Precipitated calcium carbonate production process

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 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 ... 

In the thermoplastics area, precipitated calcium carbonate is principally used in PVC applications, a market with which it has been associated since the early days of the polymer. Despite some erosion by coated natural products, the combination of small particle size and fatty acid coating continues to give a unique blend of properties in both unplasticised and plasticised PVC formulations. The advantages include easier processing, better surface finish, good low temperature properties and resistance to crease whitening and to scratching. 

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... 

The production of valuable carbonate products implies in practice the production of a valuable (precipitated) calcium carbonate. When producing these from calcium-containing waste materials, several process parameters have a direct influence on product quantity and quality. Many test results and product analyses have been reported, mainly for low-value feedstock materials such a cement waste, ashes and slags from iron- and steel production, and the carbonation processes are practically all based on aqueous systems operating at conditions up to 473 K, 20 MPa. 

Figure 14.1 The precipitated calcium carbonate (PCC) production process A schematic representation, according to the acetic acid route [21, 51].

The industrial process by which large quantities of sodium hydroxide are made consists in treating a 10 per cent solution of sodium carbonate with an excess of calcium hydroxide (milk of lime). After the reaction is complete the mixture is filtered to remove the precipitated calcium carbonate and excess of calcium hydroxide. This process involves a most important application of the principle of solubility product calcium hydroxide continues to dissolve and calcium carbonate to precipitate according to the reaction... 

In most processes, the precipitated calcium carbonate is a waste product. It does not meet the stringent requirements for PCC. At least one company calcines the precipitate and re-uses the resulting quicklime [31.23]. 

Briefly, paper is made from a very dilute aqueous suspension of anionically charged cellulosic fibres which, after water removal, fam a fibrous network, i.e., a paper sheet. In many cases, filler particles such as ground or precipitated calcium carbonate or clay are added to the fibre suspension to enhance the optical performance or printability of the paper. Also, a variety of other components are added to improve specific properties of the paper sheet (e.g., wet and dry strength agents) or to facilitate the paper production process (e.g., retention aids to minimize the loss of fines and filler material to the process water, dewatering aids or defoaming chemicals). The majority of these chemical additives are polymers. 

Precipitated calcium carbonates are produced by controlled precipitation from calcium hydroxide solution by carbonation. The products of these processes are fine particles (0.05-0.2 pm) and are often coated with a fatty acid (stearic) or a reactive resin (carboxylated polybutadiene). Uncoated grades are also available. 

Precipitated calcium carbonate Pure CaCOs prepared by chemical processes (see chapter on limestone, lime manufacturing and products) is preferred to gypsum as diluent in pharmaceuticals. 

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. 

PCC (Precipitated Calcium Carbonate) is by definition a very fine, high purity processed calcium carbonate with controlled morphology, particle size and particle size distribution. PCC is often used in the production of paper [1], but can also be used in different fields of applications, mainly as fillers (in paints, polymers...). There is therefore a need for Lhoist to further improve its expertise in the field of synthetic carbonates and to develop innovative synthetic carbonates with new properties and especially new morphologies. For this purpose, an area in which Lhoist does not have much experience has been explored, that is the production of synthetic carbonates starting from a natural dolomite (CaC03.MgC03) instead of limestone (CaCOs). 

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