Method for evaluating harmfulness of characteristic heavy metals in steel slag based on leaching characteristics and biological effective state

Abstract

The invention provides a method for evaluating harmfulness of characteristic heavy metals in steel slag based on leaching characteristics and biological effective state, which comprises the following steps: S1, pretreating steel slag and preparing a sample, collecting the steel slag sample and pretreating to prepare a steel slag sample meeting the requirements of leaching toxicity and biological effective state detection; s2, evaluating the leaching toxicity of the steel slag characteristic heavy metal, and evaluating the bioavailability of the steel slag characteristic heavy metal at the same time; s3, comprehensively evaluating the harmfulness of the steel slag characteristic heavy metal based on the steel slag characteristic heavy metal leaching toxicity evaluation result and the steel slag characteristic heavy metal bioavailability evaluation result. The method for evaluating the harmfulness of the characteristic heavy metals of the steel slag is wide in applicability, high in operability and reliable in evaluation effect.

Description

Technical Field

[0001] The present invention relates to the technical field of environmental pollution prevention and control, and particularly relates to a method for evaluating the hazards of characteristic heavy metals in steel slag based on leaching characteristics and bioavailability assessment. Background Art

[0002] China is the world's largest steel producer. In 2022, the crude steel output reached 1.013 billion tons, accounting for more than 53% of the global total output. During the steel smelting process, about 10%-15% of steel slag is produced for every 1 ton of crude steel produced. Based on this estimation, China's annual steel slag output exceeds 150 million tons. Although steel slag can be used to replace natural aggregates in fields such as building materials and roadbeds, its resource utilization rate has been less than 30% for a long time. In recent years, due to fluctuations in the demand of the construction industry and restrictions on building material standards, the actual consumption of steel slag has further decreased. A large amount of unused steel slag is mainly stored in the open air, occupying more than 12,000 hectares of land area, and problems such as dust and leachate are likely to occur during the storage process, exacerbating the environmental burden.

[0003] The main components of steel slag are calcium silicate, iron oxides, free calcium oxide, etc., but at the same time, it may enrich characteristic heavy metal pollutants such as chromium (Cr), nickel (Ni), lead (Pb), cadmium (Cd), etc. Taking typical steel slag as an example, the Cr content can reach 200-800 mg / kg, and the Ni content is 50-200 mg / kg, which is significantly higher than the natural soil background value. In the natural environment, heavy metals in steel slag can be leached from the steel slag through acid precipitation or surface water scouring, infiltrating into the surrounding soil and groundwater, and heavy metal pollutants such as these may pose a threat to human health through food chain enrichment.

[0004] Currently, the research on the environmental hazards assessment of heavy metals in steel slag mainly focuses on the study of their leaching concentrations. Through traditional leaching experiments (such as TCLP, SPLP), the leaching amounts of heavy metals are measured by simulating specific environmental conditions (such as acid rain pH = 4.93 or groundwater pH = 6.0), but such methods only reflect the short-term static release potential and cannot characterize the long-term dynamic release behavior of heavy metals in complex environments. The total amount of heavy metals is not completely related to their actual ecological risks, and their hazards more depend on the migratory leaching concentration and the proportion of bioavailable effective state. Especially under the action of acidic soil or organic matter, it is transformed into a more bioactive and more easily absorbed occurrence form, resulting in the underestimation of the potential risks of heavy metals by traditional leaching results. Summary of the Invention

[0005] In view of the above situation, based on the single evaluation method of leaching toxicity analysis of steel slag, combined with bioavailability analysis and evaluation, the present invention provides a comprehensive environmental risk evaluation method based on the bioavailability evaluation of heavy metal occurrence forms and the environmental hazard evaluation based on the total amount of heavy metals, which can effectively evaluate the hazards of heavy metals in steel slag.

[0006] Example 1. According to one aspect of the present invention, a method for evaluating the hazards of characteristic heavy metals in steel slag based on leaching characteristics and bioavailability is provided, including the following steps:

[0007] Step S1. Pretreatment and sample preparation of steel slag. Collect steel slag samples and perform pretreatment operations to prepare steel slag samples that meet the requirements for leaching toxicity and bioavailability detection.

[0008] Step S2. Evaluate the leaching toxicity of characteristic heavy metals in steel slag and simultaneously evaluate the bioavailability of characteristic heavy metals in steel slag.

[0009] Step S2 further includes: Step S2a1, analyze the leaching concentration of characteristic heavy metals in steel slag using the toxicity leaching method for solid waste; Step S2a2, evaluate the leaching toxicity of characteristic heavy metals in steel slag in combination with standards.

[0010] Step S2b1, analyze the bioavailable state of characteristic heavy metal pollutants in steel slag using the chemical sequential extraction method; Step S2b2, evaluate the leaching toxicity of characteristic heavy metals in steel slag according to the risk assessment coding method.

[0011] Step S3. Based on the evaluation results of the leaching toxicity of characteristic heavy metals in steel slag and the evaluation results of the bioavailability of characteristic heavy metals in steel slag, comprehensively evaluate the hazards of characteristic heavy metals in steel slag.

[0012] In an optional implementation manner, in the step S1, the collection and pretreatment operations of the steel slag samples further include: first, uniformly collect the steel slag samples, then use crushing equipment and screening equipment to crush and screen the steel slag to obtain sample particles with a particle size not greater than 3 mm, and finally perform low-temperature drying on the treated steel slag at a drying temperature of 80 - 110 °C.

[0013] In an optional implementation manner, in the step S2a1, it further includes: perform leaching analysis on the characteristic heavy metal pollutants in steel slag such as Cu, Zn, Cd, Cr, Ni, As, Hg, and Pb according to the HJ557 standard. Specifically, weigh a test sample with a dry basis weight of 100 - 200 g, place it in an extraction bottle, calculate the volume of the extraction agent required according to the liquid-solid ratio of 10:1 (L / kg) based on the moisture content of the sample, add the extraction agent and seal the extraction bottle, vertically fix the extraction bottle on a horizontal oscillation device, adjust the oscillation frequency to 110 - 200 times / min, oscillate at room temperature for 8 - 12 h, then remove the extraction bottle, let it stand for 16 - 24 h, and filter the obtained leachate using suction filtration or filter paper to detect and analyze the concentration of the test solution.

[0014] In an alternative embodiment, in the step S2a2, it further includes analyzing whether the leaching concentration of characteristic heavy metals in the steel slag exceeds the maximum allowable emission concentration in the standard according to the GB8978 standard to evaluate the harmfulness of the leaching toxicity of characteristic heavy metals in the steel slag.

[0015] In an alternative embodiment, in the step S2b1, it further includes that the occurrence forms of characteristic heavy metal pollutants in the steel slag are divided into L1 state, L2 state, L3 state and L4 state, and the occurrence forms and contents of various characteristic heavy metals in the steel slag are detected.

[0016] In an alternative embodiment, in the step S2b2, it further includes analyzing the bioavailable state of characteristic heavy metal pollutants in the steel slag to obtain the contents of each form as L 10 、L 20 、L 30 、L 40 , and calculating the effectiveness evaluation index T according to the contents of each form. The specific formula is

[0017] T = L 10 / (L 10 + L 20 + L 30 + L 40 ) * 100%,

[0018] Evaluating the pollution degree of heavy metals in the steel slag according to the evaluation criteria of the risk assessment coding method.

[0019] In an alternative embodiment, the extraction method of the L1 state is as follows: Take 1.000 g of the steel slag sample and put it into a round-bottom centrifuge tube with a capacity of 100 mL. Add 40 mL of acetic acid (HOAc) with a concentration of 0.11 mol / L. Seal the centrifuge tube and place it under oscillation at room temperature for 16 - 20 hours. After the oscillation ends, put the centrifuge tube into a centrifuge, set the rotation speed to 4000 - 4500 r / min, and the centrifugation time to 20 - 30 minutes. Filter through a 45 μm filter membrane to obtain the supernatant, add one drop of nitric acid (1 + 1), and prepare for measurement. Use ICP-MS to detect and analyze the test solution to obtain the content of the characteristic pollutant in the L1 state as L 10 (mg / kg). The remaining steel slag sample in the centrifuge tube is rinsed with 20 mL of deionized water and then centrifuged and washed again. After pouring out the supernatant, the steel slag is left for the next step.

[0020] In an alternative embodiment, the method for extracting the L2 state is as follows: add 40 mL of hydroxylamine hydrochloride solution with a concentration of 0.5 mol / L to the steel slag rinsed with deionized water, place it in an oscillator at room temperature and oscillate for 16 - 20 hours. After the oscillation ends, put the centrifuge tube into a centrifuge, set the rotation speed to 4000 - 4500 r / min, and the centrifugation time to 20 - 30 minutes. Filter through a 45 μm filter membrane to obtain the supernatant, add one drop of nitric acid (1 + 1), and prepare for testing. Use ICP-MS to detect and analyze the test solution, and the content of the characteristic pollutant L2 state is L 20 (mg / kg). The remaining steel slag sample in the centrifuge tube is rinsed with 20 mL of deionized water and then centrifuged again. After pouring out the supernatant, the steel slag is left for the next step.

[0021] In an alternative embodiment, the method for extracting the L3 state is as follows: add 10 mL of 8.8 mol / L hydrogen peroxide to the steel slag in the above step, place the centrifuge tube in a constant temperature water bath and continuously heat at 85 °C for 1 - 1.5 hours, with intermittent oscillation. When the volume of the solution in the centrifuge tube is less than 2 mL, add another 10 mL of 8.8 mol / L hydrogen peroxide and repeat the above operation. After the centrifuge tube cools, add 50 mL of ammonium acetate with a concentration of 1.0 mol / L and let it stand in a constant temperature water bath at room temperature for 16 - 20 hours, then centrifuge again. Filter the supernatant through a filter membrane, add one drop of nitric acid (1 + 1) and prepare for testing. Use ICP-MS to detect and analyze the test solution, and the content of the characteristic pollutant L3 state is L 30 (mg / kg). The remaining steel slag in the centrifuge tube is washed and centrifuged for the next step.

[0022] In an alternative embodiment, the method for extracting the L4 state is as follows: vacuum dry the centrifuge tube containing the residue from the previous step at 40 °C to constant weight, grind and sieve it, and perform total digestion of the characteristic pollutants on the remaining steel slag residue as a solid sample. The digestion method is to add 60 - 80 mL of a mixed acid of hydrofluoric acid - hydrochloric acid - nitric acid - perchloric acid to the residue, and perform pyrolysis on an electric hot plate to obtain the test solution. Then use ICP-MS to detect and analyze the test solution, and the content of the characteristic pollutant L4 state is L 40 (mg / kg).

[0023] Advantages of the present invention:

[0024] The present invention proposes a comprehensive hazard assessment method combining the assessment of the leaching toxicity of characteristic heavy metals in steel slag and the evaluation of the bioavailability of characteristic heavy metals. At the same time, two heavy metal hazard assessment methods are used to evaluate the environmental hazard of steel slag, making up for the deficiencies of single-method evaluation, and enabling a comprehensive and systematic evaluation of the heavy metal hazards of industrial solid wastes represented by steel slag.

[0025] The method described in the present invention is applicable to industrial solid wastes such as steel slag, with a wide range of applicability; by combining two evaluation methods of the toxicity leaching and bioavailability of heavy metals, the hazards of characteristic heavy metals in steel slag are evaluated, and the evaluation results are more comprehensive and reliable; at the same time, the method is simple to operate and easy to implement and promote. Description of the Drawings

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0027] Figure 1 It is a schematic flow chart of a method for evaluating the hazards of characteristic heavy metals in steel slag based on leaching characteristics and bioavailable states provided by the present invention. Detailed Embodiments

[0028] To make the objectives, technical solutions, and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention in conjunction with the specific embodiments and corresponding drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0029] According to one aspect of the present invention, a method for evaluating the hazards of characteristic heavy metals in steel slag based on leaching characteristics and bioavailable states is provided, including collecting and preprocessing steel slag to obtain steel slag samples for leaching toxicity and bioavailable state analysis; analyzing the leaching concentration of characteristic heavy metals in steel slag by using the toxicity leaching method for solid waste, and evaluating the leaching toxicity of characteristic heavy metals in steel slag in combination with the GB8978 standard; analyzing the bioavailable state of characteristic heavy metal pollutants in steel slag by using the chemical sequential extraction method, and evaluating the bioavailability of characteristic heavy metals in steel slag according to the risk assessment coding method; finally, comprehensively evaluating the hazards of characteristic heavy metals in steel slag by combining the leaching toxicity and bioavailability of characteristic heavy metals in steel slag.

[0030] Further, for the steel slag samples obtained for bioavailability analysis and leaching toxicity analysis, first, the steel slag samples, including newly generated steel slag in the factory area and steel slag stored outside the factory, are collected uniformly; then, crushing equipment such as jaw crushers and screening equipment such as vibrating screens are used to crush and screen the steel slag to obtain sample particle sizes not greater than 3 mm; finally, the processed steel slag is dried at a drying temperature of 80-110 °C.

[0031] Further, the method for leaching toxic characteristic heavy metals from steel slag is to conduct leaching analysis on characteristic heavy metal pollutants such as Cu, Zn, Cd, Cr, Ni, As, Hg, and Pb in steel slag according to HJ557 standard. The specific steps are as follows: Weigh a sample with a dry basis weight of 100 - 200 g and place it in an extraction bottle. According to the moisture content of the sample, calculate the volume of the required leaching agent according to a liquid-solid ratio of 10:1 (L / kg), add the leaching agent, tightly cover the bottle cap, and vertically fix it on a horizontal oscillation device. Adjust the oscillation frequency to 110 - 200 times / min, oscillate at room temperature for 8 - 12 h, then remove the extraction bottle and let it stand for 16 - 24 h. Filter the obtained leaching solution using suction filtration or filter paper filtration, etc., and detect and analyze to obtain the concentration of the test solution.

[0032] Further, for the assessment of the leaching toxicity of characteristic heavy metals in steel slag, it is to analyze whether the leaching concentration of characteristic heavy metals in steel slag exceeds the maximum allowable emission concentration in the standard according to GB8978 standard. The maximum allowable emission concentration of the second type of pollutants is implemented according to the first-class standard to judge the harmfulness of the leaching of characteristic heavy metals in steel slag.

[0033] Further, for the analysis of the effective states of characteristic heavy metals in steel slag, the occurrence forms of characteristic heavy metal pollutants in steel slag are divided into L1 state, L2 state, L3 state, and L4 state, and the contents of each state are L 10 、L 20 、L 30 、L 40 , respectively. The extraction steps are as follows:

[0034] Extraction method for L1 state: Take 1.000 g of steel slag sample and put it into a 100 mL round-bottom centrifuge tube. Then add 40 mL of acetic acid (HOAc) with a concentration of 0.11 mol / L, cover the lid and place it under room temperature conditions for oscillation (250 - 300 r / min to ensure that the mixture in the tube is in a suspended state), and the oscillation time is 16 - 20 hours. After the oscillation ends, put the centrifuge tube into a centrifuge, set the rotation speed to 4000 - 4500 r / min, and the centrifugation time to 20 - 30 minutes. Take the supernatant (filtered through a 45 μm filter membrane), add one drop of nitric acid (1 + 1), and prepare for testing. Use ICP-MS to detect and analyze the test solution to obtain that the content of the characteristic pollutant in L1 state is L 10 (mg / kg). The remaining steel slag sample in the centrifuge tube is rinsed with 20 mL of deionized water and then centrifuged and cleaned again. After pouring out the supernatant, leave the steel slag for the next test.

[0035] Extraction method of L2 state: Add 40 mL of hydroxylamine hydrochloride solution with a concentration of 0.5 mol / L to the steel slag rinsed with deionized water, and place it in an oscillator at room temperature and oscillate for 16 - 20 hours. After the oscillation, put the centrifuge tube into a centrifuge, set the rotation speed to 4000 - 4500 r / min, and the centrifugation time to 20 - 30 minutes. Take the supernatant (filtered through a 45 μm filter membrane), add a drop of nitric acid (1 + 1), and prepare for measurement. Use ICP - MS to detect and analyze the test solution, and the content of the characteristic pollutant L2 state is L 20 (mg / kg). The remaining steel slag sample in the centrifuge tube is rinsed with 20 mL of deionized water and centrifuged again. After pouring out the supernatant, the steel slag is left for the next test.

[0036] Extraction method of L3 state: Add 10 mL of 8.8 mol / L hydrogen peroxide to the steel slag after the above steps, place the centrifuge tube in a constant temperature water bath at 85 °C and continuously heat for 1 - 1.5 hours, with intermittent oscillation. When the volume of the solution in the centrifuge tube is less than 2 mL, add another 10 mL of 8.8 mol / L hydrogen peroxide and repeat the above operation. After the centrifuge tube cools, add 50 mL of ammonium acetate with a concentration of 1.0 mol / , and let it stand in a constant temperature water bath at room temperature for 16 - 20 hours. Then centrifuge again, take the supernatant and filter it through a filter membrane, add a drop of nitric acid (1 + 1) and prepare for measurement. Use ICP - MS to detect and analyze the test solution, and the content of the characteristic pollutant L3 state is L 30 (mg / kg). The remaining steel slag in the centrifuge tube is used for the next test after cleaning and centrifugation.

[0037] Extraction method of L4 state: Vacuum - dry the centrifuge tube containing residue from the previous step at 40 °C to constant weight, grind and sieve (80 - 100 mesh), and perform total digestion of the characteristic pollutants on the remaining steel slag residue as a solid sample. The digestion method is to add 60 - 80 mL of a mixed acid of hydrofluoric acid - hydrochloric acid - nitric acid - perchloric acid to the residue, and perform pyrolysis on an electric hot plate to obtain the test solution. Then use ICP - MS to detect and analyze the test solution, and the content of the characteristic pollutant L4 state is L 40 (mg / kg).

[0038] Furthermore, the evaluation of the bioavailability of characteristic heavy metals in the steel slag is calculated according to the risk assessment coding method. The specific calculation formula is T = L 10 / (L 10 +L 20 +L 30 +L 40 ) * 100%, and the pollution degree of heavy metals in the steel slag is evaluated according to the evaluation criteria of the risk assessment coding method in the following table. The evaluation criteria are shown in Table 1.

[0039] Evaluation Criteria of Risk Assessment Coding Method in Table 1

[0040]

[0041] Example 2. According to another aspect of the present invention, the implementation process of a method for evaluating the hazards of characteristic heavy metals in steel slag based on leaching characteristics and bioavailable forms is divided into six steps:

[0042] Step 1: Collection and pretreatment of steel slag samples. First, collect samples evenly to ensure uniform sampling of the steel slag; then use crushing equipment such as jaw crushers and screening equipment such as vibrating screens to crush and screen the steel slag; and then dry it for standby.

[0043] Step 2: Analysis of the leaching concentration of characteristic heavy metals in steel slag. Conduct a toxicity leaching experiment on the pretreated steel slag raw materials according to the solid waste heavy metal toxicity leaching method, and detect and analyze the obtained leachate.

[0044] Step 3: Analysis of the leaching concentration of characteristic heavy metals in steel slag. According to the analysis results of the characteristic heavy metals in steel slag obtained in Step 2, evaluate the leaching toxicity of the characteristic heavy metals in steel slag in combination with the GB8978 standard.

[0045] Step 4: Analysis of the occurrence forms of characteristic heavy metals in steel slag. Use the chemical sequential extraction method to analyze the bioavailable forms of characteristic heavy metals in steel slag, divide the occurrence forms of heavy metals into L1 state, L2 state, L3 state and L4 state, and detect the occurrence forms and contents of various characteristic heavy metals in the steel slag.

[0046] Step 5: Evaluation of the bioavailability of characteristic heavy metals in steel slag. Combine the analysis results of the contents of the occurrence forms of various heavy metals in the steel slag obtained in Step 4, and calculate the pollution degree index of the characteristic heavy metals in the steel slag according to the risk assessment coding method to evaluate the heavy metal pollution degree.

[0047] Step 6: Comprehensive evaluation of the hazards of characteristic heavy metals in steel slag. According to the evaluation of the leaching toxicity of the characteristic heavy metals in the steel slag and the evaluation of the bioavailability of the characteristic heavy metals in the steel slag, comprehensively evaluate the hazards of the characteristic heavy metals in the steel slag by combining the two evaluation methods.

[0048] Example 3. According to another aspect of the present invention, taking the steel slag stored in a certain steel plant as an example for analysis, the specific content is as follows:

[0049] For the steel slag samples used for bioavailability analysis and leaching toxicity analysis, first, samples of the steel slag stored in the steel plant were collected; then, the steel slag was crushed and screened using crushing equipment such as jaw crushers and screening equipment such as vibrating screens to obtain sample particle sizes not greater than 3 mm; finally, the treated steel slag was dried at a drying temperature of 80°C.

[0050] The method for leaching characteristic heavy metals toxicity of steel slag is to leach and analyze characteristic heavy metal pollutants such as Cu, Zn, Cd, Cr, Ni, As, Hg, Pb, etc. in steel slag according to HJ557 standard. The specific steps are as follows: Weigh a sample with a dry basis weight of 100 and place it in an extraction bottle. According to the moisture content of the sample, calculate the volume of the leaching agent required according to a liquid-solid ratio of 10:1 (L / kg), add the leaching agent, tighten the bottle cap, and vertically fix it on a horizontal oscillation device. Adjust the oscillation frequency to 110 times / min, oscillate for 8 h at room temperature, then remove the extraction bottle and let it stand for 16 h. Filter the obtained leachate using suction filtration or filter paper, etc., detect and analyze to obtain the concentration of the test solution. The characteristic heavy metal pollutants and leaching concentrations of the steel slag are shown in Table 2.

[0051] The evaluation of the leaching toxicity of characteristic heavy metals in steel slag is to analyze whether the leaching concentration of characteristic heavy metals in steel slag exceeds the maximum allowable emission concentration in the standard according to GB8978 standard (the maximum allowable emission concentration of the second-class pollutants is implemented according to the first-class standard), so as to judge the harmfulness of the leaching toxicity of characteristic heavy metals in steel slag. It can be seen that the leaching concentrations of characteristic heavy metals in steel slag obtained by the leaching method according to HJ557 standard are all less than the maximum allowable emission concentration in GB8978 standard, indicating that the leaching toxicity of heavy metals in steel slag is within the safe range.

[0052] Table 2 Occurrence forms and contents of various characteristic heavy metals in the steel slag of a steel plant

[0053]

[0054] Note: ND indicates not detected below the detection limit

[0055] The analysis of the effective states of characteristic heavy metals in steel slag is to divide the occurrence forms of characteristic heavy metals such as Cu, Zn, Cd, Cr, Ni, As, Hg, Pb, etc. in steel slag into L1 state, L2 state, L3 state and L4 state, and the contents of each state are L 10 、L 20 、L 30 、L 40 , and the extraction steps are as follows:

[0056] Extraction method of L1 state: Take 1.000 g of steel slag sample and put it into a round-bottom centrifuge tube with a capacity of 100 mL. Then add 40 mL of acetic acid (HOAc) with a concentration of 0.11 mol / L, cover the lid and place it in a shaker at room temperature (250 r / min to ensure the mixture in the tube is in a suspended state) for 16 hours. After shaking, put the centrifuge tube into a centrifuge, set the rotation speed to 4000 / min, and the centrifugation time to 20 minutes. Take the supernatant (filtered through a 45 μm filter membrane), add a drop of nitric acid (1+1), and prepare for measurement. Use ICP-MS to detect and analyze the test solution, and the content of the characteristic pollutant L1 state is L 10 (mg / kg). The remaining steel slag sample in the centrifuge tube is rinsed with 20 mL of deionized water and then centrifuged and washed again. After pouring out the supernatant, the steel slag is left for the next test.

[0057] Extraction method of L2 state: Add 40 mL of hydroxylamine hydrochloride solution with a concentration of 0.5 mol / L to the steel slag rinsed with deionized water, and place it in a shaker at room temperature for 16 hours. After shaking, put the centrifuge tube into a centrifuge, set the rotation speed to 4000 r / min, and the centrifugation time to 20 minutes. Take the supernatant (filtered through a 45 μm filter membrane), add a drop of nitric acid (1+1), and prepare for measurement. Use ICP-MS to detect and analyze the test solution, and the content of the characteristic pollutant L2 state is L 20 (mg / kg). The remaining steel slag sample in the centrifuge tube is rinsed with 20 mL of deionized water and then centrifuged again. After pouring out the supernatant, the steel slag is left for the next test.

[0058] Extraction method of L3 state: Add 10 mL of 8.8 mol / L hydrogen peroxide to the steel slag after the above steps, place the centrifuge tube in a constant temperature water bath at 85 °C and continuously heat for 1 - 1.5 hours with intermittent shaking. When the volume of the solution in the centrifuge tube is less than 2 mL, add another 10 mL of 8.8 mol / L hydrogen peroxide and repeat the above operation. After the centrifuge tube cools, add 50 mL of ammonium acetate with a concentration of 1.0 mol / , and let it stand in a constant temperature water bath at room temperature for 16 hours. Then centrifuge again, take the supernatant and filter it through a filter membrane, add a drop of nitric acid (1+1) and prepare for measurement. Use ICP-MS to detect and analyze the test solution, and the content of the characteristic pollutant L3 state is L 30 (mg / kg). The remaining steel slag in the centrifuge tube is used for the next test after cleaning and centrifugation.

[0059] Extraction method of L4 state: The centrifuge tube containing residues from the previous step was dried to constant weight under vacuum at 40 °C, ground and sieved (80 - 100 mesh). The total digestion of characteristic pollutants in the remaining steel slag residues was carried out according to solid samples. The digestion method was to add a mixed acid of hydrofluoric acid - hydrochloric acid - nitric acid - perchloric acid with a concentration of 60% to the residues, and pyrolyze them on a hot plate to obtain the test solution. Then, ICP - MS was used to detect and analyze the test solution, and the content of the characteristic pollutant L4 state was L 40 (mg / kg).

[0060] The evaluation of the bioavailability of characteristic heavy metals in steel slag is to combine the analysis results of the content of various occurrence forms of heavy metals in steel slag obtained from the above steps to obtain the contents of elements such as characteristic heavy metals Cu, Zn, Cd, Cr, Ni, As, Hg, Pb, etc. in steel slag. The occurrence forms and contents of various heavy metals are shown in Table 1. According to the risk assessment coding method, the bioavailability evaluation index T of steel slag heavy metal pollution was calculated. The specific calculation formula is T = L 10 / (L 10 +L 20 +L 30 +L 40 ) * 100%. And according to the evaluation criteria of the risk assessment coding method, the T values of elements such as characteristic heavy metals Cu, Zn, Cd, Cr, Ni, As, Hg, Pb, etc. in this steel slag were all less than 1%. The result analysis is shown in Table 3, and it is analyzed that there is no environmental risk for the characteristic heavy metals in this steel slag.

[0061] Table 3 Occurrence forms and contents of various characteristic heavy metals in the steel slag of a steel plant

[0062]

[0063] Analyzed by the comprehensive hazard assessment method of the present invention combining the leaching toxicity assessment of characteristic heavy metals in steel slag and the bioavailability evaluation of characteristic heavy metals, there is no environmental risk for the characteristic heavy metals in the steel slag of this experiment.

[0064] The above are only examples of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A method for evaluating the harmfulness of characteristic heavy metals in steel slag based on leaching characteristics and bioavailable states, characterized in that, It includes the following steps: Step S1. Steel slag pretreatment and sample preparation: Collect steel slag samples and perform pretreatment operations to prepare steel slag samples that meet the requirements for leaching toxicity and bioavailable state detection. Step S2. Evaluate the leaching toxicity of characteristic heavy metals in steel slag and, at the same time, evaluate the bioavailability of characteristic heavy metals in steel slag. The said Step S2 further includes: Step S2a1, analyze the leaching concentration of characteristic heavy metals in steel slag using the toxicity leaching method for solid waste; Step S2a2, evaluate the leaching toxicity of characteristic heavy metals in steel slag in combination with the standards. Step S2b1, analyze the bioavailable state of characteristic heavy metal pollutants in steel slag using the sequential extraction method; Step S2b2, evaluate the leaching toxicity of characteristic heavy metals in steel slag according to the risk assessment coding method. Step S3. Based on the evaluation results of the leaching toxicity of characteristic heavy metals in steel slag and the evaluation results of the bioavailability of characteristic heavy metals in steel slag, comprehensively evaluate the harmfulness of characteristic heavy metals in steel slag.

2. The method for evaluating the hazard of characteristic heavy metals in steel slag based on leaching characteristics and bio-available state as claimed in claim 1, wherein In the said Step S1, the collection of steel slag samples and the performance of pretreatment operations further include: First, collect the steel slag samples uniformly, then use crushing equipment and screening equipment to crush and screen the steel slag to obtain sample particles with a particle size not greater than 3 mm, and finally perform low-temperature drying on the treated steel slag at a drying temperature of 80 - 110 °C.

3. The method for evaluating the hazard of characteristic heavy metals in steel slag based on leaching characteristics and bio-available state as claimed in claim 1, wherein In the said Step S2a1, it further includes: Analyze the leaching of characteristic heavy metal pollutants in steel slag such as Cu, Zn, Cd, Cr, Ni, As, Hg, and Pb in accordance with the HJ557 standard. Specifically, it includes: Weigh a test sample with a dry basis weight of 100 - 200 g, place it in an extraction bottle, calculate the volume of the extraction agent required according to the liquid-solid ratio of 10:1 (L / kg) based on the moisture content of the sample, add the extraction agent and seal the extraction bottle, vertically fix the extraction bottle on a horizontal oscillation device, adjust the oscillation frequency to 110 - 200 times / min, oscillate at room temperature for 8 - 12 h, then remove the extraction bottle, let it stand for 16 - 24 h, and filter the obtained leachate using suction filtration or filter paper to detect and analyze the concentration of the test solution.

4. The method for evaluating the harmfulness of characteristic heavy metals in steel slag based on leaching characteristics and bioavailable state as claimed in claim 3, wherein In the said Step S2a2, it further includes: Analyze whether the leaching concentration of characteristic heavy metals in steel slag exceeds the maximum allowable discharge concentration in the standard in accordance with the GB8978 standard to evaluate the harmfulness of the leaching toxicity of characteristic heavy metals in steel slag.

5. A method for evaluating the hazard of characteristic heavy metals in steel slag based on leaching characteristics and bioavailable states as claimed in claim 1, wherein, In the said Step S2b1, it further includes: The occurrence forms of characteristic heavy metal pollutants in steel slag are divided into L1 state, L2 state, L3 state, and L4 state, and detect the occurrence forms and contents of various characteristic heavy metals in steel slag.

6. The method for evaluating the hazard of characteristic heavy metals in steel slag based on leaching characteristics and bio-available state as claimed in claim 5, wherein In the step S2b2, it further includes analyzing the bioavailable forms of the characteristic heavy metal pollutants in the steel slag to obtain the contents of each form as L 10 , L 20 , L 30 , L 40 . The effectiveness evaluation index T is calculated according to the contents of each form, and the specific formula is T = L 10 / (L 10 + L 20 + L 30 + L 40 ) * 100%, Evaluate the degree of heavy metal pollution in steel slag according to the evaluation criteria of the risk assessment coding method.

7. A method for evaluating the hazard of characteristic heavy metals in steel slag based on leaching characteristics and bio-available state as claimed in claim 6, wherein, The extraction method of L1 state is as follows: take 1.000 g of steel slag sample and put it into a round-bottom centrifuge tube with a capacity of 100 mL. Add 40 mL of acetic acid (HOAc) with a concentration of 0.11 mol / L. Seal the centrifuge tube and place it under oscillation at room temperature for 16 - 20 hours. After the oscillation is completed, put the centrifuge tube into a centrifuge, set the rotation speed to 4000 - 4500 r / min, and the centrifugation time to 20 - 30 minutes. Filter through a 45 μm filter membrane to obtain the supernatant. Add one drop of nitric acid (1 + 1) and prepare for testing. Use ICP-MS to detect and analyze the test solution to obtain that the content of the characteristic pollutant L1 state is L 10 (mg / kg). The remaining steel slag sample in the centrifuge tube is rinsed with 20 mL of deionized water and then centrifuged and washed again. After pouring out the supernatant, the steel slag is left for the next step.

8. A method for evaluating the hazard of characteristic heavy metals in steel slag based on leaching characteristics and bio-available state as claimed in claim 7, wherein The extraction method of the L2 state is as follows: Add 40 mL of hydroxylamine hydrochloride solution with a concentration of 0.5 mol / L to the steel slag rinsed with deionized water, place it in an oscillator at room temperature and oscillate for 16 - 20 hours. After the oscillation ends, put the centrifuge tube into a centrifuge, set the rotation speed to 4000 - 4500 r / min, and the centrifugation time to 20 - 30 minutes. Filter the supernatant through a 45 μm filter membrane, add one drop of nitric acid (1 + 1), and prepare for measurement. Use ICP-MS to detect and analyze the sample to be measured, and the content of the characteristic pollutant L2 state is L 20 (mg / kg). The remaining steel slag sample in the centrifuge tube is rinsed with 20 mL of deionized water and centrifuged again. After pouring out the supernatant, the steel slag is left for the next step.

9. The method for evaluating the hazards of characteristic heavy metals in steel slag based on leaching characteristics and bio-available state as claimed in claim 8, wherein The extraction method of the L3 state is as follows: Add 10 mL of 8.8 mol / L hydrogen peroxide to the steel slag in the above steps, place the centrifuge tube in a constant temperature water bath and continuously heat it at 85 °C for 1 - 1.5 hours, with intermittent oscillation. When the volume of the solution in the centrifuge tube is less than 2 mL, add another 10 mL of 8.8 mol / L hydrogen peroxide and repeat the above operation. After the centrifuge tube cools, add 50 mL of ammonium acetate with a concentration of 1.0 mol / L and let it stand in a constant temperature water bath at room temperature for 16 - 20 hours. Then centrifuge again, take the supernatant and filter it through a filter membrane, add one drop of nitric acid (1 + 1) to prepare for measurement, and use ICP-MS to detect and analyze the test solution to obtain that the content of the characteristic pollutant L3 state is L 30 (mg / kg). The remaining steel slag in the centrifuge tube is washed and centrifuged for the next step.

10. A method for evaluating the harmfulness of characteristic heavy metals in steel slag based on leaching characteristics and bio-available state as claimed in claim 9, wherein, The extraction method of the L4 state is as follows: the centrifuge tube containing residues in the previous step is vacuum-dried at 40 °C until constant weight, ground and sieved, and the total amount of characteristic pollutants in the remaining steel slag residues is digested according to solid samples. The digestion method is to add 60 - 80 mL of a mixed acid of hydrofluoric acid - hydrochloric acid - nitric acid - perchloric acid to the residues, and perform pyrolysis on an electric hot plate to obtain a test solution. Then, the test solution is detected and analyzed by ICP-MS, and the content of the characteristic pollutant in the L4 state is L 40 (mg / kg).

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