Mine Water Pollution: Understanding The Toxic Truth

Water is essential to life on Earth, and human activities such as mining threaten the water sources that we all depend on. Mining affects freshwater sources through its heavy use of water in processing ore, and through water pollution from discharged mine effluent and seepage from tailings and waste rock impoundments. Water pollution from mine waste rock and tailings may need to be managed for decades, if not centuries, after a mine has closed. There are four main types of mining impacts on water quality: acid mine drainage, heavy metal contamination and leaching, processing chemicals pollution, and erosion and sedimentation.

Acid mine drainage

AMD forms when sulfides in rocks are exposed to air and water, creating sulphuric acid. This acid then leaches from the rock and is carried off the mine site by rainwater or surface drainage, which is then deposited into nearby streams, rivers, lakes, and groundwater. The acid will continue to be produced as long as its source rock is exposed to air and water, and until the sulphides are leached out – a process that can last hundreds, or even thousands, of years.

AMD severely degrades water quality and can kill aquatic life, making water virtually unusable. It can also cause contaminated drinking water, disrupt the growth and reproduction of aquatic plants and animals, and corrode infrastructure such as bridges. The acid runoff further dissolves heavy metals such as copper, lead, mercury, arsenic, cobalt, cadmium, silver, and zinc into groundwater or surface water.

The rate and degree to which AMD proceeds can be increased by the action of certain bacteria, which accelerate the oxidation and acidification processes, leaching even more trace metals from the wastes. Colonies of bacteria and archaea, called extremophiles, occur naturally in the rock and greatly accelerate the decomposition of metal ions. These microbes thrive in waters with pH very close to zero and favour the low pH levels of abandoned mines.

Heavy metal contamination

Heavy metal pollution in water is caused by the leaching of metals, such as arsenic, cobalt, copper, cadmium, lead, silver, and zinc, from excavated rock or exposed underground mines. These metals are then carried downstream as water washes over the rock surface. While metals can become mobile under neutral pH conditions, their leaching is accelerated under low pH conditions, such as those created by acid mine drainage.

Acid mine drainage (AMD) occurs when large quantities of rock containing sulphide minerals are excavated and exposed to air and water, creating sulphuric acid. This acid then leaches heavy metals from the rock, and the resulting fluids may be highly toxic. When mixed with groundwater, surface water, and soil, they can have harmful effects on humans, animals, and plants.

The impact of heavy metal contamination from mining activities can be seen in the Tsolum River on Vancouver Island. After a small open-pit copper mine was abandoned in 1966, the river experienced toxic levels of acid mine drainage, leading to a decline in salmon and trout populations. This example illustrates the long-term environmental and ecological consequences of heavy metal contamination from mining activities.

To address heavy metal contamination in water, various physicochemical and biological methods can be employed. Physicochemical methods, such as reverse osmosis, chemical precipitation, and membrane filtration, are commonly used but are often costly and generate large amounts of secondary pollutants. On the other hand, biological methods, such as biosorption, bioaccumulation, bioreduction, phytoremediation, and mycoremediation, offer more cost-effective and eco-friendly alternatives. These methods utilise living organisms and materials, such as fungi, algae, bacteria, and plant-based biomass, to remove heavy metals from water.

Processing chemicals pollution

Water is essential to the mining industry. It is used in mineral processing to recover valuable metals from ore. However, using water in this way causes mineral contaminants and other solids to accumulate in the process water supply, leading to contaminated mining wastewater. This contaminated water cannot be reused or returned to the environment without treatment due to community health concerns and environmental regulations.

The process of extracting valuable metals from ore involves crushing the ore into finely ground tailings. The finely ground tailings are then processed with various chemicals to extract the final product. This process creates what is known as mining-influenced water (MIW), which is defined as any water that has been chemically affected by mining or mineral processing.

One of the biggest issues with MIW is processing chemicals pollution. This type of pollution occurs when chemical agents used in the extraction process spill, leak, or leach into nearby water bodies. These chemical agents, such as cyanide or sulphuric acid, can be highly toxic to humans and wildlife.

To address the issue of processing chemicals pollution, mining operations need to treat their wastewater on-site using chemicals and filtration methods. This involves restoring optimal pH levels to the water, using coagulants and flocculants to combine small metal particles and suspended solids into larger clumps, and then removing these clumps through mechanical filtration. By treating their wastewater on-site, mining operations can achieve significant cost savings, maintain full control of the treatment process, reuse the treated water, and maximize water recovery.

Erosion and sedimentation

The process of erosion involves the weathering of rock material into particles or fragments, which are then transported by water, wind, glaciers, and even plant and animal activities. In the context of water pollution, fluvial sediment refers to erosion caused primarily by water. Human activities, such as mining, can accelerate erosion rates compared to natural or geologic erosion, which occurs slowly over centuries or millennia.

During mining operations, the exposure of bare soil and the alteration of landscapes can result in increased sedimentation. Without adequate prevention and control strategies, erosion of exposed earth can carry substantial amounts of sediment into streams, rivers, and lakes. This excessive sedimentation can have several negative consequences:

• Clogging of riverbeds: Sediment can accumulate in riverbeds, reducing water depth and making navigation difficult or impossible.
• Smothering of vegetation and wildlife habitats: High concentrations of suspended sediment can smother watershed vegetation, wildlife habitats, and aquatic organisms.
• Disruption of fish populations: Sediment in the water can decrease light penetration, irritate fish gills, destroy protective mucus, increase water temperature, and bury fish eggs, all of which can lead to reduced fish survival and population decline.
• Contaminant transport: Sediment particles can absorb and transport toxic chemicals, including agricultural and industrial compounds, into water bodies. When these sediments are dredged, the released contaminants can endanger the health of aquatic life and water users.

To mitigate the impacts of erosion and sedimentation, several strategies can be implemented:

• Best practices and regulations: Strict regulations and the adoption of best practices in mining operations can help minimize erosion. This includes land reclamation, erosion control measures, and adherence to environmental impact assessments.
• Sediment control structures: Installing sediment ponds, silt fences, sediment basins, and retention ponds can capture and settle sediments before they enter water bodies, allowing for the release of cleaner water.
• Vegetation restoration: Reestablishing native plant species in mined areas can stabilize soils, prevent erosion, and restore ecological functions.
• Water management: Proper water management practices, such as the collection and treatment of runoff water, can minimize erosion and reduce the release of contaminants into nearby water bodies.
• Community engagement: Engaging with local communities, stakeholders, and environmental organizations can promote responsible mining practices, foster accountability, and encourage sustainable practices.

By implementing these strategies, it is possible to reduce the negative impacts of mining on erosion and sedimentation, promoting more sustainable mining practices that balance resource extraction with environmental protection.

Depletion of water supplies

Mining can deplete surface and groundwater supplies in several ways. Firstly, groundwater depletion is caused by excessive groundwater pumping, which lowers the water table and can cause wells to no longer reach groundwater. As the water table lowers, the water must be pumped further, increasing costs and energy usage. This can also lead to reduced surface water supplies, as groundwater and surface water are connected.

Secondly, mining processes require significant amounts of water for separating minerals, cooling machinery, and controlling dust. This heavy water usage can strain local water supplies, particularly in areas already facing high water stress. For example, lithium extraction in South America's "lithium triangle" uses up to half a million gallons of brine water to extract one ton of lithium. This has led to salinization of freshwater and depleted water supplies for local communities.

Thirdly, mining activities can cause land subsidence, which occurs when there is a loss of support below ground due to the overuse of groundwater. This can lead to soil collapse, compaction, and dropping, causing further disruptions to water supplies.

Finally, mining can also contaminate water supplies, making them unusable. Acid mine drainage, heavy metal contamination, chemical pollution, and erosion and sedimentation from mining activities can all render water supplies unusable for human consumption, agriculture, and industrial purposes.

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