Long-term management of leachates produced from highly alkaline bauxite email@example.com
Background and Rationale:
There is a global legacy of mining and mineral processing residues and wastes produced by the ever expanding need for raw materials. As former industrial and mining sites reach the end of their period of economic production, attention switches to the needs of long-term management of residues and the potential for site remediation. Some types of mineral processing residues contain toxic chemicals and produce leachates which can be harmful to the environment if not properly managed. Expectations from government and communities that these sites will be managed sustainably has never been higher.
This project is focused on the management of large volumes of residues produced during the worldwide production of aluminium. The manufacture of aluminium begins with extraction of alumina (Al2O3) from bauxite ore, which produces 1-2 tonnes of ‘red mud’ residue for each tonne of alumina produced. Rehabilitation of red mud sites is challenging and needs to be based on best scientific understanding of the geochemical evolution of leachates and mineralogy of the specific residues involved. Bauxite residues (red mud) and their associated leachates that are highly alkaline and contain high concentrations of oxyanion forming elements (e.g. Al, As, Mo, V), which can be problematic if released into the environment (Mayes et al., 2011; 2016). Although there is also potential for removal and recovery of some of these elements (Gomes et al., 2016), vanadium (as vanadate) is particularly recalcitrant to treatments (e.g. neutralisation) and can still pose an environmental risk in treated leachates (Burke et al., 2012; 2013). Therefore, there is need to investigate the fate and behaviour of trace elements during residue management and treatment, seeking to produce systems (if possible at relatively low cost) that are effective for, alkalinity reduction, metal(loid) retention, red mud stabilisation and site revegetation.
Fig 1. Rehabilitation of Rio Tinto’s old red mud impoundments a Mt. Rosser and Kirkvine, Jamaica.
This project will investigate the behaviour and mobility of selected trace elements during residue storage and leachate management. It will employ a range traditional laboratory and field based geochemical investigations, along with state of the art synchrotron and electron microscope based methods to determine the precise chemical form of the trace elements in all parts of the storage and management system (i.e. residues, leachates, precipitates). We will also investigate the likely fate of trace elements (chiefly V) in natural environments where interaction with soil minerals and organic matter is likely to control their environmental behaviour. We will seek to use this new understanding of trace element fate and behaviour to explain the observed concentrations of trace elements in on site processes and to help design future management systems with better performance and lower costs.
Fig 2. Potential environmental issues and opportunities associated with the management of alkaline red mud residues.
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.
You will primarily work under the supervision of Dr. Ian Burke and Prof Doug Stewart within the Cohen Geochemistry Group at Leeds. You will receive specialist scientific training in state-of-the-art geochemical, mineralogical, experimental and analytical techniques and synchrotron based geochemical analysis. Dr Will Mayes will lead training in fieldwork aspects of the work at bauxite residue legacy disposal sites. In addition, you will have the opportunity to be trained in a wide variety of key transferable skills within the SPHERES NERC DTP, from computer programming and modelling, to media skills and public outreach. You will also be encouraged and supported to present your research at national and international scientific conferences.
Fig 3. Diamond Light source in Oxfordshire: a powerful new facility for molecular level studies of contaminant behaviour and an example of the molecular bonding proposed for V(V) on an iron oxide surface (Peacock and Sherman, 2004) . It is only when the molecular behaviour is understood that large-scale environmental predictions can be made with certainty.
CASE partnership and fieldwork
This project has a Case (Collaborative awards in science and engineering) in place with Rio Tinto legacy management and the project findings will feed directly into their program of red mud site management at bauxite residue disposal areas across the world. The project will benefit from £10,000 of additional support from the case partner (to support the student’s travel to residue sites and laboratories, and, to enhance the student stipend). The student will be hosted by Rio Tinto for up to 4 months during the project. This work will include fieldwork at Rio Tinto’s European legacy sites (e.g. in Scotland and France), visits to analytical laboratories in the Netherlands, and desk based study at Rio Tinto offices in Paris.
The applicant must satisfy the requirements to register as a doctoral student at the University of Leeds, which involves holding appropriate Honours, Diploma or Masters Degree and having passed the appropriate English language tests. Applications are invited from graduates who have, or expect to gain, a good degree in chemistry, geology, environmental science, materials science, chemical engineering or another relevant science discipline. Relevant Masters level qualifications are also welcomed. The applicant should have a good command of both written and spoken English.
Burke I. T., Mayes, W. M., Peacock C. L., Brown A. P., Jarvis A. P. and Gruiz, K. Speciation of arsenic, chromium and vanadium in red mud samples from the Ajka spill site, Hungary, Environmental Science and Technology. (2012) 46, 3085-3092.
Burke I. T., Peacock C. L., Lockwood C. L., Stewart D. I., Mortimer R. J. G., Ward M. B., Renforth P., Gruiz, K. and Mayes, W. M. Behaviour of aluminium, arsenic and vanadium during the neutralisation of red mud leachate by HCl, gypsum, or seawater. Environmental Science and Technology (2013) 47, 6527-6535.
Gomes H. I., Jones A., Rogerson M., Burke I. T. and Mayes W. M. Vanadium removal and recovery from bauxite residue leachates by ion exchange. Environmental Science and Pollution Research (2016; in press).
Mayes, W. M., Burke I. T., Gomes, H. I., Anton A. D., Ujaczki E., Molnar M. and Feigl V. Advances in understanding environmental risks of red mud after the Ajka spill, Hungary. Journal of Sustainable Metallurgy (2016) DOI 10.1007/s40831-016-0050-z, pp1-12.
Mayes W. M., Jarvis A. P., Burke I. T., Walton M. Feigl, V., Klebercz, O. and Gruiz K. Dispersal and attenuation of trace contaminants downstream of the Ajka bauxite residue (red mud) depository failure, Hungary. Environmental Science and Technology. (2011) 45 (12) 5147-5155.
Peacock C. L. and Sherman D. M. Vanadium(V) adsorption onto goethite (alpha-FeOOH) at pH 1.5 to 12: A surface complexation model based on ab initio molecular geometries and EXAFS spectroscopy. Geochimica et Cosmochimica Acta. (2004) 68(8), 1723−1733.
Related undergraduate subjects:
- Chemical engineering
- Environmental science
- Materials science