Self-balancing production method for preparing potassium sulfate from high-nitrate and high-potassium wastewater

Abstract

The invention provides a self-balancing production method for preparing potassium sulfate from high-nitrate and high-potassium wastewater. The self-balancing production method comprises the following steps: carrying out MVR (Mechanical Vapor Recompression) evaporation and concentration on the wastewater, and separating to obtain glaserite I and mother liquor I; carrying out a conversion reaction II on the glaserite I, potassium chloride and water to obtain potassium sulfate and a potassium mother solution, adding sodium sulfate into the potassium mother solution, carrying out a conversion reaction I, evaporating, carrying out solid-liquid separation to obtain glaserite II and a mother solution II, and feeding the glaserite II back to the conversion reaction II; performing MVR evaporative crystallization on the mother liquor II to obtain industrial salt I, water and mother liquor III, adding water into the mother liquor III, and performing conversion reaction III to obtain glauberite III and mother liquor IV; the glaserite III is sent back to the conversion reaction II; part of the fourth mother liquor and the first mother liquor are exchanged and sent back to the MVR for evaporative crystallization; evaporating and crystallizing part of the mother liquor IV to obtain industrial salt II, water and mother liquor VI; and feeding the obtained water into a water storage device for recycling the above steps. High-purity potassium sulfate and industrial salt are obtained through a reasonable process, system water balance and material balance are achieved through mother liquor multi-stage backflow and water recycling, water expansion is avoided, and raw material consumption is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic chemical industry, and in particular relates to a self-balancing production method for preparing potassium sulfate by using high-nitrate and high-potassium wastewater. Background Art

[0002] Potassium sulfate (K2SO4) is an important inorganic compound with a wide range of applications across agriculture, industry, and medicine. In agriculture, it's primarily used as a potash fertilizer, providing potassium to crops. It's particularly suitable for chlorine-sensitive crops like tobacco, watermelon, and tea, and sulfur-loving crops like rapeseed and beans, preventing the degradation of crops caused by chloride ions in potassium chloride. In industry, it's used as a chemical raw material to manufacture potassium salts like potassium carbonate and potassium persulfate, and as a clarifier in glassmaking to remove bubbles from melts. In medicine and other fields, it's used as a laxative ingredient, a bulking agent, and a moisture-retaining agent in meat products.

[0003] Currently, the main methods for producing potassium sulfate are the Mannheim process and the Glauber's salt process. The Mannheim process uses potassium chloride (KCl) and sulfuric acid (H₂SO₄) as raw materials, reacting at a high temperature of 550–700°C to produce potassium sulfate (K₂SO₄) and hydrogen chloride gas. This method is technically mature, but it is characterized by high energy consumption, large equipment investment, severe equipment corrosion, high maintenance costs, difficult disposal of the byproduct hydrochloric acid, and significant environmental pressures. The Glauber's salt process simply uses the raw material, solid Glauber's salt (Na₂SO₄·10H₂O), in a double decomposition reaction with solid potassium chloride to produce potassium sulfate and sodium chloride. The unit consumption of sodium sulfate and potassium chloride is ≥0.8 (per ton of potassium sulfate), while the potassium recovery rate is less than 60%. High production costs and unstable product quality are also hindered by imperfect mother liquor treatment technologies, limiting large-scale production. Furthermore, water expansion during the production process causes system instability and compromises economic benefits.

[0004] Currently, there are processes for extracting potassium sulfate from wastewater, but the raw wastewater composition is relatively simple, primarily composed of sodium sulfate and sodium chloride. However, methods for extracting potassium sulfate from multi-component systems (such as high-nitrate and high-potassium wastewater, whose main components are Na2SO4, NaCl, and KCl) have not yet been reported. How to efficiently separate economically valuable components (such as K2SO4) from such complex wastewater, achieve stable process operation, avoid system water expansion, reduce material consumption and production costs, and simultaneously improve environmental and economic benefits remain key challenges. Summary of the Invention

[0005] In view of this, and to address the above-mentioned technical problems, the present invention proposes a self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater. Using multi-component high-nitrate and high-potassium wastewater as raw material, a rational process flow is employed to produce high-purity potassium sulfate, industrial salt, and miscellaneous salts. Simultaneously, by recycling mother liquor and water, combined with process parameter regulation, the system achieves both material and water balance, effectively preventing water expansion, ensuring stable system operation, and significantly reducing raw material consumption.

[0006] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater comprises the following steps:

[0008] S1, high nitrate and high potassium wastewater is evaporated and concentrated by MVR to obtain water and slurry; the water is sent to the water storage device, and the slurry is separated by solid-liquid separation to obtain potassium glauberite and mother liquor;

[0009] S2, adding potassium chloride and water supplied from a water storage device to Glauber's salt 1 to carry out conversion reaction 2 to obtain potassium sulfate and potassium mother liquor;

[0010] S3, sodium sulfate is added to the potassium mother liquor to carry out conversion reaction 1, and then evaporation of water and solid-liquid separation are carried out to obtain glauberite 2 and mother liquor 2; the evaporated water is sent to the water storage device, and the glauberite 2 is sent to step S2 for conversion reaction 2;

[0011] S4, mother liquor 2 is evaporated and crystallized by MVR to obtain industrial salt 1, water and mother liquor 3; water is sent to the water storage device, and water supplied by the water storage device is added to mother liquor 3 to perform conversion reaction 3 to obtain potassium glauberite 3 and mother liquor 4; potassium glauberite 3 is sent to step S2 for conversion reaction 2;

[0012] S5, a portion of the mother liquor 4 is exchanged with the mother liquor 1 to obtain the mother liquor 5, which is sent to step S4 for MVR evaporation crystallization;

[0013] S6. Another part of the mother liquor 4 is evaporated and crystallized to obtain industrial salt 2, water and mother liquor 6; the water is sent to the water storage device, and the mother liquor 6 is solidified to obtain miscellaneous salt.

[0014] In some preferred embodiments of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater of the present invention, in S1, the total dissolved solids of the high-nitrate and high-potassium wastewater is 80,000 to 180,000 mg / L, Na + The content is 12000~30000 mg / L, K + The content is 20000~40000 mg / L, Cl - Content is 40000~60000 mg / L, SO4 2-The content is 10,000 to 40,000 mg / L, and the total content of other impurities is 1,000 to 3,000 mg / L.

[0015] In some preferred embodiments of the self-balancing production method for preparing potassium sulfate using high nitrate and high potassium wastewater of the present invention, in S1, the mass ratio of water obtained by MVR evaporation and concentration of high nitrate and high potassium wastewater to high nitrate and high potassium wastewater is 0.65-0.75:1; Na in mother liquor 1 + With K + The mass ratio of Cl is 0.3~3:1, - With SO4 2- The mass ratio is 4 to 11:1.

[0016] In some preferred embodiments of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater of the present invention, in S2, the mass ratio of the added potassium chloride to water is 1:2-3.5; the mass ratio of the potassium mother liquor to potassium sulfate is 1.5-3:1.

[0017] In some preferred embodiments of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater of the present invention, in S3, the mass ratio of potassium mother liquor to sodium sulfate is 4 to 9:1; the mass ratio of evaporated water to potassium mother liquor is 0.1 to 0.3:1; Na + With K + The mass ratio of Cl is 1~3:1, - With SO4 2- The mass ratio is 4 to 8:1.

[0018] In some preferred embodiments of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater of the present invention, in S4, the mass ratio of industrial salt 1, water and mother liquor 3 is 1:1-5:6-12; the mass ratio of mother liquor 3 to water added to mother liquor 3 is 10-30:1.

[0019] In some preferred embodiments of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater of the present invention, in S5, 10% to 60% of the total mass of the mother liquor 4 is exchanged with the mother liquor 1.

[0020] In some preferred embodiments of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater of the present invention, in S6, the mass ratio of industrial salt 2, water and mother liquor 6 is 1:1-6:8-15.

[0021] In some preferred embodiments of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater of the present invention, 10% to 30% of the total mass of water extracted from the water storage device is fed into step S2 for conversion reaction 2; and 1% to 5% of the total mass of water extracted from the water storage device is fed into step S4 for conversion reaction 3.

[0022] In some preferred embodiments of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater of the present invention, the product purity of the potassium sulfate obtained in S2 is ≥98%; the product purity of the sodium chloride in the industrial salt 1 obtained in S4 and the industrial salt 2 obtained in S6 is ≥98.5%.

[0023] Compared with the prior art, the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater of the present invention has the following advantages:

[0024] (1) The present invention uses multi-component high-nitrate and high-potassium wastewater (whose main components are Na2SO4, NaCl and KCl) as raw material. Through a reasonable process flow, it achieves efficient extraction of valuable resources from the wastewater, ultimately obtaining products such as potassium sulfate, industrial salt and miscellaneous salts. The purity of the potassium sulfate product is ≥98%, and the purity of the sodium chloride product in the industrial salt is ≥98.5%. This method not only helps to conserve natural mineral resources and reduce environmental pollution, but also effectively reduces the wastewater discharge load, thus having significant environmental benefits. At the same time, each ton of potassium sulfate produced can bring economic benefits of more than 1,000 yuan, showing good prospects for resource utilization and economic benefits.

[0025] (2) The present invention realizes the material balance and water balance in the system through the recycling of water, recycling of various mother liquors and precise control of key process parameters, which is conducive to the stable operation of the system and avoidance of water expansion, providing a guarantee for the long-term stable operation of the system, and is also conducive to the unification and control of product quality; in addition, in terms of reducing raw material consumption, the method significantly improves the raw material utilization rate, so that the unit product consumption of sodium sulfate and potassium chloride is controlled at a low level, the unit consumption of sodium sulfate is ≤0.75 (calculated in tons of potassium sulfate), and the unit consumption of potassium chloride is ≤0.65 (calculated in tons of potassium sulfate), and the comprehensive utilization rate of potassium is increased to more than 75%, thereby significantly reducing production costs and enhancing the economy and sustainability of the overall process. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0027] Figure 1 Schematic diagram of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater as described in Example 1 of the present invention;

[0028] Figure 2 This is a material balance diagram of the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater as described in Example 1 of the present invention. DETAILED DESCRIPTION

[0029] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are conventional biochemical reagents; the experimental methods described, unless otherwise specified, are conventional methods.

[0030] The present invention will be described in detail below with reference to the accompanying drawings and in conjunction with embodiments.

[0031] Example 1

[0032] like Figure 1 and 2 As shown, the self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater includes the following steps:

[0033] S1, high nitrate and high potassium wastewater flow rate is 600m 3 / d, with a mass flow rate of 654094 kg / d, it is sent to the MVR evaporation and concentration device. After MVR evaporation and concentration, water and slurry are obtained; the water is sent to the water storage device, and the slurry is separated into potassium glauberite and mother liquor by solid-liquid separation; among them, the total dissolved solids (TDS) of high nitrate and high potassium wastewater is 126100 mg / L, Na + The content is 27924.5 mg / L, K + The content is 24154.4 mg / L, Cl - The content is 40925.8 mg / L, SO4 2- The content is 32157.4 mg / L, other impurities such as NH4 + 、NO3 - The total content is 1276 mg / L; the mass ratio of the obtained water to the high nitrate and high potassium wastewater is 0.72:1; the Na + The mass fraction of K is 9.53%, + The mass fraction of Cl is 3.86%, - The mass fraction of SO4 is 15.66%, 2- The mass fraction of Na is 3.48%, that is, + With K + The mass ratio of Cl is 2.5:1, - With SO4 2- The mass ratio is 4.5:1;

[0034] S2, adding potassium chloride and water supplied from the water storage device to the glauberite 1 to carry out conversion reaction 2 to obtain potassium sulfate and potassium mother liquor; wherein the mass ratio of potassium chloride to water is 1:2.5, and the extracted water accounts for 15% of the total water mass of the water storage device; the mass ratio of potassium mother liquor to potassium sulfate is 2.3:1;

[0035] S3, sodium sulfate is added to the potassium mother liquor to carry out conversion reaction 1, and then glauberite 2 and mother liquor 2 are obtained by evaporating water and solid-liquid separation; the evaporated water is sent to the water storage device, and glauberite 2 is sent to step S2 for conversion reaction 2; wherein the mass ratio of potassium mother liquor to sodium sulfate is 5.4:1; the mass ratio of evaporated water to potassium mother liquor is 0.14:1; Na in mother liquor 2 + With K + The mass ratio of Cl is 2:1, - With SO4 2- The mass ratio is 5.9:1;

[0036] S4 and mother liquor 2 are evaporated and crystallized by MVR to obtain industrial salt 1, water and mother liquor 3; the water is fed into a water storage device, and water supplied from the water storage device is added to mother liquor 3 to carry out conversion reaction 3 to obtain glauberite 3 and mother liquor 4; glauberite 3 is fed into step S2 to carry out conversion reaction 2; wherein the mass ratio of industrial salt 1, water and mother liquor 3 is 1:3.2:10.3; the mass ratio of mother liquor 3 to water added to mother liquor 3 is 26.1:1, and the extracted water accounts for 2% of the total water mass of the water storage device;

[0037] S5, 49% of the total mass of mother liquor 4 is exchanged with mother liquor 1 to obtain mother liquor 5, which is sent to step S4 for MVR evaporation crystallization;

[0038] S6 and the remaining part of the mother liquor 4 are sent to the evaporation crystallization device to obtain industrial salt 2, water and mother liquor 6 through evaporation crystallization; the water is sent to the water storage device, and the mother liquor 6 is solidified to obtain miscellaneous salt; wherein, the mass ratio of industrial salt 2, water and mother liquor 6 is 1:3.2:9.1.

[0039] The overall material balance of Example 1 is shown in Table 1, the overall water balance is shown in Table 2, and the revenue estimate is shown in Table 3.

[0040] Table 1

[0041]

[0042] Table 2

[0043]

[0044] Table 3

[0045]

[0046] Note: Revenue is estimated based on the items listed in the table. Unit consumption is calculated in tons of potassium sulfate. Annual quantities are calculated based on 300 days of annual production.

[0047] The purity of the potassium sulfate product prepared in Example 1 was tested to be 98.5%, and the purity of the sodium chloride product in the industrial salt was 98.5%. Figure 2 The material balance diagram shows that the unit consumption of sodium sulfate is 0.42 (per ton of potassium sulfate), and the unit consumption of potassium chloride is 0.65 (per ton of potassium sulfate). The comprehensive utilization rate of potassium in wastewater neutralizing the added potassium chloride is 77%. Through water recycling and various mother liquor recycling methods, material and water balances are achieved, ensuring stable system operation and preventing water expansion. Table 3 estimates that a profit of 1,235 yuan can be generated per ton of potassium sulfate (based on the items listed in the table), demonstrating high economic benefits.

[0048] Example 2

[0049] A self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater comprises the following steps:

[0050] S1, high nitrate and high potassium wastewater flow rate is 600m 3 / d, with a mass flow rate of 654094 kg / d, and sent to the MVR evaporation and concentration device. After MVR evaporation and concentration, water and slurry are obtained; the water is sent to the water storage device, and the slurry is separated into potassium glauberite and mother liquor by solid-liquid separation; among them, the total dissolved solids (TDS) of high nitrate and high potassium wastewater is 121500 mg / L, Na + The content is 20000mg / L, K + The content is 35000mg / L, Cl - Content is 50000 mg / L, SO4 2- The content is 15000 mg / L, other impurities such as NH4 + 、NO3 - The total content is 1500 mg / L; the mass ratio of the obtained water to the high nitrate and high potassium wastewater is 0.75:1; the Na + With K + The mass ratio of Cl is 1.5:1, - With SO4 2- The mass ratio is 6:1;

[0051] S2, adding potassium chloride and water supplied from the water storage device to glauberite 1 to carry out conversion reaction 2 to obtain potassium sulfate and potassium mother liquor; wherein the mass ratio of potassium chloride to water is 1:2.5, and the extracted water accounts for 13% of the total water mass of the water storage device; the mass ratio of potassium mother liquor to potassium sulfate is 2.3:1;

[0052] S3, sodium sulfate is added to the potassium mother liquor to carry out conversion reaction 1, and then glauberite 2 and mother liquor 2 are obtained by evaporating water and solid-liquid separation; the evaporated water is sent to the water storage device, and glauberite 2 is sent to step S2 for conversion reaction 2; wherein the mass ratio of potassium mother liquor to sodium sulfate is 5:1; the mass ratio of evaporated water to potassium mother liquor is 0.12:1; Na in mother liquor 2 + With K + The mass ratio of Cl is 1.8:1, - With SO4 2- The mass ratio is 6.3:1;

[0053] S4 and mother liquor 2 are evaporated and crystallized by MVR to obtain industrial salt 1, water and mother liquor 3; the water is fed into a water storage device, and water supplied from the water storage device is added to mother liquor 3 to carry out conversion reaction 3 to obtain glauberite 3 and mother liquor 4; glauberite 3 is fed into step S2 to carry out conversion reaction 2; wherein the mass ratio of industrial salt 1, water and mother liquor 3 is 1:4:11; the mass ratio of mother liquor 3 to water added to mother liquor 3 is 25:1, and the extracted water accounts for 1.5% of the total water mass of the water storage device;

[0054] S5, 45% of the total mass of mother liquor 4 is exchanged with mother liquor 1 to obtain mother liquor 5, which is sent to step S4 for MVR evaporation crystallization;

[0055] S6, the remaining part of the mother liquor four is sent to the evaporation crystallization device, and industrial salt two, water and mother liquor six are obtained through evaporation crystallization; the water is sent to the water storage device, and the mother liquor six is ​​solidified to obtain miscellaneous salt; wherein, the mass ratio of industrial salt two, water and mother liquor six is ​​1:4:10.

[0056] Testing revealed that the potassium sulfate product prepared in Example 2 had a purity of 98.7%, while the sodium chloride product in the industrial salt had a purity of 98.7%. The unit consumption of sodium sulfate was 0.53 (per ton of potassium sulfate), and the unit consumption of potassium chloride was 0.62 (per ton of potassium sulfate), resulting in a potassium utilization rate of 79%. Through water recycling and the recycling of various mother liquors, material and water balances were achieved, ensuring stable system operation and preventing water expansion. A profit of 1,289 yuan was generated per ton of potassium sulfate, demonstrating high economic efficiency.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater, characterized in that: The steps include: S1, high nitrate and high potassium wastewater is evaporated and concentrated by MVR to obtain water and slurry; the water is sent to the water storage device, and the slurry is separated by solid-liquid separation to obtain potassium glauberite and mother liquor; S2, adding potassium chloride and water supplied from a water storage device to Glauber's salt 1 to carry out conversion reaction 2 to obtain potassium sulfate and potassium mother liquor; S3, sodium sulfate is added to the potassium mother liquor to carry out conversion reaction 1, and then evaporation of water and solid-liquid separation are carried out to obtain glauberite 2 and mother liquor 2; the evaporated water is sent to the water storage device, and the glauberite 2 is sent to step S2 for conversion reaction 2; S4, mother liquor 2 is evaporated and crystallized by MVR to obtain industrial salt 1, water and mother liquor 3; water is sent to the water storage device, and water supplied by the water storage device is added to mother liquor 3 to perform conversion reaction 3 to obtain potassium glauberite 3 and mother liquor 4; potassium glauberite 3 is sent to step S2 for conversion reaction 2; S5, a portion of the mother liquor 4 is exchanged with the mother liquor 1 to obtain the mother liquor 5, which is sent to step S4 for MVR evaporation crystallization; S6. Another part of the mother liquor 4 is evaporated and crystallized to obtain industrial salt 2, water and mother liquor 6; the water is sent to the water storage device, and the mother liquor 6 is solidified to obtain miscellaneous salt.

2. The self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater according to claim 1, characterized in that: In the S1, the total dissolved solids of the high nitrate and high potassium wastewater is 80,000 to 180,000 mg / L, Na + The content is 12000~30000 mg / L, K + The content is 20000~40000 mg / L, Cl - Content is 40000~60000 mg / L, SO4 2- The content is 10,000 to 40,000 mg / L, and the total content of other impurities is 1,000 to 3,000 mg / L.

3. The self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater according to claim 1, characterized in that: In the S1, the mass ratio of water obtained by MVR evaporation and concentration of high nitrate and high potassium wastewater to high nitrate and high potassium wastewater is 0.65-0.75:1; Na in the mother liquor + With K + The mass ratio of Cl is 0.3~3:1, - With SO4 2- The mass ratio is 4 to 11:

1.

4. The self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater according to claim 1, characterized in that: In the S2, the mass ratio of potassium chloride to water is 1:2-3.5; the mass ratio of potassium mother liquor to potassium sulfate is 1.5-3:

1.

5. The self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater according to claim 1, characterized in that: In the S3, the mass ratio of potassium mother liquor to sodium sulfate is 4 to 9:1; the mass ratio of evaporated water to potassium mother liquor is 0.1 to 0.3:1; Na + With K + The mass ratio of Cl is 1~3:1, - With SO4 2- The mass ratio is 4 to 8:

1.

6. The self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater according to claim 1, characterized in that: In the S4, the mass ratio of industrial salt 1, water and mother liquor 3 is 1:1-5:6-12; the mass ratio of mother liquor 3 to water added to mother liquor 3 is 10-30:

1.

7. The self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater according to claim 1, characterized in that: In S5, 10% to 60% of the total mass of the mother liquor 4 is exchanged with the mother liquor 1.

8. The self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater according to claim 1, characterized in that: In the S6, the mass ratio of industrial salt 2, water and mother liquor 6 is 1:1-6:8-15.

9. The self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater according to claim 1, characterized in that: 10% to 30% of the total mass of water extracted from the water storage device is fed into step S2 for conversion reaction 2; 1% to 5% of the total mass of water extracted from the water storage device is fed into step S4 for conversion reaction 3.

10. The self-balancing production method for preparing potassium sulfate using high-nitrate and high-potassium wastewater according to any one of claims 1 to 9, characterized in that: The product purity of the potassium sulfate obtained in S2 is ≥98%; the product purity of the sodium chloride in the industrial salt 1 obtained in S4 and the industrial salt 2 obtained in S6 is ≥98.5%.

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