Production process for preparing sodium chloride and sodium sulfate from bittern and nitrate bittern

Abstract

The invention discloses a production process for preparing sodium chloride and sodium sulfate from bittern, nitre and bittern, and relates to the technical field of salt chemical industry. According to the process, bittern and nitrate bittern are used as raw materials at the same time, continuous separation is achieved in the same multi-effect evaporation system, and sodium chloride and sodium sulfate products are obtained respectively. The method specifically comprises the following steps: preheating bittern, then carrying out high-temperature and low-temperature evaporation salt production, and separating sodium chloride to obtain high-temperature and low-temperature salt production mother liquor; preheating the nitre halogen, then performing low-temperature evaporation nitre preparation, and separating sodium sulfate to obtain high-salt or low-salt nitre preparation mother liquor; combining the part of mother liquor with the last-effect circulating mother liquor to enter a medium-temperature nitrate preparation effect, separating out sodium sulfate again, and further recovering sodium chloride from the obtained nitrate preparation mother liquor through flash evaporation or low-temperature evaporation; and the last-effect salt-making mother liquor is returned to the medium-temperature nitrate-making effect for cyclic utilization after waste heat is recovered.

Description

Technical Field

[0001] This invention relates to the field of salt chemical technology, specifically a production process for preparing sodium chloride and sodium sulfate from brine and nitrate as dual raw materials. Background Technology

[0002] Rock salt deposits are often associated with brine and nitrate resources. Traditional mining and processing methods often treat brine and nitrate as independent systems, employing separate extraction and treatment processes. Brine is primarily composed of sodium chloride, with a small amount of sodium sulfate; nitrate is rich in sodium sulfate and contains a certain amount of sodium chloride. Due to their similar physicochemical properties, using conventional single-raw-source evaporation processes easily leads to problems such as low purity of the target product, mixed byproducts, high energy consumption, and difficulty in recycling the mother liquor.

[0003] Particularly in typical mining areas such as Huai'an, Jiangsu Province, historical mining and geological structures have resulted in a large number of old wells with complex high-salt brine composition. Meanwhile, the salt cavern gas storage projects that have been vigorously developed in the region in recent years have continuously generated low-nitrate brine with varying compositions during the cavern construction and operation. If these two types of brine cannot be utilized efficiently and in a coordinated manner, it will not only lead to a serious waste of high-quality mineral resources but also place dual pressures on environmental management and corporate economic benefits.

[0004] Currently, although relevant enterprises in the region have built nitrate separation facilities of a certain scale, their process routes are mostly designed for a single type of brine, making it difficult to efficiently process both brine and nitrate brine simultaneously. Building two separate production lines for this purpose would result in huge investments, increased land occupation, and superimposed energy consumption, and would not achieve the intrinsic coupling optimization of energy and materials, which does not meet the development requirements of green, low-carbon, and circular economy.

[0005] To address the aforementioned problems, this invention provides a production process for preparing sodium chloride and sodium sulfate from brine and nitrate as dual raw materials. Summary of the Invention

[0006] The purpose of this invention is to provide a production process for preparing sodium chloride and sodium sulfate from brine and nitrate as dual raw materials, in order to solve the problems raised in the prior art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A production process for preparing sodium chloride and sodium sulfate from brine and nitrate as dual raw materials includes the following steps: Step 1: Pretreatment of brine and initial separation of sodium chloride After the brine is preheated, it undergoes pretreatment and then enters the evaporation system to obtain sodium chloride and high-temperature salt production mother liquor. Step 2: Pretreatment of nitrate brine and initial separation of sodium sulfate After preheating the nitrate brine, it is fed into a low-temperature evaporation tank with a third-effect evaporation process to separate sodium sulfate product and obtain low-salt nitrate mother liquor. Step 3: Mixing the mother liquor with sodium sulfate for primary separation The high-temperature salt-making mother liquor obtained in step one, the low-salt nitrate-making mother liquor obtained in step two, and the final-effect salt-making mother liquor recycled from the system are all fed into the medium-temperature evaporation nitrate-making second-effect evaporator. Under these conditions, sodium sulfate crystallizes out in large quantities again to obtain sodium sulfate product, and nitrate-making mother liquor is produced at the same time. Step 4: Treatment of Nitrogenation Mother Liquor and Recycling of Sodium Chloride The nitrate mother liquor obtained in step three is processed to further recover sodium chloride and obtain low-temperature salt production mother liquor. Step 5: Final Salt Production and Mother Liquor Output The low-temperature salt production mother liquor obtained in step four is sent to the low-temperature evaporation salt production final V-effect evaporation tank for evaporation and crystallization, and sodium chloride is recovered again to obtain the final effect salt production mother liquor. Step Six: Waste Heat Recovery and Mother Liquor Circulation The mother liquor from the final effect of salt production is preheated, and the preheated mother liquor is recycled back to the second-effect evaporator for medium-temperature evaporation in step three, where it continues to participate in the reaction as part of the raw materials, thus achieving continuous production; finally, sodium chloride and sodium sulfate are recovered.

[0008] Further, step one includes the following steps: after preheating the brine, it is all fed into the low-temperature evaporation salt production IV-effect evaporator and III-effect evaporator in a horizontal flow to separate some sodium chloride and obtain low-nitrate salt production mother liquor; the mother liquor is then fed into the high-temperature evaporation salt production I-effect evaporator in a countercurrent flow to further separate sodium chloride and produce high-temperature salt production mother liquor.

[0009] Further, step one includes the following steps: after preheating the brine, the preheated brine is divided into two streams. The first stream of brine, after being preheated, flows horizontally into the low-temperature evaporation salt production IV-effect evaporator and III-effect evaporator to obtain sodium chloride and high-nitrate salt production mother liquor. The second stream of brine, after being preheated, enters the high-temperature salt production I-effect evaporator to obtain sodium chloride high-temperature salt production mother liquor.

[0010] Furthermore, in step four, the method of processing through salt production efficiency is either flash evaporation or low-temperature evaporation.

[0011] Furthermore, the temperature range of the high-temperature evaporation salt production first-effect evaporator is 100-150℃; the temperature range of the low-temperature evaporation salt production fifth-effect evaporator is 35-55℃; and the temperature range of the medium-temperature evaporation nitrate production second-effect evaporator is 80-110℃.

[0012] Furthermore, the low-temperature evaporation process involves passing the nitrate mother liquor through a low-temperature evaporation salt production III-effect evaporator and a low-temperature evaporation salt production IV-effect evaporator to obtain sodium chloride and low-temperature salt production mother liquor.

[0013] Furthermore, the temperature range of the low-temperature evaporation salt production IV-effect evaporator is 55–90°C; the temperature range of the low-temperature evaporation salt production III-effect evaporator is 45–70°C.

[0014] Furthermore, the flash evaporation includes a first-stage flash evaporation and a second-stage flash evaporation. The process involves sequentially passing the nitrate mother liquor through a first-stage flash evaporation and a second-stage flash evaporation to obtain sodium chloride and a low-temperature salt production mother liquor. The temperature range of the first-stage flash evaporation is 80-95℃, and the temperature range of the second-stage flash evaporation is 60-75℃.

[0015] Furthermore, the brine comprises, by mass-volume concentration: NaCl 280–310 g / L, Na₂SO₄ 5.0–30 g / L.

[0016] Furthermore, the components of the nitrate brine include, in terms of mass-volume concentration: NaCl 255-60 g / L, Na2SO4 65-290 g / L.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This innovative process achieves simultaneous processing and separation of two different brine components, brine and nitrate brine, within the same multi-effect evaporation system, avoiding the need for two separate units or complex pretreatment required in traditional processes. Through the systematic coupling of material and energy flows, multiple steps in nitrate separation are integrated into one, significantly simplifying the production process, reducing equipment investment and operational complexity, and resulting in a high-purity and high-recovery product.

[0018] 2. The system fully utilizes the condensate from multi-effect evaporation, secondary steam, and the flash heat from the mother liquor in the final effect to preheat the raw brine in stages. Through the rational arrangement of high, medium, and low temperatures and the countercurrent and circulation design of the mother liquor, it achieves cascaded recovery and efficient utilization of heat energy. This design significantly reduces the consumption of fresh steam, and the overall energy consumption is significantly lower than that of traditional fractional processing technology. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments, and all described quantities are by weight. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0020] Step 1: Take 160 m³ / h of brine (300 g / L NaCl, 11 g / L Na₂SO₄) as raw material, preheat it, and then flow it horizontally into the low-temperature evaporation salt production IV-effect (82℃) evaporator and III-effect (66℃) evaporator to obtain 14.14 tons / h of sodium chloride and 101 m³ / h of low-nitrate salt production mother liquor (341.65 g / L NaCl, 17.35 g / L Na₂SO₄). This low-nitrate salt production mother liquor flows countercurrently into the high-temperature salt production I-effect (118℃) evaporator to obtain 24.36 tons / h of sodium chloride and 33 m³ / h of high-temperature salt production mother liquor (316 g / L NaCl, 54 g / L Na₂SO₄). Step 2: Take 230 m³ / h of nitrate brine (240 g / L NaCl, 100 g / L Na₂SO₄) as raw material, and after preheating, enter it horizontally into a low-temperature evaporation evaporation tank with a third-effect (82℃) to obtain 13.37 tons / h of sodium sulfate and 180 m³ / h of low-salt nitrate mother liquor (306.5 g / L NaCl, 53.5 g / L Na₂SO₄). Step 3: The 33 m³ / h high-temperature salt production mother liquor obtained in Step 1, the 180 m³ / h low-salt nitrate production mother liquor obtained in Step 2, and the 973 m³ / h final-effect salt production mother liquor (294.2 g / L NaCl, 64.6 g / L Na₂SO₄) reused in Step 5 are all fed into a medium-temperature evaporation nitrate production II-effect (102℃) evaporator to obtain 11.39 tons / h of sodium sulfate and 1148 m³ / h of nitrate production mother liquor (308 g / L NaCl, 54 g / L Na₂SO₄). Step 4: The 1148 m³ / h nitrate mother liquor is subjected to first-stage (91℃) and second-stage (68℃) flash evaporation to obtain 32.33 tons / h of sodium chloride and 1071 m³ / h of low-temperature salt production mother liquor (301.1 g / L NaCl, 57.9 g / L Na2SO4). Step 5: 1071 m³ / h of low-temperature salt production mother liquor is fed into the low-temperature evaporation salt production final V-effect evaporator (48℃) to obtain 33.23 tons / h of sodium chloride and 973 m³ / h of final effect salt production mother liquor (294.2 g / L NaCl, 64.6 g / L Na2SO4). Step Six: The 973 m³ / h final-effect salt production mother liquor is preheated by the secondary steam generated by flash evaporation and then circulated to the medium-temperature evaporation tank for nitrate production in Step Three to form a dynamic balance and achieve continuous production; finally, the sodium chloride and sodium sulfate mother liquors produced by the evaporation system are dehydrated and dried to obtain industrial wet salt, industrial dry salt and sodium sulfate products, respectively. Example

[0021] Step 1: Take 160 m³ / h of brine (NaCl 300 g / L, Na₂SO₄ 11 g / L) as raw material and divide it into two streams; The first stream of brine (74.6 m³ / h) is preheated and then flows horizontally into the low-temperature evaporation salt production tanks IV (82℃) and III (66℃), yielding 17.62 tons / h of sodium chloride and 15.6 m³ / h of high-nitrate salt production mother liquor (305.4 g / L NaCl, 52.6 g / L Na₂SO₄). The second stream of brine (85.4 m³ / h) is preheated and then enters the high-temperature salt production efficiency I (118℃) evaporator to obtain 20.12 tons / h of sodium chloride and 17.4 m³ / h of high-temperature salt production mother liquor (316 g / L NaCl, 54 g / L Na2SO4). Step 2: Take 230 m³ / h of nitrate brine (240 g / L NaCl, 100 g / L Na₂SO₄) as raw material, and after preheating, enter it horizontally into a low-temperature evaporation evaporation tank with a third-effect (82℃) to obtain 13.37 tons / h of sodium sulfate and 180 m³ / h of low-salt nitrate mother liquor (306.5 g / L NaCl, 53.5 g / L Na₂SO₄). Step 3: The 17.4 m³ / h high-temperature salt production mother liquor obtained in Step 1, the 180 m³ / h low-salt nitrate production mother liquor obtained in Step 2, and the 973 m³ / h final-effect salt production mother liquor (294.2 g / L NaCl, 64.6 g / L Na₂SO₄) to be reused are all fed into the medium-temperature evaporation nitrate production II-effect (102℃) evaporator to obtain 11.39 tons / h of sodium sulfate and 1148 m³ / h of nitrate production mother liquor (308 g / L NaCl, 54 g / L Na₂SO₄). Step 4: The 1148 m³ / h nitrate mother liquor was successively treated by low-temperature evaporation salt production process III (88℃) and IV (66℃) to obtain 32.33 tons / h of sodium chloride and 1071 m³ / h of low-temperature salt production mother liquor (301.1 g / L NaCl, 57.9 g / L Na2SO4). Step 5: Combine the 1071 m³ / h low-temperature salt production mother liquor with the 15.6 m³ / h high-nitrate salt production mother liquor obtained in Step 1, and enter the low-temperature evaporation salt production final V-effect evaporator (48℃) to obtain 33.23 tons / h of sodium chloride and 973 m³ / h of final-effect salt production mother liquor (294.2 g / L NaCl, 64.6 g / L Na2SO4). Step Six: The 973 m³ / h final-effect salt production mother liquor is preheated with secondary steam from the low-temperature evaporation salt production effect and then circulated to the medium-temperature evaporation nitrate production II-effect evaporator in Step Three to form a dynamic balance and achieve continuous production; finally, the sodium chloride and sodium sulfate mother liquors produced by the evaporation system are dehydrated and dried to obtain industrial wet salt, industrial dry salt and sodium sulfate products, respectively. Example

[0022] Step 1: Take 205 m³ / h of brine (300 g / L NaCl, 15 g / L Na₂SO₄) as raw material, preheat it, and then flow it horizontally into the low-temperature evaporation salt production IV-effect (66℃) evaporator and III-effect (82℃) evaporator to obtain 13.11 tons / h of sodium chloride and 149 m³ / h of low-nitrate salt production mother liquor (324.1 g / L NaCl, 35.9 g / L Na₂SO₄). This low-nitrate salt production mother liquor flows countercurrently into the high-temperature salt production I-effect (118℃) evaporator to obtain 22.7 tons / h of sodium chloride and 86 m³ / h of high-temperature salt production mother liquor (324.1 g / L NaCl, 35.9 g / L Na₂SO₄). Step 2: Take 185 m³ / h of nitrate brine (210 g / L NaCl, 130 g / L Na₂SO₄) as raw material, preheat it and then flow it horizontally into a low-temperature evaporation evaporation tank with a secondary efficiency (100℃) to obtain 13.39 tons / h of sodium sulfate and 138 m³ / h of low-salt nitrate mother liquor (282.5 g / L NaCl, 77.5 g / L Na₂SO₄). Step 3: The 86 m³ / h high-temperature salt production mother liquor obtained in Step 1, the 138 m³ / h low-salt nitrate production mother liquor obtained in Step 2, and the 729 m³ / h final-effect salt production mother liquor (293.7 g / L NaCl, 64.97 g / L Na₂SO₄) reused in Step 5 are all fed into a medium-temperature evaporation nitrate production II-effect (100℃) evaporator to obtain 11.39 tons / h of sodium sulfate and 1154 m³ / h of nitrate production mother liquor (309.2 g / L NaCl, 54 g / L Na₂SO₄). Step 4: The 1154 m³ / h nitrate mother liquor is subjected to first-stage (90.98℃) and second-stage (67.6℃) flash evaporation to obtain 33.9 tons / h of sodium chloride and 1076 m³ / h of low-temperature salt production mother liquor (301.1 g / L NaCl, 57.9 g / L Na2SO4). Step 5: 1076 m³ / h of low-temperature salt production mother liquor is fed into the low-temperature evaporation salt production final V-effect evaporator (48℃) to obtain 33.9 tons / h of sodium chloride and 729 m³ / h of final effect salt production mother liquor (293.7 g / L NaCl, 64.97 g / L Na2SO4). Step Six: The 729 m³ / h final-effect salt production mother liquor is preheated by the secondary steam generated by flash evaporation and then circulated to the medium-temperature evaporation tank for nitrate production in Step Three to form a dynamic balance and realize continuous production of the evaporation system; finally, the sodium chloride and sodium sulfate crystals produced by the evaporation system are dehydrated and dried to obtain industrial wet salt, industrial dry salt and sodium sulfate products, respectively.

[0023] Comparative Example 1: A higher concentration of brine and nitrate brine was used as raw materials for preparation; the rest was the same as in Example 1. Specifically: Step 1: Take 160 m³ / h of brine (320 g / L NaCl, 9 g / L Na₂SO₄) as raw material, preheat it, and then flow it horizontally into the low-temperature evaporation salt production tanks IV (82℃) and III (66℃) to obtain 14.21 tons / h of sodium chloride and 98 m³ / h of low-nitrate salt production mother liquor (361.65 g / L NaCl, 15.35 g / L Na₂SO₄). This low-nitrate salt production mother liquor flows countercurrently into the high-temperature salt production tank I (118℃) to obtain 20.16 tons / h of sodium chloride and 46 m³ / h of high-temperature salt production mother liquor (331.12 g / L NaCl, 47.13 g / L Na₂SO₄). Step 2: Take 230 m³ / h of nitrate brine (260 g / L NaCl, 60 g / L Na₂SO₄) as raw material, and after preheating, enter it horizontally into a low-temperature evaporation evaporation tank with a third-effect (82℃) to obtain 14.17 tons / h of sodium sulfate and 147 m³ / h of low-salt nitrate mother liquor (325.2 g / L NaCl, 31.5 g / L Na₂SO₄). Step 3: The 46 m³ / h high-temperature salt production mother liquor obtained in Step 1, the 147 m³ / h low-salt nitrate production mother liquor obtained in Step 2, and the 845 m³ / h final-effect salt production mother liquor (207.1 g / L NaCl, 51.9 g / L Na₂SO₄) reused in Step 5 are all fed into a medium-temperature evaporation nitrate production II-effect (102℃) evaporator to obtain 10.23 tons / h of sodium sulfate and 1013 m³ / h of nitrate production mother liquor (204 g / L NaCl, 31 g / L Na₂SO₄). Step 4: Pass the 1013 m³ / h nitrate mother liquor through a first-stage (91℃) and second-stage (68℃) flash evaporation process to obtain 27.13 tons / h of sodium chloride and 1045 m³ / h of low-temperature salt production mother liquor (216.5 g / L NaCl, 50.3 g / L Na2SO4). Step 5: 1071 m³ / h of low-temperature salt production mother liquor is fed into the low-temperature evaporation salt production final V-effect evaporator (48℃) to obtain 27.13 tons / h of sodium chloride and 845 m³ / h of final effect salt production mother liquor (207.1 g / L NaCl, 51.9 g / L Na2SO4). Step Six: The 845 m³ / h final-effect salt production mother liquor is preheated by the secondary steam generated by flash evaporation and then circulated to the medium-temperature evaporation tank for nitrate production in Step Three to form a dynamic balance and achieve continuous production; finally, the sodium chloride and sodium sulfate mother liquors produced by the evaporation system are dehydrated and dried to obtain industrial wet salt, industrial dry salt and sodium sulfate products, respectively.

[0024] experiment: The mother liquor containing sodium chloride and sodium sulfate produced by the evaporation system in Examples 1-3 and Comparative Example 1 was transported to a subsequent system device for dehydration and drying to obtain the following products: industrial wet salt, industrial dry salt, and sodium sulfate. Purity tests were performed on the three products. The industrial wet salt and industrial dry salt were tested according to the national standard "Industrial Salt" (GB / T5462-2015), and the sodium sulfate was tested according to the national standard "Industrial Anhydrous Sodium Sulfate" (GB / T6009-2014). The data obtained are shown in Table 1 below.

[0025] Conclusion: The data above demonstrates that the simultaneous separation process of brine and nitrate brine proposed in this invention has achieved significant comprehensive results in actual operation. Through a unique material and heat energy coupling design, this process successfully achieves the synergistic processing and co-production of two different brine components, brine and nitrate brine, within the same evaporation system. Results show that the system can stably produce high-quality sodium chloride and sodium sulfate products, both of which exceed the national first-class product standard, with high resource recovery efficiency.

[0026] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A production process for preparing sodium chloride and sodium sulfate from brine and nitrate as dual raw materials, characterized in that: Includes the following steps: Step 1: Pretreatment of brine and initial separation of sodium chloride After the brine is preheated, it undergoes pretreatment and then enters the evaporation system to obtain sodium chloride and high-temperature salt production mother liquor. Step 2: Pretreatment of nitrate brine and initial separation of sodium sulfate After preheating the nitrate brine, it is fed into a low-temperature evaporation tank with a third-effect evaporation process to separate sodium sulfate product and obtain low-salt nitrate mother liquor. Step 3: Mixing the mother liquor with sodium sulfate for primary separation The high-temperature salt-making mother liquor obtained in step one, the low-salt nitrate-making mother liquor obtained in step two, and the final-effect salt-making mother liquor recycled from the system are all fed into the medium-temperature evaporation nitrate-making second-effect evaporator. Under these conditions, sodium sulfate crystallizes out in large quantities again to obtain sodium sulfate product, and nitrate-making mother liquor is produced at the same time. Step 4: Treatment of Nitrogenation Mother Liquor and Recycling of Sodium Chloride The nitrate mother liquor obtained in step three is processed to further recover sodium chloride and obtain low-temperature salt production mother liquor. Step 5: Final Salt Production and Mother Liquor Output The low-temperature salt production mother liquor obtained in step four is sent to the low-temperature evaporation salt production final V-effect evaporation tank for evaporation and crystallization, and sodium chloride is recovered again to obtain the final effect salt production mother liquor. Step Six: Waste Heat Recovery and Mother Liquor Circulation The mother liquor from the final effect of salt production is preheated, and the preheated mother liquor is recycled back to the second-effect evaporator for medium-temperature evaporation in step three, where it continues to participate in the reaction as part of the raw materials, thus achieving continuous production; finally, sodium chloride and sodium sulfate are recovered.

2. The production process for preparing sodium chloride and sodium sulfate from brine and nitrate brine as described in claim 1, characterized in that: Step one includes the following steps: After preheating the brine, it is all fed into the low-temperature evaporation salt production IV-effect evaporator and III-effect evaporator in a horizontal flow to separate some sodium chloride and obtain low-nitrate salt production mother liquor; the mother liquor is then fed into the high-temperature evaporation salt production I-effect evaporator in a countercurrent flow to further separate sodium chloride and produce high-temperature salt production mother liquor, wherein the temperature range of the high-temperature evaporation salt production I-effect evaporator is 100-150℃.

3. The production process for preparing sodium chloride and sodium sulfate from brine and nitrate brine as described in claim 1, characterized in that: Step one includes the following steps: After preheating the brine, the preheated brine is divided into two streams. The first stream of brine, after preheating, flows horizontally into the low-temperature evaporation salt production IV-effect evaporator and III-effect evaporator to obtain sodium chloride and high-nitrate salt production mother liquor. The second stream of brine, after preheating, enters the high-temperature salt production I-effect evaporator to obtain sodium chloride and high-temperature salt production mother liquor.

4. The production process for preparing sodium chloride and sodium sulfate from brine and nitrate brine as described in claim 1, characterized in that: In step four, the processing method is either flash evaporation or low-temperature evaporation.

5. The production process for preparing sodium chloride and sodium sulfate from brine and nitrate brine as described in claim 1, characterized in that: The temperature range of the low-temperature evaporation salt-making V-effect evaporator is 35–55℃; the temperature range of the medium-temperature evaporation nitrate-making II-effect evaporator is 80–110℃.

6. The production process for preparing sodium chloride and sodium sulfate from brine and nitrate brine as described in claim 4, characterized in that: The low-temperature evaporation process involves passing the nitrate mother liquor through a low-temperature evaporation salt production III-effect evaporator and a low-temperature evaporation salt production IV-effect evaporator to obtain sodium chloride and low-temperature salt production mother liquor.

7. The production process for preparing sodium chloride and sodium sulfate from brine and nitrate brine as described in any one of claims 2 or 3, characterized in that: The temperature range of the IV-effect evaporator for low-temperature salt production is 55–90℃; the temperature range of the III-effect evaporator for low-temperature salt production is 45–70℃.

8. The production process for preparing sodium chloride and sodium sulfate from brine and nitrate brine as described in claim 4, characterized in that: The flash evaporation includes a first-stage flash evaporation and a second-stage flash evaporation. The process involves sequentially passing the nitrate mother liquor through a first-stage flash evaporation and a second-stage flash evaporation to obtain sodium chloride and a low-temperature salt production mother liquor. The temperature range of the first-stage flash evaporation is 80-95℃, and the temperature range of the second-stage flash evaporation is 60-75℃.

9. The production process for preparing sodium chloride and sodium sulfate from brine and nitrate brine as described in claim 1, characterized in that: The brine comprises, by mass-volume concentration: NaCl 280–310 g / L, Na₂SO₄ 5.0–30 g / L.

10. The production process for preparing sodium chloride and sodium sulfate from brine and nitrate brine as described in claim 1, characterized in that: The components of the nitrate brine include, by mass-volume concentration: NaCl 255-60 g / L, Na2SO4 65-290 g / L.

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