A method for recovering and separating potassium chloride from potassium-sodium-containing wastewater and co-producing sodium carbonate

Abstract

The application provides a method for recovering and separating potassium chloride and co-producing sodium carbonate from potassium-sodium-containing wastewater, which comprises the following steps: (1) mixing an ammonium salt precipitant and potassium-sodium-containing wastewater, and filtering to obtain sodium bicarbonate and a filtrate; (2) subjecting the sodium bicarbonate in step (1) to heat treatment to obtain sodium carbonate and carbon dioxide; (3) mixing potassium hydroxide and the filtrate in step (1), and subjecting the mixture to stripping treatment to obtain ammonia gas and an ammonia-removed solution; and (4) mixing an acidic substance and the ammonia-removed solution in step (3), and subjecting the mixture to evaporation crystallization to obtain potassium chloride crude product and a sodium-containing mother liquor. The application adjusts the potassium-sodium ion content in wastewater, and then adopts a method combining chemical precipitation, stripping and evaporation crystallization, adds an ammonium salt precipitant to realize the precipitation of sodium ions in the wastewater, further heats to obtain soda ash product, and further removes sodium through evaporation crystallization and pyroantimonic acid precipitation, so that the obtained potassium chloride has high purity, and the resource utilization of the wastewater is realized.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology and relates to a method for recovering and separating potassium chloride from potassium- and sodium-containing wastewater and producing sodium carbonate. Background Technology

[0002] Industrial production processes generate large amounts of saline wastewater. Currently, the treatment of saline wastewater generally involves membrane treatment and evaporation crystallization to extract the desired components. This process generates a large amount of industrial waste salts, such as sodium chloride and potassium chloride. These industrial waste salts are generally disposed of through landfill or land reclamation. These treatment methods are highly hazardous, detrimental to environmental protection, and fail to realize the utilization of inorganic salt resources, resulting in resource waste.

[0003] my country faces an extreme shortage of potassium resources, relying heavily on imports for a significant portion of its potassium salts. The demand for potassium salts is enormous, and prices remain consistently high. Therefore, utilizing high-salinity wastewater containing both sodium chloride and potassium chloride to separate and recover potassium chloride has considerable economic and social value. Existing technologies for separating sodium chloride and potassium chloride mainly include evaporation crystallization + cooling crystallization processes and organic solvent salt precipitation processes.

[0004] CN108862325A discloses a method and equipment for recovering and treating high-salt wastewater containing sodium chloride and potassium chloride. The method includes the following steps: S1, preheating: the material is fed into the waste steam preheater and the first condensate preheater sequentially by a feed pump for preheating treatment; S2, evaporation crystallization; S3, flash crystallization. The method has the advantages of low energy consumption, avoiding blockage during crystallization, and improving yield and quality. However, the evaporation crystallization + cooling crystallization process has high energy consumption, especially when the salt concentration of the wastewater is low and the evaporation concentration ratio is high. The salt recovery rate of this process is generally ≤70%, and the remaining crystallization tail liquid has a high concentration and complex composition. Direct reuse will cause the enrichment of impurity ions, making treatment difficult.

[0005] Organic solvent salt precipitation processes often use alcohol solvents, especially methanol and ethanol. By adding organic solvents to high-salt wastewater, the solubility of sodium chloride and potassium chloride in the wastewater solution is reduced. By adjusting process parameters, sodium chloride and potassium chloride can be precipitated and recovered separately. However, this method is complicated to control, has a small salt precipitation range, is difficult to control, and the salt purity is not high. In addition, the introduction of new solvents requires subsequent evaporation, which increases energy costs and results in low economic benefits.

[0006] Therefore, there is an urgent need to develop a low-cost, low-energy-consumption, and high-recovery process for treating sodium chloride and potassium chloride, so that the salts in the wastewater can be fully recovered and utilized, and the resulting products have high utilization value. Summary of the Invention

[0007] The purpose of this invention is to provide a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and co-producing sodium carbonate. The method involves adding an ammonium salt precipitant to precipitate sodium ions in the wastewater, followed by further heating to obtain soda ash. Then, sodium is further removed by evaporation crystallization and pyroantimonic acid precipitation, resulting in high-purity potassium chloride with high product value, thus realizing the resource utilization of wastewater.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for recovering and separating potassium chloride from potassium- and sodium-containing wastewater and co-producing sodium carbonate, the method comprising the following steps:

[0010] (1) Mix ammonium salt precipitant and potassium-sodium-containing wastewater, filter and obtain sodium bicarbonate and filtrate;

[0011] (2) Heat-treat the sodium bicarbonate obtained in step (1) to obtain sodium carbonate and carbon dioxide;

[0012] (3) Mix potassium hydroxide and the filtrate from step (1), and strip the mixture to obtain ammonia gas and ammonia-removing solution;

[0013] (4) Mix the acidic substance and the ammonia removal solution described in step (3), evaporate and crystallize to obtain crude potassium chloride and sodium-containing mother liquor;

[0014] Steps (2) and (3) are not in any particular order.

[0015] The method provided by this invention combines chemical precipitation, stripping, and evaporation crystallization. By adding an ammonium salt precipitant, sodium ions in the wastewater are precipitated, and further heating yields soda ash. A small amount of potassium hydroxide is added to the remaining system to recover ammonia water for ammonium salt precipitant production. Then, by adjusting the pH of the ammonia-removing solution and evaporation crystallization, crude potassium chloride and a sodium-containing mother liquor are obtained. The sodium-containing mother liquor is returned for further treatment. The resulting products have high purity and application value, achieving resource utilization of wastewater. Simultaneously, the precipitant can be synthesized during the treatment process, effectively reducing the amount of additives used in wastewater treatment and thus lowering costs. The method is simple to operate, provides thorough separation, is suitable for treating large volumes of wastewater, and does not cause secondary pollution.

[0016] As a preferred technical solution of the present invention, the mass ratio of sodium ions to potassium ions in the potassium-containing wastewater in step (1) is 1:(20-25), for example, it can be 1:20.5, 1:21, 1:21.5, 1:22, 1:22.5, 1:23, 1:23.5, 1:24 or 1:24.5, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0017] In this invention, the sources of the potassium- and sodium-containing wastewater include wastewater neutralization treatment and / or chemical byproducts. Furthermore, before use, the mass ratio of sodium ions to potassium ions in the wastewater needs to be adjusted to within the range of 1:(20-25) to obtain saturated sodium bicarbonate, and subsequently, high-purity sodium carbonate product.

[0018] Preferably, step (1) further includes: concentrating the potassium and sodium-containing wastewater before mixing.

[0019] Preferably, after concentration, the concentration of sodium ions in the potassium-sodium wastewater is 5-20 g / L, for example, it can be 6 g / L, 7 g / L, 8 g / L, 10 g / L, 12 g / L, 15 g / L, 17 g / L or 19 g / L, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0020] As a preferred technical solution of the present invention, the ammonium salt precipitant in step (1) includes ammonium bicarbonate.

[0021] In this invention, the ammonium salt precipitant includes ammonium bicarbonate. Sodium bicarbonate is precipitated by taking advantage of the low solubility of sodium bicarbonate. At the same time, ammonia ions can be converted into ammonia gas, which can be used as a raw material for the production of ammonium bicarbonate without introducing new impurities or causing secondary pollution.

[0022] Preferably, the molar ratio of the ammonium salt precipitant and the sodium ions in the potassium-sodium wastewater in step (1) is (1-1.2):1, for example, it can be 1.02:1, 1.04:1, 1.05:1, 1.07:1, 1.09:1, 1.1:1, 1.12:1, 1.14:1, 1.15:1, 1.17:1 or 1.19:1, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0023] Preferably, the heat treatment temperature in step (2) is 60-100℃, for example, it can be 65℃, 70℃, 75℃, 80℃, 85℃, 90℃ or 95℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] As a preferred technical solution of the present invention, after mixing in step (3), the mass ratio of sodium ions to potassium ions in the filtrate is 1:(50-80), for example, it can be 1:52, 1:55, 1:57, 1:60, 1:62, 1:65, 1:67, 1:70, 1:72, 1:75, 1:77 or 1:79, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0025] Preferably, the carrier gas for the stripping process in step (3) includes air and / or water vapor.

[0026] In this invention, when air is used as the carrier gas, the flow rate is 1000-2000 m³ / h. 3 The flow rate is 90-110 kg / h, and the stripping temperature is 20-35℃. When steam is used as the carrier gas, the flow rate is 90-110 kg / h, and the stripping temperature is 90-100℃.

[0027] As a preferred technical solution of the present invention, the method further includes: mixing the carbon dioxide in step (2) and the ammonia in step (3), and obtaining ammonium bicarbonate after reaction, wherein the ammonium bicarbonate is returned to step (1) as an ammonium salt precipitant.

[0028] As a preferred technical solution of the present invention, the acidic substance in step (4) includes hydrochloric acid.

[0029] This invention uses hydrochloric acid to adjust the pH value of the system solution, thus avoiding the introduction of new impurities.

[0030] Preferably, the amount of acidic substance added in step (4) is to adjust the pH of the ammonia removal solution to 6-8, for example, it can be 6.2, 6.5, 6.7, 6.9, 7, 7.2, 7.5, 7.7 or 7.9, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] Preferably, the evaporation and crystallization temperature in step (4) is 90-120℃, for example, it can be 92℃, 95℃, 97℃, 100℃, 102℃, 105℃, 107℃, 110℃, 112℃, 115℃, 117℃ or 119℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] As a preferred technical solution of the present invention, the sodium-potassium ratio of the crude potassium chloride in step (4) is less than that of the sodium-potassium ratio of the sodium-containing mother liquor.

[0033] Preferably, the mass ratio of sodium ions to potassium ions in the crude potassium chloride product in step (4) is 1:(100-500), for example, it can be 1:150, 1:200, 1:250, 1:300, 1:350, 1:400 or 1:450, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] Preferably, the mass ratio of sodium ions to potassium ions in the sodium-containing mother liquor in step (4) is 1:(90-200), for example, it can be 1:100, 1:110, 1:120, 1:130, 1:150, 1:170, 1:180 or 1:190, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the sodium-containing mother liquor from step (4) is returned to step (1) for further processing.

[0036] As a preferred technical solution of the present invention, the method further includes: mixing pyroantimonic acid, potassium hydroxide, solvent and crude potassium chloride from step (4), and reacting to obtain sodium pyroantimonate and potassium chloride.

[0037] As a preferred technical solution of the present invention, the mass ratio of the pyroantimonic acid and crude potassium chloride is (1-1.2):1, for example, it can be 1.02:1, 1.04:1, 1.05:1, 1.07:1, 1.09:1, 1.1:1, 1.12:1, 1.14:1, 1.15:1, 1.17:1 or 1.19:1, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0038] Preferably, the mass ratio of the crude potassium hydroxide to the crude potassium chloride is (0.05-0.15):1, for example, it can be 0.06:1, 0.07:1, 0.08:1, 0.1:1, 0.11:1, 0.12:1, 0.13:1 or 0.14:1, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0039] Preferably, the reaction temperature is 90-120℃, for example, it can be 92℃, 95℃, 97℃, 100℃, 102℃, 105℃, 107℃, 110℃, 112℃, 115℃, 117℃ or 119℃, etc., but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0040] Preferably, the reaction time is 1-2 hours, for example, 1.1 hours, 1.2 hours, 1.3 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.7 hours, 1.8 hours or 1.9 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] As a preferred technical solution of the present invention, the method includes the following steps:

[0042] (1) Concentrate the potassium and sodium-containing wastewater, then mix it with an ammonium salt precipitant, filter it to obtain sodium bicarbonate and filtrate;

[0043] The mass ratio of sodium ions to potassium ions in the potassium-sodium-containing wastewater is 1:(20-25); after concentration, the concentration of sodium ions in the potassium-sodium-containing wastewater is 5-20 g / L.

[0044] The ammonium salt precipitant includes ammonium bicarbonate; the molar ratio of the ammonium salt precipitant to sodium ions in the potassium-sodium wastewater is (1-1.2):1;

[0045] (2) The sodium bicarbonate obtained in step (1) is heat-treated at a temperature of 60-100℃ to obtain sodium carbonate and carbon dioxide;

[0046] (3) Mix potassium hydroxide and the filtrate from step (1), and strip the mixture to obtain ammonia gas and ammonia-removing solution;

[0047] After mixing, the mass ratio of sodium ions to potassium ions in the filtrate is 1:(50-80);

[0048] (4) After mixing the carbon dioxide in step (2) and the ammonia in step (3), ammonium bicarbonate is obtained after the reaction. The ammonium bicarbonate is returned to step (1) as an ammonium salt precipitant.

[0049] (5) Mix the acidic substance and the ammonia removal solution described in step (4), and evaporate and crystallize at a temperature of 90-120℃ to obtain crude potassium chloride and sodium-containing mother liquor. The sodium-containing mother liquor is returned to step (1) for treatment.

[0050] The acidic substance includes hydrochloric acid; the amount of acidic substance added is such that the pH of the ammonia removal solution is adjusted to 6-8.

[0051] The sodium-potassium ratio of the crude potassium chloride is less than that of the sodium-potassium mother liquor; the mass ratio of sodium ions to potassium ions in the crude potassium chloride is 1:(100-500); the mass ratio of sodium ions to potassium ions in the sodium-containing mother liquor is 1:(90-200).

[0052] (6) Mix pyroantimonic acid, potassium hydroxide, solvent and crude potassium chloride from step (5), and react at 90-120℃ for 1-2 hours to obtain sodium pyroantimonate and potassium chloride.

[0053] The mass ratio of the crude pyroantimonic acid to crude potassium chloride is (1-1.2):1; the mass ratio of the crude potassium hydroxide to crude potassium chloride is (0.05-0.15):1.

[0054] Steps (2) and (3) are not in any particular order.

[0055] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] (1) The method provided by the present invention controls the potassium and sodium ion content in the wastewater, and then uses a combination of chemical precipitation, stripping and evaporation crystallization. By adding ammonium salt precipitant, sodium ions in the wastewater are precipitated, and further heated to obtain soda ash product; then sodium is deeply removed by evaporation crystallization and pyroantimonic acid precipitation method, and the obtained potassium chloride has a purity of ≥98%, with high product value, realizing the resource utilization of wastewater;

[0058] (2) The method provided by the present invention adds a small amount of potassium hydroxide to the filtrate system to recover ammonia water for use in the production of ammonium salt precipitant, which effectively reduces the amount of additives used in wastewater treatment, thereby reducing costs; and the method is simple to operate, separates thoroughly, is suitable for the treatment of large quantities of wastewater, and will not cause secondary pollution. Attached Figure Description

[0059] Figure 1 The process flow diagram is for the method of recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate in Example 1. Detailed Implementation

[0060] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0061] Example 1

[0062] This embodiment provides a method for recovering and separating potassium chloride from potassium- and sodium-containing wastewater and simultaneously producing sodium carbonate. The process flow diagram is shown below. Figure 1 As shown, the method includes the following steps:

[0063] (1) Concentrate the potassium and sodium-containing wastewater, then mix it with ammonium bicarbonate, filter it to obtain sodium bicarbonate and filtrate;

[0064] The mass ratio of sodium ions to potassium ions in the potassium-sodium-containing wastewater is 1:23; after concentration, the concentration of sodium ions in the potassium-sodium-containing wastewater is 10 g / L.

[0065] The molar ratio of ammonium bicarbonate to sodium ions in potassium-sodium-containing wastewater is 1.1:1;

[0066] (2) The sodium bicarbonate obtained in step (1) is heat-treated at a temperature of 80°C to obtain sodium carbonate and carbon dioxide;

[0067] (3) Mix potassium hydroxide and the filtrate from step (1) at a temperature of 25°C and a flow rate of 1500 m³ / h. 3 After the air is stripped at a rate of / h, ammonia gas and ammonia removal solution are obtained.

[0068] After mixing, the mass ratio of sodium ions to potassium ions in the filtrate is 1:65;

[0069] (4) After mixing the carbon dioxide from step (2) and the ammonia from step (3), ammonium bicarbonate is obtained after the reaction, and the ammonium bicarbonate is recycled for step (1);

[0070] (5) Mix hydrochloric acid and the ammonia removal solution described in step (4), evaporate and crystallize at a temperature of 105°C to obtain crude potassium chloride and sodium-containing mother liquor. The sodium-containing mother liquor is returned to step (1) for treatment.

[0071] The amount of hydrochloric acid added is sufficient to adjust the pH of the ammonia removal solution to 7;

[0072] The mass ratio of sodium ions to potassium ions in the crude potassium chloride product is 1:500; the mass ratio of sodium ions to potassium ions in the sodium-containing mother liquor is 1:100.

[0073] (6) Mix pyroantimonic acid, potassium hydroxide, water and the crude potassium chloride from step (4), and react at 105°C for 1.5 h to obtain sodium pyroantimonate and potassium chloride;

[0074] The mass ratio of the crude pyroantimonic acid to crude potassium chloride is 1.1:1; the mass ratio of the crude potassium hydroxide to crude potassium chloride is 0.1:1.

[0075] Steps (2) and (3) are not in any particular order.

[0076] Example 2

[0077] This embodiment provides a method for recovering and separating potassium chloride from potassium- and sodium-containing wastewater and simultaneously producing sodium carbonate, the method comprising the following steps:

[0078] (1) Concentrate the potassium and sodium-containing wastewater, then mix it with ammonium bicarbonate, filter it to obtain sodium bicarbonate and filtrate;

[0079] The mass ratio of sodium ions to potassium ions in the potassium-sodium-containing wastewater is 1:20; after concentration, the concentration of sodium ions in the potassium-sodium-containing wastewater is 5 g / L.

[0080] The molar ratio of ammonium bicarbonate to sodium ions in potassium-sodium wastewater is 1:1;

[0081] (2) The sodium bicarbonate obtained in step (1) is heat-treated at a temperature of 70°C to obtain sodium carbonate and carbon dioxide;

[0082] (3) Mix potassium hydroxide and the filtrate from step (1) at a temperature of 25°C and a flow rate of 1000 m³ / h. 3 After the air is stripped at a rate of / h, ammonia gas and ammonia removal solution are obtained.

[0083] After mixing, the mass ratio of sodium ions to potassium ions in the filtrate is 1:50;

[0084] (4) After mixing the carbon dioxide from step (2) and the ammonia from step (3), ammonium bicarbonate is obtained after the reaction, and the ammonium bicarbonate is recycled for step (1);

[0085] (5) Mix hydrochloric acid and the ammonia removal solution described in step (4), and evaporate and crystallize at a temperature of 95°C to obtain crude potassium chloride and sodium-containing mother liquor. The sodium-containing mother liquor is returned to step (1) for treatment.

[0086] The amount of hydrochloric acid added is sufficient to adjust the pH of the ammonia removal solution to 6.2;

[0087] The mass ratio of sodium ions to potassium ions in the crude potassium chloride product is 1:400; the mass ratio of sodium ions to potassium ions in the sodium-containing mother liquor is 1:195.

[0088] (6) Mix pyroantimonic acid, potassium hydroxide, water and the crude potassium chloride from step (4), and react at 90°C for 2 hours to obtain sodium pyroantimonate and potassium chloride;

[0089] The mass ratio of the crude pyroantimonic acid to crude potassium chloride is 1:1; the mass ratio of the crude potassium hydroxide to crude potassium chloride is 0.05:1.

[0090] Steps (2) and (3) are not in any particular order.

[0091] Example 3

[0092] This embodiment provides a method for recovering and separating potassium chloride from potassium- and sodium-containing wastewater and simultaneously producing sodium carbonate, the method comprising the following steps:

[0093] (1) Concentrate the potassium and sodium-containing wastewater, then mix it with ammonium bicarbonate, filter it to obtain sodium bicarbonate and filtrate;

[0094] The mass ratio of sodium ions to potassium ions in the potassium-sodium-containing wastewater is 1:25; after concentration, the concentration of sodium ions in the potassium-sodium-containing wastewater is 20 g / L.

[0095] The molar ratio of ammonium bicarbonate to sodium ions in potassium-sodium-containing wastewater is 1.2:1;

[0096] (2) The sodium bicarbonate obtained in step (1) is heat-treated at a temperature of 100°C to obtain sodium carbonate and carbon dioxide;

[0097] (3) Mix potassium hydroxide and the filtrate from step (1) at a temperature of 30°C and a flow rate of 2000 m³ / h. 3 After the air is stripped at a rate of / h, ammonia gas and ammonia removal solution are obtained.

[0098] After mixing, the mass ratio of sodium ions to potassium ions in the filtrate is 1:80;

[0099] (4) After mixing the carbon dioxide from step (2) and the ammonia from step (3), ammonium bicarbonate is obtained after the reaction, and the ammonium bicarbonate is recycled for step (1);

[0100] (5) Mix hydrochloric acid and the ammonia removal solution described in step (4), evaporate and crystallize at a temperature of 120°C to obtain crude potassium chloride and sodium-containing mother liquor. The sodium-containing mother liquor is returned to step (1) for treatment.

[0101] The amount of hydrochloric acid added is sufficient to adjust the pH of the ammonia removal solution to 7.7;

[0102] The mass ratio of sodium ions to potassium ions in the crude potassium chloride product is 1:100; the mass ratio of sodium ions to potassium ions in the sodium-containing mother liquor is 1:90.

[0103] (6) Mix pyroantimonic acid, potassium hydroxide, water and the crude potassium chloride from step (4), and react at 120°C for 1 hour to obtain sodium pyroantimonate and potassium chloride;

[0104] The mass ratio of crude pyroantimonic acid to crude potassium chloride is 1.2:1; the mass ratio of crude potassium hydroxide to crude potassium chloride is 0.15:1.

[0105] Steps (2) and (3) are not in any particular order.

[0106] Example 4

[0107] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for the mass ratio of sodium ions to potassium ions in the potassium-containing sodium wastewater in step (1) being 1:15, all other conditions are the same as in embodiment 1.

[0108] Example 5

[0109] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for the mass ratio of sodium ions to potassium ions in the potassium-containing sodium wastewater in step (1) being 1:30, all other conditions are the same as in Example 1.

[0110] Example 6

[0111] This embodiment provides a method for recovering and separating potassium chloride from potassium-sodium wastewater and producing sodium carbonate. Except for the concentration of sodium ions in the potassium-sodium wastewater after concentration in step (1) being 2 g / L, all other conditions are the same as in Example 1.

[0112] Example 7

[0113] This embodiment provides a method for recovering and separating potassium chloride from potassium-sodium wastewater and producing sodium carbonate. Except for the concentration of sodium ions in the potassium-sodium wastewater after concentration in step (1) being 30 g / L, all other conditions are the same as in Example 1.

[0114] Example 8

[0115] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for the fact that the amount of potassium hydroxide added in step (3) is too small and the mass ratio of sodium ions to potassium ions in the filtrate after mixing is 1:40, all other conditions are the same as in Example 1.

[0116] Example 9

[0117] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for step (3), where the amount of potassium hydroxide added is too large and the mass ratio of sodium ions to potassium ions in the filtrate after mixing is 1:100, all other conditions are the same as in Example 1.

[0118] Example 10

[0119] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for step (5), in which the amount of hydrochloric acid added is adjusted to adjust the pH of the ammonia-free solution to 5, all other conditions are the same as in Example 1.

[0120] Example 11

[0121] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for step (5), in which the amount of hydrochloric acid added is adjusted to adjust the pH of the ammonia-free solution to 9, all other conditions are the same as in Example 1.

[0122] Example 12

[0123] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for the absence of pyroantimonic acid in step (6), all other conditions are the same as in Example 1.

[0124] Example 13

[0125] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for the absence of potassium hydroxide in step (6), all other conditions are the same as in Example 1.

[0126] Example 14

[0127] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for the reaction temperature of 70°C in step (6), all other conditions are the same as in Example 1.

[0128] Example 15

[0129] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for the reaction temperature of 140°C in step (6), all other conditions are the same as in Example 1.

[0130] Comparative Example 1

[0131] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for step (3), in which potassium hydroxide is not added and the filtrate is directly stripped, all other conditions are the same as in Example 1.

[0132] Comparative Example 2

[0133] This embodiment provides a method for recovering and separating potassium chloride from potassium-containing sodium wastewater and producing sodium carbonate. Except for step (5), where hydrochloric acid is not added and the ammonia-free solution is directly evaporated and crystallized, all other conditions are the same as in Example 1.

[0134] The purity and recovery rate of sodium carbonate in step (2) and the purity and recovery rate of potassium chloride in step (6) of the above embodiments and comparative examples were analyzed and tested. The test results are shown in Table 1.

[0135] Table 1

[0136]

[0137]

[0138] As shown in Table 1:

[0139] (1) The method provided by the present invention for treating potassium and sodium-containing wastewater not only has high purity and high recovery rate of potassium chloride obtained by separation, but also can co-produce sodium carbonate, which has high product value and realizes the resource utilization of wastewater.

[0140] (2) Comparing Example 1 and Example 4-7, it can be seen that if the potassium and sodium ion content in the wastewater is not controlled or the sodium ion concentration is not controlled properly after concentration, some potassium ions will combine with bicarbonate ions to form potassium bicarbonate co-crystallization and precipitation, resulting in a decrease in sodium carbonate purity and a decrease in potassium chloride recovery rate.

[0141] (3) Based on the comparison of Example 1 and Example 8-9 and Comparative Example 1, it can be seen that when potassium hydroxide is not added to the system in step (3) or the amount of potassium hydroxide added is too small, the purity of potassium chloride is low and the recovery rate is low due to the high ammonia nitrogen; when the amount of potassium hydroxide added to the system in step (3) is too large, the purity of potassium chloride is low and the recovery rate decreases due to the high potassium hydroxide content.

[0142] (4) Based on the comparison of Example 1 and Example 10-11 and Comparative Example 2, it can be seen that when too much hydrochloric acid is added to the system in step (5), the potassium chloride purity is low and the recovery rate is low due to the excess of hydrogen ions; when no hydrochloric acid is added to the system in step (5) to adjust the pH or when too little hydrochloric acid is added, the potassium chloride purity is low and the recovery rate is low due to the excess of hydroxide ions.

[0143] (5) Comparing Example 1 and Example 12-13, it can be seen that when pyroantimonic acid is not added during the sodium removal process in step (5), the purity of the obtained potassium chloride is low due to the high residual sodium particles; when potassium hydroxide is not added, it cannot be converted into potassium pyroantimonate to react with sodium chloride, and sodium ions cannot be removed, resulting in the low purity of the obtained potassium chloride.

[0144] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0145] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0146] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. A method for recovering and separating potassium chloride from potassium- and sodium-containing wastewater and co-producing sodium carbonate, characterized in that, The method includes the following steps: (1) Mix ammonium salt precipitant and potassium- and sodium-containing wastewater, filter and obtain sodium bicarbonate and filtrate; (2) Heat-treat the sodium bicarbonate obtained in step (1) to obtain sodium carbonate and carbon dioxide; (3) Mix potassium hydroxide and the filtrate from step (1), and strip the mixture to obtain ammonia gas and ammonia-removing solution; After mixing in step (3), the mass ratio of sodium ions to potassium ions in the filtrate is 1:(50-80); (4) Mix the acidic substance and the ammonia removal solution described in step (3), evaporate and crystallize to obtain crude potassium chloride and sodium-containing mother liquor; The amount of acidic substance added is such that the pH of the ammonia removal solution is adjusted to 6-8; Steps (2) and (3) are not in any particular order; In step (1), the mass ratio of sodium ions to potassium ions in the potassium-containing wastewater is 1:(20-25). Step (1) before mixing also includes: concentrating the potassium and sodium-containing wastewater; After concentration, the concentration of sodium ions in the potassium-sodium wastewater is 5-20 g / L; The method further includes: mixing pyroantimonic acid, potassium hydroxide, solvent and crude potassium chloride from step (4), and reacting to obtain sodium pyroantimonate and potassium chloride; The reaction temperature is 90-120℃.

2. The method according to claim 1, characterized in that, The ammonium salt precipitant in step (1) includes ammonium bicarbonate.

3. The method according to claim 1, characterized in that, In step (1), the molar ratio of the ammonium salt precipitant to the sodium ions in the potassium-sodium wastewater is (1-1.2):

1.

4. The method according to claim 1, characterized in that, The heat treatment temperature in step (2) is 60-100℃.

5. The method according to claim 1, characterized in that, The carrier gas for the stripping process in step (3) includes air and / or water vapor.

6. The method according to claim 1, characterized in that, The method further includes: mixing the carbon dioxide from step (2) and the ammonia from step (3), reacting to obtain ammonium bicarbonate, which is returned to step (1) as an ammonium salt precipitant.

7. The method according to claim 1, characterized in that, The acidic substance mentioned in step (4) includes hydrochloric acid.

8. The method according to claim 1, characterized in that, The evaporation and crystallization temperature in step (4) is 90-120℃.

9. The method according to claim 1, characterized in that, The sodium-potassium ratio of the crude potassium chloride in step (4) is less than that of the sodium-potassium ratio of the sodium-containing mother liquor.

10. The method according to claim 1, characterized in that, In step (4), the mass ratio of sodium ions to potassium ions in the crude potassium chloride is 1:(100-500).

11. The method according to claim 1, characterized in that, In step (4), the mass ratio of sodium ions to potassium ions in the sodium-containing mother liquor is 1:(90-200).

12. The method according to claim 1, characterized in that, The sodium-containing mother liquor in step (4) is returned to step (1) for processing.

13. The method according to claim 1, characterized in that, The mass ratio of the crude pyroantimonic acid to crude potassium chloride is (1-1.2):

1.

14. The method according to claim 1, characterized in that, The mass ratio of crude potassium hydroxide to crude potassium chloride is (0.05-0.15):

1.

15. The method according to claim 1, characterized in that, The reaction time is 1-2 hours.

16. The method according to claim 1, characterized in that, The method includes the following steps: (1) The potassium and sodium-containing wastewater is concentrated, then mixed with ammonium salt precipitant, filtered to obtain sodium bicarbonate and filtrate; The mass ratio of sodium ions to potassium ions in the potassium-sodium-containing wastewater is 1:(20-25); after concentration, the concentration of sodium ions in the potassium-sodium-containing wastewater is 5-20 g / L. The ammonium salt precipitant includes ammonium bicarbonate; the molar ratio of the ammonium salt precipitant to sodium ions in the potassium-sodium wastewater is (1-1.2):1; (2) The sodium bicarbonate obtained in step (1) is heat-treated at a temperature of 60-100℃ to obtain sodium carbonate and carbon dioxide; (3) Mix potassium hydroxide and the filtrate from step (1), and strip the mixture to obtain ammonia gas and ammonia-removing solution; After mixing in step (3), the mass ratio of sodium ions to potassium ions in the filtrate is 1:(50-80); (4) After mixing the carbon dioxide in step (2) and the ammonia in step (3), ammonium bicarbonate is obtained after the reaction. The ammonium bicarbonate is returned to step (1) as an ammonium salt precipitant. (5) Mix the acidic substance and the ammonia removal solution described in step (4), and evaporate and crystallize at a temperature of 90-120℃ to obtain crude potassium chloride and sodium-containing mother liquor. The sodium-containing mother liquor is returned to step (1) for treatment. The acidic substance includes hydrochloric acid; the amount of acidic substance added is such that the pH of the ammonia removal solution is adjusted to 6-8. The sodium-potassium ratio of the crude potassium chloride is less than that of the sodium-potassium mother liquor; the mass ratio of sodium ions to potassium ions in the crude potassium chloride is 1:(100-500); the mass ratio of sodium ions to potassium ions in the sodium-containing mother liquor is 1:(90-200). (6) Mix pyroantimonic acid, potassium hydroxide, solvent and crude potassium chloride from step (5), and react at 90-120℃ for 1-2 hours to obtain sodium pyroantimonate and potassium chloride; The mass ratio of the crude pyroantimonic acid to crude potassium chloride is (1-1.2):1; the mass ratio of the crude potassium hydroxide to crude potassium chloride is (0.05-0.15):

1. Steps (2) and (3) are not in any particular order.

Images