JP2013023720A - Method of reusing wet dust present in material generated in blast furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a simple, practical, and effective method of reusing wet dust present in a material generated in a blast furnace, for effectively using wet dust collected from exhaust gas of an iron-making blast furnace, which method comprises separating the wet dust into three portions, i.e., a portion comprising iron (Fe) as a useful object, a portion comprising carbon (C) as a useful object, and a portion comprising zinc (Zn) as a useful object.SOLUTION: The wet dust is converted into a slurry state, and the resulting slurry is subjected to two steps 15, 16 of wet cyclone separation, and the effluent from the lower part of the second step cyclone is subjected to wet magnetic separation 17, whereby the wet dust is separated into three portions, i.e., a portion comprising iron (Fe) as a useful object, a portion comprising carbon (C) as a useful object, and a portion comprising zinc (Zn) as a useful object.

Description

The present invention relates to a recycling method for effectively using the products generated in the iron making process again in the iron making process. More specifically, the present invention relates to iron (Fe) and carbon (C ) And zinc (Zn) are separated from each other.

The dust collected from the blast furnace exhaust gas includes a primary dust collection dust (dry dust collection dust) that is collected in a dry manner and a fine secondary dust collection dust (wet dust collection dust, Wet dust). Most of the dry dust collection dust is reused as a sintering raw material for the recovery of Fe.
However, even if wet dust is used as a Fe source in the sintering process, it is fine and therefore has a high moisture content. Even if it is dehydrated, there is an adverse effect on the sintering operation. There are many adverse effects such as damage to furnace materials in the blast furnace and facilitating the generation of deposits on the furnace wall. Recycling as blast furnace raw materials by methods such as using it as a sintering raw material is restricted and discarded There are many things.

In order to utilize the wet dust collected from this blast furnace exhaust gas, it is necessary to perform Zn removal treatment. FIG. 4 shows an example of the entire process for utilizing the wet dust of the conventional method. In many cases, wet dust is treated in a reduction furnace. In the operation of the reduction furnace, although C is used as a reducing agent, the total amount of C charged is within an appropriate range in relation to the reduction reaction, and excessive C content causes the strength deterioration of the reduced pellets as a product. There is a problem of adversely affecting the quality.

However, the blast furnace wet dust contains a large amount of C as shown in Table 1 (cited from the Steel Handbook 4th edition), so it cannot be used in large quantities as a reducing furnace raw material due to the total amount of C charged. As shown in FIG. 4, there is a problem that a part must be discarded.

Further, when the C source is effectively used for combustion, Fe and Zn become obstacles. Fe becomes a combustion residue, Zn volatilizes and causes flue adhesion and the like, which is problematic and practically difficult to use. Therefore, in order to effectively use the three elements of Fe, C, and Zn as resources, it is necessary to separate and concentrate the three elements so that the influence of the content values of the other two elements does not substantially matter. is there. From this viewpoint, as shown in Patent Documents 1 to 7, several techniques have been proposed in the past for three-part separation techniques of Fe, C, and Zn.

Patent Document 1 is intended for recovery of C content to be activated carbon for both blast furnace primary ash (dry dust collection dust) and secondary ash (wet dust collection dust). Separation of C as a dissolved residue due to dissolution of metal oxide by acid treatment, while acid is recovered as bengara by heating iron hydroxide and iron carbonate precipitate generated by neutralization with sodium carbonate and further alkalinization. The residual liquid is further concentrated to recover zinc carbonate by adding sodium carbonate. It is also described that magnetic separation is performed before acid dissolution and the magnetic deposit is used as an iron source.

Although the concept of performing the three-way separation to use each is clearly shown, the method involves dissolution of the metal oxide by acid treatment, separation of C as a dissolution residue, dissolution There is no specific method beyond textbook chemical methods, such as neutralization of acid solution with sodium carbonate. Moreover, since it is necessary to use an acid and an alkali, it has the fault that an installation cost and an operation cost including a waste water treatment become high.

Further, Patent Document 2 proposes a method for enriching and separating Fe, Zn, and C for wet dust collecting dust of steelmaking and steelmaking. The first step is separation of iron rich dust (lower discharge) and Zn and C rich dust (upper discharge) by magnet cyclone treatment. In the second step, contact with C and flotation treatment by adding and dispersing an organic solvent such as n-hexane to the upper effluent of the previous step (in the precipitation layer; Zn-rich component, in the flotation layer; C main component dust) ).

Although a specific method of three-way separation is provided, the results presented in the examples show that the C distribution ratio to the Fe recovery side mainly composed of Fe is as high as 39 to 63%, not necessarily Fe and The separability of C is not good. In addition, there is a disadvantage that the cost is increased by using an organic solvent. Furthermore, disaster prevention, safety and hygiene considerations are also necessary when using organic solvents. For example, the hexane described is a flammable substance with a flash point of −22 ° C. and has a low explosive limit concentration in the air. Strict countermeasures are required.

Many proposals have been made for the purpose of separating two of the three elements of Fe, Zn and C, or a method of separating one component of the three from the other two. Among them, Patent Documents 3 to 7 are examples of proposals aimed at separating Zn and Fe from blast furnace dust or separating Zn from components other than Fe using a wet cyclone.
Patent Document 3 discloses a method for separating C, Fe, Zn, and Pb by a two-stage treatment of a wet cyclone. Patent Document 4 discloses a method for separating Fe and Zn by an electromagnetic cyclone having a positive magnetic field gradient. Patent Document 5 discloses a method of separating Fe and Zn by a special wet cyclone using ultrasonic treatment and negative pressure using a dispersant. Patent Document 6 discloses separation of Fe and Zn by ultrasonic treatment and hydrocyclone treatment. And in patent document 7, although the separation method of Fe and C, Zn, and Pb by the two-stage process of a hydrocyclone is shown, the wet magnetic separation is not performed but Fe and C are rich from reduced waste. Furthermore, it is not disclosed that iron and carbon are separated and used independently as raw materials.

JP-A-48-052616 Japanese Patent Laid-Open No. 53-025201 Japanese Patent Laid-Open No. 51-120466 Japanese Patent Application Laid-Open No. 53-039907 Japanese Patent Laid-Open No. 53-081479 JP 58-034051 Japanese National Patent Publication No. 8-507577

Chemical Engineering Association; Chemical Engineering Handbook 4th Edition, 1964, Maruzen

However, these are proposals of an optimum method for the purpose of separating the three parts into two, but combining the different proposals does not mean that the three-way separation of Fe, C, and Zn can be performed optimally. That is, even if these are combined, it is difficult to provide a part of the optimum three-way separation method for efficiently separating Fe, C, and Zn.
The present invention has been made in view of such circumstances, and in terms of wet dust of blast furnace exhaust gas, iron (Fe), zinc (Zn), and carbon (C) are separated from each other in order to effectively reuse them. An object of the present invention is to provide a simple, practical and effective method for reusing wet dust in blast furnace products.

The method for reusing wet dust in the blast furnace product according to the present invention in accordance with the above object is to collect wet dust (blast furnace wet dust) collected when the exhaust gas generated from the blast furnace for iron making is wet collected. The first step,
A second step of performing a first wet cyclone treatment on the slurry-like wet dust;
A third step of performing a second wet cyclone treatment on the lower discharge of the first wet cyclone treatment;
A fourth step of performing a wet magnetic separation process on the lower discharge of the second wet cyclone process,
The upper discharge generated in the first wet cyclone process and the upper discharge generated in the second wet cyclone process are defined as “part a using zinc for the purpose”, and the non-magnetized substance generated in the wet magnetic separation process Is a “part b used for the purpose of carbon”, a magnetic deposit generated by the wet magnetic separation process is called “a part c used for the purpose of iron”, and the wet dust is “a part a used for the purpose of zinc a” And “part b used for the purpose of carbon” and “part c used for the purpose of iron”.

In the method for reusing wet dust in a blast furnace product according to the present invention, the slurry wet dust is subjected to ultrasonic treatment before the first wet cyclone treatment in the second step. Is preferred.
Here, the ultrasonic treatment is performed by using an ultrasonic treatment parameter expressed by a product of “ultrasonic intensity expressed in kW per 1 m ^{3 of} slurry” and “ultrasonic irradiation time expressed in minutes”. / M ³ or more is preferable.

By the method for reusing wet dust in the blast furnace product according to the present invention, the blast furnace wet dust can be separated into three parts that are used for the purposes of Fe, Zn, and C, respectively. As a result, the adverse effects of Zn and C when recycling the main part of Fe are reduced, and the adverse effects of Fe and Zn when recycling the main part of C are reduced. Make the main parts easier to recycle. Thereby, the quantity which can utilize blast furnace wet dust effectively can be increased. In other words, there is an effect that the amount of blast furnace wet dust discarded without being used can be reduced and resources can be effectively used.

It is a flowchart which shows the process of the reuse method of the wet dust in the blast furnace product which concerns on one embodiment of this invention. It is a figure explaining the processing flow of the reuse method of the wet dust in the blast furnace product which concerns on 1st Example of this invention. It is a figure explaining the processing flow of the reuse method of the wet dust in the blast furnace product which concerns on 2nd Example of this invention. It is a flowchart which shows an example of the processing process of the wet dust in the blast furnace generated product which concerns on a prior art example.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
(Slurry conditions)
As shown in FIG. 1, dust (exhaust gas) generated in the blast furnace 10 is a thin slurry immediately after being collected by the dust catcher 11 and the wet venturi scrubber 12, so that it is usually easy to handle. In addition, after sedimentation and concentration by thickener 13, dehydration is performed by a dehydrator. In order to apply the present invention, the wet dust needs to be in a slurry state. As a method for the wet dust, the slurry collected by the wet venturi scrubber 12 may be used as it is, or a slurry that is sedimented and concentrated by the thickener 13 may be used. . A slurry concentrated or diluted by any method based on these slurries may be used.
Further, for convenience of transportation and storage, water may be added to the blast furnace wet dust that has been dewatered by a dehydrator and turned into sludge to form a slurry.

In the present invention, although not essential, it is more preferable to maintain the pH of the slurry at about 8.5 to 10. This is because, in this pH range, there is less elution of metal elements such as Fe and Zn into the liquid compared to other pH values, and the drainage treatment after the final solid-liquid separation is easy.

(Each meaning of wet magnetic separation and wet cyclone treatment)
A significant portion of the Fe content contained in the blast furnace wet dust is a ferromagnetic material. On the other hand, the C or Z content contained in the blast furnace wet dust is hardly magnetized by magnetic separation with a normal magnetic flux density gradient of 1 Tesla or less. Therefore, it is preferable to apply wet magnetic separation in order to separate the Fe content from the C content and the Zn content.

The size of particles mainly composed of Zn is 60 to 80% in terms of the mass ratio of sizes of 8 to 10 μm or less, and 60 to 80% of particles mainly composed of Fe and particles mainly composed of C exceed 15 μm. Has a diameter. Therefore, if a wet cyclone designed to have a calculated 50% classified particle size of 8 to 15 μm is used, particles mainly composed of Zn, particles mainly composed of Fe, and particles mainly composed of C can be classified and separated.

As shown in FIG. 1, the process of the method for reusing wet dust in blast furnace products according to an embodiment of the present invention applies wet cyclone treatment twice in advance (that is, first wet cyclone treatment). 15 and the second wet cyclone treatment 16), a part of the classified product, that is, the lower magnetic discharge of the second wet cyclone, the wet magnetic separation (wet magnetic separation) 17 is applied. Then, "Zinc-based recovered material (portion that uses zinc for the purpose) a", "carbon-based recovered material (portion that uses carbon for the purpose) b, which uses Zn content, C content, and Fe content, respectively. ”And“ Iron-mainly collected material (portion where iron is used for the purpose) c ”. In addition, although it is not an essential requirement, when performing the ultrasonic treatment 14 for separating each particle of the wet dust into micro, it is necessary to perform it before the wet cyclone treatment and the wet magnetic separation treatment.

(Conditions for wet cyclone treatment)
As described above, the calculated 50% classification particle size of the wet cyclone is 8 to 15 μm based on the size distribution of the particles using Zn for the purpose and the size distribution of the particles using the purpose of Fe and the particles using the purpose of C. It is preferable to do.
The calculated 50% classified particle diameter d50 ^* [μm] of the wet cyclone can be calculated using, for example, the equation (1) described in Non-Patent Document 1.

Symbols in the formula (1) mean the following matters.
Dc: inner diameter of the cyclone body [cm]
Di: Inner diameter [cm] of cyclone inlet
De: Inner diameter [cm] of the upper outlet of the cyclone
μ; viscosity of liquid [kg / m. sec]
ρp: Particle density [kg / m ³ ]
ρ: Density of liquid [kg / m ³ ]
Q: Liquid supply speed to the cyclone [liter / sec]

The solid concentration (ie, slurry concentration) of the slurry supplied to the wet cyclone is not particularly limited. However, when the solid concentration is high, handling of the slurry may be difficult, and a solid concentration of 30% or less is preferable in practice. Further, the lean side has the disadvantage that the equipment efficiency is lowered and a larger equipment is required.
In the cyclone treatment of blast furnace secondary ash, a large amount of solid phase such as C may be discharged on the lower discharge side, resulting in a slurry with a high solid concentration. Therefore, when the lower effluent from the first-stage cyclone treatment (first wet cyclone treatment 15) is subjected to the second-stage cyclone treatment (second wet cyclone treatment 16), depending on the concentration, It is preferable to dilute to such a solid concentration.

(Conditions for wet magnetic separation)
Any wet magnetic separation method such as a well-known drum-type wet magnetic separation or a filter-type wet magnetic separation can be applied as long as it is a method capable of macroscopically separating a slurry containing a large amount of Fe. Moreover, as long as it can be industrially separated, the specific conditions such as the wet magnetic separation and the magnetic flux density may be any conditions.

(Meaning of ultrasonic treatment)
As shown in the examples described later, the first and second wet cyclone treatments 15 and 16 and the wet magnetic separation treatment 17 are performed on the blast furnace wet dust that is slurried without ultrasonic treatment of the slurry. , Zn content and C content can be separated into three parts that are used for the purpose. Further, when the slurry is first subjected to ultrasonic treatment 14 and then subjected to two stages of wet cyclone treatment and wet magnetic separation treatment, each of the Fe, Zn, and C components is used for the purpose as compared with the result without the treatment. The degree of separation between the three parts is improved. In particular, the yield of Zn is improved.

The purpose and function of the ultrasonic treatment 14 is to microscopically separate various types of particles such as Fe, C, and Zn that are physically attached to each other. Here, “micro” means separation of fine particles suspended in the slurry. That is, before performing the macro wet separation such as wet magnetic separation or wet cyclone separation in order to divide the slurry or sludge with high Fe content into the slurry or sludge with high C content and the slurry or sludge with high Zn content, It has the meaning of promoting the separation of individual particles as much as possible.

(Sonication conditions)
The ultrasonic treatment is sufficient if the slurry can be substantially irradiated with ultrasonic waves. For example, the separation of Fe, C, and Zn is improved even when ultrasonic irradiation is performed for 2 to 3 minutes at an ultrasonic intensity of 1 kW per 1 m ^{3 of} slurry as compared to the case without ultrasonic irradiation. More suitable conditions will be described later.
The frequency of the ultrasonic wave to be irradiated is not particularly limited, but a relatively low frequency of 100 kHz or less is more preferable. The ultrasonic irradiation may be performed in either a batch type container or a continuous flow path. In both batch processing and continuous processing, sufficient slurry agitation is required by some method. This is because it is impossible to make the slurry uniform and, consequently, uniform ultrasonic irradiation only by the ultrasonic excitation force.

The slurry concentration at the time of ultrasonic irradiation, that is, the ratio of solid substance amount / total mass is not particularly limited. The lower the concentration, the lower the treatment efficiency and the larger the equipment scale for the same wet dust treatment amount on a dry basis, which is economically disadvantageous. Moreover, if it becomes high concentration, processing efficiency will improve, but processing, such as stirring and transfer, will become difficult. Although the effect can be obtained at any slurry concentration, it can be said that about 3 to 25% by mass is a more preferable range from these viewpoints.

(Suitable conditions for ultrasonic treatment)
The sonication condition is that the sonication parameter represented by the product of the ultrasonic intensity expressed in kW per 1 m ^{3 of} slurry and the ultrasonic irradiation time expressed in minutes is particularly less than 20 kW · min / m ^3. As the value of the sonication parameter increases, the separation result of each component is greatly improved. When the value of this sonication parameter is in an area of 20 kW · min / m ³ or more, the separation status of each component does not change much even if the value of the sonication parameter is increased further.

In the region where the value of the sonication parameter is less than 20 kW · min / m ³ , micro mutual separation of Fe-based particles, C-based particles, and Zn-based particles by sonication is still insufficient. It shows that separation progresses rapidly with increasing sonication intensity. On the other hand, if it is 20 kW · min / m ³ or more, the separation progresses somewhat as the ultrasonic treatment intensity increases, but the degree of improvement becomes small. For this reason, it can be said that it is particularly preferable to satisfy the condition that the value of the ultrasonic treatment parameter is 20 kW · min / m ³ or more industrially in consideration of the efficiency balance between the equipment cost and the effect.

Moreover, the combination of ultrasonic intensity and irradiation time is not particularly limited. As long as the condition of 20 kW · min / m ³ or more is satisfied, a long-time irradiation with a low intensity such as 4 kW / m ³ and a long-time irradiation with a high intensity such as 35 kW / m ³ There is no clear difference between and any combination can be selected.

Example 1
According to the process shown in FIG. 2, a series of separation processes were performed in which the ultrasonic treatment was performed and then the treatment was performed twice with a cyclone, and the second-stage discharge was further subjected to wet magnetic separation. Blast furnace wet dust having the composition shown in Table 2 was used.

Incidentally, the slurry containing the blast furnace wet dust having the composition shown in Table 2 was a concentrated slurry extracted from the thickener, and its mass concentration was 12%. The pH of the slurry was adjusted to 9-10. This was subjected to ultrasonic treatment for 25 minutes at an ultrasonic treatment intensity of 4 kW / m ³ . The ultrasonic treatment was performed by irradiating ultrasonic waves with a predetermined intensity for a predetermined time while impeller stirring in order to prevent the particles from settling and separating in a storage tank.
The slurry was subjected to the cyclone treatment twice, but when the cyclone treatment was performed again for the first lower discharge slurry, the mass concentration was diluted to about 12%.

Cyclone treatment is performed by using a normal type cyclone that does not use negative pressure and classifying by adjusting the flow rate so that the calculated 50% classified particle size d ₅₀ ^{* is} approximately 10 μm using the above-mentioned equation (1). It was.
As shown in the flow in FIG. 2, after the ultrasonic treatment 14, the upper discharge 15 a and the lower discharge 15 b by the first wet cyclone treatment 15 are separated from the second wet cyclone separation (second pass, respectively). Wet cyclone treatments 16a and 16) are performed. Then, each of the upper discharges 19 and 20 and the lower discharges 21 and 22 of the second wet cyclone separation (second wet cyclone treatment 16a and 16) is subjected to wet magnetic separation 24-27, The analysis was performed by separating into kimonos 28-31 and non-magnetic deposits 32-35. Wet magnetic separation 24-27 was performed with a drum type magnetic separator with a surface magnetic flux density of 0.24 Tesla. The results are shown in Table 3.

The cyclone two-stage process using the first wet cyclone process 15 and the second wet cyclone process 16, 16a was performed. As a result, the first cyclone process (the first wet cyclone process 15) was performed. All of the upper discharge 15a (= the upper discharge 19, the lower discharge 21, and the No. 1 to 4 in Table 3 when it is treated in the second stage of the cyclone, that is, the second wet cyclone treatment 16a) and The upper discharge 20 (see Nos. 5 and 6 in Table 3) in the second-stage cyclone treatment (second wet cyclone treatment 16) of the lower-stage discharge 15b of the first-stage cyclone has a larger Zn concentration than the raw blast furnace wet dust. Therefore, it was judged that the Zn recovery part should be used as a part for utilizing Zn for the purpose. When the amount distribution is calculated, about 2/3 of the total amount of Zn brought in from the raw blast furnace wet dust is included in this Zn recovery portion.

In addition, when the lower discharge 22 in the cyclone second-stage treatment of the first-stage cyclone discharge 15b in the cyclone is magnetically selected, C is concentrated to a component value of 59% in the non-magnetized material (see No. 8 in Table 3). , C was determined to be a portion to be used for the purpose of C recovery. 70% of the total amount of C brought in from the blast furnace wet dust is distributed to this part.
On the other hand, the magnetic deposit 31 (see No. 7 in Table 3) has a high Fe value of 49% by mass and a low component value of C and Zn. .

It was confirmed that the three-part separation of Fe, Zn, and C can be substantially realized by processing as described above and classifying the separated products into the above-mentioned categories.
In other words, it can be said that if the wet magnetic separation 24-27 is not performed after the cyclone treatment, it is impossible to separate the portion using C for the purpose and the portion using Fe for the purpose. Further, if the lower part of the first stage of the cyclone is directly subjected to wet magnetic separation 24-27 without performing the second stage treatment of the cyclone, the total amount of Zn in the upper discharge of the second stage of the cyclone (N05, 6 in Table 3) is 24%. It does not enter the part that uses Zn for the purpose, but is mixed in the part that uses C for the purpose and the part that uses Fe for the purpose. That is, the Zn recovery rate was reduced from 66% to 42%.

Example 2
Next, the difference in separation behavior with and without sonication was confirmed.
Using the same blast furnace wet dust as in Example 1, processing was performed according to the flow shown in FIG. The conditions for ultrasonic treatment and wet magnetic separation when performing ultrasonic treatment are the same as those in the first embodiment. Table 4 shows the results for the case with sonication, and Table 5 shows the results for the case without sonication.

In the case where the ultrasonic treatment 14 was performed before the cyclone treatments 15 and 16 and the wet magnetic separation treatment 17, as in Example 1, Zn used for the purpose of Zn was introduced into the raw material blast furnace wet dust. About 2/3 of the total amount is distributed, and more than 70% of the total amount of C brought in is allocated to the portion that uses C for the purpose.

On the other hand, even in the case where ultrasonic treatment has not been performed in advance, 70% or more of the total amount of C brought in is allocated to the portion that uses C for the purpose. It is the same. On the other hand, the distribution from the total amount of Zn brought in from the blast furnace wet dust of the raw material to the portion using Zn for the purpose is 59%, and the Zn distribution ratio is 8% as compared with the case where the ultrasonic treatment 14 is performed. It will be lowered.
Even without ultrasonic treatment in advance, although the cyclone two-stage treatment (first and second wet cyclone treatments 15 and 16) and the wet magnetic separation treatment 17 slightly reduce the Zn recovery rate, substantially Fe, Zn , C three-way separation can be realized. Considering the Zn distribution rate, it is determined that it is more preferable to perform ultrasonic treatment in advance.

10: Blast furnace, 11: Dust catcher, 12: Venturi scrubber, 13: Thickener, 14: Ultrasonic treatment, 15: First wet cyclone treatment, 15a: Upper discharge, 15b: Lower discharge, 16, 16a : Second wet cyclone treatment, 17: wet magnetic sorting, 19, 20: upper discharge, 21, 22: lower discharge, 24-27: wet magnetic separation, 28-31: magnetic deposit, 32-35: Non-magnetic kimono

Claims (3)

A first step in which wet dust collected when wet exhaust gas generated from a blast furnace for iron making is collected into a slurry,
A second step of performing a first wet cyclone treatment on the slurry-like wet dust;
A third step of performing a second wet cyclone treatment on the lower discharge of the first wet cyclone treatment;
A fourth step of performing a wet magnetic separation process on the lower discharge of the second wet cyclone process,
The upper discharge generated in the first wet cyclone process and the upper discharge generated in the second wet cyclone process are defined as “part a using zinc for the purpose”, and the non-magnetized substance generated in the wet magnetic separation process Is a “part b used for the purpose of carbon”, a magnetic deposit generated by the wet magnetic separation process is called “a part c used for the purpose of iron”, and the wet dust is “a part a used for the purpose of zinc a” And “part b used for the purpose of carbon” and “part c used for the purpose of iron”. The method for reusing wet dust in the blast furnace product 2. The method for reusing wet dust in a blast furnace product according to claim 1, wherein the slurry wet dust is subjected to ultrasonic treatment before the first wet cyclone treatment in the second step. Reusing the wet dust in the blast furnace product. 3. The method of reusing wet dust in a blast furnace product according to claim 2, wherein the ultrasonic treatment includes “ultrasonic intensity expressed in kW per 1 m ^{3 of} slurry” and “ultrasonic irradiation time expressed in minutes”. The method for reusing wet dust in a blast furnace product, wherein the ultrasonic treatment parameter represented by the product is 20 kW · min / m ³ or more.

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