A process and system for zero discharge treatment of high-salt wastewater with coexistence of potassium and sodium

Abstract

The application belongs to the technical field of industrial wastewater advanced treatment and resource utilization, and particularly relates to a potassium-sodium coexisting type high-salinity wastewater zero discharge treatment process method and system. The treatment process method comprises the following steps: potassium-sodium coexisting type high-salinity wastewater is treated by pretreatment, first-stage reverse osmosis, second-stage reverse osmosis, four-stage reverse osmosis, and the like, to obtain four-stage reverse osmosis effluent; the four-stage reverse osmosis effluent is sequentially subjected to four-stage high-density precipitation, four-stage medium filtration, four-stage ultrafiltration and evaporation crystallization treatment, to obtain sodium chloride and evaporation crystallization effluent; the evaporation crystallization effluent is subjected to cooling flash distillation to obtain potassium chloride and potassium-containing mother liquor, and the potassium-containing mother liquor is introduced into an evaporation crystallizer, and subjected to secondary evaporation crystallization and cooling flash distillation, to obtain sodium chloride and potassium chloride. The application realizes the advanced treatment of potassium-sodium coexisting type high-salinity wastewater, and obtains potassium chloride, sodium chloride and gypsum, thereby not only reducing environmental pollution and water recycling, but also efficiently extracting valuable resources such as potassium chloride as agricultural fertilizer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of industrial wastewater advanced treatment and resource utilization, and particularly relates to a potassium-sodium coexisting type high-salinity wastewater zero discharge treatment process method and system. BACKGROUND

[0002] High-salinity wastewater refers to industrial wastewater containing salt exceeding a certain concentration, and the source is very wide. The high-salinity wastewater is often accompanied by heavy metals (such as lead, cadmium, mercury) and organic pollutants, and direct discharge will cause multiple hazards to the environment and human health. The cations of most high-salinity wastewater are mainly sodium ions (divalent calcium, magnesium and other cations are replaced into sodium ions through chemical softening or ion exchange processes), such as coal chemical industry and petroleum chemical industry. The zero discharge process route of sodium type high-salinity wastewater is basically "pretreatment + membrane concentration + salt separation and crystallization", and finally the by-products sodium chloride and sodium sulfate are obtained. The salt separation methods of sodium type high-salinity wastewater mainly include thermal salt separation and nanofiltration salt separation. The thermal salt separation is to realize the separation of salts by controlling the appropriate operating temperature and concentration multiple in the crystallization process according to the concentration difference and solubility difference of different inorganic salts. The membrane salt separation is to realize the separation or enrichment of different salts in the crystallization process by membrane separation process according to the difference of ion radius or charge characteristics of chloride ions and sulfate ions, and then solid is obtained by the thermal crystallization process.

[0003] The thermal salt separation and crystallization process further includes direct evaporation crystallization process, salt-nitrate co-production salt separation and crystallization process and low-temperature crystallization process. When the content of a certain salt in the high-salinity wastewater has a large advantage, the direct evaporation crystallization process is usually used to separate and recover the advantageous salt component. When there is no salt component with a large proportion in the wastewater, the salt recovery rate of the direct evaporation crystallization process is low, and the step-by-step crystallization of sodium sulfate and sodium chloride can be used to crystallize sodium sulfate at a higher temperature and crystallize sodium chloride at a lower temperature, which is called salt-nitrate co-production process.

[0004] The low-temperature crystallization process refers to the following process: high-salt wastewater containing mixed salts of sodium sulfate and sodium chloride is concentrated to a certain degree at a relatively high temperature, and then rapidly cooled to crystallize a large amount of sodium sulfate decahydrate (mirabilite) solid. Since the mirabilite obtained by low-temperature crystallization has a relatively low market price and a high transportation cost, a hot-solution evaporation crystallization unit is usually added to obtain anhydrous sodium sulfate (sodium sulfate) to improve the product value. Since the low-temperature crystallization process can only obtain sodium sulfate solid, in order to obtain sodium chloride, the low-temperature crystallization process needs to be combined with a high-temperature crystallization process. Due to the large change in solubility, the low-temperature crystallization process can achieve a high recovery rate of sodium sulfate and sodium chloride, and the purity of the crystallized salt is also easier to control than that in the salt-mirabilite co-production process. The influence of organic matter on the whiteness of the crystallized salt in the low-temperature crystallization process is also smaller. The nanofiltration salt separation process mainly utilizes the selective interception characteristics of nanofiltration membranes for divalent salts to separate monovalent salt sodium chloride and divalent salt sodium sulfate in the liquid phase. Sodium chloride mainly enters the nanofiltration permeate, and sodium sulfate is concentrated in the nanofiltration concentrated water. By crystallizing the nanofiltration permeate and concentrated liquid respectively, sodium chloride and sodium sulfate crystallized salts can be finally recovered.

[0005] However, part of the cations in the high-salt wastewater, such as landfill leachate, contains a large amount of potassium ions in addition to sodium ions. The traditional sodium-type high-salt wastewater mainly contains three ions, namely sodium ions, chloride ions and sulfate ions, and can generate two by-products, sodium chloride and sodium sulfate, after thermal salt separation or nanofiltration salt separation. The potassium-sodium coexisting type high-salt wastewater mainly contains four ions, potassium ions, sodium ions, chloride ions and sulfate ions, which can form four by-products, sodium chloride, sodium sulfate, potassium chloride and potassium sulfate, after the combination of anions and cations. At this time, it is difficult to obtain four by-products by thermal salt separation through the difference in solubility of the four substances at different temperatures. Even if the nanofiltration salt separation process is used, sodium sulfate and potassium sulfate on the nanofiltration concentrated water side cannot be crystallized by thermal salt separation. Therefore, the zero discharge of potassium-sodium coexisting type high-salt wastewater faces great difficulties. If salt separation cannot be achieved, a large amount of mixed salt hazardous waste will be formed, which has a high disposal cost. SUMMARY

[0006] The purpose of the present application is to provide a potassium-sodium coexisting type high-salt wastewater zero discharge treatment process method and system, so as to overcome the shortcomings of the prior art, and to realize the deep treatment of potassium-sodium coexisting type high-salt wastewater, as well as the salt separation and crystallization and resource utilization.

[0007] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0008] In a first aspect, the present application provides a potassium-sodium coexisting type high-salt wastewater zero discharge treatment process method, comprising the following steps:

[0009] The pretreated potassium-sodium coexisting type high-salt wastewater is subjected to a first reverse osmosis treatment to obtain fresh water and a first reverse osmosis effluent;

[0010] The first-stage reverse osmosis effluent is sequentially subjected to a first-stage high-density precipitation, a first-stage medium filtration, a first-stage ultrafiltration, and a second-stage reverse osmosis treatment to obtain fresh water and a second-stage reverse osmosis effluent;

[0011] The second-stage reverse osmosis effluent is subjected to a second-stage calcium sulfate crystallization to obtain calcium sulfate and a second-stage calcium sulfate crystallization effluent;

[0012] The second-stage calcium sulfate crystallization effluent is sequentially subjected to a second-stage high-density precipitation, a second-stage medium filtration, a second-stage ultrafiltration, and a third-stage nanofiltration treatment to obtain a third-stage nanofiltration concentrated solution and a third-stage nanofiltration permeate;

[0013] The third-stage nanofiltration concentrated solution is subjected to a third-stage calcium sulfate crystallization treatment to obtain calcium sulfate and a third-stage calcium sulfate crystallization effluent;

[0014] The third-stage calcium sulfate crystallization effluent is sequentially subjected to a third-stage high-density precipitation, a third-stage medium filtration, and a third-stage ultrafiltration to obtain a third-stage ultrafiltration effluent;

[0015] The third-stage ultrafiltration effluent is returned and mixed with the second-stage ultrafiltration effluent, and then re-enters the third-stage nanofiltration treatment.

[0016] In some other embodiments, the third-stage nanofiltration permeate is sequentially subjected to an ion exchange resin treatment, a decarbonization, and a fourth-stage reverse osmosis treatment to obtain fresh water and a fourth-stage reverse osmosis effluent;

[0017] The fourth-stage reverse osmosis effluent is sequentially subjected to a fourth-stage high-density precipitation, a fourth-stage medium filtration, a fourth-stage ultrafiltration, and an evaporation crystallization treatment to obtain sodium chloride and an evaporation crystallization effluent;

[0018] The evaporation crystallization effluent is subjected to a cooling flash treatment to obtain potassium chloride, and the cooling flash effluent is returned to the evaporation crystallizer to be subjected to a re-evaporation crystallization to obtain sodium chloride.

[0019] In some other embodiments, the pretreatment is a hardness removal, a silicon removal, a biochemical treatment, an ozone catalytic oxidation, a medium filtration, and a hollow fiber ultrafiltration membrane filtration treatment on the potassium-sodium coexisting type high-salinity wastewater;

[0020] The agent used in the hardness removal and the silicon removal is lime milk, and the dosage is 150-250 mg / L, and the dosage concentration is 8-12%;

[0021] The total silicon of the pretreated wastewater is less than 30 mg / L, the COD is less than 20 mg / L, the SDI is less than 3, the fluorine is less than 3 mg / L, and the calcium ion is 100-200 mg / L.

[0022] In some other embodiments, the recovery rate of the first-stage reverse osmosis treatment is 70-80%, the membrane flux is 15-18 L / (m 2 ·h), and the operating pressure is 1.4-1.6 MPa;

[0023] Or, the reagent added in the first high-density precipitation is sodium hydroxide and sodium carbonate, the adding point is the mixing zone of the high-density precipitation tank, the adding amount of sodium hydroxide is 75-85 mg / L, the adding concentration is 25-35%, the adding amount of sodium carbonate is 400-450 mg / L, and the adding concentration is 18-25%;

[0024] The silicon in the effluent of the first high-density precipitation tank is less than 30 mg / L, and the calcium ion is 200-500 mg / L.

[0025] In some other embodiments, the recovery rate of the second reverse osmosis treatment is 60%-80%, the membrane flux is 15-18 L / (m 2 ·h), and the operating pressure is 1.4-1.6 MPa;

[0026] Or, the concentration of sulfate in the effluent of the second calcium sulfate crystallization is 5000-6000 mg / L, and the calcium ion is 1200-1600 mg / L;

[0027] Or, the reagent added in the second high-density precipitation is sodium carbonate, the adding amount of sodium carbonate is 1800-1900 mg / L, the adding concentration is 18-25%, the silicon in the effluent of the second high-density precipitation is less than 30 mg / L, and the calcium ion is 400-800 mg / L.

[0028] In some other embodiments, the recovery rate of the third nanofiltration is 50-75%, the membrane flux is 15-18 L / (m 2 ·h), and the operating pressure is 2.8-3.2 MPa;

[0029] Or, the reagent added in the third calcium sulfate crystallization is calcium chloride, the adding amount of calcium chloride is 16000-16500 mg / L, the adding concentration is 18-22%, the concentration of sulfate in the effluent of the third calcium sulfate crystallization is 6000-8000 mg / L, and the calcium ion is 1400-1800 mg / L;

[0030] Or, the reagent added in the third high-density precipitation is sodium carbonate, the adding amount of sodium carbonate is 1500-1600 mg / L, the adding concentration is 18-22%, and the calcium ion in the effluent of the third high-density precipitation is 800-1200 mg / L.

[0031] In some other embodiments, the hardness of the effluent of the ion exchange resin is less than 1 mg / L, the bicarbonate in the decarbonated effluent is less than 20 mg / L,

[0032] Or, the recovery rate of the fourth reverse osmosis is 40%-60%, the TDS of the effluent is 70000-80000 mg / L, the membrane flux is 15-18 L / (m 2The operating pressure is 6.8-7.2 MPa;

[0033] Alternatively, the medicament added in the four-stage high-density sedimentation tank is sodium hydroxide and sodium metaaluminate, the addition amount of sodium hydroxide is 35-45 mg / L, the addition concentration is 25-35%, the addition amount of sodium metaaluminate is 160-170 mg / L, and the addition concentration is 8-12%, and the silicon in the effluent is less than 20 mg / L.

[0034] In some other embodiments, the evaporation crystallization is carried out at a temperature of 100-110 DEG C, and the sodium chloride content is greater than 96%;

[0035] The cooling flash evaporation is carried out at a temperature of 40-50 DEG C, and the potassium oxide content is greater than 60%;

[0036] Alternatively, part of the evaporation crystallization mother liquor is subjected to external discharge and drying treatment.

[0037] In the second aspect, the application provides a potassium-sodium coexisting type high-salinity wastewater zero discharge treatment system for performing the potassium-sodium coexisting type high-salinity wastewater zero discharge treatment process method of the first aspect, which comprises, in sequence, a pretreatment unit, a first-stage reverse osmosis unit, a first-stage high-density sedimentation tank, a first-stage medium filter tank, a first-stage ultrafiltration tank, a second-stage reverse osmosis unit, a second-stage calcium sulfate crystallization tank, a second-stage high-density sedimentation tank, a second-stage medium filter tank, a second-stage ultrafiltration tank, and a third-stage nanofiltration unit.

[0038] The third-stage nanofiltration unit is provided with a permeate outlet of the third-stage nanofiltration unit and a concentrated liquid outlet of the third-stage nanofiltration unit.

[0039] Further comprising, in sequence, a third-stage calcium sulfate crystallization tank, a third-stage high-density sedimentation tank, a third-stage medium filter tank, and a third-stage ultrafiltration tank connected to the concentrated liquid outlet of the third-stage nanofiltration unit.

[0040] The effluent outlet of the third-stage ultrafiltration tank is connected to the water inlet of the third-stage nanofiltration unit.

[0041] In some other embodiments, further comprising, in sequence, an ion exchange resin membrane, a decarbonization tank, a fourth-stage reverse osmosis unit, a fourth-stage high-density sedimentation tank, a fourth-stage medium filter tank, an evaporation crystallizer, and a cooler connected to the permeate outlet of the third-stage nanofiltration unit.

[0042] The outlet of the cooler is connected to the inlet of the evaporation crystallizer.

[0043] The beneficial effects of the application are as follows:

[0044] (1) The condensate water of the first-stage reverse osmosis, the second-stage reverse osmosis, the fourth-stage reverse osmosis, and the evaporation crystallization can be recycled as high-quality reclaimed water, the wastewater is not discharged into natural water bodies, the damage of high-concentration wastewater to the water ecological environment is avoided, and the waste of potassium resources is also avoided.

[0045] (2) The recovered calcium sulfate (gypsum) byproduct of the present application can also be recycled as a building decoration material, and the sodium chloride byproduct can be recycled as a snow-melting agent or for producing acid and alkali.

[0046] (3) The present application can be widely applied to industries such as landfill leachate, waste incineration fly ash, new energy battery industry, and semiconductor industry, which have high-salinity wastewater containing potassium ions, sodium ions, chloride ions, and sulfate ions, and the concentration of sulfate ions in anions is greater than 50%, and the concentration of potassium ions in cations is also greater than 20%. The zero-emission treatment of high-salinity wastewater in these industries will be conducive to the recycling and utilization of industrial salt.

[0047] In summary, through the innovation of the treatment method and system, the present application not only realizes the deep treatment of wastewater, but also recovers byproducts such as calcium sulfate (gypsum), potassium chloride, and sodium chloride during the treatment process, avoiding the problem of difficult disposal of a large amount of mixed salt hazardous waste obtained by traditional evaporation crystallization. The recovery of valuable potassium chloride as fertilizer in potassium-sodium coexisting high-salinity wastewater has important strategic value. BRIEF DESCRIPTION OF DRAWINGS

[0048] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the present application and are incorporated in and constitute a part of this specification. The embodiments of these drawings are set forth to explain the present application and are not intended to limit the present application in any way.

[0049] Figure 1 The flow chart of the potassium-sodium coexisting high-salinity wastewater zero-emission treatment process method in Example 1 of the present application;

[0050] Figure 2 The flow chart of the potassium-sodium coexisting high-salinity wastewater zero-emission treatment process method in Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0051] Those skilled in the art will understand that the following examples are intended to be illustrative only and are not intended to limit the scope of the present application. Unless otherwise indicated, the specific conditions in the examples were carried out under conventional conditions or under the conditions recommended by the manufacturer. Unless otherwise indicated, the components used were conventional products available on the market.

[0052] The TDS in the potassium-sodium coexisting high-salinity wastewater is 2000-6000 mg / L, the main anions are chloride ions and sulfate ions, and the concentration of sulfate ions is greater than 50%; the main cations are potassium ions and sodium ions, and the concentration of potassium ions is greater than 20%. The treatment process method includes the following steps:

[0053] First, the high-salt wastewater with coexistence of potassium and sodium is pretreated to remove hardness and silicon, etc. to reduce the risk of fouling in the subsequent membrane and evaporation crystallization reactor. The pretreatment unit adopts chemical method to remove silicon and hardness simultaneously. The reagent used is lime milk (Ca(OH)2), which only removes the temporary hardness in the wastewater and retains part of the calcium ions in the wastewater to reduce the dosage of calcium chloride in the subsequent calcium sulfate crystallization unit. The calcium ion in the pretreatment unit effluent is 100-200 mg / L, and the calcium sulfate saturation is controlled to be less than 40% by adjusting the dosage of lime milk. During the hardness removal process, calcium silicate and calcium fluoride are also partially removed. The total silicon in the pretreatment unit effluent needs to be less than 30 mg / L (calculated as SiO2), and the fluorine needs to be less than 3 mg / L to avoid SiO2 and calcium fluoride fouling in the first reverse osmosis concentrated water. In addition, the pretreatment unit also needs to use biochemical treatment or advanced oxidation and other measures to control the COD to be less than 20 mg / L, and at the same time, the SDI is controlled to be less than 3 through medium filtration and ultrafiltration membrane filtration to meet the requirements of the first reverse osmosis inlet water, avoiding the first reverse osmosis fouling;

[0054] The effluent of the pretreatment unit first enters the first reverse osmosis unit for preliminary concentration. The recovery rate of the first reverse osmosis unit is 70%-80%, and the concentrations of various ions in the wastewater are enriched, and the calcium ions, silicon, fluorine and other fouling substances are also concentrated. At this time, the calcium sulfate saturation in the wastewater is less than 200%, and a conventional scale inhibitor can be used to prevent calcium sulfate fouling. To avoid fouling of the subsequent reverse osmosis membrane, the concentrated water of the first reverse osmosis unit enters the first high-density sedimentation tank for simultaneous removal of hardness and silicon, etc. The reagents used are sodium hydroxide and sodium carbonate, which not only remove the temporary hardness in the wastewater but also remove part of the permanent hardness, but retain part of the calcium ions in the wastewater to reduce the dosage of calcium chloride in the subsequent calcium sulfate crystallization unit. The calcium ion is 200-500 mg / L. The first high-density sedimentation tank unit controls the calcium sulfate saturation to be less than 100% by adjusting the dosing amount of sodium hydroxide and sodium carbonate to avoid calcium sulfate fouling before the wastewater enters the second reverse osmosis. During the hardness removal process, calcium silicate and calcium fluoride are also partially removed. The silicon in the effluent is controlled to be less than 30 mg / L (calculated as SiO2). The effluent of the first high-density sedimentation tank enters the first medium filtration unit and the first ultrafiltration unit to reduce the SDI and slow down the subsequent reverse osmosis membrane fouling. The effluent of the first ultrafiltration unit enters the second reverse osmosis unit for further concentration. The recovery rate of the second reverse osmosis unit is 60%-80%. The second reverse osmosis unit controls the calcium sulfate saturation to be 400%-500% by adjusting the recovery rate and adding high-efficiency scale inhibitor;

[0055] The concentrated water of the second-stage reverse osmosis unit enters the second-stage calcium sulfate crystallization unit. With the failure of the scale inhibitor, the supersaturated calcium sulfate will be destabilized and crystallized. At the same time, due to the lack of calcium ions and the presence of a large number of sulfate ions, it is still necessary to add calcium chloride to forcibly remove part of the sulfate and obtain by-product calcium sulfate (gypsum). The effluent of the second-stage calcium sulfate crystallization unit controls the concentration of sulfate ions at 5000-6000 mg / L and the concentration of calcium ions at 1200-1600 mg / L. The second-stage calcium sulfate crystallization unit controls the supersaturation degree of the effluent calcium sulfate at 120%-150% by adjusting the dosage of calcium chloride. To avoid the occurrence of scale and blockage in the subsequent nanofiltration unit, the effluent of the second-stage calcium sulfate crystallization unit enters the second-stage high-density sedimentation tank unit to continue to remove hardness and silicon. The dosing agent is sodium carbonate, the concentration of calcium ions is 400-800 mg / L, and the saturation degree of calcium sulfate is controlled to be less than 100% by adjusting the dosage of sodium carbonate to avoid scale formation of calcium sulfate before the wastewater enters the third-stage nanofiltration unit. During the process of removing hardness, calcium silicate and calcium fluoride are also partially removed, and the concentration of silicon in the effluent is controlled to be less than 30 mg / L (calculated as SiO2).

[0056] The effluent of the second-stage high-density sedimentation tank unit enters the second-stage medium filtration unit and the second-stage ultrafiltration unit to reduce the SDI and slow down the subsequent nanofiltration membrane fouling. The effluent of the second-stage ultrafiltration unit enters the third-stage nanofiltration unit. The third-stage nanofiltration unit concentrates sulfate ions while separating monovalent and divalent ions. The third-stage nanofiltration unit uses high-pressure nanofiltration, with a rejection rate of sulfate ions greater than 99% and no rejection or negative rejection of chloride ions. The recovery rate of the third-stage nanofiltration unit is 50-75%, and the saturation degree of calcium sulfate is controlled to be 400%-500% by adjusting the recovery rate and adding high-efficiency scale inhibitors. The concentrated water of the third-stage nanofiltration unit enters the third-stage calcium sulfate crystallization unit. With the failure of the scale inhibitor, the supersaturated calcium sulfate will be destabilized and crystallized. At the same time, due to the lack of calcium ions and the presence of a large number of sulfate ions, it is still necessary to add calcium chloride to forcibly remove part of the sulfate and obtain by-product calcium sulfate (gypsum). The effluent of the third-stage calcium sulfate crystallization unit controls the concentration of sulfate ions at 6000-8000 mg / L and the concentration of calcium ions at 1400-1800 mg / L. The third-stage calcium sulfate crystallization unit controls the supersaturation degree of the effluent calcium sulfate at 120%-150% by adjusting the dosage of calcium chloride. To avoid the occurrence of scale and blockage in the subsequent nanofiltration unit, the effluent of the third-stage calcium sulfate crystallization unit enters the third-stage high-density sedimentation tank unit to continue to remove hardness. The dosing agent is sodium carbonate, the concentration of calcium ions in the effluent is 800-1200 mg / L, and the saturation degree of calcium sulfate is controlled to be less than 100% by adjusting the dosage of sodium carbonate to avoid scale formation of calcium sulfate before the wastewater enters the nanofiltration membrane. The effluent of the third-stage high-density sedimentation tank unit enters the third-stage medium filtration unit and the third-stage ultrafiltration unit to reduce the SDI and slow down the subsequent nanofiltration membrane fouling. The effluent of the third-stage ultrafiltration unit is returned and mixed with the effluent of the second-stage ultrafiltration unit before re-entering the third-stage nanofiltration unit.

[0057] The main components of fresh water in the three-stage nanofiltration unit are sodium chloride and potassium chloride, which are subjected to deep hardness removal in the ion exchange resin, and the hardness of the effluent is less than 1 mg / L. The effluent of the resin is subjected to decarbonization in the decarbonizer, and the bicarbonate in the effluent of the decarbonizer is less than 20 mg / L. Then, the effluent is subjected to deep concentration in the four-stage reverse osmosis unit, and the recovery rate of the four-stage reverse osmosis unit is 40%-60%. The concentrated brine after deep concentration has a TDS of 70,000-80,000 mg / L. The concentrated brine is subjected to deep silicon removal in the four-stage high-density sedimentation tank, and the silicon in the effluent is less than 20 mg / L to avoid fouling in the evaporation crystallizer. After deep silicon removal, the effluent is subjected to medium filtration in the four-stage medium filtration unit and ultrafiltration in the four-stage ultrafiltration unit. The effluent of the four-stage ultrafiltration unit is first subjected to evaporation crystallization at a temperature of 100-110°C to obtain sodium chloride. The potassium-rich mother liquor is then flash evaporated at a temperature of 40-50°C to obtain potassium chloride. The obtained mother liquor is returned to the sodium chloride evaporator for recycling and temperature increase. A small amount of mother liquor is discharged for drying treatment.

[0058] The technical solutions of the present application and their effects are further illustrated by the following examples:

[0059] Example 1

[0060] A new energy battery enterprise discharges 40,000 m 3 / d of wastewater. The production process requires the addition of raw materials such as HF, HCL, H2O2, KOH, and additives in the cleaning stage of the (texturing) etching process, resulting in acid-containing wastewater (HF, HCL) and alkali-containing wastewater (KOH, organic matter). The etching process requires the addition of raw materials such as HNO3, HF, HCL, KOH, and H2SO4, resulting in alkali-containing wastewater (KOH, organic matter) and acid-containing nitrogen-containing wastewater (F - , NO3 - , SO4 2- ). The use of KOH instead of NaOH in the cleaning and etching stages helps to improve product quality, but the discharged wastewater also contains a large amount of potassium resources that can be recovered.

[0061] The final wastewater discharged by the enterprise has a COD of 160 mg / L, fluorine of 4 mg / L, total silicon (calculated as SiO2) of 100 mg / L, hardness (calculated as CaCO3) of 450 mg / L, and total salinity of 2600 mg / L (including chloride ions of 350 mg / L, sulfate ions of 1000 mg / L, bicarbonate ions of 120 mg / L, sodium ions of 230 mg / L, and potassium ions of 480 mg / L). The water quality characteristics are high total salinity, mainly containing potassium ions, sodium ions, chloride ions, and sulfate ions, and the concentration of sulfate ions in anions accounts for more than 70%. The potassium ions account for more than 60% in cations, belonging to a typical potassium-sodium coexisting high-salinity wastewater.

[0062] The discharge requirements of high-salinity wastewater are increasingly stringent. From the national standard, the first level standard of the "Integrated Wastewater Discharge Standard" (GB 8978-1996) requires that the chloride ion is ≤1000 mg / L and the sulfate is ≤600 mg / L; if the receiving water body is an agricultural irrigation water body, the "Irrigation Water Quality Standard for Farmland" (GB 5084-2021) also needs to be implemented, which requires that the total salt content is ≤1000 mg / L and the chloride ion is ≤350 mg / L. From the industry standard, the "Discharge Standard of Pollutants in Petroleum Chemical Industry" (GB 31571-2015) requires that the chloride ion is ≤500 mg / L; the coal chemical industry and the coking industry require that the TDS of the discharged wastewater after treatment of high-salinity wastewater is usually ≤1000 mg / L. From the local standard, the "Integrated Wastewater Discharge Standard for River Basin" (DB 37 / 3416-2023) of Shandong Province requires that the total salt content is less than 3000 mg / L, the "Integrated Wastewater Discharge Standard" (revised in 2019) of Shanxi Province requires that the total salt content is ≤1000 mg / L in the Fenhe River Basin, the total salt content is ≤2000 mg / L in the general area, and the total salt content is ≤1500 mg / L in the wastewater discharged into the Yellow River. Industrial parks and high-water-consuming industries (such as coal chemical industry and power industry) even require zero discharge of wastewater.

[0063] Because a large amount of potassium ions are contained in the cations, the traditional thermal method of separating salts or nanofiltration cannot realize the purification and separation of various crystalline salts under the coexistence of the four ions. In order to deeply treat the wastewater of the enterprise and recover the beneficial resources in the wastewater, the embodiment proposes a zero discharge treatment process method for high-salinity wastewater with coexisting potassium and sodium, wherein the water quantity and water quality of each main unit are as shown in Table 1, the treatment process is as shown in Figure 1 The embodiment specifically comprises the following steps:

[0064] First, the wastewater is pretreated to remove hardness and silicon, etc., so as to reduce the risk of fouling of the subsequent membrane and evaporation crystallization reactor. In the pretreatment unit, the high-density sedimentation tank process is used to remove hardness and silicon, the principle is chemical method to remove silicon and hardness, the reagent used is lime milk (Ca (OH)2), the dosage is 200 mg / L, the dosage concentration is 10%, and the dosage point is the mixing zone of the high-density sedimentation tank. The lime milk can remove the temporary hardness in the wastewater, the calcium ion in the effluent of the pretreatment unit is 147 mg / L, and the bicarbonate ion is 20 mg / L. By adjusting the dosage of lime milk, the calcium sulfate saturation is controlled to be 29%. During the process of removing hardness, calcium silicate and calcium fluoride are also partially removed. The total silicon in the effluent of the pretreatment unit is 28 mg / L (calculated as SiO2), and the fluorine is 2 mg / L, so as to avoid the SiO2 and calcium fluoride fouling of the concentrated water of the first reverse osmosis.

[0065] In addition, the pretreatment unit also needs to use AAO biochemical treatment combined with ozone catalytic oxidation process to control COD less than 20 mg / L, and to control SDI less than 3 through medium filtration and hollow fiber ultrafiltration membrane filtration to meet the influent requirements of the first-stage reverse osmosis.

[0066] The effluent of the pretreatment unit first enters the first-stage reverse osmosis unit (abbreviated as I-RO) for preliminary concentration, the recovery rate of the first-stage reverse osmosis unit is 75%, the membrane flux is 16 L / (m 2 ·h), and the operating pressure is 1.5 MPa, at this time, the ion concentration in the wastewater is enriched, and the scale-forming substances such as calcium ions, silicon, and fluorine are also concentrated; in order to avoid the scaling of the subsequent reverse osmosis membrane, the concentrated water of the first-stage reverse osmosis unit enters the first-stage high-density sedimentation tank (abbreviated as I-high-density tank) for cooperative hardness removal and silicon removal, and the reagents used are sodium hydroxide and sodium carbonate, the dosing point is the mixing zone of the high-density sedimentation tank, which not only removes the temporary hardness in the wastewater but also removes part of the permanent hardness, but retains part of the calcium ions in the wastewater to reduce the dosage of calcium chloride in the subsequent calcium sulfate crystallization unit, the calcium ion concentration of the first-stage high-density sedimentation tank effluent is 432 mg / L, the calcium sulfate saturation degree of the first-stage high-density sedimentation tank is controlled at 91%, at this time, the sodium hydroxide dosage is 80 mg / L, the dosage concentration is 30%, and the sodium carbonate dosage is 430 mg / L, the dosage concentration is 20%.

[0067] During the hardness removal process, calcium silicate and calcium fluoride are also partially removed, the silicon concentration of the effluent is controlled at 28 mg / L (calculated as SiO2), the first-stage high-density sedimentation tank effluent enters the first-stage medium filtration unit and the first-stage hollow fiber ultrafiltration unit to reduce the SDI and slow down the subsequent reverse osmosis membrane fouling, the first-stage ultrafiltration unit effluent enters the second-stage reverse osmosis unit (abbreviated as II-RO) for further concentration, the recovery rate of the second-stage reverse osmosis unit is 75%, the membrane flux is 16 L / (m 2 ·h), and the operating pressure is 3.5 MPa, the second-stage reverse osmosis unit controls the calcium sulfate saturation degree at 426% by adjusting the recovery rate and adding high-efficiency scale inhibitor (complex phosphonic acid-polycarboxylic acid type calcium sulfate high-efficiency scale inhibitor CalTreat® SC-200);

[0068] The concentrated water of the second-stage reverse osmosis unit enters the second-stage calcium sulfate crystallization unit (abbreviated as II-calcium sulfate crystallization), as the scale inhibitor is deactivated, the supersaturated calcium sulfate will crystallize, and due to the lack of calcium ions and the presence of excess sulfate ions, calcium chloride still needs to be added to remove part of the sulfate ions and obtain the byproduct calcium sulfate (gypsum), the second-stage calcium sulfate crystallization unit controls the sulfate concentration of the effluent at 5500 mg / L and the calcium ion concentration at 1400 mg / L, the second-stage calcium sulfate crystallization unit controls the supersaturation degree of the effluent calcium sulfate at 146% by adjusting the dosage of calcium chloride, at this time, the calcium chloride dosage is 10800 mg / L, the dosage concentration is 20%, and the dosing point is the mixing zone of the second-stage calcium sulfate crystallization unit.

[0069] To avoid the over-saturated calcium sulfate into the subsequent nanofiltration unit from scaling and fouling, the effluent from the second calcium sulfate crystallization unit enters the second high-density sedimentation tank unit (abbreviated as II-high-density tank) for further hardness and silicon removal. The dosing agent is sodium carbonate, and the calcium ion in the effluent is controlled at 700 mg / L. The calcium sulfate saturation is controlled at 75% by adjusting the sodium carbonate dosage, at which the sodium carbonate dosage is 1850 mg / L, the dosage concentration is 20%, and the dosing point is the mixing zone of the second high-density sedimentation tank. During the hardness removal process, calcium silicate and calcium fluoride are also partially removed, and the silicon in the effluent is controlled at 28 mg / L (calculated as SiO2).

[0070] The effluent from the second high-density sedimentation tank unit enters the second media filtration unit and the second ultrafiltration unit to reduce SDI and slow down the subsequent reverse osmosis membrane fouling. The effluent from the second ultrafiltration unit enters the third nanofiltration unit (abbreviated as III-NF). The third nanofiltration unit concentrates sulfate while separating monovalent and divalent ions. The third nanofiltration unit uses high-pressure nanofiltration, with a sulfate rejection rate of more than 99% and no rejection or negative rejection of chloride ions. The recovery rate of the third nanofiltration unit is 71%, the membrane flux is 16 L / (m 2 ·h), and the operating pressure is 3.0 MPa. The third nanofiltration unit controls the calcium sulfate saturation at 408% by adjusting the recovery rate and adding high-efficiency scale inhibitors.

[0071] The concentrated water from the third nanofiltration unit enters the third calcium sulfate crystallization unit (abbreviated as III-calcium sulfate crystallization). With the failure of scale inhibitors, the over-saturated calcium sulfate will crystallize. Due to the lack of calcium ions and the presence of excessive sulfate ions, calcium chloride needs to be added to remove part of the sulfate ions and obtain byproduct calcium sulfate (gypsum). The third calcium sulfate crystallization unit controls the concentration of sulfate ions at 7500 mg / L and the concentration of calcium ions at 1600 mg / L. The third calcium sulfate crystallization unit controls the over-saturation of calcium sulfate in the effluent at 134% by adjusting the dosage of calcium chloride, at which the calcium chloride dosage is 16400 mg / L, the dosage concentration is 20%, and the dosing point is the mixing zone of the third calcium sulfate crystallization unit.

[0072] To avoid the over-saturated calcium sulfate into the subsequent nanofiltration unit from scaling and fouling, the effluent from the third calcium sulfate crystallization unit enters the third high-density sedimentation tank unit (abbreviated as III-high-density tank) for further hardness removal. The dosing agent is sodium carbonate, and the calcium ion in the effluent is controlled at 1000 mg / L. The calcium sulfate saturation is controlled at 84% by adjusting the sodium carbonate dosage, at which the sodium carbonate dosage is 1590 mg / L, the dosage concentration is 20%, and the dosing point is the mixing zone of the third high-density sedimentation tank. The effluent from the third high-density sedimentation tank unit enters the third media filtration unit and the third ultrafiltration unit to reduce SDI and slow down the subsequent reverse osmosis membrane fouling. The effluent from the third ultrafiltration unit is mixed with the effluent from the second ultrafiltration unit and then enters the third nanofiltration unit again.

[0073] The main components of the fresh water of the three-stage nanofiltration unit are sodium chloride and potassium chloride. First, the fresh water is subjected to deep hardness removal by ion exchange resin, and the hardness of the effluent is 0.8 mg / L. The effluent of the resin is subjected to decarbonization, and the bicarbonate in the effluent of the decarbonizer is 15 mg / L. Then, the effluent is subjected to deep concentration by the four-stage reverse osmosis unit (abbreviated as IV-RO). The recovery rate of the four-stage reverse osmosis unit is 45%, the membrane flux is 16 L / (m 2 ·h), and the operating pressure is 7.0 MPa. The TDS of the concentrated brine after deep concentration is controlled to be 74,277 mg / L. The concentrated brine is subjected to deep silicon removal in the four-stage high-density sedimentation tank. Sodium hydroxide and sodium metaaluminate are used as the silicon removal agents. The dosage of sodium hydroxide is 40 mg / L, the concentration is 30%, and the addition point is the mixing zone of the four-stage high-density sedimentation tank. The dosage of sodium metaaluminate is 165 mg / L, the concentration is 10%, and the addition point is the mixing zone of the four-stage high-density sedimentation tank. The silicon in the effluent is controlled to be 15 mg / L. After deep silicon removal, the effluent is subjected to medium filtration and ultrafiltration.

[0074] The effluent of the four-stage ultrafiltration unit is subjected to evaporation and crystallization. First, sodium chloride is obtained by evaporation and crystallization at 100-110°C. The content of sodium chloride is greater than 96%. Then, the potassium-rich mother liquor is cooled to 40-50°C to obtain potassium chloride by flash evaporation. The equivalent potassium oxide content is greater than 60%. The obtained mother liquor is returned to the sodium chloride evaporator for recycling and temperature increase. A small amount of mother liquor is discharged for drying treatment.

[0075] Table 1 shows the water quantity and quality of each main unit (the flow unit is m 3 / d, and the concentration unit is mg / L).

[0076]

[0077] As shown in Table 1, the water inflow of the photovoltaic enterprise is 40,000 m 3 / d, and the main cations in the water quality are K + and Na + , and the main anions are SO4 2- and Cl - . The main components that cause membrane separation system fouling and pollution are Ca 2+ , total silicon, F - , COD, NH4-N, NO3 - , and HCO3 - . The wastewater is subjected to pretreatment before entering the membrane separation system. After pretreatment (before I-RO), Ca 2+ is reduced to 147 mg / L, total silicon is reduced to 28 mg / L, F - is reduced to 2 mg / L, COD is reduced to 20 mg / L, NH4-N is reduced to 2 mg / L, and NO3 -to 5 mg / L, HCO3 - to 20 mg / L, thus ensuring the water quality requirements of the membrane separation system, and introducing Na + to the system. + to 267 mg / L. After entering the membrane separation system, the water is concentrated to 10,000 m 3 / d, and K + reaches 1,877 mg / L, Na + reaches 1,045 mg / L, SO4 2- reaches 3,940 mg / L, and Cl - reaches 1,552 mg / L. At the same time, other main components that can cause fouling and pollution of the membrane separation system, such as Ca 2+ , total silicon, F - , COD, HCO3 - , etc., are also concentrated. In order to prevent fouling and pollution of the subsequent reverse osmosis unit, pretreatment is needed again. After pretreatment, the water enters the second RO unit for further concentration. The TDS of the concentrated water of the second RO unit reaches 35,909 mg / L, and the water volume is further concentrated to 2,500 m 3 / d. The concentrated water of the second RO unit enters the second calcium sulfate crystallization unit to precipitate calcium sulfate (gypsum). The SO4 2- in the effluent of the second calcium sulfate crystallization unit is reduced from 15,524 mg / L to 5,500 mg / L, and the Ca 2+ is reduced from 1,700 mg / L to 1,400 mg / L. The effluent of the second calcium sulfate crystallization unit enters the second high-density pool to remove hardness. The Ca 2+ is reduced from 1,400 mg / L to 700 mg / L to avoid fouling of the subsequent third NF unit. The effluent of the second high-density pool enters the third NF unit. The TDS of the permeate (fresh water) of the third NF unit is 41,513 mg / L. After deep hardness removal and decarburization, it enters the fourth RO unit for deep concentration. The TDS of the concentrated water of the fourth RO unit reaches 74,277 mg / L, and the water volume is reduced to 2,067 m 3 / d. Subsequently, it enters the evaporation crystallization unit and the cooling unit to produce sodium chloride and potassium chloride. The TDS of the concentrated liquid of the third NF unit reaches 74,610 mg / L, of which SO4 2- reaches 21,962 mg / L, and Ca 2+ reaches 1,802 mg / L. The concentrated liquid of the third NF unit enters the third calcium sulfate crystallization unit to precipitate calcium sulfate (gypsum). The SO4 2- in the effluent of the third calcium sulfate crystallization unit is reduced from 21,962 mg / L to 7,500 mg / L, and the Ca 2+ is reduced from 1,802 mg / L to 1,600 mg / L. The effluent of the third calcium sulfate crystallization unit enters the third high-density pool to remove hardness. The Ca 2+Reduced from 1600mg / L to 1000mg / L to avoid subsequent Ⅲ-NF unit fouling, Ⅲ-high density pool effluent after medium filtration and ultrafiltration returns to the Ⅲ-NF unit for recycling treatment.

[0078] The Ⅲ-NF unit is used for treating SO4 2- Further concentration, while achieving the separation of SO4 2- and Cl - , the Ⅲ-NF concentrated water is mainly composed of sodium sulfate, and the TDS reaches 82771mg / L, which can enter the subsequent evaporation crystallization unit to produce sodium sulfate; the Ⅲ-NF dilute water is mainly composed of sodium chloride, and the TDS is reduced to 34962mg / L, which needs to be concentrated by Ⅳ-RO and then enter the subsequent evaporation crystallization unit, and after being concentrated by Ⅳ-RO, the water volume is concentrated to 945m 3 / d, and the TDS reaches 76149mg / L, which can enter the subsequent evaporation crystallization unit to produce sodium chloride.

[0079] The TDS of the first reverse osmosis dilute water, the second reverse osmosis dilute water and the fourth reverse osmosis dilute water treated by the treatment method of the application is less than 200mg / L after being mixed, which can be used as high-quality desalted water to replace conventional water resources and be used as production water in enterprises, thereby reducing the consumption of fresh water resources in enterprises. Meanwhile, the potassium chloride produced after being treated by the treatment method of the application meets the first-class product requirements (potassium oxide content is greater than 60%) in the “Potassium Chloride” (GB / T6549-2011), and the sodium chloride meets the refined industrial wet salt superior standard (sodium chloride content is greater than 96%) in the “Industrial Salt” (GB / 5462-2015).

[0080] Embodiment 2

[0081] A potassium-sodium coexisting type high-salinity wastewater zero discharge treatment system, comprising a pretreatment unit, a first reverse osmosis unit, a first high-density sedimentation tank, a first medium filtration tank, a first ultrafiltration tank, a second reverse osmosis unit, a second calcium sulfate crystallization tank, a second high-density sedimentation tank, a second medium filtration tank, a second ultrafiltration tank and a third nanofiltration unit connected in sequence.

[0082] The third nanofiltration unit is provided with a permeate outlet of the third nanofiltration unit and a concentrated liquid outlet of the third nanofiltration unit.

[0083] The permeate outlet of the third nanofiltration unit is connected with an ion exchange resin membrane, a decarbonization tank, a fourth reverse osmosis unit, a fourth high-density sedimentation tank, a fourth medium filtration tank, an evaporation crystallizer and a cooler in sequence.

[0084] The outlet of the cooler is connected with the inlet of the evaporation crystallizer.

[0085] The three-stage ultrafiltration tank is connected with the water outlet of the three-stage nanofiltration unit.

[0086] The water outlet of the three-stage ultrafiltration tank is connected with the water inlet of the three-stage nanofiltration unit.

[0087] The treatment system for zero discharge of potassium-sodium coexisting high-salinity wastewater adopts existing structures and components, and the equipment used is known to those skilled in the art.

[0088] Comparative Example 1

[0089] The treatment process for treating photovoltaic solar cell wastewater in the industrial wastewater treatment plant is different from that in Example 1. Unlike Example 1, the calcium sulfate crystallization method is not used to remove SO4 2- from the wastewater. Only nanofiltration is used to separate SO4 2- and Cl - . The components of the obtained nanofiltration concentrated liquid are mainly potassium sulfate and sodium sulfate, and the difference in solubility between potassium sulfate and sodium sulfate cannot be used for evaporation crystallization at different temperatures to realize salt separation and purification. Therefore, a large amount of potassium sulfate and sodium sulfate salt will be produced, which needs to be disposed as hazardous waste, resulting in high cost. The specific treatment process is shown in Figure 2 .

[0090] The treatment process flow is as follows: the potassium-sodium coexisting high-salinity wastewater is sequentially subjected to a pretreatment unit, a first reverse osmosis unit, a first high-density sedimentation tank unit, a first medium filtration unit, a first ultrafiltration unit, and a second reverse osmosis unit (the above process flow is the same as that in Example 1). The concentrated water from the second reverse osmosis unit is subjected to a second high-density sedimentation tank for hardness removal. The water from the second high-density sedimentation tank is subjected to a second medium filtration and a second ultrafiltration for further removal of pollutants and reduction of SDI. The water from the second ultrafiltration is subjected to a third nanofiltration for salt separation. The permeate from the third nanofiltration unit is treated in the same way as in Example 1. The concentrated liquid from the third nanofiltration unit is subjected to a third high-density sedimentation tank for hardness removal, and then subjected to a third medium filtration and a third ultrafiltration for further removal of pollutants and reduction of SDI. The water from the third ultrafiltration is subjected to ion exchange resin II for deep hardness removal. The water after deep hardness removal is subjected to evaporation crystallization II to obtain potassium sulfate and sodium sulfate salt, which is disposed as hazardous waste.

[0091] The main difference between the process flow in Example 1 and the process flow in Comparative Example 1 is that the concentrated water from the second reverse osmosis unit is not subjected to the calcium sulfate crystallization method to remove SO4 2- from the wastewater. Instead, the water is subjected to a high-density sedimentation tank for hardness removal, and then subjected to a subsequent third nanofiltration unit. The concentrated liquid from the third nanofiltration unit is also not subjected to the calcium sulfate crystallization method to remove SO4 2-From the wastewater removal, only take high-density sedimentation to remove hardness, and then enter the subsequent evaporation crystallization, the composition of the obtained nanofiltration concentrated liquid is mainly potassium sulfate and sodium sulfate, which cannot be used to realize different temperature evaporation crystallization for different salt purification according to the solubility difference of potassium sulfate and sodium sulfate, so a large amount of potassium sulfate and sodium sulfate will be produced, and the mixed salt needs to be disposed according to the hazardous waste. Compared with example 1, the salt recovery rate in example 2 is less than 30%, a large amount of salt is separated from the system in the form of mixed salt, the valuable salt resource is not recycled, at the same time, the mixed salt needs to be disposed according to the hazardous waste related disposal standard, the disposal cost is high, which leads to high cost of the sewage treatment plant.

[0092] The preferred embodiments of the present application have been described above, but the present application is not limited to the above. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A zero-discharge treatment process for high-salinity wastewater with potassium and sodium coexistence, characterized in that, Includes the following steps: Pretreated high-salt wastewater containing potassium and sodium coexistence is subjected to a first-stage reverse osmosis treatment to produce fresh water and first-stage reverse osmosis effluent. The reverse osmosis effluent is sequentially subjected to a high-density sedimentation stage, a media filtration stage, an ultrafiltration stage, and a second-stage reverse osmosis treatment to produce fresh water and second-stage reverse osmosis effluent. The effluent from the second-stage reverse osmosis is subjected to second-stage calcium sulfate crystallization to obtain calcium sulfate and second-stage calcium sulfate crystallization effluent. The water from the two-stage calcium sulfate crystallization process was sequentially subjected to two-stage high-density precipitation, two-stage media filtration, two-stage ultrafiltration, and three-stage nanofiltration to obtain a three-stage nanofiltration concentrate and a three-stage nanofiltration permeate. The three-stage nanofiltration concentrate was subjected to three-stage calcium sulfate crystallization treatment to obtain calcium sulfate and three-stage calcium sulfate crystallization effluent. The effluent from the three-stage calcium sulfate crystallization process was sequentially subjected to three-stage high-density sedimentation, three-stage media filtration, and three-stage ultrafiltration to obtain three-stage ultrafiltration effluent. The effluent from the three-stage ultrafiltration is recycled and mixed with the effluent from the two-stage ultrafiltration before being re-entered into the three-stage nanofiltration process. It also includes sequentially treating the three-stage nanofiltration permeate with ion exchange resin, decarbonization, and four-stage reverse osmosis to produce fresh water and four-stage reverse osmosis effluent. The reverse osmosis effluent from the four stages is sequentially subjected to four stages of high-density sedimentation, four stages of media filtration, four stages of ultrafiltration, and evaporation crystallization to produce sodium chloride and evaporation crystallization effluent. Potassium chloride is obtained by cooling and flash evaporation of the water from the evaporation crystallization. The water from the cooled flash evaporation is returned to the evaporator crystallizer and then evaporated and crystallized again to obtain sodium chloride. The pretreatment process involves hardening and silicon removal, biochemical treatment, ozone catalytic oxidation, media filtration, and hollow fiber ultrafiltration membrane filtration of potassium and sodium coexisting high-salt wastewater. The agent used for the hardening and desilting treatment is lime milk, with a dosage of 150-250 mg / L and a concentration of 8-12%. After pretreatment, the total silicon in the wastewater should be less than 30 mg / L, COD less than 20 mg / L, SDI less than 3, fluoride less than 3 mg / L, and calcium ion concentration should be 100-200 mg / L.

2. The zero-discharge treatment process for high-salinity wastewater with potassium and sodium coexistence as described in claim 1, characterized in that, The recovery rate of the first-stage reverse osmosis treatment is 70-80%, and the membrane flux is 15-18 L / (m²). 2 (·h), operating pressure is 1.4-1.6 MPa; The reagents added during the high-density sedimentation stage are sodium hydroxide and sodium carbonate. The addition point is the mixing zone of the high-density sedimentation tank. The dosage of sodium hydroxide is 75-85 mg / L, with a concentration of 25-35%, and the dosage of sodium carbonate is 400-450 mg / L, with a concentration of 18-25%. The effluent from the high-density sedimentation tank contains less than 30 mg / L of silicon and 200-500 mg / L of calcium ions.

3. The zero-discharge treatment process for high-salinity wastewater with potassium and sodium coexistence as described in claim 1, characterized in that, The recovery rate of the two-stage reverse osmosis treatment is 60%-80%, and the membrane flux is 15-18 L / (m²). 2 (·h), operating pressure is 1.4-1.6 MPa; Alternatively, the sulfate concentration in the effluent from the two-stage calcium sulfate crystallization is 5000-6000 mg / L, and the calcium ion concentration is 1200-1600 mg / L; Alternatively, the reagent added in the two-stage high-density precipitation is sodium carbonate, with a dosage of 1800-1900 mg / L and a concentration of 18-25%. The effluent from the two-stage high-density precipitation contains less than 30 mg / L of silicon and 400-800 mg / L of calcium ions.

4. The zero-discharge treatment process for high-salinity wastewater with potassium and sodium coexistence as described in claim 1, characterized in that, The recovery rate of the three-stage nanofiltration is 50-75%, and the membrane flux is 15-18 L / (m²). 2 (·h), operating pressure is 2.8-3.2 MPa; Alternatively, the reagent added during the three-stage calcium sulfate crystallization is calcium chloride, with a dosage of 16000-16500 mg / L and a concentration of 18-22%. The sulfate concentration in the effluent from the three-stage calcium sulfate crystallization is 6000-8000 mg / L, and the calcium ion concentration is 1400-1800 mg / L. Alternatively, the reagent added to the three-stage high-density precipitation is sodium carbonate, with a dosage of 1500-1600 mg / L and a concentration of 18-22%, and the calcium ion concentration in the effluent of the three-stage high-density precipitation is 800-1200 mg / L.

5. The zero-discharge treatment process for high-salinity wastewater with potassium and sodium coexistence according to claim 1, characterized in that, The hardness of the effluent from the ion exchange resin is less than 1 mg / L, and the bicarbonate content in the effluent from the decarbonation process is less than 20 mg / L. Alternatively, the recovery rate of a four-stage reverse osmosis system is 40%-60%, the TDS of the effluent is 70,000-80,000 mg / L, and the membrane flux is 15-18 L / (m²). 2 (·h), operating pressure is 6.8-7.2 MPa; Alternatively, the reagents added to the four-stage high-density sedimentation tank are sodium hydroxide and sodium aluminate. The dosage of sodium hydroxide is 35-45 mg / L and the concentration is 25-35%. The dosage of sodium aluminate is 160-170 mg / L and the concentration is 8-12%. The silica content in the effluent is less than 20 mg / L.

6. The zero-discharge treatment process for high-salinity wastewater with potassium and sodium coexistence according to claim 1, characterized in that, The evaporation and crystallization temperature is 100-110℃, and the sodium chloride content is greater than 96%. The temperature of the cooling flash evaporation is 40-50℃, and the potassium chloride content is greater than 60%. Part of the evaporated crystallization mother liquor is discharged and dried.

7. A zero-discharge treatment system for high-salinity wastewater with potassium and sodium coexistence, characterized in that, The method for performing the zero-discharge treatment process for high-salt wastewater with potassium and sodium coexistence as described in claim 1 includes a pretreatment unit, a first-stage reverse osmosis unit, a first-stage high-density sedimentation tank, a first-stage media filtration tank, a first-stage ultrafiltration tank, a second-stage reverse osmosis unit, a second-stage calcium sulfate crystallization tank, a second-stage high-density sedimentation tank, a second-stage media filtration tank, a second-stage ultrafiltration tank, and a third-stage nanofiltration unit connected in sequence. The three-stage nanofiltration unit is provided with a permeate outlet and a concentrate outlet. It also includes a three-stage calcium sulfate crystallization tank, a three-stage high-density sedimentation tank, a three-stage media filtration tank, and a three-stage ultrafiltration tank that are sequentially connected to the concentrate outlet of the three-stage nanofiltration unit; The outlet of the three-stage ultrafiltration tank is connected to the inlet of the three-stage nanofiltration unit; It also includes the permeate outlet of the three-stage nanofiltration unit being sequentially connected to the ion exchange resin treatment unit, the decarbonization tank, the four-stage reverse osmosis unit, the four-stage high-density sedimentation tank, the four-stage media filtration tank, the four-stage ultrafiltration unit, the evaporator crystallizer, and the cooler. The outlet of the cooler is connected to the inlet of the evaporator crystallizer.

Images