Method for removing zinc and method for producing low-zinc steelmaking dust

Abstract

To provide a method for removing zinc contained in steelmaking dust and a method for producing low-zinc steelmaking dust.SOLUTION: The present invention provides methods including: a leaching step for adding acid to a suspension in which steelmaking dust containing zinc is dispersed to leach zinc into the liquid phase of the suspension; a precipitation step for adding an oxidizing agent and an alkali to a first treatment liquid obtained in the leaching step to precipitate iron in the first treatment liquid; a first solid-liquid separation step for separating a second treatment liquid obtained in the precipitation step into solids and liquids; a washing step for washing the solids separated in the first solid-liquid separation step; and a second solid-liquid separation step for separating a third treatment liquid obtained in the washing step into solids and liquids. In the washing step, the solids are washed so that the washing index h is 54 or higher, as represented by the following formula (1): h=4.26×L / S-13.4×N-0.782×t+53.3 where L / S represents the liquid-to-solid ratio of the washing water to the solids by mass; N represents the number of uses of the washing water; t represents the stirring time [minutes]).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for removing zinc and a method for producing low-zinc steelmaking dust. [Background technology]

[0002] Steel dust contains iron and can be used as an iron source in the steelmaking process. For example, the use of steel dust is sometimes desirable in the sintering process, which is the first step in the steelmaking process. However, steel dust often contains zinc. However, since there is an upper limit to the amount of zinc that can be charged into a blast furnace, steel dust containing zinc in excess of the allowable amount cannot be used as a raw material. Therefore, such steel dust must be processed externally, which not only makes it unusable as an iron source, but also requires additional processing costs.

[0003] Nowadays, a technique for removing zinc contained in iron-making dust has been proposed in order to reuse the dust (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2017-506700 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 describes a method in which zinc (Zn) contained in a starting material is leached out, and a solid (Fe) is precipitated in the liquid phase to obtain a mixture, which is then filtered. Water is poured onto the solid remaining on the filtration filter to wash away and remove the filtrate, which contains solubilized salts of chlorides and metals, including Zn, remaining in the gaps between the solid particles.

[0006] However, the method described in Patent Document 1 cannot be said to be capable of sufficiently dissolving Zn salts present in the solid particles and washing them away to remove them.

[0007] The present disclosure has been made based on the above circumstances, and aims to provide a zinc removal method that can reliably remove zinc contained in steelmaking dust. [Means for solving the problem]

[0008] A zinc removal method according to one embodiment of the present disclosure includes a leaching step of adding an acid to a suspension in which zinc-containing steel dust is dispersed to leach zinc into a liquid phase of the suspension; a precipitation step of adding an oxidizing agent and an alkali to a first treatment liquid obtained in the leaching step to precipitate iron in the first treatment liquid; a first solid-liquid separation step of performing solid-liquid separation of a second treatment liquid obtained in the precipitation step; a water washing step of washing a solid fraction separated in the first solid-liquid separation step; and a second solid-liquid separation step of performing solid-liquid separation of a third treatment liquid obtained in the water washing step, wherein the solid fraction is washed in the water washing step so that a water washing index h represented by the following formula 1 is 54 or more. h=4.26×L / S-13.4×N-0.782×t+53.3 1 In the above formula 1, L / S means the liquid-solid ratio of washing water to solids (washing water / solids) based on mass, N means the number of times washing water is used (wherein N=1 is the number of times fresh washing water is used, and N≧2 is the number of times washing water used repeatedly in the washing step), and t means the stirring time [min]. Effect of the Invention

[0009] A zinc removal method according to one embodiment of the present disclosure can reliably remove zinc contained in steelmaking dust. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a flow diagram illustrating a zinc removal method according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described.

[0012] (1) A zinc removal method according to one embodiment of the present disclosure includes a leaching step of adding an acid to a suspension in which zinc-containing steel dust is dispersed to leach zinc into a liquid phase of the suspension; a precipitation step of adding an oxidizing agent and an alkali to a first treatment liquid obtained in the leaching step to precipitate iron in the first treatment liquid; a first solid-liquid separation step of performing solid-liquid separation of a second treatment liquid obtained in the precipitation step; a water washing step of washing a solid fraction separated in the first solid-liquid separation step; and a second solid-liquid separation step of performing solid-liquid separation of a third treatment liquid obtained in the water washing step, wherein the solid fraction is washed in the water washing step so that a water washing index h represented by the following formula 1 is 54 or more. h=4.26×L / S-13.4×N-0.782×t+53.3 1 In the above formula 1, L / S means the liquid-solid ratio of washing water to solids (washing water / solids) based on mass, N means the number of times washing water is used (wherein N=1 is the number of times fresh washing water is used, and N≧2 is the number of times washing water used repeatedly in the washing step), and t means the stirring time [min].

[0013] In the zinc removal method, the solid content is washed with water in the water washing step so that the water washing index h is 54 or more, so that zinc contained in the iron-making dust can be reliably removed.

[0014] (2) In the above (1), the acid may be hydrochloric acid. By using hydrochloric acid as the acid, the zinc contained in the steel dust can be sufficiently removed, and solids having a high iron content and no desulfurization load can be obtained during recycling.

[0015] (3) In the above (1) or (2), the washing water in which the solids are immersed may be stirred in the washing step, and the separated liquid separated in the second solid-liquid separation step may be repeatedly used as washing water. In this way, by stirring the washing water in which the solids are immersed in the washing step, and repeatedly using the separated liquid separated in the second solid-liquid separation step as washing water, zinc contained in the ironworks dust can be removed more efficiently.

[0016] Another embodiment of the present disclosure provides a method for producing low-zinc ironworks dust, comprising: a leaching step of adding an acid to a suspension in which zinc-containing ironworks dust is dispersed to leach zinc into the liquid phase of the suspension; a precipitation step of adding an oxidizing agent and an alkali to a first treatment liquid obtained in the leaching step to precipitate iron in the first treatment liquid; a first solid-liquid separation step of performing solid-liquid separation of the second treatment liquid obtained in the precipitation step; a water washing step of washing the solids separated in the first solid-liquid separation step; and a second solid-liquid separation step of performing solid-liquid separation of the third treatment liquid obtained in the water washing step, wherein the solids are washed in the water washing step so that a water washing index h represented by the following formula 1 is 54 or more. h=4.26×L / S-13.4×N-0.782×t+53.3 1 In the above formula 1, L / S means the liquid-solid ratio of washing water to solids (washing water / solids) based on mass, N means the number of times washing water is used (wherein N=1 is the number of times fresh washing water is used, and N≧2 is the number of times washing water used repeatedly in the washing step), and t means the stirring time [min].

[0017] According to this method for producing low-zinc iron-making dust, iron-making dust with a reduced zinc content can be easily produced.

[0018] In this disclosure, the term "iron-making dust" refers to dust that is generated in the iron-making process and contains iron. The term "dust" also includes sludge and mill scale.

[0019] [Details of the embodiment of the present disclosure] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings as appropriate. Note that, for the numerical values ​​described in this specification, only one of the upper limit value and the lower limit value described can be adopted, or the upper limit value and the lower limit value can be arbitrarily combined. In this specification, all of the numerical ranges that can be combined are described as suitable ranges.

[0020] <Method for removing zinc and method for producing low-zinc ironmaking dust> As shown in FIG. 1, the zinc removal method includes a leaching process S1 in which an acid is added to a suspension in which zinc-containing steel dust is dispersed to leach zinc into the liquid phase of the suspension, a precipitation process S2 in which an oxidizing agent and an alkali are added to the first treatment liquid obtained in the leaching process S1 to precipitate iron in the first treatment liquid, a first solid-liquid separation process S3 in which the second treatment liquid obtained in the precipitation process S2 is subjected to solid-liquid separation, a water washing process S4 in which the solid content separated in the first solid-liquid separation process S3 is washed with water, and a second solid-liquid separation process S5 in which the third treatment liquid obtained in the water washing process S4 is subjected to solid-liquid separation.

[0021] In the zinc removal method, in the water washing step S4, the solid content is washed with water so that the water washing index h, represented by the following formula 1, is 54 or more. h=4.26×L / S-13.4×N-0.782×t+53.3 1 In the above formula 1, L / S means the liquid-solid ratio of washing water to solids (washing water / solids) based on mass, N means the number of times washing water is used (wherein N=1 is the number of times fresh washing water is used, and N≧2 is the number of times washing water used repeatedly in the washing step S4), and t means the stirring time [min].

[0022] The present inventors have intensively studied a method for removing zinc from iron-making dust so that the zinc can be used in the sintering step of the iron-making process. As a result, the present inventors have found that zinc can be easily removed to a low concentration by controlling the water washing index h in the water washing step S4. The zinc removal method can reliably remove zinc from the iron-making dust by washing the solid content with water in the water washing step S4 so that the water washing index h is 54 or more.

[0023] The steelmaking dust from which zinc has been removed by the zinc removal method can be reused as low-zinc steelmaking dust. That is, the zinc removal method can be used as a method for producing low-zinc steelmaking dust. The method for producing low-zinc steelmaking dust is one aspect of the present disclosure. According to the method for producing low-zinc steelmaking dust, steelmaking dust with a reduced zinc content can be easily produced.

[0024] Each step in the zinc removal method and the method for producing low-zinc iron-making dust will be described in detail below.

[0025] (Leaching process S1) In the leaching step S1, zinc contained in the iron dust is leached into the liquid phase of the suspension. More specifically, in the leaching step S1, zinc compounds contained in the iron dust are dissolved in the liquid phase of the suspension. The leaching step S1 can be carried out, for example, under a room temperature environment. The suspension used in the leaching step S1 may be, for example, recovered from a thickener of a blast furnace, and may be heated when recovered. For example, the initial temperature of the suspension in the leaching step S1 may be 40°C or higher and 60°C or lower.

[0026] The iron-making dust is not particularly limited, and examples thereof include blast furnace dust, cold rolling sludge, etc. The suspension may be a slurry recovered from a thickener when the iron-making dust is wet dust, or may be a suspension obtained by adding water such as industrial water to the dry dust when the iron-making dust is dry dust.

[0027] The lower limit of the liquid-solid ratio (liquid / solid) of the suspension on a mass basis is preferably 3.5, more preferably 4.0, from the viewpoint of smoothly stirring the suspension with a stirrer. On the other hand, the upper limit of the liquid-solid ratio can be determined from the viewpoint of keeping the scale of the treatment tank as small as possible and suppressing capital investment costs.

[0028] The acid to be added to the suspension may be any acid capable of leaching out zinc, such as hydrochloric acid, sulfuric acid, nitric acid, etc. Among these, hydrochloric acid is preferred from the viewpoints that it is relatively inexpensive, can selectively precipitate iron in the first treatment liquid in the precipitation step S2 described below, and can easily obtain solids without desulfurization load during recycling. By using hydrochloric acid as the acid, ironworks dust with a reduced zinc content (low-zinc ironworks dust) can be easily produced.

[0029] In the leaching step S1, it is preferable to stir the suspension after or while adding the acid to the suspension, which allows zinc to be easily and reliably leached into the liquid phase of the suspension.

[0030] The lower limit of the treatment time (mixing time) in the leaching step S1 is preferably 60 minutes, more preferably 80 minutes, and even more preferably 100 minutes, from the viewpoint of sufficiently leaching zinc into the liquid phase. On the other hand, the upper limit of the treatment time can be, for example, 200 minutes or may be 150 minutes, from the viewpoint of easily maintaining the effect of increasing the amount of zinc leached and from the viewpoint of sufficiently increasing the amount of treatment in the leaching step S1.

[0031] In the leaching step S1, the pH of the suspension is controlled by adding the acid. The lower limit of the pH of the suspension after the addition of the acid is preferably 0.5, more preferably 0.8, from the viewpoint of selectively leaching zinc while suppressing the leaching of iron, and from the viewpoint of suppressing the increase in material costs, equipment costs, etc. due to the increase in the amount of the acid added. That is, in the leaching step S1, iron may also be leached into the suspension, but it is easy to selectively leach zinc by controlling the pH. On the other hand, the upper limit of the pH is preferably 2.0, more preferably 1.5, from the viewpoint of suppressing the amount of zinc leached from being insufficient.

[0032] (Precipitation process) The treatment liquid after zinc is leached into the liquid phase of the suspension in the leaching step S1 is supplied to the precipitation step S2 as a first treatment liquid. The precipitation step S2 can be performed consecutively to the leaching step S1. In the precipitation step S2, iron (more specifically, iron hydroxide) is precipitated in the first treatment liquid, thereby increasing the iron recovery rate and improving the reuse efficiency of the iron-making dust. The precipitation step S2 can be performed, for example, in a room temperature environment.

[0033] Examples of the oxidizing agent added to the first treating liquid in the precipitation step S2 include hydrogen peroxide, hypochlorous acid, permanganic acid, chlorine, ozone, oxygen, air, etc. Examples of the alkali added to the first treating liquid in the precipitation step S2 include caustic soda, quicklime, slaked lime, limestone, magnesium hydroxide, sodium carbonate, etc.

[0034] The oxidizing agent oxidizes the iron contained in the first treatment liquid. More specifically, the oxidizing agent oxidizes the divalent iron contained in the first treatment liquid to trivalent iron. This makes it easy to selectively precipitate iron while dissolving zinc in the liquid phase of the first treatment liquid.

[0035] The alkali controls the pH of the first treatment liquid. More specifically, the alkali controls the pH of the first treatment liquid so as to selectively precipitate iron (iron(III)) in the first treatment liquid while zinc is dissolved in the liquid phase of the first treatment liquid.

[0036] The lower limit of the pH of the first treatment liquid controlled by the alkali is preferably 2.4, more preferably 2.7, from the viewpoint of sufficiently precipitating iron (iron(III)) in the first treatment liquid. On the other hand, the upper limit of the pH is preferably 4.5, more preferably 3.5, from the viewpoint of suppressing precipitation of zinc (e.g., zinc hydroxide) in the first treatment liquid. In the zinc removal method, for example, hydrochloric acid is used as the acid in the leaching step S1, and the pH of the first treatment liquid is controlled within the above range in the precipitation step S2, which makes it easy to selectively precipitate iron in the first treatment liquid.

[0037] In the precipitation step S2, after adding a certain amount of the oxidizing agent and the alkali to the first treatment liquid, one or both of the oxidizing agent and the alkali may be further added while stirring the first treatment liquid. The oxidizing agent may be added so that the ORP (Oxidation-Reduction Potential) is 600 mV or more. According to this configuration, the divalent iron contained in the first treatment liquid can be easily and reliably oxidized to trivalent iron. The alkali may be added so that the pH of the first treatment liquid is controlled within the above range. According to this configuration, iron can be selectively precipitated in the first treatment liquid. The treatment time in the precipitation step S2 (the stirring time of the first treatment liquid) can be, for example, 20 minutes or more and 60 minutes or less.

[0038] (1st solid-liquid separation step) The treated liquid from which iron has been precipitated in the precipitation step S2 is supplied as a second treated liquid to a first solid-liquid separation step S3. The first solid-liquid separation step S3 can be carried out consecutively to the precipitation step S2.

[0039] Examples of the device for performing solid-liquid separation of the second treated liquid in the first solid-liquid separation step S3 include a vacuum filter, a filter press, a belt press, a screw press, and a centrifugal dehydrator.

[0040] (Water washing process) In the water-washing step S4, the zinc compounds contained in the solid fraction separated in the first solid-liquid separation step S3 are dissolved and removed from the solid fraction. At the same time, in the water-washing step S4, the zinc contained in the filtrate and adhering to the solid fraction is removed.

[0041] As described above, in the water-washing step S4, the solid content is washed with water so that the water-washing index h, represented by the following formula 1, is 54 or more. The following formula 1 was determined by extracting three operation factors assumed in the water-washing step S4 and conducting an experiment using these as parameters. The lower limit of the water-washing index h is preferably 60, and more preferably 65. h=4.26×L / S-13.4×N-0.782×t+53.3 1 In the above formula 1, L / S means the liquid-solid ratio of washing water to solids (washing water / solids) based on mass, N means the number of times washing water is used (wherein N=1 is the number of times fresh washing water is used, and N≧2 is the number of times washing water used repeatedly in the washing step S4), and t means the stirring time [min].

[0042] In the water-washing step S4, the solid content is immersed in the wash water to wash it. The number of times of water washing in the water-washing step S4 may be one. In the water-washing index h, if L / S is large, the zinc concentration in the wash water decreases, and the dissolution rate and amount of zinc increase. Therefore, from the viewpoint of removing zinc from the solid content, it is preferable that L / S is large. On the other hand, if L / S is too large, the scale of the equipment becomes too large, the equipment costs increase, and it becomes difficult to realize. Therefore, the upper limit of L / S is preferably 15, and more preferably 10. In other words, the zinc removal method is suitable for efficiently and reliably removing zinc contained in the steel dust while suppressing equipment costs, etc.

[0043] In the water washing step S4, the separated liquid separated in the second solid-liquid separation step S5 can be repeatedly used as the washing water. In this case, N in the above formula 1 becomes N≧2 depending on the number of repetitions. In the above water washing index h, as N increases, the zinc concentration in the washing water increases, and the dissolution rate and amount of zinc decrease. Therefore, from the viewpoint of removing zinc from the solid content, it is preferable that N is small.

[0044] In the above-mentioned water washing index h, if t is large, the amount of foreign precipitates may increase. From this viewpoint, in the water washing step S4, it is desirable that t is small within a range in which the washing water can be appropriately stirred. From the viewpoint of appropriately stirring the washing water, t can be made to be larger than 0 (t>0), and the lower limit thereof may be 0.5 or 1.

[0045] In the water-washing step S4, for example, the solids are immersed in wash water, and the wash water in which the solids are immersed is stirred. That is, L / S in the above formula 1 is the value when the solids are immersed in the wash water, and t is the time for which the wash water is stirred with the solids immersed in the wash water. In this way, the zinc compounds contained in the solids can be easily and reliably dissolved in the wash water. As a result, the zinc contained in the steel dust can be more easily and reliably removed.

[0046] In the water washing step S4, the separated liquid (washing water used in the water washing step S4) separated in the second solid-liquid separation step S5 as described above is repeatedly used. This configuration reduces the total discharge amount of the separated liquid, and reduces wastewater treatment costs and the burden on the surrounding environment. In the zinc removal method, by controlling the number of times N of washing water usage and the mixing time t in the water washing step S4, it is possible to more efficiently remove zinc contained in the steel dust while effectively utilizing the separated liquid separated in the second solid-liquid separation step S5.

[0047] Examples of the washing water include desalted water, pure water, distilled water, tap water, industrial water, etc. In the zinc removal method, tap water or industrial water can be used as the first washing water (N=1).

[0048] The upper limit of the dezincing rate in the water washing step S4 is preferably 50.0%, more preferably 55.0%, further preferably 60.0%, and particularly preferably 65.0%. According to the zinc removal method, the dezincing rate in the water washing step S4 can be easily and reliably increased. The "dezincing rate" means a value calculated by the following formula 2 using the zinc concentration C1 [mass%] in the solid content to be subjected to the water washing step S4 and the zinc concentration C2 [mass%] in the solid content after the water washing step S4. Dezincification rate R [%] = (C1-C2) / C1 × 100 2

[0049] The upper limit of the zinc concentration in the solid content after the water-washing step S4 is preferably 0.35 mass%, more preferably 0.32 mass%, and even more preferably 0.28 mass%. According to the zinc removal method, the zinc concentration in the solid content after the water-washing step S4 can be easily and reliably reduced.

[0050] (Second solid-liquid separation step) The treated liquid after the completion of the washing in the water-washing step S4 is supplied to the second solid-liquid separation step S5 as the third treated liquid. That is, the third treated liquid can be in a state in which the solid content is immersed in the washing water at the completion of the water-washing step S4. The second solid-liquid separation step S5 can be carried out continuously to the water-washing step S4. The solid content separated by the second solid-liquid separation step S5 is constituted as low-zinc iron-making dust with a reduced zinc content. The separated liquid separated in the second solid-liquid separation step S5 can be used as the washing water (N≧2) in the water-washing step S4.

[0051] Examples of the device for performing solid-liquid separation of the third treated liquid in the second solid-liquid separation step S5 include a vacuum filter, a filter press, a belt press, a screw press, and a centrifugal dehydrator.

[0052] [Other embodiments] The above-mentioned embodiment does not limit the configuration of the present invention. Therefore, the above-mentioned embodiment may omit, replace or add components of each part of the above-mentioned embodiment based on the description in this specification and common technical knowledge, and it should be construed that all of these are within the scope of the present invention.

[0053] For example, the zinc removal method is not intended to exclude the use of rinsing procedures other than immersion and agitation in the rinsing step. EXAMPLES

[0054] Hereinafter, the present disclosure will be described in detail based on examples, but the present disclosure should not be construed as being limited based on the description of these examples.

[0055] (No.1 to No.27) The zinc was removed from the ironworks dust containing zinc by carrying out the above-mentioned leaching step S1, precipitation step S2, first solid-liquid separation step S3, water washing step S4, and second solid-liquid separation step S5 in this order. The ironworks dust used was a mixture of blast furnace dust containing 1.73% zinc by mass and cold-rolled sludge containing 7.27% zinc by mass in a mass ratio of 90:10.

[0056] [Leaching process] The above-mentioned iron dust and tap water were put into a 500cc glass beaker, and the liquid-solid ratio (liquid / solid) was adjusted to 4. Furthermore, hydrochloric acid (special grade hydrochloric acid reagent with a hydrogen chloride content of 35 mass% ("080-010661-0" manufactured by Matsunoen Pharmaceutical Co., Ltd.) was added to the obtained suspension, while stirring the suspension with a stirrer. In the leaching step S1, the pH of the suspension was constantly measured, and the above-mentioned hydrochloric acid was additionally added so that the pH was 1. The treatment time in the leaching step S1 was 120 minutes.

[0057] [Precipitation process] The first treatment liquid obtained in the leaching step S1 was stirred in a beaker while an oxidizing agent (special grade hydrogen peroxide solution containing 30 mass% hydrogen peroxide ("081-04215" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added. The oxidizing agent was added all at once at the beginning of the precipitation step S2.

[0058] In the precipitation step S2, an alkali (a slaked lime slurry with a slurry concentration of 23 mass %) was added while stirring the first treatment liquid. The treatment time for the precipitation step S2 was set to 30 minutes, and the alkali was added so that the pH of the first treatment liquid became 30 minutes after the start of the precipitation step S2 while constantly measuring the pH of the first treatment liquid.

[0059] [First solid-liquid separation step] In the first solid-liquid separation step S3, the second treated liquid after the completion of the precipitation step S2 was subjected to solid-liquid separation using a vacuum filter having a membrane filter (diameter 90 mmφ, pore size 0.45 μm).

[0060] [Water washing process and second solid-liquid separation process] In the water washing step S4, the solid matter separated in the first solid-liquid separation step S3 was washed with water. Specifically, the first water washing (N=1) was performed using demineralized water as the washing water and a 100cc glass beaker as the washing container so as to obtain the liquid-solid ratio (L / S) and stirring time t in Table 1. In addition, after this washing, the second solid-liquid separation step S5 was performed on the obtained third treatment liquid. The solid matter obtained in this second solid-liquid separation step S5 was used as a sample (low-zinc iron dust) with the number of uses N=1, and the obtained separated liquid was used as the washing water (N=2) for the solid matter separated in the first solid-liquid separation step S3 performed in the same manner as above to perform the water washing step S4. Furthermore, the second solid-liquid separation step S5 was performed on the third treatment liquid after washing in this water washing step S4. The obtained solid matter was used as a sample with a usage count of N=2, and the obtained separated liquid was used as washing water (N=3) for the solid matter separated in the first solid-liquid separation step S3, which was carried out in the same manner as above, to carry out the water washing step S4.

[0061] <Water wash index> The water washing index h, expressed by the following formula 1, was calculated for No. 1 to No. 27. The results are shown in Table 1. h=4.26×L / S-13.4×N-0.782×t+53.3 1 In the above formula 1, L / S means the liquid-solid ratio of washing water to solids (washing water / solids) based on mass, N means the number of times washing water is used (wherein N=1 is the number of times fresh washing water is used, and N≧2 is the number of times washing water used repeatedly in the washing step S4), and t means the stirring time [min].

[0062] <Dezincification rate> For No. 1 to No. 27, the zinc removal rate R in the water washing step S4, which is represented by the following formula 2, was determined. The results are shown in Table 1. Dezincification rate R [%] = (C1-C2) / C1 × 100 2 In the above formula 2, C1 means the zinc concentration [mass %] in the solid content to be subjected to the water-washing step S4, and C2 means the zinc concentration [mass %] in the solid content after the water-washing step S4.

[0063] <Zinc concentration> For No. 1 to No. 27, the zinc concentration C1 [mass %] in the solid content subjected to the water-washing step S4 and the zinc concentration C2 [mass %] in the solid content after the water-washing step S4 were determined. The results are shown in Table 1.

[0064] [Table 1]

[0065] <Evaluation Results> As shown in Table 1, in No. 1 to No. 9, which have a water washing index h of 54 or more in the water washing step S4, the dezincing rate can be reliably increased. [Industrial Applicability]

[0066] As described above, the zinc removal method according to one embodiment of the present disclosure is suitable for reliably removing zinc contained in steelmaking dust.

Claims

1. a leaching step in which zinc is leached into the liquid phase of a suspension in which zinc-containing steel dust is dispersed by adding an acid to said suspension; a precipitation step of precipitating iron in the first treatment liquid obtained in the leaching step by adding an oxidizing agent and an alkali to the first treatment liquid; a first solid-liquid separation step of performing solid-liquid separation on the second treated liquid obtained in the precipitation step; a water washing step of washing the solid matter separated in the first solid-liquid separation step; a second solid-liquid separation step of subjecting the third treated liquid obtained in the water washing step to solid-liquid separation; Equipped with The zinc removal method comprises washing the solid content with water in such a manner that a water washing index h, represented by the following formula 1, is 54 or more in the water washing step. h=4.26×L / S-13.4×N-0.782×t+53.3...1 In the above formula 1, L / S means the liquid-solid ratio of washing water to solids (washing water / solids) on a mass basis, N means the number of uses of washing water (wherein N=1 is the number of uses when fresh washing water is used, and N≧2 is the number of uses when washing water used in the washing step is repeatedly used), and t means the stirring time [min].

2. 2. The method for removing zinc according to claim 1, wherein said acid is hydrochloric acid.

3. In the above washing step, agitating the wash water in which the solid matter is immersed; 3. The method for removing zinc according to claim 1, wherein the separated liquid from the second solid-liquid separation step is repeatedly used as the washing water.

4. a leaching step in which zinc is leached into the liquid phase of a suspension in which zinc-containing steel dust is dispersed by adding an acid to said suspension; a precipitation step of precipitating iron in the first treatment liquid obtained in the leaching step by adding an oxidizing agent and an alkali to the first treatment liquid; a first solid-liquid separation step of performing solid-liquid separation on the second treated liquid obtained in the precipitation step; a water washing step of washing the solid matter separated in the first solid-liquid separation step; a second solid-liquid separation step of subjecting the third treated liquid obtained in the water washing step to solid-liquid separation; Equipped with The method for producing low-zinc ironworks dust comprises washing the solids with water in such a manner that a water washing index h, represented by the following formula 1, is 54 or more in the water washing step. h=4.26×L / S-13.4×N-0.782×t+53.3...1 In the above formula 1, L / S means the liquid-solid ratio of washing water to solids (washing water / solids) on a mass basis, N means the number of uses of washing water (wherein N=1 is the number of uses when fresh washing water is used, and N≧2 is the number of uses when washing water used in the washing step is repeatedly used), and t means the stirring time [min].

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