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Seasonal variations of ochreous precipitates in mine effluents in Finland
Abstract
Ochreous precipitate and water samples were collected from the surroundings of seven closed sulphide mines in Finland. In the Hammaslahti Zn–Cu–Au mine, Otravaara pyrite mine and Paroistenjärvi Cu–W–As mine, the collection was repeated in different seasons to study mineralogical and geochemical variations of precipitates. The sampling was done in 1999–2002 from the ditches and drainage ponds of the tailings and waste rock piles that are susceptible to seasonal changes. Mineralogy of the precipitates was evaluated by X-ray diffraction (XRD) and infrared spectroscopy (IR), and precipitate geochemistry was examined by selective extractions. Schwertmannite (Fe8O8(OH)6SO4) was the most typical Fe hydroxide mineral found. Goethite was almost as common as schwertmannite, was often poorly ordered, and contained up to 10 wt.% of SO4. Goethite and schwertmannite were commonly found as mixtures, and they occurred in similar pH and SO4 concentrations. Ferrihydrite (nominally Fe5HO8·4H2O) was typically found in areas not influenced by acid mine drainage, and also in acid mine waters with high organic matter or As content. Jarosite (KFe3(SO4)2(OH)6) was found only in one site. In addition, some gypsum (CaSO4·2H2O) and aluminous sulphate precipitates (presumably basaluminite, Al4(SO4)(OH)10·5H2O) were identified. Selective extractions showed that acid extracts Fetot/Stot-ratios of schwertmannite and goethite samples were similar, but the ratio of oxalate-extractable to total Fe, Feox/Fetot, of goethite samples were lower than those of the schwertmannite samples. Only Al, Si and As were bound to precipitates in substantial amounts, up to several wt.%. In schwertmannites and goethites, Al, Cu, Co, Mn and Zn were mostly structural, substituting for Fe in an Fe oxyhydroxide structure or bound to surface adsorption sites in pores limited by diffusion. In ferrihydrites, heavy metals were also partly bound in adsorbed form dissolving in acid ammonium acetate. Ferrihydrites and goethites were more enriched in Co, Mn and Zn than schwertmannites, but schwertmannites and ferrihydrites were more enriched in As than goethites. Mineralogical and geochemical evidence showed that in the spring, after the snowmelt, the acid mine drainage precipitates were predominantly schwertmannite, and were partly transformed during warm summer months to goethite. The phase transformation of precipitates was followed by a decrease in pH values and increase in SO4 concentrations of waters. Adsorbed As retarded the phase transformation.
... In mine water, the formation of ochreous precipitates varies depending on different conditions such as pH, redox reactions, desorption, absorption, and ion exchange reactions (Kumpulainen et al., 2007;Michalková & Šubrt, 2015). Singer and Stumm (1970), and Stumm and Morgan (1996) explained the processes of disulfide oxidation, including the production of acidic mine drainage and the formation of precipitates. ...
... Many studies indicate that minerals of ochreous precipitates in coal mine drainage show variations from amorphous to well-crystalline forms. There are different precipitates of Fe(III) minerals such as goethite (α-FeOOH), ferrihydrite (Fe 2 O 3 .9H 2 O), schwertmannite (Fe 8 O 8 (OH) 6 SO 4 ), hematite (α-Fe 2 O 3 ), and jarosite (KFe 3 (SO 4 ) 2 (OH) 6 ), which form at different field pH conditions and SO 4 2− concentrations of mine water (Kumpulainen et al., 2007;Peretyazhko et al., 2009). These minerals are a product of the iron oxidation process, which is catalyzed by the activity of microorganisms . ...
... For example, schwertmannite is formed in low pH conditions and then transformed into goethite when the pH of the mine water increases (Gagliano et al., 2004;Acero et al., 2006). However, the ferrihydrite formation will be more dominant if the organic carbon content is high in the mine water (Kumpulainen et al., 2007;Michalková & Šubrt, 2015). Ferric oxyhydroxides can precipitate in the mine adits or the mine drainage channels (Máša et al., 2012). ...
This study investigated the mineralogical and chemical characteristics of ochreous precipitates and mine water samples from abandoned Upper Carboniferous hard coal mines in an extensive former mining area in western Germany. Mine water characteristics have been monitored and assessed using a multi-methodological approach. Thirteen mine water discharge locations were sampled for hydrochemical analysis, with a total of 46 water samples seasonally collected in the whole study area for stable isotopic analyses. Mineralogical composition of 13 ochreous precipitates was identified by a combination of powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FE-SEM/EDS). Results showed that abandoned mine drainage was characterized by circumneutral pH, Eh values ranging from 163 to 269 mV, relatively low concentrations of Fe and Mn, and was dominated by HCO3⁻ > SO4²⁻ > Cl⁻ > NO3⁻ and Na⁺ > Ca²⁺ > Mg²⁺ > K⁺. Goethite and ferrihydrite were the dominant precipitated Fe minerals, with traces of quartz, dolomite, and clay minerals. Some metal and metalloid elements (Mn, Al, Si, and Ti) were found in the ochreous sediments. The role of bacteria in the formation of secondary minerals was assessed with the detection of Leptothrix ochracea. The δ¹⁸O and δ²H values of mine water plotted on and close to the GMWL and LMWLs indicated local derivation from meteoric water and represented the annual mean precipitation isotopic composition. Results might help to develop strategies for the management of water resources, contaminated mine water, and public health.
... 9 m above the surrounding topography, had undergone oxidation processes and elemental leaching in the surface layers of the pile. The results provided detailed information on the origin of the As contamination in the surface waters and groundwater in the Ylöjärvi mining area described by Carlson et al. (2002) and Kumpulainen et al. (2007), and also further insights into the stability of the secondary As-bearing ferric precipitates acting as an important As attenuation mechanism (Articles III and IV). ...
... Previous surface water analysis (Carlson et al., 2002;Parviainen et al., 2006;Bilaletdin et al., 2007a;Kumpulainen et al., 2007) and the systematic monitoring since 1975 (HERTTA database, unpublished data) have demonstrated that the catchment area of the Ylöjärvi mine is affected by AMD, and several seepage points around the tailings pile reduce the quality of surface waters. Nearly half a century after mine closure, As (3-2,650 μg/L) and other elements show elevated concentrations in surface water samples. ...
... However, groundwater discharge may occur below the dam structure at Haveri. At Ylöjärvi, toe seepage and groundwater discharge have been reported (Kumpulainen et al., 2007;Article III). Both tailings sites have a relatively limited scale, allowing the construction of a PRB surrounding the piles, but prior to the implementation of a PRB a hydrological study is required to delineate the flow directions. ...
... The metastable character of schwertmannite particles favours phase transformation to goethite or other iron crystalline phase within weeks or months, depending on the physico-chemical conditions and water chemistry of the AMD system. Studies by Kumpulainen et al. (2007) and Peretyazko et al. (2009) on the mineralogy of AMD precipitates showed seasonal variations in the occurrence of both mineral phases. Schwertmannite was the dominant mineral present during spring, but it was then partially transformed to goethite during the warmer summer months because of changes in the water chemistry. ...
... The concentration of trace elements in the AMD precipitate was low (Table 2) or negligible. Although a higher concentration of Cu may be expected, the measured value is comparable with the values obtained by Kumpulainen et al. (2007) for AMD precipitates collected from the surroundings of copper mines. ...
... In the case of sample T-PO, three bands were detected in this region, which might be assigned to asymmetric stretching (ν 3 ) bands (~ 1096 and ~ 1032 cm -1 ) and to a symmetric stretching (ν 1 ) band (~ 974 cm -1 ). These bands, previously identified in different studies involving synthetic (Peak et al., 1999) and natural (Kumpulainen et al., 2007) iron oxides, are indicative of the presence of adsorbed or structural sulphate groups. Splitting into separate ν 3 bands is common for iron oxides formed at low pH (Fukushi et al., 2013;Tresintsi et al., 2014) and was also observed in the synthetic schwertmannite analysed (~ 1110 and ~ 1066 cm -1 ). ...
Acid mine drainage (AMD) constitutes a serious environmental problem in mining areas due to the acidification of soils and
aquatic systems, and the release of toxic metals. Many of the pollutants that occur in AMD display a high affinity for the surfaces
of the aluminium and iron oxides that are typically present in systems affected by AMD. This binding affinity reduces the mobility
of trace metals and metalloids, such as copper and arsenic, thus helping to mitigate contamination of aquatic systems. In the present
study, water samples and iron-rich bed sediments were collected in areas affected by copper mining activities. A loose ochre-coloured
precipitate occurring on the banks of a river close to an abandoned tungsten and tin mine was also sampled. The composition of the
precipitate was established, and adsorption experiments were performed with copper and arsenate ions to determine the ability of natural
iron precipitates to reduce the concentration of these ions in solution. Surface complexation models provided a good description
of the behaviour of natural iron oxides in terms of copper and arsenate retention. Use of this type of model enables prediction of the
distribution of pollutants between the solid and solution phases and analysis of their mobility in relation to environmental conditions
(pH, ionic strength, presence of competing species, etc.)
... Bambic et al. 2006;Brake et al. 2001b;Butler et al. 2009Butler et al. , 2008Chapman et al. 1983;DaSilva et al. 2009;Desbarats et al. 2007;Hakkou et al. 2008;Kim et al. 2003Kim et al. , 2002Kim and Kim, 2004;Lawrence et al. 1998;Lee et al. 2002;Munk et al. 2002;Parker et al. 2007;Sanchez-Espana et al. 2006, 2005a, 2005bSarmiento et al. 2009;Theobald et al. 1963;Webster et al. 1994), however, few studies focus on these systems in cold climates (e.g. Graham and Kelley, 2009;Herbert, 1996;Kumpulainen et al. 2007;Kwong et al. 2009Kwong et al. , 1997Lacelle et al. 2007;Lawrence et al. 1998;Stillings et al. 2008). Here we present a geochemical characterization of an ARD creek in a northern mountain environment which showed very high dissolved zinc concentrations (up to 475 mg/L) at the Zn-Pb XY deposit in Yukon, Canada. ...
... The pH of these waters was buffered to acidic conditions due to Fe(III)-hydrolysis and precipitation, which generates H + . The hardpan precipitate at the 10 m seep was identified as a mixture of schwertmannite, K-jarosite, goethite, barite, and quartz, while both the red-brown-and orange-coloured laminae in the TIFs at 18 m were composed of schwertmannite, K-jarosite, and goethite (with minor amounts of quartz), which is in line with the mineralogy of TIFs observed elsewhere (Graham and Kelley, 2009;Fernandez-Remolar et al. 2005;Kumpulainen et al. 2007;Sanchez-Espana et al. 2007). The occurrence of TIFs in this creek is thought to be due to the highly saturated waters coupled with the seasonal hydrodynamics of the creek (i.e. ...
... Given the high concentrations of sulphate in these waters, it is likely that goethite formation at all of the sampling points in the upper reaches was due to schwertmannite recyrstallization rather than direct precipitation (Bigham et al. 1996a, Bigham et al. 1996b, Yu et al. 1999, 1996bSchwertmann and Carlson, 2005;Scroth and Parnell, 2005). Although cold temperatures have been shown to enhance the stability of schwertmannite (Jonsson et al. 2005), its recrystallization to goethite can be triggered by seasonal changes in hydrological conditions (Schroth and Parnell, 2005;Kumpulainen et al., 2007), such as wetting and drying cycles, which could be expected in this environment. The presence of jarosite was expected as it was predicted to be oversaturated in these waters due to elevated concentrations of potassium, despite the pH not being overly acidic (Barham, 1997;Wang et al. 2006). ...
Acid rock drainage (ARD) is considered to be temperature-limited due to the diminished activity of Fe(II)-oxidizing microbes at low temperatures. Nonetheless, ARD streams are present in cold climates. This study presents a geochemical characterization of a cold climate ARD creek at the Zn-Pb XY deposit in Yukon, Canada, which showed highly elevated concentrations of dissolved zinc (up to 475 mg/L). Acid rock drainage at the XY deposit is likely generated via subsurface abiotic and biotic oxidation of sulphide minerals, and then exits as seeps at the headwaters of the creek. The uppermost reaches of the creek have the lowest pH levels (pH 3.3) and highest metal concentrations, with prolific precipitation of iron-hydroxysulphate and -oxyhydroxide mineral precipitates (schwertmannite, jarosite, and goethite), present as terraced iron formations (TIFs) at one sampling location. The lower reaches of the creek show a progressive pH increase (up to pH level 4.9) which occurs due to Fe(III)- and Al-hydrolysis, the neutralizing influence of carbonate-rich strata and/or ground waters, and dilution by surface waters entering the creek. Progressive pH neutralization causes a change in precipitate mineralogy to X-ray amorphous Al-hydroxysulphates, with a composition similar to aluminite and hydrobasaluminite, and amorphous Al(OH)3. Natural attenuation of Cd, Zn, and Pb occurred downstream from the headwater seeps, which was likely influenced by adsorption reactions involving both metal-sulphate anions and metal-sulphate ternary complexes. Generally, the concentrations of Cd, Zn, and Pb in the mineral precipitates followed trends in pH, aqueous concentration, predicted speciation, and mineralogy of the precipitates. However, anomalous trace metal concentrations were observed in the precipitates at 120 m downstream and potentially reflect a local ground water input. Overall the geochemistry of this cold climate ARD creek was similar to ARD in more temperate climates, although low temperatures appear to retard the kinetics of ferrous iron oxidation and seasonal hydrodynamics may influence the formation of TIFs in these highly saturated waters.
... Adsorption of sulfate may play an important role in the formation of secondary ferric phases after jarosite dissolution (Elwood Madden 2012). Also, there can be temporal changes of mineralogical assemblages in the AMD streams caused by changes in water chemistry (Kumpulainen et al. 2007;Burton et al. 2021;Schoepfer and Burton 2021). ...
... Some ferrous iron may be oxidized before discharge from the seepage face, and there is formation of ferric iron colloids that may settle further downstream. No presence of poorly crystalline ferrihydrite in sediments was observed, perhaps due to its fast transformation to more crystalline phases like goethite (Langmuir 1997;Fukushi et al. 2003;Kumpulainen et al. 2007). ...
... Finally, local climatic conditions can control the formation of secondary minerals because the chemical composition of the draining water can vary with the season. [68,[88][89][90]. Chemical changes in water composition vary due to changes in temperature and precipitation. ...
... Chemical changes in water composition vary due to changes in temperature and precipitation. In the northern latitudes, these chemical changes may also be due to snowmelt and the subsequent infiltration and wash-off of sulphide weathering products in the springtime [71,90]. ...
In the formerly glaciated terrains in the northern hemisphere and countries such as Finland, till is the most common sediment covering the bedrock. Specifically, indicator or heavy mineral studies utilising till as a vector for mineral deposits undercover have been successful. The pyrite trace-element composition from in situ mineral analyses has been shown to be an effective discriminator between different mineral deposit types, and this has led to research using heavy mineral pyrite in till to identify potential mineral deposits in a given area. However, pyrite is easily oxidised in till beds, and thus, alternative methods should be considered. Goethite pseudomorphs are more commonly found in the till sediments as remnants after pyrite oxidation. This study evaluates trace element compositions of goethitised pyrite recovered in the till beds from central Lapland in northern Finland. Intra-grain trace-elemental variations gathered using laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) between the intact pyrite core and oxidised rim demonstrated complex dynamics and variations between different trace-element values. For example, Cu, V and Mn exhibited elevated trace-element values in the goethite rim compared to the pyrite core. However, elemental ratios such as Ni/As and Co/Ni remain stable between the pyrite core and oxidised rim. Therefore, these ratios have the potential to be used as a discriminating tool between the pyrite core and oxidised rim. In addition, nanoscale variabilities using focused ion beam (FIB) and transmission electron microscopy (TEM) were utilised to inspect possible nano inclusions within the studied heavy mineral grain. The FIB and TEM studies revealed a nanocrystalline pyrite nodule observation within the goethite rim.
... The Rudyanka River (23) Background area quartz (77), clay minerals (9), plagioclases (4) goethite (1) The Rudyanka River, mouth (24) Mine drainage quartz (27), clay minerals (11) goethite (1) The Usva River (25) Background area quartz (66), clay minerals (7), plagioclases (5) goethite (1) The Usva River, below the mouth of the River Rudyanka (26) Mine drainage, runoffs from rock dumps, contaminated river water runoff quartz (15), clay minerals (12) goethite (1.5), jarosite (1) The Bolshaya Gremyachaya River (27) Mine drainage quartz (34) jarosite (45) The Bolshaya Gremyachaya River, 5 km below discharge mine water (28) quartz (15), clay minerals (6) copiapite (2) The Vilva River (29) Background area quartz (70), plagioclases (18), clay minerals (10) goethite (<1) The Vilva River, mouth (30) ...
... Experimental studies [23] have shown that with pH increasing the desorption processes of sulfates from sediments increase, Minerals 2020, 10, 364 9 of 12 which naturally increases their content in water. Active transition to aqueous media of SO 4 2− for these sites can also be associated with the evolution of crystal mineral phases of ferrous sediments, which is described in the following studies [11,24]. For this area, changes in alluvial sediments are also due to organic matter and finely dispersed coal particles, a significant amount of which is typical for sediments from the Kizel basin rivers. ...
The development of coal deposits is accompanied by negative environmental changes. In the territory of the Kizel coal basin (Perm Region, Russia), the problem of contamination of water sources by acid mine waters and runoff from rock dumps is particularly acute. Mine waters are acidic (pH 2–3), with high mineralization (up to 25 g/L) and significant content of sulfate ions, iron, aluminum, manganese, toxic trace elements (As, Co, Ni, Pb and Zn). They are formed as a result of the interaction of underground waters from flooded mines of the Kizel basin with coal and rocks of dumps with high sulfur content (15%). Uncontrolled inflow of mine water into rivers (about 22 million m3 annually) leads to significant amounts of iron and aluminum hydroxide precipitation. These precipitations are in active interaction with river water, polluting the rivers tens of kilometers downstream and are entering the Kama reservoir. Studies of alluvial precipitation can be considered as a method of control and predictors of technogenic water pollution. The mineral composition of river sediments was studied with the application of different methods, including studies of sand-gravel and silty-clayey sediments. The sandy-gravel grains in the bottom load are mainly composed by natural minerals and are represented by a significant number of particles of coal dumps, slags and magnetic spherules. The silty-clayey material, mixed with natural minerals, contains a significant number of amorphous phases with a predominance of iron-rich substances, which may actively concentrate toxic elements. The presence of jarosite, goethite, basaluminite, lepidorocite and copiapite in silty-clayey sediments are indicators of the influence of mine waters.
... Trace elements, including Al, As, Cu, V, and Zn, may be co-precipitating with 488 schwertmannite and goethite or accumulating scale-associated biomass. For elements forming 489 oxyanions at low pH, including As and V, sorption is electrostatically favorable, and strong 490 association of As with schwertmannite has been observed in multiple experiments ( Acero et al., 491 2006;Kumpulainen et al., 2007;Antelo et al., 2013;Sanchez-Espana et al., 2016;Zhang et al., 492 2016). Uptake of di-and trivalent cations including Al, Zn, Cu, Ni, Co, Cd, and Mn has occurred 493 in schwertmannite-rich precipitates at other AMD sites, but to a lesser extent than for oxyanions 494 (Acero et al., 2006;Kumpulainen et al., 2007;Burgos et al., 2012;Antelo et al., 2013). ...
... For elements forming 489 oxyanions at low pH, including As and V, sorption is electrostatically favorable, and strong 490 association of As with schwertmannite has been observed in multiple experiments ( Acero et al., 491 2006;Kumpulainen et al., 2007;Antelo et al., 2013;Sanchez-Espana et al., 2016;Zhang et al., 492 2016). Uptake of di-and trivalent cations including Al, Zn, Cu, Ni, Co, Cd, and Mn has occurred 493 in schwertmannite-rich precipitates at other AMD sites, but to a lesser extent than for oxyanions 494 (Acero et al., 2006;Kumpulainen et al., 2007;Burgos et al., 2012;Antelo et al., 2013). 495 ...
Pipelines carrying acid mine drainage (AMD) to treatment plants commonly form pipe scale, an Fe(III)-rich precipitate that forms inside the pipelines and requires periodic and costly cleanout and maintenance. Pipelines at Iron Mountain Mine (IMM) and Leviathan Mine (LM) in California carry acidic water from mine sources to a treatment plant and have developed pipe scale. Samples of scale and AMD were collected from both mine sites for mineralogical, microbiological, and chemical analysis. The scale mineralogy was primarily schwertmannite with minor amounts of poorly crystalline goethite. Although the bulk composition of the scale was similar along the length of the pipeline at IMM, the number of iron-oxidizing bacteria and concentrations of associated trace elements decreased along the flow path inside the pipeline. Laboratory batch experiments with unfiltered AMD from IMM and LM showed that Fe(II) oxidation was driven by microbial activity when the pH was <5. A remediation strategy of decreasing the pH to <2.2 was tested through geochemical modeling and laboratory experiments. These experiments indicated that scale formation could be prevented by decreasing the pH, which could be achieved at IMM by mixing source waters. However, the presence of Fe(III)-rich scale in a pipeline buffers the pH to higher values that may affect the efficacy of this remedial approach.
... Trace elements, including Al, As, Cu, V, and Zn, may be coprecipitating with schwertmannite and goethite or accumulating scaleassociated biomass. For elements forming oxyanions at low pH, including As and V, sorption is electrostatically favorable, and strong association of As with schwertmannite has been observed in multiple experiments (Acero et al., 2006;Kumpulainen et al., 2007;Antelo et al., 2013;Sanchez-Espana et al., 2016;Zhang et al., 2016). Uptake of di-and trivalent cations including Al, Zn, Cu, Ni, Co, Cd, and Mn has occurred in schwertmannite-rich precipitates at other AMD sites, but to a lesser extent than for oxyanions (Acero et al., 2006;Kumpulainen et al., 2007;Burgos et al., 2012;Antelo et al., 2013). ...
... For elements forming oxyanions at low pH, including As and V, sorption is electrostatically favorable, and strong association of As with schwertmannite has been observed in multiple experiments (Acero et al., 2006;Kumpulainen et al., 2007;Antelo et al., 2013;Sanchez-Espana et al., 2016;Zhang et al., 2016). Uptake of di-and trivalent cations including Al, Zn, Cu, Ni, Co, Cd, and Mn has occurred in schwertmannite-rich precipitates at other AMD sites, but to a lesser extent than for oxyanions (Acero et al., 2006;Kumpulainen et al., 2007;Burgos et al., 2012;Antelo et al., 2013). Geochemical speciation calculations using PW3 water chemistry indicate that in low-pH, high-sulfate environments, many cationic metals form aqueous sulfate complexes that may make adsorption more favorable to schwertmannite at low pH (Fig. S3). ...
... Moreover, the concentration of Mn leached from an initial pH 2 (1.0637 mg.L −1 ) was 22.9-and 15.8-fold higher than that at pH 4 (46.5 µg.L −1 ) and 6.5 (67.4 µg.L −1 ), indicating that the metal solubility depended on the final pH. The retention and release of metals was pH-dependent, which is responsible for the soluble metal ions through sorption and co-precipitation processes (McGregor et al. 1998;Jönsson & Lövgren 2000;Kumpuainen et al. 2007). Pokrovsky & Schott (2002) explained that having a high concentration of H + ions in the solution (low pH) may compete with the metal ions for CO 3 2À -released from calcite and obstruct the metal-carbonate (MeCO 3 ) precipitation on the surface of the adsorbent. ...
... From these above results, the concentration of metals leached from the mixing zone tailings strongly depended on the pH of the leaching solution. The results also show that the leachate had higher concentrations of As, Cu, Pb, Mn and Ni than the TGD-PCD and the TIES, as shown in Table 2. Concentrations of transition metals, such as Cu, Zn and Ni, and metalloids, such as As, under AMD condition are generally affected by sorption and co-precipitation with hydrous iron oxides (Alpers et al. 1994;McGregor et al. 1998;Jönsson & Lövgren 2000;Kumpuainen et al. 2007). Cornell & Schwertmann (1996) reported that a large number of cations (Al, Cr, Ca, Ga, V, Mn, Co, Pb, Ni, Zn and Cd) can be substituted for iron in the goethite crystal lattice. ...
This study focused on assessing the release potential of various metals and a metalloid (arsenic; As) leached from gold mine tailings under three different degrees of acidity (pH 2, 4 and 6.5) using a synthetic precipitation leaching procedure (SPLP). Tailings were collected from four pits from 0 to 16 m depth, approximately. The samples were divided into the three types, based on their position in the tailings and on other physical characteristics, of the sulphide ( c. 5 m depth), mixing ( c. 1 m depth) and oxide ( c. 10 m depth) zones. This study was primarily concerned with the concentrations of As and Mn, which were found to exceed the Thailand Industrial Effluent Standard (TIES) in the tailings from all zones. Principal component analysis revealed that the release of metals and As from the tailings under acidic conditions, as well as the metals and As mobility, was mainly controlled by the pH and redox conditions. Moreover, the first principal component had high positive loadings of Mn, Pb, Co and Ni (R ² > 0.80), indicating that these four metals are either released into the environment from a common source or/and their geochemical behaviour in the aqueous phase is similar.
Supplementary material: Concentration of metals and As leached from the sulphide mixing and oxide zones at differing pHs are available at https://doi.org/10.6084/m9.figshare.c.3840154
... Similarly, the Zn 2+ concentration in the MD was approximately 8 mg/L from June to September but increased to approximately 9.5 mg/L in October 2022. The increase in Mn 2+ and Zn 2+ concentrations in the MD may be attributed to seasonal variations, such as snow melting, summer rain, and water temperature, which affect MD water quality [33][34][35]. ...
Elevated concentrations of manganese (Mn²⁺) and zinc (Zn²⁺) in water bodies can disrupt ecosystems and damage aquatic life. However, the mechanisms underlying the removal of Mn²⁺ and Zn²⁺ under dynamic conditions and the optimal hydraulic retention time (HRT) for passive treatment plants remain unclear. Here, a pilot-scale passive treatment system for the removal of Mn²⁺ and Zn²⁺ from legacy mine drainage in northern Japan is proposed; it was performed at circumneutral pH for 152 days. Comprehensive suspended solid mineralogy analyses and geochemical and numerical modelling were conducted to optimise the passive treatment efficiency. Mn²⁺ removal (efficiency reaching 98 %) primarily depended on the activity of Mn-oxidising bacteria. Zn²⁺ removal involved Zn²⁺ co-precipitation with birnessite combined with adsorption or ion exchange on the birnessite surface. The inverse numerical model successfully determined the Mn²⁺ oxidation rate constant, Zn mass transfer coefficient, and Zn distribution coefficient. Under dynamic conditions, HRT emerged as a key factor underlying the pilot-scale passive treatment efficiency. An HRT of 0.5 days led to optimal Mn²⁺ and Zn²⁺ removal conditions and achieved values lower than the Japanese national effluent limit. The findings provide crucial information for passive treatment strategy development and environmental management, especially when considering real-scale implementation.
... There are a lot of examples showing that in the AMD environment of temperate and polar climate, the pH of waters changes during the year (to one pH unit), and the solid sediments are composed of a metastable phase gradually transformed into a stable one. For example, it is noted that metastable schwertmannite formed during spring floods turns into goethite under quieter conditions-in summer (Northern Finland) [9] or in winter (Northern Pennsylvania) [10]. ...
Seasonal variations of drainage waters and ochreous products of their discharge from the closed abandoned old gallery at the Grantcharitsa scheelite deposit (Bulgaria) were studied by field and laboratory methods for the period 2019–2023. The drainage is generated under anoxic conditions and is inherently diluted (EC = 100–202 µS/cm) with S (6–12 mg/L), Si (6–22 mg/L), Na (6–10 mg/L), Fe (0.2–3.3 mg/L), and W (0.19–3.5 µg/L), at a pH 4.4–6.5 and temperature 7–11.5 °C, with dissolved oxygen DO (2.1–7.7 mg/L). The concentrations of Fe and W and the pH of the water are variable and reach their maximum values during the dry (autumn) season. It was found that such parameters as pH, Eh, DO, Fe and W content change dramatically at a distance of up to 3 m from the water outlet; the values of pH, DO and Eh are sharply increased with a simultaneous nearly 5–6-times reduction in iron and tungsten content. The decrease in the contents of these elements is associated with the precipitation of ochreous material consisting of nanoscale ferrihydrite with an intermediate structural ordering between 2-line and 6-line ferrihydrite (major phase), hematite, goethite, quartz, montmorillonite and magnetite. The formation of ferrihydrite occurs as a result of abiotic and biotic processes with the participation of iron-oxidizing bacteria. Besides Fe2O3 (55.5–64.0 wt.%), the ochreous sediment contains SiO2 (12.0–16.4 wt.%), SO3 (1.3–2.4 wt.%), Al2O3 (3.1–6.8 wt.%) and WO3 (0.07–0.11 wt.%). It has been shown that drainage waters and ochreous sediments do not inherently have a negative impact on the environment. The environmental problem arises with intense snowmelt and heavy rainfall, as a result of which the accumulated sediments are washed away and carried in the form of suspensions into the water systems. It is suggested that by providing atmospheric oxygen access to the closed gallery (via local boreholes), it is possible to stop the generation of iron-enriched drainage.
... Therefore, it can be concluded that the mineral in the sludge was slightly-crystallized Ferrihydrite. The chemical formula was easy to transform with the ascending pH value (Kumpulainen et al., 2007;Regenspurg et al., 2004). The amorphous sludge was made up of semi-crystalline oxyhydroxides and hydroxysulphates (Munk et al., 2002), and metals could be adsorbed by it, the sorption increasing with the pH value (Lee et al., 2002). ...
Although the metals contained in acid mine drainage (AMD) are considered environmental pollutants, they may also be valuable resources. The traditional chemical precipitation processes for AMD not only produce large amounts of sludge, but also make it difficult to recycle the waste metals. This study comprehensively investigated the recycling of Fe, Cu, Zn and Mn from AMD. Ferrous ions were first oxidised by 0.15 ml/L 30% H 2 O 2 , and then a four-step fractional precipitation was applied with the selective addition of Ca(OH) 2 and Na 2 S solutions. The Fe, Cu, Zn and Mn contents of particular sludges were 45.91%, 11.58%, 31.06% and 7.95% respectively, and the recovery efficiencies of Fe, Cu, Zn and Mn from AMD reached 99.51%, 86.09%, 87.87% and 79.71%, respectively. The metals contained in the effluent were below the Code of Federal Regulations (CFR) limits after the Mn precipitation process. Technology for the complete reuse of the sludge was also tested. Fe oxide red was obtained by roasting the Fe sludge for 30 min at a temperature of 500°C, resulting in a Fe 2 O 3 content of 85.18%. Cu and Zn crude concentrates were generated by a flotation process; the Cu and Zn contents of these concentrates were 35.72% and 55.13% respectively, and the recovery efficiencies of the Cu and Zn were 72.66% and 76.18%, respectively. The Mn sludge obtained can be used in cement mixes to replace 45% of ordinary Portland cement (OPC). Based on the technology tested, a comprehensive metal recovery process is proposed here for the control of metal pollution and metal recovery from AMD.
... This very finely dispersed sediment phase, adsorbing toxic elements, on the one hand, provides processes of self-purification of water, on the other hand, is a source of secondary water pollution in areas of active accumulation. These processes are confirmed for a number of other mining areas (coal areas in Pennsylvania, USA [2], Libiola copper mines in Italy [3], coal deposits in India [4], deposits in the Iberian pyrite belt [5], sulfide mines in Finland [6], etc.). ...
... The geochemical role of ochre is manifested in the active sorption of small elements, among which Cu, Zn, Cd, Co, Cr, Ni, Pb, As, and Sb can be present in important amounts in areas of severe technogenic pollution associated with the active inflow of mine-influenced waters. This has been confirmed by numerous studies on various mining areas around the world, including coal regions in Pennsylvania (USA) (Cravotta 2008), copper mines in Libiola, Italy (Consani et al. 2017;Marescotti et al. 2012), coal deposits in India (Sahoo et al. 2012), deposits in the Iberian Pyrite Belt (Valente et al. 2015), sulphide mines in Finland (Kumpulainen et al. 2007), and elsewhere. ...
Ochre particles in modern alluvium were studied in the area affected by the development of the Kizel coal basin deposits (Perm Krai, Russia) to establish their material composition. The purpose of this study was to determine the characteristics of the morphology and material composition of ochre particles, as well as their role as concentrators and mobilizers of toxic metals in river systems. Using scanning electron microscopy, microprobe analysis, inductively coupled plasma mass spectrometry, and x-ray diffraction analysis, we found a wide range of ochre particle types, micro- and nano-textures, and material compositions. Toxic elements found in the ochre particles include (in wt.%): Cu (up to 2.56), Zn (up to 2.04), Co (up to 0.29), Sb (up to 0.23), Hg (up to 0.13), and As (up to 0.10).The diffraction data revealed that an important portion of the substance in the ochre composition is cryptocrystalline. Terrigenous components (quartz, feldspars, plagioclases, clay minerals, hematite) and authigenic components (goethite, carbonates) dominate the composition of the crystalline part of the ochre. Ochres in this area are the main toxic element concentrators; they actively migrate in the aquatic environment over long distances and deserve special attention in environmental monitoring studies.
... It has been found that the mineralogy of iron hydroxide precipitates in the tailings ponds changes from schwetmanite (Fe 8 (OH) 5.5 (SO 4 ) 1.25 ) after melting of snow in spring to goethite (Fe(OH)O) during summer time. Moreover, seasonal variations in pH trigger fluctuations in the content of SO 4 , Al, As, Cu, and Zn in tailings water [164]. Investigations into the seasonal phenomenon and water quality in relation to the bacterial activity observed in Calumet Pb-Zn tailings in Canada revealed that SO 4 reduction by sulphide-reducing bacteria (SRB) was higher in summer than in spring owing to the higher temperature and organic carbon concentrations (impacted by an agricultural runoff). ...
This overview identified temperature and precipitation as the main seasonality triggers for changes in flotation performance. Other triggers found in the literature included total dissolved organics, amount of ultra-violent irradiation, and bacteria activity. The temperature was more frequently reported as an impactful seasonal controller, fluctuations of which cause grade, recovery, and selectivity problems in flotation: cases of laboratory and plant practices were highlighted, with some examples of ‘chemical’ solutions to low efficiency in cold flotation pulps. This overview describes seasonal cyclicity mechanisms and temperature-dependency of operations by referring to chemical and physical aspects of flotation: reactions and reagents, ore and mineral surfaces, water, bubbles, and equipment efficiency.
... The results showed that the amendment of Milli-Q water and the slight shaking had negligible effects on the aggregation kinetics of hematite nanoparticles (Fig. S2 †). The particle loading of hematite was fixed at 32 mg L −1 (FeIJIII)) in all aggregation experiments, which is within the range of nanoparticle loadings in natural aqueous environments 42,43 and the optimal particle loading for DLS measurements. Each experiment was carried out in triplicate. ...
Nanomaterials may undergo a series of changes in environmental conditions during their long-distance transport in aquatic systems, but most aggregation studies were conducted under fixed conditions. How the order of...
... Several studies have been conducted on NA in AMD; however, limited studies have followed the seasonal variation in NA processes. The seasonal variation between spring and summer changed in the hydrogeochemistry of AMD and secondary precipitated mineralogy (Kumpulainen et al., 2007). The temperature changes in winter and summer significantly affect the attenuation rates of iron and As (Chen and Jiang, 2012). ...
In Mondulkiri province, Cambodia, artisanal gold miners dump tailings and wastewater from gold processing into a tributary of the Prek Te River. In the rainy season, heavy metal concentrations in the tributary decrease below the WHO drinking water standard levels through natural attenuation; however, this does not occur in the dry season. To further understand the natural attenuation mechanism, detailed analyses of the wastewater from tailing and tributary water, tributary sediments, waste rock, and ore minerals were undertaken in both seasons. The high concentration of dissolved Fe in the contaminated tributary plays a significant role in As removal during the rainy season, whereas other elements such as Ni, Se, and Cu concentration decrease due to dilution. Schwertmannite formation, controlled by iron-oxidizing bacteria, was only found at the bottom of the tributary during the rainy season. In the dry season, As, Ni, Se, and Cu concentrations remained at their original levels because there was no formation of schwertmannite or dilution by rainwater. The existing schwertmannite also starts to dissolve as the pH decreases. Seasonal dynamics cause the failure of natural attenuation; thus, methods for maintaining its effectiveness in the dry season are needed. In addition, geochemical modeling was conducted to determine the significant roles of schwertmannite formation and dilution of rainwater in the tributary. Schwertmannite is a potential adsorbent for As removal from drainage. However, dilution provided indirect and direct impacts on the tributary, such as increasing the pH and diluting the concentration of toxic elements.
... 앞서 언급했듯이 페리하이드라이트는 준안정 광물이기 때문에 추후 결정도가 높은 적철석(hematitie, Fe 2 O 3 ) 또 는 침철석으로 전이된다. 페리하이드라이트의 전이는 pH 와 온도에 크게 영향을 받는데, pH가 중성(7-8)이고 고온 에서는 적철석으로 전이되며, pH가 산성 혹은 염기성(2-5 또는 10-14)이고 실온에서는 침철석으로 전이되는 것으로 알려져 있다 (Schwertmann and Murad, 1983;Schwertmann et al., 2004;Cudennec and Lecerf, 2006 (Schwertmann and Fischer, 1973;Schwertmann and Murad, 1983;Kumpulainen et al., 2007). (Missana et al., 2003;Tang et al., 2010;Li et al., 2011;Jiang et al., 2013;Kim and Kim, 2021). ...
... This chemically complex poorly-ordered iron-rich material (Valente et al., 2011) is usually referred to as "ochres" and serves as the natural scavenger of various migrating elements in mine water discharging from abandoned mines (Dobbie et al., 2009;Bearcock et al., 2011). Kumpulainen et al. (2007) collected ochreous precipitates in drainage ponds and indicated that poorly ordered goethite and schwertmannite were the most typical ferric minerals found. Elsewhere (Máša et al., 2012), the dominant phases of ferrihydrite with goethite or goethite with lepidocrocite were found in ochres collected from slightly acidic (pH 5.6-6.0) ...
Natural ferric ochres that precipitate in streambeds at abandoned mining sites are natural scavengers of various metals and metalloids. Thus, their chemical and structural modification via microbial activity should be considered in evaluation of the risks emerging from probable spread of contamination at mining sites. Our results highlight the role of various aspergilli strains in this process via production of acidic metabolites that affect mobility and bioavailability of coprecipitated contaminants. The Mössbauer analysis revealed subtle structural changes of iron in ochres, while the elemental analysis of non-dissolved residues of ochres that were exposed to filamentous fungi suggest coinciding bioextraction of arsenic and antimony with extensive iron mobilisation. However, the zinc bioextraction by filamentous fungi is less likely dependent on iron leaching from ferric ochres. The strain specific bioextraction efficiency and subsequent bioaccumulation of mobilised metals resulted in distinct tolerance responses among the studied soil fungal strains. However, regardless the burden of bioextracted metal(loid)s on its activity, the Aspergillus niger strain has shown remarkable capability to decrease pH of its environment and, thus, bioextract significant and environmentally relevant amounts of potentially toxic elements from the natural ochres.
... A range of (Schroll, 1978). A similar and related phenomenon associated with recent anthropogenic activity is the formation of surface Fe-rich precipitates at discharge sites of acid mine drainage (AMD) or acid rock drainage (Burgos et al., 2012;Burton et al., 2008;Marescotti et al., 2012), or other disturbed sites, such as mine pits and drained coastal lowland soils (Fitzpatrick et al., 1996;Kumpulainen et al., 2007). These anthropogenic bog ores, as they may be termed, are typically of limited extent with related deposits in Pennsylvania forming over an area of 6000 m 2 and can be up to 2 m thick (Burgos et al., 2012). ...
... This transformation, however, can cause changes in the delicate textures of the micromorphologies such that casts of cell membranes and internal cellular structures of the microbial community will be destroyed via the recrystallization process. The initial recrystallization process involves the transformation of metastable schwertmannite to goethite over a short period of time, as well as with increasing depth (Acero et al. 2006;Burton et al. 2008;Kumpulainen et al. 2007;Peretyazhko et al. 2009). We can postulate that further transformation associated with the recrystallization of goethite to hematite brought on by burial and diagenesis (e.g., Goss 1987) will further modify the micro-and macromorphologies of stromatolites and other biolaminated structures in deep time. ...
Euglena-, diatom-, and algae-dominated biofilms are the principal producers of iron-rich biolaminates that result in biosedimentary structures, or stromatolites, in an acid mine drainage (AMD) environment in Indiana. These structures are considered trace fossils because they are produced by organism-sediment interactions and record physicochemical conditions of the environment. Our purpose was to link the biofilm types to specific micro- and micromorphological features and the physicochemical conditions under which they were formed. Analyses revealed that Euglena-dominated biofilm produced thin, porous microlaminae by trapping, binding, and relocating AMD precipitates as the biofilm kept pace with chemical sedimentation. More massive microlaminae were produced by high rates of chemical sedimentation brought on by increased discharge and dilution of acidity. Diatom- and algae-dominated biofilms produced thick, mm–cm-scale, porous, spongelike micro- to macrolaminae through oxygenic photosynthesis and/or metal uptake in extracellular polymeric substances, which promoted mineral precipitation on cell walls to create a rigid, porous structure. The variations in biolaminate textures within the stromatolites record seasonal changes in the microbial populations and physicochemical conditions of the AMD environment. These iron-rich stromatolites represent trace fossils that record morphological biosignatures of eukaryote-dominated microbial biofilms and may serve as appropriate proxies in the search for similar evidence of eukaryotic life in other iron-rich paleoenvironments, such as those on early Earth and Mars.
... Macrophytes and their roots provide surfaces for precipitation of ferric oxyhydroxides and stabilize accumulated ochres (Kalin 2001;Johnson and Hallberg 2005;Sracek et al. 2011;Kříbek et al. 2011). Seasonal changes occur in the composition of ochres when more crystalline phases, e.g., goethite, are formed from less crystalline phases, e.g., ferrihydrite or schwertmannite during warmer period (Kumpulainen et al. 2007). Fast transformation of low-crystallinity ferric phases into more crystalline phases was also found in mine tailings in Namibia (Sracek et al. 2014). ...
The impact of a natural wetland (“dambo” in Zambia) on neutral mine drainage at Luanshya in the Zambian Copperbelt has been investigated during an intermediate discharge period (July) using a multi-method characterization of solid phase samples, sequential extraction analysis, X-ray diffraction, Mössbauer spectroscopy, and scanning electron microscopy combined with water analyses, isotopic analyses, and geochemical modeling. In the wetland, the principal identified solid phases in sediments were carbonates, gypsum, and ferric oxyhydroxides. A significant portion of the ochres was present as insoluble hematite. Mine drainage pH values decrease, and log values increase after inflow of water into the wetland; dissolved and suspended concentrations of Fe, Mn, Cu, and Co also decrease. Based on speciation calculations, there is no precipitation of secondary Cu and Co minerals in the period of sampling, but it can occur later in dry period when the flow rate is reduced. Concentrations of sulfate decrease, and values of δ³⁴S(SO4) in the wetland increase in parallel, suggesting sulfate reduction is occurring. In more advanced dry period, the discharge in mine drainage stream is probably much lower and water can reach supersaturation with respect to minerals such as gypsum, which has been found in sediments. Wetlands have a positive impact on mine drainage water quality due to the removal of metals by adsorption, co-precipitation, and filtration of colloids. However, there can also be a rebound of contamination by seepage inflow downstream from the wetland. Ongoing climate change with extreme hydrologic events may enhance differences between dry and rainy seasons with resulting faster mobilization of contaminants.
... Dissolved ferrous iron in mine drainage seepage from mine tailings can be oxidized and precipitate as Kjarosite in low-pH waters rich in sulfate. Under higher pH conditions, schwertmannite precipitates, then goethite and lepidocrocite precipitate at slightly acidic or neutral conditions and ferrihydrite precipitates at neutral conditions (Kumpulainen et al. 2007). In particular, ferrihydrite with a large specific surface area adsorbs and/or co-precipitates dissolved metals and metalloids (Fukushi et al. 2003;Waychunas et al. 2005;Sracek et al. 2011). ...
Acid mine drainage from mine tailings at Selebi Phikwe, eastern Botswana, has been investigated using a combination of total decomposition, sequential extraction, X-ray diffraction, Mössbauer spectroscopy, and SEM analyses of solid phase samples, water analyses, isotopic analyses, and geochemical modeling. The principal ferric phases in the seepage stream sediments are jarosite and goethite, which incorporate Ni and Cu. The Mössbauer spectroscopy (MS) indicated exclusively 3+ oxidation state of iron with typical features of ferric hydroxides/sulfates. A fraction of dissolved sulfate is also sequestered in gypsum which precipitates further downstream. Significant portions of Fe, Ni, and Cu are transported in suspension. Values of pH decreased downstream due to H+ generated by the precipitation of jarosite. Values of δ2H and δ18O indicate evaporation of pore water in the mine tailings before seepage. Values of δ34S(SO4) are consistent with the oxidation of sulfides, but sample from the seepage face is affected by dissolution of gypsum. No minerals of Ni and Cu were detected and the principal attenuation processes seem to be adsorption and co-precipitation with jarosite. Higher contents of Cu are sequestered in solid phases compared to Ni, in spite of much higher dissolved Ni concentrations. Based on the speciation calculations, seepage water is undersaturated with respect to all Ni and Cu phases and adsorption and co-precipitation with jarosite seems to be the principal attenuation processes. Direct geochemical modeling was able to reproduce downstream pH trends, thus confirming the precipitation of jarosite as the principal pH-controlling process.
... Poorly crystalline Fe (III) oxides (ferrihydrite and schwertmannite) dissolved in the preparation due to the presence of more insoluble crystalline Fe (III) oxides (e.g., goethite and hematite) (Cornell and Schwertmann, 2003); >85% of the total iron is released during this step. (3) Very ordered Fe(III) minerals: ammonium acid oxalate (Kumpulainen et al., 2007) partially dissolves sulfate-rich CMD crystalline iron precipitates (hematite and goethite) during an sequential extraction step, as reported by Dold (2003a, b). However, in the method proposed by Dold, 0.2 M NH 4 oxalate was used as the extractant for 2 h in step 2, but in this study, the samples in batch system were exposed to light and heated to 80°C in a water bath. ...
In Brazil, intense coal exploitation activities have led to environmental deterioration, including soil mortification, water contamination, loss of ecosystem, and atmospheric contamination. In addition, considerable quantities of sulfur-rich residues are left behind in the mining area; these residues pose grave environmental issues as they undergo sulfide oxidation reactions. When sulfur oxides come in contact with water, extreme acid leachate is produced with great proportions of sulfate, and hazardous elements (HEs), which are identified as coal drainage (CMD). CMD is an environmental pollution challenge, particularly in countries with historic or active coal mines. To prevent CMD formation or its migration, the source must be controlled; however, this may not be feasible at many locations. In such scenarios, the mine water should be collected, treated, and discharged. In this study, data from 2005 to 2010 was gathered on the geochemistry of 11 CMD discharges from ten different mines. There are several concerns and questions on the formation of nanominerals in mine acid drainage and on their reactions and interfaces. The detailed mineralogical and geochemical data presented in this paper were derived from previous studies on the coal mine areas in Brazil. Oxyhydroxides, sulfates, and nanoparticles in these areas possibly go through structural transformations depending on their size and formation conditions. The geochemistry of Fe-precipitates (such as jarosite, goethite, and hematite) existent in the CMD-generating coal areas and those that could be considered as a potential source of hazardous elements (HEs) (e.g., Cr) were also studied because these precipitates are relatively stable in extremely low pH conditions. To simplify and improve poorly ordered iron, strontium, and aluminum phase characterization, field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), micro-Raman spectroscopy, and X-ray diffraction (XRD) and sequential extraction (SE) studies were executed on a set CMD samples from the Brazilian mines. This study aimed to investigate the role of both nanomineral and amorphous phase distribution throughout the reactive coal cleaning rejects profile and HEs removal from the water mine to provide holistic insights on the ecological risks posed by HEs, nanominerals, amorphous phases, and to assess sediments in complex environments such as estuaries. © 2018 China University of Geosciences (Beijing) and Peking University
... Thus, jarosite is formed at pH < 3, schwertmannite is commonly formed at pH 3-4, and ferrihydrite and goethite are formed at neutral pH (Bigham and Nordstrom, 2000). Due to their metastable nature, some of the mineral phases present in AMD systems may evolve within weeks or months towards more crystalline mineral phases, depending on the pH, E h and temperature of the system (Acero et al., 2006;Antelo et al., 2013;Bigham et al., 1996;Kumpulainen et al., 2007). ...
Secondary iron minerals are important in mining areas as they are natural scavengers of many contaminants. Thus, aluminium and iron oxides derived from acid mine drainage determine the fate of trace metals commonly found in mining areas. They mainly do this via sorption processes, which prevent leaching of the metals and contamination of surface and groundwater.
In the present study, abiotic precipitates were obtained from samples of acid drainage water collected from an abandoned copper mine. Characterization of the precipitates revealed that schwertmannite was the dominant iron mineral phase present. Retention of Cu, Cd, Ni and Pb by natural iron precipitates was compared with retention of the same elements by synthetic analogues. The study findings indicate that the natural abiotic precipitates have a higher retention capacity than their synthetic analogues. Thermodynamic modelling was used to predict the geochemical behaviour of the trace metals in the presence of iron precipitates. Inclusion of adsorption and precipitation reactions in the models yielded a good description of the degree of attenuation of adverse effects of the trace metals. Under acidic conditions, the schwertmannite-like particles initially present in the natural precipitates evolve towards more crystalline mineral phases. This transformation process is accompanied by the release of sulphate ions into the solution and by a decrease in trace metal sequestration
... Given the presence of sulfate in goethite samples (S-1-2-3; Table 3), it is likely that goethite formation was due to the transformation of schwertmannite into goethite rather than direct precipitation. Although cold temperatures together with low pH (~3) have been shown to enhance the stability of schwertmannite (Jönsson et al. 2005), its recrystallization to goethite can be triggered by seasonal changes in hydrological conditions (Schroth and Parnell 2005;Kumpulainen et al. 2007), such as wetting and drying cycles, which could be expected in this environment. ...
The generation of acid rock drainage (ARD) was observed in an area of Nevado Pastoruri as a result of the oxidative dissolution of pyrite-rich lutites and sandstones. These ARDs are generated as abundant pyrite becomes exposed to atmospheric conditions as a result of glacier retreat. The proglacial zone contains lagoons, springs, streams and wetlands, scant vegetation, and intense fluvioglacial erosion. This work reports a comprehensive identification and the results of sampling of the lagoons and springs belonging to the microbasin, which is the headwaters of the Pachacoto River, as well as mapping results based on the hydrochemical data obtained in our study. The physical properties and water chemistry of 12 springs and 22 lagoons from the proglacial zone are also presented. Water springs are far from being chemically uniform, with pH and EC values ranging between 2.55-6.42 and 23-1110 μS/cm respectively, which suggests a strong geologic control on water chemistry. Fe-SO4(-2) concentrations confirm the intense process of pyrite oxidative dissolution. Many of the lagoons are affected by ARD, with low pH (~ 3), and high EC (256-1092 μS/cm) values when compared with unaffected lagoons (EC between 7 and 59 μS/cm), indicating a high degree of mineralization. The affected lagoons show higher concentrations of SO4(2-) and SiO2, and elements as Fe, Al, Mg, Mn, Zn, Co, and Ni, which are related to the alteration of pyrite and the dissolution of aluminosilicate minerals. Schwertmannite-goethite appears to be the most important mineral phases controlling the Fe solubility at a pH of 2-3.5. Moreover, they act as a sorbent of trace elements (As, Sb, V, Pb, Zn, Cr), which is an efficient mechanism of natural attenuation. Despite of this, the water flowing out from the basin is acid (pH 3.1) and contains significant concentrations of Fe (0.98 mg/L) and Al (3.76 mg/L) that confer mineral acidity to water. The Pachacoto River located 5.5 km downstream from this point showed a strong natural attenuation, with a pH of 6.9 and low concentration of metals. This mitigating process is possible due to (i) the formation of precipitates that retain toxic elements and (ii) the mixing with natural waters that promote dilution, which favor the increase of pH until circumneutral conditions.
... A range of (Schroll, 1978). A similar and related phenomenon associated with recent anthropogenic activity is the formation of surface Fe-rich precipitates at discharge sites of acid mine drainage (AMD) or acid rock drainage (Burgos et al., 2012;Burton et al., 2008;Marescotti et al., 2012), or other disturbed sites, such as mine pits and drained coastal lowland soils (Fitzpatrick et al., 1996;Kumpulainen et al., 2007). These anthropogenic bog ores, as they may be termed, are typically of limited extent with related deposits in Pennsylvania forming over an area of 6000 m 2 and can be up to 2 m thick (Burgos et al., 2012). ...
... During AAO extraction procedure, poorly-crystalline ferric and aluminum oxyhydroxysulfate phases, such as schwertmannite, hydrobasaluminite, and gibbsite, are dissolved by acid ammonium oxalate (Dold, 2003a(Dold, , 2003bGagliano et al., 2004;Caraballo et al., 2009). In the case of complex Fe(III) mineral assemblages, only the poorly-crystalline goethite is dissolved during AAO, while well-crystallized goethite particles remain in solid form (Kumpulainen et al., 2007;Peretyazhko et al., 2009). ...
... Similarly, ferrihydrite showed higher adsorption capacity for Se(VI) compared with goethite and lepidocrocite, which was attributed to the greater surface area and higher dispersive properties of ferrihydrite (Das et al., 2013). Kumpulainen et al. (2007) also reported that more As was contained in schwertmannite and ferrihydrite than goethite. ...
Mine stream precipitate collected from Ilkwang mine, Korea, contained high concentrations of arsenic (As), while water collected from the same site had negligible As concentrations, indicating natural attenuation of As occurred in the mine stream. The mechanism of attenuation was explained by comparison of X-ray absorption near edge structure (XANES) of As(V) co-precipitated with or adsorbed to iron (Fe) minerals in mine precipitates. Arsenic in the mine precipitate was present as As(V) and schwertmannite was the main Fe mineral. Arsenic co-precipitation with schwertmannite was the major mechanism of As removal in the mine stream, followed by As adsorption by goethite and As co-precipitation with ferrihydrite. Schwertmannite and ferrihydrite were formed in acid mine drainage and As was incorporated in their structure during formation. Additionally, schwertmannite and ferrihydrite may transform to goethite with As adsorbed onto the goethite surface. Based on the results of batch experiments of As co-precipitation and adsorption, co-precipitation of As with ferrihydrite and schwertmannite was the most effective As sequestration mechanism in the removal of As(V) from acid mine drainage.
... Using the modified extraction scheme of Dold (2003), not adapted specifically for As, may have overestimated the amount of As in the Fe(III)-oxyhydroxide fraction. However, use of NH 4 -oxalate has been shown to be effective for the dissolution of As-bearing Fe-hydrates (Kumpulainen et al., 2007;Keon et al., 2001;Parviainen et al., 2012). The addition of ferric sulphate (reaction (1)) to the tailings slurry prior to disposal aimed to resent As in newly formed Fe-precipitates. ...
... The metal content and pH of tailings effluents may also vary in the short-term, both seasonally and annually, due to local hydrological conditions, setting constraints for water treatment design. For example, seasonal variation in water quality, such as changes in the pH and sulphate concentration, has been observed to control trace metal adsorption on secondary precipitates (Kumpulainen et al. 2007). At the Luikonlahti mine site, the quality of tailings seepage waters was monitored 2-3 times per year from May 2003 to May 2007May (years 2003May -2006). ...
Contaminative drainage from mine sites, and particularly from mine waste deposits,
may pose risks to surface waters. Therefore, mine site risk assessment and manage
-
ment require knowledge of the whole series of processes from mine drainage forma
-
tion to contaminant transport and the eventual ecological effects. This paper summa
-
rizes some of the recent studies by the Geological Survey of Finland covering these
issues. The studies have included investigations of the mineralogical and geochemi-
cal changes in the tailings and variation in tailings effluent quality, the influence of
sedimentation dynamics on contaminant distribution in lake sediments, and the use of
sediment chemistry and biota to evaluate the environmental impact of the loading. The
results demonstrate that even though sulphide oxidation in tailings may already start
during the active disposal of tailings, the main impacts of mine drainage on surface
waters are typically associated with the post-mining period of AMD generation. This
underlines the importance of the proper design and after-care of tailings facilities. In
addition, wind-driven bottom currents were observed to have a major influence on the
sedimentation dynamics in shallow lakes, which are typical in Finland, and thus also
on the contaminant distribution in lakes, further affecting the aquatic impacts of the
mine site.
... Using the modified extraction scheme of Dold (2003), not adapted specifically for As, may have overestimated the amount of As in the Fe(III)-oxyhydroxide fraction. However, use of NH 4 -oxalate has been shown to be effective for the dissolution of As-bearing Fe-hydrates (Kumpulainen et al., 2007;Keon et al., 2001;Parviainen et al., 2012). The addition of ferric sulphate (reaction (1)) to the tailings slurry prior to disposal aimed to resent As in newly formed Fe-precipitates. ...
At a gold mine in northern Sweden, gold occurring as inclusions in pyrrhotite and arsenopyrite is leached by cyanidation of the ore. The main sulphide minerals in the ore are pyrrhotite and arsenopyrite. Effluents from the cyanidation process are treated with Fe2(SO4)3 to form Fe-precipitates suitable for the co-precipitation of As. The aim of this study was to perform static and kinetic leaching tests on the ore and tailings to define geochemical processes governing As mobility. Sequential leaching tests suggested that the majority of dissolved As deriving from the sulphide fraction in the ore was incorporated in newly formed Fe-precipitates in the tailings. The mobility of As in the tailings was therefore mainly dependent on the stability of these As-bearing Fe-precipitates. Weathering cell tests (WCT) involving 31 weekly cycles of wetting and air exposure were conducted to assess the stability of the As in the tailings under accelerated weathering conditions. The first stage of the WCT was characterized by a pH ≈5 and low As leaching, probably driven by the dissolution of amorphous Fe-As species. In the second stage of the WCT, leaching of Fe, S and As increased and the pH decreased to <3.5. An increase of the leachate's molar Fe/S-ratio suggested that pyrrhotite oxidation was occurring. The falling pH destabilized As-bearing Fe-precipitates, causing further As release. The total As release during the WCT corresponded to only a small proportion of the tailings' total As content. The accelerated As-leaching observed towards the end of the WCT could thus indicate that its release could increase progressively over time.
... The river bed ochres have started to redissolve since 2012 or even earlier, which also released their toxic load of arsenic to areas downstream, while leaving behind a matte brown Fe-oxide coating on the rocks. In conclusion, the schwertmannite deposits at Caviahue occur in a natural setting instead of in an acid mine drainage field where the mineral is commonly encountered (Yu et al. 1999;Kumpulainen et al. 2007;Jonsson et al. 2005;Gagliano et al. 2004;Brady et al. 1986;Blodau and Knorr 2006), and are ephemeral because of changing water composition trends. ...
Mars carries primary rock with patchy occurrences of sulfates and sheet silicates. Both Mg- and Fe- sulfates have been documented, the former being rather uncommon on Earth. To what extent can a natural acidic river system on Earth be a terrestrial analog for early Mars environments? Copahue volcano (Argentina) has an active acid hydrothermal system that has precipitated a suite of minerals in its hydrothermal reservoir (silica, anhydrite, alunite, jarosite). Leakage from this subterranean system through hot springs and into the crater lake have formed a strongly acidified watershed (Río Agrio), which precipitates a host of minerals during cooling and dilution downstream. A suite of more than 100 minerals has been found and conditions for precipitation of the main phases are simulated with speciation/saturation routines. The lower part of the watershed (Lake Caviahue and the Lower Río Agrio) have abundant deposits of ferricrete since 2003: hydrous ferric oxides and schwertmannite occur, their precipitation being mediated by Fe-oxidizing bacteria and photochemical processes. Further downstream, at greater degrees of dilution, hydrous aluminum oxides and sulfates form and create ‘alcretes’ lining the river bed. The watershed carries among others jarosite, hematite, anhydrite, gypsum and silica minerals and the origin of all these minerals could be modeled through cooling/dilution of the primary hot spring fluids. Single evolution (acidification through capture of volcanic gases, water rock interaction to acquire the dissolved cations) through cooling of the primary fluids could explain most of the Fe-bearing minerals, but to precipitate Mg-sulfates, evaporation and renewed interaction with olivine-rich rocks is needed to saturate some common Mg-sulfates (e.g., epsomite). The schwertmannite beds formed through processes involving Fe-oxidizing bacteria, which may be significant if this mineral was common on Mars in the past. Photochemical processes on Mars are commonly discussed in terms of photo-oxidation of Fe, but photo-reduction may be a common process as well, as was found to be the case in the Río Agrio watershed. A model of waters acidified by the capture of S-rich volcanic gases that have reacted with basaltic rocks, and then evaporated or were neutralized by higher alkalinity surface fluids may explain the origin of the sulfate mineral suites on Mars quite well.
... 3f and 6), but the others are rather indicative of SO 4 adsorption (Fig. 6). Several studies demonstrated that goethite with very high content of adsorbed SO 4 is associated with schwertmannite (Kumpulainen et al., 2007;Peretyazhko et al., 2009). Schwertmannite was found to be metastable with respect to goethite, and transforms to this more stable phase by hydrolysis within months to years depending on pH, temperature and specifically adsorbed ions (Bigham et al., 1996;Jönsson et al., 2005;Schwertmann and Carlson, 2005). ...
The mineralogical composition of mining wastes deposited in countless dumps around the world is the key factor that controls retention and release of pollutants. Here we report a multi-method data set combining mineralogical (X-ray diffraction, electron microprobe and Raman microspectrometry) and geochemical (sequential extraction and pore water analysis) methods to resolve As mobility in two 50-years-old mining waste dumps. Originally, all of the As in the mining wastes selected for the study was present as arsenopyrite and with time it has been replaced by secondary As phases. At Jedová jáma mining area, the most of As precipitated as X-ray amorphous ferric arsenate (HFA). Arsenic is also accumulated in the scorodite and Fe (hydr)oxide (with up to 3.2wt.% As2O5) that is particularly represented by hematite. Mining wastes at Dlouhá Ves contain only trace amount of scorodite. Arsenic is primarily bound to Pb-jarosite and Fe (hydr)oxides (especially goethite) with up to 1.6 and 1.8wt.% As2O5, respectively. The pore water collected after rainfall events indicated high concentrations of As (~4600μg·L(-1)) at Jedová jáma, whereas aqueous As at Dlouhá Ves was negligible (up to 1.5μg·L(-1)). Highly mobile As at Jedová jáma is attributed to the dissolution of HFA and simultaneous precipitation of Fe (hydr)oxides under mildly acidic conditions (pH~4.4); immobile As at Dlouhá Ves is due to the efficient adsorption on the Fe (hydr)oxides and hydroxosulfates under acidic pH of ~2.8. Taken together, As mobility in the ferric arsenates-containing mining wastes may significantly vary. These wastes must be kept under acidic conditions or with high aqueous Fe(III) concentrations to prevent the release of As from incongruent dissolution of ferric arsenates.
... goethite, hematite) (Cornell and Schwertmann, 2003;Silva and DaBoit, 2010). More than 85% of the total iron was released in this step; 4) Highly ordered Fe 3+ hydroxides and oxides (hematite and goethite) were partially dissolved by acid ammonium oxalate (Kumpulainen et al., 2007) using a selective extraction step described by Dold (2003). As in step 2, the extractant used was 0.2 M NH 4 -oxalate for 2 h, but in this case the samples were exposed to light and heated to 80°C in a water bath; 5) For organic matter, after steps 1-4, a 0.1-mg resultant mineral sample (five replicates) was mixed with 1 mL of dimethyl sulfoxide (DMSO). ...
... More than 85 % of the total Fe was released in this step. 4. Highly ordered Fe 3+ hydroxides and oxides (hematite and goethite) were partially dissolved by acid ammonium oxalate (Kumpulainen et al. 2007) using a SE step described by Dold (2003b). As in step 2, the extractant used was 0.2 M NH 4 -oxalate for 2 h, but in this case, the samples in batch system were exposed to light and heated to 80°C in a water bath. 5. ...
The sulfide oxidation and precipitation of Al-Fe-secondary minerals associated with abandoned acid mine drainage (AMD) from the abandoned copper mine waste pile at Touro, Spain, has been studied by sequential extraction (SE) combined with several techniques with the intent of understanding the role of these processes play in the natural attenuation of hazardous element contaminants in the AMD. In addition, the fragile nature of nanominerals and ultrafine particle (UFP) assemblages from contaminated sediment systems from the abandoned copper mine required novel techniques and experimental approaches. The investigation of the geochemistry of complex nanominerals and UFP assemblages was a prerequisite to accurately assess the environmental and human health risks of contaminants and cost-effective chemical and biogeological remediation strategies. Particular emphasis was placed on the study and characterization of the complex mixed nanominerals and UFP containing potentially toxic elements. Nanometer-sized phases in sediments were characterized using energy-dispersive X-ray spectrometer (EDS), field-emission scanning electron microscope (FE-SEM), and high-resolution transmission electron microscopy (HR-TEM) images. The identification of the geochemical and mineralogical composition of AMD in Touro, as well as the different formation mechanisms proposed, complement the existing literature on secondary mineral assemblages and provide new emphasis to increase the understanding of extreme environments. The results also demonstrated that variations in the geochemical fractionation of hazardous elements in AMD were more influenced by the secondary mineral proportion and by AMD pH.
... when dissolved in an acidified ammonium oxalate (AAO) extract in the dark ( Bigham et al., 1994Bigham et al., , 1996). Many researchers have used the AAO extraction approach to quantitatively determine poorly crystalline minerals such as schwertmannite and ferrihydrite (Bigham et al., 1990(Bigham et al., , 1994(Bigham et al., , 1996Fukushi et al., 2003;Gagliano et al., 2004;Regenspurg et al., 2004;Schroth and Parnell, 2005;Burton et al., 2007;Kumpulainen et al., 2007;Peretyazhko et al., 2009). However, they used varying extraction time periods ranging from 15 min to 4 h. ...
... They are frequently a by-product of metabolic processes in microorganisms containing iron (Fe 2? ) as an energy source [10]. The mixing and diluting of AMD with a fresh water stream, in drainage channels or in other places where mine water discharges, facilitate the formation of iron precipitates with various compositions [11]. Some of the resulting iron oxides are susceptible to external conditions (temperature, atmospheric effluence, etc.), and when these conditions are present, transformation of less stable oxides to the more stable forms takes place. ...
TG–DTA, MS detections and XRD were used to characterize thermal behaviour of iron precipitates from acid mine drainage prepared by precipitation with urea and natural iron precipitates sampled from sludge bed (settling pit Sedem žien and old abandoned adit Hodruša, mining area Banská Štiavnica, Slovakia). The high-resolution transmission electron microscopy and scanning electron microscopy (SEM) techniques were used to characterize the surface microstructure and shape of the synthesized and sampled iron precipitates. The SEM micrographs of the iron precipitates (natural and precipitated with urea) show that the samples had formed into agglomerates, probably due to attractive forces of quite large surface area. During heating of the all samples up to 200 °C, physically adsorbed water was removed. On further heating in the range from 250 to 350 °C in natural iron precipitates, the less stable forms (goethite, ferrihydrite, and schwertmannite) transform to more stable forms like hematite. In case of synthetic samples, the transformation runs in two steps: first in the range from 250 to 350 °C, and second in the range from 600 to 750 °C.
... The metastable Fe(IIII) hydroxysulfate schwertmannite [Fe 8 O 8 (OH) (8−2x) (SO 4 ) x ] is common in AMD impacted surface waters (e.g., Dold and Spangenberg, 2005;España et al., 2005España et al., , 2006Kumpulainen et al., 2007), but less common in sulfide tailings deposits (Dold and Fontboté, 2001;Hayes et al., 2014). This metastable hydroxysulfate phase forms under acidic pH conditions (2.8-3.5) by hydrolysis of Fe(III) in the presence of SO 4 (Bigham et al., 1996;Caraballo et al., 2013): Hayes et al. (2014) also observed schwertmannite formation after ferrihydrite and gypsum with decreasing pH in a sulfide-rich tailings deposit. ...
Abstract Tailings generated during processing of sulfide ores represent a substantial risk to water resources. The oxidation of sulfide minerals within tailings deposits can generate low-quality water containing elevated concentrations of SO4, Fe, and associated metal(loid)s. Acid generated during the oxidation of pyrite [FeS2], pyrrhotite [Fe(1-x)S] and other sulfide minerals is neutralized to varying degrees by the dissolution of carbonate, (oxy)hydroxide, and silicate minerals. The extent of acid neutralization and, therefore, pore-water pH is a principal control on the mobility of sulfide-oxidation products within tailings deposits. Metals including Fe(III), Cu, Zn, and Ni often occur at high concentrations and exhibit greater mobility at low pH characteristic of acid mine drainage (AMD). In contrast, (hydr)oxyanion-forming elements including As, Sb, Se, and Mo commonly exhibit greater mobility at circumneutral pH associated with neutral mine drainage (NMD). These differences in mobility largely result from the pH-dependence of mineral precipitation-dissolution and sorption-desorption reactions. Cemented layers of secondary (oxy)hydroxide and (hydroxy)sulfate minerals, referred to as hardpans, may promote attenuation of sulfide-mineral oxidation products within and below the oxidation zone. Hardpans may also limit oxygen ingress and pore-water migration within sulfide tailings deposits. Reduction-oxidation (redox) processes are another important control on metal(loid) mobility within sulfide tailings deposits. Reductive dissolution or transformation of secondary (oxy)hydroxide phases can enhance Fe, Mn, and As mobility within sulfide tailings. Production of H2S via microbial sulfate reduction may promote attenuation of sulfide-oxidation products, including Fe, Zn, Ni, and Tl, via metal-sulfide precipitation. Understanding the dynamics of these interrelated geochemical and mineralogical processes is critical for anticipating and managing water quality associated with sulfide mine tailings.
Groundwater in high-mountain areas like the Central Chilean Andes is a crucial freshwater source for downstream communities. However, its pristine reputation masks a hidden threat when metallogenic systems exist: Natural Acid Drainage (NAD). This study comprehensively investigates the hydrogeological systems and the impact of NAD on groundwater quality in this copper-rich high-altitude region from an interdisciplinary approach. Specifically, the study area lies in the El Arpa Valley, a site with minimal human influence. Isotopic and hydrogeochemical analyses of groundwater, surface water, and snow samples revealed a groundwater origin between 2900 and 3300 m a.s.l. and the influence of fractures and gullies on recharge mechanisms. Physicochemical parameters exhibit increasing mineralisation downstream (118 to 714 µS/cm) with a pH range of 3.86–7.01. SO42--Ca2+ facies and elevated aluminium (4.59–6349.31 ppb), iron (1.00–7003.24 ppb), and manganese (1.25–1098.41 ppb) contents characterise groundwater composition. Rock geochemistry and mineralogy show that phyllic alteration overprinted by supergene processes contributes to NAD by dissolving pyrite and iron oxyhydroxides. Principal component analysis on Landsat 8 images allows for identifying potential NAD areas over 11.6 % of the high Andes. The widespread occurrence challenges the perception of pristine mountain water, emphasising the potential adverse effects on human health and infrastructure, mainly due to high manganese content (>80 ppb). Findings advance the knowledge on NAD occurrence in remote mountainous regions, urging a reassessment of water quality perceptions in the presence of geogenic pollution sources, particularly considering the current threat of climate change.
Schwertmannite is an iron hydroxo sulfate secondary mineral (Fe8O8(OH)8-2x(SO4)x•nH2O; 1 ≤ x ≤ 1.75) that commonly precipitates in sulfate-rich acid and metalliferous drainage as Fe(II) oxidises to Fe(III). It displays a high capacity to incorporate a range of elements through substitution of metal cations for Fe and anionic species for inner-sphere and outer-sphere sulfate groups, and surface adsorption. Precipitates from the base to top of sediment profiles immediately downstream from the historic Sunny Corner sulfide deposit are dominated by schwertmannite, indicating the stability of this mineral over decadal time frames in the low pH and high sulfate conditions. Various mineral characterisation methods, coupled with hydroxylamine hydrochloride based sequential selective extractions, reveal two forms of schwertmannite co-existing and in similar proportions throughout the profiles. The first form of schwertmannite has a high S/Fe ratio and the pattern of release of Cu, Pb, Zn and As relative to Fe indicates such trace elements are mostly adsorbed to outer-sphere sites. By contrast, the second and more crystalline schwertmannite has lower S/Fe ratios and requires higher concentrations of hydroxylamine hydrochloride to dissolve. The second schwertmannite displays substantial substitution of arsenate for sulfate, with As/(As + S) molar ratios ranging from 0.1 to 0.6, and substantially higher concentrations of trace elements. Sequential precipitation of the two schwertmannites from the AMD appears more likely than transformation of one form to the other. At sites such as Sunny Corner, pH neutralisation or removal of sulfate from the AMD stream may result in destabilisation of the schwertmannite and release of associated trace metals.
Schwertmannite is sensitive to changes in geochemical, thermal, and microbial conditions. Changes in aqueous pH beyond its stability, i.e. pH 2.5–4.5, triggers its transformation to jarosite or goethite in highly acidic environments (pH ≤ 2.5), depending on the availability of jarosite-directing cations (Na+, NH4+, K+, etc.), while goethite is the common stable end product at pH > 7.5. Schwertmannite with degraded morphology can stably exist for years in oxic intermediate pH environments (pH 5.5–6.5), but the presence of trace amounts of Fe(II)aq yields goethite/lepidocrocite within a few hours, especially at pH ≥ 6.5. Hematite is the sole end product at ≥ 600 °C dry heating, with goethite and ferrihydrite as intermediate phases. Siderite, maghemite, and mackinawite form in anoxic microbial conditions due to dissimilatory reduction of Fe(III) and SO42− to Fe(II) and HS−, while orpiment forms from As(V)-rich schwertmannites. Sorbed contaminants enhance schwertmannite stability by restricting Fe(II)–Fe(III) electron transfer and microbial degradation by occupying surface sites. Although Fe(III) and sorbed ion mobilization typically has negligible effects on schwertmannite transformation, complete schwertmannite-SO4 release is likely in extreme conditions, and in microbial Fe(II)aq-rich media. Dissolution–reprecipitation and solid state transformation mechanisms broadly govern schwertmannite transformation.
The monograph shows the main environmental problems associated with mining activity, it's waste and environmental liabilities with emphasis on risk assessment and its environmental impact. The works analyze the application of different analytical and instrumental techniques of physical, geotechnical, chemical, geochemical and risk characterization. It is divided into 11 articles that are listed below.
1. Geological and geotechnical characteristics of tailings dams at Sierra Minera de Cartagena-La Unión (SE Spain)
2. Stability of tailings ponds in the mining district of Mazarrón (SE Spain): potential risks for the Moreras Rambla
3. Nomograms to calculate stability in slate and granite spoil heaps
4. Mine soils associated with open-cast coal mining in Spain
5. Method and instrumental techniques for the study of acidic water systems
6. Assessment of heavy metal mobility in mine tailings in the province of Huelva
7. Sequential chemical extraction of heavy metals in a study of the chemical alteration of mine tailings at Ticapampa (Huaraz, Perú)
8. The flooded pit at Aznalcóllar (Seville, Spain) and it use a dumping site for mine waste
9. Transient processes associated with the flooding of Meirama pit lake
10 Geochemical processes in acidic water caused by the weathering of metal sulphides
11. X-ray fluorescence spectrometry used to assess of the dispersion of metals within mining environments
Determining key reaction pathways involving uranium and iron oxyhydroxides under oxic and anoxic conditions is essential for understanding uranium mobility as well as other iron oxyhydroxide mediated processes, particularly near redox boundaries where redox conditions change rapidly in time and space. Here we examine the reactivity of a ferrihydrite-rich sediment from a surface seep adjacent to a redox boundary at the Rifle, Colorado field site. Iron(II)-sediment incubation experiments indicate that the natural ferrihydrite fraction of the sediment is not susceptible to reductive transformation under conditions that trigger significant mineralogical transformations of synthetic ferrihydrite. No measurable Fe(II)-promoted transformation was observed when the Rifle sediment was exposed to 30 mM Fe(II) for up to 2 weeks. Incubation of the Rifle sediment with 3 mM Fe(II) and 0.2 mM U(VI) for 15 days shows no measurable incorporation of U(VI) into the mineral structure or reduction of U(VI) to U(IV). Results indicate a significantly decreased reactivity of naturally occurring Fe oxyhydroxides as compared to synthetic minerals, likely due to the association of impurities (e.g., Si, organic matter), with implications for the mobility and bioavailability of uranium and other associated species in field environments.
Water is needed at mine sites for dust suppression, mineral processing, coal washing , and hydrometallurgical extraction. For these applications, water is mined from surface water bodies and ground water aquifers, or it is a by-product of the mine dewatering process. Open pit s and underground mining operations commonly extend below the regional water table and require dewatering during mining. In particular, mines intersecting significant ground water aquifers, or those located in wet climates, may have to pump more than 100,000 liters per minute to prevent underground workings from flooding. At some stage of the mining operation, water is unwanted and has no value to the operation. In fact, unwanted or used water needs to be disposed of constantly during mining, mineral processing, and metallurgical extraction .
The oxidative dissolution of sulfidic minerals releases the extremely acidic leachate, sulfate and potentially toxic elements e.g., As, Ag, Cd, Cr, Cu, Hg, Ni, Pb, Sb, Th, U, Zn, etc. from different mine tailings and waste dumps. For the sustainable rehabilitation and disposal of mining waste, the sources and mechanisms of contaminant generation, fate and transport of contaminants should be clearly understood. Therefore, this study has provided a critical review on (1) recent insights in mechanisms of oxidation of sulfidic minerals, (2) environmental contamination by mining waste, and (3) remediation and rehabilitation
techniques, and (4) then developed the GEMTEC conceptual model/guide [(bio)-geochemistry mine type mineralogy- geological texture-ore extraction process-climatic knowledge)] to provide the new scientific approach and knowledge for remediation of mining wastes and acid mine drainage. This study has suggested the pre-mining geological, geochemical, mineralogical and microtextural characterization of different mineral deposits, and post-mining studies of ore extraction processes, physical, geochemical, mineralogical and microbial reactions, natural attenuation and effect of climate change for sustainable rehabilitation of mining waste. All components of this model should be considered for
effective and integrated management of mining waste and acid mine drainage.
An ochreous precipitate isolated from a stream receiving acid-sulphate mine drainage was found to consist primarily of goethite and lesser amounts of ferrihydrite-like materials. The Fe-oxide fraction, including goethite, was almost totally soluble in acid ammonium oxalate. Similar materials were produced in the laboratory by hydrolysis of ferric nitrate solutions containing 250-2000 mu g/ml sulphate as Na2SO4. Initial precipitates of natrojarosite transformed to Fe-oxides upon ageing for 30 days at pH 6.0. The proportion of goethite in the final products decreased with increasing sulphate (SO4/Fe = 0.2-1.8) in the initial hydrolysis solutions; only ferrihydrite-like materials were produced at SO4/Fe ratios >1.5. Variations in SO4/Fe solution ratios also produced systematic changes in the colour (Munsell colour 10 R to 7.5 YR) and surface areas (49-310 m2/g) of the dried precipitates, even though total S contents were relatively constant at 2.5-4.0%. Water quality data and properties of stream precipitate and laboratory specimens (12) are presented.-P.Br.
PHREEQC version 2 is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations.
ABSTRACT,and anatase, but it does not sorb significantly to pure clay minerals or soil organic matter (Fordham and Nor- In order to make sound decisions regarding arsenate contamination rish, 1979, 1983; Jacobs et al., 1970). Arsenate sorption in soil and water environments, it is necessary to have a thorough understanding of the mechanisms of arsenate sorption and desorption,on soils and soil components,vs. pH increases until maxi- over extended periods. The major objectives of this sstudies by Fendorf et al. (1997), Waychunas et al. (1993),
The adsorption of Cu, Pb, Zn, and Cd on goethite (αFeOOH) from NaNO3 solutions and from major ion seawater was compared to assess the effect of the major ions of seawater (Na, Mg, Ca, K, Cl, and SO4) on the adsorption behavior of the metals. Magnesium and sulphate are the principal seawater ions which enhance or inhibit adsorption relative to the inert system. Their effect, as determined from the site-binding model of Davis et al. (1978), was a combination of changing the electrostatic conditions at the interface and decreasing the available binding sites.The basic differences between the experimental system of major ion seawater and natural seawater were examined. It was concluded that: 1) although the experimental metal concentrations in major ion seawater were higher than those found in natural seawater, estimates of the binding energy of Cu, Zn, and Cd with αFeOOH for natural seawater concentrations could be made from the data, 2) Cu, Pb, Zn, and Cd showed little or no competition for surface sites on goethite, and 3) the presence of carbonate, phosphate, and silicate had little or no effect on the adsorption of Zn and Cd on goethite.
Environmental issues have become important, if not critical, factors in the success of proposed mining projects worldwide. In an ongoing and intense public debate about mining and its perceived environmental impacts, the mining industry points out that there are many examples of environmentally responsible mining currently being carried out (e.g., Todd and Struhsacker, 1997). The industry also emphasizes that the majority of mining-environmental problems facing society today are legacies from the past when environmental consequences of mining were poorly understood, not regulated, or viewed as secondary in importance to societal needs for the resources being extracted. On the other hand, environmental organizations (e.g., Mineral Policy Center, 1999) point to recent environmental problems, such as those stemming from open-pit gold mining at Summitville, Colorado, in the late 1980s (see Summitville summaries in Posey et al., 1995; Danielson and Alms, 1995; Williams, 1995; Plumlee, 1999), or those associated with a 1998 tailings dam collapse in Spain (van Geen and Chase, 1998), as an indication that environmental problems (whether accidental or resulting from inappropriate practices) can still occur in modern mining. Recent legislation imposing a moratorium on new mining in Wisconsin, and banning new mining in Montana using cyanide heap-leach extraction methods further underscore the seriousness of the debate and its implications for mineral resource extraction.
In this debate, one certainty exists: there will always be a need for mineral resources in developed and developing societies. Although recycling and substitution will help meet some of the worlds resource needs, mining will always be relied upon to meet the remaining needs. The challenge will be to continue to improve the ways in which mining is done so as to minimize its environmental effects.
The earth, engineering, and life sciences (which we group here under the term “earth-system sciences,” or ESS for short) provide an ample toolkit that can be drawn upon in the quest for environmentally friendly mineral resource development. The papers in this two-part volume provide many details on tools in the scientific toolkit, and how these tools can be used to better understand, anticipate, prevent, mitigate, and remediate the environmental effects of mining and mineral processing.
As with any toolkit, it is the professional’s responsibility to choose the tool(s) best suited to a specific job. By describing the tools now available, we do not mean to imply that all of these tools need even be considered at any given site, nor that
Remedial functions of natural wetland complexes were studied downstream of the old Otravaara pyrite mine in eastern Finland. Surface water samplings was carried ont in three occasions at the beginning of June, August and October in 2000. The pH was measured in the field and in the lab. Concentrations of 30 elements in acidified water filtrates were measured with ICP-AES and MS-ICP. Concentrations of sulphur and metals decreased in the natural wetland complex and finally obtained the background level in the downstream lake. The retention of sulphur and metals begun after the fresh, less acidic water rich in organic matter from the background brooks mixed with the contaminated water derived from the mine area. Organo-Fe precipitates binding most of S and metals in the creek junctions drifted downstream and accumulated in the wetland area. Nevertheless, the pH remained around 3 throughout the wetland complex until to the lake where it raised up to 6. This was due to the hydrolysis of Al that stabilized the pH at the constant value. Results showed that the natural wetland complex is capable of ameliorat waters rich in sulphur and metals, but cannot neutralising the acidity.
The urgent need to provide validated and accredited methods of sample preparation and chemical analysis for environmental mapping and monitoring programmes has become evident. These problems have been addressed at the Geological Survey of Finland by developing specialized analytical procedures for various terrestrial sample materials. The use of ICP-AES is described in this paper. -after Author
A variety of minerals may form as a result of the oxidation of Fe2+ in sulfate-rich mine effluents. The oxidation reaction is bacterially mediated at pH<4.0; however, the mineralization process is extracellular and mineral speciation is controlled by geochemical parameters. The most common mineral associated with acid mine drainage (pH 3.0-4.5) is a poorly crystallized oxyhydroxysulfate of Fe with a structure similar to that of akaganeite (β=FeOOH). Jarosite or natrojarosite may form as ancillary phases at pH<3.0 if [SO2-4] is sufficiently high. Ferrihydrite is produced by rapid hydrolysis of Fe3+ and is the dominant phase at pH >5.0. Goethite occurs as a trace or secondary component in many mine drainage sediments and may be an alteration product of the other mineral phases mentioned. -from Authors
The sorption mechanism of arsenate [As(V)] on schwertmannite was investigated by means of batch sorption experiments as a
function of As(V) concentration in acidic solution at 25 °C. Structural simulation indicated that the surface sites of schwertmannite
comprised various O atom (or hydroxyl) and SO4 groups. Sorption experiments showed that the reactive sites for As(V) sorption are surface-coordinated SO4 groups rather than surface hydroxyl groups, as reported in earlier studies. The As(V) sorption mechanism involves ligand
exchange with surface-adsorbed and structural SO4. The results of the sorption experiments also suggested monodentate As(V) coordination at the surface-adsorbed SO4 sites [(Fe1)2SO4] and bidentate As(V) coordination at the structural SO4 sites [(Fe3)2SO4]. The overall ligand-exchange reaction was
where the 1 and 3 in Fe1 and Fe3 are coordination numbers. The equilibrium constant derived for the exchange reaction, log KEX = 4.96, describes the observed As(V) sorption behavior. Nanocrystalline materials like schwertmannite are widespread in nature
and typically contain significant amounts of anionic impurities, such as sulfate and silicate. Our results indicate that the
effects of impurities can be significant and should be considered in order to gain a realistic understanding of sorption processes
in natural systems.
Mineralogy and geochemistry of a sulfuric acid spring water with a pH of 3.37 to 2.89 were investigated to verify the formation processes of iron minerals and the effects of bacteria on their formation. To estimate the solubility of schwertmannnite, experimental dissolution in 10.0 mM H2SO4 was conducted and this solubility data was used for geochemical modeling. Experimental incubation of the spring water containing bacteria was also performed and compared with a simulated abiotic system to evaluate the role of bacteria in the mineral formation. The spring water seeps through cracks of hydrothermally altered andesitic rocks containing pyrite, and precipitates schwertmannite and jarosite. Schwertmannite appears as a film-like thin layer floating on the water surface and composed of aggregates of spherical particles with diameters of 1 to 5 μm. Jarosite is produced as a precipitate on submerged rock surfaces. The precipitate contains well crystallized jarosite spheres 5 to 10 μm in diameter. Some ellipsoidal to rod shaped bacteria covered or decorated by poorly ordered iron minerals are also present in close association with the schwertmannite spheres. Results of the experimental incubation demonstrate that the oxidation rates of Fe2+ are 5.3 × 103 to 7.2 × 103 times greater than those of the simulated abiotic system, suggesting that the formation of the iron minerals is promoted by bacterial oxidation of Fe2+. The dissolution experiment indicates that the solubility product of the schwertmannite having an average chemical composition of Fe8O8(OH)5.9(SO4)1.05 is approximately log Kx = 7.06 ± 0.09. Using this data, geochemical modeling reveals that the spring water is supersaturated with respect to schwertmannite and also goethite and jarosite, but undersaturated with respect to ferrihydrite. Additionally, it is confirmed that the bulk solution chemistry deviates slightly into the stability field of goethite rather than jarosite. This suggests that the aquatic environments in contact with the rock surfaces may be more acidic and/or enriched in SO24 relative to the bulk solution, which may eventually lead to the formation of jarosite instead of goethite.
The waters from abandoned coal mines and dumps contain high amounts of SO4, Al, Fe, Ca, Mg, and Mn. They are precipitated in the stream bottom as oxides and/or sulfates as brown or whitish flocculated biomats. Three types of biomats, the reddish brown, brownish yellow, and white precipitates, are found in the stream bottom of the Donghae coal mine area in Taebaek, Korea. The biomats consist mainly of ferrihydrite with small amounts of goethite and schwertmannite with minor quartz and clay minerals, and Al-sulfate. The ferrihydrite and schwertmannite were directly precipitated from acid mine drainage (AMD) containing high concentrations of Fe and SO4. Goethite was transformed to ferrihydrite and/or schwertmannite depending on pH values. Many spherical and rod-shaped bacteria were observed from the reddish brown biomats. The brownish yellow biomats are composed mainly of spherical type bacteria of 0.5–5 µm in diameter. The reddish brown and brownish yellow biomats show the characteristic shape of twisted stalks of Gallionella
ferruginea. Energy dispersive X-ray spectrometer (EDS) analysis of Gallionella
ferruginea in the reddish brown and brownish yellow biomats shows Fe>>Si>Ca>Al>P, S and Fe>>Si>S>Al>>P, Ca in concentrations, respectively.
The objective of this study was to examine the mineralogy and geochemical stability of ochreous sediments accumulated in a compost wetland constructed in 1990 for acid mine drainage treatment. Intact sediment cores were collected in 1996 and 2000 from an area that had accumulated 33 cm of ochre. Solids and pore waters were subsequently separated by centrifugation and analyzed using conventional methods, including X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and wet chemical techniques. The solid phase had an average Fe content of 585 g/kg and was predominantly schwertmannite [Fe 8O8(OH)4.8(SO4)1.6] in the upper portion of the sediment column, but transformed to goethite (α-FeOOH) with depth. The rate of transformation was calculated to be 30 mol/m3/yr in the initial 6 yr of sedimentation as compared to 10 mol/m3/yr for the 4-yr period from 1996 to 2000. Pore water composition was affected by this mineral transformation through production of acidity and the release of Fe and SO4. These results demonstrate that the sediment column was not a static environment. In addition, the transformation of schwertmannite to goethite, which has been observed under laboratory conditions, also occurs in natural systems.
Enthalpies of formation of ferrihydrite and schwertmannite were measured by acid solution calorimetry in 5 N HCl at 298 K. The published thermodynamic data for these two phases and ε-Fe2O3 were evaluated, and the best thermodynamic data for the studied compounds were selected.Ferrihydrite is metastable in enthalpy with respect to α-Fe2O3 and liquid water by 11.5 to 14.7 kJ•mol−1 at 298.15 K. The less positive enthalpy corresponds to 6-line ferrihydrite, and the higher one, indicating lesser stability, to 2-line ferrihydrite. In other words, ferrihydrite samples become more stable with increasing crystallinity. The best thermodynamic data set for ferrihydrite of composition Fe(OH)3 was selected by using the measured enthalpies and (1) requiring ferrihydrite to be metastable with respect to fine-grained lepidocrocite; (2) requiring ferrihydrite to have entropy higher than the entropy of hypothetical, well-crystalline Fe(OH)3; and (3) considering published estimates of solubility products of ferrihydrite. The ΔG°f for 2-line ferrihydrite is best described by a range of −708.5±2.0 to −705.2±2.0 kJ•mol−1, and ΔG°f for 6-line ferrihydrite by −711.0±2.0 to −708.5±2.0 kJ•mol−1.A published enthalpy measurement by acid calorimetry of ε-Fe2O3 was re-evaluated, arriving at ΔH°f (ε-Fe2O3) = −798.0±6.6 kJ•mol−1. The standard entropy (S°) of ε-Fe2O3 was considered to be equal to S° (γ-Fe2O3) (93.0±0.2 J•K−1•mol−1), giving ΔG°f (ε-Fe2O3) = −717.8±6.6 kJ•mol−1. ε-Fe2O3 thus appears to have no stability field, and it is metastable with respect to most phases in the Fe2O3-H2O system which is probably the reason why this phase is rare in nature.Enthalpies of formation of two schwertmannite samples are: ΔH°f (FeO(OH)0.686(SO4)0.157•0.972H2O) = −884.0±1.3 kJ•mol−1, ΔH°f (FeO(OH)0.664(SO4)0.168•1.226H2O) = −960.7±1.2 kJ•mol−1. When combined with an entropy estimate, these data give Gibbs free energies of formation of −761.3 ± 1.3 and −823.3 ± 1.2 kJ•mol−1 for the two samples, respectively. These ΔGf° values imply that schwertmannite is thermodynamically favored over ferrihydrite over a wide range of pH (2–8) when the system contains even small concentration of sulfate. The stability relations of the two investigated samples can be replicated by schwertmannite of the “ideal” composition FeO(OH)3/4(SO4)1/8 with ΔG°f = −518.0±2.0 kJ•mol−1.
The adsorption-desorption of the divalent metal cations (Me[sup 2+]) Co[sup 2+], Cd[sup 2+], and Pb[sup 2+] to hydrous ferric oxide (HFO) was investigated as a function of oxide aging and Me[sup 2+]-oxide residence time. The HFO was produced and stored for up to 86 wk. Periodically, Me[sup 2+] sorption was determined across the pH range of 2.5 to 12. In addition, the Me[sup 2+] ions were contacted with freshly produced HFO and stored at a pH that dictated that 80 to 100% of the Me[sup 2+] would be in the sorbed state; desorbability of the Me[sup 2+] was determined as a function of Me[sup 2+]-oxide residence time. The change in the crystallinity of the HFO as a function of time was also monitored. The HFO aged without the Me[sup 2+] ions displayed no hysteresis between the adsorption-desorption curves and no substantial shifts in fractional Me[sup 2+] adsorption were observed with pH throughout 21 wk of aging. The HFO aged with the Me[sup 2+] ions displayed increasing desorption hysteresis with time for Co[sup 2+] and Cd[sup 2+], but not Pb[sup 2+]. The magnitude of hysteresis followed the order Co > Cd > Pb, which is the inverse of the ionic radii of the metal sorbates. While oxalate-extractable Fe decreased with time during a 20-wk period, powder x-ray diffraction was unchanged during the same period. 38 refs., 11 figs., 2 tabs.
Headspace P{sub CO{sub 2}} was measured with an infrared gas analyzer over an equilibrated goethite suspension to determine adsorption of carbonate species in the pH range 3 to 8. For a 2 g/L goethite suspension in 0.1 N NaClO{sub 4} ({approximately} 3 10{sup {minus}4} M surface sites), the fraction of carbonate species adsorbed increased from 0.15 at pH 3 to a maximum of 0.56 at pH 6. In 0.01 N NaClO{sub 4}, the fraction of carbonate species adsorbed at pH 6 increased to 0.67. The total concentration of CO{sub 2} in the suspension increased from about 0.4 to 0.6 10{sup {minus}4} M in the pH range of these experiments. The development of surface charge at the goethite surface was determined in the pH range 4 to 11 by potentiometric titration under controlled low CO{sub 2} conditions. No hysteresis was observed between the acid and base legs of titrations in 0.10, 0.03, and 0.01 N NaClO{sub 4} resulting in a pH{sub pzc} of 8.9. The carbonate species adsorption data were modelled using the least squares optimization program FITEQL for the diffuse double-layer model and the triple-layer model using stoichiometries of the type Fe-OCOOH and Fe-OCOO{sup {minus}} for surface bound carbonate species. The model results are consistent with separate experiments showing a significant reduction in chromate adsorption on goethite as the partial pressure of CO{sub 2} was increased from <5 to 450 and 40,000 {mu}atm. The data suggest that mineral oxide surface sites which control solid/solute partitioning of metal ions in natural systems may be largely bound to adsorbed carbonate species.
Infrared analysis showed that the bonding habit of oxyanions with freshly precipitated hydrous ferric oxides depends upon the nature of the anion and its hydration level. Monovalent oxyanions adsorb through an electrostatic interaction with the hydrated hydrous oxide surface. All divalent oxyanions, with the exception of tellurate, coordinate directly with surface iron cations. Tellurate, an octahedral anion, apparently penetrates and incorporates in the hydrous oxide structure. The symmetry of the free anion has a significant role in determining the configuration of the resultant complex. For anions of the same charge, those with tetrahedral geometry (in uncoordinated states) show a higher degree of specificity for the surface than the trigonal planer anions. Without exception, each bidentate bridging complex forms by replacement of protonated and unprotonated hydroxyls. With the anion geometry and the charge being equal, the sus- pension pH determines the adsorption capacity of the hydrous oxide.
The surface charge of colloidal particles is usually determined by potentiometric titration. These acid-base titrations make it possible to measure the pH of point-of-zero charge (pzc) for oxide minerals. This macroscopic property is the most important parameter used in surface complexation modeling to reproduce experimental data. The pzc values of goethite reported in the literature vary between 7.0 and 9.5. Carbonate adsorption and/or surface morphology are thought to account for this wide range.
Schwertmannite precipitated from acid mine drainage at the Kristineberg Zn-Cu mine in northern Sweden has been characterised regarding elemental composition, phase transformation as a function of pH and time. SO42- release and speciation of SO42- associated with the solid. The elemental analysis gave the composition FeSOS(OH)(5.02)(-SO4)(1.49) . 0.5H(2)O where approximately 1/3 of the SO42- is adsorbed to the surface. The conversion of schwertmannite to goethite at pH 9 was complete within 187 days; at pH 6. the conversion was still incomplete after 514 days. Lower pH and relatively high SO42- concentration decreased the conversion even further. Also temperature was shown to be an important parameter for this process and low temperature (+4 degreesC) effectively stopped the transformation at pH 3. The release of SO42- was linear with pH and X-ray photoelectron spectroscopy measurements confirming that the surface bound SO42- was released before bulk SO42-. Zeta potential measurements indicate a pH(IEP) of 7.2 for the schwertmannite sample. Prior to conversion into goethite, the SO42- associated with schwertmannite was indicated by attenuated total reflectance FTIR spectroscopy to be present both as bulk and surface species. Furthermore: the speciation of surface SO42- was shown to vary with pH and two predominating species were detected. As pH increases. SO42- is increasingly Coordinated in an outer sphere mode whereas a stronger. possibly inner sphere, complex dominates. at low pH. (C) 2004 Elsevier Ltd. All rights reserved.
The point of zero charge (pzc) of synthetic Fe-oxides is well documented and usually ranges between pH 7 and 9 (Parks, 1965; Schwertmann & Taylor, 1977). In contrast, the pzc of natural Fe-oxides has only rarely been determined. Using electrophoretic mobility, Van Schuylenborgh & Arens (1950) found that a natural goethite had a much lower pzc (∼3) than synthetic goethites. They attributed this to better crystallinity of the natural goethite caused by slower crystallization. Soils dominated by Fe- (or Al-) oxides rarely have pzc values as high as those of pure oxides. This is usually attributed to the presence of negatively charged impurities such as clay silicates and organic matter (Parfitt, 1981).
Ferrihydrite, a natural, poorly-crystalline Fe-oxide mineral of bulk composition 5Fe 2 O 3 .9H 2 O, occurs in hydromorphic soils (Schwertmann et al. , 1982) and is the main component in ochrous precipitates formed when Fe-bearing fresh waters come in contact with air (Schwertmann & Fischer, 1973; Carlson & Schwertmann, 1981). Under these conditions the ferrihydrite is reasonably free of other charge-active minerals. The aim of this study was to find out if the pzc of these natural ferrihydrites differed from those of synthetic samples.
Schwertmannite (ideal formula: Fe8O8(OH)6SO4) is typically found as a secondary iron mineral in pyrite oxidizing environments. In this study, geochemical constraints upon its formation are established and its role in the geochemical cycling of iron between reducing and oxidizing conditions are discussed. The composition of surface waters was analyzed and sediments characterized by X-ray diffraction, FTIR spectroscopy and determination of the Fe:S ratio in the oxalate extractable fraction from 18 acidic mining lakes. The lakes are exposed to a permanent supply of pyritegenous ferrous iron from adjacent ground water. In 3 of the lakes the suspended matter was fractionated using ultra filtration and analyzed with respect to their mineral composition. In addition, stability experiments with synthetic schwertmannite were performed. The examined lake surface waters were O2-saturated and have sulfate concentrations (10.3 ± 5.5 mM) and pH values (3.0 ± 0.6) that are characteristic for the stability window of schwertmannite. Geochemical modeling implied that i) the waters were saturated with respect to schwertmannite, which controlled the activity of Fe3+ and sulfate, and ii) a redox equilibrium exists between Fe2+ and schwertmannite. In the uppermost sediment layers (1 to 5 cm depth), schwertmannite was detectable in 16 lakes—in 5 of them by all three methods. FTIR spectroscopy also proved its occurrence in the colloidal fraction (1–10 kDa) in all of the 3 investigated lake surface waters. The stability of synthetic schwertmannite was examined as a function of pH (2–7) by a 1-yr experiment. The transformation rate into goethite increased with increasing pH. Our study suggests that schwertmannite is the first mineral formed after oxidation and hydrolysis of a slightly acidic (pH 5–6), Fe(II)-SO4 solution, a process that directly affects the pH of the receiving water. Its occurrence is transient and restricted to environments, such as acidic mining lakes, where the coordination chemistry of Fe3+ is controlled by the competition between sulfate and hydroxy ions (i.e. mildly acidic).
Synthetic goethite prepared under highly alkaline conditions incorporates Co 3+ , Ni 2+ , Cu 2+ , Zn 2+ , Cd 2+ , and Pb 4+ into its structure by isomorphous substitution. Systematic changes of the unit-cell b -dimension with increasing substitution can be related to the ionic radii of incorporated metals. The octahedra of the goethite structure become distorted along the crystallographic a -axis by an incorporation of Cu 2+ (Jahn-Teller-effect), Zn 2+ , and Cd 2+ . For Zn- and Cd-goethite, the distortion along a can be explained by a smaller ionic size which both foreign metals exhibit in tetrahedral coordination. Thorium is postulated to be incorporated by non-structural incorporation while U is not incorporated. Non-substituted as well as Co-, Ni-, Cd-, and Pb-goethites can have a slightly variable a -dimension depending on the temperature during crystal formation. A higher a -dimension is believed to be the result of structural defects and does not indicate a separate mineral phase.
Schwertmannite precipitated from acid mine drainage at the Kristineberg Zn–Cu mine in northern Sweden has been characterised regarding elemental composition, phase transformation as a function of pH and time, SO42- release and speciation of SO42- associated with the solid. The elemental analysis gave the composition Fe8O8(OH)5.02(SO4)1.49·0.5H2O where approximately 1/3 of the SO42- is adsorbed to the surface. The conversion of schwertmannite to goethite at pH 9 was complete within 187 days; at pH 6, the conversion was still incomplete after 514 days. Lower pH and relatively high SO42- concentration decreased the conversion even further. Also temperature was shown to be an important parameter for this process and low temperature (+4 °C) effectively stopped the transformation at pH 3. The release of SO42- was linear with pH and X-ray photoelectron spectroscopy measurements confirming that the surface bound SO42- was released before bulk SO42-. Zeta potential measurements indicate a pHIEP of 7.2 for the schwertmannite sample. Prior to conversion into goethite, the SO42- associated with schwertmannite was indicated by attenuated total reflectance FTIR spectroscopy to be present both as bulk and surface species. Furthermore, the speciation of surface SO42- was shown to vary with pH and two predominating species were detected. As pH increases, SO42- is increasingly coordinated in an outer sphere mode whereas a stronger, possibly inner sphere, complex dominates at low pH.
The use of adsorption data from single sorbate systems to model metal adsorption in SO4-rich waters, such as acid mine drainage, can lead to inaccurate predictions of metal speciation. The adsorption of Cu and Zn on ferrihydrite, for example, is enhanced at low pH values in the presence of SO4. This effect can only be accurately modeled using the diffuse layer model and surface complexation theory if ternary surface complexes, ≡FeOHCuSO4 or ≡FeOHZnSO4, are taken into consideration. Intrinsic adsorption constants for the formation of these ternary complexes on ferrihydrite have been derived from experimental data. When included in the model, Cu and Zn adsorption in the presence of SO4 is accurately predicted for a wide range of metal, ferrihydrite and SO4 concentrations. Adsorption of Cu and Zn onto the SO4-rich Fe oxyhydroxide, schwertmannite, could also be accurately predicted and is indistinguishable from adsorption onto ferrihydrite in the presence of high solution SO4 concentrations (e.g. 0.01 mol kg−1 SO4).
A dissolution test with 9 natural and synthetic schwertmannite and ferrihydrite samples was performed by reaction with 0.2 M ammonium oxalate at pH 3.0 in the dark. The method was coupled with differential X-ray diffraction (DXRD) to successfully detect schwertmannite at low concentrations in oxidized mine tailings. Rapid dissolution was observed for all schwertmannites (> 94% in 60 min) and natural 2-line ferrihydrites (> 85% in 60 min); however, synthetic 2-line and 6-line ferrihydrite dissolved slower (42 and 16% after 60 min, respectively). The results showed that it was not possible to distinguish between natural schwertmannites and ferrihydrites on the basis of their dissolution kinetics. Modeling of the schwertmannite dissolution curves, examinations of mineral shape by scanning electron microscopy, and Fe/S mole ratios of the dissolved fractions indicated that two different schwertmannite particle morphologies (spherical and web-like) occurred. Collapse of spherical (sea-urchin) schwertmannite aggregates seemed to control the dissolution kinetics according to a shrinking core model. In the case of web-like schwertmannite, dissolution could be modeled with a simple first order equation, and structural SO42− may have affected the dissolution kinetics. No relationship was found between ferrihydrite particle shape and dissolution behavior in acid NH4-oxalate. A 1-h extraction with 0.2 M NH4-oxalate at pH 3.0 in the dark should be adequate to dissolve schwertmannite and natural 2-line ferrihydrite in most samples. In some cases, a fraction of secondary jarosite or goethite may also be dissolved, although at a slower rate. If only schwertmannite is of interest (e.g., determination by DXRD), a 15 min attack should be used to increase selectivity. A truly selective leach of schwertmannite and ferrihydrite should be based on dissolution tests, as a broad variety of dissolution kinetics can be observed in this mineral group.
Solutions draining the Alta Mine, Jefferson County, MT, were contaminated by acid sulfate waters (ASW) generated from anthropogenic exposure of meteoric waters to sulfidic underground mine workings and a waste-rock pile. In 1999, a remediation effort was initiated in an attempt to improve the quality of water draining the site through removal of the waste-rock pile with which these solutions come in contact. ASW were sampled in the mineshaft prior to entering the waste-rock pile and upon discharge from the waste-rock pile aquifer near the pile toe. ASW composition changed as solutions flowed through the waste-rock pile due to sulfide and silicate weathering and schwertmannite precipitation.Schwertmannite and goethite were both sampled in the waste-rock pile where a distinct field relation was observed between the two minerals. Schwertmannite was always in contact with actively flowing ASW, while goethite was never in direct contact with ASW and was generally above the waste-rock water table. Goethite is hypothesized to be re-dissolved/re-precipitated schwertmannite that was deposited under higher flow conditions and subsequently transformed to goethite through exposure to wet/dry cycling associated with seasonal fluctuations in the amount of water moving through the hydrogeologic system. Trace metal concentrations in ammonium oxalate extracts of these minerals provides the first published data on the behavior of multiple trace metals through this phase transformation, which has important ramifications for considering schwertmannite as a long term metal sink due to its known metastability with respect to goethite. A relative retention scale through this phase transformation of Pb>Zn, Mn>As, Al, Cu is potentially applicable to other ASW systems.
Rusty ferruginous precipitates deposited from soil-borne waters (in drainage ditches, from springs) at various localities, contain a ferric hydroxide rich in carbon and adsorbed water. It has up to 75% dithionite soluble Fe2O3, of which between 90 and 100% is oxalate soluble IR spectrograms do not show Fe-OH features in the OH stretching and bending range. X-ray diffraction reveals very broad lines at about 2.5 and 1.5 Å and somewhat sharper lines at 2.22, 1.97 and 1.71 Å, which are characteristic of ferrihydrite (name proposed by Chukhrov et al., 1972). These deposits are found in areas where water has percolated through acid soils rich in low molecular weight organic compounds. Furthermore, as similar material could be prepared in the laboratory by bacterial or H2O2 oxidation of ferric citrate solutions, it was concluded that the natural substance is formed by microbial decomposition of soluble iron—organic complexes. Transformation experiments suggest that aging under conditions corresponding to a humid temperate climate causes conversion to goethite. This aging process is greatly retarded by organic and other compounds retained by the hydroxide. No evidence of hematite formation could be found after 2 weeks at 70°C.
The Ylojarvi Cu-W deposit in southwest Finland is located at the western end of the Svecokarelidic Tampere schist zone, which consists of argillaceous sediments and vol-canics. The deposit was mined from 1942 to 1966. During that time a total of 4,013,500 tons of ore were hoisted, from which 128,343 tons of copper concentrate, 894 tons of scheelite concentrate, and 2,100 tons of arsenopyrite concentrate were produced. The mineralized rock is confined to a tourmaline breccia close to the Hameenkyro granodiorite, both some 1,850 m.y. in age. The breccia fragments, which are tuffite and porphyrite, are enveloped by a quartzose alteration seam about 1 cm thick. The matrix is composed of tourmaline with variable amounts of chalcopyrite, arsenopyrite, pyrrho-tite, scheelite, and some accessory ore minerals.
In natural systems iron oxides and hydroxides are frequently associated with a variety of cations which may adsorb on the mineral surfaces or replace a proportion of Fe in the oxide structure. A number of laboratory studies have established that foreign cations can influence the kinetics of iron oxide formation and determine the nature of the end-product. These studies have provided further details of the mechanisms by which iron oxides form. The present report compares the effects of a series of divalent metal ions on the kinetics and products of the transformation of ferrihydrite (5Fe2O3.9H2O) to more crystalline minerals. The ions investigated, Mn2+, Cu2+, Ni2+, Co2+ and Zn2+, have been found in association with iron oxides in soils, sediments and, in some cases, in ferromanganese nodules. -Author
The dilution factors (Di) and removal fractions (Ri) of pollutants from acid mine drainage (AMD) were quantitatively estimated using two different methods, the conservative component and mass balance method, along Imgok Creek in Korea. The conservative component method assumes that SO4 is a perfectly conservative component and calculates Di and Ri from the concentration ratios of SO4. The mass balance method solves the simultaneous equations relating the concentrations of dissolved components to their precipitation stoichiometries to obtain Di and Ri. The results from both methods are little different, indicating that SO4 concentration is a good indicator of dilution for Imgok creek. The calculated Di's of pollutants quickly decrease from the site of AMD input to the site a few km downstream, but then remain more or less constant over the reaches farther downstream. This is because Di loses its sensitivity in the reaches where difference in SO4 concentration between the main stream and combining tributaries significantly diminishes. The calculated Ri's show that approximately 90, 95, and 75% of the original Fe input were removed from the streamwater in October 1996, April 1997, and October 1997, respectively. Aluminum was almost completely removed in April 1997, but only 50% of the original Al was removed in October 1997. The removal of Fe was due to the precipitation of schwertmannite or ferrihydrite and Al due to amorphous Al4(OH)10SO4. The maximum removal fraction of dissolved SO4 was only 5%. The other metals from AMD were significantly removed from the stream water only in April 1997. These metals were removed not by precipitation but by adsorption on and/or coprecipitation with Fe/Al-compounds. The relatively abundant freshwater supply in April 1997 might raise stream pH higher than the adsorption edge and consequently, contribute to rapid metal attenuation by forcing not only more precipitation but also more adsorption of the dissolved metals.
An ochreous precipitate isolated from a stream receiving acid-sulfate mine drainage was found to consist primarily of goethite and lesser amounts of ferrihydrite-like materials. The Fe-oxide fraction, including goethite, was almost totally soluble in acid ammonium oxalate. Similar materials were produced in the laboratory by hydrolysis of ferric nitrate solutions containing 250 to 2000 μ g/ml sulfate as Na 2 SO 4 . Initial precipitates of natrojarosite transformed to Fe-oxides upon aging for 30 days at pH 6.0. The proportion of goethite in the final products decreased with increasing sulfate (SO 4 /Fe = 0.2 to 1.8) in the initial hydrolysis solutions; only ferrihydrite-like materials were produced at SO 4 /Fe ratios > 1.5. Variations in SO 4 /Fe solution ratios also produced systematic changes in the color (10R to 7.5YR) and surface areas (49 to 310 m ² /g) of the dried precipitates, even though total S contents were relatively constant at 2.5 to 4.0%.
Storage of ferrihydrite in aqueous suspensions at 24oC and pHs between 2.5 and 12 for as long as three years resulted in the formation of goethite and hematite. The proportions and crystallinity of these products varied widely with the pH. Maximum hematite was formed between pH 7 and 8, and maximum goethite at pH 4 and at pH 12. We relate the proportions of goethite and hematite to the activity of the Fe(III) ion species in solution; conditions favorable for the formation of goethite are unfavorable for that of hematite and vice versa. -from Authors
Schwertmannite is a new oxyhydroxysulphate of iron from the Pyhasalmi sulphide mine, Province of Oulu, Finland. It occurs there, and elsewhere, as an ochreous precipitate from acid, sulphate-rich waters. Associated minerals at other localities may include jarosite, natrojarosite, goethite and ferrihydrite. Schwertmannite is a poorly crystalline, yellowish brown mineral with a fibrous morphology under the electron microscope. A high specific surface area in the range of 100 to 200 m2/g, rapid dissolution in cold, 5 M HCl or in ammonium oxalate at pH 3, and pronounced X-ray diffraction line broadening are consistent with its poorly crystalline character.
The unit-cell dimensions of synthetic, Al-substituted goethites showed that the c dimension is a linear function of A1 substitution in the range 0-33 mole % A1, but that the a dimension is variable over this same range. The b dimension is also linearly related to Al substitution but is slightly more variable than the c dimension for A1 substitutions of 20-33 mole %. The variability of the a dimension is postulated to be the result of structural defects. An improved procedure for estimating Al substitution from x-ray powder diffraction positions requires (1) calculation of the c dimension from the positions of the 1 l0 and 111 diffraction lines using the formula: c = (l/d(11 l) 2 - l/d(110)2) -'h, and (2) estimation of A1 substitution from the relationship: mole % A1 = 1730 - 572.0c. The 95% confidence interval of the estimate is +2.6 mole % A1 when using this procedure, in contrast to _+4.0 mole % A1 when the position of the 111 reflection alone is used.
Many sediment and soil systems have become significantly contaminated with cadmium, and earth scientists are now required to make increasingly accurate predictions of the risks that this contamination poses. This necessitates an improved understanding of the processes that control the mobility and bioavailability of cadmium in the environment. With this in mind, we have studied the composition and structure of aqueous cadmium sorption complexes on the iron oxyhydroxide minerals goethite (α-FeOOH), lepidocrocite (γ-FeOOH), akaganeite (β-FeOOH), and schwertmannite (Fe8O8(OH)6SO4) using extended X-ray adsorption fine structure spectroscopy. The results show that adsorption to all of the studied minerals occurs via inner sphere adsorption over a wide range of pH and cadmium concentrations. The bonding mechanism varies between minerals and appears to be governed by the availability of different types of adsorption site at the mineral surface. The geometry and relative stability of cadmium adsorption complexes on the goethite surface was predicted with ab initio quantum mechanical modelling. The modelling results, used in combination with the extended X-ray adsorption fine structure data, allow an unambiguous determination of the mechanism by which cadmium bonds to goethite.
A geochemical soil survey in the vicinity of the known ore body at Lontzen (Belgium) revealed numerous lead and/or zinc anomalies. Three soil traverses were selected in this area and examined for possible contamination. Two anomalous samples from one traverse were obviously contaminated (brick fragments). A sequential selective extraction procedure was applied to the soil samples, using a modification of the method of Gatehouse et al.Using this procedure, lead anomalies related to the probable extension of a known galena-sphalerite vein appear in every dissolution step. In contrast, in contaminated samples, only the final acid digestion produced anomalous values. One may thus suppose that contamination of the sample adds metal in the form of a resistant phase which is only dissolved by strong acid reagents. It should be noted that the contrast between anomalous and background values is highest for hydroxylamine hydrochloride and about the same for all other dissolution steps.The samples were also submitted to non-sequential selective extractions. The calculation of the difference between non-sequential and sequential extractions leads to the localization of two highly contrasted peaks which correspond exactly with the ore veins.
Compositional zoning in iron oxyhydroxides precipitated from mine drainage-contaminated groundwater was studied by electron microprobe (EMP) analysis. The observed zoning is characterized by variations in Al, Fe, S, and Si concentrations, with mean precipitate concentrations of ca. 56.0 wt.% Fe, 1.1 wt.% Al, 2.0 wt.% Si, and 0.5 wt.% S. The analyses indicate an inverse relationship between Al-Si concentrations and Fe-S concentrations in the Fe oxyhydroxides. The results and groundwater data from the field site suggest that the origin of compositional zoning in the Fe oxyhydroxides is controlled by both surface complexation reactions involving Al3+ and H4SiO4, which affect goethite formation kinetics, and the Al/Fe and Si/Fe molar ratios in solution.
High concentrations of Cr (up to 812 ppm) and As (up to 6740 ppm) were detected in precipitates of the mineral schwertmannite in areas influenced by acid mine drainage. Schwertmannite may act as well as a natural filter for these elements in water as well as their source by releasing the previously bound elements during its dissolution or mineral-transformation. The mechanisms of uptake and potential release for the species arsenate and chromate were investigated by performing synthesis and stability experiments with schwertmannite.
The adsorption properties of Fe-rich precipitates in acid mine drainage (AMD) systems differ from those of pure hydrous iron(III) oxides, and this can lead to inaccurate predictions of trace metal adsorption and attenuation. Adsorption edges for Cu, Pb, Zn and Cd adsorption onto a poorly ordered, goethite-bearing iron(III) oxy hydroxy sulfate, precipitated in an AMD system in New Zealand, have been compared to those for adsorption onto synthetic schwertmannite and two-line ferrihydrite. Adsorp tion of Cu and Zn onto the AMD iron(III) oxy hydroxy sulfate was greater than onto synthetic schwertmannite, which was in turn greater than onto two-line ferrihydrite. The two factors considered most likely to enhance Cu and Zn adsorption on the AMD iron(III) oxy hydroxy sulfate were (i) the formation of ternary complexes between the oxide surface, adsorbed SO4 and the metal ion and (ii) bacterially mediated formation of the AMD precipitate. Cd adsorption was similarly enhanced on AMD iron(III) oxy hydroxy sulfate but unaffected by SO4, which did not adsorb at the relatively high pH conditions required for Cd adsorption. Although Pb did appear to form ternary complexes with SO4, Pb adsorption onto both AMD iron(III) oxy hydroxy sulfate and synthetic schwertmannite was less than adsorption onto two-line ferrihydrite.
The fate and transport of metal ions in soils and sediments may be controlled by sorption to the metastable iron (hydr)oxide, ferrihydrite. The reversibility of metal partitioning to ferrihydrite can be significantly influenced by its transformation to more thermodynamically stable structures such as goethite or hematite. We studied changes in metal partitioning during aging of coprecipitates of ferrihydrite containing Cd(II), Mn(II), Ni(II), or Pb(II) at pH 6 and tem peratures of 40 or 70 °C and as a function of metal surface loading. Aqueous metal concentrations as well as the fraction extracted by 0.2 M ammonium oxalate were continuously monitored. At the end of aging, solids were characterized by thermogravimetric analysis and X-ray diffraction. Prior to aging, the extent of metal sorption decreased in the order Pb(II) >> Ni(II) > Mn(II) Cd(II). However, with ferrihydrite transformation, the extent of sorption increased and apparent sorption reversibility decreased significantly for Mn(II) and Ni(II). Both Pb(II) and Cd(II) demonstrated net desorption with aging, and sorption reversibility remained essentially unchanged. These differ ences in metal behavior are consistent with structural incorporation of Mn(II) and Ni(II) into the goethite or hematite structure and minimal incorporation of Cd(II) and Pb(II) within these crystalline products at pH 6.
The apparent solubilities of schwertmannite and ferrihydrite were estimated from the H+, OH−, Fe3+, and SO42− activities of the natural stream waters in Korea and mine drainage in Ohio, USA. Both chemical composition of the stream waters and the mineralogy of the precipitates were determined for samples from two streams polluted by coal mine drainage. This study combines these new results with previous data from Ohio, USA to redetermine solubilities. The activities of the dissolved species necessary for the solubility determinations were calculated from the chemical compositions of the waters with the WATEQ4F computer code.Laboratory analyses of precipitates indicated that the main minerals present in Imgok and Osheep creek were schwertmannite and ferrihydrite, respectively. The schwertmannite from Imgok creek had a variable chemical formula of Fe8O8(OH)8−2x(SO4)x· nH2O, where 1.74 ≤ x ≤ 1.86 and 8.17 ≤ n ≤ 8.62. The chemical formula of ferrihydrite was Fe2O3· 1.6H2O. With known mineralogy of the precipitates from each stream, the activities of H+, OH−, Fe3+, and SO42− in the waters were plotted on logarithmic activity-activity diagrams to determine apparent solubilities of schwertmannite and ferrihydrite. The best estimate for the logarithm of the solubility product of schwertmannite, logKs, was 10.5 ± 2.5 around 15°C. This value of logKs constrains the logarithm of the solubility product of ferrihydrite, logKf, to be 4.3 ± 0.5 to maintain the stability boundary with schwertmannite observed in natural waters.
Young ochreous precipitations from Fe-bearing spring waters in Finland consist mainly of ferrihydrite. a poorly ordered Fe-oxide with a layer structure and the bulk composition 5 Fe2O3 ·9 H2O Crystallinity ranges from a reasonably well developed structure to a highly disordered one with only two prismatic reflections at 2.5 and 1.5 Å. In contrast to other Fe-oxides. ferrihydrite is highly soluble in oxalate. Electron microscopy shows spherical particles 2–5 nm in diameter forming aggregates of 100–300 nm. The specific surface ranges from 220 to 560 m2/g. During their formation, the ferrihydrites adsorb large quantities of silica, part of which is unpolymerized as indicated by Si-O-Fe bonds (i.r.), and part of which is polymerized. NaOH preferentially extracts polymerized silica causing a shift in the i.r. absorption band. Silica also causes a shift in the temperature at which ferrihydrite converts to hematite. ‘Hydrous Fe(III)-oxides’ with 0–15mol% Si prepared from Si containing Fe(III) salt solutions showed similar properties: Si-O-Fe bonds are shown by i.r. and increasing temperatures of transformation to hematite with increasing amount of Si. Adsorbed Si may also retard the transformation of ferrihydrite to the more stable goethite in nature.
Analyses of ochreous sediments and associated solutions from twenty-eight mine drainage sites showed that precipitates formed at pH 6.5 or higher were composed of ferrihydrite (nominally Fe5HO8 · 4H2O) or a mixture of ferrihydrite and goethite (α-FeOOH), whereas those precipitated from waters having pH values in the range of 2.8 to 4.5 were predominantly schwertmannite (ideally Fe8O8(OH)6SO4) with trace to minor amounts of goethite. Solutions of intermediate pH values produced mixtures of ferrihydrite and schwertmannite. Only one sample, formed at pH 2.6, contained a significant amount of jarosite (H, K, Na)Fe3(OH)6(SO4)2. A solubility window of log IAPSh = 18.0 ± 2.5 was calculated for schwertmannite from selected mine drainage solutions with pH values in the range of 2.8 to 3.2. The relationship between pH and log αFe3 over the full range of drainage waters was consistent with published results from other sources, and the combined mineralogy-chemistry data were used to compute a new pe-pH diagram for the system FeSKOH that included a field of metastability for schwertmannite. The metastable nature of schwertmannite was confirmed in a long-term (1739 d) aqueous equilibrium study wherein a pure, synthetic specimen was completely transformed to goethite over a period of 543 days. The pH and computed activity of Fe 3+ in the final equilibrium solutions yielded a log KGT = 1.40 ± 0.01 for goethite. Additional field data supporting a paragenetic relationship between jarosite, schwertmannite, ferrihydrite, and goethite were obtained from a naturally acid alpine stream. Similar results were predicted from the water chemistry using a nonequilibrium reaction path model that included appropriate solubility data for the mineral phases of interest.
At the abandoned As mine in Nishinomaki, Japan, discharged water from the mining and waste dump area is acidic and rich in As. However, the As concentration in the drainage has been decreased to below the maximum contaminant level (0.01 mg/l for drinking water, Japan) without any artificial treatments before mixing with a tributary to populated areas. This implies that the As concentration in water from the waste dump area has been naturally attenuated. To elucidate the reaction mechanisms of the natural attenuation, analysis of water quality and characterization of the precipitates from the stream floor were performed by measuring pH, ORP and electric conductivity on-site, as well as X-ray diffraction, ICP-mass spectrometry and ion-chromatography. Selective extractions and mineral alteration experiments were also conducted to estimate the distribution of As in constituent phases of the precipitates and to understand the stability of As-bearing phases, respectively. The water contamination resulted from oxidation of sulfide minerals in the waste rocks, i.e., the oxidation of pyrite and realgar and subsequent release of Fe, SO4, As(V) and proton. The released Fe(II) transformed to Fe(III) by bacterial oxidation; schwertmannite then formed immediately. While the As concentrations in the stream were lowered nearly to background level downstream, those in the ochreous precipitates were up to several tens of mg/g. The As(V) was effectively removed by the formed schwertmannite and had been naturally attenuated. Although schwertmannite is metastable with respect to goethite, the experiments show that the transformation of schwertmannite to goethite may be retarded by the presence of absorbed As(V) in the structure. Therefore, the attenuation of As in the drainage and the retention of As by schwertmannite are expected to be maintained for the long term.
A poorly crystallized oxyhydroxysulfate of Fe has been identified as the primary component of ochreous precipitates from sulfate-rich mine waters having pH values in the range of 2.5 to 4.0. The compound is characterized by rapid dissolution in acid (pH 3.0) ammonium oxalate, an Fe/S mole ratio ranging from 5 to 8, a high specific surface area (175–225 m2/g), a yellowish brown (9.0–10.0YR) color, a fibrous morphology, and a broad, 8-line X-ray diffraction profile. Analyses of synthetic analogs prepared by hydrolysis of 0.02 M FeCl3 solutions containing up to 2000 μ/mL SO4 show the material to have a tunnel structure akin to that of akaganéite (β-FeOOH). Sulfate occurs both as a bridging element between Fe atoms lining adjacent walls of the tunnels and as a specifically adsorbed surface component. Extraction of the tunnel SO4 destabilizes the structure and causes the compound to transform to goethite (α-FeOOH) under ambient conditions. Mössbauer spectra taken at 4.2 K yield hyperfine fields lower than those of even the most poorly crystallized iron oxides, indicating that SO4 inhibits magnetic ordering. A tetragonal unit cell with a0 = 1.065 and c0 = 0.604 nm is proposed to describe the structure. The corresponding unit cell formula is Fe16O16(OH)12(SO4)2 but may range to Fe16O16(OH)10(SO4)3 depending upon the degree of saturation of the tunnel and surface sites with SO4. Because of its abundance and high surface reactivity, this compound should play an important role in regulating the solubilities of both major and trace elements in surface waters impacted by acid mine drainage.