CN116143141A - Process for producing ammonium sulfate by using phosphate rock and grading and utilizing calcium element - Google Patents

Abstract

A process for producing ammonium sulfate by using phosphorite and grading and utilizing calcium element, which comprises the following steps: step S1 carbonization: reacting phosphogypsum with 45-50% ammonium carbonate solution by mass fraction to obtain a reaction material; step S2, filtering: filtering the reaction materials to obtain a calcium carbonate filter cake and an ammonium sulfate filtrate; step S3, concentration: concentrating the ammonium sulfate filtrate to obtain an ammonium sulfate concentrated solution with the mass fraction of 41% -50%; step S4, neutralization: adding sulfuric acid into the ammonium sulfate concentrated solution, and controlling the pH value to be 5.0-6.8; step S5, granulating and drying: granulating and drying the neutralized ammonium sulfate concentrate to obtain granular ammonium sulfate; step S6, grading utilization of calcium carbonate. The process for producing ammonium sulfate by using the phosphogypsum and grading the calcium element has strong adaptability to phosphogypsum and great competitive advantage of products with strong flexibility of device process.

Description

A process for producing ammonium sulfate by using phosphate stone and graded utilization of calcium element

technical field

The invention relates to the technical field of resource utilization of industrial solid waste, in particular to a method for producing ammonium sulfate and graded utilization of calcium carbonate by using phosphogypsum as a raw material.

Background technique

Phosphogypsum is a solid by-product of wet-process phosphoric acid production. For every ton of P ₂ O ₅ wet-process phosphoric acid produced, nearly 5 tons of phosphogypsum are produced, which contain a large amount of impurities (such as SiO ₂ , P, F, etc.). For a long time, stockpiling has been the mainstream disposal method of phosphogypsum. At present, the total stockpiling of phosphogypsum in China is about 600 million tons. According to reports, in 2020, the output of my country's phosphogypsum industry will be 78.1 million tons, and the comprehensive utilization will be 32.6 million tons, with a utilization rate of 44%. In 2021, the output of my country's phosphogypsum industry will be about 74.6 million tons, and the comprehensive utilization rate will be less than 48.0%. The pressure to fully utilize phosphogypsum remains enormous. With the promulgation of the environmental protection policy of "determining production by slag", the rational use of phosphogypsum has become the primary issue for the high-quality development of wet-process phosphorus chemical enterprises. For this reason, related technologies arise at the historic moment, one of which is to adopt the gypsum method to make ammonium sulfate, and by-product calcium carbonate.

Patent CN101269823A discloses a method for producing ammonium sulfate using phosphogypsum as raw material, and reacting phosphogypsum with lime and ammonium carbonate solution to obtain light calcium carbonate and crystalline ammonium sulfate.

Patent CN113336242A discloses a method of adding glass balls, phosphogypsum and ammonium bicarbonate into a ball mill to prepare ammonium sulfate for water treatment by solid phase ball milling.

Patent CN112225228A discloses a method and system for preparing ammonium sulfate by using cement kiln exhaust gas and phosphogypsum. It uses ammonia water to absorb CO ₂ in the tail gas of cement kiln to obtain ammonium carbonate solution. Then mix the ammonium carbonate solution and phosphogypsum for grinding and dipping, and obtain ammonium sulfate and solid residue after solid-liquid separation.

Ding Wenjin et al. published "Phosphogypsum Mineralization of CO ₂ to Prepare High-purity Calcium Carbonate and Product Control" using phosphogypsum as raw material to study the reaction process of ammonia water intensified phosphogypsum leachate in the ammonium chloride system to prepare high-purity CaCO ₃ .

Shi Shuang stirred and heated the washed phosphogypsum slurry in "Preparation of Light Calcium Carbonate and Its Morphology Regulation by-product Phosphogypsum", and then added ammonium carbonate solution dropwise. After the reaction, filter to obtain light calcium carbonate and ammonium sulfate.

Contents of the invention

The invention aims to provide a process for processing solid waste phosphogypsum into high value-added products.

The present invention solves its technical problems by adopting the following technical solutions.

The present invention proposes a process for producing ammonium sulfate by utilizing phosphate rock and graded calcium element, which is characterized in that it comprises the following steps:

Step S1 carbonization: reacting phosphogypsum with an ammonium carbonate solution with a mass fraction of 45-50% to obtain a reaction material;

The main component of phosphogypsum is CaSO ₄ , which contains a large amount of impurities such as SiO ₂ , SO ₄ ^2- , F, Fe, Mg, Al, K, Na and P. Among them, SiO ₂ and SO ₄ ^2- have the highest content. Carbonization refers to the reaction of ammonium carbonate solution with a mass fraction of 45-50% and phosphogypsum to generate calcium carbonate and ammonium sulfate. The reaction (formula below) is a liquid-solid two-phase exothermic reaction. Its reaction equation is:

CaSO ₄ ·2H ₂ O(s)+(NH ₄ ) ₂ CO ₃ (l)=CaCO ₃ (s)+(NH ₄ ) ₂ SO ₄ (l)+2H ₂ O(l)

Specifically, the carbonization temperature in the reaction is 40-90°C, the carbonization pressure is ≤0.3MPaG, the reaction residence time is 3-6h, and the mass fraction of the ammonium carbonate solution is 45-50%.

When the carbonization pressure is 4~90kPaG, the reaction effect is better;

Among them, the degree of carbonation of the ammonium carbonate solution (2n[NH ₃ ]/n[CO ₂ ])=(1.2~1):1, to ensure the alkalinity of the solution, which is conducive to the formation of calcium carbonate, and promotes the conversion rate of the carbonization reaction to increase . .

Preferably, because ammonium carbonate is easily decomposed at normal temperature, the ratio of the amount of (NH ₄ ) ₂ CO ₃ in the ammonium carbonate solution to the CaSO ₄ in the phosphogypsum is [(NH ₄ ) ₂ CO ₃ ]: [CaSO ₄ ]=(1~1.2):1. Because the quality of phosphogypsum is uncertain, the content of CaSO ₄ in phosphogypsum should be determined before the reaction.

Preferably, the above-mentioned carbonization is multi-stage, and the reaction effect is better. The reason is that ammonium carbonate is unstable, and it is easy to decompose when stored at room temperature, forming ammonia and ammonium bicarbonate. Adding ammonium carbonate multiple times in graded reaction can inhibit the decomposition of ammonium carbonate.

Preferably, carbonization includes:

First-stage carbonization: temperature 65~90°C, pressure ≤120kPaG, residence time 0.5~1h, add ammonia to adjust pH≥7, the amount of ammonium carbonate added is n ₁ ;

Second-stage carbonization: temperature 65~90°C, pressure ≤100kPaG, residence time 0.5~1h, add ammonia to adjust pH≥7, the amount of ammonium carbonate added is n ₂ ;

The third carbonization: temperature 50~65℃, pressure ≤80kPaG, residence time 1~2h, add ammonia to adjust pH≥7;

The fourth carbonization: temperature 40~50℃, pressure ≤40kPaG, residence time 1~2h, add ammonia to adjust pH≥7;

Among them, n ₁ : n ₂ =3~7;

Excess ammonium carbonate and phosphogypsum are reacted for 3-6 hours in four series-connected pressurized and stirred reactors to achieve full conversion of phosphogypsum. Ammonium carbonate is unstable, and it is easy to decompose when stored at room temperature, forming ammonia and ammonium bicarbonate. Ammonium carbonate is distributed into the first two stages of reaction in proportion, which can effectively inhibit the decomposition of ammonium carbonate. Ensuring that the reaction is in an alkaline environment by supplementing ammonia gas can reverse the decomposition reaction of ammonium carbonate, thereby inhibiting the decomposition of ammonium carbonate. The temperature of the material in the reaction kettle can be changed from high to low according to the flow direction of the material, that is, the first-stage carbonization reacts quickly and reduces the decomposition of ammonium carbonate. And the carbonization reaction pressure is relatively high, which can also inhibit the decomposition of ammonium carbonate.

Preferably, the material of at least one of the first-stage carbonization, second-stage carbonization, third-stage carbonization and fourth-stage carbonization is crushed by a high-speed shearing machine. The reactants and products of the carbonization reaction are both solid. In order to avoid encapsulation, breaking the solid material during the reaction can greatly speed up the reaction process.

Step S2 Filtration: the reaction material is filtered through the first step to obtain calcium carbonate filter cake and ammonium sulfate filtrate; due to excessive ammonium carbonate in the carbonization reaction, a small amount of ammonium carbonate remains in the ammonium sulfate filtrate.

Step S3 concentration: Concentrating the ammonium sulfate filtrate to an ammonium sulfate concentrate with a mass fraction of 41% to 50%; the unreacted ammonium carbonate remaining in the ammonium sulfate filtrate is decomposed by heat into ammonia entering the tail gas and hydrogen carbonate remaining in the solution Ammonium.

Preferably, the mass fraction of the ammonium sulfate concentrate is controlled to 44% to 48%. The final granulation effect of the above concentration is better.

Step S4 neutralization: add sulfuric acid to the ammonium sulfate concentrate, and control the pH=5.0~6.8; the above steps can neutralize part of the ammonium bicarbonate and a small amount of free ammonia remaining in the ammonium sulfate concentrate solution.

Preferably, phosphoric acid is added to the ammonium sulfate concentrate, and phosphoric acid and sulfuric acid jointly neutralize the ammonium sulfate concentrate; the amount of phosphoric acid added needs to meet the content of impurity ammonium phosphate in the granular ammonium sulfate, and the mass fraction of _P2O5 is _0.1 %~ 4%. Adding part of phosphoric acid to the neutralizing acid can effectively improve the particle strength of the granular ammonium sulfate obtained by granulation. And the ammonium sulfate obtained through the granulation step is convenient for transportation.

Step S5 Granulation and drying: the neutralized ammonium sulfate concentrate is dried through the second granulation to obtain granular ammonium sulfate; the neutralized ammonium sulfate concentrate can be sent into the drum granulator through the nozzle and synchronized with hot air Drying is achieved by contact, and granular ammonium sulfate is obtained.

Preferably, in step S5, one of ammonium monohydrogen phosphate, ammonium dihydrogen phosphate and potassium salt is added to obtain a compound fertilizer. Among them, ammonium monohydrogen phosphate and ammonium dihydrogen phosphate can not only be used as raw materials for compound fertilizers, but also can be used as adhesives to enhance the strength of product particles.

The graded utilization of step S6 calcium carbonate. Rational use of calcium carbonate in layers to improve utilization.

Preferably, step S6 includes preparing calcium carbonate powder: drying and pulverizing the calcium carbonate filter cake to obtain calcium carbonate powder. Wherein, the calcium carbonate filter cake is washed with clear water to remove the ammonium sulfate solution attached to it. The washing water is returned to prepare the ammonium carbonate solution required for carbonization. To improve waste utilization and save costs. The prepared calcium carbonate powder can meet the requirements of GB/T 35164-2017 "Limestone Powder Used in Cement, Mortar and Concrete".

Preferably, step S6 includes preparing calcium carbonate powder: reacting the mixed lye and calcium carbonate filter cake at 100-150°C and ≤0.65MPaG for 4-6h under pressure, and then filtering and washing to obtain refined filter cake and Sodium silicate filtrate and refined filter cake are dried and crushed to obtain calcium carbonate powder; wherein, the mixed lye contains 20-30% by mass fraction of NaOH and 0.05-0.2% by mass fraction of Na ₂ CO ₃ , or the mixed lye contains 20-30% mass fraction of KOH and 0.05-0.2 mass fraction of K ₂ CO ₃ .

Among them, when the mixed lye contains 20~30% by mass fraction of NaOH and 0.05~0.2% by mass fraction of _Na2CO3 , calcium carbonate meeting HG/T 2226-2019 and calcium carbonate meeting GB/T 4209-2008 can be produced _. Industrial Sodium Silicate. Calcium carbonate and potassium water glass meeting HG/T _2226-2019 can be produced when the mixed lye contains 20-30% by mass KOH and 0.05-0.2% by mass _K2CO3 .

Preferably, step S6 includes preparing granular heavy calcium/composite fertilizer: mixing and reacting calcium carbonate filter cake with phosphoric acid to obtain a mixture, and then drying through the first granulation to obtain granular heavy calcium.

Preferably, step S6 also includes preparing calcium nitrate crystals: mixing and reacting part of the calcium carbonate filter cake with insufficient nitric acid, and then obtaining calcium nitrate filtrate through second filtration, crystallizing, filtering, and drying to obtain calcium nitrate crystals.

Preferably, part of the calcium nitrate filtrate is extracted to the mixture, and the filter residue obtained by the second filtration is sent to the mixture, and then dried through the first granulation to obtain granular compound fertilizer;

Preferably, the calcium nitrate filtrate is reacted with barium nitrate solution before crystallization, and the obtained barium sulfate filter residue is sent to the mixture, and then dried through the first granulation to obtain granular compound fertilizer.

Compared with the prior art, the present invention has the following beneficial effects:

(1) Strong adaptability to phosphogypsum. The off-line phosphogypsum of the wet-process phosphoric acid plant reacts directly with ammonium carbonate, without the need for pretreatment processes such as water washing, lime neutralization, and flotation desiliconization. It can be applied to various qualities of phosphogypsum.

(2) The installation process is flexible. It can produce granular ammonium sulfate, granular heavy calcium, light calcium carbonate, compound fertilizer, fully water-soluble calcium nitrate and other products. The product system is rich and the quality is graded. The product structure can be adjusted according to the quality of raw materials and market demand. The impurities brought by phosphogypsum can be fully digested.

(3) The product has great competitive advantage. In the product system, granular ammonium sulfate with high particle strength, fully water-soluble calcium nitrate, high-purity light calcium carbonate, etc. have high added value. At the same time, products such as heavy calcium and compound fertilizer can fully accommodate the impurities brought by phosphogypsum. Compared with the existing devices, the economic efficiency of the method disclosed in this patent is significantly improved, which is conducive to the long-term stable operation of the phosphogypsum recycling device

Description of drawings

In order to illustrate the technical solutions of the embodiments of the present invention more clearly, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus It should be regarded as a limitation on the scope, and those skilled in the art can also obtain other related drawings based on these drawings without creative work.

Fig. 1 is the technological process schematic diagram of embodiment 1 of the present invention;

Fig. 2 is a schematic diagram of the process flow of step S1 carbonization in Example 1 of the present invention.

Implementation

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those who do not indicate the specific conditions in the examples are carried out according to the conventional conditions or the conditions suggested by the manufacturer.

Ammonium sulfate is an excellent nitrogen fertilizer (commonly known as fertilizer powder), suitable for general soil and crops, can make branches and leaves grow vigorously, improve fruit quality and yield, and enhance crop resistance to disasters. It can be used as base fertilizer, topdressing fertilizer and seed fertilizer. At the same time, it is also widely used in leather, metallurgy, biological fermentation, printing and dyeing, flame retardant and other industries. Industrially use sulfuric acid or ammonia water to absorb by-products or waste gas in production (such as sulfuric acid absorbing ammonia in coke oven gas, ammonia water absorbing sulfur dioxide in smelter flue gas, ammonia in Capron production or sulfuric acid process titanium dioxide production Sulfuric acid waste in). There are also those who adopt the gypsum method to prepare ammonium sulfate (using natural gypsum or phosphogypsum, ammonia, and carbon dioxide as raw materials), but the cost is high and there is no market advantage.

Calcium carbonate is an important chemical raw material, which is widely used in papermaking, metallurgy, glass, alkali making, rubber, medicine, food, pigment, functional material, organic chemical industry and other departments. Generally, the purity requirement is higher - ≥97%, or even ≥99.9%.

Heavy superphosphate, referred to as heavy calcium, is used as a fertilizer for various soils and crops, and can be used as a raw material for base fertilizer, topdressing fertilizer and compound (mixed) fertilizer. Widely applicable to rice, wheat, corn, sorghum, cotton, melons, fruits, vegetables and other food crops and economic crops. Also used in glass making, plastic stabilization, livestock feed supplement.

Calcium nitrate is used in the electronics industry to coat cathodes, analytical reagents and materials for fireworks. In agriculture, it is used as a quick-acting fertilizer for acidic soil and a fast-acting calcium supplement for plants. It is also a typical fast-acting foliar fertilizer. Calcium nitrate with low water insoluble matter is a high-end fully water-soluble fertilizer, which is very popular in the market.

The present invention will be further described below with reference to the accompanying drawings and embodiments, and the mode of the present invention includes but not limited to the following embodiments.

Example

This embodiment provides a process for producing ammonium sulfate by using phosphate stone and graded calcium element, which specifically includes the following steps:

Step S1 carbonization: reacting phosphogypsum with ammonium carbonate solution with a mass fraction of 48% to obtain a reaction material. Among them, the carbonation degree of the ammonium carbonate solution (2n[NH ₃ ]/n[CO ₂ ])=(1.2~1):1. The quality of phosphogypsum is uncertain, and the content of CaSO ₄ in phosphogypsum should be determined before the reaction. Specifically, this implementation adopts a four-stage carbonization reaction. According to the amount of substances, the phosphogypsum containing _100mol CaSO and the ammonium carbonate solution containing 90mol ammonium carbonate are sent to the first stage carbonization. The reaction temperature is 80°C, the residence time is 0.75h, and the pressure is 100kPaG. The output of the first stage carbonization and the ammonium carbonate solution containing 20mol ammonium carbonate enter the second stage carbonization, the temperature is 70°C, the residence time is 0.75h, and the pressure is 80kPaG. The output of the second-stage carbonization enters the third-stage carbonization with a temperature of 60°C, a residence time of 1.5h, and a pressure of 60kPaG. The discharge of the third stage carbonization enters the fourth stage carbonization, the temperature is 45°C, the residence time is 1.5h, and the pressure is 30kPaG. The above four stages of carbonization are all equipped with high-speed shearing machines to cyclically crush and disperse the materials in the kettle. Moreover, the above four-stage carbonization is passed through ammonia gas to adjust the pH at 8-9.

Step S2 Filtration: the reaction material is filtered through the first step to obtain calcium carbonate filter cake and ammonium sulfate filtrate; due to excessive ammonium carbonate in the carbonization reaction, a small amount of ammonium carbonate remains in the ammonium sulfate filtrate.

Step S3 Concentration: Concentrate the ammonium sulfate filtrate to an ammonium sulfate concentrate with a mass fraction of 46%.

Step S4 Neutralization: add sulfuric acid and phosphoric acid to the ammonium sulfate concentrate to neutralize part of the ammonium bicarbonate and a small amount of free ammonia remaining in the ammonium sulfate concentrate solution, and control the pH to 6.0. The amount of phosphoric acid added needs to meet the content of the impurity ammonium phosphate salt in the granular ammonium sulfate, and the mass fraction of P ₂ O ₅ is 0.1%~4%.

Step S5 Granulation and drying: Send the neutralized ammonium sulfate concentrate to the drum granulator through the nozzle, add ammonium monohydrogen phosphate, contact with hot air at the same time, and make 16-20 compound fertilizer through the second granulation and drying (16 means N mass fraction ≥ 16%, 20 means P ₂ O ₅ mass fraction ≥ 20%.

The grade utilization of step S6 calcium carbonate comprises:

Preparation of calcium carbonate powder: The mixed lye containing 25% NaOH and 0.12% Na ₂ CO ₃ and the washed part of the calcium carbonate filter cake were kept under pressure for 5 hours at 120°C and 0.5 MPaG, and then subjected to The third step is to filter and wash to obtain refined filter cake and sodium silicate filtrate. The sodium silicate filtrate meets the requirements of GB/T 4209-2008 for industrial sodium silicate. The refined filter cake is dried and pulverized to produce calcium carbonate powder meeting HG/T 2226-2019.

Preparation of calcium nitrate crystals: mix and react part of the washed calcium carbonate filter cake with insufficient nitric acid, and then obtain calcium nitrate filtrate through second filtration. After crystallization, filtration, and drying, high-purity calcium nitrate tetrahydrate crystals are obtained.

Preparation of granular compound fertilizer: mix and react part of the washed calcium carbonate filter cake with phosphoric acid to prepare a mixture. Simultaneously extract part of the calcium nitrate filtrate to the mixture. The remaining calcium nitrate filtrate is reacted with barium nitrate solution before crystallization, and the obtained barium sulfate filter residue is sent to the mixing material. The filter residue obtained by the second filtration is also sent to the mixture, and then dried through the first granulation to obtain granular compound fertilizer.

Example

This embodiment provides a kind of technology that utilizes phosphate stone to produce ammonium sulfate and utilizes calcium element gradedly, and its difference with embodiment 1 is:

The grade utilization of step S6 calcium carbonate comprises:

Preparation of calcium carbonate powder: The mixed lye containing 25% NaOH and 0.12% Na ₂ CO ₃ and the washed part of the calcium carbonate filter cake were kept under pressure for 5 hours at 120°C and 0.5 MPaG, and then subjected to The third step is to filter and wash to obtain refined filter cake and sodium silicate filtrate. The sodium silicate filtrate meets the requirements of GB/T 4209-2008 for industrial sodium silicate. The refined filter cake is dried and pulverized to produce calcium carbonate powder meeting HG/T 2226-2019.

Preparation of calcium nitrate crystals: mix and react part of the washed calcium carbonate filter cake with insufficient nitric acid, and then obtain calcium nitrate filtrate through second filtration. After crystallization, filtration, and drying, high-purity calcium nitrate tetrahydrate crystals are obtained.

Preparation of granular heavy calcium: mix and react part of the washed calcium carbonate filter cake with phosphoric acid to prepare a mixture. After the first granulation and drying, granular heavy calcium is obtained.

Example

This embodiment provides a kind of technology that utilizes phosphate stone to produce ammonium sulfate and utilizes calcium element gradedly, and its difference with embodiment 1 is:

The graded utilization of step S6 calcium carbonate does not comprise preparation calcium carbonate powder.

Example

This embodiment provides a kind of technology that utilizes phosphate stone to produce ammonium sulfate and utilizes calcium element gradedly, and its difference with embodiment 1 is:

The graded utilization of calcium carbonate in step S6 does not include the preparation of granular compound fertilizer.

Example

This embodiment provides a process for producing ammonium sulfate by using phosphate stone and graded utilization of calcium element. The difference from Example 2 is:

The graded utilization of calcium carbonate in step S6 does not include the preparation of calcium nitrate crystals.

Example

This embodiment provides a kind of technology that utilizes phosphate stone to produce ammonium sulfate and utilizes calcium element gradedly, and its difference with embodiment 1 is:

Step S6 Calcium carbonate powder preparation in the graded utilization of calcium carbonate is: dry and pulverize the washed calcium carbonate filter cake to obtain calcium carbonate powder.

Example

This embodiment provides a process for producing ammonium sulfate by using phosphate stone and graded calcium element, which specifically includes the following steps:

Step S1 carbonization: reacting phosphogypsum with ammonium carbonate solution with a mass fraction of 45% to obtain a reaction material. Among them, the carbonation degree of the ammonium carbonate solution (2n[NH ₃ ]/n[CO ₂ ])=(1.2~1):1. The quality of phosphogypsum is uncertain, and the content of CaSO ₄ in phosphogypsum should be determined before the reaction. Specifically, this implementation adopts a four-stage carbonization reaction. According to the amount of substances, the phosphogypsum containing _100mol CaSO and the ammonium carbonate solution containing 90mol ammonium carbonate are sent to the first stage carbonization. The reaction temperature is 65°C, the residence time is 0.5h, and the pressure is 120kPaG. The output of the first stage carbonization and the ammonium carbonate solution containing 30mol ammonium carbonate enter the second stage carbonization, the temperature is 90°C, the residence time is 0.5h, and the pressure is 100kPaG. The output of the second-stage carbonization enters the third-stage carbonization with a temperature of 65° C., a residence time of 1 hour, and a pressure of 80 kPaG. The output of the third stage carbonization enters the fourth stage carbonization, the temperature is 50°C, the residence time is 1h, and the pressure is 40kPaG. The above four stages of carbonization are all equipped with high-speed shearing machines to cyclically crush and disperse the materials in the kettle. Moreover, the above four-stage carbonization is all fed into liquid ammonia to adjust the pH at 7.

Step S2 Filtration: the reaction material is filtered through the first step to obtain calcium carbonate filter cake and ammonium sulfate filtrate; due to excessive ammonium carbonate in the carbonization reaction, a small amount of ammonium carbonate remains in the ammonium sulfate filtrate.

Step S3 Concentration: Concentrate the ammonium sulfate filtrate to an ammonium sulfate concentrate with a mass fraction of 41%.

Step S4 Neutralization: add sulfuric acid to the ammonium sulfate concentrate to neutralize part of the ammonium bicarbonate and a small amount of free ammonia remaining in the ammonium sulfate concentrate solution, and control the pH to 6.8.

Step S5 Granulation and drying: Send the neutralized ammonium sulfate concentrate to the drum granulator through the nozzle, add ammonium dihydrogen phosphate, contact with hot air at the same time, and make 16-20 compound fertilizer through the second granulation and drying .

The grade utilization of step S6 calcium carbonate comprises:

Preparation of calcium carbonate powder: The mixed lye containing 20% NaOH and 0.05% Na ₂ CO ₃ and the washed part of the calcium carbonate filter cake were reacted under pressure at 150°C and 0.65MPaG for 4 hours, and then subjected to The third step is to filter and wash to obtain refined filter cake and sodium silicate filtrate. The sodium silicate filtrate meets the requirements of GB/T 4209-2008 for industrial sodium silicate. The refined filter cake is dried and pulverized to produce calcium carbonate powder meeting HG/T 2226-2019.

Preparation of calcium nitrate crystals: mix and react part of the washed calcium carbonate filter cake with insufficient nitric acid, and then obtain calcium nitrate filtrate through second filtration. After crystallization, filtration, and drying, high-purity calcium nitrate tetrahydrate crystals are obtained.

Preparation of granular compound fertilizer: mix and react part of the washed calcium carbonate filter cake with phosphoric acid to prepare a mixture. Simultaneously extract part of the calcium nitrate filtrate to the mixture. The remaining calcium nitrate filtrate is reacted with barium nitrate solution before crystallization, and the obtained barium sulfate filter residue is sent to the mixing material. The filter residue obtained by the second filtration is also sent to the mixture, and then dried through the first granulation to obtain granular compound fertilizer.

Example

This embodiment provides a process for producing ammonium sulfate by using phosphate stone and graded calcium element, which specifically includes the following steps:

Step S1 carbonization: reacting phosphogypsum with 50% ammonium carbonate solution by mass fraction to obtain a reaction material. Among them, the carbonation degree of the ammonium carbonate solution (2n[NH ₃ ]/n[CO ₂ ])=(1.2~1):1. The quality of phosphogypsum is uncertain, and the content of CaSO ₄ in phosphogypsum should be determined before the reaction. Specifically, this implementation adopts a four-stage carbonization reaction. According to the amount of substances, the phosphogypsum containing _79mol CaSO and the ammonium carbonate solution containing 70mol ammonium carbonate are sent to the first stage carbonization. The reaction temperature is 90°C, the residence time is 1h, and the pressure is 110kPaG. The output of the first-stage carbonization and the ammonium carbonate solution containing 10mol ammonium carbonate enter the second-stage carbonization with a temperature of 65° C., a residence time of 1 hour, and a pressure of 90 kPaG. The output of the second-stage carbonization enters the third-stage carbonization with a temperature of 50°C, a residence time of 2 hours, and a pressure of 70kPaG. The discharge of the third stage carbonization enters the fourth stage carbonization, the temperature is 40°C, the residence time is 2h, and the pressure is 20kPaG. The above four stages of carbonization are all equipped with high-speed shearing machines to cyclically crush and disperse the materials in the kettle. Moreover, the above four-stage carbonization is all passed into ammonia gas to adjust the pH at 7.

Step S2 Filtration: the reaction material is filtered through the first step to obtain calcium carbonate filter cake and ammonium sulfate filtrate; due to excessive ammonium carbonate in the carbonization reaction, a small amount of ammonium carbonate remains in the ammonium sulfate filtrate.

Step S3 Concentration: Concentrate the ammonium sulfate filtrate to an ammonium sulfate concentrate with a mass fraction of 48%.

Step S4 Neutralization: add sulfuric acid and phosphoric acid to the ammonium sulfate concentrate to neutralize part of the ammonium bicarbonate and a small amount of free ammonia remaining in the ammonium sulfate concentrate solution, and control the pH to 5.0. The amount of phosphoric acid added needs to meet the content of the impurity ammonium phosphate salt in the granular ammonium sulfate, and the mass fraction of P ₂ O ₅ is 0.1%~4%.

Step S5 Granulation and drying: send the neutralized ammonium sulfate concentrate to the drum granulator through the nozzle, add KH ₂ PO ₄ slurry, contact with hot air at the same time, and make NPK compound fertilizer through the second granulation and drying (NPK compound fertilizer).

The grade utilization of step S6 calcium carbonate comprises:

Preparation of calcium carbonate powder: The mixed lye containing 30% NaOH and 0.2% Na ₂ CO ₃ and the washed part of the calcium carbonate filter cake were reacted under pressure at 100°C and 0.6MPaG for 6h, and then The third step is to filter and wash to obtain refined filter cake and sodium silicate filtrate. The sodium silicate filtrate meets the requirements of GB/T 4209-2008 for industrial sodium silicate. The refined filter cake is dried and pulverized to produce calcium carbonate powder meeting HG/T 2226-2019.

Preparation of calcium nitrate crystals: mix and react part of the washed calcium carbonate filter cake with insufficient nitric acid, and then obtain calcium nitrate filtrate through second filtration. After crystallization, filtration, and drying, high-purity calcium nitrate tetrahydrate crystals are obtained.

Preparation of granular compound fertilizer: mix and react part of the washed calcium carbonate filter cake with phosphoric acid to prepare a mixture. Simultaneously extract part of the calcium nitrate filtrate to the mixture. The remaining calcium nitrate filtrate is reacted with barium nitrate solution before crystallization, and the obtained barium sulfate filter residue is sent to the mixing material. The filter residue obtained by the second filtration is also sent to the mixture, and then dried through the first granulation to obtain granular compound fertilizer.

Example

This embodiment provides a kind of technology that utilizes phosphate stone to produce ammonium sulfate and utilizes calcium element gradedly, and its difference with embodiment 1 is:

In step S6, the graded utilization of calcium carbonate contains 25% mass fraction of NaOH and 0.12% mass fraction of Na ₂ CO The mixed lye is replaced by: containing 25% mass fraction of KOH and 0.12% mass fraction of K _{2 CO 3} Mix the lye. The product changes from GB/T4209-2008 industrial sodium silicate to potassium silicate that can meet HG/T 2226-2019.

Example

This embodiment provides a kind of technology that utilizes phosphate stone to produce ammonium sulfate and gradedly utilizes calcium element, and its difference with embodiment 7 is:

In step S6, the grading of calcium carbonate is replaced by the mixed lye containing 20% mass fraction of NaOH and 0.05% mass fraction of Na ₂ CO ₃ : containing 20% mass fraction of KOH and 0.12% mass fraction of K ₂ CO ₃ mixed lye. The product changes from GB/T4209-2008 industrial sodium silicate to potassium silicate that can meet HG/T 2226-2019.

Example

This embodiment provides a process for producing ammonium sulfate by using phosphate stone and graded utilization of calcium element. The difference from Example 8 is:

In step S6, the graded utilization of calcium carbonate contains 30% mass fraction of NaOH and 0.2% mass fraction of Na ₂ CO ₃ mixed lye is replaced by: containing 30% mass fraction of KOH and 0.2% mass fraction of K ₂ CO ₃ mixed lye. The product changes from GB/T4209-2008 industrial sodium silicate to potassium silicate that can meet HG/T 2226-2019.

Example

This embodiment provides a kind of technology that utilizes phosphate stone to produce ammonium sulfate and utilizes calcium element gradedly, and its difference with embodiment 1 is:

Step S5 Granulation and drying: the neutralized ammonium sulfate concentrate is sent to the drum granulator through the nozzle, and the granular ammonium sulfate is obtained through the second granulation and drying.

To sum up, the process of producing ammonium sulfate by using phosphate stone and utilizing calcium element by grade in the embodiment of the present invention has the advantages of strong adaptability to phosphogypsum, strong device process flexibility and great product competitiveness.

The embodiments described above are some, not all, embodiments of the present invention. The detailed description of the embodiments of the invention is not intended to limit the scope of the claimed invention but to represent only selected embodiments of the invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Claims (10)

1. A process for producing ammonium sulfate from a phosphorus stone and classifying the use of a calcium element, comprising the steps of:

step S1 carbonization: reacting phosphogypsum with 45-50% ammonium carbonate solution by mass fraction to obtain a reaction material;

step S2, filtering: the reaction materials are subjected to first filtration to obtain a calcium carbonate filter cake and an ammonium sulfate filtrate;

step S3, concentration: concentrating the ammonium sulfate filtrate to obtain an ammonium sulfate concentrated solution with the mass fraction of 41% -50%;

step S4, neutralization: adding sulfuric acid into the ammonium sulfate concentrated solution, and controlling the pH value to be 5.0-6.8;

step S5, granulating and drying: the neutralized ammonium sulfate concentrated solution is subjected to second granulation and drying to obtain granular ammonium sulfate;

step S6, grading utilization of calcium carbonate.

2. The process for producing ammonium sulfate using fluorite and classifying the calcium element according to claim 1, wherein the step S6 includes preparing calcium carbonate powder: and drying and crushing the calcium carbonate filter cake to obtain calcium carbonate powder.

3. The process for producing ammonium sulfate using fluorite and classifying the calcium element according to claim 1, wherein the step S6 includes preparing calcium carbonate powder: mixing alkali liquor with the calcium carbonate filter cake at 100-150 DEG CPressure maintaining reaction is carried out for 4-6 hours under the pressure of less than or equal to 0.65MPaG, then the third filtration and the washing are carried out, so as to obtain a refined filter cake and sodium silicate filtrate, and the refined filter cake is dried and crushed, so as to obtain calcium carbonate powder; wherein the mixed alkali solution contains 20-30% by mass of NaOH and 0.05-0.2% by mass of Na ₂ CO ₃ Or the mixed alkali solution contains 20-30% by mass of KOH and 0.05-0.2% by mass of K ₂ CO ₃ 。

4. A process for the production of ammonium sulphate by means of hawse and the fractional utilization of elemental calcium according to any one of claims 1-3 wherein step S6 comprises the preparation of granular heavy calcium/compound fertilizer: and mixing the calcium carbonate filter cake with phosphoric acid to react to obtain a mixture, and performing first granulation and drying to obtain granular heavy calcium.

5. The process for producing ammonium sulfate and classifying calcium element by use of phosphorus stone according to claim 4, wherein said step S6 further comprises preparing calcium nitrate crystals: mixing part of the calcium carbonate filter cake with insufficient nitric acid for reaction, then performing second filtration to obtain calcium nitrate filtrate, and crystallizing, filtering and drying to obtain calcium nitrate crystals;

preferably, extracting part of the calcium nitrate filtrate to the mixture, delivering the filter residue obtained by the second filtration to the mixture, and drying the mixture through the first granulation to obtain the granular compound fertilizer;

preferably, the calcium nitrate filtrate reacts with the barium nitrate solution before crystallization, and the prepared barium sulfate filter residue is sent to a mixture, and is subjected to first granulation and drying to prepare the granular compound fertilizer.

6. The process for producing ammonium sulfate by using the phosphoite and classifying the calcium element according to claim 1, wherein in the step S1, the carbonization temperature is 40-90 ℃, the carbonization pressure is less than or equal to 0.3MPaG, the reaction residence time is 3-6 h, and the mass fraction of the ammonium carbonate solution is 45-50%;

preferably, the carbonization pressure is 4-120 kPaG;

preferably, the carbonic acidDegree of carbonization of ammonium solution (2 n [ NH ] ₃ ]/n[CO ₂ ]）=（1.2~1）：1。

7. The process for producing ammonium sulfate using fluorite and classifying calcium element according to claim 1, wherein in the step S1, (NH ₄ ) ₂ CO ₃ And CaSO in the phosphogypsum ₄ The ratio of the amounts of the substances is [ (NH) ₄ ) ₂ CO ₃ ]：[CaSO ₄ ]=（1~1.2）：1。

8. The process for producing ammonium sulfate and classifying calcium element by use of phosphorus stone according to claim 7, wherein in said step S1, said carbonization is in multiple stages;

preferably, the carbonizing includes:

first-stage carbonization: the temperature is 65-90 ℃, the pressure is less than or equal to 120kPaG, the residence time is 0.5-1 h, ammonia is added to adjust the pH to be more than or equal to 7, and the amount of the added ammonium carbonate substance is n ₁ ；

Second-stage carbonization: the temperature is 65-90 ℃, the pressure is less than or equal to 100kPaG, the residence time is 0.5-1 h, ammonia is added to adjust the pH to be more than or equal to 7, and the amount of the added ammonium carbonate substance is n ₂ ；

Third-stage carbonization: the temperature is 50-65 ℃, the pressure is less than or equal to 80kPaG, the residence time is 1-2 h, and ammonia is added to adjust the pH to be more than or equal to 7;

fourth-stage carbonization: the temperature is 40-50 ℃, the pressure is less than or equal to 40kPaG, the residence time is 1-2 h, and ammonia is added to adjust the pH to be more than or equal to 7;

wherein n is ₁ ：n ₂ =3~7；

Preferably, the material of at least one of the first stage carbonization, the second stage carbonization, the third stage carbonization and the fourth stage carbonization is crushed by a high speed shearer.

9. The process for producing ammonium sulfate by using fluorite and classifying calcium according to claim 1, wherein phosphoric acid is added to the ammonium sulfate concentrate in the step S4, and the phosphoric acid neutralizes the ammonium sulfate concentrate together with the sulfuric acid.

10. The process for producing ammonium sulfate by using fluorite and classifying calcium element according to claim 1, wherein in the step S5, one of monoammonium phosphate, monoammonium phosphate and potassium salt is added to produce a compound fertilizer.

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