A method for efficiently treating iron-zinc-containing dust sludge and recovering molten iron and zinc

Abstract

The present application relates to the technical field of iron and zinc-containing dust and sludge recovery in steel plants, and particularly relates to a method for efficiently treating iron and zinc-containing dust and sludge and recovering molten iron and zinc. The present application provides a method for efficiently treating iron and zinc-containing dust and sludge and recovering molten iron and zinc, which realizes process simplification and efficiency improvement through granulation-free direct feeding, steel solid waste composite additive modification, speed-adjusting dynamic smelting and three-stage condensation recovery. Compared with the traditional rotary hearth furnace / rotary kiln process, the process method provided by the present application exhibits lower energy consumption, higher zinc recovery rate and better economic efficiency in the treatment of iron and zinc-containing dust and sludge, especially low-zinc dust and sludge, thereby providing a short-process, low-cost and high-yield industrialized solution for the resource utilization of steel solid waste. Meanwhile, the present application promotes the green and cyclic development of the metallurgical industry through the mode of "waste treatment with waste" to synergistically consume and utilize steel solid waste.

Description

Technical Field

[0001] This invention relates to the field of iron-zinc dust and sludge recovery technology in steel plants, specifically to a method for efficiently treating iron-zinc dust and sludge and recovering molten iron and zinc. Background Technology

[0002] For solid waste containing iron-containing dust or sludge, current treatment processes mainly include smelting furnace, rotary hearth furnace, and rotary kiln processes. However, smelting furnace and rotary hearth furnace processes require pre-forming into pellets or briquettes to avoid agglomeration during smelting. These pellets or briquettes are then added to the smelting furnace or rotary hearth furnace for smelting. For the rotary hearth furnace process, the metallized pellets obtained from the rotary hearth furnace smelting need to be smelted into molten iron in a blast furnace, resulting in higher production costs. Furthermore, the rotary hearth furnace process is mostly suitable for treating dust with high iron content and fine particle size, while the rotary kiln process is suitable for dust and sludge with low iron content and high zinc content. Although the smelting furnace process has no particular restrictions on the iron and zinc content of solid waste dust and sludge, it requires pelletizing the dust and sludge before feeding it into the smelting furnace for smelting, leading to increased production costs.

[0003] Therefore, the recovery rates of iron and zinc in current treatment processes still have significant room for improvement. Furthermore, the granulation stage in traditional processes suffers from drawbacks such as complex procedures, high equipment investment, and energy consumption accounting for up to 15% of total energy consumption. Ultimately, the zinc concentration in the exhaust gas remains high, failing to meet direct emission standards and requiring further treatment. Therefore, there is an urgent need to develop a treatment process applicable to all iron- and zinc-containing dust and sludge from steel plants, achieving higher zinc and iron recovery rates and a simpler process. Summary of the Invention

[0004] In view of this, the present invention provides a method for efficiently treating iron-zinc dust and recovering molten iron and zinc. This method is applicable to all iron-zinc dust in steel plants, and the recovery rate of zinc and iron is higher. It is also economical, environmentally friendly, and has a simple process.

[0005] The first aspect of this invention provides a method for efficiently treating iron-zinc-containing dust and recovering molten iron and zinc, comprising:

[0006] Iron-zinc dust, quicklime and composite additives are mixed to obtain mixed dust, which is then pre-dried in a gradient at 100℃~280℃ to obtain pretreated mixture.

[0007] Add the pretreated mixture into the pure oxygen-fuel-fired conversion furnace, and then evenly cover it with coke;

[0008] The temperature inside the ferroconversion furnace is gradually increased to 1200℃~1300℃ for preheating, and the furnace is rotated alternately in both directions at 3~4 rpm for 35~45 minutes. During this process, a slight positive pressure of 15~20 Pa is maintained inside the furnace. Then, the temperature is further increased to 1550℃~1700℃ and the furnace is rotated at 10~12 rpm for 55~65 minutes for smelting. During this process, a slight positive pressure of 20~25 Pa is maintained inside the furnace. Molten iron, slag and zinc-containing tail gas are obtained.

[0009] The molten iron obtained is transferred to a ladle for later use through the tapping port, and the slag obtained is transferred out and collected after water quenching. The zinc-containing tail gas is discharged after passing through three stages of condensation, bag filter dust removal, and purification to meet the standards. In the three-stage condensation process, particulate metallic zinc is obtained, and in the bag filter dust removal process, secondary zinc oxide dust is collected.

[0010] The present invention provides a method for efficiently treating iron-zinc dust and recovering molten iron and zinc. The method involves simply mixing the iron-zinc dust with flux and composite additives, pre-drying it, and then feeding it into a pure oxygen-fuel-fired ferroconversion furnace for smelting. No additional granulation, briquetting, or pelletizing steps are required. A layer of coke is then uniformly covered on the surface of the pre-treated mixture, gradually raising the furnace temperature to 1200℃~1300℃ for preheating. Simultaneously, the furnace rotates alternately in both directions to enhance material tumbling and mass transfer, ensuring permeability and uniform heating of the smelting material during the smelting process. This ensures efficient reaction of zinc oxide even in powdered smelting materials. The furnace is maintained at a slightly positive pressure of 15~20 Pa to guarantee efficient recovery of zinc vapor. The furnace temperature and rotation speed are then further increased to melt all unmelted raw materials and those adhering to the furnace wall during preheating, recovering molten iron. The furnace is maintained at a slightly positive pressure of 20~25 Pa to collect as much remaining zinc vapor as possible. Secondly, by using composite additives with specific compositions and dosages while controlling the amount of quicklime, the mass ratios of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide in the pretreated mixture are kept within a specific range. This allows the process to be applied to all iron- and zinc-containing sludge removal processes in steel plants. Combined with dynamic layered feeding technology, the problem of clumping in the furnace of powdered materials that have not been pre-formed is completely solved, improving the extraction efficiency of zinc and iron during smelting. Furthermore, this invention employs speed- and pressure-controlled rotary smelting during melting and a three-stage condensation process after melting. The combination of melting and condensation significantly improves the overall zinc recovery rate. After three-stage condensation treatment, the zinc concentration in the exhaust gas, after baghouse dust collection and purification, meets national standards and can be directly discharged.

[0011] In conjunction with the first aspect, the composite additive includes converter dust and blast furnace bag filter dust; the coke and quicklime can be in powder, granular, or block form.

[0012] In conjunction with the first aspect, the heating rate of the gradual heating is 10~20℃ / min.

[0013] In conjunction with the first aspect, in the mixed dust and sludge, the moisture content of the iron-zinc dust and sludge is not higher than 8%, the mass percentage of the quicklime is 8% to 10%, the mass percentage of the converter dust is 4% to 6%, and the mass percentage of the blast furnace bag filter dust is 15% to 20%.

[0014] In conjunction with the first aspect, the mass percentages of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide in the pretreated mixture meet the following criteria: total iron 35%~55%, zinc 0.5%~6%, silicon dioxide 5%~6%, calcium oxide 12%~18%, magnesium oxide 3.2%~3.6%, and aluminum oxide 2.3%~3.0%.

[0015] In conjunction with the first aspect, the gradient pre-drying specifically involves: adding the mixed dust and sludge to a multi-layer fluidized bed dryer and drying at 90℃~105℃ for 10~15 min, then raising the temperature to 190℃~210℃ for 15~20 min, and continuing to raise the temperature to 270℃~290℃ for 10~15 min; the resulting pretreated mixture has a moisture content of no more than 2%.

[0016] In conjunction with the first aspect, the furnace wall of the pure oxygen-gas-fired conversion iron furnace is equipped with a cast steel cooling wall. The inner side of the furnace wall is provided with an insulation layer and a working layer that are attached to each other from the outside to the inside. The insulation layer is obtained by casting lightweight alumina, and the working layer is formed by sintering and solidifying corundum-silicon carbide ramming material.

[0017] In conjunction with the first aspect, the oxygen flow rate during preheating is 140~160 m³ / h, and the gas flow rate is 70~80 m³ / h; the oxygen flow rate during smelting is 260~280 m³ / h, and the gas flow rate is 130~140 m³ / h.

[0018] In conjunction with the first aspect, the three-stage condensation steps are as follows: cooling the zinc-containing exhaust gas to 500℃~510℃ by water cooling, cooling the zinc-containing exhaust gas to 180℃~190℃ by air cooling, and cooling the zinc-containing exhaust gas to 80℃~90℃ by liquid nitrogen spraying.

[0019] In conjunction with the first aspect, the purification involves passing the zinc-containing exhaust gas through a wet scrubbing tower.

[0020] In conjunction with the first aspect, the molten iron, after deoxidation, is used to cast ductile iron parts, and the slag, after water quenching and granulation, is used as a concrete admixture.

[0021] The beneficial effects of this invention are as follows: The method provided by this invention eliminates the need for pre-granulation and molding processes, significantly shortening the process flow and reducing production energy consumption; by using composite additives with specific compositions and dosages while controlling the amount of quicklime, the mass ratios of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide in the pre-treated mixture are kept within a specific range, making the process applicable to all iron- and zinc-containing sludge removal processes in steel plants; simultaneously, combined with dynamic layered feeding technology, it completely solves the problems of easy agglomeration and poor permeability of powdered materials that have not been pre-agglomerated in the furnace, enabling uniform mass transfer even when the smelting raw materials are all in powder form, ensuring the extraction efficiency of zinc and iron during smelting, with a molten iron recovery rate of over 98.5% and a molten iron purity of approximately 95%; furthermore, by combining speed and pressure adjustment during rotary smelting with a three-stage condensation system, the comprehensive zinc recovery rate reaches over 99%, increasing profits by 15%, and the zinc concentration in the exhaust gas meets national emission standards. The method provided by this invention has the dual advantages of being economical and environmentally friendly. It eliminates the equipment and energy consumption required for the granulation process, reduces the cost per ton of processing by 28%, increases zinc recovery revenue by 15%, and achieves a solid waste comprehensive utilization rate of nearly 100%. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A schematic flowchart illustrating the efficient method for treating iron-zinc-containing dust and sludge and recovering molten iron and zinc provided by the present invention.

[0024] Figure 2 This is a schematic diagram of the process flow of the melting furnace in the prior art. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0026] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the meaning consistent with their meaning in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless specifically defined.

[0027] Unless otherwise specified, the raw materials, reagents and equipment used in this invention are all commercially available products.

[0028] Currently, typical treatment processes for iron-zinc-containing solid waste generated from steel smelting include the rotary hearth furnace method and the rotary kiln method. The rotary hearth furnace method primarily treats high-iron, low-zinc dust and sludge. Its process mainly consists of two parts: raw material processing and direct reduction in the rotary hearth furnace. In the raw material processing step, iron-containing raw materials are mixed with a certain proportion of reducing agent (coal, coke powder, semi-coke, etc.). Depending on the raw material being treated, certain amounts of additives and binders are added, and the mixture is then briquetteed (pressed or pelletized). The carbon-containing pellets are dried and then rapidly reduced in the rotary hearth furnace, ultimately yielding directly reduced pellets with a certain metallization rate (high impurities, metallization rate approximately 70%). The rotary kiln method primarily treats low-iron, high-zinc, and high-carbon dust and sludge. Its process involves adding zinc-containing dust and sludge, along with other auxiliary materials, in a proportionate ratio or granulating them before adding them to the rotary kiln. The zinc element in the dust and sludge is reduced into the gas phase, where it is oxidized into zinc oxide dust, which is then collected in the flue and baghouse dust collector as secondary zinc oxide powder. Iron-containing kiln slag is cooled, graded, and then sintered in a blast furnace before being used.

[0029] However, generally speaking, the rotary hearth furnace method has an iron recovery rate of about 70% and a zinc recovery rate of about 90%. It also generates new solid waste—high-chloride zinc-potassium-sodium ash. Furthermore, this method incurs energy consumption when processing the solid waste sludge into metallized pellets, and secondary energy consumption occurs when reducing the metallized pellets in a blast furnace or converter. This results in low production efficiency and energy utilization, high impurities in the finished product, and poor economic benefits. The rotary kiln method has a zinc recovery rate of about 90%, but it also generates new solid waste—high-sulfur, high-zinc kiln slag. This method incurs energy consumption during zinc removal, again during the crushing and magnetic separation of the high-sulfur, high-zinc kiln slag into reduced iron and fine powder, a third energy consumption occurs when the reduced iron is fed into the blast furnace for smelting, and a fourth energy consumption occurs when the fine powder is sintered in the furnace and then smelted in the blast furnace. Overall, the process has low production efficiency and requires multiple energy consumption steps throughout the entire process.

[0030] To address the above problems, this invention provides a method for efficiently treating iron-zinc-containing dust and recovering molten iron and zinc, comprising:

[0031] Iron-zinc dust, quicklime and composite additives are mixed to obtain mixed dust, which is then pre-dried in a gradient at 100℃~280℃ to obtain pretreated mixture.

[0032] Add the pretreated mixture into the pure oxygen-fuel-fired conversion furnace, and then evenly cover it with coke;

[0033] The temperature inside the ferroconversion furnace is gradually increased to 1200℃~1300℃ for preheating, and the furnace is rotated alternately in both directions at 3~4 rpm for 35~45 minutes. During this process, a slight positive pressure of 15~20 Pa is maintained inside the furnace. Then, the temperature is further increased to 1550℃~1700℃ and the furnace is rotated at 10~12 rpm for 55~65 minutes for smelting. During this process, a slight positive pressure of 20~25 Pa is maintained inside the furnace. Molten iron, slag and zinc-containing tail gas are obtained.

[0034] The molten iron obtained is transferred to a ladle for later use through the tapping port, and the slag obtained is transferred out and collected after water quenching. The zinc-containing tail gas is discharged after passing through three stages of condensation, bag filter dust removal, and purification to meet the standards. In the three-stage condensation process, particulate metallic zinc is obtained, and in the bag filter dust removal process, secondary zinc oxide dust is collected.

[0035] The present invention provides a method for efficiently treating iron-zinc dust and recovering molten iron and zinc. The method involves simply mixing the iron-zinc dust with flux and composite additives, pre-drying it, and then feeding it into a pure oxygen-fuel-fired ferroconversion furnace for smelting. No additional granulation, briquetting, or pelletizing steps are required. A layer of coke is then uniformly covered on the surface of the pre-treated mixture, gradually raising the furnace temperature to 1200℃~1300℃ for preheating. Simultaneously, the furnace rotates alternately in both directions to enhance material tumbling and mass transfer, ensuring permeability and uniform heating of the smelting material during the smelting process. This ensures efficient reaction of zinc oxide even in powdered smelting materials. The furnace is maintained at a slightly positive pressure of 15~20 Pa to guarantee efficient recovery of zinc vapor. The furnace temperature and rotation speed are then further increased to melt all unmelted raw materials and those adhering to the furnace wall during preheating, recovering molten iron. The furnace is maintained at a slightly positive pressure of 20~25 Pa to collect as much remaining zinc vapor as possible. Secondly, by using composite additives with specific compositions and dosages while controlling the amount of quicklime, the mass ratios of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide in the pretreated mixture are kept within a specific range. This allows the process to be applied to all iron- and zinc-containing sludge removal processes in steel plants. Combined with dynamic layered feeding technology, the problem of clumping in the furnace of powdered materials that have not been pre-formed is completely solved, improving the extraction efficiency of zinc and iron during smelting. Furthermore, this invention employs speed- and pressure-controlled rotary smelting during melting and a three-stage condensation process after melting. The combination of melting and condensation significantly improves the overall zinc recovery rate. After three-stage condensation treatment, the zinc concentration in the exhaust gas, after baghouse dust collection and purification, meets national standards and can be directly discharged.

[0036] As a specific embodiment of the method of this invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the iron-zinc dust, quicklime, and composite additives are mixed and then stirred in a twin-shaft mixer until uniformly dispersed to obtain a mixed dust. After uniform stirring, the bulk density of the mixed dust decreases by 15%, and its fluidity increases by 20%.

[0037] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the composite additives used include converter dust and blast furnace bag filter dust; the coke and quicklime used can be in powder, granular or block form.

[0038] In traditional granulation and molding processes, lignin sulfonate is required as a binder and graphite as a lubricant. This invention uses converter dust and blast furnace baghouse dust as a composite additive. Converter dust is fine dust obtained after dry dust removal of flue gas generated during converter steelmaking; its carbon and iron oxide content synergistically replaces the binding and reducing functions of lignin sulfonate. Blast furnace baghouse dust is dust collected in blast furnaces, characterized by high carbon content and a certain amount of iron oxide. The carbon and coke in the blast furnace baghouse dust can replace the fluidity of graphite, improving the function of constructing a reducing environment.

[0039] As a specific embodiment of the method of this invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the iron-zinc dust in the mixed dust contains a moisture content of no more than 8%, quicklime with a mass ratio of 8% to 10%, converter dust with a mass ratio of 4% to 6%, and blast furnace bag filter dust with a mass ratio of 15% to 20%. The mass ratios of these raw materials ensure that the iron-zinc dust is lubricated and does not clump, and that the powders are in full contact, thus guaranteeing the full reduction of iron oxides and the volatilization of zinc during the smelting process.

[0040] As a specific embodiment of the method for efficiently treating iron-zinc dust and recovering molten iron and zinc according to the present invention, the mass percentages of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide in the pretreatment mixture meet the following indicators: total iron 35%~55%, zinc 0.5%~6%, silicon dioxide 5%~6%, calcium oxide 12%~18%, magnesium oxide 3.2%~3.6%, and aluminum oxide 2.3%~3.0%. The pretreatment mixture with the above composition has better compatibility with the method for efficiently treating iron-zinc dust and recovering molten iron and zinc provided by the present invention.

[0041] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the gradient pre-drying is specifically as follows: the mixed dust is added to a multi-layer fluidized bed dryer and dried at 90℃~105℃ for 10~15 min, then the temperature is raised to 190℃~210℃ for 15~20 min, and then the temperature is further raised to 270℃~290℃ for 10~15 min; the moisture content of the resulting pretreated mixture is not higher than 2%.

[0042] Fluidized bed dryers, also known as boiling bed dryers, are mechanical devices that use fluidization technology to dry wet materials. They can be classified into various types according to their structure, such as single-layer, multi-layer, pulse, or centrifugal fluidized bed dryers. This invention employs a multi-layer fluidized bed dryer. The dynamic drying of the fluidized bed can prevent material agglomeration during the drying process. Furthermore, the gradient drying method not only allows for more thorough drying of the mixed dust and sludge but also increases thermal efficiency by 30%. The resulting mixture is loosely granular (particle size ≤ 5mm), suitable for direct feeding.

[0043] As a specific embodiment of the method of the present invention for efficiently treating iron and zinc dust and recovering molten iron and zinc, the furnace wall of the pure oxygen gas-fired conversion furnace used in the present invention is equipped with a cast steel cooling wall. The inner side of the furnace wall is provided with an insulation layer and a working layer that are attached to each other from the outside to the inside. The insulation layer is obtained by casting lightweight alumina, and the working layer is formed by sintering and solidifying corundum-silicon carbide ramming material.

[0044] A cast steel cooling wall is installed on the furnace wall. This wall can be cooled by water, keeping the furnace shell temperature below 200℃ and extending the furnace's lifespan. The working layer is obtained by sintering and solidifying corundum-silicon carbide ramming mix at 1100℃~1200℃. The corundum matrix resists zinc slag penetration, while the silicon carbide enhances thermal shock resistance and improves the furnace's resistance to zinc slag erosion. The ramming mix contains 80%~85% corundum and 10%~15% silicon carbide, as well as a phosphate binder. The phosphate binder provides high-temperature stability, erosion resistance, and bonding strength; its dosage is 5%~15% of the sum of the corundum and silicon carbide dosages.

[0045] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the thickness of the cast steel cooling wall is 75~85mm, the thickness of the insulation layer is 45~55mm, and the thickness of the working layer is 110~120mm.

[0046] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the phosphate binders used are orthophosphate binders and polyphosphate binders. The orthophosphate binders include at least one of aluminum dihydrogen phosphate (with excellent bonding performance and thermal shock resistance), aluminum monohydrogen phosphate (forming ceramic bonding at high temperatures and enhancing material density), magnesium dihydrogen phosphate (improving slag resistance and thermal stability), and industrial phosphoric acid (directly used as an acid binder, simplifying the process and with low cost). The polyphosphate binders include at least one of sodium hexametaphosphate (improving slurry fluidity and hardening speed), sodium tripolyphosphate (enhancing bonding strength at medium and low temperatures and reducing cracking tendency), and sodium pyrophosphate (improving corrosion resistance).

[0047] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, a dynamic layered feeding method is adopted to add the pretreated mixture into the pure oxygen-gas-fired blast furnace. First, the furnace body is tilted at 35°~45°, and the pretreated mixture (lower layer) and coke (upper layer) are fed in sequence by a screw feeder. The total amount of material does not exceed 75% of the furnace capacity. Among them, the volume ratio of the pretreated mixture in the whole furnace is 67%~70%, and the volume ratio of coke in the whole furnace is 5%~8%.

[0048] The pure oxygen-fired gas-fired iron conversion furnace with dual-function furnace lining used in this invention extends the lining life to 300 heats or even longer, while the life of traditional quartz lining is only about 200 heats. Secondly, the dynamic layered feeding method is adopted, where the coke layer formed by the upper layer of coke covers the pre-treated mixture in the lower layer, forming a reducing atmosphere in the furnace and inhibiting zinc vapor oxidation.

[0049] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the oxygen flow rate is 140~160m³ / h and the gas flow rate is 70~80m³ / h during preheating; and the oxygen flow rate is 260~280m³ / h and the gas flow rate is 130~140m³ / h during smelting.

[0050] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the oxygen flow rate is 160 m³ / h and the gas flow rate is 80 m³ / h during preheating; and the oxygen flow rate is 280 m³ / h and the gas power is 140 m³ / h during smelting.

[0051] During preheating, the furnace body rotates alternately in both directions to enhance the tumbling of materials and mass transfer between them, avoid local agglomeration, ensure air permeability and zinc vapor volatilization. Zinc oxide in the pretreated mixture is reduced and volatilized into zinc vapor. At the same time, the furnace pressure is monitored in real time to maintain it at a slightly positive pressure of 15~20Pa, which is then discharged through the tail gas vent. Carbon in the converter dust and blast furnace bag filter dust is simultaneously oxidized into carbon monoxide, increasing the concentration to 18%. The zinc oxide reduction rate is accelerated by 25%, and the starting temperature of zinc volatilization is reduced by 80℃.

[0052] During smelting, the furnace body rotates in one direction with adjustable speed to promote uniform heating of loose materials, achieving an iron oxide reduction efficiency of ≥98%. Simultaneously, the furnace pressure is monitored in real time to maintain a slightly positive pressure of 20-25 Pa, ensuring that zinc vapor is extracted as completely as possible. The smelting time is controlled at 55-65 minutes to compensate for the reaction time of materials that have not undergone granulation, resulting in a molten iron yield of over 93%.

[0053] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the three-stage condensation steps are as follows: cooling the zinc-containing tail gas to 500℃~510℃ by water cooling, cooling the zinc-containing tail gas to 180℃~190℃ by air cooling, and cooling the zinc-containing tail gas to 80℃~90℃ by liquid nitrogen spraying.

[0054] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the zinc-containing tail gas is introduced into a three-stage condensation tower through a water-cooled pipe (lined with silicon carbide): the first stage is water-cooled to 500°C, the second stage is air-cooled to 180°C, and the third stage is liquid nitrogen sprayed to 80°C. After three stages of condensation, the metallic zinc vapor settles in particulate form, and the secondary zinc oxide dust formed after the uncondensed zinc vapor is condensed is collected by a pulse bag filter and returned to the batching process for recycling.

[0055] By combining water cooling, air cooling, and liquid nitrogen spraying, the condensation efficiency is significantly improved, effectively preventing the escape of fine dust, and the direct recovery rate of metallic zinc is nearly 96%. In this process, the cooling fluids (such as water and air) for water cooling and air cooling flow in their own independent pipes and do not come into direct contact with zinc vapor; in the third stage of liquid nitrogen spraying condensation, the nitrogen gas that is sprayed out and vaporized forms an inert protective atmosphere for the solidified particulate metallic zinc, which can prevent the particulate metallic zinc from oxidizing.

[0056] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, purification is carried out by passing the zinc-containing tail gas through a wet scrubbing tower.

[0057] The remaining tail gas after three-stage condensation enters a wet scrubbing tower for further neutralization of acidic gases such as SO2 and HCl. The scrubbing liquid in the wet scrubbing tower is an 8%~12% sodium hydroxide solution (pH=12~13). The purified tail gas is monitored online, and it meets emission standards when the Zn concentration is ≤2mg / m³ and the SO2 concentration is ≤20mg / m³.

[0058] As a specific embodiment of the method of the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc, the molten iron is used for casting ductile iron parts after deoxidation, and the slag is used as a concrete admixture after water quenching and granulation.

[0059] After smelting, the molten iron can be poured into a preheating ladle (800℃) through the taphole for later use. The furnace body is tilted to discharge the liquid slag, which, after water quenching and granulation, can be used as a concrete admixture (activity index ≥75%), increasing the added value by 40%.

[0060] The following specific embodiments illustrate the method provided by the present invention for efficiently treating iron-zinc dust and recovering molten iron and zinc.

[0061] In the following examples and comparative examples, the contents of total iron, silicon dioxide, calcium oxide, magnesium oxide, aluminum oxide, and zinc in the converter dust, blast furnace bag filter dust, and quicklime used in the raw materials were tested in advance. The results are shown in Table 1 below:

[0062] Table 1. Percentage of each component in each raw material

[0063]

[0064] Example 1

[0065] This embodiment provides a method for efficiently treating iron-zinc-containing dust and recovering molten iron and zinc, the steps of which include:

[0066] Weigh out 52 kg of converter dust, 160 kg of blast furnace bag filter dust, and 80 kg of quicklime, and mix them with 708 kg of iron-zinc dust sludge to be treated (the mass percentages of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide are as follows: total Fe 62.62%, Zn 1.22%, SiO2 5.89%, CaO 6.67%, MgO 3.59%, Al2O3 3.21%, which is high-iron, low-zinc dust sludge) to obtain mixed dust sludge. The mixed dust and sludge were stirred at 100 rpm for 60 minutes to ensure uniform mixing of all raw and auxiliary materials. The mixture was then fed into a multi-layer fluidized bed dryer and dried at 100℃ for 15 minutes. The temperature was then increased to 200℃ for another 15 minutes, followed by further heating to 280℃ for 10 minutes. This yielded a pretreated mixture with a moisture content of 1.2% (based on testing, the mass percentages of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide in the pretreated mixture were: total Fe 52.58%, Zn 1.55%, SiO2 5.34%, CaO 12.47%, MgO 3.33%, Al2O3 2.72%), which was in the form of loose granules with particle sizes ranging from 0.5 to 3 mm. The furnace body of the pure oxygen-gas-fired blast furnace is tilted at 40°, and the pre-treated mixture is fed into the pure oxygen-gas-fired blast furnace in layers using a screw feeder (the pre-treated mixture accounts for 67% of the total volume of the blast furnace), and coke powder is evenly covered on the top layer (coke powder accounts for 5% of the total volume of the blast furnace). Ignition begins with the gas flow rate controlled at 4 m³ / h. The gas flow rate is then gradually increased, raising the furnace temperature to 1250°C at a rate of 10-15°C / min. Simultaneously, the gas flow rate is gradually increased to 80 m³ / h, and the furnace is preheated by alternating forward and reverse rotation at 3 rpm for 40 minutes. During this process, the furnace pressure is maintained at a slightly positive pressure of 15-20 Pa (i.e., 15-20 Pa higher than the external pressure). After preheating, the gas flow rate is gradually increased to 140 m³ / h, raising the furnace temperature to 1600°C. The furnace is then smelted by rotating in one direction at 11 rpm for 60 minutes, while maintaining a slightly positive pressure of 20-25 Pa (i.e., 20-25 Pa higher than the external pressure). The ratio of gas flow rate to oxygen flow rate is 1:2.

[0067] After smelting, the zinc-containing tail gas undergoes further recovery and purification. It is sequentially cooled to 500℃ by primary water cooling, 180℃ by secondary air cooling, and 80℃ by tertiary liquid nitrogen spraying. After three stages of condensation, particulate metallic zinc can be collected, with a calculated yield of 95.5%. The yield (%) is calculated as: [dry basis weight of obtained particulate metallic zinc (kg) × purity of particulate metallic zinc (%)] / [dry basis weight of pretreated mixture (kg) × mass percentage of zinc in pretreated mixture (%)] × 100%. The tail gas continues to pass through a dust collector bag to capture the secondary zinc oxide dust formed after the condensation of uncondensed zinc vapor. The total zinc recovery rate is calculated as: 99.1%. The yield (%) of secondary zinc oxide dust (based on zinc) is calculated as: [dry basis weight of obtained secondary zinc oxide dust (kg) × mass percentage of zinc in secondary zinc oxide dust (%)] / [Dry weight of pretreated mixture (kg) × mass percentage of zinc in pretreated mixture (%)] × 100%, the total zinc recovery rate is the sum of the recovery rate of particulate metallic zinc and the recovery rate of secondary zinc oxide dust. The tail gas is then passed into a wet scrubbing tower, with a 10% sodium hydroxide solution as the scrubbing liquid, for further purification. The purified tail gas has a Zn concentration of 1.8 mg / m³, SO₂ of 18 mg / m³, and dust concentration ≤ 8 mg / m³, meeting the direct discharge standard and can be directly discharged. Molten iron in the furnace flows into the preheating ladle (800℃) through the taphole. The molten iron recovery rate is calculated to be 99.2% (molten iron purity 95.2%), where molten iron recovery rate (%) = [weight of molten iron obtained (kg) × molten iron purity (%)] / [Dry weight of pretreated mixture (kg) × mass percentage of iron in pretreated mixture (%)] × 100%. The furnace body is tilted 45° to discharge the slag, which is then water-quenched and granulated before being used as an admixture for C30 concrete.

[0068] Example 2

[0069] This embodiment provides a method for efficiently treating iron-zinc-containing dust and recovering molten iron and zinc, the steps of which include:

[0070] Weigh out 52 kg of converter dust, 160 kg of blast furnace bag filter dust, and 80 kg of quicklime, and mix them with 708 kg of iron-zinc dust sludge to be treated (the mass percentages of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide are as follows: total Fe 47.52%, Zn 5.32%, SiO2 5.88%, CaO 6.65%, MgO 3.55%, Al2O3 2.81%, which is low-iron, high-zinc dust sludge) to obtain mixed dust sludge. The mixed dust and sludge were stirred at 100 rpm for 60 minutes to ensure uniform mixing of all raw and auxiliary materials. The mixture was then fed into a multi-layer fluidized bed dryer and dried at 105℃ for 10 minutes, followed by drying at 210℃ for 20 minutes, and then further dried at 290℃ for 15 minutes. This yielded a pretreated mixture with a moisture content of 1.4% (based on testing, the mass percentages of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide in the pretreated mixture were: total Fe 41.89%, Zn 12.37%, SiO2 5.33%, CaO 12.47%, MgO 3.31%, Al2O3 2.44%), which was in the form of loose granules with particle sizes ranging from 0.5 to 3 mm. The furnace body of the pure oxygen-gas-fired blast furnace is tilted at 45°, and the pre-treated mixture is fed into the pure oxygen-gas-fired blast furnace in layers using a screw feeder (the pre-treated mixture accounts for 68% of the total volume of the blast furnace), and coke is evenly covered on the top layer (coke accounts for 6% of the total volume of the blast furnace). Ignition begins with the gas flow rate controlled at 4 m³ / h. The gas flow rate is then gradually increased, raising the furnace temperature to 1250°C at a rate of 10-15°C / min. Simultaneously, the gas flow rate is gradually increased to 80 m³ / h, and the furnace is preheated by alternating forward and reverse rotation at 3 rpm for 40 minutes. During this process, the furnace pressure is maintained at a slightly positive pressure of 15-20 Pa (i.e., 15-20 Pa higher than the external pressure). After preheating, the gas flow rate is gradually increased to 140 m³ / h, raising the furnace temperature to 1600°C. The furnace is then smelted by rotating in one direction at 11 rpm for 60 minutes, while maintaining a slightly positive pressure of 20-25 Pa (i.e., 20-25 Pa higher than the external pressure). The ratio of gas flow rate to oxygen flow rate is 1:2.

[0071] After smelting, the zinc-containing tail gas undergoes further recovery and purification. It is sequentially cooled to 505℃ by primary water cooling, 185℃ by secondary air cooling, and 88℃ by tertiary liquid nitrogen spraying. After three stages of condensation, particulate metallic zinc can be collected (96.1% yield). The tail gas continues to pass through a dust collector bag to capture the zinc oxide dust formed after the condensation of uncondensed zinc vapor (total zinc recovery rate 99.4%). The tail gas is then passed through a wet scrubbing tower with a 10% sodium hydroxide solution for further purification. The purified tail gas has a Zn concentration of 1.6 mg / m³, SO₂ concentration of 15.3 mg / m³, and dust concentration ≤8 mg / m³, meeting the direct discharge standard and can be directly discharged. The molten iron in the furnace flows into the preheating ladle (850℃) through the taphole, with a calculated molten iron recovery rate of 98.6% (molten iron purity 94.8%). The furnace body is tilted 45° to discharge the slag, which is then water-quenched and granulated before being used as an admixture for C30 concrete.

[0072] The calculation methods for the yield of particulate zinc, the yield of zinc oxide dust, the total zinc recovery rate, and the molten iron recovery rate are the same as in Example 1, and will not be repeated here.

[0073] Comparative Example 1

[0074] This comparative example provides a method for treating iron-zinc-containing dust and recovering molten iron and zinc, the steps of which include:

[0075] Weigh out 52 kg of converter dust, 160 kg of blast furnace bag filter dust, and 40 kg of quicklime, and mix them with 748 kg of iron-zinc dust sludge to be treated (the mass percentages of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide are as follows: total Fe 62.62%, Zn 1.22%, SiO2 5.89%, CaO 6.67%, MgO 3.59%, Al2O3 3.21%, which is high-iron, low-zinc dust sludge) to obtain mixed dust sludge. The mixed dust and sludge were stirred at 100 rpm for 60 minutes to ensure uniform mixing of all raw and auxiliary materials. The mixture was then fed into a multi-layer fluidized bed dryer and dried at 100℃ for 15 minutes. The temperature was then increased to 200℃ for another 15 minutes, followed by further heating to 280℃ for 10 minutes. This yielded a pretreated mixture with a moisture content of 1.3% (based on testing, the mass percentages of iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide in the pretreated mixture were: total Fe 55.09%, Zn 1.60%, SiO2 5.50%, CaO 9.31%, MgO 3.28%, Al2O3 2.85%). The mixture was in the form of loose granules with particle sizes ranging from 0.5 to 3 mm. The furnace body of the pure oxygen-gas-fired blast furnace is tilted at 40°, and the pre-treated mixture is fed into the pure oxygen-gas-fired blast furnace in layers using a screw feeder (the pre-treated mixture accounts for 67% of the total volume of the blast furnace), and coke is evenly covered on the top layer (coke accounts for 5% of the total volume of the blast furnace). Ignition begins with the gas flow rate controlled at 4 m³ / h. The gas flow rate is then gradually increased, raising the furnace temperature to 1250°C at a rate of 10-15°C / min. Simultaneously, the gas flow rate is gradually increased to 80 m³ / h, and the furnace is preheated by alternating forward and reverse rotation at 3 rpm for 40 minutes. During this process, the furnace pressure is maintained at a slightly positive pressure of 15-20 Pa (i.e., 15-20 Pa higher than the external pressure). After preheating, the gas flow rate is gradually increased to 140 m³ / h, raising the furnace temperature to 1600°C. The furnace is then smelted by rotating in one direction at 11 rpm for 60 minutes, while maintaining a slightly positive pressure of 20-25 Pa (i.e., 20-25 Pa higher than the external pressure). The ratio of gas flow rate to oxygen flow rate is 1:2.

[0076] After smelting, the zinc-containing tail gas undergoes further recovery and purification. It is sequentially cooled to 500℃ by primary water cooling, 180℃ by secondary air cooling, and 80℃ by tertiary liquid nitrogen spraying. After three stages of condensation, particulate metallic zinc can be collected (direct recovery rate 95.2%). The tail gas continues to pass through a dust collector bag to capture the secondary zinc oxide dust formed after the condensation of uncondensed zinc vapor (total zinc recovery rate 98.7%). The tail gas is then passed through a wet scrubbing tower with a 10% sodium hydroxide solution for further purification. The purified tail gas has a Zn concentration of 1.7 mg / m³, SO₂ concentration of 16.2 mg / m³, and dust concentration ≤8 mg / m³, meeting the direct discharge standard and can be directly discharged. The molten iron in the furnace flows into the preheating ladle (800℃) through the taphole, with a calculated molten iron recovery rate of 94.3% (molten iron purity 94.1%). The furnace body is tilted 45° to discharge the slag, which is then water-quenched and granulated before being used as an admixture for C30 concrete.

[0077] The calculation methods for the yield of particulate zinc, the yield of zinc oxide dust, the total zinc recovery rate, and the molten iron recovery rate are the same as in Example 1, and will not be repeated here.

[0078] The difference between this comparative example and Example 1 is that the amount of each raw material in the mixed dust and sludge is different, and the mass ratio of calcium oxide in the pretreated mixture obtained in Comparative Example 1 is 9.31%, which exceeds the limited range of 12% to 18%.

[0079] Comparing Example 1 and Comparative Example 1, it can be seen that when the amount of quicklime added is small and the calcium oxide content in the pretreated mixture is less than 12%, the yield of molten iron is significantly reduced, the slag and molten iron are difficult to separate, resulting in a decrease in the yield of molten iron and an increase in the iron content in the slag.

[0080] The method provided by this invention is applicable to all iron- and zinc-containing dust and sludge generated by steel plants, eliminating the need for pre-granulation, briquetting, or pelletizing processes, significantly shortening the process flow and reducing energy consumption. By employing a specific composite additive combined with dynamic layered feeding technology, the extraction efficiency of zinc and iron during smelting is improved, achieving a molten iron recovery rate of over 98.5% and a purity of approximately 95%. Furthermore, through the combination of speed- and pressure-regulated rotary smelting and a three-stage condensation system, the total zinc recovery rate reaches over 99%, increasing revenue by 15%, and the zinc concentration in the exhaust gas meets national emission standards. The method provided by this invention has dual advantages of economy and environmental protection, eliminating the equipment and energy consumption required for granulation processes, reducing the cost per ton of processing by 28%, increasing zinc recovery revenue by 15%, and achieving a solid waste comprehensive utilization rate of nearly 100%.

[0081] In summary, the method provided by this invention for treating iron-zinc containing sludge sludge simplifies the process and improves efficiency through direct feeding without granulation, modification with composite additives for steel solid waste, speed-controlled dynamic smelting, and three-stage condensation recovery. Compared with traditional rotary hearth furnace / rotary kiln processes, the process method provided by this invention exhibits lower energy consumption, higher zinc recovery rate, and better economic performance in the treatment of iron-zinc containing sludge sludge, especially low-zinc sludge. It provides a short-process, low-cost, and high-yield industrial solution for the resource utilization of steel solid waste, and promotes the green and circular development of the metallurgical industry through the "waste-to-waste" model for the coordinated disposal of steel solid waste.

[0082] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for efficiently treating iron-zinc containing dust and sludge and recovering molten iron and zinc, characterized in that, include: Iron-zinc dust, quicklime and composite additives are mixed to obtain mixed dust, which is then pre-dried in a gradient at 100℃~280℃ to obtain pretreated mixture. Add the pretreated mixture into the pure oxygen-fuel-fired conversion furnace, and then evenly cover it with coke; The temperature inside the ferroconversion furnace is gradually increased to 1200℃~1300℃ for preheating, and the furnace is rotated alternately in both directions at 3~4 rpm for 35~45 minutes. During this process, a slight positive pressure of 15~20 Pa is maintained inside the furnace. Then, the temperature is further increased to 1550℃~1700℃ and the furnace is rotated at 10~12 rpm for 55~65 minutes for smelting. During this process, a slight positive pressure of 20~25 Pa is maintained inside the furnace. Molten iron, slag and zinc-containing tail gas are obtained. The molten iron obtained is transferred to a ladle for use after tapping, and the slag obtained is transferred out and collected after water quenching. The zinc-containing tail gas is discharged after passing through three stages of condensation, bag filter dust removal and purification to meet the standards. Particulate metallic zinc is obtained in the three-stage condensation process, and secondary zinc oxide dust is collected in the bag filter dust removal process. The oxygen flow rate during preheating is 140~160 m³ / h, and the gas flow rate is 70~80 m³ / h; the oxygen flow rate during smelting is 260~280 m³ / h, and the gas flow rate is 130~140 m³ / h. The pretreated mixture contains iron, zinc, silicon dioxide, calcium oxide, magnesium oxide, and aluminum oxide in the following proportions by mass: total iron 35%~55%, zinc 0.5%~6%, silicon dioxide 5%~6%, calcium oxide 12%~18%, magnesium oxide 3.2%~3.6%, and aluminum oxide 2.3%~3.0%.

2. The method for efficiently treating iron-zinc containing dust and sludge and recovering molten iron and zinc as described in claim 1, characterized in that, The composite additives include converter dust and blast furnace bag filter dust.

3. The method for efficiently treating iron-zinc containing dust and sludge and recovering molten iron and zinc as described in claim 2, characterized in that, In the mixed dust and sludge, the moisture content of the iron-zinc dust and sludge is not higher than 8%, the mass percentage of the quicklime is 8% to 10%, the mass percentage of the converter dust is 4% to 6%, and the mass percentage of the blast furnace bag filter dust is 15% to 20%.

4. The method for efficiently treating iron-zinc containing dust and sludge and recovering molten iron and zinc as described in claim 1, characterized in that, The gradient pre-drying specifically refers to: The mixed dust and sludge are added to a multi-layer fluidized bed dryer and dried at 90℃~105℃ for 10~15 min, then the temperature is raised to 190℃~210℃ for 15~20 min, and then the temperature is raised to 270℃~290℃ for 10~15 min; the moisture content of the resulting pretreated mixture is not higher than 2%.

5. The method for efficiently treating iron-zinc containing dust and sludge and recovering molten iron and zinc as described in claim 1, characterized in that, The furnace wall of the pure oxygen gas-fired ferroconversion furnace is equipped with a cast steel cooling wall. The inner side of the furnace wall is provided with an insulation layer and a working layer that are attached to each other from the outside to the inside. The insulation layer is made of lightweight alumina casting, and the working layer is made of corundum-silicon carbide ramming material sintered and solidified.

6. The method for efficiently treating iron-zinc containing dust and sludge and recovering molten iron and zinc as described in claim 1, characterized in that, The three-stage condensation process is as follows: cooling the zinc-containing exhaust gas to 500℃~510℃ by water cooling, cooling the zinc-containing exhaust gas to 180℃~190℃ by air cooling, and cooling the zinc-containing exhaust gas to 80℃~90℃ by liquid nitrogen spraying.

7. The method for efficiently treating iron-zinc containing dust and sludge and recovering molten iron and zinc as described in claim 1, characterized in that, The purification process involves passing the zinc-containing exhaust gas through a wet scrubbing tower.

8. The method for efficiently treating iron-zinc containing dust and sludge and recovering molten iron and zinc as described in claim 1, characterized in that, The molten iron is used for casting ductile iron parts after deoxidation, and the slag is used as a concrete admixture after water quenching and granulation.

Images