MODELING OF SOLVENT-EXTRACTION EQUILIBRIA OF ZN(II) FROM SULFATE-SOLUTIONS WITH BIS-(2-ETHYLHEXYL)-PHOSPHORIC ACID

The distribution of Zn(II) between aqueous sulfate solutions and n-dodecane solutions of bis-(2-ethylhexyl)-phosphoric acid (D2EHPA) has been measured in the range of an initial aqueous Zn(II) concentration from 1.5 X 10(-3) to 1.5 x 10(-1) M. The ionic strength I, for several experiments carried out, was adjusted to a constant value by using Na2SO4, for I = 0.1-3. The data obtained were used to find a way of calculating the equilibrium distribution over a large concentration range. In this case, for the chemical reaction between the reactive extractant D2EHPA and the bivalent metal cation Zn(II), the stoichiometry changes from 2 to 1.5 for high D2EHPA loading conditions. A model was developed, based on the law of mass action, which enables the prediction of extraction equilibria for a given system over a large range of parameters such as ionic strength, pH, D2EHPA and zinc concentrations for known initial concentrations of the components of the system.