Abstract
Noble metals including palladium, which are used in catalytic agent and electric device, have been much in demand recently, in spite of the limited natural resource in the crust. Therefore, the recovery of the noble metals from wastes such as spent catalysts or scraps has become necessary as well as the extraction from ores. Tannin gel particles with polyhydroxyphenyl groups were synthesized as the adsorbent for the new recovery system of palladium(Pd), which was simple and generated little secondary waste in comparison with the conventional recovery processes. The properties of tannin gel particles for the adsorption of Pd were examined in PdCl2 aqueous solution and resulted in that Pd is adsorbed onto the tannin gel particles as a reduced metallic Pd through redox reaction mechanism: chloropalladium(II) species are reduced to metallic Pd(0), while hydroxyl groups of tannin gel are oxidized during the adsorption. Additionally, it was observed that Pd species containing fewer Cl, such as PdCl2(H2O)2 and PdCl(H2O)3+, are more favorable for the adsorption than PdCl3(H2O)- and PdCl42-. By utilizing such characteristics of tannin gel particles, it is expected that they can be applied to recover Pd efficiently and simply with low cost.
