CN114918240A - A biochar-based heavy metal soil remediation method - Google Patents

Abstract

The invention belongs to the technical field of soil remediation, and particularly relates to a heavy metal soil remediation method based on biochar, which is used for solving the problem of heavy metal pollution of soil. According to the invention, the contaminated soil range is determined by establishing the soil heavy metal distribution three-dimensional model, and the contamination range, the contaminated heavy metal composition and the contamination severity can be accurately evaluated. Polluted soil is excavated through the soil heavy metal distribution three-dimensional model, the polluted soil and normal soil can be accurately divided, and the pertinence of soil remediation is improved; then, heavy metals are fixed or adsorbed by the passivator, or the heavy metals form insoluble salts, so that the plant absorption of the heavy metals in the polluted soil is reduced, and the effect of soil remediation is achieved.

Description

A biochar-based heavy metal soil remediation method

technical field

The invention relates to a farmland restoration method, in particular to a biochar-based heavy metal soil restoration method.

Background technique

Heavy metals are more prominent among soil inorganic pollutants, mainly because heavy metals cannot be decomposed by soil microorganisms and are easy to accumulate. They are converted into more toxic methyl compounds, and some even accumulate in the human body at harmful concentrations through the food chain, causing serious harm. Human health.

Soil heavy metal pollutants mainly include mercury, cadmium, lead, copper, chromium, arsenic, nickel, iron, manganese, zinc, etc. Although arsenic is not a heavy metal, its behavior, source and harm are similar to heavy metals, so it is usually listed in Heavy metals are discussed. As far as the needs of plants are concerned, metal elements can be divided into two categories: 1. Elements that are not needed for plant growth and development, but are more harmful to human health, such as cadmium, mercury, and lead. ② Elements required for the normal growth and development of plants, and have certain physiological functions for the human body, such as copper, zinc, etc., but too much will cause pollution and hinder the growth and development of plants.

Due to the different forms of the same metals in the soil, their migration and transformation characteristics and pollution properties are also different. Therefore, when studying the harm of heavy metals in soil, not only their total content, but also the content of various forms must be paid attention to.

There are two main ways of heavy metal elements in soil: natural sources and human interference. Among natural factors, soil-forming parent material and soil-forming process have great influence on soil heavy metal content. Among various human factors, soil heavy metal pollution caused by sources such as industry, agriculture and transportation accounts for a relatively high proportion.

1. Natural Sources

Soil is weathered from rocks, and different rocks contain various heavy metal elements. The chemical elements of the parent rock determine the initial chemical content in the soil and affect the environmental background value of heavy metal elements in the soil: at the same time, the parent rock is forming the soil. The influencing factors in the process also affect the content of heavy metals in the soil. For example, quartz rocks with strong wind resistance control the content of heavy metals in the soil developed on them, while carbonate rocks with weak wind resistance can control the content of heavy metals in the soil. The control effect of heavy metal content in the developed soil is not strong. Heavy metal dustfall in the atmosphere is also one of the main natural factors affecting the content of heavy metals in soil. Processes such as volcanic eruptions, forest fires, splashing ocean waves, vegetation discharge, and wind-blown dust have caused a lot of heavy metal dust to float in the air. Part of heavy metal elements in the air are absorbed by plants, and part of them enters water and soil through dustfall. In nature, soil pollution also affects the content of heavy metals in soil. In the deep lithosphere, complex geochemical processes such as magmatism and metamorphism may form industrial deposits rich in heavy metals. Soils developed on dispersed halos and soils developed with transported mineralized material as parent rocks tend to have abnormally high concentrations of heavy metals.

2. Soil heavy metal pollution caused by human factors

With the development of industrial and agricultural modernization and urbanization of human society, soil heavy metal pollution caused by human factors is an environmental problem that cannot be ignored in today's world. Heavy metals are mostly non-ferrous metals, which are widely used in various aspects of human production and life, but also accompanied by serious environmental pollution of heavy metals. The development and smelting of non-ferrous heavy metal deposits is the most important source of pollution to discharge heavy metals into the environment. Industrial and mining enterprises that discharge heavy metals into the environment through the "three wastes", such as mining, mineral processing, metallurgy, electroplating, electrical engineering, dyes, textiles, oil refining, etc.

Since most of these pollution sources are point pollution sources, they are uneven pollution to the soil environment, and soil heavy metal pollution may be quite serious in some areas. With the development of urbanization and the increase of various wastes discharged from industry and traffic in the city, the content of heavy metals in urban soil has increased significantly, among which mercury and lead are the most prominent. With the increase of heavy metal pollutants released into the atmosphere by human activities, soil pollution by heavy metal deposition has become more and more serious, especially the combustion of fossil fuels. For example, the mercury released by combustion accounts for 57% to 71% of the anthropogenic release. %; the input of nickel into the atmosphere from coal combustion and fuel oil accounts for 60% to 78% of the anthropogenic release; due to the addition of antiknock agents - tetramethyl lead and tetraethyl lead to the gasoline used in automobiles, the amount of nickel emitted in automobile exhaust The lead content is 20～50ug/L. In agriculture, the application of pesticides, fertilizers, sludge, and sewage irrigation are also one of the main ways to aggravate soil heavy metal pollution. In chemical fertilizers, the impurities of the raw material ore and the pollution of the production process make the content of heavy metals quite high. For example, some superphosphate fertilizers have high cadmium and arsenic content. According to the measurement results of phosphate fertilizer and lime in Guangzhou, The cadmium content is 2~3mg/kg, the arsenic content is 60~80ng/kg, and the mercury content is 1~2ng/kg. Among the pesticides, there are more mercury, arsenic and lead, such as: organic mercury-containing preparations include Sai Lisan, Xi Lisheng, etc., organic arsenic-containing preparations include rice foot green, Sunong 6401, arsenic and lead-containing arsenic acid clamp , lead arsenite, etc., and pesticides containing other heavy metals include lead and lead. Therefore, the long-term application of chemical fertilizers and pesticides can cause the soil to suffer from heavy metal pollution.

In the soil, it is generally not easy to be leached with water and cannot be decomposed by soil microorganisms; on the contrary, organisms can enrich heavy metals, often causing heavy metals to gradually accumulate in the soil environment, and even some heavy metals can be transformed into more toxic elements in the soil. Methyl compounds, and some accumulate in the human body in harmful concentrations through the food chain, seriously endangering human health. Compared with the pollution of the water environment, the pollution of heavy metals to the soil environment is more difficult to control, and the pollution is more harmful.

SUMMARY OF THE INVENTION

In view of the problems existing in the background technology, the present invention provides a biochar-based heavy metal soil remediation method, which aims to fix or adsorb heavy metals through passivating agents, or make heavy metals form insoluble salts to reduce plant absorption of heavy metals in polluted soil. .

The present invention solves the above-mentioned technical problems and provides the following technical solutions:

A biochar-based heavy metal soil remediation method, comprising the following steps:

Step 1: Perform soil sampling, heavy metal detection and 3D modeling for the contaminated area to obtain a 3D model of soil heavy metal distribution;

Step 2: Based on the three-dimensional model of soil heavy metal distribution, excavate and collect contaminated soil to obtain contaminated soil;

Step 3: Add the contaminated soil to the mixing tank, and add a passivating agent to mix for 40 minutes;

Step 4: Add diammonium phosphate and calcium oxide into the mixing tank, and stir for 20min;

Step 5: Add ferrous sulfate and magnesium oxide into the mixing tank, and stir for 20min

Step 6: Repeat steps 3 to 5, and continue to detect the heavy metal content of the soil until the heavy metal content is lower than the national standard, and the renovated soil is obtained.

After adopting this scheme, biochar is porous and rich in surface functional groups, which can adsorb organic pollutants and heavy metals in the environment, thereby effectively reducing the mobility and bioavailability of pollutants, and reducing the environmental risks of pollutants. Biochar has a high adsorption capacity for heavy metals, and adding biochar to soil can increase the adsorption capacity of soil for heavy metals. For organic pollutants, biochar prepared at high temperature generally has strong polarity and strong affinity with organic substances; biochar can improve the activity of microorganisms in soil and improve the degradation ability of organic pollutants.

The application of diammonium phosphate can make metal lead, mercury, manganese, chromium, zinc and cadmium form insoluble phosphate, and reduce the toxic effect of heavy metals in the soil.

Adding ferrous sulfate, magnesium oxide, and calcium oxide can make arsenic generate insoluble substances and fix them, thereby reducing the activity of arsenic. Ferrous sulfate and calcium oxide generate calcium sulfate hydrate in the presence of water, and the synergistic effect of calcium sulfate/calcium sulfate hydrate and iron-containing reagents can further reduce the activity of arsenic.

Preferably, the soil sampling in step 1 includes:

Set up several sampling points evenly in the polluted area;

Using the soil sampling tool, collect several soil samples at different depths at each sampling point;

Each soil sample is classified and marked according to the coordinates of the sampling point and the depth of collection.

Preferably, the coordinates of the sampling point are one of GPS coordinates or Beidou coordinates.

Preferably, the step 1 detection includes:

Detection of heavy metal content in each soil sample;

The detected heavy metal content includes mercury, cadmium, lead, chromium, and arsenic;

The detection method is one of atomic absorption spectrometry, ultraviolet-visible spectrophotometry, atomic fluorescence method, electrochemical method-anodic stripping voltammetry, X-ray fluorescence spectrometry or inductively coupled plasma mass spectrometry.

Preferably, the three-dimensional modeling of the first step includes:

According to the coordinates of the sampling point, the depth of the sampling point and the concentration of heavy metals for each soil sample, a three-dimensional model of soil heavy metal distribution was established.

Preferably, the step 2 excavation includes: according to the three-dimensional model of soil heavy metal distribution, selecting sampling points lower than the national soil heavy metal standard as excavation points, excavating the contaminated soil area corresponding to the cube wrapped by the excavation points, and obtaining contaminated soil .

After adopting the above preferred solution, by establishing a three-dimensional model of soil heavy metal distribution to determine the scope of contaminated soil, the scope of pollution, the composition of polluted heavy metals and the severity of pollution can be accurately assessed. Excavating contaminated soil through the three-dimensional model of soil heavy metal distribution can accurately segment contaminated soil and normal soil, and improve the pertinence of soil remediation.

Preferably, the continuation of step 4 also includes step 5: detecting the pH value of the refurbished soil, and adjusting the pH value to neutral by adding potassium dihydrogen phosphate, diammonium phosphate, calcium oxide, plant ash or humus.

After adopting this preferred solution, the pH may change during the soil remediation process, so the pH value of the refurbished soil is finally adjusted to make it suitable for crop growth; the passivating agent and the adjusting agent used in the present invention are both substances with fertilizer effects, and there are Helps to improve soil fertility.

Preferably, by weight, the passivating agent comprises:

60 parts of 300-500 mesh biochar and 40 parts of diatomaceous earth.

After adopting this preferred scheme, the possible mechanisms of biochar passivation of heavy metals include ion exchange, electrostatic adsorption, surface precipitation and complexation. Studies have shown that the adsorption of Pb by biochar prepared from sludge is achieved by a variety of mechanisms, the most critical of which is the exchange of Pb ₂ + with Ca ₂ +, Mg ₂ + and other cations released on the surface of biochar, promoting biological The co-precipitation and inner-layer complexation of Pb by humic substances and mineral oxides in carbon, while the complexation of Pb ₂ + with surface functional groups, physical adsorption and Pb ₂ + diffusion in biochar particles all play a role. . For different heavy metals, the mechanism of biochar passivation may be different; different biochars have differences in physicochemical properties, and their mechanisms of heavy metal passivation are also different; in addition, the properties of heavy metal-contaminated soils themselves The effect of carbon passivation of heavy metals will also have a certain impact.

The research on the relationship and interaction between biochar and heavy metals in soil continues to deepen. Through a series of test results of biochar-soil system and biochar-soil-plant system, it is shown that biochar can effectively reduce Pb in soil , Zn, Cd, Ni and other heavy metals effectiveness.

Diatomaceous earth is composed of amorphous SiO ₂ and contains a small amount of Fe ₂ O ₃ , CaO, MgO, Al ₂ O ₃ and organic impurities. Diatomaceous earth is usually light yellow or light gray, soft, porous and light. Diatomite has neutral pH, non-toxic, good suspension performance, strong adsorption performance, light bulk density, oil absorption rate of 115%, fineness of 325 mesh to 500 mesh, good mixing uniformity, and can adsorb heavy metals. It will not block the agricultural machinery pipeline, and it can moisturise the soil, loosen the soil, prolong the time of medicinal effect and fertilizer effect, and promote the growth effect of crops.

A preparation method of biochar, for preparing the biochar of claim 8, the step comprising:

drying, cutting and pulverizing bamboo to obtain bamboo particles;

Bamboo charcoal is obtained by heating the bamboo particles at 500-600 °C for 2 hours in an oxygen-free environment;

Pulverize and sieve the bamboo charcoal to obtain 300-500 mesh biochar.

To sum up, due to the adoption of the above-mentioned technical solutions, the beneficial effects of the present invention are:

1. Biochar has good physical and chemical properties and nutrient regulation ability. After being applied to the soil, due to its porous structure, it can effectively improve the physical and chemical properties and microbial activity of the soil, reduce the loss of soil nutrients, thereby improving soil fertility and promoting crop growth. .

2. The pH may change during the soil remediation process, so finally adjust the pH of the renovated soil to make it suitable for crop growth

3. Both the passivating agent and the adjusting agent used in the present invention are substances with the effect of fertilizer, which are beneficial to improve the fertility of the renovated soil.

4. By establishing a three-dimensional model of soil heavy metal distribution to determine the scope of contaminated soil, it is possible to accurately assess the scope of pollution, the composition of polluted heavy metals and the severity of pollution. Excavating contaminated soil through the three-dimensional model of soil heavy metal distribution can accurately segment contaminated soil and normal soil, and improve the pertinence of soil remediation.

Detailed ways

In order to make the technical means, features and effects realized by the present invention easier to understand, the technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to specific embodiments.

The present invention provides the following technical solutions:

A biochar-based heavy metal soil remediation method, comprising the following steps:

Step 1: Perform soil sampling, heavy metal detection and 3D modeling for the contaminated area to obtain a 3D model of soil heavy metal distribution;

Step 2: Based on the three-dimensional model of soil heavy metal distribution, excavate and collect contaminated soil to obtain contaminated soil;

Step 3: Add the contaminated soil to the mixing tank, and add a passivating agent to mix for 40 minutes;

Step 4: Add diammonium phosphate and calcium oxide into the mixing tank, and stir for 20min;

Step 5: Add ferrous sulfate and magnesium oxide into the mixing tank, and stir for 20min

Step 6: Repeat steps 3 to 5, and continue to detect the heavy metal content of the soil until the heavy metal content is lower than the national standard, and the renovated soil is obtained.

Preferably, the soil sampling in step 1 includes:

Set up several sampling points evenly in the polluted area;

Using the soil sampling tool, collect several soil samples at different depths at each sampling point;

Each soil sample is classified and marked according to the coordinates of the sampling point and the depth of collection.

Preferably, the coordinates of the sampling point are one of GPS coordinates or Beidou coordinates.

Preferably, the step 1 detection includes:

Detection of heavy metal content in each soil sample;

The detected heavy metal content includes mercury, cadmium, lead, chromium, and arsenic;

The detection method is one of atomic absorption spectrometry, ultraviolet-visible spectrophotometry, atomic fluorescence method, electrochemical method-anodic stripping voltammetry, X-ray fluorescence spectrometry or inductively coupled plasma mass spectrometry.

Preferably, the three-dimensional modeling of the first step includes:

According to the coordinates of the sampling point, the depth of the sampling point and the concentration of heavy metals for each soil sample, a three-dimensional model of soil heavy metal distribution was established.

Preferably, the step 2 excavation includes: according to the three-dimensional model of soil heavy metal distribution, selecting sampling points lower than the national soil heavy metal standard as excavation points, excavating the contaminated soil area corresponding to the cube wrapped by the excavation points, and obtaining contaminated soil .

Preferably, the continuation of step 4 also includes step 5: detecting the pH value of the refurbished soil, and adjusting the pH value to neutral by adding potassium dihydrogen phosphate, diammonium phosphate, calcium oxide, plant ash or humus.

Preferably, by weight, the passivating agent comprises:

60 parts of 300-500 mesh biochar and 40 parts of diatomaceous earth.

A preparation method of biochar, for preparing the biochar of claim 8, the step comprising:

drying, cutting and pulverizing bamboo to obtain bamboo particles;

Bamboo charcoal is obtained by heating the bamboo particles at 500-600 °C for 2 hours in an oxygen-free environment;

Pulverize and sieve the bamboo charcoal to obtain 300-500 mesh biochar.

Biochar has good physical and chemical properties and nutrient regulation ability. After being applied to the soil, due to its porous structure, it can effectively improve the physical and chemical properties and microbial activity of the soil, reduce the loss of soil nutrients, thereby improving soil fertility and promoting crop growth.

The pH may change during soil remediation, so adjust the pH of the refurbished soil at the end to make it suitable for crop growth.

Both the passivating agent and the adjusting agent used in the present invention are substances with the effect of fertilizer, which are beneficial to improve the fertility of the renovated soil.

By establishing a three-dimensional model of soil heavy metal distribution and determining the scope of contaminated soil, it is possible to accurately assess the scope of pollution, the composition of polluted heavy metals, and the severity of pollution. Excavating contaminated soil through the three-dimensional model of soil heavy metal distribution can accurately segment contaminated soil and normal soil, and improve the pertinence of soil remediation.

The following is the specific use process of this embodiment:

The present invention is a biochar-based heavy metal soil remediation method. The soil sampling, heavy metal detection and three-dimensional modeling are carried out for polluted areas to obtain a three-dimensional model of soil heavy metal distribution; based on the three-dimensional model of soil heavy metal distribution, the polluted soil is excavated and collected to obtain Contaminated soil; add the contaminated soil to the mixing tank, and add passivating agent and stir for 40 minutes; add diammonium phosphate and calcium oxide to the mixing tank and stir for 20 minutes; add ferrous sulfate and magnesium oxide to the mixing tank and stir for 20 minutes

Steps 3 to 5 are repeated, and the heavy metal content of the soil is continuously detected until the heavy metal content is lower than the national standard, and the renovated soil is obtained.

It will be apparent to those skilled in the art that the present invention is not limited to the details of the above-described exemplary embodiments, but that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments are to be regarded in all respects as illustrative and not restrictive, and the scope of the invention is to be defined by the appended claims rather than the foregoing description, which are therefore intended to fall within the scope of the claims. All changes within the meaning and scope of the equivalents of , are included in the present invention.

Claims (9)

1. a heavy metal soil remediation method based on biochar, is characterized in that: comprise the following steps: Step 1: Perform soil sampling, heavy metal detection and 3D modeling for the contaminated area to obtain a 3D model of soil heavy metal distribution; Step 2: Based on the three-dimensional model of soil heavy metal distribution, excavate and collect contaminated soil to obtain contaminated soil; Step 3: Add the contaminated soil to the mixing tank, and add a passivating agent to mix for 40 minutes; Step 4: Add diammonium phosphate and calcium oxide into the mixing tank, and stir for 20min; Step 5: Add ferrous sulfate and magnesium oxide into the mixing tank, and stir for 20min Step 6: Repeat steps 3 to 5, and continue to detect the heavy metal content of the soil until the heavy metal content is lower than the national standard, and the renovated soil is obtained. 2. A biochar-based heavy metal soil remediation method according to claim 1, characterized in that: the step 1 soil sampling comprises: Set up several sampling points evenly in the polluted area; Using the soil sampling tool, collect several soil samples at different depths at each sampling point; Each soil sample is classified and marked according to the coordinates of the sampling point and the depth of collection. 3 . The biochar-based heavy metal soil remediation method according to claim 2 , wherein the coordinates of the sampling point are one of GPS coordinates or Beidou coordinates. 4 . 4. a kind of heavy metal soil remediation method based on biochar according to claim 2 is characterized in that: described step 1 detection comprises: Detection of heavy metal content in each soil sample; The detected heavy metal content includes mercury, cadmium, lead, chromium, and arsenic; The detection method is one of atomic absorption spectrometry, ultraviolet-visible spectrophotometry, atomic fluorescence method, electrochemical method-anodic stripping voltammetry, X-ray fluorescence spectrometry or inductively coupled plasma mass spectrometry. 5. A biochar-based heavy metal soil remediation method according to claim 4, characterized in that: the three-dimensional modeling of the step 1 comprises: According to the coordinates of the sampling point, the depth of the sampling point and the concentration of heavy metals for each soil sample, a three-dimensional model of soil heavy metal distribution was established. 6. A biochar-based heavy metal soil remediation method according to claim 1, characterized in that: the step 2 excavation comprises: according to a three-dimensional model of soil heavy metal distribution, selecting a sampling point lower than the national soil heavy metal standard as an excavation point , excavating the contaminated soil area corresponding to the cube wrapped by the excavation point to obtain the contaminated soil. 7. a kind of heavy metal soil remediation method based on biochar according to claim 1 is characterized in that: continuing step 4 also comprises step 5: detecting and renovating soil pH value, by adding potassium dihydrogen phosphate, diammonium phosphate, calcium oxide , plant ash or humus to adjust the pH value to neutral. 8. a kind of heavy metal soil remediation method based on biochar according to claim 1, is characterized in that: by weight, described passivating agent comprises: 60 parts of 300-500 mesh biochar and 40 parts of diatomaceous earth. 9. A preparation method of biochar, characterized in that: for preparing the biochar according to claim 8, the step comprises: drying, cutting and pulverizing bamboo to obtain bamboo particles; Bamboo charcoal is obtained by heating the bamboo particles at 500-600 °C for 2 hours in an oxygen-free environment; Pulverize and sieve the bamboo charcoal to obtain 300-500 mesh biochar.