Donnan dialysis based separation of gold(III) from electronic waste solutions using an anion exchange pore-filled membrane

Abstract

Donnan dialysis technique was employed for the recovery of Au(III) from aqua regia solutions of electronic waste containing low concentrations of Au(III) in the presence of much higher concentrations of Cu(II) and Ni(II). The anion exchange pore-filled membrane was synthesized using in-situ photo-polymerization with polypropylene as the host membrane and (3-acrylamidopropyl)trimethyl ammonium chloride and (3-acryloxy-propyl)trimethoxysilane as the monomer and spacer, respectively. Photo-polymerization was carried out with ethylene glycol dimethacrylate as the cross-linker and 2,2-dimethoxy-2-phenyl acetophenone as the UV-initiator. The transport of Au(III) through this anion-exchange pore-filled membrane was studied using a two compartment cell where the receiver solution contained NaCl as the stripping reagent. Cu(II), which is the dominant metal ion in electronic waste solutions, did not interfere with the transport of Au(III) even at Au(III): Cu(II) mass ratios of up to 1:500. Gold from 100-fold diluted electronic waste solutions in aqua regia was successfully recovered (96.3%) after 4 cycles of Au(III) transport while at the same time insignificant fractions of the dominant metals in the electronic scrap (Cu and Ni) were transported. This study shows that Au(III) can be selectively recovered from diluted aqua regia solutions of electronic waste based on the proposed Donnan dialysis process.