Recovery of high-quality phosphate from steelmaking slag by a hydrometallurgical process

Phosphorus recovery from wastes has become a worldwide concern. The P-bearing steelmaking slag generated from steel plant is considered a potential phosphorus source. In this study, a novel process of selective leaching–precipitation–alkaline wash was proposed to recover high-quality phosphate from steelmaking slag. During leaching, most of the P was dissolved from slag and Fe was almost insoluble. Increasing temperature and solid-liquid ratio significantly suppressed the dissolution of Si due to the formation of silica sols. An excellent selective leaching of P was achieved at pH 3 and 333 K. The dissolution ratio of P reached 83.5% while only 22.6% of Si was dissolved. The residue containing 49.5% Fe₂O₃ and 0.9% P₂O₅ can be reused as a steelmaking feedstock, achieving the recycling in plant. In the dilute leachate, the precipitation of Si and Ca was significantly suppressed as the pH increased and a precipitate with higher P₂O₅ content and lower SiO₂ content was extracted. A large amount of SiO₂ was removed from the precipitate by alkaline wash. A precipitate containing 30.1% P₂O₅ and 45.5% CaO was recovered in this process. This study provided a cost-effective approach to recovering high-quality phosphate.