KR20180064753A - Methods for waste water treatment of Nitrogen trifluoride(NF3) process - Google Patents

Abstract

Provided is a process for treating wastewater by collecting, stage by stage, high purity metal, hydrofluoric acid, and ammonia components present in high concentration in wastewater generated in a process of producing nitrogen trifluoride (NF_3) gas. According to the present invention, it is possible not only to treat wastewater generated in the process of producing nitrogen trifluoride gas as a general waste according to environmental regulations, but also to reduce costs for wastewater treatment since the produced by-products can be recovered in high purity to be reused or sold outside, with little additional production of wastewater during the wastewater treatment.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for treating waste water of a nitrogen trifluoride nitrogen (NF3)

The present invention relates to a method for treating wastewater generated in a process for producing nitrogen trifluoride (NF3) gas and a method for recovering and recycling metals, hydrofluoric acid and ammonia components present in wastewater, respectively.

Nitrogen trifluoride (NF ₃ ) gas is usefully used as a dry etching agent for semiconductors, LCDs, solar cells, cleaning gas for CVD devices, and the like. Recently, it is industrially important gas that has been rapidly used in the semiconductor industry and also as an Exima laser gas.

Generally, the nitrogen trifluoride gas is produced by a method of electrolyzing an electrolytic solution containing ammonia (NH ₃ ) - hydrogen fluoride (HF) based molten salt in an electrolytic bath, and a metal plate is mainly used as an anode and a cathode electrode. The wastewater generated at this time contains ammonium and fluorine components as reaction raw materials and contains metal components eluted during electrolysis. The concentration of the fluorine component in the wastewater is generally 10 to 15 wt%, the ammonium component 1 to 2 wt%, and the metal component 0.2 wt% or less. These ingredients are very harmful to aquatic organisms and the human body, and therefore their contents are strictly regulated.

Methods for removing metals from wastewater include a method using strongly acidic cation exchange resin, a precipitation method using an acid leaching process, an electrodialysis method, and an evaporation concentration method. However, in the waste water produced in the nitrogen trifluoride manufacturing process, the fluorine component and the ammonium component There is a disadvantage that the wastewater can not be effectively treated due to the influence of the wastewater, the wastewater generated in comparison with the existing wastewater is generated, and the apparatus is corroded. In addition, the above process has a disadvantage in that the process is complicated and the possibility of metal loss is high, so that the recovery rate is low, it is difficult to treat in a large amount, and the reaction rate is slow.

As a method for removing fluorine in wastewater, there is a method in which a calcium compound such as calcium hydroxide (Ca (OH) ₂ ) or calcium chloride (CaCl ₂ ) is added to wastewater and the fluoride ion is precipitated with an insoluble calcium fluoride salt (CaF ₂ ) (Japanese Patent No. 2858478). However, since there is a high concentration of the metal component in the wastewater generated in the nitrogen trifluoride production process, it is difficult to recover it as a calcium fluoride salt of high purity.

Ammonia stripping is typically used to remove ammonium from wastewater (Korean Patent No. 10-1200156). When the pH is adjusted to 10 or more by adding a base to the wastewater, ammonium can be converted into ammonia gas and recovered. However, ammonia can not be recovered purely due to the influence of the fluorine component in the wastewater generated in the nitrogen trifluoride production process, or plugging may occur due to the influence of the metal component.

Korean Patent No. 10-0559919 discloses a method for reducing or eliminating NH ₃ / HF or NH ₃ / HF / MFz liquid waste melt in the production of nitrogen trifluoride gas, .

Korean Patent Registration No. 10-0559919 Korean Patent Registration No. 10-1200156 Japanese Patent Registration No. 2858478

The present invention relates to a method for treating waste water generated in a process for producing nitrogen trifluoride gas, wherein there is no problem of erosion of the impurities that the prior art has not solved, the wastewater is additionally generated in the wastewater treatment, And can be reused or sold externally, thereby providing a new method for reducing waste water treatment costs.

In order to solve the above problem, the present invention provides a process for recovering metal, hydrofluoric acid and ammonia components present at a high concentration in wastewater generated in a process for producing nitrogen trifluoride gas in high purity stepwise to treat wastewater.

Specifically, the method for recovering metal, hydrofluoric acid, and ammonia from wastewater generated in the process for producing nitrogen trifluoride gas according to the present invention,

a) recovering the metal from the wastewater by an organic solvent extraction method;

b) supplying a metal hydroxide to the wastewater from which the metal is recovered to convert fluorine to an insoluble metal fluoride salt and recovering the metal hydroxide; And

c) heating and stripping the wastewater from which the fluorine has been recovered to convert ammonium to ammonia and recover.

Further, according to the present invention, there is provided a method for recovering a metal-containing aqueous solution, comprising the steps of: back-extracting an organic solvent containing metal recovered in step a) with an acid to recover an aqueous solution of the metal dissolved therein; And recovering the metal from the aqueous solution in which the metal is dissolved. It is preferable that the organic solvent is added so that the aqueous phase / organic phase ratio is in the range of 0.1-1.

Preferably, in step (a), the organic solvent containing the metals is back-extracted with the sulfuric acid solution, and the metal in the back extract is extracted, whereby metal impurities can be effectively removed and recovered.

As a method for recovering the metal from the aqueous solution in which the metal is dissolved, it is more preferable to use electrolytic-winning.

In order to economically operate the present invention, it is preferable that the high purity organic solvent from which the metal is recovered is recycled and recycled in the step a).

The metal hydroxide for recovering fluorine according to the present invention is preferably calcium hydroxide (Ca (OH) ₂ ). Accordingly, the recovered fluoride metal salt is reacted with sulfuric acid at a high temperature to obtain hydrogen fluoride, which can be reused as a raw material for producing NF3.

According to the embodiment of the present invention, there is almost no wastewater additionally generated during wastewater treatment in the process of producing nitrogen trifluoride gas, and the produced by-products can be recovered in high purity and reused or sold outside, have.

Fig. 1 is a process chart of wastewater treatment and each by-product recovery.

Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention can be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below.

According to the present invention, the wastewater treatment step includes sequentially removing the metal, removing the fluorine component, and removing ammonia.

The method also includes recovering the removed metal by an electrolytic extraction method, recovering the fluorine component in the form of a metal fluoride salt, and recovering the ammonium component in high purity with ammonia.

According to one embodiment of the present invention, the metal is extracted by using an organic solvent in a continuous extractor (room temperature, atmospheric pressure, 30 stages), and the metal is solvent extracted in the range of 0.1-1. If the ratio is less than 0.1, the extraction rate may be decreased. If the ratio is more than 1, there is a large amount of solvent, which increases equipment and increases the utility cost.

The organic solvent for metal extraction according to the present invention may be an acidic solvent, a chelating agent or a mixture thereof, but is not limited thereto. The acidic solvent is preferably a hydrocarbon carboxylic acid, more preferably neodecanoic acid (trade name: versatic acid).

As the chelating agent, aliphatic hydroxyalkyloximes in a hydrocarbon group having high flash point, such as kerosene, may be further used. As the aliphatic hydroxyalkyloximes, 5,8-diethyl-7-hydroxydodecane-6-oxime is preferable (trade name Lix63, BASF).

The organic solvent may be mixed with an acidic solvent and a chelating agent in a volume ratio of 5: 9: 5-1. When the volume ratio is less than 5: 5, there is a problem that the cost is high. When the volume ratio is more than 9: 1,

It is preferable that the metal content of the metal removal wastewater after metal extraction is 5 ppm or less. If the metal content exceeds 5 ppm, it causes environmental problems and the like.

The organic solvent containing the metal is stripped using 0.5-5 M sulfuric acid in a reverse extractor (30 ° C, normal pressure, 50 stages), the solvent is recovered and reused, the metal is recovered by the electrolytic sampling method, Is recycled back to the reverse extractor. When the sulfuric acid concentration is less than 0.5M, there is a problem that the metal removal effect is insufficient. When the sulfuric acid concentration is more than 5M, the apparatus corrosion problem occurs.

The electrolytic sampling apparatus may include an electrolytic bath, a solution supply means, a power source, and a blowout unit, though not shown as a usual apparatus. The inside of the electrolytic cell is partitioned into an anode chamber and a cathode chamber by an ion permeable diaphragm, and the raw water supply means may include a pump for regulating a supply flow rate. The demixing liquid introduced into the electrolytic cell is electrolyzed into an anion and a cation component by the electrolytic currents of the anode and the cathode respectively provided in the anode chamber and the cathode chamber, and is separated and moved to the anode chamber and the cathode chamber according to the ion tendency. As a result, sulfuric acid is collected in the anode chamber, and metal components are collected in the cathode chamber.

According to an embodiment of the present invention, when fluorine is converted into an insoluble metal fluoride salt by using a metal hydroxide such as calcium hydroxide from wastewater from which a metal component is removed, the fluorine component can be recovered with high purity. The recovered fluoride metal salt can be reused as hydrogen fluoride after reacting with sulfuric acid at a high temperature.

According to an embodiment of the present invention, pure ammonia water can be obtained by heating and stripping wastewater from which metal and fluorine components have been removed. The heating temperature is in the range of 30 to 120, and the pressure is in the atmospheric pressure range. Nitrogen and air can be used.

A specific embodiment of the present invention was carried out as follows.

a) 150 L of wastewater generated in the production process of nitrogen trifluoride gas was put into the upper part of a continuous extractor (Karr Type 30), and versatic acid (versatic acid 10, Hexion) and Lix63 (BASF) in a ratio of 7: 3 was introduced into the bottom of the continuous extractor, and the plate was reciprocated at a rate of 80 rpm at room temperature and normal pressure to continuously extract the metal components.

b) 64 kg of calcium hydroxide (Ca (OH) ₂ ) was added to the wastewater from which the metal component had been removed, and the mixture was uniformly mixed while stirring slowly at 50 rpm. 33.8 kg of precipitated calcium fluoride (CaF2) precipitated by solid-liquid separation through a press filter was recovered, and 32 kg of calcium hydroxide was recovered from the remaining mixed precipitate and recovered.

c) The filtrate was poured into a stripper under heating (heating rate: 10 ° C / min) and stripped under the conditions of 1 bar and 111 ° C to recover ammonia water (9.3 kg of water and 3.1 kg of ammonia) And discharged.

100 L of the organic solvent containing the metal component extracted in step a) was introduced into the lower part and the upper part of the reverse extractor (50, Karr type) to extract 7 L of dilute sulfuric acid (36 wt%). The plate was reciprocated at a rate of 80 rpm at 30 DEG C and normal pressure to continuously back-extract the metal components.

An aqueous solution in which the metal was dissolved was introduced into the electrolytic cell and the pure metal was recovered by electrolytic collection. The recovered metal was 0.74 kg, containing 93.3% by weight of nickel, 5.52% by weight of iron and 0.85% by weight of chromium.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, It will be obvious to those of ordinary skill in the art.

Claims (8)

A method for recovering metal, hydrofluoric acid, and ammonia from wastewater generated in a process for producing nitrogen trifluoride (NF ₃ ) gas,
a) recovering the metal from the wastewater by an organic solvent extraction method;
b) supplying a metal hydroxide to the wastewater from which the metal is recovered to convert fluorine to an insoluble metal fluoride salt and recovering the metal hydroxide; And
c) heating and stripping the wastewater from which the fluorine has been recovered to convert ammonium into ammonia and recovering the wastewater.
The method of claim 1, further comprising the step of back-extracting the metal-containing organic solvent recovered in step a) with an acid to recover an aqueous solution of the metal dissolved therein; And recovering the metal from the aqueous solution in which the metal is dissolved.
The method according to claim 2, wherein the organic solvent containing the metals is back-extracted with the sulfuric acid solution and the metal in the back extract is withdrawn and recovered in the step (a).
3. The method according to claim 2, wherein the metal is recovered from the aqueous solution in which the metal is dissolved by eletro-winning.
The method according to claim 2, wherein the high purity organic solvent from which the metal is recovered is recycled in the step a)
The method for treating wastewater according to claim 1, wherein the metal hydroxide is calcium hydroxide (Ca (OH) ₂ )
The method according to claim 1, wherein the fluoride metal salt recovered in step b) is reacted with sulfuric acid at a high temperature to obtain hydrogen fluoride and reused in the nitrogen trifluoride production process.
The method according to claim 1, wherein in step a), the organic solvent is mixed in the range of the aqueous / organic phase ratio of 0.1-1.

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