Method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material

Abstract

A method for preparing electronic-grade inorganic acid using waste hydrofluoric acid liquid as a raw material, wherein an alkali metal salt containing an alkali metal fluoride and an alkali metal nitrate is added to the waste hydrofluoric acid liquid containing hydrofluoric acid, nitric acid and water, the azeotropic phenomenon of hydrofluoric acid and water is destroyed, and then hydrogen fluoride vapor is separated by distillation, and the residue is a mixed solution formed by nitric acid, water, alkali metal nitrate and alkali metal fluoride. Nitric acid and water are then evaporated from the mixed solution to form a nitric acid-water mixed solution, and alkaline earth metal nitrate is added to the nitric acid-water mixed solution to destroy the azeotropic phenomenon of nitric acid and water, and then nitric acid is separated by distillation. The separated hydrogen fluoride vapor and nitric acid vapor are respectively depleted of impurity droplets, condensed, and then concentrated with ultrapure water to obtain electronic-grade hydrofluoric acid and electronic-grade nitric acid that meet the purity standards required by the semiconductor industry.

Description

Technical Field

[0001] The invention relates to a method for treating waste hydrofluoric acid liquid in the electronics industry, in particular to a method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as a raw material. Background Art

[0002] In the manufacturing process of high-tech electronic industries such as semiconductors and solar cells, a large amount of hydrofluoric acid or a mixed acid containing hydrofluoric acid and nitric acid is used for cleaning and etching of silicon and silicon compounds, resulting in the generation of a large amount of waste hydrofluoric acid liquid. Waste hydrofluoric acid liquid contains hydrofluoric acid and water, or contains hydrofluoric acid, nitric acid and water. If the waste hydrofluoric acid liquid is directly discharged without proper treatment, it will cause waste of resources and cause serious pollution and harm to the environment. In particular, with the vigorous development of the semiconductor industry, the use of hydrofluoric acid and nitric acid has also increased, further exacerbating the generation of a large amount of waste hydrofluoric acid liquid. Therefore, how to effectively treat waste hydrofluoric acid liquid in the electronics industry, especially the treatment of waste hydrofluoric acid liquid containing hydrofluoric acid, nitric acid and water, is an important issue that urgently needs to be solved.

[0003] However, since hydrofluoric acid and water in the waste hydrofluoric acid liquid easily form an azeotrope, and nitric acid and water easily form an azeotrope, the three components of hydrofluoric acid, nitric acid and water also easily form an azeotrope, resulting in the existing electronic industry waste hydrofluoric acid liquid treatment methods, such as sulfuric acid method, reduced pressure evaporation method, ion exchange method, solvent extraction method and electrodialysis method, etc., all cannot effectively separate hydrofluoric acid and nitric acid from the waste hydrofluoric acid liquid separately, and cannot regenerate high-purity hydrofluoric acid and high-purity nitric acid, thereby limiting the application and economic benefits of the recovered acid. Summary of the invention

[0004] The inventors first aimed to solve the problem that the existing methods for treating waste hydrofluoric acid liquid in the electronics industry cannot effectively separate and recover hydrofluoric acid and nitric acid from waste hydrofluoric acid liquid containing hydrofluoric acid, nitric acid and water. Therefore, the first object of the present invention is to provide a method for preparing electronic-grade inorganic acid using waste hydrofluoric acid liquid as a raw material, wherein the method can achieve the separate separation and recovery of hydrofluoric acid and nitric acid and produce high-purity electronic-grade hydrofluoric acid and high-purity electronic-grade nitric acid.

[0005] The method of the present invention for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material comprises the following steps:

[0006] Step S1: comprising adding an alkali metal salt containing an alkali metal fluoride and an alkali metal nitrate into a waste hydrofluoric acid liquid containing hydrofluoric acid, nitric acid and water to destroy the azeotropic phenomenon of hydrofluoric acid and water, and performing a first distillation treatment in a vacuum environment to separate hydrogen fluoride vapor, and the residue is a mixed solution formed by nitric acid, water, alkali metal nitrate and alkali metal fluoride, wherein the amount of the alkali metal salt is in a range of 20 mol% to 40 mol% relative to the total molar amount of all substances in the waste hydrofluoric acid liquid and the alkali metal salt;

[0007] Step S2: comprising removing droplets containing impurities entrained in the hydrogen fluoride vapor to obtain pure hydrogen fluoride vapor;

[0008] Step S3: comprising condensing the pure hydrogen fluoride vapor and adjusting the concentration with ultrapure water to produce electronic grade hydrofluoric acid with a hydrofluoric acid concentration range of 49±0.5%;

[0009] Step S4: comprising subjecting the mixed solution formed by the nitric acid, water, alkali metal nitrate and alkali metal fluoride in step S1 to a first evaporation treatment in a vacuum environment, thereby evaporating nitric acid and water from the mixed solution to form a nitric acid-water mixed solution, and concentrating the alkali metal nitrate, alkali metal fluoride and unevaporated water to form an alkali metal salt concentrated solution, and introducing the alkali metal salt concentrated solution into the first distillation treatment of step S1 for recycling;

[0010] Step S5: adding alkaline earth metal nitrate to the nitric acid-water mixture obtained in step S4 to destroy the azeotropic phenomenon between nitric acid and water, and performing a second distillation treatment in a vacuum environment to separate nitric acid vapor, and the residue is an alkaline earth metal nitrate solution formed by alkaline earth metal nitrate and water;

[0011] Step S6: comprising removing droplets containing impurities entrained in the nitric acid vapor to obtain pure nitric acid vapor;

[0012] Step S7: comprising condensing the pure nitric acid vapor and adjusting the concentration with ultrapure water to prepare electronic grade nitric acid with a nitric acid concentration range of 70±0.5%; and

[0013] Step S8: comprising subjecting the alkaline earth metal nitrate solution obtained in step S5 to a second evaporation treatment in a vacuum environment, so that part of the water in the alkaline earth metal nitrate solution is evaporated to form an alkaline earth metal nitrate concentrated solution, and the alkaline earth metal nitrate concentrated solution is introduced into the second distillation treatment of step S5 for recycling.

[0014] The present invention discloses a method for preparing electronic grade inorganic acid by using waste hydrofluoric acid liquid as raw material. The alkali metal fluoride salt is selected from one or more of lithium fluoride, potassium fluoride and cesium fluoride, the alkali metal nitrate salt is selected from one or more of lithium nitrate, potassium nitrate and cesium nitrate, and the molar ratio of the alkali metal fluoride salt to the alkali metal nitrate salt is in the range of 0.05 to 10.

[0015] The present invention provides a method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as a raw material. In the step S1, the pressure range of the vacuum environment is 100 mmHg to 500 mmHg, the first distillation treatment is carried out in a distillation tower with a polytetrafluoroethylene liner, and the bottom temperature range of the distillation tower is 80°C to 130°C, the top temperature range is 50°C to 100°C, and the reflux ratio range is 0.5 to 3.

[0016] The present invention uses waste hydrofluoric acid liquid as a raw material to prepare an electronic grade inorganic acid. In the step S4, the temperature range of the first evaporation treatment is 130° C. to 180° C.

[0017] The present invention provides a method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as a raw material. In the step S5, the alkaline earth metal nitrate is selected from one or more of magnesium nitrate and calcium nitrate, and the amount of the alkaline earth metal nitrate is in a range of 40 mol% to 65 mol% relative to the total molar amount of the alkaline earth metal nitrate, nitric acid and water in the nitric acid-water mixture.

[0018] The present invention provides a method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as a raw material. In the step S5, the pressure range of the vacuum environment is 100 mmHg to 500 mmHg, the second distillation treatment is carried out in a distillation tower with a polytetrafluoroethylene liner, and the bottom temperature range of the distillation tower is 120°C to 140°C, the top temperature range is 70°C to 100°C, and the reflux ratio range is 0.5 to 3.

[0019] The present invention uses waste hydrofluoric acid liquid as a raw material to prepare electronic grade inorganic acid. In the step S8, the temperature range of the second evaporation treatment is 130° C. to 180° C.

[0020] In addition, the inventors have found that hydrofluoric acid can be effectively separated and recovered from waste hydrofluoric acid liquid containing hydrofluoric acid and water but not containing nitric acid by adding alkali metal salts and performing distillation. Therefore, a second object of the present invention is to provide a method for preparing electronic-grade inorganic acid using waste hydrofluoric acid liquid as a raw material, wherein the method can separate and recover hydrofluoric acid and produce high-purity electronic-grade hydrofluoric acid.

[0021] The method of the present invention for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material comprises the following steps:

[0022] Step S1: adding an alkali metal salt containing an alkali metal fluoride and an alkali metal nitrate into a waste hydrofluoric acid liquid containing hydrofluoric acid and water to destroy the azeotropic phenomenon of hydrofluoric acid and water, and performing a first distillation treatment in a vacuum environment to separate hydrogen fluoride vapor, wherein the amount of the alkali metal salt used is greater than 20 mol% relative to the total molar amount of all substances in the waste hydrofluoric acid liquid and the alkali metal salt;

[0023] Step S2: comprising removing droplets containing impurities entrained in the hydrogen fluoride vapor to obtain pure hydrogen fluoride vapor; and

[0024] Step S3: comprising condensing the pure hydrogen fluoride vapor and adjusting the concentration with ultrapure water, thereby preparing electronic grade hydrofluoric acid with a hydrofluoric acid concentration range of 49±0.5%.

[0025] The present invention provides a method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as a raw material. In the step S1, the alkali metal fluoride salt is selected from one or more of lithium fluoride, potassium fluoride and cesium fluoride, the alkali metal nitrate is selected from one or more of lithium nitrate, potassium nitrate and cesium nitrate, and the molar ratio of the alkali metal fluoride salt to the alkali metal nitrate is in the range of 0.05 to 10.

[0026] The present invention provides a method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as a raw material. In the step S1, the pressure range of the vacuum environment is 100 mmHg to 500 mmHg, the first distillation treatment is carried out in a distillation tower with a polytetrafluoroethylene liner, and the bottom temperature range of the distillation tower is 80°C to 130°C, the top temperature range is 50°C to 100°C, and the reflux ratio range is 0.5 to 3.

[0027] The beneficial effect of the present invention is that when the waste hydrofluoric acid solution contains hydrofluoric acid, nitric acid and water, the method of the present invention is carried out through the steps S1 to S8, especially in the step S1, the azeotropic phenomenon of hydrofluoric acid and water is destroyed by the alkali metal salt of a specific amount so that the first distillation treatment can separate the hydrogen fluoride vapor, and in the step S5, the azeotropic phenomenon of nitric acid and water in the nitric acid-water mixture is destroyed by the alkaline earth metal nitrate so that the second distillation treatment can separate the nitric acid vapor, and in combination with the steps S2 and S3, the hydrogen fluoride vapor is further made into high-purity electronic-grade hydrofluoric acid, and the steps S6 and S7 further make the nitric acid vapor into high-purity electronic-grade nitric acid. The high-purity electronic-grade hydrofluoric acid and electronic-grade nitric acid prepared by the method of the present invention are particularly suitable for semiconductor and solar cell processes.

[0028] Another beneficial effect of the present invention is that when the waste hydrofluoric acid liquid contains hydrofluoric acid and water, the present invention uses the steps S1 to S3, especially in the step S1, a specific amount of the alkali metal salt is used to destroy the azeotropic phenomenon between hydrofluoric acid and water so that the first distillation treatment can separate the hydrogen fluoride vapor, and cooperates with the steps S2 and S3 to further make the hydrogen fluoride vapor into high-purity electronic-grade hydrofluoric acid. The high-purity electronic-grade hydrofluoric acid obtained by the method of the present invention is particularly suitable for use in semiconductor and solar cell processes. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below.

[0030] In this article, the "waste hydrofluoric acid liquid" generally refers to the waste hydrofluoric acid [HF] generated in the process of high-tech electronic industries such as semiconductor industry or optoelectronic industry. (aq) ] and water. According to the process of producing the waste hydrofluoric acid solution, the waste hydrofluoric acid solution also contains nitric acid [HNO 3(aq) ] and at least one of fluorosilicic acid (H2SiF6). For example, the waste hydrofluoric acid solution generated in the silicon wafer cleaning process includes water, about 5wt% to 35wt% hydrofluoric acid and about 0.1wt% to 5wt% fluorosilicic acid. The waste hydrofluoric acid solution generated in the polysilicon etching process includes water, about 5wt% to 35wt% hydrofluoric acid, about 0.1wt% to 10wt% fluorosilicic acid and about 10wt% to 55wt% nitric acid.

[0031] When the waste hydrofluoric acid liquid contains hydrofluoric acid and water, the method of the present invention can separate and recycle hydrofluoric acid from the waste hydrofluoric acid liquid and regenerate it into high-purity electronic-grade hydrofluoric acid. When the waste hydrofluoric acid liquid contains hydrofluoric acid, nitric acid and water, the method of the present invention can separate and recycle hydrofluoric acid and nitric acid from the waste hydrofluoric acid liquid and regenerate it into high-purity electronic-grade hydrofluoric acid and electronic-grade nitric acid. Two embodiments of the method of the present invention are described in detail below.

[0032] The first implementation model

[0033] In a first embodiment of the present invention, the waste hydrofluoric acid solution comprises hydrofluoric acid, nitric acid and water. The method of preparing electronic grade inorganic acid using waste hydrofluoric acid solution as raw material comprises the following steps S1 to S8.

[0034] [Step S1]

[0035] Step S1: adding an alkali metal salt containing an alkali metal fluoride salt and an alkali metal nitrate into the waste hydrofluoric acid liquid to destroy the azeotropic phenomenon between hydrofluoric acid and water, and performing a first distillation treatment in a vacuum environment to separate hydrogen fluoride vapor [HF (g)], the residue is a mixed solution of nitric acid, water, alkali metal nitrate and alkali metal fluoride.

[0036] The alkali metal salt can destroy the azeotropic phenomenon of hydrofluoric acid and water in the waste hydrofluoric acid liquid and thus separate the hydrofluoric acid from the water. Moreover, compared with the use of alkali metal fluoride salt alone or alkali metal nitrate salt alone, the mixed use of alkali metal fluoride salt and alkali metal nitrate salt has a better effect on destroying the azeotropic phenomenon of hydrofluoric acid and water. It should be particularly noted that the azeotropic phenomenon of hydrofluoric acid and water is destroyed by controlling the addition ratio of the alkali metal salt. Although the alkali metal salt also changes the gas-liquid equilibrium of nitric acid and water in the waste hydrofluoric acid liquid to cause the azeotropic point to shift, it does not destroy the azeotropic phenomenon of nitric acid and water. Therefore, the first distillation treatment will not separate nitric acid vapor. Therefore, hydrogen fluoride vapor can be separated separately in the step S1. More specifically, relative to the molar sum of all substances in the waste hydrofluoric acid solution and the alkali metal salt, the amount of the alkali metal salt ranges from 20 mol% to 40 mol%. The amount of the alkali metal salt is more than 20 mol%, which can destroy the azeotropic phenomenon of hydrofluoric acid and water, separate more hydrogen fluoride vapor, and thus make the method of the present invention have a higher hydrofluoric acid recovery rate. The amount of the alkali metal salt is less than 40 mol%, which can completely avoid the separated hydrogen fluoride vapor from entraining nitric acid vapor. In addition, the alkali metal fluoride and alkali metal nitrate have the characteristics of large saturated solubility and are not easy to produce crystal precipitation. Preferably, the alkali metal fluoride is selected from one or more of lithium fluoride, potassium fluoride and cesium fluoride, and the alkali metal nitrate is selected from one or more of lithium nitrate, potassium nitrate and cesium nitrate. Preferably, the molar ratio of the alkali metal fluoride to the alkali metal nitrate is in the range of 0.05 to 10, which enables the method of the present invention to have a higher hydrofluoric acid recovery rate (up to 99% or more) and a nitric acid recovery rate (up to 95% or more), and can make the nitric acid content in the produced electronic-grade hydrofluoric acid lower, and the hydrofluoric acid content in the electronic-grade nitric acid lower.

[0037] Preferably, the pressure range of the vacuum environment is 100 mmHg to 500 mmHg, the first distillation treatment is carried out in a distillation tower with a polytetrafluoroethylene liner, and the bottom temperature range of the distillation tower is 80°C to 130°C, the top temperature range is 50°C to 100°C, and the reflux ratio range is 0.5 to 3. Among them, the reflux ratio range is 0.5 to 3, which can separate hydrogen fluoride vapor with higher purity. It is worth mentioning that by adding the alkali metal salt, the first distillation treatment can also be carried out in a low bottom temperature range and a low top temperature range, thereby achieving energy saving and reducing the corrosion of the distillation tower.

[0038] If the waste hydrofluoric acid solution also contains fluorosilicic acid, the step S1 further comprises, before adding the alkali metal salt, adding sodium hydroxide into the waste hydrofluoric acid solution to convert the fluorosilicic acid into sodium fluorosilicate, and removing the sodium fluorosilicate by filtering.

[0039] [Step S2]

[0040] Step S2: comprising removing the droplets containing impurities entrained in the hydrogen fluoride vapor to obtain pure hydrogen fluoride vapor.

[0041] The hydrogen fluoride vapor is passed through a multiple defogger to remove the droplets, and the multiple defogger includes at least two defoggers connected in series, and each defogger includes more than one packing unit. The packing unit has a carrier and a packing filled in the carrier. The material of the carrier is selected from at least one of perfluoroalkoxy vinyl ether copolymer (PFA) and modified polytetrafluoroethylene (M-PTFE). The material of the packing is selected from perfluoroalkoxy vinyl ether copolymer or modified polytetrafluoroethylene. The packing material of the packing unit in each defogger may be the same or different. The shape of the packing is a wire mesh or a 3D honeycomb, and the specific surface area of ​​the packing is in the range of 200m 2 / m 3 Up to 2000m 2 / m 3 .

[0042] [Step S3]

[0043] Step S3: comprising condensing the pure hydrogen fluoride vapor and adjusting the concentration with ultrapure water, thereby preparing electronic grade hydrofluoric acid with a hydrofluoric acid concentration range of 49±0.5%.

[0044] [Step S4]

[0045] Step S4: comprising subjecting the mixed solution formed by the nitric acid, water, alkali metal nitrate and alkali metal fluoride in step S1 to a first evaporation treatment in a vacuum environment, thereby evaporating nitric acid and water from the mixed solution to form a nitric acid-water mixed solution, and concentrating the alkali metal nitrate, alkali metal fluoride and unevaporated water to form an alkali metal salt concentrated solution.

[0046] Preferably, the temperature range of the first evaporation treatment is 130°C to 180°C, and the first evaporation treatment is performed in a vacuum evaporation kettle with a polytetrafluoroethylene liner. The temperature range of the first evaporation treatment is 130°C to 180°C, which can make the alkali metal salt concentrated solution have a high concentration, thereby facilitating the transportation of the alkali metal salt concentrated solution in equipment and pipelines.

[0047] In the step S4, the concentrated alkali metal salt solution is also recovered and introduced into the first distillation treatment of the step S1 for recycling. In more detail, the concentrated alkali metal salt solution recovered in the step S4 is used in the next step S1 to destroy the azeotropic phenomenon of hydrofluoric acid and water. Since a considerable amount of alkali metal nitrate and alkali metal fluoride will be used in the actual implementation of the method of the present invention, a considerable amount of concentrated alkali metal salt solution will be generated. Therefore, by recovering and recycling the concentrated alkali metal salt solution, it is not only possible to avoid the derivation of secondary process waste, but also more energy-saving and environmentally friendly.

[0048] [Step S5]

[0049] Step S5: adding alkaline earth metal nitrate to the nitric acid-water mixture obtained in step S4 to destroy the azeotropic phenomenon between nitric acid and water, and performing a second distillation treatment in a vacuum environment to separate nitric acid vapor [NO 3(g) ], the residue is an alkaline earth metal nitrate solution formed by alkaline earth metal nitrate and water.

[0050] In the nitric acid-water mixture obtained in step S4, nitric acid and water still have an azeotropic point. By adding the alkaline earth metal nitrate in step S5, the azeotropic phenomenon of nitric acid and water in the nitric acid-water mixture can be destroyed, thereby separating nitric acid from water. Therefore, in step S5, the nitric acid vapor can be separated from the nitric acid-water mixture alone, and water forms the alkaline earth metal nitrate solution with the alkaline earth metal nitrate. Preferably, the alkaline earth metal nitrate is selected from one or more of magnesium nitrate and calcium nitrate. Preferably, relative to the molar sum of the alkaline earth metal nitrate, nitric acid and water in the nitric acid-water mixture, the amount of the alkaline earth metal nitrate ranges from 40 mol% to 65 mol%. The amount of the alkaline earth metal nitrate is more than 40 mol%, which can separate more nitric acid vapor and thus make the method of the present invention have a higher nitric acid recovery rate. The amount of the alkaline earth metal nitrate is less than 65 mol%, which can avoid the alkaline earth metal nitrate from being too high in concentration and crystallizing to block the pipeline of the equipment.

[0051] Preferably, the pressure range of the vacuum environment is 100 mmHg to 500 mmHg, the second distillation treatment is carried out in a distillation tower with a polytetrafluoroethylene lining, and the bottom temperature of the distillation tower ranges from 120°C to 140°C, the top temperature ranges from 70°C to 100°C and the reflux ratio ranges from 0.5 to 3, wherein the reflux ratio ranges from 0.5 to 3, which can separate nitric acid vapor with higher purity.

[0052] [Step S6]

[0053] Step S6: comprising removing the mist droplets containing impurities entrained in the nitric acid vapor to obtain pure nitric acid vapor, wherein the nitric acid vapor is passed through a multiple demisting device to remove the mist droplets, and the multiple demisting device is as described above and will not be described in detail here.

[0054] [Step S7]

[0055] Step S7: comprising condensing the pure nitric acid vapor and adjusting the concentration with ultrapure water to obtain electronic grade nitric acid with a nitric acid concentration range of 70±0.5%.

[0056] [Step S8]

[0057] Step S8: comprising subjecting the alkaline earth metal nitrate solution obtained in step S5 to a second evaporation treatment, so that part of the water in the alkaline earth metal nitrate solution is evaporated and concentrated to form an alkaline earth metal nitrate concentrated solution. The temperature range of the second evaporation treatment is 130° C. to 180° C., and the second evaporation treatment is performed in a vacuum evaporator with a polytetrafluoroethylene liner.

[0058] In the step S8, the concentrated alkaline earth metal nitrate solution is recovered and introduced into the second distillation treatment of the step S5 for recycling. In more detail, the concentrated alkaline earth metal nitrate solution recovered in the step S8 is used in the next step S5 to destroy the azeotropic phenomenon of nitric acid and water. Since a considerable amount of alkaline earth metal nitrate is used in the actual implementation of the method of the present invention, a considerable amount of concentrated alkaline earth metal nitrate solution is generated. Therefore, by recovering and recycling the concentrated alkaline earth metal nitrate solution, it is not only possible to avoid the generation of secondary process waste, but also more energy-saving and environmentally friendly.

[0059] Second Implementation Model

[0060] In a second embodiment of the present invention, the waste hydrofluoric acid solution comprises hydrofluoric acid and water. The method for preparing electronic-grade inorganic acid using the waste hydrofluoric acid solution as a raw material comprises the following steps S1 to S3.

[0061] [Step S1]

[0062] Step S1: comprising adding an alkali metal salt containing an alkali metal fluoride and an alkali metal nitrate into the waste hydrofluoric acid liquid to destroy the azeotropic phenomenon between hydrofluoric acid and water, and performing a first distillation treatment in a vacuum environment to separate hydrogen fluoride vapor, and the residue is a mixed solution formed by nitric acid, water, alkali metal nitrate and alkali metal fluoride.

[0063] The alkali metal salt can destroy the azeotropic phenomenon of hydrofluoric acid and water in the waste hydrofluoric acid solution and separate hydrofluoric acid from water, and compared with the use of alkali metal fluoride salts alone or alkali metal nitrates alone, the mixed use of alkali metal fluoride salts and alkali metal nitrates has a better effect on destroying the azeotropic phenomenon of hydrofluoric acid and water. Preferably, the alkali metal fluoride salt is selected from one or more of lithium fluoride, potassium fluoride and cesium fluoride, and the alkali metal nitrate is selected from one or more of lithium nitrate, potassium nitrate and cesium nitrate. Preferably, relative to the molar sum of all substances in the waste hydrofluoric acid solution and the alkali metal salt, the amount of the alkali metal salt is more than 20 mol%, which can separate more hydrogen fluoride vapor and thus make the method of the present invention have a higher hydrofluoric acid recovery rate; more preferably, the amount of the alkali metal salt is in the range of 20 mol% to 40 mol%. Preferably, the molar ratio of the alkali metal fluoride salt to the alkali metal nitrate salt is in the range of 0.05 to 10, which enables the method of the present invention to have a higher hydrofluoric acid recovery rate.

[0064] Preferably, the pressure range of the vacuum environment is 100 mmHg to 500 mmHg, the first distillation treatment is carried out in a distillation tower with a polytetrafluoroethylene liner, and the bottom temperature of the distillation tower ranges from 80°C to 130°C, the top temperature ranges from 50°C to 100°C, and the reflux ratio ranges from 0.5 to 3, wherein the reflux ratio ranges from 0.5 to 3, which can separate hydrogen fluoride vapor with higher purity.

[0065] If the waste hydrofluoric acid solution also contains fluorosilicic acid, the step S1 further comprises, before adding the alkali metal salt, adding sodium hydroxide into the waste hydrofluoric acid solution to convert the fluorosilicic acid into sodium fluorosilicate, and removing the sodium fluorosilicate by filtering.

[0066] [Step S2]

[0067] Step S2: comprising removing the droplets containing impurities entrained in the hydrogen fluoride vapor to obtain pure hydrogen fluoride vapor.

[0068] The hydrogen fluoride vapor is passed through a multiple defogger to remove the droplets, and the multiple defogger includes at least two defoggers connected in series, and each defogger includes more than one packing unit. The packing unit has a supporting frame and a packing filled in the supporting frame. The material of the supporting frame is selected from at least one of perfluoroalkoxy vinyl ether copolymer (PFA) and modified polytetrafluoroethylene (M-PTFE). The material of the packing is selected from perfluoroalkoxy vinyl ether copolymer or modified polytetrafluoroethylene. The packing material of the packing unit in each defogger may be the same or different. The shape of the packing is a wire mesh or a 3D honeycomb, and the specific surface area of ​​the packing is in the range of 200m 2 / m3 Up to 2000m 2 / m 3 .

[0069] [Step S3]

[0070] Step S3: comprising condensing the pure hydrogen fluoride vapor and adjusting the concentration with ultrapure water to produce electronic grade hydrofluoric acid with a hydrofluoric acid concentration range of 49±0.5%.

[0071] In addition, in the second embodiment, the mixed solution obtained in step S1 can also be evaporated and concentrated and then recycled for reuse.

[0072] The present invention will be further described with reference to the following examples. However, it should be understood that the examples are only for illustration and should not be construed as limitations on the implementation of the present invention.

[0073] [Examples 1 to 3]

[0074] In Examples 1 and 2, electronic grade hydrofluoric acid and electronic grade nitric acid are prepared by performing steps S1 to S8 of the first embodiment, and electronic grade hydrofluoric acid is prepared by performing steps S1 to S3 of the second embodiment. The composition and feed amount of the waste hydrofluoric acid solution in Examples 1 to 3, the molar ratio of sodium hydroxide to silicofluoric acid in step S1, the recovery rate of hydrofluoric acid and the recovery rate of nitric acid are shown in Table 1. The full analysis results of the electronic grade hydrofluoric acid prepared in Examples 1 to 3 are shown in Table 2, and the full analysis results of the electronic grade nitric acid prepared in Examples 1 to 2 are shown in Table 3.

[0075] Wherein, the composition of the waste hydrofluoric acid solution is measured by using an automatic titrator and an ultraviolet-visible light spectrometer.

[0076] Hydrofluoric acid recovery rate = (HF concentration of electronic grade hydrofluoric acid × volume of electronic grade hydrofluoric acid) ÷ (HF concentration of waste hydrofluoric acid liquid × volume of waste hydrofluoric acid liquid).

[0077] Nitric acid recovery rate = (HNO3 concentration of electronic grade nitric acid × volume of electronic grade nitric acid) ÷ (HNO3 concentration of waste hydrofluoric acid solution × volume of waste hydrofluoric acid solution).

[0078] Among them, the full analysis of electronic-grade hydrofluoric acid is based on the SEMIC28-0618 standard analysis method, and the full analysis of electronic-grade nitric acid is based on the SEMIC35-0708 standard analysis method, and the metal ion content is measured by inductively coupled plasma mass spectrometer, the chloride ion content is measured by turbidimeter, the nitrate ion content and phosphate ion content are measured by UV-visible spectrometer, the sulfate ion content is measured by ion chromatography, and the hydrofluoric acid content, nitric acid content, ignition residue content, fluorosilicic acid content and reducing substance content are measured by automatic titrator.

[0079] Table 1

[0080]

[0081] Note: Non-volatile acids include sulfuric acid.

[0082] Referring to Table 1, the nitric acid recovery rate of Examples 1 to 2 is greater than 95% and the hydrofluoric acid recovery rate is greater than 99%, indicating that Examples 1 to 2 can effectively recover nitric acid and hydrofluoric acid from the waste hydrofluoric acid solution by performing steps S1 to S7.

[0083] The hydrofluoric acid recovery rate of Example 3 is greater than 99.5%, indicating that Example 3 can effectively recover hydrofluoric acid from the waste hydrofluoric acid solution by performing steps S1 to S3.

[0084] Table 2

[0085]

[0086] Table 3

[0087]

[0088] Referring to the full analysis results in Table 2 and Table 3, the electronic-grade hydrofluoric acid prepared in Examples 1 to 2 meets the purity standard of electronic-grade hydrofluoric acid required by the semiconductor industry, and the electronic-grade nitric acid prepared meets the purity standard of electronic-grade nitric acid required by the semiconductor industry, indicating that Examples 1 to 2 can effectively recover and regenerate hydrofluoric acid from waste hydrofluoric acid liquid to produce electronic-grade hydrofluoric acid, and recover and regenerate nitric acid to produce electronic-grade nitric acid by performing steps S1 to S7, and the electronic-grade hydrofluoric acid and electronic-grade nitric acid prepared are particularly suitable for use in the processes of high-tech electronic industries such as semiconductor processes and solar cell processes.

[0089] Referring to the full analysis results in Table 2, the electronic-grade hydrofluoric acid prepared in Example 3 meets the purity standard of electronic-grade hydrofluoric acid required by the semiconductor industry, indicating that Example 3 can effectively recover and regenerate hydrofluoric acid from waste hydrofluoric acid liquid to prepare electronic-grade hydrofluoric acid by performing steps S1 to S3, and the prepared electronic-grade hydrofluoric acid is particularly suitable for use in semiconductor processes, solar cell processes and other high-tech electronic industry processes.

[0090] In summary, the method of the present invention uses the waste hydrofluoric acid liquid generated in the process of the high-tech electronic industry as a raw material to prepare electronic-grade hydrofluoric acid and electronic-grade nitric acid. Not only the specifications of the prepared electronic-grade hydrofluoric acid and electronic-grade nitric acid meet the purity standards required by the semiconductor industry, but also the green recycling of the waste hydrofluoric acid liquid can be achieved, which makes a significant contribution to waste reduction and environmental protection. Therefore, the purpose of the present invention can be achieved.

[0091] The above description is merely a preferred embodiment of the present invention and cannot be used to limit the scope of implementation of the present invention. In other words, any simple equivalent changes and modifications made according to the claims and description of the present invention are still within the scope of the patent of the present invention.

Claims

1. A method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material, characterized in that: The method comprises the following steps: Step S1: comprising adding an alkali metal salt containing an alkali metal fluoride and an alkali metal nitrate into a waste hydrofluoric acid liquid containing hydrofluoric acid, nitric acid and water to destroy the azeotropic phenomenon between hydrofluoric acid and water, and performing a first distillation treatment in a vacuum environment to separate hydrogen fluoride vapor, wherein the residue is a mixed solution formed by nitric acid, water, alkali metal nitrate and alkali metal fluoride, wherein the amount of the alkali metal salt used is in a range of 20 mol% to 40 mol% relative to the total molar amount of all substances in the waste hydrofluoric acid liquid and the alkali metal salt; Step S2: comprising removing droplets containing impurities entrained in the hydrogen fluoride vapor to obtain pure hydrogen fluoride vapor; Step S3: comprising condensing the pure hydrogen fluoride vapor and adjusting the concentration with ultrapure water to produce electronic grade hydrofluoric acid with a hydrofluoric acid concentration range of 49±0.5%; Step S4: comprising subjecting the mixed solution formed by the nitric acid, water, alkali metal nitrate and alkali metal fluoride in step S1 to a first evaporation treatment in a vacuum environment, thereby evaporating nitric acid and water from the mixed solution to form a nitric acid-water mixed solution, and concentrating the alkali metal nitrate, alkali metal fluoride and unevaporated water to form an alkali metal salt concentrated solution, and introducing the alkali metal salt concentrated solution into the first distillation treatment of step S1 for recycling; Step S5: adding alkaline earth metal nitrate to the nitric acid-water mixture obtained in step S4 to destroy the azeotropic phenomenon between nitric acid and water, and performing a second distillation treatment in a vacuum environment to separate nitric acid vapor, and the residue is an alkaline earth metal nitrate solution formed by alkaline earth metal nitrate and water; Step S6: comprising removing droplets containing impurities entrained in the nitric acid vapor to obtain pure nitric acid vapor; Step S7: comprising condensing the pure nitric acid vapor and adjusting the concentration with ultrapure water to prepare electronic grade nitric acid with a nitric acid concentration range of 70±0.5%; and Step S8: comprising subjecting the alkaline earth metal nitrate solution obtained in step S5 to a second evaporation treatment to evaporate part of the water in the alkaline earth metal nitrate solution to concentration to form an alkaline earth metal nitrate concentrated solution, and introducing the alkaline earth metal nitrate concentrated solution into the second distillation treatment of step S5 for recycling.

2. The method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material according to claim 1, characterized in that: In step S1, the alkali metal fluoride salt is selected from one or more of lithium fluoride, potassium fluoride and cesium fluoride, the alkali metal nitrate salt is selected from one or more of lithium nitrate, potassium nitrate and cesium nitrate, and the molar ratio of the alkali metal fluoride salt to the alkali metal nitrate salt is in the range of 0.05 to 10.

3. The method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material according to claim 1, characterized in that: In step S1, the pressure range of the vacuum environment is 100 mmHg to 500 mmHg, the first distillation treatment is carried out in a distillation tower with a polytetrafluoroethylene lining, and the bottom temperature range of the distillation tower is 80°C to 130°C, the top temperature range is 50°C to 100°C, and the reflux ratio range is 0.5 to 3.

4. The method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material according to claim 1, characterized in that: In the step S4, the temperature range of the first evaporation treatment is 130°C to 180°C.

5. The method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material according to claim 1, characterized in that: In step S5, the alkaline earth metal nitrate is selected from one or more of magnesium nitrate and calcium nitrate, and the amount of the alkaline earth metal nitrate is in a range of 40 mol% to 65 mol% relative to the total molar amount of the alkaline earth metal nitrate, nitric acid and water in the nitric acid-water mixture.

6. The method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material according to claim 1, characterized in that: In step S5, the pressure range of the vacuum environment is 100 mmHg to 500 mmHg, the second distillation treatment is carried out in a distillation tower with a polytetrafluoroethylene liner, and the bottom temperature range of the distillation tower is 120°C to 140°C, the top temperature range is 70°C to 100°C, and the reflux ratio range is 0.5 to 3.

7. The method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material according to claim 1, characterized in that: In the step S8, the temperature range of the second evaporation treatment is 130°C to 180°C.

8. A method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material, comprising the following steps: Step S1: comprising adding an alkali metal salt containing an alkali metal fluoride salt and an alkali metal nitrate into a waste hydrofluoric acid liquid containing hydrofluoric acid and water to destroy the azeotropic phenomenon between hydrofluoric acid and water, and performing a first distillation treatment in a vacuum environment to separate hydrogen fluoride vapor, wherein: The amount of the alkali metal salt used is 20 mol% or more relative to the total molar amount of all substances in the waste hydrofluoric acid solution and the alkali metal salt; Step S2: comprising removing droplets containing impurities entrained in the hydrogen fluoride vapor to obtain pure hydrogen fluoride vapor; and Step S3: comprising condensing the pure hydrogen fluoride vapor and adjusting the concentration with ultrapure water, thereby preparing electronic grade hydrofluoric acid with a hydrofluoric acid concentration range of 49±0.5%.

9. The method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material according to claim 8, characterized in that: In step S1, the alkali metal fluoride salt is selected from one or more of lithium fluoride, potassium fluoride and cesium fluoride, the alkali metal nitrate salt is selected from one or more of lithium nitrate, potassium nitrate and cesium nitrate, and the molar ratio of the alkali metal fluoride salt to the alkali metal nitrate salt is in the range of 0.05 to 10.

10. The method for preparing electronic grade inorganic acid using waste hydrofluoric acid liquid as raw material according to claim 8, characterized in that: In step S1, the pressure range of the vacuum environment is 100 mmHg to 500 mmHg, the first distillation treatment is carried out in a distillation tower with a polytetrafluoroethylene lining, and the bottom temperature range of the distillation tower is 80°C to 130°C, the top temperature range is 50°C to 100°C, and the reflux ratio range is 0.5 to 3.

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