INFLUENCE OF THE AMINE NATURE ON THE COMPOSITION OF PALLADIUM COMPLEXES IN SOLVENT EXTRACTION SYSTEMS

Abstract

ABSTRACT The extraction of palladium chloro complexes by di-n-octylamine and diamines of various structure as function of the composition of the aqueous and organic phases has been studied. The compositions of the extracted species are indicated and the mechanisms of their distribution are described. It was shown that from 1 to 3 M HC1 solutions. complexes such as (R2NH2)2PdCl4 solvated by molecules of dioctvlamine chloride are extracted. With increasing the initial concentrations of palladium or decreasing acidity of the aqueous phase, a direct coordination takes place, first of one and then two molecules of amine to atom of palladium with the formation of extracted compounds such as HC1 solutions by salts of amines, diamines and QAB ionic associates such as (AmH)2PdCl4, (AmH)2)PdCl4 and (R4N)2PdCl4, respectively, are recovered into the organic phase. In systems containing trioctylamine, tetraoctylalkylenediamines (n = 4, 6) and QAB. ionic associates containing the dimeric complex anion, Pd2Cl6 2-, are also formed. When primary (n-octylaniline - OA) and secondary amines are used as extractants the formation of dimeric species in the organic phase is not observed. The extraction of palladium from weakly acidic and neutral solutions can proceed through a combination of anion-exchange and coordination mechanisms with the formation of (AmH)[Pd(Am)Cl3] in systems with primary and secondary amines, and through a coordination mechanism with the formation of complexes such as Pd(Am)2Cl2 in systems with primary, secondary and tertiary amines. When palladium is extracted by diamines with a short hydrocarbon chain (n=2) the formation of coordination compounds also takes place.