Iron is the main impurity element in precious metal solutions. Removing iron using techniques such as hydrolysis, ion exchange, and extraction may cause secondary dispersion of platinum group metals. A transconverting remelting technique without precious metal dispersion loss was investigated. The proposed separation and refining process is as follows: precious metal feed solution → transconverting remelting → ion exchange separation of base metals → S201 extraction of palladium → TBP extraction of platinum → extraction of residual liquor for rhodium refining.
Transconverting remelting: Obtaining a high-concentration, high-quality mixed solution of platinum, palladium, and rhodium;
Ion exchange removal of base metals: Using a strong acid-type styrene-based cation exchange resin (732 or 001×7 type), the solution is washed with deionized water → soaked in hydrochloric acid → washed with deionized water to pH 5-7 before being packed into an exchange column. After two ion exchange separations of the platinum-palladium-rhodium mixed solution, the effluent contains Fe, Pb, Sn, and Zn <0.0005 g/L, and Bi, Sb, Cu, Al, Mg, Ca, and Si <0.0001 g/L. The Pt content in the ion exchange process was 99.68%, 99.67%, and 99.11%, respectively. The resin regeneration solution contained 0.007 g/L P, 0.031 g/L Pd, and 0.016 g/L Rh, which were recovered by zinc replacement.
A mixed solution of platinum, palladium, and chromium can be directly reduced with hydrazine hydrate (N2H4·H2O) to produce pure ternary mixed metal powder. However, since the precursor compounds used in the production of automotive exhaust purification catalysts are mainly nitrates [Pt(NO), Pd(NO), Rh(NO)] and platinum ethanolamine, and the synthesis methods and proportions of these compounds differ, as do the order in which they are impregnated on the honeycomb carrier, the mixed solution of platinum, palladium, and chromium cannot be directly used to produce automotive exhaust purification catalysts. Further separation and refining into pure metals are required.
