TAILINGS DAMSA Review on Failure Rates, Consequences and Solutions

Vanessa ChappellPhysiology Seminar, 2017

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

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!

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.

Mining Waste

Mining extraction is never 100% efficient, so it is not possible to reclaim all reusable and expended processing reagents and chemicals.

The unrecoverable and uneconomic metals, minerals, chemicals, organics and process water are discharged, normally as slurry, to a final storage area, Tailings Storage Facility (TSF).

Both the physical and chemical characteristics of tailings and their methods of handling and storage are of great and growing concern.

How to Store Tailings

• To help determine the design requirements of a tailings storage facility, the following characteristics of the tailings will need to be established:

• Chemical composition (including changes to chemistry through mineral processing) and its ability to oxidize and mobilize metals

• Physical composition and stability (static and seismic loading)

• Behavior under pressure and consolidation rates

• Erosion stability (wind and water)

• Settling, drying time and densification behavior after deposition (getting rid of the water)

• Hard pan behavior (crust formation on top of the tailings)

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.

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)

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

Failure

Despite improvements on safe design for tailings dams. There has been reported failure almost every year for the past 30 years

How many? How often do they fail?

An estimated 3,500 active tailings impoundments stand around the world

As of 2000 these structures experience known "major" failures of about 2 to 5 annually, along with 35 "minor" failures

This failure rate is more than twice the failure rate of conventional water retention dams.

The records are very incomplete on crucial data elements: design height of dam, design foot print, construction type (upstream, downstream, center line), age,

design life, construction status, ownership status, capacity, release volume, runout, etc

Results of Failure

• The sheer magnitude and often toxic nature of the material held within tailings dams means that their failure, and the ensuing discharge into river systems, will invariably affect water and sediment quality, and aquatic and human life for potentially hundreds of km downstream (Edwards, 1996; Macklin et al., 1996, 2003, 2006; Anonymous, 2000; Hudson-Edwards et al., 2003).

• Records indicate that thousands of people have died from tailings dam failures (WISE, 2012)

Results of Failure

• Over 2000 people lost their lives between 1964-2000 due to tailings dam failures

• Between 2000-2017 tailings dam failures have caused a reported 5000 people to become homeless, 400 dead, 125 missing, 150 injured, and millions affected as a result of water and soil contamination

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

Examples of tailings impoundment failures

Failures and Causes

Design Failure

Upstream construction is one of the earliest construction types and the most common method used.

Cheap

Uses materials on site

Inactive dams are not immune

Overtopping (rain coupled with poor management)

Seismic changes

Common Reason for Active dam Failure

Seepage

Weather

Managemnt

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

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)