Enhanced fluoride removal from water by rare earth (La and Ce) modified alumina: Adsorption isotherms, kinetics, thermodynamics and mechanism.

The removal of F- from aqueous solution using lanthanum and cerium modified mesoporous alumina (La/MA and Ce/MA) was studied, and characteration of the adsorbents by XRD, BET, XRF, FTIR, TEM, XPS and the pHZPC measurements were carried out. The adsorption was investigated in both batch and column adsorption systems. Batch experimental results showed that adsorption capacities of adsorbents were recorded in the following order: La/MA > Ce/MA > mesoporous alumina (MA). Besides, adsorption datas were fitted well by Sips isotherm model and Elovich kinetics model, and the maximum adsorption capacity of La/MA was 26.45 mg·g-1 in Sips model at the dosage of 2.0 g·L-1 and near neutral condition (pH = 6.0 ± 0.1). Moreover, thermodynamic parameters were illustrated that adsorption process of fluoride ion over La/MA was spontaneous and endothermic. In the adsorption process, the interaction between metal and fluoride, the adsorption capacity was increased due to form the bond of M···F (M = La or Ce). Furthermore, the influence of coexisted anions on F- removal was investigated, and it was indicated that removal efficiency was slightly affected by the presence of Cl- and NO3-, while SO42- and CO32- caused a sharp fall in removal efficiency. Column experiments results were indicated that time of break-through of La/MA was twice as much as that of MA.