Recovery of Phosphorus from Steelmaking Slag by Combination of Chlorination, Steam Modification and Carbon Reduction

Phosphorus (P) is an essential element not only for human life but also for crop growth and for the production of functional materials. On the other hand, P is classified as a depleted element. Therefore, developing methods to recover P from secondary P resources is important. This study aimed to selectively recover of P from steelmaking slag by combining chlorination, steam reforming, and carbon reduction. First, detailed conditions were investigated to prepare Fe-free chlorinated residue by chlorination of the slag. Subsequently, the chlorinated residue was dechlorinated via steam reforming, and then selective volatilization of P were investigated by carbon reduction of the dechlorinated residue. Although chlorination of slag up to 1000°C enabled selective removal of Fe, selective separation of P was difficult during carbon reduction of this chlorinated residue. This was considered due to the residual chlorine in the chlorinated residue. Therefore, de-chlorination of the chlorinated residue via steam treatment was investigated. The results showed that heating at 1000°C could almost completely remove chlorine from the solid phase. Subsequent carbon reduction of this steam-modified chlorinated residue allowed only P to volatilize. These findings demonstrate that combining chlorination, steam reforming, and carbon reduction processes on steelmaking slag enables the selective, highly efficient volatilization, separation, and recovery of P alone.