Abstract
In the present study, we have investigated the counter-ion effect on the thermodynamics of Cr(III) sorption by macroporous resin Amberlyst-15. The exchange reaction was studied as a function of concentration of Cr(III) and nature of counter-ions at different temperatures. It was observed that nature of counter- ions have a profound effect on the exchange of Cr(III) ions. The selectivity of -Amberlyst-15 towards metal ion sorption follows the order -univalent > -divalent > trivalent forms. This trend can be associated to the electrostatic interaction of ions with the functional sites of the resin. The equilibrium pH values (pH eq) were observed to decrease with Cr3+/H+ exchange whereas an increase in pH eq was detected during the exchange of Cr3+/Li+, Cr3+/Na+, Cr3+/Ca2+ and Cr3+/Al3+. Different adsorption models such as Dubinin-Radushkevich (D-R) and Langmuir were employed to analyze the sorption data. The maximum exchange capacities (X m) and binding energy constants (K b) values were determined by using the Langmuir model. The values of both.Ho and.So were found positive inferring that the exchange process is endothermic accompanied by the dehydration of Cr(III) ions. The thermodynamic parameters revealed that the mechanism of Cr(III) sorption for all the counter ions is entropy driven ion exchange.