Method for realizing pollution reduction and carbon reduction through ardealite recycling

Abstract

The invention discloses a method for realizing pollution reduction and carbon reduction by phosphogypsum recycling. The method comprises the following steps: (1) washing phosphogypsum with water to remove soluble impurities, neutralizing residual acid, and calcining and activating; (2) pretreatment of the landfill leachate: magnesium salt and phosphate are added, the pH of the landfill leachate is adjusted, and free ammonia NH3 is released through low-temperature heating; (3) the pretreated landfill leachate is sprayed to capture CO2 in the flue gas, and a (NH4) 2CO3 solution is obtained; (4) fully mixing a (NH4) 2CO3 solution with the pretreated ardealite, and controlling the reaction conditions in a closed reactor, so that the ardealite and (NH4) 2CO3 are subjected to a heterogeneous reaction to generate CaCO3 and (NH4) 2SO4; and (5) product purification: carrying out solid-liquid separation on the mixed solution by adopting a multi-stage crystallization process to obtain a building material, and carrying out gradient cooling and recrystallization purification on the filtrate to obtain the nitrogen fertilizer. According to the method, recycling of the landfill leachate and the ardealite is achieved, and CO2 in the flue gas is efficiently removed.

Description

Technical Field

[0001] The present invention relates to the field of energy chemistry, and relates to a method for realizing pollution reduction and carbon emission reduction through the resource utilization of phosphogypsum, which is particularly applicable to the combined resource utilization of phosphogypsum, a by-product of wet-process phosphoric acid, landfill leachate and industrial flue gas. Background Art

[0002] Phosphogypsum, as a typical by-product of the wet-process phosphoric acid process, has a main chemical composition of calcium sulfate dihydrate (CaSO4·2H2O). According to industry statistics, for every 1 ton of phosphoric acid produced, 4 - 6 tons of phosphogypsum will be associated, and the global annual production has exceeded 300 million tons, while the comprehensive utilization rate is relatively low. It is worth noting that the stacking of phosphogypsum not only causes waste of land resources, but also the migratory pollutants such as soluble phosphorus, fluorides and heavy metal ions contained in it are more likely to cause regional soil degradation and water ecological imbalance through leaching. Although traditional phosphogypsum disposal technologies have been applied for many years, they are still limited by key bottlenecks such as large fluctuations in raw material impurities, high pretreatment costs and low acceptance in the downstream market. Developing a resource utilization path with high added value has become an urgent need in the industry.

[0003] On the other hand, with the acceleration of China's urbanization process and the increase in the total amount of domestic waste, the production of leachate has been increasing year by year. In 2023, the national production of landfill leachate was about 102 million tons, but the treatment volume was only 63.6 million tons, and the treatment rate was about 62%. By 2025, it is expected that the production will increase to 180 million tons, and the treatment demand will further expand. Landfill leachate, as a main ammonia-nitrogen-containing waste (hundreds to thousands of mg / L), has an imbalanced C / N ratio and is difficult to denitrify. Although China's landfill leachate treatment industry is developing rapidly under the promotion of policies, the current mainstream treatment technologies (such as membrane separation and advanced oxidation) have high energy consumption, risks of secondary pollution, and fail to realize the resource recovery of ammonia nitrogen. In the future, technological innovation is still needed to improve the treatment efficiency and reduce environmental risks.

[0004] At the same time, in terms of the demand for carbon dioxide emission reduction, power generation and manufacturing are the core fields of carbon dioxide emissions. The concentration of CO2 in the flue gas of coal-fired power plants reaches 12 - 15%, and the concentration in the tail gas of iron and steel sintering and cement kilns is even as high as 18 - 30%. Existing adsorption technologies (such as amine method capture) are costly and lack an integrated solution for co-treatment with solid waste. Based on the goals of "carbon peak" and "carbon neutrality", it is urgent to transform to more efficient CO2 adsorption technologies, which is not only an inevitable choice to address the climate crisis, but also a strategic measure to reshape industrial competitiveness and seize the high ground of new energy technologies.

[0005] In summary, the above by-products or waste have the following defects in terms of resource treatment: (1) The individual treatment costs of phosphogypsum and landfill leachate are high, and the resource treatment paths are single; (2) The co-fixation technology of ammonia nitrogen and CO2 is not yet mature; (3) There is a lack of systematic methods to simultaneously reduce pollution, lower carbon emissions, and output high-value products.

[0006] Based on the above discussion, the present invention proposes a new method for realizing pollution reduction and carbon emission reduction through phosphogypsum resource treatment, which has important practical significance. Summary of the Invention

[0007] In view of the above problems, the present invention provides a method for realizing pollution reduction and carbon emission reduction through phosphogypsum resource treatment, which not only realizes the resource treatment of landfill leachate and phosphogypsum, but also efficiently removes CO2 in flue gas.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for realizing pollution reduction and carbon emission reduction through phosphogypsum resource treatment, comprising the following steps: S1: Pretreatment of raw materials First, wash the phosphogypsum with water to remove soluble impurities; then add lime to neutralize the residual acid and adjust the pH to neutral; finally, perform high-temperature calcination activation in a calciner. S2: Pretreatment of landfill leachate Add a certain proportion of phosphate and magnesium salt to the landfill leachate and add alkali to adjust the pH of the system, and perform low-temperature drying to release free NH3, and prepare ammonia water through air stripping absorption method. S3: Fixation of CO2 Capture CO2 in flue gas by spraying the pretreated landfill leachate, and obtain (NH4)2CO3 solution after sufficient reaction. S4: Preparation of (NH4)2SO3 and CaCO3 Fully mix the (NH4)2CO3 solution with the pretreated phosphogypsum, control the reaction conditions in a closed reactor, and make the phosphogypsum undergo a heterogeneous reaction with (NH4)2CO3 to generate CaCO3 and (NH4)2SO 4； S5: Product purification: Adopt a multi-stage crystallization process to perform solid-liquid separation on the mixed solution obtained in step S4 to obtain building materials, and the filtrate is purified by gradient cooling and recrystallization to obtain nitrogen fertilizer.

[0009] Further, in step S1, the calcination temperature range is controlled at 300-800°C to dehydrate the phosphogypsum to form anhydrous phosphogypsum (CaSO4) to improve the product purity.

[0010] Further, in the pretreatment of landfill leachate in step S2, NH4 in the landfill leachate+ With the added PO4 3- and Mg 2+ satisfying NH4 + :PO4 3- :Mg 2+ The molar ratio is 1:1:1; the pH-adjusting substance is a KOH solution, and the system pH range is adjusted to 8 - 9; the temperature range for low-temperature drying is 85 - 90 °C, the drying environment is a nitrogen atmosphere, and the drying time is 4 - 6 h.

[0011] Furthermore, the liquid-gas ratio of the spray in step S3 is 8 - 10 L / m 3 .

[0012] Furthermore, in step S4, the reaction temperature is controlled at 50–80 °C, and the stirring time is about 1 - 3 h.

[0013] Furthermore, the multi-stage crystallization process in step S5 includes primary crystallization, secondary crystallization, and tertiary crystallization. Among them, primary crystallization is the rough crystallization stage; secondary crystallization is gradient cooling purification; tertiary crystallization is solvent-assisted recrystallization; the cooling rate of primary crystallization is 1 - 2 °C / min, and the solid-liquid ratio is controlled at 1.2 - 1.5 times.

[0014] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: The present invention innovatively constructs a synergistic conversion system of phosphogypsum-nitrogen-containing waste, realizes the efficient mineralization and fixation of high-concentration ammonia nitrogen pollutants, simultaneously completes the absorption of CO2 in flue gas, and finally produces nitrogen fertilizer with high added value. This technical route can greatly reduce the carbon emission intensity per ton of nitrogen product, and at the same time consume a large amount of phosphogypsum solid waste, truly realizing the triple coupling effect of "pollutant treatment - resource regeneration - carbon emission reduction".

[0015] Based on the idea of "treating waste with waste", the method of using solid waste to solve gaseous waste in the present invention not only realizes the resource utilization of landfill leachate and phosphogypsum, but also efficiently fixes and removes CO2 in flue gas, and simultaneously co-produces calcium carbonate materials and ammonium sulfate fertilizers, improving the resource utilization economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a process flow diagram for realizing pollution reduction and carbon emission reduction of phosphogypsum resource utilization in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0018] The present invention proposes an innovative solution to the current technical bottlenecks in the coordinated treatment of phosphogypsum, landfill leachate and coal-fired flue gas CO2. The existing technology has prominent problems such as high cost of by-product separation treatment, immature technology for coordinated fixation of ammonia nitrogen and CO2, and difficulty in balancing pollution reduction and carbon reduction with high value. To this end, the present invention pioneered a "waste-to-waste" recycling treatment system, and constructed a new multi-media coordinated treatment path through the coupling regulation of the activation of phosphogypsum calcium components, the directional conversion of leachate ammonia nitrogen and the mineralization and fixation of flue gas CO2. The specific process is as follows Figure 1 As shown, the following steps are included: One ton of phosphogypsum (CaSO4·2H2O content>85%) was taken from a phosphoric acid production enterprise and washed with water to remove soluble impurities (such as PO4 3- , F⁻), then add lime to adjust pH=7, and finally calcine at 700℃ in a calcining furnace for 2h; Garbage leachate (NH4⁺=1500mg / L) was added with MgCl2, K3PO4 (NH4 + :PO4 3- :Mg 2+ The molar ratio is 1:1:1), the pH of the system is adjusted to 8.5 with KOH solution, and the system is dried at 85℃ with nitrogen for 6 hours to release free NH3, and then ammonia water is prepared by gas stripping absorption method; The above spray liquid (liquid-gas ratio 9 L / m³) was used to absorb the coal-fired flue gas of a power plant (CO2 concentration range is 10-25%), generating 1.2m 3 (NH4)2CO3 solution; The generated (NH4)2CO3 solution is fully mixed with the pretreated phosphogypsum in a closed reactor. The reaction temperature is controlled at 70°C and the stirring time is about 1-3 hours, so that the phosphogypsum and (NH4)2CO3 undergo a multiphase reaction to generate CaCO3 and (NH4)2SO4. The relevant reaction is as follows: CaSO4+(NH4)2CO3→CaCO3↓+(NH4)2SO4; The product is purified using a multi-stage crystallization process: Primary crystallization: cooling rate 1-2℃ / min, solid-liquid ratio 1.2-1.5, separation of CaCO3, CaCO3 yield 92.5%, (NH4)2SO4 solution concentration 18wt%; Secondary crystallization: Gradient cooling is used to purify (NH4)2SO4. It is cooled to 5°C by gradient cooling, and the crystallization purity of (NH4)2SO4 is 99.2%. Tertiary crystallization: Solvent-assisted recrystallization is used to obtain high-purity nitrogen fertilizer.

[0019] The technical solution of the present invention has the following beneficial effects: (1) Pollution reduction: The removal rate of impurities in phosphogypsum is >90%, and the recovery rate of ammonia nitrogen in leachate is ≥95%; (2) Carbon reduction: 0.2 - 0.3 tons of CO2 can be fixed per ton of phosphogypsum; (3) Resource utilization: The purity of CaCO3 is ≥98% (usable as building materials), and (NH4)2SO4 can be used as nitrogen fertilizer; (4) Economy: The treatment cost is reduced by 40% compared with the traditional step-by-step process.

[0020] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for realizing pollution reduction and carbon emission reduction through the resource utilization of phosphogypsum, characterized in that, It includes the following steps: S1: Pretreatment of raw materials First, wash the phosphogypsum with water to remove soluble impurities; Subsequently, add lime to neutralize the residual acid and adjust the pH to neutral; finally, conduct high-temperature calcination activation in a calciner; S2: Pretreatment of landfill leachate Add a certain proportion of phosphate and magnesium salt to the landfill leachate, add alkali to adjust the pH of the system, and conduct low-temperature drying to release free NH3, and prepare ammonia water through air stripping absorption method; S3: Fixation of CO2 Capture CO2 in the flue gas by spraying the pretreated landfill leachate, and obtain (NH4)2CO3 solution after sufficient reaction; S4: Preparation of (NH4)2SO4 and CaCO3 The (NH4)2CO3 solution is fully mixed with the pretreated phosphogypsum, and the reaction conditions are controlled in a closed reactor to allow the phosphogypsum and (NH4)2CO3 to undergo a multiphase reaction to generate CaCO3 and (NH4)2SO 4； S5: Product purification: Adopt a multi-stage crystallization process to conduct solid-liquid separation on the mixed solution obtained in step S4 to obtain building materials, and the filtrate is purified by gradient cooling and recrystallization to obtain nitrogen fertilizer.

2. The method for realizing pollution reduction and carbon emission reduction through the resource utilization of phosphogypsum according to claim 1, wherein In step S1, the calcination temperature range is controlled at 300 - 800 °C to dehydrate the phosphogypsum to form anhydrous phosphogypsum, so as to improve the product purity.

3. A method for realizing pollution reduction and carbon emission reduction through the resource utilization of phosphogypsum according to claim 1, characterized in that, In the pretreatment of landfill leachate in step S2, NH4 in the landfill leachate + and the added PO4 3- and Mg 2+ satisfy that the molar ratio of NH4 + :PO4 3- :Mg 2+ is 1:1:1; the substance for adjusting the pH is KOH solution, the pH range of the system is adjusted to 8-9; the temperature range for low-temperature drying is 85-90 °C, the drying environment is a nitrogen atmosphere, and the drying time is 4-6 h.

4. A method for realizing pollution reduction and carbon emission reduction through the resource utilization of phosphogypsum according to claim 1, characterized in that, The liquid-gas ratio of the spray in step S3 is 8 - 10 L / m 3 .

5. A method for realizing pollution reduction and carbon emission reduction through the resource utilization of phosphogypsum according to claim 1, characterized in that, In step S4, the reaction temperature is controlled at 50–80 °C, and the stirring time is about 1 - 3 h.

6. A method for realizing pollution reduction and carbon emission reduction through the resource utilization of phosphogypsum according to claim 1, characterized in that, The multi-stage crystallization process in step S5 includes primary crystallization, secondary crystallization and tertiary crystallization, where primary crystallization is the rough crystallization stage; secondary crystallization is gradient cooling purification; Tertiary crystallization is solvent-assisted recrystallization; Among them, the cooling rate of primary crystallization is 1 - 2 °C / min, and the solid-liquid ratio is controlled at 1.2 - 1.5 times.

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