Use of serpentinite in the defluoridation of fluoride‐rich drinking water

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Abstract
A newly developed, HCl treated method is described for the enhancement of fluoride uptake by serpentinite in an aqueous medium. Fluoride adsorption and desorption reactions in treated serpentinite were investigated, over the range of fluoride concentrations (1–10 mg/1). The zero point charge of the variable charge components (pH0), and total surface charge (σp) of serpentinite were also investigated. At equal concentrations of total fluoride in solution, fluoride retention was greatest at pH = 5.2 and decreased both at low and high pH. Thermodynamic properties for fluoride adsorption at 25°C and 50°C were investigated. The isosteric heat of adsorption (?H) was calculated for treated surfaces and heterogeneity of this surfaces was examined. Finally, Differential Thermal Analysis (DTA) and X‐ray Diffraction (XRD) patterns were observed for raw, treated and fluoride‐contacted surfaces. According to DTA and XRD patterns, structural changes were observed with HCl treatment.