Diatomite

By Robert D. Crangle, Jr.

Domestic survey data and tables were prepared by Elsie D. Isaac, statistical assistant, and the world production table was prepared by Glenn J. Wallace, international data coordinator.

 

Production of diatomite in the United States decreased by 10% to 735,000 metric tons (t), with a corresponding value of $210 million free on board (f.o.b.) plant in 2012 compared with 813,000 t valued at $219 million f.o.b. plant in 2011 (table 1). The decrease in production was largely offset by an increase in prices. the United states was the leading producer of diatomite in 2012, accounting for 35% of total world production. Estimated world production was 2.1 million metric tons (Mt), a decrease of 3% from that of 2011. twenty-three countries reported the production of diatomite in 2012.

Diatomite used for filtration represented 56% of consumption, followed by its use as a filler (14%), as an absorbent (13%), and as a cement additive (13%). other diatomite applications, including abrasives, insecticides, insulation, and soil conditioner, accounted for the remainder (table 2). Major diatomite products were sold as various grades of calcined powders.

Encroachment into diatomite markets by natural and synthetic substitute material remained minimal, particularly for beverage filtration.

Diatomite is a chalk-like, soft, friable, earthy, very fine-grained, siliceous sedimentary rock comprised of fossilized diatom remains. Diatomite often has a light color (white if pure, commonly buff to gray in-situ, and rarely black). It is extremely lightweight because of its low density and high porosity, and essentially chemically inert. Diatomaceous earth (often abbreviated as D.E.) is a common alternate name but is more appropriate for the unconsolidated or less lithified sediment. Diatomite is also known as kieselguhr (Germany), tripolite (after an occurrence near Tripoli, Libya), and moler (an impure Danish form). Alfred Nobel named his explosive invention “dynamite” following his discovery that nitroglycerin could be stabilized if first absorbed in diatomite (Nobel, 1868). A unique attribute of diatomite is found within its microstructure, which often contains thousands of individual holes. These hollows are typically found in three distinct sizes, from micron to submicron diameters. The number and sizes of the holes vary with the species (Imerys, 2012).

Diatomite deposits form from an accumulation of amorphous hydrous silica cell walls of dead diatoms in both oceanic and fresh waters. These microscopic single-cell aquatic plants (algae) contain an internal, elaborate siliceous skeleton consisting of two frustules (valves) that vary in size from less than 1 micrometer (^m) to more than 1 millimeter in diameter but are typically 10 to 200 ^m in diameter. The frustules have a broad variety of delicate, lacy, perforated shapes, including cylinders, discs, feathers, ladders, needles, and spheres. Additional information on the environmental and physical properties of diatoms can be found in Dolley and Moyle (2003) and Moyle and Dolley (2003). The oldest occurrences of diatomite are thought to be of Cretaceous age, deposited about 66 million to 138 million years ago. Older diatomite occurrences may have been altered into other forms of silica, particularly chert, owing to diagenesis, burial, and exposure. Detailed information on the geology of diatomite can be found in Wallace (2003) and Moyle and Dolley (2003).

Production

Domestic production data for diatomite were developed by the U.S. Geological Survey (USGS) from a voluntary annual survey of U.S. diatomite-producing sites and company operations. The USGS canvass for 2012 was sent to 7 diatomite-producing companies with 10 mining areas and 9 processing facilities. All companies responded, accounting for 100% of the production listed in table 1. All percentages in this report were computed based on unrounded data.

In 2012, 735,000 t of diatomite were produced from 10 separate mining areas in California, Nevada, Oregon, and Washington. Major producers were Celite Corp. (a subsidiary of Imerys USA, Inc.) with mines and facilities in California, Nevada, and Washington; and EP Minerals, LLC (a subsidiary of EaglePicher Corp.) with operations in Nevada and Oregon. Nevada was the leading producing State, followed by California. The combined output of these two States accounted for about 77% of U.S. production in 2012.

Because U.S. diatomite occurrences are at or near the earth’s surface, recovery from most deposits is achieved through low- cost, open pit mining. outside the United States, however, underground mining is fairly common owing to deposit location and topographic constraints. Explosives are generally not required for surficial or subsurface mining because of the soft, friable nature of the deposits. In Iceland, dredging is used to recover lake-bottom diatomaceous mud deposits.

Diatomite is often processed near the mine to reduce transportation costs associated with the crude ore, which can contain up to 65% water. Processing typically involves a series of crushing, drying, size-reduction, and calcining operations, using heated air for conveying and classifying within the plant. Fine-sized diatomite grains, especially from baghouses, are used most often for filler-grade products, and coarser particles are employed for filtration purposes. In the latter processing stages, calcining is performed in rotary kilns to effect chemical and physical changes.

Diatomite production costs for the United States average 60% to 70% for processing, 20% to 30% for packing and shipping, and 10% for mining. Energy costs compose a large and increasing portion (25% to 30%) of diatomite production costs, both in the direct costs of mining and transportation, as well as within the energy-intensive calcining process. Diatomite used for cement production does not normally require calcining, and thus, processing costs are lower.

Consumption

Domestic apparent consumption of diatomite was approximately 643,000 t in 2012, a decrease of approximately 9% from 707,000 t in 2011. The total domestic and export quantity of filter-grade diatomite sold or used by U.S. producers was 415,000 t in 2012, a decrease of 16% from 500,000 t in accounting for 56% of total diatomite produced. For use in absorbents, 95,000 t of diatomite was reported, unchanged from that of 2011. Use of diatomite as a filler was 102,000 t in an increase of 3% from 99,000 t in 2011.

In antiquity, diatomite was used by the Greeks as an abrasive and in the production of lightweight building bricks and blocks. In the late 1800s, diatomite became of industrial interest in Western Europe when pulverized diatomite was the preferred absorbent and stabilizer of nitroglycerine used to make dynamite. Maryland was the site of the first U.S. production of diatomite in 1884. By the late 1880s, very pure, large deposits near Lompoc, CA, became the focus of interest and have continued to dominate world markets (Dolley and Moyle, 2003). Although diatomite is principally used as a filtration medium, it is also used as a silica additive in cement and various other compounds, a filler in a variety of products, an absorbent, an insulation medium, a mild abrasive, and an agent in the purification and extraction of DNA.

Commercial diatomite products provide fine-sized, irregular- shaped, porous noncaking particles that have a large surface area and high liquid-absorption capacity. They are relatively chemically inert, have a low refractive index, are mildly abrasive, have a low thermal conductivity with a reasonably high fusion point, can be slightly pozzolanic, are very high in silica, and can be produced and delivered at a cost consistent with customer applications. sawn shapes, which continue to account for a significant part of world diatomite production, have long been used as lightweight building material, especially in china, and primarily for thermal insulation (especially the high-clay-content Danish moler). Dried natural products and calcined products are used in building applications. The major use of diatomite continues to be as a filtration medium for beverages (especially beer and wine), sugar and sweetener liquors, oils and fats, petroleum and chemical processing (including reprocessing waste dry cleaning fluids), pharmaceuticals, and water (industrial process, potable, swimming pool, and waste). Another leading use is as an absorbent for industrial spills (oil and toxic liquids) and for pet litter.

Another important broad category of use is as a filler, often serving a dual purpose, such as an extender and flatting agent in paints and coatings; a bulking and anticaking agent in granular materials; and as a multieffect component in plastics (including preventing films from sticking). Other filler uses are as an extender and absorbent carrier for catalysts, nontoxic pesticides (as a desiccating agent), pharmaceuticals, and other chemicals.

Brightness, whiteness, and abrasive hardness are considered for specialized diatomite applications. Free-crystalline silica content, although normally low, is required to be identified, particularly for calcined products. calcining removes organics, increases filtration rate, oxidizes iron, increases specific gravity, increases particle hardness, and can lighten color. Flux-calcining significantly affects the physical and chemical properties and makes a white product. Most filter grades are calcined.

Prices

The calculated weighted average unit value of diatomite sold or used by U.S. producers during 2012, using USGS survey data and estimates, was $286 per metric ton f.o.b. plant, an increase of about 6% compared with $269 per ton in 2011 (table 3). The average values for filtration increased by 39% in 2012 to $381 per ton from $274 per ton reported in 2011. The value for diatomite used for absorbent purposes was $101 per ton, unchanged from 2011. The unit value for material used as fillers decreased by 3% to $399 per ton in 2012. The average value for specialized or other uses in 2012 decreased by 5% to $424 per ton from $446 per ton in 2011.

Foreign Trade

Export and import data presented here from the U.S. census Bureau may be of limited accuracy. This is a result of a lack of detail caused by the inclusion of diatomite with other mineral commodities within several categories in the Harmonized Tariff schedule of the United states (HTS) issued by the U.S. International Trade Commission. Exports of diatomite from the United States in 2012 were approximately 96,000 t, about 10,000 t less than those in 2011 (table 4). Exports accounted for about 13% of total domestic production sold or used. trade data were issued under heading 2512 of the HTS, described as applying to siliceous fossils, including kieselguhr, tripolite, diatomite, and similar siliceous earths of an apparent specific gravity of 1 or less. industry sources, however, indicated that exports also included some flux-calcined material, which is included under HTS code 3802.90.2000, where it is not differentiated from activated clays. similarly, heat-insulating mixtures and sawn and molded unfired shapes of diatomite are collected under HTS code 6806.90.0090 and are not exclusively identified as diatomite. Lastly, fired, sawn, and molded shapes of diatomite are covered under heading 6901, which is not exclusively used for diatomite data.

According to U.S. census Bureau data, diatomite and diatomite products were exported to 96 countries in 2012. The main export markets were Canada (17,900 t), Germany (12,000 t), Belgium (6,200 t), South Africa (4,600 t), and Russia (4,300 t). These five countries accounted for 47% of the total reported exports. Based on available census trade data, the average unit value free alongside ship of exported diatomite was $528 per ton in 2012 compared with $526 per ton in 2011 (table 4). Import data for diatomite show that 3,070 t came from 14 countries in 2012. France was the leading source with 2,110 t (69%); followed by Mexico with 456 t (15%), China with 312 t (10%), Italy with 91 t (3%), and Peru with 20 t (1%). These five countries provided 97% of the imports to the United States in 2012.

World Review

Estimated world production of diatomite in 2012 was 2.1 Mt (table 5). World reserves are thought to be almost 1 billion metric tons (Gt), which represents approximately 500 times the annual estimated world production rate. About 250 Mt, or 25% of the estimated 1 Gt of world reserves, is in the United States (Crangle, 2013). The world’s largest producing district in terms of volume is near Lompoc, CA. A resource assessment of this location suggested these deposits could meet all of the world’s current diatomite consumption for hundreds of years. compiling data regarding reserve estimates can be challenging because some data are proprietary and not released by companies or countries. Huge deposits, on the order of at least 110 mt of reserves, have been reported to occur in china (Lu, 1998, p. 53).

The United states was the leading producer of diatomite, accounting for 35% of total world production, followed by China with 20%, Denmark with 16% (all moler products), and Japan with 5%. smaller amounts of diatomite were mined in 20 additional countries.

Outlook

With the exception of depressed production during the global economic downturn in 2009 and 2010, U.S. annual production has been more than 600,000 t for many of the last 20 years, with production in several of those years exceeding 800,000 t. The economic stability of the mineral commodity was largely owing to its use as a filtration medium, where its demand remains strong, particularly in the filtration of spirits as well as human blood plasma and other biotechnical applications. Likewise, the encroachment of more advanced filter applications, including carbon membranes, ceramics, and polymers, were not a concern in 2012. the high costs associated with these alternatives and a cultural preference toward the use of diatomite in the brewing and wine industries indicate a strong likelihood for the continued widespread use of diatomite in filtration.

The associated issue of free-crystalline silica, particularly after diatomite is calcined, was expected to continue to be a concern, especially in the filler and absorbent markets. Although some diatomite deposits were reported to be low in free-crystalline silica, an effort to classify diatomite and related absorbent products as free of this material remains contentious, litigious, and, to date, unsuccessful. Adequate supplies of diatomite, owing to the large domestic and world reserves, coupled with small or no changes in demand, probably will remain available for the foreseeable future.

References Cited

Crangle, R.D., Jr., 2013, Diatomite: U.S. Geological survey mineral commodity Summaries 2013, p. 52-53.

Dolley, T.P., and Moyle, P.R., 2003, History and overview of the U.S. diatomite mining industry, with emphasis on the Western United states, in Bliss, J.D., Moyle, P.R., and Long, K.R., eds., contributions to industrial-minerals research: U.S. Geological survey Bulletin 2209, p. E1-E8.

Imerys, 2012, Diatomite: cornwall, United Kingdom, Imerys Minerals Ltd. (Accessed September 16, 2013, at http://www.imerys-perfmins.com/diatomite/eu/diatomaceous-earth.htm .)

Lu, Wen, 1998, chinese industrial minerals: surrey, United Kingdom, Industrial Minerals Information Ltd., 209 p.

Moyle, P.R., and Dolley, T.P., 2003, With or without salt—A comparison of marine and continental-lacustrine diatomite deposits, in Bliss, J.D., Moyle, P.R., and Long, K.R., eds., contributions to industrial-minerals research: U.S. Geological survey Bulletin 2209, p. D1-D11.

Nobel, Alfred, 1868, U.S. patent letter for dynamite: U.S. Patent 78,317, assigned to Julius Bandmann, 3 p.

Wallace, A.R., 2003, Regional geologic setting of late cenozoic lacustrine diatomite deposits, Great Basin and surrounding region—Overview and plans for investigation, in Bliss, J.D., Moyle, P.R., and Long, K.R., eds., contributions to industrial-minerals research: U.S. Geological survey Bulletin 2209, p. B1-B12.

GENERAL SOURCES OF INFORMATION

U.S. Geological Survey Publications

Diatomite. ch. in Mineral commodity summaries, annual.

Diatomite. ch. in United states Mineral Resources, Professional Paper 820, 1973.

Historical statistics for Mineral and Material commodities in the United States, Data Series 140.

Other

Diatomite. ch. in Industrial Minerals and Rocks (7th ed.), Society for Mining, Metallurgy, and Exploration, Inc., 2006.

Diatomite. ch. in Industrial Minerals Handbook II, Metal Bulletin plc, 1995.

Economics of Diatomite, The (8th ed.). Roskill Information services Ltd., 2005.

Mineral Products. ch. in Harmonized Tariff schedule of the United States, U.S. International Trade commission, 2011.

Oilfield Glossary. Schlumberger Ltd., 2008.