JP4650384B2 - Treatment method for fluorine-containing wastewater - Google Patents

Description

The present invention relates to a method of solid-liquid separation of fluorine by adding calcium chloride to the waste water containing fluorine as calcium fluoride insoluble (CaF _2), in particular, effectively acts to calcium chloride to fluorine in the waste water The present invention relates to a method for treating fluorine-containing wastewater that obtains high-quality treated water and at the same time generates sludge having a low moisture content.

  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). Moreover, since the reaction of calcium hydroxide and hydrofluoric acid under alkalinity is slow, while maintaining the pH acidic or neutral, 0.3 to 0.5 equivalents of calcium hydroxide is added to fluorine ions, The insoluble matter to produce | generate 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 fluorine ions, and fine calcium fluoride is precipitated, which is added to the treated water. There was a problem that the quality of treated water was not stable due to leakage. Further, in order to obtain treated water of high quality, if the generated and wait fine calcium fluoride you coagulation precipitation treatment by coagulant such as a polymer, a high water content of the resulting sludge, many waste There was a problem. In addition, in the method of adding 0.3 to 0.5 equivalents of calcium hydroxide to fluorine ions, separating the insoluble matter to be produced, and separating the insoluble matter to be produced, the method is separated from the addition step at least three times. It had to be repeated with the process, and it was necessary to repeat the treatment water fluorine concentration to 15 mg / L or less 4 to 5 times.

In the present invention, in order to obtain a stable treated water quality in a small number of steps and at the same time to produce sludge having a low water content, if the fluorine ions are first roughed, then the equivalent to or more than the remaining fluoride ions. It found that the generation of fine calcium fluoride be added calcium chloride can be suppressed, leading to solve the problems of the prior art described above. That is, the present onset bright, solid-liquid in the reaction step by the addition of calcium chloride to a fluorine-containing waste water to produce insoluble substance containing calcium fluoride, a sludge containing insolubles of the resulting calcium fluoride and separated water In the method for treating fluorine-containing wastewater, comprising a separation step of separating, and a sludge return step of returning the separated sludge as return sludge to the reaction step, the reaction step is a reaction of pH 5 ± 0.5 in two stages in series. includes a bath, the calcium chloride be less than equivalent amount of fluoride ion in the reaction vessel of the first stage, calcium ions are added to the residue 1 mg / L or higher 50 mg / L or less, a fluoride ion 80mg / L or less, and the calcium compound in the second reaction tank is equal to or more than the equivalent of fluoride ions remaining in the first reaction tank, and the fluoride ion concentration is 15 mg. It is a method of treating fluorine-containing waste water which comprises adding as less than L.

The calcium chloride in the reaction vessel of the first stage, a less than equivalent amount of fluoride ions, since calcium ions are added to the residue 1 mg / L or higher 50 mg / L or less, the generation of fine calcium fluoride and suppression can rough fluorine, the second stage reaction vessel, since the insoluble excessively fluoride ions by addition of calcium chloride to a more equivalents of fluoride ions remaining, fine fluoride The generation of calcium fluoride can be suppressed, the quality of treated water is stabilized, and at the same time, the calcium fluoride particles are grown to a large size, so that sludge having a low water content is generated. Further, when the pH of the first-stage reaction tank 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 path, 2 is a first reaction tank, 3 is a second reaction tank, 4 is a coagulation tank, 5 is a precipitation tank, 6 is a sludge return path, 7 is a calcium chloride addition pipe, and 8 is a pH adjuster injection pipe. It is.

Fluorine-containing a waste water raw water flows from the water inlet line 1 into the first reaction vessel, where together with calcium chloride of less than equivalent is added of fluoride ions, the pH pH adjusting agent is injected 3-11 More preferably, it is adjusted to 3 to 6, and calcium fluoride and fluoride ion 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 3-6, calcium fluoride can be precipitated with a small calcium chloride addition amount of fluoride ions. At that time, return sludge described later serves as a nucleus, and calcium fluoride precipitates on the surface. The generation of calcium fluoride is suppressed and at the same time, calcium fluoride particles grow greatly.

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. First, it is necessary to reduce the fluoride ion to 80 mg / L or less.

The addition amount of calcium chloride is fluoride ion concentration in the first reaction vessel is less 80 mg / L, and the residual calcium ions concentration is added to a low concentration. 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.

Next the first reaction liquid in the reaction vessel 2 which fluorine is rough, without solid-liquid separation, flow into the second reaction vessel 3, where excessive calcium chloride was added to the above equivalent of fluoride ion To insolubilize the remaining fluoride ions. 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.

The reaction solution in the second reaction tank 3 is preferably introduced into the aggregation tank 4. In addition quantity setting mistake or the like of calcium chloride in the first reaction tank 2 and the second reaction tank 3, and if it can not suppress the formation of fine calcium fluoride, for further improvement of the treated water quality, aggregation In the agent tank 4, a polymer flocculant can be added (not shown).

  Next, the agglomerated or non-aggregated reaction liquid is solid-liquid separated in the precipitation tank 5, and the insolubilized slurry containing calcium fluoride is returned to the first reaction tank 2 from the sludge return path 6 as return sludge. Calcium fluoride precipitates as a result of the reaction between calcium and fluoride ions. The amount of sludge returned is about 0.01 to 10 times the raw water flow rate, usually 0.05 to 0.5 times, and when the fluoride concentration of the raw water is high, it is also 0.1 to 10 times for dilution. Is preferred. The separated water is discharged as treated water from the treated water discharge passage 9.

  As a 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.

Example 1
The fluorine-containing wastewater in the treatment flow shown in FIG. 1 was treated.
The raw water quality is as follows.
_{^{pH: 3.4, F: 131mg /}} L, PO 4 3- -P: 1mg / L, SO 4 2-: 21.3mg / L, SiO 2: 39mg / L, TOC: 3.3mg / L.

The capacity of the first reaction tank 2, the second reaction tank 3 and the coagulation tank 4 is 1L each, the capacity of the sedimentation tank 5 is 15L, the flow rate of the raw water is 4L / Hr, and the amount of returned sludge is 0.1L / Hr. did. As the calcium compound, calcium chloride was used and added to the first reaction tank 2 and the second reaction tank 3, respectively. 0.1N sodium hydroxide was used for pH adjustment, and the pH of the first reaction tank 2 and the second reaction tank was adjusted to 5 ± 0.5. The coagulation tank 4 was not a polymer flocculant, but a mere residence tank. At the start of the treatment, calcium fluoride having an average particle size of 5 μm was added to the first reaction tank 2 as a seed crystal. The reaction liquid and treated water in the first and second reaction tanks were filtered with a membrane filter (pore diameter 0.45 μm), and the filtrate was analyzed. The results are shown in Table 1. The amount of calcium chloride added is also shown in Table 1. Further, the precipitated sludge was dehydrated at 2000 G with a centrifuge and the water content was measured and shown in Table 1.
Comparative Example 1
In Example 1, the treatment was performed in the same manner as in Example 1 except that calcium chloride was added to the second reaction tank in excess of the fluoride ion equivalent without adding calcium chloride to the second reaction tank. Table 1 shows the quality of the treated water.
Comparative Example 2
In Comparative Example 1, the same treatment as in Comparative Example 1 was performed except that 3 mg / L of the polymer flocculant Cliff Rock (registered trademark of Kurita Kogyo Co., Ltd.) PA331 (polyacrylamide partial hydrolyzate) was added to the coagulation tank 4. It was. Table 1 shows the quality of the treated water. Further, the precipitated sludge was dehydrated at 2000 G with a centrifuge and the water content was measured and shown in Table 1.

表１から、比較例１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。比較例２では、微細なフッ化カルシウム粒子を高分子凝集剤で凝集沈殿除去するために良好な処理水が得られている。しかし、微細粒子を凝集させた汚泥は水切れが悪いため、汚泥発生量が多くなることが分る。実施例１では、カルシウム総添加量は同じでも、第１反応槽でフッ素を粗取りしているので、微細なフッ化カルシウム粒子の生成を抑制し、種晶表面にフッ化カルシウムを析出させているために、良好な処理水質が得られていると思われる。

From Table 1, in Comparative Example 1, 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, It turns out that good treated water cannot be obtained. In Comparative Example 2, good treated water is obtained because fine calcium fluoride particles are coagulated and removed with a polymer flocculant. However, it can be seen that the sludge in which the fine particles are aggregated is poor in water drainage, so that the amount of sludge generated increases. In Example 1, although the total amount of calcium added is the same, since the fluorine is roughly removed in the first reaction tank, the production of fine calcium fluoride particles is suppressed, and calcium fluoride is precipitated on the seed crystal surface. Therefore, it seems that good treated water quality is obtained.

It is a systematic diagram which shows embodiment of the processing method of the fluorine-containing waste_water | drain of this invention. Is a graph showing the soluble Kaido calcium fluoride. The vertical axis represents the calcium 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 Sedimentation tank 6 Sludge return path 7 Calcium addition pipe 8 pH adjuster injection pipe 9 Treated water discharge path

Claims (1)

A reaction step of adding the calcium chloride to fluorine-containing waste water to produce insoluble substance containing calcium fluoride, a separation step of solid-liquid separation and the separated water sludge containing insolubles of the resulting calcium fluoride, separated In the method for treating fluorine-containing wastewater including the sludge returning step of returning the sludge as returned sludge to the reaction step, the reaction step includes a series of two-stage reaction tanks having a pH of 5 ± 0.5 , and the first step the calcium chloride in the reaction vessel of the eye is less than equivalent amount of fluoride ions, added as calcium ions remaining 1 mg / L or higher 50 mg / L or less, the fluoride ions remaining not more than 80 mg / L, calcium chloride in the second stage reaction vessel, be more than equivalent amount of fluoride ions remaining in the reaction vessel of the first stage, so that the fluoride ion concentration is less than 15 mg / L A method for treating fluorine-containing wastewater, which is characterized by being added to the above.

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