Method for producing calcium sulfide by reducing gypsum with ammonia gas

Abstract

The invention discloses a method for producing calcium sulfide by reducing gypsum with ammonia gas. Under the assistance of the solid-phase catalyst, the reaction of reducing the calcium sulfate by the ammonia gas at a relatively low temperature of 400-700 DEG C is realized, and the calcium sulfate is efficiently reduced into calcium sulfide. Under the dual action of the gas-phase ammonia gas and the solid-phase catalyst, calcium sulfate is in full contact with reducing gas molecules, the reaction is more sufficient, and the reaction efficiency is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of calcium sulfide preparation, and in particular relates to a method for producing calcium sulfide by reducing gypsum with ammonia. Background Art

[0002] Currently, my country's industrial by-product gypsum production and existing reserves are enormous, with approximately 138 million tons emitted annually. It exists primarily in the form of desulfurized gypsum, phosphogypsum, fluorinated gypsum, citric acid gypsum, and salt gypsum, with desulfurized gypsum and phosphogypsum accounting for approximately 85% of all industrial by-product gypsum. Desulfurized gypsum, a by-product of flue gas desulfurization (FGD) using the lime / limestone / gypsum process, contains impurities, has a high water content, and has a narrow particle size distribution, resulting in a low overall utilization rate. Phosphogypsum is a solid waste residue generated during the production of wet-process phosphoric acid and phosphate fertilizers. For every ton of wet-process phosphoric acid (measured as P2O5), 4-5 tons of phosphogypsum are produced. At present, the comprehensive utilization rate of industrial by-product gypsum is only about 38%. The phenomenon of gypsum accumulation is widespread, with the cumulative accumulation volume exceeding 300 million tons, which not only occupies land but also wastes resources. In addition, the acidic substances and other harmful substances in the gypsum may also pollute the surrounding environment. It can be seen that the accumulation of gypsum and the low utilization rate have seriously restricted the sustainable development of my country's coal-fired unit desulfurization and phosphorus chemical enterprises.

[0003] Gypsum's primary component is calcium sulfate. Producing calcium sulfide through the reduction reaction of gypsum is one way to efficiently utilize the calcium and sulfur elements in solid gypsum waste. The calcium sulfide product can be further reacted with gypsum to produce sulfuric acid-co-produced cement. Furthermore, calcium sulfide can serve as an important chemical raw material for the production of high-value-added chemicals such as thiourea, sodium sulfide, and sulfur. Because calcium sulfate's thermal decomposition temperature exceeds 1400°C, it is currently produced through high-temperature thermal reduction methods, including sulfur reduction, carbon monoxide reduction, hydrogen reduction, hydrogen sulfide reduction, and carbon reduction. CN101708825A discloses a method for producing calcium sulfide by decomposing gypsum using sulfur reduction. This method uses gaseous sulfur as a reducing agent to reduce gypsum to calcium sulfide, with the byproduct, sulfur dioxide, being used to produce sulfuric acid. CN119797287A discloses a method for producing calcium sulfide by directly reducing gypsum using solid sulfur at temperatures between 800°C and 1200°C. However, due to the cost of sulfur, the sulfur reduction method for gypsum is costly and inefficient, hindering large-scale application. CN101428767A discloses a method for preparing calcium sulfide using gypsum, that is, mixing phosphogypsum and coal in a molar ratio of 1:2 to 4, grinding them, adding water to form pellets or blocks, and calcining them at a high temperature of 800 to 1100°C to obtain a calcium sulfide product. However, the carbonaceous reducing agent itself and the reaction under high temperature conditions produce a large amount of CO2, which is not conducive to green and low-carbon production. CN119284842A discloses a method for using hydrogen to assist the reduction and decomposition of phosphogypsum, which requires a reaction at 700 to 800°C for 1 to 2.5 hours to obtain a calcium sulfide product. The reaction time is long and the efficiency needs to be improved. In addition, hydrogen is flammable and explosive, has a low volume energy density at normal temperature and pressure, high storage and transportation costs, and low safety. Therefore, a more efficient, safe, and low-cost method for preparing calcium sulfide from calcium sulfate still needs to be developed. Summary of the Invention

[0004] As a highly efficient hydrogen storage medium, ammonia offers advantages such as easy storage and transportation, low cost, and zero carbon emissions. This invention provides a method for producing calcium sulfide by reducing gypsum with ammonia. The reaction uses ammonia as a reducing agent, assisted by a solid-phase catalyst. This method aims to address technical issues such as high reaction temperature, long reaction time, low reaction efficiency, and poor quality of the calcium sulfide product in existing methods for producing calcium sulfide from calcium sulfate.

[0005] In one aspect, the present invention provides a method for producing calcium sulfide by reducing gypsum with ammonia, the method comprising the steps of contacting the gypsum with a catalyst and contacting the gypsum with an ammonia-containing gas.

[0006] In one or more embodiments, the gypsum is mainly composed of calcium sulfate, and the mass percentage of calcium sulfate in the gypsum is 50.00-99.99%; the gypsum is selected from a combination of one or more of desulfurized gypsum, phosphogypsum, natural gypsum, fluorgypsum, citric acid gypsum and salt gypsum.

[0007] In one or more embodiments, the catalyst is a solid phase catalyst comprising a catalytic component and a carrier component; wherein the catalytic component is selected from a combination of one or more of iron oxide, nickel oxide, cobalt oxide, iron sulfide and pyrite, and the carrier component is selected from a combination of one or more of aluminum oxide, silicon oxide, porous carbon and magnesium oxide.

[0008] Preferably, the mass ratio of the gypsum to the catalyst is (1-20):1.

[0009] Preferably, in the solid-phase catalyst, the content of the catalytic component is 5 to 50 wt%, and the content of the carrier component is 50 to 95 wt%.

[0010] Preferably, the solid phase catalyst is prepared by physical ball milling, wherein the ball milling time is 30 to 120 minutes.

[0011] Preferably, the gypsum and the catalyst are pulverized and then mixed uniformly. More preferably, the gypsum and the catalyst are pulverized to 100 mesh and then mixed uniformly.

[0012] In one or more embodiments, the ammonia-containing gas is ammonia or a mixture of ammonia and nitrogen, water vapor or argon. In the ammonia-containing gas, the volume proportion of ammonia is 40-100%.

[0013] In one or more embodiments, the method comprises the steps of:

[0014] S1: mixing gypsum and a catalyst to obtain a solid mixture;

[0015] S2: preheating the solid mixture and the ammonia-containing gas separately;

[0016] S3: introducing the preheated solid mixture and ammonia into a reduction reactor for a reduction reaction to obtain a calcium sulfide product and a high-temperature tail gas; the high-temperature tail gas includes unreacted ammonia.

[0017] Preferably, the high-temperature tail gas includes one or more gases selected from ammonia, hydrogen, water vapor and argon.

[0018] In one or more embodiments, the method further includes step S4: sending the calcium sulfide product to a cooling device, passing a low-temperature inert gas to cool it, obtaining a cooled calcium sulfide product and a high-temperature inert gas, passing the high-temperature inert gas into a reduction reactor to mix with the high-temperature tail gas, and then passing the high-temperature inert gas into a preheater to exchange heat with the solid mixture.

[0019] Preferably, in step S2, the preheating temperature is 400-700°C.

[0020] Preferably, in step S2, the ammonia-containing gas is preheated by a heater.

[0021] In one or more embodiments, in step S3, the temperature of the reduction reaction is 400-700°C.

[0022] In one or more embodiments, in step S3, the reduction reaction time is 3 s to 90 min.

[0023] Preferably, in step S3, the reduction reaction time is 60s to 30min.

[0024] Preferably, in step S3, the ratio of the solid mixture and the ammonia-containing gas introduced into the reduction reactor is calculated based on a molar ratio of calcium sulfate in gypsum to ammonia in the ammonia-containing gas of 2.5 to 10.

[0025] Preferably, in step S3, the oxygen content in the reduction reactor is maintained below 3 vol% during the reduction reaction.

[0026] Preferably, in step S3, the decomposition rate of calcium sulfate in the gypsum is greater than 98.5%.

[0027] Preferably, in step S4, the calcium sulfide product is cooled to room temperature by low-temperature inert gas.

[0028] Preferably, in step S4, the temperature of the gas after heat exchange is 150-350°C.

[0029] Preferably, in step S4, the purity of calcium sulfide in the calcium sulfide product is greater than 50%. More preferably, in step S4, the purity of calcium sulfide in the calcium sulfide product is greater than 90%.

[0030] Preferably, the gas after heat exchange with the solid mixture is sequentially passed into a gas dust removal device and a gas-liquid separation device to remove particles and moisture in the gas respectively, and then passed into a cooling device to cool the high-temperature calcium sulfide.

[0031] In another aspect, the present invention provides a system for producing calcium sulfide by reducing gypsum with ammonia, the system comprising a raw mill-homogenizing tank, a preheater, a heater, a reduction reactor, a cooling device, a gas dust removal device and a gas-liquid separation device, wherein the raw mill-homogenizing tank, the preheater, the reduction reactor and the cooling device are connected in sequence by pipelines, the heater and the reduction reactor are connected by pipelines, and the preheater, the gas dust removal device, the gas-liquid separation device and the cooling device are connected in sequence by separate pipelines.

[0032] In another aspect, the present invention provides a method for producing calcium sulfide by reducing gypsum with ammonia, the method comprising using the system as described in any embodiment herein, including the processes of contacting gypsum with a catalyst and contacting gypsum with ammonia.

[0033] In another aspect, the present invention provides the use of ammonia in the preparation of calcium sulfide, cement, sulfuric acid, thiourea, alkali sulfide or sulfur, wherein the ammonia is used to reduce calcium sulfate in gypsum to generate calcium sulfide.

[0034] The present invention proposes a method for producing calcium sulfide by reducing calcium sulfate with ammonia. The method comprises mixing gypsum whose main component is calcium sulfate with a solid-phase catalyst, preheating and dehydrating the mixture, and then introducing reducing ammonia at a reaction temperature of 400-700°C to achieve efficient reduction of calcium sulfate to prepare high-quality calcium sulfide.

[0035] Compared with the prior art, the method of producing calcium sulfide by reducing calcium sulfate with ammonia gas of the present invention has the following beneficial effects:

[0036] (1) With the assistance of a solid-phase catalyst, the reaction of ammonia reducing calcium sulfate can be carried out at a relatively low temperature of 400-700°C, and calcium sulfate can be almost completely reduced to calcium sulfate. The catalyst has two main functions: on the one hand, the solid-phase catalyst is a promoter of the reaction between ammonia and calcium sulfate, promoting the direct combination of ammonia molecules with oxygen atoms on the surface of calcium sulfate; on the other hand, the solid-phase catalyst can promote the catalytic decomposition of ammonia to produce nitrogen and hydrogen, which is conducive to the rapid reduction of calcium sulfate in the reducing hydrogen atmosphere of hydrogen and ammonia. Under the dual action of gaseous ammonia and solid-phase catalyst, the contact between calcium sulfate and reducing gas molecules increases, the reaction is more complete, and the reaction efficiency is significantly improved.

[0037] (2) The reduction system using ammonia is in an oxygen-deficient environment, which helps prevent calcium sulfide from oxidizing to form calcium oxide or other byproducts during the reaction, thereby solving the problem of low quality of calcium sulfide produced by existing technologies. The calcium sulfide product obtained by this method is of high quality and can be directly used as a raw material to produce cement or calcium oxide to co-produce sulfuric acid, and can also be used to prepare high-value-added chemicals such as thiourea, sodium sulfide, and sulfur.

[0038] (3) The energy density of ammonia is greater than that of hydrogen. The volume of liquid ammonia required to reduce the same mass of calcium sulfate is smaller than that of liquid hydrogen, which can reduce the floor space of storage equipment and reduce construction costs. Using ammonia as a hydrogen carrier makes it easier to store for a long time and transport over long distances, thus solving the problems of high hydrogen transportation costs and low intrinsic safety. In addition, compared with carbon-containing reducing gases, the use of ammonia can avoid carbon emissions and is conducive to sustainable production. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of the process of producing calcium sulfide by reducing gypsum with ammonia.

[0040] Figure 2 This is a system diagram for producing calcium sulfide by reducing gypsum with ammonia.

[0041] Figure 3 This is the XRD pattern of calcium sulfide product. DETAILED DESCRIPTION

[0042] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail with specific embodiments below. Those skilled in the art should understand that the content described below is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0043] In the present invention, the principle of reducing gypsum with ammonia to produce calcium sulfide is shown in the following formula (I):

[0044] 3CaSO4+8NH3→3CaS+4N2+12H2O, ΔH 298K =119.64KJ / mol(Ⅰ).

[0045] In the present invention, preferably, Figure 1 As shown, the method for producing calcium sulfide by reducing gypsum with ammonia is:

[0046] S1: mixing gypsum and a catalyst to obtain a solid mixture;

[0047] S2: preheating the solid mixture and the ammonia-containing gas separately;

[0048] S3: introducing the preheated solid mixture and ammonia-containing gas into a reduction reactor for reduction reaction to obtain a calcium sulfide product and high-temperature tail gas; the high-temperature tail gas includes unreacted ammonia.

[0049] S4: The calcium sulfide product is sent to a cooling device and cooled by passing low-temperature inert gas to obtain a cooled calcium sulfide product and high-temperature inert gas. The high-temperature inert gas is passed into a reduction reactor to be mixed with the high-temperature tail gas, and then passed into a preheater to exchange heat with the solid mixture.

[0050] In the present invention, preferably, Figure 2 As shown, the system for producing calcium sulfide by reducing gypsum with ammonia includes: a raw mill-homogenizing tank 1, a preheater 2, a heater 3, a reduction reactor 4, a cooling device 5, a gas dust removal device 6, and a gas-liquid separation device 7;

[0051] Among them, the raw mill-homogenizing tank 1, preheater 2, reduction reactor 4 and cooling device 5 are connected in sequence through pipelines, the heater 3 and the reduction reactor 4 are connected through pipelines, and the preheater 2, gas dust removal device 6, gas-liquid separation device 7 and cooling device 5 are also connected in sequence through pipelines.

[0052] The raw mill-homogenizing tank 1 is used to crush and mix gypsum and catalyst;

[0053] The preheater 2 is used to preheat the solid mixture. The preheater 2 is provided with a heating device. The preheating heat mainly comes from the high-temperature inert gas and high-temperature tail gas, and partly comes from the heating device.

[0054] The heater 3 is used to heat the ammonia-containing gas;

[0055] The reduction reactor 4 serves as a container for the reduction reaction of gypsum by the ammonia-containing gas.

[0056] The cooling device 5 is used to introduce low-temperature inert gas to cool the calcium sulfide product obtained by the reduction reaction; the "low temperature" of "low-temperature inert gas" can be understood as 0 to 50°C, preferably 5 to 35°C.

[0057] The gas dust removal device 6 is used to remove solid particles in the gas discharged from the preheater.

[0058] The gas-liquid separation device 7 is used to remove liquid from the gas discharged from the preheater.

[0059] In the present invention, the catalyst may include a catalytic component and a carrier component. Preferably, the catalytic component and the carrier component are both solid powders, and the catalyst is an integrated catalyst prepared by mixing by physical ball milling. Among them, the catalytic component plays the main role of catalyzing the reaction of ammonia and calcium sulfate and catalyzing the decomposition of ammonia into nitrogen and hydrogen; the carrier component accounts for more than 50% by mass in the catalyst, which determines the main physical properties of the catalyst. The surface of the carrier component is porous and plays the role of loading and supporting the catalytic component. When preparing the catalyst, the catalytic component is loaded onto the surface of the porous carrier component, so that the catalytic component can efficiently and stably play a catalytic role, and the surface of the obtained integrated catalyst forms a reaction interface with catalytic activity.

[0060] Example 1: Production of calcium sulfide using ammonia and an iron-based catalyst

[0061] Take 1.5 grams of iron oxide powder and 0.5 grams of iron sulfide powder as catalytic components, and 6 grams of aluminum oxide powder and 2 grams of silicon oxide powder as carrier components, and perform physical ball milling for 1 hour to obtain an iron-based catalyst; the catalytic component content accounts for 20wt%, and the carrier component content accounts for 80wt%.

[0062] Desulfurized gypsum blocks and the aforementioned iron-based catalyst are fed into a raw mill-homogenizer 1, mixed in a mass ratio of 10:1, and crushed to produce a uniform solid mixture. The solid mixture is then fed into a preheater 2, where it is preheated and dried with high-temperature gas at 600°C. Simultaneously, liquid ammonia is fed into a heater 3, heating it to 500°C ammonia gas. A reduction reactor 4, preheated and maintained at 500°C, is then fed with the preheated mixture and ammonia gas, where they react for 30 minutes to produce calcium sulfide and high-temperature tail gas. The molar amount of the ammonia gas fed is approximately three times the molar amount of the calcium sulfate in the desulfurized gypsum fed. The high-temperature tail gas primarily consists of nitrogen, hydrogen ion (H2O), hydrogen, and unreacted ammonia. The high-temperature calcium sulfide is fed to a cooling device 5, where a low-temperature inert gas (N2) is passed through the cooling device 5 to cool the calcium sulfide. The resulting high-temperature inert gas is then passed into a reduction reactor 4, mixed with the high-temperature tail gas, and then passed into a preheater 2 for heat exchange with the solid mixture. After the calcium sulfide product is cooled to room temperature in the cooling device 5, the catalyst is separated by magnetic attraction. The gas output from the preheater 2 is sequentially passed into a gas dust removal device 6 and a gas-liquid separation device 7 to remove particles and moisture, respectively, before being passed back into the cooling device 5 to cool the high-temperature calcium sulfide, achieving recycling of the inert gas.

[0063] After XRD testing, the XRD spectrum of calcium sulfide products is as follows Figure 3 As shown in the figure, after calculation, the decomposition efficiency of calcium sulfate in desulfurization gypsum reaches 99%, and the purity of calcium sulfide reaches 90%.

[0064] Example 2: Production of calcium sulfide using ammonia and nickel-based catalyst

[0065] Take 0.5 grams of nickel oxide powder as a catalytic component, and 6 grams of porous carbon powder and 3.5 grams of magnesium oxide powder as carrier components, and perform physical ball milling for 2 hours to obtain a nickel-based catalyst; the catalytic component content accounts for 5wt% and the carrier component content accounts for 95wt%.

[0066] The phosphogypsum blocks and the nickel-based catalyst are fed into a raw mill-homogenizer 1, mixed in a 1:1 mass ratio, and crushed to produce a uniform solid mixture. The solid mixture is then fed into a preheater 2, where it is preheated and dried with high-temperature gas at 700°C. Simultaneously, liquid ammonia is fed into a heater 3, heating it to 700°C ammonia gas. A reduction reactor 4, preheated and maintained at 500°C, is then fed with the preheated mixture and ammonia gas, where they react rapidly for 60 seconds to produce calcium sulfide and high-temperature tail gas. The molar amount of the ammonia gas fed is approximately 10 times the molar amount of the calcium sulfate in the phosphogypsum. The high-temperature tail gas primarily consists of nitrogen, hydrogen ion (H2O), hydrogen, and unreacted ammonia. The high-temperature calcium sulfide is fed to a cooling device 5, where a low-temperature inert gas (N2) is passed through the cooling device 5 to cool the calcium sulfide. The resulting high-temperature inert gas is then passed into a reduction reactor 4, mixed with the high-temperature tail gas, and then passed into a preheater 2 for heat exchange with the solid mixture. After the calcium sulfide product is cooled to room temperature in the cooling device 5, the catalyst is separated by magnetic attraction. The gas output from the preheater 2 is sequentially passed into a gas dust removal device 6 and a gas-liquid separation device 7 to remove particles and moisture, respectively, before being passed back into the cooling device 5 to cool the high-temperature calcium sulfide, achieving recycling of the inert gas.

[0067] After XRD detection and calculation, the decomposition efficiency of calcium sulfate in phosphogypsum is close to 100%, and the purity of calcium sulfide reaches 95%.

[0068] Example 3: Production of calcium sulfide using a mixture of ammonia and nitrogen and an iron-nickel based catalyst

[0069] Take 1.5 grams of nickel oxide powder and 1.5 grams of pyrite powder as catalytic components, and 5 grams of silicon oxide powder and 2 grams of magnesium oxide powder as carrier components, and perform physical ball milling for 1.5 hours to obtain an iron-nickel-based catalyst; the catalytic component content accounts for 30wt% and the carrier component content accounts for 70wt%.

[0070] Natural gypsum blocks and the aforementioned iron-nickel-based catalyst are fed into a raw mill-homogenizer 1, mixed in a mass ratio of 5:1, and crushed to produce a uniform solid mixture. The solid mixture is then fed into a preheater 2, where it is preheated and dried using high-temperature gas at 600°C. Simultaneously, a mixture of ammonia and nitrogen is fed into a heater 3 and heated to 600°C, with ammonia accounting for 60% of the volume of the mixture. A reduction reactor 4, preheated and maintained at 600°C, is then fed with the preheated mixture and ammonia, where a rapid reaction occurs within 3 seconds, generating calcium sulfide and high-temperature exhaust gas. The molar amount of the input ammonia is approximately 8 times that of the calcium sulfate in the natural gypsum. The high-temperature exhaust gas primarily consists of nitrogen, hydrogen, hydrogen, and unreacted ammonia. The high-temperature calcium sulfide is fed to a cooling device 5, where a low-temperature inert gas (N2) is passed through the cooling device 5 to cool the calcium sulfide. The resulting high-temperature inert gas is then passed into a reduction reactor 4, mixed with the high-temperature tail gas, and then passed into a preheater 2 for heat exchange with the solid mixture. After the calcium sulfide product is cooled to room temperature in the cooling device 5, the catalyst is separated by magnetic attraction. The gas output from the preheater 2 is sequentially passed into a gas dust removal device 6 and a gas-liquid separation device 7 to remove particles and moisture, respectively, before being passed back into the cooling device 5 to cool the high-temperature calcium sulfide, achieving recycling of the inert gas.

[0071] After XRD detection and calculation, the calcium sulfate in natural gypsum was reduced to calcium sulfide, the decomposition efficiency of calcium sulfate reached 99%, and the purity of calcium sulfide reached 96%.

[0072] Example 4: Production of calcium sulfide using a mixture of ammonia and argon and a nickel-cobalt-based catalyst

[0073] Take 3 grams of cobalt oxide powder, 2 grams of nickel oxide powder as catalytic components, and 5 grams of silicon oxide powder carrier component, and perform physical ball milling for 0.5 hours to obtain a nickel-cobalt based catalyst; the catalytic component content accounts for 50wt%, and the carrier component content accounts for 50wt%.

[0074] The citric acid gypsum blocks and the nickel-cobalt-based catalyst are fed into a raw mill-homogenizer 1, mixed in a mass ratio of 20:1, and crushed to produce a uniform solid mixture. The solid mixture is then fed into a preheater 2, where it is preheated and dried using high-temperature gas at 400°C. Simultaneously, a mixture of ammonia and argon is fed into a heater 3 and heated to 400°C, with ammonia accounting for 40% of the volume of the mixture. A reduction reactor 4, preheated and maintained at 400°C, is then fed with the preheated mixture and ammonia, where they react for 50 minutes to produce calcium sulfide and high-temperature exhaust gas. The molar amount of ammonia fed is approximately 2.7 times the molar amount of calcium sulfate in the citric acid gypsum. The high-temperature exhaust gas primarily consists of nitrogen, hydrogen, hydrogen, argon, and unreacted ammonia. The high-temperature calcium sulfide is fed to a cooling device 5, where a low-temperature inert gas (N2) is passed through the cooling device 5 to cool the calcium sulfide. The resulting high-temperature inert gas is then passed into a reduction reactor 4, mixed with the high-temperature tail gas, and then passed into a preheater 2 for heat exchange with the solid mixture. After the calcium sulfide product is cooled to room temperature in the cooling device 5, the catalyst is separated by magnetic attraction. The gas output from the preheater 2 is sequentially passed into a gas dust removal device 6 and a gas-liquid separation device 7 to remove particles and moisture, respectively, before being passed back into the cooling device 5 to cool the high-temperature calcium sulfide, achieving recycling of the inert gas.

[0075] After XRD detection and calculation, the decomposition efficiency of calcium sulfate in citric acid gypsum is close to 100%, and the purity of calcium sulfide reaches 90%.

[0076] Example 5: Production of calcium sulfide using a mixture of ammonia and argon and a cobalt-based catalyst

[0077] Take 1.5 grams of cobalt oxide powder as a catalytic component, 5 grams of aluminum oxide powder, and 3.5 grams of silicon oxide carrier component, and perform physical ball milling for 1.5 hours to obtain a cobalt-based catalyst; the catalytic component content accounts for 15wt% and the carrier component content accounts for 85wt%.

[0078] Fluorogypsum blocks and the aforementioned cobalt-based catalyst are fed into a raw mill-homogenizer 1, mixed in a mass ratio of 16:1, and crushed to produce a uniform solid mixture. The solid mixture is then fed into a preheater 2, where it is preheated and dried using high-temperature gas at 450°C. Simultaneously, a mixture of ammonia and argon is fed into a heater 3 and heated to 450°C, with ammonia comprising 90% by volume. A reduction reactor 4, preheated and maintained at 450°C, is then fed with the preheated mixture and ammonia for 35 minutes, reacting to produce calcium sulfide and high-temperature offgas. The molar amount of ammonia fed is approximately 5.5 times the molar amount of calcium sulfate in the fluorogypsum fed. The high-temperature offgas primarily consists of H2O, H2, Ar, and unreacted ammonia. The high-temperature calcium sulfide is fed to a cooling device 5, where a low-temperature inert gas (Ar) is passed through the cooling device 5 to cool the calcium sulfide. The resulting high-temperature inert gas is then passed into a reduction reactor 4 to mix with the high-temperature tail gas, and then into a preheater 2 for heat exchange with the solid mixture. After the calcium sulfide product is cooled to room temperature in the cooling device 5, the catalyst is separated by magnetic attraction. The gas output from the preheater 2 is sequentially passed into a gas dust removal device 6 and a gas-liquid separation device 7 to remove particles and moisture, respectively, before being passed back into the cooling device 5 to cool the high-temperature calcium sulfide, achieving recycling of the inert gas.

[0079] After XRD detection and calculation, the decomposition efficiency of calcium sulfate in fluorgypsum is close to 98.9%, and the purity of calcium sulfide reaches 99%.

[0080] Example 6: Production of calcium sulfide using a mixture of ammonia and water vapor and an iron-cobalt-based catalyst

[0081] Take 3.5 grams of iron oxide powder and 1 gram of cobalt oxide powder as catalytic components, and 5 grams of porous carbon and 0.5 grams of aluminum oxide powder as carrier components, and perform physical ball milling for 2 hours to obtain an iron-cobalt-based catalyst; the catalytic component content accounts for 45wt% and the carrier component content accounts for 65wt%.

[0082] The citric acid gypsum blocks and the nickel-cobalt-based catalyst are fed into a raw mill-homogenizer 1, mixed in a mass ratio of 8:1, and crushed to produce a uniform solid mixture. The solid mixture is then fed into a preheater 2, where it is preheated and dried using high-temperature gas at 650°C. Simultaneously, a mixture of ammonia and water vapor is fed into a heater 3 and heated to 650°C, with ammonia comprising 80% by volume. A reduction reactor 4, preheated and maintained at 650°C, is then fed with the preheated mixture and ammonia for 15 minutes to react, producing calcium sulfide and high-temperature exhaust gas. The molar amount of ammonia fed is approximately 8 times the molar amount of calcium sulfate in the citric acid gypsum. The high-temperature exhaust gas primarily consists of nitrogen, hydrogen, hydrogen, and unreacted ammonia. The high-temperature calcium sulfide is fed to a cooling device 5, where a low-temperature inert gas (N2) is passed through the cooling device 5 to cool the calcium sulfide. The resulting high-temperature inert gas is then passed into a reduction reactor 4, mixed with the high-temperature tail gas, and then passed into a preheater 2 for heat exchange with the solid mixture. After the calcium sulfide product is cooled to room temperature in the cooling device 5, the catalyst is separated by magnetic attraction. The gas output from the preheater 2 is sequentially passed into a gas dust removal device 6 and a gas-liquid separation device 7 to remove particles and moisture, respectively, before being passed back into the cooling device 5 to cool the high-temperature calcium sulfide, achieving recycling of the inert gas.

[0083] After XRD detection and calculation, the decomposition efficiency of calcium sulfate in citric acid gypsum is close to 99.9%, and the purity of calcium sulfide reaches 95%.

[0084] Example 7: Production of calcium sulfide using a mixture of ammonia and nitrogen and an iron-cobalt-nickel based catalyst

[0085] Take 2 grams of iron oxide powder, 1.5 grams of cobalt oxide powder, and 1 gram of nickel oxide powder as catalytic components, and 3 grams of porous carbon, 1.5 grams of aluminum oxide powder, and 1 gram of magnesium oxide powder as carrier components, and perform physical ball milling for 0.5 hours to obtain an iron-cobalt-based catalyst; the catalytic component content accounts for 40wt%, and the carrier component content accounts for 60wt%.

[0086] The phosphogypsum blocks and the nickel-cobalt-based catalyst are fed into a raw mill-homogenizer 1, mixed in a mass ratio of 12:1, and crushed to produce a uniform solid mixture. The solid mixture is then fed into a preheater 2, where it is preheated and dried using high-temperature gas at 700°C. Simultaneously, a mixture of ammonia and nitrogen is fed into a heater 3 and heated to 700°C, with ammonia accounting for 75% of the volume. A reduction reactor 4, preheated and maintained at 700°C, is then fed with the preheated mixture and ammonia for a five-minute reaction, generating calcium sulfide and high-temperature tail gas. The molar amount of ammonia fed is approximately five times the molar amount of calcium sulfate in the phosphogypsum. The high-temperature tail gas primarily consists of nitrogen, hydrogen ion (H2O), hydrogen, and unreacted ammonia. The high-temperature calcium sulfide is fed to a cooling device 5, where a low-temperature inert gas (N2) is passed through the cooling device 5 to cool the calcium sulfide. The resulting high-temperature inert gas is then passed into a reduction reactor 4, mixed with the high-temperature tail gas, and then passed into a preheater 2 for heat exchange with the solid mixture. After the calcium sulfide product is cooled to room temperature in the cooling device 5, the catalyst is separated by magnetic attraction. The gas output from the preheater 2 is sequentially passed into a gas dust removal device 6 and a gas-liquid separation device 7 to remove particles and moisture, respectively, before being passed back into the cooling device 5 to cool the high-temperature calcium sulfide, achieving recycling of the inert gas.

[0087] After XRD detection and calculation, the decomposition efficiency of calcium sulfate in phosphogypsum is close to 99.0%, and the purity of calcium sulfide reaches 98%. Comparative Example 1: Production of calcium sulfide using ammonia

[0088] Phosphogypsum blocks are fed into a raw mill-homogenizer 1 for crushing and then into a preheater 2, where they are preheated and dried with high-temperature gas at 700°C. Simultaneously, liquid ammonia is fed into a heater 3, heating it to 700°C ammonia gas. A reduction reactor 4, preheated and maintained at 500°C, is then fed with the preheated mixture and ammonia gas, where a rapid reaction takes 60 seconds to produce calcium sulfide and high-temperature exhaust gas. The molar amount of ammonia gas fed is approximately 10 times the amount of calcium sulfate in the phosphogypsum. The high-temperature exhaust gas primarily consists of nitrogen, hydrogen ion (H2O), hydrogen, and unreacted ammonia. The high-temperature calcium sulfide is fed to a cooling device 5, where low-temperature inert gas (N2) is passed through to cool the calcium sulfide. The resulting high-temperature inert gas is then passed into a reduction reactor 4 to mix with the high-temperature tail gas and then into a preheater 2 for heat exchange with the phosphogypsum blocks within the preheater. After the calcium sulfide product is cooled to room temperature in the cooling device 5, the catalyst is separated by magnetic attraction. The gas output from the preheater 2 is sequentially passed through a gas dust removal device 6 and a gas-liquid separation device 7 to remove particles and moisture, respectively, before being passed back into the cooling device 5 to cool the high-temperature calcium sulfide, thereby achieving recycling of the inert gas.

[0089] After XRD detection and calculation, the decomposition efficiency of calcium sulfate in phosphogypsum is about 50%, and the purity of calcium sulfide is about 40%. Comparative Example 2: Production of calcium sulfide using hydrogen and nickel-based catalyst

[0090] This comparative example produces calcium sulfide by referring to the method of Example 2, except that an equimolar amount of hydrogen is used instead of ammonia.

[0091] After XRD detection and calculation, the decomposition efficiency of calcium sulfate in desulfurization gypsum is about 60%, and the purity of calcium sulfide is about 50%.

[0092] It can be seen from the above embodiments and comparative examples that, in general, the calcium sulfate decomposition efficiency and calcium sulfide purity of calcium sulfide produced by mainly using ammonia to reduce gypsum are significantly better than those produced by mainly using hydrogen to reduce gypsum.

Claims

1. A method for producing calcium sulfide by reducing gypsum with ammonia, characterized in that: The method includes the steps of contacting gypsum with a catalyst and contacting gypsum with an ammonia-containing gas.

2. The method according to claim 1, wherein The gypsum is mainly composed of calcium sulfate, and the mass proportion of calcium sulfate in the gypsum is 50.00-99.99%; the gypsum is selected from a combination of one or more of desulfurized gypsum, phosphogypsum, natural gypsum, fluorinated gypsum, citric acid gypsum and salt gypsum.

3. The method according to claim 1, wherein The catalyst is a solid phase catalyst, comprising a catalytic component and a carrier component; wherein the catalytic component is selected from a combination of one or more of iron oxide, nickel oxide, cobalt oxide, iron sulfide and pyrite, and the carrier component is selected from a combination of one or more of aluminum oxide, silicon oxide, porous carbon and magnesium oxide.

4. The method according to claim 1, wherein The ammonia-containing gas is ammonia or a mixture of ammonia and nitrogen, water vapor or argon. In the ammonia-containing gas, the volume proportion of ammonia is 40-100%.

5. The method according to claim 1, wherein The method comprises the following steps: S1: mixing gypsum and a catalyst to obtain a solid mixture; S2: preheating the solid mixture and the ammonia-containing gas separately; S3: introducing the preheated solid mixture and ammonia-containing gas into a reduction reactor for reduction reaction to obtain a calcium sulfide product and high-temperature tail gas; the high-temperature tail gas includes unreacted ammonia.

6. The method according to claim 5, wherein The method further includes step S4: sending the calcium sulfide product to a cooling device, passing low-temperature inert gas to cool it, obtaining a cooled calcium sulfide product and high-temperature inert gas, passing the high-temperature inert gas into a reduction reactor to mix with the high-temperature tail gas, and then passing the high-temperature inert gas into a preheater to exchange heat with the solid mixture.

7. The method according to claim 5 or 6, characterized in that In step S3, the temperature of the reduction reaction is 400-700°C.

8. The method according to claim 5 or 6, wherein: In step S3, the reduction reaction time is 3s to 90min.

9. A system for producing calcium sulfide by reducing gypsum with ammonia, characterized in that: The system comprises a raw mill-homogenizing silo (1), a preheater (2), a heater (3), a reduction reactor (4), a cooling device (5), a gas dust removal device (6) and a gas-liquid separation device (7), wherein the raw mill-homogenizing silo (1), the preheater (2), the reduction reactor (4) and the cooling device (5) are sequentially connected via pipelines, the heater (3) and the reduction reactor (4) are connected via pipelines, and the preheater (2), the gas dust removal device (6), the gas-liquid separation device (7) and the cooling device (5) are also sequentially connected via pipelines.

10. Use of ammonia in the preparation of calcium sulfide, cement, sulfuric acid, thiourea, sodium sulfide or sulfur, characterized in that: The ammonia gas is used to reduce calcium sulfate in the gypsum to generate calcium sulfide.

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