Treatment methods for saline wastewater

Abstract

This invention relates to the field of wastewater treatment and discloses a method for treating saline wastewater. The method includes: 1) evaporating the wastewater to be treated to obtain a concentrated liquid; 2) separating the concentrated liquid into solid and liquid phases, and cooling the liquid phase obtained from the solid-liquid separation to crystallize it, obtaining a crystalline liquid; 3) separating the crystalline liquid into solid and liquid phases and evaporating the liquid phase obtained from the solid-liquid separation to obtain a concentrated liquid; 4) cooling the concentrated liquid to crystallize it, obtaining a crystalline liquid; 5) separating the crystalline liquid into solid and liquid phases, wherein, relative to the CH3COO content in 1 mol of the wastewater to be treated... ‑ The wastewater to be treated contains Cl ‑ The concentration is 0.4-5 mol. The method according to this invention is environmentally friendly and can separately recover potassium chloride and potassium acetate from wastewater, maximizing the reuse of resources in the wastewater.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment, and more specifically to a method for treating saline wastewater. Background Technology

[0002] Potassium chloride is mainly used in inorganic industries as a basic raw material for manufacturing various potassium salts or alkalis such as potassium hydroxide, potassium sulfate, potassium nitrate, potassium chlorate, and potassium dichromate. In the pharmaceutical industry, it is used as a diuretic and a drug to prevent potassium deficiency. In the dye industry, it is used to produce potassium salts and reactive dyes. In agriculture, it is a potassium fertilizer. Its fertilizer effect is rapid; direct application to farmland can raise the moisture content of the lower soil layers, providing drought resistance. However, it is not suitable for saline-alkali soils or for crops such as tobacco, sweet potatoes, and sugar beets. Potassium chloride has a similar taste to sodium chloride (bitter) and is also used as an additive in low-sodium salts or mineral water. In addition, it is used to manufacture flash suppressants for gun muzzles or cannons, heat treatment agents for steel, and in photography. It also has applications in medicine, scientific research, and food processing; potassium chloride can also partially replace sodium chloride in table salt to reduce the likelihood of high blood pressure.

[0003] Potassium acetate is an organic compound with the chemical formula CH3COOK. It is a white powder used as an analytical reagent and for adjusting pH levels. It is also used as a desiccant in the manufacture of transparent glass and in the pharmaceutical industry. Furthermore, it can be used as a buffer, diuretic, fabric and paper softener, and catalyst.

[0004] CN108264457A discloses a method for preparing potassium acetate, which uses the solubility of potassium acetate in ethanol to purify potassium acetate. However, anhydrous ethanol is used for pulping, which has drawbacks in terms of recycling.

[0005] In industrial production, large quantities of aqueous solutions containing potassium acetate and potassium chloride are generated due to production needs. These two salts are extremely similar in properties, making their separation extremely difficult. Currently, there is no mature process for separating mixed salts. Traditionally, landfill disposal using distillation is employed, which suffers from high disposal costs, potassium salt loss, and resource waste. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of high disposal costs, potassium salt loss, and resource waste in existing technologies, and to provide a new method for treating saline wastewater. This method is green and environmentally friendly, and can recover potassium chloride and potassium acetate from the wastewater separately, maximizing the reuse of resources in the wastewater.

[0007] To achieve the above objectives, the present invention provides a method for treating saline wastewater containing K. + Cl - and CH3COO - The method is characterized by the following steps:

[0008] 1) The wastewater to be treated is passed into an evaporation device for the first evaporation to obtain a first concentrated solution containing potassium chloride crystals;

[0009] 2) The first concentrated solution containing potassium chloride crystals is subjected to a first solid-liquid separation, and the liquid phase obtained from the first solid-liquid separation is subjected to a first cooling crystallization to obtain a crystalline solution containing potassium chloride crystals;

[0010] 3) The crystallization liquid containing potassium chloride crystals is subjected to a second solid-liquid separation, and the liquid phase obtained from the second solid-liquid separation is subjected to a second evaporation to obtain a second concentrated liquid containing potassium acetate;

[0011] 4) The second concentrated solution containing potassium acetate is subjected to a second cooling crystallization to obtain a crystalline solution containing potassium acetate crystals;

[0012] 5) The crystallization solution containing potassium acetate crystals is subjected to a third solid-liquid separation.

[0013] Among them, relative to the CH3COO contained in 1 mol of the wastewater to be treated - The wastewater to be treated contains Cl - It is 0.4-5 mol;

[0014] The first evaporation prevents potassium acetate from crystallizing out;

[0015] The temperature for the first solid-liquid separation is 80-90℃;

[0016] The temperature for the first cooling crystallization is 15-25℃;

[0017] The temperature for the second cooling crystallization is 5-20℃.

[0018] Preferably, relative to the amount of CH3COO contained in 1 mol of the wastewater to be treated - The wastewater to be treated contains Cl - The concentration is 0.5-4.5 mol; more preferably, relative to the CH3COO content in 1 mol of the wastewater to be treated. - The wastewater to be treated contains Cl - The concentration ranges from 0.54 to 4.2 mol.

[0019] Preferably, the conditions for the first evaporation include: a temperature of 85-100°C and a vacuum degree of 0.005-0.05 MPa; more preferably, the conditions for the first evaporation include: a temperature of 90-97°C and a vacuum degree of 0.01-0.03 MPa.

[0020] Preferably, the first evaporation causes the concentration of potassium acetate in the first concentrate to be below X, where X is the concentration of potassium acetate in the first concentrate when both potassium chloride and potassium acetate are saturated under the conditions of the first evaporation.

[0021] Preferably, the first evaporation results in a potassium acetate concentration of 0.94X-0.999X in the first concentrate.

[0022] Preferably, the first cooling crystallization time is 20-40 min; more preferably, the conditions for the first cooling crystallization include: a temperature of 20-23°C and a time of 20-30 min.

[0023] Preferably, the conditions for the second evaporation include a temperature of 55-80°C and a vacuum degree of 0.06-0.09 MPa; more preferably, the conditions for the second evaporation include a temperature of 58-70°C and a vacuum degree of 0.08-0.085 MPa.

[0024] Preferably, the second cooling crystallization time is 20-40 min; more preferably, the conditions for the second cooling crystallization include: a temperature of 8-12°C and a time of 25-35 min.

[0025] Preferably, the method further includes performing a first solid-liquid separation on the first concentrated solution containing potassium chloride crystals to obtain potassium chloride crystals.

[0026] Preferably, potassium chloride crystals are obtained by performing a second solid-liquid separation on the crystallization liquid containing potassium chloride crystals.

[0027] Preferably, the method further includes washing the obtained potassium chloride crystals.

[0028] Preferably, the potassium acetate crystals are obtained by a third solid-liquid separation process on the crystallization solution containing potassium acetate crystals.

[0029] Preferably, the method further includes washing the obtained potassium acetate crystals.

[0030] Preferably, the K in the saline wastewater + For 30g / L or more, Cl - For amounts above 30 g / L, CH3COO - The concentration is above 40 g / L; more preferably, the K in the saline wastewater + 40-180g / L, Cl - The concentration is 35-180 g / L, CH3COO - It is 50-200g / L.

[0031] Preferably, the method further includes adjusting the saline wastewater to neutral using potassium hydroxide.

[0032] Through the above technical solution, for products containing K + Cl - and CH3COO - The saline wastewater is treated by evaporation to obtain potassium chloride crystals and a first concentrated solution. After thermal separation of the first concentrated solution to obtain solid potassium chloride, further cooling and crystallization yields potassium chloride crystals and a crystallization solution. The crystallization solution is then evaporated and cooled for crystallization to obtain potassium acetate crystals. The mother liquor from crystallization can be returned to step 1) for use as wastewater. This method utilizes the concentration gradients of potassium chloride and potassium acetate in water at different temperatures to recover potassium chloride and potassium acetate from the wastewater separately, maximizing the reuse of resources in the wastewater. Furthermore, potassium chloride and potassium acetate are recovered in crystalline form, and the water obtained from distillation and the mother liquor from crystallization can be reused. The entire process generates no wastewater or waste residue, making it environmentally friendly. Detailed Implementation

[0033] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0034] This invention provides a method for treating saline wastewater containing potassium (K). + Cl - and CH3COO - The method is characterized by the following steps:

[0035] 1) The wastewater to be treated is passed into an evaporation device for the first evaporation to obtain a first concentrated solution containing potassium chloride crystals;

[0036] 2) The first concentrated solution containing potassium chloride crystals is subjected to a first solid-liquid separation, and the liquid phase obtained from the first solid-liquid separation is subjected to a first cooling crystallization to obtain a crystalline solution containing potassium chloride crystals;

[0037] 3) The crystallization liquid containing potassium chloride crystals is subjected to a second solid-liquid separation, and the liquid phase obtained from the second solid-liquid separation is subjected to a second evaporation to obtain a second concentrated liquid containing potassium acetate;

[0038] 4) The second concentrated solution containing potassium acetate is subjected to a second cooling crystallization to obtain a crystalline solution containing potassium acetate crystals;

[0039] 5) The crystallization solution containing potassium acetate crystals is subjected to a third solid-liquid separation.

[0040] Among them, relative to the CH3COO contained in 1 mol of the wastewater to be treated -The wastewater to be treated contains Cl - It is 0.4-5 mol;

[0041] The first evaporation prevents potassium acetate from crystallizing out;

[0042] The temperature for the first solid-liquid separation is 80-90℃;

[0043] The temperature for the first cooling crystallization is 15-25℃;

[0044] The temperature for the second cooling crystallization is 5-20℃.

[0045] The method provided by this invention can target substances containing K. + Cl - and CH3COO - The saline wastewater is treated to remove K. + Cl - and CH3COO - Furthermore, there are no particular limitations on the saline wastewater. Such wastewater can be, for example, synthetic wastewater.

[0046] In this invention, the first evaporation preventing potassium acetate from crystallizing means controlling the concentration of potassium acetate in the mixed system to not exceed its solubility under the evaporation conditions (including but not limited to temperature, pH, etc.), and does not exclude potassium acetate carried by potassium chloride crystals or adsorbed on the surface. Since the water content of the crystals differs after solid-liquid separation, it is generally considered that potassium acetate will not crystallize if the potassium chloride content in the obtained sodium chloride crystals is below 2% by mass (preferably below 1% by mass).

[0047] According to the present invention, the evaporation apparatus is not particularly limited and can be any type of evaporator conventionally used in the art. For example, it can be one or more selected from rising film evaporators, falling film evaporators, and scraped film evaporators.

[0048] Preferably, relative to the amount of CH3COO contained in 1 mol of the wastewater to be treated - The wastewater to be treated contains Cl - The concentration is 0.5-4.5 mol; more preferably, relative to the CH3COO content in 1 mol of the wastewater to be treated. - The wastewater to be treated contains Cl - The concentration is 0.54-4.2 mol. This is achieved by using CH3COO... - and Cl - By controlling the molar ratio within the above range, high-purity potassium chloride crystals can be obtained through evaporation, thus achieving the separation of potassium acetate and potassium chloride.

[0049] According to the present invention, the purpose of the first evaporation is to precipitate most of the potassium chloride crystals but not potassium acetate crystals, thereby separating most of the potassium chloride first.

[0050] In this invention, the evaporation conditions are not particularly limited; as long as the above-mentioned objectives are met, they can be appropriately selected as needed. To improve the evaporation efficiency, preferably, the first evaporation conditions include: a temperature of 85-100℃ and a vacuum degree of 0.005-0.05 MPa; more preferably, the first evaporation conditions include: a temperature of 90-97℃ and a vacuum degree of 0.01-0.03 MPa.

[0051] According to the present invention, the first evaporation prevents potassium acetate from crystallizing (i.e., potassium acetate does not reach supersaturation). Preferably, the concentration of potassium acetate in the first concentrate is X or less, where X is the concentration of potassium acetate in the first concentrate when both potassium chloride and potassium acetate are saturated under the conditions of the first evaporation. More preferably, the concentration of potassium acetate in the first concentrate is 0.999X or less, further preferably 0.95X-0.999X, and even more preferably 0.99X-0.994X. By controlling the degree of the first evaporation within the above range, as much potassium chloride as possible can crystallize and precipitate while ensuring that potassium acetate does not precipitate. By maximizing the crystallization of potassium chloride during the first evaporation, wastewater treatment efficiency can be improved and energy waste reduced.

[0052] In this invention, the extent of the first evaporation can be monitored by controlling the concentration of the liquid obtained from the evaporation. Specifically, by controlling the concentration of the liquid obtained from the first evaporation within the aforementioned range, the first evaporation prevents potassium acetate in the concentrate from crystallizing out. Here, the concentration of the liquid obtained from the first evaporation is monitored by measuring its density, specifically using a hydrometer.

[0053] According to the present invention, the first solid-liquid separation can be performed by methods commonly used in the art for separating solids and liquids, such as filtration and centrifugation. Furthermore, the potassium chloride crystals obtained from the first solid-liquid separation inevitably adsorb certain impurities such as acetate ions. To remove these adsorbed impurities and improve the purity of the crystals, preferably, the potassium chloride crystals are first washed with methanol or water and then dried. To avoid dissolution of the potassium chloride crystals during the washing process, preferably, the potassium chloride crystals are washed with an aqueous solution of potassium chloride.

[0054] The methods for the first solid-liquid separation and the first washing described above are not particularly limited. For example, conventional solid-liquid separation equipment in the art can be used, or it can be carried out on a segmented solid-liquid separation device such as a belt filter. Preferably, the first washing method is rinsing. The number of rinsing cycles is not particularly limited and can be more than once. To obtain potassium chloride crystals of higher purity, 2-4 cycles are preferred. During the washing process, the liquid generated during washing is preferably returned to step 1) as wastewater.

[0055] According to the present invention, potassium chloride crystals are obtained by performing a first solid-liquid separation on the first concentrated solution containing potassium chloride crystals. The purity of the potassium chloride crystals is preferably 98% by weight or more, more preferably 98.5% by weight or more, even more preferably 99% by weight or more, and even more preferably 99.5% by weight or more.

[0056] In this invention, the liquid phase obtained from the first solid-liquid separation is subjected to a first cooling crystallization to obtain a crystalline liquid containing potassium chloride crystals. The purpose of the first cooling crystallization is to precipitate a small portion of the potassium chloride crystals in the liquid phase obtained from the first solid-liquid separation, while potassium acetate hardly precipitates. The conditions for the first cooling crystallization only need to meet the above-mentioned purpose. Preferably, the first cooling crystallization time is 20-40 minutes; more preferably, the conditions for the first cooling crystallization include: a temperature of 20-23°C and a time of 20-30 minutes.

[0057] According to the present invention, the second solid-liquid separation can be performed by methods commonly used in the art for separating solids and liquids, such as filtration and centrifugation. Furthermore, the potassium chloride crystals obtained from the second solid-liquid separation inevitably adsorb certain impurities such as acetate ions. To remove these adsorbed impurities and improve the purity of the crystals, preferably, the potassium chloride crystals are subjected to a second washing with methanol or water and then dried. To avoid dissolution of the potassium chloride crystals during the washing process, preferably, the potassium chloride crystals are washed with an aqueous solution of potassium chloride.

[0058] The methods for the second solid-liquid separation and the second washing described above are not particularly limited. For example, conventional solid-liquid separation equipment in the art can be used, or it can be carried out on a segmented solid-liquid separation device such as a belt filter. Preferably, the second washing method is rinsing. The number of rinsing cycles is not particularly limited and can be more than once. To obtain potassium chloride crystals of higher purity, 2-4 cycles are preferred. During the washing process, the liquid generated during washing is preferably reused for the next batch of secondary separation.

[0059] In this invention, potassium chloride crystals are obtained by performing a second solid-liquid separation on the crystallization liquid containing potassium chloride crystals. The purity of the potassium chloride is preferably 88% by weight or more, more preferably 89% by weight or more, even more preferably 90% by weight or more, even more preferably 91% by weight or more, and even more preferably 95% by weight or more.

[0060] According to the present invention, the liquid phase obtained from the second solid-liquid separation is subjected to a second evaporation to obtain a second concentrated solution containing potassium acetate. The purpose of the second evaporation is to precipitate potassium acetate crystals.

[0061] In this invention, the evaporation conditions are not particularly limited. To improve the evaporation efficiency, preferably, the second evaporation conditions include: a temperature of 55-80°C and a vacuum degree of 0.06-0.09 MPa; more preferably, the second evaporation conditions include: a temperature of 58-70°C and a vacuum degree of 0.08-0.085 MPa.

[0062] In this invention, the second evaporation is sufficient to make the potassium acetate in the concentrate supersaturated. In a preferred embodiment of this invention, after the second evaporation continues until crystals precipitate, the second cooling crystallization is performed.

[0063] In this invention, the second concentrated solution containing potassium acetate is subjected to a second cooling crystallization to obtain a crystalline solution containing potassium acetate crystals. The purpose of the second cooling crystallization is to precipitate potassium acetate crystals. The conditions for the second cooling crystallization only need to meet the above-mentioned purpose. Preferably, the time for the second cooling crystallization is 20-40 minutes; more preferably, the conditions for the second cooling crystallization include: a temperature of 8-12°C and a time of 25-35 minutes.

[0064] In this invention, the crystallization liquid containing potassium acetate crystals undergoes a third solid-liquid separation. This third solid-liquid separation can be performed using methods commonly used in the art for separating solids and liquids, such as filtration or centrifugation. Furthermore, the potassium acetate crystals obtained from the third solid-liquid separation inevitably adsorb certain impurities such as chloride ions. To remove these adsorbed impurities and improve the purity of the crystals, preferably, the potassium acetate crystals are washed with methanol or water and then dried. To avoid dissolving potassium chloride crystals during the washing process, preferably, the potassium acetate crystals are washed with an aqueous solution of potassium acetate.

[0065] The third solid-liquid separation and second washing methods described above are not particularly limited. For example, conventional solid-liquid separation equipment in the art can be used, or the process can be carried out on a segmented solid-liquid separation device such as a belt filter. Preferably, the third washing method is rinsing. The number of rinsing cycles is not particularly limited and can be more than once. To obtain potassium chloride crystals of higher purity, 2-4 cycles are preferred. During the washing process, the solvent generated from the washing can be removed to obtain potassium acetate, and the solvent obtained from distillation can be used for washing the next batch.

[0066] In this invention, potassium acetate crystals are obtained by performing a third solid-liquid separation on the crystallization liquid containing potassium acetate crystals. The purity of the potassium acetate is preferably 98% by weight or more, more preferably 98.5% by weight or more, even more preferably 99% by weight or more, and even more preferably 99.5% by weight or more.

[0067] In addition, it is preferable to return the crystallization mother liquor obtained from the third solid-liquid separation to step 1) as wastewater, thereby maximizing the reuse of resources in the wastewater.

[0068] According to the present invention, preferably, the K in the saline wastewater + For 30g / L or more, Cl - For amounts above 30 g / L, CH3COO - The concentration is above 40 g / L; more preferably, the K in the saline wastewater + 40-180g / L, Cl - The concentration is 35-180 g / L, CH3COO - It is 50-200g / L.

[0069] In addition, the saline wastewater contains K + Cl - and CH3COO - In addition, it may contain CH3COOH, HCl, etc.

[0070] According to the present invention, when starting wastewater treatment, the saline wastewater can be used directly to begin the process. If the ion content of the saline wastewater meets the conditions of the present invention, it can be treated directly according to the conditions of the present invention. If the ion content of the saline wastewater does not meet the conditions of the present invention, for example, if the wastewater contains potassium chloride and acetic acid, potassium hydroxide can be used to adjust the saline wastewater to neutral, thereby making the wastewater meet the requirements of the present invention. Of course, in the initial stage, potassium chloride or potassium acetate can also be used to adjust the ion content in the wastewater to be treated, as long as the wastewater to be treated meets the CH3COO content of the wastewater to be treated in the present invention. - Cl - That's all that's required.

[0071] The present invention will be described in detail below through embodiments, but the present invention is not limited to the following embodiments.

[0072] Example 1

[0073] Saline wastewater (0.61L): contains 123.0 g / L potassium chloride, 221.4 g / L potassium acetate, pH = 8.07, relative to the CH3COO content in 1 mol of the wastewater to be treated. - The wastewater to be treated contains Cl - It is 0.73 mol.

[0074] 1) The saline wastewater was evaporated in an evaporation device. The degree of evaporation was monitored by a densitometer installed on the evaporation device. The evaporation was carried out until the concentration of potassium acetate in the concentrated evaporation solution was 0.993X. The solution was then rapidly filtered at 90°C. The filter cake was washed with a small amount of methanol and dried to obtain 70.3g of solid potassium chloride with a purity of 99.61% by weight. The evaporation conditions were: temperature 95°C and vacuum degree 0.02 MPa.

[0075] 2) The liquid phase obtained by filtration in step 1) is cooled and crystallized, and then the crystallized liquid is filtered by suction. After the filter cake is dried, 3.6g of solid potassium chloride is obtained. The purity of potassium chloride is 91.66% by weight. The cooling and crystallization temperature is 22℃ and the time is 25min.

[0076] 3) The mother liquor obtained in step 2) was evaporated until crystals precipitated, then cooled to 10°C and held at that temperature for 30 minutes for further cooling crystallization. The crystallized liquid was filtered, and the filter cake was washed with methanol and dried to obtain 77.76 g of potassium acetate with a purity of 98.10% by weight. The evaporation conditions were: temperature 70°C and vacuum degree 0.08 MPa. Furthermore, the methanol wash was evaporated to obtain 23.35 g of solid potassium acetate with a purity of 98.51% by weight.

[0077] In addition, the crystallization mother liquor obtained in step 3) is mixed with the next batch of wastewater and treated as saline wastewater.

[0078] Example 2

[0079] The saline wastewater (0.44L) contained 183.87 g / L potassium chloride, 149.82 g / L potassium acetate, and had a pH of 7.86. This is relative to the CH3COO content in 1 mol of the wastewater to be treated. - The wastewater to be treated contains Cl - It is 1.61 mol.

[0080] 1) The saline wastewater was evaporated in an evaporation device. The degree of evaporation was monitored by a densitometer installed on the evaporation device. The evaporation was carried out until the concentration of potassium acetate in the concentrated evaporation solution was 0.992X. The solution was then rapidly filtered at 90°C. The filter cake was washed with a small amount of methanol and dried to obtain 77.58g of solid potassium chloride with a purity of 99.65% by weight. The evaporation conditions were: temperature 95°C and vacuum degree 0.02Mpa.

[0081] 2) The liquid phase obtained by filtration in step 1) is cooled and crystallized, and then the crystallized liquid is filtered by suction. After the filter cake is dried, 3.62g of solid potassium chloride is obtained. The purity of potassium chloride is 71.00% by weight. The cooling and crystallization temperature is 22℃ and the time is 28min.

[0082] 3) The mother liquor obtained in step 2) was evaporated until crystals precipitated, then cooled to 10°C and held at that temperature for 30 minutes for further cooling crystallization. The crystallized liquid was filtered, and the filter cake was washed with methanol and dried to obtain 38.90 g of potassium acetate with a purity of 98.07% by weight. The evaporation conditions were: temperature 70°C and vacuum degree 0.08 MPa. Furthermore, the methanol wash was evaporated to obtain 16.33 g of solid potassium acetate with a purity of 98.51% by weight.

[0083] In addition, the crystallization mother liquor obtained in step 3) is mixed with the next batch of wastewater and treated as saline wastewater.

[0084] Example 3

[0085] The saline wastewater (0.355L) contained 76.14 g / L potassium chloride, 186.12 g / L potassium acetate, and had a pH of 7.93. This is relative to the CH3COO content in 1 mol of the wastewater to be treated. - The wastewater to be treated contains Cl - It is 0.54 mol.

[0086] 1) The saline wastewater was evaporated in an evaporation device. The degree of evaporation was monitored by a densitometer installed on the evaporation device. The evaporation was carried out until the concentration of potassium acetate in the concentrated evaporation solution was 0.990X. The solution was then rapidly filtered at 90°C. The filter cake was washed with a small amount of methanol and dried to obtain 23.44g of solid potassium chloride with a purity of 99.17% by weight. The evaporation conditions were: temperature 95°C and vacuum degree 0.02 MPa.

[0087] 2) The liquid phase obtained by filtration in step 1) is cooled and crystallized, and then the crystallized liquid is filtered by suction. After the filter cake is dried, 4.5g of solid potassium chloride is obtained. The purity of potassium chloride is 76.57% by weight. The cooling and crystallization temperature is 21℃ and the time is 25min.

[0088] 3) The mother liquor obtained in step 2) was evaporated until crystals precipitated, then cooled to 10°C and held at that temperature for 30 minutes for further cooling crystallization. The crystallized liquid was filtered, and the filter cake was washed with methanol and dried to obtain 49.37 g of potassium acetate with a purity of 99.45% by weight. The evaporation conditions were: temperature 60°C and vacuum degree 0.085 MPa. Furthermore, the methanol wash was evaporated to obtain 6.67 g of solid potassium acetate with a purity of 98.11% by weight.

[0089] In addition, the crystallization mother liquor obtained in step 3) is mixed with the next batch of wastewater and treated as saline wastewater.

[0090] Example 4

[0091] Saline wastewater (0.45L): contains 107.1g / L potassium chloride, 161.84g / L potassium acetate, pH=7.77, relative to the CH3COO content in 1 mol of the wastewater to be treated. - The wastewater to be treated contains Cl - It is 0.9 mol.

[0092] 1) The saline wastewater was evaporated in an evaporation device. The degree of evaporation was monitored by a densitometer installed on the evaporation device. The evaporation was carried out until the concentration of potassium acetate in the concentrated evaporation solution was 0.990X. The solution was then rapidly filtered at 85°C. The filter cake was washed with a small amount of methanol and dried to obtain 42.41g of solid potassium chloride with a purity of 99.51% by weight. The evaporation conditions were: temperature 90°C and vacuum degree 0.03Mpa.

[0093] 2) The liquid phase obtained by filtration in step 1) is cooled and crystallized, and then the crystallized liquid is filtered by suction. After the filter cake is dried, 2.53g of solid potassium chloride is obtained. The purity of potassium chloride is 91.28% by weight. The cooling and crystallization temperature is 23℃ and the time is 27min.

[0094] 3) The mother liquor obtained in step 2) was evaporated until crystals precipitated, then cooled to 10°C and held at that temperature for 30 minutes for further cooling crystallization. The crystallized liquid was filtered, and the filter cake was washed with methanol and dried to obtain 39.67 g of potassium acetate with a purity of 98.62% by weight. The evaporation conditions were: temperature 58°C and vacuum degree 0.083 MPa. Furthermore, the methanol wash was evaporated to obtain 4.51 g of solid potassium acetate with a purity of 98.21% by weight.

[0095] Example 5

[0096] Saline wastewater (0.40L): contains 237.5g / L potassium chloride, 73.5g / L potassium acetate, pH=7.59, relative to the CH3COO content in 1 mol of the wastewater to be treated. - The wastewater to be treated contains Cl - It is 4.2 mol.

[0097] 1) The saline wastewater was evaporated in an evaporation device. The degree of evaporation was monitored by a densitometer installed on the evaporation device. The evaporation was carried out until the concentration of potassium acetate in the concentrated evaporation solution was 0.990X. The solution was then rapidly filtered at 90°C. The filter cake was washed with a small amount of methanol and dried to obtain 91.80g of solid potassium chloride with a purity of 99.36% by weight. The evaporation conditions were: temperature 97°C and vacuum degree 0.01Mpa.

[0098] 2) The liquid phase obtained by filtration in step 1) is cooled and crystallized, and then the crystallized liquid is filtered by suction. After the filter cake is dried, 2.89g of solid potassium chloride salt is obtained. The purity of potassium chloride is 90.14% by weight. The cooling and crystallization temperature is 20℃ and the time is 30min.

[0099] 3) The mother liquor obtained in step 2) was evaporated until crystals precipitated, then cooled to 10°C and held at that temperature for 30 minutes for further cooling crystallization. The crystallized liquid was filtered, and the filter cake was washed with methanol and dried to obtain 3.70 g of potassium acetate with a purity of 98.52% by weight. The evaporation conditions were: temperature 58°C and vacuum degree 0.083 MPa. Furthermore, the methanol wash was evaporated to obtain 1.20 g of solid potassium acetate with a purity of 98.31% by weight.

[0100] In addition, the crystallization mother liquor obtained in step 3) is mixed with the next batch of wastewater and treated as saline wastewater.

[0101] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for treating saline wastewater containing potassium (K). + Cl - and CH3COO - Its characteristics are, This method Includes the following steps, 1) The wastewater to be treated is passed into an evaporation device for the first evaporation to obtain a first concentrated solution containing potassium chloride crystals; 2) The first concentrated solution containing potassium chloride crystals is subjected to a first solid-liquid separation, and the liquid phase obtained from the first solid-liquid separation is subjected to a first cooling crystallization to obtain a crystalline solution containing potassium chloride crystals; 3) The crystallization liquid containing potassium chloride crystals is subjected to a second solid-liquid separation, and the liquid phase obtained from the second solid-liquid separation is subjected to a second evaporation to obtain a second concentrated liquid containing potassium acetate; 4) The second concentrated solution containing potassium acetate is subjected to a second cooling crystallization to obtain a crystalline solution containing potassium acetate crystals; 5) The crystallization solution containing potassium acetate crystals is subjected to a third solid-liquid separation. Among them, relative to the CH3COO contained in 1 mol of the wastewater to be treated - The wastewater to be treated contains Cl - It is 0.4-5 mol; The first evaporation prevents potassium acetate from crystallizing out; The temperature for the first solid-liquid separation is 80-90℃; The temperature for the first cooling crystallization is 15-25℃; The temperature for the second cooling crystallization is 5-20℃.

2. The method according to claim 1, wherein, Relative to the CH3COO content in 1 mol of the wastewater to be treated - The wastewater to be treated contains Cl - The concentration ranges from 0.5 to 4.5 mol.

3. The method according to claim 2, wherein, Relative to the CH3COO content in 1 mol of the wastewater to be treated - The wastewater to be treated contains Cl - The concentration ranges from 0.54 to 4.2 mol.

4. The method according to claim 1, wherein, The conditions for the first evaporation include: a temperature of 85-100℃ and a vacuum degree of 0.005-0.05 MPa.

5. The method according to claim 4, wherein, The conditions for the first evaporation include: a temperature of 90-97°C and a vacuum degree of 0.01-0.03 MPa.

6. The method according to any one of claims 1-5, wherein, The first evaporation reduces the concentration of potassium acetate in the first concentrate to below X, where X is the concentration of potassium acetate in the first concentrate when both potassium chloride and potassium acetate are saturated under the conditions of the first evaporation.

7. The method according to claim 6, wherein, The first evaporation reduces the concentration of potassium acetate in the first concentrate to 0.94X-0.999X.

8. The method according to any one of claims 1-5, wherein, The first cooling crystallization time is 20-40 minutes.

9. The method according to claim 8, wherein, The conditions for the first cooling crystallization include: a temperature of 20-23°C and a time of 20-30 minutes.

10. The method according to any one of claims 1-5, wherein, The conditions for the second evaporation include: a temperature of 55-80℃ and a vacuum degree of 0.06-0.09 MPa.

11. The method according to claim 10, wherein, The conditions for the second evaporation include: a temperature of 58-70℃ and a vacuum degree of 0.08-0.085 MPa.

12. The method according to any one of claims 1-5, wherein, The second cooling crystallization time is 20-40 minutes.

13. The method according to claim 12, wherein, The conditions for the second cooling crystallization include: a temperature of 8-12℃ and a time of 25-35 minutes.

14. The method according to any one of claims 1-5, wherein, The method further includes performing a first solid-liquid separation on the first concentrated solution containing potassium chloride crystals to obtain potassium chloride crystals.

15. The method according to any one of claims 1-5, wherein, Potassium chloride crystals are obtained by performing a second solid-liquid separation on the crystallization liquid containing potassium chloride crystals.

16. The method according to claim 15, wherein, The method also includes washing the obtained potassium chloride crystals.

17. The method according to any one of claims 1-5, wherein, Potassium acetate crystals are obtained by performing a third solid-liquid separation on the crystallization solution containing potassium acetate crystals.

18. The method according to claim 17, wherein, The method also includes washing the obtained potassium acetate crystals.

19. The method according to any one of claims 1-5, wherein, K in the saline wastewater + For 30g / L or more, Cl - For amounts above 30 g / L, CH3COO - It is above 40g / L.

20. The method according to claim 19, wherein, K in the saline wastewater + 40-180g / L, Cl - The concentration is 35-180 g / L, CH3COO - It is 50-200g / L.

21. The method according to any one of claims 1-5, wherein, The method also includes adjusting the saline wastewater to neutral using potassium hydroxide.