CN109909281B - medicament and method for synchronously fixing and reducing trichloroethylene in soil and/or underground water - Google Patents

Abstract

The invention discloses a medicament and a method for synchronously fixing and reducing trichlorethylene in soil and/or underground water. The agent uses bentonite, persulfate and water in a specific ratio. At the same time, the bentonite uses sodium-based bentonite with specific properties. Using this specific performance of sodium-based bentonite can effectively activate persulfate to produce more strong oxidation. SO ₄ ^‑ and OH, using it to completely oxidize trichlorethylene, without producing more toxic dechlorination products such as 1,1‑dichloroethylene, 1,2‑dichloroethylene or vinyl chloride, thereby increasing DNAPL pollution sources TCE removal rate in the zone. At the same time, the sodium-based bentonite with this specific performance can maintain the pH stability of the reaction system during the process of removing trichlorethylene, so no additional addition of alkaline reagents and adjustment of the pH value are required during the reaction process. After testing, the removal rate of TCE reaches 51%-56% within 8 days and 93%-100% within 64 days.

Description

A medicament for simultaneously fixing and reducing trichlorethylene in soil and/or groundwater and method

technical field

The invention belongs to the technical field of soil and groundwater pollution risk management and control, treatment and restoration, and specifically relates to a medicament and method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, and in particular to a bentonite-coupled persulfate synchronously fixing and reducing soil And/or groundwater heavy non-aqueous phase liquid (dense non-aqueous phase liquid, DNAPL) pollution sources and methods of trichlorethylene.

Background technique

Trichloroethylene (TCE) is one of the volatile chlorinated organic compounds ubiquitous in soil and groundwater all over the world, and its pollution has become a worldwide environmental and health problem. According to incomplete statistics, high concentrations of TCE have been detected in the soil and groundwater of China, the United Kingdom, Japan, the United States, Belgium and other countries. TCE in soil and groundwater mainly comes from the leakage of storage tanks of organic solvents, dry cleaning agents and anesthetics or the waste liquid discharged without effective treatment.

TCE was listed as a "priority control compound" by the United States as early as 1976, and it was also listed as a priority pollutant for environmental monitoring and control in China by my country. It has potential carcinogenic, teratogenic, and mutagenic properties. It is a heavy non-aqueous phase liquid (dense non-aqueous phase liquid, DNAPL) with a density higher than water, with a small solubility in water (1100mg/L), higher density than water, and low viscosity. TCE migrates quickly in the soil and vadose zone, and stays in the medium gap in the form of droplets, while the part entering the groundwater will stay at the bottom of the aquifer, forming a DNAPL pollution source area, and gradually dissolves into the water as the groundwater migrates , causing secondary pollution. TCE in the DNAPL pollution source area will become a continuous and persistent source of groundwater pollution.

At present, the in-situ risk control and remediation technologies of TCE in soil and groundwater DNAPL pollution source areas mainly include barrier technology and chemical reduction technology. Among them, the barrier technology mainly relies on non-permeable materials such as clay, bentonite, cement, and fly ash to build a barrier wall to block the migration and diffusion of pollution sources to the downstream. Barrier technology can only cut off the exposure route and limit the migration of pollution plumes, but it cannot reduce the concentration of pollutants and there is a risk of pollutant leakage. In most cases, barrier technology is only used as a temporary control method in the initial stage of groundwater pollution control.

The chemical reduction technology mainly relies on the principle of zero-valent iron as an electron donor to provide electrons, and TCE as an electron acceptor to accept electrons to undergo hydrogenolysis or dechlorination. The experimental results of the granular iron column show that at the initial stage of operation (≤20 pore volumes), zero-valent iron can completely remove TCE, but when the operation reaches 90 pore volumes, the zero-valent iron is passivated, and the removal rate of TCE drops to 60%. Accompanied by cis-1,2-dichloroethylene, vinyl chloride and other chlorinated by-products. In addition, granular iron is easily oxidized by oxygen to form FeOOH or Fe(OH) ₃ , which hinders the contact of pollutants and blocks its pores, thereby reducing permeability and electrical conductivity.

In practical application, the above-mentioned technology has large pH changes, low TCE removal rate and easy generation of 1,1 - Dichloroethylene, 1,2-dichloroethylene or vinyl chloride, defects with high technical requirements for barrier wall permeability coefficient and service life.

Contents of the invention

For this reason, what the present invention is to solve is that there are large pH changes, low TCE removal rate and easy generation of 1,1-dichloride in the prior art in the process of fixing and reducing trichlorethylene in soil and groundwater heavy non-aqueous liquid pollution source areas. Ethylene, 1,2-dichloroethylene or vinyl chloride, barrier wall permeability coefficient and high service life technical requirements defects, and then provide a simultaneous fixation and reduction of trichlorethylene in soil and/or groundwater agent and method.

In order to solve the problems of the technologies described above, the technical scheme adopted in the present invention is as follows:

The medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater provided by the present invention includes bentonite, persulfate and water, and the mass ratio of bentonite and persulfate is 3000～5000:300～500, so The mass ratio of bentonite to water is 1～2:40～60;

The bentonite is sodium-based bentonite, the Na ⁺ content in the sodium-based bentonite is 2wt%-4wt%, the total organic carbon content is 10-15mg/L, the pH is 10.0-11.0, and the particle size is 75-180μm.

Further, the mass ratio of bentonite to persulfate is 3800-4200:350-400, and the mass ratio of bentonite to water is 1-2:45-55;

The bentonite is sodium-based bentonite, the Na ⁺ content in the sodium-based bentonite is 2.5wt%-3wt%, the total organic carbon content is 13-14mg/L, the pH is 10.3-10.8, and the particle size is 120-150μm.

Further, the persulfate is potassium persulfate and/or sodium persulfate, and the purity of the persulfate is ≥98wt%.

Further, the persulfate is potassium persulfate and sodium persulfate, and the mass ratio of potassium persulfate and sodium persulfate is 1:(4-5).

In addition, it should be noted that the pH test method of sodium bentonite is as follows: add ultrapure water to sodium bentonite, and control the mass ratio of sodium bentonite to ultrapure water to 1:50, and stir it with a stirrer for over 24 hours , Determination of the pH value of the water, the pH value is the pH of the sodium bentonite.

The preparation method of the above-mentioned medicament is as follows: weighing bentonite, persulfate and water according to the mass ratio, and stirring evenly at room temperature, so that the bentonite is in a suspended state, and the medicament is prepared.

In addition, the present invention also provides a method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater by using the above-mentioned medicament, comprising the following steps:

S1, mixing bentonite with water to make mud;

S2. Use cofferdams or high-pressure injection methods to pour the mud in step S1 into the soil and groundwater medium around the DNAPL pollution source area to form a vertical barrier wall and/or a horizontal barrier wall to block the migration and diffusion of DNAPL pollution sources and fix trichloride. vinyl;

S3. Inject the medicament into the DNAPL pollution source area to degrade the trichlorethylene therein.

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 ≤1×10 ^-7 cm/s, and the thickness is 9-19 cm;

The permeability coefficient of the horizontal barrier wall is ≤1×10 ^-7 cm/s, and the thickness is 9-19cm.

Further, in step S3, the mass ratio of persulfate in the medicament to trichlorethylene in the DNAPL pollution source area is 300-500:1-5.

Further, in step S2, when the burial depth of the DNAPL pollution source area is <10m, it is implemented in the form of a cofferdam; or,

In step S2, when the burial depth of the DNAPL pollution source area is 10-30 m, a high-pressure injection method is used.

Further, pouring the mud in step S1 into the vadose zone around the DNAPL pollution source area, forming a vertical barrier wall and a horizontal barrier wall in the vadose zone and around the DNAPL pollution source area; or,

The mud in step S1 is poured into the aquifer downstream of the DNAPL pollution source area to form a vertical barrier.

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

(1) The medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater provided by the present invention adopts bentonite, persulfate and water to cooperate under a specific proportion, and simultaneously bentonite adopts sodium-based bentonite with specific properties , using this specific performance of sodium bentonite can effectively activate persulfate to produce more strong oxidizing SO ₄ ^·- and ·OH, and use SO ₄ ^·- and ·OH to completely oxidize trichlorethylene without generating 1,1 - More toxic dechlorination products such as dichloroethylene, 1,2-dichloroethylene or vinyl chloride, thereby improving the removal rate of TCE in DNAPL pollution source areas. At the same time, the sodium-based bentonite with this specific performance can maintain the pH stability of the reaction system during the process of removing trichlorethylene, so no additional addition of alkaline reagents and adjustment of the pH value are required during the reaction process. After testing, the removal rate of TCE reached 51%-56% within 8 days, and 93%-100% within 64 days, and no more toxic dechlorination products such as 1,2-dichloroethylene and vinyl chloride were produced during the reaction process. Small secondary pollution, low risk to the ecological environment, high safety, and significant advantages in terms of technology and environmental protection.

(2) The medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater provided by the present invention adopts sodium bentonite, ^and optimizes Na content, total organic carbon content, pH and particle size in sodium bentonite, which can Improve the thixotropic plasticity, expansibility and cohesiveness of sodium-based bentonite, so that the sodium-based bentonite can effectively fill the gaps in soil, vadose zone and groundwater medium, and finally effectively block the migration of trichlorethylene for a long time with diffusion.

(3) the medicament of synchronously fixing and reducing trichlorethylene in soil and/or groundwater provided by the present invention, persulfate is potassium persulfate and sodium persulfate, and the mass ratio of potassium persulfate and sodium persulfate is 1:( 4-5), through the use of different types of persulfates in specific proportions, it helps to improve the removal rate of TCE in the DNAPL pollution source area.

(4) The method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater provided by the present invention first mixes bentonite with water to make mud; then adopts a cofferdam or high-pressure injection mode to pour the mud into the DNAPL pollution source In the soil and groundwater medium around the area, a vertical barrier wall and/or a horizontal barrier wall are formed to block the migration and diffusion of DNAPL pollution sources and fix trichlorethylene; finally inject the agent into the DNAPL pollution source area, and the bentonite in the agent fills the gaps in the soil and groundwater medium In the interior, persulfate is dispersed in the pollution source area by gravity and capillary phenomenon, forming a low-permeability reaction area, prolonging the residence time of trichlorethylene in the reaction area to completely oxidize and degrade trichlorethylene.

(5) The method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater provided by the present invention forms mud by mixing bentonite and water in a specific mass ratio, and this mud is suitable for pouring into soil and groundwater around the DNAPL pollution source area In the medium, a vertical barrier wall and/or a horizontal barrier wall are formed; by optimizing the permeability coefficient and thickness of the vertical barrier wall and/or horizontal barrier wall, the migration and diffusion of trichlorethylene are blocked; by limiting the persulfate and DNAPL in the medicament The mass ratio of trichlorethylene in the pollution source area can improve the removal rate of TCE in the DNAPL pollution source area.

(6) The method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater provided by the present invention does not require heating, ultraviolet light irradiation, transition metal ions and hydrogen peroxide, etc., and can be carried out under normal temperature and pressure, and the reaction system is simple , mild reaction conditions, low operation and maintenance management costs. By using the method, the technical requirements on the thickness and service life (at least 10 years) of the existing barrier wall can be significantly reduced, thereby reducing the construction cost of the barrier wall. At the same time, it can realize in-situ fixation, treatment and repair of soil and groundwater, especially deep groundwater pollutants, as well as emergency pollution treatment, and has a wide range of applications.

Description of drawings

In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the specific embodiments or prior art. Obviously, the accompanying drawings in the following description The drawings show some implementations of the present invention, and those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the schematic diagram of the structure and the layout state of trichlorethylene in the groundwater DNAPL pollution source area of the synchronous in-situ fixation and reduction of groundwater DNAPL pollution source area in combination with bentonite and persulfate in the embodiment of the present invention;

Fig. 2 is the schematic diagram of the structure and layout state diagram of trichlorethylene in the soil DNAPL pollution source area of Example 4 of the present invention combined with bentonite and persulfate synchronously in situ to fix and reduce;

Fig. 3 is the short-term variation figure of the TCE removal rate that causes in the embodiment of the present invention bentonite and persulfate combined with reaction time;

Fig. 4 is the linear fitting diagram of the kinetics of TCE oxidative degradation caused by the combination of bentonite and persulfate in the embodiment of the present invention;

Fig. 5 is the short-term variation figure of the pH of the reaction system caused by the joint use of bentonite and persulfate in the embodiment of the present invention along with the reaction time;

Fig. 6 is the long-term variation figure of the TCE removal rate that causes in the embodiment of the present invention bentonite and persulfate combined with reaction time;

Fig. 7 is the long-term variation diagram of the pH of the reaction system caused by the combination of bentonite and persulfate in the embodiment of the present invention with the reaction time;

Fig. 8 is the long-term change diagram of the reaction system Eh caused by the combination of bentonite and persulfate in the embodiment of the present invention with the reaction time;

Fig. 9 is a graph showing the long-term change of the residual amount of S ₂ O ₈ ^2- in the reaction system with the reaction time caused by the combination of bentonite and persulfate in the embodiment of the present invention;

Fig. 10 is the SEM (5000 times) morphology figure of bentonite in the embodiment of the present invention;

Fig. 11 is the EDS analysis spectrogram of bentonite in the embodiment of the present invention.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Apparently, the described embodiments are some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The term "bentonite" in the present invention is a hydrous clay mineral with montmorillonite as the main mineral component. Montmorillonite belongs to the 2:1 crystal structure and is composed of two silicon-oxygen tetrahedrons sandwiching a layer of aluminum-oxygen octahedron. The main chemical The composition is silicon dioxide, aluminum oxide and water, and also contains elements such as iron, magnesium, calcium, sodium, potassium, etc., with a hardness of 1-2 and a density of 2-3g/cm ³ . It is yellow-green, yellow-white, gray, white, etc. Color, after adding water, the volume expands several times to 20-30 times. There are certain cations in the layered structure formed by the montmorillonite unit cell, such as Cu ²⁺ , Mg ²⁺ , Na ⁺ , K ⁺ . The interaction between these cations and the montmorillonite unit cell is very unstable, and they are easily exchanged by other cations.

In the present invention, the term "heavy non-aqueous phase liquid (dense non aqueous phase liquid, DNAPL)" refers to the general term of all liquid pollutants that are insoluble in water and have a higher density than water in soil and groundwater, such as coal tar, woodgrain Oils, trichloroethylene and tetrachloroethylene, have lower solubility and higher interfacial tension.

The term "trichloroethylene (TCE)" in the present invention is a flammable and volatile liquid with a molecular formula of C ₂ HCl ₃ , a relative molecular weight of 131.39, a boiling point of 87.1°C, a melting point of -86°C, a colorless odor similar to chloroform, and is difficult to dissolve. In water, easily soluble in ethanol, ether, etc., and miscible in most organic solvents, it is one of the representative pollutants of DNAPL.

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 there is no conflict with each other.

Example 1

The present embodiment provides a medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, the medicament includes 4000g of bentonite, 384g of persulfate and water, and the mass ratio of bentonite to water is 1:50; wherein , the bentonite is sodium-based bentonite, the Na ⁺ content in the sodium-based bentonite is 2.6wt%, the total organic carbon content is 13.7mg/L, the pH is 10.5, the particle size is 150 μm, and the persulfate is sodium persulfate;

The microscopic characterization of bentonite in this embodiment is as shown in Figure 10 and Figure 11, as can be seen from Figure 10: the surface of bentonite is an irregular polygon, smooth, with edges and corners; as can be seen from Figure 11: it is mainly composed of oxygen, silicon, aluminum It is composed of and contains a small amount of sodium, potassium, iron, calcium, magnesium, etc., and conforms to the 2:1 crystal structure composed of silicon-oxygen tetrahedron sandwiching a layer of aluminum-oxygen octahedron of montmorillonite;

Simulate the application environment, apply the medicament in this embodiment to 10mg/L anaerobic groundwater containing TCE, the specific application method is as follows: add persulfate and water in the medicament to 10mg/L anaerobic groundwater containing TCE Add bentonite to oxygenated groundwater to ensure that the mass ratio of bentonite and persulfate in the agent to TCE in anaerobic groundwater containing TCE is 4000:384:2. React for 8 days under normal temperature, normal pressure, and vibration (250rpm) conditions. , the removal rate of TCE in anaerobic groundwater containing TCE reached 56%, and after 64 days of reaction, the removal rate of TCE in anaerobic groundwater containing TCE reached 100%.

Example 2

The present embodiment provides a medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, the medicament includes 4000g of bentonite, 384g of persulfate and water, and the mass ratio of bentonite to water is 1:50; wherein , the bentonite is sodium-based bentonite, the Na ⁺ content in the sodium-based bentonite is 2.6wt%, the total organic carbon content is 13.7mg/L, the pH is 10.6, the particle size is 120 μm, and the persulfate is potassium persulfate;

Simulate the application environment, apply the medicament in this embodiment to 10 mg/kg of TCE-containing soil, the specific application method is as follows: add the persulfate in the medicament to 10 mg/kg of TCE-containing soil, and then add the medicament Bentonite and water in the medicament, to ensure that the mass ratio of bentonite, persulfate and TCE-containing soil in the medicament is 4000:384:2, after reacting for 8 days under normal temperature, normal pressure, and oscillation (250rpm) conditions, the TCE-containing The removal rate of TCE in the anaerobic groundwater reaches 54%, and after 64 days of reaction, the removal rate of TCE in the anaerobic groundwater containing TCE reaches 97%.

Example 3

The present embodiment provides a medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, the medicament includes 3800g of bentonite, 400g of persulfate and water, and the mass ratio of bentonite to water is 1:55; wherein , the bentonite is sodium-based bentonite, the Na content in the sodium ^- based bentonite is 2.5wt%, the total organic carbon content is 14mg/L, the pH is 10.8, the particle size is 130 μm, and the persulfate is sodium persulfate;

Simulate the application environment, apply the medicament in this embodiment to 10mg/L anaerobic groundwater containing TCE, the specific application method is as follows: add persulfate and water in the medicament to 10mg/L anaerobic groundwater containing TCE Add bentonite to oxygenated groundwater to ensure that the mass ratio of bentonite and persulfate in the agent to TCE in anaerobic groundwater containing TCE is 3800:400:1. React for 8 days under normal temperature, normal pressure, and vibration (250rpm) conditions. , the removal rate of TCE in anaerobic groundwater containing TCE reaches 55%, and after 64 days of reaction, the removal rate of TCE in anaerobic groundwater containing TCE reaches 99%.

Example 4

The present embodiment provides a medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, the medicament includes 4200g of bentonite, 350g of persulfate and water, and the mass ratio of bentonite to water is 2:45; wherein , the bentonite is sodium-based bentonite, the Na content in the sodium ^- based bentonite is 3wt%, the total organic carbon content is 13mg/L, the pH is 10.5, the particle size is 140 μm, and the persulfate is potassium persulfate;

Simulate the application environment, apply the medicament in this embodiment to 10mg/L anaerobic groundwater containing TCE, the specific application method is as follows: add persulfate and water in the medicament to 10mg/L anaerobic groundwater containing TCE Add bentonite to oxygenated groundwater to ensure that the mass ratio of bentonite, persulfate and TCE in the anaerobic groundwater containing TCE is 4200:350:5. After reacting for 8 days under normal temperature, normal pressure and oscillation (250rpm) conditions , the removal rate of TCE in anaerobic groundwater containing TCE reached 56.7%, and after 64 days of reaction, the removal rate of TCE in anaerobic groundwater containing TCE reached 99.8%.

Example 5

The present embodiment provides a medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, the medicament includes 3000g of bentonite, 500g of persulfate and water, and the mass ratio of bentonite to water is 1:60; wherein , the bentonite is sodium-based bentonite, the Na content in the sodium ^- based bentonite is 4wt%, the total organic carbon content is 10mg/L, the pH is 11, the particle size is 75 μm, and the persulfate is sodium persulfate;

Simulate the application environment, apply the medicament in this embodiment to 10mg/L anaerobic groundwater containing TCE, the specific application method is as follows: add persulfate and water in the medicament to 10mg/L anaerobic groundwater containing TCE Add bentonite to oxygenated groundwater to ensure that the mass ratio of bentonite and persulfate in the agent to TCE in anaerobic groundwater containing TCE is 3000:500:2. React for 8 days under normal temperature, normal pressure, and vibration (250rpm) conditions. , the removal rate of TCE in anaerobic groundwater containing TCE reached 52%, and after 64 days of reaction, the removal rate of TCE in anaerobic groundwater containing TCE reached 95%.

Example 6

The present embodiment provides a medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, the medicament includes 5000g of bentonite, 300g of persulfate and water, and the mass ratio of bentonite to water is 2:40; wherein , the bentonite is sodium-based bentonite, the Na content in the sodium ^- based bentonite is 2wt%, the total organic carbon content is 15 mg/L, the pH is 10, the particle size is 180 μm, and the persulfate is potassium persulfate;

Simulate the application environment, apply the medicament in this embodiment to 10mg/L anaerobic groundwater containing TCE, the specific application method is as follows: add persulfate and water in the medicament to 10mg/L anaerobic groundwater containing TCE Add bentonite to oxygenated groundwater to ensure that the mass ratio of bentonite and persulfate in the agent to TCE in anaerobic groundwater containing TCE is 5000:300:2. React for 8 days under normal temperature, normal pressure, and vibration (250rpm) conditions. , the removal rate of TCE in anaerobic groundwater containing TCE reached 51%, and after 64 days of reaction, the removal rate of TCE in anaerobic groundwater containing TCE reached 93%.

Example 7

This embodiment provides a kind of medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, with embodiment 2, only difference is: in the present embodiment, persulfate is potassium persulfate and sodium persulfate The mixture, wherein the mass ratio of potassium persulfate to sodium persulfate is 1:4.5;

According to the method test in embodiment 2, after testing, after reacting 8 days under normal temperature, normal pressure, vibration (250rpm) condition, the removal rate of TCE in the anaerobic groundwater containing TCE reaches 56%, after reacting for 64 days, the anaerobic groundwater containing TCE removes 56%. The removal rate of TCE in oxygen groundwater reaches 99%.

Example 8

The present embodiment provides a method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, as shown in Figure 1, comprising the steps:

S1, mix bentonite and water, the mass ratio of bentonite and water is 1.5:50, and make mud;

S2. The burial depth of the DNAPL pollution source area is 10-30 m. The mud in step S1 is poured into the aquifer downstream of the DNAPL pollution source area by means of high-pressure jetting to form a vertical barrier wall. The permeability coefficient of the vertical barrier wall is 1×10 ^{- 7} cm/s, thickness 16cm, from the bottom of the vertical barrier wall to the water barrier, blocking the migration and diffusion of DNAPL pollution sources, and immobilizing trichlorethylene;

S3. Inject the medicament in Example 1 into the DNAPL pollution source area, control the mass ratio of persulfate in the medicament to trichlorethylene in the DNAPL pollution source area to be 300:5, and degrade the trichlorethylene therein;

After testing, after 64 days of reaction, the removal rate of TCE in the DNAPL pollution source area reached over 98%.

Example 9

This embodiment provides a method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, comprising the steps of:

S1, mix bentonite and water, the mass ratio of bentonite and water is 1:60, and make mud;

S2. The burial depth of the DNAPL pollution source area is 10-30 m. The mud in step S1 is poured into the aquifer downstream of the DNAPL pollution source area by means of high-pressure jetting to form a vertical barrier wall. The permeability coefficient of the vertical barrier wall is 1×10 ^{- 8} cm/s, thickness 19cm, from the bottom of the vertical barrier wall to the water barrier, blocking the migration and diffusion of DNAPL pollution sources, and immobilizing trichlorethylene;

S3. Inject the medicament in Example 2 into the DNAPL pollution source area, control the mass ratio of the persulfate in the medicament to the trichlorethylene in the DNAPL pollution source area to be 500:1, and degrade the trichlorethylene therein;

After testing, after 64 days of reaction, the removal rate of TCE in the DNAPL pollution source area reached over 98%.

Example 10

This embodiment provides a method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, comprising the steps of:

S1, mix bentonite with water, the mass ratio of bentonite to water is 2:40, and make mud;

S2. The burial depth of the DNAPL pollution source area is 10-30 m. The mud in step S1 is poured into the aquifer downstream of the DNAPL pollution source area by means of high-pressure jetting to form a vertical barrier wall. The permeability coefficient of the vertical barrier wall is 1×10 ^{- 9} cm/s, 9cm thick, from the bottom of the vertical barrier wall to the water barrier, blocking the migration and diffusion of DNAPL pollution sources, and immobilizing trichlorethylene;

S3. Inject the medicament in Example 3 into the DNAPL pollution source area, control the mass ratio of the persulfate in the medicament to the trichlorethylene in the DNAPL pollution source area to be 500:1, and degrade the trichlorethylene therein;

After testing, after 64 days of reaction, the removal rate of TCE in the DNAPL pollution source area reached over 98%.

Example 11

The present embodiment provides a method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, as shown in Figure 2, comprising the steps:

S1, mix bentonite and water, the mass ratio of bentonite and water is 1.5:55, and make mud;

S2. The burial depth of the DNAPL pollution source area is <10m, and the mud in step S1 is poured into the vadose zone around the DNAPL pollution source area by means of a cofferdam to form a vertical barrier wall and The horizontal barrier wall, the permeability coefficient of the vertical barrier wall is 1×10 ^-7 cm/s, and the thickness is 16cm. The permeability coefficient of the horizontal barrier wall is 1×10 ^-7 cm/s, and the thickness is 16cm, which blocks the migration and diffusion of DNAPL pollution sources. fixed trichlorethylene;

S3. Inject the medicament in Example 4 into the DNAPL pollution source area, control the mass ratio of the persulfate in the medicament to the trichlorethylene in the DNAPL pollution source area to be 400:3, and degrade the trichlorethylene therein;

After testing, after 64 days of reaction, the removal rate of TCE in the DNAPL pollution source area reached over 98%.

Example 12

This embodiment provides a method for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, comprising the steps of:

S1, mix bentonite and water, the mass ratio of bentonite and water is 2:50, and make mud;

S2. The burial depth of the DNAPL pollution source area is <10m, and the mud in step S1 is poured into the vadose zone around the DNAPL pollution source area by means of a cofferdam to form a vertical barrier wall and The horizontal barrier wall, the vertical barrier wall has a permeability coefficient of 1×10 ^-8 cm/s and a thickness of 14cm, and the horizontal barrier wall has a permeability coefficient of 1×10 ^-8 cm/s and a thickness of 14cm, which can block the migration and diffusion of DNAPL pollution sources, fixed trichlorethylene;

S3. Inject the medicament in Example 5 into the DNAPL pollution source area, control the mass ratio of the persulfate in the medicament to the trichlorethylene in the DNAPL pollution source area to be 450:2, and degrade the trichlorethylene therein;

After testing, after 64 days of reaction, the removal rate of TCE in the DNAPL pollution source area reached over 98%.

Comparative example 1

This comparative example provides a medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, the same as in Example 1, the only difference is that the bentonite in this comparative example is calcium-based bentonite, purchased from Zhangjiakou Hengtai bentonite limited liability company;

Simulate the application environment, apply the medicament in this comparative example to the anaerobic groundwater containing TCE at 10mg/L, the specific application method is as follows: add the persulfate and water in the medicament to the anaerobic groundwater containing TCE at 10mg/L Add calcium-based bentonite to oxygenated groundwater to ensure that the mass ratio of calcium-based bentonite and persulfate in the agent to TCE in anaerobic groundwater containing TCE is 4000:384:2. After 8 days of reaction, the removal rate of TCE in the anaerobic groundwater containing TCE reached 31%, and after 64 days of reaction, the removal rate of TCE in the anaerobic groundwater containing TCE reached 72%.

Comparative example 2

This comparative example provides a kind of medicament for synchronously fixing and reducing trichlorethylene in soil and/or groundwater, with embodiment 1, only difference is: in this comparative example, bentonite is sodium-based bentonite, Na in sodium ^- based bentonite The content is 5wt%, the total organic carbon content is 9mg/L, the pH is 10.6, and the particle size is 150μm;

Simulate the application environment, apply the medicament in this comparative example to the anaerobic groundwater containing TCE at 10mg/L, the specific application method is as follows: add the persulfate and water in the medicament to the anaerobic groundwater containing TCE at 10mg/L Add bentonite to oxygenated groundwater to ensure that the mass ratio of bentonite and persulfate in the agent to TCE in anaerobic groundwater containing TCE is 4000:384:2. React for 8 days under normal temperature, normal pressure, and vibration (250rpm) conditions. , the removal rate of TCE in anaerobic groundwater containing TCE reached 40%, and after 64 days of reaction, the removal rate of TCE in anaerobic groundwater containing TCE reached 81%.

Test Example 1: Application of bentonite coupled with persulfate to reduce trichlorethylene in groundwater pollution source areas

1. Experimental materials and instruments: TCE: Beijing Chemical Plant (purity ≥ 99.5%); Sodium persulfate: Beijing Chemical Plant (analytical pure); Potassium iodide: Beijing Chemical Plant (analytical pure); Sodium bicarbonate: Beijing Chemical Plant (analytically pure); Sodium chloride: Beijing Chemical Plant (analytical pure); Potassium sulfate: Beijing Chemical Plant (analytical pure); Magnesium sulfate: Beijing Chemical Plant (analytical pure); Calcium sulfate: Beijing Chemical Plant (analytical pure); Methanol: DIKMA Company (purity≥99.9%), American Honeywell Company (chromatographically pure); alternative standard mixture: American Chem Service Company (2000 μg/mL in methanol); 54 component volatile organic compound standard: American ChemService Company (2000 μg/mL in methanol) methanol); bentonite: Sinopharm Chemical Reagent Co., Ltd. (sodium base); experimental water: ultrapure water; helium: Beijing Huayuan Gas Co., Ltd. (purity 99.999%); gas chromatography-mass spectrometer: Agilent, 6890/5973N , the United States; headspace autosampler: Agilent, G1888, the United States; constant temperature culture shaker: Fuma, QYC-2102C, China; desktop low-speed centrifuge: Xiangyi, L550, China; desktop high-speed centrifuge: Jingli, LG16-W(Ⅰ), China; UV spectrophotometer: Shimadzu, UV-1800, Japan; anaerobic glove box: COY, 14500 Coy Drive, USA; pH meter: Sartorius, PB-10, Germany; redox potentiometer : Clean, ORP30, the United States; micro-injection needles: Hamilton, 10, 25, 100, 1000μL, Switzerland;

2. Experiment:

(1) Bentonite and persulfate reduce the short-term performance of trichlorethylene in groundwater:

Take 0.4g of bentonite and place it in a series of 20mL screw-top brown glass bottles with caps (lined with polytetrafluoroethylene/silica gel septa); add 20mL of oxygen-dispelling ultrapure water; add 100μL of 476g/L sodium persulfate mother liquor to ensure The initial concentration of persulfate is 1.9g/L; add 5μL of 40.0g/L TCE mother solution to ensure the initial concentration of TCE is 10mg/L; place the glass bottle in a constant temperature oscillator (250rpm, 25±1.0℃), and take it out regularly within 8 days And centrifuge (3000rpm, 20min); take the supernatant to detect TCE, 1,1-dichloroethylene, 1,2-dichloroethylene, vinyl chloride and pH; set 3 parallel experiments for each group;

The short-term removal effect of TCE caused by the agent in Example 1 is shown in Figure 3, and the relevant kinetic linear fitting is shown in Figure 4, and the short-term removal effect of TCE caused by a single bentonite is shown in Figure 3, and the TCE dechlorination product caused by the agent in Example 1 The changes are shown in Table 1, and the pH changes caused by the agents in Example 1 are shown in Figure 5. After 5 days of reaction, the removal rate of TCE by a single bentonite was only 3%, indicating that the adsorption of bentonite was weak (Fig. 3). Under normal temperature and pressure, sodium persulfate can only remove a small amount of TCE. After 8 days of reaction, the combined use of bentonite and persulfate had a TCE removal rate of 56%, indicating that persulfate can effectively oxidize and degrade TCE (Figure 3). The oxidative degradation of TCE by combined use of bentonite and persulfate conformed to pseudo-first-order kinetics, and the degradation rate constant was 0.094(d ^-1 ) (Fig. 4). On the other hand, when bentonite and persulfate were combined, the three dechlorinated products of 1,1-dichloroethylene, 1,2-dichloroethylene, and vinyl chloride were not detected (Table 1), proving that TCE was completely mineralized . On the other hand, in the reaction system of bentonite and persulfate, under the condition of initial pH of 10.5, the pH remained at 10.2 after 8 days (Fig. 5). It can be seen that the pH of the system does not change much with the reaction time, indicating that bentonite can ensure the system is in a stable alkaline environment, which is beneficial to the realization of alkali-activated persulfate.

The change of TCE dechlorination product caused in the embodiment 1 of table 1

Note: ND means not detected.

(2) Long-term performance of bentonite and persulfate to reduce trichlorethylene in groundwater:

Take 0.4g of bentonite and place it in a series of 20mL screw-top brown glass bottles with caps (lined with polytetrafluoroethylene/silica gel septa); add 20mL of oxygen-dispelling ultrapure water; add 100μL of 476g/L sodium persulfate mother liquor to ensure The initial concentration of persulfate is 1.9g/L; add 5μL of 40.0g/L TCE mother solution to ensure the initial concentration of TCE is 10mg/L; place the glass bottle in a constant temperature oscillator (250rpm, 25±1.0℃), and take it out regularly within 64 days And centrifuge (3000rpm, 20min); take the supernatant to detect TCE, S ₂ O ₈ ^2- , pH and Eh; set 3 parallel experiments for each group.

The long-term removal effect of TCE caused by the agent in Example 1, the change of Eh of the reaction system, the change of pH of the reaction system and the change of residual persulfate are shown in Figure 6, Figure 7, Figure 8 and Figure 9 respectively. As the reaction time was extended to 64 days, the TCE removal rate of the reagent in Example 1 reached 100% ( FIG. 6 ). The pH of the system decreased gradually, but not much, from the initial 10.5 to 9.3 (at 64 days) (Figure 7). Although persulfate is accompanied by the generation of H ⁺ (Eq. 1) during the oxidative degradation of TCE, bentonite exhibits a strong buffering effect, resulting in little change in the pH of the system. In the first 15 days, the Eh of the system gradually increased, from the initial 60.1mV to 225.6mV; after 15 days, the Eh was high and low, and the value was between 174.0 and 225.7mV (Figure 8). The increase of Eh further proves that bentonite can maintain the alkaline and oxidative environment of the system, and promote the activation of persulfate to generate SO ₄ ^·- , which in turn leads to the transformation of SO ₄ ^·- into ·OH. After 64 days, TCE was completely removed (FIG. 6), but a large amount of persulfate (residual rate greater than 90%) still remained in the system (FIG. 9). Combined with the system pH, Eh and residual persulfate, it is speculated that the system still has the ability to oxidatively degrade TCE.

SO ₄ ^·- +C ₂ HCl ₃ +4H ₂ O→2CO ₂ +9H ⁺ +3Cl ^- +6SO ₄ ^2- (1)

Apparently, the above-mentioned embodiments are only examples for clear description, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or changes derived therefrom are still within the scope of protection of the present 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.