Curing agent for repairing lead-arsenic compound polluted soil and repairing method

Abstract

The invention discloses a curing agent for repairing lead-arsenic compound polluted soil and a repairing method, and relates to the technical field of environmental geotechnical engineering.The method comprises the following steps that a Pb (NO3) 2 solution and a NaAsO2 solution are taken and added into a clean soil body, the mixture is stirred to be uniform, and polluted soil is prepared; adding an acidified Fenton reagent, uniformly stirring, and standing until complete reaction to obtain the polluted soil; uniformly mixing red mud, steel slag and modified electrolytic manganese slag to prepare an ERS curing agent, adding the ERS curing agent into the polluted soil, and adding deionized water to prepare solidified soil; and pressing to obtain a soil sample with the maximum dry density, demolding, sealing, transferring and curing. The method has the advantages of raw material saving, high efficiency and convenience, and accords with the idea of green and sustainable restoration.

Description

Technical Field

[0001] The invention relates to the technical field of environmental geotechnical engineering, and in particular to a curing agent and a repair method for repairing lead-arsenic composite contaminated soil. Background Art

[0002] According to the National Soil Pollution Survey Bulletin, lead and arsenic are typical inorganic pollutants in China's soil. Lead (Pb) is a cation that exists mainly in the form of Pb (II) in heavy metal-contaminated soil. The presence of lead in soil comes from industrial activities, including non-ferrous metal smelting, mining activities, the use of lead-containing products, and the combustion of fossil fuels. The presence of arsenic (As) in soil comes from pesticide application, fossil fuel combustion, agricultural activities, and mining activities, and exists mainly in the form of As (III) and As (V). These heavy metals are easy to accumulate in the soil and are difficult to degrade, causing potential irreversible soil pollution. Heavy metal elements can also enter the bodies of animals and plants through the soil-water-plant system, causing damage to the surrounding ecological environment and posing a threat to human health. Compared with the low-toxic and low-mobility As (V), the high toxicity and mobility of As (III) make As (III) difficult to be adsorbed by common adsorption materials (iron-based, aluminum-based materials). Studies have shown that Fenton's reagent can oxidize most of the As (III) in wastewater to more stable As (V). Fenton's reagent is a strong oxidant prepared from H2O2 and FeSO4. Zhang Wenjie and others used Fenton reagent combined with ferric chloride and cement to treat heavily arsenic-contaminated soil, and found that the fixation rate of arsenic in the repaired soil was as high as 99%. However, the large-scale use of cement and ferric chloride will significantly increase the cost of use and carbon emissions. At the same time, the large amount of iron salts (acidic when hydrolyzed) in the soil will also cause soil acidification, thereby increasing the risk of lead leaching.

[0003] Electrolytic manganese slag (EMR) is the acid leaching residue in the production process of electrolytic manganese metal (EMM). The modified electrolytic manganese slag can produce a large amount of iron / manganese oxides and silicates with heavy metal adsorption properties. Ma Ming et al. used modified electrolytic manganese slag to repair heavy metal contaminated soil. The stability rates of modified electrolytic manganese slag for Pb and As(V) were as high as 97.59% and 71.99%, respectively. However, because it contains NH4 + -N, Mn(II) and other soluble pollutants, if not properly handled, will cause harm to the environment and human health.

[0004] In addition, it is rare for a single pollutant to cause pollution in an industrial pollution site. The most significant situation is that multiple heavy metals are simultaneously present in the soil of the site. Among them, Pb and As are both typical inorganic pollutants in the soil, and both are often simultaneously present in high concentrations in industrial pollution sites.

[0005] In the existing technology, solidification / stabilization technology (S / S) is the most common remediation method in the actual application of soil remediation due to its economy, efficiency and convenience. However, most of the solidifying agents currently developed for solidifying heavy metal contaminated soil contain high-cost, high-carbon emission products such as cement and lime. With the continuous improvement of the level of solid waste resource utilization, industrial solid waste has gradually come into the public eye.

[0006] The existing technology research is mostly focused on the remediation of divalent cation contaminated soil (lead, cadmium, zinc, etc.) and As(V) contaminated soil, and the research on effective and green remediation of complex contaminated soil is also relatively scattered. Summary of the invention

[0007] The present invention aims to solve the problems that there are few reports on the remediation of composite contaminated soil at present, the commonly used curing agents for curing heavy metal contaminated soil mostly contain high-cost and high-carbon emission products such as cement and lime, and the electrolytic manganese slag is improperly handled, which is harmful to the environment and human health. The present invention provides a curing agent and a remediation method for repairing lead-arsenic composite contaminated soil.

[0008] The present invention is implemented by the following technologies: The present invention provides a method for preparing a curing agent for repairing lead-arsenic composite contaminated soil, comprising the following steps: a. Collect foundation pit soil, air-dry it, crush it, and then pass it through a 2 mm sieve to obtain clean soil. Take Pb(NO3)2 solution and NaAsO2 solution as pollution sources, add them into the clean soil and stir them evenly. The Pb content in the mixed soil is greater than or equal to 1.00%, the As content is greater than or equal to 0.21%, and the moisture content is greater than or equal to 20%. After sealing, place it in a cool place for passivation for 10 days to obtain contaminated soil.

[0009] b. Add 0-4% acidified Fenton reagent to the contaminated soil. To obtain better oxidation performance of the soil, the acidified Fenton reagent is a Fenton reagent acidified to pH 4 with dilute sulfuric acid. 2+ The molar ratio of H2O2 is 1:10; stir evenly and leave for three days to react completely to obtain contaminated soil.

[0010] c. modifying the electrolytic manganese slag to obtain modified electrolytic manganese slag; The specific steps include: ca, drying the electrolytic manganese slag in an oven at 105° C., grinding it with a crusher, and mixing the ground electrolytic manganese slag with calcium oxide in a mass ratio of 7:3 to obtain a mixed solid; cb, mixing the mixed solid with deionized water at a solid-to-liquid ratio of 1:3, stirring, and standing at room temperature for one day to achieve complete reaction, thereby obtaining a mixture; cc, filter the mixture, take the filter residue and dry it, use a crusher to crush it to obtain electrolytic manganese slag powder, and calcine it at 800°C in a muffle furnace for 2 hours to obtain modified electrolytic manganese slag.

[0011] d. Red mud that was air-dried, crushed, and passed through a 0.1 mm sieve was selected. The main elements of the red mud were SiO2, Al2O3, CaO, Fe2O3, K2O, and MgO, of which the content of SiO2 was 20.78% and the content of Al2O3 was 22.36%; The surface area of ​​slag is 429m 2 / kg, the steel slag includes SiO2, CaO, Al2O3, Fe2O3, and MgO, wherein the content of SiO2 is 14.72%, and the content of CaO is 37.39%; Red mud, steel slag and modified electrolytic manganese slag are uniformly mixed, with the red mud content being 10% to 30% and the mass ratio of modified electrolytic manganese slag to steel slag being 0.20 to 1.00, to obtain ERS curing agent, and 15% ERS curing agent is added to the contaminated soil. Since the hydration of the curing agent will consume part of the water, deionized water is added to make the moisture content reach 15 to 20%, specifically 18.05%, to obtain cured soil.

[0012] e. Press the solidified soil to obtain a soil sample with the maximum dry density, demould and seal it, and transfer it to a curing box with a relative humidity of 80-100% and a temperature of 20±2℃ for curing; The specific steps include: ea, take the solidified soil and put it into a stainless steel mold, the stainless steel mold is in the shape of a cylinder with a diameter of 50 mm and a height of 100 mm, use a hydraulic jack with a force of 20 kN to press the soil sample to a height of 50 mm, and press to obtain a soil sample with the maximum dry density; eb, demoulding, and placing the soil sample into a polyethylene bag and sealing it; ec, transferred to a curing box with a relative humidity of 95% and a temperature of 20±2℃ for curing, and the curing age was 7 days, 14 days, and 28 days.

[0013] The invention also provides a curing agent for repairing lead-arsenic composite contaminated soil.

[0014] The principle of the present invention for solidifying lead-arsenic contaminated soil is that the ERS solidifier and Fenton reagent can synergistically convert most of the highly toxic and highly mobile As(III) in the contaminated soil into low-toxic and low-mobility As(V), thereby promoting its adsorption on Fe / Mn oxides and hydroxides. After the ERS solidifier is added to the contaminated soil, the modified electrolytic manganese slag and red mud hydration reaction result in a large amount of OH - 、SO4 2- , Ca 2+ and AlO4 5-The slag is then hydrolyzed to release a large amount of Ca 2+ OH - and SiO4 4- .Ca 2+ OH - and SiO4 4- It can produce calcium silicate hydrate (CSH) by volcanic ash reaction. Calcium silicate hydrate (CSH) not only has good gel and filling properties, but also has good resistance to Pb 2+ Cations such as Ca and Mg have strong electrostatic adsorption, physical sealing and ion exchange effects. 2+ OH - and AlO4 5- It can form ettringite (AFt) with good mechanical properties, which can fill pores and improve the strength of solidified soil. In addition, AFt has good ion exchange capacity. 2+ and SO 2- Can be Pb2 2+ and AsO4 2- Substitution, forming Pb-AFt and As-AFt isomers, thereby adsorbing Pb and As. Pb and As are easily reacted with CO3 2- OH - It combines with iron, manganese and calcium oxides / hydroxides to form PbCO3, Pb(OH)2 and Fe-As, Mn-As and Ca-As precipitates.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The present invention is a curing agent and a method for repairing lead-arsenic composite contaminated soil. The chemical oxidation technology is combined with the curing / stabilization technology. That is, after using the Fenton reagent to oxidize As(III) to As(V), EMR-RM-SS (ERS ternary curing agent) is added to stabilize the lead and arsenic in the soil, so as to realize the utilization of bulk industrial solid waste that is difficult to handle, and to achieve efficient recycling and waste utilization. EMR, RM, and SS have certain complementarity in the CaO-SiO2-Al2O3-SO3 mineral system. The three have the potential to synthesize cementitious materials.

[0016] The ERS solidifying agent prepared by the present invention significantly improves the strength and stability of the lead-arsenic composite contaminated soil, and the use of the Fenton reagent can significantly improve the solidification ability of arsenic. After curing for 28 days, the unconfined compressive strength of the solidified / stabilized soil of the lead-arsenic composite contaminated soil solidified by 15% of the ERS solidifying agent and 1.92% of the Fenton reagent was 1.06 Mpa, and the leaching concentrations of As and Pb were 0.23 and 0.48 mg / L, respectively. The solidified / stabilized soil has the potential for safe reuse.

[0017] The remediation strategy of the ERS curing agent prepared by the present invention in coordination with the Fenton reagent can effectively solidify / stabilize the lead-arsenic composite contaminated soil. Moreover, compared with the method of using the traditional curing agent alone, the present invention has better economic benefits and environmental friendliness. Traditional curing agents such as cement have high carbon emissions; although magnesium phosphate cement has low carbon emissions, it is expensive. In the present invention, only a small amount of Fenton reagent and a certain amount of solid waste can be used to effectively solidify / stabilize the lead-arsenic composite contaminated soil, which is in line with the concept of green and sustainable remediation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Shows the X-ray diffraction patterns of electrolytic manganese slag and modified electrolytic manganese slag.

[0019] Figure 2 It represents the Fourier transform infrared spectra of electrolytic manganese slag and modified electrolytic manganese slag.

[0020] Figure 3 The effects of the ERS curing agent with or without Fenton's reagent on the strength of the cured soil at different curing ages in Examples 1 to 5 are shown.

[0021] Figure 4 The effects of the ERS solidifying agent with or without Fenton's reagent in Examples 1 to 5 on the leaching concentrations of lead and arsenic in the solidified soil at different curing ages are shown.

[0022] Figure 5 Shows the XPS fitting spectrum of ERS solidified / stabilized soil assisted by Fenton's reagent.

[0023] Figure 6 The effect of the traditional curing agent in comparative examples 1 to 4 and the traditional curing agent in combination with Fenton's reagent on the strength of the cured soil at different curing ages is shown.

[0024] Figure 7 The effects of the traditional curing agent and the Fenton reagent in comparative examples 1 to 4 on the leaching concentrations of lead and arsenic in the cured soil at different curing ages are shown. DETAILED DESCRIPTION

[0025] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. Example 1

[0026] A method for preparing a curing agent for repairing lead-arsenic composite contaminated soil comprises the following steps: a. Collect soil from foundation pits at construction sites. The basic physical and chemical parameters of the soil are shown in Table 1.

[0027] According to my country's "Engineering Classification Standard for Soil" (GB / T 50145), the soil was determined to be sandy low liquid limit clay. The soil was air-dried, crushed, and sieved through a 2 mm sieve to obtain clean soil. Take Pb(NO3)2 solution and NaAsO2 solution as pollution sources, add them into clean soil and stir evenly. The Pb content in the mixed soil is 1.00%, the As content is 0.21%, and the moisture content is 20%. After sealing, place it in a cool place for passivation for 10 days to obtain contaminated soil.

[0028] The quadratic polynomial regression model was used to calculate the Fenton content, the mass ratio of modified manganese slag to steel slag, and the red mud content. Specifically, the optimal experimental parameters were obtained using the response surface equation based on the Box-Behnken principle in the Design Expert 13 software.

[0029] Considering that a high amount of Fenton reagent (acidic reagent) will affect the hydration effect of alkaline solid waste-based solidifying agent; a high amount of manganese slag or red mud will make the active SiO2 / CaO content in the solidifying agent system too low, which is not conducive to the formation of hydration products. Therefore, the three independent variables are A (Fenton content is 0-4%), B (mass ratio of modified manganese slag to steel slag is 0.2:1-1:1), and C (red mud content is 10%-30%), and the dependent variables are the unconfined compressive strength (UCS) of solidified soil and the leaching concentrations of heavy metals Pb and As. The data samples are shown in Table 2. The quadratic polynomial regression model of ERS solidified soil compressive strength and heavy metal leaching concentration was obtained by Design-Expert software. Variance analysis and credibility analysis were performed on the regression model.

[0030]

[0031] The coefficients of variation Cv of the regression models for compressive strength, lead ion and arsenic ion leaching concentration were 3.12%, 9.94% and 5.88%, respectively. All Cv were less than 10%, indicating that the experimental error was small. 2 The R values ​​of the regression models for compressive strength, Ps and As leaching concentrations were 0.98, 0.99 and 0.99, respectively, indicating that the fitted model can accurately predict the test results. adj 2 The R values ​​of the regression models for compressive strength, lead ion and arsenic ion leaching concentration were 0.96, 0.99 and 0.99, respectively. pre 2 The prediction coefficients were 0.86, 0.96 and 0.98 respectively. The signal-to-noise ratios of the regression models for compressive strength, lead ion and arsenic ion leaching concentrations were 22.77, 43.96 and 58.84 respectively. adj 2 and Rpre 2 The differences between them are all less than 0.2, and the signal-to-noise ratios are all greater than 4. This shows that the fitted model of ERS-stabilized soil compressive strength and heavy metal leaching concentration can accurately predict the test results.

[0032] The Numencial function in Design-Expert software was used to optimize the model independent variable parameters, and then the optimal experimental parameters for solidification / stabilization of lead-arsenic composite contaminated soil were selected. The results showed that the optimal engineering parameters for solidification / stabilization of soil were Fenton content of 1.92%, mass ratio of manganese slag to steel slag of 0.54, and red mud content of 28.76%. At this time, the model predicted that the compressive strength of the solidified soil was 1.03 MPa, and the lead leaching concentration was 0.09 mg·L -1 The arsenic leaching concentration is 0.35 mg·L -1 Under this parameter, a verification test was carried out to verify the engineering parameters. The test results showed that the solidified soil was determined to be 1.05 MPa, and the solidified soil met the conditions for reuse as engineering filler; the leaching concentration of lead was 0.10 mg / L, and the leaching concentration of arsenic ions was 0.33 mg / L. The errors between the compressive strength of the solidified soil and the leaching concentrations of lead and arsenic and the predicted values ​​were all less than 8%. The above analysis shows that the regression model has a high reliability in predicting and optimizing the test parameters.

[0033] b. Add 1.92% of Fenton's reagent acidified to pH 4 to the contaminated soil. The Fenton's reagent is composed of commercially available H2O2 (w / v 30%) and commercially available FeSO4·7H2O (>99%). 2+ Fe:H2O2 molar ratio 1:10 2+ The molar ratio of H2O2 is 1:10; stir evenly and leave for three days to react completely to obtain contaminated soil.

[0034] c. modifying the electrolytic manganese slag to obtain modified electrolytic manganese slag; Figure 1 It can be seen that the main substances and mineral phases in electrolytic manganese slag are calcined gypsum and quartz; after chemical modification, the main substance forms and mineral phases in electrolytic manganese slag are portlandite, anhydrite and calcium silicate. In addition, a small amount of MnO2, goethite (FeOOH) and magnetite (Fe3O4) were also detected in M-EMR (modified electrolytic manganese slag); Figure 2 It can be seen that after modification, some free water and bound water bonds (1619.70cm -1 and 3395.61cm -1) has moved in intensity and position. Combined with XRD analysis, the movement is due to the hydration reaction resulting in the generation of new hydration products (hydrated calcium silicate). In addition, the absorption wavelengths of SO, Si-O, Fe-O and Mn-O bonds have also changed. EMR contains a large amount of NH 3 -N, -NH (3555.6 cm -1 ). However, these characteristic peaks were not found in M-EMR, indicating that NH3-N almost disappeared during the modification process. Therefore, after modification, EMR not only removed a large number of harmful substances, but also produced a large amount of silicates and more iron and manganese oxides, improving its ability to adsorb heavy metals.

[0035] The specific steps include: ca, electrolytic manganese slag was collected from a manganese plant in Guizhou, the electrolytic manganese slag was dried in an oven at 105°C, ground using a crusher, and the ground electrolytic manganese slag and calcium oxide were mixed in a mass ratio of 7:3 to obtain a mixed solid; cb, the mixed solid was mixed with deionized water at a solid-liquid ratio of 1:3, stirred, and allowed to stand at room temperature for one day to obtain a mixture; to achieve complete reaction, cc, filter the mixture, take the filter residue and dry it, use a crusher to crush it to obtain electrolytic manganese slag powder, and calcine it at 800°C in a muffle furnace for 2 hours to obtain modified electrolytic manganese slag.

[0036] d, red mud was collected from an aluminum plant in Shanxi Province. After air drying and crushing, the red mud was sieved through a 0.1 mm sieve. The main elements of the red mud were SiO2, Al2O3, CaO, Fe2O3, K2O, and MgO, of which the content of SiO2 was 20.78% and the content of Al2O3 was 22.36%; The steel slag was purchased from a solid waste recycling plant with a surface area of ​​429m 2 / kg, the steel slag includes SiO2, CaO, Al2O3, Fe2O3, and MgO, wherein the content of SiO2 is 14.72%, and the content of CaO is 37.39%; Red mud, steel slag and modified electrolytic manganese slag are evenly mixed in a dry material stirring pot. The red mud content is 28.76%. The mass ratio of modified electrolytic manganese slag to steel slag is 0.20-1.00, specifically 0.54, to obtain ERS curing agent. 15% ERS curing agent is added to the contaminated soil. Since the hydration of the curing agent will consume part of the water, deionized water is added to make the moisture content reach 18.05% to obtain cured soil.

[0037] e. Press the solidified soil to obtain a soil sample with the maximum dry density, demould and seal it, and transfer it to a curing box with a relative humidity of 95% and a temperature of 20±2°C for curing; The specific steps include: ea, take the solidified soil and put it into a stainless steel mold, the stainless steel mold is in the shape of a cylinder with a diameter of 50 mm and a height of 100 mm, use a hydraulic jack with a force of 20 kN to press the soil sample to a height of 50 mm, and press to obtain a soil sample with the maximum dry density; eb, demoulding, and placing the soil sample into a polyethylene bag and sealing it; ec, transferred to a curing box with a relative humidity of 95% and a temperature of 20±2℃ for curing, and the curing age was 7 days, 14 days, and 28 days.

[0038] The solidified soil obtained by curing in Example 1 was tested: 1. Unconfined compressive strength test of stabilized soil The unconfined compressive strength of the solidified soil obtained by curing in Example 1 was measured. Figure 3 As shown in the figure, the compressive strength of Pb-As composite contaminated soil solidified by ERS solidifier in cooperation with Fenton reagent reached 0.78MPa after 7 days of curing, 0.89MPa after 14 days of curing, and 1.06MPa after 28 days of curing. With the extension of curing time, the hydration reaction gradually becomes sufficient, resulting in an increase in the number of hydration products, enhanced gel bonding and filling effects, and thus enhanced the compressive strength of the soil.

[0039] 2. Toxicity leaching test The broken samples were collected for subsequent testing. The toxicity leaching test was conducted in accordance with the Chinese standard "Toxicity Leaching Method for Solid Waste Leaching", using a sulfuric acid / nitric acid solution with a mass ratio of 2:1 (pH 3.20±0.05) as the leaching solution to simulate the acid rain erosion scenario. The results are as follows Figure 4As shown in the figure, the leaching concentrations of Pb and As in the untreated contaminated soil were 65.67 and 50.00 mg / L, respectively, exceeding the safety threshold of Pb and As leaching concentrations of less than 5 mg / L specified in the Chinese Hazardous Waste Identification Standard (GB 5085.3-2007). However, after adding Fenton's reagent and ERS solidification agent to the Pb-As composite contaminated soil, the heavy metal leaching concentrations of the contaminated soil were significantly reduced. After 7 days of curing, the leaching concentrations of lead and arsenic in the ERS solidified soil treated with Fenton's reagent were 0.38 and 0.73 mg / L, respectively. The leaching concentrations of lead and arsenic in the solidified soil after 28 days were 0.23 and 0.48 mg / L, respectively, which were close to the corresponding limits of the groundwater Class IV water quality standard (Pb≤0.1 mg / L, As≤0.05 mg / L). Although arsenite may react with lead ions or other cations in the soil to generate a small amount of arsenite precipitate mainly composed of lead arsenite during the preparation of the contaminated soil. Since ERS-solidified soil is alkaline, the alkaline pore fluid in the solidified soil will dissolve lead arsenite (easily soluble in acid / alkaline solutions) and make them free ions again. Lead arsenite precipitates may exist in the contaminated soil at first, but the alkaline environment provided by the hydration of the solidifying agent will dissolve it. The contaminated ions produced by the dissolution are adsorbed and fixed by silicates and Fe / Mn oxides. Although a small amount of lead arsenite may still exist, it will dissolve during the toxic leaching experiment. This situation will lead to a decrease in the stability rate of Pb and As in the solidified soil. Despite this, the toxic leaching values ​​of arsenic and lead in the solidified soil still meet the safe treatment standards for hazardous solid wastes, which fully demonstrates the effectiveness of the remediation strategy of Fenton reagent in conjunction with ERS solidifying agent to repair lead-arsenic contaminated soil. With the increase of curing age, the content of cementitious products produced by the hydration reaction increases, which can enhance the physical encapsulation and chemical adsorption of Pb and As by the soil.

[0040] 3. XPS measurement The XPS measurements of the Fenton reagent and ERS curing agent for Pb-As composite contaminated soil were recorded using an X-ray photoelectron spectrometer (Thermo Kalpha). The binding energy was calibrated using the C1s peak of carbon at 284.8 eV. Figure 5 As shown. The relative content of As(V) (44.9 eV) in the contaminated soil treated with ERS solidifier and Fenton reagent reached 88%. The transition of As 3d binding energy shows that most of the As(III) in the contaminated soil is oxidized to As(V) by ·OH in Fenton reagent, Mn(IV) and Fe(III) in EMR. As(V) has extremely low toxicity and mobility, and is easier to coordinate with Fe / Mn elements to form more stable compounds. The 138.58 eV and 143.37 eV of Pb 4f correspond to Pb 4f 7 / 2 and Pb 4f 5 / 2The peaks of 2 and 3 indicate the presence of PbSiO3, Pb(OH)2 and PbCO3 precipitation in the ERS solidified soil synergized with Fenton reagent. The XPS results further confirmed that lead and arsenic were fixed through ion exchange and complex precipitation.

[0041] Because arsenite may react with lead ions or other cations in the soil to generate a small amount of arsenite precipitate mainly composed of lead arsenite during the preparation of lead-arsenic composite contaminated soil, contaminated soils containing only lead and only arsenic were prepared separately as controls. Example 2

[0042] In this embodiment, in step a, the content of lead in the heavy metal contaminated soil is 0%, and the content of arsenic is 0%, and the rest is exactly the same as in Example 1. Strength tests are performed on ERS solidified soil samples after curing for 7 days, 14 days, and 28 days, respectively. Example 3

[0043] In this embodiment, in step a, the content of lead in the heavy metal contaminated soil is 1%, and the content of arsenic is 0%, and the rest is exactly the same as in Example 1. Strength tests are performed on ERS solidified soil samples after curing for 7 days, 14 days, and 28 days, respectively. Example 4

[0044] In this embodiment, in step a, the content of lead in the heavy metal contaminated soil is 0%, and the content of arsenic is 0.21%. The rest is exactly the same as in Example 1. Strength tests are performed on ERS solidified soil samples after curing for 7 days, 14 days, and 28 days, respectively. Example 5

[0045] In this embodiment, Fenton's reagent was not added, and only ERS curing agent with a dosage of 15% was used. The rest was completely consistent with Example 1. Strength tests were carried out on ERS cured soil samples after curing for 7 days, 14 days, and 28 days.

[0046] Comparing Example 1 with Examples 2 to 5, Figure 3 It can be seen that the compressive strength of different soils solidified by Fenton reagent and ERS solidifier after 28 days of curing is as follows: Example 2> Example 4> Example 3> Example 1. The results show that the addition of Pb and As affects the cementing properties of ERS solidified soil and reduces the compressive strength of ERS solidified soil. Due to the influence of the relatively high heavy metal content in the solidified contaminated soil, a higher amount of precipitation is caused, thereby encapsulating the unhydrated solidifier and hindering the formation of products with gel and filling properties.

[0047] The compressive strength of soil stabilized with ERS curing agent in combination with Fenton reagent increases with the curing age. This is because as the curing time increases, the hydration reaction gradually becomes complete, resulting in an increase in the number of hydration products, enhanced gel bonding and filling effects, and thus enhanced soil compressive strength. The strength of soil stabilized with ERS curing agent in combination with Fenton reagent is 6% to 8% lower than that of soil stabilized with ERS curing agent alone, which meets the safety limit for repeated use. + and SO4 2- The Ca(OH)2 produced by ERS hydration was consumed, but the formation of more ettringite may offset some of the negative effects on the strength of the stabilized soil caused by the reduction of Ca(OH)2 content.

[0048] Depend on Figure 4 It can be seen that the stabilization effect of Fenton reagent in ERS solidification agent on Pb in Pb-As composite contaminated soil is lower than that of single Pb contaminated soil. Due to the limited hydration reaction products in the solidified soil and the potential competition between Pb(II) and As(III) for adsorption sites, the solidification / stabilization of excess Pb(II) in the soil is limited. However, the As leaching concentration of single As contaminated soil solidified / stabilized by Fenton reagent in ERS solidification agent is slightly higher than that of Pb-As composite contaminated soil solidified by Fenton reagent in ERS solidification agent. This is due to the high pH value of ERS solidified soil with an initial arsenic content of 0.21%. At the same time, with the increase of curing age, the leaching concentrations of Pb and As gradually decreased. After 28 days of treatment with ERS solidification agent at a dosage of 15%, the leaching concentrations of Pb and As reached 0.19 and 2.26 mg / L, respectively. After 28 days of treatment with ERS solidification agent at a dosage of 15%, the leaching concentration of As was high, which was easy to cause environmental pollution. Although the acidic Fenton reagent may affect the formation of Ca(OH)2, the ability of ERS to fix lead in oxidized soils has hardly decreased. This is due to the hydrolysis of Fe(II) in the Fenton reagent and the supplementation of sulfate ions, which gradually produce goethite and ettringite with strong heavy metal adsorption capacity, which have an adsorption effect on Pb. Comparative Example 1

[0049] Cement (PC) was used as a curing agent to solidify the lead-arsenic composite contaminated soil that had not been treated with Fenton's reagent. The rest of the preparation process, curing process, and sample preparation method were the same as those in Example 1. The total amount of the curing agent was 15% (relative to the dry soil mass). Comparative Example 2

[0050] Cement assisted by Fenton's reagent was used as a curing agent. The rest of the preparation process, curing process, and sample preparation method were the same as those in Example 1. The total amount of the curing agent was 15%, and the amount of the Fenton's reagent was 1.92% (relative to the dry soil mass). Comparative Example 3

[0051] Red mud-assisted magnesium phosphate cement (RM-MPC) was used as a curing agent. The rest of the preparation process, curing process, and sample preparation method were the same as those in Example 1. The total amount of the curing agent was 15% (relative to the dry soil mass). Comparative Example 4

[0052] The magnesium phosphate cement assisted by red mud and Fenton's reagent was used as the curing agent. The rest of the preparation process, curing process and sample preparation method were the same as those in Example 1. The total dosage of the curing agent was 15% (relative to the dry soil mass), and the dosage of the Fenton's reagent was 1.92%.

[0053] The strength test and toxicity leaching test were performed on the Pb-As composite contaminated soil solidified by the curing agent in Comparative Examples 1 to 4 for 28 days. Figure 6 It can be seen that cement and red mud-assisted magnesium phosphate cement are both alkaline curing agents, and Fenton's reagent will also affect its hydration reaction in the soil, thereby affecting the strength of the cured soil. The strength values ​​of the cured soil with 15% PC, RM-MPC and ERS assisted by 1.92% Fenton's reagent after 28 days of curing were 1.34, 0.85 and 1.06 MPa, respectively. The results show that the mechanical properties of the ERS-cured soil assisted by Fenton's reagent are better than those of the RM-MPC-cured soil assisted by Fenton's reagent, but lower than those of the PC-cured soil assisted by Fenton's reagent. This finding can be attributed to the high calcium content in cement. At the same curing agent dosage and curing age, the proportion of cementitious products (CSH and AFt) that may be formed in PC-cured soil is higher than that of the cured / stabilized soil using other curing agents.

[0054] Depend on Figure 7 It can be seen that the As leaching concentrations of the stabilized soil with 15% PC and RM-MPC dosages are 5.58 and 1.99 mg / L, respectively. The stabilization effect of ERS on As is better than that of PC and RM-MPC. The As leaching concentration of 1.92% Fenton's reagent in synergistic PC-stabilized soil is 4.59 mg / L. The As leaching concentration of 1.92% Fenton's reagent in synergistic RM-MPC-stabilized soil is 1.03 mg / L. The stabilization ability of PC, RM-MPC and ERS under the coordination of Fenton's reagent on As in contaminated soil increases successively, which may be due to the increase in the content of Fe / Mn oxides in PC, RM-MPC and ERS. Pb in RM-MPC stabilized soil 2+ The leaching concentration is lower than that of ERS and PC stabilized soils. This is because Pb3(PO4)2 has better stability than Pb(OH)2 in acidic environment.

[0055] The heavy metal contaminated soil remediation method of the present invention is simple, convenient, low-cost and has good performance. The SS, EMR and RM used in the present invention are all industrial solid wastes that are difficult to handle, and only the additional calcination and grinding costs need to be considered. Moreover, the amount of Fenton reagent used is only 1.92%, and the cost of use and carbon emissions are low. In contrast, the use of PC and MPC to repair contaminated soil may result in relatively high costs and carbon emissions. The remediation strategy of using Fenton reagent in conjunction with ERS curing agent not only has a good curing / stabilization effect, but also has relatively little impact on the environment and has good economic value. The present invention also provides a new research idea and technical path for the remediation of heavy metal contaminated sites. At the same time, the research results can provide a scientific basis and theoretical support for the resource utilization of hazardous solid wastes.

[0056] The scope of protection claimed by the present invention is not limited to the above specific embodiments. For those skilled in the art, the present invention may have various deformations and changes. Any modifications, improvements and equivalent substitutions made within the concept and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A curing agent for repairing lead-arsenic composite contaminated soil, It is characterized in that The following steps are involved: a, take Pb(NO 3 ) 2 Solution and NaAsO 2 The solution is added to the clean soil and stirred evenly, wherein the Pb content in the mixed soil is greater than or equal to 1.00%, the As content is greater than or equal to 0.21%, and the moisture content is greater than or equal to 20%. After sealing, the mixed soil is placed in a cool place for passivation for 10 days to obtain contaminated soil; b. Add acidified Fenton's reagent to the contaminated soil, stir evenly, and leave for three days until the reaction is complete to obtain contaminated soil; c. modifying the electrolytic manganese slag to obtain modified electrolytic manganese slag; d. Evenly mix red mud, steel slag and modified electrolytic manganese slag to prepare ERS curing agent, add ERS curing agent to the contaminated soil, add deionized water to make the moisture content reach 15-20%, and prepare cured soil; e. Press the solidified soil to obtain a soil sample with maximum dry density, demold and seal it, and transfer it to a curing box with a relative humidity of 80~100% and a temperature of 20±2℃ for curing.

2. A curing agent for repairing lead-arsenic composite contaminated soil according to claim 1, Features: Step c specifically includes the following steps: ca, drying the electrolytic manganese slag at 105° C., grinding, and mixing the ground electrolytic manganese slag and calcium oxide in a mass ratio of 7:3 to obtain a mixed solid; cb, mixing the mixed solid with deionized water at a solid-to-liquid ratio of 1:3, stirring, and standing at room temperature for one day to obtain a mixture; cc, filter the mixture, take the filter residue, dry it, and crush it to obtain electrolytic manganese slag powder, which is calcined at 800°C for 2 hours to obtain modified electrolytic manganese slag.

3. A curing agent for repairing lead-arsenic composite contaminated soil according to claim 1, Features: In step a, the clean soil is obtained by collecting foundation pit soil, air-drying it, crushing it and then passing it through a 2 mm sieve.

4. A curing agent for repairing lead-arsenic composite contaminated soil according to claim 1, Features: In step b, the acidified Fenton reagent is a Fenton reagent acidified to a pH value of 4 by dilute sulfuric acid, wherein Fe 2+ and H 2 O 2 The molar ratio is 1:10; the content of the Fenton reagent is 0-4%.

5. A curing agent for repairing lead-arsenic composite contaminated soil according to claim 1, Features: In step d, the dosage of the ERS curing agent is 15%, in which the mass ratio of modified electrolytic manganese slag to steel slag is 0.20-1.00, and the red mud content is 10%-30%; deionized water is added to make the moisture content reach 18.05%.

6. A curing agent for repairing lead-arsenic composite contaminated soil according to claim 5, Features: The red mud is air-dried, crushed, and sieved through a 0.1 mm sieve; SiO 2 The content of Al is 20.78%, 2 O 3 The content is 22.36%; The surface area of ​​the slag is 429m 2 / kg, SiO in the steel slag 2 The content of Al is 14.72%, and the content of CaO is 37.39%.

7. A curing agent for repairing lead-arsenic composite contaminated soil according to claim 1, Features: In step e, the steps are specifically performed: ea, take the solidified soil and put it into a stainless steel mold, the stainless steel mold is in the shape of a cylinder with a diameter of 50 mm and a height of 100 mm, use a hydraulic jack with a force of 20 kN to press the soil sample to a height of 50 mm, and press to obtain a soil sample with the maximum dry density; eb, demoulding, and placing the soil sample into a polyethylene bag and sealing it; ec, transferred to a curing box with a relative humidity of 95% and a temperature of 20±2℃ for curing, and the curing age was 7 days, 14 days, and 28 days.

8. A curing agent for repairing lead-arsenic composite contaminated soil.

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