Abstract: The efficient removal of high-concentration free fluoride ions from phosphogypsum leachate poses a significant environmental challenge for the phosphorus chemical industry.To achieve the goal of "waste control by waste",this study fabri cated a porous geopolymer using phosphogypsum,phosphate tailings,and blast furnace slag as primary raw materials via alkali activation and H2 O2 chemical foaming.The adsorption behavior and mechanism of the porous geopolymer towards fluoride ions were systematically investigated.Experimental results showed that the optimized porous geopolymer achieved a fluoride removal rate of 66.7% under the conditions of pH=4,initial fluoride concentration of 50 mg/L,and temperature of 25 ℃.The adsorp tion kinetics followed the pseudo-second-order model,indicating a chemisorption-dominated process.The adsorption isotherm was better fitted by the Freundlich model,suggesting multilayer adsorption on heterogeneous surfaces.Mechanistic studies re vealed that the adsorption involved synergistic effects of physical interception,ion exchange,and chemical precipitation.The dominant mechanism was identified as the chemical precipitation of CaF2 ,resulting from the reaction between Ca2+ dissolved from the geopolymer and F- in solution.This research provides a novel approach for the high-value-added utilization of phosph ogypsum and phosphate tailings,and the developed porous geopolymer demonstrates promising potential for application in fluor ide-containing wastewater treatment.

Key words: geopolymer,phosphate tailings,phosphogypsum,fluoride ions removal,adsorption mechanism,waste control by waste