Method for resource utilization of potassium-sodium mixed brine

Abstract

The present application relates to the technical field of high-salt wastewater, and particularly relates to a method for resource utilization of potassium-sodium mixed brine. The present application discloses a method for resource utilization of potassium-sodium mixed brine, which comprises the following steps: (1) adding a precipitant to the potassium-sodium mixed brine, performing solid-liquid separation after sufficient stirring and reaction to obtain a post-precipitation liquid and a precipitated solid; (2) adding an oxidant to the post-precipitation liquid to obtain an oxidized liquid after oxidation is completed; (3) separating the oxidized liquid through a separation system to obtain a concentrated liquid and high-concentration brine, and sending the high-concentration brine into an evaporation crystallizer alone for crystallization or sending the high-concentration brine and evaporation mother liquor into the evaporation crystallizer for crystallization. The method disclosed by the present application solves the problem that the potassium-sodium ratio in the concentrated brine is unbalanced and the two kinds of salts cannot be effectively separated in the traditional method.

Description

Technical Field

[0001] This invention relates to the technical field of high-salinity wastewater, and in particular to a method for the resource utilization of potassium-sodium mixed brine. Background Technology

[0002] High-salinity wastewater refers to wastewater with a total salt content greater than 3.5 wt%, mainly originating from industries such as chemical, pharmaceutical, and metal smelting. Currently, this type of wastewater exceeds 300 million cubic meters, generating over ten million tons of high-salinity hazardous waste. If these resources are not treated and utilized, they will have a significant impact on the environment and represent a huge waste of resources. Current treatment methods for high-salinity wastewater primarily involve removing impurities and then sending it to an evaporation system to crystallize potassium and sodium salts. However, the potassium and sodium salts in high-salinity wastewater cannot be completely separated, ultimately producing approximately 5-10% concentrated brine. Further crystallization of this concentrated brine produces waste salt that cannot be used; returning the concentrated brine to the mother liquor for recrystallization disrupts the potassium-sodium ratio in the system, affecting crystallization efficiency and the purity of the produced salt.

[0003] Currently, there are three main methods for treating concentrated brine produced by evaporation and crystallization: returning the mother liquor, incineration, and atomization drying. Returning the mother liquor is the simplest method, but as the evaporation and crystallization process proceeds, high-boiling-point impurities in the high-salt wastewater also accumulate and concentrate. The resulting concentrated brine affects the composition of the mother liquor, leading to low evaporation efficiency, pipeline blockage, and high levels of salt impurities, increasing operating costs and potentially causing equipment failure. Incineration is simple to operate and suitable for large-scale processing, but it requires the establishment of additional processing lines, resulting in significant equipment investment, large raw material consumption, and additional processes for treating incineration exhaust gas and sludge, leading to high energy consumption and costs. Atomization drying uses a spray dryer to dry the concentrated brine, yielding mixed salts. However, these mixed salts are hazardous waste and cannot be directly utilized, requiring landfill or outsourced further treatment.

[0004] Patent CN 118812104 A discloses a low-energy-consumption, zero-emission treatment method and system for deep concentration of wastewater coupled with evaporation and crystallization. In this system, multiple modules are coupled to treat high-salt wastewater. The concentrated mother liquor treatment module removes water from the concentrated brine produced by the system by using a spray dryer to obtain solid miscellaneous salt waste. This waste still needs to be further processed before it can be used as a secondary resource.

[0005] In summary, current methods for treating concentrated brine are relatively rudimentary, lacking targeted technologies and methods. Most methods are implemented to meet environmental requirements, resulting in large investments in production lines with low returns. Furthermore, secondary pollution from exhaust gases and dust must be prevented during treatment, leading to large quantities of waste salt, high treatment difficulty, high costs, and poor economic viability, resulting in significant resource waste. Therefore, from an economically feasible perspective, the resource utilization of potassium-sodium mixed concentrated brine is the only way to achieve industrial wastewater treatment. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for the resource utilization of potassium-sodium mixed brine. The method optimizes the composition of potassium-sodium mixed brine through steps such as chemical precipitation, oxidation treatment, and separation system, so that potassium and sodium salts can be efficiently separated during subsequent evaporation and crystallization. This solves the problem that traditional methods cannot effectively separate the two salts due to the imbalance of potassium and sodium ratios in concentrated brine.

[0007] The technical solution adopted by this application to solve its technical problem is:

[0008] A method for resource recovery from potassium-sodium mixed brine includes the following steps:

[0009] (1) Add a precipitant to a potassium-sodium mixed salt solution, stir the reaction thoroughly, and then perform solid-liquid separation to obtain a liquid after precipitation and a precipitated solid.

[0010] (2) Add an oxidant to the precipitate. The amount of oxidant added is 1%-10% of the mass of the potassium-sodium mixed brine. After oxidation, the oxidized solution is obtained.

[0011] (3) The oxidized liquid is separated by a separation system to obtain a concentrated liquid and a high-concentration brine. The high-concentration brine is sent to an evaporator crystallizer for crystallization, or the high-concentration brine and the mother liquor are mixed and then sent to an evaporator crystallizer for crystallization. The concentration of the concentrated liquid can be controlled as needed to obtain hydrochloric acid of different concentrations.

[0012] In the evaporator crystallizer, the evaporation temperature is controlled at 90℃~100℃ for evaporation. When sodium chloride crystals are saturated, the mixture is cooled to crystallize, yielding potassium chloride crystals and a primary filtrate. The primary filtrate is then further evaporated at 90℃~100℃ and filtered to obtain sodium chloride crystals.

[0013] In some specific embodiments, the potassium-sodium mixed brine in step (1) is a concentrated liquid discharged from various high-salt industrial wastewater after evaporation and crystallization.

[0014] In some specific embodiments, the mass ratio of potassium to sodium in the potassium-sodium mixed brine in step (1) is (0.8-1.5):1.

[0015] In some specific embodiments, in step (1), the precipitant is any one of potassium bicarbonate, ammonium bicarbonate, or carbon dioxide mixed with ammonia.

[0016] In some specific embodiments, in step (1), the reaction temperature is 20℃~35℃ and the reaction time is 0.5h~1.5h.

[0017] In some specific embodiments, in step (2), the oxidant is either chlorine or chlorine dioxide.

[0018] In some specific embodiments, the concentrated solution is hydrochloric acid, and the mass ratio of potassium to sodium in the high-concentration brine is (2-3):1.

[0019] In some specific embodiments, in step (3), the evaporator crystallizer is any one of an MVR evaporator crystallizer, a triple-effect evaporator crystallizer, a TVR evaporator crystallizer, or a low-temperature evaporator crystallizer.

[0020] In some specific embodiments, in step (3), the separation system includes anion exchange membranes.

[0021] In some specific embodiments, in step (3), the cooling temperature for crystallization is 0°C to 5°C.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The method described in this application has a simple process and low operating cost. While fully separating potassium and sodium in the mixed salt, it obtains hydrochloric acid with high purity, which can avoid the generation of unseparable potassium and sodium mixed salt in the chloride evaporation crystallization system and reduce the overall cost of the evaporation crystallization process. Attached Figure Description

[0024] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Figure 1 This is a process flow diagram of the method described in this application. Detailed Implementation

[0026] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments. The content mentioned in the embodiments is not intended to limit the present invention.

[0027] As used herein, “and / or” includes all combinations of any one or more of the associated listed items. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “a,” “an,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. Further understanding is needed; when used in this specification, “comprising” designates the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or combinations thereof.

[0028] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Further understanding is that terms, such as those defined in common dictionaries, are interpreted in accordance with their meaning in the context of the relevant field and are not idealized or overly formal, unless expressly defined herein.

[0029] The exemplary invention described herein may suitably omit any one or more limiting elements, which are not specifically disclosed herein. Therefore, terms such as “comprising,” “including,” “containing,” etc., should be interpreted broadly and non-limitingly. Furthermore, the terminology used herein is for descriptive purposes without limitation, and it is unintentional to use terms that do not include any equivalent characteristics, but only to describe a portion of their characteristics; however, various modifications are possible within the scope of the invention according to the claims. Therefore, while the invention has been specifically disclosed through preferred embodiments and optional features, variations of the invention embodied by the modifications disclosed herein may be noted by those skilled in the art, and such modifications and variations are considered to be within the scope of the invention.

[0030] Currently, traditional methods struggle to address the imbalance in potassium-sodium ratios in concentrated brine, hindering the effective separation of the two salts. This application provides a solution... Figure 1 The method for resource recovery of potassium-sodium mixed brine shown includes the following steps:

[0031] (1) Add a precipitant to a potassium-sodium mixed salt solution, stir the reaction thoroughly, and then perform solid-liquid separation to obtain a liquid after precipitation and a precipitated solid.

[0032] (2) Add an oxidant to the precipitate. The amount of oxidant added is 1%-10% of the mass of the potassium-sodium mixed brine. After oxidation, the oxidized solution is obtained.

[0033] (3) The oxidized liquid is separated by a separation system to obtain a concentrated liquid and a high-concentration brine. The high-concentration brine is sent separately to an evaporator crystallizer for crystallization; or the high-concentration brine and the mother liquor are mixed and then sent to an evaporator crystallizer for crystallization.

[0034] In the evaporator crystallizer, the evaporation temperature is controlled at 90℃~100℃ for evaporation. When sodium chloride crystals are saturated, the mixture is cooled to crystallize, yielding potassium chloride crystals and a primary filtrate. The primary filtrate is then further evaporated at 90℃~100℃ and filtered to obtain sodium chloride crystals.

[0035] In the above technical solution, a specific precipitant (such as potassium bicarbonate, ammonium bicarbonate, or carbon dioxide mixed with ammonia) is added to the potassium-sodium mixed brine. The precipitant reacts with sodium ions in the solution to form a sparingly soluble sodium bicarbonate precipitate, thereby effectively adjusting the potassium-sodium ratio. This process does not introduce other impurities and maintains the purity of the solution.

[0036] In the above technical solution, an oxidant (such as chlorine or chlorine dioxide) is added to the precipitated liquid to oxidize any reducing substances, such as ammonia nitrogen, that may be present. This step ensures that the purity of the product is not affected by residual reducing substances during the evaporation and crystallization process.

[0037] In the above technical solution, the separation of potassium and sodium salts by evaporation crystallization is based on the different solubilities of potassium chloride and sodium chloride at different temperatures. The solubility of potassium chloride is greatly affected by temperature, while the solubility of sodium chloride remains basically unchanged. Therefore, the evaporation crystallization process involves first heating and evaporating until sodium chloride is close to saturation, then cooling and crystallizing to allow potassium chloride to precipitate out, and then continuing to heat up and evaporate to crystallize sodium chloride.

[0038] Specifically, the potassium-sodium mixed brine mentioned in step (1) is a concentrated liquid discharged from various high-salt industrial wastewater after evaporation and crystallization. The potassium-sodium mixed brine contains sodium chloride and potassium chloride, and the mass ratio of potassium to sodium in the concentrated liquid is (0.8-1.5):1.

[0039] The precipitant is any one of potassium bicarbonate, ammonium bicarbonate, or carbon dioxide mixed with a measured amount of ammonia. In this application, potassium bicarbonate, ammonium bicarbonate, or carbon dioxide mixed with a measured amount of ammonia (ammonia to carbon dioxide feed volume ratio of 1.0:1 to 1.5:1) is used as the precipitant. This allows the precipitant to combine with sodium ions in the potassium-sodium mixed brine to form sodium bicarbonate, which has low solubility, thereby separating it from the liquid phase. This method allows for adjustment of the potassium-sodium ratio without introducing additional impurities.

[0040] In step (1), the reaction temperature is 20℃~35℃ and the reaction time is 0.5h~1.5h.

[0041] In this application, the reaction temperature is set to 20℃~35℃ and the reaction time is set to 0.5h~1.5h to ensure that the chemical reaction between the precipitant and sodium ions can proceed fully, while avoiding the influence of excessively high or low temperatures on the reaction rate and product purity.

[0042] Specifically, in step (2), the oxidant is either chlorine or chlorine dioxide.

[0043] Understandably, untreated potassium-sodium brine may contain various impurities, including high-boiling-point organic compounds and other metal ions, which can interfere with the evaporation and crystallization process and reduce product purity. Oxidation treatment removes reducing substances, thus minimizing the impact of impurities on the final product quality.

[0044] Therefore, in this application, chlorine or chlorine dioxide is used as an oxidant. These substances have strong oxidizing properties and can effectively oxidize ammonia nitrogen in potassium-sodium mixed brine into nitrogen gas, which then escapes. They can also remove other possible organic or reducing inorganic substances.

[0045] In this application, the amount of oxidant added is 1% to 10% of the mass of the potassium-sodium mixed brine, depending on the ammonia nitrogen content and the amount of other substances to be oxidized in the wastewater. An appropriate amount of oxidant ensures complete oxidation of the target substance without waste or introducing excessive chloride ions, which could affect product quality. The oxidation completion time is set at 0.5-2 hours, which is sufficient for the oxidant to fully contact and react with the reducing substances in the solution. Too short a time may lead to incomplete oxidation; while too long a time is unnecessary as it will not significantly improve the oxidation effect and will instead increase treatment costs.

[0046] Specifically, in step (3), the evaporator crystallizer is any one of an MVR evaporator crystallizer, a triple-effect evaporator crystallizer, a TVR evaporator crystallizer, or a low-temperature evaporator crystallizer. The cooling and crystallization temperature is 0℃~5℃.

[0047] Specifically, in step (3), the separation system includes anion exchange membranes. The concentrate is hydrochloric acid, and the mass ratio of potassium to sodium in the high-concentration brine is (2-3):1.

[0048] In the above technical solution, the anion exchange membrane exhibits high selectivity for chloride ions, allowing chloride ions to pass through the membrane while preventing potassium and sodium ions from passing through. This results in chloride ion accumulation on one side of the membrane, forming a concentrated solution (such as hydrochloric acid). The principle is as follows:

[0049] 1. Selective transport of chloride ions:

[0050] Anion exchange membranes exhibit high selectivity for chloride ions, allowing chloride ions to pass through while potassium and sodium ions cannot. This results in chloride ion accumulation on one side of the membrane, forming a concentrate (such as hydrochloric acid).

[0051] 2. The blocking effect of cations:

[0052] The positively charged functional groups on anion exchange membranes repel cations such as potassium and sodium ions, preventing them from passing through the membrane. Therefore, potassium and sodium ions remain in the original solution, forming a highly concentrated brine solution.

[0053] 3. Charge balance:

[0054] In the membrane separation process, in order to maintain charge balance, anions (mainly chloride ions) carry an equal amount of cations as they pass through the membrane. However, hydrogen ions have a small ionic radius and their diffusion rate is much greater than that of other metal ions. Therefore, cations such as potassium and sodium remain in the original solution in large quantities, thus obtaining hydrochloric acid concentrate and high-concentration brine, and realizing the recovery and utilization of hydrochloric acid.

[0055] The following examples and comparative examples further illustrate the method for resource utilization of potassium-sodium mixed brine described in this application. Example 1

[0056] A method for resource recovery from potassium-sodium mixed brine includes the following steps:

[0057] Step (1): The composition of the concentrated brine produced by the MVR evaporation and crystallization process of high-salt wastewater from a steel plant is shown in Table 1 below:

[0058] Table 1. Composition of Potassium-Sodium Mixed Concentrated Brine

[0059]

[0060] Take the potassium-sodium mixed brine as shown in Table 1 above, add ammonium bicarbonate to the mixed brine, and the ratio of the amount of ammonium bicarbonate added to the mass of sodium ions in the solution is 0.8:1. Stir the reaction at 20℃ for 0.5h. After the reaction is completed, perform solid-liquid separation to obtain the precipitated liquid and the precipitated solid. The precipitated liquid enters the next process, and the precipitated solid is washed with saturated sodium bicarbonate solution to obtain sodium bicarbonate product.

[0061] Step (2): Chlorine gas is introduced into the precipitated liquid to oxidize the ammonia nitrogen in the feed liquid. The chlorine gas introduction rate is 1% and the chlorine gas introduction time is 0.5h to obtain the oxidized liquid.

[0062] Step (3): The oxidized liquid obtained in step (2) is introduced into a membrane separation system composed of anion exchange membranes to obtain a concentrated liquid and a high-concentration brine; the high-concentration brine is sent to an MVR evaporator to prepare potassium and sodium salts.

[0063] Table 2 Composition of high-concentration brine

[0064]

[0065] In the evaporator crystallizer, the evaporation temperature is controlled at 90℃ for evaporation. When the sodium chloride crystals are saturated, the crystals are cooled at 0℃ and filtered to obtain potassium chloride crystals and a primary filtrate. The primary filtrate is then evaporated and filtered again at 90℃ to obtain sodium chloride crystals and a secondary filtrate. Example 2

[0066] A method for resource recovery from potassium-sodium mixed brine includes the following steps:

[0067] The composition of the concentrated brine produced by the MVR evaporation and crystallization process of high-salt wastewater from a steel plant is shown in Table 3 below:

[0068] Table 3 Composition of Potassium-Sodium Mixed Concentrated Brine

[0069]

[0070] Take the potassium-sodium mixed brine as shown in Table 3 above, add ammonium bicarbonate to the mixed brine, and the ratio of the amount of ammonium bicarbonate added to the sodium ions in the solution is 0.9:1. Stir the reaction at 25°C for 1 hour. After the reaction is completed, perform solid-liquid separation to obtain the precipitated liquid and the precipitated solid. The precipitated liquid enters the next process, and the precipitated solid is washed with saturated sodium bicarbonate solution to obtain sodium bicarbonate product.

[0071] Chlorine gas is introduced into the precipitate to oxidize the ammonia nitrogen in the feed solution. The chlorine gas flow rate is 5% and the chlorine gas flow time is 1.5 hours. After the reaction is completed, the oxidized solution is obtained. The oxidized solution is introduced into a membrane separation system composed of anion exchange membranes to obtain a concentrated solution and a high-concentration brine. The high-concentration brine is sent to an MVR evaporator to prepare potassium and sodium salts.

[0072] Table 4 Composition of High-Concentration Brine

[0073]

[0074] In the evaporator crystallizer, the evaporation temperature is controlled at 100℃ for evaporation. When sodium chloride crystals are saturated, the mixture is cooled at 5℃ to crystallize and is filtered to obtain potassium chloride crystals and a primary filtrate. The primary filtrate is then evaporated and filtered again at 100℃ to obtain sodium chloride crystals and a secondary filtrate. Example 3

[0075] A method for resource recovery from potassium-sodium mixed brine includes the following steps:

[0076] The composition of the concentrated brine produced by the MVR evaporation and crystallization process of high-salt wastewater from a steel plant is shown in Table 5 below:

[0077] Table 5 Composition of Potassium-Sodium Mixed Concentrated Brine

[0078]

[0079] Take the potassium-sodium mixed brine as shown in Table 5 above, add ammonium bicarbonate to the mixed brine, and the ratio of the amount of ammonium bicarbonate added to the sodium ions in the solution is 1:1. Stir the reaction at 35℃ for 1.5h. After the reaction is completed, perform solid-liquid separation to obtain the precipitated liquid and the precipitated solid. The precipitated liquid enters the next process, and the precipitated solid is washed with saturated sodium bicarbonate solution to obtain sodium bicarbonate product.

[0080] Chlorine gas is introduced into the precipitate to oxidize the ammonia nitrogen in the feed solution. The chlorine gas introduction rate is 10%, and the chlorine gas introduction time is 2 hours. After the reaction is completed, the oxidized solution is obtained. The oxidized solution is introduced into a membrane separation system composed of anion exchange membranes to obtain a concentrated solution and a high-concentration brine. The high-concentration brine is sent to an MVR evaporator to prepare potassium and sodium salts.

[0081] Table 6 Composition of High-Concentration Brine

[0082]

[0083] In the evaporator crystallizer, the evaporation temperature is controlled at 95℃ for evaporation. When the sodium chloride crystals are saturated, the crystals are cooled at 3℃ and filtered to obtain potassium chloride crystals and a primary filtrate. The primary filtrate is then evaporated and filtered again at 95℃ to obtain sodium chloride crystals and a secondary filtrate.

[0084] Comparative Example 1

[0085] A method for resource recovery from potassium-sodium mixed brine includes the following steps:

[0086] Step (1): The composition of the concentrated brine produced by the MVR evaporation and crystallization process of high-salt wastewater from a steel plant is shown in Table 7 below:

[0087] Table 7 Composition of Potassium-Sodium Mixed Concentrated Brine

[0088]

[0089] Step (2): Take the potassium-sodium mixed brine (concentrated brine) shown in Table 7 above, and pass chlorine gas through it to oxidize the potassium-sodium mixed brine. The chlorine gas flow rate is 1% and the chlorine gas flow time is 0.5h to obtain the oxidized liquid.

[0090] Step (3): The oxidized liquid obtained in step (2) is introduced into a membrane separation system composed of anion exchange membranes to obtain a concentrated liquid and a high-concentration brine; the high-concentration brine is sent to an MVR evaporator to prepare potassium and sodium salts.

[0091] Table 8 Composition of High-Concentration Brine

[0092]

[0093] In the evaporator crystallizer, the evaporation temperature is controlled at 90℃ for evaporation. When the sodium chloride crystals are saturated, the crystals are cooled at 0℃ and filtered to obtain potassium chloride crystals and a primary filtrate. The primary filtrate is then evaporated and filtered again at 90℃ to obtain sodium chloride crystals and a secondary filtrate.

[0094] Comparative Example 2

[0095] A method for resource recovery from potassium-sodium mixed brine includes the following steps:

[0096] Step (1): The composition of the concentrated brine produced by the MVR evaporation and crystallization process of high-salt wastewater from a steel plant is shown in Table 9 below:

[0097] Table 9 Composition of Potassium-Sodium Mixed Concentrated Brine

[0098]

[0099] Take the potassium-sodium mixed brine as shown in Table 1 above, add ammonium bicarbonate to the mixed brine, and the ratio of the amount of ammonium bicarbonate added to the mass of sodium ions in the solution is 0.8:1. Stir the reaction at 20℃ for 0.5h. After the reaction is completed, perform solid-liquid separation to obtain the precipitated liquid and the precipitated solid. The precipitated liquid enters the next process, and the precipitated solid is washed with saturated sodium bicarbonate solution to obtain sodium bicarbonate product.

[0100] Step (2): The precipitated liquid obtained in step (1) is introduced into a membrane separation system composed of anion exchange membranes to obtain concentrated liquid and high-concentration brine; the high-concentration brine is sent to an MVR evaporator to prepare potassium and sodium salts.

[0101] Table 10 Composition of High-Concentration Brine

[0102]

[0103] In the evaporator crystallizer, the evaporation temperature is controlled at 90℃ for evaporation. When the sodium chloride crystals are saturated, the crystals are cooled at 0℃ and filtered to obtain potassium chloride crystals and a primary filtrate. The primary filtrate is then evaporated and filtered again at 90℃ to obtain sodium chloride crystals and a secondary filtrate.

[0104] Comparative Example 3

[0105] A method for resource recovery from potassium-sodium mixed brine includes the following steps:

[0106] Step (1): The composition of the concentrated brine produced by the high-salt wastewater from a steel plant after the MVR evaporation and crystallization process is shown in Table 11 below:

[0107] Table 11 Composition of Potassium-Sodium Mixed Concentrated Brine

[0108]

[0109] Take the potassium-sodium mixed brine as shown in Table 1 above, add ammonium bicarbonate to the mixed brine, and the ratio of the amount of ammonium bicarbonate added to the mass of sodium ions in the solution is 0.8:1. Stir the reaction at 20℃ for 0.5h. After the reaction is completed, perform solid-liquid separation to obtain the precipitated liquid and the precipitated solid. The precipitated liquid enters the next process, and the precipitated solid is washed with saturated sodium bicarbonate solution to obtain sodium bicarbonate product.

[0110] Step (2): Chlorine gas is introduced into the precipitated liquid to oxidize the ammonia nitrogen in the feed liquid. The chlorine gas introduction rate is 1% and the chlorine gas introduction time is 0.5h to obtain the oxidized liquid.

[0111] Step (3): The oxidized liquid obtained in step (2) is sent to an MVR evaporator to prepare potassium and sodium salts.

[0112] Table 12 Composition of the Oxidized Solution

[0113]

[0114] In the evaporator crystallizer, the evaporation temperature is controlled at 90℃ for evaporation. When the sodium chloride crystals are saturated, the crystals are cooled at 0℃ and filtered to obtain potassium chloride crystals and a primary filtrate. The primary filtrate is then evaporated and filtered again at 90℃ to obtain sodium chloride crystals and a secondary filtrate.

[0115] Comparative Example 4

[0116] The difference from Example 1 is that in step (3), the high-concentration brine is evaporated at 95°C until sodium chloride is saturated, and then cooled to 3°C to precipitate potassium chloride crystals;

[0117] The filtrate was further evaporated and crystallized at 95°C to obtain sodium chloride crystals.

[0118] The potassium salts, sodium salts, and secondary filtrates obtained in Examples 1-3 and Comparative Examples 1-4 were tested, and the results are summarized in Table 13 below.

[0119] Table 13

[0120]

[0121] As can be seen from Table 13, the results of Examples 1-3 are as follows:

[0122] High purity of potassium salt: In Examples 1-3, the potassium (K) content in the potassium salt was 96.8%, 96.7% and 96.5% respectively, which indicates that after being processed by the method described in this invention, the potassium salt has very high purity and contains almost no sodium (Na), with sodium content of only 3.2%, 3.3% and 3.5% respectively.

[0123] High purity sodium salts: Similarly, the sodium (Na) content in the sodium salts is 97.5%, 97.4%, and 97.7%, respectively, while the potassium (K) content is very low, at 2.5%, 2.6%, and 2.3%, respectively. This indicates that this method can effectively separate high-purity sodium salts.

[0124] The secondary filtrate contains few impurities: Data from Examples 1-3 also show low concentrations of sodium and potassium in the secondary filtrate, at 385 mg / L and 231 mg / L, 346 mg / L and 192 mg / L, and 308 mg / L and 154 mg / L, respectively. This means that most of the potassium and sodium have been effectively separated during crystallization, leaving the filtrate with low potassium and sodium content, resulting in minimal environmental impact during further treatment or discharge.

[0125] The results of comparative examples 1-4 are as follows:

[0126] The potassium and sodium salts of Comparative Examples 1-4 had significantly lower purity than those of Examples 1-4, and the potassium and sodium content in the secondary filtrate was higher. This indicates that without the treatment method described in this invention, the potassium and sodium separation effect is poor, the product purity is low, and the difficulty and cost of subsequent processing are increased.

[0127] It is evident that the excellent results of Examples 1-3 are due to the following reasons:

[0128] Use of precipitants: Specific precipitants (such as potassium bicarbonate, ammonium bicarbonate, or carbon dioxide mixed with ammonia) were used in the examples. These precipitants react with sodium ions in the solution to form insoluble sodium bicarbonate precipitate, thereby effectively adjusting the potassium-to-sodium ratio. This step not only improves the effectiveness of subsequent separation steps but also reduces the influence of impurities.

[0129] Oxidation treatment: An oxidizing agent (such as chlorine gas or chlorine dioxide) is added to the precipitate to oxidize any reducing substances that may be present (such as ammonia nitrogen). This step ensures that the purity of the product is not affected by residual reducing substances during the evaporation and crystallization process.

[0130] An effective separation system: The oxidized liquid is further separated by a separation system (such as anion exchange membrane) to obtain a concentrated solution and a highly concentrated brine. This helps to more precisely control the composition of the material entering the evaporator crystallizer, thereby improving crystallization efficiency and product purity.

[0131] Optimized evaporation and crystallization conditions: By controlling the evaporation temperature (90℃~100℃) and the cooling crystallization temperature (0℃~5℃) in the evaporator crystallizer, high-purity potassium chloride and sodium chloride crystals can be effectively separated.

[0132] The inventors speculate that the poor results of comparative examples 1-3 are due to the following reasons:

[0133] Comparative Example 1: The potassium-sodium mixed brine was directly oxidized before entering the evaporation and crystallization process, without undergoing a precipitation step to adjust the potassium-sodium ratio. Therefore, the final product contained high levels of both sodium and potassium, resulting in low purity of both potassium and sodium salts.

[0134] Comparative Example 2: Although precipitation treatment was carried out, oxidation treatment was not carried out, resulting in the failure to remove reducing substances (such as ammonia nitrogen), which affected the product quality during the evaporation and crystallization process.

[0135] Comparative Example 3: Only precipitation and oxidation treatment were performed, but no separation system was used, resulting in the material composition entering the evaporator crystallizer being not pure enough, which affected the purity of the final product.

[0136] Comparative Example 4: Due to the adjustment of evaporation temperature (95°C) and cooling temperature (3°C), the potassium-sodium separation efficiency was slightly lower than that of Example 1. The sodium impurities in the potassium salt increased, the potassium impurities in the sodium salt increased, and the potassium concentration in the secondary filtrate increased.

[0137] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. A method for resource utilization of a potassium-sodium mixed salt water, characterized by, The method comprises the following steps: (1) adding a precipitant into the potassium-sodium mixed brine, fully stirring and reacting, and then performing solid-liquid separation to obtain a post-precipitation liquid and a precipitated solid; (2) adding an oxidant into the post-precipitation liquid, wherein the amount of the oxidant is 1%-10% of the mass of the potassium-sodium mixed brine, and a post-oxidation liquid is obtained after oxidation; (3) separating the post-oxidation liquid through a separation system to obtain a concentrated liquid and a high-concentration brine, and sending the high-concentration brine into an evaporation crystallizer alone for crystallization or sending the high-concentration brine mixed with an evaporation mother liquor into the evaporation crystallizer for crystallization; In the evaporation crystallizer, the evaporation temperature is controlled at 90-100 DEG C, and when the sodium chloride is close to saturation, cooling and crystallization are performed to obtain potassium chloride crystals and a primary filtrate; the primary filtrate is continuously evaporated at 90-100 DEG C, and filtration is performed to obtain sodium chloride crystals; In step (1), the mass ratio of potassium to sodium in the potassium-sodium mixed brine is (0.8-1.5):1; In step (2), the oxidant is any one of chlorine and chlorine dioxide; The concentrated liquid is hydrochloric acid, and the mass ratio of potassium to sodium in the high-concentration brine is (2-3):1; In step (3), the evaporation crystallizer is any one of an MVR evaporation crystallizer, a three-effect evaporation crystallizer, a TVR evaporation crystallizer or a low-temperature evaporation crystallizer; In step (3), the separation system comprises an anion exchange membrane; In step (3), the temperature for cooling and crystallization is 0-5 DEG C.

2. The method of claim 1, wherein, In step (1), the potassium-sodium mixed brine is a concentrated liquid discharged after evaporation crystallization of various high-salt industrial wastewater.

3. The method of claim 1, wherein, In step (1), the precipitant is any one of potassium bicarbonate, ammonium bicarbonate and carbon dioxide mixed with ammonia.

4. The method of claim 1, wherein, In step (1), the reaction temperature is 20-35 DEG C, and the reaction time is 0.5-1.5 h.

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