Preparation method and application of carboxyl type compound eluting agent suitable for arsenic and heavy metal contaminated soil

Abstract

The invention discloses a preparation method and application of a carboxyl type compound eluting agent suitable for arsenic and heavy metal contaminated soil. The preparation and application method of the leaching agent comprises the following steps: mixing oxalic acid (OA) and glutamic acid N, N-tetrasodium diacetate (GLDA) according to a molar concentration ratio of 2: (1-4) in an isovolumetric manner to prepare a compound leaching agent, mixing the compound leaching agent with compound polluted soil, carrying out oscillation leaching, and then carrying out solid-liquid separation to repair the polluted soil. According to the method, the compound eluting agent is developed by scientifically combining the same type of functional group eluting agent, and the synchronous removal efficiency of arsenic and heavy metal in soil is synergistically improved by utilizing the reduction effect of oxalic acid (OA) and the acid dissolution and strong complexing effect of glutamic acid N, N-tetrasodium diacetate (GLDA). Components and application conditions of the compound eluting agent are simple, the eluting effect is slightly affected by the soil pollution condition, operability is high, popularization is easy, and the compound eluting agent has good application prospects in soil arsenic and heavy metal combined pollution remediation.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal contaminated soil remediation, and specifically relates to a preparation method and application of a carboxyl type composite eluent suitable for arsenic and heavy metal contaminated soil. Background Art

[0002] The soil in mining areas and metal smelting areas is seriously contaminated by complex heavy metals, and complex pollution of anionic and cationic heavy metals / metalloids is a typical type of pollution. For example, the soil of abandoned lead-zinc mines is generally contaminated by complex arsenic (As), cadmium (Cd) and lead (Pb). As and heavy metals (such as Cd and Pb) have opposite geochemical characteristics in the soil environment and cannot be removed by the same mechanism, so it is difficult to remediate them simultaneously and efficiently. For the remediation of soil contaminated with arsenic and heavy metals, compared with the solidification / stabilization technology that leaves pollutants in the soil and may have the risk of secondary activation, the leaching technology can remove most heavy metals / metalloids. In principle, long-term monitoring is not required and it has been successfully used in the remediation of many heavy metal / metalloid contaminated sites.

[0003] Eluent is a key factor in soil leaching technology. Existing studies have shown that a single eluent with high removal rates of both anionic and cationic heavy metals / metalloids is rare. Research on leaching and remediation of anionic and cationic heavy metal / metalloid composite contaminated soils is currently focused on the development of combined eluents. In order to simultaneously and efficiently remove arsenic and heavy metals in soil, eluents that are effective against arsenic and heavy metals are usually combined in a compound or graded manner. However, the antagonistic reactions, diversity, and high concentration and high dosage of the components in the combination are usually overlooked. The literature "Comparison of Multi-stage Leaching Effects of Different Eluents on Arsenic-Contaminated Soils" shows that MGDA and KH containing different types of functional groups have good performance. 2 PO 4 The compound eluent has an antagonistic effect when eluting As. MGDA will have an elution effect on phosphate, resulting in a decrease in the As removal capacity of the combination. The invention patent with the publication number CN200810198394 discloses a chemical elution remediation method for heavy metal contaminated soil, using Na 2 The combination of EDTA, oxalic acid and KI is used to step-by-step elute arsenic and heavy metal compound contaminated soil. The three-component three-stage elution can simultaneously remove As, Cd and Pb in the soil, but the eluent components are complex and the dosage is large. The elution operation is repeated many times and takes a long time. The removal rate of arsenic and heavy metals is less than 50%. The invention patent with the publication number CN 113736469B discloses an eluent suitable for high-concentration arsenic-antimony compound contaminated soil and its preparation and application. 0.2 mol·L of the same carboxyl eluent is used. -1 of citric acid and 1 mol·L -1The oxalic acid compound elution was used to wash arsenic and antimony contaminated soil. Compared with the single eluent, the removal rate of arsenic and antimony by the compound eluent increased, but the increase was less than 5%. The eluent concentration was high, the reaction speed was large, and the time was long.

[0004] Combined carboxyl eluents have the potential to simultaneously remove arsenic and heavy metals from soils, and can weaken the antagonistic reaction between components to a certain extent. However, there are currently few studies on the use of carboxyl eluents to repair anionic and cationic heavy metal / metalloid composite contaminated soils, and the application conditions of eluents still need to be optimized. The biodegradable chelating agent glutamic acid tetrasodium N,N-diacetate (GLDA) has the same efficiency as EDTA in removing cationic heavy metals (EDTA is currently one of the most efficient eluents for the remediation of cationic heavy metal contaminated soils); the low molecular weight organic acid oxalic acid (OA) has a good removal efficiency for anionic heavy metal arsenic, and can achieve a high removal efficiency at low concentrations (0.4 mol·L in the comparative example of invention patent CN 202210073052). -1 The removal rate of arsenic by oxalic acid is 21.31%, while that by tartaric acid is only 7.99%). The two are combined and the composition ratio is adjusted to develop a composite eluent, and its remediation effect in different types of soil is explored. It has the potential to repair anion and cation heavy metal contaminated soil with simple low-concentration components, but there is no relevant eluent and its application research. Summary of the invention

[0005] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a leaching agent with simple application conditions, good remediation effect, and suitable for soils contaminated with arsenic and heavy metals. The leaching agent provided by the present invention contains a carboxyl group of the same type of functional group, and is compounded with oxalic acid (OA) with high removal efficiency for anionic metalloid arsenic in soil and glutamic acid N, N-diacetate tetrasodium (GLDA) with high removal efficiency for cationic heavy metals in soil, and synergizes the reducing effect of oxalic acid (OA) and the acid dissolution and strong complexation of glutamic acid N, N-diacetate tetrasodium (GLDA), which can simultaneously elute arsenic and heavy metals in the soil. At the same time, the leaching agent and elution conditions have little interference with the mineral structure of the soil, are environmentally friendly, have good remediation effects on different types of soils, and can effectively control the soil arsenic and heavy metal contamination.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a carboxyl-type composite eluent suitable for arsenic and heavy metal contaminated soil and its application, comprising the following steps:

[0008] (1) The composite eluent is prepared by mixing equal volumes of oxalic acid (OA) and tetrasodium glutamate N,N-diacetate (GLDA) solution.

[0009] (2) The compound eluent and the composite contaminated soil are mixed, shaken and eluted, and the solid phase is collected after centrifugation, which is the repaired soil, thus completing the elution remediation of the contaminated soil.

[0010] In the step (1), the preparation method of the composite eluent is: oxalic acid (OA) and glutamic acid N,N-diacetate tetrasodium (GLDA) are mixed in equal volumes at a molar concentration ratio of 2: (1-4), preferably at a molar concentration ratio of 2:4.

[0011] In step (1), the concentration of oxalic acid (OA) is 0.2 mol·L -1 ~0.4mol·L -1 , preferably 0.2 mol·L -1 .

[0012] In step (1), the concentration of tetrasodium glutamate N,N-diacetate (GLDA) is 0.2 mol·L -1 ~0.4mol·L -1 , preferably 0.4 mol·L -1 .

[0013] In the step (1), the pH value of the eluent is prepared by using 0.1 mol·L -1 HCl or 0.1 mol·L -1 The NaOH content is adjusted to 3-5, preferably 4.

[0014] In the step (2), the contaminated soil to be repaired is mixed with the composite eluent, and the soil-liquid ratio is 1 g: (10-30) mL, preferably 1 g: 10 mL.

[0015] In the step (2), the elution time during the oscillation elution process is 20 min to 240 min, preferably 120 min.

[0016] In the step (2), the oscillation speed during the elution process is 100 to 200 rpm, preferably 180 rpm.

[0017] In the step (2), the centrifugal speed during the centrifugation process is 3000 rpm and the centrifugal time is 2 min.

[0018] The present invention provides a method for preparing a carboxyl-type composite eluent suitable for arsenic and heavy metal contaminated soil and its application, which is used for repairing arsenic and heavy metal composite contaminated soil. The composite contaminated soil is any arsenic and heavy metal composite contaminated soil, such as arsenic-cadmium-lead and arsenic-lead composite contaminated soil.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The present invention combines oxalic acid (OA) and glutamic acid N, N-diacetate tetrasodium (GLDA) containing the same type of functional group carboxyl to form a composite eluent. The acidity and reducibility of the carboxyl group, the dynamic ionization equilibrium reaction formed by the difference in component concentration, and the ligand complexation selectivity can synergistically remove different types of heavy metals / metalloids. The chemical reaction between the composite components is weakened, and the reaction mechanism differences between oxalic acid and anionic metalloids, which are mainly reductive reactions, and glutamic acid N, N-diacetate tetrasodium (GLDA) and cationic heavy metals, which are mainly acid dissolution and ligand complexation reactions, and the synergistic effect of the ionization equilibrium reaction between the components are utilized to improve the simultaneous removal efficiency of anionic and cationic heavy metals / metalloids in composite contaminated soils, and has good application prospects.

[0021] (2) The present invention obtains an arsenic and heavy metal contaminated soil eluent by compounding carboxyl oxalic acid (OA) and glutamic acid tetrasodium diacetate (GLDA) which have high leaching efficiency for anionic and cationic heavy metals / metalloids in soil. The eluent has good remediation effects on various heavy metal pollutions in soil. The eluent concentration, solid-liquid ratio, elution time and other conditions are easy to achieve, the remediation effect is good, the eluent components are easy to obtain, the damage to the soil mineral structure is small, the environment is friendly, and the technology is easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the change of removal efficiency of As, Cd and Pb of composite eluent in As-Cd-Pb contaminated soil ZY with elution time and the kinetic fitting of the process;

[0023] Figure 2 It is the removal effect of composite eluent on different forms of As in soil ZY contaminated by As-Cd-Pb;

[0024] Figure 3 It is the removal effect of composite eluent on different forms of Cd in soil ZY contaminated by As-Cd-Pb;

[0025] Figure 4 It is the removal effect of composite eluent on different forms of Pb in As-Cd-Pb contaminated soil ZY;

[0026] Figure 5 It is the XRD spectrum of As-Cd-Pb contaminated soil ZY before and after eluting with composite eluent;

[0027] Figure 6 It is the change of As and Pb removal efficiency of composite eluent in As-Pb contaminated soil ZZ with elution time and the kinetic fitting of the process;

[0028] Figure 7 It is the removal effect of composite eluent on different forms of As in As-Pb contaminated soil ZZ;

[0029] Figure 8 It is the removal effect of composite eluent on different forms of Pb in As-Pb contaminated soil ZZ;

[0030] Fig. 9 is the XRD spectrum of As-Pb contaminated soil ZZ before and after eluting with composite eluent; DETAILED DESCRIPTION

[0031] The following is a specific description of the preparation method and application of a carboxyl-type composite eluent suitable for arsenic and heavy metal contaminated soil proposed by the present invention, but the protection scope of the present invention is not limited thereby. The experimental soil ZY used is As-Cd-Pb composite contaminated soil, the soil pH is 7.18±0.05, and the As content in the soil is 398.66±36.40 mg·kg -1 , Cd content is 26.30±1.48mg·kg -1 , Pb content 6506.52±228.88mg·kg -1 The experimental soil ZZ used was As-Pb composite contaminated soil, soil pH = 5.69 ± 0.02, and the As content in the soil was 34.26 ± 4.7 mg kg -1 , Pb content 384.99±44.05mg·kg -1 .

[0032] Example 1: Remediation effect of composite eluent on As-Cd-Pb contaminated soil

[0033] This example shows the remediation effect of OA and GLDA composite eluents on As-Cd-Pb contaminated soil ZY. The composite eluent is prepared by the method described in the claim, mixed with the contaminated soil, and the removal effect of the composite eluent on soil As, Cd and Pb is measured and analyzed after oscillation elution, including the following steps:

[0034] The test soil was the As-Cd-Pb contaminated surface soil (0-20 cm) around a mining area. It was naturally air-dried and passed through a 2 mm sieve for later use. An oscillation elution experiment was performed to add 0.2 mol·L -1 OA and 0.4 mol·L -1 GLDA and a composite eluent (pH = 4) were mixed in equal volumes. 0.5 g of the test soil was placed in a centrifuge tube, and 5 mL of the composite eluent was added at a solid-liquid ratio of 1:10. After mixing evenly, the mixture was shaken and eluted at 180 rpm at room temperature for 120 min. After centrifugal filtration, the heavy metal content of the supernatant was determined by ICP-MS, and the removal rate of heavy metals in the soil was calculated.

[0035] The removal rates of As, Cd and Pb in contaminated soil ZY by composite eluent vary with time and the kinetic fitting results are shown in Figure 2. Figure 1As shown. The removal rate of the composite eluent for total As, Cd and Pb in the soil increased with time, and the removal rates of the three heavy metals reached dynamic equilibrium after 2 hours, indicating that the composite eluent can quickly remove arsenic and heavy metals in alkaline contaminated soil in a short time. The removal rates of the composite eluent for total As, Cd and Pb in the contaminated soil were 29.04%, 75.31% and 67.75% respectively (equilibrium removal rates obtained by secondary kinetic fitting), indicating that the composite eluent can effectively remove arsenic and heavy metals in alkaline contaminated soil.

[0036] Comparative Example 1: Remediation effect of single OA and GLDA eluents on As-Cd-Pb contaminated soil

[0037] The difference between Comparative Example 1 and Example 1 is that the eluent used is a single OA or a single GLDA. This comparative example is the remediation effect of a single OA and GLDA eluent on the As-Cd-Pb contaminated soil ZY. The removal effect of a single OA and GLDA eluent on soil As, Cd and Pb was determined and analyzed by the elution method described in Example 1, including the following steps:

[0038] The test soil was the As-Cd-Pb contaminated surface soil (0-20 cm) around a mining area. It was naturally air-dried and passed through a 2 mm sieve for later use. The oscillation elution experiment was performed by adding 0.2 mol·L -1 OA or 0.4 mol·L -1 GLDA eluent. Place 0.5 g of test soil in a centrifuge tube, add 5 mL of a single eluent according to a solid-liquid ratio of 1:10, mix well, and elute at 180 rpm at room temperature for 120 min. After centrifugal filtration, use ICP-MS to determine the heavy metal content of the supernatant and calculate the removal rate of heavy metals in the soil.

[0039] The test results show that the removal rates of As, Cd and Pb in the soil by single OA leaching are 25.01%, 27.32% and 7.28% respectively. The removal rates of As, Cd and Pb in the soil by single GLDA leaching are 8.12%, 78.22% and 4.02% respectively. The removal rates of As, Cd and Pb in the soil by the composite eluent in Example 1 are higher than those of single OA, and the removal rate of Cd is basically the same as that of GLDA, while the removal rates of As and Pb are higher than those of single GLDA, indicating that the composite eluent can simultaneously and efficiently repair alkaline arsenic and heavy metal contaminated soil.

[0040] Example 2: Removal efficiency of composite eluent for different forms of As, Cd and Pb in As-Cd-Pb contaminated soil

[0041] This example shows the removal effect of OA and GLDA composite eluents on different forms of As, Cd and Pb in As-Cd-Pb contaminated soil ZY. The composite eluent is prepared by the method described in the claim, mixed with the contaminated soil, and the removal effect of the composite eluent on different forms of As, Cd and Pb in the soil is measured and analyzed after oscillation elution, including the following steps:

[0042] The test soil was the As-Cd-Pb contaminated surface soil (0-20 cm) around a mining area. It was naturally air-dried and passed through a 2 mm sieve for later use. An oscillation elution experiment was performed to add 0.2 mol·L -1 OA and 0.4 mol·L -1 GLDA and a composite eluent (pH = 4) were mixed in equal volumes. 0.5 g of the test soil was placed in a centrifuge tube, and 5 mL of the composite eluent was added at a solid-liquid ratio of 1:10. After mixing evenly, the mixture was shaken and eluted at 180 rpm for 120 min at room temperature. After centrifugation, the supernatant was discarded and the soil was dried at low temperature for later use. The BCR morphological classification method was used to determine the morphological distribution changes of Cd and Pb in the soil before and after elution (exchangeable state EXC, reducible state RED, oxidizable state OXI, residual state RES), and the Wenzel-SEP morphological classification method was used to determine the morphological distribution changes of As in the soil before and after elution (non-specific adsorption state F1, specific adsorption state F2, amorphous iron-aluminum oxide-bound state F3, crystalline iron-aluminum oxide-bound state F4, residual state F5).

[0043] The concentration changes of different forms of As, Cd and Pb in soil ZY before and after elution with composite eluent are shown in Figure 2. Figures 2 to 4 As shown. The composite eluent mainly removes As in the amorphous iron / aluminum oxide-bound state F3 and the crystalline iron-aluminum oxide-bound state F4 in the soil, both of which are insoluble arsenic forms. After leaching, the content of these two forms of As in the total amount decreased by 17.20% and 9.71%, respectively. This is mainly due to the reaction of oxalic acid in the composite eluent with arsenic-containing iron minerals, reducing iron to release arsenic and removing As in the soil. The composite eluent has a removal effect on different forms of Cd and Pb in the soil, among which the removal amount of exchangeable Cd and reducible Pb is the largest. After leaching, their forms in the total amount decreased by 61.98% and 59.64%, respectively. These two forms of heavy metals are weakly bound and easily soluble forms, mainly due to the removal of tetrasodium glutamate-N,N-diacetate in the composite eluent through acid dissolution and complexation. At the same time, GLDA can also complex with iron reduced by OA, inhibit the recombination of arsenic and iron, and synergistically improve the removal effect of arsenic.

[0044] Example 3: Removal effect of composite eluent on other heavy metals in As-Cd-Pb contaminated soil

[0045] This example shows the removal effect of OA and GLDA composite eluents on other heavy metals in composite contaminated soil ZY. The composite eluent is prepared by the method described in the claim, mixed with the contaminated soil, and the removal effect of the composite eluent on other heavy metals (Co, Cu and Zn) in the soil is measured and analyzed after oscillation elution, including the following steps:

[0046] The test soil was the As-Cd-Pb contaminated surface soil (0-20 cm) around a mining area. It was naturally air-dried and then passed through a 2 mm nylon sieve for later use. An oscillation elution experiment was performed to add 0.2 mol·L -1 OA and 0.4 mol·L -1 GLDA and a composite eluent (pH = 4) were mixed in equal volumes. 0.5 g of the test soil was placed in a centrifuge tube, and 5 mL of the composite eluent was added at a solid-liquid ratio of 1:10. After mixing evenly, the mixture was shaken and eluted at 180 rpm at room temperature for 120 min. After centrifugal filtration, the heavy metal content of the supernatant was determined by ICP-MS, and the removal rate of other heavy metals (Co, Cu and Zn) in the soil was calculated.

[0047] The test results show that the removal rates of the composite eluent for total Co, Cu and Zn in the soil are 38.10%, 52.01% and 86.72% respectively, indicating that in addition to the target pollutants, the composite eluent also has a good removal efficiency for other heavy metals in the soil and has the potential to be used for the remediation of other types of composite polluted soils.

[0048] Test Example 1: Effect of composite eluent on As-Cd-Pb soil mineral structure

[0049] This example is about the effect of OA and GLDA composite eluents on soil mineral structure. The composite eluent is prepared, mixed with contaminated soil, and the soil is shaken and eluted to analyze the change of soil mineral structure before and after elution using XRD, including the following steps:

[0050] The test soil was the As-Cd-Pb contaminated surface soil (0-20 cm) around a mining area. It was naturally air-dried and passed through a 2 mm sieve for later use. An oscillation elution experiment was performed to add 0.2 mol·L -1 OA and 0.4 mol·L -1 GLDA and a composite eluent (pH = 4) were mixed in equal volumes. 5.0 g of the test soil was placed in a centrifuge tube, and 50 mL of the composite eluent was added at a solid-liquid ratio of 1:10. After mixing evenly, the mixture was shaken and eluted at 180 rpm for 120 min at room temperature. The supernatant was discarded by centrifugation, and the eluted soil was dried at low temperature for later use. The soil before and after elution was ground through a 100-mesh nylon sieve, and the changes in the soil mineral structure before and after elution were determined using XRD (X'Pert Pro, Netherlands).

[0051] XRD spectrum analysis of soil before and after elution with composite eluent Figure 5 As shown in the figure, compared with the original soil, the position of the mineral structure peak in the soil after leaching has not changed, only the intensity of some characteristic peaks of muscovite and kaolinite has slightly decreased, indicating that the types of soil mineral components have not changed after leaching, the leaching of the composite eluent has little damage to the soil mineral structure, and the leaching process has little impact on the soil.

[0052] Example 4: Remediation effect of composite eluent on As-Pb contaminated soil

[0053] This example shows the remediation effect of OA and GLDA composite eluents on As-Pb composite contaminated soil ZZ. The composite eluent is prepared by the method described in the claim, mixed with the contaminated soil, and the removal effect of the composite eluent on soil As and Pb is measured and analyzed after oscillation elution, including the following steps:

[0054] The test soil was the As-Pb contaminated surface layer (0-20 cm) of soil around a mining area. It was naturally air-dried and then passed through a 2 mm sieve for later use. An oscillation elution experiment was performed to add 0.2 mol·L -1 OA and 0.4 mol·L -1 GLDA and a composite eluent (pH = 4) were mixed in equal volumes. 0.5 g of the test soil was placed in a centrifuge tube, and 5 mL of the composite eluent was added at a solid-liquid ratio of 1:10. After mixing evenly, the mixture was shaken and eluted at 180 rpm at room temperature for 120 min. After centrifugal filtration, the heavy metal content of the supernatant was determined by ICP-MS, and the removal rate of heavy metals in the soil was calculated.

[0055] The removal rate of As and Pb in contaminated soil ZZ by composite eluent changes with time and the kinetic fitting results are shown in Figure 6 As shown. The removal rate of total As and Pb in soil by the composite eluent increases with time. The removal rate of Pb reaches dynamic equilibrium after 1 hour, and the removal rate of As reaches dynamic equilibrium after 2 hours. This may be due to the difference in the main reaction mechanism between the composite eluent and arsenic and heavy metals. The leaching removal of arsenic is that OA breaks down iron minerals through reduction reaction to release arsenic, while heavy metals are directly released by GLDA through acid dissolution and complexation, resulting in rate differences. At the same time, it shows that the composite eluent can quickly remove arsenic and heavy metals in acidic contaminated soil in a short time. The removal rates of total As and Pb in soil by the composite eluent are 37.13% and 58.19%, respectively (equilibrium removal rates obtained by secondary kinetic fitting), indicating that the composite eluent can effectively remove arsenic and heavy metals in acidic contaminated soil.

[0056] Comparative Example 2: Remediation effect of single OA and GLDA eluents on As-Pb contaminated soil

[0057] The difference between Comparative Example 2 and Example 4 is that the eluent used is a single OA or a single GLDA. This comparative example is the remediation effect of a single OA and GLDA eluent on As-Pb contaminated soil ZZ. The removal effect of a single OA and GLDA eluent on soil As, Cd and Pb was determined and analyzed by the elution method described in Example 4, including the following steps:

[0058] The test soil was the As-Pb contaminated surface layer (0-20 cm) of soil around a mining area. It was naturally air-dried and then passed through a 2 mm sieve for later use. The oscillation elution experiment was performed by adding 0.2 mol·L -1 OA or 0.4 mol·L -1 GLDA eluent (pH = 4). Place 0.5 g of test soil in a centrifuge tube, add 5 mL of a single eluent according to a solid-liquid ratio of 1:10, mix well, shake and elute at 180 rpm at room temperature for 120 min, centrifuge and filter, and use ICP-MS to determine the heavy metal content of the supernatant to calculate the removal rate of heavy metals in the soil.

[0059] Single 0.2 mol·L -1 The removal rates of As and Pb in soil by OA leaching were 34.06% and 23.14% respectively. -1 GLDA elution, the removal rates of As and Pb in the soil were 4.55% and 44.94%. The removal of As and Pb in the soil by the composite eluent in Example 4 was higher than that of single OA and single GLDA, indicating that the composite eluent can simultaneously and efficiently repair acidic arsenic and heavy metal contaminated soil.

[0060] Example 5: Removal efficiency of composite eluent for different forms of As and Pb in As-Pb contaminated soil

[0061] This example shows the removal effect of OA and GLDA composite eluents on different forms of heavy metals in As-Pb contaminated soil ZZ. The composite eluent is prepared by the method described in the claim, mixed with the contaminated soil, and the removal effect of the composite eluent on different forms of As and Pb in the soil is measured and analyzed after oscillation elution, including the following steps:

[0062] The test soil was the As-Pb contaminated surface layer (0-20 cm) of soil around a mining area. It was naturally air-dried and then passed through a 2 mm sieve for later use. An oscillation elution experiment was performed to add 0.2 mol·L -1 OA and 0.4 mol·L -1GLDA and a composite eluent (pH = 4) were mixed in equal volumes. 0.5 g of the test soil was placed in a centrifuge tube, and 5 mL of the composite eluent was added at a solid-liquid ratio of 1:10. After mixing evenly, the mixture was shaken and eluted at 180 rpm for 120 min at room temperature. After centrifugation, the supernatant was discarded, and the soil was dried at low temperature. The BCR morphological classification method was used to determine the morphological distribution changes of Cd and Pb in the soil before and after elution (exchangeable state EXC, reducible state RED, oxidizable state OXI, residual state RES), and the Wenzel-SEP morphological classification method was used to determine the morphological distribution changes of As in the soil before and after elution (non-specific adsorption state F1, specific adsorption state F2, amorphous iron-aluminum oxide-bound state F3, crystalline iron-aluminum oxide-bound state F4, residual state F5).

[0063] The concentration changes of different forms of As and Pb in soil ZZ before and after elution with composite eluent are shown in Figure 2. Figures 7-8 As shown. The composite eluent mainly removes As in the amorphous iron / aluminum oxide-bound state F3 and the crystalline iron-aluminum oxide-bound state F4 in the soil, both of which are insoluble arsenic forms. After leaching, the proportion of these two forms of As in the total amount of the original soil decreased by 35.74% and 9.41%, respectively. This is mainly due to the reduction reaction of oxalic acid in the composite eluent with arsenic-containing iron minerals to dissolve the minerals and release arsenic, thereby removing As in the soil. The composite eluent mainly removes Pb in the reducible state RED and the oxidizable state OXI of the soil. After leaching, the proportion of these two forms of Pb in the total amount decreased by 61.94% and 6.38%, respectively. The removal is mainly based on the removal of weakly bound and easily soluble forms, which are mainly removed by acid dissolution and complexation using tetrasodium glutamate-N,N-diacetate in the composite eluent.

[0064] Example 6: Removal effect of composite eluent on other heavy metals in As-Pb contaminated soil

[0065] This example shows the removal effect of OA and GLDA composite eluents on other heavy metals in composite contaminated soil ZZ. The composite eluent is prepared by the method described in the claim, mixed with the contaminated soil, and the removal effect of the composite eluent on other heavy metals (Co, Cu and Zn) in the soil is measured and analyzed after oscillation elution, including the following steps:

[0066] The test soil was the As-Pb contaminated surface soil (0-20 cm) around a mining area. It was naturally air-dried and passed through a 2 mm nylon sieve for later use. The oscillation elution experiment was performed by adding 0.2 mol·L -1 OA and 0.4 mol·L -1GLDA and a composite eluent (pH = 4) were mixed in equal volumes. 0.5 g of the test soil was placed in a centrifuge tube, and 5 mL of the composite eluent was added at a solid-liquid ratio of 1:10. After mixing evenly, the mixture was shaken and eluted at 180 rpm at room temperature for 120 min. After centrifugal filtration, the heavy metal content of the supernatant was determined by ICP-MS, and the removal rate of other heavy metals (Co, Cu and Zn) in the soil was calculated.

[0067] The test results show that the removal rates of the composite eluent for total Co, Cu and Zn in the soil are 16.25%, 35.85% and 17.96% respectively, indicating that in addition to the target pollutants, the composite eluent also has a good removal efficiency for other heavy metals in the soil and has the potential to be used for the remediation of other types of composite polluted soils.

[0068] Test Example 2: Effect of composite eluent on As-Pb soil mineral structure

[0069] This example is about the effect of OA and GLDA composite eluents on soil mineral structure. The composite eluent is prepared, mixed with contaminated soil, and the soil is shaken and eluted to analyze the change of soil mineral structure before and after elution using XRD, including the following steps:

[0070] The test soil was the As-Pb contaminated surface layer (0-20 cm) of soil around a mining area. It was naturally air-dried and then passed through a 2 mm sieve for later use. An oscillation elution experiment was performed to add 0.2 mol·L -1 OA and 0.4 mol·L -1 GLDA and a composite eluent (pH = 4) were mixed in equal volumes. 5.0 g of the test soil was placed in a centrifuge tube, and 50 mL of the composite eluent was added at a solid-liquid ratio of 1:10. After mixing evenly, the mixture was shaken and eluted at 180 rpm for 120 min at room temperature. The supernatant was discarded by centrifugation, and the eluted soil was dried at low temperature for later use. The soil before and after elution was ground through a 100-mesh nylon sieve, and the changes in the soil mineral structure before and after elution were determined using XRD (X'Pert Pro, Netherlands).

[0071] XRD spectrum analysis of soil before and after elution with composite eluent Fig. 9 As shown in the figure, compared with the original soil, the position of the mineral structure peak in the soil after leaching has not changed, only the intensity of some characteristic peaks of muscovite has slightly decreased, indicating that the types of soil mineral components have not changed after leaching, the leaching of the composite eluent has little damage to the soil mineral structure, and the leaching process has little impact on the soil.

Claims

1. A method for preparing a carboxyl-type composite eluent suitable for arsenic and heavy metal contaminated soil, characterized in that: The preparation method of the carboxyl type composite eluent is as follows: oxalic acid (OA) and glutamic acid N,N-diacetate tetrasodium (GLDA) are mixed in equal volumes at a molar concentration ratio of 2: (1-4).

2. The method for preparing a carboxyl type composite eluent according to claim 1, wherein: The concentration of oxalic acid (OA) is 0.2 mol·L -1 ~0.4mol·L -1 .

3. The method for preparing a carboxyl type composite eluent according to claim 1, wherein: The concentration of the glutamic acid N,N-diacetate tetrasodium (GLDA) is 0.2 mol·L -1 ~0.4mol·L -1 .

4. The method for preparing a carboxyl type composite eluent according to claim 1, wherein: The pH value of the compound eluent is adjusted to 3-5 by using NaOH or HCl.

5. The use of the composite eluent prepared by the method according to claim 1, characterized in that: The composite eluent is mixed with the composite contaminated soil, eluted by oscillation, and the solid phase is collected after centrifugation to obtain the repaired soil.

6. The method according to claim 5, characterized in that The soil-liquid ratio of the composite contaminated soil and the compound leaching agent is 1g: (10-30)mL, and the elution time of the oscillation elution process is 20min-240min.

7. The method according to claim 5, characterized in that The composite contaminated soil is soil contaminated by arsenic and heavy metals, and the heavy metals include but are not limited to cadmium and lead.

8. Use of the method according to any one of claims 1 to 7 in remediating soil contaminated by arsenic and heavy metals.

Images