How to Boost Brightness in Light Calcium Carbonate Key Factors and Fixes
As a widely used inorganic filler, the whiteness of lightweight calcium carbonate is one of the key indicators for assessing product quality, directly affecting its appearance and performance. High-whiteness lightweight calcium carbonate holds greater application value in industries such as plastics, rubber, papermaking, and coatings. Multiple factors can influence the whiteness of lightweight calcium carbonate, but corresponding solutions exist for each of these factors.
Limestone Raw Material Quality
Factors influencing: Limestone is the primary factor affecting the whiteness of light calcium carbonate. Impurities such as iron, manganese, and insoluble substances in hydrochloric acid in the raw materials significantly reduce the product's whiteness. Iron in calcium carbonate primarily exists in the form of Fe3+, which is the main cause of decreased whiteness. When the iron content in limestone exceeds 0.2%, the product turns yellow or even red, with a noticeable decline in whiteness.
Solution: Select limestone with low impurity content such as iron and manganese as raw material, and ensure its purity through strict screening and classification. When the iron content in the limestone is ≤0.12%, the manganese content is ≤0.006%, and the insoluble matter in hydrochloric acid is ≤0.30%, it is generally possible to produce calcium carbonate with qualified whiteness.
Fuel Selection
Influencing factors: In the production process of calcium carbonate, the choice of fuel is also crucial. The content of impurities such as sulfur and ash in anthracite directly affects the whiteness of calcium carbonate.
Solution: Use low sulfur and low ash smokeless coal as fuel to reduce the negative impact on the whiteness of calcium carbonate. The sulfur content of smokeless coal used in production should be ≤ 1.5%, the ash content should be ≤ 25%, and the content of other impurities such as alkali stones should be ≤ 2.0%.
Calcination Conditions
Influencing factors: The calcination conditions of quicklime have a significant impact on the whiteness of calcium carbonate. The calcination temperature and time need to be strictly controlled to avoid overburning of quicklime, and impurities such as coke slag and coke nuclei in quicklime should be removed. In addition, if the quality of limestone does not meet the standard and the impurity content is too high, low melting point viscous substances will be formed during calcination, which will adhere to the surface of calcium oxide and reduce the whiteness of the product.
Solution: Strictly control the calcination temperature and time to avoid overburning of quicklime. At the same time, impurities such as coke residue and coke nuclei in quicklime are removed to improve the whiteness of calcium carbonate.
Carbonization Process
Influencing factors: During the carbonization process, the reaction between Ca (OH) 2 and CO2 must be complete to ensure no alkali return or agglomeration, thereby improving the dispersion, particle fineness, and distribution uniformity of calcium carbonate crystal particles. This is also one of the key ways to improve product whiteness.
Solution: Improve the purity of kiln gas CO2 and ensure complete reaction between Ca (OH) 2 and CO2. At the same time, optimize the carbonization reaction conditions, such as reaction temperature, pressure, and time, to improve the whiteness of the product.
Particle Size And Moisture Content
Influencing factors: The finer the particle size of the ore, the higher the whiteness usually. Meanwhile, the moisture content of ore is also an important factor affecting whiteness.
Solution: Fine grinding and grading of calcium carbonate to improve its particle uniformity and fineness. At the same time, control the moisture content of the ore to avoid excessive moisture affecting its whiteness.
Digestion And Refinement
Influencing factors: Different digestion equipment has different effects on whiteness. For example, the drum digestion machine has the greatest impact on the whiteness of calcium carbonate, while the digestion tank has the smallest impact. The refining process is one of the important factors affecting the whiteness of the slurry. The quality of refinement can greatly affect the whiteness, and the purpose of refinement is to remove yellow and black impurities. The more thoroughly removed, the higher the whiteness.
Solution: Choose a digestion device with less impact on whiteness, such as a digestion tank. At the same time, optimize the digestion process conditions to improve the whiteness of the product.
Extraction Process
Influencing factors: In the production process of pulp and other products, the refining process is one of the important factors affecting whiteness. Incomplete extraction can lead to residual impurities and reduce the whiteness of the product.
Solution: Strengthen the management and control of the refining process to ensure that impurities are fully removed. At the same time, advanced extraction techniques and equipment are adopted to improve extraction efficiency and quality.
Chemical Treatment
Influencing factors: Impurities in calcium carbonate need to be removed through chemical treatment to improve its purity.
Solution: Adopt appropriate chemical treatment methods, such as acid washing, alkali washing, etc., to remove impurities from calcium carbonate. However, attention should be paid to safety and environmental issues during the handling process.
Fluorescent Whitening Agent
Influencing factors: Fluorescent whitening agents can significantly improve the whiteness of calcium carbonate, but excessive or improper use can have a negative impact on product quality.
Solution: Use fluorescent whitening agents with caution to ensure they are within the allowed range of use. At the same time, choose reliable fluorescent whitening agent products to avoid adverse effects on product quality.
Inorganic Coating
Influencing factors: Inorganic coating can improve the whiteness of calcium carbonate, but the uniformity and thickness of the coating layer will affect the whiteness of the final product.
Solution: Adopt appropriate inorganic coating technology to ensure uniform and moderate thickness of the coating layer. At the same time, the coated calcium carbonate is finely ground and graded to improve its particle uniformity and whiteness.
From this, it can be seen that there are many factors that affect the whiteness of lightweight calcium carbonate. However, by selecting high-quality raw materials, optimizing fuel selection, improving production processes, fine grinding and grading, chemical treatment, adding fluorescent whitening agents, and coating with inorganic substances, the whiteness of calcium carbonate can be significantly improved to meet the market's demand for high-quality products.