Competitive adsorption of copper and mercury ions on natural and crosslinked chitosan membranes / Adsorção competitiva dos ions cobre e mercurio em membranas de quitosana natural e reticulada

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

Recent investigations have described chitosan, a linear polysaccharide obtained from deacetylation of chitin, as a suitable biopolymer to remove heavy metal ions from wastewater, since the amino and hydroxyl groups present in its structure can act as chelating sites. Several methods have been used to modify natural chitosan, such as crosslinking with glutaraldehyde (GLA) or epiclorohydrin (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. Chitosan membranes were prepared and used to obtain the single and binary kinetic and equilibrium 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 capacities were found for crosslinked chitosan. It is possible to notice that the presence of copper ions in the mixture has a more significant impact on mercury adsorption than the other way around. Using only the monocomponent data, the competitive adsorption effects of the different ions in mixture were evaluated using the Langmuir Extended Model and Ideal Adsorbed Solution Theory (IAST). The adsorption kinetic modeling showed that external diffusion (boundary layer) is more significant than intraparticle diffusion for copper ions and the opposite for mercury ions. By increasing the mercury concentration, the copper kinetics was strongly influenced. The best desorption results were obtained for Hg(II) ions using NaCl and KI solutions as elutants. For Cu(II) ions, the best results were obtained by using H2SO4 and thioreia solutions. These results indicated that the adsorption mechanism for Hg(II) ions on chitosan is either by chelation, ion-exchange and electrostatic attraction, while for Cu(II) ions the chelation is more significant mechanism. X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure spectroscopy (EXAFS) were used to investigate the complex properties. The XPS results showed a possible reduction of Cu(II) ions on glutaraldehydecrosslinked chitosan. The EXAFS results confirmed that copper and mercury adsorption could have happen both on amino and hydroxil groups

ASSUNTO(S)

mercurio chitosan mercury quitosana heavy metals misturas cobre metais pesados mixture adsorption copper adsorção

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