8.2 Energy resources  (Page 5/5)

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Discussion : using energy wisely

The massive power cuts or 'load shedding' that South Africans began to experience at the beginning of 2008, were a dramatic wake-up call to the growing energy crisis that the country faces.

There are alternative energy sources available, but they will take years to become functional, and many of them have their own problems. Another way to look at the problem, is to put the focus on reducing how much energy is used rather than focusing only on ways to meet the growing demand.

1. In your groups, discuss ways that each of the following groups of people could save energy.
1. industries
2. domestic users
3. farmers
2. Discuss creative incentives that could be used to encourage each of these groups to reduce their energy consumption.

Summary

• The lithosphere is the solid, outermost part of our planet and contains many important metal elements such as gold and iron, as well as products that are needed to produce energy.
• These elements are seldom found in their pure form, but rather as minerals in rocks .
• A mineral is formed through geological processes. It can either be a pure element (e.g. gold) or may consist of a number of different elements e.g. the gold-bearing mineral calaverite (AuTe ${}_{2}$ ).
• A rock is an aggregate of a number of different minerals.
• An ore is rock that contains minerals which make it valuable for mining.
• Minerals have been used throughout history . As new metals and minerals were discovered, important growth took place in industry, agriculture and technology.
• Gold is one of the most important metals in the history of South Africa. It was the discovery of gold that led to an influx of fortune-seeking foreigners, and a growth in mining villages and towns.
• Most of South Africa's gold is concentrated in the 'Golden Arc' in the area between Johannesburg and Welkom.
• Three methods are used to obtain gold from the lithosphere: panning , open cast mining and shaft mining .
• Gold ore must be processed so that the metal can be removed. One way to process the ore after it has been crushed is a method called gold cyanidation . A cyanide solution is added to the crushed ore so that a gold-cyanide solution is formed. Zinc is then added to this solution so that the gold is precipitated out.
• Gold has a number of important characteristics which make it a useful metal for jewelery and other applications. The metal is shiny, durable, malleable, ductile, is a good conductor of electricity and is also a good heat reflector.
• Gold mining has a number of environmental impacts , which include resource consumption, air pollution, poisoned water, solid waste and the destruction of biodiversity in natural areas.
• Mine rehabilitation is one way of restoring old mine sites to what they were like before.
• Iron is another important metal and is used in industry, furniture and building materials.
• Iron is usually found in minerals such as iron oxides . These minerals must be processed to remove the metal.
• When iron ore is processed , a blast furnace is used. The iron ore, carbon and a flux are added to the top of the furnace and hot air is blasted into the bottom of the furnace. A number of reactions occur in the furnace to finally remove the iron from its ore. Iron oxides are reduced by carbon monoxide to produce iron.
• Iron can occur in a number of forms, depending on its level of purity and carbon content. It can also occur in an alloy e.g. steel.
• Phosphates are found in sedimentary rock, which must be quarried to access the ore.
• Phosphates react with phosphoric acid or sulfuric acid to produce a superphosphate (Ca(H ${}_{2}$ PO ${}_{4}$ ) ${}_{2}$ ), which is an important component in fertilisers .
• The products of the lithosphere are also important in meeting energy needs . Coal and oil can be extracted from the lithosphere for this purpose.
• Coal and oil are both fossil fuels . A fossil fuel is a hydrocarbon that has been formed from the fossilsed remains of plants and animals that have been under conditions of high heat and pressure over a long period of time.
• Coal and oil are non-renewable resources , meaning that once they have been used up, no more can be produced.
• Coal can be removed from the ground using strip mining , open cast mining or underground mining .
• Coal is burned to produce energy, which can be used to generate electricity . Coal can also be used to produce liquid fuels or a syngas which can be converted into other useful products for the chemical industry.
• Some of the environmental impacts associated with coal mining include landscape scars, spontaneous combustion, acid formation and global warming.
• Oil is also a fossil fuel but it forms in the oceans . It can extracted using either pumping or drilling , depending on the pressure of the oil.
• Fractional distillation of oil can be used to make products such as diesel, gasoline and liquid petroleum gas.
• Cracking can be used to convert heavy hydrocarbons to light hydrocarbons.
• The environmental impacts of oil extraction and use are similar to those for coal.
• In view of the number of environmental impacts associated with the extraction and use of coal and oil, other alternative energy sources should be considered. These include nuclear power, biofuels, hydropower and a number of others. All of these alternatives have their own advantages and disadvantages.

Summary exercise

1. Give one word to describe each of the following phrases:
1. earth's crust together with the upper layer of the mantle
2. a mineral containing silica and oxygen
3. an alloy of iron and tin
4. a manual technique used to sort gold from other sediments
2. For each of the following questions, choose the one correct answer from the list provided.
1. One of the main reasons that South Africa's gold industry has been so economically viable is that...
1. gold panning can be used as an additional method to extract gold
2. open cast mining can be used to extract gold reserves
3. South Africa's geological history is such that its gold reserves are concentrated in large reefs
4. South Africa has large amounts of water to use in mining
2. The complete list of reactants in an iron blast furnace is...
1. carbon and oxygen
2. coal, oxygen, iron ore and limestone
3. carbon, oxygen and iron ore
4. coal, air, iron ore and slag
3. More profits, more poisons In the last three decades, gold miners have made use of cyanidation to recover gold from the ore. Over 99% of gold from ore can be extracted in this way. It allows miners to obtain gold flakes - too small for the eye to see. Gold can also be extracted from the waste of old operations which sometimes leave as much as a third of the gold behind. The left-over cyanide can be re-used, but is more often stored in a pond behind a dam or even dumped directly into a local river. A teaspoonful of 2% solution of cyanide can kill a human adult.Mining companies insist that cyanide breaks down when exposed to sunlight and oxygen which render it harmless. They also point to scientific studies that show that cyanide swallowed by fish will not 'bio-accumulate', which means it does not pose a risk to anyone who eats the fish. In practice, cyanide solution that seeps into the ground will not break down because of the absence of sunlight. If the cyanide solution is very acidic, it could turn into cyanide gas, which is toxic to fish. On the other hand, if the solution is alkaline the cyanide does not break down. There are no reported cases of human death from cyanide spills. If you don't see corpses, everything is okay.
1. What is cyanidation ?
2. What type of chemical reaction takes place during this process: precipitation, acid-base or redox?
3. Is the pH of the solution after cyanidation greater than, less than or equal to 7?
4. How is solid gold recovered from this solution?
5. Refer to cyanidation and discuss the meaning of the heading of this extract: More profits, more poisons . (DoE Grade 11 Paper 2, 2007)

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