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. mass ratio of %Al2O3 and SiO2 in the solid; N/S: mass ratio of %Na2O and SiO2 in the solid.