Calcium carbonate producers

Calcium carbonate produced by the chemical process known as precipitation. 

Not counting T, a second portion of the string subscript (the third portion, if T is present) may also be present. This will then refer to the reason for the existence of the type of mass involved. For example, consider Mcacojco mentioned previously. In this symbol, CO2 is the reason for the existence of the mass of CaC03. Thus, McacojCo is the mass of calcium carbonate produced from carbon dioxide. 

Mass of calcium carbonate produced from the precipitation of the magnesium bicarbonate removed Mass of Ca(HC03)2 removed... 

Characters and Tests.—Transparent, nearly colourless liquid. Sp. gr. 1 035. Exposed to the atmosphere, the calcium hypochlorite is decomposed by carbonic anhydride the calcium carbonate produced is deposited as a white precipitate, and the chlorine which is set free may be recognised by its odour. 

Hard water is produced when rainwater, which is weakly acidic because of the presence of dissolved carbon dioxide, falls upon limestone or chalk which are both forms of calcium carbonate. The acidic solution dissolves calcium carbonate producing a solution of calcium hydrogencarbonate, or hard water ... 

It is seen in Table 2.9, that flexural moduli improve considerably upon incorporation of 25 to 50% of glass fibre in the formulation. Epoxy resins are an exception, carbon fibre also improves the flexural modulus of PC from 2.8 to 13 GPa and with polyacetal the addition of carbon fibre improved the flexural modulus from 2.6 to 17.2 MPa. For PP the addition of 20% calcium carbonate produced hardly any change in flexural modulus. 

Lime Soda. Process. Lime (CaO) reacts with a dilute (10—14%), hot (100°C) soda ash solution in a series of agitated tanks producing caustic and calcium carbonate. Although dilute alkaH solutions increase the conversion, the reaction does not go to completion and, in practice, only about 90% of the stoichiometric amount of lime is added. In this manner the lime is all converted to calcium carbonate and about 10% of the feed alkaH remains. The resulting slurry is sent to a clarifier where the calcium carbonate is removed, then washed to recover the residual alkaH. The clean calcium carbonate is then calcined to lime and recycled while the dilute caustic—soda ash solution is sent to evaporators and concentrated. The concentration process forces precipitation of the residual sodium carbonate from the caustic solution the ash is then removed by centrifugation and recycled. Caustic soda made by this process is comparable to the current electrolytic diaphragm ceU product. 

In the commonly used Welland process, calcium cyanamide, made from calcium carbonate, is converted to cyanamide by reaction with carbon dioxide and water. Dicyandiamide is fused with ammonium nitrate to form guanidine nitrate. Dehydration with 96% sulfuric acid gives nitroguanidine which is precipitated by dilution. In the aqueous fusion process, calcium cyanamide is fused with ammonium nitrate ia the presence of some water. The calcium nitrate produced is removed by precipitation with ammonium carbonate or carbon dioxide. The filtrate contains the guanidine nitrate that is recovered by vacuum evaporation and converted to nitroguanidine. Both operations can be mn on a continuous basis (see Cyanamides). In the Marquerol and Loriette process, nitroguanidine is obtained directly ia about 90% yield from dicyandiamide by reaction with sulfuric acid to form guanidine sulfate followed by direct nitration with nitric acid (169—172). 

In addition to the main acidulation reaction, other reactions also occur. Free calcium carbonate in the rock reacts with the acid to produce additional by-product calcium compounds and CO2 gas which causes foaming. Other mineral impurities, eg, Fe, Al, Mg, U, and organic matter, dissolve, the result being that the wet-process acid is highly impure. 

Cementstone is an impure (usually argillaceous) limestone, possessing the ideal balance of siUca, alumina, and calcium carbonate for Portiand cement (qv) manufacture. When calcined it produces a hydrauHc cementing material. 

At about the same time that the Birkeland-Eyde process was developed, the Frank-Caro cyanamide process was commercialized (14). In this process limestone is heated to produce lime, which then reacts with carbon in a highly energy-demanding reaction to give calcium carbide. Reaction with N2 gives calcium cyanamide [150-62-7] which hydrolyzes to ammonia and calcium carbonate (see Cyanamides). 

Excess calcium hydroxide is precipitated by usiag carbon dioxide and the calcium carbonate, calcium hydroxide, and calcium phosphite are removed by filtration. The filtered solution is treated with an equivalent amount of sodium sulfate or sodium carbonate to precipitate calcium sulfate or carbonate. Sodium hypophosphite monohydrate [10039-56-2] is recovered upon concentration of the solution. Phosphinic acid is produced from the sodium salt by ion exchange (qv). The acid is sold as a 50 wt %, 30—32 wt %, or 10 wt % solution. The 30—32 wt % solution is sold as USP grade (Table 12) (63). Phosphinic acid and its salts are strong reduciag agents, especially ia alkaline solution (65). 

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