Nano-scale ultrafine calcium carbonate has a very small particle size (usually 1 nm to 100 nm). It is difficult to produce nano-scale ultrafine calcium carbonate by physical means, and physical methods cannot produce a highly active crystal form in particular. Therefore, chemical methods are being studied both at home and abroad, and the carbonization method is the main method for producing nano-scale ultrafine calcium carbonate. The industrialized production process of nano-calcium carbonate mainly includes intermittent bubbling carbonization, continuous spray carbonization, and high-gravity reaction crystallization.

1.1 Intermittent bubble carbonization
Intermittent bubbling carbonization is the process used by most manufacturers at home and abroad. According to whether there is stirring device in the carbonization tower, the method can be divided into ordinary intermittent bubbling carbonization method and stirring type intermittent bubbling carbonization method. In this method, a purified calcium hydroxide suspension and appropriate additives are added to a cone-bottom cylinder carbonization tower, and carbon dioxide is then passed through the bottom of the tower to “carbonize” to obtain the desired calcium carbonate product. During the reaction, it is necessary to strictly control the reaction conditions such as carbonization temperature, carbon dioxide flow rate, lime milk concentration, and stirring speed, and add appropriate additives.
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1.2 Continuous Spray Carbonization
In the continuous spray carbonization method, the milk of lime is sprayed into a spray and sprayed from the top of the tower, and a certain concentration of CO2 rises from the bottom of the tower at a certain speed and reacts with the milk of lime-like milk. A three-stage series carbonization process is generally used. Refined lime milk is sprayed from the top of the first-stage carbonization tower into droplets of 0.01 nm to 0.1 mm, and carbon dioxide is introduced from the bottom of the tower. The carbonization reaction occurs in the countercurrent contact between the two. The reaction mixture flows out from the bottom of the column and enters the slurry tank. After the appropriate dispersant is added, the mixture is sprayed into the second carbonization tower to continue the carbonization. Then, the mixture is treated with surface activity and sprayed into the tertiary carbonization tower to obtain a particle size. 40 to 80 nm final product.
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1.3 Hypergravity Reaction Crystallization
The feature of the hypergravity reaction crystallization technique is to strengthen the gas-liquid mass transfer process as the basic starting point. The core is that the carbonization reaction is carried out in a hypergravity centrifugal reactor (rotary spiral or packed bed reactor), and a high-gravity field environment can be obtained by using the tens to hundreds of times the gravitational acceleration generated by the high-speed rotation of the packed bed. The CO2 and Ca(OH)2 suspensions are countercurrently contacted in a special gravity apparatus, which greatly enhances interphase mass transfer and microscopic mixing, creating an ideal environment for uniform and rapid nucleation of CaCO3. In the hypergravity field, various transfer processes are greatly strengthened, the phase interface is rapidly updated, and the volumetric mass transfer coefficient can be increased to 10 to 1 000 times that of the normal gravity packed bed, thereby greatly improving the dissolution of Ca(OH) 2 and CO 2 . The absorption rate increases the concentration of Ca2+ and CO2-3 in the system, and increases the degree of supersaturation. At the same time, an appropriate dispersant is added to control the growth of crystals, and nano-sized calcium carbonate having an average particle size of 15 to 30 nm is finally obtained.
1.4 Non-freezing process
The main characteristics of the non-freezing nano-calcium carbonate preparation process are as follows: (1) Carbonization is carried out at normal temperature and pressure without freezing, low energy consumption, and low investment. Taking the new nano calcium carbonate plant with a capacity of 10 000 tons/year as an example, the construction investment (excluding working capital) will be around 12 million yuan, and the product cost per ton will be less than 1,000 yuan. (2) The particle size of the product can be adjusted by adjusting the formulation of the additive, and can be adjusted within a range of 10 to 100 nm as required. The particle size distribution is narrow and the operation is simple. China has abundant calcium carbonate resources. At present, China's annual output of calcium carbonate is second only to the United States, which is the second largest in the world. It has become a major producer of calcium carbonate, but it is not yet a strong producer of calcium carbonate. In China's calcium carbonate industry, precipitated calcium carbonate with a certain technological added value accounts for only 10% of the product structure, with high value-added varieties such as nano-scale calcium carbonate less than 1% of total production; at the same time, the dispersion of the product Large, poor performance stability, can not meet the market demand, still need to import more than 100,000 tons per year. Foreign nano-scale calcium carbonate has formed a large-scale industrial production. The fuel we use is mainly coal. In foreign countries, we use both coal as fuel and oil and gas.

Nano-calcium carbonate is a new type of light calcium carbonate product processed and developed using nanotechnology in the 1980s. Its particle size is usually between 20 and 100 nm. Due to the ultrafine refinement of calcium carbonate particles, the crystal structure and surface electronic structure of the calcium carbonate particles are changed, resulting in the quantum size effect, small size effect, surface effect, and macroscopic quantum effect that ordinary calcium carbonate does not have, and the particle size is fine and uniform. The narrow distribution, large specific surface area, good surface activity and dispersibility, and high surface energy enable it to exhibit more excellent properties that many ordinary calcium carbonate materials do not have in practical use, and is used more widely. Such as can be widely used in a large number of injection molding, extrusion, PVC profiles, pipes, automotive coatings, sealants, adhesive coatings, inks, rubber and other industries, the added value of calcium carbonate products has been greatly improved, and soon caused the world The general concern has now become a hot spot for inorganic non-metallic materials research and corporate competitive investment.