JP7799733B2 - Layered double hydroxide manufacturing equipment - Google Patents

Description

The present invention relates to an apparatus for producing layered double hydroxides.

Layered double hydroxides are known to have anion exchange properties. Some layered double hydroxides have the ability to immobilize arsenic, fluorine, boron, selenium, hexavalent chromium, nitrite ions, and other anionic hazardous substances through this anion exchange property, thereby contributing to improving the quality of contaminated water, preventing the leaching of hazardous substances, improving soil, and promoting the stabilization of hazardous substances at waste disposal sites. Furthermore, some layered double hydroxides have the ability to inhibit corrosion of steel materials by chloride ions when applied to them. Several methods for producing layered double hydroxides have been proposed (for example, Patent Document 1).

International Publication No. 2009/072488

Layered double hydroxides are produced by mixing an acidic solution and an alkaline solution, and by mixing different types of solutions, it is possible to produce layered double hydroxides with different properties and uses. Traditionally, producing layered double hydroxides with different properties and uses required separate production lines. Furthermore, when using a single production line to produce different layered double hydroxides, the entire production line must be cleaned when switching from producing one layered double hydroxide to producing another, which is time-consuming and labor-intensive.

In one aspect, the present invention aims to provide a layered double hydroxide production apparatus that can reduce the effort required for cleaning when changing the layered double hydroxide being produced.

Another object of the present invention is to provide a layered double hydroxide production apparatus that can appropriately treat the wastewater generated during the production of layered double hydroxide.

The first layered double hydroxide manufacturing apparatus described in this specification is an apparatus for manufacturing a layered double hydroxide by mixing an acidic solution and an alkaline solution to produce a layered double hydroxide, and includes a mixing unit that mixes the acidic solution and the alkaline solution, a first supply unit that supplies a first acidic solution toward the mixing unit, a second supply unit that supplies a second acidic solution different from the first acidic solution toward the mixing unit, and a supply switching unit that switches between a state in which the first acidic solution is supplied toward the mixing unit from a first pipe connected to the first supply unit and a state in which the second acidic solution is supplied toward the mixing unit from a second pipe connected to the second supply unit.

The second layered double hydroxide manufacturing apparatus described in this specification is a layered double hydroxide manufacturing apparatus that produces a nitric acid type layered double hydroxide by mixing an acidic solution and an alkaline solution, and includes a plurality of waste liquid tanks for storing waste liquid generated during the production of the nitric acid type layered double hydroxide, a determination unit that determines whether the waste liquid, which contains nitrate nitrogen or nitrate ions generated during the production of the nitric acid type layered double hydroxide, satisfies a predetermined standard before the waste liquid is stored in one of the plurality of waste liquid tanks, and a switching unit that switches the storage destination of the waste liquid to one of the plurality of waste liquid tanks based on the determination result of the determination unit.

The third layered double hydroxide production apparatus described in this specification is an apparatus for producing a layered double hydroxide by mixing an acidic solution and an alkaline solution, and includes a production unit for producing a first layered double hydroxide of nitric acid type by mixing a first acidic solution with the alkaline solution, or for producing a second layered double hydroxide of nitric acid type by mixing a second acidic solution different from the first acidic solution with the alkaline solution, and a plurality of drains for storing wastewater generated during the production of the first layered double hydroxide or the second layered double hydroxide. The system comprises a liquid tank, and a switching unit which, when the first layered double hydroxide is being produced in the production unit, determines whether the effluent containing nitrate nitrogen or nitrate ions generated when the first layered double hydroxide is produced satisfies a predetermined standard before the effluent is stored in one of the plurality of effluent tanks, and switches the storage destination of the effluent to one of the plurality of effluent tanks based on the determination result, and when the second layered double hydroxide is being produced in the production unit, fixes the storage destination of the effluent to a predetermined effluent tank.

The layered double hydroxide production apparatus described in this specification can reduce the effort required for cleaning when changing the layered double hydroxide being produced.

In addition, the wastewater generated during the production of layered double hydroxides can be properly treated.

FIG. 1 is a diagram showing an outline of a production line. FIG. 2 is a diagram illustrating the generating unit of FIG. FIG. 3 is a diagram illustrating the processing unit of FIG. FIG. 4 is a block diagram showing an outline of a control system for the manufacturing line shown in FIG. FIG. 5 is a flowchart showing the control procedure of each part of the manufacturing line up to the processing part in FIG. FIG. 6 is a flowchart showing a control procedure for the waste fluid reservoir.

The production line 100, which is one embodiment of a layered double hydroxide production apparatus, is described in detail below with reference to Figures 1 to 6.

In this embodiment, the production line 100 is, as an example, a production line that produces two types of layered double hydroxides.

(Layered double hydroxide)
Here, we will explain layered double hydroxides. Layered double hydroxides have the chemical formula M2 ⁺ _1- xM3 ⁺ _x ( ^OH ) ₂ ( _NO3- ) _x/n · _mH2O . ^M2+ represents a divalent metal, M3 ⁺ represents a trivalent metal, and n is a natural number. Furthermore, x is a number in the range of 0 < x < 1, generally 1/6 < x < 1/3. m is a number greater than 0. Layered double hydroxides are synthesized by mixing an acidic solution containing divalent and trivalent metal ions with an alkaline solution. These layered double hydroxides are sometimes called hydrotalcite-like compounds. Examples of divalent metal ions (M2 ⁺ ) include Mg2 ⁺ , Fe2 ⁺ , Zn2 ⁺ , Li2 ⁺ , Ni2 ⁺ , Co2 ⁺ , and Cu2 ⁺ . Examples of trivalent metal ions (M ³⁺ ) include Al ³⁺ , Fe ³⁺ , Cr ³⁺ , and Mn ³⁺ . The divalent metal ions (M ²⁺ ) and trivalent metal ions (M ³⁺ ) contained in the above general formula do not have to be of one type, and may contain multiple types. Examples of anions include HCO ₃ ^- , PO ₄ ^3- , SO ₄ ^2- , Cl ^- , NO ₂ ^- , and NO ₃ ^- .

Examples of layered double hydroxides include layered double hydroxides represented by the general formula Mg2 ⁺ _1- xAl3 ⁺ _x (OH) ₂ ( ^An- ) _{x/ n.mH2O} and layered double hydroxides represented by the general formula Zn2 ⁺ _1-xAl3 ⁺ _x (OH) ₂ ( ^An- ) _{x/ n.mH2O} ( ^An- is an n-valent anion, m>0).

For example, when producing a layered double hydroxide having the general formula Mg ²⁺ _1-x Al ³⁺ _x (OH) ₂ (A ^n- ) _x/n ·mH ₂ O (A ^n- is an n-valent anion, m>0), an acidic solution containing aluminum ions and magnesium ions is used.

The aluminum source for aluminum ions is not limited to any particular substance, as long as it generates aluminum ions in water. Examples of aluminum sources that can be used include alumina, sodium aluminate, aluminum hydroxide, aluminum chloride, aluminum nitrate, bauxite, alumina production residue from bauxite, and aluminum sludge. These aluminum sources may be used alone or in combination of two or more.

The magnesium source for magnesium ions is not limited to any specific substance, as long as it generates magnesium ions in water. For example, brucite, magnesium hydroxide, magnesite, and calcined magnesite can be used. These magnesium sources can be used alone or in combination of two or more.

The aluminum compound used as the aluminum source and the magnesium compound used as the magnesium source do not need to be completely dissolved in the acidic solution as long as aluminum ions and magnesium ions are present. Therefore, layered double hydroxides can be produced without any problems even if the acidic solution contains undissolved aluminum compounds or magnesium compounds.

Furthermore, it is known that a highly crystalline layered double hydroxide represented by Mg2 ⁺ _1- xAl3 ⁺ _x (OH) ₂ ( ^An- ) _{x/ n.mH2O} has a molar ratio of aluminum ions to magnesium ions of 1:3 (x = 0.25). Therefore, the molar ratio of aluminum ions to magnesium ions in the acidic solution is preferably in the range of 1:5 to 1:2. By setting the ratio within this range, the layered double hydroxide can be produced in an advantageous manner in terms of material balance without wasting the aluminum and magnesium sources.

To adjust the acidic solution to an acidic state, it is preferable to use nitric acid or hydrochloric acid. In this embodiment, an acidic solution adjusted to an acidic state using nitric acid is used as the first acidic solution described below, and an acidic solution adjusted to an acidic state using hydrochloric acid is used as the second acidic solution described below.

The alkaline solution used to produce the layered double hydroxide is preferably prepared with a pH of 8 to 14. The alkali contained in the alkaline solution is not limited to any particular substance, as long as it renders the aqueous solution alkaline. For example, sodium hydroxide, calcium hydroxide, etc. can be used. Sodium carbonate, potassium carbonate, ammonium carbonate, aqueous ammonia, sodium borate, potassium borate, etc. can also be used. These alkalis can be used alone or in combination of two or more.

(Regarding production line 100)
Fig. 1 is a diagram showing an overview of a production line 100. As shown in Fig. 1, the production line 100 comprises an acidic solution supply unit 10 that prepares an acidic solution serving as a raw material for the layered double hydroxide and supplies it to a production unit 28, an alkaline solution supply unit 20 that supplies an alkaline solution serving as a raw material for the layered double hydroxide to the production unit 28, a pH-adjusting solution supply unit 30 that supplies a pH-adjusting solution to the production unit 28, and the production unit 28 as a mixing unit. The production line 100 also comprises a treatment unit 52 that performs various treatments such as filtration, water washing, pressing, and drying on the layered double hydroxide produced in the production unit 28, and an effluent storage unit 60 that stores effluent (including filtrate and wash water) generated in the treatment unit 52.

(Acid solution supply unit 10)
The acidic solution supply unit 10 prepares an acidic solution that serves as a raw material for the layered double hydroxide, and supplies the acidic solution to the production unit 28. The acidic solution supply unit 10 includes a first acidic solution preparation tank 11, a first acidic solution storage tank 12, a pipe 15 (first pipe), a pump 21, a second acidic solution preparation tank 13, a second acidic solution storage tank 14, a pipe 16 (second pipe), and a pump 22. The acidic solution supply unit 10 also includes a switching valve 23 that serves as a supply switching unit. The first acidic solution preparation tank 11 and the first acidic solution storage tank 12 function as a first supply unit that supplies the first acidic solution to the production unit 28, and the second acidic solution preparation tank 13 and the second acidic solution storage tank 14 function as a second supply unit that supplies the second acidic solution to the production unit 28.

The first acidic solution preparation tank 11, also known as a make-up tank, is a tank for preparing the first acidic solution. In the first acidic solution preparation tank 11, the materials necessary to prepare the first acidic solution containing trivalent metal ions and divalent metal ions are mixed, and the solution is adjusted to an acidic state using nitric acid. In this embodiment, the first acidic solution preparation tank 11 is located above the first acidic solution storage tank 12.

The first acidic solution storage tank 12 stores the first acidic solution prepared in the first acidic solution preparation tank 11. The first acidic solution storage tank 12 has a capacity capable of storing a predetermined number of times (e.g., three times) the amount of first acidic solution that can be prepared in one batch in the first acidic solution preparation tank 11. A pipe 15 is connected to the first acidic solution storage tank 12, and when a shutter on the pipe 15 is opened and the pump 21 is activated, the first acidic solution is transported toward the switching valve 23.

The second acidic solution preparation tank 13 is a tank for preparing the second acidic solution. In this embodiment, the second acidic solution preparation tank 13 is disposed above the second acidic solution storage tank 14. In the second acidic solution preparation tank 13, the materials necessary to prepare the second acidic solution containing trivalent metal ions and divalent metal ions are mixed, and the solution is adjusted to an acidic state using hydrochloric acid. Note that the adjustment using hydrochloric acid may be omitted.

The second acidic solution storage tank 14 stores the second acidic solution prepared in the second acidic solution preparation tank 13. The second acidic solution storage tank 14 has a capacity capable of storing a predetermined number of times (e.g., three times) the amount of second acidic solution that can be prepared in one operation in the second acidic solution preparation tank 13. A pipe 16 is connected to the second acidic solution storage tank 14, and when a shutter on the pipe 16 is opened and the pump 22 is operated, the second acidic solution is transported toward the switching valve 23.

The switching valve 23 switches whether the first acidic solution or the second acidic solution is to be delivered to the production unit 28, i.e., whether the first acidic solution or the second acidic solution is to be used to produce layered double hydroxide.

(Alkaline solution supply unit 20)
The alkaline solution supply unit 20 has an alkaline solution storage tank 24 and a pump 25. The alkaline solution storage tank 24 stores the alkaline solution. A pipe is connected to the alkaline solution storage tank 24, and when a shutter provided on the pipe is opened and the pump 25 is operated, the alkaline solution is transported toward the generation unit 28.

(pH adjustment liquid supply section 30)
The pH adjusting liquid supply unit 30 has a pH adjusting liquid storage tank 26 and a pump 27. The pH adjusting liquid storage tank 26 stores the pH adjusting liquid. A pipe is connected to the pH adjusting liquid storage tank 26, and the pH adjusting liquid is transported toward the generation unit 28 by opening a shutter provided on the pipe and operating the pump 27.

(Generation unit 28)
When a first acidic solution is supplied from the acidic solution supply unit 10, the production unit 28 mixes the first acidic solution with an alkaline solution in a predetermined ratio to produce a first layered double hydroxide (hereinafter referred to as a nitric acid type layered double hydroxide). When a second acidic solution is supplied from the acidic solution supply unit 10, the production unit 28 mixes the second acidic solution with an alkaline solution in a predetermined ratio to produce a second layered double hydroxide (hereinafter referred to as a chloride type layered double hydroxide).

Figure 2 shows a schematic diagram of the generation unit 28. The generation unit 28 includes an agitation tank 117, a pH adjustment tank 118, a first supply unit 111 that supplies an acidic solution (first acidic solution or second acidic solution) to the agitation tank 117, a second supply unit 112 that supplies an alkaline solution to the agitation tank 117, and a rotary agitation unit 115 that agitates the acidic solution and alkaline solution in the agitation tank 117 to form a mixed solution.

The first supply unit 111 and the second supply unit 112 may be equipped with a flow rate regulator that appropriately adjusts the flow rate of the acidic solution and the alkaline solution. Any conventional flow rate regulator may be used, such as a flow rate regulator valve.

The rotary agitator 115 has a rotating shaft 113 and multiple blades 114 provided below the rotating shaft 113. It rotates at a predetermined speed to rapidly agitate the acidic solution and alkaline solution to produce a mixed liquid (layered double hydroxide). When a first acidic solution is supplied from the first supply unit 111, a nitric acid-type layered double hydroxide is produced. On the other hand, when a second acidic solution is supplied from the first supply unit 111, a chloride-type layered double hydroxide is produced. Since the layered double hydroxide produced tends to accumulate on the rotating shaft 113 of the rotary agitator 115, to prevent the accumulation of layered double hydroxide on the rotating shaft 113, for example, a liquid such as water may be supplied from above the rotating shaft 113 and allowed to flow, covering the surface of the rotating shaft 113. Alternatively, a liquid such as water may be supplied from below the rotating shaft 113 and allowed to flow, covering the surface of the rotating shaft 113.

A third supply unit 116 is connected to the bottom of the pH adjustment tank 118 (below the rotary agitator 115). A discharge flow path 119 is connected to the top of the pH adjustment tank 118. The third supply unit 116 is connected to the pH-adjusting liquid supply unit 30 (see FIG. 1). To stop the aging of the layered double hydroxide, a pH-adjusting liquid (e.g., water or sodium hydroxide) is supplied from the pH-adjusting liquid supply unit 30 to the third supply unit 116. The pH-adjusting liquid adjusts the hydrogen ion exponent of the mixed solution produced in the agitator 117. By quickly stopping the aging of the layered double hydroxide using the pH-adjusting liquid, layered double hydroxides with small crystallite size can be efficiently mass-produced. The shorter the aging time after production, the smaller the crystallite size of the layered double hydroxide produced. To prevent aging, the pH of the mixed solution can be lowered to a value at which crystal growth of the layered double hydroxide stops after the acidic and alkaline solutions are mixed.

The pH adjusting liquid may be any liquid with a pH below the level required to stop aging, such as water or an acidic solution. Alternatively, a gas (pH adjusting gas) or solid (pH adjusting solid) capable of lowering the pH of the mixed liquid may be used instead of the pH adjusting liquid. The third supply unit 116 may also be provided with an adjustment device for adjusting the flow rate of the pH adjusting liquid, as appropriate.

The layered double hydroxide slurry (nitrate-type layered double hydroxide or chloride-type layered double hydroxide) produced by the overflow of the mixed solution of acidic and alkaline solutions is discharged together with the pH-adjusting solution to the outside of the pH adjustment tank 118 via the discharge flow path 119. The layered double hydroxide slurry discharged to the outside of the pH adjustment tank 118 flows into the slurry tank 29 shown in FIG. 1. The layered double hydroxide slurry that flows into the slurry tank 29 is transported by the pump 31 toward the processing unit 52. A selector valve 51 is provided between the pump 31 and the processing unit 52. The selector valve 51 switches between supplying the layered double hydroxide slurry in the slurry tank 29 to the processing unit 52 or supplying the liquid in the washing water tank 41 (described below) to the processing unit 52.

The cleaning water tank 41 stores a liquid for cleaning the layered double hydroxide. In this embodiment, water is used as the liquid, and therefore the liquid stored in the cleaning water tank 41 will be referred to as cleaning water. The cleaning water stored in the cleaning water tank 41 is transported toward the treatment section 52 by the pump 42. The amount of cleaning water supplied to the treatment section 52 is 20 to 100 liters per minute, preferably 20 to 80 liters per minute, and more preferably 25 to 40 liters per minute. In order to shorten the time required to clean the layered double hydroxide, it is preferable to use a large amount of cleaning water, but in order to reduce cleaning costs, it is preferable to use a small amount of cleaning water. Therefore, the amount of cleaning water is determined taking into account the time required to clean the layered double hydroxide and the cleaning costs.

The pressure at which the cleaning water is supplied should be 0.2 MPa to 1.5 MPa, preferably 0.4 MPa to 1.0 MPa, and more preferably 0.5 MPa to 0.8 MPa. The above lower and upper limits are set because if the water pressure is below the lower limit, the aggregated layered double hydroxide will not form granules, and if the water pressure is above the upper limit, the water will not pass easily through the filter described below, making it impossible to clean the layered double hydroxide. The cleaning water may be tap water or purified water. Since the electrical conductivity of natural water is 100 μS/cm, it is preferable to use water with an electrical conductivity of 200 μS/cm or less, preferably 100 μS/cm or less, and more preferably 50 μS/cm or less. The lower limit of the electrical conductivity of water is 0.01 μS/cm, the electrical conductivity of pure water.

(Processing unit 52)
The treatment section 52 performs various treatments on the layered double hydroxide, such as filtration, washing, squeezing, and drying. Fig. 3 is a diagram showing a schematic diagram of the treatment section 52. As shown in Fig. 3, the treatment section 52 has a treatment body 152 and a filter cloth 153.

The treatment body 152 has an internal space that houses a filter cloth 153. An opening 154 is formed at the top of the treatment body 152 for supplying layered double hydroxide and cleaning water to the filter cloth 153. The treatment body 152 also has a discharge section 155 that discharges the pH adjusting solution and cleaning water supplied together with the layered double hydroxide to the outside of the internal space, and a compressed gas supply section 156 that supplies compressed gas for the squeezing process.

Chemical fibers such as nylon, polyester, polypropylene, etc. can be used for the filter cloth 153. The breathability of the filter cloth 153 can be set to, for example, 0.1 to 1 cm ³ /cm ² ·sec so that the layered double hydroxide does not flow out of the filter cloth 153.

A switching valve 51 is connected to the opening 154 of the treatment body 152, and layered double hydroxide and cleaning water are selectively supplied from the opening 154 to the filter cloth 153.

The discharge section 155 of the treatment body 152 is formed below the treatment body 152 and discharges the liquid (wastewater) that has passed through the filter cloth 153 to the outside of the treatment body 152. While two discharge sections 155 are shown in Figure 3, the number of discharge sections 155 may be one, or three or more.

The compressed gas supply unit 156 is formed above the processing body 152 and is connected to a compressed gas supply source (not shown). In this embodiment, the compressed gas supply unit 156 supplies air, but other gases may also be used. Also, while two compressed gas supply units 156 are shown in Figure 3, the number of compressed gas supply units 156 may be one, or three or more.

(Drainage reservoir 60)
Returning to FIG. 1, the waste liquid storage section 60 is for storing the waste liquid (filtrate and washing water used after washing the layered double hydroxide) discharged from the treatment section 52.

The wastewater storage unit 60 includes a pipe 81 (first drain pipe) connected to the processing unit 52, an electrical conductivity meter 61 provided within the pipe 81 for measuring the electrical conductivity of the wastewater discharged from the processing unit 52, a switching valve 62 (wastewater switching valve) connected to the pipe 81, a primary wastewater tank 63, a secondary wastewater tank 64, a pipe 82 (branch drain pipe) connecting the switching valve 62 and the primary wastewater tank 63, and a pipe 83 (branch drain pipe) connecting the switching valve 62 and the secondary wastewater tank 64.

The primary wastewater tank 63 is a tank that stores wastewater whose nitrate nitrogen concentration exceeds the standard value, and the secondary wastewater tank 64 is a tank that stores wastewater whose nitrate nitrogen concentration is below the standard value.

Here, there is a correlation between the nitrate nitrogen concentration of the effluent and the electrical conductivity of the effluent. Therefore, the electrical conductivity of the effluent discharged from the treatment unit 52 is measured using an electrical conductivity meter 61 before it reaches the switching valve 62. If the electrical conductivity exceeds a threshold value (the electrical conductivity value when the nitrate nitrogen concentration reaches the reference value), the switching valve 62 is switched so that the effluent is transported to the primary effluent tank 63. If the electrical conductivity is below the threshold value, the switching valve 62 is switched so that the effluent is transported to the secondary effluent tank 64. Specific switching methods for the switching valve 62 will be described later.

The wastewater stored in the primary wastewater tank 63 is either treated to meet wastewater standards and then discharged, or disposed of as industrial waste. On the other hand, the wastewater stored in the secondary wastewater tank 64 is discharged after its pH is adjusted.

(Control system)
FIG. 4 is a block diagram showing an outline of a control system for the manufacturing line 100 of this embodiment.

As shown in FIG. 4, the production line 100 has a control device 70 that controls all parts of the production line 100. The control device 70 is connected to an input/output device 72, an electrical conductivity meter 61, pumps 21, 22, 25, 27, 31, and 42, and switching valves 23, 51, and 62. The input/output device 72 is a terminal or the like that can be used by the manager who manages the production line 100. The manager can input to the input/output device 72 whether a nitrate-type layered double hydroxide or a chloride-type layered double hydroxide is to be produced, and can input that cleaning of the production line 100 has been completed. The control device 70 also outputs information to the input/output device 72, such as which parts of the production line 100 are available for cleaning.

The control device 70 controls the pumps 21, 22, 25, 27, 31, and 42 and the switching valves 23, 51, and 62 based on information input by the operator via the input/output device 72, measurement results from the electrical conductivity meter 61, etc.

(Regarding control by the control device 70)
Next, the control of each part of the production line 100 by the control device 70 will be described in detail with reference to the flowcharts of Figures 5 and 6. Figure 5 is a flowchart showing the control procedure of each part of the production line 100 up to the processing unit 52 in Figure 1, and Figure 6 is a flowchart showing the control procedure of the waste liquid storage unit 60. The controls in Figures 5 and 6 are executed simultaneously in parallel.

(Regarding Figure 5)
First, the control procedure of Fig. 5 will be described. The flowchart of Fig. 5 starts when the production line 100 is in an operable state (each component of the production line 100 has been cleaned). At the start of the flowchart of Fig. 5, all of the pumps 21, 22, 25, 27, 31, and 42 are stopped, the first acidic solution storage tank 12 stores the first acidic solution prepared in the first acidic solution preparation tank 11, and the second acidic solution storage tank 14 stores the second acidic solution prepared in the second acidic solution preparation tank 13. The first and second acidic solutions are adjusted in the first and second acidic solution preparation tanks 11 and 13 as appropriate, depending on the amounts of the solutions stored in the first and second acidic solution storage tanks 12 and 14, respectively. It is also assumed that the alkaline solution reservoir 24 stores an alkaline solution, the pH adjusting liquid reservoir 26 stores a pH adjusting liquid, and the cleaning water reservoir 41 stores cleaning water.

When the flowchart in Figure 5 starts, first, in step S10, the control device 70 waits until the administrator specifies the layered double hydroxide to be produced (nitrate-type layered double hydroxide or chloride-type layered double hydroxide) and inputs a command to start production into the input/output device 72. Once the administrator inputs information about the product and a command to start production into the input/output device 72, the control device 70 proceeds to step S12.

When proceeding to step S12, the control device 70 switches the switching valve 23 in the acid solution supply unit 10 to start production of the specified production target. Specifically, if a nitric acid-type layered double hydroxide is specified as the production target, the control device 70 switches the switching valve 23 so that the first acid solution is transported from the first acid solution storage tank 12 to the production unit 28; and if a chloride-type layered double hydroxide is specified as the production target, the control device 70 switches the switching valve 23 so that the second acid solution is transported from the second acid solution storage tank 14 to the production unit 28.

Next, in step S14, the control device 70 activates pump 21 or 22, pumps 25 and 27, and also operates the production unit 28. This mixes the first or second acidic solution with the alkaline solution to produce a nitrate-type or chloride-type layered double hydroxide slurry. The pH adjuster is used to prevent the layered double hydroxide from ripening. The layered double hydroxide slurry is transported to and stored in the slurry tank 29.

Next, in step S16, the control device 70 operates the processing unit 52 and starts the filtering, washing, squeezing, and drying processes.

(Filtration process)
First, the control device 70 switches the selector valve 51 and operates the pump so that the layered double hydroxide in a slurry state stored in the slurry tank 29 is supplied to the treatment section 52. As a result, filtration is carried out in the filter cloth 153 of the treatment section 52, and liquids such as the pH adjusting solution pass through the filter cloth 153 and are discharged. In this way, filtration is carried out by a filter press using the filter cloth 153.

(Cleaning treatment)
Following the filtration process, the control device 70 switches the selector valve 51 so that cleaning water is supplied from the cleaning water tank 41 to the treatment section 52, thereby cleaning (rinsing) the layered double hydroxide. When producing a nitric acid-type layered double hydroxide, mixing the first acidic solution with the alkaline solution produces not only a nitric acid-type layered double hydroxide but also _NaNO3 , and this cleaning process removes _NaNO3 . When producing a chloride-type layered double hydroxide, mixing the second acidic solution with the alkaline solution produces not only a chloride-type layered double hydroxide but also NaCl, and this cleaning process removes NaCl. At this time, NaCl adhering to the layered double hydroxide is also removed, improving the anion exchange activity of the layered double hydroxide and improving its adsorption performance for arsenic, fluorine, boron, selenium, hexavalent chromium, nitrite ions, and other anionic harmful substances.

It is preferable to perform the cleaning process after the filtration process to reduce the amount of water used, but cleaning water may be supplied to the filter cloth 153 through the opening 154 during filtration.

(Compression process)
After the cleaning treatment, the control device 70 switches the selector valve 51 so as to stop the supply of the slurry layered double hydroxide and cleaning water to the treatment section 52, and introduces compressed air from a compressed gas supply source (not shown) into the treatment section 52. Compressed air is supplied to the treatment section 52 from the compressed gas supply section 156 shown in Figure 3. This causes the layered double hydroxide contained in the treatment section 52 to be compressed. In this embodiment, the compression treatment is carried out within the treatment section 52, but the layered double hydroxide may also be contained in a container separate from the treatment section 52 and subjected to the compression treatment.

(Drying treatment)
Next, the control device 70 dries the layered double hydroxide in the treatment unit 52. The drying process may be performed outside the treatment unit 52. When performing the drying process in the treatment unit 52, for example, a vacuum suction mechanism (not shown) is used to vacuum-absorb the steam from the filter cloth 153, and a liquid at 80°C to 100°C is circulated through a flow path in the treatment unit 152, thereby vacuum-drying the layered double hydroxide. By lowering the air pressure inside the treatment unit 152 using the vacuum suction mechanism, the water vapor is converted to steam at a low temperature, enabling efficient drying. When the vacuum suction mechanism is operating, it is preferable to cover the opening 154 with a lid or the like to prevent communication with the outside of the treatment unit 152. The layered double hydroxide may be dried by blowing hot air at 80°C to 150°C, preferably 100°C to 120°C, onto the treatment unit 52, or by electromagnetic waves.

After the drying process, the layered double hydroxide may be crushed or sieved. For example, when used as a rust inhibitor for reinforcing bars, the particle size of the nitric acid-type layered double hydroxide is preferably 70 μm or less. Therefore, the crushing and sieving processes may be repeated to obtain a nitric acid-type layered double hydroxide of the desired particle size (e.g., 70 μm or less). If the nitric acid-type layered double hydroxide after the drying process meets the desired particle size, the crushing and sieving processes may not be necessary. Furthermore, when used as a water treatment agent for removing harmful substances from water to make it potable, the particle size of the chloride-type layered double hydroxide is preferably 500 μm or more and 1200 μm or less. Therefore, the crushing and sieving processes may be repeated to obtain a chloride-type layered double hydroxide of the desired particle size (e.g., 500 μm to 1200 μm). If the chloride-type layered double hydroxide has the desired particle size after drying, crushing and sieving do not need to be carried out.

After starting the filtering, washing, squeezing, and drying processes in step S16 as described above, the process proceeds to step S18, where the control device 70 waits until information regarding a change in the production target is input to the input/output device 72. In other words, the layered double hydroxide production process continues until the administrator inputs information regarding a change in the control target into the input/output device 72.

When information about the change in production target is input to the input/output device 72, the control device 70 proceeds to step S20, gradually stops the production line 100, identifies areas that can be cleaned, and outputs a cleaning instruction to the input/output device 72. For example, when information about the change in production target is input, the control device 70 stops the supply of liquid from the acidic solution supply unit 10, alkaline solution supply unit 20, and pH adjusting liquid supply unit 30 to the generation unit 28. The control device 70 then outputs to the input/output device 72 a message indicating that the piping between the switching valve 23 and the generation unit 28 can now be cleaned. This allows the administrator to clean the piping between the switching valve 23 and the generation unit 28. Note that cleaning of the piping may be performed, for example, by connecting the pH adjusting liquid storage tank 26 and the switching valve 23 with a pipe and supplying pH adjusting liquid (e.g., water) to the piping. Alternatively, cleaning may be performed by connecting the cleaning water tank 41 and the switching valve 23 with a pipe and supplying cleaning water to the piping. Furthermore, while the generation time of the generation unit 28 is approximately 1 to 3 hours, the processing time of the processing unit 52 is longer at 10 hours or more. Therefore, cleaning of the upstream side of the processing unit 52 may be performed while the processing unit 52 is processing.

Furthermore, when the layered double hydroxide production process in the production unit 28 is completed, the control unit 70 outputs to the input/output device 72 a message indicating that cleaning of the production unit 28 is now possible. Furthermore, when all of the slurry layered double hydroxide in the slurry tank 29 has been transported to the processing unit 52, the control unit 70 outputs to the input/output device 72 a message indicating that cleaning of the slurry tank 29 and the piping between the slurry tank 29 and the switching valve 51 is now possible. Furthermore, when processing in the processing unit 52 is completed, the control unit 70 outputs to the input/output device 72 a message indicating that cleaning of the processing unit 52 and the piping between the switching valve 51 and the processing unit 52 is now possible. This allows the manager to clean areas in order of their availability for cleaning, thereby enabling efficient cleaning and efficient switching of production targets. When cleaning of the entire production line 100 is completed, the manager inputs this information (that cleaning is complete) into the input/output device 72. Furthermore, if there is equipment or piping within the production line 100 that requires a long time to clean, replacement equipment or piping may be prepared separately and replaced instead of cleaning.

In this embodiment, the acidic solution supply unit 10 includes a first acidic solution preparation tank 11 and a first acidic solution storage tank 12, and a second acidic solution preparation tank 13 and a second acidic solution storage tank 14. That is, two sets of acidic solution preparation tanks and acidic solution storage tanks are provided. For example, if the acidic solution supply unit 10 only includes one set of acidic solution preparation tank and acidic solution storage tank, it would be necessary to clean the acidic solution preparation tank, acidic solution storage tank, and piping when switching between production targets, which would require time and effort. However, by including two sets of acidic solution preparation tanks and acidic solution storage tanks as in this embodiment, it is not necessary to clean the acidic solution supply unit 10 when switching between production targets.

In step S22, the control device 70 determines whether a signal indicating completion of cleaning of the entire production line 100 has been input. If the determination in step S22 is negative, the process returns to step S20. However, if the determination in step S22 is positive, the process returns to step S12. After returning to step S12, the control device 70 repeats the processing from step S12 onwards. That is, for example, if nitric acid-type layered double hydroxide was being produced using the first acidic solution until just before, the control device 70 switches the switching valve 23 (S12) and performs the production of chloride-type layered double hydroxide using the second acidic solution (S14, S16).

(Regarding Figure 6)
Next, a description will be given of the control procedure in Fig. 6. As described above, the control device 70 executes the control in Fig. 6 in parallel with the control in Fig. 5 .

When the process of FIG. 6 begins, first, in step S50, the control device 70 determines whether the product to be produced is a nitric acid-type layered double hydroxide. If the determination in step S50 is positive (the product to be produced is a nitric acid-type layered double hydroxide), the process proceeds to step S52. On the other hand, if the determination in step S50 is negative (the product to be produced is a chloride-type layered double hydroxide), the process proceeds to step S70.

In step S52, the control device 70 starts measurement using the electrical conductivity meter 61. When a nitric acid-type layered double hydroxide is produced, the effluent discharged from the treatment device 52 contains the hazardous substance _NaNO3 . In this case, if the effluent does not meet the wastewater standard (a concentration of NO3-N (nitrate nitrogen concentration) of 380 mg/L or less, or 280 mg/L or less for greater safety), the effluent must be treated to meet the standard and then discharged, or disposed of as industrial waste. In this embodiment, measurement of the electrical conductivity of the effluent is started using the electrical conductivity meter 61 installed in the piping between the treatment device 52 and the selector valve 62, before the nitric acid-type layered double hydroxide is sent to the primary effluent tank 63 or the secondary effluent tank 64, in order to measure the nitrate nitrogen concentration in real time.

Next, in step S54, the control device 70 determines whether the electrical conductivity exceeds a threshold value. Here, it was discovered that when the nitrate nitrogen concentration of the effluent is below 380 mg/L, the electrical conductivity of the effluent is 2000 μs/cm or less. Therefore, in step S54, the control device 70 determines whether the electrical conductivity measured by the electrical conductivity meter 61 exceeds the threshold value (2000 μs/cm). The control device 70 also functions as a determination unit that determines whether the effluent meets predetermined standards.

If the determination in step S54 is positive, the process proceeds to step S56, where the control device 70 switches (or maintains) the switching valve 62 so that the wastewater is transported to the primary wastewater tank 63. Then, the process proceeds to step S60, where the control device 70 determines whether the manufacturing target has been switched. If the determination in step S60 is negative, the process returns to step S54.

On the other hand, if the determination in step S54 is negative, i.e., if the electrical conductivity is below the threshold, the process proceeds to step S58, where the control device 70 switches (or maintains) the switching valve 62 so that the effluent is transported to the secondary effluent tank 64. For example, immediately after starting to wash the nitrate-type layered double hydroxide in the processing device 52, the nitrate nitrogen concentration (electrical conductivity) is high, but once the washing process has progressed to a certain extent, the nitrate nitrogen concentration (electrical conductivity) decreases. In such a case, the determination in step S54 is negative, and the process of step S58 is executed. Note that in this embodiment, the control device 70 and the switching valve 62 function as a switching unit that switches the storage destination of the effluent.

Then, the process proceeds to step S60, where the control device 70 determines whether a change in the manufacturing target has occurred. If the determination in step S60 is negative, the process returns to step S54.

Then, the processing and determination of steps S54 to S60 are repeatedly executed, and if the determination of step S60 is positive, the process proceeds to step S70.

When the determination in step S60 is affirmative or the determination in step S50 is negative and the process proceeds to step S70, the control device 70 switches (or maintains) the switching valve 62 so as to transport the wastewater to the secondary wastewater tank 64. When the process proceeds to step S70, measurement by the electrical conductivity meter 61 is not performed. Since the wastewater discharged from the processing unit 52 during the production of a chloride-type layered double hydroxide does not contain _NaNO3 , all of the wastewater is stored in the secondary wastewater tank 64.

After step S70, the process proceeds to step S72, where the control device 70 waits until the manufacturing object is switched. Then, when the manufacturing object is switched, the control device 70 proceeds to step S52.

The effluent stored in the primary effluent tank 63 has a nitrate nitrogen concentration that exceeds the effluent standard, so it is either treated to meet the effluent standard and then released, or disposed of as industrial waste. In contrast, the effluent stored in the secondary effluent tank 64 has its pH adjusted to meet the effluent standard before being released.

As described in detail above, according to this embodiment, the production line 100 comprises a generation section 28 that mixes an acidic solution and an alkaline solution to generate layered double hydroxide, a first acidic solution preparation tank 11 and a first acidic solution storage tank 12 that supply a first acidic solution toward the generation section 28, a second acidic solution preparation tank 13 and a second acidic solution storage tank 14 that supply a second acidic solution toward the generation section 28, and a switching valve 23 that switches between a state in which the first acidic solution is supplied toward the generation section 28 from a pipe 15 connected to the first acidic solution storage tank 12 and a state in which the second acidic solution is supplied toward the generation section 28 from a pipe 16 connected to the second acidic solution storage tank 14. As a result, even when switching between the production of layered double hydroxide using the first acidic solution and the production of layered double hydroxide using the second acidic solution, there is no need to clean the first and second acidic solution preparation tanks 11, 13, the first and second acidic solution storage tanks 12, 14, or the pipes 15, 16. This reduces the effort required when switching between production targets and shortens the time required for switching.

Furthermore, according to this embodiment, the production line 100 is equipped with a primary wastewater tank 63 and a secondary wastewater tank 64 for storing wastewater generated during the production of layered double hydroxide, and the control device 70 determines whether the wastewater before being stored in the primary wastewater tank 63 or the secondary wastewater tank 64 meets predetermined standards based on the measurement results of the electrical conductivity meter 61, and switches the storage destination of the wastewater based on the determination result. This allows wastewaters that require different treatment methods to be stored in separate wastewater tanks, making it possible to efficiently treat the wastewater.

In addition, according to this embodiment, the control device 70 determines whether the effluent discharged during the production of nitric acid-type layered double hydroxide satisfies predetermined standards based on the measurement results of the electrical conductivity meter 61, and based on the determination results, switches the storage destination of the effluent between the primary effluent tank 63 and the secondary effluent tank 64, while the storage destination of the effluent discharged during the production of chloride-type layered double hydroxide is fixed at the secondary effluent tank 64. This allows the effluent to be stored in an appropriate effluent tank. Furthermore, because the electrical conductivity meter 61 is not used when producing chloride-type layered double hydroxide, power consumption in the production line 100 can be reduced.

(Modification)
In the above embodiment, the case where the control device 70 controls (switches) the switching valves in the production line 100 has been described, but the present invention is not limited to this. At least some of the switching valves may be manually switched by a manager or the like. In this case, the control device 70 may notify the manager of the switching timing of the switching valves via the input/output device 72.

In the above embodiment, the acidic solution supply unit 10 has been described as having two sets of acidic solution preparation tanks and acidic solution storage tanks, but this is not limited thereto and may have three or more sets. In this way, three or more types of layered double hydroxides can be produced in the production line 100, reducing the effort required when switching between production targets.

In the above embodiment, whether the nitrate nitrogen concentration in the effluent exceeds the standard is determined based on the electrical conductivity of the effluent. However, this is not limited to this, and the nitrate ion concentration in the effluent may be measured and the determination may be made based on the measurement results.

In the above embodiment, the case where the layered double hydroxide produced on the production line 100 is two types of layered double hydroxides with different uses (nitrate-type layered double hydroxide and chloride-type layered double hydroxide) has been described, but this is not limited to this. For example, two types of layered double hydroxides with the same use may be produced. Even if the use is the same, layered double hydroxides with different particle sizes may be produced. Therefore, for example, the layered double hydroxide to be produced may be switched between shipping layered double hydroxide with a large particle size (granular) and shipping layered double hydroxide with a small particle size (powder).

In the above embodiment, the acid solution supply unit 10 is described as including the first acid solution storage tank 12 and the second acid solution storage tank 14, but this is not limited to this. For example, if the first acid solution preparation tank 11 and the second acid solution preparation tank 13 can prepare a large amount of acid solution at one time (approximately the same amount as the first acid solution storage tank 12 and the second acid solution storage tank 14 can store), the acid solution supply unit 10 does not need to be provided with the first acid solution storage tank 12 and the second acid solution storage tank 14.

In the above embodiment, the pipes 15 and 16 of the acid solution supply unit 10 may be directly connected to the generation unit 28. In this case, open/close valves may be provided midway along the pipes 15 and 16 to individually switch whether or not the acid solution is transported to the generation unit 28. This further reduces the number of pipes that need to be cleaned when switching the manufacturing target.

The above-described embodiment is a preferred example of the present invention. However, it is not limited to this, and various modifications are possible within the scope of the gist of the present invention. For example, in the case of chloride-type layered double hydroxides, harmful substances may be removed from the water to make it drinkable, so the cleaning time when switching from the production of nitric acid-type layered double hydroxides to the production of chloride-type layered double hydroxides may be longer than the cleaning time when switching from the production of chloride-type layered double hydroxides to the production of nitric acid-type layered double hydroxides.

REFERENCE SIGNS LIST 12 First acid solution storage tank 14 Second acid solution storage tank 15 Pipe 16 Pipe 23 Switching valve 28 Generation unit 62 Switching valve 63 Primary drainage tank 64 Secondary drainage tank 70 Control device 81 Pipe 82, 83 Pipe 100 Production line

Claims (10)

An apparatus for producing a layered double hydroxide by mixing an acidic solution and an alkaline solution, comprising:
a mixing unit that mixes the acidic solution and the alkaline solution;
a first supply unit that supplies a first acidic solution toward the mixing unit;
a second supply unit that supplies a second acidic solution different from the first acidic solution toward the mixing unit;
a supply switching unit that switches between a state in which the first acidic solution is supplied from a first pipe connected to the first supply unit toward the mixing unit and a state in which the second acidic solution is supplied from a second pipe connected to the second supply unit toward the mixing unit;
An apparatus for producing a layered double hydroxide comprising: The layered double hydroxide manufacturing apparatus according to claim 1, wherein the mixing section produces a nitrate-type layered double hydroxide by mixing the first acidic solution with the alkaline solution, and produces a chloride-type layered double hydroxide by mixing the second acidic solution with the alkaline solution. The layered double hydroxide manufacturing apparatus of claim 1, wherein the supply switching unit switches the state based on whether the layered double hydroxide is shipped in granular or powder form. the first supply unit includes a first preparation tank that prepares the first acidic solution and a first storage tank that stores the first acidic solution,
2. The apparatus for producing a layered double hydroxide according to claim 1, wherein the second supply unit comprises a second preparation tank that prepares the second acidic solution and a second storage tank that stores the second acidic solution. 1. An apparatus for producing a layered double hydroxide by mixing an acidic solution and an alkaline solution to produce a nitric acid type layered double hydroxide,
a plurality of wastewater tanks for storing wastewater generated during the production of the nitrate-type layered double hydroxide;
a determination unit that determines whether or not the effluent containing nitrate nitrogen or nitrate ions generated during the production of the nitric acid-type layered double hydroxide satisfies a predetermined standard before the effluent is stored in any of the plurality of effluent tanks;
a switching unit that switches the storage destination of the drainage liquid to one of the plurality of drainage tanks based on the determination result of the determination unit;
An apparatus for producing a nitric acid type layered double hydroxide, comprising: 6. The apparatus for producing a nitrate-type layered double hydroxide according to claim 5, wherein the determining unit detects the electrical conductivity of the wastewater and determines whether the electrical conductivity satisfies a predetermined standard. 6. The apparatus for producing a nitrate-type layered double hydroxide according to claim 5, wherein the switching unit comprises: a first drain pipe through which the drainage passes; a plurality of branch drain pipes branching from the first drain pipe and connected to each of the plurality of drain tanks; and a drainage switching valve for switching communication between the first drain pipe and each of the plurality of branch drain pipes. 6. The apparatus for producing a nitrate-type layered double hydroxide according to claim 5, wherein the wastewater stored in each of the plurality of wastewater tanks is treated by a different method. An apparatus for producing a layered double hydroxide by mixing an acidic solution and an alkaline solution, comprising:
a generating unit that mixes a first acidic solution with the alkaline solution to generate a first layered double hydroxide of nitric acid type , or mixes a second acidic solution different from the first acidic solution with the alkaline solution to generate a second layered double hydroxide different from the nitric acid type ;
a plurality of waste liquid tanks for storing waste liquid generated during the production of the first layered double hydroxide or the second layered double hydroxide;
a switching unit which, when the first layered double hydroxide is being produced in the production unit, determines whether the effluent containing nitrate nitrogen or nitrate ions generated when the first layered double hydroxide is produced satisfies a predetermined standard before the effluent is stored in one of the plurality of effluent tanks, and switches the storage destination of the effluent to one of the plurality of effluent tanks based on the determination result, and when the second layered double hydroxide is being produced in the production unit, fixes the storage destination of the effluent to a predetermined effluent tank;
An apparatus for producing a layered double hydroxide comprising: 10. The layered double hydroxide manufacturing apparatus according to claim 9, wherein the drainage tank in which the effluent is stored when the second layered double hydroxide is being produced in the production section is the same as the drainage tank in which the effluent is stored when the first layered double hydroxide is being produced in the production section and the effluent satisfies a predetermined standard.