JP3080947B1 - Electric furnace dust treatment method - Google Patents

Abstract

Kind Code: A1 A method for recovering zinc, which can efficiently recover pure zinc and / or zinc oxide from a raw material containing zinc or a zinc compound, and a method for treating electric furnace dust, which can effectively recycle metals using the same. I will provide a. SOLUTION: In a method for recovering zinc, a raw material containing zinc or a zinc compound is leached with nitric acid to form a zinc nitrate solution, and the solution is electrolyzed to recover pure zinc and / or zinc oxide. The method of treating electric furnace dust is to mix the dust generated from the electric furnace with diluted nitric acid, adjust the pH, and leach heavy metals other than iron contained in the dust into the diluted nitric acid to remove heavy metals excluding iron. Add zinc to the leached solution
A heavy metal having a lower ionization tendency than zinc is precipitated and recovered, and the heavy metal is removed. The solution containing zinc nitrate is electrolyzed to recover pure zinc and / or zinc oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating electric furnace dust using a method for recovering zinc by electrolysis.

[0002]

2. Description of the Related Art At present, dust generated from electric furnaces in Japan reaches about 500,000 tons per year. Since a large amount of Zn is contained in the electric furnace dust, it is necessary to recover Zn in the electric furnace dust. However, this treatment is currently performed at about 65% of the generated amount. And
The remaining 35% is landfilled untreated. As this method, a dry method is employed in which ZnO in electric furnace dust is reduced and volatilized at a high temperature to recover high-purity ZnO from the dust. In addition, Zn (Zn
Although the dust after recovery of O) contains a high concentration of iron, it has been used as landfill and roadbed material without being recycled into an electric furnace, but recently its use has seen limitations. Is coming.

[0003]

In the above-mentioned conventional dry method, very high energy is required for processing at a high temperature. Therefore, from the economic point of view, the larger the dust treatment scale is, the more efficient it is.However, in general, the amount of electric furnace dust generated from an electric furnace at a steelworks is not so large, and these are collected in one place. It is not an effective treatment method in consideration of transportation for treatment. In addition, despite the need for high energy, the present dry method has a problem that ZnO is not completely reduced and zinc cannot be sufficiently recovered. Further, the remaining dust after reduction is used as a landfill or as a roadbed material. However, in addition to unreduced zinc, lead, cadmium, chromium and the like are contained in this dust, which is not environmentally preferable. The present invention has been made in view of the above circumstances, and effectively recycles heavy metals including iron using a zinc recovery method capable of efficiently recovering zinc and / or zinc oxide from a raw material containing zinc or a zinc compound. An object of the present invention is to provide a method for treating electric furnace dust that can be performed.

[0004]

According to a first aspect of the present invention, there is provided a method for treating dust in an electric furnace, comprising mixing dust generated from an electric furnace with dilute nitric acid, adjusting the pH thereof, and including the dust in the dust. A first step of leaching heavy metals excluding iron components into the diluted nitric acid, and a second step of adding zinc to a solution in which the heavy metals excluding iron components are leached to precipitate and recover heavy metals having a smaller ionization tendency than zinc. And a third step of electrolyzing a solution containing zinc nitrate from which the heavy metals are removed to recover pure zinc and / or zinc oxide. Thereby, in the first step, heavy metals other than iron contained in the electric furnace dust are selectively leached, so that iron can be recovered as leaching residue. In the second step, a metal having a lower ionization tendency than zinc, for example, lead, copper, cadmium, or the like can be deposited. Then, in the third step, pure zinc and / or zinc oxide can be recovered by electrolyzing the solution after recovering lead, copper, cadmium and the like in the second step.

[0005] In the method for treating electric furnace dust according to the first invention, the pH is preferably in the range of 3 to 5. If the pH is less than 3, iron (Fe (III)) may leach out into the solution, while if the pH exceeds 5, metals other than iron, such as Cu ²⁺ , Pb
There is a possibility that ²⁺ , Cd ^{2+ and the} like do not leach into the solution. This makes it possible to remove iron as a precipitate in the solution. Further, in the method for treating electric furnace dust according to the first invention, the solution containing the remaining nitric acid obtained by recovering pure zinc and / or zinc oxide in the third step may be a part of the diluted nitric acid used in the first step or It can be used as a whole.
Thereby, the dilute nitric acid can be recycled.

According to a second aspect of the present invention, there is provided a method for treating dust in an electric furnace, wherein dust generated from an electric furnace is mixed with dilute nitric acid, and metals contained in the dust are leached into the dilute nitric acid. A first step, a second step of removing iron from the solution in which the metals have been leached, and a third step of adding zinc to the solution from which the iron has been removed to precipitate and recover a metal having a lower ionization tendency than zinc. And the metal is removed,
The method includes a fourth step of electrolyzing a solution containing zinc nitrate to recover pure zinc and / or zinc oxide. Thereby, the first
In the process, metals contained in the electric furnace dust are leached, so that strict control of pH is not required. Further, in the second step, only iron can be removed from the leached solution, so that iron can be recovered as a leaching residue. In the third step, a metal having a lower ionization tendency than zinc, for example, lead, copper, cadmium, or the like can be deposited. Then, in the fourth step, pure zinc and / or zinc oxide can be recovered by electrolyzing the solution after recovering lead, copper, cadmium and the like in the third step.

In the method for treating electric furnace dust according to a second aspect of the present invention, the solution containing the remaining nitric acid from which pure zinc and / or zinc oxide has been recovered in the fourth step is partially used as the diluted nitric acid used in the first step. Alternatively, it can be used as a whole. Thereby, the dilute nitric acid can be recycled.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIG. 1 is a process explanatory view of a method for treating electric furnace dust according to an embodiment of the present invention, FIG. 2 is an explanatory diagram of electrolysis in the method for treating electric furnace dust,
FIG. 3 is a process explanatory view of a method of treating electric furnace dust according to another embodiment of the present invention, and FIG. 4 is an explanatory view of electrolysis in the method of treating electric furnace dust.

As shown in FIGS. 1 and 2, in the method for treating electric furnace dust according to one embodiment of the present invention, first, about 1000 k of dust generated from an electric furnace is placed in a melting tank 10.
g. Then, the pH of the solution was adjusted to 3 to 3 by adding diluted nitric acid.
The pH is adjusted to a range of 5, for example, about pH 4. Then, stirring is performed for a predetermined time, for example, about 1 to 2 hours. Thereby, heavy metals except iron contained in electric furnace dust, for example, Z
n, Pb, Cu, Cd, etc. leach into the nitric acid solution. On the other hand, undissolved iron components including slag components such as CaO and SiO ₂ are recovered as leaching residues (first step). Here, the leaching residue is about 740 kg and the iron content is 40 to 50%, so that it can be returned to the electric furnace and reused. In addition, ZnO.Fe ₂
O _{3 is} also included, but can also be returned to the electric furnace and reused.

Next, the supernatant liquid is transferred to the cleaning tank 11 and about 20 kg of zinc is added thereto and stirred for a predetermined time (for example, about 1 to 2 hours). Zinc dissolves as a metal ion (Zn ²⁺ ) by substituting with a metal ion having a lower ionization tendency, for example, Pb ²⁺ , Cu ²⁺ , Cd ²⁺ or the like. On the other hand, heavy metals having a smaller ionization tendency than zinc precipitate. And
The supernatant (solution excluding the precipitate) was transferred to the electrolytic cell 12 used in the next step, and the deposited heavy metals (Pb, Cu, Cd
Etc.) (second step). Next, the solution from which the heavy metals have been removed (recovered) is electrolyzed in the electrolytic bath 12. As shown in FIG. 2, an electrolytic cell 12 used for electrolysis is maintained at a constant temperature, for example, about 60 ° C. by a constant temperature water tank (not shown), and heavy metals are recovered in the electrolytic cell 12 in a second step. The solution containing the zinc nitrate after the addition is introduced. Further, an anode (anode) 13 made of, for example, a platinum plate and a cathode (cathode) 14 made of, for example, aluminum are provided in the electrolytic cell 12, and the ends of the anode 13 and the cathode 14 are respectively connected to a DC power supply 15. Have been.

When electrolysis is performed using this device, the anode 13 is energized by using a DC power supply 15 to supply electricity.
On the side, a reaction of 2H ₂ O → 4H ⁺ + O ₂ + 4e ⁻ occurs to generate oxygen. On the cathode 14 side, a reaction of 2Zn ²⁺ + 4e ⁻ → 2Zn occurs, and zinc is deposited. After completion of the electrolysis, the precipitated pure zinc and / or zinc oxide is recovered (third step). Also,
4H ⁺ generated at the anode 13 is converted into 4 (NO ₃ ⁻ ) in the solution.
To regenerate nitric acid (HNO ₃ ). The regenerated solution containing nitric acid is returned to the dissolving tank 10 so that
It can be used as part or all of the diluted nitric acid added in the process.

Next, FIGS. 3 and 4 show a method of treating electric furnace dust according to another embodiment of the present invention. First, about 1000 kg of dust generated from an electric furnace is put into the melting tank 20. Next, the pH of the solution is adjusted to 1 or less, for example, about pH 1 by adding diluted nitric acid. Then, stirring is performed for a predetermined time, for example, about 1 to 2 hours. Thereby, metals contained in the electric furnace dust, for example, Zn, Fe, Pb, Cu, C
d and the like leach into the nitric acid solution. On the other hand, SiO ₂ , Ca
Since the undissolved slag such as O uses acidic leaching, it can be recovered as a highly pure leaching residue to which other metal elements are not attached (first step). Since the leach residue is about 190 kg, it can be reused as slag.

Further, the supernatant is transferred to a deironing tank 21 and Fe
By adding NaOH or the like to ³⁺ and neutralizing to about pH ₃ , it precipitates and recovers as a hydroxide of Fe (OH) ₃ . Here, a solution in which a metal is leached is mixed with an organic solvent, and only the Fe ^{3+ in} the solution is selectively removed by a solvent extraction method of extracting the metal (second step). Since this precipitate has no deposits such as ZnO and has a high iron purity, it does not need to be returned to an electric furnace and reused, and is easy to recycle. Next, the liquid from which iron has been removed is placed in a cleaning tank 22.
, And about 20 kg of zinc is added thereto, followed by stirring for a predetermined time (for example, about 1 to 2 hours). Zinc is a metal ion having a lower ionization tendency, such as Pb ²⁺ , Cu ²⁺ , Cd
It dissolves as metal ions (Zn ²⁺ ) by replacing with ^{2+ and the} like.

On the other hand, metals having a lower ionization tendency than zinc precipitate. Then, the supernatant liquid (solution excluding the precipitate) is transferred to the electrolytic cell 23 used in the next step, and the deposited metal (Pb, Cu, Cd, etc.) is collected (third step). Next, metal with a lower ionization tendency than zinc is removed (recovered)
The solution thus obtained is electrolyzed in the electrolytic cell 23. As shown in FIG. 4, the electrolytic cell 23 used for the electrolysis is maintained at a constant temperature, for example, about 60 ° C. by a constant temperature water tank (not shown), and the metal is recovered in the electrolytic cell 23 in the fourth step. The solution containing the zinc nitrate after the addition is introduced. An anode (anode) made of, for example, a platinum plate is provided in the electrolytic cell 23.
24 and a cathode made of, for example, aluminum (cathode)
An anode 24 and an end of the cathode 25 are connected to a DC power supply 26, respectively.

When electrolysis is carried out using this apparatus, the anode 24
On the side, a reaction of 2H ₂ O → 4H ⁺ + O ₂ + 4e ⁻ occurs to generate oxygen. On the cathode 25 side, a reaction of 2Zn ²⁺ + 4e ⁻ → 2Zn occurs, and zinc is deposited. After completion of the electrolysis, the deposited pure zinc and / or zinc oxide is recovered (fourth step). Also,
The 4H ⁺ generated at the anode 24 is 4 (NO ₃ ⁻ ) in the solution.
To regenerate nitric acid (HNO ₃ ). The regenerated solution containing nitric acid is returned to the dissolving tank 20 so that
It can be used as part or all of the diluted nitric acid added in the process.

By treating the dust generated from the electric furnace in the above steps, zinc, iron, lead and the like can be efficiently recovered in addition to zinc, and these can be effectively used. In addition, the diluted nitric acid used can be regenerated and used repeatedly, and the electric furnace dust can be economically treated as a whole.

[0017]

Next, an embodiment of a method for treating electric furnace dust according to the present invention will be described. Here, the following treatment was performed based on the process of FIG. 1 using electric furnace dust having the composition shown in Table 1.

[0018]

[Table 1]

First, 100 g of electric furnace dust was added to 1000 g of water.
cc, and further add nitric acid to adjust pH = 4,
Stirring was performed for minutes. Then, the components of the solution were analyzed. The results are shown in Table 2 (No. 1). Note that ND in the table is an abbreviation of Not Detected, and indicates that no detection was performed.

[0020]

[Table 2]

From the results, the Fe content was 4.4 pp.
m, which means that the iron content hardly remains in the solution. Next, in the same manner as described above, 1000 cc of water was added to 100 g of the electric furnace dust, and nitric acid was further added to adjust the pH to 4, and the mixture was stirred for 60 minutes to collect the precipitate (iron). 6 more
Stirring was performed for 0 minutes. Then, the components of the solution were analyzed. The results are shown in Table 2 (NO. 2). From these results, Cd, Pb, and Cu were clearly reduced as compared with the case where only nitric acid was added and stirred (Table 2 (NO. 1)). From this, the metal ions (Cd
²⁺ , Pb ²⁺ , and Cu ²⁺ ) were replaced with zinc, and were found to be deposited as metal.

Furthermore, zinc was recovered by electrolysis. Note that a platinum electrode was used for the anode, and an aluminum electrode was used for the cathode. The electrolyte was a solution of zinc 10 g / liter, pH 3, and was prepared by dissolving zinc oxide in dilute nitric acid. The electrolysis temperature was 60 ° C., and the electrolysis time was 1 hour by the constant current method. Thereafter, the amount of zinc deposited on the cathode was determined by chelate titration. Table 3 shows the results.

[0023]

[Table 3]

From Table 3, it can be seen that the amount of zinc deposited increases with an increase in current density, and that zinc can be easily recovered by electrolysis using nitric acid. In addition, high current efficiency was easily obtained in the electrolysis, and it was found that the electrolysis was industrially useful. The current efficiency is 1
Although it exceeds 00%, it is considered that this is partly due to the generation of monovalent Zn. In addition, the electrolysis time is 2
A similar experiment was performed at a later time, but the amount of zinc deposited increased in proportion to the quantity of electricity, but no other special changes occurred. Here, in the electrolysis according to this example, a solution obtained by dissolving zinc oxide in dilute nitric acid was used, but the electrolysis was also performed using a solution having the composition shown in Table 2 (NO. 2). Zinc can be easily recovered.

As described above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the configurations described in the above embodiments, and is described in the claims. Other embodiments and modifications that can be considered within the scope of the matter are also included. For example, although the dissolving tank and the cleaning tank are separate tanks, the treatment can be performed in the same tank. In the electrolysis, platinum was used for the anode, but a titanium alloy or stainless steel could be used, and aluminum was used for the cathode, but stainless steel could be used.

[0026]

According to the method for treating electric furnace dust according to any one of claims 1 to 3, in the first step, the dust generated from the electric furnace is mixed with dilute nitric acid, and the pH is adjusted to be included in the dust. Since heavy metals other than iron are leached in dilute nitric acid, iron contained in dust can be transferred to leaching residue, and as a result, iron (min) can be easily recovered from electric furnace dust. In addition, in the second step, zinc is added to the solution in which heavy metals other than iron are leached, and a metal having a smaller ionization tendency than zinc is precipitated and collected, so that valuable metals such as lead can be easily collected. . In the third step, the solution obtained by recovering lead, copper, cadmium and the like in the second step is electrolyzed, so that the current efficiency during electrolysis is good and the pure zinc and / or zinc oxide having high purity is further obtained. Can be recovered. Therefore,
By the processes of the first to third steps, the contained metal can be easily and efficiently recovered from the electric furnace dust, and the respective components can be effectively used.

In particular, in the method for treating electric furnace dust according to the second aspect, since the pH is in the range of 3 to 5, the iron (Fe (II)
I)) can be transferred to the leaching residue, and in a later step, a highly pure metal that does not contain iron can be recovered.

[0028] In the method for treating electric furnace dust according to claim 3, the solution containing the remaining nitric acid obtained by recovering pure zinc and / or zinc oxide in the third step is a part of the diluted nitric acid used in the first step. Alternatively, since it is used as a whole, the dilute nitric acid can be recycled, and the cost can be reduced.

In the method for treating electric furnace dust according to claims 4 and 5, in the first step, dust generated from the electric furnace is mixed with dilute nitric acid. Can be leached. Also,
In the second step, iron is removed from the solution in which the metals have been leached. Therefore, in the third step, a highly pure metal containing no iron can be recovered. Then, in the third step, zinc is added to the solution from which the iron has been removed, and a metal having a lower ionization tendency is deposited and recovered, so that a highly pure metal can be recovered. Efficiency can be increased. Further, in the fourth step, since the solution containing zinc nitrate from which the metal has been removed is electrolyzed, pure zinc and / or zinc oxide having high purity can be recovered. Therefore, from the first step to the fourth step
By the processing up to the step, the metal contained can be easily and efficiently recovered from the electric furnace dust, and the respective components can be effectively used.

In particular, in the method for treating electric furnace dust according to the fifth aspect, the solution containing the remaining nitric acid obtained by recovering pure zinc and / or zinc oxide in the fourth step is converted to the diluted nitric acid used in the first step. Since it is used as part or all, dilute nitric acid can be recycled, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a process explanatory view of an electric furnace dust treatment method according to an embodiment of the present invention.

FIG. 2 is an explanatory view of electrolysis in the electric furnace dust treatment method.

FIG. 3 is a process explanatory view of a method for treating electric furnace dust according to another embodiment of the present invention.

FIG. 4 is an explanatory view of electrolysis in the method for treating electric furnace dust.

[Explanation of symbols]

10: Dissolution tank, 11: Cleaning tank, 12: Electrolysis tank, 13: Anode, 14: Cathode, 15: DC power supply, 20: Dissolution tank, 21: Deironing tank, 22: Cleaning tank, 23: Electrolysis tank, 2
4: anode, 25: cathode, 26 DC power supply

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25C 1/16 C22B 3/00, 7/02 B09B 3/00

Claims (5)

(57) [Claims] A first step of mixing dust generated from an electric furnace with diluted nitric acid, adjusting pH, and leaching heavy metals other than iron contained in the dust into the diluted nitric acid; Add zinc to the solution from which heavy metals have been leached,
A second step of depositing and recovering a heavy metal having a smaller ionization tendency than zinc, and a third step of recovering pure zinc and / or zinc oxide by removing the heavy metal and electrolyzing a solution containing zinc nitrate. A method for treating electric furnace dust. 2. The method for treating electric furnace dust according to claim 1, wherein the pH is in the range of 3 to 5. 3. The method for treating electric furnace dust according to claim 1, wherein the solution containing the remaining nitric acid from which pure zinc and / or zinc oxide is recovered in the third step is diluted nitric acid used in the first step. A method for treating electric furnace dust, wherein the method is used as a part or all of an electric furnace. 4. A first step of mixing dust generated from an electric furnace with dilute nitric acid and leaching metals contained in the dust into the diluted nitric acid, and removing iron from the solution leached with the metals. A second step of removing, a third step of adding zinc to the solution from which the iron has been removed, and precipitating and recovering a metal having a lower ionization tendency than zinc; and A method for treating electric furnace dust, comprising a fourth step of decomposing and recovering pure zinc and / or zinc oxide. 5. The method for treating electric furnace dust according to claim 4, wherein the solution containing the remaining nitric acid from which pure zinc and / or zinc oxide has been recovered in the fourth step is one of the diluted nitric acid used in the first step. A method for treating electric furnace dust, wherein the method is used as part or all.