Solvation properties in iso-acidic media involving phosphoric acid

Abstract

Concentrated solutions of mineral acids (phosphoric, hydrochloric, perchloric, sulfuric) are characterized, for an equal value of their water activity, by an equal R0(H) acidity level (iso-acidic solutions). By mixing them, we prepare what we call iso-acidic mixtures which keep the same acidity level as the constitutive solutions whatever the proportions; their redox and solvating properties depend both on the nature and on the ratio of the constitutive solutions. Reactivity variations for ionic species: Cl−, Br−,I−, diethyldithiophosphate (LET−), Si(W3Ol0)44−, Si(W3O10)45−, Cu2+, Cu+, Pb2+, Sn2+, Cd2+, Zn2+, Ag+, Fe3+, Fe2+, UO22+, U4+ in the iso-acidic mixtures are characterized by their ƒ solvation-transfer activity coefficients. Relations between ƒ coefficient values and complexation properties are established and it is shown that phosphoric acid has comparatively weak solvating properties toward most species. The possibility for anticipating reaction changes with the iso-acidic mixture composition by using the ƒ coefficients is demonstrated in the case of cadmium ionic flotation with diethyldithiophosphate and silver extraction with dithizone in carbon tetrachloride.