Operating method of a fluorine adsorption tower

Abstract

This invention provides a method for operating a fluorine adsorption tower that requires less water to push out the alkaline aqueous solution after the fluorine desorption process using the alkaline aqueous solution, allows the pH inside the fluorine adsorption tower to decrease rapidly, and prevents deterioration of the fluorine adsorbent. [Solution] A method for operating a fluorine adsorption tower, comprising an adsorption step of passing raw water consisting of fluorine-containing wastewater through a fluorine adsorption tower filled with fluorine adsorbent material, and a regeneration step of passing an alkaline aqueous solution through the fluorine adsorption tower to desorb fluorine from the fluorine adsorbent material, wherein the regeneration step is characterized by performing a desorption step of passing an alkaline aqueous solution through the fluorine adsorption tower, then passing a washing solution through the fluorine adsorption tower, and at this time, allowing the water flowing out of the fluorine adsorption tower to flow into a neutralization tank, adding acid to the water in the neutralization tank to make water with a predetermined pH, and passing this water with a predetermined pH through the fluorine adsorption tower.

Description

Technical Field

[0001] The present invention relates to an operation method of a fluorine adsorption tower for fluorine adsorption treatment of fluorine-containing wastewater, and particularly relates to an operation method of a fluorine adsorption tower having a regeneration step and a subsequent startup (restart of raw water flow) step. Specifically, the present invention relates to an operation method of a fluorine adsorption tower filled with fluorine adsorbent-supported resin particles as an adsorbent.

Background Art

[0002] As an adsorbent for adsorbing and removing fluorine in fluorine-containing wastewater, those obtained by granulating hydrous oxides, hydroxides or gel-like oxides of rare earth elements such as cerium with ethylene-vinyl alcohol copolymer or polyacrylonitrile resin, or those obtained by supporting cerium on a carrier of styrene-based synthetic resin are known (Patent Documents 1, 2).

[0003] Patent Document 3 describes a fluorine adsorbent obtained by molding zirconium hydrate into a spherical shape using ethylene vinyl alcohol copolymer.

[0004] By passing raw water (fluorine-containing wastewater) through a fluorine adsorption tower filled with such fluorine adsorbent particles, fluorine is adsorbed and removed.

[0005] To regenerate the fluorine adsorbent in this fluorine adsorption tower, an alkaline aqueous solution such as sodium hydroxide is passed through to elute (desorb) fluorine. Then, water is passed through to extrude the alkaline aqueous solution.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

[0007] When an alkaline aqueous solution is passed through a fluorine adsorption tower that has adsorbed fluorine to desorb the fluorine, and then water is passed through to push out the alkaline aqueous solution, a large amount of water is required to sufficiently push out the alkaline aqueous solution from inside the tower.

[0008] If alkaline aqueous solution remains in the tower and the pH inside the tower is high, restarting the flow of fluorine-containing wastewater carries the risk of calcium components in the fluorine-containing wastewater precipitating within the fluorine adsorption tower.

[0009] One might consider adding acid to the water used to push out the alkaline solution to quickly lower the pH inside the fluorine adsorption tower. However, in this case, the pH inside the tower may drop excessively (for example, to less than 3), which could cause the synthetic resin constituting the fluorine adsorbent to deteriorate due to leaching or other reasons, thus compromising the durability of the fluorine adsorbent.

[0010] The present invention aims to provide a method for operating a fluorine adsorption tower that requires a small amount of water to push out the alkaline aqueous solution after the fluorine desorption process using the alkaline aqueous solution, allows the pH inside the fluorine adsorption tower to decrease rapidly, and prevents deterioration of the fluorine adsorbent. [Means for solving the problem]

[0011] The gist of this invention is as follows:

[0012] [1] An adsorption process in which raw water consisting of fluorine-containing wastewater is passed through a fluorine adsorption tower filled with fluorine adsorbent, A regeneration process is performed by passing an alkaline aqueous solution through the fluorine adsorption tower to desorb fluorine from the fluorine adsorbent. In a method for operating a fluorine adsorption tower having, In the regeneration process, A desorption process is performed by passing an alkaline aqueous solution through the fluorine adsorption tower. Next, washing water is passed through the fluorine adsorption tower, and the water flowing out of the fluorine adsorption tower at this time is introduced into a neutralization tank, and acid is added to the water in the neutralization tank to make it water with a predetermined pH. This water with a predetermined pH is passed through the fluorine adsorption tower. A method for operating a fluorine adsorption tower, characterized by the features described above.

[0013] [2] A method for operating the fluorine adsorption tower described in [1], wherein regenerated water with a Ca concentration of less than 20 mg / L is first passed through as the washing water.

[0014] [3] A method for operating the fluorine adsorption tower of [2], wherein after passing the recycled water through it, the raw water is passed through it as a second washing water.

[0015] [4] A method for operating the fluorine adsorption tower according to [3], wherein the raw water as the second washing water is supplied from the neutralization tank to the fluorine adsorption tower through the pH adjustment tank.

[0016] [5] A method for operating the fluorine adsorption tower according to [4], wherein acid is added to both the neutralization tank and the pH adjustment tank to set the pH of the water supplied to the fluorine adsorption tower to 3 to 6.

[0017] [6] The alkaline aqueous solution is obtained by adding alkali to the reclaimed water. [2] A method for operating a fluorine adsorption tower.

[0018] [7] A method for operating the fluorine adsorption tower according to [4], wherein in the adsorption step, raw water supplied to the fluorine adsorption tower is supplied to the fluorine adsorption tower through the neutralization tank and the pH adjustment tank.

[0019] [8] A method for operating the fluorine adsorption tower according to [7], wherein raw water that has passed through the pH adjustment tank is supplied to the fluorine adsorption tower through an intermediate tank.

[0020] [9] A method for operating a fluorine adsorption tower, wherein acid is added to both the neutralization tank and the pH adjustment tank to set the pH of the water supplied to the fluorine adsorption tower to 3 to 6.[7] or [8] [Effects of the Invention]

[0021] According to the operation method of the fluorine adsorption tower of the present invention, in the regeneration process of the fluorine adsorbent, after fluorine desorption, the water for extruding the alkaline aqueous solution that passes water through the fluorine adsorption tower is made to flow into the receiving tank, acid is added to make acidic water with a predetermined pH, this acidic water is passed through the fluorine adsorption tower, and the effluent water at this time is returned to the receiving tank.

[0022] According to the operation method of the fluorine adsorption tower of the present invention, since the water for extrusion and the acidic water are circulated, the amount of water used for regeneration can be reduced to be sufficient. Further, by passing the acidic water, the pH in the fluorine adsorption tower decreases at an early stage, so that the passage of fluorine-containing wastewater can be resumed at an early stage.

[0023] Also, in the operation method of the fluorine adsorption tower according to one aspect of the present invention, since the acidic water is pH-adjusted in both the neutralization tank and the pH adjustment tank to accurately reach a predetermined pH (for example, 3 to 4), deterioration of the fluorine adsorbent is also prevented (suppressed).

Brief Description of the Drawings

[0024] [Figure 1] It is a configuration diagram of a treatment system for fluorine-containing wastewater. [Figure 2] It is a water flow diagram for passing fluorine-containing wastewater. [Figure 3] It is a water flow diagram for the desorption process. [Figure 4] It is a water flow diagram for the extrusion process. [Figure 5] It is a water flow diagram for the regeneration process. [Figure 6] It is a water flow diagram for the regeneration process.

Embodiments for Carrying Out the Invention

[0025] Hereinafter, the present invention will be described in more detail.

[0026] Examples of fluorine-containing wastewater treated in this invention include wastewater from semiconductor and liquid crystal factories and other electronic component manufacturing processes, as well as wastewater from chemical and metal processing manufacturing processes, which has been treated in a primary fluorine wastewater treatment facility. The fluorine concentration of the fluorine-containing wastewater targeted by this invention is 1 to 50 mg / L as F, particularly 5 to 30 mg / L, but is not limited to this range.

[0027] Suitable fluorine adsorbents for filling the fluorine adsorption tower are those made by granulating fluorine adsorbents such as rare earth elements (preferably cerium) or zirconium metal hydrate oxides or metal hydrate fluorides with synthetic resin.

[0028] As synthetic resins, phenol resins, urea resins, melamine resins, polyester resins, diallyl phthalate resins, xylene resins, alkylbenzene resins, epoxy resins, epoxy acrylate resins, silicon resins, urethane resins, fluororesins, vinyl chloride resins, vinylidene chloride resins, polyethylene, chlorinated polyolefin, polypropylene, polystyrene, ABS resins, polyamides, methacrylic resins, polyacetals, polycarbonates, cellulose resins, polyvinyl alcohol, polyimide, polysulfone, polyacrylonitrile, etc., and copolymers of the above can be used. However, those that have appropriate water resistance and chemical resistance, are highly hydrophilic, and can form a porous structure are preferred, and polyamides, cellulose resins, polysulfone, polyacrylonitrile, vinyl chloride, vinyl alcohol copolymers, etc., are particularly preferred.

[0029] The amount of synthetic resin used is 5 to 50% by weight of the metal hydrated oxide or hydrated fluoride, particularly preferably 10 to 30% by weight. Granular fluorine adsorbent is formed from the fluorine adsorbent and the synthetic resin. The average particle size (JIS mesh) of the fluorine adsorbent is 0.35 to 1.18 mm, particularly preferably about 0.6 to 0.8 mm.

[0030] Figure 1 is a flowchart showing an example of a fluorine adsorption system that implements the operation method of the fluorine adsorption tower according to the present invention.

[0031] Fluorine-containing wastewater from the raw water tank (not shown) is introduced into the neutralization tank 2 through piping 1 from the filter (not shown). Acids such as hydrochloric acid can be added to the neutralization tank 2 from the acid addition means 3.

[0032] The water in the neutralization tank 2 is transferred to the pH adjustment tank 4. Acids such as hydrochloric acid can also be added to the pH adjustment tank 4 from the acid addition means 5.

[0033] The water in the pH adjustment tank 4 is transferred to the intermediate tank 6, and from the intermediate tank 6, it is passed through a pump (not shown) and piping 7 to the fluorine adsorption tower 8, where the treated water flows out into piping 9. The fluorine adsorption tower 8 is filled with fluorine adsorbent material.

[0034] A pipe 10 is connected to the bottom of the fluorine adsorption tower 8 for draining the desorbed wastewater during the fluorine desorption treatment in the fluorine adsorption tower 8. The pipe 10 branches into pipes 11 and 12. One pipe 11 can supply water to a regenerated wastewater tank (not shown), and the other pipe 12 can supply water to the neutralization tank 2. On / off valves (not shown) are provided on pipes 9 to 12, respectively.

[0035] Water used for desorption treatment of the fluorine adsorption tower 8 with an alkaline aqueous solution and for subsequent extrusion of the alkaline aqueous solution (hereinafter sometimes referred to as regenerated water) can be introduced into the water tank 21 via piping 20. The water in this water tank 21 can be supplied to the top of the fluorine adsorption tower 8 via a pump (not shown) and piping 22 and 23. An alkaline aqueous solution such as sodium hydroxide can be added to this piping 22 from the alkaline aqueous solution addition means 25.

[0036] Furthermore, the water in the tank 21 can be supplied to the bottom of the fluorine adsorption tower 8 via pipes 22 and 24, and the fluorine adsorption tower 8 can be backwashed.

[0037] Fluorine-containing wastewater is passed through this fluorine adsorption tower 8 for fluorine adsorption treatment. When the amount of adsorbed fluorine increases and the fluorine concentration in the treated water exceeds a specified concentration, regeneration treatment is performed using recycled water.

[0038] For recycled water, a calcium concentration of 20 mg / L or less, and especially 5 mg / L or less, is preferred. This is to prevent calcium adsorption in the fluorine adsorption tower 8.

[0039] [Fluorine adsorption treatment operation] Figure 2 shows the flow of operation during fluorine adsorption treatment using this fluorine adsorption system.

[0040] As shown in Figure 2, the raw water (fluorine-containing wastewater) flows through pipe 1, neutralization tank 2, pH adjustment tank 4, intermediate tank 6, pipe 7, and fluorine adsorption tower 8, and treated water is extracted from pipe 9.

[0041] In pH adjustment tank 4, the pH is adjusted to 6-10, particularly 6-9, by adding acid. Acid may also be added in neutralization tank 2. By adjusting the pH in both neutralization tank 2 and pH adjustment tank 4, pH fluctuations are prevented (suppressed).

[0042] This fluorine adsorption treatment operation is carried out until the fluorine concentration of the treated water reaches a specified value, or until a specified amount of raw water has been passed through.

[0043] Furthermore, the fluorine adsorption tower 8 is backwashed as needed during the water flow.

[0044] [Desorption operation of fluorine adsorption tower 8] To desorb fluorine from the fluorine adsorbent in the fluorine adsorption tower 8, as shown in Figure 3, the introduction of raw water is stopped, regenerated water is supplied from the water tank 21 to the fluorine adsorption tower 8 via pipes 22 and 23, and an alkaline aqueous solution is added to pipe 22 from the alkali addition means 25. As a result, the alkaline aqueous solution flows through the fluorine adsorption tower 8, and fluorine is desorbed from the fluorine adsorbent. The regenerated wastewater is discharged from the bottom of the fluorine adsorption tower 8 via pipes 10 and 11.

[0045] Furthermore, it is preferable that the pH of the alkaline aqueous solution supplied from pipes 22 and 23 to the fluorine adsorption tower 8 during this desorption operation be 12 to 14, particularly 13 to 14.

[0046] This de-attachment operation is carried out until the fluorine concentration in the regenerated wastewater falls below a specified value, or until a specified amount of alkaline aqueous solution is passed through.

[0047] [Extrusion and washing with alkaline aqueous solution] After the fluorine desorption operation using an alkaline aqueous solution, as shown in Figure 4, the addition of the alkaline aqueous solution from the alkali addition means 25 is stopped, and the regenerated water with a low Ca concentration in the water tank 21 is passed through pipes 22 and 23 to the fluorine adsorption tower 8. The water that is pushed out is discharged from the bottom of the fluorine adsorption tower 8 through pipes 10 and 11.

[0048] The water flow velocity to the fluorine adsorption tower 8 during extrusion is preferably 15-45% of the flow velocity during fluorine adsorption treatment operation, particularly around 20-40%.

[0049] The extrusion of this alkaline aqueous solution is carried out until the pH or alkalinity of the effluent water from the fluorine adsorption tower 8 falls within a specified range, or until a predetermined amount of regenerative water (for example, 3 to 5 times the packed bed volume in the fluorine adsorption tower 8) is passed through. After the extrusion of this alkaline aqueous solution, regenerative water may be passed through the same path as the extrusion process for a predetermined time (for example, 40 to 60 minutes) to wash the fluorine adsorbent.

[0050] [Recycled water recycling] When the extrusion process shown in Figure 4 is performed, the alkaline aqueous solution in the fluorine adsorption tower 8 is extruded, but the alkaline aqueous solution is still contained within the particles of the fluorine adsorbent in the fluorine adsorption tower 8. Therefore, even if raw water is passed through the fluorine adsorption tower 8 immediately after extrusion, the pH inside the fluorine adsorbent is high, and there is a risk that Ca will be adsorbed onto the fluorine adsorbent.

[0051] Therefore, conventionally, an acidic aqueous solution is passed through the fluorine adsorption tower after extrusion. However, this can cause the pH of the acidic aqueous solution to become excessively low, leading to deterioration of the resin that makes up the fluorine adsorbent.

[0052] Therefore, in this embodiment of the present invention, after the extrusion process shown in Figure 4, as shown in Figure 5, regenerated water with a low Ca concentration is passed through pipes 22 and 23 to the fluorine adsorption tower 8, and the effluent from the fluorine adsorption tower 8 is sent to the neutralization tank 2 through pipes 10 and 12. Then, in the neutralization tank 2 and the pH adjustment tank 4, acid is added from the acid adding means 3 and 5 to adjust the pH to 3 to 6, preferably 3 to 4. The water in the neutralization tank 2 flows from the pH adjustment tank 4 and the relay tank 6 to the fluorine adsorption tower 8 through pipe 7. As a result, the pH of the liquid in the adsorbent particles in the fluorine adsorption tower 8 also decreases rapidly.

[0053] The water flow rate through the fluorine adsorption tower 8 during this recycled water circulation is preferably 80-120%, particularly 90-100%, of the flow rate during the fluorine adsorption treatment operation. Furthermore, this recycled water circulation process is preferably carried out for 10-60 minutes, particularly 20-40 minutes.

[0054] [Raw water cycle] After the recycled water circulation process, the supply of recycled water from the water tank 21 is stopped, and raw water is supplied to the neutralization tank 2 as shown in Figure 6. The raw water is then passed from the neutralization tank 2 through the pH adjustment tank 4 and the intermediate tank 6 to the fluorine adsorption tower 8. At this time, acid is added from the acid addition means 3 and 5 to the neutralization tank 2 and the pH adjustment tank 4 to adjust the pH to 3 to 6, preferably to around 3 to 4. The effluent from the fluorine adsorption tower 8 is returned to the neutralization tank 2 via pipes 10 and 12.

[0055] By implementing this raw water recycling process, the recycling process for recycled water is shortened, resulting in a reduction in the amount of recycled water used.

[0056] The water flow rate through the fluorine adsorption tower 8 in this raw water circulation process is preferably 80-120% of the flow rate during fluorine adsorption treatment operation, and particularly preferably 90-100%. This raw water circulation process is preferably carried out for 10-60 minutes, and particularly preferably for 20-40 minutes.

[0057] [Resumption of raw water supply] After the raw water circulation process shown in Figure 6 is completed, the raw water flow operation shown in Figure 2 is resumed.

[0058] [Advantages of the above driving style] As described above, immediately after regeneration of fluorine adsorption tower 8, the discharge of regeneration sodium from the fluorine adsorbent inside fluorine adsorption tower 8 continues, and the pH is high. Therefore, if raw water is immediately passed through, there is a risk that calcium from fluorine-containing wastewater will precipitate inside the tower. To reduce this risk, the water source for washing after extrusion is first made from regeneration water, and the water quality conditions are set to Ca < 20 mg / L. After the discharge of sodium from the fluorine adsorbent is completed, the regeneration water is circulated, then raw water is circulated, and then steady-state operation is resumed.

[0059] In this embodiment, a neutralization tank 2 is installed before the pH adjustment tank 4, and acid is injected in both the neutralization tank 2 and the pH adjustment tank 4 during circulation, thereby suppressing pH fluctuations in the pH adjustment tank 4 during the adsorption and circulation processes.

[0060] In this way, the risk of increased fluorine concentration in treated water due to high pH can be avoided, and the leaching of resin from fluorine adsorbents due to low pH water can be prevented, thereby reducing the risk of decreased water volume. Furthermore, the burden of on-site adjustments to the concentration and duration of acid washing to mitigate these risks is reduced.

[0061] In this embodiment, a recycling process for reclaimed water and a recycling process for raw water are performed, but since an acid washing process like in the conventional example is not performed, an increase in regeneration time can be prevented.

[0062] In this embodiment, as described above, by setting the return destination of the circulation process to the neutralization tank 2 preceding the pH adjustment tank 4, it is possible to accurately adjust the pH at the inlet of the fluorine adsorption tower to a constant level (preferably pH 3 to 4, particularly 3 to 3.5) even during circulation.

[0063] This process of circulating low-pH water essentially also serves as a dilute acid washing process, allowing the treated water pH to drop quickly, completing the water quality adjustment phase and reducing the risk of the treated water pH becoming too high.

[0064] Furthermore, the pH of wastewater in the initial stages of the circulation process is often still high. Returning this directly to the raw water tank poses risks such as calcium deposition within the tower and deterioration of fluorine concentration in the treated water, including in other operating regeneration systems besides the one in question. Returning the circulating water to neutralization tank 2 prevents these risks. In the above embodiment, the neutralization tank 4 is installed in the path that supplies raw water to the fluorine adsorption tower 8. However, a circulation path may be provided to circulate regenerative water directly to the fluorine adsorption tower 8 without passing through the pH adjustment tank 4 or the intermediate tank 6, and the neutralization tank 4 may be installed in this circulation path. [Explanation of symbols]

[0065] 2 Neutralization tank 4 pH adjustment tank 6. Relay tank 8. Fluorine adsorption tower 21 Aquariums

Claims

1. An adsorption process in which raw water consisting of fluorine-containing wastewater is passed through a fluorine adsorption tower filled with fluorine adsorbent, A regeneration process is performed by passing an alkaline aqueous solution through the fluorine adsorption tower to desorb fluorine from the fluorine adsorbent. In a method for operating a fluorine adsorption tower having, In the regeneration process, A desorption process is performed by passing an alkaline aqueous solution through the fluorine adsorption tower. Next, washing water is passed through the fluorine adsorption tower, and the water flowing out of the fluorine adsorption tower at this time is introduced into a neutralization tank, and acid is added to the water in the neutralization tank to make it water with a predetermined pH. This water with a predetermined pH is passed through the fluorine adsorption tower. A method for operating a fluorine adsorption tower, characterized by the features described above.

2. The method for operating a fluorine adsorption tower according to claim 1, wherein, as the washing water, regenerated water with a Ca concentration of less than 20 mg / L is first passed through as the washing water.

3. A method for operating a fluorine adsorption tower according to claim 2, wherein, after passing the recycled water through it, the raw water is passed through it as a second washing water.

4. A method for operating a fluorine adsorption tower according to claim 3, wherein the raw water used as the second washing water is supplied from the neutralization tank to the fluorine adsorption tower through the pH adjustment tank.

5. A method for operating a fluorine adsorption tower according to claim 4, wherein acid is added to both the neutralization tank and the pH adjustment tank to set the pH of the water supplied to the fluorine adsorption tower to 3 to 6.

6. The method for operating a fluorine adsorption tower according to claim 2, wherein the alkaline aqueous solution is obtained by adding alkali to the regenerative water.

7. The method for operating a fluorine adsorption tower according to claim 4, wherein in the adsorption step, raw water supplied to the fluorine adsorption tower is supplied to the fluorine adsorption tower through the neutralization tank and the pH adjustment tank.

8. A method for operating a fluorine adsorption tower according to claim 7, wherein raw water that has passed through the pH adjustment tank is supplied to the fluorine adsorption tower through an intermediate tank.

9. A method for operating a fluorine adsorption tower according to claim 7 or 8, wherein acid is added to both the neutralization tank and the pH adjustment tank to set the pH of the water supplied to the fluorine adsorption tower to 3 to 6.

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