Defluoridation of drinking water by Mg/Al hydrotalcite-like compounds and their calcined products

Fluorosis, developed in the population who depends on water with high concentrations of fluoride for their daily drinking usage, is one of the most frequently occurring endemic diseases. To search for effective defluoridation agents, we studied F− adsorption by synthetic Mg/Al–CO3 hydrotalcite-like compounds (HT) and their calcined products (HTC). The adsorption experiments were carried out as a function of time, pH, and the adsorbate concentration. The affecting factors to fluoride sorption were found to be solution pH and the crystallinity of the HT. The results from our adsorption experiments indicated that F− uptake by HTC was much stronger than their precursors HT. It was further observed that the maximal adsorption takes place within the first 15 min. HTs and HTCs exhibit a reversed trend in F− uptake with regard to temperature of the hydrothermal treatment to HT. At any specific initial F− concentration, the removal efficiency of F− increases with the temperature for HTC, but decreases for HT. The removal efficiency is inversely related to the initial fluoride concentration for HTC obtained from HT synthesized at 130 °C (HTC130, the most efficient adsorbent seen in this study). The adsorption isotherm at pH 7 for HTC130 was linear and did not follow Langmuir equation; the K value (slope of the line) was calculated to be 0.46 L/g. HTC130 was shown to be able to bring F− concentration from 5 mg/L down to less than 1 mg/L in aqueous solution, suggesting that this material may be a possible candidate for F− removal.