Mining's Water Pollution: Understanding The Environmental Impact

Water is essential to life, and so it is crucial to ensure that our streams, rivers, lakes and oceans remain uncontaminated. However, human activities such as mining threaten our water sources. Water has been called mining's most common casualty as it is used in processing ore and is often polluted by discharged mine effluent and seepage from tailings and waste rock impoundments. Mining can cause water pollution in several ways, including acid mine drainage, heavy metal contamination and leaching, processing chemical pollution, and erosion and sedimentation. These issues can have severe effects on both the environment and human health, and the clean-up costs can be significant. While there have been improvements in mining practices, more needs to be done to protect our water resources.

Acid Mine Drainage

AMD has devastating effects on rivers, streams, and aquatic life. It can kill aquatic life and make water virtually unusable. It can also contaminate drinking water, disrupt the growth and reproduction of aquatic plants and animals, and corrode infrastructure such as bridges. The effects of AMD can last indefinitely, long after mining has ended.

The rate and degree of AMD 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 thrive in the low pH levels of abandoned mines.

AMD is a significant problem in many parts of the world, including the United States, Canada, the United Kingdom, South Africa, Ireland, Spain, Germany, Australia, New Zealand, and Indonesia. The cost of correcting AMD-related problems can be substantial. For example, in West Virginia's Appalachian region, the cost of addressing acidic mine drainage issues is estimated at $5-$15 billion with currently available technology.

Prevention is key to mitigating the environmental impacts of AMD. Some treatment methods for AMD include neutralization with calcium carbonate, lime, or calcium silicate, ion exchange processes, and constructed wetlands.

Heavy Metal Contamination

The proliferation of heavy metal ions, which possess toxic properties, in water bodies has become a significant global concern in recent years, owing to the exponential growth in industrialization, urbanization, and the utilization of chemical compounds in various industries. These substances can have far-reaching and detrimental effects on both the environment and living organisms and are therefore a significant concern for environmental protection.

Water contamination by these metals has become a major concern due to the accumulation of heavy metals in organisms, which pose a threat to human beings. The removal of heavy metals from wastewater has been achieved effectively through various treatment technologies, including physical adsorption using biochar, ion-exchange using zeolite, and the Advanced Oxidation Processes (AOPs).

The following paragraphs discuss the sources, toxicity, and recent advancements in the utilization of biochar-based adsorption, zeolite ion-exchange, and AOPs for the removal of heavy metals from wastewater.

Sources of Heavy Metal Pollution

The primary source of heavy metal contamination in the environment has been determined to be the exponential increase in human population, the proliferation of industrialization, and the expansion of agricultural activities. Heavy metal pollution in the aquatic environment is on the rise due to industrialization, climate change, and urbanization. Sources of pollution include mining waste, landfill leachates, municipal and industrial wastewater, urban runoff, and natural phenomena such as volcanic eruptions, weathering, and rock abrasion.

Toxicity and Effects of Heavy Metals

Heavy metals, unlike organic pollutants, are not biodegradable and tend to accumulate in living organisms when they are released into the environment, which can negatively impact the health of all forms of life, including humans, animals, and plants. Heavy metals can enter the human body through various routes such as absorption, skin contact, and inhalation, resulting in a range of health issues from mild to severe, including loose intestines, anxiety, lung disease, fatigue, kidney problems, stomach issues, skin infections, neurological issues, and malignant growth.

Recent Advancements in Heavy Metal Removal

The utilization of natural zeolites as ion exchangers has been found to be effective in removing heavy metals such as copper, cadmium, and lead from wastewater due to their high selectivity, high cation exchange capacity, and low cost. Similarly, the use of biomass-derived biochar as an adsorbent has gained significant attention in recent years due to its low cost, abundant availability, and high adsorption capacity for heavy metal ions. AOPs such as Fenton, photo-Fenton, and electro-Fenton have also been shown to be effective in removing heavy metal complexes from wastewater due to their ability to generate highly reactive oxidizing species, which can degrade complex organic pollutants and release free heavy metal ions that can be eliminated using conventional treatment methods.

Processing Chemicals Pollution

The chemicals used in mining and mineral processing include cyanide, sulfuric acid, and solvents for separating minerals from ore. Cyanide, for example, is used to separate gold from ore. In its pure form, it has no colour and smells like bitter almonds. An amount the size of a grain of rice is enough to kill a human. It often spills into waterways during gold mining, and when ponds filled with mine waste burst. Even when cyanide is no longer harmful to humans, it leaves behind other harmful chemicals.

The Canadian mineral industry generates one million tonnes of waste rock and 950,000 tonnes of tailings per day, totalling 650 million tonnes of waste per year. Waste rock, which often contains acid-generating sulphides, heavy metals, and other contaminants, is usually stored above ground in large free-draining piles. In other regions of North America, tailings also represent a major source of heavy metals contamination of waterways.

In gold mining, mercury is mixed with ores dug from the ground or stream beds to form an amalgam. The burning of the amalgam leads to the vaporisation of the elemental mercury into a toxic plume, leaving the gold behind. Mercury is also released into the environment as a result of the reprocessing of some old gold tailings dumps. Mercury can be inhaled during the mining and roasting processes and remains suspended in the air due to its volatile nature.

Erosion and Sedimentation

The increased sediment load in these water bodies can have several detrimental effects. Firstly, excessive sediment can clog riverbeds and smother vegetation, wildlife habitats, and aquatic organisms. It can also decrease water depth, making navigation difficult or impossible. Secondly, suspended sediment in the water can irritate the gills of fish, destroy the protective mucus covering their eyes and scales, and increase water temperatures by absorbing warmth from the sun. These factors can cause stress and even lead to the death of fish. In addition, high concentrations of suspended sediment can dislodge plants, invertebrates, and insects in stream beds, reducing the food source for fish and resulting in smaller and fewer fish. Furthermore, settling sediments can bury and suffocate fish eggs, and the sediment particles can carry toxic agricultural and industrial compounds, endangering the health of aquatic life.

The impact of erosion and sedimentation caused by mining activities extends beyond the immediate environment. The contamination can spread downstream, affecting agriculture, drinking water supplies, and aquatic ecosystems. Therefore, it is crucial to implement effective erosion control measures and sustainable mining practices to mitigate these far-reaching consequences.

Water Depletion

In Nevada, the driest state in the US, the Humboldt River is being drained to meet the water demands of gold mining operations along the Carlin Trend. From 1986 to 2001, mines in the northeastern Nevada desert extracted over 580 billion gallons of water—enough to supply New York City for more than a year. Similarly, groundwater withdrawal from the Santa Cruz River Basin in southern Arizona for copper mining operations is causing the water table to drop, drying up the river.

The impact of mining on water depletion is not limited to the immediate vicinity of the mine. The effects can be felt many miles away from the mine site. For example, groundwater withdrawals from mines can damage or destroy streamside habitats far from the actual mining operations. This has been observed in the case of the Humboldt River in Nevada and the Santa Cruz River Basin in Arizona.

The issue of water depletion is further compounded by the fact that mining activities can also lead to water pollution, making existing water sources unusable. Acid mine drainage (AMD), for instance, is a significant issue where sulphide-rich rocks are exposed to air and water, forming sulphuric acid. This acid can leach heavy metals from the rocks, contaminating nearby water sources. Heavy metal contamination can also occur when arsenic, cobalt, copper, cadmium, lead, silver, and zinc come into contact with water. These types of water pollution can render water unfit for human consumption, irrigation, or recreational activities such as fishing or swimming.

To address water depletion and pollution issues in the mining industry, it is essential to implement water recycling and treatment processes. Reducing water usage, diverting runoff water, and treating different types of mining water are crucial steps to mitigate the environmental and societal impacts of water depletion in mining.

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