Papers by Keyword: Bioleaching

Abstract: Solid waste from sulfuric acid production may contain relatively high levels of metals such as Fe, Zn, Co, Cu and As that are harmful if inappropriately disposed of in the environment, but may be a valuable resource if metals can be recovered. The objective of this research was to investigate the pilot-scale acid bioleaching of metals from pyritic ashes, originating from the roasting of pyrite ores for sulfuric acid production and consisting mainly of hematite. Bioleaching was carried out at 25 °C in pilot-scale continuously stirred tank reactors (CSTR), with 50 L working volume in mineral salts medium supplemented with trace elements, 1 % (w/v) elemental sulfur and with pyritic ash pulp densities 10 % and 20 %. The reactors were inoculated with a mixed culture of iron- and sulfur-oxidising acidophiles containing Acidithiobacillus (At.) ferrooxidans, At. thiooxidans/albertensis, At. caldus, Leptospirillum ferrooxidans, Sulfobacillus (Sb.) thermosulfidooxidans, Sb. thermotolerans and some members of Alicyclobacillus genus. Metal leaching yields from pyritic ashes in the CSTR after 32 days were 54.6-56.7 % Cu, 41.7-43.2 % Zn, 1.7-1.8 % Co, 3.0-5.4 % As and 0.3-0.5 % Fe. Solution pH decreased during the experiment from 2.9 to 1.9-2.2. Elemental analysis using X-ray fluorescence showed that the contents of metals, except for As, in the leach residue were below the higher guideline values given in the Government decree on the assessment of the soil contamination and remediation needs by the Ministry of the Environment, Finland. Bioleaching facilitated the extraction of metals from pyritic ashes and the mitigation of environmental risks related to the residue disposal for other metals except for As.

Abstract: The purpose of this work was to investigate the phenomenon of microbial iron reduction in industrial minerals and materials. These materials are generally not pure, often associated with impurities usually in the form of Fe³⁺. In all cases, the presence of iron affects the colour and the physical properties of the mineral and therefore lowers their industrial value and limits their application. In this study bentonite, kaolin and quartz sand sample were used for the experiments and compared in effectiveness of iron dissolution. The experimental results showed that after 30 days of bioleaching process, bacteria are able to remove 9.29% of Fe occurring in the kaolin sample (K-I) in amorphous form of oxyhydroxides and approximately 12% of Fe from the bentonite sample (B-JP) also in amorphous form of oxyhydroxides. In the quartz sand sample C3-15D, the concentration of Fe decreased by 15% after 15 days of bioleaching process and in the sample C3-30D after 30 days of bioleaching process by 24.7%.

Abstract: Since the discovery of bioleaching microorganisms and their role in metal extraction in the 1940s, a number of technical approaches have been developed to enhance microbially catalysed solubilisation of metals from ores, concentrates and waste materials. Biomining has enabled the transformation of uneconomic resources to reserves, and thus help to alleviate the challenges related to continually declining ore grades. The rapid advancement of microbial characterisation methods has vastly increased our understanding of microbial communities in biomining processes. The objective of this paper is to review the recent advances in biomining processes and microbial characterisation.

Abstract: Silver-catalyzed bioleaching of enargite concentrate with three bacteria (Acidimicrobium ferrooxidans ICP, Sulfobacillus sibiricus N1, Acidithiobacillus caldus KU) and one archaeon (Ferroplasma acidiphilum Y) was conducted in order to elucidate the catalytic mechanism of silver sulfide in enargite bioleaching. Whereas Cu recovery remained relatively low (43%) and Fe dissolved completely without silver sulfide, Cu recovery was greatly enhanced (96%) and Fe dissolution was suppressed (29%) in the presence of 0.04% silver sulfide. In the latter case, 52% of the solubilized As was re-immobilized, in contrast to only 14% As re-immobilization in the former. The silver-catalyzed bioleaching (at 0.04% silver sulfide) proceeded at low redox potentials within the optimal range, which likely promoted enargite dissolution via formation of intermediate Cu₂S. XAFS analysis revealed that As was mainly immobilized as As (V), which was in agreement with the EPMA results detecting ferric arsenate passivation on some enargite grains. Furthermore, formation of trisilver arsenic sulfide (Ag₃AsS₄) was detected by XRD and EPMA, covering the surface of enargite particles. An intermediate layer, consisting of (Cu,Ag)₃AsS₄, was also observed between the enargite grain and trisilver arsenic sulfide layer, implying that Cu in enargite may be gradually substituted by solubilized Ag. The overall mechanism of silver-catalyzed bioleaching of enargite concentrate will be proposed.

Abstract: Bioleaching was applied to mobilize metals from printed wire boards (PWBs). PWBs have a rich metal content and are produced in high volume. Operating conditions of bioleaching of PWBs using an adapted mixed culture of Acidithiobacillus ferrooxidans (A. ferrooxidans) and A. thiooxidans to recover Cu, Zn and Ni were optimized in this study. The adaptation phase began at 1 g/L PWBs powder with 10% inoculation and the final pulp density was 20 g/L after about 40 days. Optimization was performed using central composite design method to optimize four effective factors, including initial pH (1.5 to 2), pulp density (15 to 25 g/L), initial sulfur (3 to 7 g/L) and initial FeSO₄ (15 to 25g/L), to achieve maximum recoveries of Cu, Zn and Ni. Also, the present study evaluated the effect of the independent variables initial pH, pulp density, initial Fe³⁺ concentration and initial sulfur content on extraction of metals from PWBs. Results showed that with an initial pH of 1.5, 25g/L pulp density, 25 g/L of FeSO₄·7H₂O and 7 g/L of S₀, copper, zinc and nickel recoveries reached 92%, 96% and 94%, respectively, after 25 days.

Abstract: Small quantities of organic substances are inevitably entrained and dissolve in the aqueous raffinate during a copper solvent extraction (SX) operation. These organic substances contaminate the bioleaching environment through the loopback of the raffinate. The attachment of cells of Acidithiobacillus ferrooxidans (At. ferrooxidans) to the low grade chalcopyrite ores and the bioleaching of the ores under the influence of solvent extraction organic substances were investigated. The results showed that the cells of At. ferrooxidans were apt to attach on the SX organics-contaminated chalcopyrite ores with an adsorption ratio of about 83%, larger than that of 44% on the uncontaminated ores as a control. However, the bioleaching efficiency decreased from 25% to 15% under the influence of the SX organic substances. Obviously, an improvement of the cells attachment did not improve the bioleaching efficiency of the low grade chalcopyrite ores by At. ferrooxidans in the present of the SX organic substances. The SX organic substances impacted the metabolism of At.ferrooxidans and their bioleaching ability.

Abstract: In this study, two black shale copper ores from different Mid-European Kupferschiefer-type deposits and their flotation concentrates were used for bioleaching tests. All samples were subjected to stirred tank bioleaching using an acidophilic, moderately thermophilic microbial consortium. The distribution of sulfides and gangue minerals in the ores, copper concentrates and residues of both, bioleaching and sterile chemical control tests were investigated using EDX-based particle analysis. The black shale ores and the extracted copper concentrates varied in their mineralogical composition with respect to the distribution of sulfides and gangue. While the copper-bearing sulfides in the Sangerhausen black shale and concentrate were dominated by bornite and chalcopyrite, the Rudna black shale and its flotation concentrate were rich in chalcocite and bornite. Differences in the portion of gangue minerals were detected in particular for carbonates that represented the dominant mineral group in the Rudna black shale and its copper concentrate. Distinct Cu dissolution kinetics and recovery rates of Co and other associated metals were observed for the various materials processed by bioleaching. Copper sulfides were completely dissolved also in both black shale ores. However, the sulfide distribution in the bioleaching residues of the Sangerhausen concentrate revealed that a significant portion of chalcopyrite was not leached. Even higher recovery rates for copper and other metals were determined for the bioleaching tests on the Rudna concentrate, in which copper sulfides were nearly completely dissolved. Alteration of copper sulfides and the formation of calcium sulfate were in particular observed in the sterile control residue of the Rudna concentrate, due to excessively use of sulfuric acid for pH stabilization. Lead sulfate precipitates increasingly occurred in the bioleaching residues, but represented also a common secondary phase in the sterile leaching residues.

Abstract: It has been a major issue for urgent solution in China as a result of a series of poisoning cases caused by cadmium. Yet there is no effective methods for removal of cadmium from the paddy soils. Microbial leaching process as an effective approach is currently applied to remediate the contaminated soils. In this study, bioleaching of cadmium from contaminated paddy soils by consortium of autotrophic and indigenous cadmium-tolerant bacteria was applied. The bioleaching results showed that the leaching rate of cadmium was from 74.93% to 92.76%. The distribution of the Cd fractions had a significant change before and after bioleaching with the organic fraction and residues fraction mainly remained. Moreover, the microbial community analysis showed that the Acidithiobacillus and Acidiphilium became the dominant genus in the bioleaching process. The combination of bioleaching with acidophilic chemolithotrophic microorganisms and the cadmium-resistant bacteria provides a potential process for bioremediation of metal-contaminated soils.

Abstract: The mineral surface chemistry characterization is essential to describe the dissolution kinetics in leaching and bioleaching. Five different methods, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR) and Raman Spectroscopy, have been applied to study the surface chemistry changes during pyrite, sphalerite and molybdenite bioleaching. The surface characterizations have been done for samples before and after biological and chemical leaching. The SEM images illustrated that the minerals surfaces were smooth before processing, while they covered with an ash layer after biological treatment. Although EDS analysis and Raman spectrum demonstrated the potassium jarosite formation on the pyrite surface during bioleaching, the formation of jarosite layer did not occur on the sphalerite surfaces during bioleaching. On the other hand, a sulfur layer formation on the sphalerite surface was confirmed by mentioned characterization methods. Finally, according to the XRD and EDS spectrum the molybdenite surface had been covered both with sulfur and jarosite.

Abstract: A large number of microbial species commonly called phosphate solubilizing microorganisms (PSMs) are efficient at converting insoluble phosphate to soluble forms to prevent phosphorus limitation. This study examined the impact that PSMs had on a sterile and non-sterile monazite source and determined that they could be applied for bioleaching purposes to recover rare earth elements (REEs). On sterile monazite, Penicillum sp. released a total REE concentration of 12.32 mg L^-1 after incubation for 8 days, however, this doubled when inoculated on to non-sterile ore (23.7 mg L^-1). Similar results were recorded with Enterobacter aerogenes, Pantoea agglomerans and Pseudomonas putida. Abiotic controls leached a total REE level of 0.65 mg L^-1. Examination of the leachate by HPLC identified several low molecular weight organic acids that corresponded with decreases in the media pH. The presence of a native consortia from the monazite ore combined with a known PSMs was more effective at leaching REEs from the monazite matrix than a single isolates or by the native population alone.