A ferric-sulfur-based reducing agent, its preparation method and uses

Abstract

This invention provides an iron-sulfur-based reducing material, its preparation method, and its uses. The preparation method includes the following steps: (1) heating ferrous sulfate raw material under a first inert atmosphere; (2) introducing a reducing gas with a flow rate of 5-400 mL / min into the ferrous sulfate raw material and performing a calcination reduction treatment at a temperature of 400-900℃ for 0.5-5 h to obtain a solid mixture; (3) cooling the solid mixture under a second inert atmosphere to obtain the iron-sulfur-based reducing material. The preparation method of this invention has the advantages of simple preparation process, clean and environmentally friendly, and easy to achieve large-scale production; the prepared iron-sulfur-based reducing material can simultaneously provide Fe(O), Fe(II), and S(-II), greatly improving the activity and utilization rate of the iron-sulfur-based reducing material, and is suitable for application in the field of heavy metal contaminated soil and groundwater remediation.

Description

Technical Field

[0001] This invention relates to the field of environmental remediation technology, and in particular to an iron-sulfur-based reducing agent, its preparation method, and its uses. Background Technology

[0002] In recent years, environmental pollution has attracted widespread attention. Among the major pollutants exceeding standards, chromium, cadmium, and mercury, three heavy metals, are toxic in their high-valence states, but their reduced low-valence states can remain safe and stable for a long time; halogenated hydrocarbons can also be degraded through reduction. Against this backdrop, the research and application of environmentally friendly reducing materials has become a hot topic. Traditional environmental remediation methods often face a series of challenges, including low efficiency, long cycles, poor stability, limitations imposed by application conditions (pH, etc.), and susceptibility to other environmental factors. To overcome these difficulties, some novel iron-sulfur-based reducing remediation materials have emerged in recent years, attracting widespread attention due to their unique properties and application advantages.

[0003] Currently, common iron-sulfur-based reductive remediation materials mainly include zero-valent iron (ZVFe) and ferrous sulfide. Due to its highly reducing properties, ZVFe can rapidly reduce various harmful substances in certain environments, but its use is limited by slow reaction rates and short lifespans. Ferrous sulfide, due to its stable structure, can release its reducing properties over a long period, but its preparation often faces high costs and complex synthesis processes.

[0004] CN104030365A discloses a method for preparing ferrous sulfide, which mainly includes: (1) reaction: using distilled water to prepare ferrous salt and sulfide aqueous solutions respectively; adjusting the pH of the ferrous salt aqueous solution to less than 3 and adding a reducing agent; adding the sulfide aqueous solution to the ferrous salt aqueous solution and stirring to obtain ferrous sulfide as a precipitate; (2) separation: after the reaction is completed, remove the supernatant and centrifuge to separate; after centrifugation, remove the supernatant, wash the precipitate with distilled water, centrifuge and repeat three times; then add the first inert organic solvent, wash, centrifuge and separate three times to remove water from the precipitate; (3) drying: add the washed ferrous sulfide precipitate to the second inert organic solvent to form a mixture, transfer the mixture to a filter device for filtration and separation; use the third inert organic solvent to repeatedly wash the ferrous sulfide precipitate in the filter paper more than three times; grind and dry in an inert gas atmosphere, and obtain suitable ferrous sulfide powder after drying. The method for preparing ferrous sulfide in this patent is simple, but it generates a large amount of waste salt and wastewater during the preparation process, causing secondary pollution. At the same time, the formation of sodium sulfate will affect the performance of the material and salt removal is required, making the preparation process complex.

[0005] CN105414554A discloses a method for preparing an iron-ferrous sulfide composite. The method mainly includes: mixing elemental sulfur powder and micron-sized iron powder at a mass ratio of 1:5 to 60; placing the resulting mixture in a ball mill jar containing grinding media; maintaining a vacuum or inert gas atmosphere inside the jar; turning on the ball mill; grinding at 400 to 4000 rpm for 2 to 30 hours; and separating the grinding media from the product after grinding to obtain the iron-ferrous sulfide composite. This method is simple, uses inexpensive raw materials, and does not use or produce toxic or hazardous chemicals, making it a clean production process. However, this method involves mechanical mixing, resulting in an impure and unevenly shaped product, large particle size, high specific surface area, and low material application efficiency.

[0006] Therefore, in view of the above aspects, the present invention provides a simple, clean and efficient method for preparing iron-sulfur-based reducing materials, and the prepared material has controllable composition, small particle size, large specific surface area and good reactivity. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides an iron-sulfur-based reducing material, its preparation method and uses. It is obtained by direct reduction of ferrous sulfate raw material, without the need for additional iron and sulfur sources. The preparation process is simple and low in cost. The obtained iron-sulfur-based reducing material has small particle size and large specific surface area, and can simultaneously provide Fe(O), Fe(II) and S(-II). It has strong reducing properties and reaction selectivity, and has good application prospects in the remediation of heavy metal contaminated soil or heavy metal contaminated groundwater.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0010] (1) Ferrous sulfate raw material is heated under a first inert atmosphere;

[0011] (2) A reducing gas with a flow rate of 5-400 mL / min is introduced into the ferrous sulfate raw material, and a calcination reduction treatment is carried out at a temperature of 400-900℃ for 0.5-5 h to obtain a solid mixture;

[0012] (3) The solid mixture is cooled in a second inert atmosphere to obtain the iron-sulfur-based reducing material.

[0013] The preparation method of the iron-sulfur-based reducing material described in this invention is simple to operate. It directly reduces ferrous sulfate with a reducing gas to obtain the iron-sulfur-based reducing material, without requiring additional iron or sulfur sources. Under specific reducing gas flow rates, temperatures, and time conditions, reducing materials with different iron and sulfur contents can be obtained, achieving effective remediation of heavy metal-contaminated soil or groundwater. The iron-sulfur-based reducing material prepared by this invention not only has high reducing performance but also provides zero-valent iron, divalent iron ions, and negative divalent sulfur ions, exhibiting high reduction efficiency. It can rapidly reduce harmful substances such as heavy metals in soil and water, and also has a long lifespan, continuously releasing its remediation effects.

[0014] In the roasting and reduction process described in this invention, a reducing gas is introduced at a flow rate of 5–400 mL / min. If the flow rate is too low, ferrous sulfate cannot be fully reduced to an iron-sulfur-based material; if the flow rate is too high, the percentage of iron in the reduction product increases while the percentage of sulfur decreases, reducing the reduction effect and wasting hydrogen, thus increasing costs. The roasting and reduction temperature is 400–900°C. If the temperature is too low, ferrous sulfate cannot be reduced to an iron-sulfur-based material; if the temperature is too high, the reduction rate is too fast, increasing the percentage of iron and decreasing the percentage of sulfur in the reduction product, reducing the reduction effect and increasing energy consumption. The roasting and reduction time is 0.5–5 hours. If the time is too short, the reduction of ferrous sulfate is incomplete, failing to obtain an iron-sulfur-based material with the appropriate content; if the time is too long, the percentage of iron in the reduction product increases while the percentage of sulfur decreases, reducing the reduction effect.

[0015] The flow rate of the reducing gas described in this invention is 5 to 400 mL / min, for example, it can be 5 mL / min, 10 mL / min, 30 mL / min, 50 mL / min, 100 mL / min, 200 mL / min, 300 mL / min or 400 mL / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] The temperature of the calcination reduction treatment is 400 to 900°C, for example, it can be 400°C, 500°C, 600°C, 700°C, 750°C, 800°C or 900°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0017] The calcination reduction treatment time is 0.5 to 5 hours, for example, it can be 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 4 hours or 5 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the ferrous sulfate raw material in step (1) includes any one or a combination of at least two of analytical grade ferrous sulfate, industrial ferrous sulfate, or industrial ferrous sulfate waste salt. Typical but non-limiting combinations include a combination of analytical grade ferrous sulfate and industrial ferrous sulfate, a combination of industrial ferrous sulfate waste salt and analytical grade ferrous sulfate, or a combination of industrial ferrous sulfate and industrial ferrous sulfate waste salt, preferably analytical grade ferrous sulfate.

[0019] Preferably, the ferrous sulfate raw material in step (1) is pre-treated by refining before heating, so that it can be in good contact with reducing gas to obtain an iron-sulfur-based reducing material with excellent reducing performance.

[0020] Preferably, the refining pretreatment method includes: grinding the ferrous sulfate raw material to obtain ground ferrous sulfate raw material with a particle size of 1 to 10 μm, for example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 4.5 μm, 5 μm, 8 μm or 10 μm, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0021] Preferably, the first inert atmosphere in step (1) includes any one or a combination of at least two of nitrogen atmosphere, argon atmosphere or helium atmosphere, wherein typical but non-limiting combinations include a combination of nitrogen atmosphere and argon atmosphere, a combination of helium atmosphere and nitrogen atmosphere or a combination of argon atmosphere and helium atmosphere.

[0022] Preferably, in step (1), the first inert atmosphere is achieved by continuously introducing an inert gas.

[0023] Preferably, the flow rate of the inert gas is 5 to 800 mL / min, for example, it can be 5 mL / min, 10 mL / min, 50 mL / min, 100 mL / min, 300 mL / min, 500 mL / min, 700 mL / min or 800 mL / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 100 to 400 mL / min.

[0024] In this invention, ferrous sulfate raw material is preferably heated under a first inert atmosphere to eliminate the presence of oxidizing gases. If the flow rate of the inert gas is too low, the oxidizing gases cannot be completely eliminated, and they will oxidize ferrous iron to ferric iron, thus preventing the iron-based material from having a reducing effect. If the flow rate of the inert gas is too high, it will result in gas waste and increase the cost of preparing iron-sulfur-based reducing materials.

[0025] Preferably, the temperature rise to 400-900℃ in step (1) can be, for example, 400℃, 500℃, 600℃, 700℃, 750℃, 800℃ or 900℃, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the reducing gas in step (2) includes hydrogen and / or carbon monoxide, with hydrogen being the most preferred.

[0027] Preferably, the flow rate of the reducing gas in step (2) is 100 to 200 mL / min, for example, it can be 100 mL / min, 120 mL / min, 130 mL / min, 150 mL / min, 170 mL / min, 180 mL / min, 190 mL / min or 200 mL / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the temperature of the calcination reduction treatment in step (2) is 400 to 500°C, for example, it can be 400°C, 420°C, 440°C, 450°C, 470°C, 490°C or 500°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0029] Preferably, the calcination reduction treatment time in step (2) is 0.5 to 2.5 h, for example, it can be 0.5 h, 0.8 h, 1 h, 1.3 h, 1.5 h, 2 h, 2.3 h or 2.5 h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the second inert atmosphere in step (3) includes any one or a combination of at least two of nitrogen atmosphere, argon atmosphere or helium atmosphere, wherein typical but non-limiting combinations include a combination of nitrogen atmosphere and argon atmosphere, a combination of helium atmosphere and nitrogen atmosphere or a combination of argon atmosphere and helium atmosphere.

[0031] Preferably, in step (3), the second inert atmosphere is achieved by continuously introducing an inert gas.

[0032] Preferably, the flow rate of the inert gas is 5 to 800 mL / min, for example, it can be 5 mL / min, 10 mL / min, 50 mL / min, 100 mL / min, 300 mL / min, 500 mL / min, 700 mL / min or 800 mL / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 100 to 400 mL / min.

[0033] Preferably, the temperature drop to 20-30°C in step (3) can be, for example, 20°C, 22°C, 24°C, 25°C, 27°C, 29°C or 30°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] The preferred method of cooling to 20-30°C is to prevent ferrous sulfide from spontaneously combusting.

[0035] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0036] (1) The ferrous sulfate raw material is ground to obtain a ground ferrous sulfate raw material with a particle size of 1 to 10 μm, and then heated to 400 to 900 °C under a first inert atmosphere;

[0037] The ferrous sulfate raw material includes any one or a combination of at least two of analytical grade ferrous sulfate, industrial ferrous sulfate, or industrial ferrous sulfate waste salt.

[0038] The first inert atmosphere includes any one or a combination of at least two of nitrogen, argon, or helium atmospheres; the first inert atmosphere is achieved by continuously introducing an inert gas; the flow rate of the inert gas is 5–800 mL / min.

[0039] (2) A reducing gas with a flow rate of 5 to 400 mL / min is introduced into the ground and reduced ferrous sulfate raw material, and a calcination reduction treatment is carried out at a temperature of 400 to 900 °C for 0.5 to 5 h to obtain a solid mixture;

[0040] The reducing gas includes hydrogen and / or carbon monoxide;

[0041] (3) The solid mixture is cooled to 20-30°C in a second inert atmosphere to obtain the iron-sulfur-based reducing material;

[0042] The second inert atmosphere includes any one or a combination of at least two of nitrogen, argon, or helium atmospheres; the second inert atmosphere is achieved by continuously introducing an inert gas; the flow rate of the inert gas is 5 to 800 mL / min.

[0043] In a second aspect, the present invention provides an iron-sulfur-based reducing material, wherein the iron-sulfur-based reducing material is obtained by the preparation method of the iron-sulfur-based reducing material described in the first aspect;

[0044] The iron-sulfur-based reducing material comprises any one or a combination of at least two of ferrous sulfide or elemental iron; the particle size of the iron-sulfur-based reducing material is 100–500 nm; the specific surface area of ​​the iron-sulfur-based reducing material is 10–50 m². 2 / g; the iron content of the iron-sulfur-based reducing material is 63.6-100 wt.%; the sulfur content of the iron-sulfur-based reducing material is 0-36.4 wt.%.

[0045] The particle size of the iron-sulfur-based reducing material described in this invention is 100-500 nm, for example, it can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm or 500 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] The specific surface area of ​​the iron-sulfur-based reducing material is 10–50 m². 2 / g, for example, could be 10m 2 / g, 15m 2 / g, 20m 2 / g, 25m 2 / g、30m 2 / g or 50m 2 / g, etc., but not limited to the listed values, other unlisted values ​​within the range also apply.

[0047] The iron content of the iron-sulfur-based reducing material is 63.6 to 100 wt.%, for example, it can be 63.6 wt.%, 64 wt.%, 66 wt.%, 70 wt.%, 80 wt.%, 85 wt.%, 90 wt.%, or 100 wt.%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0048] The sulfur content of the iron-sulfur based reducing material is 0 to 36.4 wt.%, for example, it can be 0 wt.%, 3 wt.%, 5 wt.%, 10 wt.%, 20 wt.%, 25 wt.%, 30 wt.%, or 36.4 wt.%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0049] The iron-sulfur-based reducing material described in this invention has a small particle size and a large specific surface area. Compared with iron powder raw materials and ferrous sulfide raw materials, it can simultaneously provide Fe(O), Fe(II) and S(-II), exhibiting strong reducing properties and reaction selectivity. Moreover, it can remediate heavy metal contaminated soil or heavy metal contaminated groundwater through adsorption, reduction, co-precipitation, and other methods without requiring specific pH and temperature conditions.

[0050] Thirdly, the present invention provides an application of the iron-sulfur-based reducing material as described in the second aspect, wherein the iron-sulfur-based reducing material is used to remediate heavy metal-contaminated soil or heavy metal-contaminated groundwater.

[0051] Compared with the prior art, the present invention has at least the following beneficial effects:

[0052] (1) The preparation method of the iron-sulfur-based reducing material provided by the present invention is simple, clean and efficient. It uses reducing gas to directly reduce ferrous sulfate raw material to obtain iron-sulfur-based reducing material, without the need to provide an additional iron source and sulfur source.

[0053] (2) The iron-sulfur-based reducing material provided by the present invention has the advantages of zero-valent iron and ferrous sulfide, and overcomes their respective limitations. It can simultaneously provide Fe(0), Fe(II) and S(-II), and has a high reduction efficiency. It can efficiently remediate heavy metal contaminated soil or heavy metal contaminated groundwater without the need for specific pH and temperature conditions. Attached Figure Description

[0054] Figure 1 This is a phase diagram of the iron-sulfur-based reducing material prepared in Example 1 of the present invention.

[0055] Figure 2 This is a morphology diagram of the iron-sulfur-based reducing material prepared in Example 1 of the present invention.

[0056] Figure 3 This is a surface scan energy spectrum of the iron-sulfur-based reducing material prepared in Example 1 of the present invention.

[0057] Figure 4 This is a phase diagram of the iron-sulfur-based reducing material prepared in Example 8 of the present invention.

[0058] Figure 5 The image shows the line scan energy spectrum of the iron-sulfur-based reducing material prepared in Example 8 of this invention. Detailed Implementation

[0059] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0060] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0061] Example 1

[0062] This embodiment provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0063] (1) 5g of analytical grade ferrous sulfate was ground to obtain ground analytical grade ferrous sulfate with a particle size of 8μm, and heated to 400℃ under a nitrogen atmosphere with a flow rate of 200mL / min.

[0064] (2) Hydrogen gas with a flow rate of 100 mL / min was introduced into the ground analytical grade ferrous sulfate, and calcination and reduction treatment was carried out at a temperature of 400 °C for 2.5 h to obtain a solid mixture;

[0065] (3) The solid mixture is cooled to 20°C in a nitrogen atmosphere with a flow rate of 200 mL / min to obtain the iron-sulfur-based reducing material.

[0066] The phase diagram of the iron-sulfur-based reducing material obtained in this embodiment is as follows: Figure 1 As shown, from Figure 1 It can be seen that the main phase of the obtained iron-sulfur-based reducing material is FeS;

[0067] The morphology of the iron-sulfur-based reducing material obtained in this embodiment is shown in the figure below. Figure 2 As shown, from Figure 2 It can be seen that the morphology of the obtained iron-sulfur-based reducing material is spherical with a particle size of 100-200 nm.

[0068] The surface scan energy dispersive spectroscopy (SSD) spectrum of the iron-sulfur-based reducing material obtained in this embodiment is as follows: Figure 3 As shown, from Figure 3 It can be seen that the main elemental components of the obtained iron-sulfur-based reducing material are Fe and S, with the molar ratio of Fe to S close to 1:1.

[0069] Example 2

[0070] This embodiment provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0071] (1) 5g of analytical grade ferrous sulfate was heated to 400℃ in an argon atmosphere with a flow rate of 200mL / min;

[0072] (2) Carbon monoxide with a flow rate of 100 mL / min was introduced into the analytical grade ferrous sulfate and calcined and reduced at a temperature of 400 °C for 2.5 h to obtain a solid mixture;

[0073] (3) The solid mixture is cooled to 23°C in an argon atmosphere with a flow rate of 200 mL / min to obtain the iron-sulfur-based reducing material.

[0074] Example 3

[0075] This embodiment provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0076] (1) 5g of analytical grade ferrous sulfate was ground to obtain ground analytical grade ferrous sulfate with a particle size of 1μm, and heated to 400℃ under a helium atmosphere with a flow rate of 200mL / min.

[0077] (2) Hydrogen gas with a flow rate of 200 mL / min was introduced into the ground analytical grade ferrous sulfate, and calcination and reduction treatment was carried out at a temperature of 400 °C for 2.5 h to obtain a solid mixture;

[0078] (3) The solid mixture is cooled to 27°C in an argon atmosphere with a flow rate of 200 mL / min to obtain the iron-sulfur-based reducing material.

[0079] Example 4

[0080] This embodiment provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0081] (1) 500g of analytical grade ferrous sulfate was ground to obtain ground analytical grade ferrous sulfate with a particle size of 3μm, and heated to 400℃ under a nitrogen atmosphere with a flow rate of 400mL / min.

[0082] (2) Carbon monoxide with a flow rate of 200 mL / min was introduced into the ground analytical grade ferrous sulfate, and calcination and reduction treatment was carried out at a temperature of 400 °C for 2.5 h to obtain a solid mixture;

[0083] (3) The solid mixture is cooled to 30°C in a nitrogen atmosphere with a flow rate of 400 mL / min to obtain the iron-sulfur-based reducing material.

[0084] Example 5

[0085] This embodiment provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0086] (1) 500g of industrial ferrous sulfate was ground to obtain ground industrial ferrous sulfate with a particle size of 10μm, and then heated to 400℃ under an argon atmosphere with a flow rate of 400mL / min.

[0087] (2) Carbon monoxide with a flow rate of 200 mL / min was introduced into the ground industrial ferrous sulfate and calcined and reduced at a temperature of 400 °C for 2.5 h to obtain a solid mixture;

[0088] (3) The solid mixture is cooled to 24°C in a helium atmosphere with a flow rate of 400 mL / min to obtain the iron-sulfur-based reducing material.

[0089] Example 6

[0090] This embodiment provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0091] (1) 500g of industrial ferrous sulfate waste salt was ground to obtain ground industrial ferrous sulfate waste salt with a particle size of 8μm, and heated to 400℃ under a nitrogen atmosphere with a flow rate of 400mL / min.

[0092] (2) Hydrogen gas with a flow rate of 200 mL / min was introduced into the ground industrial ferrous sulfate waste salt, and calcination and reduction treatment was carried out at a temperature of 400 °C for 2.5 h to obtain a solid mixture;

[0093] (3) The solid mixture is cooled to 30°C in a nitrogen atmosphere with a flow rate of 400 mL / min to obtain the iron-sulfur-based reducing material.

[0094] Example 7

[0095] This embodiment provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0096] (1) 1500g of analytical grade ferrous sulfate was ground to obtain ground analytical grade ferrous sulfate with a particle size of 4.5μm, and heated to 400℃ under an argon atmosphere with a flow rate of 800mL / min.

[0097] (2) Hydrogen gas with a flow rate of 400 mL / min was introduced into the ground analytical grade ferrous sulfate, and calcination and reduction treatment was carried out at a temperature of 400 °C for 2.5 h to obtain a solid mixture;

[0098] (3) The solid mixture is cooled to 21°C in a nitrogen atmosphere with a flow rate of 800 mL / min to obtain the iron-sulfur-based reducing material.

[0099] Example 8

[0100] This embodiment provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0101] (1) 5g of analytical grade ferrous sulfate was ground to obtain ground analytical grade ferrous sulfate with a particle size of 8.8μm, and heated to 500℃ under a nitrogen atmosphere with a flow rate of 200mL / min.

[0102] (2) Hydrogen gas with a flow rate of 100 mL / min was introduced into the ground analytical grade ferrous sulfate, and calcination and reduction treatment was carried out at a temperature of 500 °C for 1 h to obtain a solid mixture;

[0103] (3) The solid mixture is cooled to 20°C in a nitrogen atmosphere with a flow rate of 200 mL / min to obtain the iron-sulfur-based reducing material.

[0104] The phase diagram of the iron-sulfur-based reducing material obtained in this embodiment is as follows: Figure 4 As shown, from Figure 4 It can be seen that the main phases of the obtained iron-sulfur-based reducing material are FeS and Fe;

[0105] The line scan energy spectrum of the iron-sulfur-based reducing material obtained in this embodiment is as follows: Figure 5 As shown, from Figure 5 It can be seen that the obtained iron-sulfur-based reducing material is Fe-encapsulated FeS, with an encapsulation layer thickness of approximately 10-20 nm.

[0106] Example 9

[0107] This embodiment provides a method for preparing an iron-sulfur-based reducing material, the method comprising the following steps:

[0108] (1) 5g of analytical grade ferrous sulfate was ground to obtain ground analytical grade ferrous sulfate with a particle size of 10μm, and heated to 500℃ under an argon atmosphere with a flow rate of 200mL / min.

[0109] (2) Hydrogen gas with a flow rate of 100 mL / min was introduced into the ground analytical grade ferrous sulfate, and calcination and reduction treatment was carried out at a temperature of 500 °C for 0.5 h to obtain a solid mixture;

[0110] (3) The solid mixture is cooled to 20°C in a nitrogen atmosphere with a flow rate of 200 mL / min to obtain the iron-sulfur-based reducing material.

[0111] The particle size, specific surface area, iron content, and sulfur content of the iron-sulfur based reducing materials obtained in Examples 1-9 are shown in Table 1.

[0112] Table 1

[0113] Example 1 150 49.5 65.22 34.78 Example 2 250 45.2 66.22 33.78 Example 3 275 40.3 68.97 31.03 Example 4 350 37.8 67.22 32.78 Example 5 415 33.6 67.87 32.13 Example 6 430 30.2 68.02 31.98 Example 7 450 25.7 68.22 31.78 Example 8 500 22.3 75.76 24.24 Example 9 300 38.6 66.72 33.28

[0114] As can be seen from Table 1, the iron-sulfur-based reducing material provided by the present invention has a small particle size and a large specific surface area. The iron content of the iron-sulfur-based reducing material is 65.22-75.76 wt.%, and the sulfur content is 24.24-34.78 wt.%, exhibiting strong reducing properties and reaction selectivity.

[0115] Comparative Example 1

[0116] This comparative example provides a 400-mesh commercial iron powder, the oxide layer of which is removed by washing with hydrochloric acid.

[0117] Comparative Example 2

[0118] This comparative example provides a ferrous sulfide, obtained using the method described in the specific embodiment of CN104030365A.

[0119] Comparative Example 3

[0120] This comparative example provides an iron-ferrous sulfide composite material, obtained by following the steps in Example 1 of CN105414554A.

[0121] Comparative Example 4

[0122] This comparative example provides a method for preparing an iron-sulfur-based reducing material. Except for the hydrogen flow rate of 2 mL / min in step (2), the preparation method is the same as that in Example 1.

[0123] Comparative Example 5

[0124] This comparative example provides a method for preparing an iron-sulfur-based reducing material. Except for the hydrogen flow rate of 450 mL / min in step (2), the preparation method is the same as that in Example 1.

[0125] Comparative Example 6

[0126] This comparative example provides a method for preparing an iron-sulfur-based reducing material. Except for the calcination reduction treatment temperature of 300°C in step (2), the preparation method is the same as that in Example 1.

[0127] Comparative Example 7

[0128] This comparative example provides a method for preparing an iron-sulfur-based reducing material. Except for the calcination reduction treatment temperature of 1000℃ in step (2), the preparation method is the same as that in Example 1.

[0129] Comparative Example 8

[0130] This comparative example provides a method for preparing an iron-sulfur-based reducing material. Except for the calcination reduction treatment time of 0.3 h in step (2), the preparation method is the same as that in Example 1.

[0131] Comparative Example 9

[0132] This comparative example provides a method for preparing an iron-sulfur-based reducing material. Except for the calcination and reduction treatment time of 6 hours in step (2), the preparation method is the same as that in Example 1.

[0133] The iron-sulfur-based reducing agents obtained in the above embodiments and comparative examples, taking Cr(VI) as an example, were examined for their removal effects in water and soil. The specific test methods are as follows:

[0134] Test method for Cr(VI) removal effect in water: 0.1g of the obtained iron-sulfur reducing material was placed in a plastic bottle containing 100mL of Cr(VI) solution with a concentration of 20mg / L. The shaking temperature was 25℃ and the rotation speed was 200rpm. After 24h of reaction, the removal effect of the material on Cr(VI) in water was determined by diphenylcarbazide spectrophotometry according to GB 7467-87.

[0135] Test method for Cr(VI) removal effect in soil: Artificial contamination was carried out on the original soil. Sodium dichromate aqueous solution was added until the chromium concentration in the soil reached 1000 mg / L. After stirring evenly and air-drying naturally, the soil was ground through a 400-mesh sieve to obtain contaminated soil after simple treatment. The iron-sulfur-based reducing agent obtained in the above examples and comparative examples was mixed evenly with the contaminated soil at a mass ratio of 1:10. The moisture content was adjusted to 10%, and the soil was placed in a ventilated outdoor area for 7 days for passivation. The moisture content and Cr(VI) content in the soil were then measured, and the Cr(VI) content in the dry weight of the soil was calculated. The method for determining the moisture content and Cr(VI) content in the soil is as follows: The Cr(VI) content in the soil was determined using HJ1082-2019 Determination of Hexavalent Chromium in Soil and Sediments - Alkali Extraction-Flame Atomic Absorption Spectrophotometry.

[0136] The results of the removal efficiency of Cr(VI) in water and the passivation efficiency of Cr(VI) in soil obtained by the above embodiments and comparative examples are shown in Table 2.

[0137] Table 2

[0138]

[0139]

[0140] As can be seen from Table 2:

[0141] (1) As can be seen from the comprehensive examples 1 to 9, the preparation method of the iron-sulfur-based reducing material provided by the present invention is simple. The iron-sulfur-based reducing material is obtained by directly reducing ferrous sulfate raw material with reducing gas. The iron-sulfur-based reducing material has a small particle size and a large specific surface area, and can simultaneously provide Fe(O), Fe(II) and S(-II). The removal efficiency of Cr(VI) in water can reach more than 90%, and the passivation efficiency of Cr(VI) in soil can reach more than 80%.

[0142] (2) It can be seen from the combined examples 1 and 3 that the removal efficiency of commercial iron powder and the ferrous sulfide and iron-ferrous sulfide composite disclosed in the existing patent for Cr(VI) in water and the passivation efficiency of Cr(VI) in soil are worse than those of the iron-sulfur-based reducing material in this application.

[0143] (3) It can be seen from the combined examples 1 and 4-9 that when the reducing gas flow rate, the temperature and time of the calcination reduction treatment are not within the range specified in this invention, the removal efficiency of Cr(VI) in water and / or the passivation efficiency of Cr(VI) in soil of the obtained iron-sulfur-based reducing material is greatly reduced.

[0144] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing an iron-sulfur-based reducing material, characterized in that, The preparation method includes the following steps: (1) The ferrous sulfate raw material is heated under a first inert atmosphere; the ferrous sulfate raw material includes any one or a combination of at least two of analytical grade ferrous sulfate, industrial ferrous sulfate or industrial ferrous sulfate waste salt; the first inert atmosphere is achieved by continuously introducing inert gas; the flow rate of the inert gas in step (1) is 5~800mL / min; (2) A reducing gas with a flow rate of 5~400 mL / min is introduced into the ferrous sulfate raw material, and a calcination reduction treatment is carried out at a temperature of 400~500℃ for 0.5~5 h to obtain a solid mixture; (3) The solid mixture is cooled in a second inert atmosphere to obtain the iron-sulfur-based reducing material; The iron-sulfur-based reducing materials include ferrous sulfide and elemental iron.

2. The preparation method according to claim 1, characterized in that, The ferrous sulfate raw material mentioned in step (1) is analytical grade ferrous sulfate.

3. The preparation method according to claim 1, characterized in that, The ferrous sulfate raw material in step (1) is pre-treated by refining before heating.

4. The preparation method according to claim 3, characterized in that, The refining and pretreatment method includes: grinding the ferrous sulfate raw material to obtain ground ferrous sulfate raw material with a particle size of 1~10µm.

5. The preparation method according to claim 1, characterized in that, Step (1) The first inert atmosphere includes any one or a combination of at least two of nitrogen atmosphere, argon atmosphere or helium atmosphere.

6. The preparation method according to claim 1, characterized in that, The flow rate of the inert gas in step (1) is 100~400 mL / min.

7. The preparation method according to claim 1, characterized in that, Step (1) involves heating the temperature to 400~500℃.

8. The preparation method according to claim 1, characterized in that, The reducing gas in step (2) includes hydrogen and / or carbon monoxide.

9. The preparation method according to claim 8, characterized in that, The reducing gas is hydrogen.

10. The preparation method according to claim 1, characterized in that, The flow rate of the reducing gas in step (2) is 100~200 mL / min.

11. The preparation method according to claim 1, characterized in that, The roasting and reduction treatment in step (2) takes 0.5 to 2.5 hours.

12. The preparation method according to claim 1, characterized in that, Step (3) The second inert atmosphere includes any one or a combination of at least two of nitrogen atmosphere, argon atmosphere or helium atmosphere.

13. The preparation method according to claim 1, characterized in that, Step (3) The second inert atmosphere is achieved by continuously introducing inert gas.

14. The preparation method according to claim 13, characterized in that, The flow rate of the inert gas in step (3) is 5~800 mL / min.

15. The preparation method according to claim 14, characterized in that, The flow rate of the inert gas in step (3) is 100~400 mL / min.

16. The preparation method according to claim 1, characterized in that, Step (3) involves cooling the temperature to 20-30°C.

17. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) The ferrous sulfate raw material is ground to obtain a ground ferrous sulfate raw material with a particle size of 1~10µm, and then heated to 400~500℃ under a first inert atmosphere; The ferrous sulfate raw material includes any one or a combination of at least two of analytical grade ferrous sulfate, industrial ferrous sulfate, or industrial ferrous sulfate waste salt. The first inert atmosphere includes any one or a combination of at least two of nitrogen atmosphere, argon atmosphere or helium atmosphere; the first inert atmosphere is achieved by continuously introducing inert gas; the flow rate of the inert gas in step (1) is 5~800mL / min; (2) A reducing gas with a flow rate of 5~400 mL / min is introduced into the ground and reduced ferrous sulfate raw material, and a calcination reduction treatment is carried out at a temperature of 400~500℃ for 0.5~5 h to obtain a solid mixture; The reducing gas includes hydrogen and / or carbon monoxide; (3) The solid mixture is cooled to 20~30°C in a second inert atmosphere to obtain the iron-sulfur-based reducing material; The second inert atmosphere includes any one or a combination of at least two of nitrogen atmosphere, argon atmosphere or helium atmosphere; the second inert atmosphere is achieved by continuously introducing inert gas; the flow rate of the inert gas in step (3) is 5~800 mL / min.

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