Enhanced removal of fluoride from water through precise regulation of active aluminum phase using CaCO3

Coagulation with aluminum salts is an important method for fluoride removal from groundwater. However, the hydration of aluminum salts generating a large number of H+ usually leads to limited defluorination performance due to the optimum pH of active aluminum phase for fluoride removal around 5.5–6.5. In this work, enhanced fluoride removal from groundwater through precise regulation of active aluminum phase by CaCO3 was investigated. Precipitation products were characterized by XPS, FTIR, XRD, and SEM, respectively, and the mechanism of the high fluoride removal efficiency was discussed and compared with the traditional coagulation of Al2(SO4)3. In the Al2(SO4)3 + CaCO3 (ASCC) system, CaCO3 can stably regulate the pH at the optimum range for active aluminum phase existence and has the best fluoride removal effect. CaCO3 accurately regulated the activity of the aluminum phase by slowly releasing OH− and fine tuning pH, thereby achieving effective fluoride removal. Undissolved CaCO3 particles exist as the carrier of defluorination flocs to accelerate precipitation and improve stability. The work here provides a new method for fluoride removal and may shed light on the application of CaCO3 coagulants for other pollutants.