Analytical Sciences

Surfactant Gel Adsorption of Platinum(II), (IV) and Palladium(II) as Chloro-complexes and Kinetic Separation of Palladium from Platinum Using EDTA

Yoshiko MURAKAMI,* Kaoru HIRAIWA,* Yoshiaki SASAKI,* Isamu FUJIWARA,** and Shoji TAGASHIRA*

*Department of Chemistry, Faculty of Science, Yamaguchi University, Yoshida, Yamaguchi 753-8512, Japan
**The Center for Waste Water Treatment, Yamaguchi University, Yoshida, Yamaguchi 753-8511, Japan

A micellar solution of cetylpyridinium chloride (CPC) can separate into two phases due to a temperature change or to the addition of salts. Platinum(II), (IV) and palladium(II) reacted with chloride ions to form stable anionic complexes of PtCl₄^2-, PtCl₆^2- and PdCl₄^2-, respectively, and were adsorbed onto the CPC gel phase. The CPC phase plays the role of an ion-exchange adsorbent for the anionic complexes. By such a procedure, the precious metals of platinum and palladium could be separated from base metals such as copper, zinc and iron. The kinetic separation was performed by a ligand exchange reaction of the palladium(II) chloro-complex with EDTA at 60°C. The anionic palladium(II)-EDTA complex could not bind the opposite charged CP⁺ and was desorbed from the CPC phase. In the aqueous phase, the recovery of palladium(II) by the double-desorption was 101.1 ± 1.2%. The platinum(II) and (IV) chloro-complexes were stable for at least 30 min and remained in the CPC phase.

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