Performance and mechanism of Mg-Ca-Fe hydrotalcite-like compounds for fluoride removal from aqueous solution

The Mg5-xCaxFe-NO3 hydrotalcite-like compounds (Mg5-xCaxFe-NO3-HTlcs, x = 0-5, x is the mol.% of Ca) were successfully synthesized by a facile co-precipitation method in this study. Mg/Ca/Fe molar ratio was studied to optimize the adsorbent. The adsorbents were characterized by Inductively coupled plasma (ICP), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR). Batch adsorption experiments were conducted to study the influence of various factors, such as contact time, adsorbent dose, temperature, initial solution pH, and coexisting anions. The experimental results demonstrated that the adsorbent obtained the maximum adsorption capacity of 248.44 mg g(-1) for fluoride with a Mg/Ca/Fe molar ratio of 1.25:3.75:1, adsorbent dose of 0.5 g L-1, contact time of 12 h and at 50 degrees C. The adsorption data were fitted well with the Freundlich isotherm and pseudo-second-order kinetic model. The adsorption mechanism involved surface/intercalation and the precipitation of releasing Ca2+ with fluoride. All results indicated that the Mg-CaFe-NO3-HTlcs can be a very promising material for fluoride removal from aqueous solution.