Method for producing briquette, briquette, and method for recovering zinc

Abstract

To provide a method for producing a briquetted ore with which the briquetted ore having high density and crushing strength can be obtained and the treating efficiency is high.SOLUTION: The method for producing the briquetted ore includes a process in which a raw material mixture containing a zinc-containing raw material and a reducing agent is pre-compacted by a pre-compacting machine, and the obtained pre-compacted product and the raw material mixture are charged into the briquetting machine, and further briquetted. The briquetted ore is obtained by further briquetting a briquetted product obtained by pre-briquetting a raw material mixture containing a zinc-containing raw material and a reducing agent, and the raw material mixture.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing high-strength agglomerates from a mixture containing a zinc-containing raw material and a reducing agent, the agglomerates obtained by the method, and a method for recovering zinc. [Background technology]

[0002] Steelmaking dust, generated when scrap iron is melted in an electric furnace to produce steel, contains valuable metals such as zinc and lead. Zinc is recovered as crude zinc oxide powder by reducing and volatilizing the steelmaking dust and then reoxidizing it. One example of a process for treating this is the Mitsui Furnace Process (MF process), currently in operation at Mitsui Mining & Smelting. This process involves mixing zinc-containing waste with a reducing agent to form agglomerates, which are then heated and melted to approximately 1,300°C in a semi-melting furnace using oxygen-enriched residual hot air, separating the waste into metallic zinc vapor and slag or matte. Because the process relies on carbothermal reduction and volatilization as its basic principle, zinc becomes metallic zinc vapor, which is then reoxidized and recovered as crude zinc oxide. This process plays a major role in recovering valuable metals from industrial waste (Non-Patent Document 1).

[0003] To ensure a uniform reduction reaction, the agglomerated ore must have a certain strength. As a method for increasing the strength of such agglomerates, Patent Document 1 discloses a manufacturing method including a step of forming primary granules using powder of metal oxides including one or more of zinc oxide, lead oxide, and titanium oxide, and iron oxide, and a step of pressing a plurality of primary granules to form secondary granules.

[0004] Patent Document 2 discloses a method for producing briquettes in which a material used as a pigment in paints, such as zinc oxide, lead oxide, or titanium oxide, is added to a powder of a metal oxide to function as a binder. The method includes: (1) producing briquettes having an apparent density of 1000 to 4000 kg / m using a powder containing one or more of zinc oxide, lead oxide, or titanium oxide and a metal oxide; 3The present invention discloses a manufacturing method including the steps of (1) forming primary granules containing one or more of zinc oxide, lead oxide, and titanium oxide, and (2) pressing the primary granules together to form secondary granules. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Surface Technology, Vol. 66, No. 3, 2015, pp. 86-90 [Patent documents]

[0006] [Patent Document 1] Patent No. 5554478 [Patent Document 2] Patent No. 5571345 Summary of the Invention [Problem to be solved by the invention]

[0007] Patent Documents 1 and 2 disclose methods for producing briquettes by granulating zinc oxide in two stages. However, it is difficult to obtain briquettes with sufficient compressive strength, and there are issues with the low filling rate during the melting reduction process, resulting in low processing efficiency. Furthermore, the use of a binder, although not insignificant, can lead to clogging of materials during briquette production and unstable supply of raw materials to the furnace due to the binder's adhesive properties. Furthermore, the use of binders increases production costs, so it is desirable to minimize the amount of binder used. [Means for solving the problem]

[0008] Under these circumstances, the inventors conducted extensive research to solve the above problems and discovered that by mixing raw materials that have not been further processed with pre-pressurized pellets, it is possible to increase the density, and as a result, it is possible to increase the compressive strength of the pellets, thereby completing the present invention. [1] A method for producing pelletized ore, comprising the steps of pre-pressurizing a raw material mixture containing a zinc-containing raw material and a reducing agent using a pre-pressurizing pelletizer, and feeding the resulting pre-pressurized pellets and the raw material mixture into a pelletizer for further pelletizing. [2] The method for producing pelletized ore according to [1], wherein the amount of pre-pressurized pellets fed into the pelletizer is 55 to 85% by mass of the total amount fed. [3] A method for producing agglomerated ore as described in [1], in which the raw material mixture is granulated in advance. [4] The method for producing pelletized ore according to [1], wherein the maximum diameter of the pre-pressurized pellets is in the range of 20 to 40 mm. [5] The method for manufacturing agglomerates according to [1], wherein the maximum diameter of the agglomerates is in the range of 50 to 100 mm. [6] A method for producing the agglomerated ore of [1], which comprises melting and reducing the agglomerated ore. [7] A method for producing agglomerated ore according to [5], in which the melting reduction treatment is carried out using a high-frequency induction furnace, a DC or AC resistance heating electric furnace, or a Mitsui-type zinc semi-blast furnace (MF furnace). [8] The method for producing agglomerates of [1], wherein the zinc-containing raw material is steelmaking dust. [9] A method for producing agglomerated ore according to [1], wherein the raw material mixture contains fly ash.

[10] A pelletized ore obtained by pre-pressurizing a raw material mixture containing a zinc-containing raw material and a reducing agent and further pelletizing the raw material mixture with the pre-pressurized pellets obtained by pre-pressurizing a raw material mixture containing a zinc-containing raw material and a reducing agent.

[11] The agglomerated ore of

[10] is obtained by further subjecting the obtained agglomerated ore to a melting reduction treatment.

[12] A method for recovering zinc from pelletized ore, comprising pelletizing a raw material mixture containing a zinc-containing raw material and a reducing agent, mixing the resulting pre-pressurized pellets with the raw material mixture to pelletize, melting and reducing the resulting pellets, and recovering the resulting crude zinc oxide by reoxidizing the metallic zinc vapor. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain pelletized ore with high density and crushing strength. As a result, it is possible to improve processing efficiency. It is also possible to significantly reduce the amount of binder itself, which makes it possible to reduce production costs. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 shows a schematic cross-sectional view of a muller used in the present invention. [Figure 2] FIG. 2 shows a schematic flow diagram of an example of the production method of the present invention. [Figure 3] FIG. 3 shows a diagram in which the ratio of the pre-pressed pellets to the raw material mixed powder and the evaluation results of the crushing strength in the examples are plotted. DETAILED DESCRIPTION OF THE INVENTION

[0011] The method for producing pelletized ore of the present invention comprises: a raw material mixture containing a zinc-containing raw material and a reducing agent is pre-pressurized and pelletized by a pre-pressurizing pelletizer; The method further comprises a step of feeding the obtained pre-pressed pellets and the raw material mixture into a pellet-making machine for further pelletization.

[0012] raw material mixture In the present invention, a zinc-containing raw material is used in the raw material mixture. Although various raw materials containing zinc can be used as the zinc-containing raw material, it is practically preferable to use steelmaking dust. Steelmaking dust is generated when iron scrap is melted in an electric furnace to produce steel, and contains approximately 10 to 40 mass% zinc.

[0013] In the present invention, fly ash can also be used. As the fly ash, zinc-containing fly ash such as incineration fly ash or molten fly ash is dechlorinated and washed with a washing solution having a pH of 10 to 12, and the dechlorinated and washed fly ash is used. The reducing agent may be, for example, a carbon-containing substance such as coal, lignite, anthracite, coke powder, steelmaking dust containing carbonaceous materials, plastic, wood powder, etc. From the viewpoint of maintaining the strength of the briquettes, it is generally desirable to use a reducing agent with a low volatile content, but there is no particular limitation.

[0014] In addition to the reducing agent, the melting furnace may contain other adjusting agents (lime, silica stone, etc.) required for the melting furnace. Furthermore, in order to improve the strength of the pelletized ore, an appropriate amount of a known binder such as starch or molasses may be mixed, if necessary.

[0015] If necessary, an appropriate amount of water may be mixed into the raw material mixture in order to improve the strength of the agglomerated ore. As for the composition of each component in the mixture, the zinc-containing raw material is preferably 10 mass% or more relative to the total amount of the raw material mixture. When the amount is within this range, processing efficiency is high and pelletized ore with high crushing strength can be obtained.

[0016] The raw material mixture may be kneaded and granulated in advance, for example, by a method such as rolling granulation. Granulation allows for efficient processing without powdering during pre-compression granulation.

[0017] ·Blanking process In the pelleting process, for example, a twin-roll pelleting machine as shown in Figure 1 can be used. Figure 1 shows a schematic diagram of a pelleting machine. As shown in Figure 1, the pelleting machine continuously compresses the mixture fed from a hopper for feeding raw materials between pocketed rolls to produce pellets. The size of the pellets is adjusted by the size of the pockets. Depending on the shape of the pockets, pellets of various shapes, such as spheres, oval spheres (bale-shaped), and cones, can be obtained. The hopper may be provided with a screw for extruding the raw materials, if necessary.

[0018] The raw material mixture is fed into a pre-pressure pelletizer and pre-pressurized to produce pre-pressurized pellets. The maximum diameter of the pre-pressed pellets is preferably in the range of 20 to 40 mm, more preferably 25 to 35 mm. In the present invention, the maximum diameter of the pellets is measured along the long side. The compressive strength of the pre-pressed pellets is in the range of 20 to 40 kgf.

[0019] The resulting mixture of pre-pressed pellets and the raw material mixture is fed into a pellet-making machine and pelletized. If a hopper equipped with a screw is used, it is also possible to directly mix the pre-pressed pellets with the raw material mixture in the hopper. The amount of pre-pressed pellets fed into the pellet-making machine is not limited as long as it allows pelletization, and is in the range of 55 to 85 mass% of the total amount fed, more preferably 55 to 80 mass%, preferably 60 to 80 mass%, and even more preferably 65 to 75 mass%. Mixing the pre-pressed pellets with the raw material mixture in the above ranges reduces the void ratio, making it possible to increase the packing density and obtain pellets with high crushing strength.

[0020] The maximum diameter of the pellets is larger than that of the pre-pressed pellets, and is in the range of 50 to 100 mm, preferably 60 to 90 mm, and more preferably 70 to 80 mm. The compression strength of the pellets is in the range of 70 to 130 kgf. The maximum diameter ratio of the pellets to the pre-pressed pellets is preferably 2 to 5 times, more preferably 3 to 4 times, of the pellets / pre-pressed pellets.

[0021] ·process The method for producing pelletized ore of the present invention will be described below with reference to Fig. 2. Fig. 2 shows a schematic flow diagram illustrating an example of the production method of the present invention. Note that in the present invention, other steps are not particularly limited as long as the pelletizing step is included. Each raw material constituting the mixed powder raw material is dried in a dryer and then pulverized. After pulverization and mixing, the raw material mixture is transferred to a tumbling granulator, granulated, and if necessary, a binder is added, and the moisture content is appropriately adjusted again in the dryer.

[0022] The obtained raw material mixture is fed into a pre-pressurized pelletizer and processed into the specified pre-pressurized pellets as described above. The pre-pressurized pellets are fed into the pelletizer together with the raw material mixture that has not been pre-pressurized, in a specified ratio. At this time, they may be mixed as appropriate. The pelletizer produces pellets of a specified shape. The pelletizer can be used as a pelletizer or a pre-pressurized pelletizer by adjusting the size of the pockets to the specified size. The pellets formed to a predetermined size may be aged in an aging bin as needed. This aging process allows the pellets to develop stable pellet strength. There are no particular restrictions on the aging conditions, but the pellets are typically left in the aging bin at room temperature for about half a day.

[0023] The resulting pellets are subjected to a melting and reducing treatment at a predetermined temperature. The evaporated metallic zinc vapor is concentrated in the dust during the smelting reduction process, and is reoxidized during the cooling process to be recovered as crude zinc oxide, which can be used in zinc smelting.

[0024] The melting reduction treatment may be carried out by any known method, but is preferably carried out using a high-frequency induction furnace, a DC or AC resistance heating electric furnace, or a Mitsui-type zinc semi-blast furnace (MF furnace). Of these, the Mitsui-type zinc semi-blast furnace (MF furnace) is preferred in terms of efficiency. In Figure 2, an MF furnace is used as an example. When coal (including coke) is used as the reducing agent, smelting reduction treatment can be carried out by melting the coal under reducing conditions, for example, at 1300°C or higher. Generally, when the treatment temperature during smelting reduction is lower than 1300°C, the metal components in the agglomerate tend to be insufficiently volatilized or melted.

[0025] According to the present invention, it is possible to provide agglomerated ore having a high density without performing a complicated process, and as a result, it is possible to increase the compressive strength of the agglomerated ore. The agglomerated ore can be used for zinc recovery and smelting.

[0026] Furthermore, according to the present invention, there is provided a method for recovering zinc from pelletized ore, which comprises pre-pressurizing a raw material mixture containing a zinc-containing raw material and a reducing agent, further pelletizing the resulting pre-pressurized pellets together with the raw material mixture, subjecting the resulting pellets to a melting reduction treatment, and recovering the resulting crude zinc oxide by re-oxidizing the metallic zinc vapor. [Example]

[0027] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples in any way.

[0028] Example Water was added to the steelmaking dust in a tumbling granulator to a concentration of 15% by mass, and the mixture was granulated. A binder was added and the mixture was dried to prepare a raw material powder mixture with a moisture content of 10% by mass. The raw material powder mixture was subjected to pre-compression pelletizing using the pelletizing machine shown in Figure 1. The pre-compression pellets were oval-spherical, with an average long side of 30 mm and a crushing strength of 30 kgf. The obtained pre-pressurized pellets were mixed with the raw material mixture powder so that the ratio of the primary pellets in the mixture was 35, 40, 42, 45, 55, 60, 65, 70, 75, 77.5, and 80% by mass, respectively, and pelletized. The pellets were oval-shaped with an average long side of 85 mm. The crushing strength of each mixture was evaluated. The crushing strength was measured using a precision load measuring instrument (Aiko Engineer).

[0029] In Figure 3, the horizontal axis shows the pre-compressed pellet content ratio and the vertical axis shows the evaluation results of crushing strength for each mixture. As a result, it was found that a pellet having high crushing strength can be obtained by mixing the pre-pressurized pellet with the raw material powder mixture in a predetermined ratio.

Claims

1. a raw material mixture containing a zinc-containing raw material and a reducing agent is pre-pressurized and pelletized by a pre-pressurizing pelletizer; The method for producing pelletized ore includes a step of feeding the obtained pre-pressurized pellets and the raw material mixture into a pelletizing machine for further pelletizing.

2. The method for producing pellets according to claim 1, wherein the amount of pre-pressurized pellets charged into the pellet making machine is 55 to 85% by mass of the total amount charged.

3. 2. The method for producing pelletized ore according to claim 1, wherein the raw material mixture is pelletized in advance.

4. 2. The method for producing pelletized ore according to claim 1, wherein the maximum diameter of the pre-pressurized pellets is in the range of 20 to 40 mm.

5. The method for producing pelletized ore according to claim 1, wherein the pellets have a maximum diameter in the range of 50 to 100 mm.

6. 2. The method for producing pelletized ore according to claim 1, wherein the pelletized ore is melted and reduced.

7. 7. The method for producing pelletized ore according to claim 6, wherein the melting reduction treatment is carried out using a high frequency induction furnace, a DC or AC resistance heating electric furnace, or a Mitsui type zinc semi-blast furnace (MF furnace).

8. 2. The method for producing granulated ore according to claim 1, wherein the zinc-containing raw material is steelmaking dust.

9. The method for producing granulated ore according to claim 1, wherein the raw material mixture contains fly ash.

10. A pelletized ore is obtained by pre-pressurizing a raw material mixture containing a zinc-containing raw material and a reducing agent and further pelletizing the raw material mixture with the pelletized product.

11. The granulated ore of claim 10, further comprising a melting reduction treatment.

12. A method for recovering zinc from pelletized ore, comprising pre-pressurizing a raw material mixture containing a zinc-containing raw material and a reducing agent, pelletizing the resulting pre-pressurized pellets with the raw material mixture, melting and reducing the resulting pellets, and recovering the resulting crude zinc oxide by re-oxidizing the metallic zinc vapor.

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