Solid State Phenomena Vol. 262

Abstract: A composed mixed acidophilic, iron-oxidizing culture (FIGB) and a thermo-acidophilic enrichment culture (TK65) were used to evaluate microbial iron(III) reduction coupled to oxidation of reduced inorganic sulfur compounds (RISCs) under high pressure. Experiments were done in batch culture in high pressure vessels at 1 and 100 bar. Microbial abundance and activity were determined by measuring iron(II) concentration, direct cell counting, T-RFLP and quantitative real-time PCR. The data indicate that both cultures are able to reduce soluble iron(III) by oxidation of sulfur compounds under anaerobic conditions. At high pressure (100 bar) these acidophiles were capable of growing and microbial ferric iron reduction was only partially inhibited. These results indicate that acidophiles can be barotolerant and their activities are contributing to sulfur and iron cycling in anaerobic environments including deep ore deposits which is highly relevant for in situ leaching operations.

Abstract: The experiment focused on the effect of pyrite on the dissolution of the ore from Saindak copper mine in Pakistan. The MLA results showed that the ore mainly consisted of chalcopyrite, which was associated closely with pyrite. The bioleaching process and galvanic promotion experiments of pyrite on the copper extraction were investigated. The data revealed that copper recovery rate could be up to 97.8% after the bioleaching process by extreme thermophilic acidophilic organisms for 30 days at 65 ^OC. The temperature and redox potential were the controlled factors to recover copper from the Saindak mineral. The phylogenetic analyses of 16S rRNA gene fragments revealed that organisms related to Metallosphaera cuprina strain Ar-4 and Sulfolobus sp. HB59 were most dominant. Pyrite could accelerate the dissolution of chalcopyrite as one galvanic assistant substance, which would be strengthened by elevating the temperature or in the presence of microorganisms.

Abstract: JOGMEC has been carrying out the study on primary copper sulfide ores leaching for recovering copper economically and efficiently by heap leaching. In our study, we have been using the primary copper sulfide ore produced in an IOCG deposit. The ore is characterized by high iron content and high acid consumption in leaching. For the optimization of the leaching, the conditions such as ore size, agglomeration, pH and irrigation rate of leaching solution were examined with column leach tests. The best result was over 80 % extraction of copper in 150 days with leaching solution of 1 M sulfuric acid and temperature of 45 °C. In this experiment, the fines of the ore sample were removed before putting it into the column to keep the permeability of the ore bed. In these column leach tests, the Fe²⁺/total-Fe ratio of PLS decreased gradually by the activity of naturally grown iron-oxidizing bacteria. The bacteria in PLS, which have the ability of iron-oxidizing and sulfur-oxidizing, were identified by next-generation sequencing as Acidithiobacillus caldus and Sulfobacillus thermosulfidooxidans. We also carried out bench-scale tests with about 200 tons of the primary copper sulfide ores. Iron-oxidizing and sulfur-oxidizing bacteria were identified in the leaching solution as same with column leach tests. It is considered that the bacteria worked in the leaching solution and on the surface of the ores.

Abstract: High-capacity polyethylenimine (PEI)/Ca-alginate blended hydrogel fibers were fabricated via three steps, viz. electrostatic blending of PEI and alginate, ionotropic gelation of alginate and CaCl₂, and fixing of PEI into the Ca-alginate matrix, using glutaraldehyde (GA) as a crosslinker. Two crosslinking approaches resulted in different stabilities and gold uptake capacities of the prepared sorbents. Post-crosslinking approach was more efficient than pre-crosslinking likely owing to the better crosslinking efficiency, leading to better stability and sorption capacity. Furthermore, X-ray diffraction (XRD) study revealed the reduction of Au (III) to metallic gold, Au (0) in the crosslinked fibers. The Au (0) predominancy was confirmed with a metal desorption study. The present study thus demonstrates the possibility of recovering metallic gold from aqueous solutions by direct adsorption-coupled-reduction approach using GA-crosslinked PEI/Ca-alginate fibers.

Abstract: Pregnant leach solutions (PLS) resulting from bioleaching of copper concentrate from Kupferschiefer are characterized by low pH and high concentrations of Fe, Cu, Zn as well as significant amounts of Ni and Co. In order to recover the valuable metals for further processing, chemical methods and a novel biological-induced technique that promotes selective metal recovery and sulfate removal from acidic liquors were applied and a process scheme was developed.

Abstract: Concentrated tailings samples resulting from the benefication of polymetallic ores (Armenia) were exposed to bioleaching in order to recover non-ferrous and precious metals. Bioleaching of concentrated tailings samples was performed by the natural microbial consortium of drainage water. It was shown that the extent of extraction of metals from two samples of concentrated tailings by the natural microbial consortium reached 55, 56% and 63, 73% for copper and zinc, respectively. However, the application of the natural microbial consortium together with an iron- oxidizing Acidithiobacillus sp.13Zn resulted in an increase of extraction of metals from concentrated tailings to 70 - 93% for Cu and 75 - 90% for Zn. Thus, to increase the recovery of non-ferrous and precious metals, the use of a natural microbial consortium of drainage water combined with an iron- and sulfur- oxidizing Acidithiobacillus sp.13Zn is proposed.

Abstract: Primary copper sulfides are recalcitrant to bioleaching, probably due to semi-conductivity or passivation effects which result in slow dissolution kinetics. The mineral dissolution strongly depends on redox reactions and, consequently, electrochemical techniques are recommendable for analyzing and processing of redox-active minerals. For this reason we installed a three electrode system into a conventional bioreactor. Electrolytic bioleaching was applied to a copper concentrate from black shale ore. First results verified the operational capability of ferric iron reduction during electrochemical leaching and that bioleaching is not hindered by the physical presence of the electrochemical setup. Although the working electrode was able to reduce ferric iron and to regenerate it as electron supply for ferrous iron oxidizing microorganisms, the electron input into the bioleaching process has to be further increased to keep up with fast biocatalytical iron oxidation.

Abstract: Heap biooxidation is the most economic option of treating processing plants tailings and refractory ores containing non-ferrous and precious metals and sulphides.Pyrite tailings of copper ore processing (Sample 1), tailings of sulphide copper-nickel ore processing (Sample 2) and double refractory gold-bearing ore (Sample 3) were studied.Autotrophic microorganisms Acidithiobacillus thiooxidans and Acidithiobacillus ferrooxidans were used for the tests. The duration of heap biooxidation tests for Samples 1, 2 and 3 was 6, 10 and 16 months, respectively. The rates of copper and zinc recovery into solution during heap biooxidation of Sample 1 were 68% and 71%, respectively; the rates of copper and nickel recovery from Sample 2 were 50% and 75%, respectively. Base metals were extracted from solution to selective high-grade concentrates after biooxidation.Biooxidation tailings of Samples 1 and 3 were leached using an alkaline sodium cyanide solution. The recovery of gold from Sample 1 and Sample 2 was 65% and 85%, respectively.

Abstract: In this study, the important variables of organic acids degradation with Phanerochaete chrysosporium were selected in refractory arsenic-bearing and carbonaceous gold ores. The eight variables of fungal degradation of carbonaceous matter were confirmed by the previous single factor experiments, which were guaiacol concentration, dextrin concentration, tween-80 concentration, oxalic acid concentration, hydrogen peroxide concentration, pulp density, fungal concentration and action time. The most important factors influencing organic acids degradation (p < 0.05), as identified by a two-level Plackett-Burman design with above-mentioned eight variables, were pulp density, oxalic acid concentration and action time. The pulp density could influence the effective contact area between organic acids and fungi, the shear stress and the mass transfer efficiency of degradation system. Oxalic acid could affect the fungal growth and the enzymes activity by adjusting pH value of degradation system. Organic acids could not be fully degraded when the fungal action time was the very short or excessively long. A long action time could lead to the lack of nutrients and the accumulation of toxic and harmful substances.

Abstract: An optimal approach to the problem of cupriferous gold ores hydrometallurgical processing is the recycling of process solutions after copper recovery and regeneration of cyanide bound in complexes. The study focuses on the copper-cyanide solutions processing technology using biogenic hydrogen sulfide for copper recovery in the form of сhalcocite, and cyanide regeneration. The strains of anaerobic sulfidogenic thermophilic microorganisms Desulfurella acetivorans and Desulfurella Kamchatkensis were used for producing hydrogen sulfide. The studies on copper precipitation and cyanide regeneration were conducted on copper-cyanide process solutions which were obtained during cyanidation of refractory cupriferous gold-bearing flotation concentrates from one of the deposits in the South Ural (Russia). Ten cycles of "Cyanidation-Regeneration" were carried out in total. The copper recovery was 86–96 %; the cyanide regeneration obtained 96 %. On an average 8.9 kg of sodium cyanide and 4.6 kg of copper sulfide were recovered from 1 m³ of solution. The sodium cyanide consumption decreased from 25.0 kg/t to 6.0 kg/t without reducing gold recovery during the CIL (carbon-in-leach) recycling process. The gold recovery was the same 63–68 %.