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

Automated summary

In this study, red mud-based geopolymer microspheres were successfully prepared and showed good adsorption properties for fluoride ions. The adsorption experiment results revealed that the microspheres could effectively remove fluoride ions from water and meet the drinking water standard within a short period of time. Furthermore, the microspheres exhibited selective adsorption for different anions in competitive adsorption experiments. Moreover, the red mud-based geopolymer microspheres demonstrated excellent fluoride removal performance in various types of water.