KR20120076781A - Method for manufacturing zinc coating solution using high purity zinc oxide recovered from recyling secondary dust - Google Patents

Abstract

PURPOSE: A method for producing a zinc plating solution is provided to reduce the amount of used zinc balls by using high-purity zinc oxide recovered from secondary dust. CONSTITUTION: A method for producing a zinc plating solution comprises the steps of: leaching secondary dust, which is produced during a recycling process of stainless byproducts, in a sulfuric acid solution to prepare an aqueous zinc solution, filtering the zinc solution and the residues to remove a first group of impurities from the zinc solution, inserting metal zinc-containing dust into the zinc solution to remove a second group of impurities, adding NaOH(Sodium Hydroxide) into the aqueous solution and melt zinc at pH 14-15 to obtain an aqueous alkali zinc solution, putting high-purity sulfuric acid zinc into the aqueous alkali zinc solution at a OH and zinc mole number ratio of 2.0-3.0 to obtain a zinc oxide solution, drying the zinc oxide solution to obtain zinc oxide, and melting the zinc oxide into sulfuric acid used for producing a zinc plating liquid.

Description

METHOD FOR MANUFACTURING ZINC COATING SOLUTION USING HIGH PURITY ZINC OXIDE RECOVERED FROM RECYLING SECONDARY DUST}

The present invention relates to a method for producing a zinc plating solution from high purity zinc oxide, and more particularly, to recovering high purity zinc oxide from secondary dust generated in a recycling process of stainless steel by-products, and converting the high purity zinc oxide into a zinc plating solution. It relates to a manufacturing method.

In order to improve corrosion resistance and paintability, and to make surface appearance beautiful, steel plate etc. which are used for automobile bodies are usually galvanized. The zinc component used in such zinc plating has usually used metal zinc balls. These zinc balls are melted using sulfuric acid in a plating bath and used as a plating solution. However, such zinc balls have a high unit price per ton, causing the price of steel sheet to rise.

On the other hand, dust generated in the steel process usually contains 15-20% of zinc to form a dust with a reducing agent and heat concentrated to recover the zinc oxide has been proposed (Korean Patent 1997-0013538, Japanese Patent Laid-Open) 1992-261590).

That is, using LD converter steel dust containing zinc and EAF steelmaking dust as raw materials, and using waste tire dry coal, waste activated carbon or coke as a reducing agent, these components are combined on a stoichiometric basis, and then pellets and briquettes are prepared. After drying, it is charged into a liquid fuel heating reduction furnace, smelted at 1000-1500 ° C. for 1-3 hours, and then the evaporated ZnO is recovered in a dust collector.

However, the zinc oxide prepared in these methods cannot be suitably used as a zinc plating solution requiring high purity zinc oxide with ZnO = 60-90%.

In addition, Japanese Laid-Open Patent Publication No. 2003-339317 or the like discloses that high-purity zinc oxide is usually prepared by volatilizing high-purity metallic zinc, and acid leaching or electro-extracting raw materials such as Zn-containing scrap having a high degree of wetness. After extraction, the activated carbon is treated again to remove impurities, and then the solution from which the impurities are removed is neutralized with an alkaline solution to obtain zinc hydroxide, and the zinc hydroxide is calcined again to form zinc oxide. A manufacturing method is disclosed.

In addition, the inventors of the present invention, in Korean Patent Application No. 1998-0056706 and Korean Patent Registration No. 409951, in the Zn plating waste solution, the number of moles of KOH corresponding to 1 / 200-1 / 50 of the number of moles of Zn is administered and stirred and aged. Treating and adsorbing impurities, and then filtering the impurities; Filtering and adding the Zn-containing solution, from which impurities were removed, to a KOH solution to maintain a pH of the solution at 13 or more, so that the neutralization reaction was performed and stirring for at least 1 hour to obtain ZnO directly from an aqueous solution; And it has been presented a method for producing a high purity zinc oxide from the by-products, including the step of repeated filtration and washing the oxide obtained above.

Zinc oxide can be obtained by the same method as described above, but it is not suggested or suggested that it can be used as a raw material for the galvanized solution of steel sheet from dust in any of the published patent documents.

The present invention provides a method for producing a galvanized plating liquid, more specifically a zinc electroplating liquid, from secondary dust generated in the recycling process of stainless by-products.

Furthermore, the present invention is to provide a method for producing a plating liquid suitable for zinc electroplating of steel sheet by improving the impurity purification technology to more economically produce high purity zinc oxide from secondary dust generated in the recycling process of stainless by-products.

The present invention relates to a method for producing a zinc plating solution from secondary dust, the method comprising leaching secondary dust generated in the process of recycling stainless steel dust with an aqueous sulfuric acid solution to dissolve zinc to make a zinc aqueous solution; Filtering the zinc aqueous solution and the residue to filter out the first group impurities from the aqueous zinc solution; Removing the second group impurities by filtering metal zinc-containing dust into the aqueous zinc solution from which the first group impurities have been removed and filtering the second group impurities; Adding NaOH to the aqueous solution from which the second group impurities have been removed, dissolving zinc in a condition of pH 14-15, and filtering to obtain an aqueous alkali zinc solution; Adding a high purity zinc sulfate to the aqueous alkali zinc solution so that the ratio of the number of moles of OH: number of zinc is 2.0-3.0 to obtain a zinc oxide solution; Drying the obtained high purity zinc oxide solution to obtain zinc oxide; And dissolving the zinc oxide with sulfuric acid to provide a zinc plating solution as a raw material.

Preferably, the step of obtaining the aqueous alkali zinc solution is the step of neutralizing and precipitating zinc and third group impurities with hydroxide by adding an alkali agent to the aqueous solution from which the second group impurities are removed; Filtering the solution in which zinc and the third group impurities are neutralized and precipitated with hydroxides; And adding NaOH to the neutralized material to dissolve zinc in a condition of pH 14-15, and filter to obtain an alkali zinc aqueous solution.

The aqueous sulfuric acid solution contains 5-18% sulfuric acid, and the pH of the leaching solution is preferably 4-6.

The first group impurity may be one or two or more of iron, chromium, nickel, lead, silicon, and fluorine, and the second group impurity may be one or more of lead and cadmium.

The residue separated from the zinc aqueous solution in which the secondary dust is leached with an acidic aqueous solution to selectively dissolve zinc may be washed with water, filtered and the filtrate obtained by filtration may be added to the aqueous zinc solution.

The high purity zinc sulfate can be obtained by dissolving zinc in sulfuric acid.

In addition, the zinc oxide in the step of obtaining the zinc oxide may be prepared in the form of pellets, powder or cake, the zinc oxide comprises Na ₂ SO ₄ .

According to the present invention, a high purity zinc oxide can be produced more economically from secondary dust generated in the recycling process of stainless by-products, and furthermore, a zinc plating solution suitable for producing a galvanized steel sheet using the obtained high purity zinc oxide. Can be prepared.

As described above, since a galvanized solution can be obtained by preparing a galvanized solution from secondary dust generated in the recycling process of stainless by-products, the use of expensive zinc balls can be reduced and economical.

Hereinafter, the present invention for preparing zinc oxide from secondary dust generated in the recycling process of stainless by-products and preparing the same as a plating solution will be described in detail.

The present invention is applied to the secondary dust generated in the recycling process of stainless by-products, more preferably the secondary dust is T-Fe 1-10%, Si 1-6%, Ca 2-8% by weight , Mn 0.1-2.0%, Zn 20-45%, Mg 1-5%, Ni 0.1-1%, Cr 0.3-2%, Cd 0.1-1%, Pb 1-8% and K 3-10% Applicable to

Table 2 shows the results of analyzing the composition of one example of the secondary dust generated in the recycling process of the stainless by-products to which the present invention is applied.

T-Fe Si Ca Mn Zn Mg Ni Cr CD Pb K Primary 7.24 4.84 7.00 0.78 30.20 3.33 0.35 1.43 0.15 3.82 6.10 Secondary 6.83 3.71 6.89 0.78 29.46 3.47 0.30 1.37 0.14 4.02 5.83

As can be seen from Table 1, the zinc concentration in the secondary dust generated in the recycling process of stainless by-products is very high, about 30%, but the content of impurities such as Si, Mn, Cr, Ni, Mg, Pb is also high, The anion contains a large amount of the F component (about 5%) and the chlorine component (about 10%). However, it is difficult to effectively remove the impurities from the secondary dust and it is very difficult to economically recycle the secondary dust.

The present invention is to improve the impurity purification technology to produce a high-purity zinc oxide in the secondary dust generated in the recycling process of stainless by-products, and to provide a more economical method for producing a zinc plating solution using this.

First, a method of producing high purity zinc oxide from secondary dust generated in a recycling process of stainless by-products will be described.

In the present invention, it is necessary to selectively dissolve zinc by leaching secondary dust generated in the process of recycling stainless steel dust with an acidic aqueous solution. As the acidic aqueous solution for leaching the stainless dust, hydrochloric acid, sulfuric acid, and nitric acid aqueous solution may be used, and as a neutralizing agent, NaOH is preferably used. Thus, when sulfuric acid is used as an acidic aqueous solution and NaOH is used as a neutralizing agent, the by-product obtained by this can be used as a galvanizing solution, and it is most preferable.

Leaching reaction is carried out using an aqueous sulfuric acid solution, and the reaction equation in the case of neutralization reaction is represented by the formulas (1) and (2).

Scheme 1

Sulfuric acid aqueous solution leaching: ZnO + H ₂ SO ₄ = ZnSO ₄

Scheme 2

Neutralization: ZnSO ₄ + 2NaOH = ZnO + Na ₂ SO ₄

As can be seen from the respective reaction schemes, the salt produced by the leaching and neutralization reaction according to each acidic aqueous solution is Na ₂ SO ₄ , of which Na ₂ SO ₄ is suitably used as a conductive assistant in an electro zinc plating bath. Since it can be used, a solution containing zinc oxide and the Na ₂ SO ₄ can be added to the electrozinc plating bath without having to be washed with water to recover zinc oxide in a subsequent process, so that zinc is leached using sulfuric acid. Do.

It is preferable to use aqueous sulfuric acid solution while maintaining pH 4-6 for leaching of the secondary dust. When the pH of the sulfuric acid aqueous solution is less than 4 during zinc leaching, a large amount of metallic impurities other than zinc flows into the leaching solution, and there is a concern that a fluorine component may be introduced rapidly. In addition, when the leaching pH exceeds 6, the acid dissolution rate is slowed, the zinc leaching rate is low, and the unfavorable result of the zinc recovery rate is lowered. Therefore, it is preferable that sulfuric acid aqueous solution has a range of pH 4-6.

More preferably, the aqueous sulfuric acid solution may be performed by adjusting the pH to 4-6 using 5-18% weak sulfuric acid. Leaching with a strong sulfuric acid aqueous solution causes a sharp drop in pH, leading to a pH of 4 or less, making it difficult to adjust the pH. Therefore, it is preferable to use weak sulfuric acid.

The primary dust that occurs in the general carbon steel manufacturing process is that since the zinc contained mostly consists of spinel phase of zinc ferrite (ZnOFe ₂ O ₃ ), a strong acidic aqueous solution should be used for zinc leaching. However, stainless steel secondary dust is composed mostly of ZnO phase and only part of ZnOFe ₂ O ₃ spinel phase. Since ZnO has an alkaline property, there is no problem with zinc leaching even if it is leached under low leaching pH conditions with a weakly acidic aqueous solution such as low sulfuric acid.

On the other hand, heavy metal impurities such as Ni, Cr, Pb, etc. are mostly present in the form of spinel phase of (NiPb) O (CrFe) ₂ O ₃ . Since such spinel phases, such as (NiPb) O (CrFe) ₂ O ₃ , are highly resistant to acids, when leaching at low pH of weak acids, these heavy metal components having spinel phases dissolve and tend to flow into the zinc solution. Extremely limited

In particular, the fluorine component is present in majority in the form of CaF _2, CaF ₂ is to leach the zinc sulfate aqueous solution because of the nature that is not a pH of less than 6, almost dissolved, and is not dissolved in a fluoride ion-phase. In addition, Si also exists in the form of SiO ₂ and does not dissolve.

Therefore, when leaching at an appropriate pH range using a weak sulfuric acid solution containing a low concentration of acid, zinc in the aqueous solution is mostly present as metal ions, while fluorine and metal components such as Ni, Pb, Cr, Fe, and Si are used. Since impurities in the solid state are present, the impurities can be removed through solid-liquid separation, thereby obtaining an aqueous zinc solution containing zinc.

In this way, zinc is selectively dissolved by leaching of an aqueous sulfuric acid solution to remove impurities (first group impurities) such as solid fluorine and metal components such as Ni, Pb, Cr, Fe, and Si in the solution. can do.

At this time, the residue (sludge) separated from the aqueous zinc solution is washed with water after being washed with water, and the filtrate obtained by the filtration may be added to the aqueous zinc solution.

However, since a small amount of the second group impurities such as Pb component and Cd component, which are not present in the spinel phase in the secondary dust, is mixed in the aqueous zinc solution, a process for removing them is required. In the removal of the second group impurities from the aqueous zinc solution, the second group impurities can be removed by introducing a dust containing metal zinc into the aqueous zinc solution obtained by the separation filtration.

Since the Pb and Cd ions are electrochemically precious metal ions, when the metal zinc is administered, the metal zinc is substituted with the metal Pb and Cd by reaction as shown in the following Reaction Formula (3) to obtain Pb and Cd of the metal. By filtration separation, it can remove completely.

Scheme 3

(Pb, Cd) SO ₄ + Zn = (Pb, Cd) ⁰ + ZnSO ₄ (3)

The amount of zinc metal to be added must be at least as high as the sum of the moles of Cd and Pb to be removed, as shown in Equation (3) above.

In this case, metal zinc for removing lead and cadmium may be used, but since it is expensive, it is more preferable to use a dust containing zinc of a metal component. Specifically, zinc slime (zinc ball residue) generated in the dust or electro zinc plating process having a metal zinc content of 40-90% obtained in the process of smelting metal zinc may be used. Dust and sludge (slime) having a metal zinc content of less than 40% are not preferable because the substitution precipitation reaction rate is slow, and dust having a metal zinc content of 90% or more is expensive and thus limited in use.

NaOH is added to the aqueous solution from which the second group impurities are removed from the secondary dust, so that the zinc is dissolved in an aqueous alkali zinc solution at a pH of 14 or more, preferably in the range of 14-15, and filtered. When the leaching pH is less than 14, zinc dissolution is incomplete and the zinc leaching recovery rate is low, so it must be leached under conditions of strong alkali pH of 14 or more.

Thus, zinc obtained by leaching a strong alkali of pH 14 or more is present in the form as shown in the following scheme 4.

Scheme 4

Zn (OH) ₂ + 6NaOH = ZnNa ₂ (OH) ₄ + 4NaOH

ZnNa ₂ (OH) ₄ is an alkali melt of zinc present in an ionic state.

In order to raise a leaching rate, it is preferable to heat, for example, it is preferable to carry out at high temperature of 30-95 degreeC. If the leaching temperature is less than 30 ℃ leaching rate is bad, if the temperature exceeds 95 ℃ is a strong alkali, it is difficult to select the filtration material.

As described above, when the caustic soda is added to the zinc aqueous solution from which lead and cadmium are removed, the reaction is stirred at a pH of 13.5 or more to obtain zinc oxide.

Secondary dust generated when recycling carbon steel dust through RHF (Rotary Hearth Furnace) has very low Mn and Mg content, so that after the acid dissolution, only the first group impurity and the second group impurity mixed into the recycling process are purified. Zinc sulfate of good purity can be obtained. In some cases, however, the color of the zinc oxide thus produced may be very dark.

As a result of analyzing dark zinc oxide, the purity is only 95% or less. If the cause is investigated, the zinc aqueous solution from which lead and cadmium are removed as mentioned above contains Mn and Mg. Mn is a big cause of whiteness fall, and Mg is a big cause of purity fall. Therefore, a separate purification process for removing such Mn and Mg is required.

In the case where the secondary dust contains a third group impurity such as Mn and Mg, an alkaline agent is added to the aqueous solution from which the second group impurity is removed as described above to neutralize and precipitate zinc and the third group impurity with hydroxide, and then the aqueous solution is Filtration can optionally add a step to obtain neutral salts and chlorides.

That is, the alkaline agent is added to the aqueous solution from which lead and cadmium are removed as described above to neutralize and precipitate zinc and impurity metal components (Mn and Mg) with hydroxides. Alkali agents that can be used include, but are not limited to, NaOH, for example. In the case of using NaOH, a neutralization reaction occurs as shown in Scheme 5, which precipitates not only zinc ions, but also manganese and magnesium as hydroxides.

Scheme 5

MSO ₄ + ZnSO ₄ + Na (OH) ₂ = M (OH) ₂ + Zn (OH) ₂ + Na ₂ SO ₄ (M = Mn, Mg, Si)

The alkali (neutralizing agent) include not particularly limited, but it is preferred to use NaOH, The reason is that is obtained by neutralizing the salt Na ₂ SO _4, that can be used as a conductive auxiliary agent in the zinc plating solution, is preferred. On the other hand, Ca (OH) ₂ may be used, but in this case, a separate washing process is required to remove Ca, and Na ₂ SO _{4, which} is a conduction aid, is lost during the washing process. It can be simplified, and it is more preferable because there is no need to add a separate conduction aid to the plating solution.

After the neutralization treatment as described above, as described above, when NaOH is added to dissolve zinc in an aqueous alkali zinc solution at a pH of 14 or more, preferably in a pH range of 14-15, and filtered, only zinc is dissolved in an aqueous alkali zinc solution. Dissolves. The filtration and separation can separate the zinc-containing alkaline solution and impurities manganese and magnesium hydroxide sludge. The zinc-containing alkaline solution contains Na ₂ SO ₄ which can be used as a conductive aid in the plating solution.

Next, zinc sulfate (ZnSO ₄ ) is added to the aqueous alkali zinc solution containing ZnNa ₂ (OH) ₄ obtained in the above reaction formula (4) so that the molar ratio of OH to zinc is 2.0-3.0. As the reaction occurs, zinc oxide is directly crystallized in an aqueous solution.

[Reaction Scheme 6]

ZnNa ₂ (OH) ₄ + ₄ NaOH + 2 ZnSO ₄ = 3ZnO + ₂ NaOH + 4Na ₂ SO ₄ (OH: zinc molar ratio = 8/3)

When the number-of-moles ratio of OH: zinc is 2.0, zinc oxide is not produced but zinc hydroxide is formed, and when it exceeds 3.0, zinc is alkali-dissolved to decrease the ZnO production yield.

Since the purity of zinc sulfate is directly related to that of zinc oxide, it is preferable to use zinc sulfate of industrial high purity (> 99%). As such high purity zinc sulfate, use zinc sulfate aqueous solution obtained by purifying waste zinc plating solution, or by reacting zinc by-product with sulfuric acid, Ni + Cr + Pb + Cd + Mn + Mg + F + Si <0.5 An aqueous zinc sulfate solution purified to be by weight may be used. Furthermore, as high purity zinc sulfate, secondary dust obtained by secondary evaporation of carbon steel dust was used as the zinc by-product, and the secondary dust was reacted with an acid to give Ni + Cr + Pb + Cd + Mn + Mg relative to the dry weight of zinc sulfate. Aqueous zinc sulfate aqueous solution can be used such that + F + Si <0.5% by weight.

As described above, the zinc aqueous solution from which the second group impurities and the third group impurities are removed is an aqueous solution containing ZnO and Na ₂ SO ₄ . The zinc oxide is dissolved in sulfuric acid, Na ₂ SO ₄ is not dissolved in sulfuric acid, after adjusting the concentration of the aqueous zinc solution, it can be used as a raw material of the zinc plating solution by dissolving in sulfuric acid. At this time, the Na ₂ SO ₄ may be used as a conductive aid in the electrogalvanized solution.

The zinc oxide aqueous solution concentration suitable for use as a zinc plating solution is preferably, for example, a zinc concentration of 40% by weight or more. Therefore, when the zinc concentration is less than 40% by weight, the obtained aqueous zinc solution may be dried to control the moisture content. In addition, preferably ZnO in the aqueous zinc solution is preferably 80% by weight or more based on the weight of the component excluding the solvent, and Na ₂ SO ₄ is preferably less than 20% by weight.

Furthermore, the zinc oxide aqueous solution may be dried and provided as a raw material of the zinc plating solution in a solid state of zinc oxide. In this case, the dried zinc oxide may include Na ₂ SO ₄ . The zinc oxide thus dried may be prepared in powder, pellet or cake form by a known method.

In this way, when supplied as a raw material of the zinc plating solution in a solid state, zinc oxide containing Na ₂ SO ₄ can be dissolved in sulfuric acid to be solution. At this time, suitable sulfuric acid conditions are not particularly limited, but it is preferable to use a high purity (> 99%) as the impurity regulation of the plating liquid is difficult. When zinc oxide is dissolved in sulfuric acid, zinc sulfate is produced by a reaction as in Scheme 7 below.

Scheme 7

ZnO + H ₂ SO ₄ = ZnSO ₄ + H ₂ O

On the other hand, in the case of preparing a plating solution using zinc balls, hydrogen gas is generated as in Scheme 8 below.

[Reaction Scheme 8]

Zn + H ₂ SO ₄ = ZnSO ₄ + H ₂

As can be seen from the above Reaction Scheme 7, zinc oxide reacts with sulfuric acid to generate water, so that an additional advantage of ensuring safety of operation can be obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

Example  One

100 g of secondary dust generated in the recycling process of the stainless by-product having the composition of Table 1 was added to sulfuric acid and dissolved for 2 hours. At this time, the amount of sulfuric acid added was changed according to the pH of the leaching sulfuric acid solution, and the amount of the final water was changed to fix the leaching solution to 1 liter.

Leaching conditions in each solution are as shown in Table 2.

For comparison, an alkali agent of NaOH instead of sulfuric acid was leached under the conditions as described in Table 2.

Thereafter, fluorine and undissolved sludge such as Ni, Pb, Cr, Fe, and Si were filtered out from the solution.

The amount of zinc eluted and the content of impurities in the resulting aqueous zinc solution were analyzed by ICP, and the results are shown in Table 2 below.

No Leaching condition Zinc and Impurity Concentrations (g / l) Leaching agent density pH Zn Si Ni Cr Fe Pb Mn Comparative Example 1 HCl 35% 1.0 30.1 0.21 0.30 0.56 2.53 1.78 0.7 Comparative Example 2 NaOH 50% > 15 25.0 1.4 Tr Tr 0.01 3.88 Tr Comparative Example 3 NaOH 15% 13.8 5.4 0.7 Tr Tr Tr 0.35 Tr Inventory 1 H ₂ SO ₄ 15% 4.0 28.5 0.12 0.10 0.11 0.14 0.13 0.3 Inventory 2 H ₂ SO ₄ 10% 5.0 25.8 0.05 0.08 0.10 0.12 0.12 0.28 Comparative Example 4 HCl 3% 6.2 7.7 0.02 0.05 0.08 0.10 0.10 0.24

In Table 2, Tr. Indicates that the content of the component is less than 0.01 g / l.

In Comparative Examples 2 and 3, the leaching reaction was performed with an alkaline agent. As can be seen from Comparative Example 2, when high concentration caustic soda is used, zinc can be leached from the secondary dust, but the amount of zinc leaching is 83% (25.0 / 2) compared to the case of leaching with high concentration hydrochloric acid of Comparative Example 1. It is understood that the leaching effect of 30.1) cannot be obtained and that Pb and Si, which are difficult to purify from the leaching solution, are leached in large quantities. Furthermore, it can be seen that the zinc leaching rate is extremely lowered when the alkali concentration is lowered as in Comparative Example 3.

As such, the reason why the zinc leaching rate decreases during the alkali leaching of dust is that the reaction rate of the leaching reaction of zinc oxide in dust as shown in Scheme 9 is slow.

Scheme 9

ZnO + 6NaOH = Zn0Na ₂ (OH) ₃ + 4NaOH

On the other hand, in leaching with sulfuric acid, as in Comparative Example 1, when the leaching reaction using concentrated sulfuric acid (35%), the pH can be lowered, the leaching rate is good, and leaching using a high concentration of alkali Compared with the case of Comparative Example 2, there is an advantage that can reduce the content of the leaching of Si or Pb, but the incorporation of Fe, Mn, F in the leaching solution is severe, there was a problem that it is difficult to adjust to the target pH level. Furthermore, since the sludge increase due to Fe, Mn, F impurities occurs in a subsequent step, it is not preferable.

On the other hand, when the leaching reaction was performed at pH 4.1 and 5.2 by lowering the acid concentration as in Inventive Examples 1 and 2, the zinc leaching rate was good, and the impurity content in the zinc aqueous solution was sharply reduced, which was advantageous for the subsequent impurity removal process. However, in the case of Comparative Example 4, the acid concentration was too low, the pH level was high, and thus the time required to leach zinc was long, and a high zinc concentration in the solution could not be obtained.

Example  2

4 g of by-products having different metal zinc contents were added to 1 liter of the leachate prepared in Inventive Example 1 and Comparative Example 2 in terms of zinc leaching amount and impurity content in the leachate of Example 1, followed by stirring to filter the solids in the solution. Removed. The elution amount and impurity degree of zinc in the leaching solution thus obtained were analyzed by ICP, and the results are shown in Table 3 below.

No Heavy metal removal condition Zinc and Impurity Concentrations (g / l) Kinds Metal Zinc Concentration Input (g) Zn Mg Fe CD Pb Mn Comparative Example 5 - - - 28.5 2.4 0.14 0.1 0.13 0.3 Inventory 3 Plating Sludge 65% 4 29.2 2.4 0.1 0.01 Tr. 0.3 Honorable 4 Smelting Dust 50% 4 29.1 2.4 0.1 0.01 Tr. 0.3 Comparative Example 6 Smelting Dust 35% 6 29.0 2.4 0.2 0.09 0.2 0.3 Inventory 5 Smelting Dust 80% 3 29.2 2.4 0.1 0.01 Tr. 0.3

As shown in Table 3, it can be seen that dust and sludge having a zinc metal content of 40% or more has a clear Pb and Cd removal effect, as compared to Comparative Example 5, in which zinc-containing dust or sludge is not added.

On the other hand, in Comparative Example 6 in which smelting dust having a zinc content of less than 40% was added, the absolute amount of zinc metal was 6g × 0.35 = 2.1g, which is higher than that of Inventive Example 4, but the effect of removing Pb and Cd was hardly exhibited. That is, it can be seen that the heavy metal removal effect is hardly seen when the metal content is lowered below a certain amount due to a large amount of oxides and the like on the surface of the metal zinc. Therefore, it can be seen that the absolute amount of zinc metal should be added more than the sum of the moles of Cd and Pb to be removed, as shown in Scheme 3.

Example  3

1 liter of NaOH 1 mol solution was added to 1 liter of the purified solution as shown in Table 3, and zinc oxide was directly synthesized while stirring at a condition of pH = 13.5 or more. However, the zinc oxide is very dark in color and zinc oxide has been found to be less than 95% pure. As a result of investigating the cause, the purified aqueous zinc solution contained Mn and Mg.

Alkaline was added to the purified aqueous solution obtained by separating lead and cadmium from Example 4 of Example 2 to neutralize and precipitate zinc, Mn, and Mg impurity metal components with hydroxide, and then, an aqueous NaOH solution was added to the obtained neutralized precipitate. Zinc was dissolved in an aqueous alkali zinc solution. The leaching pH and temperature at this time were different. Thereafter, the obtained aqueous alkali zinc solution was filtered to remove impurities such as Mn and Mg in the solution, thereby preparing a high alkali zinc aqueous solution.

The leaching solution according to alkaline leaching conditions as shown in Table 4 was analyzed by ICP, and the results are shown in Table 4 below.

Leaching condition Zinc and Impurity Concentrations (g / l) corrector Leaching agent Temperature pH Zn Si Ni Cr Fe Pb Mn Comparative Example 7 NaOH Ca (OH) ₂ 80 12.5 0.3 0.01 Tr. Tr. Tr. Tr. Tr. Inventory 6 NaOH NaOH 80 14.5 39.1 0.01 Tr. Tr. Tr. Tr. Tr. Comparative Example 8 Ca (OH) ₂ NaOH 80 14.5 39.1 0.01 Tr. Tr. Tr. Tr. Tr. Comparative Example 9 NaOH NaOH 25 14.5 28.4 0.01 Tr. Tr. Tr. Tr. Tr. Comparative Example 10 NaOH NaOH 60 13.5 15.4 0.01 Tr. Tr. Tr. Tr. Tr. Honorable 7 NaOH NaOH 45 14.8 40.0 0.01 Tr. Tr. Tr. Tr. Tr.

As shown in Table 4, in the case of Comparative Example 7 using Ca (OH) ₂ as a leaching agent it can be seen that the zinc elution hardly occurs, because the leaching pH is low.

In addition, in the case of using Ca (OH) ₂ as a neutralizing agent as in Comparative Example 8, it shows an excellent effect on zinc leaching and impurity concentration, but does not go through a washing step, so a large amount of Ca is contained in the solution, The amount of NaOH was increased relatively.

On the other hand, when the temperature of the solution is low as in Comparative Example 9, or the leaching pH is low as in Comparative Example 10 it can be seen that the leaching efficiency of zinc is very low.

On the other hand, in the case of Inventive Examples 6 and 7, it is equipped with the appropriate temperature and pH conditions, it can be seen that the high leaching rate, high zinc content, low impurity concentration, Na ₂ SO ₄ is a plating solution produced during the neutralization process It can be used as a conductive additive, and does not require a washing process.

Therefore, it is preferable to use hydrated lime as a neutralizing agent and NaOH as an alkali leaching agent so that the leaching pH is 14 or higher, and the leaching temperature is set to 30 ° C or higher. If leaching temperature exceeds 95 ℃, problems of equipment material occur, so leaching temperature is preferably 30 ℃ -95 ℃, and zinc leaching rate by alkali leaching (dissolved zinc amount / zinc content in hydroxide before reaction) Nearly 100%, there is very little zinc left in the leach residue.

Example 4

Industrial high purity zinc sulfate was added to the strong alkali zinc leaching solution obtained in Example 6 of Table 4 so as to be 2.0-3.0 while controlling the molar ratio of OH: zinc to obtain white zinc. After drying, XRD analysis showed that it contained zinc oxide and Na ₂ SO ₄ . In addition, the purity analysis by XRF showed that the content of zinc oxide is more than 85%.

Example 5

The zinc oxide and Na ₂ SO ₄ solutions obtained in Example 4 were dried to obtain a zinc concentration of 10% by weight (general plating bath composition) in the solution. In the solution, except for water, zinc oxide was 88% by weight and Na ₂ SO ₄ was 12% by weight. 15% sulfuric acid was added to the solution to pH 4.5 to dissolve zinc oxide in the solution, thereby preparing an electrogalvanized solution.

Galvanizing was performed on the steel sheet using the obtained plating bath, and visual observation was compared with the surface of the plated steel sheet subjected to electro-zinc plating using zinc balls.

As a result of observation, the steel plate plated using the plating liquid obtained in this example did not differ in the surface and plating quality of the steel plate plated using zinc balls.

Claims (11)

A zinc dissolving step of leaching secondary dust generated in the process of recycling stainless steel dust with an aqueous sulfuric acid solution to dissolve zinc to form an aqueous zinc solution;
A first group impurity removing step of filtering the first aqueous solution from the zinc aqueous solution by filtering the zinc aqueous solution and the residue;
A second group impurity removal step of removing a second group impurity by filtering metal zinc-containing dust into the aqueous zinc solution from which the first group impurity has been removed, and filtering the second group impurity;
Alkali zinc aqueous solution manufacturing step of obtaining zinc alkali aqueous solution by dissolving zinc in the condition of pH 14-15 by adding NaOH to the aqueous solution from which the 2nd group impurities were removed, and filtering it;
Preparing a zinc oxide solution to obtain a zinc oxide solution by adding a high purity zinc sulfate to the aqueous alkali zinc solution so that the ratio of OH moles: zinc moles is 2.0-3.0;
Zinc oxide manufacturing step of obtaining zinc oxide by drying the obtained zinc oxide solution; And
Method for producing a galvanized solution from the secondary dust comprising the step of dissolving the zinc oxide with sulfuric acid to provide a plating solution as a raw material for galvanizing solution.
The method of claim 1, wherein the obtaining of the alkali zinc aqueous solution
A neutralization step of neutralizing and precipitating zinc and third group impurities with hydroxide by adding an alkali agent to the aqueous zinc solution obtained in the second group impurity removing step; And
A method for producing a zinc plating solution from secondary dust, comprising the step of removing impurities from NaOH by adding NaOH and filtering zinc to obtain an alkaline zinc aqueous solution.
The method of claim 1, wherein the aqueous sulfuric acid solution contains 5-18% sulfuric acid and the leaching solution has a pH of 4-6.
The method of claim 1, wherein the first group impurities are one or two or more of iron, chromium, nickel, lead, silicon, and fluorine, and the second group impurities are one or more of lead and cadmium. Method for producing a galvanized solution from tea dust.
The method of claim 1, wherein the metal zinc-containing dust of the second group impurity removing step has a metal zinc content of 40-90% by weight.
The method of claim 1, wherein the secondary dust is leached into an acidic aqueous solution, and the residue separated from the zinc aqueous solution in which zinc is selectively dissolved is washed with water, filtered, and the filtrate obtained by filtration is added to the aqueous zinc solution. Method for producing a galvanized solution from the secondary dust, characterized in that.
The method of claim 2, wherein the alkali agent is a method for producing a galvanized solution from secondary dust, characterized in that NaOH.
3. The method of claim 2, wherein the first group impurity is one or two or more of iron, chromium, nickel, lead, silicon, and fluorine, and the second group impurity is one or more of lead and cadmium, and the third A method for producing a galvanized solution from secondary dust, characterized in that the group impurities are one or two of manganese and magnesium.
According to claim 1, The high purity zinc sulfate is zinc sulfate aqueous solution obtained by purifying the waste zinc plating solution, zinc by-products reacted with sulfuric acid zinc sulfate Ni + Cr + Pb + Cd + Mn + Mg + F + Si < The zinc sulfate aqueous solution or carbon steel dust purified to 0.5% by weight was subjected to secondary evaporation and concentrated secondary dust with acid to give Ni + Cr + Pb + Cd + Mn + Mg + F + Si <0.5% by weight Method for producing a galvanized solution from the secondary dust, characterized in that at least one selected from the group consisting of purified zinc sulfate aqueous solution.
The method of claim 1, wherein in the step of obtaining zinc oxide, zinc oxide is prepared in the form of pellets, powders or cakes.
The method according to any one of claims 1 to 10, wherein the zinc oxide comprises Na ₂ SO ₄ to prepare a galvanized solution from secondary dust.