A method for producing light magnesium carbonate and co-producing calcium carbonate by using magnesium reduction slag to store carbon dioxide

Abstract

The present invention relates to a method for producing light magnesium carbonate and co-producing calcium carbonate by sequestering carbon dioxide using magnesium reduction slag, acidic ammonium salt solution and magnesium reduction slag are added to leaching reactor, stirring and controlling pH to be 8.5-10.5, after solid-liquid separation, the solution is passed into a precipitation reactor, and industrial flue gas is passed into stirring reaction, until the system pH drops to 8, solid-liquid separation, the obtained mother liquor is used as a leaching liquid to repeatedly extract the same batch of magnesium slag, and then the mother liquor obtained after repeated extraction is used as a leaching liquid to extract multiple batches of magnesium slag, until the magnesium ion concentration in the mother liquor is greater than 0.1M, solid-liquid separation, industrial flue gas is passed into and pH is controlled to be 7.3-8.5, solid-liquid separation after reaction, ammonia is added to the obtained mother liquor and industrial flue gas is passed into, the system pH is controlled to be 9-9.5, and finally solid-liquid separation, drying, obtain light magnesium carbonate. The method is low in cost, can achieve zero emission and high value application of magnesium reduction slag, and has strong operability and is easy to realize industrialization.

Description

Technical Field

[0001] The invention relates to a method for producing light magnesium carbonate and co-producing calcium carbonate by using magnesium reduction slag to seal carbon dioxide, and belongs to the field of inorganic salt chemical industry and fertilizer production. Background Art

[0002] According to the Intergovernmental Panel on Climate Change (IPCC) report, since the mid-20th century, the extensive use of fossil fuels has led to a continuous increase in the content of atmospheric greenhouse gases, mainly carbon dioxide, which is closely related to global climate change. In order to prevent further environmental degradation caused by global climate change, it is necessary to stabilize the carbon dioxide content in the atmosphere from both the "source" and the "sink" aspects. Since fossil fuels are dominant now and even for a long time in the future, coal, oil and gas are the main energy sources. In addition, renewable energy will still be relatively expensive in the next few decades and cannot be promoted on a large scale, which leads to the inability to fully reduce carbon dioxide emissions into the atmosphere at the source. Therefore, the capture and storage of carbon dioxide in industrial flue gas has become the focus of attention and research at home and abroad.

[0003] Magnesium reduction slag is an industrial waste slag produced by silico-thermal magnesium refining. According to statistics, the production of 1 ton of raw magnesium will produce 5.5-10 tons of magnesium reduction slag. Magnesium slag is basically piled up in the open air. The naturally slow cooling magnesium slag is dusty. The huge stockpile will produce a lot of dust to pollute the environment. At the same time, the moisture absorption of magnesium slag will cause environmental problems such as soil compaction and alkalization. At present, magnesium reduction slag is mainly used in cement and concrete. It can be used as a mineralizer to promote the burning of cement clinker, as a raw material to configure cement raw materials, or use its water hardening to become a cement admixture. However, the "Standard for Magnesium Slag Portland Cement" (GB / T23933-2009) makes requirements on the magnesium content, activity and other indicators of magnesium slag in cement. The domestic silico-thermal process level is uneven, and the magnesium slag of many factories does not meet the national standard requirements and is difficult to use.

[0004] Magnesium reduction slag has high content of silicon, magnesium and calcium, which can be used to absorb carbon dioxide in flue gas and generate economically beneficial calcium magnesium carbonate. While achieving emission reduction, it is also of great significance to solving the pollution problem of magnesium reduction slag.

[0005] Light magnesium carbonate has important applications in many fields such as fine chemicals, refractory materials, rubber industry, coating industry, medicine, food, light industrial enamel, ceramics, etc. Calcium carbonate has a wide range of applications and a large demand in the chemical industry, such as ink, plastic, rubber, papermaking and other industries. At present, the production of light magnesium carbonate in my country mainly relies on calcining magnesite, and the production of calcium carbonate mainly relies on calcining limestone, both of which have the disadvantages of high energy consumption and poor product quality. Summary of the invention

[0006] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a method for preparing light magnesium carbonate and co-producing calcium carbonate by using magnesium reduction slag to seal carbon dioxide in industrial flue gas (such as cement plant flue gas, thermal power plant flue gas, etc.). The method is low-cost, can achieve zero emission and high-value application of magnesium reduction slag, and has strong operability and is easy to realize industrialization.

[0007] Technical Solution

[0008] The present invention uses magnesium reduction slag as raw material, extracts and separates calcium and magnesium elements in magnesium reduction slag through acidic ammonium salt solution, introduces industrial flue gas into the leaching solution to absorb carbon dioxide, separates calcium element and generates byproduct calcium carbonate, then continues to leach the filtrate after precipitation with ammonium salt solution, repeats the leaching precipitation process in a cycle, so that calcium element in the leaching solution is continuously separated and precipitated, and magnesium element is gradually enriched in the leaching solution, and finally adjusts the pH and temperature of the filtrate after precipitation to make magnesium ions saturated and crystallized to obtain a light magnesium carbonate product. This process can achieve zero emission and high-value utilization of magnesium reduction slag. After extracting calcium carbonate, the ammonium salt residual liquid generated by the reaction is sent back to the leaching reactor, and the magnesium reduction slag can be reabsorbed. Through the recycling of the ammonium salt solution, the industrial economic cost is reduced and the raw material utilization rate is improved. The detailed technical scheme is as follows:

[0009] A method for producing light magnesium carbonate and co-producing calcium carbonate by using magnesium reduction slag to seal carbon dioxide comprises the following steps:

[0010] (1) adding an acidic ammonium salt solution into a leaching reactor, then adding magnesium reduction slag at a solid-liquid ratio of 50-300 g / L, stirring the reaction and controlling the pH value of the solution to 8.5-10.5, and after completion, performing solid-liquid separation to obtain mother liquor I and filter residue;

[0011] (2) introducing mother liquor I into a precipitation reaction kettle and heating it to 25-60° C., then introducing industrial flue gas into mother liquor I and stirring it thoroughly. When the pH value of the reaction liquid drops to 8, the introduction of flue gas is stopped, and solid-liquid separation is performed to obtain mother liquor II and crude calcium carbonate. The crude calcium carbonate is washed and dried to obtain calcium carbonate;

[0012] (3) returning the filter residue obtained in step (1) and the mother liquor II obtained in step (2) as raw materials to the leaching reaction kettle, repeating steps (1) and (2) to obtain a calcium carbonate product and mother liquor III;

[0013] (4) adding the mother liquor III and the magnesium reduction slag to the leaching reactor, repeating steps (1) to (3) 3 to 6 times until the magnesium ion concentration in the solution is greater than 0.1 mol / L, thereby obtaining calcium carbonate and mother liquor IV;

[0014] (5) introducing the mother liquor IV into a precipitation reactor, adding ammonia water to adjust the pH value to 7.3-8.5, introducing industrial flue gas for stirring reaction, and adding ammonia water to maintain the pH value of the system at 7.3-8.5. After the reaction is completed, the solid and liquid are separated to obtain the mother liquor V and calcium carbonate;

[0015] (6) adding aqueous ammonia to the mother solution V, adjusting the pH value to 9-9.5, introducing industrial flue gas for stirring reaction, controlling the pH value of the system to be stable at 9-9.5 during the reaction process, separating the solid and the liquid after the solution becomes turbid, and drying to obtain light magnesium carbonate;

[0016] In step (1), the magnesium reduction slag is an industrial waste slag produced by silicothermic magnesium smelting in a magnesium plant, which contains 50%-60% by mass of calcium oxide, 30%-40% by mass of silicon dioxide, 4%-10% by mass of magnesium oxide, and 1%-5% by mass of aluminum oxide. Calcium mainly exists in the form of dicalcium silicate, and magnesium mainly exists in the form of magnesium oxide and magnesium silicon compounds. The particle size of the magnesium reduction slag is mainly between 50-500 meshes.

[0017] Furthermore, in step (1), the acidic ammonium salt solution contains 0.5-8 mol / L of ammonium chloride, 0.5-4 mol / L of ammonium nitrate, 0.01-1 mol / L of hydrochloric acid and 0.5-4 mol / L of acetic acid. The leaching agent is not only low in cost, but also can efficiently extract magnesium, calcium, iron and other elements from magnesium reduction slag in the leaching stage, which is convenient for subsequent carbonization precipitation extraction.

[0018] Furthermore, in step (1), the stirring reaction is carried out at a temperature of 20-40° C. and for a time of 20-60 min.

[0019] Furthermore, in step (3), step (1) and step (2) are repeated 2-5 times. The same batch of magnesium reduction slag is leached multiple times and multiple batches of leaching are performed simultaneously, so as to extract magnesium and calcium in the steel slag to the greatest extent.

[0020] Furthermore, in step (6), the drying temperature is 110-180° C. and the drying time is 0.5-4 h.

[0021] In steps (2) and (6), the industrial flue gas is the gas obtained by purification after desulfurization and denitrification in a power plant or the gas generated by burning fossil fuels in a cement plant or boiler room, wherein the volume percentage of carbon dioxide is 12 to 28%.

[0022] In step (4), the magnesium ion concentration in the solution is controlled to be greater than 0.1 mol / L, and in step (6), the pH is adjusted to be stable at 9.0-9.5, which is conducive to the preparation of light magnesium carbonate.

[0023] In step (5), the solution is controlled at 7.3-8.5 to allow a large amount of calcium ions in the solution to precipitate, which is beneficial to the preparation of light magnesium carbonate in step (6).

[0024] Beneficial effects of the present invention:

[0025] 1) The present invention provides a method for producing light magnesium carbonate and co-producing calcium carbonate by using magnesium reduction slag to seal carbon dioxide. The method has strong operability, good economic benefits, no environmental pollution, and is easy to realize industrialization.

[0026] 2) The present invention absorbs carbon dioxide in flue gas to generate thermodynamically more stable carbonates, thereby achieving permanent storage of carbon dioxide. Since there is no risk of leakage, there is no need for large investments for long-term monitoring, which reduces direct emissions of flue gas into the atmosphere and can achieve on-site storage of carbon dioxide from emission sources according to local conditions.

[0027] 3) The present invention uses magnesium reduction slag to absorb carbon dioxide, effectively utilizing a large amount of magnesium reduction slag produced during the magnesium smelting process of the magnesium plant. The raw material is very abundant and low-cost, solving the current pollution problem of magnesium reduction slag storage and converting waste slag into industrial products with economic value.

[0028] 4) The present invention adopts the technology of recycling ammonium salt, which not only saves raw materials and is conducive to integrating production processes, but also reduces the impact on the environment and produces obvious economic benefits.

[0029] 5) The purity of the calcium carbonate product prepared by the present invention is greater than 98%, and the shape is spherical or granular, with rhombic cleavage visible on the surface, and the diameter of the small particles is about 5um, and the diameter of the large particles is about 10um; the purity of the light magnesium carbonate product is 95%, and the particle diameter is about 20um. The product can be used as coating, refractory material, etc., in rubber, plastic and other industries, and has good economic utilization value. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a process flow chart of the method for producing light magnesium carbonate and co-producing calcium carbonate by using magnesium reduction slag to seal carbon dioxide in Example 1. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is described clearly and in detail below in conjunction with the embodiments and drawings.

[0032] It should be noted that in the following embodiments, the magnesium reduction slag used contains 57.69% by mass of calcium oxide, 31.85% by mass of silicon dioxide, 5.05% by mass of magnesium oxide, and 1.77% by mass of aluminum oxide, wherein calcium is mainly present in the form of dicalcium silicate, magnesium is mainly present in the form of magnesium oxide and magnesium silicon compounds, and the particle size of the magnesium reduction slag is between 50 and 500 meshes. However, the invention is not limited thereto.

[0033] Example 1

[0034] like Figure 1 A method for producing light magnesium carbonate and co-producing calcium carbonate by using magnesium reduction slag to store carbon dioxide comprises the following steps:

[0035] (1) adding 1500 mL of an acidic ammonium salt solution (containing 1.5 mol / L of ammonium chloride, 0.5 mol / L of ammonium nitrate, 0.1 mol / L of hydrochloric acid and 1 mol / L of acetic acid) into a leaching reactor, then adding 150 g of magnesium reduction slag, stirring and reacting at 25° C. for 40 min, and controlling the pH value of the solution to 9.1. After completion, solid-liquid separation was performed to obtain mother liquor I and filter residue;

[0036] (2) The mother liquor I is introduced into a precipitation reaction kettle and heated to 27° C., and then industrial flue gas is introduced into the mother liquor I and stirred thoroughly. When the pH value of the reaction liquid drops to 8, the flue gas introduction is stopped, and the solid-liquid separation is performed to obtain mother liquor II and crude calcium carbonate. The crude calcium carbonate is washed and dried to obtain 53.5 g of calcium carbonate;

[0037] (3) returning the filter residue obtained in step (1) and the mother liquor II obtained in step (2) as raw materials to the leaching reaction kettle, repeating steps (1) and (2) twice to obtain a calcium carbonate product and mother liquor III; a total of 79.14 g of calcium carbonate product was obtained, the purity of the product was greater than 98%, the shape was spherical and granular, rhombohedral cleavage was visible on the surface, the diameter of small particles was about 5 μm, and the diameter of large particles was about 10 μm;

[0038] (4) adding mother liquor III and 150 g of magnesium reduction slag to a leaching reactor, repeating steps (1) to (3) 3 to 6 times until the magnesium ion concentration in the solution is greater than 0.1 mol / L, to obtain calcium carbonate and mother liquor IV;

[0039] (5) introducing mother liquor IV into a precipitation reactor, connecting a computer program and a horizontal flow pump and measuring the pH of mother liquor III in real time with a pH meter to ensure that it is stable at 7.3, continuing to introduce industrial flue gas, and adding ammonia water to maintain the pH value of the system at 7.3. After the reaction is completed, the solid and liquid are separated to obtain mother liquor V and calcium carbonate; the calcium ion precipitation rate is measured to be as high as 99.99%;

[0040] (6) Ammonia water was added to the mother solution V to adjust the pH value to 9.0-9.2, and industrial flue gas was introduced for stirring reaction. The pH value of the reaction system was controlled to be stable at 9.0-9.2 during the reaction process. After the solution became turbid, the solid and liquid were separated and dried at 130° C. for 3 h to obtain 16.43 g of light magnesium carbonate with a purity greater than 95% and a particle size of about 20 μm.

[0041] Comparative Example 1

[0042] A method for producing light magnesium carbonate and co-producing calcium carbonate by using magnesium reduction slag to seal carbon dioxide comprises the following steps:

[0043] (1) adding 1500 mL of 1.5 mol / L ammonium chloride solution into a leaching reactor, then adding 150 g of magnesium reduction slag, stirring and reacting at 25° C. for 40 min, and controlling the pH value of the solution to 9.7. After completion, solid-liquid separation was performed to obtain mother liquor I and filter residue;

[0044] (2) introducing mother liquor I into a precipitation reactor at a reaction temperature of 27° C., then introducing pure CO2 into mother liquor I and stirring thoroughly. When the pH value of the reaction solution drops to 6.3, solid-liquid separation is performed to obtain mother liquor II and crude calcium carbonate. The crude calcium carbonate is washed and dried to obtain 32.74 g of calcium carbonate product.

[0045] (3) returning the filter residue obtained in step (1) and the mother liquor II obtained in step (2) as raw materials to the leaching reaction kettle, repeating steps (1) and (2) twice to obtain a calcium carbonate product and mother liquor III; a total of 40.83 g of calcium carbonate product was obtained, the purity of the product was greater than 98%, the shape was spherical and granular, the diameter of small particles was about 5 μm, and the diameter of large particles was about 10 μm;

[0046] (4) adding mother liquor III and 150 g of magnesium reduction slag to a leaching reactor, repeating steps (1) to (3) 3 to 6 times until the magnesium ion concentration in the solution is greater than 0.1 mol / L, to obtain calcium carbonate and mother liquor IV;

[0047] (5) introducing mother liquor IV into a precipitation reactor, connecting a computer program and a horizontal flow pump and measuring the pH of mother liquor III in real time with a pH meter to ensure that it is stable at 7.5, continuing to introduce industrial flue gas, and adding ammonia water to maintain the pH value of the system at 7.5. After the reaction is completed, the solid and liquid are separated to obtain mother liquor V and calcium carbonate; the calcium ion precipitation rate is measured to be as high as 99.99%;

[0048] (6) Ammonia water was added to the mother liquor V to adjust the pH value to 9.0-9.2, and industrial flue gas was introduced for stirring reaction. The pH value of the reaction system was controlled to be stable at 9.0-9.2 during the reaction process. After the solution became turbid, the solid and liquid were separated and dried at 130° C. for 3 h to obtain 7.48 g of light magnesium carbonate product with a purity of 75% and a particle size of about 20 μm.

Claims

1. A method for producing light magnesium carbonate and co-producing calcium carbonate by using magnesium reduction slag to seal carbon dioxide, characterized in that: The steps include: (1) adding an acidic ammonium salt solution into a leaching reactor, then adding magnesium reduction slag at a solid-liquid ratio of 50-300 g / L, stirring the reaction and controlling the pH value of the solution to 8.5-10.5, and after completion, performing solid-liquid separation to obtain mother liquor I and filter residue; (2) introducing mother liquor I into a precipitation reaction kettle and heating it to 25-60° C., then introducing industrial flue gas into mother liquor I and stirring it thoroughly. When the pH value of the reaction liquid drops to 8, the introduction of flue gas is stopped, and solid-liquid separation is performed to obtain mother liquor II and crude calcium carbonate. The crude calcium carbonate is washed and dried to obtain calcium carbonate; (3) returning the filter residue obtained in step (1) and the mother liquor II obtained in step (2) as raw materials to the leaching reaction kettle, repeating steps (1) and (2) to obtain a calcium carbonate product and mother liquor III; (4) adding the mother liquor III and the magnesium reduction slag to the leaching reactor, repeating steps (1) to (3) 3 to 6 times until the magnesium ion concentration in the solution is greater than 0.1 mol / L, thereby obtaining calcium carbonate and mother liquor IV; (5) introducing the mother liquor IV into a precipitation reactor, adding ammonia water to adjust the pH value to 7.3-8.5, introducing industrial flue gas for stirring reaction, and adding ammonia water to maintain the pH value of the system at 7.3-8.

5. After the reaction is completed, the solid and liquid are separated to obtain the mother liquor V and calcium carbonate; (6) adding aqueous ammonia to the mother solution V, adjusting the pH value to 9-9.5, introducing industrial flue gas for stirring reaction, controlling the pH value of the system to be stable at 9-9.5 during the reaction process, separating the solid and the liquid after the solution becomes turbid, and drying to obtain light magnesium carbonate; In step (1), the magnesium reduction slag contains 50%-60% by mass of calcium oxide, 30%-40% by mass of silicon dioxide, 4%-10% by mass of magnesium oxide and 1%-5% by mass of aluminum oxide.

2. The method for producing light magnesium carbonate and co-producing calcium carbonate by sequestering carbon dioxide using magnesium reduction slag as claimed in claim 1, characterized in that: In step (1), the acidic ammonium salt solution contains 0.5-8 mol / L of ammonium chloride, 0.5-4 mol / L of ammonium nitrate, 0.01-1 mol / L of hydrochloric acid and 0.5-4 mol / L of acetic acid.

3. The method for producing light magnesium carbonate and co-producing calcium carbonate by sequestering carbon dioxide using magnesium reduction slag as claimed in claim 1, characterized in that: In step (1), the stirring reaction is carried out at a temperature of 20-40° C. and for a time of 20-60 min.

4. The method for producing light magnesium carbonate and co-producing calcium carbonate by sequestering carbon dioxide using magnesium reduction slag as claimed in claim 1, characterized in that: In step (3), step (1) and step (2) are repeated 2-5 times.

5. The method for producing light magnesium carbonate and co-producing calcium carbonate by sequestering carbon dioxide using magnesium reduction slag as claimed in claim 1, characterized in that: In step (6), the drying temperature is 110-180° C. and the drying time is 0.5-4 h.

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