The efficient recovery of Au(III) ions from acidic solutions by a novel scavenger based on functionalized poly(styrene-co-maleimide) nanoparticles

Abstract Tertiary amine functionalized poly(styrene-co-maleimide) nanoparticles were readily synthesized by an organic solvent-free thermal imidization reaction. The obtained spherical nanoparticles, with average diameters of about 50 nm, were shown to be highly effective as a unique scavenger for the recovery of Au(III) ions from strong acidic solution. High equilibrium Au loading capacities (>570 mg/g) were obtained at 25 °C and the rate of metal ion uptake was remarkably fast. The Au(III) ions in the feed solutions were almost quantitatively recovered within 3-10 min, depending on the shaking speed during batch sorption. Elution of the adsorbed Au species was however incomplete with a maximum elution efficiency of 75% using acidified thiourea as eluant. XPS analysis showed that the adsorbed Au species were present as a mixture of Au(0), Au(I), and Au(III), which explained the inadequate elution. An alternative and innovative method to recover the adsorbed Au was developed consisting of digestion of the Au-loaded scavenger followed by reductive precipitation with water as reducing agent. The Au formerly loaded on the scavenger was successfully and completely recuperated as pure metallic Au. This is a step-change in the way Au is recovered from solution and eliminates the need for difficult, partial, and environmentally unfavorable elution processes of Au species strongly adsorbed on the scavenger particles.