Collaborative processing of steelmaking slag and red mud for efficient phosphorus recovery and resource utilization

Efficient recovery of phosphorus (P) from steelmaking slag (SS) is crucial for promoting resource sustainability and reducing solid waste generation in the metallurgical industry. However, the complex mineral composition of SS hinders P extraction and utilization. To solve this problem, red mud (RM), a by-product of alumina production, was added as a modifier to reconstruct the mineral phases of SS and improve P availability. SS was melted with varying additions of RM to investigate the effects of mineralogical reconstruction on P partitioning behavior. The results showed that increasing the RM addition promoted P₂O₅ enrichment in dicalcium silicate, predominantly forming the Na₂Ca₂P₂O₈ phase. The modified slags were subjected to mildly acidic leaching (pH 3.0-5.0) to evaluate the dissolution behavior of major elements. At pH 4.0, P showed high leachability with an extraction efficiency of 75%, while Fe and Al remained largely insoluble, indicating leaching selectivity. Adjusting the leachate pH to 8.0 allowed 99% P precipitation, with an overall P recovery efficiency of 74%. The recovered white precipitate was mainly hydroxyapatite, with total impurity content below 1 wt% and no detectable secondary crystalline phases in the XRD patterns. Modifying synthetic SS using RM is presented as an effective strategy to enhance P recovery, offering a sustainable and efficient approach for high-value utilization of SS.