Calcium carbonate precipitation reaction

Precipitated Calcium Carbonate. Precipitated calcium carbonate can be produced by several methods but only the carbonation process is commercially used in the United States. Limestone is calcined in a kiln to obtain carbon dioxide and quicklime. The quicklime is mixed with water to produce a milk-of-lime. Dry hydrated lime can also be used as a feedstock. Carbon dioxide gas is bubbled through the milk-of-lime in a reactor known as a carbonator. Gassing continues until the calcium hydroxide has been converted to the carbonate. The end point can be monitored chemically or by pH measurements. Reaction conditions determine the type of crystal, the size of particles, and the size distribution produced. 

Hostomsky, J. and Jones, A.G., 1993c. Ibid., Modelling of calcium carbonate precipitation in the reaction between gaseous carbon dioxide and aqueous solution of calcium hydroxide. Indem. pp. 2055-2059. 

Calcium carbonate is a common inorganic compound known as limestone. Calcium carbonate has many applications in industries such as medicine, agriculture, paint plastic and surface coatings etc. The vast majority of calcium carbonate used in industry is extracted by mining process. Pure calcium carbonate (e.g. for food or pharmaceutical use), is synthesized by passing carbon dioxide into a solution of calcium hydroxide slurry. In this process calcium carbonate precipitates out, and this grade of product is referred to as precipitate calcium carbonate (abbreviated as PCC). The common reaction is as follows ... 

The calcium levulate precipitate was separated from the reaction mixture by filtration and washed with cold water. The precipitate was suspended in water to give a thick slurry, and solid carbon dioxide added until the solution was colorless to phenolphthalein. A heavy precipitate of calcium carbonate was now present and free fructose remained in the solution. The calcium carbonate precipitate was removed by filtration, and the filtered solution was found to contain 1,436 g of fructose as determined by optical rotation. A small amount of calcium bicarbonate was present as an impurity in solution and was removed by the addition of oxalic acid solution until a test for both calcium and oxalic acid was negative. The insoluble calcium oxalate precipitate was removed by filtration. 

The kinetics of calcium carbonate precipitation in simple solutions have received less attention than those of dissolution reactions. This perhaps reflects the fact that most sedimentary carbonates are initially formed biogenically and that the primary interest in carbonate precipitation reactions has been directed at reaction... 

The combination of the sulfate reduction reaction, and reactions primarily with iron and manganese oxide minerals can lead to significant calcium carbonate precipitation. This type of net process can be represented schematically as ... 

Extracellular deposition Some bacteria and fungi contribute to calcium carbonate precipitation in the bulk phase with CO2 generated in their respiration on organic energy sources. This precipitation is dependent on a circumneutral pH range and an excess of Ca " " in the reactive zone in the bulk phase. The formation of extracellular calcium carbonate from respiratory CO2 formed by heterotrophic bacteria and fungi involves the following sequence of equilibrium reactions or variants thereof ... 

Sometimes a double-displacement reaction has one produa that is insoluble in water. As that produa forms, it emerges, or precipitates, from the solution as a solid. This process is called precipitation, such a reaaion is called a precipitation reaction, and the solid is called the precipitate. For example, when water solutions of calcium nitrate and sodium carbonate are mixed, calcium carbonate precipitates from the solution while the other product, sodium nitrate, remains dissolved. 

CaC03(r) + C02( ) + H20(/) Thus, in your hot water pipes, solid calcium carbonate precipitates from solution and collects as scale on the inside of the pipes. After we have discussed acid-base reactions in Chapter 5, it will be possible to explain how the plumber can remove this obstruction. 

CALCIUM CARBONATE, precipitated (471-34-1) CaC03 Noncombustible solid. Inconqjatible with acids (exothermic reaction... 

On the other hand, the ions present in the transported water, such as aqueous carbon dioxide and bicarbonate ion, tend to enter into the pore water. The reaction between the hydroxide ions from the pore water and the dissolved aqueous carbon dioxide and bicarbonate ion forms carbonate ion (COs "). As a result, conditions suitable for spontaneous calcium carbonate precipitation may exist in the pores, near the exposed surface. This process is called carbonation. These calcium carbonate deposits can reduce the interaction between transported water and the chemical species in the pores. 

The hydroxide ions formed by Eq. (14.3) enhance the rate of calcium carbonate precipitation through reaction in Eq. (14.4) ... 

Calcium hydroxide is relatively well soluble in water, and when water evaporates from the concrete surface a layer of portlandite can be produced. The carbonation of portlandite occurs easily in reaction with atmospheric CO2 therefore the calcium carbonate is the main component of efflorescence. The calcium ions can react with CO2 in the liquid phase of paste and calcium carbonate precipitates because of its low solubility ... 

Calcium carbonate precipitates from the calcium hydroxide solution, as it has a lower solubility than that of calcium hydroxide. The optimum reaction temperature is 80 to 90°C. The calcium carbonate is settled, and the overflow is a weak caustic soda, which is concentrated by evaporation. 

When investigating the aqueous-phase bicarbonate hydrogenation with ruthenium and rhodium complexes, Benyei and J06 observed certain activity for the reverse reaction, that is, formate decomposition. [RuCl2(mTPPMS)2]2 (mTPPMS = meta-monosulfonated triphenylphosphine) decomposed sodium formate and formic acid (41), while RhCl(mTPPMS)3 slowly decomposed calcium formate and promoted calcium carbonate precipitation (42). 

The evolved hydrofluoric acid was collected in plastic bottle containing distilled water. This acidic solution was treated with equal volume of calcium carbonate. The reaction was carried out in the pH range 1.0 to 4.5. A precipitate started to form at pH 3.0, and calcium carbonate was added with continuous stirring until the pH value reached 4.5 to assure complete precipitation. The XRD analysis of the obtained precipitate revealed that it is a pure calcium fluoridfe compound (ASTM card no. 4-0864). 

The calcium carbonate precipitated and could be removed by filtering. The solution contained potassium nitrate formed in this reaction and also present from the original decay process. Water was evaporated leaving white saltpeter to crystallize. 

Flue-Gas (Stack-Gas) Scrubbing. Flue-gas scrubbing is a refiner s last chance to keep NOx and SOx out of the air. In wet flue-gas desulfurization, gas streams containing SOx react with an aqueous slurry containing calcium hydroxide Ca(OH)2 and calcium carbonate CaCOs. Reaction products include calcium sulfite (CaSOs) and calcium sulfate (CaS04>, which precipitate from the solution. 

EDTA is also used to remove the calcium carbonate and sulfate scales that form in hot-water boilers and heaters. Calcium carbonate precipitates out when hard water is heated because the bicarbonate present in any naturally aerated water supply decomposes under the action of heat into carbonate, water, and carbon dioxide, as shown in Equation (6.15). (This reaction is the source of some of the very small bubbles that form on the sides of a beaker before water heated in it comes to a boil.) The carbonate is then available to be precipitated by calcium, magnesium, or iron cations that are often present in a natural water supply. This precipitation reaction is shown for calcium in Equation (6.16) ... 

The other form of calcium carbonate available to the alkaline papermaker is synthetically produced precipitated calcium carbonate (PCC). PCC is made from limestone that has reduced to lime in a rotary kiln, slaked to calcimn hydroxide then converted to calcium carbonate by reaction with CO2. PCC can be precipitated in many different crystal structures. The particle size and shape can be tailored to the customer s specific needs. 

Fit a 1500 ml. bolt-head flask with a reflux condenser and a thermometer. Place a solution of 125 g. of chloral hydrate in 225 ml. of warm water (50-60°) in the flask, add successively 77 g. of precipitated calcium carbonate, 1 ml. of amyl alcohol (to decrease the amount of frothing), and a solution of 5 g. of commercial sodium cyanide in 12 ml. of water. An exothermic reaction occurs. Heat the warm reaction mixture with a small flame so that it reaches 75° in about 10 minutes and then remove the flame. The temperature will continue to rise to 80-85° during 5-10 minutes and then falls at this point heat the mixture to boiling and reflux for 20 minutes. Cool the mixture in ice to 0-5°, acidify with 107-5 ml. of concentrated hydrochloric acid. Extract the acid with five 50 ml. portions of ether. Dry the combined ethereal extracts with 10 g. of anhydrous sodium or magnesium sulphate, remove the ether on a water bath, and distil the residue under reduced pressure using a Claiseii flask with fractionating side arm. Collect the dichloroacetic acid at 105-107°/26 mm. The yield is 85 g. 

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). 

Naphthalenesulfonic Acid. The sulfonation of naphthalene with excess 96 wt % sulfuric acid at < 80°C gives > 85 wt % 1-naphthalenesulfonic acid (a-acid) the balance is mainly the 2-isomer (P-acid). An older German commercial process is based on the reaction of naphthalene with 96 wt % sulfuric acid at 20—50°C (13). The product can be used unpurifted to make dyestuff intermediates by nitration or can be sulfonated further. The sodium salt of 1-naphthalenesulfonic acid is required, for example, for the conversion of 1-naphthalenol (1-naphthol) by caustic fusion. In this case, the excess sulfuric acid first is separated by the addition of lime and is filtered to remove the insoluble calcium sulfate the filtrate is treated with sodium carbonate to precipitate calcium carbonate and leave the sodium l-naphthalenesulfonate/7J(9-/4-J7 in solution. The dry salt then is recovered, typically, by spray-drying the solution. 

Causticization, the reaction of hydrated lime [1305-62-0], Ca(OH)2, with sodium carbonate to regenerate sodium hydroxide and precipitate calcium carbonate, is an important part of the Bayer process chemistry. 

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