ABSTRACT

The mode of coordination about Cu(II) adsorbed on a strongly basic anion exchange resin equilibrated in HCl aqueous solutions was determined using extended X-ray absorption fine structure (EXAFS) and Raman spectroscopies. EXAFS spectra of the adsorbed Cu chloro-complexes were constant over a wide range of HCl concentrations in contrast to stepwise Cu-Cl complexation in the solutions. The adsorbed anion species was estimated to be [CuCl₄]^2-. Its Raman spectra suggested the most plausible coordination structure of [CuCl₄]^2- was 4 Cl coordination without H₂O ligands. The change from sixfold coordination [Cu(H₂O)₆]²⁺ to fourfold coordination [CuCl₄]^2- in stepwise chloro-complexation in the aqueous phase and preferential adsorption of [CuCl₄]^2- to the resin through ion-exchange reactions in elevated HCl concentrations will result in larger mass fractionation of Cu compared to Zn, which has a tendency to form tetrahedral Zn chloro-complexes in the presence of chloride ions.