Calcium compounds are a part of our day-to-day life. Calcium is the fifth most abundant element in the earth’s crust and the human. It is a gray silvery metal element with the atomic number 20. It is the lightest alkaline earth metal. It is naturally silvery and lustrous but it oxidizes quickly and gets dull color. As it is highly reactive, it can’t be found in pure form.Calcium carbonate, which is used in the cement industry is obtained from its ores’ stalagmites and stalactites. Calcium metal is also found in various minerals such as limestone, gypsum and fluorite.

Calcium is present in a number of products in our everyday life, such as chalk, bones, teeth, cement, etc. Before 19th century, it was considered as a mineral as it rapidly forms hydroxides. The element metal is very reactive in water, as it releases hydrogen from water. It is somewhat less reactive in air. Calcium is harder than sodium metal, but softer than aluminum. It forms the body skeleton and it is a common cellular ionic messenger. It is flammable and when it burns it gives out white light generally known as limelight.

Calcium was first isolated by Sir Humphry Davy in 1808; Davy produced a calcium amalgam by electrolyzing an aqueous solution of chloride, CaCl2, using a mercury cathode such as in chlor alkali process employing a mercury cathode. After distilling mercury from the amalgam form, he obtained a pure calcium metal. He showed lime to be an oxide of calcium.

Calcium metal and calcium compounds have many industrial as well as biological uses. Pure calcium is used as an alloy agent for copper and aluminium. It also has applications as deoxidizer, decarburizer, desulfurizer, reducer, in storage battery and as dehydrogenating agent. It is used in the manufacturing of high quality low carbon steel. It serves as a starting material for many special alloys such as nickel-based, titanium-based, iron, copper, aluminum alloys, etc. It is used as a reducing agent in the preparation of several important metals.

Calcium is a highly reactive metal and can’t be found in pure form. It occurs in sedimentary rocks in the mineral forms such as calcite, dolomite and gypsum. These sources are generally employed to get various useful calcium compounds such as calcium carbonate, calcium fluoride, quicklime etc. Pure calcium metal is obtained by electrolysis and distillation processes.

1. Calcium metal by aluminothermic process (High temperature vacuum reduction calcium oxide)
2. Calcium metal from anorthositic ore

Aluminothermic process (High temperature vacuum reduction calcium oxide)

Calcium metal is produced by the aluminothermic method in which aluminum is used as reducing agent and calcium oxide is reduced in vacuum at high temperature. Calcium oxide is obtained from calcium carbonate. Calcium oxide is grounded to small particles and dry blended with the desired amount of finely divided aluminum. To ensure good contact, this mixture is compacted into briquettes or retorts (these are horizontal tubes made up of heat resistant steel). It is heated to 1100-1200°C. The open ends of retort protrude from the furnace and cooled by water jacket to condense the calcium vapor. Retorts are sealed and evacuated to pressure less than 13 Pa. After 24 hours of reaction vacuum is broken by Argon and 99% pure calcium is recovered and calcium aluminate residue is removed.

Calcium metal from anorthositic ore

Anorthositic ore is a calcium aluminum silicate containing soil. In this process an ore is first made free from iron compound impurities by a magnetic separation process and selective evaporation of some compound in vacuum at elevated temperatures.This is the preliminary step of the process.

In the first major process step reduction of silicon is carried out. The ore is dissolved in the lithium aluminum fluoride electrolyte. When exposed to liquid, the aluminum silicon oxide, part of the ore is reduced by the following reaction

3CaAl2Si2O8 + 8Al ==> 6Si + 3CaO + 7Al2O3

Silicon obtained from above reaction is in the form of hypereutectic melt of aluminum and silicon. After cooling, the silicon is precipitated and separated.
In the second major process step electrolysis of aluminum and calcium is carried out. Fluoride electrolyte containing aluminum oxide and calcium oxide is electrolyzed. At cathode aluminum and calcium are reduced into a liquid pool. Aluminum is separated as a main product and calcium and lithium are separated as a byproduct. Oxygen is evolved at anode. It is purified and obtained as byproduct.

From CreamRedistillation

When Calcium is used for the reduction of metal compounds, purity greater than 99% calcium is required. To obtain calcium metal of more than 99% purity the crude calcium metal is distilled in the retort at the pressure less than 6.6 Pa and bottom temperature 900-925°C. After distillation the volatile impurities in the distillate are separated from calcium by passing vapors over refractory oxides such as TiO2, ZrO2, and CrO3 to form nonvolatile Na2O and K2O in the absence of moisture to avoid oxidation.

Metal Industry
Steel industry

The major quantity of calcium metal is applied in the steel industry as a desulfurizer and deoxidizer agent for steel refining. It is used in the form of cored wire during the production of silicon-free steel. The Calcium Silicon alloy is used in manufacturing of high quality and low carbon steel. Calcium Silicon Alloy can also be used as the inoculants of cast iron and the additive in the production of nodular cast iron. Calcium metal controls graphite carbon in cast iron.

Lead industry

After steel industry, calcium metal is mostly consumed in lead refining. It is used for de-bismuthisation for production of lead-calcium alloys for batteries.

Reducing agent

Calcium is an excellent reducing agent. At elevated temperature, it reacts with oxides and halides of all metallic elements to give corresponding metal. It is also used to recover refractory metals such as chromium, rare earth metals and thorium from their oxides. It is used in payrometallurgy as a strong reducing agent in metallograthermic preparation of refractory metals such as Cr, Th, U, Ti, Zr and Hf.

Alloying agent

Calcium metal is used as an alloying agent for aluminum, beryllium, silicon, copper, lead, magnesium and other base metals. It is alloyed with lead employed as sheaths for telephone cables and as a grid for storage batteries of the lead-acid stationary type. Calcium Silicon Alloy is also employed as a starting material for special alloys, such as nickel base alloy and titanium base alloy.

Other applications

It is used in metallurgy as a desulfurizer for ferrous metals, as a deoxidizer for certain high temperature alloys such as copper and beryllium and for nickel, steel and tin bronze. It is used as a getter in vacuum electron tubes to fix residual gases such as oxides, nitrides and hydrides. Calcium alloyed with cerium used in making flints for cigarettes and gas lighters. It is also employed as dehydrating agent for alcohols and solvents.

Product Identification

CAS No. : 7440-70-2
Molecular Formula : Ca
Synonym : Calcium
H.S.Code : 2805.12..00

Calcium metal Specification

Appearance Silver gray granular
Calcium (as Ca) % 98.5 (min)
Fe % 0.030 (max)
Ni % 0.006 (max)
Mn % 0.020 (max)
Cu % 0.002 (max)
Mg % 0.50 (max)
Al % 0.40 (max)
Si % 0.003 (max)
Particle size mm 0-2 , 2-3. 0-3
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