tailings dam

File:Bituminous geomembrane installation on a mine tailings storage facility.jpg installation on the base and walls of a tailings storage facility.]]

Unlike water-retention dams, the height of a tailings dam is typically increased (raised) throughout the life of the particular mine. Typically, a base or starter dam is constructed, and as it fills with a mixture of tailings and water, it is raised. Material used to raise the dam can include the tailings (if their properties are suitable), earthfill, or rockfill.{{cite book |last=Blight |first= Geoffrey E. |chapter=Construction of Tailings Dams |title=Case studies on tailings management |year=1998 |publisher=International Council on Metals and the Environment |location=Paris, France |isbn=1-895720-29-X |pages=9–10 |chapter-url=https://books.google.com/books?id=qG9Bux3RYWMC&q=tailings+dam&pg=PA9 | access-date=10 August 2011}} It is increasingly common for barrier systems such as geomembranes to be incorporated into tailings dams. Impermeable barriers can prevent or reduce seepage, thereby increasing the geotechnical and environmental stability of the dam.{{cite report |last1=McLeod|first1=Harvey |last2=Bjelkevik|first2=Annika |date=2021 |title=TAILINGS DAM DESIGN Technology Update |publisher= ICOLD Committee on Tailings Dams|url= https://www.icoldchile.cl/boletines/181.pdf|doi= |page= 91}}

File:The Wheal Jane Tailings Dam - geograph.org.uk - 845826.jpg Tailings Dam, West Cornwall, England]]

There are three types of dam raises, the upstream, downstream and centerline, named according to the relative position of the new crest of the dam to the previous. The specific design used is dependent upon topography, geology, climate, the type of tailings, and cost. An upstream tailings dam consists of trapezoidal embankments being constructed on top, but toe to crest, of another, moving the crest further upstream. This creates a relatively flat downstream side and a jagged upstream side, which is supported by tailings slurry in the impoundment. The downstream design refers to the successive raising of the embankment that positions the fill and crest further downstream. A centerlined dam has sequential embankment dams constructed directly on top of each other while fill is placed on the downstream side for support and slurry supports the upstream side.{{cite web| title=Properties of Tailings Dams| url=http://www.mining.ubc.ca/faculty/meech/MINE290/Tailings%20Dam%20Construction%20Methods.pdf| publisher=NBK Institute of Mining Engineering| access-date=10 August 2011| url-status=dead| archiveurl=https://web.archive.org/web/20111001213037/http://www.mining.ubc.ca/faculty/meech/MINE290/Tailings%20Dam%20Construction%20Methods.pdf| archive-date=1 October 2011}}http://mining.ubc.ca/files/2013/03/Dirk-van-Zyl.pdf{{cite book| editor= Raj K. Singhal| title=Environmental issues and management of waste in energy and mineral production: Proceedings of the Sixth International Conference on Environmental Issues and Management of Waste in Energy and Mineral Production: SWEMP 2000; Calgary, Alberta, Canada, May 30 – June 2, 2000| year=2000| publisher=Balkema| location=Rotterdam| isbn=90-5809-085-X| pages=257–260| url=https://books.google.com/books?id=PqiYy538JFUC&q=tailings+dam&pg=PA257| access-date=9 November 2015}}

Brazil and Chile have banned the construction of upstream dams, deeming them too dangerous, and the fifty or so in the Brazilian state of Minas Gerais will have to be decommissioned by 2035.{{cite news|author=Pierre Cormon| url =https://www.entrepriseromande.ch/web/er/w/les-barrages-miniers-lourd-heritage-environnemental#:~:text=Les%20barrages%20miniers%20sont%20souvent,de%20Los%20Leones%20(Chili).&text=%23M%C3%A9taux%20Les%20r%C3%A9sidus%20de%20l,Des%20accidents%20se%20produisent%20r%C3%A9guli%C3%A8rement.| title = Les barrages miniers, lourd héritage environnemental| last1 =| first1 = | publisher = Fédération des Entreprises Romandes Genève| newspaper = Entreprise romande| date = 4 October 2024| accessdate = 5 December 2024}}

The extraction of economic minerals results in an accumulation of tailings on the surface, mostly in tailings ponds, that occupy a large amount of land.{{Cite journal |last1=Chen |first1=S. |last2=Jin |first2=A. |last3=Zhao |first3=Y. |last4=Wang |first4=J. |year=2023 |title=Formation mechanism and deformation characteristics of stratified cemented tailings backfill under noncontinuous filling system |url=https://linkinghub.elsevier.com/retrieve/pii/S0950061823013363 |journal=Construction and Building Materials |volume=389 |pages=131623 |doi=10.1016/j.conbuildmat.2023.131623 |issn=0950-0618|url-access=subscription }} Stratification is inherent to sedimentation, as the heavier particles settle before the lighter particles. Yet, tailings can also represent an untapped resource, as many tailings contain valuable secondary minerals. These could be recovered, contributing to the circular economy and reducing the need for new mining operations. Analyzing the mineralogy of tailings can reveal the presence of economically valuable minerals, such as rare earth elements or other metal resources. This is particularly important as global demand for these resources continues to grow. A thorough understanding of tailings stratigraphy helps to identify the most promising areas for recovery and informs processing methods that allow mineral recovery to be maximized while minimizing environmental issues.

File:South Africa-Gold mining-tailings-001.jpg

Tailings stratification is the layering of tailings due to the distribution in particle size as well as the difference in specific density. The compactness of the sandy to silty tailings{{Cite journal |last1=Graupner |first1=T. |last2=Kassahun |first2=A. |last3=Rammlmair |first3=D. |last4=Meima |first4=J.a. |last5=Kock |first5=D. |last6=Furche |first6=Markus |last7=F. |first7=Adrian |last8=S. |first8=Axel |last9=Melcher |first9=F. |year=2007 |title=Formation of sequences of cemented layers and hardpans within sulfide-bearing mine tailings (mine district Freiberg, Germany) |url=https://linkinghub.elsevier.com/retrieve/pii/S088329270700203X |journal=Applied Geochemistry |volume=22 |issue=11 |pages=2486–2508 |doi=10.1016/j.apgeochem.2007.07.002 |bibcode=2007ApGC...22.2486G |issn=0883-2927|url-access=subscription }} influences the permeability, which will influence the drainage ability of the tailings and thus the infiltration line.{{Cite journal |last1=Geng |first1=W. |last2=Song |first2=Z. |last3=He |first3=C. |last4=Wang |first4=H. |last5=Dong |first5=X. |year=2024 |title=The Impact of Fine-Layering of Tailings Dam on the Variation Pattern of Infiltration Lines |journal=Applied Sciences |language=en |volume=14 |issue=2 |pages=950 |doi=10.3390/app14020950 |doi-access=free |issn=2076-3417}} The infiltration line is the pathway through which water can enter in a specific area, and it affects the safety and stability of tailings ponds.

Furthermore, the tailings' compactness affects how much water they can hold. This also affects how strong and stiff they get to be. The more compact the tailings are, the smaller the permeability coefficient and the stronger the water-holding capacity. Rather than consisting of a single uniform body, tailings are usually composed of multiple layers of sediment that differ in grain size and mineralogical composition.{{Cite journal |last1=Meima |first1=J. A. |last2=Graupner |first2=T. |last3=Rammlmair |first3=D. |year=2012 |title=Modeling the effect of stratification on cemented layer formation in sulfide-bearing mine tailings |url=https://linkinghub.elsevier.com/retrieve/pii/S0883292711004148 |journal=Applied Geochemistry |volume=27 |issue=1 |pages=124–137 |doi=10.1016/j.apgeochem.2011.09.024 |bibcode=2012ApGC...27..124M |issn=0883-2927|url-access=subscription }} The grain size of tailings can show great fluctuations due to the deposition of larger and finer particles, which influences the tailings stratification and shear strength. When more fine particles settle, it weakens the tailings, which may result in the settled layer holding more water. This could create the saturation line, affecting how safely the tailings storage facility can be operated.

Mineralogical composition in tailings causes the cementation of layers. Sulfide-enriched layers can form protective cemented layers. These layers will usually not form in systems with a homogeneous distribution of iron-bearing sulfide. Therefore, tailings stratification is greatly influenced by the presence of minerals which have a great influence in the cementation of the tailings' layers, by the grain-size distribution which influences the compactness and density of the tailings. However, there are other factors that influence tailings' stratification, such as topography, geological setting, climate, tailings deposition process, and how long the tailings have been stored in the facility.

Carbon mineralization is a natural process that occurs over hundreds or thousands of years, where certain minerals, such as in mine tailings, react with atmospheric carbon dioxide to form solid carbonates. This process effectively sequesters and removes carbon dioxide from the atmosphere. Ultramafic mine tailings, rich in magnesium-bearing minerals such as serpentine, olivine, and brucite, are highly reactive due to their reduced grain size from crushing and have been historically and currently produced in substantial quantities, facilitating carbon mineralization.{{cite journal |last1=Gras |first1=A. |last2=Beaudoin |first2=G. |last3=Molson |first3=J. |last4=Plante |first4=B. |title=Atmospheric carbon sequestration in ultramafic mining residues and impacts on leachate water chemistry at the Dumont Nickel Project, Quebec, Canada |journal=Chemical Geology |date=20 July 2020 |volume=546 |pages=119661 |doi=10.1016/j.chemgeo.2020.119661 |bibcode=2020ChGeo.54619661G |url=https://doi.org/10.1016/j.chemgeo.2020.119661 |issn=0009-2541|url-access=subscription }} Using these tailings for carbon mineralization can reduce the costs associated with the extraction and processing of ultramafic rocks, which is often energy-intensive. The mineralogy of these tailings can vary substantially depending on the commodity being mined.{{cite thesis |last1=Wynands |first1=E. |date=2021 |title=Carbon mineralization in ultramafic mine tailings via CO₂ injection |url=http://hdl.handle.net/2429/79796 |journal=Science, Faculty of; Earth, Ocean and Atmospheric Sciences, Department of |publisher=University of British Columbia |doi=10.14288/1.0402341|hdl=2429/79796 }}

As an example, the Baptiste nickel project in British Columbia, Canada, is known for its potential to mineralize carbon in its tailings. Similarly, the Gahcho Kué diamond mine in the Northwest Territories, Canada, has kimberlite pipes with the potential for carbon mineralization. Tailings from this mine contain a mix of minerals that can facilitate carbon mineralization, contributing to the overall reduction of atmospheric carbon dioxide concentrations. Ultramafic mine tailings are a promising avenue for carbon mineralization, providing both an effective means of carbon sequestration and a way to use waste materials from mining operations.

Secondary mineralization in tailings involves the formation of new minerals from the alteration or weathering of primary minerals found in mine waste. These secondary minerals develop within tailings impoundments due to weathering processes following mining and milling activities. A key factor in this mineralization is the oxidation of sulfide minerals, which alters dissolved species concentrations, porewater pH, and the overall mineralogy. Within the oxidation zone, primary minerals such as sulfides and carbonates are depleted, leading to the formation of secondary minerals. These secondary minerals are critical, as they help to regulate the concentrations of dissolved species in the pore water.{{cite journal |last1=Petrunic |first1=Barbara M. |last2=Al |first2=Tom A. |last3=Weaver |first3=Louise |last4=Hall |first4=Douglas |year=2009 |title=Identification and characterization of secondary minerals formed in tungsten mine tailings using transmission electron microscopy |url=https://doi.org/10.1016/j.apgeochem.2009.09.014 |journal=Applied Geochemistry |volume=24 |issue=12 |pages=2222–2233 |doi=10.1016/j.apgeochem.2009.09.014 |bibcode=2009ApGC...24.2222P |issn=0883-2927|url-access=subscription }}

This study focused on tungsten secondary minerals in tailings generated during a two-year mining operation at the Mount Pleasant Tungsten Mine, approximately {{Convert|60|km}} south of Fredericton, New Brunswick. Initially, the tailings were submerged but were exposed to atmospheric oxygen following a dam failure in 1997. The primary mineralogy of the deposit consists mainly of quartz, topaz, fluorite, micas, clays, chlorite, K-feldspars and opaque minerals including wolframite. While the tailings are not extensively oxidized, certain areas have elevated sulfate and metal concentrations including lower pH values.

Living organisms, particularly microbes, contribute to the formation of minerals through their metabolic activities. Acidophilic chemolithotrophic bacteria like Thiobacillus are vital to mineralization processes and play a critical role in biomineralization processes in mine tailings. Examples are those found at the abandoned Kam Kotia mine near Timmins, Ontario, Canada, which has been inactive for about 30 years{{As of when|date=February 2025}}. These bacteria catalyze the production of toxic, acidic metal leachates that can severely affect natural ecosystems.{{cite journal |last1=Fortin |first1=D. |last2=Davis |first2=B. |last3=Beveridge |first3=T.J. |year=1996 |title=Role of Thiobacillus and sulfate-reducing bacteria in iron biocycling in oxic and acidic mine tailings |url= |journal=FEMS Microbiology Ecology |language=en |volume=21 |issue=1 |pages=11–24 |doi=10.1111/j.1574-6941.1996.tb00329.x}}

Under oxidizing conditions, acidophilic chemolithotrophs oxidize ferrous (Fe (II)) sulfides to produce sulfuric acid and ferric (Fe (III)) iron. These bacteria increase the rate of iron (Fe (II)) oxidation at low pH. Certain species, such as Acidithiobacillus ferrooxidans, can also reduce iron (Fe (III)) in both aerobic and anaerobic environments at very low pH. In addition, sulfate-reducing bacteria (SRB) can indirectly influence the iron cycle in mine tailings by reacting with soluble iron (Fe (II)) to form iron sulfide precipitates. Although sulfate-reducing bacteria (SRB) typically prefer neutral, reducing conditions, they have been found in acid mine drainage environments, indicating potential acid tolerance. Although oxygen generally inhibits their activity, recent{{When|date=February 2025}} studies suggest that sulfate-reducing bacteria (SRB) can remain viable in oxygenated conditions and even engage in aerobic sulfate reduction in well-oxygenated microbial mats.

{{see also|List of largest dams in the world}}

The largest three tailings dams are:

Type: TE – Earth; ER – Rock-fill; PG – Concrete gravity; CFRD – Concrete face rock fill

{{excerpt|Tailings dam failure}}

• Oil sands tailings ponds (Canada)
• Ash pond

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{{commons category|Tailings dams}}

Category:Dams by type