JPH0461043B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for continuously producing zinc white from steelmaking dust generated in a steelworks. [Prior Art] In steelmaking plants that manufacture steel using blast furnaces, open hearths, and electric furnaces, a large amount of steelmaking smoke dust is generated from the blast furnaces, open hearths, and electric furnaces during steelmaking. Previously, this steelmaking dust was released into the atmosphere, but with the recent strengthening of air pollution prevention administration, the installation of dust collectors has become mandatory.
Currently, most of it is collected without being released into the atmosphere. The recovered steelmaking smoke dust is difficult to handle because it is fine particles, contains a wide variety of metals mostly as oxides, and each of the contained metals is of low grade.Furthermore, it is a byproduct of steelmaking plants. Therefore, it has not been considered as an industrial raw material at all because of the large fluctuation in composition and the inability to obtain stable quality. However, in recent years, due to the above-mentioned physical properties of steelmaking dust and the risk of secondary pollution caused by the heavy metals it contains, it is no longer possible to dispose of it as is. On the other hand, steelmaking dust contains a large amount of zinc, and we focused on the fact that it can be reused as a zinc resource. Zinc recovery has been commercialized by the present inventor since 1966, and now 90% of the steelmaking dust generated from electric furnaces in Japan has been effectively treated. Several companies are producing electrolytic zinc ingots, distilled zinc ingots, and zinc white using crude zinc oxide produced from steelmaking dust as a raw material. Conventional methods for producing zinc white include the French method of producing from zinc ingots, the American method of producing from zinc ore or zinc dross, and the recent method of producing zinc white from steelmaking dust using an electric furnace.In addition to these methods, ,
Previously proposed by the present inventor (Special Publication No. 50-33994)
However, there is a method of producing zinc white from steelmaking dust using a three-stage rotary furnace. However, since both methods involve complicated processes and consume a large amount of energy, it is desired to provide a method for producing zinc white from steelmaking dust more effectively. [Problems to be solved by the invention] In the zinc refining industry, no matter how excellent a method is, whether or not it can be implemented on an industrial scale is largely influenced by profitability (economic efficiency). Ru. Technically, the continuous production of zinc white from steelmaking dust typically requires several processing steps and large amounts of heating energy. The important factors are how simple the process can be and how little energy can be used. From this point of view, the conventional zinc white production method and the above-mentioned
The method shown in Publication No. 33994 is simpler because zinc white is obtained only after a three-step treatment process using three rotary furnaces, and each rotary furnace requires a large amount of heating energy. There has been a desire for a process that uses less energy in total. In particular, due to the recent slump in the zinc market,
The emergence of a new manufacturing method was eagerly awaited. In addition, in the method disclosed in Japanese Patent Publication No. 50-33994, from the above-mentioned viewpoint, the target of treatment is limited to steelmaking smoke dust from open hearth furnaces and electric furnaces, which have a high zinc content, and the quality of the zinc contained is Steelmaking dust from blast furnaces, which has a low content, was not targeted. However, as mentioned above, when disposing of steelmaking dust as it is, it has become quite difficult to secure a disposal site, and depending on the disposal method, secondary
Because there is a risk of becoming a source of tertiary pollution,
It has been desired to develop a method that can sufficiently efficiently recover zinc from steelmaking dust generated from blast furnaces. In order to meet the above-mentioned demands, an object of the present invention is to provide a method that can produce zinc white from steelmaking dust extremely efficiently, using a much simpler process and using less energy than conventionally known methods. It is in. Another object of the present invention is to obtain zinc white with higher purity than conventional methods while achieving the above-mentioned economical objectives. [Means for Solving the Problems] The method for producing zinc white from steelmaking smoke dust of the present invention, which achieves the above object, comprises the following method. That is,
Steelmaking smoke dust containing iron oxide, zinc oxide, lead oxide, cadmium oxide, and sodium chloride generated during steelmaking can be reduced to 800% without adding coke as a reducing agent.
By heating to 1100°C and dry firing, lead oxide, cadmium oxide, and sodium chloride in the steelmaking dust are selectively volatilized, producing dry fired ore in which zinc oxide and iron oxide remain. the air-fired ore,
By mixing it with reducing agent coke and heating it to 900℃ to 1100℃, the zinc oxide in the air-fired ore is once reduced and selectively volatilized as metal zinc vapor, and the metal zinc vapor is passed through the furnace. A method for producing zinc white from steelmaking smoke dust, which is characterized by generating zinc white by reoxidizing it with flowing air. [Operation] The steelmaking smoke dust to be treated in the above method includes both those generated from open hearth furnaces, electric furnaces, and blast furnaces. Although there are slight differences in steelmaking smoke dust generated from open hearth furnaces and electric furnaces due to the grade quality of raw iron scrap and differences in steelmaking methods, the contained components and standard grades are generally shown in Table 1, and the amount generated is is about 1 to 2% per ton of crude steel produced.

【table】

[Table] Currently, for convenience of transportation, steelmaking dust is turned into granular pellets with a diameter of 2 to 5 mm at the generating factory.
Contains 4-7% water. In addition, steelmaking smoke dust generated from blast furnaces is currently not used as a raw material for producing zinc white due to its low zinc content; however, as described below, with the highly efficient production of zinc white by the method of the present invention,
In the future, it can be fully treated by the present invention. The standard grade of steelmaking dust generated from blast furnaces is approximately Table 2.
As shown.

【table】

[Table] In the present invention, the above-mentioned steelmaking smoke dust is
First, without adding additives, at normal pressure from 800℃
It is heated to 1100°C and baked at this temperature, and the baking time is suitably about 30 minutes to 90 minutes. The dry firing is performed while steelmaking dust is introduced from one end of the first stage heating furnace and is transferred to the other end in the first stage heating furnace. As the first stage heating furnace and the second stage heating furnace described below, a rotary kiln is preferably used, and a slightly inclined rotary kiln is particularly preferred. By using such a rotary furnace, steelmaking dust introduced from one end is naturally transferred to the other end as the furnace rotates. Generally, a batch type furnace is generally used, but a rotary furnace such as the one described above enables continuous processing.
In this dry firing, lead, cadmium, chlorine, etc. in the steelmaking smoke dust are selectively volatilized, and most of the volatile substances become lead oxide in a heated atmosphere, and some lead chloride, cadmium oxide, cadmium chloride, etc. It becomes common salt (NaCl) and is collected and recovered by the first-stage recovery device connected to the first-stage heating furnace. Zinc and iron contained in the steelmaking dust remain without being volatilized, and are taken out from the other end of the first-stage heating furnace as dry burning ore, and used as raw materials for the second-stage treatment described below. The reason why lead, cadmium, and chlorine are selectively volatilized and zinc and iron remain during the volatilization during the above-mentioned dry firing is considered to be as follows.
Investigation by the present inventor has revealed that most of the chlorine in steelmaking dust remains in the form of NaCl without forming other chlorides, and some of this NaCl and
PbO, which is contained as an oxide in steelmaking dust,
It is thought that CdO exhibits a reaction to produce chloride, and this reaction promotes the volatilization of lead, cadmium, and chlorine. This was confirmed by experimental results showing that if the raw material steelmaking dust was hot-washed in advance to remove NaCl, lead, cadmium, and chlorine were less likely to volatilize from the sample in which NaCl had been removed. The reaction that produces the above chloride is performed using PbO, CdO,
Regarding ZnO and Fe ₂ O ₃ , it is as follows. △
G° ₁ , ΔG° ₃ , ΔG° ₄ indicate standard free energy changes in each reaction. PbO + 2NaCl = PbCl ₂ + Na ₂ O (△G° ₁ ) …………(1) CdO + 2NaCl = CdCl ₂ + Na ₂ O (△G° ₂ ) …………(2) ZnO + 2NaCl = ZnCl ₂ + Na ₂ O (△G ° ₃ ) …………(3) 1/2Fe ₂ O ₃ +3NaCl=FeCl ₃ +3/2Na ₂ O (△G° ₄
)…………(4) Also, the standard free energy change (Cal) at each temperature is as shown in Table-3.

[Table] In equations (1), (2), (3), and (4) above, △ in Table-3
The smaller the value of G°, the more likely the reaction will proceed to the right, so
CdO is most easily chlorinated, PbO is slightly less chlorinated, and ZnO and Fe ₂ O ₃ are much less chlorinated than PbO and CdO. Therefore, in dry baking at the above-mentioned temperature, the reactions of formulas (1) and (2) above occur actively, but the reactions of formulas (3) and (4) hardly occur. The reactions of equations (1) and (2) are thought to play a role in promoting the volatilization of Pb, Cd, and Cl components in steelmaking dust, and as shown in the specific data in the examples below, it is actually Pb,
There are almost no Cd and Cl components, and a large amount of Zn and Fe components remain. The air-fired ore produced in the first stage treatment is extracted as having almost no lead, cadmium, and chlorine components as they have been removed, and the remaining zinc and iron contents are high. , sent to second stage processing. In the second stage treatment, coke is mixed as a reducing agent into the air-fired ore. A suitable mixing ratio of coke is about 30% by weight. The mixture is placed in a second stage heating furnace, heated to 900°C to 1100°C and maintained at this temperature. Holding time is approximately 30 minutes to 90 minutes
About a minute is appropriate. During this heating, zinc oxide in the dry ore is reduced by coke and selectively volatilized as metallic zinc vapor due to the difference in metal vapor pressure with iron. Then, in an oxidizing atmosphere, for example, with appropriate air blown into the furnace at the same time, it is immediately reoxidized to produce pure white zinc white. At this time, the heat generated when the metal zinc vapor is reoxidized is also effectively utilized. The zinc white is collected in a second-stage recovery device connected to the second-stage heating furnace, and the target zinc white is obtained. The resulting zinc white is obtained from the air-fired ore, which has already been separated from lead, cadmium, and chlorine in the first stage treatment, and is then selectively separated from iron in the second stage treatment by utilizing the difference in metal vapor pressure. Because of this, its purity is extremely high, exceeding the standards for zinc white manufactured by the American method and comparable to the zinc white produced by the French method. The energy required in the method of the present invention is mainly comprised of two parts: one for heating the steelmaking dust and coke to a predetermined temperature, and the other for reducing the zinc oxide. However, in the latter case, the generated zinc vapor and carbon monoxide are finally oxidized to zinc white and carbon dioxide by the secondary air, which generates heat again, and as a result, the coke burns and becomes carbon dioxide. An amount of energy corresponding to the amount of energy generated is generated in excess. This energy reaches 1160 KCal per 1 kg of zinc white produced, and if this energy is effectively recovered and used to heat the charge or the primary air for the heavy oil burner, energy consumption can be significantly reduced. Note that some of the coke is also consumed for the reduction of iron oxide, but compared to the case of zinc, which immediately turns into steam and leaves the reaction system after being reduced to metal, the reduction of iron oxide is extremely slow. It is gradual. In the conventional method, impurities in the crude zinc oxide produced during the first stage heating are removed by water washing and second stage heating before being sent to the third stage zinc white production process, so the number of heating times is three. The coke mixing step is also required twice. Furthermore, in the first stage crude zinc oxide recovery process, effective heat recovery is difficult due to significant volatilization of chlorine content, and although this method uses twice the amount of coke, it is difficult to effectively recover the combustion heat. Not available. In contrast, in the method of the present invention, in the first stage treatment, lead, cadmium, and chlorine components are first separated from the dry fired ore in which zinc and iron remain, and in the second stage treatment, the dry fired ore is separated. Since this method selectively separates the zinc component, a two-step process is required, simplifying the entire process. Further, the coke mixing step only needs to be carried out once. In addition, only two stages of heating are required, and the heat generated by the reoxidation of metal zinc vapor and the combustion of carbon monoxide can also be used, so the energy used to produce zinc white is approximately 2/3 compared to the three-stage conventional method described above. This results in significant savings. Incidentally, the sintered slag taken out from the second-stage heating furnace in the second-stage treatment has a significantly increased iron content, so it can be used as sintered ore and other raw materials in blast furnace operation. [Embodiments] Preferred embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show a schematic equipment system of an apparatus for carrying out the method of the invention. In the figures, 1 in FIG. 1 indicates the entire first-stage processing device, and 2 in FIG. 2 indicates the entire second-stage processing device. The first-stage treatment apparatus 1 includes a rotary kiln 3 as a first-stage heating furnace, and a washing tower 5 as a first-stage recovery apparatus connected to the rotary kiln 3 via a conduit 4. Heavy oil or kerosene is used as a heating source for the rotary kiln 3, and air is blown into the rotary kiln 3 together with heavy oil or kerosene. The heated air blown from one end of the rotary kiln 3 passes through the rotary kiln 3, passes through the conduit 4, passes through the washing tower 5, and is discharged as exhaust gas. The second-stage processing device 2 also has a substantially similar device configuration, including a rotary kiln 6 as a second-stage heating furnace, and a second stage processing device connected to the rotary kiln 6 via a conduit 7.
It has a stage recovery device 8. Heavy oil or kerosene is used as a heating source for the rotary kiln 6, and air is blown therewith, and the heated air is exhausted after passing through the second stage recovery device 8. In the rotary kilns 3 and 6, the raw material inlet side 3a and 6a are on the other end side 3.
It is installed at an angle so that it is slightly higher than b and 6b. In the rotary kilns 3 and 6, the number of revolutions can be adjusted, and the raw materials introduced from the inlets 3a and 6a are transferred inside toward the other ends 3b and 6b, but the speed, that is, The residence time in the furnace can be adjusted by changing the rotation speed. Using such an apparatus, zinc white was produced as follows. First, the steelmaking smoke dust used as a raw material was generated from an electric furnace, and its quality is as shown in Table 4.

[Table] This steelmaking dust is continuously introduced from the inlet 3a of the rotary kiln 3 without adding any additives.
In the furnace while moving the inside of the furnace toward the discharge port 3b side.
The rotary kiln 3 was heated to 800°C to 1100°C, and the rotation speed of the rotary kiln 3 was adjusted so that the baking time would be about 60 minutes at that temperature. While steelmaking dust passes through the furnace, lead,
Cadmium and chlorine were volatilized, and the volatile substances were recovered in the washing tower 5 as lead oxide, lead chloride, cadmium oxide, cadmium chloride, and salt slime. Air-fired ore in which zinc and iron components remained as non-volatile substances was obtained from the discharge port 3b. The content of each component in the obtained air-fired ore is as shown in Table-5.
Most of lead, cadmium, and chlorine were removed.

[Table] Next, the above-mentioned air-burning ore is introduced into the rotary kiln 6 through the inlet 6a with about 30% by weight of coke mixed in, and heated to 900℃ to 1100℃ in the furnace, and the coal remains in the furnace. The rotation speed of rotary kiln 6 was adjusted so that the time was approximately 60 minutes. During this heating, zinc is selectively volatilized due to the difference in metal vapor pressure, and the volatilized metal zinc vapor is reoxidized by heated air blown from the other end to produce zinc white, and the generated zinc white is It was sent along with air to the second-stage recovery equipment, where it was recovered as pure white zinc white with high purity.
At this time, the heat generated during reoxidation of the metal zinc vapor sufficiently contributed to energy savings. The air-fired ore in which the zinc component had been volatilized was discharged from the discharge port 6b as sintered ore slag. The components contained in the obtained zinc white are as shown in Table 6, and the zinc white had a high purity comparable to the specifications of zinc white manufactured by the French method.

[Table] In addition, the components contained in the residual sintered slag are shown in Table 7, and it can be seen that zinc, lead, and cadmium were volatilized with high efficiency.

[Table] Since this sinter slag has a significantly increased iron content as described above, it can be used as a raw material for sintered ore and the like. [Effects of the Invention] According to the method for producing zinc white from steelmaking dust of the present invention, lead, cadmium, and chlorine are volatilized by actively utilizing the action of NaCl coexisting in steelmaking dust.
The first step is to obtain air-fired steel consisting of FeO and ZnO, and then mix and heat air-fired steel and coke to selectively reduce zinc oxide using the difference in metal vapor pressure to produce metallic zinc. Zinc white is obtained through a two-step process including volatilization and re-oxidation to obtain zinc white, which greatly simplifies the process and equipment compared to conventional methods, and reduces the amount of energy required. It is possible to achieve the effect that it is possible to significantly reduce the cost of production, equipment costs, and economically produce zinc white. Therefore, it becomes possible to effectively utilize not only the steelmaking dust generated from open hearth furnaces and electric furnaces, but also the steelmaking dust from blast furnaces, which has hitherto been a completely unused resource. In addition, since the volatilization temperatures of ZnO and FeO are significantly different, ZnO can be extracted with high precision, and the zinc white obtained is comparable to the standards for French method zinc white.
Another effect is that the product quality can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic equipment system diagram of a first-stage processing apparatus among apparatuses for carrying out the method of the present invention, and FIG. 2 is a schematic equipment system diagram of a second-stage processing apparatus. 1... First stage processing device, 2... Second stage processing device, 3... Rotary kiln as first stage heating furnace, 4, 7... Conduit, 5... Washing tower as first stage recovery device , 6... rotary kiln as a second stage heating furnace, 8... second stage recovery device.

Claims (1)

[Claims] 1. Steelmaking dust containing iron oxide, zinc oxide, lead oxide, cadmium oxide, and sodium chloride generated during steelmaking can be treated in a simple manner without adding coke as a reducing agent.
By heating to 800℃~1100℃ and dry baking,
Lead oxide, cadmium oxide, and sodium chloride in steelmaking dust are selectively volatilized to produce air-fired ore in which zinc oxide and iron oxide remain, and then the air-fired ore is mixed with reducing agent coke. hand
By heating to 900°C to 1100°C, the zinc oxide in the air-fired ore is reduced and selectively volatilized as metallic zinc vapor, and the metallic zinc vapor is reoxidized by the air flowing in the furnace. A method for producing zinc white from steelmaking dust, characterized by producing zinc white.