Method for treating high-salinity wastewater and separating sodium sulfate salt
By adding sodium persulfate and polymerized iron sulfate solution to high-salt wastewater, the pH value is controlled and the high-temperature nitrification and low-temperature salt treatment is carried out, the problems of COD and carbonate and bicarbonate impurities in high-salt wastewater are solved, and the sodium sulfate salt is efficiently separated and the treatment cost is reduced, thereby avoiding iron ion pollution.
Patent Information
- Application Number
- CN202510557303.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-29
- Publication Date
- 2025-08-05
AI Technical Summary
The high content of COD, carbonate and bicarbonate impurities in high-salt wastewater leads to poor salt purity, poor color and odor after treatment. It is impossible to obtain economically valuable salts in the MVR evaporation system, and there is a risk of secondary pollution of iron ions.
Add sodium persulfate and polymerized iron sulfate solution to the wastewater, adjust the pH to 12-13, and then keep the heat in. After filtration, use dilute sulfuric acid to adjust the pH to acidity, then use sodium hydroxide to adjust it to 6-7. Finally, use high-temperature nitrification and low-temperature salt method to evaporate and crystallize, control the pH value during the reaction to remove impurities and separate the sodium sulfate salt.
The COD content in the wastewater is effectively reduced to below 150mg/L, and the removal rate of carbonate and bicarbonate is 96%, obtaining sodium sulfate salt with a purity of ≥98%, avoiding secondary pollution of iron ions, and low treatment cost and suitable for complex organic wastewater.
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Abstract
Description
Technical Field
[0001] The invention relates to the technical field of high-COD high-salt wastewater treatment, in particular to a method for treating high-salt wastewater and separating sodium sulfate. Background Art
[0002] Wastewater from the coal tar fractionation, needle coke pretreatment, and delayed coking processes, combined with trihydroxy wastewater, butyl octanol distillate, ammonia-containing wastewater, and vaporizer wastewater, is a complex mixture containing volatile phenols, polycyclic aromatic hydrocarbons, and heterocyclic compounds such as oxygen, sulfur, and nitrogen. Concentrations of COD, ammonia nitrogen, sulfide, phenol, and cyanide are high, and the organic composition is complex. After undergoing multiple treatment steps, including biochemical treatment, oxidation treatment, and reverse osmosis, this mixed wastewater enters the MVR evaporation process. The primary components of the wastewater entering the MVR evaporation process are chloride ions, sodium ions, sulfate, carbonate, and bicarbonate. However, the wastewater at this stage is highly acidic, has a poor color, an odor, and a high COD content. The salt obtained after treatment in the MVR evaporation system is of poor purity, color, and odor, making it impossible to obtain economically valuable salt. Therefore, this wastewater must be outsourced for treatment as solid waste, increasing treatment costs.
[0003] Based on the perspectives of resource recovery and solid waste reduction, the present invention proposes a method for treating high-salt wastewater and separating sodium sulfate salt. Summary of the Invention
[0004] The present invention aims to provide a method for treating high-salt wastewater and separating sodium sulfate. By treating the wastewater before entering the MVR process, the contents of COD, carbonate and bicarbonate impurities in the wastewater are reduced, and sodium sulfate that meets national standards is separated. In addition, the wastewater treated by the present invention will not have secondary contamination by iron ions.
[0005] In order to solve the above technical problems, the present invention provides a method for treating high-salt wastewater and separating sodium sulfate salt, the method comprising the following steps:
[0006] S1. Adding 2-4% sodium persulfate solution and 1-2% polyferric sulfate solution to wastewater, and then adjusting the pH of the wastewater to 12-13 with 30% sodium hydroxide solution; wherein the main salt component of the wastewater is sodium sulfate, and its pH is 8-9, and the main impurities in the wastewater are COD, carbonate and bicarbonate, and the COD content in the wastewater is 2000mg / L-3500mg / L;
[0007] S2, after the above-treated wastewater is kept at 80-90°C for 2-3 hours, the wastewater is cooled to room temperature and then filtered;
[0008] S3, using 10% dilute sulfuric acid to adjust the pH of the wastewater treated in S2 to acidic, and keep it at 80-90°C for 30-60 minutes, and finally using 30% sodium hydroxide solution to adjust the pH of the wastewater to 6-7;
[0009] S4. The COD content in the wastewater after treatment in S3 was tested in accordance with the national standard HJ828-2017. The COD content in the wastewater was less than 150 mg / L. The carbonate and bicarbonate contents in the wastewater after treatment in S3 were tested in accordance with the national standard DZT0064.49-2021.
[0010] S5. Using the high-temperature nitrate and low-temperature salt method, the wastewater tested in S4 is evaporated, crystallized, and dried at 95-100°C to obtain sodium sulfate;
[0011] S6. The sodium sulfate salt obtained by drying in S5 is tested in accordance with the national standard GB / T 6009-2014 to obtain sodium sulfate salt that meets the national standard Class II first-class product (purity>98%) or above.
[0012] Preferably, the content of polyferric sulfate in the polyferric sulfate solution of S1 is ≥11%.
[0013] Preferably, the ratio of the sodium persulfate solution to the polyferric sulfate solution in S1 is 2:1, and the sum of the amounts of the sodium persulfate solution and the polyferric sulfate solution is less than or equal to 10% of the amount of wastewater.
[0014] Preferably, the room temperature in S2 is 20-30°C.
[0015] Preferably, in S3, 10% dilute sulfuric acid is used to adjust the pH of the wastewater to pH = 3.8-4.2.
[0016] Preferably, in S5, the evaporated crystallized sodium sulfate salt is dried at 110-120° C. for 2-3 hours.
[0017] The beneficial effects of the present invention are:
[0018] 1. The present invention adds 2-4% sodium persulfate solution and 1-2% polyferric sulfate solution to wastewater, then uses 30% sodium hydroxide solution to adjust the pH of the wastewater to 12-13, keeps the wastewater at 80-90° C. for 2-3 hours, cools it to room temperature, and then filters it, thereby effectively reducing the COD content in the wastewater. The COD removal rate in the wastewater can reach 96%. Specifically, sodium persulfate generates highly active free radicals through the activation of iron element, thereby oxidizing and degrading organic matter, and polyferric sulfate condenses and precipitates the oxidation products and residual pollutants. The combination of the two can achieve deep removal of COD, and the iron ions in the polyferric sulfate easily react with hydroxide ions to form precipitates, which are removed by filtration. The tail water after the sodium sulfate is finally evaporated is subjected to conductivity testing. The tail water conductivity meets the conductivity of tap water. The wastewater treated by the present invention does not have secondary pollution of iron ions.
[0019] In addition, the present invention adjusts the pH of the treated wastewater to acidic by using 10% dilute sulfuric acid, keeps the wastewater at 80-90° C. for 30-60 minutes, and adjusts the pH of the wastewater to 6-7 by using 30% sodium hydroxide solution. By controlling the pH of the wastewater during the reaction process, carbonate and bicarbonate ions in the wastewater are removed, and the total removal rate of carbonate and bicarbonate ions in the wastewater can reach 96%.
[0020] 2. The present invention adopts the high-temperature nitrate and low-temperature salt method to evaporate and crystallize the wastewater that has reached a colorless and transparent state after treatment, and obtains sodium sulfate salt that meets the national standard Class II first-class product (purity>98%) or above. The present invention is suitable for treating industrial wastewater with more complex water components and more types of organic matter, and has stronger universality.
[0021] 3. The present invention is suitable for treating wastewater with a COD content of 2000 mg / L to 3500 mg / L. By controlling the ratio of sodium persulfate to polyferric sulfate to 2:1 and ensuring that the amount of the mixed solution of sodium sulfate and polyferric sulfate does not exceed 10% of the wastewater volume during the treatment process, the COD content in the wastewater can be reduced to 150 mg / L, which can effectively control the treatment cost. DETAILED DESCRIPTION
[0022] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.
[0023] Example 1
[0024] The main test items in the wastewater raw materials used are shown in Table 1.
[0025]
[0026] Table 1
[0027] In this embodiment, the above wastewater is used as raw material, and the method for treating high-salt wastewater and separating sodium sulfate salt includes the following steps:
[0028] S1. Add 3% sodium persulfate and 1.5% polyferric sulfate solution (the content of polyferric sulfate is ≥11%) to the wastewater, and then adjust the pH of the wastewater to 13 with 30% sodium hydroxide solution; the ratio of sodium persulfate solution to polyferric sulfate solution is 2:1, and the sum of the amount of sodium persulfate solution and polyferric sulfate solution is less than 10% of the amount of wastewater;
[0029] S2, keeping the wastewater treated in S1 at 85°C for 2 hours, then filtering after cooling the wastewater;
[0030] S3, using 10% sulfuric acid to adjust the pH of the wastewater treated in S2 to 4, and keeping it at 85°C for 45 minutes, and finally using 30% sodium hydroxide solution to adjust the pH of the wastewater back to 6-6.5;
[0031] S4. Detect the COD content in the wastewater treated in S3 in accordance with the national standard HJ 828-2017; detect the carbonate and bicarbonate contents in the wastewater treated in S3 in accordance with the national standard DZT0064.49-2021;
[0032] The test results showed that the COD content in the treated wastewater dropped from 2140mg / L to 80mg / L, with a removal rate of 96.3%;
[0033] The carbonate content dropped from 858 mg / L to 0, and the bicarbonate content dropped from 1168 mg / L to 129.3 mg / L, with the total removal rate of carbonate and bicarbonate reaching 93.6%;
[0034] S5. Using the high-temperature nitrate and low-temperature salt method, evaporate and crystallize the wastewater tested in S4 at 95-100°C, and keep the sodium sulfate salt obtained by evaporation and crystallization at 120°C for 2 hours to remove crystallization water;
[0035] S6. The sodium sulfate salt obtained by drying in S6 was tested in accordance with the national standard GB / T 6009-2014. The test results showed that the sodium sulfate salt obtained by evaporation could reach the national standard Class II first-class product (purity >98%) or above; the conductivity of the tail water after evaporating the sodium sulfate was tested, and the tail water conductivity was 841.9μs / cm, which is consistent with the conductivity of tap water, proving that COD is deeply removed without secondary contamination by iron ions.
[0036] Example 2
[0037] The main test items in the wastewater raw materials used are shown in Table 2.
[0038]
[0039] Table 2
[0040] This embodiment uses the above wastewater as raw material and adopts the same treatment steps as Example 1, except that: 3.5% sodium persulfate solution and 1.75% polyferric sulfate solution (polyferric sulfate content ≥11%) are used in step S1.
[0041] The results after S4 testing are:
[0042] After treatment, the COD content in the wastewater dropped from 2560 mg / L to 113 mg / L, with a removal rate of 95.6%;
[0043] The carbonate content dropped from 383 mg / L to 0, and the bicarbonate content dropped from 2964 mg / L to 113.9 mg / L. The total removal rate of carbonate and bicarbonate reached 96.6%.
[0044] The test results of S6 are: the obtained sodium sulfate salt also meets the national standard Class II first-class product (purity >98%) or above; the conductivity of the tail water after evaporating the sodium sulfate is tested, and the tail water conductivity is 912.5μs / cm, which is consistent with the conductivity of tap water, proving that COD is deeply removed without secondary contamination by iron ions.
[0045] In summary, the impurities in the wastewater treated in each embodiment are greatly reduced, and relatively pure brine is obtained. The purity of the sodium sulfate salt obtained after evaporation and crystallization of the brine reaches Class II first-class or above, effectively reducing the COD content in the wastewater. The COD removal rate in the wastewater is as high as 96%, and the total removal rate of carbonate and bicarbonate in the wastewater can be as high as 96%. In addition, the wastewater treated by the present invention will not be contaminated by secondary iron ions.
[0046] The above disclosure is merely a preferred embodiment of the present invention and certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.
Claims
1. A method for treating high-salt wastewater and separating sodium sulfate, characterized in that: The method comprises the following steps: S1. Adding 2-4% sodium persulfate solution and 1-2% polyferric sulfate solution to wastewater, and then adjusting the pH of the wastewater to 12-13 with 30% sodium hydroxide solution; wherein the main salt component of the wastewater is sodium sulfate, and its pH is 8-9, and the main impurities in the wastewater are COD, carbonate and bicarbonate, and the COD content in the wastewater is 2000mg / L-3500mg / L; S2, after the above-treated wastewater is kept at 80-90°C for 2-3 hours, the wastewater is cooled to room temperature and then filtered; S3, using 10% dilute sulfuric acid to adjust the pH of the wastewater treated in S2 to acidic, and keep it at 80-90°C for 30-60 minutes, and finally using 30% sodium hydroxide solution to adjust the pH of the wastewater to 6-7; S4. The COD content in the wastewater treated in S3 was tested in accordance with the national standard HJ828-2017. The COD in the wastewater was less than 150 mg / L. The carbonate and bicarbonate contents in the wastewater treated in S3 were tested in accordance with the national standard DZT0064.49-2021. S5. Using the high-temperature nitrate and low-temperature salt method, the wastewater tested in S4 is evaporated, crystallized, and dried at 95-100°C to obtain sodium sulfate; S6. The sodium sulfate salt obtained by drying in S5 is tested in accordance with the national standard GB / T 6009-2014 to obtain sodium sulfate salt that meets the national standard Class II first-class product (purity>98%) or above.
2. The method for treating high-salt wastewater and separating sodium sulfate according to claim 1, characterized in that: The content of polyferric sulfate in the polyferric sulfate solution of S1 is ≥11%.
3. The method for treating high-salt wastewater and separating sodium sulfate according to claim 1, characterized in that: The ratio of the sodium persulfate solution to the polyferric sulfate solution in S1 is 2:1, and the sum of the amounts of the sodium persulfate solution and the polyferric sulfate solution is less than or equal to 10% of the amount of wastewater.
4. The method for treating high-salt wastewater and separating sodium sulfate according to claim 1, wherein: The room temperature in S2 is 20-30°C.
5. The method for treating high-salt wastewater and separating sodium sulfate according to claim 1, characterized in that: In the S3, 10% dilute sulfuric acid is used to adjust the pH of the wastewater to pH=3.8-4.
2.
6. The method for treating high-salt wastewater and separating sodium sulfate according to claim 1, characterized in that: In S5, the evaporated crystallized sodium sulfate salt is dried at 110-120° C. for 2-3 hours.