Calcium economic importance

Strontianite is the naturally occurring form of strontium carbonate. It has a theoretical strontium oxide content of 70.2%, but no economically workable deposits are known. There are some naturally occurring strontium—barium and strontium—calcium isomorphs, but none has economic importance. 

Most abundant group of materials, composed of silicates of aluminium with sodium, potassium, calcium, and rarely barium. Most economically important mineral. Used for ceramics, glass, abrasive wheels, cements, insulation and fertilizer. 

For many industrial-scale operations involving the oxidation or reduction of both inorganic and organic substances, and especially for the production of the more active metals such as sodium, calcium, magnesium, and aluminum, the most cost-effective reducing agent is electrons supplied by an external power source. The two most economically important of these processes are described below. 

Economic Importance The current worldwide extraction of limestone and other calcium carbonate-containing minerals such as dolomite is estimated to be ca. 3-10 t/a, of which 950 10 t/a is in the USA. In the rock and earth extraction industry, limestone is in second place, only the mining of sand and gravel being more important. The extraction of limestone in 1995 in Western Europe was 850 10 t. The 1995 production of synthetic (precipitated) calcium carbonate in the USA was 1.483 10 t/a. 

Economic Importance Calcium oxide (quicklime) and calcium hydroxide (slaked lime, lime hydrate) are next to calcium carbonate, the most important calcium compounds, being utilized in almost all sectors of industry. The worldwide production (including calcined dolomite) was 130 10 t/a in 1994. The leading producer country is China. The most important product is quicklime, which is produced throughout the world partly in very small units, although predominantly in highly industrialized countries. 

Economic Importance. Calcium chloride is produced in large quantities as a byproduct in different chemical processes e.g. in the Solvay process or in the production of propene oxide in the chlorohydrin process, of which only a small part is processed to pure calcium chloride. In 1993 in the USA ca. 0.48 10 t (as anhydrous calcium chloride/ was produced mainly from natural sources (mainly subterranean brines and, to a lesser extent, dried out salt lakes in California). 

Recovery from Brines. Natural lithium brines are predominately chloride brines varying widely in composition. The economical recovery of lithium from such sources depends not only on the lithium content but on the concentration of interfering ions, especially calcium and magnesium. If the magnesium content is low, its removal by lime precipitation is feasible. Location and avadabiHty of solar evaporation (qv) are also important factors. 

Reaction of coke with calcium oxide gives calcium carbide, which on treatment with water produces acetylene. This was for many years an important starting point for the production of acrylonitrile, vinyl chloride, vinyl acetate and other vinyl monomers. Furthermore, during World War II, Reppe developed routes for many other monomers although these were not viable under normal economic conditions. 

Phosphate-polymer control, in industrial water treatment, 26 132-133 Phosphate recognition, 16 794 Phosphate refractory dental dies, compressive strength, 8 289t Phosphate rock, 11 119, 120 minerals in, 19 5, 14 recovery of fluoride from, 14 12-13 U.S. imports for consumption of, 19 15t U.S. production of, 19 17 Phosphates, 18 814-863 19 19. See also Phosphate Polyphosphates aluminum acid, 18 839 ammonium, 11 487 18 835-836 analysis of, 18 851-852 calcium, 18 836-839 condensed, 18 841-852 crystalline, 18 839 dispersants, 8 710t economic aspects of, 18 859-860... 

The rare earths (see table II) have a marked geochemical affinity for fluorine, calcium, titanium, niobium, zirconium, and the phosphate and carbonate ions. The most important, from an economic viewpoint, are the carbonatites and the phosphates. 

The most important industrial alkalis are the weak alkali ammonia (Section 9.3), caustic soda (sodium hydroxide), and lime (calcium oxide).1-6 For many industrial and agricultural purposes, the most economical source of alkali is lime, which is used in steelmaking and other metallurgical operations ( 45% of U.S. production of lime), in control of air pollution from smokestack gases (Chapter 8), in water and sewage treatment (Sections 9.6 and 14.5), in pulp and paper production (Section 10.4), in reduction of soil acidity, in cement and concrete manufacture (indirectly, as discussed later), and in many chemical processes such as paper making (Section 10.4). In short, lime is one of the most important of all chemical commodities. 

Units called flue gas desulfurisation (FGD) units are being fitted to some power stations throughout the world to prevent the emission of sulfur dioxide gas. Here, the sulfur dioxide gas is removed from the waste gases by passing them through calcium hydroxide slurry. This not only removes the sulfur dioxide but also creates calcium sulfate, which can be sold to produce plasterboard (Figure 11.25). The FGD units are very expensive and therefore the sale of the calcium sulfate is an important economic part of the process. 

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