Efficient reducing agent for steel dust and sludge and preparation method of efficient reducing agent

Abstract

The invention discloses an efficient reducing agent for steel dust and sludge, and relates to the technical field of steel dust and sludge treatment, the efficient reducing agent comprises lignite powder, calcium oxide, starch and urethane acrylate; the reducing agent is in a porous pellet shape, when the reducing agent is mixed with dust and sludge, a large amount of dust and sludge can be filled into gaps of the reducing agent, contact between the reducing agent and the dust and sludge is more sufficient and uniform, and the reducing effect of the dust and sludge in the calcining process is improved; according to the invention, polyurethane acrylate is added into the reducing agent to form a firm skeleton structure, polyurethane acrylate forms a film layer on the surface of the skeleton structure of the reducing agent, and the film layer has an attraction effect on steel dust, so that part of the steel dust can be fully filled into the porous skeleton, and H2 and CO can be generated by pyrolysis at high temperature; the two gases can be used as effective reducing gases of the steel dust, so that the reduction of metal oxides in the steel dust is promoted, and the recovery of metal iron and metal zinc is promoted.

Description

Technical Field

[0001] The invention relates to the technical field of steel dust treatment, and in particular to a high-efficiency reducing agent for steel dust and a preparation method thereof. Background Art

[0002] A large amount of steel dust and mud is generated during the steel production process. These dust and mud usually contain high levels of iron, carbon, zinc and other elements. If they cannot be effectively utilized, it will not only waste resources but also pollute the environment. The efficient treatment and resource utilization of steel dust and mud have always been the focus of attention in the steel industry. Traditional steel dust and mud treatment methods often have problems such as low treatment efficiency, high energy consumption, low product metallization rate, and low zinc and iron recovery rate. Therefore, the development of an efficient reducing agent and its preparation method is of great significance to improve the resource utilization efficiency of steel dust and mud and reduce production costs.

[0003] Among the existing steel dust and sludge treatment processes, the rotary kiln process in the pyrometallurgical treatment process is relatively mature. In this process, the dried dust and sludge are mixed with anthracite as a reducing agent and added to the rotary kiln. The charge is directly reduced at high temperature in the rotary kiln to form pellets. After cooling, the pellets can be screened for converter and blast furnace smelting, while the smaller particles can be used for sintering, and metal substances such as iron and zinc can be recovered.

[0004] In the rotary kiln process, the reducing agent is an important medium for reducing metals, and its composition is crucial. Existing reducing agents mostly select a mixture of carbon-containing powders, and the powder mixture is mixed with dust and mud to form granules before calcining. However, since the surface properties of various powders vary greatly, after the powders are mixed and granulated, the homogeneity of the components in the granules is poor, which affects the adequacy of reduction during the sintering process. Some dust and mud are not fully reduced due to less contact with the reducing agent, which greatly reduces the final recovery rate of metallic iron and metallic zinc. Summary of the invention

[0005] The purpose of the present invention is to provide a high-efficiency reducing agent for steel dust and a preparation method thereof, so as to solve the following technical problems: How to improve the recovery of metallic iron and metallic zinc from steel dust and sludge.

[0006] The purpose of the present invention can be achieved through the following technical solutions: In a first aspect, the present invention discloses a high-efficiency reducing agent for steel dust, comprising the following raw materials in parts by weight: 45-55 parts of lignite powder, 10-20 parts of calcium oxide, 2-4 parts of starch, and several parts of polyurethane acrylate; preferably, the lignite powder is 50 parts, the calcium oxide is 15 parts, and the starch is 3 parts.

[0007] Furthermore, the reducing agent is in the form of porous spherical particles, and a polyurethane acrylate film layer is provided on the surface of the reducing agent; the lignite powder and calcium oxide form a skeleton structure of the porous sphere, starch is used as a binder to bond and shape the lignite powder and calcium oxide, and the polyurethane acrylate forms a supporting film structure on the surface of the skeleton structure, which can improve the strength performance of the porous sphere and prevent it from being damaged during transportation or storage.

[0008] When the high-efficiency reducing agent of the present invention is used in the process of treating steel dust, the method of using the high-efficiency reducing agent is as follows: first, the steel dust and the reducing agent are added to a mixer and mixed evenly, so that the steel dust is fully mixed into the porous skeleton structure of the reducing agent; the polyurethane acrylate film layer of the outermost layer of the reducing agent has an attractive effect on the steel dust, so that part of the steel dust can be fully filled into the porous skeleton; then the mixed materials are put into a pelletizing machine for granulation and then sent to a rotary kiln for calcination treatment, so as to recover the metal zinc and metal iron in the steel dust.

[0009] During the calcination process of the high-efficiency reducing agent and steel dust mud of the present invention, the steel dust mud and the reducing agent are evenly mixed, and a large amount of steel dust mud is fully mixed into the skeleton structure of the reducing agent. Under the action of high temperature, the outermost polyurethane acrylate film layer of the reducing agent is pyrolyzed to generate hydrogen (H2) and carbon monoxide (CO). These two gases can be used as effective reducing gases for the steel dust mud to promote the reduction of oxidized metals in the steel dust mud. At the same time, the carbon element in the lignite in the reducing agent can be combined with the oxygen element in the steel dust mud at high temperature to form CO or carbon dioxide (CO2), while releasing heat. These Gases, especially CO, can undergo a reduction reaction with iron oxides in steel dust to reduce them to metallic iron; and calcium oxide can combine with acidic oxides in steel dust, such as SiO2, to form compounds such as silicates during the reduction process, thereby adjusting the alkalinity of the system, helping to promote the reduction reaction of metal oxides and improve the recovery rate of metallic iron and metallic zinc. The addition of calcium oxide can change the composition of the slag phase and regulate the melting point of the slag phase, thereby facilitating the growth and aggregation of metallic iron particles; and because the steel dust is filled in the skeleton voids of the reducing agent, the reaction is very uniform and the reduction effect is good.

[0010] In a second aspect, the present invention further discloses a method for preparing a high-efficiency reducing agent for steel dust and mud as described above, comprising the following preparation steps: Step 1: add lignite powder and calcium oxide powder to a ball mill, then add 75% ethanol aqueous solution to the ball mill, the amount added is 50% to 60% of the mixed material, the ball-to-material ratio is 20:1, the ball mill is mounted on a ball mill, the ball milling time is 1.5-2.5h, the ground powder is collected and stirred evenly with starch to obtain a mixed powder, water is added to the mixed powder, and stirred evenly to form a mixed slurry with a solid content of 25% to 35%; Preferably, the solid content of water is 30%.

[0011] The starch in the mixed slurry has a certain viscosity after being dissolved in water, which reduces the overall fluidity of the mixed slurry, prevents the lignite powder and calcium oxide powder from being deposited in a short time, and ensures the stability of the mixed slurry system.

[0012] Step 2: refrigerate the mixed slurry at 0-5°C for 4-5h, then stir it at -10°C to -5°C until it is in a fully iced state, ensuring that no droplets remain, then add it to a roller ball press at a temperature below 0°C, press it into a spherical shape at a linear ratio of 700-800Kg / cm, and keep it warm for 8-10h to obtain ice crystal balls with a particle size of 0.8-1.5cm; Preferably, the particle size of the ice crystal ball is 1.0 cm, and its size can be freely adjusted by the roller spacing of the roller ball press; In this step, the water in the mixed slurry tends to freeze under low temperature conditions. Stirring prevents the water from freezing into blocks, while ensuring that it is evenly dispersed in the mixed system in the form of ice crystals. Therefore, in the obtained ice crystal balls, the water ice crystals are in a uniformly dispersed state.

[0013] Step 3: Add the ice crystal balls into a vacuum dryer, dry at 180° C. for 3-4 hours, cool to room temperature, add them into a vibrating sieve machine for oscillation and separation, and obtain reducing agent precursor particles; During the drying process of the ice crystal ball, the water ice crystals evaporate completely, and at the same time, the starch undergoes gelatinization under the action of high temperature, causing the starch to lose its original crystalline state and produce sticky and colloid-like dextrin. The dextrin acts as a bond between the lignite powder and the calcium oxide powder in the ice crystal ball, so that the dehydrated sphere forms a solid skeleton structure. Moreover, due to the removal of water ice crystals, a coherent pore structure is formed between the skeleton structures, namely the reducing agent precursor particles.

[0014] Step 4: Soak the reducing agent precursor particles in a 15% to 20% mass fraction polyurethane acrylate solution at room temperature for 5 to 10 seconds, then immediately remove them, and then dry them at 100 to 120° C. for 30 minutes to obtain agglomerated reducing agents, and use a vibrating screen to oscillate and separate the agglomerated reducing agents to obtain a high-efficiency reducing agent for steel dust and mud; The polyurethane acrylate solution has a certain viscosity. After the reducing agent precursor particles are immersed in the polyurethane acrylate solution, a layer of polyurethane acrylate liquid film is first covered on their surface. In order to prevent the film layer from being too thick and affecting the porosity of the reducing agent, the immersion time should not be too long; the porosity of the reducing agent is also affected by the water content in the mixed slurry in step one. The larger the amount of water, the lower the viscosity of the mixed slurry, but the larger the mass share in the ice crystal ball, so the porosity of the sphere after dehydration is higher, but if the viscosity is too low, the fluidity is too large, which is easy to cause powder deposition. Therefore, in order to ensure that the effects of the two remain ideal, after multiple groups of experiments, the solid content of water in the mixed slurry was determined to be 25% to 35%, and by controlling the solid content of water, the porosity of the reducing agent can be freely regulated.

[0015] Beneficial effects of the present invention: 1. The high-efficiency reducing agent for steel dust of the present invention is in the form of porous particles. When mixed with dust, a large amount of dust can be filled into the gaps of the reducing agent, so that the contact between the reducing agent and the dust is more sufficient and uniform. Therefore, during the calcination process, the reaction between the dust and the reducing agent is more sufficient, which can avoid the situation where some dust cannot be reduced due to insufficient contact with the reducing agent. Therefore, the reduction effect of the dust during the calcination process can be improved, and the recovery rate of its metallic iron and metallic zinc can be improved.

[0016] 2. The high-efficiency reducing agent for steel dust and mud of the present invention uses starch as a binder to bond and support lignite powder and calcium oxide powder to form a solid skeleton structure. During the sintering process of starch, hydrogen, oxygen and other elements in the starch will be released in the form of gas (such as water vapor, carbon dioxide, etc.), and the remaining carbon element will gradually gather to form carbonized products, which will be recovered together with the carbon slag without generating any extra harmful substances. The released water vapor and carbon dioxide can also promote the carbonization of dust and mud and the reduction reaction during the sintering process, which is beneficial to the improvement of the sintering reaction rate.

[0017] 3. In the high-efficiency reducing agent for steel dust of the present invention, polyurethane acrylate is used to form a film layer on the surface of the skeleton structure of the reducing agent. The film layer has an attractive effect on the steel dust, so that part of the steel dust can be fully filled into the porous skeleton, and pyrolysis at high temperature will generate H2 and CO. These two gases can be used as effective reducing gases for steel dust, promote the reduction of oxidized metals in steel dust, and improve the recovery of metallic iron and metallic zinc.

[0018] 4. In the high-efficiency reducing agent for steel dust and sludge of the present invention, the addition of starch and polyurethane acrylate not only improves the reduction reaction of the dust and sludge, but also improves the overall strength of the reducing agent particles, making the reducing agent particles easy to store and transport, thereby improving its commercial value. DETAILED DESCRIPTION

[0019] The technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0021] Example 1 High-efficiency reducing agent for preparing steel dust mud: Step 1: Add 500g of lignite powder and 150g of calcium oxide to a ball mill, then add 357.5g of 75% ethanol by mass into the ball mill, with a ball-to-material ratio of 20:1, place the ball mill on a ball mill and mill for 2h, collect the ground powder and add it to a beaker, then add 30g of starch into the beaker, stir evenly with a glass rod to obtain a mixed powder, slowly add 1587g of water to the mixed powder, stirring while adding until evenly stirred to obtain a mixed slurry.

[0022] Step 2: Put the mixed slurry into a freezer, adjust the temperature of the freezer to 2°C, take it out after refrigeration for 4.5 hours, pour it into a low-temperature constant temperature magnetic stirring reaction bath and stir it at -8°C until it is in a full ice crystal state to ensure that no droplets remain. Then, add it to a roller ball press at -3°C and press it into spherical particles with a linear ratio of 750Kg / cm at a roller pressure of 750Kg / cm, and then transfer it to a freezer and keep it warm at -3°C for 9 hours.

[0023] Step 3, adding the ice crystal balls after heat preservation into a vacuum dryer, drying at 180° C. for 3.5 hours, cooling to room temperature, adding them into a vibrating sieve machine for shaking and separation, and obtaining reducing agent precursor particles; Step 4. Prepare a polyurethane acrylate solution with a mass fraction of 18% in a bucket (the polyurethane acrylate here is purchased from Kunshan Custer Polymer Materials Co., Ltd., the same below), place the reducing agent precursor particles in a sieve basket, immerse the sieve basket in the bucket and shake it for 7 seconds, then immediately take it out (the amount of polyurethane acrylate used is 21g calculated based on the volume difference), and filter out the droplets until no droplets fall from the bottom of the sieve basket, then transfer the particles in the sieve basket to a vacuum drying oven, dry at 110°C for 30 minutes, take out to obtain agglomerated reducing agent, put the agglomerated reducing agent into a vibrating screen for oscillation separation, and obtain a high-efficiency reducing agent for steel dust.

[0024] Example 2 High-efficiency reducing agent for preparing steel dust mud: Step 1: Add 450 g of lignite powder and 100 g of calcium oxide to a ball mill, then add 302.5 g of 75% ethanol to the ball mill, with a ball-to-material ratio of 20:1, place the ball mill on a ball mill and mill for 2 hours, collect the ground powder and add it to a beaker, then add 20 g of starch to the beaker, stir evenly with a glass rod to obtain a mixed powder, slowly add 1330 g of water to the mixed powder, stirring until evenly mixed to obtain a mixed slurry.

[0025] Step 2: Put the mixed slurry into a freezer, adjust the temperature of the freezer to 0°C, take it out after refrigeration for 4 hours, pour it into a low-temperature constant temperature magnetic stirring reaction bath and stir it at -10°C until it is in a full ice crystal state to ensure that there are no droplets remaining, then add it to a roller ball press at -3°C and press it into spherical particles with a particle size of 1 cm at a linear ratio of 700Kg / cm, and then transfer it to a freezer and keep it warm at -3°C for 8 hours.

[0026] Step 3, adding the ice crystal balls after heat preservation into a vacuum dryer, drying at 180° C. for 3 hours, cooling to room temperature, adding them into a vibrating sieve machine for oscillation separation, and obtaining reducing agent precursor particles; Step 4: prepare a polyurethane acrylate solution with a mass fraction of 15% in a bucket, place the reducing agent precursor particles in a sieve basket, immerse the sieve basket in the bucket and shake it for 5 seconds, then immediately take it out and filter out the droplets until no droplets fall from the bottom of the sieve basket, then transfer the particles in the sieve basket to a vacuum drying oven, dry it at 100°C for 30 minutes, take it out to obtain agglomerated reducing agent, put the agglomerated reducing agent into a vibrating screen for oscillation separation, and obtain a high-efficiency reducing agent for steel dust.

[0027] Example 3 High-efficiency reducing agent for preparing steel dust mud: Step 1. Add 550g of lignite powder and 200g of calcium oxide to a ball mill, then add 412.5g of 75% ethanol by mass into the ball mill, with a ball-to-material ratio of 20:1, place the ball mill on a ball mill and mill for 2.5h, collect the ground powder and add it to a beaker, then add 40g of starch into the beaker, stir evenly with a glass rod to obtain a mixed powder, slowly add 1843g of water to the mixed powder, stirring until evenly mixed to obtain a mixed slurry.

[0028] Step 2: Put the mixed slurry into a freezer, adjust the temperature of the freezer to 5°C, take it out after refrigeration for 5 hours, pour it into a low-temperature constant temperature magnetic stirring reaction bath and stir it at -5°C until it is in a full ice crystal state to ensure that there are no droplets remaining, then add it to a roller ball press at -3°C and press it into spherical particles with a particle size of 1 cm at a linear ratio of 800Kg / cm, and then transfer it to a freezer and keep it at -3°C for 10 hours.

[0029] Step 3, adding the ice crystal balls after heat preservation into a vacuum dryer, drying at 180° C. for 3 hours, cooling to room temperature, adding them into a vibrating sieve machine for oscillation separation, and obtaining reducing agent precursor particles; Step 4: prepare a polyurethane acrylate solution with a mass fraction of 15% in a bucket, place the reducing agent precursor particles in a sieve basket, immerse the sieve basket in the bucket and shake it for 5 seconds, then immediately take it out and filter out the droplets until no droplets fall from the bottom of the sieve basket, then transfer the particles in the sieve basket to a vacuum drying oven, dry it at 100°C for 30 minutes, take it out to obtain agglomerated reducing agent, put the agglomerated reducing agent into a vibrating screen for oscillation separation, and obtain a high-efficiency reducing agent for steel dust.

[0030] Example 4 Compared with Example 1, the only difference is that in step 1, 2024 g of water is slowly added to the mixed powder, and the other steps and conditions are exactly the same, and finally a high-efficiency reducing agent for steel dust is obtained.

[0031] Example 5 Compared with Example 1, the only difference is that in step 1, 1263 g of water is slowly added to the mixed powder, and the other steps and conditions are exactly the same, and finally a high-efficiency reducing agent for steel dust is obtained.

[0032] Comparative Example 1 Compared with Example 1, the only difference is that in step 1, 2720 g of water is slowly added to the mixed powder, and the other steps and conditions are exactly the same, and finally a high-efficiency reducing agent for steel dust is obtained.

[0033] Comparative Example 2 Compared with Example 1, the only difference is that in step 1, 1020 g of water is slowly added to the mixed powder, and the other steps and conditions are exactly the same, and finally a high-efficiency reducing agent for steel dust is obtained.

[0034] Comparative Example 3 Compared with Example 1, the only difference is that step 4 is not performed, and the other steps and conditions are exactly the same, and the obtained reducing agent precursor particles are used as the final reducing agent.

[0035] Comparative Example 4 Compared with Example 1, the only difference is that starch is not added in step 1, and the other steps and conditions are exactly the same to finally prepare the reducing agent.

[0036] Comparative Example 5 Add 500g lignite powder and 150g calcium oxide into a ball mill, then add 357.5g ethanol with a mass fraction of 75% into the ball mill, the ball-to-material ratio is 20:1, put the ball mill on a ball mill and mill for 2h, collect the ground powder and add it into a beaker, then add 30g starch and 21g polyurethane acrylate into the beaker and mix well to obtain a mixed powder reducing agent.

[0037] The reducing agents prepared in Examples 1-5 and Comparative Examples 1-5 were tested for strength and porosity using the following test methods: Compressive strength: Particle strength tester (DL-4), test 20 groups and take the average value.

[0038] Porosity: gas adsorption method (ISO 15901.3), 20 groups of tests were taken as the average value.

[0039] The test results are listed in Table 1, which is as follows:

[0040] By analyzing the data in Table 1, it can be known that the compressive strength of the high-efficiency reducing agent for steel dust prepared in Examples 1-5 all reached above 33 MPa, and the porosity all reached above 52%, and both the compressive strength and the porosity were at a relatively high level.

[0041] Compared with Example 1, although the porosity of Comparative Example 1 is higher, the compressive strength is significantly reduced. This is because the amount of water used in the mixed slurry is too much, resulting in more pores and poor strength; Compared with Example 1, although the compressive strength of Comparative Example 2 is higher, the porosity is significantly reduced. This is because the amount of water in the mixed slurry is too small, resulting in less porosity and higher strength; Compared with Example 1, the strength of Comparative Example 3 decreased significantly and the porosity decreased slightly, because the lack of starch bonding force reduced the strength; Compared with Example 1, the strength of Comparative Example 4 is significantly reduced and the porosity is slightly reduced. This is because the lack of support from the polyurethane acrylate film layer causes the strength to decrease.

[0042] The reducing agents prepared by the methods of Examples 1-5 and Comparative Examples 1-5 were respectively tested for reduction performance. The test method was as follows: homogeneous steel dust provided by Zhongke Boyi Environmental Protection Technology Co., Ltd. was mixed with the reducing agent to form granules, and then transferred to a rotary kiln (provided by Zhongke Boyi Environmental Protection Technology Co., Ltd.) for calcination, and metallic iron and metallic zinc were collected, and the obtained metallic iron and metallic zinc were weighed. The conditions of each group of tests were kept the same, and the test results were listed in Table 2. Table 2 is as follows:

[0043] By analyzing the data in Table 2, it can be seen that the recovery amounts of metallic iron and metallic zinc in Examples 1-5 are significantly higher than those in Comparative Examples 1-5, which indicates that the high-efficiency reducing agent for steel dust and sludge of the present invention has a higher reduction effect.

[0044] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A highly efficient reducing agent for steel dust and mud, characterized in that: The method comprises the following raw materials in parts by weight: 45-55 parts of lignite powder, 10-20 parts of calcium oxide, 2-4 parts of starch, and several parts of polyurethane acrylate; The high-efficiency reducing agent for steel dust is in the form of porous spherical particles.

2. The high-efficiency reducing agent for steel dust and sludge according to claim 1, characterized in that: The reducing agent is in the form of porous spherical particles, and a polyurethane acrylate film layer is provided on the surface of the reducing agent.

3. A method for preparing a high-efficiency reducing agent for steel dust and mud according to claim 1, characterized in that: The method comprises the following preparation steps: Step 1: grind the lignite powder and calcium oxide, add starch and stir evenly to obtain a mixed powder, add water to the mixed powder, stir evenly to form a mixed slurry with a solid content of 25% to 35%; Step 2: pre-cool the mixed slurry, then stir it at -10°C to -5°C until it is in a full ice crystal state, then mold it into pellets at below 0°C, and keep it warm for 8-10 hours to obtain ice crystal balls; Step 3: drying the ice crystal balls at 180° C. for 3-4 hours, cooling to room temperature, and then shaking and separating to obtain reducing agent precursor particles; Step 4: Soak the reducing agent precursor particles in the polyurethane acrylate solution for 5-10 seconds, then immediately remove them, and then dry them at 100-120° C. for 30 minutes to obtain agglomerated reducing agents, and oscillate and separate the agglomerated reducing agents to obtain a highly efficient reducing agent for steel dust and sludge.

4. The method for preparing a high-efficiency reducing agent for steel dust and sludge according to claim 3, characterized in that: In step one, the method for mixing and grinding lignite powder and calcium oxide is as follows: add the mixture of lignite powder and calcium oxide into a ball mill, then add a 75% by mass ethanol aqueous solution into the ball mill, the ball-to-material ratio is 20:1, the ball mill is mounted on a ball mill, and the ball milling time is 1.5-2.5h.

5. The method for preparing a high-efficiency reducing agent for steel dust and sludge according to claim 4, characterized in that: The amount of the ethanol aqueous solution added is 50%-60% of the mixed material.

6. The method for preparing a high-efficiency reducing agent for steel dust and sludge according to claim 3, characterized in that: In step 2, the mixed slurry is precooled by refrigerating the mixed slurry at 0-5°C for 4-5h.

7. The method for preparing a high-efficiency reducing agent for steel dust and sludge according to claim 3, characterized in that: The method for molding the whole ice crystals of the mixed slurry into spherical particles is as follows: adding the whole ice crystals of the mixed slurry into a roller ball press and rolling them at a linear pressure of 700-800 Kg / cm.

8. The method for preparing a high-efficiency reducing agent for steel dust and sludge according to claim 3, characterized in that: In step 2, the particle size of the ice crystal ball is 0.8-1.5 cm.

9. The method for preparing a high-efficiency reducing agent for steel dust and sludge according to claim 3, characterized in that: In step 3 and step 4, the oscillation separation is performed by a vibrating screen machine.

10. The method for preparing a high-efficiency reducing agent for steel dust and sludge according to claim 3, characterized in that: In step 4, the mass fraction of the polyurethane acrylate solution is 15%-20%.

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