Palladium sorption on glutaraldehyde-crosslinked chitosan

The high nitrogen content of chitosan is the main reason for its ability to sorb metal ions through several mechanisms including ion-exchange or chela tion, depending on the metal and the pH of the solution. Glutaraldehyde is used to crosslink chitosan through imine linkage between amine groups of ch itosan and aldehyde groups of the crosslinking agent. This modified biosorb ent was studied for palladium recovery in acidic medium (around pH 2). The influence of several parameters such as pH and competitor anions were studi ed with respect to sorption equilibrium. Sorption isotherms were obtained a nd modeled using the Langmuir and the Freundlich model. This study also exa mines the effect of palladium concentration, particle size, sorbent dosage, and the extent of crosslinking on sorption kinetics. Kinetic curves are mo deled using single diffusion model equations to evaluate the predominance o f either external or intraparticle mass transfer resistance. The influence of the acid used to control the pH of the solution was examined in conjunct ion with the influence of competitor anions. Sulfuric acid proves to be unf avorable to palladium sorption, in comparison with hydrochloric acid. Howev er, the addition of chloride anions in a palladium solution, whose pH is co ntrolled with sulfuric acid, enhances metal anion sorption: results are int erpreted with reference to chloropalladate speciation. (C) 2000 Elsevier Sc ience B.V. All rights reserved.