A method for recycling chemical waste salt in the PTA industry

Abstract

The application provides a PTA industry chemical waste salt resource treatment method, which comprises the following steps: firstly, dissolving and filtering the chemical waste salt containing sodium carbonate and sodium bromide; vacuum evaporating and crystallizing the filtered filtrate, controlling the evaporation ratio, and obtaining an industrial-grade sodium carbonate product with high purity; evaporating the mother liquor into a cooling crystallizer to separate and obtain sodium carbonate decahydrate for reuse; after being concentrated by an evaporation crystallizer, the cooled mother liquor is introduced into a sodium bromide cooling crystallizer to separate and obtain an industrial-grade sodium bromide product, and part of the sodium bromide crystallization mother liquor is recycled and part is taken out for drying. The crystallization process combining evaporation crystallization and cooling crystallization can effectively recover valuable components in the PTA industry chemical waste salt, without adding additional raw materials and chemical additives to assist production, without causing secondary pollution of waste water and additional solid waste output; low energy consumption and low cost realize the resource of the chemical waste salt, greatly reduce the hazardous waste treatment cost, solve the environmental protection problem, and have great economic benefits.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization, specifically to a method for the resource utilization of chemical waste salt in the PTA industry. Background Technology

[0002] Purified terephthalic acid (PTA) is an important organic synthetic monomer, widely used in the preparation of polymer resins, plasticizers, and adhesives. Its primary application is in the synthesis of polyesters, which are then used to produce polyester fibers, bottle chips, or films. With the continuous expansion of PTA production capacity, major domestic PTA manufacturers have accumulated large amounts of chemical waste salts, mainly composed of sodium carbonate, sodium bromide, and a small amount of sodium chloride, as well as trace amounts of insoluble heavy metals. Currently, manufacturers can only outsource the treatment of this waste, resulting in high processing costs and the inability to recover the economically valuable sodium carbonate and sodium bromide, leading to a significant waste of resources.

[0003] Currently, there are two treatment schemes for recovering mixed sodium carbonate and sodium bromide salts: The first is a membrane separation and crystallization process. This utilizes the differences in ionic radius or charge characteristics between carbonate and bromide ions to separate or enrich the different salts before crystallization via a membrane separation process, followed by thermal crystallization to obtain the solid. This method is costly, energy-intensive, and prone to membrane fouling, making it difficult to operate and manage, and unable to achieve long-term stable operation. The second method uses hydrobromic acid to replace sodium carbonate in the solution, followed by thermal crystallization to obtain sodium bromide. The crude sodium bromide obtained using this method has a high sodium carbonate content, requiring the addition of large amounts of hydrobromic acid. Hydrobromic acid is toxic and highly corrosive; even slight carelessness during storage and production could lead to accidents, endangering employee lives and company property. Furthermore, at current market prices, the unit price of hydrobromic acid is much higher than that of sodium carbonate and sodium bromide, resulting in high recovery costs and low resource value, making this route difficult to compete in the market.

[0004] In view of the above-mentioned problems in the existing technology, the researchers of this invention, through a large number of experiments, based on the phase rule equilibrium data of mixed salts at different temperatures and compositions, provide a method for the resource-based treatment of chemical waste salt in the PTA industry. The method adopts a crystallization process that combines evaporation crystallization and cooling crystallization, which can effectively recover sodium carbonate and sodium bromide from PTA industry waste salt. It does not require the addition of additional raw materials and chemical auxiliaries to assist production, and achieves the resource-based treatment of chemical waste salt at a low cost, with great environmental and economic benefits.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for the resource utilization of chemical waste salt in the PTA industry, which includes the following steps:

[0007] Step 1: First, the chemical waste salt containing sodium carbonate and sodium bromide is dissolved in water in a dissolving tank to prepare a mixed salt solution. The temperature of the mixed salt solution is 25-80℃ (preferably 30-60℃). The solution is then filtered to remove heavy metal salts and insoluble matter, resulting in a filtrate.

[0008] Step 2: After preheating the filtrate obtained in the above steps to the evaporation temperature, it is transported to a primary evaporation crystallization system for vacuum evaporation crystallization. The evaporation temperature is 50-120℃ (preferably 80-100℃), and the operating pressure is 20-90kPa (preferably 30-80kPa). A certain concentration ratio is controlled to obtain sodium carbonate monohydrate crystals and primary evaporation mother liquor. The sodium carbonate monohydrate crystals are centrifuged, washed, and dried to obtain a high-purity sodium carbonate product. The mass of the sodium carbonate product accounts for 35-50% (preferably 40-50%) of the total sodium carbonate in the chemical waste salt feed.

[0009] Step 3: The mother liquor obtained from the first evaporation in the above steps is pre-cooled and then transported to the first cooling crystallization system for cooling and crystallization. The cooling and crystallization temperature is -5 to 25°C (preferably 0 to 15°C) to obtain sodium carbonate decahydrate crystals and the first cooling mother liquor. After centrifugation and cleaning, the sodium carbonate decahydrate crystals are added to the solution preparation tank and dissolved in water to prepare a sodium carbonate solution for reuse.

[0010] Step 4: After preheating the primary cooling mother liquor obtained in the above steps to the evaporation temperature, it is transported to the secondary evaporation crystallization system for evaporation and crystallization. The evaporation temperature is 50-130℃ (preferably 80-120℃), and the operating pressure is 20-90kPa (preferably 30-80kPa). The evaporation ratio is controlled to increase the sodium bromide concentration in the mother liquor. When the concentration is increased to the point where the precipitated solid content is 10-30%, a small amount of mixed salt crystals mainly containing sodium carbonate and secondary evaporation mother liquor are obtained. The mixed salt crystals are centrifuged and then transported to the solution preparation tank described in Step 3 for reuse.

[0011] Step 5: After pre-cooling the secondary evaporation mother liquor obtained in the above steps, it is transported to the secondary cooling crystallization system. The cooling crystallization temperature is -5 to 25°C (preferably 0 to 15°C). Cooling crystallization is carried out at low temperature to obtain high-purity sodium bromide dihydrate crystals and secondary cooling mother liquor. The sodium bromide dihydrate crystals are separated by centrifugation, washed and dried to obtain high-purity sodium bromide product.

[0012] Step 6: A small portion of the secondary cooling mother liquor obtained in Step 5) is used as waste liquid and transported to the slag removal system for separate treatment. The remainder is returned to the secondary evaporation and crystallization system in Step 4). The amount of mother liquor extracted is determined based on the content of impurity salt ions in the secondary cooling mother liquor.

[0013] Furthermore, the main components of the chemical waste salt mentioned in step 1 are: sodium carbonate content of 80%–97% (mass percentage, the same below), sodium bromide content of 2.5%–8%, sodium chloride content of approximately 0.1%–3%, etc., and also contain trace heavy metals and a small amount of insoluble matter. Preferably, the main components of the chemical waste salt are: sodium carbonate content of 90%–97%, sodium bromide content of 2%–5%, sodium chloride content of 0.1%–0.5%, with the remainder being trace heavy metals and a small amount of insoluble matter.

[0014] The sodium carbonate content in the mixed salt solution is 10-30% (preferably 15-25%).

[0015] The filtration adopts one or more stages of filtration, and the filter type is one or more of bag filter, cartridge filter, basket filter, fully automatic cleaning filter, and mechanical filter, which can realize continuous production, automatic cleaning and slag discharge.

[0016] Furthermore, the primary evaporation crystallization system described in step 2 includes a sodium carbonate evaporator crystallizer and a sodium carbonate monohydrate centrifuge; the primary cooling crystallization system described in step 3 includes a sodium carbonate cooling crystallizer and a sodium carbonate decahydrate centrifuge; the secondary evaporation crystallization system described in step 4 includes a secondary evaporator crystallizer and a mixed salt centrifuge; and the secondary cooling crystallization system described in step 5 includes a sodium bromide cooling crystallizer and a sodium bromide dihydrate centrifuge.

[0017] Further, in step 3), the sodium carbonate crystallization decahydrate and the sodium carbonate component in the primary cooling mother liquor account for 45-60% and 2-5% of the total sodium carbonate in the chemical waste salt feed, respectively, preferably 46-56% and 3-4%, respectively.

[0018] Further, in step 4), the solids are evaporated, crystallized, and concentrated until the content of the precipitated solids is 20-25%.

[0019] Furthermore, in step 6), 1-5 wt% of the secondary cooling mother liquor is separated and used as produced waste liquid to be transported to the slag removal system for separate treatment.

[0020] Furthermore, the evaporation form of the evaporator crystallizer is any one of forced circulation evaporator, multi-effect evaporator, or MVR evaporator; the evaporator crystallizer is any one of FC continuous crystallizer, OSLO continuous crystallizer, or DTB continuous crystallizer.

[0021] Furthermore, the cooling crystallizer is any one of the OSLO continuous crystallizer, DTB continuous crystallizer, IC continuous crystallizer, or a variation thereof.

[0022] Furthermore, the centrifugal separator is any one of a pusher centrifuge, a sedimentation centrifuge, a filter centrifuge, or a scraper centrifuge, and is equipped with a fresh water and saturated solution cleaning system.

[0023] Furthermore, the sodium carbonate solution preparation tank in step 3 is a stirred tank with an outer jacket or a half-pipe.

[0024] Furthermore, the drying described in steps 2 and 4 is vacuum drying, and the dryer is one of the following types: rake dryer, disc dryer, externally heated rotary calcining furnace, vibrating fluidized bed dryer, or boiling dryer, which can achieve continuous production.

[0025] Furthermore, the secondary steam generated by the sodium carbonate evaporator and the secondary evaporator enters the steam compressor. After being compressed by the compressor, the pressure, temperature, and enthalpy increase, and it is then transported to the heating chamber of the evaporator to heat the feed liquid. After the latent heat of the secondary steam is recovered in the evaporator, the sensible heat of the high-temperature secondary steam condensate is collected to preheat the mixed salt solution and the primary cooling mother liquor. This fully recovers the latent and sensible heat of the secondary steam, minimizing the system's energy consumption. During normal operation, only a small amount of steam needs to be added. After the secondary steam condensate exchanges heat with the feed liquid, it is collected and transported to the dissolving tank for dissolving chemical waste salt, reducing the amount of fresh water used and achieving zero wastewater discharge.

[0026] Furthermore, the high-temperature primary evaporation mother liquor exchanges heat with the primary cooling mother liquor; the high-temperature secondary evaporation mother liquor exchanges heat with the secondary cooling mother liquor. Through a thermal integration scheme, the consumption of thermal and cold energy is reduced.

[0027] Furthermore, the slag removal system described in step 6 can be any one of a rake dryer, a scraper evaporator, or an evaporation crystallization kettle.

[0028] By adopting the above technical solution, compared with the prior art, the present invention has the following advantages and beneficial effects:

[0029] (1) The present invention provides a method for the resource utilization of chemical waste salt in the PTA industry, which can effectively recover sodium carbonate and sodium bromide with high economic value from PTA industry waste salt. The present invention adopts a crystallization process that combines evaporation crystallization and cooling crystallization. By controlling the evaporation ratio, the problem of low purity and high energy consumption of single evaporation crystallization products is overcome, and high-purity sodium carbonate and sodium bromide products are obtained with lower energy consumption.

[0030] (2) This invention does not require the addition of additional raw materials and chemical auxiliaries to assist production, and achieves the resource-based treatment of chemical waste salt at a low cost, resulting in significant environmental and economic benefits. It eliminates the need for complex processes such as resin adsorption, and avoids the large amounts of wastewater generated during membrane separation or resin adsorption elution and regeneration processes, which could cause secondary pollution; this invention can achieve almost zero wastewater discharge.

[0031] (3) In response to the demand for sodium carbonate recycling from PTA manufacturers, sodium carbonate products obtained through low-temperature cooling crystallization are formulated into a recovery liquid for reuse in the production line, saving a significant amount of steam energy and greatly improving the economic efficiency of waste salt resource utilization. Based on changes in the plant's demand for sodium carbonate recycling, the ratio of sodium carbonate sold externally and recycled can be adjusted in a timely manner, maximizing economic benefits while meeting production needs.

[0032] (4) The process of this invention is simple, the equipment is stable, and multiple heat integration methods are adopted to fully recover the latent heat and sensible heat of the secondary steam, thereby minimizing the energy consumption of the system, reducing costs, and improving the competitiveness of enterprises. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the process flow for a method of resource utilization of chemical waste salt in the PTA industry provided by the present invention.

[0034] In the diagram: 1. Dissolving tank; 2. Filter; 3. Sodium carbonate evaporator crystallizer; 4. Sodium carbonate centrifuge I; 5. Sodium carbonate dryer; 6. Sodium carbonate cooling crystallizer; 7. Sodium carbonate centrifuge II; 8. Solution preparation tank; 9. Secondary evaporator crystallizer; 10. Crystallization centrifuge; 11. Sodium bromide cooling crystallizer; 12. Sodium bromide centrifuge; 13. Sodium bromide dryer; 14. Slag removal system. Detailed Implementation

[0035] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0036] like Figure 1 As shown, this invention discloses a method for the resource-based treatment of chemical waste salt from the PTA industry. The chemical waste salt mainly comprises: sodium carbonate content of 80%–97% (mass percentage, the same below), sodium bromide content of 2.5%–8%, and sodium chloride content of approximately 0.1%–3%, etc., and also contains trace amounts of heavy metals and a small amount of insoluble matter. The resource-based treatment method includes the following steps:

[0037] Step 1: First, the chemical waste salt containing sodium carbonate and sodium bromide is dissolved in water in dissolving tank 1 to prepare a mixed salt solution. The sodium carbonate content in the solution is 10-30%, and the temperature of the mixed salt solution is 25-80℃. The solution is then passed through filter 2 to remove heavy metal salts and insoluble matter, yielding filter residue and filtrate.

[0038] Step 2: After preheating the filtrate obtained in the above steps to the evaporation temperature, it is sent to the sodium carbonate evaporator crystallizer 3 for vacuum evaporation crystallization. The evaporation temperature is 50-120℃, the operating pressure is 20-90kPa, and a certain concentration ratio is controlled to obtain sodium carbonate monohydrate crystals and primary evaporation mother liquor. After solid-liquid separation and washing in the sodium carbonate centrifuge 4, the sodium carbonate monohydrate crystals are sent to the sodium carbonate dryer 5 for drying to obtain high-purity sodium carbonate product. The mass of the sodium carbonate product accounts for 35-50% of the total sodium carbonate in the chemical waste salt feed.

[0039] Step 3: The mother liquor obtained from the first evaporation step above is pre-cooled and then sent to a sodium carbonate cooling crystallizer 6 for cooling and crystallization at a temperature of -5 to 25°C, resulting in sodium carbonate decahydrate crystals and a first cooling mother liquor. The sodium carbonate decahydrate crystals are centrifuged and cleaned by a sodium carbonate centrifuge 7, and then dissolved in water in a solution preparation tank 8 to prepare a sodium carbonate solution with a mass fraction of 20 to 25% for reuse. The mass of sodium carbonate in the sodium carbonate decahydrate crystals and the first cooling mother liquor accounts for 45 to 60% and 2 to 5% of the total sodium carbonate in the chemical waste salt feed, respectively.

[0040] Step 4: After preheating the primary cooling mother liquor obtained in the above steps to the evaporation temperature, it is transported to the secondary evaporation crystallizer 9 for vacuum evaporation crystallization. The evaporation temperature is 50-130℃, and the operating pressure is 20-90kPa. The evaporation ratio is controlled to increase the sodium bromide concentration in the mother liquor. When the concentration is reduced to 10-30% of the precipitated solids, a small amount of mixed salt crystals mainly containing sodium carbonate and the secondary evaporation mother liquor are collected. The sodium carbonate is centrifuged by the crystallization centrifuge 10 and then transported to the solution preparation tank 8 for reuse.

[0041] Step 5: After pre-cooling the secondary evaporation mother liquor obtained in the above steps, it is sent to the sodium bromide cooling crystallizer 11. The cooling crystallization temperature is -5 to 25℃. Cooling crystallization is carried out at low temperature to obtain high-purity sodium bromide dihydrate crystals and secondary cooling mother liquor. After centrifugation and washing by the sodium bromide centrifuge 12, the sodium bromide dihydrate crystals are sent to the sodium bromide dryer 13 for vacuum drying to obtain high-purity sodium bromide product.

[0042] Step 6: A small portion of the secondary cooling mother liquor obtained in Step 5) is used as waste liquid and transported to the slag removal system for separate treatment. The remainder is returned to the secondary evaporation and crystallization system in Step 4). The amount of mother liquor extracted is determined based on the content of impurity salt ions in the secondary cooling mother liquor.

[0043] The secondary steam condensate generated by the sodium carbonate evaporator crystallizer 3 exchanges heat with the secondary steam generated by the secondary evaporator crystallizer 9 and the mixed salt solution, recovering the latent heat and sensible heat of the secondary steam for preheating the waste salt solution; the high-temperature primary evaporation mother liquor exchanges heat with the primary cooling mother liquor, recovering the sensible heat of the high-temperature mother liquor for preheating the feed of the secondary evaporator crystallizer 9; the secondary cooling mother liquor exchanges heat with the secondary evaporation mother liquor, recovering the cold energy of the low-temperature mother liquor for precooling the feed of the sodium bromide cooling crystallizer 11; through the thermal integration scheme, the consumption of thermal and cold energy is reduced.

[0044] The saturated steam and secondary steam condensate are collected and summarized after heat exchange with the feed liquid, and then transported to the dissolving tank for dissolving chemical waste salt, reducing the amount of fresh water used and achieving zero wastewater discharge.

[0045] Example 1:

[0046] The PTA industry chemical waste salt resource utilization process in this embodiment is as follows: Figure 1 As shown in the flowchart, this invention is applied to the resource recovery treatment of 40,000 tons / year of chemical waste salt from a PTA production enterprise. The main components of this enterprise's chemical waste salt are: sodium carbonate content 95% (mass percentage, the same below), sodium bromide content 4%, sodium chloride content approximately 0.3%, and trace amounts of heavy metals and a small amount of insoluble matter accounting for 0.7%; the waste salt temperature is approximately 120℃, and the feed rate is 5 t / h. The resource recovery treatment method includes the following steps:

[0047] Step 1: First, the above-mentioned chemical waste salt containing sodium carbonate and sodium bromide is dissolved in water in dissolving tank 1 to prepare a mixed salt solution with a sodium carbonate content of 20% at a temperature of 46°C. The solution is then passed through filter 2 to remove heavy metal salts and insoluble matter, resulting in filter residue and filtrate.

[0048] Step 2: After preheating the filtrate obtained in the above steps to the evaporation temperature, it is sent to the sodium carbonate evaporator crystallizer 3 for vacuum evaporation crystallization. The evaporation temperature is 85℃, the operating pressure is 40kPa, and a certain concentration ratio is controlled to obtain sodium carbonate monohydrate crystals and primary evaporation mother liquor. After solid-liquid separation and washing in the sodium carbonate centrifuge 4, the sodium carbonate monohydrate crystals are sent to the sodium carbonate dryer 5 for drying to obtain high-purity sodium carbonate product. The mass of the sodium carbonate product accounts for 40.8% of the total sodium carbonate in the chemical waste salt feed.

[0049] Step 3: The mother liquor obtained from the first evaporation step above is pre-cooled and then sent to the sodium carbonate cooling crystallizer 6 for cooling and crystallization at a cooling temperature of 5°C, resulting in sodium carbonate decahydrate crystals and a first cooling mother liquor (the sodium carbonate content in the sodium carbonate decahydrate crystals and the first cooling mother liquor accounts for 56% and 3.2% of the total sodium carbonate in the chemical waste salt feed, respectively). After centrifugation and cleaning by the sodium carbonate centrifuge 7, the sodium carbonate decahydrate crystals are dissolved in water in the solution preparation tank 8 to prepare a sodium carbonate solution with a mass fraction of 25% for reuse. The sodium bromide content in the sodium carbonate decahydrate crystals accounts for 6.2% of the total sodium bromide in the chemical waste salt feed.

[0050] Step 4: After preheating the primary cooling mother liquor obtained in the above steps to the evaporation temperature, it is transported to the secondary evaporation crystallizer 9 for vacuum evaporation crystallization. The evaporation temperature is 90℃, the operating pressure is 20kPa, and the evaporation ratio is controlled to increase the sodium bromide concentration in the mother liquor. When the concentration is reduced to 21% of the precipitated solids, the "mixed salt crystals mainly containing sodium carbonate" and the secondary evaporation mother liquor are collected. The "mixed salt crystals mainly containing sodium carbonate" are centrifuged by the crystallization centrifuge 10 and then transported to the solution preparation tank 8 for reuse. The sodium carbonate and sodium bromide components in the "mixed salt crystals mainly containing sodium carbonate" account for approximately 3.2% and 5.86% of the total sodium carbonate and sodium bromide in the chemical waste salt feed, respectively.

[0051] Step 5: The secondary evaporation mother liquor obtained in the above steps is pre-cooled and then sent to the sodium bromide cooling crystallizer 11. The cooling crystallization temperature is 8°C. Cooling crystallization is carried out at a low temperature to obtain high-purity sodium bromide dihydrate crystals and secondary cooling mother liquor (which contains approximately 41.2% high-concentration sodium bromide, as well as concentrated impurities). After centrifugation and washing by the sodium bromide centrifuge 12, the sodium bromide dihydrate crystals are sent to the sodium bromide dryer 13 for vacuum drying to obtain high-purity sodium bromide product. The mass of sodium bromide in the sodium bromide dihydrate crystals accounts for 84.45% of the total sodium bromide in the chemical waste salt feed.

[0052] Step 6: Separate about 2 wt% of the secondary cooling mother liquor obtained in the above steps and use it as produced waste liquid to be transported to the slag removal system for separate treatment. The remainder is returned to the secondary evaporation crystallizer 9 described in step 4 for circulating evaporation.

[0053] Through the above steps, 37,620 tons of sodium carbonate and 1,360 tons of sodium bromide can be recycled annually. Testing shows that the sodium carbonate has a purity of ≥99.2% and a recovery rate of 40.8%, meeting the standards for superior industrial-grade sodium carbonate; the sodium bromide has a purity of ≥99% and a recovery rate of 84.45%, also meeting the standards for superior industrial-grade sodium bromide. All recycled products can be sold on the market.

[0054] Furthermore, in the PTA production field, if the sodium carbonate in the prepared sodium carbonate aqueous solution accounts for more than 97.5% of the total mass of the compounds excluding the solvent water, it meets the usage standards. In the production method of this application, the sodium carbonate solution prepared in step 3) has a sodium carbonate purity of more than 98% of the total mass of the compounds excluding the solvent water, meeting industrial application standards. Moreover, sodium carbonate and sodium bromide are required in the PTA production process; therefore, step 3) of this application, preparing the sodium carbonate solution, can also be considered a recovery of sodium carbonate and sodium bromide components.

[0055] In summary, according to the method steps of this invention, the overall recovery rate of sodium carbonate can reach over 99.9%, and the recovery rate of sodium bromide can reach over (84.45% + 5.86% + 6.2%) = 96.5%.

[0056] The contents described in this specification are merely an enumeration of the implementation forms of the inventive concept, and the scope of protection of this invention should not be regarded as limited to the specific forms described in the embodiments.

Claims

1. A PTA industry chemical waste salt resource treatment method, characterized in that The method comprises the following steps: 1) The PTA industry chemical waste salt mainly contains sodium carbonate and sodium bromide, which is dissolved in water to prepare a mixed salt solution, the dissolving temperature is 25-80℃, the solution is filtered to remove heavy metal salts and insoluble substances, and a filtrate is obtained; According to the weight percentage, the main components of the chemical waste salt in step 1) are as follows: the content of sodium carbonate is 80-97%, the content of sodium bromide is 2.5-8%, the content of sodium chloride is 0.1-3%, and the rest is trace heavy metals and a small amount of insoluble substances; The content of sodium carbonate in the mixed salt solution in step 1) is 10-30%; 2) The filtrate obtained in step 1) is preheated to the evaporation temperature and then sent to a primary evaporation crystallization system for vacuum evaporation crystallization, the evaporation temperature is 50-120℃, the operation pressure is 20-90kPa, and sodium carbonate monohydrate crystals and a primary evaporation mother liquor are obtained by evaporation and concentration, the sodium carbonate monohydrate crystals are centrifuged and washed and then dried to obtain a high-purity sodium carbonate product, and the mass of the sodium carbonate product accounts for 35-50% of the total amount of sodium carbonate in the chemical waste salt feed; 3) The primary evaporation mother liquor obtained in step 2) is pre-cooled and then sent to a primary cooling crystallization system for cooling crystallization, the cooling crystallization temperature is 0-15℃, sodium carbonate decahydrate crystals and a primary cooling mother liquor are obtained, the sodium carbonate decahydrate crystals are centrifuged and washed and then dissolved in water in a solution preparation tank to prepare a sodium carbonate solution for reuse; The mass of the sodium carbonate component in the sodium carbonate decahydrate crystals and the primary cooling mother liquor in step 3) accounts for 45-60% and 2-5% of the total amount of sodium carbonate in the chemical waste salt feed, respectively; 4) The primary cooling mother liquor obtained in step 3) is preheated to the evaporation temperature and then sent to a secondary evaporation crystallization system for evaporation crystallization, the evaporation temperature is 50-130℃, the operation pressure is 20-90kPa, and the concentration of sodium bromide in the upgraded mother liquor is increased by evaporation and concentration, and when the solid content is 10-30%, a small amount of mixed salt crystals mainly containing sodium carbonate and a secondary evaporation mother liquor are obtained; the mixed salt crystals are centrifuged and then sent to the solution preparation tank in step 3) for reuse; 5) The secondary evaporation mother liquor obtained in step 4) is pre-cooled and then sent to a secondary cooling crystallization system, the cooling crystallization temperature is 0-15℃, high-purity sodium bromide dihydrate crystals and a secondary cooling mother liquor are obtained, the sodium bromide dihydrate crystals are centrifuged and washed and then dried to obtain a high-purity sodium bromide product; 6) A small part of the secondary cooling mother liquor obtained in step 5) is separated and sent to a slag removal system for separate treatment as a waste liquid, and the rest is returned to the secondary evaporation crystallization system in step 4), and the amount of the mother liquor to be taken out is determined according to the content of the impurity salt ions in the secondary cooling mother liquor; In step 6), 1-5wt% of the secondary cooling mother liquor is separated and sent to a slag removal system for separate treatment as a waste liquid.

2. The PTA industry chemical waste salt resourceful treatment method according to claim 1, characterized in that According to the weight percentage, the main components of the chemical waste salt in step 1) are as follows: the content of sodium carbonate is 90-97%, the content of sodium bromide is 2-5%, the content of sodium chloride is 0.1-0.5%, and the rest is trace heavy metals and a small amount of insoluble substances.

3. The PTA industry chemical waste salt resourceful treatment method according to claim 1, characterized in that The content of sodium carbonate in the mixed salt dissolving solution is 15-25%, and the dissolving temperature is 30-60 DEG C; the filtration in step 1) is one-stage or multi-stage filtration, and the filter is one or several of bag filter, core filter, basket filter, full-automatic cleaning filter and mechanical filter, which can realize continuous production, automatic cleaning and residue discharge.

4. The PTA industry chemical waste salt resourceful treatment method according to claim 1, characterized in that The evaporation temperature in step 2) is 80-100 DEG C, and the operation pressure is 30-60 kPa; the mass of the obtained sodium carbonate product in step 2) accounts for 40-50% of the total amount of sodium carbonate in the chemical waste salt feed; the primary evaporation crystallization system in step 2) comprises a sodium carbonate evaporation crystallizer, and a sodium carbonate monohydrate centrifugal separator is used for centrifugal separation.

5. The PTA industry chemical waste salt resource treatment method according to claim 1, characterized in that The primary cooling crystallization system in step 3) comprises a sodium carbonate cooling crystallizer, and a sodium carbonate decahydrate centrifugal separator is used for centrifugal separation; the mass of the sodium carbonate decahydrate crystallization and the sodium carbonate component in the primary cooling mother liquor in step 3) accounts for 46-56% and 3-4% of the total amount of sodium carbonate in the chemical waste salt feed, respectively.

6. The PTA industry chemical waste salt resourceful treatment method according to claim 1, characterized in that The evaporation temperature in step 4) is 80-120 DEG C, and the operation pressure is 30-80 kPa; the secondary evaporation crystallization system in step 4) comprises a secondary evaporation crystallizer, and a mixed salt centrifugal separator is used for centrifugal separation; the evaporation crystallization in step 4) is concentrated to a solid content of 20-25%.

7. The PTA industry chemical waste salt resourceful treatment method according to claim 1, characterized in that The secondary cooling crystallization system in step 5) comprises a sodium bromide cooling crystallizer, and a sodium bromide dihydrate centrifugal separator is used for centrifugal separation.

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