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Extration von Hexachloroplatinat(IV) mit phoshorylierten Merrifield-Harzen aus salzsauren Lösungen
(2012)
A series of diols (diethylene glycol, triethylene glycol, butane-1,4-diol and hexane-1,6-diol) were immobilized onto Merrifield resin and subsequently phosphorylated with dialkyl chlorophosphate (alkyl = Me, Et, Bu). The resins bearing hexane-1,6-diyl groups exhibited very good extraction abilities in regard to precious metal chloro complexes like platinum(IV), palladium(II) and rhodium(III). In batch experiments, more than 98% of Pt(IV) is extracted even when the metal and the hydrochloric acid concentration is enhanced significantly. Elution can be achieved with a solution of 0.5 mol L-1 thiourea in 0.1 mol L-1 hydrochloric acid. In the presence of other noble metals, platinum(IV) is preferentially bound. The extraction yield decreases in slightly acidic solution in the following order: Pt(IV)approximate to Pd(II)>Rh(III) and changes with increasing hydrochloric acid concentration to Pt(IV)>Pd(II)>> Rh(III). At different ratios of metal and acid, the temperature has nearly no influence on the platinum extraction. On slightly acidic media, the extraction of rhodium decreases by 30% when the temperature is increased from 10 degrees C to 40 degrees C. When the acid and metal concentration is enhanced, the palladium extraction decreases by 7-9%, depending on the resin.
A series of three dialkyl phosphate resins with a Merrifield resin support was used to extract platinum from acidic media. In column operations total capacities of 85-130 mg/g were gained. The presence of palladium and rhodium results in the order: Pt(IV) > Pd(II) >> Rh(III). From a leach liquor gained from spent automotive catalysts metals forming anionic chloro complexes are co-extracted only to a small extent. However, in order to separate and enrich platinum a selective back-extraction can be done with a sodium thiocyanate solution. A second elution step with acidic thiourea leads to a mixed solution of palladium and rhodium.