Competitive sorption of platinum and palladium on chitosan derivatives

Glutaraldehyde-cross-linked chitosan (GCC), thiourea derivative of chitosan (TGC) and rubeanic acid derivative of chitosan (RADC) have previously been shown to be very efficient at removing platinum and palladium from single component dilute acidic solutions. This study examines the competitive sorp tion of these metal anions in bi-component mixtures for GCC, TGC and RADC. Palladium sorption is less sensitive to the presence of platinum than the r everse: the maximum sorption capacity decreases less for palladium than for platinum in the presence of the competitor anion (the metals being in thei r chloro-metal forms). Moreover, the Langmuir-shape of the sorption isother m for palladium is unaffected (with the usual plateau reached at low residu al palladium), while in the case of platinum sorption, the isotherms exhibi t a significant decrease of the sorption capacity at high residual platinum concentration which increases with increasing concentrations of palladium. RADC is more selective for palladium over platinum than the other chitosan derivatives. A preliminary study of the competitive sorption kinetics in b oth batch and fixed bed systems is presented for RADC and confirms the high er affinity of the sorbent for palladium than for platinum. (C) 2001 Elsevi er Science B.V. All rights reserved.