Hydrogen peroxide induces the transition of amorphous to crystalline structure of AlOx and enhanced fluoride removal efficiency in coal mine wastewater

Abstract

Reducing the concentration of F⁻ in water is crucial, given that excessive fluoride poses a threat to both the environment and human health. In this study, amorphous alumina (AlO_x) was prepared using solvothermal method and the surface hydroxyl content of calcined AlO_x was enhanced using H₂O₂ (0–5 wt%) to improve its defluoridation rate. The produced materials were gradually transformed from the amorphous form to the crystalline state. The crystalline calcined AlO_x modified with 0.5 % H₂O₂ exhibits a rapid increase in defluoridation rate, from 76.4 % to 94 %, in just 5 min at the initial fluoride concentration of 10 mg/L. Furthermore, it shows effective fluoride removal across the pH range of 3–10. The pseudo-second-order model and the Langmuir model provided an accurate representation of the kinetics and isotherms associated with adsorption, suggesting that the process is characterized by chemisorption and occurs in a monolayer. The adsorption mechanism, primarily the ion exchange between F⁻ and hydroxyl groups, is discussed. The 0.5 % H₂O₂/AlO_x adsorbent regenerated through aluminum sulfate solution showed good reusability performance, and its defluoridation rate was maintained at 79.9 % after five cycles. This indicates that enhancing hydroxyl groups content on the surface of the adsorbent enhances its defluoridation performance which is promising for practical mine water treatment.