Minerals, removal

Calcinating a mineral removes its volatile components, such as water or carbon dioxide and leaves an usually crumbly solid residue. Calcinated secondary minerals such as limestone are the basic components of building cements, and in extractive metallurgy operations they facilitate the smelting of metals. Calcinating limestone (composed of calcium carbonate), for example, drives away carbon dioxide, leaving a solid, friable residue of quicklime (composed of calcium oxide) ... 

This table is highly important, as showing the enormous quantity of soluble minerals removed from soils by cultivated crops. If th crops were removed from the ground, and no means were taken to return to the soil in some form the mineral constituents thus constantly taken off, the inevitable consequence would ultimately be utter sterility. 

Cesium-ion concentrations in distilled water and synthetic ground-waters were measured after contact with the feldspars for various periods of time, over the temperature range 150°C to 200°C. It was found that for short reaction times (< 5 days), there was little reduction in the concentration of cesium ion, i.e. little sorption of Cs+ by the minerals. Removal of Cs+ from solution was enhanced by increased mineral surface area, reaction temperature and time. It was observed that in the extreme case for powdered labradorite, 98% of an initial 10 2 mol dm 3 solution of Cs+ was sorbed after 14 days at 200°C in distilled water. The morphology, composition and chemical structure of the mineral surfaces were investigated by several analytical methods, as described below. 

In practice, for essentially all known minerals, the angles at which they diffract X-rays are known and tabulated in searchable databases. Modem diffractometers commonly use such databases to match the pattern obtained from an unknown sample to specific minerals, removing the need for calculating the crystal dimensions. 

The role of the osteoclasts is also uncertain. It is not known whether they are concerned with mineral removal, matrix removal, or both processes, which appear to proceed pari passu (C6, M5). 

Small amounts of weathered solutes reprecipitate in lower soil horizons. Examples include clay accumulation in the B horizon, silica pans (impermeable layers of soil particles indurated with silica), and the wide-spread caliche horizons of CaCC>3 accumulation in arid regions. Most solutes, however, reach the sea, where precipitation of other secondary minerals removes most of the weathered solutes except Na+, Cl-, and Mg2+. Marine sediments, in turn, are slowly convened into igneous, metamorphic, or sedimentary rocks, which form new soil parent material. Such element recycling has circulated ions many times from land to sea during the earth s histoiy. 

Finally, periodic non-destructive imaging by x-ray CT is used to view redistribution of mineral mass within the heated sample, as illustrated in Figure 2. X-ray CT records changes in density within the sample as a proxy for mineral removal or redistribution, with the scanner used in this study capable of resolving down to -1/1000 of the diameter of the sample. For sample diameters of 3-5 cm used in the following study, the minimum voxel size scales to the order of 30-50 pm. This resolution is at the limits of utility in defining mass redistribution - it is adequate to define mass redistribution in samples of Berea and limestone, but not for the relatively tighter fracture in novaculite. 

The amount of mineral matter in coking coal (Chapter 16) is an indication of the amonnt of ash that will eventually be part of the coke made from the coal. Thus, the higher the ash content of the coal, the lower the proportion of usable carbon in the coke and the more the fluxing limestone that must be added to the furnace to assist in ash (mineral) removal. However, the fouling tendency of a coal is dependent upon several factors, not the least of which is the nature of the mineral matter and the resulting ash (Beer et al., 1992). 

Similarly, when a part of leachate percolating downward through the vadose zone passes through the clay-rich subsurface layers, the clay minerals remove a part of dissolved substances from it, preventing or decreasing the pollution or contamination of ground water. 

One of the most crucial aspects of green technology is the sustainable utilization of minerals. In a sense, the concept of sustainable mineral utilization is an oxymoron because minerals removed from the geosphere are not replaced. However, the idea of sustainability can greatly extend supplies of minerals. This section addresses the approach to sustainability in obtaining minerals. The broader questions of green utilization of materials, substitution of materials, and recycling are discussed in more detail in Chapters 14 and 16. 

Rice polishings—This product, like wheat bran, contains the minerals removed from whole grains (brown rice) during milling. It Is an excellent source of iron, magnesium, and the... 

In room-and-pillar mining, the retreat or pillaring phase occurs when miners remove coal blocks originally used for support as the working section withdraws. The method requires stringent ventilation and roof control safeguards (p. 7). 

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