BINARY EXTRACTION OF PLATINUM METALS

Abstract

The equations describing the regularities of interphase distribution of platinum metals as their chloro complex acids in systems containing binary extractants have been derived. The dependencies of distribution coefficients of platinum metals on the composition of both phases, and their aqueous acidity have been determined when both binary extraction and a combination of anion-exchange and binary extraction occurred. The interrelation of the binary extraction constant of chloro complex acids of platinum metals with the extraction constant of hydrochloric acid and the anion-exchange constant is described. We studied platinum metal extraction by salts of organic acids and organic bases and showed that in the systems involving binary extractants, such as salts of quaternary ammonium bases, the distribution of platinum metals proceeds via either anion-exchange or binary mechanisms depending on the composition of the system. With increasing pH, the distribution coefficients of platinum metals decrease according to the regularities of binary extraction due to forming thermodynamicaHy stable binary extractants, R4NA When the anion-exchange extraction occurs, the distribution of complex acids of platinum metals in the systems containing binary extractants is affected by interactions of the extractants and the extracted compounds with the organic acids. Interactions between extractants in the chloride form and the molecules of organic acids have been shown to be largely responsible for the extraction characteristics. The binary extractant systems are preferred in the development of solvent extraction processes for the recovery and the stripping of platinum metals.