Thermodynamic and Kinetic Study of Ion Adsorption onto Nanofiltration Membrane

In this work, adsorption of chloride and calcium ions from NaCl and CaSO4 binary solutions onto NF45 nanofiltration membrane was studied and compared. Freundlich isotherm wasfound to well represent the sorption data. For both ions, thermodynamic parameters such as G0, H0 and S0 werecalculated and compared. It was found that for both ions the adsorption was endothermic ( H0> 0) and spontaneous ( G0< 0). Moreover, the cation adsorption was superior to the anionadsorption; i.e. it was more endothermic and feasible. On the basis of greater S0 value, more randomness was induced in thelayer adsorbed on the membrane surface by Ca+2 in comparison with Cl- ions. Kinetic studies were conducted. The obtainedresults showed when the amount of adsorbate was low, as a result of either low total solution concentration or being at early stages of adsorption, adsorption rates satisfactorily followedpseudo-second-order rate model. However, as the adsorbed amount was increased coefficient correlation was decreased and the overall trend shifted toward the lower order of adsorption rate, the pseudo-first-order rate