A method for preparing polycrystalline nanometer calcium carbonate from steel slag by carbonization in a supergravity field

Abstract

The present application belongs to the technical field of resource utilization of steel slag and preparation of nano calcium carbonate, and more particularly relates to a method for preparing polycrystalline nano calcium carbonate from steel slag through carbonization in a high gravity field. The present application couples the high gravity field with a calcium chelating agent, utilizes the synergistic effect, strengthens the control ability of the mass transfer and reaction process, effectively inhibits the rapid agglomeration and disordered growth of crystal nuclei, breaks through the technical bottleneck that it is difficult to prepare nano calcium carbonate from complex component leaching liquor of solid waste by traditional methods, and through selection of calcium chelating agents with different functional groups and cooperation with the reaction system, the growth rate of different crystal faces of calcium carbonate can be accurately controlled, so that controllable preparation of various crystal forms such as vaterite and calcite and specific nano morphology is realized.

Description

Technical Field

[0001] This invention belongs to the field of resource utilization of steel slag and preparation technology of nano-calcium carbonate, and more specifically, it relates to a method for preparing polycrystalline nano-calcium carbonate from steel slag by carbonization in a hypergravity field. Background Technology

[0002] Steel slag contains abundant calcium ions, which can react with CO2 to form calcium carbonate. By leaching calcium ions from the steel slag and then reacting it with CO2, pure calcium carbonate can be produced, achieving stable carbon sequestration. However, the calcium carbonate produced by conventional methods is the most common cubic calcite, which typically has low activity and is often used in fillers and building materials, resulting in low added value and difficulty in forming a competitive market position.

[0003] By nano-sizing calcium carbonate and altering its crystal form, it is hoped that the physicochemical properties of calcium carbonate can be improved, enabling it to meet the needs of more fields and thus significantly increasing its application value. The composition of calcium ion leachate from solid waste is complex, making the synthesis of nano-sized calcium carbonate even more difficult. Some existing technologies disclose a method for preparing high-purity nano-calcium carbonate, using calcium leachate from carbide slag or steel slag, which carbonizes to form nano-calcium carbonate under the action of ammonia, a carbonizing agent, and a crystal-directing agent. However, this method can only form cubic calcite-type calcium carbonate with a conventional crystal form. Other existing technologies disclose a method for preparing nano-calcium carbonate by capturing carbon dioxide from steel slag and its amine recycling method, utilizing ammonium bicarbonate and steel slag calcium leachate at a relatively high temperature (60-70℃) to form needle-like calcium carbonate. However, the formed calcium carbonate is a single needle-like crystal form with a major axis in the micrometer range. Therefore, how to prepare polymorphic nano-sized calcium carbonate using steel slag calcium leachate is a problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing polycrystalline nano-calcium carbonate from steel slag by carbonization in a hypergravity field, so as to solve the problems existing in the prior art and realize the controllable preparation of polycrystalline nano-calcium carbonate.

[0005] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of this invention is to provide a method for preparing polycrystalline nano-calcium carbonate from steel slag by carbonization in a hypergravity field, the steps of which include: Ammonium chloride solution and converter steel slag powder are mixed and leached with stirring to obtain calcium-rich filtrate; The calcium ion concentration in the calcium-rich filtrate was adjusted to 0.08-0.12 mol / L, and the pH was adjusted to 9.8-10.3 using ammonia. Then, a dispersant and a calcium chelating agent were added to the solution, and the solution was aged to obtain the filtrate to be reacted. The filtrate to be reacted is pumped into a high-gravity reactor, and CO2 gas is introduced at the same time. After a circulating carbonization reaction, a suspension of carbonization products is obtained. The carbonized product suspension was centrifuged, purified, and dried to obtain polycrystalline nano-calcium carbonate. The polycrystalline nano-calcium carbonate includes at least two of cubic calcite, needle-shaped calcite, and spheroidal aragonite.

[0006] Furthermore, the concentration of the ammonium chloride solution is 0.3-0.6 mol / L.

[0007] Furthermore, the liquid-to-solid ratio of the ammonium chloride solution and the converter steel slag powder is 20-30 mL:1g.

[0008] Furthermore, the stirring leaching temperature is 60-80 ℃, and the time is 10-20 min.

[0009] Furthermore, the concentration of the ammonia solution is 25 wt.%.

[0010] Furthermore, the dispersant is polyoxyethylene ether, and the amount added is 0.05-0.15 wt.% of the solution mass.

[0011] Furthermore, the calcium chelating agent includes at least one of citric acid, malic acid, tartaric acid, and a complex formed by citric acid, malic acid, or tartaric acid with EDTA-2Na.

[0012] Furthermore, the amount of the calcium chelating agent added is 0.015-0.5 wt.% of the solution mass.

[0013] Furthermore, the aging time is 1-2 hours.

[0014] Furthermore, the supergravity reactor is a supergravity rotating packed bed, and the gas and liquid are in countercurrent contact.

[0015] Furthermore, the cyclic carbonization reaction is a single carbonization reaction from the entry of the filtrate into the hypergravity reactor to its discharge, and is repeated 8-12 times at a reaction temperature of 10-20 °C.

[0016] Furthermore, the ratio of the liquid pumping flow rate of the filtrate to the gas flow rate containing CO2 in the supergravity reactor is 1:5-10.

[0017] Furthermore, the CO2 concentration of the CO2-containing gas is 10% (volume fraction).

[0018] The second technical solution of the present invention is to provide a polycrystalline nano-calcium carbonate prepared by the above method.

[0019] The present invention discloses the following technical effects: This invention couples a supergravity field with a calcium chelating agent, utilizing their synergistic effect to enhance the control of mass transfer and reaction processes, effectively suppressing the rapid aggregation and disordered growth of crystal nuclei, and breaking through the technical bottleneck of traditional methods that make it difficult to prepare nano-sized calcium carbonate from complex solid waste leachates.

[0020] This invention, by selecting calcium chelating agents with different functional groups and coordinating them with the reaction system, can precisely control the growth rate of different crystal faces of calcium carbonate, thereby achieving controllable preparation of various crystal forms and specific nanomorphologies such as aragonite and calcite. This method is highly flexible and can be used to synthesize products with different properties according to the needs of downstream applications, thus expanding the application fields and economic value. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The images shown are characterization diagrams of the nano-calcium carbonate product in Example 1, where the left image is a SEM image, the right image is a TEM image, and the inset is an XRD image.

[0022] Figure 2 The images shown are characterization diagrams of the nano-calcium carbonate product in Example 2, where the left image is a SEM image, the right image is a TEM image, and the inset is an XRD image.

[0023] Figure 3 The images shown are characterization diagrams of the nano-calcium carbonate product in Example 3, where the left image is a SEM image, the right image is a TEM image, and the inset is an XRD image.

[0024] Figure 4 The images shown are characterization diagrams of the nano-calcium carbonate product in Example 4, where the left image is a SEM image, the right image is a TEM image, and the inset is an XRD image.

[0025] Figure 5 The images show the characterization of the calcium carbonate product in Comparative Example 1, with the left image being a SEM image and the right image being an XRD image.

[0026] Figure 6 The images show the characterization of the calcium carbonate product in Comparative Example 2, with the left image being a SEM image and the right image being an XRD image.

[0027] Figure 7 The images show the characterization of the calcium carbonate product in Comparative Example 3, with the left image being a SEM image and the right image being an XRD image. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0029] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] Unless otherwise specified, all raw materials and reagents involved in the specific embodiments of this invention are commercially available products.

[0034] Unless otherwise specified, room temperature and normal temperature in the specific embodiments of this invention refer to 20-30℃.

[0035] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0036] In some specific embodiments, the present invention provides a method for preparing polycrystalline nano-calcium carbonate from steel slag by carbonization in a hypergravity field, the steps of which include: S1. Mix ammonium chloride solution with converter steel slag powder at a liquid-solid ratio of 20-30 mL: 1 g, and leach for 10-20 min with continuous stirring at 60-80 ℃. After leaching, filter to obtain calcium-rich filtrate. S2. Adjust the calcium ion concentration in the calcium-rich filtrate obtained in step S1 to 0.08-0.12 mol / L, adjust the pH with 25 wt.% ammonia water to obtain a solution with a pH of 9.8-10.3, then add 0.05-0.15 wt.% of dispersant (polyoxyethylene ether) and 0.015-0.5 wt.% of calcium chelating agent (citric acid, malic acid, tartaric acid, and at least one of the complexes formed by citric acid, malic acid, or tartaric acid and EDTA-2Na) to the solution, and age for 1-2 h to obtain the filtrate to be reacted; S3. The filtrate to be reacted obtained in step S2 is pumped into a supergravity reactor (supergravity rotating packed bed, gas-liquid countercurrent contact) through a feed pump. At the same time, CO2-containing gas (CO2 concentration of 10%) is introduced into the supergravity reactor through the gas inlet. The process of the filtrate entering and exiting the supergravity reactor is considered one reaction. The carbonization reaction is carried out 8 to 12 times in a cycle at a reaction temperature of 10-20 ℃ to obtain a carbonization product suspension. The ratio of the flow rate of the filtrate to be reacted to the flow rate of the CO2-containing gas is 1:5-10.

[0037] S4. After centrifugation, purification and drying of the carbonization product suspension, polycrystalline nano calcium carbonate is obtained. Polycrystalline nano-calcium carbonate includes at least two of cubic calcite, acicular calcite, and spheroidal aragonite.

[0038] Regarding the amount of dispersant added, when the dosage is less than 0.05 wt.%, it is difficult to coat all the crystal nuclei, resulting in low particle dispersion; when it exceeds 0.15 wt.%, the organic film adsorbed on the crystal surface will be too thick, making it difficult to separate and contaminating the product.

[0039] Regarding the amount of calcium chelating agent added, when the dosage is less than 0.015 wt.%, the nucleation inhibition effect will be reduced, resulting in larger product particle size; when it exceeds 0.5 wt.%, it will induce crystal aggregation and hinder the combination of carbonate and calcium ions, thus reducing carbonation efficiency.

[0040] In this invention, the hypergravity factor (β) is defined as: ; In the formula, β: supergravity factor; ω: angular velocity, s -1 γ: Average rotor radius, m; N: Rotor speed, rpm; ri : Rotor inner radius, m; r o : Rotor outer radius, m; g: gravitational acceleration, m / s² 2 .

[0041] The mechanism of action of this invention is as follows: The hypergravity field enhances micromixing efficiency, enabling the breakthrough of the critical value for uniform crystal nucleation and thus reducing crystal size. The steel slag leaching solution system is complex and a single liquid phase. When carbon dioxide gas is introduced, the solution rapidly becomes supersaturated, resulting in a homogeneous nucleation explosion. The collision and adsorption of numerous crystal nuclei promote crystal growth, which is detrimental to the formation of nanoparticles. This invention reduces the concentration of calcium ions and CO2 in the solution, slowing down the reaction and the rate of particle adsorption. Furthermore, by introducing an appropriate amount of calcium chelating agent, the rapid formation of crystal nuclei is slowed down, and the coating and separation of crystal nuclei by polyoxyethylene ether prevents crystal aggregation. Therefore, by combining the hypergravity field, calcium chelating agent, and dispersant, nanoscale calcium carbonate is formed in the complex steel slag leaching system.

[0042] Finally, by using and combining different calcium chelating agents, the surface-inducing effect of functional groups on calcium carbonate crystals was changed, the surface energy was reduced or a growth template was formed, resulting in polycrystalline calcium carbonate with different crystal forms and morphologies.

[0043] In the following embodiments of the present invention, the converter steel slag powder used is from Hebei Shougang Qian'an Iron and Steel Co., Ltd., and is mainly composed of CaO (40%), SiO2 (20%), Fe2O3 (25%), MgO (4%) and Al2O3 (5%), with a median particle size of 9.59 μm.

[0044] Example 1 A method for preparing polycrystalline nano-calcium carbonate from steel slag by carbonization under a hypergravity field includes the following steps: S1. A 0.5 mol / L ammonium chloride solution was mixed with converter steel slag powder at a liquid-solid ratio of 20 mL: 1 g. The mixture was continuously stirred and leached at 80 °C for 10 min. After leaching, the mixture was filtered to obtain a calcium-rich filtrate, and the calcium ion concentration was measured to be 0.21 mol / L. S2. Adjust the calcium ion concentration in the calcium-rich filtrate obtained in step S1 to 0.1 mol / L with pure water, adjust the pH with 25 wt.% ammonia water to obtain a solution with pH 10, then add 0.1 wt.% of dispersant (polyoxyethylene ether) and 0.017 wt.% of calcium chelating agent (citric acid) to the solution, and age for 1 h to obtain the filtrate to be reacted; S3. 500 mL of the filtrate obtained in step S2 is pumped into a high gravity reactor (high gravity rotating packed bed, gas-liquid countercurrent contact) at a flow rate of 0.5 L / min using a feed pump. At the same time, 10% CO2 is introduced into the high gravity reactor at a flow rate of 5 L / min through the inlet. The high gravity factor formed by the rotation of the high gravity packed bed is 200, and the reaction temperature is 20 °C. The liquid after the reaction is discharged from the outlet of the high gravity reactor into a stirred container. One reaction is completed from the entry into the reactor to the discharge from the reactor, and the time is 1 min. A total of 12 cycles of carbonization reaction are carried out to obtain a nano-calcium carbonate suspension. S4. The nano-calcium carbonate suspension was centrifuged to separate the solid and liquid phases, and then purified by washing three times with anhydrous ethanol. Subsequently, it was dried in a vacuum drying oven at 40 °C for 12 h to obtain the nano-calcium carbonate product.

[0045] Figure 1 The images show the characterization of the nano-calcium carbonate product in Example 1. The left image is a SEM image, the right image is a TEM image, and the inset is an XRD image. As can be seen from the images, the nano-calcium carbonate has a particle size of less than 200 nm and is composed of 97.5% cubic calcite and 2.5% spheroidal aragonite.

[0046] Example 2 A method for preparing polycrystalline nano-calcium carbonate from steel slag by carbonization under a hypergravity field includes the following steps: S1. A 0.5 mol / L ammonium chloride solution was mixed with converter steel slag powder at a liquid-solid ratio of 20 mL: 1 g. The mixture was continuously stirred and leached at 80 °C for 10 min. After leaching, the mixture was filtered to obtain a calcium-rich filtrate, and the calcium ion concentration was measured to be 0.21 mol / L. S2. Adjust the calcium ion concentration in the calcium-rich filtrate obtained in step S1 to 0.1 mol / L with pure water, adjust the pH with 25 wt.% ammonia water to obtain a solution with pH 10, then add 0.1 wt.% dispersant (polyoxyethylene ether) and 0.017 wt.% citric acid and 0.2 mM EDTA-2Na to the solution by mass, and age for 1 h to obtain the filtrate to be reacted; S3. 500 mL of the filtrate obtained in step S2 is pumped into a hypergravity reactor (hypergravity rotating packed bed, gas-liquid countercurrent contact) at a flow rate of 0.5 L / min using a feed pump. At the same time, 10% CO2 is introduced into the hypergravity reactor at a flow rate of 5 L / min through the inlet. The hypergravity factor formed by the rotation of the hypergravity packed bed is 200, and the reaction temperature is 10 °C. The liquid after the reaction is discharged from the outlet of the hypergravity reactor into a stirred container. The reaction time is 1 min from entering to exiting the reactor. A total of 8 cycles of carbonization reaction are carried out to obtain a nano-calcium carbonate suspension. S4. The nano-calcium carbonate suspension was centrifuged to separate the solid and liquid phases, and then purified by washing three times with anhydrous ethanol. Subsequently, it was dried in a vacuum drying oven at 40 °C for 12 h to obtain the nano-calcium carbonate product.

[0047] Figure 2 The images show the characterization of the nano-calcium carbonate product in Example 2. The left image is a SEM image, the right image is a TEM image, and the inset is an XRD image. As can be seen from the images, the nano-calcium carbonate has a particle size of less than 200 nm and is composed of 26.6% cubic calcite and 73.4% spheroidal aragonite.

[0048] Example 3 A method for preparing polycrystalline nano-calcium carbonate from steel slag by carbonization under a hypergravity field includes the following steps: S1. A 0.5 mol / L ammonium chloride solution was mixed with converter steel slag powder at a liquid-solid ratio of 20 mL: 1 g. The mixture was continuously stirred and leached at 80 °C for 10 min. After leaching, the mixture was filtered to obtain a calcium-rich filtrate, and the calcium ion concentration was measured to be 0.21 mol / L. S2. Adjust the calcium ion concentration in the calcium-rich filtrate obtained in step S1 to 0.1 mol / L with pure water, adjust the pH with 25 wt.% ammonia water to obtain a solution with pH 10, then add 0.1 wt.% of dispersant (polyoxyethylene ether) and 0.05 wt.% of calcium chelating agent (malic acid) to the solution, and age for 1 h to obtain the filtrate to be reacted; S3. 500 mL of the filtrate obtained in step S2 is pumped into a high gravity reactor (high gravity rotating packed bed, gas-liquid countercurrent contact) at a flow rate of 0.5 L / min using a feed pump. At the same time, 10% CO2 is introduced into the high gravity reactor at a flow rate of 5 L / min through the inlet. The high gravity factor formed by the rotation of the high gravity packed bed is 200, and the reaction temperature is 20 °C. The liquid after the reaction is discharged from the outlet of the high gravity reactor into a stirred container. One reaction is completed from the entry into the reactor to the discharge from the reactor, and the time is 1 min. A total of 12 cycles of carbonization reaction are carried out to obtain a nano-calcium carbonate suspension. S4. The nano-calcium carbonate suspension was centrifuged to separate the solid and liquid phases, and then purified by washing three times with anhydrous ethanol. Subsequently, it was dried in a vacuum drying oven at 40 °C for 12 h to obtain the nano-calcium carbonate product.

[0049] Figure 3 The images show the characterization of the nano-calcium carbonate product in Example 3. The left image is a SEM image, the right image is a TEM image, and the inset is an XRD image. As can be seen from the images, the nano-calcium carbonate has a particle size of less than 200 nm and is composed of 24.8% cubic calcite and 75.2% spheroidal aragonite.

[0050] Example 4 A method for preparing polycrystalline nano-calcium carbonate from steel slag by carbonization under a hypergravity field includes the following steps: S1. A 0.5 mol / L ammonium chloride solution was mixed with converter steel slag powder at a liquid-solid ratio of 20 mL: 1 g. The mixture was continuously stirred and leached at 80 °C for 10 min. After leaching, the mixture was filtered to obtain a calcium-rich filtrate, and the calcium ion concentration was measured to be 0.21 mol / L. S2. Adjust the calcium ion concentration in the calcium-rich filtrate obtained in step S1 to 0.1 mol / L with pure water, adjust the pH with 25 wt.% ammonia water to obtain a solution with pH 10, then add 0.1 wt.% of dispersant (polyoxyethylene ether) and 0.15 wt.% of calcium chelating agent (citric acid) to the solution, and age for 1 h to obtain the filtrate to be reacted; S3. 500 mL of the filtrate obtained in step S2 is pumped into a high gravity reactor (high gravity rotating packed bed, gas-liquid countercurrent contact) at a flow rate of 0.5 L / min using a feed pump. At the same time, 10% CO2 is introduced into the high gravity reactor at a flow rate of 5 L / min through the inlet. The high gravity factor formed by the rotation of the high gravity packed bed is 200, and the reaction temperature is 20 °C. The liquid after the reaction is discharged from the outlet of the high gravity reactor into a stirred container. One reaction is completed from the entry into the reactor to the discharge from the reactor, and the time is 1 min. A total of 12 cycles of carbonization reaction are carried out to obtain a nano-calcium carbonate suspension. S4. The nano-calcium carbonate suspension was centrifuged to separate the solid and liquid phases, and then purified by washing three times with anhydrous ethanol. Subsequently, it was dried in a vacuum drying oven at 40 °C for 12 h to obtain the nano-calcium carbonate product.

[0051] Figure 4 The images show the characterization of the nano-calcium carbonate product in Example 4. The left image is a SEM image, the right image is a TEM image, and the inset is an XRD image. As can be seen from the images, the nano-calcium carbonate is mainly composed of needle-shaped calcite, accounting for 85.5%, with the remainder being 14.5% spheroidal aragonite. The nano-calcium carbonate has a width of approximately 100 nm and a length of approximately 500 nm.

[0052] Comparative Example 1 The preparation steps of calcium carbonate include: S1. A 0.5 mol / L ammonium chloride solution was mixed with converter steel slag powder at a liquid-solid ratio of 20 mL: 1 g. The mixture was continuously stirred and leached at 80 °C for 10 min. After leaching, the mixture was filtered to obtain a calcium-rich filtrate, and the calcium ion concentration was measured to be 0.21 mol / L. S2. Adjust the calcium ion concentration in the calcium-rich filtrate obtained in step S1 to 0.1 mol / L with pure water, adjust the pH with 25 wt.% ammonia water to obtain a solution with pH 10, then add 0.1 wt.% of dispersant (polyoxyethylene ether) and 0.017 wt.% of calcium chelating agent (citric acid) to the solution, and age for 1 h to obtain the filtrate to be reacted; S3. Place 500 mL of the filtrate obtained in step S2 into a stirred reactor. At the same time, introduce 10% CO2 into the stirred reactor at a rate of 5 L / min through the inlet. The reaction temperature is 20 °C and the carbonation time is 12 min to obtain a calcium carbonate suspension. S4. Centrifuge the calcium carbonate suspension to separate the solid and liquid phases, and purify it by washing it three times with anhydrous ethanol. Then dry it in a vacuum drying oven at 40 °C for 12 h to obtain the calcium carbonate product.

[0053] Figure 5 The figures show the characterization of the calcium carbonate product in Comparative Example 1. The left image is a SEM image, the right image is a TEM image, and the inset is an XRD image. As can be seen from the figures, the calcium carbonate product is calcium carbonate with a particle size greater than 1 μm (97% calcite, 3% aragonite).

[0054] Comparative Example 2 The preparation steps of calcium carbonate include: S1. A 0.5 mol / L ammonium chloride solution was mixed with converter steel slag powder at a liquid-solid ratio of 20 mL: 1 g. The mixture was continuously stirred and leached at 80 °C for 10 min. After leaching, the mixture was filtered to obtain a calcium-rich filtrate, and the calcium ion concentration was measured to be 0.21 mol / L. S2. Adjust the calcium ion concentration in the calcium-rich filtrate obtained in step S1 to 0.1 mol / L with pure water, and adjust the pH with 25 wt.% ammonia water to obtain a filtrate with a pH of 10. S3. 500 mL of the filtrate obtained in step S2 is pumped into a high gravity reactor (high gravity rotating packed bed, gas-liquid countercurrent contact) at a flow rate of 0.5 L / min using a feed pump. At the same time, 10% CO2 is introduced into the high gravity reactor at a flow rate of 5 L / min through the inlet. The high gravity factor formed by the rotation of the high gravity packed bed is 200, and the reaction temperature is 20 °C. The liquid after the reaction is discharged from the outlet of the high gravity reactor into a stirred container. The reaction time is 1 min from entering to exiting the reactor. A total of 12 cycles of carbonation reaction are carried out to obtain a calcium carbonate suspension. S4. Centrifuge the calcium carbonate suspension to separate the solid and liquid phases, and purify it by washing it three times with anhydrous ethanol. Then dry it in a vacuum drying oven at 40 °C for 12 h to obtain the calcium carbonate product.

[0055] Figure 6 The figures show the characterization of the calcium carbonate product in Comparative Example 2, with the left image being the SEM image and the right image being the XRD pattern. As can be seen from the figures, the calcium carbonate product is 0.5-2 μm aragonite with a purity of 98%.

[0056] Comparative Example 3 The preparation steps of calcium carbonate include: S1. A 0.5 mol / L ammonium chloride solution was mixed with converter steel slag powder at a liquid-solid ratio of 20 mL: 1 g. The mixture was continuously stirred and leached at 80 °C for 10 min. After leaching, the mixture was filtered to obtain a calcium-rich filtrate, and the calcium ion concentration was measured to be 0.21 mol / L. S2. Adjust the calcium ion concentration in the calcium-rich filtrate obtained in step S1 to 0.1 mol / L with pure water, adjust the pH with 25 wt.% ammonia water to obtain a solution with pH of 10, then add 0.017 wt.% calcium chelating agent (citric acid) to the solution and age for 1 h to obtain the filtrate to be reacted. S3. 500 mL of the filtrate obtained in step S2 is pumped into a high gravity reactor (high gravity rotating packed bed, gas-liquid countercurrent contact) at a flow rate of 0.5 L / min using a feed pump. At the same time, 10% CO2 is introduced into the high gravity reactor at a flow rate of 5 L / min through the inlet. The high gravity factor formed by the rotation of the high gravity packed bed is 200, and the reaction temperature is 20 °C. The liquid after the reaction is discharged from the outlet of the high gravity reactor into a stirred container. The reaction time is 1 min from entering to exiting the reactor. A total of 12 cycles of carbonation reaction are carried out to obtain a calcium carbonate suspension. S4. Centrifuge the calcium carbonate suspension to separate the solid and liquid phases, and purify it by washing it three times with anhydrous ethanol. Then dry it in a vacuum drying oven at 40 °C for 12 h to obtain the calcium carbonate product.

[0057] Figure 7 The figures show the characterization of the calcium carbonate product in Comparative Example 3, with the left image being the SEM image and the right image being the XRD image. As can be seen from the figures, the calcium carbonate product in Comparative Example 3 is micron-sized (>2 μm) spindle-shaped calcite formed by the directional aggregation of cubic calcite particles with a diameter of less than 200 nm.

[0058] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0059] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing polycrystalline nano-calcium carbonate from steel slag by carbonization under a hypergravity field, characterized in that the steps include... include: Ammonium chloride solution and converter steel slag powder are mixed and leached with stirring to obtain calcium-rich filtrate; The calcium ion concentration in the calcium-rich filtrate was adjusted to 0.08-0.12 mol / L, and the pH was adjusted to 9.8-10.3 using ammonia. Then, a dispersant and a calcium chelating agent were added to the solution, and the solution was aged to obtain the filtrate to be reacted. The filtrate to be reacted is pumped into a high-gravity reactor, and CO2 gas is introduced at the same time. After a circulating carbonization reaction, a suspension of carbonization products is obtained. The carbonized product suspension was centrifuged, purified, and dried to obtain polycrystalline nano-calcium carbonate. The polycrystalline nano-calcium carbonate includes at least two of cubic calcite, needle-shaped calcite, and spheroidal aragonite.

2. The method as described in claim 1, characterized in that, The concentration of the ammonium chloride solution is 0.3-0.6 mol / L; the liquid-to-solid ratio of the ammonium chloride solution to the converter steel slag powder is 20-30 mL:1g.

3. The method as described in claim 1, characterized in that, The stirring leaching temperature is 60-80 ℃, and the time is 10-20 min.

4. The method as described in claim 1, characterized in that, The concentration of the ammonia solution is 25 wt.%.

5. The method as described in claim 1, characterized in that, The dispersant is polyoxyethylene ether, and the amount added is 0.05-0.15 wt.% of the solution mass.

6. The method as described in claim 1, characterized in that, The calcium chelating agent includes at least one of citric acid, malic acid, tartaric acid, and a complex formed by citric acid, malic acid, or tartaric acid and EDTA-2Na; the amount of calcium chelating agent added is 0.015-0.5 wt. of the solution mass.

7. The method as described in claim 1, characterized in that, The aging time is 1-2 hours.

8. The method as described in claim 1, characterized in that, The cyclic carbonization reaction is a single carbonization reaction from the entry of the filtrate into the hypergravity reactor to its discharge, and is repeated 8-12 times at a temperature of 10-20 ℃.

9. The method as described in claim 1, characterized in that, The ratio of the liquid pump flow rate of the filtrate to the gas flow rate containing CO2 in the supergravity reactor is 1:5-10. And / or, the CO2 concentration of the CO2-containing gas is 10%.

10. A polycrystalline nano-calcium carbonate prepared by the method according to any one of claims 1-9.

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