CN109909281B - medicament and method for synchronously fixing and reducing trichloroethylene in soil and/or underground water - Google Patents
medicament and method for synchronously fixing and reducing trichloroethylene in soil and/or underground water Download PDFInfo
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- CN109909281B CN109909281B CN201910195313.XA CN201910195313A CN109909281B CN 109909281 B CN109909281 B CN 109909281B CN 201910195313 A CN201910195313 A CN 201910195313A CN 109909281 B CN109909281 B CN 109909281B
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Abstract
The invention discloses a medicament and a method for synchronously fixing and reducing trichloroethylene in soil and/or underground water. The medicament adopts bentonite, persulfate and water to be matched in a specific ratio, and simultaneously, the bentonite adopts sodium bentonite with specific performance, and the sodium bentonite with specific performance can effectively activate the persulfate to generate more SO with strong oxidizing property4 ·‑and OH, which is used for completely oxidizing trichloroethylene, so that dechlorination products with stronger toxicity, such as 1, 1-dichloroethylene, 1, 2-dichloroethylene or chloroethylene, are not generated, and the removal rate of TCE in a DNAPL polluted source region is improved. Meanwhile, the sodium bentonite with specific performance can maintain the pH stability of a reaction system in the process of removing trichloroethylene, so that an alkali reagent is not required to be additionally added in the reaction process, and the pH value is not required to be adjusted. Tests show that the removal rate of TCE reaches 51-56% in 8 days and 93-100% in 64 days.
Description
Technical Field
the invention belongs to the technical field of soil and underground water pollution risk management and control and remediation, and particularly relates to a medicament and a method for synchronously fixing and reducing trichloroethylene in soil and/or underground water, in particular to a medicament and a method for synchronously fixing and reducing trichloroethylene in a soil and/or underground water heavy non-aqueous phase liquid (DNAPL) pollution source region by coupling bentonite and persulfate.
Background
trichloroethylene (TCE) is one of the volatile chlorinated organics ubiquitous in soil and groundwater worldwide, and its pollution has become a worldwide environmental and health problem. According to incomplete statistics, high concentrations of TCE were detected in soil and groundwater in China, British, Japan, the United states, Belgian, and other countries. TCE in soil and groundwater is mainly derived from leaks in organic solvents, dry cleaning agents and narcotics storage tanks or waste streams that are discharged without being effectively treated.
TCE was listed as a "priority control compound" in the United states as early as 1976, and is also listed as a priority pollutant for monitoring and controlling Chinese environment in China, and has potential carcinogenic, teratogenic and mutagenic properties. It is a heavy non-aqueous phase liquid (DNAPL) having a density greater than that of water, and has a low solubility in water (1100mg/L), a density greater than that of water, and a low viscosity. TCE has high migration speed in soil and aeration zone, stays in medium gap in the form of liquid drop, and part of TCE entering underground water stays at the bottom of the water-containing layer to form DNAPL pollution source zone, and gradually dissolves into water along with the migration of the underground water to cause secondary pollution. TCE in the DNAPL polluted source region can become a continuous and durable underground water pollution source.
At present, the in-situ risk management and control and treatment repair technology of TCE in a DNAPL (deoxyribonucleic acid PL) polluted source area of soil and underground water mainly comprises a blocking technology, a chemical reduction technology and the like. The separation technology mainly depends on clay, bentonite, cement, mixed fly ash and other non-permeable materials to construct a separation wall to block the downstream migration and diffusion of the pollution source. The blocking technique can only cut off the exposure path, limiting the migration of the pollution plume, but cannot reduce the concentration of the pollutants and risks causing the leakage of the pollutants. In most cases, the barrier technology is used as a temporary control method only in the early stage of groundwater pollution control.
The chemical reduction technology mainly relies on the principle that zero-valent iron serves as an electron donor to provide electrons, and TCE serves as an electron acceptor to accept electrons, so that hydrogenolysis or dechlorination is carried out. The experimental research result of the granular iron column shows that the zero-valent iron can completely remove TCE at the initial stage of operation (less than or equal to 20 pore volumes), but when the operation is carried out to 90 pore volumes, the zero-valent iron is passivated, the removal rate of the TCE is reduced to 60 percent, and the chlorinated byproducts such as cis-1, 2-dichloroethylene, chloroethylene and the like are generated along with the passivation. In addition, granular iron is susceptible to oxidation by oxygen to form FeOOH or Fe (OH)3Blocking the contaminants from contacting them and blocking their voids, thereby reducing permeability and conductivity, among other things.
in practical application, the technology has the defects of large pH change, low TCE removal rate, easy generation of 1, 1-dichloroethylene, 1, 2-dichloroethylene or chloroethylene, high barrier wall permeability coefficient and high service life technical requirement in the process of fixedly reducing trichloroethylene in a soil and underground water heavy non-aqueous phase liquid (DNAPL) pollution source region.
Disclosure of Invention
Therefore, the invention aims to solve the defects of large pH change, low TCE removal rate, easy generation of 1, 1-dichloroethylene, 1, 2-dichloroethylene or chloroethylene, high barrier wall permeability coefficient and high service life technical requirement in the process of fixing and reducing trichloroethylene in a heavy non-aqueous phase liquid pollution source region of soil and underground water in the prior art, and further provides a medicament and a method for synchronously fixing and reducing the trichloroethylene in the soil and/or the underground water.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
The medicament for synchronously fixing and reducing the trichloroethylene in the soil and/or underground water comprises bentonite, persulfate and water, wherein the mass ratio of the bentonite to the persulfate is 3000-5000: 300-500, wherein the mass ratio of the bentonite to the water is 1-2: 40-60;
The bentonite is sodium bentonite, and Na in the sodium bentonite+the content is 2 wt% -4 wt%, the total organic carbon content is 10-15 mg/L, the pH is 10.0-11.0, and the particle size is 75-180 mu m.
Further, the mass ratio of the bentonite to the persulfate is 3800-4200: 350-400, wherein the mass ratio of the bentonite to the water is 1-2: 45-55;
The bentonite is sodium bentonite, and Na in the sodium bentonite+the content is 2.5 wt% -3 wt%, the total organic carbon content is 13-14 mg/L, the pH is 10.3-10.8, and the particle size is 120-150 mu m.
Further, the persulfate is potassium persulfate and/or sodium persulfate, and the purity of the persulfate is more than or equal to 98 wt%.
further, the persulfate is potassium persulfate and sodium persulfate, and the mass ratio of the potassium persulfate to the sodium persulfate is 1: (4-5).
In addition, the pH test method of sodium bentonite is as follows: adding ultrapure water into sodium bentonite, and controlling the mass ratio of the sodium bentonite to the ultrapure water to be 1: and 50, after the stirrer stirs for over 24 hours, measuring the pH value of the water, wherein the pH value is the pH value of the sodium bentonite.
The preparation method of the medicament comprises the following steps: weighing bentonite, persulfate and water according to the mass ratio, and stirring uniformly at room temperature to make the bentonite in a suspension state to prepare the medicament.
in addition, the invention also provides a method for synchronously fixing and reducing the trichloroethylene in the soil and/or the underground water by adopting the medicament, which comprises the following steps:
S1, mixing bentonite and water to prepare slurry;
s2, pouring the slurry obtained in the step S1 into soil and underground water media around the DNAPL pollution source region by adopting a cofferdam or high-pressure spraying mode to form a vertical barrier wall and/or a horizontal barrier wall, blocking migration and diffusion of the DNAPL pollution source, and fixing trichloroethylene;
s3, injecting the medicament into a DNAPL polluted source region, and degrading trichloroethylene in the DNAPL polluted source region.
Further, in step S1, the mass ratio of bentonite to water is 1-2: 40-60.
further, in step S2, the permeability coefficient of the vertical barrier wall is less than or equal to 1 × 10-7cm/s and the thickness is 9-19 cm;
the permeability coefficient of the horizontal barrier wall is less than or equal to 1 multiplied by 10-7cm/s and a thickness of 9-19 cm.
further, in step S3, the mass ratio of the persulfate in the chemical to the trichloroethylene in the DNAPL polluted source region is 300-500: 1 to 5.
Further, in step S2, when the DNAPL contamination source region burial depth is less than 10m, the step is implemented in a cofferdam manner; or the like, or, alternatively,
In the step S2, when the buried depth of the DNAPL polluted source region is 10-30 m, a high-pressure injection mode is adopted.
Further, the slurry in the step S1 is poured into the air-entrained zone around the DNAPL contaminated source region, and vertical and horizontal barrier walls are formed in the air-entrained zone and around the DNAPL contaminated source region; or the like, or, alternatively,
and (4) pouring the slurry obtained in the step S1 into an aquifer downstream of the DNAPL polluted source region to form a vertical barrier wall.
Compared with the prior art, the invention has the following beneficial effects:
(1) The medicament for synchronously fixing and reducing the trichloroethylene in the soil and/or underground water provided by the invention adopts bentonite, persulfate and water to be matched in a specific proportion, and simultaneously adopts sodium bentonite with specific performance, and the sodium bentonite with the specific performance can effectively activate the persulfate to generate more SO with strong oxidizing property4 ·-And OH, making use of SO4 ·-And OH thoroughly oxidizes trichloroethylene without generating dechlorination products with stronger toxicity, such as 1, 1-dichloroethylene, 1, 2-dichloroethylene or chloroethylene, so that the removal rate of TCE in a DNAPL polluted source region is improved. Meanwhile, the sodium bentonite with specific performance can maintain the pH stability of a reaction system in the process of removing trichloroethylene, so that an alkali reagent is not required to be additionally added in the reaction process, and the pH value is not required to be adjusted. Tests show that the removal rate of TCE reaches 51-56% in 8 days and 93-100% in 64 days, dechlorination products with stronger toxicity, such as 1, 2-dichloroethylene, chloroethylene and the like, are not generated in the reaction process, the secondary pollution is small, the ecological environment risk is small, the safety is high, and the method has remarkable advantages in technical and environmental protection.
(2) the agent for synchronously fixing and reducing the trichloroethylene in the soil and/or the underground water adopts sodium bentonite and optimizes Na in the sodium bentonite+The content, the total organic carbon content, the pH value and the particle size can improve the properties of the sodium bentonite such as thixoplasticity, expansibility, cohesiveness and the like, so that the sodium bentonite can effectively fill the gaps of soil, an aeration zone and a groundwater medium, and finally the migration and diffusion of trichloroethylene can be effectively blocked for a long time.
(3) The invention provides a medicament for synchronously fixing and reducing trichloroethylene in soil and/or underground water, wherein persulfate is potassium persulfate and sodium persulfate, and the mass ratio of the potassium persulfate to the sodium persulfate is 1: (4-5), the removal rate of TCE in the DNAPL polluted source region is improved by matching different types of persulfate according to a specific proportion.
(4) The method for synchronously fixing and reducing the trichloroethylene in the soil and/or the underground water, provided by the invention, comprises the steps of mixing bentonite and water to prepare slurry; then, pouring the slurry into soil and underground water medium around the DNAPL pollution source region by adopting a cofferdam or high-pressure spraying mode to form a vertical barrier wall and/or a horizontal barrier wall, blocking migration and diffusion of the DNAPL pollution source, and fixing trichloroethylene; and finally, injecting the medicament into a DNAPL (deoxyribonucleic acid-propylene polymer) polluted source region, filling bentonite in the medicament into gaps of soil and underground water media, dispersing persulfate in the polluted source region by virtue of the gravity action and the capillary phenomenon to form a low-permeability reaction region, and prolonging the retention time of trichloroethylene in the reaction region so as to completely oxidize and degrade the trichloroethylene.
(5) The method for synchronously fixing and reducing the trichloroethylene in the soil and/or the underground water provided by the invention is characterized in that bentonite and water are mixed according to a specific mass ratio to form slurry, and the slurry is suitable for being poured into soil and underground water media around a DNAPL pollution source area to form a vertical barrier wall and/or a horizontal barrier wall; blocking migration and diffusion of trichloroethylene by optimizing permeability coefficient and thickness of the vertical barrier walls and/or the horizontal barrier walls; by limiting the mass ratio of the persulfate in the medicament to the trichloroethylene in the DNAPL polluted source region, the removal rate of TCE in the DNAPL polluted source region can be improved.
(6) the method for synchronously fixing and reducing the trichloroethylene in the soil and/or the underground water can be carried out at normal temperature and normal pressure without heating, ultraviolet irradiation, transition metal ions, hydrogen peroxide and the like, and has the advantages of simple reaction system, mild reaction conditions and low operation, maintenance and management cost. By using the method, the technical requirements on the thickness and service life (at least 10 years) of the existing barrier wall can be obviously reduced, and further the construction cost of the barrier wall is reduced. Meanwhile, the in-situ fixation, treatment and restoration of soil and underground water, particularly deep underground water pollutants, and emergent pollution treatment can be realized, and the application range is wide.
drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a diagram showing a structural schematic and a layout state of bentonite and persulfate combined synchronous in-situ fixation and reduction of trichloroethylene in a DNAPL pollution source region of underground water in an embodiment of the invention;
FIG. 2 is a diagram showing a structural representation and a layout state of bentonite and persulfate in combination for synchronous in-situ fixation and reduction of trichloroethylene in a soil DNAPL pollution source region in example 4 of the present invention;
FIG. 3 is a graph of the short term change in TCE removal rate with reaction time for a combination of bentonite and persulfate salts in an example of the invention;
FIG. 4 is a linear fit graph of the TCE oxidative degradation kinetics induced by the combination of bentonite and persulfate in the examples of the present invention;
FIG. 5 is a graph showing the short-term change of pH of the reaction system with reaction time due to the combination of bentonite and persulfate in the example of the present invention;
FIG. 6 is a graph of the long term change in TCE removal rate with reaction time for a combination of bentonite and persulfate salts in an example of the invention;
FIG. 7 is a graph showing the change of pH of the reaction system with time due to the combination of bentonite and persulfate in the example of the present invention;
FIG. 8 is a graph showing the secular change of Eh of a reaction system with respect to reaction time, which is caused by the combination of bentonite and persulfate in the example of the present invention;
FIG. 9 shows a reaction system S caused by the combination of bentonite and persulfate in the example of the present invention2O8 2-Long-term change of residual amount with reaction time;
FIG. 10 is an SEM (5000X) topography of bentonite in an example of the invention;
FIG. 11 is an EDS analysis spectrum of bentonite in the example of the present invention.
Detailed Description
the technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
the term "bentonite" in the present invention is a hydrous clay mineral having montmorillonite as a main mineral component, the montmorillonite being 2: the crystal structure of type 1 comprises two silicon-oxygen tetrahedrons sandwiching a layer of aluminum-oxygen octahedron, the main chemical components are silicon dioxide, aluminum oxide and water, and the crystal structure also contains elements such as iron, magnesium, calcium, sodium, potassium and the like, the hardness is 1-2, and the density is 2-3 g/cm3the water-soluble film is yellow green, yellow white, gray, white and the like, and the volume of the water-soluble film is expanded by a plurality of times to 20-30 times after the water is added. The layered structure formed by the montmorillonite unit cell has some cations, such as Cu2+、Mg2+、Na+、K+. These cations are not very stable in their interaction with the montmorillonite unit cell and are easily exchanged with other cations.
The term "heavy non-aqueous phase liquid (DNAPL)" as used herein refers to a generic term for all water-insoluble liquid contaminants in soil and groundwater having a density greater than that of water, such as coal tar, wood oil, trichloroethylene and tetrachloroethylene, which have low solubility and high interfacial tension.
The term "Trichloroethylene (TCE) in the present invention is of the formula C2HCl3The DNAPL has the relative molecular weight of 131.39, the boiling point of 87.1 ℃, the melting point of-86 ℃, is colorless, is a flammable and volatile liquid with the smell similar to chloroform, is insoluble in water, is easily soluble in ethanol, ether and the like, can be dissolved in most organic solvents, and is DNAPL representing one of pollutants.
In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
Example 1
This embodiment provides a synchronous fixation andA medicament for reducing trichloroethylene in soil and/or groundwater, the medicament comprising 4000g of bentonite, 384g of persulfate and water, the mass ratio of bentonite to water being 1: 50; wherein the bentonite is sodium bentonite, and Na in the sodium bentonite+The content is 2.6 wt%, the total organic carbon content is 13.7mg/L, the pH is 10.5, the particle size is 150 mu m, and the persulfate is sodium persulfate;
The microscopic characterization of bentonite in this example is shown in fig. 10 and 11, and it can be seen from fig. 10 that: the surface of the bentonite is irregular polygon, smooth and angular; from fig. 11, it can be seen that: it is mainly composed of oxygen, silicon and aluminum and contains a small amount of sodium, potassium, iron, calcium, magnesium and the like, and is in accordance with 2: a type 1 crystal structure;
The application environment is simulated, and the medicament in the embodiment is applied to 10mg/L of anaerobic underground water containing TCE, and the specific application method is as follows: adding persulfate and water in the medicament into 10mg/L anaerobic underground water containing TCE, and then adding bentonite, so as to ensure that the mass ratio of the bentonite and the persulfate in the medicament to the TCE in the anaerobic underground water containing TCE is 4000: 384: 2, after reacting for 8 days under the conditions of normal temperature, normal pressure and oscillation (250rpm), the removal rate of TCE in the anaerobic underground water containing TCE reaches 56 percent, and after reacting for 64 days, the removal rate of TCE in the anaerobic underground water containing TCE reaches 100 percent.
Example 2
The embodiment provides a medicament for synchronously fixing and reducing trichloroethylene in soil and/or underground water, which comprises 4000g of bentonite, 384g of persulfate and water, wherein the mass ratio of the bentonite to the water is 1: 50; wherein the bentonite is sodium bentonite, and Na in the sodium bentonite+the content is 2.6 wt%, the total organic carbon content is 13.7mg/L, the pH value is 10.6, the particle size is 120 mu m, and the persulfate is potassium persulfate;
The application environment is simulated, and the medicament in the embodiment is applied to the TCE-containing soil of 10mg/kg, and the specific application method is as follows: adding persulfate in the preparation into 10mg/kg of TCE-containing soil, and then adding bentonite and water in the preparation to ensure that the mass ratio of the bentonite and the persulfate in the preparation to the TCE in the TCE-containing soil is 4000: 384: 2, after reacting for 8 days under the conditions of normal temperature, normal pressure and oscillation (250rpm), the removal rate of TCE in the anaerobic underground water containing TCE reaches 54 percent, and after reacting for 64 days, the removal rate of TCE in the anaerobic underground water containing TCE reaches 97 percent.
example 3
the embodiment provides a medicament for synchronously fixing and reducing trichloroethylene in soil and/or underground water, which comprises 3800g of bentonite, 400g of persulfate and water, wherein the mass ratio of the bentonite to the water is 1: 55; wherein the bentonite is sodium bentonite, and Na in the sodium bentonite+The content is 2.5 wt%, the total organic carbon content is 14mg/L, the pH value is 10.8, the particle size is 130 mu m, and the persulfate is sodium persulfate;
the application environment is simulated, and the medicament in the embodiment is applied to 10mg/L of anaerobic underground water containing TCE, and the specific application method is as follows: adding persulfate and water in the medicament into 10mg/L anaerobic underground water containing TCE, and then adding bentonite, so as to ensure that the mass ratio of the bentonite and the persulfate in the medicament to the TCE in the anaerobic underground water containing TCE is 3800: 400: 1, after reacting for 8 days under the conditions of normal temperature, normal pressure and oscillation (250rpm), the removal rate of TCE in the anaerobic underground water containing TCE reaches 55%, and after reacting for 64 days, the removal rate of TCE in the anaerobic underground water containing TCE reaches 99%.
Example 4
The embodiment provides a medicament for synchronously fixing and reducing trichloroethylene in soil and/or underground water, which comprises 4200g of bentonite, 350g of persulfate and water, wherein the mass ratio of the bentonite to the water is 2: 45, a first step of; wherein the bentonite is sodium bentonite, and Na in the sodium bentonite+The content is 3 wt%, the total organic carbon content is 13mg/L, the pH value is 10.5, the particle size is 140 mu m, and the persulfate is potassium persulfate;
the application environment is simulated, and the medicament in the embodiment is applied to 10mg/L of anaerobic underground water containing TCE, and the specific application method is as follows: adding persulfate and water in the medicament into 10mg/L anaerobic underground water containing TCE, and then adding bentonite, so as to ensure that the mass ratio of the bentonite and the persulfate in the medicament to the TCE in the anaerobic underground water containing TCE is 4200: 350: 5, after reacting for 8 days under the conditions of normal temperature, normal pressure and oscillation (250rpm), the removal rate of TCE in the anaerobic underground water containing TCE reaches 56.7 percent, and after reacting for 64 days, the removal rate of TCE in the anaerobic underground water containing TCE reaches 99.8 percent.
example 5
the embodiment provides a medicament for synchronously fixing and reducing trichloroethylene in soil and/or underground water, which comprises 3000g of bentonite, 500g of persulfate and water, wherein the mass ratio of the bentonite to the water is 1: 60, adding a solvent to the mixture; wherein the bentonite is sodium bentonite, and Na in the sodium bentonite+the content is 4 wt%, the total organic carbon content is 10mg/L, the pH value is 11, the particle size is 75 mu m, and the persulfate is sodium persulfate;
The application environment is simulated, and the medicament in the embodiment is applied to 10mg/L of anaerobic underground water containing TCE, and the specific application method is as follows: persulfate and water in the medicament are added into 10mg/L of anaerobic underground water containing TCE, bentonite is added, and the mass ratio of the bentonite and the persulfate in the medicament to the TCE in the anaerobic underground water containing TCE is 3000: 500: 2, after reacting for 8 days under the conditions of normal temperature, normal pressure and oscillation (250rpm), the removal rate of TCE in the anaerobic underground water containing TCE reaches 52 percent, and after reacting for 64 days, the removal rate of TCE in the anaerobic underground water containing TCE reaches 95 percent.
Example 6
the embodiment provides a medicament for synchronously fixing and reducing trichloroethylene in soil and/or underground water, which comprises 5000g of bentonite, 300g of persulfate and water, wherein the mass ratio of the bentonite to the water is 2: 40; wherein the bentonite is sodium bentonite, and Na in the sodium bentonite+The content is 2 wt%, the total organic carbon content is 15mg/L, the pH value is 10, the particle size is 180 mu m, and the persulfate is potassium persulfate;
The application environment is simulated, and the medicament in the embodiment is applied to 10mg/L of anaerobic underground water containing TCE, and the specific application method is as follows: adding persulfate and water in the medicament into 10mg/L anaerobic underground water containing TCE, and then adding bentonite, so as to ensure that the mass ratio of the bentonite and the persulfate in the medicament to the TCE in the anaerobic underground water containing TCE is 5000: 300: 2, after reacting for 8 days under the conditions of normal temperature, normal pressure and oscillation (250rpm), the removal rate of TCE in the anaerobic underground water containing TCE reaches 51 percent, and after reacting for 64 days, the removal rate of TCE in the anaerobic underground water containing TCE reaches 93 percent.
Example 7
the present embodiment provides an agent for synchronously immobilizing and reducing trichloroethylene in soil and/or groundwater, which is different from embodiment 2 only in that: in this embodiment, the persulfate is a mixture of potassium persulfate and sodium persulfate, wherein the mass ratio of potassium persulfate to sodium persulfate is 1: 4.5;
According to the test method in the embodiment 2, after 8 days of reaction under the conditions of normal temperature, normal pressure and oscillation (250rpm), the removal rate of TCE in the anaerobic underground water containing TCE reaches 56 percent, and after 64 days of reaction, the removal rate of TCE in the anaerobic underground water containing TCE reaches 99 percent.
example 8
The embodiment provides a method for synchronously fixing and reducing trichloroethylene in soil and/or underground water, as shown in figure 1, comprising the following steps:
S1, mixing bentonite and water, wherein the mass ratio of the bentonite to the water is 1.5: 50, preparing slurry;
S2, filling the slurry obtained in the step S1 into a water-bearing layer at the downstream of the DNAPL polluted source region by adopting a high-pressure spraying mode, wherein the burial depth of the DNAPL polluted source region is 10-30 m, and forming a vertical partition wall, wherein the permeability coefficient of the vertical partition wall is 1 multiplied by 10-7cm/s, the thickness is 16cm, the vertical barrier wall is perpendicular to the bottom of the water-resisting layer, the migration and the diffusion of a DNAPL pollution source are blocked, and trichloroethylene is fixed;
S3, injecting the medicament in the embodiment 1 into a DNAPL polluted source region, and controlling the mass ratio of persulfate in the medicament to trichloroethylene in the DNAPL polluted source region to be 300: 5, degrading trichloroethylene in the solution;
Tests show that after 64 days of reaction, the removal rate of TCE in the DNAPL polluted source region reaches more than 98%.
Example 9
The embodiment provides a method for synchronously fixing and reducing trichloroethylene in soil and/or underground water, which comprises the following steps:
s1, mixing bentonite and water, wherein the mass ratio of the bentonite to the water is 1: 60, preparing slurry;
S2, filling the slurry obtained in the step S1 into a water-bearing layer at the downstream of the DNAPL polluted source region by adopting a high-pressure spraying mode, wherein the burial depth of the DNAPL polluted source region is 10-30 m, and forming a vertical partition wall, wherein the permeability coefficient of the vertical partition wall is 1 multiplied by 10-8cm/s, the thickness of 19cm, the vertical barrier wall bottom to the water-resisting layer, block DNAPL pollution source migration diffusion, fix trichloroethylene;
S3, injecting the medicament in the embodiment 2 into a DNAPL polluted source region, and controlling the mass ratio of persulfate in the medicament to trichloroethylene in the DNAPL polluted source region to be 500: 1, degrading trichloroethylene in the solution;
Tests show that after 64 days of reaction, the removal rate of TCE in the DNAPL polluted source region reaches more than 98%.
Example 10
The embodiment provides a method for synchronously fixing and reducing trichloroethylene in soil and/or underground water, which comprises the following steps:
s1, mixing bentonite and water, wherein the mass ratio of the bentonite to the water is 2: 40, preparing slurry;
s2, filling the slurry obtained in the step S1 into a water-bearing layer at the downstream of the DNAPL polluted source region by adopting a high-pressure spraying mode, wherein the burial depth of the DNAPL polluted source region is 10-30 m, and forming a vertical partition wall, wherein the permeability coefficient of the vertical partition wall is 1 multiplied by 10-9cm/s and the thickness of 9cm, and is vertical to the bottom of the barrier wall to the water-resisting layer, so that the migration and diffusion of a DNAPL pollution source are blocked, and trichloroethylene is fixed;
S3, injecting the medicament in the embodiment 3 into a DNAPL polluted source region, and controlling the mass ratio of persulfate in the medicament to trichloroethylene in the DNAPL polluted source region to be 500: 1, degrading trichloroethylene in the solution;
Tests show that after 64 days of reaction, the removal rate of TCE in the DNAPL polluted source region reaches more than 98%.
Example 11
The embodiment provides a method for synchronously fixing and reducing trichloroethylene in soil and/or underground water, as shown in fig. 2, comprising the following steps:
s1, mixing bentonite and water, wherein the mass ratio of the bentonite to the water is 1.5: 55, preparing slurry;
S2, DNAPL pollution source region buried depth<10m, pouring the slurry obtained in the step S1 into an air-entrapping zone around the DNAPL polluted source region in a cofferdam mode, and forming a vertical barrier wall and a horizontal barrier wall around the DNAPL polluted source region in the air-entrapping zone, wherein the permeability coefficient of the vertical barrier wall is 1 x 10-7cm/s, thickness of 16cm, and permeability coefficient of 1 × 10-7cm/s, the thickness is 16cm, migration and diffusion of DNAPL pollution sources are blocked, and trichloroethylene is fixed;
s3, injecting the medicament in the embodiment 4 into a DNAPL polluted source region, and controlling the mass ratio of persulfate in the medicament to trichloroethylene in the DNAPL polluted source region to be 400: 3, degrading trichloroethylene in the solution;
tests show that after 64 days of reaction, the removal rate of TCE in the DNAPL polluted source region reaches more than 98%.
Example 12
The embodiment provides a method for synchronously fixing and reducing trichloroethylene in soil and/or underground water, which comprises the following steps:
s1, mixing bentonite and water, wherein the mass ratio of the bentonite to the water is 2: 50, preparing slurry;
S2, DNAPL pollution source region buried depth<10m, pouring the slurry obtained in the step S1 into an air-entrapping zone around the DNAPL polluted source region in a cofferdam mode, and forming a vertical barrier wall and a horizontal barrier wall around the DNAPL polluted source region in the air-entrapping zone, wherein the permeability coefficient of the vertical barrier wall is 1 x 10-8cm/s, thickness of 14cm, and permeability coefficient of 1 × 10-8cm/s and a thickness of 14cm, blocking migration and diffusion of DNAPL pollution sources, and fixing trichloroethylene;
S3, injecting the medicament in the embodiment 5 into a DNAPL polluted source region, and controlling the mass ratio of persulfate in the medicament to trichloroethylene in the DNAPL polluted source region to be 450: 2, degrading trichloroethylene in the solution;
Tests show that after 64 days of reaction, the removal rate of TCE in the DNAPL polluted source region reaches more than 98%.
Comparative example 1
this comparative example provides an agent for simultaneous fixation and reduction of trichloroethylene in soil and/or groundwater, the only difference being as in example 1: the bentonite in the comparative example is calcium bentonite, and is purchased from Zhang Jiakongtai Bentonite GmbH;
The medicament in the comparative example is applied to 10mg/L of anaerobic underground water containing TCE by simulating the application environment, and the specific application method is as follows: adding persulfate and water in the medicament into 10mg/L anaerobic underground water containing TCE, and adding calcium bentonite, so as to ensure that the mass ratio of the calcium bentonite and the persulfate in the medicament to the TCE in the anaerobic underground water containing TCE is 4000: 384: 2, after reacting for 8 days under the conditions of normal temperature, normal pressure and oscillation (250rpm), the removal rate of TCE in the anaerobic underground water containing TCE reaches 31 percent, and after reacting for 64 days, the removal rate of TCE in the anaerobic underground water containing TCE reaches 72 percent.
comparative example 2
This comparative example provides an agent for simultaneous fixation and reduction of trichloroethylene in soil and/or groundwater, the only difference being as in example 1: in the comparative example, the bentonite is sodium bentonite, and Na in the sodium bentonite+The content is 5 wt%, the total organic carbon content is 9mg/L, the pH value is 10.6, and the particle size is 150 mu m;
The medicament in the comparative example is applied to 10mg/L of anaerobic underground water containing TCE by simulating the application environment, and the specific application method is as follows: adding persulfate and water in the medicament into 10mg/L anaerobic underground water containing TCE, and then adding bentonite, so as to ensure that the mass ratio of the bentonite and the persulfate in the medicament to the TCE in the anaerobic underground water containing TCE is 4000: 384: 2, after reacting for 8 days under the conditions of normal temperature, normal pressure and oscillation (250rpm), the removal rate of TCE in the anaerobic underground water containing TCE reaches 40%, and after reacting for 64 days, the removal rate of TCE in the anaerobic underground water containing TCE reaches 81%.
Test example 1: application of bentonite coupled persulfate in reduction of trichloroethylene in underground water pollution source region
1. experimental materials and instruments: TCE: beijing chemical plant (purity is more than or equal to 99.5%); sodium persulfate: beijing chemical plant (analytical grade); potassium iodide: beijing chemical plant (analytical grade); sodium bicarbonate: beijing chemical plant (analytical grade); sodium chloride: beijing chemical plant (analytical grade); potassium sulfate: beijing chemical plant (analytical grade); magnesium sulfate: beijing chemical plant (analytical grade); calcium sulfate: beijing chemical plant (analytical grade); methanol: DIKMA (purity is more than or equal to 99.9%), Honeywell in USA (chromatographic purity); alternative standard mixtures: chem Service Inc. USA (2000. mu.g/mL in methanol); mixing 54 components of volatile organic compounds: ChemStavice, USA (2000. mu.g/mL in methanol); bentonite: national chemical group chemical reagents ltd (sodium-based); water for experiment: ultrapure water; helium gas: beijing Huayuan gas Co., Ltd. (purity 99.999%); gas chromatography-mass spectrometer: agilent, 6890/5973N, USA; headspace autosampler: agilent, G1888, usa; constant temperature cultivation shaking table: fuma, QYC-2102C, china; desk-top low-speed centrifuge: hunan instrument, L550, china; a desk-top high-speed centrifuge: jingli, LG16-W (I), China; ultraviolet spectrophotometer: shimadzu, UV-1800, Japan; anaerobic box glove box: COY, 14500 cov Drive, usa; a pH meter: sartorius, PB-10, germany; oxidation-reduction potentiometer: clean, ORP30, usa; a micro sample injection needle: hamilton, 10, 25, 100, 1000 μ L, switzerland;
2. experiment:
(1) bentonite and persulfate cut short-term performance of chlorotrifluoroethylene in groundwater:
0.4g of bentonite is respectively put into a series of 20mL of brown glass bottles with screw openings and covers (lined with polytetrafluoroethylene/silica gel spacers); adding 20mL of oxygen-driving ultrapure water; adding 100 mu L of 476g/L of sodium persulfate mother liquor to ensure that the initial concentration of persulfate is 1.9 g/L; adding 5 mu L of 40.0g/L TCE mother solution to ensure that the initial concentration of TCE is 10 mg/L; placing the glass bottle in a constant temperature oscillator (250rpm, 25 + -1.0 deg.C), taking out periodically for 8 days, and centrifuging (3000rpm, 20 min); taking supernatant to detect TCE, 1-dichloroethylene, 1, 2-dichloroethylene, chloroethylene and pH; each set of experiments was set to 3 replicates;
Short-term effects of TCE removal induced by the agents of example 1 are shown in FIG. 3, and a linear fit on the kinetics is shownthe short-term TCE removal effect of the single bentonite is shown in FIG. 3, the TCE dechlorinated product change caused by the agent in example 1 is shown in Table 1, and the pH change caused by the agent in example 1 is shown in FIG. 5. After 5 days of reaction, the removal rate of TCE by single bentonite is only 3%, which indicates that the adsorption effect of bentonite is weak (figure 3). At room temperature and pressure, only a small amount of TCE was removed by sodium persulfate alone. When the reaction is carried out for 8 days, the removal rate of TCE by combining bentonite and persulfate reaches 56 percent, which shows that the persulfate can effectively oxidize and degrade the TCE (figure 3). The combined oxidative degradation of the bentonite and the persulfate to TCE accords with the quasi-first-order reaction kinetics, and the degradation rate constant is 0.094 (d)-1) (FIG. 4). On the other hand, when bentonite and persulfate were used in combination, 3 dechlorinated products such as 1, 1-dichloroethylene, 1, 2-dichloroethylene, and vinyl chloride were not detected (Table 1), and it was confirmed that TCE was completely mineralized. In yet another aspect, in a bentonite and persulfate reaction system, the pH remained at 10.2 after 8 days at an initial pH of 10.5 (fig. 5). Therefore, the change of the pH of the system along with the reaction time is not large, which shows that the bentonite can ensure that the system is in a stable alkaline environment, and is favorable for realizing the alkali activation of persulfate.
TABLE 1 changes in TCE dechlorinated products caused in example 1
Note: ND means not detected.
(2) Bentonite and persulfate cut the long-term performance of trichloroethylene in groundwater:
0.4g of bentonite is respectively put into a series of 20mL of brown glass bottles with screw openings and covers (lined with polytetrafluoroethylene/silica gel spacers); adding 20mL of oxygen-driving ultrapure water; adding 100 mu L of 476g/L of sodium persulfate mother liquor to ensure that the initial concentration of persulfate is 1.9 g/L; adding 5 mu L of 40.0g/L TCE mother solution to ensure that the initial concentration of TCE is 10 mg/L; placing the glass bottle in a constant temperature oscillator (250rpm, 25 + -1.0 deg.C), taking out periodically for 64 days, and centrifuging (3000rpm, 20 min); taking supernatant to detect TCE and S2O8 2-pH and Eh; each set of experiments was set to 3 replicates.
Practice ofThe long-term TCE removal effect, the change in Eh reaction system, the change in pH reaction system, and the change in the residual amount of persulfate caused by the agent in example 1 are shown in fig. 6, 7, 8, and 9, respectively. The agent of example 1 achieved 100% removal of TCE with the extended reaction time of 64 days (figure 6). The pH of the system gradually decreased, but the amplitude was not large, from the initial 10.5 to 9.3 (at 64 days) (FIG. 7). Although persulfate salts are accompanied by the formation of H in the oxidative degradation of TCE+(equation 1), however, bentonite exhibits a strong buffering effect, so that the pH of the system does not change much. The Eh of the system gradually increases from the initial 60.1mV to 225.6mV in the first 15 days; after 15 days, the Eh is high and the Eh is low, and the value is 174.0-225.7 mV (FIG. 8). The rise of Eh further proves that the bentonite can maintain the alkaline and oxidizing environment of the system, and promote persulfate to be activated to generate SO4 ·-further cause SO4 ·-Is converted into OH. TCE was completely removed after 64 days (fig. 6), however, a large amount of persulfate remained in the system (more than 90% residual) (fig. 9). The system is presumed to still have the capability of oxidatively degrading TCE by combining the pH of the system, the Eh and the residual amount of persulfate.
SO4 ·-+C2HCl3+4H2O→2CO2+9H++3Cl-+6SO4 2- (1)
it should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications therefrom are within the scope of the invention.
Claims (10)
1. The medicament for synchronously fixing and reducing the trichloroethylene in the soil and/or underground water comprises bentonite, persulfate and water, wherein the mass ratio of the bentonite to the persulfate is 3000-5000: 300-500, wherein the mass ratio of the bentonite to the water is 1-2: 40-60;
The above-mentionedThe bentonite is sodium bentonite, and Na in the sodium bentonite+The content is 2 wt% -4 wt%, the total organic carbon content is 10-15 mg/L, the pH is 10.0-11.0, and the particle size is 75-180 mu m.
2. The medicament according to claim 1, wherein the mass ratio of the bentonite to the persulfate is 3800-4200: 350-400, wherein the mass ratio of the bentonite to the water is 1-2: 45-55;
the bentonite is sodium bentonite, and Na in the sodium bentonite+The content is 2.5 wt% -3 wt%, the total organic carbon content is 13-14 mg/L, the pH is 10.5-10.8, and the particle size is 120-150 mu m.
3. The agent according to claim 1 or 2, wherein the persulfate is potassium persulfate and/or sodium persulfate, and the purity of the persulfate is 98 wt% or more.
4. the agent according to claim 3, wherein the persulfate is potassium persulfate and sodium persulfate, and the mass ratio of the potassium persulfate to the sodium persulfate is 1: (4-5).
5. A method for synchronously fixing and reducing the content of the trichloroethylene in the soil and/or the underground water by using the agent of any one of claims 1 to 4, comprising the following steps:
s1, mixing bentonite and water to prepare slurry;
S2, pouring the slurry obtained in the step S1 into soil and underground water media around the DNAPL pollution source region by adopting a cofferdam or high-pressure spraying mode to form a vertical barrier wall and/or a horizontal barrier wall, blocking migration and diffusion of the DNAPL pollution source, and fixing trichloroethylene;
S3, injecting the medicament into a DNAPL polluted source region, and degrading trichloroethylene in the DNAPL polluted source region.
6. The method according to claim 5, wherein in the step S1, the mass ratio of the bentonite to the water is 1-2: 40-60.
7. The method as claimed in claim 5 or 6, wherein the permeability coefficient of the vertical barrier wall is ≦ 1 × 10 in step S2-7cm/s and the thickness is 9-19 cm;
The permeability coefficient of the horizontal barrier wall is less than or equal to 1 multiplied by 10-7cm/s and a thickness of 9-19 cm.
8. The method according to claim 5 or 6, wherein in step S3, the mass ratio of the persulfate in the medicament to the trichloroethylene in the DNAPL contaminated source region is 300-500: 1 to 5.
9. The method according to claim 5 or 6, wherein in step S2, when the DNAPL contamination source region burial depth is less than 10m, the method is implemented by using a cofferdam mode; or the like, or, alternatively,
in the step S2, when the buried depth of the DNAPL polluted source region is 10-30 m, a high-pressure injection mode is adopted.
10. The method of claim 5 or 6, wherein the slurry of step S1 is poured into an air-entrained band around the DNAPL contaminated source region, forming vertical and horizontal barriers at the air-entrained band and around the DNAPL contaminated source region; or the like, or, alternatively,
and (4) pouring the slurry obtained in the step S1 into an aquifer downstream of the DNAPL polluted source region to form a vertical barrier wall.
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