JP2019060019A - Separation method of zinc, manufacturing method of zinc material, and manufacturing method of iron material - Google Patents

Abstract

To provide a separation method of zinc capable of separating zinc from an iron-making dust at high recovery rate and good efficiency.SOLUTION: There is provided a separation method of zinc including a zinc leaching process for leaching zinc contained in an iron-making dust by adding acid to the iron-making dust and adjusting pH to 1.0 or more, an iron deposition process for depositing iron by adding first alkali and an oxidant to a treated liquid after the zinc leaching process, a first solid and liquid separation process for solid and liquid separating a treated liquid after the iron deposition process, a zinc deposition process for depositing zinc by adding second alkali to a treated liquid after the first solid and liquid separation process, and a second solid and liquid separation process for solid and liquid separating a treated liquid after the zinc deposition process, in which a reaction divided into a plurality or sections is used and the addition of the first alkali is conducted in at least 2 sections of the plurality of sections in the iron deposition process.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method of separating zinc, and more particularly, to a method of separating zinc which can efficiently separate zinc from iron dust by adjusting pH with high accuracy. The present invention also relates to a method for producing a zinc material and a method for producing an iron material, using the above-described method for separating zinc.

  Iron, which is a typical base metal, is used in various industrial fields. Iron has abundant resources compared to rare metals called rare metals, but with the rise of emerging countries, the balance between supply and demand has changed dramatically. As a result, high-quality iron ore resources are depleted, and it is becoming necessary to use inferior grade ores.

  In view of such circumstances, in addition to refining iron ore, attempts have been made to recycle industrial wastes and by-products from steelmaking facilities composed of multicomponent metals including iron as iron sources. There is. For example, dust generated by ironworks such as blast furnace dust, converter dust, electric furnace dust, etc. contains iron, zinc, carbon etc. These dusts (hereinafter referred to as "iron making dust") are re-used as iron making raw materials It is resourced.

  However, since zinc in iron making dust forms deposits in the blast furnace and adversely affects blast furnace operation, the amount of iron making dust recycled has been limited. Therefore, there is a need for a technology for separating and recovering zinc from steelmaking dust.

  Methods of separating zinc from steelmaking dust are roughly classified into dry methods and wet methods. The dry method is a technology of reducing iron-making dust at high temperature, volatilizing zinc, and separating and recovering it. However, separation and recovery of zinc by a dry process requires a large-scale high-temperature reduction apparatus, and there has been a problem that blast furnace dust and converter dust having a zinc content of about several% can not be economically realized.

  Therefore, in order to solve the above-mentioned problems, a method of separating zinc from iron making dust by a wet method has been studied. In the wet method, acid is added to iron-making dust to elute zinc, and then zinc is precipitated and recovered by adding an alkali.

  For example, Patent Documents 1 and 2 propose that in the recovery rate of zinc by a wet method, the iron dissolved together with zinc when the zinc is eluted is precipitated and removed prior to the zinc precipitation treatment.

JP-A-53-004705 Japanese Patent Application Laid-Open No. 61-261446

  According to the methods proposed in Patent Documents 1 and 2, it is expected that zinc can be recovered at a high concentration because iron precipitated together with zinc is removed in advance by precipitation. However, in practice, it has been found that the conventional methods as described in Patent Documents 1 and 2 have a problem that the recovery of zinc and iron becomes lower than expected. This problem is particularly noticeable when scaling up from laboratory tests to actual equipment levels, and further improvement is required for practical use.

  Therefore, an object of the present invention is to provide a method for separating zinc which can efficiently separate zinc from iron dust at a high recovery rate. Another object of the present invention is to provide a method for producing a zinc material and a method for producing an iron material, using the method for separating zinc.

  The present inventors diligently studied ways to solve the above problems, and obtained the following findings.

(1) In the conventional method, there was a problem in the accuracy of pH adjustment at the time of precipitating iron prior to precipitation and separation of zinc. That is, when iron is precipitated by adding an alkali to the treatment liquid, if the pH is too low, iron can not be sufficiently precipitated and removed, and as a result, the recovery rate of iron decreases. On the other hand, if the pH is too high, not only iron but also zinc is precipitated, and as a result, the recovery rate of zinc decreases. Therefore, when iron is precipitated, it is necessary to precisely control the pH.

(2) However, in the actual treatment, there is a time lag until the treatment solution is mixed and the neutralization reaction is completely completed after the alkali is added. Therefore, the alkali is monitored while monitoring the pH of the treatment solution. Even if it adds, it is difficult to adjust pH correctly. In addition, since the treatment solution has a constant volume, it is difficult to make the pH of the entire treatment solution completely uniform even if alkali is added while stirring, and depending on the location, the pH may be low or high. There is a place.

(3) As a result of investigating the relationship between the pH and the redox potential (ORP) in the iron precipitation step, it became clear that the ORP tends to be higher as the pH of the treatment liquid is lower. As described later, it is preferable to control the addition amount of the oxidizing agent based on the ORP, but if a place with a low pH locally occurs in the reaction tank, the addition amount of the oxidizing agent is too small even if the ORP is monitored. As a result, the iron recovery rate decreases.

(4) Therefore, the pH adjustment in the iron precipitation step is carried out by the simple method of using the reaction vessel divided into a plurality of compartments and performing the addition of the first alkali in at least two of the plurality of compartments The accuracy of the system can be significantly improved, and as a result, the recovery of zinc and iron can be effectively improved.

  The present invention has been made on the basis of the above-described findings, and the summary of the invention is as follows.

1. A zinc leaching step of adjusting the pH to 1.0 or more by adding an acid to iron making dust, and leaching the zinc contained in the iron making dust;
An iron precipitation step of precipitating iron by adding a first alkali and an oxidant to the treatment liquid after the zinc leaching step;
A first solid-liquid separation step of solid-liquid separation of the treatment liquid after the iron precipitation step;
A zinc precipitation step of precipitating zinc by adding a second alkali to the treatment liquid after the first solid-liquid separation step;
And d) a second solid-liquid separation step of solid-liquid separation of the treatment liquid after the zinc precipitation step;
The method for separating zinc according to claim 1, wherein in the iron precipitation step, the reaction vessel divided into a plurality of sections is used, and the addition of the first alkali is performed in at least two of the plurality of sections.

2. The method for separating zinc according to the above 1, wherein the pH is adjusted to 2.0 or more and 3.0 or less in the zinc leaching step.

3. The method for separating zinc according to the above 1 or 2, wherein the leaching time in the zinc leaching step is 15 minutes or more and 120 minutes or less.

4. 5. The method for separating zinc according to any one of the above 1 to 3, wherein in the iron precipitation step, the pH of the treatment liquid is adjusted to 4.0 or more and 6.0 or less.

5. 5. The method for separating zinc according to any one of the above 1 to 4, wherein in the iron precipitation step, the redox potential is controlled to 550 mV or more.

6. In the zinc precipitation step, the method for separating zinc according to any one of the above 1 to 5, wherein the pH of the treatment liquid is adjusted to 8.0 or more and 12.0 or less.

7. The above 1 to 4, further comprising one or both of a ferrous iron recovery step of recovering iron separated in the first solid-liquid separation step and a zinc recovery step of recovering zinc separated in the second solid-liquid separation step. The method for separating zinc according to any one of 6.

8. The method for separating zinc according to any one of the above 1 to 7, further comprising a third solid-liquid separation step of solid-liquid separation of the treatment liquid between the zinc leaching step and the iron precipitation step.

9. 9. The method for separating zinc according to the above 8, further comprising a ferric iron recovery step of recovering iron separated in the third solid-liquid separation step.

10. The manufacturing method of the zinc material which isolate | separates and collect | recovers zinc from iron-making dust with the isolation | separation method of zinc as described in any one of said 1-9.

11. The manufacturing method of the iron material which isolate | separates and collect | recovers iron from iron-making dust with the isolation | separation method of the zinc as described in any one of said 1-9.

  According to the present invention, zinc can be efficiently separated from steelmaking dust with a high recovery rate.

It is a flowchart which shows the isolation | separation method of zinc in 1st Embodiment. It is a figure which shows the observation image of blast furnace dust with a scanning electron microscope, and the elemental mapping of zinc and iron. It is an electric potential-pH figure of iron in the aqueous solution of 25 degreeC. It is an electrical potential-pH figure of zinc in the aqueous solution of 25 degreeC. It is a flowchart which shows the isolation | separation method of zinc by 2nd Embodiment. It is a figure which shows the relationship between pH at the time of a leaching process, 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 the pH of calcium hydroxide, and the leaching rate of iron and zinc. It is a figure which shows the precipitation rate of iron and zinc in an iron precipitation process.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. Note that the following description shows a preferred embodiment of the present invention, and the present invention is not limited to this.

First Embodiment
FIG. 1 is a flow chart showing a method of separating zinc in an embodiment of the present invention. As shown in the flowchart, in the method for separating zinc in the present embodiment, the ironmaking dust is sequentially subjected to the processes in the following steps (S1) to (S5).
(S1) Zinc leaching process (S2) Iron precipitation process (S3) first solid-liquid separation process (S4) zinc precipitation process (S5) second solid-liquid separation process

  In addition, the process of said (S1)-(S5) can be implemented by arbitrary systems. For example, all of the steps (S1) to (S5) may be performed batchwise or continuously. Moreover, one part process can be performed by a batch type among the processes of said (S1)-(S5), and a remaining process can also be performed by a continuous type. However, the iron making dust is generated continuously in the iron making process, and it is desirable to treat the generated dust one by one. Therefore, it is preferable to perform the process of said (S1)-(S5) continuously from a viewpoint of processing efficiency.

  Each of the steps (S1) to (S5) can be performed using any device unless otherwise specified. It is preferable that an apparatus or device such as a reaction tank used in each process is made of a material having chemical resistance that is not attacked by a drug (such as alkali) used in each process, or be provided with a chemical resistant lining. The shape of the reaction vessel is also not particularly limited, and can be freely determined according to the installation place and the like.

Iron-making dust
The iron-making dust in the present invention is not particularly limited, and any dust can be used as long as it is dust generated in an iron-making process. As a typical thing of iron making dust, blast furnace dust, converter dust, electric furnace dust etc. are mentioned, for example.

Among them, it is preferable to use one or both of blast furnace dust and converter dust as the iron making dust. Although the blast furnace dust and converter dust have a low zinc content of several mass%, as described later, about 70% of the total zinc is present as zinc oxide (ZnO). Therefore, it can be easily leached even at relatively high pH as compared with other forms of zinc such as zinc sulfide (ZnS) and zinc ferrite (ZnFe ₂ O ₄ ). As a result, despite the low zinc content of the dust itself, the zinc purity of the precipitate finally obtained in the zinc precipitation step is extremely high and is particularly suitable for recycling as a zinc source.

  The iron-making dust can be used in any form, but it is preferable to mix it with water and use it as a slurry from the viewpoint of ease of processing in the subsequent steps. At this time, the ratio (solid-liquid ratio) of iron dust and water (solid-liquid ratio) can be any ratio, but it is desirable to determine so that uniform mixing can be performed.

  Here, the result of having investigated zinc contained in the above-mentioned iron-making dust is demonstrated. FIG. 2 shows an observation image of blast furnace dust with a scanning electron microscope (SEM), and elemental mapping of zinc and iron. In the 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 scarcely present in blast furnace dust particles and concentrated on the surface in any of particles having a diameter of about 1 μm and particles having a diameter of about 20 μm. Also, 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 ratio of ZnO was determined by quantifying the dissolved zinc. As a result, it was found that about 70% of zinc was present as zinc oxide (ZnO). The same was true for converter dust.

  As shown in the examples below, the zinc leaching rate rises with the drop in pH in the zinc leaching step, reaching 70% at pH = 2, and almost all of the zinc present as zinc oxide is leached out. In addition, the leaching rate does not increase even when the pH is 1, and the zinc leaching rate is saturated at pH = 2. Such a tendency was the same as in the case of converter dust.

[Zinc leaching process]
An acid is added to the iron making dust to adjust the pH to 1.0 or more, and zinc contained in the iron making dust is leached (zinc leaching step).

  The acid is not particularly limited, and any acid can be used as long as it can leach zinc. For example, hydrochloric acid, sulfuric acid, nitric acid or the like can be used. However, hydrochloric acid may cause corrosion of equipment, and there is a problem that nitric acid is more expensive than hydrochloric acid and sulfuric acid. Therefore, it is preferable to use sulfuric acid as the acid added in the zinc leaching step.

  In the zinc leaching step, the pH is adjusted to 1.0 or more. If the pH is less than 1.0, the leaching of iron increases, the final iron recovery rate decreases, and the purity of the recovered zinc decreases. Moreover, in order to make pH less than 1.0, since it is necessary to add a large amount of acids, consumption of a chemical | medical agent increases and processing cost increases.

  As described later, the leaching rate of zinc when pH was lowered was saturated at pH = 2.0, and did not increase any more even if it was less than 2.0, and only the consumption of the drug increased Do. Therefore, in the zinc leaching step, it is preferable to adjust the pH to 2.0 or more. On the other hand, since it becomes difficult to leach zinc when pH exceeds 5.0, it is preferable to adjust pH to 5.0 or less in a zinc leaching process. In addition, if the pH is 3.0 or less, the leaching rate is about 60%, and zinc having a more preferable concentration for reuse as a raw material can be leached. Therefore, it is more preferable to adjust the pH to 3.0 or less. It is more preferable to adjust pH to 2.0 or more and 3.0 or less in terms of zinc leaching rate and processing cost. In addition, pH shall refer to pH of the mixture which mixed iron-making dust and an acid here.

  Although the addition method of the acid in the said zinc leaching process is not specifically limited, For example, it can carry out using a pump. The pump is not particularly limited, and a general pump can be used. In addition, also in each process other than a zinc leaching process like the addition of the said acid, when adding chemical | medical agents, such as an alkali, arbitrary apparatuses, such as a pump, can be used.

  When adding an acid, it is preferable to monitor the pH with a pH meter and to control the amount of acid added based on the result. For example, when adding an acid to iron making dust in a reaction tank, it is preferable to install a pH meter in the reaction tank to monitor the pH. In addition, it is preferable to monitor pH by pH meter, when adding chemical | medical agents, such as an alkali, also in each process other than a zinc leaching process similarly to addition of the said acid.

  In addition, since iron making dust contains iron or the like having a large specific gravity and tends to settle, it is preferable to perform stirring when adding an acid in the zinc leaching step. For example, when adding an acid in a reaction tank, it is preferable to install stirring means in the reaction tank and add the acid while stirring. Although the method of stirring is not particularly limited, for example, it can be carried out using a general stirrer or the like. It is desirable that the stirring speed be determined so that the concentration distribution in the tank becomes uniform in consideration of the ratio of iron making dust and water. In addition, also in each process other than a zinc leaching process like the addition of the said acid, when adding chemical | medical agents, such as an alkali, it is preferable to stir by arbitrary methods.

  The solid-liquid ratio of the iron-making dust and the water can be any ratio as long as uniform mixing can be performed.

  The leaching time (time to shift to the next pH adjustment step) in the zinc leaching step is not particularly limited, but is preferably 15 minutes or more and 120 minutes or less. By setting the leaching time to 15 minutes or more, zinc contained in the iron-making dust can be leached more sufficiently. On the other hand, by setting the leaching time to 120 minutes or less, zinc can be leached more effectively while suppressing the amount of leached iron.

  The reaction temperature in the zinc leaching step can be arbitrarily set in a temperature range in which water does not coagulate or evaporate.

[Iron precipitation process]
Next, a first alkali and an oxidizing agent are added to the treatment liquid after the zinc leaching step to precipitate iron (iron precipitation step). The zinc leaching process is aimed at leaching zinc with acid, but it is difficult to completely prevent leaching of iron. Therefore, iron ions are also contained in the treatment solution in addition to zinc ions, the content of iron contained in the residue obtained by leaching zinc with acid decreases, and the recycling rate as a steelmaking material also decreases. In addition, when adding an alkali to the above-mentioned processing solution and precipitating and recovering zinc, not only zinc but also iron is simultaneously precipitated, so that mixing with iron reduces the value as a zinc raw material, which is also uneconomical .

  So, in this invention, the iron precipitation process which selectively precipitates iron contained in a process liquid is performed prior to a zinc precipitation process. By this step, it is possible to separate iron from the treatment solution and separate zinc of sufficient purity for reuse as a resource in the subsequent zinc precipitation step.

  Furthermore, in the present invention, in the iron precipitation step, the reaction vessel divided into a plurality of compartments is used, and the addition of the first alkali is performed in at least two of the plurality of compartments. In the iron precipitation step, as the reaction tank becomes larger, unevenness in pH in the reaction tank is more likely to occur. For example, the pH tends to be high in the vicinity of the position where the first alkali is added, and tends to be low in the vicinity of the position away from the position or the position where the treatment liquid after the zinc leaching step in the previous stage flows. Therefore, by using the reaction vessel divided into a plurality of compartments as described above, the pH can be controlled in a compartment of a smaller volume as compared to the case of using the whole reaction vessel without partitioning, so the accuracy of pH adjustment The pH of the entire reaction vessel can be made uniform. And as a result, the recovery of zinc and iron can be effectively improved.

  The method of division into the plurality of compartments is not particularly limited and may be arbitrarily selected, but it is preferable to divide the whole reaction vessel so that the volumes of the respective compartments become substantially the same. Also, the number of sections can be any number of two or more. Although depending on the volume of the whole reaction vessel, it is also preferable to set it to 3 or more or 4 or more from the viewpoint of improving the accuracy of pH adjustment. On the other hand, even if the division into more than necessary divisions saturates the effect and the equipment becomes complicated, the number of divisions is preferably 10 or less.

  The plurality of sections may be used independently, and the iron precipitation step may be individually performed in each section. However, from the viewpoint of improving the accuracy of pH adjustment and continuous processing, it is preferable to use a cascade method in which each section is connected and iron precipitation processing is performed while flowing the processing solution from the upstream section toward the downstream section . In that case, the method of flowing the treatment liquid between the compartments is not particularly limited, but for example, a partition plate (a weir) of an appropriate height is provided between adjacent compartments, and the treatment liquid overflows the partition plate. It can be in the form of flowing to the next section sequentially to the next section.

  The arrangement of the respective compartments is not particularly limited. For example, all the compartments can be arranged in series, or some or all of the compartments can be arranged in parallel. When the partition plate is used to divide the sections, the partition plates can be arranged in parallel, but can also be arranged to intersect.

  The addition of the first alkali is performed in at least two of the plurality of compartments. For example, in the cascade reaction vessel, it is preferable to perform the addition of the first alkali at least in the most upstream section and the most downstream section. Moreover, from the viewpoint of improving the accuracy of pH adjustment, it is preferable to perform the addition of the first alkali in all the sections.

  The first alkali used in the iron precipitation step is not particularly limited, and any desired one can be used. As the first alkali, one or more selected from the group consisting of an alkali metal hydroxide and an alkaline earth metal hydroxide is preferably used, and among them, at least one of calcium hydroxide and sodium hydroxide is preferable. It is more preferable to use Since these alkalis can be obtained inexpensively, the processing cost can be reduced.

  In addition, although the kind and density | concentration of a compound can be independently selected independently for every division, it is preferable to use the same alkali from a viewpoint of a simplification of an installation and a process to each division.

  Further, as described above, since the iron-making dust contains iron or the like having a large specific gravity and is easily sedimented, it is preferable to stir the inside of the tank when performing pH adjustment.

  The method of adding the first alkali is not particularly limited, but can be performed using a general pump or the like. At that time, it is preferable to monitor the pH of the compartment to be added with a pH meter and to control the amount of addition of the first alkali based on the result.

The pH (pH _S3 ) adjusted in the iron precipitation step is not particularly limited, and may be arbitrarily selected in consideration of various conditions so that iron can be selectively precipitated. The specific preferable range of pH _S3 is demonstrated below.

  FIG. 3 is a potential-pH diagram showing the state of iron present in an aqueous solution at 25 ° C., with pH on the horizontal axis and the redox potential (ORP) on the vertical axis. FIG. 4 is a potential-pH diagram showing the presence of zinc in an aqueous solution at 25 ° C. The shaded portions in FIG. 3 indicate regions where iron precipitates, and similarly, the hatched portions in FIG. 4 indicate regions where zinc precipitates.

  As can be seen from FIG. 3 and FIG. 4, the area where iron precipitates and the area where zinc precipitates overlap most of the time, so zinc tends to be precipitated simultaneously under iron precipitation conditions. However, in the region surrounded by thick lines in FIG. 3, that is, the region where the pH is low and the ORP is under oxidative conditions, mainly iron can be selectively precipitated. Therefore, in the iron precipitation step, it is preferable to add an alkali so as to be the condition of the region surrounded by the thick line in FIG.

Specifically, in the iron precipitation step, it is preferable to add the first alkali so that the pH is 4.0 or more and 6.0 or less (4.0 ≦ pH _S3 ≦ 6.0). By setting the pH to 4.0 or more, iron can be efficiently precipitated. Further, by setting the pH to 6.0 or less, only iron can be precipitated more efficiently without precipitating zinc.

  Further, as apparent from FIG. 3, whether iron precipitates depends not only on pH but also on redox potential. Therefore, in the iron precipitation step, the oxidation reduction potential (ORP) of the treatment liquid is controlled by further adding an oxidizing agent. Since iron in the treatment solution is generally present in the form of divalent iron ions, the iron ion is surely precipitated by raising the ORP of the treatment solution (to make it an oxidizing atmosphere) to make the iron ions trivalent. It can be done.

The oxidizing agent is not particularly limited and any one may be used. As the oxidizing agent, for example, one or more selected from the group consisting of hydrogen peroxide, hypochlorite, O ₂ (oxygen) containing gas, O ₃ (ozone) containing gas is preferably used. As the hypochlorite, it is preferable to use one or more selected from the group consisting of alkali metal salts and alkaline earth metal salts of hypochlorous acid, and sodium hypochlorite is more preferable. preferable. As the O ₂ -containing gas, O ₂ gas itself may be used, but it is preferable to use air. In other words, a gas (for example, air) containing O ₂ as an oxidizing agent can be added to the processing solution. Similarly, as the O _3, can also be used the O ₃ gas itself, it is also possible to use a gas containing O _3. When a gas such as air is used as the oxidizing agent, it is preferable to add the oxidizing agent by blowing the gas into the treatment liquid. Among them, it is preferable to use, as the oxidizing agent, one or more selected from the group consisting of hydrogen peroxide, sodium hypochlorite, and air from the viewpoint of easy availability and cost.

  The addition amount of the oxidizing agent is preferably controlled so that the ORP of the treatment liquid has a value suitable for iron precipitation. The optimal ORP value varies with the pH of the treatment solution. Therefore, it is preferable to experimentally determine the optimum ORP according to the pH of the treatment liquid.

  The reaction temperature in the iron precipitation step can be arbitrarily set in a temperature range in which the treatment liquid does not coagulate or evaporate. The reaction time is preferably 15 minutes or more and 120 minutes or less in view of the treatment efficiency.

[First solid-liquid separation step]
Subsequently, the treatment liquid after the iron precipitation step is subjected to solid-liquid separation (first solid-liquid separation step). In this step, the treatment liquid is separated into a filtrate mainly containing zinc ions, and a zinc leaching residue in the zinc leaching step and solids precipitated in the iron precipitation step (iron precipitate).

  The main component of the zinc leaching residue produced in the zinc leaching step is iron, which contains almost no zinc. Therefore, it can be reused as a steelmaking raw material through a sintering process. Moreover, the solid content produced | generated in the iron precipitation process contains highly pure iron, and it can recycle | reuse as an iron-making raw material through a sintering process like zinc leaching residue.

  Therefore, it is preferable to further include a ferrous iron recovery step of recovering iron separated in the first solid-liquid separation step. Thereby, the separated iron can be recovered and reused as a resource.

  The solid-liquid separation method used in the first solid-liquid separation step is not particularly limited, and any method can be used. For example, methods such as gravity sedimentation, filtration, centrifugation, filter press, etc. can be used alone or in combination.

[Zinc precipitation process]
Next, a second alkali is added to the treatment liquid after the first solid-liquid separation step to precipitate zinc (zinc precipitation step). Here, the “treatment liquid after the first solid-liquid separation step” refers to the liquid portion (filtrate) after the solid content is separated in the first solid-liquid separation step.

  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 treatment liquid after the first solid-liquid separation step is , Almost only zinc is dissolved. Therefore, only zinc can be selectively precipitated by adding an alkali to the treatment solution.

  The second alkali used in the zinc precipitation step is not particularly limited and any desired one can be used. As the second alkali, one or more selected from the group consisting of an alkali metal hydroxide and an alkaline earth metal hydroxide is preferably used, and among them, at least one of calcium hydroxide and sodium hydroxide is preferable. It is more preferable to use Since these alkalis can be obtained inexpensively, the processing cost can be reduced.

When sulfuric acid is used in the zinc leaching step, when an alkaline earth metal hydroxide is used as the second alkali, a water-insoluble salt such as CaSO ₄ is formed to precipitate together with zinc. And as a result, there exists a problem that the zinc concentration (purity) of solid content (precipitate) obtained by a zinc precipitation process will fall. On the other hand, if sodium hydroxide is used as the second alkali, such a problem does not occur because Na ₂ SO ₄ is soluble in water. Therefore, when using sulfuric acid in the zinc leaching step, it is preferable to use sodium hydroxide as the second alkali in the zinc precipitation step.

  The pH adjusted in the zinc precipitation step is not particularly limited, and may be any value as long as it can precipitate zinc. Specifically, the pH is 8.0 or more and 12.0 or less It is preferable to By setting the pH to 8.0 or more, zinc can be efficiently precipitated. In addition, by setting the pH to 12.0 or less, it is possible to prevent zinc that has once precipitated from being redissolved in the treatment liquid, and to further improve the zinc recovery rate.

  The reaction temperature in the zinc leaching step can be arbitrarily set in a temperature range in which the treatment liquid does not coagulate or evaporate. Moreover, about reaction time, it is preferable to set it as 15 minutes or more and 120 minutes or less in view of the precipitation formation time of zinc, and a process efficiency.

[Second solid-liquid separation step]
Finally, the treatment liquid after the zinc precipitation step is subjected to solid-liquid separation (second solid-liquid separation step). Thereby, solid content (zinc precipitate) is separated from the treatment liquid.

  The solid-liquid separation method used in the second solid-liquid separation step is not particularly limited, and any method can be used. For example, methods such as gravity sedimentation, filtration, centrifugation, filter press, etc. can be used alone or in combination.

  By the above procedure, zinc can be efficiently separated from steelmaking dust. The zinc precipitate separated by the method of the present invention contains zinc at a high concentration of 40% or more, and is valuable as a zinc raw material. Therefore, by further providing a zinc recovery step of recovering the zinc separated in the second solid-liquid separation step, it is possible to recycle as zinc raw material through zinc smelting and the like.

Second Embodiment
FIG. 5 is a flow chart showing a zinc separation method according to another embodiment of the present invention. As shown in the flow chart, in the method of separating zinc according to the present embodiment, the third solid-liquid separation step (solid-liquid separation step) is performed between the zinc leaching step (S1) and the pH adjustment step (S2). S11) is further provided.

  In the first embodiment described above, in the first solid-liquid separation step, the zinc leaching residue produced in the zinc leaching step and the solid substance produced in the iron precipitation step are simultaneously subjected to solid-liquid separation. In the third solid-liquid separation step after the zinc leaching step, the zinc leaching residue is solid-liquid separated, and in the first solid-liquid separation step, only the solid content generated in the iron precipitation step is solid-liquid separated.

  The solid-liquid separation method used in the third solid-liquid separation step is not particularly limited, and any method can be used. For example, methods such as gravity sedimentation, filtration, centrifugation, filter press, etc. can be used alone or in combination.

  When the third solid-liquid separation step is performed, it is preferable to further include a ferric iron recovery step of recovering iron (zinc leaching residue) obtained in the third solid-liquid separation step. Thereby, a sintering process is performed with respect to a zinc leaching residue, and it can recycle | reuse as resources as iron-making raw materials.

  The other points than the above can be the same as those of the first embodiment.

(Method of manufacturing zinc material)
The method for producing a zinc material according to the present invention is characterized in that zinc is separated and recovered from steelmaking dust by the above-described method for separating zinc. Thereby, the zinc contained in iron-making dust can be concentrated, and a zinc material with a zinc content rate of 40% or more can be manufactured.

(Method of manufacturing 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 above-described method for separating zinc. This makes it possible to recover and recycle all of the iron contained in the steelmaking dust.

  Next, the following experiment was performed to examine suitable conditions in the method for separating zinc of the present invention.

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

  FIG. 6 shows the relationship between pH during leaching treatment and the leaching rate of iron and zinc. It can be seen from FIG. 6 that the leaching rates of iron and zinc rise with the decrease in pH at the time of leaching, and reach 7% and 70% at pH = 2, respectively.

FIG. 7 shows the proportions of zinc compounds before and after sulfuric acid leaching. Generally, among zinc, zinc oxide, zinc sulfide and zinc-iron complex oxide (ZnFe ₂ O ₄ ), acid-soluble substances are zinc and zinc oxide, but zinc oxide in blast furnace dust after acid leaching The proportion of the solution significantly decreased and almost all dissolved. Therefore, it is understood that particularly preferable pH is 2.0 or more and 3.0 or less.

  Next, after leaching at pH = 2, component analysis results of the zinc leaching residue obtained by performing the solid-liquid separation step (third solid-liquid separation step) are shown in Table 2. As shown in this table, since the zinc content in the residue after zinc leaching is less than 0.4% which is generally said to be recyclable as iron making material, it is possible to totally recycle as iron making material I understand.

  Furthermore, while adding hydrogen peroxide water as an oxidizing agent to the treatment liquid (filtrate) after the above solid-liquid separation step (third solid-liquid separation step), 10 mass% calcium hydroxide is pH = 3, 4, After adding to become 5, 6, 7 and stirring for 60 minutes, the recovery of iron and zinc was investigated. The reaction pH during the experiment was controlled to be constant by a pH controller.

  FIG. 8 shows the relationship between pH after addition of calcium hydroxide and the precipitation rate of iron and zinc in the iron precipitation step. From FIG. 8, the precipitation rate of iron falls rapidly below pH = 4, while the precipitation rate of zinc rises with pH. In particular, when the pH exceeded 6, the precipitation rate significantly increased, and when the pH was 7, almost all of the precipitates were precipitated. That is, it was found that the preferred pH for selectively precipitating iron alone without precipitating zinc is pH 4.0 to 6.0.

  The "precipitation rate" of zinc and iron in the above experiment means the ratio of the amount of Zn or Fe precipitated in the iron precipitation step to the amount of Zn or Fe contained in the treatment liquid subjected to the iron precipitation step. Specifically, it was determined according to the following procedure.

(Zinc precipitation rate)
Zn concentration in the treated liquid (filtrate) after the third solid-liquid separation step: _Zn , ₀ (mg / L) and Zn concentration in the treated liquid (filtrate) after the first solid-liquid separation step: C _Zn , ₁ (mg / L) was measured by inductively coupled plasma mass spectrometry (ICP-MS). From the obtained values, the precipitation rate of Zn was calculated by the following equation (1).
Precipitation rate of zinc (%) = ( _Czn , _{0- Czn} , ₁ / _Czn , ₀ ) x 100 (1)

(Iron deposition rate)
As in the case of zinc, Fe concentration in the treated liquid (filtrate) after the third solid-liquid separation step: C 2 _{Fe 0} (mg / L) and the treated liquid after the first solid-liquid separation step (filtrate) Fe concentration in C): C 2 _{Fe 1} (mg / L) was measured by inductively coupled plasma mass spectrometry (ICP-MS). From the obtained values, the precipitation rate of Fe was calculated by the following equation (2).
Precipitation rate of iron (%) = (C _Fe , ₀ -C _Fe , ₁ / C _Fe , ₀ ) × 100 (2)

(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 prepare slurry of blast furnace dust: water = 1: 10 (weight ratio). Thereafter, 3 mol / L of sulfuric acid was added to the slurry to adjust to pH = 2.0, and zinc contained in blast furnace dust was leached out (zinc leaching step).

  An alkali was added to the treatment liquid after the zinc leaching step to precipitate iron (iron precipitation step). In the iron precipitation step, a reaction vessel divided into two compartments of the same volume by partition plates was used. The concrete procedure of the process is as follows. First, the treatment liquid after the zinc leaching step was received in one section of the reaction tank, and hydrogen peroxide and a 10 wt% calcium hydroxide slurry were added to the treatment liquid of the section so that the pH was 4.5. . Then, the treatment liquid adjusted to pH: 4.5 is received in the other section of the reaction vessel, and hydrogen peroxide and 10 wt% calcium hydroxide slurry are further added so that the pH is 5.0. did. The amount of hydrogen peroxide solution added was such that the iron concentration in the treatment solution of each section was quantified in advance, and the amount was sufficient to react with all the iron ions.

  Thereafter, the treatment liquid after the iron precipitation step was subjected to solid-liquid separation (first solid-liquid separation step).

  An aqueous solution of 2.5 mol / L sodium hydroxide was added to the obtained treatment liquid (filtrate) so that the pH was 9.0, and zinc contained in the treatment liquid was precipitated (zinc precipitation step) .

  Finally, solid-liquid separation was performed on the treatment liquid obtained in the zinc precipitation step to separate the precipitated zinc (second solid-liquid separation step).

<Settling rate of iron and zinc>
The precipitation rates of iron and zinc in the above iron precipitation step are shown in FIG. From this result, it can be seen that according to the method of the present invention, iron can be completely precipitated and removed in the iron precipitation step with little precipitation of zinc.

  In the same manner as the experiment described above, the “precipitation rate” of zinc and iron in this example refers to the iron precipitation step with respect to the amount of Zn or Fe contained in the treatment solution subjected to the iron precipitation step. It is the proportion of the amount of Zn or Fe precipitated. However, since the third solid-liquid separation step was not performed in this example, the treatment liquid after the zinc leaching step was used as the treatment liquid subjected to the iron precipitation step. Specifically, it is as follows.

(Zinc precipitation rate)
Zn concentration in treatment solution (filtrate) after zinc leaching step: _Zn , ₀ (mg / L) and Zn concentration in treatment solution (filtrate) after first solid-liquid separation step: C _Zn , ₁ (Mg / L) was measured by inductively coupled plasma mass spectrometry (ICP-MS). From the obtained values, the precipitation rate of Zn was calculated by the following equation (1).
Precipitation rate of zinc (%) = ( _Czn , _{0- Czn} , ₁ / _Czn , ₀ ) x 100 (1)

(Iron deposition rate)
As in the case of zinc, Fe concentration in the treated liquid (filtrate) after the zinc leaching step: C 2 _{Fe 0} (mg / L) and in the treated liquid (filtrate) after the first solid-liquid separation step Fe concentration: C 2 _{Fe 1} (mg / L) was measured by inductively coupled plasma mass spectrometry (ICP-MS). From the obtained values, the precipitation rate of Fe was calculated by the following equation (2).
Precipitation rate of iron (%) = (C _Fe , ₀ -C _Fe , ₁ / C _Fe , ₀ ) × 100 (2)

<Zinc content rate>
The component analysis of the precipitate which precipitated by the said zinc precipitation process was performed. The component analysis results are shown in Table 3. From Table 3, the obtained precipitate is concentrated to 42.6% of zinc, and exceeds the zinc content of 40%, which is considered to have a high recovery value as a zinc raw material, and zinc separated from iron dust Can be recycled as a zinc source.

(Comparative example)
For comparison, zinc was separated from blast furnace dust under the same conditions as in the above-mentioned invention example except that the inside of the reaction tank used in the iron precipitation step was used without separation. In addition, the volume of the whole reaction tank was made the same as the volume of the whole reaction tank used by the said invention example.

  The zinc removal rate and the iron recycling rate were measured in the following procedures for each of the invention example and the comparative example. The measurement results are shown in Table 4.

<Zinc removal rate>
The zinc removal rate refers to the ratio of the amount of zinc not recovered as solids (precipitate) in the first solid-liquid separation step to the amount of zinc contained in the iron-making dust before treatment. The solid content recovered in the first solid-liquid separation step is composed of a residue (zinc leaching residue) not dissolved in the zinc leaching step and a solid content precipitated in the iron precipitation step, and is recovered as an iron material is there. Therefore, the amount of zinc not contained in the solid content obtained in the first solid-liquid separation step can be regarded as the amount of zinc which could be removed.

That is, the zinc removal rate is determined as follows: Zn concentration in iron dust before treatment: C _Zn , _a (mass%), Zn concentration in solid separated in the first solid-liquid separation step: C _Zn , _b (mass% ) Was measured and calculated by the following equation (3).
Zinc removal rate (mass%) = 100-( _Czn , _b / _Czn , _a ) x 100 (3)

<Iron recycling rate>
The iron recycling rate refers to the ratio of the amount of iron recovered as the solid content (precipitation) in the first solid-liquid separation step to the amount of iron contained in the iron-making dust before treatment. As described above, the solid content recovered in this first solid-liquid separation step is composed of the residue not dissolved in the zinc leaching step (zinc leaching residue) and the solid content precipitated in the iron precipitation step, and the iron material It will be collected as In other words, the ratio of the amount of Fe remaining on the treatment liquid side without being collected as solid in the first solid-liquid separation step can be said to be the ratio of iron that has not been recycled, so the value is subtracted from 100 The iron recycling rate can be determined by

That is, the iron recycling rate is determined by separating the treatment solution after the zinc leaching step and filtering the Fe concentration in the filtrate: C _Fe , _a (mass%), the treatment solution after the first solid-liquid separation step Fe concentration: C 2 _Fe , _b (mass%) was measured, and calculated according to the following equation (4).
Iron recycling rate (mass%) = 100- (C _Fe , _b / C _Fe , _a ) × 100 (4)

  As can be seen from the results shown in Table 4, in the comparative example, the zinc removal rate was as low as 37%, but in the invention example, the zinc removal rate was improved by almost 30% over the comparative example. It is considered that this is because in the comparative example in which the reaction vessel divided into a plurality of parts in the iron precipitation step is not used, pH adjustment can not be accurately performed, and Zn as well as Fe is precipitated. As the cause, as described above, the variation of pH depending on the position in the reaction tank, the error of pH control due to the time lag for completing the neutralization reaction, etc. can be considered. In addition, since the addition of an alkali such as calcium hydroxide is usually performed by making the alkali into a slurry as in this example, calcium hydroxide is unreacted before the first solid-liquid separation after the iron precipitation step. It is also conceivable that the reaction occurs in the process, and the pH rises to precipitate zinc. On the other hand, in the example of the invention using the reaction vessel divided into a plurality of sections, since the amount of treatment liquid per section is small, the pH can be controlled with high precision without being adversely affected as described above. As a result, it is considered that the zinc removal rate could be significantly improved.

  As described above, according to the present invention, zinc can be efficiently separated from steelmaking dust at a high recovery rate, which is useful in the steelmaking industry.

Claims (11)

A zinc leaching step of adjusting the pH to 1.0 or more by adding an acid to iron making dust, and leaching the zinc contained in the iron making dust;
An iron precipitation step of precipitating iron by adding a first alkali and an oxidant to the treatment liquid after the zinc leaching step;
A first solid-liquid separation step of solid-liquid separation of the treatment liquid after the iron precipitation step;
A zinc precipitation step of precipitating zinc by adding a second alkali to the treatment liquid after the first solid-liquid separation step;
And d) a second solid-liquid separation step of solid-liquid separation of the treatment liquid after the zinc precipitation step;
The method for separating zinc according to claim 1, wherein in the iron precipitation step, the reaction vessel divided into a plurality of sections is used, and the addition of the first alkali is performed in at least two of the plurality of sections.   The method for separating zinc according to claim 1, wherein the pH is adjusted to 2.0 or more and 3.0 or less in the zinc leaching step.   The zinc separation method according to claim 1, wherein the leaching time in the zinc leaching step is set to 15 minutes or more and 120 minutes or less.   The zinc separation method according to any one of claims 1 to 3, wherein the pH of the treatment liquid is adjusted to 4.0 or more and 6.0 or less in the iron precipitation step.   The zinc separation method according to any one of claims 1 to 4, wherein the redox potential is controlled to 550 mV or more in the iron precipitation step.   The method for separating zinc according to any one of claims 1 to 5, wherein in the zinc precipitation step, the pH of the treatment liquid is adjusted to 8.0 or more and 12.0 or less.   The method further includes one or both of a ferrous iron recovery step of recovering iron separated in the first solid-liquid separation step and a zinc recovery step of recovering zinc separated in the second solid-liquid separation step. The isolation | separation method of the zinc as described in any one of -6.   The zinc separation method according to any one of claims 1 to 7, further comprising a third solid-liquid separation step of solid-liquid separation of the treatment liquid between the zinc leaching step and the iron precipitation step.   The zinc separation method according to claim 8, further comprising a ferric iron recovery step of recovering iron separated in the third solid-liquid separation step.   The manufacturing method of the zinc material which isolate | separates and collect | recovers zinc from iron-making dust with the isolation | separation method of zinc as described in any one of Claims 1-9.   The manufacturing method of an iron material which isolate | separates and collect | recovers iron from iron-making dust with the isolation | separation method of zinc as described in any one of Claims 1-9.