Authors: Tutu, H; Cukrowska, EM; McCarthy, TS

Paper is not available for download
Contact Us

DOI https://doi.org/10.36487/ACG_repo/852_58

Cite As:
Tutu, H, Cukrowska, EM & McCarthy, TS 2008, 'Geochemical Modeling of the Speciation of Uranium in an Acid Mine Drainage Environment in the Witwatersrand Basin', in AB Fourie, M Tibbett, I Weiersbye & P Dye (eds), Mine Closure 2008: Proceedings of the Third International Seminar on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 631-638, https://doi.org/10.36487/ACG_repo/852_58

Download citation as:   ris   bibtex   endnote   text   Zotero


Abstract:
Gold tailings dams from the Witwatersrand Basin usually contain elevated amounts of heavy metals and radionuclides. Uranium, in the form of uraninite (UO2) and brannerite (UTi2O6), is normally associated with gold-bearing ores in the basin. As a result of acid mine drainage (AMD), uranium is released into groundwater and fluvial systems. Its transport, retardation and immobilization depend strongly on the uranium species and prevailing geochemical conditions. This study was aimed at the quantitative assessment of the distribution of uranium and the modeling of its geochemical speciation. Geochemical analyses of tailings, water and sediment in areas of previous mining were performed. The results indicate that there is active leaching of uranium from the tailings, transport of soluble uranium species through water systems, with subsequent deposition of insoluble uranium species in sediments of fluvial systems. Analysis of tailings material indicated that mobilization and transportation of uranium from the tailings resulted in its decoupling from its progeny which remained largely unaffected by the weathering effects. Mobilization occurs as uranium is oxidized to the U(VI) state which dominates aqueous chemistry. The U(VI) is reduced to U(IV) which is immobile and is subsequently deposited in the wetland sediments downstream from the primary acid mine drainage. Geochemical modeling of uranium speciation revealed the two most influential hydrogeochemical facies in uranium mobility, namely a sulphate-dominated AMD system; and lime-neutralized carbonate-dominated system. In both cases the uranium was shown to be soluble throughout a very wide pH regime, thus yielding important information for risk assessment considerations.

References:
Atomic Energy Corporation of South Africa Ltd (1986) Uranium in South Africa, Pretoria, South Africa.
Cole, D.I. (1998) Uranium in Wilson, M.G.C. and Anhausser, C.R. (eds), The mineral resources of South Africa:
Handbook. Council for Geoscience, 16, pp. 642-652.
Ford, M.A. (1993) Uranium in South Africa. Journal of the South African Institute of Mining and Metallurgy 93 (2),
pp. 37-58.
Hermond, H.F. and Fechner-Levy, E.J. (2000). Chemical fate and transport in the environment. Academic Press, San
Diego, U.S.A.
Jones, G.A., Brierley, S.E., Geldenhuis, S.J.J. and Howard, J.R. (1988) Research on the contribution of mine dams to
the mineral pollution load in the Vaal Barrage, Report to the Water Research Commission, WRC Report No.
136/1/89, Pretoria, South Africa.
Kempe, J.O. (1983) Review of water pollution problems and control strategies in the South African Mining Industry.
Water Science and Technology 15, pp. 27-58.
Langmuir, D. (1978) Uranium solution-mineral equilibria at low temperatures with applications to sedimentary ore
deposits. Geochimica et. Cosmochimica Acta 49, pp. 1931-1941.
Geochemical Modeling of the Speciation of Uranium in an Acid Mine Drainage Environment H. Tutu et al.
in the Witwatersrand Basin
Marsden, D.D. (1986) The current limited impact of Witwatersrand gold-mine residues on water pollution in the Vaal
River system. Journal of the South African Institute of Mining and Metallurgy, 86, pp. 481-504.
Mphephu, N.F. (2004) Geotechnical environmental evaluation of mining impacts on the Central Rand. PhD Thesis
submitted to the University of the Witwatersrand, Johannesburg.
Mrost, M. (1973) The rehabilitation of gold mine tailings deposits. SACIE 5th Quinquennial Convention, Div. of Soil
Mechanics and Foundation Engineering Speciality Session: Engineering aspects of erosion.
Naicker, K., Cukrowska, E. and McCarthy, T.S. (2003) Acid mine drainage arising from gold mining activities in
Johannesburg, South Africa and environs. Journal of Environmental Pollution, 122, pp. 29-40.
Rosner, T., Boer, R., Reyneke, R., Aucamp, P. and Vermaak, J. (2001) A preliminary assessment of pollution contained
in the unsaturated and saturated zone beneath reclaimed gold-mine residue deposits. Water Research
Commission Report No. 797/01/01, Pretoria, 210.
Tutu, H., McCarthy, T.S. and Cukrowska, E.M. (2008) The chemical characteristics of acid mine drainage with
particular reference to sources, distribution and remediation: the Witwatersrand Basin, South Africa as a case
study. Applied Geochemistry (in press).
Winde, F. (2001) Slimes dams as sources of uranium contamination of streams – the Koekemoerspruit (Klerksdorp gold
field) as a case study. Chamber of Mines of South Africa Conference on Environmentally Responsible Mining in
Southern Africa, 25-28 September 2001, Muldersdrift, Johannesburg, 1, 2C1-2C10.
Winde, F. (2002) Uranium contamination in fluvial systems – mechanisms and processes. Part I: Geochemical mobility
of uranium along the water path – the Koekemoerspruit (South Africa) as a case study in Cuardernos de
Investigacion Geografica 28, pp. 49-57.
Winde, F. and de Villiers, A.B. (2002) The nature and extent of uranium contamination from tailings dams in the
Witwatersrand gold mining area (South Africa) in B.J. Merkel, B. Planer-Friedrich, and C. Wolkersdorfer (eds),
Uranium in the Aquatic Environment, Berlin, Heidelberg, 889-897.
Winde, F. and Sandham, L.A. (2004) Uranium pollution of South African streams – an overview of the situation in gold
mining areas of the Witwatersrand. GeoJournal, 61, pp. 131-149.
Winde, F., Wade, P. and van der Walt, I.J. (2004) Gold tailings as a source of water-borne uranium contamination of
streams – the Koekemoerspruit (South Africa) as a case study. Water SA, 30(2), pp. 219-239.
World Nuclear Association (WNA) (2005) The Global Nuclear Fuel Cycle.
Wymer, D. (2001) The impact of gold mining on radioactivity in water and foodstuffs. Chamber of Mines of South
Africa, 1, Conference on Environmentally Responsible Mining in Southern Africa, Muldersdrift, Johannesburg,
25-28 September 2001, 2C-19-2C-30.




© Copyright 2022, Australian Centre for Geomechanics (ACG), The University of Western Australia. All rights reserved.
Please direct any queries or error reports to repository-acg@uwa.edu.au