Property and Application Inventory of Precipitated Calcium Carbonate

Production Method of Precipitated Calcium Carbonate

Precipited Calcium Carbonate (PCC), also known as light calcium carbonate, is produced by burning raw materials such as limestone to produce lime (mainly composed of calcium oxide) and carbon dioxide, then adding water to digest the lime to produce lime milk (mainly composed of calcium hydroxide), and then carbonizing the lime milk with carbon dioxide to produce calcium carbonate precipitate. Finally, it is dehydrated, dried, and crushed to produce calcium carbonate precipitate. Alternatively, it can be obtained by first decomposing sodium carbonate and calcium chloride to produce calcium carbonate precipitate, which is then dehydrated, dried, and crushed. There are various methods for producing light calcium carbonate, but the main industrial production method in China is carbonization.

1. Carbonization method: Limestone and other raw materials are calcined to produce lime (mainly composed of calcium oxide) and carbon dioxide, and then water is added to digest the lime to produce lime milk (mainly composed of calcium hydroxide). Then, carbon dioxide is introduced to carbonize the lime milk to produce calcium carbonate precipitate. Finally, the calcium carbonate precipitate is dehydrated, dried, and crushed to produce light calcium carbonate.
2. Soda ash (Na2CO3) calcium chloride method: Adding calcium chloride to an aqueous solution of soda ash can generate calcium carbonate precipitate.
3. Caustic alkali method: During the production of caustic soda (NaOH), a by-product, light calcium carbonate, can be obtained. Adding hydrated lime to a pure alkali aqueous solution can generate calcium carbonate precipitate, and at the same time obtain a caustic soda aqueous solution. Finally, the calcium carbonate precipitate is dehydrated, dried, and crushed to produce light calcium carbonate.
4. Calcium chloride method: Treat hydrated lime with hydrochloric acid to obtain calcium chloride solution. After inhaling ammonia gas, carbonize the calcium chloride solution with carbon dioxide to obtain calcium carbonate precipitate.
5. Solvay method: During the production of soda ash, a by-product, light calcium carbonate, can be obtained. Saturated saline solution is carbonized with carbon dioxide after inhaling ammonia gas, resulting in the precipitation of heavy alkali (sodium bicarbonate) and ammonium chloride solution. Adding lime milk to ammonium chloride solution yields calcium chloride ammonia solution, which is then carbonized with carbon dioxide to obtain calcium carbonate precipitate.

Characteristics of Precipitated Calcium Carbonate Powder

Due to the larger settling volume of light calcium carbonate (2.4-2.8 mL/g) compared to heavy calcium carbonate (1.1-1.4 mL/g), it is called light calcium carbonate. The chemical formula of calcium carbonate is CaCO3. Calcium carbonate reacts with all strong acids to produce water and corresponding calcium salts (such as calcium chloride CaCl2), while releasing carbon dioxide; At room temperature (25 ℃), the concentration product of calcium carbonate in water is 8.7 × 1029, the solubility is 0.0014, the pH value of calcium carbonate aqueous solution is 9.5-10.2, and the pH value of air saturated calcium carbonate aqueous solution is 8.0-8.6. Calcium carbonate is non-toxic, odorless, and non irritating, usually white in color, with a relative density of 2.7-2.9. The settling volume of lightweight calcium carbonate is above 2.5ml/g, and the specific surface area is about 5m2/g (tested using the BET method of the fully automatic F-Sorb 2400 specific surface area meter produced by Beijing Jin'epu Technology). Light calcium carbonate particles are fine and have a rough surface, with a large specific surface area, resulting in a high oil absorption value of around 60-90ml/100g.

The shape of light calcium carbonate can be divided into spindle shaped, cubic shaped, needle shaped, chain shaped, spherical shaped, flake shaped, and square column shaped calcium carbonate according to the different grain shapes of calcium carbonate. These different crystal forms of calcium carbonate can be prepared by controlling the reaction conditions. Light calcium carbonate is divided into three types based on its original average particle size (d): fine calcium carbonate (5 μ m), micro calcium carbonate (1-5 μ m), micro calcium carbonate (0.1-1 μ m), ultrafine calcium carbonate (0.02-0.1 μ m), and ultrafine calcium carbonate (0.02 μ m). The particle shape is regular and can be regarded as a monodisperse powder; The particle size distribution is narrow and the particle size is small.

Basic Uses of Precipitated Calcium Carbonate

Papermaking

The paper industry is one of the largest markets for calcium carbonate, and heavy calcium carbonate fillers are mainly used for printing paper, advertising paper, office paper, writing paper, etc., in addition to cigarette paper, filter paper, and special low basis weight information paper. Light calcium carbonate has better quality compared to heavy calcium carbonate, with advantages such as fine particle size, high whiteness, low price, low foaming ability, and good printing adaptability. It is very suitable for use as a papermaking filler and can basically meet the requirements of paper printing and optical performance.

Relevant analysis shows that spindle shaped ultrafine grained calcium carbonate can improve the quality and wear resistance of high-grade paper without modification. Moreover, filling spindle shaped calcium carbonate in pulp can simulate fine fibers and create a large number of small air chambers, resulting in excellent smoothness and printability.

Rubber

Lightweight calcium carbonate is widely used in rubber products, such as tires, conveyor belts, rubber hoses, adhesive tapes, and medical rubber products. It can reduce the amount of rubber used, lower costs, and also play a role in reinforcement and semi reinforcement. Filling lightweight calcium carbonate into rubber can achieve higher tensile strength, wear resistance, tear strength than pure rubber sulfides, and has a significant reinforcing effect in natural rubber and synthetic rubber, while also adjusting viscosity.

Relatively speaking, the reinforcing and toughening properties of needle shaped calcium carbonate are stronger than those of ordinary fillers. After filling in the material, it can improve the strength, hardness, and wear resistance of the material.

Plastic

Lightweight calcium carbonate can serve as a skeleton in plastic products, greatly improving the dimensional stability of plastic products, increasing their hardness, and enhancing their surface gloss and smoothness. Adding calcium carbonate to general plastic products can improve their heat resistance. As lightweight calcium carbonate has a whiteness of over 90%, it can also replace expensive white pigments and have a certain whitening effect.

Paint and Coatings

Calcium carbonate is an important filler in paint production, and its fineness and particle distribution determine the transparency of the paint. Lightweight calcium carbonate is widely used in the paint industry and is an indispensable skeleton. It is used in over 30% of thick paints, 4-7% of phenolic enamel paints, and over 39% of phenolic fine patterned and wrinkled paints.

Compared to heavy calcium, light calcium is artificially synthesized and its crystal structure and composition are easy to control, thus endowing it with multiple functions. Its relatively high specific surface area makes the powder's reinforcement effect in coatings significantly better than that of heavy calcium. Ordinary light calcium is mainly used in anti-corrosion coatings (including ship coatings, container coatings, vehicle primers, bridge and steel structure anti-corrosion coatings, etc.), in addition to being partially used in architectural coatings, paper coatings, and powder coatings. Ultra fine light calcium not only serves as a filler, but also has certain water resistance and corrosion inhibition.

Ink

Lightweight calcium carbonate applied to ink can make the paint film glossy and long-lasting; Make the printing tone of ink elegant and uniform, and its good translucency, glossiness, and flowability can also reduce the cost of coating and ink. Spherical and cubic nano calcium carbonate have better dispersibility, transparency, glossiness, and coverage than other fillers, and are widely used in high-quality inks for rapid printing and laser typesetting.

Medicine

Light calcium carbonate is used in pharmaceutical formulations as a neutralizing agent, filter aid, buffering and dissolving agent, as well as a filler and calcium source supplement. And the hollow structure of calcium carbonate has good biocompatibility and can be used as a drug delivery and diagnostic biomarker.

Food

Lightweight calcium carbonate is widely used in the modern life calcium supplement and nutritional food industry. It is a high-quality nutritional reinforcement additive for dairy products, meat and flour products, dairy milk powder, dairy tablets and other industries. In the process of preparing penicillin, streptomycin, and oxytetracycline, a large amount of calcium carbonate is required.

As an additive in food to ensure the necessary calcium intake for the human body, such as in chewing gum, chocolate and yogurt, calcium tablets, jelly and other beverages as fortifiers to meet the body's calcium needs. Light calcium carbonate is used as an alkaline agent, nutritional supplement, dough conditioner, curing agent, yeast nutrient, anti caking agent, loosening agent, gum sugar additive, and modifier in food processing. Edible grade calcium carbonate has high content and low impurities, with particularly low indicators such as Pb, As, Hg, Fe, etc.

Feed

Light calcium carbonate is used as a calcium supplement in feed processing. Feed grade lightweight calcium carbonate must meet the following standards: calcium carbonate (CaCO3) content ≥ 98%; Calcium carbonate (Ca) content ≥ 39.2%; Moisture content ≤ 1%; Hydrochloric acid content ≤ 0.2%; Heavy metal content (Pb) ≤ 0.003%; Arsenic (As) ≤ 0.0002%; Barium salt (Ba) ≤ 0.030%.

Toothpaste

Light calcium carbonate can be used in daily chemical products such as tooth powder, toothpaste, cosmetics, etc. Lightweight calcium carbonate is used as a friction agent in toothpaste, which can not only remove dental plaque and residue, polish teeth without damaging the enamel, but also has good aroma permeability and paste diffusion; In addition, it is slightly alkaline and can neutralize acidic metabolites such as citric acid from plaque bacteria, reducing oral pH and having multiple effects such as clearing acidic plaque and neutralizing acidic metabolites in the oral cavity.

Sealing Adhesive

Calcium carbonate, as a semi reinforcing filler used in adhesives, can change the properties of the adhesive layer, reduce adhesive costs, and basically do not react with the base material. Adding a certain amount of calcium carbonate to the adhesive can increase its bonding strength, hardness, heat resistance, dimensional stability, reduce curing shrinkage rate, and linear expansion coefficient. As for commonly used glass adhesives, without the use of reinforcing fillers, the bonding strength becomes very poor. Adding industrial calcium carbonate can improve the strength of the bonding joint, increase surface hardness, viscosity and thermal conductivity, increase impact toughness and wear resistance, improve the medium resistance of the adhesive, and reduce costs. Light calcium, especially nanoscale light calcium, has good particle size stability and uniform dispersion, providing excellent elasticity, waterproofness, airtightness, and rheological properties for sealants, making it an ideal sealing material.

Ceramic

Developing cubic calcium carbonate with uniform particle distribution, which can be used for the production of densified ceramics at low temperatures of 600 ℃.

Cable

Lightweight calcium carbonate in cable products can improve electrical insulation performance, with moderate acidity and alkalinity, good compatibility with resins, increase filling volume, and reduce costs. It is particularly suitable for filling PVC wire and cable materials.

Other

Light calcium carbonate is also widely used in organic synthesis, metallurgy, glass and asbestos production. It can also be used as a seeding agent for industrial wastewater and as an SO2 eliminating agent for SO2 containing waste gas.