Diatomaceous earth
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Diatomaceous earth, also known as diatomite, kieselguhr, kieselgur, and Celite, is a naturally occurring, soft, chalk-like, sedimentary rock mineral that is easily crumbled into a fine white to off-white powder. This powder has an abrasive feeling similar to pumice powder and is very light-weighed due to its high porosity. It is made primarily of silica and consists of fossilized remains of diatoms, a type of hard-shelled algae. It is used as a filtration aid, as a mild abrasive, as a mechanical insecticide, as an absorbent for liquids, as cat litter, and as a component of dynamite.
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Applications
Filtration
Probably the most common use of diatomaceous earth is a filter medium. Diatomaceous earth has a high porosity because it is made of microscopically small coffin-like hollow particles. It used in chemistry as a filtration aid to filter very fine particles that would otherwise pass or clog the filter paper. It also used to filter water and other liquids such as beer.
Abrasive
The oldest use of diatomite is as a very mild abrasive and for this purpose has been used in toothpaste and metal polishes.
Diatomaceous earth is also used as an insecticide due to its abrasive properties. The fine powder causes small cuts in the waxy outer layer of insects, causing them to dehydrate. It is sometimes mixed with an attractant or other additives to increase its effectiveness.
Absorbent
Its absorbent qualities make it useful for spill cleanup and the U.S. Center for Disease Control recommends it to clean up toxic liquid spills.
More recently, diatomaceous earth has been employed as a primary ingredient in a type of cat litter. The type of silica used in cat litter comes from freshwater sources and does not pose a significant health risk to pets or humans.
In 1867, Alfred Nobel discovered that nitroglycerin could be made much more stable if absorbed in diatomaceous earth. He patented this mixture as dynamite.
Geology
Because diatomaceous earth forms from the remains of water-borne diatoms, it is found in proximity to either current or former bodies of water. Diatomaceous earth is generally divided into two categories based upon source: freshwater and saltwater. Freshwater diatomaceous earth is mined from dry lakebeds and is characteristically low in crystalline silica content. Saltwater diatomaceous earth, in contrast, contains a high crystalline silica content making it a useful material for filters due to the sieve-like features of the crystals.
Specific varieties
- Tripolite refers to the variety found in Tripoli, Libya.
- Bann clay refers to the variety found in the Lower Bann valley in Ireland.
Safety Considerations
The absorbent qualities of diatomaceous earth can result in a significant drying of the hands if handled without gloves. The saltwater form contains the highly crystalline form of silica resulting in sharp edges. The sharpness of this version of the material makes it dangerous to breathe and a dust mask is recommended when working with it.
See also
External links
- Diatomite. Statistics and Information (http://minerals.usgs.gov/minerals/pubs/commodity/diatomite/)
- Tripolite: Tripolite mineral data (http://www.mindat.org/min-9855.html) Citat: "...A diatomaceous earth consisting of opaline silica..."
- The Lough Neagh & Lower Bann Advisory Committees: Diatomite (http://www.loughneagh.com/diatomite.htm) Quote: "...Diatomite, or Bann clay as it is known locally..."da:Moler