Synthesis and alumina leaching mechanism of calcium sulphoaluminate

Calcium sulphoaluminate (3CaO·3Al₂O₃·CaSO₄, abbreviated as C₄A₃S) was synthesized by sintering at 1375 °C for 2 h with analytically pure carbonate calcium, alumina and dihydrate calcium sulfate. The crystal structure of C₄A₃S was characterized by XRD, SEM and TEM. Alumina leaching properties in Na₂CO₃ solution were studied, and the leaching mechanism was investigated by means of Raman spectrum and XRD. The results show that C₄A₃S has porous morphology. The polycrystallines and single crystals coexist in C₄A₃S and grow along different directions. The alumina leaching rate of C₄A₃S is 98.41%, which is higher than that of 12CaO·7Al₂O₃ under the optimal condition. The aluminum and sulfur elements exist in the leaching solution in the form of $\text{Al}{\left(\text{OH}\right)}_4^{?}$ and $\text{S}{\text{O}}_4^{2?}$, respectively, and the calcium exists as CaCO₃ in the leaching residues.