Adsorption recovery of rhodium(III) in acidic chloride solutions by amine‐modified tannin gel

Abstract

AbstractA tannin gel (TG), synthesized from condensed tannin molecules, has the remarkable ability to adsorb various metal ions in aqueous solutions. In the present study, the adsorption behavior of rhodium ion [Rh(III)] in acidic chloride solutions was investigated using an amine‐modified tannin gel (ATG) prepared by the ammonia treatment of a TG. The ATG was able to adsorb Rh(III) in strong hydrochloric acid solutions, whereas the TG failed to adsorb it. This is because the amino group in the ATG can form a stable complex with Rh(III) compared to the hydroxy group. With increasing chloride ion concentration, the adsorption amount of Rh(III) onto the ATG decreased somewhat, while the number of chloride ligands in the Rh(III) complex was expected to increase. This suggests that the Rh(III) complexes with fewer chloride ligands are more favorable for adsorption onto the ATG. Also, the Rh(III) adsorbability of the ATG decreased significantly with decreasing initial pH because of the protonation of the hydroxy and amino groups in the ATG. The results obtained here indicate that in the Rh(III) adsorption onto the ATG, the solution pH is more influential than the chloride ion concentration. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012