Resourceful treatment method of chemical waste salt

Abstract

The invention relates to the technical field of waste salt recovery, and discloses a resourceful treatment method of chemical waste salt. The treatment method comprises the following steps: sequentially carrying out high-temperature treatment and salt leaching on the waste salt; freezing and crystallizing the salt-leached saline water to separate out sodium sulfate, and sequentially carrying out activated carbon adsorption and evaporative crystallization; the high-temperature treatment is carried out under the condition that the oxygen content is lower than 2vol%. The method can overcome the influence of fluctuation of the ratio of salt to nitrate on the quality of salt products in the feeding process, and compared with a common cold and hot salt separation process, the method reduces 40-70% of the amount of salt water entering a freezing process, and reduces the energy consumption cost of salt separation. Meanwhile, the method can realize the recycling of process water in the system and the resource utilization of inorganic carbon formed by pyrolysis.

Description

Technical Field

[0001] The present invention relates to the technical field of waste salt recovery, and in particular to a resource treatment method for chemical waste salt. Background Art

[0002] Chemical waste salt mainly comes from the pesticide, pharmaceutical, dye, coal chemical and other industries. It has complex composition and is difficult to treat, especially for the treatment of organic pollutants. The resource treatment of mixed waste salt generally adopts a combination of processes such as drying-incineration-dissolution-filtration-salt separation. CN111467725A discloses a comprehensive treatment method for pesticide waste salt, which adopts a combination of processes such as high-temperature heat treatment-dissolution-electrochemical oxidation and concentrated crystallization to realize the resource utilization of waste salt. However, there are problems such as high air consumption during high-temperature heat treatment and the introduction of new impurities such as potassium sulfate and ammonium persulfate during electrochemical oxidation, which will affect the quality of the recovered waste salt; CN114368763A discloses a comprehensive treatment method for industrial waste salt, which adopts a combination of processes such as dissolution-granulation incineration-redissolution-membrane separation-evaporation crystallization to separate sodium sulfate and sodium chloride. The process flow is complex, the combination of four membrane processes is difficult to operate, and stability is difficult to ensure. It also involves multiple waste salt dissolution processes, and the heat consumption during the phase change process is large. The investment cost and operating cost are very high; CN1 14558878A discloses a waste salt resource utilization system and a treatment method thereof, which adopts pyrolysis, dissolution, reaction precipitation and evaporation crystallization processes to treat mixed waste salt, but has problems such as low pyrolysis temperature, incomplete oxidation of organic matter, and unguaranteed quality of calcium sulfate products prepared by calcium salt; CN110054203B discloses a resource utilization method for industrial waste salt, which adopts a dissolution-then-incineration process. This method is mainly aimed at waste salt with a single component. Although the solid-liquid co-incineration has a high efficiency in removing organic matter, it has high treatment costs and cannot separate salt; CN113560314A discloses a semi-dissolution method for recycling waste salt, which adopts a combined process of heat treatment-semi-dissolution-pretreatment-recovery system to realize waste salt resource utilization, but the organic matter in the waste salt is not completely oxidized during the heat treatment process and will continue to accumulate in the recovery system, ultimately affecting the quality of the finished salt. CN110127925A discloses a method for resource-based mixed salt produced by waste acid treatment, which adopts extraction + dissolution + adsorption / oxidation + frozen crystallization + evaporative crystallization to finally achieve the separation of sodium chloride and sodium sulfate. However, due to the high power required for frozen crystallization, the brine is completely frozen to separate the sodium sulfate, which greatly increases the operating cost. In addition, ultrasonic extraction suffers from incomplete oxidation of organic matter, which affects the quality of the final finished salt. CN111559823A discloses a resource-based harmless treatment system and treatment method for mixed salt, which is mainly aimed at mixed salt produced by zero-emission coal chemical industry and oil refining chemical industry, and adopts a combined process with nanofiltration membrane as the core. However, this combined process is only suitable for mixed salt with low organic pollutant content and relatively stable composition in waste salt.

[0003] There are many types of organic pollutants in chemical waste salt, and the composition is complex and difficult to remove. The salt-nitrate ratio of the waste salt (i.e. the mass ratio of sodium chloride to sodium sulfate) is difficult to stabilize. When the existing technology treats waste salt with a wide salt-nitrate ratio range, the cost of using full frozen crystallization to separate the salt is relatively high. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems existing in the prior art and provide a resource-based treatment method for chemical waste salt. The treatment method can overcome the instability of the waste salt treatment effect caused by fluctuations in the salt-nitrate ratio and improve the quality stability of the salt product.

[0005] In order to achieve the above object, the first aspect of the present invention provides a method for treating waste salt, the method comprising: sequentially subjecting the waste salt to high temperature treatment and salt washing;

[0006] The brine after salt washing is frozen and crystallized to separate sodium sulfate, and then activated carbon adsorption and evaporation crystallization are carried out in sequence;

[0007] The high temperature treatment is performed under the condition that the oxygen content is lower than 2 vol%.

[0008] The second aspect of the present invention provides the application of the above-mentioned treatment method in the resource recovery treatment of waste salt.

[0009] Through the above technical solution, the present invention can achieve at least the following beneficial effects:

[0010] The method provided by the present invention can process chemical waste salts with different salt-nitrate ratios, can overcome the influence of the fluctuation of the salt-nitrate ratio during the incoming material process on the quality of the salt product, and the obtained product has higher purity.

[0011] Furthermore, under the condition that the sodium sulfate content of the waste salt is 5wt%-10wt%, the amount of brine entering the freezing process is reduced by 40%-70% compared with the ordinary hot and cold salt separation process, thereby reducing the energy consumption cost of salt separation.

[0012] In some particularly preferred embodiments of the present invention, zero wastewater discharge is achieved by recycling the evaporated condensate and the evaporated mother liquor. Reusing the inorganic carbon formed after high-temperature treatment not only improves the brine's impurity removal efficiency but also enables resource utilization of the inorganic carbon. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 1 is a schematic flow chart of the waste salt treatment method of Example 1. DETAILED DESCRIPTION

[0014] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0015] A first aspect of the present invention provides a method for treating waste salt, the method comprising: sequentially subjecting the waste salt to high-temperature treatment and salt washing;

[0016] The brine after salt washing is frozen and crystallized to separate sodium sulfate, and then activated carbon adsorption and evaporation crystallization are carried out in sequence;

[0017] The high temperature treatment is performed under the condition that the oxygen content is lower than 2 vol%.

[0018] In the present invention, the waste salt is derived from the production processes of industries such as pesticides, pharmaceuticals, dyes, and coal chemical industry, and its main components include sodium chloride, sodium sulfate, and organic pollutants. The above treatment method can overcome the instability of waste salt treatment caused by fluctuations in the salt-nitrate ratio (i.e., the mass ratio of sodium chloride to sodium sulfate), thereby improving the quality stability of the salt product. Compared with conventional process flows, this treatment method can also reduce the processing volume of the freeze crystallization process, thereby lowering processing costs.

[0019] In the present invention, the high-temperature treatment converts organic matter in the waste salt into inorganic carbon, which can effectively remove TOC from the waste salt. The high-temperature treatment is carried out under conditions of isolation from air and / or oxygen. This condition can be provided by a protective atmosphere or by physically isolating the air and / or oxygen using a heating device.

[0020] In the present invention, preferably, the high temperature treatment is carried out under a protective atmosphere, preferably provided by nitrogen.

[0021] In the present invention, preferably, the high temperature treatment is performed under the condition that the oxygen content is 0-1 vol%.

[0022] In the present invention, the TOC and sodium sulfate contents of the waste salt can be selected in a wide range. All types of waste salt can be treated using the above method.

[0023] According to the present invention, preferably, the TOC of the waste salt is 1500-30000 mg / kg, and the content of sodium sulfate is 5-20 wt%.

[0024] According to the present invention, preferably, the temperature of the high temperature treatment is 500-700° C., and the treatment time is 0.5-2.5 h.

[0025] In the present invention, the high-temperature treatment conditions are within the above range, which is more conducive to the full conversion of TOC in the waste salt into inorganic carbon.

[0026] According to the present invention, preferably, the high temperature treatment carbonizes TOC in the waste salt into inorganic carbon with a conversion rate of 30-60%. The conversion rate refers to the mass ratio of the inorganic carbon obtained after the high temperature treatment to the total organic carbon.

[0027] In the present invention, the waste gas generated after high-temperature treatment enters the secondary combustion chamber and waste gas treatment units such as desulfurization and denitrification, where it is purified and discharged to meet emission standards. The waste gas treatment units can be conventional in the field and are not described in detail in this invention. The waste salt after high-temperature treatment is washed to dissolve the sodium sulfate in the waste salt.

[0028] According to the present invention, preferably, the conditions for washing salt include: the mass ratio of the waste salt to the detergent is 1:1-4.

[0029] According to the present invention, preferably, the lotion is a sodium chloride aqueous solution.

[0030] According to the present invention, preferably, the concentration of sodium chloride in the lotion is 22-27 wt % based on the total mass of the lotion.

[0031] In the present invention, the salt washing process is continued until the concentration of sodium sulfate in the washing agent reaches 5-7 wt %.

[0032] In the present invention, most of the sodium sulfate in the waste salt is dissolved after salt washing and exists in the brine, which also contains inorganic carbon and part of TOC.

[0033] According to the present invention, preferably, the treatment method further comprises: filtering the brine after salt washing to separate the inorganic carbon, and using the inorganic carbon in the activated carbon adsorption process.

[0034] In the present invention, the brine after salt washing can be filtered after the hardness of the brine is reduced by adjusting the pH to 11-13.

[0035] In the present invention, the filtration can be carried out by selecting a conventional filtration method in the field. Preferably, the brine after salt washing is filtered by plate and frame filter press.

[0036] Preferably, the operating pressure of the plate and frame filter press is 0.5-1.5 MPa.

[0037] In the present invention, the inorganic carbon formed after high-temperature treatment is used in the activated carbon adsorption process, thereby realizing resource utilization of the inorganic carbon. The activated carbon can be mixed with various additives (such as dispersants and / or binders) and then used in the activated carbon adsorption process to improve the adsorption performance of the inorganic carbon.

[0038] In the present invention, preferably, the inorganic carbon is mixed with carboxymethyl cellulose and / or polyvinyl alcohol fiber and then used in the activated carbon adsorption process. The types of the carboxymethyl cellulose and polyvinyl alcohol fiber can be conventionally selected in the field and can be obtained commercially, as long as the purpose of the present invention can be achieved.

[0039] In some specific embodiments of the present invention, the inorganic carbon is mixed with carboxymethyl cellulose and polyvinyl alcohol fiber and then used in the activated carbon adsorption process, wherein the mass ratio of the inorganic carbon, carboxymethyl cellulose and polyvinyl alcohol fiber is 100:0.01-0.02:0.005-0.01.

[0040] According to the present invention, preferably, the treatment method further comprises: sequentially dissolving and centrifuging the solid phase salt obtained after salt washing.

[0041] In the present invention, the conditions for the dissolution and centrifugation are not particularly limited, and the purpose is to remove insoluble impurities in the solid phase salt. Preferably, the dissolution conditions are such that the sodium chloride concentration of the brine is 20-26.8 wt %. The centrifugation speed is 5500-7500 rpm.

[0042] Further preferably, the clear liquid after centrifugal separation enters the activated carbon adsorption process.

[0043] In the present invention, the brine after washing (optionally filtered) is subjected to freeze crystallization in order to separate the sodium sulfate in the brine.

[0044] According to the present invention, preferably, the temperature of the freeze crystallization is -10°C to 0°C.

[0045] In the present invention, the freeze crystallization time is not particularly limited. The main purpose is to crystallize the sodium sulfate in the brine as quickly as possible and separate it from the brine. Those skilled in the art can determine the freeze crystallization time based on actual conditions. Preferably, the freeze crystallization conditions are such that the sodium sulfate content in the brine after freeze crystallization is 0.6-1.2 wt %.

[0046] In the present invention, the sodium sulfate after freeze crystallization is evaporated and dried to obtain a sodium sulfate product.

[0047] In the present invention, activated carbon adsorption is performed on the brine after freezing and crystallizing to separate the sodium sulfate solid and / or the clear liquid after centrifugal separation.

[0048] In the present invention, the activated carbon adsorption method is to contact the salt water with the activated carbon, and the contact method can be a conventional choice in the field. Preferably, the activated carbon is fixed in an activated carbon adsorption tower, and the salt water passes through the adsorption tower to undergo the activated carbon adsorption process.

[0049] According to the present invention, preferably, the activated carbon adsorption conditions include: a hydraulic retention time of 0.4-1.25 hours per unit volume of activated carbon. The hydraulic retention time refers to the average time it takes for brine to pass through a unit effective volume (BV) of activated carbon.

[0050] In the present invention, the brine after adsorption by the activated carbon is evaporated and crystallized.

[0051] According to the present invention, preferably, the treatment method further comprises: subjecting the brine after activated carbon adsorption to ion exchange and then evaporation and crystallization.

[0052] In the present invention, the conditions and resin types of the ion exchange process are conventionally selected in the art, as long as the purpose of the present invention can be achieved. Preferably, the ion exchange process makes the TOC in the brine less than 50 mg / L and the hardness less than 5 mg / L.

[0053] Preferably, the resin used in the ion exchange process is an aminocarboxylic acid chelating resin and / or a macroporous ion exchange resin.

[0054] According to the present invention, preferably, the raw steam pressure of the evaporative crystallization is 0.1-0.5 MPa, and the evaporation temperature is 90-100°C.

[0055] Further preferably, the raw steam pressure of the evaporative crystallization is 0.3-0.5 MPa, and the evaporation temperature is 95-100°C.

[0056] Preferably, the evaporative crystallization adopts triple-effect evaporation.

[0057] In the present invention, during the evaporation crystallization process, TOC continuously accumulates in the mother liquor. When the TOC in the evaporated mother liquor reaches 5,000-30,000 mg / L, the evaporated mother liquor is subjected to catalytic wet oxidation. Prior to the catalytic wet oxidation treatment, the evaporated mother liquor is diluted to a TOC of 2,000-12,000 mg / L and a salinity of 5-10%, where salinity refers to the mass content of soluble inorganic salts in the evaporated mother liquor.

[0058] According to the present invention, preferably, the treatment method further comprises: subjecting the mother liquor after evaporation and crystallization to catalytic wet oxidation treatment.

[0059] In the present invention, the catalytic wet oxidation treatment can further remove the remaining TOC in the evaporation mother liquor, thereby reducing the pressure of mother liquor treatment in actual production and improving the resource utilization rate of the entire process.

[0060] According to the present invention, preferably, the temperature of the catalytic wet oxidation is 150-320° C., the pressure is 1-15 MPa, the pH is 6-7, and the time is 0.5-2 h.

[0061] In the present invention, the oxidant for catalytic wet oxidation is a conventional choice in the art, for example, the oxidant may be oxygen.

[0062] In the present invention, the catalyst for catalytic wet oxidation is not particularly limited and can be any conventional catalyst in the art as long as the purpose of the present invention can be achieved.

[0063] According to the present invention, preferably, at least a portion of the condensate after evaporation and crystallization is recycled to at least one of the processes of solid-phase salt dissolution, catalytic wet oxidation, and salt washing.

[0064] According to the present invention, preferably, the treatment method further comprises: recycling at least part of the effluent from the catalytic wet oxidation to the salt washing process.

[0065] In the present invention, the condensate after evaporation and crystallization and the effluent of catalytic wet oxidation are reused to achieve zero wastewater discharge in the entire process.

[0066] Further preferably, the treatment method further comprises: recycling all the effluent from the catalytic wet oxidation into the salt washing process.

[0067] In some specific embodiments of the present invention, the condensed water from the evaporation process is recycled to the salt dissolving unit, the catalytic wet oxidation unit, and the salt washing unit in a volume ratio of 2.6:(0.2-0.4):(0.3-0.6).

[0068] The second aspect of the present invention provides the application of the above-mentioned treatment method in the resource recovery treatment of waste salt.

[0069] In the present invention, the treatment method can be used to treat various types of chemical waste salts, including but not limited to chemical waste salts from the pesticide, pharmaceutical, dye, coal chemical and other industries. The components of the waste salts can be as described above.

[0070] The present invention will be described in detail below through examples. It should be understood that the following examples are only used to further explain and illustrate the present invention, and are not intended to limit the present invention.

[0071] Unless otherwise specified, the reagents and materials used in the following examples were purchased from regular chemical reagent suppliers and were of analytical grade.

[0072] In the following examples, carboxymethyl cellulose was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. with the brand name C294622;

[0073] Polyvinyl alcohol fiber was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. with the brand name P434370.

[0074] In the following examples, the aminocarboxylic acid chelating resin filled in the ion exchange unit was purchased from Shaanxi Lanshen Special Resin Co., Ltd., with the brand LS-1000; the macroporous ion exchange resin was purchased from Shaanxi Lanshen Special Resin Co., Ltd., with the brand LS-109D.

[0075] In the following examples, the purity of the sodium chloride product was tested according to GB / T 13025.5, General Test Methods for Salt Production Industry.

[0076] The test method for the purity of sodium sulfate products refers to GB / T 13025.8 General test methods for salt production industry.

[0077] Example 1

[0078] This example is used to illustrate the effect of the method of the present invention on the treatment of by-product chemical waste salt of a pesticide production enterprise. The sodium sulfate content of the waste salt is 5wt% and the TOC is 20000mg / kg. The process of the treatment method is as follows Figure 1 shown.

[0079] S1. Waste salt is heated at 650°C under oxygen-free conditions (N2 atmosphere) for 1.5 hours. The TOC content of the waste salt after heating is 330 mg / kg, and the conversion rate of TOC carbonization to inorganic carbon is 55%. The waste gas generated enters the secondary combustion chamber and desulfurization and denitrification waste gas treatment units for purification and then meets the emission standards.

[0080] S2. The waste salt temperature at the high-temperature pyrolysis outlet is 220°C. It enters the salt washing unit and is washed with a 26.8wt% sodium chloride solution with a mass ratio of 1:1 to the waste salt. The salt washing temperature is 50°C, and the salt washing process continues until the sodium sulfate concentration in the liquid phase reaches 5.3wt%.

[0081] S3. After washing, sodium hydroxide solution is added to the brine to make the pH reach 12, and then the brine enters the plate and frame filter press to separate the inorganic carbon (the filtration pressure is 1.0 MPa). 0.02 wt% of carboxymethyl cellulose and 0.01 wt% of polyvinyl alcohol fiber are added to the inorganic carbon, and the mixture is mixed and then added to the activated carbon adsorption unit.

[0082] S4. The brine after plate and frame filtration in step S3 enters the freezing crystallization unit. The brine volume is 1 t / ton of salt and the freezing temperature is -5°C. The obtained sodium sulfate crystals are dried and dehydrated to obtain anhydrous sodium sulfate product with a purity of 94.2%.

[0083] The solid phase salt after washing in step S3 is added with evaporated condensed water to prepare a salt solution with a sodium chloride concentration of 26.8 wt %, and the salt solution is centrifuged at a rotation speed of 6600 rpm.

[0084] S5. The brine after the sodium sulfate crystals separated in step S4 is mixed with the brine after the salt solution is centrifuged and impurities are removed, and then enters the activated carbon unit. The hydraulic retention time of the brine in the activated carbon unit is 1.25 hours. The brine at the outlet of the activated carbon unit enters the ion adsorption unit. The flow rate of the ion exchange unit is 1 BV / h. The TOC of the brine at the outlet of the ion exchange unit is 50 mg / L, and the hardness is 4 mg / L.

[0085] S6. The effluent from the ion exchange unit in step S5 enters an evaporation and crystallization unit, which uses triple-effect evaporation, controlled at a temperature of 95°C and a steam pressure of 0.3 MPa. When the TOC in the mother liquor reaches 5000 mg / L, the mother liquor is diluted with evaporated condensate to a salinity of 10% and a TOC of 2000 mg / L before entering a catalytic wet oxidation unit. The resulting sodium chloride product has a purity of 96%.

[0086] S7, the catalyst for catalytic wet oxidation is copper sulfate, Cu 2+ The concentration is 400 mg / L, the reaction temperature is 280℃, the pH is 7, the pressure is 6 MPa, and the time is 1 hour. Air is introduced during the process. The TOC of the brine after degradation is 300 mg / L, and it is recycled to the salt washing unit.

[0087] S8. In step S6, the condensed water from the evaporation process is recycled to the salt dissolving unit, the catalytic wet oxidation unit and the salt washing unit in a volume ratio of 2.6:0.2:0.3, thereby achieving zero discharge of wastewater.

[0088] Example 2

[0089] This example is used to illustrate the effect of the method of the present invention on treating chemical waste salt produced as a by-product of a pesticide production enterprise. The raw salt of the waste salt has a sodium sulfate content of 10 wt% and a TOC content of 15000 mg / kg.

[0090] S1. Waste salt is heated at 550°C under oxygen-free conditions (N2 atmosphere) for 1 hour. The TOC content of the waste salt after heating is 280 mg / kg, and the conversion rate of TOC carbonization to inorganic carbon is 53%. The waste gas generated enters the secondary combustion chamber and desulfurization and denitrification waste gas treatment units for purification and then meets the emission standards.

[0091] S2. The waste salt temperature at the high-temperature pyrolysis outlet is 200°C. It enters the salt washing unit and is washed with a 26.5wt% sodium chloride solution with a mass ratio of 2:1 to the waste salt. The salt washing temperature is 35°C, and the salt washing process continues until the sodium sulfate concentration in the liquid phase reaches 6wt%.

[0092] S3. After washing, sodium hydroxide solution is added to the brine to make the pH reach 12, and then the brine enters the plate and frame filter press to separate the inorganic carbon (the filtration pressure is 1.2 MPa). 0.02 wt% of carboxymethyl cellulose and 0.01 wt% of polyvinyl alcohol fiber are added to the inorganic carbon, and the mixture is mixed and then added to the activated carbon adsorption unit.

[0093] S4. The brine after plate and frame filtration in step S3 enters the freezing crystallization unit. The brine volume is 1.7t / ton of raw salt and the freezing temperature is -5°C. The obtained sodium sulfate crystals are dried and dehydrated to obtain anhydrous sodium sulfate product with a purity of 93.1%.

[0094] The solid phase salt after washing in step S3 is added with evaporated condensed water to prepare a salt solution with a sodium chloride concentration of 26.5 wt %, and the salt solution is centrifuged at a rotation speed of 6600 rpm.

[0095] S5. The brine after the sodium sulfate crystals separated in step S4 is mixed with the brine after the salt solution is centrifuged and impurities are removed, and then enters the activated carbon unit. The hydraulic retention time of the brine in the activated carbon unit is 1 hour. The brine at the outlet of the activated carbon unit enters the ion adsorption unit. The flow rate of the ion exchange unit is 1 BV / h. The TOC of the brine at the outlet of the ion exchange unit is 45 mg / L, and the hardness is 3.5 mg / L.

[0096] S6. The effluent from the ion exchange unit in step S5 enters an evaporation and crystallization unit, which uses triple-effect evaporation, controlled at a temperature of 95°C and a steam pressure of 0.3 MPa. When the TOC in the mother liquor reaches 5000 mg / L, the mother liquor is diluted with evaporated condensate to a salinity of 10% and a TOC of 2000 mg / L before entering a catalytic wet oxidation unit. The resulting sodium chloride product has a purity of 93.4%.

[0097] S7, the catalyst for catalytic wet oxidation is copper sulfate, Cu 2+ The concentration is 500 mg / L, the reaction temperature is 280℃, the pH is 7, the pressure is 6 MPa, the time is 1 hour, and the TOC of the brine after degradation is 280 mg / L, which is recycled to the salt washing unit.

[0098] S8. In step S6, the condensed water from the evaporation process is recycled to the salt dissolving unit, the catalytic wet oxidation unit and the salt washing unit in a volume ratio of 2.6:0.4:0.6, thereby achieving zero discharge of wastewater.

[0099] Example 3

[0100] This example is used to illustrate the effect of the method of the present invention on treating by-product chemical waste salt of a pesticide production enterprise. The sodium sulfate content of the waste salt is 10wt%, and the TOC is 10000mg / kg.

[0101] S1. Waste salt is heated at 500℃ under oxygen-free conditions (N2 atmosphere) for 1h. The TOC content in the waste salt after heating is 250mg / kg, and the conversion rate of TOC carbonization to inorganic carbon is 60%. The waste gas generated enters the secondary combustion chamber and desulfurization and denitrification waste gas treatment units for purification and then meets the emission standards.

[0102] S2. The waste salt temperature at the high-temperature pyrolysis outlet is 195°C. It enters the salt washing unit and is washed with a 26.4wt% sodium chloride solution with a mass ratio of 2:1 to the waste salt. The salt washing temperature is 20°C, and the salt washing process continues until the sodium sulfate concentration in the liquid phase reaches 6wt%.

[0103] S3. After washing, sodium hydroxide solution is added to the brine to make the pH reach 12, and then the brine enters the plate and frame filter press to separate the inorganic carbon (the filtration pressure is 0.8 MPa). 0.02 wt% of carboxymethyl cellulose and 0.01 wt% of polyvinyl alcohol fiber are added to the inorganic carbon, and the mixture is mixed and then added to the activated carbon adsorption unit.

[0104] S4. The brine after plate and frame filtration in step S3 enters the freezing crystallization unit. The brine volume is 1.4 t / ton of raw salt and the freezing temperature is -5°C. The obtained sodium sulfate crystals are dried and dehydrated to obtain anhydrous sodium sulfate product with a purity of 93.3%.

[0105] The solid phase salt after washing in step S3 is added with evaporated condensed water to prepare a salt solution with a sodium chloride concentration of 26.4 wt %, and the salt solution is centrifuged at a rotation speed of 6600 rpm.

[0106] S5. The brine after the sodium sulfate crystals separated in step S4 is mixed with the brine after centrifugal impurity removal from the salt solution and enters the activated carbon unit together. The hydraulic retention time of the brine in the activated carbon unit is 0.5h. The brine at the outlet of the activated carbon unit enters the ion adsorption unit. The ion exchange unit uses aminocarboxylic acid chelating resin and macroporous ion exchange resin. The flow rate is 1BV / h. The TOC of the brine at the outlet of the ion exchange unit is 40mg / L and the hardness is 3.2mg / L.

[0107] The effluent from the ion exchange units in S6 and S5 enters the evaporation and crystallization unit, which uses triple-effect evaporation, controlled at 95°C and a steam pressure of 0.3 MPa. When the TOC in the mother liquor reaches 5000 mg / L, it is diluted with evaporated condensate to a salinity of 10% and a TOC of 2000 mg / L before entering the catalytic wet oxidation unit. The resulting sodium chloride product has a purity of 97%.

[0108] S7, the catalyst for catalytic wet oxidation is copper sulfate, Cu 2+The concentration is 800 mg / L, the reaction temperature is 280℃, the pH is 7, the pressure is 6 MPa, the time is 1.5h, and the TOC of the brine after degradation is 190 mg / L, which is recycled to the salt washing unit.

[0109] S8. In step S6, the condensed water from the evaporation process is recycled to the salt dissolving unit, the catalytic wet oxidation unit and the salt washing unit in a volume ratio of 2.6:0.3:0.4, thereby achieving zero discharge of wastewater.

[0110] Comparative Example 1

[0111] In this comparative example, the waste salt (sodium sulfate content 5 wt %, TOC 20000 mg / kg) of Example 1 was treated using a conventional hot and cold salt separation process.

[0112] S1. Waste salt is heated at 650°C under oxygen-free conditions (N2 atmosphere) for 1.5 hours. The TOC content of the waste salt after heating is 330 mg / kg, and the conversion rate of TOC carbonization to inorganic carbon is 55%. The waste gas generated enters the secondary combustion chamber and desulfurization and denitrification waste gas treatment units for purification and then meets the emission standards.

[0113] S2. The waste salt temperature at the high-temperature pyrolysis outlet is 220°C. After heat exchange, it enters the salt dissolving unit and dissolves into saturated brine with 24.2% sodium chloride and 5.3% sodium sulfate. The brine temperature is 50°C.

[0114] S3. Add sodium hydroxide solution to the brine to make the pH reach 12, then enter the plate and frame filter press (filter pressure is 1.0 MPa) to separate the inorganic carbon and impurities, and then add hydrochloric acid to adjust to neutral.

[0115] S4. The brine after plate and frame filtration in step S3 enters the freezing crystallization unit, and the brine volume is 3.5t / ton of raw salt. The brine volume entering the freezing unit is increased by 250% compared with Example 1, and the direct operation energy consumption is increased by 47%; the freezing temperature is -5°C, and the obtained sodium sulfate crystals are dried and dehydrated to obtain anhydrous sodium sulfate product with a purity of 89%.

[0116] S5. The frozen crystallization mother liquor in step S4 enters the evaporation crystallization unit, which adopts triple-effect evaporation, controls the temperature at 95° C., and the steam pressure at 0.3 MPa. When the TOC in the evaporation mother liquor reaches 5000-30000 mg / L, it is discharged for disposal, and the purity of the obtained sodium chloride product is 90%.

[0117] Comparative Example 2

[0118] In this comparative example, the waste salt of Example 2 (sodium sulfate content of 10 wt %, TOC of 15000 mg / kg) was treated by a conventional hot and cold salt separation process.

[0119] S1. Waste salt is heated at 550°C under oxygen-free conditions (N2 atmosphere) for 1 hour. The TOC content of the waste salt after heating is 280 mg / kg, and the conversion rate of TOC carbonization to inorganic carbon is 53%. The waste gas generated enters the secondary combustion chamber and desulfurization and denitrification waste gas treatment units for purification and then meets the emission standards.

[0120] S2. The waste salt temperature at the high-temperature pyrolysis outlet is 200°C. After heat exchange, it enters the salt dissolving unit and dissolves into saturated brine with 23.5% sodium chloride and 6% sodium sulfate. The brine temperature is 35°C.

[0121] S3. Add sodium hydroxide solution to the brine to make the pH reach 12, then enter the plate and frame filter press (filter pressure is 1.2MPa) to separate the inorganic carbon and impurities, and then add hydrochloric acid to adjust to neutral.

[0122] S4. The brine after plate and frame filtration in step S3 enters the freezing crystallization unit, with a brine volume of 3.4 t / ton of raw salt. The brine volume entering the freezing unit is increased by 100% compared with Example 2, and the direct operation energy consumption is increased by 34%. The freezing temperature is -5°C, and the obtained sodium sulfate crystals are dried and dehydrated to obtain anhydrous sodium sulfate product with a purity of 88%.

[0123] S5. The frozen crystallization mother liquor in step S4 enters an evaporation crystallization unit. The evaporation crystallization unit adopts triple-effect evaporation, controls the temperature at 95° C., and the steam pressure at 0.3 MPa. When the TOC in the evaporation mother liquor reaches 5000-30000 mg / L, it is discharged for disposal. The purity of the obtained sodium chloride product is 88.2%.

[0124] Comparative Example 3

[0125] This comparative example uses a common cold and hot salt separation process (without a salt washing process) to treat the waste salt of Example 3 (the waste salt has a sodium sulfate content of 10 wt % and a TOC of 10,000 mg / kg).

[0126] S1. Waste salt is heated at 500℃ under oxygen-free conditions (N2 atmosphere) for 1h. The TOC content in the waste salt after heating is 250mg / kg, and the conversion rate of TOC carbonization to inorganic carbon is 60%. The waste gas generated enters the secondary combustion chamber and desulfurization and denitrification waste gas treatment units for purification and then meets the emission standards.

[0127] S2. The waste salt temperature at the high-temperature pyrolysis outlet is 195°C. After heat exchange, it enters the salt dissolving unit and dissolves into saturated brine with 22.5% sodium chloride and 7.5% sodium sulfate. The brine temperature is 20°C.

[0128] S3. Add sodium hydroxide solution to the brine to make the pH reach 12, then enter the plate and frame filter press (filter pressure is 0.8MPa) to separate the inorganic carbon and impurities, and then add hydrochloric acid to adjust to neutral.

[0129] S4. The brine after plate and frame filtration in step S3 enters the freezing crystallization unit, with a brine volume of 3.3 t / ton of raw salt. The brine volume entering the freezing unit is increased by 136% compared with Example 3, and the direct operation energy consumption is increased by 40%; the freezing temperature is -5°C, and the obtained sodium sulfate crystals are dried and dehydrated to obtain anhydrous sodium sulfate product with a purity of 90.1%.

[0130] S5. The frozen crystallization mother liquor in step S4 enters the evaporation crystallization unit, which adopts triple-effect evaporation, controls the temperature at 95° C., and the steam pressure at 0.3 MPa. When the TOC in the evaporation mother liquor reaches 5000-30000 mg / L, it is discharged for disposal. The purity of the obtained sodium chloride product is 90.1%.

[0131] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for treating waste salt, characterized in that: The treatment method comprises: sequentially subjecting waste salt to high-temperature treatment and salt washing; The brine after salt washing is frozen and crystallized to separate sodium sulfate, and then activated carbon adsorption and evaporation crystallization are carried out in sequence; The high temperature treatment is performed under the condition that the oxygen content is lower than 2 vol%.

2. The processing method according to claim 1, wherein The waste salt has a TOC content of 1500-30000 mg / kg and a sodium sulfate content of 5-20 wt%.

3. The processing method according to claim 1, wherein: The temperature of the high temperature treatment is 500-700°C and the treatment time is 0.5-2.5h; And / or, the high temperature treatment carbonizes TOC in the waste salt into inorganic carbon with a conversion rate of 30-60%.

4. The processing method according to claim 1 or 2, wherein: The conditions for washing salt include: The mass ratio of the waste salt to the detergent is 1:1-4; Preferably, the lotion is an aqueous solution of sodium chloride; Preferably, the concentration of sodium chloride in the lotion is 22-27 wt % based on the total mass of the lotion.

5. The processing method according to claim 1 or 2, wherein: The temperature of the freezing crystallization is -10°C to 0°C; And / or, the activated carbon adsorption conditions include: a hydraulic retention time of 0.4-1.25 h per unit volume of activated carbon.

6. The processing method according to claim 1 or 2, wherein: The raw steam pressure of the evaporation crystallization is 0.1-0.5 MPa, and the evaporation temperature is 90-100°C.

7. The processing method according to claim 1 or 2, wherein: The treatment method further comprises: filtering the salt water after salt washing to separate the inorganic carbon, and using the inorganic carbon in the activated carbon adsorption process; And / or, the treatment method further comprises: sequentially dissolving and centrifuging the solid phase salt obtained after salt washing; Preferably, the clear liquid after centrifugal separation enters the activated carbon adsorption process.

8. The processing method according to claim 7, wherein: The treatment method further comprises: subjecting the brine after activated carbon adsorption to ion exchange and then evaporation and crystallization; And / or, the treatment method further comprises: subjecting the mother liquor after evaporation and crystallization to catalytic wet oxidation treatment; Preferably, the treatment method further comprises: recycling at least part of the condensate after evaporation and crystallization to at least one of the processes of dissolving the solid salt, catalytic wet oxidation and washing the salt; Preferably, the treatment method further comprises: reusing at least part of the effluent from the catalytic wet oxidation to the salt washing process.

9. The processing method according to claim 8, wherein: The temperature of the catalytic wet oxidation is 150-320° C., the pressure is 1-15 MPa, the pH is 6-7, and the residence time is 0.5-2 h.

10. Application of the treatment method according to any one of claims 1 to 9 in waste salt resource treatment.

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