Calcium carbonate manufacturing processPosted: 2020-01-07

  • Calcium carbonate is usually divided into heavy calcium carbonate/ ground calcium carbonate powder and light calcium carbonate/ precipitated calcium carbonate. Heavy calcium carbonate is also called ground calcium carbonate, referred to as heavy calcium carbonate/ ground calcium carbonate powder, which is produced by physical processing method; light calcium carbonate is also called precipitated calcium carbonate, which is chemically processed. Made. Heavy calcium / heavy calcium powder is widely used in many fields because of its many advantages. The true value of heavy calcium carbonate/ ground calcium carbonate powder is its deep-processed products, that is, ultra-fine, high-purity, surface-modified products. Added value ultra-fine, high-purity heavy calcium carbonate/ ground calcium carbonate powder products have good industrial application prospects.
    calcium carbonate manufacturing process
     

    1. Manufacturing process of heavy calcium carbonate



    The production methods of heavy calcium carbonate are usually divided into two methods, dry method and wet method.

    The characteristics of heavy calcium carbonate dry production:
    1) low investment and mass production of stable quality products;
    2) can flexibly control production conditions and produce at a lower cost according to different use requirements Products with different requirements;
    3) The product can be surface modified to improve the performance of the product.


    The heavy calcium carbonate wet production method is to extract the extracted natural calcium carbonate through primary, secondary pulverization and washing, and then select and enter the wet grinding equipment for grinding, and then mix with the dispersant for secondary grinding.

    The product is obtained after precipitation, and its production characteristics are:
    1) large-scale production and low cost;
    2) product quality parameters can be adjusted according to product requirements;
    3) extremely fine granularity can be achieved;
    4) product transportation difficulties, such as Drying increases investment and production costs, so wet products should be produced and used locally.

    In addition, the dry method is suitable for producing fine heavy calcium with an average particle size larger than 3um. For powders below 3um, it is technically feasible, but the cost is too high and it is not economically feasible. The wet method is mainly used to produce average particle size Fillers less than 2um and maximum particle size less than 10um and coating-grade heavy calcium are mostly used in papermaking and high-grade coatings. Therefore, different production methods can be adopted according to different needs.
     

    2. The main process of wet grinding heavy calcium carbonate



    (1) Raw ore → jaw crusherRaymond mill → Wet stirring mill or chipping machine (intermittent, multi-stage or cycle) → Wet classifier → Screening → Drying → Activation → Bagging Heavy calcium powder). A wet ultra-subdivision level is added to this process, which can timely sort out qualified products and improve efficiency. Wet ultra-subdivided equipment mainly includes small-diameter cyclones, horizontal spiral classifiers, and disc classifiers. The classified pulp concentration is relatively thin, and sometimes a sedimentation tank is required. The process has good economic indicators, but the classification is difficult to operate. At present, there is no very effective wet ultra-fine segmentation equipment.


    (2) Raw ore → jaw crusher → Raymond mill → wet stirring mill → sieving → drying → activation → bagging (filler grade heavy calcium carbonate / heavy calcium powder).


    (3) Raw ore → jaw crusher → Raymond mill → wet stirring mill or chipping machine (intermittent, multi-stage or cycle) → sieving (paper-making coating-grade heavy calcium slurry).


    Wet production of heavy calcium carbonate can be produced in filler grade and coating grade depending on the process selected. Filler grade heavy calcium carbonate / heavy calcium powder generally can meet the requirements of the product after one grinding. The coated grade heavy calcium carbonate needs to be ground again after grinding. In addition, in wet production, process control is relatively complicated, and appropriate production processes should be selected according to raw materials, media, grinding equipment, product use, etc.
     

    3. Research status of wet grinding heavy calcium carbonate 


     
    In order for the wet-processed papermaking cloth-grade heavy calcium products to meet the technical indicators, we must choose many key influencing factors such as raw materials, grinding equipment, grinding aids, and grinding media.


    (1) Selection of raw materials. Calcium carbonate crystals with high purity, crystalline form, and high utilization value in nature are mainly calcite, marble, and ice. At present, the raw materials of heavy calcium carbonate / calcium powder in China are all derived from carbonate metamorphism and thermal contact metamorphism. Marble type calcite deposits and a few are hydrothermal vein-like calcite deposits. The available minerals are Calcite. Calcite is mostly in the form of grains and flakes, and has excellent optical properties. It is suitable for high-end applications, such as papermaking, especially flake calcite, commonly known as large calcite. Practice has proved that due to its flaky structure and three rhombohedron cleavage structures, it has high whiteness and hiding power, which is very suitable for filling and coating of high-grade white cardboard, and its ore source is relatively small, so the price is relatively Higher. Relatively speaking, granular calcite is commonly known as small calcite, followed by hiding power, and more importantly, the large calcite has a slower settlement speed and slower solution, which is conducive to pulp dispersion.


    (2) Selection of grinding equipment. It has been mentioned that the grinding equipment for wet grinding of heavy calcium carbonate / heavy calcium powder mainly includes chippers, agitating mills, and sand mills, but no matter which equipment is selected, the purity of the heavy calcium carbonate / heavy calcium powder must be The whiteness and whiteness are not contaminated. For example, the inner lining of the cylinder and the grinding disc or agitator are made of polyurethane, ceramics or other highly wear-resistant materials, and the mill can run stably under the conditions of high solid content, high viscosity, and small grinding media. The large vertical wet ultra-fine mill developed by Changsha Taiye Research Institute is a new type of high-efficiency ultra-fine grinding equipment. It can be used for wet ultra-fine grinding of non-metallic ore. It is also used in many current ultra-fine grinding equipment. A device with a high rate and fine granularity of the product has a simple structure and convenient operation and maintenance. The mill consists of a transmission part (including a motor and a reducer), a barrel and a combined agitator. The motor drives the combined agitator through a reducer, which is filled with a certain grinding medium (corundum balls, zirconium balls or glass balls) and the material being milled in the cylinder at high speed, and the centrifugal extrusion caused by the heavy pressure of the grinding medium and the rotation of the mixer Under friction, use friction, impact and shear to effectively grind materials. After experiments and production practice verification, the superfine grinding equipment can be used to produce filler grade and primer coating grade (-2um> = 60% -90%) papermaking heavy calcium products after a period of grinding. Therefore, the superfine grinding equipment has a very Good industrial application prospects. In addition, there are more sand mills for wet grinding heavy calcium applications. At present, the more advanced sand mills in China are modified MB300 sand mills, which are characterized by the input power of the mills acting directly on the agitator. Thus, the grinding medium is pushed at a high speed to achieve the purpose of ultra-fine grinding. The high-speed rotation of the agitator causes the grinding medium to have the dual effects of impact and grinding, effectively grinding the material and dispersing it uniformly. The superfine grinding equipment can reach filler grade and base coating grade papermaking calcium product after first or second stage grinding, and can reach top coating grade papermaking calcium product after grinding.


    (3) Selection of grinding aids. Grinding aids are essential for wet ultrafine grinding of powders. We generally divide grinding aids into grinding aids and dispersants, and their mechanisms of action are not the same.


    Regarding the action mechanism of grinding aids, according to the existing research results, there are two representative theories: the first is the "adsorption reduction hardness" theory led by Repinzaire, that is, the grinding aids on the particles Adsorption reduces the surface energy of the particles, or causes dislocation migration of the surface lattice, resulting in point or line defects, thereby reducing the strength and hardness of the particles, promoting the production and expansion of cracks, thereby reducing the energy consumption of the grinding and improving the grinding. Mineral effect; the second is the "slurry rheology adjustment" doctrine headed by Krampal, which believes that the grinding aid can adjust the fluidity of the slurry, between the particles, between the particles and the grinding medium and the liner Reunion and adhesion.


    In production practice, the role of grinding aids is mainly reflected in the following three aspects: 1) Change the rheological properties of the slurry and the electrical properties of the particle surface, thereby reducing the viscosity of the slurry, improving the dispersibility of the slurry, and reducing production The resistance of pipelines and inlets and outlets in the system improves the stability of the system; 2) due to the reduction of slurry viscosity, the resistance of the medium is reduced, and the impact of the relative motion of the medium on the slurry particles and the grinding effect are improved; Adsorption on the surface of new particles greatly reduces the unsaturated surface energy on the surface of the microparticles, thus preventing agglomeration of the particles. For wet grinding of ultra-fine heavy calcium, dispersants are generally used as grinding aids, and polycarboxylic acids or polyacrylic acids and their sodium salts with high purity and stability should be selected as far as possible.


    (4) Selection of grinding media. The hardness of the wet ground heavy calcium raw material is between Mohs hardness of 2.6-3.0, so the grinding medium must have appropriate hardness and toughness. If the hardness is too large, the mill barrel and the agitator or the grinding disc will wear too much; while if the toughness is not good, the grinding medium will be easily broken. According to experience, the optimal hardness of the grinding medium is three times that of the material. For heavy calcium, commonly used grinding media include corundum balls, zirconium balls and glass beads. As for the size of the grinding medium, in general, the size is small, the number of contact points is high, the grinding efficiency is high, but too small grinding medium will increase the small particle portion of the slurry, and for large particles, the small size grinding medium cannot Provide sufficient kinetic energy to break, agree with the widened product particle distribution, and easy to block the separation system of the grinding medium and slurry. Therefore, for a certain range of fineness products, there is an optimal grinding medium diameter, which has been in practical production. Verified. In the case of multiple mills, a correspondingly smaller grinding medium is selected as the feed particles at each level gradually become smaller.


    (5) Optimal configuration of some process parameters. Such as the size of the ore, the spindle speed of the mill, the concentration of the ore, the mass ratio of the grinding medium to the raw material, the grinding time, the amount of dispersant and grinding aid, and so on.
     

    4. Development of wet grinding of heavy calcium carbonate



    The true value of heavy calcium carbonate application is its deep-processed products, that is, ultra-fine, high-purity, surface-modified products, while the wet produced heavy calcium carbonate products have high purity, fine particle size, and Uniform, good grain shape and stable quality, achieve the purpose of deep processing of the product. Therefore, wet grinding of heavy calcium carbonate has broad prospects.


     (1) Large-scale production, large-scale equipment, automated and intelligent production processes, and improved economic efficiency;


     (2) Adopt advanced equipment to improve grinding effect and reduce energy consumption;


     (3) Adopting advanced process flow to optimize the configuration of various process parameters and improve production efficiency;


     (4) Develop more effective grinding aids to better improve the rheology of the pulp and provide paper mills with excellent dispersion of heavy calcium pulp;


     (5) Establish a satellite supply system to reduce losses caused by transportation and subsequent processing.
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