Could tailings dam failures, and their subsequent fallout, be completely avoided?
Tailings Dam Failure
There’s been more than 220 tailings dam failures in the last 55 years resulting in 2,033 known deaths and an immense impact on wildlife, water supplies and the environment.
A tailings pond, the wet storage area for processing tailings that allows them to be continuously submerged, contains finely ground rock particles and chemicals used to extract the valuable mineral or oil being processed. These are essentially the excess of the mineral or oil which cannot or have not been extracted as part of the standard processing.
The Impact of Tailings Dam Failures
Tailings ponds are used globally for the storage of mining byproducts. Damage to tailings ponds can cause them to release large volumes of their toxic contents into the environment.
In some cases, tailings dams fail due to sinkholes and earthquakes. In many cases, failure is purely do to the volume of waste and the pace of production. Essentially, the dams are overfilled.
Tailings ponds can also leak gradually. A Canadian federal study released in early 2014 found evidence that strongly suggested that the contents of Alberta’s tailings ponds are seeping into the Athabasca River. The study found oilsands compounds with chemical signatures matching the tailings ponds in upward flowing groundwater less than a metre below the river.
The mining and processing byproducts collected in tailings dams are not part of the aerobic ecological systems, and are unstable. They may damage the environment by releasing toxic metals (arsenic and mercury among others), by acid drainage (usually by microbial action on sulfide ores), or by damaging aquatic wildlife that rely on clear water.
Tailings ponds can also be a source of acid drainage, leading to the need for permanent monitoring and treatment of water passing through the tailings dam. For instance in 1994 the operators of the Olympic Dam mine, Western Mining Corporation, admitted that their uranium tailings containment had released of up to 5 million m3 of contaminated water into the subsoil. The cost of mine cleanup has typically been 10 times that of mining industry estimates when acid drainage was involved.
SAMARCO TAILINGS DAM FAILURE 2015
Why do tailings dam fail?
Simply put, the more efficient the processing of minerals and oil are, the less tailings there will be. Less waste results in a smaller volume of tailings to manage and less burden on the tailings dams.
Traditional measurement of mineral processing is via a nuclear density gauge, which is notoriously inefficient. Nuclear density meters do not have a real time measurement, the response time can be ten minutes and in some cases even longer. This is not useful for understanding the composition of a slurry. In addition to having a long reaction time, nuclear density gauges have a less than ideal accuracy. In some cases, the accuracy has been below 80% and gets even worse with increased percentages of solids. Nuclear density meters also irradiate the slurry as it is being measured. This has its own ecological concerns and can raise the already high cost of disposal.
Beyond this, nuclear density gauges are also cloaked in red tape. Multiple levels of paperwork are required for maintenance, use and disposal. Fees tied to the paperwork add up just as quickly. Nuclear density meters required full time supervision and are restricted to one location. In some instances, two mile detours have been used so that the nuclear density meter does not have to be used. This two mile detour adds both error and delay into the system; neither of which are ideal for understanding how the slurry is composed.
This combination of inefficient and environmentally dangerous measurement of the slurry means on average, 20% of the usable mineral is being disposed as waste. Not only are processors throwing these valuable minerals away, they then have to pay to store and dispose of them in tailings ponds. When the tailings dams fail, they have to pay up substantially more for the repercussions of the failure.
How can tailings dam failures be avoided?
A Red Meters non-nuclear density measurement system is the preferred method to measure the density of a slurry with an accuracy greater than 99%. The increased accuracy of the RM system is due to the fact that it measures the entire volume of the pipeline and not just a small sample. An RM system also works in real time; there is no delay between when the measurement is taken and when the reading is available. This allows for instantaneous information to be available to the operator. Knowing the exact composition of the tailings allows for better decision making in regards to impoundment management and dewatering processes.
- Chronology of major tailings dam failures (last updated 22 Sep 2016) http://www.wise-uranium.org/mdaf.html
- Tailings Dam Casualties https://en.wikipedia.org/wiki/Tailings_dam#Casualties
- Profiling Oil Sands Mixtures from Industrial Developments and Natural Groundwaters for Source Identification http://pubs.acs.org/doi/abs/10.1021/es500131k
- Environmental Aspects of Uranium Mining http://www.world-nuclear.org/information-library/nuclear-fuel-cycle/mining-of-uranium/environmental-aspects-of-uranium-mining.aspx