JP7274379B2 - water treatment method - Google Patents

Description

The present invention relates to a water treatment method for treating water containing fluoride ions and sulfate ions.

In coal-fired power plants, coke plants, steel plants, and the like, flue gas desulfurization wastewater containing sulfate ions and fluorine ions is generated by desulfurizing exhaust gas generated by burning coal or coke. Flue gas desulfurization effluent usually contains tens of thousands mg/L or more of sulfate ions, and further contains several tens of mg/L to several hundreds of mg/L of fluoride ions. Therefore, it is necessary to remove fluorine ions from the waste water before discharging it.

Conventionally, various methods have been proposed as methods for removing fluoride ions from flue gas desulfurization wastewater. For example, Patent Document 1 discloses a treatment method in which calcium ions are added to wastewater containing fluoride ions, magnesium ions and sulfate ions to adjust the pH to 9.4 to 9.8. Patent Document 2 discloses a method for removing fluoride ions from flue gas desulfurization wastewater using magnesium hydroxide as a desulfurizing agent, wherein suspended solids in the wastewater are separated into solid and liquid, and water is added to the solid-liquid separated liquid. A treatment method is disclosed in which sodium oxide is added to adjust the pH to 9 or higher, fluorine ions are adsorbed on the precipitates formed, and solid-liquid separation is performed. Patent Document 3 discloses a flue gas desulfurization wastewater treatment method including a COD component decomposition step, a first coagulation-sedimentation step, a second coagulation-sedimentation step, and a fluorine adsorption step.

On the other hand, a method for removing fluorine ions using a fluorine adsorbent is also known as a method for treating fluorine-containing waste liquids discharged from etching cleaning waste liquids, aluminum electrolytic refining processes, glass manufacturing processes, etc. in the field of semiconductor manufacturing and the like. For example, Patent Document 4 discloses a treatment method in which fluorine-containing water is reacted with a calcium compound to be converted into calcium fluoride, solid-liquid separated, and then the separated liquid is brought into contact with a fluorine adsorbent. Patent Document 5 discloses a process of separating fluorine-containing water into low-concentration fluorine-containing water and high-concentration fluorine-containing water, adding a calcium compound to the low-concentration fluorine-containing water, performing solid-liquid separation, and contacting the separated liquid with a fluorine adsorbent. a step of regenerating the fluorine adsorbent; and a step of adding the regeneration waste liquid of the fluorine adsorbent to the high-concentration fluorine-containing water and then passing the liquid through a tank filled with calcium carbonate crystal seeds. is disclosed. Patent Document 6 describes a method for removing fluorine from water in which fluorine-containing water to be treated is passed through an adsorption tower filled with a fluorine adsorbent to produce treated water with reduced fluorine, in which fluorine is removed by adsorption in the adsorption tower. Disclosed is a method for removing fluorine from water in which the fluorine concentration of the fluorine-containing water to be treated at the inlet of the adsorption tower is adjusted to 15 mg/L or less by mixing the treated water in which fluorine is reduced generated by It is

JP-A-8-57486 JP-A-2000-176241 JP-A-11-137958 JP-A-5-92187 JP-A-5-253575 JP 2006-314957 A

Conventionally, fluorine removal treatment using a fluorine adsorbent has been performed on water to be treated that has a relatively low concentration of fluorine ions. When treating water with a high concentration of fluoride ions, usually first the fluoride ions are insolubilized by coagulation sedimentation or coprecipitation to remove the fluoride ions to some extent, and then the water with a reduced concentration of fluoride ions is treated. is brought into contact with an adsorbent to remove fluoride ions to a high degree. The reasons for this type of treatment are that fluorine ions can be removed to a higher degree by using an adsorbent compared to coagulation-sedimentation or co-precipitation treatment, and that water to be treated with a high concentration of fluoride ions can be treated by coagulation-sedimentation or co-precipitation. It is difficult to stably obtain treated water in which the fluorine concentration is sufficiently reduced if the water is brought into direct contact with the adsorbent without undergoing such pretreatment. In particular, when the concentration of coexisting ions other than fluorine ions is high, there is concern about the effect on the fluorine adsorption treatment.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for removing fluorine ions from water to be treated that contains fluoride ions and a high concentration of sulfate ions, and is stabilized by a fluorine adsorbent. To provide a water treatment method capable of treating as

The water treatment method of the present invention, which was able to solve the above-mentioned problems, is to introduce the water to be treated containing fluoride ions and sulfate ions into an adsorption tower filled with a fluorine adsorbent, and remove the fluorine ions in the water to be treated. and a pretreatment step of introducing the first treated water obtained in the adsorption step into the adsorption tower before the adsorption step, and introducing the water into the adsorption tower. The first treated water introduced into the adsorption tower has a sulfate ion concentration of 30,000 mg/L or more.

If the water to be treated contains sulfate ions at a high concentration of 30,000 mg/L or more together with fluoride ions, the fluoride ions cannot be sufficiently adsorbed and removed if the water is suddenly introduced into an adsorption tower filled with a fluorine adsorbent for treatment. Especially at the initial stage when the water to be treated is introduced into the adsorption tower, the fluorine ion concentration of the treated water becomes high. However, in the water treatment method of the present invention, prior to the fluorine adsorption treatment of the water to be treated, the treated water for the adsorption treatment is prepared in advance, and the treated water is introduced into the adsorption tower filled with the fluorine adsorbent. ing. That is, before the adsorption step, a pretreatment step of introducing the first treated water obtained in the adsorption step into the adsorption tower is provided, and the first treated water introduced into the adsorption tower in the pretreatment step has a sulfate ion concentration of 30 ,000 mg/L or more. By providing the pretreatment step in this way, when the water to be treated is introduced into the adsorption tower in the adsorption step, fluorine ions are preferably adsorbed and removed from the beginning of the adsorption step, and the fluorine ion concentration is sufficiently reduced. Water can be obtained stably.

In the pretreatment step, the fluorine ion concentration of the first treated water introduced into the adsorption tower is preferably 15 mg/L or less. Moreover, the pH of the first treated water introduced into the adsorption tower is preferably 2.0 or more and 3.5 or less. In the pretreatment step, the first treated water may be introduced while being circulated to the adsorption tower.

It is preferable to perform the adsorption step when the pH of the second treated water discharged from the adsorption tower in the pretreatment step becomes 4.0 or less.

In the adsorption step, the fluorine ion concentration of the water to be treated introduced into the adsorption tower is preferably 50 mg/L or more. Moreover, the pH of the water to be treated introduced into the adsorption tower is preferably 2.0 or more and 3.5 or less. A cerium-based adsorbent is preferably used as the fluorine adsorbent.

The water treatment method of the present invention comprises a desorption step in which an alkaline solution is introduced into the adsorption tower after the adsorption step to desorb fluorine ions from the fluorine adsorbent, and an acid treatment in which an acid solution is introduced into the adsorption tower after the desorption step. It is preferable that the pretreatment step is performed after the acid treatment step, and then the adsorption step is performed again.

The water treatment method of the present invention comprises a desorption step in which an alkaline solution is introduced into the adsorption tower after the adsorption step to desorb fluorine ions from the fluorine adsorbent, and an acid treatment in which an acid solution is introduced into the adsorption tower after the desorption step. A first adsorption tower and a second adsorption tower are provided as adsorption towers, and the following stages (1) to (4) are repeated in order, so that the first adsorption tower and the second adsorption tower Each step may be performed.
(1) The first adsorption tower and the second adsorption tower are connected in series in this order, the water to be treated is sequentially introduced into the first adsorption tower and the second adsorption tower, the adsorption step is performed in the first adsorption tower, and the A pretreatment step is performed in two adsorption towers.
(2) The desorption step and the acid treatment step are performed in the first adsorption tower, and the water to be treated is introduced into the second adsorption tower to perform the adsorption step.
(3) The second adsorption tower and the first adsorption tower are connected in series in this order, the water to be treated is sequentially introduced into the second adsorption tower and the first adsorption tower, the adsorption step is performed in the second adsorption tower, and the A pretreatment step is performed in one adsorption tower.
(4) The desorption step and the acid treatment step are performed in the second adsorption tower, and the water to be treated is introduced into the first adsorption tower to perform the adsorption step.

In the case of processing as described above, in the stage (1), the fluorine ion concentration of the first treated water discharged from the first adsorption tower is measured, and when the fluorine ion concentration exceeds a predetermined value, the stage of (2) , and in the stage (3), the fluorine ion concentration of the first treated water discharged from the second adsorption tower is measured, and when the fluorine ion concentration exceeds a predetermined value, it is preferable to move to the stage (4). . Alternatively, in stage (1), when the cumulative adsorption amount of fluorine ions adsorbed by the adsorbent in the first adsorption tower exceeds a predetermined value, the stage moves to (2), and in stage (3), the second adsorption If the cumulative adsorption amount of fluorine ions adsorbed by the adsorbent in the tower exceeds a predetermined value, the process may proceed to stage (4).

As the water to be treated containing sulfate ions at a relatively high concentration together with fluoride ions, it is preferable to use flue gas desulfurization wastewater discharged from flue gas desulfurization equipment.

According to the water treatment method of the present invention, even if the water to be treated contains a high concentration of sulfate ions, when the water to be treated is introduced into the adsorption tower filled with the fluorine adsorbent and treated, the water is stable. treated water with a reduced fluoride ion concentration can be obtained.

Fluoride ion concentration and pH of the treated water containing a high concentration of sulfate ions were measured when the adsorption step was performed without performing the pretreatment step and when the adsorption step was performed after the pretreatment step. represents the change over time. 1 shows a configuration example of a water treatment system used in the water treatment method of the present invention. 1 shows a configuration example of a water treatment system used in the water treatment method of the present invention. 1 shows a configuration example of a water treatment system used in the water treatment method of the present invention.

The present invention relates to a water treatment method for treating water containing fluoride ions and sulfate ions. Specifically, water to be treated containing sulfate ions at a high concentration of 30,000 mg/L or more together with fluoride ions is introduced into an adsorption tower filled with a fluorine adsorbent, and at least a portion of the fluorine ions in the water to be treated is It relates to a water treatment method for removing

Coal-fired power plants, coke plants, steel plants, etc., emit exhaust gas containing sulfur and fluorine by burning coal and coke. Flue gas desulfurization effluent containing high concentrations of ions and fluoride ions is generated. As a desulfurization method in flue gas desulfurization equipment, a wet treatment method using calcium hydroxide, magnesium hydroxide, or sodium hydroxide is known. Flue gas desulfurization wastewater containing ions and sulfate ions at a concentration of tens of thousands of mg/L or more is generated.

Conventionally, when removing fluorine ions from such flue gas desulfurization effluent, usually first, fluorine ions are insolubilized by coagulation sedimentation, coprecipitation, etc. to remove fluorine ions to some extent, and then, if necessary, fluorine ions Fluoride ions have been removed to a high degree by contacting treated water with a reduced concentration with an adsorbent. The reasons for this type of treatment are that fluorine ions can be removed to a higher degree by using an adsorbent compared to coagulation-sedimentation or co-precipitation treatment, and that water to be treated with a high concentration of fluoride ions can be treated by coagulation-sedimentation or co-precipitation. If the water is brought into direct contact with the adsorbent without undergoing such pretreatment, it may not be possible to obtain treated water with a sufficiently reduced fluorine ion concentration. On the other hand, when flue gas desulfurization wastewater is treated by coagulation sedimentation, coprecipitation, or the like, both fluorine ions and sulfate ions are insolubilized, generating a large amount of sludge. As a result, the cost of sludge disposal increases, leading to an increase in treatment costs.

The inventors of the present invention have investigated a method for stably removing fluorine when treating water containing a high concentration of sulfate ions as well as fluorine ions by introducing it into an adsorption tower filled with a fluorine adsorbent. . However, if the water to be treated, which contains a high concentration of sulfate ions as well as fluoride ions, is immediately introduced into an adsorption tower filled with a fluorine adsorbent for treatment, the fluorine ions may not be sufficiently adsorbed and removed. It was found that the fluorine ion concentration in the treated water tends to increase at the initial stage when the water to be treated is introduced into the adsorption tower. As a countermeasure against this, it is effective to prepare the treated water for the adsorption treatment in advance prior to the fluorine adsorption treatment of the water to be treated, and introduce the treated water into an adsorption tower filled with a fluorine adsorbent. It became clear. That is, the water treatment method of the present invention comprises introducing water to be treated containing fluoride ions and sulfate ions into an adsorption tower filled with a fluorine adsorbent, and removing at least part of the fluorine ions in the water to be treated. and a pretreatment step of introducing the first treated water obtained in the adsorption step into the adsorption tower prior to the adsorption step, wherein the water to be treated is introduced into the adsorption tower in the adsorption step. has a sulfate ion concentration of 30,000 mg/L or more, and the first treated water (treated water obtained in the adsorption step) introduced into the adsorption tower in the pretreatment step has a sulfate ion concentration of 30,000 mg/L or more. There is something.

When the fluorine adsorption treatment of the water to be treated is performed using a fluorine adsorbent, fluorine ions are removed from the water to be treated by ion exchange with the anions of the adsorbent. Since the anions possessed by the fluorine adsorbent are usually hydroxide ions, when the fluorine ions are adsorbed by the fluorine adsorbent, the hydroxide ions are desorbed from the fluorine adsorbent, increasing the pH of the water to be treated. tend to On the other hand, the fluorine adsorbent has a pH range suitable for adsorbing and removing fluorine ions, and when the pH of the water to be treated rises, the pH deviates from the optimum pH range, making it difficult to adsorb and remove fluorine ions sufficiently. Such an increase in pH becomes more conspicuous as the fluorine ion concentration in the water to be treated increases, because the amount of exchange with hydroxide ions increases.

On the other hand, when the present inventors performed fluorine adsorption treatment on various waters to be treated, it was found that when water to be treated containing sulfate ions at a high concentration of 30,000 mg/L or more was treated with a fluorine adsorbent, It was found that even when the fluorine ion concentration of the water to be treated is low, the pH of the treated water rises and the fluorine ion adsorption performance decreases. When we investigated the cause of this, we found that although the fluorine adsorbent preferentially adsorbs fluorine ions, if the concentration of sulfate ions in the water to be treated is excessively high, the adsorption of sulfate ions to the fluorine adsorbent cannot be ignored. As a result, it was considered that a large amount of hydroxide ions were desorbed from the adsorbent and the pH of the treated water increased. In this case, the amount of sulfate ions adsorbed by the fluorine adsorbent is only a small portion of the amount of sulfate ions contained in the water to be treated. As a countermeasure, a pretreatment step may be provided prior to the fluorine adsorption treatment of the water to be treated in the adsorption step to forcibly replace the hydroxide ions in the fluorine adsorbent with sulfate ions. proved to be effective. As a result, the fluorine adsorbent has sulfate ions as anions. After that, when the water to be treated is brought into contact with the fluorine adsorbent, the sulfate ions in the adsorbent are ion-exchanged with the fluorine ions, suppressing the increase in the pH of the treated water. be able to. In order to replace the hydroxide ions possessed by the fluorine adsorbent with sulfate ions, it is efficient to use treated water obtained by bringing the water to be treated containing a high concentration of sulfate ions into contact with the fluorine adsorbent. It became clear that the

FIG. 1 shows the case where the water to be treated with a sulfate ion concentration of 30,000 mg/L or more was subjected to the adsorption step without performing the pretreatment step and the case where the adsorption step was performed after the pretreatment step. , the measurement results of the fluoride ion concentration and pH of the treated water obtained. The fluorine ion concentration of the water to be treated was 100 mg/L, and the water to be treated was introduced into the adsorption tower at a space velocity (SV) of 20 hr ^-1 . As can be seen from the results shown in FIG. 1, by providing the pretreatment step, the increase in pH of the treated water, especially in the initial stage of the adsorption step, can be suppressed, and treated water from which fluorine ions are highly removed can be easily obtained. can be done. Further, by using the treated water obtained in the adsorption step to modify the fluorine adsorbent in the pretreatment step, the fluorine adsorbent can be easily modified. Hereinafter, the water treatment method of the present invention will be described in detail.

In the adsorption step, water to be treated containing fluorine ions and sulfate ions is introduced into an adsorption tower filled with a fluorine adsorbent to obtain first treated water from which at least part of the fluorine ions in the water to be treated has been removed. The treated water discharged from the adsorption tower in the adsorption step is referred to as "first treated water". The water to be treated is not particularly limited as long as it contains at least fluoride ions and sulfate ions. It is preferable to use flue gas desulfurization effluent from a steel factory or the like.

The sulfate ion concentration of the water to be treated introduced into the adsorption tower in the adsorption step is 30,000 mg/L or more, but the sulfate ion concentration may be higher than this, for example, 35,000 mg/L or more. , 40,000 mg/L or greater, or 50,000 mg/L or greater. Although the upper limit of the sulfate ion concentration of the water to be treated is not particularly limited, it may be, for example, 150,000 mg/L or less, 100,000 mg/L or less, or 80,000 mg/L or less. In the present invention, the sulfate ion concentration means the concentration including not only the free ion form but also the salt-formed form, and the sulfate ion concentration can be determined by ion chromatography or the like.

The fluorine ion concentration of the water to be treated introduced into the adsorption tower in the adsorption step is not particularly limited, and may be, for example, 10 mg/L or more, 15 mg/L or more, 20 mg/L or more, or 25 mg/L or more. may In addition, the effect of the present invention, that is, the effect that the fluorine ion concentration of the first treated water obtained in the adsorption step can be sufficiently reduced by combining the pretreatment step is more effective. is preferably 50 mg/L or more, more preferably 60 mg/L or more, and even more preferably 70 mg/L or more. According to the present invention, fluorine ions can be adsorbed and removed to a high degree even in the water to be treated having such a high fluorine ion concentration. On the other hand, the upper limit of the fluorine ion concentration of the water to be treated is preferably 200 mg / L or less, more preferably 150 mg / L or less, and further preferably 120 mg / L or less, in order to stably obtain the first treated water with a low fluorine concentration. Preferably, 100 mg/L or less is even more preferable. The fluorine ion concentration can be determined by ion chromatography or the like.

The water to be treated may contain magnesium ions, sodium ions, and the like. When the water to be treated includes flue gas desulfurization effluent from coal-fired power plants, coke plants, steel plants, etc., the water to be treated may contain sulfate ions as well as magnesium ions and sodium ions. When the flue gas desulfurization effluent uses magnesium hydroxide as a desulfurizing agent, the content ratio of magnesium ions and sulfate ions in the water to be treated is, for example, a magnesium ion/sulfate ion molar ratio of 2/8 to 8/. A range of 2 is preferred, a range of 3/7 to 7/3 is more preferred, and a range of 4/6 to 6/4 is even more preferred. When the flue gas desulfurization effluent uses sodium hydroxide as a desulfurizing agent, the content ratio of sodium ions and sulfate ions in the water to be treated is, for example, a sodium ion/sulfate ion molar ratio of 3/7 to 9/. A range of 1 is preferred, a range of 4/6 to 8/2 is more preferred, and a range of 5/5 to 7/3 is even more preferred. The water to be treated preferably contains flue gas desulfurization effluent using magnesium hydroxide as a desulfurizing agent. It becomes easier to suppress the outflow of active ingredients (metallic components).

As the fluorine adsorbent, a known adsorbent capable of adsorbing fluorine ions may be used. For example, an alumina-based adsorbent, a ferrite iron-based adsorbent, a zirconium-based adsorbent, a cerium-based adsorbent, etc. may be used. can. Among them, it is preferable to use a cerium-based adsorbent as an adsorbent capable of adsorbing and removing fluorine ions to a high degree. Cerium- _based adsorbents include those containing cerium oxide ( _CeO2 ), particularly hydrous cerium oxide ( _CeO2.nH2O ). The adsorbent contains a resin, and cerium oxide or hydrous cerium oxide may be immobilized or reinforced by the resin.

The pH of the water to be treated is preferably 2.0 or higher, more preferably 2.1 or higher, and still more preferably 2.2 or higher, in order to ensure that the adsorption and removal of fluorine ions by the adsorbent is performed favorably. 3.5 or less is preferable, 3.3 or less is more preferable, and 3.1 or less is even more preferable. When the pH of the water to be treated is high, the pH of the water to be treated may be adjusted by adding an acid, and it is preferable to use hydrochloric acid or sulfuric acid as the acid. Conversely, when the pH of the water to be treated is low, the pH of the water to be treated may be adjusted by adding an alkali. As the alkali, an alkali metal hydroxide is preferably used, and sodium hydroxide is preferably used. is more preferred. When flue gas desulfurization effluent is used as the water to be treated, the pH of the flue gas desulfurization effluent is not always in such a range. It is preferable to adjust the pH to a predetermined range by

Adjustment of the pH of the water to be treated may be performed by providing a pH adjustment means in front of the adsorption tower. As the pH adjusting means, a pH adjusting tank having an acid or alkali addition means may be provided before the adsorption tower, or an acid or alkali addition means may be provided in the flow path for supplying the water to be treated to the adsorption tower. The means for adding acid or alkali includes a chemical feeding pump and the like. Further, as pH adjusting means, pH measuring means may be provided together with acid or alkali adding means. It is preferable that the pH measuring means is installed in the pH adjusting tank or between the acid or alkali adding means and the adsorption tower in the channel for supplying the water to be treated to the adsorption tower.

Prior to introducing the water to be treated into the adsorption tower, the oxidation-reduction potential of the water to be treated may be adjusted. For example, if the water to be treated contains a large amount of reducing substances, metals such as cerium that make up the fluorine adsorbent are likely to leach out. Elution of metals from the adsorbent can be suppressed. From such a point of view, the oxidation-reduction potential of the water to be treated is preferably 600 mV or higher, more preferably 700 mV or higher. On the other hand, the redox potential of the water to be treated is preferably 1000 mV or less, more preferably 950 mV or less, from the viewpoint of suppressing deterioration of the fluorine-adsorbing resin (for example, deterioration of the resin constituting the fluorine-adsorbing agent). You may make it the to-be-processed water adjust an oxidation-reduction potential with pH.

As a chemical for adjusting the oxidation-reduction potential of the water to be treated, it is convenient to use a chlorine-based oxidizing agent such as sodium hypochlorite. The chemical is preferably supplied to the water to be treated before the water to be treated is introduced into the adsorption tower. The oxidation-reduction potential of the water to be treated can be adjusted by installing an oxidation-reduction potentiometer in the water-to-be-treated channel communicating with the inlet side of the adsorption tower and measuring the oxidation-reduction potential of the water to be treated. Further, instead of measuring the oxidation-reduction potential of the water to be treated, or in addition to measuring the oxidation-reduction potential, it is also preferable to adjust the residual chlorine concentration of the water to be treated. In this case, the residual chlorine concentration of the water to be treated introduced into the adsorption tower is preferably 0.5 mg/L or more, more preferably 1.0 mg/L or more, and preferably 18 mg/L or less, more preferably 15 mg/L or less. .

The water to be treated is brought into contact with the fluorine adsorbent by introducing the water to be treated into an adsorption tower filled with the fluorine adsorbent. The water to be treated may be passed through the adsorption tower in an upward flow manner or a downward flow manner. The flow rate at this time may be appropriately set according to the properties of the water to ^be treated and the filling amount of the fluorine adsorbent ^. Just do it. From the viewpoint of preventing the adsorption tower equipment from becoming excessively large, the space velocity (SV) is preferably 3 hr ^-1 or more, more preferably 5 hr ^-1 or more, still more preferably 8 hr ^-1 or more, and further preferably 12 hr ^-1 or more. more preferred. In addition, from the viewpoint of easily obtaining the first treated water in which the fluorine ion concentration is stably reduced, the space velocity (SV) is preferably 40 hr ^-1 or less, more preferably 30 hr ^-1 or less, and further 25 hr ^-1 or less. preferable.

By introducing the water to be treated into the adsorption tower and bringing it into contact with the fluorine adsorbent, the first treated water having a reduced fluorine ion concentration is obtained. The fluorine adsorption treatment using the adsorption tower may be performed in one stage or in multiple stages (two or more stages). In particular, when the fluorine ion concentration of the water to be treated is high, the water to be treated is treated with multi-staged adsorption towers, or the water is treated by combining treatment with one stage of adsorption towers and treatment with multi-staged adsorption towers. preferably. This makes it possible to stably reduce the fluorine ion concentration of the first treated water. The number of adsorption towers connected in multiple stages should be two or more, but if the number of adsorption towers connected in series (that is, the number of adsorption towers through which the water to be treated passes) is too large, the management of the adsorption towers becomes complicated. Therefore, it is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less.

When the adsorption towers are connected in series in multiple stages, the water to be treated may be adjusted in pH before being introduced into each adsorption tower connected in series in multiple stages. At this time, as described above, each pH is preferably 2.0 or more, more preferably 2.1 or more, further preferably 2.2 or more, and preferably 3.5 or less, and 3.3 or less. More preferably, 3.1 or less is even more preferable. In the water treatment method of the present invention, the pH change is small when the water to be treated is passed through the adsorption tower in the adsorption step, and usually, the pH is adjusted only when the water to be treated is first introduced into the adsorption tower. is sufficient.

The fluorine ion concentration of the first treated water obtained in the adsorption step is basically lower than the fluorine ion concentration of the water to be treated introduced into the adsorption tower. It is preferable that the first treated water obtained by the adsorption step has a fluorine ion concentration reduced to a level suitable for discharge into the environment. For example, according to the uniform wastewater standards set by the Ministry of the Environment, the permissible limit for fluorine and its compounds is 15 mgF/L for those discharged into sea areas, and 8 mgF/L for those discharged into public water areas other than sea areas. defined as L. Therefore, the fluorine ion concentration of the first treated water is preferably 15 mg/L or less, more preferably 8 mg/L or less. The fluorine ion concentration of the first treated water may be lower, such as 5 mg/L or less, 3 mg/L or less, or 1 mg/L or less. When adsorption treatment is performed by connecting multiple adsorption towers in series, the concentration of fluorine ions in the first treated water obtained from the rearmost adsorption tower should be within such a range. In addition, the sulfate ion concentration of the first treated water obtained in the adsorption step is generally not significantly different from the sulfate ion concentration of the water to be treated.

A pretreatment step is performed prior to the adsorption step. In the pretreatment step, the first treated water obtained in the adsorption step is introduced into the adsorption tower. The treated water discharged from the adsorption tower in the pretreatment step is referred to as "second treated water". By introducing the first treated water into the adsorption tower in the pretreatment step, the hydroxide ions of the fluorine adsorbent packed in the adsorption tower can be replaced with sulfate ions. As a result, when the fluorine adsorbent adsorbs fluorine ions in the adsorption step that follows the pretreatment step, the resulting first treated water is prevented from increasing in pH, and the fluorine ions in the water to be treated are highly adsorbed and removed. becomes possible. The second treated water discharged from the adsorption tower in the pretreatment step can be discharged out of the system as treated water from which fluorine ions have been removed.

The first treated water introduced into the adsorption tower in the pretreatment step may be the first treated water obtained by performing the adsorption step in the same adsorption tower, or the first treated water obtained by performing the adsorption step in another adsorption tower. It may be the first treated water. In the latter case, the water to be treated introduced into another adsorption tower in the adsorption step has the same origin as the water to be treated introduced into the adsorption tower when the adsorption step is performed in the adsorption tower into which the first treated water is introduced. is preferably

The first treated water introduced into the adsorption tower in the pretreatment step has a sulfate ion concentration of 30,000 mg/L or more, but the sulfate ion concentration may be higher than this, for example, 35,000 mg/L or more. may be 40,000 mg/L or higher, or 50,000 mg/L or higher. Although the upper limit of the sulfate ion concentration of the water to be treated is not particularly limited, it may be, for example, 150,000 mg/L or less, 100,000 mg/L or less, or 80,000 mg/L or less.

As described above, the fluorine ion concentration of the first treated water introduced into the adsorption tower in the pretreatment step is preferably 15 mg/L or less, more preferably 8 mg/L or less. The fluorine ion concentration of the first treated water may be lower, such as 5 mg/L or less, 3 mg/L or less, or 1 mg/L or less. By introducing the first treated water having a low fluorine ion concentration into the adsorption tower in the pretreatment step in this way, even if the fluorine ions in the first treated water are not removed by adsorption in the pretreatment step, they are discharged from the adsorption tower. The fluoride ion concentration of the second treated water becomes sufficiently low.

The pH of the first treated water introduced into the adsorption tower in the pretreatment step is preferably 2.0 or higher, more preferably 2.1 or higher, still more preferably 2.2 or higher, and preferably 3.5 or lower. .3 or less is more preferable, and 3.1 or less is even more preferable. When the pH of the first treated water is high, the pH of the first treated water may be adjusted by adding an acid, and it is preferable to use hydrochloric acid or sulfuric acid as the acid. Conversely, when the pH of the first treated water is low, the pH of the first treated water may be adjusted by adding an alkali. As the alkali, an alkali metal hydroxide is preferably used, and sodium hydroxide is used. It is more preferable to use By adjusting the pH of the first treated water introduced into the adsorption tower in this manner, the hydroxide ions of the fluorine adsorbent can be efficiently replaced with sulfate ions in the pretreatment step.

The first treated water may be passed through the adsorption tower in an upward flow manner or may be passed in a downward flow manner. At this time, the liquid permeation rate may be appropriately adjusted, for example, in the range of 1 hr ^-1 to 100 hr ^-1 as a space velocity (SV). The space velocity (SV) is preferably 3 hr ^-1 or more, and 5 hr ^-1 or more from the viewpoint of shortening the time required for the pretreatment step and suppressing an excessive increase in the pH of the second treated water discharged from the adsorption tower. is more preferable, 8 hr ^-1 or more is more preferable, and 12 hr ^-1 or more is even more preferable. In addition, from the viewpoint of increasing the efficiency of replacing hydroxide ions in the adsorbent with sulfate ions, the space velocity (SV) is preferably 70 hr ^-1 or less, more preferably 50 hr ^-1 or less, and even more preferably 30 hr ^{-1 or} less. .

In the pretreatment step, the first treated water may be introduced while being circulated to the adsorption tower. For example, a holding tank for the first treated water can be prepared and the first treated water can be circulated between the holding tank and the adsorption tower. In this case, the second treated water discharged from the adsorption tower is reused as the first treated water introduced into the adsorption tower in the pretreatment step. Of course, without circulating the first treated water to the adsorption tower, the second treated water discharged from the adsorption tower may be discharged as it is to the outside of the system as treated water from which fluorine ions have been removed.

In the pretreatment step, all of the first treated water obtained in the adsorption step may be introduced into the adsorption tower, or only a portion thereof may be introduced into the adsorption tower. When the hydroxide ions of the fluorine adsorbent are sufficiently replaced with sulfate ions in the pretreatment step, the supply of the first treated water to the adsorption tower may be stopped and the pretreatment step may be terminated.

The timing of completion of the pretreatment process can be determined by measuring the pH of the second treated water. The second treated water has a high pH at the beginning of the pretreatment process, or the pH increases, for example, the pH is about 6-9. On the other hand, as the pretreatment step continues, the amount of hydroxide ions in the fluorine adsorbent exchanged with sulfate ions decreases, and the pH of the second treated water gradually decreases. Therefore, when the pH of the second treated water becomes equal to or lower than the predetermined value in the pretreatment process, the pretreatment process can be terminated and the adsorption process can be started. The pH of the second treated water, which is a standard, is preferably 4.0 or less, more preferably 3.8 or less, and even more preferably 3.5 or less.

The timing for ending the pretreatment step may be determined based on the amount of first treated water supplied to the adsorption tower. For example, the amount (volume) of the first treated water supplied to the adsorption tower in the pretreatment step is preferably at least 20 times the apparent volume of the fluorine adsorbent packed in the adsorption tower, more preferably at least 30 times. , more preferably 40 times or more. The upper limit of the amount of the first treated water supplied to the adsorption tower is not particularly limited, but since the effect of introducing the first treated water is not so improved even if it is supplied in excess, the first treated water is supplied to the adsorption tower. is preferably 200 times or less, more preferably 150 times or less, and even more preferably 100 times or less the apparent volume of the fluorine adsorbent packed in the adsorption tower. The supply amount of the first treated water to the adsorption tower described here means the total amount of the first treated water introduced into the adsorption tower when the first treated water is circulated and supplied to the adsorption tower.

By performing the pretreatment step as described above, the fluorine adsorbent has sulfate ions as anions. Thereafter, when the water to be treated is brought into contact with the fluorine adsorbent in the adsorption step, the sulfate ions contained in the adsorbent are ion-exchanged with the fluorine ions, and the increase in pH of the first treated water can be suppressed. Therefore, it becomes easy to maintain the pH of the first treated water in a pH range suitable for removing fluorine by adsorption, and the adsorption and removal of fluorine from the water to be treated can be stably performed.

The pretreatment step may be performed after the adsorption step, desorbing and regenerating the fluorine adsorbent, and before carrying out the fluorine adsorption treatment in the next adsorption step. In this case, in the water treatment method of the present invention, after the adsorption step, an alkaline solution is introduced into the adsorption tower to desorb fluorine ions from the fluorine adsorbent, and after the desorption step, an acid solution is introduced into the adsorption tower. After the acid treatment step, the pretreatment step is performed, and then the adsorption step is performed again. By thus providing the desorption step and the acid treatment step after the adsorption step, the fluorine adsorbent can be used repeatedly.

In the desorption step, the adsorbent that has adsorbed fluorine ions in the adsorption step is brought into contact with an alkaline solution. As a result, fluorine ions are desorbed from the adsorbent to obtain a desorbed liquid containing fluorine ions. The desorbed liquid thus obtained can concentrate fluorine ions more than the water to be treated, and becomes a high-purity fluorine ion-containing liquid, so that fluorine can be efficiently recovered.

As the alkaline solution, it is preferable to use a solution of an alkali metal hydroxide. As the alkali metal hydroxide, lithium hydroxide, potassium hydroxide, sodium hydroxide, rubidium hydroxide, cesium hydroxide, etc. can be used, and these may be used alone or in combination of two or more. You may In addition, it is preferable to use sodium hydroxide as an alkali metal hydroxide from the aspect of cost.

As the alkali solution used in the desorption step, it is preferable to use an alkali solution having a relatively high hydroxide ion concentration, because the higher the hydroxide ion concentration, the higher the concentration of fluorine ions in the desorbed solution. The hydroxide ion concentration of the alkaline solution is, for example, preferably 0.05 mol/L or higher, more preferably 0.1 mol/L or higher, and even more preferably 0.2 mol/L or higher. On the other hand, considering the handling properties of the alkaline solution and the influence on the equipment specifications, the hydroxide ion concentration of the alkaline solution is preferably 3 mol/L or less, more preferably 1 mol/L or less.

The adsorbent from which fluorine ions have been desorbed in the desorption step can be used again as a fluorine adsorbent by contacting it with an acid solution in the acid treatment step. As the acid at this time, it is preferable to use hydrochloric acid or sulfuric acid. The hydrogen ion concentration of the acid solution is, for example, preferably higher than 0.01 mol/L, more preferably 0.03 mol/L or more, and preferably 2.0 mol/L or less, more preferably 1.0 mol/L or less. Before the acid treatment step, the adsorbent from which fluorine ions have been desorbed in the desorption step may be washed with water. Moreover, after the acid treatment step, the adsorbent may be washed with water.

After the acid treatment step, the pretreatment step described above is performed. When washing with water after contacting with the acid solution in the acid treatment step, the pretreatment step is performed after this washing with water. By performing the pretreatment step after regenerating the fluorine adsorbent in this manner and then performing the adsorption step again, the first treated water in which the fluorine ion concentration is sufficiently reduced from the initial stage can be obtained in the adsorption step performed again. will be available.

In addition, when sulfuric acid is used in the acid treatment process, it was examined whether the acid treatment process can also serve as the pretreatment process described above. could not obtain the same effect. That is, when the adsorption step is performed without performing the pretreatment step after performing the acid treatment step, the pH of the first treated water increases in the adsorption step, especially at the beginning of the adsorption step. Fluoride ion concentration tended to increase.

It is effective to carry out the above-described pretreatment step before performing the first adsorption step with the fluorine adsorbent, or after regenerating the fluorine adsorbent and before performing the first adsorption step. Therefore, when the adsorption step is temporarily interrupted and then resumed, the pretreatment step may not be performed before the resumed adsorption step.

Next, a system configuration example used in the water treatment method of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiments shown in the drawings.

The water treatment system shown in FIG. 2 has an adsorption tower 11 filled with a fluorine adsorbent and a water flow path 21 that communicates with the inlet side of the adsorption tower 11 and supplies the water 1 to be treated. . The water to be treated 1 introduced into the adsorption tower 11 contains at least fluorine ions and sulfate ions, and has a sulfate ion concentration of 30,000 mg/L or more. By introducing the water 1 to be treated into the adsorption tower 11 and bringing it into contact with the fluorine adsorbent, the first treated water 2 with reduced fluorine ion concentration is obtained (adsorption step). The first treated water 2 has a fluorine ion concentration reduced to such an extent that it can be discharged into the environment. The first treated water 2 is obtained through a treated water flow path 22 provided in communication with the outlet side of the adsorption tower 11 , and at least part of it is temporarily stored in a treated water tank 23 .

It is preferable that a pH adjusting means 12 for adjusting the pH of the water 1 to be treated is provided on the inlet side of the adsorption tower 11 . Examples of the pH adjusting means 12 include a chemical injection pump for adding acid or alkali. The acid or alkali may be supplied into the piping of the water flow path 21 to be treated, or a pH adjustment tank may be provided in the water flow path 21 to supply the acid or alkali to the pH adjustment tank. At this time, it is preferable to supply acid or alkali while measuring the pH of the water 1 to be treated. Therefore, it is preferable to provide a pH meter on the entrance side of the adsorption tower 11 . By adjusting the pH of the water to be treated 1 to a range suitable for adsorption, fluorine ions can be efficiently adsorbed and removed when the water to be treated 1 is introduced into the adsorption tower 11 .

A fluorine ion concentration meter is preferably provided on the exit side of the adsorption tower 11 . By measuring the fluorine ion concentration of the first treated water 2 with a fluorine ion concentration meter, it is possible to determine the timing for ending the adsorption step. For example, a reference value for the fluorine ion concentration of the first treated water 2 is determined in advance, and the adsorption step can be terminated when the reference value is exceeded. In addition, a fluorine ion concentration meter may be provided on the inlet side of the adsorption tower 11, and the difference between the fluorine ion concentration of the water to be treated 1 and the fluorine ion concentration of the first treated water 2 and the supply amount of the water to be treated 1 (or The cumulative adsorption amount of fluorine ions to the adsorbent filled in the adsorption tower 11 is calculated from the discharge amount of the first treated water 2), and when the cumulative adsorption amount exceeds a predetermined value, the adsorption step is terminated. good too.

The adsorbent that has adsorbed fluorine ions can be desorbed from the adsorbent by bringing it into contact with an alkaline solution (desorption step). Therefore, it is preferable that the inlet side of the adsorption tower 11 is provided with the chemical liquid flow path 25 in communication therewith. It is preferable that the exit side of the adsorption tower 11 is provided in communication with a waste liquid flow path 26 for discharging the alkaline solution, that is, the desorbed liquid 3 that has come into contact with the adsorbent. In addition, in FIG. 2, the chemical liquid flow path 25 is directly connected to the inlet side of the adsorption tower 11, but it may be connected to the water flow path 21 to be treated. When the alkaline solution is supplied from the chemical liquid channel 25, the supply of the water 1 to be treated to the adsorption tower 11 is stopped, and the desorbed liquid 3 discharged from the adsorption tower 11 through the waste liquid channel 26 is recovered.

The adsorbent that has desorbed fluorine ions is regenerated by bringing it into contact with an acid solution, and is given fluorine adsorption capacity again (acid treatment step). In FIG. 2, the acid solution can be supplied from the chemical liquid channel 25, and the acid solution in contact with the adsorbent, that is, the acid cleaning waste liquid 4 is discharged through the waste liquid channel 26. In FIG. The acid solution may be supplied to the adsorption tower 11 through a channel different from that for the alkaline solution, and the acid washing waste liquid 4 may be discharged from the adsorption tower 11 through a channel different from that for the desorbed liquid 3 . Moreover, prior to supplying the acid solution to the adsorption tower 11 , water may be supplied to the adsorption tower 11 to wash away the alkaline solution in the adsorption tower 11 . The adsorbent brought into contact with the acid solution has hydroxide ions at the adsorption sites of fluorine ions.

The adsorbent regenerated by contact with the acid solution can be used again to adsorb and remove fluorine ions in the water 1 to be treated. The first treated water 2 stored in is introduced into the adsorption tower 11 through the return flow path 24 (pretreatment step). A second treated water 5 is obtained from the adsorption tower 11 . The first treated water 2 has a sulfate ion concentration of 30,000 mg/L or higher. Hydroxide ions of the packed adsorbent are replaced with sulfate ions. As a result, when the water to be treated 1 is subsequently introduced into the adsorption tower 11, the increase in pH of the first treated water 2 discharged from the adsorption tower 11 is suppressed, and fluorine ions are stably released from the water to be treated 1. It can be removed by adsorption. It is also preferable to supply water to the adsorption tower 11 to wash away the acid solution in the adsorption tower 11 after the contact with the acid solution and before the introduction of the first treated water 2 .

The timing of the end of the pretreatment process can be determined by providing a pH meter on the outlet side of the adsorption tower 11 and measuring the pH of the second treated water 5 . Specifically, when the pH of the second treated water 5 becomes equal to or lower than a predetermined value (for example, the pH is 4.0 or lower), the pretreatment step can be terminated and the adsorption step can be started. The amount of the first treated water 2 supplied to the adsorption tower 11 in the pretreatment step is preferably 20 times or more the apparent volume of the adsorbent filled in the adsorption tower 11 .

Another example of the water treatment system of the present invention will be described with reference to FIGS. 3 and 4. FIG. In the following description, the description of the parts overlapping with FIG. 2 will be omitted.

In the configuration example shown in FIG. 3, a first adsorption tower 11A and a second adsorption tower 11B are provided in parallel as adsorption towers. A treated water channel 22 , a treated water tank 23 , a return channel 24 , a chemical solution channel 25 and a waste liquid channel 26 are provided. According to the configuration example shown in FIG. 3, the adsorption step and the desorption/acid washing/pretreatment step can be performed in each of the first adsorption tower 11A and the second adsorption tower 11B. Therefore, it is possible to perform the adsorption treatment in the first adsorption tower 11A and the desorption/regeneration treatment and the pretreatment of the adsorbent in the second adsorption tower 11B at the same time, and vice versa. Continuous adsorption treatment becomes possible.

In the configuration example shown in FIG. 3, two adsorption towers, the first adsorption tower 11A and the second adsorption tower 11B, are alternately subjected to the adsorption process and the desorption/acid washing/pretreatment process, thereby continuously However, three or more adsorption towers can be used to continuously adsorb the water to be treated. For example, when three adsorption towers, a first adsorption tower, a second adsorption tower, and a third adsorption tower, are used, the adsorption step is performed by connecting the first adsorption tower and the second adsorption tower in series in this order. Desorption, acid washing and pretreatment are carried out in the adsorption tower, then adsorption is carried out by connecting the second adsorption tower and the third adsorption tower in series in this order, and desorption, acid washing and pretreatment are carried out in the first adsorption tower. By repeating the steps of performing the steps, then performing the adsorption step by connecting the third adsorption tower and the first adsorption tower in series in this order, and performing the desorption, acid washing, and pretreatment steps in the second adsorption tower. , three adsorption towers can be used for continuous adsorption treatment of the water to be treated. When four or more adsorption towers are used, adsorption treatment may be performed by connecting three or more adsorption towers in series in multiple stages. good too.

FIG. 4 shows a configuration example in which adsorption towers are connected in series in multiple stages. In FIG. 4, a first adsorption tower 11A and a second adsorption tower 11B are provided as adsorption towers, and a series connection flow path 27 is provided to communicate with the outlet side of the first adsorption tower 11A and the inlet side of the second adsorption tower 11B. Thus, the first adsorption tower 11A and the second adsorption tower 11B can be connected in series in this order. When the adsorption towers are connected in series in this way, the water to be treated 1 is introduced into the first adsorption tower 11A and the adsorption step is performed in the first adsorption tower 11A to obtain the first treated water 2A. 1 Treated water 2A can be introduced into the second adsorption tower 11B through the series connection channel 27, and a pretreatment step can be performed in the second adsorption tower 11B. Therefore, installation of a treated water tank for the first treated water 2A for carrying out the pretreatment process becomes unnecessary. The second treated water 5B discharged from the second adsorption tower 11B can be discharged into the environment. In addition, in the 2nd adsorption tower 11B, it is preferable to perform a desorption process and an acid treatment process prior to introduce|transducing 2 A of 1st treated water into the 2nd adsorption tower 11B. Therefore, while the desorption step and the acid treatment step are being performed in the second adsorption tower 11B, the first treated water 2A discharged from the first adsorption tower 11A is directly outside the system without passing through the second adsorption tower 11B. Ejection is preferred.

In FIG. 4, a series connection flow path 28 is further provided in communication with the outlet side of the second adsorption tower 11B and the inlet side of the first adsorption tower 11A, whereby the second adsorption tower 11B and the first adsorption tower are connected. 11A can be connected in series in this order. When the adsorption towers are connected in series in this way, the water to be treated 1 is introduced into the second adsorption tower 11B and the adsorption step is performed in the second adsorption tower 11B to obtain the first treated water 2B. 1 Treated water 2B can be introduced into the first adsorption tower 11A through the series connection channel 28, and a pretreatment step can be performed in the first adsorption tower 11A. Therefore, installation of a treated water tank for the first treated water 2B for performing the pretreatment process is not required. The second treated water 5A discharged from the first adsorption tower 11A can be discharged into the environment. In addition, prior to introducing the first treated water 2B into the first adsorption tower 11A, it is preferable to perform the desorption step and the acid treatment step in the first adsorption tower 11A. Therefore, while the desorption step and the acid treatment step are being performed in the first adsorption tower 11A, the first treated water 2B discharged from the second adsorption tower 11B is discharged from the system as it is without passing through the first adsorption tower 11A. Ejection is preferred.

In the configuration example shown in FIG. 4, specifically, it is preferable to perform an adsorption step, a desorption step, an acid treatment step, and a pretreatment step in each adsorption tower as follows. That is, by performing the following stages (1) to (4) in order, each step of the adsorption step, the desorption step, the acid treatment step, and the pretreatment step is performed in the first adsorption tower 11A and the second adsorption tower 11B. is preferred. (1) The first adsorption tower 11A and the second adsorption tower 11B are connected in series in this order, the water to be treated 1 is sequentially introduced into the first adsorption tower 11A and the second adsorption tower 11B, and the first adsorption tower 11A An adsorption step is performed, and a pretreatment step is performed in the second adsorption tower 11B. (2) The desorption process and the acid treatment process are performed in the first adsorption tower 11A, and the water to be treated 1 is introduced into the second adsorption tower 11B to perform the adsorption process. (3) The second adsorption tower 11B and the first adsorption tower 11A are connected in series in this order, the water to be treated 1 is sequentially introduced into the second adsorption tower 11B and the first adsorption tower 11A, and An adsorption step is performed, and a pretreatment step is performed in the first adsorption tower 11A. (4) The desorption step and the acid treatment step are performed in the second adsorption tower 11B, and the water to be treated 1 is introduced into the first adsorption tower 11A to perform the adsorption step. These stages (1) to (4) can be repeated, that is, after stage (4) is completed, stage (1) can be returned to. As a result, the frequency of desorption/regeneration treatment in the adsorption tower can be reduced, and fluorine ions can be efficiently removed from the water to be treated.

In stage (1), the first adsorption tower 11A and the second adsorption tower 11B are connected in series in this order, and the water to be treated 1 is sequentially introduced into the first adsorption tower 11A and the second adsorption tower 11B. In the stage (1), first, the water to be treated 1 having a sulfate ion concentration of 30,000 mg / L or more is introduced into the first adsorption tower 11A, and at least part of the fluorine ions is removed from the water to be treated 1. A treated water 2A is obtained. The fluoride ion concentration of the first treated water 2A is removed to the extent that it can be discharged into the environment, and the sulfate ion concentration is maintained at 30,000 mg/L or more. The first treated water 2A obtained in the first adsorption tower 11A is introduced into the second adsorption tower 11B, and the second treated water 5B is obtained from the second adsorption tower 11B. The second treated water 5B is discharged out of the system through the treated water flow path 22 . In the second adsorption tower 11B, a pretreatment step is performed prior to the adsorption step being performed in the next stage (2), and hydroxide ions possessed by the adsorbent packed in the second adsorption tower 11B are converted to sulfuric acid. replaced by ions.

In the stage (1), by measuring the pH of the second treated water 5B discharged from the second adsorption tower 11B, the hydroxide ions of the adsorbent packed in the second adsorption tower 11B are converted into sulfate ions. It is possible to grasp how much the replacement of has progressed. The pH of the second treated water 5B normally once increases to about 6 to 9, and then decreases as the treatment continues. The stage (1) is preferably performed until the pH of the second treated water 5B becomes a predetermined value or less (for example, pH is 4.0 or less). In the stage (1), even if the pH of the second treated water 5B becomes equal to or lower than the predetermined value, the introduction of the first treated water 2A into the second adsorption tower 11B may be continued. As a result, if the fluorine ion concentration of the first treated water 2A discharged from the first adsorption tower 11A exceeds the reference value, the first treated water 2A is introduced into the second adsorption tower 11B, Fluorine ions contained in the first treated water 2A can be removed by adsorption by the second adsorption tower 11B.

Stage (1) WHEREIN: At the stage where the adsorption-removal performance of the fluorine ion of 11 A of 1st adsorption towers fell, or the stage before it falls, it moves to the stage of (2). For example, in the stage (1), the fluorine ion concentration of the first treated water 2A discharged from the first adsorption tower 11A is measured, and when the fluorine ion concentration exceeds a predetermined value, the stage is shifted to (2). do it. Alternatively, in the stage (1), when the cumulative adsorption amount of fluorine ions adsorbed by the adsorbent in the first adsorption tower 11A exceeds a predetermined value, the stage may be shifted to (2). The cumulative adsorption amount of fluorine ions adsorbed by the adsorbent of the first adsorption tower 11A is the difference between the fluorine ion concentration of the water to be treated 1 and the fluorine ion concentration of the first treated water 2A, and It can be obtained from the amount supplied to 11A (or the amount of discharge of the first treated water 2A).

In the stage (2), desorption/regeneration treatment of the adsorbent in the first adsorption tower 11A is performed, and fluorine ion adsorption treatment of the water 1 to be treated is performed in the second adsorption tower 11B. In the second adsorption tower 11B, even if the water to be treated 1 containing sulfate ions at a high concentration of 30,000 mg/L or more is introduced due to the pretreatment step being performed in the stage (1), , the increase in pH of the first treated water 2B obtained is suppressed, and the first treated water 2B from which fluorine ions are removed to the extent that it can be discharged into the environment is obtained.

After the desorption/regeneration treatment of the adsorbent in the first adsorption tower 11A is completed in the stage (2), the process proceeds to the stage (3). In the stage (3), the second adsorption tower 11B and the first adsorption tower 11A are connected in series in this order, and the water to be treated 1 is sequentially introduced into the second adsorption tower 11B and the first adsorption tower 11A. In the stage (3), first, the water to be treated 1 having a sulfate ion concentration of 30,000 mg / L or more is introduced into the second adsorption tower 11B, and at least part of the fluorine ions is removed from the water to be treated 1. Treated water 2B is obtained. The fluoride ion concentration of the first treated water 2B is removed to the extent that it can be discharged into the environment, and the sulfate ion concentration is maintained at 30,000 mg/L or more. The first treated water 2B obtained in the first adsorption tower 11B is introduced into the first adsorption tower 11A, and the second treated water 5A is obtained from the first adsorption tower 11A. In the first adsorption tower 11A, a pretreatment step is performed subsequent to the desorption step and the acid treatment step performed in the stage (2), and hydroxide ions possessed by the adsorbent packed in the first adsorption tower 11A are replaced by sulfate ions.

In the stage (3), by measuring the pH of the second treated water 5A discharged from the first adsorption tower 11A, the hydroxide ions of the adsorbent packed in the first adsorption tower 11A are converted into sulfate ions. It is possible to grasp how much the replacement of has progressed. The pH of the second treated water 5A normally once increases to about 6 to 9, and then decreases as the treatment continues. The stage (3) is preferably performed until the pH of the second treated water 5A becomes a predetermined value or less (for example, pH is 4.0 or less). In stage (3), even if the pH of the second treated water 5A becomes equal to or lower than the predetermined value, the introduction of the first treated water 2B into the first adsorption tower 11A may be continued. As a result, if the fluorine ion concentration of the first treated water 2B discharged from the second adsorption tower 11B exceeds the reference value, the first treated water 2B is introduced into the first adsorption tower 11A, Fluorine ions contained in the first treated water 2B can be removed by adsorption by the first adsorption tower 11A.

Stage (3) WHEREIN: At the stage where the adsorption removal performance of the fluorine ion of the 2nd adsorption tower 11B falls, or the stage before it falls, it moves to the stage of (4). For example, in the stage (3), the fluorine ion concentration of the first treated water 2B discharged from the second adsorption tower 11B is measured, and when the fluorine ion concentration exceeds a predetermined value, the stage is moved to (4). do it. Alternatively, in stage (3), if the cumulative adsorption amount of fluorine ions adsorbed by the adsorbent in second adsorption tower 11B exceeds a predetermined value, stage (4) may be performed. The cumulative adsorption amount of fluorine ions adsorbed by the adsorbent of the second adsorption tower 11B is the difference between the fluorine ion concentration of the water to be treated 1 and the fluorine ion concentration of the first treated water 2B and the second adsorption tower of the water to be treated 1 11B (or the discharge amount of the first treated water 2B).

In the stage (4), desorption/regeneration treatment of the adsorbent in the second adsorption tower 11B is performed, and fluorine ion adsorption treatment of the water 1 to be treated is performed in the first adsorption tower 11A. In the first adsorption tower 11A, even if the water to be treated 1 containing sulfate ions at a high concentration of 30,000 mg/L or more is introduced due to the pretreatment step being performed in the stage (3), , the increase in pH of the first treated water 2A to be obtained is suppressed, and the first treated water 2A from which fluorine ions have been removed to the extent that it can be discharged into the environment is obtained.

After the desorption/regeneration treatment of the adsorbent in the second adsorption tower 11B is completed in the stage (4), the process proceeds to the stage (1) again. By repeating the cycle consisting of stages (1) to (4) in this way, the frequency of desorption/regeneration treatment of the adsorbent packed in the adsorption tower is reduced, and fluorine ions are efficiently removed from the water to be treated. becomes possible. A reduction in the frequency of desorption/regeneration treatment of the adsorbent leads to extension of the life of the adsorbent, thereby reducing treatment costs.

In the configuration example shown in FIG. 4, the adsorption towers are connected in series in two stages, but the adsorption towers may be connected in series in three or more stages. In this case, in the stages corresponding to the above stages (1) and (3), the pretreatment process is performed in the last adsorption tower, and the first adsorption tower performs the desorption process and the acid treatment process in the next stage. should be done.

INDUSTRIAL APPLICABILITY The present invention can be used to treat flue gas desulfurization wastewater from coal-fired power plants, coke plants, steel plants, and the like.

1: water to be treated 2, 2A, 2B: first treated water 3: desorption liquid 4: acid washing waste liquid 5, 5A, 5B: second treated water 11: adsorption tower, 11A: first adsorption tower, 11B: second 2 adsorption tower 12: pH adjusting means 21: water to be treated channel 22: treated water channel 23: treated water tank 24: return channel 25: chemical solution channel 26: waste liquid channel 27, 28: series connection channel

Claims (13)

an adsorption step of introducing water to be treated containing fluorine ions and sulfate ions into an adsorption tower filled with a fluorine adsorbent to obtain first treated water from which at least part of the fluorine ions in the water to be treated has been removed;
Before the adsorption step, a pretreatment step of introducing the first treated water obtained in the adsorption step into the adsorption tower,
The water to be treated introduced into the adsorption tower has a sulfate ion concentration of 30,000 mg/L or more,
A water treatment method, wherein the first treated water introduced into the adsorption tower has a sulfate ion concentration of 30,000 mg/L or more. 2. The water treatment method according to claim 1, wherein in said pretreatment step, the first treated water introduced into said adsorption tower has a fluorine ion concentration of 15 mg/L or less. The water treatment method according to claim 1 or 2, wherein in the pretreatment step, the first treated water introduced into the adsorption tower has a pH of 2.0 or more and 3.5 or less. 4. The water treatment method according to claim 3, wherein the adsorption step is performed when the second treated water discharged from the adsorption tower in the pretreatment step has a pH of 4.0 or less. The water treatment method according to any one of claims 1 to 4, wherein in the pretreatment step, the first treated water is introduced into the adsorption tower while being circulated. After the adsorption step, a desorption step of introducing an alkaline solution into the adsorption tower to desorb fluorine ions from the fluorine adsorbent;
After the desorption step, further comprising an acid treatment step of introducing an acid solution into the adsorption tower,
The water treatment method according to any one of claims 1 to 5, wherein the pretreatment step is performed after the acid treatment step, and then the adsorption step is performed again. The water treatment method according to any one of claims 1 to 6, wherein in the adsorption step, the water to be treated introduced into the adsorption tower has a fluorine ion concentration of 50 mg/L or more. The water treatment method according to any one of claims 1 to 7, wherein in the adsorption step, the water to be treated introduced into the adsorption tower has a pH of 2.0 or more and 3.5 or less. The water treatment method according to any one of claims 1 to 8, wherein the fluorine adsorbent is a cerium-based adsorbent. After the adsorption step, a desorption step of introducing an alkaline solution into the adsorption tower to desorb fluorine ions from the fluorine adsorbent;
After the desorption step, further comprising an acid treatment step of introducing an acid solution into the adsorption tower,
A first adsorption tower and a second adsorption tower are provided as the adsorption towers, and each step is performed in the first adsorption tower and the second adsorption tower by repeating the following stages (1) to (4) in order. 10. The water treatment method according to any one of 1 to 9.
(1) The first adsorption tower and the second adsorption tower are connected in series in this order, the water to be treated is sequentially introduced into the first adsorption tower and the second adsorption tower, the adsorption step is performed in the first adsorption tower, and the A pretreatment step is performed in two adsorption towers.
(2) The desorption step and the acid treatment step are performed in the first adsorption tower, and the water to be treated is introduced into the second adsorption tower to perform the adsorption step.
(3) The second adsorption tower and the first adsorption tower are connected in series in this order, the water to be treated is sequentially introduced into the second adsorption tower and the first adsorption tower, the adsorption step is performed in the second adsorption tower, and the A pretreatment step is performed in one adsorption tower.
(4) The desorption step and the acid treatment step are performed in the second adsorption tower, and the water to be treated is introduced into the first adsorption tower to perform the adsorption step. In the stage (1), the fluorine ion concentration of the first treated water discharged from the first adsorption tower is measured, and when the fluorine ion concentration exceeds a predetermined value, the stage moves to (2),
In the stage (3), the fluorine ion concentration of the first treated water discharged from the second adsorption tower is measured, and when the fluorine ion concentration exceeds a predetermined value, the stage (4) is performed. The described water treatment method. In the stage (1), when the cumulative adsorption amount of fluorine ions adsorbed by the adsorbent of the first adsorption tower exceeds a predetermined value, the stage moves to (2),
The water treatment method according to claim 10 or 11, wherein in the stage (3), when the cumulative adsorption amount of fluorine ions adsorbed by the adsorbent in the second adsorption tower exceeds a predetermined value, the stage (4) is performed. . The water treatment method according to any one of claims 1 to 12, wherein the water to be treated is flue gas desulfurization effluent discharged from flue gas desulfurization equipment.

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