Characterisation of Radioactivity in Bauxite and Red Mud Tailings (2D2)

Project Status: Complete
Project Participants: Alcoa, ANSTO
Project Leader: Merrill Ford (ANSTO)

Previous work by ANSTO in 2002 showed that:

• Radioactivity occurs in significantly higher concentrations in the bauxite ores and leach residues at some Alcoa sites, such as Wagerup;
• The majority of the radioactivity in the Alcoa Western Australian bauxites examined was due to the presence of 232Th and its decay chain;
• The 232Th chain radioactivity appears to be in secular equilibrium and reports, in equilibrium, to the process red mud product; and
• The relatively less significant 238U decay chain activity is not in equilibrium in the leach residues, as it is leached to a small degree from the ore and reports, to some extent, to the caustic digestion liquor (the majority of 238U chain activity still reports to the leach residue).

In the longer term, there is a need to better understand the nature of radioactivity contained in bauxite ore and caustic leach residue (red mud) to:

• Avoid ore and red mud being ‘classified’ as radioactive from a regulatory viewpoint;
• Allow red mud to be more easily considered (from a radiological perspective) for wider end-use application; and
• Reduce the future risk associated with the presence of radioactivity in processes and products.

This project focused on these longer term issues. A better understanding may also open the way to opportunities for separation/removal of radioactivity from bauxite and/or red mud. The outcome from the work was a reduction in the risks associated with the presence of radioactivity, so that issues such as potential end-product applications for red mud are addressed in a more informed manner.

The research objectives were to:

• Gain a better understanding of the mineral phases, which host radioactivity (232Th and 238U) in bauxite ores and leach residues (red mud).
• Understand how these mineral phases behave/change during processing, by also examining the corresponding bauxite ore and red mud residues.
• Gain a broader understanding of how Alcoa compares, in regard to the issue of NORM, with other aluminium companies, and other mineral industries in general.