Layered composite bimetallic oxide as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of adsorption materials, and particularly relates to a layered composite bimetallic oxide as well as a preparation method and application thereof. The preparation method of the layered composite bimetallic oxide provided by the invention comprises the following steps: mixing magnesium oxide and a hydrate of magnesium salt, and then carrying out ball milling to obtain a ball-milled material; mixing the ball-milled material with a hydrate of a manganese salt, and performing wet milling to obtain a composite bimetallic oxide precursor; roasting the composite bimetal oxide precursor to obtain a layered composite bimetal oxide; the molar ratio of the magnesium element in the magnesium oxide to the magnesium element in the magnesium salt is (1-6): 1. The preparation method provided by the invention is convenient and free of wastewater generation, and the prepared composite metal oxide shows excellent performance in synchronous remediation of cadmium-arsenic combined pollution, that is, the material can realize treatment of cadmium while remediation of arsenic pollution; an effective solution is provided for solving the problem that cadmium and arsenic pollution is difficult to treat at the same time at present.

Description

Technical Field

[0001] The invention belongs to the technical field of adsorption materials, and specifically relates to a layered composite bimetallic oxide and a preparation method and application thereof. Background Art

[0002] Heavy metal ions in aqueous solutions exist in the form of cations or metal oxygen-containing anions. Among them, cadmium is highly toxic. Excessive intake of cadmium may cause cadmium poisoning, muscle atrophy and joint deformity. In addition, arsenic heavy metal has been identified as a "known human carcinogen". Long-term intake of drinking water with excessive arsenic content can cause chronic poisoning of the body. Compared with the cationic Cd form that is easily removed by adsorption or precipitation, the oxygen-containing anion form AsO2 - It has higher solubility and environmental mobility and can migrate freely in the environment.

[0003] At present, there are various materials used for adsorption and solidification of heavy metals in water / soil, such as metal organic framework materials (MOFs), activated carbon, layered composite metal hydroxides (LDHs) and iron-manganese-based oxides, etc. Among them, LDHs are a type of clay compound assembled by main layers and interlayer anion intercalation. Due to its special two-dimensional layered structure, it can remove heavy metals in a variety of ways, such as interlayer anion exchange, memory effect, isomorphous substitution, etc., and has shown good application prospects in the field of heavy metal contaminated water remediation.

[0004] However, the restoration of the coexistence system of heavy metals arsenic and cadmium is very difficult and is a bottleneck problem in the field of heavy metal pollution control. This is mainly due to the differences in the pH and redox potential (Eh) dependence of the two heavy metals arsenic and cadmium: arsenic and cadmium are affected by pH and Eh in completely opposite ways. Arsenic is more stable under acidic conditions, while cadmium is more stable under alkaline conditions. This makes it difficult to prepare suitable repair agents to jointly treat complex heavy metals, thereby reducing harm to the human body. At present, there are great problems in the preparation of materials for adsorbing heavy metals. For example, the preparation process of MOFs or covalent organic frameworks (COF) materials with porous structures is complicated, and the raw materials used are mainly expensive organic matter, resulting in high material costs and easy production of wastewater containing organic matter, leading to pollution. For common inorganic materials, salt-alkali coprecipitation reaction or hydrothermal reaction is mainly used, and a large amount of saline wastewater will be generated during the preparation process. With the increasingly stringent environmental protection requirements, the discharge of saline wastewater is also an issue that needs to be addressed urgently. More importantly, the adsorption sites of the adsorbent materials currently prepared are single, that is, they can only selectively adsorb cadmium or have relatively good adsorption capacity for arsenic, but it is difficult to have good adsorption performance for cadmium and arsenic at the same time. Therefore, it is urgent to develop a green and convenient synthesis method to have adsorbent materials with the function of composite repair of heavy metals. Summary of the invention

[0005] The purpose of the present invention is to provide a layered composite bimetallic oxide and a preparation method and application thereof. The method for preparing the layered composite bimetallic oxide provided by the present invention is simple, and the prepared layered composite bimetallic oxide can simultaneously remove arsenic and cadmium.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing a layered composite bimetallic oxide, comprising the following steps: The magnesium oxide and the hydrate of the magnesium salt are mixed and then ball-milled to obtain a ball-milled material; The ball mill material and the hydrate of the manganese salt are mixed and wet-milled to obtain a composite bimetallic oxide precursor; calcining the composite bimetallic oxide precursor to obtain a layered composite bimetallic oxide; The molar ratio of the magnesium element in the magnesium oxide to the magnesium element in the magnesium salt is 1-6:1.

[0007] Preferably, the magnesium salt includes at least one of magnesium chloride, magnesium sulfate, magnesium carbonate and magnesium nitrate.

[0008] Preferably, the manganese salt includes at least one of manganese chloride, manganese nitrate, manganese sulfate and manganese carbonate.

[0009] Preferably, the molar ratio of manganese element in the manganese salt to magnesium element in the ball-milled material is 1:10-1:5.

[0010] Preferably, the ball-to-material ratio of the ball milling and wet milling is independently 5-20:1; the rotation speed of the ball milling and wet milling is independently 400-800 rpm; the material of the grinding balls in the ball milling and wet milling is zirconium oxide; and the diameter of the grinding balls is independently 1-10 mm.

[0011] Preferably, the calcination temperature is 300-500° C., and the calcination holding time is 2-6 h.

[0012] Preferably, the heating rate to the calcining temperature is 3-10° C. / min.

[0013] The present invention provides a layered composite bimetallic oxide prepared by the preparation method described in the above technical scheme, wherein the layered composite bimetallic oxide is a magnesium-manganese layered bimetallic oxide, and the molar ratio of manganese element to magnesium element in the magnesium-manganese layered bimetallic oxide is 1:10-1:5.

[0014] Preferably, the BET specific surface area of ​​the layered composite bimetallic oxide is 50 to 200 m 2 / g.

[0015] The present invention provides a layered composite bimetallic oxide prepared by the preparation method described in the above technical solution or the use of the layered composite bimetallic oxide described in the above technical solution in the simultaneous removal of arsenic and cadmium.

[0016] The present invention provides a method for preparing a layered composite bimetallic oxide, comprising the following steps: mixing magnesium oxide and a hydrate of a magnesium salt and then ball milling to obtain a ball milled material; mixing the ball milled material and a hydrate of a manganese salt and then wet milling to obtain a composite bimetallic oxide precursor; calcining the composite bimetallic oxide precursor to obtain a layered composite bimetallic oxide; the molar ratio of the magnesium element in the magnesium oxide to the magnesium element in the magnesium salt is 1 to 6:1. In the synthesis process of the layered composite bimetallic oxide, the hydrate of magnesium oxide and magnesium salt at the above molar ratio can activate magnesium oxide by utilizing the acidic characteristics of the magnesium salt, obtain a large number of active sites on its surface, form abundant magnesium defect sites, and then chemically react under the action of crystal water in the magnesium salt and manganese salt to form a pure phase composite metal hydroxide without over-oxidizing it to positive tetravalent manganese to form a manganese oxide heterophase (MnO2). In addition, in the reaction process, manganese ions are first adsorbed on the surface of magnesium oxide, react with the free magnesium ions to form a composite bimetallic hydroxide, and the composite bimetallic hydroxide can obtain a layered composite bimetallic oxide by simple calcination. Compared with conventional strong alkalis such as sodium hydroxide or potassium hydroxide, the suitable alkalinity of magnesium oxide will not lead to the formation of manganese oxide impurities, and saves a large amount of alkali. At the same time, the application of mechanical grinding methods (ball milling or wet grinding) avoids the generation of wastewater, reduces the preparation cost, and reduces environmental pressure. In summary, the preparation method provided by the present invention is not only convenient but also does not generate wastewater. In addition, the data of the embodiment show that the composite metal oxide prepared by the present invention exhibits excellent performance in the simultaneous repair of cadmium and arsenic composite pollution, that is, the material can achieve the treatment of cadmium while repairing arsenic pollution, and provides an effective solution to the problem that cadmium and arsenic pollution are difficult to treat simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 is the XRD pattern of the magnesium-manganese bimetallic oxide obtained in Example 1; Figure 2 TEM image of the magnesium-manganese bimetallic oxide obtained in Example 1; Figure 3is the BET diagram of the magnesium-manganese bimetallic oxide obtained in Example 1; Figure 4 It is a kinetic curve diagram of arsenic adsorption by the magnesium-manganese bimetallic oxide obtained in Application Example 1; Figure 5 This is a comparison chart of the adsorption capacity of magnesium-manganese bimetallic oxide on As in Application Example 2 and other adsorbents on As; Figure 6 It is a kinetic curve diagram of the composite adsorption of arsenic and cadmium by magnesium-manganese bimetallic oxide in Application Example 2; Figure 7 This is the XRD diagram of the magnesium-manganese bimetallic oxide after adsorption of cadmium and arsenic in Application Example 2. DETAILED DESCRIPTION

[0019] The present invention provides a method for preparing a layered composite bimetallic oxide, comprising the following steps: The magnesium oxide and the hydrate of the magnesium salt are mixed and then ball-milled to obtain a ball-milled material; The ball mill material and the hydrate of the manganese salt are mixed and wet-milled to obtain a composite bimetallic oxide precursor; calcining the composite bimetallic oxide precursor to obtain a layered composite bimetallic oxide; The molar ratio of the magnesium element in the magnesium oxide to the magnesium element in the magnesium salt is 1-6:1.

[0020] As an embodiment of the present invention, the magnesium salt may include at least one of magnesium chloride, magnesium sulfate, magnesium carbonate and magnesium nitrate; in the embodiment of the present invention, the hydrate of the magnesium salt is specifically described by taking magnesium chloride hexahydrate or magnesium nitrate hexahydrate as an example. As an embodiment of the present invention, the average particle size of the magnesium oxide may be 20 to 500 nm; in the embodiment of the present invention, it is specifically described by taking 50 nm magnesium oxide as an example. As an embodiment of the present invention, the molar ratio of the magnesium element in the magnesium oxide to the magnesium element in the magnesium salt may be 1 to 6:1, specifically 1:1, 2:1, 3:1, 4:1, 5:1 or 6:1.

[0021] As an embodiment of the present invention, the ball-to-material ratio of the ball milling can be 5-20:1, specifically 5:1, 10:1, 15:1, 20:1; the rotation speed of the ball milling can be 400-800 rpm, specifically 400 rpm, 500 rpm, 600rpm, 700 rpm or 800 rpm; the time of the ball milling can be 4-6 h, specifically 4h, 5h or 6h; the material of the grinding balls of the ball milling is zirconium oxide; the diameter of the grinding balls can be 1-10 mm, specifically 1 mm, 5 mm or 10 mm; in the embodiment of the present invention, the mass proportion of the diameter of the zirconium oxide ball is 15%, the mass proportion of the diameter ...

[0022] After the ball-milled material is obtained, the invention mixes the ball-milled material and a manganese salt and then wet-mills the mixture to obtain a composite bimetallic oxide precursor.

[0023] As an embodiment of the present invention, the manganese salt may include at least one of manganese chloride, manganese nitrate, manganese sulfate and manganese carbonate; in the embodiment of the present invention, the hydrate of the manganese salt is specifically described by taking tetrahydrated manganese nitrate or tetrahydrated manganese chloride as an example. As an embodiment of the present invention, the molar ratio of the manganese element in the manganese salt to the magnesium element in the ball mill material may be 1:10 to 1:5, specifically 1:9, 1:8, 1:7, 1:6 or 1:5.

[0024] As an embodiment of the present invention, the ball-to-material ratio of the wet grinding can be 5-20:1, specifically 5:1, 10:1, 15:1, 20:1; the medium of the wet grinding can include anhydrous ethanol; the rotation speed of the wet grinding can be 400-800 rpm, specifically 400 rpm, 500 rpm, 600 rpm, 700 rpm or 800 rpm; the time of the wet grinding can be 3-5 h, specifically 3 h, 4 h or 5 h; the material of the wet grinding ball is zirconium oxide; the diameter of the grinding ball can be 1-10 mm, specifically 1 mm, 5 mm or 10 mm; in the embodiment of the present invention, the mass proportion of the diameter of the zirconium oxide ball is 15%, the mass proportion of the diameter ...

[0025] As an embodiment of the present invention, the wet grinding further includes: centrifuging the product after the wet grinding treatment, washing and then drying to obtain the composite bimetallic oxide precursor; the reagents used for the washing can be deionized water and ethanol in sequence; the drying method can be drying; the drying temperature can be 40~90°C, specifically 60°C; the drying time can be 6~24 h, specifically 12 h.

[0026] After obtaining the composite bimetallic oxide precursor, the present invention bakes the composite bimetallic oxide precursor to obtain a layered composite bimetallic oxide.

[0027] As an embodiment of the present invention, the calcination temperature can be 300-500°C, specifically 300°C, 400°C or 500°C; the calcination holding time can be 2-6 h, specifically 2 h, 3 h, 4 h, 5 h or 6 h; the heating rate to the calcination can be 3-10°C / min, specifically 5°C / min. The present invention is calcined under the above conditions, and the layered composite bimetallic oxide can be successfully prepared on the basis of low energy consumption. In addition, the above calcination temperature range can avoid the appearance of manganese oxide impurities in the composite material, and at the same time, the above heating rate can effectively avoid the sintering phenomenon of the material caused by too fast heating rate (sintering phenomenon will reduce the specific surface area of ​​the material), and at the same time, the above heating rate can improve the preparation efficiency.

[0028] As an embodiment of the present invention, the roasting further includes cooling; the present invention does not specifically limit the cooling method, and natural cooling can be used.

[0029] The present invention provides a layered composite bimetallic oxide prepared by the preparation method described in the above technical solution. As an embodiment of the present invention, the molar ratio of manganese element to magnesium element in the magnesium-manganese layered bimetallic oxide can be 1:10 to 1:5, specifically 1:5, 1:7 or 1:10.

[0030] As an embodiment of the present invention, the BET specific surface area of ​​the layered composite bimetallic oxide magnesium manganese bimetallic oxide can be 50 to 200 m 2 / g, specifically 185 m 2 / g.

[0031] The composite bimetallic oxide obtained by the present invention has a larger specific surface area and abundant active sites (including oxidation sites and adsorption sites) than magnesium manganese layered double hydroxide (MgMn-LDH), which is beneficial for treating the composite pollution of heavy metal arsenic and cadmium.

[0032] The present invention provides the application of the layered composite bimetallic oxide prepared by the preparation method described in the above technical solution in the simultaneous removal of arsenic and cadmium from water. The present invention does not specifically limit the specific application of the layered composite bimetallic oxide, and a method familiar to those skilled in the art can be used.

[0033] The magnesium-manganese composite oxide obtained by the present invention can react with water molecules on the surface to hydroxylate the magnesium-manganese composite oxide due to its high catalytic activity in aqueous solution. During the hydroxylation process, arsenite and arsenate are very easy to react with hydroxyl groups, so that ions such as arsenite and arsenate are adsorbed in the magnesium-manganese composite oxide. At the same time, during the hydration process of the magnesium-manganese composite oxide, arsenic pollutants in anion state can also enter the interlayer, that is, the magnesium-manganese composite oxide presents multiple channels for the removal of arsenic, so that its adsorption amount is much greater than the removal amount of arsenic by the existing adsorbent. On the other hand, magnesium ions and cadmium ions have relatively similar ionic radii and similar coordination numbers, and the solubility of magnesium hydroxide is greater than the solubility of cadmium hydroxide, so that cadmium ions are easy to react with active magnesium ions, that is, cadmium ions enter the crystal lattice of the magnesium-manganese composite oxide, and during the hydroxylation process, cadmium-containing composite hydroxides are formed, thereby achieving the simultaneous removal of cadmium and arsenic.

[0034] In summary, the magnesium-manganese composite oxide obtained in the present invention can remove arsenic by hydroxyl complexation and interlayer confinement, and remove cadmium by equivalent isomorphous substitution, and has good application prospects in the simultaneous removal of arsenic and cadmium in water.

[0035] In order to further illustrate the present invention, the scheme of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be understood as limiting the protection scope of the present invention.

[0036] Example 1 1.21 g (0.03 mol) of nano magnesium oxide (particle size of 50 nm) and 2.03 g (0.01 mol) of magnesium chloride hexahydrate were placed in a 316L stainless steel grinding jar, wherein the total mass of the zirconium oxide balls was 20 g, the mass of the zirconium oxide balls with a diameter of 1 mm accounted for 15%, the mass of the diameter of 5 mm accounted for 25%, and the mass of the diameter of 10 mm accounted for 60%. After ball milling at a speed of 600 rpm for 4 h, the ball milling jar was opened, 1.58 g (0.008 mol) of manganese chloride tetrahydrate was placed in the above-opened ball milling jar, 3 mL of anhydrous ethanol was added, and after mixing evenly, the ball milling was continued at a speed of 600 rpm for 6 h, and then centrifuged. The obtained precipitate was washed with deionized water and ethanol three times respectively, and then the precipitate was placed in an oven at 60 ° C and dried for 12 h to obtain a magnesium manganese bimetallic oxide precursor (magnesium manganese layered double hydroxide MgMn-LDH). The Mg in the obtained magnesium manganese bimetallic oxide precursor was 1.58 g (0.008 mol) of manganese chloride tetrahydrate. 2+ :Mn 2+ The molar ratio is 5: 1. The magnesium-manganese bimetallic oxide precursor is placed in a muffle furnace, heated to 350 °C at 5 °C / min, calcined at 350 °C for 3 h, and then naturally cooled to obtain a layered magnesium-manganese bimetallic oxide (the molar ratio of manganese element to magnesium element in the layered magnesium-manganese bimetallic oxide is 1:5).

[0037] Figure 1 is the XRD pattern of the magnesium-manganese bimetallic oxide obtained in Example 1, Figure 1 It can be seen that when the calcination temperature is 350°C, layered MgMn-LDO is formed (spectrum information: 2θ=18.7°, 29.8°, 32.9°, 36.9°, 43.3° and 62.8°).

[0038] Figure 2 TEM image of the magnesium manganese bimetallic oxide obtained in Example 1 clearly shows that there is no significant difference in the morphology of the irregular hexagonal nanosheets of the magnesium manganese bimetallic oxide obtained in Example 1 and MgMn-LDH. However, unlike the smooth surface of the MgMn-LDH nanosheets, the magnesium manganese bimetallic oxide nanosheets obtained in Example 1 are formed by the aggregation of a large number of nanoparticles and present a porous structure.

[0039] Figure 3 is the BET diagram of the magnesium-manganese bimetallic oxide obtained in Example 1, Figure 3 It can be seen that the BET specific surface area of ​​magnesium-manganese bimetallic oxide is 185 m 2 / g, which is about three times that of the magnesium-manganese bimetallic oxide precursor (MgMn-LDH).

[0040] Example 2 2.42 g (0.06 mol) of nano magnesium oxide (particle size of 50 nm) and 2.56 g (0.01 mol) of magnesium nitrate hexahydrate were placed in a 316 L stainless steel grinding jar, wherein the total mass of the zirconium oxide balls was 20 g, the total mass of the zirconium oxide balls was 20 g, the mass proportion of the diameter of the zirconium oxide balls was 15%, the mass proportion of the diameter of the balls was 5 mm, and the mass proportion of the diameter of the balls was 10 mm. The ball mill was opened after ball milling at a speed of 600 rpm for 5 h, and 2.51 g (0.01 mol) of manganese nitrate tetrahydrate was placed in the above-opened ball mill, 5 mL of anhydrous ethanol was added, and after mixing evenly, the ball milling was continued at a speed of 700 rpm for 6 h, centrifuged, and the obtained precipitate was washed with deionized water and ethanol three times respectively, and the precipitate was placed in an oven at 60 ° C for 12 h to obtain a magnesium-manganese bimetallic oxide precursor. The Mg in the magnesium-manganese bimetallic oxide precursor was 1.5%. 2+ :Mn 2+ The molar ratio is 7: 1. The magnesium-manganese bimetallic oxide precursor is placed in a muffle furnace, heated to 350 °C at 5 °C / min, calcined at 350 °C for 3 h, and then naturally cooled to obtain a layered magnesium-manganese bimetallic oxide (the molar ratio of manganese to magnesium in the layered magnesium-manganese bimetallic oxide is 1:7).

[0041] Application Example 1 Adsorption of arsenic by the magnesium-manganese bimetallic oxide obtained in Example 1: 0.1 g of the magnesium-manganese bimetallic oxide obtained in Example 1 was placed in a 200 mL beaker, and 100 mL of sodium arsenite solution was added, wherein the arsenic concentration was 10-2000 mg / L. After magnetic stirring at room temperature for 12 h to reach adsorption equilibrium, the upper layer solution was filtered with a 0.22 µm filter membrane and the As concentration was measured by inductively coupled plasma technology (ICP-OES). The adsorption amount of arsenic at different concentrations is shown in Figure 4 As shown in Figure 2, the maximum adsorption capacity is calculated to be 662.4 mg / g, which is much larger than other adsorbents reported so far (see Figure 5 ).

[0042] Application Example 2 Adsorption of arsenic and cadmium composite heavy metals by the magnesium-manganese bimetallic oxide obtained in Example 2: 0.1 g of the magnesium-manganese bimetallic oxide obtained in Example 2 was placed in a 200 mL beaker, and 100 mL of a sodium arsenite-cadmium nitrate mixed solution was added, wherein the concentration of arsenic was 100 mg / L and the concentration of cadmium was 200 mg / L. The pH value of the mixed solution was adjusted to about 5, and after magnetic stirring for 12 h at room temperature to reach adsorption equilibrium, the upper layer solution was filtered with a 0.22 µm filter membrane and the concentrations of As and Cd therein were measured by ICP-OES. The removal rate results at different time periods are shown as follows: Figure 6 As shown by Figure 6 It can be seen that the magnesium-manganese bimetallic oxide in Example 2 can reach adsorption equilibrium for the composite heavy metals of arsenic and cadmium within 10 minutes. The addition of Cd greatly increases the adsorption rate of arsenic by the magnesium-manganese bimetallic oxide, indicating that the magnesium-manganese bimetallic oxide has a strong affinity for the composite heavy metals of arsenic and cadmium.

[0043] Figure 7 is the XRD diagram of magnesium-manganese bimetallic oxide after adsorption of cadmium and arsenic in Example 2, Figure 7 It can be seen that after adsorbing arsenic, the XRD diffraction spectrum of the magnesium-manganese bimetallic oxide shows the characteristic diffraction peaks of typical hydrotalcites, indicating that the adsorption mechanism of the prepared magnesium-manganese bimetallic oxide on cadmium-arsenic composite pollution is significantly different from that of existing materials. By analyzing the XRD spectrum, it can be seen that in the process of adsorbing cadmium-arsenic composite pollutants, the magnesium-manganese bimetallic oxide undergoes a phase topological transformation process, and the cadmium ions in the solution replace the magnesium in the magnesium-manganese bimetallic oxide to form a magnesium-cadmium-manganese ternary hydrotalcite, which is consistent with the equivalent isomorphism in geology, rather than conventional materials adsorbing cadmium ions on the surface. This special adsorption method makes cadmium fixed in the lattice. In view of the rich coordination bonds between the lattices and the interaction between the host and the guest, it is extremely difficult for the cadmium ions to be desorbed; at the same time, the XRD diagram can also show that the interlayer spacing is significantly increased, indicating that there are interlayer guest molecules with larger sizes entering the interlayer. According to the type of anions in the reaction system, the guest anions are arsenate ions or arsenite ions, indicating that the pollutant arsenic is confined in the limited space between the layers. The above results show that magnesium-manganese bimetallic oxide achieves simultaneous adsorption through different adsorption pathways when treating cadmium-arsenic combined pollution, solving the problem that the original materials are difficult to effectively and simultaneously adsorb cadmium and arsenic.

[0044] It can be seen from Application Examples 1-2 that the magnesium-manganese bimetallic oxide exhibits excellent performance in treating arsenic pollutants alone and simultaneously treating cadmium-arsenic composite pollutants, further indicating that the simultaneous adsorption of cadmium-arsenic pollutants by the material provided by the present invention is carried out through different adsorption mechanisms.

[0045] Application Example 3 Remediation of soil contaminated by arsenic and cadmium composite heavy metals using the magnesium-manganese bimetallic oxide obtained in Example 2: Take 500 g of cadmium-arsenic composite contaminated soil sample and 10 g of magnesium-manganese bimetallic oxide obtained in Example 2 in a beaker and mix them thoroughly. Then add 300 mL of deionized water and continue stirring until it is in a muddy state and then leave it naturally. After natural drying, the soil sample is used to plant madou. After the madou seedlings emerge, they continue to grow for 20 days. The madou seedlings are carefully pulled out with their roots, the soil is washed and naturally dried. After weighing, the cadmium and arsenic contents in the madou seedlings are determined by the national standard method. Among them, the cadmium content is 0.021 mg / kg, and the arsenic content is 0.11 mg / kg, which meets the national standard limit values ​​of the cadmium and arsenic contents of vegetables that shall not exceed (the cadmium content shall not exceed 0.1 mg / kg, and the arsenic content shall not exceed 0.5 mg / kg).

[0046] Comparative Example In order to further illustrate the effect of magnesium-manganese bimetallic oxide in the remediation of cadmium-arsenic contaminated soil, a comparative example was carried out. The difference between this comparative example and Application Example 3 is that magnesium-manganese bimetallic oxide is not added to the contaminated soil, and other operations are the same.

[0047] Take 500g of cadmium and arsenic composite heavy metal contaminated soil in a beaker, mix it thoroughly, add 300mL of deionized water, continue stirring until it becomes a paste, and then leave it naturally. After it dries naturally, use the soil sample to plant magnolia. After the magnolia sprouts, continue to grow for 20 days. Carefully pull out the magnolia seedlings with their roots, wash off the soil, and dry them naturally. After weighing, use the national standard method to determine the cadmium and arsenic contents in the magnolia seedlings. The cadmium content is 0.283mg / kg, and the arsenic content is 0.741mg / kg. Compared with the national standard, they exceed the maximum limit and are vegetables that do not meet national requirements. They are very likely to cause harm to human health after consumption.

[0048] By comparing Application Example 3 and the comparative example, it can be proved that the magnesium-manganese bimetallic oxide provided by the present invention has a very good effect in the remediation of cadmium and arsenic contaminated soil.

[0049] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a layered composite bimetallic oxide, comprising the following steps: The magnesium oxide and the hydrate of the magnesium salt are mixed and then ball-milled to obtain a ball-milled material; The ball mill material and the hydrate of the manganese salt are mixed and wet-milled to obtain a composite bimetallic oxide precursor; calcining the composite bimetallic oxide precursor to obtain a layered composite bimetallic oxide; The molar ratio of the magnesium element in the magnesium oxide to the magnesium element in the magnesium salt is 1-6:

1.

2. The preparation method according to claim 1, characterized in that The magnesium salt includes at least one of magnesium chloride, magnesium sulfate, magnesium carbonate and magnesium nitrate.

3. The preparation method according to claim 1, characterized in that: The manganese salt includes at least one of manganese chloride, manganese nitrate, manganese sulfate and manganese carbonate.

4. The preparation method according to claim 1, characterized in that: The molar ratio of the manganese element in the manganese salt to the magnesium element in the ball-milled material is 1:10 to 1:

5.

5. The preparation method according to any one of claims 1 to 4, characterized in that The ball-to-material ratio of the ball mill and the wet mill is independently 5-20:1; the rotation speed of the ball mill and the wet mill is independently 400-800 rpm; the material of the grinding balls in the ball mill and the wet mill is zirconium oxide; the diameter of the grinding balls is independently 1-10 mm.

6. The preparation method according to claim 1, characterized in that: The calcination temperature is 300-500°C, and the calcination holding time is 2-6 h.

7. The preparation method according to claim 6, characterized in that: The heating rate to the calcination temperature is 3-10°C / min.

8. The layered composite bimetallic oxide prepared by the preparation method according to any one of claims 1 to 7, wherein the layered composite bimetallic oxide is a magnesium-manganese layered bimetallic oxide, characterized in that: The molar ratio of manganese element to magnesium element in the magnesium-manganese layered bimetallic oxide is 1:10-1:

5.

9. The layered composite bimetallic oxide according to claim 8, characterized in that: The BET specific surface area of ​​the layered composite bimetallic oxide is 50-200 m 2 / g.

10. Use of the layered composite bimetallic oxide prepared by the preparation method according to any one of claims 1 to 7 or the layered composite bimetallic oxide according to claim 8 or 9 in the simultaneous removal of arsenic and cadmium.

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