Use of Binary Extractants for Extraction and Separation of Noble Metals

Abstract

The distribution of platinum metals and gold in the systems with binary extractants (salts of amines, quaternary ammonium bases (QAB), and organic acids) in toluene has been studied. It was shown that anion exchange mechanism complicated by interactions of components in organic phase is realized during metal extraction from 1–3 M HCl solutions. When acidity of aqueous phase decreases distribution coefficients of noble metals are decreased according to binary extraction regularities of mineral acids in (he systems with salts of trioctylamine and QAB. In the systems with caprylate and alkylphenolate of dioctylamine in the region of high pH values of aqueous phase, palladium distribution coefficients are increased due to formation in the organic phase of complexes with direct coordination of amine molecules to atoms of palladium and their stability is, obviously, higher than that of dioctylamine salts with corresponding organic acids. From the investigated binary extractants, the salts of quaternary ammonium bases and strong organic acids (alkylphosphoric, alkylbenzolsulfonic acids) are of great interest for practice. It was shown during extraction of Pt (IV), Pd (II), Ir (IV) and Au (III) chlorocomplexes by 0.1 M solutions of trialkylbenzylammonium alkylsulphonate, metal distribution coefficients in the acidic region are changed from 5 to 150 while distribution coefficients for Rh(III) and Ir(III) did not exceed 0.1 and that creates possibilities for separation of platinum metals. Noble metals are lightly stripped from organic phase by water that it is impossible for initial systems with mineral salts of quaternary ammonium bases. The comparison of the systems with binary extractants and TBP has shown the advantage of binary extraction for obtaining more concentrated stripping solutions.