Factors affecting the whiteness of calcium carbonate
1
Limestone quality
Limestone is the main factor affecting the whiteness of light calcium carbonate. The main chemical components affecting its whiteness are impurities such as iron, manganese and hydrochloric acid insolubles. Iron is mainly present in the form of Fe3+ in calcium carbonate, which is the main cause of the decrease in whiteness of calcium carbonate. Therefore, the whitening of calcium carbonate is the removal of iron by physical and chemical methods.
2
Calcination
In the beneficiation stage, the quality of limestone is not up to standard, the impurity content is too high, and many harmful impurities such as silica, alumina, iron oxide, etc., will combine with calcium oxide to form a low-melting viscous material during calcination, causing the vertical kiln to occur. In the case of nodulation, the tumor adheres to the surface of calcium oxide, reducing the whiteness of the product.
3
digestion
Different digestive equipments have different effects on whiteness, the influence of the digesting tank is the smallest, the pulp is digested and the second, and the drum digestive machine has the greatest influence.
4
refined
The refining process is one of the important factors affecting the whiteness of the slurry. The quality of the refining process can make the whiteness greatly different. Refining is to get out the yellow and black impurities. The more thorough the removal, the higher the whiteness.
Method for improving calcium dioxide whiteness
The use of limestone to produce light calcium carbonate, the quality of the ore, directly affects the whiteness of the product. Therefore, increasing the whiteness of calcium carbonate begins with the choice of ore. When the limestone iron content is ≤0.12%, the manganese content is ≤0.06%, and the hydrochloric acid insoluble content is ≤0.30%, the light calcium carbonate which is qualified for whiteness can be basically satisfied.
When the iron content exceeds 0.2%, the product will be yellow or even red, causing a decrease in whiteness. At this time, it is necessary to remove iron by chemical agents. If iron pollution is caused by equipment, it can be treated in the same way. If it is not excessively high, it cannot be used. The method handles, otherwise it will reduce the whiteness.
If other impurities in the ore exceed the standard, the whiteness will not be high. At this time, the whiteness should be increased as much as possible by multi-stage de-slag treatment. Generally, the increase is limited, and it is better to change the ore. If it contains high color minerals, bleaching techniques should be used to increase the whiteness of calcium carbonate products.
Then, according to the pigment ions contained in the limestone and the product calcium carbonate, reduction bleaching or oxidative bleaching or a bleaching method is used respectively. In addition, it is necessary to strengthen management and improve equipment levels, and timely maintenance and maintenance of equipment is also important.
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