Limestone, Metal Extraction & Uses: A Chemistry Exploration
Limestone and Its Uses
Limestone is made of calcium carbonate. Limestone is widely used in the building industry. The calcium carbonate in limestone breaks down when heated strongly to make calcium oxide and carbon dioxide. The reaction is called thermal decomposition.
Reactions of Carbonates
Carbonates react with dilute acid to form a salt, water, and carbon dioxide. Limewater turns cloudy in the test for carbon dioxide gas. A precipitate of insoluble calcium carbonate causes the cloudiness. Metal carbonates decompose on heating to form the metal oxide and carbon dioxide.
The Limestone Reaction Circle
When water is added to calcium oxide, it produces calcium hydroxide. Calcium hydroxide is alkaline, so it can be used to neutralize acids. The reactions of limestone:
- Heat calcium carbonate to get calcium oxide and release carbon dioxide.
- Add water to calcium oxide to get calcium hydroxide.
- Add more water and filter to get limewater (calcium hydroxide solution).
- Add carbon dioxide to get limestone (calcium carbonate).
Cement and Concrete
Cement is made by heating limestone with clay in a kiln. Mortar is made by mixing cement and sand with water. Concrete is made by mixing crushed rocks or small stones called aggregate, cement, and sand with water.
Limestone Quarrying: Benefits and Issues
There are good and bad points about quarrying for limestone. For example, more jobs will be created, but there will be a large scar on the landscape. Limestone, cement, and concrete all have useful properties for use as building materials, but the mining and processing of limestone and its products has a major effect on our environment.
Extracting Metals from Ores
A metal ore contains enough of the metal to make it economic to extract the metal. Ores are mined and might need to be concentrated before the metal is extracted and purified. Gold and other unreactive metals can be found in their native state. The reactivity series helps decide the best way to extract a metal from its ore. The oxides of metals below carbon in the series can be reduced by carbon to give the metal element. Metals more reactive than carbon cannot be extracted from their ores using carbon.
Iron and Steels
Iron is extracted from iron ore by reducing it using carbon in a blast furnace. Pure iron is too soft to be very useful. Carefully controlled quantities of carbon and other elements are added to iron to make alloys of steel with different properties. Important examples of steels are:
- Low carbon steels: easily shaped
- High carbon steels: very hard
- Stainless steels: resistant to corrosion
Aluminium and Titanium
Aluminium and titanium are useful because they resist corrosion. Aluminium requires the electrolysis of molten aluminium oxide to extract it, as it is too reactive to reduce using carbon. Aluminium and titanium are expensive because extracting them from their ores involves many stages and requires large amounts of energy.
Extracting Copper
Most copper is extracted by smelting copper-rich ores, although supplies of these ores are becoming scarce. Copper can be extracted from copper solutions by electrolysis or by displacement using scrap iron. Electrolysis is also used to purify impure copper. Scientists are developing ways to extract copper that use low-grade copper ores. Bacteria are used in bioleaching, and plants in phytomining.
Useful Metals: Transition Metals
The transition metals are found in the central block of elements in the periodic table. Transition metals have properties that make them useful for building and making things. Copper, gold, and aluminium are all alloyed with other metals to make them harder.
Social and Environmental Issues of Metal Extraction
There are social, economic, and environmental issues associated with exploiting metal ores. Plants can remove metals from low-grade ores. The metals can be recovered by processing the ash from burning the plants. Recycling metals saves energy and limited metal ores (and fossil fuels). The pollution from extracting metals is also reduced. There are drawbacks as well as benefits from the use of metals in structures.