Diatomaceous earth (also known as DE, diatomite, diahydro, kieselguhr, kieselgur, and celite) is a soft, chalk-like sedimentary rock. It consists of the fossilized remains of diatoms, a type of hard-shelled algae. White to off-white in color, it is easily crumbled into a fine powder. The powder is highly porous and very light, and it has an abrasive feel, similar to pumice powder.
Diatomaceous earth is useful for many applications. It is used as a filtration aid, mild abrasive, absorbent for liquids, and insecticide. It is a component of cat litter and dynamite. Given its resistance to heat, it can be used as a thermal insulator.
Given that diatomite is produced from the remains of waterborne diatoms, it is found close to current and former bodies of water. Based on the source, it is divided into two general categories: freshwater and saltwater. Freshwater diatomite is mined from dry lakebeds and is characteristically low in its content of crystalline silica. By contrast, saltwater diatomite contains a high content of crystalline silica, making it a useful material for filters, due to the sieve-like features of the crystals.
Diatomite is highly porous, because it is composed of microscopically small, coffin-like hollow particles. In addition, it is a good absorbent and is resistant to heat. Its typical chemical composition is 86 percent silica, five percent sodium, three percent magnesium, two percent iron, and other minor constituents.
Several varieties of diatomite have been found. They include the following types.
Given its high porosity, diatomaceous earth is most commonly used (65-70 percent) as a filter medium, especially for swimming pools. It is a filtration aid in chemistry, to separate very fine particles that would otherwise pass or clog filter paper. It is also used to filter water, particularly in the drinking water treatment process, 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 fulling material.
The oldest use of diatomite is as a mild abrasive. This application includes its use in toothpaste, metal polishes, and some facial scrubs.
Diatomite is also used as an insecticide, taking advantage of its physico-sorptive properties. The fine powder absorbs lipids from the cuticle (the waxy outer layer of insect exoskeletons), causing them to dehydrate. The lowering of water pressure kills arthropods. This approach also works against gastropods and is commonly employed to defeat garden slugs. However, since slugs inhabit humid environments, efficacy is very low. Beekeepers are experimenting with it, to see if it will prevent 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 animals and humans. It is also used to help control and eventually eliminate a cockroach infestation.
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.
Given its heat resistance, diatomite can be used as the barrier material in some fire-resistant safes.
Freshwater diatomite can be used as a growing medium in hydroponic gardens.
The Earth's climate depends greatly on the amount of dust in the atmosphere, and locating major sources of dust are of great interest for climatology. Recent research indicates that surface deposits of diatomaceous earth play a dominant role.
A major example is the Bodélé depression in a part of the Sahara belonging to Chad. Here, storms push diatomite gravel over dunes, and dust is abraded, leading to the largest single influx of dust into the atmosphere.
The absorbent qualities of diatomite can result in a significant drying of the hands, if handled without gloves. The saltwater (industrial) 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. 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 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.
All links retrieved October 24, 2017.
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