pH-driven ionic barrier-based techniques to recover precious metals from urban mines

Precious metals (PMs) including Au, Pd, Pt are naturally occurring elements of high economic values. However, they face future supply-chain risks due to their limited abundance in the earth’s crust. Meanwhile, frequent replacements of electrical and electronic devices are leading to accumulated amounts of e-wastes, with PM contents gradually superseding natural ore deposits. Urban mining is the act of recovering PMs from e-wastes. This technique is important from circular economic and environmental remediation viewpoints, owing to the prospects of generating income through recycling and protecting the environment from pollution dangers. This project utilizes the properties and advantages of adsorption and hydroxide recipitation to design internal pH-driven ionic barrier-based protocols to recover PMs from urban mines (e-wastes). The proposed techniques will involve the fabrication of polyelectrolyte complex (PEC) capsules using poly(diallyldimethylammonium chloride), PDADMAC and poly(styrenesulfonate), PSS. Here, a new concept of “ionic barrier” will be combined with metal-hydroxide formation to help retain high internal pH within the PEC capsules. The capsules will create ionic barriers that will promote selective passage of PMs and reject heavy metals such as Cd, Pb, Hg etc., whilst the high internal pH will induce hydrolysis and metal hydroxide formation between OH ions and the penetrated PMs within the capsules. For further improvement of the recovery efficiency, the functional polymer, polyethyleneimine (PEI) will be immobilized. Strategic recovery techniques will be designed via sequential desorption and adsorption-coupled incineration to obtain elemental PMs. Consequently, these protocols are expected to enhance separation and recovery of PMs, and eliminate the hydroxide sludge and sulfide gases that usually accompany the precipitation process. Moreover, it will help to salvage the supply-chain risk associated with PMs, and keep their continuous supply to industries.