Slurry Precipitated Calcium Carbonates

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. 

Figure 2.8 Particle mass flux during slurry sedimentation of precipitated calcium carbonate (Coulson and Richardson, 1991)...

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 ... 

Ground calcium carbonate, extracted from the earth, is present in practically every country in the world in varying quantities in the form of limestone, marble, dolomite or chalk. Following the extraction, GCC needs to be ground. Dry grinding, the cheaper alternative, is often limited to a minimum particle size of 2- 3 microns. Wet grinding, more expensive, is used for fine and ultra fine material or when the final product must be a slurry (paper or paint application). Precipitated calcium carbonate is produced by chemical reaction between... 

Absorption of C02 in aqueous slurry of lime for the manufacture of precipitated calcium carbonate (which is reused in large quantities as a rubber filler, a pigment, etc.). Here lime is sparingly soluble in water and the reaction occurs between the dissolved carbon dioxide and OH" ions. 

Chem. Descrip. Precipitated calcium carbonate slurry CAS 471-34-1 EINECS/ELINCS 207-439-9 Uses Coating pigment for glossy, high brightness coated paper and board applies. 

Lazy Slurry. A dilatant body which remains fluid when still or slowly stirred, but solidifies if stirred rapidly. It comprises about 100 parts of precipitated calcium carbonate (depending on the particle size) 10 parts of 5% ZnNOs 20 parts 5% Calgon 40 parts water. 

MAGNUM GLOSS 72% Precipitated Calcium Carbonate Slurry ... 

Precipitated Calcium Carbonate Mississippi 72% M60 Slurry Typical Physical Analysis ... 

In the process, the cement kiln dust is collected in a recycling stream of slurry which contacts the flue gas. Carbon dioxide is absorbed in the alkaline solution and reacts with calcium sulfote and calcium hydroxide to precipitate calcium carbonate and release sulfitte ions. Sulfur dioxide is absorbed and is then oxidized by oxygen from the flue gas stream to form additional sulfate ions. The sulfate rmaains in solution as the very soluble potassium sulfate. 

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. 

Pre-liming. Lime slurry, 0.25% lime on juice (0.250 g of CaO/100 g juice), is added to bring the pH of the mixture into the alkaline range. Insoluble calcium salts are precipitated as finely dispersed coUoids. Calcium carbonate in the form of recycled first carbonation sludge is added to provide coUoid absorption and stabilization. Temperature may be cool (50°C) or hot (80°C) depending on the temperature of the next step, or occasionally on the type of diffusion equipment. Retention time is 15 to 30 min. 

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. 

Merseburg A process for making ammonium sulfate fertilizer from gypsum. The gypsum is slurried with water and ammonium carbonate solution added. Calcium carbonate precipitates and is removed, any excess of ammonium carbonate is neutralized with sulfuric acid, and the solution is concentrated until it crystallizes ... 

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 packed tower is compact and efficient for air stripping. The waste water, in a lime slurry (for phosphate removal and pH control), is first sent to a mixing tank and then to a shell settling tank to settle out calcium phosphate and calcium carbonate. The clarified waste water enters near the top ofthe packed tower, while air is introduced countercurrently atthe bottom of the tower. Waste water product is then sent to a recarbonation basin so that calcium carbonate may be precipitated, removed, and reused. 

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