Preparation Process of Activated Calcium Carbonate Powder
Activated calcium carbonate powder is a novel functional material characterized by high purity, excellent dispersibility, and high reactivity, making it promising for a wide range of applications. Its preparation primarily involves two methods: the wet process and the dry process. This paper provides a detailed discussion of the underlying principles and the control of process parameters for both methods.
I. Wet-Method Preparation
Wet-process preparation refers to the production of precipitated calcium carbonate powder under liquid-phase conditions. The main steps include formulation of the reactants, reaction, filtration, and drying.
In the wet-process preparation of precipitated calcium carbonate powder, calcium carbonate powder, an acidic substance (such as hydrochloric acid or nitric acid), and a calcium salt solution (such as calcium chloride or calcium nitrate) are used. The calcium carbonate powder serves as the reactant, the acidic substance facilitates the conversion of calcium carbonate into soluble calcium chloride or calcium nitrate, and the calcium salt solution provides the calcium source for the reaction. During the process, the calcium carbonate powder is first mixed with the acidic substance to initiate the reaction, producing soluble calcium chloride or calcium nitrate. The resulting solution is then added dropwise to a suspension of calcium carbonate, where a chemical reaction occurs to form the precipitated calcium carbonate powder. Throughout the reaction, parameters such as temperature, reaction time, and atmosphere must be carefully controlled to ensure complete reaction and high product quality. After the reaction is complete, the reaction mixture is filtered and washed to remove impurities and unreacted materials. The dried product is then milled and packaged to yield the final precipitated calcium carbonate powder.
II. Dry-Method Preparation
Dry-process preparation refers to the production of precipitated calcium carbonate powder under dry conditions. The main steps include formulation of the reactants, reaction, calcination, and grinding.
In the dry-process preparation of activated calcium carbonate powder, calcium carbonate powder, calcium oxide, sodium hydroxide, or other alkaline substances are used. Among these, calcium carbonate powder serves as the reactant, while the alkaline substances enhance the reactivity of the reactants and accelerate the reaction. During the process, the calcium carbonate powder is first mixed with the alkaline substance and subjected to ball milling to ensure thorough blending. The resulting mixture is then calcined to induce a chemical reaction that produces activated calcium carbonate powder. Throughout the reaction, parameters such as calcination temperature, duration, and atmosphere must be carefully controlled to ensure complete conversion and high product quality. After the reaction is complete, the product undergoes further calcination to develop a uniform crystalline structure and particle morphology. Finally, the calcined product is milled and screened to obtain the finished activated calcium carbonate powder.
III. Control of Preparation Process Parameters
Whether active calcium carbonate powder is prepared by the wet or dry method, control of the process parameters is crucial. The following lists several key parameters.
Reaction temperature: The reaction temperature affects both the reaction rate and the quality of the product. An excessively high reaction temperature can degrade the product’s structure and particle morphology, while an excessively low temperature can hinder complete reaction and compromise product quality. In general, for wet-chemical synthesis, the reaction temperature is typically maintained between 20°C and 60°C, whereas for dry-chemical synthesis, the calcination temperature is usually in the range of 500°C to 1000°C.
Reaction time: Reaction time refers to the duration of the reaction. If the reaction time is too short, the reactants may not fully convert; if it is too long, it results in unnecessary waste of time and energy. Generally, wet-chemical synthesis requires a reaction time of 30 minutes to 4 hours, while dry-chemical calcination typically takes 1 to 4 hours.
Reactant Ratio: The reactant ratio refers to the proportion of different raw materials. This ratio influences both the chemical composition and the structure of the product. In general, for wet-process preparation, the amount of calcium carbonate powder should be appropriate; the amount of acidic substance should be properly balanced with the calcium carbonate powder; and the concentration of the calcium salt solution should be moderate. For dry-process preparation, the amount of alkaline substance should be appropriate, and the amount of calcium carbonate powder should be moderate.
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