Process method for preparing superfine calcium carbonate and co-producing ammonium sulfate from ardealite
Through a process method including preparation of ammonium carbonate for production, waste residue slurry washing and purification, and conversion of multiphase reactors, the problems of low efficiency and impurities exceeding the standard in the preparation of ultrafine calcium carbonate co-product ammonium sulfate in phosphogypsum are solved, and the problem of inefficiency and impurities exceeding the standard in the process of preparing ultrafine calcium carbonate co-product ammonium sulfate is achieved. Efficient and low-cost production improves product quality.
Patent Information
- Application Number
- CN202411795559.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-09
- Publication Date
- 2025-02-14
AI Technical Summary
The existing process for preparing ultrafine calcium carbonate co-production ammonium sulfate in phosphogypsum has problems such as low efficiency of reaction stirrer, low calcium carbonate conversion rate and ammonium sulfate yield, and excessive impurities of finished products, which are difficult to promote and apply.
A multi-phase reactor that includes the preparation of ammonium carbonate, waste residue slurry cleaning and purification, purifying phosphogypsum into a continuous reaction multi-phase reactor for conversion of insoluble compounds, producing calcium carbonate and ammonium sulfate solutions, and through multi-effect evaporation process and replacement Process method for obtaining finished products by method crystallizer.
Improve production efficiency, reduce operating costs, and add an anti-float removal process, remove solid impurities in phosphogypsum raw materials, improve calcium carbonate conversion rate and ammonium sulfate yield, and solve the problem of excessive impurities in finished products. , product quality has been greatly improved.
Smart Images
Figure FT_1
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of solid waste disposal and carbon dioxide capture and mineralization utilization, and specifically to a process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum. Background Art
[0002] Phosphogypsum is the waste residue discharged by nitrophosphate fertilizer and wet phosphoric acid production enterprises. The production of 1 ton of phosphoric acid (calculated as 100% P2O5) produces 4.8 to 5.0 tons of phosphogypsum. The treatment and utilization of phosphogypsum has always been a global problem. According to international practice, the annual output of phosphogypsum in the world has exceeded 280 million tons, and my country's output has exceeded 75 million tons, with a comprehensive utilization rate of less than 30%. The main component of phosphogypsum waste residue is calcium sulfate dihydrate, which contains a small amount of harmful impurities such as phosphorus, fluorine, iron, aluminum, magnesium, and silicon, with a pH value of 4 to 5. Phosphogypsum is mainly used as a cement retarder, gypsum bricks and other building materials, but the characteristics of phosphogypsum containing impurities such as phosphorus and fluorine seriously restrict its large-scale use in the construction industry. Therefore, it is necessary to develop different ways to expand the comprehensive utilization of phosphogypsum. In addition to phosphogypsum, calcium sulfate waste residues generated in various industrial scenarios, such as calcium sulfate waste residues generated by the neutralization of titanium dioxide acidic wastewater, calcium sulfate dihydrate waste residues generated during lactic acid production, and desulfurization gypsum, all have technical difficulties in comprehensive utilization.
[0003] At present, the commonly used methods for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum are mainly double decomposition method, conversion reaction method or phase transfer precipitation method.
[0004] The double decomposition method includes two main steps: double decomposition reaction to produce ammonium sulfate and recycling of crude calcium carbonate. This method solves the problem of removing insoluble impurities through strong acid leaching, but it also brings about the problem of purification and recycling of the generated CO2: the process includes strong acid leaching and two carbonization reactions, the process is long, the cost is high, and there is secondary pollution.
[0005] Conventional conversion reaction method or phase transfer precipitation method usually converts phosphogypsum into a soluble calcium ion solution through the conversion reaction of phosphogypsum and ammonium bicarbonate, and then adds a carbonizing agent to the soluble calcium ion solution to form a precipitate. The filter residue after solid-liquid separation is calcium carbonate, which is washed and purified to be a finished product; the filtrate mainly contains ammonium sulfate, which is concentrated, crystallized and dried to be a finished product. Due to the lack of strict impurity removal treatment, it is difficult to remove soluble and insoluble impurities in the phosphogypsum raw material, and the impurity content is high, which affects the quality of the product ammonium sulfate and calcium carbonate. And because the precipitation reaction is a reversible reaction to a certain extent, with the continuous production of calcium carbonate, the forward progress of the precipitation reaction is inhibited, affecting the formation of calcium carbonate. It is necessary to strengthen the stirring during the reaction process as calcium carbonate is generated and accumulated continuously, otherwise the yield of calcium carbonate will be low. Moreover, the precipitation reaction is mostly stirred by a reaction tank, a reaction tank or a reaction kettle, and intermittent production. Although strong stirring can improve the conversion rate of calcium carbonate and the yield of ammonium sulfate to a limited extent, it is still difficult to solve the problem of low production efficiency and inability to produce on a large scale continuously.
[0006] Existing studies have shown that when the particle size of phosphogypsum is 80-100 mesh, the mass ratio of phosphogypsum to ammonium carbonate is 2:1, the amount of ammonium carbonate is 103%-105% of the theoretical amount, the reaction temperature is 65℃-70℃, and the reaction time is 2.5-3h, the conversion rate of phosphogypsum can reach more than 96%, and the product quality of the solid calcium sulfate obtained by the reaction can meet the requirements of first-class products in GB535-1995.
[0007] Existing studies have also shown that if ultrafine calcium carbonate is produced using by-product calcium carbonate slag without prior treatment of the phosphogypsum raw material such as impurities removal, the product cannot meet the national standard requirements for ultrafine calcium carbonate products with a purity of more than 97% and a whiteness value greater than 92.
[0008] In summary, the current process of preparing calcium carbonate and ammonium sulfate from phosphogypsum has a series of problems that are not conducive to its promotion and application, such as low efficiency of the reaction agitator, low calcium carbonate conversion rate and ammonium sulfate yield, and excessive impurities in the finished product. Summary of the invention
[0009] 1. Technical issues to be resolved In view of the shortcomings of the prior art, the present invention provides a process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum, which solves a series of problems that are not conducive to promotion and application, such as low efficiency of reaction agitator, low calcium carbonate conversion rate and ammonium sulfate yield, and excessive impurities in finished products.
[0010] (II) Technical solution To achieve the above objectives, the present invention is implemented by the following technical scheme: A process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum, comprising the following steps: S1. Preparation of ammonium carbonate for production: adding ammonia water or a mixture of ammonia gas and water, and additives into a supergravity carbonization reactor, and simultaneously introducing low concentration of carbon dioxide, to form ammonium carbonate after chemical reaction, the reaction formula is as follows: 2NH3+CO2+H2O→(NH4)2CO3; S2, slurry preparation, washing and purification of waste residue: After the waste residue is crushed and ball-milled, it is first mixed with water to form a slurry with a solid content of 20% to 30%, and then enters the reverse flotation device for impurity removal, and organic matter, soluble impurities and fine mud are removed from the overflow, and the remainder is pumped into the cyclone separator. The slurry flowing out from the bottom of the cyclone separator is filtered and then washed with an appropriate amount of water in the washing tank to obtain purified phosphogypsum. The wastewater is purified and reused for slurrying and washing; S3, the purified phosphogypsum solid phase enters a multiphase reactor capable of continuous reaction, where the insoluble compounds are converted to generate calcium carbonate and ammonium sulfate solution, and then the ammonium carbonate in S1 is injected into the multiphase reactor. In the multiphase reactor, the phosphogypsum and ammonium carbonate undergo a stable chemical reaction to generate calcium carbonate and ammonium sulfate. The reaction formula is as follows: CaSO4•2H2O+(NH4)2CO3→(NH4)2SO4+CaCO3+ 2H2O After the reaction is completed, the reaction product in the multiphase reactor is separated into a filter cake and a filtrate by solid-liquid separation; S4, the filter cake is broken up, dried, ground, deagglomerated, collected, packaged and stored as a finished product; S5. After the filtrate is cooled by a heat exchanger, it is injected into a substitution method crystallizer, where it reacts with methanol to precipitate ammonium sulfate. After separation by a centrifuge, solid ammonium sulfate is obtained, which is dried to obtain the finished product; S6, the methanol-containing aqueous solution coming out of the crystallizer in S5 is heated by a heat exchanger to reach the boiling point of methanol and evaporated, and the vaporized methanol is precipitated after distillation in an ultra-gravity distillation reactor and recycled; S7. After removing the methanol by distillation, the remaining liquid is cooled by a heat exchanger and then sent back to the ultra-gravity carbonization reactor to prepare ammonium carbonate for production.
[0011] Preferably, the additive in S1 is triethanolamine, and the added amount is 0.2% to 1%.
[0012] Preferably, the waste residue in S2 is one of phosphogypsum, dihydrate gypsum or desulfurized gypsum.
[0013] Preferably, the temperature of the solution in the multiphase reactor in S3 is 65°C to 70°C, the chemical reaction time of the phosphogypsum and ammonium carbonate in S3 is 0.5 to 3 hours; ammonia water is continuously added during the chemical reaction, and the pH of the solution is 7 to 12 during the chemical reaction.
[0014] Preferably, the finished product in S4 is further classified and selected to obtain high-purity ultrafine calcium carbonate.
[0015] Preferably, the filtrate in S5 can also be crystallized by a multiple-effect evaporation process, and after the ammonium sulfate crystallization reaches the requirement, it is vacuum dried to prepare a finished product.
[0016] (III) Beneficial effects The present invention provides a process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum. It has the following beneficial effects: 1. The process system has low operating costs. Since the ammonium carbonate used in the reaction is self-produced in a supergravity carbonization reactor by the carbon fixation method, and the reaction device into which the purified phosphogypsum solid phase enters is a multiphase reactor capable of continuous reaction, the production efficiency is greatly improved, the operating costs are reduced, and a reverse flotation impurity removal process is added to remove solid impurities in the phosphogypsum raw materials.
[0017] 2. The process equipment is sealed, which improves the yield of ammonia, reduces the residual ammonia in the tail gas, and reduces unorganized emissions such as ammonia escape.
[0018] 3. The temperature control range is precise during the reaction process. The multiphase reactor can greatly shorten the production time, improve the calcium carbonate conversion rate and ammonium sulfate yield, and solve the problem of low purity of the produced ultrafine calcium carbonate.
[0019] 4. Using low concentration of carbon dioxide will make the carbon fixation effect more obvious.
[0020] 5. This process adopts solvent substitution method, which greatly reduces heating costs.
[0021] 6. The product quality has been greatly improved. The ultrafine calcium carbonate products and high-purity ammonium sulfate obtained by this process are both high value-added chemical products. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 The present invention provides a process flow diagram of a process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum. DETAILED DESCRIPTION
[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0024] like Figure 1 As shown, the embodiment of the present invention provides a process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum, comprising the following steps: S1. Preparation of ammonium carbonate for production: adding ammonia water or a mixture of ammonia gas and water and an additive into a supergravity carbonization reactor, wherein the additive is triethanolamine in an amount of 0.4%, and simultaneously introducing low concentration of carbon dioxide to form ammonium carbonate after chemical reaction, and the reaction formula is as follows: 2NH3+CO2+H2O→(NH4)2CO3; S2, slurry preparation, washing and purification of phosphogypsum waste residue: After the phosphogypsum waste residue is crushed and ball-milled, it is first mixed with water to form a slurry with a solid content of 25%, and then enters the reverse flotation device for impurity removal, and organic matter, soluble impurities and fine mud are removed from the overflow, and the remainder is pumped into the cyclone separator. The slurry flowing out from the bottom of the cyclone separator is filtered and then washed with an appropriate amount of water in the washing tank to obtain purified phosphogypsum. The wastewater is purified and reused for slurrying and washing; S3, the purified phosphogypsum solid phase enters a multiphase reactor capable of continuous reaction, where the insoluble compounds are converted at 65°C to generate calcium carbonate and ammonium sulfate solution. The ammonium carbonate in S1 is then injected into the multiphase reactor, and ammonia water is injected simultaneously to keep the pH of the reaction solution at 8. In the multiphase reactor, the phosphogypsum and ammonium carbonate undergo a stable chemical reaction to generate calcium carbonate and ammonium sulfate. The reaction formula is as follows: CaSO4•2H2O+(NH4)2CO3→(NH4)2SO4+CaCO3+ 2H2O The reaction time is 1 hour. After the reaction is completed, coarse calcium carbonate crystals are obtained. The reaction product in the multiphase reactor is separated into a filter cake and a filtrate by solid-liquid separation. S4, the filter cake is broken up, dried, ground, depolymerized, collected, packaged and stored as a finished product, and the finished product is further graded and selected to obtain high-purity ultrafine calcium carbonate; S5. After the filtrate is cooled by a heat exchanger, it is injected into a substitution crystallizer, reacted with methanol in the crystallizer to precipitate ammonium sulfate, separated by a centrifuge to obtain solid ammonium sulfate, and dried to obtain the finished product. It can also be crystallized by a multi-effect evaporation process, and then after the processes of solution saturation, crystal nucleus formation, crystal nucleus growth, etc., the ammonium sulfate crystals that meet the requirements are obtained, and the ammonium sulfate crystals are vacuum dried to obtain the finished product; S6, the methanol-containing aqueous solution coming out of the crystallizer in S5 is heated by a heat exchanger to reach the boiling point of methanol and evaporated, and the vaporized methanol is precipitated after distillation in an ultra-gravity distillation reactor and recycled; S7. After removing the methanol by distillation, the remaining liquid is cooled by a heat exchanger and then sent back to the ultra-gravity carbonization reactor to prepare ammonium carbonate for production.
[0025] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.
Claims
1. A process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum, characterized in that: The following steps are involved: S1. Preparation of ammonium carbonate for production: adding ammonia water or a mixture of ammonia gas and water, and additives into a supergravity carbonization reactor, and simultaneously introducing low concentration of carbon dioxide, to form ammonium carbonate after chemical reaction, the reaction formula is as follows: 2NH3+CO2+H2O→(NH4)2CO3; S2, slurry preparation, washing and purification of waste residue: After the waste residue is crushed and ball-milled, it is first mixed with water to form a slurry with a solid content of 20% to 30%, and then enters the reverse flotation device for impurity removal, and organic matter, soluble impurities and fine mud are removed from the overflow, and the remainder is pumped into the cyclone separator. The slurry flowing out from the bottom of the cyclone separator is filtered and then washed with an appropriate amount of water in the washing tank to obtain purified phosphogypsum. The wastewater is purified and reused for slurrying and washing; S3, the purified phosphogypsum solid phase enters a multiphase reactor capable of continuous reaction, where the insoluble compounds are converted to generate calcium carbonate and ammonium sulfate solution, and then the ammonium carbonate in S1 is injected into the multiphase reactor. In the multiphase reactor, the phosphogypsum and ammonium carbonate undergo a stable chemical reaction to generate calcium carbonate and ammonium sulfate. The reaction formula is as follows: CaSO4•2H2O+(NH4)2CO3→(NH4)2SO4+CaCO3+ 2H2O After the reaction is completed, the reaction product in the multiphase reactor is separated into a filter cake and a filtrate by solid-liquid separation; S4, the filter cake is broken up, dried, ground, deagglomerated, collected, packaged and stored as a finished product; S5. After the filtrate is cooled by a heat exchanger, it is injected into a substitution method crystallizer, where it reacts with methanol to precipitate ammonium sulfate. After separation by a centrifuge, solid ammonium sulfate is obtained, which is dried to obtain the finished product; S6, the methanol-containing aqueous solution coming out of the crystallizer in S5 is heated by a heat exchanger to reach the boiling point of methanol and evaporated, and the vaporized methanol is precipitated after distillation in an ultra-gravity distillation reactor and recycled; S7. After removing the methanol by distillation, the remaining liquid is cooled by a heat exchanger and then sent back to the ultra-gravity carbonization reactor to prepare ammonium carbonate for production.
2. The process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum according to claim 1, characterized in that: The additive in S1 is triethanolamine, and the added amount is 0.2% to 1%.
3. The process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum according to claim 1, characterized in that: The waste residue in S2 is one of phosphogypsum, dihydrate gypsum or desulfurized gypsum.
4. The process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum according to claim 1, characterized in that: The temperature of the solution in the multiphase reactor in S3 is 65°C to 70°C, and the chemical reaction time of the phosphogypsum and ammonium carbonate in S3 is 0.5 to 3 hours; ammonia water is continuously added during the chemical reaction, and the pH value of the solution is 7 to 12 during the chemical reaction.
5. The process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum according to claim 1, characterized in that: The finished product in S4 is further classified and selected to obtain high-purity ultrafine calcium carbonate.
6. The process for preparing ultrafine calcium carbonate and co-producing ammonium sulfate from phosphogypsum according to claim 1, characterized in that: The filtrate in S5 can also be crystallized through a multi-effect evaporation process. After the ammonium sulfate crystals meet the requirements, they are vacuum dried to produce a finished product.