Polymer pendant ligand chemistry .4. Recovery of precious metal ions from strongly acidic solution with a polymer-supported o-phenylenediamine hydrochloride ligand

We report on the synthesis and reactivity of a polymer-supported o-phenylenediamine hydrochloride ligand, PS-PDHC, using macroporous 6% crosslinked polystyrene-divinylbenzene beads. The PS-PDHC ligand was found to be highly selective to AuCl4- ions in strongly acidic solutions in the presence of other precious metal ions, PdCl42-, PtCl42-, RhCl63-, and RuCl52- (selectivity values: 2.5, Au/Pd; 7.5, Au/Pt; 7, Au/Rh; 2.2, Au/Ru) as well as other transition metal ions, Fe3+, Cr3+, Cu2+, Ni2+, and Mn2+. The sorption capacity, selectivity, kinetics of removal and recovery, and solution isotherms have been determined for AuCl4- ions in competition with the above-mentioned metal ions. The relative ease of formation of the anionic complex in 0.5 M HCl, AuCl4-, was thought to be the primary reason for its selective ability to bind to the PS-PDHC ligand by an anion-exchange mechanism. Therefore, the effect of the HCl concentration on the kinetics of AuCl4- ion removal from solution was also investigated to clearly show that raising the pH from 0 to 5 caused a dramatic decrease in rate. The AuCl4- ion can be recovered quantitatively from the PS-PDHC beads using a 5% thiourea solution in 0.1 M HCl, allowing the polymer-supported ligand to be reused.