The object of our research was the low-grade quartzite ore with a gold content (0.7-0.8 g/t) from the Bolnisi-Kazreti gold mining enterprise located in the industrial region of Georgia. The aim was to extract gold from the abovementioned ore using microbiological methods which are mainly applied through two approaches: heap leaching and percolation leaching. In this study, both methodologies were investigated. The heap leaching process of gold (grinding fineness of 0.074 mm) was carried out for 30 days, until the gold content was concentrated in the solution. The liquid-to-solid ratio was 1:2. The recovery reached 92%. Activated carbon was used as a sorbent. The heap leaching methodology is cost-effective, simple, and environmentally safe. Its main drawback is the long duration of the leaching process. Under the percolation methodology, gold leaching (grinding fineness of 0.074 mm) was carried out over a period of 35 days. The liquid-to-solid ratio was 1:1. Gold recovery in the solution reached 97%. Activated carbon and zinc powder were used as sorbents. Based on the results, preference was given to activated carbon. The aim of the study was to replace the cyanide method for processing low-grade quartzite ores with a microbiological process employing a strain of autotrophic silicate bacteria, which is a safe, cost-effective and environmentally sound approach. The actuality of the research lies in the fact that, the minimum quantity of ingredients was determined for both methodologies, specifically with regard to the liquid-to-solid ratio, gold ore, bacterial culture, and nutrient medium. As a result, optimal conditions were established for both methodologies. The percentage of gold recovery complies with internationally accepted standards. Modern physicochemical analytical methods were used in the study: atomic absorption spectrometry (Perkin Elmer), X-ray fluorescence spectrometry (Sky-ray Instruments USA- EDX3600H X-ray), electron microscopy (NSX-100), biological microscopy (MI-5200STD), and quantitative chemical analysis.
Gigauri et al. (Thu,) studied this question.