Recovery of gold ions from discarded mobile phone leachate by solvent extraction and polymer inclusion membrane (PIM) based separation using an amic acid extractant

This paper reports on the selective separation and recovery of gold ions from leachates of discarded mobile phones using liquid-liquid extraction and a polymer inclusion membrane (PIM) transport system. The collected mobile phones were crushed by a mill and the obtained powder was calcinated. After leaching with aqua regia, the metal composition of the leachate was analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The analysis results confirmed that the mobile phone waste contained 397 g/ton of gold. Liquid-liquid extraction and PIM-based separation procedures for the selective recovery of gold(III) from synthetic and actual leachates were developed. The extracting organic solution and the PIM incorporated the newly synthesized extractant N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG) which exhibited high selectivity for the gold(III) ion over the other metal ions present in much higher concentrations in the leachates. The compositions of the feed and receiving solutions in both the liquid-liquid and PIM based extraction and back-extraction of the gold(III) ions were optimized. It was established that optimal extraction required a HCl concentration in the feed solution of 2 mol/L and that a receiving solution containing 0.1 M thiourea in 1 M HCl was capable of back-extracting gold(III) quantitatively. Membrane transport experiments with a synthetic leachate as the feed solution demonstrated that 96% of the gold(III) ions was selectively transported into the receiving solution of the transport cell thus leaving all other metal ions in the leachate.