KR102356642B1 - Method of recovering high quality sodium fluoride by treating waste water including fluorine compound with ammonium ion - Google Patents

Abstract

A method for recovering sodium fluoride from an ammonium-based fluorine compound-containing waste solution, the method comprising: a) preparing a solution containing sodium sulfate by adding sulfuric acid to an aqueous solution of a sodium-based alkali compound; b) obtaining a product containing sodium fluoride by dropping an ammonium-based fluorine compound waste solution thereto while stirring the solution containing sodium sulfate to proceed with a fixing reaction; c) filtering the mixture containing the product to separate the product containing the sodium fluoride in solid form and washing the product; and d) drying a product comprising said sodium fluoride in solid form. This method effectively detoxifies and neutralizes waste liquid containing ammonium-based fluorine compounds generated in the etching or cleaning process of glass or semiconductor substrates during the display and semiconductor device manufacturing process, and converts the fluorine component into a form of high-quality sodium fluoride with good crystallinity. can be recovered with

Description

Method of recovering high quality sodium fluoride by treating waste water including fluorine compound with ammonium ion

The present invention relates to a method for detoxifying and neutralizing waste liquid containing ammonium-based fluorine compounds generated in the etching or cleaning process of glass or semiconductor substrates during display and semiconductor device manufacturing processes, and at the same time recovering fluorine components as high-quality sodium fluoride. .

In the conventional semiconductor and display manufacturing process, _{hydrofluoric acid is used to etch a silicon dioxide (SiO 2} ) film or glass, for example, a high-concentration hydrofluoric acid solution where a high etching rate is required, and a diluted hydrofluoric acid solution (HF) where a low etching rate is required. solution) was used. However, for fine and precise etching and cleaning, an ammonium-based fluorine compound-containing solution in which 49% hydrofluoric acid solution and 40% ammonium fluoride solution (NH ₄ F) are mixed in various proportions depending on the purpose of the process is widely used. As such, a diluted hydrofluoric acid solution and a buffered oxide etchant (BOE) are widely used for wet etching or cleaning of a silicon dioxide film or glass, which are currently widely used in semiconductor and display device manufacturing processes, and BOE is NH in HF solution. _{It is} a typical etching/cleaning solution containing an ammonium-based fluorine compound made by mixing 4 F solution in an appropriate ratio. As such, the main purpose of preparing and using a buffer solution instead of the HF solution is to control the pH and to obtain a stable etching rate through this, while _{NH 4 F continuously supplements the fluoride ions that become insufficient as the process progresses.} It also has advantages that it does not have.

In this case, ammonium fluoride is usually mixed in excess of hydrofluoric acid and used, for example, 40% ammonium fluoride solution and 49% hydrofluoric acid solution 4:1, 10:1, 20:1, 50:1 and 100:1 It is mixed and used in various ratios, including At this time, since hydrofluoric acid is combined with ammonium fluoride _{and exists in an acidic ammonium fluoride (NH 4} HF ₂ ) state, the volatility of hydrofluoric acid is almost eliminated and work safety is increased. In addition, an aqueous solution prepared by dissolving solid acidic ammonium fluoride may be used instead of hydrofluoric acid for the purpose of etching or cleaning glass, silicon dioxide, and the like. Likewise, the etching rate is not as rapid as compared to hydrofluoric acid, so process management is convenient, and the working environment is improved because hydrofluoric acid is not volatilized.

On the other hand, Korean Patent Publication No. 2019-0067507 by the present inventor, whose title is 'a method of treating waste liquid containing ammonium-based fluorine compound with improved eco-friendliness and solid-liquid separation performance', contains a large amount of fluorine components and ammonia, etc. Disclosed is a method for environmentally friendly, economical and efficient treatment of waste liquids containing ammonium-based fluorine compounds, which were difficult to treat. This method is a method of obtaining _{CaF 2} having improved filterability using calcium compounds such as Ca(OH) ₂ , CaCO ₃ , and CaO and inorganic acids such as sulfuric acid, hydrochloric acid, and nitric acid. However, because CaF ₂ sludge to a large quantity of fluorine waste solution generated in the semiconductor and the display device caused by treatment with a Ca compound is introduced to the cement while areas to the free or processing costs, easy yimajeodo in a state of CaF ₂ oversupply. For reference, as of 2017, domestic companies accounted for about 21% of global semiconductor sales (64.5% if only memory semiconductors are counted), resulting in a large amount of semiconductor device production and a large amount of fluorine-containing waste liquid that is used and discarded.

Korean Patent Laid-Open No. 2016-0122031 by the present inventor, whose title is 'Method for Producing Sodium Fluoride from Fluorine-Contained Waste Slurry', is an etching process of tempered glass for touch panel that etches a large amount of glass or glass etching for flat panel display Disclosed is a method for treating waste slurry generated in the process. In this method, the solid content of the waste slurry _{is mostly silicofluoride such as Na 2} SiF ₆ or K ₂ SiF _{6 ,} and in order to treat these compounds, 2 ~ It was necessary to proceed with the reaction for a long time, about 4 hours.

Therefore, there is still a need for a method capable of treating waste liquid containing ammonium-based fluorine compounds that can obtain a more useful product in a gentle, energy-saving and efficient manner.

Accordingly, it is an object of the present invention to detoxify and neutralize waste liquids containing ammonium-based fluorine compounds generated in the etching or cleaning process of glass or semiconductor substrates in a display and semiconductor device manufacturing process in a gentle, energy-saving and efficient way and simultaneously with fluorine component To provide a method for recovering in the form of sodium fluoride.

In order to solve the above problems, the present invention

A method for recovering an ammonium-based fluorine compound-containing waste liquid, comprising:

a) preparing a solution containing sodium sulfate by adding sulfuric acid to an aqueous solution of a sodium-based alkali compound;

b) obtaining a product containing sodium fluoride by adding an ammonium-based fluorine compound waste solution dropwise thereto while stirring the solution containing sodium sulfate over 1 to 2 hours to proceed with a fixing reaction;

c) filtering the mixture containing the product to separate the product containing the sodium fluoride in solid form and washing the product; and

d) drying the product comprising sodium fluoride in solid form.

In one embodiment of the present invention, in step a), the sodium-based alkali compound may be at least one selected from soda _{ash (Na 2} CO _{3 ) and caustic soda (NaOH).}

In one embodiment of the present invention, the input amount of the sodium-based compound in step a) is the sodium required for the fixed reaction according to Scheme 1 below with the fluorine component contained in the ammonium-based fluorine compound waste solution added in step b) It is in the range of 85% to 95% of the theoretical molar amount of the compound,

Na ⁺ + F ^- --> NaF (1),

In step a), the amount of sulfuric acid added is 85% to 100% of the theoretical molar amount of sulfuric acid required to proceed with the fixed reaction according to the following Scheme 2 with the ammonium ion component contained in the ammonium-based fluorine compound waste solution added in step b) It is preferred that the range is:

2NH ₄ ⁺ + SO ₄ ^2- --> (NH ₄ ) ₂ SO ₄ (2).

In one embodiment of the present invention, the reaction proceeding in step b) is preferably carried out in a temperature range of 60 to 70 ℃ and a pH range of 6.0 to 7.0.

In one embodiment of the present invention, in adjusting the pH, it is preferable to use sulfuric acid to lower the pH, and to use ammonia water to increase the pH.

In one embodiment of the present invention, the ammonium-based fluorine compound in step b) may be at least one selected from ammonium fluoride and ammonium bifluoride.

In one embodiment of the present invention, the drying step in step d) may be carried out under conditions in which moisture is removed and impurities are removed by thermal decomposition.

In one embodiment of the present invention, the conditions are conditions carried out at a temperature of 110 ℃ or more, and the impurities may include NH ₄ HCO ₃ and (NH ₄ ) ₂ CO ₃ .

By detoxifying and neutralizing waste liquid containing ammonium-based fluorine compounds with the recovery method according to the present invention, high-purity sodium fluoride with increased crystal size can be obtained, and the production of hydrofluoric acid and ammonia gas is suppressed during treatment to prevent the occurrence of hydrofluoric acid and ammonia gas in the working environment or surrounding environment. This can be greatly improved. In addition, the obtained sodium fluoride particle size is increased and the filterability is improved, so that the filtration time can be significantly shortened and the filtration process can be greatly improved. Sodium fluoride has many uses, such as being recycled as various preservatives, caries preventives, and disinfectants in fermentation. can do.

Hereinafter, a method for recovering sodium fluoride from an ammonium-based fluorine compound-containing waste liquid according to the present invention will be described in more detail.

A method for recovering a waste solution containing an ammonium-based fluorine compound according to the present invention comprises the steps of: a) preparing a solution containing sodium sulfate by adding sulfuric acid to an aqueous solution of a sodium-based alkali compound; b) obtaining a product containing sodium fluoride by adding an ammonium-based fluorine compound waste solution dropwise thereto while stirring the solution containing sodium sulfate over 1 to 2 hours to proceed with a fixing reaction; c) filtering the mixture containing the product to separate the product containing the sodium fluoride in solid form and washing the product; and d) drying the product comprising said sodium fluoride in solid form.

That is, in the recovery method according to the present invention, the ammonium-based fluorine compound-containing waste solution used in the etching or cleaning process of silicon dioxide film or glass performed in the manufacturing process of a display or semiconductor device is treated with soda ash (Na ₂ CO ₃ ) or caustic soda ( NaOH) can be used to prepare sodium fluoride and neutralize at the same time, and sulfuric acid can be used to fix ammonia in the form of ammonium sulfate. Thereby, the waste liquid containing the ammonium-based fluorine compound can be effectively and efficiently treated.

In step a), sulfuric acid is added to an aqueous solution of a sodium-based alkali compound in advance to prepare a solution containing _{sodium sulfate (Na 2} SO _{4 ).} In this step, when the sodium-based alkali compound solution and the ammonium-based fluorine compound are in direct contact with each other, ammonia or hydrofluoric acid is released when a rapid reaction occurs, which may deteriorate the working environment, so it is to be suppressed. This step is also a step for preparing in advance so that sodium fluoride crystals can grow significantly and efficiently by allowing only a small amount of precipitation nuclei to form when sodium fluoride is generated by adding the ammonium-based fluorine compound waste solution in step b). The sodium-based alkali compound that may be used in this step may be _{at least one selected from soda ash (Na 2} CO ₃ ) and caustic soda (NaOH). The present inventors claim that the amount of sodium-based compound added in this step is 85% to 95% of the theoretical molar amount of the sodium-based compound required for the fixed reaction according to the following Scheme 1 with the fluorine component contained in the ammonium-based fluorine compound waste solution added in step b) It has been found desirable to control in the range of %: Na ⁺ + F ^- --> NaF (1). For example, in Scheme 1, it is preferable to adjust 0.85 to 0.95 moles of sodium ions to be added to 1 mole of fluoride ions. The present inventors also found that the amount of sulfuric acid added in this step is 85% to 100% of the theoretical molar amount of sulfuric acid required to proceed with the fixed reaction according to the following Scheme 2 with the ammonium ion component contained in the ammonium-based fluorine compound waste solution added in step b) It has been found that a range of: 2NH ₄ ⁺ + SO ₄ ^2- --> (NH ₄ ) ₂ SO ₄ (2). For example, in Scheme 2, it is preferable to adjust the amount of sulfuric acid added so that 0.85 to 1 mole of sulfate ions are added with respect to 2 moles of ammonium ions.

In step b), _{while slowly stirring the solution containing sodium sulfate (Na 2} SO ₄ ) prepared in step a), the ammonium-based fluorine compound waste solution is slowly added dropwise over 1 to 2 hours to proceed with the fixing reaction to obtain sodium fluoride. to obtain a product comprising The stirring speed controls the rotation speed of the stirrer to a level of 30-50 rpm, and when the ammonium-based fluorine compound waste liquid is added dropwise, if it is added at a too fast speed, ammonium sulfate may be generated in the reactor, so it is observed that white smoke does not occur. Slowly drop and react. If the reaction proceeds slowly under such a slow stirring rate and dropping rate, the number of crystal nuclei of sodium fluoride produced can be reduced, and the crystal size can be increased. When the crystal size is increased, it is easy to wash with water, so that high purity sodium fluoride can be obtained, and the filtration time can be shortened and drying can be facilitated.

By the fixing reaction of this step, the fluorine component contained in the ammonium-based fluorine compound waste solution _{reacts with sodium sulfate (Na 2} SO ₄ ) according to Scheme 1 to form sodium fluoride crystals, and along with this, according to Scheme 2, ammonium-based fluorine The ammonium ion component contained in the compound waste solution and sodium sulfate (Na ₂ SO ₄ ) react to form ammonium sulfate ((NH ₄ ) ₂ SO ₄ ). The ammonium-based fluorine compound contained in the waste solution in this step may include ammonium fluoride and ammonium bifluoride. The reaction proceeding in this step is preferably carried out in a temperature range of 60 to 70 °C, and in a pH range of 6.0 to 7.0. When the temperature range of 60 to 70 ° C. is controlled, the purity of sodium fluoride crystals can be increased by allowing reactants and/or products that may exist other than the precipitated sodium fluoride crystals to exist in a dissolved state in the solution without precipitation. See Table 1 for this. Table 1 summarizes the solubility (unit: g) in water according to the temperature of substances that may be present in the reaction mixture. The present inventors have found that when a mild pH range of 6.0 to 7.0 is applied, the emission of ammonia gas is suppressed, thereby greatly improving the working environment or the surrounding environment.

0℃ 15℃ 20℃ 60℃ 100℃ sodium fluoride
(NaF) - - 4.04 - 5.05 soda ash
(Na ₂ CO ₃ ) - 16.4 - 45.62 - anhydrous forget-me-not
(Na ₂ SO ₄ ) 4.76 - 13.9 - 42.7 Malthorn Heptahydrate
(Na ₂ SO _{4 ㆍ} 7H ₂ O) 19.5 - 44 - - Ammonium Sulfate
((NH ₄ ) ₂ SO ₄ ) 70.6 - 74.4 - 103.6

Referring to Table 1, in the temperature range of 20 ° C. to 100 ° C., sodium fluoride has a low solubility with solubility of about 4 to 5 g and a small change in solubility according to temperature, soda ash (Na ₂ CO ₃ ), Mangocho (Na ₂ SO) ₄ ), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), etc., have higher solubility as the temperature increases, and almost all exist in a solution state above 60 ℃, so if the reaction temperature is controlled to a low temperature range of 60 to 70 ℃ It can be confirmed that the purity of the sodium fluoride crystals can be increased.

When the pH of the reaction mixture is maintained in a pH range of 6.0 to 7.0 in order to suppress ammonia release, sulfuric acid is used to lower the pH, and ammonia water is preferably used to increase the pH. When ammonia is used to increase the pH, even if unreacted sulfuric acid is present, it reacts with the ammonia to be converted to ammonium sulfate with very good solubility, so it is removed during filtration and washing in the subsequent step, thereby reducing the effect on the purity of sodium fluoride. Accordingly, the purity of the sodium fluoride recovered in the present invention is advantageous in satisfying the KS standard for sodium fluoride summarized in Table 2 below.

Specification of sodium fluoride (KS M 1404;2012)

Item standard Moisture (wt%) 0.5 or less Free acid (HF) (wt%) 0.1 or less Free alkali (Na ₂ CO ₃ ) (% by weight) 0.5 or less Sodium silicate fluoride (Na ₂ SiF ₆ ) (wt%) 1.5 or less Sulfate (SO ₄ ) (wt%) 0.1 or less Sodium Fluoride (NaF) (After Drying) (wt%) 97.0 or higher

In step c), the reaction mixture containing the product is filtered to separate a product containing sodium fluoride in a solid form and washed with water. Specifically, the reaction mixture solution on which the fixed reaction of step b) is completed is immediately filtered so that the temperature of the reaction mixture solution does not cool down. Pressure filtration is preferred over reduced pressure filtration to minimize temperature drop. The purpose of minimizing the temperature drop is to pass impurities other than sodium fluoride through the filtrate as described above and to obtain pure sodium fluoride crystals as the filtered solid as possible. When the filtration is completed, water, for example, deionized or distilled water, or general water is added to wash with water and re-filtered if necessary.

Finally, the product comprising sodium fluoride crystals in solid form in step d) is dried. In this step, the drying _{may be carried out under conditions in which moisture is removed and impurities such as NH 4} HCO ₃ and (NH ₄ ) ₂ CO ₃ can be removed by thermal decomposition. The condition may be a condition in which the water of the filtered NaF crystals falls within the specifications of Table 2, for example, at a temperature of 110° C. for 1 hour or more, preferably for 2 hours or more. _{Under such conditions, sodium fluoride obtained by decomposing impurities such as NH 4} HCO ₃ , (NH ₄ ) ₂ CO ₃ and the like, which may exist in a trace amount at high temperature and being released into the gas phase, may satisfy the specifications of Table 2 above.

The sodium fluoride recovered in this way can be used as a flux in the manufacturing process of steel or aluminum, as a preservative for wood, as a fluoridation agent for tap water, and as an emulsion agent for enamel. Ammonium sulfate (milk) separated from the filtrate can be used as a fertilizer through concentration and crystallization.

Hereinafter, the present invention will be described in more detail through the following examples. However, the following examples are for illustrative purposes only and not for limiting the scope of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and matters reasonably inferred therefrom.

For the BOE waste solution used in the experiment, the BOE waste solution used as an etchant in Company S was used, and the components are shown in Table 3 below.

Composition of BOE waste liquid used in the experiment

ingredient Hydrofluoric acid (HF, wt%) Total Fluorine (F, wt%) Ammonium (NH ₄ ⁺ , % by weight) value 7.2 17.0 9.6

preliminary experiment

When NaF is manufactured using sodium compounds such as soda ash or caustic soda from such BOE waste liquid, the pH of the reaction solution rises to 9 or higher, and ammonia gas is generated, which greatly deteriorates the working environment. Therefore, by adding sulfuric acid to this reaction, ammonia gas was prevented by fixing ammonium ions in the form of ammonium sulfate.

However, depending on the method of adding sulfuric acid, a difference may occur in the NaF crystals produced. In order to investigate this, the following test was performed.

Example One

In a 2L beaker made of polypropylene (PP), put 170.7 g of soda ash (a sodium compound equivalent to 90 mol% of the amount of sodium required to react with the fluorine component in 400 g of BOE waste solution) and 170 g of distilled water, and bathe in water at 70°C. while stirring slowly. In the beaker, 208.6 g of 47.6 wt% of spent sulfuric acid (sulfuric acid corresponding to 95 mol% of the amount of sulfuric acid required to react with the ammonium component contained in 400 g of BOE waste solution) was added to produce Na ₂ SO ₄ .

_{When the reaction of sulfuric acid and soda ash was completed, 400 g of BOE waste solution (F: 17.0 wt %, NH 4} : 9.6 wt %) was dropped over about 1 hour with a 500 mL separatory funnel made of PP material, and the mixture in the beaker was reacted while slowly stirring. . After the input of the BOE waste solution was completed, when about 1 hour had elapsed, 28 wt% aqueous ammonia was added to neutralize the pH of the mixed solution to 7.5.

Thereafter, while maintaining the temperature of the reaction mixture at about 70° C., vacuum filtration was performed using a 110 mm Buchner funnel made of PP and 5A filter paper. The solid was washed with 170 g of distilled water while vacuum filtration. The filtered solid was put in a centrifugal dehydrator and dehydrated for about 20 minutes. After drying the dehydrated solid at about 110° C. for about 1 hour, the moisture content was measured.

comparative example One

In a 2L beaker made of PP material, 170.7 g of soda ash (a sodium compound corresponding to 90 mol% of the amount of sodium required to react with fluorine in 400 g of BOE waste solution) and 170 g of distilled water were put and stirred slowly while taking a water bath at 70°C.

Separately, 400 g of BOE waste solution and 208.6 g of 47.6 wt% of waste sulfuric acid (sulfuric acid equivalent to 95 mol% of the amount of sulfuric acid required to react with ammonium in 400 g of BOE waste solution) were mixed to obtain a mixed solution, and then 500 mL of PP material The mixed solution was added dropwise to the beaker over 1 hour using a separatory funnel. When about 1 hour has elapsed after the mixture of BOE waste liquid and sulfuric acid was completely added, 28 wt% aqueous ammonia was added to the beaker to neutralize the pH of the mixture to 7.5.

Thereafter, while maintaining the temperature of the reaction mixture at about 70° C., vacuum filtration was performed using a 110 mm Buchner funnel made of PP and 5A filter paper. The solid was washed with 170 g of distilled water while vacuum filtration. The filtered solid was put in a centrifugal dehydrator and dehydrated for about 20 minutes. After drying the dehydrated solid at about 110° C. for about 1 hour, the moisture content was measured.

comparative example 2

In order to minimize the generation of ammonia gas, only an amount of soda ash corresponding to the equivalent of sulfuric acid was added, and the remaining sodium ions were _{supplemented with sodium bicarbonate (NaHCO 3} ) to react. Since sodium bicarbonate is less alkaline than soda ash, ammonia generation can be further reduced by not raising the pH of the solution much.

Specifically, 107.4 g of soda ash and 170 g of distilled water were put into a 2L beaker made of PP material and stirred slowly while taking a water bath at 70°C. In the beaker, 208.6 g of 47.6 wt% spent sulfuric acid (sulfuric acid corresponding to 95 mol% of the amount of sulfuric acid required to react with ammonium contained in 400 g of BOE waste solution) was added to produce Na ₂ SO ₄ . After the reaction of sulfuric acid and soda ash was completed, _{100.3 g of sodium bicarbonate (NaHCO 3} ) was further added to the beaker.

With a 500 mL separatory funnel made of PP material, 400 g of BOE waste solution was added dropwise to the beaker over 1 hour, and the mixture in the beaker was slowly stirred to react. When the BOE waste liquid was completely added and about 1 hour had elapsed, the solids were vacuum filtered through a 110 mm Buchner funnel made of PP and 5A filter paper while maintaining the temperature of the mixed solution in the beaker at 70°C. While vacuum filtering the solid, the solid was washed with 170 g of distilled water. At this time, the solid was put in a centrifugal dehydrator and dehydrated for about 20 minutes. After drying the dehydrated solid at 110° C. for about 1 hour, the moisture content was measured.

Table 4 shows the chemical input amount and the moisture content after drying in Example 1 and Comparative Examples 1 and 2.

Sulfuric acid (47.6% by weight)
input soda ash
input baking soda
input BOE waste fluid
input manufacturing method Moisture content after dehydration
(weight%) Example 1 208.6g
(95 mol%) 170.7g
(90 mol%) 0g 400g After the Na ₂ SO ₄ reaction
NaF production 11.9% Comparative Example 1 208.6g
(95 mol%) 170.7g
(90 mol%) 0g 400g BOE waste liquid and sulfuric acid
Preparation of NaF after mixing 22.5% Comparative Example 2 208.6g
(95 mol%) 107.4g 100.3g 400g _{Na 2} SO ₄ reaction with sulfuric acid and soda ash, sodium bicarbonate is added
NaF production by input 23.6%

Table 5 shows the results of analysis on whether or not the standard of sodium fluoride according to KS M 1404 was met for the solid after drying.

Item NaF standard Example 1 Comparative Example 1 Comparative Example 2 moisture
(weight%) 0.5 or less 0.3 1.3 0.9 free acid (HF)
(weight%) 0.1 or less 0.02 0.01 0.01 Free alkali (Na ₂ CO ₃ )
(weight%) 0.5 or less N.D. N.D. N.D. sodium silicate
(weight %) 1.5 or less 0.01 0.01 0.01 sulfate
(weight %) 0.1 or less 0.05 0.8 0.6 sodium fluoride
(weight %) 97 or higher 98.9 97.1 97.8

N.D. (not detectable): Not detectable.

In Example 1, sulfuric acid was added to soda ash to first generate sodium sulfate according to the reaction formula of _{Na 2} CO ₃ + H ₂ SO ₄ → Na ₂ SO ₄ , and then BOE waste solution was added to _{the remaining Na 2} CO ₃ and Na ₂ SO _{4 .} The reaction expected to produce NaF solution can be expressed as

Na ₂ SO ₄ + 2NH ₄ F → 2NaF + (NH ₄ ) ₂ SO ₄

In Comparative Example 1, sulfuric acid is first mixed with BOE waste solution, ammonium ions are fixed with ammonium sulfate, and then reacted with soda ash to produce NaF. The reaction formula can be expressed as follows.

H ₂ SO ₄ + 2NH ₄ F → (NH ₄ ) ₂ SO ₄ + 2HF

2HF + Na ₂ CO ₃ → 2NaF + H ₂ O + CO ₂

In Comparative Example 2, when sodium ions required for the reaction were added to minimize ammonia gas generation, only soda ash equivalent to sulfuric acid equivalent was first added, and the remaining sodium ions were _{supplemented with sodium bicarbonate (NaHCO 3} ) for reaction. This is because sodium bicarbonate has weaker alkalinity than soda ash and does not increase the pH of the solution much, so it is expected that ammonia generation can be further reduced, and the expected reaction formula can be expressed as follows.

Na ₂ CO ₃ + H ₂ SO ₄ → Na ₂ SO ₄ + H ₂ O + CO ₂

Na ₂ SO ₄ + 2NH ₄ F → 2NaF + (NH ₄ ) ₂ SO ₄

NaHCO ₃ + HF → NaF + H ₂ O + CO ₂ .

Referring to Tables 4 and 5, compared to Example 1, Comparative Examples 1 and 2 had fine sodium fluoride crystal particles, and thus the dehydration properties were not good. Comparative Examples 1 and 2 had a high water content of 22.5% and 23.6%, respectively, even after dehydration, so that a lot of ammonium sulfate dissolved in the residual water remained after washing, and as a result, a lot of ammonium sulfate salt remained even after drying. It was confirmed that the remaining sulfate was also out of specification (0.1%).

By comparing the results of Example 1 and Comparative Examples 1 and 2, when NaF is produced via sodium sulfate, the size becomes larger than that of sodium fluoride crystals made using soda ash or sodium bicarbonate, so dehydration is improved, and the sulfate remaining as a result of the analysis is also specified ( 0.1%) was confirmed (Example 1). Na ₂ SO ₄ are difficult solubility of 13.9g / 100mL (20 ℃) with (NH _{4) 2} is much less than the solubility of 75.4g / 100mL (20 ℃) of SO ₄ removal of the water washing. Since the KS standard for NaF specifies that the SO ₄ content is 0.1% or less, it is necessary to experimentally adjust the sulfuric acid input. Experiments were carried out by controlling the amount of sulfuric acid to be added through Examples and Comparative Examples below.

Example 2 to 5 and comparative example 3 to 4

The following series of experiments were performed to investigate the effect of changes in the amount of sulfuric acid input during NaF production using BOE waste liquid.

Except for changing the amount of sulfuric acid, the experiment was carried out using the same drug as in Example 1 and the same method. The changed input amount of each drug is summarized in Table 6, and the analysis results according to KS M 1404 for solids after drying at 110° C. for 1 hour are shown in Table 7.

Comparing Example 2 and Comparative Example 3, compared to Example 1 in which the sulfuric acid input was adjusted to 95% of the theoretical molar amount of sulfuric acid required to proceed with the fixed reaction with the ammonium ion component, 85 mol% and 80 mol%, respectively It can be seen that the moisture content of the sample after dehydration was increased in both Example 2 and Comparative Example 3 compared to that of Example 1. In addition, in the case of Comparative Example 3, since the water content was high, the amount of sulfate ions remaining in the sample was higher than that of Example 2 when the amount of sulfuric acid input was small, but when the sample was washed with the same amount of water. This is presumably because the dissolved ammonium sulfate salt was contained in the solid. It is estimated that if the amount of sulfuric acid input is less than an appropriate value, dehydration of the produced NaF becomes difficult and the residual probability of impurities increases. On the other hand, in the case of Comparative Example 4 in which 105 mol% of sulfuric acid was added, it was found that a large amount of unreacted sulfuric acid remained in NaF after drying. From this, it was confirmed that the appropriate range of sulfuric acid was 85 to 100 mol% of the theoretical molar amount of sulfuric acid reacting with ammonium ions.

Sulfuric acid dosage
(47.6% by weight) soda ash
input BOE
input washing liquid
input after dehydration
moisture content remaining
sulfuric acid concentration Comparative Example 3 175.7g
(80 mol%) 170.7g 400g 170g 14.8% by weight 0.04% Example 2 186.7g
(85 mol%) 170.7g 400g 170g 12.7% by weight N.D. Example 3 197.6g
(90 mol%) 170.7g 400g 170g 11.9% by weight 0.01% Example 4 208.6g
(95 mol%) 170.7g 400g 170g 10.5% by weight 0.08% Example 5 219.6g
(100 mol%) 170.7g 400g 170g 10.3% by weight 0.10% Comparative Example 4 230.6g
(105 mol%) 170.7g 400g 170g 10.2% by weight 0.7%

* The amount of sulfuric acid input is mol% of the theoretical amount of sulfuric acid that will react with the ammonium ions in the BOE waste liquid.

Item KS standard Comparative Example 3 Example 2 Example 3 Example 4 Example 5 Comparative Example 4 moisture
(weight%) 0.5 or less 0.4 0.2 0.2 0.3 0.2 0.2 Free acid (HF)
(weight%) 0.1 or less N.D. 0.02 0.01 0.02 0.03 0.03 Free alkali (Na ₂ CO ₃ )
(weight%) 0.5 or less 0.1 N.D. N.D. N.D. N.D. N.D. silicification
salt
(weight%) 1.5 or less 0.02 0.01 N.D. N.D. N.D. 0.01 sulfate
(weight%) 0.1 or less 0.07 N.D. 0.01 0.08 0.10 0.70 sodium fluoride
(weight%) 97 or higher 98.1 98.8 98.7 98.5 98.8 96.8

Example 6 to 7 and comparative example 5

The following series of experiments were performed to investigate the effect of changes in the amount of sodium compound input during NaF production using BOE waste liquid.

85 mol% (Example 6), 95 mol% (Example 7), 100 mol% (Comparative Example 5) relative to the theoretical amount of the sodium compound required for the reaction with the fluorine component contained in the BOE waste liquid were added to each. The amount of sulfuric acid input was fixed at 95 mol% of the amount of sulfuric acid required to react with ammonium ions contained in the BOE waste solution. The detailed reaction procedure was the same as in Example 1. The changed input amount of each drug is summarized in Table 8, and the analysis results according to KS M 1404 for solids after drying at 110° C. for 1 hour are shown in Table 9.

Sulfuric acid (47.6% by weight)
input BOE
input soda ash
input yield
(dry weight) Example 6 208.6g 400g 161.3 g (85 mol%) 88.6g Example 7 208.6g 400g 180.2 g (95 mol%) 99.7g Comparative Example 5 208.6g 400g 189.7 g (100 mol%) 106.8g

Item NaF standard Example 6 Example 7 Comparative Example 5 Moisture (wt%) 0.5 or less 0.2 0.2 0.3 Free acid (HF) (wt%) 0.1 or less 0.02 0.02 N.D. Free alkali (Na ₂ CO ₃ )
(weight%) 0.5 or less N.D. N.D. 1.2 sodium silicate
(weight%) 1.5 or less 0.01 0.02 0.01 sulfate
(weight%) 0.1 or less N.D. 0.05 0.05 sodium fluoride
(weight%) 97 or higher 98.5 98.4 97.6

Referring to the results of Tables 8 and 9, in Comparative Example 5 in which 100 mol% of the sodium compound was added (soda ash), the soda ash (Na ₂ CO ₃ ) remaining in the NaF obtained after drying the solid was KS M 1404 standard. appeared to exceed. On the other hand, as the input amount of soda ash decreased, the yield of NaF decreased, and 85% to 95% of the theoretical molar amount of the sodium-based compound required to react with the fluorine component contained in the BOE waste liquid was confirmed as a suitable input range.

As described above, if the waste liquid containing ammonium-based fluorine compounds is detoxified and neutralized using the recovery method of the present invention, high-quality sodium fluoride with increased crystal size can be efficiently obtained, and hydrofluoric acid and ammonia gas during treatment It can be seen that the work environment or surrounding environment can be greatly improved by suppressing the occurrence of In addition, it can be confirmed that the obtained sodium fluoride particle size is increased and the filterability is improved, so that the filtration time can be significantly shortened and the filtration process can be greatly improved.

Claims (9)

A method for recovering sodium fluoride from an ammonium-based fluorine compound-containing waste solution, the method comprising:
a) preparing a solution containing sodium sulfate by adding sulfuric acid to an aqueous solution of a sodium-based alkali compound;
b) obtaining a product containing sodium fluoride by dropping an ammonium-based fluorine compound waste solution thereto while stirring the solution containing sodium sulfate to proceed with a fixing reaction;
c) filtering the mixture containing the product to separate the product containing the sodium fluoride in solid form and washing the product; and
d) drying a product comprising said sodium fluoride in solid form;
The input amount of the sodium-based compound in step a) is 85% of the theoretical molar amount of the sodium-based compound required for the fixed reaction according to the following Reaction Scheme 1 with the fluorine component contained in the ammonium-based fluorine compound waste solution added in step b) to 95% of the range,
Na ⁺ + F ^- --> NaF (1),
The amount of sulfuric acid added in step a) is 85% to 100% of the theoretical molar amount of sulfuric acid required for the fixed reaction according to Scheme 2 below with the ammonium ion component contained in the ammonium-based fluorine compound waste solution added in step b) A recovery method characterized in that the range:
2NH ₄ ⁺ + SO ₄ ^2- --> (NH ₄ ) ₂ SO ₄ (2). The method of claim 1, wherein the sodium-based alkali compound in step a) is _{at least one selected from soda ash (Na 2} CO ₃ ) and caustic soda (NaOH). delete The recovery method according to claim 1, wherein in step a), the ammonium-based fluorine compound waste solution is dripped over 1 to 2 hours. The recovery method according to claim 1, wherein the reaction proceeding in step b) is carried out at a temperature range of 60 to 70 °C and a pH range of 6.0 to 7.0. The recovery method according to claim 5, wherein in adjusting the pH, sulfuric acid is used to lower the pH, and ammonia water is used to increase the pH. The recovery method according to claim 1, wherein the ammonium-based fluorine compound in step b) is at least one selected from ammonium fluoride and ammonium bifluoride. The recovery method according to claim 1, wherein the drying step in step d) is carried out under conditions in which moisture is removed and impurities are removed by thermal decomposition. The recovery method according to claim 8, wherein the condition is performed at a temperature of 110° C. for 1 hour or more, and the impurities include NH ₄ HCO ₃ and (NH ₄ ) ₂ CO _{3 .}