Preparation, Separation And Application Of Superfine Calcium Carbonate

This thesis has skillfully employed the amphoteric characteristic of glycine, to extract and purify calcium from lime or the waste of calcium carbide slag, and to form ultrafine calcium carbonate:the former, extraction and purification of calcium, is accomplished by using carboxyl group of glycine to react with calcium hydroxide in carbide slag or lime to form soluble calcium salt, and later, to form ultrafine calcium carbonate, is accomplished by using the ammino group of glycine, to react with acid to precipitate Ca2+ by pumping CO? into calcium solution inside the in-loop ultrasonic reactor, glycine is recycled and reused to dissolve calcium carbide slag. A new approach to both recycling the waste of calcium carbide slag and to form calcium carbonate is developed conveniently. This glycine method is in low cost and high value-added.This thesis has the following high lights:1、Under the condition of pH 6.5-7, the ultrafine calcium carbonate particle is formed with an average size of 10μm, which is easier to filter. The slurry of this calcium carbonate has a good stability for storage, it can be used directly.2、The ultrafine calcium carbonate purity is above 98% and the whiteness is above 96%, both are better than China National Standard.3、The pilot test’s production of calcium carbonate has good dispersive, shows excellent performances in plastic, rubber, dope and papermaking etc.4、The engineering and technological condition of carbonation reaction has an important effect on the nucleation and surface topography of calcium carbonate. The in-loop ultrasonic reactor is very suitable for preparing nanometer particle in mass production.5、We have studied the four methods of formation of ultrafine calcium carbonate, glycine method (HOOCCH2NH2-Ca(OH)2-CO2), ammonium chloride method (CaCl2-NH3-CO2), carbon dioxide method (Ca(OH)2-CO2) and alkali method (Na2CO3-Ca(OH)2-CO2), all the four methods have been passed pilot tests. The result of the comparison of the four methods shows that under the same conditions, only glycine method could generate spherical calcium carbonate, whereas other methods all generate calcite, in addition the slurry of glycine method and alkali method’s ultrafine calcium carbonate are stable, whereas other methods’ultrafine calcium carbonate are unstable. This concludes that surface modification of glycine has the most critical effect on the surface topography and characteristics of calcium carbonate.6、The application of ultrafine calcium carbonate in the water coatings shows that:when the titanium dioxide and other expensive powders have been replaced by the slurry of calcium carbonate, the coating’s properties are completely qualified, and even better, but the cost can be reduced greatly, which gives good competitiveness in waterborne coatings market.In summary, the preparation. purification and application of ultra-fine calcium carbonate have been studied deeply, the rule of calcium carbonate’s nucleation and growth is summarized. and the filtration problems are solved. A new way of using ultra-fine calcium carbonate directly has been proposed. it will bring prosperity and development in the industry. All of these open a gate for producing calcium carbonate and other ultra-fine power in large scale, high value-added and low cost. The research has theoretical and practical values, as well as economic, environment protection, social benefit.