A method for continuously and controllably preparing uniform zinc phosphate by using wet-process phosphoric acid

Abstract

The application discloses a method for continuously and controllably preparing uniform crystal zinc phosphate by using wet-process phosphoric acid, which comprises the following steps: S1, pre-purification; S2, solution decalcification; S3, deep purification; S4, mixed crystal zinc phosphate preparation; and S5, crystal type reconstruction, so as to obtain the uniform crystal zinc phosphate product. The zinc phosphate is prepared by using low-cost wet-process phosphoric acid and calcium alkali as raw materials, the use amount of high-price hot-process phosphoric acid and sodium alkali or other alkalis is greatly reduced, and the production cost of the zinc phosphate is significantly reduced. Meanwhile, the method can realize the continuous and controllable preparation of the zinc phosphate, the prepared zinc phosphate product has complete crystal morphology, the crystal type is uniform and controllable, and the quality of the zinc phosphate product is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of fine phosphate production, in particular to a method for continuously and controllably preparing isomorphous zinc phosphate by using wet-process phosphoric acid. BACKGROUND

[0002] Zinc phosphate can replace toxic zinc chromate or red lead and other toxic antirust raw materials, and is used for producing water-soluble coatings and non-toxic antirust pigments, and can also be used in the fields of photocatalysis, medicine and dental adhesive.

[0003] The traditional preparation process of zinc phosphate is direct reaction of industrial phosphoric acid and zinc oxide. This process is simple, but the conversion rate is not easy to control, and zinc oxide is easily wrapped by zinc phosphate, which causes passivation phenomenon and reduces the product quality of zinc phosphate.

[0004] Patent CN201910061247.7 discloses a method for preparing zinc phosphate. The raw materials used in the patent are phosphoric acid and zinc oxide, and citric acid is introduced as a dissolving dispersant in the reaction system. The temperature is 55-65℃, the reaction time is 10-30min, and the generated zinc phosphate dihydrate crystals are dried at 90℃ to obtain zinc phosphate dihydrate product.

[0005] Patent CN202111533322.9 discloses a high-activity zinc phosphate and a preparation method thereof. The patent first slurries water and zinc oxide; the zinc oxide slurry is added to a reaction kettle, stirring is started, and heating is performed, then phosphoric acid solution is slowly added, and the reaction is kept warm. After filtration, washing and drying, high-activity zinc phosphate is obtained.

[0006] Patent CN201410699100.8 discloses a preparation method of nanosheet-shaped zinc phosphate. The patent comprises the following steps: (1) dissolving zinc oxide; (2) preparing nanosheet-shaped zinc phosphate precursor; (3) preparing nanosheet-shaped zinc phosphate. The zinc phosphate prepared by the present application has a clear sheet structure and no obvious agglomeration.

[0007] The raw materials used in the above technologies are all zinc oxide and phosphoric acid, and the reaction process is difficult to be continuous and controllable. The zinc phosphate produced inevitably contains more or less zinc oxide, which affects the product quality. In addition, the raw material acid is pure phosphoric acid, which has high production cost and no market competitiveness.

[0008] Patent with application number 200910114623.0 discloses a method for producing high-purity zinc phosphate. The patent uses soluble zinc salt, soluble carbonate or bicarbonate as raw materials to react in aqueous solution to generate zinc carbonate or basic zinc carbonate precipitate, and then reacts with phosphoric acid to generate zinc phosphate. The product yield reaches more than 95%, the content of dihydrate zinc phosphate is more than 98%, the content of sulfate is less than 0.05%, the content of chloride ion is less than 0.05%, lead is less than or equal to 0.0025%, and cadmium is less than or equal to 0.0025%, which can be used as raw material for high-grade coatings.

[0009] F. Xie et al. synthesized ultrafine zinc phosphate by hydrothermal method using sodium phosphate dibasic and zinc sulfate as raw materials and emulsifier OP-10 as surfactant.

[0010] A. Q. Yuan et al. synthesized spherical nano zinc phosphate crystals by solid-state reaction using trisodium phosphate and zinc sulfate as raw materials.

[0011] CN201610429078.4 discloses a process for producing high-quality zinc phosphate by indirect method. The technology is to obtain zinc sulfate solution by reacting zinc-containing waste residue with dilute sulfuric acid; to prepare sodium phosphate dibasic solution by mixing phosphoric acid with caustic soda; to add the prepared sodium phosphate dibasic solution and aqueous caustic soda to the metered zinc sulfate solution, and to obtain the product zinc phosphate after separation, drying and grinding.

[0012] Patent CN202211722799.6 discloses a method for producing high-quality zinc phosphate from low-grade zinc ore. The patent dries and grinds the low-grade zinc ore into ore powder, prepares an ammonia-carbon ammonium solution with pH of 9-10, dissolves the ore powder in the ammonia-carbon ammonium solution, filters out insoluble slag to obtain zinc liquid; adds zinc powder with purity not less than 90% to the zinc liquid under stirring to remove metal impurities; adds phosphoric acid dropwise to the zinc liquid under stirring, the ratio of zinc liquid to phosphoric acid satisfies n(Zn):n(H3PO4)=1:1; then filters under vacuum to obtain zinc phosphate, which is dried after washing to obtain zinc phosphate containing 2 crystal waters.

[0013] Patent CN201810365094.0 discloses a zinc phosphate containing crystal water, its preparation method and use as a photocatalyst. The patent first prepares a certain concentration of zinc nitrate solution, adds an appropriate amount of diammonium hydrogen phosphate to the solution to make the molar concentration ratio of zinc nitrate to diammonium hydrogen phosphate 3:2, and then performs constant temperature hydrothermal reaction at 170-190℃ for 23-25 hours; after the reaction is completed, the solution is naturally cooled to room temperature, washed, centrifuged and dried to obtain Zn3(PO4)2·4H2O product with excellent photocatalytic activity.

[0014] Patent CN201210455288.2 discloses a method for preparing zinc phosphate from low-grade zinc oxide ore. The technology uses low-grade zinc oxide ore as raw material, obtains ammonia leaching purified liquid by ammonia-ammonium salt leaching and purification, generates zinc ammonium double salt intermediate precipitate by adding precipitant, then fully dissolves the intermediate and reacts with trisodium phosphate solution to generate zinc phosphate solid precipitate, and obtains PO4 3- content ≥45%, Zn 2+ content ≥45% high-purity powdery zinc phosphate product, which can be used as raw material for high-grade anticorrosive paint.

[0015] Patent CN200610010775.2 discloses a method for producing zinc phosphate with phosphate fertilizer. The technology dissolves fertilizer grade ammonium phosphate salt and soluble zinc salt in hot water to obtain ammonium phosphate solution and zinc salt solution, the molar ratio of phosphate ion to zinc ion is 0.7-1:1, the obtained two solutions are added into a reactor, the reaction temperature is 50-80℃, the pH value of the mixture is adjusted to 6.5-8.5 by alkali, the mixture is aged for 10-20 minutes and then filtered, the filter cake is washed with hot water and dried to obtain zinc phosphate product.

[0016] Patent CN201210569946.0 discloses a preparation method of high-efficiency zinc phosphate micro-nano anticorrosive agent. The technology uses ultrasonic wave and high-temperature and high-pressure water bath to synchronously and cooperatively control, uses zinc nitrate and trisodium phosphate as raw materials to prepare high-efficiency zinc phosphate micro-nano anticorrosive agent. The two effects are synchronously and cooperatively used to better disperse the product system and ensure the uniformity of crystal nucleation, effectively solve the problem that the particle size and crystallization degree of nanocrystal are difficult to be synchronously controlled, and the product is dried by microwave heating to reduce the agglomeration. The prepared micro-nano zinc phosphate product has the advantages of high purity, complete crystallinity, narrow particle size distribution range and good dispersity.

[0017] In summary, the prior art is to use soluble zinc salt and phosphate salt to carry out displacement reaction, the used phosphate salt is pure raw material, the production cost is high, and the competitiveness is low. Moreover, the prepared zinc phosphate has incomplete crystal morphology, and the particles cannot be uniformly controlled. SUMMARY

[0018] The purpose of the present application is to solve the problems of poor quality of zinc phosphate and high production cost in the prior art, and to provide a method for continuously and controllably preparing uniform crystal zinc phosphate by using wet-process phosphoric acid.

[0019] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a method for continuously and controllably preparing uniform crystal zinc phosphate by using wet-process phosphoric acid, comprising the following steps:

[0020] S1, pre-purification: reacting wet-process phosphoric acid with calcium alkali, and then filtering and washing to obtain solid phase I which is fertilizer grade phosphate salt and liquid phase I which is pre-purification liquid saturated with calcium dihydrogen phosphate; the reaction conditions are as follows: the concentration of phosphoric acid (P2O5) is 3-20%, the reaction temperature is 40-70℃, the reaction time is 0.5-2 hours, and the end point pH is 2-3.5;

[0021] S2, solution decalcification: configuring a sulfate solution, and continuously and slowly adding the sulfate solution and the liquid phase I obtained in S1 into a reactor by using a peristaltic pump, controlling SO3 at 1-6%, and reacting at 50-80℃ for 1-5 hours to obtain white gypsum and liquid phase II by filtering and washing;

[0022] S3, deep purification: the liquid phase II obtained from S2 is reacted with a base, the reaction temperature is controlled at 50-100℃, the reaction time is 0.5-3 hours, the end point pH is 4.0-9.0, filtration and washing are performed to obtain liquid phase III and solid III, and the solid III is a plant nutrient;

[0023] S4, mixed crystal zinc phosphate preparation: a zinc salt solution is configured, and the zinc salt solution and the liquid phase III obtained from S3 are continuously and slowly added into a reactor by using a peristaltic pump, the pH of the system is controlled at 1.0-4.0, the reaction temperature is controlled at 50-90℃, the reaction time is 1-4 hours, and filtration is performed to obtain solid phase IV with incomplete crystal form and liquid phase IV;

[0024] S5, crystal form reconstruction: the solid phase IV is uniformly dispersed in pure dilute phosphoric acid for crystal form reconstruction, the reconstruction time is controlled at 1-3 hours, and filtration, washing and drying are performed to obtain the uniform crystal zinc phosphate product.

[0025] Preferably, the calcium base is one of apatite, calcium carbonate, calcium oxide and calcium hydroxide.

[0026] Preferably, the sulfate is one of ammonium sulfate, sodium sulfate and potassium sulfate, and the SO3 concentration in the liquid phase is controlled at 1-10%.

[0027] Preferably, the base in S3 is one of gaseous ammonia, aqueous ammonia, ammonium carbonate, ammonium bicarbonate, sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate and potassium hydroxide.

[0028] Preferably, the zinc salt in S4 is one of zinc sulfate, zinc nitrate, zinc acetate, zinc citrate and zinc chloride.

[0029] Further preferably, if the liquid phase IV contains a sulfate, part of the solution is returned to the liquid phase I for decalcification, and the remaining solution is concentrated to obtain a water-soluble sulfate, nitrate, acetate, citrate or chloride product.

[0030] Further preferably, in S5, the pure dilute phosphoric acid is hot-process phosphoric acid or refined phosphoric acid, the concentration is 1-5%, the liquid-solid ratio for crystal form reconstruction is 2-5:1, the temperature is controlled at 60-100℃, the time is 1-3 hours, and the stirring intensity (Reynolds number Re) is controlled at 1x10 4 The above.

[0031] The present application has the beneficial effects that: the present application uses low-cost wet-process phosphoric acid and a calcium base as raw materials to prepare zinc phosphate, greatly reduces the use amount of high-priced hot-process phosphoric acid and sodium base or other bases, and significantly reduces the production cost of zinc phosphate; meanwhile, the present application can realize continuous and controllable preparation of zinc phosphate, the prepared zinc phosphate product has complete crystal morphology, the crystal form is uniform and controllable, and the quality of the zinc phosphate product is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A flow chart for the continuous and controllable preparation of uniform crystal zinc phosphate using wet-process phosphoric acid. DETAILED DESCRIPTION

[0033] The application will be further described below in connection with the accompanying drawings and specific examples.

[0034] Example 1

[0035] Pre-purification: Take 1000g of wet-process phosphoric acid I, add 104.8g of calcium carbonate with a purity of 95% (add 157.2g of water to make a slurry), control the temperature at 40-45°C, the reaction time is 1.0 hour, adjust the intermediate pH to 2.3 with lime milk, after the reaction is completed, filter and wash, the solid phase I is fertilizer-grade calcium hydrogen phosphate, the weight (dry basis) is 83.5g, containing P2O5 29.0%, continue to adjust the pH of the filtrate to 2.7 with lime milk, filter, obtain liquid phase I (containing washing liquid) with a weight of 2500.0g, containing P2O5 7.11%, CaO 1.87% (see Table 3 for index data), which is used to produce gypsum dihydrate, the filter cake is dissolved with 1000g of wet-process phosphoric acid I to form wet-process phosphoric acid I for continuous circulation;

[0036] Solution decalcification: take 118.5g of sodium sulfate, dissolve in 1340g of water to configure a solution. Continuously add liquid phase I and the sodium sulfate solution into the reaction tank with a peristaltic pump, control the temperature at 70±1°C, the solution SO3 is 2%, the reaction time is 4 hours, filter and wash to obtain gypsum dihydrate 137.37g, liquid phase II 4154.1g, containing P2O5 4.26% (see Table 4 for index data), continue to purify the clear liquid deeply;

[0037] Deep purification: place liquid phase II in the reaction tank, control the temperature to 80°C, neutralize to pH=6.0 with sodium carbonate, filter and wash, the solid phase III is slow-release type phosphate fertilizer (weight 80.2g, containing phosphorus 36.0%), the weight of liquid phase III is 4581.6g, containing P2O5 3.1% (see Table 5 for data index), which is used as raw material for the production of mixed crystal zinc phosphate;

[0038] Preparation of mixed crystal zinc phosphate: take 550.0g of zinc sulfate dihydrate and place it in a dissolving tank, add 1300g of zinc phosphate washing liquid, continuously and slowly add the zinc sulfate solution and liquid phase III into the reactor with a peristaltic pump, control the system temperature at 70°C, the reaction time is 2 hours, the end point pH is 2.6. After the reaction is completed, filter to obtain solid phase IV (mixed crystal zinc phosphate 438.0g). Neutralize liquid phase IV with sodium carbonate, filter, part of the solution returns to the decalcification of liquid phase I, the remaining solution is concentrated to produce mirabilite product 333.8g (see Table 5 for data index);

[0039] Reconstruction of crystal form: 45 g of thermal phosphoric acid (85%) was diluted with 584 g of water to prepare a dilute phosphoric acid solution with a concentration of 4.4% (P2O5), and heated to 90°C. Solid phase IV was dispersed in the solution, and the stirring intensity (Reynolds number Re) was controlled at 1 x 105, and the crystal conversion time was controlled at 2 hours. After filtration, washing and drying, 430.0 g of zinc phosphate dihydrate product was obtained (see Table 6 for the quality index).

[0040] The flow chart for the continuous controllable preparation of uniform crystal zinc phosphate using wet-process phosphoric acid is shown in Figure 1. Figure 1

[0041] The components and amounts of the wet-process phosphoric acid used in this example are shown in Table 1.

[0042] Table 1 Components and amounts of wet-process phosphoric acid

[0043] Composition P2O5 CaO MgO Al2O3 Fe2O3 F Amount of phosphoric acid used in the test Content % 20.20 0.31 0.62 0.41 0.80 1.18 1000.0

[0044] Examples 2-5

[0045] Examples 2-5 were prepared in the same manner as Example 1, and the amounts and components of the wet-process phosphoric acid used were the same as in Example 1 (see Table 1 for details). The difference between Examples 2-5 and Example 1 was in the test conditions, which are shown in Table 2, and the test and analysis results are shown in Tables 3-6.

[0046] Table 2 Test conditions for Examples 2-5

[0047]

[0048] Table 3 Material data for the pre-purification stage of Examples 1-5

[0049]

[0050] Table 4 Material data for the dihydrate gypsum of Examples 1-5

[0051]

[0052] Table 5 Material data for the deep purification and preparation of mixed crystal zinc phosphate of Examples 1-5

[0053]

[0054]

[0055] * The amount of material returned to the decalcification process.

[0056] Table 6 Weight and composition of the uniform crystal zinc phosphate prepared in Examples 1-5

[0057]

[0058] ​In conclusion, the application realizes the continuous controllable preparation of zinc phosphate by using wet-process phosphoric acid and calcium alkali as raw materials, the product has complete and controllable crystal form, the quality of the zinc phosphate product is significantly improved, and the preparation method is simple, the raw material is low, and the production cost is effectively reduced.

[0059] The specification and drawings of the application are considered to be illustrative rather than restrictive, and on the basis of the application, those skilled in the art can make some substitutions and modifications to some technical features according to the disclosed technical content without creative labor, which are all within the protection scope of the application.

Claims

1. A method for the continuous and controllable preparation of homogeneous zinc phosphate using wet-process phosphoric acid, characterized in that, Includes the following steps: S1. Pre-purification: Wet phosphoric acid is reacted with calcium alkali, then filtered and washed to obtain solid phase I, which is fertilizer-grade phosphate, and liquid phase I, which is a pre-purified liquid saturated with calcium dihydrogen phosphate. The reaction conditions are: phosphoric acid (P2O5) concentration of 3~20%, reaction temperature of 40~70℃, reaction time of 0.5~2 hours, and final pH of 2~3.

5. S2, Solution decalcification: Prepare a sulfate solution, and continuously and slowly add the sulfate solution and liquid phase I obtained from S1 to the reactor using a peristaltic pump. The SO3 content is controlled at 1~6%, and the reaction is carried out at 50~80℃ for 1~5 hours. After filtration and washing, white dihydrate gypsum and liquid phase II are obtained. S3, Deep purification: The liquid phase II obtained from S2 is reacted with alkali, the reaction temperature is controlled at 50~100℃, the time is 0.5~3 hours, the endpoint pH = 4.0~9.0, and the liquid phase III and solid III are obtained by filtration and washing. Solid III is a plant nutrient. S4. Preparation of mixed crystal zinc phosphate: Prepare a zinc salt solution, and use a peristaltic pump to continuously and slowly add the zinc salt solution and liquid phase III obtained in S3 into the reactor. Control the pH of the system to 1.0~4.0, the reaction temperature to 50~90℃, and the reaction time to 1~4 hours. Filter to obtain solid phase IV and liquid phase IV with incomplete crystal development. S5. Crystal Reconstruction: Solid phase IV is uniformly dispersed in pure dilute phosphoric acid for crystal reconstruction. The reconstruction time is controlled within 1 to 3 hours. After filtration, washing and drying, homogeneous zinc phosphate product is obtained.

2. The method according to claim 1, characterized in that, The calcium alkali is one of apatite, calcium carbonate, calcium oxide, and calcium hydroxide.

3. The method according to claim 1, characterized in that, The sulfate is one of ammonium sulfate, sodium sulfate, and potassium sulfate, and the SO3 concentration in the liquid phase is controlled at 1-10%.

4. The method according to claim 1, characterized in that, The alkali in S3 is one of the following: gaseous ammonia, ammonia water, ammonium carbonate, ammonium bicarbonate, sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium carbonate, and potassium hydroxide.

5. The method according to claim 1, characterized in that, The zinc salt in S4 is one of zinc sulfate, zinc nitrate, zinc acetate, zinc citrate, and zinc chloride.

6. The method according to claim 1, characterized in that, If liquid phase IV contains sulfate, part of the solution is returned to liquid phase I for decalcification, and the remaining solution is concentrated to obtain water-soluble sulfate, nitrate, acetate, citrate or chloride products.

7. The method according to claim 1, characterized in that, In step S5, the pure dilute phosphoric acid is either thermally produced phosphoric acid or refined phosphoric acid, with a concentration of 1-5%, a liquid-to-solid ratio for crystal reconstruction of 2-5:1, a temperature controlled at 60-100℃, a time of 1-3 hours, and a stirring intensity with a Reynolds number Re controlled at [value missing]. above.

Images