Mobilisation of arsenic from bauxite residue (red mud) affected soils : effect of pH and redox conditions

Lockwood, Cindy L.; Mortimer, Robert J.G.; Stewart, Douglas I.; Mayes, William M.; Peacock, Caroline L.; Polya, David A.; Lythgoe, Paul R.; Lehoux, Alizée P.; Gruiz, Katalin; Burke, Ian T.

Abstract

The tailings dam breach at the Ajka alumina plant, western Hungary in 2010 introduced ∼1 million m³ of red mud suspension into the surrounding area. Red mud (fine fraction bauxite residue) has a characteristically alkaline pH and contains several potentially toxic elements, including arsenic. Aerobic and anaerobic batch experiments were prepared using soils from near Ajka in order to investigate the effects of red mud addition on soil biogeochemistry and arsenic mobility in soil–water experiments representative of land affected by the red mud spill. XAS analysis showed that As was present in the red mud as As(V) in the form of arsenate. The remobilisation of red mud associated arsenate was highly pH dependent and the addition of phosphate to red mud suspensions greatly enhanced As release to solution. In aerobic batch experiments, where red mud was mixed with soils, As release to solution was highly dependent on pH. Carbonation of these alkaline solutions by dissolution of atmospheric CO₂ reduced pH, which resulted in a decrease of aqueous As concentrations over time. However, this did not result in complete removal of aqueous As in any of the experiments. Carbonation did not occur in anaerobic experiments and pH remained high. Aqueous As concentrations initially increased in all the anaerobic red mud amended experiments, and then remained relatively constant as the systems became more reducing, both XANES and HPLC–ICP-MS showed that no As reduction processes occurred and that only As(V) species were present. These experiments show that there is the potential for increased As mobility in soil–water systems affected by red mud addition under both aerobic and anaerobic conditions.

Citation

Lockwood, C. L., Mortimer, R. J., Stewart, D. I., Mayes, W. M., Peacock, C. L., Polya, D. A., …Burke, I. T. (2014). Mobilisation of arsenic from bauxite residue (red mud) affected soils : effect of pH and redox conditions. Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry, 51(December), 268-277. https://doi.org/10.1016/j.apgeochem.2014.10.009

• Journal Article Type: Article
• Online Publication Date: Oct 20, 2014
• Publication Date: 2014-12
• Deposit Date: Nov 11, 2015
• Publicly Available Date: Nov 23, 2017
• Journal: Applied geochemistry
• Print ISSN: 0883-2927
• Electronic ISSN: 1872-9134
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 51
• Issue: December
• Pages: 268-277
• DOI: https://doi.org/10.1016/j.apgeochem.2014.10.009
• Keywords: Red mud; Ajka red mud spill; Hungary; Arsenic
• Public URL: https://hull-repository.worktribe.com/output/381171
• Publisher URL: http://www.sciencedirect.com/science/article/pii/S0883292714002418
• Additional Information: Copy of article first published in: Applied geochemistry, 2014, v.51, December.