SEQUESTRATION OF CADMIUM FROM AQUEOUS SOLUTION USING GLUTARALDEHYDE CROSS-LINKED CHITOSAN HYDROGEL

Abstract

In this research work, comparative adsorption studies of Cd(II) ions on snail shell derived chitosan and glutaraldehyde crosslinked chitosan from aqueous solution were performed. Chitosan was extracted from snail shells by deproteination, demineralization, deacetylation and purification using suitable solvents. The degree of deacetylation of chitosan was calculated from FTIR spectrum of chitosan using Kasaii equation. The adsorbents were characterised by FTIR and SEM techniques. Batch adsorption experiments were performed as a function of pH ranging from 1 to 7, contact time ranging from 5 minutes to 6 h, initial Cd(II) ions concentrations of 10, 25, 50, 100 and 200 ppm, and temperature ranging from 298 K to 338 K. Equilibrium data were fitted using Langmuir, Freundlich, and Temkin isotherm models and were also tested with pseudo-first order, pseudo-second-order, Elovich and the intraparticle diffusion kinetic models. The experimental data were best represented by using a pseudo-second order kinetic model and a Freundlich isotherm model for both adsorbents. The reuse of chitosan and crosslinked chitosan adsorbents for the adsorption of Cd(II) ions from aqueous solution was experimented. EDTA, HCl and NaOH at different concentrations were used as desorbing agents. The data obtained for the adsorption studies were subjected to students’ t-test at 95 % significant level. The degree of deacetylation of chitosan was calculated to be approximately 62 %. Optimum adsorption was achieved at pH 5, 3 h of contact, and a concentration of 10 ppm at room temperature. The negative value of enthalpy change (Ho), negative values of free energy change (Go) increasing with increasing temperature from -6.491 KJ mol-1 at 298 K to -0.046 kJ mol-1 at 338 K for chitosan and from -5.307 KJ mol-1 at 298 K to 0.560 KJ mol-1 at 338 K for cross-linked chitosan showed the adsorption process was exothermic, spontaneous and feasible. Moreover, the obtained negative entropy change (So) showed the decreased randomness at the solid-solution.