Unwanted minerals

The rest of the chapter has been devoted to special topics and in materials science there are many possibilities. Those selected include the mechanism of the flotation of minerals in which the addition of a certain organic to the solution causes a specific mineral to become hydrophobic so that it is exposed to air bubbles, the bubbles stick to it and buoy the mineral up to the surface, leaving unwanted minerals on the bottom of the tank. It turns out that the mechanism of this phenomenon involves a mixed-potential concept in which the anodic oxidation of the organic collector, often a xanthate, allows it to form a hydrophobic film upon a semiconducting sulfide or oxide, but only if there is a partner reaction of oxygen reduction. This continues until there is almost full coverage with the dixanthate, and the surface is thereby made water-repelling. 

Iron ore, which contains unwanted minerals as well as the iron compounds, is commonly refined in a blast furnace, a crude but most efficient instrument. 

When coal bums, it releases carbon dioxide and other emissions in flue gas. Some clean coal technologies purify the coal before it burns. One type of coal preparation, coal washing, removes unwanted minerals by mixing crushed coal with a liquid and allowing the impurities to separate and settle (Luttrell et al., 2006). 

The breakdown of an ore with a concentrated acid, on an industrial scale, is only justified if the mineral values are fairly high in concentration and of some economic importance. A high acid wastage upon unwanted minerals, e.g. carbonates, oxides, sulphates, phosphates and silicates, can normally be expected if these are present, and in any case the quantity of acid required merely to wet the ore and form a workable pulp is of necessity high. Corrosion problems are generally more severe than with dilute leaching acids and require more expensive materials of construction. 

Contamination in this context refers specifically to the debasing of the purity of steam and condensate. Contamination may occur in the presence of unwanted steam volatile materials (such as silica volatiles), minerals carried over with BW, oil and process materials infiltrating the steam-water circuit, or by the results of corrosion processes. 

Copper, Cu, is unreactive enough for some to be found as the metal, but most is produced from its sulfides, particularly the ore cbalcopyrite, CuFeS2 (Fig. 16.10). The crushed and ground ore is separated from excess rock by froth flotation, a process that depends on the ability of sulfide ores to be wetted by oils but not by water. In this process, the powdered ore is combined with oil, water, and detergents (Fig. 16.1 l). Then air is blown through the mixture the oil-coated sulfide mineral floats to the surface with the froth, and the unwanted copper-poor residue, which is called gangue, sinks to the bottom. 

A major consequence of the activities associated with the exploitation of mineral deposits (i.e., exploration, the development of mines and processing facilities, the extraction and concentration, which is also called beneficiation, of ores containing the desired minerals, and the decommissioning or abandonment of mine facilities) is the production of extremely large volumes of unwanted materials. Waste volumes vary from ca. 30% of the mass of the ore in the case of gypsum and other non-metals, to about 50% for base metals to more than 80% for strip-mined... 

Because many elderly persons experience constipation, laxative use is sometimes viewed as a normal part of daily life. However, mineral oil can be a special hazard in bedridden elderly persons because it can lead to pneumonia through inhalation of oil droplets into the lungs. Lactulose may be a better choice in this situation. Regular use of any laxative that affects fluid and electrolytes may result in significant unwanted adverse effects. 

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