Display omitted •BOF slag and phosphate tailings were synergistically treated to recover P.•P2O5 was concentrated in a specific mineral phase in the synthetic slag.•Selective leaching was applied for separation of the P-rich phase.•Undissolved synthetic slag can be reutilized as a flux in steel plants.•The precipitate extracted from the leachate can be used as a P-Si fertilizer. To efficiently recover phosphorus from industrial solid wastes, the collaborative processing of P-bearing steelmaking slag and phosphate tailings was proposed. Steelmaking slag and phosphate tailings were remelted to make P enrich in a specific mineral phase and then selective leaching was adopted to separate the P-concentrating mineral phase. The P-concentrating leachate can be used to recover calcium phosphate by chemical precipitation. It shows that the P was mainly concentrated in the dicalcium silicate after remelting of steelmaking slag and phosphate tailings and it could be selectively leached. When the mass ratio of the original BOF slag to phosphate tailings was 7:3, the mixed slag with basicity of 2.3 was obtained. The dissolution efficiency of P from this mixed slag reached 89.2% whereas Fe was barely leached at pH 1. The residue containing 68.6% FetO and 15.6% MgO can be reused in the metallurgical process. When the pH of leachate was adjusted to 7, more than 89.3% of phosphate ions precipitated in the form of calcium phosphate, and the obtained precipitate containing 28.8% CaO, 19.8% P2O5, and 47.2% SiO2, could be a potential P-Si fertilizer. The total recovery ratio of P from mixed slag was approximately 80% and other components could be reused in steel plants, achieving the comprehensive utilization of steelmaking slag and phosphate tailings.