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.
This research work has developed a processing technology for full oxidation of the biocake from gold-arsenic flotation concentrate with high pyrrhotite content by neutrophilic association of microorganisms, which oxidize elemental sulphur and antimony sulphide at a high rate. Biocake, which is produced as a result of oxidizing the sulphides in the flotation concentrate at pH 1,7 – 1,9 by acidophilic bacteria of chemolithotrophic microorganisms and containing around 3%-5% of elemental sulphur, is then fully oxidized by association of neutrophilic bacteria at рН 7,0-8,0.
Using molecular genetic methods, 10 species wereidentified in the community of neutrophilic microorganisms isolated from thebioreactor during the process of biooxidation of gold-arsenicpyrrhotite-bearing sulfide ore flotation concentrate. The microbial communitywas composed of chemolithotrophs oxidizing elemental sulfur and its reducedcompounds and chemoorganotrophs. The predominant S0-oxidizingchemolithotrophic strain and 3 strains of chemoorganotrophs were isolated inpure cultures. Phylogenetic identification of the pure cultures revealed thechemolithotrophic microorganism to belong to Thermithiobacillus tepidarius,while organotrophic microorganisms were identified as Parapedobacter sp.,Nocardioides nitrophenolicus, and Nocardioides sp. Themorphological and physiological characteristics of Thermithiobacillustepidarius and Nocardioides nitrophenolicus, the culturespredominant in the community of neutrophilic microorganisms, were studied.Active growth of T. tepidarius occurs within a temperature range of38–48°C at the optimal pH value of 7.0–7.5. The maximal specific growth rate ofT. tepidarius on sulfur and on solid residue which remains after theprocess of bioleaching/biooxidation of sulfide ore flotation concentrate (biooxidationresidue) was 0.13 and 0.135 h-1, respectively. The average maximalrate of S0 oxidation in the biooxidation residue was 0.107 g S0oxidizedper g S0initial h-1. The ability of Nocardioidesnitrophenolicus to destruct thiocyanate was shown.
The first production shop in Russia of refractory gold ores biooxidation using chemoautotrophic microorganisms association was launched in 2001 at Olimpiada gold recovery plant. The shop was designed for treatment of 3 million tons of Olimpiada deposit “Vostochniy” pit primary sulphide ore per year. In 2007 the BIO-2 shop designed for treatment of 5 million tons of primary sulphide ore was launched. Total capacity of the two bio-processing unit is 8 million tons of sulphide ores per year. A more advanced concept of BIO-3 shop was developed based on industrial operation and performance analysis of BIO-1 and BIO-2. The concept was based on biooxidation process automatisation with displaying control and managing parameters of the process on the monitors in control room. This allows to keep main process parameters within the specified limits and maintain process in a stable high-performance state. Installation of the automatisation systems in BIO-1 and BIO-2 shops allowed increasing the throughput of all flotation concentrate treatment shops from 870 t/day to 1200-1300 t/day. This led to production of more than 26 tons of gold in 2016. Currently JSC “Polyus” is copyright holder of patented refractory gold sulphide ores concentrate treatment technology, patented microbial association carrying out the process, and the technology itself is protected by the trademark "BIONORD".
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