A harmless treatment method for waste salt containing metallic sodium

Abstract

The present application relates to the technical field of waste salt treatment in waste treatment, and specifically discloses a harmless treatment method for waste salt containing metallic sodium. The method specifically includes the following steps: pretreatment: crushing and grinding the waste salt containing metallic sodium to obtain the ground waste salt; the particle size of the ground waste salt is not more than 50 meshes; static oxidation: placing the ground waste salt in a dry environment for static oxidation; the static oxidation time is 8-16h; the stacking thickness is not more than 2mm, and the waste salt after static oxidation is obtained; the dry environment is: the humidity is less than 30%, and the temperature is 10-30℃. The method provided in the present application is used to safely dispose of hazardous wastes containing metallic sodium waste salts, which are byproducts of the sodium reduction method for preparing tantalum powder, to remove the reactivity of metallic sodium in such hazardous wastes, and to achieve harmless treatment.

Description

Technical Field

[0001] The present application relates to the technical field of waste salt treatment in hazardous waste treatment, and more specifically, to a harmless treatment method for waste salt containing metallic sodium. Background Art

[0002] Tantalum powder is primarily used in the manufacture of high-quality electrolytic capacitors. The capacitance of electrolytic capacitors made with tantalum powder is over five times greater than that of conventional capacitors of the same size. Tantalum powder is widely used in military equipment and high-tech fields, such as missiles, spacecraft, televisions, and computers. Currently, the production of tantalum powder is primarily based on the sodium reduction method using potassium fluorotantalate. This method involves reacting potassium fluorotantalate with sodium to produce tantalum, potassium fluoride, and sodium fluoride. The reaction is as follows: .

[0003] As can be seen, in addition to obtaining tantalum metal products, this process also produces a large amount of waste salt. The waste salt consists of sodium chloride, potassium chloride, potassium fluoride, sodium fluoride, and small amounts of sodium and tantalum metal. According to the hazardous waste catalog, this waste salt is classified as hazardous waste.

[0004] The main difficulty in treating the waste salt generated during the production of tantalum powder is that the waste salt contains metallic sodium, which will react with water. Sodium can produce flames or sparks and a large amount of smoke when in contact with water, which is reactive. In addition, fluoride will also have an impact on the ecological environment.

[0005] Related technology CN102336438A discloses a method for treating the aforementioned waste salts, namely, a method for preparing potassium fluorotantalate by recycling the byproduct of tantalum powder production through sodium reduction. The waste salts produced as a byproduct of the sodium reduction process are crushed, dissolved in water, and filtered. The resulting filtrate is heated, evaporated, cooled, and centrifuged to obtain a mixed salt. This mixed salt is then used in the production of potassium fluorotantalate, resulting in a final product. However, the application scope of this method is limited to the production of potassium fluorotantalate.

[0006] Related technology CN102352444A discloses another method for treating the above-mentioned waste salt, namely, a method for producing composite salt using tantalum metallurgical by-products, comprising the following steps: adding pure water to a dissolving tank, then adding tantalum metallurgical by-product waste salt, stirring while adding until the tantalum metallurgical by-product waste salt is completely dissolved, and standing to clarify for 6-10 hours; releasing the supernatant liquid of the solution, performing precision filtration, and then entering the acid adjustment tank after filtration; stirring the remaining slag-containing solution, performing coarse filtration, and then performing precision filtration on the filtrate, and the filtered clear liquid enters the acid adjustment tank; after adjusting the pH value of the clear liquid to 7-9 in the acid adjustment tank, the clear liquid is evaporated and concentrated, centrifuged and dried to obtain composite salt crystals, and then dried. The composite salt crystals produced by this method meet all the requirements for use and are suitable for producing diluents for K2TaF7 and metallurgical-grade tantalum powder. The final product obtained by this method is also a mixed salt, without separation, with low product value and limited application range.

[0007] The two aforementioned waste salt treatment methods, besides recovering a mixed salt product, fail to address the reactivity of elemental sodium metal with water, posing a safety risk. Therefore, it is necessary to find a suitable treatment method for the safe disposal of this type of waste salt. Summary of the Invention

[0008] This application provides a method for the harmless disposal and resource recovery of waste salts containing metallic sodium. This method is used to safely dispose of hazardous wastes containing metallic sodium salts, a byproduct of the sodium reduction process for preparing tantalum powder, by removing the reactivity of metallic sodium in such hazardous wastes and achieving harmless treatment.

[0009] Waste salt containing metallic sodium, primarily composed of sodium chloride, potassium chloride, potassium fluoride, sodium fluoride, and small amounts of metallic sodium and tantalum. The waste salt contains metallic sodium, which reacts with water. Contact with water can produce flames or sparks, and generate significant amounts of smoke. This reactive nature makes it a hazardous waste.

[0010] In addition, the waste salt containing metallic sodium is a hard irregular block with a diameter of 200-500 mm. The elemental metallic sodium is evenly distributed inside the waste salt block, with a content of about 0.1-0.5 wt%.

[0011] In addition, the present application also separates and recycles the mixed salt, and the recovered products are converted from mixed salts into separate salts, thereby realizing resource utilization and increasing the value of the product.

[0012] The present application provides a method for harmless treatment and resource recovery of waste salt containing metallic sodium, which adopts the following technical solution:

[0013] A method for harmlessly treating waste salt containing metallic sodium comprises the following steps:

[0014] Pretreatment: crushing and grinding the waste salt containing metallic sodium to obtain ground waste salt; the particle size of the ground waste salt is not greater than 50 mesh;

[0015] Static oxidation: the ground waste salt is placed in a dry environment for static oxidation; the static oxidation time is 8-16 hours; the stacking thickness is not greater than 2mm, and the waste salt after static oxidation is obtained; the dry environment is: humidity is less than 30%, and the temperature is 10-30°C.

[0016] The processing method provided in the present application includes pretreatment and static oxidation, wherein the pretreatment includes crushing and grinding.

[0017] Crushing breaks down large chunks of sodium metal waste salt into granules for subsequent grinding. Grinding also exposes the sodium metal trapped within the salt, increasing its contact area with air during the static oxidation step. Furthermore, during the grinding process, the sodium on the surface of the salt is oxidized to sodium oxide through contact with air. Furthermore, grinding facilitates dissolution in water for subsequent resource recovery.

[0018] Through the crushing and grinding process, the metallic sodium is initially oxidized, and then static oxidation in a dry environment is carried out to completely oxidize the elemental sodium. This avoids the process of elemental sodium directly contacting water to react and produce sparks, eliminates the reactivity of the waste salt, and facilitates subsequent resource utilization.

[0019] During the static oxidation process, metallic sodium reacts with oxygen in the air to form sodium oxide. The reaction is as follows:

[0020] 4Na+O2=2Na2O.

[0021] The environment for static oxidation is required to be kept dry to prevent the risk of explosion after the hydrogen generated by the reaction of metallic sodium and water vapor accumulates. In this application, the dry environment is defined as: humidity is less than 30%, and temperature is 10-30°C. When the humidity is greater than 30%, the amount of water vapor in contact with the sodium element increases, and a certain amount of hydrogen is produced. In order to prevent the accumulation of hydrogen to the explosion limit, the humidity must be strictly controlled and the air must be ventilated in time; when the temperature is greater than 30°C, it is higher than room temperature and an additional heat source needs to be provided for heating, which increases the cost; when the temperature is lower than 10°C, it will affect the oxidation time of the elemental sodium, reduce the oxidation reaction rate, and prolong the time required for the static oxidation process.

[0022] After grinding and static oxidation, the vast majority of the sodium metal in the sodium metal waste salt has been oxidized to sodium oxide. This removes its reactivity, reduces safety risks, and allows for subsequent resource utilization.

[0023] Preferably, the particle size of the ground waste salt is 100-200 mesh.

[0024] In a specific embodiment, the particle size of the ground waste salt can be 50 mesh, 100 mesh, 200 mesh, or 250 mesh.

[0025] In some specific embodiments, the particle size of the ground waste salt can be 50-100 mesh, 50-200 mesh, 50-250 mesh, 100-200 mesh, 100-250 mesh, or 200-250 mesh.

[0026] Preferably, the static oxidation time is 8-11 hours.

[0027] In a specific embodiment, the static oxidation time can be 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or 16h.

[0028] In some specific embodiments, the time for static oxidation can be 8-9h, 8-10h, 8-11h, 8-12h, 8-13h, 8-14h, 8-15h, 8-16h, 9-10h, 9-11h, 9-12h, 9-13h, 9-14h, 9-15h, 9-16h, 10-11h, 10-12h, 10-13h, 10-14h, 10-15h, 10-16h, 11-12h, 11-13h, 11-14h, 11-15h, 11-16h, 12-13h, 12-14h, 12-15h, 12-16h, 13-14h, 13-15h, 13-16h, 14-15h, 14-16h, 15-16h.

[0029] Preferably, the stacking thickness is no more than 1.5 mm.

[0030] In a specific embodiment, the stacking thickness may be 0.5 mm, 1 mm, 1.5 mm, or 2 mm.

[0031] In some specific embodiments, the stacking thickness can be 0.5-1 mm, 0.5-1.5 mm, 0.5-2 mm, 1-1.5 mm, 1-2 mm, or 1.5-2 mm.

[0032] Furthermore, the static oxidation step further comprises the following steps:

[0033] Dissolving: dissolving the waste salt after static oxidation in water to obtain a mixed salt solution; adjusting the pH to neutral;

[0034] Filtration and separation: filtering and separating the insoluble matter in the mixed salt solution;

[0035] Preparation of mixed salt solution: Detection of Na in the mixed salt solution + and F - The molar amount of the mixed salt solution is then adjusted according to the test results to obtain a prepared salt solution; the prepared salt solution contains Na + and F - The molar amounts are the same;

[0036] Evaporation and concentration: The prepared salt solution is evaporated and concentrated, and the sodium fluoride is precipitated almost completely; after fine solid-liquid separation, the solid phase is sodium fluoride and the liquid phase is chloride ions and potassium ions; the liquid phase is further concentrated to obtain potassium chloride.

[0037] This application not only removes the reactivity of metallic sodium in metallic sodium waste salt to achieve harmless treatment, but also further provides a subsequent treatment method, thereby achieving resource utilization while achieving harmless treatment and increasing the value of the recovered products.

[0038] The resource recovery process provided by this application includes dissolution, filtration separation, preparation of mixed salt solutions, and evaporation concentration. In the dissolution step, sodium hydroxide is generated due to the reaction of sodium oxide generated during the static oxidation process with water. Therefore, the mixed salt solution obtained by dissolution is alkaline, and the pH is adjusted to neutral by adding hydrochloric acid. The components of the mixed salt solution are NaCl, KF, NaF, and KCl. There will be a small amount of insoluble matter at the bottom, which is composed of NaF and metallic tantalum. Among them, the solubility of NaF is much lower than that of the other three salts, and is only about 4% at room temperature, and it will precipitate at room temperature.

[0039] During the resource utilization process, the more valuable tantalum-containing insoluble matter is first separated, and then the four compounds in the soluble matter are separated according to the specified route, and finally sodium fluoride and potassium chloride products are obtained, realizing resource utilization and obtaining high-value products with a wide range of applications.

[0040] The mixed salt solution insoluble matter is separated by filtration and mainly includes Na + , K + 、F - 、Cl - Four ions. If evaporation and concentration are performed directly, the product obtained is a mixed salt containing a variety of mixtures. In order to facilitate the separation of different types of salts, it is necessary to detect the Na in the mixed salt solution. + and F - The molar amount of the mixed salt solution is then adjusted according to the test results to make the Na + and F - The molar amount is the same. According to the balance of anions and cations, the K + and Cl - The molar amounts are the same.

[0041] Due to the solubility and common ion effect of different compounds, as the prepared salt solution concentrates, the solubility of sodium fluoride is much lower than that of the other three compounds. The presence of chloride ions further reduces the solubility of sodium fluoride, so sodium fluoride will precipitate and crystallize first. As evaporation continues, the salt solution continues to concentrate, and fluoride ions and sodium ions continue to combine and precipitate as crystals. Due to the common ion effect of fluoride and chloride ions, sodium fluoride will precipitate nearly completely. Fine solid-liquid separation will reveal sodium fluoride crystals in the solid phase, while the solution will mainly contain chloride ions and potassium ions. Further concentration will produce potassium chloride product.

[0042] Preferably, the mixed salt solution is prepared as follows: + and F - The molar amounts are counted as a and b respectively;

[0043] ① When a>b, add (ab)mol F - , so that the Na + and F - The molar amounts are the same;

[0044] ② When a<b, add (ba)mol Na + , so that the Na + and F - The molar amounts are the same;

[0045] ③When a=b, no mixing is required.

[0046] During the preparation of the mixed salt solution, the F - and Na + Molar amount, add Na according to the result + or F - , so that it reaches equilibrium. By utilizing the characteristic that the solubility of sodium fluoride is much lower than that of the other three salts, sodium fluoride can be guaranteed to precipitate and crystallize first to obtain sodium fluoride product. Then, according to the balance of anions and cations, the remainder is potassium chloride product. If this balance adjustment is not performed, the final product ratio cannot be determined, and what is obtained is a mixture of multiple salts, and the separation of mixed salts cannot be achieved.

[0047] Detection of Na in mixed salt solution + and F - The molar amount of F - The molar amount is greater than Na + Molar amount, Na + The molar amount is greater than F - The molar weight and molar weight of the two ions are equal. The preparation process of the mixed salt solution is to make the Na + Molar amount and F- The molar amounts are equal. + The molar amount is greater than F - When the molar amount is greater than 1%, additional F is required. - When F - The molar amount is greater than Na + molar amount, additional Na + ; When the molar amounts of the two ions are equal, no mixing is required.

[0048] Preferably, when a>b, F is supplemented by adding KF - .

[0049] Preferably, when a<b, NaCl is added to supplement Na + .

[0050] According to the sodium reduction reaction equation, the molar number of fluoride ions is greater than the molar number of sodium ions. The diluents are potassium chloride and potassium fluoride, and no sodium ions are introduced. Therefore, in actual situations, the molar number of fluoride ions is often greater than the molar number of sodium ions. Therefore, the main situation in the concentration preparation of the mixed salt solution is that the molar number of fluoride ions is greater than the molar number of sodium ions. It is necessary to prepare it by adding sodium ions to make the Na in the prepared salt solution + and F - The molar amount is the same. That is, sodium chloride is added to the solution, and the cost of sodium chloride is relatively low, which can reduce the cost consumption.

[0051] Preferably, in the dissolving step, the weight ratio of the waste salt after static oxidation to the water is 1:(2-3).

[0052] Preferably, in the dissolving step, hydrochloric acid is added to the mixed salt solution to adjust the pH.

[0053] In summary, this application has the following beneficial effects:

[0054] 1. The method provided in this application is used to safely dispose of hazardous wastes such as metallic sodium waste salts, which are by-products of the sodium reduction method for preparing tantalum powder. The metallic sodium waste salts are crushed, ground, and the particle size of the ground particles is controlled. At the same time, they are placed in a dry environment for static oxidation treatment. After the sodium element in the metallic sodium waste salts reacts with air and is oxidized, it will no longer produce hydrogen when it comes into contact with water. The reactivity of metallic sodium in such hazardous wastes is removed, and the disposal risk is greatly reduced, thereby achieving safe disposal of metallic sodium waste salts and solving the treatment problems of related enterprises.

[0055] 2. This application not only realizes the harmless treatment of waste salt containing metallic sodium, but also further treats the waste salt after harmless treatment as a resource, by preparing the mixed salt solution containing sodium + and F -The molar amount of the two is equal, and with evaporation and concentration, sodium fluoride precipitates first and almost completely, depending on the solubility of different compounds. Filtration can separate the sodium chloride and the solution, and further evaporation and concentration can produce potassium chloride. Compared with the mixed salts recovered in related technologies, the products recovered in this application are separate salts, which increases the value of the product and realizes resource utilization. DETAILED DESCRIPTION

[0056] This application provides a method for harmlessly treating waste salt containing metallic sodium. Specifically, it comprises the following steps:

[0057] (1) Pretreatment, including crushing and grinding the waste salt containing metallic sodium. Elemental metallic sodium is evenly distributed inside the waste salt block, with a content of about 0.1-0.5wt%.

[0058] Crushing: First, the large pieces of waste salt containing sodium metal (diameter 200-500mm) are crushed into small particles of waste salt of 20-30mm;

[0059] Grinding: Grind the small particles of waste salt to no more than 50 meshes to obtain the ground waste salt.

[0060] Preferably, the particle size of the ground waste salt is 100-200 mesh.

[0061] (2) Static oxidation

[0062] The ground waste salt is placed in a dry environment for static oxidation. The static oxidation time is 8-16 hours. The stacking thickness is no greater than 2 mm, and the waste salt after static oxidation is obtained. The dry environment has a humidity of less than 30% and a temperature of 10-30°C. In this application, the static oxidation process is carried out indoors, and the indoor temperature and humidity are regulated by an indoor temperature and humidity control system.

[0063] Preferably, the static oxidation time is 8-11 hours. Preferably, the stacking thickness is no more than 1.5 mm.

[0064] Furthermore, based on the above-mentioned harmless treatment method for waste salt containing metallic sodium, the present application further carries out resource treatment of waste salt. That is, after the static oxidation step, the following steps are also included:

[0065] (1) Dissolution

[0066] Dissolve the waste salt after static oxidation in water, with the weight ratio of waste salt to water being 1:(2-3), and stir at the same time to accelerate dissolution to obtain a mixed salt solution, and add hydrochloric acid to adjust the pH to neutral.

[0067] At this point, the components of the mixed salt solution are NaCl, KF, NaF, and KCl, with a small amount of insoluble matter at the bottom.

[0068] (2) Filtration separation

[0069] The insoluble matter in the mixed salt solution is filtered and separated. The insoluble matter accounts for approximately 2-5% of the total waste salt. The main components of the insoluble matter are sodium fluoride and tantalum metal, with small amounts of other impurities. The tantalum metal content accounts for 2-5% of the insoluble matter and has a high recovery value, so it is recycled and reused.

[0070] (3) Preparation of mixed salt solution

[0071] The details are as follows:

[0072] 1. Detection: Detection of Na in mixed salt solution + and F - The molar amount of the mixed salt solution is then adjusted according to the test results to obtain the adjusted salt solution.

[0073] 2. The deployment method is as follows:

[0074] Will Na + and F - The molar amounts are counted as a and b respectively;

[0075] ① When a>b, then, in the mixed salt solution, add (ab) mol KF, that is, add (ab) mol F - , so that the Na + and F - The molar amount is the same. According to the balance of anions and cations, the K + and Cl - The molar amounts are the same.

[0076] ② When a<b, similarly, in the mixed salt solution, add (ba) mol NaCl, that is, add (ba) mol Na + , so that the Na + and F - The molar amount is the same. According to the balance of anions and cations, the K + and Cl - The molar amounts are the same.

[0077] ③When a=b, no mixing is required.

[0078] (4) Evaporation and concentration

[0079] The prepared salt solution is concentrated by evaporation.

[0080] The solubility of each substance in the prepared salt solution is shown in Table 1.

[0081] Table 1 Solubility of various substances

[0082]

[0083] According to the solubility and common ion effect of the different compounds in Table 1, as the prepared salt solution concentrates, the solubility of sodium fluoride is much lower than that of the other three compounds. The presence of chloride ions further reduces the solubility of sodium fluoride, so sodium fluoride will precipitate and crystallize first. As evaporation continues, the salt solution continues to concentrate, and fluoride ions and sodium ions continue to combine and precipitate as crystals. Due to the common ion effect of fluoride and chloride ions, sodium fluoride will precipitate nearly completely. Fine solid-liquid separation will result in sodium fluoride crystals in the solid phase, while the solution will mainly contain chloride ions and potassium ions. Further concentration will produce potassium chloride product.

[0084] The present application is further described in detail below with reference to the embodiments.

[0085] Example Example 1

[0086] This example provides a method for harmlessly treating waste salt containing metallic sodium. The source of the waste salt containing metallic sodium in this example is a tantalum powder factory in Ningxia. The sodium content of the waste salt is 0.5 wt%.

[0087] The sodium content in the waste salt containing metallic sodium is detected by dissolving the waste salt containing metallic sodium in water, titrating the solution to neutrality using an acid solution, and recording the molar amount of acid consumed in the titration.

[0088] The sodium content in the waste salt containing metallic sodium is calculated as follows:

[0089] W=(M×23) / m×100%.

[0090] Where W represents the sodium content of the sodium metal waste salt; M is the molar mass of hydrogen ions consumed in the titration; 23 is the atomic mass of sodium; and m is the total amount of the sodium metal waste salt sample. Note: The sodium content calculated here includes the sodium element within the sodium metal waste salt and a small amount of sodium oxide on its surface.

[0091] The above harmless treatment method specifically includes the following steps:

[0092] (1) Preprocessing

[0093] Crushing: Crushing the waste salt containing metallic sodium into small particles of 20-30mm.

[0094] Grinding: Grind the small particles of waste salt to 50 mesh to obtain the ground waste salt.

[0095] (2) Static oxidation

[0096] The ground waste salt is placed in air for static oxidation. The static oxidation environment must be kept dry, with a controlled temperature of 20°C and a humidity of 20%. The ground waste salt is piled to a thickness of 2mm to obtain the waste salt after static oxidation.

[0097] After 8 hours of static oxidation, samples were taken every hour to detect the oxidation of metallic sodium in the waste salt, and the time for complete oxidation of metallic sodium in the waste salt was recorded.

[0098] The test method is as follows: Use the water spray method to test the reactivity of the sodium metal in the waste salt and observe whether sparks are generated and the number of sparks. If no sparks are generated during the test, it indicates that the sodium metal is completely oxidized.

[0099] Take 5g of the statically oxidized waste salt sample and spread it flat on the bottom of a 500ml beaker. Slowly spray water over the surface of the waste salt until it is submerged. Observe for sparks. In this example, after 16 hours of static oxidation, the metallic sodium in the waste salt is completely oxidized.

[0100] Example 2-12

[0101] Examples 2-12 each provide a harmless treatment method for waste salt containing metallic sodium. These methods differ from Example 1 in terms of the sodium content of the waste salt containing metallic sodium, the particle size of the small particles of waste salt after grinding, the thickness of the accumulated waste salt after static oxidation, and the time required to detect complete oxidation of the elemental sodium in the waste salt. All other conditions are the same as in Example 1, as shown in Table 2.

[0102] Examples 13-25

[0103] Examples 13-25 each provide a method for harmlessly treating waste salt containing metallic sodium. These methods differ from Example 1 in the temperature or humidity used for static oxidation, and the time or result for detecting complete oxidation of the elemental sodium in the waste salt. All other methods are the same as in Example 1, as shown in Table 2.

[0104] Table 2 Parameters in Examples 1-25 and Comparative Examples 1-6

[0105]

[0106] By comparing the test results of Examples 1-4 and Comparative Example 2, it can be seen that the present application controls the particle size of the waste salt after grinding to no more than 50 mesh, which can ensure that the elemental sodium in the waste salt containing metallic sodium can be completely oxidized. Furthermore, the present application controls the particle size of the waste salt after grinding to 100-200 mesh, which can effectively shorten the time for complete oxidation of the elemental sodium in the waste salt containing metallic sodium.

[0107] By comparing the test results of Examples 3, 5-7, 17-25 and Comparative Example 3, it can be seen that when the stacking thickness during static oxidation is controlled to be no more than 2 mm, the elemental sodium in the waste salt containing metallic sodium can be completely oxidized. Furthermore, the present application controls the stacking thickness during static oxidation to be no more than 1.5 mm, which can effectively shorten the time for complete oxidation of the elemental sodium in the waste salt containing metallic sodium.

[0108] By comparing the test results of Examples 6, 8-12 and Comparative Example 1, it can be seen that the treatment object of the present application is waste salt containing metallic sodium with a sodium content of less than 0.54%, which can ensure that the elemental sodium in the waste salt containing metallic sodium can be completely oxidized. Furthermore, the lower the sodium content of the treatment object, the shorter the time it takes for the elemental sodium in the waste salt containing metallic sodium to be completely oxidized.

[0109] By comparing the test results of Examples 6, 13-16 and Comparative Examples 3-5, it can be seen that the static oxidation conditions of the present application are controlled to be a temperature of 10-30°C and a humidity of less than 30%, which can ensure that the elemental sodium in the waste salt containing metallic sodium can be completely oxidized. When the static oxidation conditions do not meet the above conditions, it is not conducive to the complete oxidation of the elemental sodium in the waste salt containing metallic sodium.

[0110] Comparative Example

[0111] Comparative Examples 1-3 provide a harmless treatment method for waste salt containing metallic sodium. These methods differ from Example 1 in terms of the sodium content in the waste salt containing metallic sodium, the particle size of the small particles of waste salt after grinding, the thickness of the accumulated waste salt after static oxidation, and the time required to detect complete oxidation of the elemental sodium in the waste salt. All other conditions are the same as in Example 1, as shown in Table 1.

[0112] Comparative Examples 4-5

[0113] Comparative Examples 4-6 provide a method for harmlessly treating waste salt containing metallic sodium. These methods differ from Example 1 in the temperature and humidity used for static oxidation, as well as the time or result required to detect complete oxidation of the elemental sodium in the waste salt. All other methods are the same as in Example 1, as shown in Table 1.

[0114] Examples 26-30

[0115] Examples 26-30 provide methods for harmless treatment and resource recovery of sodium metal waste salts. The difference between these methods is that the resource recovery treatment is performed after the harmless treatment of sodium metal waste salts provided in Examples 6 and 8-12, respectively. The results of the resource recovery process are shown in Table 3.

[0116] The above resource processing process specifically includes the following steps:

[0117] (1) Dissolution

[0118] Dissolve the waste salt after static oxidation in 200 ml of water while stirring to accelerate dissolution to obtain a mixed salt solution, and add hydrochloric acid to adjust the pH to neutral. At this point, the components of the mixed salt solution are NaCl, KF, NaF, KCl, and there will be a small amount of insoluble matter at the bottom.

[0119] (2) Filtration separation

[0120] The insoluble matter in the mixed salt solution is filtered and separated. The insoluble matter accounts for approximately 2-5% of the total waste salt. The main components of the insoluble matter are sodium fluoride and tantalum metal, with small amounts of other impurities. The tantalum metal content accounts for 2-5% of the insoluble matter and has a high recovery value, so it is recycled and reused.

[0121] (3) Preparation of mixed salt solution

[0122] The details are as follows:

[0123] 1. Detection: Detection of Na in mixed salt solution + and F - The molar amount of the mixed salt solution is then adjusted according to the test results to obtain the adjusted salt solution.

[0124] 2. The deployment method is as follows:

[0125] Will Na + and F - The molar amounts are counted as a and b respectively;

[0126] ① When a>b, then, in the mixed salt solution, add (ab) mol KF, that is, add (ab) mol F - , so that the Na + and F - The molar amount is the same. According to the balance of anions and cations, the K + and Cl - The molar amounts are the same.

[0127] ② When a<b, similarly, in the mixed salt solution, add (ba) mol NaCl, that is, add (ba) mol Na + , so that the Na + and F - The molar amount is the same. According to the balance of anions and cations, the K + and Cl - The molar amounts are the same.

[0128] ③When a=b, no mixing is required.

[0129] (4) Evaporation and concentration

[0130] The prepared salt solution is evaporated and concentrated. Sodium fluoride is precipitated almost completely. After fine solid-liquid separation, the solid phase is sodium fluoride and the liquid phase is chloride ions and potassium ions. The liquid phase is further concentrated to obtain potassium chloride.

[0131] Among them, recovery rate = (recovery amount × purity) / mixed salt solution after preparation

[0132] Table 3 Resource recovery results in Examples 26-30

[0133]

[0134] As can be seen from the table above, using the resource recovery method provided by this application to treat waste salt, the purity of the recovered sodium fluoride can reach 95-98%, and the recovery rate can reach over 97%; the purity of the recovered potassium chloride can reach 93-95%, and the recovery rate can reach 98%. As can be seen from the above, the methods provided by this application can efficiently recover sodium fluoride and potassium chloride, and both are of high purity.

[0135] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for harmlessly treating waste salt containing sodium metal, characterized in that: The specific steps include: Pretreatment: crushing and grinding the waste salt containing metallic sodium to obtain ground waste salt; the particle size of the ground waste salt is not greater than 50 meshes; Static oxidation: the ground waste salt is placed in a dry environment for static oxidation; the static oxidation time is 8-16 hours; the stacking thickness is not more than 2mm, and the waste salt after static oxidation is obtained; the dry environment is: the humidity is less than 30%, and the temperature is 10-30°C; Dissolving: dissolving the waste salt after static oxidation in water to obtain a mixed salt solution; adjusting the pH to neutral; Filtration and separation: filtering and separating the insoluble matter in the mixed salt solution; Preparation of mixed salt solution: Detection of Na in the mixed salt solution + and F - The molar amount of the mixed salt solution is then adjusted according to the test results to obtain a prepared salt solution; the prepared salt solution contains Na + and F - The molar amounts are the same; Evaporation and concentration: The prepared salt solution is evaporated and concentrated, and the sodium fluoride is almost completely precipitated; after fine solid-liquid separation, the solid phase is sodium fluoride, and the liquid phase is chloride ions and potassium ions; The liquid phase is further concentrated to obtain potassium chloride.

2. The harmless treatment method for waste salt containing metallic sodium according to claim 1, characterized in that: The particle size of the ground waste salt is 100-200 meshes.

3. The harmless treatment method for waste salt containing metallic sodium according to claim 1, characterized in that: The static oxidation time is 8-11 hours.

4. The harmless treatment method for waste salt containing metallic sodium according to claim 1, characterized in that: The stacking thickness is no more than 1.5 mm.

5. The harmless treatment method for waste salt containing metallic sodium according to claim 1, characterized in that: The mixed salt solution is prepared as follows: + and F - The molar amounts are counted as a and b respectively; ① When a>b, add (ab) mol F - , so that the Na + and F - The molar amounts are the same; ②When a<b, add (ba)mol Na + , so that the Na + and F - The molar amounts are the same; ③When a=b, no adjustment is required.

6. The harmless treatment method for waste salt containing metallic sodium according to claim 5, characterized in that: When a>b, F is supplemented by adding KF - .

7. The harmless treatment method for waste salt containing metallic sodium according to claim 5, characterized in that: When a<b, NaCl is added to supplement Na + .

8. The harmless treatment method for waste salt containing metallic sodium according to claim 1, characterized in that: In the dissolution step, the weight ratio of the waste salt after static oxidation to the water is 1:(2-3).

9. The harmless treatment method for waste salt containing metallic sodium according to claim 1, characterized in that: In the dissolving step, hydrochloric acid is added to the mixed salt solution to adjust the pH.

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