Method for treating monopotassium phosphate crystallization mother liquor

Abstract

The invention discloses a method for treating monopotassium phosphate crystallization mother liquor, which comprises the following steps: adding potassium hydroxide into the monopotassium phosphate crystallization mother liquor, converting phosphoric acid in the mother liquor into monopotassium phosphate, carrying out vacuum concentration and filtration on the conversion liquid to remove calcium and magnesium salt impurities, and carrying out vacuum concentration and cooling crystallization on the obtained filtrate to obtain a monopotassium phosphate filter cake; and washing and drying the filter cake to obtain a potassium dihydrogen phosphate crude product. According to the treatment method disclosed by the invention, the monopotassium phosphate in the monopotassium phosphate crystallization mother liquor can be recycled, so that the yield of the monopotassium phosphate is increased, and the economic value of the crystallization mother liquor is increased.

Description

Technical Field

[0001] The invention relates to the technical field of mother liquor treatment, and in particular to a method for treating potassium dihydrogen phosphate crystallization mother liquor. Background Art

[0002] Inositol, chemically known as cyclohexanehexol, is an important vitamin required by higher animals. Inositol can promote fat metabolism and reduce the cholesterol content in the blood. It is also used as an anti-fatty liver drug for the treatment of cirrhosis, hepatitis, high cholesterol, excessive fat and vascular sclerosis. In addition to being used directly as a drug (such as inositol tablets, hepatol, liver-soothing tablets, etc.), inositol can also be used as a pharmaceutical intermediate to make many drugs, such as nicotinic acid inositol ester, pulsetong, anticancer drug paclitaxel, etc.

[0003] Potassium dihydrogen phosphate is used as a buffer and culture agent in industry; it is used as a high-efficiency phosphorus-potassium compound fertilizer in agriculture. It is widely applicable to various types of economic crops, such as grain, fruits, vegetables, etc. It has many excellent effects such as significantly increasing production and income, improving quantity / optimizing quality, resisting lodging, resisting diseases and pests, and preventing premature aging. It also has the effect of overcoming nutritional deficiencies caused by the aging of the root system and the decreased absorption capacity in the later stages of crop growth.

[0004] Inositol and potassium dihydrogen phosphate can be obtained by hydrolysis of potassium phytate. In the prior art, the hydrolysis process of potassium phytate mainly includes phytase hydrolysis and high temperature and high pressure hydrolysis. The mixed liquid of inositol and potassium dihydrogen phosphate is obtained by hydrolysis. The mixed liquid of inositol and potassium dihydrogen phosphate is obtained by separation (such as multi-stage charge membrane separation). The inositol liquid and potassium dihydrogen phosphate liquid are then vacuum concentrated and cooled and crystallized to obtain wet products of inositol and potassium dihydrogen phosphate and their crystallization mother liquors. The amount of inositol crystallization mother liquor is small and can be sold to feed and fertilizer companies for further preparation of subsequent high value-added products. The amount of potassium dihydrogen phosphate crystallization mother liquor is large, and the mother liquor contains more calcium, magnesium and protein. In addition, there are about 5% of inositol and 30% of potassium dihydrogen phosphate in the mother liquor. The current treatment method is to treat the waste mother liquor at a low price, resulting in the waste of high-value components in the potassium dihydrogen phosphate crystallization mother liquor.

[0005] Therefore, it is urgent to establish a method for treating potassium dihydrogen phosphate crystallization mother liquor in the prior art to recover high-value inositol and potassium dihydrogen phosphate in the mother liquor and improve the economic value of the mother liquor. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a method for treating potassium dihydrogen phosphate crystallization mother liquor, which overcomes the technical problems in the prior art that valuable components in the potassium dihydrogen phosphate crystallization mother liquor cannot be fully utilized and the economic efficiency is not high.

[0007] In order to achieve the above object, the present invention provides a method for treating potassium dihydrogen phosphate crystallization mother liquor, comprising the following steps:

[0008] Add potassium hydroxide to the potassium dihydrogen phosphate crystal mother liquor to adjust the pH to 5.0-5.2, and react to obtain a conversion solution;

[0009] The conversion liquid is subjected to a first vacuum concentration, and when crystals are precipitated in the conversion liquid, the vacuum is turned off and the conversion liquid is heated to 85-95° C., and the conversion liquid is filtered while hot to remove calcium and magnesium salts to obtain a filtrate;

[0010] The filtrate is subjected to a second vacuum concentration to obtain a concentrated solution;

[0011] Adding a crystallization solvent to the concentrated solution, cooling the solution to 30° C. for crystallization, and filtering the solution to obtain a potassium dihydrogen phosphate filter cake and a second filtrate;

[0012] The potassium dihydrogen phosphate filter cake is eluted with an organic solvent and dried to obtain a crude potassium dihydrogen phosphate product.

[0013] The processing method of potassium dihydrogen phosphate crystallization mother liquor provided by the present invention first adds potassium hydroxide to the potassium dihydrogen phosphate crystallization mother liquor, and by controlling the pH of the solution, phosphoric acid (inorganic phosphorus) in the mother liquor is converted into potassium dihydrogen phosphate, and the obtained conversion liquid is vacuum concentrated, and by controlling the vacuum degree and temperature, the solubility of potassium dihydrogen phosphate is improved, and calcium and magnesium salts (mainly calcium phosphate and magnesium phosphate) are supersaturated and precipitated, and calcium and magnesium salt impurities are removed by hot filtration. The obtained filtrate is then vacuum concentrated and cooled and crystallized to obtain a potassium dihydrogen phosphate filter cake, and inositol is retained in the crystallization mother liquor, and the filter cake is washed and dried to obtain a crude potassium dihydrogen phosphate product. The processing method of the present invention can recycle the potassium dihydrogen phosphate in the potassium dihydrogen phosphate crystallization mother liquor, improve the yield of potassium dihydrogen phosphate, and also improve the economic value of the crystallization mother liquor. It has been determined that the content of potassium dihydrogen phosphate in the crude potassium dihydrogen phosphate obtained by the present invention can reach about 77%. DETAILED DESCRIPTION

[0014] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0015] The present invention provides a method for treating potassium dihydrogen phosphate crystallization mother liquor, which specifically comprises:

[0016] Add potassium hydroxide to the potassium dihydrogen phosphate crystal mother liquor to adjust the pH to 5.0-5.2, and react to obtain a conversion solution;

[0017] The conversion liquid is subjected to a first vacuum concentration, and when crystals are precipitated in the conversion liquid, the vacuum is turned off and the conversion liquid is heated to 85-95° C., and the conversion liquid is filtered while hot to remove calcium and magnesium salts to obtain a filtrate;

[0018] The filtrate is subjected to a second vacuum concentration to obtain a concentrated solution;

[0019] Adding a crystallization solvent to the concentrated solution, cooling the solution to 30° C. for crystallization, and filtering the solution to obtain a potassium dihydrogen phosphate filter cake and a second filtrate;

[0020] The potassium dihydrogen phosphate filter cake is eluted with an organic solvent and dried to obtain a crude potassium dihydrogen phosphate product.

[0021] The present invention first adds potassium hydroxide to potassium dihydrogen phosphate crystallization mother liquor to adjust the pH to 5.0-5.2, and reacts to obtain a conversion solution. In the present invention, the potassium dihydrogen phosphate crystallization mother liquor is a crystallization mother liquor obtained by hydrolyzing potassium phytate to obtain inositol and potassium dihydrogen phosphate, and then recovering inositol and potassium dihydrogen phosphate through crystallization; generally, the crystallization mother liquor contains 30-60 g / L of inositol, 10-20% of inorganic phosphorus, 4-12% of protein and 15000-30000 ppm of chloride ions. In the present invention, the potassium hydroxide is preferably solid potassium hydroxide or potassium hydroxide solution; wherein the concentration of the potassium hydroxide solution is preferably 30-40% (w / w); the purpose of adding potassium hydroxide to the crystallization mother liquor is to convert the inorganic phosphorus (phosphoric acid) in the crystallization mother liquor into potassium dihydrogen phosphate under specific pH conditions. Too high or too low pH will lead to the production of impurity dipotassium hydrogen phosphate or tripotassium phosphate byproducts; the present invention has no special restrictions on the reaction time, temperature and pressure, and conventional neutralization reaction time, normal temperature and pressure can be used. The present invention also includes stirring after adding solid potassium hydroxide or potassium hydroxide solution to the crystallization mother liquor. Preferably, the stirring rate is 20-100rpm; the purpose of stirring in the present invention is to promote the uniformity of the solution, so that the subsequent pH determination is more timely and accurate, and the reaction is more uniform. The present invention has no special restrictions on the reaction time, for example, it can be 0.5-2h.

[0022] After obtaining the conversion liquid, the present invention performs a first vacuum concentration on the conversion liquid, and when crystals are precipitated in the conversion liquid, the vacuum is turned off and the conversion liquid is heated to 85-95°C, and the conversion liquid is filtered while hot to remove calcium and magnesium salts to obtain a filtrate. In the present invention, the vacuum degree of the first vacuum concentration is preferably ≤-0.09MPa, and the temperature is preferably 70-80°C; the present invention has no special limitation on the equipment for the first vacuum concentration, and conventional concentration equipment in the art can be used; the hot filtration is preferably performed by centrifuge filtration, the centrifuge speed is preferably 600-1000rpm, and the filter cloth pore size is preferably 800-1000 mesh. When crystals are precipitated in the conversion liquid in the present invention, it refers to the precipitation of calcium magnesium salts. Specifically, it refers to concentrating the conversion liquid to a volume of 85-90% of the original volume. The precipitation process of calcium magnesium salts is also accompanied by the precipitation of potassium dihydrogen phosphate. Therefore, the present invention stops concentrating after the precipitation of calcium magnesium salts, closes the vacuum and raises the temperature, so that the potassium dihydrogen phosphate is redissolved, while the calcium magnesium salts will not be redissolved. At this time, filtering is performed while hot to obtain a calcium magnesium salt filter cake and a filtrate.

[0023] After obtaining the filtrate, the present invention performs a second vacuum concentration on the filtrate to obtain a concentrated solution. In the present invention, the vacuum degree of the second vacuum concentration is preferably ≤-0.09MPa, and the temperature is preferably 80-90°C; the present invention has no special limitation on the equipment for the second vacuum concentration, and conventional concentration equipment in the art can be used. In the present invention, the density of the concentrated solution is preferably 1.35-1.5g / ml.

[0024] After obtaining the concentrated solution, the present invention adds a crystallization solvent to the concentrated solution, cools and crystallizes to 30°C, and then filters to obtain a potassium dihydrogen phosphate filter cake and a second filtrate. In the present invention, the crystallization solvent is preferably methanol or ethanol, and the concentration of the crystallization solvent is preferably 90-95% (v / v); the volume ratio of the crystallization solvent to the concentrated solution is preferably (1.25-1.4): 1. In the present invention, the rate of the cooling crystallization is preferably 20-30°C / h; the present invention does not specifically limit the crystallization equipment, and the commonly used crystallization equipment in the art can be used, such as a crystallization kettle. In the present invention, the filtration is preferably carried out by centrifuge filtration, the centrifuge speed is preferably 600-1000rpm, and the filter cloth pore size is preferably 800-1000 mesh. In the present invention, the cooling crystallization process preferably also includes: stirring at a stirring rate of 500-1000rpm.

[0025] After obtaining the potassium dihydrogen phosphate filter cake, the present invention rinses the potassium dihydrogen phosphate filter cake with an organic solvent, and obtains a crude potassium dihydrogen phosphate product after drying. In the present invention, the organic solvent is preferably methanol or ethanol, and the concentration of the organic solvent is preferably 90-95% (v / v); the amount of the organic solvent is 1.25-1.4BV of the volume of the potassium dihydrogen phosphate filter cake. The purpose of the present invention using an organic solvent for elution is to reduce the content of protein and inositol in the filter cake and improve the purity of potassium dihydrogen phosphate. The present invention does not specifically limit the temperature and equipment for the drying, and conventional drying equipment and drying temperature in the art can be used.

[0026] After filtering to obtain a potassium dihydrogen phosphate filter cake and a second filtrate, the present invention further comprises: performing a third vacuum concentration on the second filtrate to obtain an organic solvent and a concentrated solution. In the present invention, the temperature of the third vacuum concentration is preferably 60-80°C, and the vacuum degree is preferably ≤-0.09MPa; the present invention does not specifically limit the equipment for the third vacuum concentration, and conventional concentration equipment in the art can be used. The purpose of the present invention performing vacuum concentration on the second filtrate is to distill out the crystallization solvent used in the crystallization process in order to recover it; and the obtained concentrated solution contains a certain amount of inositol, which can be sold directly.

[0027] In order to better illustrate the technical solution of the present invention, the present invention also provides the following specific examples. It should be understood that the raw materials used in the following examples are all commercially available raw materials unless otherwise specified.

[0028] Example 1

[0029] S1. Add 75.2 g of potassium hydroxide to 2000 ml of potassium dihydrogen phosphate crystallization mother liquor (inositol 31.2 g / L, inorganic phosphorus 10.5%, protein 6.2%, chloride ion 16707 ppm), and react for 1 h at 80 rpm stirring and pH 5.1 to obtain a conversion solution;

[0030] S2. Take 2000 ml of the conversion solution and perform the first vacuum concentration at -0.09 MPa and 80 ° C. When crystals are precipitated in the conversion solution, turn off the vacuum and raise the temperature of the conversion solution to 95 ° C. The conversion solution is filtered while hot (centrifugal speed is 800 rpm, filter cloth pore size is 900 mesh), and 163 g of calcium and magnesium salt filter cake (after drying) and 1780 ml of filtrate are obtained;

[0031] S3. The filtrate was concentrated under vacuum for the second time at -0.09MPa and a temperature of 85°C, and the concentration was stopped when the material density reached 1.4g / ml to obtain 1450ml of concentrated solution;

[0032] S4. 1957.5 ml of methanol solution (90% (v / v)) was added to the above concentrate, and the mixture was crystallized at a cooling rate of 25°C / h to 30°C (stirring rate 1000 rpm), and filtered (centrifugal speed of 800 rpm, filter cloth pore size 900 mesh) to obtain 743.6 g of potassium dihydrogen phosphate filter cake (before drying) and 3320 ml of the second filtrate;

[0033] S5. The potassium dihydrogen phosphate filter cake was rinsed with 50 ml of methanol solution (95% (v / v)) and dried to obtain 571.6 g of crude potassium dihydrogen phosphate.

[0034] The results of testing showed that the crude potassium dihydrogen phosphate product contained 4.3% inositol, 39.8% inorganic phosphorus (76.4% when converted into potassium dihydrogen phosphate), 2.3% protein and 1902 ppm chloride ion.

[0035] Example 2

[0036] S1. Add 136 g of potassium hydroxide to 2000 ml of potassium dihydrogen phosphate crystallization mother liquor (inositol 46.5 g / L, inorganic phosphorus 19.9%, protein 10.7%, chloride ion 101409 ppm), stir at 100 rpm, react for 2 h at pH 5.0 to obtain a conversion solution;

[0037] S2. Take 2000 ml of the conversion solution and perform the first vacuum concentration at -0.095 MPa and 75 ° C. When crystals are precipitated in the conversion solution, turn off the vacuum and raise the temperature of the conversion solution to 90 ° C. The conversion solution is filtered while hot (the centrifugal speed is 600 rpm and the filter cloth pore size is 800 mesh) to obtain 171 g of calcium and magnesium salt filter cake (after drying) and 1805 ml of filtrate;

[0038] S3. The filtrate was concentrated under vacuum for the second time at -0.095MPa and a temperature of 90 ° C. The concentration was stopped when the material density reached 1.35g / ml to obtain 1520ml of concentrated solution;

[0039] S4. 1900 ml of methanol solution (95% (v / v)) was added to the above concentrate, and the mixture was crystallized at a cooling rate of 20°C / h to 30°C (stirring rate of 800 rpm), and filtered (centrifugal speed of 1000 rpm, filter cloth pore size of 800 mesh) to obtain 772.3 g of potassium dihydrogen phosphate filter cake (before drying) and 3380 ml of the second filtrate;

[0040] S5. The potassium dihydrogen phosphate filter cake was rinsed with 50 ml of ethanol solution (90% (v / v)) and dried to obtain 594.4 g of crude potassium dihydrogen phosphate.

[0041] The results of testing showed that the crude potassium dihydrogen phosphate contained 6.7% inositol, 40.2% inorganic phosphorus (77.2% when converted into potassium dihydrogen phosphate), 3.7% protein and 6475 ppm chloride ion.

[0042] Example 3

[0043] S1. Add 250 ml of potassium hydroxide solution (concentration 40% (w / w)) to 2000 ml of potassium dihydrogen phosphate crystallization mother liquor (inositol 52.6 g / L, inorganic phosphorus 13.7%, protein 4.5%, chloride ion 29365 ppm), and react for 0.5 h under stirring at 20 rpm and pH 5.2 to obtain a conversion solution;

[0044] S2. Take 2250 ml of the conversion solution and perform the first vacuum concentration at -0.010 MPa and 70 ° C. When crystals are precipitated in the conversion solution, turn off the vacuum and raise the temperature of the conversion solution to 95 ° C. The conversion solution is filtered while hot (centrifugal speed is 1000 rpm, filter cloth pore size is 1000 mesh), and 121 g of calcium magnesium salt filter cake (after drying) and 1822 ml of filtrate are obtained;

[0045] S3. The filtrate was concentrated under vacuum for a second time at -0.010MPa and a temperature of 80 ° C. The concentration was stopped when the material density reached 1.5g / ml to obtain 1340ml of concentrated solution;

[0046] S4. Add 1876 ml of ethanol solution (93% (v / v)) to the above concentrate, crystallize to 30 ° C at a cooling rate of 30 ° C / h (stirring rate 500 rpm), filter (centrifugal speed 600 rpm, filter cloth pore size 1000 mesh) to obtain ***g potassium dihydrogen phosphate filter cake (before drying) and 3010 ml of the second filtrate;

[0047] S5. The potassium dihydrogen phosphate filter cake was rinsed with 50 ml of ethanol solution (95% (v / v)) and dried to obtain 592.4 g of crude potassium dihydrogen phosphate.

[0048] The results of testing showed that the crude potassium dihydrogen phosphate contained 6.9% inositol, 37.2% inorganic phosphorus (71.4% converted into potassium dihydrogen phosphate), 3.6% protein and 7674 ppm chloride ion.

[0049] Example 4

[0050] S1. The 3320 ml second filtrate obtained in Example 1 was subjected to a third vacuum concentration at -0.09 MPa and 70°C to obtain 2165 ml of methanol solution and 910 ml of concentrated solution.

[0051] After testing, the inositol content in the concentrated solution is 38.2 g / L, inorganic phosphorus is 1.5%, protein is 11.5%, and chloride ion is 29182 ppm.

[0052] Example 5

[0053] S1. The second filtrate obtained in Example 2 was subjected to a third vacuum concentration at -0.095 MPa and 60° C. to obtain 2180 ml of methanol solution and 1000 ml of concentrated solution.

[0054] After testing, the inositol content in the concentrated solution was 51 g / L, inorganic phosphorus was 2.8%, protein was 8.4%, and chloride ion was 1758 ppm.

[0055] Example 6

[0056] S1. The 3380 ml second filtrate obtained in Example 3 was subjected to a third vacuum concentration at -0.010 MPa and 80° C. to obtain 2265 ml of ethanol solution and 565 ml of concentrated solution.

[0057] After testing, the inositol content in the concentrated solution is 64.4 g / L, the inorganic phosphorus is 10.3%, the protein is 13.2%, and the chloride ion is 32137 ppm.

[0058] Comparative Example 1

[0059] The step S1 in Example 1, "adding potassium hydroxide to the potassium dihydrogen phosphate crystallization mother liquor, adjusting the pH to 5.1 and reacting" is adjusted to "adding potassium hydroxide to the potassium dihydrogen phosphate crystallization mother liquor, adjusting the pH to 5.7 and reacting", and other conditions remain unchanged.

[0060] Finally, 502.3 g of crude potassium dihydrogen phosphate was obtained; after testing, it was found that the crude potassium dihydrogen phosphate had an inositol content of 4.5%, an inorganic phosphorus content of 39.5% (converted to 75.9% of potassium dihydrogen phosphate), a protein content of 2.2%, and a chloride ion content of 1966 ppm.

[0061] In Comparative Example 1, after the pH of the potassium dihydrogen phosphate crystallization mother liquor was increased, the amount of crude potassium dihydrogen phosphate finally obtained was reduced. The reason for this was that when the pH was 5.7, the process of generating potassium dihydrogen phosphate would cause a side reaction to produce part of dipotassium hydrogen phosphate, thereby reducing the recovery amount and recovery rate of potassium dihydrogen phosphate.

[0062] Comparative Example 2

[0063] The step of “turning off the vacuum and raising the temperature of the conversion liquid to 90° C.” in Example 2 was adjusted to “turning off the vacuum and keeping the temperature of the reaction liquid unchanged”, and other conditions remained unchanged.

[0064] Finally, 192g of calcium and magnesium salt filter cake (after drying) and 533.2g of crude potassium dihydrogen phosphate were obtained; after testing, it was found that the crude potassium dihydrogen phosphate had an inositol content of 6.9%, inorganic phosphorus of 38.2% (73.3% converted into potassium dihydrogen phosphate), protein of 3.6%, and chloride ion of 7643ppm. The crude product was turbid after 10% water dissolution, proving that there were still a lot of calcium and magnesium ions in the crude product.

[0065] In Comparative Example 2, the solution was not heated after the vacuum was turned off. The results showed that the amount of calcium magnesium salt filter cake obtained increased and the amount of crude potassium dihydrogen phosphate decreased. This is because if the solution is not heated, part of the potassium dihydrogen phosphate will not be redissolved into the solution during the crystallization process, but will crystallize with the calcium magnesium salt and enter the calcium magnesium salt filter cake, resulting in a decrease in the final amount of potassium dihydrogen phosphate.

[0066] Test Case

[0067] A. Inositol is tested according to GB1903.42-2020;

[0068] B. Protein was tested according to GB5009.5-85;

[0069] C. Chloride ion detection:

[0070] 1. Take 5 ml, add it into a 50 ml volumetric flask, add purified water to make up to 50 ml, and shake well (i.e. dilute 10 times);

[0071] 2. Take 1 ml of the above solution, add it into a conical flask, add purified water to make up to 50 ml, and shake well;

[0072] 3. Add 2 drops of phenolphthalein, shake well, then add 2 drops of sodium hydroxide solution, it turns purple-red;

[0073] 4. Add 1-2 drops of nitric acid, shake well, and turn colorless;

[0074] 5. Add potassium chromate solution with a dropper length of about 2 cm, shake well, and turn bright yellow;

[0075] 6. Titrate with 0.01033 mol / L silver nitrate standard solution until the color changes from bright yellow to dark yellow. Record the volume of silver nitrate titrant consumed.

[0076] 7. Chloride ion = 0.01033*35.45*1000*10 (diluted 10 times)*V = 3661.985*V.

[0077] Inorganic phosphorus detection:

[0078] 1. Under acidic conditions, inorganic phosphorus reacts with molybdic acid to form yellow ammonium phosphomolybdate, which is then reduced to dark blue molybdenum blue with an appropriate reducing agent. The higher the phosphorus content, the more molybdenum blue substances are formed, and the darker the blue color. The absorbance is measured at 650nm with a spectrophotometer, and the content of inorganic phosphorus in the solution can be calculated;

[0079] 2. Reagent preparation: Reagent 1: A weigh 24g of ammonium molybdate, dissolve it in an appropriate amount of purified water and dilute it to 240ml, B slowly pour 360ml of concentrated sulfuric acid into 240ml of purified water, mix A and B, and store them in a brown glass bottle; Reagent 2: weigh 0.8g of metol, 4g of anhydrous sodium sulfite, dissolve them in 40ml of purified water, weigh 176g of sodium bisulfite (or sodium bisulfite), dissolve it in 760ml of purified water, mix the two solutions and filter them, store the filtrate in a brown glass bottle and keep it away from light;

[0080] 3. Pipette 5ml of the supernatant from the centrifugation of the sample into a 50ml volumetric flask, add 10ml of 10% trichloroacetic acid solution, heat in a boiling water bath for 7min, add purified water to the mark, shake well, and filter. Pipette 2ml of the filtrate into a 25ml volumetric flask, add 1ml each of phosphorus reagents 1 and 2, and then add 6ml of purified water, shake well, heat in a boiling water bath for 30min, take out and cool, add purified water to the mark, shake well, and measure the absorbance at 650nm with a 721 spectrophotometer, using purified water as a blank control. Obtain the measurement results based on the standard curve.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention is described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for treating potassium dihydrogen phosphate crystallization mother liquor, characterized in that: The steps include: Add potassium hydroxide to the potassium dihydrogen phosphate crystal mother liquor to adjust the pH to 5.0-5.2, and react to obtain a conversion solution; The conversion liquid is subjected to a first vacuum concentration, and when crystals are precipitated in the conversion liquid, the vacuum is turned off and the conversion liquid is heated to 85-95° C., and the conversion liquid is filtered while hot to remove calcium and magnesium salts to obtain a filtrate; The filtrate is subjected to a second vacuum concentration to obtain a concentrated solution; Adding a crystallization solvent to the concentrated solution, cooling the solution to 30° C. for crystallization, and filtering the solution to obtain a potassium dihydrogen phosphate filter cake and a second filtrate; The potassium dihydrogen phosphate filter cake is eluted with an organic solvent and dried to obtain a crude potassium dihydrogen phosphate product.

2. The method according to claim 1, characterized in that: The potassium hydroxide is solid potassium hydroxide or a potassium hydroxide solution; wherein the concentration of the potassium hydroxide solution is 30-40% (w / w).

3. The method according to claim 1, characterized in that: The vacuum degree of the first vacuum concentration is ≤-0.09MPa and the temperature is 70-80°C; and / or, The hot filtration is carried out by centrifuge filtration, and the pore size of the filter cloth is 800-1000 meshes.

4. The method according to claim 1, characterized in that: The vacuum degree of the second vacuum concentration is ≤-0.09MPa and the temperature is 80-90°C; and / or, The density of the concentrate is 1.35-1.5 g / ml.

5. The method according to claim 1, characterized in that: The crystallization solvent is methanol or ethanol, and the concentration of the crystallization solvent is 90-95% (v / v); and / or, The volume ratio of the crystallization solvent to the concentrated solution is (1.25-1.4):

1.

6. The method according to claim 1, characterized in that The rate of the cooling crystallization is 20-30°C / h; and / or, The filtration is carried out using a centrifuge filter cloth, and the pore size of the filter cloth is 800-1000 meshes.

7. The method according to claim 1 or 6, characterized in that: The cooling crystallization process also includes: stirring at a stirring rate of 500-1000 rpm.

8. The method according to claim 1, characterized in that The organic solvent is methanol or ethanol, and the concentration of the organic solvent is 90-95% (v / v); and / or, The amount of the organic solvent used is 1.25-1.4 BV of the volume of the potassium dihydrogen phosphate filter cake.

9. The method according to claim 1, characterized in that: After filtering to obtain potassium dihydrogen phosphate filter cake and second filtrate, the method further comprises: The second filtrate is subjected to a third vacuum concentration to obtain an organic solvent and a concentrated solution.

10. The method according to claim 9, characterized in that The vacuum degree of the third vacuum concentration is ≤-0.09MPa, and the temperature is 60-80°C.