Palladium and platinum recovery from bicomponent mixtures using chitosan derivatives

Chitosan has been used as a base material for the preparation of platinum and palladium sorbents. Chitosan derivatives were obtained by glutaraldehyde cross-linking (GA), by poly(ethyleneimine) grafting (PEI), and by thiourea grafting (TDC). These sorbents were tested for the recovery of platinum group metals (PGMs) in batch systems and column systems from bicomponent mixtures at the optimum pH (ca. pH 2). Sorption isotherms were determined in batch systems, considering the impact of the excess of one metal on the sorption of the second. The sorbents have a marked preference for palladium over platinum. In most cases, the total sorption capacity (taking into account both Pd and Pt sorption) was comparable to that of each metal individually, indicating that the metals compete for the same sorption sites, regardless of the type of sorbent. In fixed-bed systems, similar effects were observed, with typical profiles driven by the displacement of platinum by palladium, attributed to the greater affinity of the sorbents for palladium. The sorbents (especially GA and TDC) have a greater selectivity for Pd than for Pt, compared to PEI, which has greater sorption capacities. Metal desorption was tested using several eluants, none of which allowed the complete removal of the metals from loaded sorbent, nor the selective desorption of either. A complete separation of the metals was not obtained, but by combination of sorption and desorption conditions, a concentration of Pd of 10- to 20-fold was achieved.