Extraction and purification of gold from raw acidic electronic leachate using an aqueous biphasic system

Abstract

This work presents a new method for gold extraction and purification from scrap central processing units (CPUs) by using an aqueous biphasic system (ABS) consisting of a biodegradable copolymer and ions already present in the CPU leachate (chloride and nitric acid). In the first step of the gold extraction, 100% of gold is extracted into the macromolecule-rich top phase (TP), without the use of any auxiliary extractants, using the ABS formed from the raw CPU acidic leachate, L64 triblock copolymer, and lithium sulfate. However, gold purity is only 7%(w/w). Therefore, three subsequent steps are necessary to enable gold purification. At the end of the fourth step, 96% of gold is extracted from the raw leachate with 94%(w/w) of purity. Extraction of gold into the TP of the ABS is mainly possible due to the interaction of the negatively charged or neutral gold species, respectively, with pseudopolycation or micelle hydrophobic core present in the TP. Additionally, copper can be recovered during the extraction with purities ranging from 83 to 99%.