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

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 degrees 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.(c) 2023 The Ceramic Society of Japan. All rights reserved.