Solid State Phenomena Vol. 262

Abstract: The bio-treatment of double refractory gold ores (DRGO) to reduce preg-robbing needs to account for the heterogeneity of the ore so as to acquire a much more complete picture of the system. To this end, the effects of ferrous ion additives on the degradation of powdered activated carbon (PAC) by cell-free spent medium (CFSM) was studied. Au(CN)₂^- adsorption and Raman spectrometric results suggest that the ferrous salt could have possibly reacted with some biogenic hydrogen peroxide to aid in the degradation of PAC. The bio-treatment produced mixed solid residues containing some partially degraded aromatic compounds which were soluble in alkaline solutions. Ultimately, biodegradation of PAC using CFSM in the presence of 50 µM FeSO₄.7H₂O for 7 days followed by washing with 3 mM NaOH reduced Au(CN)₂^- uptake by 80%.

Abstract: Microbial population performing biooxidation of flotation concentrate of gold bearing sulfide ore containing pyrite, arsenopyrite, and pyrrhotite was studied using cultural and molecular biological (metagenomics sequencing of V3-V4 fragments of 16S rRNA gene) approaches. The biooxidation of the concentrate was conducted at temperatures from 38 to 42°C. Strains of Acidithiobacillus thiooxidans, Acidiphilium multivorum, Leptospirillum ferriphilum, Sulfobacillus thermotolerans, Ferroplasma acidarmanus, and Ferroplasma acidiphilum were isolated from the samples of the pulp from biooxidation reactors. It was shown that optimum temperatures of isolated strains were from 38 to 40°C. Metagenomic analysis demonstrated predominance of the genera Acidiferrobacter, Acidithiobacillus, Acidiphilum, Leptospirillum, and Ferroplasma. According to results of molecular biological analysis, share of the genus Acidithiobacillus was of 0 to 25%, share of the genus Acidiferrobacter was of 7 to 56%, share of the genus Acidiphilum was of 0.03 to 36%, share of the genus Leptospirillum was of 0.7 to 7%, whereas share of the archaea of the genus Ferroplasma was of 33 to 94%. Thus, it was shown that representatives of the genus Ferroplasma can play significant role in bioleach process. Representatives of the genus Acidiferrobacter were previously detected in acid mine drainages, acid soils as well as in bioleach heaps and reactors, whereas data on predominance of the genus in tank bioleach processes have not been presented in the literature. In the present study, strains of the genus Acidiferrobacter were not isolated despite application of the nutrient media recommended for Acidiferrobacter and their properties were not studied. Nevertheless, results of the present study suggest that representatives of the genus Acidiferrobacter have a great impact on industrial bioleach processes.

Abstract: In the present study, we investigated the bioleaching of arsenopyrite with or without pyrite by moderate thermophiles. In both chemical leaching and bioleaching, the addition of pyrite decreased the leaching rate of arsenopyrite. The arsenic speciation and minerology changes in the residues were analysed by X-ray Absorption Near Edge Structure (XANES) Spectroscopy, X-ray Photoelectron Spectroscopy (XPS) and powder X-ray Diffraction (XRD). The XANES analysis showed no detectable arsenopyrite in the final residues from the experiments without pyrite. However, there was still 21.7% of arsenic species presented as arsenopyrite after bioleaching, when the initial arsenopyrite/pyrite ratio was 1:5. The XPS analysis revealed there was only As(V) on the surface of most of the residues, except on one chemically leached sample where As(III) was found.

Abstract: The H2020 BioMOre project (www.biomore.info, Grant Agreement #642456) tests the feasibility of in-situ bioleaching of copper in deep subsurface deposits in the Rudna Mine, Poland. Copper is leached using biologically produced ferric iron solution, which is recycled back to the in-situ reactor after re-oxidation by iron-oxidizing bacteria (IOB). From a post operational point of view, it is important that the biological processes applied during the operation can be controlled and terminated. Our goal was to determine the possibility to use natural saline mine water for the inactivation of introduced IOB remaining in the in-situ reactor after completion of the leaching process of the Kupferschiefer ore. Aerobic and anaerobic microcosms containing acid-leached (pH 2) sandstone or black shale from the Kupferschiefer in the Rudna mine were further leached with the effluent from an iron-oxidizing bioreactor, at a temperature of 30°C, for 10 days, to simulate in-situ leaching. After the removal of the iron solution, residing IOB were inactivated by filling the microcosms with saline water (65 g L^-1 Cl^-) originating from the mine. The saline water completely inactivated the IOB and the naturally occurring saline water of the mine can be used for long-term post process inactivation of bioleaching microorganisms.

Abstract: Bioleaching is applied mainly for copper recovery from low-grade sulfide ores via heap leaching. The main copper processing route includes pyrometallurgy and the remaining copper slag from smelting may still contain copper in amounts found in the ore. Here bioleaching of copper slag material with a copper content of about 1 % (grain size < 63 µm) and fayalite (Fe₂SiO₄) und magnetite (Fe₃O₄) as main mineral phases was tested in aerobic shake flask experiments with a mixed culture of Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Acidiphilium spp..To additionally test for reductive bioleaching, experiments under anaerobic conditions (80% N₂, 20% CO₂, v/v) with or without addition of elemental sulfur were run. The pH was adjusted to < 3 by addition of sulfuric acid. After the incubation period of more than 50 days at 30°C cell growth was observed in all biological assays. The redox potential was above 800 mV SHE in the aerobic biological assays and dropped to around 500 mV in the chemical control assays as well as in the anaerobic biological and chemical assays. A significant copper bioleaching was observed in the aerobic experiments with 91 % copper release (max. 35 % in the chemical controls). Anaerobic bioleaching experiments did not show a significant copper release, however the release of iron (as iron(II)) and sulfate was much higher than in the abiotic assays and several fold higher than in the classical aerobic bioleaching experiments. Overall the results show that copper bioleaching from slag material is possible, however the economic feasibility needs to be demonstrated.

Abstract: The Sawayardun Gold Mine, the first Muruntau type gold mine in China, was located in the south Tianshan Mountain, Xinjiang Province. The gold reserve was 127 t with an average gold grade of 2.36 g/t. Due to the high content of arsenic and antimony, the traditional flotation-roasting-cyanidation process was not suitable. The direct cyanidation gold extraction for the raw ore was 44.70 %. Thus, biooxidation experiments in shaker flasks were conducted for this ore. The optimum conditions were obtained as inoculation volume 10 %, initial pH 1.7, pulp density 15 %, temperature 33 °C, leaching time 10 days, with the arsenic oxidation rate of 75.12 %. Then the biooxidation residues were test for gold leaching using NaCN, green gold leaching agent and thiourea. After 24 h leaching rate at pulp density of 33%, gold leaching agent dosage of 2 kg/t ore, the gold extraction for NaCN, green gold leaching agent and thiourea were 91.50 %, 86.23 % and 91.09 %, respectively. The high gold extraction showed a bright future for the whole-ore heap biooxidation of this refractory gold ore.

Abstract: The major objective of the EU Horizon 2020 project “BioMOre” is the technical realization of indirect in situ leaching of Kupferschiefer sandstone and black shale ore by a ferric iron lixiviant generated by a mixed culture of autotrophic, acidophilic, iron-oxidizing bacteria and archaea in a ferric iron-generating bioreactor (FIGB). These organisms could colonize the deeply buried geological formations even under anaerobic conditions as most are able to grow by coupling the reduction of ferric iron to the oxidation of reduced sulfur compounds in the absence of oxygen. Development of an inhibition protocol to eliminate these allochthonous microbial bioreactor populations subsequent to the completion of in situ bioleaching was therefore investigated. Column bioleaching experiments using a laboratory-scale FIGB confirmed not only that metals were solubilised from both the sandstone and shale ores, but also that significant numbers of bacteria were released from the FIGB. The efficacy of 13 different chemical compounds in inhibiting microbial iron oxidation has been tested at different concentrations in shake flask and FIGB-coupled columns. Iron-oxidation activity, microcalorimetrically-determined activity and ATP measurements, in combination with microscopic cell counts and biomolecular analysis (T-RFLP, qPCR), plate counts and most-probable-number (MPN), were used to monitor the inhibiting effects on the acidophiles. Complete inhibition of metabolic activity of iron-oxidizing acidophiles was achieved in the presence of 0.4 mM formate, 300 mM chloride, 100 mM nitrate, 10 mM of primary C₆ to C₈ alcohols, 100 mM 1-butanol, 100 mM 1-pentanol, 0.1 mM SDS or 0.35 mM benzoic acid. No inhibition was found for 0.6 mM acetic acid and 200 mM methanol. Based on these results a recipe for the chemical composition of the “decommissioning solution” is proposed.

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: The ability of Acidithiobacillus ferrooxidans to remove chromium and other metals from LD slag was examined. Additionally the option to retrieve P from LD slag was evaluated. Due to the facts that A. ferrooxidans is a facultative anaerobic microorganism and LD slag is an alkaline and oxidic material, both oxidative and reductive bioleaching experiments were carried out. In the reductive mode, four different gas atmospheres (nitrogen, carbon dioxide, air and a mixture of N₂ and CO₂) were considered. Promising results were obtained by reductive bioleaching with A. ferrooxidans and a pure carbon dioxide atmosphere, 83 % chromium could be removed. In comparison, only 27 % Cr were removed by oxidative bioleaching. The degree of P removal could not be easily determined due to imbalanced data obtained.

Abstract: Mineral separation by froth flotation is widely used around the world for the beneficiation of sulfide ores. Flotation products (typically concentrate) are subjected to metallurgical processes for metal extractions. Bioleaching as a metallurgical procedure indicated many advantages over other traditional techniques (pyro- and hydro-metallurgy). However, organic flotation reagent residuals on the surface of minerals are effective on biological activities of microorganisms. In this work, to extensively study these effects, typical sulfide flotation collectors (Sodium ethyl-xanthate, Potassium isopropyl-xanthate, Potassium isobutyl-xanthate, Potassium amyl-xanthate, and Dithiophosphate (Aero)), and frothers (pine oil (PO) and methyl isobutyl Carbinol (MIBC)) were used in the presence of various bacteria (Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans) to investigate their effects on bio-oxidation. The results of this investigation can be used to better understand the mechanisms of bio-activities when reagent residues are on the surface of flotation products and they will feed to the bioleaching process.