Stirred-tank bioleaching of copper and cobalt from mine tailings in Chile

Metals from low-grade sulfide ores, electronic waste and mine tailings can be recovered using biohydrometallurgy. In this study, acidophilic microbial consortia of mesophiles and moderate thermophiles were applied in shake flasks as well as in stirred tank reactors (STR) to bioleach cobalt and copper from mine tailings in Chile. The mine tailings near Taltal contained considerable amounts of copper (similar to 5000 ppm) and cobalt (similar to 115 ppm). After adaptation of the mesophilic consortium, 38% of Co and 86% of Cu were recovered in 2-L STR at 10% solid load after 12 days bioleaching at 30.C. In a mini-pilot test in 20-L STR at 15% solid load, Co and Cu extraction reached 49% and 83%, respectively. Improved metal recovery was obtained by using a moderate thermophilic microbial consortium at 42.C, reaching 74% of Co and almost 100 % Cu in 2-L STR at 10% solid load. Low Fe dissolution below 14% for all tests was observed which may favor the downstream processing of Cu and Co. Together with the results from chemical leaching, the data indicated that Cu was mainly leached by sulfuric acid (acid leaching) while a high Co extraction required Fe(II)-oxidizing microbial activity (bioleaching).