Separation and recovery of phosphorus from steelmaking slag via a selective leaching–chemical precipitation process

Abstract

Steelmaking slag, a significant by-product of steelmaking, contains a certain amount of phosphorus, which makes it a potential phosphate source. To achieve its high value-added utilization, the P-concentrated C2S–C3P solid solution in slag is commonly separated. In this study, we adopted a selective leaching–chemical precipitation process to recover P from steelmaking slag. The effects of the acid, pH, and valence of Fe in slag on the leaching characteristics of P were first investigated. Chemical precipitation was then adopted to extract P from the leachate. The characteristics of the final product were evaluated. The results indicate that the P-concentrated solid solution was readily leached, whereas the Fe-rich magnesioferrite was resistant to dissolution in each acid solution. In view of the utilization of the residue and reducing the production costs, hydrochloric acid was considered the optimum leaching agent for dissolving the slag. The dissolution of steelmaking slag in the hydrochloric acid solution increased with a decrease in pH. In addition, 81.6% of the P in slag was dissolved at pH 3, whereas the Fe leaching was negligible, exhibiting an improved selective leaching. Further, the P-removed steelmaking slag can be reutilized in a steel plant to achieve waste-free steelmaking. In the following precipitation at pH 7, most of the P in the leachate was transformed into an insoluble calcium phosphate. This process provides more than a 70% P recovery from steelmaking slag. The P2O5 content in the product obtained reached 20.2 mass%, which can be applied as a fertilizer.