Deep Removal of Fluoride by Highly Activated Magnesium Oxide

Activated MgO was prepared from calcination of alkaline magnesium carbonate for the removal of a low concentration of fluorion. MgO calcinated at 500 °C showed the highest adsorption capacity and fastest adsorption rate for fluorion. The removal rate of F^– reached 98.35% with the maximum adsorption capacity of 19.3 mg·g^–1 with an initial F^– concentration of 20 mg/L in a wide range of pH. The adsorption of F^– by MgO is less affected by Cl^–, CO₃^2–, and HCO₃^–. SO₄^2– and NO₃^– have a negative effect on the adsorption of F^– on activated MgO. The adsorption process of F^– on MgO follows the proposed second-order kinetic model and Langmuir isotherm model. The adsorption of F^– on activated MgO has two stages. Surface and intraparticle diffusion are the rate limiting steps in the first and second stage, respectively. FTIR and XPS results of MgO and used MgO inferred that O–H···F bonds formed between F^– and MgO during the defluorination process.