Method for treating nickel-containing waste electrolyte in electrolytic fluorine production

Abstract

The invention relates to an electrolytic fluorine-making nickel-containing waste electrolyte treatment method which comprises the following steps: heating a fluorine-making electrolytic cell to 80-95 DEG C, completely melting the electrolyte, standing for layering, and taking out the colorless electrolyte on the upper layer; excessive fluorine gas is introduced into the electrolytic cell, and ferrous ions in the remaining electrolyte are converted into iron ions; electrolyte in the electrolytic bath is guided into an anti-corrosion container, deionized water is added into the anti-corrosion container, and the electrolyte is completely dissolved; adjusting the pH value of the solution in the container to 3-4, fully precipitating, and carrying out solid-liquid separation to obtain a solid A and a filtrate A; adjusting the pH value of the filtrate A to 9-11, fully precipitating, and carrying out solid-liquid separation to obtain a solid B and a filtrate B; and adjusting the ion molar ratio of F <-> to K < + > in the filtrate B to be 2: 1, then carrying out evaporative crystallization, and drying obtained crystals to obtain products of potassium hydrogen difluoride and potassium fluoride. The waste electrolyte can be effectively treated, and resources are efficiently recycled and reutilized.

Description

Technical Field

[0001] The invention relates to the technical field of electrolytic fluorine production, and in particular to a method for treating nickel-containing waste electrolyte in electrolytic fluorine production. Background Art

[0002] Fluorine gas is one of the most important raw materials for fluorine chemical industry. With the development of fluorine chemical technology, nickel anode electrolysis fluorine production technology is also receiving more and more attention from fluorine chemical enterprises in terms of high-purity fluorine gas and stable operation of fluorine electrolytic cells. However, when metal nickel is used as the anode of fluorine electrolytic cells, nickel will be gradually consumed as the fluorine electrolytic cells are operated and become nickel fluoride and complexes. At the same time, the carbon steel of the electrolytic cell cathode and the cell body will also be consumed during the operation, shutdown, and maintenance of the electrolytic cell, producing iron fluoride and complexes. The above-mentioned metal fluorides are highly toxic and corrosive, and will also cause great damage to the natural environment. Therefore, a method for effectively and environmentally friendly treatment of nickel-containing waste electrolytes for electrolytic fluorine production is needed.

[0003] The composition of nickel slag is relatively complex, mainly containing electrolyte and nickel fluoride, among which the content of ammonium bifluoride and hydrogen fluoride is about 50-60%, and the remaining solids are about 60-70% nickel fluoride, 10-20% ferric fluoride or ferrous fluoride and other solids. Chinese patent CN106854765A discloses a process for recycling waste electrolyte in the fluorine gas production process. The method includes: 1. Dissolving the waste electrolyte, placing the dissolution reactor in a hot water bath, heating and keeping it warm to 70℃-90℃, the dissolution time is 6h~10h; and performing a coarse filtration treatment; 2. Placing the aging reactor in a hot water bath, heating and keeping it warm to 70℃-90℃, and adding an appropriate amount of KOH to the aging reactor to adjust the pH value of the filtrate obtained by coarse filtration to 3-5, the aging time is 4h-8h, and fine filtration treatment; 3. Crystallizing the filtrate, drying and packaging. Chinese patent CN111020632B discloses a method for recovering waste electrolyte from fluorine production by electrolysis. It includes the following steps: (1) dissolving waste electrolyte; (2) adjusting pH; (3) crystallizing potassium difluoride; a clarified electrolyte solution can be obtained by dissolving and filtering. By adjusting pH to 3-4, controlling pH to 10-12 for copper removal, and adjusting pH to 3-4 before crystallization, a recovered electrolyte with indicators similar to those of a newly purchased electrolyte can be obtained. In the above-mentioned prior art, when treating electrolyte waste residues, the treated electrolyte waste residues are mostly waste electrolytes that do not contain nickel fluoride produced by using carbon anodes, and there are few nickel-containing waste electrolytes produced by electrolysis processes that do not involve the use of nickel anodes. In addition, when treating nickel-containing waste electrolytes, the waste residues are not completely dissolved, resulting in a waste of resources when recovering the electrolyte. Summary of the invention

[0004] In order to overcome the above-mentioned problems existing in the prior art, the purpose of the present invention is to provide a method for treating waste nickel-containing electrolyte from electrolytic fluorine production, solve the technical problem that electrolyte waste residue is not easy to completely dissolve, and can effectively and environmentally friendly treat waste nickel-containing electrolyte from electrolytic fluorine production.

[0005] To achieve the purpose of the present invention, the specific technical solutions provided by the present invention are as follows:

[0006] A method for treating waste nickel-containing electrolyte for electrolytic fluorine production, the method comprising the following steps:

[0007] S1. Heat the fluorine production electrolytic cell to 80-95°C to completely melt the nickel-containing waste electrolyte for electrolysis of fluorine production, let it stand for stratification, and take out the colorless electrolyte on the upper layer;

[0008] S2, introducing excess fluorine gas into the electrolytic cell to convert the ferrous ions in the remaining electrolyte into ferric ions;

[0009] S3, introducing the electrolyte in the electrolytic cell into an anti-corrosion container, and adding deionized water into the anti-corrosion container to dissolve all the electrolyte;

[0010] S4, adjusting the pH of the solution in the container to 3-4, after sufficient precipitation, performing solid-liquid separation to obtain solid A and filtrate A; then adjusting the pH of the filtrate A to 9-11, after sufficient precipitation, performing solid-liquid separation to obtain solid B and filtrate B;

[0011] S5, F in filtrate B - and K + The ion molar ratio is adjusted to 2:1, and then evaporation crystallization is performed, and the obtained crystals are dried to obtain potassium difluoride containing a small amount of potassium fluoride.

[0012] Preferably, in step S2, fluorine gas is introduced into the electrolytic cell, the volume of the fluorine gas introduced is 1 / 4-1 / 2 of the volume of the electrolytic cell, the fluorine gas is introduced below the electrolyte liquid level, and the pressure of the electrolytic cell is maintained at ≤0.03MPa, and the reaction is carried out for 0.5-3h.

[0013] Preferably, in step S3, the anti-corrosion container is a polytetrafluoroethylene lined reactor, the container temperature is maintained at 80-95°C, deionized water is added to the container, and the volume ratio of electrolyte to deionized water is 1:4, so that the electrolyte is completely dissolved.

[0014] Preferably, in step S3, the anti-corrosion container is a polytetrafluoroethylene lined reactor, the container temperature is maintained at 80-95°C, deionized water is added to the container, the volume ratio of electrolyte to deionized water is 1:4, and then anhydrous hydrogen fluoride is added to the container to make the hydrogen ion concentration 0.1-0.3 mol / L until the electrolyte is completely dissolved.

[0015] Preferably, in step S4, a potassium hydroxide solution is used to adjust the pH value of the solution, and the concentration of the potassium hydroxide solution is 1-2 mol / L.

[0016] Preferably, in step S4, solid A is ferric hydroxide, solid B is nickel hydroxide, the water content of solid A and solid B is less than 10%, and after solid A and solid B are dried, the purity of ferric hydroxide and nickel hydroxide is greater than 98%.

[0017] Preferably, in step S4, when performing solid-liquid separation, a belt filter is used for filtration.

[0018] Preferably, in step S5, hydrogen fluoride is used to adjust F - and K + The ion molar ratio was adjusted to 2:1.

[0019] Preferably, in step S5, potassium dihydrogen fluoride containing a small amount of potassium fluoride is obtained, wherein the mass content of potassium dihydrogen fluoride is greater than 95%.

[0020] Preferably, the upper layer of colorless electrolyte, potassium dihydrogen fluoride and potassium fluoride are recycled to other electrolytic fluorine production electrolytic cells.

[0021] The method for treating waste nickel-containing electrolyte for fluorine production by electrolysis of the present invention has the following beneficial effects:

[0022] 1. The present application dissolves the electrolyte by heating and melting, introducing fluorine gas into the oxidation reaction, and adding deionized water, and finally adding anhydrous hydrogen fluoride, which effectively solves the technical problem that the waste residue in the nickel-containing waste electrolyte of electrolytic fluorine production is not easy to be completely dissolved. At the same time, the electrolyte can be recovered and directly reused during the heating process of the waste electrolyte; the addition of anhydrous hydrogen fluoride adjusts the hydrogen ion concentration of the solution to 0.1-0.3 mol / L, ensuring that the fluorides of nickel and iron can be completely dissolved, thereby improving the processing efficiency and resource recovery rate.

[0023] 2. This application utilizes the difference in solubility product constants between nickel hydroxide and ferric hydroxide to successfully separate high-purity ferric hydroxide and nickel hydroxide (with purity greater than 98%) through a step-by-step precipitation method, thus achieving effective recycling and reuse of resources. - and K + ion molar ratio and evaporated and crystallized to obtain a potassium difluoride product containing a small amount of potassium fluoride, further improving the economic value.

[0024] 3. In the present application, the nickel-containing waste electrolyte generated by the use of nickel anodes can be effectively treated. During the entire treatment process, no waste is generated or discharged, and there is no pollution to the environment. The safety and environmental protection of the treatment process are ensured, the requirements of sustainable development are met, environmental protection problems are solved, and economic benefits are brought to the enterprise through efficient recycling and reuse of resources. DETAILED DESCRIPTION

[0025] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation method, structure, characteristics and effects of the present invention are described in detail below in combination with the preferred embodiments.

[0026] Example 1

[0027] This embodiment provides a method for treating waste nickel-containing electrolyte for fluorine production by electrolysis, the method comprising the following steps:

[0028] S1. After the nickel anode electrolytic cell has been used for 10 million ampere-hours, heat the cell to 85°C, use a copper rod to detect the electrolyte at the bottom of the cell to ensure that it is completely melted, and measure the electrolyte brought out to determine the liquid level of the waste electrolyte at the bottom; according to the liquid level of the waste electrolyte, insert the transfer tube above the liquid level of the waste electrolyte, maintain a negative pressure of -0.06MPa in the receiving tank, and transfer the upper colorless electrolyte in the fluorine-producing electrolytic cell to the receiving tank. The colorless electrolyte can be directly used in other electrolytic fluorine-producing electrolytic cells.

[0029] S2. Introduce 1 cubic meter of fluorine gas below the level of the waste electrolyte through the HF feeding port of the fluorine production electrolytic cell, maintain the pressure of the fluorine production electrolytic cell ≤ 0.03MPa, and let it stand for 3 hours to convert the ferrous ions in the cell into ferric ions.

[0030] S3. Use a pneumatic diaphragm pump to transfer all the remaining electrolyte in the fluorine production electrolytic cell to a 500L polytetrafluoroethylene-lined reactor. The volume of the electrolyte is measured to be 50L. Maintain the reactor temperature at 85°C, slowly introduce 200L of 85°C deionized water into the reactor and stir continuously. The electrolyte is not completely dissolved. Determine the H + Ion concentration, H + Ion concentration <0.1mol / L, H + Insufficient ion concentration, H + When the ion concentration is not within the range of 0.1-0.3 mol / L, the metal fluoride cannot be completely dissolved when the hydrogen ion concentration is low. Anhydrous HF needs to be added until the electrolyte is completely dissolved. The H + Ion concentration, H + The ion concentration is 0.18mol / L.

[0031] S4, adding a potassium hydroxide solution with a concentration of 2 mol / L to the solution, adjusting the pH of the solution in the kettle to between 3-4, standing for 2 h to precipitate, and after sufficient precipitation, filtering using a belt filter to obtain a precipitated filter cake A and a filtrate A, drying the filter cake A, and weighing the filter cake A after drying to obtain a weight of 14.3 kg, and the water content of the filter cake A before drying was 8.5%. After testing, it was determined that the filter cake A was a ferric hydroxide precipitate, and the mass content of ferric hydroxide was 98.9%;

[0032] The filtrate A was further treated with a potassium hydroxide solution having a concentration of 2 mol / L, and the pH value of the solution in the kettle was adjusted to between 9 and 11. The solution was allowed to stand for 2 hours for precipitation. After sufficient precipitation, a filtration operation was performed using a roller filter to obtain a precipitated filter cake B and a filtrate B. The filter cake B was dried. After drying, the weight of the filter cake B was found to be 226.5 kg by weighing. The water content of the filter cake B before drying was 7.9%. After further testing, it was determined that the filter cake B was a nickel hydroxide precipitate, in which the mass content of nickel hydroxide was 99.3%.

[0033] S5. First, determine the F in filtrate B. - and K + ion concentration, and then use hydrogen fluoride to remove the F - and K + The molar ratio of the ions is adjusted to 2:1, the solution is subjected to an evaporation and crystallization operation, the obtained crystals are separated and dried, and the obtained potassium dihydrogen fluoride and potassium fluoride can be reused. The weight of potassium dihydrogen fluoride and potassium fluoride is 19.8 kg, of which the mass content of potassium dihydrogen fluoride is 97.8%.

[0034] Example 2

[0035] S1. Heat the fluorine-producing electrolytic cell to 95°C, use a copper rod to detect the electrolyte at the bottom of the fluorine-producing electrolytic cell to ensure that it is completely melted, and measure the electrolyte brought out to determine the liquid level of the waste electrolyte at the bottom; according to the liquid level of the waste electrolyte, insert the transfer tube above the liquid level of the waste electrolyte, maintain a negative pressure of -0.06MPa in the receiving tank, and transfer the upper colorless electrolyte in the fluorine-producing electrolytic cell to the receiving tank. The colorless electrolyte can be directly used in other electrolytic fluorine-producing electrolytic cells.

[0036] S2. Introduce 0.5 cubic meters of fluorine gas below the level of the waste electrolyte through the HF feeding port of the fluorine production electrolytic cell, maintain the pressure of the fluorine production electrolytic cell ≤ 0.03MPa, and let it stand for 0.5 hours to convert the ferrous ions in the cell into ferric ions.

[0037] S3. Use a pneumatic diaphragm pump to transfer all the remaining electrolyte in the fluorine production electrolytic cell to a 500L polytetrafluoroethylene-lined reactor. The volume of the electrolyte is measured to be 50L. Maintain the reactor temperature at 95°C, slowly introduce 200L of 95°C deionized water into the reactor and stir continuously. Since the electrolyte contains about 40% HF, the electrolyte is completely dissolved and the H content of the solution is measured. + Ion concentration, H + The ion concentration is 0.21mol / L.

[0038] S4, adding a potassium hydroxide solution with a concentration of 1.5 mol / L to the solution, adjusting the pH of the solution in the kettle to between 3-4, standing for 2 h to precipitate, after sufficient precipitation, using a belt filter to filter, to obtain a precipitated filter cake A and a filtrate A, drying the filter cake A, and weighing the filter cake A after drying to obtain a weight of 14.8 kg, a water content of 8.9%, and then determining that the filter cake A is a ferric hydroxide precipitate after testing, wherein the mass content of ferric hydroxide is 98.6%;

[0039] The filtrate A was further treated with a potassium hydroxide solution with a concentration of 1.5 mol / L, and the pH value of the solution in the kettle was adjusted to between 9 and 11. The solution was allowed to stand for 2 hours for precipitation. After sufficient precipitation, a roller filter was used for filtering to obtain a precipitated filter cake B and a filtrate B. The filter cake B was dried. After drying, the weight of the filter cake B was found to be 237.3 kg by weighing, and the water content was 8.1%. After further testing, it was determined that the filter cake B was a nickel hydroxide precipitate, in which the mass content of nickel hydroxide was 98.9%.

[0040] S5. First, determine the F in filtrate B. - and K + ion concentration, and then use hydrogen fluoride to remove the F - and K + The molar ratio of the ions is adjusted to 2:1, the solution is subjected to an evaporation and crystallization operation, the obtained crystals are separated and dried, and the obtained potassium difluoride and potassium fluoride can be reused. The weight of potassium difluoride and potassium fluoride is 17.8 kg, wherein the mass content of potassium difluoride is 98.3%.

[0041] Example 3

[0042] S1. After the electrolytic cell for fluorine production by electrolysis has been used for 10 million ampere-hours, the fluorine production electrolytic cell is heated to 80°C, and a copper rod is used to detect the electrolyte at the bottom of the fluorine production electrolytic cell to ensure that it is completely melted. The electrolyte brought out is measured to determine the liquid level of the waste electrolyte at the bottom; according to the liquid level of the waste electrolyte, the transfer tube is inserted above the liquid level of the waste electrolyte, and the negative pressure of the receiving tank is maintained at -0.05MPa. The upper colorless electrolyte in the fluorine production electrolytic cell is transferred to the receiving tank. The colorless electrolyte can be directly used in other electrolytic fluorine production electrolytic cells.

[0043] S2. Introduce 0.8 cubic meters of fluorine gas below the level of the waste electrolyte through the HF feeding port of the fluorine production electrolytic cell, maintain the pressure of the fluorine production electrolytic cell ≤ 0.03 MPa, and let it stand for 2 hours to convert the ferrous ions in the cell into ferric ions.

[0044] S3. Use a pneumatic diaphragm pump to transfer all the remaining electrolyte in the fluorine production electrolytic cell to a 500L polytetrafluoroethylene-lined reactor. The volume of the electrolyte is measured to be 55L. Maintain the reactor temperature at 80°C, slowly introduce 220L of 80°C deionized water into the reactor and stir continuously. The electrolyte is not completely dissolved. Determine the H + Ion concentration, H + Ion concentration <0.1mol / L, H + Insufficient ion concentration, H + When the ion concentration is not within the range of 0.1-0.3 mol / L, the metal fluoride cannot be completely dissolved when the hydrogen ion concentration is low. Anhydrous HF needs to be added until the electrolyte is completely dissolved. The H + Ion concentration, H + The ion concentration is 0.13 mol / L.

[0045] S4, adding a potassium hydroxide solution with a concentration of 1 mol / L to the solution, adjusting the pH of the solution in the kettle to 3-4, standing for 2 h to precipitate, after sufficient precipitation, using a belt filter to filter, to obtain a precipitated filter cake A and a filtrate A, the filter cake A was dried, and after drying, the weight of the filter cake A was obtained by weighing to be 14.9 kg, and the water content was 7.6%. After testing, it was determined that the filter cake A was a ferric hydroxide precipitate, wherein the mass content of ferric hydroxide was 99.1%;

[0046] The filtrate A was further treated with a potassium hydroxide solution with a concentration of 1 mol / L, the pH value of the solution in the kettle was adjusted to 9-11, and the solution was allowed to stand for 2 hours for precipitation. After sufficient precipitation, a filtration operation was performed using a roller filter to obtain a precipitated filter cake B and a filtrate B. The filter cake B was dried and weighed to obtain a weight of 240.3 kg and a water content of 8.3%. After further testing, it was determined that the filter cake B was a nickel hydroxide precipitate, in which the mass content of nickel hydroxide was 99.4%.

[0047] S5. First, determine the F in filtrate B. - and K + ion concentration, and then use hydrogen fluoride to remove the F - and K + The molar ratio of the ions is adjusted to 2:1, the solution is subjected to an evaporation crystallization operation, the obtained crystals are separated and dried, and the obtained potassium dihydrogen fluoride and potassium fluoride can be reused. The weight of potassium dihydrogen fluoride and potassium fluoride is 21.3 kg, of which the mass content of potassium dihydrogen fluoride is 98.6%.

[0048] Comparative Example 1

[0049] Compared with Example 1, in step S2, 0.3 m 3 The remaining steps remain unchanged. After testing, the quality and purity of the iron hydroxide obtained in step S4 are reduced, the quality of the nickel hydroxide is increased, but the purity is reduced; in step S5, the quality and purity of the potassium difluoride obtained are reduced.

[0050] Comparative Example 2

[0051] Compared with Example 1, in step S5, no hydrogen fluoride is added to adjust the F in the filtrate B. - and K + The concentration of the ion is reduced, and the other steps remain unchanged. Through evaporation and crystallization operation, the mass content of potassium dihydrogen fluoride in the obtained mixture of potassium dihydrogen fluoride and potassium fluoride is 56.1%, and the purity is greatly reduced.

[0052] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for treating nickel-containing waste electrolyte in electrolytic fluorine production, characterized in that: The method comprises the following steps: S1. Heat the fluorine production electrolytic cell to 80-95°C to completely melt the nickel-containing waste electrolyte from electrolysis fluorine production, let it stand for stratification, and take out the colorless electrolyte on the upper layer; S2, introducing excess fluorine gas into the electrolytic cell to convert the ferrous ions in the remaining electrolyte into ferric ions; S3, introducing the electrolyte in the electrolytic cell into an anti-corrosion container, and adding deionized water into the anti-corrosion container to dissolve all the electrolyte; S4, adjusting the pH of the solution in the container to 3-4, after sufficient precipitation, performing solid-liquid separation to obtain solid A and filtrate A; then adjusting the pH of the filtrate A to 9-11, after sufficient precipitation, performing solid-liquid separation to obtain solid B and filtrate B; S5, F in filtrate B - and K + The ion molar ratio is adjusted to 2:1, and then evaporation crystallization is performed, and the obtained crystals are dried to obtain potassium difluoride containing a small amount of potassium fluoride.

2. The method for treating nickel-containing waste electrolyte in electrolytic fluorine production according to claim 1, characterized in that: In step S2, fluorine gas is introduced into the electrolytic cell. The volume of the fluorine gas introduced is 1 / 4-1 / 2 of the volume of the electrolytic cell. The fluorine gas is introduced below the electrolyte liquid level and the pressure of the electrolytic cell is maintained at ≤0.03MPa. The reaction is carried out for 0.5-3h.

3. The method for treating nickel-containing waste electrolyte in electrolytic fluorine production according to claim 1, characterized in that: In step S3, the anti-corrosion container is a polytetrafluoroethylene lined reactor, the container temperature is maintained at 80-95°C, deionized water is added to the container, the volume ratio of electrolyte to deionized water is 1:4, and the electrolyte is completely dissolved.

4. The method for treating nickel-containing waste electrolyte in electrolytic fluorine production according to claim 1, characterized in that: In step S3, the anti-corrosion container is a polytetrafluoroethylene lined reactor, the container temperature is maintained at 80-95°C, deionized water is added to the container, the volume ratio of electrolyte to deionized water is 1:4, and then anhydrous hydrogen fluoride is added to the container to make the hydrogen ion concentration 0.1-0.3 mol / L until the electrolyte is completely dissolved.

5. The method for treating nickel-containing waste electrolyte in electrolytic fluorine production according to claim 1, characterized in that: In step S4, a potassium hydroxide solution is used to adjust the pH value of the solution, and the concentration of the potassium hydroxide solution is 1-2 mol / L.

6. The method for treating nickel-containing waste electrolyte in electrolytic fluorine production according to claim 1, characterized in that: In step S4, solid A is ferric hydroxide, solid B is nickel hydroxide, the water content of solid A and solid B is less than 10%, and after solid A and solid B are dried, the purity of ferric hydroxide and nickel hydroxide is greater than 98%.

7. The method for treating nickel-containing waste electrolyte in electrolytic fluorine production according to claim 1, characterized in that: In step S4, when solid-liquid separation is performed, filtration is performed using a tape filter.

8. The method for treating nickel-containing waste electrolyte in electrolytic fluorine production according to claim 1, characterized in that: In step S5, hydrogen fluoride is used to adjust F - and K + The ion molar ratio was adjusted to 2:

1.

9. The method for treating nickel-containing waste electrolyte in electrolytic fluorine production according to claim 1, characterized in that: In step S5, potassium dihydrogen fluoride containing a small amount of potassium fluoride is obtained, wherein the mass content of potassium dihydrogen fluoride is greater than 95%.

10. The method for treating nickel-containing waste electrolyte in electrolytic fluorine production according to claim 1, characterized in that: The removed upper colorless electrolyte is reused in other electrolytic fluorine production electrolytic cells.