A method for preparing nano-calcium carbonate

Abstract

This invention provides a method for preparing nano-calcium carbonate, comprising the following cyclical processes: (1) pretreatment of dry carbide slag raw materials; (2) leaching Ca from the dry carbide slag with ammonium chloride solution. 2+ And perform solid-liquid separation to obtain a high-purity calcium chloride solution and ammonia. (3) Use the ammonia in (2) to absorb low-concentration CO2 flue gas to obtain a mixed solution of ammonium carbonate and ammonium bicarbonate; (4) Mix the mixed solution of ammonium carbonate and ammonium bicarbonate obtained in (3) with the calcium chloride solution obtained in (2) to obtain calcium carbonate precipitate and ammonium chloride solution; (5) Use the ammonium chloride solution obtained in (4) to evaporate and concentrate, and return to step (2) to complete the entire cycle process. This method uses the escaped ammonia produced by the traditional ammonium chloride leaching CO2 to dry carbide slag to absorb flue gas to prepare ammonium carbonate and ammonium bicarbonate. It not only achieves efficient conversion of low-concentration flue gas CO2, significantly reduces conversion costs, and improves economic feasibility, but also uses the high-concentration ammonium carbonate of the conversion product to produce nano-CaCO3, which has significant environmental and economic benefits.

Description

Technical Field

[0001] This invention relates to the fields of waste utilization and carbon emission reduction, and specifically to a method for preparing nano-calcium carbonate. Background Technology

[0002] Dry calcium carbide slag is a typical byproduct of industrial production processes. It is the core solid waste from the hydrolysis of calcium carbide to produce acetylene (reaction formula: (CaC2 + 2H2O → C2H2↑ + Ca(OH)2). Its main component is Ca(OH)2, containing small amounts of CaCO2, aluminosilicates, and moisture. Traditional disposal methods present problems such as land occupation, alkaline pollution, and resource waste. Flue gas CO2 originates from industrial processes involving fossil fuels or carbon-containing raw materials and is a core greenhouse gas contributing to global climate change.

[0003] Therefore, achieving the synergistic recovery and comprehensive utilization of dry carbide slag and flue gas CO2 has become a key path to achieving the triple goals of "solid waste resource utilization + high value-added products + carbon emission reduction". There are many reports on the preparation of calcium carbonate from dry carbide slag, which can be mainly divided into calcination and leaching methods. The principle of the calcination method is to calcine the dry carbide slag at high temperature to obtain quicklime, and then pass CO2 or other carbonizing agents through it to obtain calcium carbonate. The leaching method for preparing calcium carbonate usually includes two stages: the leaching stage and the carbonation stage. In the leaching stage, calcium ions are leached out using a leaching agent, and in the carbonation stage, calcium carbonate is obtained using a carbonizing agent. Common leaching agents include dilute hydrochloric acid and ammonium chloride. For example, CN101264920B discloses a method for preparing fine and ultrafine calcium carbonate of different crystal forms from dry carbide slag. This method obtains a calcium chloride solution by adding hydrochloric acid dropwise, and then produces calcium carbonate precipitate by adding sodium carbonate solution dropwise in the presence of an activator. Although the process is simple, it continuously consumes hydrochloric acid and sodium carbonate, and generates sodium chloride waste liquid, making it unsuitable for large-scale production from a resource utilization and environmental perspective. There are many patents using ammonium chloride to leach calcium carbonate from dry carbide slag, such as CN116119701A (a method for preparing nano-calcium carbonate from dry carbide slag) and CN119841341A (a method for preparing nano-calcium carbonate from blast furnace slag through resource utilization). These patents often use ammonium chloride as the leaching agent to extract calcium ions from the dry carbide slag. During the reaction, ammonium chloride easily generates ammonia water with a pungent odor, posing a risk of ammonia escape and affecting the recycling and reuse of ammonium chloride, thus impacting the environmental friendliness and operational safety of the process. All of the above patents focus on how to efficiently leach calcium carbonate. 2+ However, the problem of ammonia escape was overlooked.

[0004] Based on this, developing a green preparation process that enables the recycling of ammonium chloride, efficient conversion of low-concentration flue gas CO2, and avoids ammonia escape is of great significance for promoting the resource utilization of dry carbide slag and industrial carbon emission reduction. Summary of the Invention

[0005] To address the existing problem of ammonia escape, the present invention aims to provide a method for preparing nano-calcium carbonate.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing nano-calcium carbonate, the method comprising the following steps: (1) Pretreatment of dry carbide slag: The dry carbide slag obtained after dehydration in industrial production is subjected to wet hydrolysis to remove a small amount of unreacted carbide.

[0007] Preferably, in step (1), the dry carbide slag is placed in a sealed reactor, and warm water (40-60°C) is added in proportion and stirred to ensure complete hydrolysis of the residue. The acetylene gas produced by the reaction is collected and can be reused as fuel or chemical raw material.

[0008] (2) Ca in dry carbide slag 2+ Leaching: The pretreated carbide slag hydrolysis slurry and excess ammonium chloride solution are placed in a reaction vessel and stirred. During the process, the temperature of the reaction vessel is increased to decompose the ammonia water. After the reaction is completed, the solid and liquid are separated to obtain a filtrate containing calcium chloride and ammonium chloride and an insoluble filter residue.

[0009] Preferably, in step (2), a certain amount of ammonium chloride is weighed and dissolved in distilled water, and then added to the carbide slag hydrolysis slurry, with the dry carbide slag:ammonium chloride:water ratio being 5:6:35. The Ca leaching process is then carried out. 2+ The equipment used is a stirred reactor with a heating jacket, with a leaching temperature of 25-40℃ and a stirring speed of 300 rpm. The leaching time is 30-40 minutes, and the pH of the solution is controlled at 7-9 during the leaching process to prevent impurities such as iron and aluminum ions from the dry carbide slag from entering the filtrate. Solid-liquid separation after leaching is performed using a plate and frame filter press.

[0010] (3) Using low-concentration flue gas CO2 and ammonia to prepare a mixed solution of ammonium carbonate and ammonium bicarbonate: The ammonia obtained from the leaching of dry carbide slag in (2) and the flue gas CO2 were respectively passed into the absorption tower to prepare a mixed solution of ammonium carbonate and ammonium bicarbonate.

[0011] Preferably, the equipment selected in step (3) for generating ammonia water and ammonium carbonate is a counter-current spray tower. The ammonia gas escaped from the leaching of dry carbide slag enters from the bottom of the spray tower and comes into counter-current contact with deionized water to generate ammonia water. Low-concentration flue gas CO2 enters from the bottom of the counter-current spray tower and comes into counter-current contact with the ammonia water for absorption. During the absorption process, the pH of the absorption liquid needs to be controlled at 8-11, the molar ratio of ammonia gas to CO2 is 1.5-2:1, and the spray density is set to 5-20 L / m³. 3 The gas velocity in the empty tower is 0.5 to 2 m / s. The ammonia gas obtained from the leaching of dry carbide slag in (2) is transported to the spray tower using an ammonia compressor.

[0012] In step (3), the exhaust gas containing unabsorbed ammonia and carbon dioxide from the top of the spray tower also needs to be treated by first absorbing with water, then absorbing with acid, and finally venting. The low-concentration ammonium chloride solution obtained after acid absorption can also be recycled.

[0013] (4) Nano calcium carbonate prepared by reacting calcium chloride with ammonium carbonate: The ammonium carbonate solution obtained above and the calcium chloride solution obtained after filtration in (2) are placed in a reaction vessel for stirring and reaction. After solid-liquid separation, a white precipitate and ammonium chloride solution are obtained. Nano calcium carbonate is obtained by drying.

[0014] Preferably, in step (4), the high-concentration ammonium carbonate solution prepared in (3) and the calcium chloride solution obtained after filtration in (2) are mixed and stirred in a 1:1 ratio in a stirred reactor. The reaction temperature is controlled at 20-30°C, the stirring rate is 600-1000 rpm, and the residence time is 2-20 min. After the reaction is completed, the solution is pumped into a filter press by a diaphragm pump for solid-liquid separation.

[0015] (5) The ammonium chloride solution obtained above is concentrated and returned to step (2) to complete the entire recycling process of ammonium chloride.

[0016] The process route and method provided by this invention have the following advantages compared with the prior art: (1) The present invention uses ammonium chloride as a leaching agent, which can not only efficiently leach calcium ions but also adjust the pH value of the system, which is helpful for subsequent processing. The ammonium chloride solution after separating calcium carbonate can be recycled.

[0017] (2) In the present invention, the low-concentration flue gas CO2 reacts with ammonia water to prepare a mixed solution of ammonium carbonate and ammonium bicarbonate, which prevents ammonia escape caused by carbonation or leaching in general methods. This not only achieves efficient conversion of low-concentration flue gas CO2, but also the mixed solution of ammonium carbonate and ammonium bicarbonate of the conversion product is used to produce nano-CaCO3, which has significant environmental and economic benefits.

[0018] (3) The nano-calcium carbonate in this invention is prepared by the liquid-liquid reaction of ammonium carbonate and calcium chloride. Compared with the gas-liquid reaction of the common carbonation method, the reaction conditions are relatively mild and easy to control, and the reaction rate is faster. Ammonium carbonate and calcium chloride can fully react the calcium ions and carbonate ions in the solution to generate calcium carbonate precipitate. The reaction is more thorough and the purity is higher.

[0019] (4) The preparation method described in this invention can prepare nano-CaCO3 in a green, efficient, batch and low-cost manner. The equipment covered are all industrial applications, including storage tanks, diaphragm pumps, filter presses, reaction kettles, spray towers, etc. The preparation method described in this invention has the characteristics of low toxicity and recyclability, which can greatly promote the development of resource utilization of solid waste in dry carbide slag industry and CO2 gas capture and utilization. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of a method for preparing nano-calcium carbonate according to the present invention; Detailed Implementation

[0021] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to specific implementation methods.

[0022] All the raw materials, instruments, and equipment used in this invention can be purchased from the market or prepared by existing methods. Example

[0023] A method for preparing nano-calcium carbonate using dry carbide slag includes the following steps: (1) Pretreatment of dry carbide slag: The dry carbide slag needs to be placed in a closed reactor, and warm water (40-60°C) is added in proportion. The mixture is stirred to ensure that the residue is fully hydrolyzed. The acetylene gas produced by the reaction can be collected and reused as fuel or chemical raw material.

[0024] (2) Ca in dry carbide slag 2+ Leaching: 100 kg of dry calcium carbide slag raw material and 2.8 mol / L ammonium chloride solution were added to a reaction vessel to leach Ca. 2+ The equipment used was a stirred reactor with a heating jacket, with a leaching temperature of 40℃ and a stirring speed of 300 rpm. The leaching time was 40 minutes, and the solution pH was controlled at 9 during the leaching process. Under these conditions, the Ca content in the dry carbide slag was... 2+ The leaching rate was 81.72%. During the leaching process, ammonia water can be completely decomposed into ammonia gas at 40℃. After the leaching is completed, solid-liquid separation is performed using a plate and frame filter press to obtain a calcium chloride solution with high purity.

[0025] (3) Preparation of a mixed solution of ammonium carbonate and ammonium bicarbonate from low-concentration flue gas CO2 and ammonia: The ammonia generated in the reactor is compressed by an ammonia compressor and pumped from the bottom into a countercurrent spray tower to obtain 10-14% ammonia water. The ammonia water enters from the top of the second spray tower, and then flue gas CO2 is introduced from the bottom. During the absorption process, the pH of the absorbent needs to be controlled at 8, the molar ratio of ammonia to CO2 is 1.5, and the spray density is set to 10 L / m³. 3The empty tower gas velocity is 1 m / s. The absorption rate of low-concentration CO2 in flue gas can reach 85%.

[0026] (4) Preparation of nano-calcium carbonate: The prepared ammonium carbonate and ammonium bicarbonate mixed solution and the calcium chloride solution obtained after leaching were mixed and stirred in a stirred reactor at a ratio of 1:1. The reaction temperature was 20℃, the stirring speed was 600 rpm, and the stirring time was 15 min. After the reaction was completed, the mixture was pumped into a filter press for solid-liquid separation by a diaphragm pump. After drying, nano-calcium carbonate of different phases was obtained.

[0027] (5) The ammonium chloride solution is concentrated and returned to the leaching step to complete the entire recycling process of ammonium chloride.

[0028] Table 1 Results data for Example 1

[0029] Depend on Figure 1 The results in Table 1 demonstrate that the process flow and operating details provided by this invention are feasible.

[0030] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0031] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing nano-calcium carbonate, characterized by comprising the following steps: (1) Pretreatment of dry carbide slag raw materials; (2) Extracting Ca from dry carbide slag by leaching with ammonium chloride solution 2+ Solid-liquid separation was performed to obtain a high-purity calcium chloride solution and ammonia gas; (3) The ammonia gas obtained in (2) is used to absorb low-concentration CO2 flue gas to obtain a mixed solution of ammonium carbonate and ammonium bicarbonate; (4) The high-concentration ammonium carbonate solution obtained in (3) is mixed with the calcium chloride solution obtained in (2) to react and obtain calcium carbonate precipitate and ammonium chloride solution; (5) The ammonium chloride solution obtained in (4) is concentrated and returned to step (2) to complete the entire cycle.

2. The method for preparing nano-calcium carbonate according to claim 1, characterized in that... In step (2), the ratio of dry carbide slag: ammonium chloride: water consumption is 5:6:

35.

3. The method for preparing nano-calcium carbonate according to claim 1, characterized in that... In step (2), the pH of the solution is controlled to be 7-9 during the leaching process to prevent impurity ions such as iron and aluminum in the dry carbide slag from entering the filtrate.

4. The method for preparing nano-calcium carbonate according to claim 1, characterized in that... In step (2), Ca is leached. 2+ The equipment used is a stirred reactor with a heating jacket, with a leaching temperature of 25-40℃, a stirring speed of 300rpm, and a leaching time of 30-40min, ensuring that all ammonia water is converted into ammonia gas during the leaching process.

5. The method for preparing nano-calcium carbonate according to claim 1, characterized in that... In step (3), the equipment is a counter-current spray tower. During the absorption process, the pH of the absorbent needs to be controlled at 8-11, the molar ratio of ammonia to CO2 is 1.5-2:1, and the spray density is set to 5-20 L / m³. 3 The air velocity in the empty tower is 0.5–2 m / s.

6. The method for preparing nano-calcium carbonate according to claim 1, characterized in that... In step (4), a 1:1 mixing and stirring reaction is carried out in a stirred reactor.

7. The method for preparing nano-calcium carbonate according to claim 1, characterized in that... In step (4), the reaction temperature is controlled at 20-30℃, the stirring rate is 600-1000rpm, and the residence time is 2-20min.

8. The method for preparing nano-calcium carbonate according to claim 1, characterized in that... In step (5), the ammonium chloride solution is concentrated and returned to the leaching stage for recycling.

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