A method for preparing feed-grade dibasic calcium phosphate from low-grade phosphate ore through high-value comprehensive utilization

Abstract

The application belongs to the technical field of comprehensive utilization of phosphoric acid, and particularly relates to a method for preparing feed-grade calcium hydrogen phosphate by high-value comprehensive utilization of low-grade phosphate rock. The method comprises the following steps: (1) secondary decomposition of phosphate rock by nitric acid: low-grade phosphate rock powder is respectively added with nitric acid for first acidolysis and second acidolysis; (2) two-stage countercurrent extraction: two-stage countercurrent extraction is performed on the acidolysis liquid by using an extractant, the liquid and solid are separated after first-stage extraction, and purified acidolysis liquid from which iron, magnesium and aluminum impurities are removed is obtained, and the crystal slurry is filtered after two-stage extraction of the purified acidolysis liquid to obtain feed-grade calcium hydrogen phosphate product. The application utilizes nitric acid to decompose phosphate rock through secondary circulation cross flow, and removes nitric acid in the acidolysis liquid by adopting a two-stage countercurrent extraction mode, thereby not only realizing efficient and high-value utilization of calcium resources in the phosphate rock, but also reducing consumption of additional calcium resources and saving economic cost, and providing a brand-new approach for production of feed-grade calcium hydrogen phosphate.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of comprehensive utilization of phosphoric acid, and relates to a method for preparing feed-grade calcium hydrogen phosphate from low-grade phosphate ore (P2O5 content is less than 30%) through high-value comprehensive utilization. BACKGROUND

[0002] As a poultry and livestock feed additive rich in phosphorus and calcium nutrients, calcium hydrogen phosphate can increase the average yield of milk, eggs and meat of poultry and livestock by 15-20% when 1-3% of the total amount of feed is added to animal feed. With the continuous improvement of people's living standards, the rapid development of animal husbandry has directly promoted the sharp increase in demand for feed-grade calcium hydrogen phosphate. The production of feed-grade calcium hydrogen phosphate is mainly divided into hot-process phosphoric acid and wet-process phosphoric acid technology. The hot-process phosphoric acid technology is restricted by the state due to the three high problems, and the mainstream method at present is the wet-process phosphoric acid technology, the main process of which is to use sulfuric acid or hydrochloric acid to extract phosphate ore to obtain crude phosphoric acid, to remove fluorine from the crude phosphoric acid by a fluorine removal agent, and then to neutralize the crude phosphoric acid after fluorine removal with lime milk, calcium oxide or calcium carbonate to obtain feed-grade calcium hydrogen phosphate.

[0003] In the mainstream production method of existing feed-grade calcium hydrogen phosphate, the following deficiencies need to be further improved: first, a large amount of by-product phosphogypsum is brought in the process of preparing crude phosphoric acid by decomposing phosphate ore with sulfuric acid, which not only leads to insufficient utilization of calcium resources in phosphate ore, but also brings serious potential harm to the surrounding ecological environment; second, since feed-grade calcium hydrogen phosphate has a requirement for fluorine content, the crude phosphoric acid needs to be treated by a fluorine removal agent, which leads to high economic cost and causes phosphorus loss; third, in the existing production process, calcium sources such as lime milk and calcium oxide need to be additionally introduced and reacted with the crude phosphoric acid, which causes an increase in resource consumption and economic cost; fourth, in the process of producing calcium hydrogen phosphate by using hydrochloric acid method or nitric acid method, the by-products are mainly calcium chloride and calcium nitrate, which cannot realize high-value conversion and utilization of by-products and efficient utilization of calcium resources in phosphate ore, and the economic benefit of the process needs to be further improved. SUMMARY

[0004] The purpose of the present application is to provide a method for preparing feed-grade calcium hydrogen phosphate from low-grade phosphate ore through high-value comprehensive utilization, so as to realize efficient and high-value utilization of low-grade phosphate ore resources, save production cost, simplify production process and improve high-value conversion and utilization of by-products.

[0005] The present application can be realized by the following technical scheme: a method for preparing feed-grade calcium hydrogen phosphate from low-grade phosphate ore through high-value comprehensive utilization is provided, which comprises the following steps:

[0006] (1) Nitric acid secondary decomposition of phosphate rock: low-grade phosphate rock powder is added with 30-40% mass concentration nitric acid for first acidolysis, after reaction, filtration is performed to separate the first acidolysis residue and the first acidolysis solution;

[0007] The first acidolysis residue is added into a second acidolysis tank, and 30-40% mass concentration nitric acid is added for second acidolysis, after reaction, filtration is performed to separate the calcium fluoride-containing residue and the second acidolysis solution, and the second acidolysis solution is added into the first acidolysis tank;

[0008] In the above reaction, the main chemical reaction equation is:

[0009] Ca5F(PO4)3+10HNO3→H3PO4+5Ca(NO3)2+HF↑

[0010] 7H3PO4+Ca5F(PO4)3→5Ca(H2PO4)2+HF↑

[0011] CaCO3+2HNO3→Ca(NO3)2+H2O+CO2↑

[0012] CaCO3+2H3PO4→Ca(H2PO4)2+H2O+CO2↑

[0013] CaCO3+2HF→CaF2↓+H2O+CO2↑

[0014] 4HF+SiO2→SiF4↑+H2O

[0015] H2SiF6+CaCO3→CaSiF6+H2O+CO2↑

[0016] CaSiF6+2Ca(NO3)2+2H2O→3CaF2↓+4HNO3+SiO2

[0017] (2) Preparation of feed-grade dicalcium phosphate by secondary countercurrent extraction: the first acidolysis solution is added into a primary extraction tank, and an extractant is added for primary extraction, after extraction, the extractant, the first acidolysis solution and the residue are separated to obtain a first purified acidolysis solution;

[0018] The first purified acidolysis solution is added into a secondary extraction tank for secondary extraction, after extraction, the crystal slurry is filtered to obtain the extractant, a first mother liquor and feed-grade dicalcium phosphate, and the feed-grade dicalcium phosphate is separated, and the first mother liquor is returned to the first acidolysis tank to prepare a nitric acid solution.

[0019] The beneficial effects of the above technical scheme are: the nitric acid is used to decompose the phosphate ore, and the product calcium nitrate after the reaction can be dissolved in the acidolysis solution, thereby avoiding the generation of by-product phosphogypsum in the process of decomposing the phosphate ore by the sulfuric acid method, significantly reducing the harm of the by-product to the surrounding ecological environment, and being an environment-friendly green process; meanwhile, the method for twice circulating and decomposing the phosphate ore avoids the excessive consumption of acid by calcium oxide in the phosphate ore in the traditional one-time acidolysis process, improves the phosphoric acid extraction efficiency, and realizes efficient removal of fluorine in the acidolysis solution, thereby avoiding the use of a defluorination agent in the conventional process, and finally the phosphoric acid extraction rate is more than 98%, the fluorine content in the acidolysis solution is reduced to below 0.15% (0.08-0.15%), the efficient use of the phosphorus resource is improved, and the economic cost is saved; the two-stage countercurrent extraction method is used to remove the nitric acid in the acidolysis solution, the phosphate ore resource is used in a graded and efficient manner, and more importantly, the additional addition of a calcium source and a crude phosphoric acid solution for neutralization to obtain the feed-grade dicalcium phosphate is avoided in the conventional process, not only the calcium resource in the phosphate ore is used in an efficient and high-value manner, but also the consumption of the additional calcium resource is reduced, the economic cost is saved, and a brand-new way is provided for the production of the feed-grade dicalcium phosphate.

[0020] In one specific embodiment of the present application, the following steps are further included:

[0021] (3) Extracting nitric acid to prepare co-production potassium nitrate: potassium chloride is used to back-extract the extractant containing nitric acid after the completion of the two-stage extraction, and after the extraction is completed, filtration separation is performed to obtain the extractant and a potassium nitrate solution, and the extractant is returned to the first extraction tank;

[0022] The seed crystal is added to the potassium nitrate solution, and the second mother liquor containing the seed crystal is cooled and crystallized, and cooled to a temperature of 20-25 DEG C, and the second mother liquor and the crystal are separated, and the obtained crystal is the potassium nitrate product.

[0023] The beneficial effects of the above technical scheme are: in the production process of dicalcium phosphate by using the hydrochloric acid method or the nitric acid method, the by-product is mainly calcium chloride or calcium nitrate, and the by-product has not been used in a high-value manner, and the present application obtains potassium nitrate by adding potassium chloride to react with nitric acid in the extractant, thereby realizing the high-value use of the by-product.

[0024] In one specific embodiment of the present application, the following steps are further included:

[0025] (4) Ammonia gas neutralization reaction to prepare co-production ammonium chloride: ammonia gas is introduced into the second mother liquor to react, the reaction is terminated when the pH of the third mother liquor is 7-8, the reaction temperature is 50-70 DEG C, and the reaction time is 30-60 min, and after the reaction, the third mother liquor is concentrated to precipitate crystals, cooled and crystallized, cooled to a final temperature of 20-25 DEG C, and separated to obtain the crystal ammonium chloride product.

[0026] The beneficial effect of the above technical scheme is that: the mother liquor containing hydrochloric acid is reacted with ammonia gas to obtain ammonium chloride product, realizing green comprehensive utilization of by-products and improving the additional economic value of the process.

[0027] In one specific embodiment of the present application, in step (1), the conditions of the first acidolysis and the second acidolysis are as follows: the amount of nitric acid added is limited by the pH of the reaction solution being 2-2.5, the liquid-solid ratio of the nitric acid to the low-grade phosphate rock powder is 2-2.5 (mass ratio), and the reaction temperature is 50-80 DEG C.

[0028] The beneficial effect of the above technical scheme is that: the method for decomposing phosphate rock through secondary circulation avoids the excessive consumption of acid by calcium oxide in the traditional one-time acidolysis process, thereby reducing the waste of acid resources and the extraction efficiency of phosphoric acid, and through the regulation of a suitable liquid-solid ratio, the extraction efficiency of phosphoric acid is improved while the efficient removal of fluorine in the acidolysis liquid is realized, thereby avoiding the use of a defluorination agent in the conventional process, and finally the extraction rate of phosphoric acid is more than 98%, the fluorine content in the acidolysis liquid is reduced to less than 0.15%, and the efficient utilization of phosphorus resources is improved and the economic cost is saved.

[0029] In one specific embodiment of the present application, in step (2), the extractant is composed of trioctylamine, triamylamine, kerosene and short carbon chain alcohol (C4-C8), and the volume ratio of the trioctylamine, triamylamine, kerosene and short carbon chain alcohol (C4-C8) is 25-40:10-25:20-40:10-30.

[0030] The beneficial effect of the above technical scheme is that: the selected extractant has high selectivity for nitric acid, and can well separate nitric acid from the acidolysis liquid into the extractant, thereby realizing the efficient removal of nitric acid in the acidolysis liquid.

[0031] In one specific embodiment of the present application, in step (2), the conditions for performing the first countercurrent extraction are as follows: the amount of the extractant added is limited by the pH of the first purified acidolysis liquid after extraction being 1.8-2.4, the extraction temperature is 40-70 DEG C, the extraction time is 10-60 min, and the volume ratio of the extractant to the first acidolysis liquid is 1.5-6:1.

[0032] In one specific embodiment of the present application, in step (2), the conditions for performing the second countercurrent extraction are as follows: the amount of the extractant added is limited by the pH of the second purified acidolysis liquid after extraction being 4-5, the extraction temperature is 40-70 DEG C, the extraction time is 30-60 min, and the volume ratio of the extractant to the second acidolysis liquid is 1.5-6:1.

[0033] The beneficial effects of the above technical scheme are: the present application removes nitric acid in the acidolysis solution by the way of secondary countercurrent extraction, reduces the pH of the acidolysis solution in stages, and makes the white fertilizer residue containing metal impurity ions and the feed-grade calcium hydrogen phosphate precipitate in turn, so that the phosphorite resources are used efficiently in stages, and more importantly, the additional calcium source and the crude phosphoric acid solution for neutralization to obtain the feed-grade calcium hydrogen phosphate are avoided in the conventional process, not only the calcium resources in the phosphorite are used efficiently and in high value, but also the consumption of the additional calcium resources is reduced, the economic cost is saved, and a new way for the production of the feed-grade calcium hydrogen phosphate is provided.

[0034] In one specific embodiment of the present application, in the step (3), the conditions for the back extraction are: the back extraction temperature is 50-60 DEG C, the back extraction time is 30-60 min, and the addition amount of potassium chloride is 1-1.1:1 of the molar ratio of potassium ions to nitrate ions in the extractant.

[0035] In one specific embodiment of the present application, in the step (3), the seed crystal is industrial-grade potassium nitrate, and the addition amount of the seed crystal is 1%-5% of the mass of potassium nitrate contained in the potassium nitrate aqueous solution.

[0036] The beneficial effects of the present application are: the present application uses nitric acid to decompose the phosphorite through secondary circulation cross flow, removes the nitric acid in the acidolysis solution by the way of secondary countercurrent extraction, effectively improves the extraction efficiency of the phosphoric acid, and also realizes the efficient removal of fluorine in the acidolysis solution, avoids the use of the defluorination agent in the conventional process, and more importantly, the additional calcium source and the crude phosphoric acid solution for neutralization to obtain the feed-grade calcium hydrogen phosphate are avoided in the conventional process, not only the calcium resources in the phosphorite are used efficiently and in high value, but also the consumption of the additional calcium resources is reduced, the economic cost is saved, and a new way for the production of the feed-grade calcium hydrogen phosphate is provided. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The process flow chart of the method for the high-value comprehensive utilization of the low-grade phosphorite to prepare the feed-grade calcium hydrogen phosphate of the present application. DETAILED DESCRIPTION

[0038] To make the purpose, technical scheme and advantages of the present application more clear, the technical scheme of the present application will be described in detail below. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor belong to the scope protected by the present application.

[0039] The low-grade phosphorite powder used in the following embodiments mainly contains the following components (mass fraction, %):

[0040]

[0041] The mass concentration of the nitric acid used is 30-40%.

[0042] Example 1

[0043] A method for preparing feed-grade dicalcium phosphate by high-value comprehensive utilization of low-grade phosphate rock, comprising the following steps:

[0044] (1) Take 30 g of low-grade phosphate rock powder, add 20 mL of 30% mass concentration nitric acid for first acidolysis, the temperature during acidolysis is 70°C, and after acidolysis is completed, the pH of the solution is 2.1. The first acidolysis is followed by filtration, and the separated filter residue is introduced into the second acidolysis tank, and the separated first acidolysis solution is introduced into the first extraction tank. The first acidolysis filter residue is added to the second acidolysis tank, and 40 mL of 30% mass concentration nitric acid is added for second acidolysis, the temperature during acidolysis is 70°C, and after acidolysis is completed, the pH of the solution is 2.1. The second acidolysis is followed by filtration, and the separated filter residue containing calcium fluoride is obtained, and the filtered second acidolysis solution is returned to the first acidolysis tank.

[0045] (2) The first acidolysis solution in step (1) is subjected to secondary countercurrent extraction using an extractant composed of trioctylamine, triamylamine, n-butanol and kerosene, with a volume ratio of 3:2:1:4, and the volume ratio of the extractant to the first acidolysis solution is 4:1, the extraction temperature is 50°C, the extraction time is 30 min, and the pH of the acidolysis solution after first extraction is 2.1. After extraction, the extractant, the first acidolysis solution and the filter residue are separated to obtain the first purified acidolysis solution from which iron, magnesium and aluminum impurities are removed. Subsequently, the first purified acidolysis solution is introduced into the second extraction tank, the extraction temperature is 50°C, the extraction time is 40 min, the volume ratio of the extractant to the second acidolysis solution is 4:1, and the pH of the acidolysis solution after second extraction is 4.5. After the second purified acidolysis solution is extracted, the crystal slurry is filtered to obtain the feed-grade dicalcium phosphate product, and the first mother liquor is returned to the first acidolysis tank to prepare a nitric acid solution.

[0046] It is calculated that the recovery rate of phosphorus pentoxide in the phosphate rock in this embodiment is 98.5% (the calculation method is: recovery rate = phosphorus pentoxide content in the acidolysis solution entering the first extraction / phosphorus pentoxide content in the phosphate rock * 100), the fluorine content in the first acidolysis solution is 0.1%, and the recovery rate of phosphorus pentoxide in the feed-grade dicalcium phosphate is 75%.

[0047] Example 2

[0048] A method for preparing feed-grade dicalcium phosphate by high-value comprehensive utilization of low-grade phosphate rock, comprising the following steps:

[0049] (1) take 30g low-grade phosphate rock powder, add 20ml of 30% mass concentration nitric acid for the first acidolysis, the temperature is 70℃ during acidolysis, the solution pH = 2.1 after acidolysis, wherein, the first acidolysis is filtered, the obtained filter residue is put into the second acidolysis tank, and the first acidolysis solution is separated and obtained into the first extraction tank; the first acidolysis filter residue is added into the second acidolysis tank, 40ml of 30% mass concentration nitric acid is added for the second acidolysis, the temperature is 70℃ during acidolysis, the solution pH = 2.1 after acidolysis, the second acidolysis is filtered, and the obtained filter residue containing calcium fluoride is separated, and the second acidolysis solution after filtration is returned to the first acidolysis tank;

[0050] (2) the first acidolysis solution in step (1) is subjected to secondary countercurrent extraction with an extractant, the extractant is composed of trioctylamine, triamylamine, n-butanol and kerosene, the volume ratio is 3:2:1:4, the volume ratio of the extractant and the first acidolysis solution is 4:1, the extraction temperature is 50℃, the extraction time is 30min, the pH of the acidolysis solution after the first extraction is 2.1, the extractant, the first acidolysis solution and the filter residue are separated after extraction, the first purified acidolysis solution in which the iron, magnesium and aluminum impurities are removed is obtained, then the first purified acidolysis solution is put into the second extraction tank, the extraction temperature is 50℃, the extraction time is 40min, the volume ratio of the extractant and the second acidolysis solution is 4:1, the pH of the acidolysis solution after the second extraction is 4.5, the second purified acidolysis solution is filtered after the extraction is completed, and the feed-grade dicalcium phosphate product is obtained, and the first mother liquor is returned to the first acidolysis tank to prepare a nitric acid solution.

[0051] (3) the extractant containing nitric acid after the second extraction is back-extracted with a potassium chloride aqueous solution, the back-extraction temperature is 50℃, the back-extraction time is 40min, the amount of potassium chloride added is that the molar ratio of potassium ions to nitrate ions in the extractant is 1.05:1, then the extractant and the potassium nitrate solution after back-extraction are filtered and separated, and the extractant is returned to the first extraction tank in step (2);

[0052] (4) crystal seeds are added to the potassium nitrate solution separated in step (3), the amount of the crystal seeds added is 2.1% of the mass of the potassium nitrate contained in the second mother liquor, then the second mother liquor containing the crystal seeds is cooled and crystallized, the final temperature is 22℃, and the second mother liquor and the crystal are separated, and the obtained crystal is a potassium nitrate product;

[0053] (5) ammonia gas is passed into the second mother liquor separated in step (4) to react, the pH of the third mother liquor after the reaction is terminated is 7.5, wherein the reaction temperature is 60℃, and the reaction time is 30min, the third mother liquor after the reaction is concentrated until a small amount of crystal is precipitated, then cooled and crystallized, the final temperature is 22℃, and the separated crystal is an ammonium chloride product, and the third mother liquor is returned to step (3) to prepare a potassium chloride solution.

[0054] Example 3

[0055] A method for preparing feed-grade dibasic calcium phosphate from low-grade phosphate ore through high-value comprehensive utilization, comprising the following steps:

[0056] (1) Take 30g of low-grade phosphate ore powder, add 25mL of 30% mass concentration nitric acid for first acidolysis, the temperature during acidolysis is 70℃, after acidolysis, the pH of the solution is 2.0, wherein, after the first acidolysis, filtration is performed, the obtained filter residue is introduced into the second acidolysis tank, and the obtained first acidolysis solution is introduced into the first extraction tank; the first acidolysis filter residue is added into the second acidolysis tank, 40mL of 40% mass concentration nitric acid is further added for second acidolysis, the temperature during acidolysis is 70℃, after acidolysis, the pH of the solution is 2.1, after the second acidolysis, filtration is performed, the obtained filter residue containing calcium fluoride is separated, and the filtered second acidolysis solution is returned to the first acidolysis tank;

[0057] (2) The first acidolysis solution in step (1) is subjected to secondary countercurrent extraction using an extractant, the extractant is composed of trioctylamine, triamylamine, n-butanol and kerosene, the volume ratio of the extractant is 3:2:2:3, the volume ratio of the extractant to the first acidolysis solution is 5:1, the extraction temperature is 50℃, the extraction time is 40min, the pH of the acidolysis solution after the first extraction is 2.0, after extraction, the extractant, the first acidolysis solution and the filter residue are separated to obtain the first purified acidolysis solution from which iron, magnesium and aluminum impurities are removed, then the first purified acidolysis solution is introduced into the second extraction tank, the extraction temperature is 50℃, the extraction time is 40min, the volume ratio of the extractant to the second acidolysis solution is 5:1, the pH of the acidolysis solution after the second extraction is 4.7, after the second purified acidolysis solution is extracted, the crystal slurry is filtered to obtain the feed-grade dibasic calcium phosphate product, and the first mother liquor is returned to the first acidolysis tank to prepare a nitric acid solution;

[0058] (3) The extractant containing nitric acid after the secondary extraction is back-extracted using a potassium chloride aqueous solution, the back-extraction temperature is 50℃, the back-extraction time is 40min, the amount of potassium chloride added is such that the molar ratio of potassium ions to nitrate ions in the extractant is 1.1:1, then the back-extracted extractant and the potassium nitrate solution are filtered and separated, and the extractant is returned to the first extraction tank in step (2);

[0059] (4) Crystal seeds are added to the potassium nitrate solution separated in step (3), the amount of the crystal seeds added is 2.5% of the mass of potassium nitrate contained in the second mother liquor, then the second mother liquor containing the crystal seeds is cooled and crystallized, the final temperature is 22℃, and the second mother liquor and the crystal are separated, and the obtained crystal is a potassium nitrate product;

[0060] (5) the second mother liquor separated in step (4) is reacted with ammonia gas, and after the reaction is terminated, the pH of the third mother liquor is 7.8, wherein the reaction temperature is 60°C, and the reaction time is 30 min; the third mother liquor after the reaction is concentrated to have a small amount of crystals precipitated, and then cooled and crystallized, and the final temperature is cooled to 22°C; the separated crystals are ammonium chloride products, and the third mother liquor is returned to step (3) to prepare a potassium chloride solution.

[0061] It is calculated that the recovery rate of the phosphorus pentoxide in the phosphorite in the embodiment is 98.9%, the fluorine content in the first acidolysis solution is 0.09%, and the recovery rate of the phosphorus pentoxide in the feed-grade dicalcium phosphate is 77%.

[0062] Embodiment 4

[0063] A method for preparing feed-grade dicalcium phosphate by comprehensively utilizing low-grade phosphorite at high value, comprising the following steps:

[0064] (1) 30 g of low-grade phosphorite powder is taken, and 10 mL of nitric acid with a mass concentration of 30% is added for first acidolysis, and the temperature during acidolysis is 70°C; after the acidolysis is completed, the pH of the solution is 2.2; wherein, after the first acidolysis, filtration is performed, the separated filter residue is fed into a second acidolysis tank, and the separated first acidolysis solution is fed into a first extraction tank; the first acidolysis filter residue is added into the second acidolysis tank, and 50 mL of nitric acid with a mass concentration of 30% is further added for second acidolysis, and the temperature during acidolysis is 70°C; after the acidolysis is completed, the pH of the solution is 2.2; after the second acidolysis, filtration is performed, and the separated filter residue containing calcium fluoride is obtained, and the filtered second acidolysis solution is returned to the first acidolysis tank;

[0065] (2) the first acidolysis solution in step (1) is subjected to secondary countercurrent extraction by using an extractant, the extractant is composed of trioctylamine, triamylamine, n-butanol and kerosene, and the volume ratio of the extractant is 3:2:1:4; the volume ratio of the extractant to the first acidolysis solution is 4.5:1; the extraction temperature is 60°C; the extraction time is 30 min; after the first extraction, the pH of the acidolysis solution is 2.2; after the extraction, the extractant, the first acidolysis solution and the filter residue are separated, and the first purified acidolysis solution in which iron, magnesium and aluminum impurities are removed is obtained; subsequently, the first purified acidolysis solution is fed into a second extraction tank, the extraction temperature is 60°C, the extraction time is 40 min, the volume ratio of the extractant to the second acidolysis solution is 4.5:1, and the pH of the acidolysis solution after the secondary extraction is 4.8; after the second purified acidolysis solution is extracted, the crystal slurry is filtered to obtain feed-grade dicalcium phosphate products, and the first mother liquor is returned to step (1) to prepare a nitric acid solution;

[0066] (3) using potassium chloride aqueous solution to back-extract the extractant containing nitric acid after the secondary extraction, the back-extraction temperature is 60°C, the back-extraction time is 40 min, the adding amount of potassium chloride is that the molar ratio of potassium ion to nitrate ion in the extractant is 1.1:1, then the back-extracted extractant and potassium nitrate solution are filtered and separated, and the extractant returns to the primary extraction tank in step (2);

[0067] (4) adding crystal seeds to the potassium nitrate solution separated in step (3), the adding amount of the crystal seeds is 2.8% of the mass of potassium nitrate contained in the second mother liquor, then the second mother liquor containing the crystal seeds is cooled and crystallized, the cooling is to the final temperature of 22°C, and the second mother liquor is separated from the crystals, and the obtained crystals are the potassium nitrate product;

[0068] (5) passing ammonia gas into the second mother liquor separated in step (4) to react, after the reaction is terminated, the pH of the third mother liquor is 8, the reaction temperature is 60°C, and the reaction time is 30 min, the third mother liquor after the reaction is concentrated to have crystals precipitated, then cooled and crystallized, the cooling is to the final temperature of 22°C, and the separated crystals are the ammonium chloride product, and the third mother liquor returns to step (3) to prepare the potassium chloride solution.

[0069] It is calculated that the recovery rate of the phosphorus pentoxide in the phosphorite in the embodiment is 99.2%, the fluorine content in the first acid hydrolysis solution is 0.08%, and the recovery rate of the phosphorus pentoxide in the feed-grade dicalcium phosphate is 80%.

Claims

1. A method for preparing feed-grade dicalcium phosphate through high-value comprehensive utilization of low-grade phosphate rock, characterized in that, include: (1) Secondary decomposition of phosphate rock with nitric acid: Add nitric acid with a mass concentration of 30-40% to low-grade phosphate rock powder for the first acid hydrolysis. After the reaction is completed, filter to separate the first acid hydrolysis residue and the first acid hydrolysis liquid. The first acid hydrolysis filter residue is added to the second acid hydrolysis tank, and then nitric acid with a mass concentration of 30-40% is added for the second acid hydrolysis. After the reaction is completed, the filter is filtered to separate the calcium fluoride filter residue and the second acid hydrolysis solution. The second acid hydrolysis solution is added to the first acid hydrolysis tank. (2) Preparation of feed-grade dicalcium phosphate by two-stage countercurrent extraction: The first acid hydrolysate is added to the first-stage extraction tank, and then an extractant is added for first-stage extraction. After extraction, the extractant, the first acid hydrolysate and the filter residue are separated to obtain the first purified acid hydrolysate. The first purified acid hydrolysate is then added to the secondary extraction tank for secondary extraction. After extraction, the crystal slurry is filtered to obtain the extractant, the first mother liquor, and feed-grade dicalcium phosphate. Feed-grade dicalcium phosphate is separated, and the first mother liquor is returned to the first acid hydrolysate tank to prepare nitric acid solution. In step (2), the extractant is composed of trioctylamine, triammonium amine, kerosene and C4-C8 short-chain alcohol, and the volume ratio of the trioctylamine, triammonium amine, kerosene and C4-C8 short-chain alcohol is 25-40:10-25:20-40:10-30.

2. The method for preparing feed-grade dicalcium phosphate by high-value comprehensive utilization of low-grade phosphate rock according to claim 1, characterized in that, it further... include: (3) Extraction of nitric acid to produce potassium nitrate: Potassium chloride is used to back-extract the extractant containing nitric acid after the secondary extraction. After extraction, the extractant and potassium nitrate solution are obtained by filtration. The extractant is returned to the primary extraction tank. Seed crystals are added to the potassium nitrate solution, and then the second mother liquor containing the seed crystals is cooled to crystallize. The temperature is cooled to 20-25°C, and the second mother liquor and crystals are separated. The resulting crystals are potassium nitrate products.

3. The method for preparing feed-grade dicalcium phosphate by high-value comprehensive utilization of low-grade phosphate rock according to claim 2, characterized in that, it further... include: (4) Preparation of co-produced ammonium chloride by neutralization reaction with ammonia: Ammonia is introduced into the second mother liquor to carry out the reaction. The reaction is terminated when the pH of the third mother liquor is 7-8. The reaction temperature is 50-70℃ and the reaction time is 30-60min. After the reaction, the third mother liquor is obtained. The third mother liquor is concentrated until crystals precipitate. It is cooled to crystallize. It is cooled to a final temperature of 20-25℃ and separated to obtain crystalline ammonium chloride product.

4. The method for preparing feed-grade dicalcium phosphate by high-value comprehensive utilization of low-grade phosphate rock according to claim 1, characterized in that, In step (1), the conditions for the first acidolysis and the second acidolysis reaction are as follows: the amount of nitric acid added is limited to the pH of the reaction solution being 2-2.5, the liquid-solid ratio of the nitric acid to the low-grade phosphate rock powder is 2-2.5, and the reaction temperature is 50-80℃.

5. The method for preparing feed-grade dicalcium phosphate by high-value comprehensive utilization of low-grade phosphate rock according to claim 1, characterized in that, In step (2), the specific conditions for performing primary countercurrent extraction are as follows: the amount of extractant added is such that the pH of the first purified acid hydrolysate after extraction is 1.8-2.4, the extraction temperature is 40-70℃, the extraction time is 10-60min, and the volume ratio of extractant to the first acid hydrolysate is 1.5-6:

1.

6. The method for preparing feed-grade dicalcium phosphate by high-value comprehensive utilization of low-grade phosphate rock according to claim 1, characterized in that, In step (2), the specific conditions for performing secondary countercurrent extraction are as follows: the amount of extractant added is limited to the pH of the second purified acid hydrolysate after extraction being 4-5, the extraction temperature is 40-70℃, the extraction time is 30-60min, and the volume ratio of extractant to second acid hydrolysate is 1.5-6:

1.

7. The method for preparing feed-grade dicalcium phosphate by high-value comprehensive utilization of low-grade phosphate rock according to claim 2, characterized in that, In step (3), the back-extraction conditions are: back-extraction temperature is 50-60℃, back-extraction time is 30-60min, and the amount of potassium chloride added is based on the molar ratio of potassium ions to nitrate ions in the extractant as 1-1.1:

1.

8. The method for preparing feed-grade dicalcium phosphate from low-grade phosphate rock through high-value comprehensive utilization according to claim 2 or 7, characterized in that, In step (3), the seed crystal is industrial-grade potassium nitrate, and the amount of seed crystal added is 1%-5% of the mass of potassium nitrate contained in the potassium nitrate aqueous solution.

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