CN115446104A - Composition for post-repair site chemical resistance control layer, preparation method and application thereof - Google Patents
Composition for post-repair site chemical resistance control layer, preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to a composition for a post-repair site chemical resistance control layer, a preparation method and application thereof, and belongs to the field of environmental risk control and environmental functional materials. The invention provides a composition, which comprises a chemical resistance control material, clay and clean soil. The invention also provides a preparation method of the chemical resistance and control material, and application of the composition in a chemical resistance and control layer after resistance and control of heavy metal pollution remediation. The composition for the post-repair site chemical resistance control layer provided by the invention has the advantages of convenient material acquisition, low cost, simple synthesis, durable performance, convenient operation, wide application and the like. In addition, the chemical resistance control material can capture (adsorb) heavy metal pollution in a targeted manner, limit the migration and the transformation of the heavy metal pollution in a repaired site, further prolong the repair effect and ensure the safety of the repaired site in the recycling process.
Description
Technical Field
The invention relates to a composition for a post-repair site chemical resistance control layer, a preparation method and application thereof, and belongs to the technical field of environmental risk control and environmental functional materials.
Background
With the development of industrialization, the number of the existing polluted sites is continuously increased, and particularly, the environmental problems are increasingly prominent due to the heavy metal polluted sites. At present, a restoration solidification/stabilization restoration technology is often adopted for restoration of heavy metal contaminated sites, and although the restoration target can be quickly realized at relatively low cost, the leaching concentration of heavy metals is reduced to the acceptance standard, but the reduction of heavy metals in soil cannot be realized. It has been found that there is a risk of reactivation of heavy metals that have been solidified/stabilized under external environmental stress. For example, the heavy metal chromium alternately increases the leaching concentration of chromium in the solidified/stabilized soil in flooding and dry-wet states, and facilitates the change of the appearance of the solidified/stabilized chromium. Particularly, in south China, the field is subjected to high temperature and rainy days and frequent hydrothermal exchange, and after solidification/stabilization repair, the field is eroded by flooding, alternation of wetting and drying, underground water level change and the like for a long time, so that the oxidation-reduction potential, pH, iron oxide morphology and the like of soil in the field are influenced, the change of occurrence morphology of heavy metals in the soil is promoted, the return tendency of the heavy metals in the environment is influenced finally, and potential environmental risks are generated.
In order to block the way of migration and diffusion of heavy metal pollutants in a soil medium, isolate the polluted medium from the surrounding environment, and avoid the pollutants from contacting with human bodies and causing harm to the human bodies and the surrounding environment along with precipitation or entering underground water, engineering measures are generally adopted to physically block the pollutants in the horizontal direction or the vertical direction. The most common physical barrier measure at present is the physical barrier engineering of 'two cloths and one film', and the permeability coefficient of the physical barrier engineering can reach 1.0 multiplied by 10 -12 . However, the physical barrier engineering does not effectively reduce the content of the pollutants, and the physical barrier layer has risks of breakage and pollution exposure. In addition, after physical barrier measures are implemented, the site often has seepage prevention and completion of the physical barrier layerThe integrity and the like put forward corresponding management requirements, such as forbidding excavation of the site, piling and the like, which result in the damage or penetration of the physical barrier layer. In addition, in the urban management and construction process, the construction requirements of the sponge city are met in the process of re-developing and utilizing the repaired site. This is contrary to the barrier requirements of physical barrier measures. Further restricting the subsequent reutilization, development and design, construction and the like of the repaired site. Therefore, how to implement separation on heavy metal pollutants and simultaneously realize migration control and concentration reduction on the pollutants, avoid the operation contradiction with site later development and construction as much as possible, ensure the long-term up-to-standard management and control effect of the repair effect, and be an important breakthrough for improving the comprehensive treatment efficiency of the heavy metal pollution site.
Therefore, the method meets the requirements for disposing the heavy metal polluted site, ensuring the long-term stability of the polluted site after restoration, and safely recycling the site after restoration. The invention provides a preparation method of a composition for chemical resistance control after heavy metal contaminated site restoration and an application mode applicable to the chemical resistance control after heavy metal contaminated site restoration, so that efficient risk resistance control and pollution factor cooperative reduction of heavy metal pollutants in the restored site are realized, construction difficulty is reduced for post-development construction of the site, and safe utilization of the restored contaminated site is continuously ensured for a long time.
Disclosure of Invention
Technical problem to be solved
In order to solve the problems in the prior art, the invention provides a composition for a post-remediation site chemical resistance and control layer, a preparation method and application thereof in the post-remediation site chemical resistance and control layer, and particularly aims at environmental risk control after heavy metal pollution site remediation.
(II) technical scheme
In order to achieve the purpose, the invention adopts the main technical scheme that:
the composition for repairing the chemical resistance and control layer of the post-repairing site comprises, by mass, 60-90 parts of clean soil, 15-40 parts of clay and 0.5-5 parts of chemical resistance and control material.
The composition as described above, preferably, the clean soil is in-situ soil of the repaired site area, and the clay is any one or a mixture of any several of montmorillonite, bentonite, attapulgite, illite, sepiolite, hydromica or kaolinite.
The total concentration of heavy metals in-situ soil in a repaired site area meets the corresponding land use requirements of soil risk management and control standards (trial) for soil environmental quality construction (GB 36600-2018), furthermore, a leaching experiment is carried out on the soil by using a solid waste leaching toxicity leaching method horizontal oscillation method (HJ 557-2010), the content of heavy metals in the leachate is detected, and the IV standard in the surface water quality standard (GB 3838-2002) is met.
The composition as described above, preferably, the chemical resistance control material is a heavy metal stabilizing material;
the heavy metal stabilizing material is a magnetic biochar material, iron-doped hydroxyapatite and the like. Further, preferably, the magnetic biochar material is prepared by adopting a 'dipping + hydrothermal method'.
The preparation method comprises the following steps:
s1, adding water into ground biochar, adding alkali to adjust the pH value to be alkaline to form a suspension, adding ferrous salt into the suspension, and stirring to obtain a suspension;
and S2, reacting the suspension under a heating condition, cooling after the reaction, and performing solid-liquid separation to obtain a solid substance, namely the magnetic biochar material.
In the above preparation method, preferably, in step S1, the biochar is wood biochar, coal biochar, or straw biochar, and water is added to the biochar in a mass ratio of biochar to water of 1:1 to 10.
In the preparation method described above, preferably, in step S1, the alkali is one or more of ammonia water, KOH and NaOH, the pH value is 10 to 11, and the ferrous salt is FeSO 4 、FeCl 2 、Fe(NO 3 ) 2 Any one or mixture of any more of the above, the addition amount of ferrous salt is according to the biochar5 to 40 percent of the mass of the mixture.
In the preparation method, the reaction temperature is preferably 120-180 ℃ and the reaction time is preferably 10-16 h in step S2.
The composition is applied to a repaired site, is uniformly mixed and then is used as a barrier layer for covering soil after curing/stable repair of a heavy metal contaminated site to realize risk control and prolonged curing/stable repair of heavy metal in-situ contaminated soil, namely is used as a chemical resistance control layer, and has a permeability coefficient K of 1 x 10 -5 ～1×10 -6 cm/s。
Use of a composition as described above in a post-remediation site, preferably the composition is applied horizontally and/or vertically over the post-remediation soil area; when the composition is in the condition of no groundwater immersion, the thickness of the chemical resistance control layer can be set to be 50-200 mm; when the composition is likely to be soaked in groundwater when the paving position is deep or the groundwater level is shallow, the thickness of the composition may be set to 100mm to 300mm.
According to a large amount of experimental researches, the clay used in the invention can be any one or a mixture of any several of montmorillonite, bentonite, attapulgite, illite, sepiolite, hydromica or kaolinite, and the clay substances can form ion exchange and have a certain function of capturing heavy metals. In addition, the clay mainly has the function of adjusting the permeability of the soil, and the permeability coefficient of the clay can reach 1.0 multiplied by 10 -7 cm/s, the clay content is large, and the influence of rainwater on heavy metal can be reduced by compacting in the laying process.
The composition is used as a barrier layer for covering soil after the heavy metal polluted site is cured/stably repaired, is paved to a certain thickness, and has the following functions: (1) Prevent the infiltration of rainwater from leading to the activation of heavy metal after the restoration. (2) The resistance control layer has certain thickness and can form certain strength, and migration of polluted particles caused by runoff, wind blowing and the like can be effectively avoided. (3) In the low-groundwater-level area, the fluctuation of the groundwater level easily causes the alternation of dry and wet soil after restoration and the change of the oxidation-reduction potential of the soil, so that some heavy metals are reactivated. Therefore, the thickness of the barrier layer in the low groundwater level region is preferably as thick as 100mm to 300mm.
(III) advantageous effects
The invention has the beneficial effects that:
1. the composition for the post-repair site chemical resistance control layer has the advantages of low material cost, convenience in material acquisition, multiple functions, lasting performance, convenience in operation and the like. The clean soil is used as a main matrix material of the chemical resistance control layer, the materials can be obtained in situ, and the materials and the economic cost can be saved. The clay is added into the chemical resistance control layer, so that the permeability coefficient of the chemical resistance control layer can be reduced, and the plasticity of the chemical resistance control layer is increased. In addition, in the composition, the addition of the heavy metal stabilizing material can effectively control and assist in reducing pollution factors, so that the risk control of the heavy metal polluted site after restoration and the safe recycling of the site are realized.
2. The composition for the post-repair site chemical resistance and control layer provided by the invention takes the chemical resistance and control material as a heavy metal stabilizing material, and can treat heavy metal pollutants in a targeting manner. Preferably, the magnetic biochar material can be targeted on chemical resistance control of a chromium pollution remediation site. The iron-based nano material in the magnetic biochar is a high-activity magnetic material, has good adsorption performance and ultrahigh reduction activity due to the specific surface and size effects, can reduce hexavalent chromium into trivalent chromium through reduction, and simultaneously generates Fe 3+ Capable of reacting with Cr produced by reduction 3+ A coprecipitation is formed. The biochar has large specific surface area, multiple pores, various functional groups on the surface, good ion exchange capacity of the adsorbent, wide raw material source and low price, so the biochar is greatly valued and widely applied to the soil heavy metal remediation aspect. Loading iron on the biochar by adopting a dipping and hydrothermal method, wherein the process comprises the steps of adding alkaline substances to have a precipitation effect with iron ions, uniformly distributing the precipitate on the biomass by high-speed stirring, and carrying out hydrothermal reaction to obtain the magnetic biochar. Magnetic biochar material prepared by 'dipping + hydrothermal method' on the surface of biocharThe surface oxygen-containing functional groups are obviously increased, and a more stable complex can be formed with heavy metals in the adsorption process; the nano iron particles on the surface of the biochar are not agglomerated any more, and the iron base can perform electrophilic reaction with heavy metal ions, so that a more stable coordination chelate is formed. The iron-containing biochar material has magnetism, is easy to physically separate and regenerate, and can be recycled.
3. According to the composition for the repaired site chemical barrier control layer, the clay can be selected from various feasible types, and the clay types have the characteristics of hypotonic property and strong ion exchange, so that heavy metal ions are captured, and the stabilization process of the reactivated heavy metal ions in the repaired site soil is favorably realized.
4. The application of the chemical resistance control layer provided by the invention aims at the application of the heavy metal polluted site after solidification/stabilization restoration, and is suitable for various sites after heavy metal pollution restoration, especially sites which cannot be implemented by a physical resistance control technology or are inconvenient to construct, such as sponge city construction, arbor planting and the like. Meanwhile, the application of the chemical barrier layer can overcome the defects that the traditional physical barrier layer is damaged due to long-term use or is excavated in the process of site follow-up development and recycling, the perforated part of the barrier layer and pollutants caused by pile driving construction and the like are exposed and difficult to repair, the barrier layer can be repaired in a mode of refilling materials when the barrier layer is damaged, and the barrier layer is convenient and fast to use and has no missing leakage points.
5. Aiming at the risk control engineering measures of the site after the heavy metal pollution remediation, the composition for the chemical resistance control layer of the site after the remediation is adopted to separate and control the heavy metal pollutants in the site soil, so that the safe reutilization of the site after the remediation is ensured.
Drawings
Fig. 1 is a schematic view of the composition of a chemical resistance control layer material provided in example 1 of the present invention.
FIG. 2 is a schematic diagram of the column experiment provided in example 1 of the present invention.
Figure 3 is an XRD characterization of the magnetic biochar provided in example 2 of the invention.
Fig. 4 is an SEM characterization of coal-made magnetic biochar provided in example 2 of the present invention.
Fig. 5 is an SEM characterization of the wooden magnetic biochar provided in example 2 of the present invention.
FIG. 6 is an SEM representation of magnetic biochar made from straw as provided in example 2 of the present invention.
Fig. 7 is an XPS survey of magnetic biochar provided in example 2 of the invention.
Fig. 8 is an XPS peak of the C element of the magnetic biochar material provided in example 2 of the present invention.
Fig. 9 is an XPS peak of the O element of the magnetic biochar material provided in example 2 of the present invention.
Fig. 10 is an XPS peak of the N element of the magnetic biochar material provided in example 2 of the present invention.
Fig. 11 is an XPS peak of Fe element of the magnetic biochar material provided in example 2 of the present invention.
Fig. 12 is a schematic view of the treatment of the chemical barrier layer after the chromium contaminated site is repaired according to embodiment 6 of the present invention.
Fig. 13 shows an adsorption experiment of biochar by a magnet.
Detailed Description
The embodiment of the invention provides a composition for a repaired site chemical resistance control layer, a preparation method and application thereof in the repaired site chemical resistance control layer, and aims to overcome the defects of a physical resistance control technology and the technical defect of difficulty in implementation in the prior art.
Aiming at the engineering measures of risk management and control of the site after heavy metal pollution remediation, the chemical resistance and control material and the chemical resistance and control layer constructed by the chemical resistance and control material are adopted to separate and control heavy metal pollutants in the site soil, so that the safety of the site after heavy metal pollution remediation in re-development and utilization is guaranteed. The wood biochar, coal biochar and straw biochar in the following examples are commercially available products.
For the purpose of better explaining the present invention and to facilitate understanding, the present invention will be described in detail by way of specific embodiments with reference to the accompanying drawings.
EXAMPLE 1 preparation of chemical resistance control layer
The embodiment is directed at the application of chemical resistance control of the site after heavy metal pollution restoration, the chemical resistance control layer of the site after the restoration is formed by 'clean soil + clay + heavy metal stabilizing material', and the composition schematic diagram of the chemical resistance control layer is shown in fig. 1.
Firstly, in-situ clean soil of the repaired site is taken as a matrix material of a chemical barrier control layer, and the repaired site is from a certain chromium-polluted site of Hunan Tan in Hunan province. The method comprises the steps of mixing the polluted soil with reducing agents such as ferrous sulfate, sodium metabisulfite/sodium bisulfite and the like through solidification/stabilization remediation, reducing Cr (VI) in the polluted soil into low-toxicity and stable Cr (III), solidifying, and backfilling the repaired soil to an excavation area.
The current situation of the repaired site is obviously yellow when the soil is accumulated in water after being leached by rainwater. Namely, the dissolution of hexavalent chromium occurs in the field, and the phenomenon of obvious yellowing occurs. The analysis shows that the Cation Exchange Capacity (CEC) in the soil is 16.6cmol/kg; the pH was 10.2; the total content of Cr is 537mg/kg; the content of Cr (VI) is 10.3mg/kg; the leaching concentration of Cr (VI) in the soil is further analyzed by a method of 'solid waste leaching toxicity leaching method horizontal oscillation method' (HJ 557-2010) and is 0.576mg/L, which exceeds 11.5 times of the III-type standard limit value (0.05 mg/L) in 'surface water environmental quality standard' (GB 3838-2002). Therefore, an area where 'yellowing' does not occur is selected to be excavated, the average content of total Cr in the excavated soil is 18.96mg/kg through detection, further, a leaching experiment is carried out by further adopting a solid waste leaching toxicity leaching method horizontal oscillation method (HJ 557-2010) aiming at the soil, the content of Cr (VI) in the leachate is detected, the concentration of Cr (VI) in the leachate is 0.02mg/L, and the II-type standard in the ground surface water quality standard (GB 382002) is met, so that the excavated soil can be used as a filler of a chemical resistance control layer, and the using amount of the excavated soil is 60-90 parts by mass.
And secondly, selecting bentonite as a clay component to be mixed with clean soil to be used as a filler of the chemical resistance control layer so as to reduce the total permeability of the material, wherein the using amount is 15-40 parts by mass.
And finally, adding an active material of the chemical pore-blocking layer into the mixed material of the clean soil matrix and the clay for adsorption and stabilization treatment of heavy metal pollutants. The active material is a magnetic biochar material which is used for providing a targeted heavy metal stabilizing material, and the using amount of the active material is 0.5-5 parts by mass.
The simulation can be performed by a column experiment, the experimental schematic diagram is shown in fig. 2, and the permeability coefficient K of the chemical resistance control layer is calculated by using darcy's law according to the following formula.
In the formula: k is the permeability coefficient of the chemical resistance control layer, and the unit is m/d; v-volume of water discharged within time t, unit is m 3 (ii) a L is the distance between two measuring points on the experimental column, and the unit is m; a-area of water passing section of experimental column, unit is m 2 (ii) a t-time of water flow through the medium in units of d; h is the water head difference between the two measuring points, and the unit is m.
The permeability coefficient K of the chemical resistance control layer is measured and calculated to be 1.0 multiplied by 10 -5 ～1.0×10 -6 cm/s。
Example 2 preparation of chemical resistance control Material (preparation of magnetic biochar)
Respectively taking 100g of biochar materials, namely wooden biochar, coal-made biochar and straw-made biochar (biochar fired by corn straws), and carrying out ball milling; adding purified water or distilled water into the ball-milled biochar according to the mass ratio of 1; 20g of FeSO were added to the suspension 4 Stirring the mixture for 4 hours on a magnetic stirrer at the speed of 300 to 400r/min to obtain suspension; then the suspension is transposed and reacted in a reaction kettle for 12 hours at the temperature of 150 ℃; and after the reaction kettle is cooled, carrying out solid-liquid separation to obtain a solid substance, namely the iron-loaded biochar material.
Taking 5mg of powder sample of the obtained iron-loaded biochar material, placing the powder sample on a carrying plate of an instrument, setting the test, and carrying out X-ray diffraction (XRD) detection within the range of 5-65 DEGThe phase composition thereof, the XRD results obtained are shown in FIG. 3. The result shows that the XRD peaks of the three different biomass raw materials are basically consistent under the action of the 'immersion and hydrothermal method'. In addition, fe 2+ The modified biochar obtained by loading the biochar is found to be Fe by comparison 3 O 4 (JCPDS: 75-1609) indicating the presence of Fe on its surface 3 O 4 Description of Fe 3 O 4 Successfully loaded on the biochar, and the obtained magnetic biochar material is also shown by the adsorption of the magnet on the biochar (as shown in figure 13).
For the magnetic biochar material obtained above, a 1mg sample was taken, the powder sample was dipped on a conductive gel with a glass rod, and the powder that was not stuck was purged with an ear-washing ball. After the gold spraying, a Scanning Electron Microscope (SEM) test was performed, and the results are shown in fig. 4 to 6. From the SEM structure of the prepared material, the main appearance of the magnetic biochar is an irregular blocky structure. In addition, fe is uniformly distributed on the surface of the biochar 3 O 4 Nanoparticles, this is due to the presence of Fe 2+ In reaction with alkali, fe (OH) is produced 2 Can be evenly deposited on the surface of the biochar, and then Fe is obtained through hydrothermal action 3 O 4 And (3) nanoparticles.
The obtained magnetic biochar material was subjected to BET test, and the BET analysis procedure was as follows:
1) The sample to be tested (about 100 mg) was loaded into the sample tube.
2) Setting test parameters and starting adsorption and desorption test processes.
3) And after the test is finished, taking out the sample in the sample tube, and cleaning the sample tube.
The results are shown in Table 1. Comparing the three magnetic biochar materials, the magnetic biochar prepared from coal has the largest specific surface area of 561.3m compared with the magnetic biochar prepared from wood and straws 2 (iv) g; the specific surface areas of the wooden magnetic biochar and the magnetic biochar prepared from straws are respectively 26.41m 2 G, and 47.526m 2 (ii) in terms of/g. And the adsorption effect of the magnetic biochar made of coal on heavy metals is judged more favorably in predictability.
Table 1 BET results for the magnetic biochar material prepared in example 2
| Name (R) | Magnetic charcoal made from coal | Wooden magnetic charcoal | Magnetic biochar prepared from straw |
| BET specific surface area (m) 2 /g) | 561.3 | 26.41 | 47.526 |
| Total pore volume (cm) 3 /g) | 0.2442 | 0.0133 | 0.0233 |
| Micro pore volume (cm) 3 /g) | 128.96 | 6.0679 | 10.919 |
| Average pore diameter (nm) | 1.7405 | 2.0151 | 1.9643 |
The obtained magnetic biochar material is subjected to an X-ray photoelectron spectroscopy (XPS) test, and the XPS analysis process is as follows:
1) Directly sticking a sample to be detected (about 10mg of the obtained powder sample) on a sample table of the double-sided carbon conductive adhesive;
2) Setting test parameters, and starting to perform full-spectrum and high-resolution spectrum test.
3) And after the test is finished, taking out the sample, and cleaning the sample table.
The results are shown in fig. 7 to 11, and the results show that in XPS characterization of the magnetic biochar made of coal, characteristic peaks of C, O, fe, and N elements are shown in fig. 7. FIG. 8 is a high-resolution spectrum of C element, the binding energy corresponding to the 1s peak of C is 285.5eV, which is divided into the binding energy of C-C single bond in the biochar structure; in addition, a C = C double bond is also present on the surface of the biochar material, which corresponds to a binding energy of 286.3eV, and-COOH, which corresponds to a binding energy of 290.5eV, is also present on the surface of the biochar material during the hydrothermal process. FIG. 9 is a high resolution spectrum of O element, with a binding energy of 532.1eV corresponding to the 1s peak of O, which is classified as the binding energy of-OH in the biochar structure; in addition, at the lower binding energy of 530.5eV, the bonding of the oxygen element and the iron element, that is, fe-O, is mainly exhibited. FIG. 10 is a high resolution spectrum of N element, and the 1s peak of N corresponds to a binding energy of 399.5eV, which is mainly the binding energy of C-N on the surface of the biochar. FIG. 11 is a high-resolution spectrum of Fe element, in which the 2p peak of Fe is divided into 2p due to spin-orbit splitting 3/2 Peak sum 2p 1/2 Peaks corresponding to binding energies of 712.7eV and 726.3eV, respectively, and mainly of ferric (Fe (iii)) and ferrous (Fe (ii)). In addition, fe 2+ The binding energy corresponding to the satellite peak of (2) was 720.5eV. So that the magnetic biochar contains ferrous iron which has the capability of reducing hexavalent chromium through XPS analysis. The method shows that the Fe (II) contained in the magnetic biochar can effectively reduce hexavalent chromium (Cr (VI)), and can be selected as a chemical resistance control material after the Cr-polluted site is repaired to inhibit the phenomenon of yellowing after the Cr-polluted site is repaired.
Furthermore, the content of each element on the surface of the magnetic biochar made of coal is shown in table 2 by XPS characterization. The magnetic biochar surface mainly comprises C and O elements, and the reason is that more oxygen-containing functional groups such as-OH, -COOH and-C = O can be formed on the biochar surface easily to form a chemical adsorption effect on heavy metals due to a hydrothermal method. In addition, the content of the Fe element on the surface of the biochar reaches 6.70 percent by a deposition and hydrothermal method. The magnetic biochar material contains a large number of C, O and N functional group adsorption sites, the functional groups can form stable chemical bonds with adsorbed heavy metal ions under conventional conditions, stable chemical adsorption is carried out on the heavy metal ions, the heavy metal ions can be released due to reactivation in field soil bodies after targeted capture and restoration, secondary release is not formed in the using process to limit migration and diffusion of the heavy metals, and the inhibition and control effect of a chemical inhibition and control layer is improved.
TABLE 2 content ratio of each element on the surface of coal biochar
| Element(s) | C | O | N | Fe |
| Content ratio (%) | 70.26 | 20.79 | 2.25 | 6.70 |
Example 3
0.5g of each of the three magnetic biochar materials prepared in example 2 was used to treat 100mL of 10mg/L aqueous hexavalent chromium solution, samples were taken after reacting for 2 hours, 4 hours, and 6 hours in a constant temperature shaking table at 30 ℃, and the concentration of hexavalent chromium in the filtrate was measured by dibenzoyl dihydrazide spectrophotometry, and the results are shown in Table 3. The color of the solution can be seen to change from yellow (color of hexavalent chromium solution) to colorless (color of trivalent chromium) before and after the reaction, which indicates that the magnetic biochar has the reduction effect. The coal-made magnetic biochar has the best hexavalent chromium removal effect, after 6 hours of adsorption, the hexavalent chromium removal rate reaches 100%, and the wood-made magnetic biochar and the straw-made magnetic biochar have good hexavalent chromium removal effects, and the removal rates are 99.85% and 99.99%, respectively.
TABLE 3 magnetic biochar materials for treatment of hexavalent chromium in water
Example 4
100g of soil to be tested (namely the soil in example 1, the Cation Exchange Capacity (CEC) in the soil is 16.6cmol/kg; the pH is 10.2, the total content of Cr is 537mg/kg; the content of Cr (VI) is 10.3mg/kg; the leaching concentration of Cr (VI) in the soil is further analyzed by a method of solid waste leaching toxicity leaching method horizontal oscillation (HJ 557-2010) and is 0.576mg/L, which is more than 11.5 times of the III type standard limit (0.05 mg/L) in the surface water environmental quality standard (GB 3838-2002), 0.5g of the three magnetic biochar prepared in example 2 of the invention are respectively added, the mixture is uniformly mixed, watering and maintenance is carried out, the water content of the restored soil is kept between 20 and 40 percent during watering and maintenance, and the watering and maintenance time is between 7 and 14 days. Meanwhile, the leaching condition of Cr (VI) in the soil to be tested is analyzed by adopting a solid waste leaching toxicity leaching method horizontal oscillation method (HJ 557-2010) in 7 days and 14 days of maintenance, and the soil without the magnetic biochar material is used as a blank control. As shown in table 4. The magnetic biochar material can effectively inhibit leaching of hexavalent chromium in soil, only 0.5% of the material based on the mass of the soil is added, the leaching concentration of the hexavalent chromium in the soil is obviously reduced after 7 days of treatment, and the treatment effect is over 70%. Wherein, the coal-made magnetic biochar has the best hexavalent chromium removal effect, and the removal rate is as high as 85.59%; after 14 days, the leaching concentration of hexavalent chromium in the soil is 0mg/L, cr (VI) is completely removed, and the removal rate reaches 100%. The magnetic biochar material can effectively inhibit the dissolution of Cr (VI) in the repaired site.
TABLE 4 effect of magnetic biochar material on soil after remediation
Example 5 verification of the Effect of the chemical resistance control layer
In order to verify the application effect of the chemical resistance control layer in the repaired field, a laboratory small test column experiment is adopted for verification and evaluation. The evaluation of the chemical resistance control layer was performed by solution leaching using a column experimental set-up (see fig. 2), and the chemical resistance control material was loaded into the column. The chemical resistance control material is the material provided in example 1, and comprises 80 parts of clean soil, 19 parts of clay and 1 part of coal magnetic biochar (prepared by the method of example 2). The feed water was a Cr (VI) solution, the concentrations were 0.5mg/L and 5mg/L, respectively, the volume was 1L, the flow rate of a peristaltic pump was 0.3mL/min, the column inner diameter was 5cm, the total height was 30cm, the thickness of the chemical barrier layer was 30cm, water samples were taken through the side walls at positions 5cm,10cm,2 cm and 30cm, respectively, the concentration of hexavalent chromium in the water was measured by dibenzoyl dihydrazide spectrophotometry, the barrier efficiency was determined according to the following formula, and the results are shown in Table 5. When the concentration of Cr (VI) is 0.5mg/L, the migration of Cr (VI) can be well limited by only laying a chemical resistance control layer with the thickness of 5cm, and the resistance control efficiency reaches 100%; when the Cr (VI) concentration is 5mg/L, the chemical resistance control layer with the thickness of 10cm can resist the migration of 99.48 percent of Cr (VI). The migration of Cr (VI) can be completely limited by laying the layer with the thickness more than 10 cm.
TABLE 5 TEST EFFECT OF CHEMICAL RESISTANCE-CONTROLLING LAYER
After the column experiment reaction was completed, the chemical barrier control layer was collected, left to stand for 7 days or 14 days, and then the leaching of Cr (vi) in the chemical barrier control layer was analyzed by the "solid waste leaching toxicity leaching method horizontal oscillation method" (HJ 557-2010), and the results are shown in table 6. The results show that after 7 days and 14 days, the leaching concentration of Cr (VI) in the chemical resistance control layer is 0mg/L, the chemical resistance control layer has a strong resistance control effect on the Cr (VI), the Cr (VI) can be stabilized for a long time, and the site safety after repair is guaranteed.
TABLE 6 stabilizing effect of chemical resistance control layer
| Time | Leaching concentration (mg/L) |
| 7 |
0 |
| 14 |
0 |
Example 6
According to the treatment results of the chemical resistance control layer verified by the experimental laboratory, a chemical resistance control layer pilot test is performed by selecting a length × width (1 m × 1 m) area in the field after repair in example 1. In the construction process, firstly, the target area is excavated, the surface impurities are removed, then, the chemical resistance control material (wherein, 80 parts of clean soil, 19 parts of clay, and 1 part of coal magnetic biochar (prepared by the method of embodiment 2)) is prepared according to the steps in embodiment 1 to serve as a chemical resistance control layer, the thickness of the chemical resistance control layer is designed to be 0.2m, and after the chemical resistance control layer is completely laid, 0.5m of clean soil is laid above the chemical resistance control layer, as shown in fig. 12. And (3) arranging a surface soil sampling area in the chemical resistance control area, wherein the surface soil sampling depth is 10cm, and the sampling period is 6 months, wherein the sampling is carried out once every 30 days. The leaching of Cr (vi) in the soil layer was analyzed by the "solid waste leaching toxicity leaching method horizontal oscillation method" (HJ 557-2010), and the results are shown in table 7. The result shows that the leaching concentration of Cr (VI) in the soil is 0mg/L after 180 days, which indicates that the chemical resistance control layer has stronger resistance control effect on the Cr (VI), can effectively inhibit the Cr (VI) in the repaired site from being dissolved out, limit the migration of the Cr (VI), effectively control the site to turn yellow, and simultaneously can keep the stability of the effect after repair for a long time, thereby really ensuring the safety of the site after repair in re-development and utilization.
TABLE 7 Pilot test Effect of chemical resistance control layer
| Time (sky) | Cr (VI) concentration | Resistance control efficiency (%) |
| 30 | 0 | 100 |
| 60 | 0 | 100 |
| 90 | 0 | 100 |
| 120 | 0 | 100 |
| 150 | 0 | 100 |
| 180 | 0 | 100 |
Comparative example 1
In the patent application with the application number of 201911319646.5 in the prior art, a preparation and use method of magnetic porous biochar for removing chromium in water discloses that Fe (III) is used as a magnetic precursor, and the artemia egg shells are prepared into the magnetic porous biochar by a method of slow pyrolysis and in-situ carbon reduction after impregnation and loading, the magnetic porous biochar can be used for removing Cr (VI) and Cr (III) in water, when the magnetic porous biochar is used, the biochar is placed in the chromium-containing water, and an adsorbent is magnetically separated or is statically placed for precipitation separation after a certain time, so that chromium removal is completed.
Compared with the invention, the magnetic biochar material prepared by the dipping and hydrothermal method adopts the dipping method to mix Fe 2+ Ions are uniformly loaded on the surface of the biochar, and more functional groups containing O and N are introduced on the surface of the biochar by a hydrothermal method. The invention is to put biomass (artemia cysts) into FeCl 3 And (3) dipping, drying the obtained estimation, then placing the estimation in a tubular furnace, introducing nitrogen for protection, heating to perform slow pyrolysis and in-situ carbon reduction to obtain the magnetic biochar.
At present, the impregnation and high-temperature thermal reduction method is widely used for preparing the loaded magnetic biochar, and the method is approximately to put biomass powder such as straws, camphor leaves or tea tree shells and the like into a ferric iron-containing solution for impregnation for a plurality of hours, and then dry the solution to enable Fe 3+ Loaded on biomass, and then CO and H generated by high temperature (the temperature is more than 500 ℃) under the anaerobic condition 2 Isoreduction ofThe gas of nature will Fe 3+ Reducing to prepare the loaded magnetic biochar. However, this method has several disadvantages: (1) less reducing gas, low content of reducing iron in the magnetic biochar, and other magnetic substances, such as alpha-Fe 2 O 3 ，γ-Fe 2 O 3 The ratio of the components is higher; (2) most of Fe due to low specific surface area and few active sites of biomass 3+ Still in solution, if the solution is dried directly, a large amount of Fe will be produced 3+ Stacking on part of the biomass, resulting in uneven distribution of subsequent iron on the magnetic biochar; (3) in addition, added Fe-containing 3+ The volume of the solution is difficult to control, and if the added volume is too low or too high, the stirring is not uniform or the energy consumption is large.
In the preparation of the magnetic biochar, a chemical precipitation method is utilized, namely, sodium hydroxide (NaOH), potassium hydroxide (KOH) and ammonia water (NH) are added 3 ·H 2 O) and other alkaline substances and metal ions are precipitated, and the metal ions in the solution are trapped. The chemical precipitation method is combined into the dipping and hydrothermal reduction method, and Fe is firstly treated by using alkali solution 2+ Conversion to Fe (OH) 2 Precipitating, and stirring at high speed to make Fe (OH) 2 The precipitate is evenly distributed on the biochar, and finally the solid matter is collected through centrifugal separation, so that the iron-containing compound is evenly distributed on the biochar, and the defect of directly drying the solution can be avoided. Meanwhile, a hydrothermal reduction method introduces more functional groups on the surface of the biochar, and finds chemical adsorption with heavy metals, so that the performance of the material is improved.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. However, any simple modification, equivalent change and modification of the above embodiments according to the technical essence of the present invention will still fall within the protection scope of the technical solution of the present invention.
Claims (10)
1. The composition for repairing the post-site chemical resistance control layer is characterized by comprising 60-90 parts by mass of clean soil, 15-40 parts by mass of clay and 0.5-5 parts by mass of chemical resistance control materials.
2. The composition for remediating a post-remediation site chemical barrier as recited in claim 1, wherein the clean soil is in situ soil in the area of the remediating site, and the clay is any one or a mixture of montmorillonite, bentonite, attapulgite, illite, sepiolite, hydromica, or kaolinite; the chemical resistance control material is a heavy metal stabilizing material.
3. The composition for the chemical resistance and control layer of the repaired site as claimed in claim 2, wherein the concentration of the total heavy metals in-situ soil in the site area after repair meets the corresponding site requirements of soil risk control standards (trial) for soil environmental quality construction (GB 36600-2018), the soil is subjected to leaching experiments by using solid waste leaching toxicity leaching method horizontal oscillation method (HJ 557-2010), and the content of the heavy metals in the leachate is detected, so that the IV-type standards in surface water quality standards (GB 3838-2002) are met.
4. The composition for repairing a post-yard chemical barrier coating according to claim 2, wherein the heavy metal stabilizing material is a magnetic biochar material or iron-doped hydroxyapatite.
5. The composition for repairing a post-construction site chemical barrier layer according to claim 4, wherein the magnetic biochar material is prepared by the following method:
s1, adding water into ground biochar, adding alkali to adjust the pH value to be alkaline to form a suspension, adding ferrous salt into the suspension, and stirring to obtain a suspension;
and S2, reacting the suspension under a heating condition, cooling after the reaction, and performing solid-liquid separation to obtain a solid substance, namely the magnetic biochar material.
6. The composition for repairing a post-construction site chemical resistance control layer according to claim 5, wherein in step S1, the biochar is wood biochar, coal biochar or straw biochar, and water is added to the biochar according to a mass ratio of biochar to water of 1:1 to 10.
7. The composition for repairing a post-site chemical resistance control layer according to claim 5, wherein in step S1, the base is one or more of ammonia, KOH and NaOH, the pH is 10 to 11, and the ferrous salt is FeSO 4 、FeCl 2 、Fe(NO 3 ) 2 The ferrous salt is added according to the proportion of 5 to 40 percent of the mass of the biochar.
8. The composition for repairing a post-construction site chemical barrier layer according to claim 5, wherein the reaction temperature in step S2 is 120 ℃ to 180 ℃ and the reaction time is 10h to 16h.
9. The composition of claim 1, wherein the composition is used as a barrier layer for soil coverage after curing/stabilizing remediation of a heavy metal contaminated site, so as to realize risk management and control of heavy metal in-situ contaminated soil and prolong curing/stabilizing remediation.
10. The use of claim 9, wherein: the composition is horizontally and/or vertically covered on the soil area after remediation; when the composition is in a state of being soaked without groundwater, the thickness of the composition may be set to 50mm to 200mm; when the composition is likely to be soaked in groundwater when the paving position is deep or the groundwater level is shallow, the thickness of the composition is set to be 100 mm-300 mm.
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