Tailings
Primary reference(s)
ICMM, 2019. Tailings management. International Council on Mining and Minerals (ICMM). Accessed 21 November 2019.
Additional scientific description
Tailings are the fine-grained waste material remaining after the metals and minerals recoverable with the technical processes applied have been extracted. The material is rejected at the ‘tail end’ of the process with a particle size normally ranging from 10 μm to 1.0 mm (UNECE, 2014:3). Tailings are mixtures of crushed rock and processing fluids from mills, washeries or concentrators that remain after the extraction of economic metals, minerals, mineral fuels or coal from the mine (Kossoff et al., 2014).
Tailings are the by-product of several extractive industries, including those for aluminium, coal, oil sands, uranium and precious and base metals (Kossoff et al., 2014). The chemical composition of tailings depends on the mineralogy of the ore body, the nature of the processing fluids used to extract the economic metals, the efficiency of the extraction process and the degree of weathering during storage in the dammed impoundment. Major components usually include such elements as silica also known as silicon dioxide (SiO2), iron (Fe), oxygen (O), aluminium (Al), calcium (Ca), potassium (K), magnesium (Mg), manganese (Mn), sodium (Na), phosphorus (P), titanium (Ti) and sulphur (S) (Kossoff et al., 2014). Tailings may also contain toxic elements such as arsenic (As) or chemical reagents such as cyanide (CN−) which can be toxic in sufficient concentrations (Jewell, 1998).
As an example, uranium tailings are radioactive and can retain the majority of the radioactivity of the ore from which they are derived. In parallel, their radioactivity is very long-lived; they contain a range of biotoxic heavy metals and other compounds; they may contain sulphidic minerals and so generate acid mine drainage; their granular to slime constituency makes them readily leachable, erodible or collapsible under different conditions; the common method of surface disposal exposes a large surface area to the natural elements and thus increases the risk releasing radiation flux, radioactive and geochemically toxic dusts, and interaction with surface water systems; and the large surface area of these generally thin tailings deposits (or ‘piles’) adversely affects large areas of land and renders potentially valuable land unfit for other uses (IAEA, 2004:6).
Tailings are also of concern due to the danger of tailing dam failures (one of the most common tailings storage methods). Failure of mining dams and the release of toxic waves of material can claim thousands of lives, affect water and sediment quality, fish, terrestrial animal life and plant life, cause irreversible environmental damage, and negatively impact biodiversity and the reputation of the mining industry.
Metrics and numeric limits
For every tonne of ore, the extraction of metal concentrates results in about 850 kg of residual solid waste and an equal amount of water containing slightly less than 1 kg of residual chemicals (Jewell, 1998). The total global volume is unknown (UNEP, 2017) and environmentally acceptable storage constitutes a significant challenge.
At the time of writing, the International Council on Mining and Metals (ICMM), the United Nations Environment (UN Environment) and the Principles for Responsible Investment (PRI) were co-convening a global tailings review to establish an international standard (Global Tailings Review, 2019).
Key relevant UN convention / multilateral treaty
Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter (1972), also referred as the ‘London Convention’ prevents dumping of waste at sea. At the time of writing, there were 87 parties to the London Convention (IMO, 2019).
UNECE Convention on the Transboundary Effects of Industrial Accidents (1992) at the time of writing had 41 Parties (UN Treaty Collection, 1992a).
Convention on the Protection and Use of Transboundary Watercourses and International Lakes (1992) also referred as the ‘Water Convention’, applies as industrial accidents at tailings management facilities may lead to water pollution (UNECE, 2014). Serviced by the United Nations Economic Commission for Europe (UNECE), it started as a regional convention but was opened up to countries outside the UNECE region in 2016. At the time of writing it had 43 parties (UN Treaty Collection, 1992b).
Directive 2006/21/EC on the management of waste from the extractive industries also referred as the Extractive Waste Directive (2006) (European Commission, 2019).
Directive 2012/18/EU on the control of major-accident hazards involving dangerous substances, amending and subsequently repealing Council Directive 96/82/EC Text with EEA relevance also referred as the Seveso III Directive includes in its scope operational tailings disposal facilities, including tailing ponds or dams, containing dangerous substances (European Commission, 2019).
Examples of drivers, outcomes and risk management
Approaches to the handling and storage of tailings can include riverine disposal, submarine disposal, wetland retention, backfilling, dry stacking, and most commonly used – storage behind dammed impoundments – ‘tailing ponds’ or ‘tailing dams’ (Kossoff et al., 2014).
Tailings are usually stored under water to prevent the formation of surface dusts and acid mine drainage (by forestalling oxidation), especially when large amounts of acid-generating pyrite and pyrrhotite are present (Kossoff et al., 2014).
Mine wastes and their storage facilities require particularly careful management for preventing and minimising air, water, and soil contamination. The rate of failure is one in 700 to one in 1750 with a significantly higher failure rate for water-retaining dams – one in 10,000 (David, 2003). Causes of failure include overtopping, poor maintenance, breach following heavy rain, breach following earthquake, foundation failure, and retention wall failure (Kossoff et al., 2014). Furthermore, abandoned mining sites and mining waste storage facilities may contain chemicals and other elements which may be dangerous to human and animal health and to the wider environment.
Effective legal and institutional frameworks for dam safety and environmental protection, implementation and enforcement of relevant laws and safety standards, adequate tailing dam designs based on accurate risk assessments, regular inspections and special monitoring systems are of critical importance for sound tailings management (Centre for Economic Development, Transport and the Environment, 2012).
Application of technology-driven solutions such as remote sensing methods has shown significant development for tailing dam monitoring and early warning systems to prevent their failure. More attention needs to be given to monitoring of the leachate coming out of the ponds/dams.
References
Blowes, D.W., C.J. Ptacek, J.L. Jambor and C.G. Weisener, 2003. The Geochemistry of Acid Mine Drainage. Treatise on Geochemistry 9:612. Accessed 26 November 2019.
Centre for Economic Development, Transport and the Environment, 2012. Dam Safety Guide. Accessed 25 February 2021.
David, C.P., 2003. Heavy metal concentrations in growth bands of corals: a record of mine tailings input through time (Marinduque Island, Philippines). Marine Pollution Bulletin, 46:187-196.
European Commission, 2019. Extractive Waste. Accessed 26 November 2019.
Global Tailings Review, 2019. Establishing an international standard for the safer management of tailings storage facilities. Accessed 26 November 2019.
IAEA, 2004. Environmental Contamination from Uranium Production Facilities and their Remediation. International Atomic Energy Agency (IAEA). Accessed 25 February 2021.
IMO, 2019. Convention on the prevention of marine pollution by dumping of wastes and other matter. International Maritime Organization (IMO). Accessed 26 November 2019.
Jewell, R.J., 1998. An introduction to tailings. In: Case Studies on Tailings Management. International Council on Metals and the Environment, 7-8.
Kossoff, D., W.E. Dubbin, M. Alfredsson, S.J. Edwards, M.G. Macklin and K.A. Hudson-Edwards, 2014. Mine tailings dams: characteristics, failure, environmental impacts, and remediation. Applied Geochemistry, 51:229-245.
UN Treaty Collection, 1992a. Environment: Chapter XXVII. Convention on the transboundary effects of industrial accidents. Accessed 26 November 2019.
UN Treaty Collection, 1992b. Chapter XXVII. Environment: Convention on the protection and use of transboundary watercourses and international lakes. Accessed 26 November 2019.
UNECE, 2014. Safety guidelines and good practices for tailings management facilities. United Nations Economic Commission for Europe (UNECE). Accessed 26 November 2019.
UNEP, 2017. New report urges global action on mining pollution. United Nations Environment Programme (UNEP). Accessed 26 November 2019.