Phosphate Removal from Steelmaking Slag Using Molten CaCl<sub>2</sub>

Steelmaking slag contains valuable components. Its high phosphorus content hinders its reutilization in the steelmaking process. This study proposes an efficient phosphate removal process using molten CaCl2 as the reaction medium, aiming to enable slag recycling and P recovery. Experimental results show that nearly all P-bearing phases in steelmaking slag are leached into molten CaCl2 under the tested conditions (850 to 1000 °C, slag/CaCl2 mass ratios 1:10 to 1:2.5). The leaching mechanism involves the reaction of slag's P-bearing phases with CaCl2 to form intermediates (Ca2PO4Cl and Ca3SiO4Cl2), which dissociate into PO43– and other ions in the melt. For other elements: Si(IV) leaches continuously but incompletely; Fe(II) and Mn(II) concentrations in the melt first increase then decrease, attributed to the evaporation of volatile FeCl2 and MnCl2; Mg and Al remain nearly unleachable. After leaching, adding carbon to the P-enriched melt achieves complete P(V) removal via carbothermal reduction. This molten CaCl2-based approach provides a sustainable alternative to conventional technologies, offering valuable insights for the comprehensive utilization of P-bearing solid wastes.