Preparation process of potassium dihydrogen phosphate and potassium dihydrogen phosphate

Abstract

The application discloses a preparation process of potassium dihydrogen phosphate and the potassium dihydrogen phosphate and belongs to the technical field of potassium dihydrogen phosphate production. The application solves the problem of how to provide a potassium dihydrogen phosphate production method with simple process, low cost, high product purity, low energy consumption and environmental protection. The application comprises the following steps: S1, mixing calcium hydrogen phosphate and hemihydrate phosphoric acid solution under the temperature condition of 70-85 DEG C to obtain a pre-dissolved mixed bottom liquid; S2, mixing a potassium bisulfate solution with the pre-dissolved mixed bottom liquid, keeping the temperature condition of 70-85 DEG C and continuously reacting to obtain a double decomposition liquid and double decomposition residue; S3, desulfurizing the double decomposition liquid to obtain a desulfurized liquid and desulfurized residue; S4, neutralizing and removing impurities from the desulfurized liquid to obtain a potassium dihydrogen phosphate clear liquid; S5, concentrating and crystallizing the potassium dihydrogen phosphate clear liquid to obtain a concentrated and crystallized liquid; and S6, performing solid-liquid separation on the concentrated and crystallized liquid and drying the concentrated and crystallized liquid to obtain a potassium dihydrogen phosphate product. The application can increase the recovery rate of phosphorus and potassium, increase the product purity and reduce the production cost.

Description

Technical Field

[0001] This invention belongs to the field of potassium dihydrogen phosphate production technology, specifically relating to a preparation process of potassium dihydrogen phosphate and potassium dihydrogen phosphate. Background Technology

[0002] Potassium dihydrogen phosphate (chemical formula: KH2PO4) is a highly efficient and pure inorganic compound widely used in agriculture, food, medicine, and industry. Traditional methods for producing potassium dihydrogen phosphate include neutralization, metathesis, and direct acid hydrolysis. Neutralization involves the reaction of phosphoric acid with potassium hydroxide or potassium carbonate. This method has high raw material costs (requiring pure phosphoric acid and potassium alkali) and produces a large amount of wastewater as a byproduct. Metathesis involves the reaction of calcium dihydrogen phosphate with salts such as potassium sulfate, but the product has low purity and is difficult to separate. Direct acid hydrolysis uses phosphate rock (whose main component is fluorapatite, Ca2+) as a raw material. 10 (PO4)6F2 reacts with inorganic acids (such as sulfuric acid, hydrochloric acid, and nitric acid) and then combines with potassium salts, but the product purity is low, there are many by-products, and purification is difficult.

[0003] Industrial production of potassium dihydrogen phosphate typically employs a wet-process phosphoric acid + potassium hydroxide neutralization route. While the process is mature and cost-effective, potassium hydroxide is expensive (compared to potassium chloride and potassium sulfate), and the wet-process phosphoric acid requires purification before use, necessitating additional impurity removal steps, which increases production costs.

[0004] Therefore, developing a simple, low-cost, high-purity, low-energy-consumption, and environmentally friendly method for producing potassium dihydrogen phosphate, and overcoming the shortcomings of existing technologies, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the problem of how to provide a simple, low-cost, high-purity, low-energy-consumption, and environmentally friendly method for producing potassium dihydrogen phosphate, this invention provides a preparation process and potassium dihydrogen phosphate, aiming to increase phosphorus and potassium recovery rates, increase product purity, reduce production costs, and produce a byproduct, gypsum dihydrate, with a whiteness of over 90%, which can be used as an excellent building sound insulation material to generate economic value.

[0006] The technical solution adopted in this invention is as follows:

[0007] A process for preparing potassium dihydrogen phosphate includes the following steps:

[0008] S1: Mix dicalcium phosphate with a hemihydrate phosphoric acid solution at a temperature of 70~85℃ to obtain a pre-dissolved mixed base solution;

[0009] S2: Mix potassium hydrogen sulfate solution with pre-dissolved mixed base liquid, and continue the reaction at a temperature of 70~85℃ to obtain double decomposition solution and double decomposition residue;

[0010] S3: Desulfurize the compounding solution to obtain desulfurized liquid and desulfurized residue;

[0011] S4: Neutralize and remove impurities from the desulfurization liquid to obtain potassium dihydrogen phosphate solution and neutralized filter residue;

[0012] S5: Concentrate and crystallize the potassium dihydrogen phosphate solution to obtain a concentrated crystallized solution;

[0013] S6: After solid-liquid separation and drying of the concentrated crystallization liquid, potassium dihydrogen phosphate product is obtained.

[0014] After adopting this technical solution, dicalcium phosphate and hemihydrate phosphoric acid solution are mixed at a temperature of 70~85℃. This is because if the temperature is too low, the potassium dihydrogen phosphate reacted will crystallize, resulting in large losses, low solution concentration, and increased concentration costs in the later stage; if the temperature is too high, water will be lost quickly, which is not conducive to maintaining the stability of the system.

[0015] Preferably, in S1, the mass ratio of P2O5 contained in dicalcium phosphate to that in the hemihydrate phosphoric acid solution is 1:0.2~0.5, based on the mass of P2O5.

[0016] After adopting this technical solution, the coarse calcium hydride is easily encapsulated by the generated calcium sulfate. When the calcium hydride is ground into finer particles, some of the later-reacting particles are easily encapsulated by the first-generated calcium sulfate. Therefore, phosphoric acid is used to pre-dissolve the calcium hydride to reduce encapsulation and increase the yield of phosphorus. However, excessive hemihydrate phosphoric acid will increase the overall cost. Therefore, the mass ratio of calcium hydride to P2O5 in the hemihydrate phosphoric acid solution is controlled to be 1:0.2~0.5.

[0017] Preferably, in S2, the pre-dissolved mixed base solution and potassium bisulfate solution are mixed in a P:K molar ratio of 1:1.0~1.4, and the mass concentration of potassium bisulfate is controlled at 30%~45%.

[0018] After adopting this technical solution, potassium sulfate is used instead of potassium hydroxide to reduce costs. However, excessive potassium sulfate will reduce the amount of sulfuric acid used. Since the Ca / S ratio is fixed, the P / K ratio needs to be controlled within a certain range to achieve both the lowest cost and a high P recovery rate.

[0019] Preferably, in S1, dicalcium phosphate is added to a hemihydrate phosphoric acid solution for mixing, and the feeding time is 0.5h~1.0h.

[0020] By adopting this technical solution, adding dicalcium phosphate to the hemihydrate phosphoric acid solution can effectively prevent the formation of encapsulation, which would lead to a decrease in decomposition rate and an increase in phosphorus loss rate.

[0021] Preferably, in step S2, potassium bisulfate solution is added to the pre-dissolved mixed substrate for acid hydrolysis, and the potassium bisulfate solution is added dropwise over a period of 1 to 4 hours.

[0022] Furthermore, S2 also includes adding potassium hydrogen sulfate solution to the pre-dissolved mixed base liquid using a peristaltic pump for precise and uniform dripping, adding baffles to the reaction vessel, and using multi-layer stirring to ensure that the slurry can be fully mixed from top to bottom, and reacting for 1 to 4 hours after the addition is completed.

[0023] Preferably, the P2O5 mass concentration of the hemihydrate phosphoric acid solution in S1 is ≥9%, and the particle size of dicalcium phosphate is ≥30 mesh.

[0024] When using this technical solution, the particle size of dicalcium phosphate cannot be too coarse; the larger the mesh number, the finer the particle size.

[0025] As a preferred method, in S2, 98% acid is first slowly added to water and stirred evenly according to a molar ratio of 1:0.5~1, then potassium sulfate is added, and the mixture is heated to 50~80℃ and reacted until it becomes clear and transparent to obtain a potassium bisulfate solution.

[0026] Furthermore, S2 also includes the requirement that after the potassium bisulfate solution reacts until it becomes clear and transparent, it must be kept at a temperature above 40°C to ensure that the potassium bisulfate does not precipitate crystals due to cooling, and the reaction must continue for at least 0.5 hours after the addition of the materials.

[0027] Preferably, in step S3, desulfurization is carried out by adding barium carbonate, and the barium carbonate is added according to the molar ratio of Ba to S in the reaction system of 0.90~1:1; in step S4, the desulfurization liquid is neutralized and impurities are removed by adding potassium hydroxide, and the potassium hydroxide is added according to the molar ratio of K to P of 0.95~1.05:1; in step S5, the potassium dihydrogen precipitate is concentrated to a specific gravity of 1.30~1.50; in step S6, the centrifugation speed is 2000~3000 r / min, the centrifugation time is 3~6 min, the drying temperature is 50~80℃, and the drying time is 2~6 h.

[0028] Furthermore, S3 also includes 30%~60% pre-dissolved barium carbonate (powder, effective content 99%) in the metathesis solution, which is slowly added under stirring to prevent the reaction foam from encapsulating the barium carbonate. After pre-dissolution, the barium carbonate is added dropwise over 2~4 hours using a peristaltic pump, and the reaction is allowed to proceed for more than 0.5 hours after the addition is completed.

[0029] Furthermore, S4 also includes preparing a KOH solution with a mass concentration of 40% to 60% using water, adding it dropwise over 0.5 to 2 hours using a peristaltic pump, and then allowing the reaction to proceed for at least 0.5 hours after the addition is complete.

[0030] Furthermore, the final temperature of cooling crystallization in S5 is 55~65℃, and potassium dihydrogen phosphate product is obtained by centrifugation and drying.

[0031] As a preferred option, the metathesis residue and desulfurization residue obtained in S2 and S3 are subjected to a secondary washing reaction (the filtered filter cake is rinsed with clean water), and the reaction time is 2-4 hours. The resulting washing liquid and filtrate are used as the original liquid for neutralizing the filter cake washing.

[0032] After adopting this technical solution, a certain amount of clean water is used to first stir and wash the metathesis residue and desulfurization residue, and then a certain amount of clean water is used for rinsing to avoid phosphorus and potassium being carried into the filter cake due to the liquid being absorbed. The two liquids are combined and used as the washing liquid for neutralizing the filter cake, and the liquid after washing and neutralizing the filter cake is used as the supplementary liquid for the metathesis reaction.

[0033] Preferably, the neutralized filter residue obtained in S4 is washed with the original solution of the secondary washing reaction for more than 0.5 hours. The filter cake after washing and filtration is rinsed with clean water, and the washing solution and filtrate are used as supplementary solutions for the pre-dissolution reaction in S1.

[0034] Preferably, the centrifuged mother liquor obtained in S6 is returned to S4 for recycling.

[0035] A potassium dihydrogen phosphate, prepared using the same process as potassium dihydrogen phosphate.

[0036] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0037] 1. This invention explores a metathesis method (reaction of dicalcium phosphate with phosphoric acid and potassium salts) as the basic process, using dicalcium phosphate and hemihydrate phosphoric acid as phosphorus sources and potassium sulfate as the potassium source to prepare high-quality potassium dihydrogen phosphate. By optimizing the process route and experimental conditions, potassium dihydrogen phosphate is obtained through multiple purification processes including metathesis, desulfurization, concentration, and neutralization. This invention avoids the disadvantages of the metathesis method, such as high phosphorus and potassium residue in the filter residue, low recovery rate, and numerous product impurities. Furthermore, it has a lower production cost than the neutralization method, providing a lower-cost technical route for preparing high-quality potassium dihydrogen phosphate.

[0038] 2. This invention uses hemihydrate acid to predissolve dicalcium phosphate, which actually partially generates calcium dihydrogen phosphate. At a temperature of 70~85℃, the solubility of calcium dihydrogen phosphate is about 130 times that of dicalcium phosphate, which can increase the reactivity, reduce insoluble phosphorus, and improve the yield of P and K.

[0039] 3. This invention uses the water required to replenish the system as the washing liquid for the previous filter cake, which can not only recover P and K, reduce external discharge and environmental risks, but also recover P and K in multiple levels and to the maximum extent.

[0040] 4. This invention uses clean water to wash the metabolite cake, first stirring and then rinsing, which reduces the P and K carried by the filter cake in the late-stage liquid, resulting in a final late-stage liquid of clean water. The collected filtrate is acidic, and washing and neutralizing the filter cake can recover the effective components discharged due to the pH change caused by impurity removal (meaning that a large amount of KOH is added during the neutralization process, turning the original acidic solution into an alkaline solution, with the pH rising from approximately 1.5 to above 8.0. This process causes a large number of metal ions (such as iron and magnesium) to precipitate into the filter cake). The filter cake is then stirred, rinsed, and then washed with clean water. Water rinsing maximizes the recovery of effective components such as phosphorus and potassium. However, the pH of the washing liquid for metathesis cake is approximately 2.5. After washing, some impurities that precipitate due to the high pH will dissolve in the washing liquid. Nevertheless, it can still maximize the recovery of components such as phosphorus and potassium. The collected washing liquid is used as the reaction water for metathesis. During the metathesis stage, precipitates can be generated and discharged from the system with the filter cake. The collected neutralized wash water is used as the replenishment liquid for the next metathesis reaction. This not only achieves water balance and eliminates wastewater discharge, reducing energy consumption and saving costs, but also maximizes the recovery of phosphorus and potassium, resulting in a high recovery rate for the system.

[0041] 5. In the metathesis process, some of the neutralization wash water used as a supplementary liquid will be discharged with the metathesis residue due to the impurities carried out by the washing and neutralization filter cake. The washing residue is clear liquid, while the filter cake impurities will continue to exist in the filter cake and be discharged to the slag field. The metathesis filtrate undergoes desulfurization and KOH neutralization for multi-stage impurity removal, resulting in a low impurity content in the clear liquid. After concentration, crystallization, and centrifugation, the impurities enter the mother liquor. The mother liquor is returned to the neutralization stage to further remove impurities together with the new slurry, achieving the effect of impurity separation and resulting in high product purity. Attached Figure Description

[0042] Figure 1 This is a process flow diagram of the present invention;

[0043] Figure 2 The figure shows the results of the cyclic experiment in Example 1. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0045] Example 1

[0046] like Figure 1 As shown, a process for preparing potassium dihydrogen phosphate includes the following steps:

[0047] S1: Weigh out the hemihydrate phosphoric acid with dicalcium phosphate and phosphoric acid hemihydrate at a P2O5 content ratio of 1:0.4. Mix the hemihydrate phosphoric acid with acid hydrolysis water (reaction replenishment water, initial reaction replenishment water, and subsequent cycle replenishment of neutralization filter cake washing liquid instead of water) to obtain a hemihydrate phosphoric acid solution with a P2O5 mass concentration of 10%. Under the condition of water bath at 80℃, slowly add dicalcium phosphate to the hemihydrate phosphoric acid solution over 1.5h. After the addition is completed, continue the reaction for 0.5h. After the reaction is completed, a pre-dissolved mixture is obtained.

[0048] S2: Weigh potassium sulfate according to a P:K molar ratio of 1:1.2, and weigh 98% sulfuric acid according to a potassium sulfate:sulfuric acid molar ratio of 1:1. Slowly add the 98% sulfuric acid to the demineralized water, stir evenly, then add potassium sulfate. Heat to 60℃ and stir continuously until the solution is clear and transparent. Stop stirring and maintain the temperature at 40℃ (after the solution is clear and transparent, potassium bisulfate solution can be added. Maintaining the temperature is only to prevent tube blockage caused by potassium bisulfate crystallization due to cooling. This temperature is not fixed; it may be higher in winter, and in summer, if there is no tube blockage, the temperature does not need to be maintained). Then, under the condition of 80℃ water bath, add the evenly mixed potassium bisulfate solution dropwise to the pre-dissolved mixture at a peristaltic pump at a uniform rate (dropping rate of 600g / h, to be completed within 4 hours) for acid hydrolysis. After the addition is completed, continue the reaction for 2 hours. After the reaction is completed, filter to obtain the metathesis solution and metathesis filter residue.

[0049] S3: Weigh barium carbonate according to a molar ratio of Ba:S of 1.0. Take 50% of the metathesis solution to pre-dissolve barium carbonate. During pre-dissolution, slowly add barium carbonate under stirring to prevent reaction foam from encapsulating the barium carbonate. After pre-dissolution, use a peristaltic pump to add the barium carbonate dropwise over 3 hours. After the addition is complete, react for 0.5 hours. After the reaction is complete, filter to obtain desulfurization liquid and desulfurization slag. Mix the desulfurization slag and metathesis slag and wash them twice (stirring and rinsing). The total water volume for stirring and rinsing is 90% of the initial water volume (the acid hydrolysis water added in S1). Based on this, the water ratio for stirring and rinsing is 8:2 (or 7:3 in other embodiments). The reaction time is 2 hours. After the reaction is complete, filter. The filtrate is secondary washing water, and the filter cake is purified filter cake, which is sent to the downstream gypsum section.

[0050] S4: Weigh KOH according to the P:K molar ratio of 1:1, and prepare a 60% mass concentration using water and the centrifugal mother liquor obtained in S6 (use water first, then use the centrifugal mother liquor first, and add water as needed). Add the solution dropwise using a peristaltic pump over 1 hour. After the addition is complete, react for 0.5 hours. Filter to obtain neutralized liquid and neutralized residue. Use 80% of the secondary washing water as the stirring liquid for 0.5 hours, 20% as the rinsing liquid, and then use 10% of the initial water volume as the secondary rinsing liquid for rinsing. After completion, obtain neutralized wash water. Collect the neutralized wash water as a supplementary liquid for the pre-dissolution stage, and send the neutralized residue to the slag yard.

[0051] S5: Concentrate and crystallize the potassium dihydrogen phosphate solution to a specific gravity of 1.40 to obtain a concentrated crystallized solution;

[0052] S6: Cool the concentrate to crystallize at the final crystallization temperature of 60℃, centrifuge at 2000 r / min for 3 min, dry at 50℃ for 2 h to obtain potassium dihydrogen phosphate product; return the centrifuged mother liquor to the neutralization stage of S4 for recycling (return to S4 and mix with the new desulfurization liquid, then start adding KOH solution dropwise).

[0053] The detection results of the process products and the final potassium dihydrogen phosphate product obtained in this embodiment are shown in Tables 1-3:

[0054] Table 1

[0055]

[0056] Table 2

[0057]

[0058] Table 3

[0059]

[0060] From Table 1-3 and Figure 2 It can be seen that this process can stably produce high-quality potassium dihydrogen phosphate using relatively inexpensive raw materials. After eight cycles of testing, the proportion of impurities in the centrifuged mother liquor showed a slow upward trend. After a certain number of cycles, pre-purification of the mother liquor with potassium hydroxide can be performed. Magnesium and sodium accumulation was relatively slow, and the overall cycle was stable and feasible.

[0061] Example 2

[0062] A process for preparing potassium dihydrogen phosphate includes the following steps:

[0063] S1: Weigh out the hemihydrate phosphoric acid with dicalcium phosphate and hemihydrate phosphoric acid at a P2O5 content ratio of 1:0.4. Mix the hemihydrate phosphoric acid with acid hydrolysis water to obtain a hemihydrate phosphoric acid solution with a P2O5 concentration of 10%. Under the condition of water bath at 80℃, slowly add dicalcium phosphate to the hemihydrate phosphoric acid solution over 1.5 hours. After the addition is completed, continue the reaction for 0.5 hours. After the reaction is completed, a pre-dissolved mixture is obtained.

[0064] S2: Weigh potassium sulfate according to a P:K molar ratio of 1:1.0, and weigh 98% sulfuric acid according to a potassium sulfate:sulfuric acid molar ratio of 1:1.1. Slowly add the 98% sulfuric acid to the demineralized water, stir evenly, then add potassium sulfate. Heat to 60℃ and stir continuously until the solution is clear and transparent. Stop stirring and maintain the temperature at 40℃. Then, under the condition of 80℃ water bath, add the evenly mixed potassium hydrogen sulfate solution dropwise to the pre-dissolved mixture at a peristaltic pump at a rate of 600g / h, to be completed within 4 hours for acid hydrolysis. After the addition is completed, continue the reaction for 2 hours. After the reaction is completed, filter to obtain the metathesis solution and metathesis filter residue.

[0065] S3: Weigh barium carbonate according to a molar ratio of Ba:S of 1.0. Take 50% of the metathesis solution to pre-dissolve barium carbonate. During pre-dissolution, slowly add barium carbonate under stirring to prevent reaction foam from encapsulating the barium carbonate. After pre-dissolution, use a peristaltic pump to add the barium carbonate dropwise over 3 hours. After the addition is complete, react for 0.5 hours. After the reaction is complete, filter to obtain desulfurization liquid and desulfurization slag. Mix the desulfurization slag and metathesis slag and wash them twice (stirring and rinsing). The total water volume for stirring and rinsing is 90% of the initial water volume (the acid hydrolysis water added in S1). Based on this, the water ratio for stirring and rinsing is 8:2 (or 7:3 in other embodiments). The reaction time is 2 hours. After the reaction is complete, filter. The filtrate is secondary washing water, and the filter cake is purified filter cake, which is sent to the downstream gypsum section.

[0066] S4: Weigh KOH according to the P:K molar ratio of 1:1, and prepare a solution with a mass concentration of 60% using water and the centrifuged mother liquor obtained in S6 (using water initially, and then adding water as needed). Add the solution dropwise using a peristaltic pump over 1 hour. After the addition is complete, react for 0.5 hours. Filter to obtain a neutralized solution and a neutralized residue. Use 80% of the secondary washing water as the stirring liquid for 0.5 hours, and 20% as the rinsing liquid. Then use 10% of the initial water volume as the secondary rinsing liquid for rinsing. After completion, obtain neutralized wash water. Collect the neutralized wash water as a supplementary liquid for the pre-dissolution stage, and send the neutralized residue to the slag yard.

[0067] S5: Concentrate and crystallize the potassium dihydrogen phosphate solution to a specific gravity of 1.40 to obtain a concentrated crystallized solution;

[0068] S6: Cool the concentrate to crystallize at a final crystallization temperature of 60℃, centrifuge at 2000 r / min for 3 min, dry at 50℃ for 2 h to obtain potassium dihydrogen phosphate product; return the centrifugation mother liquor to the neutralization stage of S4 for recycling.

[0069] The detection results of the process products and the final potassium dihydrogen phosphate product obtained in this embodiment are shown in Table 4-6:

[0070] Table 4

[0071]

[0072] Table 5

[0073]

[0074] Table 6

[0075]

[0076] As can be seen from Table 4-6, this process can stably produce high-quality potassium dihydrogen phosphate products using relatively inexpensive raw materials.

[0077] Table 7

[0078]

[0079] As shown in Table 7, the cost of potassium dihydrogen phosphate obtained using the process of this invention is 6526.56 yuan / ton, while the production cost of MKP potassium dihydrogen phosphate prepared using semi-finished MAP is 8396.75 yuan / ton, the production cost of MKP potassium dihydrogen phosphate prepared using wet phosphoric acid desulfurization is 8085.40 yuan / ton, and the production cost of potassium dihydrogen phosphate prepared using Nanzhang potassium diammonium phosphate is 8049.73 yuan / ton. It can be seen that the cost of preparing potassium dihydrogen phosphate is effectively reduced by using the process of this invention.

[0080] To demonstrate the important role of each parameter in this invention, corresponding embodiments and comparative examples are also provided. Embodiments 3-9 and Comparative Examples 1-11 are basically the same as Embodiment 1, with differences and effect data shown in Table 8:

[0081] Table 8

[0082]

[0083] As shown in Table 8, this invention systematically investigated the effects of the mass ratio of dicalcium phosphate to phosphoric acid, reaction temperature, P / K molar ratio in step S2, Ba / S molar ratio in step S3, P / K molar ratio in step S4, and process circulation mode on the yield and purity of the product as P2O5 using a single-factor variable method. The results show that each process parameter and circulation step has a significant regulatory effect on the reaction effect. Under the optimized conditions of the examples, the product yield was higher than 91.77%, and the purity was not lower than 97.48%. Among them, when the mass ratio of dicalcium phosphate to phosphoric acid was 1:0.4, the reaction temperature was 80℃, the P / K molar ratio in step S2 was 1:1.2, the Ba / S molar ratio in step S3 was 1:1, and the P / K molar ratio in step S4 was 1:1, the yield reached 97.13%, and the purity was as high as 99.89%, showing the best overall performance. Too little phosphoric acid will lead to insufficient pre-dissolution reaction and significantly reduce the yield; the reaction rate is slow and the yield is low when the reaction temperature is 70℃, and there is no significant improvement in yield and purity when the temperature is increased to 85℃. 80℃ is the optimal reaction temperature.

[0084] In process S2, a P / K molar ratio below or above 1:1.2, and in process S3, a Ba / S molar ratio below 1:1, will both lead to a simultaneous decrease in yield and purity. This is because a P / K ratio below 1.2 primarily results in increased potassium hydroxide supplementation in the later stages, leading to higher costs. It also increases the amount of neutralized filter cake, causing more entrainment and generating impurities similar to ferric phosphate, thus reducing phosphorus recovery. Furthermore, excessive potassium sulfate supplementation in the early stages leads to an excess of sulfate ions, which can easily cause encapsulation during the fine desulfurization stage, reducing the desulfurization rate and increasing water-insoluble matter in the later stages, thus lowering purity. In process S4, a P / K molar ratio slightly deviating from 1:1 can slightly increase the yield, but the purity will decrease significantly. This is because a P / K ratio above 1.2 increases the amount of calcium hydrogen phosphate added in the early stages, reduces the metathesis rate, decreases the phosphorus recovery, increases the amount of calcium calcium phosphate introduced, and reduces the amount of calcium sulfate. The calcium calcium phosphate remaining in the solution can easily form calcium hydrogen phosphate during crystallization, thus reducing product purity. Comparative results show that reversing the process sequence and severely imbalanced raw material molar ratios lead to a significant decrease in product purity, and may even cause reaction termination and a yield of 0 (in Comparative Example 5, the theoretical pH range for potassium dihydrogen phosphate was exceeded, resulting in a 0% yield). Temperatures that are too low make the reaction difficult to proceed, while temperatures that are too high easily trigger side reactions that reduce purity. Crucially, using secondary washing solutions from metathesis residue and desulfurization residue to wash the neutralized filter residue, and then recycling the washing solution, filtrate, and S6 centrifugal mother liquor to the corresponding processes, can significantly reduce phosphorus loss and greatly increase yield. Eliminating the recycling process or using only clean water for washing leads to a sharp drop in yield. In summary, appropriate raw material ratios, reaction temperature, strict control of process molar ratios, and reasonable recycling of washing solution and mother liquor are the core conditions for achieving high-purity, high-yield preparation of dicalcium phosphate.

[0085] In each embodiment, the whiteness of the secondary washing cake (dry basis, i.e., dihydrate gypsum) was approximately 91%. The testing method referenced GB / T 5950-2008 "Methods for measuring the whiteness of building materials and non-metallic mineral products".

[0086] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A process for preparing potassium dihydrogen phosphate, characterized in that: Includes the following steps: S1: Mix dicalcium phosphate with a hemihydrate phosphoric acid solution at a temperature of 70~85℃ to obtain a pre-dissolved mixed base solution; S2: Mix potassium hydrogen sulfate solution with pre-dissolved mixed base liquid, and continue the reaction at a temperature of 70~85℃ to obtain double decomposition solution and double decomposition residue; S3: Desulfurize the compounding solution to obtain desulfurized liquid and desulfurized residue; S4: Neutralize and remove impurities from the desulfurization liquid to obtain potassium dihydrogen phosphate solution and neutralized filter residue; S5: Concentrate and crystallize the potassium dihydrogen phosphate solution to obtain a concentrated crystallized solution; S6: After solid-liquid separation and drying of the concentrated crystallization liquid, potassium dihydrogen phosphate product is obtained.

2. The preparation process of potassium dihydrogen phosphate according to claim 1, characterized in that: In S1, based on the mass of P2O5, the mass ratio of P2O5 contained in dicalcium phosphate to phosphoric acid hemihydrate solution is 1:0.2~0.

5.

3. The preparation process of potassium dihydrogen phosphate according to claim 1, characterized in that: In S2, the pre-dissolved mixed base solution and potassium bisulfate solution are mixed at a P:K molar ratio of 1:1.0~1.4, and the mass concentration of potassium bisulfate solution is controlled at 30%~45%.

4. The preparation process of potassium dihydrogen phosphate according to claim 1, characterized in that: The metathesis residue and desulfurization residue obtained in S2 and S3 are subjected to a secondary washing reaction, and the resulting washing liquid and filtrate are used as the raw liquid for neutralizing and washing the filter residue.

5. The preparation process of potassium dihydrogen phosphate according to claim 1, characterized in that: The neutralized filter residue obtained in S4 is washed with the original solution from the secondary washing reaction of metathesis residue and desulfurization residue. The filter cake after washing and filtration is rinsed with clean water. The washing solution and filtrate are used as supplementary solutions for the pre-dissolution reaction in S1.

6. A process for preparing potassium dihydrogen phosphate according to any one of claims 1-5, characterized in that: In S1, dicalcium phosphate is added to the hemihydrate phosphoric acid solution for mixing, and the addition time is 0.5h~1.0h. In S2, potassium bisulfate solution is added to the pre-dissolved mixed base solution for acid hydrolysis, and the potassium bisulfate solution is added dropwise over 1~4h.

7. A process for preparing potassium dihydrogen phosphate according to any one of claims 1-5, characterized in that: In S2, 98% acid is slowly added to water at a molar ratio of 1:0.5~1 and stirred until homogeneous. Then potassium sulfate is added, and the mixture is heated to 50~80℃ until it becomes clear and transparent to obtain potassium hydrogen sulfate solution.

8. A process for preparing potassium dihydrogen phosphate according to any one of claims 1-5, characterized in that: In step S3, desulfurization is achieved by adding barium carbonate, with the barium carbonate added according to a Ba to S molar ratio of 0.90 to 1:1 in the reaction system. In step S4, potassium hydroxide is added to neutralize and remove impurities from the desulfurization liquid, with the potassium hydroxide added according to a K to P molar ratio of 0.95 to 1.05:

1. In step S5, the potassium dihydrogen precipitate is concentrated to a specific gravity of 1.30 to 1.

50. In step S6, the centrifugation speed is 2000 to 3000 r / min, the centrifugation time is 3 to 6 min, the drying temperature is 50 to 80℃, and the drying time is 2 to 6 h.

9. A process for preparing potassium dihydrogen phosphate according to any one of claims 1-5, characterized in that: The centrifuged mother liquor obtained in S6 is returned to S4 for recycling.

10. A potassium dihydrogen phosphate, characterized in that: It is prepared using the potassium dihydrogen phosphate preparation process according to any one of claims 1-9.

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