diatomaceous earth

A sample of diatomaceous earth

Diatomaceous earth (pronounced /ˌdaɪ.ətɵˌmeɪʃəs ˈɜrθ/) — also known as DE, TSS, diatomite, diahydro, kieselguhr, kieselgur, brand names include Celatom or celite — is a naturally occurring, soft, chalk-like sedimentary rock that is easily crumbled into a fine white to off-white powder, with a particle size extending from less than 1 to over 100 microns, but typically around 2 to 10 microns. ^[1] This powder has an abrasive feel, similar to pumice powder, and is very light, due to its high porosity. The typical chemical composition of diatomaceous earth is 86% silica, 5% sodium, 3% magnesium and 2% iron.

Diatomaceous earth 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, as an activator in blood clotting studies, and as a component of dynamite. As it is also heat-resistant, it can be used as a thermal insulator.

Applications

Industrial

In 1866, Alfred Nobel discovered that nitroglycerin could be made much more stable if absorbed in diatomite. This allows much safer transport and handling than nitroglycerin in its raw form. He patented this mixture as dynamite in 1867, and the mixture is also referred to as guhr dynamite.

Filtration

Individual diatom cell walls often maintain their shape even in commercially processed filter media, such as this one for swimming pools

The most common use (68%)^{[citation needed]} of diatomaceous earth is as a filter medium, especially for swimming pools. It has a high porosity, because it is composed of microscopically-small, coffin-like, hollow particles. It is used in chemistry under the brand name Celatom or Celite as a filtration aid, to filter very fine particles that would otherwise pass through or clog filter paper. It is also used to filter water, particularly in the drinking water treatment process and in fish tanks, and other liquids, such as beer and wine. It can also filter syrups and sugar. Other industries such as paper, paints, ceramics, soap and detergents use it as a fulling material.

Abrasive

The oldest use of diatomite is as a very mild abrasive and, for this purpose, it has been used both in toothpaste and in metal polishes, as well as in some facial scrubs.

Pest control

Diatomite is also used as an insecticide, due to its physico-sorptive properties. The fine powder absorbs lipids from the waxy outer layer of insects' exoskeletons, causing them to dehydrate. Arthropods die as a result of the water pressure deficiency, based on Fick's law of diffusion. This also works against gastropods and is commonly employed in gardening to defeat slugs. However, since slugs inhabit humid environments, efficacy is very low. 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. It is most commonly used in lieu of boric acid, and can be used to help control and eventually eliminate a cockroach infestation. This material has wide application for insect control in grain storage.^[2]

Absorbent

Its absorbent qualities make it useful for spill clean-up and the U.S. Centers for Disease Control recommends it to clean up toxic liquid spills. These qualities also lend themselves to use in facial masks to absorb excess oils.

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.

Thermal

Its thermal properties enable it to be used as the barrier material in some fire resistant safes.

DNA purification

Diatomite (Celite) can be used for the removal of DNA in the presence of a highly concentrated chaotropic agent such as sodium iodide, guanidinium hydrochloride and guanidinium thiocyanate. As with other silicates, the diatomites will remove double stranded DNA but not RNA or proteins. The DNA can be extracted from the diatomites using low ionic strength buffers, including water, at neutral to slightly alkaline pH. Crude diatomites of a uniform size must first be washed in a heated acid such as 5M HCl^[3]. Calcination can further improve consistency of the material, while mild caustic treatment may improve adsorption with lower levels of chaotrophs.

Use in agriculture

Natural freshwater diatomaceous earth is used in agriculture for grain storage as an anti-caking agent, as well as insecticide.^[4] It is approved by the US Department of Agriculture as a feed supplement.

It is also used as a neutral anthelmentic (de-wormer). Some farmers add it to their livestock and poultry feed to improve the health of animals.^[5] "Food Grade Diatomaceous Earth" is widely available in agricultural feed supply stores. It is acceptable as organic feed additive for livestock.

Hydroponics

Freshwater diatomite can be used as a growing medium in hydroponic gardens.

It is also used as a growing medium in potted plants, particularly as bonsai soil. Bonsai enthusiasts use it as a soil additive, or pot a bonsai tree in 100% Diatomaceous earth. Like perlite, vermiculite, and expanded clay, it retains water and nutrients while draining fast and freely allowing high oxygen circulation within the growing medium.

Marker in Livestock Nutrition Experiments

Natural diatomaceous earth (dried, not calcined) is regularly used in livestock nutrition research as a source of acid insoluble ash (AIA), which is used as an indigestible marker. By measuring the content of AIA relative to nutrients in test diets and feces or digesta sampled from the terminal ileum (last third of the small intestine) the percentage of that nutrient digested can be calculated using the following equation:

% Nutrient Digestibility = (1 - (% Nutrient_{feces/digesta} / % Nutrient_feed) X (% AIA_feed / % AIA_{feces/digesta})) X 100

Natural diatomaceous earth (freshwater) is preferred by many researchers over chromic oxide, which has been widely used for the same purpose, but which is also a known carcinogen and therefore a potential hazard to research personnel.

Geology

Please help improve this article by expanding it. Further information might be found on the talk page. (January 2007)

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. Saltwater diatomite is mined from areas that were once covered in seawater. Both freshwater and saltwater (marine) diatomite can be processed into material suitable for filtering.

Specific varieties

• Tripolite 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.

Climatologic importance

The Earth's climate is affected by dust in the atmosphere, so locating major sources of atmospheric dust is important for climatology. Recent research indicates that surface deposits of diatomaceous earth play an important role. For instance, the largest single atmospheric dust source is the Bodélé depression in Chad, where storms push diatomite gravel over dunes, generating dust by abrasion.^[6]

Safety considerations

The absorbent qualities of diatomite can result in a significant drying of the hands if handled without gloves. The flux-calcined form contains a 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 poses a serious inhalation hazard because it can cause silicosis. Amorphous silica can cause dusty lungs, but does not carry the same degree of risk as crystalline silica. Natural or dried diatomite generally contains very low percentages of crystalline silica. Diatomite produced for pool filters is treated with high heat (calcining) and a fluxing agent (soda ash), causing the formerly amorphous silicon dioxide to assume its crystalline form.

In the United States, the crystalline silica content in the dusts is regulated by the Occupational Safety and Health Administration (OSHA), and there are guidelines for the maximum amounts allowable in the product and in the air near the breathing zone of workers.^[7]

See also

• Biomineralization
• Diatom
• Fuller's earth
• Perlite

References

External links

• International Chemical Safety Card 0248
• Diatomite: Statistics and Information - USGS
• Tripolite: Tripolite mineral data Citat: "...A diatomaceous earth consisting of opaline silica..."
• DIATOMACEOUS EARTH: A Non Toxic Pesticide
• Photograph of diatomite deposits along River Bann, Ireland
• Raising Poultry using Diatomacious Earth - Article by the Poultry Youth Association