A method for preparing potassium dihydrogen phosphate by using raffinate acid

Abstract

The application provides a method for preparing potassium dihydrogen phosphate by using raffinate acid, and belongs to the technical field of fine phosphate production. The method for preparing potassium dihydrogen phosphate by using raffinate acid comprises the following steps: mixing raffinate acid and a purifying agent, carrying out impurity removal and purification to obtain purified raffinate acid; the purifying agent comprises ethanol, n-propanol and isopropanol; mixing the purified raffinate acid and phosphate rock powder, carrying out acidolysis reaction, and then filtering to obtain insoluble impurities and a filtrate; carrying out crystallization on the filtrate to obtain heavy calcium; carrying out defluorination on the heavy calcium to obtain defluorinated heavy calcium; mixing the defluorinated heavy calcium, a potassium salt and water, carrying out double decomposition reaction, and then filtering to obtain potassium dihydrogen phosphate and a calcium salt. The water purifying agent used in the application has a polarity lower than that of the raffinate acid, and can form a co-mixed system with the raffinate acid; the solubility of strong polar substances such as metal phosphates in the raffinate acid is lower in the co-mixed system, and the strong polar substances can form a precipitate and be separated, so that the raffinate acid can be purified and impurities removed.

Description

Technical Field

[0001] This invention belongs to the field of fine phosphate production technology, specifically relating to a method for preparing potassium dihydrogen phosphate using residual raffinate. Background Technology

[0002] Among various phosphoric acid purification processes, solvent extraction has become the mainstream process for producing refined phosphoric acid in domestic phosphate chemical enterprises due to its advantages of high capacity, low energy consumption, and low pollution. Solvent extraction utilizes the difference in partition coefficients between phosphoric acid and various impurity ions in the organic and aqueous phases of wet-process phosphoric acid. Phosphoric acid is extracted into the organic phase for purification and impurity removal, and then back-extracted to obtain refined phosphoric acid. However, 40-45% of the phosphoric acid remains in the aqueous phase after extraction, and impurity ions that are insoluble or slightly soluble in organic solvents, as well as solids, are enriched in the aqueous phase, forming raffinate with high viscosity, high impurities, and high solids content.

[0003] Currently, domestic phosphate chemical companies mainly recover phosphorus resources from raffinate by using it as a raw material to produce fertilizer-grade ammonium phosphate. However, due to factors such as overcapacity in phosphate compound fertilizers and large fluctuations in market prices, the advantages of using raffinate to produce ammonium phosphate are gradually decreasing. Therefore, how to process raffinate to increase its added value has become an urgent technical problem to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing potassium dihydrogen phosphate using residual raffinate. The method provided by this invention enables the preparation of potassium dihydrogen phosphate using residual raffinate, thereby increasing the added value of the residual raffinate.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing potassium dihydrogen phosphate using residual raffinate, comprising the following steps:

[0007] (1) Mix the residual raffinate and the purifying agent to purify and remove impurities, and obtain purified residual raffinate; the purifying agent includes ethanol, n-propanol and isopropanol;

[0008] (2) The purified residual acid obtained in step (1) is mixed with phosphate rock powder, and acid hydrolysis reaction is carried out. Then the mixture is filtered to obtain insoluble impurities and filtrate.

[0009] (3) Crystallize the filtrate obtained in step (2) to obtain heavy calcium carbonate;

[0010] (4) The heavy calcium carbonate obtained in step (3) is defluorinated to obtain defluorinated heavy calcium carbonate;

[0011] (5) Mix the defluorinated heavy calcium, potassium salt and water obtained in step (4) and carry out a metathesis reaction, then filter to obtain potassium dihydrogen phosphate and calcium salt.

[0012] Preferably, in step (1), the volume ratio of ethanol to n-propanol is (1~2.5):1, and the volume ratio of ethanol to isopropanol is (1~5):1.

[0013] Preferably, in step (1), the volume ratio of the purifying agent to the residual acid is (1~5):1.

[0014] Preferably, the purification temperature in step (1) is 40~70℃ and the purification time is 60~150min.

[0015] Preferably, in step (2), the mass ratio of purified residual acid to phosphate rock powder is (4~6):1.

[0016] Preferably, the acid hydrolysis reaction in step (2) is carried out at a temperature of 75~85℃ and for a time of 90~140min.

[0017] Preferably, the defluorination temperature in step (4) is 50~80℃ and the defluorination time is 1~2 days.

[0018] Preferably, the substance used for defluorination in step (4) is phosphate rock powder, and the mass of the phosphate rock powder is 1 to 2% of the mass of heavy calcium carbonate.

[0019] Preferably, in step (5), the mass ratio of defluorinated heavy calcium salt to potassium salt is (0.84~0.93):1.

[0020] Preferably, the temperature of the metathesis reaction in step (5) is 45~55℃ and the time of the metathesis reaction is 90~150min.

[0021] This invention provides a method for preparing potassium dihydrogen phosphate using residual raffinate, comprising the following steps: mixing residual raffinate and a purifying agent for purification to obtain purified residual raffinate; the purifying agent includes ethanol, n-propanol, and isopropanol; mixing the purified residual raffinate with phosphate rock powder for acid hydrolysis, followed by filtration to obtain insoluble impurities and filtrate; crystallizing the filtrate to obtain heavy calcium carbonate; defluorinating the heavy calcium carbonate to obtain defluorinated heavy calcium carbonate; mixing the defluorinated heavy calcium carbonate, potassium salt, and water for metathesis reaction, followed by filtration to obtain potassium dihydrogen phosphate and calcium salt. The water purification agent used in this invention includes ethanol, n-propanol, and isopropanol, which have lower polarity than raffinate and can form a co-mixing system with it. The various highly polar substances in the raffinate, such as metal phosphates, have lower solubility in this system and will precipitate out, thus purifying the raffinate. The purified raffinate is then mixed with phosphate rock powder for acid hydrolysis, followed by filtration and crystallization to obtain heavy calcium carbonate (HCC) with calcium dihydrogen phosphate as the main component. After defluorination to remove fluorine impurities, it undergoes a metathesis reaction with potassium salt to obtain potassium dihydrogen phosphate. This method of preparing potassium dihydrogen phosphate using raffinate increases the added value of the raffinate. Experimental results show that the purity of potassium dihydrogen phosphate obtained using the method provided by this invention reaches 99.2%, and the P2O5 recovery rate reaches 94.3%. Attached Figure Description

[0022] Figure 1 This is a process flow diagram of the preparation of potassium dihydrogen phosphate using residual raffinate according to the present invention. Detailed Implementation

[0023] This invention provides a method for preparing potassium dihydrogen phosphate using residual raffinate, comprising the following steps:

[0024] (1) Mix the residual raffinate and the purifying agent to purify and remove impurities, and obtain purified residual raffinate; the purifying agent includes ethanol, n-propanol and isopropanol;

[0025] (2) The purified residual acid obtained in step (1) is mixed with phosphate rock powder, and acid hydrolysis reaction is carried out. Then the mixture is filtered to obtain insoluble impurities and filtrate.

[0026] (3) Crystallize the filtrate obtained in step (2) to obtain heavy calcium carbonate;

[0027] (4) The heavy calcium carbonate obtained in step (3) is defluorinated to obtain defluorinated heavy calcium carbonate;

[0028] (5) Mix the defluorinated heavy calcium, potassium salt and water obtained in step (4) and carry out a metathesis reaction, then filter to obtain potassium dihydrogen phosphate and calcium salt.

[0029] Unless otherwise specified, the present invention does not have any special limitations on the source of the raw materials used, and commercially available products or well-known preparation methods familiar to those skilled in the art can be used.

[0030] The method provided by this invention is applicable to the residual acid, a byproduct obtained from the purification of wet-process phosphoric acid. This invention does not impose any specific limitations on the composition of the residual acid; any residual acid well-known to those skilled in the art can be used.

[0031] This invention involves mixing residual raffinate and a purifying agent to purify and remove impurities, thereby obtaining purified residual raffinate.

[0032] In this invention, the purifying agent comprises ethanol, n-propanol, and isopropanol; the preferred volume ratio of ethanol to n-propanol is (1~2.5):1; the preferred volume ratio of ethanol to isopropanol is (1~5):1. The water purification agent used in this invention comprises ethanol, n-propanol, and isopropanol, which have lower polarity than raffinate, yet can form a co-mixing system with raffinate. Various highly polar substances such as metal phosphates in the raffinate have lower solubility in this system, resulting in precipitation and thus achieving purification and impurity removal from the raffinate. By controlling the volume ratios of ethanol to n-propanol and ethanol to isopropanol within the aforementioned ranges, the polarity of the purifying agent solution can be adjusted, thereby regulating the rate of co-mixing with the raffinate and the precipitation effect of metal phosphate impurities, thereby improving the purification and impurity removal effect.

[0033] In one embodiment, the volume ratio of ethanol to n-propanol can be 1.5:1 or 2:1; the volume ratio of ethanol to isopropanol can be 2:1, 2.5:1, 3:1 or 4:1.

[0034] In this invention, the preferred volume ratio of the purifying agent to the residual raffinate is (1~5):1. As one embodiment, the volume ratio of the purifying agent to the residual raffinate can be 1.8:1, 2:1, 3:1, or 4:1. Limiting the volume ratio of the purifying agent to the residual raffinate within the above range further improves the purification and impurity removal effect.

[0035] The present invention does not have any special limitations on the operation of mixing the residual acid and the purifying agent; any technical solution for preparing the mixture well known to those skilled in the art can be used.

[0036] In this invention, the preferred purification temperature is 40-70°C; the preferred purification time is 60-150 min. As one embodiment, the purification temperature can be 45°C, 50°C, 55°C, 60°C, or 65°C; the purification time can be 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, or 140 min. Limiting the purification temperature and time to the above ranges further improves the purification effect.

[0037] In this invention, the purification and impurity removal are preferably carried out under stirring conditions. This invention does not impose a particular limitation on the stirring rate; stirring operations well-known to those skilled in the art can be used.

[0038] After purification and impurity removal, the present invention preferably filters and evaporates the product obtained by purification and impurity removal in sequence to obtain purified residual acid.

[0039] The present invention does not impose any special limitations on the filtration operation; any operation well known to those skilled in the art can be used to obtain the filtrate.

[0040] In this invention, the vacuum degree of the evaporation and concentration is preferably 0.05~0.08 MPa; the temperature of the evaporation and concentration is preferably 50~80℃. This invention does not have a specific limitation on the evaporation and concentration time; evaporation and concentration until the TOC (total organic carbon) content in the residual acid is <0.5% is sufficient. This invention uses evaporation and concentration to remove the purifying agent from the residual acid, achieving the recovery of the purifying agent.

[0041] In one embodiment, the vacuum degree of the evaporation and concentration can be 0.06 MPa or 0.07 MPa; the temperature of the evaporation and concentration can be 55°C, 60°C, 65°C, 70°C or 75°C.

[0042] After obtaining purified residual acid, the present invention mixes the purified residual acid with phosphate rock powder, performs acid hydrolysis reaction, and then filters to obtain insoluble impurities and filtrate.

[0043] In this invention, the reaction equation for the acidolysis reaction is as follows:

[0044] 7H3PO4+Ca5(PO4)3F=5Ca(H2PO4)2+HF.

[0045] In this invention, the preferred mass content of phosphorus pentoxide in the phosphate rock powder is 29.3% to 33.6%; the preferred particle size of the phosphate rock powder is 25 to 149 μm. As one embodiment, the mass content of phosphorus pentoxide in the phosphate rock powder can be 29.5%, 30.0%, 30.5%, 31.0%, 31.5%, 32.0%, 32.5%, 33.0%, or 33.5%; the particle size of the phosphate rock powder can be 34.3 μm.

[0046] In this invention, the preferred mass ratio of purified raffinate acid to phosphate rock powder is (4~6):1. As one embodiment, the mass ratio of purified raffinate acid to phosphate rock powder can be 4.5:1, 5:1, or 5.5:1.

[0047] The present invention does not have any special limitations on the operation of mixing the purified residual acid with phosphate rock powder; any technical solution for preparing the mixture well known to those skilled in the art can be used.

[0048] In this invention, the preferred temperature for the acidolysis reaction is 75-85°C; the preferred time for the acidolysis reaction is 90-140 min. As one embodiment, the temperature for the acidolysis reaction can be 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, or 84°C; the preferred time for the acidolysis reaction can be 100 min, 110 min, 120 min, or 130 min. By limiting the temperature and time of the acidolysis reaction to the above ranges, this invention can increase the degree of acidolysis, thereby increasing the content of calcium dihydrogen phosphate in the superphosphate.

[0049] In this invention, the acidolysis reaction is preferably carried out under stirring conditions. This invention does not impose a particular limitation on the stirring rate; any stirring operation well-known to those skilled in the art can be used.

[0050] The present invention does not impose any special limitations on the filtration operation; any operation well known to those skilled in the art can be used to obtain the filtrate.

[0051] After obtaining the filtrate, the present invention crystallizes the filtrate to obtain heavy calcium carbonate.

[0052] In this invention, the crystallization is preferably carried out by cooling crystallization; the cooling crystallization is preferably carried out by naturally cooling to room temperature, followed by aging and filtration.

[0053] In this invention, the aging time is preferably 2 to 3 hours. As one embodiment, the aging time can be 2.5 hours.

[0054] The present invention does not impose any special limitations on the filtration operation; any operation known to those skilled in the art can be used to obtain the filter residue.

[0055] After obtaining the heavy calcium carbonate, the present invention defluorinates the heavy calcium carbonate to obtain defluorinated heavy calcium carbonate.

[0056] In this invention, the material used for defluorination is preferably phosphate rock powder; the mass of the phosphate rock powder is preferably 1-2% of the mass of the heavy calcium carbonate. As one embodiment, the mass of the phosphate rock powder can be 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, or 1.9% of the mass of the heavy calcium carbonate. Limiting the mass of the phosphate rock powder within the above range further improves the defluorination effect.

[0057] In this invention, the preferred mass content of phosphorus pentoxide in the phosphate rock powder is 29.3% to 33.6%; the preferred particle size of the phosphate rock powder is 25 to 149 μm. As one embodiment, the mass content of phosphorus pentoxide in the phosphate rock powder can be 29.5%, 30.0%, 30.5%, 31.0%, 31.5%, 32.0%, 32.5%, 33.0%, or 33.5%; the particle size of the phosphate rock powder can be 34.3 μm.

[0058] In this invention, the defluorination temperature is preferably 50-80°C; the defluorination time is preferably 1-2 days. Limiting the defluorination temperature and time to the above ranges further improves the defluorination effect.

[0059] In one embodiment, the defluorination temperature can be 55°C, 60°C, 65°C, 70°C, or 75°C; the defluorination time can be 1.5 days.

[0060] After obtaining the defluorinated calcium carbonate, the present invention mixes the defluorinated calcium carbonate, potassium salt and water, performs a metathesis reaction, and then filters to obtain potassium dihydrogen phosphate and calcium salt.

[0061] In this invention, the potassium salt is preferably potassium sulfate; the preferred mass ratio of the defluorinated calcium carbonate to the potassium salt is (0.84~0.93):1. As one embodiment, the mass ratio of the defluorinated calcium carbonate to the potassium salt can be 0.85:1, 0.86:1, 0.87:1, 0.88:1, 0.89:1, 0.90:1, 0.91:1, or 0.92:1. Limiting the mass ratio of the defluorinated calcium carbonate to the potassium salt within the above range further enhances the degree of metathesis reaction and increases the yield.

[0062] In this invention, the preferred mass ratio of the total mass of the defluorinated calcium carbonate and potassium salt to water is 1:(3~6). As one embodiment, the mass ratio of the total mass of the defluorinated calcium carbonate and potassium salt to water can be 1:4, 1:4.5, or 1:5. The use of water in this invention facilitates slurry preparation, which is beneficial for the metathesis reaction.

[0063] The present invention does not have any special limitations on the operation of mixing the defluorinated heavy calcium carbonate, potassium salt and water, and any technical solution for preparing the mixture well known to those skilled in the art can be used.

[0064] In this invention, the preferred temperature for the metathesis reaction is 45-55°C; the preferred time for the metathesis reaction is 90-150 min. As one embodiment, the temperature for the metathesis reaction can be 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, or 54°C; the preferred time for the metathesis reaction can be 100 min, 110 min, 120 min, 130 min, or 140 min. By limiting the temperature and time of the metathesis reaction to the above ranges, this invention can further increase the extent of the metathesis reaction, thereby increasing the yield of potassium dihydrogen phosphate.

[0065] The present invention does not impose any special limitations on the filtering operation; any operation known to those skilled in the art can be used.

[0066] After filtration, the present invention preferably performs crystallization and first filtration on the filtrate obtained by filtration in sequence to obtain impurities and first filtrate. Then, the first filtrate is subjected to evaporation and concentration, cooling and crystallization, second filtration, washing and drying in sequence to obtain potassium dihydrogen phosphate.

[0067] In this invention, the pH value during crystallization is preferably 4.5-5; the pH value is preferably adjusted using potassium carbonate; the crystallization temperature is preferably 40-60℃, more preferably 50℃. As one embodiment, the pH value can be 4.6, 4.7, 4.8, or 4.9. This invention utilizes crystallization to ensure that all phosphorus in the filtrate is converted to hydrogen sulfide (H₂PO₄). - It exists in the form of K + The combination generates KH2PO4 crystals, which precipitate out and thus improves the yield of potassium dihydrogen phosphate.

[0068] The present invention does not impose any special limitations on the operation of the first filtering; any operation known to those skilled in the art can be used.

[0069] The present invention does not impose any special limitations on the temperature and time of the evaporation and concentration, and the concentration is made up to the point that the P2O5 concentration in the filtrate is ≥19.95%.

[0070] In this invention, the cooling crystallization is preferably carried out by natural cooling to room temperature, followed by aging; the aging time is preferably 2-3 hours. This invention does not have any particular limitation on the natural cooling to room temperature operation; any operation well-known to those skilled in the art can be used. As one embodiment, the aging time can be 2.5 hours.

[0071] The present invention does not impose any special limitations on the operation of the second filtering; any operation known to those skilled in the art can be used.

[0072] The present invention does not impose any special limitations on the washing operation; washing until neutral is sufficient.

[0073] The present invention does not impose any special limitations on the drying operation; drying to a constant weight is sufficient.

[0074] The method provided by this invention can solve the current difficulties in utilizing residual acid and the low added value of the product, and provides a new production process for preparing potassium dihydrogen phosphate from residual acid, thus promoting the sustainable development of the wet process phosphate chemical industry.

[0075] This invention uses residual phosphate rock, phosphate rock powder, and potassium sulfate as raw materials to produce potassium dihydrogen phosphate, and the produced potassium dihydrogen phosphate meets the requirements of fertilizer grade superior products specified in HG / T 2321-2016.

[0076] The process flow diagram for preparing potassium dihydrogen phosphate using residual raffinate in this invention is shown below. Figure 1 As shown. From Figure 1 As can be seen, the residual raffinate and the purifying agent are mixed for purification and impurity removal to obtain purified residual raffinate; then the purifying agent is recovered by evaporation and concentration, and then mixed with phosphate rock powder for acid hydrolysis reaction, followed by filtration to obtain insoluble impurities and filtrate; the filtrate is cooled and crystallized (precipitated), and filtered to obtain heavy calcium carbonate; subsequently, the heavy calcium carbonate is defluorinated using phosphate rock powder to obtain defluorinated heavy calcium carbonate; then the defluorinated heavy calcium carbonate, potassium sulfate and water are mixed for metathesis reaction, followed by filtration to obtain filter residue and calcium sulfate; finally, the filter residue is purified and concentrated for crystallization to obtain potassium dihydrogen phosphate.

[0077] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0078] The composition of the residual acid in Examples 1-7 is shown in Table 1.

[0079] Table 1. Composition of residual acid in Examples 1-7

[0080]

[0081] Example 1

[0082] A method for preparing potassium dihydrogen phosphate using residual raffinate comprises the following steps:

[0083] (1) Measure 250 mL of raffinate acid into a 1000 mL three-necked flask, measure 250 mL of ethanol, 250 mL of n-propanol, and 250 mL of isopropanol, mix them evenly, and then heat them in a water bath at 50 °C for 120 min to remove impurities. Then filter to remove insoluble impurities. The filtrate is evaporated and concentrated in a rotary evaporator to recover the purifying agent until the TOC (total organic carbon) content in the raffinate acid is <0.5%, and a purified raffinate acid with a P2O5 content of 45 wt% is obtained. The purification and impurity removal are carried out under stirring conditions. The vacuum degree of evaporation and concentration is 0.05 MPa. The evaporation and concentration temperature is 80 °C.

[0084] (2) Weigh 160g of phosphate rock powder (P2O5 content is 33.5% and particle size is 34.3μm) and 960g of purified raffinate, place them in a three-necked flask, stir at 80℃ for 120min for acid hydrolysis, and then filter while hot to obtain filtrate;

[0085] (3) Cool the filtrate obtained in step (2) to room temperature naturally, then age it for 3 hours, and then filter it to obtain heavy calcium carbonate;

[0086] (4) Mix 80g of the heavy calcium carbonate obtained in step (3) with 0.8g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and defluorinate to obtain defluorinated heavy calcium carbonate; wherein, the defluorination temperature is 60℃ and the defluorination time is 1d;

[0087] (5) Place 50g of the defluorinated heavy calcium carbonate obtained in step (4) into a 500mL three-necked flask, then add 54g of potassium sulfate and 520g of water and mix. Perform a double decomposition reaction at 50℃ for 120min, then filter while hot to obtain calcium sulfate and filtrate. Then add potassium carbonate to the filtrate to adjust the pH value to 5, crystallize at 50℃, filter again, evaporate and concentrate the filtrate to a P2O5 concentration of 19.95%, then cool naturally to room temperature, then age for 3h, then filter, wash with water and dry to obtain potassium dihydrogen phosphate.

[0088] The potassium dihydrogen phosphate prepared in Example 1 had a purity of 99.2 wt%, a K2O mass fraction of 34.3% (calculated from K in potassium dihydrogen phosphate), a chloride mass fraction of 0.08%, a P2O5 recovery rate of 90.3%, water-insoluble matter below the detection limit, and a pH value of 4.6, meeting the requirements for superior fertilizer grade as specified in HG / T 2321-2016.

[0089] Example 2

[0090] A method for preparing potassium dihydrogen phosphate using residual raffinate comprises the following steps:

[0091] (1) Measure 250 mL of raffinate acid into a 1000 mL three-necked flask, measure 375 mL of ethanol, 187.5 mL of n-propanol, and 187.5 mL of isopropanol, mix them evenly, and then heat them in a water bath at 40 °C for 90 min to remove impurities. Then filter to remove insoluble impurities. The filtrate is evaporated and concentrated in a rotary evaporator to recover the purifying agent until the TOC (total organic carbon) content in the raffinate acid is <0.5%, and a purified raffinate acid with a P2O5 content of 45 wt% is obtained. The purification and impurity removal are carried out under stirring conditions. The vacuum degree of evaporation and concentration is 0.06 MPa. The evaporation and concentration temperature is 80 °C.

[0092] (2) Weigh 160g of phosphate rock powder (P2O5 content is 33.5% and particle size is 34.3μm) and 960g of purified raffinate, place them in a three-necked flask, stir at 80℃ for 120min for acid hydrolysis, and then filter while hot to obtain filtrate;

[0093] (3) Cool the filtrate obtained in step (2) to room temperature naturally, then age it for 3 hours, and then filter it to obtain heavy calcium carbonate;

[0094] (4) Mix 80g of the heavy calcium carbonate obtained in step (3) with 0.8g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and defluorinate to obtain defluorinated heavy calcium carbonate; wherein, the defluorination temperature is 50℃ and the defluorination time is 2d;

[0095] (5) Place 50g of the defluorinated heavy calcium carbonate obtained in step (4) into a 500mL three-necked flask, then add 54g of potassium sulfate and 520g of water and mix. Perform a double decomposition reaction at 50℃ for 120min. Then filter while hot to obtain calcium sulfate and filtrate. Then add potassium carbonate to the filtrate to adjust the pH value to 4.8. Perform crystallization at 50℃, filter again, and evaporate and concentrate the filtrate to a P2O5 concentration of 19.95%. Then cool naturally to room temperature and age for 3h. Then filter, wash with water and dry to obtain potassium dihydrogen phosphate.

[0096] The potassium dihydrogen phosphate prepared in Example 2 had a purity of 98.3 wt%, a K2O mass fraction of 34.1% (calculated from K in potassium dihydrogen phosphate), a chloride mass fraction of 0.08%, a P2O5 recovery rate of 89.6%, water-insoluble matter below the detection limit, and a pH value of 4.6, meeting the requirements for superior fertilizer grade as specified in HG / T 2321-2016.

[0097] Example 3

[0098] A method for preparing potassium dihydrogen phosphate using residual raffinate comprises the following steps:

[0099] (1) Measure 250 mL of raffinate acid into a 1000 mL three-necked flask, measure 250 mL of ethanol, 100 mL of n-propanol, and 100 mL of isopropanol, mix them evenly, and then heat them in a water bath at 40 °C for 60 min to remove impurities. Then filter to remove insoluble impurities. The filtrate is evaporated and concentrated in a rotary evaporator to recover the purifying agent until the TOC (total organic carbon) content in the raffinate acid is <0.5%, and a purified raffinate acid with a P2O5 content of 45 wt% is obtained. The purification and impurity removal are carried out under stirring conditions. The vacuum degree of evaporation and concentration is 0.06 MPa. The evaporation and concentration temperature is 60 °C.

[0100] (2) Weigh 160g of phosphate rock powder (P2O5 content is 33.5% and particle size is 34.3μm) and 960g of purified raffinate, place them in a three-necked flask, stir at 80℃ for 120min for acid hydrolysis, and then filter while hot to obtain filtrate;

[0101] (3) Cool the filtrate obtained in step (2) to room temperature naturally, then age it for 3 hours, and then filter it to obtain heavy calcium carbonate;

[0102] (4) Mix 80g of the heavy calcium carbonate obtained in step (3) with 0.8g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and defluorinate to obtain defluorinated heavy calcium carbonate; wherein, the defluorination temperature is 80℃ and the defluorination time is 1d;

[0103] (5) Place 50g of the defluorinated heavy calcium carbonate obtained in step (4) into a 500mL three-necked flask, then add 59.4g of potassium sulfate and 520g of water and mix. Perform a double decomposition reaction at 50℃ for 120min. Then filter while hot to obtain calcium sulfate and filtrate. Then add potassium carbonate to the filtrate to adjust the pH value to 5. Perform crystallization at 50℃. After filtration, evaporate and concentrate the filtrate to a P2O5 concentration of 19.95%. Then cool naturally to room temperature and age for 3h. Then filter, wash with water and dry to obtain potassium dihydrogen phosphate.

[0104] The potassium dihydrogen phosphate prepared in Example 3 had a purity of 98.7 wt%, a K2O mass fraction of 34.2% (calculated from K in potassium dihydrogen phosphate), a chloride mass fraction of 0.12%, a P2O5 recovery rate of 94.3%, water-insoluble matter below the detection limit, and a pH value of 5, meeting the requirements for superior fertilizer grade as specified in HG / T 2321-2016.

[0105] Example 4

[0106] A method for preparing potassium dihydrogen phosphate using residual raffinate comprises the following steps:

[0107] (1) Measure 250 mL of raffinate acid into a 1000 mL three-necked flask, measure 250 mL of ethanol, 250 mL of n-propanol, and 250 mL of isopropanol, mix them evenly, and then heat them in a water bath at 50 °C for 120 min to remove impurities. Then filter to remove insoluble impurities. The filtrate is evaporated and concentrated in a rotary evaporator to recover the purifying agent until the TOC (total organic carbon) content in the raffinate acid is <0.5%, and a purified raffinate acid with a P2O5 content of 45 wt% is obtained. The purification and impurity removal are carried out under stirring conditions. The vacuum degree of evaporation and concentration is 0.06 MPa. The evaporation and concentration temperature is 80 °C.

[0108] (2) Weigh 160g of phosphate rock powder (P2O5 content is 33.5% and particle size is 34.3μm) and 720g of purified raffinate, place them in a three-necked flask, stir at 75℃ for acid hydrolysis reaction for 90min, and then filter while hot to obtain filtrate;

[0109] (3) Cool the filtrate obtained in step (2) to room temperature naturally, then age it for 3 hours, and then filter it to obtain heavy calcium carbonate;

[0110] (4) Mix 80g of the heavy calcium carbonate obtained in step (3) with 0.8g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and defluorinate to obtain defluorinated heavy calcium carbonate; wherein, the defluorination temperature is 50℃ and the defluorination time is 2d;

[0111] (5) Place 50g of the defluorinated heavy calcium carbonate obtained in step (4) into a 500mL three-necked flask, then add 54g of potassium sulfate and 420g of water and mix. Perform a double decomposition reaction at 50℃ for 120min, then filter while hot to obtain calcium sulfate and filtrate. Then add potassium carbonate to the filtrate to adjust the pH value to 4.5, crystallize at 50℃, filter again, evaporate and concentrate the filtrate to a P2O5 concentration of 19.95%, then cool naturally to room temperature, then age for 3h, then filter, wash with water and dry to obtain potassium dihydrogen phosphate.

[0112] The potassium dihydrogen phosphate prepared in Example 4 had a purity of 96.5 wt%, a K2O mass fraction of 33.4% (calculated from K in potassium dihydrogen phosphate), a chloride mass fraction of 0.27%, a P2O5 recovery rate of 93.1%, a water-insoluble matter mass fraction of 0.2%, and a pH value of 4.9, meeting the requirements for superior fertilizer grade products specified in HG / T 2321-2016.

[0113] Example 5

[0114] A method for preparing potassium dihydrogen phosphate using residual raffinate comprises the following steps:

[0115] (1) Measure 250 mL of raffinate acid into a 1000 mL three-necked flask, measure 250 mL of ethanol, 250 mL of n-propanol, and 250 mL of isopropanol, mix them evenly, and then heat them in a water bath at 50 °C for 120 min to remove impurities. Then filter to remove insoluble impurities. The filtrate is evaporated and concentrated in a rotary evaporator to recover the purifying agent until the TOC (total organic carbon) content in the raffinate acid is <0.5%, and a purified raffinate acid with a P2O5 content of 45 wt% is obtained. The purification and impurity removal are carried out under stirring conditions. The vacuum degree of evaporation and concentration is 0.06 MPa. The evaporation and concentration temperature is 80 °C.

[0116] (2) Weigh 160g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and 800g of purified raffinate, place them in a three-necked flask, stir at 80℃ for acid hydrolysis reaction for 120min, and then filter while hot to obtain filtrate;

[0117] (3) Cool the filtrate obtained in step (2) to room temperature naturally, then age it for 3 hours, and then filter it to obtain heavy calcium carbonate;

[0118] (4) Mix 80g of the heavy calcium carbonate obtained in step (3) with 0.8g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and defluorinate to obtain defluorinated heavy calcium carbonate; wherein, the defluorination temperature is 80℃ and the defluorination time is 2d;

[0119] (5) Place 50g of the defluorinated heavy calcium carbonate obtained in step (4) into a 500mL three-necked flask, then add 54g of potassium sulfate and 350g of water and mix. Perform a double decomposition reaction at 55℃ for 90min, then filter while hot to obtain calcium sulfate and filtrate. Then add potassium carbonate to the filtrate at 50℃ to adjust the pH to 5, crystallize at 50℃, filter again, evaporate and concentrate the filtrate to a P2O5 concentration of 19.95%, then cool naturally to room temperature, then age for 3h, then filter, wash with water and dry to obtain potassium dihydrogen phosphate.

[0120] The potassium dihydrogen phosphate prepared in Example 5 had a purity of 98.6 wt%, a K2O mass fraction of 34.1% (calculated from K in potassium dihydrogen phosphate), a chloride mass fraction of 0.16%, a P2O5 recovery rate of 91.8%, water-insoluble matter below the detection limit, and a pH value of 4.4, meeting the requirements for superior fertilizer grade as specified in HG / T 2321-2016.

[0121] Example 6

[0122] A method for preparing potassium dihydrogen phosphate using residual raffinate comprises the following steps:

[0123] (1) Measure 250 mL of raffinate acid into a three-necked flask, measure 780 mL of ethanol, 312 mL of n-propanol, and 158 mL of isopropanol, mix them evenly, and then heat them in a water bath at 50 °C for 120 min to remove impurities. Then filter to remove insoluble impurities. The filtrate is evaporated and concentrated in a rotary evaporator to recover the purifying agent until the TOC (total organic carbon) content in the raffinate acid is <0.5%, and a purified raffinate acid with a P2O5 content of 45 wt% is obtained. The purification and impurity removal are carried out under stirring conditions. The vacuum degree of evaporation and concentration is 0.06 MPa. The evaporation and concentration temperature is 80 °C.

[0124] (2) Weigh 160g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and 960g of purified raffinate, place them in a three-necked flask, stir at 85℃ for acid hydrolysis reaction for 140min, and then filter while hot to obtain filtrate;

[0125] (3) Cool the filtrate obtained in step (2) to room temperature naturally, then age it for 3 hours, and then filter it to obtain heavy calcium carbonate;

[0126] (4) Mix 80g of the heavy calcium carbonate obtained in step (3) with 0.8g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and defluorinate to obtain defluorinated heavy calcium carbonate; wherein, the defluorination temperature is 80℃ and the defluorination time is 1d;

[0127] (5) Place 50g of the defluorinated heavy calcium carbonate obtained in step (4) into a 500mL three-necked flask, then add 54g of potassium sulfate and 420g of water and mix. Perform a double decomposition reaction at 45℃ for 150min, then filter while hot to obtain calcium sulfate and filtrate. Then add potassium carbonate to the filtrate at 50℃ to adjust the pH to 5, crystallize at 50℃, filter again, evaporate and concentrate the filtrate to a P2O5 concentration of 19.95%, then cool naturally to room temperature, then age for 3h, then filter, wash with water and dry to obtain potassium dihydrogen phosphate.

[0128] The potassium dihydrogen phosphate prepared in Example 6 had a purity of 98.7 wt%, a K2O mass fraction of 34.1% (calculated from K in potassium dihydrogen phosphate), a chloride mass fraction of 0.13%, a P2O5 recovery rate of 93.7%, water-insoluble matter below the detection limit, and a pH value of 4.5, meeting the requirements for superior fertilizer grade as specified in HG / T 2321-2016.

[0129] Example 7

[0130] A method for preparing potassium dihydrogen phosphate using residual raffinate comprises the following steps:

[0131] (1) Measure 250 mL of raffinate acid into a 1000 mL three-necked flask, measure 250 mL of ethanol, 250 mL of n-propanol, and 250 mL of isopropanol, mix them evenly, and then heat them in a water bath at 50 °C for 120 min to remove impurities. Then filter to remove insoluble impurities. The filtrate is evaporated and concentrated in a rotary evaporator to recover the purifying agent until the TOC (total organic carbon) content in the raffinate acid is <0.5%, and a purified raffinate acid with a P2O5 content of 45 wt% is obtained. The purification and impurity removal are carried out under stirring conditions. The vacuum degree of evaporation and concentration is 0.08 MPa. The evaporation and concentration temperature is 50 °C.

[0132] (2) Weigh 160g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and 800g of purified raffinate, place them in a three-necked flask, stir at 80℃ for acid hydrolysis reaction for 120min, and then filter while hot to obtain filtrate;

[0133] (3) Cool the filtrate obtained in step (2) to room temperature naturally, then age it for 3 hours, and then filter it to obtain heavy calcium carbonate;

[0134] (4) Mix 80g of the heavy calcium carbonate obtained in step (3) with 0.8g of phosphate rock powder (P2O5 mass content is 33.5% and particle size is 34.3μm) and defluorinate to obtain defluorinated heavy calcium carbonate; wherein, the defluorination temperature is 80℃ and the defluorination time is 1d;

[0135] (5) Place 50g of the defluorinated heavy calcium carbonate obtained in step (4) into a 500mL three-necked flask, then add 54g of potassium sulfate and 616g of water and mix. Perform a double decomposition reaction at 50℃ for 120min, then filter while hot to obtain calcium sulfate and filtrate. Then add potassium carbonate to the filtrate to adjust the pH value to 5, crystallize at 50℃, filter again, evaporate and concentrate the filtrate to a P2O5 concentration of 19.95%, then cool naturally to room temperature, then age for 2h, then filter, wash with water and dry to obtain potassium dihydrogen phosphate.

[0136] The potassium dihydrogen phosphate prepared in Example 7 had a purity of 98.5 wt%, a K2O mass fraction of 34.2% (calculated from K in potassium dihydrogen phosphate), a chloride mass fraction of 0.05%, a P2O5 recovery rate of 92.6%, water-insoluble matter below the detection limit, and a pH value of 4.5, meeting the requirements for superior fertilizer grade as specified in HG / T 2321-2016.

[0137] As can be seen from the above embodiments, the method provided by the present invention can prepare potassium dihydrogen phosphate using residual raffinate, thereby increasing the added value of residual raffinate.

[0138] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing potassium dihydrogen phosphate using residual raffinate, characterized in that, Includes the following steps: (1) Mix the residual raffinate and the purifying agent to purify and remove impurities, and obtain purified residual raffinate; the purifying agent includes ethanol, n-propanol and isopropanol; (2) The purified residual acid obtained in step (1) is mixed with phosphate rock powder, and acid hydrolysis reaction is carried out. Then the mixture is filtered to obtain insoluble impurities and filtrate. (3) Crystallize the filtrate obtained in step (2) to obtain heavy calcium carbonate; (4) The heavy calcium carbonate obtained in step (3) is defluorinated to obtain defluorinated heavy calcium carbonate; (5) Mix the defluorinated heavy calcium, potassium salt and water obtained in step (4) to carry out a metathesis reaction, and then filter to obtain potassium dihydrogen phosphate and calcium salt; In step (1), the volume ratio of the purifying agent to the residual acid is (1~5):1; In step (2), the mass ratio of purified residual acid to phosphate rock powder is (4~6):1; The substance used for defluorination in step (4) is phosphate rock powder, and the mass of the phosphate rock powder is 1-2% of the mass of heavy calcium carbonate. In step (5), the mass ratio of defluorinated heavy calcium carbonate to potassium salt is (0.84~0.93):

1.

2. The method according to claim 1, characterized in that, In step (1), the volume ratio of ethanol to n-propanol is (1~2.5):1, and the volume ratio of ethanol to isopropanol is (1~5):

1.

3. The method according to claim 1, characterized in that, The purification temperature in step (1) is 40~70℃, and the purification time is 60~150min.

4. The method according to claim 1, characterized in that, The acid hydrolysis reaction in step (2) is carried out at a temperature of 75~85℃ and for a time of 90~140min.

5. The method according to claim 1, characterized in that, The defluorination temperature in step (4) is 50~80℃, and the defluorination time is 1~2 days.

6. The method according to claim 1, characterized in that, The temperature of the metathesis reaction in step (5) is 45~55℃, and the reaction time is 90~150min.

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