Simultaneous Reduction of PO and FeO from CaO–SiO–FeO–PO Synthesized Slag by Carbothermic Reduction

Steelmaking slag is considered an attractive phosphorus secondary resource since it contains relatively high phosphorus content and a fairly fixed composition with the negligibly small hazardous element. The carbothermic reductions of CaO–SiO–FeO–PO slags were carried out to investigate the reduction behavior of phosphorus from steelmaking slags. During the carbothermic reduction process of the slags, iron oxides and phosphorus oxides were reduced to metallic iron and phosphorus gases. The generated phosphorus gases dissolved into the reduced iron, and some escaped into the gas phase. The phosphorus content in the reduced iron increased until FeP is formed but could not dissolve anymore. It was found that the amount of phosphorus dissolution into the reduced iron and that escaped into the gas phase was comparable. The phosphorus content in the reduced iron is possibly determined by the balance between the carbon and phosphorus dissolution rates into the reduced iron. In other words, the phosphorus content in the reduced iron was determined by kinetics but not thermodynamics. The findings in the present study indicate that the carbothermic reduction of 2CaO·SiO–3CaO·PO solid solution separated from steelmaking slags will be the plausible approach to recover phosphorus from steelmaking slags.