Abstract
Fluoride is an anionic pollutant found in high concentrations (>2 mg/l) in the Shilabati river basin of West Bengal, India, which has reported numerous serious cases of skeletal fluorosis and bone deformation in recent years. This study investigated fluoride adsorption on kaolinite lithomarge (red and white laterite) from Paschim Medinapore (West Bengal, India), exploring both kinetic and equilibrium facets with a series of batch tests and a fixed bed column study using natural water. Based on the X-ray Powder Diffraction analysis, Alpha SiO2 with trigonal structure and Alpha Al2O3 with hexagonal structure of this natural adsorbent played a critical role in fluoride absorption mechanism. Experimental results showed that based on pH values relevant to the fluoride enriched groundwater, kaolinite lithomarge of red type was the most efficient having an effective removal efficiency (98.32 %) at pH 6.58 whereas the white type demonstrated the highest removal efficacy of 95.31 % at pH 6.51. The modelled breakthrough curves were obtained, and they were in good accordance with the corresponding experimental data. Finally, water samples were collected from 11 sites from the fluoride contaminated zone within the river basin and natural groundwater was filtered using kaolinite lithomarge of red type obtaining a removal capacity of 97.13 % within 30 min, for the initial concentration of 2.37 mg/l. The prototype tested in the laboratory showed promising contaminant removal as a low-cost, time saving, natural filtration option supplying a liter of fluoride free water for 0.0015 USD.
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