CN111517832A - Separation method of P and Ca in medium and low grade phosphate rock and method for producing fertilizer - Google Patents

Abstract

The invention relates to a separation method of P, Ca in medium and low grade phosphorite and a method for producing fertilizer, belonging to the technical field of phosphorite cleaning processing and utilization. The separation method of P, Ca in the medium and low grade phosphate ore comprises the following steps: (1) mixing phosphorite and nitric acid solution, reacting for 0.5-2 h at 30-70 ℃, and carrying out solid-liquid separation to obtain an acid insoluble substance and an acidolysis clear solution; (2) neutralizing the acidolysis clear solution, and controlling the pH of the solution to be not less than 3.5 and not more than 6.5; then, performing solid-liquid separation to obtain a solid phase I and a liquid phase I; (3) mixing the solid phase I and a nitric acid solution, and reacting for 0.3-2 h at 30-70 ℃ to obtain a second-stage acidolysis solution; (4) cooling the secondary acidolysis solution to-10-0 ℃ for crystallization; and after the crystallization is finished, carrying out solid-liquid separation to obtain a solid phase II and a liquid phase II. The process greatly improves the separation rate of P, Ca of the medium and low grade phosphorite, improves the resource utilization rate of P, Ca and the like, and opens up a new technical route for processing the medium and low grade phosphorite by a nitric acid method.

Description

Separation method of P and Ca in medium and low grade phosphate rock and method for producing fertilizer

technical field

The invention relates to a method for separating P and Ca in low-grade phosphate rock and a method for producing fertilizer, belonging to the technical field of clean processing and utilization of phosphate rock.

Background technique

Phosphate resource is an important strategic resource of the country and the material basis of the phosphorus chemical industry. It is non-renewable. my country is rich in phosphate rock, but more than 80% of it is medium and low-grade phosphate rock that is difficult to use directly.

The processing and utilization of phosphate rock mainly include thermal method and wet method, and the wet method mainly includes hydrochloric acid method, sulfuric acid method and nitric acid method. The vast majority of phosphate rock processing enterprises in my country adopt acid wet process. For every ton of phosphoric acid (calculated as P ₂ O ₅ ) produced by the sulfuric acid method, 5 to 5.5 tons of phosphogypsum waste residue will be discharged, with a total annual discharge of nearly 88 million tons, accumulative storage of hundreds of millions of tons, and a comprehensive utilization rate of less than 30%. Phosphogypsum is mainly discharged in the open air, occupying a lot of land and polluting the ecological environment. Therefore, there is an urgent need to develop clean processing technology for phosphate rock, reduce solid waste discharge in the production process, and achieve environmental protection, cleanliness, safety and green development in the process of phosphate rock processing. Wet-process phosphoric acid by hydrochloric acid method is hardly affected by raw materials, does not require high grade of phosphate rock, and does not produce phosphogypsum solid waste. However, due to the presence of chloride ions in the hydrochloric acid method, the equipment will be corroded, and the calcium chloride produced by the process is difficult to separate and directly use, and the production and application limitations are very obvious. Compared with the sulfuric acid method and the hydrochloric acid method, the nitric acid method does not have high requirements on the grade of phosphate rock, and the decomposition rate of the phosphate rock is high, so it is more meaningful and promising to deal with the phosphate rock. Nitric acid plays a dual role in the process of treating phosphate rock. It not only uses the chemical energy of nitric acid to decompose phosphate rock, but also converts it into nitrogen fertilizer for use, which improves the utilization rate of raw materials, and the nitric acid method does not produce solid waste, so it is a clean and efficient phosphate rock. processing technology.

Nitrophosphate fertilizer refers to the general term for fertilizers containing nitrogen and phosphorus produced by decomposing phosphate rock with nitric acid. Nitrophosphate fertilizer developed rapidly in Europe, which lacked sulfur resources. In the 1970s and 1980s, due to the oil crisis, the price of sulfur rose. Nitrophosphate fertilizer has developed rapidly in many countries, and many large-scale production facilities have also been built. Judging from the composition of nitrophosphate fertilizer, it not only has quick-acting NO ₃ ^- , NH ₄ ⁺ and water-soluble P ₂ O ₅ , but also has long-lasting citric-soluble P ₂ O ₅ and Ca ²⁺ , which is suitable for dryland crops. The molar ratio of CaO/P ₂ O ₅ in the phosphate rock is generally above 3.33:1. If the acid hydrolyzate of the phosphate rock is directly ammoniated and neutralized by nitric acid, the P ₂ O ₅ will be precipitated as CaHPO ₄ as citric acid-soluble phosphorus, and even degenerate into insoluble phosphorus. Therefore, industrially, various methods are taken to remove CaO. According to different treatment methods, there are mainly freezing method, nitric acid-sulfate method, nitric acid-phosphoric acid method, nitric acid-carbonization method, nitro calcium superphosphate method, etc.

The key technology of nitrophosphate fertilizer is the separation of calcium nitrate in acid hydrolyzate. The separation rate of calcium nitrate is low, the content of water-soluble phosphorus in nitrophosphate fertilizer is low, and the product is difficult to meet the requirements of qualified products (25-10-0) in GB/T 10510-2007 standard. Therefore, in actual production, enterprises use high-quality phosphate rock to increase the concentration of phosphoric acid in the acid hydrolyzate and improve the separation rate. According to the phase diagram of the CaO-P ₂ O ₅ -N ₂ O ₆ -H ₂ O system shown in Figure 2 of the specification, the concentration of phosphoric acid in the acid hydrolysis solution has a great influence on the solubility of calcium nitrate tetrahydrate. In acidic medium, phosphate in Ca(NO ₃ ) ₂ ·4H ₂ O crystallization zone has a salting-out effect on calcium nitrate. In the presence of phosphoric acid and nitric acid, the solubility of calcium nitrate is significantly reduced. The higher the concentration of phosphoric acid, the more crystals of Ca(NO ₃ ) ₂ ·4H ₂ O precipitated, generally n[H ₆ (PO ₄ ) ₂ ]:n[H ₆ (NO ₃ ) ₆ ]=0.53～0.6 phosphoric acid is more suitable. Therefore, properly increasing the concentration of phosphoric acid in the acid hydrolysis solution in the theoretical crystallization zone and reducing the dissolved amount of calcium nitrate in phosphoric acid are the prerequisites for producing qualified nitrophosphate fertilizers.

CN109160828A discloses a method for twice ammonia neutralization and concentration of mother liquor in the process of freezing method nitrophosphate fertilizer. The preparation method is as follows: the acid hydrolyzate obtained by decomposing phosphate rock with nitric acid to filter out acid insoluble matter is frozen to separate the mother liquor of calcium nitrate Add ammonium nitrate solution and ammonia to the neutralization tank, and neutralize until the solution is 1.0≤pH≤2.5. After the neutralization slurry is evaporated and concentrated, the second neutralization reaction is carried out with ammonia in a tubular reactor, and the neutralization is performed until the slurry is 5.0≤pH≤6.5. Due to the presence of Ca ²⁺ and other metal ions in the decalcification mother liquor, the viscosity of the slurry increases with the increase of solution pH. The addition of ammonium nitrate solution overcomes the problem of clogging caused by the increase of viscosity and increases the nitrogen content in the product. . In this process, the evaporation process is between the two ammonia neutralization processes, which overcomes the problem of the slurry clogging the pipeline during the evaporation and concentration process.

CN105198503A discloses a system and method for improving the water solubility of nitrophosphate fertilizer product P ₂ O ₅ . The preparation method is as follows: acid hydrolyzate obtained by filtrating phosphate rock with nitric acid to remove acid insoluble matter, and separating the mother liquor of calcium nitrate and nitric acid by freezing Ammonium solution, potassium sulfate solution and ammonia are added to the neutralization tank, and potassium sulfate is used to precipitate calcium ions in the solution to reduce the generation of citric acid-soluble and insoluble calcium phosphate salts, thereby improving the water solubility of the product. The water solubility of the product can reach 80%, reaching the standard of high-grade nitrophosphate fertilizer.

CN104909841A discloses a method for producing nitrophosphate fertilizer by-product gypsum by decomposing phosphate rock with nitric acid. The preparation method is as follows: adding ammonium sulfate or sulfuric acid to the acid hydrolyzate obtained by filtering phosphate rock with nitric acid to remove acid-insoluble matter, and after filtering and separating A gypsum solid phase is obtained, and the filtrate is neutralized, evaporated and granulated to obtain a nitrophosphate fertilizer.

CN 1067644 A discloses a production method of nitrophosphate fertilizer. The preparation method is as follows: firstly, a circulating solution containing calcium dihydrogen phosphate, calcium nitrate and nitric acid is prepared, and calcium nitrate is precipitated by freezing at -5°C to 25°C, and the filtrate is mixed with nitric acid. After nitric acid decomposes phosphate rock, the acid hydrolyzate containing calcium dihydrogen phosphate and calcium nitrate is mixed, and then filtered to obtain calcium dihydrogen phosphate. Part of the filtrate is used to decompose phosphate rock, and the other part is used as a circulating solution after supplementing nitric acid to produce calcium nitrate and calcium nitrate. Calcium dihydrogen phosphate. In the aqueous solution containing saturated monoammonium phosphate and ammonium chloride, add a certain amount of calcium nitrate solution and freeze to 0 ~ 25 ° C, filter and separate the crystallized calcium nitrate tetrahydrate, separate the mother liquor after evaporating part of the water at 20 ~ 55 ° C Add ammonium nitrate and calcium dihydrogen phosphate metathesis reaction to obtain monoammonium phosphate crystal, which is the final nitrophosphate fertilizer product. The separated mother liquor is used as a circulating liquid to continue producing calcium nitrate and monoammonium phosphate.

CN 102731191 A discloses an ammonia neutralization process for nitrophosphate fertilizer mother liquor, the preparation method of which is as follows: acid slurry obtained by carrying out normal pressure neutralization reaction with gas ammonia and phosphoric acid mother liquor from a calcium nitrate filtration process in a first-stage neutralization device , and then sent to the second-stage forced circulation device to continue the ammoniation and neutralization reaction so that the pH of the outlet slurry is 5.6-6.0, and the water content is 10%-15%. And carry out absorption and purification, the tail gas from the first stage of neutralization enters the neutralization tail gas for washing, and is washed and absorbed by the nitric acid aqueous solution and then discharged, and the washing liquid is sent to the second-stage neutralization device.

CN 102351590 B discloses a method for producing highly water-soluble nitric phosphate fertilizer by decomposing phosphate rock calcium nitrate with nitric acid, and the preparation method is as follows: adding sodium nitrate to defluoride the acid hydrolyzate obtained by decomposing phosphate rock with nitric acid and filtering acid-insoluble matter into the mother liquor, The defluorination slag is separated by filtration; the obtained defluorination liquid is cooled and crystallized, and ammonium sulfate is added to the decalcified mother liquor after filtration and separation to carry out metathesis for further decalcification; the filtrate after filtration and separation of calcium sulfate is neutralized with ammonia water to remove impurities, calcium ions and metals Impurity ions generate phosphate precipitation to separate the system, and the filtrate is evaporated, concentrated and crystallized to obtain nitrophosphate fertilizer with a water solubility of 99%.

The above-mentioned patents are improved and upgraded on the basis of the traditional nitric acid method for processing phosphate rock, but they all use high-quality phosphate rock; my country is mainly based on medium and low-grade phosphate rock, and flotation is required to obtain high-quality phosphate rock. It not only produces a large amount of tailings by-product, which poses a threat to the environment, but also reduces the utilization rate of elements such as calcium and phosphorus in medium and low-grade phosphate rock.

CN101486595A discloses a process method for producing high-concentration nitrophosphate fertilizer. The preparation method is as follows: acid hydrolyzate obtained by decomposing low-grade phosphate rock with nitric acid and filtering out acid-insoluble matter; The precipitated calcium ions are removed by the reaction, and calcium sulfate precipitate and filtrate are obtained after filtration and separation. The filtrate is neutralized with ammonium nitrate solution and gas ammonia to obtain nitrophosphate fertilizer slurry, which is concentrated, granulated and dried to obtain nitrophosphate fertilizer. The phosphoric acid concentration obtained by this technology is low, and the concentration process needs to consume a lot of energy.

CN 104909841 A discloses a method for preparing ammonium calcium magnesium phosphate and ammonium calcium magnesium nitrate by decomposing middle and low grade phosphate rock with nitric acid. Neutralize directly with ammonia to 5.0≤pH≤7.0, filter and wash the solid phase obtained as calcium-magnesium phosphate mixture, evaporate the filtrate and granulate to obtain ammonium nitrate, calcium-magnesium mixture.

CN 109251062 A discloses a kind of nitric acid phosphate fertilizer with low water insoluble content, and its preparation method is as follows: acid hydrolysis filtration obtained by decomposing middle and low grade phosphate rock with nitric acid, sedimentation and plate and frame filter filter to remove acid insoluble matter to ensure acid hydrolysis solution The acid-insoluble content in the acid solution accounts for ≤5% of the weight of the acid hydrolyzate; the acid hydrolyzate filtrate is frozen and crystallized at -10°C to 0°C, and most of the calcium nitrate is separated out by vacuum filtration at -2 to 1°C; Neutralize the decalcified mother liquor to pH=5～7 with an alkaline substance, and the insoluble content in the liquid phase is lower than 0.1%; the filtrate obtained after the neutralization slurry is filtered and separated is concentrated, heated, melted and granulated to obtain water insoluble Nitrophosphate fertilizer with a content of less than 0.2%.

The above two patents use nitric acid to decompose phosphate rock, and the raw materials are medium and low-grade phosphate rock. The latter obtains nitrophosphate fertilizer with low water-insoluble content; according to the phase diagram theory of water-salt system, since this technology uses nitric acid to decompose medium and low-grade phosphate rock, the concentration of phosphoric acid in the acid hydrolyzate is low, and the tetrahydrate nitric acid is removed by freezing. Calcium is limited. The patent neutralizes the decalcification mother liquor with an alkaline substance, so that the calcium ions in it are combined with phosphate to form calcium phosphate precipitation, and then the deep decalcification mother liquor is used to produce nitrophosphate fertilizer. The water-soluble nitrophosphate fertilizer produced by this patent has a low yield and a large amount of Phosphorus generates insoluble calcium phosphate salt, which is difficult to produce good economic benefits.

SUMMARY OF THE INVENTION

In view of the above problems, the present invention provides a method for separating P and Ca in low-grade phosphate rock and improving the utilization rate of elements such as P and Ca.

For nitric acid decomposing medium and low-grade phosphate rock technology, the present invention proposes: first neutralize the acid hydrolyzate from which acid-insoluble matter is separated out to all phosphorus precipitation with an alkaline substance, filter and separate to obtain precipitation and filtrate I, and carry out secondary precipitation with nitric acid After acid hydrolysis, the calcium nitrate is separated by freezing, and the filtrate II after the separation of calcium nitrate is filtered and neutralized with ammonia to produce nitrophosphate fertilizer. Filtrate I and the calcium nitrate precipitated by freezing crystallization are used to produce fully water-soluble calcium ammonium nitrate fertilizer. The present invention can directly utilize medium and low grade phosphate rock, and no phosphogypsum is produced in the process, and N, P and Ca in the raw material are finally turned into products; , Phosphorus and other elements utilization rate is greatly improved. The invention can open up a new economical and feasible technical route for processing low-grade phosphate rock by nitric acid method.

The method for separating P and Ca in low-grade phosphate rock comprises the following steps:

(1) Primary acid hydrolysis: mix phosphate rock and nitric acid solution, react at 30-70 °C for 0.5-2 h, and then separate solid-liquid to obtain acid-insoluble matter and acid-lysed clear liquid;

(2) Neutralization: neutralize the acid hydrolyzed clear liquid, and control the solution to be 3.5≤pH≤6.5; and then separate solid-liquid to obtain solid phase I and liquid phase I;

(3) Secondary acid hydrolysis: Mix solid phase I and nitric acid solution, and react at 30～70° C. for 0.3～2h to obtain secondary acid hydrolysis solution;

(4) Frozen crystallization: the secondary acid hydrolyzate is cooled to -10°C to 0°C for crystallization; after the crystallization is completed, the solid-liquid separation is performed to obtain solid phase II and liquid phase II;

Wherein, the liquid phase I is a calcium-containing liquid, the liquid phase II is a phosphorus-containing liquid, and the solid phase II is a calcium-containing solid.

In a specific embodiment, in step (1), the phosphate rock is in the form of powder or slurry, and the water content in the phosphate rock is 0-40 wt %; the nitric acid concentration is 30-70 wt %.

In a specific embodiment, in step (1), the amount of nitric acid is 0.9 to 1.2 times the theoretical acid consumption for the complete reaction of phosphate rock; more preferably, the amount of nitric acid is 0.9 to 0.9 to 1.2 times the theoretical acid consumption for the complete reaction of phosphate rock 1.1 times.

In a specific embodiment, in step (1), the solid-liquid separation is performed in two steps, firstly performing sedimentation separation, and then filtering and separating the liquid after sedimentation and separation.

In a specific embodiment, in step (2), an alkaline neutralizer is used for the neutralization; preferably, the alkaline neutralizer is ammonia gas, ammonia water, limestone, milk of lime, ammonium carbonate and At least one of ammonium bicarbonate.

In a specific embodiment, in step (3), the concentration of the nitric acid solution is 30 to 70 wt %, and the amount of nitric acid is 0.9 to 1.2 times the theoretical acid consumption of the solid phase I complete reaction; Phase 1 completely reacts 0.9 to 1.1 times of the theoretical acid consumption.

In a specific embodiment, in step (4), the secondary acid hydrolysis solution is cooled to -5°C to 0°C for crystallization.

The invention also provides a method for producing fertilizer by utilizing medium and low grade phosphate rock.

The method for producing fertilizer, firstly adopts the separation method of P and Ca in the described medium and low grade phosphate rock to obtain liquid phase I, liquid phase II and solid phase II; neutralize liquid phase II to obtain nitrophosphate fertilizer; Phase II and liquid phase I are mixed to obtain calcium-containing fertilizer.

In a specific embodiment, when the liquid phase II is neutralized, the neutralizing agent used is at least one of gas ammonia, ammonia water, ammonium carbonate or ammonium bicarbonate.

In a specific embodiment, the neutralized liquid phase II is concentrated and dried to obtain nitrophosphate fertilizer.

In a specific embodiment, after the solid phase II and the liquid phase I are mixed, a substance containing nutrient elements is added to adjust the nutrients of the product to obtain calcium nitrate fertilizer or calcium ammonium nitrate fertilizer; The substance is at least one of ammonia, ammonium nitrate and calcium nitrate.

Beneficial effects of the present invention:

1. The present invention can directly utilize medium and low grade phosphate rock of various grades, and does not need to carry out flotation of medium and low grade phosphate rock;

2. The utilization rate of calcium, phosphorus and other elements in medium and low grade phosphate rock is greatly improved, which has good economic benefits;

3. The present invention can reduce the energy consumption required for freezing and reduce the cost;

4, the calcium content is low in the nitrophosphate fertilizer obtained by the present invention;

5. The process has low comprehensive cost and basically no solid waste, realizes the clean processing and utilization of phosphate rock, and has good economic and social benefits and broad industrial application prospects.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

Figure 2 is the phase diagram of the CaO-P ₂ O ₅ -N ₂ O ₆ -H ₂ O system at 0°C, 5°C, 25°C and 50°C.

Detailed ways

The method for separating P and Ca in low-grade phosphate rock comprises the following steps:

(1) Primary acid hydrolysis: mix phosphate rock and nitric acid solution, react at 30-70 °C for 0.5-2 h, and then separate solid-liquid to obtain acid-insoluble matter and acid-lysed clear liquid;

(2) Neutralization: neutralize the acid-degraded clear liquid, and control 3.5≤pH≤6.5; and then separate solid-liquid to obtain solid phase I and liquid phase I;

(3) Secondary acid hydrolysis: Mix solid phase I and nitric acid solution, and react at 30～70° C. for 0.3～2h to obtain secondary acid hydrolysis solution;

(4) Frozen crystallization: the secondary acid hydrolyzate is cooled to -10°C to 0°C for crystallization; after the crystallization is completed, the solid-liquid separation is performed to obtain solid phase II and liquid phase II;

Wherein, the liquid phase I is a calcium-containing liquid, the liquid phase II is a phosphorus-containing liquid, and the solid phase II is a calcium-containing solid.

The method for separating P and Ca in the low-grade phosphate rock of the present invention can separate phosphorus and calcium in the phosphate rock as much as possible, improve the utilization rate of phosphorus, and reduce the content of citric acid-soluble calcium phosphate in the subsequently prepared nitrophosphate fertilizer.

Wherein, in step (1), the main reaction that occurs is:

Ca ₅ F(PO ₄ ) ₃ +10HNO ₃ =5Ca(NO ₃ ) ₂ +3H ₃ PO ₄ +HF↑;

In step (2), the acid hydrolyzate is neutralized to 3.5≤pH≤6.5, the purpose of which is to precipitate phosphorus. Neutralize with ammonia, after solid-liquid separation, the solid phase I is mainly CaHPO ₄ and CaF ₂ ; the liquid phase I solution is mainly NH ₄ ⁺ , NO ₃ ^- , Ca ²⁺ , and a trace amount of H ₂ PO ₄ ^- , HPO ₄ ^2- .

Wherein, the pH value after neutralization is controlled to be less than or equal to 6.5 in the present invention, and if the pH value is too high, the precipitation of impurities will increase.

In step (3), solid phase I is subjected to secondary acidolysis with nitric acid, and calcium phosphate is dissolved;

In step (4), after the secondary acid hydrolyzate is frozen and crystallized, a large amount of Ca ²⁺ crystallizes out, and when the nitric acid phosphate fertilizer is prepared by using the filtrate, the content of water-insoluble phosphorus in the product is reduced, which greatly increases the water solubility of the nitric acid phosphate fertilizer.

The traditional method for separating calcium from phosphate rock is as follows: firstly, acidly hydrolyze the low-grade phosphate rock, and the obtained acid hydrolyzate is directly subjected to freezing crystallization to precipitate CaNO ₃ ·4H ₂ O, but the precipitation rate of directly frozen crystalline calcium nitrate is low, Even when using high-quality phosphate rock (high-quality phosphate rock refers to concentrate, less impurities, high grade, _P2O5 content>30wt%, MgO< _5wt %, _R2O3 <3wt%, _acid insoluble matter<3wt% ), the highest freezing precipitation rate is only about 80%, and the excess calcium ions remain in the solution to finally generate calcium phosphate salts that exist in the nitrophosphate fertilizer, which affects the water solubility of the product.

By using the method of the present invention, compared with the traditional method, the calcium precipitation rate is greatly increased. The reason is: the CaO/P ₂ O ₅ molar ratio of calcium fluorophosphate in apatite is 3.33:1. Generally, phosphate rock contains a certain amount of calcium carbonate. In fact, CaO/P ₂ O in medium and low grade phosphate rock ₅ molar ratio is above 3.6. And the present invention has ammoniation neutralization and precipitation calcium hydrogen phosphate (CaO/P ₂ O ₅ molar ratio is 2:1) and freeze crystallization twice to remove calcium. )/3.6=44.4% of calcium is left in the neutralization solution and separated from phosphorus; the process of freezing and separating calcium nitrate after calcium hydrogen phosphate is acidlyzed by nitric acid, according to the phase diagram at 0°C in Fig. At the point of Y=0.6, along with the precipitation of calcium nitrate, the liquid phase composition changes with [H ₆ (PO ₄ ) ₂ ] along this point, and the liquid phase composition can reach Y=0.82, and the calcium ion precipitation rate at this point up to 67% (and the lower the freezing temperature, the higher the precipitation rate). The acid hydrolyzate is separated from calcium and phosphorus twice, and its separation rate is higher than 81.6%! Therefore, the water solubility of the product of the method of the present invention is better than that of the traditional product.

In a specific embodiment, in step (1), the phosphate rock is in the form of powder or slurry. When the water content in the phosphate rock is 0%, it is in the form of powder, and as the water content increases, the phosphate rock is in the form of powder. It will become a slurry, for example, when the water content of the phosphate rock is 40%, it is a slurry. In the method of the present invention, the concentration of the nitric acid solution needs to be strictly controlled. The concentration of the nitric acid solution is 30-70wt% based on the water content in the phosphate rock of 0-40wt%, that is to say, when the water content in the raw phosphate rock is 0-40wt%, the concentration of the nitric acid solution is controlled to be 30-70wt% If the water content in the raw phosphate rock exceeds 40wt%, the concentration of the nitric acid solution needs to be calculated according to the water content in the phosphate rock. For example, when the water content in the raw phosphate rock is 50wt%, the concentration of the raw nitric acid solution needs to be appropriately increased. In actual production, it can be calculated according to the dosage ratio of phosphate rock and nitric acid.

In a specific embodiment, in step (1), the amount of nitric acid is 0.9 to 1.2 times of the theoretical acid consumption for the complete reaction of the phosphate rock; preferably, the amount of nitric acid is 0.9 to 1.1 times the theoretical acid consumption for the complete reaction of the phosphate rock. times.

The theoretical acid consumption for the complete reaction of phosphate rock can be calculated according to the content of each component in the phosphate rock. For example, it is detected that the main components reacting with acid in a phosphate rock are calcium oxide, magnesium oxide, iron oxide and aluminum oxide. According to the content of the above components, the calcium oxide, magnesium oxide, iron oxide, The theoretical acid consumption of the complete reaction of alumina, that is, the theoretical acid consumption of the complete reaction of phosphate rock.

In a specific embodiment, in step (1), the solid-liquid separation is performed in two steps, firstly performing sedimentation separation, and then filtering and separating the liquid after sedimentation and separation.

In a specific embodiment, in step (2), an alkaline neutralizer is used for the neutralization; preferably, the alkaline neutralizer is ammonia gas, ammonia water, limestone, milk of lime, ammonium carbonate and At least one of ammonium bicarbonate; more preferably, the alkaline neutralizing agent is ammonia gas, ammonia water, ammonium carbonate or ammonium bicarbonate; the components in the above-mentioned neutralizing agent can be used as the subsequent preparation of calcium nitrate or calcium ammonium nitrate active ingredients for efficient use.

In a specific embodiment, in step (3), the concentration of the nitric acid solution is 30 to 70 wt %, and the amount of nitric acid is 0.9 to 1.2 times the theoretical acid consumption of the solid phase I complete reaction; Phase 1 completely reacts 0.9 to 1.1 times of the theoretical acid consumption.

Wherein, the complete theoretical acid consumption of solid phase I described in step (3) can calculate the Ca content in solid phase I according to the weight of solid phase I, and then press HNO ₃ and the mol ratio of ^{Ca 2+ is} 2:1 , calculate the amount of HNO ₃ , that is, the theoretical acid consumption.

In a specific embodiment, in step (4), the secondary acid hydrolysis solution is cooled to -5°C to 0°C for crystallization.

The invention also provides a method for producing fertilizer by utilizing medium and low grade phosphate rock.

The method for producing fertilizer, adopts the separation method of P and Ca in the described low-grade phosphate rock, obtains liquid phase I, solid phase II and liquid phase II, and neutralizes liquid phase II to obtain nitrophosphate fertilizer;

In order to make full use of other elements such as calcium in phosphate rock, solid phase II and liquid phase I are mixed to obtain calcium-containing fertilizer.

In a specific embodiment, when liquid phase II is neutralized, the neutralizing agent used is at least one of gas ammonia, ammonia water, ammonium carbonate and ammonium bicarbonate.

In another specific embodiment, the neutralized liquid phase II is concentrated and dried to obtain nitrophosphate fertilizer. In a specific embodiment, according to actual needs, additives containing nutrient elements such as ammonium nitrate solution can be added to the neutralized liquid phase II to prepare nitrophosphate fertilizer.

In a specific embodiment, the solid phase II and the liquid phase I can be mixed according to the actual specific requirements of the fertilizer components, and then a substance containing nutrient elements is added to adjust the product nutrients to prepare calcium nitrate fertilizer or calcium ammonium nitrate fertilizer; The production of calcium nitrate and calcium ammonium nitrate fertilizers can be prepared by using existing methods. Preferably, the nutrient element-containing substances may be conventional substances such as ammonia, ammonium nitrate, calcium nitrate and the like.

Wherein, the main reaction of producing calcium ammonium nitrate is as follows:

H ⁺ +NH ₃ +NO ₃ ⁻ +Ca ²⁺ → 5Ca(NO ₃ ) ₂ ·NH ₄ NO ₃ ·10H ₂ O.

Phosphate rock commonly used in the art is suitable for the present invention. In a specific embodiment, the P ₂ O ₅ content in the phosphate rock is 15-30 wt %; preferably, the F content in the phosphate rock is 1.5-3.0 wt %.

The specific embodiments of the present invention will be further described below with reference to the examples, but the present invention is not limited to the scope of the described examples.

The available phosphorus in the embodiment includes water-soluble phosphorus and citrate-soluble phosphorus, excluding insoluble phosphorus.

The specific components of the phosphate rock used in the following examples are shown in Table 1.

Full analysis of phosphate rock used in each example of Table 1

Example 1

In this example, the content of phosphate rock P ₂ O ₅ , CaO, MgO, Fe ₂ O ₃ , Al ₂ O ₃ , SiO ₂ and F was 27.96%, 41.30%, 1.48%, 1.94%, 1.03%, 9.93%, 2.99%, made into phosphate rock powder. The specific process is as follows:

(1) Primary acid hydrolysis: Mix phosphate slurry with a water content of 21% and nitric acid solution, react at 50°C for 1.5 hours to obtain a solid-liquid mixture, and obtain acid-insoluble matter and acid hydrolyzate after solid-liquid separation; among them, phosphorus The mineral powder is 100g, the nitric acid solution is 212g, and the concentration is 50wt%; the mass of the acidolysis solution is _315.4g , the content of _P2O5 in the acidolysis solution is 8.7%, and the content of CaO is 12.8%;

(2) neutralization: the liquid phase obtained in step (1) is neutralized to solution pH=3.7 with ammonia; then solid-liquid separation is carried out to obtain liquid phase I and 63g solid phase I;

(3) Secondary acid hydrolysis: Mix solid phase I with 92.5 g of nitric acid solution with a concentration of 50 wt %, and react at 50° C. for 0.5 h.

(4) Freezing crystallization: the acid hydrolyzate obtained in step (3) is cooled to -5°C to carry out crystallization reaction; after crystallization is completed, solid-liquid separation is performed to obtain liquid phase II and 58 g of solid phase II;

(5) Ammoniation and neutralization: The liquid phase II obtained in (4) was neutralized with ammonia to pH=5.8, and then evaporated, concentrated and spray-dried to obtain 213.4 g of nitrophosphate fertilizer. Among them, the content of available phosphorus (calculated as P ₂ O ₅ ) was 12.2%, the content of nitrogen was 26.2%, and the content of Ca was 2.27%.

(6) Dissolving solid phase II in liquid phase I, adding additives to prepare calcium ammonium nitrate fertilizer or calcium nitrate fertilizer.

Example 2

In this example, the content of phosphate rock P ₂ O ₅ , CaO, MgO, Fe ₂ O ₃ , Al ₂ O ₃ , SiO ₂ and F is 18.12%, 29.46%, 2.74%, 1.63%, 3.73%, 34.53%, 1.62%, made into phosphate rock powder. The specific process is as follows:

(1) Primary acid hydrolysis: Mix phosphate rock slurry with a water content of 40% and nitric acid solution, react at 60°C for 1 hour to obtain a solid-liquid mixture, and obtain acid-insoluble matter and acid hydrolyzate after solid-liquid separation; The powder is 100g; the nitric acid solution is 145.5g, the concentration is 70wt%; the quality of the acidolysis solution is _266.7g , the _P2O5 content in the acidolysis solution is 6.7%, and the CaO content is 10.8%;

(2) neutralization: the liquid phase obtained in step (1) is neutralized to solution pH=3.6 with ammonium carbonate; then solid-liquid separation is carried out to obtain liquid phase I and 40.4g solid phase I;

(3) Secondary acid hydrolysis: Mix solid phase I with 42.5 g of a 70 wt% nitric acid solution, and react at 60° C. for 0.5 h.

(4) frozen crystallization: the acid hydrolyzed solution obtained in step (3) was cooled to 0° C. to carry out a crystallization reaction; after the crystallization was completed, solid-liquid separation was performed to obtain liquid phase II and 37 g of solid phase II;

(5) Ammoniation and neutralization: The liquid phase II obtained in (4) was neutralized with ammonia to pH=5.6, and then evaporated, concentrated and spray-dried to obtain 135.7 g of nitrophosphate fertilizer. Among them, the content of available phosphorus (calculated as P ₂ O ₅ ) was 12.30%, the content of nitrogen was 26.3%, and the content of Ca was 2.29%.

(6) Dissolving solid phase II in liquid phase I, adding additives to prepare calcium ammonium nitrate fertilizer or calcium nitrate fertilizer.

Example 3

In this example, the content of phosphate rock P ₂ O ₅ , CaO, MgO, Fe ₂ O ₃ , Al ₂ O ₃ , SiO ₂ and F is 19.42%, 27.99%, 0.44%, 1.51%, 3.36%, 41.44%, 1.45%, made into phosphate rock powder. The specific process is as follows:

(1) First-level acid hydrolysis: Mix the non-aqueous phosphate slurry and nitric acid solution, and react at 70°C for 0.5 h to obtain a solid-liquid mixture. 100g; 241g of nitric acid solution with a concentration of 30wt%; wherein the mass of the acidolysis solution is _282g , the content of _P2O5 in the acidolysis solution is 6.6%, and the content of CaO is 9.5%;

(2) neutralization: the liquid phase obtained in step (1) is neutralized to solution pH=4.4 with ammonia; then solid-liquid separation is performed to obtain liquid phase I and 43.8g solid phase I;

(3) Secondary acid hydrolysis: Mix solid phase I with 107 g of 30 wt% nitric acid solution, and react at 70° C. for 0.5 h.

(4) Freezing crystallization: the acid hydrolyzed solution obtained in step (3) is cooled to -7°C to carry out crystallization reaction; after crystallization is completed, solid-liquid separation is performed to obtain liquid phase II and 40.3 g of solid phase II;

(5) Ammoniation and neutralization: The liquid phase II obtained in (4) was neutralized with ammonia to pH=6.5, and then evaporated, concentrated and spray-dried to obtain 143.5 g of nitrophosphate fertilizer. Among them, the content of available phosphorus (P ₂ O ₅ ) was 12.6%, the content of nitrogen was 26.4%, and the content of Ca was 2.34%.

(6) Dissolving solid phase II in liquid phase I, adding additives to prepare calcium ammonium nitrate fertilizer or calcium nitrate fertilizer.

Example 4

In this example, the content of phosphate rock P ₂ O ₅ , CaO, MgO, Fe ₂ O ₃ , Al ₂ O ₃ , SiO ₂ and F is 26.70%, 41.53%, 2.34%, 0.60%, 0.53%, 19.75%, 2.50%, made into phosphate rock powder. The specific process is as follows:

(1) Primary acid hydrolysis: Mix phosphate slurry with a water content of 30% and nitric acid solution, and react at 60 °C for 1.2 h to obtain a solid-liquid mixture. The mineral powder is 100g; the nitric acid solution is 218.8g, the concentration is 50wt% _; the quality of the acidolysis solution is 331g, the _P2O5 content in the acidolysis solution is 7.8%, and the CaO content is 12.2%;

(2) neutralization: the liquid phase obtained in step (1) is neutralized to solution pH=4.2 with ammonium carbonate; then solid-liquid separation is carried out to obtain liquid phase I and 60.2g solid phase I;

(3) Secondary acid hydrolysis: Mix the solid phase I with 88.5 g of a 60 wt% nitric acid solution, and react at 60° C. for 0.5 h.

(4) Freezing crystallization: the acid hydrolyzed solution obtained in step (3) is cooled to -2°C to carry out crystallization reaction; after crystallization is completed, solid-liquid separation is performed to obtain liquid phase II and 55.5 g of solid phase II;

(5) Ammoniation and neutralization: The liquid phase II obtained in (4) was neutralized with ammonia to pH=5.5, and then evaporated, concentrated and spray-dried to obtain 200.5 g of nitrophosphate fertilizer. Among them, the available phosphorus (P ₂ O ₅ ) content was 12.4%, the nitrogen content was 26.2%, and the Ca content was 2.31%.

(6) Dissolving solid phase II in liquid phase I, adding additives to prepare calcium ammonium nitrate fertilizer or calcium nitrate fertilizer.

Comparative Example 1

In this example, the content of phosphate rock P ₂ O ₅ , CaO, MgO, Fe ₂ O ₃ , Al ₂ O ₃ , SiO ₂ and F was 27.96%, 41.30%, 1.48%, 1.94%, 1.03%, 9.93%, 2.99%, made into phosphate rock powder. The specific process is as follows:

(1) Primary acid hydrolysis: Mix phosphate slurry with a water content of 21% and nitric acid solution, react at 50°C for 1.5 hours to obtain a solid-liquid mixture, and obtain acid-insoluble matter and acid hydrolyzate after solid-liquid separation; among them, phosphorus The mineral powder is 100g and the 50wt% nitric acid solution is 212g; the acid hydrolysis solution has a mass of 315.4g, the P ₂ O ₅ content in the acid hydrolysis solution is 8.7%, and the CaO content is 12.8%;

(2) Frozen crystallization: the acid hydrolyzed solution is cooled to -5° C. to carry out crystallization reaction; after the crystallization is completed, solid-liquid separation is performed to obtain liquid phase I and solid phase I. The solid phase I was Ca(NO ₃ ) ₂ ·4H ₂ O, and the mass was 122 g. The nitrophosphate fertilizer prepared by this method has high calcium content and poor water solubility, which affects fertilizer efficiency.

Claims (10)

1. the separation method of P, Ca in low-grade phosphate rock, is characterized in that, may further comprise the steps: (1) Primary acid hydrolysis: mix phosphate rock and nitric acid solution, react at 30-70 °C for 0.5-2 h, and then separate solid-liquid to obtain acid-insoluble matter and acid-lysed clear liquid; (2) Neutralization: neutralize the acid hydrolyzed clear liquid, and control the solution to be 3.5≤pH≤6.5; and then separate solid-liquid to obtain solid phase I and liquid phase I; (3) Secondary acid hydrolysis: Mix solid phase I and nitric acid solution, and react at 30～70° C. for 0.3～2h to obtain secondary acid hydrolysis solution; (4) Frozen crystallization: the secondary acid hydrolyzate is cooled to -10°C to 0°C for crystallization; after the crystallization is completed, the solid-liquid separation is performed to obtain solid phase II and liquid phase II; Wherein, the liquid phase I is a calcium-containing liquid, the liquid phase II is a phosphorus-containing liquid, and the solid phase II is a calcium-containing solid. 2. the separation method of P, Ca in low-grade phosphate rock according to claim 1, is characterized in that, in step (1), phosphate rock is powdery or slurry; Based on 40 wt %, the concentration of nitric acid is 30-70 wt %. 3. the separation method of P, Ca in low-grade phosphate rock according to claim 1 and 2, is characterized in that, in step (1), nitric acid consumption is 0.9～1.2 times of phosphate rock complete reaction theoretical acid consumption ; Preferably, the amount of nitric acid is 0.9 to 1.1 times the theoretical acid consumption for the complete reaction of phosphate rock. 4. the separation method of P, Ca in the middle and low grade phosphate rock according to claim 1, is characterized in that, in step (1), solid-liquid separation is carried out in two steps, first carry out sedimentation separation, then after sedimentation separation The liquid is filtered and separated. 5. The method for separating P and Ca in the medium and low-grade phosphate rock according to any one of claims 1 to 4, wherein in step (2), an alkaline neutralizer is used for the neutralization; preferably , the alkaline neutralizer is at least one of gas ammonia, ammonia water, limestone, lime milk, ammonium carbonate and ammonium bicarbonate. 6. the separation method of P, Ca in the middle and low grade phosphate rock according to claim 1, is characterized in that, in step (3), the concentration of nitric acid solution is 30～70wt%, and nitric acid consumption is solid phase 1 complete reaction 0.9 to 1.2 times the theoretical acid consumption; preferably, the nitric acid consumption is 0.9 to 1.1 times the theoretical acid consumption of the solid phase I complete reaction. 7. the separation method of P, Ca in the low-grade phosphate rock according to claim 1～6, is characterized in that, in step (4), the secondary acid hydrolyzate is cooled to -5 ℃～0 ℃ to carry out crystallization . 8. the method for producing fertilizer, it is characterized in that, adopt the separation method of P, Ca in the low-grade phosphate rock described in any one of claim 1～7, after obtaining liquid phase I, solid phase II and liquid phase II, The liquid phase II is neutralized to obtain a nitrophosphate fertilizer; the solid phase II and the liquid phase I are mixed to obtain a calcium-containing fertilizer. 9. The method for producing fertilizer according to claim 8, wherein when liquid phase II is neutralized, the neutralizing agent employed is at least one of gas ammonia, ammoniacal liquor, ammonium carbonate and ammonium bicarbonate. 10. the method for producing fertilizer according to claim 8 or 9, is characterized in that, after solid phase II and liquid phase I are mixed, add the material containing nutrient element again to adjust product nutrient, obtain calcium nitrate fertilizer or calcium ammonium nitrate Fertilizer; preferably, the nutrient element-containing substance is at least one of ammonia, ammonium nitrate and calcium nitrate.

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