JP2024176830A - Zinc removal method and method for producing low-zinc ironmaking dust - Google Patents

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

This disclosure relates to a method for removing zinc and a method for producing low-zinc ironmaking dust.

Since steel dust contains iron, it 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, there is an upper limit to the amount of zinc that can be charged into a blast furnace, so steel dust that contains more zinc than the allowable amount cannot be used as a raw material. As a result, such steel dust must be processed externally, which not only means that it cannot be used as an iron source, but also requires additional processing costs.

Today, technology has been proposed to remove zinc from steel dust in order to reuse the dust (see Patent Document 1).

Special table 2017-506700 publication

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

However, the method described in Patent Document 1 does not seem to be able to sufficiently dissolve the Zn salts present in the solid particles and wash them away to remove them.

This disclosure was made based on these circumstances, and aims to provide a zinc removal method that can reliably remove zinc contained in steelmaking dust.

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) 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].

The zinc removal method according to one aspect of the present disclosure can reliably remove zinc contained in steelmaking dust.

FIG. 1 is a flow diagram illustrating a zinc removal method according to one embodiment of the present disclosure.

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

(1) A zinc removal method according to one aspect of the present disclosure includes a leaching step of adding an acid to a suspension in which zinc-containing steelmaking 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) 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].

In this zinc removal method, the solids are washed in the water washing step so that the water washing index h is 54 or more, so that the zinc contained in the steel dust can be reliably removed.

(2) In the above (1), it is preferable that the acid is hydrochloric acid. In this way, by using hydrochloric acid as the acid, the zinc contained in the steel dust can be sufficiently removed, and solids with a high iron content can be obtained that do not impose a desulfurization load when recycled.

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

A method for producing low-zinc ironworks dust according to another embodiment of the present disclosure includes a leaching step of adding an acid to a suspension in which zinc-containing ironworks 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 component 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 component 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) 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].

This method for producing low-zinc ironmaking dust makes it easy to produce ironmaking dust with a reduced zinc content.

In this disclosure, "iron-making dust" refers to dust that is generated during the iron-making process and contains iron. "Dust" also includes sludge and mill scale.

[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.

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

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) on a mass basis, N means the number of times washing water has been 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 in the washing step S4 is repeatedly used), and t means the stirring time [min].

The inventors have conducted extensive research into methods for removing zinc from ironmaking dust so that it can be used in the sintering step of the ironmaking process. As a result, the inventors have discovered that zinc can be easily removed to a low concentration by controlling the water washing index h in the water washing step S4. This zinc removal method can reliably remove zinc from the ironmaking dust by washing the solids in the water washing step S4 so that the water washing index h is 54 or more.

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

The zinc removal method and each step in the method for producing low-zinc ironmaking dust are explained in detail below.

(Leaching step 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.

The above-mentioned iron-making dust is not particularly limited, and examples thereof include blast furnace dust, cold rolling sludge, etc. As the above-mentioned suspension, if the above-mentioned iron-making dust is wet dust collection, an example thereof is a slurry recovered from a thickener. Furthermore, if the above-mentioned iron-making dust is dry dust collection, an example thereof is a suspension obtained by adding water such as industrial water to the dry dust collection.

The lower limit of the liquid-solid ratio (liquid/solid) of the suspension by mass 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 size of the treatment tank as small as possible and suppressing capital investment costs.

The acid to be added to the suspension may be any acid capable of leaching zinc, such as hydrochloric acid, sulfuric acid, and nitric acid. Among these, hydrochloric acid is preferred because 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, ironmaking dust with a reduced zinc content (low-zinc ironmaking dust) can be easily produced.

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

The lower limit of the processing 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 processing 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 processing amount in the leaching step S1.

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 increases in material costs, equipment costs, etc. due to an increase in the amount of the acid added. That is, in the leaching step S1, iron may also be leached into the suspension, but by controlling the pH, it becomes easy to selectively leach zinc. On the other hand, the upper limit of the pH is preferably 2.0, more preferably 1.5, from the viewpoint of suppressing an insufficient amount of zinc leaching.

(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 dust. The precipitation step S2 can be performed, for example, in a room temperature environment.

The oxidizing agent added to the first treatment liquid in the precipitation step S2 may be, for example, hydrogen peroxide, hypochlorous acid, permanganic acid, chlorine, ozone, oxygen, air, etc. Furthermore, the alkali added to the first treatment liquid in the precipitation step S2 may be, for example, caustic soda, quicklime, slaked lime, limestone, magnesium hydroxide, sodium carbonate, etc.

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 easier to selectively precipitate iron while dissolving zinc in the liquid phase of the first treatment liquid.

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.

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.

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, for example, so that the ORP (Oxidation-Reduction Potential) is 600 mV or more. With this configuration, the divalent iron contained in the first treatment liquid can be easily and reliably oxidized to trivalent iron. In addition, the alkali may be added, for example, so that the pH of the first treatment liquid is controlled within the above range. With this configuration, iron can be selectively precipitated in the first treatment liquid. The treatment time in the precipitation step S2 (stirring time of the first treatment liquid) can be, for example, 20 minutes or more and 60 minutes or less.

(First 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 may be carried out consecutively to the precipitation step S2. can.

Examples of devices that separate the second treatment liquid into solid and liquid in the first solid-liquid separation step S3 include a vacuum filter, a filter press, a belt press, a screw press, a centrifugal dehydrator, etc.

(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.

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) on a mass basis, N means the number of times washing water has been 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 in the washing step S4 is repeatedly used), and t means the stirring time [min].

In the water washing step S4, the solids are immersed in the wash water to wash them. The number of washes in the water washing step S4 may be one. In the water washing index h, if the 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 solids, it is preferable that the L/S is large. On the other hand, if the L/S is too large, the equipment scale becomes excessive, the equipment costs increase, and it becomes difficult to realize. Therefore, the upper limit of the 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.

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.

In the above water washing index h, as t increases, the amount of foreign precipitates may increase. From this perspective, 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 perspective of appropriately stirring the washing water, t can be greater than 0 (t>0), and the lower limit thereof may be 0.5 or 1.

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.

In addition, 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 water washing step S4, the zinc removal method controls the number of times N the wash water is used and the mixing time t, thereby making effective use of the separated liquid separated in the second solid-liquid separation step S5 and more efficiently removing zinc contained in the steel dust.

Examples of the above-mentioned 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 washing water for the first time (N=1).

The upper limit of the dezincing rate in the water washing step S4 is preferably 50.0%, more preferably 55.0%, even more 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 x 100 ... 2

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 this zinc removal method, the zinc concentration in the solid content after the water washing step S4 can be easily and reliably reduced.

(Second solid-liquid separation step)
The treated liquid after the completion of the washing in the washing step S4 is supplied to the second solid-liquid separation step S5 as a third treated liquid. The solid matter separated by the second solid-liquid separation step S5 may be in a state of being immersed in water. The second solid-liquid separation step S5 may be performed continuously after the water washing step S4. The resulting low-zinc iron-making dust has a reduced zinc content. The separated liquid in the second solid-liquid separation step S5 can be used as washing water (N≧2) in the water-washing step S4.

Examples of devices that separate the third treatment liquid into solid and liquid in the second solid-liquid separation step S5 include a vacuum filter, a filter press, a belt press, a screw press, a centrifugal dehydrator, etc.

[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 understood that all of these are within the scope of the present invention.

For example, the zinc removal method is not intended to exclude the use of water washing procedures other than immersion and agitation in the water washing step.

The present disclosure will be described in detail below based on examples, but the present disclosure should not be interpreted in a restrictive manner based on the description of these examples.

(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.

[Leaching process]
The above-mentioned iron dust and tap water were put into a 500 cc 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 hydrochloric acid was additionally added so that the pH was 1. The treatment time in the leaching step S1 was 120 minutes.

[Precipitation process]
The first treatment liquid obtained in the leaching step S1 was stirred in a beaker, and an oxidizing agent (special grade hydrogen peroxide solution containing 30% by mass of 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.

In the precipitation step S2, an alkali (a hydrated lime slurry with a slurry concentration of 23% by 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 reached 30 minutes after the start of the precipitation step S2 while constantly measuring the pH of the first treatment liquid.

[First solid-liquid separation step]
In the first solid-liquid separation step S3, the second treatment 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).

[Water washing step and second solid-liquid separation step]
In the water washing step S4, the solid matter separated in the first solid-liquid separation step S3 was washed with water. Specifically, desalted water was used as the washing water, and a 100 cc glass beaker was used as the washing container, and the washing water was washed with the water shown in Table 1. The first water washing (N=1) was carried out so that the liquid-solid ratio (L/S) and the stirring time were t. After this water washing, the third treated liquid obtained was subjected to a second solid-liquid separation process. The solid fraction obtained in the second solid-liquid separation step S5 was used as a sample (low-zinc ironworks dust) with N=1 use, and the separated liquid was separated in the same manner as above. The washing step S4 was carried out using the water (N=2) for washing the solid matter separated in the first solid-liquid separation step S3. The liquid separation step S5 was carried out. The obtained solid matter was used as a sample with N=2 usage times, and the obtained separated liquid was washed with water (N = 3) was used to carry out the water washing step S4.

<Water washing index>
The water washing index h, represented 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) on a mass basis, N means the number of times washing water has been 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 in the washing step S4 is repeatedly used), and t means the stirring time [min].

<Dezincification rate>
For No. 1 to No. 27, the dezincing 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 x 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.

<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.

<Evaluation Results>
As shown in Table 1, in No. 1 to No. 9 in which the water washing index h in the water washing step S4 is 54 or more, the dezincing rate can be reliably increased.

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 (4)

a leaching step of adding an acid to a suspension in which zinc-containing steel dust is dispersed to leach zinc into the liquid phase of the 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 performing solid-liquid separation on the third treated liquid obtained in the water washing step,
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]. The method for removing zinc according to claim 1, wherein the acid is hydrochloric acid. 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. a leaching step of adding an acid to a suspension in which zinc-containing steel dust is dispersed to leach zinc into the liquid phase of the 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 performing solid-liquid separation on the third treated liquid obtained in the water washing step,
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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