Salt separation treatment method and treatment system for mixed solution of sodium oxalate and sodium sulfate

Abstract

The invention relates to the technical field of salt-containing wastewater resource recovery and treatment, and provides a salt separation treatment method and system for a mixed solution of sodium oxalate and sodium sulfate. According to the mass concentration ratio of sodium sulfate to sodium oxalate, the method can provide a salt separation treatment scheme for a mixed salt solution with any composition: if the mass ratio of sodium sulfate to sodium oxalate is lower than a certain numerical value (R), separation is carried out according to a process S2; otherwise, separating according to a process S3. In the two salt separation processes, separation and purification of sodium oxalate and sodium sulfate can be realized by controlling the temperature of feed liquid in the evaporation and cooling processes and taking the density of the feed liquid as a key control index, the industrial grade standard is reached, and high-quality utilization of salt resources is realized while water resource recycling is realized. Meanwhile, based on the salt separation control method, the invention provides a corresponding process treatment system, high-purity anhydrous sodium sulfate and anhydrous sodium oxalate crystals can be obtained through separation, and the method is environmentally friendly and economical.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater resource recovery and treatment, and provides a salt separation treatment method for a mixed solution of sodium oxalate and sodium sulfate and a treatment system thereof. Background Art

[0002] With the development of electric vehicles, mobile and stationary energy storage with rechargeable batteries has become a topic of broad social and economic significance. Lithium-ion battery technology is at the forefront of development, but the massively growing market has put severe pressure on resources and supply chains. Compared with lithium batteries, sodium-ion batteries are a lower-cost alternative that is less susceptible to resource and supply risks. However, due to limitations in electrical capacity and electrical conversion rate, the commercialization of sodium batteries has been slow. In order to solve the problem of poor electrochemical performance of sodium-ion batteries, people have conducted a lot of research on positive electrode materials. Adding sodium oxalate as a supplementary sodium source to sodium-ion battery materials can improve battery cycling performance. Novel Na2Co(C2O4)(SO4) - The xH2O electrode material has good electrochemical properties and is a promising sodium ion electrode material. This new type of sodium battery will produce a large amount of high-salinity wastewater containing Na2C2O4 and Na2SO4 during the production process.

[0003] The application fields of sodium oxalate and sodium sulfate cover many industries such as chemical, textile, papermaking, and medicine, and they are indispensable raw materials for these industries. With the development of technology and changes in market demand, their application scope will be further expanded. However, there is still a lack of in-depth research on the separation of salt resources in mixed solutions of sodium sulfate and sodium oxalate. During the concentration and crystallization process of sodium oxalate and sodium sulfate in wastewater, as the concentration multiple continues to increase, if the salt separation treatment is not properly controlled, the impurity salt will tend to saturate and precipitate in the form of mixed salt, reducing the purity and utilization value of the product, and even increasing the cost of treating waste salt. If the step-by-step separation of the two salts can be controlled, it will not only reduce the cost burden brought by solid waste treatment, but also turn waste into treasure and realize the simultaneous recycling of salt resources and water resources.

[0004] Therefore, the present invention provides a method and a processing system for treating a mixed solution of sodium oxalate and sodium sulfate with any mass concentration ratio, so as to solve the problems of difficulty in purifying salt products, high impure salt content and large amount of solid waste in the mixture of two inorganic salts in the prior art. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for treating a mixed solution of sodium oxalate and sodium sulfate and a treatment system thereof. The separation process is selected by comparing the mass concentration ratio of sodium sulfate and sodium oxalate in the mixed solution of sodium oxalate and sodium sulfate with the R value, and the density of the feed liquid is strictly controlled in the process, so that pure sodium oxalate crystals and sodium sulfate crystals are finally obtained, and the amount of impure salts in the obtained crystals is small, and less solid waste is generated during the separation process.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] A method for separating salt from a mixed solution of sodium oxalate and sodium sulfate, comprising:

[0008] (1) Detecting the mass concentration ratio of sodium oxalate and sodium sulfate in the sodium oxalate and sodium sulfate mixed solution A, and selecting a salt separation process after comparing the mass concentration ratio with the R value, wherein the R value is the mass concentration ratio of sodium sulfate and sodium oxalate in the solution when both sodium sulfate and sodium oxalate reach saturation under the temperature conditions corresponding to the high-temperature evaporation of the sodium oxalate and sodium sulfate mixed solution A in process S2 or process S3, and the value range is 30 to 150. If it is higher than the R value, separation is carried out according to process S3, and if it is lower than the R value, separation is carried out according to process S2.

[0009] (2) Process S2 specifically comprises: evaporating the mixed solution A of sodium oxalate and sodium sulfate at high temperature, controlling the feed liquid temperature to 70-105°C and the density to 1150-1350 kg / m 3 The evaporation is stopped when the sodium oxalate is supersaturated and the sodium sulfate is nearly saturated to obtain a crystal slurry B1, and then the crystal slurry B1 is flash evaporated, cooled to 30-60°C, and then centrifuged to obtain a solid D1 and a mother liquor C1. The solid D1 is washed with salt and dried to obtain sodium oxalate crystals; the mother liquor C1 is evaporated at high temperature to control the feed liquid temperature to 70-105°C and the density to 1280-1350 kg / m 3 When the evaporation is stopped, the evaporation slurry B2 is obtained, and the solid D2 and the mother liquor C2 are obtained by centrifugation. The solid D2 is washed with salt and dried to obtain sodium sulfate crystals, and the mother liquor C2 is refluxed and mixed with the slurry B1 for circulation;

[0010] (3) Process S3 specifically comprises: performing high temperature evaporation on the mixed solution A of sodium oxalate and sodium sulfate, controlling the feed liquid temperature to be 70-105°C and the density to be 1280-1350 kg / m 3The evaporation is stopped at 30 to 60°C to obtain a slurry B3 in a supersaturated state of sodium sulfate and a nearly saturated state of sodium oxalate. The slurry B3 is centrifuged to obtain a solid D3 and a mother liquor C3. The solid D3 is washed with salt and dried to obtain sodium sulfate crystals. The mother liquor C3 is flash evaporated and cooled to 30 to 60°C to obtain a slurry B4. The slurry B4 is centrifuged to obtain a solid D4 and a mother liquor C4. The solid D4 is washed with salt and dried to obtain sodium oxalate crystals. The mother liquor C4 is refluxed to circulate with the mixed solution A of sodium oxalate and sodium sulfate.

[0011] The salt separation treatment method of the sodium oxalate and sodium sulfate mixed solution A provided by the present invention, before selecting the salt separation treatment, the mass ratio of sodium sulfate and sodium oxalate in the system should be determined. The mixed solution treatment process of the present invention is selected based on the mass concentration ratio of sodium sulfate and sodium oxalate in the sodium oxalate and sodium sulfate mixed solution A under the temperature conditions corresponding to high-temperature evaporation.

[0012] The present invention provides a salt separation treatment method for a mixed solution A of sodium oxalate and sodium sulfate. In the process S2, if the feed liquid temperature and density are lower than the temperature and density, the sodium oxalate in the solution cannot be completely precipitated; if they are higher than the temperature and density, the precipitated solid contains sodium sulfate solid; if the cooling temperature and density are higher than the temperature, the sodium oxalate cannot be completely precipitated.

[0013] The present invention provides a method for separating the salt of a mixed solution A of sodium oxalate and sodium sulfate. In the process S3, if the feed liquid temperature and density are higher than the temperature and density, sodium oxalate is precipitated in the solution; if the feed liquid temperature and density are lower than the temperature and density, sodium sulfate cannot be completely precipitated in the solution; if the cooling temperature and density are higher than the temperature range, sodium oxalate cannot be completely precipitated.

[0014] Furthermore, the evaporation of the sodium oxalate and sodium sulfate mixed solution A and the mother liquor C1 in the processes S2 and S3 adopts mechanical vapor recompression (MVR) technology or multiple-effect evaporation technology.

[0015] Furthermore, in the processes S2 and S3, the cooling of the slurry B1 and the mother liquor C3 adopts cooling crystallization technology or flash cooling crystallization technology.

[0016] Furthermore, the total mass concentration of sodium oxalate and sodium sulfate in the sodium oxalate and sodium sulfate mixed solution A accounts for more than 90% of the total soluble solid content in the solution.

[0017] On the other hand, the present invention provides a processing system for the salt separation treatment method, including a process S2 processing system and a process S3 processing system, wherein the process S2 processing system includes a first evaporator, a second evaporator, a first cooling crystallizer, a first centrifuge, a second centrifuge, a first salt washing tank, a second salt washing tank, a first dryer and a second dryer, wherein the first evaporator is used to evaporate a solution A mixed with sodium oxalate and sodium sulfate, and obtain a crystal slurry B1 in a supersaturated state of sodium oxalate and a state close to saturation of sodium sulfate; the second evaporator is used to evaporate the mother liquor C1 obtained by centrifugation in the first centrifuge to precipitate a solid D2; the first cooling crystallizer is used to cool and crystallize the crystal slurry B1 / reflux mother liquor C2, and continue to precipitate out sodium oxalate crystals; the first centrifuge is used to centrifuge the crystal slurry B1 to obtain solid D1 and mother liquor C1; the second centrifuge is used to centrifuge the crystal slurry B2 to obtain solid D2 and reflux mother liquor C2; the first salt washing tank is used to wash the solid D1 separated by the first centrifuge to obtain purified sodium oxalate crystals; the second salt washing tank is used to wash the solid D2 separated by the second centrifuge to obtain purified sodium sulfate crystals; the first dryer is used to dry the sodium oxalate crystals obtained by the first salt washing tank to obtain dry sodium oxalate crystal products; the second dryer is used to dry the sodium sulfate crystals obtained by the second centrifuge to obtain dry sodium sulfate crystals.

[0018] The processing system of the process S3 includes a third evaporator, a second cooling crystallizer, a third centrifuge, a fourth centrifuge, a third salt washing tank, a fourth salt washing tank, a third dryer and a fourth dryer. The third evaporator is used to evaporate the mixed solution A of sodium oxalate and sodium sulfate, and obtain a crystal slurry B3 in which sodium sulfate is supersaturated and sodium oxalate is nearly saturated; the second cooling crystallizer is used to cool and crystallize the mother liquor C3 to precipitate sodium oxalate crystals; the third centrifuge is used to centrifuge the crystal slurry B3 to obtain solid D3 and mother liquor C3; the fourth centrifuge is used to centrifuge the crystal slurry B4 obtained by the second cooling crystallizer to obtain solid D4; the third salt washing tank is used to wash the solid D3 to obtain purified sodium sulfate crystals; the fourth salt washing tank is used to wash the solid D4 to obtain purified sodium oxalate crystals; the third dryer is used to dry the washed sodium sulfate crystals to obtain a dry sodium sulfate product; the fourth dryer is used to dry the washed sodium oxalate crystals to obtain a dry sodium oxalate product;

[0019] Furthermore, the processing system also includes: a raw material tank, a first mother liquor tank and a second mother liquor tank, the raw material tank is used to store a mixed raw material liquid of sodium oxalate and sodium sulfate; the first mother liquor tank is used to recover the mother liquor C2 in the process S2 and transport it to the first cooling crystallizer; the second mother liquor tank is used to recover the mother liquor C4 in the process S3 and transport it to the third evaporator.

[0020] Furthermore, the first evaporator, the second evaporator and the third evaporator are MVR evaporators.

[0021] Furthermore, the first cooling crystallizer and the second cooling crystallizer are flash cooling crystallizers or cooling crystallization kettles.

[0022] Furthermore, in the process S2 treatment system, the first salt washing tank and the second salt washing tank can be disposed of separately or together.

[0023] Furthermore, in the salt separation method of the mixed solution of sodium oxalate and sodium sulfate, the mother liquor reflux can be carried out in the form of full reflux or partial reflux.

[0024] Furthermore, the sodium oxalate product obtained by crystallization in the salt separation treatment method of the mixed solution of sodium oxalate and sodium sulfate is anhydrous sodium oxalate crystals, and the sodium sulfate product obtained by crystallization is anhydrous sodium sulfate crystals.

[0025] The advantages and positive effects of the present invention are:

[0026] (1) The salt separation treatment method of the mixed solution of sodium oxalate and sodium sulfate provided by the present invention is based on the concentration ratio of sodium sulfate and sodium oxalate in the mixed solution, and the classification treatment is carried out; by controlling the density of the concentrated end point solution, while one salt is precipitated, the other salt is controlled not to precipitate in the solution (unsaturated state), and the separation and preparation of sodium oxalate crystals and sodium sulfate crystals are realized by combining evaporation crystallization technology and cooling crystallization technology, and sodium oxalate and sodium sulfate with higher purity can be separated, and the sodium sulfate reuse value is higher. When used to treat mixed salts or saline wastewater of sodium oxalate and sodium sulfate, the cost of solid waste treatment can be reduced, and efficient utilization of water resources and salt resources can be achieved; at the same time, the mother liquor treated by the process described in the present invention can be mixed with upstream materials in a reflux manner to achieve circulation, and the evaporated condensed water can be reused in other production sections to achieve "zero emission" or "near zero emission" in the experimental process. The product of the treatment method described in the present invention has less salt and less solid waste, and has minimal environmental pollution.

[0027] (2) The treatment system of the sodium oxalate and sodium sulfate mixed solution provided by the present invention is a set of process treatment system composed of the treatment method of the sodium oxalate and sodium sulfate mixed wastewater of the present invention, which can separate anhydrous sodium oxalate crystals and anhydrous sodium sulfate crystals with higher purity, has the value of conventional industrial production, and can realize the resource utilization of wastewater and waste salt, reduce waste discharge, and meet the needs of green chemical development. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a process flow chart of the salt separation treatment method of the mixed solution of sodium oxalate and sodium sulfate provided by the present invention;

[0029] Figure 2It is a schematic diagram of the structure of a treatment system corresponding to process S2 of the treatment method using a mixed solution of sodium oxalate and sodium sulfate provided by the present invention;

[0030] Figure 3 It is a schematic diagram of the structure of a treatment system corresponding to process S3 of the treatment method using a mixed solution of sodium oxalate and sodium sulfate provided by the present invention;

[0031] Reference numerals:

[0032] 1: raw material tank; 2: first evaporator; 3: first cooling crystallizer; 4: first centrifuge; 5: second evaporator; 6: second centrifuge; 7: second salt washing tank; 8: second dryer; 9: first salt washing tank; 10: first dryer; 11: first mother liquid tank; 12: third evaporator; 13: third centrifuge; 14: third salt washing tank; 15: third dryer; 16: second cooling crystallizer; 17: fourth centrifuge; 18: fourth salt washing tank; 19: fourth dryer; 20: second mother liquid tank. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Embodiment 1:

[0035] A method for separating salt from a mixed solution of sodium oxalate and sodium sulfate, comprising:

[0036] (1) The concentrations of the two salts in the sodium oxalate and sodium sulfate mixed solution A are quantitatively analyzed by a chemical analysis method. The total mass concentration of the two salts of sodium oxalate and sodium sulfate in the sodium oxalate and sodium sulfate mixed solution A accounts for 95% of the total soluble solid content in the solution, and the mass concentration ratio of sodium sulfate to sodium oxalate is 20. The R value at the high-temperature evaporation temperature of 70° C. is 58. If the value is lower than the R value, process S2 is selected for treatment;

[0037] (2) Process S2 specifically comprises: using an MVR evaporator to evaporate and concentrate the mixed solution A of sodium oxalate and sodium sulfate, controlling the feed liquid temperature to 70°C and the density to 1350 kg / m 3 When , evaporation is stopped, and a slurry B1 in which sodium oxalate is supersaturated and sodium sulfate is unsaturated is obtained;

[0038] The slurry B1 is transported to the first cooling crystallizer 3 (DTB flash cooling crystallizer), cooled to 30°C, and sodium oxalate crystals are continuously precipitated. The cooled slurry is centrifuged to obtain solid D1 and mother liquor C1;

[0039] The solid D1 is washed with salt in a first salt washing tank 9 to obtain purified sodium oxalate crystals, and then passed through a first dryer 10 to obtain a dry anhydrous sodium oxalate product;

[0040] The mother liquid C1 obtained by the first centrifuge 4 is sent to the second evaporator 5, and the feed liquid temperature is controlled to be 70°C and the density is 1280kg / m 3 When the evaporation is stopped to obtain the slurry B2, the evaporated slurry B2 is sent to the second centrifuge 6, and the solid D2 and the mother liquor C2 are obtained by centrifugation. The mother liquor is stored in the mother liquor tank and circulated back into the slurry B1 for circulation;

[0041] The solid D2 obtained by centrifugation is washed in the second salt washing tank 7 and dried in the second dryer 8 to obtain anhydrous sodium sulfate product.

[0042] The purities of the anhydrous sodium oxalate and anhydrous sodium sulfate products obtained in step S2 are 99.3% and 98.9% respectively.

[0043] Embodiment 2:

[0044] The mixed solution of sodium oxalate and sodium sulfate to be treated is consistent with that in Example 1. The R value is 29 when the high-temperature evaporation temperature is 105°C. Process S2 is used for treatment. The mixed solution A of sodium oxalate and sodium sulfate is evaporated and concentrated by MVR evaporator to control the feed liquid temperature to 105°C and the density to 1150kg / m 3 When the evaporation is stopped, the evaporation is stopped, and a slurry B1 in which sodium oxalate is supersaturated and sodium sulfate is unsaturated is obtained; the slurry B1 is transported to the first cooling crystallizer 3 (DTB flash cooling crystallizer), cooled to 60°C, sodium oxalate crystals continue to precipitate, and the cooled slurry is centrifuged to obtain solid D1 and mother liquor C1. The remaining operations are consistent with those in Example 1. Finally, the purities of the obtained anhydrous sodium oxalate and anhydrous sodium sulfate products can reach 98.9% and 98.4%, respectively.

[0045] Embodiment 3:

[0046] A method for separating salt from a mixed solution of sodium oxalate and sodium sulfate, comprising:

[0047] (1) The concentrations of the two salts in the mixed solution A of sodium oxalate and sodium sulfate are quantitatively analyzed by chemical analysis method. The total mass concentration of the two salts of sodium oxalate and sodium sulfate in the solution to be treated accounts for 90% of the total soluble solid content in the solution. The concentration ratio of sodium sulfate to sodium oxalate in the salt-containing solution is determined to be 300, and the R value when the high-temperature evaporation temperature is 70° C. is 58. If the value is higher than the R value, process S3 is selected for treatment;

[0048] (2) Process S3 specifically comprises: using an MVR evaporator to evaporate and concentrate the mixed solution A of sodium oxalate and sodium sulfate, controlling the feed liquid temperature to 70°C and the density to 1350 kg / m 3 When the evaporation is stopped, a slurry B3 in which sodium sulfate is supersaturated and sodium oxalate is unsaturated is obtained;

[0049] The slurry B3 is transported to the third centrifuge 13 for centrifugal separation to obtain solid D3 and mother liquor C3. The solid D3 is a crude sodium sulfate crystal product. After being washed with salt in the third salt washing tank 14 and dried in the third dryer 15, an anhydrous sodium sulfate crystal product is obtained.

[0050] The mother liquor C3 is transported to the second cooling crystallizer 16 (DTB flash cooling crystallizer), flash cooled to 30°C to obtain slurry B4, the slurry B4 is centrifuged to obtain solid D4 and mother liquor C4, and the mother liquor C4 is refluxed to circulate with the mixed solution A of sodium oxalate and sodium sulfate;

[0051] The solid D4 is a crude sodium oxalate crystal product, which is washed with salt in a fourth salt washing tank 18 and dried in a fourth dryer 19 to obtain an anhydrous sodium oxalate crystal product.

[0052] The purities of the anhydrous sodium oxalate and anhydrous sodium sulfate products obtained through process S3 can reach 98.4% and 95.4% respectively.

[0053] Embodiment 4:

[0054] The mixed solution of sodium oxalate and sodium sulfate to be treated A is consistent with that in Example 3. The R value is 29 when the high-temperature evaporation temperature is 105°C. The mixed solution of sodium oxalate and sodium sulfate is evaporated and concentrated by MVR evaporator. The feed liquid temperature is controlled to be 105°C and the density is 1280 kg / m 3 When the evaporation is stopped, the slurry B3 in which the sodium sulfate is supersaturated and the sodium oxalate is unsaturated is obtained; the slurry B3 is transported to the third centrifuge 13, and centrifuged to obtain solid D3 and mother liquor C3, and the mother liquor C3 is transported to the second cooling crystallizer 16 (DTB flash cooling crystallizer), flash cooled to 60°C, to obtain slurry B4, and the slurry B4 is centrifuged to obtain solid D4 and mother liquor C4, and the mother liquor C4 is refluxed to the sodium oxalate and sodium sulfate mixed solution A. The remaining operations are consistent with those in Example 3. Finally, the purities of the obtained anhydrous sodium oxalate and anhydrous sodium sulfate products can reach 98.3% and 93.1%, respectively.

[0055] Comparative Example 1:

[0056] The mixed solution A of sodium oxalate and sodium sulfate to be treated is consistent with that in Example 2, and is treated by process S2. The mixed solution A of sodium oxalate and sodium sulfate is evaporated and concentrated by an MVR evaporator to control the feed liquid temperature to 105°C and the density to 1101 kg / m 3 When the evaporation is stopped, the evaporation is stopped, and a slurry B1 in a supersaturated state of sodium oxalate and an unsaturated state of sodium sulfate is obtained; the slurry B1 is transported to the first cooling crystallizer 3 (DTB flash cooling crystallizer), cooled to 60°C, and sodium oxalate crystals continue to precipitate, and the cooled slurry B2 is centrifuged to obtain solid D1 and mother liquor C2. The remaining operations are consistent with those in Example 1. Finally, the first evaporator (MVR evaporator) of process S2 does not evaporate completely, and sodium oxalate remains in the mother liquor C1, resulting in a decrease in yield and a decrease in the purity of anhydrous sodium sulfate. The purities of anhydrous sodium oxalate and anhydrous sodium sulfate products are 98.5% and 85.3%, respectively.

[0057] Comparative Example 2:

[0058] The mixed solution of sodium oxalate and sodium sulfate to be treated A is consistent with that in Example 3, and is treated by process S3. The mixed solution of sodium oxalate and sodium sulfate is evaporated and concentrated by MVR evaporator to control the feed liquid temperature to 70°C and the density to 1405 kg / m 3 , and obtain supersaturated slurry B3; convey the slurry B3 to the third centrifuge 13, centrifuge to obtain solid D3 and mother liquor C3, solid D3 is crude sodium sulfate crystal, washed with salt in the third salt washing tank 14, centrifuged and dried in the third dryer 15 to obtain anhydrous sodium sulfate crystal product; convey the mother liquor C3 to the second cooling crystallizer 16 (DTB flash cooling crystallizer), flash cool to 40 ° C, density 1405kg / m 3 Excessive evaporation caused sodium oxalate crystals to precipitate during the evaporation stage, and no sodium oxalate crystals were obtained. Finally, the anhydrous sodium sulfate product was obtained with a purity of 98.2%.

[0059] A processing system for realizing a salt separation treatment method of a mixed solution of sodium oxalate and sodium sulfate, comprising a raw material tank 1, a process S2 processing system and a process S3 processing system, wherein the process S2 processing system comprises a first evaporator 2, a second evaporator 5, a first cooling crystallizer 3, a first centrifuge 4, a first mother liquid tank 11, a second centrifuge 6, a first salt washing tank 9, a second salt washing tank 7, a first dryer 10 and a second dryer 8, such as Figure 2The schematic diagram of the processing system structure of process S2 shown in the figure, the mixed solution A of sodium oxalate and sodium sulfate in the raw material tank 1 enters the first evaporator 2 for high-temperature evaporation to obtain a supersaturated state of sodium oxalate and a slurry B1 of sodium sulfate close to a saturated state; the slurry B1 of the first evaporator 2 and the reflux mother liquor C2 enter the first cooling crystallizer 3 for cooling and crystallization, and sodium oxalate crystals continue to precipitate; the first centrifuge 4 centrifuges the cooled slurry B1 to obtain a solid D1 and a mother liquor C1; the first salt washing tank 9 washes the solid D1 separated by the first centrifuge 4 to obtain purified sodium oxalate crystals, and the first dryer 10 The sodium oxalate crystals obtained by the first salt washing tank 9 are dried to obtain anhydrous sodium oxalate crystal products; the second evaporator 5 evaporates the mother liquor C1 obtained by centrifugation in the first centrifuge 4 to obtain crystal slurry B2, the second centrifuge 6 centrifuges the crystal slurry B2 to obtain solid D2 and reflux mother liquor C2; the second salt washing tank 7 washes the solid D2 separated by the second centrifuge 6 to obtain purified sodium sulfate crystals; the second dryer 8 is used to dry the sodium sulfate crystals obtained by the second centrifuge 6 to obtain anhydrous sodium sulfate crystals; the first mother liquor tank 11 recovers the mother liquor C2 and transports it to the first cooling crystallizer 3.

[0060] like Figure 3 The schematic diagram of the processing system structure of process S3 is shown, and the processing system of process S3 includes a third evaporator 12, a second cooling crystallizer 16, a third centrifuge 13, a fourth centrifuge 17, a third salt washing tank 14, a fourth salt washing tank 18, a third dryer 15 and a fourth dryer 19. The mixed solution A of sodium oxalate and sodium sulfate in the raw material tank 1 enters the third evaporator 12 for evaporation, and obtains a slurry B3 with supersaturated sodium sulfate and nearly saturated sodium oxalate; the third centrifuge 13 centrifuges the slurry B3 to obtain a solid D3 and a mother liquor C3; the third salt washing tank 14 The solid D3 is washed to obtain purified sodium sulfate crystals, and the third dryer 15 dries the washed sodium sulfate crystals to obtain a dry anhydrous sodium sulfate product; the second cooling crystallizer 16 cools and crystallizes the mother liquor C3, precipitates sodium oxalate crystals to obtain crystal slurry B4; the fourth centrifuge 17 centrifuges the crystal slurry B4 obtained by the second cooling crystallizer 16 to obtain solid D4 and mother liquor C4; the fourth salt washing tank 18 washes the solid D4 to obtain purified sodium oxalate crystals; the fourth dryer 19 dries the washed sodium oxalate crystals to obtain anhydrous sodium oxalate product. The second mother liquor tank 20 recovers the mother liquor C4 and transports it to the third evaporator 12.

[0061] The processing system of the sodium oxalate and sodium sulfate mixed solution provided in the specific implementation case of the present invention is a set of process processing system composed of an evaporator, a cooling crystallizer, a centrifuge, a salt washing tank, a dryer and a mother liquor recovery tank. Through the operation steps of evaporation, cooling crystallization, centrifugal separation, salt washing, purification and drying, it can realize the step-by-step separation and preparation of sodium oxalate and sodium sulfate crystal products with higher purity. The reuse value of the two salt resources is high, and it has good environmental and economic benefits.

[0062] In the embodiment of the present invention, the evaporator is an MVR evaporator, and other evaporators may also be used. The cooling crystallizer is a DTB flash cooling crystallizer or a cooling crystallization kettle, and other cooling crystallizers may also be used.

[0063] After obtaining crude sodium oxalate crystals and crude sodium sulfate crystals in the embodiment of the present invention, the process also includes: washing the crude sodium oxalate crystals and crude sodium sulfate crystals to remove solid impurities adsorbed on the surface and entrained mother liquor, then centrifuging the obtained slurry, and drying the obtained solid to obtain sodium oxalate crystals and sodium sulfate crystals with high purity. The purpose of this process is to further improve the purity of the obtained crystals and obtain sodium oxalate and sodium sulfate products with high purity. According to the above steps, the sodium oxalate and sodium sulfate mixed salts are separated and purified, and the prepared sodium oxalate and sodium sulfate have high purity, and the solid phase purity obtained after washing the salt can reach more than 98%.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating a mixed solution of sodium oxalate and sodium sulfate by separating salts, characterized in that: include: (1) detecting the mass concentration ratio of sodium sulfate to sodium oxalate in the sodium oxalate and sodium sulfate mixed solution A, comparing the mass concentration ratio with the R value and selecting a salt separation process; if the mass concentration ratio is lower than the R value, separation is performed according to process S2; if the mass concentration ratio is higher than the R value, separation is performed according to process S3, wherein the R value is the mass concentration ratio of sodium sulfate to sodium oxalate in the solution when both sodium sulfate and sodium oxalate reach saturation under the temperature conditions corresponding to the high-temperature evaporation of the sodium oxalate and sodium sulfate mixed solution A in process S2 or process S3, and the value range is 30 to 150; (2) Process S2 specifically comprises: evaporating the mixed solution A of sodium oxalate and sodium sulfate at high temperature, controlling the feed liquid temperature to 70-105°C and the density to 1150-1350 kg / m 3 The evaporation is stopped when the sodium oxalate is supersaturated and the sodium sulfate is nearly saturated to obtain a crystal slurry B1, and then the crystal slurry B1 is flash evaporated, cooled to 30-60°C, and centrifuged to obtain a solid D1 and a mother liquor C1. The solid D1 is washed with salt and dried to obtain sodium oxalate crystals; the mother liquor C1 is evaporated to control the feed liquid temperature to 70-105°C and the density to 1280-1350 kg / m 3 When the evaporation is stopped, the crystal slurry B2 is obtained, and the solid D2 and the mother liquor C2 are obtained by centrifugation. The solid D2 is washed with salt and dried to obtain sodium sulfate crystals, and the mother liquor C2 is refluxed and mixed with the crystal slurry B1 for circulation; (3) Process S3 specifically comprises: performing high temperature evaporation on the mixed solution A of sodium oxalate and sodium sulfate, controlling the feed liquid temperature to be 70-105°C and the density to be 1280-1350 kg / m 3 The evaporation is stopped when evaporation is stopped to obtain a slurry B3 in a supersaturated state of sodium sulfate and a nearly saturated state of sodium oxalate. The slurry B3 is centrifuged to obtain a solid D3 and a mother liquor C3. The mother liquor C3 is flash evaporated and cooled to 30-60°C to obtain a slurry B4. Solid D4 and mother liquor C4 are obtained by centrifugation. Solid D3 and solid D4 are washed with salt and dried to obtain sodium sulfate crystals and sodium oxalate crystals, respectively. The mother liquor C4 is refluxed and mixed with the sodium oxalate and sodium sulfate mixed solution A and then circulated.

2. The salt separation treatment method according to claim 1, characterized in that: The operations of process S2 and process S3 can selectively perform the following treatments on the obtained sodium oxalate crystals and sodium sulfate crystals, respectively, based on the impurity content of the mixed solution and the product standards: washing the sodium oxalate crystals and sodium sulfate crystals, and drying the washed slurry to obtain a crystal product, and the obtained sodium oxalate and sodium sulfate products meet industrial grade standards, respectively.

3. The salt separation treatment method according to claim 1, characterized in that: In the process S2 and the process S3, the high temperature evaporation of the sodium oxalate and sodium sulfate mixed solution A and the mother solution C1 adopts mechanical vapor recompression technology or multiple effect evaporation technology.

4. The salt separation treatment method according to claim 1, characterized in that: In the process S2 and the process S3, the cooling of the slurry B1 and the mother liquor C3 adopts the cooling crystallization technology or the flash cooling crystallization technology.

5. The salt separation treatment method according to claim 1, characterized in that: The total mass concentration of sodium oxalate and sodium sulfate in the sodium oxalate and sodium sulfate mixed solution A accounts for more than 90% of the total soluble solid content in the solution.

6. A treatment system for the salt separation treatment method according to any one of claims 1 to 3, characterized in that: Including process S2 processing system and process S3 processing system, The process S2 treatment system comprises: A first evaporator (2) evaporates a solution A containing sodium oxalate and sodium sulfate, and obtains a slurry B1 in which sodium oxalate is in a supersaturated state and sodium sulfate is in a nearly saturated state; The first cooling crystallizer (3) cools and crystallizes the slurry B1 / refluxing mother liquor C2 to continue precipitating sodium oxalate crystals; A first centrifuge (4) is used to centrifuge the slurry B1 to obtain a solid D1 and a mother liquor C1; The first salt washing tank (9) washes the solid D1 separated by the first centrifuge (4) to obtain purified sodium oxalate crystals. A first dryer (10) is used to dry the sodium oxalate crystals obtained from the first salt washing tank (9) to obtain an anhydrous sodium oxalate crystal product; A second evaporator (5) evaporates the mother liquor C1 obtained by centrifugation in the first centrifuge (4) to obtain a slurry B2, which is then centrifuged to obtain a solid D2 and a mother liquor C2; A second centrifuge (6) is used to centrifuge the slurry B2 to obtain a solid D2 and a reflux mother liquor C2; A second salt washing tank (7) is used to wash the solid D2 separated by the second centrifuge (6) to obtain purified sodium sulfate crystals; a second dryer (8) for drying the sodium sulfate crystals obtained by the second centrifuge (6) to obtain anhydrous sodium sulfate crystals; The process S3 treatment system comprises: A third evaporator (12) evaporates the mixed solution A of sodium oxalate and sodium sulfate to obtain a slurry B3 in which sodium sulfate is supersaturated and sodium oxalate is nearly saturated; a third centrifuge (13) for centrifuging the slurry B3 to obtain a solid D3 and a mother liquor C3; The third salt washing tank (14) washes the solid D3 to obtain purified sodium sulfate crystals. a third dryer (15) for drying the washed sodium sulfate crystals to obtain a dry anhydrous sodium sulfate product; A second cooling crystallizer (16) is used to cool and crystallize the mother liquor C3 to precipitate sodium oxalate crystals to obtain slurry B4; A fourth centrifuge (17) is used to centrifuge the slurry B4 obtained by the second cooling crystallizer (16) to obtain solid D4 and mother liquor C4; A fourth salt washing tank (18) is used to wash the solid D4 to obtain purified sodium oxalate crystals; The fourth dryer (19) dries the washed sodium oxalate crystals to obtain anhydrous sodium oxalate product.

7. The processing system according to claim 6, characterized in that Also includes: A raw material tank (1), used for storing a mixed solution A of sodium oxalate and sodium sulfate; A first mother liquid tank (11), used for recovering the mother liquid C2 in the step S2 and conveying it to the first cooling crystallizer (3); The second mother liquid tank (20) is used to recover the mother liquid C4 in the process S3 and transport it to the third evaporator (12).

8. The processing system according to claim 6, characterized in that The evaporator is an MVR evaporator.

9. The processing system according to claim 6, characterized in that The first cooling crystallizer (3) and the second cooling crystallizer (16) are flash cooling crystallizers or cooling crystallization kettles.

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