Separation / recovery method of zinc and metal iron

Abstract

To provide a method for separating zinc in steelmaking dust by a small chemical dosage, and recovering zinc and metal iron.SOLUTION: A method has the steps of: allowing steelmaking dust slurry to flow into a wet cyclone, separating the steelmaking dust slurry into metal iron diluted dust slurry and metal iron concentrated dust slurry, and recovering them; adding oxidizer to metal iron diluted dust slurry to adjust an oxidation-reduction potential; adjusting pH of adjusted zinc-containing dust slurry to leach zinc, and obtaining zinc leachate and zinc leach residue; performing solid-liquid separation into zinc leachate and zinc leach residue; adjusting pH of the zinc leachate to precipitate zinc as zinc precipitate; performing solid-liquid separation of the zinc leachate into zinc precipitate and filtrate to recover the zinc precipitate; and performing solid-liquid separation of the metal iron concentrated dust slurry into metal iron concentrated dust and filtrate to recover the metal iron concentrated dust.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for separating and recovering zinc and metallic iron, and more particularly to a method for separating and recovering zinc and metallic iron in dust. [Background technology]

[0002] Zinc-containing dust generated from steelmaking furnaces such as converters, hot metal pretreatment furnaces, and electric furnaces contains a large amount of iron dust, making it a promising recycling source for the steelmaking process. However, if all of the zinc-containing dust is recycled, the zinc from the raw materials will accumulate as it continues to circulate within the steelworks, and if the amount of accumulation becomes excessive, it will cause operational problems in the blast furnace. Therefore, when recycling zinc-containing dust, it is necessary to separate the zinc beforehand.

[0003] Patent Document 1 proposes a technique for separating zinc from zinc-containing dust, in which zinc-containing steelmaking dust is brought into contact with and mixed with water in a reaction vessel while being stirred by blowing air into the dust, the hydrogen ion concentration of the water is adjusted to a pH of 3 to 6 to leach the zinc in the dust into the solution, the water in which the zinc has been dissolved is separated from the iron-containing dust, and the hydrogen ion concentration of the water in which the zinc has been dissolved is subsequently adjusted to a pH of 7 to 9 to separate the zinc by precipitating it.

[0004] Furthermore, Patent Document 2 proposes a method in which zinc-containing collected dust from an electric furnace or the like is adjusted to a pH of 4 in a reaction vessel using sulfuric acid, by using aeration or an oxidizing agent in combination, thereby eluting zinc while suppressing the elution of iron.

[0005] Furthermore, Patent Document 3 proposes a method in which zinc-containing ironmaking dust is concentrated with a wet cyclone to extract zinc, the pH is adjusted to 1.0 or higher to leach the zinc, an alkali is added to precipitate iron and perform solid-liquid separation, and then another alkali is added to precipitate and separate the zinc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-309831 [Patent Document 2] Japanese Patent Application Publication No. 2-250928 [Patent Document 3] Japanese Patent Publication No. 2022-105980 Summary of the Invention [Problem to be solved by the invention]

[0007] However, in the methods described in Patent Documents 1 and 2, most of the iron in the zinc-containing dust is in the form of metallic iron or wüstite, which is easily soluble in acid, increasing the hydrogen ion concentration of the water to the acidic side. Therefore, approximately 2–4% of the iron, the main component of the dust, is leached into the solution. The iron leaching consumes hydrogen ions in the water, significantly increasing the amount of acid added to control the hydrogen ion concentration of the water. Furthermore, the iron leached into the solution also precipitates during zinc precipitation and separation, significantly reducing the purity of the recovered zinc. Furthermore, metallic iron is oxidized to iron oxide, which necessitates the use of additional reducing agents when recycling the zinc leaching residue as an iron source within the steelworks.

[0008] Furthermore, in the method described in Patent Document 3, unlike when blast furnace dust is used, when steelmaking dust is used, zinc and iron are partially chemically bonded to each other and the difference in particle size is small, so it is not possible to separate and concentrate zinc from iron using a hydrocyclone. Furthermore, because steelmaking dust is mostly made up of metallic iron or wustite, which is easily soluble in acid, adding acid to the iron in its intact form, as described above, significantly increases the amount of acid added when controlling the hydrogen ion concentration in water.

[0009] The present invention has been developed in view of the above circumstances, and has as its object to provide a method for recovering zinc and metallic iron while separating zinc from steelmaking dust using a small amount of chemicals. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the present inventors have conducted extensive research into a method for separating zinc from steelmaking dust while reducing the amount of chemicals used and recovering metallic iron. As a result, they have come up with a technology that can improve zinc separation ability while suppressing the amount of acid consumed for dissolving iron by first passing the steelmaking dust through a hydrocyclone to separate it into a metallic iron-enriched dust slurry and a metallic iron-diluted dust slurry, and then increasing the oxidation-reduction potential of the metallic iron-diluted dust slurry to oxidize the iron on the dust surface to magnetite or hematite, which are insoluble in acid. The gist of this technology is as follows.

[0011] [1] A method for separating and recovering zinc and metallic iron from steelmaking dust containing zinc dust and iron dust, comprising: a wet separation step of causing a steelmaking dust slurry containing the steelmaking dust to flow into a hydrocyclone, separating the steelmaking dust slurry into a metallic iron-diluted dust slurry in which the concentrations of the metallic iron and the steelmaking dust are diluted, and a metallic iron-enriched dust slurry in which the concentrations of the metallic iron and the steelmaking dust are concentrated, and recovering the metallic iron-diluted dust slurry from an upper outlet of the hydrocyclone and the metallic iron-enriched dust slurry from a lower outlet of the hydrocyclone, respectively; an oxidation-reduction potential adjusting step of adjusting the oxidation-reduction potential by adding an oxidizing agent to the diluted metallic iron dust slurry; a zinc leaching step of adjusting the pH of the adjusted zinc-containing dust slurry whose oxidation-reduction potential has been adjusted in the oxidation-reduction potential adjusting step to leach zinc, thereby obtaining a zinc leachate and a zinc leach residue; a first solid-liquid separation step of separating the zinc leaching solution and the zinc leaching residue into solid-liquid phases; a zinc precipitation step of adjusting the pH of the separated zinc leach solution to precipitate zinc as a zinc precipitate; a second solid-liquid separation step of separating the pH-adjusted zinc leachate into the zinc precipitate and a filtrate, and recovering the separated zinc precipitate; a third solid-liquid separation step of separating the metallic iron-enriched dust slurry into a metallic iron-enriched dust and a filtrate, and recovering the separated metallic iron-enriched dust; A method for separating and recovering zinc and metallic iron.

[0012] [2] The method for separating and recovering zinc and metallic iron according to [1] above, wherein the diameter of the lower outlet of the hydrocyclone is adjusted to 7 mm or more and 12 mm or less.

[0013] [3] The method for separating and recovering zinc and metallic iron according to [1] or [2], wherein in the oxidation-reduction potential adjustment step, the oxidation-reduction potential of the steelmaking dust slurry is adjusted to an oxidation-reduction potential that causes hematite to form on the surface of the iron dust. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a method for recovering zinc and metallic iron while separating zinc from steelmaking dust using a small amount of chemicals. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a flowchart of a method for separating and recovering zinc and metallic iron according to the present invention. [Figure 2] FIG. 1 is a schematic diagram of a typical hydrocyclone. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 shows a flowchart of a method for separating and recovering zinc and metallic iron according to the present invention. The method for separating and recovering zinc and metallic iron according to the present invention is a method for separating and recovering zinc and metallic iron from steelmaking dust containing zinc dust and iron dust, and includes a wet separation step of causing a steelmaking dust slurry containing the steelmaking dust to flow into a hydrocyclone, separating the steelmaking dust slurry into a metallic iron-diluted dust slurry in which the concentrations of metallic iron and the steelmaking dust are diluted, and a metallic iron-enriched dust slurry in which the concentrations of metallic iron and the steelmaking dust are concentrated, and recovering the metallic iron-diluted dust slurry from the upper outlet of the hydrocyclone and the metallic iron-enriched dust slurry from the lower outlet of the hydrocyclone, respectively; and a step of adding an oxidizing agent to the diluted slurry to adjust the oxidation-reduction potential. a zinc leaching step of adjusting the pH of the adjusted zinc-containing dust slurry, the oxidation-reduction potential of which has been adjusted in the oxidation-reduction potential adjusting step, to leach zinc and obtain a zinc leach solution and a zinc leach residue; a first solid-liquid separation step of performing solid-liquid separation into the zinc leach solution and the zinc leach residue; a zinc precipitation step of adjusting the pH of the separated zinc leach solution to precipitate zinc as a zinc precipitate; a second solid-liquid separation step of performing solid-liquid separation of the pH-adjusted zinc leach solution into a zinc precipitate and a filtrate and recovering the separated zinc precipitate; and a third solid-liquid separation step of performing solid-liquid separation of the metallic iron-enriched dust slurry into a metallic iron-enriched dust and a filtrate and recovering the separated metallic iron-enriched dust.

[0017] <Wet separation process> First, in step S1, a steelmaking dust slurry containing steelmaking dust is introduced into a hydrocyclone, and the steelmaking dust slurry is separated into a metallic iron-diluted dust slurry in which the metallic iron and steelmaking dust concentrations have been diluted (increased), and a metallic iron-enriched dust slurry in which the metallic iron and steelmaking dust concentrations have been concentrated (increased), and the metallic iron-diluted dust slurry is recovered from the upper outlet of the hydrocyclone, and the metallic iron-enriched dust slurry is recovered from the lower outlet of the hydrocyclone (wet separation step).

[0018] The steelmaking dust to be treated includes zinc dust and iron dust. Examples of steelmaking dust include converter dust and electric furnace dust. Steelmaking dust is usually recovered as a slurry using a scrubber or the like, so the steelmaking dust can be directly introduced into the hydrocyclone.

[0019] Figure 2 shows a schematic diagram of a typical hydrocyclone. As shown in Figure 2, the hydrocyclone has an inlet (inlet) for the steelmaking dust slurry on the upper side of the device, and outlets (outlets) for the separated dust at both the top and bottom of the device. In this process, the centrifugal force acting on the steelmaking dust slurry as it flows into the hydrocyclone is used to preferentially concentrate and separate metallic iron, which has high density and particle size, at the lower outlet of the hydrocyclone. In this process, although zinc has a low particle size as an element, most of it is chemically bound to iron, making it almost impossible to preferentially concentrate and separate it at the upper outlet of the hydrocyclone.

[0020] The diameter of the lower outlet of the hydrocyclone significantly affects the separation behavior of the steelmaking dust slurry. The smaller the diameter of the lower outlet, the more concentrated metallic iron can be at the lower outlet, and the greater the mass fraction of zinc recoverable at the upper outlet. However, if the diameter of the lower outlet is too small, not only will the passage for the metallic iron-enriched dust slurry become narrower, but the dust concentration will also increase, potentially causing the metallic iron-enriched dust slurry to clog the passage. Therefore, it is desirable for the diameter of the lower outlet to be 7 mm or greater. On the other hand, if the diameter of the lower outlet is too large, it will be difficult to concentrate metallic iron at the lower outlet, and the mass fraction of zinc recoverable at the upper outlet will also be reduced. Therefore, it is desirable for the diameter of the lower outlet to be 12 mm or less.

[0021] If the subsequent oxidation-reduction potential adjustment process is carried out without going through this wet separation process, metallic iron, which is contained in the steelmaking dust at a rate of about 5 to 20 mass %, will not be separated in advance, and therefore the oxidizing agent will be consumed in the oxidation of metallic iron, and the amount of metallic iron that can be recycled within the steelworks will decrease, making this uneconomical.

[0022] <Oxidation-reduction potential adjustment step> Next, in step S2, an oxidizing agent is added to the metallic iron diluted dust slurry separated and recovered in the wet separation step to adjust the oxidation-reduction potential (oxidation-reduction potential adjustment step).

[0023] In this process, an oxidizing agent is added to adjust the redox potential of the diluted metallic iron dust slurry. More specifically, the redox potential of the diluted metallic iron dust slurry is increased. The oxidizing agent added for this purpose can be any of hydrogen peroxide, hypochlorous acid, ozone, air, etc., but from the viewpoints of ease of handling and wastewater treatment, it is preferable to use hydrogen peroxide or air.

[0024] The oxidation-reduction potential of the diluted metallic iron dust slurry is preferably adjusted to a value that allows hematite to form on the surface of the iron dust. Specifically, when the pH is approximately 8 or higher and 11 or lower, the oxidation-reduction potential of the diluted metallic iron dust slurry is preferably set to -300 mV or higher, at which point magnetite or hematite predominates. This makes it easier to suppress the leaching of iron into the diluted metallic iron dust slurry. It is more preferable to increase the oxidation-reduction potential of the diluted metallic iron dust slurry to 280 mV or higher. This allows magnetite or hematite to be stably formed on the dust surface.

[0025] If acid is added in the subsequent zinc leaching step without increasing the redox potential of the water, the iron remaining on the dust surface and iron from iron compounds that are easily soluble in acid, such as wustite, will be leached along with the zinc. This not only results in excessive consumption of chemicals for iron leaching, but also reduces the zinc concentration of the zinc-enriched residue compared to the initial dust in the subsequent zinc precipitation step. The inclusion of iron reduces the value of the zinc as a raw material, making it uneconomical.

[0026] <Zinc leaching process> Next, in step S3, the pH of the adjusted zinc-containing dust slurry whose oxidation-reduction potential has been adjusted in the oxidation-reduction potential adjusting step is adjusted to leach zinc, thereby obtaining a zinc leachate and a zinc leach residue (zinc leaching step).

[0027] The pH of the adjusted zinc-containing dust slurry can be adjusted by adding an acid to the adjusted zinc-containing dust slurry. The acid to be added can be any of inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids such as citric acid and butyric acid. Among them, sulfuric acid is preferably used as the acid from the viewpoint of cost and wastewater treatment.

[0028] In this step, it is preferable to adjust the pH of the adjusted zinc-containing dust slurry to 3 or more and 5 or less. By adjusting the pH of the adjusted zinc-containing dust slurry to 3 or more, it is possible to suppress leaching of iron into the slurry regardless of the form of the compound. Furthermore, by adjusting the pH of the adjusted zinc-containing dust slurry to 5 or less, it is possible to increase the leaching rate of zinc.

[0029] Furthermore, the reaction time after adding the acid to the adjusted zinc-containing dust slurry is preferably 20 minutes or more and 120 minutes or less from the viewpoint of the zinc leaching rate and treatment efficiency.

[0030] <First solid-liquid separation step> Subsequently, in step S4, solid-liquid separation is carried out into the zinc leaching solution obtained in the zinc leaching step and the zinc leaching residue (first solid-liquid separation step).

[0031] The solid-liquid separation can be carried out by any commonly used method, such as filtration, filter press, centrifugation, or gravity settling.

[0032] <Zinc precipitation process> Thereafter, in step S5, the pH of the separated zinc leachate is adjusted to precipitate zinc as a zinc precipitate (zinc precipitation step).

[0033] The pH of the zinc leaching solution can be adjusted by adding an alkali to the zinc leaching solution. Any common alkali, such as sodium hydroxide, calcium hydroxide, or potassium hydroxide, can be added. Because zinc is an amphoteric element and dissolves in both strong acids and strong alkalis, it is preferable to adjust the pH of the zinc leaching solution to between 8 and 10. This minimizes the solubility of zinc, allowing it to be precipitated and separated at a high precipitation rate, thereby increasing the zinc recovery rate.

[0034] <Second solid-liquid separation step> Subsequently, in step S6, the zinc leachate whose pH has been adjusted in the zinc precipitation step is subjected to solid-liquid separation into a zinc precipitate and a filtrate, and the separated zinc precipitate is recovered (second solid-liquid separation step).

[0035] In this step, the zinc precipitate is separated into a zinc precipitate and a filtrate from which zinc ions have been precipitated and removed, and the zinc precipitate is recovered. As with the first solid-liquid separation step, the solid-liquid separation method can be selected from any of the general methods, such as filtration, filter press, centrifugation, and gravity sedimentation.

[0036] <Third solid-liquid separation process> Then, in step S7, the metallic iron-enriched dust slurry separated and recovered in the wet separation step is subjected to solid-liquid separation into metallic iron-enriched dust and filtrate, and the separated metallic iron-enriched dust is recovered (third solid-liquid separation step).

[0037] In this step, the metallic iron-enriched dust slurry separated in the wet separation step is subjected to solid-liquid separation into a metallic iron-enriched dust and a filtrate from which the metallic iron-enriched dust has been removed, and the separated metallic iron-enriched dust is recovered. As in the first solid-liquid separation step, the solid-liquid separation method can be arbitrarily selected from common methods such as filtration, filter press, centrifugation, and gravity settling.

[0038] It should be noted that either the steps from the oxidation-reduction potential adjustment step to the second solid-liquid separation step or the third solid-liquid separation step may be carried out first and then the other, or both may be carried out simultaneously. [Example]

[0039] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0040] (Example 1) First, converter dust with a zinc concentration of 1 to 2 mass% and an iron concentration of 60 to 70 mass% was prepared as steelmaking dust. 30 L of distilled water was added to 6 kg of each converter dust to prepare converter dust slurry samples.

[0041] Next, a sample of the adjusted converter dust slurry was flowed into a hydrocyclone with a diameter of 7 mm at the lower outlet, and separated into a metallic iron-concentrated dust slurry and a metallic iron-diluted slurry. The metallic iron-diluted dust slurry was recovered from the upper outlet of the hydrocyclone, and the metallic iron-concentrated dust slurry was recovered from the lower outlet (wet separation step).

[0042] Subsequently, the metallic iron-enriched dust slurry separated and recovered in the wet separation step was subjected to solid-liquid separation into metallic iron-enriched dust and filtrate, and the metallic iron-enriched dust was recovered (third solid-liquid separation step).

[0043] In addition, hydrogen peroxide was added to the metallic iron diluted dust slurry separated and recovered in the wet separation process to increase the redox potential to 100 mV or higher (redox potential adjustment process). Then, sulfuric acid was added to the adjusted zinc-containing dust slurry with the adjusted redox potential, and the pH of the slurry was maintained at a constant pH of 3 for one hour (zinc leaching process). After one hour, the zinc leachate and zinc leach residue were separated by filtration (first solid-liquid separation process). Sodium hydroxide was added to the resulting zinc leachate to maintain the pH of the zinc leachate at a constant pH of 10 for one hour (zinc precipitation process). After one hour, the pH-adjusted zinc leachate was separated by filtration into a zinc precipitate and a filtrate, and the zinc precipitate was recovered (second solid-liquid separation process). Details of Example 1 are shown in Table 1. The metallic iron concentration in the recovered metallic iron-enriched dust and the zinc concentration in the zinc precipitate were analyzed by inductively coupled plasma (ICP) atomic emission spectroscopy. The pH of the slurry was controlled to be constant using a pH controller, and the oxidation-reduction potential of the slurry was measured using an oxidation-reduction potentiometer (ORP meter).

[0044] [Table 1]

[0045] (Example 2) Zinc and metallic iron were separated and recovered from steelmaking dust in the same manner as in Example 1. However, the diameter of the lower outlet of the hydrocyclone used in the wet separation process was 12 mm. All other conditions were the same as in Example 1. Details of Example 2 are shown in Table 1.

[0046] (Comparative Example 1) Zinc and metallic iron were separated and recovered from steelmaking dust in the same manner as in Example 1. However, the wet separation step and the third solid-liquid separation step were not performed, and the converter dust slurry was subjected to the oxidation-reduction potential step. All other conditions were the same as in Example 1. Details of Comparative Example 1 are shown in Table 1.

[0047] (Comparative Example 2) Zinc and metallic iron were separated and recovered from steelmaking dust in the same manner as in Example 1. However, the diameter of the lower outlet of the hydrocyclone used in the wet separation process was set to 5 mm. All other conditions were the same as in Example 1. Details of Comparative Example 2 are shown in Table 1.

[0048] (Comparative Example 3) Zinc and metallic iron were separated and recovered from steelmaking dust in the same manner as in Example 1. However, the diameter of the lower outlet of the hydrocyclone used in the wet separation process was 16 mm. All other conditions were the same as in Example 1. Details of Comparative Example 3 are shown in Table 1.

[0049] Comparative Example 4 Zinc and metallic iron were separated and recovered from steelmaking dust in the same manner as in Example 1. However, the oxidation-reduction potential adjustment step was not performed, and sulfuric acid was added to the diluted metallic iron dust slurry in the zinc leaching step. All other conditions were the same as in Example 1. Details of Comparative Example 4 are shown in Table 1.

[0050] (Comparative Example 5) Zinc and metallic iron were separated and recovered from steelmaking dust in the same manner as in Example 1. However, the oxidation-reduction potential adjustment step was not performed, and in the zinc leaching step, the same amounts of sulfuric acid and hydrogen peroxide as in Example 1 were simultaneously added to the diluted metallic iron dust slurry, and additional sulfuric acid was added as needed to maintain the pH at 3. All other conditions were the same as in Example 1. Details of Comparative Example 5 are shown in Table 1.

[0051] Referring to Table 1, Examples 1 and 2 consumed less chemicals and had a higher metallic iron recovery rate than Comparative Example 1. On the other hand, Comparative Example 1 used chemical treatment without prior separation and recovery of metallic iron using a hydrocyclone. This resulted in excessive consumption of hydrogen peroxide for metallic iron oxidation, presumably resulting in a lower metallic iron recovery rate. In Comparative Example 2, the diameter of the lower outlet of the hydrocyclone was too small compared to Examples 1 and 2, causing clogging of the metallic iron-enriched dust slurry and preventing recovery. In Comparative Example 3, the diameter of the lower outlet of the hydrocyclone was too large compared to Examples 1 and 2, resulting in poor classification accuracy of the hydrocyclone and insufficient concentration of metallic iron at the lower outlet, presumably resulting in a lower metallic iron recovery rate. Comparative Example 4 consumed more chemicals and had a lower zinc concentration level compared to Examples 1 and 2. In Comparative Example 4, the oxidation-reduction potential was not adjusted, and the pH of the water after acid addition was lowered to 3 while the dust slurry still contained a large amount of metallic iron and wüstite. This is thought to have resulted in some iron leaching, and the iron leached during alkali addition precipitated together with zinc, resulting in a lower zinc concentration in the zinc-enriched residue relative to the initial dust. In Comparative Example 5, the oxidation-reduction potential was not adjusted, and the pH of the water after acid addition was lowered to 3 while the dust slurry still contained a portion of metallic iron and wüstite. This is thought to have resulted in some iron leaching, and the iron surface was newly exposed by the leaching, so oxidation of the iron surface could not keep up, and iron continued to leach, as in Comparative Example 4. The iron leached during alkali addition precipitated together with zinc, resulting in a lower zinc concentration in the zinc-enriched residue relative to the initial dust. [Industrial Applicability]

[0052] According to the present invention, it is possible to provide a method for recovering zinc and metallic iron while separating zinc from steelmaking dust using a small amount of chemicals.

Claims

1. A method for separating and recovering zinc and metallic iron from steelmaking dust containing zinc dust and iron dust, comprising: a wet separation step of causing a steelmaking dust slurry containing the steelmaking dust to flow into a hydrocyclone, separating the steelmaking dust slurry into a metallic iron-diluted dust slurry in which the concentrations of the metallic iron and the steelmaking dust are diluted, and a metallic iron-enriched dust slurry in which the concentrations of the metallic iron and the steelmaking dust are concentrated, and recovering the metallic iron-diluted dust slurry from an upper outlet of the hydrocyclone and the metallic iron-enriched dust slurry from a lower outlet of the hydrocyclone, respectively; an oxidation-reduction potential adjusting step of adjusting the oxidation-reduction potential by adding an oxidizing agent to the diluted metallic iron dust slurry; a zinc leaching step of adjusting the pH of the adjusted zinc-containing dust slurry whose oxidation-reduction potential has been adjusted in the oxidation-reduction potential adjusting step to leach zinc, thereby obtaining a zinc leach solution and a zinc leach residue; a first solid-liquid separation step of separating the zinc leaching solution and the zinc leaching residue into solid-liquid phases; a zinc precipitation step of adjusting the pH of the separated zinc leach solution to precipitate zinc as a zinc precipitate; a second solid-liquid separation step of separating the pH-adjusted zinc leachate into a zinc precipitate and a filtrate, and recovering the separated zinc precipitate; a third solid-liquid separation step of separating the metallic iron-enriched dust slurry into a metallic iron-enriched dust and a filtrate, and recovering the separated metallic iron-enriched dust; A method for separating and recovering zinc and metallic iron.

2. 2. The method for separating and recovering zinc and metallic iron according to claim 1, wherein the diameter of the lower outlet of the hydrocyclone is adjusted to 7 mm or more and 12 mm or less.

3. 3. The method for separating and recovering zinc and metallic iron according to claim 1, wherein the oxidation-reduction potential of the steelmaking dust slurry is adjusted to an oxidation-reduction potential that causes hematite to form on the surface of the iron dust in the oxidation-reduction potential adjustment step.

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