Complexes of cadmium with phosphoric acid

Abstract

We have investigated the behaviour of109Cd, in two-phase systems: (HDEHP−C6 H6/ H3 PO4−HClO4−LiOH, μ=0.2), as a function of the independent equilibrium parameters which define the system: pH, equilibrium concentration of H3 PO4 and total concentration of HDEHP in the organic phase. The data have been interpreted in terms of the existence of phosphoric complexes characterized by their order 1 with regard to H3 PO4 and their charge z. The l and z. values are: 0<1<2, z=−2, 0, 1, 2 for the following ranges: 0.7<pH<2.7 and CH3 PO4<4M. Stability constants of the predominant complexes have been obtained. Finally, a formulation of these complexes has been proposed on the basis of partial charge of the atoms. Some complexes, could be formulated as hydroxy-phosphoric species, resulting from competition between hydroxy and dihydrogenophosphate anions. In concentrated phosphoric acid (CH3 PO4=4M), complexation of cadmium is not more than 25%.