RETENTION OF PALLADIUM WITHIN CONDENSED-TANNIN GEL BY REDOX MECHANISM AND SEPARATION OF Pd AND Au IN CHLORIDE SOLUTION

摘要

We have developed the novel recovery system of palladium from wastes, which is simple and generates little secondary waste in comparison with the conventional recovery processes, using tannin gel particles synthesized from condensed-tannin molecules. Pd is adsorbed onto the tannin gel particles through inner-sphere redox reaction mechanism: two-electron transfer from tannin gel to Pd(II) species, accompanied by ligand exchange between chloropalladium(II) complexes and tannin molecules. In addition, we propose the separation system of Pd and Au from Pd-Au mixture, which is feasible due to the difference in oxidization and reduction potential between Pd and Au species: (PdCl{sub}3(H{sub}2O)){sup}- and (PdCl{sub}4){sup}2- are less adsorbable than Pd species containing fewer Cl, such as PdCl{sub}2(H{sub}2O){sub}2 and (PdCl(H{sub}2O){sub}3){sup}+, while such a distinct difference between Au species is not observed.