Evaluation of manganese bioleaching and silver extraction in mining tailings by native bacteria using a flooded system

Abstract

During the silver extraction process in mining, the generated residues (called tailings) still contain approximately 100-140 g/ton of silver due to the presence of refractory materials that trap this metal and prevent its solubilization by conventional methods. These residues can be treated by biohydrometallurgical processes allowing, together with the cyanidation process, an increase in the efficiency of silver extraction by eliminating refractory materials such as manganese, which is present as pyrolusite (MnO2, 3.78 %). Pyrolusite can change from manganese (IV) to manganese (II) when solubilized by bioleaching. This research analyzed the effects of bioleaching using native bacteria on the concentration of silver extraction from the removal of manganese in mining tailings. The native bacteria ITDBC2, ITDBC5, and ITDBC6 were identified as Leptospirillum ferriphilum by amplification of the 16S gene corroborated by bioinformatic analysis. The experimentation was carried out using a flooded bioleaching system (9.43 L) to resemble the industrial geometry with the following variables: concentration of ferrous ions (2, 7, and 14 g/L), pH (2, 4, and 6) and agitation time at 100 rpm (2, 4 and 6 min/day). The experimentation lasted 18 days. The removal of manganese and silver extraction was 71.84 and 55.53 %, respectively. The scaled-up of the evaluated bioprocess could reduce energy consumption and process larger amounts of pulp than the reported at the laboratory scale.