Investigate closure techniques for the Rusal Aughinish Bauxite Residue Disposal Area (B.R.D.A.) & show the impact on the surrounding environment post-closure

McGrath, Michael (2012) Investigate closure techniques for the Rusal Aughinish Bauxite Residue Disposal Area (B.R.D.A.) & show the impact on the surrounding environment post-closure. DProf thesis, Middlesex University.

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Abstract

Rusal Aughinish operates an alumina refinery situated on Aughinish Island on the south side of the Shannon estuary. The company submitted an application to extend the Bauxite Residue Disposal Area (B.R.D.A.) by another 80 hectares in 2006. Space to store residue was estimated to run out in 2011, thus requiring the construction of the extra 80 hectares which needed planning permission and an extension of the licence. It was vital to get planning permission and licence extension. There is a large volume of residual alkalinity, held in a soluble and solid phase, retained in the bauxite. The E.P.A. has requested a Residuals Management Plan which included, as a minimum, a scope statement for the plan. The criteria, which defines the successful decommissioning of the activity or part thereof, ensures minimum impact to the environment. However, this is subject to: the provision of a sustainable vegetation cover; and demonstration of leachate attenuation to below pH 9.0 within 5 years. Residue neutralisation methods were also investigated. Rusal Aughinish has determined that the restoration of the B.R.D.A. surface will support a “nature conservation” end-use (AAL, 2005d). Therefore, sustainable re-vegetation of the B.R.D.A. was required to support this goal. Small plot trials (2m x1m) and larger plot trials (10m x 2m) were established, which were amended with gypsum, process sand, and spent mushroom compost which lowered the pH, exchangeable sodium percentage (ESP) and the availability of Al and Fe in the residue. The newly created soil (bauxite residue mixed with process sand, gypsum and organic waste) was seeded. Results show that the establishment of vegetation was achievable. Additionally, investigations were carried out into the use of machinery on the residue. Two Demonstration Cells were constructed within the confines of the B.R.D.A. (0.6ha). The sides and floor of the cells were lined and a leachate collection system was installed on the floor of the cells. Monitoring of pH, electrical conductivity, and soda was conducted in run-off and leachate before and after vegetation growth on the residue in the cell. No reduction was noted in leachate or run-off pH since monitoring commenced in 2007. Following research into neutralization methods the use of sulphuric acid was the best option, but only partial neutralization was achieved, due to the large volume of acid required for full neutralization. There was also the likelihood of creating pH conditions that would lead to H2S odour problems. Carbonation would also be possible, but would require the construction of a plant or the importation of liquid CO2. Seawater neutralisation using water from the Shannon estuary is prohibited by costs. An initial modelling project looked at groundwater flow within the B.R.D.A. in two dimensions and assumptions were made as to the physical stratification and structure of the B.R.D.A. Mud-farming commenced and was evaluated. In conclusion, direct vegetation was found to be feasible, and so avoiding the high cost of topsoil. Soil construction and plant establishment was demonstrated. Demonstration Cells were constructed as per design and monitoring for pH, conductivity and soda of the leachate and run-off was conducted before and after vegetation growth. This monitoring is still ongoing. Filling of the cell with residue was determined by the stacking angle of the residue. Controlling percentage solids of the residue is very important in order to achieve proper stacking of the residue, Leachate pH may take years to drop from 13 to 9.0 or below. Recommendations to the company include further monitoring of Demonstration Cell leachate, run-off, and the vegetation cover on the residue. Finally, it is recommended to continue investigation into residue neutralisation methods.

Item Type:Thesis (DProf)
Research Areas:Institute of Work Based Learning > Work Based Learning
Theses
ID Code:9237
Deposited On:12 Jul 2012 08:59
Last Modified:15 Aug 2012 14:20

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