Gillow, J & Horst, J 2008, 'Harnessing Iron Mineral Transformations for the Geochemical Stabilization of Mining Impacts', 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. 539-545, https://doi.org/10.36487/ACG_repo/852_49
Engineering a successful treatment strategy for inorganics associated with mining residuals requires that
equal consideration be given to the solid and dissolved phases. Because of its chemistry and relative
abundance, the role of iron in controlling the mobility of many other elements is pronounced. This applies to
a variety of metals, radionuclides, and certain non-metals. This paper discusses the potential for harnessing
biologically-mediated iron mineral transformations in order to stabilize metal impacts stemming from
mining activities, and presents several examples.
Iron minerals can be harnessed through biologically-mediated transformations within, and down-gradient of
an in situ anaerobic treatment zone. This process involves a variety of possible products, but of primary
importance are the formation of iron sulphide mineral phases within the anaerobic zone, and the formation
of oxy-hydroxide mineral phases in the down-gradient redox recovery zone. These biologically-mediated
mineral phases can be used to sequester sulphur derived from sulphate, create a long-term source of
reductive poise which can help immobilize certain minerals, or create sorptive capacity to control the
mobility of various inorganics. These reactions may utilize natural iron present in aquifer soil and available
sulphate – such as acid rock drainage, but can also be engineered with a supplemental source of iron and/or
One example where this concept applies is uranium. Uranium is highly soluble across a wide pH range and
under oxic conditions due to the propensity of the uranyl cation to form complexes with a variety of common
ligands (carbonate, phosphate, and hydroxide) as well as a multitude of low molecular weight organics and
natural organic matter. All of these uranium complexes persist in oxidizing environments and can be
resistant to surface reactions. In contrast, the in situ precipitation of insoluble forms of uranium can be
accomplished under anaerobic and reducing conditions, but a critical component to this approach is the
creation of excess reductive poise (through the concurrent mineralization of iron sulphides) to buffer the
environment over the long term and mitigate re-oxidation of the precipitated uranium phases. Also important
is the additional sorptive capacity that can be created to control the mobility of any uranium that is
re-oxidized. This same approach can be applied to other metals that are conducive to precipitation as
sulphides themselves, where the excess iron sulphide phases can increase the long-term stability of other
sulphide mineral phases present.
The success of this type of approach requires an adequate understanding of site mineralogical and
hydrological characteristics, speciation of the dissolved phases being targeted, and the mineralization
dynamics and associated biogeochemistry. This will allow development of an integrated and effective
treatment design for difficult mine-related soil and groundwater impacts from metals and radionuclides.
Andersen, M.S., Larsen, F. and Postma, D. (2001) Pyrite Oxidation in Unsaturated Aquifer Sediments. Reaction
Stoichiometry and Rate of Oxidation, Environmental Science and Technology, 35, pp. 4074-4079.
Casas, I., De Pablo, J., Gimenez, J., Torrero, M., Bruno, J., Cera, E., Finch, R. and Ewing, R. (1998) The Role of pe,
pH, and Carbonate on the Solubility of UO2 and Uraninite Under Nominally Reducing Conditions, Geochimica
et Cosmochimica Acta, 62, pp. 2223-2231.
Druschel, G.K., Baker, B.J., Gihring, T.M. and Banfield, J.F. (2004) Acid Mine Drainage Biogeochemistry at Iron
Mountain, California, Geochemical Transactions, 5, p. 13.
Gillow, J.B. (2006) Biotransformation of Plutonium Colloids in the Environment, Ph.D. Thesis, Colorado School of
Johnson, B.D. and Hallberg, K.B. (2005) Acid Mine Drainage Remediation Options: A Review, Science of the Total
Environment, 338, pp. 3-14.
Michel, F.M., Ehm, L., Liu, G., Han, W.Q., Antao, S.M., Chupas, P.J., Lee, P.L., Knorr, K., Eulert, H., Kim, J., Grey,
C.P., Celestian, A.J., Gillow, J., Shoonen, M.A.A., Strongin, D.R. and Parise, J.B. (2007) Similarities in 2- and
6-Line Ferrihydrite Based on Pair Distribution Function Analysis of X-ray Total Scattering, Chemistry of
Materials, 19, pp. 1489-1496.
Naveau, A., Monteil-Rivera, F., Guillon, E. and Dumonceau, J. (2007) Interactions of Aqueous Selenium (-II) and (IV)
with Metallica Sulphide Surfaces, Environmental Science and Technology, 41, pp. 5376-5382.
O’Day, P.A., Vlassopoulos, D., Root, R. and Rivera, N. (2004) The Influence of Sulfur and Iron on Dissolved Arsenic
Concentrations in the Shallow Subsurface Under Changing Redox Conditions, Proceedings of the National
Academy of Sciences, 101, pp. 13,703-13,708.
O’Loughlin, E.J., Kelly, S.D., Cook, R.E., Csencsits, R. and Kemner, K.M. (2003) Reduction of Uranium(VI) by Mixed
Iron(II)/Iron(III) Hydroxide (Green Rust): Formation of UO2 Nanoparticles, Environmental Science and
Technology, 37, pp. 721-727.
Sposito, G. (1989) Chemistry of Soils, Oxford University Press, 304 p.
Suthersan, S.S. and Payne, F.C. (2004) In Situ Remediation Engineering, CRC Press, 536 p.
Zehnder, A. and Stumm, W. (1989) Geochemistry and Biogeochemistry of Anaerobic Habitats, Anaerobic
Microbiology, 2nd Edition, Zehnder (ed), Wiley Interscience.