Method for recovering nitric acid containing hydrofluoric acid

Abstract

The invention provides a hydrofluoric acid-containing nitric acid recovery method. The method comprises the following steps: preheating a hydrofluoric acid-containing nitric acid waste liquid to 50-80 DEG C, feeding the hydrofluoric acid-containing nitric acid waste liquid into a reaction bed from the bottom of the reaction bed, and carrying out a reaction on glass fragments; sending the settled acid liquor into a calcification kettle, adding calcium hydroxide slurry accounting for 1-3% of the total acid amount, and completely reacting a small amount of hydrofluoric acid in the acid liquor; carrying out layering separation on the reacted material in the calcification kettle; upper-layer acid liquor enters a rectifying tower to be subjected to reduced-pressure rectifying operation, nitric acid refining is completed, and a concentrated nitric acid finished product with the nitric acid content larger than 70% is obtained; and drying the lower-layer slurry, adding water for dissolving, crystallizing, separating, and finally drying to obtain pure calcium fluosilicate and calcium fluoride finished products. And adding water for dissolving, crystallizing, separating and drying for 2-3 times to obtain a finished product with the purity of more than 99%. The method has the advantages of simple reaction process, few treatment steps, reduction of energy consumption and medicament consumption, reduction of the treatment cost, improvement of the recovery rate, reduction of secondary pollution and realization of resource recovery.

Description

Technical field

[0001] The present invention relates to the technical field of chemical separation and purification, and in particular 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 have produced a large amount of wastewater containing hydrofluoric acid (HF) and other acidic substances (such as HNO3). These wastewaters not only contain high concentrations of harmful components, but also have strong corrosiveness and toxicity, causing serious pollution to the environment. For example, hydrofluoric acid is increasingly used for etching in the electronics industry, and nitric acid is needed for pickling in subsequent processes, which will produce a large amount of nitric acid containing hydrofluoric acid. Some etching solution formulas are produced with nitric acid and hydrofluoric acid as the main raw materials. Therefore, a large amount of nitric acid waste acid containing hydrofluoric acid will be produced. Due to the great harm of hydrofluoric acid, the disposal of waste nitric acid containing hydrofluoric acid has become a major problem. At the same time, the recycling value of waste glass products is low, the transportation cost is extremely high, the disposal cost is high, the glass recovery rate in many places is extremely low, the properties of glass are relatively stable, and it is difficult to degrade naturally, which brings great hidden dangers to the environment. The present invention provides a method for recovering nitric acid containing hydrofluoric acid, which can effectively convert hydrofluoric acid and then complete the purification and recovery of nitric acid.

[0003] Nitric acid waste liquid containing hydrofluoric acid contains a large amount of hydrofluoric acid, which is extremely corrosive. Due to the strong corrosiveness and toxicity of hydrofluoric acid, the waste acid after recovery is extremely difficult to dispose of. This type of waste acid is extremely corrosive and requires extremely high storage equipment. Storage also carries great risks. If it is not effectively disposed of, it will cause long-term accumulation of inventory, which may eventually lead to major leakage accidents. Currently, the main methods for treating this type of wastewater include chemical precipitation, adsorption, ion exchange, membrane separation, etc.:

[0004] Chemical precipitation: This method removes harmful components by adding an alkaline reagent to the wastewater, causing the metal ions to form insoluble precipitates. While this method is simple to operate and widely applicable, it also produces a large amount of sludge, resulting in high treatment costs and difficulty in resource recovery.

[0005] Adsorption: This method uses porous materials such as activated carbon and molecular sieves to selectively adsorb harmful components in wastewater. The advantage is that the adsorbent can be recycled and the treatment effect is good, but the adsorption capacity is limited, and the treatment effect is not good for high-concentration wastewater.

[0006] Ion exchange: 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 cost of resin regeneration and replacement is relatively high.

[0007] Membrane separation: Utilizing reverse osmosis membranes, nanofiltration membranes, and other methods to separate wastewater, effectively recovering useful substances. While these methods offer advantages such as high separation efficiency and stable operation, they are prone to clogging and high maintenance costs.

[0008] Although these methods can reduce environmental pollution to a certain extent, they generally have problems such as many steps, multiple types of chemicals, high cost, 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, which has a simple reaction process, fewer processing steps, reduced energy consumption and reagent consumption, can improve the recovery rate while reducing processing costs, reduce secondary pollution, and realize resource recovery.

[0010] The present invention is achieved in that:

[0011] A method for recovering nitric acid containing hydrofluoric acid, the method being based on a nitric acid recovery system. The nitric acid recovery system comprises a reactor assembly, an intermediate product tank, a calcification kettle, and a distillation tower. The reactor assembly comprises a cullet tank, a feed auger, a reaction bed, and a settling tank. The cullet tank is connected to the upper end of the reaction bed via the feed auger. A waste acid feed pipe is provided at the bottom of the reaction bed. 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 pipeline. The intermediate product tank is connected to the upper end of the calcification kettle via a calcification feed pump. The upper end of the calcification kettle is also connected to a calcium hydroxide slurry pipeline. The bottom of the calcification kettle is respectively connected to a slurry pipeline and a clear liquid pipeline. The clear liquid pipeline is connected to the distillation tower via a distillation feed pump.

[0012] The recovery method steps are as follows:

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

[0014] Step 2: preheat the nitric acid waste liquid containing hydrofluoric acid to 50-80°C and enter the reaction bed from the bottom to react with the glass fines fed by the auger; then the reaction liquid enters the sedimentation tank from the top to remove the glass fines 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: The settled acid solution is fed into an intermediate product tank; the acid solution is then fed into a calcification kettle via a calcification feed pump, and a calcium hydroxide slurry with a total acid content of 1-3% is added to completely react the unreacted hydrofluoric acid in the acid solution;

[0019] Step 4: Separate the materials after the reaction in the calcification kettle into layers to obtain an upper layer of acid solution and a lower layer of mud;

[0020] Step 4.1: The upper acid solution enters a distillation tower for vacuum distillation to complete the purification of nitric acid and obtain a concentrated nitric acid product containing more than 70% nitric acid; the residual liquid at the bottom of the distillation tower contains sodium fluorosilicate and a small amount 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 of more than 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 fluosilicate and calcium fluoride products; and after 2-3 times of dissolving in water, crystallizing, separating, and drying, a finished product with a purity of >99% can be obtained.

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

[0023] Furthermore, the mesh size of the glass after crushing is not greater than 20 meshes.

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

[0025] Furthermore, two reaction beds are used in series, and two groups of broken glass tanks, feed auger and sedimentation tanks are provided.

[0026] Furthermore, a sight glass is provided at the bottom of the sedimentation tank, and the amount of cullet added to the reaction bed is adjusted by observing the amount of cullet at the bottom of the sedimentation tank through the sight glass.

[0027] Furthermore, the material coming out of the top of the distillation tower 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, the processing steps are few, and only discarded glass and calcium hydroxide slurry are used in the recovery process, which reduces energy consumption and reagent consumption. The overall processing cost is reduced by more than 30% compared with traditional methods.

[0030] 2) The recovery rate of the materials is improved. While obtaining a concentrated nitric acid product containing more than 70% nitric acid, sodium fluorosilicate, calcium fluorosilicate and calcium nitrate products with a purity of more than 95% are also obtained.

[0031] 3) Resource recovery is achieved, and basically no excess waste is generated. The obtained high-concentration nitric acid products and high-purity sodium fluorosilicate, calcium fluorosilicate, and calcium nitrate products can be directly used in production, thereby improving resource utilization, having certain economic benefits, and reducing environmental pressure.

[0032] 4) Reduce secondary pollution. Through efficient treatment process, the generation and discharge of waste are minimized to meet environmental protection requirements.

Brief Description of the Drawings

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

[0034] Figure 1 Schematic diagram of the nitric acid recovery system of the present invention.

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

[0036] 1-reactor assembly, 11-crushed glass tank, 12-feed auger, 13-reaction bed, 14-sedimentation tank, 15-waste acid feed pipe, 16-bubble cap support plate, 2-intermediate product tank, 3-calcification kettle, 4-distillation tower, 5-calcification feed pump, 6-calcium hydroxide slurry pipeline, 7-mud pipeline, 8-clear liquid pipeline, 9-distillation feed pump. [Specific implementation method]

[0037] The following will be combined with the Figure 1 The technical solutions of the present invention are clearly and completely described in the following and in detail. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work are within the scope of protection of the present invention. If specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0038] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present 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 the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0040] See Figure 1 , the present invention relates to a method for recovering nitric acid containing hydrofluoric acid, the recovery method is based on a nitric acid recovery system, the nitric acid recovery system comprises a reactor assembly 1, an intermediate product tank 2, a calcification kettle 3 and a distillation tower 4, the reactor assembly 1 comprises a cullet tank 11, a feed auger 12, a reaction bed 13 and a sedimentation tank 14; the cullet tank 11 is connected to the upper end of the reaction bed 13 through the feed auger 12, a waste acid feed pipe 15 is provided at the bottom of the reaction bed 13, the upper end of the reaction bed 13 is connected to the upper end of the sedimentation tank 14; the upper end of the sedimentation tank 14 is connected to the intermediate product tank 2 through a pipeline, the intermediate product tank 2 is connected to the upper end of the calcification kettle 3 through a calcification feed pump 5, the upper end of the calcification kettle 3 is also connected to a calcium hydroxide slurry pipeline 6, the bottom of the calcification kettle 3 is respectively connected to a mud pipeline 7 and a clear liquid pipeline 8, and the clear liquid pipeline 8 is connected to the distillation tower 4 through a distillation feed pump 9;

[0041] The recovery method steps are as follows:

[0042] Step 1: crush the recycled glass, wash it, dry it, and add it to the cullet jar 11 for later use; the cullet jar 11 can be replenished with glass cullet raw materials intermittently; the main components of the glass are calcium silicate, sodium silicate and silicon dioxide;

[0043] Step 2: Preheat the nitric acid waste liquid containing hydrofluoric acid to 50-80°C and enter the reaction bed 13 from the bottom to react with the glass cullets fed by the auger feed 12; then the reaction liquid enters the sedimentation tank 14 from the top to remove the glass cullets carried out; two reactor assemblies 1 are used in series, that is, two reaction beds 13 are used in series, and two groups of cullet tanks 11, feed auger 12 and sedimentation tanks 14 are provided, and the upper end of the sedimentation tank 14 of the first group is connected to the bottom of the reaction bed 13 of the second group 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: The settled acid solution is fed into the intermediate product tank 2; the acid solution is then fed into the calcification kettle 3 via the calcification feed pump 5, and a calcium hydroxide slurry with a total acid content of 1-3% is added to completely react the unreacted hydrofluoric acid in the acid solution;

[0048] Step 4: Separate the materials after the reaction in the calcification kettle 3 into layers to obtain an upper layer of acid solution and a lower layer of mud;

[0049] Step 4.1: The upper acid liquid enters the distillation tower 4 through the clear liquid pipeline 8 for vacuum distillation to complete the nitric acid purification and obtain a concentrated nitric acid product containing more than 70% nitric acid; the residual liquid at the bottom of the distillation tower 4 contains sodium fluorosilicate and a small amount 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 of more than 95%;

[0050] Step 4.2: The lower layer of mud is sent out from the mud pipe 7 for crystallization and purification. That is, after drying, it is dissolved in water, crystallized, separated, and finally dried to obtain relatively pure calcium fluosilicate and calcium fluoride products. After 2-3 rounds of water dissolution, crystallization, separation, and drying, a finished product with a purity of >99% can be obtained.

[0051] In a specific implementation, a preferred embodiment is that the amount of cullet in the reaction bed 13 is 50-80% of the bed height.

[0052] In a specific implementation, a preferred embodiment is that the mesh size of the glass after crushing is not greater than 20 meshes.

[0053] In a specific implementation, a preferred embodiment is as follows: a bubble support plate 16 is provided at the lower end of the reaction bed 13 to prevent glass fragments from falling into the bottom and causing blockage, while ensuring that the nitric acid waste liquid containing hydrofluoric acid passes smoothly; a diversion partition is provided at the upper end to reduce the amount of glass fragments carried out by the acid liquid.

[0054] In a specific implementation, a preferred embodiment is as follows: a sight glass is provided at the bottom of the sedimentation tank 14 , and the amount of cullet added to the reaction bed 13 is adjusted by observing the amount of cullet at the bottom of the sedimentation tank 14 through the sight glass.

[0055] In a specific implementation, a preferred embodiment is as follows: the material coming out of the top of the distillation tower in step 4.1 can be sent to 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, and only waste glass and calcium hydroxide slurry are used in the recovery process, which reduces energy consumption and reagent consumption. The overall processing cost is reduced by more than 30% compared with traditional methods.

[0058] 2) The recovery rate of the materials is improved. While obtaining a concentrated nitric acid product containing more than 70% nitric acid, sodium fluorosilicate, calcium fluorosilicate and calcium nitrate products with a purity of more than 95% are also obtained.

[0059] 3) Resource recovery is achieved, and basically no excess waste is generated. The obtained high-concentration nitric acid products and high-purity sodium fluorosilicate, calcium fluorosilicate, and calcium nitrate products can be directly used in production, thereby improving resource utilization, having certain economic benefits, and reducing environmental pressure.

[0060] 4) Reduce secondary pollution. Through efficient treatment process, the generation and discharge of waste are minimized to meet environmental protection requirements.

[0061] Although the specific embodiments of the present invention are described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included 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 tower. The reactor assembly includes a cullet tank, a feed auger, a reaction bed, and a settling tank. The cullet tank is connected to the upper end of the reaction bed via the feed auger, a spent acid feed pipe is provided 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 pipeline, and the intermediate product tank is connected to the upper end of the calcification kettle via a calcification feed pump. The upper end of the calcification kettle is also connected to a calcium hydroxide slurry pipeline. The bottom of the calcification kettle is respectively connected to a mud pipeline and a clear liquid pipeline, and the clear liquid pipeline is connected to the distillation tower via a distillation feed pump. The recovery method steps are as follows: Step 1: crush the recycled glass, wash it, dry it, and add it to a cullet jar for later use; the cullet jar can be replenished with glass cullet material intermittently; the main components of the glass are calcium silicate, sodium silicate and silicon dioxide; Step 2: preheat the nitric acid waste liquid containing hydrofluoric acid to 50-80°C and enter the reaction bed from the bottom to react with the glass fines fed by the auger; then the reaction liquid enters the sedimentation tank from the top to remove the glass fines 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: The settled acid solution is fed into an intermediate product tank; the acid solution is then fed into a calcification kettle via a calcification feed pump, and a calcium hydroxide slurry with a total acid content of 1-3% is added to completely react the unreacted hydrofluoric acid in the acid solution; Step 4: Separate the materials after the reaction in the calcification kettle into layers to obtain an upper layer of acid solution and a lower layer of mud; Step 4.1: The upper acid solution enters a distillation tower for vacuum distillation to complete the purification of nitric acid and obtain a concentrated nitric acid product containing more than 70% nitric acid; the residual liquid at the bottom of the distillation tower contains sodium fluorosilicate and a small amount 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 of more than 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 fluosilicate and calcium fluoride products; and after 2-3 times of dissolving in water, crystallizing, separating, and drying, a finished product with a purity of >99% can be obtained.

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

3. A method for recovering nitric acid containing hydrofluoric acid according to claim 1, wherein: The mesh number of the glass after crushing is not greater than 20 meshes.

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

5. A method for recovering nitric acid containing hydrofluoric acid according to claim 1, characterized in that: Two reaction beds are used in series, and two groups of broken glass tanks, feed auger and sedimentation tanks are provided.

6. A method for recovering nitric acid containing hydrofluoric acid according to claim 1, characterized in that: A sight glass is provided at the bottom of the sedimentation tank, and the amount of glass cullets added to the reaction bed is adjusted by observing the amount of glass cullets at the bottom of the sedimentation tank through the sight glass.

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

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