Kinetic and thermodynamic studies for fluoride removal using a novel bio-adsorbent from possotia (Vitex negundo) leaf

Abstract

Possotia leaf powder (PLP), a novel biosorbent obtained from a locally available wild plant with environment friendly and low cost nature, has found to be effective to remove fluoride from fluoride contaminated drinking water. The kinetic and thermodynamic parameters for the adsorption have been studied. Its fluorideabsorption efficiency is found to be nearly 75% at natural pH range and is affected by the parameters likecontact time, absorbent dose, solution temperature and initial fluoride concentration. The optimum contact time and absorbent dose were found to be 120 min and 3gm/L, respectively.Langmuir, Freundlich and Temkin isotherm are studied through this experimental data and found to be well followed. The adsorption kinetics data were fitted to pseudo first order, pseudo second order, and intraparticle diffusion models and was best fitted for pseudo second order model. The thermodynamic study points out the efficiency of this bio-adsorbent at low temperatureindicating the physical nature of adsorption with weak adsorbent-adsorbate force of attraction. By studyingenthalpy, entropy and Gibb’s free energy via van’t Hoff plot, it was observed that the adsorption process wasfavorable and exothermic in nature.