Cadmium-polluted farmland remediation method

Abstract

The invention discloses a cadmium-polluted farmland remediation method, which relates to the technical field of soil pollution treatment and environmental remediation, and mainly comprises the following steps: S1, dividing a cadmium-polluted land into a plurality of operation land parcels; s2, any one of the operation plots is divided into layered soil not smaller than three layers from top to bottom according to the cadmium content, the first layer of soil is cadmium-contaminated soil, the last layer of soil is clean soil, and the middle layer of soil is buffer layer soil; s3, the multiple layers of soil of the first operation land parcel are dug out in sequence to form pit slots, and the multiple layers of soil are stored separately; s4, the multiple layers of soil of the next operation land parcel are dug out in sequence to form pit slots, and the multiple layers of soil are inversely backfilled into the pit slots of the previous operation land parcel; and S5, the step S4 is repeated till backfilling of all the operation land parcels is completed. The method has the advantages of being high in operability, free of secondary pollution, economical and efficient, the problem of cadmium pollution of plots can be thoroughly solved, and the workload is small.

Description

Technical Field

[0001] The present invention relates to the technical field of soil pollution control and environmental restoration, and in particular to a method for restoring cadmium-contaminated farmland. Background Art

[0002] Common heavy metals include Cd, Hg, As, Cu, Pb, Cr, Zn, and Ni. They are all highly biologically toxic, and cadmium is recognized as one of the most toxic heavy metals in the world. The point-level exceeding rate of cadmium contaminated soil in my country is the highest, ranking first among the eight major inorganic pollutants. Cadmium contamination of farmland has posed a serious threat to the ecological environment, the quality and safety of agricultural products, and people's health.

[0003] At present, contaminated soil is usually repaired by a layered replacement remediation method, that is, the shallow contaminated soil and the deep clean soil are shoveled out and piled separately by the excavator bucket, and then the shallow contaminated soil that has been solidified is backfilled to the deep position for compaction, and then the original deep clean soil is backfilled on it, thereby realizing the layered replacement of shallow contaminated soil and deep clean soil. This method can better ensure that the soil is free of secondary pollution and has a better pollution treatment effect. However, this method requires accurate calculation of the clear dividing point between contaminated soil and clean soil, and the workload is large.

[0004] Therefore, a method for remediating cadmium-contaminated farmland is needed that is highly practical, has no secondary pollution, and only requires a rough calculation of soil stratification points, reducing workload. Summary of the invention

[0005] The purpose of the present invention is to provide a method for repairing cadmium-contaminated farmland to solve the problems existing in the above-mentioned prior art. The method has the advantages of strong operability, no secondary pollution, and economical and high efficiency. It can more thoroughly solve the problem of cadmium contamination of land and has a small workload.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] The present invention provides a method for repairing cadmium-contaminated farmland, comprising the following steps:

[0008] S1: Divide the cadmium-contaminated plot into multiple operation plots;

[0009] S2: Divide any of the operating plots into no less than three layers of soil from top to bottom according to the cadmium content, the first layer of soil is cadmium-contaminated soil, the last layer of soil is clean soil, and the middle layer of soil is buffer soil;

[0010] S3: digging out multiple layers of soil from the first operation plot in sequence to form pits, and storing the multiple layers of soil separately;

[0011] S4: digging out multiple layers of soil from the next operation plot in sequence to form a pit, and inverting and backfilling the multiple layers of soil into the pit of the previous operation plot;

[0012] S5: Repeat step S4 until all the operation plots are backfilled.

[0013] Preferably, the plurality of operating plots are long strip-shaped operating plots of the same size.

[0014] Preferably, the width of the long strip operating plot is 2-5m.

[0015] Preferably, before step S1, step S01 is also included:

[0016] The cadmium-contaminated land was investigated and the excavation depth was determined, which was 0.9-1.8m.

[0017] Preferably, before step S1, and after step S01, step S02 is further included:

[0018] Select stabilization agents to stabilize cadmium-contaminated soil.

[0019] Preferably, the operating plot is divided into three layers from top to bottom according to the cadmium content, the upper soil layer is cadmium-contaminated soil, the middle soil layer is buffer soil, the lower soil layer is clean soil, and a geomembrane is used to store the excavated soil.

[0020] Preferably, an enclosure is placed in the pit of the first operating plot, and the outer wall of the enclosure fits the side wall of the pit.

[0021] Preferably, the height of the enclosure is 60-120 cm, and is the same as the sum of the heights of the upper soil layer and the middle soil layer of the operating plot.

[0022] Preferably, after the upper soil and the middle soil of the next operation plot are backfilled into the first operation plot, the enclosure is pulled out and the backfilled soil is compacted;

[0023] Repeat the above steps until all the operation plots are backfilled.

[0024] Preferably, after step S5, the method further includes step S6:

[0025] Mature the surface soil and restore its farming function.

[0026] Compared with the prior art, the present invention has achieved the following technical effects:

[0027] The present invention first divides a cadmium-contaminated plot into a plurality of operating plots of equal size, and then divides any operating plot into no less than three layers of layered soil from top to bottom according to the cadmium content, wherein the first layer of soil is cadmium-contaminated soil, the last layer of soil is clean soil, and the middle soil is buffer layer soil, and then the first layer of soil, the middle soil, and the last layer of soil of an operating plot are dug out in sequence and stored separately, and then the first layer of soil, the middle soil, and the last layer of soil of the operating plot adjacent to the operating plot to be backfilled are filled into the operating plot to be backfilled in sequence, so that the clean soil is located at the top layer of the operating plot to be backfilled, and the subsequent operations are the same, and the first layer of soil, the middle soil, and the last layer of soil of the operating plot are dug out in sequence. The soil of adjacent plots is backfilled in turn, and the setting of the buffer layer of soil makes it unnecessary to conduct very precise testing on the cadmium-contaminated soil, and only a rough test is needed. The soil of each layer is dug out and stored separately, and then backfilled in an orderly manner. This can place the clean soil on the top of the plot to be backfilled, effectively blocking the impact of the bottom polluted soil on the upper environment, speeding up the pollution control and improving the control efficiency. The soil of adjacent plots is backfilled in turn, making full use of existing resources, avoiding the cost and time consumption of additional search for clean soil for backfilling, and having strong operability, no secondary pollution, economical and efficient, and can more thoroughly solve the problem of cadmium contamination of the plot with less workload. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 Schematic diagram of the process of repairing cadmium-contaminated farmland in some embodiments of the present invention; DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] The purpose of the present invention is to provide a method for repairing cadmium-contaminated farmland to solve the problems existing in the prior art. The method has the advantages of strong operability, no secondary pollution, and economical and high efficiency. It can more thoroughly solve the problem of cadmium contamination of land and has a small workload.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0033] like Figure 1 The present invention provides a method for repairing cadmium-contaminated farmland, comprising the following steps:

[0034] S1: Divide the cadmium-contaminated plot into multiple operation plots, specifically, divide the cadmium-contaminated plot into multiple operation plots of equal size. Dividing the operation plots into equal-sized operation plots can make the entire pollution control process more standardized, and the staff can handle each operation plot according to unified standards. For example, when excavating, transporting and backfilling soil, the operating parameters and work flow of the equipment can be relatively fixed. For the excavation equipment, it is easier to determine the excavation depth, range and speed parameters when processing plots of the same size each time, thereby improving work efficiency;

[0035] S2: Divide any operating plot into no less than three layers of soil from top to bottom according to the cadmium content. The first layer of soil is cadmium-contaminated soil, the last layer of soil is clean soil, and the middle layer of soil is buffer soil. The setting of the buffer layer soil makes it unnecessary to conduct very precise testing of cadmium-contaminated soil, and only rough testing is required, which reduces the workload;

[0036] S3: digging out multiple layers of soil from the first operation plot in sequence to form pits, and storing the multiple layers of soil separately;

[0037] S4: digging out multiple layers of soil from the next operation plot in sequence to form a pit, and inverting and backfilling the multiple layers of soil into the pit of the previous operation plot, that is, filling the first layer of soil, the middle layer of soil, and the last layer of soil into the pit of the previous operation plot in sequence, so that the clean soil is at the top;

[0038] S5: Repeat step S4 until all the operating plots are backfilled, dig out each layer of soil in turn and store them separately, and then backfill in an orderly manner, so that the clean soil can be placed on the top layer of the plot to be backfilled, effectively blocking the impact of the bottom polluted soil on the upper environment, accelerating the speed of pollution control, and improving the control efficiency. The soil of adjacent plots is backfilled in turn, making full use of existing resources, avoiding the cost and time consumption of additional search for clean soil for backfilling, and having strong operability, no secondary pollution, economical and efficient, and can more thoroughly solve the problem of cadmium contamination of the plot.

[0039] In some embodiments, the plurality of operating plots are elongated operating plots of the same size. The elongated operating plots are more maneuverable for excavation equipment (such as an excavator).

[0040] In some embodiments, the width of the long strip operating plot is 2-5m, an excavator is used as the excavation tool, and the bucket of the excavator is toothless, such as a mud bucket, in order to prevent the shovel of the bucket from digging into other layers of soil, causing soil mixing and affecting the processing effect. This width can make full use of the arm length of the excavator and avoid repeated adjustments. The specific width can be adjusted according to the arm length of the excavator.

[0041] In some embodiments, before step S1, step S01 is also included: investigate the cadmium-contaminated plots and determine the excavation depth, which is 0.9-1.8m, specifically to conduct relevant investigations on soil physical and chemical properties, farming habits, hydrogeology, etc., to determine the degree of pollution, depth, lower soil conditions, groundwater conditions, etc.; and detect the texture, physical and chemical properties, degree of soil pollution and depth of each layer in the vertical direction of the soil (one sample every 10 cm in the vertical direction). For plant growth, the excavation at this depth can also create a relatively clean growth environment for plant roots. Plant roots are mainly distributed in the upper soil. By removing this part of the contaminated soil, plants can be prevented from absorbing too much cadmium and cadmium can be prevented from being transmitted to humans and other animals through the food chain. For example, the roots of vegetable crops are generally concentrated in the soil layer of about 0-0.6m, and the excavation depth of 0.9-1.8m can well ensure the soil quality of the vegetable planting area. At the same time, the depth of cadmium-contaminated soil is generally about 0.2m, and the deepest is generally about 0.7m. The excavation depth of 0.9-1.8m can remove most of the upper soil with serious cadmium pollution.

[0042] In some embodiments, before step S1 and after step S01, step S02 is also included: selecting a stabilization agent to stabilize the cadmium-contaminated soil, which can reduce the mobility and toxicity of the cadmium pollution, reduce the leaching rate, prevent it from being taken up by plants, and migrate to deep soil and even groundwater.

[0043] In some embodiments, the operating plot is divided into three layers from top to bottom according to the cadmium content, the upper soil is cadmium-contaminated soil, the middle soil is buffer soil, and the lower soil is clean soil, and the excavated soil is stored using a geomembrane, and the width of the geomembrane is adjusted according to the division width of the operating plot. Generally, the width of the three geomembranes is set to a total width of not less than 5m, and the three geomembranes are used to store the upper soil, the middle soil, and the lower soil, respectively, and the geomembrane has good anti-seepage performance. Using a geomembrane to store the excavated soil can effectively prevent the cadmium in the soil from diffusing into the surrounding environment due to rainwater scouring, infiltration, etc. during the storage process, thereby avoiding the occurrence of secondary pollution.

[0044] It should be noted that the operating plot can also be divided into multiple layers according to the cadmium content, such as four layers, five layers, etc. More layers can make the soil treatment effect better. However, in order to consider the workload and treatment effect, dividing the operating plot into three layers according to the cadmium content is the best treatment.

[0045] In some embodiments, the soil of the first operating plot is dug out to form a pit, and a fence is placed in the pit. The outer wall of the fence fits the side wall of the pit. After the fence is placed, the fence can separate the operating plot to be backfilled from the adjacent operating plot, thereby preventing sudden collapse into the adjacent plot and affecting the treatment effect.

[0046] In some embodiments, the height of the enclosure is 60-120 cm, preferably 90 cm, which is generally two-thirds of the soil excavation depth to prevent collapse. At the same time, it isolates the upper soil of the adjacent operating plot filled in the pit from the lower clean soil of the adjacent operating plot, and is the same as the sum of the heights of the upper soil and the middle soil of the operating plot, which can fully protect the bottom clean soil of the adjacent operating plot.

[0047] In some embodiments, after the upper soil and middle soil of the second operation plot adjacent to the first operation plot are backfilled into the first operation plot, the enclosure is pulled out, and the backfilled soil is compacted. The subsequent operation plots are the same. The enclosure can be four separate retaining steel plates, including at least two. After the soil of the first long strip operation plot is dug out, a steel plate with a width of 90 cm is used as the lower enclosure of the pit to prevent collapse, and at the same time isolates the upper soil of the adjacent operation plot filled in the pit from the lower clean soil of the adjacent operation plot, waiting for the second long strip operation plot. After the upper and middle layers of soil of the plot are filled into the first long strip operating plot, the remaining three steel plates except the steel plate between the first long strip operating plot and the second long strip operating plot are pulled out. After all the soil of the second long strip operating plot is filled into the first long strip operating plot, three retaining steel plates are placed in the second long strip operating plot. After the upper and middle layers of soil of the third long strip operating plot are filled into the second long strip operating plot, the steel plate between the first long strip operating plot and the second long strip operating plot is pulled out, and so on.

[0048] The specific operation process is as follows:

[0049] Use an excavator to excavate the first operation plot in layers and pile up each layer of soil in a corresponding temporary storage area. After excavating to the designed depth, place enclosures and empty the pit after the first operation plot is excavated;

[0050] Use an excavator to scrape (clean or dig) the upper soil of the adjacent second operating plot into the pit after the first operating plot is hollowed out, and level it at any time. After the upper soil of the second operating plot is cleaned and the first operating plot is leveled, compact it.

[0051] Use an excavator to scrape (clean or dig) the middle layer of soil from the adjacent second operation plot into the pit of the first operation plot, and level it at any time. When it is filled to the same level as the enclosure, compact it and remove the remaining steel plates except the steel plate between the first long strip operation plot and the second long strip operation plot;

[0052] Use an excavator to dig the lower soil of the adjacent second operation plot into the pit of the first operation plot, and level it at any time. After digging to the designed depth, install the next enclosure, and clean the pit after the second operation plot is hollowed out. After the upper soil and middle soil of the third operation plot are filled into the second operation plot, pull out the steel plate between the first and second operation plots, and so on;

[0053] Fill the upper soil dug out from the first operating plot into the pit of the last operating plot, level it and compact it at any time, then fill the middle layer of soil from the first operating plot into the pit of the last operating plot, level it and compact it at any time, remove the steel plate, fill the lower clean soil of the first operating plot into the pit of the last operating plot, and level it.

[0054] In some embodiments, after step S5, step S6 is further included:

[0055] Maturating the clean soil on the surface can restore its farming function. Maturating the clean soil can promote the growth and reproduction of soil microorganisms and benefit plant growth.

[0056] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for repairing cadmium-contaminated farmland, characterized in that: The following steps are included S1: Divide the cadmium-contaminated plots into multiple operation plots; S2: Divide any of the operating plots into no less than three layers of soil from top to bottom according to the cadmium content, the first layer of soil is cadmium-contaminated soil, the last layer of soil is clean soil, and the middle layer of soil is buffer soil; S3: digging out multiple layers of soil from the first operation plot in sequence to form pits, and storing the multiple layers of soil separately; S4: digging out multiple layers of soil from the next operation plot in sequence to form a pit, and inverting and backfilling the multiple layers of soil into the pit of the previous operation plot; S5: Repeat step S4 until all the operation plots are backfilled.

2. The method for repairing cadmium-contaminated farmland according to claim 1, characterized in that: The plurality of operation plots are long strip operation plots of the same size.

3. The method for repairing cadmium-contaminated farmland according to claim 2, characterized in that: The width of the long strip operation plot is 2-5m.

4. The method for repairing cadmium-contaminated farmland according to claim 1, characterized in that: Before step S1, the method further includes step S01: The cadmium-contaminated land was investigated and the excavation depth was determined, which was 0.9-1.8m.

5. The method for remediating cadmium-contaminated farmland according to claim 4, characterized in that: Before step S1, and after step S01, the method further includes step S02: Select stabilization agents to stabilize cadmium-contaminated soil.

6. The method for remediating cadmium-contaminated farmland according to claim 1, characterized in that: The operation plot is divided into three layers from top to bottom according to the cadmium content, the upper soil layer is cadmium-contaminated soil, the middle soil layer is buffer soil, the lower soil layer is clean soil, and the excavated soil is stored using a geomembrane.

7. The method for remediating cadmium-contaminated farmland according to claim 6, characterized in that: An enclosure is placed in the pit of the first operating plot, and the outer wall of the enclosure fits the side wall of the pit.

8. The method for remediating cadmium-contaminated farmland according to claim 7, characterized in that: The height of the enclosure is 60-120 cm and is the same as the sum of the heights of the upper soil layer and the middle soil layer of the operation plot.

9. The method for remediating cadmium-contaminated farmland according to claim 8, characterized in that: After backfilling the upper soil and middle soil of the next operation plot into the first operation plot, the enclosure is pulled out and the backfilled soil is compacted; Repeat the above steps until all the operation plots are backfilled.

10. The method for remediating cadmium-contaminated farmland according to claim 1, characterized in that: After step S5, the method further includes step S6: Mature the surface soil and restore its farming function.

Images