CN115634923A - Method for repairing heavy metal contaminated soil around coal-based solid waste storage yard - Google Patents
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Abstract
The invention discloses a method for restoring heavy metal polluted soil around a coal-based solid waste storage yard, and belongs to the field of soil metal pollution treatment. According to the pollution range and degree of the soil around the coal-based solid waste storage yard at the stage and the diffusion condition of heavy metals in the coal-based solid waste storage yard to the surroundings within a period of time, through sampling, constructing an inversion model, combining a statistical method and multivariate statistical analysis, selecting a proper plant configuration mode and planting density, the aims of avoiding further aggravation of the pollution degree during restoration and reducing the pollution degree of the soil around the storage yard to a clean or clean level after a period of time are achieved. The method has the advantages of simple steps, convenience in implementation, high reliability and high economical efficiency.
Description
Technical Field
The invention relates to a method for restoring heavy metal polluted soil around a coal-based solid waste storage yard, and belongs to the field of soil metal pollution treatment.
Background
Mineral resource development plays an important role in economic development, but activities involving the coal industry also cause serious pollution to the surrounding environment. The release of heavy metal elements in the long-term storage process of the coal-based solid and the environment accumulation effect cannot be ignored. Heavy metal pollution is an important type of soil pollution, and heavy metals not only can affect the growth and development of plants, but also can enter human bodies through the accumulation of food chains, and finally harm the health of the human bodies. For example, lead can be harmful to a number of systems in the human body, including nerves, cardiovascular, liver, vision, etc.; cadmium damages the kidney, causes osteoporosis, or causes cancer, etc. Therefore, proper technologies need to be selected to manage and control the heavy metals in the soil around the coal-based solid waste storage yard.
The super-accumulation plant can extract heavy metals from large-range soil and store the heavy metals in vivo, the concentration of the metals in vivo is 100 times higher than that of common plants, and the super-accumulation plant has super-enrichment capacity and super-tolerance to the heavy metals. By utilizing the characteristic of super-accumulation plants, the heavy metals can be removed from the heavy metal contaminated soil, and phytoremediation is realized. However, the remediation of heavy metal contaminated soil by using super-accumulative plants has the following disadvantages: 1. most of the super-accumulation plants only have good enrichment effect on one or a few heavy metals, and have poor remediation effect on soil which is polluted by a plurality of heavy metals and has low content of each heavy metal; 2. most super-accumulative plants are native plants in the south, have high requirements on humidity and temperature, are narrow in applicable pH value range and are difficult to grow under the environment condition in the north; 3. after the heavy metal contaminated soil is phytoremediation, most super-accumulated plants have low heavy metal content (in mg of heavy metal/kg of plant), but the biomass (in kg of plant) is not large, so that the heavy metal extraction amount (in mg of heavy metal) is not large, and the heavy metal in the soil can be reduced to a target level by planting multiple crops.
The heavy metal contaminated soil is repaired by adopting a plant extraction technology, and super-accumulation plants with good enrichment effect on heavy metals are usually required to be planted. However, the remediation of heavy metal contaminated soil by using super-accumulative plants has the following disadvantages: 1. most of the super-accumulation plants have good enrichment effect only on one or a few heavy metals, and have poor remediation effect on soil which is subjected to multiple heavy metal combined pollution and has low content of each heavy metal; 2. most super-accumulative plants are native plants in the south, have high requirements on humidity and temperature, are narrow in adaptive pH value range and are difficult to grow under the environment condition in the north; 3. after the heavy metal contaminated soil is phytoremediation, most super-accumulated plants have low heavy metal content (in mg of heavy metal/kg of plant), but the biomass (in kg of plant) is not large, so that the heavy metal extraction amount (in mg of heavy metal) is not large, and the heavy metal in the soil can be reduced to a target level by planting multiple crops.
Disclosure of Invention
The technical problem is as follows: the invention provides a method for repairing heavy metal contaminated soil around a coal-based solid waste storage yard, aiming at the existing technical problems, the matching planting proportion and planting density are determined according to the heavy metal contamination degree, the method can be used for repairing the soil around the coal-based solid waste in the north, and a better repairing effect can be obtained.
The technical scheme is as follows: in order to achieve the aim, the method for restoring the heavy metal polluted soil around the coal-based solid waste storage yard comprises the following steps:
step 1, determining the pollution range and the pollution degree of soil around a coal-based solid waste storage yard through a plurality of sampling of field areas;
step 2, marking the content of various heavy metals in the soil in each polluted area, performing area division on the coal-based solid waste storage yard according to the determined pollution range and pollution degree, evaluating the ecological risk in each area around the storage yard by using a single-factor index method and an internal Mei Luo comprehensive pollution index method, and dividing a slightly polluted area, a moderate polluted area and a heavily polluted area through the ecological risk; then predicting the change of a heavy metal polluted area without intervention according to the condition that heavy metals in the coal-based solid waste storage yard diffuse to the periphery of the coal-based solid waste storage yard;
the method comprises the following steps of determining the condition that heavy metals diffuse to the periphery of a coal-based solid waste storage yard in a preset time period by utilizing a column type test: firstly, investigating dumping plans and dumping records of a storage yard, determining types of solid wastes contained in filling materials in the coal-based solid waste storage yard and proportions of various solid wastes, preparing the same filling materials and loading the filling materials into leaching columns, wherein the horizontal diffusion of heavy metals in the coal-based solid waste storage yard is mainly driven by rainfall action, so that water is leached from the upper parts of the leaching columns according to rainfall of areas where the storage yard is located, leaching liquid water samples are taken from transverse sampling ports with different heights of the leaching columns, and the horizontal diffusion conditions of various heavy metals in the leaching liquid water samples are analyzed to simulate the diffusion conditions of the heavy metals to the surroundings of the coal-based solid waste storage yard.
Step 3, in different polluted areas, selecting proper extensive accumulation plants and super accumulation plants according to local natural environment to extract heavy metal pollution in soil, then testing the change condition of the extraction capacity of the selected extensive accumulation plants and super accumulation plants to various heavy metals along with time, calculating the amount of heavy metals to be removed in unit time of each area according to the information of diffusion of the heavy metal pollution to the periphery of the area to ensure that the heavy metal pollution in the soil is not diffused, and finally determining plant species, plant configuration modes and planting density in different areas according to the test result; the heavy metal pollution degree of the surrounding soil of the coal-based solid waste storage yard is prevented from further aggravating during the restoration period, and the extraction capacity of the plants exceeds the diffusion speed of the heavy metal by reasonably matching the planted plants, so that the pollution degree of the surrounding soil of the coal-based solid waste storage yard is reduced to a clean or clean level after a period of time.
Further, sampling points are reasonably arranged in a research area, soil samples are collected, the soil samples are taken back to a laboratory to measure soil reflection spectrum and soil heavy metal content, an inversion model of the soil heavy metal content is constructed by combining a partial least square regression method, sample point data of unknown content is predicted according to an optimal inversion model of each heavy metal, and then the pollution range and the pollution degree of the heavy metal are researched by combining a geostatistics method and multivariate statistical analysis.
Further, with respect to single heavy metal contamination: cd. Hg, as, pb, cr, cu, ni, zn; areas with light, moderate and severe pollution levels are demarcated around the waste dump according to a single factor index method, and are respectively marked as follows in the map: mild single, moderate single and severe single three grades;
the method comprises the following steps of evaluating the condition that various heavy metals such As Cd, hg, as, pb, cr, cu, ni and Zn exist in the composite heavy metal contaminated soil at the same time by utilizing an internal Mei Luo comprehensive pollution index method, delimiting areas with mild pollution, moderate pollution and severe pollution levels around a waste storage yard, and respectively marking the areas As follows in a map: mild degree, moderate degree, and severe degree;
the single heavy metal contaminated area and the area conforming to the heavy metal contaminated area are integrated, and the final light contamination, moderate contamination and severe contamination are respectively marked as follows in the map: mild total, moderate total and severe total, the formula is as follows:
severe total = severe mono-to-severe.
Further, sampling points are reasonably arranged in a slightly polluted area, a medium polluted area and a heavily polluted area around the storage yard respectively, soil samples are collected from the sampling points, the soil samples are brought back to a laboratory to measure the soil reflection spectrum and the soil heavy metal content, and after the content of various heavy metals in the soil around the storage yard is measured, the ecological risk in each area around the storage yard can be evaluated according to a single-factor index method and an internal Mei Luo comprehensive pollution index method. The calculation formula is as follows:
P i ＝C i /S i 
in the formula: p i Is the single factor pollution index of heavy metal i; c i The measured content (mg/kg) of the heavy metal i; s i An evaluation standard value (mg/kg) of the heavy metal i; i is the comprehensive pollution index of the inner Mei Luo of various heavy metals; p max Is the maximum index among the single factor pollution indexes; p is ave The average of each single factor contamination index. P i The relationship between the size of I and the pollution condition is shown in tables 1 and 2;
TABLE 1 contamination with certain heavy metals
| Single factor pollution index P i Size and breadth | Pollution level of such heavy metals |
| P i ≤1 | No pollution |
| 1＜P i ≤2 | Slight pollution |
| 2＜P i ≤3 | Moderate pollution |
| P i ＞3 | Severe pollution |
TABLE 2 comprehensive contamination of various heavy metals
Selecting heavy metal with the highest single-factor pollution index, and defining areas with light pollution, moderate pollution and severe pollution grades of the heavy metal, wherein the areas are respectively called light single, moderate single and severe single;
in terms of the risk of compound heavy metal pollution, an internal Mei Luo comprehensive pollution index method is used for evaluating, and areas with light pollution, moderate pollution and severe pollution grades are defined and are respectively called light internal, moderate internal and severe internal;
according to the results of the single factor index method and the inner Mei Luo comprehensive pollution index method, final mild pollution, moderate pollution and severe pollution grade areas are defined and respectively called as mild total, moderate total and severe total, and the formula is as follows:
severe total = severe mono-to-severe.
An inversion model of the soil various heavy metal single-factor pollution indexes and the internal Mei Luo comprehensive pollution indexes is constructed by combining a partial least square regression method, sample point data with unknown content is predicted according to the optimal inversion model of each heavy metal, and then the pollution range and the pollution degree of the heavy metal are researched by combining a geostatistics method and multivariate statistical analysis.
Further, the specific content of obtaining the diffusion situation of heavy metal through the column type test is as follows:
reducing relevant parameters of the coal-based solid waste storage yard and the pollution range thereof according to the same proportion to design a column type test model, wherein the column type test model comprises an L-shaped leaching column, a coal-based solid waste filling material is filled in a left side column of the L-shaped leaching column to simulate the coal-based solid waste storage yard higher than the ground, and soil is filled in a right side column of the L-shaped leaching column to simulate the polluted soil around the coal-based solid waste storage yard; the height of the coal-based solid waste filling material in the upright column is a yard height analog value reduced according to an actual proportion, and the height of the soil filled in the horizontal column is a soil depth analog value reduced according to the actual proportion; a spray header for simulating rainwater is arranged at the top of the upright post, and a device for collecting leachate is arranged at the rightmost side of the horizontal post;
according to the rainfall of the area where the storage yard is located, water is sprayed through the spray header, a sprayed liquid water sample is collected, and the horizontal diffusion condition of various heavy metals in the sprayed liquid water sample is analyzed so as to simulate the condition that the heavy metals in the coal-based solid waste storage yard diffuse to the periphery of the coal-based solid waste storage yard;
if the annual average precipitation of the location of the coal-based solid waste storage yard is L decimeter and the diameter of the top of the leaching column is d decimeter, the total leaching water volume of the column test can be calculated to be pi d 2 L/4 liter. Opening a sampling port on the side surface of the eluviation column to sample by using a measuring cylinder while eluviating each time, and recording the volume of the eluviation liquid received in the measuring cylinder on days d1, d2,. And dn; analysis of concentration C of 8 heavy metals in water sample i (i = Cd, hg, as, pb, cr, cu, ni, zn in mg/L), the diffusion condition of the heavy metal to the water outlet of the leaching column in the horizontal direction can be obtained, namely the condition that the heavy metal in the coal-based solid waste storage yard horizontally diffuses to the periphery is simulated: thereby drawing the mass flow rho of various heavy metals i (i = Cd, hg, as, pb, cr, cu, ni, zn in mg/d) As a function of time. If the mass of the soil on the side surface of the leaching column is m, setting a parameter y i ＝ρ i (i = Cd, hg, as, pb, cr, cu, ni, zn in mg [ heavy metals ]]* kg (soil)] -1 *d -1 ) Y of various heavy metals can be drawn i Fitted curve over time.
Further, in areas of different pollution levels: planting different plant types in three regions of mild total, moderate total and severe total to extract heavy metals in soil:
growing extensively accumulated plants in lightly contaminated areas: ryegrass, calendula, zinnia; the widely accumulated plants can have certain enrichment effect on various heavy metals and are suitable for the northern climate; the fertilizer is easy to grow, large in population density, large in biomass and developed in root system; the super-accumulation plants and the wide-accumulation plants are planted in a matching way in the moderate pollution area and the severe pollution area, and the planting density in the severe pollution area is higher than that in the moderate pollution area. The planting scheme can achieve the aims of avoiding further aggravation of the pollution degree during restoration and reducing the pollution degree of the soil around the storage yard to a clean or clean level after a period of time.
Has the advantages that:
aiming at different heavy metal pollution risk areas and main heavy metal pollutants, different super-accumulation plants and 'wide accumulation plants' are selected for matched planting, the pertinence is strong, and the heavy metal extraction effect is good. The 'widely accumulated plants' comprise garden crops such as ryegrass, calendula, zinnia and the like, and play a role in beautifying the environment while repairing the heavy metals in the soil.
Drawings
FIG. 1 is a schematic flow chart of the method for remediating heavy metal contaminated soil around a coal-based solid waste yard according to the present invention;
FIG. 2 is a schematic diagram of the division of the pollution area around the yard according to the single-factor pollution index of Cd in the embodiment of the present invention;
FIG. 3 is a schematic diagram of the method for dividing the pollution area around the yard according to the comprehensive pollution index of Mei Luo in the embodiment of the present invention;
FIG. 4 is a schematic diagram of the method for dividing the pollution area around the yard by combining the single-factor pollution index of Cd and the comprehensive pollution index of inner Mei Luo;
FIG. 5 is a schematic diagram of a column test used in an embodiment of the present invention;
FIG. 6 is a schematic diagram of a plant configuration used in an embodiment of the present invention;
FIG. 7 is a fitting curve a of Cd in the design scheme of the embodiment of the invention 3 And fitting curve 1 schematic;
FIG. 8 is a fitting curve b of Cd in the design scheme of the embodiment of the invention 3 And fitting curve 1 schematic;
FIG. 9 is a fitting curve c of Cd in the test design scheme of the embodiment of the invention 3 And fitting curve 1.
Detailed Description
Embodiments of the invention are further described below with reference to the accompanying drawings:
the coal-based solid waste pile is arranged, 8 heavy metals of Cd, hg, as, pb, cr, cu, ni and Zn are mainly diffused to the periphery, and the surrounding soil is mainly polluted by the 8 heavy metals:
the invention relates to a method for restoring heavy metal contaminated soil around a coal-based solid waste storage yard, which comprises the following specific steps
Step 1: determining extent and degree of contamination
Firstly, reasonably arranging sampling points in a research area, collecting soil samples, bringing the soil samples back to a laboratory to measure soil reflection spectrum and soil heavy metal content, constructing an inversion model of the soil heavy metal content by combining a partial least squares regression method, predicting sample point data of unknown content according to an optimal inversion model of each heavy metal, and then obtaining a content distribution spectrogram of each heavy metal in the research area by combining a geostatistics method and multivariate statistical analysis.
Substituting the calculation formulas of the single-factor pollution index and the inner Mei Luo comprehensive pollution index into the model to obtain a single-factor pollution index distribution spectrogram and an inner Mei Luo comprehensive pollution index distribution spectrogram of various heavy metals,
if the single-factor pollution index of the Cd is the highest, the surrounding of the storage yard can be divided into a mild single area, a moderate single area and a severe single area (in the mild single area, the single-factor pollution index P of the Cd is Cd Satisfy 1 < P Cd Less than or equal to 2; in the medium single region, P Cd Satisfy 2 < P Cd Less than or equal to 3; in a severe single region, P Cd Satisfy P Cd > 3). The regions are shown in figure 1.
Then, substituting a calculation formula of the inner Mei Luo comprehensive pollution index into a model, dividing the periphery of the yard into a mild inner area, a moderate inner area and a severe inner area (in the mild inner area, the inner Mei Luo comprehensive pollution index I satisfies 1 < I < 2; in the moderate inner area, I satisfies 2 < I < 3; and in the severe inner area, I satisfies I > 3) according to the inner Mei Luo comprehensive pollution index I of 8 heavy metals of Cd, hg, as, pb, cr, cu, ni and Zn, wherein the areas are shown in FIG. 2.
Then, the single-factor pollution index of Cd and the comprehensive pollution index of Mei Luo of 8 heavy metals are combined, and the periphery of the storage yard is divided into three areas of mild total, moderate total and severe total according to the following formula. The area is shown as 3.
Severe total = severe mono-to-severe.
Step 2: column test
As shown in FIG. 4, the diffusion of heavy metals is known by column tests to avoid further aggravation of the contamination during the repair process. The method comprises the steps of designing a column type test model by reducing relevant parameters of a coal-based solid waste storage yard and a pollution range of the coal-based solid waste storage yard according to the same proportion (assuming that the reduction multiple is k), investigating a dumping plan and a dumping record of the storage yard, determining solid waste types contained in filling materials in the coal-based solid waste storage yard and the proportion of various solid wastes, and preparing the same filling materials to be filled into an L-shaped leaching column. The horizontal diffusion of the heavy metals in the coal-based solid waste storage yard is mainly driven by rainfall effect, so that water is drenched from the upper part of the leaching column according to the rainfall of the area where the storage yard is located, a leaching liquid water sample is taken from a side sampling port of the leaching column, and the horizontal diffusion conditions of various heavy metals in the leaching liquid water sample are analyzed to simulate the condition that the heavy metals in the coal-based solid waste storage yard diffuse to the periphery of the leaching liquid water sample.
If the annual average precipitation of the location of the coal-based solid waste storage yard is L decimeter and the diameter of the top of the leaching column is d decimeter, the total leaching water volume pi d of the column test can be calculated 2 L/4L. And opening a sampling port on the side surface of the eluviation column to sample by using the measuring cylinder while eluviating each time, and recording the volume of the eluviation liquid received in the measuring cylinder on days d1, d 2. Analysis of concentration C of 8 heavy metals in water sample i (i＝Cd、Hg、As, pb, cr, cu, ni and Zn in mg/L), and obtaining the diffusion condition of heavy metal to the water outlet of the leaching column in the horizontal direction (namely simulating the condition that the heavy metal in the coal-based solid waste storage yard diffuses horizontally to the periphery): the mass flow rho of various heavy metals can be drawn i (i = Cd, hg, as, pb, cr, cu, ni, zn in mg/d) As a function of time. If the mass of the soil on the side surface of the leaching column is m, setting a parameter y i ＝ρ i (i = Cd, hg, as, pb, cr, cu, ni, zn in mg [ heavy metals ]]* kg (soil)] -1 *d -1 ) Y of various heavy metals can be drawn i Fitted curve over time.
And step 3: planting test
Two small-range test areas are selected within the pollution range of the coal-based solid waste storage yard, a plurality of plants of the rhodiola rosea with Cd super accumulation are planted in the test area A, and ryegrass with the wide accumulation plant is planted in the test area B. In the test area A, 1 rhodiola sachalinensis is taken on d1, d2, d.and dn days after sowing, and the biomass (unit is kg [ plants ]) and the content of various heavy metals in vivo (unit is mg [ heavy metals ]/kg [ plants ]) of the rhodiola sachalinensis are measured; similarly, in test area B, 1 ryegrass was taken on days d1, d2,. And dn after sowing, and the biomass (in kg of plants) and the content of various heavy metals in vivo (in mg of heavy metals/kg of plants) were measured. Then, a fitting curve of the extraction amount of the sedum aizoon (in mg of heavy metal) of various heavy metals along with the change of time and a fitting curve of the extraction amount of the ryegrass (in mg of heavy metal) of various heavy metals along with the change of time can be drawn.
Plan to grow ryegrass (widely accumulated plants) and sedum aizoon (Cd super-accumulated plants) in a severe total area; planting ryegrass (widely accumulated plants) and sedum spectabile (Cd super-accumulated plants) in a moderate total area, wherein the planting density of the area is less than that of a severe total area; ryegrass was planted in the light areas and the plant configuration is shown in figure 5.
And 4, step 4: checking whether the designed scheme can achieve the target
The plant repair achieves the following aims: not only can avoid further aggravation of the pollution degree during the restoration, but also can reduce the pollution degree of the soil around the storage yard to a clean or not clean level after a period of time. Next, a method for determining whether the plant species, plant configuration pattern, and planting density of the current design can achieve the phytoremediation goal will be described.
Assuming that the evaluation standard value of the soil Cd in the area of the coal-based solid waste storage yard is S Cd mg/kg. In a severe general area, the average content of Cd in the soil is
In order to achieve the goal of phytoremediation in the heavy total area, firstly, the extraction capacity of Cd by the plants planted in the heavy total area is greater than the diffusion capacity of Cd from the coal-based solid waste storage yard to the area (so as to avoid further expansion of the pollution range), and secondly, the plants planted in the heavy total area are also capable of reducing the content of Cd in soil in the area (so that the pollution degree of the soil around the storage yard is reduced to a clean or clean level).
By column experiments to give y Cd (y Cd ＝ρ Cd M, m is the mass of the soil on the side surface of the leaching column) and the change condition of time (the curve equation is y = y (t)), and predicting the coal-based solid waste storage yard y Cd Time-related changes (referred to as fitted curve 1 y = k × y (t), k being the scaling of the column model compared to the actual yard).
Planting Sedum spectabile P in severe general area 1 Planting ryegrass q 1 And (4) strain. And the change of the extraction amount of heavy metal Cd of a single plant of sedum aizoon with time is known in advance through planting tests (called as a fitting curve a) 1 : y = f (t)), and the extraction of heavy Cd from ryegrass as a function of time (referred to as the fitted curve a) 2 : y = g (t)). Calculating the change of the total extraction flux of all plants in the severe total area along with time (called a fitted curve a) 3 ：y＝p 1 f(t)+q 1 g(t))。
Fitting the curve 1 and the curve a 3 Plotted in the same graph (ordinate unit is mg heavy metal]* kg [ soil ]] -1 *d -1 The abscissa has the unit d), as shown in fig. 6. FittingCurve 1 is substantially at the fitted curve a 3 And the heavy metals diffused to the heavy total area from the coal-based solid waste storage yard can be extracted by the plants in the area in large quantity, and the pollution degree of the heavy total area cannot be further increased. Order to
(lower integration limit d1 and upper integration limit dn are the time of the first sampling and the last sampling of the column test and the planting test, respectively), and Δ C Cd1 Satisfy the requirements of
It can be ensured that the single-factor contamination index of Cd in the heavy total area can be reduced to below 1 after a certain period of time, reaching a clean or still clean level. Otherwise, the planting density of the area should be increased (i.e. p should be increased) 1 、q 1 )。
In the medium total area, the average content of Cd in the soil is
Similarly, the sedum aizoon p is planted in the middle total area 2 Planting ryegrass q 2 And (4) strain. Calculating the change of the total extraction flux of all plants in the area along with the time (called a fitting curve b) 3 ：y＝p 2 f(t)+q 2 g (t)). The fitting curve 1 and the fitting curve b 3 Plotted in the same graph as shown in fig. 7. Order to
While being Delta C Cd2 Satisfy the requirement of
The target can be achieved. Otherwise, the planting density of the area should be increased (i.e. p should be increased) 2 、q 2 )。
In the light total area, the average content of Cd in the soil is
Similarly, planting ryegrass in the light total areaq 3 And (4) strain. Calculating the change of the total extraction flux of all plants in the area along with the time (called a fitted curve c) 3 ： y＝q 3 g (t)). The fitting curve 1 and the fitting curve c 3 Plotted in the same figure as shown in fig. 8. Order to
At the same time,. DELTA.C Cd3 Satisfy the requirements of
The target can be achieved. Otherwise, the planting density of the area should be increased (namely, q is increased) 3 )。
Similarly, the fitting curve graphs of Hg, as, pb, cr, cu, ni and Zn in the severe total, moderate total and mild total areas are drawn continuously, so that the fitting curve 1 in each area is ensured to be basically in the fitting curve a 1 、b 1 、c 1 Below, and satisfy
(i = Cd, hg, as, pb, cr, cu, ni, zn), various heavy metals can be targeted. Otherwise, the planting density of the corresponding area should be increased.
When the single-factor pollution index of several heavy metals with larger single-factor pollution indexes is reduced to a clean or clean level, finally, the inner Mei Luo comprehensive pollution index is also reduced to a clean or clean level according to a calculation formula of the inner Mei Luo comprehensive pollution index.
Claims (6)
1. A method for restoring heavy metal contaminated soil around a coal-based solid waste storage yard is characterized by comprising the following steps:
step 1, determining the pollution range and the pollution degree of soil around a coal-based solid waste storage yard through a plurality of sampling of field areas;
step 2, marking the content of various heavy metals in soil in each polluted area, performing area division on the coal-based solid waste storage yard according to the determined pollution range and the pollution degree, evaluating the ecological risks in each area around the storage yard by using a single-factor index method and an inner Mei Luo comprehensive pollution index method, and dividing a slightly polluted area, a moderately polluted area and a heavily polluted area through the ecological risks; then predicting the change of a heavy metal polluted area without intervention according to the condition that heavy metals in the coal-based solid waste storage yard diffuse to the periphery of the coal-based solid waste storage yard;
the method comprises the following steps of determining the condition that heavy metals diffuse to the periphery of a coal-based solid waste storage yard in a preset time period by utilizing a column type test: firstly, surveying a dumping plan and a dumping record of a storage yard, determining the types of solid wastes contained in filling materials in the coal-based solid waste storage yard and the proportion of various solid wastes, preparing the same filling materials, and loading the filling materials into leaching columns, wherein the horizontal diffusion of heavy metals in the coal-based solid waste storage yard is mainly driven by rainfall action, so that water is leached from the upper parts of the leaching columns according to the rainfall of the area where the storage yard is located, leaching liquid water samples are taken from transverse sampling ports with different heights of the leaching columns, and the horizontal diffusion conditions of various heavy metals in the leaching liquid water samples are analyzed to simulate the diffusion conditions of the heavy metals in the coal-based solid waste storage yard to the periphery of the leaching columns.
Step 3, in different polluted areas, selecting proper extensive accumulation plants and super accumulation plants according to local natural environment to extract heavy metal pollution in soil, then testing the change condition of the extraction capacity of the selected extensive accumulation plants and super accumulation plants to various heavy metals along with time, calculating the amount of heavy metals to be removed in unit time of each area according to the information of diffusion of the heavy metal pollution to the periphery of the area to ensure that the heavy metal pollution in the soil is not diffused, and finally determining plant species, plant configuration modes and planting density in different areas according to the test result; the heavy metal pollution degree of the surrounding soil of the coal-based solid waste storage yard is prevented from further aggravating during the restoration period, and the extraction capacity of the plants exceeds the diffusion speed of the heavy metal by reasonably matching the planted plants, so that the pollution degree of the surrounding soil of the coal-based solid waste storage yard is reduced to a clean or clean level after a period of time.
2. The method for remediating heavy metal contaminated soil around a coal-based solid waste storage yard according to claim 1, wherein the method comprises the following steps: sampling points are reasonably arranged in a research area, soil samples are collected, the soil samples are brought back to a laboratory to measure soil reflection spectrum and soil heavy metal content, an inversion model of the soil heavy metal content is constructed by combining a partial least square regression method, sample point data of unknown content is predicted according to an optimal inversion model of each heavy metal, and then the pollution range and the pollution degree of the heavy metal are researched by combining a geostatistics method and multivariate statistical analysis.
3. The method for remediating heavy metal contaminated soil around a coal-based solid waste yard according to claim 1, wherein the method comprises the following steps:
for single heavy metal contamination: cd. Hg, as, pb, cr, cu, ni, zn; areas with light, moderate and severe pollution levels are demarcated around the waste dump according to a single factor index method, and are respectively marked as follows in the map: mild single, moderate single and severe single three grades;
the method comprises the following steps of evaluating the condition that various heavy metals such As Cd, hg, as, pb, cr, cu, ni and Zn exist in the composite heavy metal contaminated soil at the same time by utilizing an internal Mei Luo comprehensive pollution index method, delimiting areas with mild pollution, moderate pollution and severe pollution levels around a waste storage yard, and respectively marking the areas As follows in a map: mild degree, moderate degree, and severe degree;
the single heavy metal polluted area and the area conforming to the heavy metal pollution are integrated, and the final light pollution, the moderate pollution and the severe pollution are respectively marked as follows in a map: mild total, moderate total and severe total, the formula is as follows:
severe total = severe mono-to-severe.
4. The method for remediating heavy metal contaminated soil around a coal-based solid waste yard according to claim 3, wherein the method comprises the following steps: sampling points are reasonably arranged in a slightly polluted area, a moderately polluted area and a heavily polluted area around the storage yard respectively, soil samples are collected from the sampling points, the soil samples are taken back to a laboratory to measure the soil reflection spectrum and the soil heavy metal content, and after the content of various heavy metals in the soil around the storage yard is measured, the ecological risk in each area around the storage yard can be evaluated according to a single-factor index method and an inner Mei Luo comprehensive pollution index method. The calculation formula is as follows:
P i ＝C i /S i 
in the formula: p i Is the single factor pollution index of heavy metal i; c i The measured content (mg/kg) of the heavy metal i; s i An evaluation standard value (mg/kg) of the heavy metal i; i is the comprehensive pollution index of the inner Mei Luo of various heavy metals; p max Is the maximum index among the single factor pollution indexes; p ave The average of each single factor contamination index. P i The relationship between the size of I and the pollution condition is shown in tables 1 and 2;
TABLE 1 contamination with certain heavy metals
TABLE 2 comprehensive contamination of various heavy metals
Selecting heavy metal with the highest single-factor pollution index, and defining areas with light pollution, moderate pollution and severe pollution grades of the heavy metal, wherein the areas are respectively called light single, moderate single and severe single;
in terms of the risk of compound heavy metal pollution, an internal Mei Luo comprehensive pollution index method is used for evaluating, and areas with light pollution, moderate pollution and severe pollution grades are defined and are respectively called light internal, moderate internal and severe internal;
according to the results of the single factor index method and the inner Mei Luo comprehensive pollution index method, final mild pollution, moderate pollution and severe pollution grade areas are defined and respectively called as mild total, moderate total and severe total, and the formula is as follows:
severe total = severe mono £ severe.
An inversion model of the soil various heavy metal single-factor pollution indexes and the internal Mei Luo comprehensive pollution indexes is constructed by combining a partial least square regression method, sample point data with unknown content is predicted according to the optimal inversion model of each heavy metal, and then the pollution range and the pollution degree of the heavy metal are researched by combining a geostatistics method and multivariate statistical analysis.
5. The method for remediating heavy metal contaminated soil around a coal-based solid waste storage yard according to claim 1, wherein the specific content of obtaining the diffusion situation of the solution heavy metal through a column test is as follows:
reducing relevant parameters of the coal-based solid waste storage yard and the pollution range thereof according to the same proportion to design a column type test model, wherein the column type test model comprises an L-shaped leaching column, a coal-based solid waste filling material is filled in a left side column of the L-shaped leaching column to simulate the coal-based solid waste storage yard higher than the ground, and soil is filled in a right side column of the L-shaped leaching column to simulate the polluted soil around the coal-based solid waste storage yard; the height of the coal-based solid waste filling material in the upright column is a yard height analog value reduced according to an actual proportion, and the height of the soil filled in the horizontal column is a soil depth analog value reduced according to the actual proportion; a spray header for simulating rainwater is arranged at the top of the upright post, and a device for collecting leachate is arranged at the rightmost side of the horizontal post;
according to the rainfall of the area where the storage yard is located, water is sprayed through the spray header, a sprayed liquid water sample is collected, and the horizontal diffusion condition of various heavy metals in the sprayed liquid water sample is analyzed so as to simulate the condition that the heavy metals in the coal-based solid waste storage yard diffuse to the periphery of the coal-based solid waste storage yard;
if the annual average precipitation of the location of the coal-based solid waste storage yard is L decimeters, the top of the leaching columnThe diameter is d decimeters, the total leaching water volume pi d of the column test can be calculated 2 L/4L. Opening a measuring cylinder for sampling at a sampling port on the side surface of the eluviation column during eluviation each time, and recording the volume of the eluviation liquid received in the measuring cylinder on days d1, d2,. Ang.d.dn; analysis of the concentration C of 8 heavy metals in a Water sample i (i = Cd, hg, as, pb, cr, cu, ni, zn, in mg/L), the diffusion situation of heavy metals to the water outlet of the leaching column in the horizontal direction can be obtained, namely the situation of heavy metals to diffuse horizontally to the periphery in the simulated coal-based solid waste storage yard: thereby drawing the mass flow rho of various heavy metals i (i = Cd, hg, as, pb, cr, cu, ni, zn in mg/d) As a function of time. If the mass of the soil on the side surface of the leaching column is m, setting a parameter y i ＝ρ i (i = Cd, hg, as, pb, cr, cu, ni, zn in mg [ heavy metals ]]* kg (soil)] -1 *d -1 ) Y of various heavy metals can be drawn i Fitted curve over time.
6. The method for remediating heavy metal contaminated soil around a coal-based solid waste yard according to claim 1, wherein the method comprises the following steps: in areas of different contamination levels: planting different plant types in three regions of mild total, moderate total and severe total to extract heavy metals in soil:
growing extensive accumulation of plants in lightly contaminated areas: ryegrass, calendula, zinnia; the widely accumulated plants can have certain enrichment effect on various heavy metals and are suitable for the northern climate; the fertilizer is easy to grow, large in population density, large in biomass and developed in root system; the super-accumulation plants and the wide-accumulation plants are planted in a matching way in the moderate pollution area and the severe pollution area, and the planting density in the severe pollution area is higher than that in the moderate pollution area. The planting scheme can achieve the aims of avoiding further aggravation of the pollution degree during restoration and reducing the pollution degree of the soil around the storage yard to a clean or clean level after a period of time.
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