Resourceful treatment method for high-salinity wastewater

Abstract

The invention provides a resourceful treatment method of high-salinity wastewater, which comprises the following steps: (1) mixing the high-salinity wastewater and a precipitator, stirring for reaction, and then carrying out solid-liquid separation to obtain primary filtrate; (2) performing freezing crystallization on the primary filtrate, and performing solid-liquid separation to obtain sodium sulfate and secondary filtrate; (3) carrying out multi-effect evaporation on the secondary filtrate, and carrying out solid-liquid separation to obtain sodium chloride and a tertiary filtrate; (4) carrying out cooling crystallization on the third filtrate, and carrying out solid-liquid separation to obtain potassium chloride and a fourth filtrate; the fourth filtrate is reused for freezing crystallization in the step (2). By means of freezing crystallization, multi-effect evaporation, cooling crystallization and recycling which are sequentially carried out, sodium, potassium and other components in the high-salinity wastewater can be effectively separated and recycled, sodium sulfate, sodium chloride and potassium chloride products with industrial value are produced, the salt content in the wastewater is reduced, and resource utilization of the wastewater is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial wastewater treatment, and specifically relates to a resource treatment method for high-salt wastewater. Background Art

[0002] With the rapid development of industry, the amount of high-salinity wastewater is increasing, and its treatment has become a major challenge in the field of environmental protection. High-salinity wastewater mainly comes from industries such as chemical, pharmaceutical, petroleum, papermaking, dairy processing, and food canning. These wastewaters contain a large amount of soluble inorganic salts, such as sodium chloride, sodium sulfate, etc., and may also contain a certain proportion of organic matter.

[0003] At present, high-salt wastewater treatment technology has problems such as resource waste, incomplete treatment and environmental pollution. In particular, it is difficult to balance economic efficiency and environmental protection requirements in the effective recovery of sodium and potassium salts in high-salt and high-sulfur wastewater. Traditional treatment methods include: (1) Direct evaporation concentration method: This method evaporates the water in the wastewater by heating and concentrates it to obtain sodium and potassium salts, but its energy consumption is extremely high and the economic cost is relatively high; in addition, due to the scaling problem caused by high-concentration salt during the evaporation process, the equipment maintenance is frequent, which reduces the feasibility and stability of the process. (2) Chemical precipitation method: By adding chemical agents to the wastewater, the heavy metal ions in the wastewater are formed into insoluble precipitates to reduce the heavy metal content, but this method is not suitable for the precipitation of sodium and potassium salts. (3) Membrane separation method: Membrane separation technology (such as reverse osmosis, nanofiltration, electrodialysis, forward osmosis, etc.) is often used for the preliminary treatment of high-salt wastewater. The advantage of this method is that the energy consumption is relatively low, but under high salt concentration conditions, the membrane is easily contaminated and blocked, and needs to be frequently replaced and cleaned, resulting in increased operating costs; in addition, the membrane separation method is difficult to achieve for the precise separation of sodium and potassium salts, and the product purity is not high. (4) Combination of multi-effect evaporation and crystallization: In the existing technology, the process of combining multi-effect evaporation with crystallization is used for the resource treatment of wastewater. Different salts are separated by step evaporation and crystallization. Compared with single-effect evaporation, this method has lower energy consumption, but it still faces problems such as high energy consumption, complex equipment, and high operating and maintenance costs.

[0004] Although the above treatment methods can achieve wastewater treatment to a certain extent, there are a series of problems in practical application, such as: (1) High energy consumption: Traditional evaporation concentration method and multi-effect evaporation process both consume a lot of heat energy, especially for the treatment of high salt concentration solution, resulting in high operating costs of the overall process; (2) Low product purity: Chemical precipitation method and membrane separation method are difficult to ensure the high purity of the final product. The purity of sodium salt and potassium salt is often low due to impurities or differences in membrane selectivity, which limits their industrial application value; (3) Frequent equipment maintenance: There are scaling and clogging problems in the evaporation and membrane separation process, and the equipment needs to be cleaned and maintained frequently, which not only increases the operating cost of the equipment, but also affects the continuity and stability of the process; (4) Environmental pollution: The chemical precipitation method will produce a large amount of solid waste. If it is not handled properly, it will cause secondary pollution to the environment; and the direct discharge of high-salt wastewater after evaporation and concentration will also cause serious harm to the surrounding environment.

[0005] In summary, the development of an efficient, economical and environmentally friendly high-salt wastewater treatment technology has important practical significance and broad application prospects. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for resource-based treatment of high-salt wastewater. The present invention can effectively separate and recover sodium, potassium and other components in high-salt wastewater through sequential freezing crystallization, multi-effect evaporation, cooling crystallization and recycling, produce sodium sulfate, sodium chloride and potassium chloride products with industrial value, reduce the salt content in wastewater, and realize resource utilization of wastewater.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for recycling high-salinity wastewater, which comprises the following steps:

[0009] (1) mixing high-salt wastewater and a precipitant, stirring for reaction, and then performing solid-liquid separation to obtain a primary filtrate;

[0010] (2) subjecting the primary filtrate obtained in step (1) to freeze crystallization, and obtaining sodium sulfate and a secondary filtrate after solid-liquid separation;

[0011] (3) subjecting the secondary filtrate obtained in step (2) to multi-effect evaporation to obtain sodium chloride and a tertiary filtrate after solid-liquid separation;

[0012] (4) cooling and crystallizing the tertiary filtrate obtained in step (3), and obtaining potassium chloride and the fourth filtrate after solid-liquid separation;

[0013] The four filtrates are recycled for the freeze crystallization in step (2).

[0014] In the present invention, the step-by-step recovery of sodium sulfate, sodium chloride and potassium chloride is achieved by combining freezing crystallization, evaporation crystallization and cooling crystallization, and the recovery rates of sodium sulfate, sodium chloride and potassium chloride are not less than 90%, meeting the use standards of the chemical, agricultural and food industries;

[0015] In addition, the present invention adopts multi-effect evaporation technology to significantly reduce energy consumption, and can reduce the amount of steam used by about 30 to 50°C compared to traditional single-effect evaporation;

[0016] Moreover, the resource recovery treatment method provided by the present invention removes heavy metals in wastewater by using a precipitant, with a removal rate of not less than 95%, effectively reducing the impact of heavy metals on subsequent crystallization processes; in addition, by recycling the filtrate four times, zero discharge of waste liquid is achieved during the treatment process, significantly reducing the pollution load on the environment.

[0017] The high-salt wastewater of the present invention comes from the solution of zinc oxide collected from a rotary kiln after alkali washing.

[0018] As a preferred technical solution of the present invention, the ions in the high-salt wastewater include K + 、Na + , Cl - 、SO4 2- and heavy metal ions.

[0019] Preferably, the heavy metal ions include As, Zn 2+ , Pb 2+ 、Cd 2+ And Tl + .

[0020] It is worth noting that As in the heavy metal ions is mainly present in the form of AsO 4 3- , H 2 AsO 3 - exists in the form of.

[0021] As a preferred technical solution of the present invention, the precipitant in step (1) includes sodium hydroxide and / or sodium sulfide and polyacrylamide.

[0022] Preferably, the mass ratio of sodium hydroxide, sodium sulfide and polyacrylamide is 1:1:1-3, for example, 1:1:1, 1:1:1.4, 1:1:1.8, 1:1:2.2, 1:1:2.6 or 1:1:3, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0023] Preferably, the mass ratio of the precipitant to high-salt wastewater is 1.5 to 2.5:1000, for example, it can be 1.5:1000, 1.7:1000, 1.9:1000, 2.1:1000, 2.3:1000 or 2.5:1000, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] In the present invention, the precipitant is a mixture of sodium hydroxide, sodium sulfide and polyacrylamide, wherein the sodium hydroxide reacts with the heavy metal ions in the high-salt wastewater to form insoluble hydroxides, thereby achieving the removal of heavy metals; at the same time, the pH value of the high-salt wastewater can be increased to promote the precipitation of heavy metal ions in the wastewater; the sodium sulfide can react with ions such as lead, zinc, and cadmium to generate insoluble metal sulfides, thereby effectively removing the heavy metal ions in the high-salt wastewater; the polyacrylamide, as a polymer flocculant, has a strong coagulation effect and can promote the coagulation and sedimentation of suspended matter in the wastewater by physical or chemical adsorption; and the polyacrylamide can also enhance the flocculation effect of the precipitate formed by sodium hydroxide and sodium sulfide, making the precipitate easier to separate, thereby enhancing the removal of heavy metal ions; in short, the three components in the precipitant complement each other and are indispensable, which can not only ensure the efficient progress of the precipitation reaction, but also have excellent flocculation effect, thereby achieving the efficient removal of heavy metal ions in the high-salt wastewater.

[0025] As a preferred technical solution of the present invention, the stirring rate of the stirring reaction in step (1) is 400-600 r / min, for example, it can be 400 r / min, 440 r / min, 480 r / min, 520 r / min, 560 r / min or 600 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the stirring reaction time in step (1) is 15 to 30 min, for example, 15 min, 18 min, 21 min, 24 min, 27 min or 30 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] As a preferred technical solution of the present invention, the temperature of the freezing crystallization in step (2) is -5 to 0°C, for example, it can be -5°C, -4°C, -3°C, -2°C, -1°C or 0°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, the freezing crystallization time in step (2) is 0.5 to 1.5 h, for example, 0.5 h, 0.7 h, 0.9 h, 1.1 h, 1.3 h or 1.5 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] In the present invention, sodium sulfate is firstly recovered by freezing crystallization, and its purpose is that: the solubility of sodium sulfate decreases significantly with decreasing temperature, while the solubility of other impurities changes less, and the removal of sodium sulfate reduces its influence on the subsequent sodium chloride and potassium chloride recovery process; and the temperature of the freezing crystallization is -5 to 0 DEG C. If the temperature of the freezing crystallization is too high, the crystallization speed will be slowed down, thereby affecting the crystallization efficiency and purity; conversely, if the temperature of the freezing crystallization is too low, it will affect the quality of the crystallization and cause the crystal to be too small; other impurities will also crystallize, and the purity of the product will decrease.

[0030] As a preferred technical solution of the present invention, the multi-effect evaporation in step (3) includes triple-effect evaporation.

[0031] Preferably, the temperature of the multi-effect evaporation in step (3) is 90-110°C, for example, 90°C, 94°C, 98°C, 102°C, 106°C or 110°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0032] Preferably, the time of the multi-effect evaporation in step (3) is 20 to 40 minutes, for example, 20 minutes, 24 minutes, 28 minutes, 32 minutes, 36 minutes or 40 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0033] In the present invention, sodium chloride in wastewater is recovered by multi-effect evaporation. If the temperature during the evaporation process is too high, it will lead to excessive evaporation of water, which may cause KCl crystallization and interfere with the recovery process of NaCl. If the temperature is too low, it will lead to insufficient evaporation of water, affecting the recovery effect of NaCl. The evaporation time is too long, which increases energy consumption, and too much NaCl is retained in the solution under low temperature conditions.

[0034] As a preferred technical solution of the present invention, step (4) further includes flash evaporation of the tertiary filtrates before the cooling crystallization.

[0035] Preferably, the terminal temperature of the flash evaporation treatment is 45-65°C, for example, 45°C, 49°C, 53°C, 57°C, 61°C or 65°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0036] As a preferred technical solution of the present invention, the cooling crystallization temperature in step (4) is 45-65°C, for example, it can be 45°C, 49°C, 53°C, 57°C, 61°C or 65°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0037] Preferably, the cooling crystallization time in step (4) is 10 to 30 minutes, for example, 10 minutes, 14 minutes, 18 minutes, 22 minutes, 26 minutes or 30 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0038] In the present invention, potassium chloride in wastewater is recovered by cooling crystallization. If the temperature of the cooling crystallization is too high, the solubility of KCl will be high, resulting in slow crystallization and reduced recovery rate. If the temperature is too low, KCl will be excessively precipitated and impurities will also be precipitated, affecting product quality and continuous production.

[0039] In the present invention, the cold source used in the freezing crystallization and cooling crystallization process includes industrial cooling water or mechanical refrigeration. The present invention further reduces energy consumption through reasonable cooling design. Compared with the traditional high-temperature evaporation process, the application of low-temperature cold source significantly improves the energy-saving effect of the wastewater resource utilization process and reduces the steam usage (about 30% to 50%), so that the present invention has a greater advantage in energy efficiency.

[0040] As a preferred technical solution of the present invention, the resource treatment method of high-salt wastewater provided by the present invention comprises the following steps:

[0041] (1) mixing a precipitant and high-salt wastewater in a mass ratio of 1.5 to 2.5:1000, stirring the mixture at a stirring rate of 400 to 600 r / min for 15 to 30 minutes, and then performing solid-liquid separation to obtain a primary filtrate;

[0042] The precipitant comprises sodium hydroxide, sodium sulfide and polyacrylamide in a mass ratio of 1:1:1 to 3;

[0043] (2) subjecting the primary filtrate obtained in step (1) to freeze crystallization for 0.5 to 1.5 hours at -5 to 0° C., and obtaining sodium sulfate and a secondary filtrate after solid-liquid separation;

[0044] (3) subjecting the secondary filtrate obtained in step (2) to multi-effect evaporation at 90 to 110° C. for 20 to 40 minutes to obtain sodium chloride and a tertiary filtrate after solid-liquid separation;

[0045] (4) flash evaporating the tertiary filtrate obtained in step (3), cooling and crystallizing the filtrate at 45 to 65° C. for 10 to 30 minutes, and obtaining potassium chloride and the fourth filtrate after solid-liquid separation;

[0046] The four filtrates are recycled for the freeze crystallization in step (2).

[0047] The device system used in the resource treatment method of the high-salt wastewater includes: a heavy metal removal unit, a freezing crystallization unit, an evaporation crystallization unit and a cooling crystallization unit which are sequentially connected through a conveying pipeline.

[0048] Preferably, the heavy metal removal unit comprises a stirred reactor and a solid-liquid separator which are sequentially connected.

[0049] Preferably, a flow control device is provided at the inlet of the stirred reactor to control the flow rate of the high-salinity wastewater flowing into the stirred reactor, so as to ensure the adequacy of the stirring reaction in the high-salinity wastewater.

[0050] Preferably, the freezing crystallization unit comprises a cooling crystallization pool and a crystallization separation device which are connected in sequence.

[0051] Preferably, a cooling circulation device is provided in the cooling crystallization pool to provide and maintain a low temperature environment of the cooling crystallization pool.

[0052] Preferably, the cooling circulation device includes a cooling water circulation pump or a heat exchanger.

[0053] Preferably, the evaporation crystallization device comprises a multiple-effect evaporator and a crystallization separator which are connected in sequence.

[0054] Preferably, the evaporation crystallization device further comprises a steam compressor for compressing the steam generated in the multi-effect evaporation process to improve the energy efficiency of the device system.

[0055] Preferably, the cooling crystallization unit comprises a cooler and a solid-liquid separation device which are connected in sequence.

[0056] Preferably, the liquid outlet of the solid-liquid separation device is provided with a circulation pump for pumping the fourth filtrate back into the cooling crystallization pool to form a closed-loop circulation, thereby achieving zero wastewater discharge.

[0057] Preferably, the cooler includes a cooling water circulation device to provide a low-temperature cooling source required for cooling crystallization to ensure a stable cooling crystallization process.

[0058] Preferably, the device system further comprises a control system for monitoring and adjusting the delivery flow and delivery pressure of the four filtrates during the reuse process of step (4) to ensure the continuous operation of the device system.

[0059] Preferably, the delivery flow rate is 12 to 16 m 3 / h, for example, it can be 12m 3 / h、13m 3 / h、14m 3 / h、15m 3 / h or 16m 3 / h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0060] Preferably, the delivery pressure is 165-170 KPa, for example, it can be 165 KPa, 166 KPa, 167 KPa, 168 KPa, 169 KPa or 170 KPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] It is worth noting that the resource recovery treatment method of the present invention is a continuous treatment method. By adopting a continuously connected device, continuous treatment of wastewater is achieved, thereby further improving the treatment efficiency.

[0062] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] (1) The resource recovery treatment method provided by the present invention first effectively removes heavy metals in wastewater through a precipitant (removal rate of more than 95%) to ensure that the subsequent crystallization process is not polluted; then, by combining freezing crystallization, multi-effect evaporation and cooling crystallization, the crystallization recovery of different components in high-salinity wastewater is achieved, and the scaling problem is reduced;

[0065] (2) The present invention combines freezing crystallization, multiple-effect evaporation and cooling crystallization to achieve step-by-step crystallization recovery of sodium sulfate, sodium chloride and potassium chloride using different temperature ranges, and the recovery rates of sodium sulfate, sodium chloride and potassium chloride are not less than 90%, meeting the use standards of the chemical, agricultural and food industries, ensuring that the recovered products have high industrial application value;

[0066] (3) The resource recovery treatment method provided by the present invention forms a closed loop by recycling the filtrate from the fourth step for freezing and crystallization, thereby achieving zero discharge of wastewater and full recovery of resources, significantly improving the overall resource utilization rate, reducing environmental pollution, and meeting environmental protection requirements;

[0067] (4) The resource recovery method provided by the present invention significantly improves the energy saving effect and reduces the steam usage (30-50%) by rationally utilizing the low-temperature cold source for freezing crystallization and cooling crystallization compared with the traditional high-temperature evaporation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Figure 1 This is a flow chart of the method for resource recovery treatment of high-salt wastewater provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0069] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0070] The ion composition and content in the high-salt wastewater treated by the following examples and comparative examples are shown in Table 1:

[0071] Table 1

[0072] <![CDATA[K + ]]> <![CDATA[Na + ]]> <![CDATA[Cl - ]]> <![CDATA[SO4 2- ]]> <![CDATA[Pb 2+ ]]> <![CDATA[Cd 2+ ]]> <![CDATA[Tl + ]]> <![CDATA[Zn 2+ ]]> As Content (mg / L) 32440 68790 109890 32150 1.0 0.5 6.0 4.0 0.3

[0073] Example 1

[0074] This embodiment provides a method for recycling high-salinity wastewater. Figure 1 As shown, the resource processing method includes the following steps:

[0075] (1) mixing a precipitant and high-salt wastewater in a mass ratio of 2:1000, stirring the mixture for 25 minutes at a stirring rate of 500 r / min, and then performing solid-liquid separation to obtain a primary filtrate;

[0076] The precipitant comprises sodium hydroxide, sodium sulfide and polyacrylamide in a mass ratio of 1:1:2;

[0077] (2) subjecting the primary filtrate obtained in step (1) to freeze crystallization at -3°C for 1 hour to obtain sodium sulfate and a secondary filtrate after solid-liquid separation;

[0078] (3) subjecting the secondary filtrate obtained in step (2) to triple-effect evaporation at 100° C. for 30 min to obtain sodium chloride and a tertiary filtrate after solid-liquid separation;

[0079] (4) flash evaporating the tertiary filtrate obtained in step (3), cooling and crystallizing the filtrate at 55° C. for 20 min, and obtaining potassium chloride and the fourth filtrate after solid-liquid separation;

[0080] The four filtrates are recycled for the freeze crystallization in step (2).

[0081] Example 2

[0082] This embodiment provides a method for recycling high-salinity wastewater, which comprises the following steps:

[0083] (1) mixing a precipitant and high-salt wastewater in a mass ratio of 1.5:1000, stirring the mixture for 30 minutes at a stirring rate of 400 r / min, and then performing solid-liquid separation to obtain a primary filtrate;

[0084] The precipitant comprises sodium hydroxide, sodium sulfide and polyacrylamide in a mass ratio of 1:1:1;

[0085] (2) subjecting the primary filtrate obtained in step (1) to freeze crystallization for 0.5 h at -5°C to obtain sodium sulfate and a secondary filtrate after solid-liquid separation;

[0086] (3) subjecting the secondary filtrate obtained in step (2) to triple-effect evaporation at 90° C. for 40 min to obtain sodium chloride and a tertiary filtrate after solid-liquid separation;

[0087] (4) flash evaporating the tertiary filtrate obtained in step (3), cooling and crystallizing the filtrate at 45° C. for 10 min, and obtaining potassium chloride and the fourth filtrate after solid-liquid separation;

[0088] The four filtrates are recycled for the freeze crystallization in step (2).

[0089] Example 3

[0090] This embodiment provides a method for recycling high-salinity wastewater, which comprises the following steps:

[0091] (1) mixing a precipitant and high-salt wastewater in a mass ratio of 2.5:1000, stirring the mixture at a stirring rate of 600 r / min for 15 min, and then performing solid-liquid separation to obtain a primary filtrate;

[0092] The precipitant comprises sodium hydroxide, sodium sulfide and polyacrylamide in a mass ratio of 1:1:3;

[0093] (2) subjecting the primary filtrate obtained in step (1) to freeze crystallization for 1.5 h at 0° C. to obtain sodium sulfate and a secondary filtrate after solid-liquid separation;

[0094] (3) subjecting the secondary filtrate obtained in step (2) to triple-effect evaporation at 110° C. for 20 min to obtain sodium chloride and a tertiary filtrate after solid-liquid separation;

[0095] (4) flash evaporating the tertiary filtrate obtained in step (3), cooling and crystallizing the filtrate at 65° C. for 30 min, and obtaining potassium chloride and the fourth filtrate after solid-liquid separation;

[0096] The four filtrates are recycled for the freeze crystallization in step (2).

[0097] Example 4

[0098] This embodiment provides a resource treatment method for high-salinity wastewater, which differs from the resource treatment method in embodiment 1 only in that:

[0099] In this embodiment, the temperature of the freezing crystallization in step (2) is adjusted to -8°C.

[0100] Example 5

[0101] This embodiment provides a resource treatment method for high-salinity wastewater, which differs from the resource treatment method in embodiment 1 only in that:

[0102] In this embodiment, the temperature of the freezing crystallization in step (2) is adjusted to 2°C.

[0103] Example 6

[0104] This embodiment provides a resource treatment method for high-salinity wastewater, which differs from the resource treatment method in embodiment 1 only in that:

[0105] In this embodiment, the temperature of the multi-effect evaporation in step (3) is adjusted to 80°C.

[0106] Example 7

[0107] This embodiment provides a resource treatment method for high-salinity wastewater, which differs from the resource treatment method in embodiment 1 only in that:

[0108] In this embodiment, the temperature of the multi-effect evaporation in step (3) is adjusted to 120°C.

[0109] Example 8

[0110] This embodiment provides a resource treatment method for high-salinity wastewater, which differs from the resource treatment method in embodiment 1 only in that:

[0111] In this embodiment, the temperature of the cooling crystallization in step (4) is adjusted to 40°C.

[0112] Example 9

[0113] This embodiment provides a resource treatment method for high-salinity wastewater, which differs from the resource treatment method in embodiment 1 only in that:

[0114] In this embodiment, the temperature of the cooling crystallization in step (4) is adjusted to 70°C.

[0115] Example 10

[0116] This embodiment provides a resource treatment method for high-salinity wastewater, which differs from the resource treatment method in embodiment 1 only in that:

[0117] In this embodiment, the precipitant in step (1) is adjusted to: sodium hydroxide and sodium sulfide in a mass ratio of 1:1.

[0118] Embodiment 11

[0119] This embodiment provides a resource treatment method for high-salinity wastewater, which differs from the resource treatment method in embodiment 1 only in that:

[0120] In this embodiment, sodium hydroxide and sodium sulfide in the precipitant of step (1) are omitted.

[0121] Example 12

[0122] This embodiment provides a resource treatment method for high-salinity wastewater, which differs from the resource treatment method in embodiment 1 only in that:

[0123] In this embodiment, the mass ratio of the precipitant and the high-salt wastewater in step (1) is adjusted to 5:1000, and the precipitant includes sodium hydroxide, sodium sulfide and polyacrylamide in a ratio of 2:1:3.

[0124] Comparative Example 1

[0125] This comparative example provides a resource treatment method for high-salinity wastewater, which differs from Example 1 only in that:

[0126] In this comparative example, the process of mixing the precipitant and stirring the reaction in step (1) is omitted, that is, the high-salinity wastewater is directly subjected to freeze crystallization.

[0127] Comparative Example 2

[0128] This comparative example provides a resource treatment method for high-salinity wastewater, which differs from Example 1 only in that:

[0129] In this comparative example, the operation sequence of freezing crystallization and multiple-effect evaporation is changed, that is, the primary filtrate obtained in step (1) is subjected to multiple-effect evaporation, and then freezing crystallization and cooling crystallization are carried out.

[0130] Comparative Example 3

[0131] This comparative example provides a resource treatment method for high-salinity wastewater, which differs from Example 1 only in that:

[0132] In this comparative example, the operation sequence of the multiple-effect evaporation and cooling crystallization is changed, that is, the secondary filtrate obtained in step (2) is cooled and crystallized, and then the multiple-effect evaporation is performed.

[0133] Comparative Example 4

[0134] This comparative example provides a resource treatment method for high-salinity wastewater, which differs from Example 1 only in that:

[0135] In this comparative example, the operation process is adjusted as follows: the primary filtrate obtained in step (1) is subjected to multiple-effect evaporation, cooling crystallization and freezing crystallization in sequence.

[0136] Performance testing:

[0137] The purity and yield of the sodium sulfate, sodium chloride and potassium chloride obtained in the above examples and comparative examples were tested, and the results are shown in Table 2.

[0138] Table 2

[0139]

[0140]

[0141] According to Table 1, we can know the following points:

[0142] (1) Comprehensive analysis of Examples 1-3 shows that the resource recovery method provided by the present invention can realize the step-by-step crystallization recovery of sodium sulfate, sodium chloride and potassium chloride, and the recovery rate is not less than 99%, which meets the use standards of the chemical, agricultural and food industries, ensuring that the recovered products have high industrial application value;

[0143] (2) Comprehensive analysis of Example 1 and Examples 4-5 shows that in the process of high-salt wastewater treatment, when the temperature of the freezing crystallization is too high, the crystallization rate will be reduced, thereby increasing energy consumption; on the contrary, when the temperature of the freezing crystallization is too low, impurities will be precipitated, resulting in a decrease in the purity of sodium sulfate;

[0144] (3) Comprehensive analysis of Example 1 and Examples 6-7 shows that in the process of high-salt wastewater treatment, when the temperature of the multi-effect evaporation is too high, it will lead to excessive evaporation of water, a small amount of KCl crystallization, and thus affect the purity of NaCl; conversely, when the temperature of the multi-effect evaporation is too low, it will lead to insufficient evaporation of water, affecting the recovery effect of NaCl;

[0145] (4) Comprehensive analysis of Example 1 and Examples 8-9 shows that in the process of high-salt wastewater treatment, when the cooling crystallization temperature is high, the solubility of KCl will be high, resulting in slow crystallization; conversely, when the cooling crystallization temperature is low, KCl will be excessively precipitated, impurities will also be precipitated, affecting product quality;

[0146] (5) Comprehensive analysis of Example 1 and Examples 10-12 shows that during the treatment of high-salt wastewater, adjusting the composition of the precipitant will affect the separation effect of heavy metal ions in the wastewater;

[0147] If the use of polyacrylamide is omitted, the flocculation effect will be reduced, so that the particulate impurities in the wastewater cannot be completely removed, resulting in a decrease in the purity and yield of the obtained product;

[0148] If sodium hydroxide and sodium sulfide are omitted, it will result in the inability to form incompatible hydroxides or metal sulfides, resulting in incomplete removal of some heavy metal ions, resulting in reduced purity of the obtained product;

[0149] When the content of sodium hydroxide in the precipitant is too high, the precipitate in the wastewater will be finer and more viscous, increasing the difficulty of separation;

[0150] (6) Comprehensive analysis of Example 1 and Comparative Example 1 shows that mixing the precipitant and high-salt wastewater for stirring reaction can effectively remove heavy metals in wastewater. If this step is omitted, it will lead to crystallization of heavy metal salts, affecting product quality;

[0151] (7) Comprehensive analysis of Example 1 and Comparative Examples 2-4 shows that changing the processing order of freezing crystallization, multi-effect evaporation and cooling crystallization in the resource recovery treatment provided by the present invention will lead to uneven crystallinity of each ion in the solution, thereby failing to achieve effective separation of the three high-purity salt products; (1) If cooling crystallization is performed first, KCl in a solution of 45 to 65°C cannot meet the crystallization conditions; (2) If multi-effect evaporation is performed first, during evaporation, not only NaCl will precipitate, but also Na 2 SO 4 (3) If freezing crystallization is first performed and then cooling crystallization is performed to precipitate KCl, since the solution has not been concentrated, KCl cannot be crystallized within the temperature range of 45 to 65°C.

[0152] In summary, the present invention can effectively separate and recover sodium, potassium and other components in high-salt wastewater through sequential freezing crystallization, multi-effect evaporation, cooling crystallization and recycling, produce sodium sulfate, sodium chloride and potassium chloride products with industrial value, reduce the salt content in wastewater, and realize resource utilization of wastewater.

[0153] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for recycling high-salt wastewater, characterized in that: The resource processing method comprises the following steps: (1) mixing high-salt wastewater and a precipitant, stirring for reaction, and then performing solid-liquid separation to obtain a primary filtrate; (2) subjecting the primary filtrate obtained in step (1) to freeze crystallization, and obtaining sodium sulfate and a secondary filtrate after solid-liquid separation; (3) subjecting the secondary filtrate obtained in step (2) to multi-effect evaporation to obtain sodium chloride and a tertiary filtrate after solid-liquid separation; (4) cooling and crystallizing the tertiary filtrate obtained in step (3), and obtaining potassium chloride and the fourth filtrate after solid-liquid separation; The four filtrates are recycled for the freeze crystallization in step (2).

2. The method for recycling high-salt wastewater according to claim 1, characterized in that: The ions in the high-salinity wastewater include K + 、Na + , Cl - 、SO4 2- and heavy metal ions; Preferably, the heavy metal ions include Zn 2+ , As, Pb 2+ 、Cd 2+ And Tl + .

3. The method for recycling high-salt wastewater according to claim 1 or 2, characterized in that: The precipitant in step (1) comprises sodium hydroxide, sodium sulfide and polyacrylamide; Preferably, the mass ratio of sodium hydroxide, sodium sulfide and polyacrylamide is 1:1:1-3; Preferably, the mass ratio of the precipitant to high-salt wastewater is 1.5-2.5:1000.

4. The method for recycling high-salt wastewater according to any one of claims 1 to 3, characterized in that: The stirring rate of the stirring reaction in step (1) is 400-600 r / min; Preferably, the stirring reaction time in step (1) is 15 to 30 minutes.

5. The method for recycling high-salt wastewater according to any one of claims 1 to 4, characterized in that: The temperature of the freezing crystallization in step (2) is -5 to 0°C; Preferably, the freezing crystallization time in step (2) is 0.5 to 1.5 hours.

6. The method for recycling high-salt wastewater according to any one of claims 1 to 5, characterized in that: The multi-effect evaporation in step (3) includes triple-effect evaporation.

7. The method for recycling high-salt wastewater according to any one of claims 1 to 6, characterized in that: The temperature of the multiple-effect evaporation in step (3) is 90-110° C. Preferably, the time for the multiple-effect evaporation in step (3) is 20 to 40 minutes.

8. The method for recycling high-salinity wastewater according to any one of claims 1 to 7, characterized in that: Step (4) also includes flash evaporating the tertiary filtrates before cooling and crystallizing; Preferably, the terminal temperature of the flash evaporation treatment is 45-65°C.

9. The method for recycling high-salt wastewater according to any one of claims 1 to 8, characterized in that: The temperature of the cooling crystallization in step (4) is 45-65° C. Preferably, the cooling crystallization time in step (4) is 10 to 30 minutes.

10. The method for recycling high-salt wastewater according to any one of claims 1 to 9, characterized in that: The resource processing method comprises the following steps: (1) mixing a precipitant and high-salt wastewater in a mass ratio of 1.5 to 2.5:1000, stirring the mixture at a stirring rate of 400 to 600 r / min for 15 to 30 minutes, and then performing solid-liquid separation to obtain a primary filtrate; The precipitant comprises sodium hydroxide, sodium sulfide and polyacrylamide in a mass ratio of 1:1:1 to 3; (2) subjecting the primary filtrate obtained in step (1) to freeze crystallization for 0.5 to 1.5 hours at -5 to 0° C., and obtaining sodium sulfate and a secondary filtrate after solid-liquid separation; (3) subjecting the secondary filtrate obtained in step (2) to multi-effect evaporation at 90 to 110° C. for 20 to 40 min to obtain sodium chloride and a tertiary filtrate after solid-liquid separation; (4) flash evaporating the tertiary filtrate obtained in step (3), cooling and crystallizing the filtrate at 45 to 65° C. for 10 to 30 minutes, and obtaining potassium chloride and the fourth filtrate after solid-liquid separation; The four filtrates are recycled for the freeze crystallization in step (2).

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