Phosphogypsum resource comprehensive utilization method and application thereof

Abstract

The application discloses a phosphogypsum resource comprehensive utilization method and application thereof, and belongs to the technical field of phosphogypsum resource utilization. The method comprises the following steps: S1, mixing phosphogypsum and a reducing agent to obtain a mixture; S2, performing high-temperature decomposition treatment on the mixture under an inert atmosphere to obtain a decomposition gas and a decomposition product; and S3, preparing sulfuric acid and / or carbon disulfide by using the decomposition gas as raw material, and using the decomposition product for metallurgical steelmaking. The application realizes comprehensive utilization of calcium and sulfur resources of phosphogypsum solid waste by using ferrous sulfide as a reducing agent and reducing the phosphogypsum into calcium oxide and calcium ferrite under an inert atmosphere, and recovers generated sulfur dioxide tail gas. The recovered sulfur dioxide can be used for preparing sulfuric acid and / or carbon disulfide, meanwhile, the calcium oxide and calcium ferrite can be used as a binder and a slagging agent for efficient metallurgical steelmaking, and the phosphogypsum resource comprehensive utilization method has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of phosphogypsum resource utilization technology, specifically relating to a comprehensive utilization method of phosphogypsum resources and its application. Background Technology

[0002] Phosphogypsum is an industrial byproduct of the wet process production of phosphoric acid from phosphate rock and sulfuric acid, produced in large quantities. Its main components are CaSO4·2H2O or CaSO4·0.5H2O. Untreated phosphogypsum is mainly disposed of through land stockpiling and dumping into the sea, leading to a series of pollution problems such as soil, water, and air pollution. With increasing environmental awareness and the growing economic potential of phosphogypsum, its application as a raw material in various fields has become a research hotspot. Current technologies primarily utilize the calcium and sulfur in phosphogypsum as building materials, but the presence of sulfate and fluoride ions limits its application areas.

[0003] Currently, the reduction and pyrolysis of phosphogypsum using a reducing agent is the main approach for the resource utilization of phosphogypsum. For example, Chinese patent application CN118341349A discloses a reactor and method for the reduction and pyrolysis of phosphogypsum, which utilizes one or any combination of hydrogen, methane, hydrogen sulfide, sulfur vapor, and a carrier gas containing mixed pyrite powder to reduce and pyrolyze phosphogypsum into CaS and SO2 within the reactor. However, this method suffers from problems such as incomplete pyrolysis of phosphogypsum and environmental pollution from the generated exhaust gas.

[0004] In view of this, it is necessary to provide a comprehensive utilization method for phosphogypsum resources to address the shortcomings of existing technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a method for the comprehensive utilization of phosphogypsum resources and its application. This method addresses the problems of incomplete pyrolysis and environmental pollution caused by exhaust gases in existing methods of resource utilization through phosphogypsum reduction pyrolysis.

[0006] In a first aspect, the present invention provides a method for the comprehensive utilization of phosphogypsum resources, comprising the following steps: S1, mixing phosphogypsum and a reducing agent to obtain a mixture; S2, subjecting the mixture to high-temperature decomposition treatment under an inert atmosphere to obtain decomposition gas and decomposition products; S3, using the decomposition gas as raw material to prepare sulfuric acid and / or carbon disulfide, and using the decomposition products in metallurgical steelmaking; wherein, in step S1, the reducing agent includes ferrous sulfide; in step S2, the decomposition gas includes sulfur dioxide; and the decomposition products include at least one of calcium oxide and calcium ferrite.

[0007] In this invention, the inventors discovered that by using ferrous sulfide as a reducing agent under an inert atmosphere, phosphogypsum can be reduced to calcium oxide and calcium ferrite, and the generated sulfur dioxide tail gas can be recovered, thus realizing the comprehensive utilization of calcium and sulfur resources from phosphogypsum solid waste. The recovered sulfur dioxide can be used to prepare sulfuric acid and / or carbon disulfide, while calcium oxide and calcium ferrite can be used as binders and slagging agents in high-efficiency metallurgical steelmaking.

[0008] In some embodiments, in step S1, the molar ratio of calcium sulfate to ferrous sulfide in phosphogypsum is 1:(0.4-0.6), preferably 1:0.4.

[0009] In this invention, the inventors further discovered that controlling the molar ratio of calcium sulfate to ferrous sulfide in phosphogypsum within a specific range can completely decompose phosphogypsum, further improving its utilization rate; and increasing the content of ferrous sulfide can increase the content of calcium ferrite.

[0010] In some embodiments, in step S1, the mass content of calcium sulfate dihydrate in phosphogypsum is 90-95%, preferably 89.71%; and the phosphogypsum is ground and sieved into phosphogypsum powder of 80-120 mesh (preferably 100 mesh); the purity of ferrous sulfide is 60-72%, preferably 65%; and the ferrous sulfide is ground and sieved into ferrous sulfide powder of 80-120 mesh (preferably 100 mesh).

[0011] In this invention, by grinding and sieving phosphogypsum and ferrous sulfide, phosphogypsum powder and ferrous sulfide powder with significantly increased specific surface area can be obtained, which facilitates full contact and uniform mixing of the two, and is beneficial for subsequent full reduction reaction.

[0012] In some embodiments, in step S2, the inert gas includes nitrogen, and the flow rate of the nitrogen is 8-12 ml / min, preferably 10 ml / min; the high-temperature decomposition treatment specifically includes: decomposing for 200-300 min, preferably 240 min, at a temperature of 1050-1200℃ (preferably 1100℃).

[0013] In this invention, the inventors further discovered that by controlling the flow rate of nitrogen gas, the temperature of the high-temperature decomposition process, and the time within a specific range, the raw materials can be completely reduced, ensuring the complete decomposition of phosphogypsum and further improving its utilization rate. Simultaneously, the concentration of SO2 obtained from the decomposition is moderate, which can be used for the catalytic oxidation synthesis of sulfuric acid or for a high-temperature reduction reaction with natural gas to synthesize CS2.

[0014] Understandably, the steps for preparing sulfuric acid can be routinely adjusted according to actual usage needs, as long as sulfuric acid with high purity and yield can be obtained. For example, the catalyst used in the method for preparing sulfuric acid is a diatomaceous earth catalyst supported on V2O5 active components, wherein the mass of the active components is 20-40% of the mass of the diatomaceous earth.

[0015] In some implementation schemes, step S3, preparing carbon disulfide from decomposed gas, specifically includes: mixing decomposed gas, natural gas, and a catalyst, followed by a high-temperature reduction reaction to obtain carbon disulfide; wherein the catalyst uses Ti-MWW molecular sieve as a support, loading CeO2 active component, and the mass of CeO2 active component is 20-40% of the mass of Ti-MWW molecular sieve; the high-temperature reduction reaction specifically includes: a temperature of 550-650℃, a pressure of 0.1-0.5 MPa, and a space velocity of 200-500 h⁻¹. -1 The concentration of the decomposed gas is determined by absorption with an alkaline solution. The concentration of the alkaline solution is 0.05-0.15 mol / L, preferably 0.1 mol / L, and the alkaline solution is selected from at least one of sodium hydroxide solution and potassium hydroxide solution.

[0016] In this invention, the chemical reaction formula for preparing carbon disulfide using decomposition gas as a raw material is as follows:

[0017] 3CH4+4SO2→CS2+2H2S+2CO2+2H2O;

[0018] The catalyst used is prepared using conventional catalyst preparation methods in the field (such as calcination).

[0019] Understandably, the concentration and type of alkaline solution can be routinely adjusted according to actual usage needs, as long as the concentration of sulfur dioxide can be measured. In this invention, the concentration of the alkaline solution is preferably 0.05-0.15 mol / L, and the alkaline solution is preferably selected from at least one of sodium hydroxide solution and potassium hydroxide solution.

[0020] In some embodiments, in step S1, the reducing agent also includes coal powder, and the molar ratio of calcium sulfate and ferrous sulfide in phosphogypsum to coal powder is 1:(0.05-0.4):0.8, preferably 1:0.3:0.8; and the coal powder is ground and sieved into 80-120 mesh (preferably 100 mesh) coal powder.

[0021] In this invention, the inventors further discovered that by using ferrous sulfide and coal powder simultaneously as reducing agents, and under alternating inert and oxidizing atmospheres, phosphogypsum can be efficiently reduced to calcium oxide and calcium ferrite, while recovering the generated sulfur dioxide and carbon dioxide tail gas. This further realizes the comprehensive utilization of calcium and sulfur resources from phosphogypsum solid waste. In addition, the addition of coal powder can reduce the amount of ferrous sulfide required, thereby lowering costs. At the same time, the synergistic effect between ferrous sulfide and coal powder completely degrades phosphogypsum, further improving the utilization rate of phosphogypsum and controlling the gas composition.

[0022] In this invention, by grinding and sieving coal powder, coal powder with a significantly increased specific surface area can be obtained, which facilitates its full contact and uniform mixing with other raw materials, and is beneficial for subsequent full reduction reaction.

[0023] In some embodiments, in step S2, the mixture is subjected to high-temperature decomposition treatment under alternating inert and oxidizing atmospheres to obtain decomposition gas and decomposition products; wherein the inert gas includes nitrogen and the oxidizing gas includes air, and the gas is introduced in the order of first nitrogen and then air, with the carrier gas being switched every 50-70 minutes; the high-temperature decomposition treatment specifically includes: decomposition for 200-300 minutes at a temperature of 1050-1200℃; the decomposition gas includes sulfur dioxide and carbon dioxide.

[0024] In this invention, the inventors further discovered that by controlling the flow rate of nitrogen or air, the temperature and time of the high-temperature decomposition treatment within a specific range, the raw materials can be ensured to undergo a complete reduction reaction, resulting in the complete decomposition of phosphogypsum and further improving the utilization rate of phosphogypsum. By controlling the circulation of nitrogen and air, the concentration of SO2 generated can be controlled.

[0025] In some embodiments, in step S3, the concentration of the decomposed gas is determined by alkaline absorption, wherein the concentration of the alkaline solution is 0.05-0.15 mol / L, preferably 0.1 mol / L, and the alkaline solution is selected from at least one of sodium hydroxide solution and potassium hydroxide solution.

[0026] Understandably, the concentration and type of alkaline solution can be routinely adjusted according to actual usage needs, as long as the concentration of sulfur dioxide can be measured. In this invention, the concentration of the alkaline solution is preferably 0.05-0.15 mol / L, and the alkaline solution is preferably selected from at least one of sodium hydroxide solution and potassium hydroxide solution.

[0027] In a second invention, the present invention provides the application of the decomposition gas obtained by any of the above-described methods for the comprehensive utilization of phosphogypsum resources in the preparation of sulfuric acid and / or carbon disulfide.

[0028] In a third aspect, the present invention provides the application of the decomposition products obtained by any of the above-described methods for the comprehensive utilization of phosphogypsum resources in metallurgical steelmaking.

[0029] In some implementations, the decomposition products include at least one of calcium oxide and calcium ferrite.

[0030] In this invention, when calcium oxide and calcium ferrite are applied in blast furnace steelmaking, calcium ferrite is the most important binder phase in sinter. Its low melting point and rapid formation rate reduce the amount of calcium orthosilicate in the sinter, ensuring both its strength and reducibility. It is the optimal binder phase for ensuring good metallurgical properties in high-basicity sinter and achieving low-consumption blast furnace smelting. Calcium oxide reacts with sulfides in the molten iron produced in blast furnace steelmaking to form calcium sulfide, effectively removing sulfur. Through reaction with carbon in the molten iron, it helps reduce the carbon content to achieve the required steel grades. It can also help regulate the furnace temperature through endothermic or exothermic reactions, ensuring the steelmaking process takes place at an optimal temperature, which is crucial for obtaining ideal steel properties. Furthermore, calcium oxide and calcium ferrite can act as catalysts, promoting various chemical reactions in the steelmaking process, accelerating the reaction rate, and improving production efficiency.

[0031] Furthermore, in this invention, calcium ferrite and calcium oxide can also be used as slag-forming agents in steelmaking. They can quickly form slag, providing optimal slag-forming conditions for steelmaking, improving lime utilization efficiency, and saving lime consumption. They can also create favorable dephosphorization conditions, improve the dephosphorization rate, and react with impurities such as sulfur and phosphorus in the molten iron produced by blast furnace steelmaking to generate stable compounds. These compounds have low melting points and are easy to separate from the molten steel, forming slag that is removed, which helps improve the quality of steel. In addition, they can reduce furnace lining erosion and environmental pollution, and shorten the smelting cycle.

[0032] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention uses ferrous sulfide as a reducing agent to reduce phosphogypsum to calcium oxide and calcium ferrite under an inert atmosphere, and recovers the generated sulfur dioxide tail gas, thus achieving comprehensive utilization of calcium and sulfur resources from phosphogypsum solid waste. Furthermore, by controlling the concentration of sulfur dioxide in the gaseous products, high-purity sulfuric acid or CS2 products can be prepared. Simultaneously, calcium oxide and calcium ferrite can be used as binders and slagging agents in efficient metallurgical steelmaking. This comprehensive utilization method for phosphogypsum resources has good application prospects. Attached Figure Description

[0033] Figure 1 This is a flowchart of the comprehensive utilization method of phosphogypsum resources in this invention;

[0034] Figure 2 This is the ternary phase diagram of the CaSO4-FeS-CaO system in Example 1 of the present invention;

[0035] Figure 3 The XRD pattern of the phosphogypsum powder in this invention is shown.

[0036] Figure 4 The ternary phase diagram of the CaSO4-CaS-FeS system in Example 3 of this invention;

[0037] Figure 5 The XRD pattern of the decomposition product prepared in Example 1 of this invention;

[0038] Figure 6 The XRD pattern of the decomposition product prepared in Example 3 of this invention;

[0039] Figure 7 The XRD pattern of the decomposition product prepared in Example 5 of this invention;

[0040] Figure 8 This invention relates to a reaction furnace for the decomposition of phosphogypsum coupled with steelmaking.

[0041] The meanings of the reference numerals in the attached figures are as follows:

[0042] 1: Reactor; 11: Raw material inlet; 12: Gas inlet; 13: Gas outlet; 14: Flue gas zone; 15: Molten pool. Detailed Implementation

[0043] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] Experimental methods not specified in the examples are generally performed under conventional conditions and as described in the manual, or as recommended by the manufacturer. Unless otherwise specified, the general equipment, materials, reagents, etc. used are commercially available.

[0045] Please see Figure 1 The flowchart below illustrates the comprehensive utilization method of phosphogypsum resources according to the present invention. Specifically, the comprehensive utilization method of phosphogypsum resources includes the following steps: S1, mixing phosphogypsum and a reducing agent to obtain a mixture; S2, subjecting the mixture to high-temperature decomposition treatment under an inert atmosphere to obtain decomposition gas and decomposition products; S3, using the decomposition gas as raw material to prepare sulfuric acid and / or carbon disulfide, and using the decomposition products in metallurgical steelmaking.

[0046] In this invention, the elemental composition of phosphogypsum used in the following examples and comparative examples was analyzed using X-ray fluorescence (XRF), and the results are shown in Table 1 below.

[0047] Table 1 Chemical composition of phosphogypsum

[0048]

[0049] Example 1

[0050] This embodiment provides a method for the comprehensive utilization of phosphogypsum resources, which uses ferrous sulfide (FeS) as a reducing agent and reacts with phosphogypsum (PG) to produce sulfur dioxide, calcium oxide and calcium ferrite.

[0051] Specifically, it includes the following steps:

[0052] S1. Using Factsage thermodynamic calculation software, a theoretical simulation was performed to conduct a systematic thermodynamic study on the elemental forms present during the reaction of ferrous sulfide and phosphogypsum, resulting in the ternary phase diagram of the CaSO4-FeS-CaO system (see...). Figure 2 According to point 1 in the ternary phase diagram of the CaSO4-FeS-CaO system, the raw material reaction ratio was prepared, and 2g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71% was taken (after sieving through a 100-mesh sieve, its XRD pattern is shown in the figure). Figure 3 In addition, according to the molar ratio of calcium sulfate to ferrous sulfide in phosphogypsum being 1:0.4, ferrous sulfide with a purity of 65% was weighed as a reducing agent and sieved into 100-mesh powder. It was then mixed evenly with phosphogypsum powder to obtain a mixture.

[0053] S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, introduce nitrogen gas at a rate of 10 ml / min into the tube furnace, and raise the temperature to 1100℃ to carry out the reduction and decomposition of phosphogypsum. The reaction time is 240 min, and decomposition products containing calcium oxide and calcium ferrite and sulfur dioxide tail gas are obtained.

[0054] S3. Pass the sulfur dioxide tail gas obtained in step S2 into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and determine the concentration of sulfur dioxide.

[0055] Using 20% ​​SO2 as raw material, natural gas as reducing agent, and Ti-MWW molecular sieve loaded with CeO2 active component as catalyst, wherein the mass of active component is 20-40% of the molecular sieve mass, the catalyst was developed at a temperature of 600℃, a pressure of 0.3MPa, and a space velocity of 300h⁻¹. -1 Under certain conditions, a high-temperature catalytic reduction reaction is carried out to produce carbon disulfide and hydrogen sulfide.

[0056] Measurements showed that the reduction rate of SO2 reached over 90%.

[0057] Example 2

[0058] This embodiment provides a method for the comprehensive utilization of phosphogypsum resources, which uses ferrous sulfide (FeS) as a reducing agent and reacts with phosphogypsum (PG) to produce sulfur dioxide, calcium oxide and calcium ferrite.

[0059] Specifically, it includes the following steps:

[0060] S1. Using Factsage thermodynamic calculation software, a theoretical simulation was performed to conduct a systematic thermodynamic study on the elemental forms present during the reaction of ferrous sulfide and phosphogypsum, resulting in the ternary phase diagram of the CaSO4-FeS-CaO system (see...). Figure 2 According to point 4 in the ternary phase diagram of the CaSO4-FeS-CaO system, the raw material reaction ratio was prepared, and 2g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71% was taken (after sieving through a 100-mesh sieve, its XRD pattern is shown in the figure). Figure 3 In addition, according to the molar ratio of calcium sulfate to ferrous sulfide in phosphogypsum being 1:0.6, ferrous sulfide with a purity of 65% was weighed as a reducing agent and sieved into 100-mesh powder. It was then mixed evenly with phosphogypsum powder to obtain a mixture.

[0061] S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, introduce nitrogen gas at a rate of 10 ml / min into the tube furnace, and raise the temperature to 1100℃ to carry out the reduction and decomposition of phosphogypsum. The reaction time is 240 min, and decomposition products containing calcium oxide and calcium ferrite and sulfur dioxide tail gas are obtained.

[0062] S3. Pass the sulfur dioxide tail gas obtained in step S2 into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and determine the concentration of sulfur dioxide.

[0063] Using 20% ​​SO2 as raw material, natural gas as reducing agent, and Ti-MWW molecular sieve loaded with CeO2 active component as catalyst, wherein the mass of active component is 20-40% of the molecular sieve mass, the catalyst was developed at a temperature of 600℃, a pressure of 0.3MPa, and a space velocity of 300h⁻¹. -1 Under certain conditions, a high-temperature catalytic reduction reaction is carried out to produce carbon disulfide and hydrogen sulfide.

[0064] Measurements showed that the reduction rate of SO2 reached over 90%.

[0065] Example 3

[0066] This embodiment provides a method for the comprehensive utilization of phosphogypsum resources, which uses ferrous sulfide (FeS) and coal powder (C) as reducing agents to react with phosphogypsum (PG) to produce sulfur dioxide, carbon dioxide, calcium oxide and calcium ferrite.

[0067] Specifically, it includes the following steps:

[0068] S1. Using Factsage thermodynamic calculation software, a theoretical simulation was conducted to systematically study the existence forms of elements during the reaction of ferrous sulfide, coal powder, and phosphogypsum, resulting in the ternary phase diagram of the CaSO4-CaS-FeS system (see...). Figure 4 The ratio of C to CaSO4 was fixed at 0.8:1, and the ratio of CaS generated was calculated. The raw material reaction ratio was configured according to point 1 in the ternary phase diagram of the CaSO4-CaS-FeS system. 2g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71% was taken. In addition, according to the molar ratio of calcium sulfate, calcium sulfide and ferrous sulfide in phosphogypsum of 1:0.66:0.05, ferrous sulfide with a purity of 65% was weighed as a reducing agent and sieved into 100-mesh powder. The powder was then mixed evenly with the phosphogypsum powder to obtain a mixture.

[0069] S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, and introduce nitrogen or air into the tube furnace at a rate of 10 ml / min. Change the carrier gas every 60 min in the order of nitrogen-air. Produce the temperature to 1100℃ to reduce and decompose phosphogypsum. The reaction time is 240 min. The decomposition products containing calcium oxide and calcium ferrite, as well as sulfur dioxide and carbon dioxide tail gas are obtained.

[0070] S3. The sulfur dioxide and carbon dioxide tail gas obtained in step S2 are passed into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and the concentration of sulfur dioxide is determined.

[0071] Using 20% ​​SO2 as raw material, natural gas as reducing agent, and Ti-MWW molecular sieve loaded with CeO2 active component as catalyst, wherein the mass of active component is 20-40% of the molecular sieve mass, the catalyst was developed at a temperature of 600℃, a pressure of 0.3MPa, and a space velocity of 300h⁻¹. -1 Under certain conditions, a high-temperature catalytic reduction reaction is carried out to produce carbon disulfide and hydrogen sulfide.

[0072] Measurements showed that the reduction rate of SO2 reached over 90%.

[0073] Example 4

[0074] This embodiment provides a method for the comprehensive utilization of phosphogypsum resources, which uses ferrous sulfide (FeS) and coal powder (C) as reducing agents to react with phosphogypsum (PG) to produce sulfur dioxide, carbon dioxide, calcium oxide and calcium ferrite.

[0075] Specifically, it includes the following steps:

[0076] S1. Using Factsage thermodynamic calculation software, a theoretical simulation was conducted to systematically study the existence forms of elements during the reaction of ferrous sulfide, coal powder, and phosphogypsum, resulting in the ternary phase diagram of the CaSO4-CaS-FeS system (see...). Figure 4 The ratio of C to CaSO4 was fixed at 0.8:1, and the ratio of CaS generated was calculated. The raw material reaction ratio was configured according to point 2 in the ternary phase diagram of the CaSO4-CaS-FeS system. 2g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71% was taken. In addition, according to the molar ratio of calcium sulfate, calcium sulfide and ferrous sulfide in phosphogypsum of 1:0.66:0.1, ferrous sulfide with a purity of 65% was weighed as a reducing agent and sieved into 100-mesh powder. The powder was then mixed evenly with the phosphogypsum powder to obtain a mixture.

[0077] S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, and introduce nitrogen or air into the tube furnace at a rate of 10 ml / min. Change the carrier gas every 60 min in the order of nitrogen-air. Produce the temperature to 1100℃ to reduce and decompose phosphogypsum. The reaction time is 240 min. The decomposition products containing calcium oxide and calcium ferrite, as well as sulfur dioxide and carbon dioxide tail gas are obtained.

[0078] S3. The sulfur dioxide and carbon dioxide tail gas obtained in step S2 are passed into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and the concentration of sulfur dioxide is determined.

[0079] Using 20% ​​SO2 as raw material, natural gas as reducing agent, and Ti-MWW molecular sieve loaded with CeO2 active component as catalyst, wherein the mass of active component is 20-40% of the molecular sieve mass, the catalyst was developed at a temperature of 600℃, a pressure of 0.3MPa, and a space velocity of 300h⁻¹. -1 Under certain conditions, a high-temperature catalytic reduction reaction is carried out to produce carbon disulfide and hydrogen sulfide.

[0080] Measurements showed that the reduction rate of SO2 reached over 90%.

[0081] Example 5

[0082] This embodiment provides a method for the comprehensive utilization of phosphogypsum resources, which uses ferrous sulfide (FeS) and coal powder (C) as reducing agents to react with phosphogypsum (PG) to produce sulfur dioxide, carbon dioxide, calcium oxide and calcium ferrite.

[0083] Specifically, it includes the following steps:

[0084] S1. Using Factsage thermodynamic calculation software, a theoretical simulation was conducted to systematically study the existence forms of elements during the reaction of ferrous sulfide, coal powder, and phosphogypsum, resulting in the ternary phase diagram of the CaSO4-CaS-FeS system (see...). Figure 4 The ratio of C to CaSO4 was fixed at 0.8:1, and the ratio of CaS generated was calculated. The raw material reaction ratio was configured according to point 3 in the ternary phase diagram of the CaSO4-CaS-FeS system. 2g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71% was taken. In addition, according to the molar ratio of calcium sulfate, calcium sulfide and ferrous sulfide in phosphogypsum of 1:0.66:0.3, ferrous sulfide with a purity of 65% was weighed as a reducing agent and sieved into 100-mesh powder. The powder was then mixed evenly with the phosphogypsum powder to obtain a mixture.

[0085] S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, and introduce nitrogen or air into the tube furnace at a rate of 10 ml / min. Change the carrier gas every 60 min in the order of nitrogen-air. Produce the temperature to 1100℃ to reduce and decompose phosphogypsum. The reaction time is 240 min. The decomposition products containing calcium oxide and calcium ferrite, as well as sulfur dioxide and carbon dioxide tail gas are obtained.

[0086] S3. The sulfur dioxide and carbon dioxide tail gas obtained in step S2 are passed into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and the concentration of sulfur dioxide is determined.

[0087] Using 20% ​​SO2 as raw material, oxygen as oxidant, and diatomaceous earth supported on V2O5 active components as catalyst, wherein the mass of the active components is 20-40% of the mass of the diatomaceous earth, the reaction was carried out at a temperature of 700℃, a pressure of 0.3MPa, and a space velocity of 20000h⁻¹. -1 Under certain conditions, a high-temperature catalytic oxidation reaction is carried out to produce sulfur trioxide, which is then absorbed by water to obtain sulfuric acid.

[0088] Measurements showed that the oxidation rate of SO2 reached over 90%.

[0089] Example 6

[0090] This embodiment provides a method for the comprehensive utilization of phosphogypsum resources, which uses ferrous sulfide (FeS) and coal powder (C) as reducing agents to react with phosphogypsum (PG) to produce sulfur dioxide, carbon dioxide, calcium oxide and calcium ferrite.

[0091] Specifically, it includes the following steps:

[0092] S1. Using Factsage thermodynamic calculation software, a theoretical simulation was conducted to systematically study the existence forms of elements during the reaction of ferrous sulfide, coal powder, and phosphogypsum, resulting in the ternary phase diagram of the CaSO4-CaS-FeS system (see...). Figure 4 The ratio of C to CaSO4 was fixed at 0.8:1, and the ratio of CaS generated was calculated. The raw material reaction ratio was configured according to point 4 in the ternary phase diagram of the CaSO4-CaS-FeS system. 2g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71% was taken. In addition, according to the molar ratio of calcium sulfate, calcium sulfide and ferrous sulfide in phosphogypsum of 1:0.66:0.4, ferrous sulfide with a purity of 65% was weighed as a reducing agent and sieved into 100-mesh powder. The powder was then mixed evenly with the phosphogypsum powder to obtain a mixture.

[0093] S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, and introduce nitrogen or air into the tube furnace at a rate of 10 ml / min. Change the carrier gas every 60 min in the order of nitrogen-air. Produce the temperature to 1100℃ to reduce and decompose phosphogypsum. The reaction time is 240 min. The decomposition products containing calcium oxide and calcium ferrite, as well as sulfur dioxide and carbon dioxide tail gas are obtained.

[0094] S3. The sulfur dioxide and carbon dioxide tail gas obtained in step S2 are passed into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and the concentration of sulfur dioxide is determined.

[0095] Using 20% ​​SO2 as raw material, oxygen as oxidant, and diatomaceous earth supported on V2O5 active components as catalyst, wherein the mass of the active components is 20-40% of the mass of the diatomaceous earth, the reaction was carried out at a temperature of 700℃, a pressure of 0.3MPa, and a space velocity of 20000h⁻¹. -1 Under certain conditions, a high-temperature catalytic oxidation reaction is carried out to produce sulfur trioxide, which is then absorbed by water to obtain sulfuric acid.

[0096] Measurements showed that the oxidation rate of SO2 reached over 90%.

[0097] Comparative Example 1

[0098] The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 1. The difference is that in step S1, the raw material reaction ratio is configured according to point 2 in the ternary phase diagram of the CaSO4-FeS-CaO system. According to the molar ratio of calcium sulfate to ferrous sulfide in phosphogypsum of 1:0.2, ferrous sulfide with a purity of 65% is weighed as a reducing agent and sieved into 100-mesh powder. It is then uniformly mixed with phosphogypsum powder to obtain a mixture.

[0099] Comparative Example 2

[0100] The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 1. The difference is that in step S1, the raw material reaction ratio is configured according to point 3 in the ternary phase diagram of the CaSO4-FeS-CaO system. According to the molar ratio of calcium sulfate to ferrous sulfide in phosphogypsum being 1:0.3, ferrous sulfide with a purity of 65% is weighed as a reducing agent and sieved into 100-mesh powder. It is then uniformly mixed with phosphogypsum powder to obtain a mixture.

[0101] Comparative Example 3

[0102] The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 1. The difference is that in step S2, the temperature is increased to 1000℃ to carry out the reduction and decomposition of phosphogypsum.

[0103] Comparative Example 4

[0104] The method for the comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 1, except that the reaction time in step S2 is 120 min.

[0105] Comparative Example 5

[0106] The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 3. The difference is that in step S2, the temperature is increased to 1000℃ to carry out the reduction and decomposition of phosphogypsum.

[0107] Comparative Example 6

[0108] The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 3, except that the reaction time in step S2 is 120 min.

[0109] Comparative Example 7

[0110] The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 5. The difference is that in step S2, the temperature is increased to 1000℃ to carry out the reduction and decomposition of phosphogypsum.

[0111] Comparative Example 8

[0112] The method for the comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 5, except that the reaction time in step S2 is 120 min.

[0113] Performance testing

[0114] For example, the decomposition products containing calcium oxide and calcium ferrite prepared in Examples 1, 3, and 5 were subjected to XRD tests, and the results are as follows: Figure 5-7 As shown.

[0115] from Figure 5 As can be seen from the example, in Example 1, after ferrous sulfide was used as a reducing agent to react with phosphogypsum, the phosphogypsum was completely decomposed, and the product contained only calcium oxide and calcium ferrite.

[0116] from Figure 6 As can be seen from the example, in Example 3, after reacting with a small amount of ferrous sulfide and coal powder as reducing agents, the phosphogypsum was not completely decomposed, and the product contained a certain amount of calcium sulfate impurities in addition to calcium oxide.

[0117] from Figure 7 As can be seen from Example 5, after reacting with phosphogypsum using sufficient ferrous sulfide and coal powder as reducing agents, the phosphogypsum completely decomposes, and the product contains only calcium oxide and calcium ferrite.

[0118] Furthermore, the decomposition rate, calcium oxide content, and sulfur dioxide absorption of phosphogypsum in Examples 1-2 and Comparative Examples 1-4 were tested, and the results are shown in Table 2 below.

[0119] Table 2 Performance Test Results

[0120]

[0121] As shown in Table 2, the decomposition rate of phosphogypsum in Examples 1-2 was 100%, and the generated sulfur dioxide was absorbed well. In Comparative Examples 1-2, the content of added ferrous sulfide was low, and the decomposition rate of phosphogypsum decreased significantly, leading to a reduction in the overall utilization rate of phosphogypsum. In Comparative Examples 3-4, the temperature or reaction time was too low, resulting in incomplete decomposition of phosphogypsum and a significant decrease in its decomposition rate, which also led to a reduction in the overall utilization rate of phosphogypsum. The above results indicate that controlling the amount of ferrous sulfide added, the temperature and time of the decomposition reaction within a specific range can ensure the complete decomposition of phosphogypsum and improve its overall utilization rate.

[0122] Furthermore, the decomposition rate of phosphogypsum, calcium oxide content, sulfur dioxide and carbon dioxide absorption in Examples 3-6 and Comparative Examples 5-8 were tested, and the results are shown in Table 3 below.

[0123] Table 3 Performance Test Results

[0124]

[0125] As shown in Table 3, the phosphogypsum in Examples 3-6 exhibited good decomposition rates and demonstrated effective absorption of the generated sulfur dioxide and carbon dioxide. Furthermore, the decomposition rate of phosphogypsum significantly increased with increasing ferrous sulfide content. In Comparative Examples 5-8, excessively low temperatures or reaction times resulted in incomplete decomposition of phosphogypsum, leading to a significant decrease in its decomposition rate and consequently, a reduction in its overall utilization rate. These results indicate that adding coal powder reduces the amount of ferrous sulfide required, lowering costs. Simultaneously, the synergistic effect between ferrous sulfide and coal powder further enhances the utilization rate of phosphogypsum by completely degrading it.

[0126] The results from the embodiments of this invention show that ferrous sulfide reduction of phosphogypsum can yield products such as calcium oxide or calcium ferrite, which can be practically applied in steelmaking processes as the main binder phase in sintered ore, improving metallurgical performance and achieving low-consumption blast furnace smelting. Sulfur dioxide is also effectively recovered and can be used as a raw material for the production of sulfuric acid and carbon disulfide. Based on the above examples of phosphogypsum reduction, and considering the needs of steelmaking processes, this invention provides a reactor for phosphogypsum reduction coupled with a steelmaking process, such as... Figure 8 As shown, phosphogypsum, reducing agent, and iron ore can be added to the reactor 1 simultaneously from the raw material inlet 11 as raw materials. Hot air (nitrogen or air) is introduced through the gas inlet 12. The phosphogypsum is reduced in the molten pool 15. Then, the iron ore is heated, reduced, slag-forming, desulfurized, and melted to obtain molten iron. The generated sulfur dioxide or carbon dioxide gas is discharged from the gas outlet 13 through the flue gas zone 14. This is a new measure to further expand the decomposition products of phosphogypsum to practical application fields.

[0127] In summary, this invention achieves comprehensive utilization of calcium and sulfur resources from phosphogypsum solid waste by using ferrous sulfide as a reducing agent to reduce phosphogypsum to calcium oxide and calcium ferrite under an inert atmosphere, and recovering the generated sulfur dioxide tail gas. The recovered sulfur dioxide can be used to prepare sulfuric acid and / or carbon disulfide, while calcium oxide and calcium ferrite can be used as binders and slagging agents in efficient metallurgical steelmaking.

[0128] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0129] The embodiments described above are merely illustrative of implementation methods of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for comprehensive utilization of phosphogypsum resources, characterized in that, The method comprises the following steps: S1, mixing phosphogypsum and a reducing agent to obtain a mixture; S2, performing high-temperature decomposition treatment on the mixture under an inert atmosphere to obtain a decomposition gas and a decomposition product; S3, preparing sulfuric acid and / or carbon disulfide from the decomposition gas, and using the decomposition product for metallurgical steelmaking; In step S1, the reducing agent comprises ferrous sulfide; in step S2, the decomposition gas comprises sulfur dioxide; and the decomposition product comprises at least one of calcium oxide and calcium ferrite; In step S1, the reducing agent further comprises coal powder, the molar ratio of calcium sulfate in the phosphogypsum, the ferrous sulfide, and the coal powder is 1:(0.3-0.4):0.8; and the coal powder is ground and sieved into coal powder with a particle size of 80-120 mesh; In step S1, the mass content of dihydrate calcium sulfate in the phosphogypsum is 90-95%, and the phosphogypsum is ground and sieved into phosphogypsum powder with a particle size of 80-120 mesh; The purity of the ferrous sulfide is 60-72%, and the ferrous sulfide is ground and sieved into ferrous sulfide powder with a particle size of 80-120 mesh; In step S2, the mixture is subjected to high-temperature decomposition treatment under an alternating inert atmosphere and an oxidation atmosphere to obtain a decomposition gas and a decomposition product; The inert gas comprises nitrogen, the oxidation gas comprises air, and the gas is introduced in the order of nitrogen first and then air, and the carrier gas is switched every 50-70 min; The high-temperature decomposition treatment specifically comprises: decomposing for 200-300 min at a temperature of 1050-1200℃; The decomposition gas comprises sulfur dioxide and carbon dioxide.

2. The method according to claim 1, characterized in that, In step S2, the inert gas comprises nitrogen, and the flow rate of the nitrogen introduced is 8-12 ml / min.

3. The method according to claim 1, characterized in that, In step S3, preparing carbon disulfide from the decomposition gas specifically comprises: mixing the decomposition gas, natural gas, and a catalyst, and then performing a high-temperature reduction reaction to obtain carbon disulfide; The catalyst has Ti-MWW molecular sieve as a carrier, and loads CeO2 active component, and the mass of the CeO2 active component is 20-40% of the mass of the Ti-MWW molecular sieve; the high-temperature reduction reaction specifically includes that the temperature of the high-temperature reduction reaction is 550-650 DEG C, the pressure is 0.1-0.5 MPa, the space velocity is 200-500 h -1 . The concentration of the decomposition gas is determined by alkali absorption, the concentration of the alkali is 0.05-0.15 mol / L, and the alkali is at least one of a sodium hydroxide solution and a potassium hydroxide solution.

4. The method according to claim 3, characterized in that, In step S3, the concentration of the decomposition gas is determined by alkali absorption, the concentration of the alkali is 0.05-0.15 mol / L, and the alkali is at least one of a sodium hydroxide solution and a potassium hydroxide solution.

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