Chemistry of inorganic compounds – With additive – Coating or binder
Reexamination Certificate
2001-10-31
2004-09-14
Hendrickson, Stuart (Department: 1754)
Chemistry of inorganic compounds
With additive
Coating or binder
C423S432000
Reexamination Certificate
active
06790424
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the production of precipitated calcium carbonate from a calcium carbonate-rich by-product generated in an industrial process, specifically, a by-product generated by a nitrophosphate plant in the fertilizer industry.
BACKGROUND OF THE INVENTION
Precipitated calcium carbonate finds varied commercial uses, including the manufacture of paper, rubber, plastics, glass, textiles, putties, chalks, sealant, adhesives, paints, inks, varnishes, food, cosmetics, dentrifices, chemicals and pharmaceuticals.
Commercial applications of precipitated calcium carbonate require well-defined powder characteristics, particularly, fine particles with a narrow size distribution, uniform shape and crystallinity. Marentette J. M. et al. (“Crystallization of Calcium Carbonate in the presence of PEO-block-PMAA copolymers”,
Adv. Mater
., 9, 647, 1997) have shown that these characteristics play a crucial role in product properties and that their control is important for the preparation of industrially useful products. Precipitated calcium carbonate must also be substantially free of impurities to be useful for various commercial applications. Several physical and chemical processes have been reported for the treatment of solid waste containing calcium carbonate.
Physical processes require drying and grinding to a fineness that allows impurities to be removed by screening, classification, magnetic separation, hydrocyclone and floatation separation. The disadvantages of these physical methods include the requirement of special equipment and the required maintenance thereof. Other disadvantages of existing processes include unpredictable process efficiencies, variable results in the quantities of impurities removed and the expenses associated with employing such physical techniques.
Chemical processes for the purification of calcium carbonate-rich waste involve leaching or bleaching of impurities using special reagents. Disadvantages of these methods include the requirment of a number of unit operations to perform the treatment. Moreover, a single chemical process may not be suitable for removal of all the impurities. Removal and separation of excess chemical reagents after the treatment is another disadvantage.
Another previously known and widely used method for the treatment of calcium carbonate-rich waste is reburning within the kiln and removing the reburned waste after cooling to obtain calcium oxide. The calcium oxide is then recycled in a causticizing process in producing paper pulp or it is subjected to hydration followed by carbonation to produce precipitated calcium carbonate.
In the process of Richard Woode (U.S. Pat. No. 4,018,877), an aqueous suspension of calcium hydroxide at 25° C. was agitated vigorously and reacted with a mixture of air and carbon dioxide. After 15 minutes (following the ‘primary nucleation stage’) a complex-forming agent, such as a hydroxy carboxylic acid, particularly a hydroxy poly-carboxylic acid (, e.g., citric acid and malic acid) which complexes calcium ions. The complexing agent was added in a concentration range of 0.001 to 5 wt. %, preferably in the range 0.03 to 0.2 wt. % based on the weight of the calcium carbonate produced. The carbonation was stopped after about 50 minutes when the reaction mixture had just become acid to a phenolphthalein indicator. The mixture was then heated to 85° C. over a period of 20 minutes and was allowed to age for 30 minutes. Carbonation was restarted at a much lower rate, maintaining the temperature at 85° C. After 20 to 40 minutes the pH of the batch had fallen below 8.0. At this stage, 0.8% stearic acid in ammonia solution was added and the mixture was stirred at 85° C. for about 3 hours. The suspension was filtered. The filter cake was extruded through {fraction (5/16)} inch diameter holes to yield “granules” which were dried in an oven overnight at 130° C. on a gauze-tray to produce calcium carbonate having 0.72 relative granule hardness and 0.07 micron ultimate particle size with a soft texture. The drawbacks of this process are that the total batch/production time is more than 5 hours during which time the temperature is maintained at 85° C. for a period of 4 hours. In addition, the process requires drying of the product overnight at 130° C. This process is thus highly energy consuming and is therefore unattractive.
Hiroji Shibazaki et al. (U.S. Pat. No. 4,133,894), disclose that precipitates of uniform particle size can be continuously produced by repeating the step of carbonation reaction. In the first step of the process, a suspension of calcium hydroxide having a solids concentration 0.1 to 10 weight % and a temperature of 15 to 30° C. is sprayed in the form of droplets of about 0.2 to 1.0 mm in diameter against a gas containing 10 to 40 volume % carbon dioxide in countercurrent contact therewith. The gas is passed at a specified superficial velocity of about 0.02 to 0.5 m/sec. By this process, 5 to 15% of the calcium hydroxide is converted to calcium carbonate. In the second step of this process, the suspension resulting from the first step is sprayed in the form of droplets of about 1.0 to 1.5 mm diameter against a gas containing 15 to 35 volume % of carbon dioxide and passed upward through the column at a superficial velocity of about 1.5 to 2.5 m/sec whereby growth of crystals is accomplished. In the third step of this process, the suspension resulting from second step is sprayed at a temperature of up to 30° C. in the form of droplets of about 1.5 to 2.0 mm in diameter into a column in countercurrent contact at a superficial velocity of about 1.5 to 3.0 m/sec whereby the carbonation is completed. Thus, superfine calcium carbonate having an average particle size of less than about 0.1 to 3.0 microns is produced. The main drawback of this process is that it requires control of number of parameters such as solids concentration, droplet size, temperature of suspension, gas velocity of carbon dioxide containing gas etc. for three columns. Another drawback is the requirement of multi-step carbonation which is more expensive in terms of operating cost for columns and pumps than a single stage carbonation.
Bleakley, Ian S. et al. (U.S. Pat. No. 5,342,600) describe a method of preparing precipitated calcium carbonate which comprises: (1) slaking quick lime in an aqueous medium, (2) subjecting the aqueous medium to continuous agitation during said slaking, (3) passing a suspension of calcium hydroxide obtained after slaking through a sieve having an aperture size of 40-70 microns, (4) subjecting the suspension to high energy high shear agitation with an impeller having a peripheral speed of 40-70 m/sec., so as to obtain finely dispersed calcium hydroxide, (5) terminating the said high energy high shear agitation on achieving finely dispersed slaked lime, (6) carbonating the finely dispersed slaked lime by passing therethrough sufficient gas comprising carbon dioxide to neutralize the pH of the suspension during said carbonation step, (7) subjecting the suspension to continuous agitation with an impeller speed of 200-700 cm/sec to maintain the suspension, and (8) separating the precipitated calcium carbonate formed in the process. The disadvantage associated with this method is requirement for generating high energy high shear agitation during slaking and carbonation.
The use of additives to control the morphology and particle size is also reported. Bleakley Ian S. et al. (U.S. Pat. No. 5,558,850) disclose a process wherein 0.1 to 2.0% by weight of a reagent having one or more active hydrogen atoms e.g., polyhydric alcohol or phenol is added to the aqueous medium in which the quick lime is slaked. Chapnerkar Vasant D. et al. (U.S. Pat. No. 5,332,564) disclose a process wherein quicklime is slaked in an aqueous solution containing about 0.1 to 2.0%, by weight of a sugar for the production of rhombic shaped precipitated calcium carbonate. Bleakley Ian S. et al. (U.S. Pat. No. 5,232,678), disclose a process wherein 0.01 to 1.5% by weight of triethanolamine, man
Ayyer Jayalekshmy
Badheka Yogi M.
Chunnawala Jatin R.
Jasra Raksh Vir
Oza Pravinchandra M.
Council of Scientific and Industrial Research
Hendrickson Stuart
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