Adsorption characteristics of activated red mud for fluoride removal
活化赤泥的除氟性能

Red mud, a waste tailing from alumina production, was activated with calcination and acid treatment for fluoride removal from water solution. Factors affecting fluoride adsorption on activated red mud were investigated, including reaction time, dosage of adsorbent, initial fluoride concentration, temperature, coexisting anions, and pH. Results showed that fluoride adsorption onto activated red mud generally achieved equilibrium at about 18 h. The kinetic data revealed that adsorption kinetics agreed well with the expression of Lagergren second-order rate. The higher the initial fluoride concentration, the greater the adsorption capacity was. The adsorption isotherm can be better described by Langmuir isotherm model, in comparison with Freundich isotherm model. Its maximum adsorption capacity was up to 2.71 mg/g. In addition, the coexistence of SO42-, Cl-, and NO3-(< 1 000 mg/L) had no significant effects on F- adsorption. However, HCO3- and PO43- showed negative effects on fluoride removal. It demonstrated that fluoride adsorption was relatively independent on pH between 3.5 and 11.0. In summary, the activated red mud is an environmental-friendly fluoride adsorbent with high and stable adsorption capacity, which is of great advantage in practical application.