The feasibility of fluoride adsorption from aqueous solutions using naturally available bentonite clay in both modified and unmodified forms is investigated in this report. SEM, EDX, XRD, and FT-IR analysis are applied to describe the structure and nature of unmodified and modified bentonite clay. The physicochemical characteristics of the adsorbent were also investigated by its moisture content, pH, apparent density, specific surface area, cation exchange capacity and its point of -zero charge determination. SEM image reveals particles are dispersed homogeneously and are irregular in shape. XRD and EDX analyses reveal that the bentonite is composed of seven materials: Calcite, Silica, Alumina, Hematite, bornite and Green cinnabar, and Chloride are considered as impurity. Raw bentonite (RB) clays have shown very low fluoride removal efficiency (47.19%). Modification of the clay surface with HCl (ATB) and aluminum oxide (AOMB), on the other hand, increased fluoride removal efficiency to 79.77% and 94.38%, respectively. At 5 mg/L initial fluoride concentration, 10 cm bed depth packed dose of adsorbent, and 180 min breakthrough time, a 2.88 mg/g of fluoride removal capacity was observed. As the result, aluminum oxide modified bentonite clay was chosen for further investigation and its result is not presented here.

Using small-scale batch tests, various researchers investigated the adsorptive removal of fluoride using low-cost clay minerals, such as Bentonite. In this study, Column adsorption studies were used to investigate the removal of fluoride from aqueous solution using acid-treated Bentonite (ATB). The effects of initial fluoride concentration, flow rates, and bed depth on fluoride removal efficiency (R) and adsorption capability (qe) in continuous settings were investigated, and the optimal operating condition was determined using central composite design (CCD). The model’s suitability was determined by examining the relationship between experimental and expected response values. The analysis of variance was used to determine the importance of independent variables and their interactions. The optimal values were determined as the initial concentration of 5.51 mg/L, volumetric flow rate of 17.2 mL/min and adsorbent packed-bed depth of 8.88 cm, with % removal of 100, adsorptive capacity of 2.46 mg/g and desirability of 1.0. This output reveals that an acid activation of Bentonite has made the adsorbent successful for field application.

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