Method for preparing vaterite calcium carbonate by submerged supergravity carbonization

Abstract

The application discloses a method for preparing vaterite calcium carbonate by submerged supergravity carbonization, which comprises the following steps: 1) taking ammonium salt with content of 95% or above, water, wet calcium carbide slag or ground and calcined dolomite for standby; 2) mixing the ammonium salt, water, wet calcium carbide slag or dolomite, heating and continuously stirring, and obtaining calcium-containing filtrate after filtration; 3) passing the calcium-containing filtrate obtained in the step 2) into a liquid submerged supergravity reactor, passing CO2 gas to perform carbonization reaction after the temperature of the material liquid in the supergravity reactor is stabilized, and collecting the calcium carbonate filter cake after filtration, washing and carbonization liquid; 4) mixing the filter cake, water and modifier, heating and beating to modify, and obtaining the vaterite calcium carbonate after filtration, washing and drying. The method does not need to use additional additives in the carbonization process, and the prepared vaterite calcium carbonate has a particle size of 2-5 um and can be stored stably for 30 days or above.

Description

Technical Field

[0001] This invention relates to the field of solid waste and calcium-containing ore resource utilization technology, specifically to a method and application of immersion-type supergravity carbonation for preparing aragonite calcium carbonate. Background Technology

[0002] Calcium carbonate, a highly sought-after industrial material, is widely used in plastics, rubber, coatings, inks, papermaking, sealants, pharmaceuticals, and fiber materials. Calcium carbonate exists in three crystal forms due to differences in its internal atomic arrangement: trigonal calcite, orthorhombic aragonite, and hexagonal aragonite. Calcite and aragonite are the most stable and least stable phases, respectively. Spherical aragonite is considered the most promising structure, but other structures include platy, disc-shaped, and hexagonal forms. All aragonite structures exhibit poor thermal stability; its metastable state determines its high solubility and surface free energy. Especially in humid environments, it readily transforms into the more stable calcite, resulting in its near-absence in nature and significant challenges in artificial preparation, thus hindering efficient and low-cost large-scale industrial production.

[0003] Calcium carbonate can be classified into heavy calcium carbonate and light calcium carbonate based on its preparation method. Heavy calcium carbonate is obtained by physically grinding and crushing natural limestone, resulting in a wide particle size distribution and coarse morphology. Light calcium carbonate, on the other hand, is obtained through a chemical precipitation reaction, resulting in a narrower particle size distribution and a more uniform morphology. Common methods for preparing light calcium carbonate include the solution method and the carbonation method. The solution method follows a liquid-liquid reaction route, saturating the calcium carbonate with calcium... 2+ and CO3 2- The two raw materials react directly to produce calcium carbonate precipitate; while the carbonation method follows a gas-liquid reaction route, in which CO2 reaction gas is continuously passed into a Ca-containing solution. 2+ Liquid calcium carbonate precipitates, and due to the advantages of simple process, low cost, high yield and high purity, the carbonation method has become one of the most widely used methods for producing light calcium in industry.

[0004] Calcium carbide slag is a widespread industrial solid waste. It is a waste residue mainly composed of calcium hydroxide, produced by the hydrolysis of calcium carbide (CaC2) and water to produce acetylene. Acetylene is an important raw material for the production of polyvinyl chloride (PVC) and vinyl acetate. PVC, due to its advantages such as good processing performance, excellent mechanical properties, good chemical stability, and environmental friendliness, has become one of the most widely produced synthetic plastic polymers in the world. Statistics show that every ton of PVC produced generates 1.7 tons of calcium carbide slag, demonstrating its huge industry scale and considerable output. Furthermore, other processes that produce acetylene using the calcium carbide method also generate large amounts of calcium carbide slag. Therefore, calcium carbide slag is an inevitable alkaline industrial waste residue produced in the production of the core product, acetylene.

[0005] Dolomite is a mineral resource in China with reserves exceeding 20 billion tons, concentrated in North China, South China, and Central China. It is a double salt of calcium carbonate and magnesium carbonate, with its main chemical component being CaMg(CO3)2. However, the utilization efficiency of dolomite is relatively low. It is generally used as a filler in the chemical or building materials industries, failing to realize its true economic value. This leads to serious loss of calcium and magnesium resources, and even causes environmental burden and waste of mineral resources. Therefore, current research urgently focuses on maximizing the high added value of dolomite.

[0006] Calcium carbide slag and dolomite are rich in active calcium resources, offering unique advantages in the preparation of high-value-added products such as calcium carbonate. They also bring significant economic benefits in terms of land resource utilization and ecological environmental protection. However, both materials have complex compositions and contain many impurities, which can adversely affect crystal growth and crystal form control during calcium carbonate synthesis, making them unsuitable for direct production of high-purity calcium carbonate. Therefore, leaching treatment of the solid raw materials is necessary to separate the calcium source from impurities as much as possible. Currently, accurately and scientifically understanding the composition and properties of raw materials and developing a complete set of solid raw material resource utilization technologies has become a research hotspot.

[0007] In recent years, the technology for preparing calcium carbonate has been continuously improving, resulting in a series of patented inventions. Chinese patent application CN121361822A discloses a method for synthesizing high-value amorphous calcium carbonate by carbon fixation of carbide slag. The patent describes leaching carbide slag with ammonium chloride, using anhydrous ethanol and magnesium chloride as additives, and then passing CO2 gas to fix calcium into mixed-crystalline and amorphous nano-calcium carbonate products.

[0008] Chinese patent publication number CN114408960A discloses a method for preparing cubic nano-calcium carbonate by supergravity-micro-interface mass transfer enhanced carbonation. The technology discloses a method for preparing cubic nano-calcium carbonate by supergravity carbonation using Ca(OH)2 as raw material and glucose as additive.

[0009] Chinese patent CN115583665B discloses a method for preparing high-quality calcium carbonate and magnesium building material raw materials by co-producing dolomite. The technology discloses that dolomite is calcined at 950℃ for 1 hour to obtain calcium and magnesium oxides, which are then reacted with ammonium sulfate solution at 40℃ for 1 hour and filtered to obtain active magnesium oxide. The filtrate is then carbonized to obtain calcium carbonate filler product with a D50 of 20-30 μm.

[0010] In summary, the existing technologies for producing calcium carbonate have the following drawbacks: Patent CN121361822A adds anhydrous ethanol and magnesium chloride as additives during the carbonation process, and it is impossible to obtain single-crystal calcium carbonate; Patent CN114408960A uses glucose as an additive when preparing nano-calcium carbonate by conventional hypergravity carbonation, and it cannot guarantee 100% CO2 utilization; Patent CN115583665B uses dolomite as raw material, and the calcium carbonate prepared by carbonation has a particle size D50 of 20-30 μm.

[0011] It is evident that it is difficult to achieve the effect of calcium carbonate crystals being of the single aragonite form with a particle size of 2-5 μm and CO2 utilization rate of 100% when using conventional stirring or ordinary high-gravity equipment and without additives. Summary of the Invention

[0012] The technical problem to be solved by this invention is to provide a method for preparing aragonite calcium carbonate by immersion-based supergravity carbonation. The aragonite calcium carbonate prepared by this method has stable properties, a narrow crystal size distribution, requires no additional additives during the carbonation process, and exhibits high conventional carbonation efficiency. In short, this invention successfully prepares aragonite-type calcium carbonate with uniform morphology, uniform size distribution, 100% CO2 utilization, and stable storage without any additives. The aragonite-type calcium carbonate particles obtained by this invention have a size of 2-5 μm and can be stably stored for ≥30 days.

[0013] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing calcium carbonate from spheroidal aragonite by immersion-based supergravity carbonization includes the following steps: 1) Raw material preparation: Weigh out ammonium salts with a content ≥95%, water, wet carbide slag, or ground and calcined dolomite for later use; 2) Extraction: Ammonium salt, water, wet carbide slag or dolomite are mixed, heated and stirred continuously, and filtered to obtain calcium-containing filtrate; 3) Carbonization: The calcium-containing filtrate obtained in step 2) is passed into a liquid-immersed supergravity reactor. After the temperature of the filtrate in the supergravity reactor stabilizes, CO2 gas is passed through to carry out a carbonization reaction. After the carbonization reaction is completed, the filtrate is filtered, washed, and the calcium carbonate filter cake is collected. At the same time, the carbonized liquid is collected. 4) Modification: The filter cake, water, and modifier are mixed, heated, and pulped for modification. Then, the mixture is filtered, washed, and dried to obtain calcium carbonate in the spheroidal aragonite crystal form.

[0014] Preferably, in step 1), the ammonium salt is selected from one or more of ammonium formate, ammonium acetate, and ammonium chloride.

[0015] Preferably, in step 1), the dry weight ratio of the ammonium salt, water, wet carbide slag (the actual material already takes the moisture content into account, so the theoretical calculation is based on dry basis) or ground and calcined dolomite is: ammonium salt / dry carbide slag = 1.2-2.0; water / dry carbide slag = 5.2-10.0.

[0016] Preferably, in step 2), the temperature for heating is 35-75°C.

[0017] Preferably, in step 2), the continuous stirring speed is 260-400 rpm.

[0018] Preferably, in step 2), the continuous stirring time is 40-90 minutes.

[0019] Preferably, in step 3), the flow rate of the calcium-containing filtrate is 1.0-3.5 L / min.

[0020] Preferably, in step 3), the flow rate of the CO2 gas is 1.0-5.0 L / min.

[0021] Preferably, in step 3), the temperature of the carbonization reaction is 20-35°C.

[0022] Preferably, in step 3), the rotor speed of the hypergravity reactor is 1000-2000 rpm.

[0023] Preferably, in step 3), when the pH of the feed solution is 7.5, the input of CO2 gas is turned off to terminate the carbonization reaction.

[0024] Preferably, in step 3), the washing liquid is tap water, and the washing is performed 2-6 times; Preferably, in step 3), the collected carbonized liquid is adjusted in concentration and then used for carbide slag leaching.

[0025] Preferably, in step 4), the solid content of the mixture of filter cake, water and modifier is 6.0-15.0%; the water is tap water.

[0026] Preferably, in step 4), the modifier is selected from one or more of aluminate coupling agents, titanate coupling agents, and boric acid coupling agents.

[0027] Preferably, in step 4), the amount of modifier added is 0.8-3.0% of the dry basis calcium carbonate mass.

[0028] Preferably, in step 4), the temperature for modification is 50-70°C.

[0029] Preferably, in step 4), the modification time is 20-65 minutes.

[0030] Preferably, in step 4), the stirring speed during the heating and pulping modification process is 350-550 rpm.

[0031] Preferably, in step 4), the washing liquid is tap water, and the washing is performed 3-6 times; the drying temperature is 100-110℃, and the drying time is 12-24 hours.

[0032] Any range described in this invention includes the endpoint, any value between the endpoints, and any subrange consisting of the endpoint or any value between the endpoints.

[0033] Unless otherwise specified, all raw materials used in this invention can be obtained commercially, and the equipment used in this invention can be conventional equipment in the relevant field or refer to existing technology in the relevant field.

[0034] Compared with the prior art, the present invention has the following beneficial effects: 1) The solid raw material of this invention can be selected from chemical waste carbide slag or natural ore dolomite. The leaching agent can be selected from industrial grade ammonium acetate or ammonium chloride, both of which can achieve a leaching rate of 80%. The requirements for raw materials are wide. The recycling of carbonized liquid can not only reduce production costs, but also achieve the expected leaching rate.

[0035] 2) The process of preparing calcium carbonate from aragonite by liquid immersion supergravity carbonation has not been reported in the prior art. The method of the present invention can achieve 100% CO2 utilization rate and realize efficient conversion.

[0036] 3) The prepared aragonite calcium carbonate has a particle size of 2-5 μm and a uniform and complete morphology. After modification, it can be stably stored for at least 30 days, which solves the problem that aragonite calcium carbonate cannot be stably stored. The crystallization phenomenon and conditions of aragonite under different environments were also investigated.

[0037] 4) The carbonization process does not require any additives, and the water used in the entire experiment is tap water, which lays the foundation for industrial production. Attached Figure Description

[0038] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. Figure 1 This is a process flow diagram for preparing aragonite calcium carbonate using immersion-gravity carbonation according to the present invention. Figure 2 SEM image of calcium carbonate prepared in Example 1; Figure 3 SEM image of calcium carbonate prepared in Example 2; Figure 4 SEM image of calcium carbonate prepared in Example 3; Figure 5 SEM image of calcium carbonate prepared in Example 4; Figure 6 SEM image of calcium carbonate prepared in Example 5; Figure 7 SEM image of the filter cake prepared in Example 6 after being stored directly in a PE sealed bag for 2 days and dried at 105°C for 24 hours; Figure 8 SEM image of the filter cake prepared in Example 6 after being stored directly in a PE sealed bag for 7 days and dried at 105°C for 24 hours; Figure 9 SEM image of the filter cake prepared in Example 6, which was dispersed in water with a solid content of 8-10% and left to stand for 2 days, and then dried at 105°C for 24 hours. Figure 10 SEM image of the filter cake prepared in Example 6, which was dispersed in water with a solid content of 8-10% and left to stand for 7 days, and then dried at 105°C for 24 hours. Figure 11 SEM image of the filter cake prepared in Example 6, which was dispersed in ethanol with a solid content of 8-10% and left to stand for 2 days, and then dried at 105°C for 24 hours. Figure 12 SEM image of the filter cake prepared in Example 6, which was dispersed in ethanol with a solid content of 8-10% and left to stand for 7 days, and then dried at 105°C for 24 hours. Figure 13 SEM image of calcium carbonate prepared in Comparative Example 1; Figure 14 SEM image of calcium carbonate prepared in Comparative Example 2. Detailed Implementation

[0039] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0040] As one aspect of the present invention, a method for preparing spheroidal calcium carbonate by submerged supergravity carbonization includes the following steps: 1) Raw material preparation: Weigh out ammonium salts with a content ≥95%, water, wet carbide slag, or ground and calcined dolomite for later use; 2) Leaching: Mix ammonium salt, water, wet carbide slag or dolomite, heat and stir continuously, and filter to obtain calcium-containing filtrate; 3) Carbonization: The calcium-containing filtrate obtained in step 2) is passed into a liquid-immersed centrifugal reactor. After the temperature of the filtrate in the centrifugal reactor stabilizes, CO2 gas is passed through to carry out the carbonization reaction. After the carbonization reaction is completed, the filtrate is filtered, washed, and the calcium carbonate filter cake is collected. At the same time, the carbonized liquid is collected. 4) Modification: Mix filter cake, water and modifier, heat and slurry to modify, then filter, wash and dry to obtain calcium carbonate in the spheroidal aragonite crystal form.

[0041] According to certain embodiments of the present invention, in step 1), the ammonium salt is selected from one or more of ammonium formate, ammonium acetate, and ammonium chloride.

[0042] According to certain embodiments of the present invention, in step 1), the dry weight ratio of the ammonium salt, water, wet carbide slag (the actual material already takes the moisture content into account, so the theoretical calculation is based on dry basis) or ground and calcined dolomite is: ammonium salt / dry carbide slag = 1.2-2.0; water / dry carbide slag = 5.2-10.0.

[0043] According to some embodiments of the present invention, in step 2), the temperature of the heating is 35-75°C.

[0044] According to certain embodiments of the present invention, in step 2), the continuous stirring speed is 260-400 rpm.

[0045] According to some embodiments of the present invention, in step 2), the continuous stirring time is 40-90 min.

[0046] According to certain embodiments of the present invention, in step 3), the flow rate of the calcium-containing filtrate is 1.0-3.5 L / min.

[0047] According to some embodiments of the present invention, in step 3), the flow rate of the CO2 gas is 1.0-5.0 L / min.

[0048] According to certain embodiments of the present invention, in step 3), the temperature of the carbonization reaction is 20-35°C.

[0049] According to certain embodiments of the present invention, in step 3), the rotor speed of the hypergravity reactor is 1000-2000 rpm.

[0050] In this invention, the liquid-immersed hypergravity reactor is a prior art, such as the immersed hypergravity reactor disclosed in Chinese patent application CN121288736A, or the hypergravity reactor disclosed in Chinese patent application CN113477188A.

[0051] According to certain embodiments of the present invention, in step 3), when the pH of the feed solution is 7.5, the input of CO2 gas is turned off to terminate the carbonization reaction.

[0052] According to some embodiments of the present invention, in step 3), the washing liquid is tap water, and the washing is performed 2-6 times; According to certain embodiments of the present invention, in step 3), the collected carbonized liquid is adjusted in concentration and then used for carbide slag leaching.

[0053] According to certain embodiments of the present invention, in step 4), the solid content of the mixture of filter cake, water and modifier is 6.0-15.0%; the water is tap water.

[0054] According to certain embodiments of the present invention, in step 4), the modifier is selected from one or more of aluminate coupling agents, titanate coupling agents, and boric acid coupling agents.

[0055] According to certain embodiments of the present invention, in step 4), the amount of modifier added is 0.8-3.0% of the dry basis calcium carbonate mass.

[0056] According to some embodiments of the present invention, in step 4), the temperature at which the modification is performed is 50-70°C.

[0057] According to some embodiments of the present invention, in step 4), the modification time is 20-65 minutes.

[0058] According to some embodiments of the present invention, in step 4), the stirring speed during the heating and pulping modification process is 350-550 rpm.

[0059] According to some embodiments of the present invention, in step 4), the washing liquid is tap water, and the washing is performed 3-6 times; the drying temperature is 100-110℃, and the drying time is 12-24h.

[0060] Example 1 A method for preparing calcium carbonate from spheroidal aragonite by immersion-based supergravity carbonization includes the following steps: 1) Raw material preparation: Weigh out 2 kg of wet carbide slag, 1.68 kg of ammonium chloride with a content of ≥95%, and 6.68 kg of water for later use; 2) Leaching: Mix the wet carbide slag, ammonium chloride and water weighed in step 1), heat the mixture to 35°C, and stir at 260 rpm for 40 minutes at this temperature. Then filter the mixture, collect the filter residue and calculate the leaching rate to be 80.7%. Seal and store the calcium-containing filtrate. 3) Carbonation: Weigh 2L of the calcium-containing filtrate from step 2), add 1L of water, mix well, and then circulate it into the centrifugal reactor at a flow rate of 1.0L / min. When the temperature of the filtrate stabilizes at 20℃, introduce CO2 gas at a flow rate of 1.0L / min and set the centrifugal rotation speed to 1000rpm. Stop the gas supply when the pH of the slurry drops to 7.5, and the carbonation reaction is complete. Filter and wash the slurry to obtain calcium carbonate filter cake. Recover the carbonation liquid for leaching of carbide slag in step 1).

[0061] 4) Modification: Weigh the filter cake from step 3), and beat the filter cake at 50°C for 20 minutes with a calcium carbonate solid content of 6.0% and a modifier content of 0.8% at a stirring speed of 350 prm. Filter, wash and dry the slurry to obtain modified aragonite-type calcium carbonate with a calcium carbonate yield of 80.1% and an aragonite particle size of 2.7-4.7 μm.

[0062] The calcium carbide slag used in this embodiment has a moisture content of approximately 30%, and all water used is tap water.

[0063] Figure 2 This is a SEM image of the calcium carbonate prepared in Example 1.

[0064] Example 2 A method for preparing calcium carbonate from spheroidal aragonite by immersion-based supergravity carbonization includes the following steps: 1) Raw material preparation: Weigh out 2 kg of wet carbide slag, 2.24 kg of ammonium chloride with a content of ≥95%, and 10.04 kg of water for later use; 2) Leaching: Mix the wet carbide slag, ammonium chloride and water weighed in step 1), heat the mixture to 55°C, and stir at 330 rpm for 60 min at this temperature. Then filter the mixture, collect the filter residue and calculate the leaching rate to be 82.7%. Seal and store the calcium-containing filtrate. 3) Carbonation: Weigh 2L of the calcium-containing filtrate from step 2), add 1L of water, mix well, and then circulate it into the centrifugal reactor at a flow rate of 2.3L / min. When the temperature of the filtrate stabilizes at 27℃, introduce CO2 gas at a flow rate of 2.5L / min and set the centrifugal rotation speed to 1500rpm. Stop the gas supply when the pH of the slurry drops to 7.5. The carbonation reaction is then complete. Filter and wash the slurry to obtain calcium carbonate filter cake. Recover the carbonation liquid for leaching of carbide slag in step 1). 4) Modification: Weigh the filter cake from step 3), and beat the filter cake at 60°C for 45 minutes with a calcium carbonate solid content of 10.5% and a modifier content of 1.8% at a stirring speed of 450 prm. Filter, wash and dry the slurry to obtain modified aragonite-type calcium carbonate with a calcium carbonate yield of 82.8% and aragonite particle size of 2.5-4.1 μm.

[0065] The calcium carbide slag used in this embodiment has a moisture content of approximately 30%, and all water used is tap water.

[0066] Figure 3 This is a SEM image of the calcium carbonate prepared in Example 2.

[0067] Example 3 A method for preparing calcium carbonate from spheroidal aragonite by immersion-based supergravity carbonization includes the following steps: 1) Raw material preparation: Weigh out 2 kg of wet carbide slag, 2.80 kg of ammonium chloride with a content of ≥95%, and 13.40 kg of water for later use; 2) Leaching: Mix the wet carbide slag, ammonium chloride and water weighed in step 1), heat the mixture to 75°C, and stir at 400 rpm for 90 min at this temperature. Then filter the mixture, collect the filter residue and calculate the leaching rate to be 81.9%. Seal and store the calcium-containing filtrate. 3) Carbonation: Weigh 2L of the calcium-containing filtrate from step 2), add 1L of water, mix well, and then circulate it into the centrifugal reactor at a flow rate of 3.5L / min. When the temperature of the filtrate stabilizes at 35℃, introduce CO2 gas at a flow rate of 5.0L / min and set the centrifugal rotation speed to 2000rpm. Stop the gas supply when the pH of the slurry drops to 7.5. The carbonation reaction is complete. Filter and wash the slurry to obtain calcium carbonate filter cake. Recover the carbonation liquid for leaching of carbide slag in step 1). 4) Modification: Weigh the filter cake from step 3), and beat the filter cake at 70°C for 65 minutes with a calcium carbonate solid content of 15.0% and a modifier content of 3.0%, stirring at a speed of 550 prm. Filter, wash and dry the slurry to obtain modified aragonite-type calcium carbonate with a calcium source utilization rate of 83.0% and an aragonite particle size of 3.0-4.8 μm.

[0068] The calcium carbide slag used in this embodiment has a moisture content of approximately 30%, and all water used is tap water.

[0069] Figure 4 This is a SEM image of the calcium carbonate prepared in Example 3.

[0070] Example 4 A method for preparing calcium carbonate from spheroidal aragonite by immersion-based supergravity carbonization includes the following steps: 1) Raw material preparation: Weigh out 2 kg of wet carbide slag, 2.24 kg of ammonium chloride with a content of ≥95%, and 10.04 kg of water for later use; 2) Leaching: Mix the wet carbide slag, ammonium chloride and water weighed in step 1), heat the mixture to 55°C, and stir at 330 rpm for 60 min at this temperature. Then filter the mixture, collect the filter residue and calculate the leaching rate to be 82.7%. Seal and store the calcium-containing filtrate. 3) Carbonation: Weigh 2L of the calcium-containing filtrate from step 2), add 1L of water, mix well, and then circulate it into the centrifugal reactor at a flow rate of 2.3L / min. When the temperature of the filtrate stabilizes at 27℃, introduce CO2 gas at a flow rate of 2.5L / min and set the centrifugal rotation speed to 2000rpm. Stop the gas supply when the pH of the slurry drops to 7.5, and the carbonation reaction is complete. Filter and wash the slurry to obtain calcium carbonate filter cake. Recover the carbonation liquid for leaching of carbide slag in step 1). 4) Modification: Weigh the filter cake from step 3), and beat the filter cake at 60°C for 45 minutes with a calcium carbonate solid content of 10.5% and a modifier content of 1.8% at a stirring speed of 450 prm. Filter, wash and dry the slurry to obtain modified aragonite-type calcium carbonate with a calcium carbonate yield of 82.4% and aragonite particle size of 2.5-4.6 μm.

[0071] The calcium carbide slag used in this embodiment has a moisture content of approximately 30%, and all water used is tap water.

[0072] Figure 5 This is a SEM image of the calcium carbonate prepared in Example 4.

[0073] Example 5 A method for preparing calcium carbonate from spheroidal aragonite by immersion-based supergravity carbonization includes the following steps: 1) Raw material preparation: Weigh out 2 kg of wet carbide slag, 2.24 kg of ammonium chloride with a content of ≥95%, and 10.04 kg of water for later use; 2) Leaching: Mix the wet carbide slag, ammonium chloride and water weighed in step 1), heat the mixture to 55°C, and stir at 330 rpm for 60 min at this temperature. Then filter the mixture, collect the filter residue and calculate the leaching rate to be 82.7%. Seal and store the calcium-containing filtrate. 3) Carbonation: Weigh 2L of the calcium-containing filtrate from step 2), add 1L of water, mix well, and then circulate it into the centrifugal reactor at a flow rate of 3.5L / min. When the temperature of the filtrate stabilizes at 27℃, introduce CO2 gas at a flow rate of 5.0L / min and set the centrifugal rotation speed to 1500rpm. Stop the gas supply when the pH of the slurry drops to 7.5. The carbonation reaction is then complete. Filter and wash the slurry to obtain calcium carbonate filter cake. Recover the carbonation liquid for leaching of carbide slag in step 1). 4) Modification: Weigh the filter cake from step 3), and beat the filter cake at 60°C for 45 minutes with a calcium carbonate solid content of 10.5% and a modifier content of 1.8% at a stirring speed of 450 prm. Filter, wash and dry the slurry to obtain modified aragonite-type calcium carbonate with a calcium carbonate yield of 81.5% and aragonite particle size of 2.6-4.5 μm.

[0074] The calcium carbide slag used in this embodiment has a moisture content of approximately 30%, and all water used is tap water.

[0075] Figure 6 This is a SEM image of the calcium carbonate prepared in Example 5.

[0076] Example 6 Repeat Example 2), except that the stability of the aragonite was examined using the filter cake obtained in step 3). The specific steps are as follows: A. Store the filter cake in a PE sealed bag for 2 days and 7 days, then dry at 105℃ for 24 hours and measure SEM. B. Disperse the filter cake in water with a solid content of 8-10%, let it stand for 2 days and 7 days, filter it, dry it at 105℃ for 24 hours and measure SEM. C. Disperse the filter cake in ethanol with a solid content of 8-10%, let it stand for 2 days and 7 days, filter it, dry it at 105℃ for 24 hours and measure SEM. Figure 7 SEM image of the filter cake prepared in Example 6 after being stored directly in a PE sealed bag for 2 days and dried at 105°C for 24 hours. Figure 8 SEM image of the filter cake prepared in Example 6 after being stored directly in a PE sealed bag for 7 days and dried at 105°C for 24 hours; Figure 9 SEM image of the filter cake prepared in Example 6, which was dispersed in water with a solid content of 8-10% and left to stand for 2 days, and then dried at 105°C for 24 hours. Figure 10 SEM image of the filter cake prepared in Example 6, which was dispersed in water with a solid content of 8-10% and left to stand for 7 days, and then dried at 105°C for 24 hours. Figure 11 SEM image of the filter cake prepared in Example 6, which was dispersed in ethanol with a solid content of 8-10% and left to stand for 2 days, and then dried at 105°C for 24 hours. Figure 12 The filter cake prepared in Example 6 is dispersed in ethanol with a solid content of 8-10% and left to stand for 7 days. It is then dried at 105°C for 24 hours, and the resulting image is an SEM image.

[0077] Comparative Example 1 Example 2 was repeated, except that in step 1), 1.0 kg of ammonium chloride was weighed, the filter residue was collected, and the leaching rate was calculated to be 69.4%, the calcium carbonate yield was 71.3%, and the aragonite particle size was 5.5-9.4 μm.

[0078] The data for Comparative Example 1 are shown in Table 1.

[0079] Figure 13 This is a SEM image of the calcium carbonate prepared in Comparative Example 1.

[0080] Comparative Example 2

[0081] Example 2 was repeated, except that in step 3), after the mixture was homogeneous, it was circulated into the hypergravity reactor at a flow rate of 1.0 L / min and the gas flow rate was 5.0 L / min. The calcium carbonate yield was calculated to be 78.6% and the aragonite particle size was 5.3-13.6 μm.

[0082] Figure 14This is a SEM image of the calcium carbonate prepared in Comparative Example 2.

[0083] Table 1 below shows the comparative data of the preparation of spheroidal calcium carbonate by immersion-gravity carbonization in various embodiments and comparative examples: Table 1

[0084] Therefore, in Comparative Example 1, the decrease in the ammonium slag ratio led to adverse consequences such as a decrease in the calcium carbide slag leaching rate, a decrease in calcium carbonate yield, an increase in calcium carbonate particle size to 9.4 μm, and a decrease in aragonite stability to 78.3%. In Comparative Example 2, the rapid increase in the carbonation gas-liquid ratio led to adverse consequences such as a decrease in calcium carbonate yield, an increase in aragonite particle size to 13.6 μm, and a decrease in aragonite stability to 43.1%.

[0085] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is impossible to exhaustively list all embodiments here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing spheroidal calcium carbonate by immersion-gravity carbonization, characterized in that, Includes the following steps: 1) Raw material preparation: Weigh out ammonium salts with a content ≥95%, water, wet carbide slag, or ground and calcined dolomite for later use; 2) Extraction: Ammonium salt, water, wet carbide slag or dolomite are mixed, heated and stirred continuously, and filtered to obtain calcium-containing filtrate; 3) Carbonization: The calcium-containing filtrate obtained in step 2) is passed into a liquid-immersed supergravity reactor. After the temperature of the filtrate in the supergravity reactor stabilizes, CO2 gas is passed through to carry out a carbonization reaction. After the carbonization reaction is completed, the filtrate is filtered, washed, and the calcium carbonate filter cake is collected. At the same time, the carbonized liquid is collected. 4) Modification: The filter cake, water, and modifier are mixed, heated, and pulped for modification. Then, the mixture is filtered, washed, and dried to obtain calcium carbonate in the spheroidal aragonite crystal form.

2. The method for preparing calcium carbonate aragonite according to claim 1, characterized in that: In step 1), the ammonium salt is selected from one or more of ammonium formate, ammonium acetate, and ammonium chloride.

3. The method for preparing calcium carbonate aragonite according to claim 1, characterized in that: In step 1), the dry weight ratio of the ammonium salt, water, wet carbide slag, or ground and calcined dolomite is: ammonium salt / dry carbide slag = 1.2-2.0; water / dry carbide slag = 5.2-10.

0.

4. The method for preparing aragonite calcium carbonate according to claim 1, characterized in that: In step 2), the temperature for heating is 35-75℃; Preferably, in step 2), the continuous stirring speed is 260-400 rpm; Preferably, in step 2), the continuous stirring time is 40-90 minutes.

5. The method for preparing calcium carbonate aragonite according to claim 1, characterized in that: In step 3), the flow rate of the calcium-containing filtrate is 1.0-3.5 L / min; Preferably, in step 3), the flow rate of the CO2 gas is 1.0-5.0 L / min; Preferably, in step 3), the temperature of the carbonization reaction is 20-35°C; Preferably, in step 3), the rotor speed of the hypergravity reactor is 1000-2000 rpm; Preferably, in step 3), when the pH of the feed solution is 7.5, the input of CO2 gas is turned off to terminate the carbonization reaction.

6. The method for preparing calcium carbonate aragonite according to claim 1, characterized in that: In step 3), the washing solution is tap water, and the washing is performed 2-6 times; Preferably, in step 3), the collected carbonized liquid is adjusted in concentration and then used for carbide slag leaching.

7. The method for preparing calcium carbonate aragonite according to claim 1, characterized in that: In step 4), the solid content of the mixture of filter cake, water and modifier is 6.0-15.0%; the water is tap water.

8. The method for preparing calcium carbonate aragonite according to claim 1, characterized in that: In step 4), the modifier is selected from one or more of aluminate coupling agents, titanate coupling agents, and boric acid coupling agents.

9. The method for preparing calcium carbonate aragonite according to claim 1, characterized in that: In step 4), the amount of modifier added is 0.8-3.0% of the dry basis calcium carbonate mass.

10. The method for preparing aragonite calcium carbonate according to claim 1, characterized in that: In step 4), the temperature for modification is 50-70℃; Preferably, in step 4), the modification time is 20-65 minutes; Preferably, in step 4), the stirring speed during the heating and pulping modification process is 350-550 rpm; Preferably, in step 4), the washing liquid is tap water, and the washing is performed 3-6 times; the drying temperature is 100-110℃, and the drying time is 12-24 hours.

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