Treatment method for ironmaking dust

Abstract

To provide a treatment method for iron-making dust which can simply separate zinc contained in ion-making dust at low cost.SOLUTION: A treatment method of iron-making dust includes: a dust mixing step of a converter dust slurry containing converter dust and a blast furnace dust slurry containing blast furnace dust, and converting the mixture into a mixed dust slurry; a wet classification step of separating the mixed dust slurry into a coarse dust slurry containing coarse dust with little zinc, and a fine dust slurry containing fine dust with much zinc; a fine dust concentration step of concentrating the separated fine dust slurry, and converting it into the concentrated fine dust slurry; a coarse dust dilution step of mixing water with the separated coarse dust slurry, diluting the mixture, and converting it into a diluted coarse dust slurry; a fine dust dehydration step of dehydrating the concentrated fine dust slurry, and obtaining a fine dust dehydrated case; and a coarse dust dehydration step of dehydrating the diluted coarse dust slurry, and obtaining a coarse dust dehydrated cake.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for treating iron-making dust. [Background technology]

[0002] Dust (steel dust) generated during steelmaking processes such as the blast furnace and converter processes mainly contains iron, so efforts have long been made to recycle it by returning it to the steelmaking process.

[0003] However, the amount of steel dust that can be recycled is limited by the zinc content of the dust, which forms deposits inside the blast furnace and adversely affects its operation. Therefore, in order to promote the recycling of steel dust, it is necessary to remove the zinc from the dust.

[0004] Furthermore, due to growing demands for CO2 reduction in the steelmaking process, the use of scrap iron has increased in recent years. Because scrap iron is coated with zinc, the amount of zinc contained in converter dust is expected to increase in the future.

[0005] There are many different methods for separating zinc from steel dust, but the hydrocyclone method, which can separate zinc using simple equipment, is widely used. This method separates and recovers zinc by centrifugal sieving (classifying) the iron dust into coarse and fine particles, since the zinc in the iron dust is mainly fine particles.

[0006] For the purpose of further increasing the efficiency of zinc separation, Patent Document 1, for example, proposes a method in which slurry-like wet blast furnace dust is subjected to ultrasonic treatment and then passed through a wet cyclone, with the upper recovered material being a zinc-based recovered material and the lower recovered material being again subjected to wet cyclone treatment and magnetic separation treatment, thereby separating the material into a zinc-based recovered material, an iron-based recovered material, and a carbon-based recovered material. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-023720 Summary of the Invention [Problem to be solved by the invention]

[0008] The zinc recovery method of Patent Document 1 requires multiple wet classification processes to separate zinc, making the process complicated. Furthermore, dilution is required before the second wet classification process, and there is a concern that the expected zinc separation ability will not be achieved unless an appropriate dilution concentration is set depending on the results of the first classification process. Furthermore, there is a concern that zinc physically or chemically bound to the surface of magnetic metallic iron (M.Fe) or ferrous oxide (FeO) particles will migrate to the iron-based recovered product along with M.Fe or FeO during magnetic separation, resulting in a decrease in zinc separation efficiency.

[0009] Therefore, an object of the present invention is to propose a method for treating iron-making dust that can separate zinc contained in the iron-making dust simply and at low cost. [Means for solving the problem]

[0010] The present inventors have conducted extensive research into ways to solve the above problems, and as a result have found that it is extremely effective to first mix blast furnace dust and converter dust, and then wet classify the mixed dust into fine dust and coarse dust, thereby completing the present invention.

[0011] The gist and configuration of the present invention are as follows. [1] A dust mixing step of mixing a converter dust slurry containing converter dust and a blast furnace dust slurry containing blast furnace dust to form a mixed dust slurry; a wet classification step of separating the mixed dust slurry into a coarse dust slurry containing coarse dust with a low zinc content and a fine dust slurry containing fine dust with a high zinc content; a fine dust concentrating step of concentrating the separated fine dust slurry to form a concentrated fine dust slurry; a coarse dust dilution step of mixing the separated coarse dust slurry with water to dilute it to form a diluted coarse dust slurry; a fine dust dehydration step of dehydrating the concentrated fine dust slurry to obtain a dehydrated fine dust cake; a coarse dust dewatering step of dewatering the diluted coarse dust slurry to obtain a coarse dust dewatered cake; A method for treating ironmaking dust, comprising:

[0012] [2] The method for treating iron-making dust described in [1], wherein the dust mixing step is carried out so that the total Fe (T.Fe) concentration of the resulting mixed dust slurry is 25 mass% or more and 60 mass% or less.

[0013] [3] The method for treating iron-making dust according to [1] or [2], wherein the dust mixing step is carried out so that the concentration of the resulting mixed dust slurry is 5% by mass or more and 40% by mass or less.

[0014] [4] The method for treating iron manufacturing dust according to any one of [1] to [3] above, wherein the wet classification step is carried out using a wet cyclone.

[0015] [5] A method for treating iron manufacturing dust according to any one of [1] to [4], wherein the fine dust concentration step is carried out so that the concentration of the concentrated fine dust slurry obtained is 10% by mass or more and 50% by mass or less.

[0016] [6] A method for treating iron manufacturing dust according to any one of [1] to [5], wherein the coarse dust dilution step is carried out so that the concentration of the diluted coarse dust slurry obtained is 10% by mass or more and 50% by mass or less.

[0017] [7] The method for treating iron manufacturing dust according to any one of [1] to [6], wherein the water used in the coarse dust dilution step is water produced in the fine dust concentration step.

[0018] [8] A method for treating iron-making dust according to any one of claims [1] to [7], wherein the fine dust dewatering step is carried out so that the moisture content of the resulting fine dust dewatered cake is 35 mass% or less.

[0019] [9] A method for treating iron manufacturing dust according to any one of claims [1] to [8], wherein the coarse dust dewatering step is carried out so that the moisture content of the resulting coarse dust dewatered cake is 35 mass% or less.

[0020]

[10] The method for treating iron manufacturing dust according to any one of [1] to [9], wherein the coarse dust dewatered cake obtained in the coarse dust dewatering step is fed into a sintering machine, a rotary hearth furnace, or a rotary kiln, and reused as an iron source.

[0021]

[11] The method for treating iron manufacturing dust according to any one of [1] to [9], wherein the coarse dust dewatered cake obtained in the coarse dust dewatering step is mixed with at least a portion of the fine dust dewatered cake obtained in the fine dust dewatering step to form a mixed dewatered cake, and the mixed dewatered cake is fed into a sintering machine, a rotary hearth furnace, or a rotary kiln to be reused as an iron source. [Effects of the Invention]

[0022] According to the present invention, zinc contained in iron-making dust can be separated simply and at low cost. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a flowchart showing a preferred example of a method for treating iron manufacturing dust according to the present invention. [Figure 2] FIG. 1 is a graph showing the correlation between the T.Fe concentration of a mixed dust slurry and the mass ratio of blast furnace dust to converter dust. [Figure 3] FIG. 10 is a diagram showing the correlation between the T.Fe concentration of a mixed dust slurry and the T.Fe concentration of a coarse dust slurry. [Figure 4] FIG. 10 is a flowchart showing another preferred example of a method for treating iron manufacturing dust according to the present invention. [Figure 5] FIG. 10 is a flowchart showing yet another preferred example of a method for treating iron manufacturing dust according to the present invention. [Figure 6] FIG. 1 is a flowchart showing a method for treating iron manufacturing dust used in a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0024] (Method of treating iron-making dust) DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Figure 1 shows a flowchart of a preferred example of a method for treating iron manufacturing dust according to the present invention. The method for treating steelmaking dust according to the present invention includes a dust mixing step (step S1) of mixing a converter dust slurry containing converter dust with a blast furnace dust slurry containing blast furnace dust to form a mixed dust slurry; a wet classification step (step S2) of separating the mixed dust slurry into a coarse dust slurry containing coarse dust with low zinc content and a fine dust slurry containing fine dust with high zinc content; a fine dust concentration step (step S3) of concentrating the separated fine dust slurry to form a concentrated fine dust slurry; a coarse dust dilution step (step S4) of mixing the separated coarse dust slurry with water to dilute it to form a diluted coarse dust slurry; a fine dust dewatering step (step S5) of dewatering the concentrated fine dust slurry to form a dewatered fine dust cake; and a coarse dust dewatering step (step S6) of dewatering the diluted coarse dust slurry to form a dewatered coarse dust cake.

[0025] The present inventors have conducted extensive research into a simple and low-cost method for separating zinc from steelmaking dust. Blast furnace dust and converter dust are usually recovered as slurries using a scrubber or the like. The present inventors passed a blast furnace dust slurry containing only blast furnace dust, a mixed dust slurry containing a mixture of blast furnace dust and converter dust, and a converter dust slurry containing only converter dust through a hydrocyclone, and classified the slurry into a fine dust slurry containing zinc-rich fine dust and a fine dust slurry containing zinc-poor coarse dust, and investigated their behavior.

[0026] As a result, when only the blast furnace dust slurry was passed through, and when a mixed dust slurry of blast furnace dust and converter dust was passed through, zinc was concentrated in the fine dust slurry, whereas when only the converter dust slurry was passed through, zinc was hardly concentrated in the fine dust slurry. This is thought to be because the particle size of the iron-based particles contained in the converter dust slurry is similar to that of zinc. Furthermore, the iron concentration in the coarse dust slurry was highest in the converter dust slurry, followed by the mixed dust slurry containing blast furnace dust and converter dust, and then the blast furnace dust slurry.

[0027] Furthermore, analysis of metallic iron (M.Fe) concentrations before and after cyclone classification revealed that, as shown in Table 1, the M.Fe concentration in the coarse dust slurry increased compared to before cyclone classification at all levels, with M.Fe particularly concentrating in the coarse particles. Furthermore, calculation of the ratio of M.Fe to total Fe (T.Fe) revealed that the ratio of M.Fe to T.Fe in the coarse dust increased compared to before cyclone classification. This suggests that a reduction in the reducing agent ratio (the amount of coke and auxiliary fuel used) can be expected when the coarse dust is returned to the blast furnace as an iron source, improving its value as an iron source. In other words, to achieve both zinc separation and the recycling benefits of the iron source, it was found that mixing blast furnace dust slurry and converter dust slurry to prepare a mixed dust slurry and then passing the resulting mixed dust slurry through a hydrocyclone was sufficient.

[0028] [Table 1]

[0029] However, because the concentrations of the blast furnace dust slurry and the converter dust slurry vary depending on the operating conditions, it is difficult to maintain a constant mixing ratio by simple flow rate control, etc. However, research by the present inventors has revealed that there is a certain correlation between the T.Fe concentration of the mixed dust slurry and the mass ratio of blast furnace dust to converter dust (blast furnace dust / converter dust), as shown in Figure 2. By adjusting the mixing ratio of the blast furnace dust slurry and the converter dust slurry based on this correlation and introducing them into a hydrocyclone, it has been found that zinc can be efficiently separated by adjusting the T.Fe concentration of the resulting mixed dust slurry to 25 mass% or more and 60 mass% or less, more preferably 30 mass% or more and 55 mass% or less.

[0030] As described above, the present inventors have found that zinc can be separated simply and at low cost by mixing a blast furnace dust slurry and a converter dust slurry to prepare a mixed dust slurry and then subjecting the mixed dust slurry to a wet classification treatment, and have thus completed the present invention.

[0031] <Dust mixing process> First, in step S1, a converter dust slurry containing converter dust and a blast furnace dust slurry containing blast furnace dust are mixed to prepare a mixed dust slurry (dust mixing step).

[0032] The mixing ratio of the blast furnace dust slurry and the converter dust slurry is preferably determined by the T.Fe concentration of the mixed dust slurry, rather than the mass or volume ratio of these dust slurries. This is because the T.Fe concentrations of these dusts vary depending on the operating conditions of the blast furnace and converter. This process is preferably performed so that the T.Fe concentration of the resulting mixed dust slurry is 60% by mass or less. This is because if the T.Fe concentration of the mixed dust slurry exceeds 60% by mass, the proportion of converter dust is expected to be high, which reduces the particle size difference between zinc and iron-based particles and reduces the classification efficiency. From the perspective of classification efficiency, this process is more preferably performed so that the T.Fe concentration of the mixed dust slurry is 55% by mass or less. However, if the T.Fe concentration of the mixed dust slurry is reduced too much, the difference in specific gravity between zinc and other elements will be reduced, thereby reducing the classification efficiency of the subsequent hydrocyclone. Furthermore, as shown in Fig. 3, if the T.Fe concentration of the mixed dust slurry is reduced too much, the T.Fe concentration of the resulting coarse dust slurry will also decrease, which may result in a decrease in its value as an iron source. Therefore, this step is preferably carried out so that the T.Fe concentration of the mixed dust slurry is 25% by mass or more, and more preferably 30% by mass or more.

[0033] Furthermore, taking into consideration the subsequent wet classification step, this step is preferably carried out so that the concentration of the resulting mixed dust slurry is 5% by mass or more and 40% by mass or less. Furthermore, this step is more preferably carried out so that the concentration of the mixed dust slurry is 5% by mass or more and 40% by mass or less, while the T.Fe concentration is 60% by mass or less. In this specification, the "concentration of the mixed dust slurry" means the ratio of the mass of the mixed dust (solid content) to the total mass of the mixed dust slurry.

[0034] The method for mixing the converter dust slurry and the blast furnace dust slurry is not particularly limited, but it is preferable to use a general stirring tank and stirrer to mix the blast furnace dust slurry and the converter dust slurry as uniformly as possible.

[0035] <Wet classification process> Next, in step S2, the mixed dust slurry is separated into a coarse dust slurry containing coarse dust with little zinc and a fine dust slurry containing fine dust with a lot of zinc (wet classification step).

[0036] In this step, the mixed dust slurry is separated (by particle size classification) into a coarse dust (low-zinc dust) slurry and a fine dust (high-zinc dust) slurry. In the present invention, "coarse dust" refers to dust with a particle size of 20 μm or more, and "fine dust" refers to dust with a particle size of less than 20 μm.

[0037] Particle size classification can be performed using a sieve or by utilizing the difference in sedimentation or movement speed of particles in a fluid (fluid classification). Fluid classification is broadly divided into methods that use gravity and methods that use centrifugal force. There are no particular restrictions on the classification method, but fluid classification, especially wet cyclone classification that uses centrifugal force, is preferred.

[0038] As will be explained later, zinc exists as fine particles of about a few micrometers in size. When using a sieve for classification, zinc can be selectively recovered if the sieve openings are a few micrometers in size. However, because the sieve openings are so fine, they tend to clog easily, making stable processing difficult.

[0039] The gravity method utilizes differences in settling speed to separate the dust particles, but if the entire amount of mixed dust is to be classified by gravity settling, a huge settling tank is required, and the classification accuracy is insufficient.

[0040] In contrast, hydrocyclones are advantageous in that they can classify large amounts of slurry using small-scale equipment. Furthermore, the particle size of the particles to be classified can be estimated, for example, by using the equation described in Plitt, LR: A mathematical model of the hydrocyclone classifier, CIM Bulletin (1976), pp. 114-123. In other words, by appropriately setting the cyclone's lower outlet diameter, inlet flow rate, slurry concentration, etc., with reference to the equation described in the above literature, hydrocyclones have the advantage of easily controlling the classification performance. For these reasons, it is preferable to carry out this process using a hydrocyclone.

[0041] The concentration of the mixed dust slurry supplied to the wet cyclone is not particularly limited, but if the concentration is too low, the number of cyclones required increases, reducing equipment efficiency. Conversely, if the concentration of the mixed dust slurry is too high, it can cause equipment problems such as blockage. Therefore, as described above, it is preferable to adjust the concentration of the mixed dust slurry to 5% by mass or more and 40% by mass or less before supplying it to the wet cyclone. The concentration of the mixed dust slurry to be adjusted to within the range of 5% by mass or more and 40% by mass or less is preferably determined by referring to the formula in Non-Patent Document 1, etc.

[0042] When the mixed dust slurry flows through a hydrocyclone, particles with larger specific gravity and particle size are concentrated near the wall of the hydrocyclone, while particles with smaller specific gravity and particle size are concentrated near the center. The fine particles with small specific gravity present in the center ride the upward flow within the hydrocyclone and are collected from the top of the hydrocyclone as a fine dust slurry containing fine dust. On the other hand, the coarse particles with large specific gravity present near the wall of the hydrocyclone ride the downward flow within the hydrocyclone and are collected as a coarse dust slurry containing coarse dust.

[0043] Zinc volatilized in blast furnaces and converters generally exists as fine particles of a few micrometers in size and tends to have a lower specific gravity than iron. As a result, fine dust contains more zinc than coarse dust. In contrast, iron, especially metallic iron, has a higher specific gravity than zinc, so it tends to migrate more to the coarse dust side. In other words, coarse dust has a lower zinc concentration than blast furnace dust before passing through the hydrocyclone, making it possible to reuse it as a raw material for steelmaking.

[0044] <Fine dust concentration process> Subsequently, in step S3, the separated fine dust slurry is concentrated to form concentrated fine dust slurry (fine dust concentration step).

[0045] The fine dust slurry has a lower concentration than the mixed dust slurry before wet classification, and if it is transferred to a dehydrator in the subsequent fine dust dehydration process without being concentrated, the dehydration efficiency will be poor. Therefore, the fine dust slurry is concentrated to increase its concentration before being transferred to the fine dust dehydration process. This process is carried out by discharging a certain amount of water from the fine dust slurry.

[0046] The concentration method is not particularly limited, but may be, for example, concentration using a settling tank. Specifically, the fine dust slurry is introduced into a settling tank to settle the fine dust, the resulting supernatant water is discharged by overflow, and the fine dust, which is the solid content, is drawn out from the bottom of the tank, thereby increasing the concentration.

[0047] Regarding the concentration of the concentrated fine dust slurry, which is the fine dust slurry after concentration, if the concentration is too high, handling becomes difficult, so this step is preferably carried out so that the concentration of the obtained concentrated fine dust slurry is 10% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 40% by mass or less. In this specification, "concentration of concentrated fine dust slurry" means the ratio of the mass of fine dust (solid content) to the total mass of the concentrated fine dust slurry.

[0048] <Coarse dust dilution process> In parallel with step S3, in step S4, the separated coarse-particle dust slurry is mixed with water to dilute it, thereby forming a diluted coarse-particle dust slurry (coarse-particle dust dilution step).

[0049] In contrast to fine dust slurry, coarse dust slurry has a very high slurry concentration, which may cause problems such as equipment blockage during transportation. Therefore, in this process, the coarse dust slurry is diluted to a concentration that is easy to handle.

[0050] Regarding the concentration of the diluted coarse dust slurry, which is the coarse dust slurry after dilution, if the concentration is too low, the efficiency of dewatering in the subsequent stage will be poor. Therefore, this step is preferably carried out so that the concentration of the obtained diluted coarse dust slurry is 10% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 40% or less. In this specification, the "concentration of the diluted coarse dust slurry" means the ratio of the mass of coarse dust (solid content) to the total mass of the diluted coarse dust slurry.

[0051] The water used for dilution may be new industrial water or the like, but from the viewpoint of saving water resources, it is preferable to use water generated when concentrating the fine dust slurry, and it is more preferable to use supernatant water generated when concentrating the fine dust slurry in a settling tank, for example, as shown in Figure 4. When diluting, it is preferable to stir the coarse dust slurry and water in a stirring tank until they become homogeneous.

[0052] The fine dust concentration step in step S3 and the coarse dust dilution step in step S4 may be carried out in parallel at the same time as described above, or one step may be carried out first and the other step may be carried out later.

[0053] <Fine dust dehydration process> After step S3, in step S5, the concentrated fine dust slurry is dehydrated to obtain a dehydrated fine dust cake (fine dust dehydration step).

[0054] In this step, the water content of the concentrated fine dust slurry is reduced by mechanically removing the water from the slurry, and a residue, a dehydrated fine dust cake, is obtained. The method for dehydrating the concentrated fine dust slurry is not particularly limited, but may be a filter press, which squeezes out the water from the slurry by compression, or a centrifugal dehydration method, which separates the slurry into water and solids by centrifugal force and then drains the water.

[0055] If the moisture content of the dehydrated fine dust cake obtained in this step is high, the dust will adhere to the bucket of the transport vehicle, etc., resulting in a poor yield. Therefore, this step is preferably carried out so that the moisture content of the dehydrated fine dust cake is 35% by mass or less. Conversely, if the moisture content is too low, fine powder may fly around during transport. Therefore, this step is preferably carried out so that the moisture content of the dehydrated fine dust cake is 10% by mass or more.

[0056] <Coarse dust dehydration process> After step S4, in step S6, the diluted coarse dust slurry is dewatered to obtain a dewatered coarse dust cake (coarse dust dewatering step).

[0057] In this step, the water in the diluted coarse dust slurry is mechanically removed to reduce the moisture content of the slurry, and a coarse dust dewatered cake is obtained as a residue. The dewatering method for the diluted coarse dust slurry is not limited, as in the case of the concentrated fine dust slurry, and methods such as a filter press and centrifugal dewatering can be used. The moisture content of the coarse dust dewatered cake is also the same as that of the fine dust dewatered cake. Therefore, this step is preferably carried out so that the moisture content of the coarse dust dewatered cake is 35% by mass or less. Furthermore, this step is preferably carried out so that the moisture content of the coarse dust dewatered cake is 10% by mass or more.

[0058] Since the zinc concentration in the coarse dust is reduced compared to before classification, the coarse dust dewatered cake obtained in the coarse dust dewatering step can be fed into a sintering machine, a rotary hearth furnace, or a rotary kiln in step S7 and reused as an iron source.

[0059] Alternatively, when there is a surplus in the upper limit of zinc charging capacity of the blast furnace, the coarse dust dewatered cake obtained in the coarse dust dewatering step may be mixed with at least a portion of the fine dust dewatered cake obtained in the fine dust dewatering step until the upper limit of zinc charging is reached, as shown in Fig. 5, to form a mixed dust dewatered cake, which may then be fed into a sinter machine, a rotary hearth furnace, or a rotary kiln and reused as an iron source. By performing such an operation, it is possible to increase the amount of recycled dust compared to when only coarse dust is reused. [Example]

[0060] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0061] Example 1 According to the flow chart shown in Figure 1, blast furnace dust slurry and converter dust slurry were mixed so that the total iron (T.Fe) concentration was 55% by mass or less (dust mixing process). The resulting mixed dust slurry was then passed through a wet cyclone and separated into a fine dust slurry and a coarse dust slurry (wet classification process). The resulting fine dust slurry was concentrated in a settling tank (fine dust concentration process) and then dehydrated using a filter press to obtain a fine dust dehydrated cake (fine dust dehydration process). Meanwhile, the coarse dust was diluted with industrial water (coarse dust dilution process) and then dehydrated using a filter press in the same way as the fine dust to obtain a coarse dust dehydrated cake (coarse dust dehydration process). Portions of the resulting fine dust dehydrated cake and coarse dust dehydrated cake were sampled to measure the total zinc (T.Zn) and total iron (T.Fe) concentrations.

[0062] Table 2 shows the total Zn and total Fe concentrations, median Fe concentration, slurry concentration, and moisture content of the dehydrated cake for the mixed dust slurry and the coarse and fine dust slurries obtained after the wet classification process. Table 2 also shows the Zn removal rate, calculated using the following formula from the total Zn concentration. The "Zn removal rate" defined here refers to the proportion of Zn that migrates to the fine dust slurry when the Zn contained in the mixed dust is taken as 100.

number

[0063] [Table 2]

[0064] As shown in Table 2, 61.8% of the Zn contained in the mixed dust slurry was removed.

[0065] Table 2 also shows the percentage of M.Fe contained in T.Fe, calculated from the T.Fe concentration and M.Fe concentration using the following formula:

number

[0066] As shown in Table 2, the ratio of M.Fe to T.Fe in the coarse dust was found to be higher than that before passing through the cyclone (mixed dust slurry). In other words, it was found that a reduction in the reducing agent ratio (amount of coke and auxiliary fuel used) can be expected when the coarse dust is returned to the blast furnace as an iron source.

[0067] Example 2 The steelmaking dust was treated in the same manner as in Example 1. However, the treatment was carried out according to the flow shown in Figure 4, and the supernatant water generated in the fine dust concentration step was used as part of the water used to dilute the coarse dust slurry in the coarse dust dilution step. All other conditions were the same as in Example 1.

[0068] Table 3 shows the concentration of each slurry, total Zn concentration, total Fe concentration, metal Fe concentration, Zn removal rate, water content of each dehydrated cake, and the percentage of metal Fe in total Fe.

[0069] Table 4 shows the results of a comparison between Example 1 and Example 2 regarding the amount of industrial water used in the coarse dust dilution step.

[0070] As shown in Table 3, the Zn removal rate was as high as 71.0% even when using the method following the flow shown in Figure 4. Furthermore, as in Example 1, the ratio of M.Fe to T.Fe in the coarse dust was higher than that before passing through the cyclone (mixed dust slurry). Furthermore, as shown in Table 4, the amount of industrial water used to dilute the coarse dust was reduced by approximately 30%, demonstrating that treating dust according to the flow shown in Figure 4 also makes it possible to reduce the amount of industrial water used.

[0071] [Table 3]

[0072] [Table 4]

[0073] Example 3 Steelmaking dust was treated in the same manner as in Example 1. However, the process was carried out according to the flow shown in Figure 5, and the supernatant water generated in the fine dust concentration process was used as part of the water used to dilute the coarse dust slurry in the coarse dust dilution process. The obtained coarse dust dewatered cake was entirely sintered and recycled as an iron source to the blast furnace. Meanwhile, the obtained fine dust dewatered cake was mixed with coarse dust until the upper limit of zinc charging in the blast furnace was reached, and then charged into the blast furnace. All other conditions were the same as in Example 1.

[0074] A comparison of the amount of recycled dust is shown in Table 5. The amount of recycled dust is shown as a relative value when Examples 1 and 2 are set to 1.

[0075] [Table 5]

[0076] As shown in Table 5, by following the flow shown in Figure 5, the amount of dust recycled can be increased by 1.4 times.

[0077] (Comparative Example) The steelmaking dust was treated in the same manner as in Example 1. However, the treatment was carried out according to the flow shown in Figure 6, except that the dust mixing step was not carried out, and the blast furnace dust slurry and the converter dust slurry were separately transported to the wet classification step and passed through the wet cyclone. All other conditions were the same as in Example 1.

[0078] Table 6 shows the concentration, total Zn concentration, total Fe concentration, Zn removal rate, and moisture content of each dehydrated cake for blast furnace dust slurries. Table 7 shows the concentration, total Zn concentration, total Fe concentration, total Fe concentration, and Zn removal rate for each slurry, moisture content of each dehydrated cake, and the percentage of total Fe in total Fe for converter dust slurries.

[0079] [Table 6]

[0080] [Table 7]

[0081] As shown in Table 6, the Zn removal rate of the blast furnace dust slurry was high at 70.5%. On the other hand, as shown in Table 7, the Zn removal rate of the converter dust slurry was found to be low at 47.5%. This is presumably because the particle size difference between Zn and Fe in the converter dust slurry is small, so Zn and Fe are mixed and classified.

[0082] On the other hand, since the original M.Fe concentration of the blast furnace dust slurry is low, M.Fe is somewhat concentrated in the coarse dust, but the concentration is low at 0.3%, and it has become clear that its value as an Fe source is hardly improved compared to before it was passed through the cyclone.

[0083] As described above, the present invention makes it possible to separate zinc from blast furnace dust and converter dust simply and at low cost. [Industrial Applicability]

[0084] INDUSTRIAL APPLICABILITY The present invention is useful in the steel industry because it enables zinc contained in steelmaking dust to be separated simply and at low cost.

Claims

1. a dust mixing step of mixing a converter dust slurry containing converter dust and a blast furnace dust slurry containing blast furnace dust to form a mixed dust slurry; a wet classification step of separating the mixed dust slurry into a coarse dust slurry containing coarse dust with a low zinc content and a fine dust slurry containing fine dust with a high zinc content; a fine dust concentrating step of concentrating the separated fine dust slurry to form a concentrated fine dust slurry; a coarse dust dilution step of mixing the separated coarse dust slurry with water to dilute it to form a diluted coarse dust slurry; a fine dust dehydration step of dehydrating the concentrated fine dust slurry to obtain a dehydrated fine dust cake; a coarse dust dewatering step of dewatering the diluted coarse dust slurry to obtain a coarse dust dewatered cake; Including, A method for treating iron-making dust, characterized in that the dust mixing step is carried out so that the total Fe (T.Fe) concentration of the resulting mixed dust slurry is 25 mass % or more and 60 mass % or less.

2. 2. The method for treating iron manufacturing dust according to claim 1, wherein the dust mixing step is carried out so that the concentration of the resulting mixed dust slurry is 5% by mass or more and 40% by mass or less.

3. 3. The method for treating iron manufacturing dust according to claim 1, wherein the wet classification step is carried out using a wet cyclone.

4. 3. The method for treating iron manufacturing dust according to claim 1, wherein the fine dust concentration step is carried out so that the concentration of the concentrated fine dust slurry obtained is 10% by mass or more and 50% by mass or less.

5. 3. The method for treating iron manufacturing dust according to claim 1, wherein the coarse dust dilution step is carried out so that the concentration of the diluted coarse dust slurry obtained is 10% by mass or more and 50% by mass or less.

6. 3. The method for treating iron manufacturing dust according to claim 1, wherein the water used in the coarse dust dilution step is water produced in the fine dust concentration step.

7. 3. The method for treating iron manufacturing dust according to claim 1, wherein the fine dust dewatering step is carried out so that the moisture content of the resulting dewatered fine dust cake is 35% by mass or less.

8. 3. The method for treating iron manufacturing dust according to claim 1, wherein the coarse dust dewatering step is carried out so that the moisture content of the resulting dewatered coarse dust cake is 35 mass % or less.

9. 3. The method for treating iron manufacturing dust according to claim 1, wherein the coarse dust dewatered cake obtained in the coarse dust dewatering step is fed into a sintering machine, a rotary hearth furnace, or a rotary kiln to be reused as an iron source.

10. 3. The method for treating iron manufacturing dust according to claim 1, wherein the coarse dust dewatered cake obtained in the coarse dust dewatering step is mixed with at least a portion of the fine dust dewatered cake obtained in the fine dust dewatering step to form a mixed dewatered cake, and the mixed dewatered cake is fed into a sintering machine, a rotary hearth furnace, or a rotary kiln to be reused as an iron source.

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