A carbonation consolidation method for improving pellet strength

Abstract

The present invention proposes a carbonation consolidation method for improving the strength of pellets. By changing the carbonation consolidation reaction system, the main reactants of the reaction process, calcium and CO2, are added to the raw balls in an ionic state. The carbonation reaction occurs in the ball-making process, and the reaction is in an ionic state. The reaction efficiency is much higher than the gas-solid reaction efficiency. The reaction is continued in depth during the drying and consolidation process to further improve the strength of the pellets, and ultimately improve the production efficiency of metallurgical solid waste carbonation consolidation and shorten the production cycle. Compared with ordinary carbonation consolidation, the pellets prepared by the process of the present invention have the characteristics of faster and more uniform carbonation reaction, higher pellet strength, and higher production efficiency.

Description

Technical Field

[0001] The invention relates to a pellet carbonation consolidation method, in particular to a high-strength pellet carbonation consolidation method, and belongs to the technical field of metallurgy. Background Art

[0002] The process of extracting metallic iron from iron-containing minerals (mainly iron oxides) mainly includes blast furnace method, direct reduction method, smelting reduction method, etc. From a metallurgical point of view, ironmaking is the reverse behavior of iron rusting and gradual mineralization. Simply put, it is the reduction of pure iron from iron-containing compounds. The production process of reducing iron ore with a reducing agent at high temperature to obtain pig iron. The main raw materials for ironmaking are iron ore and coke; the role of coke is to provide heat and produce reducing agents. Oxidation carbon .

[0003] Metallurgical solid waste generally contains a high content of alkali metals, which makes it difficult to return to the metallurgical process for direct use and needs to be removed in advance. Metallurgical solid waste containing alkali metals is removed by calcification oxidation roasting or calcification reduction roasting. A large amount of calcium-containing substances need to be added in the process of removing alkali metals, which are used to replace the alkali metals in the complex multi-component solid solution under high-temperature oxidation or reduction atmosphere, so that it is converted into a simple alkali metal compound, and then removed by leaching or reduction volatilization. Before high-temperature roasting, calcium-containing pellets need to be dried first and ensure that the pellets have a certain compressive and falling strength. Because the raw balls contain a high proportion of calcium hydroxide, it is appropriate to use the carbonation consolidation method to improve the strength of the dried balls. The carbonation consolidation process of metallurgical solid waste mainly occurs in the reaction of Ca(OH)2 combining with CO2 to form CaCO3. The carbonation consolidation process of traditional pellets is carried out at a lower temperature (50-70°C) and a relatively concentrated CO2 atmosphere (25%-30%), and it is necessary to keep the pellets containing a certain amount of water or in a water vapor environment. In the reaction process, CO2 diffuses from the outside of the pellet to the inside and contacts and reacts with calcium hydroxide in the pellet, which belongs to the typical unreacted core model. It is very easy to form a dense calcium carbonate film on the outer surface of the pellet first, which hinders the diffusion of CO2 gas into the inside of the pellet, greatly slowing down the overall carbonation process of the pellet. In order to ensure that the water in the pellet does not lose too fast to slow down the carbonation reaction rate, and when the strength of calcium carbonate microcrystals has not been established due to excessive drying, it is difficult for the dried calcium hydroxide to maintain the pellet strength during the drying and consolidation process. The temperature of the carbonation consolidation process needs to be maintained at a relatively low temperature, which results in extremely low drying and consolidation efficiency. It takes dozens of hours of drying and consolidation or long-term storage and slow reaction to make the pellet reach the required strength. If the reaction efficiency is to be improved, a higher temperature or a very high concentration of CO2 atmosphere is required, the conditions are harsh, and it is also difficult to ensure the pellet strength during the drying and consolidation process, resulting in the pellet material height being severely limited during the drying and consolidation process, and the production efficiency is not high. Therefore, it is difficult for traditional carbonation consolidation to balance the raw ball strength, the ball strength during the drying and consolidation process, the dry ball strength and the production efficiency.

[0004] In order to achieve low-temperature consolidation of metallurgical solid waste, researchers and practitioners have proposed some technical measures. Patent CN102732670A proposes a method for recycling iron-containing dust by using a carbonation process. The iron-containing dust and active lime are mixed to form balls, and then carbonation consolidation is carried out in a carbonation reaction tank at a temperature of 500℃-600℃ and a gas environment with a CO2 concentration greater than 50%. After the pellets have a certain strength, they replace the calcium-containing flux in converter steelmaking and shorten the converter steelmaking cycle. Patent CN1842604B proposes self-reducing cold consolidation pellets and their manufacturing methods. Cement clinker is used as a binder, mixed with mineral powder to form balls, and then CO2-containing gas is introduced into the curing device at a temperature of 100℃-300℃ for consolidation for 24h-96h, so that the pellets have higher strength. In the article “Research and Analysis on Preparation of Converter Slag-Forming Agent by Carbonation of Converter Dust” published by Zhang Zhixia in Shanxi Metallurgy (2012, 194(6): 28-29), converter dust and lime were pressed into blocks with a pressure greater than 2000N, and then reacted at 600℃ in 75% CO2 gas for 60min to obtain agglomerates with a compressive strength greater than 100N, which can meet the requirements of converter smelting for slag-forming agents.

[0005] The carbonation consolidation of the prior art is controlled by the diffusion of CO2 gas, with a low reaction rate and a low internal carbonation degree. The CO2 that reacts with Ca(OH)2 during the carbonation consolidation process comes from the reaction atmosphere, gradually diffuses from the outside of the pellet to the inside of the pellet and participates in the reaction, which belongs to the typical unreacted core model. The outer layer of the pellet first undergoes carbonation reaction, forming a dense calcium carbonate film, which hinders the further diffusion of gas into the interior of the pellet, resulting in a slow internal carbonation reaction and a low reaction degree.

[0006] The production efficiency and pellet strength of the existing technology cannot be taken into account at the same time. It is one of the necessary conditions for the carbonation consolidation reaction that the pellets contain some water or are in a water vapor environment. In order to ensure that the water in the pellets is not lost too quickly, the existing carbonation consolidation is carried out at a relatively low temperature. The low temperature will reduce the carbonation reaction rate, and it takes dozens of hours of drying and consolidation or long-term storage for slow reaction, resulting in low production efficiency. If the reaction temperature is increased and the carbonation consolidation rate is increased with high-purity CO2 gas in the presence of water vapor, the calcium hydroxide inside the pellets will be rapidly dehydrated, and the strength of the calcium hydroxide in the dry state will be low. The calcium carbonate crystallites inside the dried pellets after the water is quickly removed are not fully developed and cannot provide strength support. The strength of the bonding bridge of the dried calcium hydroxide is extremely low, resulting in extremely low pellet strength during the drying process. The material layer height during the drying and consolidation process is severely limited, and a large amount of powder is easily generated, which will also cause low production efficiency.

[0007] The conventional heating environment of the prior art causes the slow development of calcium carbonate crystallites and low strength, resulting in low strength of carbonated consolidation balls. The strength of carbonated consolidation balls is provided by the gradual formation and growth of calcium carbonate crystallites generated by the reaction. Under conventional heating conditions, newly formed calcium carbonate crystallites develop and grow on their own at a slow speed, and the temperature inside the balls is low, the carbonation reaction proceeds slowly, and the newly formed calcium carbonate is small in amount and low in strength. The consolidated balls tend to become a double-layer structure, with a high degree of carbonation and high strength in the outer layer, and a low degree of carbonation and low strength in the inner core. This double-layer ball with a hard outer layer and a loose inner layer has poor falling strength and is very easy to break during the belt transport and falling process, producing a large amount of broken balls and powder, affecting production efficiency. Summary of the invention

[0008] In view of the technical problems in the prior art, the strength of the prepared pellets is low, the pellets are easily broken in the drying and consolidation process, which is not conducive to the removal of alkali metals, affects the subsequent reduction process, and has a large amount of dust. The present invention proposes a carbonation consolidation method for improving the strength of the pellets. By changing the carbonation consolidation reaction system, the main reactants calcium and CO2 in the reaction process are added to the raw balls in an ionic state. Carbonation reaction occurs in the ball making process, and the reaction is in an ionic state. The reaction efficiency is much higher than the gas-solid reaction efficiency. The reaction continues in depth during the drying and consolidation process to further improve the strength of the pellets, and finally improve the production efficiency of carbonation consolidation of metallurgical solid waste and shorten the production cycle. Compared with ordinary carbonation consolidation, the pellets prepared by the process of the present invention have the characteristics of faster and more uniform carbonation reaction, higher pellet strength, and higher production efficiency.

[0009] A carbonation consolidation method for improving pellet strength, the method comprising the following steps:

[0010] (1) dissolving calcium oxide and / or calcium hydroxide in an aqueous solution to obtain raw water containing calcium hydroxide;

[0011] (2) dissolving the acid solution in water to obtain ball-making water containing the acid solution;

[0012] (3) uniformly mixing the iron-containing raw material, raw water containing calcium hydroxide, a binder, and a fuel to obtain a pelletizing raw material;

[0013] (4) mixing the pelletizing water containing the acid solution with the pelletizing raw materials to perform pelletizing to obtain pellets;

[0014] (5) subjecting the pellets to a drying and consolidation process to obtain consolidated pellets; and, during the drying and consolidation process, introducing a gas containing CO2 and water vapor; and the gas containing CO2 and water vapor is transported to the water in step (2) after the drying and consolidation process.

[0015] Preferably, the drying and consolidation process described in step (5) is heated by microwaves. The pellets are transported to a microwave device; a gas containing CO2 and water vapor is introduced into the microwave device to dry and consolidate the pellets, and then discharged from the microwave device and transported to step (2), where CO2 is dissolved in the aqueous solution to obtain pelletizing water containing an acid solution.

[0016] Preferably, the drying and consolidation process described in step (5) adopts hot air pre-drying and microwave drying and consolidation. The pellets are transported to a hot air pre-drying device for pre-drying, and the pre-dried pellets are transported to a microwave device for drying and consolidation, and then consolidated pellets are obtained. The gas containing CO2 and water vapor is transported to a microwave device to dry and consolidate the pellets, and then discharged from the microwave device, and then transported to a hot air pre-drying device to pre-dry the pellets. The gas containing CO2 and water vapor discharged from the pre-drying device is transported to step (2), CO2 is dissolved in the aqueous solution, and pelletizing water containing an acid solution is obtained.

[0017] In the present invention, the mass concentration of calcium hydroxide in the raw water containing calcium hydroxide obtained in step (1) is 0.01 to 0.18%, preferably 0.02 to 0.16%.

[0018] In the present invention, the acid solution in step (2) is oxalic acid and / or acetic acid.

[0019] Preferably, the mass concentration of acid in the ball-making water containing the acid solution is 5-80%, preferably 10-70%. In step (5), the gas containing CO2 and water vapor is dissolved in the ball-making water containing the acid solution, wherein the solubility of CO2 is 0.1m 3 CO2 / m 3 H2O~1.7m 3 CO2 / m 3 H2O, preferably 0.5m 3 CO2 / m 3 H2O~1.5m 3 CO2 / m 3 H2O.

[0020] In the present invention, in the pelletizing raw material of step (3), the weight ratio of the raw water containing calcium hydroxide to the iron-containing raw material is 3 to 20:100, preferably 5 to 18:100.

[0021] In the present invention, in the pelletizing raw material of step (3), the weight ratio of the iron-containing raw material to the binder is 1:0.1-1, preferably 1:0.2-0.5.

[0022] In the present invention, in step (4), the weight ratio of the pelletizing water containing the acid solution to the pelletizing raw materials is 3 to 20:100, preferably 5 to 10:100.

[0023] In the present invention, the particle size of the pellets is 2 to 15 mm, preferably 3 to 8 mm.

[0024] In the present invention, the volume concentration of CO 2 in the gas containing CO 2 and water vapor is 10 to 50%, preferably 20 to 40%.

[0025] In the present invention, the humidity of the gas containing CO2 and water vapor is 10g / m 3 ~100g / m 3 , preferably 20g / m 3 ~50g / m 3 .

[0026] In the present invention, the gas containing CO2 and water vapor is one or more of hot air with added water vapor and CO2, hot tail gas after combustion of blast furnace gas, coke oven gas or converter gas, direct reduction hot tail gas, and lime kiln hot tail gas.

[0027] In the present invention, when microwave heating is used for drying and consolidation, the temperature is 100°C to 500°C, preferably 300°C to 400°C. The drying and consolidation time is 10min to 60min, preferably 20min to 40min. The microwave power density is 5kw / m 3 ~50kw / m 3 , preferably 20kw / m 3 ~30kw / m 3 .

[0028] In the present invention, when hot air pre-drying and microwave drying consolidation are adopted: the hot air temperature is 60℃~300℃, preferably 100℃~250℃. The hot air pre-drying time is 5min~50min, preferably 10min~20min. The moisture content in the pellets after hot air pre-drying is 2%~8%, preferably 3%~6%. The microwave drying consolidation temperature is 200℃~500℃, preferably 300℃~400℃. The drying consolidation time is 5min~40min, more preferably, 10min~30min. The microwave power density is 5kw / m 3 ~50kw / m 3 , preferably 20kw / m 3 ~30kw / m 3 .

[0029] Preferably, bicarbonate or a mixture of bicarbonate and carbonate is added to the pelletizing raw material in step (3).

[0030] Preferably, the amount of bicarbonate or a mixture of bicarbonate and carbonate added is 1% to 50% by weight of the iron-containing raw material, preferably 5% to 45%, and more preferably 10% to 40%.

[0031] Preferably, a high-temperature gas slow-release agent is also added to the pelletizing raw materials in step (3).

[0032] Preferably, the addition amount of the high temperature gas slow-release agent is 1% to 30% by weight of the iron-containing raw material, preferably 5% to 25%, and more preferably 8% to 20%.

[0033] In the present invention, the bicarbonate is Ca(HCO3)2 and / or Mg(HCO3)2. The bicarbonate-carbonate mixture is one or more of Ca(HCO3)2-FeCO3, Mg(HCO3)2-FeCO3, Ca(HCO3)2-Mg(HCO3)2, and Ca(HCO3)2-FeCO3-Mg(HCO3)2.

[0034] In the present invention, the high temperature gas slow-release agent is one or more of ferroxene, hydrated iron oxide, diolite, and tremolite.

[0035] In the present invention, the iron-containing raw material is slag and / or metallurgical dust.

[0036] Preferably, the iron-containing raw material is one or more of vanadium-extracting tailings, copper slag, steel slag, and zinc-containing dust.

[0037] In the present invention, the binder is calcium oxide or a calcium salt, preferably one or more of calcium oxide, calcium hydroxide, calcium carbonate, calcium chloride, and calcium sulfate, more preferably calcium hydroxide.

[0038] In the present invention, the fuel is a carbon-containing solid fuel, preferably coke.

[0039] In the present invention, the microwave device comprises n sections, where n is 1-5.

[0040] Preferably, the microwave device comprises three sections, namely, a microwave drying section (101), a microwave drying consolidation section I (102), and a microwave drying consolidation section II (103). The pellets are sequentially passed through the microwave drying section (101), the microwave drying consolidation section I (102), and the microwave drying consolidation section II (103) to obtain consolidated pellets. The gas containing CO2 and water vapor is transported to the microwave drying consolidation section II (103), transported from the microwave drying consolidation section II (103) to the microwave drying consolidation section I (102), discharged from the microwave drying consolidation section I (102) and then transported to the microwave drying section (101), and discharged from the microwave drying section (101) and then transported to step (2), CO2 is dissolved in the aqueous solution, and pelletizing water containing an acid solution is obtained.

[0041] In the present invention, the temperature of the microwave drying section (101) is 100°C to 200°C, and the material running time is 2min to 20min.

[0042] In the present invention, the temperature of the microwave drying and consolidation stage I (102) is 200°C to 350°C, and the material running time is 5min to 20min.

[0043] In the present invention, the temperature of the microwave drying and consolidation stage II (103) is 350°C to 500°C, and the material running time is 3min to 20min.

[0044] In the present invention, the hot air pre-drying device is m sections, and m is 1-3.

[0045] Preferably, the hot air pre-drying device is composed of two sections, namely a hot air drying section (201) and a hot air drying consolidation section (202). The pellets are sequentially conveyed to the microwave device after passing through the hot air drying section (201) and the hot air drying consolidation section (202). The gas discharged from the microwave device is conveyed to the hot air drying consolidation section (202), the gas discharged from the hot air drying consolidation section (202) is conveyed to the hot air drying section (201), and the gas discharged from the hot air drying section (201) is conveyed to step (2), CO2 is dissolved in the aqueous solution, and pelletizing water containing an acid solution is obtained.

[0046] In the present invention, the temperature of the hot air drying section (201) is 60°C to 100°C, and the material running time is 2min to 20min.

[0047] In the present invention, the temperature of the hot air drying consolidation section (202) is 100°C to 300°C, and the material running time is 3min to 30min.

[0048] In the present invention, after the pellets pass through the hot air pre-drying device, the moisture content in the pellets is 2% to 8%, more preferably 3% to 6%.

[0049] In the prior art, the low strength of the pellets is mainly caused by the following reasons: during the drying and consolidation process of the pellets, CO2 gas can only diffuse from the outside of the pellets to the inside of the pellets, causing the binder (such as calcium hydroxide) in the outer layer of the outer pellet to react with CO2 preferentially to form a dense calcium carbonate layer, which hinders the CO2 gas from continuing to diffuse into the interior of the pellets, resulting in the inability to form calcium carbonate inside the pellets, affecting the overall strength of the pellets.

[0050] The present invention firstly washes the carbonation-solidified tail gas with water to dissolve the CO2 therein, so that it is converted into carbonic acid and dissolved in water, and this part of water is used as ball-making water. It has two functions. First, CO2 in the tail gas can be absorbed by water washing to reduce carbon emissions and realize the recycling of part of CO2 in the tail gas; second, CO2 dissolved in water is converted into carbonic acid, and this part of water is used as ball-making water. During the ball-making process, carbonate ions in the water after CO2 is dissolved come into contact with calcium ions or calcium hydroxide in the raw materials, and a carbonation reaction occurs. The ionic carbonate dissolved in the water has a strong ability to react with calcium, and calcium carbonate can be quickly formed and crystallized. Carbonation consolidation reaction occurs inside the pellets while the raw balls grow, and the pellet strength is improved.

[0051] The present invention uses an aqueous solution dissolved with calcium hydroxide as pelletizing raw material water and mixes it with the raw material. The calcium hydroxide aqueous solution is adsorbed on the surface of the raw material particles during the mixing process of the raw materials and exists in the raw materials in the form of molecular water. In this way, a large amount of calcium ions are evenly distributed on the surface of the raw material particles, thereby avoiding the situation that the calcium component in the conventional raw materials is mainly in the calcium hydroxide particles and there is basically no calcium ion in the molecular water on the surface of the raw material particles. The molecular water does not flow on the particle surface. In the process of adding the ball-making water during ball-making, the ball-making water is adsorbed on the surface of the raw material particles and migrates between the particles. Once the calcium ions uniformly dispersed in the molecular water on the surface of the raw material particles contact the carbonate in the ball-making water, the calcium ions and the carbonate ions undergo a carbonation reaction to generate calcium carbonate. In the precipitation process of the newly formed calcium carbonate, the raw material particles in contact with each other are bonded together, thereby improving the carbonation consolidation rate and the strength of the pellets.

[0052] In the present invention, the water added in the whole process of manufacturing pellets is divided into raw water and pelletizing water. The raw water mainly plays a role in wetting and mixing iron-containing raw materials, binders and fuels, and the pelletizing water is mainly used for the molding and granulation of pellets. In the present invention, calcium hydroxide is added to the raw water, and the mass concentration of calcium hydroxide is controlled to be 0.01-0.18% (preferably 0.02-0.16%), so that the raw water contains dispersed and free calcium hydroxide molecules, and the calcium hydroxide is attached to the surface of the raw material along with the water molecules to form a single raw material particle wrapped by calcium hydroxide. In the pelletizing water, an acid solution is added, and CO2 is dissolved. CO2 is dissolved in water to form carbonate ions. The carbonate ions and other acid radical ions in the pelletizing water are all present in the pelletizing water in an ionic state. In the pelletizing process, the pelletizing raw material is mixed with the pelletizing water, and the powerful carbonate ions and other acid radical ions in the pelletizing water directly react with the calcium hydroxide coating layer on the surface of the raw material in the pelletizing raw material. The pelletizing process is a process in which single-particle pelletizing raw materials are aggregated into agglomerates. In this process, while single-particle pelletizing raw materials are aggregated into agglomerates, calcium hydroxide, carbonate ions or other acid ions are included between the particle pelletizing raw materials. The calcium hydroxide between the particles and the carbonate ions or other acid ions directly react in the drying and consolidation process to form calcium carbonate with higher strength, thereby achieving a direct reaction inside the pellet to form a product of strongly consolidated pellets, thereby improving the strength inside the pellets. In addition, in the pelletizing process, products of the reaction of calcium hydroxide with carbonate ions or other acid ions also begin to form between the particle pelletizing raw materials. The formed products are solidified in the drying and consolidation process, which plays a role in strengthening the strength of the pellets.

[0053] Compared with the prior art, the drying and consolidation of the pellets can only be achieved by diffusion of CO2 in the atmosphere into the pellets, reacting with the binder in the pellets to form a consolidation product to solidify the pellets; the technical solution of the present invention, in the process of pelletizing, one of the reactants forming the consolidation material (calcium hydroxide) is attached to the surface of the single particle raw material, and the ball-making water contains another reactant (carbonate or) other acid ions forming the consolidation material. At the same time of ball formation, the two reactants are already dispersed between the raw material particles in the pellets. In the drying and consolidation process, the reactants between the raw material particles directly react to form the consolidation material, which plays the role of consolidating the pellets; avoiding the disadvantage that the reactants need to diffuse from the outside of the pellets to the inside of the pellets to react. In addition, in the technical solution of the present invention, the reactants undergoing the consolidation reaction are in an ionic state, and in the consolidation process, a liquid-liquid reaction occurs. Compared with the gas-solid reaction in the prior art, the reaction rate has been greatly improved. By adopting the technical solution of the present invention, the reaction of consolidating the pellets to form the consolidated material is carried out simultaneously outside, inside, and from inside to outside of the pellets, thus overcoming the technical problem of the prior art that there is a dense layer of calcium carbonate that hinders the process from outside to inside.

[0054] A certain amount of acid solution (such as oxalic acid or acetic acid, etc.) is added to the ball-making water used in the present invention, which is a soluble organic acid with a carboxyl group. In the ball-making process, because a large amount of binder (such as calcium hydroxide) is added to the raw materials, when the molecules of oxalic acid, acetic acid, etc. in the ball-making water come into contact with the calcium hydroxide particles or molecular water containing calcium hydroxide in the raw materials, the pH value of the aqueous solution is strongly alkaline. In this process, the following reactions occur:

[0055] ① Oxalic acid or acetic acid combines with calcium ions to form precipitation reaction of calcium oxalate or calcium acetate:

[0056] H2C2O4+Ca(OH)2=CaC2O4↓+2H2O (oxalic acid combines with calcium to form calcium oxalate)

[0057] 2CH3COOH+Ca(OH)2=Ca(CH3COO)2↓+2H2O (acetic acid combines with calcium to form calcium acetate)

[0058] ②Decarboxylation reaction of carboxyl group in alkaline environment and CO2 dissolution reaction:

[0059] R-COOH→RH+CO2 (decarboxylation reaction)

[0060] CO2+H2O=2H + +CO3 2- (CO2 dissolution reaction)

[0061] ③ The carbonate ions dissolved in the water between the particles react with the calcium ions to form a carbonation reaction:

[0062] CO3 2- +Ca 2+ =CaCO3↓(carbonate reacts with calcium ions)

[0063] Therefore, during the green ball nucleation and green ball growth stages, calcium oxalate or calcium acetate will be generated inside the green ball, and a carbonation reaction will occur. The newly generated calcium oxalate / calcium acetate / calcium carbonate will bond the raw material particles together and improve the strength of the pellets.

[0064] In addition, the first type of substance added in the pelletizing process of the present invention is a CHO low-temperature release agent (bicarbonate or a mixture of bicarbonate-carbonate). In the pellet drying and consolidation process, the CHO low-temperature release agent in the core (inside) of the pellet can release CO2 and H2O under the low temperature conditions of drying and consolidation, and the released CO2 and H2O react with the binder (such as calcium hydroxide) in the pellet to form a calcium carbonate consolidation structure uniformly in the entire pellet; so that in the entire pellet, each position forms a high-strength calcium carbonate consolidation, thereby improving the strength of the entire pellet. In the technical solution of the present invention, the CHO low-temperature release agent between the raw material particles is converted into CO2 and H2O during the drying and consolidation process, directly providing the CO2 gas and H2O vapor environment required for the carbonation reaction inside the pellet, changing the previous unreacted core model, avoiding the situation where the traditional CO2 needs to diffuse from the outside of the pellet into the inside, and the outside and inside of the pellet are carbonated synchronously, without the influence of the outer dense calcium carbonate film hindering gas diffusion, and reducing the diffusion resistance of CO2 inside the pellet. In addition, from the analysis of reaction kinetics, compared with the diffusion of CO2 gas from the outside of the pellet to the inside of the pellet, the technical solution of the present invention is used to release CO2 and H2O from the inside of the pellet, and it is much easier for CO2 and H2O inside the pellet to diffuse outward, thereby making it easier for the binder (such as calcium hydroxide) in the pellet to react with CO2 in the presence of water vapor, and the obtained calcium carbonate consolidation material is more uniform.

[0065] In the present invention, the CHO low-temperature release agent is solid at room temperature. During the drying and consolidation process, the bicarbonate or carbonate is decomposed by heat to release carbon dioxide and / or water. The released carbon dioxide reacts with the binder in the pellets under the action of water vapor to form a compound that has a consolidation effect. For example, the Ca(HCO3)2 used in this application begins to decompose at 250°C, releasing CO2 and H2O; Mg(HCO3)2 begins to decompose at about 90°C, releasing CO2 and H2O; FeCO3 begins to decompose at 320°C, releasing CO2. The CHO low-temperature release agent is in solid state at room temperature, and is convenient for mixing with iron-containing raw materials to form pellets. After the CHO low-temperature release agent is mixed with the iron-containing raw materials and other additives to form pellets, it gradually begins to decompose under the elevated temperature conditions of the drying and consolidation process to release CO2 and H2O, thereby achieving the technical effect of the pellets self-releasing CO2 and H2O during the drying and consolidation process. Moreover, unlike the method of introducing CO2 and H2O from the outside, the pellets of the present invention release CO2 and H2O from the inside of the pellets, and the consolidation process is carried out simultaneously inside and outside the pellets, so that the pellets after drying and consolidation have a structure with uniform strength from the inside to the outside, thereby overcoming the technical problem of "hard outside and loose inside". At the same time, the decomposition temperature of the CHO low-temperature release agent used in the present invention cannot be too high, because the drying temperature of the pellets is generally controlled below 500°C (preferably 400°C). If bicarbonate or carbonate with a decomposition temperature that is too high (over 500°C) is used, it cannot be decomposed to release CO2 and H2O during the drying and consolidation process, thereby failing to achieve the technical purpose and effect of releasing CO2 and H2O from the inside of the pellets. After continuous experiments by the inventors, compounds or compositions of Ca(HCO3)2, Mg(HCO3)2, Ca(HCO3)2-FeCO3, Mg(HCO3)2-FeCO3, Ca(HCO3)2-Mg(HCO3)2 or Ca(HCO3)2-FeCO3-Mg(HCO3)2 are added in the process of preparing pellets. Such substances can release CO2 and H2O within the temperature range of the pellet drying and consolidation process. The decomposition temperature of such substances coincides with the temperature of the drying and consolidation process. Under the temperature conditions of the drying and consolidation process, they begin to release CO2 and H2O, providing the CO2 and H2O required for consolidation inside the pellets.

[0066] In the present invention, Ca(HCO3)2-FeCO3 refers to a mixture of Ca(HCO3)2 and FeCO3, Mg(HCO3)2-FeCO3 refers to a mixture of Mg(HCO3)2 and FeCO3, Ca(HCO3)2-Mg(HCO3)2 refers to a mixture of Ca(HCO3)2 and Mg(HCO3)2, and Ca(HCO3)2-FeCO3-Mg(HCO3)2 refers to a mixture of Ca(HCO3)2, FeCO3 and Mg(HCO3)2. Experimental verification shows that the CHO low-temperature release agents in the above 6 material forms can achieve the technical effects of the present application. The dosage ratio in the mixture does not affect the effect of the technical solution of the present application.

[0067] In the present invention, in the pellets, based on weight percentage, the addition amount of bicarbonate or a mixture of bicarbonate and carbonate can be 1 weight part, 2 weight parts, 3 weight parts, 4 weight parts, 5 weight parts, 6 weight parts, 7 weight parts, 8 weight parts, 9 weight parts, 10 weight parts, 12 weight parts, 15 weight parts, 18 weight parts, 20 weight parts, 23 weight parts, 25 weight parts, 28 weight parts, 30 weight parts, 32 weight parts, 35 weight parts, 38 weight parts, 40 weight parts, 42 weight parts, 45 weight parts, or 50 weight parts per 100 weight parts of iron-containing raw material.

[0068] After drying and consolidation, the pellets prepared by the present invention enter the reduction process. In the prior art, the iron-containing raw materials in the pellets are reduced by the internal carbon (fuel) in the pellets; the reduction process is that the internal carbon reacts with the air outside the pellets to produce CO, and the CO then starts to reduce the oxides in the pellets from the outside; then the CO diffuses from the outside of the pellets to the inside of the pellets to reduce the oxides inside the pellets. In the prior art, there is also a technical solution using hydrogen-based reduction, specifically: by introducing hydrogen into the reduction device, the hydrogen starts to reduce the oxides in the pellets from the outside of the pellets, and then the hydrogen diffuses from the outside of the pellets to the inside of the pellets to reduce the oxides inside the pellets. In the prior art, whether carbon-based reduction or hydrogen-based reduction is used, the reduction process is carried out from the outside to the inside.

[0069] The inventors of the present application have discovered through experiments that, during the preparation of pellets, a substance containing water of crystallization (high-temperature gas slow-release agent) is added, and the substance containing water of crystallization decomposes and releases H2O in the reduction stage, and H2O directly reacts with the internal carbon in the pellets to generate H2 and CO. The generated H2 and CO immediately undergo a reduction reaction with the oxides in the pellets, thereby achieving the technical effect of reducing the oxides from the inside of the pellets.

[0070] The second type of substance added in the pelletizing process of the present invention is a high-temperature gas slow-release agent, which can release H2O under high temperature conditions in the reduction process. In the reduction stage, as the material temperature rises, the high-temperature gas slow-release agent inside the pellet decomposes to release H2O, and at the same time, the calcium carbonate formed in the consolidation process decomposes to release CO2, which reacts with the carbon added inside the pellet to form reducing gases H2 and CO, thereby increasing the partial pressure of the reducing gas inside the pellet. The reducing gas contacts the material particles inside the pellet and undergoes a reduction reaction, thereby improving the reaction mode of the traditional reduction process in which only CO or H2 is used as a reducing agent and diffuses from the outside of the pellet to the inside, achieving uniform and rapid reduction inside the pellet, and avoiding the formation of a dense shell layer on the outer layer of the pellet during the reduction process that hinders the reduction reaction.

[0071] In the present invention, the substance used to release H2O in the reduction stage is a substance containing crystal water with a decomposition temperature of 500-1200°C. The high-temperature gas slow-release agent is stable and does not decompose in the drying and consolidation stage (below 500°C); after the pellets enter the reduction process, they begin to decompose and release H2O, which reacts with carbon (fuel) to form H2 and CO with reducing properties. CO has the characteristics of strong reducing power, and H2 has the advantage of fast reduction speed. By reducing the oxides in the pellets from both inside and outside the pellets, the reduction rate of the pellets is greatly improved.

[0072] Further experimental verification shows that ferroxene, hydrated iron oxide, diolite, and tremolite all meet the requirements of the high-temperature gas slow-release agent of the present invention, and can achieve the effects of stabilization in the drying and consolidation stage and release of H2O in the reduction stage in the present invention.

[0073] Further preferably, the high temperature gas slow release agent can be Fe7Si8O 22 (OH)2, Fe2O3·nH2O, Fe 18 Si 12 O 40 (OH) 10 、2CaO·5MgO·8SiO2·H2O One or more of them. The decomposition temperature of this kind of substances is between 500℃-1000℃. They are added in the process of pelletizing, and are in a stable state after the drying and consolidation process. They begin to decompose in the reduction process and gradually release H2O.

[0074] In the present invention, in the pellets, based on weight percentage, the addition amount of the high temperature gas slow-release agent for 100 parts by weight of iron-containing raw material can be 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, 5 parts by weight, 5.5 parts by weight, 6 parts by weight, 6.5 parts by weight, 7 parts by weight, 7.5 parts by weight, 8 parts by weight, 8.5 parts by weight, 9 parts by weight, 9.5 parts by weight, 10 parts by weight, 12 parts by weight, 15 parts by weight, 18 parts by weight, 20 parts by weight, 23 parts by weight, 25 parts by weight, 28 parts by weight, and 30 parts by weight.

[0075] In the prior art, the pellets are generally dried and consolidated by only hot air drying and consolidation. The hot air drying results in a higher temperature on the surface of the pellets and a lower temperature inside the pellets, resulting in a large temperature difference. In order to achieve the drying effect inside the pellets, the temperature outside the pellets needs to be further increased, resulting in a rapid reaction of CO2 on the surface of the pellets with the binder to form a dense calcium carbonate layer, further hindering the formation of the consolidation structure inside the pellets. In the preferred embodiment of the present invention, a "microwave" drying and consolidation technical means is added, using microwave drying and consolidation, or using a hot air pre-drying + microwave drying and consolidation method.

[0076] Compared with hot air drying, which is only a physical heat, drying and consolidating the pellets by heat transfer; microwaves are an energy field, and microwaves can directly act on the inside of the pellets to stimulate the reaction of calcium hydroxide and carbonate ions between the raw material particles inside the pellets. The present invention adopts a microwave heating method in the carbonation process of pellet drying and consolidation. Microwave heating can achieve simultaneous heating of the inside and outside of the pellets, avoiding the high temperature and fast reaction of the outside in the traditional heating process to form a dense spherical shell, which affects the internal reaction. The carbonate ions dissolved in the raw ball water during the rapid heating process inside the pellets can also quickly undergo a carbonation consolidation reaction with calcium hydroxide, making the newly formed calcium carbonate inside the pellets uniform, without a double-layer pellet structure, and improving the overall strength of the pellets.

[0077] In addition, the CHO low-temperature release agent inside the microwave pellets decomposes. Therefore, by means of microwave heating, drying and consolidation, the temperature of the outside and inside of the pellets can be uniform, so that the outside and inside of the pellets can be dried and consolidated at the same time. Through microwave heating, the consolidation material reactants between the particles in the pellets are coordinated, and the technical means of adding CHO low-temperature release agents are used. The microwaves directly act on the CHO low-temperature release agent. While drying, the CHO low-temperature release agent synchronously decomposes and releases CO2 and H2O. Therefore, drying and consolidation are carried out simultaneously. Microwaves not only play a heating role, but also ensure the uniformity of the temperature inside and outside the pellets, thereby ensuring that the calcium hydroxide and acid ions between the pellet particles react directly; at the same time, the CHO low-temperature release agents at different positions in the pellets are decomposed at the same time, so that each position of the pellets is consolidated at the same time, forming a consolidated pellet with uniform strength.

[0078] Carbonation consolidation process of the present invention adopts the mode of consolidation under microwave action, and under microwave action, the reactant between raw material particles in pellet directly receives energy, reacts, forms consolidation material, plays the effect of strengthening pellet strength. In addition, in preferred embodiment, CHO low temperature release agent (mixture of bicarbonate or bicarbonate-carbonate) inside pellet is evenly decomposed and converted into CO2 and H2O, avoids the problem of asynchronous reaction of pellet outer layer and internal material caused by traditional heat conduction mode from outside to inside, so pellet inside and outside all meet temperature, CO2 atmosphere condition, carbonation reaction rate is consistent, and double-layer structure of hard outside and loose inside will not appear. In addition under microwave action, high temperature, high CO2, high water vapor, high calcium reaction environment are formed in pellet internal micro-region, carbonation reaction is carried out quickly, generates calcium carbonate crystallites, microwave can drive particle migration, crystallites grow up quickly, adjacent particles are closely connected together, and high strength guarantee is provided for pellet.

[0079] Therefore, by placing microwave + reactants between the raw material particles in the pellets (preferably also including CHO low-temperature release agent), the pellets are made into a homogeneous structure, avoiding the technical problem of uneven quality caused by pellet stratification, while ensuring that the pellets have high-strength structures both inside and outside, thus playing a synergistic role.

[0080] The inventor further discovered through experiments that, compared with the method of using hot air drying and consolidation alone or microwave drying and consolidation alone, the drying and consolidation method using hot air + microwave is particularly effective. If the hot air drying and consolidation method is used alone, the pellets are dried and consolidated by physical heat transfer, and there is a technical problem of uneven temperature inside and outside the pellets, and the consolidation strength inside the pellets is low. If the microwave drying and consolidation method is used alone, the moisture inside the pellets will be lost too quickly, and the moisture in the gaps between the molecules of the material in the pellets will be suddenly lost, which will also affect the consolidation effect between the molecules of the material in the pellets. Through experiments, it was found that the pellets were first dried by hot air drying and consolidation, so that the moisture in the gaps between the molecules of the material in the pellets evaporated at a slower rate, and the molecules in the material slowly gathered together, reducing the distance between the molecules in the material; and then, through the action of microwaves, the calcium hydroxide and carbonate ions or other acid ions between the raw material particles in the pellets reacted to form a consolidated material. After adding CHO low-temperature release agent, microwaves stimulate the CO2, H2O released by the CHO low-temperature release agent to react with the binder, forming a consolidated structure between the molecules of the material. Through the drying consolidation method combining hot air + microwaves, the strength of the consolidated pellets is greatly improved.

[0081] Further experiments have shown that by using a hot air + microwave drying and consolidation method, the pellets are first dried by hot air drying and consolidation until the moisture content in the pellets is 2% to 8% (preferably 3% to 6%), and then dried and consolidated by microwaves, the strength of the consolidated pellets can reach above 300N / P.

[0082] The technical solution provided by the present invention can be used for the reduction of all ores, and is particularly suitable for the reduction of iron oxide ores. The inventor further experimented that since metallurgical solid waste contains relatively high alkali metals, it is necessary to first treat the alkali metals and then use the metallurgical solid waste for the next step of resource recycling. Metallurgical solid waste is used as iron-containing raw material. Since metallurgical solid waste is raw material particles with smaller particle size, an aqueous solution containing calcium hydroxide is added to the raw water added when the raw materials are mixed, and CO2 and acid solution are added to the balling water added during the balling process. The calcium hydroxide and carbonate ions or other acid radical ions between the raw material particles react directly to form a product that plays a curing role, thereby improving the consolidation strength of the pellets. In the preferred technical solution, CHO low-temperature release agent is added to the metallurgical solid waste, and microwave drying consolidation or hot air pre-drying + microwave drying consolidation is used. The obtained consolidated pellets have high strength and a high lift-out rate for alkali metals. By adding HO high-temperature gas slow-release agent to the pellets, the metallization rate of the obtained product is greatly improved.

[0083] The technical solution provided by the present invention can be used to treat ore refining tailings, such as vanadium tailings, copper slag, and steel slag; it can also be used to treat dust collected in metallurgical fields, such as zinc-containing dust; and to remove zinc from zinc-containing dust.

[0084] In the present invention, the fuel is a carbon-containing solid fuel; for example, coke, coal, biochar.

[0085] The present invention proposes a method for preparing pellets, and the detailed steps are as follows:

[0086] Dissolve one or more of oxalic acid, acetic acid or other soluble organic acids containing carboxyl groups in water in a certain proportion, then wash the carbonated solid tail gas with water to dissolve the CO2 in the organic acid solution, and use it as ball-making water. The proportion of organic acids such as oxalic acid and acetic acid to water is 5g / 100g water to 80g / 100g water, preferably 10g / 100g water to 70g / 100g water; the concentration of CO2 in the ball-making water is 0.1m 3 CO2 / m 3 H2O~1.7m 3 CO2 / m 3 H2O, preferably 0.5m 3 CO2 / m 3 H2O~1.5m 3 CO2 / m 3 H2O.

[0087] (2) Calcium oxide and calcium hydroxide are dissolved in water and used as raw water. One or more of alkali-containing metallurgical solid wastes such as vanadium tailings, copper slag, steel slag, zinc-containing dust, etc. are mixed with raw water in a certain proportion, and then mixed with one or more calcium salts such as calcium oxide, calcium hydroxide, calcium carbonate, calcium chloride, calcium sulfate, etc., and used as pelletizing raw materials. Among them, the Ca(OH)2 concentration in the raw water is 0.01% to 0.18%, preferably 0.02% to 0.16%; the particle size of metallurgical solid waste is -200 mesh ≥50%, preferably -325 mesh ≥80%; the ratio of metallurgical solid waste to raw water is 100:3 to 100:15, preferably 100:5 to 100:10; the particle size of calcium salt is -200 mesh ≥50%, preferably -325 mesh ≥80%; the ratio of metallurgical solid waste to calcium salt is 1:0.1 to 1:1, preferably 1:0.2 to 1:0.5; the mixing equipment can be a drum mixer, a strong mixer, etc.

[0088] (3) The mixed raw materials and ball-forming water are ball-formed on a disc ball-forming machine, wherein the pellet size is 3 mm to 8 mm. The ball-forming water is added in the form of atomized water in the disc ball-forming process. Atomized water is added to the raw material distribution area and the 2 mm to 4 mm particle size area in the ball disc respectively. The amount of ball-forming water added is 5% to 20% of the raw ball mass, preferably 5% to 10%.

[0089] (4) The prepared green pellets are dried and consolidated by microwave or hot air pre-drying and consolidation plus microwave drying and consolidation. During the drying and consolidation process, a gas containing CO2 and water vapor is introduced. The drying and consolidation can be carried out by a chain grate machine, a steel mesh belt machine, etc. in combination with microwaves. The material height is 10 mm to 200 mm, preferably 100 mm to 150 mm. The gas can be hot air with added water vapor and CO2, hot tail gas after combustion of blast furnace gas / coke oven gas / converter gas, etc., hot tail gas from direct reduction, hot tail gas from lime kiln, etc. The CO2 concentration is 10% to 50%; the humidity is 10 g / m 3 ~100g / m 3 , preferably 20g / m 3 ~50g / m 3 ; Gas flow rate is 0.1m / s~5m / s.

[0090] The schematic diagram of the consolidation process by microwave drying is shown in Figure 2 As shown, 101 is a microwave drying section, 102 is a microwave drying consolidation section I, 103 is a microwave drying consolidation section II, L1, L2, L3, L4 are gases with water vapor and CO2, the temperature of section 101 is 100℃~200℃, the material running time is 2min~20min, the temperature of section 102 is 200℃~350℃, the material running time is 5min~20min, the temperature of section 103 is 350℃~500℃, the material running time is 3min~20min, and the microwave power density of sections 101, 102, and 103 is 5kw / m 3 ~50kw / m 3 , better, 20kw / m 3 ~30kw / m 3 . L4 is used as a gas source for dissolved CO2 in the pelletizing water.

[0091] The schematic diagram of the consolidation process by hot air pre-drying + microwave drying is shown in Figure 3 As shown, 201 is a hot air drying section, 202 is a hot air drying consolidation section, 203 is a microwave drying consolidation section I, 204 is a microwave drying consolidation section II, L201, L202, L203, L204, L205 are gases with water vapor and CO2, the temperature of section 201 is 60℃~100℃, the material running time is 2min~20min, the temperature of section 202 is 100℃~300℃, the material running time is 3min~20min, the moisture content of the pellets after hot air drying is 2%~8%, and the optimal 3%~6%; the temperature of section 203 is 250℃~350℃, the material running time is 2min~20min, the temperature of section 204 is 350℃~500℃, the material running time is 5min~20min, and the microwave power density of sections 203 and 204 is 5kw / m 3~50kw / m 3 , better, 20kw / m 3 ~30kw / m 3 . L205 is used as the gas source for dissolving CO2 in the pelletizing water.

[0092] Preferably, atomized water is added in the disc ball making process, and atomized water is added to the raw material distribution area and the 2mm-4mm particle size area in the ball disc respectively. The amount of atomized water added is determined according to the moisture content of the raw materials and the ball making state.

[0093] The prepared green balls are dried and consolidated by microwave or by hot air pre-drying and consolidation plus microwave drying and consolidation. Drying and consolidation can be carried out by a chain grate machine, a steel mesh belt machine or the like in combination with microwaves. The material height is 10 mm to 200 mm, preferably 100 mm to 150 mm.

[0094] The present invention proposes a prepared pellet, wherein the diameter of the pellet is 1-20 mm (preferably 2-10 mm, and more preferably 3-8 mm), and the pellet consolidation method is carbonation consolidation. Compared with ordinary carbonation low-temperature consolidation, the pellet prepared by the present invention has the characteristics of faster and more uniform carbonation reaction, higher pellet strength, and higher production efficiency.

[0095] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0096] 1. The present invention washes the carbonation-solidified tail gas with water to dissolve the CO2 therein, so that it is converted into carbonic acid and dissolved in water, and this part of water is used as ball-making water.

[0097] 2. The present invention uses an aqueous solution of calcium hydroxide as the raw material water for pelletizing and mixes it with the raw material. The aqueous solution of calcium hydroxide will be adsorbed on the surface of the raw material particles during the mixing process of the raw materials and exist in the raw materials in the form of molecular water. In this way, a large amount of calcium ions will be evenly distributed on the surface of the raw material particles.

[0098] 3. The water added in the whole pellet manufacturing process is divided into raw water and pelletizing water; calcium ions are added to the raw water and evenly distributed on the surface of the particles; carbonic acid, oxalic acid, acetic acid, etc. are added to the pelletizing water; the two undergo carbonation consolidation reaction during the pelletizing process, which plays a role in strengthening the strength of the pellets.

[0099] 4. The present invention adds "CHO ​​low temperature release agent" into the pellets. The CHO low temperature release agent can release CO2 and H2O during the low temperature drying and consolidation process, and can significantly improve the carbonation consolidation efficiency and the strength of the dried consolidated balls.

[0100] 5. The present invention adds a "high temperature gas slow release agent" into the pellets. The high temperature gas slow release agent can release H2O during the high temperature reduction process, and can significantly increase the partial pressure of the reducing gas inside the pellets and promote the rapid reduction reaction.

[0101] 6. The present invention adopts a microwave drying or hot air + microwave drying consolidation process, and microwaves strengthen the carbonation consolidation reaction inside the pellets to improve the overall strength of the pellets. BRIEF DESCRIPTION OF THE DRAWINGS

[0102] Figure 1 The present invention is a process flow chart of a carbonation consolidation method for improving pellet strength;

[0103] Figure 2 It is a schematic diagram of the structure of a microwave device used for carbonation consolidation of the present invention;

[0104] Figure 3 It is a schematic structural diagram of the hot air pre-drying device used for carbonation consolidation of the present invention.

[0105] Reference numerals:

[0106] 101: microwave drying section; 102: microwave drying consolidation section I; 103: microwave drying consolidation section II; 201: hot air drying section; 202: hot air drying consolidation section. L1, L2, L3, L4, L201, L202, L203, L204, L205: gas transmission pipelines with water vapor and CO2. DETAILED DESCRIPTION

[0107] The technical solution of the present invention is illustrated below by way of example, and the scope of protection requested by the present invention includes but is not limited to the following embodiments.

[0108] Example 1

[0109] (1) Dissolve oxalic acid in water at a ratio of 10 g / 100 g water, then wash the carbonated solid tail gas with water to dissolve the CO2 in the organic acid solution. The CO2 concentration in the ball making water is 0.8 m 3 CO2 / m 3 H2O. Calcium hydroxide is dissolved in water, and the concentration of Ca(OH)2 is 0.15%, which is used as raw water. A mixture of vanadium tailings and coking coal with a mesh size of ≥80% of -325 mesh is mixed with raw water at a weight ratio of 100:15, and then mixed with calcium hydroxide at a ratio of 1:0.4 using a powerful mixer. The mixed raw materials and ball making water are balled on a disc ball making machine, wherein the pellet size is 3mm to 8mm. The ball making water is added in the form of atomized water in the disc ball making process, and atomized water is added to the raw material distribution area and the 2mm to 4mm particle size area in the ball disc, respectively. The amount of ball making water added is 7.5% of the raw ball mass.

[0110] (2) Dry and consolidate the green pellets by hot air drying and consolidation; the material height is 100 mm; the temperature during the drying and consolidation process is 300°C, the CO2 content is 30%, and the humidity is 40 g / m 3 The hot air flow has an air flow velocity of 0.5m / s and a time of 30min.

[0111] Example 2

[0112] Example 1 was repeated, except that in step (2), the prepared green pellets were dried and consolidated by microwaves. During the drying and consolidation process, a gas containing CO2 and water vapor was introduced. The material height was 100 mm; the CO2 concentration was 30% and the humidity was 40 g / m 3 , gas velocity is 0.5m / s; Figure 2 The microwave device shown in FIG. 101 has a temperature of 80°C to 180°C and a microwave power density of 10 kW / m 3 , the material running time is 5min, the temperature of section 102 is 180℃~300℃, and the microwave power density is 20kw / m 3 , the material running time is 10min, the temperature of section 103 is 300℃~350℃, and the microwave power density is 15kw / m 3 , the material running time is 5min.

[0113] Example 3

[0114] Example 1 was repeated, except that the drying and consolidation method in step (2) was: hot air pre-drying and consolidation + high-frequency electromagnetic field drying and consolidation. Figure 3 The hot air pre-drying device-microwave device shown; the process conditions of drying and consolidation are:

[0115] During the drying and consolidation process, gas containing CO2 and water vapor is introduced, and the material height is 100mm; the CO2 concentration of L1 gas is 30%, and the humidity is 40g / m 3 The gas flow rate is 0.3m / s, the temperature of section 201 is 80℃~100℃, the material running time is 5min, the temperature of section 202 is 100℃~250℃, the material running time is 10min, and the moisture content of the pellets after hot air drying is 4%; the temperature of section 203 is 250℃~300℃, and the microwave power density is 15kw / m 3 The material running time is 5min, the temperature of section 204 is 300℃~350℃, and the microwave power density is 25kw / m 3 , the material running time is 15min.

[0116] Example 4

[0117] Example 3 was repeated except that 30% by weight of Ca(HCO3)2 based on the iron-containing raw material was also added to the granulation raw material in step (1).

[0118] Example 5

[0119] Example 3 was repeated except that 30% by weight of Mg(HCO3)2 based on the iron-containing raw material was also added to the granulation raw material in step (1).

[0120] Example 6

[0121] Example 3 was repeated, except that 30% of Ca(HCO3)2-FeCO3 (the mixing mass ratio of Ca(HCO3)2 and FeCO3 was 1:1) was added to the granulation raw material in step (1) based on the weight ratio of the iron-containing raw material.

[0122] Example 7

[0123] Example 3 was repeated, except that Mg(HCO3)2-FeCO3 (the mixing mass ratio of Mg(HCO3)2 and FeCO3 was 1:1) was also added to the granulation raw material in step (1) at a weight ratio of 30% based on the iron-containing raw material.

[0124] Example 8

[0125] Example 3 was repeated, except that Ca(HCO3)2-Mg(HCO3)2 (the mixing mass ratio of Ca(HCO3)2 and Mg(HCO3)2 was 1:1) was also added to the granulation raw material in step (1) at a weight ratio of 30% based on the iron-containing raw material.

[0126] Example 9

[0127] Example 3 was repeated, except that Ca(HCO3)2-FeCO3-Mg(HCO3)2 (the mixing mass ratio of Ca(HCO3)2, FeCO3, and Mg(HCO3)2 was 1:1:1) at a weight ratio of 30% based on the iron-containing raw material was also added to the granulation raw material in step (1).

[0128] Example 10

[0129] Example 4 was repeated except that the consolidated pellets obtained in step (2) were reduced at 1100° C. for 90 min in a rotary kiln with 50% coal added thereto to obtain a reduced material.

[0130] Embodiment 11

[0131] Example 10 was repeated, except that ferroamphetite (Fe7Si8O 22 (OH)2 content is 90%).

[0132] Example 12

[0133] Example 10 was repeated, except that hydrated iron oxide (Fe2O3·nH2O content of 90% and water content of 15%) accounting for 10% by mass of the vanadium extraction tailings was added to the raw materials in step (1).

[0134] Embodiment 13

[0135] Example 10 was repeated except that 10% of the mass ratio of Dierite (Fe) to the vanadium extraction tailings was added to the raw materials in step (1). 18 Si 12 O 40 (OH) 10 The content is 90%).

[0136] Embodiment 14

[0137] Example 10 was repeated, except that tremolite (2CaO·5MgO·8SiO2·H2O content: 90%) accounting for 10% by mass of the vanadium extraction tailings was further added to the raw material in step (1).

[0138] Embodiment 15

[0139] Example 3 was repeated except that the Ca(OH)2 concentration in the raw water was 0.08%.

[0140] Example 16

[0141] Example 3 was repeated, except that acetic acid was used instead of oxalic acid in the pelletizing water, and the ratio of oxalic acid dissolved in water was 30 g / 100 g water.

[0142] Embodiment 17

[0143] Example 3 was repeated except that the CO2 concentration in the pelletizing water was 1.2 m 3 CO2 / m 3 H2O.

[0144] Embodiment 18

[0145] Example 3 was repeated except that the weight ratio of the raw water containing calcium hydroxide to the iron-containing raw material was 1:10.

[0146] Embodiment 19

[0147] Example 3 was repeated except that the amount of pelletizing water added was 5% of the raw pellet mass.

[0148] Embodiment 20

[0149] Example 3 was repeated except that copper slag was used as the iron-containing raw material in step (1).

[0150] Embodiment 21

[0151] Example 3 was repeated except that steel slag was used as the iron-containing raw material in step (1).

[0152] Embodiment 22

[0153] Example 3 was repeated except that copper slag was used as the iron-containing raw material in step (1).

[0154] Embodiment 23

[0155] Example 3 was repeated except that zinc-containing dust was used as the iron-containing raw material in step (1).

[0156] Comparative Example 1

[0157] (1) A mixture of vanadium tailings and coking coal with a mesh size of ≥80% of -325 mesh is mixed with water in a weight ratio of 100:15, and then mixed with calcium hydroxide in a ratio of 1:0.4 using a powerful mixer. The mixed raw materials and ball making water are balled on a disc ball making machine, wherein the pellet size is 3mm to 8mm, and the water is added in the form of atomized water in the ball disc, and atomized water is added to the raw material distribution area and the 2mm to 4mm particle size area, respectively, and the amount of ball making water added is 7.5% of the raw ball mass.

[0158] (2) Dry and consolidate the green pellets by hot air drying and consolidation; the material height is 100 mm; the temperature during the drying and consolidation process is 300°C, the CO2 content is 30%, and the humidity is 40 g / m 3 The hot air flow has an air flow velocity of 0.5m / s and a time of 30min.

[0159] The vanadium extraction tailings used in the present invention are all tailings after sodium vanadium extraction from the same batch, the iron amphibole is all from the same batch of mineral raw materials, the hydrated iron oxide is all from the same batch of mineral raw materials, the dillite is all from the same batch of mineral raw materials, and the tremolite is all from the same batch of mineral raw materials. The coking coal is all from the same batch of raw materials. The calcium hydroxide is all obtained by digesting the same batch of quicklime through the same process. The mixing equipment, disc pelletizing machine, chain grate drying system, microwave device, and rotary kiln used are all the same equipment, and experiments and effect verification are carried out, and the results are as follows:

[0160]

[0161]

[0162] It should be noted that the inventors of the present application conducted experiments using copper slag, steel slag, and zinc-containing dust as iron-containing raw materials and obtained experimental results similar to those mentioned above, which will not be repeated here.

[0163] In the present invention, the compressive strength is tested according to the GB / T14201-93 standard. The drop strength is tested according to the GB / T14201-93 standard.

[0164] In the present invention, the sodium removal rate is: (1-sodium content in pellets / sodium content in the whole raw material)*100%; wherein: the whole raw material includes iron-containing raw materials, fuel, binder and additives (CHO low-temperature release agent and HO high-temperature gas slow release agent); the sodium content can be detected by an analytical detector in the prior art.

[0165] The metallization rate of iron in the reducing material refers to the weight percentage of elemental iron in the total iron element components in the entire reducing material (slag phase).

Claims

1. A carbonation consolidation method for improving pellet strength, the method comprising the following steps: (1) dissolving calcium oxide and / or calcium hydroxide in an aqueous solution to obtain raw water containing calcium hydroxide; (2) dissolving the acid solution in water to obtain ball-making water containing the acid solution; (3) uniformly mixing the iron-containing raw material, raw water containing calcium hydroxide, a binder, and a fuel to obtain a pelletizing raw material; (4) mixing the pelletizing water containing the acid solution with the pelletizing raw materials to perform pelletizing to obtain pellets; (5) subjecting the pellets to a drying and consolidation process to obtain consolidated pellets; and, during the drying and consolidation process, introducing a gas containing CO2 and water vapor; and the gas containing CO2 and water vapor is transported to the water in step (2) after the drying and consolidation process; The acid solution in step (2) is oxalic acid and / or acetic acid solution.

2. The carbonation consolidation method according to claim 1, wherein: The drying and consolidation process described in step (5) adopts microwave heating; the pellets are transported to a microwave device; a gas containing CO2 and water vapor is introduced into the microwave device to dry and consolidate the pellets, and then discharged from the microwave device and transported to step (2), CO2 is dissolved in the aqueous solution, and pelletizing water containing an acid solution is obtained; or The drying and consolidation process described in step (5) adopts hot air pre-drying and microwave drying and consolidation; the pellets are transported to the hot air pre-drying device for pre-drying, and the pre-dried pellets are transported to the microwave device for drying and consolidation, and then consolidated pellets are obtained; the gas containing CO2 and water vapor is transported to the microwave device to dry and consolidate the pellets, and then discharged from the microwave device, and then transported to the hot air pre-drying device to pre-dry the pellets, and the gas containing CO2 and water vapor discharged from the pre-drying device is transported to step (2), CO2 is dissolved in the aqueous solution, and pelletizing water containing acid solution is obtained.

3. The carbonation consolidation method according to claim 1 or 2, characterized in that: The raw water containing calcium hydroxide obtained in step (1) has a mass concentration of calcium hydroxide of 0.01 to 0.18%; and / or The mass concentration of acid in the ball-making water containing the acid solution in step (2) is 5-80%; the gas containing CO2 and water vapor in step (5) is dissolved in the ball-making water containing the acid solution, wherein the solubility of CO2 is 0.1m 3 CO2 / m 3 H2O~1.7m 3 CO2 / m 3 H2O.

4. The carbonation consolidation method according to claim 3, characterized in that: The mass concentration of calcium hydroxide is 0.02-0.16%; and / or The mass concentration of acid in the ball-making water containing the acid solution in step (2) is 10-70%; the gas containing CO2 and water vapor in step (5) is dissolved in the ball-making water containing the acid solution, wherein the solubility of CO2 is 0.5m 3 CO2 / m 3 H2O~1.5m 3 CO2 / m 3 H2O.

5. The carbonation consolidation method according to any one of claims 1-2 and 4, characterized in that: In the pelletizing raw material of step (3), the weight ratio of raw water containing calcium hydroxide to iron-containing raw material is 3 to 20:100; and / or In the pelletizing raw materials of step (3), the weight ratio of the iron-containing raw materials to the binder is 1:0.1-1.

6. The carbonation consolidation method according to claim 3, characterized in that: In the pelletizing raw material of step (3), the weight ratio of raw water containing calcium hydroxide to iron-containing raw material is 3 to 20:100; and / or In the pelletizing raw materials of step (3), the weight ratio of the iron-containing raw materials to the binder is 1:0.1-1.

7. The carbonation consolidation method according to claim 5, characterized in that: In the pelletizing raw material of step (3), the weight ratio of raw water containing calcium hydroxide to iron-containing raw material is 5 to 18:100; and / or In the pelletizing raw materials of step (3), the weight ratio of the iron-containing raw materials to the binder is 1:0.2-0.

5.

8. The carbonation consolidation method according to claim 6, characterized in that: In the pelletizing raw material of step (3), the weight ratio of raw water containing calcium hydroxide to iron-containing raw material is 5 to 18:100; and / or In the pelletizing raw materials of step (3), the weight ratio of the iron-containing raw materials to the binder is 1:0.2-0.

5.

9. The carbonation consolidation method according to any one of claims 1-2, 4, 6-8, characterized in that: In step (4), the weight ratio of the pelletizing water containing the acid solution to the pelletizing raw material is 3 to 20:100; and / or The particle size of the pellets is 2 to 15 mm.

10. The carbonation consolidation method according to claim 3, characterized in that: In step (4), the weight ratio of the pelletizing water containing the acid solution to the pelletizing raw material is 3 to 20:100; and / or The particle size of the pellets is 2 to 15 mm.

11. The carbonation consolidation method according to claim 9, characterized in that: In step (4), the weight ratio of the pelletizing water containing the acid solution to the pelletizing raw material is 5 to 10:100; and / or The particle size of the pellets is 3 to 8 mm.

12. The carbonation consolidation method according to claim 10, characterized in that: In step (4), the weight ratio of the pelletizing water containing the acid solution to the pelletizing raw material is 5 to 10:100; and / or The particle size of the pellets is 3 to 8 mm.

13. The carbonation consolidation method according to any one of claims 1-2, 4, 6-8, 10-12, characterized in that: The volume concentration of CO2 in the gas containing CO2 and water vapor is 10-50%; the humidity of the gas containing CO2 and water vapor is 10g / m 3 ~100g / m 3 ; and / or The gas containing CO2 and water vapor is one or more of hot air with added water vapor and CO2, hot tail gas after combustion of blast furnace gas, coke oven gas or converter gas, direct reduction hot tail gas, and lime kiln hot tail gas.

14. The carbonation consolidation method according to claim 3, characterized in that: The volume concentration of CO2 in the gas containing CO2 and water vapor is 10-50%; the humidity of the gas containing CO2 and water vapor is 10g / m 3 ~100g / m 3 ; and / or The gas containing CO2 and water vapor is one or more of hot air with added water vapor and CO2, hot tail gas after combustion of blast furnace gas, coke oven gas or converter gas, direct reduction hot tail gas, and lime kiln hot tail gas.

15. The carbonation consolidation method according to claim 13, characterized in that: The volume concentration of CO2 in the gas containing CO2 and water vapor is 20-40%; the humidity of the gas containing CO2 and water vapor is 20g / m 3 ~50g / m 3 .

16. The carbonation consolidation method according to claim 14, characterized in that: The volume concentration of CO2 in the gas containing CO2 and water vapor is 20-40%; the humidity of the gas containing CO2 and water vapor is 20g / m 3 ~50g / m 3 .

17. The carbonation consolidation method according to claim 2, characterized in that: When microwave heating is used for drying and consolidation: the temperature is 100℃~500℃; the drying and consolidation time is 10min~60min; the microwave power density is 5kw / m 3 ~50kw / m 3 ; and / or When hot air pre-drying and microwave drying consolidation are used: the hot air temperature is 60℃~300℃; the hot air pre-drying time is 5min~50min; the moisture content in the pellets after hot air pre-drying is 2%~8%; the microwave drying consolidation temperature is 200℃~500℃; the drying consolidation time is 5min~40min; the microwave power density is 5kw / m 3 ~50kw / m 3 .

18. The carbonation consolidation method according to claim 17, characterized in that: When microwave heating is used for drying and consolidation: the temperature is 300℃~400℃; the drying and consolidation time is 20min~40min; the microwave power density is 20kw / m 3 ~30kw / m 3 ; and / or When hot air pre-drying and microwave drying consolidation are used: the hot air temperature is 100℃~250℃; the hot air pre-drying time is 10min~20min; the moisture content in the pellets after hot air pre-drying is 3%~6%; the microwave drying consolidation temperature is 300℃~400℃; the drying consolidation time is 10min~30min; the microwave power density is 20kw / m 3 ~30kw / m 3 .

19. The carbonation consolidation method according to any one of claims 1-2, 4, 6-8, 10-12, 14-18, characterized in that: In step (3), bicarbonate or a mixture of bicarbonate and carbonate is further added to the pelletizing raw material; the amount of bicarbonate or the mixture of bicarbonate and carbonate added is 1% to 50% by weight of the iron-containing raw material; and / or A high-temperature gas slow-release agent is also added to the pelletizing raw material in step (3); the amount of the high-temperature gas slow-release agent added is 1% to 30% by weight of the iron-containing raw material.

20. The carbonation consolidation method according to claim 19, characterized in that: The amount of bicarbonate or bicarbonate-carbonate mixture added is 5% to 45% by weight of the iron-containing raw material; and / or The added amount of the high temperature gas slow-release agent is 5% to 25% of the weight ratio of the iron-containing raw material.

21. The carbonation consolidation method according to claim 20, characterized in that: The amount of bicarbonate or a mixture of bicarbonate and carbonate added is 10% to 40% by weight of the iron-containing raw material; and / or The added amount of the high temperature gas slow-release agent is 8% to 20% of the weight ratio of the iron-containing raw material.

22. The carbonation consolidation method according to claim 19, characterized in that: The bicarbonate is Ca(HCO3)2 and / or Mg(HCO3)2; the bicarbonate-carbonate mixture is one or more of Ca(HCO3)2-FeCO3, Mg(HCO3)2-FeCO3, Ca(HCO3)2-Mg(HCO3)2, Ca(HCO3)2-FeCO3-Mg(HCO3)2; and / or The high temperature gas slow-release agent is one or more of ferroxene, hydrated iron oxide, diolite and tremolite.

23. The carbonation consolidation method according to claim 20 or 21, characterized in that: The bicarbonate is Ca(HCO3)2 and / or Mg(HCO3)2; the bicarbonate-carbonate mixture is one or more of Ca(HCO3)2-FeCO3, Mg(HCO3)2-FeCO3, Ca(HCO3)2-Mg(HCO3)2, Ca(HCO3)2-FeCO3-Mg(HCO3)2; and / or The high temperature gas slow-release agent is one or more of ferroxene, hydrated iron oxide, diolite and tremolite.

24. The carbonation consolidation method according to any one of claims 1-2, 4, 6-8, 10-12, 14-18, 20-22, characterized in that: The iron-containing raw material is slag and / or metallurgical dust; and / or The binder is one or more of calcium oxide, calcium hydroxide, calcium carbonate, calcium chloride and calcium sulfate; and the fuel is a carbon-containing solid fuel.

25. The carbonation consolidation method according to claim 24, characterized in that: The iron-containing raw material is one or more of vanadium extraction tailings, copper slag, steel slag, and zinc-containing dust; and / or The binder is calcium hydroxide; the fuel is coke.

26. The carbonation consolidation method according to claim 2, characterized in that: The microwave device comprises n segments, where n is 1-5.

27. The carbonation consolidation method according to claim 26, characterized in that: The microwave device comprises three sections, namely a microwave drying section (101), a microwave drying consolidation section I (102), and a microwave drying consolidation section II (103); the pellets are sequentially passed through the microwave drying section (101), the microwave drying consolidation section I (102), and the microwave drying consolidation section II (103) to obtain consolidated pellets; the gas containing CO2 and water vapor is transported to the microwave drying consolidation section II (103), then transported from the microwave drying consolidation section II (103) to the microwave drying consolidation section I (102), then discharged from the microwave drying consolidation section I (102) and then transported to the microwave drying section (101), then discharged from the microwave drying section (101) and then transported to step (2), CO2 is dissolved in the aqueous solution to obtain pelletizing water containing an acid solution.

28. The carbonation consolidation method according to claim 26 or 27, characterized in that: The temperature of the microwave drying section (101) is 100°C to 200°C, and the material running time is 2min to 20min; The temperature of the microwave drying and consolidation stage I (102) is 200°C to 350°C, and the material running time is 5min to 20min; The temperature of the microwave drying and consolidation stage II (103) is 350°C to 500°C, and the material running time is 3min to 20min.

29. The carbonation consolidation method according to claim 2, characterized in that: The hot air pre-drying device has m sections, where m is 1-3.

30. The carbonation consolidation method according to claim 29, characterized in that: The hot air pre-drying device is composed of two sections, namely a hot air drying section (201) and a hot air drying consolidation section (202); the pellets are transported to the microwave device after passing through the hot air drying section (201) and the hot air drying consolidation section (202) in sequence; the gas discharged from the microwave device is transported to the hot air drying consolidation section (202), the gas discharged from the hot air drying consolidation section (202) is transported to the hot air drying section (201), and the gas discharged from the hot air drying section (201) is transported to step (2), CO2 is dissolved in the aqueous solution, and pelletizing water containing an acid solution is obtained.

31. The carbonation consolidation method according to claim 29 or 30, characterized in that: The temperature of the hot air drying section (201) is 60°C to 100°C, and the material running time is 2min to 20min; The temperature of the hot air drying consolidation section (202) is 100°C to 300°C, and the material running time is 3min to 30min; After the pellets pass through the hot air pre-drying device, the moisture content in the pellets is 2% to 8%.

32. The carbonation consolidation method according to claim 31, characterized in that: After the pellets pass through the hot air pre-drying device, the moisture content in the pellets is 3% to 6%.

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