Extraction of gold from electronic scraps: a biohydrometallurgical process overview

The explosive growth in the electronics industries has revolutionized modern human life. This has resulted in the enhanced electronic wastes (E-wastes) generation which affects adversely on the global environment. The E-wastes are the end life electronics devices like computers, televisions, VCRs, stereos, copiers, mobile phones, and fax machines, generally discarded without following the standard procedure established by the environmental protection agencies of different countries. They are assembled of different materials which compose various toxic metals and organic compounds; therefore, there is the risk of environmental leaching problems when discarded as such without precaution. There are different policies and steps established for the E-wastes management and the recovery of valuable metals from them is one of the suitable steps. They contain different valuable metals like copper, silver, gold, palladium, rhodium and harmful substances like beryllium, cadmium, mercury, and lead. Gold is a precious metal, which can be recovered by applying conventional techniques such as pyro- and hydro- metallurgy. However, environmental risks are always associated with the above techniques. Bio-hydrometallurgy technique has potential to overcome the issues related to the conventional techniques. Different microorganisms help directly or indirectly in the dissolution reactions of gold from the E-wastes. Acidophilus microorganisms, such as Chromobacterium violaceum, Acidithiobacillus thiooxidans, Acidithiobacillus ferrooxidans, Aspergillus niger, Penicillium simplicissimum and many more, have proved their gold dissolution properties. However it is a slow process compared to that in the conventional techniques, which should be addressed comprehensively.