Modified diatomite for repairing arsenic pollution of water and soil as well as preparation method and application of modified diatomite

Abstract

The invention relates to modified diatomite for repairing arsenic pollution of water and soil as well as a preparation method and application of the modified diatomite. The modified diatomite comprises diatomite as well as granular iron oxide and granular magnesium oxide which are loaded on the surface of the diatomite. According to the modified diatomite disclosed by the invention, the diatomite is subjected to composite modification by utilizing a hydrothermal method and an iron-magnesium compound, the modified diatomite is large in specific surface area, rough in surface and relatively strong in granular sensation, the fixing performance and the adsorption capacity on As (V) and As (III) are remarkably enhanced, and compared with single iron modification or magnesium modification or other metal modification, the modified diatomite has the advantages that the adsorption capacity is greatly improved; the effect of repairing arsenic-polluted water and arsenic-polluted soil is better when being applied to repairing arsenic-polluted water and arsenic-polluted soil. The preparation method of the modified diatomite is simple, high in operability and high in application adaptability; meanwhile, raw material sources are wide, and adaptability is wide.

Description

Technical Field

[0001] The present invention belongs to the technical field of water and soil heavy metal remediation, and relates to a modified diatomaceous earth for remediating arsenic pollution in water and soil, and a preparation method and application thereof. Background Art

[0002] Heavy metal arsenic (As) is a highly toxic heavy metal and a ubiquitous element. It exists in various forms of inorganic arsenic and organic arsenic. Inorganic arsenic is more toxic than organic arsenic. Among them, trivalent arsenic (arsenite) has the strongest mobility, while pentavalent arsenic (arsenate) is the most stable.

[0003] Arsenic poses a serious threat to human health by contaminating soil and groundwater. Ingestion of inorganic arsenic is highly harmful, potentially leading to esophagitis, gastritis, liver disease, kidney damage, nerve damage, and even cancer. Arsenic contamination can also harm the growth of plants and animals, ultimately harming human health through the food chain.

[0004] Arsenic accumulates mainly through natural and anthropogenic sources and enters the environment through soil as the main medium. Natural sources of arsenic pollution in soil include mineral decomposition, erosion and geological activities, bonfires and particulate pollution from vegetation, while anthropogenic sources of arsenic pollution include industrial activities such as mining and smelting, or agriculture (i.e. the use of herbicides, phosphate fertilizers, wood preservatives and pesticides). Arsenic in soil is mainly present as As 3+ and As 5+ As exists as inorganic compounds and can enter the human body through the food chain of irrigation water, aquatic organisms, and plant-based agricultural products, increasing ecological risks. Therefore, remediation of As-contaminated water and soil is crucial to ensuring water environmental safety, the sustainable use of soil resources, and ecological health.

[0005] Currently, there are many approaches to removing arsenic from contaminated water, including oxidation, co-precipitation, membrane filtration, ion exchange, adsorption, and microbial treatment. Among these technologies, adsorption offers advantages over other methods, including high efficiency, ease of operation, minimal pollution, low cost, and regeneration potential.

[0006] The key to adsorption is the selection of adsorption materials, which include both organic and inorganic materials, such as graphene, magnetic nanotubes, fly ash, diatomaceous earth, activated carbon, and more. Diatomaceous earth is a natural soft siliceous sediment composed of the fossilized remains of diatoms. It is chemically stable and possesses unique physical properties, such as high permeability, high porosity, small particle size, low thermal conductivity, high adsorption capacity, and high specific surface area.

[0007] However, natural pure diatomaceous earth has certain limitations in its adsorption capacity for arsenic due to the presence of impurities, lack of surface hydroxyl groups and available active sites, and limited specific surface area. Its adsorption effect often cannot meet the needs of practical applications and needs further improvement.

[0008] Mineral modification methods are increasingly attracting attention in the pollution control field. CN111377780A discloses a natural sodium-based bentonite soil passivator and its preparation method. This passivator can passivate heavy metals and reduce their bioavailability, thereby reducing the absorption of heavy metals by plants and improving the quality of agricultural products. CN105984977A discloses a treatment process for copper-containing wastewater, which uses a modified montmorillonite heavy metal adsorbent to effectively reduce the Cu content in the water. CN109777428A discloses a preparation method for an Fe3O4-based diatomaceous earth heavy metal passivator, which can improve the adsorption of heavy metals Pb and Cd. The removal rate can reduce the accumulation of heavy metals in agricultural products; CN116875317A discloses a soil heavy metal passivator. Although it can reduce the effective content of heavy metals in soil, the sludge in its material often contains a large amount of toxic and harmful heavy metals and even organic pollutants. Long-term input can produce certain cumulative risks and safety hazards to agricultural land. Creating green, risk-free and low-cost adsorption / passivation materials suitable for water and soil pollution control of arsenic and other heavy (type) metals, restoration of contaminated farmland and safe utilization, and promoting their large-scale application have become future industry needs and development goals.

[0009] Up to now, there has been little research on the use of diatomaceous earth modified materials in existing clay mineral passivators for As pollution remediation. The development of corresponding technologies and products is expected to make up for the shortcomings and defects of the industry and help remediate the As-contaminated water and soil environment. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a modified diatomaceous earth for remediating arsenic contamination in water and soil, as well as its preparation method and application. The modified diatomaceous earth provided by the present invention features low cost, a simple preparation process, high efficiency, environmental friendliness, pollution-free operation, and improved soil fertility. While immobilizing heavy metal ions, it poses no risk of secondary pollution and can be used to remediate arsenic-contaminated water and soil.

[0011] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present invention provides a modified diatomaceous earth for repairing arsenic contamination of water and soil. The modified diatomaceous earth comprises diatomaceous earth and granular iron oxide and granular magnesium oxide loaded on the surface of the diatomaceous earth.

[0013] The modified diatomaceous earth involved in the present invention utilizes a hydrothermal method and iron-magnesium compounds to carry out composite modification of diatomaceous earth. The modified diatomaceous earth has a large specific surface area, a rough surface, and a strong granular feel. The fixation performance and adsorption capacity for As(V) and As(III) are significantly enhanced. Compared with single iron modification, magnesium modification, or other metal modification, the modified diatomaceous earth is more effective in repairing arsenic-contaminated water and arsenic-contaminated soil.

[0014] Preferably, the molar ratio of the iron oxide to the magnesium oxide is (3-5): (1-2); the specific point values ​​in (3-5) can be selected from 3, 3.2, 3.3, 3.5, 3.6, 3.8, 4, 4.2, 4.5, 4.8, 5, etc.; the specific point values ​​in (1-2) can be selected from 1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, etc.; other unlisted point values ​​within this numerical range can be selected and will not be repeated here.

[0015] In a second aspect, the present invention provides a method for preparing the modified diatomaceous earth for remediating arsenic contamination of soil and water according to the first aspect, the preparation method comprising the following steps:

[0016] (1) mixing a diatomaceous earth material, a water-soluble iron salt or a hydrate thereof, a water-soluble magnesium salt or a hydrate thereof, a dispersion stabilizer, an alkaline precipitant, and water to obtain a mixed solution, and performing a first reaction to obtain a composite diatomaceous earth solution;

[0017] (2) subjecting the composite diatomite solution to an anaerobic pyrolysis reaction to obtain the modified diatomite.

[0018] The preparation method of the modified diatomite involved in the present invention is simple, highly operable and has strong application adaptability; at the same time, the raw material source is wide and the adaptability is wide.

[0019] Preferably, the water-soluble iron salt or its hydrate is selected from ferric chloride or its hydrate, ferric sulfate or its hydrate, ferric nitrate or its hydrate (eg ferric chloride hexahydrate).

[0020] Preferably, the water-soluble magnesium salt or its hydrate is selected from magnesium chloride or its hydrate, magnesium sulfate or its hydrate, magnesium nitrate or its hydrate (eg magnesium chloride hexahydrate).

[0021] Preferably, the dispersion stabilizer includes citrate or a hydrate thereof (eg, sodium citrate, potassium citrate, sodium citrate dihydrate).

[0022] Preferably, the alkaline precipitant includes any one of urea, ammonia water or sodium hydroxide, or a combination of at least two of them.

[0023] Preferably, the diatomaceous earth material is dry diatomaceous earth of 100-200 mesh (eg, 100 mesh, 120 mesh, 140 mesh, 160 mesh, 180 mesh, 200 mesh, etc.).

[0024] Preferably, the amount ratio of the diatomaceous earth material, the water-soluble iron salt or its hydrate, and the water-soluble magnesium salt or its hydrate is (0.5-2) g: (0.3-0.5) mol: (0.1-0.2) mol; wherein the specific point value in (0.5-2) can be selected from 0.5, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc.; wherein (0.3-0.5) The specific point values ​​can be selected from 0.3, 0.32, 0.34, 0.35, 0.38, 0.4, 0.42, 0.45, 0.47, 0.48, 0.5, etc.; the specific point values ​​in (0.1-0.2) can be selected from 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, etc.; other unlisted point values ​​within this numerical range can be selected and will not be listed here.

[0025] Preferably, the mass ratio of the dispersing stabilizer to the diatomaceous earth material is (0.01-0.03):(0.5-2); the specific point values ​​in (0.01-0.03) can be selected from 0.01, 0.015, 0.02, 0.025, 0.03, etc.; the specific point values ​​in (0.5-2) can be selected from 0.5, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc.; other unlisted point values ​​within this numerical range can be selected and will not be repeated here.

[0026] Preferably, the mass ratio of the alkaline precipitant to the diatomaceous earth material is (0.03-0.09):(0.5-2); the specific point values ​​in (0.03-0.09) can be selected from 0.03, 0.04, 0.05, 0.06, 0.065, 0.07, 0.075, 0.08, 0.085, 0.09, etc.; the specific point values ​​in (0.5-2) can be selected from 0.5, 0.8, 1, 1.2, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, etc.; other unlisted point values ​​within this numerical range can be selected and will not be repeated here.

[0027] Preferably, the pH value of the mixed solution of the first reaction is 6-8, for example, pH=6, pH=6.5, pH=7, pH=7.5, pH=8, etc.

[0028] Preferably, the first reaction is carried out at 20-35°C (e.g., 20°C, 22°C, 25°C, 28°C, 30°C, 33°C, 35°C, etc.) for 10-20h (e.g., 10h, 12h, 14h, 16h, 18h, 20h, etc.).

[0029] In the present invention, the first reaction removes ash from the diatomite. Simultaneously, it causes some alkaline substances in the diatomite to react with acids to form soluble salts, which can be removed during post-processing. Furthermore, iron and magnesium elements, as well as their hydrated forms, can be loaded onto the diatomite material.

[0030] Preferably, the anaerobic pyrolysis reaction is carried out at 130-180°C (e.g., 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, etc.) for 12-30h (e.g., 12h, 15h, 18h, 20h, 25h, 30h, etc.).

[0031] Other unlisted point values ​​within the above numerical range can be selected and will not be described in detail here.

[0032] In the present invention, the oxygen-free pyrolysis is preferably carried out in a muffle furnace.

[0033] Preferably, after the anaerobic pyrolysis reaction is completed, solid-liquid separation, washing, drying and crushing are performed.

[0034] In the present invention, the washing agent is preferably deionized water; the number of washings is preferably 3-5 times. In the present invention, the washing can remove the water-soluble iron salt and water-soluble magnesium salt that are not loaded on the original diatomaceous earth material.

[0035] In the present invention, the solid-liquid separation method is preferably vacuum filtration; the drying temperature is preferably 70-90°C. The present invention does not impose any specific restrictions on the drying time, as long as the moisture can be completely removed. The present invention does not impose any specific restrictions on the grinding parameters, as long as the ground product can be 100-200 mesh.

[0036] In the present invention, the oxygen-free pyrolysis reaction can ultimately convert the iron and magnesium salts or their hydrates in the diatomaceous earth composite into stable iron and magnesium oxides, which are more firmly supported on the surface of the diatomaceous earth in the form of particles.

[0037] In the present invention, the water-soluble iron salt or its hydrate, the water-soluble magnesium salt or its hydrate, the dispersion stabilizer, and the alkaline precipitant can be mixed in the form of an aqueous solution. The concentration of the water-soluble iron salt aqueous solution is preferably 0.2-0.3 mol / L; the concentration of the water-soluble magnesium salt aqueous solution is preferably 0.05-0.1 mol / L; the concentration of the sodium citrate dihydrate aqueous solution is preferably 0.01-0.02 mol / L; and the concentration of the urea aqueous solution is preferably 0.2-0.3 mol / L.

[0038] In a third aspect, the present invention provides the use of the modified diatomaceous earth described in the first aspect or the preparation method described in the second aspect in the remediation of arsenic contamination in soil or water.

[0039] Preferably, the modified diatomaceous earth is used to remediate soil arsenic contamination, and the ratio of the modified diatomaceous earth to arsenic-containing soil is 166-1666 kg / mu (for example, 166 kg / mu, 200 kg / mu, 300 kg / mu, 400 kg / mu, 600 kg / mu, 800 kg / mu, 1000 kg / mu, 1666 kg / mu, etc.).

[0040] Preferably, the modified diatomaceous earth is used to repair arsenic pollution in water, and the ratio of the modified diatomaceous earth to arsenic-containing water is 0.1-5 g / L (for example, 0.1 g / L, 0.5 g / L, 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 4 g / L, 4.5 g / L, 5 g / L, etc.).

[0041] Other unlisted point values ​​within the above numerical range can be selected and will not be described in detail here.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] The modified diatomite disclosed herein utilizes a hydrothermal method and a composite modification of iron and magnesium compounds to produce a large specific surface area, a rough surface, and a strong granular feel. The modified diatomite significantly enhances its As(V) and As(III) fixation and adsorption capacity, significantly improving its effectiveness in remediating arsenic-contaminated water and soil compared to single iron, magnesium, or other metal modifications. The modified diatomite disclosed herein has a simple preparation method, strong operability, and broad application adaptability. Furthermore, the modified diatomite is readily available from a wide variety of sources and has broad applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a SEM image of the original diatomite at 20,000 times the size;

[0045] Figure 2 This is a 20,000-fold SEM image of modified diatomaceous earth;

[0046] Figure 3 are the XRD spectra of original diatomite (DE) and modified diatomite (FMDE);

[0047] Figure 4 This is the evaluation result of the recycling ability of modified diatomaceous earth for removing As(V);

[0048] Figure 5 This is a graph showing the evaluation results of the recyclable regeneration ability of modified diatomaceous earth for removing As(III). DETAILED DESCRIPTION

[0049] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0050] Example 1

[0051] This embodiment provides a modified diatomaceous earth, and the preparation method thereof is as follows:

[0052] (1) washing the raw diatomaceous earth, drying it at 80° C., and crushing it through a 100-mesh sieve to obtain the diatomaceous earth raw material;

[0053] (2) Take 10g of the obtained diatomite raw material, add Fe 3+ / Mg 2+ 200 mL of a mixed solution of ferric chloride hexahydrate and magnesium chloride hexahydrate at a molar ratio of 3:1 (total molar amount 4 mol) was added; then 50 mL of a mixed aqueous solution of 0.01 mol / L sodium citrate dihydrate and 0.3 mol / L urea was added; the pH of the solution was adjusted to pH = 7 and stirred uniformly at 25°C under magnetic stirring for 12 hours;

[0054] (3) The obtained reaction liquid was placed in a polytetrafluoroethylene-lined stainless steel autoclave, placed in a muffle furnace, and subjected to anaerobic pyrolysis at 150°C for 24 hours. After cooling to 25°C, the reaction liquid was taken out, and a vacuum pump was used to separate the solid and liquid by vacuum filtration to obtain a solid substance. The solid substance was repeatedly washed with deionized water, dried at 80°C, and ground through a 100-mesh sieve to obtain a modified diatomaceous earth material.

[0055] The specific surface area of ​​the prepared modified diatomite material and the diatomite raw material was characterized by a fully automatic specific surface and porosity analyzer BET (Micromeritics ASAP 2460, USA). The specific surface area of ​​the modified diatomite material was 223.89 m 2 ·g -1 Compared with the unmodified carbonized composite, it increased by 111 times. The increase in specific surface area increased the adsorption sites on the surface of the modified diatomite, which is beneficial to improving the adsorption performance of the modified diatomite for arsenic.

[0056] The prepared modified diatomite material and diatomite raw material were characterized by SEM, and the material morphology and surface element distribution were observed using a field emission scanning electron microscope SEM (TESCAN MIRA LMS, Czech Republic). Figure 1 This is a 20,000-fold SEM image of diatomaceous earth raw material; Figure 2 This is a 20,000-fold SEM image of modified diatomite; Figure 1 and Figure 2 It can be seen that the modified diatomaceous earth is diatomaceous earth with a smooth surface and rough granular iron oxide and magnesium oxide supported on the surface of the diatomaceous earth.

[0057] The prepared modified diatomite material and diatomite raw material were characterized by XRD, such as Figure 3 As shown, DE represents unmodified diatomaceous earth and FMDE represents modified diatomaceous earth; Figure 3 It can be seen that iron and magnesium in modified diatomaceous earth mainly exist in the form of oxides.

[0058] Example 2

[0059] This embodiment provides a modified diatomaceous earth, and the preparation method thereof is as follows:

[0060] (1) washing the raw diatomaceous earth, drying it at 80° C., and crushing it through a 100-mesh sieve to obtain the diatomaceous earth raw material;

[0061] (2) Take 10g of the obtained diatomite raw material, add Fe 3+ / Mg 2+ 200 mL of a mixed solution of ferric chloride hexahydrate and magnesium chloride hexahydrate at a molar ratio of 5:2 (total molar amount 4 mol) was added; then 50 mL of a mixed aqueous solution of 0.02 mol / L sodium citrate dihydrate and 0.15 mol / L urea was added; the pH of the solution was adjusted to pH = 6, and the mixture was stirred uniformly at 30°C under magnetic stirring for 10 hours;

[0062] (3) The obtained reaction liquid was placed in a polytetrafluoroethylene-lined stainless steel autoclave, placed in a muffle furnace, and subjected to anaerobic pyrolysis at 170°C for 20 hours. After cooling to 25°C, the reaction liquid was taken out, and a vacuum pump was used to separate the solid and liquid by vacuum filtration to obtain a solid substance. The solid substance was repeatedly washed with deionized water, dried at 80°C, and ground through a 100-mesh sieve to obtain a modified diatomaceous earth material.

[0063] Example 3

[0064] This embodiment provides a modified diatomite, and the preparation method thereof is different from that of embodiment 1 only in that in step (2), 10 g of the obtained diatomite raw material is taken, Fe 3+ / Mg2+ Prepare a 1:1 molar ratio of ferric chloride hexahydrate and magnesium chloride hexahydrate (200 mL, total molar weight 4 mol). Add 50 mL of a 0.01 mol / L aqueous solution of sodium citrate dihydrate and 0.3 mol / L urea. Adjust the pH of the solution to 7 and stir uniformly at 25°C under magnetic stirring for 12 hours. All other steps remain unchanged.

[0065] Comparative Example 1

[0066] This comparative example provides a modified diatomaceous earth. The preparation method thereof differs from that of Example 1 only in that, in step (2), 10 g of the obtained diatomaceous earth raw material is added sequentially to 200 mL of ferric chloride hexahydrate solution (molar weight 4 mol); then, 50 mL of a mixed aqueous solution of sodium citrate dihydrate with a concentration of 0.01 mol / L and urea with a concentration of 0.3 mol / L is added; the pH of the solution is adjusted to pH = 7, and the mixture is uniformly stirred at 25° C. under magnetic stirring for 12 h. The other steps remain unchanged.

[0067] Comparative Example 2

[0068] This comparative example provides a modified diatomaceous earth. The preparation method thereof differs from that of Example 1 only in that, in step (2), 10 g of the obtained diatomaceous earth raw material is added sequentially to 200 mL of a magnesium chloride hexahydrate solution (molar weight 4 mol); then, 50 mL of a mixed aqueous solution of 0.01 mol / L sodium citrate dihydrate and 0.3 mol / L urea is added; the pH of the solution is adjusted to pH = 7, and the mixture is uniformly stirred at 25° C. under magnetic stirring for 12 h. The other steps remain unchanged.

[0069] Test Example 1

[0070] Changes in the adsorption of arsenic by modified diatomaceous earth materials over time:

[0071] Weigh 0.02 g of diatomaceous earth (DE) and modified diatomaceous earth (FMDE) obtained in Example 1, place them in 50 mL centrifuge tubes, and add 20 mL of 50 mg·L -1 As(V) solution and 30 mg·L -1 As(III) solution was stirred at 25°C at 180 r·min -1 The mixture was oscillated at a constant speed for 5, 10, 20, 30, 50, 70, 100, 150, 200, 300, and 360 min, respectively, and then centrifuged. The supernatant was filtered and the arsenic content was determined by atomic fluorescence spectrometry. The adsorption amount was calculated based on the difference with the initial concentration. Each treatment was repeated 3 times. The results are shown in Tables 1 and 2. Table 1 shows the adsorption amount of As(V) by diatomaceous earth and modified diatomaceous earth, and Table 2 shows the adsorption amount of As(III) by diatomaceous earth and modified diatomaceous earth.

[0072] Table 1

[0073]

[0074] Table 2

[0075]

[0076] It can be seen from the data results in Table 1 and Table 2 that the modified diatomaceous earth provided by the present invention has a much higher adsorption capacity for As(V) and As(III) than that of the unmodified diatomaceous earth.

[0077] Test Example 2

[0078] Removal capacity of modified diatomaceous earth materials for different concentrations of arsenic in polluted water:

[0079] 0.02 g of diatomaceous earth (DE) and the modified diatomaceous earth obtained in Examples 1-3 and Comparative Examples 1-3 were taken and placed in a 50 mL centrifuge tube. 20 ml of 0.1, 0.5, 1, 2, 5, 10, 20, 40, 60, and 80 ppm As(V) solution and As(III) solution were added, respectively. Each treatment was repeated 3 times. After shaking at 25° C. for 12 h, the mixture was taken out and centrifuged and filtered. The arsenic concentration in the filtrate was measured. The removal rate of arsenic in contaminated water by the two materials was compared. The results are shown in Table 3.

[0080] Table 3

[0081]

[0082]

[0083] As can be seen from the data results in Table 3, when the arsenic concentration in the water is 0.1-80 ppm, the modified diatomaceous earth involved in the present invention has a much higher removal rate for As(V) and As(III) than the unmodified diatomaceous earth and the modified diatomaceous earth prepared in the comparative example; as the arsenic concentration in the water increases, the arsenic removal rates of the modified diatomaceous earth and diatomaceous earth are both on a downward trend, but the arsenic removal rate of the modified diatomaceous earth is still much higher than that of the unmodified diatomaceous earth and the modified diatomaceous earth prepared in the comparative example.

[0084] Test Example 3

[0085] The removal capacity of modified diatomaceous earth materials in different dosages for arsenic in contaminated water:

[0086] Weigh 0.002 g, 0.01 g, 0.02 g, 0.04 g, 0.08 g, and 0.1 g of diatomaceous earth (DE) and modified diatomaceous earth (FMDE) obtained in Example 1, respectively, and place them in 50 mL centrifuge tubes. Add 20 mL of 50 mg·L -1As(V) solution and 20 mL of 30 mg·L -1 As(III) solution was stirred at 25°C at 180 r·min -1 The mixture was shaken at a constant speed for 12 hours, then centrifuged. The supernatant was filtered and the arsenic content was determined using an atomic fluorescence spectrometer. The arsenic removal rates of the two materials were compared. Each treatment was repeated three times. The results are shown in Table 4.

[0087] Table 4

[0088]

[0089]

[0090] From the data results in Table 4, it can be seen that the adsorption effect of modified diatomaceous earth on As(V) solution and As(III) solution is much higher than that of diatomaceous earth, and the adsorption effects of diatomaceous earth and modified diatomaceous earth on As(V) solution and As(III) solution increase with the increase of adsorbent dosage. The removal rate of diatomaceous earth for As(V) solution is 1.12%-8.57%, and the removal rate of modified diatomaceous earth for As(V) solution is 6.64%-76.89%; the removal rate of diatomaceous earth for As(III) solution is 4.95%-25.14%, and the removal rate of modified diatomaceous earth for As(III) solution is 39.11%-67.79%. With the increase of material dosage, its adsorption effect on arsenic is significantly improved.

[0091] Test Example 4

[0092] Effect of modified diatomaceous earth materials on soil arsenic fixation:

[0093] (1) Test soil

[0094] Two soil types were selected, soil S1 and soil S2. The collected soil samples were naturally air-dried and passed through a 2 mm sieve for later use. 100 g of soil was passed through a 0.149 mm sieve and the relevant indicators were determined using conventional soil agrochemical analysis methods. Among them, S1 was an As-contaminated paddy soil in the south, with a total As content of 204.9 mg kg -1 , water-soluble As content 0.40 mg·kg -1 ; S2 soil As contaminated vegetable soil in northern China was prepared by adding a certain concentration of Na3AsO5 solution and aging for 3 months, and then air-drying, grinding and sieving. The total As content of As contaminated soil S2 was 185.2 mg·kg -1 , the water-soluble As content is 3.40 mg·kg -1 The basic properties of the soil are shown in Table 5.

[0095] Table 5

[0096]

[0097]

[0098] (2) Test materials

[0099] The modified diatomaceous earth obtained in Examples 1-3 and Comparative Examples 1-3 was selected.

[0100] (3) Soil culture experiment

[0101] Two types of soil were selected for the incubation experiment, As-contaminated soil S1 and As-contaminated soil S2. 120 g of soil was accurately weighed and placed in a 250 mL beaker. Subsequently, each group of modified diatomaceous earth was applied to the soil at different mass ratios (0.1%, 0.5%, 1% or 5%). The modified diatomaceous earth and soil were fully mixed. At the same time, a blank soil control (CK) treatment was set up. All treatments maintained 70% of the field water holding capacity and were placed in a constant temperature incubator for incubation. Each treatment was repeated three times. Water was added by constant weight method to maintain 70% of the field water holding capacity for incubation. Samples were taken when the incubation was carried out for 15 days, and the available As content in the soil (mg kg -1 ).

[0102] The above arsenic contents were determined using hydride generation-atomic fluorescence spectrometry (HG-AFS 9120, Beijing Jitian Instruments, with a detection limit of <0.02 μg·L -1 ) determination.

[0103] The calculation formula for the passivation efficiency η of modified diatomite material on soil As is:

[0104] η=(C0-C e ) / C0×100%;

[0105] Where C0 and C e The available As content (mg·kg -1 ).

[0106] The results are shown in Tables 6 and 7.

[0107] Table 6

[0108]

[0109]

[0110] Table 7

[0111]

[0112] The data in Tables 6 and 7 show that, for As-contaminated soils S1 and S2, application of the modified diatomaceous earth according to the present invention significantly reduced the water-soluble As content in the soils compared to application of the modified diatomaceous earth prepared in the comparative example. This reduction in water-soluble As content increased with increasing application of the modified diatomaceous earth. The modified diatomaceous earth according to the present invention demonstrated excellent passivation performance for As in both soils, with the passivation efficiency ranking as follows: As-contaminated soil S1 > As-contaminated soil S2. Therefore, the application of the modified diatomaceous earth according to the present invention significantly reduced the available arsenic content in different soil types, thereby immobilizing the active arsenic in the soil to a certain extent.

[0113] Test Example 5

[0114] Recycling performance of modified diatomite materials:

[0115] 0.02 g of the modified diatomaceous earth prepared in Example 1 was added to 20 mL of an As(V) solution with an initial concentration of 50 ppm and an As(III) solution with an initial concentration of 30 ppm, respectively. After 12 h of adsorption equilibrium, 0.1 mol / L HCl was selected as the decomposition agent, and four adsorption and decomposition cycles were performed. The samples were taken and filtered, and the As concentration in the solution was determined to explore the cyclic regeneration adsorption performance of the modified material.

[0116] The experimental results are as follows Figure 4 and Figure 5 As shown. The modified diatomaceous earth of the present invention exhibits a gradually decreasing adsorption capacity for As(V) removal with increasing cycle number. After four adsorption-desorption cycles, the adsorption capacity remains at 89.65% of the initial adsorption capacity. Similarly, the modified diatomaceous earth of the present invention exhibits a gradually decreasing adsorption capacity for As(III) removal with increasing cycle number. After multiple adsorption-desorption cycles, the adsorption capacity remains at 83.19% of the initial adsorption capacity. This finding confirms the good reusability of the modified diatomaceous earth of the present invention for As adsorption.

[0117] The applicant declares that the present invention is illustrated by the above-described embodiments, but the present invention is not limited to the above-described embodiments. This does not mean that the present invention must rely on the above-described embodiments in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent replacements for raw materials in the present invention, additions of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

[0118] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.

[0119] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

Claims

1. A modified diatomaceous earth for repairing arsenic pollution in water and soil, characterized in that: The modified diatomaceous earth comprises diatomaceous earth and granular iron oxide and granular magnesium oxide supported on the surface of the diatomaceous earth.

2. The modified diatomaceous earth for repairing arsenic pollution in water and soil according to claim 1, characterized in that: The molar ratio of the iron oxide to the magnesium oxide is (3-5):(1-2).

3. The method for preparing modified diatomaceous earth for repairing arsenic contamination of water and soil according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: (1) mixing a diatomaceous earth material, a water-soluble iron salt or a hydrate thereof, a water-soluble magnesium salt or a hydrate thereof, a dispersion stabilizer, an alkaline precipitant, and water to obtain a mixed solution, and performing a first reaction to obtain a composite diatomaceous earth solution; (2) subjecting the composite diatomite solution to an anaerobic pyrolysis reaction to obtain the modified diatomite.

4. The preparation method according to claim 3, characterized in that The water-soluble iron salt or its hydrate is selected from ferric chloride or its hydrate, ferric sulfate or its hydrate, ferric nitrate or its hydrate; The water-soluble magnesium salt or its hydrate is selected from magnesium chloride or its hydrate, magnesium sulfate or its hydrate, magnesium nitrate or its hydrate.

5. The preparation method according to claim 3 or 4, characterized in that The dispersion stabilizer includes citrate or its hydrate; Preferably, the alkaline precipitant includes any one of urea, ammonia water or sodium hydroxide, or a combination of at least two of them.

6. The preparation method according to any one of claims 3 to 5, characterized in that The diatomaceous earth material is 100-200 mesh dry diatomaceous earth; Preferably, the usage ratio of the diatomaceous earth material, the water-soluble iron salt or its hydrate, and the water-soluble magnesium salt or its hydrate is (0.5-2) g: (0.3-0.5) mol: (0.1-0.2) mol; Preferably, the mass ratio of the dispersion stabilizer to the diatomaceous earth material is (0.01-0.03):(0.5-2); Preferably, the mass ratio of the alkaline precipitant to the diatomaceous earth material is (0.03-0.09):(0.5-2).

7. The preparation method according to any one of claims 3 to 6, characterized in that The pH value of the mixed solution of the first reaction is 6-8; Preferably, the first reaction is carried out at 20-35°C for 10-20h; Preferably, the anaerobic pyrolysis reaction is carried out at 130-180° C. for 12-30 hours; Preferably, after the anaerobic pyrolysis reaction is completed, solid-liquid separation, washing, drying and crushing are performed.

8. Use of the modified diatomaceous earth according to claim 1 or the preparation method according to any one of claims 3 to 7 in the remediation of arsenic contamination in soil or water.

9. The use according to claim 8, characterized in that The modified diatomaceous earth is used to repair soil arsenic pollution, and the ratio of the modified diatomaceous earth to arsenic-containing soil is 166-1666 kg / mu.

10. The use according to claim 8, characterized in that The modified diatomaceous earth is used for repairing arsenic pollution in water bodies, and the ratio of the modified diatomaceous earth to arsenic-containing water bodies is 0.1-5 g / L.

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