A process and system for preparing nano calcium carbonate based on carbide slag

Abstract

The application relates to the technical field of solid waste resource utilization and carbon emission reduction, and provides a nano calcium carbonate preparation process and system based on carbide slag, which comprises the following steps: firstly, pretreating the carbide slag; secondly, gradient screening the ball-milled carbide slag and removing impurities; thirdly, treating the screened material by using an ultrasonic-assisted acid leaching process to dissolve metal oxides in the material; fourthly, performing dynamic aging treatment to make residual metal ions precipitate; and finally, obtaining a high-purity calcium-containing solution. The treated calcium-containing solution is introduced into a three-stage series carbonization reaction system to perform reaction under different temperature, stirring speed, gas flow and additive conditions; the first-stage reactor is responsible for crystal nucleus generation, the second-stage reactor controls directional growth of the crystal nucleus, and the third-stage reactor completes a crystal ripening reaction. Finally, high-quality nano calcium carbonate products are prepared through post-processing steps such as centrifugal separation, ethanol washing and drying.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization and carbon emission reduction, and more particularly to a nano calcium carbonate preparation process and system based on carbide slag. BACKGROUND

[0002] Carbide slag is a major industrial by-product in the production process of acetylene gas, and its chemical composition is mainly calcium hydroxide. In addition to the main component calcium hydroxide, carbide slag also contains calcium carbonate, various silicon oxides, incompletely reacted carbon materials, and various metal oxide impurities such as iron oxide, aluminum oxide, and magnesium oxide.

[0003] If such industrial solid waste is not properly disposed of, it can easily cause a series of serious environmental problems: its storage not only occupies a large amount of land resources, but also the silicate components contained therein can easily penetrate into the soil, thereby changing the soil structure; harmful elements such as heavy metals can also migrate with rainwater and pollute groundwater; in addition, the dust phenomenon of carbide slag storage site can also increase the concentration of suspended particulate matter in the local atmosphere, thereby posing a potential threat to the local ecological environment and public health.

[0004] Although various resource utilization approaches for carbide slag have been reported, these methods generally face challenges such as low reaction efficiency and poor product quality stability. Therefore, developing a new process path that can achieve efficient conversion and ensure product quality stability is of great practical significance and application prospect for promoting the high-value utilization of carbide slag. SUMMARY

[0005] In order to overcome the above-mentioned defects of the prior art, the present application provides a nano calcium carbonate preparation process and system based on carbide slag. A three-step method of "gradient screening-ultrasonic acid leaching-dynamic aging" is used for pretreatment, and a three-stage series carbonization reactor is designed to control the conditions of different reaction stages, thereby preparing a nano calcium carbonate with better crystal form and particle size.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] A nano calcium carbonate preparation process based on carbide slag, comprising the following steps:

[0008] Step one, pretreating the carbide slag to obtain a calcium-containing solution. The pretreatment step aims to remove impurities from the carbide slag and improve the purity of the raw material for the subsequent carbonation reaction, laying the foundation for the preparation of high-quality nano calcium carbonate. The pretreatment step specifically includes gradient screening step, ultrasonic acid leaching step and dynamic aging step in sequence.

[0009] As a further scheme of the present application, the gradient screening step comprises: ball milling the carbide slag for 1-12 hours at a rotation speed of 200-1000 rpm; and screening the ball-milled carbide slag through a 100-150 mesh screen to remove large-particle impurities. The ball milling can effectively reduce the particle size of the carbide slag and increase its specific surface area, which is conducive to the subsequent acid leaching reaction. Screening through a screen of a specific mesh number can effectively remove large-particle impurities such as incompletely reacted carbon residues and large-particle silicon oxides in the carbide slag, and preliminarily purify the calcium hydroxide.

[0010] As a further scheme of the present application, the ultrasonic acid leaching step comprises: placing the carbide slag treated by the gradient screening step in a reaction container, adding an acid solution prepared by one or two reagents selected from dilute hydrochloric acid, ammonium chloride, ammonium citrate and ammonium sulfate, and performing acid leaching treatment under ultrasonic conditions at a frequency of 40 kHz to dissolve the iron oxide and aluminum oxide in the carbide slag while avoiding excessive reaction of the calcium hydroxide. The cavitation effect of the ultrasonic wave can intensify the mass transfer process and accelerate the reaction rate of the acid solution and the metal oxides in the carbide slag, thereby efficiently dissolving the main impurity oxides such as Fe and Al that affect the whiteness of the product. Selecting appropriate acid solution and its concentration and controlling the reaction conditions can achieve selective dissolution of impurities while minimizing the loss of the main component calcium hydroxide.

[0011] As a further scheme of the present application, the dynamic aging step comprises: bubbling carbon dioxide gas into the slurry treated by the ultrasonic acid leaching step until the pH value of the slurry is 9-10, so that the residual Mg 2+ ions and Fe 3+ ions in the slurry preferentially precipitate. By precisely controlling the pH value, the difference in the formation of carbonate or hydroxide precipitates of Mg 2+ , Fe 3+ ions and Ca 2+ ions under different pH conditions is utilized to achieve selective precipitation removal of these residual metal ions, further improving the purity of the calcium solution.

[0012] After the above pretreatment steps, a filtration step is further included to separate the solid and liquid, and the filtrate is the desired calcium-containing solution for the subsequent carbonization reaction.

[0013] Step two: performing a three-stage serial carbonization reaction on the calcium-containing solution to generate nano calcium carbonate. The three-stage serial carbonization reaction realizes precise regulation of the crystal form and particle size of the nano calcium carbonate by controlling the reaction conditions in stages. The three-stage serial carbonization reaction step specifically comprises: performing a crystal nucleus generation reaction in a first reactor, then introducing the reaction liquid of the first reactor into a second reactor for crystal nucleus directional growth reaction, and then introducing the reaction liquid of the second reactor into a third reactor for crystal ripening.

[0014] As a further scheme of the present application, before the three-stage series carbonation reaction step is carried out, the calcium-containing solution obtained by pretreatment is adjusted with deionized water, so that the Ca 2+ ion concentration reaches 0.5 mol·L -1 -3 mol·L -1 , and the calcium-containing solution is injected into the inlet of the three-stage series carbonation reactor. Adjusting the calcium ion concentration is an important means of controlling the subsequent calcium carbonate generation rate and supersaturation, and a suitable calcium ion concentration is conducive to the formation and growth control of the subsequent crystal nucleus.

[0015] As a further scheme of the present application, the conditions for the crystal nucleus generation reaction in the first reactor are: the reaction temperature is controlled at 5-10℃, the gas flow is controlled at 10-100 mL / min, the stirring speed is controlled at 100-200 rpm, the reaction time is 5-20 minutes, and 0.5% EDTA disodium salt by mass percentage is added to the reaction system to generate CaCO3 crystal nucleus. Low temperature conditions are conducive to increasing the solubility of CO2 in the solution and reducing the critical nucleation radius of the crystal nucleus, thereby forming a large number of fine crystal nuclei. EDTA disodium salt, as a complexing agent, can form a complex with Ca 2+ ions, regulate the concentration of free Ca 2+ ions in the solution, and thereby control the generation rate and number of crystal nuclei, laying the foundation for the subsequent preparation of nano calcium carbonate with specific morphology and size.

[0016] As a further scheme of the present application, the reaction liquid after the reaction of the first reactor is introduced into the second reactor for crystal nucleus directional growth reaction, and the conditions for the crystal nucleus directional growth reaction in the second reactor are: the reaction temperature is controlled at 20-30℃, the carbon dioxide gas flow is controlled at 100-300 mL / min, the stirring speed is controlled at 300-500 rpm, and the reaction time is 0.5-1 hour; and an additive is added to the reaction system, the additive being one or a combination of polyacrylic acid sodium, sodium tripolyphosphate, polyethylene glycol, pentaerythritol, sodium laurate, sodium oleate, and sodium dodecyl sulfonate, and the additive being added in an amount of 1%-5% of the theoretical mass of calcium carbonate generated. In the second reactor, the temperature and CO2 flow are appropriately increased, and an additive is introduced, aiming to promote the preferential growth of the crystal nucleus generated in the first reactor according to a specific crystal form, and control the growth rate, thereby regulating the particle size and morphology of the final product. These additive molecules can selectively adsorb on different crystal faces of the calcium carbonate crystal, inhibiting or promoting the growth of certain crystal faces, thereby achieving the purpose of controlling the crystal form and particle size.

[0017] As a further scheme of the present application, the reaction solution after the reaction in the secondary reactor is introduced into the tertiary reactor for crystal ripening reaction, and the conditions for the crystal ripening reaction in the tertiary reactor are as follows: the reaction temperature is controlled at 50-80℃, the carbon dioxide gas flow is controlled at 200-500 mL / min, the stirring speed is controlled at 500-800 rpm, and the reaction time is 0.5-1 hour; after the reaction, the carbon dioxide is stopped, stearic acid is added to the reaction system, the addition amount of which is 1-3% of the mass of the theoretically generated calcium carbonate, and an ethanol with the same volume as the reaction solution is added, and the stirring is performed for 3-10 hours, and then the heating and stirring are stopped, and the natural cooling to room temperature is performed. The high-temperature rapid carbonation is beneficial to the further growth and perfection of the crystal, i.e. the crystal ripening process, which can reduce the crystal defects and improve the stability of the product. Then, the stearic acid is added to coat the surface of the nano calcium carbonate particles, which can improve the dispersibility of the nano calcium carbonate in the organic phase, reduce the surface energy, prevent the particle agglomeration, and endow the nano calcium carbonate with specific application performance. The addition of ethanol is usually to help the better dissolution and dispersion of the stearic acid.

[0018] Step three, the solution after the reaction in the tertiary reactor is subjected to post-treatment to obtain a nano calcium carbonate sample. This step is to separate, purify and dry the final nano calcium carbonate product from the reaction solution.

[0019] As a further scheme of the present application, the post-treatment in step three includes: the solution after the reaction in the tertiary reactor is placed in a centrifuge tube and subjected to high-speed centrifugal separation on a centrifuge to obtain a solid after centrifugation; the solid after centrifugation is subjected to multiple centrifugal washing with ethanol; and the washed solid is dried at 105℃ for 6-24 hours to obtain the nano calcium carbonate product. The high-speed centrifugal separation can effectively separate the generated nano calcium carbonate solid from the reaction mother liquor. The purpose of the ethanol washing is to remove the soluble impurities and unreacted additives remaining on the surface of the solid, and to further improve the product purity. The final drying step is to remove the water and residual ethanol in the solid to obtain a dry nano calcium carbonate powder sample.

[0020] A nano calcium carbonate preparation system based on carbide slag, comprising:

[0021] A carbide slag pretreatment module adapted to sequentially perform gradient screening treatment, ultrasonic acid leaching treatment and dynamic aging treatment on the carbide slag to obtain a calcium-containing solution after filtration;

[0022] A tertiary series carbonation reactor for receiving the calcium-containing solution and performing a tertiary series carbonation reaction to generate nano calcium carbonate, the tertiary series carbonation reactor comprising:

[0023] A primary reactor, whose working conditions are: temperature 5-10 DEG C, gas flow 10-100 mL / min, stirring speed 100-200 rpm, and adding EDTA disodium, so that the calcium-containing solution reacts to generate calcium carbonate crystal nucleus;

[0024] A secondary reactor, which is connected in series with the primary reactor, whose working conditions are: temperature 20-30 DEG C, carbon dioxide gas flow 100-300 mL / min, stirring speed 300-500 rpm, and adding selected crystal form control agent, for promoting the directional growth of the calcium carbonate crystal nucleus;

[0025] A tertiary reactor, which is connected in series with the secondary reactor, whose working conditions are: temperature 50-80 DEG C, carbon dioxide gas flow 200-500 mL / min, stirring speed 500-800 rpm, for completing crystal ripening, after the reaction is completed, stopping the carbon dioxide from being fed, adding stearic acid to the reaction system, the adding amount is 1-3% of the mass of the generated calcium carbonate, and adding ethanol with the same volume as the reaction liquid, after stirring for 3-10 hours, the heating and stirring are turned off, and the system is naturally cooled to room temperature;

[0026] A product post-processing module, which is used for performing post-processing on the reaction liquid containing nano calcium carbonate from the tertiary series carbonation reactor, so as to obtain nano calcium carbonate product.

[0027] Compared with the prior art, the nano calcium carbonate preparation process and system based on carbide slag has the beneficial effects that:

[0028] The present application realizes the targeted removal of impurities by adopting the three-step method of "gradient screening-ultrasonic acid leaching-dynamic aging" for pretreatment of carbide slag, and combines the designed three-stage series carbonation reactor to segmentally and precisely control the carbonation process. Compared with the problems of low reaction efficiency and difficult high-value utilization in the resource utilization of carbide slag in the prior art, the present application can convert industrial waste into high-value materials, not only significantly improves the utilization value of carbide slag, but also effectively reduces the exploitation of natural limestone resources and reduces the carbon dioxide emissions in the production process, has significant environmental protection benefits and resource comprehensive utilization advantages.

[0029] The application forms a complete process-design-formula integrated innovation from raw material treatment to final product preparation through fine design of calcium carbide slag pretreatment process, innovative structure of multi-stage carbonization reactor and synergistic optimization of reaction conditions at each stage of carbonization. In view of the industry pain points that calcium carbide slag is difficult to be high-value utilized and the production cost of nano calcium carbonate is high, the core technical scheme of "impurity targeted removal-reaction process segmented regulation" proposed by the application not only builds a solid technical barrier, but also effectively improves the stability and controllability of product quality, reduces the production cost, and shows outstanding technical advancement and broad commercial application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A flowchart of a nano calcium carbonate preparation process based on calcium carbide slag according to the application.

[0031] Figure 2 A structure diagram of a system for preparing nano calcium carbonate based on calcium carbide slag according to the application. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments will be described in detail below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0033] Embodiment 1

[0034] A nano calcium carbonate preparation process based on calcium carbide slag includes the following steps:

[0035] Step one, take 200g of calcium carbide slag for ball milling, the ball milling time is 6 hours, and the ball milling rotation speed is 1000rpm. After ball milling, screen the calcium carbide slag to remove large particle impurities through a 150 mesh screen to obtain pretreated calcium carbide slag for standby use.

[0036] Step two, take 20g of screened calcium carbide slag and put it in a reaction container, add 300mL of 5% concentrated hydrochloric acid, and treat it under ultrasonic conditions at a frequency of 40kHz for 2 hours. Then, pass CO2 into the slurry until the pH value of the slurry is 9-10, so that the residual Mg 2+ ions and Fe 3+ ions are precipitated. Filter and collect the filtrate for standby use.

[0037] Step three, take 200mL of prepared CaCl2 solution, and adjust the concentration of Ca 2+ ions in the system to 1mol·L -1The calcium chloride solution was injected into the inlet of a three-stage series carbonization reactor. In the first reactor, 0.5% disodium EDTA was added. The reaction temperature was controlled at 10°C, the gas flow rate was 50 mL / min, the stirring speed was 200 rpm, and the reaction time was 20 minutes to form CaCO3 crystal nuclei. The liquid after the reaction was recorded as a.

[0038] Step 4: Introduce reaction solution a into a secondary reactor. In the secondary reactor, control the reaction temperature to 30°C, the carbon dioxide gas flow rate to 200 mL / min, the stirring speed to 300 rpm, and the reaction time to 1 hour. Add an additive, which is a combination of sodium polyacrylate and sodium tripolyphosphate. The amount of sodium polyacrylate added is 0.5% of the theoretical mass of calcium carbonate generated, and the amount of sodium tripolyphosphate added is 1% of the theoretical mass of calcium carbonate generated. The liquid after the reaction is recorded as b.

[0039] Step 5, reactant liquor b is introduced into a three-stage reactor. In the three-stage reactor, it is controlled to be 50 DEG C, the carbon dioxide gas flow rate is 500mL / min, the stirring speed is 800rpm, and the reaction time is 1 hour. After the reaction is completed, carbon dioxide is stopped from being passed through, stearic acid is added to the reaction system in an amount of 1.5% of the theoretically generated calcium carbonate mass, and ethanol equal to the volume of reactant liquor b is added and stirred for 5 hours. Heating and stirring are then turned off, and the reactant liquor is allowed to cool naturally to room temperature. The reacted liquid is recorded as c.

[0040] Step 6: Reaction solution c is placed in a centrifuge tube and centrifuged at high speed to obtain a solid. Ethanol is then added to the solid for centrifugal washing. The washed solid is dried in an oven at 105°C for 12 hours to obtain a nano-calcium carbonate sample.

[0041] Example 2

[0042] A process for preparing nano calcium carbonate based on carbide slag comprises the following steps:

[0043] Step 1: 200g of carbide slag was ball-milled for 6 hours at a speed of 1000rpm. After ball-milling, the product was sieved to remove large particles of impurities through a 150-mesh sieve to prepare the pretreated carbide slag.

[0044] Step 2: Take 20g of sieved calcium carbide slag and put it in a reaction container. Add 0.5% EDTA disodium by mass, then add 300mL of 3.2mol / L ammonium chloride solution, and treat it under ultrasonic conditions of 40kHz for 2 hours. Then, introduce CO2 into the slurry until the pH value of the slurry is 9-10, so that the residual Mg 2+ ions and Fe3+ Ion precipitation. Filtration was performed, and the filtrate was collected for later use.

[0045] Step three, 200 mL of the prepared CaCl2 solution was removed, and the Ca2+ ion concentration in the system was adjusted to 0.5 mol·L-1 by using deionized water. 2+ The Ca2+ ion concentration in the system was adjusted to 0.5 mol·L-1 by using deionized water. -1 The calcium chloride solution was injected into the inlet of the three-stage series carbonation reactor. In the first reactor, the reaction temperature was controlled at 10℃, the gas flow rate was 50 mL / min, the stirring speed was 200 rpm, and the reaction time was 20 minutes to generate CaCO3 crystal nuclei. The liquid after the reaction was recorded as a.

[0046] Step four, the reaction liquid a was introduced into the second reactor. In the second reactor, the reaction temperature was controlled at 30℃, the carbon dioxide gas flow rate was 200 mL / min, the stirring speed was 300 rpm, and the reaction time was 1 hour. An additive was added, which was a combination of sodium tripolyphosphate and polyethylene glycol, wherein the addition amount of sodium tripolyphosphate was 1% of the theoretical mass of generated calcium carbonate, and the addition amount of polyethylene glycol was 1% of the theoretical mass of generated calcium carbonate; the liquid after the reaction was recorded as b.

[0047] Step five, the reaction liquid b was introduced into the third reactor. In the third reactor, the reaction temperature was controlled at 60℃, the carbon dioxide gas flow rate was 500 mL / min, the stirring speed was 800 rpm, and the reaction time was 1 hour. After the reaction was completed, the carbon dioxide was stopped, stearic acid was added to the reaction system, the addition amount was 2% of the theoretical mass of generated calcium carbonate, and an ethanol with the same volume as the reaction liquid b was added, and stirred for 5 hours. Then the heating and stirring were turned off, and the reaction liquid was naturally cooled to room temperature. The liquid after the reaction was recorded as c.

[0048] Step six, the reaction liquid c was placed in a centrifuge tube and placed on a centrifuge for high-speed centrifugal separation to obtain a solid after centrifugation. The solid after centrifugation was washed by repeatedly adding ethanol. The washed solid was placed in an oven at 105℃ and dried for 12 hours to obtain a nano calcium carbonate sample.

[0049] Example 3

[0050] A calcium carbonate nanometer preparation process based on carbide slag, comprising the following steps:

[0051] Step one, 200g of carbide slag was ball milled for 6 hours at a speed of 1000 rpm. After ball milling, the large particle impurities were removed through a 150 mesh sieve to obtain pretreated carbide slag for later use.

[0052] Step 2: Take 20g of sieved calcium carbide slag and put it in a reaction container. Add 0.5% EDTA disodium by mass, then add 300mL of 4mol / L ammonium citrate solution, and treat it under ultrasonic conditions of 40kHz for 2 hours. Then, introduce CO2 into the slurry until the pH value of the slurry is 9-10, so that the residual Mg 2+ ions and Fe 3+ Ion precipitation. Filter and collect the filtrate for later use.

[0053] Step 3: Take 200mL of the prepared CaCl2 solution and adjust the Ca content in the system with deionized water. 2+ The concentration of ions is up to 1 mol·L -1 The calcium chloride solution was injected into the inlet of a three-stage series carbonization reactor. In the first reactor, the reaction temperature was controlled at 10°C, the gas flow rate was 50 mL / min, the stirring speed was 200 rpm, and the reaction time was 20 minutes to form CaCO3 crystal nuclei. The liquid after the reaction was recorded as a.

[0054] Step 4: Introduce reaction solution a into a secondary reactor. In the secondary reactor, control the reaction temperature to 30°C, the carbon dioxide gas flow rate to 200 mL / min, the stirring speed to 300 rpm, and the reaction time to 1 hour. Add an additive, which is a combination of polyethylene glycol and sodium dodecyl sulfate. The amount of polyethylene glycol added is 1% of the theoretical mass of calcium carbonate generated, and the amount of sodium dodecyl sulfate added is 1.5% of the theoretical mass of calcium carbonate generated. The liquid after the reaction is recorded as b.

[0055] Step 5, reactant liquor b is imported into three-stage reactor.In three-stage reactor, control reaction temperature is 60 DEG C, carbon dioxide gas flow is 500mL / min, stirring speed is 800rpm, and reaction time is 1 hour.After reaction terminates, stop passing into carbon dioxide, add stearic acid to reaction system, its addition amount is 2% of theoretical generation calcium carbonate quality, and add ethanol equal to reaction liquor b volume, stir for 5 hours.Then turn off heating and stirring, and allow reaction liquor to cool to room temperature naturally.The reacted liquid is recorded as c.

[0056] Step 6: Reaction solution c is placed in a centrifuge tube and centrifuged at high speed to obtain a solid. Ethanol is then added to the solid for centrifugal washing. The washed solid is dried in an oven at 105°C for 12 hours to obtain a nano-calcium carbonate sample.

[0057] Example 4

[0058] A process for preparing nano calcium carbonate based on carbide slag comprises the following steps:

[0059] Step one, 200 g of carbide slag was ball milled for 6 hours at a rotation speed of 1000 rpm. After ball milling, the sample was sieved to remove large particles through a 150 mesh sieve, and the pretreated carbide slag was obtained for later use.

[0060] Step two, 20 g of the sieved carbide slag was placed in a reaction vessel, and 300 mL of 5% hydrochloric acid was added. The mixture was treated under ultrasonic conditions at a frequency of 40 kHz for 2 hours. Then CO2 was introduced into the slurry until the pH value of the slurry was 9-10, and the residual Mg 2+ ions and Fe 3+ ions were precipitated. Filtration was performed, and the filtrate was collected for later use.

[0061] Step three, 200 mL of the prepared CaCl2 solution was removed, and the concentration of Ca 2+ ions in the system was adjusted to 1 mol·L -1 using deionized water. The calcium chloride solution was injected into the inlet of a three-stage series carbonation reactor. In the first reactor, 0.5% EDTA disodium was added, the reaction temperature was controlled at 10℃, the gas flow rate was 50 mL / min, the stirring speed was 200 rpm, and the reaction time was 20 minutes to generate CaCO3 nuclei. The liquid after the reaction was denoted as a.

[0062] Step four, the reaction liquid a was introduced into the second reactor. In the second reactor, the reaction temperature was controlled at 30℃, the carbon dioxide gas flow rate was 200 mL / min, the stirring speed was 300 rpm, and the reaction time was 1 hour. An additive was added, which was a combination of sodium polyacrylate and sodium tripolyphosphate, wherein the addition amount of sodium polyacrylate was 0.5% of the theoretical mass of generated calcium carbonate, and the addition amount of sodium tripolyphosphate was 1% of the theoretical mass of generated calcium carbonate; the liquid after the reaction was denoted as b.

[0063] Step five, the reaction liquid b was introduced into the third reactor. In the third reactor, the reaction temperature was controlled at 80℃, the carbon dioxide gas flow rate was 500 mL / min, the stirring speed was 800 rpm, and the reaction time was 1 hour. After the reaction, the introduction of carbon dioxide was stopped, stearic acid was added to the reaction system in an amount of 1.5% of the theoretical mass of generated calcium carbonate, and an amount of ethanol equal to the volume of the reaction liquid b was added, and the mixture was stirred for 5 hours. Then the heating and stirring were turned off, and the reaction liquid was naturally cooled to room temperature. The liquid after the reaction was denoted as c.

[0064] Step six, the reaction liquid c was placed in a centrifuge tube and subjected to high-speed centrifugal separation on a centrifuge to obtain a solid after centrifugation. The solid after centrifugation was washed with ethanol multiple times. The washed solid was placed in an oven at 105℃ and dried for 12 hours to obtain a sample of nano calcium carbonate.

[0065] Example 5

[0066] A process for preparing nano calcium carbonate based on carbide slag comprises the following steps:

[0067] Step 1: 200g of carbide slag was ball-milled for 6 hours at a speed of 1000rpm. After ball-milling, the product was sieved to remove large particles of impurities through a 150-mesh sieve to prepare the pretreated carbide slag.

[0068] Step 2: Take 20g of sieved carbide slag and place it in a reaction vessel. Add 300mL of 5% dilute hydrochloric acid and treat it under ultrasonic conditions at a frequency of 40kHz for 2 hours. Then, introduce CO2 into the slurry until the pH value of the slurry is 9-10, so that the residual Mg 2+ ions and Fe 3+ Ion precipitation. Filter and collect the filtrate for later use.

[0069] Step 3: Take 200mL of the prepared CaCl2 solution and adjust the Ca content in the system with deionized water. 2+ The concentration of ions is up to 1 mol·L -1 The calcium chloride solution was injected into the inlet of a three-stage series carbonization reactor. In the first reactor, 0.5% disodium EDTA was added. The reaction temperature was controlled at 10°C, the gas flow rate was 50 mL / min, the stirring speed was 200 rpm, and the reaction time was 20 minutes to form CaCO3 crystal nuclei. The liquid after the reaction was recorded as a.

[0070] Step 4: Introduce reaction solution a into a secondary reactor. In the secondary reactor, control the reaction temperature to 30°C, the carbon dioxide gas flow rate to 200 mL / min, the stirring speed to 300 rpm, and the reaction time to 1 hour. Add an additive, which is a combination of sodium polyacrylate and sodium tripolyphosphate. The amount of sodium polyacrylate added is 0.5% of the theoretical mass of calcium carbonate generated, and the amount of sodium tripolyphosphate added is 1% of the theoretical mass of calcium carbonate generated. The liquid after the reaction is recorded as b.

[0071] Step five, the reaction solution b is introduced into a three-stage reactor. In the three-stage reactor, the reaction temperature is controlled to be 50 DEG C, the carbon dioxide gas flow rate is 500mL / min, the stirring speed is 500rpm, and the reaction time is 1 hour. After the reaction is completed, carbon dioxide is stopped from being passed through, stearic acid is added to the reaction system in an amount of 1.5% of the theoretically generated calcium carbonate mass, and ethanol equal to the volume of the reaction solution b is added and stirred for 5 hours. Heating and stirring are then turned off, and the reaction solution is allowed to cool naturally to room temperature. The reacted liquid is recorded as c.

[0072] Step six, take the reaction liquid c in the centrifuge tube, put on the centrifuge for high speed centrifugal separation, get the centrifugal after solid. Again add ethanol to the centrifugal after solid for centrifugal washing. The washed solid is placed in a 105°C oven and dried for 12 hours to obtain a sample of nano calcium carbonate.

[0073] Example 6

[0074] A calcium carbonate nanometer preparation process based on carbide slag, comprising the following steps:

[0075] Step one, take 200g of carbide slag for ball milling, the ball milling time is 6 hours, and the ball milling speed is 1000rpm. After ball milling, screen to remove large particle impurities through a 150 mesh screen to obtain pretreated carbide slag for standby.

[0076] Step two, take 20g of screened carbide slag and put it in a reaction container, add 300mL of 5% concentrated hydrochloric acid, and treat it under ultrasonic conditions at a frequency of 40kHz for 2 hours. Then pass CO2 into the slurry until the pH value of the slurry is 9-10, so that the residual Mg 2+ ions and Fe 3+ ions are precipitated. Filter and collect the filtrate for standby.

[0077] Step three, take 200mL of prepared CaCl2 solution, adjust the concentration of Ca 2+ ions in the system to 1mol·L -1 with deionized water. Inject the calcium chloride solution into the inlet of the three-stage series carbonization reactor. In the first reactor, add 0.5% EDTA disodium by mass fraction, control the reaction temperature to 10°C, the gas flow to 50mL / min, the stirring speed to 200rpm, and the reaction time to 20 minutes to generate CaCO3 nuclei. The reacted liquid is recorded as a.

[0078] Step four, introduce reaction liquid a into the second reactor. In the second reactor, control the reaction temperature to 30°C, the carbon dioxide gas flow to 200mL / min, the stirring speed to 300rpm, and the reaction time to 1 hour. Add an additive, which is a combination of sodium polyacrylate and sodium tripolyphosphate, wherein the addition amount of sodium polyacrylate is 0.5% of the theoretical mass of generated calcium carbonate, and the addition amount of sodium tripolyphosphate is 1% of the theoretical mass of generated calcium carbonate; the reacted liquid is recorded as b.

[0079] Step five, the reaction liquid b is introduced into a three-stage reactor. In the three-stage reactor, the reaction temperature is controlled at 50°C, the carbon dioxide gas flow rate is 500 mL / min, the stirring speed is 800 rpm, and the reaction time is 1 hour. After the reaction is completed, the carbon dioxide is stopped, and no stearic acid or ethanol is added. Then the heating and stirring are turned off, and the reaction liquid is naturally cooled to room temperature. The liquid after the reaction is denoted as c.

[0080] Step six, the reaction liquid c is placed in a centrifuge tube and placed on a centrifuge for high-speed centrifugal separation to obtain a centrifuged solid. The centrifuged solid is washed by centrifugation with ethanol multiple times. The washed solid is placed in an oven at 105°C and dried for 12 hours to obtain a nano calcium carbonate sample.

[0081] Example 7

[0082] A process for preparing a nano calcium carbonate based on carbide slag, comprising the following steps:

[0083] Step one, 200 g of carbide slag is ball milled for 6 hours at a speed of 1000 rpm. After ball milling, the large particle impurities are removed by passing through a 150 mesh sieve to obtain a pretreated carbide slag for later use.

[0084] Step two, 20 g of the sieved carbide slag is placed in a reaction container, 0.5% EDTA disodium salt by mass percentage is added, and 300 mL of 3.2 mol / L ammonium chloride solution is added. Under the condition of ultrasonic treatment at a frequency of 40 kHz for 2 hours, CO2 is introduced into the slurry until the pH value of the slurry is 9-10, so that the residual Mg 2+ ions and Fe 3+ ions are precipitated. Filtration is performed, and the filtrate is collected for later use.

[0085] Step three, 200 mL of the prepared CaCl2 solution is removed and the concentration of Ca 2+ ions in the system is adjusted to 0.5 mol·L -1 using deionized water. The calcium chloride solution is injected into the inlet of a three-stage series carbonation reactor. In the first reactor, the reaction temperature is controlled at 10°C, the gas flow rate is 50 mL / min, the stirring speed is 200 rpm, and the reaction time is 2 hours to generate CaCO3 nuclei. The liquid after the reaction is denoted as a.

[0086] Step four, the reaction liquid a is introduced into the secondary reactor. In the secondary reactor, the reaction temperature is controlled at 30℃, the carbon dioxide gas flow rate is 200 mL / min, the stirring speed is 300 rpm, and the reaction time is 1 hour. An additive is added, which is a combination of sodium tripolyphosphate and polyethylene glycol, wherein the addition amount of sodium tripolyphosphate is 1% of the theoretical mass of generated calcium carbonate, and the addition amount of polyethylene glycol is 1% of the theoretical mass of generated calcium carbonate; the liquid after reaction is recorded as b.

[0087] Step five, the reaction liquid b is introduced into the tertiary reactor. In the tertiary reactor, the reaction temperature is controlled at 60℃, the carbon dioxide gas flow rate is 500 mL / min, the stirring speed is 800 rpm, and the reaction time is 1 hour. After the reaction is completed, the carbon dioxide is stopped, stearic acid is added to the reaction system, the addition amount is 2% of the theoretical mass of generated calcium carbonate, and an ethanol equal to the volume of the reaction liquid b is added, and stirred for 5 hours. Then the heating and stirring are turned off, and the reaction liquid is naturally cooled to room temperature. The liquid after reaction is recorded as c.

[0088] Step six, the reaction liquid c is placed in a centrifuge tube and placed on a centrifuge for high-speed centrifugal separation to obtain a centrifuged solid. The centrifuged solid is washed by centrifugation with ethanol multiple times. The washed solid is placed in an oven at 105℃ and dried for 12 hours to obtain a nano calcium carbonate sample.

[0089] Effect verification: particle size, whiteness, purity and impurity content test

[0090] The nano calcium carbonate samples prepared by Examples 1-7 are tested for particle size, whiteness, purity and impurity content. The specific test methods are as follows: the particle size is tested using a transmission electron microscope, and the particle size test is tested according to the relevant method in GB / T19590-2023. The whiteness of the obtained product is tested using a whiteness meter according to the provisions in GB / T19281-2014. The product purity and impurity content are tested by titration and spectrophotometer according to the provisions in GB / T19281-2014. The test results are shown in the following table:

[0091] Table 1-Comparison of particle sizes of nano calcium carbonate samples

[0092] Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Particle size 110 nm 140 nm 160 nm 210 nm 145 nm 400 nm 170 nm Whiteness 96.5 97.8 97.6 96.6 96.5 94.2 94.8 Purity 95.2 95.9 96.8 96.8 96.3 94.1 94.2 Mg content (mass fraction) 0.08% 0.05% 0.04% 0.06% 0.07% 0.08% 0.08 Fe content (mass fraction) 0.06% 0.05% 0.03% 0.05% 0.06% 0.06% 0.07%

[0093] Examples 1-3 of the present application are specific preferred embodiments of the present application, and Examples 4-7 are comparative examples for investigating the effect of specific process parameters on product performance.

[0094] Example 1 and Example 4 are both based on the preparation conditions of Example 1, but there is a difference in the reaction temperature in the third reactor. Example 1 controls the reaction temperature in the third reactor at 50°C, and the particle size of the obtained sample is 110 nm. Example 4 increases the reaction temperature to 80°C, resulting in a significant increase in the particle size of the obtained sample to 210 nm. This comparison shows that controlling the temperature in the third reaction stage is a key technical point for realizing the refinement of the crystal particle size and preparing high-quality nano calcium carbonate.

[0095] Example 1 and Example 5 are both based on the preparation conditions of Example 1, but there is a difference in the stirring speed in the third reactor. Example 1 controls the stirring speed at 800 rpm, and the particle size of the obtained sample is 110 nm. Example 5 reduces the stirring speed to 500 rpm, and the particle size of the obtained sample increases to 145 nm. This comparison reveals the importance of the stirring speed in the third reaction stage for the control of the particle size of nano calcium carbonate.

[0096] Example 1 and Example 6 differ in the post-treatment step of the product. Example 1 adds 1.5% by mass of stearic acid and an equal volume of ethanol for surface treatment after the end of the third reaction, and the particle size of the obtained sample is 110 nm, the whiteness is 96.5, and the purity is 95.2. Example 6 omits this post-treatment step, and the results show that the particle size of the product is as high as 400 nm, and the whiteness and purity are reduced to 94.2 and 94.1, respectively. This proves the importance of the stearic acid surface treatment process for preventing the agglomeration of nano calcium carbonate and maintaining a small particle size, and also has a positive effect on the whiteness and purity of the product.

[0097] Example 2 and Example 7 are based on similar preparation conditions, but there is a difference in the reaction time in the first reactor. Example 2 controls the reaction time in the first reactor at 20 minutes, and the particle size of the obtained product is 140 nm, the whiteness is 97.8, and the purity is 95.9. Example 7 extends the reaction time to 2 hours, and the particle size of the obtained sample increases to 170 nm, the whiteness is 94.8, and the purity is 94.2. This comparison shows that the reaction time in the first reactor has an important influence on the growth of the crystal nucleus, and too long a reaction time can lead to excessive growth of the crystal nucleus, which is not conducive to the control of the particle size of the final product, and also has a certain influence on the whiteness and purity of the product.

[0098] It can be seen that by precisely controlling the key process parameters of the three stages of crystal nucleus generation, crystal nucleus growth, and crystal maturation, especially the reaction temperature, stirring speed, reaction time, and the final surface modification step, the agglomeration of particles can be effectively inhibited, and high-quality nano calcium carbonate can be stably prepared.

[0099] The above merely provides the specific implementation of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, and all of them should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0100] Finally, the above merely provides the preferred embodiments of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A process for preparing nano calcium carbonate based on carbide slag, characterized in that: The following steps are involved: Step 1: pretreating carbide slag to obtain a calcium-containing solution, wherein the pretreatment step includes a gradient screening step, an ultrasonic acid leaching step for dissolving iron and aluminum oxides, and a dynamic aging step for selectively precipitating magnesium ions and iron ions by introducing carbon dioxide. Step 2: performing a three-stage series carbonization reaction on the calcium-containing solution to generate nano-calcium carbonate. The three-stage series carbonization reaction includes: performing a crystal nucleation reaction in a primary reactor, adding disodium EDTA to generate CaCO3 crystal nuclei, then introducing the reaction liquid of the primary reactor into a secondary reactor for crystal nucleus directional growth reaction, adding an additive to the reaction system in the secondary reactor, wherein the additive is one or more of sodium polyacrylate, sodium tripolyphosphate, polyethylene glycol, pentaerythritol, sodium laurate, sodium oleate, and sodium dodecyl sulfate; and then introducing the reaction liquid of the secondary reactor into a tertiary reactor for crystal aging reaction. Step 3, taking the solution after the reaction in the three-stage reactor and performing post-treatment to obtain a nano-calcium carbonate sample; Wherein, after the crystals are matured, stearic acid and ethanol are added to the three-stage reactor to perform in-situ surface modification on the generated nano-calcium carbonate.

2. A nano calcium carbonate preparation process based on carbide slag according to claim 1, characterized in that, The gradient screening includes: ball milling the carbide slag for 1-12 hours at a ball milling speed of 200-1000 rpm; and screening the ball milled carbide slag through a 100-150 mesh screen to remove impurities.

3. A nano calcium carbonate preparation process based on carbide slag according to claim 1, characterized in that, The ultrasonic acid leaching comprises: placing carbide slag processed by the gradient screening step into a reaction container, adding an acidic solution prepared by one or two reagents selected from dilute hydrochloric acid, ammonium chloride, ammonium citrate, and ammonium sulfate, and performing acid leaching under ultrasonic conditions with a frequency of 40 kHz.

4. A nano calcium carbonate preparation process based on carbide slag according to claim 1, characterized in that, The dynamic aging includes: introducing carbon dioxide gas into the slurry after the ultrasonic acid leaching step until the pH value of the slurry is 9-10, so as to precipitate the residual Mg²⁺ ions and Fe³⁺ ions in the slurry.

5. A nano calcium carbonate preparation process based on carbide slag according to claim 1, characterized in that, Before the three-stage series carbonization reaction, the calcium-containing solution obtained by pretreatment is adjusted with deionized water to make the Ca²⁺ ion concentration reach 0.5mol·L⁻¹-3mol·L⁻¹, and the calcium-containing solution is injected into the inlet of the three-stage series carbonization reactor.

6. A process for preparing nano-calcium carbonate based on carbide slag according to claim 1, characterized in that, The conditions for the CaCO3 nucleation reaction in the primary reactor are: the reaction temperature is controlled at 5-10°C, the carbon dioxide gas flow rate is controlled at 10-100 mL / min, the stirring speed is controlled at 100-200 rpm, the reaction time is 5-20 minutes, and EDTA disodium is added to the reaction system at a mass percentage concentration of 0.5%.

7. A process for preparing nano-calcium carbonate based on carbide slag according to claim 1, characterized in that: The reaction liquid after the reaction in the primary reactor is introduced into the secondary reactor for a crystal nucleus oriented growth reaction. The conditions of the crystal nucleus oriented growth reaction in the secondary reactor are: the reaction temperature is controlled at 20-30°C, the carbon dioxide gas flow rate is controlled at 100-300 mL / min, the stirring speed is controlled at 300-500 rpm, and the reaction time is 0.5-1 hour; and an additive is added to the reaction system, and the amount of the additive added is 1%-5% of the theoretical mass of the generated calcium carbonate.

8. A process for preparing nano-calcium carbonate based on carbide slag according to claim 1, characterized in that: The reaction liquid after the reaction in the secondary reactor is introduced into the tertiary reactor to complete the crystal aging reaction. The conditions of the crystal aging reaction in the tertiary reactor are as follows: the reaction temperature is controlled at 50-80°C, the carbon dioxide gas flow rate is controlled at 200-500 mL / min, the stirring speed is controlled at 500-800 rpm, and the reaction time is 0.5-1 hour; after the reaction is completed, the introduction of carbon dioxide is stopped, and stearic acid is added to the reaction system in an amount of 1-3% of the theoretical mass of calcium carbonate generated, and ethanol is added in an amount equal to the volume of the reaction liquid, stirred for 3-10 hours, and then the heating and stirring are turned off, and naturally cooled to room temperature.

9. A process for preparing nano-calcium carbonate based on carbide slag according to claim 1, characterized in that: The post-treatment in step 3 includes: placing the solution after the reaction in the three-stage reactor into a centrifuge tube, placing it on a centrifuge for centrifugal separation, and obtaining a solid after centrifugation; Washing the centrifuged solid with ethanol; The washed solid is dried at 105° C. for 6-24 hours to obtain the nano calcium carbonate product.

10. A system for preparing nano-calcium carbonate based on carbide slag, for performing the process according to any one of claims 1 to 9, characterized in that: include: A carbide slag pretreatment module is suitable for sequentially performing gradient screening treatment, ultrasonic acid leaching treatment and dynamic aging treatment on the carbide slag to obtain a calcium-containing solution after filtration; A three-stage series carbonization reactor is used to receive the calcium-containing solution and perform a three-stage series carbonization reaction to generate nano-calcium carbonate. The three-stage series carbonization reactor includes: The primary reactor has the following operating conditions: temperature 5-10°C, gas flow rate 10-100 mL / min, stirring speed 100-200 rpm, and disodium EDTA is added to react the calcium-containing solution to form calcium carbonate crystal nuclei; The secondary reactor is connected in series with the primary reactor, and its operating conditions are: temperature 20-30°C, carbon dioxide gas flow rate 100-300 mL / min, stirring speed 300-500 rpm, and a selected crystal form control agent is added to promote the directional growth of the calcium carbonate crystal nuclei; A third-stage reactor is connected in series with the second-stage reactor, and its operating conditions are: temperature 50-80°C, carbon dioxide gas flow rate 200-500mL / min, and stirring speed 500-800rpm, which is used to complete crystal ripening. After the reaction is completed, the carbon dioxide is stopped, and stearic acid is added to the reaction system in an amount of 1-3% of the theoretical mass of calcium carbonate produced. Ethanol is added in an amount equal to the volume of the reaction solution, and after stirring for 3-10 hours, heating and stirring are turned off, and the reaction mixture is naturally cooled to room temperature. The product post-processing module is used to perform post-processing on the reaction liquid containing nano-calcium carbonate from the three-stage series carbonization reactor to obtain a nano-calcium carbonate product.

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