Zinc collection method

Abstract

To provide a new method in which zinc is collected from a steelmaking dust.SOLUTION: Halogen is removed from a steelmaking dust including zinc and halogen by washing the dust using a cleaning solution. A zinc solution containing the zinc and iron is obtained by dissolving the washed steelmaking dust using an acid. An impurity element contained in the zinc solution is deposited on the surface of the zinc metal by adding the zinc metal to the zinc solution. The iron contained in the zinc solution is deposited as an iron deposit. By electrolyzing the zinc solution with an electrode inside, the zinc contained in the zinc solution is deposited on the surface of the electrode.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for recovering zinc.

Background Art

[0002] Fine powders generated in the iron-making process are recovered as iron-making dust using a collecting device such as a dust collector. Since iron-making dust contains a large amount of zinc, it has attracted attention as a resource, and conventionally, methods for recovering zinc from iron-making dust have been proposed (Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventors of the present invention examined a method for recovering zinc from iron-making dust by dissolving the iron-making dust using an acid, placing a cathode (aluminum electrode) and an anode (lead electrode) in the obtained zinc solution, and electrolyzing to deposit zinc on the cathode surface.

[0005] As a result, it was found that iron-making dust contains a large amount of halogen (fluorine, chlorine, etc.), and this halogen can cause various problems. For example, fluorine (F) corrodes the cathode surface, causes adhesion between the cathode surface and the deposited zinc, and makes it difficult to peel the deposited zinc from the cathode surface. In addition, chlorine (Cl) corrodes the anode (lead electrode), causes contamination of lead into the zinc solution (and thus the deposited zinc), and reduces the purity of the recovered zinc.

[0006] The present invention has been made in view of the above points, and an object thereof is to provide a novel method for recovering zinc from iron-making dust.

Means for Solving the Problems

[0007] As a result of intensive studies, the present inventors have found that the above object can be achieved by adopting the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to

[10] . [1] A method for recovering zinc, comprising: washing iron-making dust containing zinc and halogen with a washing liquid to remove the halogen; dissolving the washed iron-making dust with an acid to obtain a zinc solution containing zinc and iron; adding metallic zinc to the zinc solution to deposit impurity elements contained in the zinc solution on the surface of the metallic zinc; depositing iron contained in the zinc solution as an iron precipitate; and electrolyzing the zinc solution by inserting an electrode therein to deposit zinc contained in the zinc solution on the surface of the electrode. [2] The zinc recovery method according to [1], wherein the temperature of the washing liquid is 50°C or higher. [3] The zinc recovery method according to [1] or [2], wherein the washing liquid is alkaline. [4] The zinc recovery method according to any one of [1] to [3], wherein the iron-making dust is secondary dust obtained by reducing primary dust recovered from an iron-making furnace. [5] The zinc recovery method according to any one of [1] to [3], wherein the iron-making dust is electric furnace dust. [6] The zinc recovery method according to any one of [1] to [5], wherein the mass ratio of the iron-making dust to the washing liquid (iron-making dust / washing liquid) is 1 / 100 to 1 / 1. [7] The zinc recovery method according to any one of [1] to [6], wherein the addition amount of the metallic zinc is 1 to 10 g / L with respect to the zinc solution. [8] The zinc recovery method according to any one of [1] to [7], wherein when adding the metallic zinc, the pH of the zinc solution is adjusted to 2.5 to 6.5. [9] The number of times of adding the metallic zinc to the zinc solution to precipitate the impurity elements is 2 or more, and the zinc recovery method according to any one of [1] to [8] above.

[10] By precipitating iron hydroxide as the iron precipitate and separating the precipitated iron hydroxide from the zinc solution, the iron contained in the zinc solution is removed, and the zinc recovery method according to any one of [1] to [9] above.

Effects of the Invention

[0008] According to the present invention, a novel method for recovering zinc from iron-making dust can be provided.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0010] [Zinc Recovery Method] The zinc recovery method of this embodiment will be described with reference to FIG. 1. FIG. 1 is a flowchart showing the flow of the zinc recovery method.

[0011] 〈Preparation of Iron-Making Dust〉 First, prepare iron-making dust that is the target for recovering zinc. The iron-making dust is dust recovered by using a collecting device such as a dust collector for fine powder generated in an iron-making process using an iron-making furnace such as a blast furnace. Examples of the iron-making dust include blast furnace dust recovered from a blast furnace; converter dust recovered from a converter; electric furnace dust recovered from an electric furnace; secondary dust obtained by reducing the iron-making dust (primary dust) recovered from these iron-making furnaces using a reduction furnace; and the like.

[0012] 《Component Composition of Iron-Making Dust Before Cleaning》 The iron-making dust contains iron (Fe) and also contains zinc (Zn). For example, in an electric furnace, iron scrap or the like is melted to produce molten iron. Since the iron scrap contains zinc plating, the electric furnace dust contains a large amount of zinc derived therefrom.

[0013] The iron-making dust further contains halogens such as fluorine (F) and chlorine (Cl). Since the iron-making dust has a high halogen content, it can cause the above-mentioned problems.

[0014] (F content of the iron-making dust before washing) The fluorine (F) content of the iron-making dust before washing is, for example, 0.050 mass% or more, preferably 0.080 mass% or more, more preferably 0.110 mass% or more, still more preferably 0.140 mass% or more, and particularly preferably 0.170 mass% or more. The upper limit is not particularly limited. However, the F content of the iron-making dust before washing is, for example, 0.400 mass% or less, and may be 0.300 mass% or less.

[0015] (Cl content of the iron-making dust before washing) The chlorine (Cl) content of the iron-making dust before washing is, for example, 0.400 mass% or more, preferably 0.600 mass% or more, more preferably 0.800 mass% or more, still more preferably 1.000 mass% or more, and particularly preferably 1.200 mass% or more. The upper limit is not particularly limited. However, the F content of the iron-making dust before washing is, for example, 4.500 mass% or less, and may be 3.500 mass% or less.

[0016] In addition, for the component compositions of solids such as iron-making dust and liquids such as the zinc solution described later, unless otherwise specified, metal elements are quantified using ICP-OES (inductively coupled plasma optical emission spectrometry), and elements such as fluorine and chlorine are determined using ion chromatography (combustion ion chromatography when the object is a solid) (the same applies hereinafter).

[0017] In this embodiment, it is preferable to use only iron-making dust as the object (zinc source) for recovering zinc. That is, in this embodiment, it is preferable to subject only iron-making dust to the washing described later without using zinc ores such as sphalerite and heteropolarite; mixtures of zinc ores and iron-making dust; and the like.

[0018] 〈Washing of Iron-Making Dust: Removal of Halogens〉 In this embodiment, the above-described iron-making dust is washed with a washing liquid. Thereby, halogens (such as F and Cl) are removed from the iron-making dust, so that the halogen content of the obtained zinc solution is reduced, and the occurrence of the above-described problems can be suppressed.

[0019] 《Mode of Washing》 As the washing liquid, for example, water or an aqueous solution is used. As a method of washing, for example, a method of stirring a mixture (slurry) of iron-making dust and a washing liquid and then separating the iron-making dust from the slurry can be mentioned. In this case, the stirring time is, for example, 0.5 to 10 hours, but is not limited thereto, and is appropriately adjusted according to the washing effect and the like. The method of separating the iron-making dust from the slurry (solid-liquid separation) after stirring is not particularly limited, and a conventionally known method (for example, filtration) can be adopted. The separated iron-making dust may be further rinsed with a washing liquid.

[0020] 《Temperature of Washing Liquid》 The temperature of the washing liquid is, for example, normal temperature (5 to 35°C). However, for the reason that the washing effect is more excellent, the temperature of the washing liquid is preferably 40°C or higher, more preferably 50°C or higher, and still more preferably 60°C or higher. On the other hand, from the viewpoint of suppressing the energy required for maintaining the temperature, the temperature of the washing liquid is preferably 90°C or lower, more preferably 80°C or lower, and still more preferably 70°C or lower.

[0021] Note that the temperature of the cleaning liquid actually means the temperature of the cleaning liquid during cleaning. Therefore, when cleaning in the above-described manner (the manner of stirring the slurry), it actually means the temperature of the slurry. This also applies to the pH of the cleaning liquid described later.

[0022] 《pH of the Cleaning Liquid》 For the reason that the cleaning effect (especially the effect of removing F) is more excellent, the cleaning liquid is preferably alkaline. Specifically, the pH of the cleaning liquid is preferably more than 7.0, more preferably 8.0 or more, still more preferably 9.0 or more, particularly preferably 9.5 or more, and most preferably 10.0 or more. On the other hand, if the pH of the cleaning liquid is too high, not only the cost increases, but also zinc, which is an amphoteric metal, may dissolve in the cleaning liquid and cause loss. Therefore, the pH of the cleaning liquid is preferably 13.0 or less, more preferably 12.0 or less.

[0023] In this embodiment, for pH adjustment, for example, alkaline agents such as sodium hydroxide and calcium hydroxide; acidic agents such as dilute sulfuric acid and dilute hydrochloric acid; etc. are used (the same applies hereinafter).

[0024] Note that depending on the iron-making dust used, when the iron-making dust is mixed with the cleaning liquid, the pH of the cleaning liquid (slurry) may be high due to the calcium (Ca) component contained in the iron-making dust. In that case, it may not be necessary to further adjust the pH.

[0025] 《Mass Ratio (Iron-Making Dust / Cleaning Liquid)》 If the amount of the cleaning liquid relative to the iron-making dust is too small, it may be difficult to efficiently obtain the cleaning effect. On the other hand, if this amount is too large, for example, the total amount of the slurry during cleaning may become excessive, which may cause problems in handleability. Therefore, the mass ratio of the iron-making dust to the cleaning liquid (iron-making dust / cleaning liquid) is preferably 1 / 100 to 1 / 1, more preferably 1 / 60 to 1 / 2, still more preferably 1 / 40 to 1 / 3, particularly preferably 1 / 16 to 1 / 4, and most preferably 1 / 12 to 1 / 6.

[0026] "Component Composition of Ironmaking Dust after Washing" As described above, the halogen in the ironmaking dust is removed by washing, and the halogen content decreases.

[0027] (F Content of Ironmaking Dust after Washing) The fluorine (F) content of the ironmaking dust after washing is preferably 0.045% by mass or less, more preferably 0.040% by mass or less, still more preferably 0.030% by mass or less, and particularly preferably 0.025% by mass or less.

[0028] (Cl Content of Ironmaking Dust after Washing) The chlorine (Cl) content of the ironmaking dust after washing is preferably 0.012% by mass or less, more preferably 0.010% by mass or less, still more preferably 0.008% by mass or less, and particularly preferably 0.006% by mass or less.

[0029] 〈Dissolution of Ironmaking Dust: Obtaining Zinc Solution〉 Next, the ironmaking dust after washing is dissolved using an acid to obtain a zinc solution. The obtained zinc solution contains at least zinc (Zn) and iron (Fe) as elements leached from the ironmaking dust.

[0030] Examples of the acid include sulfuric acid, but it is not limited thereto, and known acids capable of dissolving ironmaking dust can be appropriately used.

[0031] The method of dissolution is not particularly limited. For example, a method of stirring a mixture (slurry) of ironmaking dust and an acid (e.g., sulfuric acid) and then separating the ironmaking dust from the slurry can be mentioned. In this case, the stirring time is, for example, 0.5 to 5 hours. The pH of the slurry is, for example, 2.5 or less, and may be 2.0 or less. The temperature of the slurry is, for example, 30 to 70°C, and may be 40 to 60°C. The mass ratio of ironmaking dust to acid (ironmaking dust / acid) is preferably 1.5 / 14 to 1.5 / 6, and more preferably 1.5 / 12 to 1.5 / 8. However, these conditions are just examples and can be changed as appropriate. The method for separating iron-making dust from the slurry after stirring (solid-liquid separation) is not particularly limited, and a conventionally known method (for example, filtration) can be adopted. When filtration is adopted, the filtrate is obtained as a zinc solution.

[0032] 《Composition of the zinc solution obtained by dissolving the iron-making dust after washing》 As described above, the zinc solution obtained by dissolving the iron-making dust after washing contains at least zinc (Zn). In addition, since the halogen has been removed from the iron-making dust after washing, the amount of halogen (F, Cl, etc.) is small.

[0033] (Zn concentration) The zinc (Zn) concentration of the zinc solution obtained by dissolving the iron-making dust after washing is preferably 50,000 to 150,000 mg / L, and more preferably 100,000 to 140,000 mg / L.

[0034] (F concentration) The fluorine (F) concentration of the zinc solution obtained by dissolving the iron-making dust after washing is preferably 80 mg / L or less, more preferably 60 mg / L or less, still more preferably 40 mg / L or less, and particularly preferably 25 mg / L or less.

[0035] (Cl concentration) The chlorine (Cl) concentration of the zinc solution obtained by dissolving the iron-making dust after washing is preferably 100 mg / L or less, more preferably 80 mg / L or less, still more preferably 60 mg / L or less, and particularly preferably 40 mg / L or less.

[0036] 〈Addition of metallic zinc: precipitation of impurity elements〉 Next, metallic zinc is added to the zinc solution. As the metallic zinc, for example, zinc powder, zinc granules, zinc plates, etc. are used. Thereby, the impurity elements contained in the zinc solution are precipitated on the surface of the added metallic zinc by utilizing the ionization tendency. This is also referred to as "cementation".

[0037] Here, the impurity elements are basically elements with a lower ionization tendency than zinc (Zn), such as nickel (Ni), tin (Sn), lead (Pb), copper (Cu), etc. That is, by adding metallic zinc to a zinc solution, the ions of the impurity elements (elements with a lower ionization tendency than zinc) contained in the zinc solution are reduced and deposited on the surface of the metallic zinc. Instead, a part of the metallic zinc is ionized (dissolved) and released into the zinc solution. Thereafter, the metallic zinc with the impurity elements deposited on its surface is separated from the zinc solution (solid-liquid separation). The method of solid-liquid separation is not particularly limited, and a conventionally known method (for example, filtration) can be adopted. In this way, at least a part of the impurity elements contained in the zinc solution is removed.

[0038] 《pH of the Zinc Solution When Adding Metallic Zinc》 When adding metallic zinc, it is preferable to adjust the pH of the zinc solution. At this time, if the pH of the zinc solution is too high, it may be difficult to obtain the effect of depositing the impurity elements. Therefore, the pH of the zinc solution is preferably 6.5 or less, more preferably 5.0 or less, and still more preferably 4.5 or less. On the other hand, if the pH of the zinc solution is too low, the dissolution of the added metallic zinc becomes dominant, and again, it is difficult to obtain the effect of depositing the impurity elements. Therefore, the pH of the zinc solution is preferably 2.5 or more, more preferably 3.0 or more, and still more preferably 3.5 or more.

[0039] 《Temperature of the Zinc Solution When Adding Metallic Zinc》 From the viewpoint of promoting the effect of depositing the impurity elements, when adding metallic zinc, the temperature of the zinc solution is preferably 20°C or higher, more preferably 30°C or higher, and still more preferably 40°C or higher. The upper limit is not particularly limited, for example, it can be 80°C or 70°C.

[0040] 《Addition Amount of Metallic Zinc》 If the amount of metallic zinc added to the zinc solution is too small, the entire amount of metallic zinc is likely to dissolve, and it may be difficult to obtain the effect of precipitating impurity elements. Therefore, the addition amount of metallic zinc is preferably 1 g / L or more, more preferably 3 g / L or more, based on the zinc solution. On the other hand, since metallic zinc is expensive, from the perspective of cost, the addition amount of metallic zinc is preferably 10 g / L or less, more preferably 8 g / L or less, still more preferably 6 g / L or less, based on the zinc solution.

[0041] 《Number of Additions》 The number of times of adding metallic zinc (including subsequent solid-liquid separation) is not limited to once, and from the perspective of sufficiently removing impurity elements, it is preferably 2 times or more, and may be 3 times or more.

[0042] 〈Precipitation of Iron Precipitate〉 Iron (Fe) contained in the zinc solution is an impurity element with a lower ionization tendency than zinc (Zn), but it cannot be sufficiently removed only by the addition of the above-mentioned metallic zinc and remains. Therefore, the iron remaining in the zinc solution is precipitated as an iron precipitate, and the precipitated iron precipitate is separated (solid-liquid separation). The method of solid-liquid separation is not particularly limited, and a conventionally known method (for example, filtration) can be adopted. In this way, the iron contained in the zinc solution is further removed.

[0043] The iron precipitate is, for example, iron hydroxide such as iron(III) hydroxide. As a method for precipitating iron hydroxide, a conventionally known method can be appropriately adopted. For example, referring to the potential-pH diagram, the pH and oxidation-reduction potential (ORP) of the zinc solution are adjusted and stirred. As a method for adjusting the oxidation-reduction potential, for example, a method of adding hydrogen peroxide can be mentioned. Thereby, only iron among zinc (Zn) and iron (Fe) contained in the zinc solution is precipitated.

[0044] 〈Electrolysis of Zinc Solution: Precipitation of Zinc〉 Next, electrodes (cathode and anode) are placed in a zinc solution from which impurity elements such as iron have been removed, and electrolysis is carried out. Thereby, zinc (Zn) contained in the zinc solution is deposited on the cathode surface.

[0045] The conditions of the electrodes are not particularly limited. For example, an aluminum electrode is used as the cathode, and a lead-silver electrode is used as the anode. When electrolyzing, the zinc solution may be diluted with water to adjust the zinc concentration to, for example, 50 - 80 g / L. The sulfuric acid concentration of the zinc solution is, for example, 150 - 200 g / L, and the temperature (liquid temperature) of the zinc solution is preferably 30 - 50 °C. Additives such as glue and gelatin may be added to the zinc solution. The electrolysis is carried out, for example, at a current density of 300 - 700 A / m 2 and is carried out as constant current electrolysis.

[0046] Thereafter, the deposited zinc (deposited zinc) is peeled off from the cathode surface. In this way, zinc can be recovered from the iron-making dust. At this time, as described above, since halogen (such as F and Cl) has been removed from the iron-making dust by washing in advance, the halogen concentration of the zinc solution obtained from the iron-making dust is also low. As a result, the occurrence of problems caused by halogen (such as the adhesion between the cathode surface and the deposited zinc, and the decrease in the purity of the deposited zinc) is suppressed.

Examples

[0047] Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples described below.

[0048] 〈Preparation of Iron-Making Dust〉 As the iron-making dust, dust A1, which is secondary dust obtained by reducing primary dust, was used. A part of the component composition of dust A1 is shown in Table 1 below.

[0049]

Table 1

[0050] 〈Washing of Iron Dust〉 Next, Dust A1 was washed using a cleaning solution. More specifically, first, Dust A1 and the cleaning solution were mixed at a mass ratio of 1 / 10 (Dust A1 / cleaning solution) to obtain a slurry. As the cleaning solution, water with no pH adjustment was used. The obtained slurry was stirred for 1 hour while controlling the temperature at 70°C. Then, Dust A1 was separated from the slurry by solid-liquid separation. The washing (the process from mixing to solid-liquid separation) was repeated 3 times. The component composition (only F and Cl) of Dust A1 after washing is shown in Table 2 below.

[0051]

Table 2

[0052] From the results shown in Table 1 and Table 2 above, it was found that by washing Dust A1, the halogen (F and Cl) content of Dust A1 decreased, indicating that halogen was removed from Dust A1. Also, it was found that by increasing the number of washing times, the effect of removing halogen increased.

[0053] Next, as cleaning solutions, in addition to the above-mentioned water with no pH adjustment (pH: 6.29), a plurality of types of alkaline aqueous solutions obtained by adding sodium hydroxide to water were used to wash Dust A1 under the same conditions (such as a temperature of 70°C) as above. As the component composition of the cleaning solution after washing, typically, the F concentration (unit: mg / L) was measured. The results are shown in Figure 2.

[0054] Figure 2 is a graph showing the relationship between the pH of the cleaning solution and the F concentration of the cleaning solution after washing. As shown in the graph of Figure 2, as the pH of the cleaning solution increased, the F concentration of the cleaning solution after washing increased, indicating that more halogen (such as F) was removed from Dust A1.

[0055] Based on the above results, the dust A1 was washed again. Specifically, using an alkaline aqueous solution with a pH of 11.0, the dust A1 and the cleaning solution were mixed at a mass ratio of 1 / 10 (dust A1 / cleaning solution), and the resulting slurry was stirred for 1 hour while controlling the temperature at 70°C. Then, the dust A1 was separated from the slurry by solid-liquid separation. The cleaning (the process from mixing to solid-liquid separation) was repeated 3 times.

[0056] 〈Dissolution of Iron Dust〉 Next, the washed dust A1 was dissolved using an acid (sulfuric acid) to obtain a zinc solution B1. Specifically, the dust A1 and sulfuric acid were mixed at a mass ratio of 1.5 / 10 (dust A1 / sulfuric acid), and the resulting slurry (pH: 1.9) was stirred for 1 hour while controlling the temperature at 50°C. Then, the residue of the dust A1 was separated by solid-liquid separation, and the filtrate was recovered as the zinc solution B1. The component composition (only F and Cl) of the zinc solution B1 is shown in Table 3 below.

[0057] For comparison, the component compositions of the zinc solutions B2 and B3 are also shown in Table 3 below. The zinc solution B2 is a zinc solution obtained by washing the dust A1 at room temperature (25°C) instead of 70°C and then dissolving the dust A1 with sulfuric acid in the same manner as the zinc solution B1. The zinc solution B3 is a zinc solution obtained by dissolving the dust A1 with sulfuric acid in the same manner as the zinc solution B1 without washing the dust A1.

[0058]

Table 3

[0059] As can be seen from the results shown in Table 3 above, it was found that in the zinc solutions B1 - B2 obtained from the washed dust A1, the halogens (F, Cl) could be reduced compared to the zinc solution B3 obtained from the unwashed dust A1.

[0060] 〈Addition of Metallic Zinc and Precipitation of Iron Precipitates〉 Next, metallic zinc was added to zinc solution B1 to perform cementation. Specifically, after adjusting the pH of zinc solution B1 to 4.0, while controlling the temperature of zinc solution B1 at 70°C, zinc powder was added as metallic zinc and stirred for 2 hours. The addition amount of metallic zinc was 5 g / L with respect to zinc solution B1. In this way, impurity elements such as lead (Pb) contained in zinc solution B1 were precipitated on the surface of the added metallic zinc (zinc powder). Then, the metallic zinc (zinc powder) on which the impurity elements had precipitated was separated from zinc solution B1 by solid-liquid separation. The addition of metallic zinc (including the subsequent solid-liquid separation) was repeated twice. A part of the component composition of zinc solution B1 after the addition of metallic zinc is shown in Table 4 below. Note that Table 4 also shows the component composition before the addition of metallic zinc.

[0061] Next, iron precipitates were precipitated in zinc solution B1. Specifically, after raising the pH of zinc solution B1 to 4.3, hydrogen peroxide was added. At this time, hydrogen peroxide was added until the oxidation-reduction potential measured using an ORP meter stopped rising. Then, it was stirred for 30 minutes to precipitate iron hydroxide as iron precipitates. Then, the iron precipitates (iron hydroxide) were separated from zinc solution B1 by solid-liquid separation. A part of the component composition of zinc solution B1 after the precipitation of iron precipitates (including the subsequent solid-liquid separation) is shown in Table 4 below.

[0062]

Table 4

[0063] As shown in Table 4 above, it was found that lead (Pb), tin (Sn), iron (Fe), etc. decreased due to the addition of metallic zinc and the precipitation of iron precipitates, and these impurity elements were removed from zinc solution B1. The increase in zinc is due to the fact that a part of the added metallic zinc (zinc powder) dissolved in the zinc solution B1 and eluted.

[0064] Based on the component composition of dust A1 (see Table 1) and the component composition of the zinc solution B1 before the addition of metallic zinc (see Table 3), the leaching rate of zinc was 98% by mass.

[0065] 〈Electrolysis of Zinc Solution〉 Next, electrodes (cathode and anode) were placed in the zinc solution B1 and electrolysis was carried out. Specifically, a zinc solution B1 diluted with pure water to adjust the zinc concentration to 65 g / L was used as the electrolyte and introduced into a 500 mL electrolytic cell. Plate-shaped electrodes (cathode and anode) with an effective electrode area of approximately 50 mm × 50 mm were placed therein. An aluminum electrode was used as the cathode, and a lead electrode (lead-silver electrode) added with 0.8% by mass of silver was used as the anode. The distance between the electrodes was 30 mm. Gelatin was added at an addition amount of 0.1 g / L, the liquid temperature was controlled at 40 °C, and constant-current electrolysis was continuously carried out at a current density of 500 A / m 2 for 24 hours. After 11 hours had elapsed since the start of electrolysis, half of the electrolyte was withdrawn and replaced with a zinc solution B1 adjusted to a zinc concentration of 130 g / L to maintain the zinc concentration of the electrolyte.

[0066] In this way, by carrying out continuous electrolysis for 24 hours, zinc was deposited on the surface of the cathode (aluminum electrode). Thereafter, the deposited zinc was peeled off from the cathode surface. At this time, excessive adhesion between the cathode surface and the deposited zinc was not observed, and the deposited zinc could be easily peeled off from the cathode surface and recovered. The mass of the recovered deposited zinc was 45.9 g. The current efficiency was 94%.

[0067] The recovered deposited zinc was qualitatively analyzed using ICP-MS to identify trace metal elements, and then quantitatively analyzed. The Zn content of the recovered deposited zinc was calculated by the difference method of subtracting the content of the detected trace metal elements from 100% by mass. The results are shown in Table 5 below.

[0068]

Table 5

[0069] As shown in Table 5 above, it was found that the Zn content of the recovered precipitated zinc was very high, and high-purity zinc could be recovered from only the iron-making dust (dust A1).

Claims

1. Subjecting iron-making dust containing zinc and halogen to washing with a washing liquid to remove the halogen, dissolving the washed iron-making dust using an acid to obtain a zinc solution containing zinc and iron, adding metallic zinc to the zinc solution to deposit impurity elements contained in the zinc solution on the surface of the metallic zinc, precipitating iron contained in the zinc solution as an iron precipitate, A zinc recovery method in which an electrode is inserted into the zinc solution and electrolyzed to deposit zinc contained in the zinc solution on the surface of the electrode.

2. The zinc recovery method according to Claim 1, wherein the temperature of the washing liquid is 50°C or higher.

3. The zinc recovery method according to Claim 1 or 2, wherein the washing liquid is alkaline.

4. The zinc recovery method according to Claim 1 or 2, wherein the iron-making dust is secondary dust obtained by reducing primary dust recovered from an iron-making furnace.

5. The zinc recovery method according to Claim 1 or 2, wherein the iron-making dust is electric furnace dust.

6. The zinc recovery method according to Claim 1 or 2, wherein the mass ratio of the iron-making dust to the washing liquid (iron-making dust / washing liquid) is 1 / 100 to 1 / 1.

7. The zinc recovery method according to Claim 1 or 2, wherein the addition amount of the metallic zinc is 1 to 10 g / L with respect to the zinc solution.

8. The zinc recovery method according to Claim 1 or 2, wherein when adding the metallic zinc, the pH of the zinc solution is adjusted to 2.5 to 6.

5.

9. The zinc recovery method according to Claim 1 or 2, wherein the number of times of adding the metallic zinc to the zinc solution to precipitate the impurity elements is 2 or more.

10. Precipitating iron hydroxide as the iron precipitate and separating the precipitated iron hydroxide from the zinc solution to remove iron contained in the zinc solution. The zinc recovery method according to Claim 1 or 2.

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