A New Method for Producing Al–Si–Ca Alloys, AlF3, and MgF2 Using Diamond Wire Saw Si Powder and CaF2–MgO Waste Slag

Diamond wire saw Si powder (DWSSP) is a valuable secondary resource rich in Si, but it is also a hazardous air pollutant. CaF₂–MgO waste slag containing F is produced during the steelmaking process. This study presents a new low–cost method for recovering both DWSSP and CaF₂–MgO waste slag. The Al reduction smelting process was used to prepare Al–Si–Ca alloy, AlF_3, and MgF₂ from the CaF₂–MgO slag and DWSSP, and these fluorides were volatilized under negative pressure (P = 2.46 × 10⁴ Pa). Additionally, the study investigated the effects of holding time and CaF₂–MgO slag compositions on O removal, preparation of Al–Si–Ca alloys. The results demonstrated that upon 120 min of smelting using solely CaF₂ slag at 1450℃, the deoxygenation efficiency reached 99.89%, with the O concentration in the alloy being reduced to 170 ppmw. Compared to CaF₂ slag, when CaF₂–30 wt.% MgO slag was employed, the deoxygenation efficiency was enhanced to 99.98%, resulting in an O concentration of merely 24 ppmw in the alloy. The alloy produced using CaF₂–12 wt.% MgO slag exhibited the highest Si extraction efficiency from DWSSP, reaching 93.65%. When using CaF₂ slag, the products obtained were Al-Si-Ca alloy and AlF₃. In contrast, the use of CaF₂-MgO slag enabled the simultaneous preparation of Al-Si-Ca alloy, AlF₃, and MgF₂. Finally, the reaction mechanism of the approach was revealed through thermodynamic analysis.