A process for recovering nitric acid containing hydrogen fluoride

Abstract

The application provides a method for recovering nitric acid containing hydrogen fluoride, and the steps are as follows: the waste liquid of nitric acid containing hydrogen fluoride is preheated to 50-80 DEG C and then enters a reaction bed from the bottom of the reaction bed to react with glass powder; then the acid liquid after precipitation is sent into a calcification kettle, and 1-3% of calcium hydroxide slurry of the total acid amount is added to completely react with a small amount of hydrogen fluoride in the acid liquid; then the material after reaction in the calcification kettle is separated by layering; the acid liquid in the upper layer is sent into a rectifying column to perform vacuum rectification operation, nitric acid refining is completed, and concentrated nitric acid products containing nitric acid > 70% are obtained; the mud in the lower layer is dried, then dissolved in water, crystallized, separated, and finally dried to obtain relatively pure calcium fluorosilicate and calcium fluoride products; and through 2-3 times of water dissolving, crystallizing, separating and drying, products with purity > 99% can be obtained. The reaction process is simple, the treatment steps are few, the energy consumption and the consumption of reagents are reduced, the recovery rate can be improved while the treatment cost is reduced, secondary pollution is reduced, and resource recovery is realized.

Description

[Technical Field]

[0001] This invention relates to the field of chemical separation and purification technology, specifically to a method for recovering nitric acid containing hydrofluoric acid. [Background Technology]

[0002] With the rapid development of the electronics industry, industries such as semiconductors and photovoltaics generate large amounts of wastewater containing hydrofluoric acid (HF) and other acidic substances (such as HNO3). This wastewater not only contains high concentrations of harmful components but also exhibits strong corrosiveness and toxicity, causing serious environmental pollution. For example, hydrofluoric acid is increasingly used for etching in the electronics industry, and subsequent processes require nitric acid for pickling, generating large amounts of nitric acid containing hydrofluoric acid. Some etching solutions are formulated using nitric acid and hydrofluoric acid as the main raw materials. Therefore, a large amount of waste nitric acid containing hydrofluoric acid is generated. Due to the extreme hazard of hydrofluoric acid, the disposal of waste nitric acid containing hydrofluoric acid has become a major challenge. At the same time, the recycling value of waste glass products is low, transportation costs are extremely high, and disposal costs are also high. In many places, the glass recycling rate is extremely low, and glass is relatively stable and difficult to degrade naturally, posing a significant environmental hazard. This invention provides a method for recovering nitric acid containing hydrofluoric acid, which can effectively convert hydrofluoric acid and thus purify and recover nitric acid.

[0003] Nitric acid wastewater containing hydrofluoric acid contains a significant amount of this highly corrosive acid. Due to the strong corrosiveness and toxicity of hydrofluoric acid, the recovered waste acid is extremely difficult to dispose of. This type of waste acid is highly corrosive, requiring extremely sophisticated storage equipment and posing significant storage risks. If not effectively disposed of, it can lead to long-term accumulation and potentially cause a major leak. Currently, the main methods for treating this type of wastewater include chemical precipitation, adsorption, ion exchange, and membrane separation.

[0004] Chemical precipitation: This method removes harmful components by adding alkaline reagents to cause metal ions in wastewater to form insoluble precipitates. Its advantages include simple operation and wide applicability, but it generates large amounts of sludge, has high treatment costs, and is difficult to recycle.

[0005] Adsorption method: This method utilizes porous materials such as activated carbon and molecular sieves to selectively adsorb harmful components in wastewater. Its advantages include the ability to regenerate and reuse the adsorbent, resulting in relatively good treatment performance. However, its adsorption capacity is limited, and it is not effective for treating high-concentration wastewater.

[0006] Ion exchange method: This method effectively removes specific ions from wastewater through the selective adsorption of ion exchange resins. Its advantages include high removal rates and strong selectivity, but the regeneration and replacement costs of the resin are relatively high.

[0007] Membrane separation: This method uses reverse osmosis membranes, nanofiltration membranes, etc., to separate wastewater and effectively recover useful substances. Its advantages include high separation efficiency and stable operation, but membrane modules are prone to clogging, resulting in higher maintenance costs.

[0008] While these methods can reduce environmental pollution to some extent, they generally suffer from problems such as multiple steps, various types of reagents used, high costs, low efficiency, and secondary pollution. Therefore, there is an urgent need to develop more efficient and economical treatment methods. [Summary of the Invention]

[0009] The technical problem to be solved by the present invention is to provide a method for recovering nitric acid containing hydrofluoric acid. The reaction process is simple, the processing steps are few, energy consumption and reagent consumption are reduced, the recovery rate can be improved while reducing the processing cost, reducing secondary pollution, and realizing resource recovery.

[0010] This invention is implemented as follows:

[0011] A method for recovering nitric acid containing hydrofluoric acid is disclosed. The recovery method is based on a nitric acid recovery system, which includes a reactor assembly, an intermediate product tank, a calcification kettle, and a distillation column. The reactor assembly includes a broken glass tank, a feed auger, a reaction bed, and a settling tank. The broken glass tank is connected to the upper end of the reaction bed via the feed auger. A waste acid feed pipe is installed at the bottom of the reaction bed, and the upper end of the reaction bed is connected to the upper end of the settling tank. The upper end of the settling tank is connected to the intermediate product tank via a pipe. The intermediate product tank is connected to the upper end of the calcification kettle via a calcification feed pump. A calcium hydroxide slurry pipe is also connected to the upper end of the calcification kettle. A mud pipe and a clear liquid pipe are connected to the bottom of the calcification kettle, and the clear liquid pipe is connected to the distillation column via a distillation feed pump.

[0012] The recycling method involves the following steps:

[0013] Step 1: Crush, wash, and dry the recycled glass, then add it to a glass shard jar for later use; the glass shard jar can be replenished intermittently; the main components of the glass are calcium silicate, sodium silicate, and silicon dioxide.

[0014] Step 2: The nitric acid waste liquid containing hydrofluoric acid is preheated to 50-80℃ and enters the reaction bed from the bottom to react with the glass fragments fed in by the auger; then the reaction liquid enters the settling tank from the top to remove the glass fragments carried out; the reaction in the reaction bed is as follows:

[0015] HF + SiO2 = SiF4 + H2O;

[0016] 6HF+Na2SiO3=2NaF+SiF4+3H2O;

[0017] 6HF+CaSiO3=CaF2↓+SiF4+3H2O;

[0018] Step 3: Send the settled acid solution into the intermediate product tank; then send the acid solution into the calcification reactor through the calcification feed pump, and add 1-3% of calcium hydroxide slurry to completely react the unreacted hydrofluoric acid in the acid solution.

[0019] Step 4: Separate the material after the reaction in the calcification kettle into layers to obtain an upper layer of acid and a lower layer of slurry.

[0020] Step 4.1: The upper acid liquid enters the distillation column for vacuum distillation to complete the purification of nitric acid and obtain concentrated nitric acid product with a nitric acid content >70%; the residue at the bottom of the distillation column contains sodium fluorosilicate and a small amount of calcium fluorosilicate and calcium nitrate, which are separated by concentration and crystallization to obtain sodium fluorosilicate, calcium fluorosilicate and calcium nitrate products with a high purity >95%;

[0021] Step 4.2: After the lower layer of mud is dried, it is dissolved in water, crystallized, separated, and finally dried to obtain relatively pure calcium fluorosilicate and calcium fluoride products; and after 2-3 times of adding water to dissolve, crystallize, separate and dry, a product with a purity of >99% can be obtained.

[0022] Furthermore, the amount of broken glass in the reaction bed is 50-80% of the bed height.

[0023] Furthermore, the mesh size of the crushed glass is no greater than 20 mesh.

[0024] Furthermore, a bubble cap support plate is provided at the lower end of the reaction bed, and a flow divider is provided at the upper end.

[0025] Furthermore, the two reaction beds are used in series, and two sets of glass crushing tanks, feed augers, and settling tanks are also provided.

[0026] Furthermore, a sight glass is provided at the bottom of the settling tank to observe the amount of glass fragments at the bottom of the settling tank, thereby adjusting the amount of glass fragments added to the reaction bed.

[0027] Furthermore, the material exiting the top of the distillation column in step 4.1 can be fed into a calcium hydroxide slurry tank.

[0028] The present invention has the following advantages:

[0029] 1) Reduced processing costs: Through reasonable process design, the reaction process is simple and the processing steps are few. Only waste glass and calcium hydroxide slurry are used in the recycling process, which reduces energy consumption and reagent consumption. The overall processing cost is reduced by more than 30% compared with traditional methods.

[0030] 2) Improved material recovery rate. While obtaining concentrated nitric acid product with a nitric acid content of >70%, sodium fluorosilicate, calcium fluorosilicate, and calcium nitrate products with a purity of >95% were also obtained.

[0031] 3) Resource recycling has been achieved, with virtually no excess waste generated. The high-concentration nitric acid product and high-purity sodium fluorosilicate, calcium fluorosilicate, and calcium nitrate products obtained can be directly used in production, improving resource utilization and generating certain economic benefits while reducing environmental pressure.

[0032] 4) It reduces secondary pollution. Through an efficient treatment process, it minimizes the generation and discharge of waste, thus meeting environmental protection requirements. [Attached Image Description]

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0034] Figure 1 This is a schematic diagram of the nitric acid recovery system of the present invention.

[0035] The numbers in the image are as follows:

[0036] 1-Reactor assembly, 11-Crushed glass jar, 12-Feed auger, 13-Reaction bed, 14-Settling tank, 15-Waste acid feed pipe, 16-Bubble cap support plate, 2-Intermediate product tank, 3-Calcification kettle, 4-Distillation column, 5-Calcification feed pump, 6-Calcium hydroxide slurry pipeline, 7-Slurry pipeline, 8-Clear liquid pipeline, 9-Distillation feed pump.

Detailed Implementation Methods

[0037] The following will be combined with the appendix Figure 1 The technical solution of the present invention will be clearly and completely described in detail with specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0038] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0040] See Figure 1 This invention relates to a method for recovering nitric acid containing hydrofluoric acid. The recovery method is based on a nitric acid recovery system, which includes a reactor assembly 1, an intermediate product tank 2, a calcification kettle 3, and a distillation column 4. The reactor assembly 1 includes a broken glass tank 11, a feed auger 12, a reaction bed 13, and a settling tank 14. The broken glass tank 11 is connected to the upper end of the reaction bed 13 via the feed auger 12. A waste acid feed pipe 15 is provided at the bottom of the reaction bed 13, and the upper end of the reaction bed 13 is connected to the upper end of the settling tank 14. The upper end of the settling tank 14 is connected to the intermediate product tank 2 via a pipe. The intermediate product tank 2 is connected to the upper end of the calcification kettle 3 via a calcification feed pump 5. The upper end of the calcification kettle 3 is also connected to a calcium hydroxide slurry pipe 6. The bottom of the calcification kettle 3 is connected to a mud pipe 7 and a clear liquid pipe 8, respectively. The clear liquid pipe 8 is connected to the distillation column 4 via a distillation feed pump 9.

[0041] The recycling method involves the following steps:

[0042] Step 1: Crush, clean, and dry the recycled glass, then add it to glass jar 11 for later use; glass jar 11 can be replenished with glass shards intermittently; the main components of the glass are calcium silicate, sodium silicate, and silicon dioxide.

[0043] Step 2: The nitric acid waste liquid containing hydrofluoric acid is preheated to 50-80℃ and enters the reaction bed 13 from the bottom to react with the glass fragments fed by the auger feed 12. Then the reaction liquid enters the settling tank 14 from the top to remove the glass fragments carried out. The two reactor components 1 are used in series, that is, two reaction beds 13 are used in series. At the same time, two sets of glass shard tank 11, feed auger 12 and settling tank 14 are set up. The upper end of the settling tank 14 of the first set is connected to the bottom of the reaction bed 13 of the second set to ensure that the hydrofluoric acid participates in the reaction as completely as possible. The reaction in the reaction bed 13 is as follows:

[0044] HF + SiO2 = SiF4 + H2O;

[0045] 6HF+Na2SiO3=2NaF+SiF4+3H2O;

[0046] 6HF+CaSiO3=CaF2↓+SiF4+3H2O;

[0047] Step 3: Send the settled acid solution into intermediate product tank 2; then send the acid solution into calcification kettle 3 through calcification feed pump 5, and add 1-3% of calcium hydroxide slurry to completely react the unreacted hydrofluoric acid in the acid solution.

[0048] Step 4: Separate the material after the reaction in calcification kettle 3 into layers to obtain an upper layer of acid and a lower layer of slurry.

[0049] Step 4.1: The upper acid liquid enters the distillation column 4 through the clear liquid pipe 8 for vacuum distillation to complete the nitric acid purification and obtain concentrated nitric acid product with a nitric acid content >70%; the residual liquid at the bottom of the distillation column 4 contains sodium fluorosilicate and a small amount of calcium fluorosilicate and calcium nitrate, which are separated by concentration and crystallization to obtain sodium fluorosilicate, calcium fluorosilicate and calcium nitrate products with higher purity >95%;

[0050] Step 4.2: The lower layer of mud is sent out through mud pipe 7 for crystallization and purification. That is, after drying, water is added to dissolve, crystallize, separate, and finally dry to obtain relatively pure calcium fluorosilicate and calcium fluoride products. After 2-3 times of adding water to dissolve, crystallize, separate, and dry, a product with a purity of >99% can be obtained.

[0051] In a preferred embodiment, the amount of broken glass in the reaction bed 13 is 50-80% of the bed height.

[0052] In a preferred embodiment, the mesh size of the crushed glass is no greater than 20 mesh.

[0053] In a preferred embodiment, the reaction bed 13 is provided with a bubble cover support plate 16 at its lower end, which can prevent glass fragments from falling below and causing blockage, and can also ensure the smooth passage of nitric acid waste liquid containing hydrofluoric acid; a diversion baffle is provided at the upper end, which can reduce the glass fragments being carried out by the acid liquid.

[0054] In a preferred embodiment, the bottom of the settling tank 14 is provided with a sight glass. The amount of glass fragments at the bottom of the settling tank 14 is observed through the sight glass to adjust the amount of glass fragments added to the reaction bed 13.

[0055] In a preferred embodiment, the material exiting the top of the distillation column in step 4.1 can be fed into a calcium hydroxide slurry tank.

[0056] In summary, the present invention has the following advantages:

[0057] 1) Reduced processing costs: Through reasonable process design, fewer processing steps are required. The recycling process only uses waste glass and calcium hydroxide slurry, reducing energy consumption and reagent consumption. The overall processing cost is reduced by more than 30% compared with traditional methods.

[0058] 2) Improved material recovery rate. While obtaining concentrated nitric acid product with a nitric acid content of >70%, sodium fluorosilicate, calcium fluorosilicate, and calcium nitrate products with a purity of >95% were also obtained.

[0059] 3) Resource recycling has been achieved, with virtually no excess waste generated. The high-concentration nitric acid product and high-purity sodium fluorosilicate, calcium fluorosilicate, and calcium nitrate products obtained can be directly used in production, improving resource utilization and generating certain economic benefits while reducing environmental pressure.

[0060] 4) It reduces secondary pollution. Through an efficient treatment process, it minimizes the generation and discharge of waste, thus meeting environmental protection requirements.

[0061] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for recovering nitric acid containing hydrofluoric acid, characterized in that: The recovery method is based on a nitric acid recovery system, which includes a reactor assembly, an intermediate product tank, a calcification kettle, and a distillation column. The reactor assembly includes a broken glass tank, a feed auger, a reaction bed, and a settling tank. The broken glass tank is connected to the upper end of the reaction bed via the feed auger. A waste acid feed pipe is installed at the bottom of the reaction bed, and the upper end of the reaction bed is connected to the upper end of the settling tank. The upper end of the settling tank is connected to the intermediate product tank via a pipe. The intermediate product tank is connected to the upper end of the calcification kettle via a calcification feed pump. A calcium hydroxide slurry pipe is also connected to the upper end of the calcification kettle. A mud pipe and a clear liquid pipe are connected to the bottom of the calcification kettle, and the clear liquid pipe is connected to the distillation column via a distillation feed pump. The recycling method involves the following steps: Step 1: Crush, wash, and dry the recycled glass, then add it to a glass shard jar for later use; the glass shard jar can be replenished intermittently; the main components of the glass are calcium silicate, sodium silicate, and silicon dioxide. Step 2: The nitric acid waste liquid containing hydrofluoric acid is preheated to 50-80℃ and enters the reaction bed from the bottom to react with the glass fragments fed in by the auger; then the reaction liquid enters the settling tank from the top to remove the glass fragments carried out; the reaction in the reaction bed is as follows: HF + SiO2 = SiF4 + H2O; 6HF+Na2SiO3=2NaF+ SiF4+3H2O; 6HF+CaSiO3=CaF2↓+ SiF4+3H2O; Step 3: Send the settled acid solution into the intermediate product tank; then send the acid solution into the calcification reactor through the calcification feed pump, and add 1-3% of calcium hydroxide slurry to completely react the unreacted hydrofluoric acid in the acid solution. Step 4: Separate the material after the reaction in the calcification kettle into layers to obtain an upper layer of acid and a lower layer of slurry. Step 4.1: The upper acid solution enters a distillation column for vacuum distillation to complete the nitric acid purification, obtaining concentrated nitric acid product with a nitric acid content >70%; the residue at the bottom of the distillation column contains sodium fluorosilicate and small amounts of calcium fluorosilicate and calcium nitrate, which are separated by concentration and crystallization to obtain high-purity sodium fluorosilicate, calcium fluorosilicate, and calcium nitrate products with a purity >95%; Step 4.2: After the lower layer of mud is dried, it is dissolved in water, crystallized, separated, and finally dried to obtain relatively pure calcium fluorosilicate and calcium fluoride products; and after 2-3 times of adding water to dissolve, crystallize, separate and dry, a product with a purity of >99% can be obtained.

2. The method for recovering nitric acid containing hydrofluoric acid according to claim 1, characterized in that: The amount of broken glass in the reaction bed is 50-80% of the bed height.

3. The method for recovering nitric acid containing hydrofluoric acid according to claim 1, characterized in that: The mesh size of the crushed glass is no greater than 20 mesh.

4. The method for recovering nitric acid containing hydrofluoric acid according to claim 1, characterized in that: The reaction bed is provided with a bubble cap support plate at the lower end and a flow divider plate at the upper end.

5. The method for recovering nitric acid containing hydrofluoric acid according to claim 1, characterized in that: There are two reaction beds, which are connected in series. There are also two sets of glass crushing tanks, feeding augers and settling tanks.

6. The method for recovering nitric acid containing hydrofluoric acid according to claim 1, characterized in that: A sight glass is installed at the bottom of the settling tank. The amount of glass fragments at the bottom of the settling tank can be observed through the sight glass to adjust the amount of glass fragments added to the reaction bed.

7. The method for recovering nitric acid containing hydrofluoric acid according to claim 1, characterized in that: In step 4.1, the material coming out of the top of the distillation column can be sent to the calcium hydroxide slurry tank.

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