Equilibrium, kinetic, and thermodynamic studies on nickel removal from aqueous solutions using Ca-bentonite

Sorption using natural materials such as clay minerals is generally regarded as a suitable method for wastewater treatment. Equilibrium nickel (Ni) sorption on Ca-bentonite was determined in solutions with initial Ni concentrations ranging from 0-100 mg L-1. The effect of contact time and temperature on Ni sorption was also investigated. The equilibrium capacity of the bentonite for Ni removal was 2.93, 3.91, and 6.00 mg g(-1) at 278, 298, and 318 K, respectively, showing sorption enhancement with rising temperature. The results obtained from the kinetic tests indicated that major Ni removal occurred within the first 2 h, but the equilibrium condition was not attained before 24 h. Negative changes in Gibbs free energy (Delta G degrees) of sorption indicated that Ni sorption on Ca-bentonite was a spontaneous reaction. The positive values of both Delta H degrees and Delta S degrees suggest the endothermic nature of the Ni sorption and increased randomness at the solid-solution interface during the Ni chemisorption on the Ca-bentonite, respectively. In conclusion, Ca-bentonite is a potential sorbent for removal of Ni from wastewaters with the most favorable removal behavior at higher temperatures.