When applied to wastewater treatment, natural gibbsite has a low fluorine capacity and is therefore rarely used. In this work, the gibbsite was calcined at different temperatures to improve the fluoride adsorption capacity. The adsorption responsible parameters, such as calcination temperature and time, initial fluoride concentration, dosage, reaction time and temperature were optimized. The results showed that the adsorption capacity of fluorine ion varies significantly by the gibbsite calcined at different temperatures. The best fluorine removal effect is the gibbsite calcined at 573 K for 0.75 h and its adsorption fluoride capacity of 8.3470 mg/g, which is 7.4 times that of natural gibbsite under the same conditions. Calcination temperature on its structural properties by means of scanning electron microscopy (SEM), thermogravimetric and differential thermal analysis (TGA/DSC), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) for the gibbsite were investigated. The results of characterization analysis showed that the phase composition of gibbsite calcined at different temperatures is different and the significantly different effect of fluorine removal may be attributed to the increase of specific surface area after calcination. The pseudo-second-order kinetic model and Langmuir adsorption isotherm model can better describe the fluorine removal process of gibbsite calcined at high temperature.

In order to improve the fluorine removal performance of bauxite, the effects of different calcination temperatures and several acids (HCl, H 2 SO 4 , H 2 C 2 O 4 ) on the fluorine removal performance of bauxite were investigated. It was found that the calcination temperature of 500 C and the modification of H 2 SO 4 had the best fluorine removal performance. Under the same experimental conditions, the fluoride removal rate of the modified bauxite could reach 99.54%, which was much higher than that of unmodified bauxite (52.69%). The adsorbent was characterized by XRD, FTIR, BET, TG/DSC, and XRF. The influence of the addition amount of adsorbent, initial concentration of fluorine, adsorption time, and temperature on fluorine removal performance was studied. The adsorption process reached equilibrium in 32 min, and the inhibition order of coexisting anions was H 2 PO 4 À < HCO 3 À < CO 3 2À < Cl À . The pseudo-secondorder kinetic model was more suitable for the fluoride removal process of modified bauxite. Thermal regeneration had better regeneration performance than alkali leaching regeneration.