Method for preparing high-dispersibility calcium carbonate based on direct mineralization of carbide slag

Abstract

The purpose of this invention is to provide a method for preparing highly dispersible calcium carbonate based on direct mineralization of calcium carbide slag, belonging to the field of highly dispersible calcium carbonate production technology. The method includes a first-stage activation process: calcium carbide slag, sodium tripolyphosphate, sodium oleate, and water are mixed to form a slurry, and CO2 is introduced to carbonize the slurry, achieving initial dispersion of calcium carbonate. A second-stage activation process involves adding stearate to the mineralized carbonized slurry for in-situ activation. Finally, the slurry is filtered and dried to obtain the highly dispersible calcium carbonate product. The advantages of this invention are that the synergistic effect between the two-stage activation processes inhibits the agglomeration of calcium carbonate particles, and the process and equipment are simple, highly practical, and easy to industrialize.

Description

Technical Field

[0001] This invention belongs to the field of highly dispersible calcium carbonate production technology, specifically relating to a method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag. Background Technology

[0002] The CO2-mineralized calcium carbide slag for calcium carbonate production is an environmentally friendly technology that reacts the industrial byproduct calcium carbide slag with CO2 to generate high-purity, high-whiteness calcium carbonate. Calcium carbonate, as an important industrial filler and functional powder material, is widely used in plastics, rubber, coatings, papermaking, and ink industries. Its market value and application performance largely depend on the product's physicochemical properties, such as purity, whiteness, particle size distribution, and dispersibility in the matrix. Good dispersibility is crucial to ensuring that calcium carbonate effectively reinforces, toughens, and improves gloss in composite materials.

[0003] The direct mineralization of calcium carbonate from carbide slag still faces significant challenges. Existing carbide slag mineralization processes primarily focus on improving conversion rates, lacking effective control over crystal growth and interparticle interactions. Furthermore, carbide slag has a complex composition, often containing impurities such as silicon, magnesium, iron, and aluminum, as well as incompletely reacted carbon particles. These impurities can act as heterogeneous nuclei during mineralization, interfering with the normal growth of calcium carbonate crystals, resulting in uneven particle size distribution, irregular morphology, and a high tendency for hard agglomeration. This inherent agglomeration tendency severely degrades the dispersion performance of the final product, limiting its application in high-end fields and confining it to low-value-added fillers, failing to fully realize its potential value.

[0004] Currently, the conventional method for improving the dispersibility of calcium carbonate is to mechanically pulverize the dried powder after carbonation and then perform dry surface organic coating. However, mechanical pulverization is energy-intensive and difficult to effectively break up native nanoscale agglomerates; dry modification is also prone to problems such as uneven coating and weak binding of modifiers, resulting in unsatisfactory effects and increased processes and costs. To overcome these limitations, research has developed a variety of surface modification pathways, mainly including organic coating, coupling agent treatment, polymer grafting, in-situ coprecipitation modification, and mechanochemical activation. However, each of these methods has its advantages and disadvantages: for example, stearic acid modification is low-cost but has poor thermal stability; coupling agents can form strong chemical bonds but are expensive; in-situ modification has good uniformity but requires strict process control; these single modifiers or methods generally face problems such as performance limitations, high costs, and narrow applicability. Summary of the Invention

[0005] This invention addresses the agglomeration problem in existing methods for the direct mineralization of calcium carbonate from carbide slag, and provides a method for preparing highly dispersible calcium carbonate based on the direct mineralization of carbide slag. This invention employs a two-stage activation process to improve the dispersibility of calcium carbonate prepared by direct CO2 mineralization of carbide slag.

[0006] The present invention adopts the following technical solution: A method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag includes the following steps: The first step is to dry the carbide slag in a dryer and store it in a material silo for later use. The second step is to introduce water into a reactor equipped with a stirrer and start stirring. Add surfactant A to the reactor and stir for 5 minutes. Then add surfactant B to the reactor and continue stirring for 5 minutes to form a homogeneous solution in the reactor. The third step is to add dried carbide slag to the reactor to form a carbide slag slurry with a solid content of 1%-10%, and continue stirring for 5 minutes. Step 4, primary activation: The carbide slag slurry is fed into the carbonization reactor, stirred and continuously fed with a mixture of CO2 and N2 gas until the pH of the slurry reaches 7, at which point the feeding of the mixed gas is stopped. Step 5, secondary activation: Add surfactant C to the carbide slag slurry after primary activation to activate the slurry, and continue stirring for 60-90 minutes; The sixth step is to filter the activated slurry to obtain a filter cake, and then dry and grind the filter cake to obtain highly dispersible calcium carbonate.

[0007] Furthermore, in the first step, the drying temperature is 80-150℃ and the drying time is 4-8 hours.

[0008] Furthermore, in the second step, the stirring speed is 600-1200 rpm.

[0009] Furthermore, in the second step, the surfactant A is sodium tripolyphosphate, and the amount added is 1.5-2.5% of the mass of carbide slag.

[0010] Furthermore, in the second step, the surfactant B is a 1% (w / w) sodium oleate aqueous solution, and the amount added is 1.5-2.5% of the mass of carbide slag.

[0011] Furthermore, in the fourth step, the volume percentage of CO2 in the mixed gas is 30-95%; CO2 gas is introduced at a flow rate of 1-5 L / min per kilogram of carbide slag.

[0012] Furthermore, in the fifth step, the surfactant C is stearate, and the amount added is 1-3% of the mass of carbide slag; the stirring speed is 600-1200 rpm.

[0013] Furthermore, the stearate includes sodium stearate or calcium stearate.

[0014] Furthermore, in the sixth step, the filtration method includes any one of vacuum filtration, centrifugal filtration, and pressure filtration; the drying method includes any one of heating drying, vacuum drying, and conveyor belt drying, with a drying temperature of 85-150℃ and a drying time of 3-6 hours.

[0015] The beneficial effects of this invention are as follows: 1. This invention employs a two-stage activation method to improve the dispersibility of calcium carbonate produced from the direct mineralization of carbide slag. The first-stage modification, through synergistic optimization of carbonation process parameters and the introduction of the highly efficient and inexpensive composite surfactant STP-OA, inhibits crystal growth and agglomeration at the source. The second-stage activation utilizes the chemical adsorption or surface reaction between stearate and wet calcium carbonate particles to form a uniform and robust monolayer hydrophobic coating. The two-stage activation works synergistically to achieve full-process inhibition of agglomeration of calcium carbonate particles from nucleation to the final product. Due to the uniform molecular-scale coating achieved in a liquid environment, the final product exhibits excellent dispersibility.

[0016] 2. The in-situ activation step of the slurry can be completed in a mineralization reactor or a stirred reactor, without the need for additional complex equipment. Although this method increases energy consumption and time slightly, it eliminates the need for subsequent dry modification processes and complex grinding treatments, resulting in lower overall costs and no dust pollution, making it suitable for large-scale industrial production.

[0017] 3. In this invention, the mineralization reaction is carried out in a mineralization reactor at a mild temperature. By optimizing key mineralization reaction process parameters, the mass transfer efficiency and reaction efficiency are significantly improved. The prepared modified calcium carbonate particles have uniform morphology, narrow particle size distribution, and good dispersibility, with a specific surface area of ​​25.5-29.2 m². 2 / g. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the preparation process of the present invention; Figure 2 SEM image of calcium carbonate prepared in Example 1; Figure 3 SEM image of calcium carbonate prepared in Comparative Example 1; Figure 4 SEM image of calcium carbonate prepared in Comparative Example 2. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 A method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag includes the following steps: a) Dry the carbide slag in a dryer and store it in a material silo for later use. The drying temperature is 105℃ and the time is 8 hours. b) Pass water into the reactor equipped with a stirrer and start stirring at a speed of 900 rpm. Add sodium tripolyphosphate at 2% of the mass of carbide slag to the reactor and stir for 5 minutes. Then add sodium oleate aqueous solution at 2% of the mass of carbide slag (1% mass concentration) to the reactor and continue stirring for 5 minutes to form a uniform solution in the reactor. c) Add dried carbide slag to the reactor to form a slurry with a solid content of 1%, and continue stirring for 5 minutes at a stirring speed of 900 rpm. d) Pass the carbide slag slurry into the carbonization reactor, stir and continuously pass a mixture of CO2 and N2 gas, with CO2 accounting for 95% of the volume in the mixture. The flow rate is calculated as 3 L / min of CO2 gas per kilogram of carbide slag, and the passage is stopped when the pH of the slurry reaches 7. e) Add sodium stearate at 2.0% of the mass of carbide slag to the mineralized slurry and continue stirring for 75 minutes. f) Filter the activated slurry to obtain a filter cake, and then dry and grind the filter cake to obtain a highly dispersible calcium carbonate product.

[0021] The filtration method described in step f) above is vacuum filtration; the drying method is vacuum drying, with a drying temperature of 85℃ and a drying time of 3 hours.

[0022] Figure 2 The image shows a SEM image of the calcium carbonate sample prepared in this embodiment. As can be seen from the image, the obtained calcium carbonate is in the form of short rods and has good dispersibility. The average particle size of the calcium carbonate sample was measured to be 0.9 µm, and the specific surface area was 29.2 m². 2 / g.

[0023] Example 2 A method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag includes the following steps: a) Dry the carbide slag in a dryer and store it in a material silo for later use. The drying temperature is 80℃ and the time is 4 hours. b) Pass water into the reactor equipped with a stirrer and start stirring at a speed of 600 rpm. Add sodium tripolyphosphate at 1.5% of the mass of carbide slag to the reactor and stir for 5 minutes. Then add sodium oleate aqueous solution at 1.5% of the mass of carbide slag (1% mass concentration) to the reactor and continue stirring for 5 minutes to form a uniform solution in the reactor. c) Add dried carbide slag to the reactor to form a slurry with a solid content of 1%, and continue stirring for 5 minutes at a stirring speed of 600 rpm. d) Pass the carbide slag slurry into the carbonization reactor, stir and continuously pass a mixture of CO2 and N2 gas. The volume ratio of CO2 in the mixture is 30%. The flow rate is calculated as 1 L / min of CO2 gas per kilogram of carbide slag. Stop passing the gas when the pH of the slurry is 7. e) Add 1.0% (by weight of carbide slag) of calcium stearate to the mineralized slurry and continue stirring for 60 minutes. f) Filter the activated slurry to obtain a filter cake, and then dry and grind the filter cake to obtain a highly dispersible calcium carbonate product.

[0024] The filtration method described in step f) above is centrifugal filtration; the drying method is heating drying, with a drying temperature of 150℃ and a drying time of 6 hours.

[0025] The obtained calcium carbonate is cubic in shape, has good dispersibility, an average particle size of 1.5 µm, and a specific surface area of ​​25.5 m². 2 / g.

[0026] Example 3 A method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag includes the following steps: a) Dry the carbide slag in an oven and store it in a desiccator for later use. The drying temperature is 150℃ and the time is 8 hours. b) Pass water into the reactor equipped with a stirrer and start stirring at a speed of 1200 rpm. Add sodium tripolyphosphate at a mass of 2.5% of the carbide slag to the reactor and stir for 5 minutes. Then add sodium oleate aqueous solution at a mass concentration of 1% at a mass of 2.5% of the carbide slag to the reactor and continue stirring for 5 minutes to form a homogeneous solution in the reactor. c) Add dried carbide slag to the reactor to form a slurry with a solid content of 10%, and continue stirring for 5 minutes at a stirring speed of 1200 rpm. d) Pass the carbide slag slurry into the carbonization reactor, stir and continuously pass a mixture of CO2 and N2 gas, with CO2 accounting for 95% of the volume in the mixture. The flow rate is calculated as 5 L / min of CO2 gas per kilogram of carbide slag, and the gas is stopped when the pH of the slurry reaches 7. e) Add sodium stearate at 3.0% of the mass of carbide slag to the mineralized slurry and continue stirring for 90 minutes. f) Filter the activated slurry to obtain a filter cake, and then dry and grind the filter cake to obtain a highly dispersible calcium carbonate product.

[0027] The filtration method described in step f) above is pressure filtration; the drying method is vacuum drying, with a drying temperature of 105℃ and a drying time of 4 hours.

[0028] The obtained calcium carbonate is cubic in shape, has good dispersibility, an average particle size of 1.3 µm, and a specific surface area of ​​26.8 m². 2 / g.

[0029] Example 4 A method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag includes the following steps: a) Dry the carbide slag in a dryer and store it in a material silo for later use. The drying temperature is 125℃ and the time is 5 hours. b) Pass water into the reactor equipped with a stirrer and start stirring at a speed of 1050 rpm. Add sodium tripolyphosphate at a mass of 2% of the carbide slag to the reactor and stir for 5 minutes. Then add sodium oleate aqueous solution at a mass of 2% of the carbide slag (1% mass concentration) to the reactor and continue stirring for 5 minutes to form a uniform solution in the reactor. c) Add dried carbide slag to the reactor to form a slurry with a solid content of 5%, and continue stirring for 5 minutes at a stirring speed of 1050 rpm. d) Pass the carbide slag slurry into the carbonization reactor, stir and continuously pass a mixture of CO2 and N2 gas, with CO2 accounting for 95% of the volume in the mixture. The flow rate is calculated as 3 L / min of CO2 gas per kilogram of carbide slag, and the passage is stopped when the pH of the slurry reaches 7. e) Add sodium stearate at 2.0% of the mass of carbide slag to the mineralized slurry and continue stirring for 80 minutes. f) Filter the activated slurry to obtain a filter cake, and then dry and grind the filter cake to obtain a highly dispersible calcium carbonate product.

[0030] The filtration method described in step f) above is vacuum filtration; the drying method is conveyor belt drying, the drying temperature is 125℃, and the drying time is 5h.

[0031] The obtained calcium carbonate is in the form of short rods, with good dispersibility, an average particle size of 1.1 µm, and a specific surface area of ​​27.8 m². 2 / g.

[0032] Example 5 A method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag includes the following steps: a) Dry the carbide slag in an oven and store it in a desiccator for later use. The drying temperature is 105℃ and the time is 6 hours. b) Pass water into the reactor equipped with a stirrer and start stirring at a speed of 750 rpm. Add sodium tripolyphosphate at 2% of the mass of carbide slag to the reactor and stir for 5 minutes. Then add sodium oleate aqueous solution at 2% of the mass of carbide slag (1% mass concentration) to the reactor and continue stirring for 5 minutes to form a uniform solution in the reactor. c) Add dried carbide slag to the reactor to form a slurry with a solid content of 3%, and continue stirring for 5 minutes at a stirring speed of 750 rpm. d) Pass the carbide slag slurry into the carbonization reactor, stir and continuously pass a mixture of CO2 and N2 gas, with CO2 accounting for 60% of the volume of the mixture. The flow rate is calculated as 5 L / min of CO2 gas per kilogram of carbide slag, and the gas is stopped when the pH of the slurry reaches 7. e) Add sodium stearate at 2.0% of the mass of carbide slag to the mineralized slurry and continue stirring for 60 minutes. f) Filter the activated slurry to obtain a filter cake, and then dry and grind the filter cake to obtain a highly dispersible calcium carbonate product.

[0033] The filtration method described in step f) above is pressure filtration; the drying method is vacuum drying, with a drying temperature of 105℃ and a drying time of 4 hours.

[0034] The obtained calcium carbonate is cubic in shape, has good dispersibility, an average particle size of 1 µm, and a specific surface area of ​​28.2 m². 2 / g.

[0035] Comparative Example 1 a) Dry the carbide slag in a dryer and store it in a material silo for later use. The drying temperature is 105℃ and the time is 8 hours. b) Pass water into the reactor equipped with a stirrer and start stirring at a speed of 900 rpm. Add sodium tripolyphosphate at a mass of 2% of the carbide slag to the reactor and stir for 5 minutes. Then add sodium oleate aqueous solution at a mass of 2% of the carbide slag (1% mass concentration) to the reactor and continue stirring for 5 minutes to form a uniform solution in the reactor. c) Add dried carbide slag to the reactor to form a slurry with a solid content of 1%, and continue stirring for 5 minutes at a stirring speed of 900 rpm. d) The carbide slag slurry is fed into the carbonization reactor, stirred and continuously fed with a mixture of CO2 and N2 gas. The volume percentage of CO2 in the mixture is 95%. The flow rate is calculated as 3 L / min of CO2 gas per kilogram of carbide slag. The feeding is stopped when the pH of the slurry reaches 7.

[0036] The SEM images of the obtained samples are as follows Figure 3 As shown, according to Figure 3 As can be seen, the calcium carbonate particles of the mineralized product are relatively uniform in size and are short rod-shaped. However, compared with the product after secondary activation, the agglomeration of calcium carbonate particles shown in the figure is more severe.

[0037] Comparative Example 2 A method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag includes the following steps: a) Dry the carbide slag in a dryer and store it in a material silo for later use. The drying temperature is 125℃ and the time is 5 hours. b) Pass water into the reactor equipped with a stirrer and start stirring at a speed of 1050 rpm. Add sodium tripolyphosphate at a mass of 2% of the carbide slag to the reactor and stir for 5 minutes. Then add sodium oleate aqueous solution at a mass of 2% of the carbide slag (1% mass concentration) to the reactor and continue stirring for 5 minutes to form a uniform solution in the reactor. c) Add dried carbide slag to the reactor to form a slurry with a solid content of 5%, and continue stirring for 5 minutes at a stirring speed of 1050 rpm. d) The carbide slag slurry is fed into the carbonization reactor, stirred and continuously fed with a mixture of CO2 and N2 gas. The volume percentage of CO2 in the mixture is 95%. The flow rate is calculated as 3 L / min of CO2 gas per kilogram of carbide slag. The feeding is stopped when the pH of the slurry reaches 7.

[0038] The SEM images of the obtained samples are as follows Figure 4 As shown, according to Figure 4 It can be seen that the calcium carbonate particles are rod-shaped, and while the dispersibility between particles is weakened, the particle size of calcium carbonate increases significantly.

[0039] Comparative Examples 1 and 2 both involved only one-stage activation. Compared to two-stage activation, single-stage activation is more significantly affected by process conditions. Figure 3 Figure 4 It can be seen that as the stirring speed increases, the agglomeration of calcium carbonate particles is significantly aggravated. After secondary activation, the dispersibility of calcium carbonate particles is further enhanced, and the influence of process conditions is also reduced.

[0040] The above description only illustrates the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag, characterized in that: Includes the following steps: The first step is to dry the carbide slag in a dryer and store it in a material silo for later use. The second step is to introduce water into a reactor equipped with a stirrer and start stirring. Add surfactant A to the reactor and stir for 5 minutes. Then add surfactant B to the reactor and continue stirring for 5 minutes to form a homogeneous solution in the reactor. The third step is to add dried carbide slag to the reactor to form a carbide slag slurry with a solid content of 1%-10%, and continue stirring for 5 minutes. Step 4, primary activation: The carbide slag slurry is fed into the carbonization reactor, stirred and continuously fed with a mixture of CO2 and N2 gas until the pH of the slurry reaches 7, at which point the feeding of the mixed gas is stopped. Step 5, secondary activation: Add surfactant C to the carbide slag slurry after primary activation to activate the slurry, and continue stirring for 60-90 minutes; The sixth step is to filter the activated slurry to obtain a filter cake, and then dry and grind the filter cake to obtain highly dispersible calcium carbonate.

2. The method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag according to claim 1, characterized in that: In the first step, the drying temperature is 80-150℃ and the drying time is 4-8 hours.

3. The method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag according to claim 1, characterized in that: In the second step, the stirring speed is 600-1200 rpm.

4. The method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag according to claim 1, characterized in that: In the second step, the surfactant A is sodium tripolyphosphate, and the amount added is 1.5-2.5% of the mass of carbide slag.

5. The method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag according to claim 1, characterized in that: In the second step, the surfactant B is a 1% sodium oleate aqueous solution, and the amount added is 1.5-2.5% of the mass of carbide slag.

6. The method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag according to claim 1, characterized in that: In the fourth step, the volume percentage of CO2 in the mixed gas is 30-95%; CO2 gas is introduced at a flow rate of 1-5 L / min per kilogram of carbide slag.

7. The method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag according to claim 1, characterized in that: In the fifth step, the surfactant C is stearate, and the amount added is 1-3% of the mass of carbide slag; the stirring speed is 600-1200 rpm.

8. The method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag according to claim 7, characterized in that: The stearate includes sodium stearate or calcium stearate.

9. The method for preparing highly dispersible calcium carbonate based on direct mineralization of carbide slag according to claim 1, characterized in that: In step six, the filtration method includes any one of vacuum filtration, centrifugal filtration, and pressure filtration; the drying method includes any one of heating drying, vacuum drying, and conveyor belt drying, with a drying temperature of 85-150℃ and a drying time of 3-6 hours.

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