Nowadays, large amount of municipal solid waste is because of electrical scraps (i.e. waste electrical and electronic equipment) that contain large quantities of electrical conductive metals like copper and gold. Recovery of these metals decreases the environmental effects of waste electrical and electronic equipment (also called E-waste) disposal, and as a result, the extracted metals can be used for future industrial purposes. Several studies reported in this review, demonstrated that the biohydrometallurgical processes were successful in efficient extraction of metals from electrical and electronic wastes. The main advantages of biohydrometallurgy are lower operation cost, less energy input, skilled labour, and also less environmental effect in comparison with pyro-metallurgical and hydrometallurgical processes. This study concentrated on fundamentals and technical aspects of biohydrometallurgy. Some points of drawbacks and research directions to develop the process in the future are highlighted in brief.

In the present study, the potential application of Acidithiobacillus ferrooxidans for elimination of ash and sulfur from bitumen was investigated in batch experiments. A comparison between the bioleaching and abiotic treatments indicated that A. ferrooxidans cells enhanced ash and pyritic sulfur removal by 20 and 59%, respectively. The X-ray diffraction profiles of the samples indicated the precipitation of some mineral elements inside of bitumen decreased the bioleaching performance after 9 days from beginning of the experiments. The effects of bitumen particle size (X 1 ), agitation speed (X 2 ) and initial pH (X 3 ) as interfacial factors each at three levels on the ash removal (Y 1 ) and pyritic sulfur removal (Y 2 ) were investigated by response surface methodology (RSM) as a statistical design of the experiment. On the basis of quadratic models applied to the performance of the bioleaching process, 66.42% of the pyritic sulfur and 50.88% of the ash could be removed after 9 days under optimal conditions, namely a bitumen particle size of 100 µm, an agitation speed of 80 rpm, and in initial pH of 2.