Phosphogypsum resource comprehensive utilization method and application thereof

Abstract

The invention discloses an ardealite resource comprehensive utilization method and application thereof, and belongs to the technical field of ardealite resource utilization. The method comprises the following steps: S1, mixing ardealite and a reducing agent to obtain a mixture; s2, performing high-temperature decomposition treatment on the mixture in an inert atmosphere to obtain decomposed gas and a decomposed product; s3, sulfuric acid and / or carbon disulfide are / is prepared with the decomposition gas as the raw material, and the decomposition product is used for metallurgical steelmaking; according to the method, ferrous sulfide is used as a reducing agent, under the inert atmosphere, phosphogypsum is reduced into calcium oxide and calcium ferrite, generated sulfur dioxide tail gas is recycled, and comprehensive utilization of calcium and sulfur resources of phosphogypsum solid waste is achieved; the recycled sulfur dioxide can be used for preparing sulfuric acid and / or carbon disulfide, meanwhile, calcium oxide and calcium ferrite can serve as an adhesive and a slag former to be used for efficient metallurgical steelmaking, and the comprehensive utilization method for ardealite resources has a good application prospect.

Description

Technical Field

[0001] The present invention belongs to the technical field of phosphogypsum resource utilization, and particularly relates to a phosphogypsum resource comprehensive utilization method and application thereof. Background Art

[0002] Phosphogypsum is an industrial by-product of the wet production of phosphoric acid from phosphate rock and sulfuric acid. It has a huge output and its main component is CaSO4·2H2O or CaSO4·0.5H2O. Untreated phosphogypsum is mainly disposed of by land storage and dumping into the sea, which will lead to a series of pollution such as soil, water and air pollution. With the increasing awareness of environmental protection and the highlighting of the potential economic value of phosphogypsum, the application of phosphogypsum as a raw material in various fields has become a research hotspot. In the existing technology, the resource utilization of calcium and sulfur in phosphogypsum is mainly to use it as a construction raw material. However, the presence of sulfate, fluoride ions, etc. in phosphogypsum limits the application of phosphogypsum.

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

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

[0005] The purpose of the present invention is to provide a method for comprehensive resource utilization of phosphogypsum and its application, so as to solve the problems of incomplete pyrolysis of phosphogypsum and environmental pollution caused by the exhaust gas generated in the resource utilization of phosphogypsum through reduction pyrolysis.

[0006] In a first aspect, the present invention provides a method for comprehensive resource utilization of phosphogypsum, comprising the following steps: S1, mixing phosphogypsum and a reducing agent to obtain a mixture; S2, subjecting the mixture to a high-temperature decomposition treatment under an inert atmosphere to obtain a decomposition gas and decomposition products; S3, using the decomposition gas as a raw material to prepare sulfuric acid and / or carbon disulfide, and using the decomposition products for 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 the present invention, the inventors have discovered that by using ferrous sulfide as a reducing agent, phosphogypsum can be reduced to calcium oxide and calcium ferrite in an inert atmosphere, and the generated sulfur dioxide tail gas is recovered, thereby achieving the comprehensive utilization of the calcium and sulfur resources of the phosphogypsum solid waste; the recovered sulfur dioxide can be used to prepare sulfuric acid and / or carbon disulfide, and at the same time, calcium oxide and calcium ferrite can be used as binders and slag-forming agents for efficient metallurgical steelmaking.

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

[0009] In the present 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 the phosphogypsum and further improve the utilization rate of the phosphogypsum; 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 the 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 the present invention, by grinding and screening 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 conducive to subsequent sufficient 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 at a temperature of 1050-1200°C (preferably 1100°C) for 200-300 min, preferably 240 min.

[0013] In the present invention, the inventors further discovered that by controlling the nitrogen flow rate, pyrolysis temperature, and duration within specific ranges, the complete reduction reaction of the raw materials can be ensured, leading to complete decomposition of the phosphogypsum and further improving its utilization. Furthermore, the SO₂ produced by decomposition has a moderate concentration, making it suitable for use in the catalytic oxidation synthesis of sulfuric acid or for the high-temperature reduction reaction with natural gas to synthesize CS₂.

[0014] It is understood that the steps for preparing sulfuric acid can be adjusted based on actual application needs, as long as sulfuric acid of high purity and yield is obtained. For example, the catalyst used in the method for preparing sulfuric acid is a diatomaceous earth catalyst loaded with a V2O5 active component, where the mass of the active component is 20-40% of the mass of the diatomaceous earth.

[0015] In some embodiments, in step S3, preparing carbon disulfide using decomposition gas as a raw material specifically includes: mixing the decomposition gas, natural gas and a catalyst, and performing a high-temperature reduction reaction to obtain carbon disulfide; wherein the catalyst uses Ti-MWW molecular sieve as a carrier, loads CeO2 active components, and the mass of the CeO2 active components is 20-40% of the mass of the Ti-MWW molecular sieve; the high-temperature reduction reaction specifically includes: the temperature of the high-temperature reduction reaction is 550-650°C, the pressure is 0.1-0.5 MPa, and the space velocity is 200-500h -1 The concentration of the decomposition gas is measured by alkali absorption, the concentration of the alkali solution is 0.05-0.15 mol / L, preferably 0.1 mol / L, and the alkali solution is selected from at least one of sodium hydroxide solution and potassium hydroxide solution.

[0016] In the present invention, the chemical reaction formula for preparing carbon disulfide using decomposition gas as raw material is as follows: 3CH4+4SO2→CS2+2H2S+2CO2+2H2O; The catalyst used is prepared by conventional catalyst preparation methods in the art (such as calcination method).

[0017] It is understood that the concentration and type of the alkali solution can be adjusted according to actual use needs, as long as the concentration of sulfur dioxide can be measured. In the present invention, the concentration of the alkali solution is preferably 0.05-0.15 mol / L, and the alkali solution is preferably selected from at least one of sodium hydroxide solution and potassium hydroxide solution.

[0018] In some embodiments, in step S1, the reducing agent further includes coal powder, and the molar ratio of calcium sulfate and ferrous sulfide in the phosphogypsum to the 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.

[0019] In the present invention, the inventors further discovered that by using ferrous sulfide and coal powder as reducing agents at the same time, in the presence of alternating inert atmosphere and oxidizing atmosphere, phosphogypsum can be efficiently reduced to calcium oxide and calcium ferrite, and the generated sulfur dioxide and carbon dioxide tail gas can be recovered, thereby further realizing the comprehensive utilization of calcium and sulfur resources of phosphogypsum solid waste. In addition, after adding coal powder, the amount of ferrous sulfide added can be reduced, thereby reducing costs. At the same time, the ferrous sulfide and coal powder can completely degrade the phosphogypsum through synergistic action, further improving the utilization rate of the phosphogypsum and controlling the gas composition at the same time.

[0020] In the present invention, by grinding and screening the coal powder, the coal powder with significantly increased specific surface area can be obtained, which facilitates the coal powder to fully contact and mix evenly with other raw materials, and is conducive to the subsequent sufficient reduction reaction.

[0021] In some embodiments, in step S2, the mixture is subjected to a high-temperature decomposition treatment in the alternating presence of an inert atmosphere and an oxidizing atmosphere to obtain decomposition gas and decomposition products; wherein, the inert gas includes nitrogen, and the oxidizing gas includes air, and ventilation is performed in the order of first introducing nitrogen and then introducing air, and the carrier gas is switched every 50-70 minutes; the high-temperature decomposition treatment specifically includes: decomposition at a temperature of 1050-1200°C for 200-300 minutes; the decomposition gas includes sulfur dioxide and carbon dioxide.

[0022] In the present invention, the inventors have further discovered that by controlling the flow rate of nitrogen or air, and the temperature and duration of the pyrolysis treatment within specific ranges, the raw materials can be completely reduced, completely decomposing the phosphogypsum, and further improving the utilization rate of the phosphogypsum. By controlling the circulation of nitrogen and air, the concentration of the generated SO2 gas can be controlled.

[0023] In some embodiments, in step S3, the concentration of the decomposition gas is measured by alkaline solution absorption, 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.

[0024] It is understood that the concentration and type of the alkali solution can be adjusted according to actual use needs, as long as the concentration of sulfur dioxide can be measured. In the present invention, the concentration of the alkali solution is preferably 0.05-0.15 mol / L, and the alkali solution is preferably selected from at least one of sodium hydroxide solution and potassium hydroxide solution.

[0025] In the second invention, the present invention provides the use of the decomposition gas obtained by any of the above-mentioned methods for comprehensive utilization of phosphogypsum resources in the preparation of sulfuric acid and / or carbon disulfide.

[0026] In a third aspect, the present invention provides the use of a decomposition product obtained by any of the above-mentioned methods for comprehensive utilization of phosphogypsum resources in metallurgy and steelmaking.

[0027] In some embodiments, the decomposition products include at least one of calcium oxide and calcium ferrite.

[0028] In the present invention, when calcium oxide and calcium ferrite are applied to blast furnace metallurgy and steelmaking, calcium ferrite is the most important binding phase of sintered ore, has a low melting point and a fast generation rate, can reduce the calcium orthosilicate in the sintered ore, can ensure the strength of the sintered ore, and can ensure the reducibility of the sintered ore, and is the best binding phase to ensure that the high-basicity sintered ore has good metallurgical properties and realize low-consumption smelting in the blast furnace; calcium oxide reacts with sulfides in molten iron produced by blast furnace metallurgy and steelmaking to form calcium sulfide, effectively removing sulfur, and helps to reduce the carbon content by reacting with carbon in the molten iron to achieve the required steel grade specifications; it can also help regulate the temperature in the furnace through endothermic or exothermic reactions, ensuring that the steelmaking process is carried out at an optimal temperature, which is crucial for obtaining ideal steel properties; and calcium oxide and calcium ferrite can also serve as catalysts to promote various chemical reactions in the steelmaking process, accelerate the reaction rate, and improve production efficiency.

[0029] Furthermore, in the present invention, calcium ferrite and calcium oxide can also be used as slag-forming agents for steelmaking, which can quickly form slag, provide optimal slag-forming conditions for steelmaking, improve lime utilization efficiency, and save lime consumption; they can also create good dephosphorization conditions, improve the dephosphorization rate, and react with impurity elements such as sulfur and phosphorus in molten iron produced by blast furnace metallurgy and steelmaking to form stable compounds. These compounds have low melting points and are easy to separate from molten steel to form slag that is removed, which helps to improve the quality of steel. In addition, they can reduce furnace lining erosion and environmental pollution and shorten the smelting cycle.

[0030] The beneficial effects of the present invention are as follows: different from the prior art, the present invention uses ferrous sulfide as a reducing agent, reduces phosphogypsum to calcium oxide and calcium ferrite under an inert atmosphere, and recovers the generated sulfur dioxide tail gas, thereby realizing the comprehensive utilization of calcium and sulfur resources of phosphogypsum solid waste; further, the concentration of sulfur dioxide in the gas product is controlled, and sulfuric acid or CS2 products with high purity and yield can be prepared; at the same time, calcium oxide and calcium ferrite can be used as binders and slag-forming agents for efficient metallurgical steelmaking. The method for comprehensive utilization of phosphogypsum resources has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of the comprehensive utilization method of phosphogypsum resources in the present invention; Figure 2 is a ternary phase diagram of the CaSO4-FeS-CaO system in Example 1 of the present invention; Figure 3is the XRD spectrum of the phosphogypsum powder in the present invention; Figure 4 is the ternary phase diagram of the CaSO4-CaS-FeS system in Example 3 of the present invention; Figure 5 is the XRD spectrum of the decomposition product prepared in Example 1 of the present invention; Figure 6 is the XRD spectrum of the decomposition product prepared in Example 3 of the present invention; Figure 7 is the XRD spectrum of the decomposition product prepared in Example 5 of the present invention; Figure 8 The reactor for phosphogypsum decomposition coupled with steelmaking of the present invention; The meanings of the reference numerals are as follows: 1: Reactor; 11: Raw material inlet; 12: Gas inlet; 13: Gas outlet; 14: Flue gas area; 15: Molten pool. DETAILED DESCRIPTION

[0032] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] For experimental methods in the examples where specific conditions are not specified, generally conventional conditions and conditions described in the manual or conditions recommended by the manufacturer were followed. The general equipment, materials, reagents, etc. used were all commercially available unless otherwise specified.

[0034] See also Figure 1 , which is a flow chart of the comprehensive resource utilization method for phosphogypsum according to the present invention. Specifically, the comprehensive resource utilization method for phosphogypsum comprises the following steps: S1. Mixing phosphogypsum and a reducing agent to obtain a mixture; S2. High-temperature decomposing the mixture under an inert atmosphere to obtain decomposition gas and decomposition products; S3. Using the decomposition gas as a raw material to prepare sulfuric acid and / or carbon disulfide, and using the decomposition products for metallurgical steelmaking.

[0035] In the present invention, the elemental composition of the phosphogypsum used in the following examples and comparative examples was analyzed using an X-ray fluorescence spectrometer (XRF). The results are shown in Table 1 below.

[0036] Table 1 Chemical composition of phosphogypsum

[0037] Example 1 This embodiment provides a method for comprehensive resource utilization of phosphogypsum, which uses ferrous sulfide (FeS) as a reducing agent and reacts with phosphogypsum (PG) to produce sulfur dioxide, calcium oxide, and calcium ferrite.

[0038] Specifically, the steps include: S1. Theoretical simulation was performed using Factsage thermodynamic calculation software to conduct a systematic thermodynamic study on the existence forms of elements in the reaction process of ferrous sulfide and phosphogypsum, and the ternary phase diagram of the CaSO4-FeS-CaO system was obtained (see Figure 2 ), according to the point 1 in the ternary phase diagram of the CaSO4-FeS-CaO system, the raw material reaction ratio is configured, and 2g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71% (sieved through 100 mesh, its XRD spectrum is shown in Figure 3 ), according to the molar ratio of calcium sulfate to ferrous sulfide in the phosphogypsum being 1:0.4, ferrous sulfide with a purity of 65% was weighed as a reducing agent, and sieved into a powder of 100 mesh, and uniformly mixed with the phosphogypsum powder to obtain a mixture; 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 program the temperature to 1100° C. to perform reduction decomposition of the phosphogypsum for 240 min to obtain decomposition products containing calcium oxide, calcium ferrite, and sulfur dioxide tail gas; S3, passing the sulfur dioxide tail gas obtained in step S2 into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and measuring the concentration of sulfur dioxide; Using 20% SO2 as raw material, natural gas as reducing agent, Ti-MWW molecular sieve loaded with CeO2 active component as catalyst, where the mass of active component is 20-40% of the mass of molecular sieve, at temperature of 600℃, pressure of 0.3MPa, and space velocity of 300h -1 Under the conditions of high temperature catalytic reduction reaction, carbon disulfide and hydrogen sulfide are generated.

[0039] It has been determined that the reduction rate of SO2 reaches more than 90%.

[0040] Example 2 This embodiment provides a method for comprehensive resource utilization of phosphogypsum, which uses ferrous sulfide (FeS) as a reducing agent to react with phosphogypsum (PG) to produce sulfur dioxide, calcium oxide, and calcium ferrite.

[0041] Specifically, the steps include: S1. Theoretical simulation was performed using Factsage thermodynamic calculation software to conduct a systematic thermodynamic study on the existence forms of elements in the reaction process of ferrous sulfide and phosphogypsum, and the ternary phase diagram of the CaSO4-FeS-CaO system was obtained (see Figure 2 ), according to the point 4 in the ternary phase diagram of the CaSO4-FeS-CaO system, the raw material reaction ratio is configured, and 2g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71% (sieved through 100 mesh, its XRD spectrum is shown in Figure 3 ), according to the molar ratio of calcium sulfate to ferrous sulfide in the phosphogypsum being 1:0.6, ferrous sulfide with a purity of 65% was weighed as a reducing agent, and sieved into a powder of 100 mesh, and uniformly mixed with the phosphogypsum powder to obtain a mixture; 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 program the temperature to 1100° C. to perform reduction decomposition of the phosphogypsum for 240 min to obtain decomposition products containing calcium oxide, calcium ferrite, and sulfur dioxide tail gas; S3, passing the sulfur dioxide tail gas obtained in step S2 into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and measuring the concentration of sulfur dioxide; Using 20% SO2 as raw material, natural gas as reducing agent, Ti-MWW molecular sieve loaded with CeO2 active component as catalyst, where the mass of active component is 20-40% of the mass of molecular sieve, at temperature of 600℃, pressure of 0.3MPa, and space velocity of 300h -1 Under the conditions of high temperature catalytic reduction reaction, carbon disulfide and hydrogen sulfide are generated.

[0042] According to the measurement, the reduction rate of SO2 reaches more than 90%.

[0043] Example 3 This embodiment provides a method for comprehensive resource utilization of phosphogypsum, which uses ferrous sulfide (FeS) and coal powder (C) as reducing agents and reacts with phosphogypsum (PG) to produce sulfur dioxide, carbon dioxide, calcium oxide and calcium ferrite.

[0044] Specifically, the steps include: S1. Theoretical simulation was performed using Factsage thermodynamic calculation software to conduct a systematic thermodynamic study on the existence forms of elements in the reaction process of ferrous sulfide, coal powder and phosphogypsum, and the ternary phase diagram of the CaSO4-CaS-FeS system was obtained (see Figure 4), fixing the ratio of C to CaSO4 at 0.8:1, and converting the ratio of CaS to be generated, configuring the raw material reaction ratio according to point 1 in the ternary phase diagram of the CaSO4-CaS-FeS system, taking 2 g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71%, and weighing 65% pure ferrous sulfide as a reducing agent based on a molar ratio of calcium sulfate, calcium sulfide, and ferrous sulfide in the phosphogypsum of 1:0.66:0.05, and sieving it into a 100-mesh powder, and uniformly mixing it with the phosphogypsum powder to obtain a mixture; S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, introduce 10 ml / min of nitrogen or air into the tube furnace, switch the carrier gas once every 60 minutes in the order of nitrogen-air, and program the temperature to 1100° C. to perform reduction decomposition of phosphogypsum. The reaction time is 240 minutes to obtain decomposition products containing calcium oxide and calcium ferrite, as well as sulfur dioxide and carbon dioxide tail gas; S3, passing the sulfur dioxide and carbon dioxide tail gas obtained in step S2 into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and measuring the concentration of sulfur dioxide; Using 20% SO2 as raw material, natural gas as reducing agent, Ti-MWW molecular sieve loaded with CeO2 active component as catalyst, where the mass of active component is 20-40% of the mass of molecular sieve, at temperature of 600℃, pressure of 0.3MPa, and space velocity of 300h -1 Under the conditions of high temperature catalytic reduction reaction, carbon disulfide and hydrogen sulfide are generated.

[0045] It has been determined that the reduction rate of SO2 reaches more than 90%.

[0046] Example 4 This embodiment provides a method for comprehensive resource utilization of phosphogypsum, which uses ferrous sulfide (FeS) and coal powder (C) as reducing agents and reacts with phosphogypsum (PG) to produce sulfur dioxide, carbon dioxide, calcium oxide and calcium ferrite.

[0047] Specifically, the steps include: S1. Theoretical simulation was performed using Factsage thermodynamic calculation software to conduct a systematic thermodynamic study on the existence forms of elements in the reaction process of ferrous sulfide, coal powder and phosphogypsum, and the ternary phase diagram of the CaSO4-CaS-FeS system was obtained (see Figure 4), fixing the ratio of C to CaSO4 at 0.8:1, and converting the ratio of CaS to be generated, configuring the raw material reaction ratio according to point 2 in the ternary phase diagram of the CaSO4-CaS-FeS system, taking 2 g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71%, and weighing 65% pure ferrous sulfide as a reducing agent based on a molar ratio of calcium sulfate, calcium sulfide, and ferrous sulfide in the phosphogypsum of 1:0.66:0.1, and sieving it into a 100-mesh powder, and uniformly mixing it with the phosphogypsum powder to obtain a mixture; S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, introduce 10 ml / min of nitrogen or air into the tube furnace, switch the carrier gas once every 60 minutes in the order of nitrogen-air, and program the temperature to 1100° C. to perform reduction decomposition of phosphogypsum. The reaction time is 240 minutes to obtain decomposition products containing calcium oxide and calcium ferrite, as well as sulfur dioxide and carbon dioxide tail gas; S3, passing the sulfur dioxide and carbon dioxide tail gas obtained in step S2 into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and measuring the concentration of sulfur dioxide; Using 20% SO2 as raw material, natural gas as reducing agent, Ti-MWW molecular sieve loaded with CeO2 active component as catalyst, where the mass of active component is 20-40% of the mass of molecular sieve, at temperature of 600℃, pressure of 0.3MPa, and space velocity of 300h -1 Under the conditions of high temperature catalytic reduction reaction, carbon disulfide and hydrogen sulfide are generated.

[0048] It has been determined that the reduction rate of SO2 reaches more than 90%.

[0049] Example 5 This embodiment provides a method for comprehensive resource utilization of phosphogypsum, which uses ferrous sulfide (FeS) and coal powder (C) as reducing agents and reacts with phosphogypsum (PG) to produce sulfur dioxide, carbon dioxide, calcium oxide and calcium ferrite.

[0050] Specifically, the steps include: S1. Theoretical simulation was performed using Factsage thermodynamic calculation software to conduct a systematic thermodynamic study on the existence forms of elements in the reaction process of ferrous sulfide, coal powder and phosphogypsum, and the ternary phase diagram of the CaSO4-CaS-FeS system was obtained (see Figure 4), fixing the ratio of C to CaSO4 at 0.8:1, and converting the ratio of CaS to be generated, configuring the raw material reaction ratio according to point 3 in the ternary phase diagram of the CaSO4-CaS-FeS system, taking 2 g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71%, and weighing 65% pure ferrous sulfide as a reducing agent based on a molar ratio of calcium sulfate, calcium sulfide, and ferrous sulfide in the phosphogypsum of 1:0.66:0.3, and sieving it into a 100-mesh powder, and uniformly mixing it with the phosphogypsum powder to obtain a mixture; S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, introduce 10 ml / min of nitrogen or air into the tube furnace, switch the carrier gas once every 60 minutes in the order of nitrogen-air, and program the temperature to 1100° C. to perform reduction decomposition of phosphogypsum. The reaction time is 240 minutes to obtain decomposition products containing calcium oxide and calcium ferrite, as well as sulfur dioxide and carbon dioxide tail gas; S3, passing the sulfur dioxide and carbon dioxide tail gas obtained in step S2 into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and measuring the concentration of sulfur dioxide; With 20% SO2 as raw material, oxygen as oxidant, diatomaceous earth loaded with V2O5 active component as catalyst, the mass of active component is 20-40% of the mass of diatomaceous earth, temperature is 700℃, pressure is 0.3MPa, and space velocity is 20000h -1 Under the conditions of high temperature catalytic oxidation reaction, sulfur trioxide is generated, which is then absorbed by water to obtain sulfuric acid.

[0051] It has been determined that the oxidation rate of SO2 reaches over 90%.

[0052] Example 6 This embodiment provides a method for comprehensive resource utilization of phosphogypsum, which uses ferrous sulfide (FeS) and coal powder (C) as reducing agents and reacts with phosphogypsum (PG) to produce sulfur dioxide, carbon dioxide, calcium oxide and calcium ferrite.

[0053] Specifically, the steps include: S1. Theoretical simulation was performed using Factsage thermodynamic calculation software to conduct a systematic thermodynamic study on the existence forms of elements in the reaction process of ferrous sulfide, coal powder and phosphogypsum, and the ternary phase diagram of the CaSO4-CaS-FeS system was obtained (see Figure 4), fixing the ratio of C to CaSO4 at 0.8:1, and converting the ratio of CaS to be generated, configuring the raw material reaction ratio according to point 4 in the ternary phase diagram of the CaSO4-CaS-FeS system, taking 2 g of phosphogypsum powder with a CaSO4·2H2O mass content of 89.71%, and weighing 65% pure ferrous sulfide as a reducing agent based on a molar ratio of calcium sulfate, calcium sulfide, and ferrous sulfide in the phosphogypsum of 1:0.66:0.4, and sieving it into a 100-mesh powder, and uniformly mixing it with the phosphogypsum powder to obtain a mixture; S2. Add the mixture obtained in step S1 to a thermal reduction tube furnace, introduce 10 ml / min of nitrogen or air into the tube furnace, switch the carrier gas once every 60 minutes in the order of nitrogen-air, and program the temperature to 1100° C. to perform reduction decomposition of phosphogypsum. The reaction time is 240 minutes to obtain decomposition products containing calcium oxide and calcium ferrite, as well as sulfur dioxide and carbon dioxide tail gas; S3, passing the sulfur dioxide and carbon dioxide tail gas obtained in step S2 into a 0.1 mol / L sodium hydroxide aqueous solution for absorption, and measuring the concentration of sulfur dioxide; With 20% SO2 as raw material, oxygen as oxidant, diatomaceous earth loaded with V2O5 active component as catalyst, the mass of active component is 20-40% of the mass of diatomaceous earth, temperature is 700℃, pressure is 0.3MPa, and space velocity is 20000h -1 Under the conditions of high temperature catalytic oxidation reaction, sulfur trioxide is generated, which is then absorbed by water to obtain sulfuric acid.

[0054] It has been determined that the oxidation rate of SO2 reaches over 90%.

[0055] Comparative Example 1 The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 1, except 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, and the molar ratio of calcium sulfate to ferrous sulfide in the phosphogypsum is 1:0.2. Ferrous sulfide with a purity of 65% is weighed as a reducing agent, sieved into a powder of 100 mesh, and uniformly mixed with the phosphogypsum powder to obtain a mixture.

[0056] Comparative Example 2 The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 1, except 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, and the molar ratio of calcium sulfate to ferrous sulfide in the phosphogypsum is 1:0.3. Ferrous sulfide with a purity of 65% is weighed as a reducing agent, sieved into a powder of 100 mesh, and uniformly mixed with the phosphogypsum powder to obtain a mixture.

[0057] Comparative Example 3 The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 1, except that, in step S2, the temperature is programmed to 1000° C. for reduction and decomposition of the phosphogypsum.

[0058] Comparative Example 4 The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 1, except that, in step S2, the reaction time is 120 min.

[0059] Comparative Example 5 The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 3, except that, in step S2, the temperature is programmed to 1000° C. for reduction and decomposition of the phosphogypsum.

[0060] Comparative Example 6 The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 3, except that, in step S2, the reaction time is 120 min.

[0061] Comparative Example 7 The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 5, except that, in step S2, the temperature is programmed to 1000° C. for reduction and decomposition of the phosphogypsum.

[0062] Comparative Example 8 The method for comprehensive utilization of phosphogypsum resources provided in this comparative example is basically the same as that in Example 5, except that, in step S2, the reaction time is 120 min.

[0063] Performance Testing 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 were as follows: Figure 5-7 shown.

[0064] from Figure 5 It can be seen that in Example 1, after ferrous sulfide is used as a reducing agent to react with phosphogypsum, the phosphogypsum is completely decomposed, and the product contains only calcium oxide and calcium ferrite.

[0065] from Figure 6 It can be seen that in Example 3, after a small amount of ferrous sulfide and coal powder were used as reducing agents to react with phosphogypsum, the phosphogypsum was not completely decomposed, and the product contained a certain amount of calcium sulfate impurities in addition to calcium oxide.

[0066] from Figure 7It can be seen that in Example 5, after sufficient ferrous sulfide and coal powder are used as reducing agents to react with phosphogypsum, the phosphogypsum is completely decomposed and the product contains only calcium oxide and calcium ferrite.

[0067] Furthermore, the decomposition rate, calcium oxide content, and sulfur dioxide absorption of the phosphogypsum in Examples 1-2 and Comparative Examples 1-4 were tested, and the results are shown in Table 2 below.

[0068] Table 2 Performance test results

[0069] As can be seen from Table 2, the decomposition rate of phosphogypsum in Examples 1-2 was 100%, and the generated sulfur dioxide was well absorbed. In Comparative Examples 1-2, the added ferrous sulfide content was relatively low, and the results showed that the decomposition rate of phosphogypsum decreased significantly, resulting in a reduction in the comprehensive utilization rate of phosphogypsum. In Comparative Examples 3-4, the temperature was too low or the reaction time was too low, resulting in incomplete decomposition of phosphogypsum, a significant decrease in the decomposition rate, and a reduction in the comprehensive utilization rate of phosphogypsum. These results demonstrate that controlling the amount of ferrous sulfide added, the temperature, and the time of the decomposition reaction within specific ranges can completely decompose phosphogypsum and improve its comprehensive utilization rate.

[0070] Furthermore, the decomposition rate, calcium oxide content, sulfur dioxide and carbon dioxide absorption of the phosphogypsum in Examples 3-6 and Comparative Examples 5-8 were tested, and the results are shown in Table 3 below.

[0071] Table 3 Performance test results

[0072] As can be seen from Table 3, the phosphogypsum in Examples 3-6 has a good decomposition rate and can effectively absorb the generated sulfur dioxide and carbon dioxide. Furthermore, the decomposition rate of phosphogypsum increases significantly with increasing ferrous sulfide content. In Comparative Examples 5-8, the temperature was too low or the reaction time was too low, resulting in incomplete decomposition of the phosphogypsum, a significant decrease in its decomposition rate, and a reduction in the overall utilization rate of the phosphogypsum. These results demonstrate that the addition of coal powder can reduce the amount of ferrous sulfide added, lowering costs. Furthermore, the synergistic effect between ferrous sulfide and coal powder completely degrades the phosphogypsum, further improving its utilization rate.

[0073] From the results of the examples of the present invention, it was observed that ferrous sulfide can reduce phosphogypsum to produce products such as calcium oxide or calcium ferrite, which can be actually used in the steelmaking process as the main binder phase in sintered ore, improving metallurgical properties and achieving low-consumption smelting in blast furnaces; 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 corresponding examples of phosphogypsum reduction mentioned above, considering the needs of the steelmaking process, the present invention provides a reactor for phosphogypsum reduction and coupling with the steelmaking process, such as Figure 8 As shown, phosphogypsum, a reducing agent, and iron ore can be simultaneously added as raw materials to the reactor 1 from the raw material inlet 11, and hot air (nitrogen or air) is introduced from the gas inlet 12 to reduce the phosphogypsum in the molten pool 15. The iron ore is then heated, reduced, slag-formed, desulfurized, and melted to obtain molten iron. The generated sulfur dioxide or carbon dioxide gas passes through the flue gas zone 14 and is discharged from the gas outlet 13. This is a new initiative to further expand the practical application of phosphogypsum decomposition products.

[0074] In summary, the present invention reduces phosphogypsum to calcium oxide and calcium ferrite in an inert atmosphere by using ferrous sulfide as a reducing agent, and recovers the generated sulfur dioxide tail gas, thereby achieving the comprehensive utilization of calcium and sulfur resources of phosphogypsum solid waste; the recovered sulfur dioxide can be used to prepare sulfuric acid and / or carbon disulfide, and at the same time, calcium oxide and calcium ferrite can be used as binders and slag-forming agents for efficient metallurgical steelmaking.

[0075] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For any details not described in individual embodiments, reference may be made to the description in other embodiments.

[0076] The above-described embodiments merely illustrate the implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for comprehensive utilization of phosphogypsum resources, characterized in that: The steps include: S1. Mixing phosphogypsum and a reducing agent to obtain a mixture; S2. Under an inert atmosphere, performing a high-temperature decomposition treatment on the mixture to obtain a decomposition gas and a decomposition product; S3, preparing sulfuric acid and / or carbon disulfide using the decomposition gas as a raw material, and using the decomposition product for metallurgical steelmaking; Wherein, in step S1, the reducing agent includes ferrous sulfide; in step S2, the decomposition gas includes sulfur dioxide; and the decomposition product includes at least one of calcium oxide and calcium ferrite.

2. The method for comprehensive utilization of phosphogypsum resources according to claim 1, characterized in that: In step S1, the molar ratio of calcium sulfate in the phosphogypsum to the ferrous sulfide is 1:(0.4-0.6).

3. The method for comprehensive utilization of phosphogypsum resources according to claim 1, characterized in that: In step S1, the mass content of calcium sulfate dihydrate in the phosphogypsum is 90-95%, and the phosphogypsum is ground and sieved to obtain phosphogypsum powder of 80-120 mesh; The purity of the ferrous sulfide is 60-72%, and the ferrous sulfide is ground and sieved to obtain ferrous sulfide powder with a mesh size of 80-120.

4. The method for comprehensive utilization of phosphogypsum resources according to claim 1, characterized in that: In step S2, the inert gas includes nitrogen, and the flow rate of the nitrogen is 8-12 ml / min; The high-temperature decomposition treatment specifically includes: decomposing at a temperature of 1050-1200° C. for 200-300 minutes.

5. The method for comprehensive utilization of phosphogypsum resources according to claim 1, characterized in that: In step S3, preparing carbon disulfide using the decomposition gas as a raw material specifically includes: mixing the decomposition gas, natural gas and a catalyst, and performing a high-temperature reduction reaction to obtain carbon disulfide; The catalyst is supported by Ti-MWW molecular sieve and loaded with 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: the temperature of the high-temperature reduction reaction is 550-650 ° C, the pressure is 0.1~0.5 MPa, and the space velocity is 200-500h -1 ; The concentration of the decomposition gas is measured by alkaline solution absorption, the concentration of the alkaline solution is 0.05-0.15 mol / L, and the alkaline solution is selected from at least one of sodium hydroxide solution and potassium hydroxide solution.

6. The method for comprehensive utilization of phosphogypsum resources according to claim 1, characterized in that: In step S1, the reducing agent further includes coal powder, and the molar ratio of calcium sulfate in the phosphogypsum, the ferrous sulfide and the coal powder is 1:(0.05-0.4):0.8; and the coal powder is ground and sieved into 80-120 mesh coal powder.

7. The method for comprehensive utilization of phosphogypsum resources according to claim 6, characterized in that: In step S2, the mixture is subjected to a high-temperature decomposition treatment in the presence of an alternating inert atmosphere and an oxidizing atmosphere to obtain a decomposition gas and a decomposition product; The inert gas includes nitrogen, the oxidizing gas includes air, and the ventilation is performed in the order of first introducing nitrogen and then introducing air, and the carrier gas is switched every 50-70 minutes; The high temperature decomposition treatment specifically includes: decomposing at a temperature of 1050-1200° C. for 200-300 minutes; The decomposition gas includes sulfur dioxide and carbon dioxide.

8. The method for comprehensive utilization of phosphogypsum resources according to claim 7, characterized in that: In step S3, the concentration of the decomposition gas is measured by alkaline solution absorption, the concentration of the alkaline solution is 0.05-0.15 mol / L, and the alkaline solution is selected from at least one of sodium hydroxide solution and potassium hydroxide solution.

9. Use of the decomposition gas obtained by the method for comprehensive utilization of phosphogypsum resources according to any one of claims 1 to 8 in the preparation of sulfuric acid and / or carbon disulfide.

10. Use of the decomposition product obtained by the method for comprehensive utilization of phosphogypsum resources according to any one of claims 1 to 8 in metallurgy and steelmaking.

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