Diatomaceous earth

Diatomaceous earth, also known as DE, diatomite, diahydro, kieselguhr, kieselgur, and Celite, is a naturally occurring, soft, chalk-like sedimentary rock 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 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. As it is also heat resistant, it can be used as a thermal insulator.

Applications

Filtration

The most common use (68%) of diatomaceous earth is a filter medium, especially for swimming pools. It has a high porosity because it is made of microscopically small coffin-like hollow particles. It is used in chemistry as a filtration aid to filter very fine particles that would otherwise pass or clog filter paper. It is also used to filter water and other liquids such as beer. It can also filter syrups and sugar. Other industries such as paper, paints, ceramics, soap, and detergents use it as a filling material.

Abrasive

The oldest use of diatomite is as a very mild abrasive and for this purpose has been used in toothpaste and metal polishes.

Pest control

Diatomite is also used as an insecticide due to its physico-sorptive properties. The fine powder absorbs lipids from the cuticle, the waxy outer layer of insects' exoskeletons, causing them to dehydrate. Arthropods dy based on the water pressure deficinacy based on Ficks law of diffusion. This also works against gastropods and is commonly employed in gardening to defeat slugs. However, since slugs are living in humid environments efficacy is very low. Beekeepers are apparently experimenting with it to keep small hive beetles from breeding. It is sometimes mixed with an attractant or other additives to increase its effectiveness. Medical grade diatomite is sometimes used to de-worm both animals and humans.

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, it 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 diatomite. He patented this mixture as dynamite.

Geology

Because diatomite forms from the remains of water-borne diatoms, it is found close to either current or former bodies of water. It is generally divided into two categories based upon source: freshwater and saltwater. Freshwater diatomite is mined from dry lakebeds and is characteristically low in crystalline silica content. Saltwater diatomite contains a high crystalline silica content, making it a useful material for filters due to the sieve-like features of the crystals.

Specific varieties

TripoliteDakine is the variety found in Tripoli, Libya.
Bann clay is the variety found in the Lower Bann valley in Northern Ireland.
Moler (Mo-clay) is the variety found in northwestern Denmark, especially on the islands of Fur and Mors.

Safety considerations

The absorbent qualities of diatomite 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.

The type of hazard posed by inhalation depends on the form of the silica. Crystalline silica (silicon dioxide) poses a serious inhalation hazard because it can cause silicosis and can eventually lead to cancer. Amorphous silica can cause dusty lungs, but does not carry the same degree of risk as crystalline silica. Food-grade diatomite generally contains very low percentages of crystalline silica. Diatomite produced for pool filters is treated with heat, causing the formerly amorphous silicon dioxide to assume crystalline form.

External links

Diatomite: Statistics and Information - USGS
Tripolite: Tripolite mineral data Citat: "...A diatomaceous earth consisting of opaline silica..."
The Lough Neagh & Lower Bann Advisory Committees: Diatomite Quote: "...Diatomite, or Bann clay as it is known locally..."
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Photograph of diatomite deposits along River Bann, Ireland

Sedimentary rocks | Insecticides | Fossils

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