Synthesis and characterization of a thiourea derivative of chitosan for platinum recovery

Chitosan is effective at removing platinum from dilute solutions, but sorpt ion properties are significantly affected by the presence of competitor ani ons, such as chloride and, especially, sulfate anions. Sorption capacities in such complex solutions are enhanced by grafting thiourea through glutara ldehyde linkage. The influence of the amount of glutaraldehyde and thiourea in the impregnation bath was investigated and optimized with special atten tion to the composition of the solution and the type of acid used for pH co ntrol. This modification involves a change in the sorption mechanism: While glutaraldehyde-crosslinked chitosan adsorbs platinum through an ion-exchan ge mechanism, the thiourea derivative of chitosan acts as a chelating resin , less sensitive to ionic strength and competitor anions. Platinum sorption is also less sensitive to pH, and increasing the sulfate anion concentrati on has a limited effect on platinum sorption in comparison with the crossli nked sorbent. Thiourea grafting seems to increase sorption kinetics, especi ally in solutions controlled with sulfuric acid. SEM-EDAX techniques as wel l as FTIR analyses were used to characterize chemical modifications of the sorbent. (C) 2000 John Wiley & Sons, Inc.