Purification method of sodium sulfide as raw material for preparing zinc sulfide

Abstract

The invention provides a method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, comprising the following steps: S10, mixing sodium sulfide and water to obtain a sodium sulfide solution; S20, filtering the sodium sulfide solution to obtain a clarified sodium sulfide solution; S30, mixing the clarified sodium sulfide solution with disodium ethylenediaminetetraacetate and filtering to obtain a secondary clarified sodium sulfide liquid; S40, filtering the secondary clarified sodium sulfide liquid through a nanofiltration membrane to obtain a deeply impurity-removed sodium sulfide solution; S50, sequentially subjecting the deeply impurity-removed sodium sulfide solution to evaporation, crystallization and centrifugation to obtain sodium sulfide crystals. The invention removes heavy metal ions in the sodium sulfide by filtering and adding disodium EDTA, and then deeply removes impurities by filtering through a nanofiltration membrane to ensure the purity of the final sodium sulfide solution. Finally, after evaporation, crystallization and centrifugation, the quality of the sodium sulfide crystals can be made purer and more stable. The prepared sodium sulfide crystals have high purity and a metal ion content of less than 0.5ppm.

Description

Technical Field

[0001] The invention relates to the technical field of inorganic fine chemical industry, and in particular to a method for purifying sodium sulfide used as a raw material for preparing zinc sulfide. Background Art

[0002] Sodium sulfide (Na2S) is an important sulfide compound that is widely used in the chemical industry. Its purity is crucial for its application in the fields of medicine, electronic materials, high-performance polymers, etc. High levels of metal impurities will reduce the purity of sodium sulfide products, affect their electrical properties and chemical stability, and may even lead to unstable product quality or failure to meet specific industry standards. Currently, the most common types are red flaky sodium sulfide and yellow flaky sodium sulfide, of which the iron content of red flaky sodium sulfide is about 300ppm, and the iron content of yellow flaky sodium sulfide is about 30ppm. However, in industries such as pharmaceutical intermediates, electrolysis, and the synthesis process of sulfur-containing polymers that require higher quality sodium sulfide, industrial sodium sulfide is limited in application due to its high impurity content. In industries such as sulfur dyes and leather making, such as the need to produce high-quality advanced sulfur dyes, produce soft and good-touch leather, and improve the quality of leather products, the iron content of sodium sulfide products is required to be less than 10ppm. Sodium sulfide is also the raw material for producing pigment-grade zinc sulfide. Since zinc sulfide has high requirements for whiteness, the content of metal ions such as iron and nickel in sodium sulfide is required to be less than 0.5ppm. Polyphenylene sulfide (PPS) is one of the most widely used special engineering plastics. The industrial production method of PPS is mainly the sodium sulfide method. However, PPS has very high requirements for the raw material crystal sodium sulfide. The high metal content in sodium sulfide will affect the purity of PPS products and reduce its electrical properties.

[0003] At present, due to the existing method of producing high-purity sodium sulfide, the purity or cost of high-purity sodium sulfide cannot meet normal demand due to various defects. For example, patent CN110155954B discloses a method for preparing high-purity sodium sulfide crystals, by adding sodium hydroxide to remove sodium sulfate, sodium hydrosulfide, etc. in the concentrated solution, but adding sodium hydroxide can not effectively remove sodium sulfate, and new harmful impurities (such as sodium hydroxide products often carry impurities such as sodium sulfate and sodium chlorate) can be brought into it at the same time, which can affect its application in industries with high requirements for impurity content such as sulfur-containing polymers such as medicine, polyphenylene sulfide, and the removal degree of metal impurities of the above method and its limited. Patent CN115784169B discloses a method for purifying sodium sulfide crystals, by adding sodium citrate in sodium sulfide concentrated solution, using sodium citrate to remove impurities by the complexing ability of metal ions such as iron ions, barium ions, and calcium ions, but the method can only reduce iron to 1ppm, and the requirement of pigment industry to sodium sulfide cannot be met. Therefore, there is an urgent need in the art for a low-cost, deep purification method for removing sodium sulfide crystals. Summary of the invention

[0004] In view of this, the present invention proposes a method for purifying sodium sulfide as a raw material for preparing zinc sulfide, wherein heavy metal ions in sodium sulfide are removed by filtering and adding disodium EDTA, and then deep impurities are removed by nanofiltration membrane filtration to ensure the purity of the final sodium sulfide solution. Finally, after evaporation, crystallization and centrifugation, the quality of sodium sulfide crystals can be made purer and more stable. The sodium sulfide crystals prepared in the present application have high purity and a metal ion content of less than 0.5ppm.

[0005] The technical solution of the present invention is achieved as follows: The present invention provides a method for purifying sodium sulfide as a raw material for preparing zinc sulfide, comprising the following steps:

[0006] S10, mixing sodium sulfide and water to obtain a sodium sulfide solution;

[0007] S20, filtering the sodium sulfide solution to obtain a clarified sodium sulfide solution;

[0008] S30, mixing and filtering the clarified sodium sulfide solution and disodium ethylenediaminetetraacetate to obtain a secondary clarified sodium sulfide solution;

[0009] S40, filtering the sodium sulfide secondary clarified liquid through a nanofiltration membrane to obtain a sodium sulfide solution after deep impurity removal;

[0010] S50, subjecting the sodium sulfide solution after deep impurity removal to evaporation, crystallization and centrifugation in sequence to obtain sodium sulfide crystals.

[0011] In the above technical scheme, disodium ethylenediaminetetraacetic acid (disodium EDTA) is mainly achieved by chelation when removing heavy metals in sodium sulfide solution. Chelation refers to a chemical reaction formed by coordination bonds, in which the atoms of one or more ligands form stable complexes with metal ions by sharing a pair of electrons. In this case, the EDTA molecule in disodium EDTA contains multiple coordination sites, which can form stable complexes with heavy metal ions. When disodium EDTA contacts heavy metal ions in sodium sulfide solution, the carboxyl and amino groups in EDTA will react with heavy metal ions to form complexes. These complexes have high stability and can effectively separate heavy metal ions from sodium sulfide solution, thereby achieving the purpose of removing heavy metals. Wherein, disodium EDTA is food grade.

[0012] The present invention removes heavy metal ions in sodium sulfide by filtering and adding disodium EDTA, and then removes impurities by filtering through a nanofiltration membrane to ensure the purity of the final sodium sulfide solution. Finally, after evaporation, crystallization and centrifugation, the quality of the sodium sulfide crystals can be made purer and more stable. The sodium sulfide crystals prepared by the present application have high purity and a metal ion content of less than 0.5ppm.

[0013] On the basis of the above technical solution, preferably, in step S10,

[0014] The temperature condition when sodium sulfide and water are mixed is 70-80°C and the mixing time is 30-60 minutes; and / or,

[0015] Sodium sulfide and water need to be stirred when mixed, and the stirring speed is 50-70 rpm; and / or,

[0016] The mass concentration of the obtained sodium sulfide solution is 10-20%.

[0017] On the basis of the above technical solution, preferably, in step S20, the sodium sulfide solution is filtered through a plate-frame filter press, the filter cloth pore size of the plate-frame filter press is 1-10 μm, and the pressure of the plate-frame filter press when in use is 0.3-1.6 MPa; preferably, the filter cloth pore size of the plate-frame filter press is 5-10 μm, and the pressure of the plate-frame filter press when in use is 0.5-0.6 MPa; and / or,

[0018] In step S20, the temperature of the sodium sulfide solution during filtration is 70-80°C.

[0019] On the basis of the above technical solution, preferably, in step S30, the clarified sodium sulfide solution is mixed with disodium ethylenediaminetetraacetate in a de-impurity tank; and / or,

[0020] In step S30, the mixing temperature of the clarified sodium sulfide solution and disodium ethylenediaminetetraacetate is 30-50° C. In this technical solution, the mixing temperature of 30-50° C. helps to increase the reaction rate, promotes the reaction of disodium ethylenediaminetetraacetate with heavy metal ions in the solution, accelerates the formation rate of the complex, and helps to improve the efficiency of removing heavy metals. At the same time, the mixing temperature of 30-50° C. also helps to maintain the stability of the reaction system, avoid unnecessary side reactions, and ensure the quality and purity of the product; and / or,

[0021] In step S30, the step of mixing the clarified sodium sulfide solution with disodium ethylenediaminetetraacetate includes stirring for 100-120 minutes, settling for 10-12 hours, and then filtering to obtain a secondary clarified sodium sulfide solution; and / or,

[0022] In step S30, the filtering tool is a plate and frame filter press.

[0023] In the present invention, the meaning of "and / or" in the whole text includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0024] On the basis of the above technical scheme, preferably, in step S30, the clarified sodium sulfide solution contains iron ions, nickel ions, calcium ions and chromium ions, and the molar ratio of the disodium ethylenediaminetetraacetic acid to the total content of the iron ions, nickel ions, calcium ions and chromium ions is (2-5):1. In this technical scheme, before adding disodium ethylenediaminetetraacetic acid, it is necessary to first determine the total content of iron ions, nickel ions, calcium ions and chromium ions contained in the clarified sodium sulfide solution by atomic absorption.

[0025] On the basis of the above technical solution, preferably, in step S40, the sodium sulfide secondary clarified liquid is injected into a nanofiltration membrane for filtration by a high pressure pump with a pressure of 2-4 MPa; and / or,

[0026] In step S40, the nanofiltration membrane is made of acid- and alkali-resistant polymer material, and the cut-off molecular weight of the nanofiltration membrane is 400-1000 Da, wherein the polymer material is a high molecular polymer material.

[0027] On the basis of the above technical scheme, preferably, in step S40, the filtration temperature of the nanofiltration membrane is 20-45°C, and the filtration pressure is 2.4-3.2MPa. Limiting the filtration temperature of the nanofiltration membrane to 20-45°C helps to maintain the stability of the solute in the solution and avoid the precipitation or denaturation of the solute, thereby ensuring the filtration effect and product quality; at the same time, since conventional nanofiltration membranes generally limit the temperature to below 45°C, higher temperatures will damage the performance of the filter membrane, leading to aging and degradation of the membrane material, and reducing the service life of the membrane. Preferably, the nanofiltration membrane has better performance at a temperature of 30-35°C; an appropriate filtration pressure range (2.4-3.2MPa) can increase the filtration rate of the nanofiltration membrane and promote the speed at which the solution passes through the filter membrane, while also helping to ensure the filtration effect and improve production efficiency; reasonable filtration conditions can effectively remove impurities and particles in the solution, ensure the purity and quality of the product, and make the final sodium sulfide solution purer and more stable.

[0028] On the basis of the above technical solution, preferably, in step S50, the evaporation step of the deeply impurity-removed sodium sulfide solution is to evaporate the deeply impurity-removed sodium sulfide solution through an electric furnace to a mass concentration of 38-41%.

[0029] On the basis of the above technical scheme, preferably, in step S50, the sodium sulfide solution after deep impurity removal is evaporated, stirred and cooled, and then sent to a crystallizer for crystallization. The crystallization end temperature is 50-80°C, the crystallization time is 3-4h, and stirring is continued during the cooling and crystallization process.

[0030] On the basis of the above technical solution, preferably, in step S50, after the sodium sulfide solution after deep impurity removal is evaporated and crystallized, a centrifuge is used to separate the crystallized product into solid and liquid to obtain sodium sulfide crystals.

[0031] A chip and a preparation method thereof of the present invention have the following beneficial effects compared with the prior art:

[0032] (1) The present invention removes heavy metal ions in sodium sulfide by filtering and adding disodium EDTA, and then removes impurities by nanofiltration to ensure the purity of the final sodium sulfide solution. Finally, after evaporation, crystallization and centrifugation, the quality of the sodium sulfide crystals can be made purer and more stable. The sodium sulfide crystals prepared by the present invention have high purity and a metal ion content of less than 0.5 ppm.

[0033] (2) The mixing temperature of the clarified sodium sulfide solution and disodium ethylenediaminetetraacetate of the present invention is 30-50° C. The mixing temperature of 30-50° C. helps to increase the reaction rate, promotes the reaction of disodium ethylenediaminetetraacetate with heavy metal ions in the solution, accelerates the formation rate of the complex, and helps to improve the efficiency of removing heavy metals. At the same time, the mixing temperature of 30-50° C. also helps to maintain the stability of the reaction system, avoid unnecessary side reactions, and ensure the quality and purity of the product.

[0034] (3) The filtration temperature of the nanofiltration membrane of the present invention is 20-45°C, and the filtration pressure is 2.4-3.2 MPa. Limiting the filtration temperature of the nanofiltration membrane to 20-45°C helps to maintain the stability of the solute in the solution and avoid the precipitation or denaturation of the solute, thereby ensuring the filtration effect and product quality. At the same time, since conventional nanofiltration membranes generally limit the temperature to below 45°C, higher temperatures will damage the performance of the filter membrane, leading to aging and degradation of the membrane material and reducing the service life of the membrane. Preferably, the nanofiltration membrane has better performance at a temperature of 30-35°C. Reasonable filtration conditions can effectively remove impurities and particles in the solution, ensure the purity and quality of the product, and make the final sodium sulfide solution purer and more stable.

[0035] (4) The process is easy to operate, the equipment is simple, and continuous operation can be achieved, which greatly improves the operating efficiency. The deeply purified and impurity-free sodium sulfide can be used as the raw material for the production of polyphenylene sulfide and pigment-grade zinc sulfide. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 The present invention is a schematic flow diagram of a method for purifying sodium sulfide used as a raw material for preparing zinc sulfide. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Example 1

[0040] A method for purifying sodium sulfide as a raw material for preparing zinc sulfide, such as Figure 1 As shown, the following steps are included:

[0041] 1) Hot dissolution: add industrial sodium sulfide to distilled water, dissolve at 70°C for 30 minutes, stir at 50 rpm to obtain a dissolved sodium sulfide solution, the mass concentration of the sodium sulfide solution is 10%;

[0042] 2) Plate and frame filter press: The dissolved sodium sulfide solution is sent to a plate and frame filter press with a filter cloth pore size of 5 μm, and filtered at a pressure of 0.5 MPa and a temperature of 70°C to obtain a clarified sodium sulfide solution, and the content of iron ions, nickel ions, calcium ions, and chromium ions is detected by atomic determination method;

[0043] 3) Complexation precipitation: send the clarified sodium sulfide solution into a decontamination tank, slowly add disodium ethylenediaminetetraacetate at a molar ratio of 2:1, stir for 100 minutes at 30°C, then settle for 10 hours, and obtain a secondary clarified sodium sulfide solution by plate and frame filter press;

[0044] 4) Nanofiltration separation: The secondary clarified sodium sulfide liquid is injected into a nanofiltration membrane through a high-pressure pump at a pressure of 2.4 MPa for nanofiltration separation treatment. The separation temperature is 30°C to remove high-valent cations to obtain a deeply purified and impurity-free sodium sulfide solution, and the contents of iron ions, nickel ions, calcium ions, and chromium ions are detected;

[0045] 5) Crystallization: The sodium sulfide solution after deep purification and impurity removal is evaporated on an electric furnace to a concentration of 38%, and sent to a crystallizer for crystallization. The crystallization end temperature is 50° C., the crystallization time is 3 hours, and stirring is continued during the cooling and crystallization process; the product after crystallization is separated into solid and liquid by a centrifuge to obtain white sodium sulfide crystals.

[0046] Example 2

[0047] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide comprises the following steps:

[0048] 1) Hot dissolution: add industrial sodium sulfide to distilled water, dissolve at 75°C for 50 minutes, stir at 60 rpm to obtain a dissolved sodium sulfide solution, the mass concentration of the sodium sulfide solution is 15%;

[0049] 2) Plate and frame filter press: The dissolved sodium sulfide solution is sent to a plate and frame filter press with a filter cloth pore size of 8 μm, and filtered at a pressure of 0.55 MPa and a temperature of 75°C to obtain a clarified sodium sulfide solution, and the content of iron ions, nickel ions, calcium ions, and chromium ions is detected by atomic determination method;

[0050] 3) Complexation precipitation: send the clarified sodium sulfide solution into a decontamination tank, slowly add disodium ethylenediaminetetraacetate at a molar ratio of 3:1, stir for 110 minutes at 40°C, then settle for 11 hours, and obtain a secondary clarified sodium sulfide solution by plate and frame filter press;

[0051] 4) Nanofiltration separation: The secondary clarified sodium sulfide liquid is injected into a nanofiltration membrane through a high-pressure pump at a pressure of 3 MPa for nanofiltration separation treatment. The separation temperature is 33°C to remove high-valent cations to obtain a deeply purified and impurity-free sodium sulfide solution, and the contents of iron ions, nickel ions, calcium ions, and chromium ions are detected;

[0052] 5) Crystallization: The sodium sulfide solution after deep purification and impurity removal is evaporated on an electric furnace to a concentration of 40%, and sent to a crystallizer for crystallization. The crystallization end temperature is 60° C., the crystallization time is 3.5 hours, and stirring is continued during the cooling and crystallization process; the product after crystallization is separated into solid and liquid by a centrifuge to obtain white sodium sulfide crystals.

[0053] Example 3

[0054] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide comprises the following steps:

[0055] 1) Hot dissolution: add industrial sodium sulfide to distilled water, dissolve at 80°C for 60 minutes, stir at 70 rpm to obtain a dissolved sodium sulfide solution, the mass concentration of the sodium sulfide solution is 20%;

[0056] 2) Plate and frame filter press: The dissolved sodium sulfide solution is sent to a plate and frame filter press with a filter cloth pore size of 10 μm, and filtered at a pressure of 0.6 MPa and a temperature of 80°C to obtain a clarified sodium sulfide solution, and the content of iron ions, nickel ions, calcium ions, and chromium ions is detected by atomic determination method;

[0057] 3) Complexation precipitation: send the clarified sodium sulfide solution into a de-impurity tank, slowly add disodium ethylenediaminetetraacetate at a molar ratio of 5:1, stir for 120 minutes at 50°C, then settle for 12 hours, and obtain a secondary clarified sodium sulfide solution by plate and frame filter press;

[0058] 4) Nanofiltration separation: The secondary clarified sodium sulfide liquid is injected into a nanofiltration membrane through a high-pressure pump at a pressure of 3.4 MPa for nanofiltration separation treatment. The separation temperature is 35°C to remove high-valent cations to obtain a deeply purified and impurity-free sodium sulfide solution, and the contents of iron ions, nickel ions, calcium ions, and chromium ions are detected;

[0059] 5) Crystallization: The sodium sulfide solution after deep purification and impurity removal is evaporated on an electric furnace to a concentration of 41%, and sent to a crystallizer for crystallization. The crystallization end temperature is 80° C., the crystallization time is 4 hours, and stirring is continued during the cooling and crystallization process; the product after crystallization is separated into solid and liquid by a centrifuge to obtain white sodium sulfide crystals.

[0060] Example 4

[0061] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide comprises the following steps:

[0062] 1) Hot dissolution: add industrial sodium sulfide to distilled water, dissolve at 80°C for 60 minutes, stir at 50 rpm to obtain a dissolved sodium sulfide solution, the mass concentration of the sodium sulfide solution is 10%;

[0063] 2) Plate and frame filter press: The dissolved sodium sulfide solution is sent to a plate and frame filter press with a filter cloth pore size of 10 μm, and filtered at a pressure of 0.6 MPa and a temperature of 70°C to obtain a clarified sodium sulfide solution, and the content of iron ions, nickel ions, calcium ions, and chromium ions is tested;

[0064] 3) Complexation precipitation: send the clarified sodium sulfide solution into a decontamination tank, slowly add disodium ethylenediaminetetraacetate at a molar ratio of 2:1, stir for 120 minutes at 30°C, then settle for 10 hours, and obtain a secondary clarified sodium sulfide solution by plate and frame filter press;

[0065] 4) Nanofiltration separation: The secondary clarified sodium sulfide liquid is injected into a nanofiltration membrane through a high-pressure pump at a pressure of 2.4 MPa for nanofiltration separation treatment. The separation temperature is 35°C to remove high-valent cations to obtain a deeply purified and impurity-free sodium sulfide solution, and the contents of iron ions, nickel ions, calcium ions, and chromium ions are detected;

[0066] 5) Crystallization: The sodium sulfide solution after deep purification and impurity removal is evaporated on an electric furnace to a concentration of 38%, and sent to a crystallizer for crystallization. The crystallization end temperature is 50° C., the crystallization time is 3 hours, and stirring is continued during the cooling and crystallization process; the product after crystallization is separated into solid and liquid by a centrifuge to obtain white sodium sulfide crystals.

[0067] Example 5

[0068] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, wherein the steps are the same as those of Example 4), except that, in step 3), the clarified sodium sulfide solution is fed into a decontamination tank, and disodium ethylenediaminetetraacetate is slowly added at a molar ratio of 4:1.

[0069] Example 6

[0070] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, wherein the steps are the same as those of Example 4), except that, in step 3) of complex precipitation, the clarified sodium sulfide solution is fed into a decontamination tank, and disodium ethylenediaminetetraacetate is slowly added at a molar ratio of 5:1.

[0071] Example 7

[0072] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, wherein the steps are the same as those of Example 4), except that, in step 3), the clarified sodium sulfide solution is fed into a decontamination tank, disodium ethylenediaminetetraacetate is slowly added in a molar ratio of 2:1, and the mixture is stirred for 120 minutes at 50°C and then allowed to settle for 10 hours.

[0073] Comparative Example 1

[0074] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, wherein the steps are the same as those of Example 4, except that in step 2), there is no need to detect the contents of iron ions, nickel ions, calcium ions, and chromium ions, and there is no need to add disodium ethylenediaminetetraacetate to the clarified sodium sulfide solution obtained in step 2), that is, the complex precipitation step is deleted.

[0075] Comparative Example 2

[0076] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, wherein the steps are the same as those in Example 4), except that the nanofiltration separation step is deleted and the obtained sodium sulfide secondary clarified liquid is directly subjected to the crystallization step.

[0077] Comparative Example 3

[0078] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, wherein the steps are the same as those of Example 4), except that, in step 3), the clarified sodium sulfide solution is fed into a decontamination tank, disodium ethylenediaminetetraacetate is slowly added in a molar ratio of 2:1, and the mixture is stirred for 120 minutes at 80°C and then allowed to settle for 10 hours.

[0079] Comparative Example 4

[0080] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, wherein the steps are the same as those of Example 4), except that, in step 3), the clarified sodium sulfide solution is fed into a decontamination tank, disodium ethylenediaminetetraacetate is slowly added in a molar ratio of 2:1, and the mixture is stirred for 120 minutes at 20°C and then allowed to settle for 10 hours.

[0081] Comparative Example 5

[0082] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, wherein the steps are the same as those of Example 4), except that, in step 3), the clarified sodium sulfide solution is fed into a decontamination tank, and disodium ethylenediaminetetraacetate is slowly added at a molar ratio of 6:1.

[0083] Comparative Example 6

[0084] A method for purifying sodium sulfide used as a raw material for preparing zinc sulfide, wherein the steps are the same as those of Example 4), except that, in step 3), the clarified sodium sulfide solution is fed into a decontamination tank, and disodium ethylenediaminetetraacetate is slowly added in a molar ratio of 1:1.

[0085] Performance testing and results

[0086] The impurity ion content of the sodium sulfide solution before crystallization and concentration in Examples 1-7 and Comparative Examples 1-6 was measured by atomic absorption determination. The results are shown in Table 1.

[0087] Table 1 shows the impurity ion content of sodium sulfide solution before crystallization and concentration

[0088] Group Fe / ppm Ni / ppm Cd / ppm Ca / ppm Cr / ppm Mn / ppm Example 1 0.44 0.36 0.25 0.32 0.48 0.06 Example 2 0.32 0.22 0.20 0.23 0.33 0.05 Example 3 0.15 0.13 0.16 0.21 0.29 0.03 Example 4 0.36 0.25 0.23 0.30 0.43 0.05 Example 5 0.24 0.20 0.21 0.24 0.34 0.05 Example 6 0.20 0.18 0.17 0.22 0.31 0.04 Example 7 0.30 0.23 0.21 0.26 0.37 0.05 Comparative Example 1 4.23 0.89 0.98 2.31 0.78 0.15 Comparative Example 2 1.11 0.75 0.84 1.34 0.67 0.15 Comparative Example 3 0.39 0.31 0.25 0.32 0.44 0.05 Comparative Example 4 0.66 0.45 0.33 0.42 0.55 0.11 Comparative Example 5 0.35 0.24 0.22 0.30 0.42 0.05 Comparative Example 6 0.68 0.37 0.41 0.39 0.41 0.09

[0089] As can be seen from Table 1, by comparing Example 1 with Example 4, it can be found that the impurities such as Fe and Ni in Example 4 are slightly lower than those in Example 1, which indicates that heating can increase the flux of nanofiltration membrane filtration, reduce the filtration time, and reduce the redissolution of Fe and Ni in the sodium sulfide solution, thereby improving the impurity removal rate. By comparing Example 4, Example 5 and Example 6, the Fe, Ni and Ca contents of the sodium sulfide solution prepared in Example 6 are lower than those in Example 4 and Example 5, indicating that increasing the addition amount of disodium ethylenediaminetetraacetic acid is beneficial to the removal of metal ions, thereby improving the purity of sodium sulfide crystals. Compared with Example 5, Example 4 further increases disodium ethylenediaminetetraacetic acid to a molar ratio of 6:1, and the content of impurities such as Fe and Ni does not change much; by comparing Example 4 with Comparative Example 6, the content of disodium ethylenediaminetetraacetic acid is reduced to a molar ratio of 1:1, the complexation reaction is insufficient, and the impurity removal effect of Fe, Ni and Ca is poor; by comparing Example 4 with Comparative Example 1, disodium ethylenediaminetetraacetic acid is not added for impurity removal, and the impurity content, especially the content of Ni, is too high. By comparing Example 4 and Example 7, it can be found that increasing the complex reaction temperature from 30 to 50°C can improve the impurity removal efficiency, but further increasing it to 80°C (Comparative Example 3) will increase the impurity content of the product, mainly because the high temperature causes the redissolution of Fe, Ni, etc. Compared with Comparative Example 4, the complex temperature is reduced to 20°C, the complex reaction is not sufficient, resulting in limited removal of impurity content. Comparing Example 4 and Comparative Example 2, only complex precipitation impurity removal is performed without nanofiltration separation, and the Fe content is 1.11ppm and the Ni content is 0.75ppm.

[0090] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for purifying sodium sulfide as a raw material for preparing zinc sulfide, characterized in that: The following steps are involved: S10, mixing sodium sulfide and water to obtain a sodium sulfide solution, wherein the temperature condition when the sodium sulfide and water are mixed is 70-80° C., the mixing time is 30-60 min, and the sodium sulfide and water need to be stirred when mixed, and the stirring speed is 50-70 rpm, and the mass concentration of the sodium sulfide solution is 10-20%; S20, filtering the sodium sulfide solution, filtering the sodium sulfide solution through a plate-frame filter press, wherein the filter cloth pore size of the plate-frame filter press is 1 to 10 μm, the pressure of the plate-frame filter press during use is 0.3 to 1.6 MPa, and the temperature during filtration is 70 to 80° C., to obtain a clarified sodium sulfide solution; S30, mixing and filtering the clarified sodium sulfide solution with disodium ethylenediaminetetraacetate to obtain a secondary clarified sodium sulfide solution; the clarified sodium sulfide solution contains iron ions, nickel ions, calcium ions and chromium ions, and the molar ratio of the disodium ethylenediaminetetraacetate to the sum of the iron ions, nickel ions, calcium ions and chromium ions is (2-5):1; S40, filtering the sodium sulfide secondary clarified liquid through a nanofiltration membrane to obtain a sodium sulfide solution after deep impurity removal; injecting the sodium sulfide secondary clarified liquid into a nanofiltration membrane for filtration through a high-pressure pump with a pressure of 2 to 4 MPa, wherein the nanofiltration membrane is made of an acid- and alkali-resistant polymer material, and the cut-off molecular weight of the nanofiltration membrane is 400 to 1000 Da, the filtration temperature of the nanofiltration membrane is 20 to 45° C., and the filtration pressure is 2.4 to 3.2 MPa; S50, subjecting the deeply impurity-removed sodium sulfide solution to evaporation, crystallization and centrifugation in sequence, evaporating the deeply impurity-removed sodium sulfide solution through an electric furnace to a mass concentration of 38-41%; after evaporation, stirring and cooling the deeply impurity-removed sodium sulfide solution, sending it into a crystallizer for crystallization, the crystallization terminal temperature is 50-80° C., the crystallization time is 3-4h, and stirring is continuously performed during the cooling and crystallization process; using a centrifuge to separate the crystallized product into solid and liquid to obtain sodium sulfide crystals.

2. The method for purifying sodium sulfide as a raw material for preparing zinc sulfide according to claim 1, characterized in that: In step S30, the clarified sodium sulfide solution is mixed with disodium ethylenediaminetetraacetate in a decontamination tank; and / or, In step S30, the mixing temperature of the clarified sodium sulfide solution and disodium ethylenediaminetetraacetate is 30-50° C.; and / or, In step S30, the step of mixing the clarified sodium sulfide solution with disodium ethylenediaminetetraacetate includes stirring for 100-120 minutes, settling for 10-12 hours, and then filtering to obtain a secondary clarified sodium sulfide solution; and / or, In step S30, the filtering tool is a plate and frame filter press.

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