CN107115840B

CN107115840B - Carbon-based composite material for repairing arsenic-cadmium contaminated soil and application thereof

Info

Publication number: CN107115840B
Application number: CN201710243623.5A
Authority: CN
Inventors: 吴萍萍; 李录久; 李敏
Original assignee: Institute of Soil and Fertilizer of Anhui Academy of Agricultural Sciences
Current assignee: Institute of Soil and Fertilizer of Anhui Academy of Agricultural Sciences
Priority date: 2017-04-14
Filing date: 2017-04-14
Publication date: 2020-03-27
Anticipated expiration: 2037-04-14
Also published as: CN107115840A

Abstract

The invention discloses a carbon-based composite material for repairing arsenic-cadmium polluted soil and application thereof. The carbon-based composite material is prepared by taking crop straws as raw materials, carbonizing the crop straws to prepare biochar, mixing the biochar with a ferric salt solution according to a certain solid-to-liquid ratio, adjusting the pH value of the solution in the process to ensure that the biochar and the ferric salt solution are coprecipitated, and pyrolyzing the coprecipitated solution to form the carbon-based composite material. The carbon-based composite material prepared by the invention is applied to arsenic-cadmium composite polluted soil, can obviously reduce the content of effective arsenic and cadmium by combining methods of ploughing, watering and the like, enables the arsenic and cadmium in the soil to be converted to a direction with lower biotoxicity and mobility, can improve the physical and chemical properties of the soil to a certain extent, and is suitable for being applied to various types of soil. Can effectively remove arsenic and cadmium ions in water, and has the advantages of simple operation steps, wide material sources, low production cost and environmental protection in the preparation process.

Description

Carbon-based composite material for repairing arsenic-cadmium contaminated soil and application thereof

Technical Field

The invention relates to the field of heavy metal contaminated soil remediation, in particular to a carbon-based composite material for remediation of arsenic and cadmium contaminated soil and application thereof.

Background

As is listed As a priority pollutant by WHO due to its high carcinogenicity and genotoxicity to humans. In south and southeast Asia, contamination of groundwater with As by geochemistry has resulted in chronic poisoning of As by millions of people, becoming the most serious environmental disaster event in human history. As pollution is caused by chemical fertilizer and pesticide application, pesticide production, coal combustion, long-term mining and metallurgy activities and the like. The long-term chronic arsenic poisoning of human body can cause serious diseases such as liver cancer, skin cancer and the like, and is accompanied with teratogenesis and mutagenesis. Cd is also one of the most toxic heavy metals to humans. Cd entering a human body forms Cd sulfur protein in the human body, reaches the whole body through blood, selectively accumulates in kidney and liver to cause kidney damage, and seriously hinders the growth and metabolism of bones to cause osteodynia and even bone cancer.

The soil pollution problem is usually mainly caused by a certain pollutant, and other pollutants, namely a composite pollution problem, exist at the same time. The reported cultivated land area polluted by Cd, As, Cr, Pb and other heavy metals in China is nearly 2500 kilohm²About 1/5% of the total cultivated area. About half of farmlands in south China are polluted by toxic heavy metals such As Cd and As, and most farmlands in Yangtze river delta areas are polluted by more than two kinds of heavy metals, so that the soil heavy metal combined pollution becomes an important environmental problem and poses serious threats to human health and national food safety. At present, the treatment approach of the heavy metal pollution of the soil is mainly to passivate the pollutants by changing the existing form of the heavy metal in the soil, thereby reducing the mobility and bioavailability of the heavy metal in the soil. The common treatment means comprises physical remediation, chemical remediation, biological remediation, agricultural measure remediation and the like, wherein the chemical remediation is realized by applying a proper conditioner to the soil according to the properties of the soil and the heavy metals, and has the advantages of low cost, easiness in implementation, small disturbance to the soil, wide source range of the conditioner and the like. The biochar is a porous, highly aromatic and insoluble solid substance formed by carrying out low-temperature (< 700 ℃) thermal cracking and carbonization on agricultural wastes and the like under the condition of limited oxygen or no oxygen, is a potential application in the environmental field and the agricultural field, and is widely researched and applied to adsorption of various inorganic pollutants and organic pollutants in water and soil. The biochar has good adsorption effect on heavy metal cations such as Cd, Pb and Cu, and the adsorption capacity is superior to that of other most agricultural and forestry wastes and activated carbon. However, there is little or no adsorption of anionic As. The iron compound has strong selective coordination effect on As, but the particles of the iron compound are extremely fine (nanometer-scale particle size), are easy to lose in practical application and are difficult to be directly applied to industrialization. Therefore, the carbon-based composite material taking the biochar as the main body and loaded with the iron compound is prepared, and can adsorb water andheavy metal pollutants such As As and Cd in the soil reduce the biological effectiveness, can improve the physical and chemical properties of the soil, and has great application potential for repairing As and Cd combined polluted soil.

Disclosure of Invention

The invention provides a carbon-based composite material for repairing arsenic-cadmium polluted soil and application thereof, and has the advantages of capability of simultaneously repairing As and Cd polluted soil, improvement of physical and chemical properties of soil, simple operation steps, wide sources of prepared materials and the like. The invention mainly solves the technical problems that: the activity of anions As and cations Cd in the heavy metal combined polluted soil can be effectively reduced, the content of nutrients such As soil organic matters and quick-acting potassium is improved, and the problems of soil acidification or substantial reduction of the content of total nitrogen and alkaline hydrolysis nitrogen are avoided.

The technical scheme adopted by the invention is as follows:

the carbon-based composite material for repairing arsenic-cadmium contaminated soil is characterized by being prepared by the following method, and comprising the following specific operation steps:

(1) the preparation method of the biochar comprises the steps of cutting crop straws into small sections of about 3-5cm, cleaning, naturally drying in the air, putting the small sections into a carbonization furnace for pyrolysis, keeping the temperature rise rate at 4-6 ℃/min to enable the final pyrolysis temperature to be 500 ℃ plus 300 ℃, taking out the small sections after pyrolysis for 1-2 h, and naturally cooling to room temperature to obtain the biochar raw material;

(2) preparing iron salt solution and weighing a certain mass of Fe (NO)₃)₃Adding deionized water into the reagent to completely dissolve the reagent to prepare an iron salt solution with the molar concentration of 0.4 mol/L;

(3) coprecipitation, the prepared straw biochar is sieved by a sieve with the thickness of 0.4-0.6mm, and the weight ratio of the obtained straw biochar to the straw biochar is 1: (9-11) adding the solid-liquid ratio into the prepared ferric salt solution, uniformly stirring, then dropwise adding 5mol/L NaOH solution, controlling the dropwise adding rate to be 1-2 drops per second, gradually forming red precipitate in the process, continuously stirring to fully contact the generated iron compound with the biochar until the final pH value is stabilized at 7.00 +/-0.02, and standing at room temperature for 23-25 h;

(4) and (3) carrying out suction filtration on the solution after the reaction to remove supernatant, placing the solution in an open container, drying the solution in an oven at 75-85 ℃, cooling the solution to remove salting-out substances on the surface layer, washing the solution for 1-2 times by using deionized water to remove unsupported iron compounds, drying the solution at 75-85 ℃, and grinding the solution by using a 0.4-0.6mm sieve to obtain a solid substance, namely the carbon-based composite material containing the biochar and the ferrihydrite.

The heating rate of the carbonization furnace in the step (1) is 5 ℃/min.

The pyrolysis final temperature in the step (1) is 500 ℃.

The solid-liquid ratio in the step (3) is 1: 10.

The screen size of the biochar in the step (4) is 0.5 mm.

The application of the carbon-based composite material for repairing the arsenic-cadmium polluted soil to the arsenic-cadmium composite polluted soil is characterized by comprising the following specific operations:

(1) the remediation of the arsenic-cadmium composite polluted soil avoids the rainy and windy weather, and is carried out according to the soil pollution degree and the physicochemical property of 22.5-67.5 t/hm²Uniformly spreading the carbon-based composite material on the surface of the composite contaminated soil, immediately turning over the soil with the surface of 0-10cm to uniformly mix the carbon-based composite material with the surface soil, determining whether to spray water according to the soil moisture condition after turning over the soil, ensuring that the water content of the soil is 65-75% of the maximum field water capacity, but not irrigating the field, completing the passivation of As and Cd after balancing for 30 days, and applying a chemical fertilizer or planting crops to the field after the restoration is completed As much As possible;

(2) weighing the carbon-based composite material for removing arsenic and cadmium in the water body, putting the carbon-based composite material in a triangular flask, adding wastewater solution with the concentration of 1-50mg/L containing As (III), As (V) or Cd (II) according to the solid-to-liquid ratio of 2.5g/L, controlling the pH value of the solution to be 5.0-7.0, and oscillating for 4-24 h at room temperature to remove arsenic and cadmium in the solution.

The invention has the advantages that:

(1) the carbon-based composite material prepared by the method has stable performance and high iron loading strength, no iron ion dissolution is found at the pH of 3-9, and only a very small amount of iron (C) is present at the pH of 10-12<0.02%) dissolved. Loading iron as amorphous ferrihydrite (Fe)₁₀O₁₅·9H₂O) is mainly used, has high adsorption efficiency on As and Cd in water body, and canSimultaneously reduces the activity of two heavy metals with different chemical properties, namely As and Cd in the soil, and has wide application range. Meanwhile, the fertilizer can also adsorb heavy metal ions such as Cu, Zn and the like, and is suitable for heavy metal composite polluted soil;

(2) compared with other iron-based materials, the carbon-based composite material prepared by the invention has neutral final pH value, has little influence on the pH value of soil, does not cause the problems of soil acidification, reduction of oxidation-reduction potential and the like, and is suitable for being applied in soil, while the carbon-based composite material applied in the past is mostly used for removing heavy metals in water; meanwhile, the carbon-based composite material takes the straw biochar as a main body, contains abundant C, K and other elements, can improve the content of soil organic matters and quick-acting potassium, and adopts ferric nitrate in the preparation of the iron salt solution in the preparation step, so that the content of N element in the obtained carbon-based composite material is improved, and the defect that part of the biochar material reduces the content of soil total nitrogen or alkaline hydrolysis nitrogen can be overcome; in addition, physical properties of soil such as porosity, water retention, aggregate composition and the like are improved to different degrees;

(3) when the carbon-based composite material is actually applied, measures such as plowing and sprinkling are combined, so that the composite material and soil particles are fully and uniformly mixed, and compared with the modes such as direct field soaking or large water flood irrigation after spreading, the method can not cause the repairing material to float on the soil surface or migrate to a water body along with wind and water, and is more favorable for the safety of ecological environment;

(4) in the existing preparation process of the iron-carbon composite material, the preparation is mostly realized by adding reducing agents such as sodium borohydride and the like or reacting in a high-pressure reaction kettle, and the preparation process is relatively complicated. The preparation method of the carbon-based composite material is simple and feasible, has simple and convenient operation steps, and only needs three key steps of carbonization, coprecipitation and pyrolysis; meanwhile, the needed crop straws, reagents and instruments are easy to obtain, the sources are wide, the cost is low, the requirements on production equipment and materials are not high, and the popularization and the application are facilitated;

(5) the carbon-based composite material prepared by the invention is an environment-friendly material, mainly comprises straw biochar and amorphous ferrihydrite, wherein the straw biochar is a resource utilization product of agricultural wastes, and the amorphous ferrihydrite is an intermediate transition state of stable iron oxide and commonly exists in soil, so that secondary pollution cannot be caused after the carbon-based composite material is applied to the soil.

Drawings

FIG. 1 is a Scanning Electron Microscope (SEM) of a carbon-based composite material in example 1 of the present invention;

FIG. 2 is an X-ray diffraction pattern (XRD) of the carbon-based composite material of example 1 of the present invention;

FIG. 3 is an EDS (elemental distribution System) diagram showing the main elements of the carbon-based composite material according to example 1 of the present invention.

Detailed Description

The present invention is further illustrated by the following examples.

Example 1

Preparation of the carbon-based composite material of the invention

(1) Cutting wheat straws into small sections of about 4cm, cleaning, naturally drying in the air, putting into a vacuum tube furnace for pyrolysis, keeping the temperature at 400 ℃ for 1.5h, taking out, naturally cooling to room temperature, and sieving the prepared straw biochar by a 0.5mm sieve;

(2) 16.16g of analytically pure Fe (NO) are weighed out accurately₃)₃·9H₂Adding 100mL of deionized water into the O reagent in a glass beaker for complete dissolution, and uniformly stirring to obtain 0.4mol/L of iron salt solution;

(3) weighing 10g of sieved biochar, adding the biochar into a prepared ferric salt solution, placing the solution on a magnetic stirrer to be continuously stirred, enabling the pH value of the solution to be about 1.7-1.9, then dropwise adding 5mol/L NaOH solution to enable the final pH value to be stable at 7.00 +/-0.02, and standing the solution at room temperature for 24 hours;

(4) and (3) carrying out suction filtration on the reaction solution by using a vacuum suction flask, drying the reaction solution in an oven at 80 ℃ after removing supernatant, removing salting-out substances on the surface layer after cooling, and cleaning the reaction solution for 2 times by using deionized water until the pH value is not obviously changed. Drying at 80 ℃, and grinding through a 0.5mm sieve to obtain the carbon-based composite material;

(5) observing the surface morphology of the carbon-based composite material by using a scanning electron microscope, and finding that the iron compound uniformly covers the surface of the biochar (figure 1); the mineral composition is analyzed and found by an X-ray powder diffractometer (figure 2), Fe in the prepared carbon-based composite material mainly exists in an amorphous form and belongs to an unstable state, a large number of tetrahedral structural units exist on the surface, the crystallinity is poor, the specific surface area is large, and the prepared carbon-based composite material can provide more active adsorption sites as an adsorption main body; the main element composition is measured by an energy spectrometer (figure 3), and the contents of C and Fe in the carbon-based composite material are high and reach 33.2 percent and 16.88 percent respectively.

Example 2

Adsorption performance of carbon-based composite material to As and Cd in water body

0.10g of the carbon-based composite material prepared above is weighed in a 50mL centrifuge tube, 40mL of As (III) or Cd simulated wastewater solution with the initial concentration of 1, 5 and 10mg/L respectively is added, and 0.01mol/L of NaNO is added₃The solution is used as supporting electrolyte, and the pH of the solution is 0.01mol/L NaOH or HNO₃Adjusting the solution to 5.8 +/-0.2, oscillating for 24h at room temperature, centrifugally filtering, and measuring the concentration of arsenic and cadmium in the supernatant. The result shows that the carbon-based composite material prepared by the invention has good removal effect on As and Cd in water, the removal efficiency is respectively 92.1-98.4% and 96.0-97.1%, the maximum adsorption capacity can reach more than 95% within 4h, and the adsorption reaction is rapid. The saturated adsorption capacity of the carbon-based composite material to As and Cd in a water body is high and is respectively 15.22 mg/g and 15.19mg/g through model fitting.

Example 3

Remediation of arsenic and cadmium polluted soil by carbon-based composite material

Collecting the As and Cd combined pollution soil near the mining area, wherein the Cd content of the soil is 31.3 times of the national soil environment quality second-level standard (GB 15618-. Setting the adding amount of the carbon-based composite material to be 1 percent (w/w), which is about 22.5t/hm which is equivalent to the field application amount². The soil and the carbon-based composite material are fully and uniformly mixed and then are filled in a plastic pot, the plastic pot is sealed by a plastic film, and a plurality of small holes are punched to ensure that air inside and outside the pot freely circulates. Periodically adding deionized water to keep the water content at 70% of the maximum field water capacity of the soil, and culturing at room temperature for 30 d.

The results (table 1) show that after the carbon-based composite material is applied to the composite contaminated soil, the contents of the available As and the available Cd in the soil are respectively reduced by 17.0% and 16.7%, and the contents of the stable As and the stable Cd are respectively improved by 31.5% and 85.7%. The carbon-based composite material prepared by the method can effectively reduce the content of effective As and Cd in soil, and improve the content of stable As and Cd, so that the content is converted to a direction with low biological toxicity and mobility.

TABLE 1 influence of carbon-based composites on As, Cd contents in the soil in the active and steady state

Table 2 shows that, after the carbon-based composite material is applied, the pH value of the soil is slightly increased, the difference is 0.14 unit, the contents of organic matter, available phosphorus and available potassium are respectively increased by 12.5%, 7.5% and 19.8%, and the content of alkaline hydrolysis nitrogen is slightly decreased, with the amplitude of 1.5%. The carbon-based composite material prepared by the invention can improve the content of soil nutrients to different degrees while passivating heavy metals, and has small influence on the pH value and the content of alkaline nitrogen.

TABLE 2 influence of carbon-based composites on the main physicochemical properties of the contaminated soil

Claims

1. The carbon-based composite material for repairing arsenic-cadmium contaminated soil is characterized by being prepared by the following method, and comprising the following specific operation steps:

(2) weighing a certain mass of Fe (NO3)3 reagent in the ferric salt solution preparation, adding deionized water for complete dissolution, and preparing the ferric salt solution with the molar concentration of 0.4 mol/L;

2. The carbon-based composite material for repairing arsenic-cadmium polluted soil as claimed in claim 1, wherein: the heating rate of the carbonization furnace in the step (1) is 5 ℃/min.

3. The carbon-based composite material for repairing arsenic-cadmium polluted soil as claimed in claim 1, wherein: the pyrolysis final temperature in the step (1) is 500 ℃.

4. The carbon-based composite material for repairing arsenic-cadmium polluted soil as claimed in claim 1, wherein: the solid-liquid ratio in the step (3) is 1: 10.

5. The carbon-based composite material for repairing arsenic-cadmium polluted soil as claimed in claim 1, wherein: the screen size of the biochar in the step (4) is 0.5 mm.

6. The application of the carbon-based composite material for repairing arsenic-cadmium polluted soil as claimed in claim 1 on arsenic-cadmium composite polluted soil is characterized by comprising the following specific operations:

(1) the remediation of the arsenic-cadmium composite contaminated soil avoids the weather of heavy weather of plum rain, according to the soil pollution degree and the physicochemical property, the carbon-based composite material is uniformly scattered on the surface of the composite contaminated soil according to the application amount of 22.5-67.5 t/hm2, then the soil with the surface of 0-10cm is immediately ploughed, so that the carbon-based composite material and the surface soil are uniformly mixed, whether water is sprayed or not is determined according to the field soil moisture condition after the soil is ploughed, the water content of the soil is 65-75% of the maximum field water capacity, but the soil cannot be watered to soak the field, the passivation of As and Cd can be completed after 30 days of balance, and the application of chemical fertilizers or planting crops is carried out after the remediation is completed As much As;