Throughout the mining industry, tailings dams are a requirement for the storage of by-products from operations in the form of liquids and slurries. Depending on the size and operation, there may be one or many tailing storage facilities. Some of them may be located many kilometres from the mine itself.
Typically, tailings dams are designed for permanent storage of varied potentially toxic waste contaminants. With the increasing development of operations, tailings dams are continually increasing in size from different construction processes creating embankments many kilometres in length. Construction methods commonly use compacted earth, and generally one of three methods – upstream, downstream and centreline – determined by the geology of the land, climate, materials used and cost.
The attention of tailings dams has risen in recent times due to the large storage area of toxic materials and failures at numerous locations around the world. One example being, the Brazilian Brumadinho dam disaster, which resulted in over 100 deaths, many more people unaccounted for, and the release of millions of cubic meters of iron waste into the local ecosystem.
Legislation of the monitoring of tailings dams is now more focused due to the heightened spotlight of these failures, and for the protection of the environment and safety of personnel. Mining operators now requires the monitoring of tailings dams, and the feeds into these dams, as a pivotal part of the risk management of daily mining operations.
Monitoring methods of tailings dams
Monitoring of tailings dams can be performed by various methods depending on actual mining operation procedures. Common parameters are slope stability, ground water and level of dam. Capturing these parameters is usually done via data loggers, or dedicated measuring techniques such as piezometers that require the running of cables between sensors and controller.
Due to the large area, the running of cables along the slope of the dams creates problems as they are difficult to maintain, costly and hard to adapt to the changing structures. This creates potential risks in cable integrity and cable failure can also go undetected for periods of time.
The use of data loggers has allowed for reduced cable runs, however, it does not always produce a real-time approach to the collection and processing of data points. Data collection from loggers can be via 3 common methods:
1. Direct connection: dfirectly connecting PC to logger requiring personnel to be removed from current operations. Poses potential safety risk of getting to devices. If a logger is used, provides real-time data collection but not reporting.
2. Short range wireless i.e. Bluetooth: still has requirement of personnel going to device. Provides real-time data collection but not reporting.
3. Remote connection via UHF/ cellular technologies: these methods of connection provide real time-data collection and reporting if required. Distances personnel from risks and provides better workplace efficiency.
Wireless technologies
When it comes to industrial applications with wireless technologies in mind, it is important that the wireless network does not become the weakest link in an already potentially hazardous situation. The following points should be considered:
• Data to be captured and transmitted: size of data frame.
• Distances to be transmitted across: short range – hundreds of metres, long range 10’s of kilometres.
• Future planning: how will the topology look in the future? Dam wall increasing in size, more sensors to interconnect.
• What else is in the immediate vicinity: have you considered the flow rates and possible pipeline leakage of the product being placed into the tailings dam?
• Environmental: automatic weather stations to provide external data that could affect both the stability and levels of tailings dam.
It is not uncommon for tailing dams to have areas of greater than 2 km across and wall heights in excess of 50 m. To be able to effectively provide reliable data, which can be transmitted in real time between sensors located in hard to reach locations is both challenging and requires wireless devices using robust sensitivity and high RF power.
It must be ensured that the correct technology is chosen for a tailings dam application, as it is critical that it be able to operate 24/7/365. Wireless technologies such as Bluetooth, 802.11.15 and WLAN are commonly used for short distances and are typically not suitable for operating in and around tailings dams due to lower RF power, poor propagation and low immunity to noise and interference.
With the emergence of cellular technology, it is not always the case that there is a guarantee of availability in worsening weather conditions, when it is critical to the operation.
LPWAN (low power wide area network) technologies have seen a step increase in use over the past few years. Low power consumption makes it an attractive proposition, however, many of these technologies are either application specific or also require the use of 3rd party hosting/ backbone connectivity. Around many mine sites, this infrastructure may not be present, or costly to implement for the project.
Licenced/licence-free ISM band radios are available around the world. Advantages include high RF power, and excellent receiver sensitivity allow for more reliable communications. Along with Monitoring and Control features inbuilt into the radios allowing action to be taken directly from the radio unit itself. ISM Banded radios can operate over distances of 30km / 18miles also utilising repeater functionality which can be especially useful for the pipeline monitoring that is feeding tailings dams.
Network deployment
As mining businesses expand operations, so the need for tailings dams increases, either by increasing in volume or additional structures built further away. Being able to move and adjust with these changes is as important as finding the initial solution. What often gets overlooked is future communication paths and how the system can grow without becoming the Achilles heel limit to effectiveness.
The monitoring of tailings dams, if not managed properly, could be catastrophic to a company’s reputation due to the high potential of environmental and human safety factors. The simple steps described above ensure wireless monitoring systems can grow with the operation to ensure the timely and accurate delivery of information, regardless of weather, time or other conditions.
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