Calcium natural deposits

Group II hydrogencarbonates have insufficient thermal stability for them to be isolated as solids. However, in areas where natural deposits of calcium and magnesium carbonates are found a reaction between the carbonate, water and carbon dioxide occurs ... 

Calcium sulfate [7778-18-9J, CaSO, ia mineral form is commonly called gypsum and occurs abundandy ia many areas of the wodd. In natural deposits, the main form is the dihydrate. Some anhydrite is also present ia most areas, although to a lesser extent. Mineral composition can be found ia Table 1. 

C18-0131. Limestone caverns are formed by the reaction of H2 O and CO2 with natural deposits of calcium... 

In addition to climate change, the increased atmospheric concentration of C02 is likely to have wide-spread ecological effects in various environments, since C02 is a physiologically active gas, in plants as well as animals. The acidic nature of C02 will also lead to changes in the chemistry of the ocean s surface, which is in equilibrium with the atmosphere. Once the shift in the oceanic chemical balance becomes significant, it will affect ecosystems. It has been shown, for example, that doubling C02 concentration in the atmosphere will reduce the rate of calcium carbonate deposition in coral reefs by 30-40% (Langdon et al., 2000). 

Acid rain has resulted in the loss of life in a number of lakes. The ability of a lake to withstand the impacts of acid rain is related to the geology of the lake s basin. In areas with limestone (calcium carbonate) deposits, a lake has a natural buffering capacity. The buffering capacity refers to the ability to resist changes in pH. In well-buffered lakes, calcium carbonate reacts... 

CALCIUM SULFATE. CAS. 10101 -1 1-4], Calcium sulfate, CaSOj. in mineral form is commonly called and occurs abundantly in many areas of the world. In natural deposits, the main form is the dihydrale. Some anhydrite is also present in most areas, although to a lesser extent. Mineral composition can be found in Table 1. The hemihydrate is normally produced by heal conversion of the dihydrale from which HiO is removed as vapor. The resulting powder is also known as plaster of Paris. Stucco has the greatest commercial significance of these materials. It is the primary constituent used to fabricate products and in formulated plasiers used in job or shop-site applications. 

Many cooling system operators use either lean water, with very low natural hardness, or ion-exchange softened water as a makeup source. Also, there are some authorities that require softened water makeup, say less than 5 to 10 ppm total hardness (TH), for comfort cooling systems on the basis that this will minimize the risk of calcium carbonate deposits, the presence which could in turn increase the risk of Legionella proliferation. 

Layer or layers of minerals (especially calcium carbonate) deposited, by the throwing down, or precipitation, onto a heat-transfer surface, reducing its U value. Scales are often hard and dense and difficult to remove. The scale can be crystalline in nature (a solid body having a characteristic internal structure, with symmetrically arranged plane surfaces and definite angles), or amorphous (lacking any characteristic crystalline shape). 

The raw minerals mined from natural deposits comprise mixtures of different specific minerals. An early step in mineral processing is to use crushing and grinding to free these various minerals from each other. In addition, these same processes may be used to reduce the mineral particle sizes to make them suitable for a subsequent separation process. Non-ferrous metals such as copper, lead, zinc, nickel, cobalt, molybdenum, mercury, and antimony are typically produced from mineral ores containing these metals as sulfides (and sometimes as oxides, carbonates, or sulfates) [91,619,620], The respective metal sulfides are usually separated from the raw ores by flotation. Flotation processes are also used to concentrate non-metallic minerals used in other industries, such as calcium fluoride, barium sulfate, sodium and potassium chlorides, sulfur, coal, phosphates, alumina, silicates, and clays [91,619,621], Other examples are listed in Table 10.2, including the recovery of ink in paper recycling (which is discussed in Section 12.5.2), the recovery of bitumen from oil sands (which is discussed further in Section 11.3.2), and the removal of particulates and bacteria in water and wastewater treatment (which is discussed further in Section 9.4). 

Recent pelagic sediments containing over 30% calcium carbonate, by dry weight, cover a quarter of the surface of the earth (see Figure 1). These sediments make up a vast and chemically reactive carbonate reservoir which has a major influence on the chemistry of the oceans and atmosphere. In order to have a predictive understanding of the natural carbon dioxide system and the influence of man on it, the chemical dynamics of calcium carbonate deposition in the deep ocean basins must be known in detail. 

Calcite and whitings (RI 1.5-1.7) are naturally occurring calcium carbonate deposits. The lowest cost grades are ground limestone or the mixed calcium magnesium carbonate ore, dolomite. Synthetic calcium carbonate is also used as an extender, but it is more expensive. 

The starting material calcium carbonate occurs naturally as calcite and more rarely as aragonite and vaterite. In natural deposits calcium carbonate is often found as mixtures with magnesium carbonate. The mineral CaMg(C()3)2 is known as dolomite. 

The SEM micrographs shown in Figure 3 provide evidence for the proposed prevention of calcification by citrate anions. It can be seen that the calcium phosphate deposits formed on PHEMA in the presence of citric acid are much lower in amount and smaller in size (Figure 3C). In other words, under the action of citrate anions, the extent of the deposition of calcium phosphates was significantly reduced and the nature of the deposits modified. This is confirmed by the veiy low calcium contents of the calcium phosphate deposits over the whole range of calcification times (see Figure 4), as determined by XPS. It should be mentioned here that after 5 weeks of calcification time, at least one layer of calcium phosphate (with a thickness of 0.4 pm (33)) was deposited on the surface of PHEMA containing no citric acid. Thus, it is anticipated that the calcium content of the calcium phosphate deposits tends to plateau after 5 weeks in SBF solution. 

Primary hyperoxaluria has been defined by Archer et al. (A7, A9) as a clinical entity characterized by progressive calcium oxalate urolithiasis and nephrocalcinosis beginning in early childhood. It might be associated with disseminated extrarenal calcium oxalate deposits, a condition known as oxalosis (A7) it is not known whether oxalosis always represents a stage in the natural history of primary hyperoxaluria (S9). 

Classification. Extenders are mainly natural minerals that are converted into a usable form by working natural deposits, separating secondary constituents, and comminution (micronization). Synthetic products such as precipitated carbonates [e.g., calcium carbonicum praecipitatum (ccp), precipitated sulfates (e.g., blanc fixe), precipitated and pyrogenic silica, and silicates are used for optical brightening. Synthetic fibers (generally organic) are used for reinforcement. The classification of extenders used in surface coatings is summarized in Table 4.1. 

The two parameters that control corrosivity of soft waters are the pH and the dissolved oxygen concentration. In hard waters, however, the natural deposition on the metal surface of a thin diffusion-barrier film composed largely of calcium carbonate (CaCOs) protects the underlying metal. This film retards diffusion of dissolved oxygen to cathodic areas, supplementing the natural corrosion barrier of Fe(OH)2 mentioned earlier (Section 7.2.3). In soft water, no such protective film of CaCOs can form. But hardness alone is not the only factor that determines whether a protective film is possible. Ability of CaCOs to precipitate on the metal surface also depends on total acidity or alkalinity, pH, and concentration of dissolved solids in the water. For given values of hardness, alkalinity, and total dissolved salt concentration, a value of pH, given the symbol pHs, exists at which the water is in equilibrium with solid CaCOs. When pH > pHs, the deposition of CaCOs is thermodynamically possible. 

At natural ambient temperatures, calcium-rich deposits form (mainly CaCOs) on the cathode, whereas at higher temperatures mainly magnesium compounds (Mg(OH)2) are separated. These processes are also observed when cathodic protection is used. 

During natural deposition of carbonates, when magnesium salts are present, a mixture of magnesium and calcium carbonates are precipitated, which is known as dolomite. Dolomite contains about 40 to 45 % MgCOj and 55 to 60 % CaCOg. Its properties are close to those of natural calcium carbonate, except that it is slightly denser and less bright and less sensitive to acid than calcium carbonate. 

Ionic compounds occur throughout Earth s crust as minerals. Examples include limestone (CaC03), a type of sedimentary rock gibbsite [Al(OH)3], an aluminum-containing mineral and soda ash (Na2C03), a natural deposit. We can also find ionic compounds in the foods that we eat. Examples include sodium chloride (NaCl), which is table salt calcium carbonate (CaCOs), a source of calcium necessary for bone health and potassium chloride (KCl), a source of potassium necessary for fluid balance and... 

A distinction must be made between a thick layer of deposit, whether calcium carbonate or any other material, and a protective layer. The ideal protection in fact consists of layers of negligible thickness which do not impede water or heat flow and which are self-healing. This is difficult to achieve with natural waters. A water which is exactly in equilibrium with respect to calcium carbonate is normally corrosive to steel because it has no power to form a calcium carbonate deposit. Supersaturated waters, on the other hand, unless suitably treated, will form a substantial scale, but whether this inhibits corrosion or not depends on its adherence to the metal and its porosity. 

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