CN110369473B - Remediation method for heavy metal contaminated soil of coastal mud flat - Google Patents
Remediation method for heavy metal contaminated soil of coastal mud flat Download PDFInfo
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- CN110369473B CN110369473B CN201910809186.8A CN201910809186A CN110369473B CN 110369473 B CN110369473 B CN 110369473B CN 201910809186 A CN201910809186 A CN 201910809186A CN 110369473 B CN110369473 B CN 110369473B
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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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- 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
Abstract
The invention provides a remediation method for heavy metal contaminated soil of coastal beaches, which belongs to the field of environmental science and comprises the steps of providing soil modification and reducing the viscosity of the beaches soil; leaching is provided, and mobile heavy metal with higher activity is removed; providing a heavy metal stabilizer, and fixing and stabilizing heavy metals; the heavy metal stabilizer comprises an acid carbonized porous biomass matrix and a fixing agent with a multilayer film structure. The repair method provided by the invention can immobilize heavy metal elements; the continuity of soil capillaries is damaged, the porosity of soil is increased, and the migration path of heavy metal is damaged and the migration performance of heavy metal is reduced; the activity of phosphatase in the soil is enhanced, and the effectiveness of organic matters and phosphorus in the soil is improved; the provided heavy metal stabilizer can enhance the activity of urease and catalase in soil, improve the soil fertility and the capability of preventing hydrogen peroxide from being poisoned by plants, and the contained fixing agent can be recycled and reused, so that the soil remediation cost is reduced, and the preparation method can reduce the acid consumption and the production cost.
Description
Technical Field
The invention belongs to the field of environmental science, and particularly relates to a remediation method for heavy metal contaminated soil on coastal mudflats.
Background
The beach reclamation and development is one of the main ways for supplementing cultivated land in coastal areas of China, and has important strategic significance for sustainable development of agriculture and economy in coastal areas of China. The tidal flat area of China is about 250 kilohm2And at 5000hm per year2The landing speeds of the left and right extend to the sea. Since most of the mudflats are formed by coastal reclamation, high salt content of soil, high mineralization degree of underground water and heavy metal pollution are serious main limiting factors for the utilization of the mudflats. By far, the utilization rate of mudflat development in our country is less than 50%. As the beach saline-alkali soil belongs to sandy silty soil and is barren, nutrients required by plant growth are difficult to provide, and a large amount of domestic and industrial sewage is discharged, the beach saline-alkali soil has high content of heavy metals and toxic and harmful substances, and simultaneously contains rich organic matters and N, P and other nutrient substances. N, P and other nutrient substances in the soil are easy to leach out along with tail water, and secondary pollution is generated to surrounding water bodies; heavy metals are difficult to decompose in natural environment, can change the dominant species of soil microorganisms after entering soil, can enter plant bodies through plant absorption, and indirectly react with each other through food chainsThe human body poses threat, enters the water body to pollute the ecological environment of aquatic organisms, enters the human body through the biological chain amplification, and causes harm to the human body. Heavy metal pollution is different from organic matter pollution, heavy metal is difficult to degrade and is easy to produce enrichment effect through plants or animals, so that the treatment difficulty of the heavy metal pollution of soil is higher. At present, in common treatment of heavy metal pollution of soil, agricultural ecological engineering measures are adopted, special plants and microorganisms are propagated on the soil polluted by the heavy metal, and the heavy metal in the soil is absorbed or degraded through the special plants and microorganisms, so that the aim of purifying the soil is fulfilled.
Disclosure of Invention
The invention aims to provide a fixing and stabilizing device which can fix and stabilize heavy metal elements; the continuity of soil capillaries can be damaged, the porosity of the soil is increased, the migration path of the heavy metal is damaged, and the migration performance of the heavy metal is reduced; the heavy metal stabilizer used in the method can enhance the activity of urease and catalase in the soil, improve the soil fertility and the capability of preventing the hydrogen peroxide from being poisoned by plants, and the contained fixing agent can be recycled and reused, thereby reducing the soil remediation cost.
The technical scheme adopted by the invention for realizing the purpose is as follows:
the method for restoring heavy metal contaminated soil on the coastal mudflat comprises the following steps: soil modification is provided, and the viscosity of mud flat soil is reduced; leaching is provided, and mobile heavy metal with higher activity is removed; providing a heavy metal stabilizer, and fixing and stabilizing heavy metals; the heavy metal stabilizer comprises an acid carbonized porous biomass matrix and a fixing agent with a multilayer film structure. The method reduces the activity of heavy metal ions (such as lead, zinc, copper, cadmium, arsenic and the like) in the soil by modifying, leaching and stabilizing the soil polluted by the heavy metal, replaces the inactivated heavy metal elements into the porous carrier, reduces the mobility and the biological activity of the heavy metal elements, reduces the absorption of plants and animals to the heavy metal, completes the fixation and stabilization of the heavy metal, repairs the heavy metal pollution in the soil of a tidal flat high-tide zone, a middle-tide zone and a low-tide zone, does not cause secondary pollution in the repair process, and has wider applicability in the soil repair engineering.
In some embodiments, the soil modification step is as follows: screening the coal cinder, selecting coal cinder particles with the particle size of less than 5mm, stirring and crushing polluted soil with the particle size of 0-10cm on the surface layer of a region to be repaired, adding the coal cinder into the soil according to the dry basis weight ratio of the coal cinder to the soil of 1:1-3, uniformly mixing, spraying water on the surface layer according to the solid-liquid ratio of 1:1-3, and then aging and maintaining for 5-10 days to obtain the modified soil. The coal cinder is industrial solid waste, the main components are silicate, iron, calcium and the like, and the alkaline mineral components have strong affinity to heavy metals, so that the acid heavy metal environment can be improved, the subsequent leaching operation can be facilitated, the phenomenon of discarding and accumulating the coal cinder is avoided, and the resource waste and the environmental risk are reduced.
In some embodiments, the rinsing step is as follows: diluting hydrochloric acid, bamboo vinegar and sulfuric acid at a weight ratio of 1:1-2:1-3 to prepare 0.3-1.0% leacheate, leaching the modified soil by 2-5 times, repeating the leaching for 1-2 times at an interval of 10-12h, and collecting the leacheate and the solid soil after solid-liquid separation. The acid solution can complex heavy metals, wash out small parts of heavy metals with high activity and strong mobility in the soil, and meanwhile, the residues such as bamboo vinegar can improve the content of organic matters and quick-acting nitrogen, phosphorus and potassium in the soil, thereby being beneficial to ecological restoration of the soil.
In some embodiments, the method of use of the heavy metal stabilizer in soil remediation is as follows: s1, ploughing and drying the field, crushing the washed solid soil into blocks, and then uniformly spreading the heavy metal stabilizer according to the amount of 200-300 kg/mu; s2, after the heavy metal stabilizer is sown, deep ploughing the soil, wherein the depth of surface soil of the deep ploughing is 10-40cm, and repeating for 2-3 times to ensure that the soil is uniformly mixed horizontally and vertically; s3, after deep ploughing, adding water until the water level is 10-20cm higher than the soil surface, and aging the soil for 10-15 days; and S4, draining water and drying the land after the aging is finished. The stabilizer and the heavy metal in the soil are subjected to physical and chemical actions such as chelation, precipitation, adsorption and the like, and the inactivated heavy metal elements are replaced into the porous carrier, so that the exchangeable state quantity of heavy metal pollutants is effectively reduced, the treatment efficiency is high, the stability and the effectiveness are realized for a long time, and the effect of remediation and treatment is achieved.
In some embodiments, 25 to 35wt% of the acid-carbonized porous biomass matrix and 40 to 60wt% of the multi-layer film structured immobilizing agent are included in the heavy metal stabilizer. The biomass matrix and the fixing agent can enrich the heavy metal elements by utilizing the active groups of the biomass matrix and the fixing agent, and then exchange or adsorb the heavy metal elements into the porous carrier, so that the heavy metal elements are synergistically stabilized in the carrier, the heavy metal elements are prevented from being accumulated in plants or animals, the purpose of purifying soil is achieved, and the heavy metal stabilizing agent has small disturbance on the soil and is beneficial to the subsequent ecological restoration of the soil.
In some specific embodiments, the heavy metal stabilizer further comprises at least one of sulfur powder, zeolite powder, carbide slag and limestone. The stabilizer contains natural materials with good compatibility and easy dispersion, can form a stable complex with heavy metals, greatly improves the adsorption rate and the adsorption capacity of the heavy metals, and has better passivation stabilization improvement effect on the polluted soil.
In some embodiments, the acid carbonized porous biomass substrate comprises the biomass substrate, residual acid from the acid carbonization process, and ammonium species formed from the residual acid amination reaction. The biomass substrate carbonized by the acid generates a microporous structure, the residual acid in the pore volume can enrich heavy metal elements and form a combined state to lose activity, and can also generate ammoniation reaction with ammonia to form ammonium substances, and the ammonium substances are adsorbed on the carbon substrate and are slowly released and provide nutrients when the material is applied to soil, so that the growth of plants is promoted.
In some embodiments, biomass substrates include, but are not limited to, forest and agricultural waste residues such as sawdust, corn stover, and the like, food waste, livestock waste, agricultural product waste such as bagasse, grain residues, and the like, aquatic product waste such as seaweed, and the like, industrial waste such as sugar processing residues, and the like.
In some embodiments, the acid used for acid carbonization is sulfuric acid and/or phosphoric acid. If sulfuric acid is used, the ammonium substance formed by ammoniation reaction is ammonium sulfate, and the sulfuric acid and lignin exposed in the biomass can form lignosulfonate, so that the effects of improving the pH value of soil and salinization are achieved; if phosphoric acid is used, the ammonium species formed by the ammoniation reaction is monoammonium phosphate or diammonium phosphate.
In some specific embodiments, the acid-carbonized porous biomass matrix is prepared by the steps of: adding 20-70 wt% of acid into the biomass matrix for carbonization for 10-30min, wherein the mass concentration of the acid is 40-80%, introducing anhydrous gaseous ammonia accounting for 15-40 wt% of the biomass matrix into the system after the reaction is completed, reacting for 30-60min, recovering residual liquid, and taking out and drying the precipitate to obtain the biomass-based catalyst.
In some embodiments, the acid used for acid carbonization contains 0.05-0.1mM of tert-butylhydroquinone and 0.03-0.08mM of methyl naphthol, and the two have a synergistic effect during acid carbonization, so that the combination of lignin and hemicellulose is depolymerized, the lignin is favorably exposed and forms lignosulfonate with sulfuric acid, the carbonization degree of the acid on biomass fibers can be controlled, the acid using amount and the production cost are reduced, and on the other hand, the activity of urease and catalase in the soil can be continuously enhanced after the two are slowly released into the soil from the biomass matrix, so that the soil fertility and the hydrogen peroxide poisoning prevention capability of plants are improved, and the purpose of soil remediation is achieved.
In some embodiments, the fixative of the multilayer film structure includes an ethylene-vinyl acetate copolymer particle core having a particle size of 2 to 6mm, a filler layer formed from a glycoconjugate, and a tie layer formed from a polyhydroxylated acid. The jointing layer enriches heavy metals, and the heavy metals are replaced into the grain cores through the filling layer for immobilization, so that the toxicity of the heavy metals to plants is reduced, meanwhile, the jointing layer and the filling layer can be naturally decomposed in soil, nutrient elements are provided for the plants, the soil fertility is increased, the grain cores can be recycled and reused, and the soil remediation cost is reduced.
In some embodiments, the filler layer and the bonding layer of the fixing agent of the multilayer film structure are sequentially coated on the surface layer of the particle core by means of spraying; the filling layer and the jointing layer are respectively 5-10% and 8-15% of the weight of the grain core.
In some specific embodiments, the polyhydroxy acid used in the tie layer is a condensation polymer of one or more hydroxy acids, preferably hydroxy acids including, but not limited to, glycolic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxyisobutyric acid, or a combination of two or more thereof. The polyhydroxy hydrocarbon acid is a biodegradable polymer, can produce and enrich heavy metal elements, and forms high-affinity and stable complex precipitates with heavy metal ions, so that the harm to plants is reduced.
In some specific embodiments, the glycoconjugate used in the filling layer comprises one or more substances comprising glycosidic linkages including, but not limited to, glucose, starch, pectin, alginic acid or a salt thereof, xanthan gum, or a combination of two or more thereof. Preferably, the glycoconjugate is a starch. The filling layer can increase the adhesion between the grain core and the jointing layer, and meanwhile, a channel is established between the jointing layer and the grain core, so that heavy metal elements are replaced into the grain core from the surface layer of the fixing agent, and the fixation and stabilization of heavy metals are achieved.
The invention has the beneficial effects that:
1) the repairing method provided by the invention reduces the migration and biological activity of heavy metal ions in the soil by modifying, leaching and stabilizing the soil polluted by the heavy metal, reduces the absorption of plants and animals to the heavy metal, and completes the fixation and stabilization of the heavy metal;
2) according to the remediation method provided by the invention, the acidic heavy metal environment can be improved through soil modification, the phenomenon of coal cinder abandoning and accumulation is avoided, the resource waste and the environmental risk are reduced, the continuity of soil capillaries can be damaged through leaching, the porosity of the soil is increased, the migration performance of the heavy metal is reduced through damaging the migration path of the heavy metal, the activity of phosphatase in the soil can be enhanced, and the circulation of organic phosphorus in the soil is accelerated, so that the effectiveness of organic matters and phosphorus in the soil is improved, and the ecological restoration of the soil is facilitated;
3) the heavy metal stabilizer provided by the invention can effectively reduce the exchangeable state quantity of heavy metal pollutants, has high treatment efficiency, is stable and effective for a long time, improves the adsorption rate and adsorption capacity of heavy metals, has small disturbance to soil, is beneficial to subsequent ecological restoration of soil, and can provide nutrient elements for plants and increase the soil fertility;
4) the acid carbonized porous biomass matrix in the heavy metal stabilizer provided by the invention can enhance the activity of urease and catalase in soil and improve the soil fertility and the capability of preventing hydrogen peroxide from being poisoned by plants, the preparation method can reduce the acid dosage and the production cost, and the fixing agent with a multilayer film structure can be recycled and reused, thereby reducing the soil remediation cost.
The invention adopts the technical scheme to provide the remediation method for heavy metal contaminated soil on the coastal mudflat, overcomes the defects of the prior art, and has reasonable design and convenient operation.
Drawings
FIG. 1 is a schematic illustration of the effect of different remediation methods on urease activity in soil;
FIG. 2 is a schematic representation of the effect of different remediation methods on catalase activity in soil;
FIG. 3 is a graph showing the effect of different remediation methods on phosphatase activity in soil.
Detailed Description
The technical solution of the present invention is further described in detail below with reference to the following detailed description and the accompanying drawings:
example 1:
the method for restoring heavy metal contaminated soil on the coastal mudflat comprises the following steps: soil modification is provided, and the viscosity of mud flat soil is reduced; leaching is provided, and mobile heavy metal with higher activity is removed; providing a heavy metal stabilizer, and fixing and stabilizing heavy metals; the heavy metal stabilizer comprises an acid carbonized porous biomass matrix and a fixing agent with a multilayer film structure. The method reduces the activity of heavy metal ions (such as lead, zinc, copper, cadmium, arsenic and the like) in the soil by modifying, leaching and stabilizing the soil polluted by the heavy metal, replaces the inactivated heavy metal elements into the porous carrier, reduces the mobility and the biological activity of the heavy metal elements, reduces the absorption of plants and animals to the heavy metal, completes the fixation and stabilization of the heavy metal, repairs the heavy metal pollution in the soil of a tidal flat high-tide zone, a middle-tide zone and a low-tide zone, does not cause secondary pollution in the repair process, and has wider applicability in the soil repair engineering.
The soil modification steps are as follows: screening the coal cinder, selecting coal cinder particles with the particle size of less than 5mm, stirring and crushing polluted soil with the surface layer of a region to be repaired being 10cm, adding the coal cinder into the soil according to the dry basis weight ratio of the coal cinder to the soil being 1:2, uniformly mixing, spraying water on the surface layer according to the solid-liquid ratio of 1:2, and then aging and maintaining for 10 days to obtain the modified soil. The coal cinder is industrial solid waste, the main components are silicate, iron, calcium and the like, and the alkaline mineral components have strong affinity to heavy metals, so that the acid heavy metal environment can be improved, the subsequent leaching operation can be facilitated, the phenomenon of discarding and accumulating the coal cinder is avoided, and the resource waste and the environmental risk are reduced.
The leaching steps are as follows: diluting hydrochloric acid, bamboo vinegar and sulfuric acid at a weight ratio of 1:1:2 to prepare an eluent with a concentration of 1.0%, then leaching the modified soil by 4 times, repeating for 2 times at an interval of 12h, and after solid-liquid separation, respectively collecting the eluent and the solid soil. The acid solution can complex heavy metals, wash out small parts of heavy metals with high activity and strong mobility in the soil, and meanwhile, the residues such as bamboo vinegar can improve the content of organic matters and quick-acting nitrogen, phosphorus and potassium in the soil, thereby being beneficial to ecological restoration of the soil.
The application method of the heavy metal stabilizer in soil remediation is as follows: s1, ploughing and drying the land, smashing the washed solid soil block mass, and then uniformly spreading the heavy metal stabilizer according to the amount of 300 kg/mu; s2, after the heavy metal stabilizer is sown, deep ploughing the soil, wherein the depth of surface soil of the deep ploughing is 30cm, and the deep ploughing is repeated for 3 times to ensure that the soil is uniformly mixed horizontally and vertically; s3, after deep ploughing, adding water until the water level is 10cm higher than the soil surface, and aging the soil for 15 d; and S4, draining water and drying the land after the aging is finished. The stabilizer and the heavy metal in the soil are subjected to physical and chemical actions such as chelation, precipitation, adsorption and the like, and the inactivated heavy metal elements are replaced into the porous carrier, so that the exchangeable state quantity of heavy metal pollutants is effectively reduced, the treatment efficiency is high, the stability and the effectiveness are realized for a long time, and the effect of remediation and treatment is achieved.
The heavy metal stabilizer comprises 35wt% of acid carbonized porous biomass matrix and 50 wt% of fixing agent with a multilayer film structure. The biomass matrix and the fixing agent can enrich the heavy metal elements by utilizing the active groups of the biomass matrix and the fixing agent, and then exchange or adsorb the heavy metal elements into the porous carrier, so that the heavy metal elements are synergistically stabilized in the carrier, the heavy metal elements are prevented from being accumulated in plants or animals, the purpose of purifying soil is achieved, and the heavy metal stabilizing agent has small disturbance on the soil and is beneficial to the subsequent ecological restoration of the soil.
The heavy metal stabilizer also comprises 5wt% of sulfur powder and 10 wt% of limestone. The stabilizer contains natural materials with good compatibility and easy dispersion, can form a stable complex with heavy metals, greatly improves the adsorption rate and the adsorption capacity of the heavy metals, and has better passivation stabilization improvement effect on the polluted soil.
The acid carbonized porous biomass matrix comprises a biomass matrix, residual acid in the acid carbonization process and ammonium substances formed by ammoniation reaction of the residual acid. The biomass substrate carbonized by the acid generates a microporous structure, the residual acid in the pore volume can enrich heavy metal elements and form a combined state to lose activity, and can also generate ammoniation reaction with ammonia to form ammonium substances, and the ammonium substances are adsorbed on the carbon substrate and are slowly released and provide nutrients when the material is applied to soil, so that the growth of plants is promoted.
Such biomass substrates include, but are not limited to, forest and agricultural waste residues such as sawdust, corn stover, and the like, food waste, livestock waste, agricultural product waste such as bagasse, grain residues, and the like, aquatic product waste such as seaweed, and the like, industrial waste such as sugar processing residues, and the like.
The acid used for acid carbonization is sulfuric acid and phosphoric acid with the weight ratio of 1:1. If sulfuric acid is used, the ammonium substance formed by ammoniation reaction is ammonium sulfate, and the sulfuric acid and lignin exposed in the biomass can form lignosulfonate, so that the effects of improving the pH value of soil and salinization are achieved; if phosphoric acid is used, the ammonium species formed by the ammoniation reaction is monoammonium phosphate or diammonium phosphate.
The preparation steps of the acid carbonized porous biomass matrix are as follows: adding 30 wt% of acid into the biomass matrix for carbon 15min, wherein the mass concentration of the acid is 50%, introducing 20 wt% of anhydrous gaseous ammonia into the biomass matrix after the reaction is completed, reacting for 40min, recovering residual liquid, and drying the precipitate to obtain the biomass-based catalyst.
The acid used for acid carbonization contains 0.07mM of tert-butyl hydroquinone and 0.08mM of methyl naphthol, and the two have a synergistic effect during acid carbonization, so that the combination of lignin and hemicellulose is depolymerized, lignin is favorable for forming lignosulfonate with sulfuric acid after being exposed, the carbonization degree of the acid to biomass fibers can be controlled, the acid using amount and the production cost are reduced, and on the other hand, the two can continuously enhance the activities of urease and catalase in soil after being slowly released from a biomass matrix into the soil, so that the soil fertility and the hydrogen peroxide toxicity prevention capability of plants are improved, and the purpose of soil restoration is achieved.
The fixing agent of the multilayer film structure comprises an ethylene-vinyl acetate copolymer particle core with the particle diameter of 5mm, a filling layer formed by a glycoconjugate and a jointing layer formed by polyhydroxy hydrocarbon acid. The jointing layer enriches heavy metals, and the heavy metals are replaced into the grain cores through the filling layer for immobilization, so that the toxicity of the heavy metals to plants is reduced, meanwhile, the jointing layer and the filling layer can be naturally decomposed in soil, nutrient elements are provided for the plants, the soil fertility is increased, the grain cores can be recycled and reused, and the soil remediation cost is reduced.
The filler layer and the bonding layer in the fixing agent of the multilayer film structure are sequentially coated on the surface layer of the particle core in a spraying mode; the filler layer and the binder layer were used in amounts of 10% and 10% by weight of the core, respectively.
The polyhydroxylic acid used in the above-mentioned jointing layer is a polycondensate of one or more kinds of hydroxycarboxylic acids, preferably, the hydroxycarboxylic acid is hydroxybutyric acid. The polyhydroxy hydrocarbon acid is a biodegradable polymer, can produce and enrich heavy metal elements, and forms high-affinity and stable complex precipitates with heavy metal ions, so that the harm to plants is reduced.
The glycoconjugate used in the filling layer comprises one or more substances containing glycosidic bonds, and preferably, the glycoconjugate is starch. The filling layer can increase the adhesion between the grain core and the jointing layer, and meanwhile, a channel is established between the jointing layer and the grain core, so that heavy metal elements are replaced into the grain core from the surface layer of the fixing agent, and the fixation and stabilization of heavy metals are achieved.
Example 2:
the method for restoring heavy metal contaminated soil on the coastal mudflat comprises the following specific steps:
(1) screening coal slag, selecting coal slag particles with the particle size of less than 5mm, stirring and smashing polluted soil with the surface layer of a region to be repaired being 10cm, adding the coal slag into the soil according to the dry basis weight ratio of the coal slag to the soil being 1:1.5, spraying water to the surface layer according to the solid-liquid ratio of 1:1.5 after uniformly mixing, and then aging and maintaining for 7d to obtain modified soil;
(2) diluting hydrochloric acid, bamboo vinegar and sulfuric acid at a weight ratio of 1:2:1.5 to prepare 0.5% leacheate, leaching the modified soil by 3 times, repeating the leaching for 2 times at a time interval of 10 hours, and respectively collecting the leacheate and the solid soil after solid-liquid separation;
(3) adding 35% by weight of acid into a biomass matrix for carbonization for 30min, introducing 25% by weight of anhydrous gaseous ammonia into a system after the reaction is completed for reaction for 45min, recovering residual liquid, and drying a precipitate to obtain an acid carbonized porous biomass matrix, wherein the acid used for acid carbonization is sulfuric acid and phosphoric acid in a weight ratio of 1:1, the mass concentration of the acid is 45%, and the acid contains 0.05mM of tert-butylhydroquinone and 0.05mM of methyl naphthol;
(4) selecting an ethylene-vinyl acetate copolymer with the particle size of 5mm as a particle core, spraying and coating starch with the weight of 8% of the weight of the particle core on the surface layer of the particle core to form a filling layer, and then spraying and coating polyhydroxypropionic acid with the weight of 12% of the weight of the particle core on the outside of the filling layer to form a bonding layer, so as to prepare the fixing agent with the multilayer film structure;
(5) uniformly mixing 35wt% of acid carbonized porous biomass matrix, 45 wt% of fixing agent with a multilayer film structure, 10 wt% of sulfur powder, 5wt% of zeolite powder and 5wt% of carbide slag in sequence to prepare a heavy metal stabilizer;
(6) ploughing and drying the field, crushing the washed solid soil into blocks, and then uniformly spreading the heavy metal stabilizer according to the amount of 250 kg/mu; after the heavy metal stabilizer is sowed, deep ploughing the soil, wherein the depth of surface soil subjected to deep ploughing is 15cm, and repeating for 2 times to ensure that the soil is uniformly mixed horizontally and vertically; after deep ploughing, adding water until the water level is 15cm higher than the soil surface, and aging the soil for 14 d; and after aging, draining water and drying the land.
Example 3:
this embodiment differs from embodiment 2 only in that: the leacheate used in the step (2) also comprises furoic acid and ethoxyquin, wherein the weight of the furoic acid and the ethoxyquin are respectively 0.04% of that of hydrochloric acid, and the synergistic effect of the furoic acid and the ethoxyquin can be used for embedding functional groups into the coal cinder structure during leaching, destroying the continuity of soil capillaries by using hydrophilicity of different degrees, increasing the porosity of soil, further destroying the migration path of heavy metals and reducing the migration performance of the heavy metals, and on the other hand, the two can enhance the activity of phosphatase in the soil and accelerate the circulation of organic phosphorus in the soil, so that the phosphorus effectiveness and the soil fertility in the soil are improved.
Example 4:
this embodiment differs from embodiment 2 only in that: the acid used in the acid carbonization in the step (3) is not added with tert-butylhydroquinone and methyl naphthol.
Example 5:
this embodiment differs from embodiment 2 only in that: the acid used in the acid carbonization in the step (3) is not added with tert-butylhydroquinone and alpha naphthol, the mass concentration of the acid used in the acid carbonization is 55%, and the acid dosage is 65% of the weight of the biomass matrix.
Example 6:
this embodiment differs from embodiment 2 only in that: the concrete measures of the step (5) are as follows: uniformly mixing 80 wt% of acid carbonized porous biomass matrix, 10 wt% of sulfur powder, 5wt% of zeolite powder and 5wt% of carbide slag in sequence to obtain a heavy metal stabilizer; namely, the heavy metal stabilizer is not added with a fixing agent with a multilayer film structure.
Example 7:
this embodiment differs from embodiment 2 only in that: the concrete measures of the step (5) are as follows: uniformly mixing 80 wt% of a fixing agent with a multilayer film structure, 10 wt% of sulfur powder, 5wt% of zeolite powder and 5wt% of carbide slag in sequence to obtain a heavy metal stabilizer; namely, the porous biomass matrix which is not carbonized by acid is added in the heavy metal stabilizer.
Test example 1:
detection of heavy metal content in soil under different remediation methods
The test method comprises the following steps: the soil repaired in each example was randomly taken as a test sample, copper, zinc, lead and chromium were measured by inductively coupled plasma emission spectrometry, cadmium was measured by flameless atomic absorption spectrophotometry and arsenic and mercury were measured by atomic fluorescence with reference to part 5 of the marine test specifications (GB 17378.5-2007). The statistics of the detection results are shown in table 1.
TABLE 1 detection results of heavy metal content in soil
As can be seen from the above table, the heavy metal content in the repaired soil meets the level II standard of GB15618-1995 soil environmental quality standard. The repairing results of examples 2-5 are significantly better than those of examples 6 and 7, which shows that the heavy metal stabilizer in examples 2-5 has significantly better immobilization effect on heavy metal elements than the heavy metal stabilizer used in examples 6 and 7. The repair results of example 2 and example 5 are not significantly different, but the amount and concentration of acid in example 5 are higher than in example 2, which illustrates that the method of preparing the acid carbonized porous biomass matrix in example 2 can reduce the amount of acid compared to example 5, and can significantly reduce the production cost in actual production. Compared with the examples 3 and 4, the embodiment 2 has the best repairing result, the embodiment 2 has the second time, and the embodiment 4 has the worst repairing result, which shows that the repairing method in the embodiment 3 has better repairing effect than the embodiment 2, can reduce the migration of heavy metal, and achieves the effect of fixing and stabilizing heavy metal; compared with example 4, the embodiment 2 shows that the heavy metal stabilizer repair effect in the embodiment 2 is better than that in the embodiment 4, and the repair method in the embodiment 2 is more worthy of popularization and application.
Test example 2:
effect of different remediation methods on soil porosity
The test method comprises the following steps: after the test soil was washed according to the methods of examples 2 and 3, respectively, the solid soil obtained by washing was collected, and the soil that was not washed was used as a control group. Respectively randomly selecting soil with the same weight for sampling, after the sample is dried in the air, sieving the soil sample by using a sieve with the specification of 0.25mm, then packaging by using a sealed polyethylene bag, and storing at 4 ℃ for later use; and then measuring the total porosity of the soil by adopting a cutting ring method. Statistics and analysis of results are shown in table 2.
TABLE 2 determination of soil porosity under different remediation methods
As can be seen from the above table, the remediation methods of examples 2 and 3 can increase the porosity of the soil compared with the control group, and the increased porosity of the soil has a moderate proportion, which is beneficial to reducing the migration of heavy metals; compared with the embodiment 2, the repairing method of the embodiment 3 has the advantages that the increase range of the porosity of the soil after being washed by the method of the embodiment 3 is larger, the porosity is higher, and the capillary continuity of the soil can be damaged, so that the aim of damaging the migration path of the heavy metal to reduce the migration performance of the heavy metal is fulfilled.
Test example 3:
effect of different remediation methods on enzymatic Activity in soil
(1) After soil was restored by the methods of examples 2 and 4, respectively, unrepaired soil was used as a control group. And detecting the activity of urease and catalase in the soil at each stage of soil modification, leaching and application of the heavy metal stabilizer, wherein the activity of the urease is detected by a sodium phenolate colorimetric method, and the activity of the catalase is detected by a potassium permanganate titration method. The statistics and analysis results are shown in fig. 1 and 2.
FIG. 1 is a schematic diagram showing the effect of different remediation methods on urease activity in soil, and FIG. 2 is a schematic diagram showing the effect of different remediation methods on catalase activity in soil. As can be seen from the figure, the activity difference of the urease and the catalase in the soil is not obvious in the examples 2 and 4 and the control group before the application of the heavy metal stabilizer, the activity of the urease and the activity of the catalase fluctuate between 0.4 mg/g and 0.8mg/g and 0.4 mg/g and 0.9mg/g respectively, after the application of the stabilizer, the activity of the urease and the activity of the catalase in the example 4 and the control group are still within the normal fluctuation range, and the activity of the urease and the activity of the catalase in the example 2 are increased to 1.23mg/g and 1.35mg/g respectively, so that the increase range is larger, and the difference is obvious. Compared with the embodiment 4, the repairing method in the embodiment 2 can enhance the activities of urease and catalase in the soil, thereby improving the soil fertility and the poison prevention capability on hydrogen peroxide and achieving the aim of repairing the soil.
(2) After soil was restored by the methods of examples 2 and 3, respectively, unrepaired soil was used as a control group. And detecting the activity of phosphatase in the soil at each stage of soil modification, leaching and application of the heavy metal stabilizer, wherein the phosphatase activity adopts a disodium phenylphosphate colorimetric method. The statistics and analysis results are shown in fig. 3.
FIG. 3 is a graph showing the effect of different remediation methods on phosphatase activity in soil. As can be seen from the figure, the phosphatase activity difference in the tested soil is not obvious before the washing of the examples 2 and 3 and the control group, the phosphatase activity fluctuates between 1.2 and 1.7mg/g, after the washing, the phosphatase activity of the example 2 and the control group is still within the normal fluctuation range, while the phosphatase activity of the example 3 is increased to 2.3mg/g, the increase range is large, the difference is obvious, and the high activity of the phosphatase can be continuously maintained after the stabilizer is applied. Compared with the embodiment 2, the remediation method in the embodiment 3 can enhance the activity of phosphatase in the soil, so that the circulation of organic phosphorus in the soil is accelerated, and the effectiveness and the fertility of phosphorus in the soil are improved.
Conventional techniques in the above embodiments are known to those skilled in the art, and therefore, will not be described in detail herein.
The above embodiments are merely illustrative, and not restrictive, and those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention, and the protection scope of the present invention should be defined by the claims.
Claims (8)
1. The method for restoring heavy metal contaminated soil on the coastal mudflat comprises the following steps:
soil modification is provided, and the viscosity of mud flat soil is reduced;
leaching is provided, and mobile heavy metal with higher activity is removed;
providing a heavy metal stabilizer, and fixing and stabilizing heavy metals;
the heavy metal stabilizer comprises 25-35wt% of acid carbonized porous biomass matrix and 40-60wt% of fixing agent with a multilayer film structure;
the acid carbonized porous biomass matrix comprises a biomass matrix, residual acid in the acid carbonization process and ammonium substances formed by ammoniation reaction of the residual acid;
the acid used for preparing the acid carbonized porous biomass matrix is at least one of sulfuric acid and phosphoric acid, and the mass concentration of the acid is 40-80%; the acid used for acid carbonization contains 0.05-0.1mM of tert-butylhydroquinone and 0.03-0.08mM of methyl naphthol;
the concentration of an eluent used for leaching is 0.3-1.0%, and the eluent comprises hydrochloric acid, bamboo vinegar and sulfuric acid in a weight ratio of 1:1-2: 1-3;
the leacheate also comprises furoic acid and ethoxyquinoline which respectively account for 0.04% and 0.06% of the weight of the hydrochloric acid.
2. The remediation method for heavy metal contaminated soil of coastal beaches according to claim 1, wherein: the soil modification steps are as follows: screening the coal cinder, selecting coal cinder particles with the particle size smaller than 5mm, stirring and smashing the polluted soil with the particle size of 0-10cm on the surface layer of the area to be repaired, adding the coal cinder into the soil according to the dry basis weight ratio of the coal cinder to the soil =1:1-3, uniformly mixing, spraying water on the surface layer according to the solid-liquid ratio of 1:1-3, and then aging and maintaining for 5-10d to obtain the modified soil.
3. The remediation method for heavy metal contaminated soil of coastal beaches according to claim 1, wherein: the application amount of the heavy metal stabilizer in the soil is 200-300 kg/mu; after the heavy metal stabilizer is applied, deep ploughing is carried out on surface soil with the depth of 10-40cm, and water is added for aging for 10-15 days.
4. The remediation method for heavy metal contaminated soil of coastal beaches according to claim 1, wherein: the preparation steps of the acid carbonized porous biomass matrix are as follows: adding 20-70 wt% of acid into the biomass matrix for carbonization for 10-30min, introducing anhydrous gaseous ammonia accounting for 15-40 wt% of the biomass matrix into the system after the reaction is completed, recovering residual liquid after the reaction is carried out for 30-60min, and taking out and drying the precipitate to obtain the biomass-based catalyst.
5. The remediation method for heavy metal contaminated soil of coastal beaches according to claim 1, wherein: the fixing agent of the multilayer film structure comprises an ethylene-vinyl acetate copolymer particle core with the particle diameter of 2-6mm, a filling layer formed by a glycoconjugate and a jointing layer formed by polyhydroxy hydrocarbon acid.
6. The remediation method for heavy metal contaminated soil of coastal beaches according to claim 1, wherein: the filler layer and the bonding layer in the fixing agent of the multilayer film structure are sequentially coated on the surface layer of the particle core in a spraying mode; the filling layer and the jointing layer are respectively 5-10% and 8-15% of the weight of the grain core.
7. The remediation method for heavy metal contaminated soil of coastal beaches according to claim 5, wherein: the polyhydroxyhydrocarbon acid is a polycondensate of a polyhydroxyhydrocarbon acid; the hydroxy acid is selected from glycolic acid, hydroxy propionic acid, hydroxy butyric acid, hydroxy isobutyric acid, or their combination.
8. The remediation method for heavy metal contaminated soil of coastal beaches according to claim 5, wherein: the glycoconjugate is selected from glucose, starch, pectin, alginic acid or its salt, xanthan gum, or a combination of two or more thereof.
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