JP4110604B2 - Fluorine-containing water treatment method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a treatment method for desalinating fluorine-containing water with a reverse osmosis membrane, and more particularly to a method for desalting fluorine-containing water with a reverse osmosis membrane to treat it into drinking water.
[0002]
[Prior art]
A reverse osmosis membrane (hereinafter referred to as RO membrane) is a semipermeable membrane having pores that allow water to permeate and block the permeation of salt. To press water from the raw water side and permeate water to perform desalting. It is used for. Such a desalting technique using a reverse osmosis membrane is generally applied as a means for removing salt. However, in a system containing calcium and fluorine, when the concentration is increased, calcium fluoride becomes a scale and precipitates on the membrane surface. In order to prevent the permeation, the operation is performed at a concentration that does not generate calcium fluoride scale, and the water recovery rate is low. As described above, the RO method has problems such as an increase in membrane replacement cost due to scale adhesion to the membrane, an increase in the frequency of washing, and a low water recovery rate, thereby raising the water production cost.
[0003]
On the other hand, as a conventional technology for removing fluorine from groundwater or river water to make drinking water, water supply facility design guidelines and explanations (Japan Water Works Association (1990), pages 313 to 314) include water with an aluminum-based flocculant. A method is shown in which flocs of aluminum oxide are generated, and fluorine is adsorbed on the generated flocs for solid-liquid separation. However, in this method, since the amount of fluorine adsorption of aluminum hydroxide is small, it is necessary to add a large amount of chemicals. As a result, a lot of aluminum hydroxide sewage is generated, and the disposal requires excessive cost.
[0004]
As another conventional method, a method of adsorbing fluorine using activated alumina or bone charcoal as a filter medium has been proposed. However, since activated sulfate method uses aluminum sulfate to regenerate the filter medium, excessive sludge is generated by neutralization of the regenerated wastewater. appear. Further, in the bone charcoal method, performance degradation (decrease in adsorption amount) occurs due to repeated regeneration, and it cannot withstand long-term use.
In addition, as a conventional method, there has been proposed a method in which calcium carbonate is added to raw water to be electrolyzed and insolubilized and separated as calcium fluoride. In this method, MgCl ₂ and NaCl are also added during the electrolytic treatment. Increases in hardness and salt, and is unsuitable for drinking water.
[0005]
[Problems to be solved by the invention]
The object of the present invention is to efficiently treat fluorine-containing water with the RO membrane without clogging the RO membrane to increase the water recovery rate, and to treat fluorine contained in the raw water efficiently with a small amount of chemicals. It is to obtain a method for treating fluorine-containing water that can be insolubilized.
[0006]
[Means for Solving the Problems]
In the present invention, fluorine- containing water having fluorine of 1 to 20 mg / l and calcium of 2 to 50 mg / l is brought into contact with a Na-type strongly acidic cation exchange resin, and calcium ions in raw water are exchanged and adsorbed to obtain softened treated water. Ion exchange process,
A regeneration step in which a cation exchange resin exchanged and adsorbed with calcium ions is brought into contact with a 5 to 20% by weight aqueous sodium chloride solution to regenerate it into Na form ;
A reverse osmosis process in which softened water in the ion exchange process is separated into a permeate and a concentrate by reverse osmosis membrane separation,
Reacting the concentrated liquid in the reverse osmosis process with the regenerated effluent discharged from the regenerating process to insolubilize the fluorine in the concentrated liquid as calcium fluoride, and the solid-liquid separation to separate the reaction liquid in the insolubilizing process into solid and liquid A process for treating fluorine-containing water comprising a step.
[0007]
In the present invention, the fluorine-containing water to be treated is water mainly containing fluorine as fluoride ions, and examples thereof include river water, lake water, and groundwater, but are not limited thereto. Fluorine-containing water suitable as a treatment target includes 1-20 mg / l fluorine such as river water, lake water, and groundwater, and 2-50 mg / l calcium fresh water, and the present invention treats these raw waters for drinking water. It is suitable to be applied to other systems for obtaining water.
[0008]
In general, such fresh water contains about 1 to 10 mg / l of fluorine and 2 to 50 mg / l of calcium. When this is concentrated by the RO membrane, calcium fluoride is precipitated and the RO membrane is clogged. In the present invention, calcium is removed to prevent this. Although it is difficult to remove the low-concentration fluorine as described above, calcium can be removed by ion exchange to such an extent that precipitation of calcium fluoride can be prevented.
[0009]
Therefore, in the present invention, in the ion exchange step, fluorine-containing water (raw water) is brought into contact with the Na-type strongly acidic cation exchange resin, and calcium ions in the raw water are exchanged and adsorbed to obtain softened treated water.
[0010]
The method for contacting the raw water with the cation exchange resin is not particularly limited. For example, a softening tower filled with Na-type strongly acidic cation exchange resin can be used in the tower, and can be carried out by passing the raw water through the softening tower. . The water flow may be upward or downward. By passing water, an ion exchange reaction occurs, calcium ions are adsorbed and removed from the ion exchange resin, and decalcified water (softened treated water) is obtained as treated water.
[0011]
As the ion exchange process continues, the amount of calcium ions adsorbed on the ion exchange resin approaches saturation, and calcium ions begin to leak (flow point). At this point of time or periodically, the process proceeds to an ion exchange resin regeneration step.
[0012]
Regeneration can be performed by bringing a cation exchange resin having exchanged and adsorbed calcium ions into contact with a regenerant. The regenerant to play Na form, 5 to 20 wt% aqueous sodium chloride solution can use. The sodium chloride concentration of the regenerant is preferably around 10% by weight . By playing as this, regeneration effluent is obtained which contains calcium ions.
[0013]
The softened water in the ion exchange step is supplied to the RO membrane device to perform membrane separation, and is separated into a permeate and a concentrate. RO membrane removes fluorine by desalting the softened water in the ion exchange process, and is generally used for desalting, such as cellulose acetate, polyamide, polysulfone, etc. having pores of 0.5 to 100 nm. Is used. As the form of the RO membrane, those generally used for desalting such as a flat membrane, a spiral, a hollow fiber, and a tubular shape are used.
[0014]
By subjecting the softened water in the ion exchange process to membrane separation with an RO membrane, fluorine and other salts are concentrated on the concentrate side, and a permeate containing no fluorine is obtained. At this time, the concentrated solution is adjusted to pH 4 to 6, preferably pH 4.5 to 5.5 with an acid to prevent precipitation of calcium fluoride and other insolubilized materials on the RO membrane. Membrane separation is operated to allow 80-95% of the separation liquid to permeate and leave 5-20% as a concentrate. The permeate is used for drinking and other irrigation water as the final treated water.
[0015]
In the insolubilization step, the concentrated solution is insolubilized as calcium fluoride by reacting the regenerated drainage liquid in the regenerating step with calcium fluoride. The reaction can be carried out by mixing the concentrated liquid and the regenerated waste liquid, whereby the fluorine being concentrated reacts with the calcium in the regenerated discharged liquid and is insolubilized as calcium fluoride.
[0016]
The reaction solution in the insolubilization step is subjected to solid-liquid separation in the solid-liquid separation step, and separated into a separation solution and sludge. As the solid-liquid separation means, precipitation is generally used, but centrifugation, filtration separation, membrane separation and the like can be used. The separation liquid may be discharged out of the system as a treatment liquid, or may be mixed with raw water and treated again. The separated sludge can be easily post-treated such as dehydration and used as a calcium source or a fluorine source.
[0017]
As described above, in the present invention, when the fluorine-containing water is separated by the RO membrane, the calcium ion in the raw water is previously ion-exchanged and adsorbed by the softening treatment in order to prevent the calcium fluoride generated by the membrane concentration from being scaled. Calcium in the effluent is insolubilized as calcium fluoride by reacting with fluorine in the membrane concentrate so that calcium in the raw water can be reused, reducing the amount of chemicals used and reducing sludge generation. It is done.
[0018]
【The invention's effect】
As described above, according to the present invention, fluorine-containing water having fluorine of 1 to 20 mg / l and calcium of 2 to 50 mg / l is brought into contact with the Na-type strongly acidic cation exchange resin to exchange and remove calcium ions in the raw water. An ion exchange process for obtaining softened treated water, a regeneration process for regenerating the cation exchange resin that has exchanged and adsorbed calcium ions with a 5 to 20 wt% sodium chloride aqueous solution to form Na, and a softened treated water for the ion exchange process in a reverse osmosis membrane Reverse osmosis process that separates and separates into permeate and concentrated liquid, and reacts the concentrated liquid in the reverse osmosis process with the regenerated effluent discharged from the regenerative process to insolubilize the fluorine in the concentrated liquid as calcium fluoride. step, and because it contains a solid-liquid separation step of the reaction solution to solid-liquid separation of insoluble step, the fluorine containing water without clogging of the RO membrane is treated efficiently by the RO membrane water Yield can be enhanced, fluorine can be insolubilized efficiently processed to a small chemical amount contained in the raw water.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a system diagram showing a method for treating fluorine-containing water according to an embodiment. In FIG. 1, reference numeral 1 denotes a softening tower, which is filled with Na-type strongly acidic cation exchange resin to form a cation exchange resin layer 2. 3 is a circulation tank, 4 is an RO membrane device, 5 is a reaction tank, and 6 is a precipitation tank.
[0020]
The treatment method is an ion exchange step, in which raw water (fluorine-containing water) is introduced from the raw water channel 11 into the softening tower 1, and the cation exchange resin layer 2 is passed in a downward flow to exchange and adsorb calcium ions. Removes and softens calcium. Thereby, the softening process water with which the calcium concentration became substantially zero is obtained.
[0021]
The form of calcium ions in the raw water has a primary hardness [Ca (HCO ₃ ) ₂ ] and a secondary hardness [CaCl ₂ , CaSO ₄ , Ca (NO ₃ ) ₂ ], which pass through the cation exchange resin layer 2. At the time, it is adsorbed and adsorbed on Na-type strongly acidic cation exchange resin. This reaction is represented by the formula (1).
[Chemical 1]
2R-Na ⁺ + Ca ²⁺ → R ₂ -Ca ²⁺ + Na ⁺ (1)
[0022]
The softened water subjected to the ion exchange treatment is introduced into the circulation tank 3 from the system path 12 and temporarily stored, and then supplied from the system path 13 to the RO membrane device 4 to be desalted by the RO membrane 14. In the RO membrane device 4, the permeate that has passed through the RO membrane 14 is taken out from the treatment water channel 15 as desalted treated water, and the concentrated solution enriched with fluorine is circulated from the circulation channel 16 to the circulation tank 3.
[0023]
In the RO membrane 14, 80 to 95% of the inflow water becomes the permeate (treated water), and the remaining 5 to 20% becomes the concentrate. The membrane material, type, and shape of the RO membrane 14 are not limited.
The concentrated solution is concentrated to about 5 to 20 times the fluorine concentration of the raw water.
[0024]
After the ion exchange treatment by the softening tower 1 continues, the amount of calcium ions adsorbed on the ion exchange resin layer 2 approaches saturation and reaches a penetration point where calcium ions begin to leak, or after a predetermined period of time has passed, ion exchange The Na-type strongly acidic cation exchange resin that forms the resin layer 2 is regenerated.
[0025]
Regeneration is performed by introducing a sodium chloride aqueous solution as a regenerant from the chemical injection channel 21 to the softening tower 1 and passing the ion exchange resin layer 2 in a downward flow. By this regeneration treatment, the cation exchange resin having adsorbed calcium ions is regenerated into Na form, and the regenerated drainage liquid in which calcium ions are concentrated is discharged. The regenerated effluent is concentrated to a calcium concentration of about 5 to 20 times the raw water calcium concentration. The regeneration reaction is represented by the formula (2).
[Chemical formula 2]
R ₂ −Ca ²⁺ + 2NaCl → 2R-Na ⁺ + Ca ²⁺ + 2Cl ⁻
... (2)
[0026]
The regenerated effluent discharged from the softening tower 1 is introduced into the reaction tank 5 from the system path 22, mixed with the solution in the circulation tank introduced into the reaction tank 5 from the circulation tank 3 through the system path 23, and stirred with the stirrer 24. .
In the reaction tank 5, calcium ions contained at a high concentration in the regeneration waste liquid react with fluorine ions contained at a high concentration in the liquid in the circulation tank, and insoluble calcium fluoride is generated and deposited. To do. This reaction is represented by Formula (3).
[Chemical 3]
Ca ²⁺ ＋ 2F ⁻ → CaF ₂ ↓ (3)
[0027]
The reaction liquid in the reaction tank 5 enters the precipitation tank 6 from the system path 25 and is separated into solid and liquid, the supernatant liquid is taken out from the treatment water path 26 as treated water, and the separated sludge is taken out from the sludge path 27.
The raw water is passed through the regenerated cation exchange resin layer 2 in the same manner as above to restart the treatment.
[0028]
【Example】
Examples of the present invention will be described below.
Example 1
Groundwater with a fluorine concentration of 4 mg / l, a Ca ion concentration of 7 mg / l, and a pH of 7.8 is passed through a softening tower packed with Na-type strongly acidic cation exchange resin at SV = 8 liter / hr, and below the detection limit of Ca ion concentration. Softened water was obtained. This softened water was passed through the polyamide RO membrane at a recovery rate of 90% to obtain permeated water having a fluorine concentration of 0.2 mg / l and concentrated water having a fluorine concentration of 39 mg / l.
[0029]
Ca leak occurred at the time when 200 bed volume (Bed Volume) of the resin volume was passed through, and regeneration with saline was performed. The Ca concentration in the regenerated effluent was 75 mg / l.
The regenerated effluent and the membrane concentrated water were mixed, stirred, and allowed to stand to obtain supernatant water and precipitated sludge.
The supernatant water had a fluorine concentration of 11 mg / l and a Ca concentration of 45 mg / l, and 28 mg / l of fluorine reacted with Ca and could be precipitated and removed as CaF ₂ .
[Brief description of the drawings]
FIG. 1 is a system diagram showing a method for treating fluorine-containing water according to an embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Softening tower 2 Cation exchange resin layer 3 Circulation tank 4 RO membrane apparatus 5 Reaction tank 6 Precipitation tank 11 Raw water channel 12, 13, 22, 23, 25 System route 14 RO membrane 15, 26 Treatment water channel 16 Circulation channel 21 Chemical injection channel 24 Stirrer 27 Sludge path

Claims (1)

An ion exchange step of obtaining softened treated water by bringing fluorine-containing water of fluorine 1 to 20 mg / l and calcium 2 to 50 mg / l into contact with a Na-type strongly acidic cation exchange resin to exchange and remove calcium ions in raw water;
A regeneration step in which a cation exchange resin exchanged and adsorbed with calcium ions is brought into contact with a 5 to 20% by weight aqueous sodium chloride solution to regenerate Na form ;
A reverse osmosis process in which softened water in the ion exchange process is separated into a permeate and a concentrate by reverse osmosis membrane separation,
Reacting the concentrated liquid in the reverse osmosis process with the regenerated effluent discharged from the regenerating process to insolubilize the fluorine in the concentrated liquid as calcium fluoride, and the solid-liquid separation to separate the reaction liquid in the insolubilizing process into solid and liquid The processing method of fluorine-containing water including a process.

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