Efficient brine refining process

Abstract

The invention relates to the technical field of salt-containing wastewater treatment, and particularly discloses an efficient brine refining process. The invention relates to an efficient brine refining process which comprises the following steps: sequentially carrying out air flotation treatment, oxidation treatment, coagulating sedimentation and reverse osmosis membrane concentration on salt-containing wastewater to obtain reverse osmosis concentrated water; wherein a composite flocculating agent is used during coagulating sedimentation, and the raw material of the composite flocculating agent comprises a mixture consisting of polyaluminum chloride, polyacrylamide, ferrous sulfate, diatomite, nano silicon dioxide and activated carbon; carrying out nanofiltration membrane separation on the reverse osmosis concentrated water to obtain sodium sulfate-containing concentrated water and sodium chloride-containing clear water; the method comprises the following steps: oxidizing sodium chloride-containing clear water, evaporating and crystallizing to obtain mother liquor A and crystals A, and drying the crystals A to obtain sodium chloride; performing freezing crystallization on the sodium sulfate-containing concentrated water to obtain mother liquor B and crystals B, and performing salt melting crystallization and drying on the crystals B to obtain sodium sulfate; and concentrating the mother liquor A and the mother liquor B, performing evaporative crystallization, and drying to obtain the carnallite.

Description

Technical Field

[0001] The present application relates to the technical field of saline wastewater treatment, and in particular to a high-efficiency brine refining process. Background Art

[0002] Shale oil wastewater is mainly produced in the process of hydraulic fracturing operations, and its main characteristics are: first, high viscosity, high iron, high suspended matter, and high salt; second, complex composition, with more than 20 chemical additives, including friction reducers, cross-linking agents, scale inhibitors, etc. At the same time, due to contact with formation water, it contains a variety of mineral elements and soluble substances in oil and gas reservoirs; third, the water quality fluctuates greatly. During the backflow process of the fracturing fluid, the composition of the fracturing backflow fluid itself will continue to change. The initial backflow fluid composition is basically the same as the fracturing fluid composition. In the middle and late stages of the backflow process, the ion concentration shows a trend of continuous increase, and in different reservoirs, its physical and chemical properties will also vary to a certain extent; fourth, the discharge volume of the backflow fluid varies greatly. Because it is affected by the different well locations of the oil and gas reservoirs, the discharge volume of the backflow fluid will also vary greatly. In some cases, no backflow fluid even appears.

[0003] Through oil separation, oxidation, flocculation flotation, multi-media filtration or membrane treatment, shale oil wastewater can achieve multiple treatment goals such as reinjection, re-dispensing, reuse or external discharge of return fluid. However, the previous treatment of shale oil wastewater was "heavy on water and light on mud". The large amount of salt contained in shale oil wastewater was generally treated by a combination of concentration and evaporation crystallization. The by-product crystalline salt appeared in a mixed form, resulting in a low yield of the target products sodium chloride and sodium sulfate. Summary of the invention

[0004] In order to improve the yield of target products sodium chloride and sodium sulfate, the present application provides a high-efficiency brine refining process.

[0005] The present application provides a high-efficiency brine refining process, which adopts the following technical solution: A high-efficiency brine refining process comprises the following steps: Pretreatment: The saline wastewater is subjected to flotation treatment, oxidation treatment, coagulation and sedimentation, and reverse osmosis membrane concentration in sequence to obtain reverse osmosis concentrated water; a composite flocculant is used during coagulation and sedimentation, and the raw materials of the composite flocculant include a mixture of polyaluminium chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano-silicon dioxide, and activated carbon; Nanofiltration: The reverse osmosis concentrated water is separated by nanofiltration membrane to obtain concentrated water containing sodium sulfate and clear water containing sodium chloride; Preparation of sodium chloride: oxidize and evaporate the sodium chloride-containing water to obtain mother liquor A and crystal A, and dry the crystal A to obtain sodium chloride; Preparation of sodium sulfate: Firstly freeze and crystallize the concentrated water containing sodium sulfate to obtain mother liquor B and crystal B, then perform salt melting crystallization on the crystal B and dry it to obtain sodium sulfate; Preparation of impure salts: concentrate mother liquor A and mother liquor B, evaporate and crystallize them, and dry them to obtain impure salts.

[0006] By adopting the above technical scheme, the combination of polyaluminium chloride, polyacrylamide, ferrous sulfate and diatomaceous earth is used to make the composite flocculant have a good flocculation effect. Nano-silicon dioxide can improve the adsorption performance and stability of diatomaceous earth, further enhancing the flocculation effect of the composite flocculant on suspended particles in wastewater. Activated carbon has excellent adsorption performance. Therefore, the composite flocculant in the present application can effectively remove suspended particles and other pollutants in wastewater, thereby effectively improving the final yield of sodium chloride and sodium sulfate.

[0007] In a specific embodiment, the weight ratio of polyaluminium chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano-silicon dioxide and activated carbon in the composite flocculant is 1: (0.1-0.3): (0.1-0.2): (0.4-0.5): (0.1-0.2): (0.05-0.08).

[0008] By adopting the above technical scheme, the proportion of polyaluminium chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano-silicon dioxide and activated carbon in the composite flocculant is further limited, so that the flocculation effect of the composite flocculant can be further improved.

[0009] In a specific embodiment, the preparation method of the composite flocculant comprises the following steps: Firstly, nano silicon dioxide is added to diatomaceous earth, and the mixture is stirred and evenly mixed to obtain a composite material; polyacrylamide, ferrous sulfate, the composite material and activated carbon are added to polyaluminium chloride, and the mixture is stirred and evenly mixed to obtain a composite flocculant.

[0010] By adopting the above technical scheme, nano silicon dioxide is first mixed into diatomaceous earth to obtain a composite material, and then polyacrylamide, ferrous sulfate, the composite material and activated carbon are added into polyaluminium chloride, stirred and mixed evenly to obtain a composite flocculant with good flocculation effect.

[0011] In a specific embodiment, the addition amount of the composite flocculant is 50-60 mg / L.

[0012] By adopting the above technical solution, the usage of the composite flocculant is further limited, so that the composite flocculant can perform flocculation and precipitation better.

[0013] In a specific embodiment, in the sodium sulfate preparation step, mirabilite seed crystals are added during freeze crystallization.

[0014] By adopting the above technical solution, the addition of mirabilite seed crystals can significantly promote the freeze crystallization process, improve the crystallization efficiency and purity of sodium sulfate, and thus improve the quality and yield of the product.

[0015] In a specific embodiment, polyethylene is deposited on the surface of the mirabilite seed crystals.

[0016] By adopting the above technical solution and using polyethylene to modify the mirabilite seed crystals, the contact state between the seed crystals and the solution can be improved, and the crystallization efficiency and crystal quality can be improved.

[0017] In a specific embodiment, the added amount of the mirabilite seed crystals accounts for 0.1%-0.3% by weight of the concentrated water containing sodium sulfate.

[0018] By adopting the above technical solution, the amount of sodium sulfate seed added is further limited, thereby further improving the yield of the product.

[0019] In a specific embodiment, the steps of preparing the impure salt are: concentrating mother liquor A and mother liquor B, evaporating and crystallizing to obtain mother liquor C and crystal C, drying crystal C to obtain impure salt, and adding mother liquor C to concentrated water containing sodium sulfate to continue freezing and crystallizing.

[0020] By adopting the above technical solution, the mother liquor C is added into concentrated water containing sodium sulfate to continue freezing and crystallizing, so as to further improve the yield of the obtained product.

[0021] In summary, the present application includes at least one of the following beneficial technical effects: 1. In the present application, the composite flocculant has a good flocculation effect by using polyaluminium chloride, polyacrylamide, ferrous sulfate and diatomaceous earth. Nano-silicon dioxide can improve the adsorption performance and stability of diatomaceous earth, further enhancing the flocculation effect of the composite flocculant on suspended particles in wastewater. Activated carbon has excellent adsorption performance. Therefore, the composite flocculant in the present application can effectively remove suspended particles and other pollutants in wastewater, thereby effectively improving the final yield of sodium chloride and sodium sulfate. 2. In this application, polyethylene is used to modify the mirabilite seed crystals, which can improve the contact state between the seed crystals and the solution, and improve the crystallization efficiency and crystal quality; 3. In the present application, the mother liquor C is added to the concentrated water containing sodium sulfate to continue freezing and crystallizing, which can further improve the yield of the product. DETAILED DESCRIPTION

[0022] The present application is further described in detail below with reference to the embodiments.

[0023] All raw materials in the examples are commercially available.

[0024] Preparation Example Preparation Example 1 Preparation Example 1 provides a method for preparing a composite flocculant, comprising the following steps: First, nano silicon dioxide is added to diatomaceous earth, and the mixture is stirred and mixed to obtain a composite material; polyacrylamide, ferrous sulfate, the composite material and activated carbon are added to polyaluminium chloride, and the mixture is stirred and mixed to obtain a composite flocculant; wherein the weight ratio of polyaluminium chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano silicon dioxide and activated carbon is 1:0.1:0.1:0.4:0.1:0.05.

[0025] Preparation Example 2 Preparation Example 2 provides a method for preparing a composite flocculant, comprising the following steps: First, nano silicon dioxide is added to diatomaceous earth, and the mixture is stirred and mixed to obtain a composite material; polyacrylamide, ferrous sulfate, the composite material and activated carbon are added to polyaluminium chloride, and the mixture is stirred and mixed to obtain a composite flocculant; wherein the weight ratio of polyaluminium chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano silicon dioxide and activated carbon is 1:0.2:0.15:0.45:0.15:0.06.

[0026] Preparation Example 3 Preparation Example 3 provides a method for preparing a composite flocculant, comprising the following steps: First, nano silicon dioxide is added to diatomaceous earth, and the mixture is stirred and mixed to obtain a composite material; polyacrylamide, ferrous sulfate, the composite material and activated carbon are added to polyaluminium chloride, and the mixture is stirred and mixed to obtain a composite flocculant; wherein the weight ratio of polyaluminium chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano silicon dioxide and activated carbon is 1:0.3:0.2:0.5:0.2:0.08.

[0027] Preparation Example 4 Preparation Example 4 provides a method for preparing a composite flocculant, comprising the following steps: Add polyacrylamide, ferrous sulfate and diatomaceous earth into polyaluminium chloride, stir and mix evenly to obtain a composite flocculant; wherein the weight ratio of polyaluminium chloride, polyacrylamide, ferrous sulfate and diatomaceous earth is 1:0.1:0.1:0.4. Example

[0028] Example 1 Example 1 provides a brine efficient refining process, comprising the following steps: Pretreatment: subjecting the saline wastewater to dissolved air flotation treatment to reduce the suspended solids content in the wastewater to 1900 mg / L; subjecting the wastewater after flotation treatment to oxidation treatment using ozone oxidation technology, wherein the ozone oxidation device adopts a contact oxidation tank, the ozone oxidant is provided by an ozone generator, the dosage of the ozone oxidant is 80 mg / L of wastewater, and the residence time of the wastewater in the contact oxidation tank is 30 min; adding the composite flocculant in Preparation Example 1 to the oxidized wastewater, flocculating and precipitating, filtering and removing the generated precipitate; subjecting the wastewater after flocculation treatment to reverse osmosis membrane concentration, the operating pressure of the reverse osmosis membrane concentration is 10 MPa, and obtaining reverse osmosis concentrated water; wherein the addition amount of the composite flocculant is 50 mg / L; Nanofiltration: The reverse osmosis concentrated water is separated by nanofiltration membrane. The operating pressure of nanofiltration is 5.0Mpa to obtain concentrated water containing sodium sulfate and clear water containing sodium chloride. Preparation of sodium chloride: firstly oxidize the sodium chloride-containing water with ozone, then evaporate and crystallize at 50°C and 0.04Mpa to obtain mother liquor A and crystal A, and then dry the crystal A to obtain sodium chloride; Preparation of sodium sulfate: Firstly freeze and crystallize concentrated water containing sodium sulfate at 0°C to obtain mother liquor B and crystal B, and then perform salt melting crystallization on crystal B and dry it to obtain sodium sulfate; Preparation of impure salts: Mother liquor A and mother liquor B are first concentrated, and then evaporated and crystallized at 60°C and a pressure of 0.06 MPa to obtain mother liquor C and crystal C. Crystal C is dried to obtain impure salts.

[0029] Example 2 The difference between Example 2 and Example 1 is that, pretreatment: the salt-containing wastewater is subjected to dissolved air flotation treatment to reduce the suspended matter content in the wastewater to 1900 mg / L; the wastewater after flotation treatment is oxidized by ozone oxidation technology, the ozone oxidation device adopts a contact oxidation tank, the ozone oxidant is provided by an ozone generator, the dosage of the ozone oxidant is 80 mg / L of wastewater, and the residence time of the wastewater in the contact oxidation tank is 30 min; the composite flocculant in Preparation Example 2 is added to the oxidized wastewater, flocculation and precipitation are carried out, and the generated precipitate is removed by filtration; the wastewater after flocculation treatment is subjected to reverse osmosis membrane concentration, the operating pressure of the reverse osmosis membrane concentration is 10 MPa, and reverse osmosis concentrated water is obtained; wherein the addition amount of the composite flocculant is 50 mg / L; the remaining steps are consistent with Example 1.

[0030] Example 3 The difference between Example 3 and Example 1 is that, pretreatment: the salt-containing wastewater is subjected to dissolved air flotation treatment to reduce the suspended matter content in the wastewater to 1900 mg / L; the wastewater after flotation treatment is oxidized by ozone oxidation technology, the ozone oxidation device adopts a contact oxidation tank, the ozone oxidant is provided by an ozone generator, the dosage of the ozone oxidant is 80 mg / L of wastewater, and the residence time of the wastewater in the contact oxidation tank is 30 min; the composite flocculant in Preparation Example 3 is added to the oxidized wastewater, flocculation and precipitation are carried out, and the generated precipitate is removed by filtration; the wastewater after flocculation treatment is subjected to reverse osmosis membrane concentration, the operating pressure of the reverse osmosis membrane concentration is 10 MPa, and reverse osmosis concentrated water is obtained; wherein the addition amount of the composite flocculant is 50 mg / L; the remaining steps are consistent with Example 1.

[0031] Example 4 The difference between Example 4 and Example 2 is that, pretreatment: the salt-containing wastewater is subjected to dissolved air flotation treatment to reduce the suspended matter content in the wastewater to 1900 mg / L; the wastewater after flotation treatment is oxidized by ozone oxidation technology, the ozone oxidation device adopts a contact oxidation tank, the ozone oxidant is provided by an ozone generator, the dosage of the ozone oxidant is 80 mg / L of wastewater, and the residence time of the wastewater in the contact oxidation tank is 30 min; the composite flocculant in Preparation Example 2 is added to the oxidized wastewater, flocculation and precipitation are carried out, and the generated precipitate is removed by filtration; the wastewater after flocculation treatment is subjected to reverse osmosis membrane concentration, the operating pressure of the reverse osmosis membrane concentration is 10 MPa, and reverse osmosis concentrated water is obtained; wherein the addition amount of the composite flocculant is 55 mg / L; the remaining steps are consistent with Example 2.

[0032] Example 5 The difference between Example 5 and Example 2 is that, pretreatment: the salt-containing wastewater is subjected to dissolved air flotation treatment to reduce the suspended matter content in the wastewater to 1900 mg / L; the wastewater after flotation treatment is oxidized by ozone oxidation technology, the ozone oxidation device adopts a contact oxidation tank, the ozone oxidant is provided by an ozone generator, the dosage of the ozone oxidant is 80 mg / L of wastewater, and the residence time of the wastewater in the contact oxidation tank is 30 min; the composite flocculant in Preparation Example 2 is added to the oxidized wastewater, flocculation and precipitation are carried out, and the generated precipitate is removed by filtration; the wastewater after flocculation treatment is subjected to reverse osmosis membrane concentration, the operating pressure of the reverse osmosis membrane concentration is 10 MPa, and reverse osmosis concentrated water is obtained; wherein the addition amount of the composite flocculant is 60 mg / L; the remaining steps are consistent with Example 2.

[0033] Example 6 The difference between Example 6 and Example 4 is that, in the preparation of sodium sulfate, concentrated water containing sodium sulfate is first subjected to freeze crystallization at 0°C to obtain mother liquor B and crystal B, and the crystal B is subjected to salt melt crystallization and dried to obtain sodium sulfate; wherein during the freeze crystallization, mirabilite seed crystals are added, and the amount of mirabilite seed crystals added is 0.1% by weight of the concentrated water containing sodium sulfate; and the remaining steps are consistent with Example 4.

[0034] Example 7 The difference between Example 7 and Example 4 is that, in the preparation of sodium sulfate, concentrated water containing sodium sulfate is first subjected to freeze crystallization at 0°C to obtain mother liquor B and crystal B, and the crystal B is subjected to salt melt crystallization and dried to obtain sodium sulfate; wherein during the freeze crystallization, mirabilite seed crystals are added, and the amount of mirabilite seed crystals added is 0.2% by weight of the concentrated water containing sodium sulfate; and the remaining steps are consistent with Example 4.

[0035] Example 8 The difference between Example 8 and Example 4 is that, in the preparation of sodium sulfate, concentrated water containing sodium sulfate is first subjected to freeze crystallization at 0°C to obtain mother liquor B and crystal B, and the crystal B is subjected to salt melt crystallization and dried to obtain sodium sulfate; wherein during the freeze crystallization, mirabilite seed crystals are added, and the amount of mirabilite seed crystals added is 0.3% by weight of the concentrated water containing sodium sulfate; and the remaining steps are consistent with Example 4.

[0036] Example 9 The difference between Example 9 and Example 7 is that, in the preparation of sodium sulfate, concentrated water containing sodium sulfate is first subjected to freeze crystallization at 0°C to obtain mother liquor B and crystal B, and the crystal B is subjected to salt melt crystallization and dried to obtain sodium sulfate; wherein during the freeze crystallization, mirabilite seed crystals are added, the amount of mirabilite seed crystals added is 0.3% by weight of the concentrated water containing sodium sulfate, and polyethylene is deposited on the surface of the mirabilite seed crystals, and the thickness of the polyethylene is 0.01 mm; the remaining steps are consistent with Example 7.

[0037] Example 10 The difference between Example 10 and Example 9 is that, in the preparation of the impure salt, the mother liquor A and the mother liquor B are first concentrated, and then evaporated and crystallized at 60° C. and a pressure of 0.06 MPa to obtain mother liquor C and crystal C, the crystal C is dried to obtain the impure salt, the mother liquor C is oxidized with ozone and then added to concentrated water containing sodium sulfate to continue freezing and crystallization; the remaining steps are consistent with Example 9.

[0038] Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that, pretreatment: the salt-containing wastewater is subjected to dissolved air flotation treatment to reduce the suspended matter content in the wastewater to 1900 mg / L; the wastewater after flotation treatment is oxidized by ozone oxidation technology, the ozone oxidation device adopts a contact oxidation tank, the ozone oxidant is provided by an ozone generator, the dosage of the ozone oxidant is 80 mg / L of wastewater, and the residence time of the wastewater in the contact oxidation tank is 30 min; polyaluminum chloride is added to the oxidized wastewater, flocculation and precipitation are carried out, and the precipitate produced is removed by filtration; the wastewater after flocculation treatment is subjected to reverse osmosis membrane concentration, the operating pressure of the reverse osmosis membrane concentration is 10 MPa, and reverse osmosis concentrated water is obtained; wherein the amount of polyaluminum chloride added is 50 mg / L; the remaining steps are consistent with Example 1.

[0039] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that, pretreatment: the salt-containing wastewater is subjected to dissolved air flotation treatment to reduce the suspended matter content in the wastewater to 1900 mg / L; the wastewater after flotation treatment is oxidized by ozone oxidation technology, the ozone oxidation device adopts a contact oxidation tank, the ozone oxidant is provided by an ozone generator, the dosage of the ozone oxidant is 80 mg / L wastewater, and the residence time of the wastewater in the contact oxidation tank is 30 min; the composite flocculant in Preparation Example 4 is added to the oxidized wastewater, flocculation and precipitation are carried out, and the generated precipitate is removed by filtration; the wastewater after flocculation treatment is subjected to reverse osmosis membrane concentration, the operating pressure of the reverse osmosis membrane concentration is 10 MPa, and reverse osmosis concentrated water is obtained; wherein the addition amount of the composite flocculant is 50 mg / L; the remaining steps are consistent with Example 1.

[0040] Performance test yield: Test the yield of sodium chloride and sodium sulfate in the product. The higher the yield, the better the effect of the refining process.

[0041] Table 1 Performance test results of products sample Sodium chloride yield (%) Sodium sulfate yield (%) Example 1 93.1 90.3 Example 2 94.3 91.0 Example 3 93.6 90.5 Example 4 95.5 91.7 Example 5 95.6 91.8 Example 6 95.4 92.3 Example 7 95.4 92.5 Example 8 95.5 92.6 Example 9 95.5 93.2 Example 10 95.4 93.7 Comparative Example 1 83.5 85.3 Comparative Example 2 89.2 87.7 In combination with Example 1 and Comparative Examples 1-2, the yields of sodium chloride and sodium sulfate in Example 1 are the highest. It can be seen that when a flocculant is used for flocculation precipitation, a composite flocculant composed of polyaluminum chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano-silicon dioxide and activated carbon is selected. Nano-silicon dioxide can improve the adsorption performance and stability of diatomaceous earth, further enhancing the flocculation effect of the composite flocculant on suspended particles in wastewater. Activated carbon has excellent adsorption performance. The combination of polyaluminum chloride, polyacrylamide, ferrous sulfate and diatomaceous earth makes the composite flocculant have a good flocculation and adsorption effect, thereby effectively improving the final yield of sodium chloride and sodium sulfate.

[0042] Combined with Examples 1-3, the yields of sodium chloride and sodium sulfate in Example 2 are the highest. It can be seen that when preparing the composite flocculant, the ratio of polyaluminium chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano-silicon dioxide and activated carbon in Preparation Example 2 is optimal.

[0043] Combining Example 2, Example 4 and Example 5, it can be seen that when the flocculant is used for flocculation precipitation, when the addition amount of the composite flocculant is 50-60 mg / L, increasing the usage amount of the composite flocculant can increase the yield of the product.

[0044] Combining Example 4 with Examples 6-8, the yield of sodium sulfate in Examples 6-8 is higher. It can be seen that when performing freeze crystallization, adding mirabilite seed crystals can significantly promote the freeze crystallization process and increase the yield of sodium sulfate.

[0045] Combining Example 7 and Example 9, the yield of sodium sulfate in Example 9 is higher. It can be seen that when performing freeze crystallization, adding polyethylene-modified sodium sulfate seeds can improve the contact state between the seeds and the solution, thereby further improving the yield of sodium sulfate.

[0046] Combining Example 9 and Example 10, the yield of sodium sulfate in Example 10 is higher, which shows that when preparing impure salts, adding the obtained mother liquor C to concentrated water containing sodium sulfate to continue freezing and crystallizing can further improve the yield of sodium sulfate.

[0047] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A high-efficiency brine refining process, characterized in that: The steps include: Pretreatment: The saline wastewater is subjected to flotation treatment, oxidation treatment, coagulation and sedimentation, and reverse osmosis membrane concentration in sequence to obtain reverse osmosis concentrated water; a composite flocculant is used during coagulation and sedimentation, and the raw materials of the composite flocculant include a mixture of polyaluminium chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano-silicon dioxide, and activated carbon; Nanofiltration: The reverse osmosis concentrated water is separated by nanofiltration membrane to obtain concentrated water containing sodium sulfate and clear water containing sodium chloride; Preparation of sodium chloride: oxidize and evaporate the sodium chloride-containing water to obtain mother liquor A and crystal A, and dry the crystal A to obtain sodium chloride; Preparation of sodium sulfate: Firstly freeze and crystallize the concentrated water containing sodium sulfate to obtain mother liquor B and crystal B, then perform salt melting crystallization on the crystal B and dry it to obtain sodium sulfate; Preparation of impure salts: concentrate mother liquor A and mother liquor B, evaporate and crystallize them, and dry them to obtain impure salts.

2. A brine efficient refining process according to claim 1, characterized in that: The weight ratio of polyaluminium chloride, polyacrylamide, ferrous sulfate, diatomaceous earth, nano-silicon dioxide and activated carbon in the composite flocculant is 1: (0.1-0.3): (0.1-0.2): (0.4-0.5): (0.1-0.2): (0.05-0.08).

3. A brine efficient refining process according to claim 2, characterized in that: The preparation method of the composite flocculant comprises the following steps: Firstly, nano silicon dioxide is added to diatomaceous earth, and the mixture is stirred and evenly mixed to obtain a composite material; polyacrylamide, ferrous sulfate, the composite material and activated carbon are added to polyaluminium chloride, and the mixture is stirred and evenly mixed to obtain a composite flocculant.

4. A brine efficient refining process according to claim 3, characterized in that: The addition amount of the composite flocculant is 50-60 mg / L.

5. The high-efficiency brine refining process according to claim 1, characterized in that: In the sodium sulfate preparation step, mirabilite seed crystals are added during freezing crystallization.

6. A brine efficient refining process according to claim 5, characterized in that: Polyethylene is deposited on the surface of the mirabilite seed crystals.

7. A brine efficient refining process according to claim 6, characterized in that: The added amount of the mirabilite seed crystals accounts for 0.1%-0.3% of the weight fraction of the concentrated water containing sodium sulfate.

8. The high-efficiency brine refining process according to claim 1, characterized in that: The preparation steps of the impure salt are as follows: concentrating mother liquor A and mother liquor B, evaporating and crystallizing to obtain mother liquor C and crystal C, drying crystal C to obtain impure salt, and adding mother liquor C into concentrated water containing sodium sulfate to continue freezing and crystallizing.