JP4766457B2 - Method and apparatus for treating fluorine-containing wastewater - Google Patents

Description

  The present invention relates to a fluorine-containing wastewater treatment method and apparatus, and more particularly to a fluorine-containing wastewater treatment method and apparatus for treating fluorine-containing wastewater discharged from a semiconductor manufacturing factory or the like.

  In semiconductor manufacturing factories and related factories, a large amount of an etchant mainly composed of hydrogen fluoride or ammonium fluoride is used. For this reason, the fluorine-containing waste water which has hydrogen fluoride and ammonium fluoride as a main component is discharged | emitted in factory waste water, The process which removes fluorine from this fluorine-containing waste water is needed.

  Conventionally, treatment of fluorine-containing wastewater has been carried out by coagulation sedimentation, etc., and calcium salts such as calcium hydroxide are added to fluorine-containing wastewater to form poorly soluble calcium fluoride, and this calcium fluoride is agglomerated. By doing so, the fluorine component is removed. However, this method has a problem that a large amount of sludge with poor sedimentation is generated, and it is necessary to reduce the amount of sludge generated.

  Therefore, a method using a calcium carbonate packed tower has been proposed as a method for reducing the amount of sludge generated. In this method, fluorine-containing waste water is passed through a calcium carbonate packed tower to convert fluorine into granular calcium fluoride and remove it.

However, the above method has a problem that the fluorine treatment cannot be stably performed for a long period of time. That is, in the fluorine-containing wastewater, acids such as hydrochloric acid and nitric acid coexist in addition to hydrofluoric acid, and calcium carbonate is dissolved by the acid, so that the fluorine treatment cannot be stably performed for a long time. there were. In order to cope with this, a method has been proposed in which an alkali agent is added in an amount equal to or greater than the equivalent of an acid other than hydrofluoric acid contained in fluorine-containing wastewater (see Patent Document 1).
JP-A-5-293475

  However, this method has an effect on the quality of treated water depending on the properties of the fluorine-containing wastewater. When the acid content other than hydrofluoric acid is contained in the fluorine-containing wastewater, calcium carbonate is excessively dissolved.

  When most of the fluorine contained in the fluorine-containing wastewater is derived from ammonium fluoride, the fluorine treatment performance is lowered, and fluorine remains at a high concentration.

  In addition, if treated water containing excess fluorine is passed from a calcium carbonate packed tower to a crystallization tower for precipitating fluoroapatite, the amount of phosphate chemical and calcium compound to be added is insufficient, and fluorine remains in the treated water. Or turbidity is generated in the crystallization tower.

  Further, when calcium aggregation / solid-liquid separation treatment is performed between the calcium carbonate packed tower and the crystallization tower in order to sufficiently reduce the fluorine concentration before passing through the crystallization tower, an acid component other than hydrofluoric acid. There is a problem that a large amount of turbidity is generated when wastewater containing a large amount of wastewater flows. In other words, the crystallization is caused by the soluble calcium in the treated water of the calcium carbonate packed tower due to excessive dissolution of calcium carbonate, the calcium compound added in the next aggregation / solid-liquid separation treatment, and the calcium compound added in the subsequent crystallization treatment. The calcium concentration in the precipitation tower increases and turbidity is generated.

  In addition, fluorine-containing wastewater discharged from semiconductor manufacturing factories and related factories generally contains hydrofluoric acid, ammonium fluoride, and acids other than hydrofluoric acid, but the concentration of each component is discharged at a constant level. Is rare.

  As described above, due to excessive dissolution of calcium carbonate, residual fluorine, and turbidity generation in the crystallization tower, the fluorine-containing waste water is sequentially passed from the calcium carbonate packed tower to the crystallization tower for advanced fluorination treatment. Was difficult.

  The present invention has been made in view of such circumstances, and by appropriately controlling the fluorine concentration and calcium concentration of treated water that is passed to the crystallization tower, high fluorine removal performance can be obtained, and carbonic acid can be obtained. It aims at providing the processing method and apparatus of fluorine-containing wastewater which can improve the utilization efficiency of calcium and reduction of sludge generation amount.

  In order to achieve the above object, the invention according to claim 1 is a method for treating fluorine-containing wastewater that removes fluorine from fluorine-containing wastewater. The pH and fluorine ion concentration of the fluorine-containing wastewater are measured, and the measured fluorine Calculate the pH of the hydrofluoric acid solution when all of the ion concentration is derived from hydrofluoric acid and do not contain other acids, and the difference is the difference in the measured pH of the fluorine-containing wastewater relative to the calculated pH of the hydrofluoric acid solution Calcium carbonate packed tower treatment step of passing a fluorine-containing waste water whose pH is adjusted so that the difference pH falls within the range of -0.5 to +1.0 to the calcium carbonate packed tower, and the calcium carbonate filling A coagulation / separation step in which a calcium compound is added to the tower treated water to treat the fluorine concentration to 20 mg / L or less, and the fluorine-containing wastewater after the coagulation / separation step is treated with phosphoric acid. It characterized in that it and a crystallization step of Rohm added to crystallize 析塔 at least phosphoric acid drugs of the agent and the calcium compound.

  According to the invention of claim 1, the pH and fluorine ion concentration of the fluorine-containing wastewater are measured, and the hydrofluoric acid solution when all the measured fluorine ion concentrations are derived from hydrofluoric acid and do not contain other acids. Calculating the pH, obtaining the difference pH, which is the difference in the measured pH of the fluorine-containing wastewater relative to the calculated pH of the hydrofluoric acid solution, and adjusting the pH so that the difference pH is within the range of -0.5 to +1.0 The waste water is passed through a calcium carbonate packed tower, a calcium compound is added, the fluorine concentration is aggregated and separated to 20 mg / L or less, and at least a phosphate-based drug is added out of the phosphate-based drug and calcium compound. By passing water through the crystallization tower, it is possible to prevent excessive dissolution of calcium carbonate, deterioration of the fluorine treatment performance, and generation of turbidity. Here, the “hydrofluoric acid solution” is a virtual solution and is not actually prepared. In addition, although the setting of the difference pH of the fluorine-containing waste water in a calcium carbonate packed tower processing process is the range of -0.5- + 1.0, Preferably it is the range of -0.5- + 0.5. Further, as described above, in the fluorine-containing waste water that satisfies the difference pH in the range of −0.5 to +1.0, the fluorine ion concentration and the calcium concentration of the treated water after passing through the calcium carbonate packed tower are It has a fluorine ion concentration curve and a calcium concentration curve that have a low concentration and a substantially constant slope in a pH range of −0.5 to +1.0. Therefore, by setting the difference pH within a range of −0.5 to +1.0 to a predetermined difference pH, the fluorine ion concentration and the calcium concentration in the treated water that has passed through the calcium carbonate packed tower are set to the difference pH. It can be controlled indirectly depending on how many are set. Thereby, since the addition amount etc. of the calcium compound in a post process can be adjusted, it can contribute to the improvement in utilization efficiency of calcium carbonate, reduction of sludge generation, and prevention of occurrence of turbidity.

  Calcium carbonate packed tower treatment process Fluorine concentration in coagulation / solid-liquid separation treated water by adding calcium compound to remove fluorine remaining in calcium carbonate packed tower treated water as calcium fluoride in the next aggregation / separation process To 20 mg / L or less. The calcium compound is added in excess of the amount of calcium necessary for the fluorine to become calcium fluoride, and the fluorine is reduced to 20 mg / L or less, which is the concentration at which the agglomerated solid-liquid separation treated water can pass through the crystallization tower. It is preferable to remove. The calcium remaining here can be used in a subsequent crystallization tower, and is a calcium compound addition that takes it into account, and does not lead to an increase in running cost due to excessive addition of chemicals. In this way, when the treated water in which fluorine remains excessively is passed from the calcium carbonate packed tower to the crystallization tower for precipitating fluoroapatite, the amount of the phosphoric acid agent and calcium compound to be added is insufficient. The problem that fluorine remains in the crystallization tower and turbidity is generated in the crystallization tower can be solved.

  Then, fluorine can be suitably treated by a crystallization step in which at least a phosphoric acid chemical agent is added to the treated water and water is passed through the crystallization tower. If calcium is insufficient, a calcium compound is further added to highly treat fluorine.

  As described above, by treating the fluorine-containing wastewater with the method for treating fluorine-containing wastewater of the present invention, it is possible to prevent excessive dissolution of calcium carbonate, reduce the amount of sludge generated, and reduce the cost of added chemicals. In addition, it can be highly fluorinated.

  The invention according to claim 2 is the invention according to claim 1, wherein the addition of the calcium compound in the aggregation / separation step is equivalent to the amount of fluorine ion remaining in the calcium carbonate packed tower treated water being calcium fluoride. More than 50 mg / L of calcium, and the calcium dissolved in the calcium carbonate packed tower treated water and the added calcium are combined so as not to exceed 500 mg / L.

  According to the invention of claim 2, by adding the calcium compound in the aggregation / separation step within the above range, the fluorine concentration of the packed tower treated water can be treated to 20 mg / L or less. It does not cause white turbidity when passing through the crystallization tower. In addition, since the calcium concentration in the treated water of the calcium carbonate packed tower can be estimated by adjusting the fluorine-containing waste water to a predetermined difference pH, a special measure such as monitoring the dissolved calcium concentration of the treated water in the calcium carbonate packed tower Control is not necessary.

  A third aspect of the present invention is characterized in that in the first or second aspect, in the aggregation / separation step, at least one of an inorganic flocculant and a polymer flocculant is added together with the addition of the calcium compound.

  According to claim 3, it is preferable to add at least one of an inorganic flocculant and a polymer flocculant in the flocculation / separation step.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein 300 mg / of the equivalent of calcium required to produce fluoroapatite with fluorine ions remaining in the fluorine-containing wastewater after the aggregation / separation step is provided. When calcium of more than L is dissolved, the calcium compound is not added in the crystallization step.

  If more than 300 mg / L of calcium is dissolved in the fluorine ion remaining in the fluorine-containing wastewater after the coagulation / separation step, the amount of calcium is more than 300 mg / L than the equivalent amount of calcium necessary to produce fluoroapatite, There is a possibility that white turbidity may occur in the precipitation tower, and since the dissolved calcium can be sufficiently treated with fluorine, the fluorine can be treated by passing water through the crystallization tower without adding a calcium compound. be able to. Therefore, according to claim 4, when 300 mg / L more calcium is dissolved than the equivalent amount of calcium required to produce fluoroapatite with the fluorine ions remaining in the fluorine-containing wastewater after the aggregation / separation step, In the crystallization step, the running cost due to the dissolution of calcium carbonate can be suppressed by adding only the phosphoric acid-based agent without adding the calcium compound.

  In order to achieve the above object, the invention according to claim 5 is a fluorine-containing wastewater treatment apparatus for removing fluorine from fluorine-containing wastewater, a pH measuring means for measuring the pH of the fluorine-containing wastewater, and a fluorine ion concentration. Fluorine ion concentration measuring means for measuring, and calculating the pH of the hydrofluoric acid solution when all of the measured fluorine ion concentrations are derived from hydrofluoric acid and do not contain other acids, and the calculated pH of the hydrofluoric acid solution A calculation means for obtaining a difference pH, which is a difference in measured pH of the fluorine-containing wastewater, and a drainage adjustment means for adjusting the pH of the fluorine-containing wastewater so that the difference pH falls within a range of −0.5 to +1.0. A pH adjusting tank equipped with, a calcium carbonate packed tower through which fluorine-containing wastewater adjusted in pH in the pH adjusting tank is passed, and a fluorine containing water after passing through the calcium carbonate packed tower A flocculant tank for aggregating calcium fluoride sludge from fluorine and the calcium compound in the fluorine-containing wastewater by adding a calcium compound for converting the fluorine remaining in water into calcium fluoride; and the agglomerated fluoride Crystallization equipped with a precipitation tank for precipitating calcium sludge, and an addition means for adding at least a phosphoric acid-based chemical among a phosphoric acid-based chemical and a calcium compound to the fluorine-containing wastewater after passing through the precipitation tank And a tower.

  According to a sixth aspect of the present invention, in the fifth aspect of the present invention, the calcium compound addition means in the coagulation tank is configured so that the fluorine ions remaining in the calcium carbonate packed tower treated water are more than the equivalent amount of calcium necessary for generating calcium fluoride. More than 50 mg / L, and the calcium compound is added so that the calcium dissolved in the fluorine-containing wastewater after passing through the pH adjusting tank and the calcium to be added do not exceed 500 mg / L. .

  The invention according to claim 7 is the invention according to claim 5 or 6, wherein more than 300 mg / L of calcium is dissolved than the equivalent amount of calcium necessary for producing fluoroapatite with fluorine ions remaining in the treated water in the settling tank. The calcium compound is not added to the crystallization tower.

  Claims 5 to 7 are the inventions of the methods according to claims 1 to 4. By treating fluorine with such a treatment apparatus, it is possible to highly treat fluorine while preventing excessive dissolution of calcium carbonate, reducing the amount of sludge generated, and reducing the cost of added chemicals.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to obtain high fluorine removal performance, the processing method and apparatus of fluorine-containing wastewater which can improve the utilization efficiency of calcium carbonate and reduce sludge generation amount can be provided.

  Preferred embodiments of a fluorine-containing wastewater treatment method and apparatus according to the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 schematically shows the configuration of the waste water treatment apparatus of the present embodiment. As shown in the figure, the waste water treatment apparatus 10 mainly includes a pH adjustment tank (also referred to as a raw water tank) 12, a calcium carbonate packed tower 13, a coagulation tank 14, a precipitation tank 15, and a crystallization tank 16. And the processing method of the fluorine-containing waste_water | drain of this invention is equipped with the calcium carbonate packed tower processing process A, the aggregation / separation process B, and the crystallization process C, as shown in the figure.

  The fluorine-containing wastewater stored in the raw water tank 12 is sent to the calcium carbonate packed tower 13 where it is treated in an upward flow and discharged from the upper part. In addition, a circulation line 46 for feeding the solution in the calcium carbonate packed tower from the upper part of the calcium carbonate packed tower 13 and the lower part of the treated water discharge port to the lower part of the tower is provided by the circulation pump 42. The particles of calcium carbonate filled by this circulating flow are floated to form an expanded bed, thereby preventing the calcium carbonate from adhering to each other and accumulation of carbon dioxide gas discharged from the calcium carbonate in the calcium carbonate packed layer.

  Circulation can be carried directly from the upper part of the calcium carbonate packed tower 13 to the lower part, but a circulation tank (not shown) is installed, the circulating liquid is allowed to overflow from the upper part of the calcium carbonate packed tower, and the circulation tank is pumped by a circulation pump. Water can also be sent to the bottom of the calcium carbonate packed tower. When a circulation tank is installed, the treated water is discharged from the circulation tank, not from the top of the calcium carbonate packed tower.

  The raw water tank 12 is provided with a pH meter 20 and a fluorine ion concentration meter 22, and when the calculation device 24 determines that all of the measured fluorine ion concentration is derived from hydrofluoric acid and does not contain other acids. Calculate the pH of the acid solution, determine the difference pH, which is the difference between the measured pH of the fluorine-containing wastewater relative to the calculated pH of the hydrofluoric acid solution, and adjust the pH so that the difference pH is within the range of -0.5 to +1.0. Fluorine-containing wastewater whose pH is adjusted by adding or adjusting acid or alkali such as sodium hydroxide is passed through a calcium carbonate packed tower, and the difference pH is preferably in the range of -0.5 to +1.0, More preferably, it is in the range of -0.5 to +0.5.

  The raw water tank 12 is connected to an acid storage tank 28 via a pipe 26 and is connected to an alkali storage tank 32 via a pipe 30. Pumps 34 and 36 are respectively provided in the pipes 26 and 30. By driving the pumps 34 and 36, an acid solution (for example, hydrochloric acid) in the acid storage tank 28 and an alkali solution ( For example, sodium hydroxide) is added to the raw water tank 12. The pumps 34 and 36 are respectively connected to the control device 24, and the pumps 34 and 36 are controlled by the control device 24 to adjust the amount of acid or alkali added to the raw water tank 12.

  For example, when the difference pH is set to −0.3, all of the fluorine ion concentrations obtained by the arithmetic unit 24 from the fluorine ion concentration of the wastewater measured by the fluorine ion concentration meter 22 are derived from hydrofluoric acid and other When the pH of the hydrofluoric acid solution when it does not contain an acid is 2.5, the pH of the wastewater may be adjusted to 2.2. The set value may be set based on the water quality desired to be obtained as the treated water from the calcium carbonate packed tower 13, whereby the fluorine ion concentration and calcium ion concentration of the treated water from the calcium carbonate packed tower can be indirectly controlled. When the fluorine ion concentration contained in the fluorine-containing wastewater is relatively stable, the fluorine ion concentration meter 22 is not necessarily installed, and the pH difference from the hydrofluoric acid solution is obtained from the measured value of the pH meter 20, The pH of the fluorine-containing wastewater can be adjusted.

  The treated water flowing out from the calcium carbonate packed tower 13 flows into the flocculation tank 14 through the treated water pipe 44, and an inorganic flocculant such as a calcium compound and PAC (polyaluminum chloride) and / or a polymer flocculant is added. In the precipitation tank 15, the calcium fluoride sludge and the water supplied to the crystallization tower 16 described below are agglomerated and solid-liquid separated.

  The coagulation tank 14 is connected to the calcium compound storage tank 50 via a pipe 52 and is connected to a coagulant storage tank 56 via a pipe 58. The pipes 52 and 58 are provided with pumps 54 and 60, respectively. By driving the pumps 54 and 60, the calcium compound in the calcium compound reservoir 50, the inorganic flocculant in the coagulant reservoir 56, and / or Alternatively, a polymer flocculant is added to the aggregation tank 14.

  Calcium compounds can be monitored by monitoring the calcium concentration contained in the treated water from the calcium carbonate packed tower 13 and the amount of addition can be controlled so as to achieve a predetermined calcium concentration in the agglomeration tank 15. A combined method may be used.

  The amount of the calcium compound added is 50 mg / L or more of fluorine ions remaining in the treated water of the calcium carbonate packed tower more than the equivalent amount of calcium necessary to produce calcium fluoride, and after passing through the calcium carbonate packed tower It is preferable that the calcium dissolved in the fluorine-containing waste water and the calcium to be added do not exceed 500 mg / L.

  The crystallization tower 16 is connected from the agglomeration tank 15 through a treated water pipe 62. A pipe 66 is connected to the treated water pipe 62, and is connected to the calcium compound reservoir 50 via a pump 68 disposed in the pipe 66. Further, piping 76 and 82 are disposed in the circulation line 70 described later. The pipes 76 and 82 are provided with pumps 78 and 84, respectively, and by driving the pumps 78 and 84, the phosphate drug in the phosphate drug reservoir 74 and the sodium hydroxide reservoir 80 are provided. The sodium hydroxide inside is added to the crystallization tower 16 via the circulation line 70.

  Calcium compound, phosphoric acid-based chemical and sodium hydroxide as pH adjuster are added to the water supplied to the calcium carbonate packed tower 13 and the crystallization tower 16 which has been agglomerated and solid-liquid separated. The treated water from which fluorine has been removed from the upper part after being treated with a stream is discharged. In addition, a circulation line 70 is provided for feeding the liquid in the crystallization tower from the upper part of the crystallization tower 16 to the lower part of the tower below the treated water discharge port, and the crystallization material filled by this circulation flow is floated. The expanded bed is formed, and the crystallized materials are solidified to prevent drifting.

  In the crystallization tower 16, for example, the total concentration of calcium ions in the calcium carbonate packed tower treated water and the calcium compound added in the flocculation / solid-liquid separation treatment is treated by the crystallization tower 16 after the flocculation / solid-liquid separation treatment. It is possible to eliminate the need for the addition of a calcium compound to the crystallization tower 16 by setting the calcium ion concentration to a sufficient level. When 300 mg / L or more of calcium is dissolved in the fluorine ion remaining in the treated water in an amount of 300 mg / L or more than the equivalent amount of calcium necessary for producing fluoroapatite, it is possible to add phosphoric acid without adding a calcium compound. preferable.

  In this case, the concentration of calcium ions in the aggregation / solid-liquid separation treatment is high, and the fluorine ion concentration of the treated water can be reduced from the relationship of the solubility product, so that the fluorine load on the crystallization tower 16 can be reduced. There is also an advantage.

  According to the present invention, since the fluorine concentration and calcium concentration discharged from each process can be controlled, high fluorine removal performance can be obtained, and calcium carbonate utilization efficiency can be improved and sludge generation amount can be reduced.

  Next, the operation of the wastewater treatment apparatus 10 configured as described above will be described based on the results of tests.

  In this embodiment, when the fluorine-containing wastewater whose pH difference of hydrofluoric acid solution is adjusted to ± 0 pH is passed, the wastewater whose pH difference of hydrofluoric acid solution in the calcium carbonate packed tower is adjusted to +1.2 pH is calcium carbonate. When water was passed through the packed tower, the fluorine treatment performance decreased, and the treated water fluorine ion concentration increased from the beginning of the water flow. In order to make the treated water of the calcium carbonate packed tower 13 treated in such a manner that it can be supplied to the subsequent crystallization tower 16, a large amount of calcium compound is added in the next stage of aggregation / solid-liquid separation of the calcium carbonate packed tower 13. It becomes necessary and it turns out that the amount of sludge generation increases.

  The drainage in which the pH difference of the hydrofluoric acid solution was adjusted to ± 0 pH had good fluorine treatment performance, and the filled calcium carbonate could be used for a long time. Next, the fluoride ion concentration of the treated water obtained by adding 100 mg-Ca / L of calcium chloride as the calcium compound and 100 mg / L of PAC as the inorganic flocculant to the treated water of the calcium carbonate packed tower becomes 14 mg / L, and the crystallization tower supply water As a result, the fluorine concentration could be reduced to a sufficient level. The sludge generated by the treatment so far is about 250 mg / L as SS, and it was confirmed that the amount of sludge generated can be greatly reduced as compared with the conventional calcium coagulation sedimentation treatment. Furthermore, final treated water having a fluorine ion concentration of 4 mg / L or less and SS of 1 mg / L or less was obtained by passing the coagulation / solid-liquid separation treated water through the crystallization tower. By treating the fluorine-containing wastewater according to the present invention, the fluorine concentration and calcium concentration are controlled by the calcium carbonate packed tower and the coagulation / solid-liquid separation treatment, and stable crystallization tower supply water is obtained. There were no problems such as high concentration of fluorine in the crystallization tower treated water due to fluctuations or the occurrence of turbidity.

  FIG. 2 shows the relationship between the difference pH between the fluorine-containing wastewater and the hydrofluoric acid solution, and FIG. 3 shows the relationship between the pH difference between the fluorine-containing wastewater and the hydrofluoric acid solution. Is shown.

  Calcium carbonate packed tower 13 by limiting the fluorine concentration in fluorine-containing wastewater within a certain range, and changing the difference pH from the hydrofluoric acid solution of fluorine-containing wastewater by the mixing ratio of hydrofluoric acid and ammonium fluoride, the kind and concentration of acid. It was confirmed that there is a relationship between the pH difference from the hydrofluoric acid solution and the calcium ion concentration of the treated water. Further, when the difference pH from the hydrofluoric acid solution is ± 0 or less and the calcium ion concentration of the treated water suddenly increases, and the difference pH from the hydrofluoric acid solution falls below −0.5, the crystallization tower 16 in the latter stage becomes turbid. It can be seen that the quality exceeds the calcium ion concentration where the quality tends to occur.

  When the pH difference from the hydrofluoric acid solution is -0.5, the dissolution of calcium carbonate is large, so the reduction of calcium carbonate is large, and treatment with calcium carbonate filled at an early stage becomes impossible.

  However, an increase in the calcium concentration in the treated water of the calcium carbonate packed tower leads to a decrease in the concentration of fluorine ions in the treated water. Furthermore, in such a case, in the next aggregation / solid-liquid separation treatment, the addition amount of the calcium compound may be reduced or the aggregation / solid-liquid separation treatment with an inorganic flocculant such as PAC may be performed without adding, The same treatment can be performed in the water flow to the crystallization tower 16, and the running cost is not increased due to dissolution of calcium carbonate.

  Regarding the fluorine ion concentration of the treated water, the difference between the pH difference from the hydrofluoric acid solution exceeded +1.0, and the difference was caused by the two types of drainage fluorine concentrations of A and B. It was confirmed that the effect of was small. Similarly, when the pH difference from the hydrofluoric acid solution exceeds +1.0, the treated water fluoride ion concentration tends to increase rapidly. When the treated water fluoride ion concentration becomes high, the calcium carbonate filling It can be seen that the amount of sludge generated increases in the agglomeration tank 14 and the sedimentation tank 25 in the next aggregation / solid-liquid separation step of the tower 13.

  From the above results, it is possible to roughly estimate the calcium ion concentration and the fluorine ion concentration in the treated water with the difference pH from the hydrofluoric acid solution of the fluorine-containing wastewater. By adjusting the difference pH with the hydrofluoric acid solution, It was confirmed that the water quality of the calcium packed tower treated water can be controlled. Thereby, the amount of chemicals added in the coagulation / solid-liquid separation treatment step and the crystallization step can be determined, and the quality of treated water in each step can be controlled, so that stable treatment is possible.

The figure which shows the structure of the waste water treatment equipment of this Embodiment The figure which shows the relationship between the difference between the fluorine-containing wastewater pH and the pH of the hydrofluoric acid solution and the calcium ion concentration of the treated water The figure which shows the relationship between the difference between the fluorine-containing wastewater pH and the pH of the hydrofluoric acid solution and the fluorine ion concentration of the treated water

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Waste water treatment apparatus, 12 ... pH adjustment tank (raw water tank), 13 ... Calcium carbonate packed tower, 14 ... Coagulation tank, 15 ... Precipitation tank, 16 ... Crystallization tower, 18 ... Raw water piping, 20 ... pH meter, 22 DESCRIPTION OF SYMBOLS ... Fluorine ion concentration meter, 24 ... Control apparatus, 28 ... Acid storage tank, 32 ... Alkali storage tank (sodium hydroxide storage tank), 44 ... Treatment water piping, 46 ... Circulation line, 48 ... Pump, 50 ... Calcium compound storage Tank, 56 ... flocculant reservoir, 62 ... treated water piping, 64 ... calcium compound reservoir, 72 ... pump, 74 ... phosphoric acid chemical reservoir, 80 ... sodium hydroxide reservoir, A ... calcium carbonate packed tower treatment Process, B ... Aggregation / separation process, C ... Crystallization process

Claims (7)

In the treatment method of fluorine-containing wastewater that removes fluorine from fluorine-containing wastewater,
The pH and fluorine ion concentration of the fluorine-containing wastewater are measured, and the pH of the hydrofluoric acid solution is calculated when all of the measured fluorine ion concentrations are derived from hydrofluoric acid and do not contain other acids. A difference pH, which is a difference in measured pH of the fluorine-containing wastewater with respect to the calculated pH of the acid solution, is obtained, and the fluorine-containing wastewater whose pH is adjusted so that the difference pH is in the range of −0.5 to +1.0 is obtained by calcium carbonate. A calcium carbonate packed tower treatment step for passing water through the packed tower;
An aggregation / separation step of adding a calcium compound to the calcium carbonate packed tower treated water to treat the fluorine concentration to 20 mg / L or less;
A crystallization step of adding at least a phosphoric acid-based agent out of a phosphoric acid-based agent and a calcium compound to the fluorine-containing wastewater after the aggregation / separation step, and allowing water to pass through a crystallization tower. Treatment method for fluorine-containing wastewater. The addition of the calcium compound in the aggregation / separation step is as follows:
Fluorine ions remaining in the calcium carbonate packed tower treated water are added by 50 mg / L or more than the equivalent amount of calcium necessary to make calcium fluoride, and added with calcium dissolved in the calcium carbonate packed tower treated water. The treatment method of fluorine-containing wastewater according to claim 1, wherein calcium is combined so as not to exceed 500 mg / L. In the aggregation / separation step,
The method for treating fluorine-containing wastewater according to claim 1 or 2, wherein at least one of an inorganic flocculant and a polymer flocculant is added together with the addition of the calcium compound. When 300 mg / L or more of calcium is dissolved in the fluorine ion remaining in the fluorine-containing wastewater after the coagulation / separation step, more than 300 mg / L of calcium equivalent to the amount of calcium necessary to produce fluoroapatite,
The method for treating fluorine-containing wastewater according to any one of claims 1 to 3, wherein the calcium compound is not added in the crystallization step. In a fluorine-containing wastewater treatment device that removes fluorine from fluorine-containing wastewater,
A pH measuring means for measuring the pH of the fluorine-containing wastewater, a fluorine ion concentration measuring means for measuring the fluorine ion concentration, and all the measured fluorine ion concentrations are derived from hydrofluoric acid and do not contain other acids. A calculation means for calculating a pH of the hydrofluoric acid solution and calculating a difference pH which is a difference of the measured pH of the fluorine-containing wastewater with respect to the calculated pH of the hydrofluoric acid solution; and the difference pH is -0.5 to +1.0 Drainage adjusting means for adjusting pH of fluorine-containing drainage so as to be in the range of
A calcium carbonate packed tower through which fluorine-containing wastewater whose pH is adjusted in the pH adjusting tank is passed;
Calcium fluoride sludge is added from the fluorine in the fluorine-containing wastewater and the calcium compound by adding a calcium compound for converting the fluorine remaining in the fluorine-containing wastewater after passing through the calcium carbonate packed tower to calcium fluoride. A coagulation tank for coagulating
A settling tank for precipitating the agglomerated calcium fluoride sludge;
A crystallization tower provided with an adding means on the upstream side for adding at least a phosphoric acid-based chemical among a phosphoric acid-based chemical and a calcium compound to the fluorine-containing wastewater after passing through the settling tank, Fluorine-containing wastewater treatment equipment. The calcium compound addition means of the aggregation tank is
More than 50 mg / L of fluorine ions remaining in the calcium carbonate packed tower treated water than the equivalent amount of calcium required to produce calcium fluoride, and dissolved in the fluorine-containing wastewater after passing through the pH adjustment tank The apparatus for treating fluorine-containing wastewater according to claim 5, wherein the calcium compound is added so that the combined calcium and the added calcium do not exceed 500 mg / L. In the case where 300 mg / L or more of calcium is dissolved in the fluorine ions remaining in the treated water in the settling tank, more than 300 mg / L of calcium equivalent to the amount of calcium necessary to produce fluoroapatite,
The apparatus for treating fluorine-containing wastewater according to claim 5 or 6, wherein the calcium compound is not added to the crystallization tower.

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