Extraction, separation and recovery of palladium and platinum by a kinetic method combined with ultrafiltration

Abstract

A method is presented allowing separation of palladium from platinum based on the different kinetic lability of the two metals. These are let to react with PADA (trans-pyridine-2-azo-p-dimethylaniline) in the presence of SDS micelles. The kinetic study of the PADA binding to Pd(II) and Pt(II), both in form of chlorocomplexes, shows that the reactivity of PdCl42− is about 4×103-fold higher than that of PtCl42−. The Pd(II)–PADA complex is completely formed in about 30min and adsorbed on the micelle surface. In this lapse of time less than 2% of Pt(II) is complexed. The separation of the two metals is then accomplished by ultrafiltration. With this procedure 98% of platinum can be recovered in the filtrate. Palladium, present in the retentate, is then recovered using a stripping agent and a multi-step ultrafiltration procedure. The most efficient among the stripping reagents tested is HCl 0.05M (yield 90% after three steps). The extraction yield is independent of the concentration of the SDS micelles ([SDS]=0.01–0.04M), thus allowing low concentrations of surfactant to be used with excellent yields.