Diatomaceous earth
Diatomaceous earth, also known as diatomite, celite, or kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3 mm to less than 1 μm, but typically 10 to 200 μm. Depending on the granularity, this powder can have an abrasive feel, similar to pumice powder, and has a low density as a result of its high porosity. The typical chemical composition of oven-dried diatomaceous earth is 80–90% silica, with 2–4% alumina, and 0.5–2% iron oxide.
Diatomaceous earth consists of the fossilized remains of diatoms, a type of hard-shelled microalgae, that have accumulated over millions of years. It is used as a filtration aid, mild abrasive in products including metal polishes and toothpaste, mechanical insecticide, absorbent for liquids, matting agent for coatings, reinforcing filler in plastics and rubber, anti-block in plastic films, porous support for chemical catalysts, cat litter, activator in coagulation studies, a stabilizing component of dynamite, a thermal insulator, and a soil for potted plants and trees as in the art of bonsai. It is also used in gas chromatography packed columns made with glass or metal as stationary phase.
Composition
Diatomaceous earth consists of the fossilized remains of diatoms that accumulated over millions of years. It is usually composed of 80% to 90% silica, 2% to 4% alumina minerals, and 0.5% to 2% iron oxide, although the precise composition of every deposit is different. Deposits may contain different amounts of silica depending on the sedimentation conditions, the presence of other sediments, and the age of the deposit. The species of diatom may also differ among deposits. The species of diatom is dependent upon the age and paleoecology of the deposit. In turn, the shape of a diatom is determined by its species.Many deposits throughout British Columbia, such as Red Lake Earth, are from the Miocene epoch and contain a species of diatom known as Melosira granulata. These diatoms have a small globular shape. A deposit containing diatoms from this epoch can provide certain benefits over others. For example, diatoms from the Eocene epoch are not as effective in their ability to absorb fluids because as older diatoms recrystallize, their small pores become filled with silica.
Formation
Diatomite forms by the accumulation of the amorphous silica remains of dead diatoms in lake sediment or marine sediments. The fossil remains consist of a pair of symmetrical shells or frustules. Marine diatomites are found in association with a wide variety of other rock types but lacustrine diatomites are almost always associated with volcanic rock. Diatomaceous chert consists of diatomite that has been cemented with silica.Diatoms are able to extract silica from water that is less than 1% saturated in amorphous silica. Their frustules remain undissolved because they are surrounded by an organic matrix. Clay minerals may also precipitate on the frustules and protect them from dissolution in sea water. When the diatom dies, the frustule is stripped of its organic layer and exposed to sea water. As a result, only 1% to 10% of frustules survive long enough to be buried under sediments and some of this is dissolved within the sediments. Only an estimated 0.05% to 0.15% of the original amount of silica produced by diatoms is preserved in the sedimentary record.
Discovery
In 1836 or 1837, German peasant Peter Kasten discovered diatomaceous earth (German: Kieselgur when sinking a well on the northern slopes of the Haußelberg hill, on Lüneburg Heath in North Germany.The extraction site on Lüneburg Heath from 1863–1994 was Neuohe, while the storage sites were:
| Storage site | from | to |
| Wiechel | 1871 | 1978 |
| Hützel | 1876 | 1969 |
| Hösseringen | 1894 | |
| Hammerstorf | 1920 | |
| Oberohe | 1884 | 1970 |
| Schmarbeck | 1896 | |
| Steinbeck | 1897 | 1928 |
| Breloh | 1907 | 1975 |
| Schwindebeck | 1913 | 1973 |
| Hetendorf | 1970 | 1994 |
The deposits are up to thick and are all of freshwater diatomaceous earth.
Until World War I, almost the entire worldwide production of diatomaceous earth was from this region.
Other deposits
In Poland diatomaceous earth deposits are found in Jawornik, and are composed mostly of diatomaceous skeletons.In Germany, diatomaceous earth was also extracted at on the Vogelsberg and at Klieken.
There is a layer of diatomaceous earth more than thick in the nature reserve of Soos in the Czech Republic.
Deposits on the Isle of Skye, off the west coast of Scotland, were mined until 1960.
In Colorado and in Clark County, Nevada, United States, there are deposits that are up to several hundred meters thick in places. Marine deposits have been worked in the Sisquoc Formation in Santa Barbara County, California near Lompoc and along the Southern California coast. This is the world's largest deposit of diatomite. Additional marine deposits have been worked in Maryland, Virginia, Algeria and the MoClay of Denmark. Freshwater lake deposits occur in Nevada, Oregon, Washington and California. Lake deposits also occur in interglacial lakes in the eastern United States, in Canada and in Europe in Germany, France, Denmark and the Czech Republic. The worldwide association of diatomite deposits and volcanic deposits suggests that the availability of silica from volcanic ash may be necessary for thick diatomite deposits.
Diatomaceous earth is sometimes found on desert surfaces. Research has shown that the erosion of diatomaceous earth in such areas is one of the most important sources of climate-affecting dust in the atmosphere.
The siliceous frustules of diatoms accumulate in fresh and brackish wetlands and lakes. Some peats and mucks contain a sufficient abundance of frustules such that they can be mined. Most of Florida's diatomaceous earths have been found in the muck of wetlands or lakes. The American Diatomite Corporation, from 1935 to 1946, refined a maximum of 145 tons per year from their processing plant near Clermont, Florida. Muck from several locations in Lake County, Florida was dried and burned to produce the diatomaceous earth.
It was formerly extracted from Lake Mývatn in Iceland.
The commercial deposits of diatomite are restricted to Tertiary or Quaternary periods. Older deposits from as early as the Cretaceous Period are known, but are of low quality.
Diatomite deposits rich in fossils have been located in New Zealand, but mining of the Foulden Maar deposits on an industrial scale, for conversion to animal feed, has drawn strong opposition.
Commercial form
Diatomaceous earth is available commercially in several formats:- granulated diatomaceous earth is a raw material simply crushed for convenient packaging
- milled or micronized diatomaceous earth is especially fine and used for insecticides
- calcined diatomaceous earth is heat-treated and activated for filters
Usage
Explosives
In 1866, Alfred Nobel discovered that nitroglycerin could be made more stable if absorbed in diatomite. This allowed safer transport and handling than pure nitroglycerin in liquid form. Nobel patented this mixture as dynamite in 1867; the mixture is also called guhr dynamite in reference to the kieselguhr.Filtration
The Celle engineer, Wilhelm Berkefeld, recognized the ability of the diatomaceous earth to filter and developed tubular filters fired from diatomaceous earth. During the cholera epidemic in Hamburg in 1892, these Berkefeld filters were used successfully.One form of diatomaceous earth is used as a filter medium, especially for swimming pools. It has a high porosity because it is composed of microscopically small, hollow particles. Diatomaceous earth is used in chemistry as a filtration aid, to increase flow rate, and 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, sugar, and honey without removing or altering their color, taste, or nutritional properties.
Abrasive
The oldest use of diatomite is as a very mild abrasive and has been used in toothpaste, metal polishes, and some facial scrubs.Pest control
Diatomite is of value as an insecticide because of its abrasive and physico-sorptive properties. The fine powder adsorbs lipids from the waxy outer layer of the exoskeletons of many species of insectswhich layer acts as a barrier that resists the loss of water vapour from the insect's body. Damaging the layer increases the evaporation of water from their bodies, so that they dehydrate, often fatally.This also works against gastropods and is commonly employed in gardening to defeat slugs. However, since slugs inhabit humid environments, efficacy is low. Diatomaceous earth is sometimes mixed with an attractant or other additives to increase its effectiveness.
The shape of diatoms has not been proven to affect their functionality as regarding adsorption of lipids. However, certain applications, such as that for slugs and snails, work best when a particularly shaped diatom is used, suggesting that lipid adsorption is not the only factor involved. For example, in the case of slugs and snails, large, spiny diatoms work best to lacerate the epithelium of the mollusk. Diatom shells will work to some degree on the vast majority of animals that undergo ecdysis in shedding cuticle, such as arthropods or nematodes. It also may have other effects on lophotrochozoans, such as mollusks or annelids.
Medical-grade diatomite has been studied for its efficacy as a deworming agent in cattle; in both studies cited the groups being treated with diatomaceous earth did not fare any better than control groups. It is commonly used in lieu of boric acid and can be used to help control and possibly eliminate bed bugs, house dust mite, cockroach, ant, and flea infestations.
Diatomaceous earth is widely applied for insect control in grain storage. It is used to control cannibalistic behaviors in confused flour beetles, which infest flour storages.
To be effective as an insecticide, diatomaceous earth must have a mean particle size below about 12 μm ; and it must be uncalcinated.
Although considered to be relatively low-risk, pesticides containing diatomaceous earth are not exempt from regulation in the United States under the Federal Insecticide, Fungicide, and Rodenticide Act and must be registered with the Environmental Protection Agency.