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Written by Administrator
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Thursday, 17 September 2009 23:04 |
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Because copper reacts readily with other substances, it can be found in a variety of ways in the Earth's crust. It is often found in deposits with other metals such as lead, zinc, gold and silver. By far the largest amounts of copper are found in the crust in bodies known as porphyry copper deposits. These deposits were once large masses of molten rock that cooled and solidified deep in the Earth's crust. As they cooled, some large crystals grew, which were then surrounded by smaller crystals — geologists call these rocks porphyries.  At first, the molten rock contained a small amount of copper. As it cooled and crystals began to form the amount of fluid became smaller. The copper remained in the fluid, becoming more and more concentrated. When the rock was almost completely solid, it contracted and cracked and the remaining copper-rich fluid was squeezed into the cracks, where it too finally solidified.
Over many millions of years the rocks covering these deposits eroded away and the deposits eventually appeared at the surface.
These deposits can contain 2 billion tonnes of rock which, when processed, gives 30 million tonnes of copper metal. |
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Last Updated on Thursday, 17 September 2009 23:13 |
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Bentonite Physico-chemical properties & composition |
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Written by Administrator
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Thursday, 17 September 2009 22:18 |
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Bentonite is a naturally occurring material consisting predominantly of the clay mineral montmorillonite. Montmorillonite is a material species in the family of sheet silicates called smectites. Other smecitite group minerals include hectorite, stevensite and saponite.
Indeed, the definition of bentonite can be expanded to include these other smectites, but deposits in which they predominate are more commonly referred to by other names (hectorite, urasite, etc...) Smectites are three-layer clay minerals. They consist of two tetrahedral layers of interconnected SiO4-tetrahedrons which enclose a central M(O,OH)6 -octahedron layer (M=Al, Fe, Mg and others). The silicate layers have a slightly negative charge that is compensated by exchangeable ions in the intermediate layers. The charge is so weak that the cations (in natural form, predominantly Ca2+-, Mg2+- or Na+-ions) can be adsorbed with an associated hydrate shell (innercrystalline swelling).  An essential characteristic of all smectite minerals is their ability to absorb tremendous amounts of water and other liquids into their sheet structures. This gives bentonite extraordinary swelling and adhesive properties that are exploited commercially by many industries. The ability of smectite to absorb water is due in part to by the inherently small grain size of individual smectite crystals (typically much less that 2µ) and to the fact that individual sheets possess a negative surface charge which tends to attract polar molecules (Figure). This negative charge is also responsible for another essential attribute of smectite - its ability to absorb positively charged ions from solutions, an attribute which, like adhesion, is also exploited commercially.
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Last Updated on Thursday, 17 September 2009 22:33 |
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