How to Extract Limestone

Limestone is a sedimentary rock composed of calcium carbonate (CaCO3). Limestone comes from the shells of dead marine organisms such as clams, oysters, crayfish, brachiopods, bryozoa, crinoids and corals. Such animals live on the bottom of the sea and after death their shells accumulate into piles, forming beds of limestone. Some limestone is pure calcium carbonate, but most is actually tainted with other minerals from the sea bed, such as silicone dioxide (sand), iron oxides and silt.



Calcium carbonate is used in toothpaste, chewing gum, soap, glue and antacids; in its purest form, it is simply white marble.



To get pure calcium carbonate, you can either mine it from areas known for their pure limestone, such as the Peak District in the U.K., or you can extract it from impure limestone.

Things You'll Need

• Hydrochloric acid
• Filter paper
• Oxalic acid
• Deionized water
• Beakers
• Drying oven

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Instructions

• 1

  Crush the limestone and dissolve in dilute hydrochloric acid. Filter any insoluble materials, such as silica, with filter paper.

• 2

  Add oxalic acid (H2C2O4), which will react with the remaining calcium to form calcium oxalate (CaC2O4) as a solid precipitate. Wash this precipitate with deionized water and transfer it to a beaker.

• 3

  Add dilute hydrochloric acid (HCl) to calcium oxalate to form calcium chloride (CaCl2).

• 4

  Add concentrated sodium carbonate (Na2CO3) to calcium chloride to form calcium carbonate (CaCO3) as a precipitate.

• 5

  Filter off this precipitate and wash it. Dry the calcium carbonate in an oven at 120 degrees Celsius (248 degrees Fahrenheit).