216

14 Recovery of Precious Metals from Electronic and Other Secondary Solid Waste

obtained from bioleaching of e-wastes and presented based on the type of e-waste,

microorganism, and bioleaching method. Bioleaching process that uses acidophiles

causes metal solubilization via thiosulfate or polysulfide pathway by generating sul-

furic and ferric acids. Chemolithoautotrophs and heterotrophs are the two groups

of microorganisms used for bioleaching of e-waste. Various groups of these microor-

ganisms use different mechanisms to solubilize metals such as the heterotrophic

fungi uses mechanisms such as acidolysis and complexolysis, redoxolysis and bioac-

cumulation. At present, bioleaching process is studied substantially on wastes from

various wastes generated, especially from the e-wastes for extracting precious metals.

However, large-scale application is very limited due to the slow rate of this bioleach-

ing process. Therefore, several researchers have been using various methods such as

addition of catalysts, prior adaptation of microorganisms, ultrasonic treatment, opti-

mizing process parameters, to improve the efficiency of process, and the results were

highly effective. The limitations and challenges faced in this approach including

toxic to microbes, precipitation and variation must be described properly. Indus-

trial development in the contemporary world causes natural resources depletion on

one side, and on the other side, the amount of waste generated increases at high

pace. Hence, bioleaching is the most effective and a sustainable approach to meet

the upcoming needs of our future generation. Future studies must emphasis more on

process used for retrieval of precious metals using bioleaching approach and also the

omics approaches. This requires a deepened knowledge about the role of microor-

ganism in this field and also toward their bioleaching ability by alteration of their

genetic makeup.

List of Abbreviations

EEE

electronic and electrical equipment

WEEE

waste electronic and electrical equipment

PCB

printed circuit boards

References

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