Basic knowledge of calcium carbonate

Basic knowledge of calcium carbonate:

1. Overview: Calcium carbonate (CAS number 471-34-1): is a very common inorganic compound widely distributed on Earth. Molecular formula: CaCO3； Molecular weight: 100.09. According to its molecular weight, the calcium content of calcium carbonate is 40%.

Note: CAS number refers to the numbering of all chemical substances in the American Chemical Abstracts.

2. Classification of calcium carbonate:

2.1 Classified by preparation process, it can be divided into two types: light calcium carbonate and heavy calcium carbonate.

2.2.1 Light calcium carbonate:

The calcium carbonate obtained through chemical synthesis is called light calcium carbonate (LCC) or precipitated calcium carbonate (PCC). There are mainly two methods for its production process:

a. Precipitation method: The starting material is limestone (with a bluish gray or black appearance), which is calcined to produce calcium oxide (while releasing carbon dioxide). Calcium oxide+water produces calcium hydroxide, which is then combined with carbon dioxide to synthesize calcium carbonate. The reaction equation is as follows:

CaCO₃                   CaO+ CO₂;

CaO+H₂O         Ca(OH)₂;

Ca(OH)₂ + CO₂                  CaCO₃;

The raw material calcium carbonate of Zhejiang Jiande Zhengfa Pharmaceutical Co., Ltd. adopts this process route.

The advantages and disadvantages of this method are:

The advantages are: low starting material prices; The synthesis process has lower costs; No added substances, no need to remove residual impurities.

Disadvantages: This process has poor impurity removal ability, and product quality mainly depends on raw materials.

b. Calcium chloride process:

Calcium carbonate is synthesized by adding calcium chloride and ammonium bicarbonate, and the reaction equation is as follows

CaCl₂+ NH₄HCO₃                  CaCO₃+ NH₄Cl

The advantages and disadvantages of this method are:

Advantages: Short production process and one-step synthesis.

Disadvantages: Under the same specifications, the price of starting materials is generally higher than that of finished products, which is not economically feasible; There are a large number of chloride ions present in the product, which require repeated washing and are costly (previously, this process was used to produce calcium carbonate for reagents, and it is said that 15 tons of water are needed to wash each ton of calcium carbonate). Due to drug standards, chloride ions are required (not exceeding 0.03%); The byproduct of the reaction, ammonium chloride, is unstable and easily decomposes to produce ammonia gas, resulting in an unpleasant odor in the product.

2.2.2 Heavy Calcium Carbonate:

The calcium carbonate obtained by physically grinding natural calcite ore is called Heavy Calcium Carbonate (HCC), and there is also an English translation for Ground Calcium Carbonate (GCC).

The advantages and disadvantages of this process:

Advantages: Simple production process; The starting material has high purity and few impurities, resulting in a higher content and impurity level of the finished product than light calcium carbonate.

Disadvantages: High specific gravity, fast settling in water, and cannot be used in many liquid products; Without a chemical synthesis process, it is not possible to declare the raw material calcium carbonate product (according to the current chemical raw material declaration requirements in China).

2.2 Other classification methods:

The classification of calcium carbonate is generally based on the preparation process. At present, there are other classification methods in China:

According to the particle size of the powder, it can be divided into conventional calcium carbonate (average particle size 5-10 microns), fine calcium carbonate (average particle size 0.1-1 microns), and ultrafine calcium carbonate (average particle size not exceeding 0.1 microns, also known as nano calcium carbonate).

Classified by product usage, it can be divided into industrial calcium carbonate, food additive calcium carbonate, raw material calcium carbonate, etc.