Biohydrometallurgical Recovery of Metals from Waste Electronic Equipment: Current Status and Proposed Process

Electronic waste (e-waste) is an emerging health and environmental burden due to the toxic substances present within e-wastes. To address this burden, e-wastes contain various base, rare earth and noble metals, which can be recovered from these substances, thus serving as secondary sources of metals. Pyrometallurgical and hydrometallurgical processes have been developed to extract metals from e-waste. However, these techniques are energy-intensive and produce secondary wastes, which will add to the operating costs of the process. However, the biohydrometallurgical approach has been deemed as an eco-friendly, cost-effective, and environmentally friendly process that does not produce large quantities of secondary waste. However, research has focused chiefly on one-stage bioprocesses to recover the metals of interest and majorly on base metals recovery. Hence, this review proposes a two-stage bio-hydrometallurgical process where the first stage will consist of acidophilic iron and sulphur oxidising organisms to extract base metals, followed by the second stage which will consist of cyanide-producing organisms for the solubilisation of rare earth and precious metals. The solid waste residue that is produced from the system can be used in the synthesis of silica nanomaterials, which can be utilised for various applications.