RETENTION OF PALLADIUM WITHIN CONDENSED-TANNIN GEL BYREDOX MECHANISM AND SEPARATION OF Pd AND Au IN CHLORIDESOLUTION

摘要

We have developed the novel recovery system of palladium from wastes, which is simple andgenerates little secondary waste in comparison with the conventional recovery processes, usingtannin gel particles synthesized from condensed-tannin molecules. Pd is adsorbed onto thetannin gel particles through inner-sphere redox reaction mechanism: two-electron transfer fromtannin 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 Aufrom Pd-Au mixture, which is feasible due to the difference in oxidization and reductionpotential between Pd and Au species: PdCl3(H2O)– and PdCl42– are less adsorbable than Pdspecies containing fewer Cl, such as PdCl2(H2O)2 and PdCl(H2O)3+, while such a distinctdifference between Au species is not observed.