Separation and purification system and separation and purification method suitable for sodium chloride-sodium sulfate mixed waste salt

Abstract

The invention discloses a separation and purification system and a separation and purification method suitable for sodium chloride-sodium sulfate mixed waste salt, and belongs to the technical field of environmental protection, the separation and purification system comprises a mixed waste salt pyrolysis salt-dissolving module, a chemical impurity removal module, a membrane purification module and a product separation module which are communicated; the mixed waste salt pyrolysis salt-dissolving module comprises a pyrolysis treatment device and a salt-dissolving dissolving tank; the chemical impurity removal module comprises an oxidation tank, a magnesium removal reaction tank, a fluorine and phosphorus removal reaction tank and the like which are arranged in sequence. A salt dissolving and impurity removing process is adopted, impurities in mixed waste salt are effectively removed mainly through a chemical impurity removing module composed of an oxidation tank, a magnesium removal reaction tank, a fluorine and phosphorus removal reaction tank, a heavy metal and calcium removal reaction tank, a sulfur removal reaction tank and the like which are sequentially arranged, and a subsequent membrane purification module and a product separation module are matched; efficient separation of sodium chloride and sodium sulfate is achieved, the quality of the obtained product is remarkably improved, and the industrial use requirement is met.

Description

Technical Field

[0001] This application belongs to the field of environmental protection technology, specifically relating to a separation and purification system and method suitable for mixed waste salt of sodium chloride and sodium sulfate. Background Technology

[0002] Industrial waste salt containing sodium chloride and sodium sulfate is mainly generated in chemical, coal chemical, pharmaceutical, and agrochemical production processes. These processes produce saline waste liquids and solids containing organic matter and other toxic and harmful components, which are then treated to form this type of waste salt. Because the waste salt contains various organic impurities, it cannot be used directly, which not only causes a serious waste of resources but also harms the environment.

[0003] Currently, there are few technically and economically feasible disposal routes for industrial waste salt, and enterprises face numerous difficulties in disposing of it. At present, enterprises mainly use landfill to dispose of waste salt, while some processes employ precipitation or membrane treatment methods for separation and purification. However, these methods are not ideal for treating mixed sodium chloride and sodium sulfate waste salts, resulting in products with high impurity content that cannot meet the requirements for direct industrial use. Summary of the Invention

[0004] This application aims to at least partially address one of the technical problems in related technologies. Therefore, the purpose of this application is to propose a separation and purification system and method suitable for mixed sodium chloride and sodium sulfate waste salts. This application employs a chemical purification process, primarily using a chemical purification module consisting of sequentially arranged oxidation tanks, magnesium removal reaction tanks, fluoride and phosphorus removal reaction tanks, heavy metal and calcium removal reaction tanks, and sulfur removal reaction tanks to effectively remove impurities from the mixed waste salts. Combined with subsequent membrane purification and product separation modules, this not only achieves efficient separation of sodium chloride and sodium sulfate but also significantly improves the quality of the obtained product, meeting industrial application requirements.

[0005] In the first aspect, this application proposes a separation and purification system suitable for mixed waste salt of sodium chloride and sodium sulfate, the separation and purification system comprising a pyrolysis salting module, a chemical impurity removal module, a membrane purification module and a product separation module connected in series; The mixed waste salt pyrolysis salt dissolving module includes a pyrolysis treatment device and a salt dissolving tank; The chemical impurity removal module includes, in sequence, an oxidation tank, a magnesium removal reaction tank, a fluorine and phosphorus removal reaction tank, a heavy metal and calcium removal reaction tank, a sulfur removal reaction tank, a flocculation tank, a sedimentation tank, and a pH adjustment tank. The membrane purification module includes an ultrafiltration membrane device and a secondary nanofiltration membrane device; The product separation module includes a cryo-crystallizer, a nanofiltration membrane device, and an ion-exchange membrane electrolysis device.

[0006] This application provides a separation and purification system suitable for mixed sodium chloride and sodium sulfate waste salts. The separation and purification system mainly uses a chemical impurity removal module composed of an oxidation tank, a magnesium removal reaction tank, a fluorine and phosphorus removal reaction tank, a heavy metal and calcium removal reaction tank, and a sulfur removal reaction tank arranged in sequence to effectively remove impurities from the mixed waste salts. Combined with a subsequent membrane purification module and product separation module, it not only achieves efficient separation of sodium chloride and sodium sulfate, but also significantly improves the quality of the obtained product, meeting the requirements of industrial use.

[0007] In addition, the separation and purification system for mixed sodium chloride-sodium sulfate waste salt provided in this application may also have the following additional technical features: In some specific embodiments of this application, the pyrolysis treatment device is connected to the salt dissolving tank via a conveying device, and the salt dissolving tank is connected to the chemical impurity removal module via a No. 1 brine pump.

[0008] In some specific embodiments of this application, the solution in the mixed waste salt pyrolysis salt module is introduced into the oxidation tank after passing through a filtration device; The oxidation tank is connected to the magnesium removal reaction tank. The solution in the magnesium removal reaction tank is sequentially pumped into the fluoride and phosphorus removal reaction tank, the heavy metal and calcium removal reaction tank and the sulfur removal reaction tank, which are arranged in series, through the No. 2 brine pump. The desulfurization reaction tank is connected to the buffer tank. The buffer tank is connected to the brine filter press (No. 2) via a No. 3 brine pump. The brine filter press (No. 2) is connected to the filtrate tank. The filtrate tank is connected to the flocculation tank via a No. 4 brine pump. The flocculation tank is connected to the sedimentation tank and the pH adjustment tank in sequence.

[0009] In some specific embodiments of this application, the sedimentation tank is connected to the sludge tank via sludge pump #4, the magnesium removal reaction tank, the fluoride and phosphorus removal reaction tank, the heavy metal and calcium removal reaction tank, and the sulfur removal reaction tank are all connected to the sludge tank via sludge pump #1, the sludge tank is connected to brine filter press #1 via sludge pump #2, the brine filter press #1 is connected to the sludge filter press, and the sludge filter press is connected to the salt dissolving tank via sludge pump #3.

[0010] In some specific embodiments of this application, the pH adjustment tank is connected to the intermediate water tank, and the intermediate water tank is connected to the ultrafiltration membrane device and the secondary nanofiltration membrane device in sequence through a No. 5 brine pump.

[0011] In some specific embodiments of this application, the secondary nanofiltration membrane device is connected to a concentrate tank, the concentrate tank is connected to the cryogenic crystallizer via a concentrate transfer pump, and the cryogenic crystallizer is connected in sequence to a centrifuge and the nanofiltration membrane device.

[0012] In some specific embodiments of this application, the nanofiltration membrane device is connected to a secondary brine treatment device, and the secondary brine treatment device is connected to an ion-exchange membrane electrolysis device; The secondary nanofiltration membrane device is sequentially connected to an activated carbon adsorption tower, a macroporous adsorption resin tower, and a product water tank. The product water tank is connected to a product water transfer pump and a salt dissolving tank.

[0013] Secondly, this application proposes a separation and purification method suitable for mixed sodium chloride and sodium sulfate waste salts. This method employs the separation and purification system for mixed sodium chloride and sodium sulfate waste salts described in the first aspect. Therefore, this separation and purification method significantly improves the quality of the obtained product. Specifically, the inorganic pollutant content in the product obtained by this method is less than 0.2% by mass, and the obtained sodium sulfate decahydrate and sodium chloride products have high purity. Furthermore, the sodium sulfate decahydrate product after dehydration treatment meets the standard of "Regenerated Industrial Salt - Sodium Sulfate" T / ZGZS0303-2023, and its sodium chloride content is not higher than 0.5% by mass.

[0014] In addition, the separation and purification method for mixed waste salts of sodium chloride and sodium sulfate provided in this application may also have the following additional technical features: In some specific embodiments of this application, the percentage of dry sodium chloride W1 in the mixed sodium chloride-sodium sulfate waste salt to be treated, by mass percentage, satisfies: 80% ≤ W1 < 100%; By mass percentage, the dry basis sodium sulfate content W2 in the mixed sodium chloride-sodium sulfate waste salt to be treated satisfies: 0% < W2 ≤ 20%; The total organic carbon content of the mixed waste salt of sodium chloride and sodium sulfate after pyrolysis treatment is 20~160ppm; The operating parameters of the salt dissolving tank include: temperature ≤ 60℃, time 2~6h.

[0015] In some specific embodiments of this application, the operating conditions of the pyrolysis treatment device include: a temperature of 300~800℃ and a time of 1~2h; The operating conditions of the oxidation tank include: the added oxidant is sodium hypochlorite, and the mass percentage concentration of the oxidant is ≥8%; The operating conditions of the magnesium removal reaction tank include: the added magnesium removal agent includes calcium hydroxide, and the amount of the precipitant added is 1.5 to 2.0 times the molar amount of magnesium ions in the solution to be treated; The operating conditions of the defluorination and phosphorus removal reaction tank include: the added defluorination and phosphorus removal agent includes calcium chloride, and the amount of the added defluorination and phosphorus removal agent is 4 to 5.5 times the total molar amount of fluorine and phosphorus in the solution to be treated; The operating parameters of the heavy metal and calcium removal reaction tank include: the added heavy metal and calcium removal agent includes sodium sulfide and sodium carbonate, the amount of sodium sulfide added is 1.1 to 1.5 times the molar amount of heavy metal ions in the solution to be treated, and the amount of sodium carbonate added is 1.0 to 1.2 times the molar amount of calcium ions in the solution to be treated; that is, the molar ratio of sodium sulfide to sodium carbonate is (1.1 to 1.5) molar amount of heavy metal ions: (1.0 to 1.2) molar amount of calcium ions, and the amount of the heavy metal and calcium removal agent added is 1.1 times the molar amount of heavy metal ions + 1.0 times the molar amount of calcium ions to 1.5 times the molar amount of heavy metal ions + 1.2 times the molar amount of calcium ions; The operating conditions of the desulfurization reaction tank include: the added desulfurizing agent includes ferric chloride, and the amount of the added desulfurizing agent is 0.8 to 1.33 times the molar amount of sulfide in the solution to be treated; The operating conditions of the flocculation tank include: the added coagulant includes at least one of polyaluminum chloride and polyacrylamide, wherein the concentration of polyaluminum chloride in the solution to be treated is 5~50 mg / L, and the concentration of polyacrylamide in the solution to be treated is 0.1~5 mg / L; The operating parameters of the pH adjustment tank include: adjusting the pH to 5.5-7.5; The operating conditions of the cryo-crystallizer include: temperature ≤ 30℃.

[0016] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0017] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the technical solutions in conjunction with the following drawings, wherein: Figure 1 This is a schematic diagram of the separation and purification system for mixed waste salts of sodium chloride and sodium sulfate provided in this application.

[0018] Explanation of reference numerals in the attached figures: Figure 1In the middle section: 1-Conveying device; 2-Salt dissolving tank; 3-No. 1 brine pump; 4-Filtration device; 5-Oxidation tank; 6-Magnesium removal reaction tank; 7-No. 2 brine pump; 8-Fluoride and phosphorus removal reaction tank; 9-Heavy metal and calcium removal reaction tank; 10-Sulfur removal reaction tank; 11-No. 1 sludge pump; 12-Sludge tank; 13-No. 2 sludge pump; 14-No. 1 brine filter press; 15-Sludge filter press; 16-No. 3 sludge pump; 17-Buffer tank; 18-No. 3 brine pump; 19-No. 2 brine filter press; 20-Filtrate tank; 21-No. 4 brine pump ; 22-Flocculation tank; 23-Sedimentation tank; 24-Sludge pump #4; 25-pH adjustment tank; 26-Intermediate water tank; 27-Brine pump #5; 28-Ultrafiltration membrane device; 29-Secondary nanofiltration membrane device; 30-Concentrate tank; 31-Concentrate water transfer pump; 32-Freezing crystallizer; 33-Centrifuge; 34-Nanofiltration membrane device; 35-Secondary brine treatment device; 36-Ion-ion membrane electrolysis device; 37-Activated carbon adsorption tower; 38-Macroporous adsorption resin tower; 39-Product water tank; 40-Product water transfer pump; 41-Pyrolysis treatment device. Detailed Implementation

[0019] The specific embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The specific embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0020] Firstly, this application proposes a separation and purification system suitable for mixed waste salts of sodium chloride and sodium sulfate, such as... Figure 1 As shown, the separation and purification system includes a connected mixed waste salt pyrolysis salting module, a chemical impurity removal module, a membrane purification module, and a product separation module; The mixed waste salt pyrolysis salt dissolving module includes a pyrolysis treatment device 41 and a salt dissolving tank 2; The chemical impurity removal module includes, in sequence, an oxidation tank 5, a magnesium removal reaction tank 6, a fluorine and phosphorus removal reaction tank 8, a heavy metal and calcium removal reaction tank 9, a sulfur removal reaction tank 10, a flocculation tank 22, a sedimentation tank 23, and a pH adjustment tank 25. The membrane purification module includes an ultrafiltration membrane device 28 and a secondary nanofiltration membrane device 29; The product separation module includes a cryo-crystallizer 32, a nanofiltration membrane device 34, and an ion-exchange membrane electrolysis device 36.

[0021] This application provides a separation and purification system suitable for mixed waste salt of sodium chloride and sodium sulfate. The separation and purification system mainly uses a chemical impurity removal module consisting of an oxidation tank 5, a magnesium removal reaction tank 6, a fluorine and phosphorus removal reaction tank 8, a heavy metal and calcium removal reaction tank 9, and a sulfur removal reaction tank 10 arranged in sequence to effectively remove impurities (including organic matter, nitrogen, magnesium, fluorine, phosphorus, heavy metals, calcium and other elements) from the mixed waste salt. With the subsequent membrane purification module and product separation module, not only is the efficient separation of sodium chloride and sodium sulfate achieved, but the quality of the obtained product is also significantly improved, meeting the requirements of industrial use.

[0022] In addition, the separation and purification system for mixed sodium chloride-sodium sulfate waste salt provided in this application may also have the following additional technical features: In some specific embodiments of this application, such as Figure 1 As shown, the pyrolysis treatment device 41 is connected to the salt dissolving tank 2 via the conveying device 1, and the salt dissolving tank 2 is connected to the chemical impurity removal module via the No. 1 brine pump 3. Thus, the mixed sodium chloride-sodium sulfate waste salt to be treated, after pyrolysis treatment, initially achieves the removal of organic matter, facilitating subsequent chemical impurity removal.

[0023] In some specific embodiments of this application, the solution in the mixed waste salt pyrolysis module is introduced into the oxidation tank 5 after passing through the filtration device 4; the oxidation tank 5 is connected to the magnesium removal reaction tank 6, and the solution in the magnesium removal reaction tank 6 is sequentially introduced into the fluoride and phosphorus removal reaction tank 8, the heavy metal and calcium removal reaction tank 9, and the desulfurization reaction tank 10, which are arranged in series, via a brine pump 7 (#2); the desulfurization reaction tank 10 is connected to the buffer tank 17, which is connected to the brine filter press 19 (#2) via a brine pump 18 (#3), and the brine filter press 19 is connected to the filtrate pool 20; the filtrate pool 20 is connected to the flocculation tank 22 via a brine pump 21 (#4), and the flocculation tank 22 is sequentially connected to the sedimentation tank 23 and the pH adjustment tank 25. Thus, this application effectively removes nitrogen, magnesium, fluorine, phosphorus, heavy metals, calcium, and other elements through the above-mentioned specific sequence of chemical impurity removal steps, improving the quality of the obtained product.

[0024] In some specific embodiments of this application, the sedimentation tank 23 is connected to the sludge tank 12 via sludge pump 24 (No. 4). The magnesium removal reaction tank 6, the fluoride and phosphorus removal reaction tank 8, the heavy metal and calcium removal reaction tank 9, and the sulfur removal reaction tank 10 are all connected to the sludge tank 12 via sludge pump 11 (No. 1). The sludge tank 12 is connected to brine filter press 14 (No. 1) via sludge pump 13 (No. 2). The brine filter press 14 is connected to the sludge filter press 15 (No. 15). The sludge filter press 15 is connected to the salt dissolving tank 2 (No. 3) via sludge pump 16 (No. 3). This achieves secondary treatment of the sludge and improves the utilization rate of the sodium chloride-sodium sulfate mixed waste salt.

[0025] In some specific embodiments of this application, the pH adjustment tank 25 is connected to the intermediate water tank 26, and the intermediate water tank 26 is connected to the ultrafiltration membrane device 28 and the secondary nanofiltration membrane device 29 in sequence via a No. 5 brine pump 27. This allows the chemically purified solution to enter the subsequent membrane purification module.

[0026] In some specific embodiments of this application, the secondary nanofiltration membrane device 29 is connected to the concentrate tank 30, the concentrate tank 30 is connected to the freeze crystallizer 32 via a concentrate transfer pump 31, and the freeze crystallizer 32 is sequentially connected to the centrifuge 33 and the nanofiltration membrane device 34. This application obtains sodium sulfate decahydrate by separating sodium sulfate decahydrate from nanofiltration concentrate through methods such as freeze crystallization, thus obtaining the sodium sulfate decahydrate product.

[0027] In some specific embodiments of this application, the nanofiltration membrane device 34 is connected to the secondary brine treatment device 35, which is connected to the ion-exchange membrane electrolysis device 36; the secondary nanofiltration membrane device 29 is sequentially connected to the activated carbon adsorption tower 37, the macroporous adsorption resin tower 38, and the product water tank 39, which is connected to the salt dissolving tank 2 via a product water transfer pump 40. Thus, a high-quality sodium chloride product is obtained.

[0028] In some specific embodiments of this application, the above-mentioned separation and purification system for mixed sodium chloride and sodium sulfate waste salts includes the following processes during actual operation: The mixed waste salt of sodium chloride and sodium sulfate to be treated is pyrolyzed in pyrolysis treatment device 41 to obtain salt residue. It is then conveyed to salt dissolving tank 2 by a conveying device 1 such as a screw conveyor. Water is added to salt dissolving tank 2 and the mixture is stirred. The sodium chloride and sodium sulfate in the salt residue gradually dissolve in salt dissolving tank 2 with stirring. A brine pump 3 is used to pump the solution from salt dissolving tank 2 into a filtration device 4 such as a carbon blackboard frame filter press for filtration (the resulting filter residue is processed externally). The filtrate enters oxidation tank 5 and reacts with added oxidants such as sodium hypochlorite to remove nitrogen-containing compounds (mainly small molecule nitro compounds, amides / carbamates, amines, etc., such as nitromethane, formamide, methylpyridine, methylamine, etc.) and organic matter (mainly amino / amide compounds, hydroxyl / aldehyde compounds, double / triple bond compounds, sulfur compounds, etc., such as proteins, benzene, etc.) from the solution. After the oxidation reaction (containing phenols, unsaturated fatty acids, thiols, etc.), the solution flows by gravity into the magnesium removal reaction tank 6 to react with the added calcium hydroxide and generate magnesium hydroxide precipitate. Then, the solution in the magnesium removal reaction tank 6 is pumped into the fluoride and phosphorus removal reaction tank 8, the heavy metal and calcium removal reaction tank 9, and the sulfur removal reaction tank 10 by the No. 2 brine pump 7. The solution reacts with the calcium chloride pumped into the fluoride and phosphorus removal reaction tank 8, the sodium sulfide and sodium carbonate pumped into the heavy metal and calcium removal reaction tank 9, and the ferric chloride pumped into the sulfur removal reaction tank 10, respectively. Each of these reactions produces calcium chloride and calcium phosphate precipitates (reaction products in the fluoride and phosphorus removal reaction tank 8), heavy metal precipitates and calcium carbonate precipitates (reaction products in the heavy metal and calcium removal reaction tank 9), and ferric sulfide precipitates (reaction products in the sulfur removal reaction tank 10). The sludge precipitate in the magnesium removal reaction tank 6 and the sludge precipitates in the fluoride and phosphorus removal reaction tank 8, the heavy metal and calcium removal reaction tank 9, and the sulfur removal reaction tank 10 are pumped into the sludge tank 12 by the No. 1 sludge pump 11. The sludge in sludge tank 12 is pumped into brine filter press 14 by sludge pump 2#13 for filtration (the resulting filter residue is outsourced for processing). The filtrate enters sludge filter press 15 and is sent into salt dissolving tank 2 by sludge pump 3#16.The solution after passing through the desulfurization reaction tank 10 enters the buffer tank 17, and is then pumped into the brine filter press 19 by the #3 brine pump 18 for filtration (the resulting filter residue is processed externally). The filtrate enters the filtrate tank 20, and is then pumped into the flocculation tank 22 by the #4 brine pump 21, where a coagulant aid (such as polyaluminum chloride (PAC) or polyacrylamide (PAM)) has been added. After a certain flocculation reaction time, the solution flows by gravity into the sedimentation tank 23 for sludge sedimentation. The settled sludge is then discharged... The sludge is pumped into sludge tank 12 by sludge pump #4 (24). The solution flowing out of sedimentation tank 23 enters pH adjustment tank 25 with added hydrochloric acid. After the pH is adjusted by staying in the adjustment tank for a period of time, it flows by gravity into intermediate water tank 26. The solution is then passed through ultrafiltration membrane device 28 containing an ultrafiltration membrane and secondary nanofiltration membrane device 29 containing a secondary nanofiltration membrane to remove some soluble organic matter (this organic matter mainly includes small molecule fluorinated organic matter, small molecule oxygenated organic matter, and chlorinated byproducts such as nitro compounds) by brine pump #5 (27). The nanofiltration concentrate contains methane, acetic acid, propionic acid, chloroacetic acid, and some dissolved salts (mainly divalent / polyvalent salts and heavy metal salts such as Na2SO4, CaCl2, CdSO4, etc.). The concentrate is stored in the concentrate tank 30 and pumped into the freeze crystallizer 32 by the concentrate transfer pump 31. The sodium sulfate decahydrate and sodium chloride solution precipitated from the freeze flow together into the centrifuge 33 for solid-liquid separation. The separated solid is sodium sulfate decahydrate. The mother liquor after separation is sent to the nanofiltration membrane device 34 containing a nanofiltration membrane for further separation. The nanofiltration concentrate is recycled back into the freeze crystallizer 32. The nanofiltration permeate is treated by a secondary brine treatment device 35 (mainly containing chelating resin) with the addition of sodium hydroxide and hydrochloric acid. Finally, sodium chloride product is obtained by the ion-exchange membrane electrolysis device 36. After passing through the secondary nanofiltration membrane device 29, the nanofiltration permeate is successively treated by the activated carbon adsorption tower 37 and the macroporous adsorption resin tower 38. The solution enters the permeate tank 39 and is finally sent to the salt dissolution tank 2 by the permeate transfer pump 40 as a solution to dissolve salt residue. This achieves the separation and purification of mixed sodium chloride and sodium sulfate waste salts, resulting in a product with an inorganic pollutant content of less than 0.2% by mass, and high purity sodium sulfate decahydrate and sodium chloride products. Specifically, the dehydrated sodium sulfate product meets the T / ZGZS0303-2023 standard for "Regenerated Industrial Salt - Sodium Sulfate", and its sodium chloride content is not higher than 0.5% by mass. Meanwhile, the activated carbon adsorption tower 37 and macroporous resin adsorption tower 38 require backwashing after a period of use to restore their adsorption performance; the ultrafiltration membrane device 28, the secondary nanofiltration membrane device 29, and the nanofiltration membrane device 34 also require backwashing after a period of use to restore their filtration performance.

[0029] Secondly, this application proposes a separation and purification method suitable for mixed sodium chloride and sodium sulfate waste salts. This method employs the separation and purification system for mixed sodium chloride and sodium sulfate waste salts described in the first aspect. Therefore, this separation and purification method significantly improves the quality of the obtained product. Specifically, the inorganic pollutant content in the product obtained by this method is less than 0.2% by mass, and the obtained sodium sulfate decahydrate and sodium chloride products have high purity. Furthermore, the sodium sulfate decahydrate product after dehydration treatment meets the standard of "Regenerated Industrial Salt - Sodium Sulfate" T / ZGZS0303-2023, and its sodium chloride content is not higher than 0.5% by mass.

[0030] In addition, the separation and purification method for mixed waste salts of sodium chloride and sodium sulfate provided in this application may also have the following additional technical features: In some specific embodiments of this application, the dry basis sodium chloride percentage W1 in the mixed sodium chloride-sodium sulfate waste salt to be treated satisfies: 80%≤W1<100%, for example, it can be 85%, 90%, etc. By mass percentage, the dry basis sodium sulfate content W2 in the mixed sodium chloride-sodium sulfate waste salt to be treated shall satisfy: 0% < W2 ≤ 20%, for example, it can be 5%, 10%, 15%, etc. The total organic carbon (TOC) content of the mixed sodium chloride-sodium sulfate waste salt after pyrolysis treatment is 20~160ppm, for example, it can be 40ppm, 60ppm, 80ppm, 100ppm, etc. The operating adjustment parameters of the salt dissolving tank include: temperature ≤ 60℃ (e.g., 40℃, 45℃, etc.), and time 2~6h (e.g., 3h, 5h, etc.).

[0031] In some specific embodiments of this application, the operating conditions parameters of the pyrolysis treatment device include: a temperature of 300~800℃ (e.g., 300℃, 400℃, 500℃, 700℃, 800℃ or any range between the above values), and a time of 1~2h (e.g., 1h, 1.5h, 2h, etc.). The operating conditions of the oxidation tank include: the added oxidant is sodium hypochlorite, and the mass percentage concentration of the oxidant is ≥8%, for example, 10%, 12%, 15%, etc. The operating conditions of the magnesium removal reaction tank include: the added magnesium removal agent includes calcium hydroxide, and the amount of the precipitant added is 1.5 to 2.0 times the molar amount of magnesium ions; The operating parameters of the defluorination and phosphorus removal reaction tank include: the added defluorination and phosphorus removal agent includes calcium chloride, and the amount of the defluorination and phosphorus removal agent added is 4 to 5.5 times the total molar amount of fluorine and phosphorus in the solution to be treated, preferably 2.92 times F + 1.75 times PO4. 3-~3xF + 2xPO4 3- ; The operating parameters of the heavy metal and calcium removal reaction tank include: the added heavy metal and calcium removal agent includes sodium sulfide and sodium carbonate, the weight ratio of sodium sulfide and sodium carbonate is a molar ratio of heavy metal ion molar amount (1.1~1.5): calcium ion molar amount (1.0~1.2), and the amount of heavy metal and calcium removal agent added is 1.1 times the heavy metal ion molar amount + 1.0 times the calcium ion molar amount to 1.5 times the heavy metal ion molar amount + 1.2 times the calcium ion molar amount; The operating conditions of the desulfurization reaction tank include: the added desulfurizing agent includes ferric chloride, and the amount of the added desulfurizing agent is 6.1 to 10.1 times the amount of sulfide; The operating parameters of the flocculation tank include: the added coagulant includes at least one of polyaluminum chloride and polyacrylamide, if it is polyaluminum chloride, then 5~50 mg / L, if it is polyacrylamide, then 0.1~5 mg / L; The operating parameters of the pH adjustment tank include: adjusting the pH to 5.5-7.5; The operating conditions of the cryo-crystallizer include: temperature ≤ 30℃.

[0032] In some specific embodiments of this application, the operating conditions of the secondary brine treatment device include: countercurrent flow, flow rate 5~15 BV / h, temperature 40~50℃, and pressure 0.1~0.2 MPa; the operating conditions of the ion-exchange membrane electrolysis device include: operating temperature 85~95℃ and current density 3~6 kA / m³. 2 The voltage of the cell is 2.8~3.2V / single cell. The operating conditions of the activated carbon adsorption tower include: co-current flow, empty bed contact time of 10~20min, filtration rate of 5~10m / h, operating temperature of 20~40℃, and operating pressure of 0.1~0.2MPa. The operating conditions of the macroporous adsorption resin tower include: counter-current flow, empty bed contact time of 15~30min, filtration rate of 3~8m / h, operating temperature of 25~40℃, and operating pressure of 0.1~0.5MPa.

[0033] The embodiments of this application are described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. In addition, unless otherwise specified, all reagents used in the following embodiments are commercially available or can be synthesized according to the methods described herein or known methods. For reaction conditions not listed, they are also readily available to those skilled in the art.

[0034] Example 1 This embodiment provides a separation and purification system and method suitable for mixed waste salts of sodium chloride and sodium sulfate, such as... Figure 1As shown, it includes the following steps: The mixed waste salt of sodium chloride and sodium sulfate to be treated (by mass percentage, the dry basis sodium chloride percentage W1 is 87.5% and the dry basis sodium sulfate percentage W2 is 6.9%) was pyrolyzed in pyrolysis treatment device 41 at a temperature of 800℃ for 2 hours to obtain salt residue. Analysis of the salt residue showed that the high-chlorine waste sodium salt containing organic matter had a TOC content of 45 ppm, a sodium chloride content of 92.6%, a sodium sulfate content of 7.3%, and other impurities of 1.0%.

[0035] The waste sodium chloride and sodium sulfate mixed salt residue with a particle size of less than 5 mm after pyrolysis is then transported to the salt dissolving tank 2 by a conveying device 1 such as a screw conveyor. Water is added to the salt dissolving tank 2 and the mixture is stirred. The sodium chloride and sodium sulfate in the salt residue gradually dissolve in the salt dissolving tank 2 with stirring. The reaction time is 0.5 h and the residence time is 6 h. The solution comes from municipal tap water or filtrate after pressure filtration and water from the product water tank.

[0036] The solution in the salt dissolving tank 2 is pumped into a filtration device 4, such as a carbon blackboard frame filter press, using a No. 1 brine pump 3 for filtration (the resulting filter residue is outsourced for processing). The filtration time is 0.5 hours, with an intermittent interval of 1 hour. An automatic diaphragm filter press is used. The filtrate enters the oxidation tank 5 and reacts with added sodium hypochlorite oxidant. The sodium hypochlorite reacts to remove nitrogen and organic matter from the solution. The reaction time is 0.5 hours. The amount of sodium hypochlorite added is 0.2 L of sodium hypochlorite solution with 10% available chlorine per liter of waste salt solution.

[0037] After the oxidation reaction is complete, the solution flows by gravity into magnesium removal reaction tank 6 to react with the added calcium hydroxide and form magnesium hydroxide precipitate. The residence time is 2 hours, and the amount of calcium hydroxide added is Mg. 2+ 1.05 times the molar mass. Then, the solution in the magnesium removal reaction tank 6 is pumped into the fluoride and phosphorus removal reaction tank 8, the heavy metal and calcium removal reaction tank 9, and the sulfur removal reaction tank 10 via brine pump #2 7, respectively, and reacted with the calcium chloride (added at 2.94 times the amount of F) pumped into the fluoride and phosphorus removal reaction tank 8. - +1.8x PO4 3 The reaction process involves: 1 hour of reaction of sodium sulfide and sodium carbonate (sodium sulfide added at 1.2 times the molar amount of heavy metal ions and sodium carbonate added at 1.1 times the molar amount of calcium ions) pumped into heavy metal and calcium removal reaction tank 9; 1 hour of reaction of ferric chloride (added at 1.0 times the molar amount of sulfide) pumped into desulfurization reaction tank 10; and 1 hour of reaction of ferric chloride. Each reaction produces calcium chloride and calcium phosphate precipitates (reaction products in fluorine and phosphorus removal reaction tank 8), heavy metal precipitates and calcium carbonate precipitates (reaction products in heavy metal and calcium removal reaction tank 9), and ferric sulfide precipitates (reaction products in desulfurization reaction tank 10).

[0038] The sludge sediment from magnesium removal reactor 6, along with the sludge sediment from fluoride and phosphorus removal reactor 8, heavy metal and calcium removal reactor 9, and sulfur removal reactor 10, is pumped into sludge tank 12 via sludge pump 11. The sludge in sludge tank 12 is then pumped into brine filter press 14 via sludge pump 2 (the resulting filter residue is outsourced for processing). The filtrate enters sludge filter press 15 and is then pumped into salt dissolution tank 2 via sludge pump 3. The solution after passing through the desulfurization reaction tank 10 enters the buffer tank 17, and is then pumped into the brine filter press 19 by the brine pump 18 (the resulting filter residue is processed externally). The filtrate enters the filtrate tank 20, and is then pumped into the flocculation tank 22 by the brine pump 21, which contains coagulant aids (polyaluminum chloride and polyacrylamide, with polyaluminum chloride added at 15 mg / L and polyacrylamide added at 2 mg / L). After a certain period of flocculation, the solution flows by gravity into the sedimentation tank 23 for sludge sedimentation. The settled sludge is then pumped into the sludge tank 12 by the sludge pump 24. The solution flowing out of the sedimentation tank 23 enters the pH adjustment tank 25, which contains hydrochloric acid. After the pH is adjusted to 7-8 in the adjustment tank for a period of time, the solution flows by gravity into the intermediate water tank 26.

[0039] The solution in the intermediate water tank 26 is sequentially passed through an ultrafiltration membrane device 28 containing an ultrafiltration membrane and a secondary nanofiltration membrane device 29 containing a secondary nanofiltration membrane to remove some soluble organic matter and some dissolved salts. The nanofiltration concentrate is stored in a concentrate tank 30. The concentrate is then pumped into a cryogenic crystallizer 32 by a transfer pump 31 (the operating conditions of the cryogenic crystallizer 32 include: operating temperature -2℃, 101.3 kPa, crystallization time 2h, 50 rpm). The sodium sulfate decahydrate and sodium chloride solution precipitated from the freeze-drying process flow together into a centrifuge. Solid-liquid separation is performed at unit 33, and the separated solid is sodium sulfate decahydrate. The mother liquor after separation is sent to nanofiltration membrane unit 34 containing a nanofiltration membrane for further separation. The nanofiltration concentrate is recycled into the cryogenic crystallizer 32. The nanofiltration permeate passes through a secondary brine treatment unit 35 (mainly containing chelating resin, operating parameters include: countercurrent, flow rate 10 BV / h, temperature 40℃, operating pressure 0.1 MPa) with added sodium hydroxide and hydrochloric acid. Finally, it passes through an ion-exchange membrane electrolysis unit 36 ​​(operating parameters include: operating temperature 85℃, current density 4 KA / m³). 2Sodium chloride is produced by a process with a cell voltage of 3.0V / single cell. The nanofiltration permeate after passing through a two-stage nanofiltration membrane device 29 sequentially enters an activated carbon adsorption tower 37 (operating conditions include: co-current flow, empty bed contact time of 15 min, filtration rate of 8 m / h, operating temperature of 30℃, and operating pressure of 0.1 MPa) and a macroporous adsorption resin tower 38 (operating conditions include: counter-current flow, empty bed contact time of 20 min, filtration rate of 5 m / h, operating temperature of 30℃, and operating pressure of 0.2 MPa). The resulting solution then enters a permeate tank 39 and, via a permeate water transfer pump 40, finally enters a salt dissolving tank 2 to dissolve salt residue. This process achieves the separation and purification of mixed sodium chloride and sodium sulfate waste salts.

[0040] After treatment: the purity of sodium chloride is 99.4%, the TOC content is 2.56 ppm, and other impurities are 0.6%; the sodium sulfate decahydrate content in Glauber's salt is 99.6%, the TOC content is 3.28 ppm, and other impurities are 0.4%. The treated sodium chloride meets the requirements of Grade I industrial dry salt (sodium chloride content ≥98.5%, moisture ≤0.5%, other impurities ≤1%). The dehydrated Glauber's salt meets the requirements of "Regenerated Industrial Salt Sodium Sulfate" (T / ZGZS0303-2023), as shown in Table 1.

[0041] Comparative Example 1 This comparative example provides a separation and purification system and method suitable for mixed sodium chloride and sodium sulfate waste salts, which differs from Example 1 only in that: (1) The order of setting the magnesium removal reaction tank, fluorine removal and phosphorus removal reaction tank, heavy metal removal and calcium removal reaction tank and sulfur removal reaction tank in the chemical impurity removal module is different. The order adjustment is as follows: "magnesium removal reaction tank - heavy metal removal and calcium removal reaction tank - sulfur removal reaction tank - fluorine removal and phosphorus removal reaction tank".

[0042] After treatment: the TOC content in sodium chloride was 12.6 ppm, and the other impurities were 4.2%; the TOC content in sodium sulfate decahydrate in Glauber's salt was 16.8 ppm, and the other impurities were 3.6%; as shown in Table 1.

[0043] Table 1

[0044] As shown in Table 1, compared with Comparative Example 1, the separation and purification system for mixed waste salt of sodium chloride and sodium sulfate using the embodiments of this application can significantly improve the quality of the obtained product. This indicates that the salt removal process used in this application mainly removes impurities from the mixed waste salt through a chemical removal module consisting of an oxidation tank, a magnesium removal reaction tank, a fluorine and phosphorus removal reaction tank, a heavy metal and calcium removal reaction tank, and a sulfur removal reaction tank arranged in sequence.

[0045] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0046] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A separation and purification system suitable for mixed waste salts of sodium chloride and sodium sulfate, characterized in that, It includes a connected mixed waste salt pyrolysis salting module, a chemical impurity removal module, a membrane purification module, and a product separation module; The mixed waste salt pyrolysis salt dissolving module includes a pyrolysis treatment device and a salt dissolving tank; The chemical impurity removal module includes, in sequence, an oxidation tank, a magnesium removal reaction tank, a fluorine and phosphorus removal reaction tank, a heavy metal and calcium removal reaction tank, a sulfur removal reaction tank, a flocculation tank, a sedimentation tank, and a pH adjustment tank. The membrane purification module includes an ultrafiltration membrane device and a secondary nanofiltration membrane device; The product separation module includes a cryo-crystallizer, a nanofiltration membrane device, and an ion-exchange membrane electrolysis device.

2. The separation and purification system for mixed sodium chloride-sodium sulfate waste salt according to claim 1, characterized in that, The pyrolysis treatment device is connected to the salt dissolving tank via a conveying device, and the salt dissolving tank is connected to the chemical impurity removal module via a No. 1 brine pump.

3. The separation and purification system for mixed sodium chloride-sodium sulfate waste salt according to claim 2, characterized in that, The solution in the mixed waste salt pyrolysis salt-making module is filtered before being introduced into the oxidation tank. The oxidation tank is connected to the magnesium removal reaction tank. The solution in the magnesium removal reaction tank is sequentially pumped into the fluoride and phosphorus removal reaction tank, the heavy metal and calcium removal reaction tank and the sulfur removal reaction tank, which are arranged in series, through the No. 2 brine pump. The desulfurization reaction tank is connected to the buffer tank. The buffer tank is connected to the brine filter press (No. 2) via a No. 3 brine pump. The brine filter press (No. 2) is connected to the filtrate tank. The filtrate tank is connected to the flocculation tank via a No. 4 brine pump. The flocculation tank is connected to the sedimentation tank and the pH adjustment tank in sequence.

4. The separation and purification system for mixed sodium chloride-sodium sulfate waste salt according to claim 3, characterized in that, The sedimentation tank is connected to the sludge tank via sludge pump #4. The magnesium removal reaction tank, the fluoride and phosphorus removal reaction tank, the heavy metal and calcium removal reaction tank, and the sulfur removal reaction tank are all connected to the sludge tank via sludge pump #1. The sludge tank is connected to brine filter press #1 via sludge pump #2. Brine filter press #1 is connected to sludge filter press. The sludge filter press is connected to the salt dissolution tank via sludge pump #3.

5. The separation and purification system for mixed sodium chloride-sodium sulfate waste salt according to claim 4, characterized in that, The pH adjustment tank is connected to the intermediate water tank, which is connected to the ultrafiltration membrane device and the secondary nanofiltration membrane device in sequence via a No. 5 brine pump.

6. The separation and purification system for mixed sodium chloride-sodium sulfate waste salt according to claim 5, characterized in that, The secondary nanofiltration membrane device is connected to the concentrate tank, which is connected to the freeze crystallizer via a concentrate transfer pump. The freeze crystallizer is connected in sequence to the centrifuge and the nanofiltration membrane device.

7. The separation and purification system for mixed sodium chloride-sodium sulfate waste salt according to claim 6, characterized in that, The nanofiltration membrane device is connected to the secondary brine treatment device, and the secondary brine treatment device is connected to the ion membrane electrolysis device. The secondary nanofiltration membrane device is sequentially connected to an activated carbon adsorption tower, a macroporous adsorption resin tower, and a product water tank. The product water tank is connected to a product water transfer pump and a salt dissolving tank.

8. A method for separating and purifying mixed waste salts of sodium chloride and sodium sulfate, characterized in that, The separation and purification method uses the separation and purification system suitable for mixed waste salt of sodium chloride and sodium sulfate as described in any one of claims 1 to 7.

9. The method for separating and purifying mixed waste salts of sodium chloride and sodium sulfate according to claim 8, characterized in that, By mass percentage, the dry basis sodium chloride content W1 in the mixed sodium chloride-sodium sulfate waste salt to be treated satisfies: 80% ≤ W1 < 100%; By mass percentage, the dry basis sodium sulfate content W2 in the mixed sodium chloride-sodium sulfate waste salt to be treated satisfies: 0% < W2 ≤ 20%; The total organic carbon content of the mixed waste salt of sodium chloride and sodium sulfate after pyrolysis treatment is 20~160ppm; The operating parameters of the salt dissolving tank include: temperature ≤ 60℃, time 2~6h.

10. The method for separating and purifying mixed waste salts of sodium chloride and sodium sulfate according to claim 8, characterized in that, The operating parameters of the pyrolysis treatment device include: temperature of 300~800℃ and time of 1~2h; The operating conditions of the oxidation tank include: the added oxidant is sodium hypochlorite, and the mass percentage concentration of the oxidant is ≥8%; The operating conditions of the magnesium removal reaction tank include: the added magnesium removal agent includes calcium hydroxide; The operating conditions of the defluorination and phosphorus removal reaction tank include: the added defluorination and phosphorus removal agent includes calcium chloride, and the amount of the added defluorination and phosphorus removal agent is 4 to 5.5 times the total molar amount of fluorine and phosphorus in the solution to be treated; The operating conditions of the heavy metal and calcium removal reaction tank include: the added heavy metal and calcium removal agents include sodium sulfide and sodium carbonate, the amount of sodium sulfide added is 1.1 to 1.5 times the molar amount of heavy metal ions in the solution to be treated, and the amount of sodium carbonate added is 1.0 to 1.2 times the molar amount of calcium ions in the solution to be treated; The operating conditions of the desulfurization reaction tank include: the added desulfurizing agent includes ferric chloride, and the amount of the added desulfurizing agent is 0.8 to 1.33 times the molar amount of sulfide in the solution to be treated; The operating conditions of the flocculation tank include: the added coagulant includes at least one of polyaluminum chloride and polyacrylamide, wherein the concentration of polyaluminum chloride in the solution to be treated is 5~50 mg / L, and the concentration of polyacrylamide in the solution to be treated is 0.1~5 mg / L; The operating parameters of the pH adjustment tank include: adjusting the pH to 5.5-7.5; The operating conditions of the cryo-crystallizer include: temperature ≤ 30℃.

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