CN110125156B

CN110125156B - Method for treating heavy metal pollution in soil by carbon dioxide filling technology

Info

Publication number: CN110125156B
Application number: CN201810128992.4A
Authority: CN
Inventors: 那平; 王淳; 乔斌
Original assignee: Tianjin University
Current assignee: Shandong Tianda Taize Environmental Protection Technology Co.,Ltd.
Priority date: 2018-02-08
Filing date: 2018-02-08
Publication date: 2021-03-30
Anticipated expiration: 2038-02-08
Also published as: CN110125156A

Abstract

The invention discloses a method for treating heavy metal pollution in soil by a carbon dioxide filling technology, which comprises the following steps: constructing a bagged sand well, paving a clay working cushion layer on the ground surface, setting a sleeve, excavating a depth groove, paving a plastic film on the upper part of the working cushion layer, perforating the position of the sleeve on the plastic film, introducing carbon dioxide into an outer pipe, controlling the flow and the introduction time of the carbon dioxide, maintaining the state for a period of time after the introduction is stopped, starting a vacuum system, controlling the vacuum degree and the vacuumizing time, and the like. After the treatment process is finished, heavy metal ions generated by the reaction of the heavy metal in the soil and the carbon dioxide aqueous solution are transferred to the liquid in the soil and are extracted to the treatment discharge liquid through vacuum, so that the heavy metal in the soil can be effectively removed, an eluent is not newly introduced, and the groundwater pollution caused by the downward movement of water containing the heavy metal ions is avoided.

Description

Method for treating heavy metal pollution in soil by carbon dioxide filling technology

Technical Field

The invention belongs to the technical field of soil treatment, and particularly relates to a method for treating heavy metal pollution in soil by using a carbon dioxide filling technology.

Background

With the development and utilization of mineral resources in large quantities, the rapid development of industrial production and the wide use of various chemical products, pesticides and chemical fertilizers, pollutants containing heavy metals enter the environment through various ways, and the heavy metal pollution of soil, especially farmland soil, is increasingly serious. At present, the soil of various countries in the world has different degrees of pollution, and Hg is about 1.5 multiplied by 104t, Cu is about 340 ten thousand t, Pb is about 500 ten thousand t, Mn is about 1500 ten thousand t and Ni is about 100t which are discharged in the world on average each year. In europe, there are millions of hectares in heavy metal contaminated farmlands; the farmland area polluted by Cd, Cu, As and the like in Japan is 7224 hm². At present, the cultivated land area polluted by Cd, Hg, As, Cr and Pb in China is about 2000 x 104hm²The grain lost due to heavy metal pollution is about 1000 x 104t each year, the polluted grain is as much as 1200 x 104t, and the economic loss is at least 200 x 108 yuan.

At present, the technology for remedying the heavy metal pollution of farmland soil by various countries in the world mainly comprises physical, chemical, biological, agricultural and ecological technologies, combined remediation technologies and the like.

Physical repair technique

The physical repair technology mainly comprises engineering measures (soil replacement, soil replacement and deep ploughing and turning) and thermal desorption. The engineering measures have the advantages of thoroughness and stability, but the engineering quantity is large, the investment is high, the soil body structure is easy to damage, the soil fertility is reduced, and the polluted soil needs to be treated in a centralized manner in order to avoid secondary pollution. Therefore, the method is only suitable for repairing the severely polluted soil with small area; thermal desorption is a method for heating polluted soil and desorbing some volatile heavy metals such As Hg, As, Se and the like from the soil, and the method has the advantages of simple process, high energy consumption and high operation cost, is only suitable for volatile pollutants, and the desorbed gas needs to be collected and treated.

Chemical repair technique

Chemical repair techniques include electrokinetic repair, leaching techniques, and stabilization/solidification repair techniques.

The electric restoration is to apply direct current voltage to two sides of the polluted soil to form electric field gradient, heavy metal pollutants in the soil are brought to two ends of an electrode in an electric field effect in a mode of electromigration, electroosmotic flow or electrophoresis, and then concentrated collection treatment is carried out, so that the soil is cleaned. The method is particularly suitable for clay and silt with low permeability, and can control the flowing direction of pollutants. At present, some exploratory work has been carried out on the aspects of cell body design, electric process and mechanism thereof, model establishment and the like. The electric restoration is an in-situ restoration technology, can remove heavy metals and organic pollutants simultaneously, does not stir the soil layer, is simple to operate, has high treatment efficiency, is an economical and feasible restoration technology, and easily causes the change of the physical and chemical properties of the soil. The electric restoration efficiency is probably caused by the adsorption of soil surface particles to pollutants and H at two ends of the electrode⁺(Positive electrode) and OH^-The (negative) aggregation effect is reduced. Since acid and alkali may cause changes in the physicochemical properties of soil, additives such as chelating agents, complexing agents, surfactants, and oxidation/reduction agents (H) are added₂O₂、NaMnO₄、KMnO₄、Fe⁰) So that the heavy metal and the compound form stable and soluble compounds in a wider pH range, and the aim of efficiently removing the heavy metal in the soil is fulfilled by enhancing the migration of the heavy metal. Researches find that the electric method has the advantages of good removal effect, high economic benefit and the like, and also has a plurality of defects, such as reverse seepage caused by system acidification; precipitation easily occurs in the alkaline zone; some contaminants in the soil are difficult to resolve, etc.

The soil leaching technique comprises adding water or chelating agent (citric acid, EDTA, DTPA, EDDS) containing washing auxiliary agent, and acid/alkali solution (H)₂SO₄、HNO₃) Complexing agent (acetic acid, ammonium acetate)Cyclodextrin), surfactants) (APG, SDS, SDBS, DDT, rhamnolipids) and the like into contaminated soil or sediments, and eluting and cleaning the contaminants in the soil. The key of the technology is to find an eluent which can extract heavy metals in various forms and does not damage the soil structure. The study showed that 0.1 mol. L^-1The removal rates of HCl as an eluting agent to Cu, Ni, Pb and Zn are respectively 92%, 77%, 79% and 75%; the common artificial chelating agent, such as Ethylene Diamine Tetraacetic Acid (EDTA), can achieve ideal leaching effects on Pb and Cd. A large number of engineering practices show that the soil leaching technology is a quick and efficient method. The soil remediation effect is poor for the soil with heavy geological viscosity and poor permeability. The high-efficiency eluting agent is expensive, and the eluting waste liquid can cause secondary pollution to soil and underground water. At present, the soil leaching technology capable of being applied in a large scale and the complete equipment development are relatively lagged, and further improvement and perfection are urgently needed.

The soil stabilization/solidification remediation technology refers to a remediation technology that fixes harmful pollutants in soil by a physical or chemical method, or converts the pollutants into a chemically inactive form to prevent the pollutants from moving, diffusing and the like in the environment, thereby reducing the toxic degree of the pollutants. Common curing agents fall into 4 categories: inorganic binding substances (such as cement, lime, etc.), organic binders (such as thermoplastic materials like asphalt), thermosetting organic polymers (such as urea, phenolics, epoxies, etc.), vitreous substances. Chemical fixation is mainly achieved by adding chemical agents or materials and utilizing the fact that insoluble or poorly mobile and less toxic substances are formed between the chemical agents or materials and heavy metals, so that the bioavailability and the mobility of the chemical agents or materials in soil are reduced. A large number of modifying materials, such as various metal oxides, clay minerals, organic materials, polymeric materials, and biomaterials, have been used. The key point of the technology is to find the modifier which is low in price and environment-friendly. The stable/solidified soil restoration technology is in-situ restoration, is simple and feasible, but is not a permanent restoration measure, and because the existing form of heavy metal is only changed, heavy metal elements still remain in the soil and are easy to reactivate to generate secondary pollution.

Bioremediation technique

Bioremediation refers to a biological measure for realizing environmental purification and ecological effect restoration by utilizing specific organisms to absorb, convert, clear or degrade environmental pollutants, and mainly comprises phytoremediation, microbial remediation and animal remediation. The method has the advantages of low cost, simple operation, no secondary pollution, good treatment effect, large-area popularization and application and the like, and has great attention on mechanism research and application prospects.

Plant volatilization is to utilize plant roots to absorb metals and convert the metals into gaseous substances to volatilize into the atmosphere so as to reduce soil pollution, but is easy to cause secondary pollution. The microorganism remediation is to reduce the heavy metal pollution degree by utilizing the adsorption or conversion of active microorganisms to heavy metals into low-toxicity products. However, microorganisms are small and difficult to separate from soil, and they compete with indigenous strains on the restoration site. The agricultural ecological restoration mainly comprises two aspects: the first is an agronomic remediation measure. Secondly, ecological restoration. The technology is mature, the cost is low, the disturbance to the soil environment is small, the repair cycle is long, and the effect is not obvious.

Combined repair technique

Currently, the most studied combination techniques include bio-combination techniques, physicochemical combination techniques, and physicochemical-bio combination techniques. The technology mostly stays in a laboratory research stage, and the technical means is immature.

The above prior art has the following disadvantages;

1. high energy consumption and high operation cost

2. Soil leaching technology capable of being applied in large scale and relative lag of complete equipment development

3. Easy reactivation to produce secondary pollution

4. Long repairing period and no obvious effect

5. The leacheate can not be controlled by organized flow and can easily flow into the groundwater environment to pollute the groundwater.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for treating heavy metal pollution in soil by using a carbon dioxide filling technology, which can efficiently remove the heavy metal pollution in the soil and does not introduce an eluent to cause secondary pollution.

The invention is realized by the following technical scheme:

a method for treating heavy metal pollution in soil by using a carbon dioxide filling technology is characterized in that the water content of the soil is not lower than 28%, and the method comprises the following steps:

step 1, vertically constructing bagged sand wells on the surface of soil to be treated, wherein the depth of the bagged sand wells reaches the junction of a mellow soil layer of a raw soil layer, the well spacing between the sand wells is 1-3 m, and the sand wells are symmetrically arranged in a circular or square mode;

step 2, paving a deep silty clay working cushion layer on the ground surface, wherein the thickness of the working cushion layer is 5-10 cm;

step 3, arranging a sleeve in the sand well, wherein the lower end of the sleeve is positioned at the bottom of the sand well, the sleeve comprises an inner pipe and an outer pipe, the upper end of the sleeve is exposed out of the working cushion layer, the outer pipe is connected with a carbon dioxide generating device through a hose, and the inner pipe is connected with a vacuum system through a hose;

step 4, excavating a groove with the depth of 30-50 cm around the soil to be treated, paving a plastic film on the upper part of a working cushion layer, embedding the periphery of the plastic film into the groove, forming a hole in the position of the sleeve on the plastic film, and enabling the upper end of the sleeve to extend out of the plastic film, so that the construction of a vacuum pre-pressing system is completed;

step 5, starting the vacuum system, and checking the tightness of the vacuum preloading system;

step 6, starting the carbon dioxide generating device, introducing the carbon dioxide into the outer pipe, and controlling the flow rate to enable the flow rate of the carbon dioxide to be 0.1-10 cm³Controlling the carbon dioxide introduction time to be 30-200 min, stopping introducing the carbon dioxide, and maintaining the state for 10-20 h;

step 7, starting the vacuum system under the condition that the carbon dioxide inlet of the outer pipe is closed, controlling the absolute vacuum degree to be 3-80 kPa, and controlling the suction filtration speed to be 2-5 cm/s;

step 8, after vacuum filtration is carried out for 30-90 min, closing the vacuum system;

in the technical scheme, the depth of the sand well is 20-50 cm, and the diameter of the sand well is 5-20 cm.

In the technical scheme, the outer wall of the part, extending into the mellow soil, of the outer pipe is provided with vent holes, the distance between the vent holes is 1-5 cm, and the diameter of each vent hole is 1-5 mm.

In the technical scheme, the pipe diameter of the inner pipe is 2-17 cm, and the pipe diameter of the outer pipe is 5-20 cm.

In the above technical scheme, the casing pipe is a PVC pipeline.

In the above technical solution, the length of the part of the outer tube wrapped by the hose should be not less than 5cm, and the method according to claim 1, wherein the length of the part of the inner tube wrapped by the hose should be not less than 5 cm.

In the above technical scheme, the vacuum system comprises a vacuum pump and a gas-liquid separation device.

In the technical scheme, the carbon dioxide generator is an HT-1 type carbon dioxide generator, solid ammonium bicarbonate is charged at one time, and dilute sulfuric acid is added into an acid storage barrel to generate carbon dioxide gas.

In the technical scheme, the vacuum degree and the vacuumizing time of the vacuum system are determined by drawing a vacuum pressure-time change curve and an earth surface sedimentation-time curve, observing the vacuum pressure and the earth surface sedimentation of each stratum depth in the soil foundation, and drawing the vacuum pressure-time change curve and the earth surface sedimentation-time change curve of each stratum depth.

In the above technical scheme, the treated discharge water is collected in the gas-liquid separation device.

The invention has the advantages and beneficial effects that:

the method comprises the following steps: the method comprises the steps of vertically arranging a sleeve in the soil to be treated, paving a plastic film on the surface of the soil, checking the system tightness, filling carbon dioxide gas, extracting liquid and the like, wherein the carbon dioxide is used as a gas fertilizer and does not influence the environment and the soil.

CO₂The heavy metal is filled into the soil and then synthesized into bicarbonate with the heavy metal, the heavy metal is transferred into soil water in an ion form, and then the polluted water is pumped away in a vacuum mode, so that the heavy metal in the soil is treated, and the problem of heavy metal pollution in the soil is solved. The method can effectively remove heavy metals in the soil, and no eluting agent is newly introduced, so that the groundwater is prevented from being polluted by the downward movement of water containing heavy metal ions.

In addition, use the outer tube as gas tube and inner tube as two into one as the pipeline that draws water, the sealed soil of plastics seal membrane, keep apart with atmospheric pressure, when adopting the evacuation equipment evacuation, pressure reduces rapidly, the pore water pressure in the soil forms pressure gradient along with the reduction of pressure in the inner tube, the water that contains heavy metal ion passes through the inner tube and discharges, the method that adopts vertical straight vacuum tube has eliminated horizontal sand bed course, filter tube and filter membrane among the vacuum pressure transmission process loss to vacuum energy, and it is very little along the vertical direction pressure drop, the utilization efficiency of vacuum pressure has been improved. In addition, one vertical pipeline is shared; not only reduces the equipment cost, but also reduces the occupied area, wherein the inner pipe and the outer pipe can be repeatedly utilized, and the treatment cost is reduced.

In conclusion, the invention has the advantages that the heavy metal elements in the soil can be efficiently treated, and the secondary pollution to the surrounding environment and underground water can be avoided.

Drawings

Fig. 1 is a schematic diagram of a first embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a bushing according to a first embodiment of the present invention.

Wherein:

1: a green soil layer, 2: mature soil layer, 3: working cushion layer, 4: plastic film, 5: outer tube, 6: inner tube, 7: carbon dioxide generation device, 8: vent hole, 9: hose, 10: gas-liquid separation device, 11: a vacuum pump.

For a person skilled in the art, other relevant figures can be obtained from the above figures without inventive effort.

Detailed Description

In order to make the technical solution of the present invention better understood, the technical solution of the present invention is further described below with reference to specific examples.

Example one

The heavy metal content of the sampled soil sample is Pb: 78mg/kg, Cd: 0.2mg/kg, Cr: 96mg/kg, Cu: 60mg/kg, 1270mg/kg Zn, and 28 percent of soil water content.

Step 1, punching bagged sand wells with the diameter of 7cm and the depth of 40cm on 3m by 0.4m planting land, wherein the well spacing is 1.3m, and 9 sand wells are arranged in a square form;

step 2, paving a deep silty clay working cushion layer on the ground surface, wherein the thickness of the working cushion layer is 5 cm;

step 3, arranging a sleeve in the sand well, wherein the lower end of the sleeve is positioned at the bottom of the sand well, the sleeve comprises an inner pipe and an outer pipe, the diameter of the inner pipe is 5cm, the diameter of the outer pipe is 7cm, the upper end of the sleeve is exposed out of the working cushion layer by 7cm, the outer pipe is connected with a carbon dioxide generation device through a hose, the inner pipe is connected with a vacuum system through a hose, the part of the outer pipe, which is wrapped by the hose, is 5cm, the part of the inner pipe, which is wrapped by the hose, is 5cm, the part, which is embedded into the mellow soil, of the outer pipe is drilled with holes with the diameter of 2mm every 1cm, and the outer pipe is used as;

step 4, excavating a groove with the depth of 30cm around the soil to be treated, paving a plastic film on the upper part of a working cushion layer, embedding the periphery of the plastic film into the groove, forming a hole in the position of the sleeve on the plastic film, and enabling the upper end of the sleeve to extend out of the plastic film, so that the construction of a vacuum preloading system is completed;

step 6, using an HT-1 type carbon dioxide generator, charging 0.85kg of solid ammonium bicarbonate once, adding 0.85kg of dilute sulfuric acid into an acid storage barrel to generate 0.37kg of carbon dioxide gas, introducing the carbon dioxide into the outer tube, and controlling the flow rate to enable the flow rate of the carbon dioxide to be 0.1cm³Min, controlling the carbon dioxide introduction time to be 8Stopping introducing carbon dioxide for 0min, and maintaining the state for 12 h;

step 7, starting the vacuum system under the state that the carbon dioxide inlet of the outer tube is closed, and controlling the absolute vacuum degree to be 3.5 kPa;

step 8, after vacuum filtration for 40min, closing the vacuum system;

the drained water is collected. And sampling and detecting the heavy metal content in the land. According to detection, in soil, the removal rate of lead reaches 96%, the removal rate of chromium reaches 96%, the removal rate of copper reaches 94%, the removal rate of zinc reaches 97%, and the removal rate of cadmium reaches 93%.

Sampling the water quality in the raw soil layer, and detecting no heavy metal bicarbonate.

Example two

The heavy metal content of the sampled soil sample is Pb: 86mg/kg, Cd: 0.1mg/kg, Cr: 86mg/kg, Cu: 60mg/kg, Zn 1600mg/kg and soil water content 31 percent.

Step 1, punching bagged sand wells with the diameter of 10cm and the depth of 50cm on 8m by 0.5m planting land, wherein the well spacing is 1.5m, and 16 sand wells are arranged in a square form;

step 2, paving a deep silty clay working cushion layer on the ground surface, wherein the thickness of the working cushion layer is 7 cm;

step 4, excavating a groove with the depth of 40cm around the soil to be treated, paving a plastic film on the upper part of a working cushion layer, embedding the periphery of the plastic film into the groove, forming a hole in the position of the sleeve on the plastic film, and enabling the upper end of the sleeve to extend out of the plastic film, so that the construction of a vacuum preloading system is completed;

step 6, using an HT-1 type carbon dioxide generator, charging 8kg of solid ammonium bicarbonate at one time, adding 8kg of dilute sulfuric acid into an acid storage barrel to generate 3.4kg of carbon dioxide gas, introducing the carbon dioxide into the outer tube, and controlling the flow rate to enable the flow rate of the carbon dioxide to be 0.2cm³Min, wherein the carbon dioxide is introduced for 100min, the introduction of the carbon dioxide is stopped, and the state is maintained for 16 h;

step 7, starting the vacuum system under the state that the carbon dioxide inlet of the outer tube is closed, and controlling the absolute vacuum degree to be 15 kPa;

step 8, after vacuum filtration for 80min, closing the vacuum system;

the drained water is collected. And sampling and detecting the heavy metal content in the land. According to detection, in soil, the lead removal rate reaches 92%, the chromium removal rate reaches 89%, the copper removal rate reaches 90%, the zinc removal rate reaches 95%, and the cadmium removal rate reaches 88%.

EXAMPLE III

The heavy metal content of the sampled soil sample is Pb: 85mg/kg, Cd: 0.15mg/kg, Cr: 95mg/kg, Cu: 60mg/kg, 1270mg/kg Zn, 29 percent soil water content

Step 1, punching bagged sand wells with the diameter of 7cm and the depth of 50cm on 3m by 0.4m planting land, wherein the well spacing is 1.3m, and 9 sand wells are arranged in a square form;

step 3, arranging a sleeve in the sand well, wherein the lower end of the sleeve is positioned at the bottom of the sand well, the sleeve comprises an inner pipe and an outer pipe, the diameter of the inner pipe is 5cm, the diameter of the outer pipe is 7cm, the upper end of the sleeve is exposed out of the working cushion layer by 7cm, the outer pipe is connected with a carbon dioxide generating device through a hose, the inner pipe is connected with a vacuum system through a hose, the part of the outer pipe, which is wrapped by the hose, is 5cm, the part of the inner pipe, which is wrapped by the hose, is 5cm, the part, which is embedded into the mellow soil, of the outer pipe is provided with holes with the diameter of 2mm every 1.5cm, the outer pipe is used as an;

step 4, excavating a groove with the depth of 50cm around the soil to be treated, paving a plastic film on the upper part of a working cushion layer, embedding the periphery of the plastic film into the groove, forming a hole in the position of the sleeve on the plastic film, and enabling the upper end of the sleeve to extend out of the plastic film, so that the construction of a vacuum preloading system is completed;

step 6, using an HT-1 type carbon dioxide generator, charging 0.85kg of solid ammonium bicarbonate once, adding 0.85kg of dilute sulfuric acid into an acid storage barrel to generate 0.37kg of carbon dioxide gas, introducing the carbon dioxide into the outer tube, and controlling the flow rate to enable the flow rate of the carbon dioxide to be 0.15cm³Min, wherein the carbon dioxide is introduced for 90min, the introduction of the carbon dioxide is stopped, and the state is maintained for 16 h;

step 8, after vacuum filtration for 40min, closing the vacuum system;

the drained water is collected. And sampling and detecting the heavy metal content in the land. According to detection, in soil, the removal rate of lead reaches 95%, the removal rate of chromium reaches 96%, the removal rate of copper reaches 95%, the removal rate of zinc reaches 98%, and the removal rate of cadmium reaches 93%.

The invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.

Claims

1. A method for treating heavy metal pollution in soil by using a carbon dioxide filling technology comprises the following steps:

and 8, after vacuum filtration is carried out for 30-90 min, closing the vacuum system.

2. The method of claim 1, wherein the sand well depth is 20-50 cm and the sand well diameter is 5-20 cm.

3. The method as claimed in claim 1, wherein the outer pipe is provided with vent holes penetrating into the outer wall of the mellow soil part, the distance between the vent holes is 1-5 cm, and the diameter of the vent holes is 1-5 mm.

4. The method according to claim 1, wherein the inner pipe has a pipe diameter of 2-17 cm and the outer pipe has a pipe diameter of 5-20 cm.

5. The method of claim 1, wherein the sleeve is PVC tubing.

6. The method of claim 1, wherein the length of the portion of the outer tube wrapped by the hose is not less than 5cm, and the length of the portion of the inner tube wrapped by the hose is not less than 5 cm.

7. The method of claim 1, wherein the vacuum system comprises a vacuum pump and a gas-liquid separation device.

8. The method as claimed in claim 1, wherein the carbon dioxide generator is a HT-1 type carbon dioxide generator, solid ammonium bicarbonate is charged at one time, and dilute sulfuric acid is added to an acid storage tank to generate carbon dioxide gas.

9. The method of claim 1, wherein the vacuum degree and the vacuum pumping time of the vacuum system are determined by plotting a vacuum pressure-time variation curve and a surface subsidence-time curve, observing the vacuum pressure and the surface subsidence at each depth of the ground in the soil foundation, and plotting a vacuum pressure-time variation curve and a surface subsidence-time variation curve at each depth of the ground.