Immobilizing thiourea onto chitosan allowed using the polymer for the recovery of platinum groups metals (PGMs) in acidic solutions (up to 1-2M HCl concentrations). At low HCl concentration protonated amine groups may sorb chloroanionic metal species (electrostatic attraction mechanism); however, most of sorption proceeds through chelation on sulfur containing groups (less sensitive to acidic conditions). The bi-site Langmuir equation was used for fitting sorption isotherms. The sorption of PGMs was weakly affected by the composition of the solution (presence of high concentration of anions and base metals). Maximum sorption capacities for Pd(II) and Pt(IV) ranged between 274 and 330 mg g(-1) in 0.25M HCl solutions and decreased to 150-198 mg g(-1) in 2M HCl solutions: Pd(II) sorption was systematically higher than Pt(IV) sorption. The pseudo-second rate equation was used for modeling the uptake kinetics. Agitation speed hardly affected uptake kinetics indicating that external diffusion resistance is not the rate controlling step. Desorption yield higher than 85% were obtained using thiourea in 0.1M HCI solution. The adsorbents could be reused for at least three cycles. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 3318-3330, 2010