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.