Abstract
Red mud is a highly alkaline (pH >12) waste product from bauxite ore processing. The red mud spill at Ajka, Hungary, in 2010 released 1 million m3 of caustic red mud into the surrounding area with devastating results. Aerobic and anaerobic batch experiments and solid phase extraction techniques were used to assess the impact of red mud addition on the mobility of Cu and Ni in soils from near the Ajka spill site. Red mud addition increases aqueous dissolved organic carbon (DOC) concentrations due to soil alkalisation, and this led to increased mobility of Cu and Ni complexed to organic matter. With Ajka soils, more Cu was mobilised by contact with red mud than Ni, despite a higher overall Ni concentration in the solid phase. This is most probably because Cu has a higher affinity to form complexes with organic matter than Ni. In aerobic experiments, contact with the atmosphere reduced soil pH via carbonation reactions, and this reduced organic matter dissolution and thereby lowered Cu/Ni mobility. These data show that the mixing of red mud into organic rich soils is an area of concern, as there is a potential to mobilise Cu and Ni as organically bound complexes, via soil alkalisation. This could be especially problematic in locations where anaerobic conditions can prevail, such as wetland areas contaminated by the spill.Electronic supplementary materialThe online version of this article (doi:10.1007/s11356-015-4282-4) contains supplementary material, which is available to authorized users.
Highlights
The accidental release of ~1 million m3 (Reeves et al 2011; Adam et al 2011) of bauxite processing residue from the Ajkai Timfoldgyar Zrt alumina plant in Ajka, western Hungary, in October 2010 focused world attention on the public health and environmental hazards associated with red mud
This paper reports results from long-term aerobic and anaerobic batch experiments that investigate the mobility of Cu and Ni in red mud-contaminated soil-water systems that are representative of soil conditions after the Ajka disaster remediation efforts
When red mud was added to the anaerobic soil-water systems, there was an immediate increase in pH which was related to the red mud loading, after which the pH remained relatively constant throughout the incubation period
Summary
The accidental release of ~1 million m3 (Reeves et al 2011; Adam et al 2011) of bauxite processing residue (red mud) from the Ajkai Timfoldgyar Zrt alumina plant in Ajka, western Hungary, in October 2010 focused world attention on the public health and environmental hazards associated with red mud. At Ajka, the red mud had a pH >12 (Adam et al 2011), making it a hazardous substance as defined by the Basel Convention (Secretariat of the Basel Convention 2011). It is highly saline and sodic (e.g. Ajka leachate had conductivity of up to 160 mS cm−2); Na stress to soils and plants has been noted as a consequence of the Ajka spill (Ruyters et al 2011)
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