Mechanisms of Neutralization of Bauxite Residue by Carbon Dioxide

Bauxite residue (red mud), an alkaline slurry from alumina refining, is produced in large volumes and disposed of in large surface impoundments. The objectives of this study were to measure the extent of neutralization of bauxite residue by carbon dioxide as a function of C O2 partial pressure and to determine the geochemical reactions responsible for carbon sequestration. Bauxite residue was exposed to carbon dioxide (C O2 ) at partial pressures ranging from 10−3.5 to 1 atm and the residue pore-water pH was measured until a steady state pH was achieved. Using pure C O2 ( PC O2 =1 atm) , a steady state pH of 7.7 was established in 1 day while it took 9 days to reach a pH of 9.8 at PC O2 = 10−3.5 atm . The pH rebounded to 9.9 after 1 day when bauxite residue first neutralized at PC O2 of 1, 0.1, or 0.01 atm for 10 days was subsequently exposed to PC O2 = 10−3.5 atm , indicating that the pH change during short-term carbonation (t⩽10 days) was due to reactions of carbonic acid and O H− in the pore water. A l...