8.3.3: Mineral Resources(mineral, ore)

[Note: I added a B-head about the human use of minerals, which is distinct from the geologic processes that cause mineral resources to be unevenly distributed. This is a $2.5 trillion enterprise – it needs its own B-head. It is also where the PE MS-ESS3-4 gets addressed. Nuclear fission, on the other hand, is insignificant in comparison, in terms of importance. I am not sure that it even needs its own B-head, except that it is a good example that combines a mineral resource/energy/and issues concerning human impacts (the questions of what to do with nuclear waste).]

Take a look around you, right now, wherever you are reading this. Where did everything you see come from? Walls, paint, buildings, computers, cars, schools, the list is endless. Other than paper and wood (from trees) and clothing (from cotton and wool), most of the physical things we use in our lives originally come from the ground. As an old mining phrase goes, “If you don’t grow it, you mine it.” In fact, on average over 11 tons of minerals, metals, and other rocks (not including fossil fuels) are pulled out of the ground every year for each person in the United States. That totals to almost 4 billions tons of Earth’s materials to make our homes, cars, roads, buildings, and almost everything else we use. To provide a sense of scale, this amount of rock is ten times larger than the total amount of rock and sediment carried to the sea each year by the entire Mississippi River system, the largest river in North America.

[Graphic: picture of a city]

Why are Mineral Resources Unevenly Distributed?Suppose you wanted to make a pure gold wedding band. On average, gold is only about 3 parts per billion, by weight, of the earth’s crust. This means that to make a wedding band you would have to grind up an enormous amount of rock, about the

size of a three-story house, and extract all the gold out of it! If this were how we got gold, almost no one would be able to afford a gold wedding ring! Fortunately, we can go to places on Earth where there are high concentrations of gold, and just mine the gold. This is because there are geologic processes that concentrate gold and other metals. The earth does the work for us! In fact, for every mineral and metal resource that we need, there are geologic processes that concentrate the resources enough that we can inexpensively mine them.

However, different geologic processes occur in different parts of the earth, so different regions, including different countries, have different amounts of the different minerals. The same holds true for the fossil fuels you previously learned about. For example, there is a lot of coal in the state of West Virginia because of the unique geologic history of that region. Likewise, there was a lot of concentrated gold discovered in California and Alaska because of the unique geologic histories there. We mine salt in places like Texas because it had a different geologic history. By understanding the geologic processes needed to create and/or concentrate different minerals, as well as the geologic histories of different parts of the world, we can predict and discover the different kinds of mineral resources than can be obtained from each different part of the world.

Humans use many different kinds of mineral resources, and these are concentrated by many different geologic processes. Here are a few of them.

Crystallization from magma When molten magma cools underground it forms hard strong rocks called igneous rocks. These rocks are sometimes used for the construction of buildings, such as the stone granite, but are also ground up as gravel to make concrete, which is used in many different ways for construction. The atoms of many useful metals, like gold, silver, platinum, copper, etc., are relatively large and don’t fit well within the atomic structures of the minerals that make up most of

the crust (called silicate minerals). As a result, these metals usually remain in the last bit of magma to crystallize, causing them to become concentrated into a smaller region.

Precipitation from water The table salt you put on food, sodium chloride, was most likely mined from underground. It crystallized from a closed ocean basin when the sea water evaporated away, leaving just the salts behind. If you go swimming in the ocean, you can taste the salt dissolved in the sea water. You can do an experiment to replicate the crystallization of ocean salt: leave a bowl of salty water out for a week or until all the water evaporates. The sides of the bowl will be coated with salt grains that crystallized when the water evaporated. There are many other useful kinds of salts besides sodium chloride. Plaster is made from the salt gypsum. Electric cars use batteries made of lithium, which is usually mined in the form of lithium salts. In fact, the largest source of the world’s lithium (more than 1/3) is from two giant salt flats, the Atacama and Uyuni salt flats, which sit at the top of the Andes Mountains in South America.

Weathering Some useful minerals form from the weathering of other minerals. A good example is of clay minerals, which are used to make pottery plates and cups, among other times. Most clay minerals form from the mineral feldspar, which is a major component of the common rock granite. So, when granite weathers and erodes, the feldspar minerals become clays, which we use to make pottery. Weathering can also act to concentrate valuable metals if they are insoluble, such as

gold. Surrounding rocks erode away, causing the gold to accumulate in concentrations known as placer deposits.

By far, however, the most useful product of weathering is soil. When solid rock slowly weathers and breaks down, it becomes soil, which we use to grow our food in. Incidentally, sand is also a product of weathering—it comes from the quartz grains in granite and other igneous rocks when they weather and break apart.

Sedimentation Some mineral resources form from the process of sedimentation, where new rock is made from the weathered or dissolved minerals of previous rocks. Two of the most common sedimentary rocks are limestone and sandstone, both of which are commonly used for the construction of buildings. Limestone is also used to make lime, a mixture of calcium and oxygen, that is used for many purposes such as agriculture, making concrete, refining sugar, and the treatment of waste water.

High pressure During the geologic process of metamorphism, high pressures and temperatures create totally new rocks and minerals out of old ones. For example, when clay gets squeezed and heating during metamorphism it becomes a new rock, slate, which is used for paving stones and roof tiles. Limestone, when metamorphosed, becomes the rock marble, which is used for sculptures and decorative stone for construction. Most valuable mineral gemstones like diamonds, sapphires, and garnets cannot form at the surface—they only form deep within the earth at high pressures. To find them, you have to go to regions where rocks that were once deep within the earth are now found at the surface.

Hydrothermal processes – Hot water has the chemical ability to dissolve minerals more easily than cold water. Hot water within rock will also tend to dissolve large atoms that don’t fit well within the atomic crystal structure of most minerals. These are the metals like gold, silver, platinum, copper, etc., which were mentioned previously for rocks crystallizing from magma. Regions around volcanoes tend to have hot water circulating underground, driven by the heat of the magma. This water becomes enriched in heavy metals, concentrating the metals even further when the water cools and the metals precipitate out. Veins of the mineral quartz can be found containing high concentrations of valuable metals in regions that once had volcanic activity.

Plate Tectonics The process of plate tectonics is very efficient at concentrating minerals and metals, through the combined geologic processes operating at mid-ocean ridges and subduction zones. At a oceanic mid-ocean ridge there is very active hydrothermal circulation of water through the ocean crust, driven by the magma under the ridge. This hot water removes so many minerals out of the ocean crust that when the water shoots up into the ocean in the form of mid-ocean ridge thermal vents, it is black with all the dissolved minerals. This rich deposit of minerals falls to the ocean sea floor, where it may sit for more than a 100 million years, slowly moving away from the mid-ocean ridge, before eventually reaching a subduction zone. There, the surface layer of the sea floor, containing the rich minerals, is often scraped off to become part of the accretionary wedge of the overriding plate. This regionally concentrates the minerals. If these deposits become the site of volcanic activity, which is common at subduction zones, the minerals can become concentrated even further.

Human processes Of course, now that humans are removing so much rock, we are altering the distribution of mineral resources by removing them from some parts of the earth and dumping them in others. We now do this on a very big scale. For example, look at the photo of the giant Bingham Copper mine, outside of Salt Lake City, Utah. The pit left over after mining is a kilometer deep and 4 kilometers across.

[graphics: wedding ring; mining operation; granite building (this is the DC Smithsonian Natural History building); Uyuni salt flat; clay; Taj Mahal (marble); gems; pegmatite quartz vein with minerals; plate tectonics and hydrothermal circulation; mid-ocean ridge thermal vent; Bingham Copper mine]

How do Humans Use Mineral Resources?There are 93 naturally occurring elements; most of them have unique properties that make them useful and valuable for one application or another. For example, does your family use a mobile phone? If so, you depend on the availability of many different elements in order for that phone to be able to make a phone call. The cell phone electronics uses many expensive metals such as gold, silver, platinum, tungsten, palladium, and copper because of their electronic properties. The phone also uses strong magnets made from neodymium and dysprosium, elements from a group of metals known as Rare Earth elements. The phone receiver and amplifier use arsenic and gallium. The casing uses magnesium compounds. The battery is made of lithium. The liquid display uses indium. All of these minerals have to be mined and refined just to make a phone.

In addition, each of these mineral resources has many other industrial uses, as do most other minerals. For example, there is a rapid increase in the use of fiber optic cables for telecommunication, but these all require the use of the element erbium because of its unique optical properties. The element Europium is used as a red phosphor in LCD screens. Cerium is used to polish almost all lenses and mirrors because of its physical properties. Lanthanum is used to make nickel-metal hydride batteries, such as those used in many hybrid cars. Platinum and other platinum-group metals such as rhodium are used to catalyze many industrial chemical reactions. Platinum is also used in the catalytic converters of all diesel cars; rhodium is used in removing nitrous oxides from the emissions of engines. Phosphorus is used to make matches, detergents, and pesticides, but is most important in making fertilizers for agriculture. A long list could be made for the many uses of each element. As mentioned before, Americans use 4 billion tons of rocks and minerals each year for most everything that we do.

[Indium:]

[Europium:]

[Erbium:]

[Cerium:]

[Platinum/Rhodium:]

[Lanthanum:]

There is another important aspect to these mineral resources, however, that expends beyond the science and engineering. For most of the elements just mentioned, the United States has to import most or all of them from other countries, and they are getting very expensive. The total yearly cost of minerals and mineral based products in the U.S. is now over $2.5 trillion, which is about 1/6 of the total U.S. economy. Of some concern is that the readily available reserves of many of these minerals will only last decades at current rates of mining and production. This doesn’t mean that we will run out of these minerals, just the high concentrations of them that have been created by slow geologic processes. We will have to dig deeper, and dig greater volumes of rock to get the mineral resources we need, like with the

example of grinding up a house-sized volume of rock to get the gold for a wedding ring. As a result, engineers are constantly looking at ways to use minerals more efficiently and to engineer alternatives for minerals that becoming hard to obtain.

It is important to remember that even though these mineral resources are formed and concentrated by natural geologic processes, these processes occur so slowly that the mineral resources are non-renewable over human time scales. Some processes, like plate tectonics, occur over many millions of years. Some processes, like the formation of soil, only take thousands of years. However, this is still a very long time compared to human time scales, so we have to consider the rich topsoil needed for agriculture to be a non-renewable resource. Poor farming practices of the past resulted in the loss of billions of tons of much-needed topsoil to erosion. Newer farming practices are reducing this loss. There are over 7 billion humans on Earth, and we eat a lot of food. We use 40% of the land to grow crops or raise livestock for our food, and have to take great care of our valuable soil resources.

Another important issue concerning the use of so many mineral resources is what we do with them after they are used. There are about 320 million people in the U.S. and we generate about 225 million metric tons of garbage (municipal solid waste) every year. That amounts to about 2/3 of a ton of garbage per person per year, or 2 kg of garbage per person per day. Where does this garbage go? Most of it, 120 million metric tons per year, goes into landfills. A growing amount, now about 80 million metric tons per year, is now recycled. Recycling not only reduces the amount of new land needed to store the waste, it also reduces the demand and cost of obtaining new mineral resources. In 1985, American’s only recycled 10% of their waste. That number is now above 35%, and steadily increasing. As we will see in the topic on Human Impacts on the Environment, all aspects of industry involving mineral resources affect the earth and its systems.

[Graphics : photo of cell phone, outside and inside; pictures of various elements discussed (europium, erbium, cesium, platinum, etc.); photo of a landfill; graph of municipal solid waste]

How are Mineral Resources Needed for Nuclear Energy?A good example of our dependence upon a mineral resource for human purposes is the need to mine uranium ore to fuel nuclear fission electricity power plants. The U.S. gets about 100 gigawatts of electricity, almost 20% of its electricity needs, from nuclear power. This is a non-renewable energy source, however, because there are limited geologic resources of uranium ore. An ore is a rock that contains economically important minerals with important elements including metals. Uranium is commonly found in in the form of oxides, and though it is rare, it is 500 times more abundant than gold. However, uranium is not evenly distributed around the world. The countries of Australia, Kazakhstan, and Canada have 2/3 of the world’s available uranium.

[Open-air uranium mine in Namibia]

Only the isotope U-235 can be used for nuclear power, but it is just 0.7% of naturally occurring uranium. Most uranium, 99.3%, occurs in the form of the isotope U-238. Rock needs to contain at least 3% U-235 before it can be used in a nuclear reactor, so no geologic processes will naturally concentrate the rock high enough in U-235. Humans have to increase the concentration of U-235 by physically or chemically removing U-238 from it in a process called enrichment. The process has to be done carefully because uranium is radioactive, naturally giving off high-energy electromagnetic radiation in the form of gamma rays.

Nuclear fission power is generated by splitting apart atoms of U-235 when high-energy neutrons are fired at them. The uranium atom splits into smaller elements such as krypton and barium and additional neutrons. These neutrons then collide with other U-235 atoms, causing them to split and release more neutrons; the result is called a chain reaction because the splitting of atoms continuous on its own once it is started. When an atom of U-235 is split, a tiny amount of mass is converted into energy. The amount of energy can be calculated using Albert Einstein’s famous equation, E = mc2. The E stands for the energy created, m is the amount of mass destroyed, and c is the constant for the speed of light in a vacuum, which is 3 x 108 m/s. Because c2 is such a large number (9 x 1016), a tiny amount of destroyed mass still releases a lot of energy. In theory, nuclear power could also be generated by fusing hydrogen atoms to form helium in a process called nuclear fusion. This process occurs within stars and creates the energy we see as light. Humans have not yet engineered a way to harness nuclear fusion to commercially produce electricity.

Nuclear fission power is generated within a large building called a nuclear reactor. The enriched uranium is put into fuel rods, which give off heat that boils water and drives a steam turbine to generate electricity. The tall towers of the reactor are

cooling towers, which allow the steam to condense into water before going back in contact with the uranium fuel rods. In a few catastrophic instances, the temperature of the uranium fuel rods has gotten so hot that the rock has melted and broken out of the containment chamber in a process called a meltdown. The two most famous cases of a meltdown occurred in Chernobyl, Russia, in 1986, and in Fukushima, Japan, in 2011. The Fukushima meltdown followed a large M9 earthquake and resulting tsunami that damaged the power plant.

As a source of energy, nuclear fission has the advantage that you get a great deal of energy from a tiny amount of uranium. One kilogram of uranium can produce as much electricity as more than 15,000 kg of coal, and unlike the coal, there is no release of carbon dioxide. The big disadvantage with nuclear fission, however, is that many of the end waste products of the fission reactions are highly radioactive isotopes of plutonium, neptunium, and other elements. These radioactive wastes will continue to emit dangerous levels of radioactivity for hundreds of thousands of years. Many scenarios have been discussed for how best to store away the radioactive wastes, such as burying them deep underground. Currently, however, there is no place in the U.S. where these dangerous wastes can be taken to, so the

accumulating radioactive wastes are just stored on site at the 100 operating U.S. nuclear reactors.

[Nuclear waste buried underground in an old salt mine in Morsleben, Germany]

[Graphics: uranium mine, uranium ore, enriched uranium pellet, chain reaction, nuclear reactor, nuclear fuel rods, barrels of nuclear waste]

Assessment1. a. Construct an Explanation As the graph in Figure XX showed, the amount

of recycling of garbage has increased from 10% to 35% over the past 30 years. The amount of garbage going into landfills, however, has not been decreasing but has been staying at roughly the same amount each year. Explain why this might be so.b. Extrapolate What kinds of political tensions might occur if countries with the greatest reserves of a mineral resource decide not to trade that resource with other countries?

2. a. Defend an Argument Choose an optimal geographic place for the long-terms storage of the radioactive wastes from nuclear fission. Assume that some amount of leaking is always a possibility. Defend your choice of a location.b. CCC (Cause and Effect) Explain how volcanic processes can cause some metals to become highly concentrated.

Study Guide3.3 Mineral ResourcesWhy are Mineral Resources Unevenly Distributed? Mineral resources are created and concentrated naturally by geologic processes; a geographic region’s minerals resources are therefore dependent upon the current and past geologic

processes operating there.How do Humans Use Mineral Resources? Humans use mineral resources for almost all aspects of their lives; these resources are finite at economically workable concentrations, and the disposal of these resources as waste impacts Earth’s systems.How are Mineral Resources Needed for Nuclear Energy? Electricity from the nuclear fission of uranium requires the mining and refining of uranium ore; these resources and the end products of the reaction process are highly radioactive and must be carefully managed.