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Gypsum addition to soils contaminated by red mud: implications for aluminium, arsenic, molybdenum and vanadium solubility

Lehoux, Alizée P.; Lockwood, Cindy L.; Mayes, William M.; Stewart, Douglas I.; Mortimer, Robert J. G.; Gruiz, Katalin; Burke, Ian T.

Authors

Alizée P. Lehoux

Cindy L. Lockwood

Douglas I. Stewart

Robert J. G. Mortimer

Katalin Gruiz

Ian T. Burke



Abstract

Red mud is highly alkaline (pH 13), saline and can contain elevated concentrations of several potentially toxic elements (e.g. Al, As, Mo and V). Release of up to 1 million m3 of bauxite residue (red mud) suspension from the Ajka repository, western Hungary, caused large-scale contamination of downstream rivers and floodplains. There is now concern about the potential leaching of toxic metal(loid)s from the red mud as some have enhanced solubility at high pH. This study investigated the impact of red mud addition to three different Hungarian soils with respect to trace element solubility and soil geochemistry. The effectiveness of gypsum amendment for the rehabilitation of red mud-contaminated soils was also examined. Red mud addition to soils caused a pH increase, proportional to red mud addition, of up to 4 pH units (e.g. pH 7 → 11). Increasing red mud addition also led to significant increases in salinity, dissolved organic carbon and aqueous trace element concentrations. However, the response was highly soil specific and one of the soils tested buffered pH to around pH 8.5 even with the highest red mud loading tested (33 % w/w); experiments using this soil also had much lower aqueous Al, As and V concentrations. Gypsum addition to soil/red mud mixtures, even at relatively low concentrations (1 % w/w), was sufficient to buffer experimental pH to 7.5–8.5. This effect was attributed to the reaction of Ca2+ supplied by the gypsum with OH− and carbonate from the red mud to precipitate calcite. The lowered pH enhanced trace element sorption and largely inhibited the release of Al, As and V. Mo concentrations, however, were largely unaffected by gypsum induced pH buffering due to the greater solubility of Mo (as molybdate) at circumneutral pH. Gypsum addition also leads to significantly higher porewater salinities, and column experiments demonstrated that this increase in total dissolved solids persisted even after 25 pore volume replacements. Gypsum addition could therefore provide a cheaper alternative to recovery (dig and dump) for the treatment of red mud-affected soils. The observed inhibition of trace metal release within red mud-affected soils was relatively insensitive to either the percentage of red mud or gypsum present, making the treatment easy to apply. However, there is risk that over-application of gypsum could lead to detrimental long-term increases in soil salinity.

Citation

Lehoux, A. P., Lockwood, C. L., Mayes, W. M., Stewart, D. I., Mortimer, R. J. G., Gruiz, K., & Burke, I. T. (2013). Gypsum addition to soils contaminated by red mud: implications for aluminium, arsenic, molybdenum and vanadium solubility. Environmental Geochemistry and Health, 35(5), 643-656. https://doi.org/10.1007/s10653-013-9547-6

Journal Article Type Article
Acceptance Date Feb 18, 2013
Online Publication Date Jun 23, 2013
Publication Date 2013-10
Deposit Date Apr 2, 2019
Journal Environmental Geochemistry and Health
Print ISSN 0269-4042
Publisher Springer (part of Springer Nature)
Peer Reviewed Peer Reviewed
Volume 35
Issue 5
Pages 643-656
DOI https://doi.org/10.1007/s10653-013-9547-6
Keywords Alkaline red mud; Contaminated soils; Gypsum; Toxic trace elements; Arsenic; Vanadium; Aluminium; Organic matter leaching; pH reduction
Public URL https://hull-repository.worktribe.com/output/1529707
Publisher URL https://link.springer.com/article/10.1007%2Fs10653-013-9547-6
Related Public URLs http://eprints.whiterose.ac.uk/78585/