Method for preparing superfine calcium carbonate powder by using carbide slag ammonium salt circulation method

Abstract

The invention relates to a method for preparing superfine calcium carbonate powder by using a carbide slag ammonium salt circulation method, and belongs to the field of inorganic material preparation. The calcium carbide slag is used as a raw material, calcium in the calcium carbide slag is leached out through an ammonium salt solution, and a refined calcium salt solution is obtained after impurity removal and refining. Then, the nucleation particles are subjected to carbonization reaction with carbonizers of different systems in a stator-rotor reactor, and the particle size, dispersity and morphology of the nucleation particles are effectively controlled by adjusting the rotating speed, the recycle ratio and the temperature in the reaction process to strengthen the gas-liquid mass transfer and micro-mixing process. And after the reaction is finished, filtering, washing and drying to obtain the superfine calcium carbonate powder. The mother liquor can be recycled. By adopting the stator-rotor reactor, the reaction efficiency is greatly improved, the reaction time is shortened, and the prepared calcium carbonate powder has the characteristics of small particle size and good dispersity. The method realizes resource utilization of industrial waste residues and emission reduction of carbon dioxide, has the advantages of low cost, no pollution and environmental protection, and is suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic material preparation, and more specifically to a method for preparing ultrafine calcium carbonate powder using a carbide slag ammonium salt circulation process. The method is characterized by using a stator-rotor device as a core crystallization reactor, resulting in a low-cost, pollution-free process, and belongs to the fields of materials and chemical engineering. Background Art

[0002] Calcium carbonate is a widely used and important inorganic chemical product. Its low price, widespread availability, and low manufacturing costs have led to significant production capacity and usage in China. Industries using calcium carbonate as a raw material, such as coatings, papermaking, plastics, rubber, and inks, have a significant demand for high-quality calcium carbonate. Calcium carbonate also plays a vital role in the pharmaceutical and food sectors.

[0003] Nano-calcium carbonate, with particle sizes ranging from 1 to 100 nm, is a newly developed powder material developed in the 1980s. Compared to ordinary calcium carbonate, nano-calcium carbonate has a unique crystal structure and surface electronic structure, exhibiting excellent quantum size effects, surface effects, and small size effects. It is widely used in chemical engineering, catalysis, optics, medicine, building materials, and material additives.

[0004] At present, there are two main methods for synthesizing nano calcium carbonate: double decomposition method and carbonization method. There are three main reaction systems used: Ca 2+ -H2O-CO3 2- Reaction system, Ca 2+ -R-CO3 2- Reaction system and Ca(OH)2-H2O-CO2 reaction system. Nano calcium carbonate prepared by double decomposition method has good dispersibility. However, this method will introduce other impurity ions and is difficult to be applied in large-scale industrial production. From the actual industrial production of nano calcium carbonate preparation methods at home and abroad, carbonization method is currently the leading production process. Among them, the Ca(OH)2-H2O-CO2 carbonization reaction system has the advantages of low cost, large-scale production and high yield, but there are still problems such as serious agglomeration of the prepared nano calcium carbonate particles, large particle size (micrometer level), uneven particle size distribution, and unclear reaction mechanism.

[0005] Traditionally, calcium carbonate is produced by calcining limestone, a process that is energy-intensive and highly polluting. In recent years, research on the use of industrial waste residues to produce calcium carbonate has gained momentum. Carbide slag, a calcium-rich industrial waste residue, offers advantages such as widespread availability and low cost. Summary of the Invention

[0006] In view of the above, the object of the present invention is to provide a method for preparing ultrafine calcium carbonate powder by utilizing carbide slag ammonium salt circulation method, adopting novel carbonization reaction equipment: stator-rotor reactor (patent number ZL200410042631.6) in the reaction crystallization process of calcium carbonate, which greatly strengthens the mass transfer process and micro-mixing process, significantly improves the reaction rate, shortens the time of crystal nucleus growth after crystallization, effectively controls the particle size and morphology of nucleated particles, and prepares ultrafine calcium carbonate powder with high dispersibility and small particle size. The whole process material is recycled, low in cost, pollution-free, and can realize the resource utilization of carbide slag and the efficient and green preparation of ultrafine calcium carbonate powder.

[0007] The process flow adopted by the present invention has the following key process steps:

[0008] 1. A method for preparing ultrafine calcium carbonate powder by using a carbide slag ammonium salt circulation method, which is characterized by adopting the following process:

[0009] (A) under heating condition, use ammonium salt solution to dissolve carbide slag, make rough calcium salt solution, after carrying out impurity removal and purification, obtain refined calcium salt solution;

[0010] (B) rapidly mixing the refined calcium salt solution and the carbonizing agents of different systems in a stator-rotor reactor at a certain temperature, and controlling the temperature and setting a certain rotation speed so that the slurry reacts in the enhanced reactor;

[0011] (C) The mixed reaction solution undergoes a carbonization process for a certain period of time, and the reaction endpoint is detected using a pH meter;

[0012] (D) filtering and separating the carbonized reaction solution to obtain a solid product, washing it 3-4 times with deionized water, and drying it to obtain an ultrafine calcium carbonate powder product;

[0013] (E) The mother liquor obtained by filtration is reused to dissolve the calcium carbide slag (step A).

[0014] 2. The method for preparing the ultrafine calcium carbonate powder according to claim 1, wherein the heating temperature in step A is in the range of 50-100° C., the mass concentration of the ammonium salt solution is in the range of 25-35%, the ammonium salt solution is one of ammonium acetate, ammonium nitrate, and ammonium chloride, and the dissolution time is 1-2 h.

[0015] 3. The method for preparing the ultrafine calcium carbonate powder according to claim 1, wherein the reaction system in step B comprises the following three types: calcium salt-ammonia water-carbon dioxide, calcium salt-ammonia gas-carbon dioxide, and calcium salt-ammonium bicarbonate, the carbonizing agent is carbon dioxide or ammonium bicarbonate, the rotation speed of the stator-rotor reactor in step B is in the range of 300-3000 rpm, and the reaction temperature is in the range of 15-50°C.

[0016] 4. The method for preparing the ultrafine calcium carbonate powder according to claim 1, wherein the carbonization process in step C is performed under the following conditions: the carbonization reaction time is 15-60 min, the gas-liquid ratio is 0.2-5.5, and the reaction is stopped when the reaction end point pH is 7.5-8.5.

[0017] 5. The method for preparing the ultrafine calcium carbonate powder according to claim 1, wherein the drying condition in step D is 80-100° C. for 4-6 hours.

[0018] Beneficial effects of the present invention:

[0019] 1. The process of the present invention realizes the resource utilization of industrial waste residues, reduces carbon dioxide emissions, contributes to environmental protection and resource conservation, and achieves a win-win situation in economic and environmental benefits.

[0020] 2. The present invention realizes the recycling of ammonium salt in the production process, reduces production costs and avoids environmental pollution.

[0021] 3. The present invention adopts a stator-rotor carbonization reactor, which greatly enhances the gas-liquid mass transfer process and the micro-mixing process, improves the carbonization efficiency, shortens the time of crystal nucleus growth after crystallization, effectively controls the particle size and morphology of the nucleated particles, and the prepared nano calcium carbonate has a small particle size, good dispersibility, and high slurry solid-liquid separation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the preparation process of the ultrafine calcium carbonate powder provided by the present invention.

[0023] Figure 2 Schematic diagram of the process flow of the stator-rotor reactor reaction.

[0024] Figure 3 This is the SEM image of the nano-calcium carbonate prepared in Example 1.

[0025] The numbers in the accompanying drawings are as follows:

[0026] 1-Pump, 2-Pump, 3-Stator-Rotor Carbonization Reactor, 4-Storage Tank, 5-Pump, 6-pH Meter, 7-Exhaust, 8-Gas Flow Meter, 9-Carbon Dioxide, 10-Cooling Water, 11-Cooling Water DETAILED DESCRIPTION

[0027] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with the embodiments and drawings. Similar components in the drawings are represented by the same reference numerals. It should be understood by those skilled in the art that the content described below is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0028] Figure 2 The process flow diagram of the present invention using a stator-rotor reactor for reactive crystallization is shown below. The specific implementation scheme is as follows:

[0029] The impurity-removed leachate is poured into the circulation storage tank 4, the stator-rotor reactor 3 is turned on, and the rotation speed is adjusted to the preset value. The leachate in the circulation storage tank 4 passes through the circulation pump 5 and the liquid flow meter, and enters the inner ring of the rotor of the stator-rotor reactor 3 after the circulation ratio is controlled by the regulating valve. In the reactor, the leachate collides with the rotor and stator repeatedly and is continuously dispersed, crushed, and cut to form a large number of small droplets with rapidly renewed surfaces, thereby significantly enhancing the mass transfer and micro-mixing process, shortening the reaction time, and effectively controlling the particle size, dispersion and morphology of the nucleated particles. The reacted calcium carbonate slurry returns to the circulation storage tank 4 and is pumped into the stator-rotor reactor 3 again through the circulation pump 5 to achieve multiple cycle reactions to ensure that the calcium ions are fully reacted and precipitated.

[0030] After the reaction is complete, the calcium carbonate slurry is drained and transferred to a beaker for solid-liquid separation by filtration. The resulting mother liquor can be reused to dissolve carbide slag, significantly reducing costs. The filter cake is washed multiple times with deionized water and ethanol to obtain a highly dispersed calcium carbonate filter cake. Finally, it is dried to obtain highly dispersed, high-purity ultrafine calcium carbonate powder.

[0031] Example 1

[0032] Using carbide slag as the raw material, a leaching agent prepared with ammonium salt is added. The molar ratio of ammonia concentration to calcium in the carbide slag is controlled at 2:1. Leaching is carried out at 50°C for 1 hour, and the carbide slag leachate is filtered to obtain. The leachate is purified by adding quicklime and hydrogen peroxide, then its concentration is adjusted to 2.2 mol / L and placed in a stator-rotor reactor. A circulating pump is started at a speed of 1500 rpm and a circulation volume of 80 L / h. Carbon dioxide is introduced at a rate of 1200 ml / min. The pH of the reaction system is monitored in real time, and the reaction is terminated when the pH reaches 7.5-8.5.

[0033] After the reaction is completed, the slurry is filtered to obtain a calcium carbonate filter cake, which is then washed and dried to obtain a highly dispersed calcium carbonate powder. Finally, the obtained calcium carbonate powder is characterized by SEM. The results are shown in the attached manual. Figure 3 .

Claims

1. A method for preparing ultrafine calcium carbonate powder by using carbide slag ammonium salt circulation method, which is characterized by adopting the following process: (A) Under heating conditions, carbide slag is dissolved in an ammonium salt solution to prepare a crude calcium salt solution, which is then purified by impurity removal. Obtaining a refined calcium salt solution; (B) rapidly mixing the refined calcium salt solution and the carbonizing agent under different systems in a stator-rotor reactor at a certain temperature, and controlling the temperature and setting a certain rotation speed so that the slurry reacts in the enhanced reactor; (C) The mixed reaction solution is subjected to a carbonization process for a certain period of time, and a pH meter is used to detect the reaction endpoint; (D) filtering and separating the carbonized reaction solution to obtain a solid product, washing it 3-4 times with deionized water, and drying it to obtain an ultrafine calcium carbonate powder product; (E) The mother liquor obtained by filtration is reused to dissolve the calcium carbide slag (step A).

2. The method for preparing the ultrafine calcium carbonate powder according to claim 1, wherein: In step A, the heating temperature ranges from 50 to 100° C., the mass concentration range of the ammonium salt solution is from 25 to 35%, the ammonium salt solution is one of ammonium acetate, ammonium nitrate, ammonium chloride, etc., and the dissolution time is 1 to 2 hours.

3. The method for preparing the ultrafine calcium carbonate powder according to claim 1, wherein: The reaction system in step B includes the following three types: calcium salt-ammonia water-carbon dioxide, calcium salt-ammonia-carbon dioxide, and calcium salt-ammonium bicarbonate. The carbonizing agent is carbon dioxide or ammonium bicarbonate. The speed range of the stator-rotor reactor equipment in step B is 300-3000r / min, and the reaction temperature range is 15-50°C.

4. The method for preparing the ultrafine calcium carbonate powder according to claim 1, wherein: The conditions of the carbonization process in step C are as follows: the carbonization reaction time is 15-60 min, the gas-liquid ratio is 0.2-5.5, and the reaction is stopped when the reaction end point pH is 7.5-8.

5.

5. The method for preparing the ultrafine calcium carbonate powder according to claim 1, wherein: The drying condition in step D is drying at 80-100° C. for 4-6 hours.

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