2016 Volume 56 Issue 8 Pages 1436-1444
Steelmaking slag with high P2O5 content is considered as an alternative resource of P. In such slag, P is mainly concentrated in 2CaO·SiO2-3CaO·P2O5 (C2S–C3P) solid solution, which has higher water solubility than other mineralogical phases, which indicates the possibility of selective leaching of P. In order to recover P from steelmaking slag, its dissolution ratio from C2S–C3P into aqueous solutions must be increased. In this study, the effects of acid as leaching agent, high temperature modification of C2S–C3P by Na2SiO3, and pH on the dissolution behavior of C2S–C3P in aqueous solutions have been investigated. The obtained results show that when oxalic acid (H2C2O4) or citric acid (H3C6H5O7) was used to leach P from C2S–C3P, dissolved Ca2+ ions were removed by CaC2O4 precipitation or by the formation of CaC6H5O7− complex, respectively. As a result, the precipitation of phosphates was suppressed, and P dissolution increased dramatically. On the other hand, the P-rich phase changed from the original C2S–C3P into 2CaO·SiO2-2CaO·Na2O·P2O5 with higher water solubility after Na2SiO3 addition, thus improving P dissolution in the H2C2O4 and H3C6H5O7 solution. At higher pH (pH ≥ 7), H2C2O4 was beneficial for P dissolution from the modified C2S–C3P. However, at lower pH (5 ≤ pH < 7), H3C6H5O7 was an optimal leaching agent for extracting soluble P. At pH 5, the dissolution ratio of P from the modified C2S–C3P in the H3C6H5O7 solution reached 85.7%.