Mining of Ores (College Board AP® Environmental Science) : Study Guide
Impacts of mining lower grade ores
What are lower grade ores?
Lower grade ores contain smaller concentrations of valuable minerals
This means they require more extensive processing to extract usable material
As high-grade ores become depleted, mining companies must turn to lower quality deposits
Environmental impacts of mining lower grade ores
Increased resource consumption
More energy is required to extract and process lower-grade ores
Higher water usage is needed for chemical separation processes, increasing strain on local water sources
Greater waste production
Mining lower-grade ores generates larger amounts of waste rock and tailings
Tailing ponds hold toxic slurry, which can leak into surrounding ecosystems
Higher pollution levels
More fossil fuels are burned to power mining equipment and ore processing
This contributes to higher CO₂ emissions
The use of chemicals like cyanide and sulfuric acid in ore extraction increases the risk of soil and water contamination
Economic and social impacts
Rising mining costs
Extracting minerals from lower-grade ores increases operational costs, as more ore must be processed to obtain the same yield
These higher costs can lead to increased consumer prices for metals and minerals
Land degradation and habitat destruction
Larger mining operations are required to process more ore, leading to expanded deforestation, habitat destruction, and soil erosion
Example: In regions like the Amazon rainforest, lower-grade gold mining contributes to widespread deforestation
Surface mining
What is surface mining?
Surface mining involves the removal of large sections of soil and rock (known as overburden) to access minerals near the Earth’s surface
It is used for extracting coal, gold, copper, and other valuable minerals
More common than underground mining because it is cheaper and safer, but it has significant environmental impacts
Types of surface mining
Strip mining
Removes long strips of land to extract minerals located close to the surface
Destroys vegetation and topsoil, leading to increased erosion and habitat loss
Open-pit mining
Excavates large, deep pits to access ore deposits
Used for gold, copper, and iron ore mining
Generates massive amounts of waste rock, altering landscapes permanently
Environmental impacts of surface mining
Habitat destruction
Deforestation and removal of vegetation disrupt ecosystems and wildlife populations
Loss of biodiversity as species are displaced from their natural habitats
Soil erosion and degradation
Exposed soil after mining is prone to erosion, leading to loss of fertile land
Mining spoils (waste materials) are often acidic and prevent plant regrowth
Water pollution
Heavy metals and chemicals from mining runoff contaminate rivers and groundwater
Acid mine drainage (AMD) occurs when exposed rock reacts with air and water, releasing toxic sulfuric acid
Case Study
Berkeley Pit, Montana: Water pollution from mining waste
Location:
Berkeley Pit is an abandoned open-pit copper mine in Butte, Montana.
Issue:
After mining ceased in 1982, groundwater began flooding the pit
This lead to the accumulation of highly acidic water (pH ~2.5) mixed with heavy metals such as arsenic, lead, and cadmium
Environmental impacts:
The toxic water poses a serious threat to local water systems if it overflows or seeps into surrounding groundwater
In 1995, a flock of snow geese landed in the pit and over 300 of the geese died from exposure to the contaminated water
Management:
After the 1995 incident, officials implemented bird deterrent measures
These include loud noises, lasers, and trained personnel using shotguns to fire non-lethal rounds to scare birds away
The pit is part of the Superfund cleanup program, with water treatment efforts in place to prevent contamination spread
Pumps and treatment plants help remove heavy metals and neutralize acidity before releasing water into the environment
Mining wastes
Mining wastes are the unwanted materials left behind after extracting valuable minerals from ore
These wastes include overburden, tailings, and slag, each of which poses environmental risks
Types of mining wastes
Overburden
Soil and rock layers removed to reach ore deposits
Often piled into spoil heaps, which can lead to habitat destruction
Tailings
Finely ground rock and chemical byproducts left after ore processing
Contain heavy metals, cyanide, and sulfur compounds, which can leach into water sources
Stored in tailing ponds, which risk leakage, dam failure, and water contamination
Slag
Residue left after smelting ores, mainly composed of metal oxides
Can contain toxic elements like arsenic and lead, contaminating soil and groundwater
Managing and reducing mining waste
Recycling mine waste: Some tailings and slag can be reused in construction materials or road-building
Land reclamation: Restoring mined lands by planting vegetation and stabilizing waste piles
Better waste storage: Improved tailing dam designs reduce the risk of spills and contamination
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