Adsorption of atrazine from aqueous solution using unmodified and modified bentonite clays

Properties of raw bentonite clay of Afuze in Edo state which are abundant and cheap bentonite mineral in Nigeria as adsorbents for the removal of atrazine in aqueous solution were investigated. The bentonite clay-types were characterized using scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectrophotometry and X-ray diffraction (XRD). Batch adsorption experiments were carried out to determine the equilibrium characteristics, thermodynamics and kinetics of the sorption processes. The data obtained were subjected to Langmuir, Freundlich and Temkin isotherm equations, while pseudo-first-order, pseudo-second-order rate equations, intra-particle diffusion and Elovich models were considered for kinetics and mechanism. The results showed that the adsorption processes were described by different isotherm models; they were all spontaneous (∆G ranges from − 938.34 to − 6263.58 kJ/mol) and exothermic (range of ∆H is − 252.73 to − 1057.08 kJ/mol), and with decreased randomness, ∆S (− 3.110 to − 0.581 J.mol/K). Pseudo-second-order kinetics model gave the better fit for all the sorption processes which implies physisorption process as the rate limiting step. Thus, bentonite clay-types can be used to adsorb atrazine.