South African Journal of Chemical Engineering (Apr 2023)
Comparative adsorptive performance of adsorbents developed from kaolin clay and limestone for de-fluoridation of groundwater
Abstract
Excessive fluoride in potable groundwater is a serious health problem in rural areas of many developing countries. This research was designed to assess the efficiency of low-cost adsorbents for the removal of fluoride ions by using natural kaolin clay and limestone. The kaolin clay and limestone were first, subject to a beneficiated process to remove impurities. Then the thermal process was conducted at 750 °C for adsorbent preparation. The crystalline structure of thermally treated and raw materials was analyzed using X-ray diffraction (XRD). The functional groups before and after fluoride adsorption were determined by Fourier transform infrared spectroscopy (FTIR). The chemical composition and thermal stability of the adsorbent material were also investigated using atomic absorption spectroscopy (AAS), and differential thermal analysis (DTA) respectively. The prepared adsorbent materials were subjected to batch adsorption studies with different adsorption parameters including contact time, pH, adsorbent dosage, and temperature. The optimal fluoride removals in both adsorbents were obtained at a temperature of 60 °C, pH 5, a dose of 0.6 g, and at 60 min contact time. The optimum fluoride adsorption capacity was found 3.58 mg/g and 1.85 mg /g for kaolin clay and limestone, respectively. The adsorption process follows Freundlich isotherm models and Pseudo-Second-order kinetic model. The interaction effects with a 3D plot of operating parameters on the defluoridation capacity were analyzed using a design expert and confirmed that there were significant effects on fluoride adsorption. It can be concluded that kaolin and limestone showed the best results in terms of cost-effectiveness, adsorption efficiency and reusability for fluoride ion adsorption.
