Bentonite , named after the benton formation in the Fort Benton clays of Montana (USA), is a rock that is a mixture of different clay minerals and contains montmorillonite (60% to 80%) as the most important component , which is its strong water absorption - and the ability to swell explained. Further accompanying minerals are quartz , mica , feldspar , pyrite or calcite . It is created by weathering from volcanic ash .
The inner surface of one gram is 400 m² to 600 m² (normal clay: 2 m²). It therefore forms particularly valuable clay-humus complexes , so that uncontaminated bentonite is also a good addition to the compost .
If bentonite is stirred into water, a non-Newtonian fluid with thixotropic properties develops . It behaves like a liquid as long as it is shaken or stirred, but changes to a solid structure at rest. Because of this property, bentonite-water mixtures are used, among other things, in civil engineering as a support fluid when creating diaphragm walls . It is also suitable for supporting uncased bored piles or for shield driving in tunnel construction.
Bentonite deposits are always found where (not only) volcanic ash has been altered by hydrothermal activities and acids. One of the largest European deposits is on the Greek island of Milos . Bentonite, quartz and perlite are found there in minable quantities. Associated gold deposits have also been identified.
In Germany there are minable deposits in Lower Bavaria ( Mainburg , Landshut and south of Landau an der Isar ) and in eastern Upper Bavaria and near Thannhausen . According to Baier, these occurrences were related to the Ries event and were formed from glass caused by the impact ; According to Unger, on the other hand, the bentonites in Eastern Bavaria were caused by volcanism in the Pannonian Plain .
Bentonite has an important application in construction technology , including building waterproofing and building dikes . Because of their color, such seals are also known as brown tubs . Bentonite is used as a lubricant when driving tunnels and pipes , vibrating in narrow walls . When heat is obtained from geothermal energy through the use of heat pumps, the collector pipes of the geothermal probes are often coated with bentonite, because this binds the water and prevents the formation of cavities when freezing. Bentonite is a mineral sealant with a wide range of uses, such as the immobilization of pollutants and the encapsulation of contaminated sites.
Mining and drilling technology
In drilling fluids for boreholes and in support fluids for unsupported diaphragm walls .
In the beverage industry (in winemaking and in the production of fruit juices) as well as in cocoa butter , bentonite is used as a fining agent (i.e. as a clarifying and precipitating agent) (no longer present in the end product). It is used as a release agent in food . It is also known as a food additive under the name E 558 . E 558 has not been approved in the EU since May 31, 2013 .
Garden ponds and aquariums
The clay mineral montmorillonite is an important component in aquariums and garden ponds, especially for Koi . The mineral is sprinkled into the pond in the form of special dried and ground clay powder. While the distributed clay powder sinks to the bottom of the pond, it absorbs heavy metals, toxins and other suspended matter and binds them. The clay sludge can be vacuumed from time to time.
Bentonite, as a natural clay mineral mixture, is the basic material of many cosmetics, as it has a stabilizing effect in emulsions due to its strong swelling and water absorption capacity. The INCI name is bentonite .
In ceramics , bentonite is used in small proportions (up to approx. 5%) as an aggregate in order to give otherwise very lean masses malleable properties (" plasticity ").
Other possible uses are given by the use as an adsorbent than are:
- Oil and beverage refining
- Foundry additive
- Paper additives and specialties
- Horticulture, to improve sandy soils
- Civil engineering
- Detergent additives
- Wastewater treatment
- Pharmacy and diagnostics / electronics and logistics
- Lacquers and paints
- Plastic additives
- Nanotechnology - surface coatings
- cat litter
- Desiccants , e.g. B. as a dry bag in packaging
Some of these applications use bentonite treated with quaternary ammonium compounds . Furthermore, bentonite is used as an artificial barrier in the final storage of radioactive waste .
- RE Grim, N. Güven: Bentonites - geology, mineralogy and uses. Developments in Sedimentology. In: Elsevier. Amsterdam 24. ISSN 0922-3444
- Decher, Andreas; Friedrich, Günther (1991) Bentonites from the Cabo de Gata. The Earth Sciences; 9, 10; 305-316; doi : 10.2312 / geosciences . 1991.9.305 .
- Mindat - Bentonite (English)
- ^ Thomas A. Drean: Wyoming State Geological Survey. Retrieved December 4, 2019 .
- ^ Mindat - Bentonite and type locality Fort Benton shales, Wyoming, USA
- ↑ Alwin Seifert: Gardening - fields without poison .
- ↑ Milos: Where Greece is still very rich , accessed on April 18, 2015
- ↑ Johannes Baier: The ejection products of the Ries impact, Germany in Documenta Naturae , Vol. 162, Munich, 2007; ISBN 978-3-86544-162-1 .
- ↑ Johannes Baier: On the origin and importance of the Ries ejection products for the impact mechanism. In: Annual reports and communications from the Upper Rhine Geological Association. 91, 2009, pp. 9-29, doi : 10.1127 / jmogv / 91/2009/9 .
- ↑ Explanations of the Geological Map of Bavaria, 4th revised edition, editor and publisher: Bayerisches Geologisches Landesamt, Munich 1996. There chapter 4.4.4, sub-item “Bentonites of the east molasses”, by Heinz Josef Unger.
- ↑ bentonite
- ↑ EU Regulation No. 380/2012 of the Commission of May 3, 2012 with regard to the conditions and quantities of use for food additives containing aluminum (PDF)
- ↑ Interview with Janne Mokka, interview conducted by: SEBASTIAN BALZTER: ATOM PIONEER FINLAND: “Our repository will be ready soon” . In: Frankfurter Allgemeine Zeitung , FAZ F + from 14.06.2020 . June 14, 2020 (Finland is building the world's first nuclear waste repository. The residents are satisfied with it, the Finns even have the costs under control. A conversation with Janne Mokka, head of the operating company.).