Process method for extracting anhydrous sodium sulfate and sodium carbonate from mixed waste liquid containing sodium sulfate and sodium carbonate

Abstract

The invention relates to the technical field of chemical waste liquid treatment, and discloses a process method for extracting anhydrous sodium sulfate and sodium carbonate from mixed waste liquid containing sodium sulfate and sodium carbonate, which comprises the following steps: evaporating the mixed waste liquid containing sodium sulfate and sodium carbonate to prepare double salt 2Na2SO4. Na2CO3, then infiltrating the double salt 2Na2SO4. Na2CO3 by using the mixed waste liquid, controlling the infiltrating temperature, and extracting the anhydrous sodium sulfate and sodium carbonate from the mixed waste liquid. The method comprises the following steps: adding sodium carbonate into a sodium carbonate solution, centrifuging, filtering, leaching and drying to obtain an anhydrous sodium sulfate product and a mother solution, evaporating the mother solution to obtain a sodium carbonate-rich mother solution and double salt 2Na2SO4. Na2CO3, finally adding solid barium carbonate into the sodium carbonate-rich mother solution, removing residual sulfate ions in the sodium carbonate-rich mother solution, and carrying out MVR evaporation, leaching and drying to obtain an anhydrous sodium carbonate product. According to the method, anhydrous sodium sulfate is generated by a one-step method through double salt circulation, energy consumption is greatly reduced, high energy consumption of traditional mirabilite dehydration is avoided, refrigeration equipment or introduction of impurity chemical agents is not needed, the product purity is high, the industrial standard is met, no wastewater is discharged in the whole process, the cost is low, and green and efficient resource utilization of waste liquid is achieved.

Description

Technical Field

[0001] This invention relates to the field of chemical wastewater treatment technology, specifically to a process for extracting anhydrous sodium sulfate and sodium carbonate from a mixed wastewater containing sodium sulfate and sodium carbonate, which is particularly suitable for the resource-based treatment of mixed wastewater containing sodium sulfate and sodium carbonate in chemical production. Background Technology

[0002] Mixed wastewater containing sodium sulfate (Na₂SO₄) and sodium carbonate (Na₂CO₃) is widely found in industries such as chemical, coking, coal-to-oil, and pharmaceutical. For example, in the crude phenol recovery process of coking plants, the reaction of sulfuric acid with sodium phenolate produces high-salinity wastewater with a sodium sulfate concentration exceeding 20%, accompanied by sodium carbonate. Direct discharge or mixed treatment of this type of wastewater would paralyze wastewater treatment systems due to its high salinity and waste of resources. Therefore, efficient separation and recovery of sodium sulfate and sodium carbonate is crucial for achieving zero discharge and resource utilization of industrial wastewater.

[0003] In the prior art, Chinese patent CN211545967U discloses a production system for extracting sodium carbonate and sodium sulfate from cyclohexanone incineration waste alkali. After the waste alkali ash is completely dissolved, it is cooled and crystallized to extract sodium carbonate. Sulfuric acid is added to the mother liquor after sodium carbonate extraction, and the pH is maintained at 7.0-7.1 to allow the sodium carbonate and sulfuric acid to react fully and generate sodium sulfate. The resulting solution is then evaporated to dryness in an MVR system to obtain sodium sulfate. This method involves adding sulfuric acid to adjust the pH of the mother liquor, which results in the loss of sodium carbonate product and an increase in cost.

[0004] Chinese patent CN117509683A discloses a method and apparatus for separating sodium sulfate and sodium carbonate from waste liquid. The method involves evaporating, concentrating, and crystallizing engineering wastewater to obtain a double salt slurry; cooling and crystallizing the mother liquor to obtain sodium carbonate decahydrate; dissolving the double salt in water, cooling it, and then centrifuging it to obtain sodium sulfate decahydrate. This method requires cooling equipment during the separation process, resulting in high energy consumption and increased operating costs. Furthermore, the obtained product is sodium sulfate decahydrate, which requires additional equipment and costs for dehydration.

[0005] Therefore, it is necessary to develop a green, environmentally friendly, efficient, and energy-saving process that is simple, low-energy, and low-cost to recover anhydrous sodium sulfate and sodium carbonate from waste liquid. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a process for extracting anhydrous sodium sulfate and sodium carbonate from a mixed waste liquid containing sodium sulfate and sodium carbonate. Sodium sulfate is separated in one step through a double salt cycle, avoiding the high energy consumption of traditional Glauber's salt dehydration. No reagents or freezing are required; the process is simple, requires fewer devices, and has low energy consumption. The separated products meet the quality requirements of sodium sulfate (GB / T 6009-2014) and sodium carbonate (GB / T 210-2022). This invention proposes a new resource utilization method that addresses waste liquid disposal, reduces treatment costs, and generates economic benefits.

[0007] The technical solution adopted by this invention to solve the technical problem is as follows:

[0008] This invention provides a process for extracting anhydrous sodium sulfate and sodium carbonate from a mixed waste liquid containing sodium sulfate and sodium carbonate, the steps of which are as follows:

[0009] (1) Prepare the double salt 2Na2SO4·Na2CO3 by evaporating the mixed waste liquid containing sodium sulfate and sodium carbonate;

[0010] (2) The double salt 2Na2SO4·Na2CO3 is added to a mixed waste liquid at 35-60℃ for leaching, stirring, centrifugation, and filtration to obtain mother liquor and wet anhydrous sodium sulfate. The wet anhydrous sodium sulfate is washed and dried to obtain anhydrous sodium sulfate product. The mass ratio of the double salt 2Na2SO4·Na2CO3 to the mixed waste liquid is 1:1 to 1:2.5.

[0011] (3) The mother liquor obtained in step (2) is evaporated and concentrated to obtain sodium carbonate-rich mother liquor and double salt 2Na2SO4·Na2CO3;

[0012] (4) Add solid barium carbonate to the sodium carbonate-rich mother liquor for aging and conversion, filter, and then evaporate, rinse and dry the filtrate to obtain anhydrous sodium carbonate product.

[0013] Preferably, the specific components and proportions of the mixed waste liquid containing sodium sulfate and sodium carbonate are as follows: w(Na2CO3) = 2-5%, w(Na2SO4) = 10-15%, w(NaCl) = 0.1-1%, w(K2CO3) = 0.1-0.2%, and w(K2SO4) = 0.1-0.2%.

[0014] Preferably, in the preparation method of the double salt 2Na2SO4·Na2CO3 in step (1), the mass ratio of Na2SO4 to Na2CO3 in the mixed waste liquid is controlled to be 1:8-8:1, and Glauber's salt or anhydrous sodium carbonate is added to the mixed waste liquid during the process.

[0015] Preferably, the evaporation temperature of the double salt 2Na2SO4·Na2CO3 in step (1) is 75-85℃.

[0016] Preferably, the filtration method in step (2) is to use heat-insulated centrifugal filtration, and the temperature is controlled to be no less than 35°C.

[0017] Preferably, the rinsing in step (2) is performed using a 50°C saturated sodium sulfate solution.

[0018] Preferably, the evaporation and concentration temperature in step (3) is 90-95℃, and the crystallization temperature is 95-110℃.

[0019] Preferably, the evaporator used in step (3) is an MVR evaporator or a MED evaporator.

[0020] Preferably, the double salt 2Na2SO4·Na2CO3 obtained in step (3) is returned to step (2) for use, and the residual heat of the sodium carbonate-rich mother liquor is used to heat step (2) through a heat exchanger. More preferably, the heat exchanger is one of a tubular heat exchanger, a plate heat exchanger, or a heat pipe heat exchanger.

[0021] Preferably, in step (4), the mass ratio of solid barium carbonate to sodium carbonate-rich mother liquor is 1:800-1200.

[0022] This invention achieves a one-step production of anhydrous sodium sulfate through a double salt cycle. The process is as follows: the double salt 2Na₂SO₄·Na₂CO₃ is dissolved in a hot water bath to form a solid salt Na₂SO₄, while Na₂CO₃ dissolves into the solution. At temperatures above 35°C, the solid Na₂SO₄ exists as an anhydrous salt, thus achieving the preparation of anhydrous Na₂SO₄ solid.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) Energy-saving and efficient, low cost: Anhydrous sodium sulfate is generated in one step through double salt cycle, which greatly reduces energy consumption, avoids the high energy consumption of traditional sodium sulfate dehydration, and does not require refrigeration equipment or the introduction of impurity chemical agents.

[0025] (2) High product purity: The product has high purity due to the use of centrifugal filtration process. Sodium sulfate and sodium carbonate meet the industrial standards of GB / T6009-2014 and GB / T 210-2022, respectively.

[0026] (3) Green, environmentally friendly and pollution-free: No wastewater is discharged throughout the process, realizing the resource utilization of waste liquid. Attached Figure Description

[0027] Figure 1 This is a process flow diagram of the present invention;

[0028] Figure 2 The X-ray diffraction pattern of the anhydrous sodium sulfate product prepared in Example 1 of this invention;

[0029] Figure 3 The image shows the X-ray diffraction pattern of the anhydrous sodium carbonate product prepared in Example 1 of this invention. Detailed Implementation

[0030] The present invention will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0031] Example 1

[0032] A process for extracting anhydrous sodium sulfate and sodium carbonate from a mixed waste liquid containing sodium sulfate and sodium carbonate, comprising the following steps:

[0033] (1) Take 1128g of mixed waste liquid, add 53g of anhydrous sodium carbonate, stir until the anhydrous sodium carbonate is completely dissolved. At this time, the mass ratio of Na2SO4 and Na2CO3 in the mixed waste liquid is 1.45:1, the MVR evaporation temperature is 82℃, and 519g of double salt 2Na2SO4·Na2CO3 is filtered out while hot.

[0034] (2) Mix 519g of double salt 2Na2SO4·Na2CO3 and 1128g of waste liquid for leaching. Control the temperature at 50±0.5℃, stir for 4h, keep warm at 50℃ and filter out 269g of wet anhydrous sodium sulfate and 1378g of mother liquor. Rinse with 50℃ saturated sodium sulfate solution, repeat three times, and dry to obtain anhydrous sodium sulfate.

[0035] (3) The mother liquor from (2) is concentrated by MVR distillation at a concentration temperature of 95°C, with a water output of 599g, yielding 519g of double salt 2Na2SO4·Na2CO3 and 260g of sodium carbonate-rich mother liquor. The obtained double salt 2Na2SO4·Na2CO3 is returned to step (2) for recycling, and the residual heat of the sodium carbonate-rich mother liquor is used to heat step (2) through a tubular heat exchanger.

[0036] (4) Add 0.3g of solid barium carbonate to the sodium carbonate mother liquor for aging and conversion. After removing sulfate ions from the sodium carbonate mother liquor, the product is obtained by MVR evaporation.

[0037] Example 2

[0038] A process for extracting anhydrous sodium sulfate and sodium carbonate from a mixed waste liquid containing sodium sulfate and sodium carbonate, comprising the following steps:

[0039] (1) Take 11.5 kg of mixed waste liquid, add 1.42 kg of sodium carbonate decahydrate, stir until sodium carbonate decahydrate is completely dissolved. At this time, the mass ratio of Na2SO4 and Na2CO3 in the mixed waste liquid is 1.35:1, the MVR evaporation temperature is 78℃, and filter out 5.22 kg of double salt 2Na2SO4·Na2CO3 while it is hot.

[0040] (2) Mix 5.22 kg of double salt 2Na2SO4·Na2CO3 and 11.5 kg of waste liquid for conversion, control the temperature at 50±0.5℃, stir for 6 h, keep warm at 50℃ and filter out 2.71 kg of wet anhydrous sodium sulfate and 14.01 kg of mother liquor. Rinse with 50℃ saturated sodium sulfate solution, repeat three times, and dry to obtain anhydrous sodium sulfate.

[0041] (3) The 14.01 kg mother liquor from (2) is concentrated by MVR distillation at a concentration temperature of 95°C and the output water is 6.06 kg, resulting in 5.22 kg of double salt 2Na2SO4·Na2CO3 and 2.73 kg of sodium carbonate-rich mother liquor. The obtained double salt 2Na2SO4·Na2CO3 is returned to step (2) for recycling, and the residual heat of the sodium carbonate-rich mother liquor is used to heat step (2) through a plate heat exchanger.

[0042] (4) Add 3.2g of solid barium carbonate to 2.73kg of sodium carbonate mother liquor for aging and conversion. After removing sulfate ions from the sodium carbonate mother liquor, the product is obtained by MVR evaporation.

[0043] Example 3

[0044] A process for extracting anhydrous sodium sulfate and sodium carbonate from a mixed waste liquid of sodium sulfate and sodium carbonate, comprising the following steps:

[0045] (1) Take 28.2 kg of waste liquid, add 3.51 kg of sodium carbonate decahydrate, stir until sodium carbonate decahydrate is completely dissolved. At this time, the mass ratio of Na2SO4 and Na2CO3 in the mixed waste liquid is 1.5:1. The MVR evaporation temperature is 80℃. Filter out 12.72 kg of double salt 2Na2SO4·Na2CO3 while it is hot.

[0046] (2) Add 12.72 kg of double salt 2Na2SO4·Na2CO3 to 28.2 kg of waste liquid for mixing and conversion. Control the temperature at 60±1℃ and stir for 8 hours. Keep the temperature at 60℃ and filter to obtain 6.61 kg of wet anhydrous sodium sulfate and 34.31 kg of mother liquor. Rinse with 60℃ saturated sodium sulfate solution, repeat three times, and dry to obtain anhydrous sodium sulfate.

[0047] (3) The 34.31 kg mother liquor from (2) is concentrated by MVR distillation at a concentration temperature of 95°C, with a water output of 14.78 kg, yielding 12.72 kg of double salt 2Na2SO4·Na2CO3 and 6.81 kg of sodium carbonate-rich mother liquor. The obtained double salt 2Na2SO4·Na2CO3 is returned to step (2) for recycling, and the residual heat of the sodium carbonate-rich mother liquor is used to heat step (2) through a heat pipe heat exchanger.

[0048] (4) Add 7.61g of solid barium carbonate to 6.81kg of sodium carbonate mother liquor for aging and conversion. After removing sulfate ions from the sodium carbonate mother liquor, the product is obtained by MVR evaporation.

[0049] Comparative Example 1

[0050] The only difference from Example 1 is that in step (2), a mixed waste liquid at 33°C is added.

[0051] Comparative Example 2

[0052] The only difference from Example 1 is that in step (2), a mixed waste liquid at 62°C is added.

[0053] Comparative Example 3

[0054] The only difference from Example 1 is that the mass ratio of the double salt 2Na2SO4·Na2CO3 and the mixed waste liquid in step (2) is 1.5:1.

[0055] The purity of the anhydrous sodium sulfate and anhydrous sodium carbonate prepared in the examples and comparative examples is shown in Table 1.

[0056] Table 1

[0057]

[0058]

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. A process for extracting anhydrous sodium sulfate and sodium carbonate from a mixed waste liquid containing sodium sulfate and sodium carbonate, characterized in that, Includes the following steps: (1) Prepare the double salt 2Na2SO4·Na2CO3 by evaporating the mixed waste liquid containing sodium sulfate and sodium carbonate; (2) The double salt 2Na2SO4·Na2CO3 is added to a mixed waste liquid at 35-60℃ for leaching, stirring, centrifugation, and filtration to obtain mother liquor and wet anhydrous sodium sulfate. The wet anhydrous sodium sulfate is washed and dried to obtain anhydrous sodium sulfate product. The mass ratio of the double salt 2Na2SO4·Na2CO3 to the mixed waste liquid is 1:1 to 1:2.

5. (3) The mother liquor obtained in step (2) is evaporated and concentrated to obtain sodium carbonate-rich mother liquor and double salt 2Na2SO4·Na2CO3; (4) Add solid barium carbonate to the sodium carbonate-rich mother liquor for aging and conversion, filter, and then evaporate, rinse and dry the filtrate to obtain anhydrous sodium carbonate product.

2. The process method according to claim 1, characterized in that, In the preparation method of the double salt 2Na2SO4·Na2CO3 in step (1), the mass ratio of Na2SO4 and Na2CO3 in the mixed waste liquid is controlled to be 1:8-8:1, and Glauber's salt or anhydrous sodium carbonate is added to the mixed waste liquid during the process.

3. The process method according to claim 1, characterized in that, The evaporation temperature of the double salt 2Na2SO4·Na2CO3 in step (1) is 75-85℃.

4. The process method according to claim 1, characterized in that, Step (2) uses insulated centrifugal filtration.

5. The process method according to claim 1, characterized in that, Step (3) Evaporation and concentration temperature: 90-95℃, crystallization temperature: 95-110℃.

6. The process method according to claim 1, characterized in that, The evaporator used in step (3) is an MVR evaporator or a MED evaporator.

7. The process method according to claim 1, characterized in that, The double salt 2Na2SO4·Na2CO3 obtained in step (3) is returned to step (2) for use, and the residual heat of the sodium carbonate mother liquor is used to heat step (2) through a heat exchanger.

8. The process method according to claim 7, characterized in that, The heat exchanger is one of a tubular heat exchanger, a plate heat exchanger, or a heat pipe heat exchanger.

9. The process method according to claim 1, characterized in that, In step (4), the mass ratio of solid barium carbonate to sodium carbonate mother liquor is 1:800-1200.

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