What Is Dolomitic Limestone?

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What Is Dolomitic Limestone?
Dolomitic limestone contains 35 per cent to 40 per cent magnesium oxide. (limestone Jurassic rocks image by Maria Brzostowska from Fotolia.com)

Dolomitic limestone is a type of limestone that contains dolomite, a crystalline mineral that contains calcium magnesium carbonate. When processed into dolomitic lime, this mineral becomes a white or grey to pink powder that is used in agriculture, gardening and lawn care to reduce the acidity of soil.

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Origins

Dolomite appears in many places and geological formations. Researchers are not sure where or how it forms, but it appears to form under different conditions today than it did when it formed the bulk of ancient rock formations. Dolomitic limestone is formed when dolomite precipitates into limestone formations and partially replaces the limestone.

Dolomitic Lime

Dolomitic lime is manufactured from dolomitic limestone. The process produces a powdered mixture of lime and 35 to 40 per cent magnesium oxide. Because most dolomitic limestone is too highly crystalline, it cannot be calcined (burnt) using the high-temperature lime-processing methods used for other types of limestone. The heat causes the crystals to break up explosively and doesn't let the carbon dioxide escape fast enough to produce the final powdered lime product, which needs to be low in carbon dioxide. Most dolomitic lime is produced at lower temperatures in rotary kilns to create a more reactive product. Dolomitic limestone fired at higher temperatures results in a denser product better for some applications.

Manufacturing

More plants make quicklime than dolomitic lime because dolomitic limestone is harder to obtain and dolomitic lime has fewer uses. It's primary use is in the steel industry as a flux mixed with regular lime to remove impurities in the steel. Dolomitic lime is also used as a binder for forming pellets in iron-making and as a slag component in production of ferromanganese or ferrochrome.

Agriculture

Dolomitic limestone products are also used for agricultural purposes where magnesium oxide is lacking in soil that is too acidic. In some locations, excessive rain leaches the soil and depletes calcium and magnesium. Decaying crop residues, animal waste and other organic matter combined with nitrogen fertilisers further increase acidity in the soil. Dolomitic limestone products are used in these areas to replace lost minerals and reduce the acidity of the soil.

Precautions

Dolomitic lime can cause eye, skin, respiratory and gastrointestinal irritation. It contains small amounts of crystalline quartz silica, so it has been classified as a carcinogen and in some forms and applications may cause silicosis. If brought into contact with strong acids, dolomite lime can react violently. The product should be used in a well-ventilated area with a dust mask and eye protection. Skin and eyes should be washed thoroughly after contact with any lime product.

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