Abstract: In order to establish the optimization method of zeolite FeCl₃ modification conditions, improve the phosphorus adsorption efficiency, and elucidate the phosphorus adsorption mechanism, the response surface method was used to investigate the effects of four factors, namely, FeCl₃ concentration, modification time, modification rotational speed, and modification temperature on the phosphorus adsorption effect of modified zeolite, and to establish the multiple regression model to determine the optimal combinations of the modification conditions. The characterization techniques of SEM, BET, XRD, and FTIR combined with isothermal adsorption and adsorption kinetic modeling, were used to elucidate the phosphorus adsorption mechanism of FeCl₃-modified zeolite. The results showed that four factors had significant effects on the phosphorus adsorption of FeCl₃-modified zeolite, and the multiple regression model between the modification conditions and the phosphorus adsorption rate was 0.987 9 for R²_（TP%） and 0.975 9 for R_adj²_（TP%）, which was a good fit, and the optimal modification conditions after the response surface optimization were the FeCl₃ concentration of 3.8 mol/L, the modification time of 6 h, the modification temperature of 32 ℃, and the modification speed of 186 r/min. The characterization results showed that the FeCl₃ modification did not destroy the skeleton structure of zeolite, and the Fe₂O₃ loading on the surface of zeolite increased the specific surface area, and the complex adsorption with phosphorus could improve the adsorption efficiency of phosphorus. The R² of the Langmuir and Freundlich equations were 0.995 95 and 0.985 66, respectively, which indicated that both the monolayer and the multilayer adsorption existed at the same time. The R² of the second-stage kinetic model was 0.870 09, which was larger than that of the first-stage kinetic model （0.501 53）, indicating that the second-stage kinetic model could better characterize the adsorption kinetics of FeCl₃-modified zeolite on phosphate, and that the adsorption of phosphate by FeCl₃-modified zeolite was dominated by chemisorption.

Key words: FeCl₃-modified zeolite, preparation conditions, optimization, phosphorus, response surface method, adsorption mechanism