CN115055510B - Restoration method and application of heavy metal contaminated soil - Google Patents
Restoration method and application of heavy metal contaminated soil Download PDFInfo
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- CN115055510B CN115055510B CN202210672928.9A CN202210672928A CN115055510B CN 115055510 B CN115055510 B CN 115055510B CN 202210672928 A CN202210672928 A CN 202210672928A CN 115055510 B CN115055510 B CN 115055510B
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/08—Reclamation of contaminated soil chemically
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/02—Extraction using liquids, e.g. washing, leaching, flotation
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
- B09C—RECLAMATION OF CONTAMINATED SOIL
- B09C1/00—Reclamation of contaminated soil
- B09C1/06—Reclamation of contaminated soil thermally
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Abstract
The present disclosure relates to a repair method and application of heavy metal contaminated soil, the repair method comprising the steps of: (1) Mixing hydrofluoric acid and soil to be treated and reacting; (2) Carrying out solid-liquid separation on the treated soil, and collecting solid components; (3) And leaching the collected solid components by using a leaching agent to obtain the restored soil. According to the method, the silicate lattice in the soil can be broken through by utilizing hydrofluoric acid and preferably matching with microwave heating treatment, and the residual cadmium is promoted to be converted into cadmium in other forms, so that the overall activity of the cadmium in the cadmium polluted soil is improved, the removal rate of the cadmium in the soil is effectively improved, the content of the cadmium in the soil is reduced as much as possible, and the potential risk caused by the cadmium is avoided.
Description
Technical Field
The disclosure relates to the technical field of heavy metal contaminated soil remediation, in particular to a heavy metal contaminated soil remediation method and application, and especially relates to a heavy metal contaminated selenium-rich soil remediation method and application.
Background
Soil heavy metal pollution is a serious environmental problem at present, and cadmium pollution is particularly prominent. Heavy metal cadmium is a target which needs to be focused in soil pollutants because of strong biotoxicity; therefore, reasonable soil restoration means and prevention measures are adopted to cope with the cadmium pollution of the soil, and the method has extremely important significance for the development and utilization of soil resources and the health of human beings.
For severely and extremely contaminated soil, the removal of heavy metals to reduce the content thereof is a currently accepted restoration strategy, and the stabilization method commonly used in soil restoration does not completely remove heavy metal ions from the soil when treating the severely and particularly extremely severely heavy metal contaminated soil, and still has potential environmental risks, for example, CN110871213a discloses a restoration method for stabilizing/solidifying lead contaminated soil, which can reduce the mobility of lead in the soil by adding ferrous sulfate to the heavy metal lead contaminated soil and adding biochar and phosphate to stabilize the lead ions, but does not completely remove the lead ions, and the lead ions still have the possibility of migrating to the environment as the oxidizing environment of the soil changes later; compared with other restoration methods, the plant extraction restoration method and the chemical leaching restoration method can thoroughly remove heavy metals in soil, but because the heavy metals tend to exist in the soil in different forms, and the migration and activity differences of the heavy metals in different forms are larger, when heavy metal compounds exist in a residue state after being coated by silicon dioxide or silicate minerals, the heavy metal compounds are difficult to be directly absorbed by plant roots for removal, for example, CN109365494A discloses a plant restoration method for treating cadmium-manganese-chromium composite contaminated soil, which selects hyper-enriched plant celosia and Arabidopsis thaliana as experimental plants to absorb cadmium-manganese-chromium in the contaminated soil, experiments prove that celosia and Arabidopsis thaliana have better enrichment effect on cadmium-manganese-chromium in the soil, but only the content of active cadmium-manganese-chromium in the soil is found to be obviously reduced, and the residue state cadmium removal effect is extremely poor; CN104472161a discloses a method for remedying the soil polluted by medium and slight cadmium by intercropping capsicum and corn, the method utilizes capsicum to absorb and enrich heavy metal in the soil, reduces the heavy metal content of intercropping plants, has simple operation and strong practicability, but is only applicable to the soil with light cadmium pollution degree; the method for cooperatively removing arsenic, cadmium and lead in the field soil by utilizing the combined leaching agent is disclosed in CN112108509, the combined leaching agent is prepared by combining a biodegradable chelating agent and a low-molecular organic acid, the removal rate of cadmium and lead reaches 60%, but the content of residual heavy metals in the soil before and after leaching is relatively stable, and the residual heavy metals are difficult to be leached and removed.
The occurrence forms of heavy metals in soil are mainly divided into four types: an acid extractable state, a reducible state, an oxidizable state, and a residue state. The residual cadmium exists mainly in crystal lattices of silicate, mineral or sediment, the crystal structure of silicate mineral is very stable, the conventional acid-base treatment cannot be completely destroyed, and the activity is the worst in four forms and is extremely difficult to remove.
Therefore, it is a technical problem to provide a remediation method capable of removing the residual heavy metal (residual cadmium) contaminated soil.
Disclosure of Invention
In order to solve the technical problems, the disclosure provides a restoration method and application of heavy metal contaminated soil.
In a first aspect, the present disclosure provides a method for repairing heavy metal contaminated soil, the method comprising the steps of:
(1) Mixing hydrofluoric acid and soil to be treated and reacting;
(2) Carrying out solid-liquid separation on the treated soil, and collecting solid components;
(3) And leaching the collected solid components by using a leaching agent to obtain the restored soil.
The soil remediation method provided by the disclosure not only can remove heavy metals which are easily removed, such as acid extractable state, reducible state and the like, but also can realize the removal of residual heavy metals. The residual heavy metal in the heavy metal contaminated soil does not mean that all the heavy metal in the soil is in a residual state, but means that the heavy metal form part existing in the heavy metal contaminated soil is in a residual state; the heavy metal in the residue state is extremely stable, has extremely poor activity and is not easy to remove.
In the method, before the leaching agent is used for leaching the soil, hydrofluoric acid is used as an activating agent for activating the residual heavy metal, silicate lattices in the soil can be broken, the residual cadmium is promoted to be changed into cadmium in other forms, and then the leaching agent is used for leaching the soil, so that the repairing effect of the leaching agent on the residual heavy metal polluted soil can be remarkably improved.
The hydrofluoric acid is hydrogen fluoride gas aqueous solution, the hydrofluoric acid is not excessively limited, and common commercial products can meet the requirements, and preferably analytically pure hydrofluoric acid.
For fully activating the residual heavy metals in the soil, as a preferred technical scheme of the disclosure, the mass ratio of the volume of the hydrofluoric acid to the soil to be treated is (0.01-10): 1, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, etc., preferably (6-10): 1. In the present disclosure, if the addition amount of hydrofluoric acid is excessively large, loss of solid components of soil may be caused. The volume-mass ratio of the composite material is mL/g.
As a preferred embodiment of the present disclosure, the step (1) further includes performing microwave heating while mixing.
The method and the device have the advantages that the activity of the residual heavy metal (especially metal cadmium) can be further improved by utilizing the microwave heating to cooperate with hydrofluoric acid to activate the residual heavy metal polluted soil, so that the leachable property of the heavy metal is enhanced, and the aim of thoroughly removing cadmium pollution in the soil is fulfilled.
As a preferred embodiment of the present disclosure, the microwave heating temperature is 120-180deg.C, such as 130 deg.C, 140 deg.C, 150 deg.C, 160 deg.C, 170 deg.C, etc., preferably 160-180deg.C.
As a preferred technical scheme of the disclosure, the time of microwave heating is 10-30min, for example 12min, 15min, 18min, 20min, 22min, 25min, 28min and the like, preferably 10-20min. The time described in the present disclosure refers to a heat preservation time after microwave heating to a set temperature, and does not include a heating time of microwave heating.
As a preferred embodiment of the present disclosure, the microwave heating is performed at a pressure of 300-600psi, such as 350psi, 400psi, 450psi, 500psi, 550psi.
As a preferred embodiment of the present disclosure, the pH of the rinse agent is 1.0-9.0, e.g., 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, etc., preferably 2.0-4.0.
As a preferred technical solution of the present disclosure, the mass ratio of the volume of the leaching agent to the solid component is (1-40): 1, for example, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, etc., preferably 10:1, and the volume-mass ratio of the present disclosure is mL: g.
As a preferred embodiment of the present disclosure, the eluting agent comprises Na 2 Any one or a combination of at least two of EDTA solution, citric acid solution, tartaric acid solution or ferric chloride solution, preferably Na 2 EDTA solution.
As a preferred embodiment of the present disclosure, the concentration of the eluting agent is 0.01 to 0.1mol/L, for example 0.02mol/L, 0.03mol/L, 0.04mol/L, 0.05mol/L, 0.06mol/L, 0.07mol/L, 0.08mol/L, 0.09mol/L, etc., preferably 0.08 to 0.1mol/L.
As a preferred technical solution of the present disclosure, the rinsing is performed by oscillation rinsing, preferably the rate of oscillation is 100-200r/min, for example 120r/min, 140r/min, 150r/min, 160r/min, 180r/min, etc.
As a preferred embodiment of the present disclosure, the temperature of the rinsing is 15-35 ℃, e.g., 16 ℃, 18 ℃, 20 ℃, 22 ℃, 24 ℃, 26 ℃, 28 ℃,30 ℃, 32 ℃, etc.
As a preferred embodiment of the present disclosure, the rinsing time is 4-12h, e.g. 5h, 6h, 8h, 10h, 11h, etc., preferably 8-12h.
As a preferred technical scheme of the disclosure, the solid-liquid separation method adopts a centrifugal mode, preferably the centrifugal rotating speed is 3000-4000r/min, such as 3200r/min, 3400r/min, 3500r/min, 3600r/min, 3800r/min and the like, preferably the centrifugal times are 1-3 times, such as 2 times, preferably the centrifugal time is 5-10min, such as 6min, 7min, 8min, 9min and the like.
As a preferred technical solution of the present disclosure, the heavy metal includes any one or a combination of at least two of mercury (Hg), cadmium (Cd), lead (Pb), chromium (Cr), arsenic (As), copper (Cu) and nickel (Ni), preferably cadmium.
As a preferred technical solution of the present disclosure, the repair method further includes: step (1') is performed before step (1): grinding and sieving the soil to be treated;
as a preferred technical scheme of the present disclosure, the mesh number of the sieving is 50-100 mesh.
As a specific embodiment of the present disclosure, the repair method includes the steps of:
(1') grinding the soil to be treated, and then sieving the ground soil with a 50-100 mesh sieve;
(1) Mixing the sieved soil with hydrofluoric acid (1) (0.01-10) according to the mass ratio of (g: mL), and performing microwave heating treatment at 120-180 ℃ and 300-600psi for 10-30min;
(2) Centrifuging the treated soil for 5-10min at a rotating speed of 3000-4000r/min to realize solid-liquid separation, wherein the centrifuging time is 1-3 times, and collecting solid components;
(3) And (3) carrying out oscillation leaching on the collected solid components for 4-12h at 15-35 ℃ by using a leaching agent with the pH value of 1.0-9.0 and the concentration of 0.01-0.1mol/L, wherein the oscillation rate is 100-200r/min, and the liquid-solid ratio (mL: g) of the leaching agent to the solid components is (1-10): 1, so as to obtain the restored soil.
As a preferred technical scheme of the present disclosure, the method further comprises solid-liquid separation, high-purity water cleaning and drying after leaching.
In a second aspect, the present disclosure provides an application of the repairing method of the first aspect in preparing ceramic daily necessities, chinese herbal medicine planting soil or tea planting soil.
The restoration method provided by the disclosure can thoroughly remove heavy metal pollution of soil, and can be applied to industries such as Chinese herbal medicine planting and ceramic daily necessities manufacturing which are harsh to heavy metal content in soil.
Compared with the prior art, the technical scheme provided by the embodiment of the disclosure has the following advantages:
(1) In the method, hydrofluoric acid is used as an activating agent to activate the residual heavy metal, silicate crystal lattices in the soil can be broken, the residual cadmium is promoted to be changed into cadmium in other forms, and then the eluting agent is used for eluting the soil, so that the removing effect of the eluting agent on the residual heavy metal can be remarkably improved, and the method has a good repairing effect on the selenium-rich soil;
(2) The microwave heating is used for carrying out the activation treatment on the residual heavy metal in cooperation with hydrofluoric acid, so that the activity of the residual heavy metal (especially metal cadmium) can be further improved, the leachable property of the heavy metal is enhanced, and the aim of thoroughly removing cadmium pollution in soil is fulfilled;
(3) The restoration method provided by the disclosure can thoroughly remove heavy metal pollution of soil, and can be applied to industries such as Chinese herbal medicine planting and ceramic daily necessities manufacturing which are harsh to heavy metal content in soil.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the disclosure and together with the description, serve to explain the principles of the disclosure.
In order to more clearly illustrate the embodiments of the present disclosure or the solutions in the prior art, the drawings that are required for the description of the embodiments or the prior art will be briefly described below, and it will be obvious to those skilled in the art that other drawings can be obtained from these drawings without inventive effort.
FIG. 1 is a graph showing the effect of the repair methods provided in the examples and comparative examples of the present disclosure on the occurrence of cadmium in the raw soil;
FIG. 2 is a plot of cadmium removal from raw soil for the repair methods provided by examples and comparative examples of the present disclosure;
FIG. 3 is a graph showing the result of the concentration of the leaching agent versus the removal rate of cadmium in the soil;
FIG. 4 is a graph of the solid to liquid ratio of the eluent to the soil versus the removal rate of cadmium from the soil;
FIG. 5 is a graph showing the results of leaching time versus cadmium removal from soil;
FIG. 6 is a graph showing the result of the leaching agent pH versus the removal rate of cadmium from the soil;
FIG. 7 is a graph of cadmium release versus soak time for ceramic samples prepared according to the present disclosure when soaked in water at 90 ℃.
Detailed Description
In order that the above objects, features and advantages of the present disclosure may be more clearly understood, a further description of aspects of the present disclosure will be provided below. It should be noted that, without conflict, the embodiments of the present disclosure and features in the embodiments may be combined with each other.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure, but the present disclosure may be practiced otherwise than as described herein; it will be apparent that the embodiments in the specification are only some, but not all, embodiments of the disclosure.
In the following examples and comparative examples, soil samples were taken from cadmium contaminated plots of Shanxi province, the soil samples used were surface soil (0-20 cm), and branches, stones and other impurities in the soil samples were removed in a laboratory, naturally dried, and ground and sieved (2 mm) for use.
The total cadmium content of the soil sample is measured to be 12.97mg/kg, and the total cadmium content of the soil is measured by referring to the soil pollution risk control standard (trial) of agricultural land with soil environmental quality (GB 15618-2018), and the total cadmium content of the soil far exceeds the agricultural land risk control value specified in the standard, which belongs to the soil with severe pollution level;
the method for testing the total cadmium content in the soil sample comprises the following steps: the method comprises the steps of adding acid into soil to completely digest, and then testing cadmium in the digestion liquid by adopting an Atomic Fluorescence (AFS) spectrometry.
In the examples described below, hydrofluoric acid (analytically pure) was used as a commercially available product.
Example 1
The embodiment provides a method for repairing cadmium-polluted soil.
(1) Grinding the soil to be treated, and then sieving with a 50-mesh sieve;
(2) Mixing the sieved soil with hydrofluoric acid according to the mass to volume (g: mL) of 1:10, and simultaneously carrying out microwave heating treatment for 20min at 180 ℃ and 600psi (heating by microwaves for 15min and preserving heat for 20 min);
(3) Centrifuging the treated soil twice at a rotating speed of 4000r/min for 10min each time to realize solid-liquid separation, and collecting solid components;
(4) By Na having a pH of 6.0 and a concentration of 0.1mol/L 2 And (3) carrying out oscillation leaching on the collected solid components by using the EDTA solution at 25 ℃ for 8 hours, wherein the oscillation speed is 200r/min, the liquid-solid ratio of the leaching agent to the solid components is 10:1 (mL: g), and then carrying out centrifugal separation, high-purity water cleaning and drying to obtain the restored soil.
Examples 2 to 5
The embodiment provides a method for repairing residual cadmium-polluted soil.
The difference from example 1 is that in this example, the screened soil and hydrofluoric acid are 1:2 (example 2), 1:4 (example 3), 1:6 (example 4), 1:8 (example 5) by mass.
Example 6
The embodiment provides a method for repairing residual cadmium-polluted soil.
The difference from example 1 is that in this example, the step of microwave heating is not included, and only the sieved soil is mixed with hydrofluoric acid and soaked for 35min.
Examples 7 to 8
The embodiment provides a method for repairing residual cadmium-polluted soil.
The difference from example 1 is that in this example, the microwave heating temperatures are 160 ℃ (example 7), 170 ℃ (example 8).
Examples 9 to 10
The embodiment provides a method for repairing residual cadmium-polluted soil.
The difference from example 1 is that in this example, the incubation time for microwave heating was 10min (example 9) and 30min (example 10).
Comparative example 1
The comparative example provides a method for repairing the residual cadmium-polluted soil.
The difference from example 1 is that in this comparative example hydrofluoric acid was replaced with an equal volume of deionized water.
Performance test 1
(1) Repairing the residual cadmium-polluted soil according to the repairing methods provided in examples 1-5 and comparative example 1, and analyzing the occurrence form of cadmium in the solid component collected in the step (3), wherein the method comprises the following steps:
the method adopts a continuous extraction method to analyze the occurrence form of cadmium in a soil sample, and comprises the following specific steps:
s1 (extraction of exchangeable states): weighing 1.000g of sample into a 100mL polypropylene centrifuge tube, adding 40mL of 0.11mol/L HAc extracting solution, oscillating for 16h at room temperature (250 r/min, ensuring that the mixture in the tube is in a suspension state), centrifuging at 4000r/min for 20min, pouring out supernatant into a polyethylene bottle, and storing in a refrigerator at 4 ℃ for testing;
s2 (extraction of the reducible state): washing the residue of step (1) with 20mL of high purity water, shaking for 20min, centrifuging, discarding the washing solution, and adding 0.5mol/L NH to the residue 2 40mL of OH HCl extracting solution, oscillating for 16h, centrifugally separating for 20min at 4000r/min, pouring out supernatant liquid into a polyethylene bottle, and storing in a refrigerator at 4 ℃ for testing;
s3 (extraction of the oxidizable state): washing the residue of step (1) with 20mL of high purity water, shaking for 20min, centrifuging, discarding the washing solution, and slowly adding 10mL of H to the residue 2 O 2 Covering a surface dish, occasionally oscillating, digesting for 1H at room temperature, heating to 85deg.C in water bath, digesting for 1H, removing the surface dish, heating to near dryness, and adding 10ml H 2 O 2 Repeating the above steps, cooling, adding 1mol/L NH 4 50mL of OAc extracting solution, oscillating for 16h, centrifuging for 20min at 4000r/min, pouring out supernatant, placing in a polyethylene bottle, and storing in a refrigerator at 4 ℃ for testing;
s4 (calculation of the residual state): subtracting the content of exchangeable, reducible and oxidizable cadmium from the total cadmium content in the soil sample, wherein the residual cadmium content is the content of residual cadmium.
S5: the concentration of heavy metal Cd in the solution was detected by Atomic Fluorescence (AFS) spectroscopy.
The cadmium content of the untreated soil in different forms is shown in table 1:
TABLE 1
| Total cadmium content | Acid extractable state | Reducible state | Oxidizable state | Residue state |
| 12.97ppm | 1.16ppm | 4.1ppm | 0.7ppm | 7.62ppm |
From table 1, it can be known that, for the heavy metal cadmium in the soil sample provided by the disclosure, the activities of the oxidizable cadmium and the residual cadmium are the worst, and the oxidizable cadmium and the residual cadmium are not easy to be absorbed and eluted and repaired by plants, and the low-activity cadmium accounts for 64.15%, which indicates that the polluted soil sample is difficult to achieve a better repairing effect if the traditional plant extraction method and the eluting method are adopted for repairing.
The results of cadmium-forming morphology detection for examples 1-5, comparative example 1 and untreated soil are shown in FIG. 1;
as can be seen from fig. 1, the activation method provided by the present disclosure is used to activate cadmium in heavy metal cadmium contaminated soil, so as to greatly reduce the content of residual cadmium. Meanwhile, as can be seen from comparison of examples 1 to 5, in the preferred scope of the present disclosure, the residual cadmium in the original soil can be reduced to about 11% in proportion up to 56%, which greatly increases the mobility of cadmium in the soil and provides better conditions for subsequent leaching work.
(2) Repairing the residual cadmium polluted soil according to the repairing method provided in examples 7-10, analyzing the occurrence form of cadmium in the solid component collected in the step (3), comparing with untreated soil, and calculating the ratio of the residual cadmium to the total cadmium, wherein the result is shown in Table 2:
TABLE 2
| Repair method | Residual cadmium content/% |
| Example 7 | 15 |
| Example 8 | 14 |
| Example 9 | 10 |
| Example 10 | 11 |
As can be seen from a comparison of the embodiment 1 and the embodiments 7-10, the microwave heating temperature of 160-180 ℃ is preferred, and the heat preservation is preferably carried out for 10-30min in the microwave heating heat preservation process, so that the purposes of accelerating the reaction speed, shortening the hydrofluoric acid treatment time, further greatly reducing the content of residual cadmium and greatly increasing the mobility of cadmium in soil are achieved.
Comparative example 2
The comparative example provides a method for repairing the residual cadmium-polluted soil.
The difference from example 1 is that in this comparative example, steps (2) to (3) were not performed, and step (4) was directly performed.
Performance test 2
(1) The appearance of cadmium in the soil finally repaired by the repair method provided in comparative example 2 is analyzed, the analysis method refers to performance test 1, and the result is shown in table 3:
TABLE 3 Table 3
| Pre-rinse content/ppm | Post-rinse content/ppm | Removal rate/% | |
| Acid extractable cadmium | 1.16 | 0.10 | 91.38 |
| Oxidizable cadmium | 4.1 | 0.27 | 93.41 |
| Reducible cadmium | 0.7 | 0.29 | 58.57 |
| Residual cadmium | 7.62 | 5.77 | 24.28 |
| Total cadmium | 12.97 | 6.43 | 50.41 |
As can be seen from Table 3, na is used 2 EDTA is used as a leaching agent to carry out leaching restoration on the cadmium-polluted soil, and the cadmium removal rate reaches 50.41%, so that the leaching method has a good effect of removing cadmium elements in the cadmium-polluted soil.
Meanwhile, as can be seen from the table 3, the content of the acid extractable state and the oxidizable state cadmium after leaching is greatly reduced, the removal rate is more than 91%, the content of the reducible state cadmium is also greatly reduced, and the removal rate of the residual state cadmium is only 24.28%, which is far lower than that of other three forms of cadmium; therefore, the removal of the residual cadmium can not be realized in a better way only by leaching.
(2) Meanwhile, the residual cadmium-polluted soil is repaired according to the repairing methods provided in examples 1-6 and comparative examples 1-2, the cadmium content in the soil before and after treatment is detected, and the cadmium removal rate is calculated, and the results are shown in Table 4 and FIG. 2;
TABLE 4 Table 4
| Repair method | Cadmium removal rate/% |
| Example 1 | 82.13 |
| Example 2 | 60.81 |
| Example 3 | 62.83 |
| Example 4 | 73.95 |
| Example 5 | 78.21 |
| Example 6 | 75.62 |
| Comparative example 1 | 52.80 |
| Comparative example 2 | 50.41 |
FIG. 2 is a graph showing the cadmium removal rate of the original soil by the repair methods provided in examples and comparative examples, and as can be seen from Table 4 and FIG. 2, the repair methods provided in the present disclosure can improve the cadmium removal rate to more than 80%, and simultaneously, as can be seen from FIG. 1 and Table 3, by using the repair methods provided in the present disclosure, hydrofluoric acid and microwave heating are utilized first and then leaching is performed, so that a large amount of residual cadmium is released from the mineral lattice, the activity of cadmium in the soil is greatly enhanced, the mobility is improved, and the cadmium is easily transferred from the solid phase to the liquid phase, and then the cadmium is mixed with Na 2 EDTA is subjected to complexation reaction, so that Na can be greatly improved 2 The leaching efficiency of EDTA greatly improves the removal rate of residual cadmium.
Comparative examples 3 to 6
The comparative example provides a method for repairing the residual cadmium-polluted soil.
The difference from comparative example 2 is that in this comparative example, the eluent was employed as citric acid (comparative example 3), tartaric acid (comparative example 4), ferric chloride (comparative example 5), deionized water (comparative example 6) at a concentration of 0.1mol/L.
Performance test 3
Taking kaolin, sieving with a 2mm sieve, and weighing CdCl 2 The method comprises the steps of preparing a cadmium standard solution with the concentration of 1000mg/L, adding a certain amount of the cadmium standard solution into kaolin, uniformly stirring, aging for 3 months at a shade and dry place, grinding and sieving for standby, and measuring that the total cadmium content test result of the soil sample is up to 53.41mg/kg, which is far more than the maximum risk management and control value of the cadmium pollution of the agricultural soil specified in soil environmental quality agricultural soil pollution risk management and control standard (trial) (GB 15618-2018), and belongs to severely polluted soil.
(1) Repairing the soil by the repairing method provided by the reference comparative examples 2-6, exploring the occurrence form of cadmium in the finally repaired soil, and performing the analysis method by referring to the performance test 1, wherein the result is shown in Table 5;
TABLE 5
| Repair method | Eluting agent | Cadmium removal/ppm |
| Comparative example 2 | Na 2 EDTA solution | 38.12 |
| Comparative example 3 | Citric acid solution | 12.06 |
| Comparative example 4 | Tartaric acid solution | 34.07 |
| Comparative example 5 | Ferric chloride solution | 21.25 |
| Comparative example 6 | Deionized water | 1.12 |
| Raw soil | - | 53.41 (cadmium content) |
As can be seen from table 5, the different types of leaches have a large difference in performance under the same leaching conditions, wherein the heavy metal cadmium cannot be removed basically by leaching with deionized water, which indicates that only part of the cadmium which is adsorbed on the surface of the soil particles and is most easily migrated can be eluted by the deionized water; as is clear from the comparison of comparative examples 2 to 6, na was used 2 EDTA (ethylene diamine tetraacetic acid) serving as eluent is used for leaching and repairing cadmium-polluted soil, has a better removal effect, and presumably because the EDTA contains more carboxyl groups in the molecular formula and can be complexed with more cadmium ions, and meanwhile, H + The presence of (2) can lower the pH of the soil and thereby promote desorption of heavy metal ions.
(2) On the basis of comparative example 2, other conditions are kept unchanged, the concentration of the eluent is changed to be respectively 10mmol/L, 20mmol/L, 40mmol/L, 60mmol/L and 80mmol/L, and the removal rate of cadmium in soil is explored, and the result is shown in figure 3;
fig. 3 is a graph showing the result of the concentration of the leaching agent on the removal rate of cadmium in the soil, and as can be seen from fig. 3, the leaching agent with the concentration of preferably 0.08-0.1mol/L is preferred, and the removal rate of cadmium is higher and can reach more than 70%.
In the initial stage of leaching, the cadmium removal rate is obviously increased along with the increase of concentration, and the removal rate is faster, because the cadmium in the soil is mainly in an acid extractable state which is easy to leach at the initial stage of leaching, the cadmium is active and has strong mobility and is easy to be leached and removed, and the cadmium in the soil is mainly in a stable residue state and an oxidizable state along with the continuous leaching, and the cadmium removal rate is only slightly increased when the concentration of the leaching agent is increased, so that the leaching agent with the concentration of 0.08-0.1mol/L is preferred based on the industrial production application.
(3) On the basis of comparative example 2, other conditions are kept unchanged, the addition amount of the eluent is changed, the liquid-solid ratio (mL: g) is 5:1, 20:1, 30:1 and 40:1, and the removal rate of cadmium in soil is explored, and the result is shown in FIG. 4;
FIG. 4 is a graph showing the results of the solid-to-liquid ratio of the leaching agent to the soil versus the removal rate of cadmium in the soil, and as can be seen from FIG. 4, when the solid-to-liquid ratio is reduced from 1:5 to 1:10, the removal rate of cadmium is increased from 59.1% to 67.4%; however, when the solid-liquid ratio is further reduced, the increasing rate of the cadmium removal rate gradually slows down, and when the solid-liquid ratio is reduced from 1:10 to 1:40, the cadmium removal rate is increased from 67.4% to 71.3%, namely, the solid-liquid ratio is reduced by four times, and meanwhile, the cadmium removal rate is increased by only 3.9%.
In view of poor selectivity of the eluent, and in the case where the addition amount of the eluent is too large, since cadmium ions in the soil have approached the desorption equilibrium, the cadmium removal rate is slowly increased, and therefore, the solid-liquid ratio of the present disclosure is preferably 1:10 from the viewpoints of the cadmium removal rate and the application cost in view of practical application.
(4) On the basis of comparative example 2, other conditions are kept unchanged, the leaching time is changed to 0.5h, 1h, 2h, 4h, 6h, 10h and 24h, and the removal rate of cadmium in soil is explored, and the result is shown in figure 5;
fig. 5 is a graph showing the result of the leaching time on the cadmium removal rate in the soil, and as shown in fig. 5, the cadmium removal rate is rapidly increased along with the increase of the leaching time, the cadmium removal rate is increased rapidly in the stage of leaching within 2h, and the main reason is that the acid with stronger mobility in the soil is more in the initial leaching stage, the cadmium with weaker acting force with the soil is easily leached and desorbed into solution, along with the extension of the leaching time, the cadmium element which is originally combined with the soil tightly is gradually released into the leaching solution under the leaching of the oscillation and the complexing agent, and the cadmium removal rate is gradually stable in the final leaching stage, and the leaching reaches balance, so the leaching time of 8h or more is preferred, and the cadmium removal rate can reach 70% or more at this time.
(5) On the basis of comparative example 2, other conditions are kept unchanged, nitric acid or sodium hydroxide is added to change the pH of the eluent to 2, 4, 8 and 10, and the removal rate of cadmium in soil is explored, and the result is shown in FIG. 6;
FIG. 6 is a graph showing the result of the pH of the leaching agent on the removal rate of cadmium in soil, and as can be seen from FIG. 6, the pH of the leaching agent is preferably 2-6, and the removal rate of cadmium can reach more than 60%; meanwhile, it is understood from the graph that the eluting agent has a superior effect of removing cadmium under acidic conditions (ph=2 to 4), presumably because the Zeta potential of the surface of the cadmium-contaminated soil particles is small, the ion exchange and dissolution effects play a major role, H + The ion exchange can be carried out with heavy metal cations adsorbed on the surfaces of soil particles, so that heavy metal cadmium is released into the leaching solution, and EDTA complexation removal is facilitated; in addition, the lower pH environment can reduce the negative charges on the surfaces of soil particles and organic matters in the soil, so that the iron-manganese oxidation state cadmium in the cadmium polluted soil is promoted to be dissolved into the cadmium with stronger activity, and the overall mobility of the cadmium is enhanced; when the pH of the system is increased, the proton number in the soil solution is reduced, the acidification effect is also eliminated, and heavy metal ions are easy to form precipitation in an overbased environment, so that the leaching removal rate is reduced.
Application example
The application example provides a method for preparing ceramic by using restored soil.
And (3) drying the soil repaired in the embodiment 1 by a conventional ceramic making process to prepare a clay blank, sintering the clay blank in a nitrogen atmosphere, and preserving the temperature for 1h at 1100 ℃ to obtain a ceramic sample.
Comparative application example
The ceramic samples were prepared directly using the original earth reference application examples.
Performance test 4
(1) The cadmium content in the ceramic samples in the application examples and the comparative application examples is detected, and the results are shown in Table 6:
TABLE 6
| Sample of | Cadmium content/ppm |
| Application example | 7.32 |
| Comparative application example | 0.27 |
As can be seen from Table 6, the cadmium content in the ceramics prepared by the restored soil is far lower than that of the ceramics prepared by taking the original soil as the raw material, and the reduction of the cadmium content can reach more than 96%.
(2) Soaking the prepared ceramic sample in water at 90 ℃, sampling at different soaking times, and detecting the content of released cadmium, wherein the result is shown in figure 7;
as can be seen from FIG. 7, although the ceramics prepared using the restored soil still had trace cadmium release, the cadmium release amount was only 0.0041ppm at the soaking time of 48 hours.
From tables 6 and 7, it can be seen that the restoration of the soil of the ceramic raw material can effectively reduce the cadmium content in the ceramic and the cadmium release amount when the ceramic is soaked in water, and improve the safety of the ceramic daily necessities to human bodies.
It should be noted that in this document, relational terms such as "first" and "second" and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
The foregoing is merely a specific embodiment of the disclosure to enable one skilled in the art to understand or practice the disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown and described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (7)
1. The repair method of the residual heavy metal contaminated soil is characterized in that the heavy metal is cadmium, and comprises the following steps:
(1') grinding the soil to be treated, and then sieving the ground soil with a 50-100 mesh sieve;
(1) Mixing the sieved soil with hydrofluoric acid with the volume of 1 (6-10), and performing microwave heating treatment at 160-180 ℃ and 300-600psi for 10-30min;
(2) Centrifuging the treated soil for 5-10min at a rotating speed of 3000-4000r/min to realize solid-liquid separation, wherein the centrifuging time is 1-3 times, and collecting solid components;
(3) With a pH of 1.0-9.0 and a concentration of 0.01-0.1 mol-The collected solid components are leached by shaking at 15-35 ℃ for 4-12h, the shaking speed is 100-200r/min, the liquid-solid ratio of the leaching agent to the solid components is (1-10): 1, the repaired soil is obtained, and the leaching agent is Na 2 EDTA solution.
2. The repair method of claim 1, wherein the microwave heating time is 10-20min.
3. The repair method of claim 1 wherein the pH of the eluent is 2.0-4.0;
and/or the mass ratio of the volume of the eluent to the solid component is 10:1;
and/or the concentration of the eluent is 0.08-0.1mol/L.
4. The repair method of claim 1, wherein the time for rinsing is 8-12 hours.
5. The repair method according to claim 1, wherein in the step (2), the time for each centrifugation is 5 to 10 minutes.
6. The repair method of claim 1 wherein the mesh number of the screen is 50-100 mesh.
7. Use of the repair method according to any one of claims 1 to 6 for the preparation of ceramic-like commodity, chinese herbal medicine planting soil or tea planting soil.
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