Desilication and recycling of alkali-silicate solution seeded with red mud for low-grade bauxite utilization

Abstract

When low-grade high-silica bauxite undergoes desilication by alkaline leaching, a large amount of alkali-silicate solution will be produced. To realize its recycling, the alkali-silicate solution needs to be desiliconized. In this study, the effectiveness of red mud and a mixture of red mud and CaO as desilication reagents of the alkali-silicate solution are compared and the desilication mechanisms were analyzed. Results show that when adding 30–50 g/L of red mud, the desilication rate is only 36–38% while adding 30 g/L of red mud and CaO mixture with a calcium-silicon ratio of 1 reaches a desilication rate of ∼89%. Analyses by SEM-EDS and other mean show that this is mainly due to the growth of sodalite seed crystals in red mud and its synergistic desilication with CaO. Bauxite underwent cyclic desilication and the alumina/silica ratio was increased from ∼4.1 to >7.5. Effective utilization of red mud and alkali-silicate solution greatly reduces the cost of the desilication process, thereby making it applicable to low-grade bauxite in the Bayer process.