Arsenic adsorbents and methods of making and using the same

Abstract

This invention provides an arsenic adsorbent, its preparation method, and its applications. The arsenic adsorbent uses nano-γ-Al₂O₃ as a carrier, with an iron-copper sulfide active phase having an electron-rich Fe-Cu-S interface loaded on its surface. The preparation method of the arsenic adsorbent includes the following steps: dispersing an iron source, a copper source, and nano-γ-Al₂O₃ in a solvent, followed by ultrasonic treatment and drying to obtain a precursor; mixing the precursor with a sulfur source and then calcining to obtain the arsenic adsorbent. This adsorbent exhibits high adsorption capacity and wide temperature range adaptability for both trivalent and pentavalent arsenic in flue gas, and its performance is stable and even promoted under SO₂ atmosphere, capable of converting gaseous arsenic into a stable crystalline phase for fixation.

Description

Technical Field

[0001] This invention belongs to the field of flue gas treatment technology, specifically relating to an arsenic adsorbent, its preparation method, and its application. Background Technology

[0002] In recent years, with increasingly stringent environmental protection requirements, the removal of gaseous arsenic pollutants (mainly As2O3 and As2O5) from industrial flue gas from smelting, coal combustion, and other industries has received widespread attention. Metal oxide adsorbents, such as Fe2O3 and Al2O3, have become a research hotspot due to their wide availability and low cost. Among them, activated alumina (γ-Al2O3) is often used as a carrier to load active components and improve dispersibility and adsorption performance due to its large specific surface area, well-developed pore structure, and abundant hydroxyl sites on its surface. However, the arsenic adsorption capacity of traditional single-metal supported oxide adsorbents is still limited in the medium-low temperature range (150-400℃), and in actual flue gas environments, especially in the presence of high concentrations of SO2, their active sites are easily occupied by sulfides or undergo sulfation, leading to deactivation; therefore, poor sulfur resistance has become a key bottleneck restricting their industrial application.

[0003] Therefore, it is necessary to provide an arsenic adsorbent, its preparation method, and its application to solve the technical problem of how to achieve high-capacity adsorption of trivalent and pentavalent arsenic in a wide temperature range at medium and low temperatures while endowing the material with excellent sulfur resistance properties. Summary of the Invention

[0004] The main objective of this invention is to provide an arsenic adsorbent, its preparation method, and its application, aiming to solve the technical problem of how to achieve high-capacity adsorption of trivalent and pentavalent arsenic in a wide temperature range at medium and low temperatures while endowing the material with excellent sulfur resistance properties.

[0005] To achieve the above objectives, the present invention provides a method for preparing an arsenic adsorbent, comprising the steps of: dispersing an iron source, a copper source, and nano-γ-Al2O3 in a solvent, loading iron and copper onto the nano-γ-Al2O3, and then subjecting the mixture to ultrasonic treatment and drying treatment in sequence to obtain a precursor;

[0006] The precursor is mixed with a sulfur source and then calcined to obtain the arsenic adsorbent; wherein the molar ratio of sulfur in the sulfur source to iron in the iron source is 4-12:1.

[0007] Furthermore, the ratio of the total mass of the iron source and copper source to the mass of the nano-γ-Al2O3 is 1.0-1.8:1.

[0008] Furthermore, the iron source includes ferric nitrate, the copper source includes copper nitrate, and the sulfur source includes thiourea;

[0009] The molar ratio of iron in the iron source to copper in the copper source is 0.8-1.2:1.

[0010] Furthermore, the calcination temperature is 200-600℃, and the calcination time is 1-5h.

[0011] This invention provides an arsenic adsorbent prepared by the arsenic adsorbent preparation method described above. The arsenic adsorbent comprises a γ-Al2O3 matrix and an iron-copper sulfide active phase supported on the surface of the γ-Al2O3 matrix. The iron-copper sulfide active phase comprises CuFe2S3, and the CuFe2S3 forms an electron-rich Fe-Cu-S interface.

[0012] Furthermore, the arsenic adsorbent has a saturated arsenic adsorption capacity greater than 18 mg / g for pentavalent arsenic and a saturated arsenic adsorption capacity greater than 30 mg / g for trivalent arsenic.

[0013] The present invention provides an application of the arsenic adsorbent described above in removing arsenic from arsenic-containing flue gas, comprising the steps of: contacting the arsenic adsorbent with the arsenic-containing flue gas; wherein the arsenic-containing flue gas contains at least one of trivalent arsenic and pentavalent arsenic.

[0014] Furthermore, the arsenic concentration in the arsenic-containing flue gas is not higher than 35 ppm; during the contact process, the reaction temperature is 150-400℃; and the contact duration is 30-180 min.

[0015] During the contact process, some arsenic is chemically adsorbed by the active phase of iron-copper sulfides, and then mineralized and fixed into a stable crystalline phase, which includes Cu. 12 As4S 12 At least one of Cu3AsS4 and Cu3(AsO4)2.

[0016] Furthermore, the arsenic-containing flue gas also includes sulfur dioxide; the concentration of sulfur dioxide in the arsenic-containing flue gas is not higher than 800 ppm.

[0017] Furthermore, the arsenic-containing flue gas also includes at least one of NO, HCl, and O2.

[0018] Compared with the prior art, the present invention has at least the following advantages:

[0019] The preparation method provided by this invention successfully prepares nano-γ-Al2O3-supported iron-copper sulfide adsorbents through a two-step process of loading followed by sulfidation.

[0020] On the one hand, this invention achieves a significant improvement in arsenic adsorption capacity and high-efficiency adsorption over a wide temperature range. The arsenic adsorbent prepared by this invention exhibits excellent adsorption performance for gaseous arsenic, with a saturated adsorption capacity of not less than 18 mg / g for As₂O₅ and not less than 30 mg / g for Al₂O₃, which is several times higher than that of unsulfurized FeCu / Al₂O₃ (4.92 mg / g). Simultaneously, this adsorbent maintains high adsorption activity over a wide temperature range of 150-400℃, demonstrating good temperature adaptability and thermal stability, thus meeting the practical requirements for arsenic removal from medium- and low-temperature flue gas.

[0021] On the other hand, this invention endows the adsorbent with unique sulfur resistance and synergistic sulfur properties. The arsenic adsorbent prepared by this invention completely reverses the predicament of traditional metal oxides being easily deactivated in the presence of SO2. In a flue gas atmosphere containing SO2, the adsorption performance of FeCuS-8 / Al2O3 on As2O3 is not only not inhibited, but is actually promoted. This proves that the adsorbent has excellent sulfur resistance and can even utilize SO2 in the flue gas, maintaining a high adsorption capacity even in the real and complex smelting flue gas environment (containing SO2, NO, HCl, and O2), thus solving the core bottleneck of poor sulfur resistance of traditional adsorbents.

[0022] It should be noted that the fundamental reason for achieving the above-mentioned excellent performance lies in the fact that this invention successfully constructed a matrix of sulfide crystal phases such as CuFe2S3, rich in low-valence metals (Fe) on the surface of a γ-Al2O3 support using a sulfidation process. 2+ / Cu + ) and unsaturated sulfur species (S 2- / S2 2- The Fe-Cu-S electron-rich interface acts as both an electron donor and a reaction center, and its mechanism of action is as follows:

[0023] For As₂O₅: Electrons in the interface transfer to the O atoms of As₂O₅, promoting the breaking of the As-O bond. As then combines with interfacial sulfur and is eventually fixed as Cu. 12 As4S 12 Stable crystalline phase.

[0024] For As2O3: interfacial unsaturated sulfur first adsorbs As2O3 and catalyzes its dissociation. The resulting active oxygen species further oxidize the interfacial metal, ultimately driving arsenic to mineralize and be fixed in the form of Cu3AsS4 and Cu3(AsO4)2.

[0025] This interface adaptively converts gaseous arsenic into a thermodynamically stable solid phase through electron transfer and sulfur coordination, achieving permanent fixation. Therefore, this invention not only provides an efficient preparation method, but also fundamentally solves the three major technical challenges of high adsorbent capacity, wide temperature range, and synergistic sulfur resistance by constructing a specific active interface. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 The XRD patterns of γ-Al2O3, FeCu / Al2O3 and FeCuS-8 / Al2O3 in Example 1 of this invention are shown below.

[0028] Figure 2 The XRD patterns of FeS-8 / Al2O3 and CuS-8 / Al2O3 in Example 1 of this invention are shown below;

[0029] Figure 3 Raman plots of γ-Al2O3 and FeCuS-8 / Al2O3 in Example 1 of this invention;

[0030] Figure 4 (a) is the SEM image of γ-Al2O3 in Analytical Example 1 of the present invention, (b) is the SEM image of FeCu / Al2O3 in Analytical Example 1 of the present invention, (c) is the SEM image of FeCuS-8 / Al2O3 in Analytical Example 1 of the present invention, (d) and (e) are the TEM images of FeCu / Al2O3 in Analytical Example 1 of the present invention and their corresponding mapping images, respectively, (f) is the high-resolution TEM image of FeCu / Al2O3 in Analytical Example 1 of the present invention, (g) and (h) are the TEM images of FeCuS-8 / Al2O3 in Analytical Example 1 of the present invention and their corresponding mapping images, respectively, and (i) is the high-resolution TEM image of FeCuS-8 / Al2O3 in Analytical Example 1 of the present invention;

[0031] Figure 5 The graph shows the arsenic adsorption performance of FeCuS-x / Al2O3 with different sulfidation ratios in Example 2 of this invention.

[0032] Figure 6 As in Example 3 of the present invention 5+ Arsenic adsorption performance of FeCuS-8 / Al2O3 at different temperatures when the standard solution is the arsenic source;

[0033] Figure 7 As in Example 3 of the present invention 5+ Arsenic adsorption performance of FeCuS-8 / Al2O3 at different arsenic concentrations when the standard solution is the arsenic source;

[0034] Figure 8 As in Example 3 of the present invention5+ Arsenic adsorption performance of FeCuS-8 / Al2O3 at different reaction times when the standard solution is the arsenic source;

[0035] Figure 9 As in Example 4 of this invention 3+ Arsenic adsorption performance of FeCuS-8 / Al2O3 at different arsenic concentrations when the standard solution is the arsenic source;

[0036] Figure 10 As in Example 4 of this invention 3+ Arsenic adsorption performance of FeCuS-8 / Al2O3 at different reaction temperatures when the standard solution is the arsenic source;

[0037] Figure 11 As in Example 4 of this invention 3+ Arsenic adsorption performance of FeCuS-8 / Al2O3 under different atmospheres when the standard solution is the arsenic source;

[0038] Figure 12 This is a comparison chart of the arsenic removal performance of FeCuS-8 / Al2O3 with other adsorbents in Example 4 of this invention.

[0039] Figure 13 (a) and (b) are SEM images of FeCuS-8 / Al2O3 after adsorption in Example 5 of the present invention, and (c) is an EDS image of FeCuS-8 / Al2O3 after adsorption in Example 5 of the present invention.

[0040] Figure 14 The XRD patterns of FeCuS-8 / Al2O3 before and after As2O5 adsorption in Example 5 of this invention are shown below.

[0041] Figure 15 The XRD patterns of FeCuS-8 / Al2O3 before and after As2O3 adsorption are shown in Example 6 of this invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0044] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of the invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to the methods, devices, and materials in the embodiments of the present invention.

[0045] This invention provides a method for preparing an arsenic adsorbent, comprising the following steps:

[0046] S1. Disperse an iron source, a copper source, and nano-γ-Al2O3 in a solvent, so that iron and copper are loaded on the nano-γ-Al2O3, and then subject them to ultrasonic treatment and drying treatment in sequence to obtain a precursor.

[0047] In some embodiments, the iron source includes ferric nitrate, and the copper source includes copper nitrate. For example, the iron source may be Fe(NO3)3·9H2O, and the copper source may be Cu(NO3)2·3H2O.

[0048] In some embodiments, the solvent includes water.

[0049] In some embodiments, the iron source and the copper source can be dissolved in a solvent, and the ratio of the volume of the solvent to the total mass of the iron source and the copper source can be 1.0-1.5 mL: 1 g; after the iron source and the copper source are completely dissolved, a bimetallic reagent is obtained, and nano-γ-Al2O3 is added dropwise to the bimetallic reagent to obtain a mixed system.

[0050] In some embodiments, the ratio of the total mass of the iron source and the copper source to the mass of nano-γ-Al2O3 can be 1.0-1.8:1. For example, the ratio can be 1.0-1.5:1, and even more specifically, it can be 1.2-1.3:1.

[0051] In some embodiments, the molar ratio of iron in the iron source to copper in the copper source is 0.8-1.2:1. Exemplarily, the molar ratio of iron in the iron source to copper in the copper source is 0.9-1.1:1, 0.8-1.1:1, 0.8-1.0:1, 0.9-1.2:1, or 1.0-1.2:1.

[0052] In some embodiments, the mixture is thoroughly stirred to fully load the copper and iron sources onto nano-γ-Al₂O₃, followed by ultrasonic treatment and drying to obtain the precursor. The ultrasonic treatment can last from 30 min to 2 h, the drying temperature can be 60-90 °C, and the drying time can be 10-14 h.

[0053] S2. The precursor is mixed with a sulfur source and then calcined to obtain the arsenic adsorbent; wherein the molar ratio of sulfur in the sulfur source to iron in the iron source is 4-12:1.

[0054] In some embodiments, the precursor can be ground into powder and then thoroughly ground and mixed with sulfur. The mixture of precursor and sulfur is then placed in a tube furnace and calcined to obtain an arsenic adsorbent.

[0055] For example, the rate of heating to the calcination temperature can be 4-10°C / min; another example is that the rate of heating to the calcination temperature can be 4-8°C / min. For example, nitrogen can be used as the calcination atmosphere.

[0056] In some embodiments, the molar ratio of sulfur in the sulfur source to iron in the iron source can be 6-10:1. For example, the molar ratio of sulfur in the sulfur source to iron in the iron source can be 7-9:1.

[0057] In some embodiments, the sulfur source includes thiourea.

[0058] In some embodiments, the calcination temperature is 200-600°C, and the calcination duration is 1-5 hours. Exemplarily, the calcination temperature can be 300-500°C, and even more exemplaryly, the calcination temperature can be 350-450°C. Exemplarily, the calcination duration can be 1-3 hours.

[0059] This invention provides an arsenic adsorbent prepared by the method described above, comprising a γ-Al2O3 matrix and an iron-copper sulfide active phase supported on the surface of the γ-Al2O3 matrix, wherein the iron-copper sulfide active phase comprises CuFe2S3, and the CuFe2S3 forms an electron-rich Fe-Cu-S interface.

[0060] In some embodiments, the arsenic adsorbent has a saturated arsenic adsorption capacity greater than 18 mg / g for pentavalent arsenic and a saturated arsenic adsorption capacity greater than 30 mg / g for trivalent arsenic.

[0061] This invention provides an application of any of the above-described arsenic adsorbents in removing arsenic from arsenic-containing flue gas, comprising the steps of: the arsenic adsorbent contacting the arsenic-containing flue gas; the arsenic-containing flue gas containing at least one of trivalent arsenic and pentavalent arsenic, the arsenic concentration in the arsenic-containing flue gas not exceeding 35 ppm, the reaction temperature during the contact process being 150-400℃, and the contact duration being 30-180 min.

[0062] In some embodiments, the arsenic concentration in the arsenic-containing flue gas may be 5-25 ppm, 5-25 ppm, 5-23 ppm, 15-25 ppm, 18-25 ppm, or 18-23 ppm. For example, if the arsenic in the arsenic-containing flue gas is trivalent arsenic, the arsenic concentration may be 16-20 ppm; if the arsenic in the arsenic-containing flue gas is pentavalent arsenic, the arsenic concentration may be 20-35 ppm.

[0063] In some embodiments, the reaction temperature during the contact process can be 200-400℃, 250-400℃, 250-350℃, 300-400℃, or 280-380℃.

[0064] In some embodiments, the contact duration may be 50-150 min, 60-150 min, 60-120 min, or 80-120 min.

[0065] In some embodiments, the trivalent arsenic exists in the arsenic-containing flue gas in the form of As2O3, and the pentavalent arsenic exists in the arsenic-containing flue gas in the form of As2O5.

[0066] In some embodiments, during the contact process, some arsenic is chemically adsorbed by the iron-copper sulfide active phase, and then mineralized and fixed into a stable crystalline phase, wherein the crystalline phase includes Cu. 12 As4S 12 At least one of Cu3AsS4 and Cu3(AsO4)2.

[0067] In some embodiments, the arsenic-containing flue gas further includes sulfur dioxide, and the concentration of sulfur dioxide in the arsenic-containing flue gas is not higher than 800 ppm. In some embodiments, the concentration of sulfur dioxide in the arsenic-containing flue gas can be 200-800 ppm, 300-800 ppm, 200-600 ppm, or 300-600 ppm.

[0068] In some embodiments, the arsenic-containing flue gas also includes at least one of NO, HCl, and O2.

[0069] To facilitate a further understanding of the present invention by those skilled in the art, the following examples are provided:

[0070] Example 1

[0071] A method for preparing an arsenic adsorbent, comprising the following steps:

[0072] S1. Weigh 0.396g Fe(NO3)3·9H2O and 0.236g Cu(NO3)2·3H2O and dissolve them in 0.7mL of deionized water. After complete dissolution, add the solution dropwise to 0.5g of nano-γ-Al2O3. Stir and impregnate thoroughly, then sonicate for 1h. Place the solution in an oven and dry at 100℃ for 12h. After drying, grind it into powder to obtain the precursor.

[0073] S2. Weigh 0.4g of precursor powder and grind and mix it thoroughly with 0.14-0.42g of sulfur. Then place it in a tube furnace and calcine it at 400℃ for 2h in a N2 atmosphere at a rate of 100mL / min and a temperature increase of 5℃ / min to obtain FeCuS-x / Al2O3, where x represents the S / Fe molar ratio.

[0074] With a sulfur mass of 0.14 g and an S / Fe ratio of 4 / 1, FeCuS-4 / Al2O3 was prepared.

[0075] With a sulfur mass of 0.28 g and an S / Fe ratio of 8 / 1, FeCuS-8 / Al2O3 was prepared.

[0076] With a sulfur mass of 0.42 g and an S / Fe ratio of 12 / 1, FeCuS-12 / Al2O3 was prepared.

[0077] Comparative Example 1

[0078] FeCuS-1 / Al2O3, FeCuS-2 / Al2O3 and FeCuS-16 / Al2O3 were prepared.

[0079] Compared to Example 1, the remaining steps remain unchanged, except for the mass of sulfur in step S2:

[0080] With a sulfur mass of 0.035 g and an S / Fe ratio of 1 / 1, FeCuS-1 / Al2O3 was prepared.

[0081] With a sulfur mass of 0.07 g and an S / Fe ratio of 2 / 1, FeCuS-2 / Al2O3 was prepared.

[0082] With a sulfur mass of 0.56 g and an S / Fe ratio of 16 / 1, FeCuS-16 / Al2O3 was prepared.

[0083] Comparative Example 2

[0084] Preparation of FeS-8 / Al2O3.

[0085] Compared to Example 1, all other steps remain unchanged, except for step S1, which is adjusted as follows:

[0086] S1. Weigh 0.396g Fe(NO3)3·9H2O and dissolve it in 0.7mL deionized water. After complete dissolution, add it dropwise to 0.5g nano γ-Al2O3. Stir and impregnate thoroughly, then sonicate for 1h. Place it in an oven and dry at 100℃ for 12h. After drying, grind it into powder to obtain the precursor.

[0087] S2. Weigh 0.4g of precursor powder and 0.28g of sulfur, grind and mix thoroughly, then place in a tube furnace and calcine at 400℃ for 2h in a N2 atmosphere at a rate of 5℃ / min to obtain FeS-8 / Al2O3.

[0088] Comparative Example 3

[0089] Preparation of CuS-8 / Al2O3.

[0090] Compared to Example 1, all other steps remain unchanged, except for step S1, which is adjusted as follows:

[0091] S1. Weigh 0.236g Cu(NO3)2·3H2O and dissolve it in 0.7mL deionized water. After complete dissolution, add it dropwise to 0.5g nano γ-Al2O3. Stir and impregnate thoroughly, then sonicate for 1h. Place it in an oven and dry at 100℃ for 12h. After drying, grind it into powder to obtain the precursor.

[0092] S2. Weigh 0.4g of precursor powder and 0.28g of sulfur, grind and mix thoroughly, then place in a tube furnace and calcine at 400℃ for 2h in a N2 atmosphere at a rate of 5℃ / min to obtain CuS-8 / Al2O3.

[0093] The FeCuS-4 / Al2O3, FeCuS-8 / Al2O3, and FeCuS-12 / Al2O3 mentioned in Examples 1-6 below were prepared in Example 1 of this invention;

[0094] The FeCuS-1 / Al2O3, FeCuS-2 / Al2O3 and FeCuS-16 / Al2O3 mentioned in the following analytical examples 1-6 were prepared by Comparative Example 1 of the present invention;

[0095] The FeS-8 / Al2O3 mentioned in the following analytical examples 1-6 was prepared by Comparative Example 2 of the present invention;

[0096] The CuS-8 / Al2O3 mentioned in the following analytical examples 1-6 was prepared by Comparative Example 3 of the present invention.

[0097] Analysis example 1

[0098] Characterization analysis.

[0099] like Figure 1 As shown, commercial γ-Al₂O₃ exhibits distinct diffraction peaks around 37.1°, 39.3°, 45.8°, and 66.9°, which match well with the PDF#47-1770 of γ-Al₂O₃, and the peak shape is broad, consistent with the peak shape characteristics of nano-γ-Al₂O₃. After loading with iron-copper oxides, FeCu / Al₂O₃ still exhibits the γ-Al₂O₃ phase, and no new phases related to iron-copper oxides appear. This indicates that the iron-copper oxides on the FeCu / Al₂O₃ surface are dispersed and uniform, which is beneficial for fully exposing active sites and enhancing the synergistic effect of iron-copper oxides. At the same time, it does not block the pore structure of γ-Al₂O₃, which is conducive to the diffusion of arsenic oxide.

[0100] The sulfidated FeCuS-8 / Al2O3 exhibited new diffraction peaks near 29.4°, 33.6°, 49.1°, 57.9°, and 78.4°, corresponding to the (111), (200), (220), (311), and (331) crystal planes of CuFe2S3 (PDF#27-0166), respectively. At the same time, the γ-Al2O3 phase was detected, indicating that the iron / copper compound was successfully sulfided on the γ-Al2O3 surface and a new, more active phase was generated.

[0101] like Figure 2 As shown, the XRD phases of Fe / Cu sulfidation were investigated. In addition to the phase of Al2O3 support, new sulfide phases appeared in both FeS-8 / Al2O3 and CuS-8 / Al2O3, namely FeS2 (PDF#47-1770) and Cu9S5 (PDF#25-0283), respectively. The arsenic adsorption activity of the sulfide supported by alumina was much higher than that of the oxide.

[0102] like Figure 3 As shown, Raman spectroscopy was performed on γ-Al₂O₃ and FeCuS-8 / Al₂O₃. Compared with γ-Al₂O₃, FeCuS-8 / Al₂O₃ showed better performance at 670 cm⁻¹. -1 The presence of Fe-Cu-S stretching vibrations on both sides further indicates the formation of iron-copper sulfides on the Al2O3 surface, proving the accuracy of the XRD results.

[0103] The changes in the surface morphology and microstructure of the adsorbent before and after sulfidation were further investigated using SEM and TEM, such as Figure 4 As shown. Figure 4(a) is the SEM image of γ-Al2O3, (b) is the SEM image of FeCu / Al2O3, and (c) is the SEM image of FeCuS-8 / Al2O3. It can be seen that γ-Al2O3, FeCu / Al2O3, and FeCuS-8 / Al2O3 all exhibit fine granular structures. Commercial γ-Al2O3 has a smaller particle size, while FeCu / Al2O3 and FeCuS-8 / Al2O3 have relatively larger particle sizes. This is because the high-temperature calcination process inevitably causes the alumina particles to aggregate and increase in size, but their pore structure does not collapse, thus having a relatively small impact on the exposure of active sites.

[0104] Figure 4 (d) and (e) are TEM images of FeCu / Al2O3 and their corresponding mapping images, respectively. It can be seen that the calcined alumina particles aggregate into rods, and the Fe and Cu elements on the surface are relatively uniformly distributed. (f) is a high-resolution TEM image of FeCu / Al2O3. Its surface lattice is disordered, which is a typical lattice feature of nano Al2O3. No lattice spacing related to iron and copper oxides is found, which indirectly confirms the results in the XRD pattern.

[0105] Figure 4 In the middle (g) and (h), respectively, are the TEM images of FeCuS-8 / Al2O3 and their corresponding mapping images. The alumina particles after sulfidation did not aggregate into rods like FeCu / Al2O3, but were in a dispersed state, which is more conducive to the exposure and adsorption of active sites. The mapping image shows that Fe, Cu and S are uniformly dispersed on the alumina surface, proving that the new iron-copper sulfide species were successfully loaded on the alumina surface. Figure 4 In (i), a high-resolution TEM image of FeCuS-8 / Al2O3 is shown. Two lattice spacings of 0.296 nm and 0.259 nm appear on its surface, corresponding to the (111) and (200) planes of CuFe2S3, respectively (PDF#27-0166), which are consistent with the XRD results.

[0106] Analysis example 2

[0107] Arsenic adsorption performance test.

[0108] With 1 g / L of As 5+ The standard solution was used as the arsenic source. The arsenic adsorption performance of FeCuS-x / Al2O3 with different sulfidation ratios was tested under the conditions of a flue gas As concentration of 12.58 ppm, a reaction time of 90 min, a reaction temperature of 300℃, and an N2 atmosphere. The results were compared with those of commercial γ-Al2O3, FeCu / Al2O3, FeS-xAl2O3, and CuS-xAl2O3. Figure 5As shown, compared with unsulfurized FeCu / Al2O3, the arsenic adsorption capacity of materials with any sulfidation ratio is improved. Furthermore, with increasing sulfidation ratio, the arsenic adsorption capacity of FeCuS-x / Al2O3 first increases and then decreases. When the S / Fe ratio is 8:1, the arsenic adsorption capacity of FeCuS-8 / Al2O3 reaches its maximum of 16.01 mg / g, which is 3.25 times higher than that of FeCu / Al2O3 (4.92 mg / g). Compared with FeS-8 / Al2O3 and CuS-8 / Al2O3, FeCuS-8 / Al2O3 has a higher arsenic adsorption capacity, indicating that Fe and Cu have a synergistic effect during adsorption, and their interaction is beneficial to improving adsorption activity.

[0109] Analysis example 3

[0110] Performance test of FeCuS-8 / Al2O3 adsorption of As2O5.

[0111] like Figure 6 The arsenic adsorption capacity of FeCuS-8 / Al2O3 at different temperatures (150-400℃) was tested. The adsorption capacity was calculated using 1 g / L of As... 5+ The standard solution was used as the arsenic source. Under the N2 atmosphere with an As concentration of 12.58 ppm in the flue gas, the arsenic adsorption capacity at 150℃ was only 5.65 mg / g. As the temperature gradually increased to 400℃, the arsenic adsorption capacity of FeCuS-8 / Al2O3 showed a trend of increasing and then decreasing. The adsorption capacity reached its maximum at 300℃, which was 16.01 mg / g. As the temperature continued to rise, the adsorption capacity gradually decreased.

[0112] This is likely because as temperature increases, the diffusion and surface mass transfer rates of arsenic oxide molecules accelerate. Simultaneously, high temperatures provide higher activation energies for electron transfer between the adsorbent and gaseous arsenic oxide molecules, thus accelerating the surface chemical reaction rate and promoting the capture of arsenic oxide molecules in the early stages of heating. With further increases in reaction temperature, the iron-copper sulfide active phase migrates, aggregates, and gradually grows, reducing the number of reactive sites and blocking the alumina pore structure, hindering the diffusion of arsenic oxide molecules and leading to a decrease in arsenic adsorption capacity. Furthermore, excessively high temperatures may cause desorption reactions, which are detrimental to the adsorption and fixation of arsenic oxide.

[0113] like Figure 7 As shown, the arsenic adsorption capacity of FeCuS-8 / Al2O3 was tested under different gaseous arsenic concentrations. This was achieved by adjusting the As... 5+ The amount of standard solution injected is used to control the concentration of gaseous arsenic in the high-temperature fixed-bed reactor. When As... 5+When the standard solution was injected at a volume of 1 mL, the concentration of gaseous arsenic in the reactor was calculated to be 6.29 ppm. The concentration of gaseous arsenic was calculated based on this when other volumes were injected.

[0114] The adsorption capacity reached its maximum of 18.99 mg / g when the gaseous arsenic concentration was 18.87 ppm. As the gaseous arsenic concentration continued to increase, the adsorption capacity decreased slightly and then reached equilibrium, indicating that the arsenic adsorption capacity of FeCuS-8 / Al2O3 had reached saturation at this point. Therefore, the saturated adsorption capacity of FeCuS-8 / Al2O3 for As2O5 is 18.99 mg / g.

[0115] like Figure 8 As shown, the arsenic adsorption capacity of FeCuS-8 / Al2O3 at different reaction times was measured. With fixed As... 5+ With a standard solution injection volume of 3 mL, the reaction time was adjusted by setting the injection pump's liquid delivery time; the reaction temperature was 300℃. Within a reaction time range of 30-120 min, the arsenic adsorption capacity of FeCuS-8 / Al2O3 remained relatively stable, consistently exceeding 16 mg / g. The highest adsorption capacity, at 18.99 mg / g, was observed at a reaction time of 90 min.

[0116] When the reaction time was further extended to 180 min, the adsorption capacity decreased slightly to 14.47 mg / g, and then remained stable. This may be due to the presence of active sulfur species (S) on the adsorbent surface under prolonged high-temperature conditions. 2- / S2 2- The slow reaction of FeCuS-8 / Al2O3 with water vapor or residual trace amounts of O2 in the reactor causes some loss of active sites, and prolonged high temperature may also trigger a slow sintering process. It can be concluded that the reaction time has little effect on the arsenic adsorption performance; under prolonged high temperature reaction conditions, FeCuS-8 / Al2O3 still exhibits good adsorption performance, indicating its good thermal stability.

[0117] In summary, using As 5+ When arsenic standard solution is used as the volatilization source of As2O5, FeCuS-8 / Al2O3 exhibits the best adsorption capacity of 18.99 mg / g at a reaction temperature of 300℃, a reaction time of 90 min, and an arsenic concentration of 18.87 ppm in the flue gas.

[0118] Analysis example 4

[0119] Performance test of FeCuS-8 / Al2O3 adsorption of As2O3.

[0120] like Figure 9As shown, the arsenic adsorption capacity of FeCuS-8 / Al2O3 under different gaseous arsenic concentrations was measured. The reaction time was fixed at 90 min, and the reaction temperature at 300℃. The arsenic adsorption capacity of FeCuS-8 / Al2O3 was measured by adjusting the As... 3+ The concentration of gaseous As₂O₃ in the high-temperature fixed-bed reactor is controlled by the amount of standard solution injected. For example, 1 mL of As₂O₃ is injected... 3+ Based on the standard solution concentration of 6.29 ppm in the reactor, the calculated concentration of gaseous As2O3 in the reactor when 2-5 mL is added is 12.58-31.25 ppm.

[0121] The adsorption capacity changes with gaseous arsenic concentration in a similar trend to that of As₂O₅, initially increasing and then stabilizing. However, the adsorption capacity of FeCuS-8 / Al₂O₃ for As₂O₃ is significantly higher than that for As₂O₅. When the gaseous arsenic concentration is 18.87 mg / g, the adsorption capacity of As₂O₅ reaches its maximum value of 18.99 mg / g, still lower than the adsorption capacity of As₂O₃ at this point (25.35 mg / g), and the As₂O₃ adsorption capacity has not yet reached saturation. As the gaseous arsenic concentration continues to rise to 22.02 mg / g, the As₂O₃ adsorption capacity reaches its maximum of 30.66 mg / g. When the gaseous arsenic concentration further increases, the As₂O₃ adsorption capacity of FeCuS-8 / Al₂O₃ remains essentially balanced. Therefore, FeCuS-8 / Al₂O₃ exhibits better removal performance for As₂O₃ than As₂O₅, with a saturated adsorption capacity reaching 30.66 mg / g.

[0122] like Figure 10 As shown, the arsenic adsorption capacity of FeCuS-8 / Al2O3 at different temperatures (150-400℃) was tested. Under N2 atmosphere, a reaction time of 90 min, and a gaseous arsenic concentration of 22.02 ppm, the effect of temperature on the adsorption performance of FeCuS-8 / Al2O3 on As2O3 was less than that on As2O5. Within a wide temperature range of 150-400℃, the As2O3 adsorption capacity of FeCuS-8 / Al2O3 remained above 20 mg / g, reaching a maximum of 30.66 mg / g at a reaction temperature of 300℃. When the temperature exceeded 300℃, the adsorption capacity did not decrease but remained around 30 mg / g, indicating that FeCuS-8 / Al2O3 exhibits better thermal stability for As2O3 adsorption. Therefore, the optimal temperature for FeCuS-8 / Al2O3 to remove As2O3 is consistent with that of As2O5, both being 300℃, and it demonstrates better thermal stability compared to As2O5.

[0123] like Figure 11As shown, the effects of typical smelting flue gas components on the As2O3 removal performance of FeCuS-8 / Al2O3 were tested. Under the conditions of a reaction temperature of 300℃, a reaction time of 90 min, and a gaseous arsenic concentration of 25.16 mg / g, unlike the traditional metal oxide adsorption performance which is significantly inhibited by SO2, SO2 promoted the adsorption performance of FeCuS-8 / Al2O3 on As2O3 under both low and high concentration conditions. This is because the sulfur atoms on the surface of iron-copper sulfides have steric hindrance, which can prevent competitive adsorption of SO2. At the same time, SO2 is reduced on the adsorbent surface, replenishing the consumed unsaturated sulfur sites and promoting the improvement of adsorption capacity.

[0124] NO, HCl, and O2 all inhibit the adsorption performance of As2O3, with O2 showing the most significant inhibitory effect. This is because O2 removes the highly active metal sites (Fe) on the adsorbent surface. 2+ / Cu + and unsaturated sulfur sites (S 2- / S2 2- Oxidation disrupts the electron-rich interface formed by sulfidation, significantly reducing the adsorbent's ability to capture arsenic. Both NO and HCl compete with As₂O₃ for adsorption, occupying some active sites. Furthermore, NO's oxidizing properties also disrupt the Fe-Cu-S electron-rich interface, further decreasing the adsorption capacity. In addition, when a complex flue gas composition of 5% SO₂, 600 ppm NO, 30 ppm HCl, and 5% O₂ is simultaneously introduced, the As₂O₃ adsorption capacity is 25.32 mg / g, slightly lower than that under a pure N₂ atmosphere.

[0125] Figure 12 The arsenic removal performance of FeCuS-8 / Al2O3 was compared with that of some arsenic adsorbents reported in the literature. It can be seen that in the medium and low temperature range of 150-400℃, FeCuS-8 / Al2O3 has excellent adsorption performance for both As2O3 and As2O5, and its adsorption capacity is significantly higher than that of other adsorbents such as carbon-based adsorbents and metal oxides.

[0126] In summary, using As 3+ When arsenic standard solution is used as the volatilization source of As2O3, FeCuS-8 / Al2O3 exhibits the best adsorption capacity (30.66 mg / g and 97.33%) at a reaction temperature of 300℃, a reaction time of 90 min, and an arsenic concentration of 22.02 ppm in the flue gas. Simultaneously, FeCuS-8 / Al2O3 demonstrates excellent resistance to SO2 and maintains a high arsenic adsorption capacity even in complex flue gas environments.

[0127] Analysis example 5

[0128] Analysis of the adsorption mechanism of pentavalent arsenic.

[0129] like Figure 13 As shown, the surface morphology of FeCuS-8 / Al2O3 after adsorption of As2O5 was first observed by SEM. Figure 13 (a) and (b) are SEM images of FeCuS-8 / Al2O3 after adsorption. It can be seen that FeCuS-8 / Al2O3 after the reaction still presents fine particles, and the size is almost the same as before the reaction, indicating that the reaction process did not change the morphology of FeCuS-8 / Al2O3. Figure 13 Image (c) shows the EDS image of FeCuS-8 / Al2O3 after adsorption. The presence of As indicates that FeCuS-8 / Al2O3 successfully adsorbed As2O5. In addition, it can be seen that the S, Fe, Cu, As and other elements on the surface of the adsorbent are uniformly distributed and without aggregation, indicating that the active sites dispersed on the surface of the support are fully utilized.

[0130] like Figure 14 As shown, the phase changes of the adsorbent before and after the reaction were investigated by XRD. Before the reaction, FeCuS-8 / Al2O3 had phase structures of γ-Al2O3 and CuFe2S3. After the reaction, the γ-Al2O3 phase, which acts as the support, remained intact, consistent with the pre-reaction phase, while the CuFe2S3 phase disappeared, indicating that CuFe2S3 is the reactive phase of the adsorbent. Furthermore, a new peak appeared near 30.3° after the reaction, attributed to Cu... 12 As4S 12 (PDF#73-1689) New peaks appear near 35.6°, 57.3°, and 62.8°, corresponding to the (311), (511), and (440) crystal planes of Fe3O4 (PDF#75-0449), respectively. The formation of the new phase further proves that CuFe2S3 is the reactive phase of the adsorbent, and that Cu, Fe, and S sites all participate in the adsorption reaction. 12 As4S 12 The presence of the phase indicates that As eventually formed a stable ternary compound with S and Cu, and the presence of Fe3O4 indicates that Fe changed from a low oxidation state in the previous sulfide to a higher mixed oxidation state in the oxide (Fe3O4). 2+ / Fe 3+ The results indicate that Fe participates in the electron transfer process of arsenic adsorption. These conclusions demonstrate that the Fe-Cu-S electron-rich interface formed by sulfidation is the fundamental reason for the excellent As2O5 adsorption performance of FeCuS-8 / Al2O3.

[0131] The changes in the valence states of elements on the surface of the adsorbent before and after As2O5 adsorption were quantitatively analyzed. The fine XPS spectra of O1s, Fe2p, and Cu2p before and after the reaction were fitted by peak separation, and the fitting results are summarized in Table 1. This proves that the Fe-Cu-S electron-rich interface formed by sulfidation provides electrons to arsenic species as an electron donor during the adsorption process, thereby capturing arsenic species.

[0132] Table 1. Valence ratio of adsorbent surface elements before and after FeCuS-8 / Al2O3 adsorption of As2O5.

[0133]

[0134] In summary, when As 5+ When the standard solution is the arsenic source, the main arsenic species in the flue gas is As₂O₅. The adsorption of As₂O₅ from the flue gas by FeCuS-8 / Al₂O₃ is a multi-step process driven by a reducing electron-rich interface, involving electron transfer, arsenic sulfidation fixation, and ultimately the formation of a stable crystalline phase. In the initial stage, after gaseous arsenic oxide comes into contact with FeCuS-8 / Al₂O₃, the O atoms in the arsenic oxide gain electrons from the Fe-Cu-S electron-rich interface and combine with Fe and S to form Fe₃O₄ and SO₄, respectively. 2- During the reaction of O with Fe / S, the As-O bond breaks, and As tends to react with S, which has a stronger Lewis base. 2- / S2 2- Combined, forming S-As / S=As bonds, generating [AsS x ] n- Intermediates. Then, at high temperatures, these intermediates further recrystallize with copper ions, gradually forming the thermodynamically stable ternary mineral phase Cu. 12 As4S 12 This fixes arsenic in the crystal lattice.

[0135] Analysis example 6

[0136] Analysis of the adsorption mechanism of trivalent arsenic.

[0137] like Figure 15As shown, the phase changes of FeCuS-8 / Al2O3 before and after As2O3 adsorption were first investigated by XRD. Similar to the adsorption of As2O5, the γ-Al2O3 phase, which serves as the support, still exists after As2O3 adsorption, while the CuFe2S3 phase disappears, indicating that CuFe2S3 is the reactive phase for As2O3 adsorption. New characteristic peaks appeared near 27.8°, 31.4°, 31.7°, 32.1°, and 35.6° after the reaction, indicating the formation of new phases. The peaks at 27.8° and 31.4° belong to the (210) and (211) crystal planes of Cu3AsS4 (PDF#85-1603), respectively, while the peaks at 31.7° and 32.1° correspond to the (004) and (031) crystal planes of Cu3(AsO4)2 (PDF#73-1689), respectively. The peak at 35.6° belongs to the (110) crystal plane of Fe2O3 (PDF#73-0603). Unlike the adsorption of As2O5, the adsorption of As2O3, in addition to forming the ternary compound Cu3AsS4 of As, Cu, and S, also produces Cu3(AsO4)2, indicating that in the reaction process, in addition to bonding with S, some As... 3+ It will also be oxidized to As 5+ Arsenate is formed. The formation of Fe₂O₃ after the reaction indicates that Fe participates in the electron transfer process of arsenic adsorption, transforming from low-valent iron in sulfides to high-valent iron in oxides. The participation of Cu, Fe, and S sites in the As₂O₃ adsorption reaction suggests that the electron-rich Fe-Cu-S interface is the main reason for the high arsenic removal activity of FeCuS-8 / Al₂O₃.

[0138] The changes in the valence states of elements on the surface of the adsorbent before and after As2O3 adsorption were quantitatively analyzed. The fine XPS spectra of O1s, Fe2p, and Cu2p before and after the reaction were fitted with peaks and the fitting results are summarized in Table 2. This further illustrates that the Fe-Cu-S electron-rich interface plays an important role as an electron donor in the adsorption process, promoting the capture of arsenic species.

[0139] Table 2. Valence ratio of adsorbent surface elements before and after FeCuS-8 / Al2O3 adsorption of As2O5.

[0140]

[0141] In summary, when As 3+When the standard solution is the arsenic source, the arsenic species in the flue gas is As2O3. The adsorption of As2O3 in the flue gas by FeCuS-8 / Al2O3 is a process from the catalytic dissociation of As2O3 to the synergistic oxidation on the surface, ultimately achieving the mineralization and fixation of arsenic. After As2O3 diffuses to the surface of the adsorbent, it is first chemically adsorbed by coordinated unsaturated sulfur, and then dissociates under the catalytic action of high temperature and the electron-rich interface of Fe-Cu-S, producing highly active atomic O species, which has strong oxidizing properties and will capture Fe from the surface. 2+ Cu + and some As that has not yet combined with sulfur 3+ The electrons are drawn, causing the As to transform into a higher oxidation state, and further generate Fe2O3 and Cu3(AsO4)2 on the adsorbent surface. Another portion of the As is adsorbed by unsaturated sulfur... 3+ Then it further reacts with unoxidized Cu + It combines to form Cu3AsS4.

[0142] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. A method for preparing an arsenic adsorbent, characterized in that, The steps include: dispersing an iron source, a copper source, and nano-γ-Al2O3 in a solvent, loading iron and copper onto the nano-γ-Al2O3, and then sequentially subjecting the mixture to ultrasonic treatment and drying to obtain a precursor; The precursor is mixed with a sulfur source and then calcined to obtain the arsenic adsorbent. The molar ratio of sulfur in the sulfur source to iron in the iron source is 4-12:1, and the molar ratio of iron in the iron source to copper in the copper source is 0.8-1.2:1; the iron source is ferric nitrate, the copper source is copper nitrate, and the sulfur source is sulfur; the calcination temperature is 300-500℃, and the calcination time is 1-5 hours.

2. The method for preparing the arsenic adsorbent according to claim 1, characterized in that, The ratio of the total mass of the iron source and copper source to the mass of the nano-γ-Al2O3 is 1.0-1.8:

1.

3. An arsenic adsorbent, prepared by the method for preparing the arsenic adsorbent according to any one of claims 1-2, characterized in that, The arsenic adsorbent comprises a γ-Al2O3 matrix and an iron-copper sulfide active phase supported on the surface of the γ-Al2O3 matrix. The iron-copper sulfide active phase comprises CuFe2S3, and the CuFe2S3 forms an electron-rich Fe-Cu-S interface.

4. The arsenic adsorbent according to claim 3, characterized in that, The arsenic adsorbent has a saturated arsenic adsorption capacity greater than 18 mg / g for pentavalent arsenic and a saturated arsenic adsorption capacity greater than 30 mg / g for trivalent arsenic.

5. The application of the arsenic adsorbent as described in claim 3 or 4 in removing arsenic from arsenic-containing flue gas, characterized in that, The method includes the following steps: contacting the arsenic adsorbent with the arsenic-containing flue gas; wherein the arsenic-containing flue gas contains at least one of trivalent arsenic and pentavalent arsenic.

6. The application of the arsenic adsorbent according to claim 5 in removing arsenic from arsenic-containing flue gas, characterized in that, The arsenic concentration in the arsenic-containing flue gas is no higher than 35 ppm; the reaction temperature during the contact process is 150-400℃; and the contact duration is 30-180 min. During the contact process, some arsenic is chemically adsorbed by the active phase of iron-copper sulfides, and then mineralized and fixed into a stable crystalline phase, which includes Cu. 12 As4S 12 At least one of Cu3AsS4 and Cu3(AsO4)2.

7. The application of the arsenic adsorbent according to claim 5 in removing arsenic from arsenic-containing flue gas, characterized in that, The arsenic-containing flue gas also contains sulfur dioxide; the concentration of sulfur dioxide in the arsenic-containing flue gas is not higher than 800 ppm.

8. The application of the arsenic adsorbent according to claim 5 in removing arsenic from arsenic-containing flue gas, characterized in that, The arsenic-containing flue gas also includes at least one of NO, HCl and O2.

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