The differences in the competitive reactions of hydrogarnet and quicklime when reacting with titanium- containing and silicon-containing minerals during the Bayer digestion process were investigated. Thermodynamic analysis, artificial mineral experiments, and an evaluation of the digestion effect of natural diasporic bauxite were conducted. The results indicate that hydrogarnet shows a preferential reaction with anatase, and this preference becomes more pronounced as the silicon saturation coefficient increases. In contrast, quicklime participates in non-selective reactions with both anatase and desilication products (DSP). The preference of hydrogarnet for anatase significantly enhances the utilization efficiency of CaO in the high-temperature Bayer digestion process.