Method for producing zinc-containing material, method for producing electrogalvanized bath, and method for producing electrogalvanized steel sheet

Abstract

The present invention provides a zinc-containing material which can be used for the production of an electrolytic zinc-plated steel sheet that has a beautiful and bright appearance. The present invention comprises: a zinc leaching step for leaching zinc contained in iron-making dust into an acidic aqueous solution by bringing the iron-making dust into contact with the acidic aqueous solution; a first impurity precipitation step for having impurities precipitated in a state in which the pH of a first treatment liquid obtained in the zinc leaching step is 4.0 to 6.0 (inclusive); a second impurity precipitation step for having impurities precipitated by adding 0.10 g / L or more of a chelating agent, in a state in which the pH is 4.0 to 6.0 (inclusive), to a second treatment liquid obtained in the first impurity precipitation step; a first solid-liquid separation step for subjecting a third treatment liquid obtained in the second impurity precipitation step to solid-liquid separation; a zinc precipitation step for having a zinc-containing material precipitated in a state in which the pH of a fourth treatment liquid obtained in the first solid-liquid separation step is 8.0 to 12.0 (inclusive); and a second solid-liquid separation step for separating a fifth treatment liquid obtained in the zinc precipitation step into the zinc-containing material and a residual liquid.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a zinc-containing material, a method for producing an electrogalvanized bath, and a method for producing an electrogalvanized steel sheet. [Background technology]

[0002] Zinc, a typical base metal, is used in a variety of industrial fields. In particular, in the steel industry, zinc has a low electrical potential relative to iron and exhibits sacrificial corrosion protection, providing excellent corrosion resistance. For this reason, zinc is used as a plating material for the surface of steel sheets, and is widely used in automobiles, home appliances, building materials, and other applications.

[0003] Commonly used methods for producing galvanized steel sheets include the hot-dip galvanizing method, in which a zinc coating layer is formed on the surface of the steel sheet by immersing the steel sheet in a hot-dip galvanizing bath, and the electrogalvanizing method, in which a steel sheet is immersed in an acidic solution containing zinc ions and a zinc coating layer is deposited on the surface of the steel sheet through an electrochemical reaction. In both methods, metallic zinc is often used as the zinc raw material, but in recent years, the rise of emerging countries has changed the supply and demand balance, causing the price of metallic zinc to rise.

[0004] In response to this situation, attempts have been made to separate and recover industrial waste and steelworks by-products composed of other metals containing zinc instead of metallic zinc as a zinc source. For example, steelmaking dust such as blast furnace dust, converter dust, and electric furnace dust contains zinc derived from galvanized steel sheet scrap and iron ore, and techniques have been reported for separating and recovering zinc from the steelmaking dust as a zinc source. For example, Patent Document 1 describes a method for separating steelmaking dust into coarse dust and fine dust, contacting the fine dust with acid to leach zinc into the acid, and then repeatedly adding alkali and performing solid-liquid separation to separate and recover zinc. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-105980 Summary of the Invention [Problem to be solved by the invention]

[0006] Among zinc-coated steel sheets, electrogalvanized steel sheets are often used without painting after chemical conversion treatment, and therefore require excellent surface appearance. Whiteness is an important factor, and lightness (L value) is typically used as an indicator of whiteness. As a result of studies by the present inventors, it was found that when zinc separated and recovered by the method described in Patent Document 1 is used as the zinc source for an electrogalvanized bath, the L value of the plated surface decreases due to the influence of impurity metals (e.g., Pb and Cd) believed to be derived from steelmaking dust, and the plated appearance becomes darker than that of conventional electrogalvanized steel sheets. Therefore, when electrogalvanized steel sheets are produced using a zinc-containing material made from zinc separated and recovered from steelmaking dust by the method described in Patent Document 1, the desired appearance cannot be obtained.

[0007] Therefore, an object of the present invention is to provide a zinc-containing material made from steelmaking dust that can be used to produce electrogalvanized steel sheets having a beautiful bright appearance. [Means for solving the problem]

[0008] The present inventors have intensively investigated ways to solve the above-mentioned problems. As a result, they have found that a zinc-containing material free of impurity metals can be obtained by contacting steel dust with an acidic aqueous solution to leach zinc contained in the steel dust into the acidic aqueous solution, adjusting the pH of the resulting treatment solution (first treatment solution) to 4.0 or more and 6.0 or less, adding a predetermined amount of a chelating agent to the resulting treatment solution (second treatment solution) to precipitate impurity metals as hydroxides and chelate compounds while maintaining the zinc concentration in the treatment solution, subjecting the resulting treatment solution (third treatment solution) to solid-liquid separation, adjusting the pH of the resulting treatment solution (fourth treatment solution) to 8.0 or more and 12.0 or less, and then performing solid-liquid separation on the resulting treatment solution (fifth treatment solution). The present inventors have also found that an electrogalvanized steel sheet having a beautiful and bright appearance can be produced by using the resulting zinc-containing material as a zinc source in an electrogalvanizing process, which led to the completion of the present invention.

[0009] That is, the gist and configuration of the present invention are as follows. [1] a zinc leaching step in which ironmaking dust is brought into contact with an acidic aqueous solution to leach zinc contained in the ironmaking dust into the acidic aqueous solution; a first impurity precipitation step in which impurities are precipitated in the first treatment solution obtained in the zinc leaching step at a pH of 4.0 or more and 6.0 or less; a second impurity precipitation step of adding 0.10 g / L or more of a chelating agent to the second treatment liquid obtained in the first impurity precipitation step at a pH of 4.0 to 6.0 to precipitate impurities; a first solid-liquid separation step of performing solid-liquid separation on the third treated liquid obtained in the second impurity precipitation step; a zinc precipitation step of precipitating a zinc-containing substance in a state where the pH of the fourth treated liquid obtained in the first solid-liquid separation step is 8.0 or more and 12.0 or less; a second solid-liquid separation step of separating the fifth treated liquid obtained in the zinc precipitation step into a zinc-containing substance and a residual liquid; A method for producing a zinc-containing material, comprising:

[0010] [2] A method for producing a zinc-containing material as described in [1] above, further comprising a classification step of separating ironmaking dust into coarse dust and fine dust prior to the zinc leaching step, and using the fine dust obtained in the classification step as the ironmaking dust used in the zinc leaching step.

[0011] [3] A method for producing a zinc-containing material described in [1] or [2], wherein at least one of the chelating agents added to the second treatment liquid in the second impurity precipitation step is a chelating agent that forms a chelate compound with at least one of Cd and Pb.

[0012] [4] The method for producing a zinc-containing material according to any one of [1] to [3], wherein at least one of the chelating agents added to the second treatment liquid in the second impurity precipitation step is a compound partially having a structure represented by the following general formula (I): 1 and R 2 represents an optionally substituted alkyl group, M + indicates a monovalent cation. [ka]

[0013] [5] A method for preparing an electrogalvanizing bath, comprising: adding a zinc-containing material prepared by the method for preparing a zinc-containing material according to any one of [1] to [4] above to an electrogalvanizing bath; and the pH of the electrogalvanizing bath is 0.5 or more and 3.5 or less.

[0014] [6] A method for producing an electrogalvanized steel sheet, characterized in that the electrogalvanized steel sheet is produced by electrogalvanizing the surface of a steel sheet using an electrogalvanized bath prepared by the method for preparing an electrogalvanized bath described in [5] above. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a zinc-containing material made from steelmaking dust, which can be used to produce electrogalvanized steel sheets having a beautiful bright appearance. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a flowchart showing an example of a method for producing a zinc-containing material according to the present invention. [Figure 2] FIG. 1 is a flowchart showing a preferred example of a method for producing a zinc-containing material according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] (Method of producing zinc-containing materials) Hereinafter, embodiments of the present invention will be described. Note that the present invention is not limited to the following embodiments. Furthermore, in this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0018] FIG. 1 shows a flow chart of an example of a method for producing a zinc-containing material according to the present invention. The method for producing a zinc-containing material according to the present invention includes a zinc leaching step (step S1) in which ironmaking dust is brought into contact with an acidic aqueous solution to leach zinc contained in the ironmaking dust into the acidic aqueous solution; a first impurity precipitation step (step S2) in which impurities are precipitated in a first treated solution obtained in the zinc leaching step at a pH of 4.0 or higher and 6.0 or lower; a second impurity precipitation step (step S3) in which impurities are precipitated by adding 0.10 g / L or more of a chelating agent to the second treated solution obtained in the first impurity precipitation step at a pH of 4.0 or higher and 6.0 or lower; a first solid-liquid separation step (step S4) in which a third treated solution obtained in the second impurity precipitation step is subjected to solid-liquid separation; a zinc precipitation step (step S5) in which a zinc-containing material is precipitated in a fourth treated solution obtained in the first solid-liquid separation step at a pH of 8.0 or higher and 12.0 or lower; and a second solid-liquid separation step (step S6) in which the fifth treated solution obtained in the zinc precipitation step is separated into a zinc-containing material and a residue.

[0019] <Zinc leaching process> First, in step S1, iron manufacturing dust is brought into contact with an acidic aqueous solution to leach zinc contained in the iron manufacturing dust into the acidic aqueous solution (zinc leaching step).

[0020] As the raw material iron-making dust, blast furnace dust, converter dust, electric furnace dust, etc. can be used.

[0021] The acidic aqueous solution used in this zinc leaching step can be a common acidic aqueous solution such as sulfuric acid or hydrochloric acid. From the viewpoint of using the finally recovered zinc-containing material in an electrogalvanizing bath, it is desirable to use an acid containing the same type of anion as the electrogalvanizing bath to be used. When a sulfuric acid bath is used as the electrogalvanizing bath, it is preferable to use sulfuric acid as the acidic aqueous solution, and when a chloride bath is used as the electrogalvanizing bath, it is preferable to use hydrochloric acid as the acidic aqueous solution.

[0022] Although there is no particular limitation on the lower limit of the pH of the acidic aqueous solution used for zinc leaching, if the pH is below 1.0, the consumption of chemicals increases, leading to higher processing costs. Therefore, the pH of the acidic aqueous solution used for zinc leaching is preferably 1.0 or higher, and more preferably 2.0 or higher. On the other hand, if the pH of the acidic aqueous solution used for zinc leaching exceeds 5.0, zinc becomes difficult to leach, making it impossible to efficiently recover zinc. Therefore, the pH of the acidic aqueous solution used for zinc leaching is preferably 5.0 or lower, more preferably 4.0 or lower, and even more preferably 3.5 or lower.

[0023] The zinc leaching time is preferably 10 minutes or longer. By setting the zinc leaching time to 10 minutes or longer, the zinc can be sufficiently leached into the acidic aqueous solution, allowing for efficient recovery of the zinc. On the other hand, although there is no particular upper limit to the zinc leaching time, it is preferably 120 minutes or shorter in order to avoid prolonging the treatment time.

[0024] The reaction temperature during zinc leaching can be set arbitrarily within a temperature range in which the acidic aqueous solution does not solidify or evaporate. Considering the ability to maintain a constant temperature, the reaction temperature during zinc leaching is preferably 30°C or higher, and is preferably 90°C or lower, since too high a temperature increases the amount of evaporation of the acidic aqueous solution. It is also preferable to stir the acidic aqueous solution during the leaching process. While there are no particular limitations on the method for stirring the acidic aqueous solution, examples include methods using a stirrer mixer, a propeller mixer, a pump, or the like.

[0025] <First impurity precipitation process> Next, in step S2, impurities are precipitated in the first treatment solution obtained in the zinc leaching step while the pH is kept at 4.0 or more and 6.0 or less (first impurity precipitation step).

[0026] The first treatment solution obtained in the zinc leaching process is thought to contain impurities in the form of metal ions that inevitably leach into the acidic aqueous solution along with zinc from steelmaking dust. These impurities are thought to precipitate on the steel sheet along with the zinc during electroplating, lowering the L value of the galvanized steel sheet. Therefore, reducing these impurities is essential to obtaining electrogalvanized steel sheets with a beautiful, bright appearance. However, if zinc is also precipitated during the precipitation of impurities, the recycling rate for use as a raw material for galvanizing will also decrease. Therefore, it is necessary to precipitate impurities while maintaining the zinc concentration in the first treatment solution.

[0027] The present inventors conducted extensive research into conditions for precipitating and separating only impurities while maintaining the zinc concentration in the first treatment solution. As a result, they found that by adjusting the pH of the first treatment solution to 4.0 to 6.0 (first impurity precipitation step), adding a predetermined amount of a chelating agent to the resulting treatment solution (second treatment solution) to precipitate impurities (second impurity precipitation step), precipitating impurity elements other than zinc as hydroxides and chelate compounds, subjecting the resulting treatment solution (third treatment solution) to solid-liquid separation (first solid-liquid separation step), and then adjusting the pH of the resulting treatment solution (fourth treatment solution) to 8.0 to 12.0 and then subjecting the resulting treatment solution (fifth treatment solution) to solid-liquid separation (second solid-liquid separation step), a zinc-containing product free of impurity metals can be obtained. This results in a zinc-containing product suitable for producing electrogalvanized steel sheets with a beautiful, bright appearance.

[0028] Therefore, in this first impurity precipitation step, the pH of the first treatment solution obtained in the zinc leaching step is adjusted to 4.0 or more and 6.0 or less, thereby precipitating impurities (mainly Fe) as hydroxides while maintaining the zinc concentration contained in the first treatment solution. Since the pH of the first treatment solution is adjusted to 4.0 or more, Fe can be efficiently precipitated, so the pH of the first treatment solution is set to 4.0 or more. The lower limit of the pH of the first treatment solution is preferably 4.3, more preferably 4.5. Furthermore, since the pH of the first treatment solution is adjusted to 6.0 or less, zinc precipitation is suppressed, the zinc concentration in the solution is maintained, and zinc can be efficiently recovered, so the pH of the first treatment solution is set to 6.0 or less. The upper limit of the pH of the first treatment solution is preferably 5.8, more preferably 5.5.

[0029] If the pH of the first treatment solution obtained in the zinc leaching step is less than 4.0, it is necessary to adjust the pH of the first treatment solution to 4.0 or more and 6.0 or less, and one method for adjusting the pH is to add a general alkaline aqueous solution such as sodium hydroxide or calcium hydroxide. On the other hand, if the pH of the first treatment solution obtained in the zinc leaching step is within the range of 4.0 or more and 6.0 or less, it is not necessary to adjust the pH.

[0030] The temperature of the first treatment liquid in the first impurity precipitation step can be set arbitrarily within a temperature range in which the first treatment liquid does not solidify or evaporate. The temperature of the first treatment liquid is preferably 30°C or higher in consideration of maintaining a constant temperature, and is preferably 90°C or lower because an excessively high temperature increases the amount of evaporation of the first treatment liquid. Furthermore, the reaction time of the first impurity precipitation step is preferably 10 minutes or more and 120 minutes or less in consideration of the time required for impurity precipitation and treatment efficiency.

[0031] <Second impurity precipitation process> Subsequently, in step S3, 0.10 g / L or more of a chelating agent is added to the second treatment liquid obtained in the first impurity precipitation step at a pH of 4.0 to 6.0 to precipitate impurities (second impurity precipitation step).

[0032] Although some of the impurities (mainly Fe) can be precipitated as hydroxides in the first impurity precipitation step, heavy metal elements such as Cd and Pb remain in the solution without being precipitated. Therefore, in the second impurity precipitation step, a chelating agent is added to the second treatment liquid obtained in the first impurity precipitation step, thereby precipitating heavy metal elements such as Cd and Pb as chelate compounds.

[0033] For the above-mentioned purpose, it is preferable that at least one of the chelating agents added to the second treatment solution in the second impurity precipitation step is a chelating agent that forms a chelate compound with at least one of Cd and Pb. By using such a chelating agent, heavy metal elements such as Cd and Pb can be efficiently precipitated as a chelate compound.

[0034] In the present invention, it is more preferable that at least one of the chelating agents added to the second treatment liquid in the second impurity precipitation step is a compound partially having a structure represented by the following general formula (I): 1 and R 2 represents an alkyl group which may be substituted. +represents a monovalent cation, such as a proton, an alkali metal ion, an ammonium ion, etc. The compound may contain two or more structures represented by general formula (I).

[0035] [ka]

[0036] The structure represented by the above general formula (I) is thought to easily form stable complexes with heavy metal elements such as Cd and Pb, since the compound contains a total of three nitrogen atoms and sulfur atoms, each of which has a lone pair of electrons necessary for forming a coordinate bond with a metal.

[0037] Compounds having such a structure include dimethyldithiocarbamates, diethyldithiocarbamates, dipotassium piperazine-1,4-dicarbodithioate, potassium diethylamine-N-carbodithioate, and ammonium 1-pyrrolidinecarbodithioate.

[0038] The amount of chelating agent added to the second treatment solution is preferably 0.10 g / L or more to sufficiently reduce impurity elements. The amount of chelating agent added is more preferably 0.20 g / L or more, and even more preferably 0.50 g / L or more. There is no particular upper limit to the amount of chelating agent added, but from the perspective of treatment costs, it is preferably 5.00 g / L or less.

[0039] In this second impurity precipitation step, a chelating agent is added to the second treatment solution obtained in the first impurity precipitation step at a pH of 4.0 or higher and 6.0 or lower. By maintaining the pH of the second treatment solution at 4.0 or higher when the chelating agent is added, decomposition of the chelating agent added in the second impurity precipitation step is suppressed, and the chelating agent can stably form complexes with heavy metal elements and efficiently remove them. The lower limit of the pH of the second treatment solution is preferably 4.3, more preferably 4.5. Furthermore, at a pH above 6.0, zinc precipitates, reducing the zinc concentration in the solution and the zinc recovery rate; therefore, the pH of the second treatment solution must be maintained at 6.0 or lower. The upper limit of the pH of the second treatment solution is preferably 5.8, more preferably 5.5.

[0040] The pH of the second treatment liquid obtained in the first impurity precipitation step is preferably maintained between 4.0 and 6.0 until the chelating agent is added. As described above, the pH of the second treatment liquid needs to be maintained at 6.0 or less, but the pH of the second treatment liquid may temporarily become less than 4.0 as long as the pH is between 4.0 and 6.0 when the chelating agent is added.

[0041] The reaction time for the second impurity precipitation step is preferably 10 minutes or longer. By setting the reaction time to 10 minutes or longer, the impurities contained in the second treatment liquid can be sufficiently precipitated. There is no particular upper limit to the reaction time, but it is preferably 120 minutes or shorter to avoid prolonging the treatment time. The temperature of the second treatment liquid in the second impurity precipitation step can be set arbitrarily within a temperature range in which the second treatment liquid does not solidify or evaporate. Considering the ability to maintain a constant temperature, the temperature of the second treatment liquid is preferably 30°C or higher, and is preferably 90°C or lower because an excessively high temperature increases the amount of evaporation of the second treatment liquid.

[0042] <First solid-liquid separation step> Subsequently, in step S4, the third treated liquid obtained in the second impurity precipitation step is subjected to solid-liquid separation (first solid-liquid separation step).

[0043] This solid-liquid separation step is a step of separating the third treated liquid obtained in the second impurity precipitation step into a precipitated solid (hydroxides and chelate compounds of impurities) and a fourth treated liquid. The method of solid-liquid separation is not particularly limited, and any method can be selected, such as gravity settling, filtration, centrifugation, or filter press.

[0044] <Zinc precipitation process> Thereafter, in step S5, zinc-containing substances are precipitated in the fourth treatment liquid obtained in the first solid-liquid separation step, with the pH being in the range of 8.0 to 12.0 (zinc precipitation step).

[0045] In this step, the pH of the fourth treatment liquid obtained in the first solid-liquid separation step is adjusted to 8.0 or more and 12.0 or less, thereby precipitating the zinc contained in the fourth treatment liquid as a zinc-containing substance. By adjusting the pH of the fourth treatment liquid to 8.0 or more, zinc can be efficiently precipitated, so the pH of the fourth treatment liquid is set to 8.0 or more. The lower limit of the pH of the fourth treatment liquid is preferably 8.3, more preferably 8.5. Furthermore, by adjusting the pH of the fourth treatment liquid to 12.0 or less, re-dissolution of zinc can be suppressed, so the pH of the fourth treatment liquid is set to 12.0 or less. The upper limit of the pH of the fourth treatment liquid is preferably 11.8, more preferably 11.5.

[0046] If the pH of the fourth treated liquid obtained in the first solid-liquid separation step is less than 8.0, the pH of the fourth treated liquid needs to be adjusted to 8.0 or more and 12.0 or less, and examples of a method for adjusting the pH include adding a general alkaline aqueous solution of sodium hydroxide, calcium hydroxide, etc. On the other hand, if the pH of the fourth treated liquid obtained in the first solid-liquid separation step is within the range of 8.0 or more and 12.0 or less, it is not necessary to adjust the pH.

[0047] The temperature of the fourth treatment liquid in the zinc precipitation step can be set arbitrarily within a temperature range in which the fourth treatment liquid does not solidify or evaporate. Considering the ability to maintain a constant temperature, the temperature of the fourth treatment liquid is preferably 30°C or higher. On the other hand, if the temperature of the fourth treatment liquid becomes too high, the amount of evaporation of the fourth treatment liquid increases. Therefore, the temperature of the fourth treatment liquid is preferably 90°C or lower. Furthermore, taking into account the time required for impurity precipitation and treatment efficiency, the reaction time of the zinc precipitation step is preferably 10 minutes or more and 120 minutes or less.

[0048] <Second solid-liquid separation step> Finally, in step S6, the fifth treated liquid obtained in the zinc precipitation step is recovered by solid-liquid separation (second solid-liquid separation step).

[0049] The second solid-liquid separation step is a step of separating the fifth treatment liquid obtained in the zinc precipitation step into a zinc-containing material and a residual liquid. The method of solid-liquid separation is not particularly limited, and any method can be selected, such as gravity settling, filtration, centrifugation, or a filter press. Note that since the zinc-containing material obtained in the second solid-liquid separation step contains water, a drying treatment may be performed after the second solid-liquid separation step, if necessary.

[0050] In this way, zinc-containing materials can be produced from steelmaking dust.

[0051] In the present invention, the zinc recovery rate is the ratio of the amount of zinc contained in the zinc-containing material to the amount of zinc contained in the steelmaking dust, expressed as a percentage. From the viewpoint of processing costs, the zinc recovery rate is preferably 10% by mass or more, and more preferably 20% by mass or more.

[0052] The zinc-containing material obtained by the present invention can be used as part of an electrogalvanizing bath, or as part of a plating bath for electroplating a metal containing zinc, such as Fe-Zn electroplating or Ni-Zn electroplating, and can also be used in the production of electroplated steel sheets having such an electroplated layer on at least one side.

[0053] <Classification process> Fig. 2 shows a flowchart of a preferred example of the method for producing a zinc-containing material according to the present invention. As shown in Fig. 2, in the present invention, it is preferable to separate the iron-making dust into coarse dust and fine dust in step S7, which is a step prior to the zinc leaching step (classification step). It is then preferable to use the fine dust obtained in this classification step as the iron-making dust to be used in the zinc leaching step, which is a step subsequent to this classification step.

[0054] Zinc volatilized during the steelmaking process generally exists as fine particles of a few micrometers in size, and its specific gravity tends to be lower than that of iron. As a result, fine dust contains more zinc than coarse dust. Furthermore, because fine dust has a smaller average particle size than coarse dust, it is more reactive with the acidic aqueous solution in the subsequent zinc leaching process, which increases the processing efficiency of the zinc leaching reaction.

[0055] In the present invention, when the fine dust obtained in the classification step is used as the ironmaking dust to be used in the zinc leaching step, the average particle size of the fine dust is not particularly limited. However, from the viewpoint of a high zinc content and high reactivity in the zinc leaching step, the average particle size of the fine dust is preferably 100 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less.

[0056] There are no particular limitations on the method used in this classification process. For example, the ironworks dust can be separated into coarse and fine particles by using a sieve or by utilizing the difference in the settling or movement speed of particles in a fluid (fluid classification).

[0057] (Method for preparing electrogalvanizing bath) The method for preparing an electrogalvanizing bath according to the present invention is characterized in that the electrogalvanizing bath contains a zinc-containing material prepared by the method for preparing a zinc-containing material according to the present invention described above, and the pH of the electrogalvanizing bath is 0.5 or more and 3.5 or less.

[0058] In addition to the zinc-containing material of the present invention, other zinc sources that can be used in the electrogalvanizing bath used in the present invention include, for example, zinc granules, zinc sulfate (heptahydrate), zinc chloride, and zinc carbonate. Furthermore, it is preferable to use an acidic bath, which has excellent productivity, as the type of electrogalvanizing bath, and a sulfate bath, a chloride bath, or a mixture thereof can be used. However, since chloride baths require treatment of chlorine gas generated when an insoluble anode is used, it is more preferable to use a sulfate bath.

[0059] The pH of the electrogalvanizing bath is adjusted to a range of 0.5 to 3.5, preferably 1.0 to 3.0. By adjusting the pH of the electrogalvanizing bath to a range of 0.5 to 3.5, active hydrogen generation and a decrease in current efficiency can be suppressed, while plating burn on the plating layer can be suppressed, resulting in a beautiful plating appearance. The pH is preferably adjusted using an acid appropriate for the type of electrogalvanizing bath; for example, when the type of electrogalvanizing bath is a sulfuric acid bath, the pH is preferably adjusted with sulfuric acid.

[0060] The method for incorporating the zinc-containing material produced by the method for producing a zinc-containing material according to the present invention as a zinc source in an electrogalvanizing bath is not particularly limited, and one possible method is to add the zinc-containing material to an acidic bath prepared using a zinc source other than the zinc-containing material and then adjust the pH.

[0061] The proportion of the zinc-containing material contained as a zinc source in the electrogalvanizing bath is preferably 1.0 mass% or more in terms of the total zinc sources. This is because a zinc-containing material content of 1.0 mass% or more provides sufficient cost benefits according to the present invention. However, there is no upper limit to the proportion of the zinc-containing material, and the electrogalvanizing bath may be prepared using only the zinc-containing material as a zinc source.

[0062] The zinc concentration in the electrogalvanizing bath is preferably 0.5 mol / L or more. If the zinc concentration is 0.5 mol / L or more, there is no shortage of zinc ions near the steel sheet to be plated during electrolysis, and plating burn can be suppressed. There is no upper limit to the zinc concentration, but from the viewpoint of processing costs, it is preferably 2 mol / L or less.

[0063] In addition, the temperature of the electrogalvanizing bath is preferably 30°C or higher in consideration of maintaining a constant temperature. Although there is no particular upper limit for the temperature of the electrogalvanizing bath, a temperature of up to about 90°C is practical and preferable because an increase in temperature increases the amount of evaporation of the plating bath.

[0064] Furthermore, if necessary, a conductivity aid can be added to the plating bath. This is because it can improve the conductivity of the plating bath. Examples of the conductivity aid include sodium sulfate, ammonium sulfate, and potassium sulfate. However, if the amount added is too large, the whiteness of the plating may decrease when electrolytic treatment is performed at a high current density. Therefore, the amount of the conductivity aid added is preferably 0.5 mol / L or less.

[0065] The preferred range of the concentrations of impurity elements (Pb, Cd, Fe) contained in the plating bath is 1.0 ppm or less for Pb and Cd. If the concentrations of these impurity elements exceed 1.0 ppm, the L value of the plating surface may decrease. For the same reason, the Fe concentration is preferably 1000 ppm or less.

[0066] On the other hand, electrogalvanized steel sheets with a more beautiful surface can be obtained by adding inorganic components containing Sn, In, Bi, or Sb, or organic components having a 2-benzothiazolylthio group, as needed, to the plating bath. The concentrations of these inorganic and organic components are preferably controlled within the range of 0.01 to 3 ppm. The addition form of these components is not particularly limited. The inorganic components may be added in the metallic state or in the form of sulfates, chlorides, carbonates, oxides, etc. However, when using salts, it is preferable to use salts appropriate for the type of electrogalvanized bath. As the organic component having a 2-benzothiazolylthio group, 2-mercaptobenzothiazole (MBT) or its salts can be used.

[0067] (Method of manufacturing electrogalvanized steel sheets) The method for producing an electrogalvanized steel sheet according to the present invention is characterized in that the electrogalvanized steel sheet is produced by electrogalvanizing the surface of a steel sheet using an electrogalvanizing bath prepared by the method for preparing an electrogalvanized bath according to the present invention described above. When producing an electrogalvanized steel sheet, electroplating may be carried out after preparing an electrogalvanizing bath using a zinc-containing material and a zinc source other than the zinc-containing material, such as zinc grains or zinc sulfate. Alternatively, a zinc source containing the zinc-containing material prepared by the method for preparing a zinc-containing material according to the present invention may be additionally added to the electrogalvanizing bath in the electrogalvanized steel sheet production line.

[0068] The current density during electrolysis is 10 to 130 A / dm 2 The range is preferably 10 to 100 A / dm 2 It is more preferable to set the current density during electrolysis to 10 A / dm 2 By setting the current density at 130 A / dm or more, it is possible to prevent a decrease in current efficiency and a prolonged time required to secure a predetermined plating coating weight. 2 By setting the following, it is possible to suppress the occurrence of plating burn.

[0069] The type of counter electrode (anode) is not particularly limited, but considering the dissolution of impurities into the plating bath, it is preferable to use an iridium oxide electrode. Also, from the viewpoint of thinning the diffusion layer at the electrolytic interface, a plating bath flow rate of 1.0 m / s or more is preferable.

[0070] Thus, an electrogalvanized steel sheet can be produced using the electrogalvanizing bath prepared by the method for preparing an electrogalvanizing bath according to the present invention.

[0071] A surface-treated steel sheet can also be obtained by forming a chemical conversion coating on the surface of the electrogalvanized steel sheet produced as described above. The chemical conversion coating can be formed, for example, by a chromium-free chemical conversion treatment in which a chromium-free chemical conversion solution is applied and then heated and dried at a steel sheet temperature of 80 to 300°C without rinsing with water. The chemical conversion coating can be a single layer or a multi-layer, and in the case of a multi-layer, multiple chemical conversion treatments can be performed sequentially.

[0072] Furthermore, depending on the intended use of the electrogalvanized steel sheet, a single-layer or multi-layer coating containing an organic resin can be formed on the surface of the plating layer or chemical conversion coating of the electrogalvanized steel sheet produced as described above to produce a surface-treated steel sheet. Examples of such coatings include polyester-based resin coatings, epoxy-based resin coatings, acrylic-based resin coatings, urethane-based resin coatings, and fluorine-based resin coatings. Also applicable are coatings in which part of the above resins is modified with another resin, such as epoxy-modified polyester-based resin coatings. Furthermore, the above resins can be supplemented with curing agents, curing catalysts, pigments, additives, and the like, as needed.

[0073] The coating method for forming the coating film is not particularly limited, but examples of the coating method include roll coater coating, curtain flow coating, spray coating, etc. For example, a coating material containing an organic resin can be applied to the surface of the plating layer or chemical conversion coating of an electrogalvanized steel sheet, and then heated and dried by means of hot air drying, infrared heating, induction heating, etc. to form a coating film.

[0074] The above-described method for producing a surface-treated steel sheet is an example, and the present invention is not limited to this. [Example]

[0075] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0076] First, electric furnace dust (zinc content: 40% by mass, average particle size: 10 μm) was added to a sulfuric acid aqueous solution adjusted to pH 2.0 and stirred for one hour to leach zinc into the sulfuric acid aqueous solution (zinc leaching process). The resulting solution was then adjusted under various conditions, and impurity precipitation processes (first impurity precipitation process and second impurity precipitation process) were carried out. Table 1 lists the types of chelating agents, and Table 2 lists the amount of electric furnace dust added, the type of alkaline aqueous solution used to adjust the pH in the first impurity precipitation process, the pH of the solution after pH adjustment, and the type and amount of chelating agent added in the second impurity precipitation process. The structural formulas of A1 to A4 in Table 1 are also listed. Both the first impurity precipitation process and the second impurity precipitation process were carried out with stirring for one hour after bath adjustment at a solution temperature of 50°C. The solution was then subjected to solid-liquid separation using a suction filter (first solid-liquid separation step), and the pH of the resulting solution was adjusted to 9.0 (zinc precipitation step). The resulting solution was then subjected to solid-liquid separation using a suction filter (second solid-liquid separation step), and the resulting solid was dried at 105°C to obtain a zinc-containing product. The pH adjustment in the zinc precipitation step was performed using an aqueous sodium hydroxide solution. The zinc recovery rate from the electric furnace dust and the proportions of Fe, Cd, and Pb contained in the zinc-containing product for each number are shown in Table 2.

[0077] [Table 1]

[0078] [Table 2]

[0079] [ka]

[0080] [ka]

[0081] [ka]

[0082] [ka]

[0083] An electrogalvanizing bath was prepared using the zinc-containing material and zinc sulfate heptahydrate obtained as described above, with the zinc concentration in the bath adjusted to the concentration shown in Table 2. Electrogalvanizing was then carried out under the conditions shown below to produce electrogalvanized steel sheets. A cold-rolled steel sheet with a thickness of 0.7 mm, produced by a conventional method, was used as the base sheet for plating. Test pieces (150 mm x 70 mm) for batch electrogalvanizing were cut out from this steel sheet, degreased, pickled, and then electrogalvanized. The zinc coating weight per side was 20 g / m2 in all cases. 2 It was decided.

[0084] Electrolysis conditions Current density: 50A / dm 2 Bath temperature: 50℃ Electrode: Iridium oxide Flow velocity: 2.0m / sec

[0085] Furthermore, the plated surface of the obtained electrogalvanized steel sheet was coated with epoxy resin (trade name: jER1009, manufactured by Japan Epoxy Resin Co., Ltd.) to prepare a chromium-free chemical conversion treated steel sheet.

[0086] The lightness (L value) of the obtained electrogalvanized steel sheets and chrome-free chemical conversion treated steel sheets was measured using a spectrocolorimeter (SD5000 manufactured by Nippon Denshoku Industries Co., Ltd.) with SCE (specular reflection excluded) in accordance with JIS Z8722:2009. For electrogalvanized steel sheets, an L value of 80 or more was evaluated as ◎, an L value of 76 or more but less than 80 was evaluated as ◯, and an L value of less than 76 was evaluated as ×. For chrome-free chemical conversion treated steel sheets, an L value of 60 or more was evaluated as ◎, an L value of 56 or more but less than 60 was evaluated as ◯, and an L value of less than 56 was evaluated as ×. ◎, ◯, and × indicate better performance in that order.

[0087] No. 1 in Table 2 is a comparative example of electrogalvanized steel sheet and chromium-free chemically treated steel sheet that were electrogalvanized without either the first or second impurity precipitation steps. Because the zinc-containing material contains many impurities, the impurity concentration in the electrogalvanizing bath is also high, resulting in a low L value. No. 2 is a comparative example in which only the first impurity precipitation step was performed. Although the Fe content in the zinc-containing material is reduced, Cd and Pb still remain, resulting in high Cd and Pb concentrations in the electrogalvanizing bath and a low L value. No. 3 is a comparative example in which only the second impurity precipitation step was performed. However, due to the low pH and decomposition of the chelating agent, the impurity content in the zinc-containing material is high, similar to No. 1. As a result, the impurity concentration in the electrogalvanizing bath is also high and the L value is low. No. 4 is a comparative example in which the pH was outside the lower limit in the first impurity precipitation step. Although the Fe content in the zinc-containing material decreased, the pH was low and the chelating agent decomposed, resulting in Cd and Pb remaining in the zinc-containing material, and the L value was also low. No. 5 is a comparative example in which the pH was outside the upper limit in the first impurity precipitation step. The zinc recovery rate was significantly reduced, making it unsuitable as a zinc source for electrogalvanization. No. 6 is a comparative example in which the chelating compound addition amount was outside the lower limit, but the Cd and Pb content in the zinc-containing material was not sufficiently reduced, and the L value was also low. On the other hand, in the invention examples Nos. 7 to 22, the proportions of Fe, Cd, and Pb were reduced without significantly reducing the Zn concentration in the zinc-containing material, and the impurity concentrations in the electrolytic zinc plating bath were also sufficiently low, resulting in high L values. Nos. 23 and 24 are examples in which the ratio of the zinc-containing material used as a zinc source to the electrogalvanizing bath was 1.1% by mass, near the lower limit of the preferred range of the present invention. No. 23 is a comparative example prepared without performing either the first or second impurity precipitation steps. The low L value indicates that the impurity concentration in the electrogalvanizing bath is outside the allowable range due to the influence of impurities contained in the zinc-containing material. On the other hand, in Example No. 24, in which both the first and second impurity precipitation steps were performed, the proportions of Fe, Cd, and Pb in the electrogalvanizing bath were successfully reduced, resulting in a high L value. Furthermore, No. 25 is an example in which the electrogalvanizing bath was prepared using only the zinc-containing material. However, the proportions of Fe, Cd, and Pb in the zinc-containing material were sufficiently low, resulting in a low impurity concentration in the electrogalvanizing bath, resulting in a high L value. Furthermore, No. 26 is an invention example in which MBT has been added to No. 10, and it can be seen that the L value is increased compared to No. 10, which does not contain MBT. [Industrial Applicability]

[0088] According to the present invention, it is possible to provide a zinc-containing material made from steelmaking dust, which can be used to produce electrogalvanized steel sheets having a beautiful bright appearance.

Claims

1. a zinc leaching step of contacting iron manufacturing dust with an acidic aqueous solution to leach zinc contained in the iron manufacturing dust into the acidic aqueous solution; a first impurity precipitation step in which impurities are precipitated in the first treatment solution obtained in the zinc leaching step at a pH of 4.0 or more and 6.0 or less; a second impurity precipitation step of adding 0.10 g / L or more of a chelating agent to the second treatment solution obtained in the first impurity precipitation step at a pH of 4.0 to 6.0 to precipitate impurities; a first solid-liquid separation step of performing solid-liquid separation on the third treated liquid obtained in the second impurity precipitation step; a zinc precipitation step of precipitating a zinc-containing substance in a state where the pH of the fourth treated liquid obtained in the first solid-liquid separation step is 8.0 or more and 12.0 or less; a second solid-liquid separation step of separating the fifth treated liquid obtained in the zinc precipitation step into a zinc-containing substance and a residual liquid; A method for producing a zinc-containing material, comprising:

2. 2. The method for producing a zinc-containing material according to claim 1, further comprising a classification step prior to the zinc leaching step of separating ironmaking dust into coarse dust and fine dust, and the fine dust obtained in the classification step is used as the ironmaking dust used in the zinc leaching step.

3. A method for producing a zinc-containing material as described in claim 1, wherein at least one of the chelating agents added to the second treatment liquid in the second impurity precipitation process is a chelating agent that forms a chelate compound with at least one of Cd and Pb.

4. A method for producing a zinc-containing material as described in claim 2, wherein at least one of the chelating agents added to the second treatment liquid in the second impurity precipitation step is a chelating agent that forms a chelate compound with at least one of Cd and Pb.

5. The method for producing a zinc-containing material according to any one of claims 1 to 4, wherein at least one of the chelating agents added to the second treatment solution in the second impurity precipitation step is a compound having a structure represented by the following general formula (I) in a part thereof: １ and R ２ represents an alkyl group which may be substituted, and M ＋ indicates a monovalent cation. 【Chemistry 1】

6. A method for preparing an electrogalvanizing bath, comprising: containing a zinc-containing material prepared by the method for preparing a zinc-containing material according to any one of claims 1 to 4 in an electrogalvanizing bath; and the pH of the electrogalvanizing bath is 0.5 or more and 3.5 or less.

7. A method for preparing an electro-galvanized bath, characterized in that the electro-galvanized bath contains a zinc-containing material prepared by the method for preparing a zinc-containing material described in claim 5, and the pH of the electro-galvanized bath is 0.5 or more and 3.5 or less.

8. A method for producing an electrogalvanized steel sheet, comprising electroplating a surface of a steel sheet using an electrogalvanized bath prepared by the method for preparing an electrogalvanized bath according to claim 6, thereby producing an electrogalvanized steel sheet.

9. A method for producing an electro-galvanized steel sheet, characterized in that the electro-galvanized steel sheet is produced by electro-galvanizing the surface of a steel sheet using an electro-galvanized bath prepared by the method for preparing an electro-galvanized bath described in claim 7.

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