Kinetics and isotherm studies for the adsorption of boron from water using titanium dioxide

Abstract

AbstractBoron is a necessary element for plants that are generally found in the ground and seawater, but it can also be poisonous in large doses. Contamination of water with boric acid or borate ions is a global concern. Due to the absence of the chemical charge that boron possesses, its removal is often difficult. To investigate boron's adsorption characteristics, kinetic, isotherm, and isothermal studies were performed. The adsorption of boron was shown to be a pH‐dependent mechanism, with the best results at around pH 9.0. About 47% of the boron from a solution of 50 mg L−1 was removed using 5 g titanium dioxide in 30 min. It was also demonstrated that boron adsorption kinetics increased with temperature, which is best described by the pseudo‐second‐order kinetic model (R2 > 0.98) and also fits well with Elovich and pseudo‐first‐order models (R2 > 0.94) at pH 9.0. Equilibrium was reached in about 40 min for all the samples. The film boundary layer diffusion step limits the rate. Experimental results correspond well to the Freundlich isotherm (R2 = 0.95–0.99). Langmuir and Temkin's isotherms also fitted reasonably well (R2 = 0.94–0.98). The Freundlich and Langmuir constants indicate favourable adsorption. The Gibbs free energy (ΔG) values increased negatively (from −11.47 to −15.63 kJ mol−1) with increasing temperature, signifying a feasible and spontaneous process. The enthalpy change (ΔH) value of about 30.35 kJ mol−1 indicated endothermic physical adsorption. The results indicate that titanium dioxide is an excellent and safe adsorbent for the removal of boron from water.