Regulating the digestion of high silica bauxite with calcium ferrite addition

The digestion reactions of diasporic bauxite with A/S* of 5.96 was studied by adding calcium ferrite. With increasing addition of calcium ferrite, A/S and N/S* in the red mud are reduced. Under the conditions of higher digestion temperature and longer time, A/S in the red mud is also reduced with lower bauxite addition and higher soda in the liquor. Larger-scale experiments have been done with adding calcium ferrite under the conditions of 250 °C, 60 min which results in A/S in the red mud = 0.69 and N/S = 0.21. The main silicon mineral of red mud is ferrite hydrogarnet through analysis of XRD and energy-dispersive XRF. The coefficient of SiO2 approaches 1, Al2O3 0.22, and Fe2O3 0.73 in iron hydrogarnet. It is because the structure of the silicon mineral is changed that A/S and N/S in the red mud are greatly reduced.*A/S: mass ratio of %Al2O3 and SiO2 in the solid; N/S: mass ratio of %Na2O and SiO2 in the solid.

Research highlights
► The digestion reactions of diasporic bauxite with A/S* of 5.96 was studied by adding calcium ferrite. With increasing addition of calcium ferrite, A/S and N/S* in the red mud is reduced. Under the conditions of higher digestion temperature and longer time, A/S in the red mud is also reduced with lower bauxite addition and higher soda in the liquor. Larger scale experiments have been done with adding calcium ferrite under the conditions of 250 °C, 60 min which results in A/S in the red mud = 0.69 and N/S = 0.21. The main silicon mineral of red mud is ferrite hydrogarnet through analysis of XRD and energy-dispersive XRF. The coefficient of SiO2 approaches 1, Al2O3 0.22, Fe2O3 0.73 in iron hydrogarnet. It is because the structure of the silicon mineral is changed that A/S and N/S in the red mud is greatly reduced.