Method for producing zinc oxide

Abstract

To recover zinc with a permissible purity for downstream purification, while reducing total waste liquid amount in producing high-concentration zinc oxide from a stock solution containing zinc, chlorine, and organic solvent.SOLUTION: The present invention provides a method for producing zinc oxide and related technologies, the method including: a mixing step of mixing a stock solution containing zinc, chlorine, and an organic solvent with a hydroxide salt solution to adjust the pH of the mixture to 9 or higher; a solid-liquid separation step of recovering precipitates obtained in the mixing step; a drying step of heating to remove the organic solvent contained in the precipitates; and a water washing step of washing the solid matter obtained in the drying step with water.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing zinc oxide.

Background Art

[0002] Claim 1 of Patent Document 1 describes that zinc is recovered by adding sodium carbonate to a zinc chloride solution having a high chlorine concentration while restricting the aluminum concentration in the solution to precipitate basic zinc carbonate under a liquid property of pH 6 or higher.

[0003] Paragraph 0028 of Patent Document 1 describes the following content. Sodium carbonate is added to a zinc-containing hydrochloric acid solution in which the aluminum concentration has been reduced to 200 mg / L or less, and the mixture is stirred and adjusted to pH 6 or higher, preferably pH 8 or higher. The zinc compound contained in the solution is hydrolyzed to form a precipitate of basic zinc carbonate [Zn5(CO3)2(OH)6]. Most of the aluminum in the solution and the sodium from sodium carbonate remain in the solution, and the amount mixed into the precipitate is small, generally 0.1 wt% (expressed as mass% in this specification) or less.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a result of investigations by the present inventors, the following problems have been clarified.

[0006] When the solution to be treated, which contains zinc and chlorine, consists only of an aqueous phase as in the examples of Patent Document 1, if the technique described in Patent Document 1 is used, the amount of precipitated sodium mixed in is small.

[0007] On the other hand, according to the investigation by the present inventors, when the solution to be treated contains a large amount of an organic solvent such that the organic solvent forms a phase, even if the technique described in Patent Document 1 is used, the dissolution of sodium carbonate is inhibited due to the coexistence of the organic solvent, and thus it has been revealed that it is difficult to produce zinc carbonate. In this specification, the solution to be treated is also referred to as the stock solution.

[0008] To promote the dissolution of sodium carbonate, it is possible to add water, but this is not preferable because the amount of waste liquid containing the organic solvent increases during zinc recovery.

[0009] Also, when the reaction system contains an organic solvent, it has been found that the recovered zinc also contains the residual organic solvent. These organic solvents are not preferable because they inhibit the purification of zinc in the subsequent process.

[0010] In response to this new problem, the present inventors further studied. To remove the remaining organic solvent, it was considered effective to introduce a drying process to remove the organic solvent. However, as will be described later, the removal of the organic layer from zinc carbonate requires a high drying temperature, which is not preferable.

[0011] In response to this new problem, the present inventors further studied. To remove the remaining organic solvent, it was considered effective to introduce a water washing process to remove the organic solvent. However, as will be described later, it was difficult to reduce the amount of sodium mixed into zinc by water washing. This is presumably because the coexistence of the organic solvent inhibits the dissolution of unreacted sodium carbonate. These sodiums are not preferable because they inhibit the purification of zinc in the subsequent process.

[0012] From the above, it has been found that when the stock solution to be treated contains a large amount of an organic solvent such that the organic solvent forms a phase, the zinc concentration as expected from the examples in Patent Document 1 where the treatment target consists only of an aqueous phase cannot be obtained.

[0013] An object of the present invention is to provide a technique for recovering zinc with a purity acceptable in a subsequent purification step while suppressing the total amount of waste liquid when obtaining high-concentration zinc oxide from a stock solution containing zinc, chlorine, and an organic solvent. **Means for Solving the Problems**

[0014] A first invention for solving the above problems is a mixing step of mixing a stock solution containing zinc, chlorine, and an organic solvent with a hydroxide salt solution to make the pH of the mixed solution 9 or more; a solid-liquid separation step of recovering the precipitate obtained in the mixing step; a drying step of heating and removing the organic solvent contained in the precipitate; a water washing step of washing the solid obtained in the drying step with water; and is a method for producing zinc oxide.

[0015] A second invention is the method for producing zinc oxide according to the first invention, wherein the hydroxide salt is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide.

[0016] A third invention is the method for producing zinc oxide according to the first or second invention, wherein the heating temperature in the drying step is 100°C or more and less than 250°C.

[0017] A fourth invention is the method for producing zinc oxide according to any one of the first to third inventions, wherein the stock solution contains 10% or more of zinc by mass ratio.

[0018] A fifth invention is the method for producing zinc oxide according to any one of the first to fourth inventions, wherein the stock solution contains 10 to 25% of zinc by mass ratio.

[0019] A sixth invention is the method for producing zinc oxide according to any one of the first to fifth inventions, wherein the organic solvent contains alcohol.

[0020] The seventh invention is wherein the water washing step is a repulping step of crushing the obtained solid matter and stirring and washing it with water in an amount in the range of a solid-liquid mass ratio of 1:1 or more, a dehydration step of dehydrating the solid matter obtained in the repulping step, a washing step of passing water through the dehydrated matter obtained in the dehydration step and washing it, and is a method for producing zinc oxide according to any one of the first to sixth inventions having the above steps.

[0021] The eighth invention is wherein the heating temperature in the drying step is 100°C or more and less than 250°C, the stock solution contains 20 to 50% of zinc by mass ratio, the volume ratio of the organic solvent to the stock solution is 0.45 or more, the organic solvent mainly contains alcohol, the hydroxide salt mainly contains sodium hydroxide, wherein the water washing step is a repulping step of crushing the obtained solid matter and stirring and washing it with water in an amount in the range of a solid-liquid mass ratio of 1:1 or more, a dehydration step of dehydrating the solid matter obtained in the repulping step, a washing step of passing water through the dehydrated matter obtained in the dehydration step and washing it, and is a method for producing zinc oxide according to any one of the first to seventh inventions having the above steps.

Advantages of the Invention

[0022] According to the present invention, when obtaining high-concentration zinc oxide from a stock solution containing zinc, chlorine, and an organic solvent, it is possible to recover zinc with a purity acceptable in the subsequent purification process while suppressing the total amount of waste liquid.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0024] Hereinafter, this embodiment will be described. "~" indicates a value greater than or equal to a predetermined numerical value and less than or equal to a predetermined numerical value. This embodiment will list the overall configuration and then list other preferred examples and specific examples.

[0025] Figure 1 is a flowchart of a method for manufacturing zinc oxide according to this embodiment.

[0026] The method for manufacturing zinc oxide according to this embodiment includes a mixing step of mixing a stock solution containing zinc, chlorine, and an organic solvent with a hydroxide salt solution, a solid-liquid separation step of recovering a precipitate from the mixed solution after the mixing step, a drying step of heating and removing the organic solvent contained in the precipitate, and a water washing step of washing the solid obtained in the drying step with water.

[0027] Incidentally, when mixing a carbonate solution instead of a hydroxide salt solution, due to the organic solvent contained in the stock solution, the carbonate to be mixed in the mixing step will be difficult to dissolve in the stock solution without any treatment. Then, as described in Patent Document 1, it becomes difficult to generate zinc carbonate from the stock solution. To promote the dissolution of the carbonate, it is possible to add water, but the total amount of waste liquid in the neutralization step will increase.

[0028] On the other hand, in this embodiment, a hydroxide salt solution is mixed. In this case, regardless of the volume ratio of the organic solvent, a hydroxide salt equivalent to or more than the molar equivalent of zinc in the stock solution can be rapidly mixed. In particular, when the organic solvent is alcohol, sodium hydroxide and potassium hydroxide have high solubility in alcohol and can be rapidly dissolved. This means that the temperature of the stock solution to be treated can be normal temperature (for example, 25°C).

[0029] By mixing the hydroxide salt solution, when obtaining high-concentration zinc oxide from a stock solution containing zinc, chlorine, and an organic solvent, zinc with a purity acceptable in the subsequent purification process can be recovered while suppressing the total amount of waste liquid.

[0030] When the organic solvent contained in the stock solution described in the items of the examples shown below is alcohol (isopropyl alcohol (IPA), ethanol, or methanol), theoretically, the organic solvent can be removed at 100°C.

[0031] In the comparative example in the items of the examples shown below, sodium carbonate, which is a carbonate, is mixed in the mixing step. In the comparative example, the main component of the precipitate after the solid-liquid separation step and before the drying step is zinc carbonate (ZnCO3). In the example in the items of the examples shown below, an aqueous sodium hydroxide solution, which is a hydroxide salt solution, is mixed in the mixing step. In the example, the main component of the precipitate after the solid-liquid separation step and before the drying step is zinc hydroxide (Zn(OH)2).

[0032] Pyrolysis-gas chromatography / mass spectrometry (Py-GC / MS) was performed on the precipitate after the solid-liquid separation step and before the drying step in the comparative example where sodium carbonate was mixed. As a result, it was found that in the temperature range of 250 to 270°C, the volatilization of IPA occurred together with the release of CO2.

[0033] As described above, IPA usually volatilizes at 100°C. Nevertheless, the example described in the above paragraph means that, in other words, the volatilization of IPA is not completely carried out until the temperature range of 250 to 270°C is reached.

[0034] Among the temperature range of 250 to 270 °C, 250 °C overlaps with the temperature during the morphological change from zinc carbonate (ZnCO3) to zinc oxide (ZnO). That is, during this morphological change, it is presumed that, for example, the volatilization of IPA adsorbed to zinc carbonate (ZnCO3) scientifically or physically occurs.

[0035] Figure 2 is a diagram showing a TG curve (vertical axis: TGA (mg), horizontal axis: temperature (°C)) which shows the result of performing TG analysis (thermogravimetric measurement) on the precipitate after the solid-liquid separation step and before the drying step in the example of mixing an aqueous sodium hydroxide solution.

[0036] The weight loss starting from around 105 °C in Figure 2 according to the example is presumed to be due to the morphological change from zinc hydroxide (Zn(OH)2) to zinc oxide (ZnO) and the volatilization of the organic solvent adsorbed to zinc hydroxide (Zn(OH)2). Note that the morphological change from zinc hydroxide (Zn(OH)2) to zinc oxide (ZnO) is theoretically around 125 °C.

[0037] The present inventor focused on this point and found that in the example of the present invention where the morphological change from zinc hydroxide (Zn(OH)2) to zinc oxide (ZnO) starts from around 100 °C, the volatilization of IPA can be promoted in the vicinity of this temperature (even if it is as high as 180 °C).

[0038] That is, · Lowering the temperature of the morphological change from hydroxide to oxide by mixing a hydroxide salt solution · Residual organic solvent at 100 °C or higher · Removal of the organic solvent accompanying the morphological change from hydroxide to oxide Combining the above-mentioned multiple findings and the high solubility of the hydroxide salt solution in the organic solvent led to the conception of the present embodiment.

[0039] Figure 3 is a diagram showing XRD spectra (vertical axis: intensity, horizontal axis: 2θ (degrees)) when the pH of the mixed solution after the mixing step is set to 7.0, 9.0, and 12.0 in the recovered product obtained in the water washing step and the subsequent drying step.

[0040] In this embodiment, it is preferable to adjust the pH of the mixed solution to 9 or higher in the mixing step. If the pH is 9 or higher, most of the zinc-containing compounds in the recovered product obtained in the water washing step and the subsequent drying step will be zinc oxide (ZnO). When the pH is about 7, some Zn5(OH)8Cl2·H2O is generated together with zinc oxide (ZnO).

[0041] The temperature at which Zn5(OH)8Cl2·H2O transforms into zinc oxide (ZnO) is 500 to 600°C. Therefore, at a drying temperature of 100°C to 250°C for the purpose of removing the organic solvent, Zn5(OH)8Cl2·H2O cannot be transformed into zinc oxide (ZnO), resulting in the residual chlorine in the recovered zinc.

[0042] When chlorine remains in the recovered zinc, it will inhibit the purification of zinc in the subsequent process. Therefore, it is preferable to recover zinc at a pH that can suppress the generation of Zn5 (OH)8Cl2·H2O.

[0043] As a result, when the pH is 9 or higher, 10 or higher, 11 or higher, 12 or higher, or 13 or higher, high-concentration zinc hydroxide (Zn(OH)2) can be obtained, and high-concentration zinc oxide (ZnO) can be obtained by the drying step.

[0044] Hereinafter, other preferred examples and specific examples of the embodiment related to the method for manufacturing zinc oxide will be described.

[0045] In the mixing step, a stock solution containing zinc, chlorine, and an organic solvent is mixed with a hydroxide salt solution. There is no limitation on the "stock solution containing zinc, chlorine, and an organic solvent".

[0046] As an example of the stock solution, waste liquid generated in the manufacturing process of an organic synthesis catalyst or a refrigerant can be mentioned. Hereinafter, the stock solution will refer to this example. Specifically, a slurry in which zinc chloride and an organic solvent (alcohol) are mixed is treated as the stock solution to be processed by the method for manufacturing zinc oxide according to this embodiment.

[0047] Another example of the stock solution is the one described in Patent Document 1. That is, by heat-treating iron-making dust in a reduction furnace, a reduction roasting furnace, or the like, a metal oxide (crude zinc oxide) mainly composed of zinc can be obtained. This crude zinc oxide contains a large amount of chlorine. Then, this crude zinc oxide is heated to volatilize and separate it as a chloride containing lead and zinc, and the solution leached with warm water may be used as the stock solution.

[0048] There is no limitation on the pH of the stock solution. For example, in the case of the above slurry, the pH is less than 4 (or 1 or less). In the mixing step, a hydroxide salt (sodium hydroxide and / or potassium hydroxide) solution and the stock solution are mixed, and the pH of the stock solution (mixed solution) increases.

[0049] As a mode of mixing the hydroxide salt solution into the stock solution, a mode of adding the hydroxide salt solution to the stock solution may be used, or conversely, a mode of adding the stock solution to the hydroxide salt (water) solution may also be used. The powdery (solid) hydroxide salt and the stock solution may be mixed.

[0050] The stock solution may contain 10% or more (or 15% or more, 20% or more) of zinc by mass ratio. There is no limitation on the upper limit, and for example, 30% and 27.5% can be mentioned.

[0051] The stock solution may contain 20 - 50% in terms of zinc chloride (ZnCl2) conversion and 10 - 25% in terms of zinc conversion by mass ratio.

[0052] The volume ratio of the organic solvent to the stock solution may be 0.45 or more.

[0053] The organic solvent may contain alcohol and may mainly contain alcohol. There is no limitation on the specific composition of the alcohol. Examples of the alcohol include isopropyl alcohol, ethanol, methanol, etc. Hereinafter, the case where the alcohol is isopropyl alcohol (IPA) will be exemplified.

[0054] The hydroxide salt may be an alkali metal hydroxide and / or an alkaline earth metal hydroxide. The alkali metal hydroxide may be at least one selected from the group consisting of sodium hydroxide and potassium hydroxide, and the main component of the hydroxide salt may be sodium hydroxide. Hereinafter, the case where the hydroxide salt is sodium hydroxide will be exemplified.

[0055] The "main component" in this specification refers to the substance that contains a predetermined compound in the highest proportion of existence. As an example, it is a substance in which the proportion of the predetermined compound exceeds 50% by mass. The above definition of the main component is also applicable to the expression of the main component described below. When referring to the main component of an element, the above expression of the compound may be replaced with the element and applied.

[0056] Regarding the solid-liquid separation step, there is no limitation on the specific method as long as the precipitate can be recovered from the mixed solution after the mixing step. For example, known suction filtration, filter press, centrifugation, etc. may be used.

[0057] Regarding the drying step, there is no limitation on the specific method as long as the organic solvent can be removed by heating from the recovered precipitate, and there is also no limitation on the heating time and heating temperature. A known drying furnace may be used. The heating time may be, for example, 30 minutes (or 2 hours) to 5 hours. The heating temperature may be, for example, 80°C or higher (or 100°C or higher, preferably 180°C or higher, at which zinc oxide can be generated from zinc hydroxide) and 250°C or lower (or 200°C or lower), which is a temperature at which alcohol can be removed.

[0058] During the drying step, zinc hydroxide changes to zinc oxide while the organic solvent is removed. Even after passing through the subsequent water washing step, the main component of the solid is zinc oxide.

[0059] Regarding the water washing step, there is no limitation on the specific method as long as the solid obtained in the drying step can be washed with water.

[0060] The water washing process preferably includes a repulping process of crushing the obtained solid matter and stirring and washing it with water in an amount such that the solid-liquid mass ratio is 1:1 or more, a dehydration process of dehydrating the solid matter obtained by the repulping process, and a washing process of passing water through the dehydrated matter obtained by the dehydration process for washing. The solid-liquid mass ratio of 1:1 or more means an amount of water equal to or more than the same mass as the obtained solid matter. There is no upper limit to the amount of water, but examples of the upper limit include 1:12 or 1:8.

[0061] By the repulping process, impurities contained in the solid matter can be sufficiently removed from the solid matter. By the dehydration process and the washing process, impurities can be further removed from the solid matter. For the specific working contents of these processes, known methods may be adopted.

[0062] There is no limit to the number of times of the washing process, but from the viewpoint of concentrating zinc in zinc oxide obtained by sufficiently removing impurities from the solid matter, it is preferable to perform the washing process 5 times or more.

[0063] Incidentally, the definition of the number of times of this washing process may be defined from the relationship between the water retention amount of the cake and the amount of washing water. For example, in the washing process of Example 1 described below, the amount of water used per time is 500 mL, that is, the total amount of water used in the washing process is 2500 mL. However, calculating from the water retention amount of the solid matter that is the object of the washing process in Example 1, the amount of water per time for the number of times of water replacement contained in the solid matter is 420 mL. That is, when 2500 mL of the total water amount is divided by 420 mL, it is about 6. According to the above definition, in Example 1 described below, it can be said that the washing process was performed 6 times or more.

[0064] The water washing process in this embodiment is not limited to a specific configuration as long as impurities can be removed (desalted) from the obtained solid matter. As an example, it may include at least a repulping process, a subsequent dehydration process, and a subsequent washing process. For example, after passing through the dehydration process after the repulping process, the repulping process and the dehydration process may be performed again, and then the washing process may be performed. Also, after passing through the dehydration process after the repulping process, the washing process may be performed multiple times. Also, after performing the washing process multiple times, the repulping process and the dehydration process may be performed again.

[0065] When handling solids in a dry manner, it is necessary to separately perform crushing on the solids. On the other hand, along with performing a water washing step as in the method for producing zinc oxide according to the present embodiment, the solids are naturally crushed. In this regard as well, the method for producing zinc oxide according to the present embodiment has an advantageous effect.

[0066] An example of the specific content of the water washing step is as follows. Repulp in water to make it into a slurry and wash. When dehydrating using a pressure filter, after dehydration, water may be added to the cake and then re-dehydrated and washed. When dehydrating using suction filtration or a filter press, after dehydration, water may be sent to the cake for washing.

[0067] In the method for producing zinc oxide according to the present embodiment, after passing through a mixing step and then through a drying step for the precipitate recovered in the solid-liquid separation step, it is also one of the features to perform a water washing step again.

[0068] Due to this feature, the amount of sodium precipitate mixed in can be reduced to less than 1 / 6. That is, even if the stock solution to be treated contains a large amount of an organic solvent to the extent of forming a phase, zinc can be sufficiently concentrated.

[0069] The solid obtained after the water washing step (as an example, after the washing step) may be dried to obtain zinc oxide (drying step). The drying step may also serve as a dehydration step for the solid after the washing step. Alternatively, after separately performing a dehydration step after the water washing step to obtain a solid, a (second) drying step may be performed on the solid.

[0070] The technical scope of the present invention is not limited to the above-described embodiment, and also includes forms in which various changes and improvements are made within the scope where specific effects obtained by the constituent elements of the invention and their combinations can be derived.

Examples

[0071] Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. Also, the following comparative examples are not known examples.

[0072] (Example 1) A mixing step of a slurry (total amount 400 mL) containing zinc, chlorine and an organic solvent and sodium hydroxide was carried out. The details of the stock solution, which is the stock solution to be treated in this example, are as follows. · IPA: Containing 45% by mass · Zinc chloride: Containing 50% by mass · Liquid temperature: 25 °C (room temperature) · pH: 0.68

[0073] The grades and COD of zinc, chlorine, sodium, and fluorine in the stock solution are as shown in Table 1 below.

Table 1

[0074] An aqueous sodium hydroxide solution providing hydroxide ions in an amount equimolar to zinc was mixed with the slurry to form a precipitate of zinc hydroxide. The pH of the mixed solution (during neutralization) before the solid-liquid separation step was 11.1.

[0075] A solid-liquid separation step of recovering the precipitate from the mixed solution after the mixing step was carried out by suction filtration.

[0076] Thereafter, as a drying step, without washing the precipitate, it was heated and dried in a heating furnace at 300 °C for 6 hours.

[0077] Water (2.1 L) in an amount such that the solid-liquid mass ratio was 1:10 was used, and the solid obtained after drying and heating was repulped (re-pulped again) and washed with running water (repulping step). Thereafter, it was dehydrated by suction filtration (dehydration step), and further washed with running water 5 times using water (0.5 L) in an amount such that the solid-liquid mass ratio was 1:1 (washing step).

[0078] The solid matter after the washing process was dried overnight at 105 °C in a dryer. The solid matter obtained after drying was measured in the same manner as described above.

[0079] The grades of zinc, chlorine, sodium, and fluorine and the COD in the solid matter are as shown in Table 2 below. Also, the grade of fluorine and the COD in the post-liquid after the repulping process are also shown in Table 2 below. Table 2 below also shows each example in the items of the examples.

Table 2

[0080] In this example, TG analysis (thermogravimetric measurement) was performed on the precipitate before the drying process. As a result, weight loss occurred at 100 °C or higher. This is presumably due to the change in form from zinc hydroxide to zinc oxide. When XRD analysis was performed on the precipitate after the drying process, zinc oxide was confirmed. Therefore, it was confirmed that in this example through the above drying process, zinc oxide was finally obtained.

[0081] (Comparative Example 1) A mixing process was performed between the slurry (total volume 400 mL) used as the stock solution in Example 1 and an aqueous sodium carbonate (soda ash) solution (total volume 2400 mL).

[0082] An aqueous sodium hydroxide solution providing hydroxide ions in an amount equivalent to the molar amount of zinc was mixed with the slurry to form a precipitate of zinc hydroxide.

[0083] A solid-liquid separation process for recovering the precipitate from the mixed solution after the mixing process was performed by suction filtration.

[0084] Thereafter, using water (2.1 L) in an amount such that the solid-liquid mass ratio was 1:10, the precipitate was repulped (repulped again) and washed with running water (repulping process). Thereafter, it was dehydrated (dehydration process), and further washed with running water 5 times using water (0.5 L) in an amount such that the solid-liquid mass ratio was 1:1 (washing process).

[0085] Thereafter, as a drying process, the obtained solid was heated and dried in a heating furnace at 300 °C for 5 hours.

[0086] (Comparative Example 2) A solid was obtained in the same manner as in Comparative Example 1, except that the drying process in Comparative Example 1 was performed at 800 °C for 2 hours.

[0087] In Comparative Example 1 where the conditions of the drying process were 300 °C and 5 hours, sodium was 6.5% as an analytical value of the produced zinc oxide. This was more than 100 times the value of 0.04% in Example 1. Also, fluorine was 0.3%. This was 5 times the value of 0.06% in Example 1. Also, COD was 0.36 mg / g. This was 7 times the value of 0.05 mg / g in Example 1.

[0088] In Comparative Example 2 where the conditions of the drying process were 800 °C and 2 hours at high temperature, sodium was 6.9% as an analytical value of the produced zinc oxide. This was more than 100 times the value of 0.04% in Example 1.

[0089] (Example 2) A mixing step of a slurry (total amount 400 mL) containing zinc, chlorine and an organic solvent and sodium hydroxide was performed. The details of the stock solution to be treated in this example are as follows. Contents not described below are the same as in Example 1. · IPA: containing 5% by mass · Zinc chloride: containing 30% by mass · Ethanol: containing 55% by mass · Methanol: containing 10% by mass · Liquid temperature: 25 °C (room temperature) · pH: 1.0

[0090] An aqueous sodium hydroxide solution providing hydroxide ions in an amount equivalent to the molar amount of zinc was mixed with the slurry to form a precipitate of zinc hydroxide. The pH of the mixed solution (at the time of neutralization) before the solid-liquid separation step was 13.1.

[0091] (Reference Example 1) The reference example described below is an example in which a slurry containing zinc and chlorine but not containing an organic solvent to the extent of forming an organic solvent is the treatment target.

[0092] A mixing step of a slurry containing zinc and chlorine (total amount 400 mL) and sodium hydroxide was performed. The details of the stock solution to be treated in this example are as follows. The main component of the stock solution is water. The content not described below is the same as in Example 1. ·Zinc chloride: Containing 30% by mass ·Liquid temperature: 25 °C (room temperature) ·pH: 1.0

[0093] An aqueous sodium hydroxide solution providing hydroxide ions in an amount equivalent to the moles of zinc was mixed with the slurry to form a precipitate of zinc hydroxide. The pH of the mixed solution (during neutralization) before the solid-liquid separation step was 6.7.

[0094] (Reference Example 2) In Reference Example 2, an aqueous sodium carbonate solution was used instead of the aqueous sodium hydroxide solution in Reference Example 1. And the temperature of the stock solution was raised to 40 °C. Otherwise, it was the same as in Example 2. The pH of the mixed solution (during neutralization) before the solid-liquid separation step was 5.5.

[0095] When the stock solution does not contain an organic solvent, even if there is a difference in the temperature of the stock solution, zinc can be concentrated more when using an aqueous sodium carbonate solution than when using an aqueous sodium hydroxide solution. On the other hand, as shown in the above examples and comparative examples, when the stock solution contains an organic solvent, the result is reversed. This reversed relationship is also one of the factors that gave rise to the present invention.

Claims

1. A mixing step of mixing a stock solution containing zinc, chlorine, and an organic solvent with a hydroxide salt solution to make the pH of the mixed solution 9 or higher; A solid-liquid separation step of recovering the precipitate obtained in the mixing step; A drying step of heating and removing the organic solvent contained in the precipitate; A water washing step of washing the solid obtained in the drying step with water; A method for producing zinc oxide, comprising the above steps.

2. The method for producing zinc oxide according to claim 1, wherein the hydroxide salt is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide.

3. The method for producing zinc oxide according to claim 1 or 2, wherein the heating temperature in the drying step is 100°C or higher and less than 250°C.

4. The method for producing zinc oxide according to claim 1 or 2, wherein the stock solution contains 10% or more of zinc by mass ratio.

5. The method for producing zinc oxide according to claim 1 or 2, wherein the stock solution contains 10 - 25% of zinc by mass ratio.

6. The method for producing zinc oxide according to claim 1 or 2, wherein the organic solvent contains alcohol.

7. The water washing step includes: A repulping step of crushing the obtained solid and stirring and washing with water in an amount in the range of a solid-liquid mass ratio of 1:1 or more; A dehydration step of dehydrating the solid obtained in the repulping step; A washing step of washing the dehydrated product obtained in the dehydration step by passing water through it. The method for producing zinc oxide according to claim 1 or 2, comprising the above steps.

8. The heating temperature in the drying step is 100°C or higher and less than 250°C; The stock solution contains 10 - 25% of zinc by mass ratio; The volume ratio of the organic solvent to the stock solution is 0.45 or more; The organic solvent mainly contains alcohol; The hydroxide salt mainly contains sodium hydroxide; The water washing step includes: A repulping step of crushing the obtained solid and stirring and washing with water in an amount in the range of a solid-liquid mass ratio of 1:1 or more; A dehydration step of dehydrating the solid obtained in the repulping step; A washing step of washing the dehydrated product obtained in the dehydration step by passing water through it. The method for producing zinc oxide according to claim 1 or 2, comprising the above steps.

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