CN112453041A - Soil heavy metal eluting agent, eluting method of heavy metal contaminated soil and application - Google Patents
Soil heavy metal eluting agent, eluting method of heavy metal contaminated soil and application Download PDFInfo
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- CN112453041A CN112453041A CN202011209664.0A CN202011209664A CN112453041A CN 112453041 A CN112453041 A CN 112453041A CN 202011209664 A CN202011209664 A CN 202011209664A CN 112453041 A CN112453041 A CN 112453041A
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- soil
- heavy metal
- leaching
- ferric nitrate
- citric acid
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- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims abstract description 264
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical group [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 claims abstract description 186
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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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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K17/00—Soil-conditioning materials or soil-stabilising materials
- C09K17/40—Soil-conditioning materials or soil-stabilising materials containing mixtures of inorganic and organic compounds
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/3103—Atomic absorption analysis
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N21/3577—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light for analysing liquids, e.g. polluted water
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/16—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using titration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/24—Earth materials
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
- G01N2021/3595—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using FTIR
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Abstract
The invention belongs to the technical field of heavy metal contaminated soil remediation, and discloses a soil heavy metal eluting agent, an eluting method of heavy metal contaminated soil and application thereof, wherein the soil heavy metal eluting agent is ferric nitrate and citric acid; collecting a heavy metal contaminated soil sample, air-drying, and sieving; removing Cu, Zn, Pb and Cd in the polluted soil by adopting ferric nitrate and citric acid; detecting the influence of leaching concentration, solid-liquid ratio and leaching time on leaching effect, and determining leaching mechanism of ferric nitrate and citric acid by using Fourier transform infrared spectroscopy; and analyzing the soil, and detecting the influence of ferric nitrate or citric acid on the soil fertility and the potential ecological risk of the heavy metal after the soil is leached. The invention can provide insight for the potential of using ferric nitrate as an effective soil heavy metal eluting agent, and the key for reducing the harm of heavy metal to the environment and human health is to select a proper eluting agent to repair the heavy metal contaminated soil.
Description
Technical Field
The invention belongs to the technical field of heavy metal contaminated soil remediation, and particularly relates to a soil heavy metal eluting agent, an eluting method of heavy metal contaminated soil and application.
Background
At present, heavy metal contaminated soil is one of the major environmental problems worldwide, mainly due to the development of mining industry, irrigation of wastewater and unreasonable use of chemical fertilizers and pesticides. Organic compounds biodegrade over time, and unlike organics, heavy metals are not biodegradable, which poses a threat to the environment and human health. Among the numerous heavy metals, Cu, Zn, Pb and Cd are attracting much attention. Zinc and copper are essential trace elements for biological metabolism. However, excessive amounts of copper and zinc can have toxic effects on the body. For example, copper can cause vomiting, diarrhea, stomach cramps, nausea and even death. The high toxicity of lead and cadmium can cause renal insufficiency, cancer, hypertension and other diseases. Therefore, an environment-friendly, low-cost and more efficient method for repairing heavy metal contaminated soil is urgently needed.
The remediation technology of the heavy metal contaminated soil comprises chemical, physical and biological technologies. Among these methods, soil washing is considered as one of the most time-saving, economical and durable techniques for removing heavy metals from soil. Heavy metals in soil are typically leached with chelating agents, inorganic leachants or surfactants. Some of these eluents still have some drawbacks, which have been demonstrated by previous studies. Studies have shown that 1, 2, 3 and 6M HCl extracts 35%, 57%, 79% and 83% Pb from contaminated soil, respectively, but that the final soil pH after washing drops below 1, which is detrimental to soil fertility, plant productivity, vegetation restoration and microstructure. EDTA is difficult to degrade in soil and may cause secondary pollution of groundwater. Surfactants such as rhamnolipids remove heavy metals, and most surfactants are relatively expensive and difficult to apply on a large scale. Among inorganic eluents, iron nitrate has the following advantages and is widely spotlighted in soil remediation. (1) Good leaching effect, proper acidity, small secondary pollution, low price and the like. (2) In the Ca-, Mg-, Na-, K-, Fe-salts, the pKa value of trivalent iron (Fe (III)) is low. Fe (iii) can also form iron (oxygen) -rich hydroxides. (3) Fe (III)) can generate hydrogen ions in the precipitation process, and the generated hydrogen ions can reduce the pH value of the solution and improve the metal extraction rate. (4) Nitrogen is an essential nutrient for rice growth. In addition, it is reported that organic acids can replace strong acids and chelating agents. Organic acids, especially citric acid, are more beneficial to plant growth than HCl, EDTA and NTA. In addition, as a low-molecular organic acid, citric acid is easy to degrade in the environment, has little harm to soil and is low in price.
The content of quick-acting nitrogen, phosphorus and potassium in soil is an important fertility index of soil, and the deficiency of the content is one of the main factors for limiting the yield of crops. Notably, after soil leaching, heavy metals may be converted from stable to unstable components, which have strong fluidity, toxicity and bioavailability. Duan considers soil enzyme activity to be one of the most direct reactions to micro-ecological conditions. The change of the biochemical characteristics of the soil is a good index of the soil quality. Therefore, the removal rate of heavy metals, the potential ecological risks of heavy metals and the physicochemical properties of the soil after being washed are important indexes for selecting the soil washing agent.
However, comparative studies on removal of heavy metals from soil by ferric nitrate and other chemicals have not been reported. Therefore, the method is worthy of comparative study by preliminarily discussing the leaching mechanism of the ferric nitrate and the citric acid, and the properties of the leached soil and the potential ecological risks of the heavy metals.
Through the above analysis, the problems and defects of the prior art are as follows: comparative studies on removal of heavy metals from soil by ferric nitrate and other chemicals have not been reported.
The difficulty in solving the above problems and defects is: many eluents are used in the treatment of heavy metal contaminated soil, but not all of the washed soil can be reused. In general, there are problems in that (1) the eluting agent is hardly degraded in soil, resulting in secondary pollution of soil and contamination of groundwater. (2) Easily resulting in soil disintegration, as well as substantial mineral dissolution and nutrient loss. (3) Is expensive and not suitable for large-area use.
The significance of solving the problems and the defects is as follows: an efficient, low-cost and environment-friendly soil eluting agent is searched.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a soil heavy metal eluting agent, an eluting method of heavy metal contaminated soil and application thereof.
The invention is realized by the following steps that the soil heavy metal eluting agent is ferric nitrate and citric acid.
The invention also aims to provide the application of the soil heavy metal eluting agent in removing Cu, Zn, Pb and Cd in soil.
The invention also aims to provide a method for leaching heavy metal contaminated soil, which comprises the following steps:
step one, collecting a heavy metal contaminated soil sample from a surface layer of 0-20cm, air-drying, and passing through a 2mm screen.
And step two, removing Cu, Zn, Pb and Cd in the polluted soil by using ferric nitrate and citric acid.
And step three, detecting the influence of the leaching concentration, the liquid-solid ratio and the leaching time on the leaching effect, and determining the leaching mechanism of the ferric nitrate and the citric acid by utilizing Fourier transform infrared spectroscopy.
And step four, analyzing the soil, and detecting the influence of ferric nitrate or citric acid on the soil fertility and the potential ecological risk of the heavy metal after the soil is leached.
Further, in the third step, the method for detecting the influence of the leaching concentration, the liquid-solid ratio and the leaching time on the leaching effect is carried out in a 100 ml conical flask in a constant-temperature shaking instrument.
Further, the oscillation condition is: at 25 ℃ at room temperature, 150 rpm, and then centrifuged at 4000rpm for 20 min. After centrifugation, the supernatant was discharged.
Further, in the third step, in the method for detecting the influence of the leaching concentration, the liquid-solid ratio and the leaching time on the leaching effect, the leaching experiment is performed according to the following parameters:
(1) in concentration experiments, the concentrations of the citric acid and the ferric nitrate are respectively 0, 0.01, 0.03, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7 and 1 mol/L.
(2) In the liquid-solid ratio experiment, the liquid-solid ratio was set to 3, 5, 7, 9, 11, 13, 15, 17, 20, 25, 30 v/w.
(3) In the time experiment, the treatment time was set to 5, 30, 90, 150, 180, 240, 300, 360, 720, 1440 minutes.
Further, in the third step, the method for detecting the influence of the leaching concentration, the liquid-solid ratio and the leaching time on the leaching effect further comprises:
(1) the soil was washed with distilled water at a solid-to-liquid ratio of 1:10 (w/v). The washing process was repeated twice, and then the washed soil was air-dried at room temperature.
(2) All experiments were performed in parallel in triplicate with two blank controls. And finally, measuring the concentrations of Cu, Zn, Pb and Cd in the soil before and after leaching by using a flame atomic absorption spectrophotometer.
Further, in step three, the infrared spectrum analysis is that the supernatant fluid leached by soil under the optimal condition and the eluent solution with the optimal concentration are dried in a freeze dryer, and Fourier transform infrared spectrum FTIR of the sample is obtained by using perkinelmer 580B.
Further, in step four, the method for analyzing soil comprises:
(1) with HF-HNO3-HClO4After digestion, the total metal content was determined using a flame atomic absorption spectrophotometer. Strips with pH meter at soil/water ratio of 1:2.5And measuring the pH value of the soil under the condition.
(2) Measuring the content of organic matters by adopting a potassium dichromate-sulfuric acid heating method, and measuring the content of quick-acting nitrogen in soil by adopting an alkaline hydrolysis diffusion method; the content of the available phosphorus is determined by adopting a molybdenum-antimony colorimetric method, and the content of the available potassium is determined by adopting a flame atomic absorption spectrophotometry method.
(3) Soil enzyme activities such as soil urease, invertase, catalase and acid phosphatase were determined by standard methods.
(4) Determining the activity of the invertase by using a 3, 5-dinitrosalicylic acid colorimetric method; by adopting KMnO4Measuring the activity of catalase in soil by a titration method; measuring the activity of the acid phosphatase by a colorimetric method; urease activity was measured by ammonium colorimetry.
Further, in the fourth step, the distribution of Cu, Zn, Pb and Cd in the original soil and the treated soil is analyzed by adopting an improved BCR method, and the method is divided into the following steps: exchanged and acid soluble state F1, reducible state F2, oxidizable state F3 and residual state F4.
Further, in step four, the potential ecological risk index
Directly used for evaluating the toxicity and the mobility of the heavy metal. Potential ecological risk index
The following formula can be used for calculation:
wherein the content of the first and second substances,
given the toxic response coefficient of a given metal (Cu-5, Zn-1, Pb-5, Cd-30),
(mg/kg) is the average concentration of heavy metals in the soil,
heavy metals calculated by A sigma + BConcentration correction index, a is the percentage of F1 component calculated according to the BCR program, B is 1-a, σ is the toxicity index of a given metal F1 moiety,
(mg/kg) is the limit for metals in the soil, copper 30.7mg/kg, zinc 83.6mg/kg, lead 26.7mg/kg, cadmium 0.172 mg/kg; the σ value varies with increasing metal content in the F1 component; when the content is 1 percent<When F1 is less than or equal to 10%, the value of sigma is 1.0; when the F1 is more than or equal to 11 percent and less than or equal to 30 percent, the value of sigma is 1.2; when the F1 is more than or equal to 31 percent and less than or equal to 50 percent, the value of sigma is 1.4; when F1>At 50%, σ has a value of 1.6;
The invention also aims to provide a leaching device for implementing the method for leaching the heavy metal contaminated soil by using the ferric nitrate and the citric acid.
By combining all the technical schemes, the invention has the advantages and positive effects that: the method for leaching the heavy metal polluted soil by using the ferric nitrate and the citric acid provided by the invention adopts the ferric nitrate and the citric acid to remove Cu, Zn, Pb and Cd in the polluted soil. The influence of the leaching concentration, the liquid-solid ratio and the leaching time on the leaching effect is examined. In addition, the influence of ferric nitrate and citric acid on the soil fertility and the potential ecological risk of the heavy metal after the soil is washed are researched. In the ferric nitrate repair, the optimal removal rates of Cu, Zn, Pb and Cd were 78.68%, 58.96%, 48.53% and 80.86%, respectively. In the citric acid restoration, the optimal removal rates of Cu, Zn, Pb and Cd are 66.59%, 43.10%, 37.95% and 77.48%, respectively. The leaching of ferric nitrate or citric acid can significantly reduce the potential ecological risk of heavy metals in the soil, while ferric nitrate shows better effect than citric acid in reducing the risk of heavy metals. The physicochemical properties of the soil are improved to a certain extent, including invertase activity, acid phosphatase activity, quick-acting phosphorus and quick-acting nitrogen. The results show that the leaching performance of the ferric nitrate is better than that of the citric acid. Research shows that the ferric nitrate can be used as a proper eluent for the heavy metal contaminated soil.
Meanwhile, the invention also discusses the optimal leaching conditions of the citric acid and the ferric nitrate; the influence of leaching on the potential ecological risk of the soil is analyzed through chemical morphology; the influence of the two eluents on the physical and chemical properties of the eluents is compared; the elution mechanism of ferric nitrate and citric acid is researched by utilizing Fourier transform infrared spectroscopy. The research result of the invention can provide insight for the potential of using ferric nitrate as an effective soil heavy metal eluting agent, and the key for reducing the harm of heavy metal to the environment and human health is to select a proper eluting agent to repair the heavy metal contaminated soil.
Technical effect or experimental effect of comparison. Currently, organic acids (citric acid and oxalic acid), chelating agents (EDTA), inorganic acids (hydrochloric acid), surfactants (sodium lauryl sulfate and Triton X-100), and partially inorganic salts (calcium chloride) have been widely used as eluents. However, the soil shows stronger acidity after washing with inorganic acid. EDTA and other chelating agents have low biodegradability and are easy to cause secondary soil pollution. Artificial biodegradable chelating agents are relatively environmentally friendly, but are relatively expensive. Thus, ferric nitrate and citric acid are better eluents than other eluents. In the research, compared with citric acid, ferric nitrate has a better effect of removing Cu, Zn, Pb and Cd in soil. The optimal removal rates of Cu, Zn, Pb and Cd in the ferric nitrate restoration are 78.68%, 58.96%, 48.53% and 80.86% respectively; the optimal removal rates of Cu, Zn, Pb and Cd by citric acid were 66.59%, 43.10%, 37.95% and 77.48%, respectively. The potential ecological risks of the ferric nitrate and the citric acid to the heavy metals in the soil are both obviously reduced, and the potential ecological risk reducing effect of the ferric nitrate to the heavy metals in the soil is better than that of the citric acid. The citric acid and the ferric nitrate improve the invertase activity, the acid phosphatase activity, the quick-acting phosphorus and the quick-acting nitrogen of the soil to a certain degree. The leaching result shows that the leaching effect of the ferric nitrate is better than that of the citric acid. The ferric nitrate can be used as a better heavy metal contaminated soil eluting agent.
(1) The washing effect of citric acid and ferric nitrate on complex heavy metals Cu, Zn, Pb and Cd is researched. There is currently no similar study by reading the large body of literature. (2) Comprehensively compares the washing effect of ferric nitrate and citric acid on soil. Besides the total amount of heavy metals, the fertilizer also comprises heavy metal forms, organic matters, quick-acting nitrogen, phosphorus, potassium and enzyme activity, thereby providing a basis for secondary utilization of soil. The mechanism of action was analyzed by fourier transform infrared spectroscopy (FTIR). The result shows that the agent contains hydroxyl which can be used as a heavy metal contaminated soil remediation eluent. (3) In conventional studies, the concentration, time, and solid-to-liquid ratio range is small, or the gradient is large, which may cause variation in the optimum conditions. In the research, the concentration range is 0.01-1mol/L, the solid-liquid ratio is 3-30, the gradient is small, and the optimal condition can be obtained more accurately.
Drawings
FIG. 1 is a schematic diagram illustrating the effect of the eluent concentration on the Cu, Zn, Pb, and Cd removal rate according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating the influence of the solid-liquid ratio of the eluent on the Cu, Zn, Pb and Cd removal rate according to the embodiment of the present invention.
FIG. 3 is a schematic diagram illustrating the effect of the time of the eluent on the Cu, Zn, Pb, and Cd removal rates provided by embodiments of the present invention.
Fig. 4 is a schematic diagram illustrating the effect of different leachates on soil available potassium, available nitrogen, available phosphorus and organic matter.
FIG. 5 shows 4 soil enzyme activities in raw and treated soils as provided by the examples of the present invention: schematic representation of catalase, acid phosphatase, urease activity and invertase activity.
FIG. 6 is a schematic infrared spectrum of a solution of citric acid and ferric nitrate provided in an example of the present invention before and after soil washing.
Fig. 7 is a flow chart of a method for washing heavy metal contaminated soil by using ferric nitrate and citric acid, which is provided by the embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Aiming at the problems in the prior art, the invention provides a soil heavy metal eluting agent, an eluting method of heavy metal contaminated soil and application thereof, and the invention is described in detail with reference to the accompanying drawings.
The invention provides a soil heavy metal eluting agent which is composed of ferric nitrate and citric acid. The application of the soil heavy metal eluting agent in removing Cu, Zn, Pb and Cd in soil.
The present invention will be further described with reference to the following examples.
The key point for reducing the harm of heavy metal to the environment and human health is to select a proper eluent to repair the soil polluted by the heavy metal. In the invention, ferric nitrate and citric acid are adopted to remove Cu, Zn, Pb and Cd in the polluted soil. The influence of the leaching concentration, the liquid-solid ratio and the leaching time on the leaching effect is examined. In addition, the influence of ferric nitrate or citric acid on the soil fertility and the potential ecological risk of the heavy metal after the soil is washed are researched. In the ferric nitrate repair, the optimal removal rates of Cu, Zn, Pb and Cd were 78.68%, 58.96%, 48.53% and 80.86%, respectively. In the citric acid restoration, the optimal removal rates of Cu, Zn, Pb and Cd are 66.59%, 43.10%, 37.95% and 77.48%, respectively. The leaching of ferric nitrate or citric acid can significantly reduce the potential ecological risk of heavy metals in the soil, while ferric nitrate shows better effect than citric acid in reducing the risk of heavy metals. The physicochemical properties of the soil are improved to a certain extent, including invertase activity, acid phosphatase activity, quick-acting phosphorus and quick-acting nitrogen. The results show that the leaching performance of the ferric nitrate is better than that of the citric acid. Research shows that the ferric nitrate can be used as a proper eluent for the heavy metal contaminated soil.
Therefore, the invention discusses the optimal leaching conditions of the citric acid and the ferric nitrate; the influence of leaching on the potential ecological risk of the heavy metal in the soil is analyzed through the chemical form of the heavy metal; the influence of the two eluents on the physical and chemical properties of the eluents is compared; the elution mechanism of ferric nitrate and citric acid is researched by utilizing Fourier transform infrared spectroscopy. The research result of the invention can provide insight for the potential of utilizing ferric nitrate as an effective soil heavy metal eluting agent.
1. Materials and methods
1.1 soil Properties
Collecting heavy metal contaminated soil samples from waste farmlands around a mining area in northern lake province. Samples were collected from the surface layer (0-20cm), air dried, and then passed through a 2mm screen. The test soil was laterite. The physicochemical properties of the soil sample are shown in Table 1.
TABLE 1 physicochemical Properties of the soil
1.2 soil Leaching test
The influence of the eluting agent concentration, the eluting time and the liquid-solid ratio on the removal of the heavy metal is researched by the system. All elution experiments were performed in 100 ml Erlenmeyer flasks in a constant temperature shaker. The shaking conditions were: at room temperature (25 ℃ C.), 150 rpm. Then centrifuged at 4000rpm for 20 min. After centrifugation, the supernatant was discharged. The leaching experiment was carried out with the following parameters:
in concentration experiments, the concentrations of the citric acid and the ferric nitrate are respectively 0, 0.01, 0.03, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7 and 1 mol/L.
In the liquid-solid ratio experiment, the liquid-solid ratio was set to 3, 5, 7, 9, 11, 13, 15, 17, 20, 25, 30 v/w.
In the time experiment, the treatment time was set to 5, 30, 90, 150, 180, 240, 300, 360, 720, 1440 minutes.
The soil was then rinsed with distilled water at a soil to liquid ratio of 1:10 (w/v). The washing process was repeated twice and the washed soil was then air dried at room temperature for subsequent analysis. All experiments were performed in parallel in triplicate with two blank controls. And finally, measuring the concentrations of Cu, Zn, Pb and Cd in the soil before and after leaching by using a flame atomic absorption spectrophotometer.
1.3 heavy Metal forms
The distribution of Cu, Zn, Pb and Cd in the original soil and the treated soil was analyzed by the improved BCR method. The method comprises the following steps: exchanged and acid soluble states (F1), reducible state (F2), oxidizable state (F3) and residual state (F4).
1.4 soil analysis
With HF-HNO3-HClO4After digestion, the total metal content was determined using a flame atomic absorption spectrophotometer. The soil pH was measured with a pH meter at a soil/water ratio of 1: 2.5. And (3) measuring the organic matter content by adopting a potassium dichromate-sulfuric acid heating method. And (3) determining the content of the quick-acting nitrogen in the soil by an alkaline hydrolysis diffusion method. And (4) measuring the content of the quick-acting phosphorus by adopting a molybdenum-antimony colorimetric resistance method. The content of the quick-acting potassium is measured by adopting a flame atomic absorption spectrophotometry. Soil enzyme activities, including soil urease, invertase, catalase and acid phosphatase activities were determined according to the standard methods of the present invention. The activity of the invertase was determined by 3, 5-dinitrosalicylic acid colorimetry. By adopting KMnO4The catalase activity in the soil was determined by titration. The acid phosphatase activity was determined by colorimetry. Urease activity was measured by ammonium colorimetry.
1.5 Infrared Spectroscopy
The supernatant from the soil washing under optimal conditions and the eluent solution at optimal concentration were dried in a lyophilizer and fourier transform infrared spectroscopy (FTIR) of the samples was obtained using perkinelmer 580B.
2. Results
2.1 Leaching of the soil
2.1.1 Effect of citric acid and ferric nitrate concentration
Leaching tests show that ferric nitrate and citric acid have a certain removing effect on Cu, Zn, Pb and Cd in soil. In the control treatment without addition of citric acid or ferric nitrate solution, the removal rate of Cu, Zn, Pb, and Cd was low. In the control experiment of the citric acid, the removal rates of Cu, Zn, Pb and Cd are respectively 1.07%, 0.82%, 0.65% and 1.14%. In the ferric nitrate control experiment, the removal rates of Cu, Zn, Pb, and Cd were 0.85%, 0.61%, 0.47%, and 0.87%, respectively. As shown in FIG. 1, when the concentration of ferric nitrate or citric acid is increased from 0.01mol/L to 1mol/L, the leaching efficiency of Cu, Zn, Pb and Cd is correspondingly improved. When the concentration of the citric acid or ferric nitrate solution is less than 0.3mol/L, the removal rate of Cu, Zn, Pb and Cd is rapidly increased. For citric acid, the higher the concentration of the eluent, the more heavy metal ions can be bound, which directly promotes the heavy metal ions and the chelation reaction. On the other hand, during the experiment, as the concentration of citric acid increases, the amount of hydrogen ions increases, and the hydrogen ions can release heavy metal ions from the soil. In the ferric nitrate, Fe (III) replaces heavy metal ions adsorbed on soil adsorption sites, so that the dissolution of soil organic matters is promoted, and the metal ions combined with the organic matters are released.
The contents of Cu, Zn, Pb and Cd in the soil were 350, 212.5, 173.9 and 21mg/kg, respectively. Wherein, the concentrations of Cu, Zn, Pb and Cd are respectively 7 times, 1.06 times, 2.48 times and 70 times of soil pollution risk control standards (trial) of soil environmental quality agricultural land. Under the optimal leaching conditions, the removal rates of Cu, Zn, Pb and Cd by citric acid are 66.59%, 43.10%, 37.95% and 77.48%, respectively, and the removal rates of Cu, Zn, Pb and Cd by ferric nitrate are 78.68%, 58.96%, 48.53% and 80.86%, respectively. After being washed by citric acid or ferric nitrate, the concentration of copper in the soil is in the standard range of an orchard in management and control standard (trial) for soil pollution risk in soil environment quality agricultural land (150mg/kg), and the content of zinc in the soil is also in the standard range of management and control standard (trial) for soil pollution risk in soil environment quality agricultural land (200 mg/kg). The high leaching efficiency of copper may be high copper content in the soil and instability of the composition. However, the removal rate of zinc is not high, probably because Zn and Cd have similar chemical properties, Zn can compete with Cd for adsorption sites, and the concentration of Zn in soil in the research is 212.5mg/kg, which is far higher than 21mg/kg of Cd. Therefore, the adsorption capacity of the soil surface to Zn is stronger than that to Cd, so that the removal rate of Zn by ferric nitrate or citric acid is much lower. Although the lead content is reduced after washing, the lead content does not meet the soil pollution risk control standards (trial) of soil environment quality agricultural land. This may be due to the stable morphology of lead in the soil, resulting in a lower lead removal rate from the soil. Cadmium is removed in the highest rate compared to lead, copper and zinc because cadmium has an active chemical property and is the weakest to be adsorbed to soil. However, cadmium remains in a high risk state after leaching. Therefore, the temperature of the molten metal is controlled,the soil can be leached for a plurality of times, so that the content of lead and cadmium in the soil reaches the management and control standard (trial) of soil pollution risk of soil in agricultural land for soil environmental quality. The results show that ferric nitrate has a higher leaching effect than citric acid. The results may be due to the following reasons: after the soil is respectively washed by citric acid and ferric nitrate, the pH value of the soil is reduced from 5.2 to 3.11 and 2.7, wherein the citric acid mainly releases H through-COOH+Iron nitrate releases H by hydrolysis+. H released by ferric nitrate according to the pH value of the leached soil+More. On the other hand, citric acid is a carboxylic acid containing three carboxyl groups, and is less effective in removing heavy metals in combination with other cations.
2.1.2 Effect of liquid-to-solid ratio
The influence of the liquid-solid ratio on the removal rate of the heavy metal is analyzed. The result shows that the removal rates of Cu, Zn, Pb and Cd are improved along with the increase of the liquid-solid ratio until the stable state is reached. As shown in fig. 2, the optimum liquid-to-solid ratios of ferric nitrate and citric acid were 7 and 25, respectively. The removal rate of Cu, Zn, Pb and Cd is improved with the increase of the liquid-solid ratio, but in consideration of the relationship between the treatment efficiency and the treatment cost, a higher liquid-solid ratio can generate more wastewater, and in consideration of the water and energy consumption, the availability of mechanical equipment and the convenience of wastewater treatment, the liquid-solid ratio of citric acid is set to be 25, and the liquid-solid ratio of ferric nitrate is set to be 7, so that the field operation has cost benefit.
2.1.3 Effect of time
According to the optimal concentration and the liquid-solid ratio, the influence of the leaching time on the removal rate is analyzed, as shown in fig. 3, the removal rate of the heavy metal of the citric acid is remarkably improved between 0 and 720 minutes, and the increase speed is reduced as the time is prolonged to 1440 minutes. The rate of ferric nitrate removal slowed down after 240 minutes of rinsing. When the leaching time was increased from 240 minutes to 1440 minutes, the removal rates of Cu, Zn, Pb, and Cd increased only 8.9%, 7%, 3.58%, and 6.04%, respectively. The reason for this may be that the weak bound heavy metals in the soil are rapidly desorbed in the first stage, and the strong bound heavy metals are slowly released in the soil in the second stage. Therefore, in view of the practical application of this technique, the present invention suggests that the citric acid treatment time be 720 minutes and the ferric nitrate treatment time be 240 minutes.
2.2 distribution of heavy metals in soil and environmental risks
Table 2 lists the concentrations, distributions and potential ecological risks of Cu, Zn, Pb and Cd in the original soil and the treated soil
Potential ecological risk index
Directly used for evaluating the toxicity and the mobility of the heavy metal. Potential ecological risk index
The following formula can be used for calculation:
in the formula (I), the compound is shown in the specification,
given the toxic response coefficient of a given metal (Cu-5, Zn-1, Pb-5, Cd-30),
(mg/kg) is the average concentration of heavy metals in the soil, Ω is the heavy metal concentration correction index calculated by a σ + B (a is the percentage of F1 component calculated according to BCR program, B is 1-a, σ is the toxicity index of the given metal F1 fraction),
(mg/kg) is the limit for metals in soil in Hubei province (copper 30.7mg/kg, zinc 83.6mg/kg, lead 26.7mg/kg, cadmium 0.172 mg/kg). The σ value varied with increasing metal content in the F1 component. When the content is 1 percent<When F1 is less than or equal to 10%, the value of sigma is 1.0; when the F1 is more than or equal to 11 percent and less than or equal to 30 percent, the value of sigma is 1.2; when the F1 is more than or equal to 31 percent and less than or equal to 50 percent, the value of sigma is 1.4; when F1>At 50%, σ has a value of 1.6.
Indicating a low risk for a single metal, 40-80 indicating a moderate risk for that metal, 80-160 indicating a substantial risk, 160-320 indicating a high risk, and greater than 320 indicating a very high risk.
In the original soil, Cu and Cd mainly exist in the forms of F1 and F2. The stability of F1 and F2 is not as stable as that of residue, and the stability is sensitive to the change of environmental conditions, which indicates that the removal rate of Cu and Cd in soil is high. The reason why the removal rate of lead and zinc is low is that most of lead and zinc exist in a residue state.
In the original soil, Cd has a high risk to the environment, Cu has a moderate risk to the environment, and lead and zinc have a low risk to the environment. After being washed by ferric nitrate or citric acid, the potential environmental risks of Cu, Zn, Pb and Cd are all reduced, the potential ecological risk of Cu is reduced from medium to low, the potential ecological risk of Cd is obviously reduced, but Cd still has higher environmental risk, which is probably caused by lower allowable concentration (0.172mg/kg) of Cd and higher soil toxicity. The soil should be washed for many times, so that the cadmium content in the soil meets the relevant regulations of Hubei province. The potential ecological risks of Cu, Zn, Pb and Cd in the original soil after washing with citric acid or ferric nitrate are shown in Table 2.
TABLE 2 potential ecological risks of Cu, Zn, Pb and Cd in raw soil and in soil washed with citric acid or ferric nitrate
2.3 Effect of soil washing on soil physicochemical Properties
2.3.1 Effect of soil washing on physicochemical Properties of soil
In the soil leaching process, the leaching agent has certain influence on the physical and chemical properties of the soil. Fig. 4 shows the changes of the soil quick-acting potassium, quick-acting nitrogen, quick-acting phosphorus and organic matter before and after leaching. The organic content does not vary much. After being washed by ferric nitrate, the content of the quick-acting potassium in the soil is reduced from 107.69mg/kg to 51.51 mg/kg. After the citric acid is washed, the content of the quick-acting potassium in the soil is reduced from 107.69mg/kg to 84.39 mg/kg. This is due to K during the rinsing process+Desorption from the soil colloid results in a decrease in the concentration of rapid-acting potassium in the soil. In contrast, the content of available nitrogen and available phosphorus in the soil increases. This is probably due to the fact that the pH of the soil after washing is lowered (after washing with ferric nitrate and citric acid, the pH is lowered to 2.7 and 3.11, respectively) converting the unavailable nitrogen and phosphorus in the soil into fast-acting nitrogen and phosphorus. Another reason for the increase in fast-acting nitrogen after leaching with ferric nitrate is the increase in nitrate nitrogen content in the soil. In order to ensure the growth and development of crops, the fertilizer must be applied after rinsing.
2.3.2 Effect of soil Leaching on soil Biochemical Properties
Enzyme activity is an important biochemical indicator. The enzyme activity affects various reactions such as decomposition of organic residues and nutrient circulation in the soil-plant system. The activities of catalase, urease, invertase and acid phosphatase before and after the soil washing were investigated, and as shown in fig. 5, the results showed that the activities of acid phosphatase and invertase were increased after the washing with ferric nitrate or citric acid. After rinsing with ferric nitrate or citric acid, urease and catalase activities were slightly decreased. The increase in acid phosphatase activity was due to a decrease in pH and an increase in available phosphorus after washing. The reason for the increased activity of invertase may be that some cadmium stress can promote the activity of specific enzyme in soil, because the enzyme is a relatively stable protein, and the metal ion with potential toxicity can be used as an auxiliary group to form a coordination bond between the center of the enzyme and the substrate, thereby maintaining a certain specific structure between the active center of the enzyme and the enzyme molecule, thereby changing the balance between the surface charge of the enzyme protein and the enzyme reaction, and finally achieving the purpose of the enzymatic reaction. The washing treatment had no significant effect on urease activity, a result which may be related to the presence of lead in the soil. The catalase activity decreased due to the decrease in pH, which was in a reverse trend to the acid phosphatase activity.
3. Mechanism of heavy metal removal
Iron nitrate is an inorganic salt, and citric acid is a typical low molecular organic acid. Therefore, the leaching mechanism of ferric nitrate and citric acid to soil is different. The elution mechanism of citric acid isTwo aspects are to be included. (1) During the rinsing process, reactive functional groups in the citric acid may bind to heavy metal ions. Alikhani and Manceron reported that carboxyl groups may complex with metal ions. (2) Hydroxyl groups can also interact with metal ions by ion exchange. In the case of ferric nitrate, ferric nitrate is a strong acid, weak base salt that releases a large amount of hydrogen ions in solution. Furthermore, most heavy metal ions are in a cationic state in solution under low pH conditions. H+Ions can compete with heavy metal ions for adsorption sites to influence the exchange adsorption of the heavy metal ions, so that the desorption of the heavy metal ions in the soil is promoted. The infrared spectrum of citric acid in combination with heavy metal ions is shown in FIG. 6. The following features can be observed in the spectra: (a) at 3380cm-1A strong, broad band is observed, typically due to O-H stretching; (b) about 3280cm-1And 3160cm-1The two bands at (a) are due to aliphatic C-H group stretch; (C) about 2680cm-1And 2560cm-1The absorption band at (a) is due to C ═ O stretching in the phenolic hydroxyl group; (d) centered at 1730cm-1And 1530cm-1The band at (a) is mainly due to C ═ O stretching of the carboxyl group. The infrared spectrum of the ferric nitrate is also shown in fig. 6. The ferric nitrate is 3600cm-1A broad peak appears, which may be due to the O-H stretching vibration band of the dried sample absorbing water in the air. One strip is about 1400cm long-1Is generally considered to be
After leaching, the peak values of the groups are changed to a certain extent, which indicates that the heavy metal is combined with the active groups or chemically reacts in the leaching process.
4. The invention analyzes the removal effect of ferric nitrate and citric acid on Cu, Zn, Pb and Cd in soil. The influence of the factors such as the concentration of the leacheate, the liquid-solid ratio, the leaching time and the like on the leaching effect is examined, and the optimal process parameters are determined. After being washed by ferric nitrate or citric acid, the potential ecological risk index of the heavy metal is obviously reduced due to the removal of unstable components. In general, compared with citric acid, ferric nitrate has better capacity of removing heavy metals from soil and shows better performance in reducing the potential ecological risks of heavy metals. In terms of soil properties, ferric nitrate has a greater advantage in improving invertase activity, acid phosphatase activity, quick-acting nitrogen and quick-acting phosphorus than citric acid. The results show that ferric nitrate is an effective soil heavy metal remover.
As shown in fig. 7, the method for washing the heavy metal contaminated soil by using the ferric nitrate and the citric acid provided by the embodiment of the present invention includes the following steps:
s101, collecting a heavy metal contaminated soil sample from the surface layer of 0-20cm, air-drying, and passing through a 2mm screen.
S102, removing Cu, Zn, Pb and Cd in the polluted soil by using ferric nitrate and citric acid.
S103, detecting the influence of the leaching concentration, the liquid-solid ratio and the leaching time on the leaching effect, and determining the leaching mechanism of the ferric nitrate and the citric acid by utilizing Fourier transform infrared spectroscopy.
And S104, analyzing the soil, and detecting the influence of the ferric nitrate and the citric acid on the soil fertility and the potential ecological risk of the heavy metal after the soil is leached.
The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. The soil heavy metal eluting agent is characterized by comprising ferric nitrate and citric acid.
2. An application of a soil heavy metal eluting agent in removing Cu, Zn, Pb and Cd in soil.
3. The method for leaching the heavy metal contaminated soil is characterized by comprising the following steps:
collecting a heavy metal contaminated soil sample from the surface layer of 0-20cm, air-drying, and sieving;
removing Cu, Zn, Pb and Cd in the polluted soil by adopting ferric nitrate and citric acid;
detecting the influence of leaching concentration, solid-to-liquid ratio and leaching time on leaching, and determining the leaching mechanism of ferric nitrate and citric acid by utilizing Fourier transform infrared spectroscopy;
and analyzing the soil, detecting the influence of ferric nitrate or citric acid on the soil fertility, and analyzing the toxicity and the mobility of the heavy metal after the soil is washed.
4. The method for washing the heavy metal contaminated soil according to claim 3, wherein the method for detecting the influence of washing concentration, liquid-solid ratio and washing time on the washing effect is carried out in a 100 ml conical flask in a constant-temperature shaking instrument;
the oscillation conditions are as follows: at the room temperature of 25 ℃, 150 rpm, and then centrifuging for 20min at 4000 rpm; after centrifugation, the supernatant was discharged.
5. The method for washing heavy metal contaminated soil according to claim 1, wherein in the method for detecting the influence of washing concentration, liquid-solid ratio and washing time on washing effect, washing experiment is carried out according to the following parameters:
(1) in concentration experiments, the concentrations of the citric acid and the ferric nitrate are respectively 0, 0.01, 0.03, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.7 and 1 mol/L;
(2) in the liquid-solid ratio experiment, the liquid-solid ratio is set to be 3, 5, 7, 9, 11, 13, 15, 17, 20, 25 and 30 v/w;
(3) in the time experiment, the treatment time was set to 5, 30, 90, 150, 180, 240, 300, 360, 720, 1440 minutes.
6. The method for washing heavy metal contaminated soil according to claim 1, wherein the method for detecting the influence of washing concentration, liquid-solid ratio and washing time on washing effect further comprises:
(1) the soil was rinsed with distilled water at a soil to liquid ratio of 1:10 (w/v). The leaching process is repeated twice, and then the leached soil is air-dried at room temperature;
(2) all experiments were performed in parallel in triplicate with two blank controls; and finally, measuring the concentrations of Cu, Zn, Pb and Cd in the soil before and after leaching by using a flame atomic absorption spectrophotometer.
7. The method for washing heavy metal contaminated soil according to claim 1, wherein said infrared spectroscopic analysis is performed by drying the supernatant washed from the soil under optimal conditions and the eluent solution of optimal concentration in a freeze dryer, and fourier transform infrared spectroscopy FTIR of the sample is obtained by using perkinelmer 580B.
8. The method for washing heavy metal contaminated soil according to claim 1, wherein said method for analyzing soil comprises:
(1) with HF-HNO3-HClO4After digestion, the total metal content was determined using a flame atomic absorption spectrophotometer. Measuring the pH value of the soil by using a pH meter under the condition that the soil/water ratio is 1: 2.5;
(2) measuring the content of organic matters by adopting a potassium dichromate-sulfuric acid heating method, and measuring the content of quick-acting nitrogen in soil by adopting an alkaline hydrolysis diffusion method; measuring the content of the available phosphorus by adopting a molybdenum-antimony colorimetric method and measuring the content of the available potassium by adopting a flame atomic absorption spectrophotometry;
(3) urease, invertase, catalase and acid phosphatase activities were determined by standard methods;
(4) determining the activity of the invertase by using a 3, 5-dinitrosalicylic acid colorimetric method; by adopting KMnO4Measuring the activity of catalase in soil by a titration method; measuring the activity of the acid phosphatase by a colorimetric method; urease activity was measured by ammonium colorimetry.
The chemical forms of Cu, Zn, Pb and Cd in original soil and treated soil are analyzed by adopting an improved BCR method, and the method is divided into the following steps: exchanged and acid soluble state F1, reducible state F2, oxidizable state F3 and residual state F4.
9. Drenching of heavy metal contaminated soil according to claim 1Washing method, characterized in that said potential ecological risk index
Directly evaluating the toxicity and the mobility of the heavy metal; potential ecological risk index
Calculated using the following formula:
wherein the content of the first and second substances,
given the toxic response coefficient of a given metal (Cu-5, Zn-1, Pb-5, Cd-30),
the average concentration of heavy metals in the soil;
omega heavy metal concentration correction index calculated by a sigma + B, a being the percentage of component F1 calculated according to the BCR program, B being 1-a, sigma being the toxicity index of a given metal F1 moiety,
is the limit value of metals in soil, copper is 30.7mg/kg, zinc is 83.6mg/kg, lead is 26.7mg/kg, and cadmium is 0.172 mg/kg; the σ value varies with increasing metal content in the F1 component; when the ratio of 1% < F1 is less than or equal to 10%, the value of sigma is 1.0; when the F1 is more than or equal to 11 percent and less than or equal to 30 percent, the value of sigma is 1.2; when the F1 is more than or equal to 31 percent and less than or equal to 50 percent, the value of sigma is 1.4; when F1 > 50%, the value of σ is 1.6;
10. A leaching device for implementing the leaching method of the heavy metal contaminated soil according to any one of claims 3 to 9.
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