Biooxidation of a Gold-Arsenic Sulphide Concentrate by a Two-Stage Oxidation Using Consecutively Acidophilic and Neutrophilic Bacteria

Abstract

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.

Toward Sustainable Solution for Biooxidation of Waste and Refractory Materials Using Neutrophilic and Alkaliphilic Microorganisms—A Review

“…The definition of refractory applies to gold ores when the conventional cyanidation recovers around 80% of gold after fine grinding . Refractory materials include the submicroscopic or occlusion of fine-grained gold, presence of tellurides, carbonaceous matter, clays, arsenic, iron and base-metal sulfides, silica encapsulation, and incomplete oxidation of elemental sulfur. − Most refractory ores are composed of sulfide and carbonaceous matter combined with gangue materials, which prevents effective leaching from lixiviants due to preg-robbing and the occlusion of gold. , Further, carbonaceous matter adsorbs the aurocyanide complex behaving like activated carbon . These factors result in lower lixiviant leaching efficiencies, higher lixiviant consumption, and boosting operating costs.…”

“…Isolated from industrial wastewater, this species grows between pH 6.0 and 10.0 (optimum at pH 8.0) and 15–40 °C (optimum at 30 °C). − Currently, the salinity requirements are unknown. Nocardioides nitrophenolicus was a bacterial species isolated from the neutrophilic community obtained from the sulfide flotation concentrate bioreactor by Belyi et al and attributed to the oxidation of the biocake tests . Belyi et al also investigated thiocyanate degradation ability of Nocardioides nitrophenolicus and 500 mg/L SCN – was reduced to zero concentration in about 32 days.…”

“…Parapedobacter species grow between pH 6.0 and 9.0, 15–45 °C, and up to 0.86 M Na + . Their ability to oxidize reduced sulfur compounds is unknown; however, it was observed in the neutrophilic community where it was isolated from the sulfide flotation concentrate bioreactor and the oxidation of the biocake. , …”

“…Three studies have reported oxidative abilities of Thermithiobacillus tepidarius . Belyi et al isolated and identified Thermithiobacillus tepidarius as the dominant SOB in the neutrophilic community responsible for the oxidation of the sulphide flotation concentrate. This culture, along with the neutrophilic community, successfully oxidized the biocake produced by the flotation concentrate …”

“…However, these studies have led to the improvement of oxidizing refractory gold ore and sulfide concentrates. The use of acidic and neutral SOB together by performing oxidation in a 2-stage process utilizing acidophilic and neutrophilic bacteria consecutively has led to increased oxidation for refractory gold ore and sulfide concentrates. , Further, altering the medium used to grow the sulfur-oxidizing microorganisms can enhance their oxidative capabilities. , The energy sources used by microorganisms for growth can affect the performance of the bacteria by increasing oxidation of certain sulfur species. For materials with high sulfide content, a two-step oxidation process was designed to reduce sulfide toxicity for SOB. , This process, successfully performed in both neutral and alkaline conditions, includes an initial abiotic oxidation followed by biotic oxidation.…”