Migration and distribution of saline ions in bauxite residue during water leaching

Bauxite residue, a highly saline solid waste produced from digestion of bauxite for alumina production, is hazardous to the environment and restricts vegetation establishment in bauxite residue disposal areas. A novel water leaching process proposed here was used to investigate the dynamic migration and vertical distribution of saline ions in bauxite residue. The results show that water leaching significantly reduced the salinity of bauxite residue, leaching both saline cations Na+, K+, Ca2+ and anions CO2−3, SO2−4, HCO−3. Na+ and K+ migrated from 40-50 to 20-30 cm of the column, presenting a high migration capacity. The migration capacity of Ca2+ was lower and accumulated at 30-40 cm of the column. CO2−3 initially distributed at 20-30 cm of the column, subsequently transported to 30-40 cm of the column, and finally returned to 20-30 cm of the column along with evaporation. SO2−4 was originally distributed at 40-50 cm, but finally migrated to 20-30 cm of the column. Nevertheless, HCO−3 remained at the bottom of the column, and its migratory was less affected by evaporation.