CN114988380A - Method for producing food-grade monopotassium phosphate and co-producing high-purity gypsum by using feed-grade calcium hydrophosphate - Google Patents
Method for producing food-grade monopotassium phosphate and co-producing high-purity gypsum by using feed-grade calcium hydrophosphate Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/32—Phosphates of magnesium, calcium, strontium, or barium
- C01B25/322—Preparation by neutralisation of orthophosphoric acid
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F11/00—Compounds of calcium, strontium, or barium
- C01F11/46—Sulfates
- C01F11/468—Purification of calcium sulfates
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- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
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- C01P2006/60—Optical properties, e.g. expressed in CIELAB-values
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
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- Y02A40/00—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production
- Y02A40/10—Adaptation technologies in agriculture, forestry, livestock or agroalimentary production in agriculture
- Y02A40/20—Fertilizers of biological origin, e.g. guano or fertilizers made from animal corpses
Abstract
The invention discloses a method for producing food-grade monopotassium phosphate and co-producing high-purity gypsum by utilizing feed-grade calcium hydrophosphate, which comprises the following steps of: (1) mixing feed grade calcium hydrophosphate slurry and concentrated sulfuric acid for reaction, and filtering to obtain filtrate and high-purity gypsum; (2) mixing the filtrate with desulfurizer slurry and an alkaline solution of a heavy metal remover until complete precipitation is achieved, adjusting the pH value, carrying out solid-liquid separation, and concentrating the liquid phase to obtain a concentrated solution; (3) adjusting the pH value of the concentrated solution, concentrating, cooling, and performing solid-liquid separation to obtain a potassium dihydrogen phosphate semi-finished product; (4) and recrystallizing the potassium dihydrogen phosphate semi-finished product. The purity of the calcium sulfate obtained by the method reaches more than 95 percent, the whiteness of the gypsum reaches more than 90 percent, all indexes are superior to those of natural gypsum, and the content of the obtained food-grade monopotassium phosphate is high; the invention has simple process and low cost, and is convenient for large-scale industrial application.
Description
Technical Field
The invention belongs to the technical field of phosphate preparation, and particularly relates to a method for producing food-grade monopotassium phosphate and co-producing high-purity gypsum by utilizing feed-grade calcium hydrophosphate.
Background
Potassium dihydrogen phosphate is a chemical with a chemical formula of KH 2 PO 4 . The compound fertilizer is industrially used as a buffering agent and a culture agent, is also used as a flavoring agent for synthesizing sake by using a bacterial culture agent, is a raw material for preparing potassium metaphosphate, a culture agent, an enhancer, a leavening agent, a fermentation aid and the like of brewing yeast, is used as a high-efficiency phosphorus-potassium compound fertilizer in agriculture, and has wide application in the fields of food, medicine, fertilizer and the like. At present, food-grade monopotassium phosphate is mainly produced by neutralization of phosphoric acid and potassium hydroxide through a thermal method in China, and the method has the advantages of high production cost, violent reaction, easy corrosion of equipment and high danger. In recent years, the production of potassium dihydrogen phosphate by adopting calcium hydrophosphate becomes a research direction for the product development of calcium hydrophosphate enterprises, but the prior production of potassium dihydrogen phosphate by adopting calcium hydrophosphate has the defects of low product quality and high production cost, and the industrial production cannot be realized.
Patent No. CN104445124B discloses a method for producing potassium dihydrogen phosphate by using feed-grade calcium hydrogen phosphate and applying a supergravity technology, which is not beneficial to large-scale production due to high investment cost of equipment adopting the supergravity technology.
Patent No. CN106744764B discloses a process for preparing potassium dihydrogen phosphate from feed-grade calcium hydrogen phosphate and potassium hydrogen sulfate, but the process does not consider impurities in calcium hydrogen phosphate, and only industrial-grade potassium dihydrogen phosphate is finally obtained.
The method for efficiently removing impurities in the calcium hydrophosphate and then converting the calcium hydrophosphate into a high-value-added product is an effective method for utilizing the calcium hydrophosphate at a high value, but the calcium hydrophosphate has more impurities and has higher difficulty in the separation process. Patent No. CN103879980B discloses a method for producing potassium dihydrogen phosphate by using feed grade calcium hydrophosphate, which considers the removal of impurities, but has more impurity removal steps, complex process and higher cost.
Therefore, it is urgently needed to develop a method which can fully remove impurities in calcium hydrophosphate, and has simple process and low cost.
Disclosure of Invention
The invention mainly solves the technical problem of providing a method for producing food-grade potassium dihydrogen phosphate and co-producing high-purity gypsum by utilizing feed-grade calcium hydrophosphate, which can effectively reduce the heavy metal content in the calcium hydrophosphate reclaimed material and obtain high-whiteness high-purity calcium sulfate and products with higher added values.
In order to solve the technical problems, the invention adopts a technical scheme that:
a method for producing food-grade monopotassium phosphate and co-producing high-purity gypsum by utilizing feed-grade calcium hydrophosphate comprises the following steps:
(1) mixing feed-grade calcium hydrophosphate slurry and concentrated sulfuric acid for reaction, and performing solid-liquid separation to obtain dilute phosphoric acid A;
(2) mixing the dilute phosphoric acid A, desulfurizer slurry and an alkaline solution of a heavy metal remover until the precipitation is complete, adding alkali or alkali liquor to adjust the pH value, carrying out solid-liquid separation, and concentrating the liquid phase to obtain concentrated phosphoric acid A; (ii) a
(3) Mixing the concentrated phosphoric acid A with alkali or phosphoric acid until the pH value is 3.5-5, concentrating, cooling and crystallizing to obtain a monopotassium phosphate semi-finished product; (ii) a
(4) And recrystallizing the potassium dihydrogen phosphate semi-finished product.
Further, in the step (1), the mixing reaction conditions of the feed-grade calcium hydrophosphate slurry and the concentrated sulfuric acid are as follows: reacting for 2-6 h at 60-90 ℃;
further, SO in the reaction system is controlled in the reaction process 3 The mass fraction is 0.1-7%.
SO in the invention 3 The content of (b) is substantially indicative of SO in the system 4 2- In the field and industry of phosphorus chemical industry, SO 4 2- In general as SO 3 According to SO 3 Calculating the content of sulfate ions; the content includes mass fraction and molar quantity.
Further, the solid-liquid separation is realized by adopting a sedimentation filtration method, the top is supernatant, the solid-liquid mixture at the bottom is subjected to plate-and-frame filter pressing and/or centrifugation to obtain thick slurry and solid impurities, and the thick slurry returns to the sedimentation filtration unit.
Further, (1) the reaction conditions are as follows: the temperature is 70-85 ℃, and the time is 2-6 h;
the solid content of the feed-grade calcium hydrophosphate slurry is 30-80%, and preferably 40-70%.
In the specific embodiment of the invention, in the step (2), the solid content of the desulfurizer slurry is 5-70%, preferably 10-60%;
the desulfurizer is barium carbonate; the heavy metal remover is selected from one of potassium sulfide, sodium sulfide, phosphorus pentasulfide and hydrogen sulfide;
further, the solvent in the alkaline solution in the heavy metal remover is potassium hydroxide.
In the step (2), the barium carbonate is SO 3 The molar ratio is 1: 1.
Desulfurizing agent and heavy metal removing agent are adopted for simultaneous desulfurization and heavy metal removal, barium sulfate crystals formed by desulfurization are utilized to promote fine arsenic sulfide and lead sulfide precipitates formed by heavy metal removal to be precipitated simultaneously along with barium sulfate, and the problems of slow fine precipitation, filtering and percolation and the like of crystals are avoided; in the specific embodiment of the invention, the molar amount of the heavy metal removing agent is 3-5 times of that of the heavy metal contained in the dilute phosphoric acid A;
further, the mass fraction of the heavy metal remover alkaline solution is 0.1-5%.
In the step (2), the reaction conditions of the mixing are as follows: the temperature is 40-60 ℃, the time is 0.5-3 h, and the steam pressure is 0.6-1.0 MPa;
further, the stirring speed during mixing is 0.1 to 2 m/s.
In the step (2), the solute of the alkali or the alkali liquor for adjusting the pH value is selected from one or more of potassium hydroxide, potassium carbonate and potassium bicarbonate.
In the step (2), the concentrated phosphoric acid A is concentrated until the mass fraction of the concentrated phosphoric acid A is 33-55%.
In the step (3), the alkali or the phosphoric acid is used until the pH value is 3.8-4.8; the phosphoric acid is hot phosphoric acid;
further, in the step (3), the mixture is concentrated until the mass fraction of the monopotassium phosphate is 30-50% and then cooled, and preferably, the mixture is concentrated until the mass fraction of the monopotassium phosphate is 35-40% and then cooled;
furthermore, the temperature reduction rate is 5-20 ℃/hour.
In the step (4), the recrystallization comprises the steps of dissolving, cooling and crystallizing;
the amount of the dissolved solvent is used for saturating the potassium dihydrogen phosphate; the dissolving temperature is 60-80 ℃.
The filtrate obtained by filtering in the production process can be recycled.
The invention has the following beneficial effects:
(1) the monopotassium phosphate product obtained by the method can meet the food-grade quality standard of GB 25560-.
(2) The method effectively reduces the heavy metal content in the calcium hydrophosphate reclaimed material, avoids the heavy metal content from being high and causes adverse effect on the ecological environment during discharge treatment.
(3) The calcium sulfate obtained by the method has high whiteness, does not contain organic matters, has the purity of more than 95 percent, has the whiteness of more than 90 percent, has various indexes superior to those of natural gypsum, can effectively replace the natural gypsum, and saves gypsum ore resources.
(4) The method has the advantages of simple process, low energy consumption and low cost, and is convenient for realizing industrial production.
Detailed Description
The technical solutions of the present invention are described clearly and completely below, and it is obvious that the described embodiments are some, not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Example 1
(1) Preparing high-purity gypsum by sulfuric acid extraction: adding water into calcium hydrogen phosphate to prepare solidAdding concentrated sulfuric acid into slurry with the content of 40% in a reaction tank containing the slurry, and controlling SO in a reaction system 3 The mass fraction is 0.1 percent, the reaction is carried out for 2 hours at the temperature of 70 ℃, the high-purity gypsum is obtained by washing and filtering after the reaction is finished, and the liquid phase is diluted phosphoric acid A.
(2) Removing impurities from dilute phosphoric acid, concentrating and concentrating to prepare concentrated phosphoric acid: preparing slurry with solid content of 10% by using barium carbonate serving as a desulfurizing agent, and mixing dilute phosphoric acid A, the slurry serving as the desulfurizing agent and a potassium hydroxide solution serving as a heavy metal removal agent (the mass fraction of the potassium hydroxide solution serving as a solvent is 0.01%) until complete precipitation is achieved, wherein the reaction temperature is 40 ℃ and the reaction time is 0.5 h; the stirring speed is 0.1-2 m/s;
barium carbonate and SO 3 The molar ratio is 1:1, the molar amount of the heavy metal removing agent is 3 times of that of the heavy metal contained in the dilute phosphoric acid A, potassium hydroxide is added to adjust the pH value to 4.0, solid-liquid separation is carried out, and the dilute phosphoric acid B is concentrated by adopting steam wall heat exchange under the steam pressure of 0.6MPa to obtain the concentrated phosphoric acid A with the mass fraction of 33%.
(3) Concentrating, crystallizing and separating a product: adding potassium hydroxide, potassium carbonate, potassium bicarbonate or thermal phosphoric acid into the concentrated phosphoric acid A until the pH value is 3.8, carrying out steam partition wall heat exchange to concentrate slurry, adding the concentrated slurry into a crystallizer, concentrating until the mass fraction of the monopotassium phosphate is 30-50%, slowly crystallizing at the cooling speed of 5 ℃/hour, filtering and separating the crystallized slurry to obtain a solid phase which is a monopotassium phosphate semi-finished product, and returning the mother liquor to the step (2) for recycling.
(4) And (3) recrystallizing and purifying a product: dissolving the potassium dihydrogen phosphate semi-finished product obtained in the step (3) with water, heating to 60 ℃ to saturate the concentration of the potassium dihydrogen phosphate, crystallizing the potassium dihydrogen phosphate at a cooling speed of 5 ℃/h, filtering, separating and crystallizing to obtain a potassium dihydrogen phosphate product, and returning the mother liquor to the step (3) for recycling.
The purity of the obtained high-purity gypsum is 96.8 percent, the whiteness is 92.3 percent, the monopotassium phosphate reaches the national food-grade standard GB 25560-.
Example 2
(1) Preparing high-purity gypsum by sulfuric acid extraction: adding water into calcium hydrogen phosphate to prepare slurry with solid content of 70%, adding concentrated sulfuric acid into a reaction tank containing the slurry, and controlling SO in a reaction system 3 The mass fraction is 4 percent, the reaction is carried out for 6 hours at the temperature of 85 ℃, the high-purity gypsum is obtained by washing and filtering after the reaction is finished, and the liquid phase is diluted phosphoric acid A.
(2) Removing impurities from dilute phosphoric acid, concentrating and preparing concentrated phosphoric acid: preparing slurry with solid content of 60% by using barium carbonate serving as a desulfurizing agent, mixing dilute phosphoric acid A, the slurry serving as the desulfurizing agent and a potassium hydroxide solution serving as a heavy metal removal agent (the mass fraction of the potassium hydroxide solution serving as a solvent is 1%) until complete precipitation is achieved, and reacting at the temperature of 60 ℃ for 3 hours; the stirring speed is 0.1-2 m/s;
barium carbonate and SO 3 The molar ratio is 1:1, the molar amount of the heavy metal removing agent is 5 times of that of the heavy metal contained in the dilute phosphoric acid A, potassium hydroxide is added to adjust the pH value to 7.0, solid-liquid separation is carried out, and the dilute phosphoric acid B is concentrated by adopting steam wall heat exchange under the steam pressure of 1MPa to obtain concentrated phosphoric acid A with the mass fraction of 55%.
(3) Concentrating, crystallizing and separating a product: adding potassium hydroxide, potassium carbonate, potassium bicarbonate or thermal phosphoric acid into the concentrated phosphoric acid A until the pH value is 4.8, carrying out heat exchange by adopting a steam partition wall to concentrate slurry, adding the concentrated slurry into a crystallizer, concentrating until the mass fraction of the potassium dihydrogen phosphate is 30-50%, slowly crystallizing at a cooling speed of 20 ℃/h, filtering and separating the crystallized slurry to obtain a solid phase which is a potassium dihydrogen phosphate semi-finished product, and returning the mother liquor to the step (2) for recycling.
(4) And (3) recrystallizing and purifying a product: dissolving the potassium dihydrogen phosphate semi-finished product obtained in the step (3) with water, heating to 80 ℃, crystallizing the potassium dihydrogen phosphate at a cooling speed of 20 ℃/hour after the concentration of the potassium dihydrogen phosphate reaches saturation, filtering, separating and crystallizing to obtain a potassium dihydrogen phosphate product, and returning the mother liquor to the step (3) for recycling.
The purity of the obtained high-purity gypsum is 97.1 percent, the whiteness is 92.1 percent, the monopotassium phosphate reaches the food-grade national standard GB 25560-.
Example 3
(1) Preparing high-purity gypsum by sulfuric acid extraction: adding water into calcium hydrogen phosphate to prepare slurry with solid content of 50%, adding concentrated sulfuric acid into a reaction tank containing the slurry, and controlling SO in a reaction system 3 The mass fraction is 2 percent, the reaction is carried out for 4 hours at the temperature of 75 ℃, the high-purity gypsum is obtained by washing and filtering after the reaction is finished, and the liquid phase is diluted phosphoric acid A.
(2) Removing impurities from dilute phosphoric acid and concentrating to prepare concentrated phosphoric acid: preparing slurry with solid content of 30% by using barium carbonate serving as a desulfurizing agent, and mixing dilute phosphoric acid A, the slurry serving as the desulfurizing agent and a potassium hydroxide solution serving as a heavy metal removal agent (the mass fraction of the potassium hydroxide solution serving as a solvent is 0.5%) until complete precipitation is achieved, wherein the reaction temperature is 50 ℃ and the reaction time is 3 hours; the stirring speed is 0.1-2 m/s;
barium carbonate and SO 3 The molar ratio is 1:1, the molar amount of the heavy metal removing agent is 5 times of that of the heavy metal contained in the dilute phosphoric acid A, potassium hydroxide is added to adjust the pH value to 5.0, solid-liquid separation is carried out, and the dilute phosphoric acid B is concentrated by adopting steam wall heat exchange under the steam pressure of 1MPa to obtain the concentrated phosphoric acid A with the mass fraction of 44%.
(3) Concentrating, crystallizing and separating a product: adding potassium hydroxide, potassium carbonate, potassium bicarbonate or thermal phosphoric acid into the concentrated phosphoric acid A until the pH value is 4, carrying out heat exchange on the concentrated slurry by adopting a steam partition wall, adding the concentrated slurry into a crystallizer, concentrating until the mass fraction of the potassium dihydrogen phosphate is 30-50%, slowly crystallizing at a cooling speed of 10 ℃/h, filtering and separating the crystallized slurry to obtain a solid phase which is a potassium dihydrogen phosphate semi-finished product, and returning the mother liquor to the step (2) for recycling.
(4) And (3) recrystallizing and purifying a product: dissolving the potassium dihydrogen phosphate semi-finished product obtained in the step (3) with water, heating to 70 ℃ to saturate the concentration of the potassium dihydrogen phosphate, crystallizing the potassium dihydrogen phosphate at a cooling speed of 15 ℃/h, filtering, separating and crystallizing to obtain a potassium dihydrogen phosphate product, and returning the mother liquor to the step (3) for recycling.
The purity of the obtained high-purity gypsum is 97.5%, the whiteness is 92.8%, the monopotassium phosphate reaches the food-grade national standard GB25560-2010, the purity is 98.6%, and the heavy metals in the waste liquid left after the high-purity gypsum and the monopotassium phosphate are prepared are low in arsenic and lead content, wherein the arsenic content is 2ppm, and the lead content is 1 ppm.
Example 4
(1) Preparing high-purity gypsum by sulfuric acid extraction: adding water into calcium hydrogen phosphate to prepare slurry with solid content of 60%, adding concentrated sulfuric acid into a reaction tank containing the slurry, and controlling SO in a reaction system 3 The mass fraction is 1.5%, the reaction is carried out for 3 hours at the temperature of 70-85 ℃, the high-purity gypsum is obtained by washing and filtering after the reaction is finished, and the liquid phase is dilute phosphoric acid A.
(2) Preparing slurry with solid content of 50% by using barium carbonate serving as a desulfurizing agent, and mixing dilute phosphoric acid A, the slurry serving as the desulfurizing agent and a potassium hydroxide solution serving as a heavy metal removal agent (the mass fraction of the potassium hydroxide solution serving as a solvent is 0.3%) until complete precipitation is achieved, wherein the reaction temperature is 55 ℃ and the reaction time is 2 hours; the stirring speed is 0.1-2 m/s;
barium carbonate and SO 3 The molar ratio is 1:1, the molar amount of the heavy metal removing agent is 3 times of that of the heavy metal contained in the dilute phosphoric acid A, potassium hydroxide is added to adjust the pH value to 6.0, solid-liquid separation is carried out, and the dilute phosphoric acid B is concentrated by adopting steam wall heat exchange under the steam pressure of 0.6MPa to obtain concentrated phosphoric acid A with the mass fraction of 40%.
(3) Concentrating, crystallizing and separating a product: adding potassium hydroxide, potassium carbonate, potassium bicarbonate or thermal phosphoric acid into the concentrated phosphoric acid A until the pH value is 4.5, carrying out steam partition wall heat exchange to concentrate slurry, adding the concentrated slurry into a crystallizer, concentrating until the mass fraction of the monopotassium phosphate is 30-50%, slowly crystallizing at the cooling speed of 10 ℃/hour, filtering and separating the crystallized slurry to obtain a solid phase which is a monopotassium phosphate semi-finished product, and returning the mother liquor to the step (2) for recycling.
(4) And (3) recrystallizing and purifying a product: dissolving the potassium dihydrogen phosphate semi-finished product obtained in the step (3) with water, heating to 65 ℃ to saturate the concentration of the potassium dihydrogen phosphate, crystallizing the potassium dihydrogen phosphate at a cooling speed of 10 ℃/h, filtering, separating and crystallizing to obtain a potassium dihydrogen phosphate product, and returning the mother liquor to the step (3) for recycling.
The purity of the obtained high-purity gypsum is 96.7%, the whiteness is 91.5%, the monopotassium phosphate reaches the food-grade national standard GB25560-2010, the purity is 98.8%, and the heavy metals in the waste liquid left after the high-purity gypsum and the monopotassium phosphate are prepared are low in arsenic and lead content, wherein the arsenic content is 1.5ppm, and the lead content is 0.5 ppm.
Comparative example 1
(1) Adding water into the calcium hydrogen phosphate reclaimed material for pulping to obtain reclaimed material slurry with the solid content of 70 percent, adding the reclaimed material slurry into a reaction tank, adding concentrated sulfuric acid into the reaction tank, and controlling SO in a reaction system 3 The concentration is 6 percent, the reaction is carried out for 6 hours at the temperature of 100 ℃, the high-purity gypsum is obtained by washing and filtering after the reaction is finished, and the liquid phase is dilute phosphoric acid A.
Steps (2) to (4) were the same as in example 1.
The purity of the obtained high-purity gypsum is 94.5%, and the whiteness is 88.2%.
Comparative example 2
Compared with example 1, the desulfurizing agent in (2) has solid content, barium carbonate and SO 3 The molar ratio is different.
Dilute phosphoric acid A was obtained according to the procedure (1) in example 1.
(2) Removing impurities from dilute phosphoric acid and concentrating to prepare concentrated phosphoric acid: preparing slurry with solid content of 70% by using barium carbonate serving as a desulfurizing agent, and mixing dilute phosphoric acid A, the slurry serving as the desulfurizing agent and a potassium hydroxide solution (the mass fraction of a potassium hydroxide solution serving as a solvent) serving as a heavy metal removing agent until precipitation is complete, wherein the reaction temperature is 40 ℃, and the reaction time is 0.5 h; the stirring speed is 0.1-2 m/s;
barium carbonate and SO 3 The molar ratio is 2:1, the molar amount of the heavy metal removing agent is 3 times of that of the heavy metal contained in the dilute phosphoric acid A, potassium hydroxide is added to adjust the pH value to 4.0, solid-liquid separation is carried out, and the dilute phosphoric acid B is concentrated by adopting steam wall heat exchange under the steam pressure of 0.6MPa to obtain the concentrated phosphoric acid A with the mass fraction of 33%.
Steps (3) and (4) were the same as in example 1.
The purity of the obtained monopotassium phosphate is 97.2 percent, and the arsenic content and the lead content in the heavy metal in the waste liquid left after the high-purity gypsum and the monopotassium phosphate are prepared are 8ppm and 9ppm respectively.
Comparative example 3
The concentrated phosphoric acid A solution before concentration in (3) had a different pH value compared with that in example 1.
Concentrated phosphoric acid A was obtained according to the steps (1) and (2) of example 1.
(3) Concentrating, crystallizing and separating a product: adding potassium hydroxide, potassium carbonate, potassium bicarbonate or thermal phosphoric acid into the concentrated phosphoric acid A until the pH value is 3, carrying out heat exchange on the concentrated slurry by adopting a steam partition wall, adding the concentrated slurry into a crystallizer, concentrating until the mass fraction of the potassium dihydrogen phosphate is 30-50%, slowly crystallizing at a cooling speed of 5 ℃/h, filtering and separating the crystallized slurry to obtain a solid phase which is a potassium dihydrogen phosphate semi-finished product, and returning the mother liquor to the step (2) for recycling.
(4) The same as in example 1.
The purity of the obtained potassium dihydrogen phosphate is 95.4%.
Comparative example 4
The concentrated phosphoric acid A solution before concentration in (3) had a different pH value compared with that in example 1.
Concentrated phosphoric acid A was obtained according to the steps (1) and (2) of example 1.
(3) Concentrating, crystallizing and separating a product: adding potassium hydroxide, potassium carbonate, potassium bicarbonate or thermal phosphoric acid into the concentrated phosphoric acid A until the pH value is 6, carrying out heat exchange on the concentrated slurry by adopting a steam partition wall, adding the concentrated slurry into a crystallizer, concentrating until the mass fraction of the potassium dihydrogen phosphate is 30-50%, slowly crystallizing at a cooling speed of 5 ℃/h, filtering and separating the crystallized slurry to obtain a solid phase which is a potassium dihydrogen phosphate semi-finished product, and returning the mother liquor to the step (2) for recycling.
(4) The same as in example 1.
The purity of the obtained potassium dihydrogen phosphate is 95.7%.
Comparative example 5
The heating temperature and the cooling rate in (4) were different from those in example 1.
Concentrated phosphoric acid A was obtained according to the steps (1), (2) and (3) of example 1.
(4) And (3) recrystallizing and purifying a product: dissolving the potassium dihydrogen phosphate semi-finished product obtained in the step (3) with water, heating to 100 ℃, crystallizing the potassium dihydrogen phosphate at a cooling speed of 30 ℃/hour after the concentration of the potassium dihydrogen phosphate reaches saturation, filtering, separating and crystallizing to obtain a potassium dihydrogen phosphate product, and returning the mother liquor to the step (3) for recycling.
The purity of the obtained potassium dihydrogen phosphate is 97.4%.
The purity of the high-purity gypsum obtained by the method is 96.7-97.5%, the whiteness is 91.5-92.8%, all indexes are superior to those of natural gypsum, the monopotassium phosphate reaches the food-grade national standard GB 25560-.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.
Claims (10)
1. A method for producing food-grade monopotassium phosphate and co-producing high-purity gypsum by utilizing feed-grade calcium hydrophosphate is characterized by comprising the following steps:
(1) mixing feed-grade calcium hydrophosphate slurry and concentrated sulfuric acid for reaction, and carrying out solid-liquid separation to obtain dilute phosphoric acid A;
(2) mixing the dilute phosphoric acid A, desulfurizer slurry and an alkaline solution of a heavy metal remover until the precipitation is complete, adding alkali or alkali liquor to adjust the pH value, carrying out solid-liquid separation, and concentrating the liquid phase to obtain concentrated phosphoric acid A; (ii) a
(3) Mixing the concentrated phosphoric acid A with alkali or phosphoric acid until the pH value is 3.5-5, concentrating, cooling and crystallizing to obtain a monopotassium phosphate semi-finished product; (ii) a
(4) And recrystallizing the potassium dihydrogen phosphate semi-finished product.
2. The method according to claim 1, wherein in (1), the mixing reaction conditions of the feed grade calcium hydrophosphate slurry and the concentrated sulfuric acid are as follows: reacting for 2-6 h at 60-90 ℃;
further, SO in the reaction system is controlled in the reaction process 3 The mass fraction is 0.1-7%.
3. The method according to claim 1, wherein in (1), the reaction conditions are: the temperature is 70-85 ℃, and the time is 2-6 h;
the solid content of the feed-grade calcium hydrophosphate slurry is 30-80%, and preferably 40-70%.
4. The method according to claim 1, wherein in the step (2), the solid content of the desulfurizer slurry is 5 to 70 percent, preferably 10 to 60 percent;
the desulfurizer is barium carbonate; the heavy metal remover is selected from one of potassium sulfide, sodium sulfide, phosphorus pentasulfide and hydrogen sulfide;
further, the solvent in the alkaline solution in the heavy metal remover is potassium hydroxide.
5. The method according to claim 1, wherein in the step (2), the barium carbonate is SO 3 The molar ratio is 1: 1; the molar amount of the heavy metal removing agent is 3-5 times of that of the heavy metal contained in the dilute phosphoric acid A; the mass fraction of the heavy metal remover alkaline solution is 0.1-5%.
6. The method of claim 1, wherein in step (2), the reaction conditions of the mixing are as follows: the temperature is 40-60 ℃, the time is 0.5-3 h, and the steam pressure is 0.6-1.0 MPa;
further, the stirring speed during mixing is 0.1-2 m/s.
7. The method of claim 1, wherein in the step (2), the solute of the alkali or lye for adjusting the pH value is selected from one or more of potassium hydroxide, potassium carbonate and potassium bicarbonate.
8. The method according to claim 1, wherein in the step (2), the concentrated phosphoric acid A is concentrated to 33-55% by mass.
9. The method according to claim 1, wherein in the step (3), the alkali or phosphoric acid is used in an amount of 3.8 to 4.8 in terms of pH; the phosphoric acid is hot phosphoric acid;
further, in the step (3), the mixture is concentrated until the mass fraction of the monopotassium phosphate is 30-50% and then cooled, and preferably, the mixture is concentrated until the mass fraction of the monopotassium phosphate is 35-40% and then cooled;
further, the cooling rate is 5-20 ℃/hour.
10. The method according to claim 1, wherein in the step (4), the recrystallization comprises the steps of dissolving, cooling and crystallizing; the amount of the dissolved solvent is used for saturating the potassium dihydrogen phosphate; the dissolving temperature is 60-80 ℃.
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| CN115535979A (en) * | 2022-10-18 | 2022-12-30 | 新希望化工投资有限公司 | Potassium dihydrogen phosphate and method for preparing potassium dihydrogen phosphate by using calcium hydrophosphate |
| CN115676788A (en) * | 2022-10-18 | 2023-02-03 | 新希望化工投资有限公司 | High-purity monopotassium phosphate and preparation method thereof |
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| CN115676788B (en) * | 2022-10-18 | 2024-02-02 | 新希望化工投资有限公司 | High-purity potassium dihydrogen phosphate and preparation method thereof |
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