Sorption of calcium by chitosan hydrogel: Kinetics and equilibrium

One of the major applications of chitosan is based on its ability to bind ions. In essence, the presence of active hydroxyl groups (-OH) and amino groups (-NH2), chitosan coordinates easily e.g. with transition metal ions, meanwhile it has a weak adsorption properties towards to alkaline earth metals. In this paper, a batch adsorption system was applied to study the adsorption of Ca(II) ions from aqueous solution by thermosensitive chitosan hydrogels. Due to the presence of sodium β-glycerophosphate (β-GP) in the sol structure, chitosan salts respond with phase transition and obtain thermosensitive properties, including changes in sorption abilities. Experimental research (the maximum adsorption capacity obtained 1.157 g g−1) and theoretical investigation on sorption of calcium in range of concentrations of CaCl2 solution, has been studied. Equilibria were described by Langmuir, Freundlich, Toth, Redlich-Peterson, Dubinin-Radushkevich, Radke-Praushnitz, Fritz-S, Langmuir-Freundlich, Marczewski-Jaroniec, Bi-Langmuir isotherm equations. Whereas, to describe sorption kinetics an original model was proposed, which combine chemical reaction on sorbent surface and intraparticle diffusion. The process of sorption was described by two parameters: diffusion coefficient DAB = 2.967·10−9 m2 s−1 and surface process rate constant kv = 9.129·10−5 s−1.