Abstract
In the 5 years since the 2010 Ajka red mud spill (Hungary), there have been 46 scientific studies assessing the key risks and impacts associated with the largest single release of bauxite-processing residue (red mud) to the environment. These studies have provided insight into the main environmental concerns, as well as the effectiveness of remedial efforts that can inform future management of red mud elsewhere. The key immediate risks after the spill were associated with the highly caustic nature of the red mud slurry and fine particle size, which once desiccated, could generate fugitive dust. Studies on affected populations showed no major hazards identified beyond caustic exposure, while red mud dust risks were considered equal to or lesser than those provided by urban dusts of similar particle size distribution. The longer-term environmental risks were related to the saline nature of the spill material (salinization of inundated soils) and the release and the potential cycling of oxyanion-forming metals and metalloids (e.g., Al, As, Cr, Mo, and V) in the soil–water environment. Of these, those that are soluble at high pH, inefficiently removed from solution during dilution and likely to be exchangeable at ambient pH are of chief concern (e.g., Mo and V). Various ecotoxicological studies have identified negative impacts of red mud-amended soils and sediments at high volumes (typically >5 %) on different test organisms, with some evidence of molecular-level impacts at high dose (e.g., genotoxic effects on plants and mice). These data provide a valuable database to inform future toxicological studies for red mud. However, extensive management efforts in the aftermath of the spill greatly limited these exposure risks through leachate neutralization and red mud recovery from the affected land. Monitoring of affected soils, stream sediments, waters and aquatic biota (fungi, invertebrates and fish) have all shown a very rapid recovery toward prespill conditions. The accident also prompted research that has also highlighted potential benefits of red mud use for critical raw material recovery (e.g., Ga, Co, V, rare earths, inform), carbon sequestration, biofuel crop production, and use as a soil ameliorant.
Highlights
The contributing editor for this article was Yiannis Pontikes.The Ajka red mud spill in western Hungary in October 2010 was the largest documented release of alumina industry by-products into the environment, with around 1 million m3 of red mud suspension breaching the failed depository wall [1]
Studies on affected populations showed no major hazards identified beyond caustic exposure, while red mud dust risks were considered equal to or lesser than those provided by urban dusts of similar particle size distribution
The circumstances surrounding the failure of the retaining wall of Cell X [1] at the depository are not representative of modern bauxite residue disposal area (BRDA) management practices elsewhere, the numerous scientific studies in the aftermath of the spill have revealed much about the risks and environmental behavior of bauxite processing residue
Summary
The contributing editor for this article was Yiannis Pontikes. The Ajka red mud spill in western Hungary in October 2010 was the largest documented release of alumina industry by-products into the environment, with around 1 million m3 of red mud suspension breaching the failed depository wall [1]. Longer-term measures included channel dredging, the recovery of red mud from affected floodplain areas, and the plowing of red mud into topsoil in areas of shallow (\50 mm) deposits to minimize fugitive dust generation [7, 8]. The latter was based on a three-tiered risk assessment [8] for assessing potential ecological and public health impacts, along with risks of secondary salinization of soils [9]. This paper reviews the main environmental impacts of the Ajka spill and considers both: (a) the environmental behavior of red mud, and (b) the effectiveness of remedial efforts, to highlight key lessons and opportunities for future bauxite residue management
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