Analysis of Preparation Technology of Nano Calcium Carbonate

Nano-calcium carbonate is also known as ultra-fine calcium carbonate, and its average particle diameter is about 40nm. The preparation of superfine calcium carbonate in the process laboratory usually adopts three methods: carbonization method, double decomposition method and microemulsion method, and carbonization method is generally used in industry.

1, the preparation method of nanometer calcium carbonate

(1) Double decomposition method

 The double decomposition method is to prepare water-soluble calcium salts (such as calcium chloride, calcium sulfate, etc.) and water-soluble carbonates (such as ammonium carbonate, sodium carbonate, etc.) through the reaction process from liquid phase to solid phase under certain conditions. Nano calcium carbonate. When the laboratory uses this method to prepare calcium carbonate, it can be obtained by controlling the concentration of reactants, reaction temperature, supersaturation of the product and adding appropriate additives. Good solubility amorphous calcium carbonate product.

 The nano calcium carbonate prepared by this method has relatively high purity and good whiteness, but it requires high cost when producing products with different crystal forms, so at present, this method is rarely used for industrial production of nano calcium carbonate at home and abroad. calcium carbonate.

(2) Carbonization method

① The intermittent bubbling carbonization method is different from the metathesis method. The intermittent bubbling carbonization method is currently a widely used method for preparing nano-calcium carbonate at home and abroad. The operation steps are to first cool down the 1.04-1.06g/cm3 Ca(OH)2 slurry to below 25°C, then put the slurry into the carbonization tower, pay attention to maintain a certain liquid level, and then flow from the bottom of the carbonization tower to the tower Introducing CO2 or a mixed gas of CO2 and air, controlling reasonable solution concentration, reaction temperature, gas-liquid ratio and additives, can produce nano-scale calcium carbonate intermittently.

②The continuous spray method is also to produce nano-calcium carbonate by carbonization. The step is to spray the Ca(OH)2 slurry from the top of the carbonization tower through a pressure nozzle in a mist form, and at the same time pass it upward from the bottom of the tower. Inject CO2 or a mixed gas of CO2 and air to make the sprayed Ca(OH)2 slurry fully contact with CO2 to react. This method significantly increases the contact area between CO2 gas and Ca(OH)2 slurry. The reaction process can be controlled at room temperature by controlling the concentration of lime milk, droplet diameter, flow rate, reaction gas-liquid ratio, and other conditions. -0.08μm nano calcium carbonate.

The CaCO3 produced by the continuous spray method has a narrow particle size distribution, regular particle shape, and is easy to disperse. The overall quality is better than that of the intermittent bubbling method. Amount of production costs, it is difficult to popularize.

(3) Microemulsion method

The microemulsion method is a method for preparing nanoparticles that has just been developed in recent years. The operation steps of this method are respectively dissolving soluble carbonate and soluble calcium salt into two microemulsions with exactly the same composition, and performing mixing reaction under certain conditions. In this way, the nucleation and growth of crystal grains can be controlled in a small area. After the crystal grains are separated from the solvent, nano calcium carbonate particles can be obtained, and the particle size is almost controlled between a few nanometers and tens of nanometers.

2. The process of preparing nano-calcium carbonate in industry

(1) Process flow

Technological process A certain amount of quicklime is put into hot water at 80°C for digestion according to the water-cement ratio of 8:1. After completion, a rough solution of calcium hydroxide is obtained, which is aged for 24 hours and screened through a 200-mesh sieve. Sieve through a net to obtain refined calcium hydroxide slurry. Put the refined calcium hydroxide slurry into the glass reactor, add an appropriate amount of additives, set the appropriate carbonization temperature, adjust the appropriate stirring speed, and feed the mixed gas of carbon dioxide and nitrogen or pure carbon dioxide gas through the rotameter to start carbonization reaction. When the reaction system is acidic, that is, after the pH value drops below 7, carbonization is continued for 15 minutes to obtain a nano-calcium carbonate solution. The temperature of the obtained slurry is raised to 80℃., a certain amount of sodium stearate is added to keep the temperature for 2 hours, and the nano-calcium carbonate solid is obtained after filtering, drying and pulverizing.