The investigation of kinetic and isotherm of fluoride adsorption onto functionalize pumice stone

In this research work, pumice that is functionalized by the cationic surfactant, hexadecyltrimethyl ammonium (HDTMA), is used as an adsorbent for the removal of fluoride from drinking water. This work was carried out in two parts. The effects of HDTMA loading, pH (3–10), reaction time (5–60min) and the adsorbent dosage (0.15–2.5gL⁻¹) were investigated on the removal of fluoride as a target contaminate from water through the design of different experimental sets in the first part. The results from this first part revealed that surfactant-modified pumice (SMP) exhibited the best performance at dose 0.5gL⁻¹, pH 6, and it adsorbs over 96% of fluoride from a solution containing 10mgL⁻¹ fluoride after 30min of mixing time. The four linear forms of the Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherms model were applied to determine the best fit of equilibrium expressions. Apart from the regression coefficient (R²), four error functions were used to validate the isotherm and kinetics data. The experimental adsorption isotherm complies with Langmuir equation model type 1. The maximum amount of adsorption (Qₘₐₓ) was 41mgg⁻¹. The kinetic studies indicated that the adsorption of fluoride best fitted with the pseudo-second-order kinetic type 1. Thermodynamic parameters evaluation of fluoride adsorption on SMP showed that the adsorption process under the selected conditions was spontaneous and endothermic. The suitability of SMP in defluoridation at field condition was investigated with natural groundwater samples collected from a nearby fluoride endemic area in the second part of this study. Based on this study's results, SMP was shown to be an affordable and a promising option for the removal of fluoride in drinking water.