Minerals in Mine Wastes: Resources, Recycling, Remediation
Karen Hudson-Edwards
Department of Earth and Planetary Sciences, Birkbeck, University of London, Malet St., London WC1E 7HX,
UK. k.hudson-edwards@bbk.ac.uk
Wastes produced from the mining and extraction of metal, industrial mineral and energy resources
constitute one of the largest waste streams on Earth. The volumes of these ‘mine wastes’ are predicted
to increase at least two-fold over the next 100 years due to increasing demands for minerals and
energy, and lower ore grades. Mine wastes can be gases, fluids (e.g. acid, circumneutral or basic mine
drainage) and solids (flue ashes and dusts, slags, tailings, sludges and waste rock). Solid mine wastes
contain a variety of minerals that can be considered as resources (and thus re-processed or re-mined)
or can be recycled. These minerals can also react with water and air to yield secondary minerals that
contain metallic and metalloid elements, and can thus also be considered as resources, be recycled, or
require remediation. This presentation makes the case that knowledge of the minerals in mine wastes
will significantly enhance the design of re-processing, recycling and remediation programmes.
The major minerals of mine wastes can be sub-divided into four categories, namely primary
sulphides, primary non-sulphides, compounds produced from ore processing and secondary minerals
(Jamieson, 2011). Many of these are micro- to nano-sized and are not easily characterised using
traditional methods. A variety of traditional (e.g. X-ray diffraction, scanning electron microscopy,
electron probe micro-analysis and X-ray mapping, etc.) and non-traditional methods (e.g. X-ray
absorption spectroscopy, CT scanning, atomic force microscopy, etc.) are needed for this purpose.
To be able to extract economic metals and commodities from mine wastes, it is important to
know how they are hosted. Bioleaching of copper-bearing mine wastes, for example, is most effective
when the copper-bearing minerals are well-characterised, and the mechanisms by which bacteria
interact with the mineral surfaces are understood and can be managed. An understanding of the
concentrations, types, sizes and bonding environments of impurities in these copper-bearing minerals
is also important in terms of understanding how these might negatively impact on the bacteria. Metal
recovery from acid mine drainage wastes relies on knowledge of which minerals can precipitate from
these fluids, and how they can sorb and host the metallic elements.
A thorough understanding of the minerals is necessary in order to be able to safely (i.e., no
negative environmental impacts) and effectively use them in recycling programmes. For example, the
recycling of iron oxide- and oxyhydroxide-bearing mine wastes as pigments is being piloted, but relies
on these phases being insoluble and unreactive, since they can contain contaminants such as
chromium, copper and cobalt that could potentially be released to the environment.
The development of remediation technologies can also benefit from a thorough understanding
of the mine waste minerals. For example, characterisation of the sulphides and gangue minerals
present helps in the prediction of acid, neutral or basic mine drainage, the concentrations of potentially
toxic elements (e.g., arsenic, antimony, thallium) in these fluids (e.g., Kossoff et al., 2011), and the
design of appropriate remediation schemes. In cases where remediation is not possible due to the
large-scale and/or dynamic nature of mine waste-affected environments (e.g., river systems),
management of the contamination is most desirable. In these situations, knowledge of the stability of
the mineral contaminant hosts is important for prediction of the contaminants most likely to be
mobilised.
The talk will present the above material and examples, and outline the ways forward for
research in this area.
References
Jamieson, H.E. (2011) Geochemistry and mineralogy of solid mine waste: essential knowledge for predicting environmental
impact. Elements, 7, 381-386.
Kossoff, D., Hudson-Edwards, K.A., Dubbin, W.E., Alfredsson, M. (2011) Incongruent weathering of Cd and Zn from mine
tailings: a column leaching study. Chemical Geology, 281, 52-71.