Fluoride removal performance of a novel Fe–Al–Ce trimetal oxide adsorbent

A trimetal oxide was developed as a fluoride adsorbent by coprecipitation of Fe(II), Al(III) and Ce(IV) salt solutions with a molar ratio of 1:4:1 under alkaline condition. The material retained amorphous structure and maintained relatively stable fluoride adsorption performance at calcination temperatures lower than 600 °C. The optimum pH range for fluoride adsorption was 6.0–6.5 and the adsorbent also showed high defluoridation ability around pH 5.5–7.0, which is preferable for actual application. A high fluoride adsorption capacity of 178 mg g−1 was acquired under an equilibrium fluoride concentration of 84.5 mg l−1, adsorbent dose of 150 mg l−1 and pH 7.0. The adsorption isotherm could be better described by the two-site Langmuir model than the one-site model, suggesting the existence of two types of active sites on the adsorbent surface. Coexistence of high concentrations of phosphate or arsenate only led to partial inhibition of fluoride adsorption, which further suggests the existence of heterogeneous adsorption sites. Sulfate and chloride did not affect fluoride adsorption, and nitrate influenced it only when the concentration of NO3-–N exceeded 50 mg l−1. A high desorption efficiency of 97% was achieved by treating fluoride loaded Fe–Al–Ce oxide with NaOH solution at pH 12.2. A column experiment using the adsorbent fabricated into 1 mm pellets was performed at an initial fluoride concentration of 5.5 mg l−1, space velocity of 5 h−1 and pH of 5.8, and 2240 bed volumes were treated with the effluent fluoride under 1.0 mg l−1.