Efficient preparation of red mud-based geopolymer microspheres (RM@GMs) and adsorption of fluoride ions in wastewater

In this paper, red mud-based geopolymer microspheres (RM@GMs: 75-150 mu m) was prepared by dispersion -suspension-solidification method to remove fluoride ions (F-). It was found that RM@GMs still had good me-chanical properties and better F- removal effect at RM content reached 80 % of the total solid mass. The batch adsorption experiment results showed that the F- concentration (< 1.5 mg/L) reached the drinking water standard in 45 min at pH = 2 and RM@GMs dosage was 1 g/L. RM@GMs showed maximum adsorption capacity of 76.57 mg/g for F-, and the adsorption kinetics and isotherm fitted the pseudo-second-order kinetic and Langmuir isotherm model, respectively. RM@GMs exhibited excellent dynamic separation effect at the flow rate of 4 mL/min and column height of 1 cm. In addition, RM@GMs had good selectivity for F- in the competitive adsorption experiments and followed an order of: PO43-> > SO42-. NO3 - . Cl-. In real seawater, natural surface water and tap water, RM@GMs still had excellent F- removal effect. The adsorption mechanism revealed that