Sequestration of carbon dioxide in red mud

ABSTRACT

In Bayer process of obtaining alumina from bauxite, the insoluble product generated after bauxite digestion with sodium hydroxide at elevated temperature and pressure is known as “red mud” or “bauxite residue.” It is an alkaline residue with a high pH of 10.5–12.5. It is disposed as dry or semi dry material in red mud pond or abandoned bauxite mines. The environmental concerns which are related to the disposal of red mud are its large quantity and causticity resulting in soil and groundwater pollution. At present, there is no viable process developed for utilizing the bauxite residue, consequently, this large quantity of waste material is required to be disposed economically and safely to the environment. In this view, a pH-reduction processing step is incorporated to ameliorate the red mud by sequestrating it with CO₂. By mixing carbon dioxide into the bauxite residue, the compound’s pH level can be reduced to levels normally found in alkaline soil. It was seen that full neutralization of red mud takes place following CO₂ carbonation, but the pH rebound of carbonated mixtures takes place and the pH drifts upward to a value of 9.4–9.7 with time when solution and solid remains in contact. Chemical, mineralogical, and morphological analysis of neutralized red mud is also studied in the paper.

Keywords:

• Bauxite residue
• Red mud
• pH
• pH rebound
• CO₂ neutralization