Calcium is an element with metallic properties. It’s highly reactive, so it doesn’t occur in elemental form in nature. Limestone is a naturally occurring mineral high in calcium carbonate, or CaCO3. It’s possible to extract pure calcium from calcium carbonate through a multi-stage process requiring special equipment. Pure calcium reacts very quickly with the oxygen in the air, so you must store it in a non-reactive atmosphere, such as in a vacuum container.
Reduce the limestone ore to a fine powder and add dilute hydrochloric acid. This will cause the limestone to give off carbon dioxide and increase the purity of the calcium carbonate. Filter this mixture to remove the remaining silica and other insoluble material.
Add oxalic acid, or H2C204, to the refined limestone ore from step 1. This reaction will produce solid calcium oxalate, or CaC2O4, and aqueous carbonic acid, or H2C03, according to the following reaction: CaC03 + H2C2O4 -> CaC2O4 + H2CO3.
Rinse the calcium oxalate precipitate with deionized water and pour it into a beaker. Add hydrochloric acid to the precipitate, which will produce calcium chloride, or CaCl2, according to the following reaction: CaC2O4 + 2HCl -> CaCl2 + 2CO2 + H2.
Add sodium carbonate, Na2CO3, to the calcium chloride you obtained in step 3. This will produce calcium carbonate, or CaCO3, according to the following reaction: Na2CO3 + CaCl2 -> CaCO3 + 2NaCl. Filter this solution to obtain the calcium carbonate precipitate. Heat the calcium carbonate at 248 degrees Fahrenheit to dry it.
Heat the calcium carbonate from step 4 to 1,832 degrees Fahrenheit to obtain lime, or CaO. The following equation shows this reaction: CaCO3 -> CaO + CO2.
Place the lime you obtained in step 5 into a vacuum container and add aluminum. Heat this mixture to 2,552 degrees Fahrenheit to obtain pure calcium according to this equation: 5CaO + 2Al -> Al2O3 + 2CaO + 3Ca.
- limestone rocks image by Maria Brzostowska from Fotolia.com