JP2021016847A - Water treatment method - Google Patents

Abstract

To provide a water treatment method for removing fluorine ions from water to be treated that contains fluorine ions and a high concentration of sulfate ions, which method makes it possible to treat water in a stable manner by the use of a fluorine adsorbent.SOLUTION: A water treatment method comprises: an adsorption step in which water 1 to be treated that contains fluorine ions and sulfate ions is introduced into an adsorption column 11 filled with fluorine adsorbent to obtain a first treated water 2 from which at least part of the fluorine ions contained in the water 1 to be treated has been removed; and a pretreatment step in which the first treated water 2 obtained in the adsorption step is introduced into the adsorption column 11 prior to the adsorption step, wherein the sulfate ion concentration of the water 1 to be treated introduced into the adsorption column 11 is 30,000 mg/L or more, and wherein the sulfate ion concentration of the first treated water 2 introduced into the adsorption column 11 is 30,000 mg/L or more.SELECTED DRAWING: Figure 2

Description

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

In coal-fired power plants, coke factories, steel mills, etc., flue gas desulfurization wastewater containing fluorine ions as well as sulfate ions is generated by desulfurizing the exhaust gas generated by burning coal or coke. The flue gas desulfurization wastewater usually contains tens of thousands of mg / L or more of sulfate ions, and further contains tens of mg / L to several hundreds of mg / L of fluorine ions. Therefore, when releasing this, it is necessary to remove fluorine ions from the wastewater.

Various methods have been conventionally proposed as methods for removing fluorine ions from flue gas desulfurization wastewater. For example, Patent Document 1 discloses a treatment method for adjusting the pH to 9.4 to 9.8 by adding calcium ions to wastewater containing fluorine ions, magnesium ions and sulfate ions. Patent Document 2 describes a method of removing fluorine ions from flue gas desulfurized wastewater using magnesium hydroxide as a desulfurizing agent. Suspended substances in the wastewater are solid-liquid separated, 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 generated precipitate, and solid-liquid separation is performed. Patent Document 3 discloses a method for treating flue gas desulfurized wastewater, which includes a COD component decomposition step, a first coagulation sedimentation step, a second coagulation sedimentation step, and a fluorine adsorption step.

On the other hand, as a method for treating the etching cleaning waste liquid and the fluorine-containing waste liquid discharged from the aluminum electrolytic refining process, the glass manufacturing process, and the like in the field of semiconductor manufacturing, a method for removing fluorine ions using a fluorine adsorbent is also known. For example, Patent Document 4 discloses a treatment method in which fluorine-containing water is reacted with a calcium compound to convert it into calcium fluoride for solid-liquid separation, and then the separated solution is brought into contact with a fluorine adsorbent. Patent Document 5 describes a step 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, then solid-liquid separation, and contacting the separated liquid with a fluorine adsorbent. A method for treating fluorine-containing water, which comprises a step of regenerating the fluorine adsorbent, a step of adding a recycled waste liquid of the fluorine adsorbent to high-concentration fluorine-containing water, and then passing the liquid through a calcium carbonate crystal seed filling tank. Is disclosed. In Patent Document 6, in a method for removing fluorine in water in which fluorine-containing water to be treated is passed through an adsorption tower filled with a fluorine adsorbent to generate treated water in which fluorine is reduced, fluorine is adsorbed and removed by the adsorption tower. Disclosed is a method for removing fluorine in water, which adjusts the fluorine concentration of the fluorine-containing treated water at the inlet of the adsorption tower to 15 mg / L or less by mixing the treated water with reduced fluorine generated in the process with the fluorine-containing treated water. Has been done.

Japanese Unexamined Patent Publication No. 8-57486 Japanese Unexamined Patent Publication No. 2000-176241 Japanese Unexamined Patent Publication No. 11-13795 Japanese Unexamined Patent Publication No. 5-92187 Japanese Unexamined Patent Publication No. 5-253575 Japanese Unexamined Patent Publication No. 2006-314957

Conventionally, fluorine removal treatment using a fluorine adsorbent has been performed on water to be treated having a relatively low fluorine ion concentration. When treating water to be treated with a high fluorine ion concentration, usually, first, insolubilization treatment of fluorine ions is performed by coagulation precipitation or coprecipitation to remove fluorine ions to some extent, and then the treated water having a reduced fluorine ion concentration. Is brought into contact with an adsorbent to perform advanced removal of fluorine ions. The reason why such treatment is performed is that fluorine ions can be removed to a higher degree by using an adsorbent compared to treatment by coagulation sedimentation or coprecipitation, and water to be treated having a high fluorine ion concentration is coagulation sedimentation or coprecipitation. If it is suddenly brought into contact with an adsorbent without undergoing pretreatment such as, it is difficult to stably obtain treated water having a sufficiently reduced fluorine concentration. In particular, when the concentration of coexisting ions other than fluorine ions is high, there is concern about the influence on the fluorine adsorption treatment.

The present invention has been made in view of the above circumstances, and an object thereof is a method for removing fluorine ions from water to be treated containing fluorine ions and a high concentration of sulfate ions, and is stable with a fluorine adsorbent. The purpose is to provide a water treatment method that can be treated.

The water treatment method of the present invention that has been able to solve the above problems is that water to be treated containing fluorine ions and sulfate ions is introduced into an adsorption tower filled with a fluorine adsorbent, and the fluorine ions in the water to be treated are treated. It has an adsorption step of obtaining the first treated water from which at least a part has been removed, and a pretreatment step of introducing the first treated water obtained in the adsorption step into the adsorption tower before the adsorption step. It is characterized in that the sulfate ion concentration of the water to be treated is 30,000 mg / L or more, and the sulfate ion concentration of the first treated water introduced into the adsorption tower is 30,000 mg / L or more.

When the water to be treated containing fluorine ions and sulfate ions at a high concentration of 30,000 mg / L or more is suddenly introduced into an adsorption tower filled with a fluorine adsorbent and treated, the fluorine ions cannot be sufficiently adsorbed and removed. In particular, the fluorine ion concentration of the treated water becomes high at the initial stage when the water to be treated is introduced into the adsorption tower. However, in the water treatment method of the present invention, the treated water for the adsorption treatment is prepared in advance prior to the fluorine adsorption treatment of the water to be treated, 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 sulfate ion concentration of the first treated water introduced into the adsorption tower in the pretreatment step is 30. It is 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 initial stage 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. Further, 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 in the adsorption tower.

When the pH of the second treated water discharged from the adsorption tower in the pretreatment step becomes 4.0 or less, it is preferable to carry out the adsorption step.

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. The pH of the water to be treated introduced into the adsorption tower is preferably 2.0 or more and 3.5 or less. As the fluorine adsorbent, it is preferable to use a cerium-based adsorbent.

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

The water treatment method of the present invention includes a desorption step of introducing an alkaline solution into the adsorption tower after the adsorption step to desorb fluorine ions from the fluorine adsorbent, and an acid treatment of introducing an acid solution into the adsorption tower after the desorption step. The first adsorption tower and the second adsorption tower are provided as the adsorption towers, and the steps (1) to (4) below are repeated in order to form 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, and the adsorption step is performed in the first adsorption tower. 2 Perform the pretreatment step in the adsorption tower.
(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, and the adsorption step is performed in the second adsorption tower. 1 Perform the pretreatment step in the 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 treatment 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 (2) It is preferable to measure the fluorine ion concentration of the first treated water discharged from the second adsorption tower in the stage (3), and move to the stage (4) when the fluorine ion concentration exceeds a predetermined value. .. Alternatively, in the stage (1), when the cumulative adsorption amount of fluorine ions adsorbed by the adsorbent in the first adsorption tower exceeds a predetermined value, the process moves to the stage (2), and in the stage (3), the second adsorption When the cumulative amount of fluorine ions adsorbed by the adsorbent in the column exceeds a predetermined value, the stage (4) may be started.

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

According to the water treatment method of the present invention, even water to be treated containing a high concentration of sulfate ions is stable when the water to be treated is introduced into an adsorption tower filled with a fluorine adsorbent and treated. It is possible to obtain treated water having a reduced fluorine ion concentration.

The fluorine ion concentration and pH of the treated water when the adsorption step is performed without performing the pretreatment step and when the adsorption step is performed after the pretreatment step is performed on the water to be treated containing sulfate ions at a high concentration. Represents the change over time. A configuration example of the water treatment system used in the water treatment method of the present invention is shown. A configuration example of the water treatment system used in the water treatment method of the present invention is shown. A configuration example of the water treatment system used in the water treatment method of the present invention is shown.

The present invention relates to a water treatment method for treating water to be treated containing fluorine 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 fluorine ions is introduced into an adsorption tower filled with a fluorine adsorbent to introduce at least a part of the fluorine ions in the water to be treated. It relates to a water treatment method for removing water.

In coal-fired power plants, coke factories, steel mills, etc., exhaust gas containing sulfur and fluorine is emitted by burning coal and coke, but when the exhaust gas is desulfurized by a flue gas desulfurization device, sulfuric acid is emitted. Flue gas desulfurization wastewater containing high concentrations of ions and fluorine ions is generated. As a desulfurization method in a flue gas desulfurization apparatus, a method of wet treatment using calcium hydroxide, magnesium hydroxide or sodium hydroxide is known, but when magnesium hydroxide or sodium hydroxide is used as a desulfurization agent, fluorine is used. Flue gas desulfurization wastewater containing sulfate ions at a concentration of tens of thousands of mg / L or more is generated together with ions.

Conventionally, when removing fluorine ions from such flue gas desulfurized wastewater, usually, first, insolubilization treatment of fluorine ions is performed by coagulation precipitation or coprecipitation to remove fluorine ions to some extent, and then, if necessary, fluorine ions. Fluorine ions have been highly removed by contacting the water to be treated with a reduced concentration with an adsorbent. The reason why such treatment is performed is that fluorine ions can be removed to a higher degree by using an adsorbent compared to treatment by coagulation sedimentation or coprecipitation, and water to be treated having a high fluorine ion concentration is coagulation sedimentation or coprecipitation. If it is suddenly brought into contact with an adsorbent without undergoing pretreatment such as, it may not be possible to obtain treated water having a sufficiently reduced fluorine ion concentration. On the other hand, when the flue gas desulfurized wastewater is treated by coagulation sedimentation or coprecipitation, sulfate ions are insolubilized together with fluorine ions, and a large amount of sludge is generated. Therefore, the cost of sludge disposal becomes high, which leads to an increase in treatment cost.

The present inventors have investigated a method for stably removing fluorine when the water to be treated containing a high concentration of sulfate ions as well as fluorine ions is introduced into an adsorption tower filled with a fluorine adsorbent and treated. .. As a result, if the water to be treated, which contains a high concentration of sulfate ions together with fluorine ions, is suddenly introduced into an adsorption tower filled with a fluorine adsorbent and treated, the fluorine ions may not be sufficiently adsorbed and removed. It was found that the fluorine ion concentration of the treated water tended to increase at the initial stage when the water to be treated was introduced into the adsorption tower. Then, as a countermeasure, 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 to introduce the treated water into the adsorption tower filled with the fluorine adsorbent. It became clear. That is, in the water treatment method of the present invention, the water to be treated containing fluorine ions and sulfate ions was introduced into an adsorption tower filled with a fluorine adsorbent, and at least a part of the fluorine ions in the water to be treated was removed. It has an adsorption step of obtaining 1 treated water and a pretreatment step of introducing the first treated water obtained in the adsorption step into the adsorption tower before the adsorption step, and the water to be treated introduced into the adsorption tower in the adsorption step. The sulfate ion concentration of is 30,000 mg / L or more, and the sulfate ion concentration of the first treated water (treated water obtained in the adsorption step) introduced into the adsorption tower in the pretreatment step is 30,000 mg / L or more. There is.

When the fluorine adsorbing treatment of the water to be treated is carried out with a fluorine adsorbent, the fluorine ions are removed from the water to be treated by ion exchange with the anions of the adsorbent. Since the anion contained in the fluorine adsorbent is usually a hydroxide ion, when the fluorine ion is adsorbed by the fluorine adsorbent, the hydroxide ion is desorbed from the fluorine adsorbent and the pH of the water to be treated rises. Show a tendency to do. 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, it deviates from the optimum pH range and it becomes difficult for fluorine ions to be sufficiently adsorbed and removed. Such an increase in pH becomes more pronounced as the concentration of fluorine ions in the water to be treated increases, because the amount of exchange with hydroxide ions increases.

On the other hand, when the present inventors have performed fluorine adsorption treatment on various waters to be treated, the case where the water to be treated containing sulfate ions at a high concentration of 30,000 mg / L or more is treated with a fluorine adsorbent. It was found that the pH of the treated water increased even when the fluorine ion concentration of the treated water was low, and the adsorption performance of the fluorine ions decreased. As a result of investigating the cause of this, although the fluorine adsorbent preferentially adsorbs fluorine ions, if the sulfate ion concentration 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 ion adsorbed on the fluorine adsorbent is only a small part of the sulfate ion contained in the water to be treated. Then, as a countermeasure, a pretreatment step is provided prior to performing the fluorine adsorption treatment of the water to be treated in the adsorption step, and the hydroxide ion of the fluorine adsorbent is forcibly replaced with the sulfate ion. It turned out to be effective. As a result, the fluorine adsorbent has sulfate ions as anions, and when the water to be treated is subsequently brought into contact with the fluorine adsorbent, the sulfate ions of the adsorbent are ion-exchanged with the fluorine ions to suppress the pH rise of the treated water. be able to. Then, in order to replace the hydroxide ion contained in the fluorine adsorbent with sulfate ion, it is efficient to use the treated water obtained by contacting the treated water containing sulfate ion at a high concentration with the fluorine adsorbent. It became clear that it was a target.

FIG. 1 shows a case where the water to be treated having a sulfate ion concentration of 30,000 mg / L or more is adsorbed without performing the pretreatment step, and a case where the adsorption step is performed after performing the pretreatment step. , The measurement results of the fluorine ion concentration and pH of the obtained treated water are shown. 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 pH increase of the treated water at the initial stage is suppressed particularly in the adsorption step, and the 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 for modifying 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 a part of 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 fluorine ions and sulfate ions, but in the present invention, the water to be treated is a coal-fired power plant or a coke factory as water to be treated containing such ions at a relatively high concentration. It is preferable to use flue gas desulfurization wastewater from coal and steel factories.

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. It may be 40,000 mg / L or more, or 50,000 mg / L or more. The upper limit of the sulfate ion concentration of the water to be treated is not particularly limited, but 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 a concentration including not only a free ion form but also a salt-forming 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. You may. Since 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 steps, is more effective, the fluorine ion concentration of the water to be treated 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, even in water to be treated having such a high fluorine ion concentration, fluorine ions can be highly adsorbed and removed. 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 from the viewpoint of stably obtaining the first treated water having 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 contains flue gas desulfurization wastewater from coal-fired power plants, coke factories, steel mills, etc., magnesium ions and sodium ions may be contained in the water to be treated as well as sulfate ions. When the flue gas desulfurization wastewater uses magnesium hydroxide as a desulfurization agent, the content ratio of magnesium ions to sulfate ions in the water to be treated is, for example, 2/8 to 8/8 / molar ratio of magnesium ions / sulfate ions. The range of 2 is preferable, the range of 3/7 to 7/3 is more preferable, and the range of 4/6 to 6/4 is further preferable. When the flue gas desulfurization wastewater uses sodium hydroxide as the desulfurization agent, the content ratio of sodium ion and sulfate ion in the water to be treated is, for example, 3/7 to 9 / in the molar ratio of sodium ion / sulfate ion. The range of 1 is preferable, the range of 4/6 to 8/2 is more preferable, and the range of 5/5 to 7/3 is further preferable. The water to be treated preferably contains flue gas desulfurized wastewater using magnesium hydroxide as a desulfurizing agent, whereby the life of the adsorbent can be extended, and for example, it contributes to the adsorption of fluorine from the adsorbent. It becomes easier to suppress the outflow of the active ingredient (metal component).

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, or the like may be used. it 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. Examples of the cerium-based adsorbent include an adsorbent containing cerium oxide (CeO ₂ ), particularly cerium-containing hydroxide (CeO ₂ · nH ₂ O). The adsorbent may contain a resin, and cerium oxide or cerium hydroxide may be immobilized or reinforced by the resin.

The pH of the water to be treated is preferably 2.0 or more, more preferably 2.1 or more, still more preferably 2.2 or more, from the viewpoint of allowing the adsorption and removal of fluorine ions to be preferably performed by the adsorbent. It is preferably 3.5 or less, more preferably 3.3 or less, and even more preferably 3.1 or less. 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 hydrochloric acid or sulfuric acid is preferably used as the acid. On the contrary, 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, and it is preferable to use an alkali metal hydroxide as the alkali, and sodium hydroxide should be used. Is more preferable. When flue gas desulfurized wastewater is used as the water to be treated, the pH of the flue gas desulfurized wastewater is not always in such a range. Therefore, acid or alkali is added to the water to be treated introduced into the adsorption tower. It is preferable to adjust the pH to a predetermined pH range.

The pH of the water to be treated may be adjusted by providing a pH adjusting means in front of the adsorption tower. As the pH adjusting means, a pH adjusting tank provided with an acid or alkali adding means may be provided in front of the adsorption tower, or an acid or alkali adding means may be provided in the flow path for supplying the water to be treated to the adsorption tower. Examples of the acid or alkali addition means include a chemical injection pump and the like. Further, as the pH adjusting means, a pH measuring means may be provided together with the acid or alkali adding means. The pH measuring means is preferably installed in a pH adjusting tank or between the acid or alkali adding means and the adsorption tower in the flow path for supplying the water to be treated to the adsorption tower.

The redox potential of the water to be treated may be adjusted prior to introducing the water to be treated into the adsorption tower. For example, if the water to be treated contains a large amount of reducing substances, metals such as cerium constituting the fluorine adsorbent are likely to elute. Therefore, by adjusting the redox potential of the water to be treated to a predetermined value or more, fluorine Elution of metal from the adsorbent can be suppressed. From such a viewpoint, the redox potential of the water to be treated is preferably 600 mV or more, more preferably 700 mV or more. On the other hand, from the viewpoint of suppressing deterioration of the fluorine-adsorbing resin (for example, deterioration of the resin constituting the fluorine adsorbent), the redox potential of the water to be treated is preferably 1000 mV or less, more preferably 950 mV or less. The water to be treated may adjust the redox potential together with the pH.

As a chemical for adjusting the redox 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 redox potential of the water to be treated can be adjusted by installing an oxidation-reduction potential meter in the water flow path to be treated which is connected to the entrance side of the adsorption tower and measuring the redox potential of the water to be treated. Further, instead of measuring the redox potential of the water to be treated, or while measuring the redox 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, preferably 18 mg / L or less, and more preferably 15 mg / L or less. ..

The contact between the water to be treated and the fluorine adsorbent is performed 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 by an upward flow type or by a downward flow type. The liquid passing rate at this time may be appropriately set according to the properties of the water to be treated, the filling amount of the fluorine adsorbent, etc. For example, the space velocity (SV) should be appropriately adjusted in the range of ¹ hr ^{-1 to} 50 hr ^-1. Just do it. From the viewpoint of the avoid excessive adsorption column system, the space velocity (SV) is preferably at least 3 hr ^-1, more preferably 5 hr ^-1 or more, more preferably -8 hr ^-1 or more, 12hr ^-1 or more More preferred. Also, from a stable fluoride ion concentration is easy to obtain a first treated water which is reduced in view, the space velocity (SV) is preferably 40 hr ^-1 or less, more preferably 30 hr ^-1 or less, 25Hr ^-1 or less is more 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 can be obtained. The fluorine adsorption treatment by 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 by a multi-stage connected adsorption tower, or the water to be treated is treated by combining the treatment by one stage of the adsorption tower and the treatment by the adsorption tower connected in multiple stages. It is preferable to do so. 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 may 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, 5 or less is preferable, 4 or less is more preferable, and 3 or less is further preferable.

When the adsorption towers are connected in series in multiple stages, the pH of the water to be treated may be adjusted before being introduced into each of the adsorption towers connected in series in multiple stages. As described above, each pH at this time 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 further preferable. In the water treatment method of the present invention, the pH change when the water to be treated is passed through the adsorption tower in the adsorption step is small, and usually, the pH is only adjusted when the water to be treated is introduced into the first adsorption tower. Is enough.

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 being discharged into the environment. For example, according to the uniform effluent standard set by the Ministry of the Environment, the permissible limit of fluorine and its compounds is set at 15 mgF / L for those discharged into the sea area, and 8 mgF / L for those discharged into public water areas other than the sea area. It is 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 than that, for example, 5 mg / L or less, 3 mg / L or less, or 1 mg / L or less. When the adsorption towers are connected in series in multiple stages to perform the adsorption treatment, the fluorine ion concentration of the first treated water obtained from the adsorption tower in the latter stage may be in such a range. The sulfate ion concentration of the first treated water obtained in the adsorption step is usually 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 ion contained in the fluorine adsorbent filled in the adsorption tower can be replaced with sulfate ion. As a result, when the fluorine adsorbent adsorbs fluorine ions in the adsorption step performed following the pretreatment step, the pH increase of the first treated water obtained is suppressed, and the fluorine ions in the water to be treated are highly adsorbed and removed. It becomes possible. The second treated water discharged from the adsorption tower in the pretreatment step can be discharged to the outside 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 may be obtained by performing the adsorption step in another adsorption tower. It may be the first treated water obtained. 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 preferable.

The sulfate ion concentration of the first treated water introduced into the adsorption tower in the pretreatment 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. It may be 40,000 mg / L or more, or 50,000 mg / L or more. The upper limit of the sulfate ion concentration of the water to be treated is not particularly limited, but 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 than that, for example, 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, even if the fluorine ions in the first treated water are not adsorbed and removed in the pretreatment step, they are discharged from the adsorption tower. The fluorine 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 more, more preferably 2.1 or more, further preferably 2.2 or more, and preferably 3.5 or less. It is more preferably 0.3 or less, and further preferably 3.1 or less. 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 hydrochloric acid or sulfuric acid is preferably used as the acid. On the contrary, when the pH of the first treated water is low, the pH of the first treated water may be adjusted by adding an alkali, and it is preferable to use an alkali metal hydroxide as the alkali, and sodium hydroxide is used. It is more preferable to use it. By adjusting the pH of the first treated water introduced into the adsorption tower in this way, the hydroxide ion contained in the fluorine adsorbent can be efficiently replaced with sulfate ion in the pretreatment step.

The first treated water may be passed through the adsorption tower by an upward flow type or by a downward flow type. The liquid passing speed at this time may be appropriately adjusted in the range of ¹ hr ^{-1 to} 100 hr ^-1 as the space velocity (SV), for example. The space velocity (SV) is preferably 3 hr ^-1 or higher, preferably 5 hr ^-1 or higher, 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. still more preferably, -8 hr ^-1 or more, and even more preferably 12hr ^-1 or more. Further, in view of enhancing the replacement efficiency of the sulfate ion of the hydroxide ions with the adsorbent, the space velocity (SV) is preferably 70Hr ^-1 or less, more preferably 50 hr ^-1 or less, more preferably 30 hr ^-1 or less ..

In the pretreatment step, the first treated water may be introduced while being circulated in 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 will be used again as the first treated water introduced into the adsorption tower in the pretreatment step. Of course, instead of circulating and supplying 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 part thereof may be introduced into the adsorption tower. If the hydroxide ion contained in the fluorine adsorbent is sufficiently replaced with the sulfate ion 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 the end of the pretreatment step can be determined by measuring the pH of the second treated water. The pH of the second treated water is high or the pH rises at the initial stage of the pretreatment step, and the pH is, for example, about 6 to 9. On the other hand, when the pretreatment step is continued, the amount of hydroxide ion exchanged with the sulfate ion of the fluorine adsorbent decreases, and the pH of the second treated water gradually decreases. Therefore, when the pH of the second treated water becomes equal to or less than a predetermined value in the pretreatment step, the pretreatment step can be terminated and the process can proceed to the adsorption step. The pH of the second treated water as a guide is preferably 4.0 or less, more preferably 3.8 or less, and even more preferably 3.5 or less.

The timing of the end of the pretreatment step may be determined based on the amount of the 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 20 times or more, more preferably 30 times or more the apparent volume of the fluorine adsorbent filled in the adsorption tower. , 40 times or more is more preferable. 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 excessively supplied, the first treated water is supplied to the adsorption tower. The supply amount of the fluorine adsorbent is preferably 200 times or less, more preferably 150 times or less, still more preferably 100 times or less, the apparent volume of the fluorine adsorbent filled in the adsorption tower. The amount of the first treated water supplied to the adsorption tower described here means the total amount of the first treated water to be 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 a sulfate ion as an anion. After that, when the water to be treated is brought into contact with the fluorine adsorbent in the adsorption step, the sulfate ion of the adsorbent is ion-exchanged with the fluorine ion, and the pH increase 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 it becomes possible to stably remove fluorine by adsorption from the water to be treated.

The pretreatment step may be performed after the adsorption step, before the fluorine adsorbent is desorbed and regenerated, and before the fluorine adsorption treatment is performed in the next adsorption step. In this case, the water treatment method of the present invention introduces an alkaline solution into the adsorption tower after the adsorption step to desorb fluorine ions from the fluorine adsorbent, and introduces an acid solution into the adsorption tower after the desorption step. The acid treatment step is further provided, and the pretreatment step is performed after the acid treatment step, and then the adsorption step is performed again. By providing the desorption step and the acid treatment step after the adsorption step in this way, 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 the 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 is 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 alkali metal hydroxide. As the alkali metal hydroxide, lithium hydroxide, potassium hydroxide, sodium hydroxide, rubidium hydroxide, cesium hydroxide and the like can be used, and only one of these may be used, or two or more thereof may be used in combination. You may. As the alkali metal hydroxide, it is preferable to use sodium hydroxide from the viewpoint of cost.

As the alkaline solution used in the desorption step, it is preferable to use an alkaline solution having a somewhat high hydroxide ion concentration because a desorbed solution containing a higher concentration of fluorine ions can be obtained as the hydroxide ion concentration increases. The hydroxide ion concentration of the alkaline solution is, for example, preferably 0.05 mol / L or more, more preferably 0.1 mol / L or more, still more preferably 0.2 mol / L or more. On the other hand, in consideration of the handleability 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 the fluorine ions have been desorbed in the desorption step can be used again as the fluorine adsorbent by contacting it with the 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, preferably 2.0 mol / L or less, and more preferably 1.0 mol / L or less. Before the acid treatment step, the adsorbent to which the fluorine ions have been desorbed in the desorption step may be washed with water. Further, the adsorbent may be washed with water after the acid treatment step.

After the acid treatment step, the pretreatment step described above is performed. When washing with water after contacting with an acid solution in the acid treatment step, a pretreatment step is performed after this washing with water. By performing the pretreatment step after the fluorine adsorbent is regenerated in this way 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 to be performed again. Will be able to.

In addition, when sulfuric acid was used in the acid treatment step, it was examined whether the acid treatment step could also serve as the pretreatment step described above, but when the pretreatment step was performed even if sulfuric acid was used in the acid treatment step. It was not possible to obtain the same effect as. That is, when the adsorption step is performed without performing the pretreatment step after the acid treatment step, the pH of the first treated water is increased in the adsorption step, and the pH of the first treated water is particularly increased at the initial stage of the adsorption step. It showed a tendency for the fluorine ion concentration to increase.

It is effective that the pretreatment step described above is performed before the first adsorption step is performed by the fluorine adsorbent, or after the fluorine adsorbent is regenerated and before the first adsorption step is performed. Therefore, when the adsorption step is interrupted once and then the adsorption step is restarted, the pretreatment step may not be performed before the restarted 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. 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 to be treated, which communicates with the inlet side of the adsorption tower 11 and supplies 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 to be treated 1 into the adsorption tower 11 and bringing it into contact with the fluorine adsorbent, the first treated water 2 having a reduced fluorine ion concentration can be 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 a part thereof is temporarily stored in the treated water tank 23.

It is preferable that the pH adjusting means 12 for adjusting the pH of the water to be treated 1 is provided on the entrance side of the adsorption tower 11. Examples of the pH adjusting means 12 include a chemical injection pump that adds an acid or an alkali. The acid or alkali may be supplied into the pipe of the water flow path 21 to be treated, or a pH adjustment tank may be provided in the water flow path 21 to be treated and the acid or alkali may be supplied in the pH adjustment tank. At this time, it is preferable to supply the acid or alkali while measuring the pH of the water to be treated 1. 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.

It is preferable that a fluorine ion densitometer is provided on the outlet 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 at which the adsorption step is completed. For example, a reference value for the fluorine ion concentration of the first treated water 2 can be set in advance, and the adsorption step can be terminated when the reference value is exceeded. A fluorine ion concentration meter may also be provided on the entrance 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. May be good.

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

The adsorbent desorbed from fluorine ions is regenerated by contacting it with an acid solution, and the fluorine adsorbing ability is imparted again (acid treatment step). In FIG. 2, the acid solution can be supplied from the chemical flow path 25, and the acid solution in contact with the adsorbent, that is, the acid cleaning waste liquid 4, is discharged through the waste liquid flow path 26. The acid solution may be supplied to the adsorption tower 11 through a flow path different from that of the alkaline solution, and the acid cleaning waste liquid 4 may be discharged from the adsorption tower 11 through a flow path different from that of the desorption liquid 3. Further, prior to the supply of 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 for adsorbing and removing fluorine ions in the water to be treated 1, but prior to introducing the water to be treated 1 into the adsorption tower 11, the treated water tank 23 The first treated water 2 stored in the water is introduced into the adsorption tower 11 through the return flow path 24 (pretreatment step). The second treated water 5 is obtained from the adsorption tower 11. The sulfate ion concentration of the first treated water 2 is 30,000 mg / L or more, and by introducing the first treated water 2 containing sulfate ions at a high concentration into the adsorption tower 11, the adsorption tower 11 can be reached. The hydroxide ion contained in the packed adsorbent is replaced with sulfate ion. As a result, when the water to be treated 1 is subsequently introduced into the adsorption tower 11, the increase in the pH of the first treated water 2 discharged from the adsorption tower 11 is suppressed, and the fluorine ions from the water to be treated 1 are stabilized. It becomes possible to remove 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 step 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 a predetermined value or less (for example, the pH is 4.0 or less), the pretreatment step can be terminated and the process can be started to the adsorption step. 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.

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

In the configuration example shown in FIG. 3, the first adsorption tower 11A and the second adsorption tower 11B are provided in parallel as the adsorption tower, and the water flow path 21 to be treated is provided in each of the first adsorption tower 11A and the second adsorption tower 11B. A treated water flow path 22, a treated water tank 23, a return flow path 24, a chemical liquid flow path 25, and a waste liquid flow path 26 are provided. According to the configuration example shown in FIG. 3, the adsorption step and the desorption / acid cleaning / pretreatment step can be performed in each of the first adsorption tower 11A and the second adsorption tower 11B, respectively. Therefore, at the same time as the adsorption treatment is performed in the first adsorption tower 11A, the desorption / regeneration treatment and the pretreatment of the adsorbent can be performed in the second adsorption tower 11B, and vice versa. Continuous adsorption processing becomes possible.

In the configuration example shown in FIG. 3, the two adsorption towers of the first adsorption tower 11A and the second adsorption tower 11B are alternately subjected to the adsorption step and the desorption / acid cleaning / pretreatment step to continuously perform the water to be treated. It is possible to carry out a continuous adsorption treatment of the water to be treated by using three or more adsorption towers. For example, when three adsorption towers of the first adsorption tower, the second adsorption tower, and the third adsorption tower are used, the first adsorption tower and the second adsorption tower are connected in series in this order to perform the adsorption step, and the third adsorption step is performed. The adsorption tower performs desorption, acid cleaning, and pretreatment, then the second adsorption tower and the third adsorption tower are connected in series in this order to perform the adsorption process, and the first adsorption tower desorbs, acid cleans, and pretreats. By performing the step, then the third adsorption tower and the first adsorption tower are connected in series in this order to perform the adsorption step, and then the desorption, acid cleaning, and pretreatment steps are repeated in the second adsorption tower. The water to be treated can be continuously adsorbed using the three adsorption towers. When four or more adsorption towers are used, three or more adsorption towers may be connected in series in multiple stages to perform adsorption treatment, and two or more adsorption towers are subjected to desorption, acid cleaning, and pretreatment steps. May be good.

FIG. 4 shows a configuration example in which the adsorption towers are connected in series in multiple stages. In FIG. 4, a first suction tower 11A and a second suction tower 11B are provided as suction towers, and a series connection flow path 27 is provided so as to communicate with the outlet side of the first suction tower 11A and the entrance side of the second suction tower 11B. As a result, the first suction tower 11A and the second suction 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, and then the obtained first. 1 The treated water 2A can be introduced into the second adsorption tower 11B through the series connection flow path 27, and the pretreatment step can be performed in the second adsorption tower 11B. Therefore, it is not necessary to install a treated water tank for the first treated water 2A for performing the pretreatment step. The second treated water 5B discharged from the second adsorption tower 11B can be discharged into the environment. Prior to introducing the first treated water 2A into the second adsorption tower 11B, it is preferable to perform the desorption step and the acid treatment step in the second adsorption tower 11B. Therefore, during the desorption step and the acid treatment step in the second adsorption tower 11B, the first treated water 2A discharged from the first adsorption tower 11A goes out of the system as it is without going through the second adsorption tower 11B. It is preferable to discharge.

In FIG. 4, a series connection flow path 28 is further provided so as to communicate with the outlet side of the second suction tower 11B and the entrance side of the first suction tower 11A, whereby the second suction tower 11B and the first suction tower 11B and the first suction tower are provided. 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, and then the obtained first. 1 The treated water 2B can be introduced into the first adsorption tower 11A through the series connection flow path 28, and the pretreatment step can be performed in the first adsorption tower 11A. Therefore, it is not necessary to install a treated water tank for the first treated water 2B for performing the pretreatment step. The second treated water 5A discharged from the first adsorption tower 11A can be discharged into the environment. It is preferable that the desorption step and the acid treatment step are performed in the first adsorption tower 11A prior to introducing the first treated water 2B into the first adsorption tower 11A. Therefore, during the desorption step and the acid treatment step in the first adsorption tower 11A, the first treated water 2B discharged from the second adsorption tower 11B goes out of the system as it is without going through the first adsorption tower 11A. It is preferable to discharge.

In the configuration example shown in FIG. 4, specifically, it is preferable to perform the adsorption step, the desorption step, the acid treatment step, and the pretreatment step in each adsorption tower as follows. That is, by sequentially performing the following stages (1) to (4), 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 preferable. (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 The adsorption step is performed, and the pretreatment step is performed in the second adsorption tower 11B. (2) The desorption step and the acid treatment step 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 step. (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 the second adsorption tower 11B The adsorption step is performed, and the 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, when the stage (4) is completed, the stage (1) can be returned to the next stage. As a result, the frequency of desorption / regeneration treatment of the adsorption tower can be reduced, and efficient fluorine ion removal from the water to be treated becomes possible.

In the 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, water 1 to be treated having a sulfate ion concentration of 30,000 mg / L or more was introduced into the first adsorption tower 11A, and at least a part of fluorine ions was removed from the water 1 to be treated. Treated water 2A is obtained. The fluorine ion concentration of the first treated water 2A is such that fluorine ions are 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 to the outside 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 the hydroxide ion contained in the adsorbent filled in the second adsorption tower 11B is sulfate. It is replaced by an ion.

In the stage (1), by measuring the pH of the second treated water 5B discharged from the second adsorption tower 11B, the hydroxide ion contained in the adsorbent filled in the second adsorption tower 11B becomes sulfate ion. It is possible to grasp how much the replacement of is progressed. The pH of the second treated water 5B usually rises to about 6 to 9 once, and then decreases as the treatment is continued. The stage (1) is preferably performed until the pH of the second treated water 5B becomes a predetermined value or less (for example, the 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 a 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 1 treated water 2A can be adsorbed and removed by the second adsorption tower 11B.

In the stage (1), the stage moves to the stage (2) at the stage where the adsorption / removal performance of fluorine ions of the first adsorption tower 11A is lowered or before the deterioration. 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 process moves to the stage (2). do it. Alternatively, in the stage (1), when the cumulative adsorption amount of the fluorine ions adsorbed by the adsorbent of the first adsorption tower 11A exceeds a predetermined value, the stage may be moved to the stage (2). The cumulative 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 the first adsorption tower of the water to be treated 1. It can be obtained from the supply amount to 11A (or the discharge amount of the first treated water 2A).

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

After the desorption / regeneration treatment of the adsorbent of 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, water 1 to be treated having a sulfate ion concentration of 30,000 mg / L or more was introduced into the second adsorption tower 11B, and at least a part of fluorine ions was removed from the water 1 to be treated. Treated water 2B is obtained. The fluorine ion concentration of the first treated water 2B is such that fluorine ions are 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 following the desorption step and the acid treatment step performed in the stage (2), and the hydroxide ion contained in the adsorbent filled in the first adsorption tower 11A is generated. It is replaced with sulfate ion.

In the stage (3), by measuring the pH of the second treated water 5A discharged from the first adsorption tower 11A, the hydroxide ion contained in the adsorbent filled in the first adsorption tower 11A becomes sulfate ion. It is possible to grasp how much the replacement of is progressed. The pH of the second treated water 5A usually rises to about 6 to 9 once, and then decreases as the treatment is continued. The stage (3) is preferably performed until the pH of the second treated water 5A becomes a predetermined value or less (for example, the pH is 4.0 or less). In the stage (3), even if the pH of the second treated water 5A falls below a 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 1 treated water 2B can be adsorbed and removed by the first adsorption tower 11A.

In the stage (3), the stage moves to the stage (4) at the stage where the adsorption / removal performance of fluorine ions of the second adsorption tower 11B is lowered or before the deterioration. 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 process moves to the stage (4). do it. Alternatively, in the stage (3), when the cumulative adsorption amount of the fluorine ions adsorbed by the adsorbent in the second adsorption tower 11B exceeds a predetermined value, the stage may be moved to the stage (4). The cumulative 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 1 to be treated. It can be obtained from the supply amount to 11B (or the discharge amount of the first treated water 2B).

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

After the desorption / regeneration treatment of the adsorbent of 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 the stages (1) to (4) in this way, the frequency of desorption / regeneration treatment of the adsorbent filled in the adsorption tower is reduced, and efficient fluorine ion removal from the water to be treated. Is possible. The reduction in the frequency of desorption / regeneration treatment of the adsorbent also leads to a longer life of the adsorbent, which can reduce the treatment cost.

In the configuration example shown in FIG. 4, the suction towers are connected in series in two stages, but the suction towers may be connected in series in three or more stages. In this case, in the stages corresponding to the above-mentioned stages (1) and (3), the pretreatment step is performed in the adsorption tower at the last stage, and the adsorption tower at the front stage is the desorption step and the acid treatment step in the next stage. You just have to do.

The present invention can be used for treating flue gas desulfurization wastewater from coal-fired power plants, coke factories, steel mills, and the like.

1: Water to be treated 2, 2A, 2B: First treated water 3: Desorbed liquid 4: Acid cleaning waste liquid 5, 5A, 5B: Second treated water 11: Adsorption tower, 11A: First adsorption tower, 11B: No. 2 Adsorption tower 12: pH adjusting means 21: Water flow path to be treated 22: Treated water flow path 23: Treated water tank 24: Return flow path 25: Chemical solution flow path 26: Waste liquid flow path 27, 28: Series connection flow path

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 a first treated water from which at least a part of fluorine ions in the water to be treated has been removed.
Prior to the adsorption step, there is a pretreatment step of introducing the first treated water obtained in the adsorption step into the adsorption tower.
The sulfate ion concentration of the water to be treated introduced into the adsorption tower is 30,000 mg / L or more.
A water treatment method characterized in that the sulfate ion concentration of the first treated water introduced into the adsorption tower is 30,000 mg / L or more. The water treatment method according to claim 1, wherein in the pretreatment step, the fluorine ion concentration of the first treated water introduced into the adsorption tower is 15 mg / L or less. The water treatment method according to claim 1 or 2, wherein in the pretreatment step, the pH of the first treated water introduced into the adsorption tower is 2.0 or more and 3.5 or less. The water treatment method according to claim 3, wherein when the pH of the second treated water discharged from the adsorption tower in the pretreatment step becomes 4.0 or less, the adsorption step is performed. The water treatment method according to any one of claims 1 to 4, wherein in the pretreatment step, the first treated water is introduced while being circulated in the adsorption tower. After the adsorption step, an alkaline solution is introduced into the adsorption tower to desorb fluorine ions from the fluorine adsorbent, and a desorption step.
After the desorption step, an acid treatment step of introducing an acid solution into the adsorption tower is further provided.
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 fluorine ion concentration of the water to be treated introduced into the adsorption tower is 50 mg / L or more. The water treatment method according to any one of claims 1 to 7, wherein in the adsorption step, the pH of the water to be treated introduced into the adsorption tower is 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, an alkaline solution is introduced into the adsorption tower to desorb fluorine ions from the fluorine adsorbent, and a desorption step.
After the desorption step, an acid treatment step of introducing an acid solution into the adsorption tower is further provided.
A first suction tower and a second suction tower are provided as the suction tower, and each step is performed by the first suction tower and the second suction tower by repeating the following stages (1) to (4) in order. 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, and the adsorption step is performed in the first adsorption tower. 2 Perform the pretreatment step in the adsorption tower.
(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, and the adsorption step is performed in the second adsorption tower. 1 Perform the pretreatment step in the 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 process proceeds to the stage (2).
In the step (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 process proceeds to the stage (4). The water treatment method described. In the stage (1), when the cumulative adsorption amount of fluorine ions adsorbed by the adsorbent in the first adsorption tower exceeds a predetermined value, the process proceeds to the stage (2).
The water treatment method according to claim 10 or 11, wherein when the cumulative adsorption amount of fluorine ions adsorbed by the adsorbent of the second adsorption tower in the stage (3) exceeds a predetermined value, the stage moves to the stage (4). .. The water treatment method according to any one of claims 1 to 12, wherein the water to be treated is flue gas desulfurization wastewater discharged from a flue gas desulfurization facility.

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