Project Description
Bentonite is a rock composed of minerals from the clay group. Their internal structure of superimposed layers of different chemical composition defines their key characteristic: their capacity to absorb a quantity of water several times greater than their own volume. This is produced through storage of fluid in the spaces that exist between the different layers. Bentonites originate from the alteration of volcanic rocks, also through processes of hydrothermal alteration (rise of hot solutions through fractures) or also through weathering alteration (due to the action of meteoric water). The special composition of the Cabo de Gata volcanic complex means that within it the greatest concentration of bentonite deposits in Spain formed. In fact, they constitute the only exploited industrial minerals that exist within the Natural Park.
The Cabo de Gata bentonites are by nature around 75% to 95% Calcium-SodiumMagnesium types, and the rest of the rock consists of other types of clays and small quantities of other minerals originating from volcanic rocks. They display various colours, from reds, greens, yellows and blacks, to whites. The deposits have an irregular and stratified morphology
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Bentonite mining is carried out through an open cast quarry method. In a modern quarry the following activities are undertaken:
◗ Conditioning and preparation The discovery of productive layers takes place with the help of excavating machines or mechanized tractors.
◗ Extraction Once the surface is cleaned off, quarrying is carried out by cutting down benches lengthwise along the face, with a height of about 10 metres and a length close to 50 metres.
◗ Drying and classification The material quarried in this way is spread out across large areas or “heaps”, cleaned of impurities and classified by qulaity according to the use for which it is destined.
◗ Storage The dried and classified material is stored in large uncovered piles ready for transport to treatment plants or for direct sale.
USES AND APPLICATIONS
Bentonite clays, due to their physical properties, are utilised in many industrial fields.
◗ In the smelting industry they are used, along with siliceous sand, to prepare the mould of manufacture parts, in that they are capable of fusing together the sand, without altering the composition of the cast.
◗ Addition to cements allows mortars to remain fluid for a longer period of time, for which its use is essential in special cements.
◗ As an integral part of drilling mud. Due to its addition, the viscosity of the drilling mud increases and is capable of pulling out broken components more easily. Additionally, it is capable of covering and keeping the walls of the borehole intact when drilling of the borehole finishes.
◗ Its addition to powdered irons minerals means that they can be recovered in a profitable way from smelting.
◗ Their capacity for absorbing water and ionic exchange means that they can serve as cleansing aids and fertilizers, also as discolourants and clarifiers of wines and oils.
◗ Properly compacted it is an excellent impermeable material, used to this end for holding back and securing residues in storage containers and potentially contaminant substances.
References
Geology of the arid zone of Almeria. 2003
