Recovery of platinum, palladium and rhodium from acidic chloride leach solution using ion exchange resins

• Simultaneous adsorption of Pt, Pd and Rh from acidic chloride leach solution
• High adsorption affinity to chloride complexes of Pt and Pd but weaker for Rh
• Pt and Pd effectively eluted with acidic thiourea but desorption of Rh difficult

The objective of this study was to investigate the applicability and performance of the selected ion exchangers with different physicochemical characteristics and functional groups to simultaneously recover three different platinum group elements (PGE), platinum(IV), palladium(II) and rhodium(III), present in a chloride solution produced by the leaching of spent automotive catalysts. The tested ion exchangers included a resin with a quaternary ammonium functional group (Lewatit MonoPlus (M +) MP 600), a resin with a polyamine functional group (Purolite S985) and a resin with a thiouronium functional group (XUS 43600.00). The study also focused on the achievable desorption from the loaded resins using different eluent systems. The leach solution was chlorine-saturated and contained 2.35 mol/L hydrochloric acid, platinum and palladium in concentrations of 0.13 mmol/L, and rhodium 0.03 mmol/L. It was found that XUS 43600.00 showed the best adsorption performance for platinum(IV) and palladium(II) chloride complexes among the investigated resins, but weak affinity for rhodium(III) chloride complexes was observed for all three resins. The adsorption kinetics were found to obey the Ho pseudo-second order expression. For Lewatit MonoPlus (M +) MP 600 and Purolite S985 the adsorption was best described by the Freundlich isotherm, while for XUS 43600.00 the Langmuir isotherm was more apt. Desorption of the PGE was examined using four different elution agents: sodium thiocyanate (2 mol/L), hydrochloric acid (2 mol/L), thiourea (1 mol/L) in hydrochloric acid (2 mol/L), and thiourea (1 mol/L) in sodium hydroxide (2 mol/L). The results showed that platinum and palladium can be fully eluted with the acidic thiourea but desorption of rhodium proved difficult with all the eluents.