Activation and removal of silicon in kaolinite by thermochemical process

The structural changes and phase transition of kaolinite during thermal treatment were investigated by thermogravimetric analysis, differential thermal analysis, infrared spectroscopy, X-ray diffraction (XRD) and solid-state Si-29 magic angle spinning nuclear magnetic resonance in this paper. It was found that kaolinite experiences solid phase chemical transformation on heating, during which silicon in kaolinite-layered structure is activated. The thermal treatment of kaolinite at a temperature of above 980degreesC results in the formation of amorphous SiO2. The recrystallization of mullite occurred when the temperature exceeded 1100degreesC. Quartz keeps unchanged below 1200degreesC. The thermochemical (TC) process provides an avenue for the removal of silicon in kaolinite. The appropriate conditions for kaolinite activation were found to be 1050-11 00degreesC and 90-60 min. The XRD patterns of solid leached residue revealed that amorphous SiO2 could be efficiently removed by alkali leaching. The TC process was applied to desilication of kaolinite type bauxite ores. Above 50% silica total removal and 9-10 A/S ratio of desilication product were obtained at the heat conditions of 1050-11 00degreesC and 90-60 min for an ore sample bearing 19.4% kaolinite and 4.6% quartz and with the 4.4 A/S ratio.