Iron oxide / lDHs composite material, preparation method and application

Abstract

The application provides an iron oxide / LDHs composite material, a preparation method and application. The preparation method of the iron oxide / LDHs composite material comprises the following steps: co-ball milling iron oxide and magnesium-aluminum hydrotalcite to obtain the iron oxide / LDHs composite material; wherein the mass percentage of the iron oxide and the magnesium-aluminum hydrotalcite is 1-15%. The iron oxide / LDHs composite material provided by the application can improve the synchronous treatment efficiency of cadmium and arsenic; the iron oxide / LDHs composite material not only can remove cadmium and arsenic in water, but also can stabilize the effective cadmium and arsenic in soil.

Description

Technical Field

[0001] This invention belongs to the field of material preparation and cadmium and arsenic remediation, and particularly relates to an iron oxide / LDHs composite material, its preparation method and application. Background Technology

[0002] Excessive levels of heavy metals pose a potential threat to humans, animals, plants, and ecosystems. Cadmium and arsenic, among other heavy metals, are typical pollutants produced during industries such as electroplating, battery manufacturing, mining, fossil fuel combustion, and pesticide use. Cadmium and arsenic can coexist in smelting processes and mine wastewater, leading to dual pollution of soil and water. The coexistence of these pollutants poses a greater threat to the ecological environment and human health than when they exist alone. Therefore, it is necessary not only to remove cadmium and arsenic from water bodies but also to stabilize available cadmium and arsenic in the soil. However, the chemical behavior of anionic arsenic differs significantly from that of cationic cadmium, making the simultaneous stabilization of cadmium and arsenic extremely difficult.

[0003] Chemical stabilization technology has gained popularity among researchers due to its advantages in remediation cost, efficiency, and ease of implementation. Commonly used soil remediation stabilizers include alkaline regulators such as lime, fly ash, silicon fertilizer, and calcium carbonate; phosphate stabilizers such as phosphate rock, hydroxyapatite, and dicalcium phosphate; and adsorption stabilizers such as metal oxides and biomaterials. However, traditional soil stabilizers suffer from problems such as inability to simultaneously stabilize cadmium and arsenic, susceptibility to environmental impacts, secondary pollution, and long remediation cycles. Therefore, researching efficient, green, stable soil remediation stabilizers that can simultaneously remove cadmium and arsenic pollution is crucial for solving the problem of soils contaminated with multiple heavy metals.

[0004] Therefore, it is necessary to provide an iron oxide / LDHs composite material, its preparation method, and its application to solve or at least alleviate the aforementioned technical defects of low efficiency in simultaneous cadmium and arsenic treatment. Summary of the Invention

[0005] The main objective of this invention is to provide an iron oxide / LDHs composite material, its preparation method, and its application, aiming to solve or at least alleviate the aforementioned technical problem of low efficiency in simultaneous cadmium and arsenic treatment.

[0006] To achieve the above objectives, the present invention provides a method for preparing an iron oxide / LDHs composite material, comprising: ball milling iron oxide and magnesium aluminum hydrotalcite together to obtain an iron oxide / LDHs composite material; wherein the mass percentage of the iron oxide and the magnesium aluminum hydrotalcite is 1-15%.

[0007] Furthermore, in the magnesium-aluminum hydrotalcite, the molar ratio of magnesium to aluminum is less than 3.

[0008] Furthermore, in the magnesium-aluminum hydrotalcite, the molar ratio of magnesium to aluminum is 1.5-2.5:1.

[0009] Furthermore, the mass percentage of the iron oxide and the magnesium aluminum hydrotalcite is 8-12%.

[0010] Furthermore, the ball mill rotates at a speed of 200-800 rpm, and the ball milling time is 1-8 hours.

[0011] Furthermore, the ball mill uses a ball-to-material ratio of 10-20:1.

[0012] The present invention also provides an iron oxide / LDHs composite material, which is prepared by any of the preparation methods described above.

[0013] The present invention also provides the application of the iron oxide / LDHs composite material as described above in the removal and / or stabilization of cadmium and arsenic.

[0014] The present invention also provides a method for removing cadmium and arsenic, comprising: mixing the iron oxide / LDHs composite material as described above into cadmium and arsenic wastewater to remove cadmium and arsenic from the cadmium and arsenic wastewater.

[0015] The present invention also provides a method for stabilizing cadmium and arsenic, comprising: mixing an iron oxide / LDHs composite material as described above into cadmium and arsenic soil to stabilize cadmium and arsenic in the soil.

[0016] Compared with the prior art, the present invention has at least the following advantages:

[0017] The iron oxide / LDHs composite material provided by this invention can improve the simultaneous treatment efficiency of cadmium and arsenic. It can not only remove cadmium and arsenic from water bodies but also stabilize available cadmium and arsenic in soil. Specifically, this invention prepares a novel remediation agent by selecting specific magnesium aluminum hydrotalcite and ball milling iron oxide and magnesium aluminum hydrotalcite in a specific ratio to achieve the goal of removing arsenic and cadmium from water bodies or stabilizing cadmium-arsenic co-contaminated soil. Furthermore, the preparation method and operation process provided by this invention are simple, resulting in less secondary pollution, shorter synthesis time, higher yield, and wider applicability compared to chemical synthesis methods. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0019] Figure 1The images shown are SEM and EDS images of the iron oxide / LDHs composite material in Example 1 of this invention; the scale bar in the SEM image is 500 nm.

[0020] Figure 2 The images show the XRD patterns of magnesium aluminum hydrotalcite (before ball milling) and iron oxide / LDHs composite material (after ball milling) in Example 1 of this invention.

[0021] Figure 3 This is a graph showing the effect of the amount of iron oxide added and the removal rate of cadmium and arsenic in Example 2 of the present invention;

[0022] Figure 4 This is a graph showing the effect of ball milling time on cadmium and arsenic removal rate in Example 3 of the present invention;

[0023] Figure 5 This is a graph showing the effect of ball milling speed and cadmium and arsenic removal rate in Example 4 of the present invention;

[0024] Figure 6 This is a comparison chart of the stability rates of available cadmium in soil by magnesium aluminum hydrotalcite (before ball milling) and iron oxide / LDHs composite material (after ball milling) in Example 5 of the present invention.

[0025] Figure 7 This is a comparison chart of the stability rates of available arsenic in soil by magnesium aluminum hydrotalcite (before ball milling) and iron oxide / LDHs composite material (after ball milling) in Example 5 of the present invention.

[0026] Figure 8 This is a comparison chart of the stability rates of available cadmium in soil by magnesium aluminum hydrotalcite (before ball milling) and iron oxide / LDHs composite material (after ball milling) in Example 6 of the present invention.

[0027] Figure 9 This is a comparison chart of the stability rates of available arsenic in soil by magnesium aluminum hydrotalcite (before ball milling) and iron oxide / LDHs composite material (after ball milling) in Example 6 of the present invention.

[0028] Figure 10 This is a graph showing the stability rate of available cadmium and arsenic in soil under different soil-water ratios in Example 7 of the present invention.

[0029] Figure 11 This is a graph showing the stability rate of available cadmium and arsenic in soil under different soil-water ratios in Example 8 of the present invention.

[0030] Figure 12 This is a graph showing the stability rate of available cadmium and arsenic in the soil at different remediation times in Example 9 of the present invention.

[0031] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0034] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention, as well as the prior art known to those skilled in the art and the description of this invention, may be implemented using any prior art methods, devices, and materials similar to or equivalent to those described, used, or made of materials in the embodiments of this invention.

[0035] It should be noted that the reagents, medicines, instruments, etc. involved in this invention are all commercially available products.

[0036] The chemical formula of the magnesium aluminum hydrotalcite used in Examples 1-9 and Comparative Examples 2-3 of this invention is [Mg4Al2(OH)]. 12 CO3]·3H2O; The chemical formula of the magnesium aluminum hydrotalcite used in Comparative Example 1 of this invention is [Mg6Al2(OH)]. 16 [CO3]·4H2O. In this invention, the iron oxide is ferric oxide (Fe2O3).

[0037] In the embodiments and comparative examples of this invention, available cadmium in the soil was extracted using the DTPA method, and available arsenic was extracted using the 0.5M sodium bicarbonate method, thereby determining the stability rate of cadmium and arsenic. The DTPA extraction process is as follows: weigh 0.5g of soil, add 5mL of DTPA, shake for 2 hours, and filter the supernatant after extraction. The 0.5M sodium bicarbonate extraction process is as follows: weigh 0.5g of soil, add 5mL of 0.5M sodium bicarbonate, shake for 2 hours, and filter the supernatant after extraction. The cadmium / arsenic stability rate refers to the percentage decrease in the concentration of available cadmium extracted using DTPA, or the percentage decrease in the concentration of available arsenic extracted using sodium bicarbonate, compared to a control group without remediation materials. The control group refers to a group that, compared to the group where stability rate needs to be measured, only lacks remediation materials (the materials to be tested), while maintaining the same soil-to-water ratio, remediation time, and other parameters and conditions. For cases where stabilization rate data are provided, a control group is simultaneously set up in this invention. In this invention, soil pH refers to the physicochemical properties of the soil itself, obtained by measuring a mixture of soil and water at a mass ratio of 1:1.5.

[0038] This invention provides a method for preparing an iron oxide / LDHs composite material, comprising: ball milling iron oxide and magnesium aluminum hydrotalcite together to obtain the iron oxide / LDHs composite material.

[0039] The iron oxide and the magnesium aluminum hydrotalcite are present in a mass percentage of 1-15% or 1-12%. To further obtain a material with better treatment effect on cadmium and arsenic, the mass percentage of iron oxide and magnesium aluminum hydrotalcite can be 8-12%.

[0040] As an explanation of the magnesium-aluminum hydrotalcite, it can be industrial-grade or analytically pure magnesium-aluminum hydrotalcite. In the experimental process of this invention, analytically pure magnesium-aluminum hydrotalcite was specifically used. The molar ratio of magnesium to aluminum in the magnesium-aluminum hydrotalcite is less than 3. Further, the molar ratio of magnesium to aluminum can be 1.5-2.5:1, thereby ensuring the cadmium and arsenic treatment effect of the iron oxide / LDHs composite material.

[0041] It should be noted that the present invention requires the iron oxide and the magnesium aluminum hydrotalcite to be ball-milled together in order to obtain the iron oxide / LDHs composite material, thereby achieving efficient treatment of cadmium and arsenic; if only a mixture of the iron oxide and the magnesium aluminum hydrotalcite is obtained, the technical effect of the present invention cannot be achieved.

[0042] Specifically, the ball mill rotation speed can be 200-800 rpm, preferably 500-800 rpm, 550-800 rpm, or 650-800 rpm; the ball milling time can be 1-8 hours, preferably 2-8 hours; the ball-to-material ratio used in the ball milling can be 10-20:1; the ball milling method is dry milling; the ball mill rotation direction can be alternating forward and reverse cycles. In this invention, the ball milling time in both rotation directions is equal during each alternating forward and reverse cycle; and the duration of each alternating forward and reverse cycle is also equal; in the embodiments and comparative examples of this invention, the ball milling time for each alternating forward and reverse cycle is 30 minutes.

[0043] It should be noted that preliminary studies show that unmilled magnesium-aluminum hydrotalcite has a layered structure, a relatively uniform structure, and a relatively high degree of crystallinity, resulting in a small specific surface area. However, this invention uses iron oxide in the ball milling process, which breaks down the layered structure of the magnesium-aluminum hydrotalcite, resulting in a larger specific surface area compared to before milling. This leads to a higher removal rate of cadmium and arsenic in the material obtained by this invention. Furthermore, the inclusion of iron ions in the material not only eliminates the negative effect of increased As migration in the soil caused by the addition of magnesium-aluminum hydrotalcite but also effectively stabilizes arsenic. Additionally, the ball milling method used in this invention is more environmentally friendly, and the synthesis process is faster and more efficient.

[0044] This invention also provides an iron oxide / LDHs composite material, prepared using any of the preparation methods described above. The iron oxide and magnesium aluminum hydrotalcite materials provided by this invention are used to synthesize a novel composite material using a simple ball milling method. This material is suitable for the remediation and stabilization of cadmium and arsenic-contaminated soils and water bodies, exhibiting good stabilization effect, high stability, and is environmentally friendly with no secondary pollution. Its application method is also simple.

[0045] The present invention also provides the application of the iron oxide / LDHs composite material as described above in the removal and / or stabilization of cadmium and arsenic; the removal of cadmium and arsenic can be carried out in water containing cadmium and arsenic; the stabilization of cadmium and arsenic can be carried out in soil containing cadmium and arsenic.

[0046] As one specific application of the above, the present invention also provides a method for removing cadmium and arsenic, comprising: mixing the iron oxide / LDHs composite material as described above into cadmium and arsenic wastewater to remove cadmium and arsenic from the cadmium and arsenic wastewater.

[0047] The cadmium-arsenic wastewater contains cadmium and arsenic. Cadmium may be divalent, and arsenic may be trivalent or pentavalent, specifically pentavalent. The concentration of cadmium and arsenic is 20-200 ppm, and the pH of the wastewater is 4-6. The solid-liquid ratio of the iron oxide / LDHs composite material to the cadmium-arsenic wastewater is 1 mg:0.5-1.5 mL. To achieve complete removal of cadmium and arsenic, the iron oxide / LDHs composite material can be mixed with the wastewater for 12-36 hours.

[0048] As another specific application of the above, the present invention also provides a method for stabilizing cadmium and arsenic, comprising: mixing the iron oxide / LDHs composite material as described above into cadmium and arsenic soil to stabilize cadmium and arsenic in the cadmium and arsenic soil; the stabilization treatment time may be 5-50 days.

[0049] The arsenic-free soil contains cadmium and arsenic, with cadmium content ranging from 0.3 to 5 mg / kg and arsenic content ranging from 12 to 45 mg / kg; the content of available cadmium is 0.183 to 3.182 mg / kg and the content of available arsenic is 0.356 to 1.291 mg / kg.

[0050] During the process of mixing the iron oxide / LDHs composite material into the cadmium-arsenic soil, water can also be mixed into the cadmium-arsenic soil, or the cadmium-arsenic soil can be kept containing water. The mass ratio of the cadmium-arsenic soil to the water can be 1:0.3-1.5; the pH of the cadmium-arsenic soil can be 5-6.5 (which is obtained by measuring the soil and water after mixing at a mass ratio of 1:1.5).

[0051] The mass ratio of the iron oxide / LDHs composite material to the cadmium-arsenic soil (unhydrated) can be 1-8:100.

[0052] The following are specific examples of the present invention:

[0053] Example 1

[0054] 5g of magnesium aluminum hydrotalcite (magnesium aluminum molar ratio of 4:2) and 0.5g of iron oxide were mixed evenly and placed in a ball mill jar. Ball milling balls were added at a ball-to-material ratio of 20:1 (mass ratio). Then, solid-phase ball milling was performed for 2 hours at a speed of 550 rpm with four cycles of alternating forward and reverse rotation to obtain the iron oxide / LDHs composite material.

[0055] The iron oxide / LDHs composite material in this embodiment was analyzed and tested using SEM, EDS, and XRD.

[0056] See Figure 1 As shown, in the iron oxide / LDHs composite material, iron oxide is uniformly dispersed on the surface of magnesium aluminum talc; and, by mass percentage, Mg accounts for 8.18%, Al accounts for 4.09%, and Fe accounts for 2.61%.

[0057] See Figure 2 As shown, compared with magnesium aluminum hydrotalcite (before ball milling), the iron oxide / LDHs composite material (after ball milling) mainly exhibits hydrotalcite and iron oxide peaks, and the composite material has a weaker crystal structure, with the interlayer spacing increasing from the original 0.75 nm to 0.76 nm.

[0058] In this embodiment, the surface areas of magnesium aluminum hydrotalcite (before ball milling) and iron oxide / LDHs composite material (after ball milling) are shown in Table 1:

[0059] Table 1 Surface area of ​​materials before and after ball milling

[0060]

[0061] As shown in Table 1, the specific surface area of ​​the material after ball milling is about twice that of the material before ball milling, and the pore size and pore volume are significantly increased.

[0062] Example 2

[0063] 1. Mix 5g of magnesium aluminum hydrotalcite (magnesium aluminum molar ratio of 4:2) with a set mass of iron oxide and place them evenly in a ball mill jar. Add grinding balls at a ball-to-material ratio of 20:1. Then, ball mill the mixture for 2 hours at a speed of 550 rpm and with the ball mill rotating in alternating directions for four cycles to obtain the repair material.

[0064] In this embodiment, the set amounts of iron oxide are 0.1g (2% addition), 0.2g (4% addition), 0.3g (6% addition), 0.4g (8% addition), 0.5g (10% addition), and 0.6g (12% addition); the repair material is prepared under each set amount in this embodiment.

[0065] 2. Each of the above-mentioned remediation materials was used as a test material for cadmium and arsenic removal tests. The specific test procedures are as follows:

[0066] Weigh 0.025g of the test material into a centrifuge tube and add 25mL of a cadmium-arsenic mixed solution with a cadmium concentration of 50mg / L. Then, place the centrifuge tube in a shaker and shake for 24 hours. The cadmium and arsenic concentrations are determined by ICP-OES. The cadmium-arsenic mixed solution is prepared by CdNO3 and AsNa3O4·12H2O and has a pH of 5.5.

[0067] SeeFigure 3 As shown, the cadmium removal rates corresponding to addition amounts of 2%, 4%, 6%, 8%, 10%, and 12% were 89.08%, 90.8%, 94.38%, 97.22%, 99.26%, and 99.49%, respectively; and the arsenic removal rates corresponding to addition amounts of 2%, 4%, 6%, 8%, 10%, and 12% were 79.62%, 83.48%, 91.67%, 96.0%, 99.81%, and 96.58%, respectively.

[0068] Example 3

[0069] 1. Mix 5g of magnesium aluminum hydrotalcite (magnesium aluminum molar ratio of 4:2) and 0.5g (addition amount of 10%) of iron oxide evenly in a ball mill jar, and add grinding balls at a ball-to-material ratio of 20:1; then, perform solid-phase ball milling for a set time at a speed of 550rpm and alternating forward and reverse rotation to obtain the repair material.

[0070] In this embodiment, the solid-phase ball milling time is set to 1h, 2h, 4h, 6h, and 8h respectively; the repair material is prepared under each set time.

[0071] 2. Each of the above-mentioned remediation materials was used as a test material for cadmium and arsenic removal tests. The specific test procedures are as follows:

[0072] Weigh 0.025g of the test material into a centrifuge tube and add 25mL of a cadmium-arsenic mixed solution with a cadmium concentration of 50mg / L. Then, place the centrifuge tube in a shaker and shake for 24 hours. The cadmium and arsenic concentrations are determined by ICP-OES. The cadmium-arsenic mixed solution is prepared by CdNO3 and AsNa3O4·12H2O and has a pH of 5.5.

[0073] See Figure 4 As shown, the cadmium removal rates corresponding to solid-phase ball milling times of 1h, 2h, 4h, 6h, and 8h were 93.59%, 99.83%, 99.47%, 99.83%, and 99.4%, respectively; the arsenic removal rates corresponding to solid-phase ball milling times of 1h, 2h, 4h, 6h, and 8h were 90.47%, 99.8%, 99.86%, 99.88%, and 99.94%, respectively.

[0074] Example 4

[0075] 1. Mix 5g of magnesium aluminum hydrotalcite (magnesium aluminum molar ratio of 4:2) and 0.5g (addition amount of 10%) of iron oxide evenly in a ball mill jar, and add grinding balls at a ball-to-material ratio of 20:1; then, ball mill for 2 hours at a set speed with the ball mill rotation direction alternating between forward and reverse for a total of four cycles to obtain the repair material.

[0076] In this embodiment, the rotation speeds are set to 350 rpm, 450 rpm, 550 rpm, 650 rpm, and 750 rpm; the repair material is prepared at each set rotation speed.

[0077] 2. Each of the above-mentioned remediation materials was used as a test material for cadmium and arsenic removal tests. The specific test procedures are as follows:

[0078] Weigh 0.025g of the test material into a centrifuge tube and add 25mL of a cadmium-arsenic mixed solution with a cadmium concentration of 50mg / L. Then, place the centrifuge tube in a shaker and shake for 24 hours. The cadmium and arsenic concentrations are determined by ICP-OES. The cadmium-arsenic mixed solution is prepared by CdNO3 and AsNa3O4·12H2O and has a pH of 5.5.

[0079] See Figure 5 As shown, the cadmium removal rates corresponding to rotation speeds of 350 rpm, 450 rpm, 550 rpm, 650 rpm, and 750 rpm were 84.14%, 87.59%, 99.83%, 99.92%, and 98.62%, respectively; the arsenic removal rates corresponding to rotation speeds of 350 rpm, 450 rpm, 550 rpm, 650 rpm, and 750 rpm were 94.49%, 96.21%, 99.39%, 99.83%, and 99.4%, respectively.

[0080] Example 5

[0081] Magnesium aluminum hydrotalcite (magnesium aluminum molar ratio of 4:2) and iron oxide / LDHs composite material (prepared in the same way as in Example 1) were used as test materials for cadmium and arsenic stability tests, as follows:

[0082] The test material was mixed into the cadmium-arsenic soil according to the set mass percentage to stabilize the cadmium-arsenic. The available cadmium-arsenic contents in the cadmium-arsenic soil were 3.182 mg / kg and 1.291 mg / kg, respectively, and the total cadmium-arsenic contents were 4.3 mg / kg and 43 mg / kg, respectively. The pH of the cadmium-arsenic soil was 5.8. Before mixing in the test material, water was added to the cadmium-arsenic soil to control the soil-water mass ratio of the cadmium-arsenic soil to be 1:1.

[0083] The set mass percentage refers to the mass percentage of the test material and the cadmium-arsenic soil (excluding the mass of water); in this embodiment, the set mass percentages are 1%, 2%, 4%, 6%, and 8%, respectively, and the cadmium-arsenic stability test is carried out at each set mass percentage.

[0084] See the results of the measurements after 7 days of stabilization. Figure 6 and Figure 7As shown, at mass percentages of 1%, 2%, 4%, 6%, and 8%, the cadmium stability rates of the material before ball milling were 8.88%, 10.62%, 14.08%, 13.6%, and 17.44%, respectively, while the arsenic stability rates were -4.06%, -4.19%, -15.98%, -18.51%, and -13.75%, respectively. Therefore, the material before ball milling caused the leaching of available arsenic from the cadmium-arsenic co-contaminated soil.

[0085] At mass percentages of 1%, 2%, 4%, 6%, and 8%, the cadmium stability rates of the ball-milled materials were 34.5%, 39.37%, 50.48%, 57.73%, and 61.2%, respectively, and the arsenic stability rates were 12.67%, 33.2%, 43.37%, 49.03%, and 45.48%, respectively.

[0086] Example 6

[0087] Compared to Example 5, this embodiment only replaces the cadmium-arsenic soil, while keeping other conditions unchanged. In this embodiment, the available cadmium and arsenic contents in the cadmium-arsenic soil are 0.183 mg / kg and 0.356 mg / kg, respectively, and the total cadmium and arsenic contents are 0.362 mg / kg and 12.7 mg / kg, respectively. The pH of the cadmium-arsenic soil is 5.53.

[0088] See the results of the measurements after 7 days of stabilization. Figure 8 and Figure 9 As shown, at mass percentages of 1%, 2%, 4%, 6%, and 8%, the cadmium stability rates of the material before ball milling were 4.71%, 8.67%, 14.58%, 20.53%, and 27.55%, respectively, while the arsenic stability rates were -8.38%, -11.83%, -1.6%, -7.8%, and -4.74%, respectively. Therefore, the material before ball milling caused the leaching of available arsenic from the cadmium-arsenic co-contaminated soil.

[0089] At mass percentages of 1%, 2%, 4%, 6%, and 8%, the cadmium stability rates of the ball-milled materials were 29.95%, 32.73%, 41.15%, 52.26%, and 57.92%, respectively, and the arsenic stability rates were 8.61%, 9.73%, 7.53%, 8.19%, and 10.73%, respectively.

[0090] Example 7

[0091] The iron oxide / LDHs composite material (prepared in the same way as in Example 1) was used as the test material for cadmium and arsenic stability testing, as follows:

[0092] The test material was mixed into the cadmium-arsenic soil (excluding water mass) at a mass percentage of 4% to stabilize the cadmium-arsenic content. The available cadmium-arsenic content in the cadmium-arsenic soil was 3.182 mg / kg and 1.291 mg / kg, respectively, and the total cadmium-arsenic content was 4.3 mg / kg and 43 mg / kg, respectively. The pH of the cadmium-arsenic soil was 5.8. Before mixing in the test material, water was added to the cadmium-arsenic soil according to the set soil-water mass ratio to control the soil-water ratio of the cadmium-arsenic soil.

[0093] In this embodiment, the soil-to-water mass ratios were set to 1:0.3, 1:0.6, 1:1, 1:1.25, and 1:1.5, respectively. Cadmium-arsenic stability tests were conducted at each of the set soil-to-water mass ratios.

[0094] See the results of the measurements after 7 days of stabilization. Figure 10 As shown, at soil-to-water ratios of 1:0.3, 1:0.6, 1:1, 1:1.25, and 1:1.5, the cadmium stability rates were 39.22%, 44.70%, 56.29%, 57.94%, and 59.26%, respectively, while the arsenic stability rates were 24.81%, 37.97%, 45.49%, 45.49%, and 43.61%, respectively.

[0095] Example 8

[0096] Compared to Example 7, this embodiment only replaces the cadmium-arsenic soil, while keeping other conditions unchanged. In this embodiment, the available cadmium and arsenic contents in the cadmium-arsenic soil are 0.183 mg / kg and 0.356 mg / kg, respectively, and the total cadmium and arsenic contents are 0.362 mg / kg and 12.7 mg / kg, respectively. The pH of the cadmium-arsenic soil is 5.53.

[0097] The test results were obtained after 7 days of stabilization. Figure 11 As shown, at soil-to-water ratios of 1:0.3, 1:0.6, 1:1, 1:1.25, and 1:1.5, the cadmium stability rates were 17.97%, 47.16%, 47.18%, 52.47%, and 52.45%, respectively, while the arsenic stability rates were 2.78%, 13.08%, 7.53%, 10.51%, and 13.73%, respectively.

[0098] Example 9

[0099] The iron oxide / LDHs composite material (prepared in the same way as in Example 1) was used as the test material for cadmium and arsenic stability testing, as follows:

[0100] The test material was mixed into the cadmium-arsenic soil (excluding water) at a mass percentage of 4% to stabilize the cadmium-arsenic. The available cadmium-arsenic content in the soil was 3.182 mg / kg and 1.291 mg / kg, respectively, and the total cadmium-arsenic content was 4.3 mg / kg and 43 mg / kg, respectively. The pH of the soil was 5.8. Water was added to the soil before mixing in the test material to control the soil-water mass ratio at 1:1. Samples were taken for analysis at remediation times of 7, 14, 21, 28, and 42 days.

[0101] See the test results. Figure 12 As shown, the cadmium stability rates on days 7, 14, 21, 28, and 42 were 50.36%, 52.35%, 62.53%, 64.74%, and 72.9%, respectively, while the arsenic stability rates were 44.97%, 47.24%, 50.25%, 41.15%, and 43.59%, respectively.

[0102] The treated soil was tested for cadmium and arsenic content in dry soil, and the specific results are as follows:

[0103] On days 7, 14, 21, 28, and 42, the contents of available cadmium in the soil were 1.58 mg / kg, 1.52 mg / kg, 1.19 mg / kg, 1.12 mg / kg, and 0.86 mg / kg, respectively, and the contents of available arsenic in the soil were 0.71 mg / kg, 0.68 mg / kg, 0.64 mg / kg, 0.76 mg / kg, and 0.73 mg / kg, respectively.

[0104] Comparative Example 1

[0105] Mix 5g of magnesium aluminum hydrotalcite (magnesium aluminum molar ratio of 6:2) and 0.5g of iron oxide evenly in a ball mill jar, and add milling balls at a ball-to-material ratio of 20:1; then, ball mill the mixture for 2 hours at a speed of 550 rpm with four alternating forward and reverse rotations to obtain the repair material.

[0106] Weigh 0.025g of the remediation material into a centrifuge tube, add 25mL of a cadmium-arsenic mixed solution with a concentration of 50mg / L for both cadmium and arsenic; then, place the centrifuge tube in a shaker and shake for 24 hours, and determine the cadmium and arsenic concentrations using ICP-OES. The cadmium-arsenic mixed solution was prepared from CdNO3 and AsNa3O4·12H2O, and the pH of the cadmium-arsenic mixed solution was 5.5.

[0107] In this comparative example, the cadmium removal rate of the remediation material was 99.26%, and the arsenic removal rate was 61.53%.

[0108] Comparative Example 2

[0109] 5g of magnesium-aluminum hydrotalcite (magnesium-aluminum molar ratio of 4:2) was placed in a ball mill jar, and milling balls were added at a ball-to-material ratio of 20:1. Then, solid-phase ball milling was performed for 2 hours at a speed of 550rpm with four cycles of alternating forward and reverse rotation to obtain the repair material.

[0110] Weigh 0.025g of the remediation material into a centrifuge tube, add 25mL of a cadmium-arsenic mixed solution with a concentration of 50mg / L for both cadmium and arsenic; then, place the centrifuge tube in a shaker and shake for 24 hours, and determine the cadmium and arsenic concentrations using ICP-OES. The cadmium-arsenic mixed solution was prepared from CdNO3 and AsNa3O4·12H2O, and the pH of the cadmium-arsenic mixed solution was 5.5.

[0111] In this comparative example, the cadmium removal rate of the remediation material was 68.04%, and the arsenic removal rate was 40.67%.

[0112] Comparative Example 3

[0113] Mix 5g of magnesium aluminum hydrotalcite (magnesium aluminum molar ratio of 4:2) and 0.5g of iron oxide evenly to obtain the repair material.

[0114] Weigh 0.025g of the remediation material into a centrifuge tube, add 25mL of a cadmium-arsenic mixed solution with a concentration of 50mg / L for both cadmium and arsenic; then, place the centrifuge tube in a shaker and shake for 24 hours, and determine the cadmium and arsenic concentrations using ICP-OES. The cadmium-arsenic mixed solution was prepared from CdNO3 and AsNa3O4·12H2O, and the pH of the cadmium-arsenic mixed solution was 5.5.

[0115] In this comparative example, the cadmium removal rate of the remediation material was 71.18%, and the arsenic removal rate was 48.12%.

[0116] The above technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made under the technical concept of the present invention using the contents of the present invention specification and drawings, or direct / indirect applications in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. The application of an iron oxide / LDHs composite material in the removal and / or stabilization of cadmium and arsenic, characterized in that, The preparation method of the iron oxide / LDHs composite material includes: ball milling iron oxide and magnesium aluminum hydrotalcite together to obtain the iron oxide / LDHs composite material; wherein the mass percentage of the iron oxide and the magnesium aluminum hydrotalcite is 1-15%.

2. The application according to claim 1, characterized in that, In the magnesium-aluminum hydrotalcite, the molar ratio of magnesium to aluminum is less than 3.

3. The application according to claim 2, characterized in that, In the magnesium-aluminum hydrotalcite, the molar ratio of magnesium to aluminum is 1.5-2.5:

1.

4. The application according to claim 1, characterized in that, The mass percentage of the iron oxide and the magnesium aluminum hydrotalcite is 8-12%.

5. The application according to claim 1, characterized in that, The ball mill rotates at a speed of 200-800 rpm, and the milling time is 1-8 hours.

6. The application according to claim 1, characterized in that, The ball mill uses a ball-to-material ratio of 10-20:

1.

7. A method for removing cadmium and arsenic, characterized in that, include: Iron oxide / LDHs composite material is mixed into cadmium and arsenic wastewater to remove cadmium and arsenic from the wastewater; The preparation method of the iron oxide / LDHs composite material includes: ball milling iron oxide and magnesium aluminum hydrotalcite together to obtain the iron oxide / LDHs composite material; wherein the mass percentage of the iron oxide and the magnesium aluminum hydrotalcite is 1-15%.

8. The method for removing cadmium and arsenic according to claim 7, characterized in that, In the magnesium-aluminum hydrotalcite, the molar ratio of magnesium to aluminum is less than 3.

9. The method for removing cadmium and arsenic according to claim 8, characterized in that, In the magnesium-aluminum hydrotalcite, the molar ratio of magnesium to aluminum is 1.5-2.5:

1.

10. The method for removing cadmium and arsenic according to claim 7, characterized in that, The mass percentage of the iron oxide and the magnesium aluminum hydrotalcite is 8-12%.

11. The method for removing cadmium and arsenic according to claim 7, characterized in that, The ball mill rotates at a speed of 200-800 rpm, and the milling time is 1-8 hours.

12. The method for removing cadmium and arsenic according to claim 7, characterized in that, The ball mill uses a ball-to-material ratio of 10-20:

1.

13. A method for stabilizing cadmium arsenic, characterized in that, include: Iron oxide / LDHs composite material is mixed into cadmium-arsenic soil to stabilize cadmium and arsenic in the soil. The preparation method of the iron oxide / LDHs composite material includes: ball milling iron oxide and magnesium aluminum hydrotalcite together to obtain the iron oxide / LDHs composite material; wherein the mass percentage of the iron oxide and the magnesium aluminum hydrotalcite is 1-15%.

14. The method for stabilizing cadmium arsenic according to claim 13, characterized in that, In the magnesium-aluminum hydrotalcite, the molar ratio of magnesium to aluminum is less than 3.

15. The method for stabilizing cadmium arsenic according to claim 14, characterized in that, In the magnesium-aluminum hydrotalcite, the molar ratio of magnesium to aluminum is 1.5-2.5:

1.

16. The method for stabilizing cadmium arsenic according to claim 13, characterized in that, The mass percentage of the iron oxide and the magnesium aluminum hydrotalcite is 8-12%.

17. The method for stabilizing cadmium arsenic according to claim 13, characterized in that, The ball mill rotates at a speed of 200-800 rpm, and the milling time is 1-8 hours.

18. The method for stabilizing cadmium arsenic according to claim 13, characterized in that, The ball mill uses a ball-to-material ratio of 10-20:1.

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