Production of Precipitated Calcium Carbonate

The production of precipitated calcium carbonate (PCC) is categorised as a use of slaked lime and is described in section 31.2. However, PCC is clearly a limestone in terms of its chemical analysis and competes with whiting in a number of applications (the applications of both whiting and PCC are outlined in section 12.9). 

Two techniques are used — screening and classification. Dry screening is routinely practised at sizes down to about 3 mm and can be extended to as low as 300 pm with dry products. Screening at smaller apertures causes blinding of the screen. Wet screening is widely used for sizes as low as about 0.5 mm. Classification of suspensions in water or air is used to divide at smaller particle sizes. 

Screening involves passage of particles over apertures in a screen deck (or mat ), which allow particles smaller than the aperture size to pass through the deck, thereby dividing the product into undersize and oversize fractions [5.4-5.6]. The apertures may be square, rectangular, or circular. 

The screen deck may be made from woven or welded steel wire mesh with square apertures. Such decks have a high proportion of open area and are relatively inexpensive. However, they have a low resistance to wear and corrosion and produce high noise levels when vibrated. Woven wire decks with rectangular apertures are sometimes used to reduce pegging. 

Punched steel plates are very robust, but have a low proportion of open area. They are often used for screening larger sizes of stone and in trommel screens (see section 5.5.2.3), where robustness is important. Increasingly, moulded decks made from rubber or polymers (e.g. polyurethane) are used because of their resistance to wear and corrosion, and their surface properties which reduce blinding and noise emission. Their disadvantages are higher initial cost and a lower proportion of open area. 

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This process takes place in a lime kiln in the production of precipitated calcium carbonate at temperatures of from 500°C to 900°C. Carbon dioxide is also produced as a by-product in fermentation reactions to produce alcohols. An example is the fermentation of glucose, H to ethanol ( H ) H 2 1. 2C H OH. + 2CO. Carbon dioxide... 

Figure 2.16 shows a schematic diagram of the production of precipitated calcium carbonate. Such grades are also termed synthetic calcium carbonate since several chemical operations are performed. The first operation is calcination which is performed in a kiln at 900°C. At this stage, calcium carbonate is decomposed to... 

Figure 2.16. Schematic diagram showing the production of precipitated calcium carbonate. Courtesy ofSolvay GmbH, Rheinberg, Germany.

Nanocellulosic fibrils can be used as a substrate for the production of precipitated calcium carbonate-nanocellulose composites. These, PCC-nanocellulose composites can contribute toward increasing the strength and optical properties of paper. We investigated formation and properties of a new composite paper composed of fibrillar fines and calcium carbonate as the base furnish in combination with cellulosic fibres as reinforcing elements. 

Abstract A new low density mineral material has been synthesized via a simple, flexible, cheap and easy to control process. This material is a synthetic carbonate produced by carbonation of a solid phase composed of a calcic part and a magnesian part. Typically, its production process includes the calcination of a raw dolomite (general formula CaC03.MgC03) into the oxide form, followed by an at least partial hydration of this oxide and a subsequent carbonation step. This process is thus close to the well-known process used for the production of Precipitated Calcium Carbonate (PCC), a common filler and pigment in plastic, paper and rubber, except that the raw material is a dolomite instead of a limestone. It has to be pointed out that flue gases from different industries can be used as a source of CO2 for the carbonation. 

Let us add the moles of precipitated calcium carbonate as a sixth variable x6, modify the calcium and carbonate conservation equations f2(x) and /3(x) in order to account for solid phase contribution, and use the expression of the solubility product as a sixth equation. The six equations to be solved read... 

Calcium carbonate occurs in nature as hmestone in various forms, such as marble, chalk, and coral. It is probably the most widely-used raw material in the chemical industry. It has numerous apphcations, primarily to produce cement, mortars, plasters, refractories, and glass as budding materials. It also is used to produce quicklime, hydrated lime and a number of calcium compounds. It is produced either as powdered or precipitated calcium carbonate. The latter consists of finer particles of greater purity and more uniform size. They also have many important commercial apphcations. Various grades of precipitated calcium carbonate are used in several products, such as textiles, papers, paints, plastics, adhesives, sealants, and cosmetics. 

The principal U.S producers of ground calcium carbonate are Columbia River Carbonates. ECC International, franklin Limestone Company, Gen-star Stone Products, Georgia Marble Company. J.M. Huber Corporation. Calcium Carbonates Division, James River Limestone Company. Inc., OMYA Inc. (Pluess-Staufer), and MTI Inc. The principal U.S. producers of precipitated calcium carbonate are Mississippi Lime Company and MTI Inc. 

In order to convert the henzalchloride into henzaldehyde, the crude product thus obtained is treated in a round flask provided with an effective reflux condenser, with 500 c.c. of water and 150 grammes of precipitated calcium carbonate (or floated chalk or finely pulverised marble) and the mixture heated four hours in a hemispherical oil-bath to 130° (thermometer in the oil). Without further heating, steam is passed through the hot contents of the flask until no more oil distils over. For this purpose the apparatus necessary (cork with a glass tube) has been prepared before the heating in the oil-bath. 

Spontaneous precipitation by the mixing of two concentrated solutions of calciiun and carbonate results in a gelatinous matter when ionic activity product exceeds the solubility product of amorphous calcium carbonate. 

Whiting at one time coimoted only a very fine form of chalk of micrometer sizes but the term is now used more broadly to include all finely divided, meticulously milled carbonates derived from high calcium or dolomitic limestone, marble, shell, or chemically precipitated calcium carbonate. Unlike all of the above natural forms of limestone, it is strictly a manufactured product. 

The key difference between the brine process and seawater process is the precipitation step. In the latter process (Fig. 6) the seawater is first softened by a dding small amounts of lime to remove bicarbonate and sulfates, present as MgSO. Bicarbonate must be removed prior to the precipitation step to prevent formation of insoluble calcium carbonate. Removal of sulfates prevents formation of gypsum, CaS02 2H20. Once formed, calcium carbonate and gypsum cannot be separated from the product. 

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. 

Natural ground calcium carbonate has been used for years as the primary constituent of putty. Since 1945, the processing of natural calcium carbonate has seen the introduction of beneficiation by flotation (qv) to remove impurities and the development of grinding processes to manufacture finer products. Precipitated calcium carbonate was first introduced in England in 1850 commercial production started in the United States in about 1913. 

Calcium carbonate is one of the most versatile mineral fillers (qv) and is consumed in a wide range of products including paper (qv), paint (qv), plastics, mbber, textiles (qv), caulks, sealants (qv), and printing inks (qv). High purity grades of both natural and precipitated calcium carbonate meet the requirements of the Food Chemicals Codex and the United States Pharmacopeia and are used in dentifrices (qv), cosmetics (qv), foods, and pharmaceuticals (qv). 

Both natural ground or precipitated calcium carbonate are available as dry products shipped in 22.7 kg multiwaH bags, supersacks, or in bulk via tmck and railcar. Calcium carbonate slurry, primarily used by the paper industry, is shipped by tmck and rail. The soflds content of these slurries is typically >70% by weight for ground products and 20—50% for precipitated. In the 1980s small precipitation plants were built at the site of large North American papermills. 

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