The synergistic impact of mechanical ball milling and flue gas desulfurization (FGD) gypsum on the dealkalization of bauxite residue was investigated through integrated analyses of solution chemistry, mineralogy, and microtopography. The results showed a significant decrease in Na₂O content (>30 wt.%) of FGD gypsum-treated bauxite residue after 30 min of mechanical ball milling. Mechanical ball milling resulted in differentiation of the elemental distribution, modification of the minerals in crystalline structure, and promotion in the dissolution of alkaline minerals, thus enhancing the acid neutralization capacity of bauxite residue. 5 wt.% FGD gypsum combined with 30 min mechanical ball milling was optimal for the dealkalization of bauxite residue.