Carbamazepine sorption characteristics onto bentonite clay: Box-Behnken process design

Abstract

A comprehensive study has been hold as a function of ionic strength, pH, equilibrium (Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models), kinetic (pseudo-first order, pseudo-second order and intraparticular kinetic models) and thermodynamic for the removal of carbamazepine (CBZ) from its aqueous solutions onto bentonite. A statistical experimental design method (Box-Behnken) has been applied for the optimal adsorption conditions (0.089 g resin/10.31 mL solution under 144 rpm mixing speed of shaking bath) in order to achieve the maximum yield (≈80% removal). Partition coefficient (PC) was also employed for the evaluation of the bentonite clay's performance. The equilibrium time was determined as 15 min depending on the kinetic study, where the maximum adsorption capacity (2.3550 mg g-1) and PC (0.0684 mg g-1 μM-1) were achieved for an initial CBZ concentration of ≈30 mg L-1. Effects of pH (3, 5, 7, 9 and 11) and ions (chloride, fluoride and lead) on the CBZ adsorption have been explored. The acidic media (pH ~ 3) enhanced the removal, while ionic strength caused to drop the adsorption from 22 to 51% depending on the ion and its concentration (0.17, 0.86 and 1.71 mol L-1 for chloride; 0.24, 0.48 and 0.95 mol L-1 for floride; 0.03, 0.15 and 0.30 mol L-1 for lead) in the solution. Finally, the nature of the adsorption process for the CBZ removal onto bentonite has been detected to be a non-spontaneous and endothermic, having a tendency to an irregular structure.