Fluoride removal from aqueous solutions by magnesium, nickel, and cobalt calcined hydrotalcite-like compounds

Magnesium, nickel and cobalt hydrotalcite-like compounds (MgHT, NiHT, and CoHT), with similar M2+:Al3+ ratios were synthesized and characterized by XRD. It was confirmed from XRD that the materials have hydrotalcite-like structure. MgHT, NiHT, and CoHT were calcined and treated with fluoride solutions in a batch system. F- ions were determined in the remaining solutions using a fluoride ion selective electrode. The kinetics of the fluoride ions sorption on calcined hydrotalcite-like compounds (CHT) was best described by the pseudo-second order model and the equilibrium was reached in less than 300 minutes in all cases (MgCHT, NiCHT, and CoCHT). The sorption isotherms of the fluoride by hydrotalcite like compounds can be explained by the Langmuir-Freundlich model and, the highest fluoride sorption capacity was obtained for NiCHT (1.202 mgF/gCHT). The fluoride removal from aqueous solutions by calcined hydrotalcite-like compounds depends on the adsorption properties of the thermal decomposition products and the regeneration reaction mechanism of the hydrotalcite-like compounds.