Heavy Metal Extraction from E-Waste Through Bioleaching: A Promising Ecofriendly Approach

E-waste refers to waste from electronic devices and electrical appliances that are widely discarded. It includes televisions, washing machines, refrigerators, air conditioners, printers, cell phones, computers, and monitors. Currently, increasing technological developments reduce the lifespan of electronic and electrical equipment. Hence, much more e-waste is being produced. Based on recent statistics, the worldwide production of e-waste is increasing at a rate of 4.6% annually, and it is expected to reach about 52.2 metric tons in 2021. Its processing produces a sludge that is a great threat to the environment since it contains numerous toxic heavy metals. For environmental protection, physical methods have been extensively implemented by some enterprises that dismantle e-waste. The alkali and acid reagents used to extract metals from e-waste are quite costly. However, research communities globally are focusing on bio-hydrometallurgical techniques to treat e-waste for ecofriendly treatment and safe disposal. Although several treatment techniques are applied to leach heavy metals from e-wastes, this chapter focuses on bacterial leaching, colloquially called bioleaching. This method is proven and can be effectively applied for leaching heavy metals from e-waste. Three sections are developed in this chapter. First, the sources of various e-wastes and their heavy metal contents are examined. Second, the specific microorganisms that can be applied for bioleaching processes are discussed. Last, the optimal conditions, bioleaching mechanisms, and influences are presented.