Equilibrium and Kenitic Modeling of Cd(II) Adsorption from Aqueous Solution using Tricalcium Phosphate

Abstract

The performance of adsorption of Cd(II) from aqueous solutions onto tricalcium phosphate Ca₃(PO₄)₂ (TCP) have been determined and studied with kinetic and isotherm models. The effect of contact time, concentration of Cd(II) was studied. Extraction kinetics is very fast, Indeed t=5 mn. The amount of TCP sorbed per gram of Cd(II) qt (mg/g) increased with increasing initial Cd(II) concentration. The adsorption of Cd(II) by TCP followed pseudo-second order kinetics. Diffusion intraparticle is the only rate-controlling step. Adsorption equilibrium data were analyzed by Langmuir, Frendlich and Temkin isotherm equation using regression analysis. Langmuir found to best represent the data for Cd(II) adsorption onto TCP. The negative value of change in Gibbs free energy (?G°=-4.249 Kj/mol) indicates the feasible and spontaneous adsorption. The positive value of the variation of adsorption energy ?Q=31.48 Kj/mol indicate that the adsorption reaction is exothermic.

Keywords: Cd(II) adsorption, Isotherm, Kenitic, Tricalcium phosphate