Effect of BOF Slag Modification on the Dissolution Behavior of Phosphorus from Practical Dephosphorization Slag

Dephosphorization slag which is generated in large quantities is considered as a potential phosphorous source. If phosphorus is separated from De–P slag, the obtained P can be reused in phosphate industry and the P-removal slag can be recycled in plant. To promote the comprehensive utilization of De–P slag, selective leaching was adopted to separate the P-bearing phase from the practical De–P slag. Due to the lower slag basicity, the practical De–P slag was modified by the BOF slag with high basicity. In this study, the effect of slag basicity on the dissolution behavior of practical De–P slag was investigated under different pH conditions. The high-temperature remelting process was beneficial for the formation of P-rich phase in slag, resulting in a higher dissolution ratio of P during leaching. When the De–P slag was modified, the dissolution ratio of P was high and the dissolution of Fe from slag was significantly inhibited. At pH 1, the dissolution ratio of P from the modified De–P slags exceeded 81 pct while only 1.5 pct of Fe was dissolved, achieving the selective leaching of P. After leaching, the Fe-rich residue with extremely low P content is suitable for the reutilization in steelmaking. Thermodynamic analysis showed that most of the Ca- and P-bearing phases in slag could be dissolved in this case. However, due to the precipitation of iron phosphates and aluminum phosphates, the dissolution ratio of P was not high at a higher pH condition. To achieve selective leaching of P from the practical De–P slag, properly increasing slag basicity and lowering pH were necessary.