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Bentonite

 

Bentonite is a type of clay consisting predominantly of montmorillonite.  Bentonite’s mineral and chemical compositions vary considerably with montmorillonite comprising typically between 40% to 65% together with variable amounts of illite, kaolinite, aluminosilicates and minor amounts of gypsum, sodium chlorite and calcium carbonate.  The bentonitic clays of Cyprus were deposited as deep-water sediments from the alteration of volcanic ash during the Upper Cretaceous period (approximately 90 million years ago), roughly contemporaneously with the Upper Pillow Lavas or locally with the umber and radiolarites of the Perapedhi Formation. They were then either reworked or directly overlain by the pinkish clay and chalk of the Lefkara Formation.

 

Bentonite has a very high plasticity, good swelling properties and variable colour from greenish grey/yellowish brown to khaki or pinkish.  The key property of bentonite that makes it an industrial mineral with a variety of uses is the ability to swell with absorption of water and shrink with the expulsion of water.  The amount of water it can absorb reaches five times its weight and is associated with an increase of its volume of up to 15 times.  This property can be repeated many times.  To be suitable for commercial exploitation the raw bentonitic clay material should have the following properties: low calcium carbonate, high montmorillonite content, low soluble salts (chlorides and gypsum) and high plasticity.  Tests used on raw bentonite include moisture content, Atterberg limit, swelling properties (absorption rate), montmorillonite content, chemical analysis particularly for carbonate content and water-soluble salts and water absorption.

 

Bentonite is excavated periodically from shallow quarries and transported to factories where it is laid down to dry and is blended before processing.  Most of the bentonitic clays from Cyprus are exported for use as pet litter.  However, a sodium activation process has been developed to improve the properties of the natural bentonite.  The main uses of bentonite internationally include drilling muds, foundry sand binders, civil engineering and iron ore pelletisation.  Small quantities of bentonitic clays are used in Cyprus for geotechnical works such as dam construction.

 

Bentonite outcrops widely around the Troodos Mountains, covering an area of about 80 km2.  Taking account of other geological constraints the total resource is estimated around 2 billion tonnes.  The deposits vary considerably in size and in distribution but comprise more or less regular layers that may reach more than 50 m in total thickness.  Some gypsiferous bentonite outcrops south of Arsos village in the Famagusta district with an estimated reserve of about 400,000 tonnes.

 

 

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