Fundamental Experiment to Extract Phosphorous Selectively from Steelmaking Slag by Leaching

Steelmaking slag, including hot metal dephosphorization slag, is usually in the dicalcium silicate (C2S) saturated composition range. C2S is known to form a pseudo-binary solid solution with tricalcium phosphate (C3P) over a wide composition range, and most of the phosphorus in the slag forms a solid solution. The authors investigated the dissolution behavior of the solid solution and matrix phases in aqueous solutions, and the dissolution ratio of each element in matrix phase was much lower than that in the solid solution at every pH. To clarify the possibility of selective extraction of the solid solution from slag, leaching experiments were conducted on the steelmaking slag. The CaO-SiO2-Fe2O3 steelmaking slag system was made by a mixture of reagents and ground into particles smaller than 53 mu m. After immersion, holes were observed on the surface of the slag particles. The area that selectively dissolved is considered as the solid solution phase prior to leaching. At pH 3, most of the Ca and Si in the solid solution dissolved after 120 min; however, the dissolution ratio of P was approximately 65% smaller than that of Ca. Compared to the matrix composition, the CaO/SiO2 ratio in the residue was close to the matrix and P2O5/Fe2O3 ratio was slightly larger than that of the matrix. XRD analysis revealed that the peak corresponding to the solid solution disappeared in the residue. The mass ratio of the residue to the dissolved slag was close to the ratio of the matrix to the solid solution before leaching.