Pathways of fluoride removal and MgF2 recovery from fluoride-containing wastewater using different magnesium sources

Removing fluoride from fluoride-containing wastewater while recovering fluorine resources is important for both environmental protection and resource utilization. Here, three magnesium sources (MgO, MgCl 2 , and MgSO 4 ) were compared for fluoride removal and magnesium fluoride (MgF 2 ) recovery, and the roles of different Mg 2+ supply pathways in MgF 2 recovery were clarified. At pH 1.6–2.4, the hydration products of MgO drive MgF 2 precipitation via acid-promoted dissolution and interfacial F - enrichment, whereas the two soluble magnesium salts provide a stable supply of dissolved Mg 2+ at pH 5–8, thus favoring MgF 2 nucleation and crystal growth. All three magnesium sources yielded rutile-type MgF 2 with purities of 88.3 %–90.5 %, as determined by chemical composition analysis, and all recovered products met the MF-2 grade requirement. Appropriate magnesium source selection, through distinct Mg 2+ supply pathways, broadened the operable pH range for fluoride removal and MgF 2 recovery. Additionally, the anions introduced by the magnesium sources exerted stage-specific effects on MgF 2 crystallization, with Cl - promoting nucleation and SO 4 2- facilitating early crystal growth and particle aggregation. These findings provide mechanistic insight into MgF 2 recovery from complex fluoride-containing wastewater matrices and practical guidance for magnesium source selection.