A method for preparing high-purity basic magnesium carbonate from low-grade magnesite.

Abstract

This invention belongs to the field of environmental protection and resource recycling technology, specifically relating to a method for preparing high-purity basic magnesium carbonate from low-grade magnesite. The method includes the following steps: S1, crushing the low-grade magnesite and mixing it with an acid solution for acid leaching to obtain an acid leaching solution; S2, removing impurities from the acid leaching solution to obtain a refined solution; S3, absorbing the carbon dioxide gas released during the acid leaching step using an absorbent to obtain a carbon dioxide-loaded solution; S4, mixing the refined solution and the carbon dioxide-loaded solution for precipitation to obtain basic magnesium carbonate product and a protonated absorbent solution; S5, recovering the acid and regenerating the absorbent solution from the protonated absorbent solution using a bipolar membrane electrodialysis device. This invention utilizes the CO2-loaded solution as a precipitant to react with the Mg in the refined solution. 2+ The reaction produces basic magnesium carbonate. The reaction conditions are mild, and the crystal morphology and particle size are easy to control, thus obtaining a high-value-added product that meets market demands.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection and resource recycling technology, specifically relating to a method for preparing high-purity basic magnesium carbonate from low-grade magnesite. Background Technology

[0002] Basic magnesium carbonate, as an important inorganic compound, has wide applications in various fields such as rubber, building materials, pharmaceuticals, wastewater treatment, and waste gas treatment. With technological advancements and increasingly stringent environmental protection requirements, the demand for high-purity basic magnesium carbonate is growing daily. Magnesite, as one of the world's abundant magnesium resources, is also seeing continuous development in its mining and processing technologies. However, low-grade magnesite, due to its complex composition and high impurity content, presents numerous challenges for direct use in the preparation of high-purity basic magnesium carbonate.

[0003] Currently, the main methods for preparing basic magnesium carbonate include traditional processes such as dolomite carbonation, magnesite ammonium bicarbonate process, and magnesite powder-sulfuric acid-ammonium bicarbonate process. While these methods can achieve the preparation of basic magnesium carbonate to some extent, they suffer from problems such as high production costs, long process flows, large equipment requirements, complex procedures, difficulty in controlling product quality, and serious industrial waste pollution. These problems are particularly pronounced when using low-grade magnesite. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for preparing high-purity basic magnesium carbonate using low-grade magnesite. This method is carried out under mild conditions, does not emit carbon dioxide during the process, and also enables the recovery and recycling of auxiliary raw materials, thus saving costs.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for preparing high-purity basic magnesium carbonate from low-grade magnesite, comprising the following steps: S1. Acid leaching step: Low-grade magnesite is crushed and mixed with acid solution for acid leaching reaction. Solid-liquid separation is performed to obtain acid leaching solution and acid leaching residue. S2. Purification step: Remove impurities from the acid leaching solution to obtain a refined solution; S3, Carbon capture step: Use an absorbent to absorb the carbon dioxide gas released in the acid leaching step to obtain a carbon dioxide loaded liquid; S4. Precipitation step: The purified liquid is mixed with the carbon dioxide supported liquid to carry out a precipitation reaction, and the solid and liquid are separated to obtain basic magnesium carbonate product and protonated absorption liquid. S5. Regeneration step: The protonated absorbent is processed through a bipolar membrane electrodialysis device to obtain recovered acid and regenerated absorbent solution. The recovered acid is recycled for the acid leaching step, and the regenerated absorbent solution is recycled for the carbon capture step.

[0007] In the above technical solution, the magnesium oxide content in the low-grade magnesite is further 25%-35%.

[0008] In the above technical solution, the acid solution is one or more of hydrochloric acid, sulfuric acid, and acetic acid, and the concentration of the acid solution is 25wt%-40wt%; if the concentration of the acid solution is too high, impurities will be excessively leached, and if the concentration is too low, the leaching rate will be insufficient.

[0009] In the above technical solution, the specific steps of the impurity removal treatment are as follows: First, oxalic acid is added to the immersion solution, and the molar ratio of oxalic acid to calcium ions in the immersion solution is controlled to be 1:1-1.1:1, so as to ensure that calcium is completely precipitated while minimizing the introduction of new organic impurities by excessive oxalic acid. Then, hydrogen peroxide is added to oxidize ferrous ions in the solution to ferric ions. Subsequently, magnesium hydroxide is added to adjust the pH to 3.5-4.5. After solid-liquid separation, a purified solution is obtained.

[0010] In the above technical solution, the absorbent solution is further described as an aqueous solution of one or more organic amine absorbents and amino acid salt absorbents, and the concentration of the absorbent solution is 20wt%-30wt%; the organic amine absorbent includes monoethanolamine or diethanolamine, and the amino acid salt absorbent includes sodium glycine or potassium proline.

[0011] In the above technical solution, further, in the precipitation step, when the purified solution is mixed with the carbon dioxide-supported solution, the molar ratio of magnesium ions to carbonate ions is controlled to be 1:1.1-1:1.3, with a slight excess of carbonate ions to ensure that the Mg in the solution is in sufficient quantity. 2+ Complete precipitation increases magnesium yield, while excessive amounts can lead to increased solution alkalinity, promoting co-precipitation of more impurities and increasing the regeneration load of the absorbent. The reaction temperature is 50-70℃, and the reaction time is 1-2 hours.

[0012] Furthermore, in the above technical solution, the operating conditions of the bipolar membrane electrodialysis device are: voltage 30-35V, current density 50-60mA / cm². 2 .

[0013] The beneficial effects of this invention are as follows: 1. This invention utilizes a CO2-supported liquid as a precipitant to react with Mg in the purified liquid. 2+ The reaction produces basic magnesium carbonate. The reaction conditions are mild, and the crystal morphology and particle size are easy to control, thus obtaining high-value-added products that meet market demands. Moreover, it does not require calcination of magnesite or hydrothermal treatment, effectively reducing process energy consumption.

[0014] 2. This invention uses low-grade magnesite as raw material, which is abundant and low in cost, and solves the problem of mining rich magnesite and discarding poor magnesite that is common in the current magnesite mining process.

[0015] 3. The method of the present invention can utilize renewable energy for the regeneration of acids and bases, and the CO2 generated in the process is captured and reused, showing obvious low-carbon characteristics.

[0016] 4. The product obtained by this invention has high purity, wide range of uses, and good industrial application prospects. Attached Figure Description

[0017] Figure 1 This is a flowchart of the method for preparing high-purity basic magnesium carbonate using low-grade magnesite according to the present invention. Figure 2 The image shows the XRD pattern of basic magnesium carbonate prepared in Example 1. Figure 3 This is a SEM image of the basic magnesium carbonate prepared in Example 1. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments.

[0019] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0020] Example 1 This embodiment provides a method for preparing high-purity basic magnesium carbonate using low-grade magnesite, including the following steps: S1. Acid leaching step: Crush 500g of low-grade magnesite (MgO content 40%, CaO content 3%, Fe2O3 content 1.5%) to 100 mesh, add 2L of hydrochloric acid (concentration 30wt%), react at a stirring rate of 300r / min and a temperature of 60℃ for 6 hours, and filter to obtain an acid leaching solution and acid leaching residue containing magnesium ions. S2. Purification step: First, add oxalic acid to the acid leaching solution obtained in step S1, controlling the reaction between oxalic acid and Ca. 2+ The molar ratio was 1.05:1, and the mixture was stirred at a stirring rate of 200 r / min for 30 minutes to remove Ca. 2+ Add 50 ml of 5 wt% hydrogen peroxide and continue stirring for 30 minutes. Then add magnesium hydroxide powder to adjust the pH to between 3.5 and 4.5. Let it stand at room temperature for 2 hours, then filter to obtain the purified solution (testing showed that the purified solution contained Mg). 2+ (Concentration is 1.2 mol / L). S3, Carbon capture step: Use a 20wt% monoethanolamine (MEA) aqueous solution to absorb the CO2 gas released in the acid leaching step S1 until the pH of the absorbent drops to 8.0, to obtain a CO2-loaded solution; S4. Precipitation Step: Heat the purified solution to 50°C and slowly add the CO2 loading solution (according to n(Mg)). 2+ (n(CO2)=1:1.2), stirring rate 200r / min, reaction for 1 hour, white precipitate precipitates in the solution, continue to keep warm and stir for 30 minutes to convert the precipitate into basic magnesium carbonate, filter to obtain basic magnesium carbonate product and protonated absorption liquid; S5. Regeneration Step: The filtered protonated absorbent is introduced into a bipolar membrane electrodialysis device with three compartments, and the reaction is carried out at a voltage of 30V and a current density of 50mA / cm². 2 After 2 hours of treatment, hydrochloric acid (concentration of 25 wt%) is recovered in the acid chamber, and MEA solution (concentration of 18 wt%) is recovered and regenerated in the alkali chamber. These solutions are then recycled to the acid leaching and carbon capture steps, respectively.

[0021] The XRD test results of the product obtained in Example 1 are as follows: Figure 2 As shown, the product is confirmed to be basic magnesium carbonate, and the absence of impurity peaks indicates its high purity. The SEM image of the basic magnesium carbonate obtained in Example 1 is shown below. Figure 3 As shown, this method successfully prepared petal-shaped basic magnesium carbonate powder, which consists of lamellae with a particle size of 5-10 μm.

[0022] The Ca of basic magnesium carbonate obtained in Example 1 2+ Fe 3+ The content was tested, and the IPC test result was: Ca 2+ <0.05%, Fe 3+ <0.03%.

[0023] Example 2 This embodiment provides a method for preparing high-purity basic magnesium carbonate using low-grade magnesite, including the following steps: S1. Acid leaching step: Crush 800g of low-grade magnesite (MgO content 38%, CaO content 4%, Fe2O3 content 2%) to 150 mesh, add 3L of sulfuric acid (concentration 25wt%), react for 7 hours at a stirring rate of 350r / min and a temperature of 55℃, and filter to obtain an acid leaching solution and acid leaching residue containing magnesium ions. S2. Purification step: First, add oxalic acid to the acid leaching solution obtained in step S1, controlling the reaction between oxalic acid and Ca. 2+ The molar ratio was 1.1:1, and the mixture was stirred at a stirring rate of 200 r / min for 40 minutes to remove Ca. 2+Add 50 ml of 5 wt% hydrogen peroxide and continue stirring for 30 minutes. Then add magnesium hydroxide powder to adjust the pH to between 3.5 and 4.5. Let it stand at room temperature for 1 hour, then filter to obtain the purified solution (testing showed that the purified solution contained Mg). 2+ (Concentration is 1.0 mol / L). S3, Carbon capture step: Use a mixed aqueous solution of diethanolamine (DEA) and sodium glycine (NaGly) (DEA:NaGly molar ratio of 1:1, total concentration of 25wt%) to absorb the CO2 gas released in step S1 acid leaching until the pH of the absorbent drops to 8.0, to obtain a CO2 loaded solution; S4. Precipitation Step: Heat the purified solution to 60℃ and slowly add the CO2 loading solution (according to n(Mg)). 2+ (n(CO2)=1:1.3), stirring rate 250r / min, reaction time 1.5 hours, to convert the precipitate into basic magnesium carbonate, and after filtration, basic magnesium carbonate product and protonated absorption liquid are obtained; S5. Regeneration Step: The filtered protonated absorbent is introduced into a bipolar membrane electrodialysis device with three compartments, and the reaction is carried out at a voltage of 35V and a current density of 60mA / cm². 2 After 2 hours of treatment, sulfuric acid (concentration of 20 wt%) was recovered in the acid chamber, and DEA-NaGly solution (concentration of 22 wt%) was recovered and regenerated in the alkali chamber. These solutions were then recycled to the acid leaching and carbon capture steps, respectively.

[0024] The Ca of basic magnesium carbonate obtained in Example 2 2+ Fe 3+ The content was tested, and the IPC test result was: Ca 2+ <0.03%, Fe 3+ <0.02%.

[0025] Example 3 This embodiment provides a method for preparing high-purity basic magnesium carbonate using low-grade magnesite, including the following steps: Amino acid salt absorption system using acetic acid as the acid extractant S1. Acid leaching step: Crush 1000g of low-grade magnesite (MgO content 35%, CaO content 2.5%, Fel2O3 content 2%) to 80 mesh, add 4L of acetic acid (concentration 40wt%), react for 5 hours at a stirring rate of 250r / min and a temperature of 70℃, and filter to obtain an acid leaching solution and acid leaching residue containing magnesium ions. S2. Purification step: First, add oxalic acid to the acid leaching solution obtained in step S1, controlling the reaction between oxalic acid and Ca. 2+ The molar ratio was 1:1, and the mixture was stirred at a stirring rate of 250 r / min for 20 minutes to remove Ca. 2+Add 50 ml of 5 wt% hydrogen peroxide and continue stirring for 30 minutes. Then add magnesium hydroxide powder to adjust the pH to between 3.5 and 4.5. Let it stand at room temperature for 3 hours, then filter to obtain the purified solution (testing showed that the purified solution contained Mg). 2+ (Concentration is 0.8 mol / L). S3, Carbon capture step: Use potassium proline (KPro) aqueous solution (concentration 30wt%) to absorb the CO2 gas released in step S1 acid leaching step until the pH of the absorbent drops to 6.5, to obtain CO2 loaded solution; S4. Precipitation Step: Heat the purified solution to 70°C and slowly add the CO2 loading solution (according to n(Mg)). 2+ (n(CO2)=1:1.1), stirring rate 150r / min, reaction time 2 hours, to convert the precipitate into basic magnesium carbonate, filter to obtain basic magnesium carbonate product and protonated absorption liquid; S5. Regeneration Step: The filtered protonated absorbent is introduced into a bipolar membrane electrodialysis device with three compartments, and the reaction is carried out at a voltage of 35V and a current density of 60mA / cm². 2 After 3 hours of treatment, sulfuric acid (concentration of 35 wt%) was recovered in the acid chamber, and DEA-NaGly solution (concentration of 28 wt%) was recovered and regenerated in the alkali chamber. These solutions were then recycled to the acid leaching and carbon capture steps, respectively.

[0026] The Ca of basic magnesium carbonate obtained in Example 3 2+ Fe 3+ The content was tested, and the IPC test result was: Ca 2+ <0.03%, Fe 3+ <0.05%.

[0027] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A method for preparing high-purity basic magnesium carbonate from low-grade magnesite, characterized in that, Includes the following steps: S1. Acid leaching step: Low-grade magnesite is crushed and mixed with acid solution for acid leaching reaction. Solid-liquid separation is performed to obtain acid leaching solution and acid leaching residue. S2. Purification step: Remove impurities from the acid leaching solution to obtain a refined solution; S3, Carbon capture step: Use an absorbent to absorb the carbon dioxide gas released in the acid leaching step to obtain a carbon dioxide loaded liquid; S4. Precipitation step: The purified liquid is mixed with the carbon dioxide supported liquid to carry out a precipitation reaction, and the solid and liquid are separated to obtain basic magnesium carbonate product and protonated absorption liquid. S5. Regeneration step: The protonated absorbent is processed through a bipolar membrane electrodialysis device to obtain recovered acid and regenerated absorbent solution. The recovered acid is recycled for the acid leaching step, and the regenerated absorbent solution is recycled for the carbon capture step.

2. The method according to claim 1, characterized in that, The low-grade magnesite contains 25%-35% magnesium oxide.

3. The method according to claim 1, characterized in that, The acid solution is one or more of hydrochloric acid, sulfuric acid, and acetic acid, and the concentration of the acid solution is 25wt%-40wt%.

4. The method according to claim 1, characterized in that, The specific steps of the impurity removal process are as follows: First, oxalic acid is added to the immersion solution, and the molar ratio of oxalic acid to calcium ions in the immersion solution is controlled to be 1:1-1.1:

1. Then, hydrogen peroxide is added to oxidize ferrous ions in the solution to ferric ions. Subsequently, magnesium hydroxide is added to adjust the pH to 3.5-4.

5. After solid-liquid separation, a purified solution is obtained.

5. The method according to claim 1, characterized in that, The absorbent solution is an aqueous solution of one or more organic amine absorbents or amino acid salt absorbents, and the concentration of the absorbent solution is 20wt%-30wt%.

6. The method according to claim 5, characterized in that, The organic amine absorbent includes monoethanolamine or diethanolamine, and the amino acid salt absorbent includes sodium glycine or potassium proline.

7. The method according to claim 1, characterized in that, In the precipitation step, when the purified liquid is mixed with the carbon dioxide-supported liquid, the molar ratio of magnesium ions to carbonate ions is controlled to be 1:1.1-1:1.3, the reaction temperature is 50-70℃, and the reaction time is 1-2 hours.

8. The method according to claim 1, characterized in that, The operating conditions for the bipolar membrane electrodialysis device are: voltage 30-35V, current density 50-60mA / cm². 2 .

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