JP3266309B2 - Treatment method for acidic fluorine-containing water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved method for treating acidic fluorine-containing water. More specifically,
The present invention relates to a method for recovering fluorine ions in acidic fluorine-containing water discharged from, for example, a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In recent years, semiconductor manufacturing fields and related fields,
In the field of surface treatment of various metal materials, single crystal materials, etc., a large amount of etchant is used, mainly hydrogen fluoride or a mixed solution of ammonium fluoride and hydrogen fluoride, and a mixed solution containing acetic acid, nitric acid, etc. A variety of miscellaneous compositions are discharged as waste liquid. When this waste liquid is contact-reacted with calcium carbonate to form calcium fluoride, and when fluorine is insolubilized and fixed on the surface of the filter medium, the reaction state changes depending on the composition and concentration of the undiluted solution, especially when an acid such as nitric acid is contained. As a result, a phenomenon occurs in which the filter medium collapses and the surface of the filter medium flows out into the treated water, resulting in emulsified treated water.
As a result, calcium carbonate is converted into calcium fluoride, and finally calcium fluoride having a high purity and a low water content is produced. For example, even if it is intended to reuse this as a raw material such as HF, Fluorine recovery decreases due to filter media collapse. In addition, a separate coagulation sedimentation process is required to recover the emulsified calcium fluoride that has flowed out, and even if collected by coagulation sedimentation, only low-grade, high-moisture-content aggregates are obtained, and fluorine is reused. Was inappropriate. This phenomenon is a defect that appears particularly in HF-based etchant waste liquid.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a method of recovering calcium fluoride by contacting fluorine in an etchant waste liquid with a calcium filler to prevent collapse of the filter medium and to reduce the water content of the filter medium from low. An object of the present invention is to recover calcium fluoride and enable reuse such as hydrogen fluoride production.

[0004]

Means for Solving the Problems The inventors of the present invention consider that it is important to prevent the disintegration of the filter agent in order to achieve the above object, and fix fluorine as calcium fluoride from acidic fluorine-rich wastewater. For this reason, it has been found that if an alkaline agent is added to raw water in advance and then water is passed through a calcium carbonate filler, collapse of the filter medium can be prevented, and based on this finding, the present invention has been completed.

That is, the present invention provides (1) a method of removing acidic fluorine-containing water by passing acidic fluorine-containing water in an etchant waste liquid through a calcium carbonate-filled tank to remove fluorine as calcium fluoride. A method for treating acidic fluorine-containing water, comprising adding an ammonia-based or caustic-based alkali agent in an amount equal to or more than the equivalent of an acid other than the acid to the acidic fluorine-containing water in advance to remove fluorine as calcium fluoride. ,
And (2) in a method of removing acidic fluorine-containing water from calcium fluoride by passing acidic fluorine-containing water through a calcium carbonate-filled tank, wherein an alkali having an amount equal to or more than the equivalent of an acid other than hydrofluoric acid contained in the acidic fluorine-containing water. A method of pre-adding an agent to the acidic fluorine-containing water, wherein the whole or a part of the alkaline agent is an ammonia-containing gas recovered from a filling tank effluent. , Is provided. The type of acid in the acidic fluorine-containing water can be analyzed or determined from the type of acid used in the factory, but typically includes hydrofluoric acid, nitric acid and silicic acid.

A process flow according to one embodiment of the present invention will be described with reference to the drawings. First, raw water containing fluorine enters the raw water tank 1,
Calcium carbonate packed tower 2, 2 '
Removes fluorine. The fluorine-containing water targeted by the present invention contains an acid such as nitric acid or silicic acid, and is usually
It has a pH of about 1 to 4. In the present invention, such an acidic fluorine-containing water is neutralized to a pH of about 4.5 to 8.5 by adding an alkaline agent before passing the water through a calcium carbonate packed tower. That is, in the raw water tank 1, an alkali agent having an equivalent amount or more of all acids other than hydrofluoric acid in the raw water is supplied through the supply pipe 10. Examples of such an alkaline agent include ammonia gas, ammonium hydroxide, sodium hydroxide, and potassium hydroxide. It is desirable to provide a stirrer or the like to increase the contact between the alkaline agent and the raw water (not shown).

Next, the water thus neutralized is passed through the raw water pump 4 to the calcium carbonate packed tower 2. Either an upward flow or a downward flow may be applied to the packed tower, but gas such as CO ₂ may be generated by the reaction with calcium carbonate, preventing water drainage in the tower and mixing and fluidizing the filler. For this purpose, upward flow water is more desirable. Although the number of towers is two in the drawing, one or two or more towers can be used in a multistage process. The calcium carbonate layer used in the present invention is not particularly limited as long as it has a structure in which the calcium carbonate layer comes into contact with a liquid. For example, a slurry type precipitation tank method using fine calcium carbonate instead of a packed tower is used. The present invention can be applied to a single-stage or multi-stage calcium carbonate-filled tank of a reaction tank and a precipitation tank. The particle size of the calcium carbonate particles to be filled in the calcium carbonate tower is 0.3.
Calcium carbonate particles of 1-0.5 mm are preferred. The water flow rate is set to SV 0.1 to 5 hr ^-1 , preferably about SV ¹ to 3 hr ^-1 .

[0008] The treated water from which fluorine has been removed as calcium fluoride, when an ammonia-based compound is added as an alkaline agent, is sent to a treated water tank 3 as necessary to remove the ammonia component contained in the water. Specifically, the treated water from which fluorine has been removed in the calcium carbonate packed tower 2 is sent to the treated water tank 3 and aerated by a blower 8 or the like. Ammonia in the treated water is dissolved in the form of NH ₄ HCO ₃ or (NH ₄ ) ₂ CO ₃ , so if it is aerated with a gas such as air, it can be easily volatilized as NH ₃ gas. In addition, a filler such as a plastic material or a discharge tower having a plurality of trays can be suitably used. Further, a means for increasing the aeration efficiency by providing a heating or decompression means may be used. In addition to the air aeration exemplified here, an acid stripping method or a method using an adsorbent such as zeolite can be appropriately employed depending on the treatment amount.

The treated water thus removed together with the fluorine ammonia is discharged to the outside of the system through the pipe 5 '. If necessary, the treated water is subjected to a purification treatment of ammonia, fluorine, BOD or the like, and is discharged or used as process water. Reuse. In the present invention, when an ammonia-based compound is used as the alkali agent, deammonia is preferably performed in the treatment water tank 3, and thus, in the above-described alkali agent addition step, the ammonia gas thus collected is replaced with new ammonia. Alternatively, it can be used together with new ammonia or ammonia water discharged from another process. Hereinafter, an example in which an ammonia component is separated by air aeration in a treatment water tank will be described. Exhaust gas containing ammonia gas obtained by aerating the treated water tank 3 with a blower 8 is ventilated from the bottom of the raw water tank 1 through an ammonia vent pipe 9. After the gas discharged from the raw water tank 1 is circulated a certain number of times, if the gas still contains ammonia, it is sent to the gas absorption tower 6. The gas absorbent 6 is supplied with a gas absorbent from a gas absorbent tank 7. As the absorbent, an acid such as sulfuric acid, hydrochloric acid, or nitric acid is usually used, but a part of raw water can be sprayed from the top of the tower and used as the absorbent.

The amount of ammonia gas blown into the raw water tank is equal to or more than the total amount of nitric acid other than hydrofluoric acid and silicic acid (H ₂ SiO ₃ ) contained in the raw water. However, it is not always necessary to neutralize the raw water only with this ammonia, and ammonia water, caustic soda, caustic potash, etc. separately prepared as an alkaline agent can be used alone or in combination with the aerated exhaust gas from the treated water tank.
Also in this case, ammonia water is optimal from the viewpoint of the operability of the treatment process. As an alkali agent for neutralization of the raw water tank 1, Ca
It is not preferable to use a calcium agent such as (OH) ₂ , CaO, CaCO ₃ , because it combines with fluorine in raw water to form fine calcium fluoride and SiO ₂ . Also, caustic soda and caustic potash are effective to prevent filter media collapse if added to an acid such as free nitric acid other than hydrofluoric acid that coexists, but if insufficient, treated water will be emulsified. It is difficult to control the proper addition because the fluorine removal property is deteriorated.

[0011]

EXAMPLES The present invention will be described in more detail with reference to Examples. Example 1 and Comparative Example reagents HF, using H ₂ SiO _3, HNO _3, was total fluorine concentration 10 gf / l, fluorine-containing raw water HNO ₃ concentration 3.0 g / l of (pH 3.7) was prepared. In this raw water, a nitric acid concentration of 0.048 equivalent / l, an H ₂ SiO ₃ concentration of 0.088 equivalent, and an HF concentration of 0.263 equivalent / l are present. Ammonia-containing gas is added to this raw water at a flow rate of about 2 liters / min.
Blowing was performed for 20 hours to absorb the amount indicated in Table 1. The ammonia gas-absorbing raw water was passed at a space velocity of 2 hr ^-1 through a column filled with 100 ml of calcium carbonate particles having an average particle diameter of 0.32 mm through a 30 mm-diameter column. Table 1 shows the results of the analysis and analysis of the treated water for 3 hours after the start of water passage. The acid equivalent ratio in the table indicates the amount of ammonia added to the acid in equivalent. Experiment No. 1 shows the case where ammonia was not added, and Experiment Nos. 2 to 4 show the results when ammonia was added.

[0012]

[Table 1]

According to the results of the examples, in Experiment No. 1 in which ammonia was not added, the calcium carbonate particles collapsed and flowed out into the treated water as a suspended solid (SS). According to Experiment No. 2, the amount of ammonia used is not sufficient to just neutralize nitric acid. Experiment No. 4 shows that the objective was sufficiently achieved, indicating that the amount of ammonin gas is unnecessary up to an equivalent amount for neutralizing all acids. In experiment number 4,
If more than the total of HNO ₃ and H ₂ SiO ₃ is added, 80% or more of the amount of suspended solids is suppressed as compared with the case of no addition. The component of the suspended substance of Experiment No. 4 was mainly SiO ₂ .
When the treated water of Experiment No. 4 was once again passed through a calcium carbonate packed tower of the same scale, treated water having a pH of 7.3, a fluorine concentration of 4.5 mg / l, and a suspended substance of 2000 mg / l was obtained. It can be seen that this can be adequately dealt with when the concentration of fluorine in the treated water is increased by increasing the number of the packed columns of calcium carbonate. Example 2 The present invention was carried out for a pH 3.2 electronic component etching process wastewater containing 8790 mg / liter of fluorine, 6900 mg / liter of nitric acid, and 2300 mg / liter of silicic acid (as SiO ₂ ). After adding sodium hydroxide in the amount shown in Table 2 with respect to the total amount of nitric acid and silicic acid in the wastewater, water was passed through the packed bed of calcium carbonate in the same manner as in Example 1. The results are shown in Table 2. From this, when the addition amount of sodium hydroxide is less than 1 equivalent to the total amount of nitric acid and silicic acid, a leak of the filter medium is observed,
It turns out that it is not recognized at more than 1 equivalent.

[0014]

[Table 2]

[0015]

The treatment method of the present invention is advantageous in that fine CaF ₂ fine particles do not flow into the treated water, the recovery rate of CaF ₂ is high, and there is no fine turbidity leak into the treated water. The advantage of eliminating the need for a solid-liquid separator, preferably in the case of adding ammonia, the added ammonia is circulated, so the advantage of low chemical cost and the circulating use make it easy to purify as reused water without increasing salt content. There are advantages.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a flow of an example of one embodiment for carrying out the method of the present invention.

[Description of Signs] 1 Raw water tank 2 Calcium carbonate filling tower 2 'Calcium carbonate filling tower 3 Treatment water tank 4 Pump 5 Treatment water pipe 5' Discharge water pipe 6 Gas absorption tower 7 Gas absorbent tank 8 Blower 9 Ammonia gas vent pipe 10 Supply pipe

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadashi Takadoi 3-4-7 Nishi-Shinjuku, Shinjuku-ku, Tokyo Inside Kurita Water Industries Co., Ltd. (72) Inventor Masahiro Miki 1-23 Teidukayama, Abeno-ku, Osaka-shi, Osaka No. 14-521 (72) Inventor Toshiro Fukudome 68-335 Kobuki, Chihayaakasaka-mura, Minamikawachi-gun, Osaka Prefecture 72-335 (72) Inventor Matagoro Maeno 2-42-6, Komeidai, Izumi-shi, Osaka (56) References JP JP-A-53-125993 (JP, A) JP-A-54-7762 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C02F 1/58 CDG

Claims (2)

(57) [Claims] 1. A method for removing fluorine as calcium fluoride by passing acidic fluorine-containing water of an etching agent waste liquid through a calcium carbonate-filled tank, wherein an amount of an acid other than hydrofluoric acid contained in the acidic fluorine-containing water is equal to or more than an equivalent. A method for treating acidic fluorine-containing water, characterized in that an amount of an ammonia-based or caustic-based alkaline agent is previously added to the acidic fluorine-containing water to remove fluorine as calcium fluoride. 2. A method for removing fluorine as calcium fluoride by passing acidic fluorine-containing water through a calcium carbonate-filled tank, wherein an alkali having an amount of at least an equivalent of an acid other than hydrofluoric acid contained in the acidic fluorine-containing water. A method of pre-adding an agent to the acidic fluorine-containing water, wherein the whole or a part of the alkaline agent is an ammonia-containing gas recovered from a filling tank effluent. .