<p>To further enhance the defluorination rate of bauxite sludge, preliminary studies revealed that the presence of silicon in the bauxite might reduce its fluoride removal efficiency. In this study, the bauxite was treated with a sub-molten salt mixture of NaOH and Na₂CO₃ to enhance its defluorination performance. The desiliconization rate of bauxite reached 48.38% after it was modified by NaOH-Na₂CO₃ mixed sub-molten salt. The bauxite with silicon removal exhibited excellent defluorination ability, which was comparable to that of porous alumina in removing fluorine. However, the cost of this material was much lower than that of porous alumina. When initial F^- concentration and adsorbent dosage respectively were 10&#xa0;mg/L and 2&#xa0;g/L, the defluorination rate of the modified bauxite sludge reached 97.66%. Finally, the defluorination mechanism of the modified bauxite was studied. Compared with other models, the pseudo-second-order kinetic model was more suitable for describing its adsorption process. Modified bauxite’s spontaneous fluoride adsorption is verified via adsorption thermodynamics.</p>