Method for separating dissolved species by electrodialysis

Abstract

Electrodialysis is used to separate at least one species of a first group of elements present in ionized form from at least one species of a second group of elements present in nonionized form in water-containing solutions, provided that the pH of the solutions and the oxidation state of species of the second group have the appropriate values. If necessary, either the pH, the oxidation state or both are adjusted in the solution fed to the electrodialysis unit such that species of the first group are present in ionized form and species of the second group are present in a nonionized form. The method is applicable to a large number of solutions from metallurgical and chemical processes. Species of the first group include at least one element of groups IA, except Fr, IB, IIA, IIB, IIIA except B, IIIB, IVB, VIIB and VIII except Os of the periodic table; the elements V, Cr, Sn, Pb and Bi; and acids of N, S, F, Cl, Br and I. Species of the second group comprise acids containing at least one element including B, C, Si, Ge, P, As, Sb, Se, Te and F. Electrodialysis is carried out in one of more stages at 10-500 A/m.sup.2 and 0.degree.-60.degree. C. while minimizing water splitting, and using alternating cationic and anionic permselective membranes forming alternating concentrate and diluate cells between an anode and a cathode. The ionized species migrate through the membranes from the diluate to the concentrate cells and the nonionized species remain in the diluate cells. Solution concentrated in ionic species is withdrawn from the concentrate cells, and solution containing the nonionized species is withdrawn from the diluate cells. The electrode compartments are rinsed with appropriate rinse solutions.