Different Method of Extracting MetalsObtaining metals from ores- 3 stages
1. Concentrate
2. Extract crude metal
3. Refine crude to make pure the metal
There are 2 methods for extracting metal from ores (a compound of metal mixed with large amounts of earth and rock):
1. Reducing the metal compound (ore) to the metal using carbon
2. Using electricity to decompose the molten metal compound (ore) to the metal
*The more reactive the metal is, the harder it is to extract the metal from its ore. (Very reactive metals are very difficult to split up)
Extracting Iron from Haematite
(contains iron() oxide mixed with impurities such as sand and clay)
-iron is extracted from Haematite in a blast furnace
Limestone + iron ore + coke à hot air (oxygen) + blast furnace à waste gases + slag + molten iron
*4 series of chemical reactions take place in blast furnace
1. CO2 is produced due to the burning of carbon in coke in a blast of hot air, producing much heat too.
C (s) + O2 (g) --heat--à CO2 (g)
Decomposition of limestone (CaCO3) to produce quicklime + CO2
CaCO3 (s) --heat--à CaO (s) + CO2 (g)
2. CO is produced as CO2 continues to react with more coke as it rises up the furnace.
C (s) + CO2 (g) --heat--à 2CO (g)
3. Haematite is reduced to iron due to the presence of CO.
Fe2O3 (s) + 3CO (g) --heat--à 2Fe (l) + 3CO2 (g)
Molten iron formed runs to the bottom of furnace + Hot waste
4. Impurities are removed due to the adding of limestone.
CaO (s) + SiO2 (s) --heat--à CaSiO3 (l)
gases escape from the top of furnace
Molten slag formed float on top of molten iron as it is lighter.
They are thus separated and solidified slag is mainly used for road surfacing.
Impact on Evironment
Before copper ore metals can be extracted from their copper ores, the land is mined for copper ores. Mined land is usually unsightly and it cannot support plant and animal life. Building new mines reduces the land available for agriculture, housing and industrialization.
An enormous amount of waste material is also generated from the extraction process. About 90% of the metal copper ore used for metal extraction turns out to be waste and needs to be disposed off after the metal is extracted. If not disposed carefully, the waste may leech into soil and nearby water bodies, polluting land and water. To dispose the waste, huge landfill sites need to be dug which requires large amount of money.
The smelting of copper ores causes more air pollution compared to any other industrial process. In the process of large-scale earthwork, dust emissions are inevitably a problem. These dust particles originate from the following potential sources: copper ore crushing, conveyance of crushed copper ore, loading bins, blasting, mine and motor vehicle traffic, use of hauling roads, waste rock piles, windblown tailings, and disturbed areas. Dust can contain toxic heavy metals such as arsenic, lead, and other. These toxic heavy metals, when incorporated with dust can contaminate the air. Dust can also deposit in surface water causing sedimentation and turbidity problems.
In addition, the extraction of copper from their copper ores requires a continuous supply of energy. The energy is usually generated from burning fossil fuels, which are already in scarce supply. Eventually, resources of metal would be used up.
Erosion and sedimentation present another environmental issue for mine sites. When material is disturbed in significant quantities, as it is in the mining process, large quantities of sediment are transported by water erosion. The sediment eventually drops out of solution and sedimentation occurs at some point downstream from the erosive source. The degree of erosion and sedimentation depends on: the degree to which the surface has been disturbed, the prevalence of vegetative cover, the type of soil, the slope length, and the degree of the slope.
Erosion and sedimentation affect surface water and wetlands more than any other media. Erosion can adversely affect soil organisms, vegetation, and revegetation efforts because it results in the movement of soil, including topsoil and nutrients, from one location to another.
The large disturbances caused by mining can disrupt environments, adversely affecting aquatic habitats (i.e. lakes, ponds, streams, rivers), terrestrial habitats (i.e. deserts, grasslands, forests), and wetlands that many organisms rely on for survival. The disruption of site hydrology by large consumption or release of water, manipulation of topography, and the release of particulates and chemicals can all have indirect impacts on various habitats.
Solution to the Impact
- Use advanced technology such as satellites to find new ore deposits, so that we have new supplies of metals e.g. ore
- Find substitutes to replace metals so that we ca use the existing metals more sparingly. For eg, replacing some metal parts in cars with plastic or ceramic parts. Optical fibres made of special glass are replacing the metal wires used in communications instruments.
- Recycling metals is another good method. Metals are readily recycled, old metal objects can be rushed and melted for use.
Recycling is the best way as it does not produce as much waste that might endanger human health.
Electrolysis is using electrical energy to bring about chemical changes at the electrolyte connections called the anode and cathode electrodes. An electrolyte is a conducting melt or solution of ions which carry the electric charge as part of the circuit. Scrap copper can be recycled and purified this way too, and it is also cheaper starting from copper ore and saves valuable mineral resources.
Acidic gases like sulphur dioxide from sulphide ores, can be removed by bubbling through and alkali solution such as calcium hydroxide solution (‘limewater’) where it is neutralized and oxidized to harmless calcium sulphate. Cleaning a gas in this way is called “gas scrubbing”. Any contaminated water must be purged of harmful chemicals before being released into a river or recycled via water treatment plant. The waste slag is used for road construction or filling in quarries which can then be landscaped.
Examples of disadvantages of a country exploiting it's own mineral resources and reduction of its social and environmental impact:
- Dust from mining-quarrying or processing can be reduced by air filter and precipitation systems and even hosing water on dusty areas or spoil heaps or carried away to somewhere else via tall chimneys.
- Noise from process operation or transport of raw materials and product(lorries/trucks/wagons).
Difficult to deal with, sound-proofing often not practical, but operations can be reduced for unsociable hours e.g. evening movement. - Pollution can be reduced by cleaning the 'waste' or 'used' air, water and waste gases etc. of toxic or acidic materials e.g.
Toxic carbon monoxide from the blast furnace extraction of iron, it can be burnt as a fuel, but it must not be released into the air unless converted to biologically harmless carbon dioxide. - Sulphur dioxide gas from copper extraction of its sulphide ore is an irritating poisonous gas which can also cause acid rain, but it can be converted to the useful, therefore saleable, industrial chemical concentrated sulphuric acid, so you can remove a harmful pollutant and recover back some of the metal extraction costs, good green economics? Acidic gases like sulphur dioxide can be removed by bubbling through an alkali solution such as calcium hydroxide solution ('limewater') where it is neutralised and oxidised to harmless calcium sulphate. Cleaning a gas in this way is called 'gas scrubbing'.
- Mining operations will disfigure the landscape BUT it can be re-claimed and 'landscaped' in an attempt to restore the original flora and fauna. However in the case of a limestone quarry, I'm afraid there is no way round the fact that huge chunks of beautiful hills get carted away if we want to use it as useful mineral.
For more information, please go to http://www.docbrown.info/page04/Mextract.htm .
Thanks for reading!
By: Eugenia Hou Yi Fan (6), Loh Ya Xin (12), Sheena Ting Jia Wen (16), Toh Jia Yi (23), Lim Wei Jie Nicholas (35)
