CN115856254A - Method for evaluating long-acting property of soil heavy metal pollution curing stabilization - Google Patents
Method for evaluating long-acting property of soil heavy metal pollution curing stabilization Download PDFInfo
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Abstract
The invention discloses a method for evaluating the long-acting property of soil heavy metal pollution solidification stabilization, which comprises the following steps: the preparation of the coal-based biochar comprises the following steps of: drying, crushing and sieving corn straws to obtain corn straw biomass BM, mixing and roasting the fly ash FA and sodium hydroxide for 2 hours according to a certain mass ratio, and then cooling and sieving to obtain alkali fusion fly ash AFFA; carbonizing: uniformly mixing the BM obtained in the step S11 and the AFFA in a certain mass ratio, placing the mixture in a box-type resistance furnace, and performing nitrogen atmosphere at 10 ℃ for min ‑1 The room temperature is increased to 500 ℃ for pyrolysis for 2h at the speed of the second step, the mixture is cooled under the nitrogen flow, and the mixture is taken out and sieved to obtain the coal-based biochar material AFFA/BC. The invention develops soil dry-wet alternation and freeze-thaw cycle experiments under the simulation condition, evaluates the stability of heavy metal in the soil repaired by the curing agent, provides basis for long-term application of the material applied by the curing and stabilizing technology, and has great practical value.
Description
Technical Field
The invention relates to the technical field of soil heavy metal pollution treatment, in particular to a method for evaluating the long-acting property of soil heavy metal pollution curing stabilization.
Background
At present, heavy metal pollution in soil poses a serious threat to the natural environment and human health, and has become a focus of attention. The heavy metal in the soil has the characteristics of durability, aggregation, easy absorbability and instability, and is not easy to be decomposed by bacteria in the soil, so that the heavy metal is accumulated in the soil. Therefore, the heavy metal contaminated soil remediation work is urgently carried out.
Among the methods for remedying heavy metals in soil, chemical methods are widely used at present, and the specific treatment methods thereof generally include a chemical leaching technology, a stabilization technology (chemical passivation method) and the like. The solidification and stabilization technology has the advantages of low cost, small engineering quantity, quick restoration, large restoration area and the like, and is widely applied to the restoration engineering of the heavy metal polluted soil in China. The curing and stabilizing technology can reduce the toxicity and the mobility of heavy metals in soil, the total amount of the heavy metals in the soil cannot be reduced, the passivated heavy metals can be analyzed along with the prolonging of the repairing time, heavy metal ions fixed in the soil can have activity again when the external environment changes, and the evaluation of the stability of the heavy metals in the passivated soil is a key factor for judging whether the materials applied by the curing and stabilizing technology can be applied for a long time.
There is currently no effective solution to the above problems.
Disclosure of Invention
Aiming at the technical problems in the related art, the invention provides a method for stabilizing the long-acting property of heavy metal pollution curing of valuable soil, which can overcome the defects in the prior art.
In order to achieve the technical purpose, the technical scheme of the invention is realized as follows:
a method for evaluating the long-acting property of soil heavy metal pollution solidification stabilization comprises the following steps:
s1, preparation of coal-based biochar:
s11, pretreatment: drying, crushing and sieving corn straws to obtain corn straw biomass BM, mixing and roasting the fly ash FA and sodium hydroxide for 2 hours according to a certain mass ratio, and then cooling and sieving to obtain alkali fusion fly ash AFFA;
s12, carbonizing: uniformly mixing the BM obtained in the step S11 and the AFFA in a certain mass ratio, placing the mixture in a box-type resistance furnace, and performing nitrogen atmosphere at 10 ℃ for min -1 The room temperature is increased to 500 ℃ for pyrolysis for 2h at the speed, the mixture is cooled under nitrogen airflow, and the mixture is taken out and sieved to obtain a coal-based biochar material AFFA/BC;
s2, repairing the heavy metal contaminated soil:
s21, adding the coal-based biochar material AFFA/BC obtained in the step S12 into the polluted soil, adding deionized water to keep the water content of the soil, stabilizing and repairing for 12 d, and sampling to determine and analyze the content and the form of heavy metals;
s22, adding deionized water into the soil treated in the step S21 again to enable the water content to reach 55%, respectively performing 2, 4, 6, 8, 10 and 12 rounds of dry-wet alternation and freeze-thaw cycle, and then sampling again to determine and analyze the heavy metal content and the form;
s23, comparing the measured data of the step S21 with the measured data of the step S22, the leaching concentration of the heavy metal is reduced.
Further, in the step S11, the mass ratio of FA to sodium hydroxide is 1:1.5, the roasting temperature is 350 ℃.
Further, the mass ratio range of BM to AFFA in the step S12 is (1) - (10).
Further, in the step S12, deionized water is added into the mixture of BM and AFFA, the mixture is fully stirred for 2 hours on a magnetic stirrer, and then the mixture is dried, ground and sieved by a 35-mesh sieve in a blast drying oven at 85 ℃.
Further, the addition amount of the coal-based biochar material AFFA/BC in the step S21 is 5%.
Further, in step S22, the alternate dry-wet process includes: and culturing the soil submerged by the excessive water in a dark place for 12 h, drying the soil in an oven at 40 ℃ for 12 h, and adding deionized water again to restore the water content to the initial state.
Further, the process of one freeze-thaw cycle in step S22 is as follows: freezing the soil submerged by the excessive water at-20 ℃ for 12 h, culturing for 12 h in the dark, and then adding deionized water again to restore the water content to the initial state.
Further, the determination and analysis of the heavy metal content and the form in the step S23 are to naturally air-dry the soil, grind the soil through a 2 mm sieve, determine the leaching concentration of the heavy metal by TCLP, and determine the occurrence form of the heavy metal in the soil by a BCR four-step continuous extraction method.
The invention has the beneficial effects that: the invention develops soil dry-wet alternation and freeze-thaw cycle experiments under the simulation condition, evaluates the stability of heavy metal in the soil repaired by the curing agent, provides basis for long-term application of the material applied by the curing and stabilizing technology, and has great practical value.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a graph of the effect of alternate dry and wet (a), freeze-thaw cycles (b) on the toxic leaching concentration of Pb in BC and AFFA/BC remediated soil according to the method of evaluating the long-term effectiveness of soil heavy metal contaminated solidification stabilization according to an embodiment of the present invention;
fig. 2 is a graph showing the change of extraction state of Pb in BC and AFFA/BC restored soil by alternation of dry and wet (a) and freeze-thaw cycles (b) according to the method for evaluating the long-term stability of soil heavy metal pollution solidification according to the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments that can be derived by one of ordinary skill in the art from the embodiments given herein are intended to be within the scope of the present invention.
The method for evaluating the long-acting property of the soil heavy metal pollution solidification stabilization comprises the following steps:
s1, preparation of coal-based biochar:
s11, pretreatment: drying, crushing and sieving corn straws to obtain corn straw biomass BM, mixing and roasting the fly ash FA and sodium hydroxide for 2 hours according to a certain mass ratio, and then cooling and sieving to obtain alkali fusion fly ash AFFA;
s12, carbonization: uniformly mixing the BM obtained in the step S11 and the AFFA in a certain mass ratio, placing the mixture in a box-type resistance furnace, and performing nitrogen atmosphere at 10 ℃ for min -1 The room temperature is increased to 500 ℃ for pyrolysis for 2h at the speed, the mixture is cooled under nitrogen airflow, and the mixture is taken out and sieved to obtain a coal-based biochar material AFFA/BC;
s2, repairing the heavy metal contaminated soil:
s21, adding the coal-based biochar material AFFA/BC obtained in the step S12 into the polluted soil, adding deionized water to keep the water content of the soil, stabilizing and repairing for 12 d, and sampling to determine and analyze the content and the form of heavy metals;
s22, adding deionized water into the soil treated in the step S21 again to enable the water content to reach 55%, performing 2, 4, 6, 8, 10 and 12 rounds of dry-wet alternation and freeze-thaw cycle respectively, and then sampling again to determine and analyze the heavy metal content and the form;
s23, comparing the measured data of the step S21 with the measured data of the step S22, the leaching concentration of the heavy metal is reduced.
In the examples, the mass ratio of FA to sodium hydroxide in step S11 is 1:1.5, the roasting temperature is 350 ℃.
In the embodiment, the mass ratio range of BM to AFFA in the step S12 is (1 to 10).
In the embodiment, in the step S12, deionized water is added into the mixture of BM and AFFA, the mixture is fully stirred for 2 hours on a magnetic stirrer, and then the mixture is dried, ground and sieved by a 35-mesh sieve in a forced air drying oven at 85 ℃.
In the embodiment, the addition amount of the coal-based biochar material AFFA/BC in the step S21 is 5%.
In an embodiment, the process of the step S22 includes: and culturing the soil submerged by the excessive water in a dark place for 12 h, drying the soil in an oven at 40 ℃ for 12 h, and adding deionized water again to restore the water content to the initial state.
In the embodiment, the one-time freeze-thaw cycle process in step S22 is as follows: freezing the soil submerged by the excessive water at-20 ℃ for 12 h, culturing for 12 h in the dark, and then adding deionized water again to restore the water content to the initial state.
In the embodiment, the heavy metal content and morphology determination and analysis in the step S23 is to air-dry the soil naturally, grind the soil through a 2 mm sieve, determine the leaching concentration of the heavy metal by TCLP, and determine the occurrence morphology of the heavy metal in the soil by a BCR four-step continuous extraction method.
In order to facilitate understanding of the above-described technical aspects of the present invention, the above-described technical aspects of the present invention will be described in detail below in terms of specific usage.
In specific use, the method for evaluating the long-acting property of the soil heavy metal pollution solidification stabilization is analyzed through specific examples.
Example 1:
A. preparation of coal-based biochar
The corn straw is planted in covering soil of a coal gangue yard grown in Shanxi province, corn straw Biomass (BM) is dried for 6 hours in a blast drying oven at 85 ℃, and then ground and sieved by a 18-mesh sieve.
The fly ash is from a coal-fired power plant of Shanxi province in China, and is dried and crushed by air, and after the fly ash is sieved by a 18-mesh sieve, a fly ash sample is dried in an oven at 85 ℃ for 6 hours. According to the following steps: weighing 10 g of pretreated fly ash and 15 g of sodium hydroxide according to the mass ratio of 1.5, grinding and uniformly mixing in an agate mortar, placing in a 50 mL nickel crucible, and roasting in a box-type resistance furnace at the temperature of 350 ℃ for 2 hours. And after the baking and sintering are finished, taking out the product, cooling the product to room temperature, grinding the product into powder by using an agate mortar, and sieving the powder by using a 18-mesh sieve to obtain the alkali fusion fly ash, wherein the name of the alkali fusion fly ash is AFFA.
Mixing the corn straw biomass and the alkali fusion fly ash obtained in the following steps of 5:1 mass ratio, placing in a box-type resistance furnace, and heating at 10 deg.C for min in nitrogen atmosphere -1 The temperature is increased from room temperature to 500 ℃ for pyrolysis for 2h, the mixture is cooled under nitrogen flow, and the mixture is taken out, ground and sieved by a 60-mesh sieve to obtain the coal-based biochar material named AFFA/BC.
B. Remediation of heavy metal contaminated soil
Taking the remediation of the soil on the peripheral surface layer of a certain lead-zinc ore plant of inner Mongolia as an example, the site risk assessment result shows that: the main pollutant of the polluted soil is heavy metal Pb. Collecting 0-20 cm surface soil, air drying, pulverizing, and sieving with 2 mm sieve. And adding AFFA/BC into the polluted soil according to the addition amount of 5%, and adding deionized water every 1-2 days to keep the water content of the soil. After uniformly mixing and maintaining for 12 days, adding deionized water again to enable the water content to reach 55 percent, ensuring that the soil is submerged by excessive water, after culturing for 12 hours in a dark place, drying the container in an oven at 40 ℃ for 12 hours, and then adding deionized water again to enable the water content to recover to an initial state, namely a one-time dry-wet alternating process, and performing 2, 4, 6, 8, 10 and 12 times of dry-wet alternating respectively.
Example 2
A. Preparation of coal-based biochar
The same procedure as in example 1 was followed to prepare coal-based biochar.
B. Remediation of heavy metal contaminated soil
Taking the remediation of the soil on the peripheral surface layer of a certain lead-zinc ore plant of inner Mongolia as an example, the site risk assessment result shows that: the main pollutant of the polluted soil is heavy metal Pb. Collecting 0-20 cm surface soil, air drying, pulverizing, and sieving with 2 mm sieve. And adding AFFA/BC into the polluted soil according to the addition amount of 5%, and adding deionized water every 1-2 days to keep the water content of the soil. After the mixture is uniformly mixed and maintained for 12 days, deionized water is added again to enable the water content to reach 55 percent, the soil is guaranteed to be submerged by excessive water, the mixture is frozen for 12 hours at the temperature of minus 20 ℃, then the mixture is cultured for 12 hours in a dark place, and then the deionized water is added again to enable the water content to be recovered to an initial state, namely a cycle of freeze-thaw cycle, and 2, 4, 6, 8, 10 and 12 cycles of freeze-thaw cycle are respectively carried out.
Comparative example
A. Preparation of corn stalk biochar
The corn straw is planted in covering soil of a certain coal gangue yard for Shanxi Changzhi, corn straw Biomass (BM) is dried for 6 hours in an air drying oven at 85 ℃, and then ground and sieved by a 18-mesh sieve.
Placing the corn straw biomass in a box-type resistance furnace, and performing nitrogen atmosphere at 10 ℃ for min -1 The temperature is increased from room temperature to 500 ℃ for pyrolysis for 2h, the biomass is cooled under nitrogen gas flow, and the biomass is taken out, ground and sieved by a 60-mesh sieve to obtain the corn straw biochar which is named as BC.
B. Remediation of heavy metal contaminated soil
Taking the remediation of the soil on the peripheral surface layer of a certain lead-zinc ore plant of inner Mongolia as an example, the site risk assessment result shows that: the main pollutant of the polluted soil is heavy metal Pb. Collecting 0-20 cm surface soil, air drying, pulverizing, and sieving with 2 mm sieve. BC is added into the polluted soil according to the addition amount of 5%, and deionized water is added every 1-2 days to keep the water content of the soil. After mixing and curing for 12 days, 2, 4, 6, 8, 10 and 12 rounds of dry-wet alternation and freeze-thaw cycles are respectively carried out.
And (3) performance testing:
(1) Test soil: the surface soil around a lead and zinc ore plant of inner Mongolia is collected, and the basic physicochemical properties are shown in Table 1.
TABLE 1 testing of the parameters of the basic physicochemical properties of the soil
| pH | CEC | SOM | Water content ratio | Total Pb (mg/kg) |
| 7.03 | 9.17 | 2.13 | 7.31 | 263 |
(2) The test method comprises the following steps: 200 g of contaminated soil were weighed into 9 plastic containers with holes and randomly divided into three groups. Contaminated soil of group 1-2 vessels heavy metal contaminated soil remediation was carried out according to the method of example 1-2. And then, determining the leaching concentration of the heavy metal by adopting TCLP, and determining the occurrence form of the heavy metal in the soil by adopting a BCR four-step continuous extraction method. The test results are shown in fig. 1 and 2.
FIG. 1 is a graph of the toxic leaching concentration effect of alternate dry and wet (a), freeze-thaw cycles (b) on Pb in BC and AFFA/BC remediated soil, where the histograms in CK, BC, AFFA/BC have the following meanings from left to right: the results of 12 days, 2 rounds, 4 rounds, 6 rounds, 8 rounds, 10 rounds and 12 rounds of culture.
FIG. 2 shows the change of the extraction state of Pb in BC and AFFA/BC repaired soil by alternation of dry and wet (a) and freeze-thaw cycle (b), wherein the column diagrams in CK, BC and AFFA/BC represent the following meanings from top to bottom: acid extractable, reducible, oxidizable, and residuum states.
As can be seen from fig. 1 (a), under the alternate dry-wet condition, the toxic leaching concentration of Pb in the soil gradually increases as the alternate dry-wet cycle increases, but the increase rate of the toxic leaching concentration of lead is relatively high in the early stage of the alternate dry-wet cycle, and the increase rate of the toxic leaching concentration of lead gradually decreases to zero as the cycle progresses. BC. After the contaminated soil is repaired by AFFA/BC, the toxic leaching concentrations of Pb are respectively 599.43 mu g/L and 443.78 mu g/L, after 8 rounds of dry-wet alternation, the toxic leaching concentrations of Pb are 846.88 mu g/L and 642.71 mu g/L, the amplification is 41.2 percent and 44.8 percent respectively, and from 8 rounds to 12 rounds, the toxic leaching concentrations of Pb are respectively increased by 1.9 percent and 8.3 percent. Researches prove that the dry-wet alternation can promote the release and migration of heavy metals in slag particles, the lead-polluted soil after silicate solidification is subjected to dry-wet alternation, the leaching of lead in the soil can be accelerated and repaired by the dry-wet alternation, and the dry-wet treatment of the Cd-polluted farmland soil also shows that the dry-wet alternation promotes the release of cadmium.
As can be seen from FIG. 1 (b), after the remediation by BC and AFFA/BC, the toxic leaching concentration of heavy metal Pb in soil gradually decreases with the progress of freeze-thaw cycle of soil. After 2, 4, 6, 8, 10 and 12 rounds of soil restoration by BC, the Pb concentration of the soil toxicity leaching is respectively reduced from 611.05 mu g/L to 571.86 mu g/L, 542.06 mu g/L, 506.59 mu g/L, 491.08 mu g/L, 378.62 mu g/L and 356.37 mu g/L. By 12 rounds, the toxic leaching concentration of Pb decreased by 41.7%. After AFFA/BC remediation, the leaching concentration of Pb is gradually reduced from 391.81 mu g/L to 354.12 mu g/L, 327.97 mu g/L, 341.72 mu g/L, 230.58 mu g/L, 141.24 mu g/L and 140.34 mu g/L, and after 12 rounds, the leaching concentration of Pb is reduced by 64.2%. The freeze-thaw cycle is beneficial to stabilizing and repairing lead in the contaminated soil by BC and AFFA/BC, wherein the AFFA/BC has the best effect on repairing the Pb contaminated soil along with the increase of the number of the freeze-thaw cycle. The freeze-thaw cycle reduces the leaching concentration of Pb, possibly because the freeze-thaw cycle accelerates the adsorption of Pb and causes the Pb to form a more stable precipitate in the soil.
As shown in fig. 2 (a), compared with the CK group without the added material, after 12 dry-wet cycles of the soil, BC and AFFA/BC treatment systems respectively reduce the Pb content in the soil acid extraction state by 4% and 5%; the content of reducible Pb in the soil is respectively reduced by 8 percent and 18 percent; the content of oxidizable Pb in the soil is respectively increased by 0 percent and 12 percent; the content of Pb in the residue is respectively increased by 12 percent and 11 percent; as can be seen from FIG. 2 (b), after the freeze-thaw cycle 12 cycles, the BC and AFFA/BC treatment systems reduce the content of Pb in the soil in an acid extraction state by 0 and 2.0% respectively; the content of reducible Pb in the soil is respectively reduced by 0 percent and 11 percent; the content of oxidizable Pb in the soil is respectively increased by 1.0 percent and 1.0 percent; while the Pb content in the residue was increased by-1.0% and 12.0%, respectively. After wet-dry alternation and freeze-thaw cycling, the soil with added material had less contents of less stable acid extracted and reducible Pb than the CK group without added material, which is consistent with the results of the TCLP toxicity leaching experiments. The AFFA/BC has excellent repairing effect on heavy metal Pb in soil and long-term stability under the condition that dry-wet cycle and freeze-thaw cycle simulate accelerated aging of soil.
In conclusion, by means of the technical scheme, soil dry-wet alternation and freeze-thaw cycle experiments are carried out under the simulation condition, the stability of the heavy metal in the soil repaired by the curing agent is evaluated, a basis is provided for long-term application of the material applied to the curing and stabilizing technology, and the method has great practical value.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (8)
1. A method for evaluating the long-acting property of soil heavy metal pollution solidification stabilization is characterized by comprising the following steps:
s1, preparation of coal-based biochar:
s11, pretreatment: drying, crushing and sieving corn straws to obtain corn straw biomass BM, mixing and roasting the fly ash FA and sodium hydroxide for 2 hours according to a certain mass ratio, and then cooling and sieving to obtain alkali fusion fly ash AFFA;
s12, carbonization: will be described in detailUniformly mixing BM obtained in S11 and AFFA in a certain mass ratio, placing the mixture in a box-type resistance furnace at 10 ℃ for min in a nitrogen atmosphere -1 Heating the room temperature to 500 ℃ at the rate of (2), pyrolyzing for 2h, cooling under nitrogen airflow, taking out and sieving to obtain a coal-based biochar material AFFA/BC;
s2, repairing the heavy metal contaminated soil:
s21, adding the coal-based biochar material AFFA/BC obtained in the step S12 into the polluted soil, adding deionized water to keep the water content of the soil, stabilizing and repairing for 12 d, and sampling to determine and analyze the content and the form of heavy metals;
s22, adding deionized water into the soil treated in the step S21 again to enable the water content to reach 55%, performing 2, 4, 6, 8, 10 and 12 rounds of dry-wet alternation and freeze-thaw cycle respectively, and then sampling again to determine and analyze the heavy metal content and the form;
s23, comparing the measured data of the step S21 with the measured data of the step S22, the leaching concentration of the heavy metal is reduced.
2. The method for evaluating the long-acting property of soil heavy metal pollution curing stabilization according to claim 1, wherein the mass ratio of FA to sodium hydroxide in step S11 is 1:1.5, the roasting temperature is 350 ℃.
3. The method for evaluating the long-acting property of the soil heavy metal pollution curing and stabilizing effect as claimed in claim 1, wherein the mass ratio of BM to AFFA in the step S12 is 10 (1 to 10).
4. The method for evaluating the long-acting property of the solidification and stabilization of heavy metal pollution in soil according to claim 1, wherein in the step S12, the mixture of BM and AFFA is added with deionized water, fully stirred for 2 hours on a magnetic stirrer, and then dried, ground and sieved by a 35-mesh sieve in a forced air drying oven at 85 ℃.
5. The method for evaluating the long-acting property of soil heavy metal pollution curing stabilization as claimed in claim 1, wherein the addition amount of the coal-based biochar material AFFA/BC in the step S21 is 5%.
6. The method for evaluating the long-acting property of the soil for curing and stabilizing heavy metal pollution according to claim 1, wherein the alternate dry-wet process in step S22 is as follows: and culturing the soil submerged by the excessive water in a dark place for 12 h, drying the soil in an oven at 40 ℃ for 12 h, and adding deionized water again to restore the water content to the initial state.
7. The method for evaluating the long-acting property of soil heavy metal pollution solidification stabilization according to claim 1, wherein the one-time freeze-thaw cycle process in the step S22 is as follows: freezing the soil submerged by the excessive water at-20 ℃ for 12 h, culturing for 12 h in the dark, and then adding deionized water again to restore the water content to the initial state.
8. The method for evaluating the long-acting property of soil heavy metal pollution solidification stabilization according to claim 1, wherein the analysis of the content and the morphology of the heavy metal in the soil in the step S23 is implemented by naturally air-drying the soil, grinding the soil through a 2 mm sieve, measuring the leaching concentration of the heavy metal by TCLP, and measuring the occurrence morphology of the heavy metal in the soil by a BCR four-step continuous extraction method.
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