JPS58197234A - Method for removing zinc in dust from iron making blast furnace - Google Patents

Abstract

PURPOSE:To remove zinc in titled dust without consuming fuel considerably by subjecting the dust to a mineral acid treatment to dissolve and separate the zinc in the dust and returning the dust freed from the zinc to an iron making blast furnace. CONSTITUTION:The dust carried over and discharged with a gas from an iron making blast furnace is captured in a wet dust collector and is made into a dust slurry which is supplied through a conduit 20 into an agitator 12. A mineral acid is supplied through a conduit 21 into the agitator 12, where the mineral acid is agitated and mixed with the dust slurry to form an aq. mineral acid soln. charged therein with the dust. The pH thereof is monitored with a meter 30 and the supply rate of the mineral acid is controlled. The zinc contained in the dust is thus dissolved in the aq. mineral acid soln. and the aq. mineral acid soln. and the dust freed from zinc are supplied through a conduit 22 into a thickener 13, where both are separated. The supernatant liquid is treated through a conduit 25, and part of the supernatant liquid is supplied through a conduit 26 into the agitator 12 if the pH of the liquid in the agitator 12 is too high. On the other hand, the dust freed from zinc settled on the bottom of the thickener 13 is dehydrated with a dehydrator 14 and is then returned to the blast furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for removing zinc from iron-making blast furnace dust, and in particular, a method for removing zinc from iron-making blast furnace dust, which is suitable for removing zinc from dust discharged from a steel-making blast furnace by a wet process. It is about the method.

Dust is emitted along with gas from a steelmaking blast furnace. The dust discharged from this iron-making blast furnace is mainly collected by a wet dust collector. Since the main component of the dust is iron, it is returned to the steelmaking blast furnace for reuse in order to save resources. However, the dust contains around 2% zinc, which damages the joints of heat-resistant bricks in the blast furnace. Therefore, in order to return the dust to the steelmaking blast furnace for reuse, the zinc concentration in the dust (hereinafter referred to as residual zinc concentration) must be kept below 0.2 to 0.3 inches (hereinafter referred to as permissible concentration). It is necessary to remove zinc.

Conventionally, as a method for removing zinc from iron-making blast furnace dust (hereinafter abbreviated as zinc removal method), the dust collected by a wet dust collector is dehydrated using a dehydrator, and then about 1' o o.

A commonly used method is to evaporate and remove zinc by raising the temperature to 1°C.

In this zinc removal method, the dust is heated to about 100″C.
Since it is necessary to consume a large amount of fuel such as heavy oil to raise the temperature in 100 t, there is a drawback that the running cost required to remove zinc from the dust increases significantly.

The present invention aims to eliminate the above-mentioned drawbacks, and the dust discharged from a steelmaking blast furnace is poured into a mineral acid aqueous solution, stirred and mixed, and the zinc contained in the dust is dissolved in the mineral acid aqueous solution. It is characterized by separating the mineral acid aqueous solution containing dissolved zinc from the dust from which zinc has been removed (hereinafter referred to as zinc-free dust) and re-supplying the dust to the steelmaking blast furnace, which eliminates the need for fuel such as heavy oil and reduces running costs. The present invention provides a method for removing zinc that can reduce the amount of zinc.

An embodiment of the present invention will be described with reference to FIGS. 1 to 3.

FIG. 1 is a system diagram of a zinc removal device implementing the present invention.
The zinc removal device is composed of a stirrer in which stirring blades 11 rotatably installed on a stirring shaft 10 rotated by a drive device (not shown), Shirafuna 13, and a dehydrator 14. The agitator 12 is connected to, for example, a dust slurry supply conduit 21 connected to a wet dust collector (not shown) and a mineral acid supply conduit 21, and the agitator 12 and Shirafuna 13 are connected by a conduit n. ing. Bottom of Shisofuna 13 and dehydrator 1
4 is connected to the dehydrator 14 by a conduit n, and a line of conduits for discharging zinc-removed dust is connected to the dehydrator 14. The upper part of the Shirafuna 13 is connected to a conduit that supplies a supernatant liquid of an aqueous mineral acid solution in which zinc is dissolved to a wastewater treatment device (not shown). In addition, a conduit branched from the conduit 5 is connected to the agitator 12.
is connected to.

Dust entrained in the gas heat and discharged from a steelmaking blast furnace (not shown) is collected by a wet dust collector. The collected dust becomes a dust slurry and is supplied to an agitator via a conduit. The stirrer 12 is also supplied with mineral acid, for example hydrochloric acid, via a conduit 21.

The dust slurry and hydrochloric acid are stirred and mixed by the stirring force of the rotating stirring blade 11 to form an aqueous hydrochloric acid solution into which the dust is added. The pH of this aqueous hydrochloric acid solution is monitored by a PH meter and controlled by adjusting the amount of hydrochloric acid supplied. As a result, zinc contained in the dust is selectively dissolved in the aqueous hydrochloric acid solution. Thereafter, the aqueous hydrochloric acid solution in which zinc has been dissolved and the zinc-removed dust are passed from the stirrer hill through conduit n to the Shirafuna 13.
Here, the aqueous hydrochloric acid solution in which zinc is dissolved and the zinc-removed dust are separated. The supernatant liquid of the aqueous hydrochloric acid solution in which zinc has been dissolved is sent from the Shirafuna 13 through the conduit 6 to the wastewater treatment device for treatment. In addition, a part of this supernatant liquid is
When the pH of the liquid in the stirrer 12 becomes higher than a predetermined value, the liquid is supplied to the stirrer via the conduit. On the other hand, the dezinced dust that has been separated and settled at the bottom of the Shirafuna 13 is extracted from the Shirafuna 13 through the conduit n to the dehydrator 14, where it is dehydrated and then returned to the steelmaking blast furnace through the conduit row for reuse. .

Figure 2 is a graph showing the relationship between the zinc removal rate, stirring and mixing time, and p obtained in the experiment.
After setting it to 0, add hydrochloric acid to adjust the pH of the hydrochloric acid aqueous solution to 20.
The mixture was stirred and mixed batchwise using a stirrer at a temperature of 40°C. In this case, as shown in the gJ2 diagram, the zinc removal rate is a constant 92% (
Remaining, 4.

It was found that the zinc concentration was 0.12%).

Figure 3 is a relationship diagram between the zinc removal rate and iron dissolution rate obtained in the experiment and the pH of the hydrochloric acid aqueous solution, and the experimental conditions in this case are:
The experimental conditions were the same as above, except that the stirring and mixing time was 1 hour. As shown in Figure 3, the zinc removal rate decreases as the pH of the hydrochloric acid aqueous solution decreases.

Both the dissolution rate of iron increases and the pH of the hydrochloric acid aqueous solution increases to 3.0.
If the zinc removal rate is below 80%, the residual zinc concentration will be below the allowable concentration. Also, the pH of the hydrochloric acid aqueous solution is 0.
．． When it is less than 5, the dissolution rate of iron increases significantly from about 5% to more than 10%, and the amount of iron to be recovered decreases. As a result of this experiment, the pH of the hydrochloric acid aqueous solution needs to be controlled to 3.0 or less so that the residual zinc concentration is below the allowable concentration, and
When considering the amount of iron loss, it was found that it is necessary to control the loss to 3.0 or less and 0.5 or more. In addition, an experiment similar to the above was carried out by changing the temperature of the hydrochloric acid aqueous solution from 15 ° C to 60 ° C, but as a result, although the zinc removal rate tended to increase as the temperature of the hydrochloric acid aqueous solution increased, there was no significant difference. Therefore, it was found that there is no problem even if the temperature of the hydrochloric acid aqueous solution is about 20° C., which is the normal atmospheric temperature.

In the method for removing zinc as in this example, dust discharged from a steelmaking blast furnace is poured into an aqueous hydrochloric acid solution and mixed with stirring, without raising the temperature to approximately 1000°C as in conventional methods, thereby reducing the residual zinc concentration to below the allowable concentration. Therefore, there is no need to consume a large amount of fuel such as heavy oil, and therefore, the running cost required to remove zinc from dust can be significantly reduced.

In this example, the case where hydrochloric acid was used as the mineral acid was explained, but it has been confirmed through experiments that sulfuric acid can also be used to show the same behavior and numerical values as when hydrochloric acid is used. . Further, the stirring and mixing of the dust and the mineral acid aqueous solution may be carried out using a solid-liquid fluidized bed instead of the stirrer.

As explained above, in the present invention, dust discharged from a steelmaking blast furnace is poured into a mineral acid aqueous solution, stirred and mixed to dissolve the zinc contained in the dust in the mineral acid aqueous solution, and then the zinc-dissolved mineral acid By separating the aqueous solution and the zinc-removed dust and resupplying the dust to the steelmaking blast furnace, the residual zinc concentration can be reduced to below the permissible concentration without consuming a large amount of fuel, which is necessary to remove zinc from the dust. This has the effect of significantly reducing running costs.

[Brief explanation of drawings]

Figures 1 to 3 explain one embodiment of the present invention. Figure 1 is a system diagram of a zinc removal apparatus implementing the present invention, and Figure 2 shows zinc removal rate and stirring and mixing time. Relationship diagram with
Figure 3 shows the zinc removal rate, iron dissolution rate, and P of hydrochloric acid aqueous solution.
It is a relationship diagram with H. 12... Stirrer, 13... Shisofuna,
14...Curved dehydrator, addition...conduit, (fund)...
...PH meter 1 figure 2 figure':'r3 figure PH (-)

Claims (1)

[Claims] 1. In a method for removing zinc from dust that is discharged from a steelmaking blast furnace and then re-supplied to the blast furnace, the dust discharged from the blast furnace is poured into a mineral acid aqueous solution and mixed by stirring. Iron manufacturing characterized by dissolving the zinc contained in the dust in an aqueous mineral acid solution, separating the aqueous mineral acid solution containing the zinc and the dust from which the zinc has been removed, and resupplying the dust to the blast furnace. Method for removing zinc from blast furnace dust. 2. The method for removing zinc from steelmaking blast furnace dust according to claim 1, wherein the mineral acid aqueous solution has a pH of 3.0 or less.