JP2017137578A - Method for separating zinc, method for producing zinc material, and method for producing iron material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for separating zinc from iron-making dust, a method for producing a zinc material, and a method for producing an iron material.SOLUTION: Provided is a method for separating zinc from iron-making dust comprising: a zinc leaching step (step S1) where acid is added to iron-making dust generated in an iron mill to control the pH of the acid including the iron-making dust to 1.0 or more, and zinc contained in the iron-making dust is leached into the acid; an iron precipitation step (step S2) where a first treatment liquid obtained in the zinc leaching step is added with a first alkali to precipitate iron; a first solid-liquid separation step (step S3) where a second treatment liquid obtained in the iron precipitation step is subjected to solid-liquid separation; a zinc precipitation step (step S4) where a third treatment liquid obtained in the first solid-liquid separation step is added with a second alkali to precipitate zinc; and a second solid-liquid separation step (step S5) where a fourth treatment liquid obtained in the zinc precipitation step is subjected to solid-liquid separation.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for separating zinc, a method for producing a zinc material, and a method for producing an iron material.

  A typical base metal, iron, is used in various industrial fields. Although iron has abundant resources compared to rare metals called rare metals, the balance between supply and demand is changing rapidly with the rise of emerging countries. As a result, high-quality iron ore resources are depleted and inferior quality ores are being used.

  In view of these circumstances, not only refining iron ore, but also attempts to recycle industrial waste and ironworks by-products composed of multi-component metals containing iron as iron sources. Yes. For example, ironmaking dust such as blast furnace dust, converter dust, and electric furnace dust contains iron, zinc, carbon, and the like, and is recycled as an ironmaking raw material. However, since the zinc in the ironmaking dust forms deposits in the blast furnace and adversely affects the operation of the blast furnace, the amount of ironmaking dust recycled has been limited.

  In order to solve the above problems, a technique for separating and recovering zinc from steelmaking dust is required, and such a technique is roughly classified into a dry method and a wet method. Here, the dry method is a technique in which iron-making dust is reduced at a high temperature, and zinc is volatilized and separated and recovered (see, for example, Patent Document 1).

  On the other hand, in the method for separating and recovering zinc by a wet method, after ironmaking dust is treated with an acid, it is neutralized with a magnesium-based alkali to recover zinc (see, for example, Patent Document 2). . Patent Document 3 describes a method of recovering zinc contained in a non-magnetized material with an alkali after separating the iron-treated dust treated with an acid into a magnetized material and a non-magnetized material.

JP 52-61108 A JP 7-216470 A JP 2010-001524 A

  In the separation and recovery of zinc by the dry method including Patent Document 1, a large-scale high-temperature reduction device is required, and it is not economically established with blast furnace dust or converter dust having a zinc content of about several percent. There was a problem.

  In addition, the zinc recovery method of Patent Document 2 requires the use of a magnesium-based alkali that is more expensive than sodium hydroxide or calcium hydroxide when recovering the leached zinc, which is problematic in terms of cost. .

  Furthermore, since the zinc recovery method of Patent Document 3 requires selection by magnetic force, the treatment process is complicated, and the chemical cost of sodium hydrosulfide is expensive, this method also has a problem in terms of cost. In addition, sodium hydrosulfide may generate hydrogen sulfide when used, and there is a problem in ensuring safety.

  Accordingly, an object of the present invention is to propose a zinc separation method, a zinc production method, and an iron material production method capable of separating zinc from iron-making dust simply and at low cost.

  The inventors of the present invention have intensively studied how to solve the above problems. As a result, in the zinc leaching step of leaching zinc into an acid, the pH of the acid containing ironmaking dust is adjusted to 1.0 or more, and the zinc leaching step and a zinc precipitation step of precipitating zinc leached into the acid In the meantime, it has been found that it is extremely effective to perform an iron precipitation step of precipitating iron, and the present invention has been completed.

The gist of the present invention is as follows.
(1) A zinc leaching step in which an acid is added to ironmaking dust generated at a steel mill to adjust the pH of the acid containing the ironmaking dust to 1.0 or more, and zinc contained in the ironmaking dust is leached into the acid. And an iron precipitation step of precipitating iron by adding a first alkali to the first treatment liquid obtained in the zinc leaching step, and a first liquid-solid separation of the second treatment liquid obtained in the iron precipitation step. A solid-liquid separation step, a zinc precipitation step in which zinc is precipitated by adding a second alkali to the third treatment liquid obtained in the first solid-liquid separation step, and a fourth treatment liquid obtained in the zinc precipitation step And a second solid-liquid separation step of solid-liquid separation.

(2) The zinc leaching step is performed by adjusting the pH of the acid containing the ironmaking dust to 2.0 or more and 3.0 or less. The method for separating zinc according to (1) above.

(3) The method for separating zinc according to (1) or (2), wherein a time for leaching zinc contained in the iron-making dust into the acid in the zinc leaching step is 15 minutes to 120 minutes.

(4) Any of the above (1) to (3), wherein the iron precipitation step is performed by adjusting the pH of the first treatment liquid to which the first alkali is added to 4.0 or more and 6.0 or less. The method for separating zinc according to one item.

(5) The iron precipitation step is performed by controlling an oxidation-reduction potential according to the pH of the first treatment liquid to which the first alkali is added. 2. The method for separating zinc described in 1.

(6) Any of the above (1) to (5), wherein the zinc precipitation step is performed by adjusting the pH of the third treatment liquid to which the second alkali is added to 8.0 or more and 12.0 or less. The method for separating zinc according to one item.

(7) The method further includes a first iron recovery step for recovering iron obtained in the first solid-liquid separation step, and / or a zinc recovery step for recovering zinc separated in the second solid-liquid separation step. The method for separating zinc according to any one of (1) to (6).

(8) The method further includes a third solid-liquid separation step for solid-liquid separation of the first treatment liquid between the zinc leaching step and the first solid-liquid separation step, wherein the iron precipitation step includes the third solid-liquid separation step. The method for separating zinc according to any one of (1) to (7), wherein iron contained in the fifth treatment liquid obtained in the liquid separation step is precipitated.

(9) The zinc separation method according to (8), further including a second iron recovery step of recovering iron obtained in the third solid-liquid separation step.

(10) A method for producing a zinc material, comprising separating and recovering zinc from iron-making dust by the zinc separation method according to any one of (1) to (9).

(11) A method for producing an iron material, wherein iron is separated and recovered from iron-making dust by the zinc separation method according to any one of (1) to (9).

  According to the present invention, zinc can be separated from iron-making dust easily and at low cost.

It is a figure which shows the flowchart of the separation method of zinc by one Embodiment of this invention. It is a figure which shows the observation image of the blast furnace dust by a scanning electron microscope, and elemental mapping of zinc and iron. It is a state diagram of the oxidation-reduction potential and pH of iron in an aqueous solution at 25 ° C. It is a phase diagram of the oxidation-reduction potential and pH of zinc in an aqueous solution at 25 ° C. It is a figure which shows the relationship between pH and the solubility of zinc. It is a figure which shows the flowchart of the separation method of zinc by another embodiment of this invention. It is a figure which shows the relationship between the pH of a sulfuric acid, and the leaching rate of iron and zinc. It is a figure which shows the ratio of the zinc compound before and behind sulfuric acid leaching. It is a figure which shows the relationship between leaching time and zinc leaching rate. It is a figure which shows the relationship between leaching time and an iron leaching rate. It is a figure which shows the flowchart of the separation method of zinc of a comparative example. It is a figure which shows the precipitation rate of iron and zinc in an iron precipitation process.

(Zinc separation method)
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a flowchart of a method for separating zinc according to an embodiment of the present invention. In the method for separating zinc according to the present invention, an acid is added to ironmaking dust generated at a steel mill to adjust the pH of the acid containing the ironmaking dust to 1.0 or more, and zinc contained in the ironmaking dust is converted into the acid. The zinc leaching step (step S1) to be leached, the iron precipitation step (step S2) for precipitating iron by adding the first alkali to the first treatment liquid obtained in the zinc leaching step, and the iron precipitation step. A first solid-liquid separation step (step S3) for solid-liquid separation of the obtained second treatment liquid, and a second alkali is added to the third treatment liquid obtained in the first solid-liquid separation step to precipitate zinc. It includes a zinc precipitation step (step S4) and a second solid-liquid separation step (step S5) for solid-liquid separation of the fourth treatment liquid obtained in the zinc precipitation step.

  The present inventors diligently studied a method for separating zinc contained in iron-making dust easily and at low cost. For that purpose, first, the zinc contained in the steelmaking dust was investigated in detail. FIG. 2 shows an observation image of blast furnace dust with a scanning electron microscope (SEM) and elemental mapping of zinc and iron. In this figure, the upper three images show blast furnace dust particles having a diameter of about 1 μm, and the lower three figures show blast furnace dust particles having a diameter of about 20 μm.

  From these figures, it can be seen that zinc is hardly present inside the blast furnace dust particles or blast furnace dust particles, and is concentrated and dispersed on the surface. Further, based on the method described in JP-A-10-267910, the dust was stirred in a mixed solution of iron (III) chloride solution and citric acid, and the dissolved zinc was quantified to determine the proportion of ZnO. As a result, it was found that about 70% of zinc exists as ZnO-type zinc oxide. This ZnO-type zinc oxide can be dissolved with a weak acid as compared with the case where zinc contained in ferrite is dissolved.

  As shown in the following examples, the zinc leaching rate increases with a decrease in the pH of the acid, reaches 70% at pH = 2, and almost all of the zinc oxide in the ZnO state is leached. Further, even when the pH is 1, the leaching rate does not increase and the zinc leaching rate is saturated at pH = 2. This tendency was the same for converter dust.

  In addition, as described above, in the technique described in Patent Document 2, when precipitating zinc leached into an acid, an acid is neutralized efficiently by adding an expensive magnesium-based alkali. Is precipitating. The present inventors diligently studied how to precipitate zinc efficiently without using an expensive alkali as described above. As a result, after the zinc leaching step, by performing an iron precipitation step of precipitating iron contained in the treatment liquid, an inexpensive alkali such as sodium hydroxide can be used in the subsequent zinc precipitation step, and zinc is reused as a resource. It has been found that separation can be performed at a concentration sufficient for use.

  That is, in the zinc leaching process, the purpose is to leach zinc into acid, but it is difficult to completely prevent iron leaching, and the first treatment liquid obtained by adding acid to ironmaking dust is used. Includes not only zinc ions but also iron ions. Therefore, following the zinc leaching step, the iron ions contained in the first treatment liquid are precipitated, thereby reducing the iron ion concentration contained in the third treatment liquid obtained in the first solid-liquid separation step. . As a result, since it is possible to suppress iron from being mixed into zinc precipitated in the subsequent zinc precipitation step, an inexpensive alkali such as sodium hydroxide can be used.

  In this way, the present inventors adjust the pH of an acid containing iron-making dust to 1.0 or more by adding acid to iron-making dust, and iron that precipitates iron between the zinc leaching step and the zinc precipitation step. The inventors have found that zinc can be separated easily and at low cost by performing the precipitation step, and the present invention has been completed. Hereinafter, each step will be described.

  First, in step S1, a zinc leaching step is performed in which an acid is added to ironmaking dust generated at a steelworks to adjust the pH of the acid containing the ironmaking dust to 1.0 or more, and zinc contained in the ironmaking dust is leached into the acid. I do. This step is a step of selectively leaching only zinc from an iron-making dust, which is a raw material containing iron and zinc, with an acid. At this time, it is important to selectively leach only zinc while suppressing iron leaching as much as possible.

  The iron-making dust in the present invention is iron-making dust generated from a blast furnace, converter, electric furnace or the like. Among them, it is preferable to use converter dust or blast furnace dust. Although the zinc content is as low as several mass%, about 70% of zinc dispersed on the iron surface exists as ZnO-type iron oxide, and as described above, the pH is weak at 2 or more. Although zinc can be leached with an acid, and the zinc content is low, the zinc content obtained in the zinc precipitation process should be of high purity that can be reused as a raw material. it can.

  Moreover, the acid used for the leaching of zinc is not particularly limited as long as zinc can be leached. For example, common acids such as hydrochloric acid, sulfuric acid, and nitric acid can be used.

  The pH of the acid during leaching is adjusted to 1.0 or higher. This is because, when the pH is less than 1.0, iron leaching increases and the amount of chemicals consumed increases, resulting in an increase in processing costs. Moreover, as shown in FIG. 7 of the Example mentioned later, the leaching rate of zinc does not increase even if the pH is saturated at 2.0 and falls below 2.0, and only the consumption of the drug increases. Therefore, the pH is preferably 2.0 or more. On the other hand, if the pH exceeds 5.0, zinc is difficult to leach out, so it is preferably 5.0 or less. Moreover, if it is 3.0 or less, a leaching rate will be about 60%, and zinc of sufficient density | concentration for reusing as a raw material can be leached. Therefore, it is particularly preferable to adjust the pH of the acid to 2.0 or more and 3.0 or less in terms of zinc leaching rate and processing cost. Moreover, the solid-liquid ratio of iron-making dust and moisture can be set to any ratio as long as uniform mixing is possible.

  The leaching time is preferably 15 minutes or longer and 120 minutes or shorter. Here, by setting the leaching time to 15 minutes or longer, zinc can be sufficiently leached. On the other hand, when the leaching time is 120 minutes or less, zinc leaching can be effectively performed while suppressing the amount of iron leaching. As shown in the examples below, a particularly suitable leaching time is not less than 30 minutes and not more than 90 minutes. In addition, about reaction temperature, it can set arbitrarily in the temperature range which water does not solidify or evaporate.

  Next, in step S2, an iron precipitation step is performed in which an alkali (first alkali) is added to the first treatment liquid obtained in the zinc leaching step to precipitate iron. The zinc leaching process in step S1 is intended to leach zinc into an acid, but it is difficult to prevent some iron from leaching. For this reason, the first treatment liquid contains iron ions in addition to zinc ions, the content of iron contained in the residue obtained by leaching zinc into the acid is reduced, and the recycling rate as an iron-making raw material is also reduced. In addition, when zinc is recovered by adding the first alkali to the first treatment liquid, not only zinc but also iron precipitates at the same time, so that the value as a zinc raw material is lowered due to the mixing of iron, which is also uneconomical. It is.

  Therefore, in the present invention, after the zinc leaching step, an iron precipitation step of precipitating iron contained in the first treatment liquid is performed. In this step, not only iron can be separated from the first treatment liquid, but also zinc can be precipitated using an inexpensive alkali such as sodium hydroxide in the subsequent zinc precipitation step as described above, Zinc with sufficient purity to be reused can be separated.

  As a result of intensive investigations on the conditions for precipitating and separating only iron from the first treatment liquid, the present inventors have determined that the first treatment liquid has a pH of 4.0 or more and 6.0 or less and an oxidative condition. It has been found that only iron leached in can be precipitated. Hereinafter, the details that have led to the above findings will be described.

  FIG. 3 shows a phase diagram of iron redox potential (ORP) and pH in an aqueous solution at 25 ° C. FIG. 4 shows a state diagram relating to zinc. Further, the shaded portion in FIG. 3 indicates a region where iron is precipitated, and the shaded portion in FIG. 4 indicates a region where zinc is precipitated.

  3 and 4, it can be seen that the region where iron precipitates and the region where zinc precipitates overlap to some extent, and zinc is precipitated in addition to iron except in the region surrounded by the thick line in FIG. 3. However, the inventors focused on the fact that there is a region where iron mainly precipitates in the region surrounded by the thick line in FIG. 3 where the pH is low and the ORP is in an oxidative condition. Then, it was conceived that only iron can be precipitated by adjusting the pH and ORP of the first treatment solution containing iron and zinc to the pH and ORP in the region surrounded by the thick line in FIG.

  The present inventors have further studied and found that a suitable pH of the first treatment liquid in the iron precipitation step is 4.0 or more and 6.0 or less. Here, iron can be efficiently precipitated by setting pH to 4.0 or more. Moreover, by setting the pH to 6.0 or less, only iron can be efficiently precipitated without precipitating zinc.

  As is clear from FIG. 3, the iron precipitation step is preferably performed by controlling the oxidation-reduction potential according to the pH of the first treatment liquid to which the first alkali is added. The iron in the first treatment liquid generally exists as divalent iron ions. On the other hand, in order to precipitate iron ions by adjusting the pH, the ORP of the leachate is increased (to make an oxidative atmosphere) Is necessary to make it trivalent.

  As a method for bringing the first treatment liquid into an oxidative atmosphere, any method can be selected in view of treatment costs such as air oxidation or addition of an oxidizing agent. Since the amount of air blown in the air oxidation and the optimum addition amount of the oxidizing agent vary depending on the pH of the first treatment liquid, it is possible to experimentally determine and specify an appropriate amount according to the pH of the first treatment liquid. preferable.

  Moreover, about the 1st alkali added to a 1st process liquid, common alkalis, such as calcium hydroxide and sodium hydroxide, can be used. Since such an alkali can be obtained at a low cost, the processing cost can be reduced.

  About reaction temperature, it can set arbitrarily in the temperature range which a 1st process liquid does not solidify or evaporate. About reaction time, it is preferable to set it as 15 minutes or more and 120 minutes or less in view of iron precipitation formation time and processing efficiency.

  Subsequently, in step S3, a first solid-liquid separation step of performing solid-liquid separation on the second treatment liquid obtained in the iron precipitation step is performed. This step is a step for solid-liquid separation of the filtrate mainly containing zinc ions, the zinc leaching residue in the zinc leaching step, and the solid content precipitated in the iron precipitation step (iron precipitate).

  The main component of the zinc leaching residue generated in the zinc leaching process is iron, and zinc has leached into the first treatment liquid, so that it can be reused as a raw material for iron making through the sintering process. Further, the solid content generated in the iron precipitation step also contains high-purity iron, and can be reused as a resource as an iron-making raw material through a sintering step, like the zinc leaching residue. Therefore, the separated iron can be reused as a resource by performing the first iron recovery step of recovering the iron (iron precipitate) separated in the first solid-liquid separation step.

  The solid-liquid separation method is not particularly limited, and for example, any method such as gravity sedimentation separation, filtration, centrifugation, or filter press can be selected.

  Next, in step S4, a zinc precipitation step is performed in which zinc is precipitated by adding a second alkali to the third treatment liquid obtained in the first solid-liquid separation step. This step is a step of adding zinc (second alkali) to the third treatment liquid, which is the filtrate obtained in the first solid-liquid separation step, to precipitate zinc.

  As described above, in the present invention, since the iron precipitation step is performed after the zinc leaching step and the precipitated iron is separated in the first solid-liquid separation step, the second alkali is calcium hydroxide, water. Common alkalis such as sodium oxide that are easily available can be used.

  About pH of a 3rd process liquid, it is preferable to set it as 8.0 or more and 12.0 or less. Here, zinc can be efficiently precipitated by setting the pH to 8.0 or more. In addition, by adjusting the pH to 12.0 or less, zinc can be precipitated without dissolving zinc once precipitated in the third treatment liquid again.

In addition, from the facts based on “New Pollution Prevention Technology and Regulations 2016 Water Quality-3 Technology”, Pollution Prevention Technology and Regulations Editorial Board, Industrial Management Association, the relationship between pH and Zn solubility. Is shown in FIG. As is apparent from FIG. 5, the amount of zinc present in the solution as Zn ²⁺ is the minimum near pH 9, while the amount of zinc present in the solution as HZnO ₂ ⁻ is gradually increased when the pH is 9 or more. Therefore, the pH particularly suitable for efficiently precipitating zinc is 9.0 or more and 11 or less.

  Further, the reaction temperature can be arbitrarily set in a temperature range where the third treatment liquid does not solidify or evaporate. Furthermore, the reaction time is preferably 15 minutes or longer and 120 minutes or shorter in view of the zinc precipitation time and the processing efficiency.

  Finally, in step S5, a second solid-liquid separation step for solid-liquid separation of the fourth treatment liquid obtained in the zinc precipitation step is performed. This step is a step for solid-liquid separation of the fourth treatment liquid and solid content (zinc precipitate) obtained in the zinc precipitation step. Similar to the first solid-liquid separation step, the solid-liquid separation method is not particularly limited, and for example, any method such as gravity sedimentation separation, filtration, centrifugation, and filter press can be selected.

  In this way, zinc can be separated from iron-making dust easily and at low cost. The separated zinc precipitate contains zinc at a high concentration of 40% or more, and is highly valuable as a zinc raw material. Therefore, by performing the zinc recovery step of recovering the zinc separated in the second solid-liquid separation step, it can be recycled as a zinc raw material through zinc smelting and the like.

  In the first solid-liquid separation step, the zinc leaching residue produced in the zinc leaching step and the solid matter produced in the iron precipitation step are simultaneously solid-liquid separated. As shown in FIG. 6, the zinc leaching step Thereafter, a third solid-liquid separation step (step S11) for solid-liquid separation of the zinc leaching residue is performed, and in the first solid-liquid separation step, only the solid content generated in the iron precipitation step is subjected to solid-liquid separation. May be. The solid-liquid separation method at that time is not particularly limited as in the case of the first solid-liquid separation step, and any method such as gravity sedimentation separation, filtration, centrifugation, filter press, or the like can be selected.

  When performing the third solid-liquid separation step, the second iron recovery step for recovering the iron (zinc leaching residue) obtained in the third solid-liquid separation step is performed to perform the sintering step on the zinc leaching residue. It can be reused as a resource as a steelmaking raw material.

(Manufacturing method of zinc material)
The method for producing a zinc material according to the present invention is characterized in that zinc is separated and recovered from iron-making dust by the above-described zinc separation method. Thereby, zinc contained in iron-making dust can be concentrated, and a zinc material having a zinc content of 40% or more can be manufactured. The manufactured zinc material is a solid material separated in the second solid-liquid separation step of the zinc separation method according to the present invention, for example, a material containing one or both of zinc hydroxide and zinc oxide. .

(Manufacturing method of iron material)
The method for producing an iron material according to the present invention is characterized in that iron is separated and recovered from iron-making dust by the zinc separation method. Thereby, all the iron contained in iron-making dust can be collect | recovered and recycled. The manufactured iron material is a solid material separated in the first or third solid-liquid separation step of the zinc separation method according to the present invention, and is, for example, any one of iron oxide, metallic iron, and iron hydroxide, or A material containing two or more components.

<Zinc and iron leaching rate>
After adding water to the blast furnace dust having the composition shown in Table 1 to adjust the blast furnace dust: water = 1: 10 (weight ratio), 3 mol / L sulfuric acid was adjusted to pH = 1, 2, 3, 4 After adding for 5 minutes and stirring for 60 minutes, the leaching rate of iron and zinc was investigated. The reaction pH during the experiment was controlled to be constant by a pH controller.

FIG. 7 shows the relationship between the pH of sulfuric acid and the leaching rate of iron and zinc. From FIG. 7, it can be seen that the leaching rate of iron and zinc increases with decreasing pH of the sulfuric acid and reaches 7% and 70% at pH = 2, respectively. FIG. 8 shows the ratio of zinc compound before and after leaching with sulfuric acid. In general, among zinc, zinc oxide, zinc sulfide, and zinc-iron composite oxide (ZnFe ₂ O ₄ ), acid-soluble substances are zinc and zinc oxide, but zinc oxide in blast furnace dust after acid leaching. The ratio of the amount greatly decreased, and almost the entire amount was dissolved. Therefore, it can be seen that the particularly preferable pH is 2.0 or more and 3.0 or less.

  Table 2 shows the component analysis results of the zinc leaching residue obtained by performing the solid-liquid separation step (third solid-liquid separation step) after leaching at pH = 2. As shown in this table, the zinc content is generally lower than 0.4%, which is said to be recyclable as a steelmaking raw material, and thus it can be seen that the entire amount can be recycled as a steelmaking raw material.

<Leaching time>
After adding water to the blast furnace dust having the composition shown in Table 1 to adjust the blast furnace dust: water = 1: 10 (weight ratio), 3 mol / L sulfuric acid was added so that the pH = 2. . The leaching times were 15 minutes, 30 minutes, 60 minutes, 90 minutes, and 120 minutes, and the leaching rates of iron and zinc were compared. The reaction pH during the experiment was controlled to be constant by a pH controller.

  FIG. 9 shows the relationship between leaching time and zinc leaching rate, and FIG. 10 shows the relationship between leaching time and iron leaching rate. From FIG. 9, it can be seen that there is almost no change in the leaching rate after 30 minutes from the start of leaching. On the other hand, it can be seen from FIG. 10 that the leaching rate of iron gradually increases with the passage of time from the start of leaching. Therefore, it was found that the leaching time particularly suitable for selectively dissolving zinc while suppressing iron leaching is 30 minutes or more and 90 minutes or less.

(Invention example)
Zinc was separated from blast furnace dust according to the flow shown in FIG. That is, first, water was added to blast furnace dust having the composition shown in Table 1 to adjust the blast furnace dust: water = 1: 10 (weight ratio), and then 3 mol / L sulfuric acid was adjusted to pH = 2. It was adjusted to 0, and zinc contained in the blast furnace dust was leached (step S1). Next, a third solid-liquid separation process was performed on the first processing liquid obtained in the zinc leaching process (step S11). Subsequently, an iron precipitation step is performed on the fifth treatment liquid obtained by the third solid-liquid separation step, and a 2.5 mol / L sodium hydroxide aqueous solution is added so that the pH becomes 5.0. Thereafter, hydrogen peroxide solution was added to precipitate iron contained in the fifth treatment liquid (step S2). As for the amount of hydrogen peroxide solution added, the iron concentration in the fifth treatment solution was quantified in advance, an amount sufficient to react with all iron ions was added, and the mixture was stirred for 60 minutes. Then, the 1st solid-liquid separation process was performed and the 2nd process liquid obtained at the iron precipitation process was solid-liquid separated (step S3). A zinc precipitation step was performed on the obtained third treatment liquid, and a 2.5 mol / L sodium hydroxide aqueous solution was added so as to have a pH of 9.0 to precipitate zinc contained in the third treatment liquid. (Step S4). Finally, a second solid-liquid separation step for solid-liquid separation of the fourth treatment liquid obtained in the zinc precipitation step was performed to separate the precipitated zinc (step S5).

(Comparative example)
Zinc was separated from blast furnace dust in the same manner as in the inventive examples. However, processing was performed according to the flow shown in FIG. 11, and the iron precipitation step was not performed. In the flow shown in FIG. 11, steps S21, S22, S23 and S24 correspond to steps S1, S3, S4 and S5 in the flow shown in FIG. Other processes are the same as those of the invention example.

<Precipitation rate of iron and zinc>
The precipitation rate of iron and zinc in the iron precipitation step is shown in FIG. As shown in FIG. 12, it can be seen that iron can be completely precipitated and removed with almost no precipitation of zinc.

<Zinc content>
Moreover, 2.5 mol / L sodium hydroxide aqueous solution was added to the filtrate obtained at the 2nd solid-liquid separation process so that it might become pH = 9.0, it stirred for 60 minutes, and it precipitated at the zinc precipitation process. Component analysis of the precipitate was performed. Table 3 shows the component analysis results. From Table 3, the obtained precipitate is enriched with zinc to 42.6%, exceeding the zinc content of 40%, which is said to have a high recovery value as a zinc raw material, and is separated from iron-making dust. It can be seen that can be recycled as a zinc raw material.

  Furthermore, about the invention example and the comparative example, the zinc leaching rate in the zinc leaching step, the iron recycling rate (the ratio of iron in the zinc leaching residue and the iron precipitation step to the iron in the blast furnace dust before the treatment) The zinc content in the precipitate in the zinc precipitation step was compared in terms of the total processing cost. Table 4 shows the obtained results.

<Comparison between Invention Examples and Comparative Examples>
About the leaching rate of zinc, both the invention example and the comparative example were the same as 70%. However, about the comparative example, since the iron leached in the zinc leaching process cannot be recovered, the iron recycling rate was lower than that of the invention example. In addition, for the comparative example, the zinc content in the precipitate obtained in the zinc precipitation step is far below 40%, which is said to have a high recovery value as a zinc raw material, and it is found that the value as a zinc raw material is small. It was. In this case, since the precipitate obtained in the zinc precipitation step is forced to be treated as industrial waste, the treatment cost is required to be about 1.5 times that of the invention example. The flow is not economical. As described above, according to the present invention, zinc can be separated from iron-making dust easily and at low cost.

  According to the present invention, since zinc can be separated from ironmaking dust easily and at low cost, it is useful in the steel industry.

Claims (11)

  A zinc leaching step of adjusting the pH of the acid containing the ironmaking dust to 1.0 or more by adding an acid to the ironmaking dust generated at the steelworks, and leaching zinc contained in the ironmaking dust into the acid; and An iron precipitation step for precipitating iron by adding a first alkali to the first treatment liquid obtained in the zinc leaching step, and a first solid-liquid separation for solid-liquid separation of the second treatment liquid obtained in the iron precipitation step A zinc precipitation step of precipitating zinc by adding a second alkali to the third treatment liquid obtained in the first solid-liquid separation step; and a fourth treatment liquid obtained in the zinc precipitation step. And a second solid-liquid separation step of separating.   The zinc leaching step is performed by adjusting the pH of the acid containing the iron dust to 2.0 or more and 3.0 or less. The method for separating zinc according to claim 1.   3. The method for separating zinc according to claim 1, wherein in the zinc leaching step, a time for leaching zinc contained in the iron-making dust into the acid is 15 minutes or longer and 120 minutes or shorter.   The zinc according to any one of claims 1 to 3, wherein the iron precipitation step is performed by adjusting a pH of the first treatment liquid to which the first alkali is added to 4.0 or more and 6.0 or less. Separation method.   The separation of zinc according to any one of claims 1 to 4, wherein the iron precipitation step is performed by controlling a redox potential according to a pH of the first treatment liquid to which the first alkali is added. Method.   The zinc according to any one of claims 1 to 5, wherein the zinc precipitation step is performed by adjusting a pH of the third treatment liquid to which the second alkali is added to 8.0 or more and 12.0 or less. Separation method.   The method further comprises a first iron recovery step for recovering iron obtained in the first solid-liquid separation step, and / or a zinc recovery step for recovering zinc separated in the second solid-liquid separation step. The method for separating zinc according to any one of 6.   The method further includes a third solid-liquid separation step for solid-liquid separation of the first treatment liquid between the zinc leaching step and the first solid-liquid separation step, and the iron precipitation step includes the third solid-liquid separation step. The separation method of zinc as described in any one of Claims 1-7 which precipitates the iron contained in the 5th process liquid obtained by above.   The zinc separation method according to claim 8, further comprising a second iron recovery step of recovering iron obtained in the third solid-liquid separation step.   A method for producing a zinc material, wherein zinc is separated and recovered from iron-making dust by the zinc separation method according to any one of claims 1 to 9.   A method for producing an iron material, wherein iron is separated and recovered from iron-making dust by the zinc separation method according to any one of claims 1 to 9.