In October 2010, a dam failure at an aluminium producing plant in western Hungary released around one million cubic metres of toxic red sludge into nearby towns and villages and across agricultural land. The sludge was a mixture of water and mining waste containing heavy metals and was deemed a threat to the environment by Hungarian officials. A large cleanup operation ensued. A team from the University of Leeds
has used Diamond’s Microfocus Spectroscopy beamline
, I18, to study samples of the red mud that escaped from the tailings dam. Their results have been published in the journal Environmental Science & Technology
Red mud is the fine material by-product of aluminium extraction from bauxite. Although in recent years there have been multiple attempts to find practical uses for red mud, the majority of it produced is stored in land based depositories or has been dumped into the sea. To prevent dust formation, red mud is often stored as wet slurry.
Following the spill, the response to remove the red mud from residential areas and fields was to prevent dust formation, which was thought to be toxic due to its highly alkaline nature and heavy metal content. However, initial investigations suggested that the likely health effects from red mud derived dusts are no greater than other urban dust sources. Despite these initial findings, the longer term behaviour and potential mobility of toxic metals in neutral red mud affected environments are still largely unknown. This research has shed light on the toxicity of red mud and how it should be dealt with in the future.
Dr Ian Burke, the lead investigator on the project, said, “Our data partially justifies the cleanup response by Hungarian officials. Compared to the less expensive route of ploughing the mud into the topsoil, the decision to remove large swaths of the red mud from the countryside probably led to less bioavailable vanadium in the soil. Our findings should have an impact on future plans for dealing with red mud.”
Dr Burke et al’s research highlights that red mud deposited in the environment poses a real danger because of the high vanadium content and therefore should be avoided. This is relevant not only to future spill scenarios but also to plans for alternative uses for red mud wastes. “For example in agriculture,” explains Dr Burke, “as soil amendment to improve water and nutrient holding capacity. Or in the neutralisation of contaminated acidic wastes, and as a low cost absorbent for waste water treatment.”
The team used I18 to determine the chemical form of arsenic, chromium and vanadium found in the red mud. Dr Burke explains, “If we know the precise chemical form of a toxic metal then we can use that information to predict how harmful these metals are likely to be in the environment.” This study aimed to predict the likely environmental mobility, fate, and long-term hazards from arsenic, chromium and vanadium contamination associated with the red mud spill.
“Our results suggest that the chemical state of the arsenic and the chromium will restrict their environmental mobility, and therefore confirm that these elements were unlikely to have presented a significant danger. However, we found that the red mud may act as a source of mobile toxic vanadium that plants and animals could absorb where the red mud deposits are not removed from affected land.”
Beamline I18 has been in operation since January 2007. It can be used by researchers to map elements in complex samples, follow chemical reactions, and study real systems such as mineral samples returned from space, environmental samples and materials in hostile environments. The technique used in this study was X-ray absorption spectroscopy (XAS), an advantage of which being the ability to analyse small concentrations of an element in a complex matrix, such as the red mud.
Image credit: Above right - D I Stewart; Above left - W M Mayes