CN112170474A

CN112170474A - Method for repairing arsenic-polluted soil by electrically-driven reinforced permeable reactive barrier

Info

Publication number: CN112170474A
Application number: CN202010925378.8A
Authority: CN
Inventors: 朱宗强; 方雅莉; 田炎; 赵宁宁; 朱义年; 王亚茹; 章俊; 张立浩; 唐沈
Original assignee: Guilin University of Technology
Current assignee: Guilin University of Technology
Priority date: 2020-09-06
Filing date: 2020-09-06
Publication date: 2021-01-05
Also published as: JP2022044528A

Abstract

The invention discloses a method for repairing arsenic-polluted soil by electrically driving a reinforced permeable reactive barrier, which is used for efficiently repairing the arsenic-polluted soil in situ by using a device for electrically driving the reinforced permeable reactive barrier. The method comprises the following specific steps: the method comprises the steps of naturally air-drying polluted arsenic soil, crushing and sieving, then mixing and stirring uniformly by deionized water to keep the water content of the mixed soil at 30% -35%, standing to balance the soil, and then repairing the soil under the voltage condition of 1-3V/cm, wherein PRB materials are wrapped by filter cloth and placed in a soil reactor, and the materials are selected according to different arsenic pollution degrees and properties of the soil. The method improves the removal rate of arsenic in the polluted soil, avoids secondary pollution, and improves the removal rate of arsenic because the permeable reaction wall is easy to replace. The method has obvious repairing effect and simple operation, and has the implementation performance on fields such as arsenic-polluted mines, arsenic-polluted chemical soil fields and the like.

Description

Method for repairing arsenic-polluted soil by electrically-driven reinforced permeable reactive barrier

Technical Field

The invention belongs to the technical field of remediation of heavy metal pollution of soil in the environment protection technology, and particularly relates to a method for remediating arsenic-polluted soil by electrically driving a reinforced permeable reactive barrier.

Background

With the gradual improvement of human environmental awareness, the problem of heavy metal pollution of soil is more and more emphasized. The sources of the arsenic pollution in the soil include metal mining and smelting, chemical industry production, heavy metal pesticide sewage irrigation, chemical fertilizer application, high geological background value and the like, wherein heavy metal waste gas sedimentation, waste water irrigation, solid waste such as waste residues and the like discharged by the non-ferrous metal mining and smelting are main ways of arsenic pollution, and the solid waste is corroded and diffused into the soil.

Arsenic can migrate in the environment, and part of arsenic in soil is absorbed by crops and part of arsenic enters a water body along with rainfall and river scouring, and finally all arsenic enters a human body through a food chain. The arsenic passively absorbed by crops has certain harm to the crops, and the excessive arsenic inhibits the absorption and transportation of water by root systems by reducing the transpiration of plants, so that the smoothness of the leaf surface, the root length, the seedling height and the like of the crops are influenced. Wherein the combination of trivalent arsenic and enzyme in human body can inhibit enzyme activity, resulting in sugar metabolism disorder, toxic neurasthenia syndrome, etc.; the toxicity of pentavalent arsenic is chronic, and can cause sequelae such as myelitis, aplastic anemia and the like. Arsenic poisoning is a systemic disease mainly caused by skin damage, and can harm the skin, respiratory, digestive, urinary, cardiovascular, nervous, hematopoietic systems, etc. of a human.

At present, the arsenic polluted soil remediation methods at home and abroad are various, and the methods mainly comprise two methods: changing the existing form of heavy metal in soil, fixing the heavy metal, reducing the mobility and bioavailability of the heavy metal in the environment and removing the heavy metal from the soil, mainly comprising physical remediation, biological remediation and chemical remediation. An electrically-driven reinforced permeable reactive barrier technology (EK-PRB) for repairing arsenic-polluted soil is a novel technology for jointly repairing the soil pollutants by combining an electric repairing technology (EK) and a permeable reactive barrier technology (PRB). The principle is that pollutants in soil to be repaired are driven by electrolyte, underground water and the like, and PRB repair is strengthened by an electric technology, so that the pollutants can directionally migrate in the soil and the underground water and reach a reaction barrier for reaction.

Disclosure of Invention

The method aims to strongly combine electric field driving with PRB technology and analyze the specific influence of the PRB on the in-situ remediation energy efficiency of the arsenic-polluted soil under the driving of the electric field; and (3) combining the purification mechanism of the PRB material to the target ions and the electric field driving action process, revealing the interactive essential relationship between the EK-PRB controllable application process and the adsorption efficiency, and constructing an in-situ repair mechanism model. Improves the efficiency of removing arsenic from soil on the basis of the original individual EK and PRB technologies, and prevents secondary pollution.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for repairing arsenic contaminated soil by electrically driving a reinforced permeable reactive barrier comprises the following steps:

firstly, hammer-crushing and sieving naturally-dried arsenic-polluted soil;

mixing the soil obtained in the step (1) with deionized water to keep the water content of the soil at 35%, uniformly stirring and standing for 7 d;

filling the uniformly mixed soil obtained in the step (2) into a soil chamber of the EK-PRB device, and vertically placing PRB materials in the middle of the soil;

fourthly, adding electrolyte into the cathode and anode chambers on the two sides of the soil chamber in the step (3), respectively inserting graphite electrodes, and switching on a power supply to start operation and repair of the device;

removing the PRB permeable reactive barrier after electrifying is finished to obtain the repaired arsenic-polluted soil.

The pH value of the arsenic-polluted soil is 6.35, and the total arsenic concentration in the soil is 250 mg/kg.

And (2) sieving the arsenic-polluted soil after the arsenic-polluted soil is hammered and crushed by a 20-mesh sieve in the step (1).

And (3) adding about 500ml of deionized water per kilogram of soil in the step (2) to ensure that the water content is suitable for ensuring the soil conductivity.

The PRB material vertically filled in the middle of the soil in the step (3) is a moso bamboo charcoal Fe/Mn-LDH composite material, and the filling thickness is about 1 cm.

And (4) the electrolyte of the electrode chambers at the two sides is 0.1mol/L potassium chloride solution, so that the stable electric driving capability is ensured.

The operation time in the step (4) is 96 h.

The two sides of the electrode inserted into the electrode chamber are graphite electrode plates.

The EK-PRB technology described in the step three of the invention is processed by adopting the following device.

The EK-PRB device adopted by the invention comprises: the device comprises a soil chamber, a cathode chamber, an anode chamber, a direct current power supply, an electrode, an overflow hole, an electrolyte tank, a peristaltic pump, a graphite electrode, a filter screen and a PRB material of Fe/Mn-LDH.

The soil chamber is filled with arsenic-polluted soil, the size ratio of the arsenic-polluted soil is 2:1:1, electrolyte is filled in the cathode chamber and the anode chamber on two sides, and the size ratio of the electrolyte chamber is 1:1: 1. PRB is wrapped by filter cloth and vertically placed in the polluted soil. Wherein, the clapboard between the soil chamber and the electrode chamber is provided with evenly distributed holes, and 300-mesh filter cloth is pasted on the clapboard to block and prevent the soil from entering the electrolysis chamber. Graphite electrode plates with the thickness of 1cm are adopted in the anode chamber and the cathode chamber and are connected with a direct current power supply through electrode wires, and the voltage gradient is 2 v/cm. The upper and lower sides of the cathode chamber and the anode chamber are respectively provided with overflow ports with the diameter of 1cm from the top and the bottom, the upper overflow ports on the upper sides ensure that the liquid levels of the electrolytes of the cathode and the anode are kept at a stable point of water pressure difference, the electric driving capacity is stable, and the lower overflow ports are connected with an electrolyte collecting tank through peristaltic pumps to supplement lost electrolyte and circulating electrolyte.

The invention has the following remarkable advantages:

1. compared with the original pure electric drive arsenic contaminated soil and single reverse osmosis barrier technology, the method has the advantage that the repair effect is 20-40% higher than that of the repair efficiency.

2. The leaching toxicity of the arsenic-polluted soil repaired by the method is reduced by about 90 percent compared with that of the original soil.

3. The method does not cause secondary pollution to the soil and has the concept of green and environment-friendly remediation.

4. The method can replace the permeable reaction wall at any time, and improves the arsenic pollution removal rate.

5. The method has the advantages of simple operation, low cost, short processing time, large-scale engineering implementation and wide application range.

Drawings

FIG. 1 is a schematic diagram of an electrically driven enhanced permeable wall reaction device used in the present invention.

FIG. 2 is a comparison graph of total arsenic in arsenic-contaminated soil after pure electric drive and EK-PRB treatment.

FIG. 3 is a comparison graph of leaching toxicity of arsenic contaminated soil after pure electric drive and EK-PRB treatment.

Detailed Description

A method for repairing arsenic-polluted soil by utilizing an electric drive reinforced permeable reactive barrier. The arsenic-polluted soil is repaired by adopting a self-made device, and the device consists of a soil chamber, two electrolysis chambers, a direct-current power supply, two peristaltic pumps and two electrolyte collecting tanks. And filling the arsenic-polluted soil into a soil chamber, putting the PRB material wrapped by the filter cloth into the soil chamber, operating at the operating voltage of 2v/cm for 96h, removing the PRB wall, separating and taking out the treated soil, and achieving the purpose of treating the arsenic from the soil. The method comprises the following specific steps:

the method comprises the steps of weighing a certain amount of clean soil from special red soil in Guangxi province, wherein the sampled soil is 5-20cm of soil on the surface layer of the soil, removing impurities such as grass roots and large stones after natural air drying, and then screening the soil through a 20-mesh screen to obtain a soil sample for storage. Weighing a certain amount of sodium arsenite, dissolving with deionized water, and fixing the volume to a certain volume. Adding 250ml arsenic solution into each kilogram of soil, mixing and stirring uniformly, standing for one week to prepare the arsenic-contaminated soil of 500 mg/kg.

The method comprises the steps of filling arsenic-polluted soil into soil chambers of the device, filling graphite electrode plates and 0.1mol/L KCl electrolyte into cathode and anode electrolytic chambers on two sides, and taking out after the device is electrified for 96 hours at a voltage of 2 v/cm.

And thirdly, digesting the soil after operation in the second step by using a aqua regia water bath method, and then measuring the sample by using ICP or atomic fluorescence. Arsenic in the soil is removed through migration to the anode and through the PRB reverse osmosis wall, and the arsenic-removed soil is obtained.

The removal rate of total arsenic in soil after remediation of soil by chemical analysis operation increased from 28.64% for pure electric drive to 48.17% for EK-PRB treatment. The arsenic leaching toxicity of the soil before and after treatment increased from 86.1% of pure electric drive to 95.7% of EK-PRB. Both the increase in the removal rate of total arsenic and the increase in the leaching toxicity rate indicate that good results are achieved both in terms of total and bioavailable quantities.

Claims

1. A method for repairing arsenic contaminated soil by electrically driving a reinforced permeable reactive barrier comprises the following steps:

(1) hammer-crushing the naturally air-dried arsenic-polluted soil, and sieving;

(2) mixing the soil obtained in the step (1) with deionized water to keep the water content of the soil at 30-40%, uniformly stirring and standing for 7-14 d;

(3) filling the uniformly mixed soil obtained in the step (2) into a soil chamber of an EK-PRB device, and vertically placing PRB materials in the middle of the soil;

(4) adding electrolyte into the cathode and anode chambers on the two sides of the soil chamber in the step (3), respectively inserting graphite electrodes, and switching on a power supply to start the operation and repair of the device;

(5) and removing the PRB permeable reactive barrier after the electrification is finished to obtain the repaired arsenic-polluted soil.

2. The method of claim 1, wherein the arsenic-contaminated soil has a pH of 6.35 and a total arsenic concentration of 250 mg/kg.

3. The method of claim 1, wherein the arsenic contaminated soil of step (1) is hammer-crushed and sieved through a 20 mesh screen to remove bulk soil.

4. The method of claim 1, wherein about 500ml of deionized water is added per kg of soil in step (2).

5. The method as claimed in claim 1, wherein the PRB material vertically filled in the middle of the soil in the step (3) is a mao bamboo charcoal/FeMn-LDH composite material or the like having a fast arsenic adsorption property, and the filling thickness is about 1 cm.

6. The method of claim 1, wherein the electrolyte in the two-sided electrode chambers in step (4) is 0.1mol/L potassium chloride solution.

7. The method of claim 1, wherein the run time in step (4) is 96 hours.

8. The method of claim 1, wherein the electrodes inserted into the electrode compartment are graphite electrodes on both sides.

9. The method as claimed in claim 1, wherein a small hole tube having a diameter of 1cm is formed 1cm from the bottom and the top, respectively, for the inlet of the electrolyte at the bottom and the equilibrium level of the electrolyte at the top.

10. The method as claimed in claim 1, wherein the electrolyte is separately circulated from the cathode and the anode through a small tube and an external peristaltic pump, and the electrolyte is replenished at any time to maintain the amount of electrolyte in the electrolytic cell.