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Influencing Factors of Whiteness of Light Calcium Carbonate

1. Limestone raw materials
Limestone is the main factor affecting the whiteness of light calcium carbonate. The main chemical constituents affecting the whiteness are impurities such as iron, manganese and insoluble hydrochloric acid. When the iron content of limestone is less than 0.12%, the manganese content is less than 0.006%, and the hydrochloric acid insoluble content is less than 0.30%, the light calcium carbonate with qualified whiteness can be basically produced.
Experienced material collectors and inspectors usually screen according to the appearance of limestone. The limestone with blue and light gray has higher purity and less impurity content. Limestones with high impurities such as iron, manganese and hydrochloric acid insoluble substances are usually yellow, brown, pink or brown.
In addition, the color of raw lime can also be distinguished, especially when containing non-ferrous metal oxides, quicklime is mostly gray yellow, light yellow to brown or even black.
2. Fuel
Anthracite is often used as fuel in the production of light calcium carbonate. The impurity content of sulfur and ash in anthracite also affects the whiteness of light calcium carbonate.

Sulfur content of anthracite for production is less than 1.5%, i.e. low sulfur anthracite, ash content of anthracite is less than 25%, and other impurities such as alkali stone are less than 2.0%, which can meet the production process requirements of light calcium carbonate with qualified whiteness.
3. Quality of Quick Lime
On the premise of guaranteeing the quality of raw materials, the calcination conditions of limestone should also be strictly controlled. Particles and powders less than 5mm in quicklime, impurities such as coke residue and coke nucleus mixed in quicklime and over-burned quicklime should also be selected as clean as possible.
4. Gas and Dust in Lime Kiln
Due to the different specifications, coal quality and operation of lime kiln, the concentration of dust-containing liquids in lime kiln gas varies, and that in ordinary kiln gas varies from 1 to 10 g/m3. In order to reduce the influence of dust in kiln gas on the whiteness of light calcium carbonate, dust removal is often carried out while kiln gas is transported.
More than 80% of dust particles in kiln gas are larger than 10 microns. Generally, the dust above 5 microns can be removed by using multi-cylinder cyclone dust remover. But the dust remover should be installed in the proximal end of the quicklime kiln. In order to improve the dust removal effect, a water bath dust removal device is usually installed in front of the kiln gas conveying mechanical compressor, and the dust removal rate can reach 98% upward.
While removing dust from kiln gas, measures should be taken to reduce the dust content in kiln gas:
Firstly, when calcining limestone, lump coal with certain particle size is used to avoid mixing into coal surface and to prevent coal dust from occurring when feeding into kiln.
Secondly, the anthracite used should have a high crushing strength to reduce the impact of materials during feeding and produce dust.

Thirdly, the coal used for calcination in lime kiln should have good thermal stability.
5. Seminal Serum Quality
The crude slurry after lime digestion contains magazines such as raw and over-burned lime, calcium oxide with poor activity, insoluble substances and cinder blocks.
Vibrating screen and three-stage cyclone separator can be set up in production to remove larger particles and produce lime emulsion semen.

6. Quality of cooked slurry
The quality of slurry depends on the operation of carbonization process. The carbonization process should ensure that Ca(OH)2 reacts completely with CO2, and does not return to alkali or reunite. It is also one of the ways to improve the whiteness of calcium carbonate by improving the dispersibility of crystalline grains, fine particles and uniform distribution.
The quality of carbonization depends on the purity of CO2 in kiln gas and the quality of semen. In this process, insoluble Fe3 + can be changed into soluble Fe2 + and the colored substances can be removed with the clear liquid to achieve the whitening purpose.
7. Smoke and Dust of Drying System
From the influence of smoke and dust on the whiteness of light calcium carbonate, especially the influence of smoke and dust leaked from heat exchange pipe of dryer on the whiteness of light calcium carbonate is the most.
How to make the heat exchange flue pipe of dryer sealed well and leak-free?
(1) The heat exchanger flue pipe of the dryer should be heated at constant temperature during the operation of the dryer heating furnace. The semi-finished products which are put into the dryer for drying should be continuous and uniform so as to avoid frequent heat expansion and cold contraction of the heat exchange flue pipe of the dryer.
(2) The leakage of fume and dust heated by dryer should also be paid attention to. Normally, the heater leaks fume and dust without negative pressure operation.

(3) The influence of high-temperature flue gas and semi-finished products in the heat exchange flue gas pipeline of dryer on the whiteness of light calcium carbonate should also be reduced or eliminated. The furnace must have good combustion conditions. That is to say, the heating furnace should maintain a certain high temperature, adequate air volume and good mixing, as well as the necessary combustion space and time, so that combustible gases and fine coal can be fully burned, to avoid 0.05-1.0 um carbon particles free, and to reduce the content of exhaust smoke and dust.
While guaranteeing the sealing quality of flue pipe and the benign operation of heating furnace, the flue gas discharged from outside should be treated by dedusting equipment before discharging, so as to reduce the content of the flue gas discharged from outside.

8. Production environment

Due to internal or external factors, dust drifting or falling in the production plant area is harmful to the quality of semi-finished products or finished products in the process. Therefore, besides some sealing measures, we should also strengthen the management of the environment of production posts in order to eliminate the pollution of environmental impurities to semi-finished products or finished products.

In addition, it is necessary to strengthen the management of two coals, which are the main raw materials for the production of light calcium carbonate, in order to prevent the two pulverized coal particles from entering the production process artificially or externally.
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