Phosphorus Separation and Recovery from Steelmaking Slag

Abstract

Iron (Fe) is a metal element which is most abundantly produced in the world. Steel is an alloy of iron and other elements and plays a crucial role in the development of sustainable society. In the iron manufacturing process, the content of phosphorus (P) in the raw materials is relatively low but is concentrated into molten iron and then removed nearly completely into steelmaking slag. Hence, steelmaking can be viewed as a P enrichment process and generates slag which has a potential to serve as a secondary resource of P. The fundamental system of steelmaking slag is CaO-FeO-SiO₂ which is formed inside the primary 2CaO・SiO₂ region, indicating that this phase precipitates at the early stage of cooling slag. P is unevenly distributed in steelmaking slag and generally concentrated in the 2CaO・SiO₂ phase as a 2CaO・SiO₂-3CaO・P₂O₅ solid solution. This evidence reveals the potential to separate P from steelmaking slag. In this chapter, various technologies for P separation and recovery from steelmaking slag are described. They include magnetic separation, capillary action, dissolution, and carbothermic reduction. Since each method has its own merits and demerits, the best choice of single or combination of the technology options is critical to effective P recovery and separation from steelmaking slag.