Bioleaching of arsenopyrite from Janggun mine tailings (South Korea) using an adapted mixed mesophilic culture

This article explores a heap bioleaching technology for the removal of arsenic (As) from mine tailings using the GEOCOAT™ technique. Small-scale columns were operated at fixed temperatures of 20 °C, 30 °C, and 45 °C and at ramped-up temperatures from 25 °C to 45 °C using a mixed mesophilic acidophilic iron and sulfur oxidizing microbial culture, adapted to high As concentration (20 g/L). The packed-bed columns were filled with inert granite pebbles coated with Janggun Mine tailings, irrigated with a 1 g/L ferrous-enriched 0 K medium and aerated with 200 mL/min compressed air. To study the microbial colonization at various stages of the leaching process relative to the initial inoculum, the ramped-up-temperature experiment was conducted in triplicate and the columns were sacrificed after different leaching periods. The fixed-temperature column samples were sampled upon the termination of each experiment, for microbial speciation of the culture attached to the mineral during the leaching of the ore. The As that was released into the solution, the iron oxidation rates, the pH and the redox potential were used to assess the leaching performance of each column. A triangulation of the results between the fixed and the ramped-up temperatures allowed determination of the influence of temperature on As leaching kinetics and microbial distribution. 94-97% As removal was achieved among the various column experiments, 88 days after inoculation. The results showed that increased temperature induced an increased lag in the As leaching phase. Temperature also affected the abundance of acidophilic microorganisms present in the combined bulk volume of the column and on the mine tailings. The mesophilic bacterial species Acidithiobacillus caldus and Leptospirillum ferriphilum were the dominant biooxidation species (> 60%) in both the inoculum applied to the columns and in Col. A operated at a fixed 20 °C. Increased incubation temperature resulted in a decrease in the number of bacterial cells; however, the number of archaeal cells remained similar with a resulting increase in the archaeal dominance at 45 °C. The ramped-up temperature study showed similar results with an increase in both cell numbers and archaeal dominance between day 42 and 84. Overall, this study demonstrated the feasibility of As detoxification from the Janggun Mine tailings using microbial heap leaching.