System and method for treating metallurgical dust sludge and ferric sulfate slag through rotary kiln

Abstract

The invention discloses a system and method for treating metallurgical dust and sludge and ferric sulfate slag through a rotary kiln, and the system comprises the rotary kiln which is used for carrying out pelletizing forming, pre-reduction desulfurization and deep reduction on the metallurgical dust and sludge and sulfuric acid slag of an iron and steel plant; the rotary kiln is sequentially provided with a pelletizing section, a pre-reduction desulfurization section, a deep reduction section and a discharging section from the kiln tail to the kiln head, and an inclined check ring is arranged in the pelletizing section; the kiln head of the rotary kiln is provided with an air nozzle, and the kiln tail is provided with a smoke outlet. The surface cooler is used for cooling the rotary kiln flue gas from the rotary kiln to obtain low-temperature flue gas; the zinc sulfate preparation module is used for treating the low-temperature flue gas and preparing a zinc sulfate product. According to the method, resource utilization and high-value utilization of the metallurgical dust sludge and the sulfuric-acid slag of the iron and steel plant can be achieved, low-sulfur and high-iron metallized pellets and zinc sulfate products are produced, and comprehensive utilization of iron, zinc and sulfur in the metallurgical dust sludge and the sulfuric-acid slag is achieved.

Description

Technical Field

[0001] The present invention relates to the field of metallurgy and chemical environmental protection technology, and more particularly to a system and method for treating metallurgical dust and ferric sulfate slag in a rotary kiln. Background Art

[0002] The steel industry, a crucial foundation for my country's economic development, is also a major emitter of solid waste, generating significant amounts of dust during its smelting process. Statistics show that the total amount of dust generated by steel companies generally accounts for 8% to 12% of steel production, with zinc-containing dust accounting for approximately 20% to 30%. Zinc-containing dust contains significant amounts of valuable elements such as iron, lead, and zinc, making it a valuable secondary resource. Therefore, achieving efficient resource utilization of metallurgical dust and sludge is a key research and development area for the metallurgical and environmental protection industries.

[0003] The rotary kiln is a highly efficient metallurgical process for recovering zinc resources, primarily used for the comprehensive utilization of secondary resources such as zinc-containing dust and electric furnace ash in steel mills. Its core principle is to separate and recover zinc from other metals, such as iron, through high-temperature reduction and volatilization of zinc oxides, achieving both environmental and economic benefits. Zinc-containing sludge primarily consists of ZnO (3%-30%), Fe₂O₃, and small amounts of Pb and Cd. Within the rotary kiln, a carbonaceous reducing agent (coke or anthracite) is mixed with the sludge, where a reduction reaction occurs at 1100-1300°C: ZnO + CO → Zn(g) + CO₂. Gaseous zinc is discharged with the flue gases and collected through bag filters as coarse zinc oxide powder (containing 50%-70% Zn). The kiln slag, representing the dezincified iron, can be returned to steel production.

[0004] my country currently produces over 18 million tons of sulfuric acid annually, with over 10 million tons of slag discharged. Effectively treating and utilizing sulphuric acid slag would not only eliminate environmental pollution but also provide the steel industry with a large supply of high-quality, low-cost ironmaking raw materials. Research and application of sulphuric acid slag in mineral processing primarily focuses on direct iron extraction. While considerable research has been conducted on iron extraction and sulfur reduction using sulphuric acid slag, and some progress has been made, the results remain unsatisfactory. The main drawbacks are relatively low iron grade and recovery, and high sulfur content in the resulting iron products.

[0005] Chinese patent application number CN202411693204.8 discloses a rotary kiln treatment system and method for zinc-containing dust and sludge, belonging to the field of industrial solid waste treatment technology. The system includes a batching system and a roasting system. The batching system is used to mix raw materials and transport them to the rotary kiln. The roasting system includes an automatic roasting temperature control system for adjusting the roasting temperature and a high-temperature section position control system for adjusting the position of the roasting section. This method is a conventional rotary kiln dust and sludge treatment process, which has disadvantages such as a long process flow and low product value.

[0006] Chinese patent application number CN202221131464.2 discloses a device for disposing zinc-containing dust sludge using a rotary kiln, which comprises a batching bin (1), a mixing pelletizing machine (2), a rotary kiln (4), a settling chamber (8), and a waste heat boiler (9). The device solves the problem of secondary utilization of zinc-containing dust sludge, one of the environmental problems that has long plagued the steel industry, and overcomes a series of problems in the blast furnace ironmaking process, such as thickening of the blast furnace shaft, difficulty in smooth operation of the blast furnace, and reduced gas utilization rate, caused by high zinc content in the raw materials. The method includes raw material pretreatment processes such as mixing and pelletizing, has a long process flow, and is essentially a supporting process for reducing the zinc load of the blast furnace, with relatively low process and technical benefits.

[0007] Chinese patent application number CN201110248301.2 discloses a method for ironmaking using sulfuric acid slag, which belongs to the field of metallurgy technology and is carried out in the following steps: (1) adding dodecylamine to sulfuric acid slag and then quenching it with water to obtain water-added sulfuric acid slag; (2) adding a desulfurizer, stirring the reaction, and then diluting it with water to obtain a desulfurized slurry; (3) diluting the desulfurized slurry with water and concentrating it to form a concentrated slurry; (4) filtering and drying it to obtain slag iron powder; (5) mixing the slag iron powder, a binder, blast furnace bag dust removal ash, borax and water to form a ball, and letting it stand to form slag pellets; (6) drying and sintering it with a chain grate to obtain sintered pellets; (7) reducing it with a rotary kiln to obtain metal pellets; (8) letting it stand for 4 to 7 hours, and then smelting it in a smelting furnace to obtain molten iron. The method of the present invention desulfurizes, concentrates and filters the sulfuric acid slag to obtain sulfuric acid slag iron powder, and then obtains molten iron through balling, sintering, reduction and smelting. The method is simple in process and suitable for industrial production. This method is a combined process of wet and fire methods, with a long process flow, high energy consumption and poor economic benefits.

[0008] In view of the above situation, there is an urgent need to study a system and method to realize the resource utilization and high-value utilization of metallurgical dust and sulfuric acid slag in steel plants, which can realize the comprehensive utilization of iron, zinc and sulfur in metallurgical dust and sulfuric acid slag and solve the problem of resource utilization of sulfur-containing raw materials. Summary of the Invention

[0009] In view of the defects existing in the prior art, the purpose of the present invention is to provide a rotary kiln treatment system and method for metallurgical dust and ferrous sulfate slag, which can realize the resource and high-value utilization of metallurgical dust and slag in steel plants, produce low-sulfur and high-iron metallized pellets and zinc sulfate products, and realize the comprehensive utilization of iron, zinc and sulfur in metallurgical dust and slag.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] The first aspect of the present invention provides a rotary kiln system for treating metallurgical dust and ferrous sulfate slag, comprising:

[0012] The rotary kiln is used to pelletize, pre-reduction desulfurize, and deep reduce the metallurgical dust and sulfuric acid slag from the steel plant. The rotary kiln is equipped with a pelletizing section, a pre-reduction desulfurization section, a deep reduction section, and a discharge section from the kiln tail to the kiln head. The pelletizing section is equipped with an inclined retaining ring. The kiln head of the rotary kiln is equipped with an air nozzle, and the kiln tail is equipped with a flue gas outlet.

[0013] Surface cooler, used to cool the rotary kiln flue gas from the rotary kiln to obtain low-temperature flue gas;

[0014] Zinc sulfate preparation module, used to treat low-temperature flue gas and prepare zinc sulfate products.

[0015] Preferably, the angle α between the inclined retaining ring and the rotary kiln wall is 40° to 50°, and the height of the inclined retaining ring is 250 to 300 mm.

[0016] Preferably, the length of the pelletizing section is 1 / 5 to 1 / 6 of the total length of the rotary kiln, the length of the pre-reduction desulfurization section is 1.5 / 5 to 1.5 / 6 of the total length of the rotary kiln, the length of the deep reduction section is 2 / 5 to 2 / 6 of the total length of the rotary kiln, and the length of the discharging section is 1 / 5 to 1 / 6 of the total length of the rotary kiln;

[0017] The pelletizing section is a special-shaped structure with an inclined retaining ring, and the pre-reduction desulfurization section, deep reduction section, and discharge section are all through-cavity structures;

[0018] The air nozzle of the rotary kiln is connected to the kiln head blower, and the smoke outlet is connected to the surface cooler through a smoke pipe.

[0019] Preferably, the surface cooler is connected to the zinc sulfate preparation module via an induced draft fan.

[0020] Preferably, the zinc sulfate preparation module includes a zinc sulfate preparation pool, a purification and impurity removal system, and an evaporation and crystallization system arranged in sequence;

[0021] The zinc sulfate preparation pool is provided with a smoke inlet and a smoke outlet, and a hollow drum inlet pump is provided in the zinc sulfate preparation pool.

[0022] A second aspect of the present invention provides a method for treating metallurgical dust and ferric sulfate slag using a rotary kiln, wherein the system for treating metallurgical dust and ferric sulfate slag using a rotary kiln as described in the first aspect of the present invention is used to perform the following steps:

[0023] S1, the metallurgical dust and sulfuric acid slag from the steel plant are added to the pelletizing section from the kiln tail of the rotary kiln for pelletizing and forming into pellets. When the material height of the pellets exceeds the height of the inclined retaining ring, the pellets enter the pre-reduction and desulfurization section. After pre-reduction and desulfurization, they enter the deep reduction section for deep reduction. The sulfur and zinc in the pellets enter the rotary kiln flue gas and are discharged from the kiln tail. The metallized pellets after deep reduction are discharged from the discharge section;

[0024] S2, the rotary kiln flue gas is cooled by the surface cooler to obtain low-temperature flue gas;

[0025] S3, the low-temperature flue gas enters the zinc sulfate preparation pool of the zinc sulfate preparation module, and the SO2 in the low-temperature flue gas dissolves into the industrial water in the zinc sulfate preparation pool to form sulfurous acid. At the same time, air is blown into the zinc sulfate preparation pool, and the oxygen in the air oxidizes the sulfurous acid into sulfuric acid. The zinc oxide in the low-temperature flue gas reacts with the sulfuric acid to form zinc sulfate;

[0026] S4, when the zinc ion concentration of the solution in the zinc sulfate preparation tank is ≥30g / L, purification, impurity removal and evaporation crystallization are carried out to obtain zinc sulfate product.

[0027] Preferably, in step S1:

[0028] The metallurgical dust and sludge of the steel plant is secondary ash from blast furnaces; the total iron grade of the secondary ash from blast furnaces is 25-30%, the zinc content is 2-5%, the chlorine content is 2-5%, and the carbon content is 25-30%; and the particle size of the secondary ash from blast furnaces is more than 90% below 5 μm;

[0029] The sulfuric acid slag has a total iron content of 45-53%, a sulfur content of 1.5-3%, and a water content of 20-25%; the particle size of the sulfuric acid slag is 0.1-1 mm;

[0030] The dry mass ratio of the steel plant metallurgical dust and the sulfuric acid slag is 100:40-50 and is added to the pelletizing section.

[0031] Preferably, in step S1:

[0032] The time for the rotary kiln to rotate one circle is 3 to 5 minutes, and the installation slope of the rotary kiln is 3.5% to 4%;

[0033] The total residence time of the material in the rotary kiln is 3.5 to 4.5 hours; the residence time of the material in the pelletizing section is 0.6 to 0.9 hours, and the temperature is 200 to 300°C; the residence time of the material in the pre-reduction desulfurization section is 0.85 to 1.35 hours, and the temperature is 400 to 1000°C; the residence time of the material in the deep reduction section is 1.15 to 1.8 hours, and the temperature is 1200 to 1220°C; the residence time of the material in the discharging section is 0.6 to 0.9 hours, and the temperature is 900 to 1000°C;

[0034] The excess air coefficient in the rotary kiln is 2.5-3.

[0035] Preferably, in step S1:

[0036] The particle size of the pellets is 6 to 12 mm, and the water content of the pellets entering the pre-reduction desulfurization section from the pelletizing section is ≤1%;

[0037] The metallized pellets have an iron grade of ≥55%, an iron content of ≥40%, a zinc content of ≤0.5%, a sulfur content of ≤0.5%, and a carbon content of ≤0.5%;

[0038] The temperature of the rotary kiln flue gas is 400-500°C.

[0039] Preferably, in step S2, the temperature of the low-temperature flue gas is 150-200°C;

[0040] Preferably, in step S3:

[0041] In the zinc sulfate preparation tank, the amount of industrial water added is controlled, and low-temperature flue gas is used to ensure that the temperature in the zinc sulfate preparation tank is between 60 and 65°C;

[0042] The pH in the zinc sulfate preparation pool was maintained at 5.0 to 5.2 by adding sulfuric acid to the pool.

[0043] Preferably, in step S4, the purity of the zinc sulfate product is ≥99%.

[0044] The effects of the present invention are as follows:

[0045] 1. The present invention realizes resource utilization and high-value utilization of metallurgical dust and slag from steel mills through a rotary kiln treatment system for metallurgical dust and slag and a relatively short process flow, produces low-sulfur and high-iron metallized pellets and zinc sulfate products, and realizes the comprehensive utilization of iron, zinc and sulfur in metallurgical dust and slag;

[0046] 2. The present invention improves the rotary kiln, realizes pelletizing and drying of raw materials in the rotary kiln, eliminates the need for an external pelletizing plate in the traditional rotary kiln, and greatly shortens the process flow;

[0047] 3. The present invention makes full use of the characteristics of various elements in blast furnace secondary ash and sulfuric acid slag. The chlorine element in the blast furnace secondary ash plays a desulfurization role within a specific temperature range, preventing sulfur from entering the metallized pellets, thereby improving the quality and value of the pellets;

[0048] 4. The present invention makes full use of the sulfur element in the flue gas and the flue gas temperature to directly prepare the zinc oxide in the flue gas into a zinc sulfate solution, and then produces high-quality solid zinc sulfate, eliminating the need for traditional desulfurization equipment for disposing of sulfur-containing raw materials, fully realizing the comprehensive recycling of multiple elements of solid waste, and saving project investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the process of treating metallurgical dust and ferric sulfate slag with a rotary kiln according to the present invention;

[0050] Figure 2 This is a schematic structural diagram of a rotary kiln system for treating metallurgical dust and ferric sulfate slag according to the present invention;

[0051] Figure 3 Schematic diagram of the inclined retaining ring of the rotary kiln;

[0052] In the figure, 1. Rotary kiln; 11. Inclined retaining ring; 2. Surface cooler; 3. Induced draft fan; 4. Zinc sulfate preparation tank; 5. Purification and impurity removal system; 6. Evaporation crystallization system; 7. Blower. DETAILED DESCRIPTION

[0053] In order to better understand the above technical solutions of the present invention, the technical solutions of the present invention are further described below with reference to the accompanying drawings and embodiments.

[0054] Combine Figure 2 As shown, the present invention provides a rotary kiln system for treating metallurgical dust and ferrous sulfate slag, comprising a rotary kiln 1, a surface cooler 2, and a zinc sulfate preparation module. The rotary kiln 1 is used to pelletize, perform pre-reduction desulfurization, and perform deep reduction on the metallurgical dust and slag from the steel plant; the rotary kiln 1 is provided with a pelletizing section, a pre-reduction desulfurization section, a deep reduction section, and a discharge section from the kiln tail to the kiln head, and an inclined retaining ring 11 is provided in the pelletizing section; the kiln head of the rotary kiln 1 is provided with an air nozzle, and the kiln tail is provided with a flue gas outlet. The surface cooler 2 is used to cool the flue gas from the rotary kiln 1 to obtain low-temperature flue gas. The zinc sulfate preparation module is used to treat the low-temperature flue gas and prepare zinc sulfate products.

[0055] Combine Figure 3 As shown, the angle α between the inclined retaining ring 11 and the kiln wall of the rotary kiln 1 is 40° to 50°, and the height of the inclined retaining ring 11 is 250 to 300 mm. The installation slope of the rotary kiln 1 is 3.5% to 4% (see Figure 2 In the rotary kiln 1, the length of the pelletizing section is 1 / 5 to 1 / 6 of the total length of the rotary kiln 1, the length of the pre-reduction desulfurization section is 1.5 to 1.5 / 6 of the total length of the rotary kiln 1, the length of the deep reduction section is 2 / 5 to 2 / 6 of the total length of the rotary kiln 1, and the length of the discharge section is 1 / 5 to 1 / 6 of the total length of the rotary kiln 1. The pelletizing section is a special-shaped structure equipped with an inclined retaining ring 11, while the pre-reduction desulfurization section, deep reduction section, and discharge section all have through-cavity structures.

[0056] Combine Figure 2 As shown, the air nozzle of the rotary kiln 1 is connected to the kiln head blower 7 to ensure sufficient oxygen for fuel combustion in the kiln. The flue gas outlet is connected to the surface cooler 2 through a flue gas duct. The flue gas from the rotary kiln 1 is discharged from the flue gas outlet at the kiln tail and then sent to the surface cooler 2.

[0057] Combine Figure 2 As shown, the surface cooler 2 is connected to the zinc sulfate preparation module through an induced draft fan 3.

[0058] Combine Figure 2As shown, the zinc sulfate preparation module includes a zinc sulfate preparation tank 4, a purification and impurity removal system 5, and an evaporation and crystallization system 6, which are arranged in sequence. The zinc sulfate preparation tank 4 is provided with a flue gas inlet and a flue gas outlet. The zinc sulfate preparation tank 4 is also provided with an air blast pump to blow air into the tank 4.

[0059] Combine Figure 1 As shown, the present invention also provides a method for treating metallurgical dust and ferric sulfate slag with a rotary kiln, wherein the above-mentioned system for treating metallurgical dust and ferric sulfate slag with a rotary kiln is used to perform the following steps:

[0060] S1, the metallurgical dust and sulfuric acid slag from the steel plant are added to the pelletizing section from the kiln tail of the rotary kiln for pelletizing and forming into pellets. When the material height of the pellets exceeds the height of the inclined retaining ring, the pellets enter the pre-reduction and desulfurization section. After pre-reduction and desulfurization, they enter the deep reduction section for deep reduction. The sulfur and zinc in the pellets enter the rotary kiln flue gas and are discharged from the kiln tail. The metallized pellets after deep reduction are discharged from the discharge section;

[0061] In this step, the metallurgical dust and sludge from the steel mill is secondary blast furnace ash. The blast furnace secondary ash has a total iron grade of 25-30%, a zinc content of 2-5%, a chlorine content of 2-5%, and a carbon content of 25-30%. The blast furnace secondary ash has a relatively fine particle size, with particles below 5 μm accounting for over 90%. The iron in the blast furnace secondary ash exists as ferric oxide and ferroferric oxide, and the zinc exists as zinc ferrite and zinc oxide.

[0062] The total iron content of the sulfate slag is 45-53%, the sulfur content is 1.5-3%, and the water content is 20-25%. The sulfate slag is in a granular form with a particle size of 0.1-1 mm. The iron in the sulfate slag mainly exists in the form of ferroferric oxide, and the sulfur exists in the form of pyrite (FeS).

[0063] Steel mill metallurgical dust and slag are added to the pelletizing stage at the rotary kiln tail at a dry weight ratio of 100:40-50. The slag, with a water content of 20-25%, provides the required moisture for pelletizing. Granular slag serves as the aggregate for pelletizing, ensuring rapid pellet formation. Carbon from the blast furnace secondary ash acts as a reducing agent, while chlorine acts as a desulfurizer.

[0064] In this step, the rotary kiln rotates one circle for 3 to 5 minutes, and the installation slope of the rotary kiln is 3.5% to 4%; the total residence time of the material in the rotary kiln is 3.5 to 4.5 hours; the residence time of the material in the pelletizing section is 0.6 to 0.9 hours, and the temperature is 200 to 300°C; the residence time of the material in the pre-reduction desulfurization section is 0.85 to 1.35 hours, and the temperature is 400 to 1000°C; the residence time of the material in the deep reduction section is 1.15 to 1.8 hours, and the temperature is 1200 to 1220°C; the residence time of the material in the discharging section is 0.6 to 0.9 hours, and the temperature is 900 to 1000°C.

[0065] Since the rotary kiln is equipped with an air burner at the kiln head, it can ensure sufficient oxygen for fuel combustion in the kiln, and the air excess coefficient in the rotary kiln is 2.5 to 3. The carbon in the pellets prepared from blast furnace secondary ash and sulfuric acid slag acts as a reducing agent and a heating agent.

[0066] Blast furnace secondary ash and sulfuric acid slag are made into pellets with a particle size of 6 to 12 mm through the action of retaining rings in the pelletizing section. The pellets can ensure close contact between carbon, zinc, chlorine and sulfur elements in the materials, accelerate the reaction speed, and the moisture in the materials in the pelletizing section is gradually dried during the forming process. The water content of the pellets entering the pre-reduction desulfurization section from the pelletizing section is ≤1%, avoiding the explosion of the pellets.

[0067] After the pellets enter the pre-reduction desulfurization section, they complete partial sulfur removal, partial reduction and volatilization of zinc, and pre-reduction of iron. The reactions are as follows:

[0068] 2FeS2+6KCl+5O2→2FeCl3+4SO2↑+3K2O↑

[0069] 4FeS2+11O2→2Fe2O3+8SO2↑

[0070] 3ZnFe2O4+CO=2Fe3O4+3ZnO(g)+CO2(g)

[0071] ZnO + C = Zn(g) + CO (g)

[0072] ZnO + CO = Zn (g) + CO2 (g)

[0073] PbO+C=Pb(g)+CO(g)

[0074] PbO + CO = Pb(g) + CO2 (g)

[0075] Fe3O4+3C=3FeO+3CO(g)

[0076] Fe3O4 + 3CO = 3FeO + 3CO2 (g)

[0077] Fe2O3+C=2FeO+CO(g)

[0078] Fe2O3+CO=2FeO+CO2(g)

[0079] CO2+C=2CO(g)

[0080] After the pellets complete pre-reduction and desulfurization, they enter the deep reduction stage, where the iron oxides in the pellets are reduced to metallic iron, and zinc oxide and zinc ferrite are reduced to elemental metals.

[0081] FeO+CO=Fe+CO2(g)

[0082] The metallized pellets reduced in the deep reduction section are discharged from the discharging section. The iron grade of the metallized pellets is ≥55%, the iron content is ≥40%, the zinc content is ≤0.5%, the sulfur content is ≤0.5%, and the carbon content is ≤0.5%. The metallized pellets can be used as high-quality ironmaking raw materials.

[0083] During the above process, sulfur dioxide and metallic zinc volatilized by pellet reduction enter the flue gas of the rotary kiln. The metallic zinc is oxidized into zinc oxide in the flue gas of the rotary kiln. The flue gas of the rotary kiln is discharged from the flue gas outlet at the tail of the kiln. The temperature of the flue gas of the rotary kiln is 400-500℃.

[0084] S2, the flue gas from the rotary kiln is cooled by a surface cooler to obtain low-temperature flue gas; in order to prevent condensation of sulfur-containing flue gas and corrosion of equipment, the temperature of the low-temperature flue gas shall not be lower than 150°C; in specific cases, the temperature of the low-temperature flue gas is 150-200°C.

[0085] S3, the low-temperature flue gas enters the zinc sulfate preparation pool of the zinc sulfate preparation module, and the SO2 in the low-temperature flue gas dissolves into the industrial water in the zinc sulfate preparation pool to form sulfurous acid. At the same time, air is blown into the zinc sulfate preparation pool, and the oxygen in the air oxidizes the sulfurous acid into sulfuric acid. The zinc oxide in the low-temperature flue gas reacts with the sulfuric acid to form zinc sulfate;

[0086] In this step, the temperature of the zinc sulfate preparation pool is ensured by the temperature of the low-temperature flue gas. Therefore, when adding industrial water to the zinc sulfate preparation pool, the amount of industrial water added needs to be controlled, and the low-temperature flue gas is used to ensure that the temperature in the zinc sulfate preparation pool is within the range of 60-65°C.

[0087] The SO2 in the low-temperature flue gas dissolves into the industrial water in the zinc sulfate preparation pool to form sulfurous acid (H2SO3). At this time, air is blown into the zinc sulfate preparation pool using an air pump. The oxygen in the air oxidizes the sulfurous acid into sulfuric acid (H2SO4) at 60-65°C. The reaction is as follows:

[0088] H2SO3+0.5O2=H2SO4

[0089] Zinc oxide in low-temperature flue gas neutralizes sulfuric acid in an acidic system to generate zinc sulfate, and insoluble impurities such as lead and iron are separated in the form of bottom slag through plate and frame filter press filtration.

[0090] H2SO4+ZnO=ZnSO4+H2O

[0091] To ensure that the zinc oxide is completely leached into the solution by sulfuric acid, sulfuric acid is added to the zinc sulfate preparation tank to ensure that the pH in the tank is 5.0-5.2. The zinc sulfate preparation tank is equipped with a flue gas outlet, and the treated flue gas is discharged from the flue gas outlet.

[0092] S4, when the zinc ion concentration of the solution in the zinc sulfate preparation tank is ≥30g / L, purification, impurity removal and evaporation crystallization are carried out to obtain zinc sulfate product.

[0093] In this step, the solution with a zinc ion concentration of ≥30 g / L is sent to the purification and impurity removal system. By adding zinc particles and other additives, the impurities in the solution are removed to a specified range, as shown in Table 2.

[0094] Table 1

[0095] Impurity elements Cu Cd Co Ni Sb Fe Cl content ≤1mg / L ≤2mg / L ≤2mg / L ≤2mg / L ≤1mg / L ≤3000g / L ≤600g / L

[0096] The impurity-removed solution is subjected to an evaporation crystallization process to obtain a zinc sulfate product with a purity of ≥99%, and the zinc recovery rate is above 90%.

[0097] Example 1

[0098] This embodiment adopts Figure 2 、 Figure 3 The rotary kiln system shown here for treating metallurgical dust and ferrous sulfate slag includes a rotary kiln 1, a surface cooler 2, and a zinc sulfate preparation module. From the kiln's tail to the kiln's head, the rotary kiln 1 is equipped with a pelletizing section, a pre-reduction and desulfurization section, a deep reduction section, and a discharge section. The pelletizing section is equipped with an inclined retaining ring 11. The rotary kiln 1 is equipped with an air nozzle at the kiln's head and a flue gas outlet at the kiln's tail.

[0099] Combine Figure 3 As shown, the angle α between the inclined retaining ring 11 and the kiln wall of the rotary kiln 1 is 40° to 50°, and the height of the inclined retaining ring 11 is 250 to 300 mm. The installation slope of the rotary kiln 1 is 4% (see Figure 2 In the rotary kiln 1, the length of the pelletizing section is 1 / 5 to 1 / 6 of the total length of the rotary kiln 1, the length of the pre-reduction desulfurization section is 1.5 to 1.5 / 6 of the total length of the rotary kiln 1, the length of the deep reduction section is 2 / 5 to 2 / 6 of the total length of the rotary kiln 1, and the length of the discharge section is 1 / 5 to 1 / 6 of the total length of the rotary kiln 1. The pelletizing section is a special-shaped structure equipped with an inclined retaining ring 11, while the pre-reduction desulfurization section, deep reduction section, and discharge section all have through-cavity structures.

[0100] Combine Figure 2 As shown, the air nozzle of the rotary kiln 1 is connected to the kiln head blower 7 to ensure sufficient oxygen for fuel combustion in the kiln. The flue gas outlet is connected to the surface cooler 2 through a flue gas duct. The flue gas from the rotary kiln 1 is discharged from the flue gas outlet at the kiln tail and then sent to the surface cooler 2.

[0101] Combine Figure 2 As shown, the surface cooler 2 is connected to the zinc sulfate preparation module through an induced draft fan 3.

[0102] Combine Figure 2As shown, the zinc sulfate preparation module includes a zinc sulfate preparation tank 4, a purification and impurity removal system 5, and an evaporation and crystallization system 6, which are arranged in sequence. The zinc sulfate preparation tank 4 is provided with a flue gas inlet and a flue gas outlet. The zinc sulfate preparation tank 4 is also provided with an air blast pump to blow air into the tank 4.

[0103] This embodiment uses the above-mentioned rotary kiln system for treating metallurgical dust and ferrous sulfate slag to treat metallurgical dust and slag from a steel plant. The specific process is as follows:

[0104] The steel mill's metallurgical sludge is made from secondary blast furnace ash with an iron grade of 25%, a zinc content of 2%, a chlorine content of 2.5%, and a carbon content of 25%. Over 90% of the secondary blast furnace ash has a particle size of 5μm or less. Sulfate slag has an iron grade of 53%, a sulfur content of 2.8%, and a water content of 22%. The steel mill's metallurgical sludge and sulfate slag are mixed in a dry weight ratio of 100:40. This mixture is fed into the pelletizing section at the tail of the rotary kiln, where retaining rings create pellets with a particle size of 6-12mm. The pellets entering the pre-reduction desulfurization section have a water content of ≤1%. They then undergo pre-reduction desulfurization in the pre-reduction desulfurization section and deep reduction in the deep reduction section. The rotary kiln rotates one circle for 3.2 minutes, the installation slope is 4%, the total residence time of the material is 3.5 hours, the residence time of the material in the pelletizing section is 0.6 hours, the temperature is between 200 and 300 ° C, the residence time in the pre-reduction and desulfurization section is 0.9 hours, the temperature is between 400 and 1000 ° C, the residence time in the deep reduction section is 1.3 hours, the temperature is between 1200 and 1220 ° C, the residence time in the kiln head discharging section is 0.9 hours, the temperature is 900 to 1000 ° C, the excess air coefficient is 3, and the final metallized pellets are discharged from the discharging section. The iron grade of the metallized pellets is ≥56.25%, the metallic iron content is 40.63%, the zinc content is 0.41%, the sulfur content is 0.38%, and the carbon content is 0.27%. The metallized pellets can be used as high-quality ironmaking raw materials.

[0105] The high-temperature rotary kiln flue gas discharged from the rotary kiln tail has a temperature of 410°C. After cooling through a surface cooler, it reaches a low-temperature flue gas temperature of 155°C. The low-temperature flue gas enters the zinc sulfate production tank directly. Industrial water is added to the tank to maintain a temperature between 60 and 65°C. Air is continuously introduced into the tank to oxidize the sulfurous acid into sulfuric acid. Zinc oxide reacts with sulfuric acid in an acidic system to produce zinc sulfate. Sulfuric acid is added to maintain the pH in the tank between 6 and 7. Insoluble impurities such as lead and iron are separated from the zinc sulfate solution as bottom sludge through a plate and frame filter press. When the zinc ion concentration of the zinc sulfate solution in the zinc sulfate production tank reaches ≥30g / L, a traditional purification, deslagging, concentration and crystallization process is used to produce finished zinc sulfate with a purity of ≥99%, achieving a zinc recovery rate of 91%.

[0106] Example 2

[0107] This embodiment adopts Figure 2 、 Figure 3 The rotary kiln system for treating metallurgical dust and ferrous sulfate slag shown in the figure is used to treat metallurgical dust and slag from steel plants. The specific process is as follows:

[0108] The steel mill's metallurgical sludge is made from secondary blast furnace ash with an iron grade of 28%, a zinc content of 3.5%, a chlorine content of 3.5%, and a carbon content of 28%. Over 90% of the secondary blast furnace ash has a particle size of 5μm or less. The sludge is then mixed with sludge in a dry weight ratio of 100:45. This mixture is fed into the pelletizing section at the tail of the rotary kiln, where retaining rings create pellets with a particle size of 6-12mm. The pellets entering the pre-reduction desulfurization section have a water content of ≤1%. They then undergo pre-reduction desulfurization in the pre-reduction desulfurization section and deep reduction in the deep reduction section. The rotary kiln rotates one circle for 4 minutes, the installation slope is 4%, the total residence time of the material is 4 hours, the residence time of the material in the pelletizing section is 0.8 hours, the temperature is between 200 and 300 ° C, the residence time in the pre-reduction and desulfurization section is 1.1 hours, the temperature is between 400 and 1000 ° C, the residence time in the deep reduction section is 1.5 hours, the temperature is between 1200 and 1220 ° C, the residence time in the kiln head discharging section is 0.6 hours, the temperature is 900 to 1000 ° C, the excess air coefficient is 2.8, and the final metallized pellets are discharged from the discharging section. The iron grade of the metallized pellets is ≥57.33%, the metallic iron content is 40.88%, the zinc content is 0.27%, the sulfur content is 0.40%, and the carbon content is 0.38%. The metallized pellets can be used as high-quality ironmaking raw materials.

[0109] The high-temperature rotary kiln flue gas discharged from the rotary kiln tail is at a temperature of 450°C. It is cooled by a surface cooler to a low-temperature flue gas of 180°C. The low-temperature flue gas enters the zinc sulfate production tank directly. Industrial water is added to the tank to maintain a temperature between 60 and 65°C. Air is continuously introduced into the tank to oxidize the sulfurous acid into sulfuric acid. Zinc oxide reacts with sulfuric acid in an acidic system to produce zinc sulfate. Sulfuric acid is added to maintain a pH between 6 and 7 in the tank. Insoluble impurities such as lead and iron are separated from the zinc sulfate solution as sediment through a plate and frame filter press. When the zinc ion concentration of the zinc sulfate solution in the zinc sulfate production tank reaches ≥30 g / L, a traditional purification, deslagging, concentration, and crystallization process is used to produce finished zinc sulfate with a purity of ≥99%, achieving a zinc recovery rate of 92.53%.

[0110] Example 3

[0111] This embodiment adopts Figure 2 、 Figure 3 The rotary kiln system for treating metallurgical dust and ferrous sulfate slag shown in the figure is used to treat metallurgical dust and slag from steel plants. The specific process is as follows:

[0112] The steel mill's metallurgical dust and sludge are made from secondary blast furnace ash with an iron grade of 30%, a zinc content of 5%, a chlorine content of 4.5%, and a carbon content of 30%. Over 90% of the secondary blast furnace ash has a particle size of 5μm or less. The sludge and sludge have an iron grade of 50%, a sulfur content of 2%, and a water content of 23%. The metallurgical dust and sludge are mixed in a dry weight ratio of 100:45 and fed into the pelletizing section at the tail of the rotary kiln. The retaining rings create pellets with a particle size of 6-12mm. The pellets from the pelletizing section have a water content of ≤1% before entering the pre-reduction desulfurization section. They then undergo pre-reduction desulfurization and deep reduction in the deep reduction section. The rotary kiln rotates one circle for 5 minutes, the installation slope is 3.5%, the total residence time of the material is 5 hours, the residence time of the material in the pelletizing section is 0.9 hours, the temperature is between 200 and 300 ° C, the residence time in the pre-reduction desulfurization section is 1.3 hours, the temperature is between 400 and 1000 ° C, the residence time in the deep reduction section is 1.8 hours, the temperature is between 1200 and 1220 ° C, the residence time in the kiln head discharging section is 1 hour, the temperature is 900 to 1000 ° C, the excess air coefficient is 2.5, and the final metallized pellets are discharged from the discharging section. The iron grade of the metallized pellets is ≥58.22%, the metallic iron content is 41.12%, the zinc content is 0.30%, the sulfur content is 0.41%, and the carbon content is 0.45%. The metallized pellets can be used as high-quality ironmaking raw materials.

[0113] The high-temperature rotary kiln flue gas discharged from the rotary kiln tail has a temperature of 490°C. After cooling through a surface cooler, it reaches a low-temperature flue gas temperature of 200°C. The low-temperature flue gas enters the zinc sulfate production tank directly. Industrial water is added to the tank to maintain a temperature between 60 and 65°C. Air is continuously introduced into the tank to oxidize the sulfurous acid into sulfuric acid. Zinc oxide reacts with sulfuric acid in an acidic system to produce zinc sulfate. Sulfuric acid is added to maintain the pH in the tank between 6 and 7. Insoluble impurities such as lead and iron are separated from the zinc sulfate solution as sediment through a plate and frame filter press. When the zinc ion concentration of the zinc sulfate solution in the zinc sulfate production tank reaches ≥30g / L, a traditional purification, deslagging, concentration, and crystallization process is used to produce finished zinc sulfate with a purity of ≥99%, achieving a zinc recovery rate of 92.11%.

[0114] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present invention and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A rotary kiln system for treating metallurgical dust and ferrous sulfate slag, characterized in that: include The rotary kiln is used to pelletize, pre-reduction desulfurize, and deep reduce the metallurgical dust and sulfuric acid slag from the steel plant. The rotary kiln is equipped with a pelletizing section, a pre-reduction desulfurization section, a deep reduction section, and a discharge section from the kiln tail to the kiln head. The pelletizing section is equipped with an inclined retaining ring. The kiln head of the rotary kiln is equipped with an air nozzle, and the kiln tail is equipped with a flue gas outlet. Surface cooler, used to cool the rotary kiln flue gas from the rotary kiln to obtain low-temperature flue gas; Zinc sulfate preparation module, used to treat low-temperature flue gas and prepare zinc sulfate products.

2. The rotary kiln system for treating metallurgical dust and ferrous sulfate slag according to claim 1, characterized in that: The included angle α between the inclined retaining ring and the rotary kiln wall is 40° to 50°, and the height of the inclined retaining ring is 250 to 300 mm.

3. The rotary kiln system for treating metallurgical dust and ferrous sulfate slag according to claim 1, characterized in that: The length of the pelletizing section is 1 / 5 to 1 / 6 of the total length of the rotary kiln, the length of the pre-reduction desulfurization section is 1.5 / 5 to 1.5 / 6 of the total length of the rotary kiln, the length of the deep reduction section is 2 / 5 to 2 / 6 of the total length of the rotary kiln, and the length of the discharging section is 1 / 5 to 1 / 6 of the total length of the rotary kiln; The pelletizing section is a special-shaped structure with an inclined retaining ring, and the pre-reduction desulfurization section, deep reduction section, and discharge section are all through-cavity structures; The air nozzle of the rotary kiln is connected to the kiln head blower, and the smoke outlet is connected to the surface cooler through a smoke pipe.

4. The rotary kiln system for treating metallurgical dust and ferrous sulfate slag according to claim 1, characterized in that: The surface cooler is connected to the zinc sulfate preparation module through an induced draft fan.

5. The rotary kiln system for treating metallurgical dust and ferrous sulfate slag according to claim 1, characterized in that: The zinc sulfate preparation module includes a zinc sulfate preparation tank, a purification and impurity removal system, and an evaporation and crystallization system arranged in sequence; The zinc sulfate preparation pool is provided with a smoke inlet and a smoke outlet, and a hollow drum inlet pump is provided in the zinc sulfate preparation pool.

6. A method for treating metallurgical dust and ferric sulfate slag in a rotary kiln, characterized by: The rotary kiln system for treating metallurgical dust and ferrous sulfate slag according to any one of claims 1 to 5 is used to perform the following steps: S1, the metallurgical dust and sulfuric acid slag from the steel plant are added to the pelletizing section from the kiln tail of the rotary kiln for pelletizing and forming into pellets. When the material height of the pellets exceeds the height of the inclined retaining ring, the pellets enter the pre-reduction and desulfurization section. After pre-reduction and desulfurization, they enter the deep reduction section for deep reduction. The sulfur and zinc in the pellets enter the rotary kiln flue gas and are discharged from the kiln tail. The metallized pellets after deep reduction are discharged from the discharge section; S2, the rotary kiln flue gas is cooled by the surface cooler to obtain low-temperature flue gas; S3, the low-temperature flue gas enters the zinc sulfate preparation pool of the zinc sulfate preparation module, and the SO2 in the low-temperature flue gas dissolves into the industrial water in the zinc sulfate preparation pool to form sulfurous acid. At the same time, air is blown into the zinc sulfate preparation pool, and the oxygen in the air oxidizes the sulfurous acid into sulfuric acid. The zinc oxide in the low-temperature flue gas reacts with the sulfuric acid to form zinc sulfate; S4, when the zinc ion concentration of the solution in the zinc sulfate preparation tank is ≥30g / L, purification, impurity removal and evaporation crystallization are carried out to obtain zinc sulfate product.

7. The method for treating metallurgical dust and ferric sulfate slag with a rotary kiln according to claim 6, characterized in that: In step S1: The metallurgical dust and sludge of the steel plant is secondary ash from blast furnaces; the total iron grade of the secondary ash from blast furnaces is 25-30%, the zinc content is 2-5%, the chlorine content is 2-5%, and the carbon content is 25-30%; and the particle size of the secondary ash from blast furnaces is more than 90% below 5 μm; The sulfuric acid slag has a total iron content of 45-53%, a sulfur content of 1.5-3%, and a water content of 20-25%; the particle size of the sulfuric acid slag is 0.1-1 mm; The dry mass ratio of the steel plant metallurgical dust and the sulfuric acid slag is 100:40-50 and is added to the pelletizing section.

8. The method for treating metallurgical dust and ferric sulfate slag with a rotary kiln according to claim 6, characterized in that: In step S1: The time for the rotary kiln to rotate one circle is 3 to 5 minutes, and the installation slope of the rotary kiln is 3.5% to 4%; The total residence time of the material in the rotary kiln is 3.5 to 4.5 hours; the residence time of the material in the pelletizing section is 0.6 to 0.9 hours, and the temperature is 200 to 300°C; the residence time of the material in the pre-reduction desulfurization section is 0.85 to 1.35 hours, and the temperature is 400 to 1000°C; the residence time of the material in the deep reduction section is 1.15 to 1.8 hours, and the temperature is 1200 to 1220°C; the residence time of the material in the discharging section is 0.6 to 0.9 hours, and the temperature is 900 to 1000°C; The excess air coefficient in the rotary kiln is 2.5-3.

9. The method for treating metallurgical dust and ferric sulfate slag with a rotary kiln according to claim 6, characterized in that: In step S1: The particle size of the pellets is 6 to 12 mm, and the water content of the pellets entering the pre-reduction desulfurization section from the pelletizing section is ≤1%; The metallized pellets have an iron grade of ≥55%, an iron content of ≥40%, a zinc content of ≤0.5%, a sulfur content of ≤0.5%, and a carbon content of ≤0.5%; The temperature of the rotary kiln flue gas is 400-500°C.

10. The method for treating metallurgical dust and ferric sulfate slag with a rotary kiln according to claim 6, characterized in that: In step S2, the temperature of the low-temperature flue gas is 150-200°C.

11. The method for treating metallurgical dust and ferric sulfate slag with a rotary kiln according to claim 6, characterized in that: In step S3: In the zinc sulfate preparation tank, the amount of industrial water added is controlled, and low-temperature flue gas is used to ensure that the temperature in the zinc sulfate preparation tank is between 60 and 65°C; The pH in the zinc sulfate preparation pool was maintained at 5.0 to 5.2 by adding sulfuric acid to the pool.

12. The method for treating metallurgical dust and ferric sulfate slag with a rotary kiln according to claim 6, characterized in that: In step S4, the purity of the zinc sulfate product is ≥99%.

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