design of tailing dams

1. Design of Tailing
Dams In Iron And
Uranium Mines
Presented by
ABHISEK MAHALIK
120MN0550
SURFACE MINE
ENVIRONMENTAL ENGINEERING

2. Worldwide Waste Problem
• Disposal of waste in a crowded world is
becoming more and more of a problem
• Even domestic waste in developed
countries presents complicated disposal
issues as we have seen from previous
landfill presentations

3. What are Tailings Dams?
 Mining is the extraction of minerals and
metals from earth. Manganese, tantalum,
cassiterite, copper, tin, nickel, bauxite
(aluminum ore), iron ore, gold, silver, and
diamonds are just some examples of what is
mined.
 Tailings are the waste product of mining and
consists of ground rock and process
effluents that are generated in a mine
processing plant.
 Tailings Dams are among the largest
manmade structures on Earth!

4. Uranium mining and mill tailing
Traditional uranium mining generates fine sandy tailings that contain virtually all the naturally
occurring radioactive elements found in uranium ore. These are collected in engineered tailings
dams and finally covered with a layer of clay and rock to inhibit the leakage of radon gas and
ensure their long-term stability. Over the short term, the tailings material often is covered with
water. After a few months, the tailings material contains about 75% of the radioactivity of the
original ore; these are not classified as radioactive wastes. Uranium tailings are waste by-product
materials left over from processing uranium-bearing ore. Uranium mill tailings also contain heavy
metals, such as lead and arsenic. Large mounds of uranium mill tailings have been left at many old
mining sites, and so remain a potential radiological and toxic metal hazard mainly due to the
solubilization of 226Ra, As, and Pb from ore minerals

5. Mining Waste
• Due to the nature of mining and mineral
processing the volumes of wastes from
mining operations are significantly larger
than BOTH domestic and industrial
wastes.
• Around the banks of a tailing lake in
China - seven square miles of toxic
waste shows the extent of this industry's
impact.
• 9,600 to 12,000 cubic meters of waste
gas—containing dust concentrate,
hydrofluoric acid, sulfur dioxide, and
sulfuric acid—are released with every
ton of rare metals that are mined.
• Approximately 75 cubic meters of acidic
wastewater, plus about a ton of
radioactive waste residue are also
produced.
*Vegetation appears red, grassland light is brown,
rocks are black, and water surfaces are green.

6. Structure of Tailings Dams
 Tailings Dams must provide safe and permanent storage of tailings material. This is
achieved by designing tailings embankments to withstand any potential catastrophic
event – such as an earthquake or flood – and by controlling the seepage of tailings
water.
 Unlike water dams, tailings embankments are made of rock and sand, and have a
very wide base. As the volume of tailings material contained in the storage area
grows, so must the height of the tailings embankment and the elevation of the
tailings pipeline.
 Another concern for tailings management relates to the dispersal of tailings dust.
This dispersal can be prevented by keeping the tailings material saturated at all
times.

7. Factors affecting Tailings Dam Stability
 Foundation stability
 Height and angle of outer slope
 Rate of disposition and detailed properties of tailings
 Seismic influences
 Control of hydrology (drainage system)

8. Basic Designs for Tailings Dams
A. Downstream
• successive raising of the embankment
that positions the fill and crest further
downstream.
B. Centerline
• tailings from the embankment crest form
a beach behind the dam wall. When
subsequent raising is required, material
is placed on both the tailings and the
existing embankment.
C. Upstream
• starts with a pervious (free draining)
starter dyke foundation. The tailings are
usually discharged from the top of the
dam crest creating a beach that becomes
the foundation for future embankment
raises

9. Flambeau impoundment
Figure 16.8 shows a generalized representation of water gain and loss at a tailings impoundment
(Down and Stocks, 1977b). With the exception of precipitation and evaporation, the rates and
volumes of the water can be controlled to a large extent. It is more satisfactory to attempt to
prevent the contamination of natural waters rather than to treat them afterwards, and if surface run-
off to the dam is substantial, then interception ditches should be installed. It is difficult to quantify
the amount of water lost to groundwater, but this can be minimized by selecting a site with
impervious foundations, or by sealing with an artificial layer of clay.
Figure 16.7. Flambeau impoundment

10. The tailings are often treated with lime to neutralize acids and precipitate heavy metals as insoluble
hydroxides before pumping to the dam. Such treated tailings may be thickened, and the overflow,
free of heavy metals, returned to the mill (Figure 16.9), thus reducing the water and pollutant input
to the tailings dam.
Assuming good control of the above inputs and outputs of dam water, the most important factor in
achieving pollution control is the method used to remove surplus water from the dam. Decant
facilities are required on all dams to allow excess free water to be removed. Inadequate decant
design has caused major dam failures.
Figure 16.9. Treatment of tailings with lime

11. Environmental impacts associated with tailings dam failures
Other than the possible heavy loss of life and economic losses, environmental damaging impacts associated with
structural failures in dams include:
• damage or destruction of valuable habitats and ecosystems;
• release of effluent from an impoundment may contaminate surface water
• generation and release of acid mine drainage may occur
• seepage of effluent throughout the base of the structure may contaminate groundwater
• dried tailings may be swept as dust by strong winds into neighboring habitations or ecosystems
• effluent in tailings impoundments may generate toxic gases that may poison birds attracted by water in dry
regions

12. Failures and Causes

13. Timely Remedial Action
• Timely action when warning signs first
appear can prevent costly and
sometimes fatal consequences
• Responsibility is left to the owner or
operator of the dam but there is no
substitute for a competent engineer in
the construction process
• Regular inspection is a must

14. Conclusion
 There was a lack of design ability, poor construction, poo operation/closur o a
combination in each and every case history
 If basic design and construction requirements are ignore a tailings dams opportunity
as a FAILURE is imminent
Quotes from dam operators after failures:
“A well intentioned corporation employing apparently well-qualified consultants I not adequate
insurance against serious incidents.” (Morgentsern, 1998 after the Spain Dam Failure.)
“Any attempt at construction o a tailings dam that does no ake into account the design-construct
process is in my opinion doomed to great distress.” (D’Appolonia, 1976, after the Virginia disaster)