Abstract
The feasibility of fluoride adsorption from aqueous solutions using naturally available bentonite clay in both modified and unmodified forms is investigated in this report. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy analysis was applied to describe the structure and nature of modified and unmodified bentonite clay. The physicochemical characteristics of the adsorbent were also investigated for moisture content, pH, apparent density, specific surface area, cation exchange capacity and its point-of-zero charge. SEM images reveal 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 which are considered as impurities. Raw bentonite clays have shown very low fluoride removal efficiency (47.19%). Modification of the clay surface with HCl and aluminum oxide, 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 a result, aluminum oxide modified bentonite clay was chosen for further investigation and the results are not presented here.
Highlights
Fluoride has a lot of negative effects on humans, including skeletal and dental fluorosis, but it does have some benefits for enamel strengthening at low concentrations
The apparent density, which is a measure of the compactness of the clay minerals, of the raw bentonite (RB), acid-treated bentonite (ATB), and AOMB was 2.62 g/cm3, 1.23 g/cm3, and 1.25 g/cm3, respectively
The experimental results show that ATB and AOMB clay can be used for fluoride removal as an adsorbent in a fixed-bed adsorption process
Summary
Fluoride has a lot of negative effects on humans, including skeletal and dental fluorosis, but it does have some benefits for enamel strengthening at low concentrations. Fluorosis and its complications affect over 200 million people globally (Fewtrell et al 2006). The World Health Organization (WHO) has set a fluoride limit of 1.5 mg/L in drinking water (World Health Organization 1993). The majority of which are in Southeast Asia and South Asia, have naturally contaminated drinking water supplies with fluoride (Rasool et al 2015). Countries like China, Chile, India, Bangladesh, Hungary, and Mexico have recorded fluoride concentrations greater than 1.5 mg/L (Smedley et al 2002). Like other developing countries, is dealing with a water shortage as well as fluoride pollution, especially in the Central Rift Valley.
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