Zinc recovery method and zinc ferrite decomposition method

Abstract

In a zinc recovery method or a zinc ferrite decomposition method, a raw material (1) containing a zinc component and zinc ferrite or a treated raw material (3) obtained by treating the raw material (1) is brought into contact with aqueous alkali metal hydroxide solutions (5, 14), and the raw material (1) or the treated raw material (3) and the aqueous alkali metal hydroxide solutions (5, 14) brought into contact with each other are heated. The raw material (1) or the treated raw material (3) and the alkali metal hydroxide aqueous solutions (5, 14) are heated to a temperature at which the boiling point of the water is increased, and the concentration of the alkali agent contained in the alkali metal hydroxide aqueous solutions (5, 14) when evaporation of moisture in the alkali metal hydroxide aqueous solutions (5, 14) is stopped after the temperature has reached the boiling point is maintained. In the concentration maintaining step (102c), the alkaline agent whose concentration is maintained is brought into contact with the zinc ferrite of the raw material (1) or the treated raw material (3), thereby decomposing the zinc ferrite into a zinc oxide component and an iron oxide component.

Description

Technical Field

[0001] The present invention relates to a zinc recovery method and a zinc ferrite decomposition method, and more particularly to a zinc recovery method and a zinc ferrite decomposition method for decomposing zinc ferrite, which is a hardly soluble substance contained in electric furnace dust, primary dust or secondary dust such as blast furnace dust, blast furnace / converter dust or RHF (Rotary Hearth Furnace) dust, and zinc-containing dust such as roasted ore of zinc concentrate, generated when scrap is melted and smelted in the electric furnace method, which is one of the ironmaking processes. Background Art

[0002] In the electric furnace process, one of the most common ironmaking processes, the melting and smelting of scrap produces electric furnace dust, an industrial waste product containing zinc oxide, equivalent to approximately 1.5% to 2.0% of the steel produced. This amount is estimated to be 8 million tons worldwide, with 400,000 tons generated in Japan.

[0003] Iron scrap mostly comes from abandoned buildings, appliances, and cars. The painted bases of these buildings, appliances, and cars are galvanized. Scrap also contains paint, plastics, and oil. Therefore, electric furnace dust contains not only heavy metals like zinc and lead, but also hazardous organic compounds like chlorides and dioxins. However, electric furnace dust contains approximately 20-30% iron and 20-30% zinc. Furthermore, crude zinc oxide, such as secondary dust, contains approximately 10% iron and 60% zinc. Therefore, electric furnace dust and other materials are very valuable resources.

[0004] In this case, Patent Document 1 discloses a method for producing zinc, which comprises the following steps: a zinc-containing aqueous solution generating step 102, in which an alkali metal hydroxide aqueous solution is used as an extraction solvent for selectively extracting zinc components from raw materials such as electric furnace dust; an electrolysis step 103, in which the zinc-containing aqueous solution is electrolyzed as an electrolyte to generate zinc; and a chlorine concentration adjusting step 101, in which the chlorine components contained in the raw materials such as electric furnace dust are separated at the beginning of the electrolysis step 103, thereby reducing the chlorine concentration of the zinc-containing aqueous solution.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2022 / 118927 Summary of the Invention

[0008] Problems to be solved by the invention

[0009] However, according to the research of the present inventors, it has been found that the structure disclosed in Patent Document 1 includes a zinc-containing aqueous solution generating step 102, which uses an alkali metal hydroxide aqueous solution as an extraction solvent for selectively extracting the zinc component in raw materials such as electric furnace dust. However, when filtering out solid components that are insoluble in the aqueous solution of the alkali agent 7, there is a certain limit to the filterability, and the filtration takes a certain amount of time. It is also known that compounds containing iron and zinc components, such as zinc ferrite (ZnFe2O4), which is often contained in large quantities in steelmaking soot, are not easily dissolved.

[0010] Here, the present inventors have further studied and found that by immersing electric furnace dust containing zinc ferrite, etc., in molten sodium hydroxide heated to 320°C or higher in a container and holding the mixture for approximately one hour, then lowering the temperature in the container to obtain a molten solid, and immersing the solid in water in another container, a zinc component dissolved in the sodium hydroxide aqueous solution (zinc-containing aqueous solution) and iron oxide as a residue of the solid can be obtained. However, in this method, when the sodium hydroxide aqueous solution in contact with the electric furnace dust containing zinc ferrite, etc. is heated to 320°C or higher, the latent heat of vaporization of the water contained therein, the sensible heat to the melting point, the heat of fusion, and the sensible heat from the melting point are required. This increases the energy consumption for heating, and is believed to increase not only the cost but also the environmental burden. This is also assumed to apply when recycling the electrolytic tail liquid to reduce the amount of sodium hydroxide used as an alkaline agent. On the other hand, if the evaporation rate of the water in the alkali metal hydroxide aqueous solution is reduced, the evaporation may be completed in a substantially solid state without fluidity, which is believed to hinder the decomposition of zinc ferrite. That is, according to the research of the present inventors, it is believed that there is a need for a new zinc recovery method and a zinc ferrite decomposition method for decomposing zinc ferrite, which can reduce the amount of energy consumed for heating, suppress the increase in cost and the increase in environmental burden, and can decompose the zinc ferrite into zinc oxide components and iron oxide components to recover zinc.

[0011] The present invention has been completed through the above research, and its purpose is to provide a zinc recovery method and a zinc ferrite decomposition method for decomposing zinc ferrite. The above-mentioned zinc recovery method can suppress the energy consumption of heating, suppress the increase in cost and the increase in environmental burden, and can reliably decompose the zinc ferrite contained in zinc-containing dust, etc., and can recover the zinc contained in the zinc-containing dust, etc.

[0012] Means for solving problems

[0013] To achieve the above-mentioned object, the present inventors conducted further research on decomposing zinc ferrite by contacting it with an aqueous alkali metal hydroxide solution, such as an aqueous sodium hydroxide solution. As a result, they discovered that zinc ferrite decomposition occurs at a high-temperature, high-concentration state, where the temperature reaches 150°C or higher as the boiling point rises, and the concentration of an alkaline agent, such as sodium hydroxide, in the aqueous alkali metal hydroxide solution is 70% by weight or higher. Further research on this phenomenon revealed that maintaining this high-temperature, high-concentration state for a predetermined period of time is crucial for reliably decomposing zinc ferrite. For example, in an open system, water evaporates rapidly from the aqueous alkali metal hydroxide solution, causing the water to evaporate and dry out before the decomposition reaction is complete, leading to a state in which the decomposition reaction of zinc ferrite does not proceed at all. Therefore, at the point in time when the concentration of the alkaline agent in the aqueous alkali metal hydroxide solution reaches a high concentration as the boiling point rises, it is necessary to, for example, seal the reaction vessel containing the zinc ferrite and the aqueous alkali metal hydroxide solution to create a closed system, thereby suppressing water evaporation and maintaining this high-temperature, high-concentration state until the decomposition reaction is complete. This led to the completion of the present invention.

[0014] The first aspect of the present invention provides a zinc recovery method comprising: a high-temperature high-alkali treatment step comprising: a contact step of bringing a raw material containing zinc components and zinc ferrite or a treated raw material obtained by treating the raw material into contact with an alkali metal hydroxide aqueous solution; a heating step of heating the raw material or the treated raw material and the alkali metal hydroxide aqueous solution brought into contact with each other in the contact step to a temperature reaching the boiling point of water whose boiling point is rising; and a concentration maintaining step of maintaining the concentration of the alkali metal hydroxide aqueous solution at a temperature at which evaporation of water in the alkali metal hydroxide aqueous solution stops after the temperature reaches the boiling point. The method further comprises the steps of: bringing the alkali agent, the alkali agent maintained at the above-mentioned concentration in the above-mentioned concentration maintaining step, into contact with the zinc ferrite of the above-mentioned raw material or the above-mentioned treated raw material, thereby decomposing the zinc ferrite into a zinc oxide component and an iron oxide component; a first leaching step, at a temperature lower than the above-mentioned boiling point, bringing the alkali agent, the zinc oxide component, and the above-mentioned iron oxide component into contact with water, thereby dissolving the zinc oxide component in an alkali metal hydroxide aqueous solution, thereby obtaining a first zinc-containing aqueous solution containing a zinc component, and simultaneously obtaining a sparingly soluble substance containing an iron oxide component that is insoluble in the alkali metal hydroxide aqueous solution, and separating the sparingly soluble substance from the above-mentioned first zinc-containing aqueous solution; and a zinc recovery step, wherein the zinc component is recovered from the above-mentioned first zinc-containing aqueous solution.

[0015] In addition, a second aspect of the present invention is that, in addition to the first aspect, the alkaline agent is sodium hydroxide or potassium hydroxide, and in the high-temperature high-alkali treatment step, at least one of aqueous hydrogen peroxide and sodium nitrate as an oxidizing agent, or at least one of sodium sulfite, sodium thiosulfate, sodium dithionite, hydrazine, and zinc metal as a reducing agent is added to the aqueous alkali metal hydroxide solution.

[0016] In addition, the third aspect of the present invention is that, based on the first or second aspect, the above-mentioned alkaline agent is sodium hydroxide, and before the above-mentioned high-temperature high-alkali treatment step, a halogen cleaning step is further provided: the above-mentioned raw materials are cleaned using a sodium hydroxide aqueous solution with a pH value in the range of not less than 8.5 and not more than 10.5 to clean the halogen components contained in the above-mentioned raw materials.

[0017] In addition, a fourth aspect of the present invention is that, in addition to any one of the first to third aspects, the method further comprises a purification step of bringing metallic zinc into contact with the first zinc-containing aqueous solution to reduce and precipitate metallic impurity components inactive compared to zinc in the first zinc-containing aqueous solution, thereby purifying the first zinc-containing aqueous solution.

[0018] In addition, the fifth aspect of the present invention is that, based on the fourth aspect, the zinc recovery step includes an electrolysis step: electrolysis is performed using the first zinc-containing aqueous solution or an aqueous solution obtained by purifying the first zinc-containing aqueous solution as an electrolyte to obtain electrolytically generated zinc and an electrolytic tail liquid, and the electrolytic tail liquid is transported to the high-temperature and high-alkali treatment step in a state in which an alkali metal hydroxide aqueous solution and zinc components remain, and the alkali metal hydroxide aqueous solution in the electrolytic tail liquid contacts the raw material or the treated raw material.

[0019] In addition, the sixth aspect of the present invention is that, in addition to the fourth aspect, the zinc recovery step includes a zinc carbonate separation step: the zinc component in the first zinc-containing aqueous solution or the aqueous solution obtained by purifying the first zinc-containing aqueous solution is separated as zinc carbonate, and a residual liquid from which the zinc carbonate is separated is obtained. The residual liquid, while still containing an aqueous alkali metal hydroxide solution and the zinc component, is conveyed to the high-temperature high-alkali treatment step, and the aqueous alkali metal hydroxide solution in the residual liquid contacts the raw material or the treated raw material.

[0020] In addition, the seventh aspect of the present invention is that, in addition to the first or second aspect, a second leaching step is further provided before the above-mentioned high-temperature high-alkali treatment step: the raw material or the above-mentioned treated raw material is contacted with an aqueous sodium hydroxide solution, and the zinc component contained in the above-mentioned raw material or the above-mentioned treated raw material is dissolved in the above-mentioned aqueous sodium hydroxide solution and selectively extracted to obtain a second zinc-containing aqueous solution containing the above-mentioned zinc component, and at the same time, a sparingly soluble matter containing zinc ferrite that is insoluble in the above-mentioned aqueous sodium hydroxide solution is obtained; the sparingly soluble matter and the above-mentioned second zinc-containing aqueous solution are separated, and the above-mentioned sparingly soluble matter containing zinc ferrite is conveyed to the above-mentioned high-temperature high-alkali treatment step as the above-mentioned treated raw material and decomposed into a zinc oxide component and an iron oxide component; in the above-mentioned first leaching step, the zinc oxide component is dissolved in the above-mentioned aqueous sodium hydroxide solution to obtain a fourth zinc-containing aqueous solution containing the zinc component.

[0021] According to an eighth aspect of the present invention, in addition to the seventh aspect, the fourth zinc-containing aqueous solution is transported to the second leaching step, and the zinc component contained in the fourth zinc-containing aqueous solution is selectively extracted to become part of the second zinc-containing aqueous solution.

[0022] In addition, the ninth aspect of the present invention is that, based on the seventh or eighth aspect, the alkaline agent is sodium hydroxide, and a halogen cleaning step is further provided before the second leaching step: the raw material is cleaned with a sodium hydroxide aqueous solution having a pH value in the range of 8.5 to 10.5 to clean the halogen components contained in the raw material to obtain a treated raw material.

[0023] In addition, a tenth aspect of the present invention is that, in addition to any one of the seventh to ninth aspects, the method further comprises a purification step of bringing metallic zinc into contact with the second zinc-containing aqueous solution to reduce and precipitate metallic impurity components inactive compared to zinc in the second zinc-containing aqueous solution, thereby purifying the second zinc-containing aqueous solution.

[0024] In addition, the 11th aspect of the present invention is that, based on the 10th aspect, the zinc recovery step includes an electrolysis step: electrolysis is performed using the second zinc-containing aqueous solution or an aqueous solution obtained by purifying the second zinc-containing aqueous solution as an electrolyte to obtain electrolytically generated zinc and an electrolytic tail liquid, and the electrolytic tail liquid is transported to the high-temperature and high-alkali treatment step in a state in which an alkali metal hydroxide aqueous solution and zinc components remain, and the alkali metal hydroxide aqueous solution in the electrolytic tail liquid contacts the raw material or the treated raw material.

[0025] In addition, the twelfth aspect of the present invention is that, based on the tenth aspect, the zinc recovery step includes a zinc carbonate separation step: the zinc component in the second zinc-containing aqueous solution or the aqueous solution obtained by purifying the second zinc-containing aqueous solution is separated as zinc carbonate, and a residual liquid from which the zinc carbonate is separated is obtained. The residual liquid is conveyed to the high-temperature high-alkali treatment step in a state where the alkali metal hydroxide aqueous solution and the zinc component remain, and the alkali metal hydroxide aqueous solution in the residual liquid contacts the raw material or the treated raw material.

[0026] In addition, the 13th aspect of the present invention is that, on the basis of the first or second aspect, it further comprises: a magnetic mineral separation process, before the above-mentioned high-temperature high-alkali treatment process, a magnetic force is applied to the above-mentioned raw material or the above-mentioned treated raw material by means of a magnet, and a first selected ore composed of components attached to the above-mentioned magnet is separated from a second selected ore not attached to the above-mentioned magnet according to the magnetic strength of the components in the above-mentioned raw material or the above-mentioned treated raw material; and a third leaching process, conveying the above-mentioned second selected ore, dissolving the zinc component contained in the above-mentioned second selected ore in an aqueous sodium hydroxide solution and selectively extracting it to obtain a third zinc-containing aqueous solution containing the above-mentioned zinc component, and at the same time obtaining an insoluble substance insoluble in the above-mentioned alkali metal hydroxide aqueous solution, separating the above-mentioned insoluble substance and the above-mentioned third zinc-containing aqueous solution, and conveying the above-mentioned first selected ore to the above-mentioned high-temperature high-alkali treatment process as the above-mentioned treated raw material, and the above-mentioned zinc ferrite in the above-mentioned first selected ore is decomposed into the above-mentioned zinc oxide component and the above-mentioned iron oxide component.

[0027] In addition, the 14th aspect of the present invention is that, based on the 13th aspect, the above-mentioned alkaline agent is sodium hydroxide, and before the above-mentioned third leaching step, a halogen cleaning step is further provided: the above-mentioned raw material is cleaned using a sodium hydroxide aqueous solution with a pH value in the range of 8.5 to 10.5, thereby cleaning the halogen components contained in the above-mentioned raw material to obtain a treated raw material.

[0028] In addition, the fifteenth aspect of the present invention is based on the thirteenth or fourteenth aspect, further comprising a purification step of bringing metallic zinc into contact with the third zinc-containing aqueous solution to reduce and precipitate metallic impurity components inactive compared to zinc in the third zinc-containing aqueous solution, thereby purifying the third zinc-containing aqueous solution.

[0029] In addition, the 16th aspect of the present invention is that, based on the 15th aspect, the zinc recovery step includes an electrolysis step: electrolysis is performed using the third zinc-containing aqueous solution or an aqueous solution obtained by purifying the third zinc-containing aqueous solution as an electrolyte to obtain electrolytically generated zinc and an electrolytic tail liquid, and the electrolytic tail liquid is transported to the high-temperature and high-alkali treatment step in a state in which an alkali metal hydroxide aqueous solution and zinc components remain, and the alkali metal hydroxide aqueous solution in the electrolytic tail liquid contacts the raw material or the treated raw material.

[0030] In addition, the 17th aspect of the present invention is that, based on the 15th aspect, the zinc recovery step includes a zinc carbonate separation step: the zinc component in the third zinc-containing aqueous solution or the aqueous solution obtained by purifying the third zinc-containing aqueous solution is separated as zinc carbonate, and a residual liquid from which the zinc carbonate is separated is obtained. The residual liquid is conveyed to the high-temperature high-alkali treatment step in a state in which the alkali metal hydroxide aqueous solution and the zinc component remain, and the alkali metal hydroxide aqueous solution in the residual liquid contacts the raw material or the treated raw material.

[0031] In addition, the zinc ferrite decomposition method according to the eighteenth aspect of the present invention comprises: a contacting step of contacting a zinc ferrite-containing material containing zinc ferrite with an alkali metal hydroxide aqueous solution; a heating step of heating the zinc ferrite-containing material and the alkali metal hydroxide aqueous solution brought into contact with each other in the contacting step to a temperature reaching the boiling point of water whose boiling point is rising; and a concentration maintaining step of maintaining the concentration of the alkaline agent contained in the alkali metal hydroxide aqueous solution at a concentration at which evaporation of water in the alkali metal hydroxide aqueous solution stops after the temperature reaches the boiling point, wherein the alkaline agent maintained at the concentration in the concentration maintaining step contacts the zinc ferrite in the zinc ferrite-containing material, thereby decomposing the zinc ferrite into a zinc oxide component and an iron oxide component.

[0032] Effects of the Invention

[0033] According to the first aspect of the present invention, the zinc recovery method comprises the following steps: a high-temperature high-alkali treatment step, which comprises: a contact step of bringing a raw material containing zinc components and zinc ferrite or a treated raw material that has been treated into contact with an alkali metal hydroxide aqueous solution; a heating step of heating the raw material or the treated raw material and the alkali metal hydroxide aqueous solution that have been brought into contact with each other in the contact step, raising the temperature of the raw material or the treated raw material and the alkali metal hydroxide aqueous solution to a temperature that reaches the boiling point of water that is rising in boiling point; and a concentration maintaining step of maintaining the concentration of the alkali agent contained in the alkali metal hydroxide aqueous solution at a time when evaporation of water in the alkali metal hydroxide aqueous solution stops after the temperature reaches the boiling point, wherein the concentration of the alkali agent maintained in the concentration maintaining step is maintained at a constant level with respect to the raw material or the treated raw material. The present invention relates to a process for the treatment of zinc ferrite in a raw material, wherein the zinc ferrite is contacted with water at a temperature below the boiling point, thereby decomposing the zinc ferrite into zinc oxide and iron oxide. A first leaching step involves contacting the alkaline agent, the zinc oxide, and the iron oxide with water at a temperature below the boiling point, dissolving the zinc oxide in the alkali metal hydroxide aqueous solution to obtain a first zinc-containing aqueous solution containing the zinc component, while simultaneously obtaining a poorly soluble substance containing the iron oxide that is insoluble in the alkali metal hydroxide aqueous solution, and separating the poorly soluble substance from the first zinc-containing aqueous solution. A zinc recovery step involves recovering the zinc component from the first zinc-containing aqueous solution. This process reduces heating energy consumption, increases in costs, and increases in environmental burdens, while reliably decomposing zinc ferrite contained in zinc-containing dust and the like, and recovering zinc contained in the zinc-containing dust and the like. Furthermore, in the concentration maintenance step, by maintaining the concentration of the alkaline agent in the alkali metal hydroxide aqueous solution at a temperature below the boiling point at which evaporation of water in the alkali metal hydroxide aqueous solution ceases, the pressure resistance of the reaction vessel, such as a sealed container, can be reduced at this time, thereby simplifying the structure of the reaction vessel and reducing costs.

[0034] Furthermore, according to the zinc recovery method of the second aspect of the present invention, since the alkaline agent is sodium hydroxide or potassium hydroxide, at least one of aqueous hydrogen peroxide and sodium nitrate as an oxidizing agent, or at least one of sodium sulfite, sodium thiosulfate, sodium dithionite, hydrazine, and zinc metal as a reducing agent is added to the aqueous alkali metal hydroxide solution in the high-temperature, high-alkali treatment step. This allows for more reliable decomposition of zinc ferrite contained in zinc-containing dust and the like.

[0035] Furthermore, according to the zinc recovery method of the third aspect of the present invention, since the alkaline agent is sodium hydroxide, a halogen cleaning step is further provided before the high-temperature high-alkali treatment step: the raw material is cleaned with a sodium hydroxide aqueous solution having a pH value in the range of 8.5 to 10.5 to clean the halogen components contained in the raw material, thereby enabling the halogen components contained in the zinc-containing dust and the like to be reliably dissolved and cleaned.

[0036] Furthermore, the zinc recovery method according to the fourth aspect of the present invention further comprises a purification step of bringing metallic zinc into contact with the first zinc-containing aqueous solution, reducing and precipitating metallic impurity components inactive compared to zinc in the first zinc-containing aqueous solution, and purifying the first zinc-containing aqueous solution. Therefore, zinc with reduced impurity contamination can be recovered.

[0037] Furthermore, according to the zinc recovery method of the fifth aspect of the present invention, the zinc recovery step includes an electrolysis step in which the first zinc-containing aqueous solution or an aqueous solution obtained by purifying the first zinc-containing aqueous solution is electrolyzed as an electrolyte to obtain electrolytically produced zinc and an electrolytic tail liquid. The electrolytic tail liquid is conveyed to a high-temperature, high-alkali treatment step in a state in which an alkali metal hydroxide aqueous solution and zinc components remain. The alkali metal hydroxide aqueous solution in the electrolytic tail liquid contacts the raw material or the treated raw material. Therefore, the electrolytically produced zinc with reduced impurity contamination can be recovered stably with a good yield.

[0038] Furthermore, according to the zinc recovery method of the sixth aspect of the present invention, the zinc recovery step includes a zinc carbonate separation step in which the zinc component in the first zinc-containing aqueous solution or in an aqueous solution obtained by purifying the first zinc-containing aqueous solution is separated as zinc carbonate, thereby obtaining a residual liquid from which the zinc carbonate is separated. The residual liquid, while still containing an aqueous alkali metal hydroxide solution and the zinc component, is conveyed to a high-temperature, high-alkali treatment step. The aqueous alkali metal hydroxide solution in the residual liquid contacts the raw material or the treated raw material, thereby enabling stable recovery of zinc carbonate with reduced impurity contamination at a good yield.

[0039] In addition, according to the seventh aspect of the present invention, the zinc recovery method further includes a second leaching step before the high-temperature high-alkali treatment step: the raw material or the treated raw material is contacted with an aqueous sodium hydroxide solution, the zinc component contained in the raw material or the treated raw material is dissolved in the aqueous sodium hydroxide solution and selectively extracted to obtain a second zinc-containing aqueous solution containing the zinc component, and at the same time, a sparingly soluble matter containing zinc ferrite that is insoluble in the aqueous sodium hydroxide solution is obtained, the sparingly soluble matter and the second zinc-containing aqueous solution are separated, the sparingly soluble matter containing zinc ferrite is conveyed to the high-temperature high-alkali treatment step as the treated raw material, and decomposed into a zinc oxide component and an iron oxide component, and in the first leaching step, the zinc oxide component is dissolved in the aqueous sodium hydroxide solution to obtain a fourth zinc-containing aqueous solution containing the zinc component. Therefore, the zinc ferrite contained in the zinc-containing dust, etc. can be more reliably decomposed in a manner with reduced energy consumption, and the zinc contained in the zinc-containing dust, etc. can be efficiently recovered.

[0040] Furthermore, according to the zinc recovery method of the eighth aspect of the present invention, since the fourth zinc-containing aqueous solution is transported to the second leaching step, the zinc component contained in the fourth zinc-containing aqueous solution is selectively extracted and becomes part of the second zinc-containing aqueous solution, thereby enabling zinc contained in zinc-containing dust and the like to be recovered more efficiently.

[0041] Furthermore, according to the zinc recovery method of the ninth aspect of the present invention, since the alkaline agent is sodium hydroxide, a halogen cleaning step is further provided before the second leaching step: the raw material is cleaned with a sodium hydroxide aqueous solution having a pH value in the range of not less than 8.5 and not more than 10.5, thereby cleaning the halogen components contained in the raw material and providing the treated raw material. Therefore, the halogen components contained in the zinc-containing dust, etc. can be reliably dissolved and cleaned.

[0042] Furthermore, the zinc recovery method according to the tenth aspect of the present invention further comprises a purification step of bringing metallic zinc into contact with the second zinc-containing aqueous solution, reducing and precipitating metallic impurity components inactive compared to zinc in the second zinc-containing aqueous solution, and purifying the second zinc-containing aqueous solution. Therefore, zinc with reduced impurity contamination can be recovered.

[0043] Furthermore, according to the zinc recovery method of the eleventh aspect of the present invention, the zinc recovery step includes an electrolysis step in which the second zinc-containing aqueous solution or an aqueous solution obtained by purifying the second zinc-containing aqueous solution is electrolyzed as an electrolyte to obtain electrolytically produced zinc and an electrolytic tail liquid. The electrolytic tail liquid is conveyed to a high-temperature, high-alkali treatment step in a state in which an alkali metal hydroxide aqueous solution and zinc components remain. The alkali metal hydroxide aqueous solution in the electrolytic tail liquid contacts the raw material or the treated raw material. Therefore, the electrolytically produced zinc with reduced impurity contamination can be stably recovered with a good yield.

[0044] Furthermore, according to the zinc recovery method of the twelfth aspect of the present invention, since the zinc recovery step includes a zinc carbonate separation step, the zinc component in the second zinc-containing aqueous solution or in the aqueous solution obtained by purifying the second zinc-containing aqueous solution is separated as zinc carbonate, and a residual liquid from which the zinc carbonate is separated is obtained. The residual liquid, while still containing an aqueous alkali metal hydroxide solution and the zinc component, is conveyed to a high-temperature high-alkali treatment step, and the aqueous alkali metal hydroxide solution in the residual liquid contacts the raw material or the treated raw material. Thus, zinc carbonate with reduced impurity contamination can be recovered stably with a good yield.

[0045] Furthermore, the zinc recovery method according to the 13th aspect of the present invention further comprises: a magnetic separation step in which, before the high-temperature high-alkali treatment step, a magnetic force is applied to the raw material or the treated raw material by means of a magnet, and a first selected ore composed of components adhering to the magnet is separated from a second selected ore not adhering to the magnet based on the magnetic strength of the components in the raw material or the treated raw material; and a third leaching step in which the second selected ore is conveyed, the zinc component contained in the second selected ore is dissolved in an aqueous sodium hydroxide solution and selectively extracted to obtain a third zinc-containing aqueous solution containing the zinc component, and a sparingly soluble substance insoluble in the alkali metal hydroxide aqueous solution is simultaneously obtained, the sparingly soluble substance is separated from the third zinc-containing aqueous solution, and the first selected ore is conveyed as the treated raw material to the high-temperature high-alkali treatment step, whereby the zinc ferrite in the first selected ore is decomposed into a zinc oxide component and an iron oxide component. Therefore, the zinc ferrite contained in the zinc-containing dust or the like can be more reliably decomposed with reduced energy consumption, and the zinc contained in the zinc-containing dust or the like can be efficiently recovered.

[0046] Furthermore, according to the zinc recovery method of the fourteenth aspect of the present invention, since the alkaline agent is sodium hydroxide, a halogen cleaning step is further provided before the third leaching step: the raw material is cleaned with a sodium hydroxide aqueous solution having a pH value in the range of not less than 8.5 and not more than 10.5 to clean the halogen components contained in the raw material, thereby enabling the halogen components contained in the zinc-containing dust and the like to be reliably dissolved and cleaned.

[0047] Furthermore, the zinc recovery method according to the fifteenth aspect of the present invention further comprises a purification step of bringing metallic zinc into contact with the third zinc-containing aqueous solution, reducing and precipitating metallic impurity components inactive compared to zinc in the third zinc-containing aqueous solution, and purifying the third zinc-containing aqueous solution. Thus, zinc with reduced impurity contamination can be recovered.

[0048] In addition, according to the zinc recovery method of the sixteenth aspect of the present invention, since the zinc recovery step includes an electrolysis step: electrolysis is performed using the third zinc-containing aqueous solution or an aqueous solution obtained by purifying the third zinc-containing aqueous solution as an electrolyte to obtain electrolytically produced zinc and an electrolytic tail liquid, the electrolytic tail liquid is transported to a high-temperature high-alkali treatment step in a state where an alkali metal hydroxide aqueous solution and zinc components remain, and the alkali metal hydroxide aqueous solution in the electrolytic tail liquid contacts the raw material or the treated raw material, thereby being able to stably recover the electrolytically produced zinc with reduced impurity mixing with a good yield.

[0049] Furthermore, according to the zinc recovery method of the seventeenth aspect of the present invention, since the zinc recovery step includes a zinc carbonate separation step, the zinc component in the third zinc-containing aqueous solution or in an aqueous solution obtained by purifying the third zinc-containing aqueous solution is separated as zinc carbonate, and a residual liquid from which the zinc carbonate is separated is obtained. The residual liquid, while still containing an aqueous alkali metal hydroxide solution and the zinc component, is conveyed to a high-temperature high-alkali treatment step, and the aqueous alkali metal hydroxide solution in the residual liquid contacts the raw material or the treated raw material, thereby enabling the stable recovery of zinc carbonate with reduced impurities at a good yield.

[0050] Furthermore, according to the eighteenth aspect of the present invention, the method for decomposing zinc ferrite comprises: a contacting step of bringing a zinc ferrite-containing material containing zinc ferrite into contact with an alkali metal hydroxide aqueous solution; a heating and temperature-raising step of heating the zinc ferrite-containing material and the alkali metal hydroxide aqueous solution brought into contact with each other in the contacting step to a temperature reaching the boiling point of water whose boiling point is rising; and a concentration-maintaining step of maintaining the concentration of the alkali agent contained in the alkali metal hydroxide aqueous solution at a point at which evaporation of water in the alkali metal hydroxide aqueous solution stops after the temperature reaches the boiling point. The alkali agent having the maintained concentration in the concentration-maintaining step contacts the zinc ferrite in the zinc ferrite-containing material to decompose the zinc ferrite into a zinc oxide component and an iron oxide component. Therefore, the method can suppress energy consumption for heating, increase in cost, and increase in environmental burden, and can reliably decompose zinc ferrite contained in zinc-containing dust or the like. Furthermore, in the concentration maintaining step, by maintaining the concentration of the alkaline agent contained in the aqueous alkali metal hydroxide solution at the time when evaporation of water in the aqueous alkali metal hydroxide solution stops after the temperature reaches the boiling point, the pressure resistance of the reaction container such as the sealed container at this time can be reduced, thereby simplifying the structure of the reaction container and reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 (A) is a process diagram of the zinc recovery method in the first embodiment of the present invention.

[0052] Figure 1 (B) is a process diagram of the zinc ferrite decomposition method included in the zinc recovery method in this embodiment.

[0053] Figure 2 This is a process diagram of a zinc recovery method including a zinc ferrite decomposition method in a second embodiment of the present invention.

[0054] Figure 3 This is a process diagram of a zinc recovery method including a zinc ferrite decomposition method in a third embodiment of the present invention.

[0055] Figure 4 This is a process diagram of a zinc recovery method including a zinc ferrite decomposition method in a fourth embodiment of the present invention. DETAILED DESCRIPTION

[0056] Hereinafter, the zinc recovery method and the zinc ferrite decomposition method in each embodiment of the present invention will be described in detail with reference to the accompanying drawings as appropriate.

[0057] (First embodiment)

[0058] First, refer to Figure 1 , the zinc recovery method and the zinc ferrite decomposition method in the first embodiment of the present invention are described in detail.

[0059] Figure 1 : is a diagram showing the steps of the zinc recovery method including the zinc ferrite decomposition method in this embodiment. Specifically, Figure 1 (A) is a process diagram of the zinc recovery method in this embodiment, Figure 1 (B) is a process diagram of the zinc ferrite decomposition method included in the zinc recovery method in this embodiment.

[0060] like Figure 1 As shown in (A), in the zinc recovery method of this embodiment, the dehalogenation cleaning process 101, the high temperature and high alkali treatment process 102, the electrolysis tail liquid leaching process 103, the purification process 104 and the electrolysis process 105 are performed in sequence. Here, if we focus on the decomposition of zinc ferrite, as shown in FIG. Figure 1 As shown in (B), the high-temperature high-alkali treatment step 102 corresponds to all steps of the zinc ferrite decomposition method. Furthermore, the electrolysis step 105 corresponds to the zinc recovery step. While electric furnace dust 1 is representatively used as the raw material for the recovery and decomposition methods, the raw material only needs to include at least zinc compounds such as zinc oxide, iron compounds such as iron oxide, and zinc ferrite, which is a compound of iron and zinc. In addition to electric furnace dust, primary or secondary dust such as blast furnace dust, blast furnace / converter dust, or RHF (Rotary Hearth Furnace) dust, and roasted ore for zinc concentrate can also be used as raw materials.

[0061] Specifically, first, in a dehalogenation cleaning step 101, electric furnace dust 1, which serves as a raw material and contains zinc compounds such as zinc oxide, iron compounds such as iron oxide, and zinc ferrite, a compound of iron and zinc, is cleaned with a cleaning liquid 2. Halogen components such as chlorine and fluorine adsorbed on the electric furnace dust 1 are dissolved and separated from the electric furnace dust 1, thereby obtaining cleaned electric furnace dust 3. The cleaned electric furnace dust 3 is then transferred to the subsequent high-temperature, high-alkali treatment step 102. As the cleaning liquid 2, an aqueous solution of a strong alkaline agent that is highly effective in dissolving halogen components from the electric furnace dust 1 can be suitably used. Specifically, an aqueous sodium hydroxide solution can be suitably used as the cleaning liquid 2.

[0062] Typically, electric furnace dust 1, previously crushed to a predetermined size or smaller, is immersed in a sodium hydroxide aqueous solution serving as the cleaning solution 2. The immersed electric furnace dust 1 is stirred in the sodium hydroxide aqueous solution for a predetermined time to form a slurry. Halogen components in close contact with the slurry are then eluted from the slurry. If the pH of the slurry is less than 8.5, a practical amount of halogen components cannot be achieved, and zinc and lead components may be unnecessarily eluted from the slurry. Therefore, the pH is preferably 8.5 or higher. Furthermore, if the pH of the slurry exceeds 10.5, zinc is extracted from the slurry, reducing the amount of zinc in the cleaned electric furnace dust 3 to be transported to the next step. Therefore, the pH is preferably 10.5 or lower. Correspondingly, the pH value of the aqueous sodium hydroxide solution serving as the cleaning liquid 2 is also preferably set within a range of 8.5 to 10.5. It should be noted that when the electric furnace dust 1 is cleaned with the cleaning liquid 2, the halogen components adsorbed on the electric furnace dust 1 are dissolved, and the used cleaning liquid 4 containing these halogen components can be simply discharged as waste liquid, or it can be reused as the cleaning liquid 2 for further cleaning of the electric furnace dust 1 within a range that allows for further dissolution of the chlorine component. Furthermore, the dehalogenation cleaning step 101 is placed before the high-temperature high-alkali treatment step 102 and the electrolytic tail liquid leaching step 103 to more appropriately decompose the zinc ferrite in the electric furnace dust 1 and extract the zinc component. It should be noted that when using electric furnace dust 1 in which the adhesion of halogen components such as chlorine and fluorine has been previously reduced, the dehalogenation cleaning step 101 can be omitted.

[0063] Next, the high-temperature and high-alkali treatment step 102 includes: a contact step 102a of contacting the cleaned electric furnace dust 3 with the electrolytic tail liquid 14 containing sodium hydroxide; a heating and temperature raising step 102b of heating the cleaned electric furnace dust 3 and the electrolytic tail liquid 14 that are in contact with each other in the contact step 102a to a temperature that reaches the boiling point of water with a rising boiling point; and a concentration maintaining step 102c of maintaining the concentration of the alkali agent contained in the electrolytic tail liquid 14 for a predetermined time after the temperatures of the cleaned electric furnace dust 3 and the electrolytic tail liquid 14 reach the boiling point and the evaporation of the water contained in the alkali metal hydroxide aqueous solution in the electrolytic tail liquid 14 stops. By contacting the cleaned electric furnace dust 3 with the alkali agent whose concentration is maintained in the concentration maintaining step 102c for the predetermined time, the decomposition reaction of zinc ferrite into zinc oxide components and iron oxide components is completed.

[0064] Specifically, in the contact process 102a, based on the premise that the electrolytic tail liquid 14 containing sodium hydroxide is obtained and can be used in the electrolysis process 105 that has been implemented, the electrolytic tail liquid 14, specifically the sodium hydroxide therein, is brought into contact with the cleaned electric furnace dust 3 in order to reuse the strong alkaline agent, i.e., sodium hydroxide, in the electrolytic tail liquid 14 without wasting it. Next, in the heating step 102b, the washed electric furnace dust 3 and the electrolytic tail liquid 14 containing sodium hydroxide in contact with each other are heated. In the presence of zinc ferrite, a poorly soluble substance in the washed electric furnace dust 3, the water contained in the sodium hydroxide aqueous solution in the electrolytic tail liquid 14 is evaporated as its boiling point (100°C) rises. When the temperature of the heated washed electric furnace dust 3 and the electrolytic tail liquid 14 is in the range of 150°C to 250°C, the concentration of sodium hydroxide in the electrolytic tail liquid 14 is adjusted to a concentration range of 70% by weight or more and less than 100% by weight, more preferably 80% by weight or more and less than 100% by weight, while maintaining the temperature of the washed electric furnace dust 3 and the electrolytic tail liquid 14. To adjust the concentration of sodium hydroxide in the electrolytic tail liquid 14 to this concentration range, typically, it is sufficient to wait until the water contained in the sodium hydroxide aqueous solution in the electrolytic tail liquid 14 has completely evaporated. Next, in the concentration maintenance step 102c, the lid of the container containing the cleaned electric furnace dust 3 and the electrolytic tail liquid 14 from which the water of the sodium hydroxide aqueous solution has completely evaporated is closed to make their storage space a sealed space, thereby switching their storage environment from an open system to a closed system. This closed system state, i.e., the temperature of the cleaned electric furnace dust 3 and the electrolytic tail liquid 14 is within a temperature range of 150°C to 250°C, and the concentration of sodium hydroxide in the electrolytic tail liquid 14 is within a concentration range of 70% by weight to less than 100% by weight, more preferably, within a concentration range of 80% by weight to less than 100% by weight, is maintained for a predetermined time of 15 minutes to 5 hours. Thus, after the predetermined time has elapsed and this temperature and concentration range have been maintained, the decomposition of the zinc ferrite in the cleaned electric furnace dust 3, which had begun to decompose due to continuous contact with the sodium hydroxide in the electrolytic tail liquid 14, is completed.That is, the conditions of this temperature range, concentration range, and maintaining them for a specified time are necessary for completing the decomposition of the zinc ferrite in the cleaned electric furnace dust 3. This is based on the following considerations: if the temperature of the cleaned electric furnace dust 3 and the electrolytic tail liquid 14 is less than 150°C, the zinc ferrite may not dissolve. If the temperature of the cleaned electric furnace dust 3 and the electrolytic tail liquid 14 exceeds 250°C, energy exceeding the energy required to dissolve the zinc ferrite may be unnecessarily consumed, resulting in increased energy consumption. If the concentration of sodium hydroxide in the electrolytic tail liquid 14 is less than 70% by weight, the problem of zinc ferrite not dissolving becomes significant. If the concentration of sodium hydroxide in the electrolytic tail liquid 14 is 80% by weight or more, this problem disappears. In order to contain zinc and other components other than sodium hydroxide, the concentration of sodium hydroxide in the electrolytic tail liquid 14 must be less than 100% by weight. If the specified time is less than 15 minutes, the reaction time for dissolving the zinc ferrite may be insufficient. If the specified time exceeds 5 hours, unnecessary energy may be consumed after the reaction for dissolving the zinc ferrite is completed, resulting in waste. Furthermore, in the concentration maintaining step 102c, an electrolytic tail liquid 14 containing zinc-containing solid matter 6 composed of zinc oxide components and iron oxide components after decomposition of the zinc ferrite is obtained. The electrolytic tail liquid 14 containing the zinc-containing solid matter 6 is cooled and then transported to the subsequent electrolytic tail liquid leaching step 103. It should be noted that, if it is not possible to prepare enough electrolytic tail liquid 14 for performing the electrolysis step 105 before performing the high-temperature high-alkali treatment step 102, sodium hydroxide 5 may also be used.

[0065] Here, in the high-temperature high-alkali treatment step 102, the electrolytic tail liquid 14 containing sodium hydroxide is brought into contact with the cleaned electric furnace dust 3, that is, the sodium hydroxide in the electrolytic tail liquid 14 is brought into contact with the zinc ferrite in the cleaned electric furnace dust 3, and the chemical formula when the zinc ferrite contained in the electric furnace dust 3 is decomposed into a zinc oxide component and an iron oxide component is shown below (Chemical 1).

[0066] [Chemistry 1]

[0067] ZnFe2O4+2NaOH→ZnO+2NaFeO2+H2O…(Chemical 1)

[0068] In addition to sodium hydroxide, potassium hydroxide can be used as an alkaline agent suitable for decomposing zinc ferrite in the high-temperature, high-alkali treatment step 102. Furthermore, to further promote the decomposition of zinc ferrite, the oxidizing agent added to the electrolytic tail liquid 14 containing sodium hydroxide can include at least one of sodium nitrate and hydrogen peroxide solution. Similarly, the reducing agent added to the electrolytic tail liquid 14 containing sodium hydroxide can include at least one of sodium sulfite, sodium thiosulfate, sodium dithionite, hydrazine, and zinc metal. These alkaline agents, and thus the oxidizing and reducing agents, are used separately depending on the impurity situation. Furthermore, the high-temperature, high-alkali treatment step 102 is performed under a high-temperature environment. Therefore, by introducing the electrolytic tail liquid 14 and the sodium hydroxide, which has been temporarily converted into an aqueous solution, into this step, the water contained therein evaporates and forms water vapor. Therefore, this water vapor can be passed through a heat exchanger to cool, liquefy, and return to water. Alternatively, the heat generated by the heat exchanger can be used for heating in the high-temperature, high-alkali treatment step 102 and the alkaline aqueous solution leaching step 106 described in the second embodiment.

[0069] Furthermore, in the high-temperature, high-alkali treatment step 102, it is preferred that an organic substance that reacts with chlorine to form a volatile compound is added to the electrolytic tail liquid 14 or the aqueous sodium hydroxide solution, and the cleaned electric furnace dust 3 is immersed therein. When the water in the electrolytic tail liquid 14 or the aqueous sodium hydroxide solution evaporates, the organic substance reacts with the chlorine in the cleaned electric furnace dust 3, resulting in the volatilization of a volatile organic chlorine compound. This reduces the concentration of chlorine in the cleaned electric furnace dust 3, yielding a zinc-containing solidified product 6 in which zinc ferrite is decomposed and the chlorine concentration is reduced. Ethanol is a practical and preferred example of this organic substance. In this case, the ethanol reacts with the chlorine in the cleaned electric furnace dust 3 to form chloroform, a volatile organic chlorine compound, which is then volatilized.

[0070] In the subsequent electrolytic tail liquid leaching step 103, a predetermined amount of water 7 is added to the electrolytic tail liquid 14 containing the zinc-containing solid matter 6, typically at a temperature below the boiling point of water (100°C). This produces or increases the amount of sodium hydroxide aqueous solution and the insoluble matter containing iron oxide components that is insoluble in the sodium hydroxide aqueous solution. At this point, the zinc oxide components obtained by decomposing zinc ferrite and the zinc oxide components originally contained in the electric furnace dust 1 are dissolved in the sodium hydroxide aqueous solution, resulting in a zinc-containing sodium hydroxide aqueous solution 8. The mixture of the zinc-containing sodium hydroxide aqueous solution 8 and the insoluble matter containing iron oxide components is then filtered out, and the zinc-containing sodium hydroxide aqueous solution 8 and the insoluble matter containing iron oxide components are separated by filtration (solid-liquid separation). The zinc concentration in the zinc-containing sodium hydroxide aqueous solution 8, the leachate from which the insoluble matter containing iron oxide components has been separated, is increased and is then transferred to the subsequent purification step 104. The insoluble matter containing iron oxide components is discharged as residue 9.

[0071] In the subsequent purification step 104, metallic zinc 10 is brought into contact with zinc-containing sodium hydroxide aqueous solution 8, reducing and precipitating metallic impurities in the zinc-containing sodium hydroxide aqueous solution 8 that are less reactive than zinc. This results in a zinc-containing sodium hydroxide aqueous solution 11, which is further purified from the zinc-containing sodium hydroxide aqueous solution 8, and the precipitated metallic impurities. Purification step 104 is a cementation process using metallic zinc 10. The purified zinc-containing sodium hydroxide aqueous solution 11 is then transferred to the subsequent electrolysis step 105, where the metallic impurities are discharged as residue 12. The metallic zinc 10 is typically introduced into the zinc-containing sodium hydroxide aqueous solution 8 in the form of metallic zinc powder. The zinc-containing sodium hydroxide aqueous solution 8, into which the metallic zinc powder has been introduced, is heated and stirred at high speed while maintained at a predetermined temperature. This promotes the cementation reaction, resulting in the rapid precipitation of metallic impurities in the zinc-containing sodium hydroxide aqueous solution 8 that are less reactive than zinc. Alternatively, the metallic zinc 10 can be used in the form of a metallic zinc plate rather than metallic zinc powder. In this case, the zinc-containing sodium hydroxide aqueous solution 8 flows toward the stationary metallic zinc plate, contacting the plate and similarly promoting the replacement reaction. When metallic zinc powder is used, the entire surface of the metallic zinc powder is covered with precipitated metallic impurities during the replacement reaction, and it is expected that the central portion of the metallic zinc powder will not participate in the replacement reaction. However, when a metallic zinc plate is used, the contact area with the zinc-containing sodium hydroxide aqueous solution 8 can be set with a high degree of freedom, thereby increasing the contact area, reliably promoting the replacement reaction, and rapidly replacing the metallic zinc plate after the metallic impurities have been precipitated. It should be noted that the metallic zinc plate can also rotate relative to the flow of the zinc-containing sodium hydroxide aqueous solution 8. Furthermore, if the zinc-containing sodium hydroxide aqueous solution 8 contains a low amount of metallic impurities that are less reactive than zinc, the purification step 104 can be omitted.

[0072] In addition to the replacement step, the purification step 104 may include a de-ironization / de-manganeseization step for de-ironization / de-manganeseization by air oxidation or addition of an oxidizing agent, a de-siliconization / de-fluorination step for de-siliconization / de-fluorination by addition of a reducing agent such as a calcium-based compound, and a de-chlorination step by addition of copper (I) oxide or silver nitrate. These steps may be appropriately combined as needed. However, considering that the halogen content is previously reduced in the dehalogenation cleaning step 101 and the chlorine content can be reduced in the high-temperature high-alkali treatment step 102, it is preferable to use at least one of the replacement step and the de-ironization / de-manganeseization step, or to further use the de-siliconization / de-fluorination step in an attempt to perform de-siliconization.

[0073] In the following electrolysis process 105, the purified zinc-containing sodium hydroxide aqueous solution 11 is electrolyzed as an electrolyte, and the electrolytically generated zinc 13 as an electrolytic product is precipitated on the cathode side, and its solid-liquid separation is recovered as a solid. In addition, the electrolytic tail liquid 14 as the electrolyte after the electrolytically generated zinc 13 is recovered can also be directly discharged as waste liquid, but because it contains sodium hydroxide, it is more reasonable and preferred to directly send the electrolytic tail liquid 14 back to the high-temperature high-alkali treatment process 102. Thus, typically, this electrolytic tail liquid 14 is contacted with the cleaned electric furnace dust 3 in the high-temperature high-alkali treatment process 102. In addition, there is a zinc component remaining in the electrolytic tail liquid 14, and this electrolytic tail liquid 14 containing zinc can be directly sent back to the high-temperature high-alkali treatment process 102. In this case, the electrolytic tail liquid 14 is subjected to at least a high-temperature high-alkali treatment step 102 and an electrolytic tail liquid leaching step 103 to increase the zinc concentration and is used as the electrolyte in the electrolysis step 105. Therefore, in order to reliably carry out the electrolysis, it is preferred to include sodium hydroxide with a concentration of 200 g / L or more and zinc with a concentration of 10 g / L or more.

[0074] Next, Experimental Example 1 in this embodiment will be described.

[0075] (Experimental Example 1)

[0076] In the high-temperature, high-alkali treatment step 102, the dehalogenated electric furnace dust 3 (weighing 150 g) from the dehalogenated cleaning step 101 and an electrolytic tail liquid 14 (volume 1 L) containing NaOH (concentration 400 g / L) and Zn (concentration 50 g / L) are placed in an iron crucible and heated. A thermocouple sensor is pre-installed in the electrolytic tail liquid 14 containing the electric furnace dust 3. If the electrolytic tail liquid 14 is heated until its temperature reaches 150°C, the water evaporates. Although the electrolytic tail liquid 14 initially boils due to the evaporation of water, the amount of water evaporated decreases as its boiling point rises. Evaporation of water ends after a certain period of time, when the temperature of the electrolytic tail liquid 14 reaches 160°C. In this state, the previously opened iron crucible is closed and sealed, and the temperature of the electrolytic tail liquid 14 is maintained at 160°C for one hour through constant temperature control. After one hour, heating was stopped, and the temperature of the electrolyte tail liquid 14 containing the solidified material 6 was cooled to below 100°C. Next, in the electrolyte tail liquid leaching step 103, water was added to the electrolyte tail liquid 14 containing the solidified material 6, and the volume was fixed with water 7 to dilute it to the original volume of 1L. The electrolyte tail liquid 14 was then heated and stirred until the temperature of the fixed volume reached 100°C, thereby dissolving the remaining solidified material 6 and forming a slurry. This slurry was filtered to separate into Fe residue 9 and Zn leachate 8 (Zn concentration 110 g / L). The Fe residue 9 was washed and dried. Meanwhile, in the purification step 104, the Zn leachate 8 was used as an oxidation purification solution, and an oxidant (KMnO4, H2O2) was added. After stirring for one hour, the precipitate was filtered out. Next, this leachate was used as a Ca purification solution, and CaO was added. After stirring for one hour, the precipitate was filtered out. The leachate was then placed in contact with zinc metal (powder or plate form) 10 at a liquid temperature of 60°C for 24 hours to remove impurities such as Cu, Pb, Cd, and Ni. The leachate 11, which had undergone a series of liquid purifications up to this leachate replacement, was used as an electrolyte for electrolytic extraction in an electrolysis step 105. The electrolytic extraction conditions were set at a current density of 1200A per square meter, an electrolyte concentration of 400g / L NaOH, a Zn concentration of 50g / L, and an electrolyte temperature of 40°C. Electrolysis was performed under these conditions, resulting in electrolytically produced zinc 13 with a purity of 99.995%. A feed tank was used to circulate and supply the electrolyte, maintaining a Zn concentration of 55g / L in the electrolysis feed solution and 50g / L in the electrolysis tail solution. A portion of the electrolytic tail liquid 14 is discharged and used as the alkaline aqueous solution before evaporation in the high-temperature high-alkali treatment step 102 to become the leachate 8 in the subsequent electrolytic tail liquid leaching step 103. The Zn concentration in the electrolytic tail liquid 14 is increased from 50 g / L to 110 g / L through the electrolytic tail liquid leaching.The analysis values of the leachate 11 (purified zinc-containing sodium hydroxide aqueous solution) after a series of liquid purifications up to replacement are shown below (Table 1). The concentrations of the analyzed components were all below the detection limit.

[0077] [Table 1]

[0078] Table 1

[0079] Element Fe Co Ni Cu Cd Pb g / L <0.0005 <0.0002 <0.0005 <0.0007 <0.0002 <0.008

[0080] According to the zinc recovery method of the first embodiment, the method comprises the following steps: a high-temperature high-alkali treatment step 102, which comprises: a contact step 102a, wherein the raw material 1 containing zinc components and zinc ferrite or the treated raw material 3 obtained by treating the raw material 1 is brought into contact with the alkali metal hydroxide aqueous solution 5, 14; a heating and temperature raising step 102b, wherein the raw material 1 or the treated raw material 3 and the alkali metal hydroxide aqueous solution 5, 14 brought into contact with each other in the contact step 102a are heated to a temperature reaching the boiling point of water whose boiling point is rising; and a concentration maintaining step 102c, wherein the concentration of the alkali agent contained in the alkali metal hydroxide aqueous solution 5, 14 is maintained at a concentration maintaining step 102c after the evaporation of water in the alkali metal hydroxide aqueous solution 5, 14 stops after the temperature reaches the boiling point. In step 102c, an alkali agent having a maintained concentration is brought into contact with the zinc ferrite in the raw material 1 or the treated raw material 3, thereby decomposing the zinc ferrite into a zinc oxide component and an iron oxide component. In the first leaching step 103, the alkali agent, the zinc oxide component, and the iron oxide component are brought into contact with water 7 at a temperature below the boiling point, so that the zinc oxide component is dissolved in the alkali metal hydroxide aqueous solution to obtain a first zinc-containing aqueous solution 8 containing a zinc component, and simultaneously obtains a poorly soluble matter 9 containing an iron oxide component that is insoluble in the alkali metal hydroxide aqueous solution, and separates the poorly soluble matter 9 from the first zinc-containing aqueous solution 8. In addition, a zinc recovery step is performed to recover the zinc component from the first zinc-containing aqueous solution 8. Therefore, the energy consumption for heating, the increase in cost, and the increase in environmental burden can be suppressed, and the zinc ferrite contained in the zinc-containing dust, etc. can be reliably decomposed and the zinc contained in the zinc-containing dust, etc. can be recovered. Furthermore, in the concentration maintaining step 102c, by maintaining the concentration of the alkaline agent contained in the alkali metal hydroxide aqueous solution 5, 14, 22 at the time when the evaporation of water in the alkali metal hydroxide aqueous solution 5, 14, 22 stops after the temperature reaches the boiling point, the pressure resistance of the reaction container such as the sealed container at this time can be reduced, thereby simplifying the structure of the reaction container and reducing costs.

[0081] Furthermore, the zinc ferrite decomposition method of this embodiment comprises: a contacting step 102a of bringing zinc ferrite-containing materials 1 and 3 containing zinc ferrite into contact with alkali metal hydroxide aqueous solutions 5 and 14; a heating and temperature raising step 102b of heating the zinc ferrite-containing materials 1 and 3 and the alkali metal hydroxide aqueous solutions 5 and 14 that are in contact with each other in the contacting step 102a to raise the temperature of the zinc ferrite-containing materials 1 and 3 and the alkali metal hydroxide aqueous solutions 5 and 14 to a temperature that reaches the boiling point of water that has a rising boiling point; and a concentration maintaining step. In the concentration maintaining step 102c, the concentration of the alkaline agent contained in the aqueous alkali metal hydroxide solutions 5 and 14 is maintained at the concentration at which the evaporation of water in the aqueous alkali metal hydroxide solutions 5 and 14 stops after the temperature reaches the boiling point. In the concentration maintaining step 102c, the alkaline agent having maintained its concentration contacts the zinc ferrite in the zinc ferrite-containing materials 1 and 3, thereby decomposing the zinc ferrite into zinc oxide components and iron oxide components. This reduces heating energy consumption, increases in costs, and increases in environmental burdens, while reliably decomposing the zinc ferrite contained in zinc-containing dust, etc. Furthermore, in the concentration maintaining step 102c, by maintaining the concentration of the alkaline agent contained in the aqueous alkali metal hydroxide solutions 5 and 14 at the concentration at which the evaporation of water in the aqueous alkali metal hydroxide solutions 5 and 14 stops after the temperature reaches the boiling point, the pressure resistance of the reaction vessel, such as a sealed container, can be reduced at this time, thereby simplifying the structure of the reaction vessel and reducing costs.

[0082] (Second embodiment)

[0083] Next, refer to Figure 2 The zinc recovery method and the zinc ferrite decomposition method in the second embodiment of the present invention will be described in detail.

[0084] Figure 2 It is a diagram showing the steps of the zinc recovery method including the zinc ferrite decomposition method in this embodiment.

[0085] like Figure 2 As shown, the zinc recovery method of this embodiment differs from the zinc recovery method of the first embodiment mainly in that it includes an alkaline aqueous solution leaching step 106 following the dehalogenation cleaning step 101. In this embodiment, the description will focus on this difference, and the same components are assigned the same reference numerals, and their descriptions will be omitted or simplified.

[0086] Specifically, an alkaline aqueous solution leaching step 106 is provided immediately following the dehalogenation cleaning step 101. The reason for placing the dehalogenation cleaning step 101 before the alkaline aqueous solution leaching step 106 is that the zinc content in the electric furnace dust 1 can be more effectively extracted. In the alkaline aqueous solution leaching step 106, prior to the high-temperature, high-alkali treatment step 102, the cleaned electric furnace dust 3 is brought into contact with an aqueous sodium hydroxide solution, which is an aqueous solution of sodium hydroxide 5. The zinc content contained in the cleaned electric furnace dust 3 is dissolved in the aqueous sodium hydroxide solution and selectively extracted, thereby producing a zinc-containing sodium hydroxide aqueous solution 15 containing the zinc content and, simultaneously, a poorly soluble substance 16 containing zinc ferrite that is insoluble in the aqueous sodium hydroxide solution. The mixture of the zinc-containing sodium hydroxide aqueous solution 15 and the poorly soluble substance 16 containing iron oxide components is then filtered out, and the zinc-containing sodium hydroxide aqueous solution 15 and the poorly soluble substance 16 containing iron oxide components are separated by filtration (solid-liquid separation). Sodium hydroxide is used as a strong alkaline agent because it is not only effective in extracting zinc components, but also can be used together with the components used in the high-temperature high-alkali treatment step 102. Electric furnace dust 3 is brought into contact with an aqueous sodium hydroxide solution, and the zinc components contained in the cleaned electric furnace dust 3 are dissolved in the aqueous sodium hydroxide solution and selectively extracted, thereby obtaining a zinc-containing sodium hydroxide aqueous solution 15 containing zinc components. The chemical formula in this case is shown below (Chemical 2).

[0087] [Chemistry 2]

[0088] ZnO+2NaOH+H2O→2Na + +[Zn(OH)4] 2- …(Chemistry 2)

[0089] The zinc-containing sodium hydroxide aqueous solution 15 thus obtained is fed to the subsequent purification step 104. Meanwhile, the obtained insoluble matter 16 containing zinc ferrite is fed to the high-temperature, high-alkali treatment step 102, where the zinc ferrite is decomposed into zinc oxide and iron oxide. The zinc-containing solidified material 6 formed by the decomposition of the zinc ferrite is fed to the subsequent electrolytic tail liquid leaching step 103, where it becomes zinc-containing sodium hydroxide aqueous solution 8. This solution is then fed to the alkaline aqueous solution leaching step 106, where the zinc component contained in the zinc-containing sodium hydroxide aqueous solution 8 is selectively extracted and becomes part of the zinc-containing sodium hydroxide aqueous solution 15.

[0090] In the alkaline aqueous solution leaching process 106, when the treatment of the high-temperature high-alkali treatment process 102 is carried out and the zinc-containing sodium hydroxide aqueous solution 8 is generated through the electrolytic tail liquid leaching process 103 and transported to the alkaline aqueous solution leaching process 106, the zinc-containing sodium hydroxide aqueous solution 8 can be used in combination with or without using sodium hydroxide 5 to contact the cleaned electric furnace dust 3.

[0091] Here, in addition to the high-temperature, high-alkali treatment step 102, an alkaline aqueous solution leaching step 106 is provided. Insoluble matter 16 containing zinc ferrite is transported from the alkaline aqueous solution leaching step 106 to the high-temperature, high-alkali treatment step 102. The zinc-containing solidified material 6 formed by the decomposition of the zinc ferrite is then transported to the alkaline aqueous solution leaching step 106 in the form of a zinc-containing sodium hydroxide aqueous solution 8 via the subsequent electrolytic tail liquid leaching step 103. This so-called two-stage convection treatment process is employed for the following reason: The high-temperature, high-alkali treatment step 102 requires a higher temperature environment than the alkaline aqueous solution leaching step 106, and therefore consumes more energy. Therefore, by treating the electric furnace dust 1, which is the zinc-containing raw material containing zinc ferrite, not only in the high-temperature, high-alkali treatment step 102 but also in the alkaline aqueous solution leaching step 106, the treatment time in the high-temperature, high-alkali treatment step 102 can be shortened, thereby reducing energy consumption. For example, if 88% of the zinc content in a certain electric furnace dust 1 is contained in zinc oxide and the remaining 12% is contained in zinc ferrite, then treating the zinc oxide, which can be dissolved in the alkaline aqueous solution leaching step 106 (which can be performed at a temperature of 100°C or less), in the high-temperature high-alkali treatment step 102 would be inefficient in terms of energy consumption. Therefore, if 88% of the zinc content is extracted in the alkaline aqueous solution leaching step 106 before the high-temperature high-alkali treatment step 102 (the total weight of the electric furnace dust 3 to be treated is also reduced to approximately 40%), and the zinc ferrite containing the remaining 12% of the zinc content (8% of the weight of the electric furnace dust 3 to be treated) is decomposed in the high-temperature high-alkali treatment step 102, then energy consumption can be rationalized and improved. It should be noted that, similarly to the case of the high-temperature high-alkali treatment step 102, the electrolytic tail liquid 14 is also sent back to the alkaline aqueous solution leaching step 106, and the electrolytic tail liquid 14 can be used alone or together with the sodium hydroxide aqueous solution as an alkaline aqueous solution for contacting the cleaned electric furnace dust 3.

[0092] Next, Experimental Example 2 in this embodiment will be described.

[0093] (Experimental Example 2)

[0094] In the high-temperature, high-alkali treatment step 102, alkaline aqueous solution leached dust 16 (containing zinc components, zinc oxide dissolved by leaching in the alkaline aqueous solution, and zinc components from zinc ferrite remaining; weight 70 g) and electrolytic tail liquid 14 (NaOH concentration of 450 g / L, Zn concentration of 50 g / L, volume 1 L) that had undergone the alkaline aqueous solution leaching step 106 were placed in a 500 mL airtight iron container and heated and stirred. As a result, the electrolytic tail liquid 14 in contact with the alkaline aqueous solution leached dust 16 in the opened iron container boiled. When the temperature of the electrolytic tail liquid 14 reached 200°C, the iron container was closed and sealed, and the temperature of the electrolytic tail liquid 14 was maintained within a range of 180°C to 200°C for one hour. After one hour, heating was stopped, and the temperature of the electrolytic tail liquid 14 containing the solidified material 6 was cooled to less than 110°C. Next, in the electrolytic tail liquid leaching process 103, water is added to the electrolytic tail liquid 14 containing the solidified material 6, and the volume is constant and diluted to the original volume of 100 mL. A further 100 mL of electrolytic tail liquid 14 is added to make the total volume 300 mL. The solution is heated to a liquid temperature of 100° C. while stirring. The solution is kept in this state for 1 hour. After confirming that the zinc component has dissolved, the slurry is filtered. After filtration, the filter cake of the solid (iron leaching residue 9) is washed and analyzed. The results confirm that more than 98% of the Zn in the electric furnace dust 1 is dissolved in the Zn leachate 8. In addition, the volume of the Zn leachate 8 obtained by filtering out the solid (iron residue 9) is 200 mL.

[0095] In addition, in the alkaline aqueous solution leaching step 106, the electric furnace dust 3 (weighing 175g) after the dehalogenation cleaning in the dehalogenation cleaning step 101 and the Zn leachate 8 (volume 200mL) after the high-temperature high-alkali treatment step 102 and the electrolytic tail liquid leaching step 103 are added to the electrolytic tail liquid 14 (volume 800ml). The resulting solution is placed in an iron sealed reaction vessel and heated while stirring until the liquid temperature reaches 120°C, which is maintained at this temperature for 1 hour. At this point, the reaction vessel is closed and sealed to avoid the influence of the latent heat of evaporation, while the liquid temperature reaches 120°C. The dissolved solution is then filtered to separate the solid and liquid. At this time, a solid (iron residue) 16 weighing approximately 70g by dry weight is extracted. This is used as dust that has completed the first leaching and is used as the raw material for the next step, the high-temperature high-alkali treatment step 102. Meanwhile, the Zn concentration in the liquid subjected to solid-liquid separation is raised to levels of NaOH (450 g / L) and Zn (120 g / L), resulting in a leachate 15. Next, in the purification step 104, this leachate 15 is used as an oxidation purification liquid, with oxidants (KMnO4, H2O2) added, stirred for 1 hour, and the precipitate is filtered out. Next, this leachate is used as a Ca purification liquid, with CaO added, stirred for 1 hour, and the precipitate is filtered out. Furthermore, this leachate is brought into contact with zinc metal (powder or plate-like) 10 at a liquid temperature of 60°C for 24 hours to perform a substitution, removing impurities such as Cu, Pb, Cd, and Ni. The leachate 11, resulting from the complete series of liquid purifications up to this substitution, is used as an electrolyte for electrolytic extraction in the electrolysis step 105. Electrolysis was performed under the following conditions: a current density of 12,000 A per square meter, an electrolyte concentration of 450 g / L NaOH and 55 g / L Zn, and an electrolyte temperature of 60°C. Electrolysis yielded 99.995% pure electrolytically produced zinc 13. A feed tank was used to circulate and supply the electrolyte, maintaining a Zn concentration of 55 g / L in the electrolysis feed solution and 50 g / L in the electrolysis tail solution. A portion of the electrolysis tail solution 14 was discharged and used as leachates 8 and 15 in the subsequent electrolysis tail solution leaching step 103 and alkaline aqueous solution leaching step 106, respectively, through water dissolution and alkaline aqueous solution dissolution, raising the Zn concentration from 50 g / L to 120 g / L. The analysis values of the leachate 11 (the purified zinc-containing sodium hydroxide aqueous solution) after liquid purification by substitution were similar to those shown in (Table 1) of Experimental Example 1, and the concentrations of the analyzed components were all below the detection limit.

[0096] According to the zinc recovery method of the second embodiment, the second leaching step 106 is further included before the high-temperature high-alkali treatment step 102: the raw material 1 or the treated raw material 3 is contacted with an aqueous sodium hydroxide solution, and the zinc component contained in the raw material 1 or the treated raw material 3 is dissolved in the aqueous sodium hydroxide solutions 5 and 14 and selectively extracted to obtain a second zinc-containing aqueous solution 15 containing the zinc component. At the same time, a poorly soluble matter 16 containing zinc ferrite that is insoluble in the aqueous sodium hydroxide solutions 5 and 14 is obtained. The poorly soluble matter 16 is separated from the second zinc-containing aqueous solution 15, and the poorly soluble matter containing zinc ferrite 16 is conveyed to the high-temperature high-alkali treatment step 102 as the treated raw material, where it is decomposed into a zinc oxide component and an iron oxide component. In the first leaching step 103, the zinc oxide component is dissolved in the aqueous sodium hydroxide solution to obtain a fourth zinc-containing aqueous solution 8 containing the zinc component. Therefore, the zinc ferrite contained in the zinc-containing dust, etc. can be more reliably decomposed with reduced energy consumption, and the zinc contained in the zinc-containing dust, etc. can be efficiently recovered.

[0097] (Third embodiment)

[0098] Next, refer to Figure 3 , the zinc recovery method and the zinc ferrite decomposition method in the third embodiment of the present invention are described in detail.

[0099] Figure 3 It is a diagram showing the steps of the zinc recovery method including the zinc ferrite decomposition method in this embodiment.

[0100] like Figure 3 As shown, the zinc recovery method of this embodiment differs from the zinc recovery method of the second embodiment primarily in that a magnetic separation step 107 is included between the dehalogenation cleaning step 101 and the alkaline aqueous solution leaching step 106. This embodiment will be described with a focus on this difference, with identical components designated by identical reference numerals and their descriptions omitted or simplified. It should be noted that, if magnetic separation can be performed on the pre-cleaned electric furnace dust 3, the magnetic separation step 107 may also be performed before the dehalogenation cleaning step 101. Furthermore, this magnetic separation step 107 may also be applied to the zinc recovery method of the first embodiment.

[0101] Specifically, a magnetic separation step 107 is provided immediately following the dehalogenation cleaning step 101. Prior to the alkaline aqueous solution leaching step 106, the magnetic separation step 107 typically applies magnetic force to the cleaned electric furnace dust 3 using a magnet serving as an electromagnet. Based on the magnetic strength of the components in the cleaned electric furnace dust 3, an attached beneficiated ore 18 consisting of components adhering to the magnet (primarily zinc ferrite and iron components) is separated from residual beneficiated ore 19 in the cleaned electric furnace dust 3 that is not attached to the magnet, other than the attached beneficiated ore 18. It should be noted that a commercially available wet high-magnetic-force magnetic separator can be used in the magnetic separation step 107.

[0102] The attached mineral concentrate 18 is transported to a high-temperature, high-alkali treatment step 102 and brought into contact with molten sodium hydroxide. The zinc ferrite in the attached mineral concentrate 18 is decomposed into zinc oxide and iron oxide. The zinc-containing solidified product 6 formed by the decomposition of the zinc ferrite is then transported to the subsequent electrolytic tail liquid leaching step 103. In the electrolytic tail liquid leaching step 103, water 7 is brought into contact with the zinc-containing solidified product 6 formed by the decomposition of the zinc ferrite, thereby obtaining a zinc-containing sodium hydroxide aqueous solution 8 and a residue 9 composed of insoluble substances including iron oxide. However, if the mineral separation accuracy in the magnetic mineral separation step 107 is poor and a large amount of zinc is contained in the residue 9, a portion or all of the residue 9' may be transported to an alkaline aqueous solution leaching step 106 to selectively extract the zinc.

[0103] The residual ore 19 is transported to the alkaline aqueous solution leaching step 106, where the zinc component contained in the residual ore 19 is dissolved in the sodium hydroxide aqueous solution and selectively extracted, thereby obtaining a zinc-containing sodium hydroxide aqueous solution 15 containing the zinc component and simultaneously obtaining a poorly soluble matter 16 that is insoluble in the sodium hydroxide aqueous solution. The thus obtained zinc-containing sodium hydroxide aqueous solution 15 is transported to the subsequent purification step 104, but the poorly soluble matter 16 obtained is discharged as a residue. However, if the ore separation accuracy in the magnetic ore separation step 107 is poor and the poorly soluble matter 16 contains a large amount of zinc ferrite, some or all of the poorly soluble matter 16 can be transported to the high-temperature high-alkali treatment step 102 to decompose the zinc ferrite into zinc oxide and iron oxide.

[0104] Next, Experimental Example 3 in this embodiment will be described.

[0105] (Experimental Example 3)

[0106] In the high-temperature, high-alkali treatment step 102, magnetically adsorbed dust 18 (67 g of the 175 g of electric furnace dust adhering to the magnet) and alkaline electrolytic tail liquid 14 (100 mL volume, containing 450 g / L NaOH and 50 g / L Zn) that had undergone dehalogenation cleaning in the dehalogenation cleaning step 101 and magnetic separation step 107 were placed in a 500 mL airtight iron container and heated and stirred. The electrolytic tail liquid 14, which had come into contact with the alkaline aqueous solution-leached dust 16 in the opened iron container, boiled. When the temperature of the electrolytic tail liquid 14 reached 180°C, the iron container was closed and sealed, and the temperature of the electrolytic tail liquid 14 was maintained within a range of 180°C to 200°C for one hour. After one hour, heating was stopped, and the electrolytic tail liquid 14 containing the solidified material 6 was cooled to a temperature below 120°C. Next, in the electrolytic tail liquid leaching process 103, water is added to the electrolytic tail liquid 14 containing the solidified material 6, and the volume is constant and diluted to the original volume of 100 mL. Further, 200 mL of the electrolytic tail liquid 14 is added to make the overall volume 300 mL. The solution is heated to a liquid temperature of 100° C. while stirring. In this state, the solution is kept for 1 hour. After confirming that the zinc component has dissolved, the slurry is filtered. After filtering, the filter cake of the solid (iron leaching residue 9) is washed and analyzed. As a result, it is confirmed that more than 98% of the Zn in the electric furnace dust 1 is dissolved in the Zn leachate 8. In the case where the zinc dissolution is insufficient, the iron leaching residue 9 can also be put into the alkaline aqueous solution leaching process 106.

[0107] In the alkaline aqueous solution leaching step 106, after the dehalogenation cleaning in the dehalogenation cleaning step 101 is completed, the non-magnetically adsorbed dust 19 (the portion of the total EAF dust weight of 175g that does not adhere to the magnet, weighing 108g) and the filtrate 8 (volume 300mL) from the high-temperature high-alkali treatment step 102 and the electrolytic tail liquid leaching step 103 are placed in an iron reaction vessel through a magnetic separation step 107. The filtrate 8 is heated while stirring to a temperature of 120°C, which is maintained at this temperature for one hour. After one hour, the dissolved solution is filtered for solid-liquid separation, yielding a solid 16 (iron residue). This solid 16 is mixed with the iron residue from the high-temperature high-alkali treatment step 102 and analyzed, confirming that at least 98% of the Zn in the EAF dust has dissolved. The Zn concentration in the liquid after solid-liquid separation is raised to 120g / L, creating leachate 15. Next, in the purification step 104, the leachate 15 was used as an oxidation purification liquid, an oxidizing agent (KMnO4, H2O2) was added, and after stirring for 1 hour, the precipitate was filtered out. Next, the leachate was used as a Ca purification liquid, CaO was added, and after stirring for 1 hour, the precipitate was filtered out. Furthermore, the leachate was brought into contact with zinc metal (powder or plate-like) 10 at a liquid temperature of 60°C for 24 hours to perform a substitution, removing impurities such as Cu, Pb, Cd, and Ni. The leachate 11, which had undergone the series of liquid purifications up to this substitution, was used as the electrolyte for electrowinning in the electrolysis step 105. The electrowinning conditions were a current density of 1200 A per square meter, an electrolyte concentration of 450 g / L NaOH and 55 g / L Zn, and an electrolyte temperature of 60°C. Electrolysis was performed under these conditions, resulting in electrolytically produced zinc 13 with a purity of 99.995%. As for the electrolyte concentration, a feed tank was used that circulated and supplied the electrolyte so that the Zn concentration of the electrolytic feed solution was 55 g / L and the Zn concentration of the electrolytic tail liquid was 50 g / L. A portion of the electrolytic tail liquid 14 was discharged and, after evaporation in the high-temperature and high-alkali treatment step 102, the alkaline aqueous solution was used as leachates 8 and 15 in the subsequent electrolytic tail liquid leaching step 103 and the alkaline aqueous solution leaching step 106. The Zn concentration was increased from 50 g / L to 120 g / L through water dissolution and alkaline aqueous solution dissolution. Regarding the analytical values of the leachate 11 (the purified zinc-containing sodium hydroxide aqueous solution) after liquid purification by substitution, the concentrations of the analyzed components were all below the detection limit, similar to the values shown in (Table 1) of Experimental Example 1.

[0108] According to the zinc recovery method of the third embodiment, the method further comprises: a magnetic separation step 107, which applies magnetic force to the raw material 1 or the treated raw material 3 by means of a magnet before the high-temperature high-alkali treatment step 102, and separates the first selected ore 18 composed of components adhering to the magnet from the second selected ore 19 not adhering to the magnet according to the magnetic strength of the components in the raw material 1 or the treated raw material 3; and a third leaching step 106, which conveys the second selected ore 19 and dissolves the zinc component contained in the second selected ore 19 in the sodium hydroxide aqueous solution 5, 14 to selectively The zinc ferrite in the first selected ore 18 is decomposed into zinc oxide and iron oxide, thereby more reliably decomposing the zinc ferrite contained in the zinc-containing dust and the like in a manner that consumes less energy, and efficiently recovering the zinc contained in the zinc-containing dust and the like.

[0109] (Fourth embodiment)

[0110] Next, refer to Figure 4 , the zinc recovery method and the zinc ferrite decomposition method in the fourth embodiment of the present invention are described in detail.

[0111] Figure 4 It is a diagram showing the steps of the zinc recovery method including the zinc ferrite decomposition method in this embodiment.

[0112] like Figure 4 As shown, the zinc recovery method of this embodiment differs primarily from the zinc recovery method of the third embodiment in that it includes a zinc carbonate separation step 108 in place of the electrolysis step 105, which serves as the zinc recovery step. This embodiment will be described with a focus on this difference, with identical components designated by identical reference numerals and their descriptions omitted or simplified. It should be noted that the zinc carbonate separation step 108 can also be used in place of the electrolysis step 105 of the zinc recovery methods of the first and second embodiments.

[0113] Specifically, in the zinc carbonate separation step 108 , carbon dioxide 20 is brought into contact with the zinc-containing sodium hydroxide aqueous solution 11 that has passed through the purification step 104 , and the zinc component in the zinc-containing sodium hydroxide aqueous solution 11 is separated as zinc carbonate 21 .

[0114] Typically, as shown in the following chemical formula (Chemical 3), if carbon dioxide 20 is blown into the zinc component in the zinc-containing sodium hydroxide aqueous solution 11 to precipitate zinc carbonate, and the precipitated zinc carbonate is filtered, solid zinc carbonate 21 can be obtained. Zinc carbonate 21 can also be made into a product if it is dried after washing with water. In addition, since the residual liquid 22 of the zinc carbonate separation step 108 contains sodium hydroxide, it is sent back to the high-temperature high-alkali treatment step 102. It should be noted that if the solid zinc carbonate 21 is roasted, zinc oxide can also be obtained.

[0115] [Chemistry 3]

[0116] Na2[Zn(OH)4]+CO2→ZnCO3+2NaOH+H2O…(Chemical 3)

[0117] Next, Experimental Example 4 in this embodiment will be described.

[0118] (Experimental Example 4)

[0119] As in Experimental Example 3, the Zn concentration was raised from 50 g / L to 120 g / L by dissolution with an alkaline aqueous solution, while proceeding to purification step 104. Carbon dioxide 20 was blown into the leachate 11 after liquid purification to precipitate zinc carbonate 21, which was then filtered and recovered. Furthermore, the analytical values of the leachate 11 (purified zinc-containing sodium hydroxide aqueous solution) after liquid purification by substitution were similar to those shown in (Table 1) of Experimental Example 1, with the concentrations of the analyzed components all below the lower limit of detection.

[0120] According to the zinc recovery method of the fourth embodiment, the zinc recovery step includes a zinc carbonate separation step in which the zinc component in the zinc-containing aqueous solution 8, 15 or the aqueous solution 11 obtained by purifying the zinc-containing aqueous solution 8, 15 is separated as zinc carbonate 21, and a residual liquid 22 from which the zinc carbonate 21 is separated is obtained. The residual liquid 22, while still containing an alkali metal hydroxide aqueous solution and zinc components, is conveyed to the high-temperature high-alkali treatment step 102. The alkali metal hydroxide aqueous solution in the residual liquid 22 contacts the raw material 1 or the treated raw materials 3, 16, 18. Therefore, zinc carbonate with reduced impurity content can be recovered stably with a good yield.

[0121] It should be noted that the shape, configuration, number, etc. of the constituent elements of the present invention are not limited to the above-mentioned embodiments, and can of course be appropriately changed without departing from the scope of the invention, and the constituent elements can be appropriately replaced with elements that have the same effect.

[0122] Industrial Applicability

[0123] As described above, the present invention can provide a zinc recovery method and a zinc ferrite decomposition method for decomposing zinc ferrite. The above-mentioned zinc recovery method can suppress the energy consumption of heating, suppress the increase in cost and the increase in environmental burden, and can reliably decompose the zinc ferrite contained in zinc-containing dust, etc., and can recover the zinc contained in zinc-containing dust, etc. Therefore, due to its universal properties, it is expected to be widely applicable as raw materials to electric furnace dust generated when melting and smelting scrap in the electric furnace method, which is one of the ironmaking processes, as well as primary dust or secondary dust such as blast furnace dust, blast furnace / converter dust or RHF (Rotary Hearth Furnace) dust, and zinc-containing dust such as roasted ore for zinc concentrate.

[0124] Explanation of symbols

[0125] 1… Electric furnace dust

[0126] 2…Cleaning fluid

[0127] 3…treated electric furnace dust

[0128] 4…Cleaning fluid used

[0129] 5…Sodium hydroxide

[0130] 6…Zinc-containing cured product

[0131] 7…Water

[0132] 8…Sodium hydroxide aqueous solution containing zinc

[0133] 9…residue

[0134] 10…Zinc metal

[0135] 11…Sodium hydroxide aqueous solution containing zinc

[0136] 12…residue

[0137] 13…Electrolysis to produce zinc

[0138] 14…Electrolysis tail liquid

[0139] 15…Sodium hydroxide aqueous solution containing zinc

[0140] 16…Insoluble substances

[0141] 18…Attached mineral processing

[0142] 19…Residual mineral processing

[0143] 21…Zinc carbonate

[0144] 22…Residual liquid

[0145] 101…Halogen cleaning process

[0146] 101…Dehalogenation cleaning process

[0147] 102…High temperature and high alkali treatment process

[0148] 103…Electrolysis tail liquid leaching process

[0149] 104…Purification process

[0150] 105…Zinc recovery process

[0151] 105…Electrolysis process

[0152] 106…Alkaline aqueous solution leaching process

[0153] 107…Magnetic separation process

[0154] 108…Zinc carbonate separation process

Claims

1. A zinc recovery method comprising: A high-temperature, high-alkali treatment step comprising: a contacting step of contacting a raw material containing a zinc component and zinc ferrite, or a treated raw material obtained by treating the raw material, with an alkali metal hydroxide aqueous solution; a heating step of heating the raw material or the treated raw material and the alkali metal hydroxide aqueous solution brought into contact with each other in the contacting step, raising the temperature of the raw material or the treated raw material and the alkali metal hydroxide aqueous solution to a temperature reaching the boiling point of water whose boiling point is rising; and a concentration maintaining step of maintaining the concentration of the alkali agent contained in the alkali metal hydroxide aqueous solution at a point where evaporation of water in the alkali metal hydroxide aqueous solution stops after the temperature reaches the boiling point, wherein the alkali agent maintained at the concentration in the concentration maintaining step contacts the zinc ferrite in the raw material or the treated raw material, thereby decomposing the zinc ferrite into a zinc oxide component and an iron oxide component. a first leaching step of contacting the alkaline agent, the zinc oxide component, and the iron oxide component with water at a temperature lower than the boiling point, dissolving the zinc oxide component in an alkali metal hydroxide aqueous solution to obtain a first zinc-containing aqueous solution containing the zinc component, and simultaneously obtaining a poorly soluble substance containing the iron oxide component that is insoluble in the alkali metal hydroxide aqueous solution, and separating the poorly soluble substance from the first zinc-containing aqueous solution; and The zinc recovery step recovers the zinc component from the first zinc-containing aqueous solution.

2. The zinc recovery method according to claim 1, wherein The alkaline agent is sodium hydroxide or potassium hydroxide, In the high-temperature high-alkali treatment step, at least one of hydrogen peroxide and sodium nitrate as an oxidizing agent, or at least one of sodium sulfite, sodium thiosulfate, sodium dithionite, hydrazine, and zinc metal as a reducing agent is added to the alkali metal hydroxide aqueous solution.

3. The zinc recovery method according to claim 1 or 2, wherein: The alkaline agent is sodium hydroxide, Prior to the high-temperature high-alkali treatment step, a halogen cleaning step is further provided: the raw material is cleaned with a sodium hydroxide aqueous solution having a pH value within a range of 8.5 to 10.5 to clean the halogen components contained in the raw material.

4. The zinc recovery method according to claim 1 or 2, further comprising a purification step of bringing metallic zinc into contact with the first zinc-containing aqueous solution to reduce and precipitate metallic impurity components inactive compared to zinc in the first zinc-containing aqueous solution, thereby purifying the first zinc-containing aqueous solution.

5. The zinc recovery method according to claim 4, wherein The zinc recovery process includes an electrolysis process: electrolysis is performed using the first zinc-containing aqueous solution or an aqueous solution obtained by purifying the first zinc-containing aqueous solution as an electrolyte to obtain electrolytically generated zinc and an electrolytic tail liquid. The electrolytic tail liquid is transported to the high-temperature high-alkali treatment process in a state where an alkali metal hydroxide aqueous solution and zinc components remain. The alkali metal hydroxide aqueous solution in the electrolytic tail liquid contacts the raw material or the treated raw material.

6. The zinc recovery method according to claim 4, wherein The zinc recovery step includes a zinc carbonate separation step: the zinc component in the first zinc-containing aqueous solution or the aqueous solution obtained by purifying the first zinc-containing aqueous solution is separated in the form of zinc carbonate, and a residual liquid from which the zinc carbonate is separated is obtained. The residual liquid, while still containing an alkali metal hydroxide aqueous solution and the zinc component, is transported to the high-temperature high-alkali treatment step, and the alkali metal hydroxide aqueous solution in the residual liquid contacts the raw material or the treated raw material.

7. The zinc recovery method according to claim 1 or 2, wherein: Prior to the high-temperature high-alkali treatment step, a second leaching step is further provided: the raw material or the treated raw material is contacted with a sodium hydroxide aqueous solution, the zinc component contained in the raw material or the treated raw material is dissolved in the sodium hydroxide aqueous solution and selectively extracted to obtain a second zinc-containing aqueous solution containing the zinc component, and simultaneously obtains a poorly soluble substance containing zinc ferrite that is insoluble in the sodium hydroxide aqueous solution, and the poorly soluble substance is separated from the second zinc-containing aqueous solution. The insoluble material including the zinc ferrite is transported to the high-temperature high-alkali treatment step as the treated raw material, and is decomposed into a zinc oxide component and an iron oxide component. In the first leaching step, the zinc oxide component is dissolved in the sodium hydroxide aqueous solution to obtain a fourth zinc-containing aqueous solution including a zinc component.

8. The zinc recovery method according to claim 7, wherein: The fourth zinc-containing aqueous solution is transported to the second leaching step, and the zinc component contained in the fourth zinc-containing aqueous solution is selectively extracted to become a part of the second zinc-containing aqueous solution.

9. The zinc recovery method according to claim 7, wherein: The alkaline agent is sodium hydroxide, Before the second leaching step, a halogen cleaning step is further provided: the raw material is cleaned with a sodium hydroxide aqueous solution having a pH value within a range of 8.5 to 10.5 to clean the halogen components contained in the raw material to obtain a treated raw material.

10. The zinc recovery method according to claim 7, further comprising a purification step of bringing metallic zinc into contact with the second zinc-containing aqueous solution to reduce and precipitate metallic impurity components inactive compared to zinc in the second zinc-containing aqueous solution, thereby purifying the second zinc-containing aqueous solution.

11. The zinc recovery method according to claim 10, wherein: The zinc recovery process includes an electrolysis process: electrolysis is performed using the second zinc-containing aqueous solution or an aqueous solution obtained by purifying the second zinc-containing aqueous solution as an electrolyte to obtain electrolytically generated zinc and an electrolytic tail liquid. The electrolytic tail liquid is transported to the high-temperature high-alkali treatment process in a state where an alkali metal hydroxide aqueous solution and zinc components remain. The alkali metal hydroxide aqueous solution in the electrolytic tail liquid contacts the raw material or the treated raw material.

12. The zinc recovery method according to claim 10, wherein: The zinc recovery step includes a zinc carbonate separation step: the zinc component in the second zinc-containing aqueous solution or the aqueous solution obtained by purifying the second zinc-containing aqueous solution is separated in the form of zinc carbonate, and a residual liquid from which the zinc carbonate is separated is obtained. The residual liquid, while still containing an alkali metal hydroxide aqueous solution and the zinc component, is transported to the high-temperature high-alkali treatment step, and the alkali metal hydroxide aqueous solution in the residual liquid contacts the raw material or the treated raw material.

13. The zinc recovery method according to claim 1 or 2, wherein: Also features: a magnetic separation step, prior to the high-temperature and high-alkali treatment step, applying a magnetic force to the raw material or the treated raw material by means of a magnet, and separating a first selected ore composed of components adhering to the magnet from a second selected ore not adhering to the magnet based on the magnetic strength of the components in the raw material or the treated raw material; and The third leaching step comprises conveying the second selected ore and dissolving the zinc component contained in the second selected ore in a sodium hydroxide aqueous solution to selectively extract the zinc component, thereby obtaining a third zinc-containing aqueous solution containing the zinc component and simultaneously obtaining a poorly soluble substance that is insoluble in the alkali metal hydroxide aqueous solution, and separating the poorly soluble substance from the third zinc-containing aqueous solution. The first selected ore is transported to the high-temperature high-alkali treatment step as the treated raw material, and the zinc ferrite in the first selected ore is decomposed into the zinc oxide component and the iron oxide component.

14. The zinc recovery method according to claim 13, wherein: The alkaline agent is sodium hydroxide, and before the third leaching step, a halogen cleaning step is further provided: the raw material is cleaned with a sodium hydroxide aqueous solution having a pH value within the range of 8.5 to 10.5 to clean the halogen components contained in the raw material to obtain a treated raw material.

15. The zinc recovery method according to claim 13, further comprising a purification step of bringing metallic zinc into contact with the third zinc-containing aqueous solution to reduce and precipitate metallic impurity components inactive compared to zinc in the third zinc-containing aqueous solution, thereby purifying the third zinc-containing aqueous solution.

16. The zinc recovery method according to claim 15, wherein: The zinc recovery process includes an electrolysis process: electrolysis is performed using the third zinc-containing aqueous solution or an aqueous solution obtained by purifying the third zinc-containing aqueous solution as an electrolyte to obtain electrolytically generated zinc and an electrolytic tail liquid. The electrolytic tail liquid is transported to the high-temperature high-alkali treatment process in a state where an alkali metal hydroxide aqueous solution and zinc components remain. The alkali metal hydroxide aqueous solution in the electrolytic tail liquid contacts the raw material or the treated raw material.

17. The zinc recovery method according to claim 15, wherein: The zinc recovery step includes a zinc carbonate separation step: the zinc component in the third zinc-containing aqueous solution or the aqueous solution obtained by purifying the third zinc-containing aqueous solution is separated in the form of zinc carbonate, and a residual liquid from which the zinc carbonate is separated is obtained. The residual liquid, while still containing an alkali metal hydroxide aqueous solution and the zinc component, is transported to the high-temperature high-alkali treatment step, and the alkali metal hydroxide aqueous solution in the residual liquid contacts the raw material or the treated raw material.

18. A method for decomposing zinc ferrite, comprising: a contacting step of contacting the zinc ferrite-containing material with an aqueous solution of an alkali metal hydroxide; a heating step of heating the zinc ferrite-containing material and the alkali metal hydroxide aqueous solution brought into contact with each other in the contact step to raise the temperature of the zinc ferrite-containing material and the alkali metal hydroxide aqueous solution to a temperature reaching the boiling point of water whose boiling point is increased; and a concentration maintaining step of maintaining the concentration of the alkaline agent contained in the alkali metal hydroxide aqueous solution at a time when evaporation of water in the alkali metal hydroxide aqueous solution stops after the temperature reaches the boiling point, The alkaline agent whose concentration is maintained in the concentration maintaining step contacts the zinc ferrite in the zinc ferrite-containing material, thereby decomposing the zinc ferrite into a zinc oxide component and an iron oxide component.

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