Methods and systems for zinc removal and extraction from galvanized steel sheets

Abstract

This disclosure provides a method and system for removing zinc from galvanized steel sheets, belonging to the field of resource recycling technology. The method includes: pickling and immersing the galvanized steel sheet in an inorganic acid to obtain a zinc salt solution and hydrogen gas; subjecting the zinc salt solution to multi-effect evaporation to obtain a concentrated solution and a condensate of the inorganic acid, the condensate of which is reused in the pickling process; calcining the concentrated solution to obtain solid oxides and tail gas containing hydrogen chloride or sulfur trioxide, the tail gas being reused in the pickling process; magnetically separating the solid oxides to obtain magnetic and non-magnetic oxides; and using the hydrogen gas generated from the pickling process to reduce the non-magnetic oxides, which are then collected by condensation to obtain zinc metal with a purity greater than 99%. This disclosure achieves closed-loop utilization of hydrochloric acid or sulfuric acid and water resources, with high zinc recovery rate, low energy consumption, and both economic and environmental benefits.

Description

Technical Field

[0001] This disclosure relates to the field of resource recycling technology, and in particular to a method and system for removing zinc from galvanized steel sheets. Background Technology

[0002] Zinc is a key resource for strategic industries such as galvanized steel sheet manufacturing, new energy, and electronic products, and is crucial to the development of these industries. Currently, there is a significant imbalance between zinc supply and demand. On the one hand, the annual amount of discarded galvanized steel sheets exceeds ten million tons, necessitating efficient recycling of a large amount of zinc resources; on the other hand, the industry's reliance on zinc imports is high, posing a challenge to resource security.

[0003] With increasingly stringent environmental protection requirements, green electricity has become a core support for achieving low-carbon transformation in zinc recycling. However, current mainstream zinc recycling processes generally suffer from technical pain points such as low recycling efficiency, high energy consumption, significant pollution problems, and poor compatibility with green electricity. For example, mechanical methods rely on physical stripping, with zinc recovery rates typically below 85%, and the process easily damages the substrate. Furthermore, this process is primarily mechanically powered, resulting in low demand for green electricity. While pyrometallurgical recycling can achieve large-scale processing, it requires prolonged operation at high temperatures of 800-1200℃, leading to high energy consumption and significant zinc loss. Even when powered by green electricity, the high energy consumption characteristic results in low green electricity conversion efficiency. Although electrochemical methods are beneficial for reducing energy consumption and improving electricity utilization efficiency, the process is accompanied by significant heavy metal pollution and serious waste of hydrochloric acid and water resources. In addition, current processes also have obvious application scenarios and resource utilization problems: most processes are designed for powdered or zinc slag, which is difficult to adapt to the recycling needs of blocky waste galvanized steel sheets, requiring additional investment in crushing equipment to increase costs; at the same time, the process methods focus on the single recovery of zinc, without effectively separating and utilizing resources such as iron and aluminum that may exist, resulting in a low comprehensive resource utilization rate. Summary of the Invention

[0004] In view of this, in order to at least partially solve at least one of the aforementioned technical problems, this disclosure provides a method and system for removing zinc from galvanized steel sheets.

[0005] According to one embodiment of this disclosure, a method for removing zinc from galvanized steel sheets is provided, comprising:

[0006] The galvanized steel sheet is pickled and soaked in an inorganic acid, including hydrochloric acid or sulfuric acid, to obtain a zinc salt solution and hydrogen gas.

[0007] The zinc salt solution is subjected to multi-effect evaporation to obtain a concentrated solution and an inorganic acid condensate. The inorganic acid condensate is reused for pickling and soaking.

[0008] The concentrate is roasted to obtain solid oxides and tail gas containing hydrogen chloride or sulfur trioxide. The tail gas containing hydrogen chloride or sulfur trioxide is reused for acid washing and soaking.

[0009] Solid oxides are separated by magnetic separation to obtain magnetic oxides and non-magnetic oxides;

[0010] The hydrogen generated by acid washing and soaking is used to reduce non-magnetic oxides with hydrogen, and the zinc metal with a purity greater than 99% is obtained by condensation and collection.

[0011] According to another aspect of this disclosure, a system for the above-described method of zinc removal and extraction from galvanized steel sheets is provided, wherein the system includes:

[0012] Pickling equipment is suitable for pickling and immersing galvanized steel sheets with inorganic acids, including hydrochloric acid or sulfuric acid, to obtain a zinc salt solution and hydrogen gas;

[0013] The multi-effect evaporation device is suitable for evaporating zinc salt solutions from pickling equipment to obtain concentrated solutions and inorganic acid condensates. The inorganic acid condensates are reused for pickling soaking.

[0014] Fluidized bed is suitable for roasting concentrated liquid from multi-effect evaporation unit to obtain solid oxides and tail gas containing hydrogen chloride or sulfur trioxide. The tail gas containing hydrogen chloride or sulfur trioxide is reused for acid washing and soaking.

[0015] A magnetic separation device is suitable for separating solid oxides by magnetic separation to obtain magnetic oxides and non-magnetic oxides;

[0016] The reduction device is suitable for using hydrogen generated by acid washing and soaking to reduce non-magnetic oxides from magnetic separation devices, and then collecting the condensed hydrogen to obtain zinc metal with a purity greater than 99%.

[0017] Based on the above technical solution, the zinc removal and zinc extraction method for galvanized steel sheets disclosed herein has at least one or a portion of the following beneficial effects:

[0018] (1) This disclosure obtains chlorides or sulfates obtained by acid leaching of iron, zinc and aluminum by evaporation and roasting to obtain solid oxides. The solid oxides are then separated by magnetic separation to obtain relatively pure magnetic oxides. Combined with the hydrogen reduction of non-magnetic oxides, high-purity zinc metal and aluminum oxide are obtained, thereby achieving high-purity (greater than 99%) zinc metal extraction.

[0019] (2) The entire process of this disclosed method is characterized by resource recycling and atom economy: only hydrochloric acid or sulfuric acid and galvanized steel plate are consumed as initial input materials. The zinc salt solution generated by pickling can be reused in the pickling process. The hydrochloric acid or sulfur trioxide generated in the multi-effect evaporation and roasting process can be recycled to pickling immersion. The hydrogen required in the reduction stage is generated in situ by the pickling reaction and utilized, realizing the closed-loop utilization of "chlorine-hydrogen-water" or "sulfur-hydrogen-water" elements. The pickling solution, hydrogen, hydrochloric acid or sulfuric acid are all recycled and reused, and there is no wastewater discharge. This solves the problem of pollution emissions from traditional acid process heavy metal wastewater and pyrometallurgical flue gas.

[0020] (3) The process energy consumption of the method disclosed herein is low: Compared with the pyrometallurgical zinc extraction (energy consumption > 500 kWh / ton), the method disclosed herein can make full use of waste heat through multi-effect evaporation, combined with the recycling of hydrogen and hydrochloric acid or sulfuric acid, which significantly reduces the overall energy consumption. At the same time, it saves the cost of hazardous chemical transportation and wastewater treatment, thereby optimizing the cost of processing ton steel plates. It has both resource security value and potential for large-scale industrial application. Attached Figure Description

[0021] The above and other objects, features, and advantages of this disclosure will become clearer from the following description of embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0022] Figure 1 This is a schematic diagram illustrating the zinc removal and extraction method for galvanized steel sheets disclosed in this disclosure;

[0023] Figure 2 This is a process flow diagram of the zinc removal and zinc extraction method for galvanized steel sheets disclosed herein;

[0024] Figure 3 This is a schematic diagram of the system apparatus for the zinc removal and extraction method of galvanized steel sheet disclosed herein. Detailed Implementation

[0025] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0026] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The term "comprising" as used herein indicates the presence of features, steps, or operations, but does not exclude the presence or addition of one or more other features.

[0027] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0028] In realizing the concept disclosed herein, several problems were discovered with existing technologies for recycling galvanized steel sheets: mechanical stripping methods, limited by physical forces, not only fail to completely remove the galvanized layer but also suffer from low efficiency; traditional pickling processes lack precise parameter control, easily leading to volatilization waste and equipment corrosion due to excessively high acid concentrations, or affecting metal ion leaching due to excessively low concentrations, resulting in redundant energy consumption, incomplete zinc-iron separation, and substandard purity of the final product. Furthermore, inorganic acids such as hydrochloric acid, sulfuric acid, and hydrogen rely on external transportation and storage, increasing production costs and environmental and safety risks such as leakage and volatilization. Moreover, the entire process system is not well-suited for green energy use, making it difficult to meet the demands of low-carbon production.

[0029] Based on this, this disclosure proposes a method and equipment for zinc removal and extraction from galvanized steel sheets to solve the problems of low recovery rate, high pollution, and difficulty in resource recycling in traditional processes. First, the galvanized steel sheet is soaked and cleaned with hydrochloric acid or sulfuric acid. By precisely controlling the acid concentration, liquid-to-solid ratio, and temperature, zinc and iron ions are fully dissolved to form a zinc salt solution. Then, the solution is concentrated to a preset concentration using a triple-effect evaporator, utilizing waste heat in a cascade manner to reduce energy consumption and avoid ineffective water evaporation in subsequent roasting stages. The concentrated solution is then roasted in a fluidized bed to convert it into a homogeneous solid oxide. Next, a magnetic separation process with a specific magnetic field strength is used to completely separate the magnetic oxide from the non-magnetic oxide. The non-magnetic oxide is reduced with hydrogen to obtain not only high-purity zinc metal but also alumina byproducts with a purity of 95.9%~99.0%, improving the comprehensive utilization rate of resources. Meanwhile, this disclosure allows the condensate generated from multi-effect evaporation and the tail gas containing hydrogen chloride or sulfur trioxide from the roasting process to be treated and recycled into hydrochloric acid or sulfuric acid for pickling. The generated hydrogen gas is purified and recycled to the reduction process. The entire process achieves a water recycling rate of 99.0%, realizing zero external discharge and recycling of inorganic acids and water resources. Furthermore, the equipment adopts a modular design, allowing for flexible integration with green energy systems and adapting to low-carbon production needs. This not only meets the scale requirements of continuous industrial production but also fundamentally solves the core problems of poor synergy, resource waste, and high environmental risks associated with traditional technologies.

[0030] Figure 1 This is a schematic diagram illustrating the zinc removal and extraction method for galvanized steel sheets disclosed in this invention.

[0031] Figure 2This is a process flow diagram of the zinc removal and zinc extraction method for galvanized steel sheets disclosed herein.

[0032] Specifically, according to an embodiment of one aspect of this disclosure, such as Figure 1 and Figure 2 As shown, a method for removing zinc from galvanized steel sheets is provided, including the following steps S1 to S5:

[0033] Step S1: Pickling and immersing the galvanized steel sheet in an inorganic acid, including hydrochloric acid or sulfuric acid, to obtain a zinc salt solution and hydrogen gas;

[0034] Step S2: The zinc salt solution is subjected to multi-effect evaporation to obtain a concentrated solution and an inorganic acid condensate. The inorganic acid condensate is reused for pickling and soaking.

[0035] Step S3: The concentrate is roasted to obtain solid oxides and tail gas containing hydrogen chloride or sulfur trioxide. The tail gas containing hydrogen chloride or sulfur trioxide is reused for acid washing and soaking.

[0036] Step S4: Separate the solid oxides by magnetic separation to obtain magnetic oxides and non-magnetic oxides;

[0037] Step S5: Use the hydrogen generated by acid washing and soaking to reduce the non-magnetic oxide with hydrogen, and collect it by condensation to obtain zinc metal with a purity greater than 99%.

[0038] According to some specific embodiments of this disclosure, galvanized steel sheets can also be replaced with other zinc sources, such as galvanizing slag, zinc-containing scrap steel, etc. The preferred size of the galvanized steel sheet is a side length of 50 cm or less, but it is not limited to this size range. A suitable size facilitates more uniform distribution during pickling and immersion, and, combined with stirring, allows for sufficient contact with inorganic acid solutions such as hydrochloric acid or sulfuric acid solutions, avoiding localized obstruction and uneven leaching due to excessive material size, thus ensuring efficient dissolution of zinc, iron, and other metal ions. The zinc content of the galvanized steel sheet is preferably greater than or equal to 0.5 wt%, ensuring the zinc yield after treatment, allowing subsequent processes to operate under reasonable loads, balancing recovery efficiency and economic feasibility.

[0039] According to the embodiments of this disclosure, a closed-loop process including pickling, concentration, roasting, separation, and reduction is constructed. Only hydrochloric acid and galvanized steel plate are consumed as initial input materials. The condensate of inorganic acid generated by multi-effect evaporation in step S2 and the tail gas containing hydrogen chloride or sulfur trioxide generated by roasting in step S3 are recycled to pickling and soaking in step S1, avoiding waste of hydrochloric acid or sulfuric acid resources. At the same time, the hydrogen generated by pickling in step S1 is directly used for reduction in step S5, without the need for additional purchase or storage of inorganic acid and hydrogen. Through ingenious process coupling settings, the cost and environmental safety risks of raw material transportation and storage in traditional processes are thoroughly solved, realizing the closed-loop utilization of "chlorine-hydrogen-water" or "sulfur-hydrogen-water" elements. There is no wastewater discharge throughout the process, so as to achieve zero waste of resources and zero emission of pollutants.

[0040] This disclosure ensures reaction stability through precise process coordination and internal resource recycling. Combined with the efficient separation of iron and zinc oxides via magnetic separation in step S4, and the purification design of staged condensation after reduction in step S5, it effectively avoids the problems of incomplete zinc layer removal in traditional mechanical peeling methods and low product purity in traditional pickling processes, ultimately obtaining zinc metal with a purity greater than 99%. The overall process has no additional redundant energy-consuming steps, and resource recycling significantly reduces energy consumption and raw material consumption per unit of zinc output. It balances efficient zinc extraction, economic feasibility, and environmental requirements, adapting to the needs of continuous industrial production and low-carbon development.

[0041] According to embodiments of this disclosure, during the pickling and soaking process, the concentration of hydrochloric acid (HCl) or sulfuric acid is 1~5 mol / L, and the concentration can be, for example, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, etc.; the liquid-solid ratio is (2~5):1, for example, 2:1, 3:1, 4:1, 5:1, etc.; the temperature is 0~60℃, for example, 0℃, 10℃, 20℃, 25℃, 30℃, 50℃, 60℃, etc.

[0042] According to embodiments of this disclosure, traditional mechanical stripping methods for galvanized steel sheets with high industrial demand suffer from incomplete removal of the zinc coating and low efficiency. This disclosure employs a hydrochloric acid or sulfuric acid immersion chemical dissolution method. Through a chemical reaction, the zinc (Zn) layer and a small amount of iron (Fe) substrate on the steel sheet surface dissolve, achieving complete leaching of zinc and iron ions to obtain a zinc-containing salt solution. Taking hydrochloric acid pickling as an example, the zinc-containing salt solution may contain zinc chloride (ZnCl2), ferric chloride (FeCl2), and a small amount of aluminum chloride (AlCl3). Taking sulfuric acid pickling as an example, the zinc-containing salt solution may contain zinc sulfate (ZnSO4), ferric sulfate (FeSO4), and a small amount of aluminum sulfate (Al2(SO4)3). Furthermore, by optimizing pickling conditions, pollution, corrosion, or slow leaching caused by abnormal acid concentration, as well as uneven leaching caused by imbalances in liquid-solid ratio and temperature, are avoided. A stable leaching solution provides a stable ion concentration basis for subsequent zinc-containing salt solution concentration, oxide preparation, and other processes, ensuring the overall zinc recovery efficiency and resource recycling effect.

[0043] The main reaction equations during the pickling process are:

[0044] Zn + 2HCl = ZnCl2 + H2;

[0045] Fe + 2HCl = FeCl2 + H2.

[0046] Zn + H2SO4 = ZnSO4 + H2;

[0047] Fe + H2SO4 = FeSO4 + H2.

[0048] Specifically, in practical applications, after the acid pickling and soaking reaction is completed, solid-liquid separation can be performed using filtration equipment such as a belt filter to obtain zinc ion-containing (Zn) extract. 2+ ), divalent iron ions (Fe 2+ Zinc salt solution (Zn) 2+ The initial concentration is approximately 40-60 g / L. After separation, the dezincified steel plates are rinsed with clean water until neutral, dried, and then returned to the steel smelting process for resource utilization.

[0049] The zinc salt solution can be supplemented with 1-5 mol / L hydrochloric acid or sulfuric acid to the initial concentration and reused in the pickling and soaking process, for example, 2-6 times, to increase the concentration of zinc and iron ions in the solution and reduce the consumption of water resources and inorganic acids.

[0050] According to embodiments of this disclosure, multi-effect evaporation is carried out in an evaporator with 2 to 5 effects, each effect having an evaporation temperature of 65 to 160°C and an absolute pressure of 0.02 to 0.3 MPa; and / or, the volume of the concentrate is 25% to 40% of the volume of the zinc salt solution, so that Zn2+ Concentration of 180~220 g / L, Fe 2+ The concentration is 35~50g / L.

[0051] According to some specific embodiments of this disclosure, multi-effect evaporation can be carried out in 2-effect, 3-effect, 4-effect, and 5-effect evaporators. The evaporation temperature of each effect can be 65~160℃, for example, 65℃, 70℃, 90℃, 110℃, 140℃, 160℃, etc. The absolute pressure of each effect can be 0.02~0.3MPa, for example, 0.02MPa, 0.05MPa, 0.1MPa, 0.2MPa, 0.3MPa, etc. The number of evaporation effects, temperature, and absolute pressure can be adjusted according to actual production capacity, energy consumption budget, site conditions, etc., to ensure a high degree of matching between the process and production requirements.

[0052] After multi-effect evaporation, the volume of the concentrated solution is 25% to 40% of the volume of the zinc salt solution, for example, 25%, 30%, 35%, 40%, etc., to ensure that Zn 2+ The concentration is 180~220 g / L, for example, it can be 180 g / L, 190 g / L, 200 g / L, 210 g / L, 220 g / L, etc., Fe 2+ The concentration is 35~50 g / L, for example, it can be 35 g / L, 40 g / L, 45 g / L, 50 g / L, etc.

[0053] According to embodiments of this disclosure, the optimization of multi-effect evaporation conditions can ensure that the zinc salt solution is concentrated to a suitable target concentration, forming a synergistic effect of energy consumption control, equipment protection, and tail gas utilization. If the solution concentration is too low, a large amount of energy needs to be consumed to evaporate excess water when entering the fluidized bed roasting, resulting in a significant increase in the overall energy consumption. However, the waste heat utilization of multi-effect evaporation in this disclosure has efficiently removed most of the water in the concentration stage, avoiding ineffective energy consumption in the subsequent roasting stage and achieving a reduction in overall energy consumption. If the solution concentration is too high, the strong acidity will significantly increase the corrosion resistance requirements of the fluidized bed and other roasting equipment, increasing equipment procurement and maintenance costs, and easily causing crystallization blockage in the conveying pipeline. The optimized concentration of this disclosure can balance the acidity intensity, reduce the corrosion pressure on the equipment, and the tail gas containing hydrogen chloride or sulfur trioxide generated during roasting can be converted into an inorganic acid solution of the target concentration and reused for pickling after condensation and absorption. This not only realizes the resource utilization of acidic tail gas, but also further reduces its corrosive impact on the roasting equipment.

[0054] For example, the multi-effect evaporation is preferably a triple-effect evaporation, wherein the temperature of the first effect is 130~160℃ and the absolute pressure of the first effect is 0.15~0.3MPa, the temperature of the second effect is 100~130℃ and the absolute pressure of the second effect is 0.05~0.15MPa, and the temperature of the third effect is 60~100℃ and the absolute pressure of the third effect is 0.02~0.05MPa.

[0055] According to some specific embodiments of this disclosure, the temperature of the first effect can be, for example, 130°C, 140°C, 150°C, 160°C, etc., and the absolute pressure of the first effect can be, for example, 0.15MPa, 0.2MPa, 0.25MPa, 0.3MPa, etc.; the temperature of the second effect can be, for example, 100°C, 110°C, 120°C, 130°C, etc., and the absolute pressure of the second effect can be, for example, 0.05MPa, 0.1MPa, 0.15MPa, etc.; the temperature of the third effect can be, for example, 60°C, 70°C, 80°C, 90°C, 100°C, etc., and the absolute pressure of the third effect can be, for example, 0.02MPa, 0.03MPa, 0.04MPa, 0.05MPa, etc.

[0056] According to embodiments of this disclosure, the temperature and absolute pressure of each effect gradually decrease. The first effect is heated with live steam, and the temperature and pressure of the generated secondary steam are slightly lower than those of the live steam, which can be used as a heat source for the second effect. The second effect is heated using the same secondary steam, and the temperature and pressure of the generated secondary steam are further reduced before being supplied to the third effect. Through the cascaded utilization of steam, the multi-effect evaporation process is subjected to gradient cooling and depressurization, enabling each effect to achieve evaporation at its boiling point temperature under the corresponding pressure, thereby maximizing the utilization of the latent heat of steam and avoiding energy waste.

[0057] According to embodiments of this disclosure, the calcination operation is carried out in a fluidized bed at a temperature of 800-1000°C, such as 800°C, 850°C, 900°C, 950°C, or 1000°C, for a duration of 2-8 hours, such as 2 hours, 4 hours, 6 hours, or 8 hours. Appropriate calcination temperature and time ensure that chlorides or sulfates in the fluidized bed, such as zinc chloride (ZnCl2), ferrous chloride (FeCl2), and a small amount of aluminum chloride (AlCl3), are fully converted into solid oxides. This ensures the dispersion and separation efficiency of the solid oxides during subsequent magnetic separation. The solid oxides mainly include zinc oxide (ZnO), ferric oxide (Fe2O3), and a small amount of aluminum oxide (Al2O3).

[0058] The main reaction equations in the fluidized bed are:

[0059] ZnCl2 + H2O = ZnO + 2HCl;

[0060] 4FeCl2 + O2 + 4H2O = 2Fe2O3 + 8HCl;

[0061] 2AlCl3 + 3H2O = Al2O3 + 6HCl;

[0062] ZnSO4 + H2O = ZnO + H2SO4;

[0063] 4FeSO4 + O2 + 4H2O = 2Fe2O3 + 4 H2SO4;

[0064] Al2(SO4)3+ 3H2O = Al2O3 + 3 H2SO4.

[0065] In practical applications, the concentrated liquid obtained by multi-effect evaporation can be sprayed into a fluidized bed roasting furnace through a dual-fluid atomizing nozzle at an atomization pressure of 0.3~0.5MPa for roasting. The roasting conditions can be adjusted according to the atomization amount of the solution to ensure complete decomposition of the droplets and fully convert chlorides or sulfates into a mixture of solid oxides.

[0066] According to embodiments of this disclosure, the method for removing zinc from galvanized steel sheets further includes: a multi-effect evaporation stage, where the condensate generated during the multi-effect evaporation process is collected using a temperature gradient to obtain dilute hydrochloric acid A1 or dilute sulfuric acid B1 with a concentration of 0.5~4 mol / L, which is then reused for pickling and soaking; and a fluidized bed roasting stage, where chlorides or sulfates decompose at high temperatures to generate tail gas containing hydrogen chloride or sulfur trioxide. The tail gas containing hydrogen chloride or sulfur trioxide generated during roasting is then condensed and absorbed to obtain dilute hydrochloric acid A2 or dilute sulfuric acid B2 with a concentration greater than or equal to 5 mol / L, which is then reused for pickling and soaking. These two recovery paths can specifically capture hydrogen chloride or sulfur trioxide from different process stages through condensation, preventing the loss of inorganic acids with waste liquid and tail gas, and improving the overall recovery rate of inorganic acids. No additional complex adjustment equipment needs to be developed, the method is simple, and the process equipment is highly compatible.

[0067] In some exemplary embodiments, the recovered dilute hydrochloric acid A1 and A2 or dilute sulfuric acid B1 and B2 can be transported to an acid storage tank for storing inorganic acids such as hydrochloric acid or sulfuric acid and mixed, with the ratio adjusted according to the concentration requirements for pickling. If the concentration after mixing is lower than the required concentration, fresh hydrochloric acid or sulfuric acid can be added to adjust it to the target concentration range, ensuring that when reused for pickling immersion, it can meet the requirements for efficient dissolution of the zinc plating layer while avoiding excessive corrosion of the steel substrate due to excessive concentration.

[0068] According to embodiments of this disclosure, the magnetic field strength for magnetic separation is 8000~12000 Gs, for example, it can be 8000 Gs, 9000 Gs, 10000 Gs, 11000 Gs, 12000 Gs, etc.; the magnetic oxides include ferric oxide (Fe2O3), and may also include trace amounts of iron(III) oxide (Fe3O4); the non-magnetic oxides include zinc oxide (ZnO) and aluminum oxide (Al2O3).

[0069] According to embodiments of this disclosure, under the aforementioned magnetic field strength, magnetic oxides (Fe2O) 3、 Iron oxides (Fe3O4) can be efficiently adsorbed and collected; non-magnetic oxides (ZnO, Al2O3) are separated because they cannot be adsorbed by a magnetic field. This separation method can significantly improve separation efficiency, ensure full recovery of iron oxides, improve the recovery rate of iron, and ensure the purity of the recovered iron. In addition, it can also remove the interference of iron impurities in the subsequent hydrogen reduction zinc extraction process, avoid the co-reduction of iron oxides and ZnO affecting the purity of zinc metal, and lay the foundation for the subsequent preparation of high-purity zinc.

[0070] According to embodiments of this disclosure, the hydrogen reduction temperature is 900~1200℃, for example, 900℃, 1000℃, 1100℃, 1200℃, etc., and the hydrogen reduction time is 3~6 hours, for example, 3 hours, 4 hours, 5 hours, 6 hours, etc., and the hydrogen purity is greater than or equal to 99.9%.

[0071] According to embodiments of this disclosure, under these conditions, ZnO in the non-magnetic oxide can react fully with hydrogen to directly reduce it to zinc vapor, while Al2O3, due to its stable chemical properties, does not participate in the reduction reaction and remains in solid form, thus achieving efficient separation of zinc and alumina. Appropriate temperature and time ensure complete conversion of ZnO to zinc vapor, avoiding residual ZnO due to incomplete reaction that could affect zinc recovery. High-purity hydrogen prevents the introduction of impurities, ensuring the subsequent purification through staged condensation to obtain high-purity zinc.

[0072] According to embodiments of this disclosure, the condensation collection method is stepped condensation, with the temperature decreasing step by step; and / or, the stepped condensation includes: a first stage of condensation at a temperature of 900~1200℃ and an absolute pressure of 0.07-0.10 MPa, a second stage of condensation at a temperature of 500~800℃ and an absolute pressure of 0.06-0.08 MPa, and a third stage of condensation at a temperature of 25~300℃ and an absolute pressure of 0.05-0.07 MPa.

[0073] According to some specific embodiments of this disclosure, the temperature of the first stage of condensation can be, for example, 900℃, 1000℃, 1100℃, 1200℃, etc., and the absolute pressure can be, for example, 0.07Mpa, 0.08Mpa, 0.09Mpa, 0.10Mpa, etc.; the temperature of the second stage of condensation can be, for example, 500℃, 600℃, 700℃, 800℃, etc., and the absolute pressure can be, for example, 0.06Mpa, 0.07Mpa, 0.08Mpa, etc.; the temperature of the third stage of condensation can be, for example, 25℃, 50℃, 100℃, 200℃, 300℃, etc., and the absolute pressure can be, for example, 0.05Mpa, 0.06Mpa, 0.07Mpa, etc.

[0074] According to embodiments of this disclosure, the condensation and collection of zinc vapor employs a stepped condensation method with progressively decreasing temperature: the first stage, at higher temperature and pressure, traps incompletely reacted oxide particles and other high-boiling-point impurities; the second stage, by lowering temperature and pressure, further separates medium-boiling-point impurities and collects crude zinc vapor; the third stage, at lower temperature and pressure, allows the zinc vapor to fully condense into solid zinc metal. This stepped condensation method removes impurities layer by layer based on boiling point differences, ensuring a zinc purity of over 99.9%. Simultaneously, pressure control allows for the removal of oxygen from the system. In other possible examples, an inert atmosphere can be used to protect the zinc metal during the condensation process, preventing it from re-oxidizing upon contact with oxygen and ensuring the quality stability of the final zinc product.

[0075] According to embodiments of this disclosure, the method for removing zinc from galvanized steel sheets further includes: condensing and dehydrating the hydrogen generated by pickling and soaking to make the hydrogen dew point less than or equal to -40°C, thereby purifying the hydrogen; and using the purified hydrogen as a gas source for hydrogen reduction; and / or condensing and dehydrating the tail gas generated after hydrogen reduction to make the hydrogen dew point less than or equal to -40°C, thereby purifying the hydrogen; and using the purified hydrogen for reuse in hydrogen reduction for repeated use.

[0076] According to embodiments of this disclosure, the hydrogen gas generated from pickling and the reduction tail gas are purified by condensing and dehydrating to a set dew point. This process can deeply remove impurities such as water vapor and trace amounts of hydrogen chloride from the hydrogen gas, avoiding side reactions that may occur during the reduction process and ensuring the purity of zinc extraction and the stability of the reaction. Secondly, purification can eliminate free water in the hydrogen gas, preventing it from condensing in pipelines to form acidic liquid and avoiding the risk of pipeline corrosion and leakage. In addition, the purified hydrogen gas can be recycled as a reducing gas source, effectively improving the utilization rate of hydrogen gas, reducing resource waste, and lowering the cost of purchasing external gas sources.

[0077] Figure 3 This is a schematic diagram of the system apparatus for the zinc removal and extraction method of galvanized steel sheet disclosed herein.

[0078] According to an embodiment of another aspect of this disclosure, such as Figure 3 As shown, a system for the above-mentioned method of removing zinc from galvanized steel sheets is provided, comprising:

[0079] Pickling equipment is suitable for pickling and immersing galvanized steel sheets with inorganic acids, including hydrochloric acid or sulfuric acid, to obtain a zinc salt solution and hydrogen gas;

[0080] The multi-effect evaporation device is suitable for evaporating zinc salt solutions from pickling equipment to obtain concentrated solutions and inorganic acid condensates. The inorganic acid condensates are reused for pickling soaking.

[0081] Fluidized bed is suitable for roasting concentrated liquid from multi-effect evaporation unit to obtain solid oxides and tail gas containing hydrogen chloride or sulfur trioxide. The tail gas containing hydrogen chloride or sulfur trioxide is reused for acid washing and soaking.

[0082] A magnetic separation device is suitable for separating solid oxides by magnetic separation to obtain magnetic oxides and non-magnetic oxides;

[0083] The reduction device is suitable for using hydrogen generated by acid washing and soaking to reduce non-magnetic oxides from magnetic separation devices, and then collecting the condensed hydrogen to obtain zinc metal with a purity greater than 99%.

[0084] According to some specific embodiments of this disclosure, the pickling apparatus includes an acid storage tank for storing inorganic acids such as hydrochloric acid or sulfuric acid, an pickling tank, a hydrogen storage tank, and a belt filter; wherein, the acid storage tank is also suitable for storing dilute hydrochloric acid A1 or dilute sulfuric acid B1 recovered during multi-effect evaporation and dilute hydrochloric acid A2 or dilute sulfuric acid B2 obtained after condensation and absorption of tail gas containing hydrogen chloride or sulfur trioxide recovered during roasting; the pickling tank is suitable for pickling and immersing galvanized steel sheets with inorganic acids containing hydrochloric acid or sulfuric acid; the hydrogen storage tank is suitable for collecting hydrogen gas generated after pickling and immersion from the pickling tank; and the belt filter is used for solid-liquid separation of the leachate from the pickling tank after pickling and immersion to obtain a zinc salt solution.

[0085] According to some specific embodiments of this disclosure, the system of this disclosure also includes a cyclone separator configured for a fluidized bed, suitable for collecting solid oxides obtained by calcination of the fluidized bed to obtain dry oxide particles.

[0086] According to some specific embodiments of this disclosure, the magnetic separation device includes a permanent magnet drum separator and a plate and frame filter. The permanent magnet drum separator is suitable for receiving solid oxides from a fluidized bed, wherein magnetic oxides (such as Fe2O3) are adsorbed on the surface of the drum and fall off as the drum rotates to the non-magnetic zone, while non-magnetic oxides flow into the non-magnetic product tank with the slurry. The plate and frame filter is suitable for filtering and drying the slurry from the non-magnetic product tank to obtain non-magnetic oxides.

[0087] According to some specific embodiments of this disclosure, the reduction apparatus includes a hydrogen reduction furnace, a dryer, and a staged condenser. The hydrogen reduction furnace is suitable for reducing non-magnetic oxides from a magnetic separation device (e.g., a plate and frame filter). The dryer is suitable for dehydrating the tail gas (containing unreacted hydrogen and water vapor) generated after hydrogen reduction; specifically, the dryer is a freeze dryer with a condensation temperature of -5 to 0°C, ensuring the hydrogen dew point is ≤ -40°C, thus purifying the hydrogen. The staged condenser is suitable for condensing the zinc vapor generated after hydrogen reduction in stages to obtain zinc metal with a purity greater than 99%.

[0088] According to embodiments of this disclosure, the system for zinc removal and extraction from galvanized steel sheets achieves efficient closed-loop operation throughout the entire process through the coordinated linkage of various devices. First, the pickling device, multi-effect evaporator, and fluidized bed form an internal circulation channel of "hydrochloric acid-chloride-hydrochloric acid" or "sulfuric acid-sulfate-sulfuric acid," allowing for direct reuse of dilute hydrochloric acid or dilute sulfuric acid with tail gas containing hydrogen chloride or sulfur trioxide, reducing raw material loss. The magnetic separation device matches the magnetic differences of the calcined oxides, providing pure raw materials for subsequent high-purity zinc preparation. The reduction device directly utilizes the hydrogen generated by pickling, eliminating the need for external gas supply equipment. The functions of each device are closely integrated, avoiding the problems of dispersed equipment and material transfer losses in traditional systems. Second, the system uses only galvanized steel sheets and initial inorganic acid as input, and with the full-process material circulation design, the utilization rate of "chlorine-hydrogen-water" or "sulfur-hydrogen-water" elements is significantly improved, with no wastewater or waste gas discharge, significantly reducing environmental treatment costs. In addition, the modular design allows for flexible adjustment of processing scale, ensuring continuous production and ultimately producing zinc metal with a purity of ≥99%. This not only solves the pain points of low product purity and high energy consumption in traditional systems, but also reduces equipment investment and operating costs per unit capacity through internal resource recycling, meeting the needs of large-scale and low-carbon production.

[0089] In practical applications, the device disclosed herein exhibits strong adaptability to various scenarios, making it particularly suitable for deployment in green energy production areas. Since green energy production areas largely rely on clean energy sources such as wind and solar power, the modular design of the device allows for direct connection to green energy systems without the need for complex additional power supply adaptation facilities. This not only fully utilizes local green energy resources to reduce production energy costs but also further reduces carbon emissions through green energy-driven development. Simultaneously, the device produces no wastewater or exhaust gas emissions throughout its operation, preventing damage to the surrounding ecological environment. Furthermore, the device has a small overall footprint, requiring no large-scale land leveling. Its simple structure and convenient installation place low demands on site topography. Even in mountainous areas with complex terrain and limited land resources, flexible site selection and construction are possible without incurring significant site modification costs. This effectively addresses the challenge of traditional large-scale recycling equipment being difficult to implement in mountainous regions, providing a feasible solution for resource recycling in remote green energy production areas.

[0090] The present disclosure is further illustrated below through embodiments, accompanying drawings, and related test experiments and results. In the following detailed description, numerous specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Moreover, the details in the following embodiments can be arbitrarily combined to form other feasible embodiments without conflict.

[0091] Example 1

[0092] Embodiment 1 of this disclosure provides a method for removing zinc from galvanized steel sheets, including the following steps (1) to (6):

[0093] Step (1): Soaking and pickling in hydrochloric acid

[0094] Waste galvanized steel sheets were cut into 30 cm side plates and placed into a hydrochloric acid corrosion resistant pickling tank with low-speed stirring function. A 1 mol / L hydrochloric acid solution was added at a liquid-to-solid ratio of 2:1. The pickling temperature was controlled at 0 ℃, the stirring rate was 5 r / min, and the reaction was continued for 30 min.

[0095] After the reaction was completed, solid-liquid separation was performed using a belt filter to obtain a solution containing 40 g / L zinc ions (Zn). 2+ ), 35 g / L ferrous ions (Fe 2+ The chloride solution and dezincified steel plate were separated. The dezincified steel plate was rinsed with water until pH=7, dried and then transported to the steel smelting process for resource utilization. The rinsing acid was collected and recycled and transported to step (6) for processing. The chloride solution was supplemented with 1 mol / L hydrochloric acid to the initial concentration and reused twice in the pickling and soaking process before being transferred to step (2). The tail gas hydrogen generated during the pickling process was dehydrated by a freeze dryer (condensation temperature -5℃) to make the hydrogen dew point ≤-40℃ in order to purify the hydrogen. The purified hydrogen was then transported to the reduction furnace in step (5) for later use.

[0096] Step (2): Triple-effect evaporation and concentration

[0097] The chloride solution obtained in step (1) is fed into a triple-effect evaporator for gradient evaporation and concentration. The specific evaporation conditions are as follows:

[0098] The first-effect evaporation unit operates at a temperature of 130°C and an absolute pressure of 0.3 MPa. It uses live steam for heating, and the secondary steam generated during evaporation is delivered to the second effect as a heat source.

[0099] The second-effect evaporation unit operates at a temperature of 100°C and an absolute pressure of 0.15 MPa. It utilizes the secondary steam supplied from the first effect for heating, and the generated secondary steam is further supplied to the third effect.

[0100] The third-effect evaporation unit operates at a temperature of 65°C and an absolute pressure of 0.05 MPa, and is heated by secondary steam supplied from the second effect.

[0101] By using triple-effect evaporation, the solution volume is concentrated to 40% of its original volume, of which Zn 2+ The concentration was increased to 180 g / L, Fe 2 + The concentration was increased to 35 g / L; the condensate generated during the evaporation process was collected to obtain dilute hydrochloric acid with a concentration of 0.5 mol / L, which was reused in the acid washing replenishment process of step (1).

[0102] Step (3): Fluidized bed preparation of solid oxides

[0103] The concentrate from step (2) is sprayed into a fluidized bed roasting furnace through a dual-fluid atomizing nozzle with an atomization pressure of 0.3 MPa. The temperature inside the roasting furnace is controlled at 800℃ and the roasting time is 8 h. The chlorides (ZnCl2, FeCl2) in the solution react with the air introduced into the furnace to generate a solid oxide mixture containing ZnO, Fe2O3 and a small amount of Al2O3.

[0104] The solid oxide mixture is collected by a cyclone separator (separation efficiency ≥ 99%) to obtain dry oxide particles (particle size 50~100 μm), which are sent to the magnetic separation process in step (4); the hydrogen chloride tail gas generated by roasting is absorbed by a graphite condenser (condensation temperature 20℃) to obtain hydrochloric acid with a concentration of 6 mol / L, which is recycled to the acid washing and soaking process in step (1).

[0105] Step (4): Magnetic separation to separate magnetic and non-magnetic oxides

[0106] The oxide particles collected in step (3) are fed into a permanent magnet drum separator. The magnetic field strength is controlled at 8000 Gs and the drum speed is 20 r / min. Under the action of the magnetic field, the magnetic oxide (Fe2O3) is adsorbed on the surface of the drum and falls off as the drum rotates to the non-magnetic area. After being rinsed with clean water and dried with hot air (100℃), Fe2O3 filter cake (purity 96.5%) is obtained. The non-magnetic oxide (ZnO content 88%, Al2O3 content 10%) flows into the non-magnetic product tank with the slurry. After being filtered by a plate and frame filter (filter cloth pore size 1 μm) and dried, it is ready for use.

[0107] Step (5): Preparation of high-purity zinc and alumina by hydrogen reduction

[0108] The non-magnetic oxide processed in step (4) is added to a tubular reduction furnace, and hydrogen gas with a purity ≥99.9% (hydrogen flow rate 15 m³ / h) is introduced into the furnace. 3The absolute pressure inside the reduction furnace is controlled at 0.12 MPa, the reduction temperature is maintained at 900℃, and the reduction is carried out for 6 h. Under these conditions, ZnO in the non-magnetic oxide is completely converted into zinc vapor, and Al2O3 does not participate in the reduction reaction.

[0109] Zinc vapor is transported through high-temperature resistant pipelines to a three-stage series cyclone condensation and separation system for sequential condensation, under the following conditions:

[0110] Primary condenser separator: operating temperature 900℃, absolute pressure 0.10 MPa, collects high-boiling-point impurities;

[0111] Secondary condenser separator: operating temperature 500℃, absolute pressure 0.08 MPa, collects crude zinc vapor;

[0112] Three-stage condenser separator: operating temperature 25℃, absolute pressure 0.07 MPa, to obtain zinc metal.

[0113] After the reduction furnace is cooled, the solid material remaining in the furnace is collected, which is alumina with a purity of 95.9%, which can be used as a ceramic raw material or catalyst carrier. The tail gas produced by the reduction reaction (containing unreacted hydrogen and water vapor) is dehydrated by a freeze dryer (condensation temperature 0℃) to make the hydrogen dew point ≤-40℃. The purified hydrogen is returned to the reduction furnace of this step for recycling, with a hydrogen utilization rate ≥90%.

[0114] Step (6): Waste liquid treatment and hydrochloric acid and water resource recycling

[0115] The waste liquid with a large amount of impurities accumulated after two acid washes in step (1) is first filtered through a precision filter (pore size 0.22 μm) to remove suspended solids, and then transported to the triple-effect evaporator in step (2) for co-processing. The condensate (0.5 mol / L dilute hydrochloric acid) generated during the evaporation process is recycled to the acid wash process in step (1). The hydrochloric acid generated by the fluidized bed roasting in step (3) is absorbed by a graphite condenser (condensation temperature 20℃) to obtain hydrochloric acid with a concentration of 6 mol / L, which is recycled to the acid wash process in step (1). The condensate generated in each stage of the entire process (including evaporation, condensation, and absorption stages) is filtered through a precision filter (pore size 0.22 μm) and then recycled to the solution preparation and cleaning stages of each process, with a water recycling rate of ≥99.0%.

[0116] Example 2

[0117] Embodiment 2 of this disclosure provides a method for removing zinc from galvanized steel sheets, which differs from the method in Embodiment 1 in that:

[0118] In step (1), a 3 mol / L hydrochloric acid solution is added at a liquid-to-solid ratio of 3:1; the pickling temperature is controlled at 20℃, the stirring rate is 10 r / min, and the reaction is continued for 15 min. The chloride solution is replenished with 3 mol / L hydrochloric acid to the initial concentration, and the pickling and soaking process is repeated 3 times before proceeding to step (2).

[0119] In step (2), the specific evaporation conditions are as follows:

[0120] The first-effect evaporation unit operates at a temperature of 140℃ and an absolute pressure of 0.25 MPa. It uses live steam for heating, and the secondary steam generated during evaporation is delivered to the second effect as a heat source.

[0121] The second-effect evaporation unit operates at a temperature of 110°C and an absolute pressure of 0.10 MPa. It utilizes the secondary steam supplied from the first effect for heating, and the generated secondary steam is further supplied to the third effect.

[0122] The third-effect evaporation unit operates at a temperature of 70°C and an absolute pressure of 0.04 MPa, using secondary steam supplied from the second effect for heating.

[0123] In step (3), the concentrated liquid from step (2) is sprayed into the fluidized bed calcining furnace through a dual-fluid atomizing nozzle with an atomization pressure of 0.4 MPa, and the temperature inside the calcining furnace is controlled at 900℃ and the calcination time is 6 h.

[0124] In step (4), the magnetic field strength is controlled to be 10000 Gs and the drum speed is 25 r / min.

[0125] In step (5), the hydrogen flow rate is 20 m³ / s. 3 / h, control the absolute pressure inside the reduction furnace to 0.12 MPa, maintain the reduction temperature at 900℃, and hold for 6 h.

[0126] Zinc vapor is transported through high-temperature resistant pipelines to a three-stage series cyclone condensation and separation system for sequential condensation, under the following conditions:

[0127] Primary condenser separator: operating temperature 1000℃, absolute pressure 0.09 MPa, collects high-boiling-point impurities;

[0128] Secondary condenser separator: operating temperature 600℃, absolute pressure 0.07 MPa, collects crude zinc vapor;

[0129] Three-stage condenser separator: operating temperature 100℃, absolute pressure 0.06 MPa, to obtain zinc metal.

[0130] The exhaust gas produced by the reduction reaction (containing unreacted hydrogen and water vapor) is dehydrated by a freeze dryer (condensation temperature -3℃).

[0131] The remaining steps in this embodiment 2 are the same as those in embodiment 1.

[0132] Example 3

[0133] Embodiment 3 of this disclosure provides a method for removing zinc from galvanized steel sheets, which differs from the method in Embodiment 1 in that:

[0134] In step (1), a 4 mol / L hydrochloric acid solution is added at a liquid-to-solid ratio of 4:1; the pickling temperature is controlled at 40℃, the stirring rate is 15 r / min, and the reaction is continued for 10 min. The chloride solution is replenished with 4 mol / L hydrochloric acid to the initial concentration, and the pickling and soaking process is repeated 4 times before proceeding to step (2).

[0135] In step (2), the specific evaporation conditions are as follows:

[0136] The first-effect evaporation unit operates at a temperature of 150°C and an absolute pressure of 0.20 MPa. It uses live steam for heating, and the secondary steam generated during evaporation is delivered to the second effect as a heat source.

[0137] The second-effect evaporation unit operates at a temperature of 120°C and an absolute pressure of 0.05 MPa. It utilizes the secondary steam supplied from the first effect for heating, and the generated secondary steam is further supplied to the third effect.

[0138] The third-effect evaporation unit operates at a temperature of 80°C and an absolute pressure of 0.03 MPa, and is heated by secondary steam supplied from the second effect.

[0139] In step (3), the concentrated liquid from step (2) is sprayed into the fluidized bed roasting furnace through a dual-fluid atomizing nozzle with an atomization pressure of 0.5 MPa, and the temperature inside the roasting furnace is controlled at 1000℃ and the roasting time is 8 h.

[0140] In step (4), the magnetic field strength is controlled at 12000 Gs and the drum speed is 30 r / min.

[0141] In step (5), the hydrogen flow rate is 25 m³ / s. 3 / h, control the absolute pressure inside the reduction furnace to 0.12 MPa, maintain the reduction temperature at 1100℃, and hold for 4 h for reduction.

[0142] Zinc vapor is transported through high-temperature resistant pipelines to a three-stage series cyclone condensation and separation system for sequential condensation, under the following conditions:

[0143] Primary condenser separator: operating temperature 1100℃, absolute pressure 0.08 MPa, collects high-boiling-point impurities;

[0144] Secondary condenser separator: operating temperature 700℃, absolute pressure 0.06 MPa, collects crude zinc vapor;

[0145] Three-stage condenser separator: operating temperature 200℃, absolute pressure 0.05 MPa, to obtain zinc metal.

[0146] The exhaust gas produced by the reduction reaction (containing unreacted hydrogen and water vapor) is dehydrated by a freeze dryer (condensation temperature -4℃).

[0147] The remaining steps in this embodiment 3 are the same as those in embodiment 1.

[0148] Example 4

[0149] Embodiment 4 of this disclosure provides a method for removing zinc from galvanized steel sheets, which differs from the method in Embodiment 1 in that:

[0150] In step (1), a 5 mol / L hydrochloric acid solution is added at a liquid-to-solid ratio of 5:1; the pickling temperature is controlled at 60℃, the stirring rate is 20 r / min, and the reaction is continued for 5 min. The chloride solution is replenished with 5 mol / L hydrochloric acid to the initial concentration, and the pickling and soaking process is repeated 6 times before proceeding to step (2).

[0151] In step (2), the specific evaporation conditions are as follows:

[0152] The first-effect evaporation unit operates at a temperature of 160℃ and an absolute pressure of 0.15 MPa. It uses live steam for heating, and the secondary steam generated during evaporation is delivered to the second effect as a heat source.

[0153] The second-effect evaporation unit operates at a temperature of 120°C and an absolute pressure of 0.05 MPa. It utilizes the secondary steam supplied from the first effect for heating, and the generated secondary steam is further supplied to the third effect.

[0154] The third-effect evaporation unit operates at a temperature of 90°C and an absolute pressure of 0.02 MPa, using secondary steam supplied from the second effect for heating.

[0155] In step (3), the concentrated liquid from step (2) is sprayed into the fluidized bed roasting furnace through a dual-fluid atomizing nozzle with an atomization pressure of 0.5 MPa, and the temperature inside the roasting furnace is controlled at 1000℃ and the roasting time is 8 h.

[0156] In step (4), the magnetic field strength is controlled at 12000 Gs and the drum speed is 30 r / min.

[0157] In step (5), the hydrogen flow rate is 25 m³ / s. 3 / h, control the absolute pressure inside the reduction furnace to 0.12 MPa, maintain the reduction temperature at 1200 ℃, and hold for 3 h for reduction.

[0158] Zinc vapor is transported through high-temperature resistant pipelines to a three-stage series cyclone condensation and separation system for sequential condensation, under the following conditions:

[0159] Primary condenser separator: operating temperature 1200℃, absolute pressure 0.07 MPa, collects high-boiling-point impurities;

[0160] Secondary condenser separator: operating temperature 800℃, absolute pressure 0.06 MPa, collects crude zinc vapor;

[0161] Three-stage condenser separator: operating temperature 300℃, absolute pressure 0.05 MPa, to obtain zinc metal.

[0162] The exhaust gas produced by the reduction reaction (containing unreacted hydrogen and water vapor) is dehydrated by a freeze dryer (condensation temperature -4℃).

[0163] The remaining steps in this embodiment 4 are the same as those in embodiment 1.

[0164] Example 5

[0165] Embodiment 5 of this disclosure provides a method for removing zinc from galvanized steel sheets, which differs from the method in Embodiment 1 in that:

[0166] In step (1), a 5 mol / L hydrochloric acid solution is added at a liquid-to-solid ratio of 6:1; the pickling temperature is controlled at 60℃, the stirring rate is 20 r / min, and the reaction is continued for 5 min. The chloride solution is replenished with 5 mol / L hydrochloric acid to the initial concentration, and the pickling and soaking process is repeated 6 times before proceeding to step (2).

[0167] In step (2), the specific evaporation conditions are as follows:

[0168] The first-effect evaporation unit operates at a temperature of 160℃ and an absolute pressure of 0.15 MPa. It uses live steam for heating, and the secondary steam generated during evaporation is delivered to the second effect as a heat source.

[0169] The second-effect evaporation unit operates at a temperature of 120°C and an absolute pressure of 0.05 MPa. It utilizes the secondary steam supplied from the first effect for heating, and the generated secondary steam is further supplied to the third effect.

[0170] The third-effect evaporation unit operates at a temperature of 90°C and an absolute pressure of 0.02 MPa, using secondary steam supplied from the second effect for heating.

[0171] In step (3), the concentrated liquid from step (2) is sprayed into the fluidized bed roasting furnace through a dual-fluid atomizing nozzle with an atomization pressure of 0.5 MPa, and the temperature inside the roasting furnace is controlled at 1000℃ and the roasting time is 8 h.

[0172] In step (4), the magnetic field strength is controlled at 12000 Gs and the drum speed is 30 r / min.

[0173] In step (5), the hydrogen flow rate is 25 m³ / s. 3 / h, control the absolute pressure inside the reduction furnace to 0.12 MPa, maintain the reduction temperature at 1200 ℃, and hold for 3 h for reduction.

[0174] Zinc vapor is transported through high-temperature resistant pipelines to a three-stage series cyclone condensation and separation system for sequential condensation, under the following conditions:

[0175] Primary condenser separator: operating temperature 1200℃, absolute pressure 0.07 MPa, collects high-boiling-point impurities;

[0176] Secondary condenser separator: operating temperature 800℃, absolute pressure 0.06 MPa, collects crude zinc vapor;

[0177] Three-stage condenser separator: operating temperature 300℃, absolute pressure 0.05 MPa, to obtain zinc metal.

[0178] The exhaust gas produced by the reduction reaction (containing unreacted hydrogen and water vapor) is dehydrated by a freeze dryer (condensation temperature -4℃).

[0179] The remaining steps in this embodiment 5 are the same as those in embodiment 1.

[0180] Example 6

[0181] This disclosure provides a method for removing zinc from galvanized steel sheets in Example 6, which differs from the method in Example 1 in that:

[0182] In step (1), a 4 mol / L sulfuric acid solution is added at a liquid-to-solid ratio of 4:1; the pickling temperature is controlled at 60℃, the stirring rate is 20 r / min, and the reaction is continued for 5 min. The sulfate solution is replenished with 5 mol / L sulfuric acid to the initial concentration, and the pickling and soaking process is repeated 6 times before proceeding to step (2).

[0183] In step (2), the specific evaporation conditions are as follows:

[0184] The first-effect evaporation unit operates at a temperature of 160℃ and an absolute pressure of 0.15 MPa. It uses live steam for heating, and the secondary steam generated during evaporation is delivered to the second effect as a heat source.

[0185] The second-effect evaporation unit operates at a temperature of 120°C and an absolute pressure of 0.05 MPa. It utilizes the secondary steam supplied from the first effect for heating, and the generated secondary steam is further supplied to the third effect.

[0186] The third-effect evaporation unit operates at a temperature of 90°C and an absolute pressure of 0.02 MPa, using secondary steam supplied from the second effect for heating.

[0187] In step (3), the concentrated liquid from step (2) is sprayed into the fluidized bed roasting furnace through a dual-fluid atomizing nozzle with an atomization pressure of 0.5 MPa, and the temperature inside the roasting furnace is controlled at 1000℃ and the roasting time is 8 h.

[0188] In step (4), the magnetic field strength is controlled at 12000 Gs and the drum speed is 30 r / min.

[0189] In step (5), the hydrogen flow rate is 25 m³ / s. 3 / h, control the absolute pressure inside the reduction furnace to 0.12 MPa, maintain the reduction temperature at 1200 ℃, and hold for 3 h for reduction.

[0190] Zinc vapor is transported through high-temperature resistant pipelines to a three-stage series cyclone condensation and separation system for sequential condensation, under the following conditions:

[0191] Primary condenser separator: operating temperature 1200℃, absolute pressure 0.07 MPa, collects high-boiling-point impurities;

[0192] Secondary condenser separator: operating temperature 800℃, absolute pressure 0.06 MPa, collects crude zinc vapor;

[0193] Three-stage condenser separator: operating temperature 300℃, absolute pressure 0.05 MPa, to obtain zinc metal.

[0194] The exhaust gas produced by the reduction reaction (containing unreacted hydrogen and water vapor) is dehydrated by a freeze dryer (condensation temperature -4℃).

[0195] The remaining steps in Example 6 are the same as in Example 1.

[0196] Example 7

[0197] This disclosure provides a method for removing zinc from galvanized steel sheets in Example 7, which differs from the method in Example 1 in that:

[0198] In step (1), a 5 mol / L sulfuric acid solution is added at a liquid-to-solid ratio of 5:1; the pickling temperature is controlled at 60℃, the stirring rate is 20 r / min, and the reaction is continued for 5 min. The sulfate solution is replenished with 5 mol / L sulfuric acid to the initial concentration, and the pickling and soaking process is repeated 6 times before proceeding to step (2).

[0199] In step (2), the specific evaporation conditions are as follows:

[0200] The first-effect evaporation unit operates at a temperature of 160℃ and an absolute pressure of 0.15 MPa. It uses live steam for heating, and the secondary steam generated during evaporation is delivered to the second effect as a heat source.

[0201] The second-effect evaporation unit operates at a temperature of 120°C and an absolute pressure of 0.05 MPa. It utilizes the secondary steam supplied from the first effect for heating, and the generated secondary steam is further supplied to the third effect.

[0202] The third-effect evaporation unit operates at a temperature of 90°C and an absolute pressure of 0.02 MPa, using secondary steam supplied from the second effect for heating.

[0203] In step (3), the concentrated liquid from step (2) is sprayed into the fluidized bed roasting furnace through a dual-fluid atomizing nozzle with an atomization pressure of 0.5 MPa, and the temperature inside the roasting furnace is controlled at 1000℃ and the roasting time is 8 h.

[0204] In step (4), the magnetic field strength is controlled at 12000 Gs and the drum speed is 30 r / min.

[0205] In step (5), the hydrogen flow rate is 25 m³ / s. 3 / h, control the absolute pressure inside the reduction furnace to 0.12 MPa, maintain the reduction temperature at 1200 ℃, and hold for 3 h for reduction.

[0206] Zinc vapor is transported through high-temperature resistant pipelines to a three-stage series cyclone condensation and separation system for sequential condensation, under the following conditions:

[0207] Primary condenser separator: operating temperature 1200℃, absolute pressure 0.07 MPa, collects high-boiling-point impurities;

[0208] Secondary condenser separator: operating temperature 800℃, absolute pressure 0.06 MPa, collects crude zinc vapor;

[0209] Three-stage condenser separator: operating temperature 300℃, absolute pressure 0.05 MPa, to obtain zinc metal.

[0210] The exhaust gas produced by the reduction reaction (containing unreacted hydrogen and water vapor) is dehydrated by a freeze dryer (condensation temperature -4℃).

[0211] The remaining steps in Example 7 are the same as in Example 1.

[0212] Example 8

[0213] This disclosure provides a method for removing zinc from galvanized steel sheets in Example 8, which differs from the method in Example 1 in that:

[0214] In step (1), a 6 mol / L sulfuric acid solution is added at a liquid-to-solid ratio of 6:1; the pickling temperature is controlled at 60℃, the stirring rate is 20 r / min, and the reaction is continued for 5 min. The sulfate solution is replenished with 6 mol / L sulfuric acid to the initial concentration, and the pickling and soaking process is repeated 6 times before proceeding to step (2).

[0215] In step (2), the specific evaporation conditions are as follows:

[0216] The first-effect evaporation unit operates at a temperature of 160℃ and an absolute pressure of 0.15 MPa. It uses live steam for heating, and the secondary steam generated during evaporation is delivered to the second effect as a heat source.

[0217] The second-effect evaporation unit operates at a temperature of 120°C and an absolute pressure of 0.05 MPa. It utilizes the secondary steam supplied from the first effect for heating, and the generated secondary steam is further supplied to the third effect.

[0218] The third-effect evaporation unit operates at a temperature of 90°C and an absolute pressure of 0.02 MPa, using secondary steam supplied from the second effect for heating.

[0219] In step (3), the concentrated liquid from step (2) is sprayed into the fluidized bed roasting furnace through a dual-fluid atomizing nozzle with an atomization pressure of 0.5 MPa, and the temperature inside the roasting furnace is controlled at 1000℃ and the roasting time is 8 h.

[0220] In step (4), the magnetic field strength is controlled at 12000 Gs and the drum speed is 30 r / min.

[0221] In step (5), the hydrogen flow rate is 25 m³ / s. 3 / h, control the absolute pressure inside the reduction furnace to 0.12 MPa, maintain the reduction temperature at 1200 ℃, and hold for 3 h for reduction.

[0222] Zinc vapor is transported through high-temperature resistant pipelines to a three-stage series cyclone condensation and separation system for sequential condensation, under the following conditions:

[0223] Primary condenser separator: operating temperature 1200℃, absolute pressure 0.07 MPa, collects high-boiling-point impurities;

[0224] Secondary condenser separator: operating temperature 800℃, absolute pressure 0.06 MPa, collects crude zinc vapor;

[0225] Three-stage condenser separator: operating temperature 300℃, absolute pressure 0.05 MPa, to obtain zinc metal.

[0226] The exhaust gas produced by the reduction reaction (containing unreacted hydrogen and water vapor) is dehydrated by a freeze dryer (condensation temperature -4℃).

[0227] The remaining steps in Example 8 are the same as in Example 1.

[0228] Comparative Example 1

[0229] Comparative Example 1 of this disclosure provides a method for removing zinc from galvanized steel sheets, which differs from the method in Example 1 in that:

[0230] In step (1), a 5 mol / L hydrochloric acid solution is added at a liquid-to-solid ratio of 5:1; the pickling temperature is controlled at 60℃, the stirring rate is 20 r / min, and the reaction is continued for 5 min. The chloride solution is replenished with 5 mol / L hydrochloric acid to the initial concentration, and the pickling and soaking process is repeated 6 times before proceeding to step (2).

[0231] In step (2), the specific evaporation conditions are as follows:

[0232] The first-effect evaporation unit operates at a temperature of 160℃ and an absolute pressure of 0.15 MPa. It uses live steam for heating, and the secondary steam generated during evaporation is delivered to the second effect as a heat source.

[0233] The second-effect evaporation unit operates at a temperature of 120°C and an absolute pressure of 0.05 MPa. It utilizes the secondary steam supplied from the first effect for heating, and the generated secondary steam is further supplied to the third effect.

[0234] The third-effect evaporation unit operates at a temperature of 90°C and an absolute pressure of 0.02 MPa, using secondary steam supplied from the second effect for heating.

[0235] In step (3), the concentrated liquid from step (2) is sprayed into the fluidized bed roasting furnace through a dual-fluid atomizing nozzle with an atomization pressure of 0.5 MPa, and the temperature inside the roasting furnace is controlled at 1000℃ and the roasting time is 8 h.

[0236] In step (4), the magnetic field strength is controlled to be 0 Gs and the drum speed is 30 r / min.

[0237] In step (5), the hydrogen flow rate is 25 m³ / s. 3 / h, control the absolute pressure inside the reduction furnace to 0.12 MPa, maintain the reduction temperature at 1200 ℃, and hold for 3 h for reduction.

[0238] Zinc vapor is transported through high-temperature resistant pipelines to a three-stage series cyclone condensation and separation system for sequential condensation, under the following conditions:

[0239] Primary condenser separator: operating temperature 1200℃, absolute pressure 0.07 MPa, collects high-boiling-point impurities;

[0240] Secondary condenser separator: operating temperature 800℃, absolute pressure 0.06 MPa, collects crude zinc vapor;

[0241] Three-stage condenser separator: operating temperature 300℃, absolute pressure 0.05 MPa, to obtain zinc metal.

[0242] The exhaust gas produced by the reduction reaction (containing unreacted hydrogen and water vapor) is dehydrated by a freeze dryer (condensation temperature -4℃).

[0243] The remaining steps in Comparative Example 1 are the same as in Example 1.

[0244] Table 1 compares the main process conditions and product quality of each step in the embodiments of this disclosure.

[0245] Table 1

[0246]

[0247] (Continued from the table above)

[0248]

[0249] As shown in Table 1, the zinc removal and extraction method for galvanized steel sheets disclosed in this invention achieves the core indicators of zinc recovery rate ≥92.3% and zinc purity ≥99.90% in all examples. Furthermore, it can cover different application scenarios. For example, the low-temperature, long-time pickling in Example 1 is suitable for treating steel sheets with thick galvanized layers (>100 μm), reducing excessive corrosion of the substrate. The high-temperature, short-time process in Example 4 is suitable for large-scale continuous production lines, increasing processing efficiency by approximately 6 times. In Example 5, the 6:1 liquid-to-solid ratio significantly reduces zinc purity and recovery rate compared to Example 4, significantly increases the amount of byproduct Fe2O3, and increases overall energy consumption.

[0250] In steps (1) of Examples 6, 7, and 8, sulfuric acid immersion and pickling were used. By optimizing and controlling process parameters such as the liquid-to-solid ratio, the final zinc recovery rate and zinc purity reached levels comparable to those of the hydrochloric acid system examples (≥92.3%, ≥99.90%). This confirms that sulfuric acid and hydrochloric acid are equivalent in the zinc removal and extraction process of galvanized steel sheets, and both acids can efficiently achieve selective extraction and high-purity recovery of zinc. Furthermore, in Example 6, a 4 mol / L sulfuric acid solution was used with a liquid-to-solid ratio of 4:1, which significantly improved the purity and recovery rate of zinc compared to Examples 7 and 8, while also having lower overall energy consumption and water recycling rates. Moreover, the subsequent separation, purification, and pyrolysis reduction processes of the zinc sulfate solution showed good compatibility with the zinc chloride system, further verifying the universality of the method disclosed in this paper for acid systems and providing more flexible options for process selection under different operating conditions.

[0251] In Comparative Example 1, no magnetic separation was performed in step (4), and hydrogen was used directly for reduction. Although the zinc recovery rate could reach 94.4%, the by-products iron oxide and aluminum oxide could not be efficiently separated due to the lack of magnetic separation, and the economic added value in the zinc recovery process could not be improved.

[0252] Compared to traditional pyrometallurgical zinc recovery methods (<90%) and acid-process methods (severe wastewater pollution), the method disclosed herein offers advantages such as high resource utilization, low energy consumption, and zero wastewater discharge. It can reduce the processing cost per ton of steel plate by 30%–40%, while also reducing reliance on imported zinc resources. The results of the examples verify the stability and scalability potential of the process, providing a reliable technical path for the efficient recovery and low-carbon emission of zinc resources from waste galvanized steel plates.

[0253] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A method for removing zinc from galvanized steel sheets, comprising: The galvanized steel sheet is pickled and soaked in an inorganic acid, including hydrochloric acid or sulfuric acid, to obtain a zinc salt solution and hydrogen gas. The zinc salt solution is subjected to multi-effect evaporation to obtain a concentrated solution and an inorganic acid condensate. The inorganic acid condensate is reused in the pickling and soaking process. The concentrated liquid is roasted to obtain solid oxides and tail gas containing hydrogen chloride or sulfur trioxide. The tail gas containing hydrogen chloride or sulfur trioxide is reused in the acid washing and soaking process. The solid oxide is separated by magnetic separation to obtain magnetic oxide and non-magnetic oxide; The non-magnetic oxide is reduced by hydrogen using the hydrogen generated from the acid pickling process, and the zinc metal with a purity greater than 99% is obtained by condensation and collection.

2. The method according to claim 1, wherein, During the pickling and soaking process, the concentration of hydrochloric acid or sulfuric acid is 1~5 mol / L, the liquid-solid ratio is (2~5):1, and the temperature is 0~60℃.

3. The method according to claim 1, wherein, The multi-effect evaporation is carried out in an evaporator with 2 to 5 effects, with an evaporation temperature of 65 to 160°C and an absolute pressure of 0.02 to 0.3 MPa for each effect; And / or, the volume of the concentrate is 25% to 40% of the volume of the zinc salt solution, so that Zn 2+ Concentration of 180~220 g / L, Fe 2+ The concentration is 35~50 g / L.

4. The method according to claim 3, wherein, The multi-effect evaporation is a triple-effect evaporation. The temperature of the first effect is 130~160℃ and the absolute pressure of the first effect is 0.15~0.3 MPa. The temperature of the second effect is 100~130℃ and the absolute pressure of the second effect is 0.05~0.15 MPa. The temperature of the third effect is 60~100℃ and the absolute pressure of the third effect is 0.02~0.05 MPa.

5. The method according to claim 1, wherein, The calcination operation is carried out in a fluidized bed, the calcination temperature is 800~1000℃, and the calcination time is 2~8 hours; And / or, the magnetic field strength of the magnetic separation is 8000~12000Gs; the magnetic oxide includes Fe2O3, and the non-magnetic oxide includes ZnO and Al2O3.

6. The method according to claim 1, wherein, The hydrogen reduction temperature is 900~1200℃, the hydrogen reduction time is 3~6 hours, and the hydrogen purity is greater than or equal to 99.9%.

7. The method according to claim 1 or 6, wherein, The condensation collection method is stepped condensation, in which the temperature of the stepped condensation decreases step by step; And / or, the staged condensation includes: a first stage of condensation at a temperature of 900~1200℃ and an absolute pressure of 0.07 - 0.10 MPa; a second stage of condensation at a temperature of 500~800℃ and an absolute pressure of 0.06 - 0.08 MPa; and a third stage of condensation at a temperature of 25~300℃ and an absolute pressure of 0.05 - 0.07 MPa.

8. The method according to claim 1, wherein, The method further includes: The hydrogen generated by the pickling and soaking is condensed and dehydrated to make the hydrogen dew point less than or equal to -40°C, so as to purify the hydrogen. The purified hydrogen is used as the gas source for hydrogen reduction. And / or, the tail gas generated after the hydrogen reduction is subjected to condensation and dehydration treatment to make the hydrogen dew point less than or equal to -40°C, so as to purify the hydrogen. The purified hydrogen is then reused in the hydrogen reduction process for repeated use.

9. The method according to claim 1, wherein, The method further includes: The condensate generated during the multi-effect evaporation process is collected to obtain dilute hydrochloric acid A1 or dilute sulfuric acid B1 with a concentration of 0.5~4 mol / L, which can be reused for the acid washing and soaking. The tail gas containing hydrogen chloride or sulfur trioxide generated during roasting is condensed and absorbed to obtain dilute hydrochloric acid A2 or dilute sulfuric acid B2 with a concentration of greater than or equal to 5 mol / L, which is then reused for the acid washing and soaking.

10. A system for carrying out the method for removing zinc from galvanized steel sheet as described in any one of claims 1 to 9, wherein, The system includes: A pickling apparatus suitable for pickling and immersing galvanized steel sheets in inorganic acids, including hydrochloric acid or sulfuric acid, to obtain a zinc salt solution and hydrogen gas; A multi-effect evaporation device is suitable for performing multi-effect evaporation on a zinc salt solution from the pickling device to obtain a concentrated solution and an inorganic acid condensate, wherein the inorganic acid condensate is reused in the pickling soaking process. A fluidized bed is suitable for calcining the concentrate from the multi-effect evaporator to obtain solid oxides and tail gas containing hydrogen chloride or sulfur trioxide, wherein the tail gas containing hydrogen chloride or sulfur trioxide is reused in the acid washing and soaking process. A magnetic separation device is suitable for magnetically separating the solid oxide to obtain magnetic oxides and non-magnetic oxides; The reduction device is suitable for using the hydrogen generated by the acid washing and soaking to reduce the non-magnetic oxides from the magnetic separation device with hydrogen, and then collecting the condensed zinc metal with a purity greater than 99%.

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