WO2000003952A1

WO2000003952A1 - Method for treating a fluorine-containing waste water and treating apparatus

Info

Publication number: WO2000003952A1
Application number: PCT/JP1999/003789
Authority: WO
Inventors: Arata Toyoda
Original assignee: Nec Corporation
Priority date: 1998-07-17
Filing date: 1999-07-14
Publication date: 2000-01-27
Also published as: KR20010071946A; CN1311759A; GB0101249D0; GB2354516A

Abstract

A method for treating a fluorine-containing waste water which comprises fixing a fluoride ion as potassium fluoride in a reacting tank (1), sedimenting it by using aluminum hydroxide as a coagulant aid in a sedimentation tank (3), withdrawing a part of a sediment slurry comprising potassium fluoride and aluminum hydroxide to return it to an aluminum regenerating tank (4), reacting the fluorine adsorbed on aluminum hydroxide particles with a solution containing a high concentration of calcium at a pH of 9 or lower in the aluminum regenerating tank (4), to fix the fluorine as potassium fluoride, and returning it to the reactor (1), thereby conducting circulation in a manner such that aluminum hydroxide, which has adsorptive ability for fluorine, is present at a high concentration in the whole system.

Description

Method and apparatus for treating fluorine-containing wastewater

TECHNICAL FIELD The present invention relates to a method for treating fluorine-containing wastewater, and particularly to a method for treating fluorine-containing wastewater in which most of the fluorine in the wastewater is fixed as calcium fluoride and residual fluorine is adsorbed on aluminum hydroxide. It relates to a method for reducing the amount of equipment investment and chemicals, and the amount of sludge generated during treatment. The present invention also relates to a fluorine-containing wastewater treatment apparatus suitable for the treatment method. Background art

Fluorine is a useful substance that is used in large quantities in various industrial fields, such as the chemical industry and semiconductor manufacturing, but is harmful to the human body and the environment. The Pollution Control Law limits the concentration to 15 mg / 1 or less. Also, many Japanese municipalities have stricter additional standards of less than 1 Omg / l or less than 5 mg / l, and in some cases the strictest regulatory value is less than 0.8 mg / l.

In general, the basic method of removing fluorine in wastewater is to add a calcium salt to the wastewater in the primary treatment tank 10 as shown in Fig. 6 to generate sparingly soluble calcium fluoride. . Since the generated calcium fluoride particles are very fine and easily dispersed in the liquid, about 0.1 times the aluminum salt is dissolved in the molar concentration of the generated calcium fluoride, and the water generated by neutralization is dissolved. Calcium fluoride is coagulated in the first coagulation tank 11 using aluminum oxide as a coagulation aid, and then sedimented and separated in the first settling tank 12. At this stage, most of the fluorine in the wastewater can be removed. ^ In general, the fluorine concentration in this method depends on the inhibition of the calcium fluoride production reaction by the contaminants contained in the wastewater and the solubility of calcium fluoride itself. Processing up to about 2 Omg / 1 You.

Therefore, in order to achieve the environmental standards, further advanced treatment is carried out, and a large amount of aluminum salt is dissolved in the advanced treatment tank 13 and the aluminum hydroxide produced by neutralization is allowed to adsorb fluorine in wastewater, In general, the aluminum hydroxide is coagulated in the second coagulation tank 14 and then settled and separated in the second settling tank 15.

However, this method has a problem that a large amount of aluminum hydroxide adsorbing calcium fluoride and fluorine is generated as sludge. In particular, the amount of fluorine-adsorbed aluminum hydroxide generated during advanced treatment is enormous. Against for example the full Uz of calcium that occur when processing waste water 1 0 m ³ fluorine concentration 2 1 0 mg / 1 up to 2 0 mg / 1 is about ◦. 3 9 kg (about 5 moles) , in order to process the waste water 1 0 m ³ of fluorine concentration 2 0 mg / 1 to 5 mg / 1, the Aruminiumu hydroxide takes about Al (OH) ₃ and to at least 2 kg (2 5. 6 mol) . Actually, aluminum hydroxide is gel-like and difficult to dehydrate. Even if the water content is reduced to 70%, its water content is about 5 kg, which is disposed of as sludge.

This method also has the problem of requiring two settling tanks that require a large site area. For example, as shown in Fig. 7, a calcium salt is added to a fluorine-containing wastewater in a reaction tank 16 to generate calcium fluoride, and at the same time, a large amount of aluminum salt is dissolved and neutralized to form an aluminum hydroxide. It is possible to use only one sedimentation tank by using as a flocculation aid for the precipitation and separation of calcium fluoride and to use it for the adsorption treatment of fluorine, but in that case, the adsorption site for aluminum hydroxide Is occupied by calcium fluoride, and in order to obtain sufficient fluoridation properties, a large excess of aluminum, several tens of times the molar concentration of the generated calcium fluoride, is required, and the amount of sludge increases accordingly. Would. This is why the fluorine treatment is generally divided into two stages as described above, and two huge sedimentation tanks are used. However, the drainage standard is 15 If it is not severe at about mg / 1, aluminum hydroxide does not need to be used in a large amount, so even a single-step treatment can be achieved if it is practical. In particular, when the amount of contaminants in the wastewater is small, it is possible to meet the wastewater standards by using aluminum hydroxide that is slightly larger than the required amount as a coagulation aid.

On the other hand, Japanese Patent Application Laid-Open Publication No. Hei 6-15464767 discloses that fluorine in wastewater is treated to a sufficiently low concentration without increasing the amount of aluminum salt used and the amount of sludge generated in a single-stage treatment. For this purpose, a technique has been disclosed. In this technology, as shown in Fig. 8, calcium salt and aluminum salt are added to a fluorine-containing wastewater in a reaction tank 19 to neutralize it, and the generated calcium fluoride is treated with aluminum hydroxide as a coagulant aid. After coagulation at 0, the sedimentation is separated in the sedimentation tank 21 and a part of the sediment is returned to the reaction tank and circulated through the sludge, the concentrations of calcium fluoride and aluminum hydroxide are increased, and the It improves the processability of fluorine by the seed crystal effect and the coprecipitation effect of aluminum hydroxide. Since aluminum hydroxide is circulated and used after being concentrated, it is not necessary to add a large excess of aluminum salt. According to the above-mentioned publication, aluminum hydroxide is produced by calcium fluoride. The amount is preferably from 0.11 to 1.1 times, more preferably from 0.22 to 0.46 times the molar concentration of Therefore, this technology makes it possible to treat fluorine in wastewater to a sufficiently low concentration without increasing the amount of sludge by a single-stage treatment without adding a large excess of aluminum salt.

However, although the above-mentioned technology improves the efficiency of calcium fluoride production, it does not provide a sufficient fluorine adsorption effect of aluminum hydroxide used in circulation, so that the final fluorine treatability is ideal. Even under the conditions, there is a problem that the concentration is limited to about 8 mg / 1, which is equivalent to the solubility of calcium fluoride. The reason is that when sludge consisting of calcium fluoride and fluorine-adsorbed aluminum hydroxide is returned to the reaction tank, the fluorine adsorbed on the aluminum hydroxide is also returned at the same time. While the concentration of sludge in the reaction tank increases with the ring, the fluorine concentration also increases, and the adsorption capacity of aluminum hydroxide is completely insufficient to sufficiently reduce the fluorine concentration. That is, even if aluminum hydroxide already adsorbing fluorine is returned, the aluminum hydroxide has a poor ability to adsorb fluorine any more. Although moderate treatment effects can be seen if the circulation is performed twice or more, the fluoride adsorption of aluminum hydroxide reaches saturation only by repeating the circulation several times or more, and thereafter fluorine adsorption by the circulating aluminum hydroxide No effect is obtained.

Therefore, if it is necessary to constantly treat fluorine in wastewater to a concentration lower than 8 mg / 1 for continuously generated fluorine-containing wastewater, a new aluminum salt must be added. It is necessary to increase the amount of addition or to add an advanced treatment again, in which case the amount of sludge naturally increases. Also, if the wastewater standard is about 15 mg / 1 and it is attempted to complete the treatment in one step, it is difficult to control the amount of aluminum hydroxide used, and the amount of aluminum salt added during operation will be much larger than the actual required amount. There is a problem that the amount of sludge must be increased, and the amount of sludge increases accordingly. The reason is that when the amount of fluorine in wastewater is reduced to about 15 mg / 1, the difference between the total amount of aluminum hydroxide actually required and the amount required for the aggregation of calcium fluoride is small. Fluctuations in the amount of aluminum salt added, and of course, the amount of aluminum hydroxide is insufficient when the amount of calcium fluoride generated due to fluctuations in the concentration of fluorine in the wastewater temporarily increases. This is because it is necessary to always use more to avoid the danger of doing so. Disclosure of the invention

An object of the present invention is to overcome the above-mentioned problems and constantly and stably treat fluorine to a sufficiently low concentration in a single-stage treatment of a continuously generated high-concentration fluorine-containing wastewater without requiring advanced treatment. And can be processed An object of the present invention is to provide a method capable of greatly reducing the amount of chemicals used and the amount of sludge generated due to treatment. Another object of the present invention is to provide a method capable of minimizing the amount of generated sludge by effectively controlling the optimal amount of chemicals used in accordance with the target concentration of fluorine. Is to provide.

The first method for treating fluorine-containing wastewater according to the present invention comprises: a first step of causing calcium to act on wastewater containing fluorine ions to fix most of the fluorine in the wastewater as calcium fluoride; A smaller amount of aluminum salt as aluminum than calcium fluoride newly generated in the above step is added to the treatment solution, and the calcium fluoride is coagulated and settled using the formed aluminum hydroxide as a coagulation aid to form a precipitate slurry. And a third step of solid-liquid separating wastewater containing the precipitate slurry, draining the supernatant liquid phase, and discharging the solid precipitate slurry as sludge. A method for treating a fluorine-containing wastewater, wherein a part of the sediment slurry discharged as the sludge is withdrawn, and calcium is acted on at a pH of 9 or less to treat the sediment slurry. After the fluorine adsorbed on the aluminum hydroxide is fixed as calcium fluoride, the treated precipitate slurry is returned to the first step, and the series of steps is performed. By repeating the process, the amount of aluminum hydroxide in the system is maintained at a level at least necessary for agglomeration of calcium fluoride, and the amount contributing to fluorine adsorption is increased.

Further, the second method for treating fluorine-containing wastewater of the present invention comprises: a first step of causing calcium to act on wastewater containing fluorine ions to fix most of the fluorine in the wastewater as calcium fluoride; A smaller amount of aluminum salt as aluminum is added to the treatment liquid as aluminum than calcium fluoride newly generated in the above step, and the calcium fluoride is coagulated and settled using aluminum hydroxide as an agglomeration aid to precipitate sediment slurry. A second step of forming a slurry, and a solid-liquid separation of wastewater containing the sediment slurry, draining the supernatant liquid phase, and converting the solid sediment slurry into sludge. A fluorine-containing wastewater treatment method having a third step of discharging the sludge, wherein a part of the sediment slurry discharged as the sludge is withdrawn, and calcium is acted on at a pH of 9 or less to act on the sediment slurry. After fixing the fluorine adsorbed on the contained aluminum hydroxide as calcium fluoride, the treated precipitate slurry is returned to the first step, and the series of steps is repeated. As a result, the amount of aluminum hydroxide in the system is maintained at a level at least necessary for the aggregation of calcium fluoride, but the increase in aluminum hydroxide contributing to fluorine adsorption is controlled by controlling the amount of aluminum salt added. This is a method for treating fluorine-containing wastewater.

Further, in the third treatment method of the present invention, calcium is allowed to act on a fluorine-containing wastewater containing phosphoric acid under a weak alkaline condition to fix fluoride ions and phosphoric acid as calcium fluoride and calcium phosphate. In the first step, the treatment liquid is adjusted to be weakly acidic to neutral, and the amount of aluminum is smaller than the total amount of calcium fluoride and calcium phosphate newly produced in the above step as aluminum. A second step of coagulating and sedimenting the calcium fluoride and calcium phosphate to form a precipitate slurry by using aluminum hydroxide formed by adding a salt as a coagulation aid, and solid-liquid wastewater containing the precipitate slurry A method for treating fluorine-containing wastewater comprising a third step of separating, draining a supernatant liquid phase, and discharging a solid-phase sediment slurry as sludge,

A part of the sediment slurry discharged as the sludge is withdrawn, and calcium is acted on at a pH of 9 or less to remove fluorine adsorbed on the aluminum hydroxide contained in the sediment slurry. After being fixed as calcium iodide, the treated precipitate slurry is returned to the first step, and the series of steps is repeated.

The present invention also provides a reaction tank in which calcium acts on wastewater containing fluorine ions to fix most of the fluorine in the wastewater as calcium fluoride, and aluminum hydroxide formed by adding an aluminum salt. To A fluorine-containing wastewater treatment apparatus having a flocculation tank for flocculating and precipitating the calcium fluoride as a flocculation aid, and a sedimentation tank for solid-liquid separation of the obtained precipitate slurry; Alternatively, the method is applied to the second treatment method, in which a calcium salt is added under a condition of pH 9 or less to remove fluorine adsorbed on aluminum hydroxide contained in the precipitate slurry. Means for regenerating aluminum hydroxide by fixing it as a catalyst for regenerating aluminum hydroxide, extracting a part of the precipitate slurry solid-liquid separated in the sedimentation tank, and returning it to the aluminum regeneration tank; A treatment apparatus comprising means for returning aluminum hydroxide and calcium fluoride regenerated in the regenerating tank to the reaction tank, or a fluorine-containing wastewater containing phosphoric acid A first reaction tank for fixing calcium ions and calcium phosphate as calcium fluoride and calcium phosphate by reacting calcium under weak alkaline conditions; A second reaction tank that is adjusted to neutral and adds aluminum salt to produce aluminum hydroxide; and the calcium fluoride and calcium phosphate are used as a coagulation aid using the produced aluminum hydroxide. A fluorine-containing wastewater treatment apparatus having a coagulation tank for forming a sediment slurry by coagulation and sedimentation, and a sedimentation tank for solid-liquid separation of the obtained sediment slurry, wherein the treatment apparatus is the third treatment method described above. A calcium salt is added under the condition of pH 9 or less, and the fluorine adsorbed on the aluminum hydroxide contained in the precipitate slurry is fixed as calcium fluoride. An aluminum regeneration tank for regenerating the aluminum hydroxide by means of: recovering a part of the precipitate slurry solid-liquid separated in the sedimentation tank and returning the slurry to the aluminum regeneration tank; And a means for returning the aluminum hydroxide and calcium fluoride to the first reaction tank. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a system configuration diagram of the first embodiment of the present invention. FIG. 2 is a graph schematically showing the constitution of each component present in the system in order to explain the operation of the present invention.

FIG. 3 is a system configuration diagram of the second embodiment of the present invention.

FIG. 4 is a system configuration diagram of the third embodiment of the present invention.

FIG. 5 is a graph schematically showing the configuration of each component present in the system in order to explain the operation of the fourth embodiment of the present invention.

Fig. 6 is a system configuration diagram of a general fluorine-containing wastewater treatment technology. Fig. 7 is a system configuration diagram when a general fluorine-containing wastewater treatment technology is simplified.

FIG. 8 is a system configuration diagram of a conventional technology for solving the problems of a general fluorine-containing wastewater treatment technology. BEST MODE FOR CARRYING OUT THE INVENTION In the first treatment method of the present invention, the extracted sediment slurry always contains fluorine adsorbed on aluminum hydroxide contained in the sediment slurry. Aluminum hydroxide is circulated at high concentration in the system because it is fixed as calcium fluoride by the action of calcium and then returned to the reaction tank. The concentration of fluorine in water can be reduced to a level significantly lower than the value corresponding to the solubility of calcium fluoride. Also, in this method, the main purpose is fixation by the formation of calcium fluoride, so that the newly added aluminum salt is necessary for coagulating the newly generated calcium fluoride in the reaction tank. The amount is sufficient, and the amount of sludge generated as a result can be minimized.

Further, in the second treatment method of the present invention, the width of the aluminum hydroxide to be reduced can be sufficiently widened, and the amount of aluminum hydroxide can be controlled within this range. Operational control becomes extremely easy, and at the same time, the reduced amount of aluminum hydroxide can be used directly as the amount of sludge reduction. Temporary fluctuations in the concentration of fluorine in wastewater and aluminum Even if the amount of salt added fluctuates slightly, the slurry is returned after a sufficient amount has accumulated in the settling tank, so the composition ratio of the slurry always converges to an average value, There is almost no effect on the control of the amount of aluminum oxide.

Next, an embodiment of the first processing method of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing a configuration example according to the first exemplary embodiment of the present invention. The flow of the treatment system is as follows: First, in the reaction tank 1 maintained at neutral pH, calcium ions act on the continuously flowing high-concentration fluorine-containing wastewater to remove fluorine ions in the wastewater. While fixing as calcium fluoride, an aluminum salt is added and neutralized to form aluminum hydroxide, which is used as a flocculant for calcium fluoride. Subsequently, a coagulant is added in the coagulation tank 2 to coagulate the solid components, and the sedimentation tank 3 performs solid-liquid separation as a precipitate. In the sedimentation tank 3, this sediment is sufficiently accumulated in advance.

After that, a part of the sediment is extracted, a part of the extracted sediment slurry is discharged out of the system as sludge, and the remainder is reacted through an aluminum regeneration tank 4 maintained at pH 3 to 9. Return to tank 1. In addition, a calcium salt is added to the aluminum regeneration tank 4. The calcium salt added here flows into the reaction tank 1 and acts on fluorine in the wastewater to generate calcium fluoride. Further, an aluminum salt is newly added to the reaction tank 1. By repeating the above cycle, the precipitate consisting of calcium fluoride and aluminum hydroxide is circulated in the system.

Here, the amount of calcium salt to be added to the aluminum regeneration tank 4 is such that the calcium concentration when flowing into the reaction tank 1 is equal to or more than the chemical equivalent for generating calcium fluoride from fluorine in the wastewater, and is preferably twice. Set so that it is at least equivalent. The amount of the aluminum salt to be added to the reaction tank 1 is the minimum amount required for the aluminum hydroxide generated in the coagulation tank to function as a coagulation aid for calcium fluoride. As an amount of nickel, an amount smaller than the amount of newly generated calcium fluoride is added every cycle. Preferably, the amount of aluminum is set in the range of 1 to 30% as aluminum based on the amount of newly generated calcium fluoride. Set the amount of sediment slurry discharged so that the amount of calcium fluoride newly generated in each cycle is equal to the amount of calcium fluoride contained in the sediment discharged as sludge. Further, the amount of aluminum salt added is set so that the amount of aluminum salt added and the amount of aluminum hydroxide contained in the sediment discharged as sludge are equal to aluminum.

In addition, the inflow of fluorine-containing wastewater and the return and discharge of calcium fluoride and aluminum hydroxide contained in the sediment slurry should be set to always be constant. However, the inflow of fluorine-containing wastewater> the return of sediment slurry.

In this way, by setting the inflow of fluorine-containing wastewater and the return and discharge of sediment slurry, the balance of the mass balance in the system is maintained, and the circulation of sediment slurry is repeated. However, the solid-liquid interface level of the settling tank 3 can always be kept constant.

In addition, as a method of maintaining the balance of the material balance, the sedimentation was set in order to set the discharge amount of sediment slurry, while keeping the inflow of fluorine-containing wastewater and the return amount of sediment slurry constant. Focusing on the solid-liquid interface level in Vessel 3, and adjusting the discharge amount of the sediment slurry so that the solid-liquid interface is always kept within a predetermined range when the circulation of the sediment slurry is repeated, can be broached. It is. That is, means for monitoring the solid-liquid interface level, for example, a normal level sensor, and a mechanism for controlling the removal of the sediment slurry so that the solid-liquid interface level is within a predetermined range, for example, a pump (not shown) It becomes possible by linking a valve and the like.

The capacity of each tank is not particularly limited, and can be appropriately adjusted according to the design.For example, the aluminum regeneration tank 4 is 1/10 or less of the reaction tank 1, and the sedimentation tank 3 is the reaction tank. Can be more than 5 times 1 Wear. Further, the coagulation tank 2 can be set to 1 of the reaction tank 1. The amount of sediment previously accumulated in sedimentation tank 3 shall be 10 times or more the amount of sediment newly generated in each cycle.

Next, the operation of the processing system of FIG. 1 will be described with reference to the drawings. In the reaction tank 1, most of the fluorine ions in the wastewater are fixed as calcium fluoride. Further, since the reaction tank 1 is kept neutral, the dissolved aluminum salt is neutralized to produce aluminum hydroxide. Since this acts as a coagulation aid for calcium fluoride, it is possible to easily coagulate calcium fluoride particles dispersed in the liquid.

Here, the amount of addition of the aluminum salt to the amount of calcium fluoride to be generated is only such that the effect of aluminum hydroxide as a coagulation aid of calcium fluoride can be sufficiently obtained as described above. In the case of performing the above, it is not possible to expect the treatment effect by the fluorine adsorption action of aluminum hydroxide. This is because the amount of fluorine absorbed is small because the amount of aluminum is small, and the effect of lowering the fluorine concentration is hardly obtained. Therefore, in a transient treatment, the concentration of fluorine in the treated water cannot be reduced to a value much less than about 8 mg / 1, which is equivalent to the solubility of calcium fluoride, even under ideal conditions. 0 mg / 1 is the limit. However, in the treatment system using precipitate circulation shown in Fig. 1, the concentration of calcium fluoride and aluminum hydroxide in reaction tank 1 is increased by circulating the precipitate consisting of calcium fluoride and aluminum hydroxide in the system. Can be. Here, fluorine is adsorbed on the aluminum hydroxide in the sediment stored in the settling tank 3, and the amount of fluorine is not absolutely large as described above, but the amount of fluorine adsorbed per aluminum From the viewpoint of this, it is close to the saturated adsorption amount. Therefore, this precipitate slurry is also in a state where fluorine is concentrated together with calcium fluoride and aluminum hydroxide. The fluorine adsorbed on the system is fixed here as calcium fluoride. The aluminum hydroxide returned to the reaction tank 1 can contribute to fluorine adsorption. As described above, the concentration of aluminum hydroxide in the reaction tank 1 increases due to the circulation of the sediment slurry, while the amount of fluorine to be treated is constant. Can be sufficiently reduced.

Fig. 2 shows that the amount of aluminum hydroxide that can contribute to fluorine adsorption increases when the treatment is performed while circulating a precipitate slurry consisting of calcium fluoride and aluminum hydroxide, while the treatment is performed transiently. Fig. 4 is a graph schematically showing the operation. Here, in one cycle of the slurry circulation, the amount of newly generated calcium fluoride and newly added aluminum (as aluminum salt), and the amount of calcium fluoride and aluminum (hydroxylated) contained in the discharged sludge (As aluminum) is always the same, even if the concentration of calcium fluoride and aluminum hydroxide in reaction tank 1 is high, the ratio itself is always constant, and the slurry is cycled again. However, the solid-liquid interface of the settling tank 3 does not change. If the inflow of fluorine-containing wastewater and the return and discharge of sediment slurry are always constant, the concentrations of calcium fluoride and aluminum hydroxide in the reaction tank 1 equilibrate at a constant value, and The value can be set freely by manipulating each of the above quantities.

In addition, the pH of the aluminum regeneration tank 4 is such that, in the case of strong alkalinity, aluminum hydroxide dissolves as aluminate ions and reacts with calcium ions to form stable calcium aluminate. It is important to keep the pH at 9 or less because regeneration as a fluorine adsorbent becomes impossible. Further, since the fluorine adsorption property of aluminum hydroxide is strongly pH-dependent, it is preferable to keep the pH of the reaction tank 1 in the range of 6 to 7 for efficient treatment.

As described above, in this embodiment, in addition to the system including the reaction tank, the coagulation tank, and the sedimentation tank, which corresponds to the primary treatment of the general fluorine-containing wastewater treatment system using the two-stage treatment, Much smaller than With a minimal system configuration that simply adds a luminium regeneration tank (for example, a capacity of 1/10 to 1/40 of the reaction tank), it can treat fluorine in wastewater to a sufficiently low concentration without requiring any advanced treatment. It is possible.

Note that the above description may be appropriately changed in the second and third processing methods of the present invention in accordance with the requirements of the configuration.

Example 1

One embodiment of the first processing method of the present invention will be described with reference to the processing flow of FIG.

Capacity of each tank in this embodiment, the reaction vessel 1 is 30 m ^3, flocculation tank 2 1 5 m ^3, sedimentation tank 3 is 300 m ^3, aluminum regeneration tank 4 is 2 m ^3. The fluorine-containing wastewater to be treated is introduced into the reaction tank 1 at an average fluorine concentration of 200 mg / l and a pH of 5 at an inflow of 1 m ³ / min.

First, slaked lime was added so that the calcium concentration in the reaction tank 1 became 500 mg / 1, and aluminum sulfate was further added so that the aluminum concentration became 20 mg / l. Further, the pH was adjusted with sulfuric acid so that the pH of the reaction tank 1 was always in the range of 6 to 7. In coagulation tank 2, a polyacrylamide-based polymer coagulant was added as a coagulant to coagulate calcium fluoride and aluminum hydroxide generated in reaction tank 1. The mixture of aggregated calcium fluoride and aluminum hydroxide was precipitated in settling tank 3. This operation was continued, and 100 m ³ of the precipitate was accumulated in the settling tank 3. The concentration of fluorine in the supernatant of sedimentation tank 3 was 18 mg / 1.

Then, the slurries of the precipitate from the sedimentation tank 3 withdrawal at a flow rate of ^{0. 2 1 5 6 m 3 /} min, the reaction vessel through the aluminum regeneration tank 4 a part at a flow rate of 0. 2m ³ / mi n The waste was returned to 1 and the rest was discharged out of the system as sludge. The water content of the sediment slurry was 97%. Slaked lime was added to the aluminum regeneration tank 4 so that the calcium concentration was always 3000 mg / 1, and the pH was adjusted with sulfuric acid so that the pH of the aluminum regeneration tank 4 was in the range of 8-9. Aluminum concentration in reaction tank 1 Was added so that the concentration became 2 Omg / 1. The pH was adjusted with sulfuric acid or sodium hydroxide so that the pH of the reaction tank 1 was always in the range of 6 to 7. The above operation was defined as one cycle, and the precipitate slurry was circulated in the system.

As the circulation of the sediment slurry was repeated, the concentrations of calcium fluoride and aluminum hydroxide in the reaction vessel 1 increased sharply at first, but gradually decreased and reached an equilibrium state. At this time, the concentration of calcium fluoride was 4535.lmg / l, and the concentration of aluminum hydroxide was 276.7mg / l as aluminum. This aluminum concentration includes 20 mg / 1 minute of aluminum that is newly added every cycle, but a considerable portion is considered to be in a state that can contribute to fluorine adsorption, and The fluorine concentration could be constantly reduced to 5 mgZ1.

Note that the precipitate is discharged from the system as sludge, 5. hydroxide secondary aluminum © beam and calcium fluoride is 453 1: 2 7 6 force will be included in a ratio of 7 ^s, the discharge flow rate There ^{0. 0 1 5 6 m 3 /} min, the precipitate since slurries of water content of 97%, emissions hydroxide § Rumi two © beam and calcium fluoride which it 39 8. 2 m ³ / min, is calculated to be 69. ³ m 3 / min. This value is considered to be almost equal to the newly generated amounts of calcium fluoride and aluminum hydroxide in the reaction tank 1, and the solid-liquid interface in the sedimentation tank 3 did not change even if the treatment cycle was repeated.

Example 2

Next, another embodiment of the first processing method of the present invention will be described with reference to FIG.

Referring to FIG. 3, slaked lime as a calcium salt is added not only to the aluminum regeneration tank 4 but also to the reaction tank 1 for the strongly acidic fluorine-containing wastewater. Here, the total amount of slaked lime was the same as in Example 1, and the amount of slaked lime added to reactor 1 was neutral (pH Adjust the amount to keep 6 to 7), and add the rest to the aluminum regeneration tank 4. For example, if the pH of the fluorine-containing wastewater is 2.5, the other treatment conditions are the same as in the first embodiment, and the calcium concentration in the reaction tank 1 is set to 210 mg / l, Slaked lime is added to the regenerating tank 4 so that the concentration of the potash is 1740 mg / l. In this example, the pH of the strongly acidic fluorine-containing wastewater was adjusted with slaked lime only in reaction tank 1, so that the PH adjustment operation by adding sulfuric acid or sodium hydroxide in reaction tank 1 was unnecessary. There is an advantage that it becomes. In the case of weak alkaline fluorine-containing wastewater, the pH can be similarly adjusted by using an acidic calcium salt, for example, calcium chloride.

Example 3

An embodiment of the third processing method of the present invention will be described with reference to FIG.

Referring to FIG. 4, in the first reaction tank 5 maintained at a pH of 8 to 10 with respect to wastewater containing phosphoric acid together with fluorine, calcium is actuated to remove calcium fluoride and calcium phosphate. After the formation and fixation of fluorine and phosphoric acid in the wastewater, fluorine remaining in the second reaction tank 6 maintained at pH 6 to 7 is subjected to an adsorption treatment with aluminum hydroxide. Here, the aluminum hydroxide also acts as a coagulation aid for sedimenting and separating calcium fluoride and calcium phosphate in the sedimentation tank 8. The amount of newly added aluminum salt is sufficient to coagulate and sediment the calcium fluoride and calcium phosphate newly formed in the reaction tank 1. A small amount is sufficient. Other treatment conditions are the same as in the first embodiment, but when the concentration of phosphoric acid in the wastewater is high, the amount of calcium salt added to the aluminum regeneration tank 9 is increased accordingly.

In this example, there were two reactors, one adjusted to a pH suitable for the production of calcium phosphate, and the other to the aluminum hydroxide generation. Since the pH is adjusted to a value suitable for nitrogen adsorption treatment, wastewater containing fluorine and phosphoric acid can be treated with phosphoric acid along with fluorine. A part of the generated calcium phosphate circulates in the system together with calcium fluoride and aluminum hydroxide.However, calcium phosphate has a strong effect of adsorbing fluorine, so the efficiency of fluorine treatment must be improved. There is an advantage that can be.

Example 4

An embodiment of the second processing method of the present invention will be described with reference to the drawings.

This embodiment corresponds to a case where the target value of the fluorine concentration in the treated water is 13 mg / 1, and the system configuration is the same as that of the first embodiment. However, the amount of aluminum sulfate added to reactor 1 shall be 9 mg / l as aluminum concentration. In the case of treatment based on Example 1, the amount of aluminum hydroxide that can contribute to fluorine adsorption in the reaction tank 1 becomes extremely large, so that the concentration of fluorine in the treated water decreases to 5 mg / 1, but as shown in FIG. As shown in the figure, the amount of aluminum hydroxide can be significantly reduced in order to make the fluorine concentration in the treated water 13 mg / l, and the amount of aluminum sulfate added to the reaction tank 1 was reduced from 2 Omg / 1 as aluminum concentration. By reducing the concentration to 9 mg / l, the concentration of fluorine in the treated water could be reduced to 13 mg / l or less.

When the treatment is carried out by the conventional conventional method, if the amount of aluminum sulfate added to the reaction tank is basically 9 mg / l, the concentration of fluorine in the treated water is 13 mg / 1. However, if for some reason the amount of aluminum sulfate added temporarily drops slightly and drops below 8 mg / l, the cohesiveness of calcium fluoride deteriorates rapidly, the treated water becomes cloudy and the fluorine concentration increases. Also exceeds 15 mg / l. In addition, the fluctuation of the fluorine concentration in the raw wastewater is large, and the same phenomenon occurs when the concentration temporarily exceeds 300 mg / 1.Therefore, the set value of the amount of added aluminum sulfate is 2 Omg / 1 or more with a margin. Must be set to In this embodiment, problems such as a temporary change in the fluorine concentration in the raw wastewater and fluctuations in the calcium fluoride coagulation property and fluoridation property due to fluctuations in the amount of aluminum salt added do not occur. There is an advantage that stable processing can be achieved with the amount of aluminum hydroxide used. Industrial applicability

The first effect of the present invention is to continuously and stably reduce the concentration of fluorine to a sufficiently low level using high-concentration fluorine-containing wastewater by using equipment and chemicals required for conventional primary treatment without requiring advanced treatment. Can be processed. This eliminates the need for equipment and chemicals, including huge sedimentation tanks, required for advanced treatment, and at the same time eliminates the huge sludge generated by advanced treatment.

The reason is that a small amount of aluminum hydroxide, which is used as a coagulation aid for calcium fluoride generated in the primary treatment, is circulated to a high concentration in the system while constantly regenerating, so that calcium fluoride in the system This is because the amount required for the coagulation of the particles is maintained and the portion contributing to fluorine adsorption is increased.

A second effect of the present invention is that the use amount of the pH adjuster can be optimized for a strongly acidic or weakly alkaline fluorine-containing wastewater. For this reason, the use of chemicals such as sulfuric acid and sodium hydroxide used as pH adjusters can be reduced.

The reason is that a part of the strong alkaline slaked lime or the weakly acidic calcium chloride added to generate calcium fluoride can be used for neutralizing the acid or base in the reaction tank.

A third effect of the present invention is that wastewater containing phosphoric acid in addition to fluorine can be sufficiently treated with both fluorine and phosphoric acid, and in particular, fluorine can be treated with high efficiency. Therefore, the amount of aluminum hydroxide used also as a fluorine adsorbent can be reduced.

The reason is that in the system calcium fluoride and aluminum hydroxide

17 At the same time, calcium phosphate, which has strong fluorine adsorption, is circulated at a high concentration.

The fourth effect of the present invention is that when the wastewater standard originally does not require advanced treatment, calcium fluoride due to temporary fluctuations of the fluorine concentration in raw wastewater and fluctuations in the amount of aluminum salt added, etc. A stable treatment can be achieved with a minimum amount of aluminum hydroxide without causing problems such as deterioration of cohesiveness and fluorination property. For this reason, the addition amount of aluminum sulfate, which was conventionally set relatively high in view of safety, is greatly reduced, and the sludge amount can be reduced accordingly. The reason is that by returning the slurry containing aluminum hydroxide, the width of the aluminum hydroxide to be reduced can be made sufficiently large, and the amount of aluminum hydroxide can be controlled within this range, and Since the slurry is returned after a sufficient amount has been accumulated in the settling tank, the composition of the slurry is not affected by temporary fluctuations in the fluorine concentration in the wastewater and slight fluctuations in the amount of A1 salt added. This is because the ratio always converges to an average value, and there is almost no effect on the control of the amount of aluminum hydroxide.

Claims

The scope of the claims '

1. The first step in which calcium acts on wastewater containing fluorine ions to fix most of the fluorine in the wastewater as calcium fluoride. Calcium fluoride newly generated in the above process in the treatment liquid of the above step A second step of adding a smaller amount of aluminum salt as aluminum, coagulating and sedimenting the calcium fluoride using the resulting aluminum hydroxide as a coagulation aid to form a precipitate slurry, and the precipitate slurry. A solid-liquid separation of the wastewater containing the wastewater, draining the supernatant liquid phase, and discharging the solid-phase sediment slurry as sludge.

A part of the sediment slurry discharged as the sludge is withdrawn, calcium is acted on at pH of 9 or less, and the fluorine adsorbed on the aluminum hydroxide contained in the sediment slurry is converted into calcium fluoride. After the fixing, the treated precipitate slurry is returned to the first step, and the series of steps is repeated to reduce the amount of aluminum hydroxide in the system to at least the amount required for the aggregation of calcium fluoride. A method for treating fluorine-containing wastewater, characterized in that the amount of fluorine-containing wastewater is increased while increasing the amount of fluorine-containing wastewater.

2. The inflow of fluorine ions in the wastewater containing fluorine to be treated and the return of calcium fluoride and aluminum hydroxide contained in the sediment slurry are larger than the return 2. The method for treating fluorine-containing wastewater according to claim 1, characterized in that the ratio is a fixed ratio.

3. The amount of calcium fluoride newly generated in the system by the addition of calcium salt, the amount of calcium fluoride contained in the discharged slurry, the amount of newly added aluminum and the amount of precipitated The discharge amount of the precipitate slurry is set so that the amount of aluminum contained in the waste slurry is equal to each other, and the concentration of aluminum hydroxide in the system is controlled by setting the flow rate of each. The method for treating wastewater containing fluorine according to claim 1.

4. The method for treating wastewater containing fluorine according to claim 1, wherein the return amount of the sediment slurry is set to be smaller than the inflow amount of the wastewater containing fluorine to be treated.

5. The method for treating fluorine-containing wastewater according to claim 1, wherein the pH adjustment in the first step is performed only by adding a calcium salt.

6. The first step in which calcium acts on wastewater containing fluorine ions to fix most of the fluorine in the wastewater as calcium fluoride. Calcium fluoride newly formed in the treatment liquid in the above step in the above step A second step of adding a smaller amount of aluminum salt as aluminum, coagulating and sedimenting the calcium fluoride by using the formed aluminum hydroxide as a coagulant, and forming a precipitate slurry, and A solid-liquid separation of wastewater containing waste slurry, draining the supernatant liquid phase, and discharging the solid precipitate slurry as sludge, a method for treating fluorine-containing wastewater, comprising:

A part of the sediment slurry discharged as the sludge is withdrawn, and calcium is acted on at a pH of 9 or less to fluorinate the fluorine adsorbed on the aluminum hydroxide contained in the sediment slurry. After fixing as calcium, the treated precipitate slurry is returned to the first step, and the series of steps is repeated, so that aluminum hydroxide in the system is at least necessary for agglomeration of calcium fluoride. A method for treating fluorine-containing wastewater, wherein the amount of aluminum hydroxide contributing to fluorine adsorption is limited by controlling the amount of aluminum salt added.

7. Fluorine-containing wastewater containing phosphoric acid is treated with calcium under weak alkaline conditions to fix fluoride ions and phosphoric acid as calcium fluoride and calcium phosphate. To neutrality, and add aluminum hydroxide salt in a smaller amount as aluminum than the total amount of calcium fluoride and calcium phosphate newly generated in the above process to coagulate aluminum hydroxide generated. Before A second step of coagulating and sedimenting the calcium fluoride and the calcium phosphate to form a precipitate slurry, and solid-liquid separation of wastewater containing the precipitate slurry, draining a supernatant liquid phase, and forming a solid phase. A method of treating a fluorine-containing wastewater having a third step of discharging a sediment slurry as sludge, wherein a part of the sediment slurry discharged as the sludge is withdrawn, and calcium is removed at a pH of 9 or less. After acting to fix the fluorine adsorbed on the aluminum hydroxide contained in the precipitate slurry as calcium fluoride, the treated precipitate slurry is returned to the first step, A method for treating fluorine-containing wastewater, comprising repeating a series of steps.

8. Calcium acts on wastewater containing fluoride ions to fix most of the fluorine in the wastewater as calcium fluoride, and aluminum hydroxide generated by the addition of aluminum salts is used as a flocculant. And a sedimentation tank for solid-liquid separation of the obtained sediment slurry. The treatment method according to any one of 1 to 6, wherein a calcium salt is added under a condition of pH 9 or less, and the calcium salt is adsorbed on aluminum hydroxide contained in the precipitate slurry. An aluminum regeneration tank for regenerating aluminum hydroxide by fixing the fluorine as calcium fluoride, and controlling and taking out a part of the sediment slurry separated by solid-liquid separation in the sedimentation tank; A processing apparatus comprising: means for returning aluminum hydroxide and calcium fluoride regenerated in the regeneration tank to the aluminum regeneration tank; and means for returning aluminum hydroxide and calcium fluoride regenerated in the regeneration tank to the reaction tank.

9. The treatment according to claim 8, wherein the settling tank has means for monitoring a solid-liquid interface level, and has a mechanism for controlling removal of the precipitate slurry so that the solid-liquid interface level is within a predetermined range. apparatus.

10. The processing apparatus according to claim 8, wherein the regeneration tank has a capacity of 1/10 or less of a reaction tank.

11. Under weak alkaline conditions for fluorine-containing wastewater containing phosphoric acid A first reaction tank for fixing calcium ions and phosphoric acid and phosphoric acid as calcium fluoride and calcium phosphate, and adjusting the treatment solution to be weakly acidic to neutral, and adding an aluminum salt. A second reaction vessel for producing aluminum hydroxide, a flocculation vessel for flocculating and sedimenting the calcium fluoride and calcium phosphate using the produced aluminum hydroxide as a flocculating aid, and forming a precipitate slurry; A treating apparatus for treating a fluorine-containing wastewater having a sedimentation tank for solid-liquid separation of the obtained precipitate slurry, wherein the treating method according to claim 5 is applied, wherein pH 9 Under the following conditions, a calcium salt is added, and the fluorine adsorbed on the aluminum hydroxide contained in the precipitate slurry is fixed as calcium fluoride to recycle the aluminum hydroxide. Means for controlling and taking out a part of the precipitate slurry solid-liquid separated in the sedimentation tank and returning it to the aluminum regeneration tank; and aluminum hydroxide regenerated in the regeneration tank. And a means for returning calcium fluoride to the first reaction tank.

12. The sedimentation tank according to claim 11, further comprising means for monitoring a solid-liquid interface level in the settling tank, and a mechanism for controlling removal of the sediment slurry so that the solid-liquid interface level falls within a predetermined range. Processing equipment.

13. The processing apparatus according to claim 11, wherein the regeneration tank has a capacity of 1/10 or less of a reaction tank.