Evaluation of medium and applicability of corn steep waste for biogenic cyanide production by Bacillus megaterium for sustainable gold recovery

Abstract

Bio-cyanidation, a viable alternative of hazardous cyanide, is a promising approach for effective and relatively safe extraction of gold. For the first time, corn steep, a waste of corn processing plants is used as an effective medium ingredient for the production of Bio-CN to develop cost-effective and environmentally friendlier approach for gold recovery. In this study, effect of medium ingredients on bacteria growth and cyanide production by Bacillus megaterium (B. megaterium) is explored and medium is optimized for maximum gold recovery from a sulfidic gold ore. Optimization step for gold leaching suggested a maximum recovery of about 45% using 12.49 g/L tryptone, 5.36 g/L yeast extract, 2.46 g/L NaCl, and 10.13 g/L glycine after 7 days, comparable to the previous reported studies with sulfidic ore. Kinetics study showed that the leaching is relatively slow, controlled by mixed of diffusion and chemical reaction, and no significant improvement in the recovery can be achieved after 5 days. Corn steep could successfully replace tryptone and produce high concentration of ca. 120 mg/L Bio-CN. The optimum condition at which tryptone was replaced with 5 g/L corn steep waste resulted in more economic and sustainable process for gold recovery.