A method for modifying schwertmannite and its application

Abstract

The present invention discloses a method for modifying schwertmannite and its application, belonging to the technical field of environmental governance. This method involves soaking schwertmannite in an alkaline solution with a pH of 11-12 and continuously stirring and reacting for 6-8 hours. The mixture is centrifuged and separated, and repeatedly washed with deionized water until the solution is neutral. After drying, the alkali-modified schwertmannite is obtained. When it is applied to the environmental remediation of simultaneous heavy metal arsenic and cadmium pollution, this alkali-modified schwertmannite can overcome the characteristics of the opposite chemical behaviors of heavy metal arsenic and cadmium, and simultaneously passivate heavy metal arsenic and cadmium synchronously. The alkali soaking modification method of the present invention can effectively improve the passivation ability of schwertmannite to cadmium heavy metal, prevent the increase of cadmium mobility and bioavailability during use, and effectively achieve the remediation treatment of arsenic-cadmium co-pollution.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental governance, and specifically relates to a method for modifying schwertmannite and its application. The modified schwertmannite can simultaneously repair arsenic- and cadmium-contaminated soil. Background Art

[0002] Heavy metal pollutants have a wide range of sources and are difficult to degrade and volatilize under natural environmental conditions, posing great harm. Among the many heavy metals polluting the environment, both arsenic and cadmium are highly toxic and carcinogenic, and were listed in the "List of Toxic and Harmful Water Pollutants (First Batch)" issued by the Ministry of Ecology and Environment in 2019. Arsenic and cadmium mainly come from ores, and the amount flowing into the environment through mineral mining and energy combustion worldwide each year is as high as tens of thousands of tons. Processes such as mineral mining and smelting, and fossil energy combustion have polluted the surrounding environment to varying degrees, leading to an increasingly prominent accumulation of arsenic and cadmium in the farmland soil near mining areas. In addition, human activities such as the application of pesticides and fertilizers, sewage irrigation, the use of heavy metal-containing pesticides, herbicides, and feed additives have increased the amount of arsenic and cadmium entering the geochemical cycle. As typical cationic and anionic pollutants, arsenic and cadmium have opposite chemical behaviors. Therefore, the development of passivation materials capable of simultaneously repairing arsenic- and cadmium-contaminated soil is of great significance for environmental heavy metal governance.

[0003] Schwertmannite is a naturally occurring iron-containing mineral that is commonly found in acid mine drainage. Schwertmannite is a secondary hydroxy-iron sulfate mineral with poor crystallinity and metastability, and its structure contains a large number of active functional groups such as -OH and SO4 2- etc., which has a high passivation ability for arsenic and can be used for the efficient passivation of arsenic in polluted water bodies and soils. Studies have found that the maximum adsorption capacity of schwertmannite for trivalent arsenic is as high as 100 - 250 mg / g, and its passivation ability is far higher than that of other iron minerals such as lepidocrocite, ferrihydrite, hematite, and goethite. 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 releases sulfate ions during application, which causes a decrease in the pH of the solution, resulting in a significant increase in the mobility of cadmium. Studies have shown that when pH < 5.0, the adsorption of cadmium is almost completely inhibited.

[0004] Therefore, it is necessary to provide an effective method for modifying schwertmannite to improve its passivation ability for arsenic-cadmium co-contamination and provide a feasible remediation material for the remediation of arsenic- and cadmium-contaminated soil in China. Summary of the Invention

[0005] 1. Problems to be Solved

[0006] In view of the problem that the schwertmannite in the environment cannot effectively remove the heavy metal arsenic and cadmium, the anionic and cationic pollutants, synchronously due to their opposite chemical behaviors, the present invention provides a modification method and application of schwertmannite. The modified schwertmannite can effectively and synchronously remove arsenic and cadmium in the environment.

[0007] 2. Technical Solutions

[0008] To solve the above problems, the technical solutions adopted by the present invention are as follows:

[0009] The present invention provides a modification method of schwertmannite, which is an alkali immersion modification. Specifically, it includes mixing schwertmannite with an alkali solution having a pH value of 11.0 - 12.0 for reaction, and collecting the modified schwertmannite after the reaction. The alkali solution modifies the composition and structure of schwertmannite to a certain extent, reducing the content of sulfate radicals in the mineral, thereby avoiding a sharp drop in the solution pH during use. In addition, its structure evolves into an irregular nanosphere stacking structure. Due to the action of nanoparticles and micropores, its specific surface area can be increased, and thus its adsorption effect can be improved.

[0010] Preferably, the modification method of the above schwertmannite further includes washing the collected modified schwertmannite until the pH of the elution solution reaches neutral (pH 6.5 - 7.5).

[0011] Preferably, the solid-liquid ratio of the above schwertmannite to the alkali solution is 1g:10 - 20mL.

[0012] Preferably, the above alkali solution is an alkaline solution such as sodium hydroxide, potassium hydroxide or ammonia water solution.

[0013] Preferably, the above mixing reaction time is 6 - 8h.

[0014] Preferably, stirring is also included during the above mixing reaction process.

[0015] Preferably, the above collection is to filter the mixing reaction system, and the solid after filtration is the modified schwertmannite.

[0016] Preferably, the above washing is to repeatedly wash the collected modified schwertmannite after the reaction with deionized water to remove the residual alkali solution on the surface until the pH of the elution solution reaches neutral.

[0017] Preferably, the volume ratio of the deionized water used for the above washing to the modified schwertmannite is 20 - 30mL:1g, and the number of washing times is 4 - 7 times.

[0018] Preferably, the modification method of the above schwertmannite further includes drying, and the modified schwertmannite is dried after washing.

[0019] Preferably, the above drying is complete drying carried out under the condition of 40 - 55 °C.

[0020] Preferably, the above method for modifying schwertmannite also includes a method for preparing schwertmannite. The method for preparing schwertmannite is a chemical oxidation method, which specifically includes: preparing a ferrous sulfate solution with a concentration of 10 - 70 g / L, and slowly dropping a certain amount of hydrogen peroxide solution under continuous stirring, where the molar concentration ratio of hydrogen peroxide to ferrous sulfate is 0.5 - 1.0, and the dropping rate is 2 - 6 mL / h; continuously stirring for 24 ± 2 h, and adjusting the pH of the solution every half hour during this period to keep it stable at 2.3 - 2.9; after the stirring ends, separating the formed precipitate, which is schwertmannite.

[0021] Preferably, the above stirring speed is 100 - 300 rpm.

[0022] The present invention also provides a modified schwertmannite prepared by the above method for modifying schwertmannite. This modified schwertmannite is an alkali-modified schwertmannite.

[0023] The present invention also provides a method for preparing a modified schwertmannite, which specifically includes the following steps:

[0024] S1: Preparation of schwertmannite. Prepare a ferrous sulfate solution with a concentration of 10 - 70 g / L, and slowly drop a certain amount of hydrogen peroxide solution under continuous stirring, where the molar concentration ratio of hydrogen peroxide to ferrous sulfate is 0.5 - 1.0, and the dropping rate is 2 - 6 mL / h; continuously stirring for 24 ± 2 h, and adjusting the pH of the solution every half hour during this period to keep it stable at 2.3 - 2.9; after the stirring ends, separating the formed precipitate, which is schwertmannite;

[0025] S2: Modification of schwertmannite: Mix the schwertmannite obtained in S1 with an alkali solution. The pH value of the alkali solution is 11.0 - 12.0, and the solid-liquid ratio of schwertmannite to the alkali solution is 1 g:10 - 20 mL. Mix and stir for 6 - 8 h; after the stirring ends, filter and collect the solid, and repeatedly wash it with deionized water to remove the residual alkali solution on the surface until the pH of the eluate is neutral. After complete drying, the modified schwertmannite is obtained.

[0026] The present invention also provides the application of the above method for modifying schwertmannite and / or the modified schwertmannite prepared by the above method for modifying schwertmannite.

[0027] Preferably, the above application includes repairing arsenic and / or cadmium heavy metal polluted environments.

[0028] Preferably, the above application includes repairing the environment polluted by heavy metals such as arsenic and cadmium. The modified schwertmannite can overcome the opposite chemical behaviors of arsenic and cadmium, and simultaneously repair heavy metals arsenic and cadmium. This is because the content of sulfate in the alkali-modified schwertmannite is less, and the sulfate released during its application is also reduced, avoiding the decrease of the environmental pH value. Therefore, it can repair heavy metals arsenic and cadmium simultaneously. Preferably, the above arsenic-cadmium heavy metal polluted environment includes arsenic-cadmium heavy metal polluted soil, arsenic-cadmium heavy metal polluted water body, etc.

[0029] Preferably, the above application also includes selecting a modified schwertmannite single repair agent according to the actual pollution condition of the soil, or compounding it with other passivators for a more efficient treatment effect.

[0030] 3. Beneficial effects

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) A method for modifying schwertmannite and the modified schwertmannite prepared by the present invention use alkali to modify schwertmannite. The content of sulfate in the modified schwertmannite is significantly reduced (reduced by 71.6% as described in Example 1). Therefore, during its application, the release of sulfate can be reduced, avoiding the decrease of the environmental pH value, preventing the increase of the mobility and bioavailability of cadmium during use, being able to overcome the characteristics of the opposite chemical behaviors of heavy metals arsenic and cadmium, simultaneously passivating heavy metals arsenic and cadmium synchronously, effectively improving the passivation ability of schwertmannite to cadmium heavy metal, and effectively realizing the repair treatment of arsenic-cadmium co-pollution.

[0033] (2) A method for modifying schwertmannite and the modified schwertmannite prepared by the present invention have obvious changes in their morphology, evolving from a relatively smooth elliptical spherical structure on the surface to an irregular nanosphere stacking structure. Due to the action of nanoparticles and micropores, its specific surface area is significantly increased (the specific surface area increases from 69.7 m 2 / g to 261.9 m 2 / g as described in Example 1), thereby increasing its adsorption effect.

[0034] (3) A method for modifying schwertmannite provided by the present invention uses alkali solution soaking, which is simple in operation and low in cost; at the same time, schwertmannite is a naturally occurring iron mineral, and alkali soaking treatment will not introduce other toxic and harmful substances. The use of the materials of the present invention will not cause damage to the ecological environment; at the same time, it has the characteristics of environmental protection and low pollution.

[0035] (4) An alkali-modified schwertmannite provided by the present invention has a very high adsorption capacity for arsenic, and can stably passivate arsenic for a long time during the soil remediation application process. Through the phase transformation process of the mineral, arsenic is fixed inside the mineral structure, blocking the transmission of arsenic into plants. Brief Description of the Drawings

[0036] Figure 1 Morphology diagrams of the modified schwertmannite in Example 1 and the comparative schwertmannite

[0037] Figure 2 pH changes after the modified schwertmannite in Example 1 and the comparative schwertmannite are added to different solutions

[0038] Figure 3 Passivation effects of adding 1% of the modified schwertmannite material in Example 1 on arsenic and cadmium

[0039] Figure 4 Passivation effects of adding 5% of the modified schwertmannite material in Example 2 on arsenic and cadmium

[0040] Figure 5 Passivation effects of adding 0.5%, 1% and 5% of the modified schwertmannite material in Example 3 on arsenic and cadmium Detailed Description of the Invention

[0041] The present invention will be further described below in conjunction with specific embodiments

[0042] It should be noted that the terms such as "upper", "lower", "left", "right", "middle" 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 in which the present invention can be implemented

[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 the present invention 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 reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained by 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 formats are used merely for convenience and brevity and should be interpreted flexibly as including not only the values explicitly recited as the limits of the range but also all individual values or sub-ranges subsumed within the stated range as if each value and sub-range were explicitly recited. For example, a numerical range of about 1 to about 4.5 should be interpreted as including not only the explicitly recited limits 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. Additionally, this interpretation should apply regardless of the breadth of the described range or feature.

[0048] Example 1

[0049] This example provides a method for modifying schwertmannite and the alkali-modified schwertmannite prepared thereby, specifically including the following steps:

[0050] (1) Prepare a ferrous sulfate solution with a concentration of 70 g / L. Under the condition of continuous stirring at 300 rpm, slowly add a certain amount of hydrogen peroxide solution, where the molar concentration ratio of hydrogen peroxide to ferrous sulfate is 0.5, and the dropping rate is 6 mL / h; continuously stir for 24 h, and adjust the solution pH every half hour during this period to keep it stable at 2.5; after the stirring ends, separate the formed precipitate;

[0051] (2) Mix the schwertmannite obtained in (1) with a sodium hydroxide alkali solution. The pH value of the alkali solution is 12.0, and the solid-liquid ratio of schwertmannite to the alkali solution is 1 g:20 mL, and mix and stir for 8 h;

[0052] (3) Filter and collect the schwertmannite after the reaction in (2), and repeatedly wash it with deionized water to remove the residual alkali solution on the surface until the pH of the eluate reaches 7.0, and then obtain the modified schwertmannite after completely drying at 55 °C.

[0053] Result analysis:

[0054] Taking the schwertmannite prepared in step (1) as a comparison, the composition of the alkali-modified schwertmannite obtained in this example has changed. Among them, the iron content has increased from 42.5% to 47.7%, and the sulfur content has decreased from 9.5% to 2.7%, corresponding to a 71.6% reduction in the content of sulfate radicals in the mineral.

[0055] The morphology of the alkali-modified schwertmannite has changed significantly. The mineral has evolved from an elliptical spherical structure with a relatively smooth surface to an irregular nanosphere stacking structure. The morphological structure is shown in Figure 1As shown. Due to the effects of nanoparticles and micropores, the specific surface area of schwertmannite after alkali modification increased from 69.7 m 2 / g to 261.9 m 2 / g.

[0056] Schwertmannite and alkali-modified schwertmannite were added to solutions with different initial pH values. The results are as Figure 2 shown. Compared with the control schwertmannite, when the alkali-modified schwertmannite was added to the solution, it did not cause a sharp drop in the solution pH, thus avoiding the increase in cadmium mobility caused by the decrease in the solution pH value, and it can be used for the remediation of cadmium-polluted environments.

[0057] Example 2

[0058] This example provides a method for modifying schwertmannite and the modified schwertmannite prepared thereby, which specifically includes the following steps:

[0059] (1) Prepare a 10 g / L ferrous sulfate solution. Under the condition of continuous stirring at 100 rpm, slowly add a certain amount of hydrogen peroxide solution, where the molar concentration ratio of hydrogen peroxide to ferrous sulfate is 0.8, and the dropping rate is 2 mL / h; continuously stir for 24 h. During this period, adjust the solution pH every half hour to keep it stable at 2.9; after the stirring ends, separate the formed precipitate;

[0060] (2) Mix the schwertmannite obtained in (1) with a potassium hydroxide alkali solution. The pH value of the alkali solution is 11.0, and the solid-liquid ratio of schwertmannite to the alkali solution is 1 g:10 mL. Mix and stir for 6 h;

[0061] (3) Filter and collect the schwertmannite after the reaction in (2), and repeatedly wash it with deionized water to remove the residual alkali solution on the surface until the pH of the eluate reaches 6.5. After completely drying at 40 °C, the modified schwertmannite is obtained.

[0062] Example 3

[0063] This example provides a method for modifying schwertmannite and the modified schwertmannite prepared thereby, which specifically includes the following steps:

[0064] (1) Prepare a 40 g / L ferrous sulfate solution. Under the condition of continuous stirring at 200 rpm, slowly add a certain amount of hydrogen peroxide solution, where the molar concentration ratio of hydrogen peroxide to ferrous sulfate is 0.7, and the dropping rate is 4 mL / h; continuously stir for 24 h. During this period, adjust the solution pH every half hour to keep it stable at 2.3; after the stirring ends, separate the formed precipitate;

[0065] (2) Mix the schwertmannite obtained in (1) with an ammonia alkali solution. The pH value of the alkali solution is 11.5, and the solid-liquid ratio of schwertmannite to the alkali solution is 1 g:15 mL. Mix and stir for 7 h;

[0066] (3) Filter and collect the schwertmannite after the reaction in (2), and repeatedly wash it with deionized water to remove the residual alkali solution on the surface until the pH of the eluate reaches 7.5. After completely drying at 50 °C, the modified schwertmannite is obtained.

[0067] Experimental Example 4

[0068] This example provides the application of the modified schwertmannite prepared in Example 1 in soil remediation, which specifically includes the following:

[0069] Add 1% of the modified schwertmannite material prepared in Example 1 above to the heavy metal contaminated soil containing arsenic and cadmium, and stir evenly; add deionized water to keep the soil moisture content at 70%; cure the soil, and take samples on the 20th day of curing. The soil samples are naturally air-dried, ground, and passed through a 100-mesh sieve for storage. The continuous sequential extraction method is used to study the content of non-specifically adsorbed arsenic in the soil. The specific method is as follows: Weigh 0.2 g of soil into a 10 mL centrifuge tube, extract it with 0.05 M ammonium sulfate solution at 25 °C for 4 h by shaking, then centrifuge the mixture at 3000 rpm for 15 min, and filter the obtained supernatant through a 0.45 μm filter membrane; The modified BCR sequential extraction method is used to study the content of acid-extractable cadmium. The specific method is as follows: Weigh 0.2 g of soil into a 10 mL centrifuge tube, extract it with 0.11 M acetic acid solution at 25 °C for 16 h by shaking, then centrifuge the mixture at 3000 rpm for 15 min, and filter the obtained supernatant through a 0.45 μm filter membrane. The content of arsenic and cadmium in the liquid is determined by ICP-MS, and the final results obtained by analysis are shown in Figure 3 .

[0070] After testing, after the modified schwertmannite material obtained in Example 1 was used to repair the heavy metal contaminated soil containing arsenic and cadmium, the pollutants in the soil reached a stable state after 20 days of passivation. 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. After the repair treatment, the content of non-specifically adsorbed arsenic decreased from 0.132 mg / kg to 0.063 mg / kg, and the repair rate was 52.3%; while the concentration of cadmium in weak acid extractable state decreased from 0.713 mg / kg to 0.551 mg / kg, and the repair rate was 22.7%.

[0071] Experimental Example 5

[0072] This example provides the application of the modified schwertmannite prepared in Example 2 in soil remediation, which specifically includes the following:

[0073] Add 5% of the modified schwertmannite material prepared in Example 2 above to the heavy metal contaminated soil containing arsenic and cadmium, and stir evenly; add deionized water to keep the soil moisture content at 70%; cure the soil, take samples on the 20th day of curing, air-dry the soil samples naturally, grind them and sieve them through a 100-mesh sieve for preservation. The sequential extraction method was used to study the content of non-specifically adsorbed arsenic in the soil. The specific method was as follows: Weigh 0.2 g of soil into a 10 mL centrifuge tube, extract it with 0.05 M ammonium sulfate solution at 25 °C for 4 h by shaking, then centrifuge the mixture at 3000 rpm for 15 min, and filter the obtained supernatant through a 0.45 μm filter membrane; The improved BCR sequential extraction method was used to study the content of acid-extractable cadmium. The specific method was as follows: Weigh 0.2 g of soil into a 10 mL centrifuge tube, extract it with 0.11 M acetic acid solution at 25 °C for 16 h by shaking, then centrifuge the mixture at 3000 rpm for 15 min, and filter the obtained supernatant through a 0.45 μm filter membrane. The arsenic and cadmium contents in the liquid were measured by ICP-MS, and the final results obtained by analysis are shown in Figure 4 。

[0074] After testing, after the soil was repaired with the modified schwertmannite material obtained in Example 2, the pollutants in the soil reached a stable state after 20 days of passivation. After the repair treatment, the content of non-specifically adsorbed arsenic decreased from 0.132 mg / kg to 0.016 mg / kg, and the repair rate was 87.9%; while the concentration of cadmium in weak acid extract decreased from 0.713 mg / kg to 0.545 mg / kg, and the repair rate was 23.6%.

[0075] Experimental Example 6

[0076] This example provides the application of the modified schwertmannite prepared in Example 3 in soil remediation, which specifically includes the following:

[0077] Add 0.5%, 1%, and 5% of the modified schwertmannite material prepared in Example 3 above to the heavy metal contaminated soil containing arsenic and cadmium, and stir evenly; add deionized water to keep the soil moisture content at 70%; cure the soil, take samples on the 20th day of curing, air-dry the soil samples naturally, grind them and sieve them through a 100-mesh sieve for preservation.

[0078] The contents of available arsenic and available cadmium in the soil were measured separately. The extraction method of available arsenic in the soil was as follows: Weigh 5.00 g of air-dried soil passing through a 2 mm sieve into a 100 mL conical flask, add 25 mL of 0.5 M KH2PO4, place it on a horizontal shaking shaker and shake for 2 h at a rotation speed of 180 r / min, let it stand and filter, and take the supernatant to measure the As concentration; The extraction method of available cadmium in the soil was as follows: Weigh 5.00 g of air-dried soil passing through a 2 mm sieve into a 100 mL conical flask, add 25 mL of DTPA extractant, shake and extract at 25 °C for 2 h at a frequency of 180 rpm / min. After centrifugation, take the supernatant, add 5% nitric acid and then measure. The liquid was used to measure the contents of arsenic and cadmium by ICP-MS, and the final results obtained by analysis are shown in Figure 5 .

[0079] After testing, after the modified schwertmannite material obtained in Example 3 was used for remediation, the pollutant concentration in the soil was significantly lower than that of the untreated group. After treatment with 0.5%, 1%, and 5% passivation materials, the concentration of available arsenic decreased from 6.32 mg / kg to 5.32, 4.87, and 4.17 mg / kg, corresponding to passivation efficiencies of 15.8%, 22.9%, and 34.1% respectively; The concentration of available cadmium decreased from 0.553 mg / kg to 0.460, 0.451, and 0.285 mg / kg, corresponding to passivation efficiencies of 16.8%, 18.5%, and 48.5% respectively.

[0080] In summary, the modified schwertmannite obtained by alkali soaking modification in the present invention can be used for the simultaneous passivation of arsenic and cadmium in the soil. Schwertmannite has a unique amorphous structure and is an excellent passivation agent for soil arsenic pollution. After alkali soaking treatment, it can simultaneously achieve the simultaneous passivation of cadmium, thereby realizing the simultaneous remediation of arsenic and cadmium, effectively solving the problems in the prior art.

[0081] Although the specific implementation manners of the present invention have been described in detail in conjunction with the accompanying drawings, it should not be construed as a limitation on the protection scope of this patent. Within the scope described in the claims, various modifications and deformations that can be made by those skilled in the art without creative labor still fall within the protection scope of this patent.

Claims

1. A method for modifying schwertmannite, characterized in that, The modification method is alkali immersion modification, which includes mixing and reacting schwertmannite with an alkali solution having a pH value of 11.0 to 12.0, and collecting the modified schwertmannite after the reaction; The preparation method of the schwertmannite is a chemical oxidation method, specifically including: preparing a ferrous sulfate solution with a concentration of 10-70 g / L, and slowly dropping a certain amount of hydrogen peroxide solution under continuous stirring, wherein the molar concentration ratio of hydrogen peroxide to ferrous sulfate is 0.5-1.0, and the dropping rate is 2-6 mL / h; continuously stirring for 24 h, and adjusting the solution pH every half hour during this period to keep it stable at 2.3-2.9; after the stirring ends, separating the formed precipitate to obtain schwertmannite; The solid-liquid ratio of the schwertmannite to the alkali solution is 1 g: 10-20 mL.

2. The modified method of schwertmannite according to claim 1, characterized in that, The method further includes washing the collected modified schwertmannite until the pH of the elution solution is neutral; and / or drying the collected modified schwertmannite or the washed modified schwertmannite.

3. The modification method of schwertmannite according to claim 2, wherein, The alkali solution is sodium hydroxide, potassium hydroxide or ammonia water solution.

4. The modification method of schwertmannite according to claim 3, characterized in that, The mixing reaction time is 6-8 h.

5. The modified method of schwertmannite according to claim 4, wherein The washing is to repeatedly wash the collected modified schwertmannite after the reaction with deionized water, and the volume ratio of deionized water to the modified schwertmannite is 20-30 mL: 1 g; and / or the drying is to perform complete drying at 40-55 °C.

6. An alkali-modified schwertmannite, characterized in that, Prepared by the modification method of a schwertmannite according to any one of claims 1-5 above.

7. Application of the modification method of a schwertmannite according to any one of claims 1-5 and / or the alkali-modified schwertmannite according to claim 6 in repairing arsenic and / or cadmium heavy metal contaminated environment.

8. The application according to claim 7, wherein The heavy metal contaminated environment is arsenic and cadmium heavy metal contaminated environment.

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