Boron removal from wastewater via coordinative adsorption assisted by Fenton-Induced Oxoprecipitation/Flocculation

Chemical precipitation is widely used for boron removal from water in industrial-scale processes, though a following post treatment is generally required to meet the concentration set by current international standards. In this work, chemical precipitation of boron (B) in water by different precipitating agents was combined with Fenton treatment to enhance the boron removal effectiveness. This approach achieved residual boron concentration of less than 0.5 mg/L, hard to achieve through conventional precipitation methods. Batch tests were performed at different dosage of Fenton reagents, and selected Fe2+/H2O2 weight ratios were evaluated with or without adding precipitating agents. The effect of pH on the process was also investigated, to assess the optimal conditions to maximize boron removal. At the end of the process, barium hydroxide was used to remove effectively excess sulfate ions. The sludge produced was characterized by XRD, SEM and FTIR analysis, and the mechanism of boron removal was investigated. An oxoprecipitation mechanism was induced by the Fenton process: boron-based species were converted into borate ion, thus predisposing them to a coordination-type adsorption on the surface of iron and calcium hydroxide, assisted by aluminum sulfate at pH 12.5. The process was then successfully tested on real boron −contaminated wastewater, thus confirming the effectiveness of the process while simultaneously decreasing the organic content.