JPH06304572A - Treatment of ammonium fluoride containing aqueous solution - Google Patents

Abstract

PURPOSE:To efficiently decompose and remove ammonium ion by adding a nitrite in a heating condition and under the coexistence of a solvent into an ammonium fluoride containing aq. solution of a waste solution containing an etchant used in semiconductor production field. CONSTITUTION:The ammonium fluoride containing aq. solution is treated in the heating condition and under the coexistence of the solvent by using the nitrite. A catalyst carrying platinum, palladium, ruthenium, rhodium, silver, copper or the like on a carrier such as alumina, zirconia, titania, active carbon is used. Ammonium ion is decomposed and removed by passing the ammonium fluoride containing aq. solution through a column, in which the catalyst is packed together with the nitrite of alkali metal in the heating condition to induce reaction. Sodium nitrite, potassium nitrite or the like is used as the nitrite an the quantity to be used is selected in the range of 1-1.2 times ammonium ion in terms of mol.

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 ammonium fluoride-containing water. More specifically, the present invention relates to a method for efficiently decomposing and removing ammonium ions in ammonium fluoride-containing water by decomposing and removing them using a catalyst while maintaining the activity of the catalyst for a long time. It is about.

[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 normally 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, since the materials treated with these etching agents are washed with a large amount of washing water, 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. Generally, in the treatment of ammonium fluoride-containing waste liquid, fluorine ions are recovered and removed as calcium fluoride by adding a calcium compound such as calcium hydroxide, while ammonium ions are treated by biological nitrification denitrification method, ammonia It is removed by stripping method, chlorine oxidation method, contact method, etc. Among the methods for removing ammonium ions, the biological methods are
This is a method in which ammonium ions are oxidized to nitrous acid or nitrate nitrogen by nitrifying bacteria and then reduced to nitrogen gas by denitrifying bacteria. Although this method is inexpensive, it is a microbial reaction, so if the fluorine ion concentration is 50 ppm or more, the activity decreases and it is unstable with respect to other fluctuation factors, and a large installation area is required. It has drawbacks such as Further, the ammonia stripping method is a method in which a large amount of air is brought into contact with an alkaline solution to diffuse ammonia into the atmosphere. However, this method is not economical because it requires a high alkali cost and needs to adsorb and concentrate the diffused ammonia again. On the other hand, the chlorine oxidation method is a method of oxidizing ammonium ions into nitrogen gas via chloramine by adding chlorine. This method requires about 10 times the amount of chlorine to be added to ammonia, and is not suitable for treatment with high ammonium ion concentration. The contact method is attracting attention because it is a treatment method having excellent characteristics such as a small installation area, easy operation management, and generation of substances requiring post-treatment such as sludge and residual chlorine. However, when the decomposition treatment of ammonia with a catalyst is carried out in the presence of fluorine, hydrofluoric acid is produced and the pH of the treated water is drastically lowered during the treatment, resulting in dissolution and disintegration of the catalyst carrier. Therefore, conventionally, in the decomposition method using a catalyst of ammonia in the coexistence of fluorine, first a method of making fluorine ions in water to be treated insoluble by a calcium salt such as slaked lime, solid-liquid separation, and then catalytically decomposing ammonia is examined. It had been. However, this treatment method using calcium salts results in a large amount of calcium ions being contained in the obtained treated water, and even if ammonia is subsequently removed by the contact method, the calcium salts will scale depending on the operating time and the catalytic activity will decrease. There was a problem of doing.

[0003]

DISCLOSURE OF THE INVENTION The present invention, when decomposing and removing ammonium ions in ammonium fluoride-containing water using a catalyst, prevents dissolution and disintegration of the catalyst due to hydrofluoric acid, The object of the present invention is to provide a method for treating ammonium fluoride-containing water which maintains catalytic activity for a long time and efficiently decomposes and removes the ammonium ion.

[0004]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that nitrite is an ammonium ion in ammonium fluoride-containing water under heating conditions and in the presence of a catalyst. It was found that the above can be efficiently decomposed without producing hydrofluoric acid, and the present invention has been completed based on this finding. That is, the present invention provides a method for treating ammonium fluoride-containing water, which comprises adding ammonium nitrite to ammonium fluoride-containing water under heating and in the presence of a catalyst to decompose ammonium ions. is there. Hereinafter, the present invention will be described in detail. In the method of the present invention, ammonium fluoride-containing water is treated with nitrite under heating conditions and in the presence of a catalyst. Examples of the catalyst include platinum, palladium, ruthenium, rhodium, silver, on a carrier such as alumina, zirconia, titania, silica, activated carbon or zeolite.
Those supporting copper or the like are preferably used. These catalysts are packed in a column, and it is advantageous to carry out the reaction by passing ammonium fluoride-containing water under heating together with an alkali metal nitrite. In this case, SV is usually 1-10 hours
^-1 , preferably about 5 hr ^-1 , and an upward flowing liquid is desirable. Further, as the nitrite, for example, sodium nitrite, potassium nitrite and the like are preferably used. The amount of nitrite used is usually 0.1 with respect to ammonium ion.
It is selected in the range of 5 to 2 mole times, preferably 1 to 1.2 mole times. The reaction temperature is usually selected in the range of 50 to 300 ° C, preferably 70 to 200 ° C. Thus, by treating the ammonium fluoride-containing water with the nitrite, the reaction formula nNH ₄ F + M (NO ₂ ) _n → nN ₂ + nMF + 2nH ₂ O (where M is a metal element and n is a natural number) ), Ammonium ion is decomposed to nitrogen gas without producing hydrofluoric acid. Therefore, the catalyst is not dissolved or decomposed, and the catalyst activity is maintained for a long time. On the other hand, when treated with hydrogen peroxide, hydrofluoric acid is produced, the catalyst is dissolved and decomposed, and the catalytic activity is reduced in a short time. Fluorine ions in the ammonium fluoride-containing water from which ammonium ions have been decomposed and removed in this manner are conventionally known methods, for example, a flocculation-precipitation method using calcium hydroxide, a fluorine adsorbent such as cerium oxide hydrate, and an OH-type weak base. It is removed by an adsorption method using a cationic anion exchange resin, a method of passing water through a calcium carbonate crystal packed bed, or the like. The treatment method of the present invention can be applied to wastewater containing hydrogen fluoride and ammonium fluoride, as well as wastewater containing ammonium fluoride.

[0005]

EXAMPLES The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto. Comparative Example 1 NH ₄ F aqueous solution having a pH of 5.9 (containing 1000 ppm as N)
On the other hand, H ₂ O ₂ was added at a rate of 3,600 ppm, and the column was filled with 35.0 g of titania spheres carrying 0.5 wt% Pt, and the flow rate was 3.0 ml / min (SV4.5 hr ⁻¹ ). ,
The solution was passed under the condition of a temperature of 140 ° C., continuously treated for 620 hours, and the ammonium ion concentration in the treated water was measured to examine the ammonium ion removal effect. After the test, the catalyst was taken out and the weight was measured to confirm the presence or absence of dissolution. The time-dependent change in activity when the initial catalyst activity was set to 100 is shown in a graph in FIG. 1 (solid line). As can be seen from this figure, the catalyst activity decreased significantly with the passage of time. Further, the catalyst weight after the test was reduced to 24.9 g. The treated water had a pH of 2.5 to 2.9. Example 1 NH ₄ F aqueous solution having a pH of 5.9 (containing 1000 ppm as N)
To the addition of NaNO ₂ at a ratio of 1,000 ppm (as N), it was performed in the same manner as in Comparative Example 1. The change with time of the catalytic activity is shown graphically in FIG. 1 (dotted line). As can be seen from this figure, unlike Comparative Example 1, the initial catalyst activity could be maintained even after 620 hours had elapsed. Further, the catalyst weight after the test was 34.7 g, and it was hardly dissolved. The treated water had a pH of 5.8 to 5.9, and slaked lime was added to the treated water to adjust the pH to 12, followed by solid-liquid separation to obtain a fluoride ion concentration of about 15 ppm in the treated water. .

[0006]

EFFECTS OF THE INVENTION According to the present invention, when ammonium ions in ammonium fluoride-containing water are decomposed and removed using a catalyst, the catalyst is prevented from being dissolved or decomposed due to the presence of hydrofluoric acid. The activity can be retained for a long time, and ammonium ions can be efficiently decomposed and removed.

[Brief description of drawings]

FIG. 1 is a graph showing changes with time in catalytic activity when hydrogen peroxide and sodium nitrite are added to water containing ammonium fluoride to decompose ammonium ions.

Claims (1)

[Claims] 1. A method for treating ammonium fluoride-containing water, which comprises adding ammonium nitrite to ammonium fluoride-containing water under heating conditions and in the presence of a catalyst to decompose ammonium ions.