Enhancement of simultaneous gold and copper recovery from discarded mobile phone PCBs using Bacillus megaterium: RSM based optimization of effective factors and evaluation of their interactions

•Bioleaching of Au and Cu from a toxic MPPCBs waste using B. megaterium was studied.•Response surface methodology was used to evaluate and optimize three main factors.•At optimal condition about 72% of Cu and 65g Au/ton MPPCBs were extracted.•Cu elimination from MPPCBs with high ratio of Cu/Au can improve Au recovery. Bioleaching of Au from mobile phone printed circuit boards (MPPCBs) was studied, using Bacillus megaterium which is a cyanogenic bacterium. To maximize Au extraction, initial pH, pulp density, and glycine concentration were optimized via response surface methodology (RSM). Bioleaching of Cu, an important inhibitor on Au recovery, was also examined. To maximize Au recovery, the optimal condition suggested by the models was initial pH of 10, pulp density of 8.13g/l, and glycine concentration of 10g/l. Under the optimal condition, approximately 72% of Cu and 65g Au/ton MPPCBs, which is 7 times greater than the recovery from gold mines, was extracted. Cu elimination from the MPPCBs having a rich content of Au did not cause a significant effect on Au recovery. It was found that when the ratio of Cu to Au is high, Cu elimination can considerably improve Au recovery. B. megaterium could extract the total Au from PCBs containing 130g Au/ton MPPCBs.