CN115365283A - A method for thermal desorption restoration of polycyclic aromatic hydrocarbons highly polluted and highly plastic clay - Google Patents

Abstract

The application provides a method for thermal desorption and restoration of polycyclic aromatic hydrocarbon high-pollution high-plasticity clay. The content of coarse particles with the particle size of more than 0.075mm in the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay is within 25 percent, and the liquid limit is higher than 50 percent; the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay at least comprises polycyclic aromatic hydrocarbons with 2-3 rings of aromatic hydrocarbon rings. The method comprises the following steps: performing thermal desorption repair on the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay under an inert protective atmosphere; the water content of the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay is 0.01-15%, the thermal desorption restoration temperature is 250-450 ℃, and the thermal desorption restoration time is 20-40 min. The temperature for thermal desorption repair is 250-450 ℃, the time for thermal desorption repair is 20-40 min, and the total removal rate of polycyclic aromatic hydrocarbon with 2-3 rings of aromatic hydrocarbon in the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay with the water content of 0.01-15% can be effectively removed by over 73%.

Description

A method for thermal desorption restoration of polycyclic aromatic hydrocarbons highly polluted and highly plastic clay

technical field

The present application relates to the technical field of soil remediation, in particular to a method for thermal desorption remediation of polycyclic aromatic hydrocarbon highly polluted and highly plastic clay.

Background technique

With the continuous acceleration of the industrialization process, the irrational mining of mineral resources and their smelting discharge, long-term sewage irrigation and sludge application to the soil, atmospheric deposition caused by human activities, and the application of chemical fertilizers and pesticides have caused serious soil pollution. . Soil pollution is extremely harmful to building soil.

The method of soil pollution treatment includes thermal desorption treatment and so on. However, in the related art, the overall removal rate of polycyclic aromatic hydrocarbon pollutants and the like in construction soil is not high enough, and the removal effect is not good enough.

Contents of the invention

In view of this, the purpose of this application is to propose a method for thermal desorption restoration of polycyclic aromatic hydrocarbons highly polluted and highly plastic clay.

Based on the above purpose, the present application provides a method for thermal desorption restoration of polycyclic aromatic hydrocarbon highly polluted high plastic clay, wherein the content of coarse particles with a particle size greater than 0.075mm in the polycyclic aromatic hydrocarbon highly polluted high plastic clay is 25% within and the liquid limit is higher than 50%; the polycyclic aromatic hydrocarbons highly polluted high-plastic clay at least includes polycyclic aromatic hydrocarbons with 2 to 3 rings of aromatic hydrocarbons; the method includes:

Under an inert protective atmosphere, perform thermal desorption repair on the polycyclic aromatic hydrocarbon highly polluted high plastic clay; the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is 0.01% to 15%, and the thermal desorption repair The temperature is 250-450° C., and the time for the thermal desorption repair is 20-40 minutes.

In some embodiments, the high-polycyclic aromatic hydrocarbon-polluted high-plastic clay is clay after freeze-drying treatment, and the polycyclic aromatic hydrocarbon high-polluted high-plastic clay also includes polycyclic aromatic hydrocarbons with 4 to 6 rings. ; The temperature of the thermal desorption repair is 350-450° C., and the time of the thermal desorption repair is 20-40 minutes.

In some embodiments, the temperature of the thermal desorption restoration is 400-450° C., and the time of the thermal desorption restoration is 20-40 minutes.

In some embodiments, the temperature of the thermal desorption restoration is 400-450° C., and the time of the thermal desorption restoration is 30 minutes.

In some embodiments, the polycyclic aromatic hydrocarbon highly polluted high plasticity clay has a water content of 5-15%, the temperature of the thermal desorption restoration is 350-450°C, and the thermal desorption restoration time is 30 minutes.

In some embodiments, the polycyclic aromatic hydrocarbons high-pollution high-plasticity clay also includes polycyclic aromatic hydrocarbons with 4-6 rings of aromatic hydrocarbons;

The temperature of the thermal desorption restoration is 400-450° C., and the time of the thermal desorption restoration is 30 minutes.

In some embodiments, the temperature of the thermal desorption restoration is 450° C., and the time of the thermal desorption restoration is 30 minutes.

In some embodiments, the 2-3 ring polycyclic aromatic hydrocarbons are selected from at least one of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene.

苯并[b]荧蒽、苯并[k]荧蒽、苯并[a]芘、苯并[1,2,3-cd]芘、二苯并[a,h]蒽和苯并[g,h,i]苝中的至少一种。In some embodiments, the 4-6 ring polycyclic aromatic hydrocarbons are selected from the group consisting of benzo[a]anthracene,

Benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[1,2,3-cd]pyrene, dibenzo[a,h]anthracene and benzo[g , h, i] at least one of perylene.

In some embodiments, the content of benzo[a]anthracene, benzo[b]fluoranthene, benzo[1,2,3-cd]pyrene and dibenzo[a,h]anthracene is higher than standard value.

As can be seen from the above, the method for thermal desorption repairing of polycyclic aromatic hydrocarbons highly polluted high plasticity clay provided by the present application, the temperature for thermal desorption repairing is 250-450°C, and the time for thermal desorption repairing is 20 ~40min, it can effectively remove polycyclic aromatic hydrocarbons with 2-3 rings in polycyclic aromatic hydrocarbons with a water content of 0.01%-15% in high-pollution high-plasticity clay, and the overall removal rate is over 73%.

Description of drawings

In order to more clearly illustrate the technical solutions in the present application or related technologies, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments or related technologies. Obviously, the accompanying drawings in the following description are only for this application Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

Fig. 1 is the general removal figure of the aromatic hydrocarbon of 2～3 rings of embodiment 2;

Figure 2 is a schematic diagram of the overall removal rate of aromatics except 2-3 ring aromatics in Example 3;

Fig. 3 is the schematic diagram of the overall removal rate of polycyclic aromatic hydrocarbons in water content to polycyclic aromatic hydrocarbons highly polluted high plasticity clay in embodiment 4;

Fig. 4 is the impact diagram of the toxic equivalent of PAHs in the PAHs highly polluted and highly viscous soil by thermal desorption remediation in embodiment 5;

Fig. 5 is a graph showing the influence of thermal desorption remediation in Example 6 on the screening value of PAHs-contaminated and high-viscosity soils in the first class of construction land.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application shall have the usual meanings understood by those skilled in the art to which the present application belongs. The words "comprising" or "comprising" and other similar words used in the embodiments of the present application mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects .

Thermal desorption remediation has the advantages of strong applicability, good remediation effect, and simple process, and is one of the key technical means for soil remediation of organic polluted sites. In PAH-contaminated clay, PAHs can include PAHs with different ring numbers, such as PAHs with 2-3 rings and PAHs with 4-6 rings. In related technologies, the thermal desorption remediation process for highly polluted cohesive soil cannot desorb polycyclic aromatic hydrocarbons with different ring numbers and different water contents well. Therefore, in the related art, the thermal desorption treatment of PAH pollutants in high PAH-contaminated high-plasticity clay has the problem that PAHs with different ring numbers and different water contents cannot be well desorbed.

Based on this, the embodiment of the present application provides a method for thermal desorption restoration of highly polluted polycyclic aromatic hydrocarbons and high plasticity clay, which can solve the problem of good desorption of polycyclic aromatic hydrocarbons with different ring numbers and different moisture contents to a certain extent. question.

The embodiment of the present application provides a method for thermal desorption repairing of polycyclic aromatic hydrocarbons highly polluted high plasticity clay, comprising: performing thermal desorption repairing of the polycyclic aromatic hydrocarbons highly polluted high plasticity clay under an inert protective atmosphere; The moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is 0.01%-15%, the temperature of the thermal desorption restoration is 260-450° C., and the time of the thermal desorption restoration is 20-40 minutes. Among them, polycyclic aromatic hydrocarbons include at least polycyclic aromatic hydrocarbons with 2 to 3 rings. High plastic clay can be understood as high liquid limit clay, in which the content of coarse particles larger than 0.075mm is not higher than 25%, the content of montmorillonite minerals is high, and the liquid limit is higher than 50%, that is, high polycyclic aromatic hydrocarbon pollution high plastic clay The content of coarse particles with a particle size larger than 0.075mm is within 25% and the liquid limit is higher than 50%.

The method for thermal desorption repairing of polycyclic aromatic hydrocarbons highly polluted and highly plastic clay provided in the examples of this application, the temperature of thermal desorption repairing is 250-450°C, and the time of thermal desorption repairing is 20-40 minutes, which can effectively Removal of polycyclic aromatic hydrocarbons with 2 to 3 rings of aromatic hydrocarbons in highly polluted polycyclic aromatic hydrocarbons with a water content of 0.01% to 15% and high plasticity clay, with an overall removal rate of more than 73%.

In some embodiments, the 2-3 ring polycyclic aromatic hydrocarbons may include any one of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene, or a combination of two or more. That is, the 2-3 ring polycyclic aromatic hydrocarbons may be selected from at least one of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene.

In some embodiments, the high-polycyclic aromatic hydrocarbon-polluted high-plasticity clay is clay after freeze-drying treatment, and its water content is close to 0, for example, it may be 0.001%. The temperature of the thermal desorption restoration is 350-450° C., and the time of the thermal desorption restoration is 20-40 minutes. In this way, the overall removal rate of polycyclic aromatic hydrocarbons with 2-3 rings can be more than 95%.

In some embodiments, the high-polycyclic aromatic hydrocarbon-polluted high-plastic clay is clay after freeze-drying treatment, and the polycyclic aromatic hydrocarbon high-polluted high-plastic clay also includes polycyclic aromatic hydrocarbons with 4 to 6 rings. . The temperature of the thermal desorption restoration is 350-450° C., and the time of the thermal desorption restoration is 20-40 minutes. In this way, to a certain extent, PAHs with 4-6 rings in the high-pollution PAH high-plasticity clay can be removed, and the removal rate can reach more than 69%. At the same time, polycyclic aromatic hydrocarbons with 2-3 rings Ring aromatics, the overall removal rate is over 95%. At the same time, the overall removal rate of all polycyclic aromatic hydrocarbons can be more than 74%.

苯并[b]荧蒽、苯并[k]荧蒽、苯并[a]芘、苯并[1,2,3-cd]芘、二苯并[a,h]蒽和苯并[g,h,i]苝中的至少一种。其中，苯并[a]蒽、

苯并[b]荧蒽、苯并[k]荧蒽、苯并[a]芘、苯并[1,2,3-cd]芘和二苯并[a,h]蒽均具有致癌性。热脱附修复的温度为400～450℃，所述热脱附修复的时间为20～40min。可以使具有致癌性的多环芳烃去除率达到80％以上，同时，还可以使2～3环的多环芳烃，总体的去除率为99％以上。芳烃环数为4～6环的多环芳烃，使其去除率达到86％以上。同时还能使所有的多环芳烃的总体的去除率为89％以上。In some embodiments, the polycyclic aromatic hydrocarbons of 4-6 rings may include benz[a]anthracene,

Benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[1,2,3-cd]pyrene, dibenzo[a,h]anthracene and benzo[g , h, i] at least one of perylene. Among them, benz[a]anthracene,

Benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[1,2,3-cd]pyrene, and dibenzo[a,h]anthracene are all carcinogenic. The temperature of the thermal desorption restoration is 400-450° C., and the time of the thermal desorption restoration is 20-40 minutes. The removal rate of carcinogenic polycyclic aromatic hydrocarbons can reach more than 80%, and at the same time, the overall removal rate of 2-3 ring polycyclic aromatic hydrocarbons can be more than 99%. The removal rate of polycyclic aromatic hydrocarbons with 4-6 rings can reach more than 86%. At the same time, the overall removal rate of all polycyclic aromatic hydrocarbons can be more than 89%.

In some embodiments, the high-polycyclic aromatic hydrocarbon-polluted high-plasticity clay is clay after freeze-drying treatment, the temperature of the thermal desorption restoration is 400-450° C., and the time of the thermal desorption restoration is 30 minutes. The removal rate of carcinogenic polycyclic aromatic hydrocarbons can reach more than 87%, and at the same time, the overall removal rate of 2-3 ring polycyclic aromatic hydrocarbons can be more than 99%. The removal rate of polycyclic aromatic hydrocarbons with 4 to 6 rings can reach more than 90%. At the same time, the overall removal rate of all polycyclic aromatic hydrocarbons can be more than 91%.

In some embodiments, the high-polycyclic aromatic hydrocarbon-polluted high-plasticity clay is clay after freeze-drying treatment, the temperature of the thermal desorption restoration is 450° C., and the time of the thermal desorption restoration is 30 minutes. The removal rate of carcinogenic polycyclic aromatic hydrocarbons can reach more than 98%, and at the same time, the overall removal rate of 2-3 ring polycyclic aromatic hydrocarbons can be more than 99%. The removal rate of polycyclic aromatic hydrocarbons with 4-6 rings can reach more than 99%. At the same time, the overall removal rate of all polycyclic aromatic hydrocarbons can be more than 99%.

In some embodiments, the high-polycyclic aromatic hydrocarbon-polluted high-plasticity clay may be dried clay, and the moisture content may be 5-15%. The temperature of the thermal desorption restoration is 350-450° C., and the time of the thermal desorption restoration is 30 minutes. It can make polycyclic aromatic hydrocarbons with 2 to 3 rings, and the overall removal rate is over 96%. The polycyclic aromatic hydrocarbons whose ring number is 4-6 rings can make the removal rate reach more than 67%. It can also make the overall removal rate of all polycyclic aromatic hydrocarbons more than 73%. The removal rate of carcinogenic polycyclic aromatic hydrocarbons can reach more than 62%.

In some embodiments, the highly-polluted polycyclic aromatic hydrocarbon high-plasticity clay may be clay after drying treatment, the temperature of the thermal desorption restoration is 400-450°C, and the time of the thermal desorption restoration is 30 minutes . It can make polycyclic aromatic hydrocarbons with 2 to 3 rings, and the overall removal rate is over 99%. The removal rate of polycyclic aromatic hydrocarbons with 4-6 rings can reach more than 84%. It can also make the overall removal rate of all polycyclic aromatic hydrocarbons more than 87%. The removal rate of carcinogenic polycyclic aromatic hydrocarbons can reach more than 80%.

In some embodiments, the high-polycyclic aromatic hydrocarbon-polluted high-plasticity clay may be clay after drying treatment, the temperature of the thermal desorption repair is 450° C., and the time of the thermal desorption repair is 30 minutes. It can make polycyclic aromatic hydrocarbons with 2 to 3 rings, and the overall removal rate is over 99%. The removal rate of polycyclic aromatic hydrocarbons with 4-6 rings can reach more than 98%. It can also make the overall removal rate of all polycyclic aromatic hydrocarbons more than 98%. The removal rate of carcinogenic polycyclic aromatic hydrocarbons can reach more than 98%. In this way, a removal rate of more than 98% can be achieved without completely drying the high-pollution and high-plasticity clay with polycyclic aromatic hydrocarbons, thereby saving energy.

That is, the polycyclic aromatic hydrocarbon highly polluted high plasticity clay has a water content of 0.01% to 15%, the temperature of the thermal desorption repair is 450°C, and the time of the thermal desorption repair is 30 minutes, which can achieve 98% above removal rate.

In some embodiments, the inert protective atmosphere may be nitrogen. In the process of thermal desorption repair, the throughput can be 0.3L/min.

The technical solutions of the present invention will be further described below in combination with specific embodiments.

The experimental methods in the following examples are conventional methods unless otherwise specified.

The test materials used in the following examples, unless otherwise specified, were purchased from conventional chemical reagent stores.

Example 1 Soil Plasticity Analysis and Pollutant Component Analysis of Polycyclic Aromatic Hydrocarbon Highly Contaminated Highly Plastic Clay

Test material: PAH-contaminated clay. Among them, the PAH-contaminated clay was taken from a contaminated site of a chemical plant in Xiangtan City, Hunan Province.

experiment method:

Soil plasticity analysis: Soil plasticity analysis is carried out according to the Highway Geotechnical Test Regulations (JTG 3430-2020).

Analysis of pollutant components: refer to HJ 805-2016 soil and sediment, determination of polycyclic aromatic hydrocarbons, gas chromatography-mass spectrometry, USEPA METHOD 3540C (Soxhlet extraction) for Soxhlet extraction of residual polycyclic aromatic hydrocarbons in soil; use rotary evaporation Concentrate the extract with an instrument and a nitrogen blower; purify with a silica gel chromatography column according to USEPA METHOD 3630C (silica gel chromatography column purification); and use Shimadzu GCMS-QP2010 plus for quantitative analysis of PAHs. The specific conditions are: the temperature of the injector, the interface and the ion source are all 300°C. The initial temperature of the column oven was 60°C, raised to 250°C at a speed of 10°C/min and kept at the temperature for 3 minutes, then raised to 290°C at a speed of 4°C/min and kept at the temperature for 5 minutes.

test results:

The liquid limit, plastic limit and plasticity index of polycyclic aromatic hydrocarbon contaminated clay were 56%, 24% and 31 respectively, and the organic matter content was 3.4g/kg.

There are 16 kinds of PAH pollutants in the PAH-contaminated clay. The total concentration of pollutants therein is 212.3 mg/kg (RSD=1.17%), and the specific components and the specific concentrations of each component are shown in Table 1.

Table 1 The composition and content of specific PAHs in PAH-contaminated clay

Result analysis: According to the Highway Geotechnical Test Regulations (JTG 3430-2020), the PAH-contaminated clay is high liquid limit clay, that is, high plasticity clay. Among them, the concentration of pollutants BaA, BbF, IPY, and DBA are higher than the pollution screening value of Class I construction land, which are 3.3 times, 4.0 times, 3.8 times and 39.9 times of the screening value, respectively, which is highly polluted clay. Therefore, the test material belongs to polycyclic aromatic hydrocarbons highly polluted high plasticity clay.

Example 2 Effect of thermal desorption temperature and thermal desorption time on the removal rate of 2-3 ring polycyclic aromatic hydrocarbons in high polycyclic aromatic hydrocarbon contaminated high plastic clay after freeze-drying

Test material: polycyclic aromatic hydrocarbon highly polluted high plasticity clay after freeze-drying treatment, its moisture content is about 0.01%, close to 0.

Test group:

In test group 1, the temperature of thermal desorption repair was 250°C. Including test group 1-1, the thermal desorption time is 20min. For test group 1-2, the thermal desorption time is 30 minutes. For test group 1-3, the thermal desorption time is 40min.

In test group 2, the temperature of thermal desorption repair was 350°C. Including test group 2-1, the thermal desorption time is 20min. For test group 2-2, the thermal desorption time is 30 minutes. For test group 2-3, the thermal desorption time is 40min.

In test group 3, the temperature of thermal desorption repair was 400°C. Including test group 3-1, the thermal desorption time is 20min. For test group 3-2, the thermal desorption time is 30 minutes. For test group 3-3, the thermal desorption time is 40 minutes.

Test method: raise the temperature under the continuous feeding of 0.1L/min nitrogen, stabilize to the target temperature (the temperature of thermal desorption repair), quickly push into the porcelain boat containing the contaminated clay, and continuously feed 0.3L/min Under a nitrogen atmosphere, carry out the thermal desorption treatment for the target holding time (the length of the thermal desorption repair), and after the thermal desorption is completed, cool with the furnace in the nitrogen gas that is continuously fed. After cooling, adopt the measuring method of composition and concentration as embodiment 1 to carry out composition measurement, obtain the removal rate of specific composition.

Experimental results: the overall removal rate results of 2-3 ring aromatics in Example 2 are shown in Table 2 and Figure 1 .

Table 2 The overall removal rate results of 2-3 ring aromatics

It can be seen from Table 2 that for the high-plasticity clay highly polluted by polycyclic aromatic hydrocarbons after freeze-drying treatment, when the thermal desorption repair temperature is 250-450 °C and the thermal desorption repair time is 20-40 min, the The overall removal rate of ene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene can reach more than 72%.

Further, when the temperature of thermal desorption restoration is 350-450°C and the time of thermal desorption restoration is 20-40min, the overall removal of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene The rate can reach more than 95%.

Further, when the temperature of thermal desorption restoration is 400-450°C and the time of thermal desorption restoration is 20-40min, the overall removal of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene The rate can reach more than 98.8%. It shows that the thermal desorption restoration method of the embodiment of the present application has a good overall removal rate for the 2-3 ring aromatics in the polycyclic aromatic hydrocarbon highly polluted high plasticity clay after the freeze-drying treatment.

Example 3 Effects of thermal desorption temperature and thermal desorption time on the overall removal rate of 4-6 ring PAHs and total PAHs in high polycyclic aromatic hydrocarbons highly polluted high plasticity clay after freeze-drying

Test material: polycyclic aromatic hydrocarbon highly polluted high plasticity clay after freeze-drying treatment, its moisture content is about 0.01%, close to 0.

Test group:

In test group 8, the temperature of thermal desorption repair was 350°C. Including test group 8-1, the thermal desorption time is 20min. For test group 8-2, the thermal desorption time is 30 minutes. For test group 8-3, the thermal desorption time is 40 minutes.

For test group 9, the temperature for thermal desorption repair was 400°C. Including test group 9-1, the thermal desorption time is 20min. For test group 9-2, the thermal desorption time is 30 minutes. For test group 9-3, the thermal desorption time is 40 minutes.

For test group 10, the temperature for thermal desorption repair was 450°C. Including the test group 10-1, the thermal desorption time is 20min. For test group 10-2, the thermal desorption time is 30 minutes. For test group 10-3, the thermal desorption time is 40 minutes.

Test method: same as embodiment 2.

Comparative example 1

The only difference from Example 3 is that the test group is the control group 1, and the temperature for thermal desorption repair is 250°C. Including the control group 1-1, the thermal desorption time is 20min. For control group 1-2, the thermal desorption time is 30 minutes. For control group 1-3, the thermal desorption time is 40min.

For the overall removal rate of 4-6 ring polycyclic aromatic hydrocarbons and the overall removal rate of total polycyclic aromatic hydrocarbons in Example 3 and Comparative Example 2, please refer to Table 3, Figure 1 and Figure 2 .

As shown in Figure 2, at a certain temperature, the thermal desorption of PAHs has a certain plateau, that is, after reaching a certain time, the overall removal rate remains basically unchanged as the thermal desorption time increases. The higher the temperature, the earlier the plateau period will come as time increases. For example, if 350°C is used for thermal desorption treatment, the overall removal rate of 30min and 40min thermal desorption is basically the same, while 400°C and 450°C are used for treatment. , the time increase of 20min-40min did not have a great impact on the overall removal rate of 16PAHs.

Carcinogenic polycyclic aromatic hydrocarbons (Carci.-PAHs) after thermal desorption at different temperatures and times, the trend of residual amount in soil is similar to that of 16PAHs. However, as the temperature rises, especially starting from 400°C, the proportion of non-carcinogenic PAH residues in the soil becomes smaller and smaller. At 450°C, almost all of the residual PAHs in the soil are carcinogenic Aromatics.

As shown in Figure 1, the initial concentration of polycyclic aromatic hydrocarbons with 2-3 rings in clay is 42.7 mg/kg, and that of 4-6 rings is 169.6 mg/kg. The thermal desorption treatment at 250°C can make the overall removal rate of 2-3 ring PAHs reach 72.02%-82.58%. Under the same conditions, the overall removal rate of 4-6 ring PAHs is only 33.59%-44.25%. The thermal desorption treatment at 400°C for 30 minutes can make the overall removal rate of 2-3 ring PAHs reach more than 99%, which is 99.12%, but the overall removal rate of 4-6 ring PAHs reaches more than 99%. The desorption temperature is up to 450°C.

With the overall removal rate of 90% as the critical line, for tetracyclic PAHs, BbF needs thermal desorption treatment at 450°C for 20 minutes to achieve it, while its isomer BkF only needs thermal desorption treatment at 400°C for 30 minutes. Reach; the boiling point and relative molecular mass are respectively 384 ℃, 202 and 448 ℃, and 228 FLU and CHR all reach over 90% after thermal desorption treatment at 400 ℃ for 20 minutes, while the boiling point and relative molecular mass are respectively 404°C, 202°C and 475°C, PYR and BaA of 228 were achieved after thermal desorption at 350°C for 20 min and 350°C for 30 min, respectively.

Table 3 The overall removal rate of 4-6 ring PAHs and the overall removal rate results of total PAHs

It can be seen from Table 3 that for the polycyclic aromatic hydrocarbon highly polluted high plasticity clay after freeze-drying treatment, in the test group 8, test group 9 and test group 10 in embodiment 3, when the temperature of thermal desorption repair is 350-450 ℃, when the thermal desorption repair time is 20-40min, the overall removal rate of aromatics with 4-6 rings can reach more than 69%, and the overall removal rate of carcinogenic aromatics can reach more than 65%. The overall removal rate can reach more than 74%. Compared to control group 1, both had an improvement of only 30%. It shows that for aromatic hydrocarbon pollutants with different ring numbers, the suitable thermal desorption temperature is not the same. It is suitable for the thermal desorption temperature of aromatic hydrocarbon pollutants with 2-3 rings, but not suitable for aromatic hydrocarbon pollutants with 4-6 rings.

Furthermore, when the temperature of thermal desorption repair is 400-450°C, and the time of thermal desorption repair is 20-40 minutes, the overall removal rate of aromatics with 4-6 rings can reach more than 86%, which is carcinogenic The overall removal rate of aromatics can reach more than 83%, and the overall removal rate of all aromatics can reach more than 89%.

Furthermore, when the temperature of thermal desorption restoration is 400°C-450°C and the time of thermal desorption restoration is 30 minutes, the overall removal rate of aromatics with 4-6 rings can reach more than 90%. The overall removal rate can reach more than 87%, and the overall removal rate for all aromatics can reach more than 91%.

Further, when the temperature of thermal desorption repair is 450°C and the time of thermal desorption repair is 20-40 minutes, the overall removal rate of aromatics with 4-6 rings can reach more than 97%. The overall removal rate can reach over 96%, and the overall removal rate for all aromatics can reach over 97%. It shows that the thermal desorption restoration method of the embodiment of the present application has a good overall removal rate for the removal rate of 4-6 ring aromatics, carcinogenic aromatics and all aromatics in highly polluted polycyclic aromatic hydrocarbons and high plasticity clay.

Example 4 Influence of water content on the overall removal rate of polycyclic aromatic hydrocarbons in high polycyclic aromatic hydrocarbon-polluted high-plasticity clay

Test material: polycyclic aromatic hydrocarbon highly polluted high plasticity clay after freeze-drying treatment, its moisture content is about 0.01%, close to 0. After drying, the polycyclic aromatic hydrocarbons highly polluted high plasticity clay has a moisture content of 5%. The moisture content of the high-polycyclic aromatic hydrocarbon-polluted high-plasticity clay after drying treatment is about 10%. The moisture content of the high-polycyclic aromatic hydrocarbon-polluted high-plastic clay after drying treatment is about 15%.

Test group:

In test group 5, the temperature of thermal desorption repair was 350°C, and the thermal desorption time was 30 minutes. Including test group 5-1, the moisture content of high PAH-contaminated high-plasticity clay is about 0.01%. In the test group 5-2, the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is about 5%. In the test group 5-3, the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is about 10%. In the test group 5-4, the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is about 15%.

In test group 6, the temperature for thermal desorption repair was 400°C, and the thermal desorption time was 30 minutes. Including test group 6-1, the moisture content of high PAH-polluted high-plasticity clay is about 0.01%. In test group 6-2, the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is about 5%. In the test group 6-3, the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is about 10%. In the test group 6-4, the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is about 15%.

In test group 7, the temperature for thermal desorption repair was 450°C, and the thermal desorption time was 30 minutes. Including test group 7-1, the moisture content of high PAH-contaminated high-plasticity clay is about 0.01%. In test group 7-2, the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is about 5%. In test group 7-3, the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is about 10%. In the test group 7-4, the moisture content of the polycyclic aromatic hydrocarbon highly polluted high plastic clay is about 15%.

Test method: with embodiment 2.

Test results: as shown in Table 4 and Figure 3.

It can be seen from Figure 3 and Table 4 that for 2-3 ring PAHs, at 350°C-400°C 5%wt.-15%wt, with the increase of water content, the thermal desorption efficiency of 2-3 rings shows an upward trend . Compared with 5% wt. moisture content, 15% wt. moisture content polluted clay was thermally desorbed at 350°C for 30 minutes, and the residual 2-3 ring PAHs in the soil decreased from 3.32% to 2.97%, a decrease of 0.35%; after 400°C After 30 minutes of thermal desorption, the residual 2-3 ring PAHs in clay decreased from 0.87% to 0.43%. Therefore, for clay mainly polluted by 2-3 ring PAHs, the moisture content should be controlled at 10%wt.-15%wt. during thermal desorption restoration. At this time, the drier soil can achieve similar (350°C) or better (400°C and 450°C) removal effects during thermal desorption restoration. When using this water content control method, thermal desorption at 400°C for 30 minutes can make the overall removal rate of 2-3 ring PAHs reach more than 99%, and ACY, ANA, and FLU are completely removed; continue to increase the temperature for 2-3 ring heat The improvement effect of desorption efficiency is weak. Therefore, at 400°C for 30 minutes, the residual concentration of 2-3 ring PAHs decreased from 0.80% to 0.73%-0.43% in drier soil.

For 4-6 ring PAHs, at the thermal desorption temperature of 350°C-450°C, with the increase of water content, the thermal desorption efficiency of 4-6 ring PAHs showed a trend of first increasing and then decreasing, reaching 10%wt. Therefore, for clay mainly polluted by 4-6 ring PAHs, the moisture content should be controlled at 0-10%wt. during thermal desorption restoration. When using this water content control method, BaP can be completely removed by thermal desorption repair at 450°C for 30 minutes, and the overall removal rate of 4-6 ring PAHs is higher than 99%. Compared with the dry soil, the moisture content of 5%wt. and 10%wt. can promote the desorption of PAHs contaminated cohesive soil, and the total residues of 4-6 ring PAHs decreased from 0.99% to 0.92% and 0.76%. Therefore, at 450°C for 30 minutes, the water content is further screened to be 10%wt. At this time, the residual concentration of 2-3 ring PAHs decreased from 0.99 to 0.76% in drier soil.

Table 4 Effect of water content on the overall removal rate of PAHs in high PAH-contaminated high-plasticity clay

For the 16 kinds of PAHs optimized by EPA, when the thermal desorption temperature is 350°C-400°C, the moisture content within 10%wt. will not have a great impact on the thermal desorption efficiency. The 5%wt. moisture will reduce the thermal desorption efficiency slightly, and the thermal desorption efficiency at 350℃ and 400℃ decreased by 4.37% and 1.61%, respectively. When thermal desorption of PAHs-contaminated clay was performed at 350°C, the moisture content of 10%wt. improved the thermal desorption efficiency by 1.88% compared with that of 5%wt., but it was still slightly lower than that without adding water. desorption efficiency. When using 400℃ for thermal desorption of PAHs contaminated soil, the thermal desorption efficiency of 10%wt. moisture content is basically the same as that of 5%wt., and 15%wt. moisture content will make the thermal desorption efficiency decrease obviously. Compared with no water addition, the thermal desorption efficiency at 350°C and 400°C decreased by 6.95% and 4.23%, respectively. The experiment on the effect of moisture content at 450°C for 30 minutes on the thermal desorption efficiency showed that the moisture content of 5%wt. and 10%wt. could promote the desorption of PAHs polluted cohesive soil to a certain extent, and the total residue of 16PAHs optimally controlled by EPA It decreased from 0.84% to 0.75% and 0.62%, and the total residues of carcinogenic PAHs decreased from 1.17% to 1.11% and 0.91%. Therefore, the moisture content is selected as 10%wt., and the thermal desorption temperature and time are selected as: 450°C for 30min. At this time, the thermal desorption efficiency can reach more than 99%, and the toxicity represented by TEQs is only within 1% of the contaminated clay before restoration. During the high temperature thermal desorption treatment at 450℃, the participation of water further removes the residual PAHs that were originally difficult to desorb. This shows that at a thermal desorption temperature of 450 °C, the appropriate water-contaminated clay feed ratio can improve the efficiency of soil thermal desorption remediation.

It can be seen from Table 4 that for PAH-contaminated high-plasticity clays with different water contents, when the water content is 0.01-15%, the temperature of thermal desorption restoration is 350-450°C, and the time of thermal desorption restoration is 30 minutes, The overall removal rate of aromatic hydrocarbons with 4-6 rings can reach more than 71%. The overall removal rate of carcinogenic aromatics can reach more than 62%, and the overall removal rate of all aromatics can reach more than 73%. The overall removal rate of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene can reach more than 96%. It shows that for aromatic hydrocarbons with different ring numbers, the suitable thermal desorption temperature is not the same.

Furthermore, for PAH-contaminated high-plasticity clays with different water contents, when the water content is 0.01-15%, the temperature for thermal desorption restoration is 400-450°C, and the time for thermal desorption restoration is 30 minutes, for 4 The overall removal rate of aromatic hydrocarbons with ~6 rings can reach more than 84%. The overall removal rate of carcinogenic aromatics can reach more than 80%, and the overall removal rate of all aromatics can reach more than 87%. The overall removal rate of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene can reach more than 99%. Among them, when the water content is 10-15%, the overall removal rate of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene can only be further improved. It can be seen that for thermal desorption at a temperature of 400-450° C., different water contents have different effects on the overall removal rate of PAHs with different ring numbers. For polycyclic aromatic hydrocarbons with 2-3 rings, the higher the moisture content, the better, and the lower the better. Setting the moisture content to 10-15% can avoid the heat desorption equipment caused by the clay being too high. The cohesiveness of cohesive soil, the reduction of heat transport in the thermal desorption repair process of contaminated cohesive soil caused by the agglomeration of cohesive soil; and the OH free radicals in water excited by water transpiration and high temperature or microwave radiation Thermal desorption has a certain promoting effect.

Furthermore, for PAH-contaminated high-plasticity clays with different water contents, when the water content is 0.01-15%, the temperature for thermal desorption restoration is 450°C, and the time for thermal desorption restoration is 30 minutes, for 4-6 The overall removal rate of ring aromatics can reach over 98%. The overall removal rate of carcinogenic aromatics can reach over 98%, and the overall removal rate of all aromatics can reach over 98%. The overall removal rate of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene can reach more than 99.89%. Among them, when the water content is 5-15%, compared with the water content of 0%, it can increase the efficiency of thermal desorption repair, and can further improve the overall removal rate of 4-6 ring aromatics and carcinogenic aromatics. The overall removal rate and the overall removal rate of all aromatics, and increase the overall removal rate of 2-3 ring aromatics to nearly 99%.

Furthermore, for PAH-contaminated high-plasticity clays with different water contents, when the water content is 10%, the thermal desorption repair temperature is 450°C, and the thermal desorption repair time is 30 minutes, the thermal desorption can be further improved. Efficiency, the overall removal rate of aromatics with 2-3 rings can reach more than 99.9%, and the overall removal rate of aromatics with 4-6 rings can reach more than 99%. The overall removal rate of carcinogenic aromatics can reach over 99%, and the overall removal rate of all aromatics can reach over 99%. Explain that the thermal desorption repairing method of the embodiment of the present application is aimed at 2-3 ring aromatics, 4-6 ring aromatics, carcinogenic aromatic hydrocarbons and all Aromatics all had good overall removal efficiencies.

Combining TEQ and carcinogenic risk analysis, the water content is controlled at 10% wt., and the overall removal rate of thermal desorption restoration at 450°C for 30 minutes is the highest. On this basis, if the concentration of DBA is low, 400°C for 40 minutes can be selected. For 2-3 ring PAHs, the water content is controlled at 10%wt.~15%wt., and the overall removal rate of thermal desorption repair at 400°C for 30min is the highest; for 4-6 ring PAHs, the water content is controlled at 10%wt. ., the overall removal rate of thermal desorption repair at 450℃30min is the highest. In this way, the pretreatment of the wet clay does not need to be pre-dried to be nearly completely dry, and the ideal thermal desorption repair effect can be achieved by drying to 10% wt., and it also has the advantage of energy saving.

Example 5 Effect of thermal desorption remediation on the toxic equivalent of PAHs in PAHs highly polluted and highly viscous soil

Toxic Equivalent Principle: Using the Toxic Equivalent Factor (TEF), is a method for soil risk assessment. The toxicity of mixed PAH contamination in soil in this method can be expressed as a single number, replaced by the equivalent concentration (TEQ) of the most toxic or carcinogenic congener. The equivalent concentration of PAH:BaP, which is generally considered to be the most toxic and carcinogenic, was used as the toxic equivalent TEQ of residual PAHs after thermal desorption of cohesive soil.

Test material: polycyclic aromatic hydrocarbon highly polluted high plasticity clay after freeze-drying treatment, its moisture content is about 0.01%, close to 0.

Test group: Test group 11, the temperature of thermal desorption repair is 450°C. Including test group 11-1, the thermal desorption time is 30min. For test group 11-2, the thermal desorption time is 40 minutes.

For control group 2, the temperature for thermal desorption repair is 250°C. Including the control group 2-1, the thermal desorption time is 20min. For control group 2-2, the thermal desorption time is 30 minutes. For control group 2-3, the thermal desorption time is 40min.

For control group 3, the temperature of thermal desorption repair was 350°C. Including the control group 3-1, the thermal desorption time is 20min. For control group 3-2, the thermal desorption time is 30 minutes. For control group 3-3, the thermal desorption time is 40 minutes.

For control group 4, the temperature of thermal desorption repair was 400°C. Including the control group 4-1, the thermal desorption time is 20min. For control group 4-2, the thermal desorption time is 30 minutes. For control group 4-3, the thermal desorption time is 40 minutes.

For control group 5, the temperature for thermal desorption repair was 450°C. For control group 5-1, the thermal desorption time is 20 minutes.

Test method: with embodiment 2.

Test results: as shown in Table 5 and Figure 4.

Table 5 Effect of thermal desorption remediation on the toxic equivalent of PAHs in highly PAHs-contaminated and highly viscous soils

Result analysis:

As shown in Figure 4, generally speaking, with the increase of temperature at the same time, the toxic equivalent TEQ of soil PAHs after thermal desorption showed a downward trend, and at the same temperature with the increase of time, TEQ showed a downward trend. However, at a temperature of 350 °C, increasing the thermal desorption time from 30 min to 40 min did not significantly decrease the TEQ. It has the same law as thermal desorption efficiency. Compared with time, temperature is a more decisive factor. For example, after thermal desorption treatment at 350°C for 20 minutes, the TEQ of residual PAHs in clay must be lower than 250°C for 20-40 minutes; 400°C for 20 minutes After thermal desorption treatment, the TEQ of residual PAHs in clay must be lower than 350°C for 20-40min, and so on. The thermal desorption treatment at 450°C for 30 minutes reduced the TEQ of residual PAHs to 0.45 mg/kg, which was already lower than the risk screening value of BaP in soil pollution of Class I construction land.

It can be seen from Figure 3 and Table 5 that compared with the control group 2 to the control group 5, the TEQ of the test group 11-1 and the test group 11-2 is lower than the screening value of the first-class soil for construction land. It can be seen that the thermal desorption remediation conditions of test group 11-1 and test group 11-2 can make the PAHs highly polluted and highly viscous soil meet the screening value of the first-class soil for construction land after thermal desorption remediation.

Example 6 Effect of thermal desorption remediation on the screening value of PAHs in highly polluted and highly viscous soil of PAHs construction land

Test material: polycyclic aromatic hydrocarbon highly polluted high plasticity clay after freeze-drying treatment, its moisture content is about 0.01%, close to 0.

Test group: Test group 12, the temperature of thermal desorption repair is 450°C, and the thermal desorption time is 30 minutes.

For control group 6, the temperature for thermal desorption repair was 350°C, and the thermal desorption time was 30 minutes.

For control group 7, the temperature for thermal desorption repair was 400°C, and the thermal desorption time was 30 minutes.

Test method: with embodiment 2.

Test results: as shown in Table 6 and Figure 5.

Table 6 The effect of thermal desorption remediation on the screening value of PAHs construction land in highly PAHs-contaminated and highly viscous soil

It can be seen from Table 6 and Figure 5 that compared with the control group 6 and the control group 7, the overall removal rate of DBA in the test group 12 increased by 26% and 37% respectively. All the pollutants in the test group 12 reached the screening value of Class I soil for construction land. Therefore, the thermal desorption remediation process parameters in test group 12, 450°C for 30 minutes, can make the polycyclic aromatic hydrocarbon highly polluted high plasticity clay in the embodiment of the present application reach the screening value of first-class soil for construction land after thermal desorption remediation.

The moisture content control and process method for thermal desorption restoration of polycyclic aromatic hydrocarbons highly polluted and highly plastic clay provided in the examples of this application, before performing thermal desorption restoration of PAHs polluted high viscosity clay, the pre-drying step does not need Drying until completely dry, and controlling the corresponding moisture content according to the number of rings of aromatic hydrocarbons to be removed, can obtain good thermal desorption repair efficiency, highlighting the technical advantages of thermal desorption repair.

Those of ordinary skill in the art should understand that: the discussion of any of the above embodiments is exemplary only, and is not intended to imply that the scope of the present disclosure (including claims) is limited to these examples; under the idea of the present disclosure, the above embodiments or Combinations between technical features in different embodiments are also possible, steps may be implemented in any order, and there are many other variations of the different aspects of the disclosed embodiments as described above, which are not provided in detail for the sake of brevity.

Although the disclosure has been described in conjunction with specific embodiments thereof, many alternatives, modifications and variations of those embodiments will be apparent to those of ordinary skill in the art from the foregoing description.

The disclosed embodiments are intended to embrace all such alterations, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the embodiments of the present disclosure shall fall within the protection scope of the present disclosure.

Claims (10)

1. The thermal desorption remediation method for the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay is characterized in that the content of coarse particles with the particle size of more than 0.075mm in the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay is within 25% and the liquid limit is higher than 50%; the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay at least comprises polycyclic aromatic hydrocarbons with 2-3 rings of aromatic hydrocarbon rings; the method comprises the following steps:

performing thermal desorption repair on the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay under an inert protective atmosphere; the water content of the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay is 0.01-15%, the thermal desorption restoration temperature is 250-450 ℃, and the thermal desorption restoration time is 20-40 min.

2. The method for thermal desorption remediation of the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay according to claim 1, wherein the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay is a clay subjected to freeze drying treatment, and the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay further comprises polycyclic aromatic hydrocarbons with 4-6 rings of aromatic hydrocarbon rings; the temperature of the thermal desorption repair is 350-450 ℃, and the time of the thermal desorption repair is 20-40 min.

3. The method for thermal desorption remediation of the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay according to claim 2, wherein the temperature of the thermal desorption remediation is 400-450 ℃, and the time of the thermal desorption remediation is 20-40 min.

4. The method for thermal desorption remediation of polycyclic aromatic hydrocarbon high-pollution high-plasticity clay according to claim 3, wherein the temperature of the thermal desorption remediation is 400-450 ℃, and the time of the thermal desorption remediation is 30min.

5. The method for thermal desorption remediation of the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay according to claim 1, wherein the water content of the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay is 5-15%, the temperature of the thermal desorption remediation is 350-450 ℃, and the time of the thermal desorption remediation is 30min.

6. The method for thermal desorption remediation of the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay according to claim 5, wherein the polycyclic aromatic hydrocarbon high-pollution high-plasticity clay further comprises polycyclic aromatic hydrocarbons with 4-6 rings of aromatic hydrocarbon rings;

the temperature of thermal desorption restoration is 400-450 ℃, and the time of thermal desorption restoration is 30min.

7. The method for thermal desorption remediation of polycyclic aromatic hydrocarbon high-pollution high-plasticity clay according to claim 6, wherein the temperature of the thermal desorption remediation is 450 ℃, and the time of the thermal desorption remediation is 30min.

8. The method for thermal desorption remediation of the highly-polluted and highly-plastic clay containing polycyclic aromatic hydrocarbons as claimed in claim 1, wherein the 2-3 ring polycyclic aromatic hydrocarbons are selected from at least one of naphthalene, acenaphthylene, fluorene, phenanthrene, anthracene, fluoranthene and pyrene.

9. The method for thermal desorption remediation of polycyclic aromatic hydrocarbon high-pollution high-plasticity clay according to claim 2 or 6, wherein the polycyclic aromatic hydrocarbon with 4-6 rings is selected from benzo [ a ]]Anthracene,

Benzo [ b ]]Fluoranthene, benzo [ k ]]Fluoranthene, benzo [ a ]]Pyrene, benzo [1,2,3-cd]Pyrene, dibenzo [ a, h ]]Anthracene and benzo [ g, h, i ]]At least one perylene.

10. The method for thermal desorption remediation of polycyclic aromatic hydrocarbon high-pollution high-plasticity clay according to claim 9, wherein the contents of benzo [ a ] anthracene, benzo [ b ] fluoranthene, benzo [1,2,3-cd ] pyrene and dibenzo [ a, h ] anthracene are all higher than a standard value.

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