Activation mechanism of diasporic bauxite calcined with sodium carbonate

Extraction of alumina and silica from high-silica bauxite by sintering with sodium carbonate followed by two-step leaching with water and sulfuric acid

“…In addition, the TGA/DSC results under nitrogen atmosphere are highly similar to those under air atmosphere ( Fig. 4(b) ) that we studied previously, 37 indicating that different atmospheres and variable oxygen exposure have no obvious impact on the sintering process.…”

“…16,38 In this study, both Al 2 O 3 and SiO 2 would react with Na 2 CO 3 due to the absence of CaO. Therefore, the molar 37 Therefore, the weight loss in the TG curve above 600 °C was primarily attributed to the release of CO 2 from the reaction between bauxite and Na 2 CO 3 . The third endothermic peak was located at about 849 °C, where the melting of Na 2 CO 3 signicantly increased the reaction rate between bauxite and Na 2 CO 3 , 40 resulting in a signicant increase in the weight loss rate of the TG curve.…”

“…After removing the structural water, diaspore (α-Al 2 O 3 ·H 2 O) and kaolinite (Al 2 O 3 ·2SiO 2 ·2H 2 O) were transformed into alpha-alumina (α-Al 2 O 3 ) and metakaolinite (Al 2 O 3 ·2SiO 2 ), respectively, which can further react with Na 2 CO 3 to form NaAlO 2 solid solutions (Na 2− x Al 2− x Si x O 4 , x ≤ 0.55) eventually. 37 Therefore, the weight loss in the TG curve above 600 °C was primarily attributed to the release of CO 2 from the reaction between bauxite and Na 2 CO 3 . The third endothermic peak was located at about 849 °C, where the melting of Na 2 CO 3 significantly increased the reaction rate between bauxite and Na 2 CO 3 , 40 resulting in a significant increase in the weight loss rate of the TG curve.…”

“…2(a) ) dominated by diaspore (63.4%) and kaolinite (31.2%). 37 The particle size distribution ( Fig. 2(b) ) of the high-silica bauxite indicates that 80% of the particles are distributed in the range of 3.15–21.74 μm with a D50 value of 9.48 μm.…”

“…In our previous studies, the sintering time was usually set to 30 min. 36,37 In this study, the experimental range of sintering time was set to 10-50 min.…”