Dissolution Behavior of Dicalcium Silicate and Tricalcium Phosphate Solid Solution and other Phases of Steelmaking Slag in an Aqueous Solution

Abstract

Abstract Most of the phosphorus in slag forms a solid solution of dicalcium silicate (C 2 S) and tricalcium phosphate (C 3 P), and the process used to separate this solid solution from the matrix phase is the same technology used to separate P from other valuable elements such as Mn and Cr containing in the matrix phase. Although it is known that the solubility of C 2 S in an aqueous solution is much greater than that of C 3 P, the solubility of the solid solution and that of the matrix phase have yet to be investigated. To clarify the possibility of selectively extracting P from slag through a leaching process, the dissolution behaviors of the solid solution at various compositions and that of the matrix phase were investigated. The following results were obtained: The dissolution ratio of Ca to the aqueous solution at pH = 7 was close to 1.0 in the case of pure C 2 S and decreased greatly with increasing C 3 P content. The dissolution ratio of P was about 0.1 and did not change relative to the C 3 P content. When the ratio of C 3 P in the solid solution was higher than 0.3, hydroxyapatite (HAP) formation was observed in the residue. The dissolution ratio of P increased for 30 min, and after reaching the maximum value, started to decrease owing to the precipitation of HAP. The dissolution ratio of each element from a glassy slag sample (matrix phase) was lower than that from the solid solution at every pH level. In this study, the possibility to extract a solid solution containing P without dissolving the matrix phase was found through the use of an aqueous solution at pH = 7, although the dissolution ratio of P was not sufficiently high.