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Bioleaching of complex zinc sulphides using mesophilic and thermophilic bacteria: Comparative importance of pH and iron
Abstract
This study investigates the bioleaching of the complex Pb/Zn ore/concentrate using mesophilic (at 30 jC), moderate (at 50 jC), and extreme thermophilic (at 70 jC) strains of acidophilic bacteria. The effects of bacterial strain, pH, iron precipitation, and external addition of Fe 2 + on the extraction of zinc were evaluated. The results have shown that the ore is readily amenable to the selective extraction of zinc and lead using the acidophilic strains of bacteria [i.e., majority of lead (>98%) reports to the residue]. Moderate thermophiles displayed superior kinetics of dissolution of zinc compared with the other two groups of bacteria. The pH was found to exert a profound effect on the leaching process controlling the bacterial activity and precipitation of ferric iron mainly as K-jarosite. The K + released presumably from the alteration of the silicate phases such as K-feldspar present in the ore appeared to promote the formation K-jarosite in moderately thermophilic leaching systems. The external addition of iron was shown to be required for the bacteria to efficiently drive the extraction of zinc from the bulk concentrate. These findings place the emphasis on the prime importance of ferric iron for the dissolution of zinc and of mineralogical properties (i.e., iron and silicate content) of an ore/concentrate to be treated via bioleaching processes. D 2004 Elsevier B.V. All rights reserved.
... The findings (Kandemir, 1985;Sand et al., 2001;Deveci et al., 2004b;Deveci and Ball, 2010) ...
... Bioleaching of sphalerite is a relatively slow process. It has been suggested (Fowler and Crundwell, 1998;Deveci et al., 2004b, Deveci andBall, 2010) that the rate of the oxidation of sphalerite is enhanced in the presence of ferric iron. The oxidation of sphalerite by ferric iron can be represented by the reaction below: ...
... It had been demonstrated (Deveci et al., 2004b) that the contribution of bacteria to the oxidation of the bulk concentrate (MAR-BC) was limited in connection with its low iron content (2.89%) and hence the external addition of iron was required to enhance the extraction of zinc. Therefore, in the current tests the addition of ferrous iron at the start of the bioleaching experiments was made to increase the initial iron level. ...
Magnesium compounds which are caustic magnesia, sinter or dead-burnt magnesia, magnesium chloride, magnesium hydroxide, magnesium carbonate (magnesite) are produced from seawater, lake brines and minerals deposits. Magnesite ore (MgCO3) is a natural mineral mainly composed of magnesium carbonate and it is the primary source for production of magnesium and its compounds. Magnesite ore is composed of serpentine, quartz-based silica, opal and limestone, and SiO2, Fe2O3, CaO, Al2O3 content is important to determining the quality of magnesite ore and economic evaluation is done according to these values. Beneficiation of magnesite ore is performed using physical and chemical methods to produce a high-grade product to be used in the manufacture of magnesium compounds. Magnesite ore is separated from impurity silica and iron by crushing, grinding, screening and beneficiations methods. In this study is aimed to determine that beneficiation methods which used for magnesite ore is how successful. According to experiment results, the best result has been obtained by chemical beneficiation method so it is the best suitable method for beneficiation magnesite ore.
... Dopson et al. [15] estudaram o consumo de ácido em colunas de biolixiviação. Segundo os autores, após 293 dias de experimento, o consumo de ácido para os valores de pH nos ensaios iguais a 1,5; 2,0; 2,5 e 3,0 foi de 219,0; 79,0; 15,0, e 5,0 g de H 2 SO 4 /kg de minério, respectivamente, o que também está de acordo com os resultados de Deveci et al. [16]. Miner., São Paulo, v. 14, n. 3, p. 257-263, jul./set. ...
... Foram também realizados ensaios para estudar o efeito da adição de sulfato ferroso sobre o percentual de extração de cobre nos sistemas de biolixiviação. As concentrações iniciais de Fe 2+ estudadas foram: 0; 2,0; 5,0 e 10,0 g.L -1 [16,17]. ...
... Deveci et al. [16] estudaram o efeito da concentração inicial de Fe 2+ na extração de zinco de um minério que possuía 2,89% de ferro. O ensaio controle e o experimento sem a adição de Fe 2+ alcançaram extrações de 30% e 40%, respectivamente, enquanto os ensaios com concentração de Fe 2+ na faixa 1 a 4 g.L -1 mostraram resultados de aproximadamente 100% de extração. ...
... The findings (Kandemir, 1985;Sand et al., 2001;Deveci et al., 2004b;Deveci and Ball, 2010) suggest that it occurs chemically by acid attack. The only involvement of bacteria in the dissolution of sphalerite would therefore be the oxidation of elemental sulphur formed possibly via intermediate polysulphides. ...
... Bioleaching of sphalerite is a relatively slow process. It has been suggested (Fowler and Crundwell, 1998;Deveci et al., 2004b, Deveci andBall, 2010) that the rate of the oxidation of sphalerite is enhanced in the presence of ferric iron. The oxidation of sphalerite by ferric iron can be represented by the reaction below: ...
... ferrooxidans and At. thiooxidans) was used in bioleaching experiments (Deveci et al., 2004b). The culture was continuously maintained on a Zn/Pb complex ore at 30°C. ...
Bioleaching can be suitably exploited for the treatment of difficult-to-treat ores and concentrates. In this study, bioleaching of two different concentrates (a bulk Zn/Pb concentrate and zinc concentrate with high iron content) was studied to demonstrate the importance of mineralogical characteristic with particular reference to iron content. Bioleaching tests have shown that iron content of zinc concentrates is of practical importance since the external addition of iron is required to enhance the extraction of zinc from the concentrate with a low iron content. Bench scale bioleaching tests in stirred tank reactors have revealed that increasing pulp density (up to 10% w/w) tends to adversely affect bioleaching process due apparently to the excessive increase in surface area and concomitantly, the inability of bacteria to maintain strong oxidising conditions required. Dissolution rates as high as 862 mg/L/h Zn at 10% w/w were recorded. The ability of mesophilic culture to operate at high levels of Zn in solution (up to 100 g/L) was demonstrated.
... Among various leaching processes, bioleaching as a simple, costeffective and eco-friendly operation has a good potential to extract valuable metals from low-grade and complex sulphidic ores (Mousavi et al., 2005;Wang et al., 2014;Zhen et al., 2008;Zhen et al., 2009). This process has been used commercially for the extraction of copper, uranium, gold, zinc nickel and cobalt from ores and concentrates over the past two decades (Ahmadi et al., 2015;Byekwaso et al., 2002;Cameron et al., 2009a;Cameron et al., 2009b;Deveci et al., 2004;Pradhan et al., 2008;Watling, 2006;Watling, 2008;Yang et al., 2011;Zhen et al., 2008). The microorganisms extract metals from sulphidic minerals by oxidizing ferrous iron and sulphur species, leading to the generation of high oxidation reduction potential (ORP) and acid (Halinen et al., 2009;Zammit et al., 2012). ...
... It can be concluded that moderate thermophiles are more capable of extracting copper than mesophiles. The positive effect of higher temperature on the chemical subsystem could be one of the main reasons for increasing the leaching rate of chalcopyrite at 45 • C. It has been reported that moderate thermophiles offer more benefits such as higher kinetics of dissolution and lower cooling requirements than other groups of microorganisms (Deveci et al., 2004;Dew et al., 1999). The experiments conducted to evaluate the effect of pulp density indicated that increasing the pulp density from 5 to 10% (Run 1 and Run 9) decreased nickel extraction from 62.8% to 36.3% and cobalt extraction from 74.8% to 53.7%, in the first 9 days. ...
This study investigates the influence of salinity on the bioleaching efficiency of a copper‑nickel‑cobalt bearing sulphidic tailing obtained from Golgohar iron ore desulphurization plant (Sirjan, Iran). The effects of several critical parameters including, suspension pH, nutrient medium, microorganism type, and pulp density were investigated on the extraction of copper, cobalt and nickel from the sulphidic tailing at different levels of sodium chloride concentration. Bioleaching efficiency was also evaluated in the presence of saline local and process waters. Results showed that maximum extraction of nickel (87%) and cobalt (69%) was achieved at the initial pH of 1.8, the pulp density of 10%, Norris nutrient medium containing 10 g/L sodium chloride, and using moderately thermophilic microorganisms. However, maximum copper extraction (~90%) was obtained in the presence of local water. It was also found that the local and process waters containing around 15.5 and 8.3 g/L chloride ions, respectively, increased metal extraction about 25% and 10% in comparison to distilled water at the first two days. Nevertheless, the metal extraction decreased at the end of the process in both water types mainly due to the formation of gypsum and jarosite precipitates, which were found by SEM/EDS analyses. Furthermore, at the initial pH of 1.5, the extraction of valuable metals was significantly improved (20–60% increase at first 9 days) in the presence of 5 g/L sodium chloride; whereas a further increase (to 10 g/L sodium chloride) had a negative effect on the extractions. Increasing the pulp density from 5% (w/v) to 10% decreased the nickel and cobalt extraction about 26% and 21%, respectively; however, copper extraction increased around 5% which could be related to the lower level of oxidation-reduction potential of the suspension at the higher pulp density. It can be concluded that the low levels of salinity (up to 5 g/L sodium chloride addition) could have a positive effect on the efficiency of the bioleaching process.
... The formation of jarosite will result in depletion of available K + from the solution and cause coating of the sulphide minerals and liberated gold particles. Though the kinetics of ferric iron precipitation to form jarosite is relatively slow at the operating temperatures of BIOX, studies continue to record the presence of jarosite [26,[29][30][31][32][33]. This is attributed to the longer residence time and occasional increase in reactor pH close to 2.0 in BIOX operations. ...
... Gypsum (CaSO 4 .2H 2 O) on the other hand is formed due to the addition of lime in the BIOX ® circuit to adjust the pH [31,33]. This occurs when the BIOX ® reaction leads to higher acidity than is required by the bacteria. ...
This paper presents a study on characterisation of refractory ore, biooxidation feed and product, and cyanidation tailings with the aim of understanding the causes of excessive continuous frothing, incomplete sulphide oxidation, high reagent consumption, high cyanidation residues and low overall recovery as encountered in biooxidation of refractory ores. Techniques involving carbon and sulphur speciation, Quantitative X-Ray Diffraction (QXRD), Scanning Electron Microscopy (SEM) and Optical Microscopy (OM) were used to characterise the ore samples, flotation concentrate (BIOX® feed), biooxidised product (BIOX® CIL Feed) and cyanidation tailings (BIOX® CIL Tails) from a biooxidation plant. The main minerals present in the ore were quartz (45%), chlorites (21%), plagioclase feldspar (13%), dolomite (5%), pyrite (2%) and mica group (2%). The flotation concentrate recorded 18% mica, and this was responsible for excessive frothing in the biooxidation circuit as confirmed by the QXRD analysis. The carry-over froth to the CIL circuit led to short-circuiting of poorly leached material into the cyanidation tailings, resulting in high cyanidation residues. Secondary refractory minerals; gypsum and jarosite, which were observed in the biooxidation product by the QXRD, have the potential to coat unreacted sulphide particles, leading to incomplete sulphide oxidation as observed here. Partially oxidised sulphides led to high consumption of reagents such as oxygen and cyanide during cyanidation. Gypsum and jarosite also encapsulated gold particles as observed in the BSED analysis. Coated gold particles had reduced access to lixiviants during the subsequent cyanidation process, leading to high leach residues. The biooxidised product (BIOX® CIL Feed) also recorded a high organic carbon content of 6.67, while analysis by BSED revealed the presence of graphitic carbon and coatings on gold surfaces; an indicator for high preg-robbing activities during cyanidation of the concentrate. Preg-robbing indices of 64.4% and 72.7% were recorded for the flotation concentrate (BIOX® feed) and BIOX ® CIL feed respectively. The overarching effect of all the observations is a decrease in overall gold recovery.
... Gramp et al. [33] reported that the mineralization capacity of K + is 75 and 200 times higher than those of NH4 + and Na + , respectively. The effect of the Fe 3+ concentration on biomineralization was investigated by Deveci et al. [34], who suggested that regardless of the material added, mineralization ability is limited at low Fe 3+ concentrations. In the early stages, the Fe 2+ oxidation efficiency was low, owing to the adaptation period required for A. ferrooxidans. ...
... The effect of the Fe 3+ concentration on biomineralization was investigated by Deveci et al. [34], who suggested that regardless of the material added, mineralization ability is limited at low Fe 3+ concentrations. In the early stages, the Fe 2+ oxidation efficiency was low, owing to the adaptation period required for A. ferrooxidans. ...
Acid mine drainage (AMD) is characterized by low pH, high soluble Fe, and heavy metal concentrations. Conventional lime neutralization produces large amounts of Fe(OH)2 and Fe(OH)3, which complicate subsequent disposal. Secondary iron minerals synthesized by biomineralization can reduce the concentration of soluble Fe in addition to adsorbing and removing heavy metals in AMD. Therefore, an appropriate method for improving the precipitation efficiency of Fe is urgently needed for AMD treatment. Using simulated AMD, this work analyzes the influence of quartz sand (40 g/L) on the Fe2+ oxidation and total Fe deposition efficiencies, as well as the phases of secondary iron minerals in an Acidithiobacillus ferrooxidans system including K+, Na+, or NH4+ (53.3 mmol/L). Quartz sand had no significant effect on Fe2+ oxidation and 160 mmol/L Fe2+ was completely oxidized by A. ferrooxidans in 168 h, but contributed to the oxidized product (Fe3+) mineralization, improving the total Fe removal efficiency in simulated AMD. Compared with treatments involving K+ or Na+ alone, quartz sand improved the total Fe precipitation efficiency by 26.6% or 30.2%, respectively. X-ray diffraction showed that quartz sand can promote the transformation of the biomineralization pathway from schwertmannite to jarosite with higher yields, which is important for improving the removal efficiency of heavy metals in AMD.
... Some important environmental factors such as pH, dissolved oxygen and redox potential were also monitored during bioleaching of the ore. Unlike in previous Zn-bioleaching studies (Deveci et al., 2004;Rodriguez et al., 2003) conducted at different initial pH values, sulphuric acid was repeatedly added to the bioleaching medium until the pH stabilized at 2.0, followed by pH monitoring periodically during the time course. In spite of initial acid consumption, no zinc was leached from the ore during the first seven days in the inoculated and sterile flasks, suggesting that carbonatecontaining gangue was reacting during this initial phase with the added acid. ...
... The oxidative nature of these reactions is further supported by the increase in the redox potential, suggesting that bacteria maintained a high Fe 3+ /Fe 2+ ratio in the medium, and the decrease in the dissolved oxygen concentration in inoculated media. Consistent with other reports (Deveci et al., 2004;Dew et al., 1999;Konishi et al., 1998;Witne and Phillips, 2001), the findings reported in this paper indicate that moderately thermophilic bacteria were comparatively faster than the mesophiles in the bioleaching process. ...
... Bioleaching refers to the conversion of insoluble metal sulphides into their soluble forms by microbial activity (25)(26). In this process, microorganisms gain energy from oxidation of ferrous iron and other reduced inorganic compounds (9,21) and aid in extraction of metals (25,27) either by direct or indirect mechanisms, which are described later. Using this innovative biotechnological technology, it is possible to recover metals (28)(29)(30). ...
... Extraction of metals depends of the effectiveness of the bacteria, which in turn is dependent of several factors. (27). As mentioned earlier, most of the microorganisms used for the extraction of metals are chemolithotrophic sulphur bacteria, thus, concentration of mineral nutrients in the media is crucial for their growth and metabolic rates. ...
Every year, more than 40 million metric tons of electronic wastes are discarded worldwide and these wastes represent a problem due to their improper treatment. Presence of metals, plastics and ceramics in these wastes pose a threat for health and environment. Pyrometallurgy and hydrometallurgy are employed for metal extraction from these wastes. However, of late, bioleaching is emerging one of the alternatives for recovery of metals. Chemolithotrophic bacterial strains are used and they accomplish bioleaching either by direct or indirect mechanisms. This review deals on the potential bacterial strains, their mechanism of action, factors involved, limitations and perspectives on bioleaching.
... In the indirect interaction (without physical attachment), H 2 SO 4 is produced from oxidation of elemental sulfur by bio-activity, and ferrous iron (Fe 2+ ) oxidizes to ferric iron (Fe 3+ ). In both procedures insoluble metal sulfides convert into soluble metal sulfates (Ballester et al., 2003;Barreto et al., 2005;Bosecker, 1997;Deveci et al., 2004;Keeling et al., 2005;Kinzler et al., 2003;Konishi et al., 1992;Mousavi et al., 2008;Sand et al., 1999;Sand et al., 2001;Suzuki, 2001;Tributsch, 2001). Bioleaching has several advantages over other methods such as smelting. ...
... The presence of surfactants may have essential effects (positive or negative) on bio activities involved in the bioleaching process (Dehghan and Dianati, 2015;Dong and Lin, 2012). Surfactants change properties of mineral surfaces and bioleaching conditions that can affect the growth and oxidation activity of microorganisms (Ballester et al., 2003;Deveci et al., 2004;Dew et al., 1997;Escobar et al., 2009;Tuovinen, 1978). ...
Froth flotation is the most preferred processing technique for the enrichment of low grade sulfides. Bioleaching is an eco-friendly method for metallurgical extraction from flotation
products. Flotation reagents (collectors, frothers, etc.) have various impacts on bioleaching and
bacterial activities. In this investigation, the effect of a number of sulfide flotation collectors
(potassium amyl-xanthate (KAX), potassium isobutyl-xanthate (KIBX), sodium ethyl-xanthate
(NaEX), potassium isopropyl-xanthate (KIPX) and Dithiophosphate (Aero3477)), and frothers
(pine oil (PO) and methyl isobutyl carbinol (MIBC)) with different dosages is studied on
Leptospirillum ferrooxidans activities. The results of various measurements indicated that these
flotation chemicals can have positive or negative influences on the bacterial activities, based on
their chemical compositions and/or concentrations. These results can extensively be used for the
selection of flotation reagents when bioleaching is chosen as the metallurgical extraction method
after flotation enrichment.
... There are some investigations on the effect of flotation reagents in bioleaching technology that generally focused on their impacts over the metallurgical parameters (recovery and grade of products) [1,3,[6][7][8][9][10], however, the fundamental effects of these chemicals on bacterial activities are not yet widely studied. It was reported that the recovery and grade in a bioleaching process of flotation products (in the presence of remaining surfactants) could be highly affected by type of reagents (their chemical compositions and structures), concentration of reagents, and type of microorganisms (various metabolisms, cellular membranes, strains, etc.) [1,[3][4][5][6][7][8]. ...
... ferrooxidans) was the first bacterium isolated from an acidic leaching environment for biomining, and it was used in many early bioleaching studies until Leptospirillum ferrooxidans (L. ferrooxidans) was found and it was reported that L. ferrooxidans can be the dominant iron-oxidizing bacteria in biomining processes [2,9,[11][12][13][14][15][16]. The negative effect of different collectors and frothers on A. ferrooxidans activity was observed in various investigations [3,7]. ...
Recently, extraction of metals from different resources using a simple, efficient, and low-cost technique-known as bioleaching-has been widely considered, and has turned out to be an important global technology. Leptospirillum ferrooxidans and Acidithiobacillus (Thiobacillus) ferrooxidans are ubiquitous bacteria in the biomining industry. To date, the effects of commercial flotation reagents on the biooxidation activities of these bacteria have not been thoroughly studied. This investigation, by using various systematic measurement methods, studied the effects of various collectors and frothers (collectors: potassium amylxanthate, potassium isobutyl-xanthate, sodium ethylxanthate, potassium isopropylxanthate, and dithiophosphate; and frothers: pine oil and methyl isobutyl carbinol) on L. ferrooxidans and A. ferrooxidans activities. In general, results indicate that in the presence of these collectors and frothers, L. ferrooxidans is less sensitive than T. ferrooxidans. In addition, the inhibition effect of collectors on both bacteria is recommended in the following order: for the collectors, potassium isobutyl-xanthate > dithiophosphate > sodium ethylxanthate > potassium isobutyl-xanthate > potassium amylxanthate; and for the frothers, methyl isobutyl carbinol > pine oil. These results can be used for the optimization of biometallurgical processes or in the early stage of a process design for selection of flotation reagents.
... With the reduced iron in the form of pyrite, the bacteria produce iron that oxidizes metal sulfides to sulfuric acid which further accelerates rock dissolution [152][153][154] . These species, along with those in the Sulfobacillus and Acidianus genera, as well as many iron-oxidizing bacteria, are used for the biomining of copper, zinc, uranium, nickel, aluminum, and cobalt 155 . ...
With the construction of the International Space Station, humans have been continuously living and working in space for 22 years. Microbial studies in space and other extreme environments on Earth have shown the ability for bacteria and fungi to adapt and change compared to "normal" conditions. Some of these changes, like biofilm formation, can impact astronaut health and spacecraft integrity in a negative way, while others, such as a propensity for plastic degradation, can promote self-sufficiency and sustainability in space. With the next era of space exploration upon us, which will see crewed missions to the Moon and Mars in the next 10 years, incorporating microbiology research into planning, decision-making, and mission design will be paramount to ensuring success of these long-duration missions. These can include astronaut microbiome studies to protect against infections, immune system dysfunction and bone deterioration, or biological in situ resource utilization (bISRU) studies that incorporate microbes to act as radiation shields, create electricity and establish robust plant habitats for fresh food and recycling of waste. In this review, information will be presented on the beneficial use of microbes in bioregenerative life support systems, their applicability to bISRU, and their capability to be genetically engineered for biotechnological space applications. In addition, we discuss the negative effect microbes and microbial communities may have on long-duration space travel and provide mitigation strategies to reduce their impact. Utilizing the benefits of microbes, while understanding their limitations, will help us explore deeper into space and develop sustainable human habitats on the Moon, Mars and beyond.
... These bacteria are able to produce soluble oxidized metals and sulfur as well as sulfuric acid from solid mining wastes, according to the following reactions (Eqs. (1)-(4)) (Deveci et al., 2004;Nguyen et al., 2018). ...
The aim of this study was to study and model the bioleaching of abandoned mine tailings at different pulp densities 1–20% w/v by using an autochthonous mesophilic microbial culture. Because of the importance of the ferrous-iron oxidation as sub-process on the bioleaching of sulphide mineral ores, the ferrous-iron oxidation process by the autochthonous microbial culture was studied at different ferrous-iron concentrations. A mathematical model fitted to the experimental results and the main kinetic and stoichiometric parameters were determined, being the most relevant the maximum ferrous-iron oxidation rate 5.1 (mmol Fe²⁺/mmol C·h) and the biomass yield, 0.01 mmol C/mmol Fe²⁺, values very similar to that of mixed cultured dominated by Leptospirillum strains. This autochthonous culture was used in the bioleaching experiment carried out at different pulp densities, obtaining a maximum metal recovery in the tests carried out at 1% w/v, recovering a 90% of Cd, 60% of Zn, 30% of Cu, 25% Fe and 6% of Pb. Finally, the different leaching mechanisms were modelled by using the pyrite as ore model obtaining a bioleaching rate of 0.316 mmol Fe²⁺/(L·h) for the direct mechanisms and a bioleaching rate for the indirect and cooperative leaching mechanisms of 0.055 Fe²⁺/(L·h).
... The presence of pyrite accelerated the dissolution of zinc from marmatite and sphalerite samples because of galvanic interaction (Shi et al., 2006). Deveci et al. (2004) showed that moderate thermophiles grown at 50 • C oxidized sphalerite at much fast rates as compared to mesophiles. ...
Mesophilic bacteria (Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans) and moderate thermophiles (Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans) were used in bioleaching experiments with five select sphalerite samples, which varied in the Zn- and Fe-content. Each sample was leached with and without additional Fe²⁺ and S⁰ under mesophilic and moderately thermophilic conditions. A sphalerite sample with a high Fe-content (8.95% Fe) reached a higher yield of zinc bioleaching than those with less iron (0.20–2.04% Fe). The maximum Zn recovery in the mesophilic tests was 82%, obtained with the sample of the highest Fe-content. In the moderately thermophilic experiments, the highest Zn recovery was 32%. The mesophiles increased the oxidation reduction potential due to the oxidation of Fe²⁺. The formation of jarosite-type precipitates and sulfur on sphalerite surfaces in the mesophilic tests and the formation of sulfur in the moderate thermophilic tests were indicated by analysis with powder X-ray diffraction and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy.
... 3,4 While precipitate formation can be minimized, 5,6 significant accumulation over continuous longterm operation may lead to slow kinetics and reduce the efficiency of bioleaching processes by occluding desired metals within the precipitate residue. 1,7 In recent times, due to the absence of efficient technologies to treat these iron residues, they are stored in waste dams, occupying large acres of land. 8 This poses an environmental risk with the potential for heavy metal pollution of the soil and groundwater systems. ...
The feasibility of improving typical biohydrometallurgical operation to minimize copper losses was investigated by the use of biogenic iron precipitate for the uptake of Cu(II) ions from aqueous solutions. The iron precipitate was obtained from mineral sulfide bioleaching and characterized using SEM/EDS, XRD, FTIR, BET, TGA, and pHpzc analyses. The results show that the precipitate is highly heterogeneous and that Cu(II) ion adsorption can be described by both Freundlich and Langmuir adsorption isotherms, with a maximum adsorption capacity of 7.54 mg/g at 30 °C and 150 mg/L. The sorption followed pseudo-second-order kinetics, while the major presence of −OH and −NH2 functional groups initiated a chemisorption mechanism through an ion-exchange pathway for the process. Ionic Cu(II) (radius (0.72 Å)) attached easily to the active sites of the precipitate than hydrated Cu(II) (radius (4.19 Å)). With an estimated activation energy of 23.57 kJ/mol, the obtained thermodynamic parameters of ΔS° (0.034–0.050 kJ/mol K), ΔG° (8.37–10.64 kJ/mol), and ΔH° (20.07–23.81 kJ/mol) indicated that the adsorption process was chemically favored, nonspontaneous, and endothermic, respectively. The 43% Cu(II) removal within 60 min equilibrium contact time at pH 5 was indicative of the reduced efficiency of copper extraction observed in a real-life biohydrometallurgical process due to sorption by the iron precipitate. The result of this study might provide an insight into the management of the biohydrometallurgical process to minimize copper losses. It may also help mitigate environmental pollution caused by the disposal of these biogenic iron precipitate residues.
... Esto es importante porque para la disolución de metales se requiere microorganismos adaptados previamente al ambiente específico para obtener buenos resultados (Barrie, 2006). La concentración de arsenopirita, 1%, empleada para la adaptación de A. ferrooxidans y A. thioxidans estuvo basada en que la adaptación de los microorganismos en arsenopirita puede darse entre 1 y 5% (W/V) (Masoon & Rice, 2002;Deveci et al., 2004;Shi & Fang, 2005;Shi et al., 2006;Astudillo & Acevedo, 2008). Este proceso además de acortar la fase de latencia de la curva de crecimiento es importante en la obtención de mayores valores de concentración microbiana, el mayor valor obtenido en este trabajo fue 2.12x10 8 células ml -1 a las 240 horas, superior al de 10 8 células ml -1 (Xia et al., 2008b). ...
La arsenopirita es una fuente mineral para la recuperación de oro puro, sobre ella se emplea la biooxidación, tecnología muy poco estudiada y aplicada en nuestro país a pesar que es de bajo costo, eficiente y amigable con el ambiente. Este trabajo tuvo como objetivo evaluar el grado de biooxidación en dos diferentes concentraciones de arsenopirita por cultivos microbianos de colección que previamente fueron adaptados al 1 % de arsenopirita en el medio de cultivo 0K. La arsenopirita se tamizó en un tamice Tyler menor de 200 y se agregó en concentraciones de 8 y 12 % en los biorreactores que contuvieron 700 ml de medio fermentativo (630 ml de medio de cultivo esterilizado con 70 ml de inóculo microbiano). El inóculo estuvo formado por suspensiones de un cultivo microbiano puro y de uno mixto (dos cultivos puros). La incubación se desarrolló a temperatura de ambiente durante 288 horas con aireación. Se evaluó el crecimiento microbiano, pH, hierro total, hierro II, hierro III y la formación de biofilm sobre la superficie de la arsenopirita. Se determinó que el cultivo microbiano mixto actuando sobre la arsenopirita al 8 % produjo el mayor grado de biooxidación correspondiente a una producción de 8197.7 mg L-1 de hierro III.
... (2)-(4), favoring vanadium leaching (Deveci et al., 2004;Nguyen et al., 2015;Feng et al., 2019). Fe 3+ increased significantly till the point where it slowly declined. ...
Bioleaching is promising to meet the demand of strategic vanadium both economically and environmentally. Whereas the combination of bioleaching with traditional techniques is of great interest, little is known on bioleaching of vanadium from abundant vanadium-bearing resources utilized/produced in existing processes. This study investigated the bioleaching of vanadium from vanadium-titanium magnetite, steel slag, and clinker, which are common raw mineral and intermediates used in conventional vanadium extraction process. Clinker had greater leachability by Acidithiobacillus ferrooxidans, compared to vanadium-titanium magnetite and steel slag. Pulp density, inoculum volume, initial pH and initial Fe²⁺ concentration had influencing effects on this bioleaching process. Under optimal condition with 3% pulp density, 10% inoculum volume, initial pH at 1.8, and 3 g/L initial Fe²⁺ concentration, the bioleaching of clinker achieved the maximum vanadium leaching efficiency of 59.0%. Both X-ray fluorescence and energy dispersive spectroscopy analysis confirmed the reduction of vanadium content in the solid residues after leaching. The results of Community Bureau of Reference sequential extraction suggested that vanadium in acid-soluble and oxidizable phase was more easily leachable. This study is helpful to develop sustainable and practical techniques for vanadium extraction from abundant raw materials and step forward in combining bioleaching with traditional process.
... The use of Acidithiobacillus thiooxidans (A.t.) microorganisms has aroused great interest in bio-hydrometallurgical processes, mainly due to their ability to treat complex, low-grade sulfur minerals (Potysz et al., 2018;Yang et al., 2019;Deveci et al., 2004). At present, bioleaching represents approximately 20 percent of the world's mined copper, and it is used in approximately 20 mines worldwide. ...
Acidithiobacillus thiooxidans is a microorganism of great interest in bio-hydrometallurgical processes, as it is potentially capable of treating complex, low-grade (purity) sulfur minerals. However, there are concerns in the metallurgical industry regarding the microbial manipulation due to problems arising related to cellular integrity, metabolic activities, genetic stability and maintainability of a continuous generation of microbial cultures. In this work, a spray drying (SD) process (inlet temperature: 150 °C, feed flow: 1.2 L/h, and atomization rate: 27,500 rpm) was adopted to encapsulate Acidithiobacillus thiooxidans using different biopolymers as wall materials. The physicochemical properties of the powders obtained by SD reveal water activity (aw) below 0.55 with less than 10% moisture, which ensures better stability of the powders during storage with a trapping efficiency above 80%. Morphology studies by scanning electron microscopy (SEM) of the microparticles showed defined surfaces with no collapsing structures, quasi-modal size particles, low viscosity of the reconstituted powders and fast release profiles. Calorimetric analysis confirmed the viability of A. thiooxidans to withstand the SD process. By infrared analysis, the same peaks of the functional groups corresponding to the biopolymers after spray drying were observed, which evidences the microorganism encapsulation (whose signal disappeared after SD). The presence of A. thiooxidans in the microcapsules was confirmed by Transmission Electron Microscopy (TEM). Finally, viability was verified by respiratory assessment of the bacterium rendering high survival rate (1.4 × 10⁹ Cells/mL) after the spray drying process.
... The process of dissolving metals in solution is influenced by several parameters that are related to the properties of microorganisms, chemical reactions (formation of precipitates), or the degree of friction in the suspension [8]. These include pH, particle size, pulp density, stirring frequency (rpm), temperature, nutrient concentration, oxygen content, and total bioleaching time [9][10][11]. These factors have a significant effect on the overall success of the transition of metals to the liquid phase and it is important to investigate their effect in order to achieve the highest possible yield of metals [10,12]. ...
Globally, the amounts of metal ore deposits have been declining, so the research directions investigating the extraction of metals from materials that are classified as waste are gaining more importance every year. High concentrations of Cu, Pb, Zn, and Fe were analyzed in the sludge sediment (Zlaté Hory, Czech Republic), which is a waste product of the mining industry. In the bioleaching process, bacterial cells have been established as being able to convert metals from solid to liquid phase. However, the most important parameters of bioleaching are particle size, pH, and pulp density, thus our research focused on their optimization. The acidophilic and mesophilic bacteria Acidithiobacillus ferrooxidans were applied due to the high Fe content in the sample. The recovery of metals in the leachate was determined by F-AAS and the residual metal concentrations in the waste fraction were analyzed by XRF. The grain size fractions <40 µm –200 µm were investigated. The atomic absorption spectrometry (AAS) results show that the highest Fe (76.48%), Cu (82.01%), and Pb (88.90%) recoveries were obtained at particle size of 71–100 μm. Zn was dissolved for all fractions above 90%. Experiments with different pH values were performed at a pH of 1.6–2.0. The highest dissolution rates of Zn, Fe, and Cu were achieved with a suspension pH of 1.8, where 98.73% of Zn, 85.42% of Fe, and 96.44% of Cu were recovered. Due to the high percentage dissolution of metals, experiments were performed under pilot conditions in a bioreactor at a pulp density of 2.5% and 4.2% (w/v). From an economic point of view, the leaching time of 28 days was evaluated as sufficient.
... Some reports have already suggested the potential of thermophilic microorganisms for the bioleaching of spent catalysts (Deveci, Akcil & Alp, 2004). The sulfur-oxidizing extreme thermophile Acidianus brierleyi, which grows best in pH 1-2 and temperature 60-70 °C, has been identified with a good potential to perform the recovery of metals contained in minerals (Konishi, Tokushige, Asai & Suzuki, 2001). ...
Los catalizadores, homogéneos o heterogéneos, son ampliamente utilizados para una gran variedad de procesos industriales, con el fin de producir combustibles limpios y muchos otros productos valiosos, siendo los catalizadores agotados provenientes del hidroprocesamiento los mayores residuos sólidos de la industria de la refinería y la contribución principal a la generación de catalizadores agotados. Debido a su naturaleza peligrosa, el tratamiento y la recuperación de metales de este tipo de residuos han ganado cada vez más importancia, debido al agotamiento de los recursos naturales y a la contaminación ambiental. Aunque ya existen técnicas disponibles para estos fines, éstas generan grandes volúmenes de desechos potencialmente peligrosos y producen emisiones de gases nocivos. Por lo tanto, las técnicas biotecnológicas pueden representar una alternativa promisoria para el biotratamiento y la recuperación de metales contenidos en los catalizadores agotados. Con este fin, se han analizado diversos microorganismos, que comprenden bacterias, arqueobacterias y hongos, capacitados para facilitar la eliminación de losmetales contenidos en estoscatalizadores. En estarevisión se presenta un amplio escenario sobre los avances con respecto al manejo de los catalizadores agotados y su tratamiento tradicional, seguido de una descripción detallada sobre los enfoques microbiológicos reportados hasta la actualidad.
... (1) Ferrous iron oxidation is accompanied by water formation and an increase in the pH of the solution, which results in intensified ferric iron precipitation in the form of hydrous sulfates (jarosite) according to the following reaction (Dutrizac, 1980): (2) where M = K + , Na + , or H 3 O + . Jarosite precipitation can adversely affect sulfide mineral leaching, impeding the ferric ion attack on sulfide particles (Deveci et al., 2004;Zhao et al., 2019). It also decreases the oxidizer concentration in the leaching solution. ...
... According to these reactions, iron oxidation is accompanied by the consumption of protons, while the oxidation of sulfur results in the generation of acid. Therefore, co-oxidation of sulfur and iron can reduce the precipitation of the oxidant of sulfide minerals according to reaction (5), the intensity of which increases with an increase in pH [25]. ...
A two-step process, which involved ferric leaching with biologically generated solution and subsequent biooxidation with the microbial community, has been previously proposed for the processing of low-grade zinc sulfide concentrates. In this study, we carried out the process of complete biological oxidation of the product of ferric leaching of the zinc concentrate, which contained 9% of sphalerite, 5% of chalcopyrite, and 29.7% of elemental sulfur. After 21 days of biooxidation at 40°C, sphalerite and chalcopyrite oxidation reached 99 and 69%, respectively, while the level of elemental sulfur oxidation was 97%. The biooxidation residue could be considered a waste product that is inert under aerobic conditions. The results of this study showed that zinc sulfide concentrate processing using a two-step treatment is efficient and promising. The microbial community, which developed during biooxidation, was dominated by Acidithiobacillus caldus, Leptospirillum ferriphilum, Ferroplasma acidiphilum, Sulfobacillus thermotolerans, S. thermosulfidooxidans, and Cuniculiplasma sp. At the same time, F. acidiphilum and A. caldus played crucial roles in the oxidation of sulfide minerals and elemental sulfur, respectively. The addition of L. ferriphilum to A. caldus during biooxidation of the ferric leach product proved to inhibit elemental sulfur oxidation.
... Fe(II) concentration and pH are important factors closely related to the growth of bacteria as well as the characteristic of precipitates [38]. The function of initial Fe(II) concentration (3.595-10.806 ...
... Although the iron oxidation activity was not inhibited as strongly as in case of L. ferriphilum, extraction of zinc from sphalerite in the presence of 200 mM NaCl by Sb. thermosulfidooxidans was lower than zinc extracted in the control assays. That could possibly be attributed to jarosite precipitation (being favored by sodium availability) rather than by chloride inhibition of bacterial activity (Deveci et al., 2004, Akcil et al., 2013. Biofilm formation is considered to be important in the initial steps of the interfacial process of bioleaching of metal sulfides (Bellenberg et al., 2014). ...
... Many researches (Deveci et al., 2004;Antonijevi c et al., 2008;Mahmoud et al., 2017) have shown that during bioleaching, secondary copper sulphides, and zinc and lead sulphides are leached generating their corresponding sulphates and elemental sulphur. However, primary copper sulphides, such as chalcopyrite, are highly refractory and present challenges for bioleaching processes (Panda et al., 2013;Zhou et al., 2015). ...
Flotation tailing is a problematic mining waste, because contains sulphides that exposed to oxidising conditions generate acidic drainage and the subsequent metal mobilisation. In this study, a flotation tailing produced within an integral process for the treatment of polymetallic sulphide ores is cleaned and valorised seeking a better use of natural resources and a lower environmental impact. In this work, bacterial leaching followed by brine leaching is postulated as an alternative to the flotation tailing treatment. Bioleaching destroys pyritic matrix (99% Fe) producing biogenic ferric that can be used as oxidising agent and recycling to a hydrometallurgical process. 80–90% Cu and Zn are dissolved and critical raw materials as Sb, In and Co are recovered. Brine leaching achieves Pb and Ag extractions greater than 96% and generates a solid residue mainly composed of quartz, in which gold that initially was in flotation tailing is concentrated. A clean and easily treatable for gold recovery final residue is obtained. In conclusion, pyrite matrix has been destroyed avoiding the further acid generation and reducing dramatically waste volume, metals have been valorised, and tailing hazardousness has been removed. Therefore, the proposed process is a sustainable alternative for flotation tailing management, reducing the environmental impact, the management costs, and generating income from valorisation of metals and the production of leaching agent.
... thiooxidans) to leach sulfide ore [18]. After the process of bioleaching, the solubility of the realgar ore significantly increases [19]. These species of bacteria were isolated from acidic mine drainage by oxidizing ferrous ions to obtain the energy they need [20]. ...
... In recent years, low-grade and complex refractory ore, the treatment of old abandoned deposits and other secondary resources related to mining activities in the past, and the treatment of the mine of the bacterial leaching process are its low energy demand, simple process operation, low capital investment, and reduced environmental damage, which make it effective for metal element extraction, environmental protection, and waste utilization (Li et al., 2014;Panda et al., 2015;Umanskii and Klyushnikov, 2013). Over the past few decades, bioleaching processes have been applied for the extraction of copper (Díaz et al., 2018;Gentina and Acevedo, 2016;Wang et al., 2018b;Yin et al., 2018), gold (Egan et al., 2016), zinc (Deveci et al., 2004;Ke et al., 2018;Xin et al., 2012), uranium (Anjum et al., 2012;Gilligan and Nikoloski, 2015;Qiu et al., 2011;Wang et al., 2017;Zare Tavakoli et al., 2017), cobalt (Chen et al., 2016) and nickel (Li et al., 2014). In recent years, some studies have investigated other practical applications of bacterial leaching in the recycling of resources from many industrial sectors, including electronic waste , sewage sludge (Zhang et al., 2009), municipal fly ash incinerators (Funari et al., 2017;Ishigaki et al., 2005;Li et al., 2019), and printed circuit boards (Karwowska et al., 2014;Xie et al., 2009;Zhou and Qiu, 2010). ...
This study evaluated the effectiveness of ore particle size on column bioleaching from low-grade uranium ore using an indigenous Acidithiobacillus ferrooxidans, isolated from local uranium ore. The uranium content was 0.033% by weight and ore particle size was crushed to <50 mm, <30 mm, and <15 mm. The additive content of sulfuric acid 5 g/L, Fe ³⁺ dosage of 5.0 g/L, spray strength of 2.57 L/(h·m ² ) and temperature of 25 °C were controlled. After 150 days of leaching, acid consumption amounted to 2.73 g H 2 SO 4 per kg ore, the obtained maximum uranium extraction was 64.85% with the ore particle size of <15 mm. The results showed that a smaller particle size ore had a higher uranium extraction and that an economic uranium extraction can be obtained by correctly controlling the ore granularity.
... thiooxidans) to leach sulfide ore [18]. After the process of bioleaching, the solubility of the realgar ore significantly increases [19]. These species of bacteria were isolated from acidic mine drainage by oxidizing ferrous ions to obtain the energy they need [20]. ...
Background
This paper presents micro- and nano-fabrication techniques for leachable realgar using the extremophilic bacterium Acidithiobacillus ferrooxidans (A. ferrooxidans) DLC-5.
Results
Realgar nanoparticles of size ranging from 120 nm to 200 nm were successfully prepared using the high-energy ball mill instrument. A. ferrooxidans DLC-5 was then used to bioleach the particles. The arsenic concentration in the bioleaching system was found to be increased significantly when compared with that in the sterile control. Furthermore, in the comparison with the bioleaching of raw realgar, nanoparticles could achieve the same effect with only one fifth of the consumption.
Conclusion
Emphasis was placed on improving the dissolvability of arsenic because of the great potential of leachable realgar drug delivery in both laboratory and industrial settings.
How to cite: Xu R, Song P, Wang J, et al. Bioleaching of realgar nanoparticles using the extremophilic bacterium Acidithiobacillus ferrooxidans DLC. Electron J Biotechnol 2019;38. https://doi.org/10.1016/j.ejbt.2019.01.001.
... A literature survey revealed several studies of the extraction of metals using mesophilic and thermophilic bacteria. Deveci et al., (2004) studied the bioleaching of complex zinc sulphides by mesophilic and thermophilic bacteria. Taha et al., (2014) investigated the use of thermophilic fungi to decolourize a mixture of high concentrations of azo and anthraquinone dyes at 55 °C. ...
Mesophilic biomass and thermophilic biomass samples were isolated and used to remove Dorasyn Red dye from aqueous solutions. The biosorption kinetics of dye uptake by four different types of biomass at three temperatures (20, 30, and 40 °C) were investigated using pseudo-first order kinetics, pseudo-second order kinetics, intraparticle diffusion, Elovich, and Bangham models. The pseudo-second-order kinetics model and the first stage of the intraparticle diffusion model were effective in describing the experimental kinetics data. The biosorption results showed that the mesophilic biomass samples could be useful for removing dye under acidic conditions.
... In recent years, there has been an increased number of documented studies into the hydrometallurgical processing of waste PCBs, including bio-leaching techniques (e.g. Deveci et al., 2004;Pant et al., 2012). However, most of these are limited to the leaching of the metals from finely ground material, with fewer studies reporting on the downstream processes, such as metal recovery from solution and treatment of effluent streams. ...
E-waste, or waste generated from electrical and electronic equipment, is considered as one of the fastest-growing waste categories, growing at a rate of 3–5% per year in the world. In 2016, 44.7 million tonnes of e-waste were generated in the world, which is equivalent to 6.1 kg for each person. E-waste is classified as a hazardous waste, but unlike other categories, e-waste also has significant potential for value recovery. As a result it is traded significantly between the developed and developing world, both as waste for disposal and as a resource for metal recovery. Only 20% of global e-waste in 2016 was properly recycled or disposed of, with the fate of the remaining 80% undocumented – likely to be dumped, traded or recycled under inferior conditions. This review paper provides an overview of the global e-waste resource and identifies the major challenges in the sector in terms of generation, global trade and waste management strategies. It lists the specific hazards associated with this type of waste that need to be taken into account in its management and includes a detailed overview of technologies employed or proposed for the recovery of value from e-waste. On the basis of this overview the paper identifies future directions for effective e-waste processing towards sustainable waste/resource management. It becomes clear that there is a strong divide between developed and developing countries with regard to this sector. While value recovery is practiced in centralised facilities employing advanced technologies in a highly regulated industrial environment in the developed world, in the developing world such recovery is practiced in a largely unregulated artisanal industry employing simplistic, labour intensive and environmentally hazardous approaches. Thus value is generated safely in the hi-tech environment of the developed world, whereas environmental burdens associated with exported waste and residual waste from simplistic processing remain largely in developing countries. It is argued that given the breadth of available technologies, a more systematic evaluation of the entire e-waste value chain needs to be conducted with a view to establishing integrated management of this resource (in terms of well-regulated value recovery and final residue disposal) at the appropriately local rather than global scale.
... Moreover, the bioleaching of sulfide minerals is known as a complex process with a number of factors such as pH, temperature, and oxidation-reduction potential (ORP) affecting bacterial activity and chemical dissolution in minerals. 17,3133) Thus, the present study was designed as a preliminary study of column bioleaching to obtain insight into the effects of several operating parameters on Cu dissolution from chalcopyrite ores. The tests were conducted using a batch system approach with mesophilic microorganisms preadapted to Cu and chalcopyrite. ...
This study examines the effects of several operating parameters on copper leaching from chalcopyrite ores using an adapted mesophilic bacterial culture. Three temperatures (35, 40, and 45°C), three pulp density (1, 2, and 4% (w/v)), and three initial ferrous ion (Fe(II)) concentrations (5, 10, and 20 g/L) were employed as variable parameters, and their effects on the bioleaching efficiency of chalcopyrite were investigated. After 14 days, the maximum copper bioleaching efficiency was estimated to be ∼64% at a temperature of 45°C, a pH of 1.5, an initial ferrous concentration of 5 g/L, and a pulp density of 4%. More specifically, the chalcopyrite dissolution tests conducted at different temperatures showed a minimal effect of temperature and low leaching efficiency (<20%) regardless of temperature. The trend of chalcopyrite dissolution at different pulp densities showed that Cu extraction tended to increase with increases in pulp density. Moreover, the Cu leaching efficiency associated with mesophilic microorganisms largely decreased when the initial Fe(II) concentration was greater than 10 g/L. The Cu leaching behavior in different test conditions was evalauted with concentrations of total iron (Fe), Fe(II), and ferric ions (Fe(III)), as well as the oxidation-reduction potential (ORP) of the solution used in the test. The Cu leaching rate increased under lower ORP conditions, lower Fe(III):Fe(II) ratios, and balanced Fe(II)–Fe(III) cycles.
... The Fe 2+ produced during the above reactions re-oxidizes to ferric ions by bacteria (Eq. 2) and these sustainable reactions cause sulfide mineral dissolution in the presence of iron [7]. ...
The present study investigates the influence of ferrous iron (as FeSO4) and ferric iron (as Fe2 (SO4)3), and pyrite (FeS2) on the ability of bacterial leaching of a high-grade sulfide Zn–Pb ore. In this regard, shake flask experiments were carried out at 5% (w/v) pulp density of the ore sample (having 40.7% Zn and 12.4% Pb initial metal content) using a consortium of mesophilic iron and sulfur-oxidizing acidophiles. A concentration of 0.04 mol/L of ferric iron in the leaching media was found to be optimum for zinc extraction without affecting growth of the microorganisms. Under this concentration, the dissolution of Zn, Pb, Cd, and As was found to be 57%, 0.2%, 0.03%, and 9.9% in 25 days. Using ferrous iron in the media, 0.16 mol/L of Fe²⁺ was found to be the optimum concentration for efficient bacterial growth and metal dissolution (54.6% Zn, 0.08% Pb, 0.03% Cd, and 10.2% As) from the sample in 25 days. On the other hand, using pyrite as the source of energy for bacterial growth, an initial 12-day lag period was observed when compared to the effect of ferrous iron in the media. Under the optimum concentration (test with 0.24 mol/L iron in the form of pyrite), the dissolution of Zn, Pb, Cd, and As was found to be 39.8%, 0.1%, 0.03%, and 10% in 25 days. The surface chemistry analysis indicated formation of a sulfur layer over the particle surface that hindered reagent diffusion and affected metal recovery through bioleaching.
... The pH detection is crucial due to its vital role in numerous biological and chemical processes [18][19][20][21][22][23][24][25][26]. Several methods such as acid-base indicator titration [27,28], potentiometric titration [29,30], absorption and fluorescence spectroscopy [31,32] have been used for the measurement of pH variation. ...
A new rhodamine functionalized Schiff base (3',6'-bis(diethylamino)-2-((Z)-(5-((E)-(1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)diazenyl)-2,4-dihydroxybenzylidene) amino)spiro[isoindoline-1,9'-xanthen]-3-one (1) has been synthesized and was characterized spectroscopically. The optical properties of the schiff base have been studied using UV-vis and fluorescence spectra. Schiff base 1 displayed a selective behaviour towards Th4+ ions, as evidenced by UV-vis and fluorescence spectra. It shows visible colour change from orangish-yellow to red upon addition of Th4+ ions. A strong new emission band at 586 nm and about 24-fold enhancement in fluorescence intensity was observed upon binding with Th4+ which could be quenched by subsequent addition of oxalate and chromate ions. Probe 1 also acts as a reversible pH sensor in the highly acidic region (pH < 4, pKa = 2.01) via the photophysical response to pH as well as visible detectable colour change from orangish-yellow to red to pink. The absorbance and emission intensities of 1 diminished in the pH region from 4 to 11.5 and could be recovered by adding acid to adjust the pH < 4. Probe 1 exhibited high binding constant (8.595 × 106 M-1) and low limit of detection (1.122 × 10-9) compared to most previously reported sensors for Th4+ ions. Furthermore, two multiple logic gates i.e. 3 and 5 input, have been constructed.
... This maximum dissolution after 6 days is due to the use of indigenous bacterial consortia that are more compatible to the mineralogical nature of the ore. Our results showed consistency with the findings of Bhatti et al. (1993); Deveci et al. (2004); Olubambi et al. (2008). Fluctuation in initial pH of medium shows variation in dissolution rate, it is because of the inhibitory effect of pH on bacterial metabolism. ...
Indigenous iron-oxidizing bacteria were isolated on modified selective 9KFe2+ medium from Baiyin copper mine stope, China. Three distinct acidophilic bacteria were isolated and identified by analyzing the sequences of 16S rRNA gene. Based on published sequences of 16S rRNA gene in the GenBank, a phylogenetic tree was constructed. The sequence of isolate WG101 showed 99% homology with Acidithiobacillus ferrooxidans strain AS2. Isolate WG102 exhibited 98% similarity with Leptospirillum ferriphilum strain YSK. Similarly, isolate WG103 showed 98% similarity with Leptospirillum ferrooxidans strain L15. Furthermore, the biotechnological potential of these isolates in consortia form was evaluated to recover copper and zinc from their ore. Under optimized conditions, 77.68 ± 3.55% of copper and 70.58 ± 3.77% of zinc were dissolved. During the bioleaching process, analytical study of pH and oxidation-reduction potential fluctuations were monitored that reflected efficient activity of the bacterial consortia. The FTIR analysis confirmed the variation in bands after treatment with consortia. The impact of consortia on iron speciation within bioleached ore was analyzed using Mössbauer spectroscopy and clear changes in iron speciation was reported. The use of indigenous bacterial consortia is more efficient compared to pure inoculum. This study provided the basic essential conditions for further upscaling bioleaching application for metal extraction.
... When the "A" site cation is unspecified or a generic reference to the group or minerals within the group is intended, A-jarosite will be used). A-jarosite group minerals are typically found in acidic, iron-and sulfate-rich environments such as acid mine drainage impacted sediments, acid sulfate soils, and precipitates from bioleaching systems (Bigham and Nordstrom, 2000;Deveci et al., 2004;Blodau, 2006;Fitzpatrick et al., 2017). Most minerals within the group are relatively stable under natural conditions in the approximate pH range of 1.5-3.0 ...
The purpose of this study was to characterize a series of (Na, NH4, H3O)-jarosites produced with various combinations of NH4⁺ + Na⁺ in cultures of Acidithiobacillus ferrooxidans that simulated acid solutions from bioleaching systems. The solution concentrations utilized were 6.1, 80, 160 and 320 mM for NH4⁺ and 0, 50, 100, 250 and 500 mM for Na⁺ as their respective sulfates. Media at pH 2.2 were inoculated with iron-oxidizing A. ferrooxidans and incubated in shake flasks at 22 ± 2 °C. As the bacteria oxidized ferrous sulfate, ferric iron hydrolyzed and precipitated as schwertmannite (idealized formula Fe8O8(OH)6(SO4).nH2O) and/or as solid solution jarosites [(Na, NH4, H3O)-Fe3(SO4)2(OH)6)] depending on the relative and absolute concentrations of NH4⁺ and Na⁺. The precipitates were characterized by elemental analysis, X-ray diffraction, specific surface area, and Munsell color. Schwertmannite was the dominant mineral product at low combinations of Na⁺ (≤50 mM) and NH4⁺ (≤80 mM) in the media after 2 weeks of aging. At higher single or combined concentrations and with aging for 6 and 11 weeks, the formation of yellowish, solid solution jarosites was enhanced. Precipitation of jarosite-group minerals was favored by NH4⁺ relative to Na⁺. Color (Munsell hue) was a useful tool for assessing sample mineralogy after extended aging, but the presence of abundant, poorly crystalline schwertmannite tended to mask the color of admixed jarosite-group minerals after only 2 weeks of contact with the culture media. The purest samples of jarosite-type minerals had specific surface areas <1.0 m²/g. Unit cell edge lengths and cell volume calculations from powder XRD data indicated that the jarositic phases produced were ternary (Na, NH4, H3O)-solid solutions. Most products also appeared to be deficient in structural Fe, especially at low NH4 contents. Thus, ferric iron precipitation from the simulated bioleaching systems yielded solid solutions of jarosites with chemical compositions that were dependent on the relative concentrations of Na⁺ and NH4⁺ in the synthesis media. No phase separations involving discrete, end-member Na-, NH4-, or H3O-jarosites were detected.
... mg/L, whereas slower growth kinetics was observed at concentration beyond the given range (91.71-148.85 mg/L) due to precipitation of the dissolved FeSO 4 at reaction temperature At high levels of Fe 2+ , the bioleaching of copper gets limited by the strength of inoculum (size of active population of bacteria) relative to available Fe 2+ , the availability/transfer of O 2 and CO 2 , and other factors [21]. Also almost no growth was supported below the minimum FeSO 4 concentration (63.14 mg/L) required for medium preparation. ...
Amid the plethora of initiatives and regulations targeting the minimization of electronic waste generation and its transboundary shipment, efforts to adopt a sustainable resource conservation from this emerging waste stream are considerably missing. Present study is a pioneer effort to develop a novel two stage biorecvoery process
followed by electrochemical treatment to recover copper in its reusable form from waste printed circuit board. An isolated strain USCT-R010 was employed for the leaching of copper and process parameters (reaction pH, substrate concentration, inoculum size, pulp density, agitation speed) were optimized in order to maximize bioleaching of copper. The leach liquor containing mobilized copper was subjected to purification step where biosorption was carried out using dead biomass of Aspergillus oryzae and Baker’s Yeast under optimized reaction condition. Desorption was performed using 0.1N HCl to recover pure copper from dead biomass and more than 86% copper was desorbed from both the biosorbents. Electrowinning was carried out at current: 2A and electrolysis time: 150 min to recover 92.7% Cu from eluate. Characterization studies suggested 95.2% purity of recovered copper which was reused as an antibacterial agent against Escherichia coli. Utilization of low cost biomaterial for recovery and purification of metals, eco-efficient technology with high level of purity, reusability of recovered copper and environmentally sound practices are the aided incentives associated with this novel
approach. The proposed work can be reckoned as successful demonstration of ‘Greening the waste’ concept in order to generate substantial economic, environmental and social benefits from e-waste.
... Temperature is considered to be one of the most important factors for bacterial growth [51]. The best temperature for A. ferrooxidans growth is approximately 35 °C owing to the mesophilic nature of the bacteria [52]. Previous studies have shown that the concentration of arsenic ions significantly increased from 16.4 to 37.8 mg/l as the temperature changed from 15 to 40 °C [53,54]. ...
Realgar is a naturally occurring arsenic sulfide (or Xionghuang, in Chinese). It contains over 90% tetra-arsenic tetra-sulfide (As4S4). Currently, realgar has been confirmed the antitumor activities, both in vitro and in vivo, of realgar extracted using Acidithiobacillus ferrooxidans (A. ferrooxidans). Bioleaching, a new technology to greatly improve the use rate of arsenic extraction from realgar using bacteria, is a novel methodology that addressed a limitation of the traditional method for realgar preparation. The present systematic review reports on the research progress in realgar bioleaching and its antitumor mechanism as an anticancer agent. A total of 93 research articles that report on the biological activity of extracts from realgar using bacteria and its preparation were presented in this review. The realgar bioleaching solution (RBS) works by inducing apoptosis when it is used to treat tumor cells in vitro and in vivo. When it is used to treat animal model organisms in vivo, such as mice and Caenorhabditis elegans, tumor tissues grew more slowly, with mass necrosis. Meanwhile, the agent also showed obvious inhibition of tumor cell growth. Bioleaching technology greatly improves the utilization of realgar and is a novel methodology to improve the traditional method.
... Ancak ferros demirin ferrik demire oksidasyonu asit tüketen reaksiyonlar olduğu için ortam koşullarının sabit tutulması ve ferrik demirin çökelmemesi için asit eklemek suretiyle pH'ın uygun aralıkta (<pH 2) kontrol edilmesi gerekir. Ayrıca başlangıçta ortamda yeterli miktarda çözünmüş demir bulunması liç işleminin etkin şekilde ilerlemesi için gereklidir [9]. ...
... Studies have shown that the use of both mesophilic and thermophilic digesters could help recover energy from biowastes such as livestock manure and food waste. Furthermore, the use of thermophiles for the recovery of metals from industrial and municipal wastes has also been proposed [12,13]. Bioleaching is the process through which microorganisms are used to extract metals from ores and waste products. ...
Thermophilic microorganisms are of increasing interest for many industries as their enzymes and metabolisms are highly efficient at elevated temperatures. However, their metabolic processes are often largely different from their mesophilic counterparts. These differences can lead to metabolic engineering strategies that are doomed to fail. Genome-scale metabolic modeling is an effective and highly utilized way to investigate cellular phenotypes and to test metabolic engineering strategies. In this review we chronicle a number of thermophilic organisms that have recently been studied with genome-scale models. The microorganisms spread across archaea and bacteria domains, and their study gives insights that can be applied in a broader context than just the species they describe. We end with a perspective on the future development and applications of genome-scale models of thermophilic organisms.
The aim of present article is to explore a method for efficient selective separation and extraction of valuable components in low-grade polymetallic complex chalcopyrite ore (LPCCO). Characterization techniques such as ICP-AES, XRD, chemical phase analysis, SEM–EDS were used to systematically study the mineralogical characteristics of LPCCO, such as element content, phase composition, existence state, and interphase distribution characteristics. Based on mineralogical research, with sodium lignosulfonate as an additive, the oxygen pressure acid leaching study was carried out in the H2SO4–O2 system. The results show that the occurrence phase of copper in the LPCCO is mainly chalcopyrite (CuFeS2) with a small amount of bornite (Cu5FeS4). The occurrence phase of iron is mainly pyrite (FeS2); in addition, chalcopyrite and bornite are also iron-bearing phases. Lead and zinc exist in galena (PbS) and pure sphalerite (ZnS), respectively, and other elements mainly constitute gangue. The mineral phases in the LPCCO are embedded and wrapped closely with each other, and their particle size is fine, making LPCOO difficult to be used efficiently. Also the results show that the rate of Cu leaching from LPCCO is more than 98 wt%, and the leaching rate of Zn is more than 99 wt% under the optimum leaching conditions. Lead and iron mainly enter the leaching residue in the form of lead jarosite, and the filtration rate of leaching slurry obtained can reach 328.37 L/(m2 h).Graphical Abstract
This article investigates the mineralogical characterization of a thorium ore taken from the Choghart iron mine, Yazd, Iran. The mineralogical studies revealed that the main thorium content mineral of the ore was thorite, and it was mainly disseminated as a valuable mineral in different forms in minor quantity along the edge or within the intergranular spaces of gangue silicate minerals and magnetite. The XRF analysis of a radiometric sorting concentrate sample indicated that the sample contained approximately 0.25% thorium oxide, 66.28% silicate compositions, 9.14% iron oxide and significant amounts of rare earth elements. Sink and Float tests of different sizes of the sample using diiodomethane and bromoform resulted in a 2.22% concentrate with 85.7% thorium recovery. Liberation degree studies by SEM-EDX and image processing indicated that a size range of (−125, +75) µm was the optimum liberation size, and it was recommended for further beneficiation tests.
Nowadays, regarding the increasing development of electronic devices and their expanded wastes, concerns about running out of non-renewable resources have increased the interest in recycling metal pieces of these wastes. On the other hand, compared to pyrometallurgical methods, biological destruction of wastes possess a higher potential to reduce the operational costs and energy consumption and it is the most desirable method from an environmental perspective. However, one major challenge on the way of recycling these electronic wastes is their toxic contents. Hence, the current study is aimed to investigate the application of bioleaching technology in reproducing metal compounds (cu) from electronic wastes. Furthermore, different categories of microorganisms are studied from different perspectives including type, supply, ratio of extracted metal, effect of binding type of microorganism (bacterial or non-bacterial), and being single or consortium (group) to obtain the best result over the electronic wastes. Therefore, the consortium of microorganisms offers a higher advantage for practical applications since organisms can directly harvest from their resource without any need for single organisms. On the other hand, results of a temperature comparison between microorganisms reveal that the extent of metals bioleaching from ores by absolute thermophiles is higher than that by medium thermophiles and mesophiles.
Nowadays, regarding the increasing development of electronic devices and their expanded wastes, concerns about running out of non-renewable resources have increased the interest in recycling metal pieces of these wastes. On the other hand, compared to pyrometallurgical methods, biological destruction of wastes possess a higher potential to reduce the operational costs and energy consumption and it is the most desirable method from an environmental perspective. However, one major challenge on the way of recycling these electronic wastes is their toxic contents. Hence, the current study is aimed to investigate the application of bioleaching technology in reproducing metal compounds (cu) from electronic wastes. Furthermore, different categories of microorganisms are studied from different perspectives including type, supply, ratio of extracted metal, effect of binding type of microorganism (bacterial or non-bacterial), and being single or consortium (group) to obtain the best result over the electronic wastes. Therefore, the consortium of microorganisms offers a higher advantage for practical applications since organisms can directly harvest from their resource without any need for single organisms. On the other hand, results of a temperature comparison between microorganisms reveal that the extent of metals bioleaching from ores by absolute thermophiles is higher than that by medium thermophiles and mesophiles.
The copper, cobalt and nickel ores are still currently mined in the world. Its complex mineralogy creates extraction challenges by means of conventional metallurgical methods. Meanwhile, dealing with mesophilic strains in leaching process requires a compromise between solid loading and microbiota activity and growth. That is why, the influence of solid loading with fine or coarse particulates, the cell disturbance during the metal–microbes interactions depending upon the influence of gangue nature as well as metallic ions concentration on bacterial tolerance and the chemical and biological pathways involved in bioleaching mechanism of complex ores are summarised in detail in this paper. The current trends in mechanism research and diverse discovered set of microbiota and bacterial population coupled with bacterial adaptation methods contribute to optimise and improve the metals leaching performance and knowledge. In addition, the different existing complex mineralogical structures elaborate a main indirect mechanism with two different transitory mechanisms, before metal is converted into metal sulphate as wealthily explained in this comprehensive review. More data for cost analysis concomitant with extraction efficiency of metals using mesophilic bioleaching process are needed. However, it does not mean that other options are excluded in order to set a bio-hydrometallurgical chain. In fact, to consider also the concentration and purification of the pregnant leaching solution via phase separation and solvent extraction will be helpful. This obeys to the idea of option trees, where possible options are then systematically gaged with respect to critical criteria.
Dumping of used printed circuit boards (PCB's) (diode and resistor) into the environment has been a major threat and its degradation methods are inadequate and time-consuming. Therefore development of novel strategies for the recovery of metals is the need of the hour. The current study was focused on biodegradation of waste printed circuit boards (diode and resistors) with five strains Magnetospirillum sp. RJS2 (KJ570852), Magnetospirillum sp. RJS5 (KM289194), Magnetospirillum sp. RJS6 (KT266803), Magnetospirillum sp. RJS7 (KT693285) and Magnetospirillum gryphiswaldense (MSR-1). The circuit boards were milled for size reduction and the samples were analysed using particle size analyser and X-ray powder diffraction (XRD). Heavy metals such as cadmium, copper, nickel, lead and zinc were detected in diode from PCB's, whereas arsenic, chromium, copper, lead, silicon, aluminium, silver and zinc were observed in resistors. The samples were treated with the bacterial strains (RJS2, RJS5, RJS6, RJS7 and MSR-1) individually and in consortia for 12 days. Atomic absorption spectroscopy (AAS) analysis revealed the isolate RJS2, MSR-1 and RJS6 showed maximum recovery of cadmium (97%), lead (100%) and nickel (99%) from diode respectively. Similarly from resistor the maximum recovery was observed with RJS2 (copper - 89%) and RJS6 (zinc - 88%). The overall average recovery of cadmium (80%) and lead (66%) was more from treated diode. Similarly, copper (45%) and lead (40%) were recovered from resistors. It was also observed that the isolate RJS2 was effective in metal recovery (52%) from diode and strain RJS6 (66%) for the resistor. Two groups of consortia were developed MAG1 (RJS2, RJS5 and MSR-1) and MAG2 (RJS6 and RJS7) based on their growth requirements, where MAG1 exhibited better recovery of metals such as nickel (100%), zinc (75%) from diode and cadmium (90%), nickel (22%) and zinc (47%) from resistor as compared to individual strains. MAG2 also exhibited better recovery of lead (57%) from diode and nickel (22%) from resistor. Scanning electron microscope Energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray fluorescence (XRF) analysis confirmed RJS2 and RJS6 were dominant strains in metal recovery. The study showed the efficacy of Magnetospirillum bacteria in enhanced metal recovery from PCB's, highlighting its possible role in the management of E-waste.
This study aimed to investigate the ability of pure and consortia of indigenous iron-oxidizing bacteria to enhance the dissolution of trace metals from Cu and Zn-bearing ore. Three bacterial strains Acidithiobacillus ferrooxidans strain WG101, Leptospirillum ferriphilum strain WG102, Leptospirillum ferrooxidans strain WG103 isolated from Baiyin copper mine, China were used in this study. The biotechnological potential of these indigenous isolates was evaluated both in pure and in consortia to extract cobalt, chromium, and lead from the copper and zinc bearing ore. The sulfur and iron-oxidizing bacterial isolate Acidithiobacillus ferrooxidans strain WG101 exhibited efficient dissolution compared to sole iron-oxidizing Leptospirillum ferriphilum strain WG102, and Leptospirillum ferrooxidans strain WG103. Initial medium pH, pulp density, and temperature were studied as influential parameters in bioleaching carried out by bacterial consortia. The achieved optimum conditions were; initial pH of 1.5, 10% of pulp density, and temperature 30 C with 68.7 ± 3.9% cobalt, 56.6 ± 3.9% chromium, and 36 ± 3.7% lead recovery. Analytical study of oxidation reduction potential and pH fluctuation were observed during this whole process that shows the metal dissolution efficiency of bacterial consortia. Alterations in spectral bands of processed residues were reported through FTIR analysis compared with control ore sample. M€ ossbauer spec-troscopy analysis showed the influence of bacterial consortia on iron speciation in bioleached samples. The findings confirm that the indigenous acidophilic iron-oxidizing bacterial strains are highly effective in the dissolution of trace elements present in ore samples. This study not only supports the notion that indigenous bacterial strains are highly effectual in metal dissolution but provides the basic vital conditions to upscale the bioleaching technique for metals dissolution. ARTICLE HISTORY
Bioleaching is considered to be a low-cost, eco-friendly technique for leaching valuable metals from a variety of matrixes. However, the inherent slow dissolution kinetics and low metal leaching yields have restricted its wider commercial applicability. Recent advancements in bio-hydrometallurgy have suggested that these critical issues can be successfully alleviated through the addition of a catalyst. The catalyzing properties of a variety of metals ions (Ag+, Hg++, Bi+++, Cu++, Co++ etc.) during bioleaching have been successfully demonstrated. In this article, the role and mechanisms of these metal species in catalyzing bioleaching from different minerals (chalcopyrite, complex sulfides, etc.) and waste materials (spent batteries) are reviewed, techno-economic and environmental challenges associated with the use of metals ions as catalysts are identified, and future prospectives are discussed. Based on the analysis, it is suggested that metal ion-catalyzed bioleaching will play a key role in the development of future industrial bio-hydrometallurgical processes.
The attachment and bioleaching experiments were conducted to evaluate the zinc recovery from Hualilan ore by the thermoacidophilic archaeon Acidianus copahuensis. Cells of this species pregrown on tetrathionate showed higher capability of attachment to the ore than cells pregrown on other energy sources and such attachment seemed to be mediated by the product of extracellular polymeric substances. A. copahuensis achieved a successful bioleaching of the ore reaching 100% of zinc recovery when tetrathionate was added. Simultaneous addition of yeast extract and tetrathionate maintained the zinc extraction at higher rate. Zinc dissolution kinetics was controlled by chemical reaction in cultures with the external addition of tetrathionate but by the diffusion through a product layer of jarosite in the other cultures.
-------Abstract------------------
Compared to conventional extractive techniques, bacterial assisted leaching, also called “biomining” is an eco-friendly technology that provides improved metal/solid separations. These separations are enhanced by the synergistic activities of astonishingly diverse groups of microorganisms, which lead to an extraction process with low energy consumption, low capital investment and low impact on the environment. Recently, biomining has received great attention in a variety of niche areas, especially in the mineral industries and solid industrial waste materials (e.g. galvanic sludge, sewage sludge, fly ash, electronic waste, spent petrochemical catalysts, medical waste, spent batteries, waste slag) where the metals values are low, or where the presence of certain elements would lead to smelter damage, or where environmental considerations favor biological treatments options. It allows the recovery of metal from low-grade sulfide ores and concentrates that cannot be processed economically by conventional techniques, as well as the production of concentrated metal salt solutions, which could be recycled. Bacterial assisted leaching processes are based on the ability of certain microorganisms to solubilize/or expose the metals contained in the ores and concentrates by direct oxidation, or through indirect chemical oxidation instigated by the corrosive metabolic by-products generated by an electrochemical option, or a combination of both of these. The valuable metals in solution can be recovered using conventional hydrometallurgical techniques. If the material of interest constitutes part of or is in the pre-treated residue then it can be further processed for metal recovery. The majority of microorganisms involved in bacterial assisted leaching processes are chemolithotrophs. Carbon dioxide (CO2) and oxygen (O2) are essential nutrients that are used by microorganisms for their growth, maintenance, metabolite production, and survival.
This literature review aims to provide a fundamental understanding of the various mechanisms involved in microbial leaching of sulfide minerals and provide a brief look at the various factors affecting this process. Special attention is focused on the mass transfer rates in the gas phase and how they exert a pivotal role in microbially assisted leaching of sulfide minerals. Also reviewed are the major parameters that can affect gas phase mass transfer, with particular emphasis on how it is related to the efficiency of bacterial assisted leaching.
----------Keywords--------
Biomining; Bioleaching; Biooxidation; Sulfide minerals; Microorganisms; Gas transfer
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----> This review has been written and prepared jointly by Dr. Akrama Mahmoud and Professor Andrew Hoadley (Monash University, Australia). We would like to thank all authors of the papers given in the reference list for obtaining a great deal of useful information on biomining processes, and thus in helping to prepare this paper. The principal author (Dr. Akrama Mahmoud) would like to thank Jean Michel Sorbet and Olivier Gelade for their kind technical assistance and help. Finally, Dr. Akrama Mahmoud dedicate this paper to his parents for their love and sacrifices.†
For more information, Please go to:
A review of sulfide minerals microbially assisted leaching in stirred tank reactors. International Biodeterioration & Biodegradation Volume 119, April 2017, Pages 118-146.
http://www.sciencedirect.com/science/article/pii/S0964830516304097. https://doi.org/10.1016/j.ibiod.2016.09.015
Use of microorganisms in the mineral processing industry is a new and efficient method. In this study, heterotrophic bacteria Pseudomonas aeruginosa performance in recovery of zinc from Angoran Zanjan mining tailing was studied. XRD and XRF analysis indicated that the sample containing 17% zinc which had accumulated in Smithsonite mineral. To evaluate determination how to leach mineral with organic acids, first preliminary experiments were performed with citric acid. The optimum conditions of leaching are 60 min time duration, 0.5 M citric acid concentration, 80°C temperature and -400+300 µ size fraction in 10/1 solid-liquid ratio. At first in bioleaching process Nutrient broth medium was used that with respect to weak result, replaced by combined medium containing glucose and other required materials for bacteria. Growth curve of bacteria in both culture media was determined. Effects of time, the amount of glucose in the medium and the solid- liquid ratio on bioleaching operations were studied respectively. Using bacteria and medium containing 6% glucose, solid-liquid ratio 100/1 after five days 38% of the initial zinc content of sample was extracted. Finally, after adaptation of bacteria to high concentration of zinc, 62% of zinc content of initial sample was extracted. Zinc concentration in solution is determined by Atomic Absorption analyses.
The hydrometallurgical treatment of zinc sulfide concentrates involves the separation of zinc from iron, since most zinc concentrates contain 5-12% iron. Several processes, such as hematite, magnetite, goethite and jarosite, have been developed for the removal of iron from solution prior to zinc electrolysis. The precipitation of iron is controlled by a set of thermodynamic and kinetic factors operative both in iron solutions and in precipitates. Identifying these factors and their relations is important for the control of these processes. Inbrief, thermodynamic stability regions of iron compounds formed during the jarosite and goethite processes, which are commercially used in the zinc industry, are outlined in this paper.
Bioleaching/biooxidation is essentially a dissolution process with the involvement of acidophilic bacteria acting as the "catalyst" to accelerate the dissolution of metals from sulfide minerals. The contribution of bacteria to the metal dissolution is closely controlled by the growth of bacteria, which is itself affected by the physico-chemical conditions within the bioleaching environment. There are a number of operating parameters controlling bioleaching processes, which are required to be maintained within a certain range in the leaching environment whereby the activity of bacteria with the resultant oxidation of sulfide minerals can be optimized. In this regard temperature, acidity, oxidizing conditions, availability of nutrients, oxygen and carbon dioxide, surface area and presence of toxic ions are of prime importance for control and optimization of bioleaching of sulfide ores/concentrates. Bioleaching processes are temperature and pH dependent with optimum metal dissolution occurring in a particular range where the bacterial strain is most active e.g. mesophiles at 35-40°C and pH 1.6-2.0. Provision of nutrient salts is required to maintain the optimum growth and hence metal dissolution with the quantity of nutrients apparently being dependent on the availability of substrate i.e. head grade/pulp density of an ore/concentrate. Oxygen transfer is one of the most critical factors since the oxygen levels below 1-2 mg/l may adversely affect the oxidizing activity of bacteria. Bioleaching rate tends to improve with increasing the surface area at low pulp densities but, in practice, the pulp density is limited to ~20% w/v. Increasing concentrations of ions such as Cl -may also adversely affect the oxidative activity of bacteria.
The presence of some anions and cations at certain levels in the bioleaching environment may exert an inhibitory effect on the growth and hence leaching activity of a bacterial culture. In this respect, the quality of process water available with particular reference to salinity can be of prime importance for the application or development of a bioleaching process for a particular feed at an operation site.
The current study investigates the extent to which salinity up to 8% Cl- (~80 g/l) affects the bioleaching activity of mesophilic, moderately and extremely thermophilic strains of bacteria during the bioleaching of a complex Zn/Pb sulphide ore. The results indicated that salinity can adversely influence the “optimum” bioleaching activity of mesophiles and moderate thermophiles; the extent being dependent upon the strain (and type) of bacteria and the concentration of chloride. The mesophilic WJM strain was found to oxidise the complex ore at concentrations of up to 0.8% Cl- (~8 g/l) without any significant effect on the extraction of zinc while the limited extraction of zinc by DSM 583 strain occurred at 0.2% Cl-. It was noted that mesophiles can be adapted to tolerate 0.8-1% Cl- (~8-10 g/l) in solution. The bioleaching ability of the strains of moderate themophiles was adversely influenced even at 0.2% Cl- (~2 g/l). On the other hand, the extreme thermophiles were shown to perform well under saline conditions up to 5% Cl- (~50 g/l). This probably indicates the halophilic peculiarity of the extreme thermophiles compared with the mesophiles and the moderate thermophiles.
It was examined whether gas–liquid transfer of oxygen or carbon dioxide has determined the bacterial oxidation rate of sulphide minerals in the kinetic experiments reported in the literature. Correlations available in the literature were used to estimate the gas–liquid mass transfer coefficients of oxygen and carbon-dioxide, kLa (s−1), in the reported experimental equipment (e.g. shake flasks or aerated stirred tanks). The maximum oxygen and carbon dioxide transfer rates were estimated for reported kinetic experiments with pyrite and compared with estimated maximum oxygen and carbon dioxide consumption rates that occurred in those experiments. It was concluded that gas–liquid carbon dioxide transfer limitation and exhaustion of carbon dioxide in the gas-phase, often occurred. Therefore, the observed decrease of the bacterial oxidation rate constant at increasing slurry densities was probably caused by carbon dioxide limitation. Consequently, the method presented in this work needs to be applied in order to ensure that the bioleaching kinetics are properly measured in the absence of carbon dioxide and/or oxygen transfer limitation.
McArthur River mine (MRM) was described as one of the largest sedimentary stratiform zinc-lead silver deposit known. It was originally classified as a low-grade open pit resource containing 226 Mt of ore grading 9% Zn and 4% Pb. Earlier in 1990s, it was reclassified as an underground resource of 103.7 Mt at 14.1% Zn and 6.4% Pb and 64 g/t silver. The current mining operation's proven and probable reserves are 26.6 Mt averaging 14.0% Zn, 6.2% Pb and 63 g/t Ag. It will be at its full mining capacity by the end of the end of the 1995/96 financial year. MRM is today's world newest leader in mine automation and metallurgy.
Bacteria that bring about dissimilatory transformations of iron are important from both biogeochemical and industrial perspectives (Ehrlich and Brierley, 1990; Johnson, 1995). The oxido-reduction of iron in extremely acidic (pH > 3) environments is particularly interesting because of the greater solubility of ionic (particularly ferric) iron and the relative stability of soluble ferrous iron under these conditions. Acidophilic iron-oxidizing bacteria are generally considered the most significant microorganisms in the biological processing of sulfide ores (“biomining”) in which the accelerated oxidative dissolution of sulfidic minerals (e.g., pyrite, arsenopyrite, and chalcopyrite) solubilizes (e.g., copper) or releases (refractory gold) metals, thereby facilitating their recovery (Rawlings and Silver, 1995). Most research into bacterial iron transformations at low pH has focused on mesophilic chemolithotrophs, particularly Thiobacillus ferrooxidans, though a number of physiologically and phenotypically diverse mesophilic acidophiles, it is now known, are involved in the dissimilatory oxido-reduction of iron (Johnson, 1995; Norris and Johnson, 1997; Pronk and Johnson, 1992).
This paper is a progress report on the commercialization of using bioleaching for base-metal concentrates. The paper focuses on bioleach processes for recovering copper from chalcopyrite and nickel/cobalt from pentlandite/pyrrhotite. Data is discussed from pilot-plant trials in which an overall recovery >95% was obtained for the bioleaching of copper from chalcopyrite. The pilot plant was operated in closed circuit with solvent extraction and electrowinning circuits for final metal recovery. For the bioleaching of nickel and cobalt from pentlandite/pyrrhotite, an overall recovery of 97% was achieved. Precipitation routines were used to produce a final nickel/cobalt product. The pilot plants were capable of treating a few kilograms of concentrate per day. Prominent features in the design of a 1-t/day (1.1-stpd) copper-bioleach demonstration plant for the treatment of chalcopyrite concentrate are discussed. The plant, which is now under design, will be constructed and operated based on the results obtained from the laboratory pilot-plant campaigns. Issues of scale-up for the demonstration plant, together with integration into upstream and downstream processing, are also addressed. Independently derived capital and operating costs are presented for a possible commercial plant. These cost studies indicate the principle economic issues in considering the application of bioleaching to the extraction of base metals. The benefits of bioleaching complex concentrates that are not amenable to physical beneficiation and economic treatment by conventional smelting are highlighted. Issues, such as the environmental aspects, that illustrate the benefits of bioleach technology are given.
The recovery of mineral and metal values by solution mining has been practiced for centuries. What appears at first glance to be a simple, empirical technique, is in actuality a very complicated process involving a large number of critical parameters that encompass several scientific and engineering disciplines. Hydrometallurgy, hydrology, geology and geochemistry, rock mechanics, chemistry, and environmental engineering and management are a few of the specialties utilized by modern operators.
Solution mining is conveniently divided into three main categories: heap leaching, dump leaching, and in situ leaching. In situ leaching (ISL) involves the application of a specific lixiviant to dissolve en masse minerals within the confines of a deposit or in very close proximity to its original geologic setting. Currently there is considerable interest in applying ISL technology to recover copper. Substantial research and engineering effort is being expended to recover copper from oxide ores. However, the greatest potential for copper ISL extraction remains with the deep seated deposits that would otherwise be left unmined by conventional methods.
This paper highlights some historical aspects of copper in situ leaching, and also reviews some commercial and experimental projects involving both oxide and sulfide deposits. In addition, large whole-core leaching experiments using a copper oxide ore will be described. This work has provided better understanding of the physical and chemical factors associated with the in situ leaching response.
Microbiological leaching has been used as an alternative approach to conventional hydrometallurgical methods of uranium extraction. In the microbiological leaching process, iron-oxidizing bacteria oxidize pyritic phases to ferric iron and sulfuric acid, and uranium is solubilized from the ore due to sulfuric acid attack. If uranium in the ore material is in the reduced, tetravalent form (UIV), a redox reaction is involved whereby uranium is oxidized to the hexavalent form (UVI) upon dissolution. In acid-leaching systems, the primary oxidant is ferric iron, which is reduced to ferrous iron by its chemical reaction with UIV. The ferrous iron thus formed is reoxidized to ferric iron by iron-oxidizing bacteria such as Thiobacillus ferrooxidans and Leptospirillum ferrooxidans. Nutritional requirements and responses to environmental extremes of acidophilic iron-oxidizing bacteria are appraised. The S-entity in Fe-sulfides is oxidized to sulfate by bacteria similar to Thiobacillus ferrooxidans and Thiobacillus thiooxidans. Pyrite and marcasite oxidation is a sulfuric acid forming reaction. Heap, dump and in situ leach techniques are feasible as bacterial leaching systems.
An experimental study of the bacterial oxidation of naturally occurring high-purity sulphide minerals (FeS//2, Fe//1// minus //xS, Cu//5FeS//4, ZnS) is presented using a mesophilic strain of T. ferrooxidans. As well as metal analyses and solution pH, partitioning of sulphide sulphur into elemental sulphur and sulphate has been monitored as a function of leach time. Partially oxidized sulphide substrates have been characterized, at regular time intervals, by X-ray diffraction methods and extracellular organic compounds reporting into leach solution have been identified by thin layer chromatography.
GENCOR S.A. Ltd. has pioneered the commercialization of biooxidation of refractory gold ores. Development of the BIOX® process started in the late 197os at GENCOR Process Research, in Johannesburg, South Africa. The early work was championed by Eric Livesey-Goldblatt, the manager of GENCOR Process Research who directed pioneering and innovative research into bacterial oxidation of refractory gold ores prior to cyanidation. This work was driven by the need to replace Fairview’s outmoded Edward’s roasters, which at the time were seriously contributing to pollution in the Barberton area.
Billiton Process Research has carried out extensive research over the past four years to develop new process technology using bioleaching for extraction of copper and nickel from their sulphide concentrates. Continuous pilot scale and laboratory batch testwork has been carried out with adapted mesophile bacterial cultures at 40°C - 45°C, moderate thermophile cultures at 50°C - 55°C and thermophile cultures at 65°C - 85°C. Pilot scale work has demonstrated the commercial viability of mesophile cultures for bioleaching of secondary copper sulphide and nickel sulphide concentrates. Moderate thermophiles offer benefits in terms of reduced cooling requirements for commercial reactors and, in the case of bioleaching of nickel concentrates, some selectivity over bioleaching of pyrite. Continuous pilot scale testwork has shown that thermophiles achieve efficient bioleaching of primary copper sulphide and nickel sulphide concentrates, giving much higher recoveries than achieved by bioleaching with a mesophile or moderate thermophile culture.
Currently, low-grade and complex ores and mining wastes can be processed economically by using bacteria in heap and agitation leaching processes. Bacterial leaching tests are performed on the run-of-mine ore which is a mixture of two different massive and dissemine copper ores, fed to Küre Copper Plant. In this leaching process, using "Acidithiobacillus ferrooxidans" culture, bacteria count, pH, copper and iron recoveries are monitored during the 576 hours of test period. By increasing the solid ratio (1 %→5 %) the oxidation ability of bacteria decreases, thus the leaching rate. Therefore copper and iron recoveries decreased from 68 %, 35 % and 45 %, 20 %, respectively. As a result of laboratory tests, it is found that as the pulp density increased, the efficiency of copper recovery decreased using this bacterial culture.
Scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) were used to follow the surface changes occurring in galena when the bioleaching medium contained Ag(I), Hg(II) and Bi(III) ions. The results showed that the catalyst ions Ag(I), Hg(II) and Bi(III) are incorporated into the surface irrespectively of the presence of bacteria, and different reactions take place on the surface of galena depending on the cation added to the leaching medium. When the bioleaching process takes place without catalyst or with Bi(III) the galena is transformed into PbSO4 and the growth of oxidation products is characterized by needles. Ag(I) and Hg(II) ions form a layer on the galena surface, which prevents the transformation of such surface into PbSO4. The layer formed in this process can be like a silver sulphide and a mercury sulphide depending on the ion species. Microorganisms oxidize the surface sulphur of this layer and thus decrease the S/Ag and S/HG ratios at the surface.
Bioleaching is a simple and effective technology for metal extraction from low-grade ores and mineral concentrates. Metal recovery from sulfide minerals is based on the activity of chemolithotrophic bacteria, mainly Thiobacillus ferrooxidans and T. thiooxidans, which convert insoluble metal sulfides into soluble metal sulfates. Non-sulfide ores and minerals can be treated by heterotrophic bacteria and by fungi. In these cases metal extraction is due to the production of organic acids and chelating and complexing compounds excreted into the environment. At present bioleaching is used essentially for the recovery of copper, uranium and gold, and the main techniques employed are heap, dump and in situ leaching. Tank leaching is practised for the treatment of refractory gold ores. Bioleaching has also some potential for metal recovery and detoxification of industrial waste products, sewage sludge and soil contaminated with heavy metals.
Several factors affecting the precipitation of the alkali jarosites (sodium jarosite, potassium jarosite, rubidium jarosite,
and ammonium jarosite) have been studied systematically using sodium jarosite as the model. The pH of the reacting solution
exercises a major influence on the amount of jarosite formed, but has little effect on the composition of the washed product.
Higher temperatures significantly increase the yield and slightly raise the alkali content of the jarosites. The yield and
alkali content both increase greatly with the alkali concentration to about twice the stoichiometric requirement but, thereafter,
remain nearly constant. At 97 °C, the amount of product increases with longer retention times to about 15 hours, but more
prolonged reaction times are without significant effect on the amount or composition of the jarosite. Factors such as the
presence of seed or ionic strength have little effect on the yield or jarosite composition. The amount of precipitate augments
directly as the iron concentration of the solution increases, but the product composition is nearly independent of this variable.
A significant degree of agitation is necessary to suspend the product and to prevent the jarosite from coating the apparatus
with correspondingly small yields. Once the product is adequately suspended, however, further agitation is without significant
effect. The partitioning of alkali ions during jarosite precipitation was ascertained for K:Na, Na:NH4, K:NH4, and K:Rb. Potassium jarosite is the most stable of the alkali jarosites and the stability falls systematically for lighter
or heavier congeners; ammonium jarosite is slightly more stable than the sodium analogue. Complete solid solubility among
the various alkali jarosite-type compounds was established.
The dissolution of metal sulfides is controlled by their solubility product and thus, the [H+] concentration of the solution, and further enhanced by several chemical mechanisms which lead to a disruption of sulfide chemical bonds. They include extraction of electrons and bond breaking by [Fe3+], extraction of sulfur by polysulfide and iron complexes forming reactants [Y+] and electrochemical dissolution by polarization of the sulfide [high Fe3+ concentration]. All these mechanisms have been exploited by sulfide and iron-oxidizing bacteria. Basically, the bacterial action is a catalytic one during which [H+], [Fe3+] and [Y+] are breaking chemical bonds and are recycled by the bacterial metabolism. While the cyclic bacterial oxidative action via [H+] and [Fe3+] can be called indirect, bacteria had difficulties harvesting chemical energy from an abundant sulfide such as FeS2, the electron exchange properties of which are governed by coordination chemical mechanisms (extraction of electrons does not lead to a disruption of chemical bonds but to an increase of the oxidation state of interfacial iron). Here, bacteria have evolved alternative strategies which require an extracellular polymeric layer for appropriately conditioned contact with the sulfide. Thiobacillus ferrooxidans cycles [Y+] across such a layer to disrupt FeS2 and Leptospirillum ferrooxidans accumulates [Fe3+] in it to depolarize FeS2 to a potential where electrochemical oxidation to sulfate occurs. Corrosion pits and high resolution electron microscopy leave no doubt that these mechanisms are strictly localized and depend on specific conditions which bacteria create. Nevertheless, they cannot be called ‘direct’ because the definition would require an enzymatic interaction between the bacterial membrane and the cell. Therefore, the term ‘contact’ leaching is proposed for this situation. In practice, multiple patterns of bacterial leaching coexist, including indirect leaching, contact leaching and a recently discovered cooperative (symbiotic) leaching where ‘contact’ leaching bacteria are feeding so wastefully that soluble and particulate sulfide species are supplied to bacteria in the surrounding electrolyte.
Several variables were examined in column bioleaching of a complex sulfide ore material which contained chalcopyrite, pentlandite, pyrite, pyrrhotite and sphalerite as the main sulfide minerals. Samples were used with varying proportions of pyrrhotite, pyrite, quartzite (low acid consumption) and skarn (high acid consumption). The experiments were carried out using bench-scale column leaching reactors which were inoculated with acidophilic, Fe- and S-oxidizing bacteria, initially derived from the source mine water. Leaching rates in sterile controls were negligible. In inoculated columns new solid phases (covellite, jarosite, Fe (III) oxide and elemental sulfur) were formed. Acid consumption was highest under low pH and low redox potential conditions. The solubility of ferric iron was controlled by jarosite and an Fe (III) hydroxide (initially amorphous). The leaching rates of Co (from pyrite and pentlandite), Cu (chalcopyrite), and Zn (sphalerite) showed a tendency to increase with dissolved ferric iron concentration. The leaching of Ni (from pyrrhotite and pentlandite) did not correlate with the concentration of ferric iron in solution. Microscopic counts of bacteria in solution, deemed insufficient to represent total bacterial counts, showed a tendency to be higher at the lower pH and intermediate redox potential ranges. Trickle-leaching conditions yielded higher acid production and redox-potential values compared with flood leaching. The leaching rates of Co, Cu, Ni and Zn each responded differently to redox potential and pH regimes. The accelerating effect of a decreasing particle size on the metal leaching rates was amplified by low pH values.
In the present work the applicability of bioleaching using a mixed culture of mesophilic microorganisms (Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirilum ferrooxidans) on a bulk concentrate of a Spanish complex sulphide ore was studied. The bulk concentrate mainly consisted of by chalcopyrite, sphalerite and pyrite. Effects of nutrient medium, stirring, pulp density, temperature and the addition of CO2 (1% v/v) to the air flow were also studied. The highest leaching rates and recoveries were obtained with mechanically stirred reactors at 5% pulp density and 9K medium. However, by using 9K medium higher jarosite precipitation was observed. Results showed that the optimum temperature for copper bioleaching was 30°C, whereas zinc dissolution increased with a rise in the temperature.
The current phases used for the disposal of iron and arsenical wastes, jarosite and scorodite, are examined from a thermodynamic viewpoint using critically assessed data. For scorodite, it is demonstrated that the differences in the solubility reported in the literature are due to starting phases of differing crystallinity. Contour plots of solubility vs pH and activity are presented for both scorodite and jarosite and show that the minimum solubility is achieved for pH 4–7. However, neither phase is stable towards transformation to goethite with scorodite only stable below pH 4 and jarosite below pH 7. The practicalities and implications of the disposal of these phases is discussed and recommendations for future disposal options are made.
The Ok Tedi copper concentrate was bioleached under optimal oxygen- and carbon dioxide enriched air conditions. Three cultures, T. ferrooxidans, Sulfobacillus accidophilus and Sulfolobus were employed for bioleaching process. The increase in copper leaching rates demonstrated the positive effect of using enriched air in the experiments. Galvanic interaction during the leaching of copper was suggested by the low redox potentials. The x-ray diffraction (XRD) analysis of leach residues confirmed the toxicity of metal ions and formation of precipitates.
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.
The kinetics of leaching of sphalerite by the thermophilic Acidianus brierleyi were studied in a batch stirred reactor. Experiments were done at 65°C and pH 2.0 on the adsorption of A. brierleyi onto sphalerite and the bioleaching of sphalerite particles. The distribution of A. brierleyi cells between the mineral and solution was attained within the first 30 min of exposure to sphalerite, and the equilibrium distribution data were correlated with the Langmuir isotherm. The addition of 0.3 and 1.4 kg/m3 ferric iron to the A. brierleyi culture resulted in a significant decline in the leaching rates, probably because of the formation of iron precipitates such as jarosite. Rate data collected in iron-free leach solutions were analyzed to determine microbial kinetic and stoichiometric parameters for the growth of A. brierleyi on sphalerite. These growth parameters demonstrated that the rate of bioleaching with the thermophilic A. brierleyi is about seven times that with the common leaching mesophile, Thiobacillus ferrooxidans.
Microorganisms are important in metal recovery from ores, particularly sulfide ores. Copper, zinc, gold, etc. can be recovered from sulfide ores by microbial leaching. Mineral solubilization is achieved both by ‘direct (contact) leaching’ by bacteria and by ‘indirect leaching’ by ferric iron (Fe3+) that is regenerated from ferrous iron (Fe2+) by bacterial oxidation. Thiobacillus ferrooxidans is the most studied organism in microbial leaching, but other iron- or sulfide/sulfur-oxidizing bacteria as well as archaea are potential microbial agents for metal leaching at high temperature or low pH environment. Oxidation of iron or sulfur can be selectively controlled leading to solubilization of desired metals leaving undesired metals (e.g., Fe) behind. Microbial contribution is obvious even in electrochemistry of galvanic interactions between minerals.
The bioleaching rate of pyrite (FeS2) by the acidophilic thermophile Acidianus brierleyi was studied at 65 degrees C and pH 1.5 with leach solutions supplemented with yeast extract. In the absence of yeast extract supplementation, A. brierleyi could grow autotrophically on pyrite, and the leaching percentage of pyrite particles (25-44 μm) reached 25% for 7 d. The bacterial growth and consequent pyrite oxidation were enhanced by the addition of yeast extract between 0.005 and 0.25% w/v: the pyrite particles were completely solubilized within 6 d. The bioleaching rate was enhanced by a factor of 1.5 when the yeast extract concentration was changed from 0.005 to 0.05% w/v. However, there was only a slight effect on the leaching rate at the yeast extract concentrations of 0.05 to 0. 25% w/v, suggesting that the organic supplement level was in large excess in the pyrite bioleaching. Copyright 1998 John Wiley & Sons, Inc.
It is generally accepted that iron-oxidizing bacteria, Thiobacillus ferrooxidans, enhance chalcopyrite leaching. However, this article details a case of the bacteria suppressing chalcopyrite leaching. Bacterial leaching experiments were performed with sulfuric acid solutions containing 0 or 0.04 mol/dm3 ferrous sulfate. Without ferrous sulfate, the bacteria enhance copper extraction and oxidation of ferrous ions released from chalcopyrite. However, the bacteria suppressed chalcopyrite leaching when ferrous sulfate was added. This is mainly due to the bacterial consumption of ferrous ions which act as a promoter for chalcopyrite oxidation with dissolved oxygen. Coprecipitation of copper ions with jarosite formed by the bacterial ferrous oxidation also causes the bacterial suppression of copper extraction. Copyright 1999 John Wiley & Sons, Inc.
This paper reports the results of leaching experiments conducted with and without Thiobacillus ferrooxidans at the same conditions in solution. The extent of leaching of ZnS with bacteria is significantly higher than that without bacteria at high concentrations of ferrous ions. A porous layer of elemental sulfur is present on the surfaces of the chemically leached particles, while no sulfur is present on the surfaces of the bacterially leached particles. The analysis of the data using the shrinking-core model shows that the chemical leaching of ZnS is limited by the diffusion of ferrous ions through the sulfur product layer at high concentrations of ferrous ions. The analysis of the data shows that diffusion through the product layer does not limit the rate of dissolution when bacteria are present. This suggests that the action of T. ferrooxidans in oxidizing the sulfur formed on the particle surface is to remove the barrier to diffusion by ferrous ions.
Mineral processing in bioreactors has become established in several countries during the past decade with industrial application of iron- and sulfur-oxidizing bacteria to release occluded gold from mineral sulfides. Cobalt extraction in bioreactors has also been commercialized, and development of high-temperature biooxidation of copper sulfides has reached pilot-plant scale. A variety of potentially useful mineral sulfide-oxidizing thermophiles have been recognized, but the most active strains have not been fully characterized.
Biomining is the use of microorganisms to extract metals from sulfide and/or iron-containing ores and mineral concentrates. The iron and sulfide is microbially oxidized to produce ferric iron and sulfuric acid, and these chemicals convert the insoluble sulfides of metals such as copper, nickel and zinc to soluble metal sulfates that can be readily recovered from solution. Although gold is inert to microbial action, microbes can be used to recover gold from certain types of minerals because as they oxidize the ore, they open its structure, thereby allowing gold-solubilizing chemicals such as cyanide to penetrate the mineral. Here, we review a strongly growing microbially-based metal extraction industry, which uses either rapid stirred-tank or slower irrigation technology to recover metals from an increasing range of minerals using a diversity of microbes that grow at a variety of temperatures.
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