JP6967466B2 - Dissolved aluminum removal method and equipment - Google Patents

Description

The present invention relates to a method and an apparatus for removing dissolved aluminum from water to be treated containing silica (silicon dioxide: SiO _2).

In water containing silica, even if the concentration of silica is lower than its solubility in water, the coexistence of a trace amount of aluminum (Al) easily precipitates the component containing silica. This precipitation can occur even if the aluminum concentration is about several tens of μg / L when silica is contained at, for example, several tens of mg / L.

Precipitation of silica components from water containing silica can be a problem, for example, in reverse osmosis membrane devices. When water containing silica is supplied to the reverse osmosis membrane apparatus as feed water, the silica component is deposited on the surface of the reverse osmosis membrane by the aluminum coexisting in the feed water, and the reverse osmosis membrane is closed. As a result, it causes a decrease in the amount of water permeated by the reverse osmosis membrane. It is necessary to reduce the aluminum concentration in the feed water supplied to the reverse osmosis membrane device.

By the way, aluminum may originally exist in natural water such as river water, lake water, and well water, and clear water such as tap water and drinking water by removing suspended solids from water containing suspended solids. It may also be derived from an aluminum-based flocculant such as polyaluminum chloride (PAC) used in the process of producing. Most of the aluminum-based flocculants added to coagulate and remove suspended solids are removed by precipitation and filtration together with suspended solids, but some are unreacted in clear water even after the suspended solids have been removed. It remains as it is. Since river water, lake water, well water, or clear water after removing suspended solids may be used as supply water for reverse osmosis membrane devices, aluminum is removed from these waters. Technology is desired.

It is conceivable to remove aluminum in water using ion exchange resin equipment for softening and deionization. As a technique for removing aluminum in the water to be treated using an ion exchange resin, for example, Patent Document 1 describes a salt-type strong acid cation exchange resin of an alkali metal or an alkaline earth metal and a chlorine (Cl) type strong basic anion exchange resin. by using preparative mixed bed, bicarbonate ions (HCO ₃ ^-) is adsorbed to an anion exchange resin of aluminum in the for-treatment water containing, discloses a technique for reducing the amount of aluminum in water. However, the method described in Patent Document 1 has restrictions on the ion exchange resin that can be used, so that it is necessary to adjust the ion form, and a chemical for that purpose is required. In addition, it is necessary to regenerate the ion exchange resin, which requires a chemical for regeneration. In addition, there are forms of nonionic aluminum that cannot be removed by ion exchange resin equipment for softening and deionization.

Although not related to the removal of aluminum as related to the present invention, Patent Document 2 is a technique for removing silica from water to be treated containing silica after adjusting the pH of the water to be treated to a predetermined range. Disclosed is a method of adding aluminate to precipitate a compound of silica and aluminate for separation and removal.

Japanese Unexamined Patent Publication No. 2012-223700 Japanese Unexamined Patent Publication No. 2015-223539

For applications such as water supply to reverse osmosis membrane devices, it is required to be able to reliably remove dissolved aluminum in the water to be treated, but when an ion exchange resin device for softening or deionization is used, Regeneration treatment of ion exchange resin is required, and chemicals for regeneration are required. In addition, there is a form of nonionic aluminum that cannot be removed by an ion exchange resin device.

An object of the present invention is a method and an apparatus for removing aluminum contained in water to be treated containing silica and aluminum, which does not require chemical regeneration of an ion exchange resin and can surely reduce the aluminum concentration. To provide the equipment.

The removal method of the present invention is a method for removing aluminum from water to be treated containing silica and aluminum, in which water to be treated is passed through at least an ion exchange resin layer containing an anion exchange resin to reduce aluminum. Has a water flow step, and in the water flow step, the water to be treated is passed in excess of the ion exchange capacity of the anion exchange resin.

The aluminum removing device of the present invention is an aluminum removing device that removes aluminum from water to be treated containing silica and aluminum, and is provided with an ion exchange resin layer containing at least an anion exchange resin, and the water to be treated is passed through the aluminum to be treated. It is equipped with an ion exchange device that discharges reduced water and a cleaning mechanism that is connected to the ion exchange device to clean the ion exchange resin layer with a cleaning liquid, and ionizes the water to be treated in excess of the ion exchange capacity of the anion exchange resin. Suspended substances generated in the ion exchange resin layer by passing water through the exchange resin layer are removed by washing with a washing liquid.

Aluminum is an amphoteric metal, and its dissolved state is said to have a high ratio of anions on the alkaline side and cations on the acidic side with a pH of around 6.5 as a boundary. In addition to being in the form of ions, aluminum in water may form a complex with coexisting ions, which are adsorbed on the cation exchange resin or the anion exchange resin. There is also nonionic soluble aluminum, which is not adsorbed on the ion exchange resin.

On the other hand, silica (silicon dioxide) is adsorbed on the anion exchange resin. The adsorption of silica on the anion exchange resin is considered to be electrostatic rather than due to the ion exchange reaction, and it is considered that silica is loosely bonded to the anion exchange resin by that amount. If the anion exchange resin is OH type and has a high basicity, silica is relatively well adsorbed to the anion exchange resin, but unlike the case of a normal ion exchange reaction, it is less than half of the water flow amount calculated from the ion exchange capacity. Leakage of silica begins with the amount of water flowing through.

The above description of the adsorption of aluminum and silica on the ion exchange resin is based on the case where aluminum and silica are present alone in the water to be treated. In the present invention, water to be treated containing silica and aluminum is passed through an ion exchange resin layer containing at least an anion exchange resin. Silica in the water to be treated is loosely adsorbed on the anion exchange resin. At this time, if the water to be treated contains aluminum regardless of whether it is ionic or nonionic, this aluminum reacts with the silica adsorbed by the anion exchange resin, and the general formula is xAl _2. O ₃ · ySiO ₂ · zH insoluble compound represented by the ₂ O (a type of aluminosilicate) is precipitated. As long as aluminum is supplied, aluminum and silica are adsorbed on this precipitate, and this precipitate grows and becomes a suspended solid contained in the ion exchange resin layer. Suspended solids will be accumulated in the space between the particles of the ion exchange resin constituting the ion exchange resin layer.

Ionic aluminum is also adsorbed on the anion exchange resin or the cation exchange resin depending on the pH of the water to be treated. When aluminum is adsorbed on the ion exchange resin, silica in the water to be treated precipitates around it, and then silica and aluminum are adsorbed on the precipitate to form a suspended solid similar to the above. After all, by passing water to be treated containing silica and aluminum through the ion exchange resin layer containing at least the anion exchange resin, an insoluble precipitate containing silica and aluminum is generated as a suspended substance and the ion exchange resin layer is formed. The aluminum concentration in the water to be treated will decrease.

By consuming aluminum in this way, the aluminum concentration and the silica concentration in the water passing through the ion exchange resin layer are reduced, and the aluminum is removed. With respect to silica, adsorption to the anion exchange resin proceeds at the initial stage of water flow, but in a situation where the silica concentration is significantly higher than the aluminum concentration, the silica is not adsorbed as much as aluminum thereafter. As a result, even at the stage where aluminum continues to be trapped in the ion exchange resin layer, the concentration of silica hardly changes before and after water is passed through the ion exchange resin layer. At the very early stage of water flow to the ion exchange resin layer, the adsorption of silica to the cation exchange resin is not sufficient, so that a part of aluminum permeates the ion exchange resin layer, that is, leaks, but the amount is It is a very small amount.

As water flow continues, the amount of suspended solids in the ion exchange resin layer increases, the water flow differential pressure when the water to be treated passes through the ion exchange resin layer also increases, and aluminum is removed. It will not be possible to obtain water at a practical flow rate. Although it depends on the type and particle size of the ion exchange resin constituting the ion exchange resin layer, according to the experiments by the present inventors, the total amount of aluminum trapped in the ion exchange resin layer is 1 L. When it reaches 2 g per unit (that is, when it reaches 2 g Al / L-R), the pressure difference in water flow begins to increase due to the influence of the suspended substance existing between the particles of the ion exchange resin. This is because the suspended solids accumulated in the ion exchange resin layer obstruct the flow of water. When the amount of aluminum trapped in the ion exchange resin layer reaches 3 gAl / L-R with respect to the total amount of the ion exchange resin, it becomes difficult to trap more aluminum and aluminum leakage starts. It is considered that the aluminum leak starts because the suspended solids accumulate between the particles of the ion exchange resin, and the suspended solids containing aluminum are pushed out by the saturation between the particles.

Since the suspended substance is not adsorbed to the ion exchange resin by ion exchange, the suspended substance can be removed from the ion exchange resin layer by simply washing the ion exchange resin layer. It is not necessary to regenerate the ion exchange resin in the cleaning step, and pure water can be used for cleaning, for example. It is not necessary to use chemicals (for example, sodium hydroxide or hydrochloric acid) for regenerating the ion exchange resin. Therefore, in the present invention, when the water flow differential pressure of the ion exchange resin layer reaches a predetermined value, or when the amount of trapped aluminum in the ion exchange resin layer reaches a predetermined value, the ion exchange resin layer is covered. It is preferable to stop the passage of the treated water and instead introduce a cleaning liquid such as pure water into the ion exchange resin layer to clean the ion exchange resin layer. The cleaning of the ion exchange resin layer is preferably backwashing. In this case, the water to be treated may be flowed from top to bottom in the direction of gravity to pass through the ion exchange resin layer, and a cleaning liquid such as pure water may be flowed from bottom to top during backwashing. If the fluidity of the ion exchange resin layer is poor during backwashing, the ion exchange resin layer may be loosened by bubbling or the like before backwashing. The ion exchange resin layer may be washed by scrubbing instead of backwashing.

When the suspended solid is discharged from the ion exchange resin layer by washing, the water to be treated can be passed through the ion exchange resin layer again to remove the dissolved aluminum in the water to be treated. Therefore, in the present invention, the ion exchange resin layer is washed after the water passing step and the water passing step of passing water to be treated through the ion exchange resin layer containing at least the anion exchange resin to obtain water having reduced aluminum. By repeatedly performing the cleaning step, the soluble aluminum can be continuously removed from the water to be treated containing silica. Regarding when to stop the water flow process, the amount of aluminum accumulated in the ion exchange resin layer was estimated based on the integrated flow rate, and this accumulated amount was, for example, 3 gAl / L-R with respect to the total amount of the ion exchange resin. The water flow process may be terminated at that point. Alternatively, when the differential pressure of water flow increases and the amount of treated water decreases due to the accumulation of suspended solids, the differential pressure of water flow and the amount of treated water of the ion exchange resin layer are monitored, and the differential pressure of water flow exceeds a certain value. Alternatively, the water flow process may be terminated when the amount of treated water falls below a certain amount.

In short, the present invention does not capture aluminum in the ion exchange group of the ion exchange resin, but precipitates a compound having low solubility, for example, aluminum silicate, together with silica between the particles of the ion section resin, and removes the aluminum by volume filtration. It is a thing. The water to be treated may contain general anions and cations such as sodium ion, potassium ion, calcium ion, chloride ion, carbonate ion, sulfate ion and the like in addition to silica and aluminum, but removal of aluminum. Because of the fact that ion exchange is not used, the water to be treated can pass through beyond the ion exchange capacity of the ion exchange resin layer for the removal of aluminum.

In the present invention, as described above, aluminum can be repeatedly removed from the water to be treated by cleaning the ion exchange resin layer. The wash effluent contains the suspended solids described above, including aluminum and silica. If the washing wastewater containing suspended solids is allowed to stand, it separates into a precipitate containing suspended solids and a supernatant liquid. The supernatant liquid can be returned to the water to be treated and reused.

Suspended solids in the washing wastewater may settle in the drainage facility, etc., but if there is a concern that this precipitation may cause some problems, it is conceivable to dispose of the ion exchange resin layer itself. In particular, the presence of fluorine (F) can result in the formation of less soluble precipitates. When the ion exchange resin layer is disposable, it can be disposed of as a solid-concentrated ion exchange resin. Further, assuming that the water to be treated is passed through the ion exchange resin layer by a downward flow, for example, only the upper 30 to 60% portion of the ion exchange resin layer can be exchanged. When disposable, the volume of waste can be further reduced by incinerating the ion exchange resin.

In the present invention, the ion exchange resin layer may be broken at an early stage by various anions (for example, chloride ions and carbonate ions) in the water to be treated, so that any ion form of the anion exchange resin can be used. good. When tap water is used as water to be treated, even if an OH type anion exchange resin is used, the ion type of the anion exchange resin becomes Cl type over time due to the influence of chlorine added to the tap water. Become. Silica is less likely to be adsorbed on the Cl-type anion exchange resin than in the OH-type, but the adsorption of aluminum on the ion exchange resin also acts to form a precipitate in the ion exchange resin layer, and this precipitation occurs. By adsorbing aluminum or silica to the object, removal of aluminum in the water to be treated is achieved.

In the present invention, the ion exchange resin layer may be composed of a single bed of anion exchange resin or a mixed bed of anion exchange resin and cation exchange resin. The anion exchange resin used in the present invention is preferably a strong basic anion exchange resin, and the cation exchange resin in the case of a mixed bed is preferably a strong acid cation exchange resin. In the present invention, the pH of the water to be treated containing silica is preferably 4 or more and 11 or less, the total cation concentration is preferably 500 mgCaCO ₃ / L equivalent or less, and the total anion concentration is 500 mgCaCO ₃ / L equivalent or less. Is preferable. The concentration of silica contained in the water to be treated is preferably 10 mg / L or more and 200 mg / L or less. According to the present invention, the aluminum concentration can be made less than 0.01 mg / L by treating the water to be treated containing, for example, 0.01 mg / L or more and 0.1 mg / L or less of dissolved aluminum.

According to the present invention, the concentration of aluminum in the water to be treated containing silica and aluminum can be reliably reduced without the need for chemical regeneration of the ion exchange resin.

It is a figure which shows the structure of the water treatment system which includes the aluminum removal apparatus of one Embodiment of this invention. It is a figure which shows the structure of the apparatus used in an Example.

Next, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a water treatment system in which an aluminum removing device according to an embodiment of the present invention is arranged in front of a membrane filtration device.

First, the membrane filtration device 10 in the water treatment system shown in FIG. 1 will be described. The membrane filtration device 10 removes impurities contained in the supply water, and includes a filtration unit 11 that separates the supply water into concentrated water containing impurities and permeated water from which impurities have been removed. The filtration unit 11 includes a reverse osmosis membrane (RO membrane) or a nanofiltration membrane (NF membrane). If the membrane provided in the filtration unit 11 is an RO membrane, the membrane filtration device 10 is a reverse osmosis membrane device, and if it is an NF membrane, it is a loose reverse osmosis membrane device. Further, the membrane filtration device 10 is provided with a mechanism for keeping the amount of permeated water constant.

The membrane filtration device 10 includes a plurality of lines connected to the filtration unit 11, that is, a supply line 1 for supplying supply water to the filtration unit 11, a permeation water line 2 for circulating the permeated water from the filtration unit 11. It has a concentrated water line 3 for circulating concentrated water from the filtration unit 11. In addition, the membrane filtration device 10 rings two lines branched from the concentrated water line 3, that is, a drainage line 4 that discharges a part of the concentrated water flowing through the concentrated water line 3 to the outside as drainage, and the rest of the concentrated water. It has a reflux water line 5 that is returned to the supply line 1 as running water. The recirculated water line 5 is connected to the supply line 1 on the upstream side of the pressurizing pump 21, which will be described later, after branching from the concentrated water line 3. Here, the reason why a part of the concentrated water is merged with the supply water as recirculation water is to improve the ratio of the portion obtained as the permeated water in the supply water, that is, the recovery rate, and to save water. On average over a rather long period of time, the recovery rate is consistent with the ratio of the permeated water flow rate to the sum of the permeated water flow rate and the drainage flow rate.

In the filtration unit 11, when the water temperature changes and the viscosity of the supply water changes while the water supply pressure is constant, the flow rate of the permeated water changes. Therefore, the membrane filtration device 10 has a first flow meter 12 that detects the flow rate of the permeated water flowing through the permeated water line 2 and a first that adjusts the permeated water flow rate to a set flow rate in order to keep the permeated water flow rate constant. It has a control mechanism 20. The first control mechanism 20 is provided in the supply line 1 and pressurizes based on the pressure pump 21 for adjusting the pressure of the supply water flowing through the supply line 1 and the permeated water detected flow rate by the first flow meter 12. It has a first flow rate control unit 22 that controls the pump 21. When the permeated water flow rate is controlled to be constant in this way, the concentrated water flow rate also changes. In order to avoid fluctuations in the flow rate of concentrated water, the concentrated water line 3 is provided with a constant flow rate valve 13.

Further, the membrane filtration device 10 adjusts a second flow meter 14 for detecting the flow rate of concentrated water flowing through the drainage line 4, that is, the flow rate of the wastewater, and a set flow rate of the drainage in order to control the flow rate or the recovery rate of the wastewater. It has a second control mechanism 30. The second control mechanism 30 adjusts the opening degree of the flow rate adjusting valve 31 based on the flow rate adjusting valve 31 provided in the drainage line 4 and the flow rate detected by the second flow meter 14. It has a part 32 and the like. The flow rate control of the drainage by the second control mechanism 30 is executed independently of the flow rate control of the permeated water by the first control mechanism. However, in order to suppress the generation of scale in the apparatus, it is preferable that the set flow rate of the drainage is set based on the permeated water flow rate measured by the first flow meter 12. Further, in order to adjust the pressure balance of the concentrated water flowing through the drainage line 4 and the recirculation water line 5, the recirculation line 5 is provided with a pressure adjusting valve 15.

In the membrane filtration device 10 shown in FIG. 1, in order to improve the recovery rate and realize water saving, a part of the concentrated water from the filtration unit 11 is mixed with the supplied water as circulating water and supplied to the filtration unit 11 again. There is. Since aluminum and silica do not easily pass through the filtration unit 11, the concentration of aluminum in the concentrated water, the reflux water, and the water circulating in the filtration unit 11 as supply water increases while the membrane filtration device 10 continues to operate. As a result, as described in the background technology section of the present specification, the compound containing silica and aluminum will be deposited on the surface of the RO membrane or the NF membrane. In order to prevent this precipitation, it is necessary to make the concentration of the soluble aluminum in the water supplied to the membrane filtration device 10 smaller than, for example, 0.01 mg / L. Therefore, in the water treatment system shown in FIG. 1, an aluminum removing device based on the present invention is provided in front of the membrane filtration device 10.

The aluminum removing device is composed of an ion exchange device 60 including an ion exchange resin layer 61 containing at least an anion exchange resin. A raw water tank 50 for temporarily storing raw water such as city water is provided, and the raw water in the raw water tank 50 is used as treated water in the aluminum removing device through an ion exchange device via a raw water pump 51 and a raw water supply valve 52. It is designed to be supplied to 60. The raw water contains silica at a concentration of, for example, about several tens of mg / L. The water from which aluminum has been removed by the ion exchange device 60 is supplied to the supply line 1 of the membrane filtration device 10 via the outlet valve 62 as water to be supplied to the membrane filtration device 10. The raw water, which is the water to be treated, flows from above to below in the ion exchange device 60. Further, in order to backwash the ion exchange resin layer 61 in the ion exchange device 60, a backwash pump 71 is connected to the bottom of the ion exchange device 60 via a backwash valve 72. The backwash pump 71 supplies the cleaning liquid used for backwashing to the ion exchange device 60. A discharge valve 73 is provided on the upper part of the ion exchange device 60 in order to discharge the backwash drainage generated during the backwash to the outside of the ion exchange device 60. As the cleaning liquid, pure water may be used, water to be treated (that is, raw water) may be used, or water treated by the aluminum removing device 60 may be used.

When the permeated water is generated by the membrane filtration device 10, the raw water supply valve 52 and the outlet valve 62 are opened, the check valve 72 and the discharge valve 73 are closed, and the raw water is ionized from the raw water pump 51 as the water to be treated in the aluminum removal device. It is supplied to the switching device 60. As a result, as described above, suspended solids containing silica and aluminum are generated and accumulated in the ion exchange resin layer 61, and water from which aluminum has been removed is discharged from the ion exchange device 60. The water from which the aluminum has been removed is supplied to the membrane filtration device 10 as supply water via the outlet valve 62.

As the supply of water supplied to the membrane filtration device 10 is continued, the accumulation of suspended solids in the ion exchange resin layer 61 progresses. When the amount of aluminum estimated to be trapped in the ion exchange resin layer 61 reaches a certain value, or when the water flow differential pressure of the ion exchange device 60 rises and reaches a certain value, the membrane filtration device 10 is operated. The raw water pump 51 is stopped, and the supply of raw water to the ion exchange device 60 is stopped. Further, the raw water supply valve 52 and the outlet valve 62 are closed. Although it depends on the quality of the raw water, at this point, the amount of water flowing through the ion exchange resin layer 61 usually greatly exceeds the amount corresponding to the ion exchange capacity of the ion exchange resin layer 61.

Next, the backwash valve 72 and the discharge valve 73 are opened, the backwash pump 71 is started, pure water is supplied from the bottom of the ion exchange device 60 into the ion exchange device 60, and the reverse of the ion exchange resin layer 61 is performed. Wash. By performing the backwash, the suspended solids previously accumulated in the ion exchange resin layer 61 are discharged to the outside of the ion exchange device 60 as the backwash drainage. When the backwash is completed, the backwash pump 71 is stopped, and the backwash valve 72 and the discharge valve 73 are closed. After that, by opening the raw water supply valve 52 and the outlet valve 62 again and starting the raw water pump 51, the supply water from which the aluminum has been removed can be supplied to the membrane filtration device 10.

Next, the present invention will be described in more detail by way of examples.

[Example 1]
The device shown in FIG. 2 was assembled. The apparatus shown in FIG. 2 includes a pump 81, an ion exchange resin column 82 filled with an ion exchange resin, and a differential pressure gauge 83 for measuring the differential pressure between the inlet and outlet of the ion exchange resin column 82. There is. The pump 81 supplies city water to the inlet of the ion exchange resin column 82, and the treated water is obtained from the outlet of the ion exchange resin column 82.

H-type strong acid cation exchange resin (trade name "Amberlite (registered trademark) IR120B", manufactured by Dow Chemical Co., Ltd.) 24 mL and Cl-type strong basic anion exchange resin (trade name "Amberlite (registered trademark) IRA-400 Cl" An ion exchange resin column 82 was formed by filling a resin column (inner diameter 19 mm, length 500 mm) with 118 mL (manufactured by Dow Chemical Co., Ltd.) to form a mixed bed. City A tap water (pH 7.4, electrical conductivity 250 μS / cm) having a dissolved aluminum concentration of 0.03 mg / L and a silica concentration of 42 mgSiO _{2 / L was flown to the exchange resin column 82 at a flow rate of 2.1 L / h.} This water flow was carried out until the integrated value of the aluminum supplied to the ion exchange resin column 82 became 3.5 g / L-R. This water flow condition was that of the resin per hour. Passing 15 times the volume of water to be treated, that is ^{, corresponding to SV = 15h -1} , the total anion concentration of city A tap water is 85 mgCaCO ₃ / L equivalent, and the total cation concentration is 85 mgCaCO. _{It was 3} / L equivalent.

The concentration of dissolved aluminum in the treated water flowing out from the ion exchange resin column 82 was investigated. ICP (inductively coupled plasma) emission spectroscopy was used to measure the concentration of dissolved aluminum. Further, the water flow differential pressure in the ion exchange resin column 82 was measured by the differential pressure gauge 83. Table 1 shows the transition of the dissolved aluminum concentration (Al concentration) and the water flow differential pressure in the treated water. The water flow differential pressure immediately after the start of water flow was 0.010 MPa. In Table 1, the amount of water to be treated is shown by the integrated amount of aluminum that has passed (that is, the amount of Al water flow).

In the usual method of using an ion exchange resin, the ion exchange resin is regenerated with a chemical before the ions start to leak, and the ion form is changed to H type (in the case of cation exchange resin) and OH type (in the case of anion exchange resin). Use repeatedly. When calculated from the total anion concentration and total cation concentration of the city A tap water used in this example, among the ion exchange resins of the mixed bed used, the cation exchange resin has a water flow rate of around 0.2 gAl / L-R. When it reaches, the cation exceeding the ion exchange capacity is supplied, and for the anion exchange resin, when the water flow reaches around 0.6 gAl / L-R, the cation exceeding the ion exchange capacity is supplied. .. In reality, ions gradually begin to leak before reaching these water volumes. When the ion exchange capacity is reached, the ion concentrations at the inlet and outlet of the resin layer become equal. In the vicinity of the time when the ion exchange capacity was reached, the aluminum concentration in the treated water from the outlet of the ion exchange resin column 82 was almost the same as the concentration at the inlet, and the water flow differential pressure did not change from the value immediately after the start of water flow. rice field. In this embodiment, even after ions are supplied in excess of the ion exchange capacity of the ion exchange resin and the ion exchange resin loses its ion exchange ability, water flow continues, so that the water flow differential pressure gradually increases. The aluminum concentration in the treated water was less than 0.01 mg / L. This indicates that a precipitate containing aluminum and silica is formed in the ion exchange resin layer, and the aluminum is further adsorbed on the suspended solid to remove the aluminum. That is, according to the present invention, if the increase in the water flow differential pressure is within a predetermined range, the water to be treated exceeds the ion exchange capacity, and the ion exchange resin is converted into a salt form having almost the same composition as the raw water. It was later found that aluminum could be removed.

When the pH of the water to be treated is about 7, the use of a mixed bed ion exchange resin can reduce the amount of soluble aluminum, which is, for example, 0.04 mg / L, to less than 0.01 mg / L.

[Example 2]
An apparatus was assembled which was the same as the first embodiment but had a different configuration of the ion exchange resin column 82. A Cl-type strong basic anion exchange resin (trade name "Amberlite (registered trademark) IRA-400 Cl", manufactured by Dow Chemical Co., Ltd.) is filled in a resin column (inner diameter 19 mm, length 1000 mm) with water. The ion exchange resin column 82 was treated with sodium oxide to change the ion form of the anion exchange resin to the OH type. That is, in Example 2, a single-bed anion exchange resin was used as the ion exchange resin layer. Then, the same city A tap water as in Example 1 was passed as treated water under the condition of a flow rate of 2.0 L / h. This water flow condition ^{corresponds to SV = 20h -1} . Same as Example 1. The dissolved aluminum concentration in the treated water flowing out from the ion exchange resin column 82 and the water flow differential pressure in the ion exchange resin column 82 were investigated. The results are shown in Table 2. In Table 2, the column of "water flow rate" is , The amount of water flow based on the volume of the ion exchange resin.

In Example 2, when water was passed until the Al water flow rate reached 3.5 g / L-R, the water flow differential pressure increased about 3 times as compared with the initial water flow rate, and aluminum leak was observed. Therefore, when the Al water flow rate reaches 3 g / L-R, the water flow is stopped, and instead, the cleaning liquid is flowed upward from the lower part of the ion exchange resin layer in the ion exchange resin column 82 to exchange ions. The resin layer was washed. This wash removed turbidity containing aluminum and silica. Treated water was used as the cleaning liquid. When the washing wastewater was allowed to stand, the turbidity settled, so the supernatant was returned to the water to be treated. The washing was performed at a flow rate of 10 m / h. The flow velocity may be any speed as long as the turbidity can be discharged without the ion exchange resin being washed away. Further, the frequency of cleaning can be arbitrarily set as long as the water flow differential pressure is equal to or less than the allowable water flow differential pressure of the device and does not exceed 3 times the initial differential pressure. ..

After this washing, the water to be treated was flown through the ion exchange resin column 82 again, and the water flow differential pressure and the aluminum concentration at the time when the Al water flow rate became 0.5 gAl / L-R were examined. This result is also shown in Table 2. The amount of water flowed in Table 2 is the sum of the amount of water flowed before and after cleaning.

From Table 2, it can be seen that the differential pressure of water flow is restored by cleaning, and that aluminum can be reliably removed even with the total amount of water flow where aluminum leaks can be seen if cleaning is not performed. .. That is, it can be seen that by repeating the water passing step and the washing step, aluminum can be permanently removed from the water to be treated containing silica without regenerating the ion exchange resin with a chemical.

10 Filtration device 11 Filtration unit 50 Raw water tank 51 Raw water pump 60 Ion exchange device 61 Ion exchange resin layer 71 Backwash pump 72 Backwash valve 82 Ion exchange resin column 83 Differential pressure gauge

Claims (8)

A method of removing aluminum from water to be treated containing silica and aluminum.
It has a water passing step of passing the water to be treated through an ion exchange resin layer containing at least an anion exchange resin to obtain water having reduced aluminum.
A method for passing water to be treated in excess of the ion exchange capacity of the anion exchange resin in the water flow step. After the water passage step, a cleaning step of cleaning the ion exchange resin layer is further provided.
The method according to claim 1, wherein the water flow step and the cleaning step are repeated. The method according to claim 2, wherein in the washing step, the ion exchange resin layer is washed by backwashing, and suspended solids accumulated in the ion exchange resin layer are removed in the water passing step. The method according to claim 2 or 3, wherein the water flow step and the cleaning step are repeated without regenerating the chemicals of the ion exchange resin layer. In the water flow step, when the amount of aluminum trapped in the ion exchange resin layer exceeds the first threshold value, and the water flow differential pressure to the ion exchange resin layer exceeds the second threshold value. The method according to any one of claims 1 to 4, wherein the water flow step is terminated in at least one of the cases. An aluminum removing device that removes aluminum from water to be treated containing silica and aluminum.
An ion exchange device provided with an ion exchange resin layer containing at least an anion exchange resin and through which the water to be treated is passed to discharge water with reduced aluminum.
When connected to the ion exchange device and the water to be treated exceeds the ion exchange capacity of the anion exchange resin and is passed through the ion exchange resin layer, the ion exchange resin layer is washed with a cleaning liquid to obtain the above. A cleaning mechanism that removes suspended substances formed in the ion exchange resin layer by passing water to be treated through the ion exchange resin layer, and a cleaning mechanism.
The Bei Elua aluminum removal device. The aluminum removing device according to claim 6, wherein the cleaning mechanism cleans the ion exchange resin layer by backwashing. A differential pressure gauge for measuring the water flow differential pressure of the ion exchange device through which the water to be treated is passed is provided, and when the measured value by the differential pressure gauge exceeds a predetermined value, the subject to the ion exchange device is covered. the cleaning mechanism passing water treated water is completed to start the washing of the ion exchange resin layer, an aluminum removal apparatus according to claim 6 or 7.

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