A method for preparing high-activity calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation

Abstract

This invention belongs to the field of solid waste resource utilization technology, specifically relating to a method for preparing highly active calcium oxide through low-temperature decomposition of phosphogypsum based on composite additives. The method involves uniformly mixing phosphogypsum with composite additives, followed by heating and decomposition under a non-strong reducing atmosphere to obtain a solid product containing calcium oxide. Subsequently, byproducts are selectively separated to remove the remaining product, yielding highly active calcium oxide. Compared with existing technologies, this invention eliminates the need for carbonaceous reducing agents and strong reducing gases, avoiding the formation of calcium sulfide intermediates. The synergistic effect of the composite additives enables the direct decomposition of phosphogypsum at lower temperatures, improving the reactivity and specific surface area of ​​calcium oxide, while simplifying the process and reducing energy consumption.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization technology, specifically relating to a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation. Background Technology

[0002] Industrial by-product gypsum refers to by-products or waste residues mainly composed of calcium sulfate (CaSO4) generated through chemical reactions during industrial production processes. These primarily include phosphogypsum, desulfurization gypsum, titanium gypsum, fluorogypsum, and citric acid gypsum. Among these, phosphogypsum is the main solid waste generated during the wet-process phosphoric acid production process; approximately 4-6 tons of phosphogypsum are typically produced for every ton of phosphoric acid produced. With the rapid development of the phosphoric acid chemical industry, the discharge of phosphogypsum has been continuously increasing. Long-term stockpiling not only occupies a large amount of land resources, but the residual acidic substances and impurities can also easily pollute the soil and groundwater environment. Therefore, its efficient resource utilization has become an important issue that urgently needs to be addressed.

[0003] Phosphogypsum is rich in elements such as calcium and sulfur, and its main component is calcium sulfate dihydrate (CaSO4·2H2O). Through thermal decomposition, it can be converted into important basic raw materials such as calcium oxide. Therefore, the decomposition of phosphogypsum to prepare calcium oxide is considered an important resource utilization pathway. However, calcium sulfate has high thermal stability under normal atmospheres, and direct decomposition typically requires high-temperature conditions above 1300℃. This not only results in high energy consumption but also stringent equipment requirements, hindering the widespread application of this technology.

[0004] To lower the reaction temperature and improve decomposition efficiency, existing technologies mostly employ a reduction decomposition pathway. For example, patent CN101708826B discloses a method for reducing and decomposing phosphogypsum using gaseous sulfur, generating calcium sulfide intermediates, which are then further processed at high temperatures to obtain calcium oxide; patent CN105905872A proposes using pyrite as a reducing agent to achieve the reduction and decomposition of phosphogypsum in a rotary kiln and co-produce sulfuric acid; patent CN114229877A discloses a method for reducing phosphogypsum at low temperatures in a carbon monoxide atmosphere to generate calcium sulfide, followed by an oxidation step to prepare calcium oxide; in addition, patent CN103482584B introduces a carbonaceous reducing agent and processes gypsum at high temperatures in an inert atmosphere to convert calcium sulfate into calcium oxide.

[0005] While the above methods have reduced the reaction temperature and improved the decomposition efficiency to some extent, they still have significant shortcomings: First, calcium sulfide is usually generated as an intermediate product during the reduction decomposition process, and some calcium sulfide is likely to remain in the final product, affecting the purity and performance of calcium oxide; second, over-oxidation is prone to occur in the subsequent oxidation process, causing some products to be converted back into calcium sulfate, thereby reducing the overall conversion efficiency; third, when using solid reducing agents, problems such as uneven mixing and insufficient local reaction are likely to occur, while introducing impurities and increasing the difficulty of post-processing; in addition, such methods usually involve multi-step reactions or complex atmosphere control, resulting in a long process flow and high energy consumption and operating costs.

[0006] In contrast, while direct thermal decomposition of phosphogypsum in an inert or air atmosphere can avoid the formation of sulfides, the high activation energy of the reaction often requires higher temperatures, leading to a significant increase in energy consumption. At the same time, the decomposition efficiency is low, making it difficult to achieve efficient utilization.

[0007] In recent years, some studies have attempted to improve the decomposition performance of phosphogypsum by adding additives. However, existing technologies mostly use a single additive system, which has limited ability to regulate the crystal structure of calcium sulfate, making it difficult to reduce the decomposition temperature while simultaneously improving the reaction rate and product performance.

[0008] Therefore, developing a new method that can achieve efficient decomposition of phosphogypsum at lower temperatures without relying on strong reducing conditions, effectively inhibit the formation of calcium sulfide intermediates, and obtain highly active calcium oxide has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] To address the problems of complex processes, easy formation of calcium sulfide intermediates, and high energy consumption associated with the existing reduction decomposition pathway for calcium oxide preparation, this invention aims to provide a method for preparing calcium oxide through low-temperature decomposition of phosphogypsum based on the regulation of composite additives. This method, under non-strong reducing atmosphere conditions, utilizes the synergistic effect of composite additives to regulate the decomposition pathway of calcium sulfate, achieving efficient decomposition of phosphogypsum at lower temperatures and obtaining a highly active calcium oxide product.

[0010] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation, comprising the following steps: S1. Mix phosphogypsum and composite additives evenly to obtain a mixture; S2. The mixture is subjected to a heating decomposition reaction to obtain a solid product containing calcium oxide; S3. The solid product is separated to obtain calcium oxide product.

[0011] In this invention, a composite additive system is introduced to promote the destruction of the calcium sulfate crystal structure and reduce its decomposition activation energy during heating, thereby achieving effective decomposition of phosphogypsum in the range of 700–950°C. Unlike traditional reduction decomposition methods, this invention does not rely on carbonaceous reducing agents or strong reducing gases, and calcium sulfide is not the main intermediate product during the reaction, thus avoiding sulfide residues and secondary oxidation problems.

[0012] Preferably, the phosphogypsum is dried phosphogypsum with a moisture content controlled at 1% to 10%; more preferably 2% to 5%.

[0013] Preferably, the composite additive includes any one or a combination of at least two of alkali metal salts, transition metal oxides, pore-forming components, and rare earth oxides.

[0014] As an optional implementation, the composite additive is an alkali metal salt, a transition metal oxide, and a pore-forming component, with a mass ratio of (2~3):(1~2):(4~6); more preferably, it is 5:3:10.

[0015] By combining alkali metal salts, transition metal oxides, and pore-forming components, phosphogypsum can be decomposed efficiently at low temperatures, while simultaneously improving calcium oxide formation efficiency and reactivity. This is because alkali metal salts promote the destruction of the calcium sulfate lattice to lower the decomposition activation energy, transition metal oxides catalyze the decomposition reaction to accelerate the process, and pore-forming components regulate the pore structure of the product and enhance gas diffusion. The three components work synergistically to achieve the direct decomposition of phosphogypsum at lower temperatures.

[0016] As an optional implementation, the composite additive is an alkali metal salt, a transition metal oxide, a pore-forming component, and a rare earth oxide, with a mass ratio of (2~3):(1~2):(4~6):1; more preferably, it is 5:3:10:2.

[0017] Preferably, the alkali metal salt is Na2CO3 or K2CO3.

[0018] Preferably, the transition metal oxide is Fe2O3, MnO2, or CuO.

[0019] Preferably, the pore-forming component is a biomass material.

[0020] Preferably, the biomass material is wood chips, straw powder, or starch.

[0021] The method for preparing the rare earth oxide includes the following steps: dissolving rare earth metal salt and magnesium salt in deionized water and stirring until completely dissolved to obtain a clear solution; adjusting the rotation speed and temperature, slowly adding ammonia water dropwise to the above mixed salt solution until the pH value of the system is 9.0~10.0, continuing to stir for 1~3 hours, allowing it to stand and age for 6~12 hours, filtering to obtain a precipitate, washing it with deionized water 3~5 times, drying it, calcining it, grinding it and sieving it to obtain the final product.

[0022] Preferably, the rare earth metal salt is one or more of the nitrates or carbonates corresponding to the rare earth elements Ce, Pr or Tb; more preferably, the rare earth metal salt is cerium nitrate (Ce(NO3)3·6H2O).

[0023] Preferably, the magnesium salt is magnesium nitrate (Mg(NO3)2·6H2O).

[0024] Preferably, the molar ratio of rare earth element in the rare earth metal salt to magnesium element in the magnesium salt is (2~3):1; more preferably, it is 7:3.

[0025] Based on a ternary compound of alkali metal salts, transition metal oxides, and pore-forming components, the introduction of self-made rare earth oxides significantly improves the decomposition efficiency of phosphogypsum and the activity of calcium oxide purity, while further reducing the decomposition temperature and avoiding the formation of calcium sulfide intermediates. This is because, on the one hand, rare earth oxides themselves possess redox pairs, forming a dynamic oxygen buffer mechanism that avoids deep reduction to form calcium sulfide and promotes the oxidative decomposition pathway of calcium sulfate. MgO provides alkaline sites for adsorption and fixation, and induces lattice distortion, serving as alkaline sites to preferentially capture SO3 and rapidly decompose it, preventing the reverse reaction. Simultaneously, Mg... 2+ Doping with CaO causes lattice distortion, lowers the decomposition activation energy, and inhibits calcium oxide grain sintering; CeO2 pins grain boundaries and interacts with Mg. 2+ Synergistic anti-sintering mechanism enables efficient decomposition of phosphogypsum under a non-reducing atmosphere to produce highly active calcium oxide. Furthermore, rare earth oxides and ternary components form a multi-dimensional synergistic strengthening effect, synergistically exacerbating calcium sulfate lattice distortion with alkali metal salts, thus doubly reducing the decomposition activation energy. They also construct dual catalytic active centers with transition metal oxides, accelerating calcium sulfate decomposition kinetics. In conjunction with pore-forming components, they stabilize the pore structure, enhancing gas diffusion and product activity. Simultaneously, they function as a dynamic oxygen buffer, providing in-situ sulfur fixation and inhibiting calcium oxide sintering. This four-component coupling achieves lower temperature, higher efficiency, and higher selectivity decomposition of phosphogypsum under a non-strong reducing atmosphere.

[0026] Preferably, the total mass of the rare earth metal salt and magnesium salt and the solid-liquid ratio of the deionized water are 1 g: (5~10) mL.

[0027] Preferably, the rotational speed and temperature are 300~500 r / min and 35~40℃, respectively.

[0028] Preferably, the specific drying conditions are: temperature of 100-120℃ and time of 8-12 h.

[0029] Preferably, in the preparation method of the rare earth oxide, the specific calcination conditions are as follows: heating at a rate of 5°C / min to 480~520°C, holding at that temperature for 3~5 hours, and then naturally cooling to room temperature.

[0030] Preferably, the sieving is performed through a 100-200 mesh sieve.

[0031] Preferably, the mass ratio of the composite additive to phosphogypsum is (0.05~0.30):1; more preferably, it is (0.10~0.20):1, for example, 0.10:1, 0.12:1, 0.15:1 or 0.18:1.

[0032] In some alternatives, the mixture is ball-milled or mechanically mixed for 10-40 minutes before the thermal decomposition reaction to improve the uniformity of contact between the additive and phosphogypsum.

[0033] Preferably, in step S2, the heating decomposition reaction is carried out under a non-strong reducing atmosphere.

[0034] Preferably, the non-strong reducing atmosphere is an inert gas, CO2, or an oxygen-containing gas atmosphere; the inert gas is N2; in the mixed gas, the volume fraction of the inert gas is 80%~100%, and the balance is CO2 or a small amount of O2.

[0035] Preferably, the temperature of the heating decomposition reaction is 700℃~950℃; more preferably, it is 800℃~900℃, for example, 820℃, 850℃ or 880℃.

[0036] Preferably, the heating rate of the thermal decomposition reaction is 5~15℃ / min; more preferably, it is 8~10℃ / min.

[0037] Preferably, the reaction time of the heating decomposition reaction is 30-150 min; more preferably, it is 40-120 min, for example, 120 min, 60 min or 75 min.

[0038] In some alternative embodiments, step S2 further includes a cooling step: cooling to room temperature under an inert or air atmosphere after the heating decomposition reaction to prevent calcium oxide from absorbing water or carbonizing.

[0039] In some alternative schemes, the decomposition rate of calcium sulfate during the heating decomposition reaction can reach more than 85%, preferably more than 90%, and even more preferably more than 95%.

[0040] In some alternative schemes, in step S2, the mass fraction of calcium oxide in the obtained solid product containing calcium oxide is not less than 80%, preferably 85-95%, and the specific surface area is 5-25 m² / g. The obtained calcium oxide has high reactivity and can react with water to generate calcium hydroxide in a short time.

[0041] In some alternative embodiments, the separation process in step S3 includes at least one of water washing, magnetic separation, or sieving, wherein soluble salts are removed by water washing and iron-containing components are removed by magnetic separation.

[0042] The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives specifically includes the following steps: S1. After drying the phosphogypsum, mix it with the composite additive according to the mass ratio, and then mechanically stir or ball mill it for 10~60 minutes. S2. The obtained mixture is heated to 800-900℃ at a heating rate of 5-15℃ / min under a non-strong reducing atmosphere and held at that temperature for 40-90min to complete the thermal decomposition reaction; after the reaction is completed, it is cooled to room temperature to obtain a solid product containing calcium oxide. S3. The obtained solid product is washed with water or subjected to magnetic separation to remove by-products and obtain calcium oxide product.

[0043] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. This invention significantly reduces the decomposition temperature of phosphogypsum through the synergistic effect of composite additives, enabling the reaction to be completed in the range of 800-900℃, thereby reducing energy consumption.

[0044] 2. This invention does not rely on carbonaceous reducing agents and strong reducing atmospheres, thus avoiding the large-scale generation of calcium sulfide intermediates and improving the purity and stability of calcium oxide.

[0045] 3. The calcium oxide prepared by this invention has a high specific surface area and high reactivity, and can be used in fields such as adsorption, building materials or catalysis, thereby increasing the added value of products.

[0046] 4. The process of this invention is simple, and the reaction process can be completed in a single reactor, which is convenient for industrial scale-up applications.

[0047] 5. The by-products in this invention are easy to separate and process, which is conducive to achieving efficient resource utilization and environmentally friendly production. Attached Figure Description

[0048] Figure 1 This invention provides a schematic flowchart of a method for preparing calcium oxide from phosphogypsum based on the regulation of composite additives. Detailed Implementation

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] All raw materials used in this invention are commercially available, as detailed below: The phosphogypsum, sourced from Tianan Chemical Plant under Yunnan Yuntianhua Group, was crushed, ground, and sieved through a 200-mesh sieve. It was then dried at 105°C for more than 4 hours until the moisture content was 2%, and was used in the specific embodiment.

[0051] Example 1 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation, the steps of which are as follows: S1. Mix phosphogypsum and composite additives evenly to obtain a mixture; S2. The mixture is subjected to a heating decomposition reaction to obtain a solid product containing calcium oxide; S3. The solid product is separated to obtain calcium oxide product.

[0052] The composite additive consists of alkali metal salts, transition metal oxides, pore-forming components, and rare earth oxides in a mass ratio of 5:3:10:2.

[0053] The alkali metal salt is Na2CO3.

[0054] The transition metal oxide is Fe2O3.

[0055] The pore-forming component is wood chips.

[0056] The preparation method of the rare earth oxide includes the following steps: dissolving rare earth metal salt and magnesium salt in deionized water and stirring until completely dissolved to obtain a clear solution; adjusting the rotation speed and temperature, slowly adding ammonia water dropwise to the above mixed salt solution until the pH value of the system is 9.5, continuing to stir for 2 hours, allowing it to stand and age for 10 hours, filtering to obtain a precipitate, washing it 4 times with deionized water, drying it, calcining it, grinding it and sieving it to obtain the final product.

[0057] The rare earth metal salt is Ce nitrate Ce(NO3)3·6H2O.

[0058] The magnesium salt is Mg(NO3)2·6H2O.

[0059] The molar ratio of rare earth elements in the rare earth metal salt to magnesium elements in the magnesium salt is 7:3.

[0060] The total mass of the rare earth metal salt and magnesium salt and the solid-liquid ratio of the deionized water are 1 g: 6 mL.

[0061] The ammonia concentration is 28%.

[0062] The rotational speed and temperature were 400 r / min and 40℃, respectively.

[0063] The specific drying conditions are: temperature 110℃, time 10h.

[0064] In the preparation method of the rare earth oxide, the specific calcination conditions are as follows: heating to 500°C at a heating rate of 5°C / min, holding at that temperature for 4 hours, and then naturally cooling to room temperature.

[0065] The sieving process is a 200-mesh sieve.

[0066] The mass ratio of the composite additive to phosphogypsum is 0.18:1.

[0067] The mixture is ball-milled for 45 minutes before undergoing the heating and decomposition reaction.

[0068] The specific conditions for the ball milling mixing process are: ball-to-material ratio of 2:1 and rotation speed of 300 r / min.

[0069] In step S2, the heating decomposition reaction is carried out under a non-strong reducing atmosphere.

[0070] The non-strong reducing atmosphere is an oxygen-containing gas atmosphere; the oxygen-containing gas atmosphere is air.

[0071] The temperature of the heating decomposition reaction is 900℃.

[0072] The heating rate of the thermal decomposition reaction is 10℃ / min.

[0073] The reaction time for the heating decomposition reaction is 120 min.

[0074] Step S2 further includes a cooling step: after the heating decomposition reaction, the mixture is cooled to room temperature under an inert atmosphere to prevent calcium oxide from absorbing water or carbonizing; wherein the inert atmosphere is N2 atmosphere.

[0075] In step S3, the separation process is water washing.

[0076] The specific conditions for the water washing are: solid-liquid ratio 1g:5mL, washing 3 times until neutral (pH≈7), and vacuum drying at 80℃ for 2h.

[0077] Example 2 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 1, except that: The composite additive consists of alkali metal salts, transition metal oxides, and pore-forming components in a mass ratio of 5:3:10.

[0078] Example 3 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 2, except that: The alkali metal salt is K2CO3.

[0079] Example 4 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 2, except that: The transition metal oxide is MnO2.

[0080] Example 5 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 2, except that: The pore-forming component is starch.

[0081] Example 6 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 2, except that: The temperature of the heating decomposition reaction is 750℃.

[0082] The reaction time for the thermal decomposition reaction is 90 minutes.

[0083] Example 7 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 2, except that: The temperature of the heating decomposition reaction is 850℃.

[0084] The reaction time for the thermal decomposition reaction is 45 minutes.

[0085] Example 8 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 2, except that: The mass ratio of the composite additive to phosphogypsum is 0.25:1.

[0086] Example 9 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 2, except that: The mixture is ball-milled for 60 minutes before undergoing the heating and decomposition reaction.

[0087] Comparative Example 1 This comparative example provides a method for calcining phosphogypsum without adding composite additives, the steps of which are as follows: The solid product was obtained by calcining phosphogypsum with a water content of 2% directly in air at 800℃ for 60 minutes and then naturally cooling it.

[0088] Comparative Example 2 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 2, except that: Na2CO3 was used to replace the composite additive, and the mass ratio of Na2CO3 to phosphogypsum was 0.05:1.

[0089] Comparative Example 3 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 1, except that: The composite additive consists of alkali metal salts, transition metal oxides, pore-forming components, and rare earth oxides in a mass ratio of 5:3:10:8.

[0090] Comparative Example 4 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 2, except that: The composite additive consists of alkali metal salts, transition metal oxides, and pore-forming components in a mass ratio of 5:3:1.

[0091] Comparative Example 5 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 1, except that: The transition metal oxide Fe2O3 was replaced with an equal mass of Al2O3.

[0092] Comparative Example 6 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 1, except that: The wood chips, an inorganic pore-forming agent of equal mass, were replaced with NH4HCO3, an inorganic pore-forming agent.

[0093] Comparative Example 7 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 1, except that: The molar ratio of rare earth elements in the rare earth metal salt to magnesium elements in the magnesium salt is 1:10.

[0094] Comparative Example 8 This embodiment provides a method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additives. The specific implementation method is the same as in Embodiment 1, except that: The rare earth metal salt is the nitrate of Y, Y(NO3)3.

[0095] Performance testing The samples obtained in Examples 1-9 and Comparative Examples 1-7 were subjected to performance tests, including indicators such as phosphogypsum decomposition rate, calcium oxide yield, and product specific surface area.

[0096] The content of CaSO4 in the original phosphogypsum and the residual CaSO4 content in the solid product after reaction were determined by a modified gravimetric method. The decomposition rate of phosphogypsum was calculated by comparison. The content of calcium oxide in the product was determined by the sucrose method, which involves reacting calcium oxide with sucrose solution at room temperature to generate calcium sucrose, and then calculating the calcium oxide content by titration with a standard hydrochloric acid solution, thus obtaining the calcium oxide yield. The specific surface area of ​​the obtained calcium oxide sample was determined by the BET specific surface area analysis method to characterize its pore structure and activity level. The test results are shown in Table 1.

[0097] Table 1 Performance test results of products from each embodiment and comparative example

[0098] As shown in Table 1, in Examples 1 to 9 of the present invention, the decomposition rate of phosphogypsum and the yield of calcium oxide were significantly improved by introducing a composite additive system, with the calcium oxide yield reaching a maximum of over 96%.

[0099] As can be seen from Examples 1-5, different types of composite additives have a significant impact on reaction performance. Alkali metal salts mainly reduce the decomposition temperature, transition metal oxides play a catalytic role, and pore-forming components can form a porous structure at high temperatures, increasing the reaction contact area and thus synergistically improving reaction efficiency.

[0100] As shown in Examples 6 and 7, the decomposition rate of phosphogypsum increases significantly with increasing reaction temperature. However, the increase in decomposition rate tends to level off when the temperature exceeds 850°C, indicating that the present invention can achieve efficient decomposition at relatively low temperatures. This also demonstrates that the composite additive system can achieve efficient decomposition of phosphogypsum without relying on a reducing atmosphere.

[0101] As can be seen from Examples 8 and 9, appropriately increasing the amount of composite additive and the degree of mixing uniformity is beneficial to further improve the formation efficiency and specific surface area of ​​calcium oxide.

[0102] Comparing Comparative Example 1 with Example 2, it can be seen that Comparative Example 1 did not introduce catalysis and pore-forming structure regulation, resulting in insufficient decomposition of phosphogypsum, a high residual CaSO4 content in the product, and a significant reduction in the amount of calcium oxide generated. This indicates that a single factor is difficult to achieve efficient decomposition, further verifying the necessity of the composite additive system and demonstrating that the composite additive plays a key promoting role in the reaction.

[0103] As can be seen from the comparison between Comparative Example 2 and Example 2, Comparative Example 2 lacks synergistic catalysis and structural regulation. This indicates that although a single alkali metal salt has a certain promoting effect on decomposition, it lacks the catalytic effect of transition metal oxides and the structural regulation effect of pore-forming components, making it difficult to achieve efficient decomposition and preparation of highly active products. This shows that multi-component synergistic regulation is the key to achieving efficient decomposition.

[0104] In Comparative Example 3, the proportion of rare earth oxides in the composite additive was too high; in Comparative Example 4, the proportion of pore-forming components in the composite additive was too low; in Comparative Example 5, Al2O3 was used to replace the transition metal oxide Fe2O3; in Comparative Example 6, the inorganic pore-forming agent NH4HCO3 was used to replace the pore-forming component wood chips; in Comparative Example 7, the proportion of rare earth elements in rare earth metal salts was too low; and in Comparative Example 8, the rare earth element in the rare earth oxides was Y. All the relevant data obtained were low.

[0105] In summary, this invention achieves efficient decomposition of phosphogypsum under lower temperature conditions through the regulation of composite additives, and significantly improves the activity and yield of calcium oxide. This demonstrates that the invention achieves efficient conversion and preparation of highly active products while ensuring low energy consumption.

[0106] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation, characterized in that, Includes the following steps: S1. Mix phosphogypsum and composite additives evenly to obtain a mixture; S2. The mixture is subjected to a heating decomposition reaction to obtain a solid product containing calcium oxide; S3. The solid product is separated to obtain calcium oxide product.

2. The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation according to claim 1, characterized in that, The phosphogypsum is dried phosphogypsum with a moisture content controlled at 1% to 10%.

3. The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation according to claim 1, characterized in that, The composite additive includes any one or a combination of at least two of alkali metal salts, transition metal oxides, pore-forming components, and rare earth oxides.

4. The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation according to claim 3, characterized in that, The alkali metal salt is Na2CO3 or K2CO3; the transition metal oxide is Fe2O3, MnO2 or CuO; and the pore-forming component is biomass material.

5. The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation according to claim 1, characterized in that, The mass ratio of the composite additive to phosphogypsum is (0.05~0.30):

1.

6. The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation according to claim 1, characterized in that, In step S2, the heating decomposition reaction is carried out under a non-strong reducing atmosphere.

7. The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation according to claim 6, characterized in that, The non-strong reducing atmosphere is an inert gas, CO2, or an oxygen-containing gas atmosphere; the inert gas is N2; in the mixed gas, the volume fraction of the inert gas is 80%~100%, and the balance is CO2 or a small amount of O2.

8. The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation according to claim 3, characterized in that, The method for preparing the rare earth oxide includes the following steps: dissolving rare earth metal salt and magnesium salt in deionized water and stirring until completely dissolved to obtain a clear solution; adjusting the rotation speed and temperature, slowly adding ammonia water dropwise to the above mixed salt solution until the pH value of the system is 9.0~10.0, continuing to stir for 1~3 hours, allowing it to stand and age for 6~12 hours, filtering to obtain a precipitate, washing it with deionized water 3~5 times, drying it, calcining it, grinding it and sieving it to obtain the final product.

9. The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation according to claim 1, characterized in that, The temperature of the heating decomposition reaction is 700℃~950℃; the heating rate of the heating decomposition reaction is 5~15℃ / min; and the reaction time of the heating decomposition reaction is 30~150min.

10. The method for preparing highly active calcium oxide by low-temperature decomposition of phosphogypsum based on composite additive regulation according to claim 1, characterized in that, In step S3, the separation process includes at least one of water washing, magnetic separation, or sieving.

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