Production method for zinc hydroxide

Abstract

To obtain high-quality zinc hydroxide from a stock solution containing zinc, chlorine, and an organic solvent without causing scale in a dryer.SOLUTION: A production method for zinc hydroxide includes: a mixture step of mixing a stock solution containing zinc, chlorine, and an organic solvent with an aqueous solution of an alkali metal hydroxide so that the resultant mixture liquid has a pH of 9 or more; an organic solvent recovery step of, after the mixture step, recovering the organic solvent as upper liquid from the mixture liquid; a repulp step of stirring slurry remaining after the organic solvent recovery step with water; a dehydration step of dehydrating slurry obtained in the repulp step; and a washing step of pouring water over a dehydrated product obtained in the dehydration step to wash it. There is also provided a technology related thereto.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing zinc hydroxide. [Background technology]

[0002] Claim 1 of Patent Document 1 describes a batch process for producing a mixture of zinc oxide and zinc hydroxide by adding acidic wastewater containing zinc salts to an aqueous solution of caustic soda or caustic potash, and the pH at the end of the reaction is in the range of about 9.5 to about 12.5.

[0003] Paragraph 0004 of Patent Document 1 describes the following: After completion of the reaction, the reaction mixture, a suspension of a mixture of zinc oxide and zinc hydroxide, is separated from water by an appropriate separation means, such as settling, pressure filtration, vacuum filtration, centrifugal filtration, decanter, etc., and the resulting wet cake is dried by a known means to obtain a mixture of zinc oxide and zinc hydroxide. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 4-325414 Summary of the Invention [Problem to be solved by the invention]

[0005] Intensive research by the present inventors has revealed that when the solution to be treated contains an organic solvent to the extent that it forms a phase, if the zinc oxide and zinc hydroxide mixture is separated from water in a suspension of the mixture and the resulting wet cake is dried by a known means as described in Patent Document 1, there is a risk that scale will form inside the dryer due to the organic solvent remaining in the mixture (the organic solvent in the waste liquid to be treated).In this specification, the solution to be treated is also referred to as the raw solution.

[0006] An object of the present invention is to provide a technology for obtaining high-quality zinc hydroxide without generating scale inside a dryer when obtaining zinc hydroxide from a raw solution containing zinc, chlorine, and an organic solvent. [Means for solving the problem]

[0007] The first invention to solve the above-mentioned problems is: a mixing step of mixing a stock solution containing zinc, chlorine, and an organic solvent with an aqueous solution of an alkali metal hydroxide salt, and adjusting the pH of the resulting mixture to 9 or higher; an organic solvent recovery step of recovering the organic solvent, which is the supernatant, from the mixed solution after the mixing step; a repulping step of stirring the slurry remaining after the organic solvent recovery step with water; a dewatering step of dewatering the slurry obtained in the repulping step; a washing step of passing water through the dehydrated material obtained in the dehydration step to wash it; The method for producing zinc hydroxide comprises the steps of:

[0008] The second invention is: In the method for producing zinc hydroxide according to the first aspect of the present invention, the mixing step is carried out until the reaction for producing zinc hydroxide no longer progresses in the mixed solution.

[0009] The third invention is In the method for producing zinc hydroxide according to the first or second invention, the amount of water used in the washing step is equal to or greater than the volume of the dehydrated product obtained in the dehydration step.

[0010] The fourth invention is In the method for producing zinc hydroxide according to any one of the first to third aspects of the present invention, at least one of the dehydration step and the washing step is carried out multiple times.

[0011] The fifth invention is In the method for producing zinc hydroxide according to any one of the first to fourth aspects of the present invention, the hydroxide salt is at least one selected from the group consisting of sodium hydroxide and potassium hydroxide.

[0012] The sixth invention is In the method for producing zinc hydroxide according to any one of the first to fifth aspects of the present invention, the stock solution contains zinc in a mass ratio of 10% or more.

[0013] The seventh invention is In the method for producing zinc hydroxide according to any one of the first to sixth aspects of the present invention, the stock solution contains 5 to 30% by mass of zinc.

[0014] The eighth invention is In the method for producing zinc hydroxide according to any one of the first to seventh aspects of the present invention, the stock solution contains 10 to 95% by mass of an organic solvent.

[0015] The ninth invention is The method for producing zinc hydroxide according to any one of the first to eighth aspects of the present invention, wherein the organic solvent contains an alcohol. [Effects of the Invention]

[0016] According to the present invention, when zinc hydroxide is obtained from a raw solution containing zinc, chlorine, and an organic solvent, it is possible to obtain high-quality zinc hydroxide without generating scale inside a dryer. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a flowchart of the method for producing zinc hydroxide according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention will be described below with reference to embodiments. The symbol "to" indicates a value greater than or equal to a predetermined value and less than or equal to a predetermined value. After describing the overall configuration of this embodiment, other preferred examples and specific examples will be given. In this specification, the term "major component" refers to a substance or element that contains a specific compound or element at the highest abundance ratio. For example, it refers to a substance that is present in a specific compound at an abundance ratio of more than 50 mass %.

[0019] FIG. 1 is a flowchart of the method for producing zinc hydroxide according to this embodiment.

[0020] The method for producing zinc hydroxide of the present invention comprises the steps of: a mixing step of mixing a stock solution containing zinc, chlorine, and an organic solvent with an aqueous solution of an alkali metal hydroxide salt to adjust the pH of the mixed solution to 9 or higher; an organic solvent recovery step of recovering the organic solvent, which is the supernatant, from the mixed solution after the mixing step; a repulping step of stirring the slurry remaining after the organic solvent recovery step with water; a dewatering step of dewatering the slurry obtained in the repulping step; a washing step of passing water through the dehydrated material obtained in the dehydration step to wash it; It has.

[0021] In the mixing step, a stock solution containing zinc, chlorine, and an organic solvent is mixed with an aqueous solution of a hydroxide salt. There are no limitations on the "stock solution containing zinc, chlorine, and an organic solvent," but the stock solution preferably contains 10% or more zinc by mass, or preferably 5 to 30% zinc by mass. The organic solvent contained in the stock solution is preferably present in an amount of 10 to 95% by mass, and the organic solvent preferably contains an alcohol.

[0022] An example of the stock solution is waste liquid generated in the manufacturing process of an organic synthetic catalyst or a refrigerant. Hereinafter, the stock solution will be exemplified as such. Specifically, a slurry containing zinc chloride and an organic solvent (alcohol) is treated as the stock solution to be treated in the zinc hydroxide manufacturing method according to this embodiment.

[0023] There are no limitations on the pH of the raw solution, but for example, in the case of the above-mentioned slurry, the pH is less than 4 (or 1 or less). In the mixing step, the raw solution is mixed with an aqueous solution of an alkali metal hydroxide salt (e.g., sodium hydroxide and / or potassium hydroxide), and the pH of the raw solution increases.

[0024] In this embodiment, the pH is set to 9 or higher in the mixing step. If the pH is set to 9 or higher, most of the zinc-containing compounds recovered in the subsequent drying step after the repulping step, dehydration step, and washing step will be zinc oxide (ZnO). Note that if the pH is around 7, Zn5(OH)8Cl2·H2O may be produced along with zinc oxide (ZnO).

[0025] If chlorine remains in the recovered zinc, it will hinder the purification of zinc in subsequent processes, so it is preferable to recover zinc at a pH that can suppress the production of Zn5(OH)8Cl2·H2O. For this reason, in the mixing step, if the pH is set to 9 or higher, preferably 10 or higher, more preferably 11 or higher, 12 or higher, or 13 or higher, then highly concentrated zinc hydroxide (Zn(OH)2) can be obtained.

[0026] In the mixing step, it is preferable that the reaction for producing zinc hydroxide does not proceed in the mixed solution, which can further prevent impurities such as chlorine from being mixed into the zinc hydroxide to be recovered. Here, a specific example will be described as follows. When a slurry of zinc chloride and an organic solvent (alcohol) is mixed with sodium hydroxide, the following chemical reaction occurs: ZnCl2 + 2NaOH → Zn(OH)2 + 2NaCl The above reaction proceeds between the zinc chloride and sodium hydroxide in the slurry to produce zinc hydroxide and sodium chloride, but it is preferable to carry out the mixing step until the reaction to produce these compounds stops, which can be achieved by mixing a sufficient amount of sodium hydroxide. If the above condition is not satisfied, an alkali metal hydroxide salt may be intentionally added to be mixed with the slurry.

[0027] The hydroxide salt (solution) may be mixed with the stock solution by adding the hydroxide salt (solution) to the stock solution, or conversely, by adding the stock solution to the hydroxide salt (aqueous) solution.

[0028] The concentrate may contain 5% or more (or 15% or more, or 20% or more) of zinc by mass. There is no upper limit, but examples include 25%, 27.5%, and 30%.

[0029] The stock solution may contain zinc in a mass ratio of 20 to 50% calculated as zinc chloride (ZnCl2).

[0030] The organic solvent may be contained in the stock solution in a mass ratio of 10 to 95%, preferably 30% or more, more preferably 45% or more, and particularly preferably 60% or more.

[0031] The organic solvent may contain alcohol or may be mainly composed of alcohol. There are no limitations on the specific composition of the alcohol, and examples of the alcohol include isopropyl alcohol. Hereinafter, the case where the organic solvent is isopropyl alcohol (IPA) will be described as an example.

[0032] The hydroxide salt is an aqueous solution of an alkali metal hydroxide salt. Typically, it is preferable to use one or both of sodium hydroxide and potassium hydroxide. The main component of the hydroxide salt may be sodium hydroxide.

[0033] Next, in the organic solvent recovery step, the organic solvent, which is the upper liquid, is recovered from the mixed liquid after the mixing step. The recovered organic solvent, which is the upper liquid, may contain water or a small amount of impurities. When the organic solvent is IPA, the recovered organic solvent has a high purity as IPA due to the salting-out effect of NaCl. Therefore, the organic solvent recovered in this step has great utility value. For example, it can be used as a fuel (e.g., a combustion improver). Furthermore, when the organic solvent is IPA, the IPA can be reused in a process related to the production of zinc hydroxide or for other uses.

[0034] Next, in the repulping step, the slurry remaining after the organic solvent has been recovered in the organic solvent recovery step is mixed and stirred with water, thereby crushing the solids in the slurry and sufficiently removing impurities contained within the solids.

[0035] Next, in the dewatering step, the slurry obtained in the repulping step is dewatered by solid-liquid separation, and then the dewatered product obtained in the dewatering step is subjected to a washing step in which water is passed through the dewatered product to wash it. By these dehydration and washing steps, impurities in the solid matter are further removed, and zinc hydroxide is obtained. The specific work contents of these steps may be performed by known methods.

[0036] The dehydration method is not limited to a specific method as long as it allows the recovery of the precipitate from the slurry after the mixing step. For example, known methods such as suction filtration, filter press, and centrifugation can be used. The recovered precipitate may contain 30% by mass or less of water.

[0037] The amount of water used in the washing step is preferably equal to or greater than the volume of the dehydrated product obtained in the dehydration step. For example, water can be passed through the dehydrated product in a solid-liquid volume ratio of 1:1, i.e., a volume of water equal to or greater than the volume of the dehydrated product obtained, for washing.

[0038] There is no limitation on the number of times that the dehydration step and / or the washing step are performed, but they can be performed multiple times from the viewpoint of concentrating zinc in zinc hydroxide obtained by sufficiently removing impurities from the dehydrate.

[0039] In this embodiment, it is sufficient to remove impurities from the solid content of the slurry remaining after the organic solvent recovery step (removal of the remaining organic solvent and desalting), and one example includes at least one repulping step, a subsequent dehydration step, and a subsequent washing step. For example, a dehydration step may be performed after the repulping step, and then the repulping step and dehydration step may be performed again, followed by a washing step. Alternatively, a dehydration step after the repulping step may be performed, followed by multiple washing steps. Alternatively, a repulping step and dehydration step may be performed again after multiple washing steps.

[0040] Next, the solid obtained after the washing step is dried to obtain zinc oxide (drying step). The drying step may be a method for drying the solid obtained after the washing step, or a method may be used in which a dehydration step is separately performed after the washing step to obtain a solid, and then the drying step is performed on the solid.

[0041] By applying the method for producing zinc hydroxide according to this embodiment, when zinc hydroxide is obtained from a stock solution containing zinc, chlorine, and an organic solvent, no scale is generated in the dryer, and high-quality zinc hydroxide can be obtained, as shown in the examples below. Similarly, high-quality zinc hydroxide can also be obtained by natural drying after the dehydration step without drying in a dryer.

[0042] The technical scope of the present invention is not limited to the above-described embodiments, but includes various modifications and improvements within the scope of the specific effects that can be obtained by the constituent elements of the invention and their combinations. [Example]

[0043] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0044] Example 1 As the raw solution to be treated in this example, a slurry containing zinc, chlorine, and an organic solvent was prepared. The details of this slurry are as follows: ·IPA: 45% by mass content Zinc chloride: 50% by weight Liquid temperature: 25°C (room temperature) pH: 0.68

[0045] The grades of zinc, chlorine, sodium, and fluorine and the COD of the raw solution were as shown in Table 1. The grades were obtained by COD analysis using ICP emission spectrometry and potassium permanganate titration. [Table 1]

[0046] The stock solution (total volume 400 mL) was mixed with an aqueous sodium hydroxide solution (400 mL of 25% NaOH solution) (mixing step) to obtain a mixed solution containing a zinc hydroxide precipitate. The pH of this mixed solution was 11.1.

[0047] After the mixing step, an organic solvent recovery step was carried out in which the organic solvent, which was the upper liquid, was scooped out and recovered from the mixed liquid obtained. The amount of the recovered organic solvent (phase mainly composed of IPA) was 250 mL.

[0048] The solids remaining after the organic solvent recovery process were reslurried (repulped) using water (250 mL) and washed with water (repulping process). The solids were then dehydrated using a filter press (dehydration process). The filter, with the dehydrated material still remaining on the filter, was further washed five times (1.0 L total) with water (0.2 L) to achieve a solid-liquid volume ratio of 1:1 (washing process). The volume of wastewater from the repulping process to the final washing process was 1200 mL.

[0049] The solid matter after the washing step was dried at 40°C. The solid matter obtained after drying was measured in the same manner as above, and it was confirmed that zinc hydroxide was obtained. No scale was generated during drying.

[0050] The zinc content of the solid matter was 74.6% by mass, the sodium content was 0.03% by mass, and the COD was 0.1 mg / g, all of which were low values. In this example, the amount of sodium precipitated in zinc hydroxide was reduced, and it was found that zinc could be sufficiently concentrated even when the stock solution contained a large amount of organic solvent to the extent that an organic phase was formed.

[0051] Example 2 The following is a larger scale test than Example 1. The stock solution is the same as that listed in Example 1.

[0052] The slurry (total amount 1.6 m) containing zinc, chlorine and an organic solvent according to claim 1 3(2.0 tonnes)) and sodium hydroxide (25% NaOH aqueous solution (total volume 1.6 m 3 (2.0 tons))) was mixed with approximately 3.2 m 3 The pH of the mixture was 11.3.

[0053] After the mixing step, an organic solvent recovery step was carried out to recover the upper liquid from the mixed liquid. A suspension phase was also formed between the organic solvent as the upper liquid and the aqueous phase as the lower liquid. In the organic solvent recovery step of this example, the organic solvent and the suspension phase were combined to form the upper liquid, and the resulting mixture was collected to a volume of 1.0 m. 3 It was recovered.

[0054] 1.0m, the same amount as the upper liquid recovered 3 The solids remaining after the organic solvent recovery process were reslurried (repulped) using 100 ml of water and washed with water (repulping process). After that, the solids were dehydrated using a filter press (dehydration process). The amount of wastewater after dehydration was approximately 2.0 m 3 The filter was washed with water while the dehydrated material remained on the filter. The washing process was completed when it was confirmed that the amount of organic solvent in the drained liquid after water had passed through had decreased.

[0055] Incidentally, the wastewater generated after washing with a certain amount of water can be treated with normal wastewater treatment due to the amount of compounds it contains. The wastewater generated before that can be incinerated.

[0056] The solid mass obtained after air drying was 930 kg, and the majority of the solid mass was zinc hydroxide. No scale was generated during drying.

Claims

1. a mixing step of mixing a stock solution containing zinc, chlorine, and an organic solvent with an aqueous solution of an alkali metal hydroxide salt, and adjusting the pH of the resulting mixed solution to 9 or higher; an organic solvent recovery step of recovering the organic solvent, which is the supernatant, from the mixed solution after the mixing step; a repulping step of stirring the slurry remaining after the organic solvent recovery step with water; a dewatering step of dewatering the slurry obtained in the repulping step; a washing step of passing water through the dehydrated material obtained in the dehydration step to wash it; The method for producing zinc hydroxide comprises the steps of:

2. The method for producing zinc hydroxide according to claim 1, wherein the mixing step is carried out until a reaction for producing zinc hydroxide no longer proceeds in the mixed solution.

3. 2. The method for producing zinc hydroxide according to claim 1, wherein the amount of water used in the washing step is equal to or greater than the volume of the dehydrated product obtained in the dehydration step.

4. The method for producing zinc hydroxide according to claim 1 or 2, wherein at least one of the dehydration step and the washing step is carried out multiple times.

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

6. The method for producing zinc hydroxide according to claim 1 or 2, wherein the stock solution contains zinc in a mass ratio of 10% or more.

7. The method for producing zinc hydroxide according to claim 1 or 2, wherein the stock solution contains 5 to 30% by mass of zinc.

8. The method for producing zinc hydroxide according to claim 1 or 2, wherein the stock solution contains 10 to 95% by mass of an organic solvent.

9. The method for producing zinc hydroxide according to claim 1 or 2, wherein the organic solvent comprises an alcohol.

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