Microwave-assisted energy-saving method for preparing vaterite by micro-bubble mineralization regeneration of waste stone powder

Abstract

The invention discloses a microwave-assisted energy-saving method for preparing vaterite by micro-bubble mineralization regeneration of waste stone powder, and belongs to the field of high-added-value resource utilization of solid wastes. The method comprises the following steps: mixing waste stone powder and iron-rich sludge, preheating, carrying out microwave-assisted heating, activating the waste stone powder, and pyrolyzing the iron-rich sludge into an iron-carbon material to obtain a mixed material; mixing the mixed material with a leaching agent for digestion, separating out the iron-carbon material in the digestion process, and adjusting the pH value to remove impurities; and injecting flue gas generated by heating into the digested solution in a micro-nano bubble form, stirring, adding a crystal form regulator, and reacting to obtain vaterite. According to the method, the waste stone powder and the iron-rich sludge are co-treated in a microwave-assisted pyrolysis manner, the treatment scale is large, the iron-rich sludge is carbonized, the surface iron minerals are modified, a high-energy wave-absorbing point is formed, the energy consumption is low, the obtained micro-nano vaterite and the iron-carbon material have great additional values, the product performance is good, and zero carbon emission is realized in the whole process.

Description

Technical Field

[0001] The invention belongs to the field of high value-added resource utilization of solid waste, and specifically relates to a method for preparing vaterite by microwave-assisted energy-saving waste stone powder microbubble mineralization regeneration. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Waste stone powder is a kind of industrial waste that is collected and stored by dust collection system and transported by transport tank trucks. Open-air stacking or dumping landfill is the main disposal method of waste stone powder. This is not only a waste of natural resources, but also occupies a large amount of land, destroys soil and vegetation, and with the accumulation of waste stone powder, it will gradually change the type of surface coverage, and the phenomenon of "rock desertification" will appear. At present, waste stone powder is mainly used as building filler. Since magnesium oxide in waste stone powder can easily cause cement expansion and cracking during cement hydration, it will produce alkali-aggregate reaction with aggregate when used in concrete. Therefore, the national standard has certain restrictions on the content of magnesium oxide in cement, usually requiring no more than 5.0%, which greatly limits the disposal amount of waste stone powder. And due to different geology and ore sources, the mineral composition of waste stone powder has certain fluctuations, which will cause unstable concrete quality.

[0004] The calcium component content in waste stone powder is as high as 70-80%. In this regard, the inventors have proposed a high-value large-scale resource utilization method for waste stone powder, which is used as a raw material to produce calcium carbonate. The existing raw materials for producing calcium carbonate are mainly dolomite, limestone, carbide slag, fly ash, etc. For example, patent CN112110469A discloses a method for preparing vaterite calcium carbonate using limestone. The mining, crushing and grinding processes of dolomite, limestone and other stones consume a lot of energy, the calcination process consumes a lot of energy, and the carbonization process uses pure CO. 2, high cost, and low conversion efficiency of calcium component, unsatisfactory separation effect for impurities, the particle size of calcium carbonate product generated reaches tens of microns or even millimeter level, and the crystalline phase is mostly calcite. Calcite calcium carbonate can not be effectively dispersed in water or organic matter, and has low application value. Adopt solid wastes such as carbide slag or fly ash to prepare vaterite, such as patent CN116395729A discloses a method for utilizing fly ash building materials based on the dissolution and recrystallization of vaterite. Utilize carbide slag, fly ash etc. to prepare vaterite, because of high impurity content in solid waste, need long time acid leaching, and heavy metal impurities in solid waste can not be fully removed, and then remain in calcium carbonate, reduce the purity of vaterite. Therefore, the method for preparing vaterite calcium carbonate using discarded stone powder is of great significance to improving the disposal amount of discarded stone powder, reducing energy consumption, and improving vaterite output. Summary of the invention

[0005] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a microwave-assisted energy-saving method for preparing vaterite by micro-bubble mineralization and regeneration of waste stone powder. The present invention synergistically pyrolyzes waste stone powder and iron-rich sludge to effectively activate the calcium component, and the treatment scale is large. The calcium component activated by the waste stone powder is converted into a micro-nano-scale vaterite product through digestion, carbonization, crystal form control and microwave drying, which greatly improves the value of the product.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] The first aspect of the present invention provides a method for preparing vaterite by microwave-assisted energy-saving microbubble mineralization regeneration of waste stone powder, comprising:

[0008] The waste stone powder and the iron-rich sludge are mixed and preheated, and then subjected to microwave-assisted heating; during the microwave-assisted heating process, the waste stone powder is decomposed and activated, and carbon dioxide is generated at the same time, and the iron-rich sludge is pyrolyzed into iron-carbon material in a carbon dioxide atmosphere to obtain a mixed material and flue gas containing carbon dioxide;

[0009] The mixed material is mixed with a leaching agent, digested and dissolved, filtered for the first time, insoluble matter is filtered out, and a primary filtrate is obtained; the pH of the primary filtrate is adjusted and filtered again to filter out magnesium hydroxide precipitate and aluminum hydroxide precipitate to obtain a secondary filtrate;

[0010] The flue gas containing carbon dioxide enters the micro-nano bubble generator after being cooled and harmful gases are removed to obtain micro-nano bubbles; the micro-nano bubbles are injected into the secondary filtrate under stirring, and a crystal form regulator is added to react to obtain vaterite.

[0011] In some embodiments of the present invention, the particle size of the waste stone powder is less than 0.08 mm.

[0012] In some embodiments of the present invention, the iron-rich sludge is particles with a particle size of 20-60 mm, and the mass ratio of carbon to iron in the iron-rich sludge is 3-6:1.

[0013] In some embodiments of the present invention, the mass ratio of the waste stone powder to the iron-rich sludge is 3-6:1.

[0014] In some embodiments of the present invention, the preheating is to heat the mixture of waste stone powder and iron-rich sludge to 300-400° C. and keep the temperature for 7-12 minutes;

[0015] The microwave-assisted heating is carried out at a temperature of 800-900° C. and is kept warm for 5-10 minutes.

[0016] In some embodiments of the present invention, the flue gas containing carbon dioxide preheats and cools the next batch of waste stone powder and iron-rich sludge mixture, and then enters the micro-nano bubble generator after cooling and removing harmful gases to obtain micro-nano bubbles.

[0017] In some embodiments of the present invention, the leaching agent is water, and the water-solid ratio is 6-12 L / kg.

[0018] In some embodiments of the present invention, the digestion and dissolution time is 20-40 minutes.

[0019] In some embodiments of the present invention, the pH of the primary filtrate is adjusted, including: adding ammonium chloride to the primary filtrate to lower the pH of the primary filtrate, controlling the molar ratio of ammonium ions to calcium components in the waste stone powder to be 2-2.4:1, the magnesium ions in the primary filtrate to generate magnesium hydroxide precipitate, filtering out the magnesium hydroxide precipitate, and continuing to add ammonium chloride to the filtrate to adjust the pH to 8.5-9.0 so that the aluminum ions generate aluminum hydroxide precipitate, filtering out the aluminum hydroxide precipitate, and obtaining a secondary filtrate;

[0020] In the process of adjusting the pH of the primary filtrate, the gas generated by adding ammonium chloride is collected and then introduced into the secondary filtrate simultaneously with the micro-nano bubbles.

[0021] In some embodiments of the present invention, the injection pressure is 0.1-0.3 MPa, and the micro-nano bubbles are injected at a rate of 2-5 L / min per liter of solution.

[0022] In some embodiments of the present invention, the stirring rate is 300-600 rpm.

[0023] In some embodiments of the present invention, the crystal form regulator is glycine, the molar ratio of glycine to the calcium component in the waste stone powder is 0.6-2:1, and the reaction time is 20-50 min.

[0024] In some embodiments of the present invention, after the reaction is completed, the solid and liquid are separated and dried to obtain vaterite.

[0025] Preferably, ultrasonic-assisted filtration is used for solid-liquid separation.

[0026] Preferably, the filtrate after the solid-liquid separation is recycled as a leaching agent.

[0027] Preferably, the drying is microwave drying.

[0028] Preferably, the vaterite is micro-nano-scale vaterite.

[0029] The present invention adopts microwave-assisted pyrolysis to synergistically dispose of waste stone powder and iron-rich sludge. The treatment scale is large, the iron-rich sludge is carbonized and the surface iron minerals are modified to form high-energy wave absorption points, the heating rate is fast, the pyrolysis efficiency is high, the energy consumption is low, and the subsequent products, micro-nano-level vaterite and iron-carbon materials, have great added value and good product performance.

[0030] Rich CO generated by pyrolysis of waste stone powder 2 The atmosphere provides pyrolysis conditions for the iron-rich sludge, and the high-temperature flue gas generated in the microwave-assisted heating process preheats the mixed material to achieve partial carbonization of the iron-rich sludge. The flue gas is subsequently cooled and washed to remove harmful gases, and then participates in the carbonization process of the calcium component in the form of micro-nano bubbles, thereby achieving zero carbon emissions in the process. The micro-nano bubbles can be quickly and evenly distributed in the reaction solution, accelerating the formation of vaterite, which is conducive to the formation of vaterite with smaller micro-nano particle sizes.

[0031] The beneficial effects of the present invention are:

[0032] The present invention provides a microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization regeneration of waste stone powder. The waste stone powder and iron-rich sludge are pyrolyzed in a coordinated manner. The waste stone powder is decomposed into sludge-based iron-carbon material to provide CO-rich 2 The carbonization of iron-rich sludge and the conversion of iron minerals provide high-energy wave absorption sites for the activation of waste stone powder, enhancing the effect of microwave heating. The activated waste stone powder is subsequently converted into high-value-added micro-nano-scale vaterite. In the carbonization process of waste stone powder into vaterite, the high-carbon flue gas generated by microwave-assisted heating accelerates CO 2 Dissolve and recycle high-carbon flue gas instead of traditional pure CO 2 Injection can reduce production costs and achieve zero carbon emissions in the process. At the same time, the good dispersibility of micro-nano bubbles and the disturbance effect of dissolution and rupture can be used to accelerate the formation of vaterite, control the particle size, and form more nano-scale particles.

[0033] Advantages of additional aspects of the present disclosure will be given in part in the following description and in part will become apparent from the following description or will be learned through practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] Figure 1 A process flow chart of a method for preparing vaterite by microwave-assisted energy-saving microbubble mineralization regeneration of waste stone powder provided in Example 1 of the present invention.

[0036] Figure 2 A process flow chart of a microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization regeneration of waste stone powder and simultaneously generating synthesis gas provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] In view of the large fluctuations in the composition of waste stone powder, high impurity content, difficulty in separating calcium components, low disposal volume, high energy consumption in the resource utilization process and low product added value, the present invention proposes a microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization regeneration of waste stone powder.

[0038] The first typical embodiment of the present invention provides a microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization and regeneration of waste stone powder, comprising:

[0039] The waste stone powder and the iron-rich sludge are mixed and preheated, and then subjected to microwave-assisted heating; during the microwave-assisted heating process, the waste stone powder is decomposed and activated, and carbon dioxide is generated at the same time, and the iron-rich sludge is pyrolyzed into iron-carbon material in a carbon dioxide atmosphere to obtain a mixed material and flue gas containing carbon dioxide;

[0040] The mixed material is mixed with a leaching agent, digested and dissolved, filtered for the first time, insoluble matter is filtered out, and a primary filtrate is obtained (during this process, the iron-carbon material adsorbs and precipitates trace heavy metals that may exist in the filtrate); the pH of the primary filtrate is adjusted and filtered again to filter out magnesium hydroxide precipitate and aluminum hydroxide precipitate to obtain a secondary filtrate;

[0041] The flue gas containing carbon dioxide enters the micro-nano bubble generator after being cooled and harmful gases are removed to obtain micro-nano bubbles; the micro-nano bubbles are injected into the secondary filtrate under stirring, and a crystal form regulator is added to react to obtain vaterite.

[0042] The synergistic pyrolysis of waste stone powder and iron-rich sludge can effectively activate the calcium component in the waste stone powder, and the treatment scale is large. The iron-rich sludge is carbonized to form a strong absorbing iron-carbon material, and the energy consumption of the activation of the calcium component of the waste stone powder is reduced by microwave-assisted heating, and the energy consumption of the production process is low. The calcium component activated by the waste stone powder is converted into a micro-nano-scale vaterite product through digestion, carbonization, crystal form control and drying, which greatly enhances the value of the product.

[0043] In some examples of this implementation mode, the particle size of the waste stone powder is less than 0.08 mm. The waste stone powder used in the present invention comes from a dust collecting device, belongs to industrial waste, has a powdery structure, and has a particle size of less than 0.08 mm. It does not need to be crushed or ground, thus saving raw materials and reducing the exploitation of natural resources.

[0044] In some examples of this embodiment, the iron-rich sludge is particles with a particle size of 20-60 mm, and the mass ratio of carbon to iron in the iron-rich sludge is 3-6:1.

[0045] It should be noted that during the mixing process, the iron-rich sludge delivered cannot be directly mixed with the waste stone powder. It is necessary to test its composition to determine the ratio of iron and carbon and the calorific value in the iron-rich sludge. If the ratio of iron and carbon does not reach the set ratio, the mass ratio of carbon and iron in the iron-rich sludge can be adjusted to 3-6:1 by adding industrial organic sludge. In order to improve the mixing degree of iron-rich sludge and waste stone powder and the separation of iron-carbon materials in the later stage, the iron-rich sludge after matching needs to be formed into 20-60mm particles by disc granulation.

[0046] It should be noted that during the mixing process, the waste stone powder transported also needs to be tested for composition before mixing to determine the calcium component content and impurity content of the waste stone powder, so as to control the amount of ammonium chloride and crystal form regulator added, which is conducive to separating impurities in the waste stone powder and avoiding the introduction of new impurities.

[0047] In some examples of this embodiment, the mass ratio of the waste stone powder to the iron-rich sludge is 3-6: 1. Under the condition of this mass ratio, the waste stone powder can be fully activated, reducing the influence of the fluctuation of the waste stone powder composition on the purity of the prepared vaterite, and the iron-rich sludge can be fully depyrized into iron-carbon material with low energy consumption.

[0048] In some examples of this implementation mode, the preheating is to heat the mixture of waste stone powder and iron-rich sludge to 300-400° C. and keep the temperature for 7-12 minutes;

[0049] The microwave-assisted heating is carried out at a temperature of 800-900° C. and is kept warm for 5-10 minutes.

[0050] It is understandable that a microwave rotary kiln may be used for microwave assisted heating.

[0051] During the preheating process, the high-temperature flue gas preheats the material, and the iron-rich sludge particles are partially carbonized, and the wave absorption capacity is enhanced. The temperature can be rapidly increased by microwave-assisted heating, and the pyrolysis temperature is stabilized at 800-900℃ for 5-10 minutes. In this process, the calcium component in the waste stone powder is pyrolyzed and activated, and the iron-rich sludge particles are pyrolyzed into iron-carbon materials in a carbon dioxide atmosphere, forming high-energy wave absorption sites, which enhance the effect of microwave heating.

[0052] In some examples of this implementation mode, the flue gas containing carbon dioxide preheats and cools the next batch of waste stone powder and iron-rich sludge mixture, and then enters the micro-nano bubble generator after cooling and removing harmful gases to obtain micro-nano bubbles.

[0053] Aiming at the problem of large flue gas carbon emission, high heat and difficulty in utilization in the prior art vaterite production process, the present invention proposes a flue gas recycling method. During the microwave rotary kiln heating and calcining process, the waste stone powder is thermally decomposed into iron-rich sludge carbonized to form a unique CO2-rich 2 The atmosphere is formed, that is, the flue gas produced in this process is rich in carbon dioxide. The high-temperature flue gas first preheats the material (a mixture of waste stone powder and iron-rich sludge particles). During the preheating process, the iron-rich sludge particles are pre-carbonized to enhance the wave absorption characteristics for subsequent microwave-assisted heating. At the same time, the waste stone powder is preheated to reduce the flue gas temperature. The preheated flue gas is then injected into the digested solution in the form of micro-nano bubbles after a series of treatments, acting on the carbonation process of the calcium component to make the CO in the flue gas 2 It dissolves quickly in the reaction solution, achieving efficient heat utilization and zero carbon emissions in the process.

[0054] It will be appreciated that the cooling may occur in a flue gas cooling tower and the scrubbing may occur in a scrubbing tower.

[0055] It should be noted that the micro-nano bubble generator is an existing product and can be purchased. After the flue gas is input into the micro-nano bubble generator, it is output in the form of micro-nano bubbles. Micro-nano bubble technology is a new type of artificial aeration technology. Micro-nano bubbles refer to bubbles with a bubble particle size (diameter) between 10 microns and hundreds of nanometers. Such bubbles as small as nanometers to micrometers have physical and chemical properties that conventional bubbles do not have. Such as ionization, ultrasonic properties, charge, diffusivity, oxidizability, stability, bactericidal properties, retention, physiological activity, self-pressurization, etc.

[0056] In some examples of this embodiment, the leaching agent is water, the water-to-solid ratio is 6-12 L / kg, and the digestion and dissolution time is 20-40 min. The above reaction conditions ensure that the activated calcium component can be completely dissolved in the solution to form a suspension, and the temperature of the suspension can be controlled at 60-100° C. by controlling the water-to-solid ratio.

[0057] The activated waste stone powder is used as a calcium source, and water is used as a calcium component leaching agent. The water-to-solid ratio is controlled at 6-12L / kg. Impurities are filtered out after digestion for 20-40 minutes, and iron-carbon materials are sieved and separated in the process. During the digestion process, the iron-carbon materials can adsorb and remove heavy metals that may exist in the solution due to different sources of waste stone powder.

[0058] In some examples of this embodiment, the insoluble matter includes iron-carbon material, silicon dioxide, and magnesium hydroxide.

[0059] In some examples of this embodiment, filtering out the magnesium hydroxide precipitate and the aluminum hydroxide precipitate is filtering out the magnesium hydroxide precipitate and the aluminum hydroxide precipitate respectively.

[0060] In some examples of this implementation, the adjusting the pH of the primary filtrate comprises: adding ammonium chloride to the primary filtrate to lower the pH of the primary filtrate, controlling the molar ratio of ammonium ions to calcium components in the waste stone powder to be 2-2.4:1, the magnesium ions in the primary filtrate to generate magnesium hydroxide precipitate, filtering out the magnesium hydroxide precipitate, and continuing to add ammonium chloride to the filtrate to adjust the pH to 8.5-9.0 so that the aluminum ions generate aluminum hydroxide precipitate, filtering out the aluminum hydroxide precipitate, and obtaining a secondary filtrate;

[0061] In the process of adjusting the pH of the primary filtrate, the gas generated by adding ammonium chloride is collected and then introduced into the secondary filtrate simultaneously with the micro-nano bubbles.

[0062] It is understandable that after the mixed material is mixed with the leaching agent, part of the mixed material is dissolved in the leaching agent, and the insoluble matter (ferro-carbon material, silicon dioxide and magnesium hydroxide) is removed by filtration, and the alkalinity of the obtained primary filtrate is relatively strong, and it contains metaaluminate and a small amount of magnesium ions. After adding ammonium chloride to reduce the alkalinity of the primary filtrate, by controlling the addition of ammonium chloride, the magnesium ions dissolved in the primary filtrate are generated into magnesium hydroxide precipitation, and the magnesium hydroxide precipitation is filtered out to realize the depth removal of magnesium ions. Continuing to add ammonium chloride in the filtrate causes metaaluminate to become aluminum hydroxide, and the full removal of aluminum ions is realized.

[0063] In some embodiments of this embodiment, the secondary filtrate produced by the digestion process enters the carbonizing tank and is carbonized. The secondary filtrate enters the carbonizing tank, stirs, and the micro-nano bubbles are injected into the secondary filtrate, and the gas produced by the digestion process is simultaneously input into the secondary filtrate, and a crystal form regulator is added simultaneously. The gas produced in the digestion process is mainly ammonia, because ammonia is very soluble in water, most of ammonia directly dissolves in the solution, forming ammonium ions. To avoid the waste of resources of ammonia, the gas after digestion is collected and then passed into the secondary filtrate of the carbonizing tank, so that the ammonia in the gas is all dissolved in the secondary filtrate. The ammonium ions in the secondary filtrate can be adsorbed on the surface of the vaterite particles to prevent the vaterite from converting to calcite. The present invention controls the crystal form and the particle diameter of the calcium carbonate product by micro-nano bubbles, ammonium ions, stirring and a crystal form regulator, forming a micro-nano vaterite product.

[0064] In some examples of this embodiment, the injection pressure is 0.1-0.3 MPa, and the micro-nano bubbles are injected at a rate of 2-5 L / min per liter of solution. 2 The rapid dissolution and dissolution amount of the vaterite are increased, and the crystal nucleation and growth rates are controlled, so that the morphology of the vaterite product changes to a spherical structure with a smaller particle size. The pH value of the solution is maintained above 7.5, which prevents the vaterite product from further dissolving.

[0065] Micro-nano bubbles are injected into the secondary filtrate and then burst, which not only accelerates the dissolution of carbon dioxide, replacing the traditional injection of pure carbon dioxide, reducing production costs and achieving zero carbon emissions in the process; at the same time, they can be quickly and evenly distributed in the entire reaction solution, generating disturbances and microjets when bursting, accelerating the precipitation of calcium ions, and also helping to control the particle size of the precipitated calcium carbonate and form more nano-scale particles.

[0066] In some examples of this embodiment, the stirring is carried out at a rate of 300-600 rpm to ensure that the generated particles are in a suspended state and are in full contact with the crystal form regulator, and specifically can be 300 rpm, 400 rpm, 500 rpm, 600 rpm, etc.

[0067] In some examples of this embodiment, the crystal form regulator is glycine, and the molar ratio of glycine to calcium ion is 0.6-2:1, which promotes the formation and stabilization of the product vaterite phase, and the reaction time is 20-50min. The content of vaterite is high under this molar ratio, while too low calcite content is high, and too high easily leads to insufficient ammonia water.

[0068] In some examples of this embodiment, after the reaction is completed, the solid and liquid are separated and dried to obtain vaterite.

[0069] After the reaction is completed, the suspended solution in the carbonization tank can be separated into solid and liquid by ultrasonic assisted filtration to reduce the agglomeration of vaterite particles. The separated solid particles are high-purity vaterite. The targeting and pump effect of microwave drying can be used to shorten the drying time, form loose materials, and effectively improve the storage stability of micro-nano vaterite.

[0070] In some examples of this embodiment, the filtrate after the solid-liquid separation is recycled as a leaching agent.

[0071] It can be understood that the filtrate after solid-liquid separation is water containing ammonium ions, which can be used as a leaching agent and recycled to save production costs.

[0072] In some examples of this embodiment, the vaterite is micro-nano-sized vaterite.

[0073] The principle of the present invention is:

[0074] The present invention provides a microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization regeneration of waste stone powder. After the waste stone powder is mixed with a certain proportion of iron-rich sludge, the temperature is quickly raised to 800-900°C by means of high-temperature flue gas preheating and microwave-assisted heating synergistic enhancement, thereby realizing energy-saving activation of the waste stone powder. The iron-rich sludge serves as a wave absorbing site, and the waste stone powder is decomposed into the iron-rich sludge to provide a unique CO 2 The iron-rich sludge is pyrolyzed into iron-carbon materials, and the modified biochar rich in iron minerals forms high-energy sites, which can enhance the wave absorption characteristics and improve the pyrolysis reaction efficiency, thus reducing the energy consumption of the calcination process. 2+ It exists in the form of a solution, and other impurities are removed by step-by-step filtration to achieve the effect of efficient separation and purification, and the iron-carbon material is screened out as a water treatment product. 2+ The solution enters the carbonization tank, and the high-temperature flue gas emitted during the microwave-assisted heating calcination process preheats and cools the material. After cooling in the flue gas cooling tower and removing harmful gases in the scrubbing tower, the solution enters the micro-nano bubble generator. The formed micro-nano bubbles are injected into the Ca 2+ In solution. Accelerating CO by micro-nano bubbles 2 Hydration achieves the effect of rapid carbonization and realizes zero carbon emission in the process. The calcium component carbonization process controls the crystal form and particle size of the calcium carbonate product through micro-nano bubbles, stirring and crystal form regulators to form micro-nano vaterite products. After ultrasonic assisted filtration, the filtrate re-enters the digestion step for recycling. The product is quickly dried by microwave drying and stored in a storage tank.

[0075] In some examples of this embodiment, a specific microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization and regeneration of waste stone powder is provided, comprising the following steps:

[0076] (1) The waste stone powder and iron-rich sludge transported are subjected to component testing to determine the calcium component content and impurity components of the waste stone powder and the ratio of Fe to C and calorific value in the iron-rich sludge; the mass ratio of C to Fe in the iron-rich sludge is adjusted to 3-6:1 by adding industrial organic sludge, and the iron-rich sludge after the combination is formed into 20-60 mm particles by disc granulation;

[0077] (2) Iron-rich sludge particles and waste stone powder are mixed evenly in a ratio of 1:3-6 and then put into a microwave rotary kiln. The high-temperature flue gas generated later preheats the material, and the sludge particles are partially carbonized, and the microwave absorption capacity is enhanced. The temperature is rapidly increased by microwave-assisted heating, and the pyrolysis temperature is stabilized at 800-900°C for 5-10 minutes. In this process, the calcium component in the waste stone powder is pyrolyzed and activated to release CO 2 , while the sludge particles are in CO 2 Pyrolysis into iron-carbon materials under atmosphere, forming high-energy wave-absorbing sites, enhancing the effect of microwave heating;

[0078] The chemical changes that occur during pyrolysis are:

[0079] The formation process of iron-carbon materials:

[0080]

[0081] Decomposition of main minerals in waste stone powder:

[0082]

[0083] (3) The activated waste stone powder is used as a calcium source, and water and ammonium chloride are used as calcium component leaching agents. The water-to-solid ratio is controlled at 6-12 L / kg. After digestion for 20-40 minutes, impurities are filtered out, and iron-carbon materials are sieved and separated during the process. The iron-carbon materials adsorb and remove heavy metals that may exist in the reaction solution due to different sources of waste stone powder during the digestion process; NH 4 + With Ca 2+ The molar ratio of Mg(OH) was controlled at 2-2.4:1, and ammonium chloride was slowly added and filtered to obtain Mg(OH) 2 The pH value of the reaction solution was adjusted to 8.5-9.0 to precipitate aluminum ions and then filter them; the gas (mainly NH 3 ) is passed into the subsequent carbonization tank;

[0084] The chemical changes that occur during digestion include:

[0085] Water-soluble digestion:

[0086] CaO+H 2 O→Ca(OH)2 (aq)

[0087] MgO+H 2 O→Mg(OH) 2 (aq)

[0088] Ammonium chloride is used to adjust pH twice to precipitate magnesium ions and aluminum ions respectively:

[0089] Ca(OH) 2 +Mh(OH) 2 +2NH 4 Cl+H 2 O→Mg(OH) 2

[0090] ↓+CaCl 2 +2NH 3 ·H 2 O

[0091]

[0092] Al 3+ +3OH - →Al(OH) 3 ↓

[0093] Note: Aluminum ions react with excess hydroxide in a strong alkaline solution to form aluminate. When ammonium chloride is added to adjust the pH, aluminate reacts with ammonium ions and water to form aluminum hydroxide precipitate and ammonia gas, which dissolves in water. Therefore, the overall change of aluminum ions is from aluminum ions to aluminum hydroxide precipitate.

[0094] (4) The reaction solution after digestion enters the carbonization tank, and the smoke generated during the calcination process is cooled and washed, and then injected into the reaction solution in the form of micro-nano bubbles through a micro-nano bubble generator. The injection pressure of the micro-nano bubbles is controlled at 0.1-0.3 MPa, and the micro-nano bubbles are introduced into each liter of the reaction solution at a rate of 2-5 L / min, and stirred at a stirring rate of 300-600 rpm. At the same time, a crystal form regulator is added, and the crystal form regulator is glycine, and the glycine and Ca are controlled. 2+ The molar ratio of NH 4 + It can be adsorbed on the surface of vaterite particles to prevent the transformation of vaterite to calcite. Figure 2 As shown, the gas remaining in the upper part of the carbonization tank is circulated twice and passed into the solution of the carbonization tank to fully remove carbon dioxide. The remaining gas is collected and the activated calcium component is dehumidified to remove moisture, and pure synthesis gas is obtained, which can be provided to manufacturers. The calcium component after dehumidification is digested in water together with the mixture after microwave assisted heating.

[0095] The chemical changes that occur during the carbonization process are:

[0096]

[0097] Note: During the carbonization process, glycine first reacts with ammonia water to form ammonium glycinate, which then reacts with calcium chloride to form calcium glycinate and ammonium chloride. Calcium glycinate is subsequently converted into calcium carbonate and glycine. Therefore, the above formula indicates that glycine is a catalyst.

[0098] (5) The suspended solution after the reaction in the carbonization tank is filtered with the aid of ultrasound to achieve solid-liquid separation, and the separated liquid is returned to the digestion tank for recycling. The separated solid particles are high-purity vaterite, which is dried by microwave to obtain micro-nano-scale vaterite.

[0099] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0100] Example 1

[0101] A microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization and regeneration of waste stone powder, comprising the following steps:

[0102] Municipal sludge flocculated with iron salt and ammonia sugar sludge were mixed in a mass ratio of 1:1, and the C / Fe mass ratio was 4.2:1. After sludge granulation (40mm), it was evenly mixed with waste stone powder in a mass ratio of 1:4. The composition of each solid waste material is shown in Table 1. The composition of waste stone powder is mainly calcium carbonate, magnesium carbonate and silicon dioxide.

[0103] Table 1 Solid waste material composition (wt%)

[0104]

[0105] In the microwave rotary kiln, the waste stone powder and iron-rich sludge are first preheated with high-temperature flue gas (300°C, heat preservation for 10 minutes), and then microwave-assisted heating is performed to reach the set temperature (850°C) in 3-5 minutes and heat preservation for 6 minutes. The carbonate minerals in the waste stone powder are almost completely decomposed, and the BET specific surface area of ​​the produced iron-carbon material reaches 181.15m 2 / g, in which iron minerals mainly exist in the form of FeO and nano-zero-valent iron, containing some ferrous phosphate and a small amount of residual Fe 3 O 4 .

[0106] The heated material was digested and dissolved at a water-solid ratio of 10 L / kg, and sieved to separate the iron-carbon material. The solid residue was mainly SiO 2 The calcium content in the solid residue is only 0.46%; ammonium chloride, NH4 + With Ca 2+ The molar ratio of Mg(OH) was controlled to 2:1 and filtered to obtain 2 Precipitation, control the pH value of the filtrate to 9, filter and obtain Al(OH) 3 , the presence of aluminum and iron elements was almost undetectable in the obtained filtrate, and the magnesium ion concentration was only 0.13% of the calcium ion concentration.

[0107] The digested solution enters the carbonization tank. The preheated flue gas is cooled and washed before entering the micro-nano bubble generator. The obtained micro-nano bubbles are injected into the solution. The injection pressure of the micro-nano bubbles is 0.1MPa. The micro-nano bubbles are introduced into each liter of solution at a rate of 3L / min. The gas (mainly ammonia) generated during the digestion process is also introduced into the solution. The milky white tiny bubbles are quickly distributed in the solution and circulated. The stirring rate is controlled at 300rpm. Glycine and Ca are added. 2+ The molar ratio is 2:1, and a white precipitate is quickly generated in the reaction solution. After ultrasonic-assisted filtration and microwave drying, a high-purity vaterite product is obtained, with a calcium carbonate content of 99.2% and a vaterite content of 94.7%.

[0108] Example 2

[0109] A microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization and regeneration of waste stone powder, which differs from Example 1 in that the C / Fe mass ratio of municipal sludge flocculated by iron salt and ammonia sugar sludge after mixing is 3:1, and the remaining steps are consistent with Example 1.

[0110] The BET specific surface area of ​​the produced iron-carbon material reached 116.51m 2 / g,Fe 3 O 4 The content is slightly increased. A high-purity vaterite product is obtained, with a calcium carbonate content of 98.5% and a vaterite content of 94.1%.

[0111] Example 3

[0112] A microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization and regeneration of waste stone powder, which differs from Example 1 in that the C / Fe mass ratio of municipal sludge flocculated by iron salt and ammonia sugar sludge after mixing is 6:1, and the remaining steps are consistent with Example 1.

[0113] The BET specific surface area of ​​the produced iron-carbon material reached 194.67 m 2 / g, more low-valent iron and nano-scale zero-valent iron are produced on the carbon surface. High-purity vaterite products are obtained, with a calcium carbonate content of 99.4% and a vaterite content of 94.8%.

[0114] Example 4

[0115] A microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization and regeneration of waste stone powder, which differs from Example 1 in that: after sludge granulation (40 mm), it is evenly mixed with waste stone powder in a mass ratio of 1:3, and the remaining steps are consistent with Example 1.

[0116] The solid residue after primary filtration is mainly SiO 2 The calcium content in the residue is 0.17%; a high-purity vaterite product is obtained, the calcium carbonate content reaches 99.4%, and the vaterite content is 95.0%.

[0117] Example 5

[0118] A microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization and regeneration of waste stone powder. The difference from Example 1 is that after sludge granulation (40 mm), it is evenly mixed with waste stone powder in a mass ratio of 1:6, and the remaining steps are consistent with Example 1.

[0119] The solid residue after primary filtration is mainly SiO 2 The calcium content in the residue increased slightly to 3.52%; a high-purity vaterite product was obtained, with a calcium carbonate content of 98.7% and a vaterite content of 94.3%.

[0120] Comparative Example 1

[0121] A method for preparing vaterite by microwave-assisted energy-saving waste stone powder microbubble mineralization regeneration, which is different from Example 1 in that: NH 4 + With Ca 2+ The molar ratio of is controlled to be 1:1, and the remaining steps are consistent with those of Example 1.

[0122] The vaterite product was obtained, the calcium carbonate content reached 92.3%, and the vaterite content was 37.1%.

[0123] Comparative Example 2

[0124] A method for preparing vaterite by microwave-assisted energy-saving waste stone powder microbubble mineralization regeneration, which is different from Example 1 in that: NH 4 + With Ca 2+ The molar ratio of is controlled to be 3:1, and the remaining steps are consistent with those of Example 1.

[0125] The vaterite product was obtained, the calcium carbonate content reached 95.5%, the vaterite content was 91.68%, and the calcium ion concentration in the circulating filtrate was increased by about 20%.

[0126] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A microwave-assisted energy-saving method for preparing vaterite by microbubble mineralization and regeneration of waste stone powder, characterized in that: include: The waste stone powder and the iron-rich sludge are mixed and preheated, and then subjected to microwave-assisted heating; During the microwave-assisted heating process, the waste stone powder is decomposed and activated, and carbon dioxide is produced at the same time. The iron-rich sludge is pyrolyzed into iron-carbon materials in a carbon dioxide atmosphere to obtain mixed materials and flue gas containing carbon dioxide. The mixed material is mixed with a leaching agent, digested and dissolved, filtered for the first time, insoluble matter is filtered out, and a primary filtrate is obtained; the pH of the primary filtrate is adjusted and filtered again to filter out magnesium hydroxide precipitate and aluminum hydroxide precipitate to obtain a secondary filtrate; The flue gas containing carbon dioxide enters the micro-nano bubble generator after being cooled and harmful gases are removed to obtain micro-nano bubbles; Under stirring, the micro-nano bubbles are injected into the secondary filtrate, and a crystal form regulator is added to react to obtain vaterite.

2. The method according to claim 1, characterized in that The particle size of the waste stone powder is less than 0.08 mm; Preferably, the iron-rich sludge is particles with a particle size of 20-60 mm, and the mass ratio of carbon to iron in the iron-rich sludge is 3-6:1; Preferably, the mass ratio of the waste stone powder to the iron-rich sludge is 3-6:

1.

3. The method according to claim 1, characterized in that The preheating is to heat the mixture of waste stone powder and iron-rich sludge to 300-400°C and keep it warm for 7-12 minutes; The microwave-assisted heating is carried out at a temperature of 800-900° C. and is kept warm for 5-10 minutes.

4. The method according to claim 1, characterized in that The flue gas containing carbon dioxide preheats and cools the next batch of waste stone powder and iron-rich sludge mixture, and then enters the micro-nano bubble generator after cooling and removing harmful gases to obtain micro-nano bubbles.

5. The method according to claim 1, characterized in that The leaching agent is water, and the water-to-solid ratio is 6-12L / kg; Preferably, the digestion and dissolution time is 20-40 min.

6. The method according to claim 1, characterized in that The pH of the primary filtrate is adjusted, comprising: adding ammonium chloride to the primary filtrate to reduce the pH of the primary filtrate, controlling the molar ratio of ammonium ions to calcium components in the waste stone powder to be 2-2.4:1, generating magnesium hydroxide precipitates from magnesium ions in the primary filtrate, filtering out the magnesium hydroxide precipitates, and continuously adding ammonium chloride to the filtrate to adjust the pH to 8.5-9.0 so that aluminum ions generate aluminum hydroxide precipitates, filtering out the aluminum hydroxide precipitates, and obtaining a secondary filtrate; In the process of adjusting the pH of the primary filtrate, the gas generated by adding ammonium chloride is collected and then introduced into the secondary filtrate simultaneously with the micro-nano bubbles.

7. The method according to claim 1, characterized in that The injection pressure is 0.1-0.3 MPa, and the micro-nano bubbles are injected at a rate of 2-5 L / min per liter of solution.

8. The method according to claim 1, characterized in that The stirring speed is 300-600 rpm.

9. The method according to claim 1, characterized in that The crystal form regulator is glycine, the molar ratio of glycine to the calcium component in the waste stone powder is 0.6-2:1, and the reaction time is 20-50 minutes.

10. The method according to claim 1, characterized in that After the reaction is completed, the solid and liquid are separated and dried to obtain vaterite; Preferably, ultrasonic-assisted filtration is used for solid-liquid separation; Preferably, the filtrate after the solid-liquid separation is recycled as a leaching agent; Preferably, the drying is microwave drying; Preferably, the vaterite is micro-nano-scale vaterite.

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