Method for separating and recovering zinc

Abstract

To provide a method for separating zinc in zinc-containing dust with high selectivity using a small amount of chemical agent.SOLUTION: A method for separating and recovering zinc from zinc-containing dust comprising zinc dust and iron dust includes: an oxidation-reduction potential adjustment step of adding an oxidizing agent to zinc-containing dust slurry to adjust oxidation-reduction potential; 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 adjustment step to leach zinc, thereby obtaining a zinc leachate and a zinc leaching residue; a first solid-liquid separation step of separating the zinc leachate and the zinc leaching residue; a zinc precipitation step of adjusting the pH of the separated zinc leachate to precipitate zinc as a zinc sediment; and a second solid-liquid separation step of recovering the precipitated zinc sediment.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[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, so it is a promising recycling source for the ironmaking process. However, if the entire amount of zinc-containing dust is recycled, zinc will continue to circulate within the ironworks, resulting in the accumulation of only zinc derived from raw materials. When the accumulation amount becomes excessive, it causes operating troubles in the blast furnace. Therefore, it is necessary to separate zinc in advance when recycling zinc-containing dust.

[0003] As a zinc separation technology from zinc-containing dust, Patent Document 1 discloses a method in which steelmaking dust containing zinc is brought into contact and mixed with water while blowing air into a reaction vessel and stirring, the hydrogen ion concentration of the water is adjusted from pH 3 to 6 to leach the zinc content in the dust into the solution side, then the water in which zinc is dissolved and the iron-containing dust are separated, and subsequently the hydrogen ion concentration of the water in which zinc is dissolved is adjusted from pH 7 to 9 to precipitate and separate the zinc content.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the method described in Patent Document 1, the majority of the iron in the zinc-containing dust is in the form of readily acidic metallic iron or wustite, which reduces the hydrogen ion concentration of water to the acidic side. As a result, about 2-4% of the iron, which is the main component of the dust, leaches into the solution, and since hydrogen ions in water are consumed by the leaching of iron, the amount of acid added to control the hydrogen ion concentration of water increases significantly. In addition, when zinc is precipitated and separated, the iron that has leached into the solution also precipitates, which has the disadvantage of significantly reducing the purity of the recovered zinc.

[0006] This invention was developed in view of the above circumstances, and aims to provide a method for separating zinc from zinc-containing dust with a small amount of chemical agent and with good selectivity. [Means for solving the problem]

[0007] To solve the above problems, the inventors have conducted extensive research on methods for selectively separating zinc while reducing the amount of chemical agent used. As a result, they have conceived a technique that can improve zinc separation ability while suppressing the amount of acid consumed in dissolving iron by increasing the oxidation-reduction potential of a zinc-containing dust slurry containing zinc-containing dust in advance, thereby oxidizing the iron on the dust surface to convert it into acid-insoluble magnetite or hematite. The gist of this technique is as follows.

[0008] [1] A method for separating and recovering zinc from zinc-containing dust containing zinc dust and iron dust, A process of adjusting the oxidation-reduction potential by adding an oxidizing agent to a zinc-containing dust slurry containing the aforementioned zinc-containing dust, In the aforementioned oxidation-reduction potential adjustment step, the pH of the adjusted zinc-containing dust slurry whose oxidation-reduction potential has been adjusted is adjusted to leach zinc, and a zinc leaching step is performed to obtain a zinc leaching solution and a zinc leaching residue. A first solid-liquid separation step is performed to separate the zinc leachate and the zinc leachate residue into solid and liquid components. A zinc precipitation step involves adjusting the pH of the separated zinc leachate to precipitate zinc as a zinc precipitate, A second solid-liquid separation step involves separating the pH-adjusted zinc leach into a zinc precipitate and a filtrate, and recovering the separated zinc precipitate. A method for separating and recovering zinc having [a certain characteristic].

[0009] [2] The method for separating and recovering zinc according to [1], wherein in the oxidation-reduction potential adjustment step, the oxidation-reduction potential of the zinc-containing dust slurry is adjusted to an oxidation-reduction potential that causes hematite to form on the surface of the iron dust.

[0010] [3] The method for separating and recovering zinc according to [2], wherein in the oxidation-reduction potential adjustment step, the oxidation-reduction potential of the zinc-containing dust slurry is adjusted to 280 mV or higher.

[0011] [4] The method for separating and recovering zinc according to any one of the above [1] to [3], wherein in the zinc leaching step, the pH of the adjusted zinc-containing dust slurry is adjusted to 3 or more and 5 or less.

[0012] [5] The method for separating and recovering zinc according to any one of the above [1] to [4], wherein in the zinc precipitation step, the pH of the zinc leachate is adjusted to 8 or more and 11 or less.

[0013] [6] The method for separating and recovering zinc according to any one of the above [1] to [5], wherein the zinc-containing dust is steelmaking dust generated in the steelmaking process.

[0014] [7] The method for separating and recovering zinc according to any one of the above [1] to [6], wherein the zinc-containing dust is steelmaking dust generated in the steelmaking process. [Effects of the Invention]

[0015] According to the present invention, zinc in zinc-containing dust can be separated with a small amount of chemical agent and with good selectivity. [Brief explanation of the drawing]

[0016] [Figure 1] This is a flowchart of the zinc separation and recovery method according to the present invention.

Best Mode for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The zinc separation method according to the present invention is a method for separating and recovering zinc from zinc-containing dust containing zinc dust and iron dust, and includes an oxidation-reduction potential adjustment step of adding an oxidizing agent to a zinc-containing dust slurry containing zinc-containing dust to adjust the oxidation-reduction potential, 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 adjustment step to leach zinc and obtain a zinc leachate and zinc leach residue, a first solid-liquid separation step of performing solid-liquid separation on the zinc leachate and the zinc leach residue, a zinc precipitation step of adjusting the pH of the separated zinc leachate to precipitate zinc as a zinc precipitate, and a second solid-liquid separation step of performing solid-liquid separation on the zinc leachate with adjusted pH into a zinc precipitate and a filtrate and recovering the separated zinc precipitate.

[0018] <Oxidation-Reduction Potential Adjustment Step> FIG. 1 shows a flowchart of the zinc separation and recovery method according to the present invention. First, in step S1, an oxidizing agent is added to a zinc-containing dust slurry containing zinc-containing dust to adjust the oxidation-reduction potential (oxidation-reduction potential adjustment step).

[0019] The zinc-containing dust to be treated contains zinc dust and iron dust. Examples of the zinc-containing dust include iron-making dust such as blast furnace dust and rotary hearth furnace (RHF) dust, and steel-making dust such as converter dust and electric furnace dust. One or a combination of more than one of the above can be used as the zinc-containing dust.

[0020] In this step, the oxidation-reduction potential of the zinc-containing dust slurry is adjusted by adding an oxidizing agent. More specifically, the oxidation-reduction potential of the zinc-containing dust slurry is increased. As the oxidizing agent to be added for this purpose, hydrogen peroxide, hypochlorous acid, ozone, air, etc. are all applicable, but hydrogen peroxide and air are preferable from the viewpoints of ease of handling and wastewater treatment.

[0021] The redox potential of the zinc-containing dust slurry is preferably adjusted to the redox potential for forming hematite on the surface of the iron dust. Specifically, when the pH of the zinc-containing dust slurry is about 8 or more and 11 or less, the redox potential is preferably -300 mV or more at which the form of magnetite or hematite is dominant. This makes it easier to suppress the leaching of iron into the zinc-containing dust slurry. More preferably, the redox potential of the zinc-containing dust slurry is increased to 280 mV or more. Thereby, magnetite or hematite can be stably formed on the dust surface.

[0022] If an acid is added in the subsequent zinc leaching step without increasing the redox potential of water, iron derived from easily acid-soluble iron compounds such as metallic iron and wustite remaining on the dust surface will also leach out together with zinc. Furthermore, most of the zinc-containing dust is characterized by being composed of fine particles of 100 μm or less, and the specific surface area of easily acid-soluble iron compounds such as metallic iron and wustite is also large. Therefore, when an acid is added to the zinc-containing dust, the surface area of the newly exposed easily acid-soluble iron compound form due to iron leaching is also large, and the leaching of iron and the surface generation of easily acid-soluble iron compounds will continue in a chain reaction. Therefore, if an acid is added even a little first, even if the redox potential is increased later, (1) the control of the dust surface to a poorly soluble iron compound form and (2) the surface generation of easily acid-soluble iron compounds will compete, making it difficult to suppress iron leaching by making the entire dust surface into magnetite or hematite. As a result, not only is an extra amount of chemicals consumed for iron leaching and the control of the iron compound form on the dust surface, but the zinc concentration of the zinc concentration residue with respect to the initial dust in the subsequent zinc precipitation step is also significantly lowered, and the value as a zinc raw material decreases due to the mixing of iron, which is uneconomical.

[0023] <Zinc Leaching Step> Next, in step S2, the pH of the adjusted zinc-containing dust slurry whose redox potential has been adjusted in the redox potential adjustment step is adjusted to leach zinc, and a zinc leachate and a zinc leach residue are obtained (zinc leaching step).

[0024] The pH of a zinc-containing dust slurry can be adjusted by adding an acid to it. Any inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, or any organic acid such as citric acid or butyric acid, can be used as the added acid. Among these, sulfuric acid is preferred from the viewpoint of cost and wastewater treatment.

[0025] In this process, it is preferable to adjust the pH of the adjusted zinc-containing dust slurry to between 3 and 5. By setting the pH of the adjusted zinc-containing dust slurry to 3 or higher, the leaching of iron into the slurry can be suppressed regardless of the form of the compound. Furthermore, by setting the pH of the adjusted zinc-containing dust slurry to 5 or lower, the leaching rate of zinc can be increased.

[0026] Furthermore, the reaction time after adding the acid to the prepared zinc-containing dust slurry is preferably 20 minutes or more and 120 minutes or less, from the viewpoint of zinc leaching rate and processing efficiency.

[0027] <First solid-liquid separation step> Next, in step S3, the zinc leached solution and zinc leached residue obtained in the zinc leaching process are separated into solid and liquid components (first solid-liquid separation step).

[0028] The above solid-liquid separation can be carried out by arbitrarily selecting common methods such as filtration, filter pressing, centrifugal separation, and gravity sedimentation.

[0029] <Zinc precipitation process> Subsequently, in step S4, the pH of the separated zinc leachate is adjusted to precipitate the zinc as a zinc precipitate (zinc precipitation step).

[0030] The pH of the zinc leachate can be adjusted by adding an alkali to it. Any common alkali such as sodium hydroxide, calcium hydroxide, or potassium hydroxide can be selected as the alkali. Since zinc is an amphoteric element and dissolves in both strong acids and strong alkalis, it is preferable to adjust the pH of the zinc leachate to between 8 and 10. This minimizes the solubility of zinc, allowing it to precipitate and separate with a high sedimentation rate, thereby increasing the zinc recovery rate.

[0031] <Second solid-liquid separation step> Then, in step S5, the zinc leachate whose pH has been adjusted in the zinc precipitation step is subjected to solid-liquid separation into zinc precipitate and filtrate, and the separated zinc precipitate is recovered (second solid-liquid separation step).

[0032] In this process, the zinc precipitate is separated into a solid-liquid solution and a filtrate from which the zinc ions have been precipitated and removed, and the zinc precipitate is recovered. As with the first solid-liquid separation process, any common method such as filtration, filter pressing, centrifugal separation, or gravity sedimentation can be arbitrarily selected. [Examples]

[0033] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0034] (Examples 1-5 of the invention) As zinc-containing dust, converter dust with a zinc concentration of 1-2% by mass and an iron concentration of 60-70% by mass was prepared. 150 ml of distilled water was added to 30 g of each converter dust to prepare a sample of converter dust slurry. Next, hydrogen peroxide was added to the converter dust slurry to increase the oxidation-reduction potential to over 100 mV (oxidation-reduction potential adjustment step), then sulfuric acid was added, and the pH of the slurry was controlled to a constant level of 3 (Examples 1, 2, 4, and 5) or 5 (Example 3) for 1 hour (zinc leaching step). After 1 hour, the zinc leached solution and zinc leaching residue were separated by filtration (first solid-liquid separation step), and sodium hydroxide was added to the obtained zinc leached solution to control the pH of the zinc leached solution to a constant level of 8 (Example 4), 10 (Examples 1-3), or 11 (Example 5) for 1 hour (zinc precipitation step). After 1 hour, the pH-adjusted zinc leached solution was separated by filtration into zinc precipitate and filtrate (second solid-liquid separation step) to obtain the zinc precipitate. Details of each example are shown in Table 1. In Table 1, the concentrations of zinc and iron in the converter dust were analyzed by inductively coupled plasma (ICP) 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 ORP meter.

[0035] (Comparative Example 1) Zinc was recovered from zinc-containing dust in the same manner as in Invention Example 1. However, the oxidation-reduction potential adjustment step was omitted. Instead, sulfuric acid was added to the converter dust slurry to reduce the slurry's pH to 3, and then sulfuric acid and hydrogen peroxide were added to maintain the slurry's pH at a constant level of 3 for 1 hour. All other conditions were the same as in Invention Example 1.

[0036] (Comparative Example 2) Zinc was recovered from zinc-containing dust in the same manner as in Invention Example 1. However, during the zinc leaching process, the pH of the slurry was controlled to a constant level of 2 for 1 hour. All other conditions were the same as in Invention Example 1.

[0037] (Comparative Example 3) Zinc was recovered from zinc-containing dust in the same manner as in Invention Example 1. However, during the zinc leaching process, the pH of the slurry was controlled to a constant state of 6 for 1 hour. All other conditions were the same as in Invention Example 1.

[0038] (Comparative Example 4) Zinc was recovered from zinc-containing dust in the same manner as in Invention Example 1. However, during the zinc precipitation process, the pH of the slurry was controlled to a constant level of 7 for 1 hour. All other conditions were the same as in Invention Example 1.

[0039] (Comparative Example 5) Zinc was recovered from zinc-containing dust in the same manner as in Invention Example 1. However, during the zinc precipitation process, the pH of the slurry was controlled to a constant state of 12 for 1 hour. All other conditions were the same as in Invention Example 1.

[0040] [Table 1]

[0041] In Invention Examples 1 to 5, as shown in Table 1, the amount of chemicals consumed was less compared to Comparative Example 1, and the degree of zinc concentration of the zinc precipitate relative to the initial converter dust (i.e., the ratio of the zinc content of the zinc precipitate to the zinc content of the initial converter dust) was higher. The difference is particularly significant in Invention Examples 2 to 5, where the oxidation-reduction potential of the water before sulfuric acid addition was 280 mV or higher. In Comparative Example 1, sulfuric acid was added when the oxidation-reduction potential of the slurry was low, so some iron leached out and sulfuric acid was consumed excessively. Also, in the zinc precipitation process, the iron that leached out when sodium hydroxide was added precipitated together with the zinc, so sodium hydroxide was consumed excessively, and it is thought that the degree of zinc concentration of the zinc precipitate relative to the initial converter dust was also low.

[0042] Furthermore, in Invention Examples 1 to 5 described in Table 1, the degree of zinc concentration in the zinc precipitate relative to the initial converter dust is higher compared to Comparative Examples 2 to 5. In Comparative Example 2, the pH of the slurry after sulfuric acid addition was low at 2, so some iron leached out, and the leached iron precipitated together with the zinc when sodium hydroxide was added, resulting in excessive consumption of sulfuric acid. Also, it is thought that excessive sodium hydroxide was consumed in the zinc precipitation process, resulting in a lower degree of zinc concentration in the zinc precipitate relative to the initial converter dust. In Comparative Example 3, the pH of the slurry after sulfuric acid addition was high at 6, so the zinc leaching rate was low, and it is thought that the degree of zinc concentration in the zinc precipitate relative to the initial converter dust precipitated and recovered when sodium hydroxide was added was also low. In Comparative Example 4, the pH of the slurry when sodium hydroxide was added in the zinc precipitation process was low at 7, so it is thought that some zinc remained in the liquid when sodium hydroxide was added, resulting in a lower degree of zinc concentration in the zinc precipitate relative to the initial converter dust precipitated and recovered. In Comparative Example 5, the pH of the slurry was high at 11 when sodium hydroxide was added during the zinc precipitation process. As a result, some zinc remained in the liquid when sodium hydroxide was added, and it is thought that the degree of zinc concentration in the zinc precipitate relative to the initial converter dust that was precipitated and recovered was also low. [Industrial applicability]

[0043] According to the present invention, zinc in zinc-containing dust can be separated with a small amount of chemical agent and with good selectivity.

Claims

1. A method for separating and recovering zinc from zinc-containing dust that contains zinc dust and iron dust, A redox potential adjustment step is performed by adding an oxidizing agent to a zinc-containing dust slurry containing the aforementioned zinc-containing dust to adjust the redox potential to 119 mV or higher. Following the oxidation-reduction potential adjustment step, a zinc leaching step is performed to adjust the pH of the adjusted zinc-containing dust slurry, whose oxidation-reduction potential has been adjusted in the oxidation-reduction potential adjustment step, to 3 or more and 5 or less to leach zinc, thereby obtaining a zinc leaching solution and a zinc leaching residue. A first solid-liquid separation step is performed to separate the zinc leachate and the zinc leachate residue into solid and liquid components. A zinc precipitation step is performed to adjust the pH of the separated zinc leachate to 8 or more and 11 or less to precipitate zinc as a zinc precipitate, A second solid-liquid separation step involves separating the pH-adjusted zinc leach into a zinc precipitate and a filtrate, and recovering the separated zinc precipitate. It has, A method for separating and recovering zinc, wherein the zinc-containing dust is converter dust.

2. The method for separating and recovering zinc according to claim 1, wherein in the oxidation-reduction potential adjustment step, the oxidation-reduction potential of the zinc-containing dust slurry is adjusted to 280 mV or more.

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