PhD opportunity on long-term management of bauxite residues leachates

Our team has now available a Ph.D. opportunity at the University of Leeds on “Long-term management of leachates produced from highly alkaline bauxite residues” with Dr Ian Burke (SEE), Prof Doug Stewart (Civil Eng), Dr Will Mayes (Hull) and Amiel Boullemant (Rio Tinto Legacy Management).

Project Objectives

  1. Investigate the fate and mobility of soluble metals (Al, As, Mo. V) in relevant leachate management systems (e.g. neutralisation, re-circulation) using a combination of on-site measurement and laboratory experimentation (with synchrotron and electron microscopy based characterisation of metal(loid) speciation in the solid phases produced).
  2. Determine the effectiveness of residue treatments (e.g. in situ neutralisation, carbonation reactions) for controlling trace metal(loid) leaching and their long-term role in promoting residue stability and rehabilitation/ revegetation prospects.
  3. Investigate the fate of released oxyanions (chiefly V) in natural environments receiving treated leachates in order to understand the role of interactions with soil minerals and organic matter in controlling metal(loid) mobility and risk.

Project partner(s): Rio Tinto Legacy Management

Contact email: i.t.burke@leeds.ac.uk

You can find detailed information here.

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New paper published

The paper “Advances in understanding environmental risks of red mud after the Ajka spill, Hungary” was just published in the Journal of Sustainable Metallurgy.

This paper reviews the over 45 scientific studies published in the last 5 years assessing the key risks and impacts associated with the largest single release of bauxite residue to the environment  – the 2010 Ajka red mud spill.

 

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Categories of scientific papers and conference proceedings after the Ajka spill.

 

The main environmental concerns were covered in these studies, which also evaluated the  effectiveness of the remedial actions taken. 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 dry, could generate fugitive dust. Studies on affected populations showed no major hazards identified beyond caustic exposure. The dust risks were considered equal or lesser to those provided by urban dusts.

The longer term environmental risks were related with the potential salinization of inundated soils and release and potential cycling of metals and metalloids (e.g. Al, As, Cr, Mo, V) in the soil-water environment. Of these, those that are soluble at high pH, inefficiently removed from solution by dilution and likely to be exchangeable at ambient pH are of chief concern (e.g. Mo and V).

However, extensive management efforts in the aftermath of the spill greatly limited these exposure risks through neutralisation and red mud recovery from affected land. Monitoring of affected soils, stream sediments, waters and aquatic biota (fungi, invertebrates and fish) have all shown a very rapid recovery towards pre-spill 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), carbon sequestration, biofuel crop production and use as a soil ameliorant.

 

New review paper published in Journal of Cleaner Production

jcleproA new review paper on alkaline wastes is now online, after been accepted by the Journal of Cleaner Production. This paper focuses on the environmental impacts associated with alkaline residues, such as coal fly ash, bauxite residues or red mud, steelworks slags, concrete crusher fines, flue gas desulphurisation waste, Air Pollution Control (APC) residues, Solvay process waste, and chromite ore processing residue (COPR).

While there are significant differences in bulk mineralogical composition among these residues, all are characterised by the presence of Na, Ca or Mg oxides that rapidly hydrate to produce soluble hydroxides. A large range of Ca and Na silicate, aluminate and aluminosilicate phases are also present, hydrating and dissolving to generate alkalinity. Finally, any Ca and Mg carbonates present provide a stable (low solubility) alkaline phase. Initially, dissolution of soluble Na or Ca hydroxides tends to dominate (pH > 12). The  leachates of these residues have pH above typical regulatory thresholds for discharge to water bodies (usually 9), and a major influence on the mobility of contaminants potentially soluble at high pH, because they form oxyanions (e.g. As, Cr, Mo, Se and V).

The paper discusses the environmental impacts of the residues, highlighting the acute episodes, such as the dam failure in Ajka, Hungary,  as well as the widespread chronic impact of the leachate on receiving waters, especially in old and abandoned disposal sites. Pollutant pressure and biological impacts are also reviewed.

The management options for the residues and their leachates are also discussed, distinguishing active and passive treatment options. Potential reuses of these materials, in construction materials, as agricultural amendments, and in environmental applications are identified. The mechanisms of carbon sequestration by alkaline residues are assessed, and the potential for enhancing its rate as a climate change off-setting measure for the industry is evaluated. The potential for recovery of metals critical to e-technologies, such as vanadium, cobalt, lithium and rare earths, from alkaline residues is considered. Finally, research needs are identified, including the need to better understand the biogeochemistry of highly alkaline systems in order to develop predictable passive remediation and metal recovery technologies.

Reference: Gomes, H.I., Mayes, W.M., Rogerson, M., Stewart, D.I., Burke, I.T., (2015) Alkaline residues and the environment: A review of impacts, management practices and opportunities. Journal of Cleaner Production. (In Press)

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