Fluoride removal from water by Ca-Al-CO3 layered double hydroxides and simultaneous acidification

Millions of people worldwide are exposed to excessive concentrations fluoride (F−) from groundwater sources. Ca-Al-CO3 layered double hydroxides (LDHs) have shown promising defluoridation efficiency; however, by LDHs is highly pH sensitive. This study showed that simultaneous acidification conventional acids, such as HCl and CO2 substantially increased the performance for F- removal at environmentally relevant (e.g., 10 mg/L) below WHO guideline value (1.5 mg/L), while, in comparison other acids (HNO3, H2SO4, H3PO4), use does not lead introduction potentially harmful or undesired anions. The addition suspensions did changes structure. Leaching experiments, supported PHREEQC modelling characterization (SEM-EDX, XRD FTIR), strongly suggest main mechanism was F− adsorption complexation onto/into various rehydrated mixed metal oxides which re-precipitated upon partial dissolution when acidifying.