Effect of slag composition on the dissolution of phosphorus from steelmaking slag by selective leaching

Steelmaking slag is considered a potential source of P because of its huge production. In steelmaking slag, P is mainly distributed in the C₂S-C₃P solid solution which is more water-soluble than other phases. In order to recover P and recycle steelmaking slag, we have proposed the selective leaching of the P-concentrated solid solution. To clarify the applicability of this process to steelmaking slags with various compositions, the effects of P₂O₅ content, Fe₂O₃ content, and slag basicity on the dissolution behavior of the slag modified with the addition of Na₂O were investigated in this study. It was determined that the dissolution ratio of P reached approximately 76% regardless of the P₂O₅ content in slag, while the dissolution of Fe and Mg was poor. In the case of high P₂O₅ content, a leachate with higher P concentration and lower Ca and Si concentrations was obtained, exhibiting excellent selective leaching of P. Increasing the Fe₂O₃ content in slag not only promoted the dissolution of P but also decreased the dissolution ratios of other elements. With the increase in slag basicity, the dissolution ratios of Ca, Si, and P all increased. Most of the solid solution was dissolved from each slag without a large dissolution of other phases at pH 6, indicating that selective leaching of the solid solution was achieved over a wide range of slag compositions. After leaching, a residue with low P₂O₅ content and high Fe₂O₃ content was obtained.