Calcite nanoparticle was used for fluoride removal in this study. The calcite nanoparticle was firstly characterized, including BET surface area, high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and zeta potential. pH was found to be the most important factor and neutral pH was favorable for fluoride removal. Initial fluoride concentration determined the fluoride removal mechanism. PHREEQC predicts calcium fluoride precipitate occurs for each fluoride concentration. Experimental results show that when at low-concentration fluoride (10 mg/L) it is removed by surface adsorption. Fluoride adsorption decreased with increasing ionic strength. Increase in temperature decreased the adsorption. Thermodynamic parameters showed that the adsorption of fluoride is spontaneous and exothermic. Adsorption isotherms were well-fitted by Langmuir isotherm with theoretical adsorption capacity of 4.89 mg/g. When at high-concentration fluoride (100 mg/L), calcium fluoride precipitate was found on the surface of calcite nanoparticle as shown from HRTEM. Results from X-ray photoelectron (XPS) confirm that calcium fluoride precipitated on the surface of calcite nanoparticle.

Adsorption and precipitation of fluoride at calcite nanoparticle surface: A spectroscopic study

248th National Meeting (2014)

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