Adsorption removal of fluoride from polluted drinking waters using Mn-Al-La oxide

Trimetal oxides have received high attention in treatment of fluoride-polluted drinking waters. In this study, Mn-Al-La (MAL) oxide with a mole ratio of 2:1:1 was successively prepared and characterized by XRD, FTIR, XPS, and TEM. It exhibited as cotton-like assemblages (500–800 nm of axial lengths), and BET specific surface area was 52 m 2 /g. It was used to study fluoride adsorptions in aqueous solutions by batch experiments, under different adsorbent/adsorbate levels, times, temperatures, pH and coexisting anions, and treat simulated groundwater (with 2.85 mg/L fluoride and pH 7.0) by batch and column tests. Adsorption data well fitted to pseudo-second-order rate model ( R 2 = 0.996–0.999), and Langmuir ( R 2 = 0.962 − 0.997) and Freundlich ( R 2 = 0.964–0.989) isothermal models. Their maximum adsorption capacities could reach 45–113 mg/g. Only H 2 PO 4 − anions had a restrictive impact at pH 7.0, and there was a good removal ability at pH 3–9. Adsorption processes were spontaneous, endothermic, and random. Adsorption mechanisms were electrostatic interaction and ligand exchange at pH 7.0. Adsorption capacity could reach 73% of initial value at pH 7.0, after three cycles. All application data on the polluted groundwater treatments show MAL oxide is a potential adsorbent for fluoride removals.