WO2010074516A2

WO2010074516A2 - Method for preparing high purity zinc oxide using secondary dust

Info

Publication number: WO2010074516A2
Application number: PCT/KR2009/007741
Authority: WO
Inventors: 이재영; 변태봉; 안중철; 박현; 박보하
Original assignee: 주식회사 포스코; 재단법인 포항산업과학연구원
Priority date: 2008-12-23
Filing date: 2009-12-23
Publication date: 2010-07-01
Also published as: KR101060934B1; JP5564514B2; JP2012513370A; WO2010074516A3; CN102325725A; CN102325725B; KR20100074071A

Abstract

The present invention relates to a method for preparing high purity zinc oxide used for the electronics and rubber industries, and has as its objective to provide a method for preparing high purity zinc oxide used for electronics and rubber industries by utilizing secondary dust generated in the process of recycling stainless dust. The key point of the method for preparing high purity zinc oxide of the invention is a method wherein secondary dust generated in the process of recycling stainless steel dust is leached with an aqueous solution of hydrogen chloride to selectively dissolve zinc and prepare an aqueous zinc solution, impurities including iron, chrome, fluorine, lead, and cadmium are removed, NaOH is added to dissolve zinc into an aqueous alkaline zinc solution and filtration is performed under conditions of pH 14 15, high purity zinc chloride is added so that the mole ratio of OH: zinc may reach 2.0 3.0 to prepare high purity zinc oxide directly, washing is carried out to remove NaCl, and the sludge of the high purity zinc oxide is filtered and drying is carried out to prepare high purity zinc oxide. According to the invention, the industrial byproduct dust can be turned into a resource for high purity zinc oxide so that it becomes a high-value-added product.

Description

Manufacturing method of high purity zinc oxide using secondary dust

The present invention relates to a method for producing high purity zinc oxide used in the electronics industry and the rubber industry, and more particularly, by using secondary dust generated in the recycling process of stainless steel by-products. It relates to a method for producing zinc oxide.

Dust generated in the steel process usually contains 15-20% of zinc, and the dust is formed together with the reducing material, and then heated and concentrated to recover zinc oxide (Korean Patent 1997-0013538, Japanese Patent Publication 1992). -261590).

In other words, LD converter steel dust containing zinc and EAF steel dust are used as raw materials, and waste tire dry charcoal, waste activated carbon, or coke is used as a reducing agent, and these components are combined on a stoichiometric basis to prepare ferrets and briquettes. After drying, charged into a liquid fuel heating reduction furnace and smelted at 1000-1500 ° C. for 1-3 hours, and then the evaporated ZnO is recovered in a dust collector.

However, the zinc oxide produced in these methods has a disadvantage that ZnO = 60-90% level can not be used as a raw material for ferrite, rubber that requires high purity zinc oxide.

High-purity zinc oxide is usually manufactured by volatilizing high-purity metallic zinc, and wet leaching raw materials such as Zn-containing scraps having high purity, followed by acid extraction, solvent extraction, and then activated carbon treatment to remove impurities. The method of producing a high purity zinc oxide powder, characterized in that the solution from which the impurities have been removed is neutralized with an alkali solution to obtain zinc hydroxide, and then the zinc hydroxide is calcined to zinc oxide (Japanese Patent Laid-Open No. 2003-339317). have.

The inventors have developed a method for producing high purity zinc oxide from by-products. (Korean Patent Application No. 1998-0056706, Korean Patent Registration No. 409951).

That is, the method comprises administering to the Zn plating waste liquid the number of moles of KOH corresponding to 1/200 to 1/50 of the number of moles of Zn in the waste solution, and stirring and aging to allow the impurities to be adsorbed and then filtering them; Filtering and adding the Zn-containing solution from which impurities were removed to the KOH solution to maintain neutralization reaction while maintaining the pH of the solution at 13 or above, followed by stirring for 1 hour to obtain ZnO directly from the aqueous solution; And ZnO manufacturing method comprising the step of drying the obtained oxide after repeated filtration washing.

Secondary dust from the recycling process of stainless by-products has a much higher zinc concentration (about 30%) than ordinary carbon steel dust, resulting in sufficient recycling economics for zinc recovery.

However, this dust contains high concentrations of Ni, Cr, Mn, Mg, etc. in addition to Fe, and thus it is impossible to produce high purity zinc oxide through a general impurity purification process.

An object of the present invention is to provide a method for more economically manufacturing high purity zinc oxide in secondary dust generated in a recycling process of stainless by-products by improving impurity purification techniques.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention comprises the steps of leaching secondary dust generated in the process of recycling stainless dust in an acidic aqueous solution to selectively dissolve zinc to make a zinc aqueous solution;

Filtering the zinc aqueous solution and the residue to separate and remove the first group impurities from the aqueous zinc solution;

Injecting a dust containing zinc of the metal component in the aqueous solution from which the first group impurities are removed as described above to remove the second group impurities;

Adding NaOH to the aqueous solution from which the second group impurities are removed as described above, dissolving zinc in an aqueous alkaline zinc solution and filtering under a pH of 14 or more;

Preparing a high purity zinc oxide sludge directly in an aqueous solution by adding a high purity zinc chloride to an aqueous alkaline zinc solution so that the ratio of the number of moles of zinc to the number of moles of zinc is 2.0-3.0;

Washing with high purity zinc oxide sludge to remove NaCl; And

It relates to a method for producing high purity zinc oxide using secondary dust comprising the step of filtering and drying the high purity zinc oxide sludge.

Examples of the acidic aqueous solution for leaching the secondary dust include aqueous hydrochloric acid, sulfuric acid and nitric acid, and preferred acidic aqueous solution is hydrochloric acid.

Examples of the first group impurities include one or two or more of iron, chromium, nickel, lead, silicon, and fluorine.

Examples of the second group impurities include one or two of lead and cadmium.

The high-purity zinc chloride is Ni + Cr + Pb + Cd + Mn + Mg + F + Si <0.5 wt% by weight of zinc chloride by reacting zinc chloride aqueous solution or zinc by-product obtained by purifying waste zinc plating solution with hydrochloric acid. Purified aqueous zinc chloride solution can be used.

In addition, the present invention comprises the steps of leaching secondary dust generated in the process of recycling stainless dust in an acidic aqueous solution to selectively dissolve zinc to make a zinc aqueous solution;

Removing the second group impurities by inputting dust containing zinc of a metal component into an aqueous solution in which the first group impurities are removed as described above;

Neutralizing and precipitating zinc and the third group impurities with a hydroxide by adding an alkali agent to the aqueous solution from which the second group impurities are removed as described above;

Filtering the aqueous solution to obtain a neutral salt and a chloride;

Adding NaOH to the neutralized precipitate obtained as described above, dissolving zinc in an aqueous alkaline zinc solution and filtering under conditions of pH 14 or higher;

Washing with high purity zinc oxide sludge to remove NaCl; And

Examples of the second group impurities include one or two of lead and cadmium.

Examples of the third group impurity include one or two of manganese and magnesium.

As described above, according to the present invention, high purity zinc oxide used in the electronics industry and the rubber industry in secondary dust generated in the recycling process of stainless by-products can be produced more economically.

Hereinafter, the present invention will be described in more detail.

The present invention is preferably applied to the secondary dust generated in the recycling process of stainless by-products, secondary dust that can be more preferably applied to the present invention

T-Fe: 1 to 10% by weight, Si: 1 to 6%, Ca: 2 to 8%, Mn: 0.1 to 2.0%, Zn: 20 to 45%, Mg: 1 to 5%, Ni: 0.1 ˜1%, Cr: 0.3-2%, Cd: 0.1-1%, Pb: 1-8%, and K: 3-10%.

Table 1 below shows the results of analyzing the composition of one example of the secondary dust generated in the recycling process of the stainless by-products applicable to the present invention.

Table 1

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

As shown in Table 1, the zinc concentration in the secondary dust generated in the recycling process of stainless by-products is very high, about 30%, but Si, Mn, Cr, Ni, Mg, Pb, etc. are very high, and an anion F component ( 5%) and chlorine components (about 10%) are mixed in a large amount.

However, since it is difficult to effectively remove impurities from the secondary dust, it is very difficult to economically recycle the secondary dust.

The present invention provides a method for more economically producing high purity zinc oxide in secondary dust generated in the recycling process of stainless by-products by improving impurity purification techniques.

In the present invention, it is necessary to selectively dissolve zinc by leaching secondary dust generated in the process of recycling stainless dust with an acidic aqueous solution.

As the acidic leaching aqueous solution, hydrochloric acid, sulfuric acid, nitric acid aqueous solution and the like can be used, but among these, hydrochloric acid aqueous solution is most preferred.

The reason why it is most preferable to use hydrochloric acid as an acidic leaching aqueous solution as above is demonstrated.

In the case of using an aqueous hydrochloric acid solution as the acidic leaching aqueous solution, the secondary dust contains third group impurities such as Mn, so that the neutralizing agent can be used as a neutralizing agent in the neutralization step performed to remove these impurities, and preferably, It can also reduce the environmental load.

The leaching reaction and neutralization reaction for each acidic aqueous solution are expressed as follows.

Scheme 1

Hydrochloric acid aqueous solution leaching: ZnO + 2HCl = ZnCl ₂ neutralization) ZnCl ₂ + Ca (OH) ₂ = Zn (OH) ₂ + CaCl ₂

Scheme 2

Leaching of sulfuric acid solution: ZnO + H ₂ SO ₄ = ZnSO ₄ neutralization) ZnSO ₄ + Ca (OH) ₂ = Zn (OH) ₂ + CaSO ₄

Scheme 3

Nitric acid leaching: ZnO + 2HNO ₃ = ZnNO ₃ neutralization) ZnNO ₃ + Ca (OH) ₂ = Zn (OH) ₂ + Ca (NO ₃ ) ₂

Salts produced by leaching and neutralization by acidic aqueous solution are CaCl ₂ , CaSO ₄ and Ca (NO ₃ ) ₂ .

The use of aqueous sulfuric acid solution is not preferable because a large amount of solid material CaSO ₄ is produced, it is not easy to separate and remove the zinc hydroxide and lower the leaching efficiency and increase the amount of waste sludge during strong alkali leaching.

In the case of using the aqueous nitric acid solution, the nitrate produced is soluble in water but is not preferable because biological environment treatment is required.

Thus, aqueous hydrochloric acid solution, which produces a water-soluble salt in the form of calcium chloride, is most effective.

Next, the first group impurity is separated and removed by filtering the zinc aqueous solution and the residue obtained by selectively dissolving zinc by leaching the acidic aqueous solution as described above.

At this time, the residue (sludge) separated from the aqueous zinc solution as described above may be washed with water, filtered, and the filtrate obtained by the filtration may be added to the aqueous zinc solution.

The first group impurity is an impurity which is contained in the secondary dust and does not leach into an acidic aqueous solution, and examples thereof include iron, chromium, nickel, lead, silicon and fluorine.

The pH at the time of leaching of the secondary dust is preferably 4-6, more preferably

Leaching is carried out at a pH of 4-6 with 5-18% weak hydrochloric acid.

Leaching with a strongly acidic aqueous solution, for example, a strong hydrochloric acid solution, may cause a sharp drop in pH, which may cause the pH to be 4 or less.

If the pH of the acidic solution is less than 4 during leaching, a large amount of metallic impurities other than zinc flows into the leaching solution, and especially fluorine is rapidly introduced.

If the leaching pH exceeds 6, the acid dissolution rate is slowed down, which leads to an undesirable result of a slow zinc leaching rate and a low zinc recovery rate.

The reason why the leaching rate is good even when leaching with a weakly acidic aqueous solution, for example, a weak hydrochloric acid aqueous solution is as follows.

The primary dust generated in the general carbon steel manufacturing process is that zinc is mainly composed of zinc ferrite (ZnOFe ₂ O ₃ ) spinel phase, so to leach zinc, a strong acidic solution such as strong hydrochloric acid should be used.

However, most of the stainless steel secondary dust is composed of zinc in the ZnO phase and only a part in the ZnOFe ₂ O ₃ spinel phase.

In particular, most of the heavy metal impurities Ni, Cr, Pb, etc. are present in the form of (NiPb) O (CrFe) ₂ O ₃ spinel.

The spinel phase, such as (NiPb) O (CrFe) ₂ O ₃ , has a very high resistance to acids, and therefore, metal ions are dissolved and introduced when leaching with a weak acid at low leaching pH.

However, ZnO has an alkaline property, so even if it is leached at low leaching pH conditions with a weakly acidic aqueous solution such as low concentration hydrochloric acid, there is no problem with zinc leaching.

In particular, the fluorine component is present in majority in the form of CaF _2, CaF ₂ is not a pH of less than 4 because the substantially insoluble nature of leaching when fluoride is dissolved in the ion.

In addition, Si also exists in the form of SiO ₂ and does not dissolve.

Therefore, zinc in the aqueous solution using a weakly acidic solution containing a low concentration of acid and leached under an appropriate pH is mostly present as a metal ion, while fluorine and impurity metal components (Ni, Pb, Cr, Fe, Si), etc., remain in a solid state. Therefore, the solid-liquid separation can remove a considerable amount of fluorine and impurity metal components (Ni, Pb, Cr, Fe).

However, a small amount of the second group impurity such as Pb component and Cd component, which were not spinnelized, is mixed in the aqueous zinc solution, so it must be removed.

That is, the dust containing the metal component zinc is thrown into the aqueous zinc solution separated and filtered as described above to remove the second group impurities.

The second group impurity is contained in the aqueous zinc solution, and impurities such as Pb, Cd, and the like that can be removed by adding dust containing zinc of a metal component.

Since the Pb and Cd ions are electrochemically precious metal ions, administration of a dust component containing metal zinc results in substitution precipitation of zinc with the metal Pb and Cd by the following reaction, which can be completely removed during filtration separation. have.

Scheme 4

(Pb, Cd) Cl ₂ + Zn = (Pb, Cd) ⁰ + ZnCl ₂

The dust containing zinc as a metal component to remove lead and cadmium is not particularly limited, but zinc slime generated from dust or electro zinc plating processes having a metal zinc content of 40 to 90% obtained during the smelting of metal zinc ( Zinc ball residues).

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.

On the other hand, when the secondary dust contains a third group impurities such as Mn, Mg, etc. as described above, by adding an alkali agent to the aqueous solution from which the second group impurities have been removed, neutralizing and precipitating zinc and the third group impurities with hydroxides. The step of filtering the aqueous solution to obtain neutral salts and chlorides may optionally be added.

This will be described as follows.

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

The zinc oxide thus produced was very dark in color and was only 95% pure in zinc oxide analysis.

As a result of investigating this cause, Mn, Mg, etc. were contained in the zinc aqueous solution which removed lead and cadmium as mentioned above.

The said Mn was a big cause of the whiteness fall, and the said Mg was a big cause of the fall of purity. Therefore, in order to remove said Mn and Mg, a separate purification process is performed.

That is, an alkali 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, Mg) with hydroxides.

For example, when slaked lime is administered as an alkali agent to the aqueous zinc solution, the following neutralization reactions occur.

MCl ₂ + ZnCl ₂ + Ca (OH) ₂ = M (OH) ₂ + Zn (OH) ₂ + CaCl ₂ (Mn, Mg, Si)

That is, not only zinc ions but also manganese and magnesium precipitate as hydroxides.

Next, neutralized salt (CaCl ₂ ) and chloride in the aqueous solution are removed by filtration.

The chloride was contained in the dust.

The neutralized salt with, for example, there may be mentioned, such as CaCl _2, the chloride with, for example, there may be mentioned, such as KCl.

Neutralization salts such as calcium chloride are present in the ionic phase and can be removed completely by washing with water.

That is, KCl introduced from the dust component in addition to calcium ions is also removed in this washing and filtration process.

If calcium ions are not washed with water, subsequent strong alkali leaching efficiency will be reduced.

This is because the following reaction occurs to increase the consumption of caustic soda, a subsequent strong alkali precipitant.

Scheme 5

CaCl ₂ + 2NaOH = Ca (OH) ₂ + 2NaCl

On the other hand, the alkali agent (neutralizing agent), although not particularly limited, it is preferable to use hydrated lime, because it is the cheapest among the alkaline agents for making a removable salt called calcium chloride.

In particular, when slaked lime is used as an alkali agent, slaked lime has an effect of aggregating trace amounts of Si impurities present in addition to Mn and Mg in the solution in the form of CaO · SiO ₂ , thereby achieving a Si removal effect.

The third group impurity is contained in the aqueous zinc solution, and, for example, Mn and Mg may be mentioned as impurities which form a hydroxide when an alkali agent is added.

Next, NaOH is added to the aqueous solution from which the third group impurities are removed as described above, and the zinc is dissolved in an aqueous alkaline zinc solution at a pH of 14 or more, preferably in a range of 14-15, and filtered.

At this time, leaching is preferably performed at a high temperature of 30 to 95 ° C, for example.

On the other hand, when the process of removing the third group impurity as described above is added to the neutralized precipitate (zinc, manganese, magnesium hydroxide) and neutralized salts such as CaCl ₂ and the like to remove the pH is 14 or more, preferably The pH is leached in the range of 14-15, dissolving zinc in an aqueous alkaline zinc solution and filtering.

As described above, when NaOH is added to the neutralized precipitate and leached, only zinc is dissolved in an aqueous alkaline zinc solution.

Filtration can separate the zinc-containing alkaline solution and impurities such as manganese and magnesium hydroxide sludge.

When the leaching pH is less than 14, zinc dissolution is incomplete and the zinc leaching recovery rate is low. Therefore, the leaching should be performed under the condition of strong alkali pH of 14 or more.

In leaching, zinc obtained by leaching strong alkalis with a pH above 14 is present in the following form:

Scheme 6

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

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

Warm up to speed up leaching.

It is preferable to perform the said leaching at high temperature of 30-95 degreeC, for example.

If the leaching temperature is less than 30 ℃, the leaching rate is bad. If the temperature exceeds 95 ℃, it is difficult to select the filtration material because it is strong alkali.

Next, zinc oxide (ZnCl ₂ ) is added to the aqueous alkali zinc solution obtained by the reaction formula (6) so that the ratio of the number of moles of OH and the number of moles of zinc is 2.0-3.0. The following reaction occurs and zinc oxide is directly crystallized from the aqueous solution.

Scheme 7

ZnNa ₂ (OH) ₄ + 4NaOH + 2ZnCl ₂ = 3ZnO + 2NaOH + 4NaCl (OH: zinc molar ratio = 8/3)

When the ratio of the number of moles of OH to the number of zinc is 2.0 or less, zinc oxide is not produced without zinc oxide, and when the ratio is more than 3.0, ZnO production yield is reduced due to alkali dissolution of zinc.

Since the purity of zinc chloride is directly related to the purity of zinc oxide, it is preferable to use zinc chloride for industrial high purity (> 99%).

In particular, the high-purity zinc chloride is Ni + Cr + Pb + Cd + Mn + Mg + F + Si <0.5% by weight of zinc chloride by reacting zinc chloride aqueous solution or zinc by-product obtained by purifying waste zinc plating solution with hydrochloric acid Aqueous zinc chloride solution can be used.

As the high purity zinc chloride, a secondary dust obtained by secondary evaporation of carbon steel dust as a zinc by-product is used, and the secondary dust is reacted with an acid to form Ni + Cr + Pb + Cd + Mn + relative to the dry weight of zinc chloride. An aqueous zinc chloride solution purified to be Mg + F + Si <0.5 wt% may be used.

The purified high purity zinc oxide sludge is washed with water to remove NaCl, and the high purity zinc oxide sludge is filtered and dried.

The sludge may be prepared in the form of a cake.

The sludge is preferably dried after washing with water and filtration once or more.

The zinc oxide sludge dried as described above may be pulverized and used in powder form.

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

(Example 1)

After dissolving 100 g of the secondary dust generated in the recycling process of the stainless by-product having the composition shown in Table 1 with 1 liter of concentrated hydrochloric acid (35%) and 50% 1 liter of caustic soda, the undissolved sludge was filtered and removed. The amount of elution and impurities were analyzed and the results are shown in Table 2 below.

On the other hand, after dissolving 100 g of secondary dust in water to make a 7.5% aqueous solution of hydrochloric acid concentration was added to the dust mixed solution and leached for 2 hours.

At this time, the hydrochloric acid input rate was adjusted to range the leaching pH to 1.5-6.5.

The amount of hydrochloric acid added varies depending on the leaching pH, and the leaching solution is fixed to 1 liter by changing the amount of the final water.

After the leaching reaction, the undissolved sludge and the leachate were separated by filtration.

The amount of zinc eluted in the leaching solution and the degree of impurities were analyzed by ICP and the results are shown in Table 2 below.

TABLE 2

Specimen No.	Leaching condition			Zinc and impurity concentrations (g / liter)
Specimen No.	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
Inventive Example 1	HCl	15%	4.1	28.4	0.12	0.10	0.11	0.28	0.25	0.3
Inventive Example 2	HCl	10%	5.2	25.8	0.05	0.08	0.10	0.23	0.12	0.28
Comparative Example 4	HCl	3%	6.2	7.7	0.02	0.05	0.08	0.11	0.10	0.24

In Table 2 above, Tr. Represents Tr. &Lt; 0.01 g / liter.

As shown in Table 2, leaching with alkaline agent (Comparative Example 2) allows leaching in high concentration caustic soda, but the amount of zinc leaching is only 83% (25.0 / 30.1) compared to high concentration hydrochloric acid leaching (Comparative Example 1), and Pb and Si, which are difficult to leach and purify, are leached in large amounts (Comparative Example 2).

As described above, the reason why zinc leaching rate is lowered during alkali leaching of dust is because leaching reaction of zinc oxide in dust [Reaction Formula (8)] is not leaching from hydroxide as in Reaction Formula (6). to be.

Scheme 8

ZnO + 6NaOH = Zn0Na ₂ (OH) ₃ + 4NaOH

Therefore, lowering the alkali concentration is not preferable because the zinc leaching rate is extremely reduced (Comparative Example 3).

On the other hand, in the case of hydrochloric acid leaching, if the leaching pH is low using concentrated hydrochloric acid (35%), the leaching rate is good. It is difficult to control and is not preferable because the sludge increase due to Fe, Mn, F impurities in the subsequent step (Comparative Example 1).

Therefore, when the acid concentration is lowered and leached at pH = 4-6, the zinc leaching rate is also good and the impurity content is drastically reduced, which is advantageous for the subsequent impurity removal process (Invention Examples 1 and 2).

If the acid concentration is too low and the retention pH is high, the leaching time is long and the target zinc concentration cannot be obtained (Comparative Example 4).

(Example 2)

The amount of by-products having different metal zinc contents was added to 1 liter of the leachate prepared in the best conditions (inventive example 1, comparative example 5) in terms of zinc leachate and impurity content in the leachate of Example 1 (unit: gram), type, zinc The elution amount and impurity of zinc in the leachate were added by metal concentration (unit: weight%) by ICP, and the results are shown in Table 3 below.

TABLE 3

Psalm No.	Heavy metal removal condition			Zinc and impurity concentrations (g / liter)
Psalm No.	Kinds	Zinc Metal Concentration	Input amount (g)	Zn	Mg	Fe	Ni	CD	Pb	Mn
Comparative Example 5	-	-	-	28.4	2.4	0.28	0.1	0.28	0.25	0.3
Inventive Example 3	Plated sludge	65%	4	29.2	2.4	0.1	0.05	Tr.	Tr.	0.3
Inventive Example 4	Smelting Dust	50%	4	29.1	2.4	0.1	0.06	Tr.	Tr.	0.3
Comparative Example 6	Smelting Dust	35%	6	29.0	2.4	0.2	0.09	0.2	0.2	0.3
Inventive Example 5	Smelting Dust	80%	3	29.2	2.4	0.1	0.02	Tr.	Tr.	0.3

In Table 3, Tr. Represents Tr. <0.01 g / liter.

As shown in Table 3, compared to the untreated sample (Comparative Example 5), it can be seen that dust and sludge having a zinc metal content of 40% or more have a clear effect of Pb and Cd removal.

On the other hand, in the case of smelting dust (Comparative Example 6) having a zinc content of less than 40%, the absolute amount of zinc metal (6 g * 0.35 = 2.1 g) is higher than that of Inventive Material 4, but it can be seen that there is little effect of removing Pb and Cd.

In other words, when the metal zinc has a large amount of oxides or the like and the metal content is lowered to a certain amount or less, the heavy metal removal effect is hardly seen.

The absolute dose of zinc metal should be at least as high as the sum of the moles of Cd and Pb to be removed, as shown in Scheme (4).

(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.

Mn was a major cause of whiteness deterioration and Mg was a major cause of purity deterioration.

Therefore, a separate purification process for removing Mn and Mg was introduced.

In other words, an alkali was added to the purified aqueous solution from which lead and cadmium were separated, and the impurity metal components (Mn, Mg) including zinc were neutralized and precipitated with hydroxides.

Thereafter, neutralized salt (CaCl ₂ ) and chlorides such as KCl contained in the dust were removed by filtration, and NaOH aqueous solution was added to 100 g (neutral weight: 65 g because of 35% water content) of the neutralized precipitate obtained in the filtration separation step. After leaching at high temperature, the zinc was dissolved in an aqueous alkaline zinc solution.

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

Table 4

	Leaching condition				Zinc and impurity concentrations (g / liter)
	corrector	Leaching agent	Temperature ( ^oC )	pH	Zn	Si	Ni	Cr	Fe	Pb	Mn
Comparative Example 7	NaOH	Ca (OH) ₂	80	12.5	0.3	0.05	Tr.	Tr.	Tr.	Tr.	Tr.
Inventive Example 6	Ca (OH) ₂	NaOH	80	14.5	39.1	0.01	Tr.	Tr.	Tr.	Tr.	Tr.
Comparative Example 8	NaOH	NaOH	80	14.5	39.1	0.10	Tr.	Tr.	Tr.	Tr.	Tr.
Comparative material 9	Ca (OH) ₂	NaOH	25	14.5	28.4	0.01	Tr.	Tr.	Tr.	Tr.	Tr.
Comparative Material 10	Ca (OH) ₂	NaOH	60	13.5	15.4	0.01	Tr.	Tr.	Tr.	Tr.	Tr.
Invention Material 7	Ca (OH) ₂	NaOH	45	14.8	40.0	0.01	Tr.	Tr.	Tr.	Tr.	Tr.

In Table 4, Tr. Represents Tr <0.01 g / liter.

As shown in Table 4, when Ca (OH) ₂ is used as a leaching agent, the leaching pH is low and zinc elution hardly occurs (Comparative Material 7).

In addition, the use of NaOH as a neutralizing agent is very undesirable because the removal of Si is too slow to reach the target Si concentration (Comparative Material 8), even if the temperature is low (Comparative Material 9) or the leaching pH is low (Comparative Material 10). It can be seen that the leaching efficiency is very low.

Therefore, using a lime as a neutralizing agent and NaOH as an alkali leaching agent so that the leaching pH is 14 or more and the leaching temperature is preferably 30 ^° C or more.

If the leaching temperature exceeds 90 ^o C, problems of the material of the equipment occur, so the leaching temperature is preferably 30 ^o C-90 ^o C (inventive material 6,7), and zinc leaching rate by alkali leaching (dissolved zinc Amount / amount of zinc in the hydroxide before the reaction) is almost 100% so that there is almost no zinc in the leach residue.

(Example 4)

To the strong alkali zinc leaching solution of Table 4, high-purity zinc chloride was added to 2.0-3.0 while controlling the ratio of OH mole number: zinc mole number to make white zinc. After drying, the zinc oxide was a single phase of zinc oxide and was purified by XRF. As a result, more than 99.5% of high purity zinc oxide.

When the ratio of the number of moles of OH: number of zinc in the scheme 7 is less than 2.0, zinc oxide is not produced and zinc hydroxide is formed.

If the ratio of moles of OH to number of zinc is 3.0 or more, zinc ions are lost during washing due to alkali dissolution of zinc, resulting in a decrease in ZnO production yield.

On the other hand, high-purity zinc chloride for the synthesis of zinc oxide is an aqueous zinc chloride solution obtained by purifying the waste zinc plating solution (Korean Patent Application No. 1998-0056706, Korean Patent Registration No. 409951), that is, Zn in waste liquid in an electro zinc plating waste solution. It is also possible to administer moles of KOH corresponding to 1 / 200-1 / 50 of the moles and to prepare a purified high purity zinc chloride aqueous solution. Also known as RHF (Rotary Hearth Furnace), one of zinc by-products, for example, high concentration zinc oxide dust. ) High zinc concentration (> Zn 40%) dust obtained by evaporation of carbon steel dust as dust is reacted with hydrochloric acid to refine Ni + Cr + Pb + Cd + Mn + Mg + F + Si <0.5 wt% It is preferable to use zinc chloride to reduce the cost of using byproducts rather than to use industrial high purity zinc.

Particularly, the secondary dust generated when the carbon steel dust is recycled through RHF (Rotary Hearth Furnace) has extremely low Mn and Mg content, so that the first group impurities and the second group impurities that are mixed in the recycling process after acid dissolution are dissolved. Even through purification, zinc chloride of good purity can be obtained.

Claims

Leaching secondary dust generated in the process of recycling stainless dust with an acidic aqueous solution to selectively dissolve zinc to form a zinc aqueous solution;

Filtering the zinc aqueous solution and the residue to separate and remove the first group impurities from the aqueous zinc solution;

Removing the second group impurities by inputting dust containing zinc of a metal component into an aqueous solution in which the first group impurities are removed as described above;

NaOH is added to the aqueous solution from which the second group impurities are removed as described above, dissolving zinc in an aqueous alkaline zinc solution and filtering under a condition of pH 14 to 15;

Preparing a high purity zinc oxide sludge directly in an aqueous solution by adding a high purity zinc chloride to an aqueous alkaline zinc solution so that the ratio of the number of moles of zinc to the number of moles of zinc is 2.0-3.0;

Washing with high purity zinc oxide sludge to remove NaCl; And

Method for producing high purity zinc oxide using secondary dust comprising the step of filtering and drying the high purity zinc oxide sludge.
The method of claim 1, wherein before the step of directly preparing a high purity zinc oxide sludge in an aqueous solution by adding high purity zinc chloride to the aqueous alkali zinc solution,

Neutralizing and precipitating zinc and the third group of impurities with a hydroxide by adding an alkali agent to the aqueous solution from which the second group of impurities have been removed, filtering the aqueous solution to obtain neutral salts and chlorides, and adding NaOH to the neutralizing precipitate thus obtained, The method for producing high purity zinc oxide using secondary dust, characterized in that the addition of the step of dissolving zinc in an aqueous alkaline zinc solution and filtering under conditions of 14 to 15.
The method for producing high purity zinc oxide using secondary dust according to claim 1, wherein the acidic aqueous solution for leaching the secondary dust is one of hydrochloric acid, sulfuric acid and nitric acid aqueous solution.
The method for producing high purity zinc oxide using secondary dust according to claim 2, wherein the acidic aqueous solution for leaching the secondary dust is one of hydrochloric acid, sulfuric acid and nitric acid aqueous solution.
The acidic aqueous solution for leaching the secondary dust is an aqueous hydrochloric acid solution, the aqueous hydrochloric acid solution contains 5-18% hydrochloric acid, and the leaching pH is 4-6. Method for producing high purity zinc oxide.
5. The method according to claim 4, wherein the acidic aqueous solution for leaching the secondary dust is an aqueous hydrochloric acid solution, the aqueous hydrochloric acid solution contains 5-18% hydrochloric acid, and the leaching pH is 4-6. Method for producing high purity zinc oxide.
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 two of lead and cadmium. Method for producing high purity zinc oxide using secondary dust.
3. The method of claim 2, 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 two of lead and cadmium, and The third group impurity is one or two of manganese and magnesium, the method of producing high purity zinc oxide using secondary dust.
The method according to claim 1, wherein the secondary dust is leached into an acidic aqueous solution, and the residue (sludge) separated from the zinc aqueous solution in which zinc is selectively dissolved is subjected to acid washing and filtration. The filtrate obtained by filtration is filtered into the aqueous zinc solution. A method for producing high purity zinc oxide using secondary dust, characterized in that it is added and used.
The method according to claim 2, wherein the secondary dust is leached into an acidic aqueous solution, and the residue (sludge) separated from the zinc aqueous solution in which zinc is selectively dissolved is acid washed with water and filtered, and the filtrate obtained by the filtration is filtered into the aqueous zinc solution. A method for producing high purity zinc oxide using secondary dust, characterized in that it is added and used.
8. The method for producing high purity zinc oxide using secondary dust according to claim 7, wherein the content of metal zinc in zinc-containing dust or sludge to remove one or two of the lead and cadmium is 40-90%. .
The method for producing high purity zinc oxide using secondary dust according to claim 8, wherein the content of metal zinc in zinc-containing dust or sludge to remove one or two of the lead and cadmium is 40-90%. .
12. The method of claim 11, wherein the zinc-containing dust is dust obtained in the process of smelting metal zinc, and the zinc-containing sludge is obtained from the zinc ball residue of the electro-galvanizing process, high purity oxidation using secondary dust. Method of producing zinc.
The method of claim 12, wherein the zinc-containing dust is dust obtained in the process of smelting metal zinc, and the zinc-containing sludge is obtained from the zinc ball residue of the electro-galvanizing process, high purity oxidation using secondary dust. Method of producing zinc.
The method for producing high purity zinc oxide using secondary dust according to claim 2, wherein the alkali agent for neutralizing and precipitating zinc and the third group impurities with hydroxide is hydrated lime.
The method for producing high purity zinc oxide using secondary dust according to claim 2, wherein the neutralizing salt is CaCl 2 , and the chloride is KCl.
The method according to any one of claims 1 to 16, wherein the high purity zinc chloride reacts with hydrochloric acid in an aqueous solution of zinc chloride and zinc by-product obtained by purifying a waste zinc plating solution, and thus, Ni + Cr + Pb + Cd +. A method for producing high purity zinc oxide using secondary dust, characterized in that the Mn + Mg + F + Si <0.5% by weight in one of the aqueous zinc chloride purified.
18. The method of claim 17, wherein the high-purity zinc chloride is a secondary dust obtained by secondary evaporation of carbon steel dust as zinc by-product, and reacted with hydrochloric acid to react the secondary dust with Ni + Cr + Pb +. Cd + Mn + Mg + F + Si <0.5 wt% A method for producing high purity zinc oxide using secondary dust, characterized in that the aqueous zinc chloride purified.