Talking about the influence of wet and dry processes on the performance of heavy calcium products

China Powder Network News Heavy calcium carbonate production methods mainly include dry and wet methods, dry method generally produces less than 2500 mesh of heavy calcium, if the production of more than 2500 mesh of calcium is technically feasible, but can Higher cost and cost, not economically viable. The production of ultrafine heavy calcium carbonate of 2,500 mesh or more is mainly by wet grinding, and the dry grinding is used as a front stage of wet grinding.


Dry grinding process

Dry production of heavy calcium is a common method in China at present, and the technology is also relatively mature. Generally, a processing system composed of grinding equipment and grading equipment can be used to obtain products of various sizes. The main equipments used are Raymond mill, ring roller mill, ball mill, high pressure roller mill, agitator mill, vibrating mill, impact mill, etc. The grading equipment mainly adopts impeller type super-segmentation machine. among them:

Raymond mill is used in large quantities to produce 38-74μm (200-400 mesh) products. It is also used to produce fine powder of d97=30-15μm (500-800 mesh) after modification and configuration of fine classifier.

The ball mill is the main equipment of the large heavy calcium carbonate production line. It is equipped with various classifiers to produce heavy calcium carbonate products with grades of d97=5μm, 10μm, 16μm and 45μm.

The vibration grinding configuration fine grading equipment is mainly used for the production of d97=5μm, 10μm, 16μm products, but its single machine production capacity is not as good as the ball mill;

The mechanical impact mill has a simple process, but the output is low, and it is mainly used in small and medium-sized heavy calcium carbonate production plants;

Dry agitator mills are used in large heavy calcium carbonate production plants in Europe, but they are currently used in China.

The dry production process has the characteristics of less equipment investment, mature technology, simple process, low energy consumption, and high output per unit. Generally, the conventional dry process for producing heavy calcium is shown in the figure.

Wet grinding process

With the development of heavy calcium carbonate, the traditional dry process cannot meet the requirements in terms of equipment itself and economic efficiency, so the wet grinding process came into being. The biggest difference between wet grinding and dry grinding is the difference of dispersion medium. Dry method uses air as the dispersion medium, while wet grinding uses water as the dispersion medium. With the grinding aid, the dispersion of the particles is better. Grinding efficiency is higher and the particle size is finer. The general wet grinding process is shown in the figure.

After the raw ore is washed, the two sections are crushed to about 400 mesh, and the slurry is prepared into a certain concentration. The grinding aid is added to the vertical grinding machine, and the zirconia beads are used as the grinding medium. The parameters are controlled by adjusting the parameters of the mill. Fineness, after the material is ground, it is discharged as a slurry, and after drying and dust removal, the bag is collected.

Comparison of wet and dry grinding of heavy calcium

Since the production process and grinding environment of wet grinding of heavy calcium are significantly different from that of dry grinding of heavy calcium, there are also significant differences in physical properties of the products.

1, particle size. Wet-milled ultra-fine heavy calcium has a fine particle size and mainly produces products of more than 3,000 mesh. The content of -2μm can generally reach 90%, while the dry process has a relatively coarse particle size, and mainly produces products of less than 2,500 mesh.

2. Particle size distribution. The wet-processed heavy calcium has a narrow particle size distribution and a single-peak or double-peak distribution. The dry-processed heavy calcium has a wide particle size distribution and is bimodal or multimodal.

3. Particle shape. Due to the different grinding environment and force mode of the particles during grinding, the wet-milled heavy calcium product particles generally appear spherical or spheroidal, while the dry products are mostly uncertain and have sharp edges and corners.

4. The moisture of the powder. The wet superfine heavy calcium has undergone a drying process in the production process, and the water content is generally controlled below 0.3%, but the dry calcium water produced by the dry process cannot be controlled, generally more than 1%, so the wet process during the modification process The dispersibility and fluidity of ultra-fine heavy calcium is significantly better than that produced by dry process.

Superfine heavy calcium modification process

The modification of heavy calcium carbonate is generally divided into dry modification and wet modification. Dry modification generally requires first drying calcium carbonate to remove water (if the moisture content of calcium carbonate is less than 1%, it may not be carried out. Drying, then the modifier completes the surface modification of the calcium carbonate powder in a surface modification machine. The dry modification is generally applicable to powders below 1250 mesh. If the powder is too fine, the activation of the modified product is low, and a large amount of secondary agglomerates are easily formed, which affects the performance of the product.

The wet modification is carried out by surface modification treatment in a calcium carbonate slurry, followed by filtration and drying. Since the dispersion of calcium carbonate in the liquid phase is easier than the dispersion in the gas phase, this production process has the following advantages:

1. The wet modification process is beneficial to the uniform coating of calcium carbonate particles, the surface coverage rate can reach more than 98%, and continuous production can be realized.

2. The wet modification process is beneficial to the dispersion of the production and the reduction of the particle size. After pulverization and drying, the fineness is still close to the fineness of the ultrafine abrasive slurry.

3. Due to the advantages of uniform coating and particle dispersion due to wet modification, particle agglomeration does not occur during composite modification, which creates conditions for the wide application of products in plastics and rubber processing.

4. The modification equipment is generally simple, mostly a container with a stirrer and a static mixer. Strong stirring can improve the modification activation efficiency and shorten the reaction time, but the performance requirements of the equipment are high.

The combination of ultrafine grinding and modification to produce active ultrafine calcium powder has been a research hotspot in this field. At present, dry modification is still the mainstream process for the modification of heavy calcium carbonate. The wet modification process is often used for the surface modification of ultra-fine heavy calcium carbonate by light calcium and wet grinding. With the advancement of technology and equipment, as well as the increasing demand for high-end active ultra-fine calcium powder in the plastics and rubber industries, the proportion of active ultra-fine calcium produced by wet grinding + wet modification will become more and more. The bigger. (Powder network editing finishing / orange)