Article

A Novel Bioreactor System for Simultaneous Mutli-Metal Leaching from Industrial Pyrite Ash: Effect of Agitation and Sulphur Dosage

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Abstract

Simultaneous multi-metal leaching from industrial pyrite ash is reported for the first time using a novel bioreactor system that allows natural diffusion of atmospheric O2 and CO2 along with the required temperature maintenance. The waste containing economically important metals (Cu, Co, Zn & As) was leached using an adapted consortium of meso-acidophilic Fe(2+) and S oxidising bacteria. The unique property of the sample supported adequate growth and activity of the acidophiles, thereby, driving the (bio) chemical reactions. Oxido-reductive potentials were seen to improve with time and the system's pH lowered as a result of active S oxidation. Increase in sulphur dosage (>1g/L) and agitation speed (>150rpm) did not bear any significant effect on metal dissolution. The consortium was able to leach 94.01% Cu (11.75% dissolution/d), 98.54% Co (12.3% dissolution/d), 75.95% Zn (9.49% dissolution/d) and 60.80% As (7.6% dissolution/d) at 150rpm, 1g/L sulphur, 30°C in 8days.

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... Elemental sulphur (Fischer Scientific Ltd) was used as a nutrient source for sulphur oxidising bacteria, although sulphur dosage has previously been shown to be a rate limiting factor in similar experiments. 32 Panda et al. found >1 g L −1 S 0 was required for optimum metal dissolution; 32 in this study, 5 g S 0 (in 1.2 L) was therefore used to provide excess sulphur. Experiments were conducted in duplicate, investigating variables detailed in Table 1, for 1600 h. ...
... 42 Further investigation, however, would be required to assess the role of iron oxidation in this study, for example, by parallel monitoring of FeIJII) : FeIJIII) ratios in the leach solution by chromatographic or titration methods. 32,42,43 Greater increases in acid generation were seen in inoculated flasks which were stirred and heated, and were continuing to increase at the time the experiments were terminated. In addition to oxidation of added sulphur, there may have also been oxidation of reduced sulphur present in the substrate, such as metal sulphides. ...
... 47,48 Where copper is present in more labile forms (such as 'pyrite ash' produced from the combustion of pyrite in the production of sulphuric acid), it has been shown to yield higher bioleaching efficiencies than zinc. 32 Lead leachability was particularly poor, attributed to its propensity to form a sulphate with low solubility 49 which has been observed by other investigators. 50 However, as pH values were on a downward trajectory, it may be that significant increases in solubilisation of these metals would have occurred if experiments had continued. ...
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A proof of concept study is presented, using acid mine drainage (AMD) to leach metals (Zn, Cd, Ni, Mn, Fe, Pb, Cu) from a passive treatment system substrate. The substrate, taken from a sulphate-reducing bioreactor treating mine drainage at another site, was heavily contaminated with metals and could not be disposed of in landfill under UK regulations. Laboratory scale batch leaching experiments were conducted under aerobic conditions, in order to harness microbial sulphur oxidation to generate sulphuric acid and re-mobilise metals. Acid mine drainage, normally considered to be waste or an environmental liability, was used as a microbial inoculum and leach solution for the experiments, with added zero-valent sulphur as a supplementary nutrient source for sulphur oxidising bacteria. The initial reactor pH of 4.0 decreased to ≤2.8 in inoculated reactors, whereas the final pH of the sterile controls was 4.1. Metals data showed removal efficiencies of 71–100% for Zn, Cd, Ni and Mn in inoculated reactors upon completion of the 1600 hour leach period. These findings suggest that AMD can be used as a convenient leach solution and inoculum for the leaching of these metals from spent bioreactor treatment system substrates.
... The cumulative rate of metal dissolution (CRD, mg/day) is shown in Fig. 3f. CRD is an important industrial feature to determine the productivity of the system (Panda et al. 2018 Fig. 4a-e, the dissolution (%) of metals (Cu, Ni, Zn, Al) were not significantly higher after 4 days (or 6 days for Ti) in case of Test A.Fe 3+ . Hence, considering the maximum dissolution of all the metals, the optimum time for recovery is 6 days from the IBAN sample. ...
... Also, it is interesting to note that the initial pH was not higher in case of Test A.Fe 3+ and Test A for IBAM and Test A.Fe 3+ for IBAN. This indicates that the consumption of acid will be much lesser than the other systems and is an advantage when considered for scale-up studies (Panda et al. 2018). ...
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Ferrous fractions in incinerated bottom ash (IBA) are linked to lower metal dissolution. In the present study, a novel eco-friendly biotechnological approach has been tested for multi-metal leaching using meso-acidophilic Fe²⁺/S° oxidizing bacterial consortium from magnetically separated IBA, owing to the inherent property of IBA to release Fe²⁺. Comprehensive lab-scale studies, first-of-its-kind, considered all the potential elements to understand targeted metal dissolutions from the sample under differential conditions. Concentrations of metals, Al > Ti > Ni > Zn > Cu, as analyzed by ICP-OES, were targeted to be bioleached. XRD analysis indicated the sample to be amorphous with magnetite (Fe3O4) and iron (Fe) forming major phases in the magnetic part (IBAM) and titano-magnetite (Fe3–x. TixO4) and iron (Fe) for the nonmagnetic part (IBAN). The study indicated that 73.98% Cu, 98.68% Ni, 59.09% Zn, 58.84% Al, and 92.85% Ti could be leached from IBAM when the bioleaching system operates at pH 1.5, 5% pulp density for 8 days. Under similar conditions, within 6 days, 37.55% Cu, 87.99% Ni, 45.03% Zn, 40.72% Al, and 63.97% Ti could be leached from IBAN. Two routes were identified and the mechanism of action has been proposed for the leaching of metals.
... In this process, the oxidation reaction (conversion of Fe 2+ to Fe 3+ ) takes place by inorganic acid and enzymes. The reaction rate is enhanced by the production of H + ion during the oxidation process [94]. Nevertheless, direct bioleaching of metals from e-waste utilizing At. ferrooxidans and At. ...
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There is a growing interest in electronic wastes (e-wastes) recycling for metal recovery because the fast depletion of worldwide reserves for primary resources is gradually becoming a matter of concern. E-wastes contain metals with a concentration higher than that present in the primary ores, which renders them as an apt resource for metal recovery. Owing to such aspects, research is progressing well to address several issues related to e-waste recycling for metal recovery through both chemical and biological routes. Base metals, for example, Cu, Ni, Zn, Al, etc., can be easily leached out through the typical chemical (with higher kinetics) and microbial (with eco-friendly benefits) routes under ambient temperature conditions in contrast to other metals. This feature makes them the most suitable candidates to be targeted primarily for metal leaching from these waste streams. Hence, the current piece of review aims at providing updated information pertinent to e-waste recycling through chemical and microbial treatment methods. Individual process routes are compared and reviewed with focus on non-ferrous metal leaching (with particular emphasis on base metals dissolution) from some selected e-waste streams. Future outlooks are discussed on the suitability of these two important extractive metallurgical routes for e-waste recycling at a scale-up level along with concluding remarks.
... and moderate thermophiles (τ B = −0.649) is one of the best-known bacterial metabolism indicators. Bacterial oxidation of sulfur and ferrous iron simultaneously reduces the pH and increases the oxidation potential of the medium (Chen and Lin 2004;Panda et al. 2018). The strong negative correlation between OPC and bacterial count of mesophiles (τ B = −0.819) ...
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Due to entrainment or dissolution, organic extractants can contaminate aqueous raffinate during the solvent extraction (SX) process. This study aims to evaluate the effect of conventional SX reagents on the bio-oxidation and metabolism of industrial bacteria. Evaluating the effect of LIX 984N, Chemorex CP 150, D2EHPA, and Acorga M5640 at three concentrations on mesophiles and moderate thermophiles revealed that all extractants reduced the bacterial efficiency at different extents. It was observed that organic phases at 0.02% v/v resulted in a decrement of ferrous iron bio-oxidation rate and a negligible decrease in the bacterial population. At high dosages like 2% v/v, bio-oxidation and bacterial reproduction were utterly disrupted. The oxime-based extractants had a more significant effect on bacteria due to their lower stability and production of toxic substances by hydrolysis. Organic phases more impacted moderate thermophiles at a higher temperature compared to mesophiles. The analysis of Kendall tau-b revealed a strong inter-correlation between the concentration of organic phase and bio-oxidation parameters such as pH, ORP, bacterial population, bio-oxidation rate, and iron precipitation.
... The literature on E-waste bioleaching is mainly limited to benchscale applications, with only a few efforts on bubble column bioreactors at the laboratory scales. The main function of the bioreactors is controlling the substrate and product concentration during the process and the environmental conditions [21]. By using a bioreactor, the impact of biophysical agents on cells can be studied; oxygen and nutrient limitation can be overcome. ...
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The high amount of base metals poses an important challenge in gold bioleaching from spent printed circuit boards (PCBs). The best objective in the current study is the bioleaching of important base metals (Cu, Ni, and Fe) from a mixture of spent PCBs (E-waste) using adapted Acidithiobacillus ferrooxidans in the bubble column bioreactors. The adaptation process firstly is done from 1- 15 g/L in Erlenmeyer flasks in 187 days, then the concentration of E-waste increased to 40 g/L in the bubble column bioreactors in 44 days. The concurrent recovery of copper, nickel, and iron using adapted bacterium in a bioreactor was optimized by central composite design. Various effective parameters such as aeration rate, initial ferrous sulfate concentration, and solid waste loading that significantly affected bioleaching yields were studied. 54% of Cu (6% dissolution/d), 75% of Ni (8% dissolution/d), and 55% of Fe (6.1% dissolution/d) were recovered simultaneously under the optimum condition of 20 g/L of solid content, 1.5 vvm of aeration rate, and 40 g/L of the initial concentration of ferrous sulfate after only 9 days. The results proved 100% recovery of each metal is possible separately, 100% of Cu and Fe are extracted maximally on the 4th and 13th day, respectively. Ni is recovered maximally 96% on the 17th day. This is the first report of an ecofriendly method for bioleaching of important base metals from E-waste in bubble column bioreactor. Thus, the obtained results contribute to the knowledge of microbial hydrometallurgy on large scale.
... It is of practical importance to scale up laboratory and semi-pilot scale tests for industrial applications (Panda et al., 2018). Based on the preliminary shake flask tests, semi-pilot stirred tank reactor (STR) tests were performed in the present study. ...
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Bioleaching of copper from electronic waste (e-waste) in the form of high grade waste printed circuit boards (WPCBs) collected from obsoletemobile phones is assessed using a consortium of iron (Fe2+) & sulphur (Sº) oxidizing bacteria in a semi-pilot reactor system. Results from the study indicated that the microorganisms were able to grow in the presence of WPCB and efficiently solubilize Cu from it. At a solid/liquid ratio of 10% (w/v)with a particle size of <250 μm, maximum bioleaching efficiency of around 95% Cu was observed in 8 days of leaching under oxidation-reduction potentials (ORP) of >600 mV and pH 1.8. In order to recover the metallic values, electrowinning (EW) of copper from the bioleach solutions was investigated in detail. Direct EW of the bioleach solution yielded low current efficiencies (66.1% over 4h.), ascribed due to the high concentrations of iron (i.e., 9.1 g/L). As a novel approach, a downstream purification and concentration process was further tested, that involved ferric hydroxide (Fe(OH)3) precipitation and solvent displacement crystallisation (SDC) to eliminate iron and increase the concentration of copper in solution prior to its application for EW. This significantly improved the current efficiency (by ~22%) during the EW of copper. A process flow-sheet for Cu recovery from WPCBs was developed and the downstream process was found to be profitable even though its margin was small with techno-economic analysis. It is believed that the two-step hybrid process i.e. bioleaching technique followed by the novel approach proposed (i.e., iron precipitation + SDC) can be suitably employed for the extraction of copper from WPCBs.
... wileyonlinelibrary.com/jctb that provides better insights into scale-up factors and their applicability. [59][60][61][62][63] Metal dissolution efficiencies, changes in ORP, pH, Fe (II) and dissolution of total iron [Fe (T)] under bench-scale conditions are shown in Fig. 9. The dissolution of the targeted metals in the bioreactor was greater when compared to its chemical control [ Fig. 9 (a) and (b)]. ...
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Bioleaching of spent batteries was often conducted at pulp density of 1.0% or lower. In this work, metallic ions catalytic bioleaching was used for release Zn and Mn from spent ZMBs at 10% of pulp density. The results showed only Cu(2+) improved mobilization of Zn and Mn from the spent batteries among tested four metallic ions. When Cu(2+) content increased from 0 to 0.8g/L, the maximum release efficiency elevated from 47.7% to 62.5% for Zn and from 30.9% to 62.4% for Mn, respectively. The Cu(2+) catalysis boosted bioleaching of resistant hetaerolite through forming a possible intermediate CuMn2O4 which was subject to be attacked by Fe(3+) based on a cycle of Fe(3+)/Fe(2+). However, poor growth of cells, formation of KFe3(SO4)2(OH)6 and its possible blockage between cells and energy matters destroyed the cycle of Fe(3+)/Fe(2+), stopping bioleaching of hetaerolite. The chemical reaction controlled model fitted best for describing Cu(2+) catalytic bioleaching of spent ZMBs. Copyright © 2015. Published by Elsevier B.V.
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Dumping of low-grade chalcopyrite encompasses several environmental problems. Despite slow dissolution rate, meso-acidophilic bioleaching is preferred for the extraction of copper from such ores. In the present study, meso-acidophilic bioleaching of a low-grade chalcopyrite in presence of an acid-processed waste newspaper (PWp) is discussed for the first time. The study illustrated a strong catalytic response of PWp with enhanced bio-recovery of copper from acid-conditioned chalcopyrite. A maximum of 99.13% copper recovery (0.36% Cu dissolution/day) was obtained in 6 days of bioleaching in presence of 2 gL- 1 PWp in contrast to only 5.7% copper in its absence. FTIR analysis of bioleached residues revealed similar spectral patterns to the original acid-conditioned ore in presence of PWp, thus indicating less development of passivation layer which was also confirmed through a complementary raman characterization of the bioleached residues. Further, a reaction mechanism (chemistry) was proposed suggesting the possible role of PWp as the electron donor under oxygen limiting conditions which facilitated microbial reduction of Fe (III). The resulting biochemical changes provided an energy source for the bacteria, thus allowing free flow of electrons through the ore surface, thus contributing towards enhanced bioleaching of copper.
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In Turkey, pyrite, copper melting gases and sulfur are used as a raw material in sulfuric acid production. Pyrite ashes are obtained as a result of the sulfuric acid production process during the roasting of pyrite ores. These wastes are generally landfilled or dumped into the sea.Pyrite ash wastes can be utilized as a raw material in the production of iron ore, and thus environmental pollution can be avoided; however, these wastes need to achieve certain physical and chemical properties before they are used. Pyrite ashes are agglomerated into pellets to allow them acquire the required properties for use as iron ore in a blast furnace.The essential parameters affecting the pelletization of pyrite ashes are studied using bentonite as a binder. The metallurgical properties of pyrite ash, bentonite, a mixture of pyrite ash and bentonite, and sintered pellets are studied using X-ray analyses. Wet-drop, wet-crush, dry-crush and sintered-crush tests are carried out to investigate the strength of the pyrite ash wastes pellets prepared from feeds with different sieve size and bentonite content. The results of this analysis demonstrate that pyrite ashes can be agglomerated into pellets and used as feed for the blast furnace in the iron production industry.
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Meso-acidophilic bacterial leaching of ball mill spillage (containing chalcopyrite >80%) was carried out in an innovative two-step bioleaching method. The major drawback of meso-acidophilic bioleaching limiting industrial application is the passivation phenomenon over the ore surfaces in iron-sulfur rich environments. In the present study, we present a novel wash solution that efficiently removed the passivation layer. FTIR characterization of the bioleached sample indicated that the residues could be further leached to recover extra copper after wash solution application. XRD study indicated accumulation of sulfates (SO(4)(-)) of Na, K, Fe and oxy hydroxides of iron [FeO(OH)] in the form of jarosite outlining the passivation layer. SEM, FESEM-EDS studies indicated severe corrosion effects of the wash solution on the passivation layer. Two step bioleaching of the ore sample yielded 32.6% copper in 68days in the first interlude and post wash solution application yielded 10.8% additional copper.
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Zn(II) and Pb(II) from Nigerian sphalerite and galena ores were bioleached by a mixed culture of acidophilic bacteria. The influences of pH and ferric ion on the bioleaching rates of sphalerite and galena were examined. The result shows that pH 2.1 and 2.7 are favourable for the leaching of Zn(II) and Pb(II) from sphalerite and galena, respectively. It was observed that the use of agarose-simulated media caused cells to excrete exopolymers containing ferric ions which enhanced oxidation. The oxidation equilibrium for sphalerite and galena took 3 and 4 d, respectively. About 38.3% sphalerite and 34.2% galena were leached within 1 d and approximately 92.0% Zn(II) and 89.0% Pb(II) were recovered in 5 d, respectively. The unleached residual products were examined by X-ray diffraction for sphalerite, revealing the presence of elemental sulphur(S), zinc sulphate (ZnSO4) and few traces of calcium aluminate (Ca3Al2O6). The XRD pattern also indicates the presence of elemental sulphur (S), lead sulphate (PbSO4) and few traces of itoite [Pb(S,Ge)(O,OH)4] and cobalt lead silicate [Pb8Co(Si2O7)3] in the unleached galena ore.
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The extraction of sulphur produces a hematite-rich waste, known as roasted pyrite ash, which contains significant amounts of environmentally sensitive elements in variable concentrations and modes of occurrence. Whilst the mineralogy of roasted pyrite ash associated with iron or copper mining has been studied, as this is the main source of sulphur worldwide, the mineralogy, and more importantly, the characterization of submicron, ultrafine and nanoparticles, in coal-derived roasted pyrite ash remain to be resolved. In this work we provide essential data on the chemical composition and nanomineralogical assemblage of roasted pyrite ash. XRD, HR-TEM and FE-SEM were used to identify a large variety of minerals of anthropogenic origin. These phases result from highly complex chemical reactions occurring during the processing of coal pyrite of southern Brazil for sulphur extraction and further manufacture of sulphuric acid. Iron-rich submicron, ultrafine and nanoparticles within the ash may contain high proportions of toxic elements such as As, Se, U, among others. A number of elements, such as As, Cr, Cu, Co, La, Mn, Ni, Pb, Sb, Se, Sr, Ti, Zn, and Zr, were found to be present in individual nanoparticles and submicron, ultrafine and nanominerals (e.g. oxides, sulphates, clays) in concentrations of up to 5%. The study of nanominerals in roasted pyrite ash from coal rejects is important to develop an understanding on the nature of this by-product, and to assess the interaction between emitted nanominerals, ultra-fine particles, and atmospheric gases, rain or body fluids, and thus to evaluate the environmental and health impacts of pyrite ash materials.
Article
Power plant process simulation software is well-suited for the modelling of energy systems and more importantly, tools for analysing the energy efficiency are often built into the software. This work presents the development of a simulation model for a sulphuric acid plant using a commercial software package for power plant process simulation. This will be of value to for instance small consultant and engineering companies involved with audits and analysis of energy systems. For small sized companies the cost of acquiring and maintaining many different specialised software packages will be noticeable. However, companies involved with audits and analysis of energy systems will in most cases have access to at least one software package for power plant process calculations. The use of this kind of software for also modelling chemical plants would be valuable to these companies. The results of this work shows that it is possible to use an inexpensive but powerful power plant process simulation software for modelling a common chemical process as a part of a large energy system.
Article
Bioleaching of metal sulfides is effected by bacteria, like Thiobacillus ferrooxidans, Leptospirillum ferrooxidans, Sulfolobus/Acidianus, etc., via the (re)generation of iron(III) ions and sulfuric acid.According to the new integral model for bioleaching presented here, metal sulfides are degraded by a chemical attack of iron(III) ions and/or protons on the crystal lattice. The primary iron(III) ions are supplied by the bacterial extracellular polymeric substances, where they are complexed to glucuronic acid residues. The mechanism and chemistry of the degradation is determined by the mineral structure.The disulfides pyrite (FeS2), molybdenite (MoS2), and tungstenite (WS2) are degraded via the main intermediate thiosulfate. Exclusively iron(III) ions are the oxidizing agents for the dissolution. Thiosulfate is, consequently, degraded in a cyclic process to sulfate, with elemental sulfur being a side product. This explains, why only iron(II) ion-oxidizing bacteria are able to oxidize these metal sulfides.The metal sulfides galena (PbS), sphalerite (ZnS), chalcopyrite (CuFeS2), hauerite (MnS2), orpiment (As2S3), and realgar (As4S4) are degradable by iron(III) ion and proton attack. Consequently, the main intermediates are polysulfides and elemental sulfur (thiosulfate is only a by-product of further degradation steps). The dissolution proceeds via a H2S*+-radical and polysulfides to elemental sulfur. Thus, these metal sulfides are degradable by all bacteria able to oxidize sulfur compounds (like T. thiooxidans, etc.). The kinetics of these processes are dependent on the concentration of the iron(III) ions and, in the latter case, on the solubility product of the metal sulfide.
Article
The sulfur oxidation activities of four pure thermophilic archaea Acidianus brierleyi (JCM 8954), Metallosphaera sedula (YN 23), Acidianus manzaensis (YN 25) and Sulfolobus metallicus (YN 24) and their mixture in bioleaching chalcopyrite were compared. Meanwhile, the relevant surface sulfur speciation of chalcopyrite leached with the mixed thermophilic archaea was investigated. The results showed that the mixed culture, with contributing significantly to the raising of leaching rate and accelerating the formation of leaching products, may have a higher sulfur oxidation activity than the pure cultures, and jarosite was the main passivation component hindering the dissolution of chalcopyrite, while elemental sulfur seemed to have no influence on the dissolution of chalcopyrite. In addition, the present results supported the former speculation, i.e., covellite might be converted from chalcocite during the leaching experiments, and the elemental sulfur may partially be the derivation of covellite and chalcocite.
Article
The objectives of this study were to evaluate the solubility of copper in waste printed circuit boards (PCBs) by bacterial consortium enriched from natural acid mine drainage, and to determine optimum conditions of bioleaching copper from PCBs. The results indicated that the extraction of copper was mainly accomplished indirectly through oxidation by ferric ions generated from ferrous ion oxidation bacteria. The initial pH and Fe(2+) concentration played an important role in copper extraction and precipitate formation. The leaching rate of copper was generally higher at lower PCB powder dosage. Moreover, a two-step process was extremely necessary for bacterial growth and obtaining an appropriate Fe(2+) oxidation rate; a suitable time when 6.25 g/L of Fe(2+) remained in the solution was suggested for adding PCB powder. The maximum leaching rate of copper was achieved 95% after 5 days under the conditions of initial pH 1.5, 9 g/L of initial Fe(2+), and 20 g/L of PCB powder. All findings demonstrated that copper could be efficiently solubilized from waste PCBs by using bacterial consortium, and the leaching period was shortened remarkably from about 12 days to 5 days.
Article
The Sotiel-Coronada abandoned mining district (Iberian Pyrite Belt) produced complex massive sulphide ores which were processed by flotation to obtain Cu, Zn and Pb concentrates. The crude pyrite refuses were roasted for sulphuric acid production in a plant located close to the flotation site, and waste stored in a tailing dam. The present study was focused on the measurements of flow properties, chemical characterization and mineralogical determination of the roasted pyrite refuses with the aim of assessing the potential environmental impact in case of dam collapse. Chemical studies include the determination of the total contaminant content and information about their bio-availability or mobility using sequential extraction techniques. In the hypothetical case of the tailing dam breaking up and waste spilling (ca. 4.54Mt), a high density mud flow would flood the Odiel river valley and reach both Estuary of Huelva (Biosphere Reserve by UNESCO, 1983) and Atlantic Ocean in matter of a couple of days, as it was predicted by numerical simulations of dam-break waves propagation through the river valley based on quasi-2D Saint-Venant equations. The total amount of mobile pollutants that would be released into the surrounding environment is approximately of 7.1.10(4)t of S, 1.6.10(4)t of Fe, 1.4.10(4)t of As, 1.2.10(4)t of Zn, 1.0.10(4)t of Pb, 7.4.10(3)t of Mn, 2.2.10(3)t of Cu, 1.5.10(2)t of Co, 36t of Cd and 17t of Ni. Around 90-100% of S, Zn, Co and Ni, 60-70% of Mn and Cd, 30-40% of Fe and Cu, and 5% of As and Pb of the mobile fraction would be easily in the most labile fraction (water-soluble pollutants), and therefore, the most dangerous and bio-available for the environment. This gives an idea of the extreme potential risk of roasted pyrite ashes to the environment, until now little-described in the scientific literature.
Article
In Turkey, pyrite ash is created as waste from the roasting of pyrite ores in the production of sulfuric acid. These processes generate great amounts of pyrite ash waste that creates serious environmental pollution due to the release of acids and toxic substances. Pyrite ash waste can be used in the iron production industry as a raw material because of its high Fe(2)O(3) concentration. The aim of this study was to investigate the reduction behaviour of pyrite ash pellets. The pyrite ashes were reduced to obtain the iron contained in pellets. Pyrite ashes samples were pelletized dried at 105 degrees C for 24 h and sintered at 1200 degrees C for 30 min. then reduced in a pressure of 4 atm. under argon gas. The mineralogical transformations that occurred during reduction were analysed by X-ray diffraction and X-ray fluorescence. The X-ray diffraction and X-ray fluorescence measurements of these samples showed that Fe(3)O(4) was successfully reduced to a metallic iron phase in a laboratory-scale electric arc furnace.
Article
Microorganisms that have a pH optimum for growth of less than pH 3 are termed "acidophiles". To grow at low pH, acidophiles must maintain a pH gradient of several pH units across the cellular membrane while producing ATP by the influx of protons through the F(0)F(1) ATPase. Recent advances in the biochemical analysis of acidophiles coupled to sequencing of several genomes have shed new insights into acidophile pH homeostatic mechanisms. Acidophiles seem to share distinctive structural and functional characteristics including a reversed membrane potential, highly impermeable cell membranes and a predominance of secondary transporters. Also, once protons enter the cytoplasm, methods are required to alleviate effects of a lowered internal pH. This review highlights recent insights regarding how acidophiles are able to survive and grow in these extreme conditions.
Article
Bioleaching of metals from hazardous spent hydro-processing catalysts was attempted in the second stage after growing the bacteria with sulfur in the first stage. The first stage involved transformation of elemental sulfur particles to sulfuric acid through an oxidation process by acidophilic bacteria. In the second stage, the acidic medium was utilized for the leaching process. Nickel, vanadium and molybdenum contained within spent catalyst were leached from the solid materials to liquid medium by the action of sulfuric acid that was produced by acidophilic leaching bacteria. Experiments were conducted varying the reaction time, amount of spent catalysts, amount of elemental sulfur and temperature. At 50 g/L spent catalyst concentration and 20 g/L elemental sulfur, 88.3% Ni, 46.3% Mo, and 94.8% V were recovered after 7 days. Chemical leaching with commercial sulfuric acid of the similar amount that produced by bacteria was compared. Thermodynamic parameters were calculated and the nature of reaction was found to be exothermic. Leaching kinetics of the metals was represented by different reaction kinetic equations, however, only diffusion controlled model showed the best correlation here. During the whole process Mo showed low dissolution because of substantiate precipitation with leach residues as MoO3. Bioleach residues were characterized by EDX and XRD.
Insights into heap bioleaching of low grade chalcopyrite ores: a pilot scale study
  • S Panda
  • K Sanjay
  • L B Sukla
  • N Pradhan
  • T Subbaiah
  • B K Mishra
  • M S R Prasad
  • S K Ray
S. Panda, K. Sanjay, L.B. Sukla, N. Pradhan, T. Subbaiah, B.K. Mishra, M.S.R. Prasad, S.K. Ray, Insights into heap bioleaching of low grade chalcopyrite ores: a pilot scale study, Hydrometallurgy 125-126 (2012) 157-165.
  • W Sand
  • T Gehrke
  • P G Jozsa
  • A Schippers
W. Sand, T. Gehrke, P.G. Jozsa, A. Schippers, Biochemistry of bacterial leaching-direct vs. indirect bioleaching, Hydrometallurgy 59 (2001) 159-175.