Pd and Pt recovery using chitosan gel beads. II. Influence of chemical modifications on sorption properties

Chitosan is very efficient at removing precious metals from dilute acid solutions. Its sorption properties can be improved by the chemical modification of the polymer. Several methods have been tested for chitosan modification including poly(ethylene imine) (PEI)-grafting, hydrogenation of imine function on glutaraldehyde-cross-linked chitosan, and thiourea-grafting. Depending on the modification technique, the improvement in sorption performance may consist, in an increase in sorption capacity (PEI-grafted chitosan), a change in the stability of the sorbent (hydrogenation of imine linkage) or an increase in the selectivity of sorption in the presence of co-ions (thiourea derivatives of chitosan). Chitosan gel beads were chosen rather than the flaked material, since the gel beads have enhanced diffusion properties. The influence of drying and re-hydration of the beads are studied for some of these chitosan derivatives with regard to their diffusion properties.