(521b) Kinetic and Equilibrium Adsorption Properties for Copper and Mercury Ions On Chemically-Modified Chitosan Membranes

Chitosan has recently been recognized as a biopolymer with significant potential for use as biosorbent for removal of metal ions from wastewater, due mainly to amino and hydroxyl groups present in its structure. It is possible to chemically modify the structure of this biopolymer, using processes such as crosslinking with glutaraldehyde or epichlorohydrin. This chemical modification was done in order to investigate which group is responsible for adsorbing ions or even to increase the adsorption performance. Natural and crosslinked chitosan membranes were prepared and used to get the copper and mercury kinetic and equilibrium adsorption properties. The values of adsorption capacity for mercury ions were higher than those for copper ions for all kinds of chitosan membranes. The highest adsorption capacity values were found for crosslinked chitosan. The adsorption kinetic model showed that external diffusion (boundary layer) is more significant than intraparticle diffusion for copper ions and the opposite occurs for mercury ions. The copper kinetics is strongly influenced by mercury concentration. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure spectroscopy (EXAFS) were used to investigate the biopolymer-metal complex properties. The XPS results indicated a possible reduction of Cu(II) ions on glutaraldehyde-crosslinked chitosan. The EXAFS results confirmed that copper and mercury adsorption could have happen both on amino and hydroxil groups.