Separate studies of effects of mixing and grinding on solid-state reaction of kaolinite with calcium carbonate

Abstract

The effects of mixing and grinding on solid-state reactions were separately investigated using a wet-type super atomizer for dispersing particles without breaking them. The solid-state reaction of kaolinite [Al₂Si₂O₅(OH)₄] with calcium carbonate (CaCO₃) to form metastable CaAl₂Si₂O₈ was carried out, with the raw materials being ground prior to the reaction. Notably, rough mixing of the raw materials before the reaction resulted in gehlenite (Ca₂Al₂SiO₇). After grinding methoxy-modified kaolinite, an expanded kaolinite (Ex-Kaol) swollen in methanol, and calcite particles, the resultant mixed-methanol dispersion was vigorously agitated for one pass using a wet-type super atomizer with a discharge pressure of 200 MPa. No detectable change in the X-ray diffraction (XRD) patterns was observed between the pristine and treated raw materials, indicating that the stacking order of the kaolinite, which dominates the reaction rate of metastable CaAl₂Si₂O₈, was not changed by the treatment at 200 MPa. The treated raw materials gave metastable CaAl₂Si₂O₈ after calcination at 900 °C for 4 h, although the calcined product prepared from unground raw materials treated at 200 MPa contained gehlenite. The results indicated that both grinding and mixing procedures dominated the formation of CaAl₂Si₂O₈ by the solid-state reaction of kaolinite with CaCO₃.