A mixed iron mineral for simultaneous remediation of arsenic and cadmium heavy metal pollution, its preparation method and application

Abstract

This invention discloses a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution, its preparation method, and its application, belonging to the field of environmental remediation technology. The method includes preparing a ferrous sulfate solution of a certain concentration and adjusting it to an acidic pH; adding a certain amount of hydrogen peroxide under continuous stirring to initiate the reaction; subsequently adjusting the solution pH to neutral and continuing stirring; separating the formed precipitate, and drying it to obtain the mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution. This mixed iron mineral is mainly composed of Schielene mineral and ferrihydrite. Ferrihydrite adheres to the surface of Schielene mineral, forming a "shell-core" structure, which overcomes the problem of increased cadmium mobility caused by pH reduction during the use of existing iron-based materials. It simultaneously remediates heavy metals arsenic and cadmium, effectively achieving the simultaneous passivation of arsenic and cadmium heavy metals in polluted water and soil.

Description

Technical Field

[0001] This invention belongs to the field of heavy metal pollution remediation, specifically relating to a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of industry and modern agriculture, large amounts of heavy metals have entered the environment, leading to severe heavy metal pollution in soil and water resources. Arsenic and cadmium, in particular, pose significant threats to the environment and human health, and are among the key heavy metal pollutants of concern in my country. According to the "National Soil Pollution Status Survey Bulletin" (Ministry of Environmental Protection and Ministry of Land and Resources, 2014), since 2009, the total emission of cadmium in my country has exceeded 743.77 tons; the overall exceedance rate of heavy metals in farmland soil in my country is 19.4%, with cadmium ranking first among soil pollutants at an exceedance rate of 7.0%. Meanwhile, my country is one of the countries with the most severe arsenic pollution in the world, with a soil arsenic background value of 11.2 mg / kg, far exceeding the global soil background value (5-10 mg / kg). More than 20 million people live in high-risk areas of soil arsenic pollution, and arsenic poisoning incidents are frequent. With the gradual expansion of the scope and intensification of arsenic and cadmium pollution, the treatment and remediation of arsenic- and cadmium-polluted water bodies and soils are of paramount importance.

[0003] Iron-based materials possess a strong ability to bind arsenic, making them highly efficient remediation agents for reducing arsenic concentrations in polluted water and soil. They exhibit significant effects in reducing the mobility and toxicity of arsenic. Among these, Schiele minerals have a much higher arsenic retention capacity than other iron minerals such as goethite, ferrihydrite, and magnetite. Their highly efficient arsenic adsorption mechanism lies in their unique tunnel-like structure and large specific surface area, with adsorption capacities reaching 100-300 mg / g. Numerous studies have applied Schiele minerals to the remediation of arsenic-containing water and soil. Iron-based materials have a much lower adsorption capacity for cadmium than for arsenic, typically 10-40 mg / g. For the remediation of water or soil contaminated with both arsenic and cadmium, iron-based materials are often combined with biochar, alkaline materials, etc., to achieve more efficient treatment results. The main drawback of using Schiele minerals, as a highly efficient arsenic passivating material, in cadmium pollution remediation is that the pH of the system decreases after application, leading to increased cadmium mobility.

[0004] Therefore, developing mixed iron minerals based on Scheres minerals to enhance cadmium adsorption capacity and achieve the goal of simultaneously passivating arsenic and cadmium is of great significance for the treatment of heavy metal pollution caused by arsenic and cadmium co-contamination in my country. Summary of the Invention

[0005] 1. Purpose of the invention

[0006] The purpose of this invention is to provide a mixed iron mineral that can simultaneously remediate arsenic and cadmium heavy metal pollution, as well as its preparation method and application. This mixed iron mineral can overcome the problem that when existing iron-based materials are used for the remediation of arsenic and cadmium heavy metal pollution, the pH of the system decreases, which leads to increased cadmium mobility. It can simultaneously and effectively remove arsenic and cadmium from the soil.

[0007] 2. Technical Solution

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

[0009] This invention provides a method for preparing a mixed iron mineral that can simultaneously remediate arsenic and cadmium heavy metal pollution, comprising the following steps:

[0010] (1) Prepare a ferrous sulfate solution and adjust its pH to 2.0-3.0 with dilute sulfuric acid solution;

[0011] (2) Add hydrogen peroxide under continuous stirring, and then continue stirring for 24±2h, during which the pH is kept constant at 2.0-3.5;

[0012] (3) After stirring, adjust the pH of the above mixed solution to neutral with alkaline solution and continue stirring;

[0013] (4) The precipitate formed by separation is a mixed iron mineral that can simultaneously remediate arsenic and cadmium heavy metal pollution. The main component of the mixed iron mineral is Scherstein mineral, accounting for more than 80%. After the mineral is formed, the pH of the solution is increased so that the remaining iron ions in the solution are wrapped on the surface of Scherstein mineral in the form of amorphous ferrohydrate. In addition, the alkaline solution modifies the composition and structure of Scherstein mineral to a certain extent, reducing the content of sulfate ions in the outer complex form in the surface mineral. At the same time, this treatment process does not affect the sulfate ions in the inner coordination form in the mineral structure, thus maintaining its unique arsenic fixation ability.

[0014] Furthermore, in step (1) above, the concentration of ferrous sulfate is 20-50 g / L.

[0015] Furthermore, the concentration of the dilute sulfuric acid solution in step (1) above is 0.05-2 mol / L.

[0016] Furthermore, in step (2) above, the molar ratio of hydrogen peroxide to ferrous sulfate is 0.5-0.8.

[0017] Furthermore, in step (2) above, hydrogen peroxide is added either all at once or in equal amounts in 3-6 batches within 3 hours.

[0018] Furthermore, the stirring speed in step (2) above is 100-300 rpm.

[0019] Furthermore, the alkaline solution used in step (3) above is a sodium hydroxide solution with a concentration of 0.01-1 mol / L.

[0020] Furthermore, in step (3) above, the pH of the solution after adding alkali is 6.5-7.5.

[0021] Furthermore, in step (3) above, after adding alkali, continue stirring for 0.5-1.0 h.

[0022] Furthermore, the precipitate generated in step (4) above also includes washing and drying.

[0023] Furthermore, in step (4) above, the washing is performed by rinsing with deionized water 3 to 4 times.

[0024] Furthermore, in step (4) above, drying involves completely drying the washed precipitate at 40-55°C.

[0025] The present invention also provides a mixed iron mineral prepared by the above-described method for preparing mixed iron minerals, which can simultaneously remediate arsenic and cadmium heavy metal pollution.

[0026] Furthermore, the aforementioned mixed iron minerals include Schieleite-hydrothermal mixed minerals.

[0027] The present invention also provides a method for preparing the above-mentioned mixed iron minerals and / or the application of the mixed iron minerals prepared by the method for preparing mixed iron minerals.

[0028] Furthermore, the above applications include the remediation of environments contaminated with arsenic and / or cadmium heavy metals.

[0029] Furthermore, the above applications include remediation of environments contaminated with arsenic and cadmium. The reduced sulfate content in the mixed iron minerals results in less sulfate release during application, thus avoiding a drastic drop in solution pH. This overcomes the problem of increased cadmium mobility caused by a decrease in system pH during the use of existing iron-based materials, while simultaneously remediating heavy metals arsenic and cadmium.

[0030] Furthermore, the aforementioned arsenic and cadmium heavy metal pollution includes arsenic and cadmium heavy metal contaminated soil and arsenic and cadmium heavy metal contaminated water bodies.

[0031] Furthermore, the above applications also include selecting a single modified Schiele mineral remediation agent, or using it in combination with other passivating agents, based on the actual soil pollution status, to achieve a more efficient treatment effect.

[0032] 3. Beneficial effects

[0033] Compared with the prior art, the advantages of this invention are as follows:

[0034] (1) The present invention provides a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution, its preparation method and application. The prepared iron mixed mineral is mainly composed of Scheringer mineral and ferrohydrate, with the former accounting for a larger proportion. The iron mixed mineral is not a simple mixture of Scheringer mineral and ferrohydrate, but rather ferrohydrate is attached to the surface of Scheringer mineral to form a structure similar to a "shell-core".

[0035] (2) The present invention provides a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution, its preparation method and application. The alkaline solution modifies the composition and structure of the Scheres mineral to a certain extent, reducing the content of sulfate ions in the outer complex form in the surface mineral. Less sulfate ions are released during the application process, thereby avoiding a sharp drop in the pH of the solution during the application process. This can overcome the problem of increased cadmium mobility caused by the decrease in pH of the system during the use of existing iron-based materials. At the same time, the treatment process does not affect the sulfate ions in the inner coordination form in the mineral structure, thereby maintaining its unique arsenic fixation ability. It can not only maintain its own high-efficiency adsorption capacity for arsenic, but also effectively adsorb and remove cadmium.

[0036] (3) The present invention provides a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution and its preparation method. The mixed iron mineral preparation method is simple, the reaction process does not produce secondary pollution, the raw material cost is low, the mineral generation conversion rate is high, and it can meet the actual needs of large-scale production and application. Attached Figure Description

[0037] Figure 1 The image shows the morphology of the mixed iron mineral prepared in Example 2.

[0038] Figure 2 The adsorption capacity of the mixed iron mineral material prepared in Example 1 for arsenic and cadmium is shown.

[0039] Figure 3 The effect of the mixed iron mineral material prepared in Example 2 on the treatment of arsenic and cadmium co-polluted water.

[0040] Figure 4 The passivation effect of the mixed iron mineral material prepared in Example 3 on arsenic and cadmium co-contaminated soil. Detailed Implementation

[0041] The present invention will be further described below with reference to specific embodiments.

[0042] It should be noted that terms such as "upper", "lower", "left", "right", and "middle" used in this specification are only for clarity of description and are not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of implementation of this invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0044] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0045] As used herein, the term “about” is used to provide for the flexibility and imprecision associated with a given term, measure, or value. Those skilled in the art can readily determine the degree of flexibility for a particular 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” explicitly includes only A, only B, only C, and combinations thereof.

[0047] Concentration, amount, and other numerical data may be presented in range format herein. It should be understood that such range format is used solely for convenience and brevity and should be flexibly interpreted to include not only the values ​​explicitly stated as the limits of the range, but also all individual values ​​or subranges encompassed within the range, as if each value and subrange were explicitly stated. For example, a range of values ​​from about 1 to about 4.5 should be interpreted to include not only the explicitly stated limits of 1 to 4.5, but also individual numbers (such as 2, 3, 4) and subranges (such as 1 to 3, 2 to 4, etc.). The same principle applies to ranges that describe only a single value, such as “less than about 4.5,” which should be interpreted to include all the aforementioned values ​​and ranges. Furthermore, this interpretation should apply regardless of the breadth of the range or characteristic described.

[0048] Example 1

[0049] This embodiment provides a method for preparing a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution, and the prepared mixed iron mineral, specifically including the following steps:

[0050] (1) Prepare a 20 g / L ferrous sulfate solution and adjust its pH to 2.5 with a 0.05 mol / L dilute sulfuric acid solution;

[0051] (2) Under continuous stirring at 100 rpm, hydrogen peroxide was added at once, with a molar ratio of hydrogen peroxide to ferrous sulfate of 0.5. Then, stirring was continued for 24 hours, during which the pH was kept constant at 2.0.

[0052] (3) Adjust the pH of the above mixed solution to 6.5 with 0.01 mol / L sodium hydroxide alkaline solution and continue stirring for 0.5 h;

[0053] (4) The precipitate formed by separation is then washed three times with deionized water and completely dried at 40°C to obtain mixed iron minerals.

[0054] The mixed iron minerals obtained after the reaction in step (2) were used as a control because the pH of the solution was not adjusted.

[0055] Results analysis:

[0056] By measuring the total iron ion concentration in the solution before and after adjusting the pH to 6.5 with alkali, it was found that only 35% of the iron ions in the control mineral synthesis process precipitated as Schiele minerals after step (2), while the proportion precipitated as amorphous ferrohydrate was 65%. In the example, the solution pH was controlled to be constant at 2.0 during the mineral formation process, thereby increasing the proportion of Schiele minerals in the mixed minerals to 90%, thus allowing the mixed iron minerals to retain the unique arsenic-fixing ability of Schiele minerals.

[0057] Example 2

[0058] This embodiment provides a method for preparing a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution, and the prepared mixed iron mineral, specifically including the following steps:

[0059] (1) Prepare a 50 g / L ferrous sulfate solution and adjust its pH to 2.0 with a 2 mol / L dilute sulfuric acid solution;

[0060] (2) Under continuous stirring at 300 rpm, hydrogen peroxide was added in equal amounts in 6 portions over 3 hours. The molar ratio of hydrogen peroxide to ferrous sulfate was 0.8. Then, stirring was continued for 24 hours, during which the pH was kept constant at 2.0.

[0061] (3) Adjust the pH of the above mixed solution to 7.0 with 1 mol / L sodium hydroxide alkaline solution and continue stirring for 1 h;

[0062] (4) The precipitate formed by separation is then washed three times with deionized water and completely dried at 55°C to obtain mixed iron minerals.

[0063] Using the Scheres mineral prepared in steps (1) and (2) as a control, the results were analyzed as follows:

[0064] The mixed iron mineral obtained in this embodiment exhibits certain changes in structure and morphology compared to the control Schielius mineral, such as... Figure 1As shown, the Scheres mineral control exhibits a relatively smooth ellipsoidal structure, while each spherical structure in the mixed iron mineral is covered with many nanoparticles, similar to a "core-shell" structure. Due to the effect of nanoparticles and micropores, its adsorption capacity is also significantly enhanced.

[0065] The iron content in the mixed minerals increased from 42.9% to 49.1%, while the sulfur content decreased from 10.2% to 6.0%, corresponding to a 40% reduction in the sulfate content of the minerals.

[0066] When the mixed iron minerals and Schiele minerals were added at a concentration of 1 g / L to an aqueous solution with an initial pH of 8.0, the pH of the mixed iron mineral group decreased to 6.2, while the pH of the Schiele mineral control group decreased to 3.0. This demonstrates that the addition of the mixed iron minerals to the solution does not cause a drastic drop in pH, thus achieving a certain degree of cadmium adsorption.

[0067] Example 3

[0068] This embodiment provides a method for preparing a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution, and the prepared mixed iron mineral, specifically including the following steps:

[0069] (1) Prepare a 30 g / L ferrous sulfate solution and adjust its pH to 3.0 with a 1 mol / L dilute sulfuric acid solution;

[0070] (2) Under continuous stirring at 200 rpm, hydrogen peroxide was added in three equal amounts over 3 hours. The molar ratio of hydrogen peroxide to ferrous sulfate was 0.7. Then, stirring was continued for 24 hours, during which the pH was kept constant at 3.5.

[0071] (3) Adjust the pH of the above mixed solution to 7.5 with 0.05 mol / L sodium hydroxide alkaline solution and continue stirring for 0.8 h;

[0072] (4) The precipitate formed by separation is then washed three times with deionized water and completely dried at 50°C to obtain mixed iron minerals.

[0073] Experiment Example 4

[0074] This embodiment tests the maximum adsorption capacity of the mixed minerals obtained in Example 1 for As(III) and Cd(II), specifically:

[0075] (1) Accurately weigh 0.040 g of the mixed minerals obtained in Example 1 and add them to a 40 mL gradient As(III) solution (10-300 mg / L). Adjust the pH of the solution to 6.5 and then place it in a shaker at 28 °C and 180 r / min. Use NaOH and HNO3 to maintain the pH of the reaction system at 6.5 ± 0.1. After 24 h, take a sample and filter it through a 0.45 μm filter membrane to determine the As(III) content.

[0076] (2) Accurately weigh 0.040 g of the mixed minerals and add them to 40 mL of a Cd(II)-containing solution (3-60 mg / L). Adjust the pH of the solution to 6.5, then place it in a shaker at 28℃ and 180 r / min. Maintain the pH of the reaction system at 6.5 ± 0.1 with NaOH and HNO3. After 24 h, take a sample, filter it through a 0.45 μm filter membrane, and determine the Cd(II) content. The final results obtained from the analysis are shown in […]. Figure 2 .

[0077] Results analysis: Tests showed that the mixed iron minerals obtained in Example 1 had a very high adsorption capacity for As(III), and the maximum adsorption capacity calculated by combining the adsorption isotherm with the Langmuir curve was as high as 120 mg / g; the mixed iron minerals also had a certain adsorption capacity for Cd(II), with a maximum adsorption capacity of 15 mg / g.

[0078] Experimental Example 5

[0079] This embodiment tests the treatment capacity of the mixed minerals obtained in Example 2 for arsenic and cadmium pollution, specifically as follows:

[0080] As(III) was added to Cd(II) solutions of 2.5, 5, 15, and 30 mg / L to achieve As(III) concentrations of 20 and 50 mg / L in the coexisting solutions, respectively. 0.03 g of mixed iron minerals was weighed and added to 30 mL of a mixed As(III) and Cd(II) solution, and the solution was shaken at 28℃ and 180 rpm. All solutions were prepared using a pH 6.5 MES / MOPS buffer. After 24 h, samples were filtered through a 0.45 μm filter to determine the remaining As(III) and Cd(II) concentrations in the solution. The final results are shown below. Figure 3 As shown.

[0081] Tests showed that the mixed minerals exhibited good removal effects on both arsenic and cadmium. Results indicated that when the initial Cd concentrations were 2.5, 5, 15, and 30 mg / L, and the As(III) concentration in the system was 20 mg / L, the adsorption capacities of the mixed minerals for Cd were 1.32, 1.97, 5.72, and 8.38 mg / L, respectively. When the As(III) concentration increased to 50 mg / L, the adsorption capacities of the mixed minerals for Cd were 1.56, 2.47, 6.47, and 9.18 mg / L, respectively, and the adsorption capacities of the mixed iron minerals for Cd increased by 18.34%, 25.50%, 13.20%, and 9.58%, respectively. Within different treatment groups, the removal rate of the mixed minerals for the 20 mg / L As(III) solution was greater than 97%, and the removal rate for the 50 mg / L As(III) solution was greater than 92%. This indicates that the mixed minerals can remove both As(III) and Cd(II) simultaneously, and that As(III) has a certain promoting effect on the removal of Cd(II).

[0082] Experimental Example 6

[0083] This embodiment tests the ability of the mixed iron minerals obtained in Example 3 to treat arsenic and cadmium contaminated soil, specifically as follows:

[0084] 100g of soil that has passed through a 2mm nylon sieve was weighed and placed in a culture bottle. The following treatment groups were set up: (1) Blank (CK): no material was added as a blank control; (2) 1% mixed iron minerals were added; (3) 5% mixed iron minerals were added; (4) 10% mixed iron minerals were added; each treatment was set up in 3 parallel groups. After the soil and minerals were thoroughly mixed, they were placed at room temperature (25℃) for incubation. 20mL of deionized water was added to the culture bottle to maintain the soil moisture content at 20% during the incubation process. Soil samples were collected after 3 days of incubation. The leaching concentrations of As and Cd in the soil samples were determined by the horizontal shaking method (HJ-557-2010). The final results obtained from the analysis are shown in the figure. Figure 4 .

[0085] Tests showed that the mixed iron minerals obtained in Example 3 could simultaneously remediate soil co-contaminated with arsenic and cadmium. The passivation effect of the mixed iron minerals on As and Cd significantly increased with increasing dosage. Compared with the control, the leaching concentrations of As decreased by 24.24%, 66.99%, and 79.61%, respectively, while the leaching concentrations of Cd decreased by 32.82%, 61.47%, and 75.81%, respectively. The leaching concentration of Cd was close to the surface water standard; the leaching concentration of As was lower than the Class IV water standard limit of the "Surface Water Environmental Quality Standard" (GB3838-2002).

[0086] In summary, the mixed iron minerals prepared by this invention can be used for the simultaneous passivation of arsenic and cadmium in polluted water and soil, and are an effective environmental remediation material for arsenic and cadmium pollution.

[0087] Although specific embodiments of the present invention have been described in detail with reference to the accompanying drawings, this should not be construed as limiting the scope of protection of this patent. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims still fall within the scope of protection of this patent.

Claims

1. A method for preparing a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution, characterized in that, Includes the following steps: (1) Prepare a ferrous sulfate solution and adjust its pH to 2.0-3.0 with dilute sulfuric acid solution; (2) Add hydrogen peroxide under continuous stirring, and then continue stirring for 24±2 h, during which the pH is kept constant at 2.0-3.

5. The molar ratio of hydrogen peroxide to ferrous sulfate added in step (2) is 0.5-0.

8. (3) After stirring, adjust the pH of the above mixed solution to 6.5-7.5 with alkaline solution and continue stirring; (4) The precipitate formed by separation is a mixed iron mineral that can simultaneously remediate arsenic and cadmium heavy metal pollution.

2. The method for preparing a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution according to claim 1, characterized in that, In step (1), the concentration of ferrous sulfate is 20-50 g / L.

3. The method for preparing a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution according to claim 2, characterized in that, In step (2), hydrogen peroxide is added either all at once or in equal amounts in 3-6 batches within 3 hours.

4. The method for preparing a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution according to claim 3, characterized in that, The alkaline solution used in step (3) is a sodium hydroxide solution.

5. The method for preparing a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution according to claim 4, characterized in that, In step (3), after adding alkali, continue stirring for 0.5-1.0 h.

6. The method for preparing a mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution according to claim 5, characterized in that, The precipitate generated in step (4) also includes washing and drying. The washing is done by rinsing with deionized water 3 to 4 times, and the drying is done by completely drying the precipitate at 40-55°C after washing.

7. A mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution, characterized in that, It is prepared by any one of the methods described in claims 1-6 for preparing mixed iron minerals that simultaneously remediate arsenic and cadmium heavy metal pollution.

8. A mixed iron mineral for simultaneously remediating arsenic and cadmium heavy metal pollution according to claim 7, characterized in that, The mixed iron minerals include a mixture of Schieleite and ferroalloy minerals.

9. The application of the mixed iron mineral according to any one of claims 7-8 for the remediation of arsenic and / or cadmium heavy metal contamination environments.

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