Method for evaluating long-term stability of phosphoric acid-based geopolymer acidic lead polluted soil

Abstract

The invention discloses a method for evaluating the long-term stability of phosphoric acid-based geopolymer acidic lead polluted soil, and belongs to the technical field of heavy metal polluted soil technologies. The method comprises the following steps: taking a plurality of solidified polluted soil samples with the same specification as parallel test objects, and respectively obtaining data of influences of different curing agent mixing amounts and different freezing and thawing cycle times on toxicity leaching, compressive strength, elastic modulus, resistivity, pH and conductivity of the solidified polluted soil; and carrying out fitting analysis on the macroscopic data, and evaluating the long-term stability of the phosphoric acid-based geopolymer polluted soil in a freezing and thawing cycle. According to the method, a resistivity-based solidified acid heavy metal polluted soil long-term stability evaluation model is provided, and a toxicity leaching-based solidified acid heavy metal polluted soil freeze-thaw resistance service life prediction model is established, so that the result is accurate and reliable; reliable technical guidance is provided for long-term stability and safety of the phosphoric acid-based geopolymer solidified acid heavy metal polluted soil under freezing and thawing cycles.

Description

Technical Field

[0001] The invention relates to the technical field of heavy metal contaminated soil, and more specifically to a method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil. Background Art

[0002] With the rapid growth of modern industry, the amount of soil contaminated by toxic heavy metals is increasing. Mining and metallurgical activities are the main sources of soil lead pollution. 2+ It will be absorbed and accumulated by plants and enter the human body through the food chain or drinking water, causing harm to health, such as damage to brain tissue, nervous system and reproductive system. 2+ When the content exceeds the standard, effective measures need to be taken to deal with it. Solidification / stabilization (S / S) technology is widely used in S / S treatment of contaminated soil due to its wide applicability. The curing agent used in S / S technology is mainly cement-based materials. Cement-based materials CO 2 High emissions, high energy consumption and poor acid resistance of solidified contaminated soil. In comparison, alkali-activated materials are more environmentally friendly contaminated soil treatment materials, and have higher strength, better acid resistance and lower CO 2 Carbon emissions, for Pb 2+ The S / S effect of contaminated soil is better. However, many acid mines, electroplating plants, lead-acid battery plants and other wastewater (pH <3) contaminated sites are also acidic, and the performance of cement-based materials and alkali-activated materials is obviously incompatible with the acidic contaminated soil environment. Cement-based materials and alkali-activated materials are both alkaline materials, which need to react in a strong alkaline environment to produce strength. When cement-based materials and alkali-activated materials are directly used for S / S treatment of acidic heavy metal contaminated soil, the effect will drop sharply. Phosphate-based polymers are cementitious materials with excellent mechanical properties formed in an acidic environment, and have good application prospects in acidic contaminated sites. However, previous studies have shown that the modified phosphate-based polymer (MAPG) curing agent developed based on phosphate-based polymers has no effect on acidic Pb 2+ Contaminated soil has excellent S / S effect, but the performance and effect of MAPG solidifier contaminated soil under complex environmental conditions such as freeze-thaw cycles have not yet been clarified.

[0003] Freeze-thaw cycles are a common climate change phenomenon in engineering projects. Freeze-thaw cycles are an alternating process in which the temperature fluctuates above and below 0°C, causing the soil to freeze and melt. The freeze-thaw cycle will cause the heavy metal ions in the solidified contaminated soil to be released again, causing secondary pollution of the site, thereby affecting the long-term remediation effect of the heavy metal contaminated site. At the same time, the freeze-thaw cycle also poses a major challenge to the risk assessment of the effect of solidifying contaminated soil. The freeze-thaw cycle will change the physical and chemical properties of the pollution, thereby affecting the solidification effect of heavy metals. The frost heave force generated by the capillary water in the soil under the action of the freeze-thaw cycle will have a significant effect on the pore structure of the soil, resulting in the appearance of new pore channels and cracks. At the same time, the flow of water generated by the melting of ice crystals will enhance the separation of soil aggregates, increase the hydraulic conductivity and porosity of the soil, promote the migration of heavy metal ions, and accelerate the leaching of pollution. In addition, the nitrification of soil organic matter induced by the freeze-thaw cycle will produce a large amount of H + , resulting in a decrease in soil pH. pH changes will affect the adsorption of heavy metal ions by the soil. Studies have found that as the number of freeze-thaw cycles increases, the amount of heavy metal ions adsorbed by the soil decreases. In recent years, with the escalation of the intensity of extreme weather events caused by climate change, it is crucial to evaluate the long-term stability of solidified contaminated soil under extreme environments. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and to provide an accurate, reliable and highly instructive method for evaluating the long-term stability of phosphate-based polymer-solidified acidic heavy metal contaminated soil under freeze-thaw cycles.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil is proposed. Multiple solidified contaminated soil samples of the same specifications are used as parallel test objects to obtain data on the effects of different curing agent dosages and different freeze-thaw cycle numbers on the toxic leaching, compressive strength, elastic modulus, resistivity, pH and conductivity of the solidified contaminated soil. These macro data are then fitted and analyzed to evaluate the long-term stability of the phosphate-based polymer contaminated soil under freeze-thaw cycles.

[0007] The present invention is further configured that the specific steps of the evaluation method are:

[0008] S1. MAPG curing agent was mixed with acidic lead contaminated soil to prepare cylindrical solidified contaminated soil samples with different curing agent dosages but the same specifications. After curing at room temperature under the same conditions, each solidified contaminated soil sample was subjected to multiple freeze-thaw cycles;

[0009] S2. Test the toxicity leaching, compressive strength, elastic modulus, resistivity, pH and EC of the solidified contaminated soil samples under each freeze-thaw cycle;2+ The leaching concentration was determined, and the measured data were fitted and analyzed with the curing agent dosage and the number of freeze-thaw cycles to establish a service life prediction model for the freeze-thaw resistance of solidified acidic heavy metal contaminated soil based on toxic leaching; the resistivity and elastic modulus of solidified contaminated soil were determined, and a long-term stability evaluation model for solidified acidic heavy metal contaminated soil based on resistivity was established; the pH and EC of solidified contaminated soil were determined, and the measured data were fitted and analyzed with the toxic leaching data to establish pH, ​​EC and Pb respectively. 2+ Leaching concentration fitting relationship.

[0010] The present invention is further configured such that the mass of each solidified contaminated soil sample is 210 g.

[0011] The present invention is further configured such that the amount of the curing agent used to solidify the contaminated soil sample is 6% to 12%.

[0012] The present invention is further configured such that a complete freeze-thaw cycle process in the method is: the solidified contaminated soil is placed in a standard curing box for curing for 28 days, then taken out, placed in a constant temperature and low-temperature test box at -20°C for 24 hours, then the solidified contaminated soil sample is taken out, and placed back in a constant temperature and humidity standard curing box at 21±2°C for 24 hours for thawing.

[0013] The present invention is further configured such that the number of freeze-thaw cycles is 0, 2, 4, 6, or 8 times.

[0014] The present invention is further configured that the long-term stability evaluation model expression of solidified acidic heavy metal contaminated soil based on resistivity is E 50 =-6.87+1.26ρ, where: E 50 represents the elastic modulus, ρ represents the resistivity; the prediction model expression of the freeze-thaw resistance service life of the solidified acidic heavy metal contaminated soil based on toxic leaching is C=aN+b, where: C represents the heavy metal leaching concentration, N represents the number of freeze-thaw cycles, and a and b represent the prediction model parameters for different curing agent dosages.

[0015] The present invention is further configured that the solidified contaminated soil toxicity leaching test method is: after the compressive strength test, the soil sample and three kinds of leaching solutions are added into each extraction bottle at a liquid-to-solid ratio of 1:10, the bottle caps are tightly closed and placed on a flipping instrument for flipping, after the flipping is completed, the mixed solution is filtered, and the Pb 2+ Toxic leaching.

[0016] The present invention is further configured to adopt a two-phase electrode method and use a TH2820B+ type LCR digital bridge to perform resistivity testing, with a test frequency of 10 kHz and a test voltage of 1V.

[0017] The present invention is further configured that the pH and conductivity testing method is: grinding the soil sample after the unconfined compressive strength test into fine powder; mixing the fine powder with deionized water in a ratio of 1:1, and after standing, using a Mettlertoledo pH meter to measure its pH; mixing the fine powder with distilled water in a ratio of 1:5, and after standing, using a DDS-11A conductivity meter to measure its conductivity.

[0018] In summary, the present invention has the following beneficial effects:

[0019] The present invention simulates the service environment of solidified contaminated soil under freeze-thaw cycles, obtains the effects of different solidifying agent dosages and different freeze-thaw cycle numbers on toxic leaching, compressive strength, elastic modulus, resistivity, pH and conductivity of solidified contaminated soil, proposes a long-term stability evaluation model for solidified acidic heavy metal contaminated soil based on resistivity and a freeze-thaw resistance service life prediction model for solidified acidic heavy metal contaminated soil based on toxic leaching, and the evaluation results are accurate and reliable, providing reliable technical guidance for the long-term stability and safety of phosphate-based polymer solidified acidic heavy metal contaminated soil under freeze-thaw cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a graph showing the toxicity leaching test results of solidified contaminated soil from Examples 1 to 4 in a deionized water environment;

[0021] Figure 2 This is a graph showing the toxicity leaching test results of solidified contaminated soil from Examples 1 to 4 under a sulfuric acid and nitric acid environment;

[0022] Figure 3 This is a graph showing the toxicity leaching test results of solidified contaminated soil from Example 1 to Example 4 in an acetic acid environment;

[0023] Figure 4 In the deionized water environment, Examples 1 to 4 solidify the contaminated soil Pb 2+ Fitting curve of leaching concentration and freeze-thaw cycle number;

[0024] Figure 5 In the sulfuric acid and nitric acid environment, Examples 1 to 4 solidify the contaminated soil Pb 2+ Fitting curve of leaching concentration and freeze-thaw cycle number;

[0025] Figure 6 In the acetic acid environment, Examples 1 to 4 solidify the contaminated soil Pb 2+ Fitting curve of leaching concentration and freeze-thaw cycle number;

[0026] Figure 7 The unconfined compressive strength test and resistivity test results of the solidified contaminated soil of Examples 1 to 4 under 8 freeze-thaw cycles are shown in FIG.

[0027] Figure 8 It is a fitting curve diagram of resistivity and compressive strength of solidified contaminated soil in Examples 1 to 4;

[0028] Fig. 9 It is a fitting curve diagram of the number of freeze-thaw cycles and compressive strength of the solidified contaminated soil in Examples 1 to 4;

[0029] Fig.10 It is a fitted surface graph of the dosage of the solidifying agent for solidifying the contaminated soil, the number of freeze-thaw cycles and the compressive strength of Examples 1 to 4;

[0030] Fig.11 It is a surface diagram of the dosage of the curing agent for curing the contaminated soil, the number of freeze-thaw cycles and the resistivity fitting of Examples 1 to 4;

[0031] Fig.12 The elastic modulus results of the solidified contaminated soil of Examples 1 to 4 under 8 freeze-thaw cycles are shown in FIG.

[0032] Fig.13 It is a fitting curve diagram of resistivity and elastic modulus of solidified contaminated soil in Examples 1 to 4;

[0033] Fig.14 The pH test results of the solidified contaminated soil of Examples 1 to 4 under 8 freeze-thaw cycles are shown;

[0034] Fig.15 The graph is a graph showing the EC test results of the solidified contaminated soil of Examples 1 to 4 under 8 freeze-thaw cycles;

[0035] Fig.16 The pH and EC fitting curves of the solidified contaminated soil of Examples 1 to 4;

[0036] Fig.17 In the deionized water environment, the pH and Pb of the solidified contaminated soil in Examples 1 to 4 2+ Leaching concentration fitting curve diagram;

[0037] Fig.18 In the sulfuric acid and nitric acid environment, the pH and Pb of the solidified contaminated soil in Examples 1 to 4 2+ Leaching concentration fitting curve diagram;

[0038] Fig.19 In the acetic acid environment, the pH and Pb of the solidified contaminated soil in Examples 1 to 4 2+ Leaching concentration fitting curve diagram;

[0039] Fig. 20 In the deionized water environment, Examples 1 to 4 solidify the contaminated soil EC and Pb 2+ Leaching concentration fitting curve diagram;

[0040] Fig.21 In the sulfuric acid and nitric acid environment, Examples 1 to 4 solidify the contaminated soil EC and Pb 2+ Leaching concentration fitting curve diagram;

[0041] Fig. 22 In the acetic acid environment, Examples 1 to 4 solidify the contaminated soil EC and Pb 2+ Leaching concentration fitting curve. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] The long-term stability evaluation method of phosphate-based polymer acidic lead contaminated soil of the present invention is as follows: multiple solidified contaminated soil samples of the same specifications are used as parallel test objects, and data on the effects of different curing agent dosages and different freeze-thaw cycle numbers on toxic leaching, compressive strength, elastic modulus, resistivity, pH and conductivity of the solidified contaminated soil are obtained respectively; and these macro data are then fitted and analyzed to evaluate the long-term stability of the phosphate-based polymer contaminated soil under freeze-thaw cycles.

[0044] The specific steps of this evaluation method are:

[0045] S1. MAPG curing agent was mixed with acidic lead contaminated soil to prepare cylindrical solidified contaminated soil samples with different curing agent dosages but the same specifications (the mass of each solidified contaminated soil sample was 210 g, and the curing agent dosage of the solidified contaminated soil sample was 6% to 12%). After curing at room temperature under the same conditions, each solidified contaminated soil sample was subjected to multiple freeze-thaw cycles (a complete freeze-thaw cycle process was: the solidified contaminated soil was placed in a standard curing box for 28 days, then taken out, placed in a constant temperature and low temperature test box at -20°C for 24 hours, then the solidified contaminated soil sample was taken out, and placed in a constant temperature and humidity standard curing box at 21±2°C for 24 hours for thawing);

[0046] S2. Test the toxicity leaching, compressive strength, elastic modulus, resistivity, pH and EC of the solidified contaminated soil samples under each freeze-thaw cycle; 2+The leaching concentration was determined, and the measured data were fitted and analyzed with the curing agent dosage and the number of freeze-thaw cycles to establish a service life prediction model for the freeze-thaw resistance of solidified acidic heavy metal contaminated soil based on toxic leaching; the resistivity and elastic modulus of solidified contaminated soil were determined, and a long-term stability evaluation model for solidified acidic heavy metal contaminated soil based on resistivity was established; the pH and EC of solidified contaminated soil were determined, and the measured data were fitted and analyzed with the toxic leaching data to establish pH, ​​EC and Pb respectively. 2+ Leaching concentration fitting relationship.

[0047] The long-term stability evaluation model of solidified acidic heavy metal contaminated soil based on resistivity is expressed as E 50 =-6.87+1.26ρ, where: E 50 represents the elastic modulus, ρ represents the resistivity; the prediction model expression of the freeze-thaw resistance service life of the solidified acidic heavy metal contaminated soil based on toxic leaching is C=aN+b, where: C represents the heavy metal leaching concentration, N represents the number of freeze-thaw cycles, and a and b represent the prediction model parameters for different curing agent dosages.

[0048] Example 1

[0049] The long-term stability evaluation method of the phosphate-based polymer solidified acidic heavy metal contaminated soil under freeze-thaw cycles of this embodiment is:

[0050] S1. MAPG curing agent was mixed with acidic lead contaminated soil to prepare a cylindrical solidified contaminated soil sample with a specification of 50×50 mm. After curing at room temperature for 28 days, 8 freeze-thaw cycles were performed. In this embodiment, the dosage of MAPG curing agent was 6%.

[0051] S2. The toxic leaching, compressive strength, elastic modulus, resistivity, pH and EC of the solidified contaminated soil under 0, 2, 4, 6 and 8 freeze-thaw cycles were tested respectively, and a long-term stability evaluation model of solidified acidic heavy metal contaminated soil based on resistivity and a freeze-thaw resistance service life prediction model of solidified acidic heavy metal contaminated soil based on toxic leaching were established, which is recorded as FT-6 in this embodiment.

[0052] The unconfined compressive strength was measured using a TKA-WCY1F unconfined compressive strength tester produced by Nanjing Techao Technology Co., Ltd. The loading rate was constant at 1 mm / min and each test was repeated 3 times.

[0053] The toxic leaching test process is as follows: after the unconfined compression test, the soil sample and three kinds of leaching solutions are added into the extraction bottle at a liquid-solid ratio of 1:10, the bottle cap is tightly closed and placed on a tumbling machine with a tumbling frequency of 30±2r / min for 18±2h; after the tumbling, the mixed solution is filtered through a 0.22μm filter membrane and then the Pb is detected by ICP-MS instrument. 2+ Toxic leaching.

[0054] The soil pH and electrical conductivity (EC) were tested in accordance with the Japanese Basic Manual of Soil Testing. The soil was taken from the crushed soil sample after the unconfined compressive strength test. The soil sample was ground into fine powder and mixed with deionized water for testing. The fine powder was mixed with deionized water in a ratio of 1:1, and after standing for 2 hours, the pH was measured using a Mettlertoledo pH meter. The fine powder was mixed with distilled water in a ratio of 1:5, and after standing for 2 hours, the conductivity was measured using a DDS-11A conductivity meter.

[0055] The elastic modulus test method is: obtain it from the stress-strain curve of solidified contaminated soil and use the formula Where: E 50 represents the elastic modulus, q u represents the compressive strength of solidified contaminated soil, ε 50 Indicates the axial strain value corresponding to half of the peak stress.

[0056] The resistivity test was conducted using a TH2820B+ LCR digital bridge. Before the test, the upper and lower surfaces of the sample were polished flat with sandpaper, and a rectangular graphite electrode with a side length of 5 cm and a thickness of 0.2 cm was placed between the soil sample and the copper electrode sheet. During the test, an 800g metal counterweight was placed on top of the electrode sheet to press it tightly to ensure good contact between the sample and the copper electrode sheet. During the test, an electrode clamp was used to clamp the upper and lower copper sheets. The resistivity test principle is the two-phase electrode method, the test frequency is 10kHz, and the test voltage is 1V. All sample tests were carried out at room temperature, and each sample was tested 3 times.

[0057] Example 2

[0058] The method of this embodiment is the same as that of embodiment 1, except that the dosage of MAPG curing agent is 8%, which is denoted as FT-8 in this embodiment.

[0059] Example 3

[0060] The method of this embodiment is the same as that of embodiment 1, except that the dosage of MAPG curing agent is 10%, which is denoted as FT-10 in this embodiment.

[0061] Example 4

[0062] The method of this embodiment is the same as that of embodiment 1, except that the dosage of MAPG curing agent is 12%, which is denoted as FT-12 in this embodiment.

[0063] (I) The test results are as follows: Toxicity leaching

[0064] Figures 1 to 3 The results show that MAPG solidified Pb contaminated soil under freeze-thaw cycles 2+Leaching characteristics. In deionized water environment, no Pb was detected in the leachate without freeze-thaw cycle and in the leachate after two freeze-thaw cycles. 2+ As the number of freeze-thaw cycles increases, Pb 2+ The increase in leaching concentration indicates that freeze-thaw cycles will accelerate the 2+ However, after 8 freeze-thaw cycles, the Pb content of the solidified contaminated soil with a solidifying agent content of 6%, 8%, 10% and 12% 2+ The leaching concentrations were 0.083, 0.057, 0.047 and 0.036 mg / L, respectively, all lower than the groundwater IV quality standard of 0.1 mg / L. Similarly, no Pb was detected in the leaching solution of samples without freeze-thaw cycles and samples with two freeze-thaw cycles under sulfuric acid-nitric acid environment. 2+ After 8 freeze-thaw cycles, the Pb content of the solidified contaminated soil was 6%, 8%, 10% and 12%. 2+ The leaching concentrations were 0.06, 0.055, 0.038 and 0.034 mg / L, which were far lower than the groundwater IV quality standard of 0.1 mg / L. This indicates that under the environment of surface water / groundwater erosion and acid rain erosion, the MAPG curing agent has a great influence on the acidic Pb 2+ The contaminated soil has excellent durability. However, in the acetic acid environment, when the curing agent content is low (6%), the Pb 2+ The leaching concentration after 2 freeze-thaw cycles was 5.648 mg / L, and after 8 freeze-thaw cycles, the Pb 2+ The leaching concentration increased to 9.816 mg / L, which exceeded the leaching toxicity limit of hazardous waste (5 mg / L). However, when the curing agent dosage increased to 8%, 10%, and 12%, the Pb 2+ The leaching concentrations were 4.396, 2.542 and 2.003 mg / L respectively, which did not exceed the leaching toxicity limit of hazardous waste (5 mg / L). Figures 4 to 6 The freeze-thaw cycle number N and Pb under three leaching simulation environments are shown. 2+ The fitting curve of leaching concentration and the fitting formulas are shown in Table 1. 2+ The correlations between leaching concentrations are all linear, and the fitting relationship is expressed as C = aN + b. In the three leaching environments, a and b both decrease with the increase of curing agent dosage. The a and b parameters can be used to represent the antifreeze performance of MAPG curing agent at different dosages.

[0065] Table 1 Number of freeze-thaw cycles (N) and Pb under different environments 2+ Leaching concentration (C) fitting formula

[0066]

[0067]

[0068] (II) Compressive strength and resistivity

[0069] Figure 7 The effect of freeze-thaw cycles on the compressive strength and resistivity of MAPG-solidified contaminated soil was demonstrated. Under 0 freeze-thaw cycles, the compressive strength of the solidified contaminated soil with a curing agent content of 6%, 8%, 10% and 12% was 1224, 1129.3, 1241.2 and 1401.7 kPa, respectively. After 8 freeze-thaw cycles, the strength dropped to 418.3, 646.7, 675.3 and 961 kPa, respectively, and the strength loss was 65.8%, 42.7%, 45.6% and 31.4%, respectively, indicating that with the increase of curing agent content, the strength loss of solidified contaminated soil under freeze-thaw cycles is lower. With the increase of freeze-thaw cycles, although the strength of solidified contaminated soil gradually decreases, the compressive strength of solidified contaminated soil after 8 freeze-thaw cycles is still higher than the landfill strength requirement of solidified contaminated soil recommended by the US Environmental Protection Agency of 350 kPa. Figure 8 The relationship between the compressive strength and resistivity of MAPG-solidified contaminated soil under freeze-thaw cycles is demonstrated, and the compressive strength of the solidified contaminated soil increases linearly with the increase of resistivity. Fig. 9 is the fitting relationship between the number of freeze-thaw cycles and compressive strength, and the corresponding relationship is shown in Table 6. Fig.10 , Fig.11 The three-dimensional relationships among the dosage of curing agent, number of freeze-thaw cycles and the strength and resistivity of cured contaminated soil are shown respectively.

[0070] Table 2 Freeze-thaw cycle number (N) and compressive strength (q u )Fitting formula

[0071]

[0072] According to the freeze-thaw resistance life prediction model (1) of concrete under natural conditions, the MAPG solidified acid Pb 2+ The service time t of contaminated soil under freeze-thaw cycle environment is predicted.

[0073]

[0074] In the formula: k is the rapid freeze-thaw test coefficient, which can generally be taken as 12; N is the number of freeze-thaw cycles, and M is the number of freeze-thaw cycles that concrete may experience in an actual environment in one year.

[0075] According to the relationship in Table 1, the MAPG solidified acidic Pb 2+ The service life of contaminated soil was discussed. After 8 freeze-thaw cycles of MAPG-solidified contaminated soil, Pb 2+ The leaching concentration needs to be <5 mg / L, and the service time prediction model is shown in Table 3. According to the results in Table 3, in typical freeze-thaw areas, when MAPG solidifies heavy metal contaminated soil and is eroded by groundwater and acid rain, the solidified acidic Pb2+ The service life of contaminated soil can reach 100 years. When used in the solidification of acidic Pb 2+ When the soil is contaminated, the service life is significantly reduced.

[0076] Table 3 MAPG solidification of acidic Pb 2+ Prediction of service time of contaminated soil

[0077]

[0078] (III) Elastic modulus

[0079] Elastic modulus E 50 It is an important parameter in mechanical tests. The larger the elastic modulus value, the stronger the material's ability to resist deformation. Fig.12 The elastic modulus E of MAPG-solidified contaminated soil under freeze-thaw cycles is shown. 50 It decreases with the increase of the number of freeze-thaw cycles. Before the freeze-thaw cycle, the elastic modulus of the solidified contaminated soil with a curing agent dosage of 6%, 8%, 10% and 12% were 30.43, 28.05, 37.76 and 45.40 MPa, respectively. After two freeze-thaw cycles, the elastic modulus of the solidified contaminated soil dropped sharply, and after four freeze-thaw cycles, the elastic modulus tended to be stable. The main reason for this phenomenon is that after the freeze-thaw cycle, the water and ice crystals freeze and expand, and the loose pores of the soil particles extend and connect, resulting in the weakening of the elasticity of the frozen soil. When the number of freeze-thaw cycles reaches 4-6 times, there is enough pore space inside the soil to withstand the freezing expansion, so it will not cause greater damage. In addition, since the ice crystals generate cohesive force during the freezing process, the soil particles are locally squeezed, and the increase in the local density of the soil has a certain degree of consolidation effect. The elastic modulus of the solidified contaminated soil after freeze-thaw cycles showed a downward trend overall, and the elastic modulus loss rates of the solidified contaminated soil with curing agent dosages of 6%, 8%, 10% and 12% were 72.7%, 55.3%, 56.9% and 49.9%, respectively. Fig.13 The fitting relationship between the resistivity and elastic modulus of MAPG-solidified contaminated soil under freeze-thaw cycles (E 50 =-6.87+1.26ρ, where: E 50 represents elastic modulus, and ρ represents resistivity).

[0080] (IV) pH and EC

[0081] Fig.14 and Fig.15The pH and EC variations of MAPG-solidified contaminated soil under freeze-thaw cycles are respectively presented. Adding the MAPG solidifying agent changes the pH of the solidified contaminated soil. With the increase in the dosage of the solidifying agent, the pH of the solidified contaminated soil gradually decreases. The pH of the solidified contaminated soil also decreases with the increase in the number of freeze-thaw cycles. The pH values of the solidified contaminated soil with solidifying agent dosages of 6%, 8%, 10%, and 12% are 5.65, 5.45, 5.26, and 5.25 respectively. After 8 freeze-thaw cycles, the pH values of the solidified contaminated soil decrease to 5.47, 5.18, 5.11, and 5.02 respectively. Different from the pH of the solidified contaminated soil, the EC of the solidified contaminated soil increases with the increase in both the solidifying agent dosage and the number of freeze-thaw cycles. The EC values of the solidified contaminated soil with solidifying agent dosages of 6%, 8%, 10%, and 12% are 1.502, 1.551, 1.613, and 1.647 ms / cm respectively. After 8 freeze-thaw cycles, the EC values of the solidified contaminated soil increase to 1.612, 1.655, 1.681, and 1.702 ms / cm respectively. The EC of the solidified contaminated soil decreases in a linear function with the increase in pH. The relationship between the pH and EC of MAPG-solidified contaminated soil under freeze-thaw cycles is shown in Fig.16 . Figures 17 to 22 shows the relationship between pH, EC, and the leaching concentration of Pb under three leaching simulation environments, and there is a linear relationship among pH, EC, and the leaching concentration of Pb. The leaching concentration of Pb decreases with the increase in pH and increases with the increase in EC. Tables 4 and 5 show the correlations among various indicators. The correlation between pH and the leaching concentration of Pb is lower than that between EC and the leaching concentration of Pb, indicating that EC is more suitable for evaluating the leaching of Pb in MAPG-solidified acidic lead-contaminated soil under freeze-thaw cycles. 2+ The relationship between leaching concentration, pH, EC, and the leaching concentration of Pb 2+ shows a linear relationship. The leaching concentration of Pb decreases with the increase in pH and increases with the increase in EC. Tables 4 and 5 show the correlations among various indicators. The correlation between pH and the leaching concentration of Pb 2+ is lower than that between EC and the leaching concentration of Pb 2+ , indicating that EC is more suitable for evaluating the leaching of Pb in MAPG-solidified acidic lead-contaminated soil under freeze-thaw cycles. 2+ The leaching of Pb 2+ .

[0082] Table 4 Fitting formulas for the relationship between pH and the leaching concentration (C) of Pb in different environments 2+

[0083]

[0084] Table 5 Fitting formulas for the relationship between EC and the leaching concentration (C) of Pb in different environments 2+

[0085]

[0086]

[0087] ​​The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil, characterized in that: Taking multiple solidified contaminated soil samples of the same specifications as parallel test objects, data on the effects of different curing agent dosages and different freeze-thaw cycles on the toxic leaching, compressive strength, elastic modulus, resistivity, pH and conductivity of solidified contaminated soil were obtained respectively; these macro data were then fitted and analyzed to evaluate the long-term stability of phosphate-based polymer contaminated soil under freeze-thaw cycles.

2. The method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil according to claim 1, characterized in that: The specific steps of this evaluation method are: S1. MAPG curing agent was mixed with acidic lead contaminated soil to prepare cylindrical solidified contaminated soil samples with different curing agent dosages but the same specifications. After curing at room temperature under the same conditions, each solidified contaminated soil sample was subjected to multiple freeze-thaw cycles; S2. Test the toxicity leaching, compressive strength, elastic modulus, resistivity, pH and EC of the solidified contaminated soil samples under each freeze-thaw cycle; 2+ The leaching concentration was determined, and the measured data were fitted and analyzed with the curing agent dosage and the number of freeze-thaw cycles to establish a service life prediction model for the freeze-thaw resistance of solidified acidic heavy metal contaminated soil based on toxic leaching; the resistivity and elastic modulus of solidified contaminated soil were determined, and a long-term stability evaluation model for solidified acidic heavy metal contaminated soil based on resistivity was established; the pH and EC of solidified contaminated soil were determined, and the measured data were fitted and analyzed with the toxic leaching data to establish pH, ​​EC and Pb respectively. 2+ Leaching concentration fitting relationship.

3. The method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil according to claim 1 or 2, characterized in that: The mass of each solidified contaminated soil sample is 210 g.

4. The method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil according to claim 1 or 2, characterized in that: The dosage of curing agent for curing contaminated soil samples is 6% to 12%.

5. The method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil according to claim 1 or 2, characterized in that: A complete freeze-thaw cycle in this method is as follows: the solidified contaminated soil is placed in a standard curing box for 28 days, then taken out, placed in a constant temperature and low-temperature test box at -20°C for 24 hours, then the solidified contaminated soil sample is taken out, and placed back in a constant temperature and humidity standard curing box at 21±2°C for 24 hours for thawing.

6. The method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil according to claim 1 or 2, characterized in that: The freeze-thaw cycles were 0, 2, 4, 6, and 8 times.

7. The method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil according to claim 2, characterized in that: The long-term stability evaluation model of solidified acidic heavy metal contaminated soil based on resistivity is expressed as E 50＝ -6.87+1.26ρ, where E 50 represents elastic modulus, ρ represents resistivity; The prediction model expression of the freeze-thaw resistance service life of solidified acidic heavy metal contaminated soil based on toxic leaching is C=aN+b, where C represents the heavy metal leaching concentration, N represents the number of freeze-thaw cycles, and a and b represent the prediction model parameters for different solidifying agent dosages.

8. The method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil according to claim 1 or 2, characterized in that: The toxicity leaching test method of solidified contaminated soil is as follows: after the compressive strength test, the soil sample and three kinds of leaching solutions are added into each extraction bottle at a liquid-solid ratio of 1:10, the bottle cap is tightly closed and placed on a flipping instrument for flipping. After the flipping, the mixed solution is filtered and the Pb is detected by ICP-MS instrument. 2+ Toxic leaching.

9. The method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil according to claim 1 or 2, characterized in that: The resistivity test was carried out using the two-phase electrode method, with a test frequency of 10kHz and a test voltage of 1V.

10. The method for evaluating the long-term stability of phosphate-based polymer acidic lead contaminated soil according to claim 1 or 2, characterized in that: The pH and conductivity test methods are as follows: grind the soil sample after the unconfined compressive strength test into fine powder; mix the fine powder with deionized water in a ratio of 1:1, let it stand, and then use a Mettler toledo pH meter to measure its pH; mix the fine powder with distilled water in a ratio of 1:5, let it stand, and then use a DDS-11A conductivity meter to measure its conductivity.

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