Calcium carbonate is important inorganic compound widely used in plastics, rubber, papermaking, ink, paints and coatings, and building materials, etc. It is the most commonly used filler in manufacturing and processing industries. Calcium carbonate is currently chiefly produced via two types of processes: One involves the mechanical crushing of natural limestone to produce calcium carbonate of different finenesses. This type of calcium carbonate is known as heavy calcium carbonate; its quality is determined by the quality and fineness of the natural limestone. The second process involves the calcining of selected limestone; the resulting calcium oxide (CaO) is reacted with water
(H2O) to produce calcium hydroxide (Ca(OH)2), and then reacted with carbon dioxide, which results in the precipitation of calcium carbonate. This type of calcium carbonate is known as light calcium carbonate. The quality of light calcium carbonate depends not only on the quality of the natural limestone used, but also on the conditions of calcining and other chemical reactions, and the fineness grading. There are currently two main industrial methods used to make heavy calcium carbonate: One is the dry method, and the other is the wet method. Calcium carbonate made by the dry method is widely used in the rubber, plastic, and coating industries. Calcium carbonate made by the wet method is commonly used by the papermaking industry; most product is sold to paper mills in the form of a slurry.
The following diagram may help to clear up any remaining misunderstandings about calcium carbonate.
Calcium carbonate is commonly used as an additive in the manufacture of rubber, plastic, paper, paints and coatings, and ink, etc. It is also widely used in organic synthesis, metallurgy, glassmaking, and asbestos production, etc.
Calcium carbonate already has a long history of use in plastic and rubber. Its use can cut costs, and it can improve the heat resistance, size stability, and hardness of the base material. Calcium carbonate is the filler first used by the rubber industry, and is still used in the greatest quantity. Adding large amounts of calcium carbonate to rubber can increase the product's volume, which conserves the use of expensive natural rubber and thereby cuts costs. The addition of calcium carbonate to rubber increases tensile strength, abrasion resistance, and tear resistance even more than does vulcanization. Calcium carbonate also has a significant reinforcing effect in both natural and synthetic rubber, and can improve consistency. Calcium carbonate is used in such small rubber products as oil seals and auto parts, and also in such large products as tires, tape, and rubber hoses. Not only is calcium carbonate used alone as a reinforcing filler, when needed, it may also be used together with such other fillers as carbon black, white carbon black, clay, and titanium white to achieve reinforcing, filling, coloring, improving workability, enhancing product performance, and reducing latex content. Calcium carbonate may also partially replace such more-costly white fillers as white carbon black and titanium white.
Calcium carbonate forms a kind of skeleton structure inside plastic products, and greatly improves the size stability of plastic products. It can improve product hardness, electrical performance, flame retardant performance, heat resistance, and processing performance. It can also improve products' luster and surface regularity. Adding calcium carbonate can increase the heat resistance of ordinary plastic products. And since it has a whiteness in excess of 90%, calcium carbonate can serve as a whitener in place of costly white pigments. Taking the manufacture of PVC products as an example, the rational use of heavy calcium carbonate can increase heat resistance, rigidity, size stability, and workability. In addition, the use of small quantities of light calcium carbonate can increase the tensile strength of PVC products. The addition of too great an amount of calcium carbonate to PVC products can hurt product quality, and the use of poor quality calcium carbonate can greatly reduce product quality. The addition of similar quantities of ordinary calcium carbonate, superior calcium carbonate, and inferior calcium carbonate will yield PVC products with completely different performance.
Due to technological improvements in recent years, ultrafine calcium carbonate with average particle diameter of 1 μm is now used to give products good workability and enhance luster and color stability. To cut costs, many plastic and rubber companies now use ultrafine calcium carbonate instead of light calcium carbonate. Ultrafine heavy calcium carbonate is better at absorbing oil than light calcium carbonate, and the use of heavy calcium carbonate can also reduce the need for plasticizer. And since ultrafine calcium carbonate is extremely fine, and has good dispersion and thermal stability, it is widely used in plastic and rubber. The use of ultrafine calcium carbonate has yielded good results in plastic steel with nonstandard shapes, PVC, pressed materials, and silicone rubber. It can significantly increase the impact resistance, size stability, and heat resistance of plastic and rubber, improve processing performance, and cut costs by significantly increasing filling amount (for comparison, light calcium carbonate can increasing filling amount by 100%-300%). Furthermore, since ultrafine calcium carbonate is made using the wet method, particles are relatively free of sharp edges, and the cylinders and screws of extrusion machines suffer less wear than when the plastic contains heavy calcium carbonate made using the dry method. Research on increasing toughness by adding rigid particles found that when a resin matrix containing evenly dispersed inorganic particles is impacted by an external force, crazing occurs between the particles and matrix and absorbs the energy of impact. Adding particles thus serves to increase toughness. When surface activation processing is used, ultrafine calcium carbonate particles can achieve even better dispersion in the matrix resin, and can bond better with the resin, achieving an even better increase in toughness. The smaller the particle diameter, the greater their relative surface area, and the greater the increase in toughness. Ultrafine calcium carbonate yields very good processing performance in rubber, and will not influence vulcanization. Products have a smooth surface. Ultrafine calcium carbonate can be used together with other reinforcing agents such as carbon black, white carbon black, clay, and activated calcium carbonate, etc. for oil resistance. The amount of ultrafine calcium carbonate used depends on the product. In the plastic industry, ultrafine calcium carbonate improves plastic's molding performance, and can alter viscosity and improve workability. Ultrafine calcium carbonate is primarily used as a filler by the rubber and plastic industries. 。
Ultrafine calcium carbonate used in paints and coatings has a spatial steric effect. It can partially replace titanium white (the widely used white pigment titanium oxide has high whiteness and a high index of refraction, plus stable physical and chemical properties) and lithopone (a compound pigment containing zinc sulfide and barium sulfate) in order to cut costs. The addition of ultrafine calcium carbonate to paint can cause the relatively dense lithopone to stay in suspension and not sink to the bottom. It can increase the whiteness and luster of the paint film without reducing covering ability. These performance-enhancing qualities have ensured the large-scale acceptance of ultrafine calcium carbonate by the paint industry. It can prevent settling in latex paints, and can reduce the amount of dispersant needed. The use of ultrafine calcium carbonate that has been activated by treatment with a chelated paint dispersion and coupling agent can significantly increase the paint's color intensity and reflection, and thereby enhance the luster, and also improve covering ability, abrasion resistance, adhesion, impact resistance, and flexibility. Ultrafine calcium carbonate is used even more extensively in the aqueous paint industry. It can prevent pigment settling, promote good dispersion, and improve luster. Typically 20%-60% ultrafine calcium carbonate is used in aqueous paints.
Relatively large amounts of calcium carbonate are used by the oil-based paint industry, which considers it to be an indispensable reinforcing agent. Usually more than 30% is used in viscous paints, 4%-7% in phenolic paints, and over 39% in phenolic wrinkle paints. Ultrafine heavy calcium carbonate activated with a compound coupling agent is used in ink, and can effectively cut costs, increase volume, prevent settling, and improve the ink's luster, transparency, adhesion, and color brightness.
Calcium carbonate is commonly used in conjunction with kaolin in papermaking; it can increase the luster, whiteness, opacity, and ink absorption of paper. The shift from acidic to neutral sizing methods in the papermaking industry has greatly increased demand for calcium carbonate. Calcium carbonate is chiefly used as a surface coating in the neutral papermaking process, and is also used as a filler to cut expenses. It is further used as a buffering agent and to add structure. Thanks to its good dispersion and low viscosity, calcium carbonate can be used as a partial replacement for clay. It can effectively improve paper's whiteness and opacity, enhance smoothness and softness, improve ink absorption, and boost ink retention. When used in coatings, ultrafine heavy calcium carbonate offers better whiteness, ink absorption, and air permeability than kaolin. It is suitable for use in base and surface coatings used on white cardboard and copper printing paper, and increases corrosion resistance, durability, and strength. It can significantly enhance the whiteness and smoothness of paper, reduce production costs by lessening need for glue and whitener, and improve paper's printing performance.
Use of calcium carbonate as a filler can increase insulating effect.
Calcium carbonate can serve as a supplemental source of calcium when added to animal feed.
Calcium is a necessary nutrient for plants. Together with magnesium, nitrogen, phosphorus, and potassium, calcium is one of the five title planned nutrients. Taiwan's soil is generally acidic, and crushed calcium carbonate rock is considered the most economically efficient and appropriate neutralizing agent. The simultaneous use of organic fertilizer can increase plants' absorption of calcium and reduce loss of calcium from the soil. In addition, calcium carbonate is typically added to mushroom culture medium.
Calcium carbonate provides a source of calcium when added to fish and animal feed. It is also used by the food industry as a food purifier, and can be used as a additives in beverages. Calcium carbonate used in foods must be purified; a simple extraction process can increase purity.
Calcium carbonate can be used to remove sulfur from smoke. Most thermal power plants are coal-fired, and the combustion of coal releases large amounts of sulfides into the atmosphere, causing acid rain. Limestone or powdered limestone used as an absorbent can remove sulfur dioxide from smoke, yielding plaster or other waste material and achieving desulfurization.