Variation of alkaline characteristics in bauxite residue under phosphogypsum amendment.

Aiming at alkaline problem of bauxite residue, this work focused variation of alkaline characteristics in bauxite residue through phosphogypsum treatment. The results demonstrated that the pH of bauxite residue reduced from initial 10.83 to 8.70 when 1.50 wt% phosphogypsum was added for 91 d. The removal rates of free alkali and exchangeable sodium were 97.94% and 75.87%, respectively. Meanwhile, significant positive correlations (P<0.05) existed between pH and free alkali, exchangeable sodium. The effect of free alkali composition was CO₃^2->OH-> AlO₂^->HCO₃^-. In addition, alkaline phase decreased from 52.81% to 48.58% and gypsum stably presented in bauxite residue which continuously provided Ca²⁺ to inhibit dissolution of combined alkali. Furthermore, phosphogypsum promoted formation of macroaggregate structure, increased Ca²⁺, decreased Na⁺ and Al³⁺ on the surface of bauxite residue significantly, ultimately promoting soil formation in bauxite residue. [ABSTRACT FROM AUTHOR]