Ca - Calcium
|Chemical Element||Calcium||Melting Point °C||839|
|Chemical Symbol||Ca||Boiling Point °C||1484|
|Atomic Number||20||Density g/cm3||1.6|
Calcium is a silvery, relatively soft metal which belongs to Group 2 of the Periodic Table (The Alkaline Earth Metals), and is the 5th most abundant metal in the Earth’s crust; it is a vital element for almost all living things on this planet. Calcium is present in our bones, teeth and the lens in our eyes, to name just a few, and is also very important in the function of cells, constantly moving in and out of the cells, mediating the action of nerves and muscles. Calcium is rarely seen in nature in its pure metallic form, as it is attacked by oxygen and water. Calcium, when in contact with air, decomposes quickly into calcium hydroxide and calcium carbonate, which are both chalky, white substances. On contact with water or acid, calcium metal generates hydrogen gas, similarly to the Alkali Metals of Group 1, but does so at a slower, more controlled pace, making it a useful source of small amount of hydrogen.
Lime (aka quicklime, calcium oxide, CaO) was used by all ancient civilisations to make mortar for building. Lime is obtained by heating limestone (calcium carbonate, CaCO3). Mortar was then made by mixing lime with sand and water, and for a while it would be soft and workable, but then over time, as it absorbed carbon dioxide from the air, it would form back into calcium carbonate and would revert to being solid. It was not until 1755 that modern day chemists began investigating the properties of calcium, when Joseph Black proved that when limestone was heated to produce lime, the products were calcium oxide and carbon dioxide. It was considered impossible to break lime down any further, and therefore it was listed as an element, although there was a suspicion that it was an oxide of an unknown element, but there was no method of proving this. at the time. It remained unproven until 1808, when Humphry Davy obtained calcium via electrolysis. It was not until the 20th century that commercial methods of calcium production were achieved.
Calcium as an element is found only in living creatures, but its ores are abundant and the major mined ores are calcite, dolomite, gypsum and anhydrite. The four main countries which have the facilities to produce calcium on an industrial scale are Russia, China, USA and France. The Russian calcium plant produces 4,000 tonnes per annum. The main producer, China, has significantly increased its calcium production in the last 5 to 6 years, due to the increase in companies producing aluminothermic calcium, as well as the 2 companies who have produced electrolytic calcium since the 1960’s. China now produces 30,000-35,000 tonnes per year, including 4,000-6,000 tonnes of electrolytic calcium. The USA produces around 1,000- 2,000 tonnes of aluminiothermic calcium per year, and although France has the ability to produce calcium metal, it does not currently use the facilities to produce it. Reserves are virtually unlimited, due to the presence of calcium ions in living organisms.
The largest quantity of calcium metal is consumed by the steel industry in the form of cored wire during the production of silicon-free steel. The 2nd largest calcium consumer is the lead industry for lead de- bismuthisation and for the production of lead-calcium alloys for batteries. The cost of electrolytic calcium is a lot higher than aluminothermic calcium, but is much purer, therefore certain consumers choose to pay a higher price for a purer metal. Calcium oxide, CaO, is produced by thermal decomposition of carbonated minerals in furnaces and can be used in the metallurgical industry during the reduction of ferrous alloys in high intensity light arcs, due to its unusual spectral characteristics, and industrially as a dehydrating agent. Calcium silicate is manufactured in an electric oven from lime, silica and reducing carbonate agents and is a useful steel deoxidizing agent.
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