Advances in Understanding Environmental Risks of Red Mud After the Ajka Spill, Hungary

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 molecularlevel 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.

Influence of red mud on soil microbial communities: Application and comprehensive evaluation of the Biolog EcoPlate approach as a tool in soil microbiological studies

“…Sandy soils, with little or no nutrient or water holding capacity could benefit from the uses of red mud as soil ameliorant (McPharlin et al, 1994, Barrow, 1982, Ujaczki et al, 2015, Ujaczki et al, 2016 due to the presence of sodalite in red mud, with an estimated cation exchange capacity (CEC) that exceeds the CEC of most natural clays. In addition, the alkaline nature of red mud can be used to raise the pH of organic or acidic soils (Summers et al, 1996, Snars et al, 2004, which tend to suffer from Al phytotoxicity (Alva et al, 2002).…”

“…Additionally, due to red mud mineralogy (iron and aluminium oxides, hydroxides) it can increase the phosphorus retention of sandy soils adsorbing phosphate (Summers et al, 1993, Summers andPech, 1997), thus reducing phosphate leaching and preventing eutrophication, and creating a phosphate pool that is available to plants and soil microorganisms. However, the alkalinity, the trace metal content and the naturally occurring radioactive material content of red mud may pose significant environmental risks (Akinci andArtir, 2008, Klauber et al, 2011), therefore its careful application is recommended in soil (Ruyters et al, 2011, Ujaczki et al, 2015, 2016a, Mayes et al, 2016.…”

Bauxite Residue Valorization and Best Practices: Preface for the Thematic Section and Some of the Work to Follow

“…The work continues with a paper by Mayes et al [2], providing an update on the environmental risks that are associated with the Ajka spill accident, in Hungary, in 2010. This event has been registered as the largest single release of bauxite residue to the environment, and since then there have been 46 scientific studies assessing the key risks and impacts associated with it.…”

Re‐using bauxite residues: benefits beyond (critical raw) material recovery

“…The bauxite residues are emitted as a slurry‐type paste of pH > 11, a high fine silt to clay size proportion, and a high sodium content. This leads to a preference for particle dispersion, and as a result difficulties in handling and storing residue (see below). Dry cake disposal involves thickening and pressure filtration, before using dump trucks to transfer residues to the storage area .…”