Method for manufacturing composite powder, composite powder, method for treating water to be treated, and treatment equipment for water to be treated

Abstract

To provide a method that can perform a process from generating clean treated water at a level that can be discharged to discharging the treated water at a low cost for the treated water containing sodium hypochlorite, and a catalyst suitable for the method.SOLUTION: A production method for composite powder comprises: stirring and mixing nickel oxide (II) powder in water in the presence of nickel ions and an oxidizing agent to produce a composite nickel oxide powder; and ozonating the composite nickel oxide powder in the water at pH 9-13 at 60-90°C in the presence of iron ions (II).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a composite powder, a composite powder, a method for treating water to be treated, and a treatment facility for water to be treated. [Background technology]

[0002] In a wide range of industries, compounds containing chlorine are used for various purposes, such as sterilization and synthetic intermediates, resulting in the continuous generation of water containing sodium hypochlorite and gas containing chlorine.Chlorine-containing gas is usually neutralized by contacting it with an aqueous sodium hydroxide solution in a wet scrubber or the like, and the neutralized liquid is collected at the bottom of the tower.In this process, sodium chloride and sodium hypochlorite are by-produced.In other words, water containing sodium hypochlorite is produced.

[0003] When the concentration of sodium hypochlorite contained in the above-mentioned sodium hypochlorite-containing water exceeds a certain level, it emits an unpleasant odor and is toxic to seafood, aquatic plants, etc., and when it becomes acidic, it also has the property of regenerating chlorine. Therefore, it is necessary to decompose the sodium hypochlorite before discharging it outside the system (public rivers, lakes, oceans, etc.).

[0004] As a catalyst for decomposing sodium hypochlorite in such sodium hypochlorite-containing water, Patent Document 1 proposes a pellet-shaped catalyst containing nickel sesquioxide, silicon oxide, and aluminum oxide in a predetermined ratio. The catalyst is packed into a packed tower, and the sodium hypochlorite in the liquid to be treated is decomposed by passing the liquid through the packed tower. Patent Document 2 also discloses a packed tower using a nickel oxide catalyst for treating waste liquid containing sodium hypochlorite. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 149240 / 1983 [Patent Document 2] Japanese Patent Publication No. 176592 / 1983 Summary of the Invention [Problem to be solved by the invention]

[0006] It takes a long time for sodium hypochlorite to be decomposed by a packed tower (for example, in the example of Patent Document 2, it takes more than 20 hours for sodium hypochlorite to be decomposed). In order to treat the sodium hypochlorite-containing water that is continuously generated at such a decomposition rate, it is necessary to take measures to increase the treatment volume per unit time, such as increasing the size of the packed tower or installing multiple packed towers, but this would significantly increase the cost of the treatment equipment. The treatment process for sodium hypochlorite-containing water includes decomposing sodium hypochlorite, subjecting the treated water after decomposition to any additional treatment required as appropriate, and then discharging it from the system, and the cost is considered for this entire process.

[0007] The present invention aims to provide a treatment method for treating water containing sodium hypochlorite, which can be carried out at low cost from the production of treated water that is clean enough to be discharged to the discharge of the treated water, as well as a catalyst suitable for the treatment method, a method for producing the catalyst, and treatment equipment. [Means for solving the problem]

[0008] As a means for treating the water to be treated at low cost without increasing the size / number of devices for decomposing sodium hypochlorite, it is conceivable to increase the decomposition rate of sodium hypochlorite and increase the amount of water to be treated per unit time. From this perspective, the present inventors have conducted research and have come up with the idea of ​​using a catalyst made of non-stoichiometric nickel oxide powder, which has excellent decomposition activity for sodium hypochlorite and is cost-effective and stable.

[0009] In treating water using a powder catalyst, it is common to mix and stir the water and catalyst in a reactor. However, when the non-stoichiometric nickel oxide powder is used in this method, the catalyst does not settle easily to the lower part or bottom of the reactor after the decomposition reaction of sodium hypochlorite is completed. If the treated water containing this (unsettled) catalyst is sent directly to the next process, new catalyst is required each time the water is treated, resulting in increased treatment costs. On the other hand, if the catalyst is allowed to settle in the reactor and the supernatant is sent to the next process, the time required for the decomposition of sodium hypochlorite is actually longer, resulting in increased treatment costs.

[0010] Therefore, the present inventors have conducted research to improve the settling property of the non-stoichiometric nickel oxide powder, and have come up with the idea of ​​forming a composite nickel oxide powder by attaching non-stoichiometric nickel oxide particles to the particle surfaces of nickel (II) oxide powder. However, although the settling property of the composite nickel oxide powder is superior to that of the non-stoichiometric nickel oxide powder, it is still insufficient.

[0011] After further investigation, the inventors came up with the idea of ​​a composite powder in which magnetic particles are further compounded with the constituent particles of this composite nickel oxide powder, and then came up with a process in which the composite powder is used to decompose sodium hypochlorite in the treatment water, and a considerable amount of the composite powder is allowed to settle in a short period of time, although not to a sufficient level, and then the supernatant liquid containing the composite powder that has not yet settled is subjected to magnetic separation to recover the composite powder. The water after magnetic separation treatment from which the composite powder has been removed can be discharged after appropriate filtration, etc. This process allows the decomposition of sodium hypochlorite and the recovery of the composite powder in a short period of time, so the entire process up to discharge can be carried out at low cost.

[0012] In this way, the present inventors have completed the present invention. That is, the present invention is as follows. [1] A method for producing a composite powder, comprising: stirring and mixing nickel (II) oxide powder in water in the presence of nickel ions and an oxidizing agent to produce a composite nickel oxide powder; and then treating this composite nickel oxide powder with ozone at 60 to 90°C in water having a pH of 9 to 13 in the presence of iron (II) ions.

[0013] [2] The method for producing a composite powder according to [1], wherein the nickel (II) oxide powder has a volume-based cumulative 50% particle size (D50) of 6 to 20 μm as measured by a laser diffraction scattering particle size distribution analyzer.

[0014] [3] The method for producing a composite powder according to [1] or [2], wherein the nickel (II) oxide powder and nickel ions are used in a mass ratio of 10:1 to 3:1 (nickel (II) oxide powder: nickel ions).

[0015] [4] The method for producing a composite powder according to any one of [1] to [3], wherein the oxidizing agent is sodium hypochlorite, and the amount of the sodium hypochlorite used is 12 to 20 times by mole the nickel ions.

[0016] [5] The method for producing a composite powder according to any one of [1] to [4], wherein the composite nickel oxide powder and iron (II) ions are used in a mass ratio of 100:3 to 100:10 (composite nickel oxide powder:iron (II) ions).

[0017] [6] A composite powder comprising composite nickel oxide particles, each of which has non-stoichiometric nickel oxide particles attached to the surface of a nickel (II) oxide core particle, and magnetic particles containing iron and oxygen attached to the surface of the composite nickel oxide particles.

[0018] [7] The composite powder according to [6], wherein the composite powder has a volume-based cumulative 50% particle size (D50) of 6 to 18 μm as measured by a laser diffraction / scattering particle size distribution analyzer.

[0019] [8] A method for treating water to be treated, comprising stirring the water to be treated containing sodium hypochlorite in the presence of a composite powder produced by the method for producing a composite powder according to any one of [1] to [5] or the composite powder according to [6] or [7], thereby carrying out a decomposition reaction of the sodium hypochlorite.

[0020] [9] The treatment method according to [8], wherein the decomposition reaction of sodium hypochlorite is carried out in a batch-type reaction apparatus, and after completion of the decomposition reaction, stirring of the water to be treated is stopped, and the composite powder is allowed to settle naturally for 1 to 60 minutes after the stirring is stopped.

[0021]

[10] The treatment method according to [9], wherein after the natural settling, the supernatant containing a portion of the composite powder is subjected to magnetic separation to recover the composite powder in the supernatant.

[0022]

[11] The treatment method according to any one of [8] to

[10] , wherein the decomposition reaction of sodium hypochlorite is completed within 60 minutes or less.

[0023]

[12] The treatment method according to any one of [8] to

[11] , wherein the available chlorine concentration in the water to be treated is 0.1 to 12 mass%, and the available chlorine concentration in the water to be treated after completion of the decomposition reaction of the sodium hypochlorite is less than 0.1 mass%.

[0024]

[13] A treatment facility for the water to be treated, comprising: a reactor for stirring the water to be treated containing sodium hypochlorite in the presence of the composite powder produced by the method for producing a composite powder according to any one of [1] to [5] or the composite powder according to [6] or [7], and for carrying out a decomposition reaction of the sodium hypochlorite; and a liquid delivery means for delivering the liquid from the reactor to a magnetic separation device, the reactor is configured to stop stirring the water to be treated after completion of the decomposition reaction and allow the composite powder to settle naturally for 1 to 60 minutes after the stirring is stopped, The liquid sending means is configured to send a supernatant liquid containing a portion of the composite powder from the reaction device after the natural settling to a magnetic separation device. [Effects of the Invention]

[0025] According to the present invention, there are provided a method and equipment for treating water containing sodium hypochlorite, which can be carried out at low cost from producing treated water that is clean enough to be discharged to discharging the treated water, as well as a composite powder suitable for the treatment method and a method for manufacturing the same. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, an embodiment of the present invention will be described. [1. Composite powder] As described above, the composite powder of the present invention is composed of composite nickel oxide particles, which are composed of non-stoichiometric nickel oxide particles adhered to the surface of a core particle of nickel(II) oxide (meaning an oxide of divalent nickel; the same applies hereinafter), and magnetic particles containing iron and oxygen adhered to the surface of the composite nickel oxide particles. Each component of the composite powder will be described below.

[0027] <1-1. Core particle> The core particles constituting the composite powder of the present invention are nickel(II) oxide particles, as described above. As will be described later, the composite powder is typically produced through a process of adhering non-stoichiometric nickel oxide particles to the particle surfaces of nickel(II) oxide powder, and the non-stoichiometric nickel oxide particles are likely to form and adhere to the particle surfaces of nickel(II) oxide powder.

[0028] From the viewpoint of catalytic activity, it is preferable that the non-stoichiometric nickel oxide particles are fine particles, but fine particles have poor sedimentation properties. By attaching such non-stoichiometric nickel oxide particles to the surface of core particles that are larger than the nickel particles, the sedimentation properties of the catalyst particles are improved. Furthermore, from the viewpoint of catalytic activity, it is preferable that the shape of the non-stoichiometric nickel oxide particles is approximately spherical.

[0029] <1-2. Non-stoichiometric nickel oxide particles> As described above, non-stoichiometric nickel oxide particles are attached to core particles made of nickel(II) oxide particles to form composite nickel oxide core particles. "Non-stoichiometric" refers to the property that a chemical formula cannot be expressed as a simple ratio of natural numbers.

[0030] The non-stoichiometric nickel oxide particles function as an excellent catalyst for the decomposition reaction of sodium hypochlorite. The non-stoichiometric nickel oxide particles are preferably finer than the core particles and have a large specific surface area, which also contributes to excellent catalytic activity. The non-stoichiometric nickel oxide particles may be attached to the entire surface of the core particles or to only a portion of the surface.

[0031] <1-3.Magnetic particles> The composite powder of the present invention is formed by adhering magnetic particles containing iron and oxygen to the surfaces of composite nickel oxide particles, i.e., the surfaces of non-stoichiometric nickel oxide particles and to portions of the core particles to which non-stoichiometric nickel oxide particles are not attached.

[0032] These magnetic particles have the property of being attracted to a magnet. The magnetic particles in the composite powder produced by the composite powder production method of the present invention, which will be described later, are thought to be magnetite, and can be produced inexpensively. The presence of the magnetic particles makes the composite powder as a whole magnetic (excluding paramagnetism and diamagnetism), making it possible to perform magnetic separation. Furthermore, the magnetic particles do not need to cover the entire surface of the composite nickel oxide particles; rather, from the perspective of catalytic activity, it is preferable that a certain amount of non-stoichiometric nickel oxide particles be exposed.

[0033] <1-4. Particle size of composite powder> The volume-based cumulative 50% particle size (D50) of the composite powder of the present invention, as measured by a laser diffraction / scattering particle size distribution analyzer, is preferably 6 to 18 μm, more preferably 7 to 15 μm, and particularly preferably 8 to 13 μm, from the viewpoints of catalytic activity and sedimentation.

[0034] Furthermore, the volume-based cumulative 10% particle size (D10) of the composite powder is preferably 1 to 7 μm, more preferably 2 to 6 μm, and particularly preferably 3 to 5.5 μm, from the viewpoints of catalytic activity and sedimentation.

[0035] [2. Manufacturing method of composite powder] In the method for producing a composite powder of the present invention, nickel (II) oxide powder is stirred and mixed in water in the presence of nickel ions and an oxidizing agent to produce a composite nickel oxide powder (Step 1), and this composite nickel oxide powder is then treated with ozone in water at a pH of 9 to 13 at 60 to 90°C in the presence of iron (II) ions to obtain a composite powder (Step 2).

[0036] It is believed that step 1 forms non-stoichiometric nickel oxide particles from nickel ions, and that these particles adhere to the particle surfaces of the nickel (II) oxide powder. Step 2 is a typical method for producing magnetite, and by this method, magnetic particles containing iron and oxygen are formed, and that these particles adhere to the particle surfaces of the composite nickel oxide powder. Each component of the method for producing a composite powder of the present invention will be described below.

[0037] <2-1. Nickel (II) oxide powder> The nickel (II) oxide powder, which is the starting material in the method for producing the composite powder of the present invention, is a core particle to which non-stoichiometric nickel oxide particles, which are the catalyst body, adhere. This is the same as the nickel (II) oxide powder described in the composite powder of the present invention. The nickel (II) oxide powder has a mineral form called bunsenite and is green in appearance.

[0038] Regarding the particle size of the nickel(II) oxide powder, the volume-based cumulative 50% particle size (D50) measured with a laser diffraction / scattering particle size distribution analyzer is preferably 6 to 20 μm, more preferably 8 to 16 μm, and particularly preferably 9 to 14 μm, from the viewpoints of the catalytic activity and sedimentation of the composite powder produced. Furthermore, the volume-based cumulative 10% particle size (D10) of the nickel(II) oxide powder is preferably 3 to 11 μm, more preferably 5 to 10 μm, and particularly preferably 6 to 9 μm.

[0039] <2-2. Nickel ions and oxidizing agents> Nickel ions are cations that are oxidized to form black non-stoichiometric nickel oxide particles. The source of nickel ions is not particularly limited, and examples include nickel sulfate, nickel chloride, and nickel nitrate.

[0040] The oxidizing agent is not particularly limited as long as it can oxidize nickel ions to form non-stoichiometric nickel oxide particles, and an example thereof is sodium hypochlorite.

[0041] It is believed that by oxidizing nickel ions in water in the presence of nickel(II) oxide powder, non-stoichiometric nickel oxide particles are formed and adhere to the surfaces of each particle constituting the nickel(II) oxide powder. The temperature of the water during the formation reaction of the non-stoichiometric nickel oxide particles is preferably 20 to 30°C from the viewpoint of preventing decomposition and volatilization of hypochlorous acid. The pH of the water during the formation reaction is preferably 2.5 to 6 from the viewpoints of preventing chlorine generation and ensuring good adhesion of the non-stoichiometric nickel oxide particles to the nickel(II) oxide particles. The ratio of the nickel(II) oxide powder and nickel ions used (nickel(II) oxide powder:nickel ions) is preferably 10:1 to 3:1 by mass, more preferably 7:1 to 4:1, from the viewpoints of the catalytic activity and sedimentation properties of the composite powder finally formed. To ensure sufficient formation of non-stoichiometric nickel oxide particles, the amount of oxidizing agent used, when sodium hypochlorite is used, is preferably 12 to 20 molar times, more preferably 15 to 18 molar times, the amount of nickel ions.

[0042] <2-3. Adhesion of magnetic particles> It is believed that by treating the composite nickel oxide powder obtained in step 1 with ozone in water with a pH of 9 to 13 at 60 to 90°C in the presence of iron (II) ions, magnetic particles are formed and adhered to the surface of the powder particles. This ozone treatment is a common method for producing magnetite. The source of the iron (II) ions is not particularly limited, and examples include ferrous sulfate. From the viewpoints of the catalytic activity of the composite powder formed and ease of magnetic separation, the ratio of the composite nickel oxide powder to the iron (II) ions used (composite nickel oxide powder:iron (II) ions) is preferably 100:3 to 100:10 by mass, more preferably 100:4 to 100:7.

[0043] A specific example of the ozone treatment method is to inject ozone into the water. From the viewpoint of the efficiency of producing magnetic particles, it is preferable to inject ozone into the water containing the composite nickel oxide powder and iron (II) ions while stirring and mixing the water. The time for the ozone treatment (the time for injecting ozone) and the amount of ozone supplied are not particularly limited as long as sufficient magnetic particles are formed.

[0044] In this manner, the composite powder to be produced by the composite powder production method of the present invention is obtained. The particle surfaces of the composite powder are considered to be substantially composed of magnetic particles and non-stoichiometric nickel oxide particles, and since these particles are all black, the composite powder has a black appearance.

[0045] [3. Treatment method for untreated water] As explained in the section "Background Art," water to be treated containing sodium hypochlorite is widely generated in industry. The composite powder of the present invention and the composite powder produced by the method for producing the composite powder described above are suitable as catalysts for the decomposition reaction of sodium hypochlorite, and can therefore be suitably used in the treatment process of the water to be treated. It is believed that the decomposition reaction of sodium hypochlorite produces sodium chloride and oxygen. Below, an embodiment of the entire process from the decomposition of sodium hypochlorite in the water to be treated to the discharge of the treated water after the decomposition treatment will be described.

[0046] <3-1. Treated water> The amount of sodium hypochlorite in the water to be treated in the method for treating water of the present invention is, for example, 0.1 to 12% by mass in terms of available chlorine concentration. The water to be treated in the present invention preferably has a relatively low solid content, and its turbidity (NTU) is, for example, 100 or less, preferably 50 or less, and more preferably 20 or less. A method for measuring turbidity will be described in the Examples below. If the water to be treated contains a large amount of solids or organic matter, it is preferable to reduce these contents by pretreatment.

[0047] <3-2. Decomposition of sodium hypochlorite> The water to be treated is introduced into a batch-type reaction apparatus and stirred in the presence of the composite powder. The temperature of the water to be treated (the decomposition reaction temperature of sodium hypochlorite) is preferably 35 to 50°C from the viewpoints of reaction efficiency and safety. The pH of the water to be treated during the decomposition reaction is preferably 7.5 or higher, more preferably 9 to 14, from the viewpoint of preventing the generation of hydrochloric acid and chlorine gas. Stirring during the decomposition reaction can be performed using a stirrer or a rotating blade, and the rotation speed is preferably 200 to 500 rpm from the viewpoints of decomposition efficiency and reaction time. The larger the amount of composite powder used, the better the decomposition efficiency of sodium hypochlorite. However, from the viewpoints of decomposition efficiency, reaction time, and economy, the amount of composite powder used is preferably 1 to 30 parts by mass, more preferably 4 to 22 parts by mass, per 100 parts by mass of the water to be treated.

[0048] The stirring time (decomposition reaction time) is preferably 60 minutes or less, more preferably 10 to 45 minutes, and even more preferably 15 to 30 minutes, from the viewpoint of sufficiently decomposing sodium hypochlorite in the water to be treated and from the viewpoint of the treatment efficiency of the water to be treated. The end (criteria) of the decomposition reaction will likely be determined based on the wastewater standards of each country, but for example, the end of the decomposition reaction can be determined when the available chlorine concentration becomes less than 1000 ppm (0.1% by mass). By adjusting the amount of composite powder used, for example, within the range described above, the time required for the decomposition reaction to be completed can be shortened as described above.

[0049] Furthermore, some catalysts may become unusable after several uses due to disintegration, but this does not occur with the composite powder used in the present invention, and the catalyst can be reused.

[0050] <3-3. Natural settling and magnetic separation of composite powder> After the decomposition treatment of sodium hypochlorite is completed, the stirring of the water to be treated is stopped and the composite powder is allowed to settle naturally. Because the composite powder has excellent settling properties and can be magnetically separated, it is not necessary to allow the composite powder to settle completely to the lower part or bottom of the reactor, and the time for natural settling can be, for example, 1 to 60 minutes, preferably 1.5 to 30 minutes, and more preferably 2 to 10 minutes.

[0051] Even with such a short period of natural settling, a considerable amount of composite powder settles, and the turbidity of the upper part of the treated water that has undergone the decomposition reaction (a depth of 50 or less when the depth of the treated water in the reactor is 100) becomes approximately 5 or less.

[0052] The supernatant liquid (treated water) from which the composite powder has settled still contains a small amount of composite powder, but it is sent to a magnetic separator with the powder still in it and magnetically separated. Since the composite powder is magnetic, it can be recovered by magnetic separation. A specific method of magnetic separation is as follows, for example. The treated water is passed through a flow path provided in the magnetic separator, and a magnet is placed on the wall (outside) of this flow path, causing the composite powder to adhere to the wall of the flow path. The composite powder that has adhered to the wall can be recovered manually, or it can be returned to the reactor by backwashing with water.

[0053] By natural settling in the reactor and the magnetic separation described above, substantially all of the composite powder can be recovered, and this composite powder can be reused as described above, so the treatment method for water to be treated of the present invention is also excellent in terms of catalyst costs. However, if natural settling is not performed, the load on the magnetic separation device will be large, resulting in high maintenance costs for the device, and operation will have to be stopped during maintenance, leading to a decrease in treatment efficiency.

[0054] <3-4. Filtration of water after magnetic separation treatment> If any impurities are present in the water after the magnetic separation treatment, the water may be filtered to remove them.

[0055] Since the composite powder has been sufficiently removed from the water after magnetic separation, the load on the filtration filter is small. Therefore, even when filtration is performed, the method for treating water to be treated of the present invention can reduce the frequency of replacing the expensive filter.

[0056] <3-5. Discharge of water after magnetic separation treatment> After magnetic separation, the water is filtered as needed, and if it contains metal ions or organic matter that need to be removed, these are removed. The water that has undergone such treatment can be discharged outside the system (public rivers, lakes, oceans, etc.).

[0057] [4. Treatment facilities for treated water] An example of a specific configuration of a treatment facility for carrying out the method for treating water to be treated of the present invention described above is as follows.

[0058] A treatment facility for water to be treated, comprising: a reaction device for stirring water to be treated containing sodium hypochlorite in the presence of the composite powder of the present invention or a composite powder produced by the method for producing a composite powder of the present invention, and for carrying out a decomposition reaction of the sodium hypochlorite; and a liquid transport means for transporting liquid from the reaction device to a magnetic separation device, wherein the reaction device is configured to stop stirring the water to be treated after completion of the decomposition reaction and allow the composite powder to naturally settle for 1 to 60 minutes after the stirring has stopped, and the liquid transport means is configured to send a supernatant liquid containing a portion of the composite powder from the reaction device to the magnetic separation device after the natural settling.

[0059] The reaction device may be provided with a turbidity measuring means for monitoring the degree of settling of the composite powder after the decomposition reaction of sodium hypochlorite. The treatment facility may also be provided with an available chlorine concentration measuring means. [Example]

[0060] [Comparative Example 1] <Preparing the catalyst> The following three types of commercially available catalysts for the decomposition of sodium hypochlorite were prepared.

[0061] · Catalyst manufactured by Company A···Based on the results of elemental analysis, it is believed to be a catalyst in which nickel is supported on alumina. · Catalyst manufactured by Company B ··· Based on the results of elemental analysis, it is believed to be a catalyst in which cobalt, iron, and magnesium are supported on alumina and silica. · Catalyst manufactured by Company C···Based on the results of elemental analysis, it is believed to be a catalyst in which copper and manganese are supported on alumina.

[0062] <Decomposition performance confirmation test> 30 g of each of the three catalysts was added to a sodium hypochlorite solution with an effective chlorine concentration of 6 mass% (100 g of the solution was ClO - 600 mL of a catalyst containing 6 g of HCl was added, and the mixture was stirred at 40°C with a three-paddle shaft at 100 rpm. Because the prepared catalyst is prone to breakdown, the stirring speed was slower than in the examples described below to prevent breakdown. After the start of stirring, the reaction solution was sampled at predetermined time intervals, and the available chlorine concentration in the reaction solution was measured using a Pack Test (using WAK-ClO(C) manufactured by Kyoritsu Chemical Research Institute). The pH of the reaction solution remained between 11 and 13 throughout the decomposition reaction. The measurement results are shown in Table 1 below.

[0063] [Table 1]

[0064] The catalysts manufactured by Company B and Company C had low sodium hypochlorite decomposition capabilities. Furthermore, in all cases where catalysts manufactured by Companies A to C were used, no odor was generated throughout the decomposition reaction, suggesting that chlorine was not generated. The same applies to the following Comparative Examples and Examples. Furthermore, in all cases where catalysts manufactured by Companies A to C were used, the available chlorine concentration decreased and foaming also occurred, suggesting that sodium chloride and oxygen were formed from sodium hypochlorite by the catalysts manufactured by Companies A to C. The same applies to the following Comparative Examples and Examples.

[0065] <Supernatant turbidity measurement> In the above <Decomposition Performance Verification Test>, stirring was stopped 120 minutes after the start of stirring, and the liquid (supernatant) was sampled at a depth of 30 (assuming the depth of the reaction liquid is 100) after the specified time shown in Table 2 below had elapsed after stirring was stopped, and its turbidity (NTU: Nephelometric Turbidity Units) was determined. HANNA HI93414 was used to measure the turbidity. The measurement results are shown in Table 2 below.

[0066] [Table 2]

[0067] Comparative Example 2 <Production of composite nickel oxide powder> 100 g of nickel(II) oxide powder (green) (measured with an IPS2 manufactured by Sumitomo Metal Mining Co., Ltd. and an MT3300EXII manufactured by Microtrac-Bell Corporation, with a volume-based cumulative 50% particle size (D50) of 11.5 μm and a cumulative 10% particle size (D10) of 7.5 μm) and 100 mL or 200 mL of a 1.5 mol / L nickel sulfate aqueous solution (pH: 3.0) were mixed in a 1-L conical beaker at room temperature (approximately 25°C) while stirring. A sodium hypochlorite aqueous solution with an available chlorine concentration of 12% by mass was added and stirred. When 100 mL of the nickel sulfate aqueous solution was used, the amount of sodium hypochlorite aqueous solution used was 900 mL (Case 1), and when 200 mL of the nickel sulfate aqueous solution was used, the amount of sodium hypochlorite aqueous solution used was 2100 mL (Case 2).

[0068] In the above (Case 1), the mass ratio of [nickel (II) oxide powder]:[nickel ions (nickel sulfate is considered to be 100% ionized)] was approximately 11.4:1, and the amount of sodium hypochlorite used was approximately 14 molar times the amount of nickel ions. In the above (Case 2), the mass ratio of [nickel (II) oxide powder]:[nickel ions] was approximately 5.7:1, and the amount of sodium hypochlorite used was 16 molar times the amount of nickel ions.

[0069] The powder was washed with water three times, and then a sodium hypochlorite solution with an effective chlorine concentration of 12% by mass was added to the washed powder, which was then washed with water and filtered to obtain a composite nickel oxide powder consisting of nickel (II) oxide core particles (green) with approximately spherical non-stoichiometric nickel oxide (black) particles attached to the surface. The composite nickel oxide powder was black in color. The powder obtained when 100 mL of nickel sulfate aqueous solution was used (Case 1) was designated composite nickel oxide powder A1, and the powder obtained when 200 mL of nickel sulfate aqueous solution was used (Case 2) was designated composite nickel oxide powder A2.

[0070] <Decomposition performance confirmation test> 30 g of the nickel(II) oxide powder (IPS2, manufactured by Sumitomo Metal Mining Co., Ltd.) used above, and the composite nickel oxide powder A1 or composite nickel oxide powder A2 obtained above were each taken, and 300 mL of a sodium hypochlorite aqueous solution with an available chlorine concentration of 12% by mass and 300 mL of water were added. The mixture was stirred at 40°C with a three-paddle shaft at a rotation speed of 340 rpm. After the start of stirring, the reaction solution was sampled at predetermined intervals, and the available chlorine concentration in the reaction solution was measured using a Pack Test (WAK-ClO(C), manufactured by Kyoritsu Chemical Research Institute). The pH of the reaction solution remained between 11 and 13 throughout the decomposition reaction. The measurement results are shown in Table 3 below.

[0071] [Table 3]

[0072] <Supernatant turbidity measurement> In the above <Decomposition Performance Confirmation Test>, stirring was stopped 90 minutes after the start of stirring when IPS2 was used, 90 minutes after the start of stirring when composite nickel oxide powder A1 was used, and 60 minutes after the start of stirring when composite nickel oxide powder A2 was used, and the turbidity of the supernatant was measured after the specified times had elapsed in the same manner as in Comparative Example 1. The measurement results are shown in Table 4 below.

[0073] [Table 4]

[0074] When composite nickel oxide powder A1 or A2 was used, the turbidity was greater than when IPS2 was used (except when A1 was used after 1 minute and 5 minutes). This test was conducted in a beaker, and the supernatant was sampled. However, if the water to be treated containing sodium hypochlorite were to be treated in a larger device, it would take even longer for the composite nickel oxide powder to settle to the bottom of the device, which would be a problem in terms of the treatment efficiency of the water to be treated.

[0075] [Example 1] <Manufacturing composite powder> 40 g of the composite nickel oxide powder A2 obtained in Comparative Example 2 was repulped in 1.5 L of water (60°C) placed in a 3 L Pyrex (registered trademark) beaker, and 11.6 g of ferrous sulfate heptahydrate and 7.2 g of a 48% by weight aqueous solution of sodium hydroxide were added to adjust the pH to 11. The Pyrex (registered trademark) beaker containing the resulting slurry was immersed in a 70°C water bath, and ozone was blown into the slurry (0.1 g / h), followed by aeration and stirring for 1 hour and 30 minutes. The amount of iron (II) ions in the ferrous sulfate heptahydrate relative to the composite nickel oxide powder A2 was approximately 100:5.9 (composite nickel oxide powder A2:iron (II) ions) by mass, assuming that all of the ferrous sulfate heptahydrate was ionized.

[0076] The magnetism of the composite powder obtained as described above was confirmed using a magnet. From this, it is believed that the composite powder is composed of composite nickel oxide powder A2 with magnetite attached to the particle surface. Furthermore, the (D10) and (D50) of the obtained composite powder measured in the same manner as in Comparative Example 2 were 4.6 μm and 11 μm, respectively.

[0077] <Decomposition performance confirmation test> To the total amount (48 g) of composite powder obtained above, 800 mL of an aqueous sodium hypochlorite solution with an available chlorine concentration of 6% by mass was added, and the mixture was stirred at 40°C with a three-paddle shaft at a rotation speed of 340 rpm. The available chlorine concentration in the reaction solution was measured at predetermined time intervals after the start of stirring, as in Comparative Example 2. The pH of the reaction solution remained between 11 and 13 throughout the decomposition reaction. The measurement results are shown in Table 5 below.

[0078] [Table 5]

[0079] <Supernatant turbidity measurement> In the above-mentioned <Decomposition Performance Verification Test>, stirring was stopped 60 minutes after the start of stirring, and the turbidity of the supernatant was measured after a predetermined time had elapsed, as in Comparative Example 1. Similarly, after a predetermined time had elapsed after the reaction had finished and stirring had been stopped, the supernatant was sampled as in Comparative Example 1, and this liquid was passed through a magnetic separator at a flow rate of 2 cm / s. This magnetic separator was made using a 3D printer and was capable of arranging eight 240 mT rare earth magnets on the side wall of the flow path. The flow path of the magnetic separator (cross-sectional area 2.95 cm) 2 The liquid that passed through the magnetic separation filter (height: 5 mm, width: 59 mm) was collected and its turbidity was measured.

[0080] The results of the above measurements are shown in Table 6 below.

[0081] [Table 6]

[0082] [Example 2] <Cycle test> The composite powder produced by repeating the same procedure as in Example 1 was used to carry out the following cycle test.

[0083] 80 g of composite powder was placed in a 1 L Pyrex (registered trademark) beaker, followed by 400 mL of water and 400 mL of a sodium hypochlorite aqueous solution with an available chlorine concentration of 12% by mass. The reaction temperature was maintained at 40 to 50°C, and the mixture was stirred with a stirrer to decompose the sodium hypochlorite. The decomposition time was 30 minutes. The pH of the reaction solution remained at 11 to 13 throughout the decomposition reaction.

[0084] After the 30-minute decomposition treatment, stirring was stopped and the mixture was allowed to stand for 3 minutes. Half of the liquid in which the composite powder had been settled was passed through a magnetic separator similar to that used in Example 1 at a flow rate of 2 cm / s, and the composite powder (very small amount) floating in the liquid was recovered. 400 mL of an aqueous sodium hypochlorite solution with an effective chlorine concentration of 12 mass% was added to the remaining liquid in which the composite powder had been settled (approximately 400 mL, with the composite powder settling at the bottom. The available chlorine concentration was essentially 0 mass%, and is considered to be 0 ppm in the calculation of the treatment rate in Table 7 below), and the decomposition of sodium hypochlorite was carried out again.

[0085] This cycle, which consisted of decomposing sodium hypochlorite, discharging half of the liquid in which the composite powder had been precipitated, and adding 400 mL of an aqueous sodium hypochlorite solution, was repeated.

[0086] In each cycle, the available chlorine concentration of the solution after the decomposition treatment of sodium hypochlorite was measured using Pack Test (using WAK-ClO(C) manufactured by Kyoritsu Chemical Research Institute). In addition, the turbidity of the supernatant liquid left to stand for 3 minutes after the decomposition treatment and the solution after magnetic separation treatment similar to Example 1 was measured in the same manner as in Comparative Example 1.

[0087] The above evaluation results are shown in Table 7. The treatment rate in Table 7 is the rate at which the effective chlorine concentration in the water to be treated (effective chlorine concentration 6% by mass) was reduced, and can be calculated using the following formula. Treatment rate = (60,000 ppm - effective chlorine concentration in water after decomposition treatment (ppm)) / 60,000 ppm x 100 (%)

[0088] [Table 7]

Claims

1. A method for producing a composite powder, comprising: stirring and mixing nickel (II) oxide powder in water in the presence of nickel ions and an oxidizing agent to produce a composite nickel oxide powder; and then treating the composite nickel oxide powder with ozone at 60 to 90°C in water having a pH of 9 to 13 in the presence of iron (II) ions.

2. 2. The method for producing a composite powder according to claim 1, wherein the nickel (II) oxide powder has a volume-based cumulative 50% particle size (D50) of 6 to 20 μm as measured with a laser diffraction scattering particle size distribution analyzer.

3. 3. The method for producing a composite powder according to claim 1, wherein the nickel (II) oxide powder and nickel ions are used in a mass ratio of 10:1 to 3:1 (nickel (II) oxide powder:nickel ions).

4. 4. The method for producing a composite powder according to claim 1, wherein the oxidizing agent is sodium hypochlorite, and the amount of the sodium hypochlorite used is 12 to 20 times by mole relative to the amount of the nickel ions.

5. The method for producing a composite powder according to any one of claims 1 to 4, wherein the composite nickel oxide powder and iron (II) ions are used in a mass ratio of 100:3 to 100:10 (composite nickel oxide powder:iron (II) ions).

6. A composite powder comprising magnetic particles containing iron and oxygen attached to the surface of composite nickel oxide particles, each of which comprises a core particle of nickel (II) oxide and non-stoichiometric nickel oxide particles attached to the surface of the core particle.

7. The composite powder according to claim 6, wherein the volume-based cumulative 50% particle diameter (D50) of the composite powder measured by a laser diffraction scattering particle size distribution analyzer is 6 to 18 μm.

8. A method for treating water to be treated, comprising stirring the water to be treated containing sodium hypochlorite in the presence of a composite powder produced by the method for producing a composite powder according to any one of claims 1 to 5, or the composite powder according to claim 6 or 7, thereby carrying out a decomposition reaction of the sodium hypochlorite.

9. The method for treating water to be treated according to claim 8, wherein the decomposition reaction of sodium hypochlorite is carried out in a batch-type reaction apparatus, stirring of the water to be treated is stopped after completion of the decomposition reaction, and the composite powder is allowed to settle naturally for 1 to 60 minutes after the stirring is stopped.

10. 10. The method for treating water to be treated according to claim 9, wherein after the natural settling, a supernatant liquid containing a portion of the composite powder is subjected to magnetic separation to recover the composite powder in the supernatant liquid.

11. The method for treating water to be treated according to any one of claims 8 to 10, wherein the decomposition reaction of sodium hypochlorite is completed within 60 minutes or less.

12. The method for treating water according to any one of claims 8 to 11, wherein the effective chlorine concentration in the water to be treated is 0.1 to 12% by mass, and the effective chlorine concentration in the water to be treated after completion of the decomposition reaction of sodium hypochlorite is less than 0.1% by mass.

13. A treatment facility for the water to be treated, comprising: a reaction device for stirring the water to be treated containing sodium hypochlorite in the presence of the composite powder produced by the method for producing a composite powder according to any one of claims 1 to 5 or the composite powder according to claim 6 or 7, and for carrying out a decomposition reaction of the sodium hypochlorite; and a liquid delivery means for delivering the liquid from the reaction device to a magnetic separation device, the reactor is configured to stop stirring the water to be treated after completion of the decomposition reaction and allow the composite powder to settle naturally for 1 to 60 minutes after the stirring has stopped; The treatment facility for water to be treated, wherein the liquid sending means is configured to send a supernatant liquid containing a portion of the composite powder from the reaction device after the natural settling to a magnetic separation device.

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