Benutzer:Veronika Fischer/Neuburg Siliceous Earth

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Neuburg Siliceous Earth is a natural mixture with dominant fractions of ultra-fine silica particles and 20 to 40 percent by weight kaolinite.

The only known deposits worldwide with this unique composition are found near Neuburg an der Donau. Because of its purely mineral formation, Neuburg Siliceous Earth is not like the commonly known siliceous earth or diatomaceous earth, which have biological origins and developed from diatoms. There is only one mining company left today that still mines Neuburg Siliceous Earth, Hoffmann Mineral GmbH in Neuburg an der Donau. About 55,000 tons of the purified mineral are sold annually. This requires the extraction of 120,000 t of raw siliceous earth. After gentle suspension in well water, the finest fraction of the siliceous earth is separated by means of a hydrocyclone. Neuburg siliceous earth is used as a high-quality functional filler or as a polish in many industrial applications. Thanks to its purity, it is also suitable for use as a dietary supplement.

Purified pulverised Neuburg Siliceous Earth

Geology

Neuburg siliceous earth was formed about 93 to 98 million years ago in the Cenomanian, lowest stage of the Upper Cretaceous period in a bay that was located in today's occurrence area, as the finest sediments were deposited from weathered granitic masses of the Northern Upper Palatinate. The index fossil is Inoceramus crippsi.

Fine structure under the scanning electron microscope

Mineralogy

Neuburg siliceous earth was probably already formed as a mixture of minerals. It essentially consists of very fine crypto-cristalline particles (appearing amorphous, particles smaller than 1 micrometer) and amorphous silicic acid with a total of 60 to 80 percent by weight, and the rest consists of lamellar (flaky) kaolinite. Contrary to previous assumptions, the silicic acid fraction is not composed of quartz, since the basic characteristics of quartz are lacking, but rather a special SiO₂-modification. Influences from the nearby Ries impact are being discussed, the meteor strike that lead to the formation of the Nördlinger Ries.

Finding natural mineral deposits

Neuburg siliceous earth is found in funnels and run-ins in the underlying Jura limestone. Surface-near deposits were undoubtedly already discovered long ago, since they are sometimes only covered by a thin layer of soil. The deposits still remaining today are generally found under young geological layers at a depth of five to twenty meters. In the past, exploration was achieved by taking cores with manual devices. Today, machine drilling continuously produces crushed borehole cuttings at much lower costs, whereby the siliceous earth can be easily distinguished from the soil and limestone on-site and without special analysis.

Mining

Today's open pit mining

Already the Romans used Neuburg Siliceous Earth for fire-resistant linings in kilns and for potteries. It was only around 1830 that the material was specifically extracted again. Chemists discovered the formula for producing the extremely expensive pigment ultra-marine blue, for which Neuburg siliceous earth is very suitable as a natural raw material. Bis weit ins 19. Jahrhundert erfolgte der Abbau der oberflächennahen Vorkommen überwiegend im Tagebau. Until well into the 19th century, the surface-near deposits were extracted mainly from open pit mines. Beginning at the end of the 19th century, mineral deposits were increasingly exploited through underground mining, since it was often easier to dig through thicker layers of soil than to remove it completely. When mining underground, however, large portions of the deposits could not be used, since valuable material had to remain intact for structural reasons. For this reason, modern, efficient open pit mining replaced underground mining for good with the closing of the last extraction sites operated underground in 1979. With modern surface mining, backhoe excavators not only rapidly remove the overburden layers, they also have the tremendous tear-out forces required to quarry out the raw material. Blasting is only rarely necessary.

Recultivation and renaturation

Pond habitat

The mining of Neuburg siliceous earth is an encroachment in nature, which is compensated with recultivation and renaturation. Once mining operations in a deposit have ceased, the large craters are filled with excavation material and with sands and other rocks that were separated during purification. To ensure the growth of forests or for the purpose of agricultural cultivation, humus layers are spread lastly on top. Moreover, ecologically valuable wetlands are regularly created during the course of mining operations. Such biotopes are also specifically preserved after mining operations have ceased. They offer a habitat and spawning grounds for threatened species such the yellow-bellied toad (Bombina variegata), tree frog (Hyla arborea), smooth newt (Triturus vulgaris), Alpine newt (Triturus alpestris) und crested newt (Triturus cristatus).

Purification

First, the raw material is suspended in lots of well water. The usable finest fraction is extracted in successive physical separation processes by centrifuging in hydrocyclones. Afterwards, the excess water is re-separated and pressed out, and finally the material concentrated on moist filter cakes is gently dried in a natural gas-powered turbine dryer to produce its powdery final quality.

Use

Ultramarine blue

The first use in modern times occurred around 1830, since ultra-marine blue was preferably produced in Germany using Neuburg Siliceous Earth. Before that, very expensive semi-precious stones (lapis lazuli) were used. This revolutionary discovery of the simple production method in the melt flow from aluminous silicate, sulfur and other ingredients brought on a rapid upswing for Neuburg siliceous earth, because its virtually ideal composition and great fineness make it the perfect raw material. Although this use was highly significant in the past, it does not play a role anymore today.

Polishes

Still widely used today as an abrasive in polishes and household cleaners, these applications enjoy a long tradition since the second half of the 19th century. Acetic polishes are very easy to produce thanks to the acid resistance of Neuburg siliceous earth and also its good natural polishing properties.

Fillers

Application: Automomobile seal profile

Neuburg siliceous earth is mainly used today as a filler for polymers. This application became popular in the 1920s with the widespread introduction of rubber goods. The loose powder is most notably distinguished by its good miscibility and small grain size. Automobile hoses, floorings and roof sheeting for the construction sector contain high fractions of this filler. In the paint and coatings industry, electrophoretic painting and anti-corrosion coatings are important fields of application. Thanks to its purity, Neuburg siliceous earth is good for use in materials for the food sector.

Dietary supplements

Because the silicic acid and trace elements are readily digestible and the natural properties are preserved by the gentle purification, Neuburg siliceous earth is also suitable for use as a dietary supplement.

Literature

• Schönrock, Dirk: Neuburger Kieselerde. Gewinnung, Veredelung, Anwendungen als funktioneller Füllstoff. Die Bibliothek der Technik, Bd. 308, Süddeutscher Verlag onpact, München 2008, ISBN 978-3-937889-77-1

Weblinks

Commons: Veronika Fischer/Neuburg Siliceous Earth – Sammlung von Bildern, Videos und Audiodateien

• Bavarian Ministry of Economic Affairs, Infrastructure, Transport and Technology: Karte Rohstoffe Bayern (PDF-Datei; 819 KB)
• Hoffmann Mineral