N. V. Fomchenko

Diversity of the communities of acidophilic chemolithotrophic microorganisms in natural and technogenic ecosystems

The main representatives of acidophilic chemolithotrophs oxidizing sulfide minerals, ferrous iron, elemental sulfur, and reduced sulfur compounds and forming microbial communities in the natural and technogenic ecosystems with low pH values and high concentrations of heavy metal ions are listed. The species and strain diversity of the communities and environmental factors affecting their composition (temperature, pH value, energy substrate, mineralogical composition of sulfide ore concentrates, the presence of organic substances, and level of aeration) are analyzed. Involvement of mobile genetic elements (IS elements and plasmids) in the structural changes of the chromosomal DNA in the course of switching microbial metabolism to the oxidation of new energy substrates or under increased concentrations of metal ions is shown to be a probable mechanism responsible for the intraspecific genetic heterogeneity of the populations. Importance of determination of the dominant strains of different microbial species in the communities and of their physiological peculiarities for stabilization, optimization, and enhancement of efficiency of biotechnological processes for sulfide mineral oxidation is stressed.

Biohydrometallurgical technology of copper recovery from a complex copper concentrate

Leaching of sulfide-oxidized copper concentrate of the Udokan deposit ore with a copper content of 37.4% was studied. In the course of treatment in a sulfuric acid solution with pH 1.2, a copper leaching rate was 6.9 g/kg h for 22 hours, which allowed extraction of 40.6% of copper. At subsequent chemical leaching at 80°C during 7 hours with a solution of ferric sulfate obtained after biooxidation by an association of micro-organisms, the rate of copper recovery was 52.7 g/kg h. The total copper recovery was 94.5% (over 29 hours). Regeneration of the Fe3+ ions was carried out by an association of moderately thermophilic microorganisms, including bacteria of genus Sulfobacillus and archaea Ferroplasma acidiphilum, at 1.0 g/L h at 40°C in the presence of 3% solids obtained by chemical leaching of copper concentrate. A flowsheet scheme of a complex copper concentrate process with the use of bacterial-chemical leaching is proposed.

Bioprocessing of Mining and Metallurgical Wastes Containing Non-Ferrous and Precious Metals

Mining and metallurgical treatments of sulphide ores are characterised by present significant losses of non-ferrous and precious metals as different types of waste. These elements are accumulated in heaps due to the lack of efficient technology for the recovery of the metals from metallurgical waste. The treatment of two types of industrial metallurgical waste (copper converter slag and old flotation pyrite tailings) containing non-ferrous and precious metals were examined in the laboratory. Leaching of the slag containing 2.74% Cu (as digenite, bornite, and free metal) and 2.49% Zn (as a ferrite ZnFe2O4 and silicate) by an Fe3+-containing solution was studied. The effect of various experimental parameters on the leaching dynamics of copper, zinc, and iron under batch conditions was investigated. The following experimental parameters were recommended: a pH of 1.5, a pulp density of 10% (w/v), a temperature of 70 °C, and an initial Fe3+ concentration of 15 g/L. Leaching under these conditions resulted in the solubilisation of 89.4% copper and 35.3% zinc within 2.5 hours. Percolation leaching of the pyrite tailings containing 0.29% Cu (as chalcopyrite), 0.26% Zn (as sphalerite), 0.00007% gold, and 0.00108% silver was also studied. Acidic percolation leaching and the resulting biooxidation lasting 134 days resulted in the solubilisation of 73.4% zinc and 50.8% copper. The recovery rates of gold and silver from the bioleaching residues by cyanidation were 57.2% and 50.7%, respectively. The data obtained in the present work may be used to estimate the operating parameters for the industrial-scale processing of non-ferrous and precious metals from mining and metallurgical waste.

Leaching of Nonferrous Metals from Copper Converter Slag with Application of Acidophilic Microorganisms

The leaching process of copper and zinc from copper converter slag with ferric iron in sulfuric acid solutions obtained using the association of acidophilic chemolithotrophic microorganisms was investigated. The best parameters of chemical leaching (temperature 70°C, an initial concentration of ferric iron in the leaching solution of 10.1 g/L, and a solid phase content in the pulp of 10%) were selected. Carrying out the process under these parameters resulted in the recovery of 89.4% of copper and 39.3% of zinc into the solution. The possibility of the bioregeneration of ferric iron in the solution obtained after the chemical leaching of slag by iron-oxidizing acidophilic chemolithotrophic microorganisms without inhibiting their activity was demonstrated.

Selective leaching of zinc from copper-zinc concentrate

Biooxidation of copper-zinc concentrate with the use of consortia of mesophilic and moderately thermophilic acidophilic chemolithotrophic microorganisms was studied. Pyrrhotite, sphalerite, and chalcopyrite were the main sulfide minerals of the concentrate. The possibility in principal of complete selective leaching of zinc from sulfide concentrate coupled with minimal recovery of copper (less than 20%) was demonstrated. Selective leaching of zinc could be caused by galvanic interactions between minerals of the concentrate during the biooxidation. The results can be used as the basis for the development of the technologies for production of grade copper concentrate not containing zinc from sulfide copper-zinc concentrate obtained from refractory ores.

The effects of bioleaching conditions on the nonferrous metals content in copper-zinc concentrate

The effects of pH and ferrous iron concentration in cultural medium on the bioleaching of copper-zinc concentrate by mesophilic and moderately thermophilic acidophilic microorganisms were studied. It was revealed that the optimum pH for bioleaching in presence of 5 g/L of ferrous iron was 1.4–1.5. It was shown that bioleaching under optimal conditions led to an increase in the copper content in solid phase from 10.1 to 14% and a decrease in the zinc content from 7.4 to 1.4%. The results of the present work demonstrate that acidophilic microorganisms can be used for treatment of complex sulfide concentrates containing copper and zinc.

Investigation of steps of ferric leaching and biooxidation at the recovery of gold from sulfide concentrate

We examined the ferric leaching and biooxidation steps in a two-step biooxidation process of a gold-bearing sulfide concentrate containing pyrrhotite, arsenopyrite and pyrite. Ferric leaching of the concentrate (pulp density at 200 g/L) for 2 hours at 70°C at pH 1.4 by ferric sulfate solution (initial concentration at 35.6 g/L), which was obtained by microbial oxidation of ferrous sulfate allowed to oxidize 20.4% of arsenopyrite and 52.1% of sulfur. The most effective biooxidation of ferric leached concentrate was observed at 45°C in the presence of yeast extract. Oxidation of the sulfide concentrate in a two-step process proceeded more efficiently than in one-step. In a two-step mode, gold extraction from the residue was 10% higher and the content of elemental sulfur was two times lower than in a one-step process.

Chemical leaching of copper-zinc concentrate with ferric iron biosolution

The process of leaching of copper-zinc concentrate with a solution containing biogenic iron, which is a product of the metabolism of iron-oxidizing microorganisms, was studied. The dependence of leaching rate of metals on temperature and pH was determined. It was shown that up to 98% of zinc and 70% of iron could be removed from the concentrate, while up to 7 and 4 g/L of zinc and copper, respectively, were accumulated in the liquid phase, which was sufficient for metal recovery. It was established that a copper concentrate with copper content up to 16% and only 0.5% of zinc could be obtained after chemical leaching for 340 min at 80°C.

Obtaining of copper and nickel from metallurgical waste products with the use of acidophilic chemolithotrophic microorganisms

The study concerns the leaching of copper, nickel, and cobalt from metallurgical production slag with trivalent iron sulphates prepared in the process of oxidation of bivalent iron ions with the use of associations of acidophilic chemolithotrophic microorganisms. At the same time, copper extraction in the solution reached 91.2%, nickel reached 74.9%, and cobalt reached 90.1%. Copper was extracted by cementation, and nickel as sulphate can be extracted by electrolysis. Associations of microorganisms can then completely bioregenerate the solution obtained after leaching.

Bioregeneration of the solutions obtained during the leaching of nonferrous metals from waste slag by acidophilic microorganisms

The bioregeneration of the solutions obtained after the leaching of copper and zinc from waste slag by sulfuric solutions of ferric sulfate is examined. For bioregeneration, associations of mesophilic and moderately thermqophilic acidophilic chemolithotrophic microorganisms were made. It has been shown that the complete oxidation of iron ions in solutions obtained after the leaching of nonferrous metals from waste slag is possible at a dilution of the pregnant solution with a nutrient medium. It has been found that the maximal rate of oxidation of iron ions is observed at the use of a mesophilic association of microorganisms at a threefold dilution of the pregnant solution with a nutrient medium. The application ofbioregeneration during the production of nonferrous metals from both waste and converter slags would make it possible to approach the technology of their processing using the closed cycle of workflows.