A method for preparing light magnesium carbonate and magnesium oxide nanoflower by using magnesium-containing limestone

Abstract

This invention belongs to the field of mineral resource recycling, specifically relating to a method for preparing lightweight magnesium carbonate using magnesium-containing limestone, wherein the magnesium-containing limestone is reacted with formula 1 ( Additive A with a specific structure is mixed and calcined at 1100-1400℃ to obtain a modified material. The modified material and additive B are pre-modified mechanically, then digested and carbonated, followed by solid-liquid separation to obtain a calcium-rich solid and a magnesium-rich solution. Additive B is at least one of polyacrylic acid, sodium polyacrylate, ammonium polyphosphate, and polypropylene glycol. The pH of the system at the end of the carbonation treatment is 6-7. The magnesium-rich solution and additive C are mixed and subjected to thermal conversion precipitation treatment, followed by solid-liquid separation to obtain light magnesium carbonate powder. Additive C is at least one of sodium alginate and ammonium carbonate. This invention can achieve selective separation of magnesium and calcium in magnesium-containing limestone and can resourcefully produce magnesium oxide nanoflowers with high organic matter degradation activity.

Description

A method for preparing lightweight magnesium carbonate and magnesium oxide nanoflowers using magnesium-containing limestone. Technical Field

[0001] This invention belongs to the field of mineral resource processing, specifically relating to the preparation of magnesium carbonate and magnesium oxide. Background Technology

[0002] Magnesium-bearing limestone is a natural mineral containing magnesium, such as the more common dolomite. Its main component is magnesium calcium carbonate, and it also contains small amounts of impurities such as iron and aluminum.

[0003] In industrial applications, magnesium-containing limestone is the main raw material for the preparation of magnesium carbonate and magnesium oxide. The main challenge in producing magnesium products using magnesium-containing limestone lies in achieving efficient separation of magnesium and calcium. Existing methods for calcium-magnesium separation include a series of processes such as heat treatment, digestion, and carbonation.

[0004] For example, patent document CN119490217A discloses a method for separating calcium and magnesium components of calcined dolomite based on carbon dioxide; calcined dolomite is digested with water to obtain a calcined dolomite suspension; carbon dioxide-containing raw material gas is bubbled under preset conditions to obtain fine raw material bubbles; the fine raw material bubbles and the calcined dolomite suspension are carbonized to obtain a mixed suspension; and the mixed suspension is solid-liquid separated to obtain calcium carbonate and magnesium-containing liquid phases, respectively. For example, patent document CN119390104A discloses a method for calcining dolomite, a carbonization method, a calcium-magnesium separation method, and a comprehensive utilization method; calcining dolomite powder yields calcined white powder; the calcined white powder is then subjected to digestion and aging treatments to obtain an aging liquid; the aging liquid is then carbonized to obtain a carbonization reaction liquid; the carbonization reaction liquid is subjected to solid-liquid separation to obtain heavy magnesium water and a first solid separate; the heavy magnesium water is then pyrolyzed to obtain a pyrolysis reaction liquid; the pyrolysis reaction liquid is then subjected to solid-liquid separation to obtain a decomposition liquid and a second solid separate; the second solid separate is then calcined with magnesium carbonate to obtain magnesium oxide; the magnesium oxide is then reduced to obtain metallic magnesium and magnesium aluminum spinel. For example, patent document CN118598172A discloses a method for processing dolomite, which involves subjecting dolomite raw material to a first calcination treatment at 790~810℃ to obtain calcined dolomite; preparing an emulsion by mixing the calcined dolomite with water; introducing carbon dioxide into the emulsion to obtain a carbonized liquid; and filtering the carbonized liquid to obtain refined heavy magnesium water.

[0005] In summary, although calcination-digestion-carbonation treatment of magnesium-containing limestone can effectively separate magnesium and calcium, facilitating the production of magnesium oxide and magnesium carbonate products, the selectivity of magnesium-calcium separation using existing methods still needs improvement, and the phase and structural quality of the prepared magnesium oxide and magnesium carbonate products require further optimization. Furthermore, lightweight magnesium carbonate produced by traditional methods is mostly amorphous powder or simple whisker-like particles with limited specific surface area, porosity, and structural strength, resulting in poor dispersibility and unsatisfactory reinforcing effects in composite materials. Moreover, the morphology of conventional lightweight magnesium carbonate particles is insufficient to meet the specific requirements of high-end applications (such as high-efficiency adsorption, catalyst supports, and special ceramics) for material microstructure, leading to insufficient functionalization. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for preparing lightweight magnesium carbonate using magnesium-containing limestone, aiming to obtain lightweight magnesium carbonate with high specific surface area, high porosity, and good dispersibility.

[0007] The second objective of this invention is to provide a method for preparing magnesium oxide nanoflowers using magnesium-containing limestone, with the aim of obtaining flower-shaped magnesium oxide nanoflowers with excellent application activity.

[0008] A method for preparing light magnesium carbonate using magnesium-containing limestone, comprising the following steps:

[0009] Step 1:

[0010] Magnesium-containing limestone was mixed with additive A of Formula 1 and calcined at a temperature of 1100~1400℃ to obtain modified material;

[0011] Formula 1;

[0012] In Equation 1, R1 is C6~C 20 Saturated carbon chains or partially unsaturated carbon chains; M is H, Na, K or NH4;

[0013] Step 2:

[0014] The modified material and additive B were mechanically modified in advance, and then digested and carbonized in sequence, followed by solid-liquid separation to obtain calcium-rich solid and magnesium-rich solution.

[0015] Additive B is at least one of polyacrylic acid, sodium polyacrylate, ammonium polyphosphate, and polypropylene glycol;

[0016] The pH of the system at the end of the carbonation treatment is 6-7;

[0017] Step 3:

[0018] A magnesium-rich solution and additive C were mixed and subjected to thermal conversion precipitation treatment, followed by solid-liquid separation to obtain light magnesium carbonate powder.

[0019] Additive C is at least one of sodium alginate and ammonium carbonate.

[0020] This invention innovatively modifies magnesium-containing limestone by high-temperature calcination with additive A of Formula 1, which helps to optimize the phase and surface structure of the modified material. The modified material is further mechanically modified with additive B and then subjected to digestion-carbonation treatment, which facilitates the selective separation of calcium and magnesium. The resulting magnesium-containing solution is then thermally converted with additive C, thus obtaining high-quality light magnesium carbonate. In addition, the light magnesium carbonate can be calcined and decarbonized to regenerate magnesium oxide nanoflowers with high activity, such as high organic degradation activity.

[0021] In this invention, in Equation 1, R1 is C 12 ~C 18 A saturated carbon chain or a carbon chain containing 1 to 2 unsaturated double bonds;

[0022] Preferably, Formula 1 includes at least one of Formula 1A and Formula 1B;

[0023] Formula 1A;

[0024] Formula 1B.

[0025] In this invention, the weight ratio of magnesium-containing limestone to additive A is 100:1~8; considering processing efficiency and cost, it can be further 100:1~5; it can be further 100:1.5~2.5.

[0026] Preferably, the atmosphere for calcination modification is an oxygen-containing atmosphere; for example, considering processing costs, it can be further used as air.

[0027] In this invention, the calcination temperature can be further set to 1150~1350℃.

[0028] Preferably, the calcination modification time is 2-10 h, further can be 4-8 h, and even further can be 5-6 h.

[0029] In this invention, additive B can further be polyacrylic acid and polypropylene glycol in a weight ratio of 1:0.5~2. Research in this invention shows that the preferred additive B can further optimize the selectivity of calcium-magnesium separation, improve the physicochemical structure of the final magnesium oxide, and enhance the photocatalytic degradation effect of organic matter.

[0030] Preferably, in step 2, the weight ratio of the modified material to additive B is 100:0.01~0.5; more preferably, it can be 100:0.25~0.45.

[0031] Preferably, the mechanical modification method is dry ball milling or wet ball milling.

[0032] In this invention, the rotational speed for mechanical modification can be 200~600 rpm.

[0033] In this invention, the ball-to-material ratio (ball-to-material weight ratio) of mechanical modification can be adjusted as needed, for example, it can be 10~30:1.

[0034] Preferably, the mechanical modification time is 2 to 10 hours; more preferably, it can be 3 to 6 hours.

[0035] The liquid-to-solid ratio of water and modified material added during digestion is 100:10~30;

[0036] Preferably, the temperature of the digestion process is below 100°C, more preferably 0~80°C; even more preferably 5~80°C.

[0037] Preferably, the digestion process takes more than 1 hour.

[0038] Preferably, the digestion process includes three stages, wherein the temperature of the first stage of digestion is 0~30℃ (more preferably 5~15℃); the temperature of the second stage of digestion is 60~80℃; and the third stage of digestion is carried out under ultrasound assistance at a temperature of 60~80℃.

[0039] In this invention, the first stage of digestion takes 0.5 to 1.5 hours. The second stage of digestion takes 0.5 to 1.5 hours. The third stage of digestion takes 10 to 40 minutes.

[0040] Preferably, a carbon dioxide-containing atmosphere is introduced into the digestion system for carbonation treatment; the introduction rate is controlled within the range of 0.1 to 0.5 vvm (the ratio of air volume to slurry volume per minute). Preferably, the introduction rate is 0.2 to 0.4 vvm.

[0041] Preferably, the carbonation process includes a process of pre-introducing a carbon dioxide-containing atmosphere into the digestion system for low-temperature carbonation, a process of solid-liquid separation of the low-temperature carbonation process to obtain a low-temperature carbonation solution, and a process of introducing a carbon dioxide-containing atmosphere into the low-temperature carbonation solution for high-temperature carbonation.

[0042] Preferably, the temperature of the low-temperature carbonation process is 0~20℃ (more preferably 5~15℃); the temperature of the high-temperature carbonation process is 40~80℃ (more preferably 45~60℃).

[0043] In this invention, the low-temperature carbonation time can be 0.5~2h.

[0044] In this invention, the final pH of the carbonation treatment can be 6.3 to 6.8.

[0045] In this invention, additive C can be sodium alginate and ammonium carbonate in a weight ratio of 1:0.5~2. Studies have shown that the preferred additive C helps to further optimize the physicochemical structure and morphology of the precipitate, facilitates its physicochemical modification, and helps to obtain magnesium oxide nanoflower materials with excellent activity.

[0046] Preferably, in step 3, the amount of additive C added is 0.005~0.2 mg / L; more preferably, it can be 0.05~0.15 mg / L.

[0047] Preferably, the temperature of the thermal transformation precipitation process is 70~100℃, and more preferably 80~90℃.

[0048] This invention also provides a method for preparing magnesium oxide nanoflowers using magnesium-containing limestone. The magnesium-containing limestone is processed using the method described in this invention to prepare light magnesium carbonate, and the magnesium carbonate is pyrolyzed to obtain magnesium oxide nanoflowers.

[0049] The present invention demonstrates that the magnesium oxide nanoflowers obtained by this process have a physicochemical structure adapted to the degradation of organic matter, and can unexpectedly improve the degradation ability of organic matter.

[0050] In this invention, the pyrolysis temperature is 400~550℃;

[0051] Preferably, the pyrolysis time is 2-6 hours;

[0052] Preferably, the pyrolysis process is carried out under negative pressure.

[0053] There are no special requirements for the negative pressure; for example, it can be below 0.5 atm (atm refers to standard atmospheric pressure).

[0054] Beneficial effects

[0055] This invention innovatively modifies magnesium-containing limestone by high-temperature calcination with additive A of Formula 1, which optimizes the phase and surface structure of the modified material. Further mechanical modification with additive B and subsequent digestion-carbonation treatment facilitate the selective separation of calcium and magnesium. The resulting magnesium-containing solution is then thermally converted with additive C, yielding high-quality light magnesium carbonate. Conventional calcination of this light magnesium carbonate is expected to produce magnesium oxide nanoflowers with excellent structural stability and organic matter degradation activity. Attached Figure Description

[0056] Figure 1 shows the SEM image of the light magnesium carbonate prepared in Example 1;

[0057] Figure 2 shows the SEM image of the nano-magnesium oxide prepared in Example 1. Detailed Implementation

[0058] The magnesium-containing limestone can be any known magnesium-containing limestone. As an optional option, in the following examples, the magnesium oxide content can be 15~25 wt.%.

[0059] Example 1

[0060] Step 1:

[0061] Magnesium-containing limestone and additive A (Formula 1A) are mixed in a mixer at a weight ratio of 100:2, and then kept at 1200±20℃ for 6 hours in air atmosphere to obtain modified material.

[0062] Step 2:

[0063] The modified material from step 1 was mixed with additive B (polyacrylic acid) at a weight ratio of 100:0.3 and then subjected to dry ball milling. The ball milling speed was 400 rpm, the ball milling time was 4 h, and the ball-to-material weight ratio was 20:1.

[0064] Water was then added for digestion, with a water-to-modified material liquid-to-solid ratio of 100:15; the digestion temperature was 70±5℃; and the digestion time was 4 hours.

[0065] Step 3:

[0066] Carbon dioxide gas was introduced into the digestion system of step 2 for carbonation treatment. The gas introduction rate was 0.3 vvm. The carbonation treatment included a low-temperature carbonation process and a high-temperature carbonation process. The solution after solid-liquid separation treatment following the low-temperature carbonation treatment was then subjected to high-temperature carbonation treatment. The system temperature was controlled at 10±5℃ during the low-temperature carbonation process and at 50±5℃ during the high-temperature carbonation process. The low-temperature carbonation treatment lasted for 1 hour. The final pH of the system after carbonation treatment was controlled at 6.78.

[0067] After carbonation treatment, solid-liquid separation is performed to obtain calcium-rich filter residue and magnesium-rich solution;

[0068] Step 4:

[0069] Additive C (sodium alginate, 0.01 mg / L) was added to the magnesium-rich solution in step 3, and then heated to 80-90°C for 2 hours to precipitate. Subsequently, solid-liquid separation was performed to obtain light magnesium carbonate powder.

[0070] Step 5:

[0071] The light magnesium carbonate powder obtained in step 4 was subjected to vacuum calcination at a temperature of 500±20℃ for 4 hours to obtain magnesium oxide nanoflowers.

[0072] Example 2

[0073] Compared to Example 1, the only difference is that the conditions in step 1 are changed, and the experimental groups are as follows:

[0074] Group A: Additive A was replaced with an equal amount of Formula 1B; all other operations and parameters were the same as in Example 1.

[0075] Group B: The ratio of magnesium-containing limestone to additive A was controlled at 100:5; other operations and parameters were the same as in Example 1.

[0076] Group C: The roasting temperature was changed to 1300±20℃, and the roasting time was 5h. Other operations and parameters were the same as in Example 1.

[0077] Example 3

[0078] Compared to Example 1, the only difference is that the conditions in step 2 are changed, and the experimental groups are as follows:

[0079] Group A: Additive B was replaced with polypropylene glycol; all other operations and parameters were the same as in Example 1.

[0080] Group B: Additive B was changed to a 1:1 weight ratio of polyacrylic acid and polypropylene glycol; other operations and parameters were the same as in Example 1.

[0081] Group C: The modified material from step 1 and additive B (polyacrylic acid) are in a weight ratio of 100:0.4; other operations and parameters are the same as in Example 1.

[0082] Group D: The digestion process consisted of three stages. The first stage was conducted at a temperature of 5-10°C for 1 hour. The second stage was conducted at a temperature of 70±5°C for 1 hour. The third stage was conducted with ultrasound assistance at a temperature of 70±5°C for 20-25 minutes. All other operations and parameters were the same as in Example 1.

[0083] Example 4

[0084] Compared to Example 1, the only difference is that the conditions in step 3 are changed, and the experimental groups are as follows:

[0085] Group A: The carbon dioxide inlet rate was 0.5 vvm, the reaction endpoint pH was 6.35, and other operations and parameters were the same as in Example 1.

[0086] Group B: The carbonization process is carried out at the high-temperature carbonation temperature, without low-temperature carbonation. Other operations and parameters are the same as in Example 1.

[0087] Example 5

[0088] Compared to Example 1, the only difference is that the conditions in step 4 are changed, and the experimental groups are as follows:

[0089] Group A: Additive C was changed to ammonium carbonate (concentration 0.015 mg / L); all other operations and parameters were the same as in Example 1;

[0090] Group B: Additive C was changed to ammonium carbonate and sodium alginate in a weight ratio of 1:1, and the total amount of additive C was 0.01 mg / L; other operations and parameters were the same as in Example 1.

[0091] Example 6

[0092] Compared with Example 1, the only difference is that the conditions of step 5 are changed, specifically, the pyrolysis temperature is changed to 450±20℃ and the pyrolysis time is changed to 6h. All other operations and parameters are the same as in Example 1.

[0093] Comparative Example 1

[0094] Compared with Example 1, the only difference is that additive A is missing in step 1, while the other operations and parameters are the same as in Example 1.

[0095] Comparative Example 2

[0096] Compared with Example 1, the only difference is that in step 1, the calcination temperature is 900°C, and all other operations and parameters are the same as in Example 1.

[0097] Comparative Example 3

[0098] Compared with Example 1, the only difference is that in step 1, diatomaceous earth is used to replace additive A, while other operations and parameters are the same as in Example 1.

[0099] Comparative Example 4

[0100] Compared with Example 1, the only difference is that additive B was not added in step 2, while the other operations and parameters are the same as in Example 1.

[0101] Comparative Example 5

[0102] Compared with Example 1, the only difference is that in step 2, additive B is replaced with citric acid, while other operations and parameters are the same as in Example 1.

[0103] Comparative Example 6

[0104] Compared with Example 1, the only difference is that in step 2, additive B is replaced with tartaric acid, and all other operations and parameters are the same as in Example 1.

[0105] Comparative Example 7

[0106] Compared with Example 1, the only difference is that in step 2, additive B is not added during the ball milling process, but is added in the digestion system. All other operations and parameters are the same as in Example 1.

[0107] Comparative Example 8

[0108] Compared with Example 1, the only difference is that in step 4, there is no additive C; all other operations and parameters are the same as in Example 1.

[0109] The obtained magnesium oxide nanoflowers were tested for their highly efficient catalytic degradation performance on organic dye wastewater (represented by methylene blue) under visible light irradiation. The specific operation was as follows: First, a 20 mg / L methylene blue simulated wastewater solution was prepared, and 100 mL of this methylene blue solution was placed in a quartz reactor. 20.0 mg of magnesium oxide nanoflowers (concentration 0.2 g / L) were added. The irradiation experiment was started using a xenon lamp. Two hours after irradiation, the reaction system was centrifuged, and the concentration of methylene blue in the supernatant was measured to calculate the degradation rate. The test results are shown in Table 1.

[0110] ;

[0111] As can be seen from the examples and comparative examples, the present invention innovatively modifies magnesium-containing limestone by high-temperature calcination under additive A of Formula 1, which is beneficial to optimizing the phase and surface structure of the modified material. The modified material is further mechanically modified by additive B and then subjected to subsequent digestion-carbonation treatment, which is beneficial to achieving selective separation of calcium and magnesium. The resulting magnesium-containing solution is further thermally transformed under additive C, thus obtaining high-quality light magnesium carbonate.

[0112] Through Examples 1 and 3, the use of a composite of polyacrylic acid and polypropylene glycol as additive B can further synergize and enhance the modification effect, thereby improving the physicochemical structure and properties of the subsequently prepared magnesium oxide nanoflowers.

[0113] As can be seen from Examples 1 and 4, the two-stage carbonation treatment described in this invention is more conducive to the physicochemical structure of the final magnesium oxide and its performance.

[0114] As can be seen from Examples 1 and 5, using the ammonium carbonate and sodium alginate complex described in this invention as additive C is more conducive to the physicochemical structure of the final prepared magnesium oxide and to its performance.

Claims

1. A method for preparing light magnesium carbonate using magnesium-containing limestone, characterized in that, The steps include: Step 1: Mixing magnesium-containing limestone with additive A and calcining it at a temperature of 1100~1400℃ to obtain modified material; Additive A includes at least one of Formula 1A and Formula 1B; Formula 1A Formula 1BM is H, Na, K or NH4; Step 2: The modified material and additive B are mechanically modified beforehand, then digested and carbonated in sequence, followed by solid-liquid separation to obtain calcium-rich solid and magnesium-rich solution; Additive B is at least one of polyacrylic acid, sodium polyacrylate, ammonium polyphosphate, and polypropylene glycol; The pH of the system at the end of the carbonation treatment is 6-7; Step 3: The magnesium-rich solution and additive C are mixed and subjected to thermal conversion precipitation treatment, followed by solid-liquid separation to obtain light magnesium carbonate powder; Additive C is at least one of sodium alginate and ammonium carbonate.

2. The method for preparing light magnesium carbonate using magnesium-containing limestone as described in claim 1, characterized in that, The weight ratio of magnesium-containing limestone to additive A is 100:1~8; the calcination modification atmosphere is an oxygen-containing atmosphere; the calcination modification time is 2~10 h.

3. The method for preparing light magnesium carbonate using magnesium-containing limestone as described in claim 1, characterized in that, In step 2, the additive B is polyacrylic acid and polypropylene glycol in a weight ratio of 1:0.5~2; the weight ratio of the modifier to additive B is 100:0.01~0.5; the mechanical modification method is dry ball milling or wet ball milling; the mechanical modification time is 2~10 h.

4. The method for preparing light magnesium carbonate using magnesium-containing limestone as described in claim 1, characterized in that, The liquid-to-solid ratio of water and modified material added during digestion is 100:10~30; the temperature of digestion is below 100℃; and the digestion time is more than 1 hour.

5. The method for preparing light magnesium carbonate using magnesium-containing limestone as described in claim 1 or 4, characterized in that, The digestion process consists of three stages. The temperature of the first stage is 0-30℃; the temperature of the second stage is 60-80℃; and the third stage is performed with ultrasound assistance at a temperature of 60-80℃.

6. The method for preparing light magnesium carbonate using magnesium-containing limestone as described in claim 1, characterized in that, Carbonation is performed by introducing a carbon dioxide-containing atmosphere into the digestion system. The carbonation process includes a low-temperature carbonation process by introducing a carbon dioxide-containing atmosphere into the digestion system beforehand, a solid-liquid separation process to obtain a low-temperature carbonized solution, and a high-temperature carbonation process by introducing a carbon dioxide-containing atmosphere into the low-temperature carbonized solution. The temperature of the low-temperature carbonation process is 0~20℃, and the temperature of the high-temperature carbonation process is 40~80℃.

7. The method for preparing light magnesium carbonate using magnesium-containing limestone as described in claim 1, characterized in that, In step 3, the amount of additive C added is 0.005~0.2 mg / L; the temperature of the thermal transformation precipitation process is 70~100℃.

8. A method for preparing magnesium oxide nanoflowers using magnesium-containing limestone, characterized in that, Magnesium-containing limestone is processed using the method described in any one of claims 1 to 7 to prepare light magnesium carbonate, and magnesium carbonate is pyrolyzed to obtain magnesium oxide nanoflowers.

9. The method for preparing magnesium oxide nanoflowers using magnesium-containing limestone as described in claim 8, characterized in that, The pyrolysis temperature is 400~550℃; the pyrolysis time is 2~6 h; the pyrolysis process is carried out under negative pressure.

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