1. What is a Tailings Storage Facility (TSF)?
The ore extracted from the mine is transported to the concentrator. Through a mixture of reagents and water, some of the ore is transformed into copper concentrate while the rest becomes slurry waste. The slurry waste cannot be directly disposed into nature for its adverse impact on the ecological balance; therefore, dams are constructed, and tailings cell is built to store the tailings. The term “Tailings Storage Facility” encompasses both the storage cells and the slurry waste. The term “tailings” refers to the slurry waste component within this facility.
2.What are the different types of tailings storage facilities?
There are various types of tailings storage facilities, including ponds formed by dams, and pre-existing ponds, and stored in closed open pit or underground mines. Internationally, building dams are often used as storage methods.
For example, building a dam for tailings storage in a mountainous area using the natural settings of valley fills method is used at Erdenet Mining Corporation.
At the Oyu Tolgoi mine, dams are constructed on flat surfaces, enclosed on all four sides, and tailings are stored within.
3. What type of tailings storage facility is used at Oyu Tolgoi?
Due to its location on flat terrain, the Oyu Tolgoi mine has employed a rectangular surface Tailings Storage Facility (TSF), which is deemed the most suitable method for such geographical features. This facility is designed with a downstream embankment method, aimed at mitigating the risk of structural failure with its thick base and expanding walls. With each side extending two kilometers, this facility is rectangular in shape.
4. How are dams of TSF constructed?
There are three types of tailings dam commonly used:
– Upstream method: Upstream tailings dams are built progressively “upstream” of the starter dam by incorporating tailings materials into the dam for support, it requires less land and is economically less costly. However, it has the highest risk of structure failure.
– Downstream method:
This method involves extending the dam wall outward by thickening the foundation, which requires more construction space and is economically costlier. However, it significantly reduces the risk of dam collapse.
– Centerline method: Dam building is raised vertically, and its construction combines the principles of both downstream and upstream design concepts. It is less economically costly than the downstream method but has higher risk.
5. What other industries use similar storage facilities?
In addition to mining, this type of facility is used by hydropower plants and reservoirs for water storage, thermal and power plants for waste ash storage, and sewage treatment plants for sludge storage.
6. How is the tailings transported to the Tailings Cell?
Only 2% of the transported ore reaching the concentrator turns into copper concentrate, while the remaining 98% is turned into tailings which is then transported to the TSF. The tailings constitute 60% of solid material and is transported to the Tailings cell, 5 kms away from the concentrator through a special pipe.
7. What happens when the tailings cell is full?
When the tailings cell approaches its capacity, the construction of the next cell begins. Similar to this practice, the Oyu Tolgoi mine closed Tailings Cell#1 in 2023, which had been in use since 2013. The mine is prepared to use Tailings Cell #2 and plans to operate it until 2034.
8. What are the risks of TSF?
There are risks associated with structural failure, seepage and dust. The biggest risk is structural failure, which may arise from various factors such as intense rainfall, seismic activity, inadequate engineering calculations, and insufficient monitoring.
The structural failure process begins if the TSF filter cracks. At Oyu Tolgoi, engineers and technicians monitor the TSF every day to see if there are any cracks. If there is one, they continuously monitor and measure it every day. If necessary, they will reconstruct the area to prevent damage.
There is also continuous monitoring during TSF construction and once its ready to operate around 400 monitoring tools are used to monitor for 24 hours. This is done to predict, detect many potential risks, and monitor the risk of dam failure.
The tailings, characterized as a slurry, continually seeps when it interacts with the TSF structure. If there can’t be seepage, the accumulated water increases the pressure on the walls of the dam and increases the risk of dam failure. If the seepage is not monitored there’s risk of it being released into the environment.
Therefore, at Oyu Tolgoi, an 8-12-meter-deep cut-off dyke was built to reduce the base seepage. To prevent seepage from being released into the environment, a collection system is situated beneath and outside the Tailings Cell. The collected seepage is then recycled.
Large amounts of dust can harm human health and the environment. Oyu Tolgoi’s TSF manages its dust through multiple pipelines efficiently disposing of the waste and the area is kept moist to control dust. When the TSF’s operation reaches the end, the land undergoes a closure process, including rehabilitation and covering the waste to prevent dust-related impacts.
9. What TSF standards does Oyu Tolgoi adhere to?
Since 2012, the company adhered to Rio Tinto’s D5 standard, “Management of Tailings and Water Storage Facilities”, which is rooted from the ANCOLD standard. The standard is complied with in all of Rio Tinto’s mines in Australia, Canada, America, etc.
Per the D5 standard, the construction blueprint, construction progress to operations is audited by subject matter experts with 30 years of experience. The audit process is also guided, monitored, and reviewed by experts with 40 years of experience. This extensive monitoring system is designed to reduce the risk of errors.
10. Is there a better standard than the one mentioned above?
In 2021, the world’s major mining industry representatives and investors set a comprehensive standard to reduce the risk of TSF failure and to improve controls known as GISTM /Global Industry Standard Tailings Management/. Oyu Tolgoi is preparing to comply with this standard from 2025. The standard is primarily aimed at monitoring the stability of the TSF and has the advantage of incorporating instructions to increase the participation of residents in the area.
11. What are the reagents contained in the TSF? What is their impact?
The Concentrator Plant at Oyu Tolgoi uses 10 different reagents in its Flotation process as well as to protect transmission pipelines. These reagents are not only used in very low doses but also pass multiple stages to reach the TSF. The reagents do not disseminate in the air and have no properties that accumulate in living organisms.
12. What kind of issues have been encountered at the TSF at Oyu Tolgoi?
Oyu Tolgoi identified seepage within the mine lease and in one bore 60m outside of the mine lease. It was recorded as an environmental incident following Oyu Tolgoi policies and subsequent investigation involving internal and external experts in 2021.
In accordance with the company’s policies and procedures, detailed inspections and procedures were conducted with internal and external experts and measures are being taken.
13. Has the seepage impacted the quality of livestock wells and other water supplies of the local community?
The results of the inspection confirmed that the seepage had not had any adverse effects on the quality of livestock wells and other water supplies. Click here for more information.
14. Do the locals know about the TSF?
Oyu Tolgoi has been communicating and consulting with the relevant stakeholders, including the local community representatives, government agencies, the lender, and independent auditors transparently and openly, including site visits.