CN117943392A - Method for realizing efficient leaching of heavy metal elements in polluted soil based on chlorine-containing plastic co-pyrolysis - Google Patents
Method for realizing efficient leaching of heavy metal elements in polluted soil based on chlorine-containing plastic co-pyrolysis Download PDFInfo
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- 229910001385 heavy metal Inorganic materials 0.000 title claims abstract description 145
- 239000002689 soil Substances 0.000 title claims abstract description 134
- 239000000460 chlorine Substances 0.000 title claims abstract description 110
- 229910052801 chlorine Inorganic materials 0.000 title claims abstract description 110
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 title claims abstract description 108
- 239000004033 plastic Substances 0.000 title claims abstract description 103
- 229920003023 plastic Polymers 0.000 title claims abstract description 103
- 238000000197 pyrolysis Methods 0.000 title claims abstract description 88
- 238000002386 leaching Methods 0.000 title claims abstract description 85
- 238000000034 method Methods 0.000 title claims abstract description 44
- 238000000605 extraction Methods 0.000 claims abstract description 25
- 239000000463 material Substances 0.000 claims description 31
- 238000000926 separation method Methods 0.000 claims description 17
- 239000000203 mixture Substances 0.000 claims description 13
- 239000007788 liquid Substances 0.000 claims description 11
- 238000002156 mixing Methods 0.000 claims description 8
- 239000007787 solid Substances 0.000 claims description 7
- 239000000284 extract Substances 0.000 claims description 2
- 238000011282 treatment Methods 0.000 abstract description 30
- 230000008569 process Effects 0.000 abstract description 11
- 229910052500 inorganic mineral Inorganic materials 0.000 abstract description 9
- 239000011707 mineral Substances 0.000 abstract description 9
- 239000000126 substance Substances 0.000 abstract description 7
- 239000003153 chemical reaction reagent Substances 0.000 abstract description 6
- 229910052751 metal Inorganic materials 0.000 abstract description 6
- 238000004064 recycling Methods 0.000 abstract description 6
- 239000001257 hydrogen Substances 0.000 abstract description 4
- 229910052739 hydrogen Inorganic materials 0.000 abstract description 4
- 239000002184 metal Substances 0.000 abstract description 4
- 239000013502 plastic waste Substances 0.000 abstract description 3
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 abstract description 2
- 230000007547 defect Effects 0.000 abstract description 2
- 238000006731 degradation reaction Methods 0.000 abstract description 2
- 239000002699 waste material Substances 0.000 abstract description 2
- 239000000243 solution Substances 0.000 description 24
- 230000000052 comparative effect Effects 0.000 description 20
- 229910052725 zinc Inorganic materials 0.000 description 20
- 239000011701 zinc Substances 0.000 description 20
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 19
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 19
- 229910052802 copper Inorganic materials 0.000 description 19
- 239000010949 copper Substances 0.000 description 19
- 229910052793 cadmium Inorganic materials 0.000 description 18
- 239000000047 product Substances 0.000 description 18
- BDOSMKKIYDKNTQ-UHFFFAOYSA-N cadmium atom Chemical compound [Cd] BDOSMKKIYDKNTQ-UHFFFAOYSA-N 0.000 description 17
- 239000011133 lead Substances 0.000 description 17
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 14
- 239000002253 acid Substances 0.000 description 14
- 238000005516 engineering process Methods 0.000 description 10
- 239000000843 powder Substances 0.000 description 8
- 238000001556 precipitation Methods 0.000 description 8
- 238000005119 centrifugation Methods 0.000 description 7
- 230000000694 effects Effects 0.000 description 7
- 239000002245 particle Substances 0.000 description 7
- 230000008439 repair process Effects 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- 238000009713 electroplating Methods 0.000 description 5
- 230000010355 oscillation Effects 0.000 description 5
- 238000011084 recovery Methods 0.000 description 5
- 239000010802 sludge Substances 0.000 description 5
- 230000002378 acidificating effect Effects 0.000 description 4
- 230000008901 benefit Effects 0.000 description 4
- -1 chlorine radicals Chemical class 0.000 description 4
- 238000000227 grinding Methods 0.000 description 4
- 238000007873 sieving Methods 0.000 description 4
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 3
- 238000002425 crystallisation Methods 0.000 description 3
- 230000008025 crystallization Effects 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- 238000005065 mining Methods 0.000 description 3
- 150000003254 radicals Chemical class 0.000 description 3
- 238000007789 sealing Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 239000004709 Chlorinated polyethylene Substances 0.000 description 2
- 238000007605 air drying Methods 0.000 description 2
- 239000003795 chemical substances by application Substances 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000003344 environmental pollutant Substances 0.000 description 2
- 238000009616 inductively coupled plasma Methods 0.000 description 2
- 238000005342 ion exchange Methods 0.000 description 2
- JQJCSZOEVBFDKO-UHFFFAOYSA-N lead zinc Chemical compound [Zn].[Pb] JQJCSZOEVBFDKO-UHFFFAOYSA-N 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 231100000719 pollutant Toxicity 0.000 description 2
- VWDWKYIASSYTQR-UHFFFAOYSA-N sodium nitrate Chemical compound [Na+].[O-][N+]([O-])=O VWDWKYIASSYTQR-UHFFFAOYSA-N 0.000 description 2
- 238000005303 weighing Methods 0.000 description 2
- UXVMQQNJUSDDNG-UHFFFAOYSA-L Calcium chloride Chemical compound [Cl-].[Cl-].[Ca+2] UXVMQQNJUSDDNG-UHFFFAOYSA-L 0.000 description 1
- QPCDCPDFJACHGM-UHFFFAOYSA-N N,N-bis{2-[bis(carboxymethyl)amino]ethyl}glycine Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(=O)O)CCN(CC(O)=O)CC(O)=O QPCDCPDFJACHGM-UHFFFAOYSA-N 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000006978 adaptation Effects 0.000 description 1
- 239000012670 alkaline solution Substances 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 239000013065 commercial product Substances 0.000 description 1
- 239000008367 deionised water Substances 0.000 description 1
- 229910021641 deionized water Inorganic materials 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 230000005518 electrochemistry Effects 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000001640 fractional crystallisation Methods 0.000 description 1
- 238000009854 hydrometallurgy Methods 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 239000012633 leachable Substances 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000001000 micrograph Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000004800 polyvinyl chloride Substances 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 238000007348 radical reaction Methods 0.000 description 1
- 238000005067 remediation Methods 0.000 description 1
- 239000011343 solid material Substances 0.000 description 1
- 238000000194 supercritical-fluid extraction Methods 0.000 description 1
- 239000002351 wastewater Substances 0.000 description 1
- 238000004065 wastewater treatment Methods 0.000 description 1
Classifications
-
- 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
- B09C1/065—Reclamation of contaminated soil thermally by pyrolysis
-
- 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
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Landscapes
- Life Sciences & Earth Sciences (AREA)
- Soil Sciences (AREA)
- Engineering & Computer Science (AREA)
- Environmental & Geological Engineering (AREA)
- Physics & Mathematics (AREA)
- Thermal Sciences (AREA)
- Processing Of Solid Wastes (AREA)
Abstract
The invention provides a method for realizing efficient leaching of heavy metal elements in polluted soil based on chlorine-containing plastic co-pyrolysis, and relates to the technical field of metal element extraction. The invention utilizes HCl generated by combining chlorine free radicals and hydrogen free radicals in the thermal degradation process of chlorine-containing plastics to be skillfully combined with heavy metal leaching of polluted soil, promotes dissociation-leaching of the heavy metal combined with soil mineral lattices, and overcomes the defect that a large amount of acid-base reagents are consumed in the existing chemical leaching process, thereby realizing green leaching of heavy metal elements without adding chemical reagents. And the chlorine-containing plastic can be selected from waste plastic, and the recycling treatment of plastic waste is facilitated.
Description
Technical Field
The invention relates to the technical field of metal element extraction, in particular to a method for realizing efficient leaching of heavy metal elements in polluted soil based on chlorine-containing plastic co-pyrolysis.
Background
The problem of heavy metal pollution of soil is always focused, and pollution remediation is one of effective ways for realizing safe utilization of soil. However, the soil around industrial sites, mining areas and tailing ponds is often polluted by heavy metals, and the repair cost of the heavy polluted soil is difficult to cover due to long repair period, high cost and difficult thoroughness of the heavy polluted soil. Therefore, for the severely polluted soil, researchers seldom remove treatment application from the repair treatment layer, but remove resource utilization from the perspective of separating and recycling high-value metal elements, and the method can reduce the harm of the severely polluted soil, reduce the exploitation of natural minerals, accords with the concepts of environmental protection and circular economy, and has remarkable environmental and economic benefits.
The heavy metal separation and recovery technology mainly comprises a thermal separation technology, a hydrometallurgical technology (comprising chemical leaching and biological leaching), an electrochemical technology and the like. Among them, the chemical leaching process of hydrometallurgy is the most commonly used heavy metal separation and extraction technology at present, and is the only technology which has been applied industrially. The chemical leaching technology is to mix soil with strong acid or strong alkaline solution, transfer heavy metal to liquid phase through chemical reaction, and then further recover the heavy metal through precipitation, crystallization, extraction or electrochemistry. Acid is the most common leaching agent for chemical leaching, especially high concentration hydrochloric acid (HCl). Because HCl has good extraction effect and is suitable for simultaneous leaching of various heavy metals, the HCl is often used as an optimal leaching agent for extracting and recycling the heavy metals. Although the HCl leaching process is simple and mature, the extraction rate is high, the reaction period is short, a large amount of water and chemical reagents are consumed, secondary treatment is required for generating high-salt wastewater, and the comprehensive disposal cost is high. Therefore, there is a need to improve the current technology of chemical leaching of heavy metals to achieve green and efficient leaching-extraction-recovery of various metals without using acid-base chemical reagents as much as possible.
Disclosure of Invention
The invention aims to provide a method for realizing efficient leaching of heavy metal elements in polluted soil based on chlorine-containing plastic co-pyrolysis.
In order to achieve the above object, the present invention provides the following technical solutions:
The invention provides a method for realizing efficient leaching of heavy metal elements in polluted soil based on chlorine-containing plastic co-pyrolysis, which comprises the following steps:
Mixing heavy metal contaminated soil with chlorine-containing plastic to obtain a mixed material; when the pH value of the heavy metal contaminated soil is more than 6.5, the mass of the chlorine-containing plastic accounts for 15-80% of the mass of the mixed material; when the pH value of the heavy metal contaminated soil is less than or equal to 6.5, the mass of the chlorine-containing plastic accounts for 1-60% of the mass of the mixed material;
And (3) carrying out co-pyrolysis on the mixed material, wherein the temperature of the co-pyrolysis is 300-600 ℃.
Preferably, the chlorine-containing plastics have a chlorine content of > 50% by weight.
Preferably, when the pH value of the heavy metal contaminated soil is more than 6.5, the mass of the chlorine-containing plastic accounts for 20-60% of the mass of the mixed material.
Further preferably, when the pH value of the heavy metal contaminated soil is more than 6.5, the mass of the chlorine-containing plastic accounts for 25-40% of the mass of the mixed material.
Preferably, when the pH value of the heavy metal contaminated soil is less than or equal to 6.5, the mass of the chlorine-containing plastic accounts for 1-40% of the mass of the mixed material.
Further preferably, when the pH value of the heavy metal contaminated soil is less than or equal to 6.5, the mass of the chlorine-containing plastic accounts for 3-15% of the mass of the mixed material.
Preferably, when the pH value of the heavy metal contaminated soil is more than 6.5, the temperature of the co-pyrolysis is 400-500 ℃; when the pH value of the heavy metal contaminated soil is less than or equal to 6.5, the temperature of the co-pyrolysis is 300-500 ℃.
Preferably, the heavy metal contaminated soil is heavy metal contaminated soil.
Preferably, the time of the co-pyrolysis is 1 to 2 hours.
Preferably, after the mixture is subjected to co-pyrolysis, the method further comprises the step of placing the obtained solid pyrolysis product into an extraction solution for leaching, and obtaining heavy metal extraction solution through solid-liquid separation.
Compared with the prior art, the invention has the following advantages:
The invention utilizes HCl generated by combining chlorine free radicals and hydrogen free radicals in the thermal degradation process of chlorine-containing plastics to be skillfully combined with heavy metal leaching of polluted soil, promotes dissociation-leaching of the heavy metal combined with soil mineral lattices, and overcomes the defect that a large amount of acid-base reagents are consumed in the existing chemical leaching process, thereby realizing green leaching of heavy metal elements without adding chemical reagents.
And the chlorine-containing plastic can be selected from waste plastic, and the recycling treatment of plastic waste is facilitated.
In addition, the existing thermal separation technology needs to realize separation and recovery by gasifying metal elements in solid materials at a high temperature of about 1000 ℃, and has high energy consumption and large equipment investment. Compared with the thermal separation technology, the invention only needs to pyrolyze chlorine-containing plastics, and based on free radical reaction in the pyrolysis process, the invention can dissolve out the heavy metals in the soil mineral lattice bonding state to the maximum extent, and the temperature is only 600 ℃ at the maximum.
Compared with the technologies such as bioleaching, electrochemical leaching, supercritical extraction and the like, the method has the advantages of long reaction period, low extraction rate and complex process. The method can activate the heavy metals in the soil and promote the high-efficiency dissolution of the heavy metals in the soil by only one-step co-pyrolysis, and has the advantages of simple operation, short reaction period, higher extraction rate and the like.
The invention uses the calcium chloride (CaCl 2) solution to extract the soluble heavy metal elements in the polluted soil, and the higher the content of the extracted soluble heavy metal, the greater the leaching potential of the heavy metal from the soil crystal lattice, and the easier the heavy metal is extracted and recovered. Compared with the method of co-pyrolysis without adding chlorine-containing plastics and leaching by using CaCl 2 solution, the co-pyrolysis reaction in the embodiment of the invention increases the leaching rate of heavy metal elements such as cadmium, lead, copper, zinc and the like in soil by 6 to 440 times, 138 to 530 times, 26 to 483 times and 5 to 672 times respectively. The co-pyrolysis effect of the chlorine-containing plastic can obviously increase the extraction rate of the heavy metal elements in the soil, which indicates that the leaching recovery potential of the heavy metal in the soil is greatly improved.
Drawings
FIG. 1 is a graph showing the effect of chlorine-containing plastic addition on alkaline soil heavy metal leaching rate;
FIG. 2 is a scanning electron microscope image of chlorine-containing plastics with zero add-on, 8% add-on, 30% add-on co-pyrolysis product and non-pyrolyzed alkaline soil;
FIG. 3 is a graph showing the effect of chlorine-containing plastic addition on the leaching rate of heavy metals in acid soil.
Detailed Description
The invention provides a method for realizing efficient leaching of heavy metal elements in polluted soil based on chlorine-containing plastic co-pyrolysis, which comprises the following steps:
Mixing heavy metal contaminated soil with chlorine-containing plastic to obtain a mixed material; when the pH value of the heavy metal contaminated soil is more than 6.5, the mass of the chlorine-containing plastic accounts for 15-80% of the mass of the mixed material; when the pH value of the heavy metal contaminated soil is less than or equal to 6.5, the mass of the chlorine-containing plastic accounts for 1-60% of the mass of the mixed material;
And (3) carrying out co-pyrolysis on the mixed material, wherein the temperature of the co-pyrolysis is 300-600 ℃.
The invention mixes heavy metal contaminated soil with chlorine-containing plastic to obtain a mixed material.
The invention has no special requirements on the source of the heavy metal contaminated soil. In the present invention, the heavy metal contaminated soil is preferably heavy metal contaminated soil. The invention has higher application value by adopting the heavy metal contaminated soil, can realize the recycling of pollutants on one hand, and can reduce the harm of the heavy metal in the soil on the other hand. In the invention, the heavy metal contaminated soil contains at least one of Cd, pb, cu and Zn.
The invention has no special requirement on the source of the chlorine-containing plastic, and can be a commercial product or chlorine-containing plastic waste. The invention has no special requirements on the types of the chlorine-containing plastics, and the chlorine-containing plastics well known in the art can be exemplified by polyvinyl chloride (PVC) and Chlorinated Polyethylene (CPE). In the present invention, the chlorine content of the chlorine-containing plastic is preferably > 50 wt.%, and in the examples of the present invention, the chlorine content of the chlorine-containing plastic is specifically 62.7 wt.%.
Before mixing the heavy metal contaminated soil with the chlorine-containing plastic, the chlorine-containing plastic and the contaminated soil are preferably respectively crushed, ground and sieved to obtain the particles with the particle size smaller than 100 meshes.
The invention has no special requirements on the mixing process, and the method for uniformly mixing the heavy metal contaminated soil and the chlorine-containing plastic is well known in the art.
In the present invention, when the pH value of the heavy metal contaminated soil is > 6.5, the mass of the chlorine-containing plastic is 15 to 80% of the mass of the mixture, more preferably 20 to 60%, still more preferably 25 to 40%.
When the pH value of the heavy metal contaminated soil is less than or equal to 6.5, the mass of the chlorine-containing plastic accounts for 1-60% of the mass of the mixed material, more preferably 1-40%, still more preferably 3-15%, and most preferably 3-10%.
After the mixed material is obtained, the mixed material is subjected to co-pyrolysis, and a solid pyrolysis product is further obtained.
In the present invention, the temperature of the co-pyrolysis is 300 to 600 ℃, preferably 350 to 550 ℃. As a more preferred scheme, when the pH value of the heavy metal contaminated soil is more than 6.5, the temperature of the co-pyrolysis is more preferably 400 to 500 ℃; when the pH value of the heavy metal contaminated soil is less than or equal to 6.5, the temperature of the co-pyrolysis is further preferably 300-500 ℃, and most preferably 300-400 ℃.
In the invention, the pyrolysis time is preferably 1-2 h, and can be specifically 1h, 1.5h or 2h; the pyrolysis is preferably performed under oxygen-limited conditions, which are not particularly required by the present invention, and may be any oxygen-limited pyrolysis conditions well known in the art, for example: the co-pyrolysis is carried out under the condition of passing inert gas (such as nitrogen) or under the condition of sealing. In the embodiment of the invention, the mixed material is placed in a crucible, the crucible is wrapped and sealed by a plurality of layers of tinfoil paper, and then the sealed crucible is placed in a muffle furnace for oxygen-limited co-pyrolysis.
In the present invention, the rate of heating up to the temperature of the pyrolysis is preferably 5 ℃/min. In the co-pyrolysis process, chlorine-containing plastics are decomposed to generate chlorine radicals and hydrogen radicals, and the chlorine radicals and the hydrogen radicals are combined to form HCl, so that heavy metals in soil mineral lattices can be dissociated and converted into heavy metals in ion exchange states, and the leaching potential of the heavy metals in the soil is greatly improved.
After the solid pyrolysis product is obtained, the method preferably further comprises the step of placing the solid pyrolysis product into an extraction solution for leaching, and obtaining the heavy metal extraction solution through solid-liquid separation.
In the present invention, the extraction solution is obtained by dissolving an extractant in deionized water. The invention has no special requirements on the type of the extractant and the concentration thereof, and the concentration of main cations in soil pore water can be extracted and simulated by adopting the method which is well known in the field. Specifically, the extractant may be CaCl 2、NaNO3、NH4NO3 or DTPA. In the examples of the present invention, a 0.1M CaCl 2 solution was used as the extraction solution. In the present invention, the solid-to-liquid ratio of the solid pyrolysis product to the extraction solution is preferably 1:5 to 1:10 (m/v). In the present invention, the leaching process is preferably performed under normal temperature shaking conditions. In the present invention, the leaching time is preferably 1 to 2 hours; the conditions of the oscillation are not particularly limited in the present invention, and the conditions of the oscillation extraction well known in the art may be adopted, and in the embodiment of the present invention, the rotation speed of the oscillation is specifically 200rpm.
The solid-liquid separation mode is not particularly required in the invention, and can be any solid-liquid separation mode known in the art, such as filtration or centrifugation. The invention transfers the ion exchange heavy metal in the solid pyrolysis product to the extracting solution through leaching-solid-liquid separation. In the examples of the present invention, the rotational speed of the centrifugal separation was 3500rpm and the time was 10 minutes.
After the heavy metal extracting solution is obtained, the invention preferably further comprises the step of separating the heavy metal extracting solution by adopting a fractional crystallization method or a precipitation method to respectively obtain products such as cadmium, lead, copper, zinc and the like. The method has no special requirements on the crystallization and precipitation processes of the heavy metal extracting solution, and can adopt metal element crystallization and precipitation separation methods well known in the art.
The method for realizing efficient leaching of heavy metal elements in contaminated soil based on co-pyrolysis of chlorine-containing plastics provided by the invention is described in detail below with reference to examples, but they are not to be construed as limiting the scope of the invention.
Example 1
The heavy pollution soil collected in the electronic garbage dismantling site contains heavy metals of lead, cadmium, copper and zinc with concentration of 9459.4 mg/kg, concentration of 10.7 mg/kg, concentration of 2692.1 mg/kg and concentration of 5069.7mg/kg, and the pH value of the soil is 8.19 and is alkaline. If the repair treatment is implemented on the soil with severe pollution, the repair cost is difficult to cover the repair value. Therefore, the invention provides a method for recycling heavy metals in heavily polluted soil from the separation and extraction angles to realize pollutant disposal and resource utilization.
Air-drying, grinding and sieving the polluted soil to obtain soil powder with the particle size smaller than 100 meshes for standby; meanwhile, the abandoned chlorine-containing plastics (the chlorine content is 62.7 weight percent) are crushed and ground into plastic powder with the particle size smaller than 100 meshes for standby;
Weighing soil powder and chlorine-containing plastic powder, and uniformly mixing to obtain a mixed material; wherein the mass of the chlorine-containing plastic accounts for 15% of the total mass of the mixed materials;
Placing the mixed material into a crucible, wrapping and sealing the crucible by using multi-layer tinfoil paper, placing the sealed crucible into a muffle furnace for oxygen-limited pyrolysis, heating to 500 ℃ at a speed of 5 ℃/min, carrying out pyrolysis treatment for 1h at the temperature, cooling to room temperature, grinding and sieving the pyrolysis product to obtain an activated heavy metal pollution product;
Leaching heavy metal elements in the pyrolysis product by using 0.1M CaCl 2: 1.0g of pyrolysis product is weighed, 10mL of 0.1M CaCl 2 solution is added, the solid-liquid mixture is subjected to oscillation leaching for 2 hours at 200rpm and 25 ℃, then solid-liquid separation is carried out through centrifugation, the centrifugation rotating speed is 3500rpm, the centrifugation time is 10min, and the heavy metal extracting solution is obtained, and the concentration of heavy metal in the extracting solution is measured by using an inductively coupled plasma spectrometer. The 0.1M CaCl 2 solution mainly extracts soluble heavy metals in pyrolysis products, which reflect the leachable amount of the heavy metals. The higher the solubility of the heavy metal in the soil, the greater the leaching potential of the heavy metal from the soil crystal lattice, the higher the extraction rate, and the easier the heavy metal is recycled;
The leaching solution is a mixed solution containing heavy metals of lead, cadmium, copper and zinc, and precipitation of lead, cadmium, copper or zinc is respectively obtained by a fractional precipitation method which is well known to a person skilled in the art.
Examples 2 to 7
The difference from example 1 was only that the addition amounts of chlorine-containing plastics were varied, the mass fractions of chlorine-containing plastics in the mixture being 20% (example 2), 25% (example 3), 30% (example 4), 40% (example 5), 60% (example 6) and 80% (example 7), respectively.
Comparative example 1
The difference from example 1 is only that no chlorine-containing plastic (i.e., the addition amount of chlorine-containing plastic is 0%) is added and only contaminated soil is pyrolyzed.
Comparative examples 2 to 4
The difference from example 1 was only that the addition amount of chlorine-containing plastics was changed, and the mass ratio of chlorine-containing plastics in the mixed material was 3% (comparative example 2), 8% (comparative example 3) and 10% (comparative example 4), respectively.
The effect of the addition amount of chlorine-containing plastics on the leaching rate of heavy metals in alkaline soil was compared in examples 1 to 7 and comparative examples 1 to 4, and the results are shown in Table 1 and FIG. 1. The result shows that when the addition amount of the chlorine-containing plastic is more than or equal to 15%, the leaching rate of heavy metals such as cadmium, lead, copper and zinc is obviously improved compared with the leaching rate of the heavy metals in the original alkaline soil, and the method can activate the heavy metals in the alkaline soil and promote the leaching of the heavy metals in the alkaline soil by carrying out co-pyrolysis on the heavy metal contaminated soil and a certain amount of the chlorine-containing plastic. Particularly, when the addition amount of the chlorine-containing plastic is 25-40%, the leaching rate of heavy metals cadmium, lead, copper and zinc is the largest (when the addition amount of the chlorine-containing plastic is 30%, the leaching rate of the heavy metals is respectively 159, 499, 383 and 488 times higher than that of the original soil without adding the chlorine-containing plastic), which shows that the addition of 25-40% of the chlorine-containing plastic is subjected to co-pyrolysis, so that the leaching of various heavy metals in soil mineral lattices is greatly promoted.
TABLE 1 influence of chlorine-containing Plastic addition on alkaline soil heavy metal leaching Rate (%)
The chlorine-containing plastic zero addition, 8% addition, 30% addition of the co-pyrolysis product and the raw alkaline soil which is not pyrolyzed were observed by a scanning electron microscope. As shown in figure 2, the co-pyrolysis effect of the chlorine-containing plastic is obviously promoted to form a loose and porous structure on the surface of the soil mineral particles, and the more the porous structure formed on the surface of the chlorine-containing plastic is, the more the heavy metal is dissolved out of the soil mineral lattice structure with the increase of the addition amount of the chlorine-containing plastic.
Example 8
For the activation leaching of heavy metals in acid polluted soil, acid polluted soil collected in an electronic garbage dismantling site is selected as an example, wherein the pH value of the soil is 4.31, the soil is acidic, and the concentrations of heavy metals such as lead, cadmium, copper and zinc in the soil are 3262.7 mg/kg, 9.5 mg/kg, 2883.5 mg/kg and 3302.8mg/kg respectively;
Air-drying, grinding and sieving the polluted soil to obtain soil powder with the particle size smaller than 100 meshes for standby; meanwhile, the abandoned chlorine-containing plastics (the chlorine content is 62.7 weight percent) are crushed and ground into plastic powder with the particle size smaller than 100 meshes for standby;
weighing soil powder and chlorine-containing plastic powder, and uniformly mixing to obtain a mixed material; wherein the mass of the chlorine-containing plastic accounts for 1% of the total mass of the mixed materials;
Placing the mixed material into a crucible, wrapping and sealing the crucible by using multi-layer tinfoil paper, placing the sealed crucible into a muffle furnace for oxygen-limited pyrolysis, heating to 500 ℃ at a speed of 5 ℃/min, carrying out pyrolysis treatment for 1h at the temperature, cooling to room temperature, grinding and sieving the pyrolysis product to obtain an activated heavy metal pollution product;
Leaching heavy metal elements in the pyrolysis product by using 0.1M CaCl 2: 1.0g of pyrolysis product is weighed, 10mL of 0.1M CaCl 2 solution is added, the solid-liquid mixture is subjected to oscillation leaching for 2 hours at 200rpm and 25 ℃, then solid-liquid separation is carried out through centrifugation, the centrifugation rotating speed is 3500rpm, the centrifugation time is 10min, and the heavy metal extracting solution is obtained, and the concentration of heavy metal in the extracting solution is measured by using an inductively coupled plasma spectrometer.
The leaching solution is a mixed solution containing heavy metals of lead, cadmium, copper and zinc, and precipitation of lead, cadmium, copper or zinc is respectively obtained by a fractional precipitation method which is well known to a person skilled in the art.
Examples 9 to 15
The difference from example 8 was only that the addition amount of chlorine-containing plastics was changed, and the mass ratio of chlorine-containing plastics in the mixed material was 3% (example 9), 5% (example 10), 8% (example 11), 10% (example 12), 20% (example 13), 30% (example 14) and 40% (example 15), respectively, and the other treatments were the same as in example 8.
Comparative example 5
Referring to example 8, the acid contaminated soil heavy metals of example 8 were activated to leach out, except that no chlorine-containing plastic was added.
Comparative example 6
The difference from example 8 was only that the addition amount of chlorine-containing plastic was changed, the mass ratio of chlorine-containing plastic in the mixed material was 80%, and the other treatments were the same as in example 8.
The effect of the addition amount of chlorine-containing plastics on the leaching rate of heavy metals in acidic contaminated soil was compared in examples 8 to 15 and comparative examples 5 to 6, and the results are shown in Table 2 and FIG. 3. As can be seen from Table 2 and FIG. 3, when the addition amount of the chlorine-containing plastic is 1-60%, the leaching rate of heavy metals such as cadmium, lead, copper and zinc is obviously improved compared with the leaching rate of heavy metals in the original acid soil, which shows that the leaching of various heavy metals in mineral lattices of the acid-contaminated soil can be promoted by co-pyrolysis of the heavy metal-contaminated soil and a certain amount of the chlorine-containing plastic. Especially when the addition amount of the chlorine-containing plastic is 3-10%, the leaching rate of heavy metals cadmium, lead, copper and zinc is the largest (when the addition amount of the chlorine-containing plastic is 8%, the leaching rate of the chlorine-containing plastic is respectively increased by 6 times, 138 times, 30 times and 5 times compared with the leaching rate of the lead, the cadmium, the copper and the zinc in the original soil (without adding the chlorine-containing plastic), which shows that the leaching potential of heavy metals in the acid soil can be obviously improved by adding 3-10% of the chlorine-containing plastic for co-pyrolysis.
TABLE 2 influence of chlorine-containing Plastic addition on the leaching yield (%) of heavy metals in acid soil
Example 16
The difference from example 4 is that the co-pyrolysis temperature is changed from "500 ℃ to" 400 ℃, and the other treatments are the same as in example 4.
Example 17
The rest of the treatment was identical to example 4, except that the co-pyrolysis temperature of the mixture in example 4 was changed to 300 ℃.
Example 18
The rest of the treatment was identical to example 4, except that the co-pyrolysis temperature of the mixture in example 4 was changed to 600 ℃.
Comparative example 7
The alkaline soil of example 4 was subjected to heavy metal extraction directly using 0.1M CaCl 2 without pyrolysis treatment.
The treatment conditions and soil heavy metal leaching results of example 4, examples 16 to 18, and comparative examples 1 and 7 are shown in Table 3. The leaching result shows that compared with the treatment without adding chlorine-containing plastic (comparative example 1), the leaching rate of heavy metals such as lead, cadmium, copper and zinc in alkaline soil is improved by 161 times, 530 times, 483 times and 614 times respectively by adding 30% of chlorine-containing plastic and co-pyrolyzing the chlorine-containing plastic at 400 ℃ (example 16), and the leaching rate of heavy metals in alkaline soil is obviously increased; the 400 ℃ co-pyrolysis conditions (example 16) slightly increased leaching of various heavy metals from alkaline soil compared to the 500 ℃ co-pyrolysis conditions (example 4).
Example 19
The above-mentioned mixed material was subjected to pyrolysis-leaching-recovery with reference to example 11, except that the co-pyrolysis temperature was changed from "500 ℃ to" 400 ℃, and the other treatments were the same as in example 11.
Example 20
The rest of the treatment was identical to that of example 11, except that the co-pyrolysis temperature of the mixture in example 11 was changed to 300 ℃.
Example 21
The rest of the treatment was identical to example 11, except that the co-pyrolysis temperature of the mixture in example 11 was changed to 600 ℃.
Comparative example 8
The acid soil of example 11 was subjected to heavy metal extraction directly using 0.1M CaCl 2 without pyrolysis treatment.
The treatment conditions and soil heavy metal leaching results of example 11, examples 19 to 21, comparative example 5 and comparative example 8 are shown in Table 3. The leaching result shows that compared with the treatment without adding chlorine-containing plastic (comparative example 5), the leaching rate of heavy metals such as lead, cadmium, copper and zinc in the acid soil is respectively improved by 6 times, 235 times, 26 times and 7 times by adding 8% of chlorine-containing plastic for co-pyrolysis at 400 ℃ (example 19), and the leaching rate of heavy metals in the acid soil is obviously increased; the 400 ℃ co-pyrolysis conditions (example 19) increased leaching of various heavy metals in acidic soils to some extent compared to the 500 ℃ co-pyrolysis conditions (example 11).
Example 22
Referring to example 4, the heavy metal activated leaching was performed on contaminated soil collected from a lead-zinc mining area, except that the soil used in this example was different, and the soil selected in this example was from a tailings pond of the lead-zinc mining area, was alkaline (ph=8.54), and contained heavy metals of lead, cadmium, copper, and zinc at concentrations of 4483.6, 11.9, 4804.8, and 5404.5mg/kg, respectively; further, the addition amount of chlorine-containing plastic in this example was set to 30%, and the other treatments were the same as in example 4. The leaching results show that the leaching rates of the heavy metals of lead, cadmium, copper and zinc in the soil are respectively improved by 440 times, 222 times, 169 times and 672 times by adding 30 percent chlorine-containing plastic for co-pyrolysis compared with the non-pyrolysis treatment (comparative example 9), and the leaching rate of the heavy metals in the alkaline soil is obviously improved (the results are shown in Table 3).
Comparative example 9
The alkaline soil of example 22 was subjected to heavy metal extraction directly using 0.1M CaCl 2 without pyrolysis treatment.
Example 23
Referring to example 11, the heavy metals in the electroplating sludge were activated and leached, except that the soil used in this example was different, and the soil selected in this example was acidic (ph=6.04) from the electroplating sludge generated in the electroplating wastewater treatment process, and the concentrations of heavy metals copper and zinc were 15586 and 11725mg/kg, respectively; the amount of chlorine-containing plastic added in this example was 8%, and the other treatments were the same as in example 11. The leaching results show that the addition of 8% chlorine-containing plastics by co-pyrolysis improves the leaching rate of copper and zinc in the electroplating sludge by 43 and 56 times respectively, and significantly promotes leaching of heavy metals in the electroplating sludge (see Table 3 for results) compared with the non-pyrolysis treatment (comparative example 10).
Comparative example 10
The heavy metal extraction was performed directly on the acid sludge of example 23 using 0.1M CaCl 2 without pyrolysis treatment.
TABLE 3 leaching Rate of soil heavy metals (%)
As can be seen from table 3, compared with the pyrolysis treatment and the pyrolysis treatment of the original heavy metal contaminated soil without chlorine-containing plastics, the co-pyrolysis of the chlorine-containing plastics is added to obviously improve the leaching rate of various heavy metals; by comparing the influence of different pyrolysis temperatures on the extraction and leaching of the heavy metals in the soil, the optimal pyrolysis temperature of the alkaline soil is found to be 400-500 ℃, and the optimal pyrolysis temperature of the acid soil is found to be 300-400 ℃.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (10)
1. A method for realizing efficient leaching of heavy metal elements in polluted soil based on chlorine-containing plastic co-pyrolysis comprises the following steps:
Mixing heavy metal contaminated soil with chlorine-containing plastic to obtain a mixed material; when the pH value of the heavy metal contaminated soil is more than 6.5, the mass of the chlorine-containing plastic accounts for 15-80% of the mass of the mixed material; when the pH value of the heavy metal contaminated soil is less than or equal to 6.5, the mass of the chlorine-containing plastic accounts for 1-60% of the mass of the mixed material;
And (3) carrying out co-pyrolysis on the mixed material, wherein the temperature of the co-pyrolysis is 300-600 ℃.
2. The method according to claim 1, characterized in that the chlorine-containing plastic has a chlorine content of > 50 wt.%.
3. The method according to claim 1 or 2, wherein the mass of chlorine-containing plastic is 20-60% of the mass of the mixture when the pH of the heavy metal contaminated soil is > 6.5.
4. A method according to claim 3, wherein the mass of chlorine-containing plastic is 25-40% of the mass of the mixture when the pH of the heavy metal contaminated soil is > 6.5.
5. The method according to claim 1 or 2, wherein the mass of the chlorine-containing plastic is 1-40% of the mass of the mixture when the pH of the heavy metal contaminated soil is less than or equal to 6.5.
6. The method according to claim 5, wherein the chlorine-containing plastic accounts for 3-15% of the mass of the mixture when the pH value of the heavy metal contaminated soil is less than or equal to 6.5.
7. The method of claim 1, wherein the temperature of the co-pyrolysis is 400-500 ℃ when the pH of the heavy metal contaminated soil is > 6.5; when the pH value of the heavy metal contaminated soil is less than or equal to 6.5, the temperature of the co-pyrolysis is 300-500 ℃.
8. The method according to claim 1 or 7, wherein the co-pyrolysis is performed for a period of 1 to 2 hours.
9. The method of claim 1, wherein the heavy metal contaminated soil is heavy metal contaminated soil.
10. The method of claim 1, further comprising leaching the solid pyrolysis product in an extraction solution, and performing solid-liquid separation to obtain a heavy metal extract.
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