JP4858449B2 - Treatment method for fluorine-containing wastewater - Google Patents

Description

The present invention relates to a method for solid-liquid separation of fluorine as insoluble calcium fluoride (CaF ₂ ) by adding a calcium compound such as calcium chloride or calcium hydroxide to fluorine-containing wastewater. The present invention relates to a method for treating fluorine-containing wastewater, in which a calcium compound is effectively acted to obtain high-quality treated water and at the same time, sludge having a low moisture content is generated.

  Fluorine-containing wastewater such as fluorine-containing wastewater discharged from the silicon wafer manufacturing process in semiconductor component manufacturing, pickling wastewater discharged from the stainless steel plate manufacturing process, aluminum surface treatment wastewater, hydrofluoric acid manufacturing wastewater, fertilizer manufacturing wastewater, and waste incineration wastewater Is generally processed by the following two-stage processing / multi-stage processing.

That is, first, in the first step, calcium hydroxide corresponding to 120 to 250 mg / L of excess calcium ions in the first reaction step in which calcium hydroxide is added to fluorine-containing wastewater to adjust the pH to 10 to 11 and the reaction solution. And a second reaction step of neutralizing with hydrochloric acid is employed (see, for example, Patent Document 1). In addition, since the reaction between calcium hydroxide and hydrofluoric acid under alkalinity is slow, 0.3 to 0.5 equivalents of calcium hydroxide is added to fluoride ions while maintaining the pH acidic or neutral. The insoluble matter produced | generated is isolate | separated and repeating the same process with respect to supernatant water is also performed (for example, refer patent document 2).
JP 2004-283759 (Claims, Fig. 1) Japanese Patent No. 3378362 (Claims, paragraph 13)

  When calcium hydroxide is employed as a fluorine insolubilizer that also serves as a pH adjuster that adjusts the pH to 10 to 11, it may be added in an amount equal to or greater than the equivalent of fluoride ions, and fine calcium fluoride precipitates, which is treated water. There was a problem that the quality of treated water was not stable due to leakage. In addition, when the produced fine calcium fluoride is coagulated and precipitated with a coagulant such as a polymer in order to obtain high-quality treated water, there is a problem that the moisture content of the produced sludge is high and the amount of waste increases. In addition, in the method of adding 0.3 to 0.5 equivalents of calcium hydroxide to fluoride ions, separating the insoluble matter to be produced, and separating the insoluble matter to be produced, the addition step is at least three times. It was necessary to repeat the separation step, and it was necessary to repeat 4 to 5 times in order to reduce the fluorine concentration of the treated water to 15 mg / L or less.

  In addition, calcium hydroxide added as raw water or calcium compound contains a polyvalent metal such as aluminum, and the hydroxide of this polyvalent metal precipitates on the surface of calcium fluoride, and the growth of calcium fluoride occurs. Has the problem of producing sludge with a high water content by inhibiting the water content.

In the present invention, in order to obtain a stable treated water quality in a small number of steps and at the same time produce sludge having a low water content, if fluoride ions are first roughed, then the equivalent to or more than the remaining fluoride ions. It can be found that the formation of fine calcium fluoride can be suppressed even if the calcium compound is added, and further, the growth inhibition of calcium fluoride can be suppressed by adding alkali to the returned sludge and reacting the returned sludge. It came to solve the problem of the prior art.
(1) a reaction step in which a calcium compound is added to fluorine-containing wastewater to produce an insolubilized product containing calcium fluoride, and a separation step in which solid-liquid separation is performed on sludge containing the insolubilized product of calcium fluoride and separated water. In the method for treating fluorine-containing wastewater having a sludge return process for returning a part of the separated sludge as return sludge to the reaction process, the reaction process includes a series of two-stage reaction tanks, and the sludge return process is returned. An alkali sludge adjusting tank for adding alkali to the sludge, the return sludge being returned to the first stage reaction tank, and less than the equivalent of fluoride ions contained in the fluorine-containing water; The calcium ion concentration remaining in the eye reaction tank is 1 mg / L or more and 50 mg / L or less, and the fluoride ion concentration remaining in the first-stage reaction tank is 80 mg / L or less. A calcium compound is added to the first-stage reaction tank, and the calcium compound is further added to the second-stage reaction tank in an amount equal to or greater than the equivalent of fluoride ions remaining in the first-stage reaction tank, A method for treating fluorine-containing wastewater, wherein the ion concentration is less than 15 mg / L.
(2) In the treatment method of (1), the alkali added in the alkali sludge adjusting tank is calcium hydroxide, and the fluorine-containing water is also used as the calcium compound added in the first stage. Wastewater treatment method.
(3) In the processing method of (2), a second calcium compound addition means for adding a calcium compound to the first-stage reaction tank separately from the calcium compound added via the alkaline sludge adjusting tank. And a calcium compound is added to the alkali sludge adjusting tank based on the fluoride ion concentration of fluorine-containing water, and the second is based on the fluoride ion concentration and / or calcium ion concentration of the first stage reaction tank. A method for treating fluorine-containing water, characterized in that a calcium compound is added to the first-stage reaction tank from the calcium compound addition means.
(4) The method for treating fluorine-containing wastewater according to any one of (1) to (3), wherein the pH of the first-stage reaction vessel is adjusted to 3-6.

  According to the first invention of the present application, the calcium compound is added to the first stage reaction tank so that the calcium ion is less than the equivalent of fluoride ions and the calcium ions remain at 1 mg / L or more and 50 mg / L or less. Suppressing the production of fine calcium fluoride and roughing off fluorine, the calcium ion is added to the second-stage reaction tank in excess of the equivalent of the remaining fluoride ions to remove fluoride ions. Since it is insolubilized, the production | generation of fine calcium fluoride can be suppressed and the quality of treated water can be stabilized. Furthermore, by adding alkali to the returned sludge and dissolving the hydroxide of polyvalent metal such as aluminum hydroxide adsorbed on the calcium fluoride surface, the growth inhibition of calcium fluoride crystals in the reaction process is suppressed, Calcium fluoride particles can be grown greatly and sludge with a low water content can be generated.

  According to the second invention of the present application, the alkali added to the return sludge is calcium hydroxide, so that the alkali for adjusting the pH of the alkaline sludge adjusting tank, and the calcium source added in the first stage reaction tank, It is economical because it can be used for both.

  According to the third invention of the present application, the fluoride ion concentration and / or the calcium ion concentration in the first-stage reaction tank can be easily maintained in an appropriate range.

  According to the fourth aspect of the present invention, when the pH of the first-stage reaction vessel is adjusted to 3 to 6, the amount of calcium compound added can be reduced.

  The embodiment will be described below with reference to FIG.

  FIG. 1 is a schematic diagram of the processing flow of the present invention. 1 is a raw water inflow channel, 2 is a first reaction tank, 3 is a second reaction tank, 4 is a coagulation tank, 5 is a precipitation tank, 6 is an alkali sludge adjustment tank, and 7 is an alkali sludge adjusted sludge separated in the precipitation tank 5. A sludge return path for introduction into the tank 6, 8 an alkaline sludge supply path for supplying sludge from the alkaline sludge adjusting tank 6 to the first reaction tank 2, 9 an alkali injection pipe, and 10 and 11 calcium compound addition pipes , 12 and 13 are pH adjusting agent injection pipes, 14 is a flocculant injection pipe, 15 is a treated water discharge path, and 16 is a sludge discharge path.

  Raw water that is fluorine-containing wastewater flows into the first reaction tank 2 from the raw water inflow channel 1, where a calcium compound less than the equivalent of fluoride ions is added, and a pH adjuster is injected from the pH adjuster injection pipe 12. Then, the pH is adjusted to 3 to 11, more preferably 3 to 6, and calcium ions and fluoride ions react to precipitate calcium fluoride. If the pH is less than 3, the solubility of calcium fluoride is large, and the fluoride ion concentration cannot be reduced. If the pH is more than 11, precipitation of calcium carbonate becomes remarkable, resulting in a scale problem. In the case of pH 3 to 6, calcium fluoride can be precipitated with a small calcium addition amount of fluoride ions. At that time, return sludge described later serves as a nucleus, and calcium fluoride precipitates on the surface thereof. At the same time as the generation of calcium fluoride is suppressed, the calcium fluoride particles grow greatly.

  Note that the optimum pH of the first reaction tank 2 and the second reaction tank 3 varies depending on the purpose of treatment, and is optimum when the purpose is to prevent the inhibition of aluminum hydroxide and to obtain sludge having a lower water content. The pH is about 7 to 10, and the optimum pH is about 4 to 6.5 for the purpose of enhancing the cohesiveness of sludge and obtaining a higher quality of treated water.

According to the study by the present inventors, the concentration of fluoride ions flowing into the reaction tank and the concentration of calcium ions remaining in the reaction tank are determined by the solubility curve shown in FIG. 2 (the theoretical solubility product [Ca ²⁺ ] [F ^{− −} ] ² = 4.9 x 10 ^-11 mol ³ / l ³ ) and the region that falls between the supersolubility curves, the formation of fine calcium fluoride is suppressed and calcium fluoride is precipitated on the surface of the nucleus. However, although calcium fluoride particles grew greatly, it was found that fine calcium fluoride was produced when the concentration was higher than the oversolubility curve. As shown in FIG. 2, when processing fluoride ions to less than 15 mg / L, calcium ions must be present in an amount equal to or greater than that of fluoride ions, preferably 200 to 300 mg / L in excess of the equivalent. It is necessary to reduce fluoride ions to 80 mg / L or less in the first reaction tank 1.

  The amount of calcium compound added is such that the fluoride ion concentration in the first reaction tank is 80 mg / L or less and the residual calcium ion concentration is low. That is, even if it is less than the equivalent of fluoride ions, it is added so that calcium ions remain in the first reaction tank, that is, calcium ions remain 1 mg / L or more and 50 mg / L or less. If the calcium ion is less than 1 mg / L, rough removal of fluorine may not be possible, and if it exceeds 50 mg / L, production of fine calcium fluoride may not be suppressed.

  The calcium compound in the first reaction tank can be added together with the alkaline sludge via the alkaline sludge supply path 8 by using calcium hydroxide as the alkali supplied from the alkali injection pipe 9 to the alkaline sludge adjusting tank 6. preferable. Thus, by using calcium hydroxide as the alkali to be injected into the alkaline sludge adjusting tank 6, the alkali for adjusting the pH of the alkaline sludge adjusting tank and the calcium source added in the first-stage reaction tank are combined. This is economical.

  At this time, the addition of the calcium compound from the calcium compound addition pipe 10 can be omitted, but may be used in combination. When using together, calcium fluoride concentration is measured from the alkali injection pipe 9 through the alkaline sludge supply path 8 so that the fluoride ion concentration of the raw water is measured and becomes less than the equivalent of fluoride ions based on the measured value. Add. And it is preferable to measure the calcium ion concentration and / or fluoride ion concentration in the 1st reaction tank 2, and to supply the calcium shortage from the calcium compound addition piping 10 so that these measured values may become the range mentioned above. . By adding the calcium compound in this way, it is possible to easily set the addition amount of the calcium compound so as to be within the above range even when the fluoride ion concentration of the raw water or the concentration of the calcium hydroxide slurry fluctuates. Become.

  In addition, when the alkali supplied from the alkali injection pipe 9 to the alkali sludge adjusting tank 6 is an alkali other than a calcium compound such as sodium hydroxide, the calcium compound is supplied to the first reaction tank 2 by adding the calcium compound. This is done only by the pipe 10.

  Next, the reaction liquid in the first reaction tank 2 from which the fluorine has been roughly removed flows into the second reaction tank 3 without being separated into solid and liquid, where the calcium compound is added in excess of the equivalent of fluoride ions, Residual fluoride ions are insolubilized. At that time, it is preferable to adjust the pH between pH 5.8 and 8.6 in consideration of the release of the treated water. However, as described above, when the purpose is to prevent the inhibition of aluminum hydroxide and to obtain sludge having a lower water content, the pH is increased to about 7 to 10 to increase the cohesiveness of the sludge and to achieve a higher treatment. For the purpose of obtaining water quality, the pH is preferably about 4 to 6.5.

  The reaction solution in the second reaction tank 3 is preferably introduced into the aggregation tank 4. In the case where the formation of fine calcium fluoride could not be suppressed due to an incorrect setting of the amount of calcium compound added in the first reaction tank 2 or the second reaction tank 3, or in order to further improve the quality of the treated water, 4, it is preferable to add a polymer flocculant from the flocculant injection pipe 14. The polymer flocculant is not particularly limited as long as it can be used in the flocculation treatment of the suspended waste water, but a polyacrylic acid-based anionic polymer flocculant can be preferably used.

  Next, the agglomerated or unagglomerated reaction liquid is solid-liquid separated in the sedimentation tank 5, and the insolubilized slurry containing calcium fluoride is returned as sludge from the sludge return path 7 to the alkaline sludge adjusting tank 6 and the alkaline sludge. It returns to the 1st reaction tank 2 via the supply path 8, and calcium and a fluoride ion react and it becomes a nucleus which calcium fluoride precipitates. The amount of sludge returned is about 0.01 to 10 times the raw water flow rate, usually 0.05 to 0.5 times. If the fluoride concentration of the raw water is high, it is also 0.1 to 10 times for dilution. Is preferred.

  The raw water or the calcium compound added to the system contains a polyvalent metal such as aluminum as an impurity. This polyvalent metal is adsorbed on the surface of calcium fluoride and becomes a cause of inhibiting the growth of calcium fluoride crystals in the first reaction tank 2 and the like. In the present invention, the return sludge is mixed with alkali in the alkaline sludge adjusting tank 6 to dissolve the aluminum hydroxide and the like on the surface of calcium fluoride, thereby suppressing the growth inhibition of calcium fluoride crystals in the first reaction tank 2 and the like. To do. The pH of the alkaline sludge adjusting tank 6 is adjusted to pH 7 or higher, more preferably 9 or higher, in order to dissolve aluminum hydroxide. The upper limit of the pH of the alkaline sludge adjusting tank 6 is not particularly limited, but is usually about 13 is sufficient. As described above, it is preferable to use calcium hydroxide because the alkaline compound for pH adjustment can be used together as a calcium source and is economical. In addition, if the addition amount of the calcium hydroxide added through the alkaline sludge supply path 8 is controlled based on the fluoride ion concentration of the raw water as described above, the pH of the alkaline sludge adjusting tank 6 is about 9 to 13. Held in range. However, if it falls outside this range, it is necessary to adjust by adding a pH adjuster separately.

  The separated water is discharged as treated water from the treated water discharge passage 15. The separated water is discharged from the treated water discharge passage 15 as treated water, and excess sludge is discharged from the sludge discharge passage 16 to prevent accumulation of sludge in the system. The excess sludge may be discharged periodically, but a sludge concentration meter may be provided in the sludge return path 7 or the like, and sludge may be discharged when the concentration exceeds a predetermined concentration, or sedimentation. The interface of the precipitated sludge in the tank 5 may be detected, and the sludge may be discharged when the interface of the precipitated sludge becomes a predetermined level or more. The discharged sludge is preferably dehydrated by a sludge dehydrator after removing fine particles with a centrifugal cyclone or the like. The sludge dewatering machine is not particularly limited, and a filter press dewatering machine, a centrifugal dewatering machine or the like is used, but a centrifugal dewatering machine is preferable in that pore water between sludge particles can be efficiently separated. The fine particles separated by a centrifugal cyclone or the like are preferably returned to the alkaline sludge adjusting tank 6 and used as nuclei on which calcium fluoride is deposited.

  As this calcium compound, what liberates calcium ion may be sufficient and calcium chloride and calcium hydroxide are mentioned. As the pH adjuster, alkalis such as sodium hydroxide, potassium hydroxide and calcium hydroxide, and acids such as hydrochloric acid and sulfuric acid can be used. As the alkali, sodium hydroxide, potassium hydroxide, calcium hydroxide or the like can be used.

Example 1
The fluorine-containing wastewater in the treatment flow shown in FIG. 1 was treated.

  The raw water quality is as follows.

pH: 3.5-4.0, F: 150-500 mg / L, PO ₄ ^3- -P: 0.1-1 mg / L, SO ₄ ^2- : 1.9-52.3 mg / L, NO _{3 ^{- -N: 23.7~69.5mg / L, Cl}} -: 4.5~447mg / L, SiO 2: 0.9~4mg / L, TOC: 0.4~2.3mg / L.

The capacity of the first reaction tank 2 and the second reaction tank 3 is 20 L, the capacity of the coagulation tank 4 and the alkaline sludge adjusting tank 6 is 5 L, the capacity of the sedimentation tank 5 is 40 L, and the flow rate of the raw water is 60 L / Hr, The amount of returned sludge was 12 L / Hr. As the calcium compound, calcium hydroxide was used and added to the alkaline sludge adjusting tank 6, the first reaction tank 2, and the second reaction tank 3, respectively. The amount of calcium hydroxide added to each tank is such that the pH of the alkaline sludge adjusting tank 6 is pH 11.5 to 12.5, the fluoride ion concentration of the first reaction tank 2 is 30 to 50 mg / L, and the second reaction. It set so that the calcium ion concentration of a tank might be 200-300 mg / L. As the pH adjuster, 20% hydrochloric acid and 5% sodium hydroxide were used, and the pH of the first reaction tank 2 was adjusted to 5 ± 0.5, and the pH of the second reaction tank 3 was adjusted to 7 ± 0.5. To the aggregation tank 4, 3 mg / L of a polymer flocculant Cliff Rock (registered trademark of Kurita Kogyo Co., Ltd.) PA331 (polyacrylamide partial hydrolyzate) was added. The reaction liquid and treated water in the first and second reaction tanks are filtered through a membrane filter (pore diameter 0.45 μm), the filtrate is analyzed, and the precipitated sludge is dewatered at 2000 G by a centrifuge. The moisture content of was measured. These results are shown in Table 1. In addition, the 1st reaction tank calcium compound addition amount in Example 1 in Table 1 was shown by the sum of the addition amount of the calcium compound supplied from the alkali adjustment injection pipe 9 and the calcium compound addition pipe 10. .
Comparative Example 1
In Example 1, except that the sludge was directly returned to the first reaction tank 2 without going through the alkaline sludge adjusting tank 6, and the calcium compound was added to the first reaction tank 2 only from the calcium compound addition pipe 10. The same treatment as in Example 1 was performed. The results are shown in Table 1.
Comparative Example 2
In Comparative Example 1, the same treatment as in Comparative Example 1 was carried out except that calcium hydroxide was added to the second reaction tank 3 in excess of the fluoride ion equivalent without adding calcium hydroxide to the second reaction tank 3 alone. went. The results are shown in Table 1.

表１から、比較例１ではフッ素の除去効果は高いものの、生成汚泥の含水率が高いことがわかる。また、比較例２では高濃度のフッ素と高濃度のカルシウムが反応するために微細なフッ化カルシウム粒子が生成し、処理水側にリークするために、処理水の全フッ素濃度が高く、良好な処理水が得られないことが分る。

From Table 1, although the removal effect of fluorine is high in Comparative Example 1, it can be seen that the moisture content of the generated sludge is high. Further, in Comparative Example 2, fine calcium fluoride particles are generated because high concentration fluorine and high concentration calcium react and leak to the treated water side, so that the total fluorine concentration of treated water is high and good. It turns out that treated water cannot be obtained.

  In Comparative Example 1, the sludge composition was analyzed after the generated sludge was dried. The composition analysis of the entire sludge was measured by dissolving the sludge with acid and then measuring the soluble ion concentration, and the composition analysis of the sludge surface was measured by XPS. The analysis results are shown in Table 2.

表２より、返送汚泥をアルカリ汚泥調整槽でアルカリに調整しなかった比較例１の場合の汚泥では、汚泥全体に比べて汚泥表面のアルミニウム含有率が高く、フッ化カルシウム表面に水酸化アルミニウムが析出していることがわかる。

From Table 2, the sludge in Comparative Example 1 in which the returned sludge was not adjusted to alkali in the alkaline sludge adjusting tank had a higher aluminum content on the sludge surface than the entire sludge, and aluminum hydroxide on the calcium fluoride surface. It turns out that it has precipitated.

It is a systematic diagram which shows embodiment of the processing method of the fluorine-containing waste_water | drain of this invention. It is a graph showing the solubility of calcium fluoride. The vertical axis represents the calcium ion concentration, and the horizontal axis represents the fluoride ion concentration. The broken line is the solubility curve, and the solid line is the supersolubility curve. A dotted line is an equivalent line of calcium ions and fluoride ions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw water inflow path 2 1st reaction tank 3 2nd reaction tank 4 Coagulation tank 5 Precipitation tank 6 Alkali sludge adjustment tank 7 Sludge return path 8 Alkali sludge supply path 9 Alkali injection piping 10, 11 Calcium compound addition piping 12, 13 pH adjustment Agent injection pipe 14 Coagulant injection pipe 15 Treated water discharge path 16 Sludge discharge path

Claims (4)

Separated from a reaction step of adding calcium compounds to fluorine-containing wastewater to produce an insolubilized material containing calcium fluoride, and a separation step of separating solid and liquid into sludge containing the insolubilized product of calcium fluoride and separated water In the treatment method of fluorine-containing wastewater having a sludge return process of returning a part of sludge as return sludge to the reaction step,
The reaction step includes a two-stage reaction tank in series, the sludge return step includes an alkaline sludge adjusting tank for adding alkali to the return sludge, the return sludge is returned to the first-stage reaction tank, and fluorine Less than the equivalent of fluoride ions contained in the contained water, the calcium ion concentration remaining in the first stage reaction tank is 1 mg / L or more and 50 mg / L or less, and the fluorine ion remaining in the first stage reaction tank is The calcium compound is added to the first stage reaction tank so that the chloride ion concentration is 80 mg / L or less, and the calcium compound remains in the second stage reaction tank. A treatment method for fluorine-containing wastewater, wherein the treatment is performed so that the fluoride ion concentration is equal to or more than an equivalent of fluoride ions and the fluoride ion concentration is less than 15 mg / L.   2. The method for treating fluorine-containing water wastewater according to claim 1, wherein the alkali added in the alkali sludge adjusting tank is calcium hydroxide, and the calcium compound added in the first stage is also used.   In Claim 2, it has the 2nd calcium compound addition means which adds a calcium compound to the 1st stage reaction tank separately from the calcium compound added via the said alkaline sludge adjustment tank, fluorinated water Based on the fluoride ion concentration, a calcium compound is added to the alkaline sludge adjusting tank, and the first calcium compound adding means adds the first calcium ion concentration and / or calcium ion concentration to the first reaction tank. A method for treating fluorine-containing water, characterized in that a calcium compound is added to the reaction vessel at the stage.   The method for treating fluorine-containing wastewater according to any one of claims 1 to 3, wherein the pH of the first-stage reaction tank is adjusted to 3 to 6.

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