Bioleaching of Glod from Obsolete Mobile SIM Cards

Abstract

Electronic waste is the fastest growing municipality solid waste due to high obsolescence rate of electrical and electronic items. The exponential increase in the cellular networking and advancement in the related technology has also led to an increase in waste or obsolete SIM cards which are regarded as enriched source of precious metals, especially gold. With its significant gold content, e-waste is recognized as the emerging and the fastest growing waste stream and the recovery of gold from e-waste has not only economic benefits but can also serve as secondary source for gold, hence reducing the demand on gold mining operations. Bioleaching has been used for many years to recover metals from low grade ores or low grade mineral resources. Bioleaching of gold is done by cyanidation process, where cyanogenic bacteria produce hydrogen cyanide which helps to recover gold from the e-waste. This project focused on the bioleaching of gold from obsolete mobile SIM cards by cyanogenic bacteria (Chromobacterium violaceum) involving two step leaching process, evaluation of elemental composition of obsolete SIM cards and evaluating effect of pretreatment and spent medium leaching on metals recovery through bioleaching. The SIM metal was differentiated into 3 particle sizes varying from 355 μm to 700 μm or above. Elemental composition of obsolete SIM cards was found between 0.16% to 0.42% for Au, varying due to the particle size, where maximum was found in the particle size <355 μm. The concentration of Cu was found 75% with maximum found in the particle size >700 μm. The concentration of Ag was found between 0.003% to 0.22% and maximum was reported in size <355 μm. Two-step bioleaching process lead to maximum gold mobilization i.e. 2.36% of gold from obsolete mobile SIM card with particle size >700 μm followed by 2.09% gold mobilization for a particle size <355 μm and least gold mobilization was found with the particle size 355-700 μm i.e. 0.44%. Pretreatment of e-waste led to a 72.73% reduction of Cu from e-waste, with no effect on the chemical composition of other metals like Au and Ag. Two-step bioleaching of the pretreated SIM e-waste reported a gold mobilization i.e. 0.71% with a particle size 355-700 μm. Spent medium leaching at high temperature of SIM e-waste reported a gold mobilization i.e. 0.62% with a particle size 355-700 μm, whereas PCB e-waste reported a maximum gold mobilization i.e. 34.34% which was more than the gold mobilization in two-step bioleaching. Hence increase in temperature resulted in increased metal mobilization because of the increase in the reaction velocity.