Overview of Tailings
Tailings are what remains after mining activities separate the valuable fraction of ore from the uneconomic fraction. Typically composed of fine particles, tailings are often considered a type of waste rock, although they differ significantly from overburden, which is the unprocessed material removed to access the ore.
The composition of tailings can vary greatly, containing a mix of water, fine solids, and a minimal amount of valuable minerals that were not fully extracted during the mining process. They are stored on-site at a mine in tailings dams, ponds, or heaps.
Mining processes crush ore to liberate the valuable components. The undesired part of the ore body is referred to as gangue; this is also found in tailings. After the valuable metals or minerals are extracted, the remaining slurry—a combination of water and finely ground rock—must be dealt with responsibly to minimize environmental impact.
It’s crucial to understand that tailings are not entirely useless. Efforts are ongoing in some sectors to recover residual values from tailings and to utilize them in applications such as construction materials. However, the management and storage of tailings pose significant challenges, due to their potentially hazardous nature and the vast volume that is generated from mining operations.
The monitoring and treatment of tailings are key to avoiding harmful environmental impacts, such as soil and water contamination. This makes the development and application of sustainable tailing management practices essential in modern mining operations.
Mining Processes and Tailings Generation
During the mining process, valuable minerals are extracted from ore, leaving behind a mixture of water, minerals, and other materials known as tailings. These tailings can pose environmental challenges and require careful disposal methods to mitigate potential hazards.
Comminution and Separation
Comminution is the first step in mining where the ore is broken down to separate the valuable minerals from the waste rock. This process typically involves crushing and grinding, followed by separation techniques like flotation or magnetic separation to concentrate the valuable minerals into a smaller volume known as a concentrate. The remaining slurry, a semi-liquid mixture consisting of water and finely ground waste rock, is then ready for the disposal phase.
Tailings Disposal Methods
Once separation is complete, the attention turns to the disposal of the residual materials or tailings. Disposal methods include tailings ponds and tailings dams, which are engineered structures designed to contain the mixture of water and solids safely. Another method employed is submarine tailings disposal, where the tailings are released into deep ocean waters under strict regulations to minimize environmental impact. Occasionally, mine dumps are created from coarser waste rock that has not been processed through comminution, providing another form of waste disposal. These disposal sites are closely monitored to ensure the long-term stability and that environmental harm is minimized.
Environmental and Health Risks
The extraction of valuable minerals from ores generates waste materials known as tailings, which often contain toxic substances posing significant risks to the environment and human health.
Chemical Contaminants and Reactions
Tailings typically contain heavy metals such as lead, cadmium, and mercury, as well as chemicals used in the ore separation process. Arsenic, a potent toxin, is frequently found in these materials. When exposed to the elements, chemical reactions can occur, such as the formation of acid mine drainage. This process happens when sulfide minerals in tailings react with air and water to produce sulfuric acid, which can lead to the contamination of soil and water sources, affecting aquatic wildlife and leading to loss of biodiversity. Radioactive content originating from the host ore can also be present, further endangering ecosystems and human communities.
Tailings Storage and Dam Failures
The storage method for tailings is crucial for mitigating environmental risks. Improperly managed tailings dams can experience dam failures, which have led to environmental disasters. Such failures can cause groundwater leakage and spread toxic emissions, resulting in a range of consequences such as bird death, human rights violations due to displacement, and contamination of soil and water sources. Moreover, the poor handling of these storage sites can lead to the creation of sinkholes, undermining the integrity of landscapes and potentially leading to property damage and loss of life.
Recovery and Management Strategies
Efficient recovery and management strategies for tailings are crucial to reducing environmental impact and recapturing economic value from mining waste. These strategies involve innovative techniques for recycling and utilization, as well as rehabilitation and stabilization of the tailings areas.
Recycling and Utilization
Recycling the materials found in tailings can provide substantial environmental and economic benefits. The recovery of valuable metals remains a significant aspect of this process. For instance, certain tailings materials are repurposed as inputs for cement production or other construction materials. Moreover, fly ash and sulfur can be recycled from tailings, reducing the need for virgin materials and the footprint of mining operations.
Rehabilitation and Stabilization
Rehabilitation efforts focus on stabilizing the tailings sites to prevent environmental degradation. These efforts often include the reshaping of landforms to avoid erosion, covering of tailings with soil or vegetation, and ensuring proper management of water courses. Stabilization of the physical and chemical properties of tailings is paramount to reduce the dispersion of pollutants and to support new ecosystems. Tailings management systems help monitor and maintain the stability and safety of these waste materials over time, aiming to eventually integrate the areas back into the natural environment without risking ecological integrity or public health.
Case Studies and Regulatory Perspectives
This section reviews specific historical events in the mining industry related to tailings mismanagement and outlines how they have shaped current legislation and standards aimed at preventing future incidents.
Historical Incidents
The Mount Polley disaster in 2014 stands as one of the significant environmental disasters in mining history. A breach in the tailings pond sent millions of cubic meters of toxic slurry into nearby waterways, resulting in extensive environmental damage. In Papua New Guinea, the Ok Tedi mine has faced years of criticism for its environmental impact, including sedimentation of rivers and extensive bird death due to tailings disposal that has directly affected the local communities and infringed upon human rights.
Legislation and Standards
Regulatory bodies have since implemented stringent legislation and standards to prevent such incidents. These include requirements for more secure tailings impoundment and systematic monitoring to reduce toxic emissions. There is, however, an UN-level standard that strives for a universal framework in governing tailings, which emphasizes both environmental and human safety. Diverse national regulations, like those informed by the Global Tailings Review, look to mitigate the risk of future environmental disasters by reinforcing robust design and maintenance practices for tailings storage facilities.