PAEL 312 – Environmental Management

Lesson 2: Extraction of rocks and mineral extraction

Learning Outcomes
1. Describe the following methods of extraction of rocks and minerals from the Earth: Surface
mining and sub-surface mining
2. Discuss the factors that affect the decision to extract rocks and minerals

Introduction
Hello dear students! Welcome to Lesson 2 – Environmental Management. After reading
this lesson, describe the following methods of extraction of rocks and minerals from the earth and
discuss the factors that affect the direction of extracting rocks and minerals.

Activity

Watch the link below and make a reflection.

https://www.youtube.com/watch?v=sV7ahjBhBt4

Analysis

1. What are your thoughts about the video? Explain how this extraction affects human activity.

2. As a student, how will you help the environment to minimize extraction? Defend your answer
Abstraction

Extraction
Surface mining (including pit, strip, and mountain-top removal) and underground mining are the
two main types of mining techniques (shaft). Both methods may be used by a single mine. Prior to
1900, the most common method of mining in the United States was underground mining. Surface
mining is becoming more popular as a result of the advancement of equipment that can easily
move large amounts of rock at the earth's surface. Waste rock is a large amount of rock broken up
during mining that does not contain enough mineral resources to process the rock further.

Surface mining
Surface mines are typically the largest. To remove large amounts of surface rock, heavy
machinery, and blasting procedures are used, causing significant disturbance to the land. Every
day, a typical surface mine can produce up to 150,000 tons of ore. Surface-mining processes are
sometimes used to remove entire mountains (or mountain peaks).

Underground Mining

Underground mining is the extraction of ore from beneath the Earth's surface through the use of
tunnels or vertical shafts. These shafts can go deep into the ground or sideways into a mountain.
Underground mines are typically smaller operations than surface mines, producing a few hundred
thousand to a million tons of ore over the mine's lifetime. In general, underground mining disturbs
less land than surface mining.

Potential Problem 1: Waste Rock

Waste rock can be non-ore-containing rock on top of the ore body (overburden) or ore that is not
concentrated enough to mine. Surface mining removes approximately 2--3 tons of waste rock for
every ton of ore removed. Underground mining produces less waste rock than surface mining, and
the waste rock is either moved to the surface or used to fill in areas of the mine that are no longer
in use. Waste rock piles are typically deposited near the mine. These piles can cover hundreds to
thousands of acres and reach heights of more than 100 feet.

Mining accelerates the rates of weathering and erosion. Waste rock has more surface area exposed
to chemical weathering because digging and blasting break rock into smaller pieces (mechanical
weathering). This is only a minor issue for some mining wastes. Some waste rock, on the other
hand, causes hazardous conditions when chemical weathering mobilizes metals or other
undesirable chemicals. These unfavorable chemicals may cause stream or groundwater to become
more acidic. The acidic (low pH) water may be harmful to local organisms, and many of the metals
mobilized are toxic to humans, plants, and animals.
Current mining operations in the United States carefully plan the placement and layering of waste
rock and monitor water flow through waste piles to minimize waste rock problems. However, this
may not be the case in countries without government regulations, and it was not the case in the
past in the United States. Several hazardous old waste piles exist in the United States, though some
have been remedied.

Concentration
The extracted ore is typically a mixture of the desired mineral resource and undesirable rocks and
minerals. The mineral resource is separated from other rocks and minerals and purified during
various concentration processes.

Beneficiation

Most ore look like a jumble of rock chunks when it comes out of the mine, with the desired mineral
visible only at the microscopic level. As a result, the desired mineral must be concentrated further
in a process known as beneficiation. The precise process varies depending on the mineral resource
and available technology, but it usually consists of a series of steps. The following are some
examples of beneficiation processes.

Flotation
Flotation is one method for separating the grains of the desired mineral from the grains of other
minerals. During flotation, the rock slurry is mixed with a specially selected reagent that adds
bubbles. Due to the chemistry, only the desired minerals will attach to the bubbles and float to the
top (for example, pine oil is a reagent that can be used in copper flotation; copper will attach to
bubbles of pine oil, but other minerals will not). The froth of bubbles and minerals attached to the
surface is skimmed off. The excess water and/or reagent are filtered out, and the mineral may be
concentrated further using other methods such as activated carbon, electroplating, and/or leaching
with other reagents such as sodium cyanide (discussed further below).
The slurry that remains at the bottom of the flotation tank is referred to as tailings.
Potential Problem 2: Tailings

Tailings, a byproduct of the flotation process, are typically pumped downhill into impoundments
known as tailings ponds. Tailings ponds can cover thousands of acres and have thicknesses of only
a few hundred feet.
If one of the impoundment's walls/dams fails, a large amount of contamination can be released
very quickly. Furthermore, if a tailing pond dries out, the metals may be transported as dust on the
wind and thus inhaled by nearby residents. Problems with a leaky tailings pile are particularly
problematic because sulfide minerals, which are frequently found in association with metal ores,
can occur in high concentrations within the tailings. When exposed to oxygen, sulfide minerals
can form sulfuric acid, resulting in acidic soils and waters. This may have an impact on water
quality in the area by making the waters highly acidic or by increasing the amount of dissolved
(and undesirable) metals as a result of the acidity (sulfide minerals can be the ones to cause
problems in waste rock as well).
Today, plastic liners can be installed to prevent contaminated waters from draining into the
groundwater system, and tailings pond water can be treated to neutralize the acids. Tailings ponds
are covered (capped) with an impermeable liner or soil after they have been filled, and water flow
is managed, with any water leaving the ponds being treated. However, just like with waste rock,
there is a legacy of problems associated with older and unlined/untreated tailings piles.
Leaching
The use of chemicals (such as sulfuric acid or sodium cyanide) to dissolve only the desired metals
is known as leaching. The desired metal is precipitated out of the solution after the liquid
containing the desired metal is separated from the remaining solids.
Leaching can occur in a vat after milling, instead of milling (either before or after crushing), or
even within the ground itself as a type of "in-situ" extraction.

Potential Problem 3: Leach Piles

One type of leaching is heap leaching, in which the leaching solution percolates down through a
large pile of ore. Piles can be large, covering tens to hundreds of acres, and reaching a height of a
few hundred feet. The remaining rock piles have many of the same environmental concerns as
tailings ponds after the metals have been leached out, usually after successive treatments with
recycled solution. To avoid problems, leach piles can be rinsed after leaching and built on specially
designed pads.
Smelting
The metal is separated from the mineral during the smelting process by heating the mineral in the
presence of a material known as a flux. The desired mineral settles to the melt's bottom and can be
extracted. The (unwanted) material at the melt's surface can harden into slag. The smelter is
frequently located in a different location than the mine. The desired mineral is then transported to
a refinery to be concentrated further.
Potential Problem 4: Smelter Emissions
Smelting emissions, which emit sulfur dioxide and other gases, heavy metals, and particulates, can
be a source of pollution. Since the 1970s, increased regulation and improved technologies in the
United States have resulted in a reduction in dangerous emissions.

Cleaning Up Afterward
Preparing for Mine Closure

The mine will close when the ore material runs out or becomes technologically or economically
inaccessible. The closed mine will fill with water in places where water was constantly pumped
out to keep mining operations dry.

The United States has many mines that were closed prior to the 1970s (when environmental
regulations were enacted) and have numerous environmental issues, such as acid mine drainage.
Mines operating in the United States today must meet higher standards; they must provide some
level of environmental and human health protection while in operation and implement a plan to
limit environmental and human health problems long after the mine closes. For example, while
mining is still taking place, the company will plan how they will grade slopes to reduce erosion
and make slopes more stable once the mine is closed.

Reclamation

Reclamation, or the restoration of land to either natural or useful conditions, frequently entails
the process of stabilizing soils and slopes in an area through grading (creating a different, gentler
slope) and planting trees and plants. Prior to revegetation, new soil or treatment of existing soil is
usually required. This step can begin before the mine completely closes; reclamation can take
place as sections close (either parts of the surface mine or the waste rock piles). This can also
help to improve the mine area's aesthetics while it is still open.

Remediation

The process of repairing, removing, or counteracting an environmental problem is known as