Improved Adsorption Behaviors of Amine-Modified Tannin Gel for Palladium and Platinum Ions in Acidic Chloride Solutions

A tannin gel (TG) synthesized from condensed tannin molecules has a remarkable ability to adsorb various metal ions in aqueous solutions. Previously; we found that the adsorbability of the TG for the palladium ion can be improved by the ammonia treatment (Chem. Lett. 2007, 36, 1316). In the present study, we have performed solid-state C-13 NMR measurements of the tannin gels before and after the ammonia treatment and found that some hydroxy groups in the TG are substituted by ammo groups. Using this amine modified tannin gel (ATG), we have investigated the adsorption behaviors of palladium and platinum ions, Pd(II) and Pt(IV), in acidic chloride solutions under various conditions. The adsorbability of the ATG for both precious metal ions was greatly improved compared to that of the original TG. Their adsorption amounts onto the ATG increased with increasing pH and temperature or decreasing chloride ion concentration. Under all conditions examined here, the adsorbability of the ATG for Pd(II) was much higher than that for Pt(IV), resulting in the success of the selective adsorption of Pd(II) from the solution mixture of Pd(II) and Pt(IV).