(338w) Equilibrium Adsorption Modeling of Binary Mixtures of Copper and Mercury Ions On Natural and Crosslinked Chitosan Membranes

The contamination of water streams due to uncontrolled discharge of industrial wastewaters has induced considerable changes in the regulations regarding effluent treatments. Heavy metal ions, due to their high level of toxicity, their ability to be incorporated in the food chain, and their poor biodegradability, are part of the most hazardous group of compounds, requiring treatment before being discharged in the environment to meet the strict environmental quality standards.

Recent investigations have described the use of chitosan, a linear polysaccharide based on glucosamine unit, as a suitable biopolymer for removal of heavy metal ions from wastewater, since the amino and hydroxyl groups present in its structure can act as chelation sites. It is possible to chemically modify the structure of this biopolymer, using processes such as crosslinking with glutaraldehyde (GLA) or epichlorohydrin(ECH). The adsorption of different heavy metal ions in single systems has been investigated. However, in real systems it is more common to observe several ions in solution, which may interfere and compete for adsorption sites.

The aim of this work was to study the adsorption of copper and mercury ions on natural and crosslinked chitosan membranes (single and binary systems), in order to evaluate the competition of different metallic ions for the chelation sites of chitosan. Batch adsorption experiments were carried out by soaking the pristine or crosslinked chitosan membranes with copper or mercury individual solutions or for the copper/mercury mixtures.

The Langmuir model was used to fit the monocomponent equilibrium data of mercury and copper adsorption. The adsorption capacities for mercury ions were higher than those for copper ions on all kinds of chitosan membranes. The highest adsorption capacities were found for crosslinked chitosan.

Using only these monocomponent data, the competitive adsorption effects of different ions in mixture were evaluated using the Ideal Adsorbed Solution Theory (IAST), developed by Myers and Prausnitz (1965) and adapted to dilute liquid adsorption systems by Radke and Prausnitz (1972). The multicomponent adsorption isotherms for Cu and Hg ions on natural chitosan were predicted by the IAST from monocomponent data (Vieira et al. 2007) and compared for crosslinked ones. The mixture adsorption data showed that the presence of copper ions in the mixture has a more significant impact on mercury adsorption than the other way around. These results show that the adsorption of metal ion mixtures on chitosan can be predicted reasonably well by the IAST, using only monocomponent data. Using this theory together with material balance, it is possible to estimate the initial concentrations of the different heavy metal ions necessary to reach a predetermined equilibrium concentration. This feature can assist in the design of batch experiments.

References:

Mayers, A.L.; Prausnitz, J.L.; ?Thermodinamics of mixed-gas adsorption?, AICHE Journal, 11, 121-127, 1965.

Radke. CJ.; Prausnitz, J.M.; ?Thermodynamics Of Multi-Solute Adsorption From Dilute Liquid Solutions?, AIChE Journal, 18, 761, 1972.

Vieira, R. S. ; Abreu, C. R. A. ; Beppu, M. M. . Estudo Experimental e Modelagem do Equilibrio de Adsorção de Misturas dos Íons Cobre e Mercúrio em Quitosana. In: XXXIII Congresso de Sistemas Particulados, 2007, Aracaju. Anais do XXXIII Congresso de Sistemas Particulados, 2007.