Method for evaluating environmental pollution degree of road alkali residue composite soil

Abstract

The invention belongs to the technical field of industrial solid waste recycling, and particularly discloses a road alkali residue composite soil environmental pollution degree evaluation method, which takes water body, soil body and plant growth as monitoring items of alkali residue composite soil environmental protection performance and carries out evaluation index design; and carrying out quantitative analysis on the evaluation indexes, and designing an environmental pollution degree evaluation model based on the three evaluation indexes. Analyzing the influence of the alkaline residue composite soil on water quality pollution, soil pollution and plant growth, and constructing an environmental pollution degree evaluation model of the alkaline residue composite soil; and comprehensively evaluating the environmental protection performance of the alkaline residue composite soil through the environmental pollution degree evaluation model. In the evaluation system, pollution degree indexes are subjected to hierarchical design, and evaluation indexes are divided according to different standards and are in one-to-one correspondence with pollution degrees. The pollution degree of the alkaline residue composite soil and whether the alkaline residue composite soil meets the environmental protection performance under the current regulations are accurately judged. The invention further provides a reliable basis for large-scale and ecological resource utilization of the alkaline residues in the field of road materials.

Description

Technical Field

[0001] The invention belongs to the technical field of industrial solid waste recycling and utilization, relates to research on applying solid waste alkali slag to road materials, and specifically relates to a method for evaluating the environmental pollution degree of road alkali slag composite soil. Background Art

[0002] Focusing on the treatment and potential resource utilization of alkali residue, domestic and foreign scholars have explored the preparation of adsorbents, cementitious materials, unburned bricks, and the improvement of acidic soil and engineering padding, and have achieved a lot of beneficial results. - , which makes the project prone to alkali efflux and steel bar corrosion, making it difficult for alkali slag utilization projects to take into account multiple requirements such as bearing capacity, environmental protection and large-scale disposal. At present, the comprehensive utilization rate of alkali slag is less than 15%, far lower than the national target of not less than 55% for the comprehensive utilization rate of solid waste. Studies have shown that alkali slag contains a certain amount of mineral components such as CaCO3 and Ca(OH)2, which can produce a cementing effect between soil particles and promote cement hydration, and can replace part of the lime and cement to solidify the roadbed soil. The strength requirements for road subgrade or base layer are relatively low, and steel bars are generally not laid in the layer. There is no potential risk of chloride ion corrosion, and it has the potential to absorb a large amount of solid waste alkali slag. Therefore, the road field has become a key area for the recycling of solid waste alkali slag.

[0003] Sun Xiaohai and others studied the effects of different amounts of alkali slag cement on the improvement of expansive soil, conducted expansion characteristics and shear strength tests, and determined that the optimal alkali slag content was 30-40%. Guo Qinying explored the effects of 3%, 4%, and 6% alkali slag content on the mechanical properties of alkali slag lime soil materials, and found that the mechanical properties were optimal when the alkali slag content was 6%. Li Hui explored the influence of different content on the mechanical properties of alkali slag lime soil, and found that when alkali slag: lime: soil = 6%: 6%: 100%, the mechanical properties of the material were optimal. In order to clarify the performance of cement-stabilized alkali slag modified soil in resisting freeze-thaw cycles, Zhao Xiaoqing explored the changes in the volume, mass, and apparent phenomena of cement-stabilized alkali slag modified soil during the freeze-thaw cycle test, and analyzed its freeze-thaw degradation mechanism in combination with SEM electron microscopy results. Liu Jingjing et al. conducted dry-wet cycle durability tests on cement-alkali slag improved expansive soil. The test results showed that the deterioration of engineering properties caused by reducing the cement-alkali slag mass ratio can be attributed to the fact that the cementing properties of the composite compound CaO·SiO2·CaCO3·nH2O are weaker than those of typical hydration cementing products.

[0004] Most scholars focus on the road performance of road construction materials prepared from alkali slag. When designing and processing alkali slag, they pursue economy and cost-effectiveness. For example, the high dosage of alkali slag and the minimization of the use of traditional road materials (cement, lime) while meeting the mechanical properties. However, alkali slag contains a large amount of soluble chloride ions, which will migrate and be corrosive, causing certain impacts and damage to the surrounding environment. Yu Shuijun analyzed that after alkali slag lime soil is soaked in rainwater, a certain amount of chloride salt will flow out with the water, which may cause groundwater pollution. At the same time, the seepage will cause pollution to the surrounding soil and affect the growth of surrounding crops and plants. How to realize the large-scale application of alkali slag in road materials on the basis of meeting the environmental protection performance required by the country, propose an environmental pollution evaluation method for alkali slag composite soil, and analyze the environmental protection performance of alkali slag composite soil are urgent problems that need to be solved in the large-scale recycling of alkali slag in the road field. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for evaluating the environmental pollution degree of alkali-slag composite soil for road use. The present invention quantitatively analyzes and evaluates the three single factors that the alkali-slag composite soil may cause, namely, groundwater pollution, soil pollution, and the impact on the growth of surrounding crops or plants, and finally comprehensively evaluates the environmental performance of the material. The present invention optimizes the design of the alkali-slag composite soil mix ratio and lays a foundation for the large-scale and ecological resource utilization of alkali slag in road materials.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for evaluating the environmental pollution degree of road alkali-slag composite soil comprises the following steps:

[0008] (1) Taking water, soil and plant growth as the monitoring items of the environmental performance of alkali-slag composite soil, the chloride ion content in the alkali-slag composite soil soaking solution, the chloride ion retention in the soil and the plant growth performance are monitored, and the monitoring values ​​of the chloride ion content in the alkali-slag composite soil soaking solution x1, the chloride ion retention in the soil x2, the germination rate r1, the root length r2 and the stem length r3 reflecting the plant growth performance are obtained;

[0009] (2) Construct the water body evaluation index P1 and soil body evaluation index P2 model. The specific formula is as follows:

[0010]

[0011] Where: x i —water and soil monitoring values, i=1, 2;

[0012] (3) Construction of plant growth index P3 model

[0013] (3.1) Plant germination rate, root length, and stem length evaluation formula P 3iAs shown below:

[0014]

[0015] Where: r i —plant growth performance monitoring value, i=1, 2, 3;

[0016] C1—Plant growth under irrigation with soil soaking solution;

[0017] C2—plant growth under irrigation with soaking solution in the control group;

[0018] (3.2) The overall evaluation formula for plant growth performance based on plant germination rate and root length is as follows:

[0019] P3=Max{P 3i} (12)

[0020] Where: P 3i —Evaluation indexes of plant growth in different aspects, i=1, 2, 3;

[0021] (4) Comprehensively evaluate the three single factor evaluations and express them as K to comprehensively judge the influence of alkali-slag composite soil on environmental performance. The comprehensive evaluation formula is as follows:

[0022]

[0023] Where: P n ——Single factor evaluation index, i=1, 2, 3;

[0024] (5) Design pollution degree classification, as follows:

[0025]

[0026]

[0027] Alkali-slag composite soil evaluation can only be used in non-polluted and slightly polluted areas.

[0028] A further improvement of the present invention is:

[0029] The monitoring and calculation process of the chloride ion content x1 in the alkali slag composite soil soaking solution is as follows:

[0030] A. Specimen preparation: sieve the materials to be prepared for sample preparation, configure the water and materials required for a sample according to the optimal moisture content and maximum dry density obtained from the compaction test, prepare cylindrical specimens, and carry out material weighing, mixing, stuffing, mold loading, compaction, demoulding, and curing;

[0031] B. Preparation of test solution: Dry the alkali residue composite soil with different proportions, crush and sieve for later use, take the alkali residue composite soil, add deionized water according to the soil-water ratio, cover the bottle stopper, shake well, filter, and the filtered solution is the test solution;

[0032] C. Test process: Add NaHCO3 solution to the test solution until the solution turns yellow again, then add K2CrO4 indicator, and titrate with AgNO3 standard solution until the color of the turbid solution changes from yellow-green to brick red, that is, the titration endpoint is reached, and record the volume V of AgNO3 consumed;

[0033] D. Chloride content is calculated as follows:

[0034]

[0035] Cl - (%) = Cl - (mmol / kg)×0.0355×10 -1 (4)

[0036] Cl - (mg / kg) = Cl - (%)×10000 (5)

[0037] Where: c—concentration of silver nitrate standard solution (mol / L);

[0038] V—Volume of silver nitrate solution for titration (mL);

[0039] m—the mass of dry soil equivalent to the volume of leachate taken during analysis (g);

[0040] 0.0355—Molar mass of chloride (g / mol).

[0041] Furthermore, the monitoring and calculation process of the chloride ion retention x2 in the soil is as follows:

[0042] A. Device setup: The main body of the device is a frustum-shaped structure made of resin, with a water outlet at the bottom. From top to bottom, there are aquifer, planting soil layer and drainage layer. The drainage layer is filled with gravel, and the planting soil layer is made of pollution-free Daxing farmland soil.

[0043] B. Material preparation: Take 500 kg of garden soil and spread it flat in the open space in front of the rainwater laboratory for light air drying. After natural air drying, crush the large pieces of soil and remove the debris and sieve them. The sieved garden soil is saved for later use. The preparation steps of irrigation liquid are as follows: dry the alkali residue composite soil with different proportions, crush and sieve them for later use, take the alkali residue composite soil, add deionized water according to the soil-water ratio, cover the bottle stopper, shake well, filter, and the filtered solution is the irrigation liquid;

[0044] C. Test process: A planting environment with artificial water inflow under greenhouse conditions was used. In the laboratory, natural light was ensured. Under cloudy conditions, daily management was performed to maintain soil humidity. Watering was performed once every 5 days with a water volume of 400mL-500mL, for a total of 4 times. Finally, the soil was collected, dried, and the soil test solution was prepared;

[0045] D. Test the chloride ion content of the soil test solution, specifically: add NaHCO3 solution to the test solution until the solution turns back to yellow, then add K2CrO4 indicator, and titrate with AgNO3 standard solution until the color of the turbid solution changes from yellow-green to brick red, that is, the titration endpoint is reached, and record the volume V of AgNO3 consumed;

[0046] E. Chloride content is calculated according to formula (3, 4, 5):

[0047]

[0048] Cl - (%) = Cl - (mmol / kg)×0.0355×10 -1 (4)

[0049] Cl - (mg / kg) = Cl - (%)×10000 (5)

[0050] Where: c—concentration of silver nitrate standard solution (mol / L);

[0051] V—Volume of silver nitrate solution for titration (mL);

[0052] m—the mass of dry soil equivalent to the volume of leachate taken during analysis (g);

[0053] 0.0355—Molar mass of chloride (g / mol).

[0054] Furthermore, the monitoring method of the plant growth performance r is as follows:

[0055] A. Soaking liquid treatment: Dry the alkali residue composite soil with different proportions, crush and sieve for later use, take the alkali residue composite soil, add deionized water according to the soil-water ratio, cover the bottle stopper, shake well, filter, and the filtered solution is the soaking liquid;

[0056] B. Seed treatment: Soak the seeds (preferably the seeds of local roadside plants in the potential use area of ​​alkali residue) in pure water for 1-2 hours, select the plump seeds, remove the seed coat, and place the seeds in a culture dish with two layers of filter paper; pour the soaking solution, seal the sample with sealing film, and place it in a constant temperature and light-free culture box at 25±5℃ for germination;

[0057] C. Experimental process: observe the number of germinations within 7 days, and take the radicle extending 2mm out of the seed coat as the germination standard; record the number of seeds germinated every day during the germination period, and take the radicle breaking through 2mm as the standard; count and calculate the germination rate on the 7th day, and record for a total of 7 days; after completing the germination test on the 15th day, randomly select 10 representative seedlings in each culture dish, measure the root length and stem length with a vernier caliper, calculate the average height, calculate the germination rate r1, root length r2, and stem length r3, and evaluate the plant growth.

[0058] Furthermore, the germination rate r1 is calculated according to formula (6):

[0059]

[0060] Where: N q —Number of seeds germinated in 7 days;

[0061] N—is the number of seeds tested.

[0062] Furthermore, the root length r2 index is evaluated by calculating the average root length (R), and the stem length r3 index is evaluated by calculating the average stem length (B). The average root length (R) and the average stem length (B) are calculated according to formulas (7, 8):

[0063]

[0064] Where: N g —Root length of successfully germinated vegetation in 15 days;

[0065] N—is the number of seeds tested;

[0066]

[0067] Where: N j — Length of stem of successfully germinated vegetation in 15 days;

[0068] N—is the number of seeds tested.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] The present invention establishes an evaluation system for the environmental performance of alkali slag composite soil. Through the scoring of multiple indicators and the assessment of pollution degree, it is intuitively and comprehensively obtained whether the material meets the environmental protection requirements under the current standards. Comprehensive environmental performance can be used to select cost-effective and appropriate material mix ratios according to actual conditions and requirements. This system is better improved for the ecological resource utilization of alkali slag in the field of road materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 The apparatus used in the embodiments of the present invention;

[0072] Figure 2 This is a picture of compaction experiment conducted by electric compactor;

[0073] Figure 3 Create a flow chart for the test piece;

[0074] Figure 4 Preparation process of the test solution;

[0075] Figure 5 Cl - Titration process;

[0076] Figure 6 For the seed treatment process;

[0077] Figure 7 Cl for different soil depths - content;

[0078] Figure 8 For the growth of ryegrass seeds;

[0079] Fig. 9 This is an experiment on the growth of ryegrass in alkali slag lime cement soil;

[0080] Fig.10 P n Final calculation results;

[0081] Fig.11 P n1 , P n2 Determination of pollution degree;

[0082] Fig.12 P n3 Pollution impact assessment. DETAILED DESCRIPTION

[0083] The present invention is described in detail below in conjunction with specific embodiments.

[0084] Example 1: Method for evaluating the degree of environmental pollution of road-used alkali-slag composite soil

[0085] 1. Chloride ion content in the alkali slag composite soil soaking solution

[0086] Alkali residue contains a large amount of soluble salts, of which chloride salts account for the majority and have a great impact on environmental pollution. When the road alkali residue composite soil is soaked in rainwater, the chloride salts in the material will seep into the ground with the water, causing groundwater pollution. By measuring the chloride ion content in the soaking liquid after the alkali residue composite soil is crushed, the pollution of the material to the water body can be simulated. The test method for the chloride ion content in the soaking liquid of the alkali residue composite soil is as follows.

[0087] A. Specimen preparation: According to the Highway Geotechnical Test Code JTG E40-2019, prepare cylindrical specimens with a sample size of Φ50mm×50mm. Pass the materials prepared for sample preparation through a 2mm sieve, and configure the water and materials required for a sample according to the optimal moisture content and maximum dry density obtained from the compaction test, and carry out material weighing, mixing, stuffing, mold loading, compaction, demoulding, and curing.

[0088] B. Preparation of test solution: Put different proportions of alkali residue composite soil into an oven at a constant temperature of 110℃ for drying, crush and sieve through a 1mm standard sieve for later use, put the alkali residue composite soil into a dry wide-mouth plastic bottle, add deionized water at a soil-water ratio of 1:5, cover the bottle stopper, shake vigorously for 3 minutes, pour into a funnel with clean filter paper and filter. The filtered solution is the test solution.

[0089] C. Test process: Add 0.02 mol / L NaHCO3 to the test solution until the solution turns back to yellow (pH 7), then add 0.5 mL of 5% K2CrO4 indicator, and titrate with AgNO3 standard solution until the color of the turbid solution changes from yellow-green to brick red, reaching the titration endpoint, and record the volume V of AgNO3 consumed.

[0090] D. The chloride content is calculated according to the following formula (3, 4, 5).

[0091]

[0092] Cl - (%) = Cl - (mmol / kg)×0.0355×10 -1 (4)

[0093] Cl - (mg / kg) = Cl - (%)×10000 (5)

[0094] Where: c—concentration of silver nitrate standard solution (mol / L);

[0095] V—Volume of silver nitrate solution for titration (mL);

[0096] m—the mass of dry soil equivalent to the volume of leachate taken during analysis (g);

[0097] 0.0355—molar mass of chloride (g / mol);

[0098] 2. Chloride ion retention in soil

[0099] The seepage of chlorine-containing water may also flow to the surrounding soil, causing soil pollution. Use the alkali slag composite soil to crush the test specimen and irrigate the soil with the test liquid in the form of runoff. By testing the retained chloride ion content in the soil, the possible pollution of the surrounding soil by the alkali slag composite soil is simulated and explored. The test method for the retention of chloride ions in the soil is described as follows.

[0100] A. Device setup: The main body of the device is a truncated cone-shaped structure made of resin material, with a water outlet at the bottom, and the water is received by the water tray under the flower pot tray. The pot is 29cm high, with an upper inner diameter of 23cm and a lower inner diameter of 16cm. From top to bottom, there are aquifer, planting soil layer and drainage layer. The drainage layer is 30mm high and filled with gravel with a particle size of about 10mm; the planting soil layer is 200mm high and uses pollution-free Daxing farmland soil.

[0101] B. Material preparation: Take 500 kg of farmland soil and spread it flat in front of the rainwater laboratory for light drying. After natural drying, crush the large pieces of soil and remove the stones, animal and plant remains and other debris in the soil. Then sieve the farmland soil and save it for later use. The preparation method of the irrigation solution is the same as the method of the test solution for the above specimen.

[0102] C. Experimental process: To control the experimental variables, the acute impact of a single pollution source on the matrix in the bioretention facility. The experiment adopts a planting environment with artificial water inlet under greenhouse conditions. In the laboratory, natural light is guaranteed. Under cloudy conditions, daily management is done to maintain soil humidity. Water once every 5 days, with a water volume of 400mL-500mL, for a total of 4 times. Finally, the soil is collected, dried, and the soil test solution is prepared. The chloride ion content is then tested.

[0103] D. Chloride content is calculated as above formula (3, 4, 5):

[0104] 3. Plant growth performance

[0105] If there are crops around the road section where the alkali-slag composite soil is used, the chloride salts will seep with the water and may also affect the original growth around it. Therefore, a plant salt tolerance test is carried out to determine the factors affecting the seed germination rate and growth under different salt concentrations by observing the germination rate, root and stem length indicators of the selected plants.

[0106] According to the experimental content, the growth indicators of plants or crops were observed by soaking liquid of alkali slag lime soil with different alkali slag dosages (the selection of specific plants and crops depends on the actual surrounding original plants on site), and the germination rate, root length and stem length were analyzed respectively. The plant growth performance test method is as follows.

[0107] A. Soaking liquid treatment: The soaking liquid treatment method is the same as that of the alkali-slag composite soil test liquid.

[0108] B. Seed treatment: Soak the seeds in pure water for 1-2 hours, select 25 full seeds, remove the seed coat, and place the seeds in a culture dish with two layers of filter paper; pour 10 ml of soaking solution, seal with sealing film, and place the sample in a constant temperature incubator without light at 25±5℃ for germination;

[0109] C. Test process: observe the number of germinations within 7 days, and take the radicle extending 2mm out of the seed coat as the germination standard; record the number of seeds that germinate every day during the germination period, and take the radicle breaking through 2mm as the standard; count and calculate the germination rate on the 7th day, and record for a total of 7 days. After completing the germination test on the 15th day, randomly select 10 representative seedlings in each culture dish, measure the root length and stem length with a vernier caliper, and calculate the average height respectively. Evaluate the growth of plants.

[0110] D. The germination rate and rhizome length are calculated according to the following formulas (6, 7, 8).

[0111] Germination rate: Germination rate is the percentage of the number of test seeds that germinate to the total number of test seeds, and is one of the important indicators for testing seed quality. For the calculation of germination rate (S), refer to formula (6):

[0112]

[0113] Where: N q —Number of seeds germinated in 7 days;

[0114] N—is the number of seeds tested.

[0115] Root and stem length: Root length refers to the total length of roots per unit soil volume, indicating the proportion of soil volume that supplies nutrients to the roots. Stem length refers to the length of the plant stem that extends beyond the soil surface. By observing the length of the plant roots and stems, the growth of the plant can be monitored and the degree of influence of different salt concentrations on the growth of the plant can be determined. The average root length (R) and average stem length (B) are calculated according to formulas (7, 8):

[0116]

[0117] Where: N g —Root length of successfully germinated vegetation in 15 days;

[0118] N—is the number of seeds tested.

[0119]

[0120] Where: N j — Length of stem of successfully germinated vegetation in 15 days;

[0121] N—is the number of seeds tested.

[0122] 4. Evaluation index design

[0123] The monitoring indicators are quantified and their pollution mass fractions are calculated to analyze the potential ecological risk index values ​​in a quantitative way. The evaluation indicators and their symbols corresponding to the monitoring values ​​are shown in Table 1.

[0124] Table 1 Evaluation index design

[0125]

[0126] 5. Construction of environmental pollution evaluation model for alkali-slag composite soil

[0127] (1) Single factor evaluation

[0128] A. Construction of P1 and P2 evaluation index model

[0129] The three indicators are scored and judged. Designs P1 and P2 use the same scoring standard, and P3 uses another standard. The relevant scoring critical standards refer to the surface water environmental quality standard GB 3838-2002, the farmland irrigation water quality standard GB 15618-2018, and the critical concentration of chlorine tolerance of different crops. The specific evaluation values ​​and basis are shown in Table 2 below.

[0130] Table 2 Environmental pollution assessment values ​​and basis

[0131]

[0132] The test is set up to score the chloride ion concentration in the test solution to determine the environmental performance of the alkali slag lime soil sample. The score is set to 0-1 points, where the critical values ​​of chloride ion concentration corresponding to scores of 0, 0.6, 0.7, 0.8, 0.9, and 1 are 0 mg / L, 350 mg / L, 400 mg / L, 450 mg / L, 500 mg / L, and 600 mg / L, respectively.

[0133] Different chloride ion concentrations correspond to scores one by one. The numerical difference of the concentration interval divides the corresponding score interval in half, so that each concentration has a corresponding score. i The specific formula (10) is as follows. (where i = 1, 2)

[0134]

[0135] Where: x i —water and soil monitoring values, i=1, 2;

[0136] B. Construction of P3 evaluation index model

[0137] For the determination of the influence of alkali residue composite soil on plant growth indicators, the method of comparison with the control group is adopted, that is, the critical value of the score is divided according to the different proportions of the growth of the plain soil and the control group. The evaluation score interval is set to 0-1 points. The critical values ​​of the growth standards corresponding to 0, 0.6, 0.7, 0.8, 0.9, and 1 points are respectively C1 for the growth of plants under the plain soil soaking liquid, C2 for the growth of plants under the control group without alkali residue, C290%, C280%, C270%, and C260%.

[0138] If the growth condition is better than that of the plant under the soil soaking solution, that is, the value is greater than C1, the specified score is 0, that is, no effect. Other growth conditions correspond to the score range one by one, and each 1% change corresponds to 1 point. If the growth condition is lower than 60% of the control group value, the specified score is 1 point.

[0139] Plant germination rate, root length, stem length evaluation formula P 3i As shown below (11) (where i = 1, 2, 3).

[0140]

[0141] Where: r i —plant growth performance monitoring value, i=1, 2, 3;

[0142] C1—Plant growth under irrigation with soil soaking solution;

[0143] C2—Plant growth conditions under irrigation with the soaking solution of the control group.

[0144] The overall evaluation formula for plant growth performance based on plant germination rate and rhizome length is shown below (12).

[0145] P3=Max{P 3i} (12)

[0146] Where: P 3i —Evaluation indexes of plant growth in different aspects, i=1, 2, 3;

[0147] (2) Comprehensive evaluation of three factors

[0148] The above three single factor evaluations are comprehensively evaluated and represented by K to comprehensively judge the influence of alkali-slag composite soil on environmental performance. If the three single factor evaluation values ​​are less than 0.6, the average weight is used for the final comprehensive evaluation. Otherwise, the maximum pollution index value is used as the final evaluation. The comprehensive evaluation is shown in formula (13).

[0149]

[0150] Where: P n——Single factor evaluation index, i=1, 2, 3;

[0151] 6. Classification design of environmental pollution index of alkali-slag composite soil

[0152] (1) Design basis for pollution degree classification

[0153] The degree of pollution is divided according to the critical scoring values, namely different water quality standards, surface water environmental quality standards GB 3838-2002, agricultural irrigation water quality standards GB 15618-2018, critical chlorine tolerance concentrations of different crops, and plant growth conditions in the reference group.

[0154] (2) Pollution degree classification design

[0155] 0-0.6 is the non-polluting range, 0.6-0.7 is the lightly polluted range, 0.7-0.8 is the moderately polluted range, 0.8-0.9 is the heavily polluted range, and 0.9-1.0 is the severely polluted range. It is recommended that materials be used in the non-polluting and lightly polluted ranges, which will not cause harm to the environment. See Table 3 for specific evaluation values ​​and basis. Fig.11 , Fig.12 .

[0156] Table 3 Classification design of environmental pollution degree indicators

[0157] <![CDATA[Single-factor evaluation index P n > Total pollution evaluation index K Pollution level (0，0.6] (0，0.6] No pollution (0.6-0.7] (0.6-0.7] Slightly polluted (0.7-0.8] (0.7-0.8] Moderate pollution (0.8-0.9] (0.8-0.9] Severe pollution (0.9-1.0] (0.9-1.0] Severe pollution

[0158] Example 2: Evaluation Method Verification

[0159] (1) Experimental design

[0160] The test comprehensively evaluated the environmental performance of alkali slag lime cement soil with different dosages. The method of combining chloride ion dissolution rate test with potted plant experiment was adopted. The chloride ion content in the broken specimens of alkali slag lime cement soil, the influence of the broken specimen soaking liquid on the soil, and the influence of the alkali slag lime cement soaking liquid on the germination rate, root length and stem length of ryegrass were determined. The test results were substituted into the environmental performance evaluation system of alkali slag composite soil to explore the relationship between the physical properties of alkali slag lime soil and the growth regulation mechanism of ryegrass, and finally determine the optimal alkali slag cement lime soil mix ratio that meets economic and green environmental protection conditions.

[0161] (2) Experimental material mix design

[0162] The material ratio scheme of alkali slag cement lime soil was designed. The alkali slag and lime content was fixed at 4%, and the cement content was 2%. The alkali slag content of 0%, 1%, 2%, 3%, and 4% was used to replace the lime component. The moisture content was 18.8%. The mix ratio was screened and the effects of different alkali slag content on the various properties of alkali slag cement lime soil were tested. The free Cl in the soaking liquid was investigated with the increase of alkali slag content.- The influence of alkali slag dosage on the surrounding environment is analyzed by analyzing the changes in alkali slag dosage. See Table 4 for details.

[0163] Table 4 Alkali slag cement lime soil ratio table

[0164]

[0165]

[0166] (3) Test steps

[0167] 1) Specimen preparation

[0168] like Figure 1 As shown, the main test equipment includes: sample preparation device, sample preparation mold, constant temperature and humidity curing box, balance (accurate to 0.01g) and tray, etc.

[0169] Test steps: Test method: According to the "Highway Geotechnical Test Code" JTG E40-2019 and the "Highway Engineering Inorganic Binder Stabilized Material Test Code" JTG E51-2009, the selected materials are compacted to determine the optimal moisture content and optimal dry density of the materials, such as Figure 2 shown.

[0170] The sample size is selected as Φ50mm×50mm, and the materials to be prepared for sample preparation are passed through a 2mm sieve. The water and materials required for a sample are configured according to the optimal moisture content and maximum dry density obtained from the compaction test, and the steps of weighing, mixing, stuffing, molding, compacting, demoulding, and curing are carried out. Figure 3 shown.

[0171] 2) Chloride ion content in water

[0172] Preparation of the test solution: Put different proportions of alkali residue, cement, lime soil into an oven at a constant temperature of 110℃ and dry them. Pass them through a 1mm standard sieve for later use. Put 30g of alkali residue soil into a dry wide-mouth plastic bottle, add 150g of deionized water at a soil-water ratio of 1:5, cover the bottle stopper, shake vigorously for 3min, pour into a funnel with clean filter paper and filter. The filtered solution is the test solution.

[0173] Test steps: Add 0.02 mol / L NaHCO3 to the test solution until the solution turns back to yellow (pH 7), then add 0.5 mL of 5% K2CrO4 indicator, and titrate with AgNO3 standard solution until the color of the turbid solution changes from yellow-green to brick red, reaching the titration endpoint, record the volume V of AgNO3 consumed, and calculate the chloride ion content in the material.

[0174] 3) Chloride ion retention in soil

[0175] The alkali slag cement lime soil with different dosages is crushed, sieved and air-dried for later use.

[0176] In the laboratory, ensure natural light. Under cloudy conditions, carry out daily management, maintain soil moisture, and water once every 5 days with a water volume of 400mL-500mL.

[0177] 4) Plant growth indicators

[0178] Soaking liquid treatment: The same as the soaking liquid treatment method described above.

[0179] Seed treatment: Soak the seeds in pure water for 1-2 hours; select 25 full seeds and place them in a culture dish with two layers of filter paper; seal the sample with sealing film and place it in a constant temperature and light-free incubator at 25±5℃ for germination. Figure 6 As shown; observe the number of germinations within 10 days, and take the radicle extending 2mm out of the seed coat as the germination standard; observe the average rhizome length for 15 days to evaluate the plant growth.

[0180] (4) Test results

[0181] 1) Analysis of chloride ion dissolution rules

[0182] By setting the integral specimen and the broken specimen Cl - The dissolution amount was the control group, and the Cl - The dissolution amounts were considered as worst case scenarios for road engineering applications.

[0183] Monolithic specimens of alkali slag cement lime soil with different addition amounts Cl - Dissolution amount, broken specimen Cl - The dissolution test results are shown in Table 5.

[0184] Table 5 Different alkali residue dosage Cl - content

[0185]

[0186] Note: The integral specimen with 4% alkali residue content fell apart when soaked in water.

[0187] 2) Analysis of the influence of soil physical properties

[0188] The soil matrix was irrigated with the above-mentioned broken specimens 1-5 times soaking solution, and then the Cl content in the soil matrix was measured after a period of time. - The retention volume is shown in Table 6. Figure 7 shown.

[0189] Table 6 Cl at different soil depths - content

[0190]

[0191] 3) Analysis of plant growth patterns

[0192] Growth of ryegrass planted in alkali slag cement lime soil Figure 8 The experimental results of other monitoring indicators are shown in Table 7.

[0193] Table 7 Results of the ryegrass growth experiment in alkali slag lime cement soil

[0194]

[0195] To further analyze the plant growth impact characteristics, the data were plotted, e.g. Fig. 9 shown.

[0196] (5) Calculation of risk assessment PN score

[0197] 1) Analysis of P1 value calculation results

[0198] Substituting the above experimental data into the evaluation system, the P1 value results are shown in Table 8.

[0199] Table 8 P1 value calculation results

[0200]

[0201] 2) Analysis of P2 value calculation results

[0202] Substituting the above experimental data into the evaluation system, we can get P n2 The value results are shown in Table 9.

[0203] Table 9P n2 Value calculation result

[0204]

[0205] 3) Analysis of P3 value calculation results

[0206] Substituting the above experimental data into formula (1) to calculate P n3 The results are shown in Table 10.

[0207] Table 10P n3 Value calculation result

[0208]

[0209] 4) Analysis of K value calculation results

[0210] Substituting the above P1, P2, and P3 into formula (2) can obtain the final K situation, as shown in Table 11. Fig.10 shown.

[0211] Table 11P n Value calculation result

[0212]

[0213]

[0214] It can be seen from the chart that with the increase of alkali slag content, Max(P n ) value gradually increases. When the alkali slag dosage is less than 2%, P n The situation is in an unpolluted state. When the alkali residue content is 2%, P n The situation is in a mild state. When the alkali slag content is 3% and 4%, the Pn situation is in a severe pollution state. The main influencing factor is the Cl - Therefore, in the construction of road projects, the amount of alkali residue should be strictly controlled to avoid excessive alkali residue content causing pollution to the surrounding environment.

[0215] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for evaluating the environmental pollution degree of road alkali-slag composite soil, characterized in that: The following steps are involved: (1) Taking water, soil and plant growth as the monitoring items of the environmental performance of alkali-slag composite soil, the chloride ion content in the alkali-slag composite soil soaking solution, the chloride ion retention in the soil and the plant growth performance are monitored, and the monitoring values ​​of the chloride ion content in the alkali-slag composite soil soaking solution x1, the chloride ion retention in the soil x2, the germination rate r1, the root length r2 and the stem length r3 reflecting the plant growth performance are obtained; (2) Construct the water body evaluation index P1 and soil body evaluation index P2 model. The specific formula is as follows: Where: x i —water and soil monitoring values, i=1, 2; (3) Construction of plant growth index P3 model (3.1) Plant germination rate, root length, and stem length evaluation formula P 3i As shown below: Where: r i —plant growth performance monitoring value, i=1, 2, 3; C1—Plant growth under irrigation with soil soaking solution; C2—plant growth under irrigation with soaking solution in the control group; (3.2) The overall evaluation formula for plant growth performance based on plant germination rate, root length and stem length is as follows: P3=Max{P 3i } (12) Where: P 3i —Evaluation indexes of plant growth in different aspects, i=1, 2, 3; (4) Comprehensively evaluate the three single factor evaluations and express them as K to comprehensively judge the influence of alkali-slag composite soil on environmental performance. The comprehensive evaluation formula is as follows: Where: P n ——Single factor evaluation index, i=1, 2, 3; (5) Design pollution degree classification, as follows: Alkali-slag composite soil evaluation can only be used in non-polluted and slightly polluted areas.

2. The method for evaluating the environmental pollution degree of road alkali-slag composite soil according to claim 1 is characterized by: The monitoring and calculation process of the chloride ion content x1 in the alkali slag composite soil soaking solution is as follows: A. Specimen preparation: Pass the materials to be prepared through a 2mm standard sieve, prepare the water and materials required for a specimen according to the optimal moisture content and maximum dry density obtained from the compaction test, prepare a cylindrical specimen, and carry out material weighing, mixing, stuffing, mold loading, compacting, demoulding, and curing; B. Preparation of the test solution: Dry the alkali residue composite soil with different alkali residue dosage ratios, crush and sieve for later use, take the alkali residue composite soil, add deionized water at a soil-water ratio of 1:5, cover the bottle stopper, shake well, filter, and the filtered solution is the test solution; C. Test process: Add NaHCO3 solution to the test solution until the solution turns yellow again, then add K2CrO4 indicator, and titrate with AgNO3 standard solution until the color of the turbid solution changes from yellow-green to brick red, that is, the titration endpoint is reached, and record the volume V of AgNO3 consumed; D. Chloride content is calculated as follows: Cl - (%)=Cl - (mmol / kg)×0.0355×10 -1 (4) Cl - (mg / kg)=Cl - (%)×10000 (5) Where: c—concentration of silver nitrate standard solution (mol / L); V—Volume of silver nitrate solution for titration (mL); m—the mass of dry soil equivalent to the volume of leachate taken during analysis (g); 0.0355—Molar mass of chloride (g / mol).

3. The method for evaluating the environmental pollution degree of road alkali-slag composite soil according to claim 1 is characterized by: The monitoring and calculation process of the chloride ion retention x2 in the soil is as follows: A. Device setup: The main body of the device is a frustum-shaped structure made of resin, with a water outlet at the bottom. From top to bottom, there are aquifer, planting soil layer and drainage layer. The drainage layer is filled with gravel, and the planting soil layer is the farmland soil sampled from the side of the pollution-free road. B. Material preparation: Take 500 kg of garden soil and spread it flat in the open space in front of the rainwater laboratory for light air drying. After natural air drying, crush the large pieces of soil and remove the debris, then pass through a 2 mm standard sieve. The sieved garden soil is saved for later use. The preparation steps of irrigation liquid are as follows: dry the alkali residue composite soil with different proportions, crush and sieve for later use, take the alkali residue composite soil, add deionized water according to the soil-water ratio, cover the bottle stopper, shake well, filter, and the filtered solution is the irrigation liquid; C. Test process: A planting environment with artificial water inflow under greenhouse conditions was used. In the laboratory, natural light was ensured. Under cloudy conditions, daily management was performed to maintain soil humidity. Watering was performed once every 5 days with a water volume of 400mL-500mL, for a total of 4 times. Finally, the soil was collected, dried, and the soil test solution was prepared; D. Test the chloride ion content of the soil test solution, specifically: add NaHCO3 solution to the test solution until the solution turns back to yellow, then add K2CrO4 indicator, and titrate with AgNO3 standard solution until the color of the turbid solution changes from yellow-green to brick red, that is, the titration endpoint is reached, and record the volume V of AgNO3 consumed; E. Chloride content is calculated according to formula (3, 4, 5): Cl - (%)=Cl - (mmol / kg)×0.0355×10 -1 (4) Cl - (mg / kg)=Cl - (%)×10000 (5) Where: c—concentration of silver nitrate standard solution (mol / L); V—Volume of silver nitrate solution for titration (mL); m—the mass of dry soil equivalent to the volume of leachate taken during analysis (g); 0.0355—Molar mass of chloride (g / mol).

4. The method for evaluating the environmental pollution degree of road alkali-slag composite soil according to claim 1 is characterized by: The plant growth performance testing method is as follows: A. Soaking liquid treatment: Dry the alkali residue composite soil with different proportions, crush and sieve for later use, take the alkali residue composite soil, add deionized water according to the soil-water ratio, cover the bottle stopper, shake well, filter, and the filtered solution is the soaking liquid; B. Seed treatment: Soak the seeds in pure water for 1-2 hours, select the plump seeds, remove the seed coat, and place the seeds in a culture dish with two layers of filter paper; pour in the soaking solution, seal with sealing film, and place the sample in a constant temperature and light-free culture box at 25±5℃ for germination; C. Experimental process: observe the number of germinations within 7 days, and use the root protruding 2mm out of the seed coat as the germination standard; record the number of seeds germinated every day during the germination period, and use the radicle breaking through 2mm as the standard; count and calculate the germination rate on the 7th day, and record for a total of 7 days; after completing the germination test on the 15th day, randomly select 10 representative seedlings in each culture dish, measure the root length and stem length with a vernier caliper, calculate the average height, calculate the germination rate r1, root length r2, and stem length r3, and evaluate the plant growth.

5. The method for evaluating the environmental pollution degree of road alkali-slag composite soil according to claim 4 is characterized by: The germination rate r1 is calculated by referring to formula (6): Where: N q —Number of seeds germinated in 7 days; N—is the number of seeds tested.

6. The method for evaluating the environmental pollution degree of road alkali-slag composite soil according to claim 4 is characterized by: The root length r2 index is evaluated by calculating the average root length (R), and the stem length r3 index is evaluated by calculating the average stem length (B). The average root length (R) and the average stem length (B) are calculated according to formulas (7, 8): Where: N g —Root length of successfully germinated vegetation in 15 days; N—is the number of seeds tested; Where: N j — Length of stem of successfully germinated vegetation in 15 days; N—is the number of seeds tested.

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