KR20010071946A - Method for treating a fluorine-containing waste water and treating apparatus - Google Patents

Abstract

In the reactor 1, fluorine ions in the wastewater are fixed as calcium fluoride, and aluminum hydroxide is sedimented and separated in the settling tank 3 as a flocculating aid, and a part of the slurry of calcium fluoride and aluminum hydroxide is drawn to draw an aluminum regeneration tank. It is conveyed to (4), and high concentration calcium is made to react with the fluorine adsorbed to aluminum hydroxide in the aluminum regeneration tank 4 at the pH of 9 or less, and it fixed as calcium fluoride, and then conveyed to the reaction tank 1 by The aluminum hydroxide with fluorine adsorption is circulated to a high concentration in the system.

Description

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

Fluoride is a useful substance used in large quantities in various industrial fields such as chemical industry and semiconductor manufacturing, while it is harmful to humans and the environment. Fluoride contained in various industrial effluents is 15 mg / l according to the Japanese Water Pollution Control Act. It is regulated by the following concentrations. In addition, many Japanese municipalities have more stringent standards, such as 10 mg / l or less, or 5 mg / l or less, and the most stringent regulation is 0.8 mg / l or less.

In general, as a method for removing fluorine in wastewater, as shown in FIG. 6, calcium salt is added to the wastewater in the primary treatment tank 10 to produce poorly soluble calcium fluoride. Basic Since the particles of calcium fluoride produced are easily dispersed in a liquid very finely, flocculating assistant dissolves and neutralizes aluminum hydroxide produced by neutralizing about 0.1 times the amount of aluminum salt with respect to the molar concentration of calcium fluoride produced. As a result, the calcium fluoride is agglomerated in the first flocculation tank 11 and then sedimented and separated in the first sedimentation tank 12. In this step, most of the fluorine in the wastewater can be removed, but depending on the disturbance of the calcium fluoride formation reaction due to impurities contained in the wastewater, and the solubility of the calcium fluoride itself, in the above method, the concentration of fluorine is usually about 20 mg / l. Processing is the limit.

Therefore, in order to achieve an environmental standard, as a highly advanced treatment, the aluminum hydroxide produced by dissolving and neutralizing a large amount of aluminum salt in the advanced treatment tank 13 adsorbs fluorine in the waste water to the aluminum hydroxide. Is agglomerated in the second flocculation tank 14 and then sedimentation and separation in the second settling tank 15 is common.

However, this method has a problem that a large amount of sludge is generated as aluminum hydroxide adsorbed calcium fluoride and fluorine. In particular, the amount of fluorine-adsorbed aluminum hydroxide generated in the advanced treatment is enormous. For example, calcium fluoride generated when treating 10 m 3 of fluorine concentration 210 mg / l to 20 mg / l is about 0.39 kg (about 5 mol), whereas 5 mg / l of 10 m 3 of fluorine concentration 20 mg / l is used. In order to process up to l, aluminum hydroxide requires at least about 2 kg (25.6 mol) as Al (OH) ₃ . In reality, aluminum hydroxide is gel-like and difficult to dehydrate. Even if the water content is reduced to 70%, the water weight is about 5 kg, which is disposed of as sludge.

The above method also has the problem that two sedimentation tanks requiring a large site area are required. For example, as shown in FIG. 7, in the reaction tank 16, calcium salt is added to fluorine-containing waste water to produce calcium fluoride, and a large amount of aluminum salt is dissolved and neutralized to produce aluminum hydroxide. One settling tank can be used by the flocculation aid for calcium sedimentation and the adsorption treatment of fluorine, but in this case, since the adsorption position of aluminum hydroxide is occupied by calcium fluoride, Too much aluminum, which is several tens of times the molar concentration of produced calcium fluoride, is required, and the amount of sludge increases. This is because fluorine treatment is generally divided into two stages as described above, and two large sedimentation tanks are used in particular. If the drainage standard is not as strict as 15 mg / 1, aluminum hydroxide does not have to be used in such a large amount, so a single step treatment can provide a realistic response. In particular, when there are few impurities in the wastewater, it is possible to meet the drainage standard by using slightly more aluminum hydroxide than the required amount as the flocculating aid.

On the other hand, Japanese Patent Application Laid-open No. Hei 6-154767 discloses a technique for treating fluorine in wastewater to a sufficiently low concentration without increasing the amount of aluminum salt used and sludge generation amount by one step treatment. As shown in Fig. 8, the reaction vessel 19 is neutralized by adding calcium salt and aluminum salt to the fluorine-containing wastewater in the reaction tank 19, and the resulting calcium fluoride is used as the coagulant aid in the flocculation tank 20. After agglomeration, the precipitate is sedimented and separated in the settling tank 21, and a part of the precipitate is returned to the reaction tank for circulating sludge to increase the concentration of calcium fluoride and aluminum hydroxide, and the seed crystal effect of calcium fluoride and hydroxide. The co-sedimentation effect of aluminum enhances the treatment of fluorine. Since aluminum hydroxide is circulated and concentrated to be used, the addition amount of aluminum salt does not have to be excessively excessive. According to the above publication, the amount of aluminum is preferably 0.11 to 1.1 times the molar concentration of produced calcium fluoride. Preferably, the amount is 0.22 to 0.46 times. Therefore, by the above technique, it is possible to treat the fluorine in the wastewater to a low concentration sufficiently without increasing the amount of sludge by treating the fluorine in the wastewater in one step without excessively adding aluminum salt.

However, although the above-mentioned technique improves the production efficiency of calcium fluoride, the effect of fluorine adsorption by aluminum hydroxide used in circulation cannot be sufficiently obtained. Finally, the treatability of fluorine corresponds to the solubility of calcium fluoride even under ideal conditions. There is a problem that is limited to about 8mg / l. The reason for this is that when the sludge made of calcium fluoride and fluorine-adsorbed aluminum hydroxide is returned to the reaction tank, the fluorine adsorbed on the aluminum hydroxide is also simultaneously conveyed, so that the sludge concentration in the reaction tank increases along with the sludge circulation and the fluorine concentration. This is because the adsorption capacity of aluminum hydroxide is completely deteriorated in order to sufficiently increase the fluorine concentration. That is, even when conveying aluminum hydroxide which has already adsorbed fluorine, the aluminum hydroxide lacks the ability to adsorb fluorine any more, so if it is one or two cycles as exemplified in the above-mentioned publication, Although the treatment effect can be seen in its own way, the fluorine adsorption property of the aluminum hydroxide reaches saturation only after repeating the circulation several times or more, and thereafter, the fluorine adsorption effect by the circulating aluminum hydroxide cannot be obtained at all.

Therefore, when the fluorine-containing wastewater continuously generated needs to be treated with fluorine in the wastewater stably at a concentration lower than 8 mg / l, the amount of newly added aluminum salt is increased, or further advanced treatment is performed. It is necessary to add, but in such a case, the amount of sludge increases. In addition, when the drainage standard is about 15 mg / l, when the treatment in one step is sufficient, it is difficult to control the amount of aluminum hydroxide used, and the amount of aluminum salt added must be set considerably higher than the actual required amount, and the amount of sludge increases. There is a problem. The reason is that when the fluorine is reduced to about 15 mg / l in the wastewater, there is little difference between the total amount of aluminum hydroxide actually required and the amount required for flocculation of calcium fluoride. Of course, it is necessary to always use a lot because the risk of insufficient aluminum hydroxide amount can be avoided when the amount of calcium fluoride generated by fluctuation of the fluorine concentration in the waste water temporarily increases.

The present invention relates to a method for treating fluorine-containing wastewater. In particular, in the method for treating fluorine-containing wastewater in which most of the fluorine in the wastewater is fixed as calcium fluoride and the residual fluorine is adsorbed to aluminum hydroxide, the equipment investment required for the treatment and The present invention relates to a drug amount and a method for reducing sludge amount generated by treatment. The present invention also relates to an apparatus for treating fluorine-containing wastewater suitable for the treatment method.

1 is a system configuration diagram of the first embodiment of the present invention.

2 is a graph schematically showing the configuration of each component present in the system for explaining the operation of the present invention.

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

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

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.

6 is a system configuration diagram of a general fluorine-containing wastewater treatment technology.

7 is a system configuration diagram when a general fluorine-containing wastewater treatment technique is simplified.

8 is a system configuration diagram of a conventional technique for solving the problems of a general fluorine-containing wastewater treatment technique.

It is an object of the present invention to overcome the above problems and to continuously generate high concentrations of fluorine-containing wastewater, it is possible to treat fluorine to a low enough concentration at all times in a single step without requiring advanced treatment. Furthermore, the present invention provides a method capable of significantly reducing the amount of chemicals required for treatment and the amount of sludge generated by the treatment. In addition, another object of the present invention is to provide a method capable of minimizing the amount of sludge generated by effectively controlling the optimal amount of drug used according to the target concentration of fluorine treatment.

The treatment method of the 1st fluorine-containing wastewater of this invention is a 1st process which fixes most fluorine in wastewater as calcium fluoride by acting calcium with respect to the wastewater containing a fluorine ion, and the process liquid to the process liquid of the said process And a second step of adding a smaller amount of aluminum salt as aluminum than calcium fluoride to be newly produced, and coagulating sedimentation of the calcium fluoride as a coagulant aid to form a precipitate slurry, and the precipitate slurry. A method for treating fluorine-containing wastewater, comprising a third step of solid-liquid separation of the wastewater to drain the liquid supernatant and discharge the solid precipitate slurry as sludge.

A portion of the precipitate slurry discharged as the sludge is drawn, and calcium is applied at a pH of 9 or less to fix fluorine adsorbed to aluminum hydroxide contained in the precipitate slurry as calcium fluoride, and then the treatment is performed in the first step. By returning the precipitate slurry and repeating the above series of steps, it is characterized in that the aluminum hydroxide in the system is kept at least necessary for the aggregation of calcium fluoride, while increasing the amount that contributes to fluorine adsorption.

In addition, the treatment method of the second fluorine-containing wastewater of the present invention includes a first step of applying calcium to a wastewater containing fluorine ions to fix most of the fluorine in the wastewater as calcium fluoride, and the treatment liquid of the step. The second step of adding a small amount of aluminum salt as aluminum than the newly produced calcium fluoride in the step, and coagulation sedimentation of the calcium fluoride as a coagulation aid to form a precipitate slurry, and the precipitate slurry A method for treating fluorine-containing wastewater, comprising a third step of solid-liquid separation of the wastewater to be contained, draining the liquid supernatant liquid, and discharging the solid precipitate slurry as sludge.

A portion of the precipitate slurry discharged as the sludge is drawn, and calcium is applied at a pH of 9 or less to fix fluorine adsorbed to aluminum hydroxide contained in the precipitate slurry as calcium fluoride, and then the treatment is performed in the first step. By returning the precipitate slurry and repeating the above series of steps, the aluminum hydroxide salt in the system is maintained at least necessary for the aggregation of calcium fluoride, but by controlling the addition amount of aluminum salt to increase the aluminum hydroxide which contributes to fluorine adsorption It is a method of treating fluorine-containing wastewater, characterized by being limited.

In addition, the third treatment method of the present invention comprises a first step of fixing calcium fluoride and phosphoric acid as calcium fluoride and calcium phosphate by acting calcium on fluorine-containing wastewater containing phosphoric acid under mildly alkaline conditions, and the treatment. The liquid is adjusted from weakly acidic to neutral, and the aluminum hydroxide produced by adding a small amount of aluminum salt as aluminum than the total amount of calcium fluoride and calcium phosphate newly produced in the process is agglomerated, and the calcium fluoride and calcium phosphate are agglomerated. A fluorine-containing wastewater comprising a second step of sedimentation to form a precipitate slurry and a third step of solid-liquid separation of the wastewater containing the precipitate slurry to drain the liquid supernatant and discharge the solid precipitate slurry as sludge. As a treatment method of,

A portion of the precipitate slurry discharged as the sludge is drawn, and calcium is applied at a pH of 9 or less to fix fluorine adsorbed to aluminum hydroxide contained in the precipitate slurry as calcium fluoride, and then the treatment is performed in the first step. It is characterized by conveying a precipitate slurry and repeating the said series process.

The present invention also coagulates and precipitates the calcium fluoride as a coagulation aid in a reaction tank for applying calcium to the wastewater containing fluorine ions and fixing most of the fluorine in the wastewater as calcium fluoride, and aluminum hydroxide produced by addition of aluminum salts. In the apparatus for treating fluorine-containing wastewater having a flocculation tank for making a solid and a sedimentation tank for solid-liquid separation of the precipitate slurry, the apparatus is applied to the first or second treatment method described above, and the calcium salt is used under the conditions of pH 9 or less. And an aluminum regeneration tank for regenerating aluminum hydroxide by fixing fluorine adsorbed to aluminum hydroxide contained in the precipitate slurry as calcium fluoride, and extracting a part of the solid slurry separated from the liquid precipitate in the settling tank, Means for conveying to the aluminum regeneration tank, and hydroxides regenerated in the regeneration tank Treatment apparatus characterized by having a means for conveying luminium and calcium fluoride to the said reaction tank, or fluorine ion and phosphoric acid calcium fluoride and phosphoric acid by acting calcium on weakly alkaline conditions with respect to fluorine containing wastewater containing phosphoric acid. The calcium fluoride and calcium phosphate as a coagulation aid of the first reactor to be fixed as a coagulation agent, the second reaction tank to adjust the treatment solution to weak acidity to neutrality, and to add aluminum salt to produce aluminum hydroxide; A treatment apparatus for fluorine-containing wastewater having a flocculation tank for flocculation sedimentation to form a precipitate slurry and a sedimentation tank for solid-liquid separation of the obtained precipitate slurry, wherein the treatment apparatus is applied to the third treatment method and has a condition of pH 9 or less. To the aluminum hydroxide contained in the precipitate slurry In the aluminum regeneration tank which fixes the fluorine adsorbed as calcium fluoride and regenerates aluminum hydroxide, the means which takes out the part of the slurry slurry solid-separated from the said settling tank, and conveys it to the said aluminum regeneration tank, and the said regeneration tank And a means for conveying recycled aluminum hydroxide and calcium fluoride to the first reactor.

In the first treatment method of the present invention, the drawn precipitate slurry is fluorine adsorbed to the aluminum hydroxide contained in the precipitate slurry, and is always returned to the reaction tank after being fixed as calcium fluoride by the action of calcium. Aluminum hydroxide circulating at a high concentration has sufficient fluorine adsorption property, and therefore the fluorine concentration in the treated water can be lowered to a concentration significantly lower than the value corresponding to the solubility of calcium fluoride. In the above method, since the fixation is mainly performed by the formation of calcium fluoride, the aluminum salt to be newly added can be about the amount necessary to agglomerate calcium fluoride newly formed in the reaction tank, and the amount of sludge generated as a result. Can be minimized.

In addition, in the second processing method of the present invention, the width of the amount of aluminum hydroxide to be reduced can be made large enough, and the amount of aluminum hydroxide should be controlled within the above range, so that the operational control becomes extremely easy, The reduced amount of aluminum hydroxide can be used as the amount of sludge as it is. In addition, even if there is a temporary fluctuation in the fluorine concentration in the wastewater or a slight fluctuation in the amount of aluminum salt added, the slurry is conveyed after a sufficient amount is accumulated in the sedimentation tank. There is almost no effect on the control.

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

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which shows the structural example in 1st Example of this invention. The flow of a processing system is the high concentration fluorine-containing wastewater which flows in continuously in the reactor 1 maintained at neutral pH first. Calcium is reacted to fix fluorine ions in the waste water as calcium fluoride, and aluminum salt is added and neutralized to produce aluminum hydroxide to prepare a coagulation aid of calcium fluoride. Then, a flocculant is added in the flocculation tank 2, the solid component is flocculated, and solid-liquid separation is carried out as a precipitate in the settling tank 3. In the sedimentation tank 3, the precipitate is sufficiently accumulated in advance.

Thereafter, a part of the precipitate is drawn off, and some of the drawn precipitate slurry is discharged out of the system as sludge, and the remainder is returned to the reactor 1 via an aluminum regeneration tank 4 maintained at pH 3-9. In addition, 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 wastewater, and produces | generates calcium fluoride. In addition, 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 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 producing calcium fluoride from the fluorine in the wastewater, preferably 2 times per Set to be equal to or greater than the quantity. In addition, the quantity of the aluminum salt added to the reaction tank 1 is the minimum required amount from which the function as a coagulant adjuvant of the calcium fluoride by the aluminum hydroxide produced | generated in a coagulation tank is obtained, and is less than the calcium fluoride newly produced | generated every cycle as aluminum. Add amount. Preferably, the amount of calcium fluoride to be produced is set in the range of 1 to 30 mol% as aluminum. Further, the discharge amount of the precipitate slurry is set so that the amount of calcium fluoride newly generated every one cycle and the amount of calcium fluoride contained in the precipitate discharged as sludge are equal. The addition amount of the aluminum salt is set so that the amount of aluminum salt and the amount of aluminum hydroxide contained in the precipitate discharged as sludge are the same as aluminum.

In addition, the inflow amount of fluorine-containing wastewater and the conveyance amount and discharge amount of calcium fluoride and aluminum hydroxide contained in a sediment slurry are always set to become constant ratios, respectively. However, the flow rate of the fluorine-containing wastewater> the amount of the precipitate slurry is set.

Thus, by setting the inflow amount of fluorine-containing wastewater, the conveyance amount of the sediment slurry, and the discharge amount, the balance of the mass balance in the system is maintained, so that the solid-liquid interface level of the settling tank 3 (solid- The liquid interface level can always be constant.

In addition, as a method for maintaining the balance of the mass balance, the solid-liquid interface level in the sedimentation tank 3 is set in order to set the discharge amount of the precipitate slurry after the inflow amount of the fluorine-containing wastewater and the conveyance amount of the precipitate slurry are constant. In light of this, it is also possible to adjust the discharge of the precipitate slurry so that the solid-liquid interface is always kept in a predetermined range when the circulation of the precipitate slurry is repeated. That is, a means for monitoring the solid-liquid interface level, for example, a normal level sensor or the like, and a mechanism for controlling the extraction of the precipitate slurry so that the solid-liquid interface level is within a predetermined range, for example, a pump or a valve (not shown) is interlocked. It becomes possible to let.

The capacity of each tank is not specifically defined, 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 settling tank 3 is It can be made 5 times or more of the reactor 1. In addition, the flocculation tank 2 can be made into 1/2 of the reaction tank 1. In addition, the quantity of the deposit which accumulates previously in the sedimentation tank 3 shall be 10 times or more of the precipitate newly produced | generated every cycle.

Next, the operation of the processing system of FIG. 1 will be described with reference to the drawings. In the reactor 1, most of the fluorine ions in the wastewater are fixed as calcium fluoride. In addition, since the reactor 1 remains neutral, the dissolved aluminum salt is neutralized to produce aluminum hydroxide. Since this acts as an agglomeration aid of calcium fluoride, it is possible to facilitate aggregation of calcium fluoride particles that are easy to disperse in a liquid.

Here, the addition amount of the aluminum salt with respect to the amount of calcium fluoride to generate | occur | produces only the extent to which the function as a coagulation adjuvant of calcium fluoride by aluminum hydroxide is sufficient enough, and when a process is performed transiently (non-circulated treatment) The treatment effect by the fluorine adsorption action of aluminum hydroxide cannot be expected. This is because the amount of aluminum is small, so the amount of fluorine adsorbed is small, and the effect of lowering the fluorine concentration is hardly obtained. Therefore, in the transient treatment, the concentration of fluorine in the treated water is impossible even under ideal conditions until it is significantly lower than about 8 mg / l corresponding to the solubility of calcium fluoride, and usually 15 to 20 mg / l is the limit. However, in the treatment system by the deposit circulation of FIG. 1, the concentration of calcium fluoride and aluminum hydroxide in the reaction tank 1 can be increased by circulating a precipitate composed of calcium fluoride and aluminum hydroxide in the system. Here, fluorine is adsorbed to the amount of aluminum hydroxide in the precipitate accumulated in the sedimentation tank 3, and the amount is not much as an absolute amount as described above, but it is close to the saturated adsorption amount from the viewpoint of the amount of fluorine adsorption of aluminum sugar. Therefore, in the precipitate slurry, fluorine is concentrated together with calcium fluoride and aluminum hydroxide. When calcium salt is added at a high concentration in the aluminum regeneration tank 4, the fluorine adsorbed to aluminum hydroxide 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 becomes high due to the circulation of the precipitate slurry, while the amount of fluorine to be treated is constant. Therefore, the fluorine concentration in the wastewater can be sufficiently reduced by the fluorine adsorption effect. .

FIG. 2 is a graph schematically showing an increase in the amount of aluminum hydroxide that may contribute to fluorine adsorption when the treatment is performed while circulating a precipitate slurry composed of calcium fluoride and aluminum hydroxide with respect to the case where the treatment is transiently performed. . Here, with respect to one cycle of slurry circulation, the amount of newly produced calcium fluoride and newly added aluminum (as aluminum salt) and the amount of calcium fluoride and aluminum (aluminum hydroxide salt) contained in the discharged sludge are always the same. When the calcium fluoride and aluminum hydroxide concentrations in the reaction tank 1 become high, the ratio itself is always constant, and the solid-liquid interface of the sedimentation tank 3 does not fluctuate even when the slurry circulation is repeated. In addition, if the inflow of fluorine-containing wastewater, the return amount of sediment slurry, and the discharge amount are always constant, the concentrations of calcium fluoride and aluminum hydroxide in the reaction tank 1 are equilibrated to a constant value, and the value can be freely set by operating each of the above amounts. Can be.

In addition, since the pH of the aluminum regeneration tank 4 is strong in alkalinity, aluminum hydroxide dissolves as aluminate ions and reacts with calcium ions to produce stable calcium aluminate, so that the regeneration as a fluorine adsorbent becomes impossible. It is important to keep it below 9. Moreover, since the fluorine adsorption characteristic by aluminum hydroxide is strong in pH dependence, in order to process efficiently, it is preferable to keep pH of the reaction tank 1 in the range of 6-7.

As mentioned above, in the said embodiment, in addition to the system which consists of a reaction tank, a coagulation tank, and a sedimentation tank which correspond to the primary treatment of the fluorine-containing wastewater treatment system by a general two-step process, the aluminum regeneration tank much smaller than the reaction tank is By adding (for example, the capacity of 1/10 to 1/40 of the reaction tank), it is possible to treat the fluorine in the wastewater to a sufficiently low concentration without requiring any advanced treatment by the minimum system configuration.

In addition, the above description may be appropriately changed in the second and third processing methods of the present invention according to the requirements of the configuration.

Example 1

An embodiment of the first processing method of the present invention will be described with reference to the processing flow of FIG. 1.

In this embodiment, the capacity of each tank is 30 m 3 of the reaction tank 1, 15 m 3 of the flocculation tank 2, 300 m 3 of the sedimentation tank 3, and 2 m 3 of the aluminum regeneration tank 4. . The fluorine-containing wastewater to be treated is introduced into the reaction tank 1 at an inflow rate of 1 m 3 / min at an average fluorine concentration of 200 mg / l and pH 5.

First, calcined lime was added so that the calcium concentration in the reactor 1 might be 500 mg / l, and aluminum sulfate was added so that the aluminum concentration was 20 mg / l. In addition, pH was adjusted by sulfuric acid so that the pH of the reactor 1 might always be in the range of 6-7. In the coagulation tank 2, in order to coagulate the calcium fluoride and aluminum hydroxide produced in the reaction tank 1, a polyacrylamide type polymer coagulant was added as a coagulant. The mixture of aggregated calcium fluoride and aluminum hydroxide was precipitated in the settling tank 3. The operation was continued, and 100 m 3 of precipitate was accumulated in the settling tank 3. In addition, the fluorine concentration in the supernatant liquid of the sedimentation tank 3 was 18 mg / l.

Next, the slurry of the precipitate is drawn out from the settling tank 3 at a flow rate of 0.2156 m 3 / min, and a part thereof is returned to the reaction tank 1 through the aluminum regeneration tank 4 at a flow rate of 0.2 m 3 / min, and the rest All were discharged out of the system as sludge. In addition, the water content of the precipitate slurry was 97%. To the aluminum regeneration tank 4, calcined lime was added so that the calcium concentration was always 3000 mg / l, 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 sulfate was added to the reactor 1 so that the aluminum concentration might be 20 mg / l. In addition, pH was adjusted with sulfuric acid or sodium hydroxide so that the pH of the reactor 1 might always be in the range of 6-7. The above operation was circulated in the precipitate slurry in the system as one cycle.

As the circulation of the precipitate slurry was repeated, the calcium fluoride and aluminum hydroxide concentrations in the reaction tank 1 initially increased rapidly, but gradually increased, and the equilibrium was reached. At this time, the calcium fluoride concentration was 4535.1 mg / l and the aluminum hydroxide concentration was 276.7 mg / l as aluminum. Although the value of the aluminum concentration contains 20 mg / l of aluminum which is newly added every cycle, a considerable portion of the aluminum concentration is considered to contribute to fluorine adsorption, and the concentration of fluorine in the treated water is normally increased to 5 mg / l. Could be reduced.

In addition, the sludge discharged out of the system as sludge contains calcium fluoride and aluminum hydroxide at a ratio of 4535.1: 276.7, but the calcium fluoride and aluminum hydroxide are discharged at 0.0156m 3 / min and the water content of the precipitate slurry is 97%. Emissions of are calculated as 398.2㎥ / min and 69.3㎥ / min, respectively. This value is considered to substantially correspond to the amount of new generation of potassium fluoride and aluminum hydroxide in the reaction tank 1, and the solid-liquid interface in the settling 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, calcined lime is added as a calcium salt to not only the aluminum regeneration tank 4 but also the reaction tank 1 with respect to the strongly acidic fluorine-containing wastewater. Here, the total addition amount of slaked lime is the same as in the case of Example 1, the addition amount to the reaction tank 1 is adjusted to maintain the reaction tank 1 in neutral (pH 6-7), the rest of the aluminum regeneration tank ( To 4). For example, when the pH of the fluorine-containing wastewater is 2.5, other treatment conditions are the same as those in the first embodiment, so that the calcium concentration is 210 mg / l in the reaction tank 1, and the calcium in the aluminum regeneration tank 4 is used. Add slaked lime to a concentration of 1740 mg / l.

In the above embodiment, since the pH of the strongly acidic fluorine-containing wastewater is adjusted only by slaked lime in the reaction tank 1, there is an advantage that the pH adjustment operation by adding sulfuric acid or sodium hydroxide in the reaction tank 1 is unnecessary. have. In the case of weakly alkaline fluorine-containing wastewater, pH adjustment can be similarly performed 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, first, in the first reactor 5 maintained at pH 8 to 10 for wastewater containing phosphoric acid together with fluorine, calcium is reacted to produce calcium fluoride and calcium phosphate, and the fluorine in the wastewater. And after fixing phosphoric acid, fluorine remaining in the second reactor 6 maintained at pH 6 to 7 is adsorbed with aluminum hydroxide. In addition, aluminum hydroxide here also acts as a flocculation adjuvant for segregating and separating calcium fluoride and calcium phosphate in the sedimentation tank 8. In addition, the aluminum salt newly added is possible to the extent necessary for flocculation and sedimentation of the calcium fluoride and calcium phosphate newly produced | generated in the reaction tank 1, and it is possible in small quantity as aluminum with respect to these quantities. Other treatment conditions are the same as those in the first embodiment, but when the phosphoric acid concentration in the wastewater is high, the amount of calcium salt added to the aluminum regeneration tank 9 is increased accordingly.

In the above embodiment, two reaction tanks are used, one is adjusted to a pH suitable for the production of calcium phosphate, and the other is adjusted to a pH suitable for the fluorine adsorption treatment by the production of aluminum hydroxide. For wastewater, phosphoric acid can also be treated together with fluorine. In addition, although some of the produced calcium phosphate circulates in the system together with calcium fluoride and aluminum hydroxide, calcium phosphate has an advantage of adsorbing fluorine, which has the advantage of improving the treatment efficiency of fluorine.

Example 4

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

This embodiment corresponds to the case where the target value of the fluorine concentration in the treated water is 13 mg / l, and the system configuration is the same as that of the first embodiment. However, the aluminum sulfate addition amount to the reaction tank 1 is 9 mg / l as aluminum concentration. In the case of treatment based on Example 1, since the amount of aluminum hydroxide which can contribute to fluorine adsorption in the reaction tank 1 becomes very large, the fluorine concentration in the treated water drops to 5 mg / l, but as shown in FIG. 5. In order to make the concentration of fluorine in the treated water 13 mg / l, the amount of aluminum hydroxide can be greatly reduced, and the amount of aluminum sulfate added to the reaction tank 1 is reduced to 20 mg / l to 9 mg / l as the aluminum concentration, whereby the concentration of fluorine in the treated water is reduced. Was able to be 13 mg / l or less.

In addition, in the case where the treatment is carried out by a conventional method of transient, the amount of aluminum sulfate added to the reaction tank is basically 9 mg / l as the aluminum concentration, and the fluorine concentration in the treated water can be 13 mg / l. When temporarily lowered slightly to less than 8 mg / l, the cohesiveness of calcium fluoride deteriorates rapidly, resulting in turbid treatment water and fluorine concentration exceeding 15 mg / l. In addition, since the same phenomenon occurs even when the fluorine concentration in the raw wastewater is largely changed and temporarily exceeds 300 mg / l, the set value of the aluminum sulfate addition amount should be set to 20 mg / l or more with a margin.

In the above embodiment, problems such as agitation of calcium fluoride and deterioration of fluorine treatment property caused by temporary fluctuations in fluorine concentration in raw waste water or fluctuation in aluminum salt addition and the like, and stable treatment can be performed with minimal aluminum hydroxide usage. There is an advantage.

The first effect of the present invention is to treat fluorine with high concentrations of fluorine-containing wastewater by using a facility and a medicament required for conventional primary treatment without requiring advanced treatment and continuously and stably to a sufficiently low concentration. You can do it. For this reason, the facility and the chemical | medical agent which contain huge sedimentation tank which were required for the advanced processing become unnecessary, and the massive sludge which generate | occur | produced according to the advanced processing does not generate | occur | produce.

The reason for this is that aluminum hydroxide used as a coagulant aid of calcium fluoride produced in the primary treatment is circulated to a high concentration in the system while always regenerating, thereby maintaining the amount necessary for agglomeration of calcium fluoride in the system. This is because the portion contributing to the adsorption is increased at the same time.

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

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

The third effect of the present invention is that wastewater containing phosphoric acid in addition to fluorine can be sufficiently treated together with fluorine and phosphoric acid, and in particular, fluorine can be treated with high efficiency. For this reason, the usage-amount of aluminum hydroxide which also acts as a fluorine adsorbent can be reduced.

The reason is that calcium phosphate with high fluorine adsorption circulates at a high concentration together with calcium fluoride and aluminum hydroxide in the system.

The fourth effect of the present invention is that, when the original drainage standard does not require advanced treatment, the concentration of fluorine in the raw wastewater is increased by the temporary fluctuation of the fluoride concentration and the variation in the amount of aluminum salt added. It is possible to perform a stable treatment with a minimum amount of aluminum hydroxide salt without causing problems such as deterioration. Therefore, the amount of aluminum sulfate added which has been set a lot in view of safety in the past is drastically reduced, and the amount of sludge can be reduced by that much.

The reason for this is that by conveying the slurry containing aluminum hydroxide, the width of the aluminum hydroxide to be reduced can be sufficiently increased, the amount of aluminum hydroxide can be controlled within the above range, and the slurry is sufficient in the settling tank. Since it is conveyed after this accumulation, even if there is a temporary fluctuation in the fluorine concentration in the wastewater or a slight fluctuation in the amount of Al salt added, the composition ratio of the slurry always converges to an average value, so that there is little influence on the control of the amount of aluminum hydroxide. Because.

Claims (13)

The first step of fixing calcium as a calcium fluoride to the wastewater containing fluorine ions and fixing most of the fluorine in the wastewater as a calcium fluoride, and a smaller amount of aluminum as aluminum than the calcium fluoride newly produced in the step in the treatment liquid of the step. A second step of adding precipitated aluminum hydroxide and flocculating sedimentation of the calcium fluoride as a flocculating assistant to form a precipitate slurry, and solid-liquid separation of the wastewater containing the precipitate slurry. In the method for treating fluorine-containing wastewater comprising the third step of draining the liquid supernatant and discharging the solid precipitate slurry as sludge, A portion of the precipitate slurry discharged as the sludge is drawn, and calcium is applied at a pH of 9 or less to fix fluorine adsorbed to aluminum hydroxide contained in the precipitate slurry as calcium fluoride, and then the treatment is performed in the first step. By returning the precipitate slurry and repeating the above series of steps, the fluorine-containing wastewater characterized in that the aluminum hydroxide in the system is maintained at least necessary for the aggregation of calcium fluoride, while increasing the amount that contributes to fluorine adsorption. Treatment method. The amount of fluorine ions in the fluorine-containing wastewater to be treated and the amount of transport of calcium fluoride and aluminum hydroxide contained in the precipitate slurry are set at a constant ratio such that the amount of inflow is greater than the amount of transport. A method of treating fluorine-containing wastewater. The amount of calcium fluoride newly produced in the system by the addition of calcium salt, the amount of calcium fluoride contained in the precipitate slurry to be discharged, the amount of aluminum newly added and the amount of aluminum contained in the precipitate slurry to be discharged. A method of treating fluorine-containing wastewater, wherein the discharge amount of the precipitate slurry is set to be equal to each other, and the aluminum hydroxide concentration in the system is controlled by setting the flow rate. The method for treating fluorine-containing wastewater according to claim 1, wherein the conveyance amount of the precipitate slurry is set to be smaller than the inflow amount of the fluorine-containing wastewater to be treated. The method for treating fluorine-containing wastewater according to claim 1, wherein the pH adjustment in the first step is performed only by adding calcium salt. The first step of fixing calcium as a calcium fluoride to the wastewater containing fluorine ions and fixing most of the fluorine in the wastewater as a calcium fluoride, and a smaller amount of aluminum as aluminum than the calcium fluoride newly produced in the step in the treatment liquid of the step. Adding an aluminum salt and coagulating and sedimenting the calcium fluoride as a coagulant aid to form a precipitate slurry, and solid-liquid separation of the wastewater containing the precipitate slurry to drain the liquid supernatant; In the treatment method of the fluorine-containing wastewater provided with the 3rd process which discharge | releases a solid precipitate slurry as sludge simultaneously, A portion of the precipitate slurry discharged as the sludge is drawn, and calcium is applied at a pH of 9 or less to fix fluorine adsorbed to aluminum hydroxide contained in the precipitate slurry as calcium fluoride, and then the treatment is performed in the first step. By returning the precipitate slurry and repeating the above series of steps, the aluminum hydroxide salt in the system is maintained at least necessary for the aggregation of calcium fluoride, but by controlling the addition amount of aluminum salt to increase the aluminum hydroxide which contributes to fluorine adsorption Method for treating fluorine-containing wastewater, characterized in that the restriction. A first step of fixing fluorine ions and phosphoric acid as calcium fluoride and calcium phosphate by acting calcium on fluorine-containing wastewater containing phosphoric acid under mildly alkaline conditions, and adjusting the treatment liquid to weakly acidic to neutral. A second step of coagulation and precipitation of the calcium fluoride and calcium phosphate as an agglomeration aid to form aluminum hydroxide produced by adding a small amount of aluminum salt as aluminum than the total amount of calcium fluoride and calcium phosphate newly produced in In the treatment method of fluorine-containing wastewater comprising the third step of solid-liquid separation of the wastewater containing the precipitate slurry, draining the liquid supernatant and discharging the solid precipitate slurry as sludge, A portion of the precipitate slurry discharged as the sludge is drawn, calcium is applied at a pH of 9 or less to fix fluorine adsorbed to aluminum hydroxide contained in the precipitate slurry as calcium fluoride, and then the treated A method for treating fluorine-containing wastewater, wherein the precipitate slurry is returned and the series of steps are repeated. A reaction tank for applying calcium to the wastewater containing fluorine ions to fix most of the fluorine in the wastewater as calcium fluoride, and an agglomeration tank for coagulating and precipitating the calcium fluoride as a flocculating aid of aluminum hydroxide produced by the addition of an aluminum salt; In the treatment apparatus of fluorine-containing wastewater provided with the settling tank which solid-separates the obtained deposit slurry, In the treatment apparatus, the treatment method according to any one of claims 1 to 6 is applied, and calcium salt is added under conditions of pH 9 or less, and fluorine adsorbed to aluminum hydroxide contained in the precipitate slurry is added. An aluminum regeneration tank which is fixed as calcium fluoride and regenerates aluminum hydroxide; means for controlling a part of the precipitate slurry separated from the solid-liquid separated liquid in the sedimentation tank to be taken out and conveyed to the aluminum regeneration tank; And a means for conveying aluminum hydroxide and calcium fluoride to said reactor. 9. The settling tank according to claim 8, further comprising a means for monitoring a solid-liquid interface level in the settling tank, and a mechanism for controlling the extraction of the precipitate slurry such that the solid-liquid interface level is within a predetermined range. Fluorine-containing wastewater treatment apparatus. 9. The fluorine-containing wastewater treatment apparatus according to claim 8, wherein the regeneration tank has a capacity of 1/10 or less of the reaction tank. To the fluorine-containing wastewater containing phosphoric acid, calcium is reacted under weakly alkaline conditions to fix fluorine ions and phosphoric acid as calcium fluoride and calcium phosphate, and the treatment solution is adjusted to weakly acidic to neutral and aluminum salt. A second reaction tank for adding aluminum hydroxide, a flocculation tank for coagulation and precipitation of the calcium fluoride and calcium phosphate as coagulation aids to form precipitate precipitate, and a precipitation tank for solid-liquid separation of the precipitate slurry obtained. In the fluorine-containing wastewater treatment apparatus provided, In the treatment apparatus, the treatment method according to claim 7 is applied, and calcium salt is added under the condition of pH 9 or less, and fluorine adsorbed to aluminum hydroxide contained in the precipitate slurry is fixed as calcium fluoride to give aluminum hydroxide. An aluminum regeneration tank for regenerating, means for controlling a portion of the precipitate slurry separated from the solid-liquid separated liquid in the sedimentation tank, and conveying it to the aluminum regeneration tank; and aluminum hydroxide and calcium fluoride regenerated in the regeneration tank. A device for treating fluorine-containing wastewater, comprising means for conveying it to one reactor. 12. The treatment of fluorine-containing wastewater according to claim 11, further comprising a means for monitoring a solid-liquid interface level in said settling tank, and a mechanism for controlling the extraction of the precipitate slurry such that the solid-liquid interface level is within a predetermined range. Device. The fluorine-containing wastewater treatment apparatus according to claim 11, wherein the regeneration tank has a capacity of 1/10 or less of the reaction tank.