JPH05253578A - Treatment of fluorine-containing water - Google Patents

Abstract

PURPOSE:To stably recover high purity calcium fluoride by passing fluorine-containing water through a calcium carbonate packed bed as an ascending stream to remove fluorine and continuing the passage of water until the fluorine concentration or pH values of the inlet and outlet solutions of said bed become almost same. CONSTITUTION:PH meters or fluorine concn. meters 6, 7 are provided to the inlet and outlet lines of a first stage reaction tower 5 having a calcium carbonate packed bed and the treated solution of the first stage reaction tower 5 is supplied to a second stage reaction tower 8 having the same structure as the first stage reaction tower 5. When the pH values or fluorine concns. of the inlet and outlet solutions of the first stage reaction tower 5 almost coincide with each other, the operation of a pump 4 is stopped to stop the supply of water and the packing material in the first stage reaction tower 5 is drawn out to recover calcium fluoride. The treated solution 9 of the second stage reaction tower 8 is discharged as treated water while the treatment effect thereof is confirmed by a pH meter or fluorine concn. meter 10. After the packing material of the first stage reaction tower 5 is drawn out, said tank 5 is packed with calcium carbonate and water to be treated is passed in the direction of reaction tower reaction tower 5 according to a merry-go-round system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a method for treating fluorine-containing water. More specifically, the present invention relates to a method for treating fluorine-containing water for efficiently recovering fluorine as high-purity calcium fluoride from waste liquid of a fluorine-based etching agent.

[0002]

2. Description of the Related Art In recent years, semiconductor manufacturing fields and related fields,
Alternatively, a large amount of etching agents are used in the field of surface treatment of various metal materials, single crystal materials, optical system materials, etc., and as the etching agents, hydrogen fluoride and hydrogen fluoride are mainly used. An etching agent whose main component is ammonium fluoride is used. An etching agent containing hydrogen fluoride as a main component is usually used in a large amount because it contains fluorine as HF in an amount of about 0.9% by weight, while it contains hydrogen fluoride and ammonium fluoride as main components. Etching agent (buffered hydrofluoric acid)
Although it is used in a small amount, since it usually contains about 7% by weight of fluorine as HF, these etching agents become a high-concentration fluorine-containing waste liquid when transferred to the wastewater system. On the other hand, during or after the etching, the materials treated with these etching agents are washed with a large amount of washing water, so that a large amount of low-concentration fluorine-containing waste liquid is discharged from the washing step. Conventionally, these high-concentration fluorine-containing waste liquids and low-concentration fluorine-containing waste liquids are mixed and collectively processed. For the treatment of this fluorine-containing waste liquid,
Generally, a method is used in which a calcium compound such as calcium hydroxide [Ca (OH) ₂ ] is added and precipitated as calcium fluoride (CaF ₂ ) to be removed. However, in such a method of removing precipitates as calcium fluoride, SiO ₂ contained in the fluorine-containing water is also
Since most of the calcium fluoride is insolubilized and precipitates, the recovered calcium fluoride has a low purity, and there is a problem that the reuse value is unavoidably reduced. On the other hand, a fluorine treatment method using calcium carbonate is known, and powdery or granular calcium carbonate is used in this treatment method. In the case of powdery calcium carbonate, since it is simply used as a neutralizing agent, it is added in excess, so unreacted calcium carbonate remains in the precipitate, and the calcium fluoride purity of the precipitate is low. I cannot help becoming. Also, when granular calcium carbonate is used, there is no means for predicting the conversion rate of calcium carbonate particles to calcium fluoride, and the purity of calcium fluoride in the recovered product is unstable.

[0003]

DISCLOSURE OF THE INVENTION The present invention overcomes the drawbacks of the conventional method for treating fluorine-containing water,
The object of the present invention is to provide a method for stably recovering high-purity calcium fluoride in a method for treating fluorine-containing water with calcium carbonate.

[0004]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that when fluorine-containing water is treated by passing water through a calcium carbonate packed bed in an upward flow, Approximately 100 is obtained by performing water treatment until the fluorine concentration or pH of the inlet liquid and the outlet liquid of the packed bed becomes approximately the same.
It has been found that calcium fluoride with a purity close to 100% can be recovered, and the present invention has been completed based on this finding.
That is, the present invention is to pass the fluorine-containing water through the calcium carbonate packed bed in an upward flow to remove the fluorine in the fluorine-containing water and to recover the calcium fluoride, the inlet liquid of the calcium carbonate packed layer. The present invention provides a method for treating fluorine-containing water, characterized in that water treatment is carried out until the fluorine concentration or pH of the outlet liquid becomes substantially the same.

The present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is an explanatory diagram of an example for carrying out the method of the present invention. First, fluorine-containing water (processing liquid) 1 such as etching wastewater is No. 1 processing liquid tank 2 or No. 2
It is transferred to the liquid tank 3 to be treated. This tank is installed for homogenization and stabilization of the liquid to be treated, and it is convenient to have two or more tanks. The liquid to be treated is transferred to, for example, No. 1 tank 2, and when it becomes full, it is mixed and homogenized, and the first stage filled with granular calcium carbonate having a diameter of about 0.1 to 0.5 mm by a pump 4. Supply to the reaction tower 5. On the other hand, the liquid to be newly discharged is put in the No. 2 tank 3 and stored.
It is desirable that the volumes of the liquid tanks 2 and 3 to be treated be at least three times the volume of the reaction tower.

The liquid to be treated is supplied by the pump 4 to the first-stage reaction tower 5 in an upward flow. The etching wastewater or the like usually contains hydrogen fluoride or hydrogen fluoride and ammonium fluoride, and since carbon dioxide gas is generated by the hydrogen fluoride, if the liquid to be treated is supplied in a downward flow. ,
The gas flow causes a water drainage phenomenon in the column, which causes an unbalanced flow of the feed liquid, resulting in an unfavorable situation in which the reaction is hindered. In the present invention, the supply of the liquid to be treated is
It is desirable to intermittently perform by the pump 4. Due to this intermittent flow of water, in combination with the action of carbon dioxide gas generated as described above, the lumps of calcium carbonate can be effectively loosened, and calcium carbonate is efficiently converted to calcium fluoride. .. The flow rate and time of operation-stop are influenced by the fluorine concentration in the liquid to be treated, the particle size and filling height of the filled calcium carbonate, the temperature of the liquid to be treated, etc. Good.

In the present invention, when treating a liquid to be treated having an extremely low hydrogen fluoride content, if desired,
Air may be bubbled into the reaction column continuously or intermittently, or an acid such as hydrogen chloride may be added to the liquid to be treated. The pH of the liquid to be treated is preferably in the range of 4 to 6,
If necessary, alkali or acid may be added to adjust the pH. The entire amount of the treatment liquid discharged from the first-stage reaction tower 5 flows into the second-stage reaction tower 8, and the gas generated in the first-stage reaction tower 5 is not separated, and the second-stage reaction tower 5 is not separated. It is introduced into the reaction tower 8.

In the present invention, since it is necessary to monitor the pH or the fluorine concentration of the inlet liquid and the outlet liquid of the calcium carbonate packed bed, it is necessary to monitor the pH at appropriate places in the inlet and outlet lines of the first stage reaction tower 5. And a fluorine concentration meter 6 and 7 are provided. The treatment liquid of the first-stage reaction tower 5 is supplied to the second-stage reaction tower 8, but if the pH and the fluorine concentration of the inlet liquid and the outlet liquid of the first-stage reaction tower are almost the same, stop the operation of the pump 4. The water flow is stopped, and the packing material in the first reaction column is extracted to recover calcium fluoride. At this time, it is advantageous to drain the liquid to be treated adhering to the filling material, to wash it, and then to withdraw it, because the purity of calcium fluoride is improved and it becomes a countermeasure against danger during transfer. The treatment effect of the treatment liquid 9 in the second-stage reaction tower 8 is confirmed by a pH meter and a fluorine concentration meter 10, and the treated liquid 9 is discharged as treated water.

After the pH or fluorine concentration of the inlet liquid and the outlet liquid of the first-stage reaction tower 5 are almost the same, and after the filler of the first-stage reaction tower 5 is extracted, new calcium carbonate is charged. In that case, the water to be treated is passed through the merry-go-round system in the direction of the reaction tower 8 → the reaction tower 5. In this case, the pH
The role of the meter and fluorine concentration meter will change accordingly. Further, in the method of the present invention, from the fluorine concentration at the inlet and the outlet of the reaction column, by calculating the amount of fluorine removed, it is possible to know the conversion rate of the filler in the column to calcium fluoride, As a result, the replacement date of the filler can be predicted. By such a treatment, it is possible to recover calcium fluoride having a purity of almost 100%.

[0010]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

Example 1 100 ml of granular calcium carbonate having a diameter of 0.25 mm was packed in a column having an inner diameter of 30 mm. These two columns are connected in series, and the solution to be treated is SV1hr in the first column.
Water was passed at a flow rate of ^-1 , and the treatment liquid was extracted from the second column. As the liquid to be treated, NH ₄ F, HF and H ₂ SiF ₆ were mixed and added to pure water to obtain a HF / total F molar ratio of 0.13, a fluorine concentration of 22 to 25 g · F / liter, and a SiO ₂ concentration of 0 to 2
A g / l product was prepared and used. After passing water for 48 hours, stop the operation, measure the fluorine concentration and pH of the column inlet liquid, the first-stage column outlet liquid, and the second-stage column outlet liquid, extract the packing of each column after washing with water, and fluorinate. The purity of calcium was measured. The purity of calcium fluoride was determined according to the Winrad / Winter method of JIS K-1468. The results are shown in Table 1.

[0012]

[Table 1]

It can be seen from Table 1 that the purity of calcium fluoride becomes close to 100% when the fluorine concentration of the liquid to be treated and that of the liquid to be treated in the first column are almost the same. The same applies to pH. If the removal rate of fluorine in the first-stage column is high (unsaturated), a large amount of NH ₄ CO ₃ is contained in the treatment liquid and the pH rises. However, below pH 10, fluorine is removed in the second column without adjusting the pH.
The relationship between the calcium fluoride purity and the fluorine removal rate and the relationship between the calcium fluoride purity and the pH ratio (treatment solution pH / treatment pH) are shown in FIGS. 1 and 2, respectively.

[0014]

According to the method for treating fluorine-containing water of the present invention, since calcium fluoride having a purity of nearly 100% is recovered, recycling can be facilitated. Moreover, the frequency of replacement of the filler can be predicted, and the planned operation can be performed.

[Brief description of drawings]

FIG. 1 is an illustration of an example for carrying out the method of the present invention.

FIG. 2 is a graph showing the relationship between the calcium fluoride purity and the fluorine removal rate in the examples.

FIG. 3 is a graph showing the relationship between calcium fluoride purity and pH ratio (treatment liquid pH / treatment liquid pH) in Examples.

[Explanation of symbols]

 1 treated liquid 2 No. 1 treated liquid tank 3 No. 2 treated liquid tank 4 pump 5 1st stage reaction tower 6 pH meter and / or fluorine concentration meter 7 pH meter and / or fluorine concentration meter 8 2nd stage Reaction tower 9 Treatment liquid 10 pH meter and / or fluorine concentration meter 11 Flow meter

Claims (1)

[Claims] 1. When the fluorine-containing water is passed through the calcium carbonate packed bed in an upward flow to remove fluorine in the fluorine-containing water and to recover calcium fluoride, an inlet liquid of the calcium carbonate packed layer is used. Fluorine concentration in outlet liquid or
A method for treating fluorine-containing water, characterized in that water treatment is carried out until the pH becomes almost the same.