Composite material for repairing heavy metal pollutants as well as preparation method and application of composite material

Abstract

The invention belongs to the field of environmental governance materials, and relates to a composite material for repairing heavy metal pollutants as well as a preparation method and application thereof. The technical problems that in the prior art, although modified Schwertmannite can synchronously remove arsenic and cadmium, the cadmium removal capacity is still weak, and a single sulfur modified zero-valent iron-based material is low in reaction activity and selectivity are solved. The invention provides a composite material for repairing heavy metal pollutants, the composite material comprises Schwertmannite and sulfur-doped zero-valent iron, the mass ratio of the Schwertmannite to the sulfur-doped zero-valent iron is (0.05-10): 1, the heavy metal pollutants arsenic, cadmium and lead can be synchronously removed, and the adsorbing capacity of cadmium and lead is increased. The invention further provides a preparation method of the composite material, elemental sulfur and zero-valent iron are subjected to ball milling and mixing, and sulfur-doped zero-valent iron is obtained; the composite material for repairing the heavy metal pollutants is obtained by ball-milling and mixing with the Schwertmannite, and the ball-milling modification method is simple, convenient, feasible, efficient and pollution-free. Meanwhile, the invention further provides application of the composite material for repairing the heavy metal pollutants in repairing an arsenic-cadmium-lead heavy metal polluted environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental governance materials, and specifically relates to a composite material for heavy metal pollutant remediation, a preparation method thereof, and an application thereof. Background Art

[0002] Due to human activities such as mineral extraction, smelting, and industrial waste treatment, large areas of soil globally are suffering from heavy metal pollution. Among them, lead, cadmium, and arsenic are heavy metals with extremely serious hazards. They are widely distributed and highly toxic, ranking first, eighth, and second respectively on the priority pollutant list. They can be transferred to surface and groundwater through rainfall, sedimentation, and surface runoff. Thus, the heavy metals in the soil will come into contact with plant roots. Considering the non-degradability of heavy metals, they will accumulate in the food chain and be transferred to the human body and animals through biomagnification, causing serious harm to the health of humans and animals. Lead and cadmium have very different chemical properties from arsenic, and it is difficult to stabilize them simultaneously. Therefore, it is urgent to develop feasible remediation technologies for lead-cadmium-arsenic contaminated soil.

[0003] Among many remediation technologies, the chemical stabilization method has achieved varying degrees of success and has been widely recognized. Common stabilizing materials include limestone, biochar, phosphate compounds, iron-containing materials, etc. Among them, schwertmannite is a naturally occurring iron-containing mineral that is commonly found in acid mine drainage. Schwertmannite is a secondary hydroxyl iron sulfate mineral with poor crystallinity and metastability, and its structure contains a large number of -OH and other active functional groups, which have high passivation ability for arsenic and can be used for the high-efficiency passivation of arsenic in polluted water bodies and soils. However, schwertmannite cannot be used for the passivation of heavy metal cadmium, and it may even cause an increase in the biological activity of cadmium during the soil remediation process. This is mainly because schwertmannite will release sulfate ions during the application process, which will cause a decrease in the pH of the solution, thereby leading to a significant increase in the mobility of cadmium. Research shows that when pH < 5.0, the adsorption of cadmium is almost completely inhibited. In the prior art, schwertmannite has been modified to enable the simultaneous removal of arsenic and cadmium. For example, Chinese Patent Application Publication No. CN115678560A, with an application date of November 08, 2022, and an invention title of "A Mixed Iron Mineral for Simultaneously Remediating Arsenic-Cadmium Heavy Metal Pollution, a Preparation Method Thereof, and an Application Thereof", discloses that the preparation method of the mixed iron mineral includes preparing a ferrous sulfate solution with a certain concentration and adjusting it to an acidic pH; adding a certain amount of hydrogen peroxide for reaction under continuous stirring; then adjusting the pH of the solution to neutral and continuing to stir; separating the formed precipitate and drying it to obtain a mixed iron mineral for simultaneously remediating arsenic-cadmium heavy metal pollution. The mixed iron mineral mainly consists of schwertmannite and ferrihydrite. Although it can simultaneously passivate arsenic and cadmium heavy metals in polluted water and soil, the maximum adsorption capacity for cadmium is still relatively low, only reaching 15 mg / g.

[0004] Zero-valent iron (ZVI) refers to the elemental form in which iron is in its lowest oxidation state (i.e., +0 valence). It is a pure metal iron that has received extensive attention from researchers due to its environmentally friendly, non-toxic, inexpensive, abundant, and strong reducing properties, and has been increasingly valued in the field of water treatment. Although the zero-valent iron technology has been widely applied, there are also prominent disadvantages. For example, nano zero-valent iron has a large specific surface area and high reactivity, but it is prone to agglomeration, oxidation, and poor selectivity, and the preparation process is complex, expensive, and difficult to store; micron iron is easy to prepare and store, but has poor reactivity and low utilization rate. In recent years, single heteroatoms (sulfur, nitrogen, phosphorus) and transition metals have often been used to modify zero-valent iron-based materials, and they have received extensive attention due to the advantages of improving electron transfer, enhancing hydrophobicity, and catalytic performance after modification. However, the reaction activity and selectivity of single sulfur-modified zero-valent iron-based materials are still relatively low.

[0005] Previous studies have mainly focused on the removal of single heavy metals by remediation materials, ignoring the fact that multiple metals are commonly present in the environment. Therefore, it is necessary to develop materials that can effectively remove different types of heavy metals in soil simultaneously, and break through the problems of difficult synchronous stabilization of lead, cadmium, and arsenic, and poor adsorption performance of the passivation and aging products on the surface of single zero-valent iron. Summary of the Invention

[0006] 1. Problems to be Solved

[0007] In view of the technical problems that although modified schwertmannite in the prior art can simultaneously remove arsenic and cadmium, its ability to remove cadmium is still weak, and the surface of single sulfur-modified zero-valent iron-based materials in the prior art is prone to passivation and aging, and the reaction activity and selectivity in removing heavy metal pollutants are relatively low. The composite material for repairing heavy metal pollutants provided by this application has increased reaction activity and selectivity, can simultaneously remove heavy metal pollutants arsenic, cadmium, and lead, and the adsorption amounts of cadmium and lead are increased.

[0008] This application also provides a preparation method for the composite material for repairing heavy metal pollutants, which involves ball milling and mixing schwertmannite and sulfur-doped zero-valent iron, and the operation method is simple, green, and efficient.

[0009] At the same time, this application also provides the application of the composite material for repairing heavy metal pollutants in repairing arsenic-cadmium-lead heavy metal polluted environments.

[0010] 2. Technical Solutions

[0011] To achieve the above object, the technical solution provided is:

[0012] A composite material for repairing heavy metal pollutants, comprising schwertmannite and sulfur-doped zero-valent iron, and the mass ratio of schwertmannite to sulfur-doped zero-valent iron is 0.05 - 10:1.

[0013] Sulfur-modified Zero-Valent Iron (S-ZVI) is a modified material obtained by introducing sulfur elements into Zero-Valent Iron (ZVI) to improve its performance.

[0014] Preferably, the Fe / S molar ratio of the schwertmannite is 5.7.

[0015] Furthermore, the S / Fe molar ratio in the sulfur-doped zero-valent iron is 0.25 - 0.3.

[0016] A preparation method of a composite material for heavy metal pollutant remediation includes the following steps:

[0017] Mix elemental sulfur and zero-valent iron by ball milling, where the S / Fe molar ratio of the elemental sulfur to the zero-valent iron is 0.25 - 0.3, to obtain sulfur-doped zero-valent iron;

[0018] Mix schwertmannite and the sulfur-doped zero-valent iron by ball milling to obtain a composite material for heavy metal pollutant remediation, where the mass ratio of the schwertmannite to the sulfur-doped zero-valent iron is 0.05 - 10:1.

[0019] The composite material for heavy metal pollutant remediation is the schwertmannite / sulfur-doped zero-valent iron composite material.

[0020] Furthermore, the elemental sulfur is micron-sized elemental sulfur powder; the zero-valent iron is micron-sized elemental iron powder.

[0021] Preferably, the particle size of the micron-sized elemental iron powder is 70 mesh - 100 mesh.

[0022] Furthermore, the ball milling abrasive ratio is 4 - 20:1.

[0023] Furthermore, the ball milling is carried out using a planetary ball mill, the rotation speed of the ball milling is 300 rpm - 600 rpm, and the ball milling time is 3 h - 5 h.

[0024] Furthermore, the medium for the ball milling is agate ball milling beads, and the diameter of the agate ball milling beads is 3 mm - 10 mm.

[0025] Furthermore, the agate ball milling beads include agate ball milling bead A, agate ball milling bead B, and agate ball milling bead C. The diameter of the agate ball milling bead A is 10.0 mm - 10.2 mm, the diameter of the agate ball milling bead B is 5.0 mm - 5.2 mm, and the diameter of the agate ball milling bead C is 3.0 mm - 3.2 mm.

[0026] Furthermore, the mass ratio of the agate ball milling bead A, the agate ball milling bead B, and the agate ball milling bead C is 1:3:6.

[0027] Application of a composite material for heavy metal pollutant remediation, application of the composite material for heavy metal pollutant remediation in remediating a heavy metal-polluted environment, or application of the composite material for heavy metal pollutant remediation prepared by the method in remediating a heavy metal-polluted environment; the heavy metal is one or more of arsenic, cadmium and lead.

[0028] Preferably, the application further includes selecting a single remediation agent of the composite material for heavy metal pollutant remediation or compounding it with other passivators according to the actual pollution conditions of the soil and water body to achieve a more efficient treatment effect.

[0029] 3. Beneficial effects

[0030] Adopting the technical solution provided by the present invention, compared with the existing well-known technologies, it has the following beneficial effects:

[0031] (1) The composite material for heavy metal pollutant remediation of the present invention comprises schwertmannite and sulfur-doped zero-valent iron, and the mass ratio of schwertmannite to sulfur-doped zero-valent iron is 0.05-10:1. The composite material for heavy metal pollutant remediation, i.e., the schwertmannite / sulfur-doped zero-valent iron composite material, can simultaneously solidify heavy metal cations and anions in the environment, has the ability to simultaneously remove multiple heavy metals such as arsenic, cadmium and lead, and the adsorption capacity for cadmium and lead increases, mainly due to the synergistic effect between the two in terms of structure and reaction mechanism. The mechanism of arsenic removal by schwertmannite mainly includes: ① Electrostatic adsorption: Schwertmannite is an iron(III) oxyhydroxide with a high specific surface area and abundant hydroxyl groups, and its surface is positively charged, which can effectively remove arsenic through electrostatic adsorption; ② Surface complexation: Surface hydroxyl groups form complexes with arsenic; ③ Sulfate ligand exchange. The mechanism of heavy metal removal by sulfur-doped zero-valent iron includes: ① Electrostatic adsorption; ② Surface complexation. Sulfur doping improves the conductivity and reaction activity of zero-valent iron, which is beneficial to electron migration and interfacial reaction; the S element itself can also form metal sulfide precipitates with heavy metals, with strong stability. The composite material for heavy metal pollutant remediation formed by the combination of schwertmannite and sulfur-doped zero-valent iron shows a more significant flaky structure, rich pore structure, increased specific surface area, and due to the presence of schwertmannite, the surface is rougher, generating more active sites, further improving the reaction activity, enhancing the electron transfer ability, while inhibiting the surface passivation of zero-valent iron and increasing its service life.

[0032] (2) Preparation method of the composite material for heavy metal pollutant remediation of the present invention: preparing sulfur-doped zero-valent iron material by ball-milling reaction of elemental sulfur powder and zero-valent iron is a green and efficient material modification method. The ball-milling process has high-energy impact and shear force, which can promote the uniform doping of sulfur atoms on the iron surface or the formation of Fe-S bonds (such as FeS, FeS2, etc.), avoiding the agglomeration or uneven reaction caused by simple mixing, and at the same time improving the conductivity and electron donor ability of the material; ball-milling can break zero-valent iron particles and form more surface defects and active sites, which is beneficial to the adsorption and reaction of heavy metals. The molar ratio of S / Fe in elemental sulfur and zero-valent iron is 0.25 - 0.3. Sulfur-doped zero-valent iron (S-ZVI) is a core-shell structure, the core is zero-valent iron (ZVI), and the shell is FeSx. It is actually zero-valent iron that plays a role, and the shell plays an accelerating and assisting role. Previous studies have found that if S / Fe is too small, the doping effect of S will become poor, and the obtained sulfur-doped zero-valent iron is not much different from zero-valent iron; if S / Fe is too large, FeSx will become denser, reducing the contact reaction opportunity between zero-valent iron and the outside world. Then ball-mill and mix schwertmannite with sulfur-doped zero-valent iron. The mass ratio of schwertmannite to sulfur-doped zero-valent iron is 0.05 - 10:1 to obtain a composite material for heavy metal pollutant remediation, which can realize a composite material system with clear functional zoning, good interfacial coupling, and full play of the synergistic mechanism, and significantly improve the synchronous heavy metal removal performance. The ball-milling modification method is simple and easy to implement, can be prepared in large quantities, and is efficient, pollution-free, and environmentally friendly.

[0033] (3) Application of the composite material for heavy metal pollutant remediation of the present invention: The composite material for heavy metal pollutant remediation, namely schwertmannite / sulfur-doped zero-valent iron composite material, can simultaneously remediate arsenic, cadmium, and lead heavy metal polluted environments, and has very high adsorption capacity for Cd(II) and Pb(II). The fitting values of the maximum adsorption capacity are as high as 146.4 mg / g and 204.9 mg / g, significantly higher than those of schwertmannite (19.1 mg / g and 103.3 mg / g) and sulfur-doped zero-valent iron (93.4 mg / g and 158.7 mg / g). Description of the Drawings

[0034] Figure 1 Scanning electron microscope images of the schwertmannite / sulfur-doped zero-valent iron composite material (a) and sulfur-doped zero-valent iron (b) prepared in Example 1;

[0035] Figure 2 Comparison diagrams of the adsorption of arsenic, cadmium, and lead by the schwertmannite / sulfur-doped zero-valent iron composite material, schwertmannite, and sulfur-doped zero-valent iron prepared in Examples 1 - 3 respectively;

[0036] Figure 3 Adsorption capacities of the schwertmannite / sulfur-doped zero-valent iron composite material, schwertmannite, and sulfur-doped zero-valent iron prepared in Example 1 for cadmium respectively;

[0037] Figure 4 The adsorption capacities of the schwertmannite / sulfur-doped zero-valent iron composite, schwertmannite, and sulfur-doped zero-valent iron prepared in Example 1 for lead respectively;

[0038] Figure 5 The adsorption capacities of the schwertmannite / sulfur-doped zero-valent iron composite, schwertmannite, and sulfur-doped zero-valent iron prepared in Example 1 for arsenic respectively;

[0039] Figure 6 The passivation effects of the schwertmannite / sulfur-doped zero-valent iron composite, sulfur-doped zero-valent iron, and schwertmannite prepared in Example 1 with the addition of 0.1% on arsenic (a) and lead (b). Detailed implementation manners

[0040] To further understand the content of the present invention, the present invention will be described in detail in combination with the embodiments.

[0041] The following further describes the present application in combination with specific embodiments.

[0042] It should be noted that the terms such as "upper", "lower", "left", "right", "middle", etc. cited in this specification are only for the convenience of description and are not used to limit the scope of implementation. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope of implementation of the present application.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0044] For those conditions not specified in the examples, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0045] As used herein, the term "about" is used to provide flexibility and imprecision associated with a given term, measurement, or value. Those skilled in the art can easily determine the degree of flexibility of a specific variable.

[0046] As used herein, the term "at least one of..." is intended to be synonymous with "one or more of...". For example, "at least one of A, B, and C" clearly includes only A, only B, only C, and their respective combinations.

[0047] Concentrations, amounts, and other numerical data may be presented herein in a range format. It should be understood that such range format is used merely for convenience and brevity and should be interpreted flexibly as including not only the numerical values explicitly recited as the range limits but also all individual numerical values or sub-ranges subsumed within the stated range as if each numerical value and sub-range were explicitly recited. For example, a numerical range of from about 1 to about 4.5 should be interpreted as including not only the explicitly recited limit values of 1 to about 4.5 but also the individual numbers (such as 2, 3, 4) and sub-ranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that recite only one numerical value, such as "less than about 4.5", which should be interpreted as including all of the above values and ranges. In addition, this interpretation should apply regardless of the breadth of the range or feature described.

[0048] In the following examples, the preparation method of Schwertmannite (Sch) is prior art. Refer to Chinese Patent Application Publication No. CN115920825 A, with the invention title "A Modification Method and Application of Schwertmannite".

[0049] Example 1

[0050] The preparation method of the Schwertmannite / sulfur-doped zero-valent iron composite material in this example includes the following steps:

[0051] S1. Preparation of sulfur-doped zero-valent iron

[0052] Weigh 1.6 g of elemental sulfur and 10 g of zero-valent iron and place them in a ball milling jar. The elemental sulfur is micron-sized elemental sulfur powder, and the zero-valent iron is micron-sized zero-valent iron powder. The particle size of the micron-sized zero-valent iron powder is 70 mesh to 100 mesh, and the jar is filled with argon.

[0053] The micron-sized elemental sulfur powder and iron powder have a small particle size, which significantly increases the specific surface area of the material. The larger the specific surface area, the larger the surface area of the material per unit mass in contact with the reactants, thus significantly improving the reaction efficiency. The iron powder with a particle size range of 70 mesh to 100 mesh is more easily dispersed uniformly in the composite material, increasing the uniformity and stability of the material.

[0054] Place the ball milling jar in a planetary ball mill, with a ball milling speed of 400 rpm, a ball milling time of 4 h, and a ball milling material ratio (the mass ratio of the ball milling medium to the material to be milled, i.e., the mixture of elemental sulfur powder and zero-valent iron) of 4.3:1.

[0055] After ball milling, separate the ball milling medium with a sieve to obtain sulfur-doped zero-valent iron (S-ZVI), with an S / Fe molar ratio of 0.28 (S / Fe = 0.28).

[0056] The medium for ball milling is agate ball milling beads, which include agate ball milling beads A with a particle size of 10 mm, agate ball milling beads B with a particle size of 5 mm, and agate ball milling beads C with a particle size of 3 mm; the mass ratio of agate ball milling beads A, agate ball milling beads B, and agate ball milling beads C is 1:3:6.

[0057] S2. Preparation of schwertmannite / sulfur-doped zero-valent iron composite

[0058] Weigh 8 g of sulfur-doped zero-valent iron and 0.8 g of schwertmannite and place them in a ball milling jar, which is filled with argon.

[0059] Place the ball milling jar in a planetary ball mill, with a ball milling speed of 400 rpm, a ball milling time of 4 h, and a ball milling material ratio (the mass ratio of the ball milling medium to the material to be milled, i.e., the mixture of sulfur-doped zero-valent iron and schwertmannite) of 5.68:1.

[0060] After ball milling, separate the ball milling medium with a sieve to obtain the schwertmannite / sulfur-doped zero-valent iron composite (Sch / S-ZVI). The mass ratio of schwertmannite to sulfur-doped zero-valent iron is 0.1.

[0061] The medium for ball milling is agate ball milling beads, which include agate ball milling beads A with a particle size of 10 mm, agate ball milling beads B with a particle size of 5 mm, and agate ball milling beads C with a particle size of 3 mm; the mass ratio of agate ball milling beads A, agate ball milling beads B, and agate ball milling beads C is 1:3:6.

[0062] Taking the sulfur-doped zero-valent iron prepared in step S1 as the control for result analysis:

[0063] Compared with the control sulfur-doped zero-valent iron, the structure composition and morphology of the schwertmannite / sulfur-doped zero-valent iron composite obtained in this example have changed to a certain extent. For example, Figure 1 As shown, the control sulfur-doped zero-valent iron has fewer flaky structures and a smoother surface; while the schwertmannite / sulfur-doped zero-valent iron composite shows more significant flaky structures, and due to the presence of schwertmannite, the surface is rougher; chemical reactions occur during the ball milling process of schwertmannite and sulfur-doped zero-valent iron, generating more active sites.

[0064] If elemental sulfur, sulfur-doped zero-valent iron, and schwertmannite are ball milled and mixed simultaneously, the reaction path is complex, which easily leads to structural disorder and a lack of interface regulation ability. It is difficult to control the final structure morphology and interface construction during the three-component ball milling, and the formed materials often have uneven compositions and uncontrollable properties, which is not conducive to the efficient removal of heavy metals. First, ball mill zero-valent iron and elemental sulfur to prepare structurally stable sulfur-doped zero-valent iron (S-ZVI), and then compound it with schwertmannite, which can achieve a composite material system with clear functional partitioning, good interface coupling, and full play of the synergistic mechanism, significantly improving the synchronous heavy metal removal performance.

[0065] Example 2

[0066] The preparation method of the schwertmannite / sulfur-doped zero-valent iron composite material of this embodiment includes the following steps:

[0067] S1. Preparation of sulfur-doped zero-valent iron

[0068] Weigh 1.6 g of elemental sulfur and 10 g of zero-valent iron and place them in a ball-milling tank. The elemental sulfur is micron-sized elemental sulfur powder, and the zero-valent iron is micron-sized zero-valent iron powder. The particle size of the micron-sized zero-valent iron powder is 70 mesh to 100 mesh, and the tank is filled with argon.

[0069] Place the ball-milling tank in a planetary ball mill, with a ball-milling speed of 400 rpm, a ball-milling time of 4 h, and a ball-milling material ratio (the mass ratio of the ball-milling medium to the material to be milled, i.e., the mixture of elemental sulfur powder and zero-valent iron) of 4.3:1.

[0070] After ball milling, separate the ball-milling medium with a sieve to obtain sulfur-doped zero-valent iron (S-ZVI), with an S / Fe molar ratio of 0.28 (S / Fe = 0.28).

[0071] The ball-milling medium is agate ball-milling beads, which include agate ball-milling beads A with a particle size of 10 mm, agate ball-milling beads B with a particle size of 5 mm, and agate ball-milling beads C with a particle size of 3 mm; the mass ratio of agate ball-milling beads A, agate ball-milling beads B, and agate ball-milling beads C is 1:3:6.

[0072] S2. Preparation of the schwertmannite / sulfur-doped zero-valent iron composite material

[0073] Weigh 8 g of sulfur-doped zero-valent iron and 0.4 g of schwertmannite and place them in a ball-milling tank, and the tank is filled with argon.

[0074] Place the ball-milling tank in a planetary ball mill, with a ball-milling speed of 400 rpm, a ball-milling time of 4 h, and a ball-milling material ratio (the mass ratio of the ball-milling medium to the material to be milled, i.e., the mixture of sulfur-doped zero-valent iron and schwertmannite) of 5.95:1.

[0075] After ball milling, separate the ball-milling medium with a sieve to obtain the schwertmannite / sulfur-doped zero-valent iron composite material (Sch / S-ZVI), and the mass ratio of schwertmannite to sulfur-doped zero-valent iron is 0.05.

[0076] The ball-milling medium is agate ball-milling beads, which include agate ball-milling beads A with a particle size of 10 mm, agate ball-milling beads B with a particle size of 5 mm, and agate ball-milling beads C with a particle size of 3 mm; the mass ratio of agate ball-milling beads A, agate ball-milling beads B, and agate ball-milling beads C is 1:3:6.

[0077] Example 3

[0078] The preparation of the schwertmannite / sulfur-doped zero-valent iron composite material of this embodiment includes the following steps:

[0079] S1. Preparation of sulfur-doped zero-valent iron

[0080] Weigh 1.6 g of elemental sulfur and 10 g of zero-valent iron and place them in a ball-milling tank. The elemental sulfur is micron-sized elemental sulfur powder, and the zero-valent iron is micron-sized zero-valent iron powder. The particle size of the micron-sized zero-valent iron powder is 70 mesh - 100 mesh, and the tank is filled with argon gas;

[0081] Place the ball-milling tank in a planetary ball mill. The ball-milling speed is 400 rpm, the ball-milling time is 4 h, and the ball-milling material ratio (the mass ratio of the ball-milling medium to the material to be milled, i.e., the mixture of elemental sulfur powder and zero-valent iron) is 4.3∶1;

[0082] After the ball-milling is completed, use a sieve to separate the ball-milling medium to obtain sulfur-doped zero-valent iron (S-ZVI), and the S / Fe molar ratio is 0.28 (S / Fe = 0.28).

[0083] The ball-milling medium is agate ball-milling beads, which include agate ball-milling beads A with a particle size of 10 mm, agate ball-milling beads B with a particle size of 5 mm, and agate ball-milling beads C with a particle size of 3 mm; the mass ratio of agate ball-milling beads A, agate ball-milling beads B, and agate ball-milling beads C is 1∶3∶6.

[0084] S2. Preparation of schwertmannite / sulfur-doped zero-valent iron composite

[0085] Weigh 0.8 g of sulfur-doped zero-valent iron and 8 g of schwertmannite and place them in a ball-milling tank. The tank is filled with argon gas;

[0086] Place the ball-milling tank in a planetary ball mill. The ball-milling speed is 400 rpm, the ball-milling time is 4 h, and the ball-milling material ratio (the mass ratio of the ball-milling medium to the material to be milled, i.e., the mixture of sulfur-doped zero-valent iron and schwertmannite) is 5.68∶1;

[0087] After the ball-milling is completed, use a sieve to separate the ball-milling medium to obtain schwertmannite / sulfur-doped zero-valent iron composite (Sch / S-ZVI), and the mass ratio of schwertmannite to sulfur-doped zero-valent iron is 10.

[0088] The ball-milling medium is agate ball-milling beads, which include agate ball-milling beads A with a particle size of 10 mm, agate ball-milling beads B with a particle size of 5 mm, and agate ball-milling beads C with a particle size of 3 mm; the mass ratio of agate ball-milling beads A, agate ball-milling beads B, and agate ball-milling beads C is 1∶3∶6.

[0089] Example 4

[0090] Application of the schwertmannite / sulfur-doped zero-valent iron composite in this example. The adsorption of As(III), Cd(II), and Pb(II) by the schwertmannite / sulfur-doped zero-valent iron composite includes the following steps:

[0091] Accurately weigh 0.02 g of the schwertmannite / sulfur-doped zero-valent iron composite obtained in Example 1 (Sch / S-ZVI = 0.1), 0.02 g of the schwertmannite / sulfur-doped zero-valent iron composite obtained in Example 2 (Sch / S-ZVI = 0.05), and 0.02 g of the schwertmannite / sulfur-doped zero-valent iron composite obtained in Example 3 (Sch / S-ZVI = 10), and sequentially add them to a 50 mg / L As(III)-containing solution with a volume of 50 mL, a 50 mg / L Cd(II)-containing solution with a volume of 50 mL, and a 150 mg / L Pb(II)-containing solution with a volume of 50 mL. Adjust the pH of the solution to 6.0, then place it in a shaker at 28 °C and 180 rpm and oscillate. Use 0.01 M (i.e., 0.01 mol / L) HNO3 and 0.01 M (i.e., 0.01 mol / L) NaOH to maintain the pH of the reaction system at 6.0 ± 0.1. After 18 h, take samples, filter through a 0.45 μm filter membrane, and then measure the contents of As(III), Cd(II), and Pb(II). The final results obtained by analysis are shown in Figure 2 。

[0092] Comparative Example 1

[0093] The application of schwertmannite in this comparative example, the adsorption of As(III), Cd(II), and Pb(II) by schwertmannite, includes the following steps:

[0094] Accurately weigh 0.02 g of schwertmannite, and sequentially add it to a 50 mg / L As(III)-containing solution with a volume of 50 mL, a 50 mg / L Cd(II)-containing solution with a volume of 50 mL, and a 150 mg / L Pb(II)-containing solution with a volume of 50 mL. Adjust the pH of the solution to 6.0, then place it in a shaker at 28 °C and 180 rpm and oscillate. Use 0.01 M (i.e., 0.01 mol / L) HNO3 and 0.01 M (i.e., 0.01 mol / L) NaOH to maintain the pH of the reaction system at 6.0 ± 0.1. After 18 h, take samples, filter through a 0.45 μm filter membrane, and then measure the contents of As(III), Cd(II), and Pb(II). The final results obtained by analysis are shown in Figure 2 。

[0095] Comparative Example 2

[0096] The application of sulfur-doped zero-valent iron in this comparative example, the adsorption of As(III), Cd(II), and Pb(II) by sulfur-doped zero-valent iron, the operation steps are basically the same as those in Comparative Example 1, except that:

[0097] Replace schwertmannite with the sulfur-doped zero-valent iron prepared in step S1 of Example 1; the final results obtained by analysis are shown in Figure 2 。

[0098] Results analysis of Example 4, Comparative Example 1 and Comparative Example 2: To analyze the heavy metal ion concentration in the solution, inductively coupled plasma optical emission spectrometry (ICP-OES) was used to determine the contents of As(III), Cd(II) and Pb(II). The adsorption capacities of the schwertmannite / sulfur-doped zero-valent iron composite material (Sch / S-ZVI = 0.1) obtained in Example 1 for As(III), Cd(II) and Pb(II) were 43.8 mg / g, 36.5 mg / g and 57.6 mg / g respectively; the adsorption capacities of the schwertmannite / sulfur-doped zero-valent iron composite material (Sch / S-ZVI = 0.05) obtained in Example 2 for As(III), Cd(II) and Pb(II) were 36.6 mg / g, 37.2 mg / g and 55.3 mg / g respectively; the adsorption capacities of the schwertmannite / sulfur-doped zero-valent iron composite material (Sch / S-ZVI = 10) obtained in Example 3 for As(III), Cd(II) and Pb(II) were 35.3 mg / g, 32.3 mg / g and 48.7 mg / g respectively, which were higher than the adsorption capacities of the schwertmannite group in Comparative Example 1 for As(III), Cd(II) and Pb(II) (30.0 mg / g, 6.3 mg / g, 19.8 mg / g) and the adsorption capacities of the sulfur-doped zero-valent iron group in Comparative Example 2 for As(III), Cd(II) and Pb(II) (15.8 mg / g, 20.2 mg / g, 32.9 mg / g). Among them, the adsorption capacities of the schwertmannite / sulfur-doped zero-valent iron composite material for Cd(II) and Pb(II) were more than 5 times and more than 2.5 times higher than those of the schwertmannite group respectively, and the adsorption capacity for As(III) was more than 2 times higher than that of the sulfur-doped zero-valent iron group.

[0099] Example 5

[0100] Application of the schwertmannite / sulfur-doped zero-valent iron composite material in this example, the maximum adsorption capacity of the schwertmannite / sulfur-doped zero-valent iron composite material for Cd(II), includes the following steps:

[0101] Accurately weigh 0.02 g of the schwertmannite / sulfur-doped zero-valent iron composite material obtained in Example 1 and add it sequentially to 50 mL of gradient Cd(II)-containing solutions (10 mg / L, 15 mg / L, 30 mg / L, 40 mg / L, 50 mg / L). Adjust the pH of the solution to 6.0, then place it in a shaker at 28 °C and 180 rpm to oscillate. Use 0.01 M (i.e., 0.01 mol / L) HNO3 and 0.01 M (i.e., 0.01 mol / L) NaOH to maintain the pH of the reaction system at 6.0 ± 0.1. After 24 h, take samples, filter through a 0.45 μm filter membrane, and then determine the Cd(II) content. The final results obtained by analysis are shown in Figure 3 .

[0102] The adsorption isotherm data of the schwertmannite / sulfur-doped zero-valent iron composite, schwertmannite, and sulfur-doped zero-valent iron were fitted using the Langmuir adsorption isotherm model. The model formula is as follows:

[0103]

[0104] In the formula, C e (mg / L) represents the remaining concentrations of As(III), Cd(II), and Pb(II) in the solution at the adsorption equilibrium; q e (mg / g) represents the adsorption capacity at the adsorption equilibrium; q m (mg / g) represents the maximum adsorption capacity fitted by the Langmuir adsorption isotherm; K L (L / mg) represents the adsorption constant of the Langmuir model.

[0105] Comparative Example 3

[0106] For the application of schwertmannite in this comparative example, the maximum adsorption capacity of schwertmannite for Cd(II), the operation steps were basically the same as those in Example 5, except that the schwertmannite / sulfur-doped zero-valent iron composite obtained in Example 1 was replaced with schwertmannite. The final results obtained by analysis are shown in Figure 3 .

[0107] Comparative Example 4

[0108] For the application of sulfur-doped zero-valent iron in this comparative example, the maximum adsorption capacity of sulfur-doped zero-valent iron for Cd(II), the operation steps were basically the same as those in Example 5, except that the schwertmannite / sulfur-doped zero-valent iron composite obtained in Example 1 was replaced with sulfur-doped zero-valent iron. The final results obtained by analysis are shown in Figure 3 .

[0109] Result analysis of Example 5, Comparative Example 3, and Comparative Example 4: From the fitting results, it can be seen that the Langmuir adsorption isotherm model can better describe the adsorption of Cd(II)( Figure 3 ) by the schwertmannite / sulfur-doped zero-valent iron composite, schwertmannite, and sulfur-doped zero-valent iron obtained in Example 1, and the correlation coefficient R 2 is greater than 0.9. The schwertmannite / sulfur-doped zero-valent iron composite obtained in Example 1 has a very high adsorption capacity for Cd(II), and the fitted value of the maximum adsorption capacity is as high as 146.4 mg / g, which is significantly higher than the maximum adsorption capacity of schwertmannite for Cd(II) of 19.1 mg / g and the maximum adsorption capacity of sulfur-doped zero-valent iron for Cd(II) of 93.4 mg / g.

[0110] Example 6

[0111] Application of schwertmannite / sulfur-doped zero-valent iron composite material of this embodiment, maximum adsorption capacity of schwertmannite / sulfur-doped zero-valent iron composite material for Pb(II), including the following steps:

[0112] Accurately weigh 0.02 g of the schwertmannite / sulfur-doped zero-valent iron composite material obtained in Example 1 and add it to gradient Pb(II) solutions (10 mg / L, 40 mg / L, 60 mg / L, 80 mg / L, 100 mg / L) with a volume of 50 mL in sequence. Adjust the pH of the solution to 6.0, then place it in a shaker at 28 °C and 180 rpm for oscillation. Use 0.01 M (i.e., 0.01 mol / L) HNO3 and 0.01 M (i.e., 0.01 mol / L) NaOH to maintain the pH of the reaction system at 6.0 ± 0.1. After 24 h, take samples, filter through a 0.45 μm filter membrane, and then measure the Pb(II) content. The final results obtained by analysis are shown in Figure 4 .

[0113] Comparative Example 5

[0114] Application of schwertmannite in this comparative example, maximum adsorption capacity of schwertmannite for Pb(II). The operation steps are basically the same as those in Example 6, except that the schwertmannite / sulfur-doped zero-valent iron composite material obtained in Example 1 is replaced by schwertmannite. The final results obtained by analysis are shown in Figure 4 .

[0115] Comparative Example 6

[0116] Application of sulfur-doped zero-valent iron in this comparative example, maximum adsorption capacity of sulfur-doped zero-valent iron for Pb(II). The operation steps are basically the same as those in Example 6, except that the schwertmannite / sulfur-doped zero-valent iron composite material obtained in Example 1 is replaced by sulfur-doped zero-valent iron. The final results obtained by analysis are shown in Figure 4 .

[0117] Result analysis of Example 6, Comparative Example 5 and Comparative Example 6: It can be seen from the fitting results that the Langmuir adsorption isotherm model can better describe the adsorption of Pb(II) ( Figure 4 ) by the schwertmannite / sulfur-doped zero-valent iron composite material, schwertmannite, and sulfur-doped zero-valent iron obtained in Example 1. The correlation coefficient R 2 is greater than 0.9 in all cases. The schwertmannite / sulfur-doped zero-valent iron composite material obtained in Example 1 has high adsorption ability for Pb(II). The fitting value of the maximum adsorption capacity is as high as 204.9 mg / g, which is higher than the maximum adsorption capacity of schwertmannite for Pb(II) of 103.3 mg / g and the maximum adsorption capacity of sulfur-doped zero-valent iron for Pb(II) of 158.7 mg / g.

[0118] Example 7

[0119] Application of schwertmannite / sulfur-doped zero-valent iron composite material of this embodiment, maximum adsorption capacity of schwertmannite / sulfur-doped zero-valent iron composite material for As(III), including the following steps:

[0120] Accurately weigh 0.02 g of the schwertmannite / sulfur-doped zero-valent iron composite material obtained in Example 1 and add it sequentially to gradient As(III) solutions (10 mg / L, 15 mg / L, 20 mg / L, 30 mg / L, 50 mg / L, 60 mg / L, 70 mg / L) with a volume of 50 mL. Adjust the solution pH to 6.0, then place it in a shaker at 28 °C and 180 rpm for oscillation. Use 0.01 M (i.e., 0.01 mol / L) HNO3 and 0.01 M (i.e., 0.01 mol / L) NaOH to maintain the reaction system pH at 6.0 ± 0.1. After 24 h, take samples, filter through a 0.45 μm filter membrane, and then measure the As(III) content. The final results obtained by analysis are shown in Figure 5 .

[0121] Comparative Example 7

[0122] Application of schwertmannite in this comparative example, maximum adsorption capacity of schwertmannite for As(III). The operating steps are basically the same as those in Example 7, except that the schwertmannite / sulfur-doped zero-valent iron composite material obtained in Example 1 is replaced with schwertmannite. The final results obtained by analysis are shown in Figure 5 .

[0123] Comparative Example 8

[0124] Application of sulfur-doped zero-valent iron in this comparative example, maximum adsorption capacity of sulfur-doped zero-valent iron for As(III). The operating steps are basically the same as those in Example 7, except that the schwertmannite / sulfur-doped zero-valent iron composite material obtained in Example 1 is replaced with sulfur-doped zero-valent iron. The final results obtained by analysis are shown in Figure 5 .

[0125] Result analysis of Example 7, Comparative Example 7 and Comparative Example 8: It can be seen from the fitting results that the Langmuir adsorption isotherm model can better describe the adsorption of As(III) ( Figure 5 ) by the schwertmannite / sulfur-doped zero-valent iron composite material, schwertmannite and sulfur-doped zero-valent iron obtained in Example 1. The correlation coefficient R 2 is greater than 0.9 for all. Although the maximum arsenic adsorption capacity of the schwertmannite / sulfur-doped zero-valent iron composite material (47.7 mg / g) is lower than that of schwertmannite (74.7 mg / g), it is higher than that of sulfur-doped zero-valent iron (33.8 mg / g).

[0126] Combined with Example 4, Comparative Example 1, Comparative Example 2 and Figure 2 it can be known that the adsorption amounts measured in all experiments are lower than the corresponding Langmuir qm The value conforms to the theoretical expectation. q m It represents the limiting adsorption capacity of the material under saturated conditions. Usually, a high concentration is required to approach this value. The adsorption capacity of the schwertmannite / sulfur-doped zero-valent iron composite material (Sch / S-ZVI = 0.1) for As(III) is 43.8 mg / g, which is close to its q m (47.7 mg / g), indicating that it is close to saturation at a concentration of 50 mg / L. Because of its high affinity (the Langmuir constant b is larger), high specific surface area, and the exposure of more active sites, the adsorption process is easier to carry out; the adsorption capacity of schwertmannite for As(III) is 30 mg / g, which is much lower than q m (74.7 mg / g), indicating that a higher concentration is required to reach saturation; thus, it can be seen that the schwertmannite / sulfur-doped zero-valent iron composite material has a better adsorption effect on low-concentration As(III), and its adsorption capacity is higher than that of the schwertmannite group.

[0127] Example 8

[0128] This example provides the application of the schwertmannite / sulfur-doped zero-valent iron composite material prepared in Example 1 in the remediation of arsenic- and lead-contaminated soil, including the following steps:

[0129] Add 0.1% of the schwertmannite / sulfur-doped zero-valent iron composite material (Sch / S-ZVI = 0.1) prepared in Example 1 above to the heavy metal-contaminated soil containing arsenic and lead, and stir evenly; add deionized water to keep the soil moisture content at 50%; cure the soil, take samples on the 7th day of curing, air-dry the soil samples naturally, grind them, and pass through a 10-mesh sieve for storage. The Wenzel method of continuous sequential extraction was used to study the content of non-specifically adsorbed arsenic in the soil. The specific method was as follows: Weigh 1 g of soil into a 50 mL centrifuge tube, shake it with 25 mL of 0.05 M ammonium sulfate solution at a temperature of 25 ± 3 °C for 4 h, then centrifuge the mixture at 10000 rpm for 10 min, and pass the obtained supernatant through a 0.45 μm filter membrane to obtain the content of non-specifically adsorbed arsenic in the soil; the BCR method was used to extract the content of weakly acid-soluble lead in the soil. The specific method was as follows: Weigh 0.5 g of soil into a 50 mL centrifuge tube, shake it with 20 mL of 0.11 M acetic acid solution at a temperature of 25 ± 3 °C for 16 h, then centrifuge the mixture at 10000 rpm for 10 min, and pass the obtained supernatant through a 0.45 μm filter membrane to obtain the content of weakly acid-soluble lead in the soil. The arsenic and lead contents in the liquid were determined by ICP-MS, and the final results obtained by analysis are shown in Figure 6 .

[0130] Comparative Example 9

[0131] The application of schwertmannite in the remediation of arsenic- and lead-contaminated soil provided in this comparative example is basically the same as that in Example 8, except that the schwertmannite prepared in Example 1 is replaced by schwertmannite, and the final results obtained by analysis are shown in Figure 6 .

[0132] Comparative Example 10

[0133] The application of sulfur-doped zero-valent iron in the remediation of arsenic- and lead-contaminated soil provided in this comparative example is basically the same as that in Example 8, except that the schwertmannite / sulfur-doped zero-valent iron composite material prepared in Example 1 is replaced by sulfur-doped zero-valent iron, and the final results obtained by analysis are shown in Figure 6 .

[0134] Result analysis of Example 8, Comparative Example 9 and Comparative Example 10: Non-specifically adsorbed arsenic, also known as weakly adsorbed arsenic, is mainly arsenic adsorbed on the surface of soil particles. Its bioavailability and migration ability are relatively strong, and it can enter the soil solution through ion exchange and be absorbed by plants. Weak acid state lead, also known as weakly acid extractable lead, is a chemical form of lead in the environment, referring to lead that can be extracted under weakly acidic conditions. This type of lead usually exists in exchangeable or carbonate-bound forms and belongs to the form with relatively high biological availability in the environment and is easily absorbed by plants or microorganisms. After testing, after the schwertmannite / sulfur-doped zero-valent iron composite material obtained in Example 1 was used to remediate the heavy metal-contaminated soil containing arsenic and lead, the content of non-specifically adsorbed arsenic decreased from 6.9 mg / kg to 2.4 mg / kg, and the remediation rate was 65%; while the content of weakly acid extractable lead decreased from 58.6 mg / kg to 9.9 mg / kg, and the remediation rate was 83%. After the schwertmannite was used to remediate the heavy metal-contaminated soil containing arsenic and lead, the content of non-specifically adsorbed arsenic decreased to 2.5 mg / kg and the remediation rate was 63%; the content of weakly acid extractable lead decreased to 19.2 mg / kg, and the remediation rate was 67%. After the sulfur-doped zero-valent iron was used to remediate the heavy metal-contaminated soil containing arsenic and lead, the content of non-specifically adsorbed arsenic decreased to 4.6 mg / kg and the remediation rate was 33%, and the content of weakly acid extractable lead decreased to 17.6 mg / kg and the remediation rate was 69%. It shows that after the remediation with the schwertmannite / sulfur-doped zero-valent iron composite material, while the content of arsenic pollutants in the soil remains at a relatively low level, the content of lead pollutants is significantly lower than that of the sulfur-doped zero-valent iron group and the schwertmannite group.

[0135] (Since the cadmium content in the soil had reached the standard before remediation, it could not be measured, but it can be seen from Figure 2 and Figure 3 that the adsorption capacity of cadmium by the schwertmannite / sulfur-doped zero-valent iron composite material is significantly higher than that of the schwertmannite group and the sulfur-doped zero-valent iron group.)

[0136] In summary, the present invention application utilizes ball milling modification. By regulating parameters such as the addition amount of schwertmannite, the ball milling abrasive ratio, the ball milling speed, and the ball milling time, a composite material for repairing heavy metal pollutants, namely, schwertmannite / sulfur-doped zero-valent iron composite material, can be obtained, which can be used for the treatment of arsenic-cadmium-lead co-polluted environments. The schwertmannite / sulfur-doped zero-valent iron composite material has a more significant flaky structure compared with sulfur-doped zero-valent iron. Due to the presence of schwertmannite, the surface is rougher. Chemical reactions occur during the ball milling process between schwertmannite and sulfur-doped zero-valent iron, generating more active sites. Schwertmannite has a unique amorphous structure and is an excellent passivator for soil arsenic pollution. After ball milling modification, the schwertmannite / sulfur-doped zero-valent iron composite material can overcome the characteristics of the opposite chemical behaviors of heavy metals arsenic, cadmium, and lead, achieve the synchronous passivation and repair of arsenic, cadmium, and lead, and at the same time increase the passivation and repair of cadmium and lead, effectively solving the problems in the prior art.

[0137] The above-described embodiments only represent the preferred embodiments of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations, improvements, and substitutions can be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. Composite material for heavy metal pollutant remediation, characterized in that: It contains schwertmannite and sulfur-doped zero-valent iron, and the mass ratio of schwertmannite to sulfur-doped zero-valent iron is 0.05 to 10:

1.

2. The composite material for heavy metal pollutant remediation according to claim 1, wherein: In the sulfur-doped zero-valent iron, the molar ratio of S / Fe is 0.25 to 0.

3.

3. Preparation method of composite material for heavy metal pollutant remediation, characterized in that: It includes the following steps: Mix elemental sulfur and zero-valent iron by ball milling, where the molar ratio of S / Fe of the elemental sulfur to zero-valent iron is 0.25 to 0.3, to obtain sulfur-doped zero-valent iron; Mix schwertmannite and the sulfur-doped zero-valent iron by ball milling to obtain a composite material for heavy metal pollutant remediation, where the mass ratio of schwertmannite to the sulfur-doped zero-valent iron is 0.05 to 10:

1.

4. The preparation method of the composite material for heavy metal pollutant remediation according to claim 3, wherein: The elemental sulfur is micron-sized elemental sulfur powder; the zero-valent iron is micron-sized elemental iron powder.

5. The preparation method of the composite material for heavy metal pollutant remediation according to claim 3, wherein: The ball milling abrasive ratio is 4 to 20:

1.

6. The preparation method of the composite material for heavy metal pollutant remediation according to claim 5, characterized in that: The ball milling is carried out using a planetary ball mill, the rotation speed of the ball milling is 300 rpm to 600 rpm, and the ball milling time is 3 h to 5 h.

7. The preparation method of the composite material for heavy metal pollutant remediation according to claim 6, characterized in that: The medium for the ball milling is agate ball milling beads, and the diameter of the agate ball milling beads is 3 mm to 10 mm.

8. The preparation method of the composite material for heavy metal pollutant remediation according to claim 7, characterized in that: The agate ball milling beads include agate ball milling bead A, agate ball milling bead B, and agate ball milling bead C. The diameter of agate ball milling bead A is 10.0 mm to 10.2 mm, the diameter of agate ball milling bead B is 5.0 mm to 5.2 mm, and the diameter of agate ball milling bead C is 3.0 mm to 3.2 mm.

9. The preparation method of the composite material for heavy metal pollutant remediation according to claim 8, characterized in that: The mass ratio of agate ball milling bead A, agate ball milling bead B, and agate ball milling bead C is 1:3:

6.

10. Application of the composite material for heavy metal pollutant remediation, characterized in that: The application of the composite material for heavy metal pollutant remediation described in claim 1 or 2 in remediating heavy metal-polluted environments, or the application of the composite material for heavy metal pollutant remediation prepared by the method described in any one of claims 3-9 in remediating heavy metal-polluted environments; the heavy metal is one or more of arsenic, cadmium, and lead.

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