Chapter 23 Notes Condensed

I. Central Case Study: Mining for… Cell Phones?

• We rely on tantalum for our cell phones, computer chips, DVD players, game consoles, and digital cameras. Tantalum powder is ideal for capacitors (the components that store energy and regulate current in miniature circuit boards) because it is highly heat-resistant and readily conducts electricity.

• Tantalum comes from a dull blackish mineral called tantalite, which often occurs with a mineral called columbite—so the ore is referred to as columbite-tantalite, or coltan for short.  As information technology boomed in the late 1990s, global demand for tantalum rose and market prices for the metal shot up.

• Most miners ended up with little while rebels, soldiers, and bandits enriched themselves selling coltan to traders, who sold it to processing companies in Asia, Europe, and the United States.

• Steps are now being taken to help support legitimate Congolese mines while preventing the exploitation that has defined mining there in the recent past.  These efforts and others provide an opportunity to significantly reduce trade in conflict minerals while promoting trade of minerals sourced from legitimate mines in poor nations such as the Democratic Republic of the Congo.

23.1  Earth’s Mineral Resources

A.  Rocks provide the minerals we use.

1.   A rock is a solid aggregation of minerals; a mineral is a naturally occurring solid chemical element or inorganic compound with a crystal structure, a specific chemical composition, and distinct physical properties.

2.   In some cases, the rock itself is a resource, such as the gravel used to make concrete. In other cases, valuable mineral resources, such as iron or phosphate, are embedded within rocks. To secure these minerals, miners remove the mineral-containing rock and then separate the desired mineral from the surrounding rock.

B.  We obtain minerals by mining. Mining refers to the systematic removal of rock, soil, or other material for the purpose of extracting minerals of economic interest.  We use mined materials extensively.

C.  Metals are extracted from ores. - A metal is a type of chemical element, or a mass of such an element, that typically is lustrous, opaque, and malleable, and can conduct heat and electricity. Most metals are not found in a pure state in Earth’s crust, but instead are present within ore, a mineral or grouping of minerals from which we extract metals.

E.   We process metals after mining ore.

1.   A process known as smelting heats ore beyond its melting point and combines it with other metals or chemicals. Sometimes we mix, melt, and fuse a metal with another metal or a nonmetal substance to form an alloy.

2.   Processing metals can exert substantial environmental impacts.

a.   Most methods are water-intensive and energy-intensive.

b.   Many chemical reactions and heating processes used for extracting metals from ore emit air pollution. Smelting plants in particular have long been hotspots of toxic air pollution.

c.   Soil and water commonly become polluted by tailings, portions of ore left over after metals have been extracted.

d.   Mining operations often pump a toxic slurry of tailings into large reservoirs called surface impoundments.

F.   We also mine nonmetallic minerals and fuels.

1.   Sand and gravel, the most commonly mined mineral resources, are used as fill and as construction materials for the manufacturing of products such as concrete.

2.   Gemstones are treasured for their rarity and beauty.

3.   We also mine substances such as coal and petroleum that we use for fuel.

23.2  Mining Methods and Their Impacts

A.  Strip mining removes surface layers of soil and rock.

1.   When a resource occurs in shallow horizontal deposits near the surface, the most effective mining method is often strip mining, whereby layers of surface soil and rock are removed from large areas to expose the resource.

2.   Strip mining can be economically efficient, but it obliterates natural communities over large areas, and the soil in refilled areas, called overburden, can easily erode away. Strip mining also pollutes waterways through the process of acid mine drainage, which occurs when sulfide minerals in newly exposed rock surfaces react with oxygen and rainwater to produce sulfuric acid which runs off into nearby bodies of water.

B.  In subsurface mining, miners work underground.

1.   When a resource occurs in concentrated pockets or seams deep underground, and the earth allows for safe tunneling, then mining companies pursue subsurface mining. In this approach, shafts are excavated deep into the ground, and networks of tunnels are dug or blasted out to follow deposits of the mineral.

2.   We use subsurface mining for metals such as zinc, lead, nickel, tin, gold, copper, and uranium as well as for diamonds, phosphate, salt, and potash. In addition, a great deal of coal is mined using the subsurface technique.

3.   Subsurface mining is the most dangerous form of mining and indeed one of society’s most dangerous occupations.  Even after they are closed, abandoned mines can cause structural issues at the surface as well.

4.   Occasionally, subsurface mines can affect people for years after they are closed. Acidic drainage can contaminate surface water and groundwater, sometimes for centuries, after mining operations cease. Natural disasters or accidents can lead to catastrophic releases of toxin-ladenwaters from abandoned mines.  

C.  Open pit mining can create immense holes in the ground.

1.   When a mineral is spread widely and evenly throughout a rock formation, or when the earth is unsuitable for tunneling, the method of choice is open pit mining. This essentially involves digging a gigantic hole and removing the desired ore along with waste rock that surrounds the ore.

2.   Open pit mining is used to extract copper, iron, gold, diamonds, and coal, among other resources. We also use this technique to extract clay, gravel, sand, and stone such as limestone, granite, marble, and slate, but in these cases, we generally call these pits and quarries.

3.   The sheer size of these mines means that the degree of habitat loss and aesthetic degradation is considerable. Another impact is chemical contamination from acid drainage as water runs off the waste heaps or collects in the pit.

D.  Mountaintop mining or mountaintop removal reshapes ridges and can fill valleys.

1.   When a resource occurs in underground seams near the tops of ridges or mountains, mining companies may practice mountaintop removal mining, in which several hundred vertical feet of mountaintop may be blasted off to allow recovery of entire seams of the resource.

2.   In mountaintop removal mining, a mountain’s forests are clearcut, the timber is sold, topsoil is removed, and then rock is repeatedly blasted away to expose coal for extraction.

3.   Scientists are finding that dumping tons of debris into valleys degrades or destroys immense areas of habitat, clogs streams and rivers, and pollutes waterways with acid drainage.

4.   People living in communities near the mining sites experience social and health impacts.  Critics of mountaintop removal mining argue that valley filling violates the Clean Water Act.

E.   Placer mining uses running water to isolate minerals.

1.   To search for metals and gems, miners sift through material in modern or ancient riverbed deposits, generally using running water to separate lightweight mud and gravel from heavier minerals of value. This technique is called placer mining.

2.   Besides the many social and political impacts of placer mining in places such as the Democratic Republic of the Congo, placer mining is environmentally destructive because most methods wash large amounts of debris into streams, making them uninhabitable for fish and other life for many miles downstream.

F.   Solution mining dissolves and extracts underground resources.

1.   When a deposit is especially deep and the resource can be dissolved in a liquid, miners may use a technique called solution mining. In this technique, a narrow borehole is drilled deep into the ground to reach the deposit, and water, acid, or another liquid is injected down the borehole to leach the resource from the surrounding rock and dissolve it in the liquid. The resulting solution is then sucked out, and the desired resource can be isolated.

2.   Solution mining generally exerts less environmental impact than other mining techniques because less area at the surface is disturbed.

G.  Some mining occurs in the ocean.

1.   The oceans hold many minerals useful to our society. The logistical difficulty of mining them, however, has kept their extraction too expensive thus far.  As land resources become scarcer and as undersea mining technology develops, mining companies may turn increasingly to the seas.

2.   Impacts of undersea mining are largely unknown, but increases in such mining would undoubtedly destroy marine habitats and organisms that have not yet been studied. It would also likely cause some metals to diffuse into the water column at toxic concentrations and enter the food chain.

H.  Restoration helps to reclaim mine sites.

1.   Because of the environmental impacts of mining, governments of the United States and other developed nations now require that mining companies restore or reclaim surface-mined sites following mining. The aim of such restoration or reclamation is to restore the site to a condition similar to its condition before mining.

2.   Even on sites that are restored, impacts from mining (such as soil and water damage from acid drainage) can be severe and long-lasting. It is difficult to regain the same biotic communities that were naturally present before mining.  The 1977 Surface Mining Control and Reclamation Act requires companies to cover reclamation costs before permits are issued.

3.   Water polluted by mining and acid drainage can also be reclaimed if pH can be moderated and if toxic heavy metals can be removed.

I. An 1872 law still guides US mining policy.

1.   The General Mining Act of 1872 encourages people and companies to prospect for minerals on federally owned land by allowing any US citizen or any company with permission to do business in the United States to stake a claim on any plot of public land open to mining.  It covers a wide variety of metals, gemstones, uranium, and minerals used for building materials.

2.   The law may have made sense in 1872, but the United States has changed a great deal since then, and many question the law’s suitability for today’s nation.  Critics and some legislators have tried to amend the law many times over the years, mostly without success.

23.3  Toward Sustainable Mineral Use

A.  Minerals are nonrenewable resources in limited supply.

1.   As minerals become scarcer, demand for them increases and their prices rise.

2.   Estimates of mineral resources may increase or decrease over time due to several reasons.

a.   Discovery of new reserves.

b.   New extraction technologies.

c.   Changing social and technological dynamics.

d.   Changing consumption patterns.

e.   Recycling.

B.  We can make our mineral use more sustainable.  It is possible to recycle metals, especially from e-waste.