Diatomite

Diatomit

Diatomite is used as an industrial raw material with the definitions of Kiselgur and Diatomite derived from the German words “Kieselgur” and English “Diatomaceous Earth”. In the trade, Libyan diatomite is known as Tripoli, and Danish diatomite with 20-25% plastic clay content is known as Moler. Diatomite is a rock consisting of clay, sand, volcanic ash, and other organic residues as well as diatom skeletons, which are single-celled algae species living in shallow (0-35 m) depths where photosynthesis occurs intensively in fresh and saltwater reservoirs in areas with high volcanic activity. Diatome skeletons have SiO2.nH2O content.

The chemical composition of diatomites varies depending on the environmental conditions in which they are formed. Its hardness varies between 4,5-6 in accordance with its content, hardness decreases up to 1,5 due to its brittle structure and granularity. The diatom skeletal remains that makeup diatomite vary between 5-1000 µm in size, but predominantly average sizes are between 50-100 µm; 40 billion grains can be found in one cubic inch. In diatomite, the spaces between diatoms with hollow skeletons and diatom grains constitute the total porosity, and the void value can be up to 95%. Depending on their void values, they can absorb up to three times their weight in water. Their thermal conductivity is 0.08 at 100-300º C, 0.10 at 800º C, and 0.11 Kcal/m2.c.h. at 1200º C. Depending on the impurities they contain, their melting temperatures vary between 1000-1500º. Diatomites are resistant to many chemicals, but are affected by strong bases at high temperatures, and are not resistant to hydrofluoric acid due to its chemical composition. Diatomites, whose whiteness degree can reach up to 90% depending on the content, find the opportunity to be used in many different areas of the industry with their low density, moderate refractoriness, high absorption capacity, crushability to small grain size, and high surface area value. Diatomite is used in industry;

• Natural Diatomite
• Calcined Diatomite
• White Calcine (Flaks Calcine), marketed as diatomite

In all three types, there are various diatomite products with different grain sizes, and physical and chemical properties produced by different companies in line with the requirements of the industry. The usage areas of diatomite products can be listed as follows in order of importance:

• Filter auxiliary material,
• Filling material,
• Insulation (heat, sound, electricity) material,
• Absorbent,
• Abrasive
• Catalyst carrier,
• Lightweight building material,
• Refractory material,
• Silica source,
• The regulator in fertilizers.

Filtration aids are used to remove unwanted solids suspended in water. The filtration process is mechanical, the auxiliary material (diatomite) is not chemically mixed with the liquid. In the filtration of the liquid, the aid is collected in a thin layer on the surface of the filter (fabric, sieve, porous stone or metal) together with the unwanted solids. A small amount of diatomite is added to the liquid during the filtration process. The diatomite products used have various characteristics in accordance with the liquid types and filtration processes. In general, grain size is important, coarse grains provide increased resistance and very high transparency with slow filtration. Diatomite is used as a filtration aid for sugar syrup, beer, wine, whisky, fruit juices, vegetable oils, industrial waste liquids, pool water, chemicals, varnish, and mineral oil filtration. In recent years, it has been used as a solid filter in biotechnology for cleaning environmental pollution and the regeneration of soils.

FILLING MATERIAL

Fillers are substances used to ensure the cheapness of industrial products without deteriorating their quality and to improve their performance by improving their properties. Diatomite is used as a filler in paper, rubber, plastic, pharmaceutical, cosmetic, toothpaste, polish, and various chemical industry products, especially in paint. In practice, diatomite’s lightness, durability, resistance to chemicals, heat, sound, and electrical insulation ability, and high absorbency are utilized. The degree of whiteness gains importance according to the areas of use. In the paint industry, in order to obtain smooth surfaces, diatomite is a sought-after filler although it is more expensive than materials such as chalk and clay, which it is used instead of diatomite, and diatomite with a grain size of 200-300 µm is added to the paint at a rate of 2-3%.

INSULATION MATERIAL

Diatomite is used in the production of plates for sound and heat insulation with lime and cement. At high temperatures, the air gaps in the insulation material provide intense radiation and rapid convection. The larger the air gaps, the greater the radiation; for this reason, large-sized diatomite contents are sought in diatomites to be used in insulation. Diatomite materials in the form of powder, sand, block, and plate are used in various applications in cold storage.

ABSORBENT

Diatomites have the ability to absorb liquid 3-4 times their weight. With these properties, they are used as litter for domestic animals, stables, poultry houses and especially in fur breeding farms. For example, the Danish product Moler is extensively used as animal litter in Northern Europe and Scandinavia. Nitroglycerin was first impregnated with diatomite to ensure safe transport. Acid bottles are transported in diatomite-filled packages to prevent breakage. In recent studies, zeolite material has been used instead of salting operations on highways. In this regard, diatomite can be an alternative material to zeolite.

ABRASIVE

With its soft abrasive properties, diatomite is used as a polisher, especially in the automotive industry. Cleaned natural diatomite is used as a very soft abrasive in the formulation of jewelry polishers.

CATALYSER CARRIER

Diatomite is used as a catalyst carrier for nickel catalysts in the hydrogenation process and for vanadium catalyst applications in sulphuric acid production.

LIGHTWEIGHT CONSTRUCTION AND REFRACTORY MATERIAL

Diatomite is used in lightweight construction and refractory brickmaking. British Columbia (Canada) volcanic ash diatomites are used only for this purpose. Fire resistance of buildings is provided by this application. Danish Moler diatomites, with their 20-25% plastic clay content, are the sought-after material for making bricks resistant to thermal shocks, low gas permeability, and resistant to acids.

SILICA SOURCE

With its silica content, diatomite is used in the production of synthetic silicates such as calcium and magnesium silicate. It is used as silica raw material in the ceramic and glass industry (Romania).

USE IN FERTILISERS

It is especially used to prevent caking in ammonium nitrate fertilizer.

LIGHTWEIGHT CONSTRUCTION AND REFRACTORY MATERIAL

In the cement industry, diatomite is used to remove excess water from concrete and to ensure homogeneity. When 3% diatomite is added to concrete mortar, the compressive resistance of concrete increases by 20% and tensile resistance by 10%. It is also used in the production of detergents, cleaners, harmful plants and fungicides, and ceramic glaze. In order to increase the conversion efficiency of feed to meat, 2% diatomite can be added as an additive to the feed used especially in chicken breeding. During the Hundred Years’ War in Europe, diatomite was added to flour in bread-making due to famine.

Natural diatomite is obtained by drying the raw diatomite ore and roughly separating the impurities in it. Calcined diatomite is obtained by calcining natural diatomite in rotary kilns heated with fuel oil or natural gas at an appropriate temperature of 870-1090°C depending on the properties of the raw material and the production method. In calcination, the organic substances in the diatomite shells are burnt and the skeletal pores are opened. Diatome particles shrink and harden and the crumbs come together and fuse. The material coming out of the rotary kiln in hazelnut size is cooled and crumbled, and foreign and sintered grains are separated by separators and cyclones, classified according to grain size, and packaged. In accordance with the iron oxide content of the material, calcined diatomite gets pinkish color. In order to obtain a white calcined diatomite product with a high filtration rate, 3-8% soda (NaCO3) or salt (NaCl) is added before calcination. Under the effect of alkaline salt, iron oxides are removed from the environment and white colored product is obtained. Aluminum oxides are also easily separated by separators. Product properties can be adjusted and products with different filtration properties can be obtained by changing the grouping of diatomite grains and crumbs, furnace temperature, alkali salt ratio, and calcination time in a controlled manner.

The diversification of properties in diatomite products limits their usage areas. Characteristics desired to be defined in diatomites: The diatomite grain size, size distribution, free and bound moisture, wet and dry density, liquid absorption capacity, pH value, color, chemical composition, and microscopic texture. In the calcination process, the amorphous silica in natural diatomite is transformed into crystalline silica cristobalite. Since crystalline silica causes silicosis and fibrotic lung diseases, shift hours of workers working in production and inhalable crystalline silica limits in the air have been limited. The upper limit of crystalline silica smaller than 10 microns for clean air is accepted as 150 mg/m3 by health organizations.

Turkey’s diatomite reserves are generally in the form of deposits suitable for open-pit production. Before starting the operation, the production method is determined by determining the quality and size by drilling, and production is ensured by digging and transporting construction machinery. The moisture content of the diatomite, which has a moisture content of up to 50%, is reduced by open field drying in the field and transported to the plants. The mining cost is around 10% in the production of finished goods. In the plants, production is carried out with appropriate processes selected according to the usage areas of diatomite. Turkish Sugar Factories Inc. established a pilot plant in 1974 to obtain filtration products for sugar production, the plant started production in 1980 and the plant was closed in 1994 because perlite was used instead of diatomite. Today, perlite is not used either.

Diatomite consumption areas are generally defined as filtration industry with 66%, 21% filling, 1% insulation, and 12% other uses. As a filter auxiliary material, its biggest consumer is the sugar industry, while today lime and CO2 are used for cleaning sugar syrup in Turkish Sugar Factories (e.g. Eskişehir Sugar Factory). It is mainly used in the liquid food industry, mainly in breweries and wineries.

Türkiye diatomit rezervleri genellikle açık işletme ile üretim yapmaya elverişli yataklar halindedir. İşletmeye geçilmeden önce sondajlar ile kalite ve boyut saptaması yapılarak üretim yöntemi belirlenir, kazıcı ve nakledici iş makineları ile üretim sağlanır. Nem oranı %50 ‘ye kadar çıkan diatomitin nemi sahada açık alan kurutması ile düşürülerek tesislere nakledilir. Mamul madde üretiminde madencilik maliyeti %10 civarındadır. Tesislerde, diatomitin kullanım alanlarına göre, seçilen uygun proseslerle üretim yapılır. Türkiye şeker Fabrikaları A:Ş. Şeker üretiminde filtrasyon ürünü elde etmek için 1974 yılında pilot tesisi kurmuş, tesis 1980 de üretime geçmiş ve 1994 yılında diatomit yerine perlit kullanımına geçildiği için tesis kapatılmıştır. Bugün perlit de kullanılmamaktadır.

Diatomit tüketim alanları, genelde %66 lık oranla filtrasyon sanayi, %21 dolgu, %1 izolasyon ve %12 diğer kullanım olarak tanımlanır. Filtre yardımcı malzemesi olarak en büyük tüketicisi şeker sanayi iken bugün Türkiye Şeker Fabrikalarında (Örneğin Eskişehir Şeker Fabrikası) şeker şerbetinin temizlenmesi için kireç ve CO2 kullanılmaktadır. Sıvı gıda sanayinde, başlıca bira ve şarap fabrikalarında, ağırlıklı olarak kullanılmaktadır.