Calcification-carbonation method for alumina production by using low-grade bauxite.

Increasing alumina production in China and improvements in production technology have resulted in the depletion of high-quality bauxite resources. A calcification-carbonation method is described for the treatment of middle- to low-grade bauxite and red mud. Experiments using synthetic mixtures of pure NaOH, Al(OH)3, CaO and Na2SiO3 indicated that sodium aluminosilicate hydrate was transformed into hydrogarnet with increasing additions of CaO, but the alumina-silica ratio increased and the sodium-silica ratio decreased. The hydrogarnet was decomposed with CO2 at 120 degrees C at a CO2 partial pressure of 1.2 MPa. The alumina extraction efficiency was up to 63.6% and the alumina-silica ratio of the final product was reduced to 0.54. Treatment of diasporic bauxite, gibbsite and red mud under conditions of a calcification temperature of 240 degrees C for diasporic bauxite or 180 degrees C for gibbsite and red mud, a calcium oxide/silica molar ratio of 3:0.64, a carbonation temperature of 120 degrees C, and CO2 pressure of 1.2MPa reduced the alumina/silica ratios of the final products to 0.44, 0.82 and 0.43, respectively, and the sodium oxide contents to 0.12%, 0.57% and 0.44%. The final red mud product was suitable for direct use in the cement industry.
Increasing alumina production in China and improvements in production technology have resulted in the depletion of high-quality bauxite resources. A calcification-carbonation method is described for the treatment of middle- to low-grade bauxite and red mud. Experiments using synthetic mixtures of pure NaOH, Al(OH)3, CaO and Na2SiO3 indicated that sodium aluminosilicate hydrate was transformed into hydrogarnet with increasing additions of CaO, but the alumina-silica ratio increased and the sodium-silica ratio decreased. The hydrogarnet was decomposed with CO2 at 120 degrees C at a CO2 partial pressure of 1.2 MPa. The alumina extraction efficiency was up to 63.6% and the alumina-silica ratio of the final product was reduced to 0.54. Treatment of diasporic bauxite, gibbsite and red mud under conditions of a calcification temperature of 240 degrees C for diasporic bauxite or 180 degrees C for gibbsite and red mud, a calcium oxide/silica molar ratio of 3:0.64, a carbonation temperature of 120 degrees C, and CO2 pressure of 1.2MPa reduced the alumina/silica ratios of the final products to 0.44, 0.82 and 0.43, respectively, and the sodium oxide contents to 0.12%, 0.57% and 0.44%. The final red mud product was suitable for direct use in the cement industry.