Thermophilic Bioleaching Research Articles

The effect of sulfide concentrate mineralogy and texture on Reactive Oxygen Species (ROS) generation

The generation of Reactive Oxygen Species (ROS), H2O2 and OH, has been observed from sulfide mineral containing particles in acidic solutions. The implications of this phenomenon, as a potential microbial stress-causing effect, have been studied previously with respect to thermophilic bioleaching performance in the presence of finely milled pyrite and chalcopyrite concentrates. In this study, the effect of sulfide mineralogy on ROS generation in the absence of microbes under physicochemical conditions typical for the bioleach environment was investigated. The mineralogical and elemental composition of eleven different samples containing sulfide mineral was obtained. These Au, Cu and other base metal-containing sulfide mineral concentrates as well as a milled whole ore of low Cu grade were tested for ROS generation. The whole ore sample and two refractory Au concentrates containing approximately 50% pyrite, generated significantly less ROS compared to the base metal-containing concentrates when compared on a constant surface area loading basis. Sulfide mineral-related variables were correlated with ROS generation. A significant difference was observed between FeS2 and CuFeS2 grades separately, whereas a combined measure of both minerals present in samples showed a consistently strong correlation to ROS generation. The Cu grade, total Cu-containing sulfides and the chalcopyrite content of Cu-containing samples correlated well with ROS generation. However, a common deterministic variable with a strong association to increased ROS generation was not found. A sub-set of samples were subjected to QEMSCAN® for textural analysis. Results suggested that a decrease in sulfide mineral liberation, caused by gangue silicate mineral occlusion to solution, resulted in decreased reactivity as shown in one of the Au-containing samples. Well-liberated chalcopyrite and pyrite phases corresponded to increased reactivity of samples. Pyrite, which was present in all of the reactive samples, was shown to be associated with other sulfide minerals, implicating its importance in galvanic interactions. Micro-analysis of chalcopyrite and pyrite phases from highly reactive samples showed an abundance of particles with extensive cracking and the possible presence of secondary transformation phases (szomolnokite). These results suggest that sulfide mineralogy, liberation and extent of physical processing affect sulfide mineral concentrate reactivity in acidic solutions.

Thermophilic bioleaching of spent petroleum refinery catalyst using Sulfolobus metallicus

The present investigation aimed to study the thermophilic bioleaching of spent catalyst with different size fractions in modified Kelly medium with and without iron supplement using Sulfolobus metallicus. The results obtained showed Ni and Al recovery ranging from 94 to 97% and 54 to 59% respectively, with a lower recovery of Mo and V. The difference in the leaching yield in iron free and iron supplemented growth medium at all size fractions did not show much difference stating iron free modified Kelly medium to be a suitable growth medium for bioleaching of spent catalyst. However, the leaching yield obtained from different size fractions also suggested that the particle size >212 μm could be conducive for leaching of desired metal values without any problem. The redox potential profile during the bioleaching experiments and planktonic cell count ranging from 106 to 108 cells mL−1 showed a luxuriant growth performance of the microorganisms in the experiments in iron free modified Kelly medium.La présente recherche avait pour but d’étudier la biolixiviation thermophile de catalyseur usé avec différentes fractions granulométriques dans un médium de Kelly modifié avec ou sans supplément de fer en utilisant Sulfolobus metallicus. Les résultats montrent que la récupération de Ni et d’Al variait de 94 à 97% et de 54 à 59%, respectivement, avec une plus faible récupération du Mo et du V. Le rendement de la lixiviation dans le médium de croissance avec ou sans supplément de fer dans toutes les fractions granulométriques n’a pas montré grand différence. Ceci indique que le médium de Kelly modifié sans fer est un médium de croissance approprié pour la biolixiviation de catalyseur usé. Cependant, le rendement de lixiviation obtenu à partir de différentes fractions granulométriques suggérait également qu’une taille de particule >212 micromètres pourrait conduire à la lixiviation de valeurs de métal désirées, sans problème. Le profil de potentiel redox lors des expériences de biolixiviation ainsi que le compte de cellules planctoniques de 106 à 108 cellules/mL montraient un rendement de croissance luxuriante des microorganismes des expériences dans le médium de Kelly modifié sans fer.

The generation of toxic reactive oxygen species (ROS) from mechanically activated sulphide concentrates and its effect on thermophilic bioleaching

Two types of laboratory mills, planetary and vibratory, were used to activate sulphide mineral concentrates mechanically before thermophilic (bio)leaching. These samples were analysed in terms of particle size, surface area, density, SEM, XRD line profile analysis and reactivity. The product particle size distributions indicated different particle breakage mechanisms of the two mills. The surface area for pyrite milled with the planetary mill was three fold that milled in the vibratory mill for the same length of time. Planetary milled samples showed lower densities, up to 4% less for pyrite samples, compared to vibratory milled samples. Particle surface oxidation, observed by SEM, occurred post milling. Surface oxidation products were more prevalent with planetary milled sulphide samples. XRD line profile analysis showed more line broadening effects with the planetary mill. This indicated that more bulk particle-related structural defects were present in the planetary milled samples. The reactivity in acidic solution was measured in terms of the generation of toxic reactive oxygen species (ROS): hydrogen peroxide and hydroxyl radicals. The ROS generation from milled sulphides, normalised to constant surface area loading, increased with increased mechanical activation. The planetary milled samples generated greater ROS per sample surface area than vibratory milled samples, more than 4-fold for pyrite after 60 min of milling. Increased ROS generation was postulated to result from increased surface area defects, solubilisation of iron oxidation products and bulk particle-related defects. The effect of mechanical activation on performance on thermophilic leaching and bioleaching tests was investigated using milled samples at 2% (w/v) pulp density. Short mill times improved leach rates from both mills, up to 7-fold cf. unactivated feed leach rates. Poor bioleaching performance resulted following long periods of mechanical activation (20–60 min). Pyrite and chalcopyrite bioleaching performance decreased dramatically above surface area loadings of 25 and 125 m 2/L respectively. Planetary milled samples were less amenable to bioleaching. For pyrite milled for 20 and 60 min and chalcopyrite milled for 40 min, no viable cells were observed following inoculation via fluorescence microscopy, suggesting culture death supported by compromised ferrous iron oxidation. The generation of ROS was postulated to cause poor bioleaching performance under these conditions.

Community structure and dynamics of the free and attached microorganisms during moderately thermophilic bioleaching of chalcopyrite concentrate

A mixed culture of moderately thermophiles showed good performance in bioleaching of chalcopyrite. Its community structure was investigated by amplified ribosomal DNA restriction analysis. The result shows that Leptospirillum ferriphilum and Acidithiobacillus caldus were the predominant bacteria and Ferroplasma thermophilum, the only archaea, could be always detected during bioleaching. Therefore, real-time PCR assay was performed to monitor these microorganisms’ dynamics in the solution and on the mineral surface. It is shown that both in the solution and on the mineral surface, A. caldus was the dominant species at the early stage and L. ferriphilum was the predominant species at the later stage. The amount of the same species exhibited different variation trends in the solution and on the mineral surface. The amount of attached L. ferriphilum increased faster than that of the free one, and the amount of attached F. thermophilum kept at a stable level while the free one increased rapidly at the end.

Probing the archaeal diversity of a mixed thermophilic bioleaching culture by TGGE and FISH

The archaeal community present in a sample of Mixed Thermophilic Culture-B (MTC-B) from a laboratory-scale thermophilic bioleaching reactor was investigated by temperature gradient gel electrophoresis (TGGE) and fluorescence in situ hybridisation (FISH). Both techniques were specifically adapted for use on native state bioleaching samples, with a view to establishing convenient means for monitoring culture composition. Using the TGGE protocol developed, the relative species composition of the thermophilic bioleaching sample was analysed, and included four phylotypes belonging to the Sulfolobales, which were related to Stygiolobus azoricus, Metallosphaera sp. J1, Acidianus infernus and Sulfurisphaera ohwakuensis. However, the St. azoricus-like phylotype was difficult to resolve and some micro-heterogeneity was observed within this phylotype. Specific FISH probes were designed to qualitatively assess the presence of the phylotypes in MTC-B. The sample was dominated by Sf. ohwakuensis-like Archaea. In addition, the St. azoricus-like, Metallosphaera species-like and Acidianus species-like cells appeared in similar low abundance in the community. Most strikingly, FISH identified Sulfolobus shibatae-like cells present in low numbers in the sample even though these were not detected by PCR-dependent TGGE. These results highlight the importance of using more than one molecular technique when investigating the archaeal diversity of complex bioleaching reactor samples.

Studies on Thermophilic Bioleaching of Chalcopyrite toward Heap Application

In a series of studies, various aspects of thermophilic bioleaching of chalcopyrite minerals and concentrates have been analyzed. Although the main objective was the elucidation of the catalytic effect of thermophiles in leaching chalcopyrite, various other new findings contributed to a better understanding of interactions among chemical, physicochemical and biological factors, which influence the bioleaching of chalcopyrite with thermophiles. Additionally, in order to bridge laboratory results and field applications, novel mathematical models as well as an alternative method to efficiently leach chalcopyrite without thermophiles are the contributions of this research.

Mathematical modeling of thermophilic bioleaching of chalcopyrite

Previous studies have shown that the different preferences of thermophiles to oxidize S 0 or Fe 2+ is reflected by different [Fe 3+]/[Fe 2+] levels in solution. In those studies it was concluded that [Fe 3+]/[Fe 2+] governs the thermophilic bioleaching of chalcopyrite rather than temperature or pH. Therefore, the proposed model is mainly based on the finding that thermophilic bioleaching of chalcopyrite is governed by [Fe 3+]/[Fe 2+] that result from the activity of thermophiles. A direct interaction between chalcopyrite and thermophiles is neglected because it has been reported that this is not a general behavior for all thermophiles. The case of constant temperature, initial pH 1.5–2.5, and chalcopyrite concentrates is considered. The main assumption is that chalcopyrite can be anodically oxidized or cathodically reduced depending on [Fe 3+]/[Fe 2+] in solution. When chalcopyrite is oxidized at high [Fe 3+]/[Fe 2+] levels, Cu 2+ is formed directly at low rates: CuFeS 2 + 4Fe 3+ → Cu 2+ + 5Fe 2+ + S 0. Whereas, when chalcopyrite is reduced at low [Fe 3+]/[Fe 2+] levels, an intermediate (Cu 2S) is formed at higher rates: CuFeS 2 + Fe 2+ + Cu 2+ + 2H + → Cu 2S + 2Fe 3+ + H 2S. Because the oxidation of Cu 2S is relatively fast: Cu 2S + 4Fe 3+ → 2Cu 2+ + S 0 + 4Fe 2+, its accumulation is assumed to be negligible. To take into account the possibility of chalcopyrite being oxidized or reduced depending on [Fe 3+]/[Fe 2+] in solution, the principle of mixed potentials is used. The model is validated by comparing the calculated and measured values of copper extraction, total iron in solution, and pH.

Effect of pH reduction and ferric ion addition on the leaching of chalcopyrite at thermophilic temperatures

Up to now various methods including bioleaching with thermophilic archea have been studied to enhance the leaching of chalcopyrite. However, the combined effect of pH and low ORP values at thermophilic temperatures (65–80 °C) has attracted little attention. Therefore, in this work, various chalcopyrites including two concentrates and two ore minerals were leached to study the combined effect of pH and ORP. It was found that a temperature of 65 °C at an initial pH of 1.0 can lead to copper extractions comparable to those obtained in bioleaching with A. brierleyi and S. metallicus. Furthermore, at an initial pH of 1.0, the addition of Fe 3+ (200 mg/L) at concentration much lower than the usually employed (e.g. 5000 mg/L), where formation of iron salt precipitates could be avoided and low ORP values (< 450 mV) could be induced, higher leaching yields than in thermophilic bioleaching were obtained. In addition to the low ORP values derived from the presence of low amounts of Fe 3+, the notable enhancement is attributed to the generation of sufficient amounts of Fe 3+ that resulted from the oxidation of Fe 2+ by oxygen at an initial pH of 1.0 and 65–80 °C without the aid of thermophiles. The oxidation of Fe 2+ by oxygen only took place under the presence of sulfides such as Cu 2S or CuS.

Bioleaching of chalcopyrite with thermophiles: Temperature–pH–ORP dependence

The copper extraction yield from thermophilic bioleaching of chalcopyrite depends on temperature, pH, and the oxidation-reduction potential (ORP), as well as on the activity of the thermophile used. The copper extraction yields obtained with three thermophiles under various pH and temperature conditions and with different initial amounts of Fe 3+ were studied. The results indicated that because of the low ability of Acidianus brierleyi to leach iron as Fe 3+, high biomass concentrations were reflected by ORP close to a critical value (450 mV, Ag 0/AgCl reference), at which copper extractions were highest. By contrast, because of the higher ability of Sulfolobus metallicus and Metallosphaera sedula to leach iron as Fe 3+, high biomass concentrations were reflected by high ORP which in combination with the precipitation of Fe 3+ as jarosite attenuated the leaching rates. Therefore, optimum temperatures for the growth of thermophiles did not always mean high copper extraction yields. Generally, highest copper extractions were obtained at initial pH 1.5. However, higher copper extractions were observed at initial pH 2.5 than at pH 2.0, suggesting that at high pH the bioleaching of chalcopyrite is controlled by the ORP rather than by the pH or temperature. The bioleaching capacity of A. brierleyi was reduced or suppressed when insufficient initial Fe 3+ was provided to trigger the leaching reaction, whereas S. metallicus and M. sedula were less sensitive to the initial availability of Fe 3+. This result confirmed that a direct enzymatic attack on the mineral surface could initiate the leaching reaction, but later ORP governed the leaching rate of chalcopyrite.

Modeling the auto-thermal performance of a thermophilic bioleaching heap employing mesophilic and thermophilic microbes

A model was formulated to study the auto-thermal performance of a bioleaching heap that employs mixed mesophilic and thermophilic microbes for Cu extraction from CuFeS 2. The preference of mesophiles for dissolving additional FeS 2 in conjunction with the capacity of thermophiles to dissolve CuFeS 2 enables the transition from a mesophilic to thermophilic bioleaching state where CuFeS 2 is leached at higher rates without the necessity of additional energy supply. In this sense, the mathematical description of this transition takes into consideration the dependence of the activity of both types of microbe on physicochemical factors such as the temperature and O 2 availability. The leaching kinetics is assumed to be proportional to the activity of both types of microbes and not to be dependent on the Fe 3+ concentration in solution because of the additional FeS 2 which provides Fe 3+ in excess. It was found that auto-thermal performance of a heap occurs under combined threshold conditions of minimum biomass irrigation concentrations, and maximum flow rates of leaching solution. Under these threshold conditions, the effect of the aeration rate on the Cu extractions appears to be mild. Apparently high leaching solution flow rates (> 2 kg m 2 h) decrease the heat accumulation in the heap by convection. This is reflected by prolonged transition periods to the thermophilic state where the highest Cu extractions are observed because of the simultaneous contribution of mesophiles and thermophiles. The continuous application of mixed mesophiles and thermophiles leads to uniform temperature distributions. The model is validated by comparing reported heat generations estimated from column experiments against the heat generation calculated from simulating the auto-thermal performance of a heap.

Extraction, isolation and NMR data of the tetraether lipid calditoglycerocaldarchaeol (GDNT) from Sulfolobus metallicus harvested from a bioleaching reactor

The successful extraction and isolation of the hydrolysed tetraether lipid calditoglycerocaldarchaeol (GDNT) from Sulfolobus metallicus, a key thermophilic bioleaching archaeon, is described. The archaeal biomass was recovered directly from a thermophilic (68 °C) bioleaching tank reactor used to extract nickel from a pentlandite mineral concentrate. The initial Soxhlet extraction method employed was scaled to a bench-scale extraction procedure suitable for the preparation of gram-scale quantities of GDNT. The GDNT so obtained was analysed by 1D- and 2D-NMR techniques, providing the first complete 13C and 2D-NMR data-set for GDNT, including that for the intact underivatised calditol moiety. The study demonstrates the feasibility of recovering high-quality GNDT from thermophilic archaeal-mediated bioleaching reactors. The recovery of these lipids at relatively low cost, as a by-product from bioleaching reactors used in the metals processing industry, has important implications for future tetraether lipid availability and costs.

Modeling the Auto-Thermal Performance of a Thermophilic Chalcopyrite Bioleaching Heap Employing Mesophilic and Thermophilic Microbes

A model was prepared to study the performance of a thermophilic bioleaching heap that employs mixed mesophilic and thermophilic microbes for copper extraction from CuFeS2. Mesophiles’ preference for and ease of dissolving additional FeS2 provided to the heap enables the transition from a mesophilic to a thermophilic bioleaching state without the necessity of additional energy supply. In this sense, the mathematical description of the bioleaching process is done taking into consideration the dependency of both microbes’ biological states on physicochemical factors such as the temperature and O2 availability. With regard to the flow rates of the liquid and air phases, simulation results have shown that these flow rates govern not just the heat transfer and variation of cell distribution, but also the leaching rate regardless of the fraction of CuFeS2 per FeS2 leached (FCP) which is the other variable influencing to the heat accumulation in the heap.

Archaeal diversity in two thermophilic chalcopyrite bioleaching reactors

This study used a culture-independent molecular approach to investigate the archaeal community composition of thermophilic bioleaching reactors. Two culture samples, MTC-A and MTC-B, grown with different concentrations of chalcopyrite (CuFeS2), a copper sulfidic ore, at a temperature of 78 degrees C and pH 1.6 were studied. Phylogenetic analysis of the 16S rRNA genes revealed that both cultures consisted of Archaea belonging to the Sulfolobales. The 16S rRNA gene clone library of MTC-A grown with 4% (w/v) chalcopyrite was dominated by a unique phylotype related to Sulfolobus shibatae (69% of total clones). The remaining clones were affiliated with Stygiolobus azoricus (11%), Metallosphaera sp. J1 (8%), Acidianus infernus (2%), and a novel phylotype related to Sulfurisphaera ohwakuensis (10%). In contrast, the clones from MTC-B grown with 12% (w/v) chalcopyrite did not appear to contain Sulfolobus shibatae-like organisms. Instead the bioleaching consortium was dominated by clones related to Sulfurisphaera ohwakuensis (73.9% of total clones). The remaining microorganisms detected were similar to those found in MTC-A.

Toxicity of flotation reagents to moderately thermophilic bioleaching microorganisms

The toxicity of 15 flotation reagents (including xanthates, carbamates, thiophosphates, a mercaptobenzthiazole and a frothing reagent) used for concentrating sulfide minerals to five species of mineral-oxidising, moderately thermophilic and acidophilic microorganisms was assessed. The acidophiles tested included four bacteria (a Leptospirillum isolate, Acidimicrobium ferrooxidans, Acidithiobacillus caldus and a Sulfobacillusisolate) and one archaeon (a Ferroplasma isolate). There was wide variation both in terms of the relative toxicities of the different flotation reagents and the sensitivities of the microorganisms tested. In general, the dithiophosphates and the mercaptobenzothiol were the most toxic, while the Leptospirillum and Ferroplasma isolates were the most sensitive of the acidophilic microorganisms. The significance of these findings, in view of the expanding application of ore concentrates bioprocessing, is discussed.

Development of respirometry methods to assess the microbial activity of thermophilic bioleaching archaea

Respirometry methods have been used for many years to assess the microbial activity of mainly heterotrophic bacteria. Using this technique, the consumption of oxygen and evolution of carbon dioxide for heterotrophic carbon catabolism can be used to assess microbial activity. In the case of autotrophic bioleaching bacteria, carbon dioxide is used as a carbon source resulting in the consumption of both oxygen and carbon dioxide. The use of such respirometry techniques at high temperatures (up to 80 °C) for the investigation of bioleaching Archaea, however, poses particular difficulties. At these elevated temperatures, the solubility of oxygen into the liquid phase is particularly poor. This work details specific methods by which high temperature constraints are overcome while monitoring the activity of thermophilic Archaea using a Micro-Oxymax respirometer (Columbus Instruments). The use of elevated headspace oxygen concentrations, in order to overcome low oxygen solubility, is demonstrated as well as the effect of such elevated oxygen concentrations on microbial oxygen consumption rates. The relative rates of oxygen and carbon dioxide consumption are also illustrated during the oxidation of a chalcopyrite concentrate. In addition, this paper details generic methods by which respirometry data can be used to quantify inhibitory effects of a compound such as Na 2SO 4. The further use of such data in predicting minimum hydraulic reactor retention times for continuous culture bioleaching reactors, as a function of concentration of potentially inhibitory compounds, is also demonstrated.

Bioleaching of a chalcopyrite concentrate using an extremely thermophilic culture

The ability of an extreme thermophile to oxidise a concentrate comprising of chalcopyrite (66%) and pyrite (11%) is described. A batch test at 70°C showed that a copper extraction of >98% was possible. A series of continuous tests were carried out in a three-stage pilot plant, employing standard-design mechanically agitated and aerated tanks. The effect of residence time, feed grind and the mass transfer supply of oxygen and carbon dioxide on bioleach performance were evaluated. The results showed that overall Cu extractions of 95% could be obtained. However, compared to mesophilic and moderately thermophilic bioleaching bacteria, the extreme thermophiles appeared to be more sensitive to the solids concentration employed, which may also be related to the particle size of the feed solids. Levels of oxygen consumption approaching the maximum rates currently being employed in commercial-scale bioleach tanks treating refractory gold pyritic concentrates could be achieved. To maintain these high oxidation rates, it was important to ensure that the supply rate of oxygen and carbon dioxide to the reactors was sufficient. The high copper extractions obtained in these tests showed that a process treating chalcopyrite concentrates using extreme thermophiles has the potential for further development and assessment for commercial applications.

Effect of solid loading on thermophilic bioleaching of sulfide minerals

The effect of solid loading (mineral pulp density) on thermophilic bioleaching of pyrite by Sulfolobus metallicus (BC) was investigated in a batch reactor. Different mineral pulp densities in the range 3–18% (w/v) were tested. With mineral pulp densities ranging from 3 to 9% the bioleaching proceeded in a single stage with a relatively constant rate. The bioleaching rates calculated for pulp densities of 3, 6 and 9% were 0.10, 0.11 and 0.09 kg iron m−3 h−1 respectively. By contrast the bioleaching of pyrite at pulp densities of 12 and 15% proceeded in two distinct stages. During the exponential phase of microbial growth a sharp and linear increase in concentration of released iron was achieved. This increasing trend levelled off in the presence of non-growing cells and the second stage of bioleaching continued with a slower rate. For the pulp density of 12% the bioleaching rates of the first and the second stages were 0.09 and 0.02 kg iron m−3 h−1 respectively, whereas the calculated rates in the presence of 15% mineral were 0.07 and 0.017 kg iron m−3 h−1 for the first and the second stages. Application of 18% mineral adversely influenced the activity of the cells and the extent of bioleaching in this case was insignificant. © 2000 Society of Chemical Industry

Effect of solid loading on thermophilic bioleaching of sulfide minerals

The effect of solid loading (mineral pulp density) on thermophilic bioleaching of pyrite by Sulfolobus metallicus (BC) was investigated in a batch reactor. Different mineral pulp densities in the range 3–18% (w/v) were tested. With mineral pulp densities ranging from 3 to 9% the bioleaching proceeded in a single stage with a relatively constant rate. The bioleaching rates calculated for pulp densities of 3, 6 and 9% were 0.10, 0.11 and 0.09 kg iron m−3 h−1 respectively. By contrast the bioleaching of pyrite at pulp densities of 12 and 15% proceeded in two distinct stages. During the exponential phase of microbial growth a sharp and linear increase in concentration of released iron was achieved. This increasing trend levelled off in the presence of non-growing cells and the second stage of bioleaching continued with a slower rate. For the pulp density of 12% the bioleaching rates of the first and the second stages were 0.09 and 0.02 kg iron m−3 h−1 respectively, whereas the calculated rates in the presence of 15% mineral were 0.07 and 0.017 kg iron m−3 h−1 for the first and the second stages. Application of 18% mineral adversely influenced the activity of the cells and the extent of bioleaching in this case was insignificant. © 2000 Society of Chemical Industry

An Immunological Assay for Detection and Enumeration of Thermophilic Biomining Microorganisms

A specific, fast, and sensitive nonradioactive immunobinding assay for the detection and enumeration of the moderate thermophile Thiobacillus caldus and the thermophilic archaeon Sulfolobus acidocaldarius was developed. It employs enhanced chemiluminescence or peroxidase-conjugated immunoglobulins in a dot or slot blotting system and is very convenient for monitoring thermophilic bioleaching microorganisms in effluents from industrial bioleaching processes.

Thermophilic bioleaching of arsenopyrite usingSulfolobus and a semi-continuous laboratory procedure

A laboratory equipment for pumping slurries is described. The pumping is performed semi-continuously by using a plastic syringe, a set of different valves, and a programmable electronic unit. The reproducibility of the pumping is demonstrated. Bioleaching of a gold-containing arsenopyrite slurry was done withSulfolobus at 70°C using the semi-continuous procedure and with a retention time of 100 h for the mineral. Arsenic was completely released at a rate of 109 mg l−1 h−1. The gold recovery is related to the amount of iron and arsenic dissolved and is shown to have a correlation factor of approximately one relative to the release of arsenic.