Method for synthesizing high-valued amorphous calcium carbonate through carbide slag carbon sequestration

Abstract

The invention provides a method for synthesizing high-valued amorphous calcium carbonate through carbon sequestration of carbide slag, and belongs to the technical field of carbon sequestration and high-valued utilization of industrial solid waste resources. The method comprises the following steps: carrying out active calcium extraction reaction on a dried and ball-milled carbide slag aqueous solution through ammonium chloride, stirring and filtering to obtain a calcium-containing solution; the method comprises the following steps: adding a certain amount of absolute ethyl alcohol and magnesium chloride into a calcium-containing solution, fully stirring, adjusting the pH value to a certain value, and introducing CO2 gas for mineralization reaction to obtain a turbid liquid containing calcium carbonate precipitate; and carrying out centrifugal separation, alcohol washing and drying on the turbid liquid to obtain powder calcium carbonate. According to the method disclosed by the invention, the calcium carbide slag active calcium liquid is extracted by adopting ammonium chloride, and absolute ethyl alcohol-magnesium chloride is added to precisely regulate and control the reaction steps of CO2 and the extracted calcium liquid, so that the CO2 is efficiently fixed, and meanwhile, mineralization is performed to obtain a mixed crystal type amorphous nano calcium carbonate product. According to the technology, double targets of synthesizing high-valued calcium carbonate through carbide slag carbon sequestration are achieved, and an innovative technical path is invented for current solid waste resource utilization.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of industrial solid waste resource carbon sequestration high-value utilization technology, and particularly relates to a method for synthesizing high-value amorphous calcium carbonate by calcium carbide slag carbon sequestration. BACKGROUND

[0002] Calcium carbide slag is an industrial waste produced by the calcium carbide industry, and the content of Ca(OH)2 therein is more than 70%, and contains a small amount of calcite. This is because the Ca(OH)2 on the surface of the calcium carbide slag reacts with CO2 to form calcite. In addition, it also contains a small amount of impurities such as Al2O3, SiO2, and Fe2O3. At present, about 60% of the calcium carbide slag is still treated by open-air stacking. The strong alkaline liquid stream formed by rain and moisture dissolution leads to environmental risks such as groundwater pollution, soil alkalization, and dust diffusion. The traditional utilization method is to use calcium carbide slag for building material production, flue gas desulfurization, and wastewater treatment. Due to the strong alkalinity, the overall utilization rate is not high, and there are problems such as high energy consumption and low added value. The active calcium component contained in the calcium carbide slag is a high-quality industrial raw material. Using it to collect CO2 gas can reduce carbon emissions and promote carbon cycle, which meets the current policy demand of the “double carbon target”. Further producing high-quality calcium carbonate products can greatly improve the utilization value. At present, there have been studies on the preparation of single crystal or mixed crystal calcium carbonate products by using CO2 mineralization calcium carbide slag. However, there is no report on the preparation of nanoscale amorphous calcium carbonate with higher activity by using CO2 mineralization calcium carbide slag. The present application is developed for this purpose, and a low-energy-consumption and high-benefit calcium carbide slag utilization technology is developed.

[0003] Amorphous calcium carbonate has the characteristics of large specific surface area, strong adsorption, and good biocompatibility, and has great application potential in the fields of biological medicine (such as drug carriers), environmental remediation, and functional materials. Amorphous calcium carbonate is generally generated in a highly supersaturated solution and exists as a precursor of crystalline CaCO3 (such as vaterite, calcite, and calcite). Compared with crystalline states such as calcite, the synthesis of amorphous calcium carbonate needs to be carried out under specific kinetic control conditions. However, in inorganic systems, the conversion of amorphous calcium carbonate to its crystal is very rapid (usually completed within a few seconds to a few minutes), and once the conversion is completed, the nanoscale crystals will grow to microns within a very short time, which brings great challenges to the preparation of amorphous calcium carbonate.

[0004] Therefore, it is of great significance to carry out research on the preparation of amorphous calcium carbonate by indirect mineralization of calcium carbide slag. This technology not only realizes the resource utilization of calcium carbide slag through a simple process, effectively alleviating the environmental pressure brought by it, but also produces high-value amorphous calcium carbonate products, with significant economic and ecological benefits. SUMMARY

[0005] The present application aims to provide a method for synthesizing high-value amorphous calcium carbonate by carbon sequestration of carbide slag, which extracts active calcium components from a carbide slag aqueous solution by using ammonium chloride as a carbide slag leaching agent to form a calcium-containing extract solution.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions: A method for synthesizing high-value amorphous calcium carbonate by carbon sequestration of carbide slag, comprising the following steps: The method includes the following steps: taking carbide slag as raw material and ammonium chloride as leaching agent to dissolve calcium ions rich in the carbide slag and obtain a calcium-containing solution, and the solid phase is leaching residue. Then, a certain proportion of anhydrous ethanol and magnesium chloride are added to the calcium-containing solution, the mixture is stirred, the pH of the mixture is adjusted to 13.5, CO2 gas is introduced for mineralization reaction, after the reaction is completed, centrifugal separation is performed, the sample is washed with anhydrous ethanol, and the filtered product is completely dried at 40°C.

[0007] Further, the method specifically comprises the following steps: (1) The carbide slag raw material is dried at 105°C for 3 hours, and then ball-milled (ball rotation speed 400 rpm / m, time 60 min) to obtain pretreated carbide slag.

[0008] (2) The active calcium components in the carbide slag are leached under the following conditions: the solid-liquid ratio of the carbide slag to deionized water is 1:50, the leaching time is 35 min, the stirring speed is 500 rpm / min, and the ammonium chloride concentration is controlled at 0.5 mol / L to obtain a calcium-containing solution.

[0009] (3) Anhydrous ethanol is added to the calcium-containing solution, the volume ratio of the calcium-containing solution to anhydrous ethanol is controlled in the range of 1:1-1:4, the magnesium chloride concentration is controlled at 0.04 mol / L, and the pH=9.5 is the reaction endpoint. The suspension after the carbonization reaction is completed is centrifuged and separated.

[0010] (4) The centrifuged and separated product is washed with anhydrous ethanol three times, and centrifuged and separated again.

[0011] (5) The washed product is placed in a 40°C oven and dried for 24 h.

[0012] (6) The entire leaching and mineralization reaction is carried out at room temperature.

[0013] An amorphous calcium carbonate prepared by the above method, wherein the particle size of the amorphous calcium carbonate is in the range of 50-180 nm.

[0014] Compared with the prior art, the method for preparing amorphous calcium carbonate by carbide slag leaching-mineralization provided by the present application has the following beneficial effects: Calcium carbide slag is a kind of industrial solid waste with high calcium component, which can be converted into ionic calcium solution in a short time by using ammonium chloride leaching.

[0015] Anhydrous ethanol can effectively inhibit the conversion of amorphous calcium carbonate to crystalline state without the help of synthetic additives by reducing the water content in the system. Secondly, magnesium-containing substances can extend the stability of amorphous calcium carbonate in both solution and solid phase, because magnesium ions are more resistant to dehydration than calcium ions, which means that magnesium ions are more difficult to lose their surrounding water molecules. This property can inhibit the removal of water molecules in the structure of amorphous calcium carbonate, which is conducive to maintaining the stability of amorphous calcium carbonate. In addition, Mg 2+ Amorphous calcium carbonate can also be inhibited from crystallizing by stabilizing the hydrogen bond network and affecting the local structure.

[0016] The present application has a simple process flow, easy operation and low cost in the leaching process. In the mineralization process, the sealing mineralization device is not required, and the production is easy. The whole reaction can be carried out at room temperature.

[0017] The product obtained by mineralization is nano-amorphous calcium carbonate with a particle size of 50-180 nm. It has a wide range of applications and can be converted into vaterite or calcite type calcium carbonate product according to the needs, BRIEF DESCRIPTION OF DRAWINGS

[0018] The drawings accompanying the specification are used to provide a further understanding of the application, and the illustrative embodiments thereof, and together with the description, make an explanation of the application. Among them: Figure 1 PSD (Particle size distribution) of the pretreated calcium carbide slag raw material used in the present application; Figure 2 XRD of the calcium carbonate prepared in the present application; Figure 3 SEM of the amorphous calcium carbonate prepared in the present application; Figure 4 TG-DSC of the amorphous calcium carbonate prepared in the present application; Figure 5 FT-IR of the amorphous calcium carbonate prepared in the present application. DETAILED DESCRIPTION

[0019] The embodiments described in the technical solutions of the embodiments of the present application are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0020] In the present application, a method for synthesizing high-value amorphous calcium carbonate by carbon sequestration of carbide slag. The calcium element in the raw material is leached with ammonium chloride solution as the leaching agent, and the obtained liquid phase is a calcium-containing solution. Then a certain volume ratio of anhydrous ethanol and magnesium chloride is added to the liquid phase, and the mixture is fully mixed. The pH of the mixture is adjusted to 13.5. CO2 is introduced for mineralization reaction, and the slurry obtained after the reaction is centrifuged. The sample is washed with anhydrous ethanol to remove impurities on the surface of the solid. The obtained solid is placed in a 40℃ oven for drying. The method realizes CO2 mineralization using carbide slag as raw material by indirect mineralization method and obtains amorphous calcium carbonate. At the same time, the study utilizes the morphological stability of anhydrous ethanol and magnesium chloride on amorphous calcium carbonate. Nanoscale amorphous calcium carbonate is prepared by mineralizing CO2 with carbide slag as calcium source. The present application has three advantages: 1. It absorbs and sequesters strong alkaline carbide slag solid waste resources; 2. It captures and fixes CO2 greenhouse gas; 3. It obtains high-value nanometer calcium carbonate product. It belongs to the field of solid waste resource utilization and is an innovative technology invention. Example 1

[0021] The present application provides a method for preparing mixed crystal calcium carbonate from carbide slag, which specifically comprises the following steps: Step one, carbide slag pretreatment: dry the carbide slag and ball mill to refine the particle size; In a specific embodiment of the present application, the carbide slag is dried at 105℃ for 3h to reduce the moisture and gas in the carbide slag. After ball milling, the particle size is measured by a laser particle size analyzer and is less than 510 μm.

[0022] Step two, leaching of active calcium: the ball-milled carbide slag is leached under the conditions of solid-liquid ratio of 1:50, ammonium chloride concentration of 0.5mol / L, leaching time of 35min, and stirring rate of 500rpm / min.

[0023] Step three, preparation of amorphous calcium carbonate: the calcium-containing solution obtained in step two is fully stirred with anhydrous ethanol at a volume ratio of 1:1, 0.04mol / L magnesium chloride solution is added to the mixture, and the mixture is fully stirred. A pH meter is inserted into the system, and the pH of the system is adjusted to 13.5 using NaOH, and the mixture is fully stirred. The CO2 flow rate is set to 100mL / min, and the stirring rate is set to 500rpm / min. The reaction stops when the pH decreases to 9.5. The product is washed by centrifugation and dried in a 40℃ oven for 24h to obtain a granular product.

[0024] The XRD of the nanometer CaCO3 obtained in this example is shown in (a) of Figure 2 Under the preparation conditions, the obtained calcium carbonate is a mixed crystal of vaterite and calcite, and no amorphous calcium carbonate appears. Example 2

[0025] The application provides a preparation method of amorphous calcium carbonate prepared from carbide slag. Step one, carbide slag pretreatment: the carbide slag needs to be pretreated, and the carbide slag is dried and ball milled to refine the particle size. In the specific embodiment of the application, the carbide slag is dried at 105 DEG C for 3h, so that the water content and gas content of the carbide slag are reduced. After ball milling, the particle size is less than 510 μm, which is measured by a laser particle size analyzer.

[0026] Step two, active calcium leaching: the carbide slag after ball milling is controlled at a solid-liquid ratio of 1:50, an ammonium chloride concentration of 0.5 mol / L, a leaching time of 35 min and a stirring rate of 500 rpm / min, and leaching experiments are carried out under the conditions.

[0027] Step three, preparation of amorphous calcium carbonate: the calcium-containing solution obtained in step two is fully stirred at a calcium solution to anhydrous ethanol volume ratio of 1:2, 0.04 mol / L magnesium chloride solution is added to the mixed solution, and stirring is carried out. A pH meter is inserted into the system, NaOH is used to adjust the pH of the system to 13.5, and sufficient stirring is carried out. The CO2 gas flow rate is set to 100 mL / min, and the stirring rate is set to 500 rpm / min, and the reaction is stopped when the pH is reduced to 9.5. The product is centrifuged and washed, and then dried in a 40 DEG C oven for 24h to obtain amorphous nano calcium carbonate with a particle size of 60-180 nm.

[0028] The XRD of the nano CaCO3 obtained in the embodiment is shown in (b) of FIG. 1, and the calcium carbonate obtained under the preparation conditions is a mixed crystal form of a small amount of vaterite and amorphous calcium carbonate. Figure 2 Example 3

[0029] The application provides a preparation method of amorphous calcium carbonate prepared from carbide slag. Step one, carbide slag pretreatment: the carbide slag needs to be pretreated, and the carbide slag is dried and ball milled to refine the particle size. In the specific embodiment of the application, the carbide slag is dried at 105 DEG C for 3h, so that the water content and gas content of the carbide slag are reduced. After ball milling, the particle size is less than 510 μm, which is measured by a laser particle size analyzer.

[0030] Step two, active calcium leaching: the carbide slag after ball milling is controlled at a solid-liquid ratio of 1:50, an ammonium chloride concentration of 0.5 mol / L, a leaching time of 35 min and a stirring rate of 500 rpm / min, and leaching experiments are carried out under the conditions.

[0031] ​Step three, preparation of amorphous calcium carbonate: the calcium-containing solution obtained in step two is fully stirred with anhydrous ethanol at a volume ratio of calcium solution to anhydrous ethanol of 1:3, 0.04 mol / L magnesium chloride solution is added to the mixed solution, and stirring is performed. A pH meter is inserted into the system, NaOH is used to adjust the pH of the system to 13.5, and full stirring is performed. The CO2 gas flow rate is set to 100 mL / min, the stirring rate is set to 500 rpm / min, and the reaction is stopped when the pH decreases to 9.5. The product is washed by centrifugation and dried in a 40℃ oven for 24h to obtain amorphous nano calcium carbonate with a particle size of 60-150nm.

[0032] The XRD of the nano CaCO3 obtained in this example is shown in (c) of FIG. 1. Figure 2 The calcium carbonate obtained under the preparation conditions is amorphous calcium carbonate. Embodiment

[0033] The method for preparing amorphous calcium carbonate from calcium carbide slag provided by the application comprises the following steps: Step one, pretreatment of calcium carbide slag: the calcium carbide slag needs to be pretreated, and the calcium carbide slag is dried and ball milled to refine the particle size. In a specific embodiment of the application, the calcium carbide slag is dried at 105℃ for 3h to reduce the water content and gas in the calcium carbide slag. After ball milling, the particle size is measured by a laser particle size analyzer and is less than 510 μm.

[0034] Step two, extraction of active calcium: the ball-milled calcium carbide slag is subjected to leaching under the following conditions: the concentration of ammonium chloride is 0.5 mol / L, the leaching time is 35 min, and the stirring rate is 500 rpm / min.

[0035] Step three, preparation of amorphous calcium carbonate: the calcium-containing solution obtained in step two is fully stirred with anhydrous ethanol at a volume ratio of calcium solution to anhydrous ethanol of 1:4, 0.04 mol / L magnesium chloride solution is added to the mixed solution, and stirring is performed. A pH meter is inserted into the system, NaOH is used to adjust the pH of the system to 13.5, and full stirring is performed. The CO2 gas flow rate is set to 100 mL / min, the stirring rate is set to 500 rpm / min, and the reaction is stopped when the pH decreases to 9.5. The product is washed by centrifugation and dried in a 40℃ oven for 24h to obtain amorphous nano calcium carbonate with a particle size of 60-150nm.

[0036] The XRD of the nano CaCO3 obtained in this example is shown in (d) of FIG. 1. Figure 2 The calcium carbonate obtained under the preparation conditions is amorphous calcium carbonate.

[0037] Figure 1The laser particle size analysis chart of calcium carbide slag used in the experimental research of the application is shown in the figure. The distribution of calcium carbide slag presents four distribution curves, with 3 µm, 17 µm, 100 µm and 290 µm as the center of the distribution form, accounting for 43.02 vol%, 8.64 vol%, 15.07 vol% and 23.11 vol%, respectively.

[0038] Figure 3 The SEM picture obtained in Example 2 shows that the particle size of amorphous nanometer calcium carbonate is in the range of 60-180 nm, and part of it presents agglomeration phenomenon due to the effect of surface tension.

[0039] Figure 4 The thermal gravimetric curve of amorphous nanometer calcium carbonate obtained in Example 2 shows that the product exists in an amorphous state below 346℃, contains about 10% moisture, and will keep the amorphous state well without losing water. Compared with the crystalline nanometer calcium carbonate product (decomposed at 825℃), the thermal decomposition temperature of the amorphous nanometer calcium carbonate product is significantly reduced. The decomposition is basically completed at 675-726℃.

[0040] Figure 5 The FT-IR spectrum of amorphous nanometer calcium carbonate in Example 2 shows that there are two absorption peaks belonging to amorphous nanometer calcium carbonate at 1079 cm -1 and 864 cm -1 Very obvious, combined with the XRD spectrum in (b) in Figure 2 , it is fully shown that the obtained sample belongs to amorphous nanometer calcium carbonate, non-crystalline calcium carbonate.

Claims

1. A method for synthesizing high-value amorphous calcium carbonate from carbide slag through carbon fixation, characterized in that, The method includes the following steps: (1) Extraction of calcium-containing solution: The calcium carbide slag aqueous solution is stirred and reacted with ammonium chloride solution, and then filtered to obtain calcium-containing extract; (2) Add anhydrous ethanol and magnesium chloride solution to the calcium-containing extract and mix thoroughly. (3) Adjust the pH of the mixed solution to 13.5; (4) Introduce CO2 gas into the pH-adjusted mixture to carry out the mineralization reaction until pH=9.5, then stop the reaction; (5) After the reaction is complete, the obtained calcium carbonate suspension is centrifuged to separate the liquid and solid components, washed, and then dried.

2. The method for synthesizing high-value amorphous calcium carbonate from carbide slag according to claim 1, characterized in that, The calcium carbide slag was dried at 105℃ for 3 hours, and the particle size of the calcium carbide slag after ball milling was less than 510μm; the reaction temperature was 25℃ and the leaching time was 35min.

3. The method for synthesizing high-value amorphous calcium carbonate from carbide slag according to claim 1, characterized in that, In step (1), the liquid-solid-liquid ratio in the carbide slag aqueous solution is 1:50, the stirring reaction rate is 500 rpm / min, and the concentration of the ammonium chloride solution is 0.5 mol / L.

4. The method for synthesizing high-value amorphous calcium carbonate from carbide slag according to claim 2, characterized in that, In step (2), the volume ratio of calcium-containing extract to anhydrous ethanol is 1:2-1:4, and the concentration of magnesium chloride solution is 0.04 mol / L.

5. The method for synthesizing high-value amorphous calcium carbonate from carbide slag according to claim 1, characterized in that, In step (3), the reagent used to adjust the pH of the mixed solution is NaOH.

6. The method for synthesizing high-value amorphous calcium carbonate from carbide slag according to claim 4, characterized in that, In step (4), the flow rate of CO2 gas is 100 mL / min.

7. The method for synthesizing high-value amorphous calcium carbonate from carbide slag according to claim 5, characterized in that, In step (5), the drying temperature is 40-60℃ and the drying time is 24h.

8. A method for synthesizing high-value amorphous calcium carbonate from carbide slag according to any one of claims 1-7, characterized in that, The entire reaction process was carried out at room temperature.

9. Amorphous calcium carbonate prepared by the method for synthesizing high-value amorphous calcium carbonate from carbide slag carbonation as described in any one of claims 1-8.

10. The amorphous calcium carbonate according to claim 9, characterized in that, The particle size range of the amorphous calcium carbonate is 50-180 nm.

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