TW202229172A - Method of recycling ammonia from wasting buffered oxide etchants and preparing fluoro-salt crystals and solid silicon dioxide - Google Patents

Abstract

The invention provides a method of recycling ammonia from wasting buffered oxide etchants and preparing fluoro-salt crystals and solid silicon dioxide, which comprises the following steps: introducing waste BOE silicon dioxide etching solution and sodium hydroxide into an ammonia generator, By heating the reaction liquid in the ammonia generator, the ammonia stripped by air is introduced into the ammonia absorption tower, and the ammonia absorption liquid is diffused and absorbed; and when the ammonia concentration of the reaction liquid in the ammonia generator is less than a certain concentration, it is transported to the pH adjustment tank uses hydrofluoric acid to adjust the PH value of the reaction solution, and introduces it into the solid-liquid separation and concentration equipment to obtain fluoride salt crystals and silicon dioxide solids. The invention can synthesize waste (water) liquid containing hydrofluoric acid in the wet silicon dioxide layer etching process of silicon wafer manufacturing. Compared with the conventional method, it focuses on calcium fluoride, sodium fluorosilicate, and sodium hexafluoroaluminate. These three categories can recover ammonia and prepare fluoride salt crystals and silicon dioxide solids.

Description

Method for recovering ammonia from waste BOE silicon dioxide etching solution and preparing fluorine salt crystal and silicon dioxide solid

The invention relates to a method for recycling waste silicon wafer etching solution, in particular to a method for recovering ammonia from waste BOE silicon dioxide etching solution and gradually obtaining high-purity fluorine salt and silicon dioxide from the recycling process. method.

In the wet silicon dioxide layer etching (SiO ₂ Etching) process in the silicon wafer process, the commonly used chemicals are hydrofluoric acid (HF) solution and buffered oxide etchant (Buffered Oxide Etchant, referred to as BOE).

BOE silicon dioxide etching solution is a mixed solution of hydrofluoric acid (HF) and ammonium fluoride (NH ₄ F), which has the effect of buffering. The chemical reaction formula of etching silicon dioxide layer is as follows: SiO ₂ + 4HF + 2NH ₄ F → (NH ₄ ) ₂ SiF ₆ + 2H ₂ O In the traditional mechanism of using hydrofluoric acid (HF) to etch silicon dioxide layers, the etch rate is determined by the concentration of HF. Stable, need to rely on NH ₄ F solution to provide a large amount of F ^- ions to achieve the effect of buffering, so the etching rate can be kept stable.

The BOE waste (water) liquid produced in the current silicon wafer process contains ammonia, and the nitrogen (N) in ammonia can provide a nutrient source for the growth of aquatic plants, which makes aquatic plants such as seaweed and aquatic plants abundant Reproduction, which will lead to the lack of oxygen in the waters, and then let the aquatic life die. That is, ammonia nitrogen is one of the important monitoring pollution sources in the water environment, and it is also the main nutrient source that leads to the optimization of water bodies. It has strong acute toxicity and can easily cause immediate harm to aquatic organisms. Once high-concentration ammonia nitrogen wastewater is discharged into rivers and lakes, It is easy to lead to rapid deterioration of water quality, or the proliferation of microorganisms and algae, resulting in the phenomenon of optimal nutrient and ecological balance disorders in water bodies. Therefore, the Environmental Protection Agency has regulated the discharge of ammonia nitrogen from wastewater, and the recovery of ammonia nitrogen has now become an important issue.

In the wet silicon dioxide layer etching (SiO ₂ Etching) process of silicon wafer manufacturing, the produced waste (water) liquid containing hydrofluoric acid has been applied for relevant recycling patents in China as follows: Patent number Announcement/Public Date Application Number patent name I574923 2017/03/21 105110725 A method for producing calcium fluoride from wastewater containing hydrofluoric acid, hexafluorosilicic acid and hexafluoroaluminate I529131 2016/04/11 103130633 Method for recovering sodium fluorosilicate from hydrofluoric acid waste liquid I518041 2016/01/21 103128491 Method for recovering sodium fluoroaluminate from hydrofluoric acid waste liquid I449668 2014/08/21 101112494 Preparation method of calcium fluoride

Patent No. I574923 is a method for producing calcium fluoride from wastewater containing hydrofluoric acid, hexafluorosilicic acid and hexafluoroaluminate, adding potassium fluoride to the wastewater containing hydrofluoric acid, hexafluorosilicic acid and hexafluoroaluminate , With the aid of ammonia water, calcium hydroxide and flocculants, through the process of precipitation and filtration, calcium fluoride with good purity can be produced, especially for the treatment of waste LCD panel glass etching solution to produce calcium fluoride.

Patent No. I529131 is a method for recovering sodium fluorosilicate from hydrofluoric acid waste liquid. The hydrofluoric acid waste liquid is mixed with silicon concentrate, reacted at 20 to 50 ° C for 1 to 4 hours, and the first mixture is generated and filtered. , obtain a solution of silicon carbide and fluorosilicic acid, mix sodium salt with the solution containing fluorosilicic acid, and react at 20 to 50° C. for 1 to 4 hours. Another waste can be used to precipitate fluorine from the hydrofluoric acid waste liquid, so as to achieve the effect of reducing the treatment cost of the hydrofluoric acid waste liquid.

Patent number I518041 is a kind of method that reclaims sodium fluoroaluminate from hydrofluoric acid waste liquid, mixes nickel-aluminum concentrate with sodium-containing alkali powder, reacts at 200～800 ℃ for 2～4 hours, generates the first sinter, This first sinter is immersed in the water of 60～100 ℃ and reacts 0.5～2 hour, obtains nickel concentrate and sodium aluminate solution, adds alkaline substance in this sodium aluminate solution, obtains sodium aluminate precious liquid and sodium The salts are mixed and reacted for 1 to 4 hours at 60 to 100°C. Using another waste to precipitate fluorine in the form of sodium fluoroaluminate from the hydrofluoric acid waste liquid, the effect of reducing the treatment cost of the hydrofluoric acid waste liquid is achieved.

Patent No. I449668 is a method for preparing calcium fluoride, which provides a waste liquid containing HF acid, controls the HF acid content in the waste liquid to a predetermined concentration range, adds a Ca source to the waste liquid, and simultaneously controls the relationship between Ca and HF acid. The reaction temperature is within a predetermined temperature range to generate CaF ₂ . The preparation method of calcium fluoride has the advantages of simple process, low cost, high preparation speed of CaF ₂ and extremely high and stable purity and quality.

From the above, it can be found that the recovered products of the currently approved patents focus on the three categories of calcium fluoride, sodium fluorosilicate, and sodium fluoroaluminate, but the products after ammonia recovery are not seen. It can be seen that these patented methods are not applicable. in hydrofluoric acid (HF) waste solution containing ammonium fluoride (NH ₄ F).

The object of the present invention is to provide a method for recovering ammonia from waste silicon dioxide etching solution containing ammonium and preparing fluoride salt solid and silicon dioxide (SiO ₂ ). Retain the advantage of recycling fluorine (F) and silicon (Si) into related compounds.

In order to achieve the aforementioned objects, the present invention provides a method for recovering ammonia from waste BOE silicon dioxide etching solution and preparing fluorine salt crystals and silicon dioxide solids, comprising the following steps (A) to (D).

Step (A): Introduce the waste BOE silicon dioxide etching solution into the ammonia generator, and then add sodium hydroxide (NaOH) to increase the pH value of the waste BOE silicon dioxide etching solution to above 11 (hereinafter referred to as the reaction solution), and react Liquid warming (use steam or hot kerosene for indirect heating, do not directly contact the reaction liquid). Use the air stripping method to remove ammonia, use an ammonia gas sensing electrode or ammonia nitrogen test paper, and confirm that the residual amount of ammonia nitrogen in the reaction liquid is less than 10 ppm before proceeding to the next step (B). During the reaction at this stage, sodium hydroxide should be added at any time to ensure that the pH of the reaction solution is greater than 11. That is, the air stripping method uses air stripping (air is used as a carrier) under alkaline conditions to utilize the difference between the actual concentration and equilibrium concentration of ammonia nitrogen contained in wastewater, and convert ammonia ions into ammonia molecules through an alkaline environment. Through its volatile ammonia into gas, the purpose of collecting ammonia is achieved. After stripping off ammonia, the remaining fluoride ions in the reaction liquid will combine with sodium ions to form sodium fluoride, and the silicon in the waste liquid will be decomposed in high pH environment due to the characteristics of sodium fluorosilicate (Na ₂ SiF ₆ ), which cannot be used. A precipitate of sodium fluorosilicate (Na ₂ SiF ₆ ) was formed, instead becoming an amorphous solid with a white translucent jelly-like appearance.

The ammonia dissipated after air stripping is collected, and in the ammonia absorption tower, water or hydrochloric acid can be used to absorb the stripped ammonia gas, respectively, to make ammonia water or ammonium chloride solution.

Step (B): use hydrofluoric acid (HF) to adjust the pH of the reaction solution in step (A) to between 6 and 8.

Step (C): The reaction solution in step (B) is separated by a solid-liquid separation device, the solid can obtain a silicon precipitate, and the liquid can obtain a clear and transparent liquid containing sodium fluoride.

Step (D): The silicon precipitate produced in step (C) is washed with a water washing procedure, and after removing the residual sodium fluoride aqueous solution, it is sent to a drying equipment, and dried at a temperature above 100 ° C to remove the contained sodium fluoride solution. moisture, making it a white silica powder solid.

Step (E): The sodium fluoride-containing liquid separated in step (C) is sent to the concentration equipment, so as to remove a large amount of water, so that the sodium fluoride liquid reaches a supersaturated state to produce sodium fluoride crystals.

In the present invention, the ammonia water obtained in step (A) can be used or sold for personal use after being concentrated again, the liquid containing sodium fluoride separated in step (C) can be concentrated into sodium fluoride crystals for sale, and step (D) washing The cleaned silica precipitate can be made into white silica after drying.

Hereinafter, a method for recovering ammonia from waste BOE silicon dioxide etching solution and preparing fluorine salt crystals and silicon dioxide solid will be described with reference to FIGS. 1 and 2 , in which steps S10 and S50 can be referred to in conjunction with FIG. 3 , which are shown differently. Effects of pH and different temperatures on the relative amounts of ammonia molecules and ammonium ions. Please refer to FIG. 1 and FIG. 2 , in step S10 , the waste BOE silicon dioxide etching solution and sodium hydroxide are simultaneously added to the ammonia generator 1 , and the liquid in the ammonia generator 1 is hereinafter referred to as the reaction solution.

In step S20, the reaction liquid is indirectly heated by the steam generated by the boiler 2. Under the environment of high temperature and high pH, the ammonium ions (NH ₄ ⁺ ) in the reaction liquid will become gaseous ammonia (NH ₃ ) and escape. NH ₄ F + NaOH → NaF + NH ₃ ↑ + H ₂ O (NH ₄ ) ₂ SiF ₆ + 2NaOH → Na ₂ SiF ₆ + 2NH ₃ ↑ + 2H ₂ O

In step S30, the pressure-feeding blower 3 is used to send air from below the ammonia generator 1, and the ammonia in the reaction solution is blown out by the air stripping method, and the remaining reaction solution components are mainly sodium fluoride and silicon dioxide. .

Because sodium fluorosilicate cannot exist in an alkaline environment, it will decompose into sodium fluoride and silicon dioxide, and under the action of water (H ₂ O), the silicon precipitate at this time is white and translucent jelly-like. Amorphous solid. Na ₂ SiF ₆ + 4NaOH → 6NaF + SiO ₂ ‧2H ₂ O

In step S40, the stripped ammonia gas is introduced into the ammonia absorption tower 4.

In step S50, the ammonia gas blown out in step S40 is absorbed by the ammonia absorption liquid. If the ammonia absorption liquid is water, the temperature of the ammonia absorption liquid (i.e. water) is lowered by cooling to dissolve the ammonia gas in the ammonia absorption liquid (i.e. water), and the obtained product is ammonia water: H ₂ O + NH ₃ → NH ₄ ⁺ + OH ^- (please refer to Figure 2). If the ammonia absorption liquid is hydrochloric acid, the obtained product is ammonium chloride solution: HCl + NH ₃ → NH ₄ ⁺ + Cl ^- .

In step S60, the ammonia absorption liquid is stored and stored in the ammonia absorption liquid storage tank 5 for the circulating use of the ammonia absorption tower 4, and the ammonia absorption liquid is replaced with a new ammonia absorption liquid when the ammonia absorption liquid reaches the required concentration.

In step S70, the temperature of the absorption liquid will increase after absorbing ammonia gas, thus reducing the absorption efficiency. Therefore, a cooling device, such as an ice water machine 6, is prepared in advance. Used to dissolve ammonia gas in ammonia absorption liquid (ie water).

Step S80, use ammonia nitrogen test paper or ammonia gas sensing electrode to monitor the ammonia nitrogen concentration of the reaction solution in the ammonia generator 1, and when the ammonia nitrogen concentration of the reaction solution is less than 10 ppm, transfer the reaction solution in the ammonia generator 1 to pH Adjust slot 7.

Step S90, use hydrofluoric acid (HF) to lower the pH value of the reaction solution in the pH adjustment tank 7 to between 6 and 8 (optimally 7), the purpose of which is to convert the excess NaOH remaining in the reaction solution into fluorine Sodium. HF + NaOH → NaF + H ₂ O

In step S100, the reaction solution is introduced into a solid-liquid separation device, such as a filter press 8, for solid-liquid separation to remove silicon precipitates in the sodium fluoride solution to obtain a semi-finished sodium fluoride solution.

In step S110, the semi-finished product of the sodium fluoride solution is transported to a concentration device, such as a concentration evaporation tank 9, to remove excess water, increase the concentration of sodium fluoride, and then achieve a state of a supersaturated solution in which sodium fluoride coexists in solid and liquid phases.

In step S120, the supersaturated sodium fluoride solution is introduced into a solid-liquid separation device, such as the centrifugal dehydrator 10, the solid obtained after solid-liquid separation is a finished sodium fluoride crystal, and the separated liquid can be recovered as the mother liquor of the concentration device.

In step S130, the silicon precipitate obtained in step S100 is washed with water until the residual F-ion concentration in the washing water is less than 10 ppm. The high fluoride ion concentration in the front-end washing water can be recycled into the concentration equipment, and the middle and back-end washing water can be sent to the waste water plant.

In step S140 , the silicon precipitate washed in step S130 is introduced into a drying device, such as the oven 11 , to remove the water content of the precipitate and turn it into pure white silicon dioxide powder.

In another embodiment, the sodium hydroxide (NaOH) in step S10 can be replaced by potassium hydroxide (KOH), that is, the waste BOE silicon dioxide etching solution and potassium hydroxide are added to the ammonia generator 1 at the same time; In step S120, potassium fluoride (KF) fluoride salt crystals are obtained, and silicon dioxide solid is obtained in step S140.

The above descriptions are only preferred feasible embodiments of the present invention, and therefore do not limit the scope of the patent protection of the present invention. In addition to the above-mentioned embodiments, the present invention may also have other modes, and all technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope of the present invention. The undescribed technical features of the present invention can be realized by or using the prior art, and are not repeated here.

1: Ammonia generator 2: Boiler 3: Blower 4: Ammonia absorption tower 5: Ammonia absorption liquid storage tank 6: Ice water machine 7: pH adjustment tank 8: filter press 9: Concentrated evaporation tank 10: Centrifugal dehydrator 11: Oven S10: Add waste BOE silicon dioxide etching solution and sodium hydroxide to the ammonia generator at the same time S20: Indirect heating of reaction liquid using steam generated by boiler S30: Use a pressure-feed blower to feed air from below the ammonia generator S40: introduce the stripped ammonia gas into the ammonia absorption tower S50: Absorb ammonia gas with ammonia absorption liquid S60: Ammonia absorption liquid storage tank provides ammonia absorption liquid for circulating use of ammonia absorption tower S70: Use cooling equipment to reduce the temperature of ammonia absorption liquid S80: transfer the reaction solution in the ammonia generator to the pH adjustment tank S90: adding hydrofluoric acid to lower the pH of the reaction solution S100: Introduce the reaction solution to the filter press S110: transport the semi-finished product of sodium fluoride solution to the concentrated evaporation tank S120: introduce the supersaturated sodium fluoride solution into the centrifugal dehydrator S130: Wash the silicon precipitate with water S140: Introduce the washed silicon precipitate into the oven

1 and 2 are flowcharts of a method for recovering ammonia from waste BOE silicon dioxide etching solution and preparing fluoride salt crystals and silicon dioxide solids according to an embodiment of the present invention; Figure 3 is a schematic diagram of the relative amounts of ammonia molecules and ammonium ions under different pH values and different temperature conditions.

S10: Add waste BOE silicon dioxide etching solution and sodium hydroxide to the ammonia generator at the same time

S20: Indirect heating of reaction liquid using steam generated by boiler

S30: Use a pressure-feed blower to feed air from below the ammonia generator

S40: introduce the stripped ammonia gas into the ammonia absorption tower

S50: Absorb ammonia gas with ammonia absorption liquid

S60: Ammonia absorption liquid storage tank provides ammonia absorption liquid for circulating use of ammonia absorption tower

S70: Use cooling equipment to reduce the temperature of ammonia absorption liquid

S80: transfer the reaction solution in the ammonia generator to the pH adjustment tank

S90: adding hydrofluoric acid to lower the pH of the reaction solution

S100: Introduce the reaction solution to the filter press

S110: transport the semi-finished product of sodium fluoride solution to the concentrated evaporation tank

S120: introduce the supersaturated sodium fluoride solution into the centrifugal dehydrator

S130: Wash the silicon precipitate with water

S140: Introduce the washed silicon precipitate into the oven

Claims (10)

A method for recovering ammonia from waste BOE silicon dioxide etching solution and preparing fluorine salt crystal and silicon dioxide solid, which is characterized by comprising the following steps: (A) introduce waste BOE silicon dioxide etching solution and sodium hydroxide into the ammonia production method, and introduce the ammonia after air stripping into the ammonia absorption method by heating the reaction liquid in the ammonia production method, and absorb it with the ammonia absorption liquid; (B) When the ammonia concentration of the reaction liquid in the ammonia production method is less than a certain concentration, it is sent to the pH adjustment method, the pH value of the reaction liquid is adjusted with hydrofluoric acid, and introduced into the solid-liquid separation and concentration method to obtain fluorination. Sodium fluoride salt crystals and silica solid. The method according to claim 1, wherein the sodium hydroxide in step (A) is replaced by potassium hydroxide, and the fluoride salt crystal of potassium fluoride is obtained by the solid-liquid separation and concentration method in step (B). The method as claimed in claim 1, wherein step (A) is to heat the reaction liquid through steam generated by a boiler, and use a blower to send in air to blow out ammonia in the reaction liquid. The method according to claim 1, wherein the ammonia absorption method of step (A) is to recycle the ammonia absorption liquid of the ammonia absorption liquid storage tank. The method of claim 1, wherein a cooling method is further provided to cool the ammonia absorption liquid. The method according to claim 1, wherein in the step (B), when the ammonia concentration of the reaction solution in the monitoring ammonia production method is less than 10 ppm, it is sent to a pH adjustment tank. The method according to claim 1, wherein step (B) is to adjust the pH value of the reaction solution to between 6 and 8 with hydrofluoric acid. The method according to claim 1, wherein step (B) is followed by a step (B2), the fluorine salt crystal solution obtained by solid-liquid separation is sent to the concentration method, and then the fluorine salt crystal is obtained by the solid-liquid separation method. The method according to claim 1 or 8, wherein step (B) is followed by a step (B3), wherein the silicon precipitate after solid-liquid separation is washed with water until the residual fluoride ion concentration in the washing water is less than a certain value, and a drying method is introduced to remove Moisture yields silica solids. The method of claim 9, wherein the fixed value is 10 ppm.

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