PROPERTIES OF TAILINGS DAMS
(last updated 30 Sep 2003)
> See also Tailings Dam Safety
What are tailings?
Tailings are the residue of the milling process that is used to extract metals of interest from mined ores. During this process, ores are first milled and finely ground, and then treated in a hydrometallurgical plant. Since the extracted metal represents only a small percentage of the whole ore mass, the vast majority of the material mined ends up as a fine slurry.
The tailings contain all other constituents of the ore but the extracted metal, among them heavy metals and other toxic substances. Moreover, the tailings also contain the chemicals added during the milling process. In addition, as a result of the milling process, all these contaminants now are much better available for dispersion into the environment than in the original ore. And, the mechanical stability of the tailings mass is very poor, due to its small grain size and the usually high water contents.
Most of the mill tailings mass produced worldwide is dumped in large surface impoundments ("tailings dams"). The embankments forming these impoundments are earthfill dams. Although water-retention type dams would be very suitable for tailings dams, they are not used for their high cost.
Other than water-retention type dams, tailings dams usually are not constructed initially to completion, but raised sequentially as the impoundment fills.
Upstream-type embankments are the most popular embankments for tailings dams; new parts of the embankment are built on top of the slurries impounded during the previous stage - the dam crest thus moving "upstream".
(Click image to view animation of sequential raising of upstream tailings dam )
For its low cost, the upstream embankment type is used with most tailings dams worldwide, but it bears the highest risk. Dam stability is of particular concern with this type of tailings embankments:
(see also Tailings Dam Safety)
- The phreatic surface is critical for the dam stability. Dam failure can occur, if the beach width between the decant pond and the dam crest becomes too small - from flood inflow, or from improper mill operation, for example. While the determination of phreatic surface location is so important for upstream-type embankments, it is more complex by far for this embankment type than for any other type of tailings-retention structure.
kL = permeability at the edge of the ponded water at the slimes zone
k0 = permeability at the spigot point (dam crest)
kF = permeability of foundation
kh / kv = anisotropy ratio (horizontal vs. vertical)
- Upstream dams are particularly susceptible to liquefaction under severe seismic ground motion. This motion may result from earthquakes, from nearby mine blasting, or even from nearby motion of heavy equipment, for example.
- Upstream dam stability is endangered if the raising rate of the dam is too high. Raising rates greater than 15 m/yr can be hazardous. They can produce excess pore pressure within the deposit, decreasing stability.
Comparison of Surface Impoundment Embankment Types
|Mill Tailings Requirements||Suitable for any type of tailings||At least 40-60% sand in whole tailings. Low pulp density desirable to promote grain-size segregation||Suitable for any type of tailings||Sands or low-plasticity slimes|
|Discharge Requirements||Any discharge procedure suitable||Peripheral discharge and well-controlled beach necessary||Varies according to design details||Peripheral discharge of at least nominal beach necessary|
|Water Storage Suitability||Good||Not suitable for significant water storage||Good||Not recommended for permanent storage. Temporary flood storage acceptable with proper design|
|Seismic Resistance||Good||Poor in high seismic areas||Good||Acceptable|
|Raising Rate Restrictions||Entire embankment constructed initially||Less than 4.5 - 9 m/yr most desirable. Greater than 15 m/yr can be hazardous||None||Height restrictions for individual raises may apply|
|Embankment Fill Requirements||Natural soil borrow||Natural soil, sand tailings, or mine waste||Sand tailings or mine waste if production rates are sufficient, or natural soil||Sand tailings or mine waste if production rates are sufficient, or natural soil|
|Relative Embankment Cost||High||Low||High||Moderate|
- Planning, Design, and Analysis of Tailings
Dams, by Steven G.Vick, John Wiley & Sons , New
York, 1983, 369 p., ISBN 0-471-89829-5
[the textbook on the issue !]
A reprint was published in 1990 by BiTech Publishers Ltd. , Richmond B.C., Canada (ISBN 0-921095-12-0)
- Technical Report: Design and Evaluation of Tailings
Dams, U.S.EPA Office of Solid Waste, EPA/530-R-94-038,
NTIS/PB94-201845, August 1994, 69 p. [Provides an overview
of the various methods used to dispose of mine tailings and the
types of impoundments that are used. Describes the basic
concepts used in the design of impoundments, including a number
of site-specific variables of concern. Report also discusses
tailings embankment and stability and briefly discusses water
management in tailings impoundments. Includes a case study on a
lined tailings impoundment. The report relies heavily on Steven
G.Vick's book (see above). Watch out: Figures 8-11 are mixed
Order address: National Technical Information
Also available for Download (307k PDF).
- Seminar on SAFE TAILINGS DAM CONSTRUCTIONS,
Gällivare, 20-21 September 2001, Technical Papers.
Swedish Mining Association, Naturvårdsverket, EUROPEAN COMMISSION
> Download full text (800k PDF) of selected papers
- Proceedings of the Workshop on Risk Assessment and Contingency Planning in the Management of Mine Tailings, Buenos Aires, Argentina November 5-6, 1998. ICMM ,
Ottawa, Ont., 1998, 314 p.
> Download full report (ZIP archive containing PDF file)
- Proceedings of the International Workshop on
Managing the Risks of Tailings Disposal, Stockholm,
Sweden, May 22-23, 1997. ICMM ,
Ottawa, Ont., 1997, 264 p.
> Download full report (ZIP archive containing PDF file)
- Dynamic safety of earth and rockfill dams.
Proceedings of a course, New Delhi, 16-20 August 1993. by
T.Ohmachi, J.Kuwano (Eds.), A.A. Balkema, Rotterdam 1994, 160 p.
- International Symposium on Safety and Rehabilitation
of Tailings Dams, (Sydney) 23 May 1990, Vol.1:
Presented Papers. International Commission on
Large Dams, Australian National Committee
on Large Dams (Eds.), Sydney 1990, 339 p.
- Upstream constructed tailings dams - A review of the basics, by M.P.Davies and T.E.Martin, In: Tailings and Mine Waste '00, Proceedings of the Seventh International Conference on Tailings and Mine Waste '00, Fort Collins, Colorado, USA, 23-26 January 2000, ISBN 90 5809 126 0, Rotterdam/Brookfield 2000, p. 3-15
- Some considerations in the stability analysis of upstream tailings dams, by T.E.Martin and E.C.McRoberts, In: Tailings and Mine Waste '99, Proceedings of the Sixth International Conference on Tailings and Mine Waste '99, Fort Collins, Colorado, USA, 24-27 January 1999, ISBN 90 5809 025 6, Rotterdam/Brookfield 1999, p. 287-302
- Regulatory and technical tailings design
considerations in Chile, by Alan J. Krause. In:
Tailings and Mine Waste '97, Proceedings of the Fourth
International Conference on Tailings and Mine Waste '97, Fort
Collins, Colorado, USA, 13-17 January 1997, ISBN 90 5410 857 6,
Rotterdam/Brookfield 1997, p.51-55
- Dam-break studies for mine tailings
impoundments, by Jey K.Jeyapalan. In: Geotechnical
Engineering Program, Civil Engineering Department, Colorado
State University (Ed.), Uranium Mill Tailings Management.
Proceedings of the Fifth Symposium, December 9-10, 1982, Fort
Collins, Colorado 1982, p.39-53
- Earthquake effects on uranium mill tailings
impoundments, by W.A.Charlie, R.E.Wardwell. In:
Geotechnical Engineering Program, Civil Engineering Department,
Colorado State University (Ed.), Uranium Mill Tailings
Management. Proceedings of a Symposium, November 20,21, 1978
Vol.II, Fort Collins, Colorado 1978, p.69-85
- Critical parameters for tailings
embankments, by G.B.Baecher, W.A.Marr, J.S.Lin,
J.A.Consla. U.S. Bureau of Mines (Ed.), BUMINES-OFR-135-83, 1983
- Seismic Hazard Analysis of Title II Reclamation
Plans, by D. Bernreuter, E. McDermott, and J. Wagoner;
Report prepared by Lawrence
Livermore National Laboratory for the U.S. Nuclear
Regulatory Commission, UCRL-ID-121733, 1995, 145 p.
- Recommendations Regarding Seismic Design Standards
for Uranium Mill Tailings Sites in Wyoming, by James C.
Case, Hazards Report 96-1,
State Geological Survey , Laramie, Wyoming, February 28,
(32k - WMA)
- Mine and Industrial Tailings Dams and Dumps -
Bibliography, Bulletin 44a, International Commission on Large Dams, 1982-
1989; 290 pages.
- Tailings Dams Safety - Guidelines, Bulletin
74, International Commission on Large Dams,
1989; 108 pages bilingual (French/English).
[The Bulletin examines the safety aspects relating
specifically to tailings dams in terms of design, construction,
operation and rehabilitation, which are different and usually
more complex problems than those encountered in connection with
more conventional dams. The 2 appendices deal with environmental
safety and recommended legal requirements applicable to this
type of structure]
- Tailings Dams - Design of drainage,
Bulletin 97, International Commission on Large
Dams, 1994; 120 pages bilingual (French/English).
- Tailings Dams and Seismicity: Review and
Recommendations, Bulletin 98, International Commission on Large Dams, 1995;
60 pages bilingual (French/English).
[By ICOLD's account, almost two hundred tailings dams
"have failed during earthquakes, releasing liquefied
lagoons of tailings that have caused serious damage and loss of
life... Tailings dams are very susceptible to earthquake
This brochure, in French and English, explores the reasons for
these failures and puts forth solutions for strengthening
current dams and building more stable dams. The main aspects
covered in the bulletin are: "Seismic performance of
tailings dams; seismicity assessment; geotechnical evaluation;
design and construction of tailings dam; seismic stability
analysis; and remedial measures to improve the safety of
existing tailings dams."]
- Tailings Dams. Transport, Placement, Decantation -
Review and Recommendations, Bulletin 101, International Commission on Large Dams, 1995,
- Tailings Dams and Environment: Review and
Recommendations, Bulletin 103, International Commission on Large Dams, Paris
1996, 103 pages
- A guide to tailings dams and impoundments: design,
construction, use and rehabilitation, Bulletin 106, International Commission on Large Dams, Paris,
1996, 239 p.
> Download full report (PDF)
- Design, Construction, and Inspection of Embankment Retention Systems for Uranium Mills, Regulatory Guide 3.11, U.S. NRC, Dec. 1977, 10 p.
Full text available through ADAMS , Accession No. ML003740223 (1M TIFF)
- Operational Inspection and Surveillance of Embankment Retention Systems for Uranium Mill Tailings, Regulatory Guide 3.11.1, U.S. NRC, Oct. 1980, 8 p.
Full text available through ADAMS , Accession No. ML003740229 (0.6M TIFF)
- UNEP MRF - Mining and Environment - Technical Issues: Tailings
- InfoMine TailingsMine
> see also bibliography on Decommissioning & Tailings Management !