EXTRACTION OF COPPER, CADMIUM AND RELATED METALS WITH POLY(SODIUM ACRYLATE ACRYLIC-ACID) HYDROGELS

The extraction of copper, cadmium and related metals (M(2+)) with poly (sodium acrylate - acrylic acid) PAA hydrogels has been studied. pH va riations are consistent with a cation exchange process. Saturation of the gel is achieved for a metal/carboxylate ratio R approximate to 1/2 and a gel swelling of approximate to 40 which is that of the uncharge d gel : (-C00)(2)M complexes are expected to be formed, but also compl exes of higher stoichiometry (R = 1/3 for Cu and Cd, R = 1/4 for Pb) a t low metal concentrations. The selectivity is that observed in liquid -liquid extraction of metal cations with fatty carboxylic acids (Pb, C u, Cd > Zn > Ni Co). Metal stripping from the gel is readily achieved by washing with 0.1 M HNO3. PAA hydrogel extraction allows to remove c admium from a diluted aqueous solution down to a final concentration o f 5 ppb.