CN106947487A - A kind of modifying agent and preparation and application for Compound Heavy Metals soil - Google Patents

Abstract

The invention discloses a modifier for composite heavy metal polluted soil and a method for preparing and using the modifier. The modifier is composed of the following materials in mass percentage: 30-55% of steel slag powder; 20-50% of calcium superphosphate powder; loaded phosphoric acid Salt Biochar 5‑30%. The advantages of the present invention are: firstly, the modifier can significantly reduce the mobility and toxicity leaching of heavy metals in heavy metal-contaminated soil, and is especially suitable for acid-contaminated sites with high heavy metal content and many types of pollutants. After the contaminated soil is repaired, it can be used as The resource utilization of environmentally friendly materials can significantly reduce the environmental risk in the secondary development and utilization of polluted sites; at the same time, the raw materials of the modifier are easy to obtain, low in cost, simple in preparation, convenient in use, and stable in effect, and can be widely used in compounding The solidification and stabilization of the contaminated site is under restoration.

Description

A kind of modifier for complex heavy metal polluted soil and its preparation and use method

technical field

The invention relates to the field of environmental geotechnical engineering, in particular to a modifier for composite heavy metal polluted soil and a preparation and use method.

Background technique

With the adjustment of urban functions and urban layout in our country, enterprises originally located in urban centers and suburbs, such as chemical plants, metal smelting plants, and electroplating plants, have gradually shut down or retreated from cities to parks. However, the production process of industries and enterprises for many years , A large amount of pollutants have accumulated in the land left after their relocation, which not only brings resistance to the efficient use of the leftover land, but also brings serious safety hazards to the surrounding environment. In recent years, the "Soil Pollution Prevention and Control Action Plan" (Soil Ten Articles) promulgated by the government also regards the restoration of contaminated soil as one of the current important livelihood projects, and it is imminent to carry out related pollution restoration and control work.

Heavy metal pollution in industrially polluted soil is characterized by many types of heavy metals, high content and high acidity. In the remediation of heavy metal-contaminated sites, solidification stabilization technology is widely used. Commonly used modifiers mainly include materials such as cement, lime, and phosphate, which have a good effect on the solidification and stabilization of heavy metals, but there are also a large number of disadvantages, such as high energy consumption for cement production and high greenhouse gas emissions; lime and phosphate are Non-renewable natural minerals, high cost, etc.; and the application of a large amount of phosphate will seriously change the soil structure and further cause phosphorus pollution of groundwater and surface water.

To sum up, there are many defects in traditional modifiers, and it is necessary to reduce the use of cement and phosphate materials, and find a new type of modifier that can solidify and stabilize heavy metals, and at the same time have high curing and stabilizing efficiency, low cost, stable performance, wide source of materials and environmental friendliness. Improvers have become the focus of environmental science and technology workers.

Contents of the invention

Purpose of the invention: the first purpose of the present invention is to provide a kind of improver that can significantly reduce the mobility of heavy metals in the heavy metal-contaminated soil and the amount of toxic leaching; the second purpose of the present invention is to provide the improvement of the heavy metal-contaminated soil The preparation method of agent; the third object of the present invention is to provide the using method of this heavy metal polluted soil amendment.

Technical solution: The present invention is used as an amendment for composite heavy metal polluted soil, which is composed of the following materials in mass percentage: 30-55% of steel slag powder; 20-50% of superphosphate powder; 5-30% of biochar loaded with phosphate.

The constituent materials of the improver are preferably: 35-50% of steel slag powder; 25-45% of calcium superphosphate powder; 10-25% of biochar loaded with phosphate.

The steel slag powder is activated steel slag powder prepared by the following method:

(1) One or more of high-activity steel slags such as converter slag, open hearth furnace slag and electric furnace oxide slag after magnetic separation are crushed and screened;

(2) Dry the material with a particle size of less than 2 mm in the obtained product until its moisture content is less than 2%, preferably using air drying at 100-105 ° C;

(3) The obtained product is ground and passed through a 150-200 mesh sieve (for example, ball milling can be used), and then calcined at 500-700°C for 1-2h (for example, an electric furnace can be preferably used for calcination, which is energy-saving and practical) to obtain activated steel slag powder .

The biochar loaded with phosphate is prepared by the following method:

(1) Prepare a phosphate solution with a concentration of 0.01-0.05mol/L (the phosphate is preferably potassium dihydrogen phosphate, its aqueous solution is acidic and has a better activation effect on steel slag), and the biochar is ground through a 0.1-0.3mm sieve , to obtain biochar powder;

(2) Biochar powder and aluminum sulfate are mixed according to a mass ratio of 20-30:1 to obtain a biochar powder mixture;

(3) Immerse the obtained biochar powder mixture into the phosphate solution, stir for 10-15min (until the mixture is uniform), vibrate and stir at 20-30°C for 10-15h, then stand still for 36-48h to obtain a gel-like precipitate The purpose of the two stirrings is different. The first stirring is to fully contact the solid and liquid, and the second stirring is to quickly produce gel precipitates;

(4) Dry the gelatinous precipitate with an air flow at 100-250°C until its moisture content is less than 2%, and grind the resulting product through a 150-200 mesh sieve to obtain phosphate-loaded biochar. It dries quickly, and the medicine is not easy to agglomerate, which is convenient for subsequent medicine production.

One or more of the coffee grounds, tea foam and traditional Chinese medicine grounds are dried at 100-105° C. to a constant quality, and then cracked at 400-700° C. under anaerobic conditions to produce biochar.

_The calcium superphosphate powder is prepared by the following method: the calcium superphosphate with a _P2O5 content of 14-20% is dried by an air stream at 100-250°C until its moisture content is less than 2%, and ground to 150-200 mesh screen.

The preparation method of the modifier suitable for composite heavy metal-contaminated soil comprises the following steps: mixing steel slag powder, superphosphate powder and phosphate-loaded biochar according to weight percentage, and stirring by dry method for 0.5-1h until the mixture is uniform Pass through a 150-200 mesh sieve to obtain the improver.

The method of using the modifier suitable for composite heavy metal-contaminated soil is: mixing and stirring the modifier with heavy metal-contaminated soil, wherein the amount of the modifier is 5-15% of the dry weight of heavy metal-contaminated soil, and the heavy metal The moisture content of the polluted soil is 16-30%.

The content of particles with a particle size of less than 0.075 mm in the heavy metal contaminated soil is 65-100%, wherein the content of heavy metal lead is greater than 2000 mg/kg, the content of heavy metal zinc is greater than 2000 mg/kg, the content of heavy metal copper is greater than 2000 mg/kg, and the content of heavy metal nickel is greater than 2000 mg /kg.

Beneficial effect: compared with prior art, the remarkable advantage of the present invention is:

(1) The heavy metal curing effect is good. Firstly, the steel slag involved in the present invention can have a strong adsorption effect on heavy metal ions; secondly, the agricultural grade superphosphate contains part of calcium sulfate, and under the stimulation of calcium sulfate, the steel slag can exhibit its potential gelling properties, which is beneficial to Phosphate precipitation and hydroxide precipitation of heavy metals are effectively wrapped, which greatly enhances the solidification effect of heavy metals when phosphate is used alone; again, calcium oxide dissolved in steel slag hydrates to form Ca(OH) ₂ , while The main component of superphosphate is Ca(H ₂ PO ₄ ) ₂ , and the acid-base reaction between the two will generate a large number of hydroxyapatite crystals in the aqueous environment. Hydroxyapatite can efficiently adsorb and complex heavy metals such as Pb, Zn, Cu, and Ni, and the solubility of heavy metal salts of hydroxyapatite formed with heavy metals is dozens of orders of magnitude lower than that of heavy metal hydroxides. Lower dissolution, better and more stable curing effect.

(2) Good durability. Traditional amendments are easily affected by carbon dioxide erosion and acid rain erosion, resulting in the degradation and attenuation of the environmental safety and engineering characteristics of solidified contaminated soil. The improving agent involved in the present invention can effectively overcome the above-mentioned shortcomings, because the generated heavy metal phosphate precipitates are agglomerated around the biochar, and its solubility is low in various pH environments, and in the hydration product CSH gel of steel slag Under the action of wrapping, it can effectively reduce the contact between heavy metal precipitation and acidic solution; at the same time, steel slag itself has a strong acid buffering capacity and the ability to absorb carbon dioxide. Under the action of carbon dioxide erosion, CaCO ₃ crystals are generated to further fill the pores of the solidified body, effectively reducing The amount of infiltration of acidic solution further increases the stability of the solidified body in harsh environments; in addition, the biochar loaded with phosphate also has a good buffering effect on acid rain erosion, and the loaded phosphate can effectively inhibit the desorption of adsorbed heavy metals function, further increasing the durability of the cured body.

(3) Effective utilization of waste raw materials, environment-friendly modifier. First of all, steel slag, as a kind of industrial waste, accumulates in a large area and has caused serious environmental pollution. Through the activation of steel slag, the utilization value of steel slag is effectively improved, and waste is turned into treasure. Secondly, as a highly alkaline material, steel slag is directly used in the solidification and stabilization of heavy metal-contaminated soil. The pH of the solidified soil is high, which will bring many problems to the later development and utilization of the land. While the steel slag has a solidification effect on heavy metals, it also effectively reduces the pH of the solidified soil, and through the addition of superphosphate, it can achieve the best solidification and stabilization effect on heavy metals. Thirdly, coffee grounds, tea foam and traditional Chinese medicine residues are also domestic waste residues. After being prepared into biochar through medium and high temperature pyrolysis, further modification is carried out. After being loaded with phosphate, it can effectively increase the curing effect on metals and realize the treatment of steel slag. The excitation of steel slag increases the hydration activity of steel slag and the solidification and stabilization effect on heavy metals.

detailed description

Example 1

The present invention is applicable to the modifier of composite heavy metal polluted soil, and consists of the following materials in parts by mass: 45% of steel slag powder; 35% of calcium superphosphate powder; and 20% of biochar loaded with phosphate.

The steel slag powder is activated steel slag powder prepared by the following method: the converter slag is subjected to magnetic separation and then crushed and sieved; among the obtained products, materials with a particle size of less than 2mm are placed in an oven and dried by air flow at a temperature of 105°C until the water content is 1%; the obtained product is ground and passed through a 200-mesh sieve, and then calcined in an electric furnace at 700° C. for 2 hours. The basicity value of the steel slag powder is 2.07.

The main components and content of the steel slag are shown in Table 1. It should be noted that the steel slag applicable to the present invention is not limited to the data in Table 1, and it is only the steel slag used in this embodiment:

Table 1 Main components and content of steel slag

main chemical composition CaO SiO ₂ Al ₂ O _{3 Fe2O3 _} MgO P ₂ O ₅ content(%) 36.30 16.26 3.32 18.66 8.35 1.26

The phosphate-loaded biochar is prepared by the following method: prepare a potassium dihydrogen phosphate solution with a concentration of 0.05mol/L, and grind the biochar through a 0.2mm sieve to obtain biochar powder; mix the biochar powder and sulfuric acid The aluminum is fully mixed according to the mass ratio of 30:1 to obtain a biochar powder mixture; the obtained mixture is immersed in the potassium dihydrogen phosphate solution obtained above, stirred for 15 minutes until the mixture is uniform, and shaken and stirred for 15 hours at 25 ° C. After standing still for 48 hours, a gel-like precipitate was obtained; the gel-like precipitate was dried by an air flow at 200° C. until its moisture content was 1%, and the obtained product was ground through a 200-mesh sieve to obtain biochar loaded with potassium dihydrogen phosphate. The biochar is made from selected coffee grounds, dried at 105°C until its quality does not change, and then cracked at 600°C for 6 hours under airtight anoxic conditions. Its physical and chemical properties and main chemical components are shown in Table 2 shown.

Table 2 Basic chemical properties and main element contents of biochar

The calcium superphosphate powder is prepared by the following method: the calcium superphosphate with a P ₂ O ₅ content of 20% is dried by an air flow at 250° C. to a moisture content of 1%, and ground through a 200-mesh sieve.

The improver suitable for composite heavy metal-contaminated soil is prepared by the following steps: mixing the above-mentioned activated steel slag powder, superphosphate powder and phosphate-loaded biochar by dry method for 1 hour until the mixture is uniform Pass through a 200-mesh sieve to obtain the improver.

The use method of the modifier suitable for composite heavy metal-contaminated soil is specifically: mixing and stirring the modifier and heavy-metal-contaminated soil in situ, wherein the dosage of the modifier is 5% of the dry weight of the heavy-metal-contaminated soil (accounting for the composite metal-contaminated soil). dry weight of contaminated soil). There are two kinds of heavy metal pollutants: polluted soil a, lead-zinc compound polluted soil taken from a certain industrial polluted site; polluted soil b, copper-nickel compound polluted soil taken from a second industrial polluted site. Other main physical and chemical properties are shown in Table 3.

Table 3 Main physical and chemical properties of polluted soil

Example 2

The preparation process and curing process are the same as in Example 1, except that the dosage of the modifier is 10% (the modifier accounts for the dry weight of the heavy metal and organic compound polluted soil).

Example 3

The preparation process and curing process are the same as in Example 1, except that the dosage of the modifier is 15% (the modifier accounts for the dry weight of the heavy metal and organic compound polluted soil).

Comparative example 1

Without adding any modifier, only the composite heavy metal polluted soil sample in Example 1 was taken.

Comparative example 2

The steel slag in Example 1 was used to prepare the improver without activation, and the other preparation steps remained unchanged, and the dosage was the same as that in Example 3, which was 15%.

Example 4

The present invention is suitable for the modifier of composite heavy metal polluted soil, and consists of the following materials in parts by mass: 50% of steel slag powder; 25% of calcium superphosphate powder; and 25% of biochar loaded with phosphate.

The steel slag powder is activated steel slag powder prepared by the following method: open hearth furnace slag is subjected to magnetic separation and then crushed and sieved; among the obtained products, materials with a particle size of less than 2mm are dried by air flow at a temperature of 100°C until they contain water The rate is 1.5%. The obtained product is ground and passed through a 150-mesh sieve, and then calcined in an electric furnace at 500° C. for 1 hour. The basicity value of the steel slag powder is 1.8.

The phosphate-loaded biochar is prepared by the following method: prepare a potassium dihydrogen phosphate solution with a concentration of 0.01mol/L, and grind the biochar through a 0.1mm sieve to obtain biochar powder; mix the biochar powder and sulfuric acid The aluminum is fully mixed according to the mass ratio of 20:1 to obtain the biochar powder mixture; the obtained mixture is impregnated into the potassium dihydrogen phosphate solution obtained above, stirred for 10 minutes until the mixture is uniform, and shaken and stirred for 10 hours at 20°C After standing still for 36 hours, a gel-like precipitate was obtained; the gel-like precipitate was dried by an air flow at 100° C. to a moisture content of 1.5%, and the obtained product was ground through a 150-mesh sieve to obtain biochar loaded with potassium dihydrogen phosphate.

The biochar is made by selecting coffee grounds and drying them at 100°C until their quality does not change, and then pyrolyzing them at 400°C under anaerobic conditions.

The calcium superphosphate powder is prepared by the following method: the calcium superphosphate with a P ₂ O ₅ content of 14% is dried by air flow at 100° C. to a moisture content of 1.5%, and ground through a 150-mesh sieve.

The improver suitable for composite heavy metal-contaminated soil is prepared by the following steps: mixing the above-mentioned steel slag powder, superphosphate powder and phosphate-loaded biochar by dry method for 0.5h until the mixture is uniform Pass through a 150-mesh sieve to obtain the improver.

The use method of the modifier suitable for composite heavy metal-contaminated soil is specifically: mixing and stirring the modifier and heavy-metal-contaminated soil in situ, wherein the dosage of the modifier is 5% of the dry weight of the heavy-metal-contaminated soil (accounting for the composite metal-contaminated soil). Contaminated soil dry weight), and the moisture content of this heavy metal-contaminated soil is 16%, and the heavy-metal-contaminated soil is the same as the polluted soil selected in Example 1, wherein the particle content of particle diameter less than 0.075mm in this heavy-metal-contaminated soil is 65%.

Example 5

The present invention is suitable for the modifier of composite heavy metal polluted soil, and consists of the following materials in parts by mass: 35% of steel slag powder; 45% of calcium superphosphate powder; and 20% of biochar loaded with phosphate.

The steel slag powder is activated steel slag powder prepared by the following method: open-hearth slag is subjected to magnetic separation and then crushed and sieved; among the obtained products, materials with a particle size of less than 2 mm are dried by airflow at a temperature of 150 ° C until completely dry; The obtained product is ground and passed through a 180-mesh sieve, and then calcined in an electric furnace at 600° C. for 1.5 h. The basicity value of the steel slag powder is 2.2.

The phosphate-loaded biochar is prepared by the following method: prepare a potassium dihydrogen phosphate solution with a concentration of 0.03mol/L with phosphate, and grind the biochar through a 0.3mm sieve to obtain biochar powder; Powder and aluminum sulfate are fully mixed according to the mass ratio of 25:1 to obtain a biochar powder mixture; impregnate the obtained mixture into the potassium dihydrogen phosphate solution obtained above, stir for 13 minutes until the mixture is uniform, and shake at 25°C Stirring for 12.5 hours and then standing still for 42 hours, a gel-like precipitate was obtained; the gel-like precipitate was dried by airflow at 180°C until completely dry, and the resulting product was ground through a 170-mesh sieve to obtain biochar loaded with potassium dihydrogen phosphate.

The biochar is made by selecting tea leaves and drying them at 102.5°C until their quality does not change, and then pyrolyzing them at 550°C under anoxic conditions.

The calcium superphosphate powder is prepared by the following method: the calcium superphosphate with a P ₂ O ₅ content of 17% is dried in an air flow at 150° C. until completely dry, and ground through a 170-mesh sieve.

The improver suitable for composite heavy metal-contaminated soil is prepared by the following steps: mixing the above-mentioned activated steel slag powder, superphosphate powder and phosphate-loaded biochar in parts by mass, and stirring for 0.75h by dry method until the mixture is uniform Pass through a 170-mesh sieve.

The method of using the modifier suitable for composite heavy metal-contaminated soil is specifically: mixing and stirring the modifier and heavy metal-contaminated soil in situ, wherein the dosage of the modifier is 10% of the dry weight of the heavy metal-contaminated soil (accounting for the composite metal-contaminated soil). Contaminated soil dry weight), and the moisture content of this heavy metal-contaminated soil is 23%, the heavy-metal-contaminated soil is identical with the polluted soil selected in embodiment 1, and wherein, in this heavy-metal-contaminated soil, the particle content of particle diameter less than 0.075mm is 82.5% .

Example 6

The present invention is suitable for the modifier of composite heavy metal polluted soil, and consists of the following materials in parts by mass: 40% of steel slag powder; 50% of calcium superphosphate powder; and 10% of biochar loaded with phosphate.

The steel slag powder is activated steel slag powder prepared by the following method: open-hearth slag is subjected to magnetic separation and then crushed and sieved; among the obtained products, materials with a particle size of less than 2mm are dried by air flow at a temperature of 125°C until they contain water The rate is 0.5%; the obtained product is ground and passed through a 200-mesh sieve, and then calcined in an electric furnace at 700°C for 2 hours. The steel slag powder has an alkalinity value of 2.6.

The phosphate-loaded biochar is prepared by the following method: prepare a potassium dihydrogen phosphate solution with a concentration of 0.05mol/L, and grind the biochar through a 0.2mm sieve to obtain biochar powder; mix the biochar powder and sulfuric acid The aluminum is fully mixed according to the mass ratio of 30:1 to obtain the biochar powder mixture; the obtained mixture is impregnated into the phosphate solution obtained above, stirred for 15 minutes until the mixture is uniform, at 30°C, oscillated and stirred for 15 hours and then left to stand After 48 hours, a gelatinous precipitate was obtained; the gelatinous precipitate was dried by an air flow at 250° C. to a moisture content of 0.5%, and the obtained product was ground through a 190-mesh sieve to obtain biochar loaded with potassium dihydrogen phosphate.

The biochar is made by selecting traditional Chinese medicine dregs and drying them at 105°C until their quality does not change, and then pyrolyzing them at 700°C under anoxic conditions.

The calcium superphosphate powder is prepared by the following method: calcium superphosphate with a _P2O5 content of ₁₈ % is dried by airflow at 180°C until its moisture content is 0.5%, and ground through a 190-mesh sieve to obtain calcium superphosphate pink.

The improver suitable for composite heavy metal-contaminated soil is prepared by the following steps: mixing the above-mentioned steel slag powder, superphosphate powder and phosphate-loaded biochar by dry method for 0.75h until the mixture is uniform Pass through a 190-mesh sieve to obtain the improver.

The specific method for using the modifier suitable for complex heavy metal-contaminated soil is: mixing the modifier and heavy metal-contaminated soil in situ. Wherein, the amount of the improver is 15% of the dry weight of the heavy metal-contaminated soil (accounting for the dry weight of the composite metal-contaminated soil), and the moisture content of the heavy metal-contaminated soil is 30%. The content of particles with a particle size less than 0.075mm in the heavy metal contaminated soil used is 83%, and the heavy metal contaminated soil is the same as the contaminated soil selected in Example 1, wherein the particle content with a particle size of less than 0.075mm in the heavy metal contaminated soil is 100%. .

Example 7

The present invention is suitable for the improvement agent of compound heavy metal polluted soil, which is composed of the following materials in mass parts: 30% of steel slag powder; 40% of calcium superphosphate powder; and 30% of biochar loaded with phosphate.

The steel slag powder is activated steel slag powder prepared by the following method: the oxidized slag of the electric furnace is subjected to magnetic separation and then crushed and sieved; among the obtained products, materials with a particle size of less than 2mm are dried by air flow at a temperature of 150°C until completely dry ; The obtained product is ground and passed through a 180-mesh sieve, and then calcined in an electric furnace at 600°C for 1.5h. The basicity value of the steel slag powder is 2.2.

The phosphate-loaded biochar is prepared by the following method: prepare a potassium dihydrogen phosphate solution with a concentration of 0.03mol/L with phosphate, and grind the biochar through a 0.3mm sieve to obtain biochar powder; Powder and aluminum sulfate are fully mixed according to the mass ratio of 25:1 to obtain a biochar powder mixture; impregnate the obtained mixture into the potassium dihydrogen phosphate solution obtained above, stir for 13 minutes until the mixture is uniform, and shake at 25°C Stirring for 12.5 hours and then standing still for 42 hours, a gel-like precipitate was obtained; the gel-like precipitate was dried by air flow at 180°C until completely dry, and the obtained product was ground through a 200-mesh sieve to obtain biochar loaded with potassium dihydrogen phosphate.

The biochar is made by selecting a mixture of tea foam and coffee grounds and drying it at 102.5°C until its quality does not change, and then cracking it at 600°C under anaerobic conditions.

The calcium superphosphate powder is prepared by the following method: the calcium superphosphate with a P ₂ O ₅ content of 18% is dried by an air stream at 150° C. to a moisture content of 1%, and ground through a 200-mesh sieve.

The improver suitable for composite heavy metal-contaminated soil is prepared by the following steps: mixing the above-mentioned steel slag powder, superphosphate powder and phosphate-loaded biochar by dry method for 0.75h until the mixture is uniform Pass through a 200 mesh sieve.

The use method of the modifier suitable for composite heavy metal-contaminated soil is specifically: mixing and stirring the modifier and heavy-metal-contaminated soil in situ, wherein the dosage of the modifier is 5% of the dry weight of the heavy-metal-contaminated soil (accounting for the composite metal-contaminated soil). Contaminated soil dry weight), and the moisture content of this heavy metal-contaminated soil is 25%, the heavy-metal-contaminated soil is identical with the polluted soil selected in embodiment 1, and wherein, in this heavy-metal-contaminated soil, the particle content of particle diameter less than 0.075mm is 90% .

Example 8

The present invention is suitable for the modifier of composite heavy metal polluted soil, and consists of the following materials in parts by mass: 55% of steel slag powder; 20% of calcium superphosphate powder; and 25% of biochar loaded with phosphate.

The steel slag powder is activated steel slag powder prepared by the following method: the oxidized slag of the electric furnace is subjected to magnetic separation and then crushed and sieved; among the obtained products, materials with a particle size of less than 2mm are dried by air flow at a temperature of 150°C until completely dry ; The obtained product is ground and passed through a 180-mesh sieve, and then calcined in an electric furnace at 600°C for 1.5h. The basicity value of the steel slag powder is 2.2.

The phosphate-loaded biochar is prepared by the following method: prepare a potassium dihydrogen phosphate solution with a concentration of 0.03mol/L with phosphate, and grind the biochar through a 0.3mm sieve to obtain biochar powder; Powder and aluminum sulfate are fully mixed according to the mass ratio of 25:1 to obtain a biochar powder mixture; impregnate the obtained mixture into the potassium dihydrogen phosphate solution obtained above, stir for 13 minutes until the mixture is uniform, and shake at 25°C Stirring for 12.5 hours and then standing still for 42 hours, a gel-like precipitate was obtained; the gel-like precipitate was dried by air flow at 180°C until completely dry, and the obtained product was ground through a 200-mesh sieve to obtain biochar loaded with potassium dihydrogen phosphate.

The biochar is made by selecting a mixture of coffee grounds and traditional Chinese medicine grounds and drying it at 102.5°C until its quality does not change, and then cracking it at 450°C under anoxic conditions.

The calcium superphosphate powder is prepared by the following method: calcium superphosphate with a _P2O5 content of ₁₈ % is dried by air flow at 150°C until its moisture content is 1%, and ground through a 200-mesh sieve to obtain calcium superphosphate pink.

The improver suitable for composite heavy metal-contaminated soil is prepared by the following steps: mixing the above-mentioned steel slag powder, superphosphate powder and phosphate-loaded biochar by dry method for 0.75h until the mixture is uniform Pass through a 200 mesh sieve.

The method of using the modifier suitable for composite heavy metal-contaminated soil is specifically: mixing and stirring the modifier and heavy metal-contaminated soil in situ, wherein the dosage of the modifier is 10% of the dry weight of the heavy metal-contaminated soil (accounting for the composite metal-contaminated soil). Contaminated soil dry weight), and the moisture content of this heavy metal-contaminated soil is 23%, the heavy-metal-contaminated soil is identical with the polluted soil that selects in embodiment 1, and wherein, in this heavy-metal-contaminated soil, the particle content that particle diameter is less than 0.075mm is 75% .

Example 9

The present invention is applicable to the modifier of composite heavy metal polluted soil, and consists of the following materials in parts by mass: 55% of steel slag powder; 40% of superphosphate powder; and 5% of biochar loaded with phosphate.

The steel slag powder is activated steel slag powder prepared by the following method: the oxidized slag of the electric furnace is subjected to magnetic separation and then crushed and sieved; among the obtained products, materials with a particle size of less than 2mm are dried by air flow at a temperature of 150°C until completely dry ; The obtained product is ground and passed through a 180-mesh sieve, and then calcined in an electric furnace at 600°C for 1.5h. The steel slag powder has an alkalinity value of 2.2.

The phosphate-loaded biochar is prepared by the following method: prepare a potassium dihydrogen phosphate solution with a concentration of 0.03mol/L with phosphate, and grind the biochar through a 0.3mm sieve to obtain biochar powder; Powder and aluminum sulfate are fully mixed according to the mass ratio of 25:1 to obtain a biochar powder mixture; impregnate the obtained mixture into the potassium dihydrogen phosphate solution obtained above, stir for 13 minutes until the mixture is uniform, and shake at 25°C Stirring for 12.5 hours and then standing still for 42 hours, a gel-like precipitate was obtained; the gel-like precipitate was dried by air flow at 180°C until completely dry, and the obtained product was ground through a 200-mesh sieve to obtain biochar loaded with potassium dihydrogen phosphate.

The biochar is made by selecting a mixture of tea foam and traditional Chinese medicine dregs and drying it at 102.5°C until its quality does not change, and then cracking it at 550°C under anoxic conditions.

The calcium superphosphate powder is prepared by the following method: calcium superphosphate with a _P2O5 content of ₁₈ % is dried by air flow at 150°C until its moisture content is 1%, and ground through a 200-mesh sieve to obtain calcium superphosphate pink.

The improver suitable for composite heavy metal-contaminated soil is prepared by the following steps: mixing the above-mentioned steel slag powder, superphosphate powder and phosphate-loaded biochar by dry method for 0.75h until the mixture is uniform Pass through a 200 mesh sieve.

The use method of the modifier suitable for composite heavy metal-contaminated soil is specifically: mixing and stirring the modifier and heavy metal-contaminated soil in situ, wherein the dosage of the modifier is 15% of the dry weight of the heavy-metal-contaminated soil (accounting for the composite metal-contaminated soil). Contaminated soil dry weight), and the moisture content of this heavy metal-contaminated soil is 23%, the heavy-metal-contaminated soil is identical with the polluted soil selected in embodiment 1, and wherein, in this heavy-metal-contaminated soil, the particle content of particle diameter less than 0.075mm is 82.5%

Example 10

Sample soil after implementing in embodiment 1, embodiment 2, embodiment 3, comparative example 1, comparative example 2, embodiment 4, embodiment 5, embodiment 6, embodiment 7, embodiment 8 and embodiment 9 Wrap it tightly with a fresh-keeping bag, and do a toxicity leaching test on the solidified contaminated soil after curing for 28 days at 20°C and a humidity greater than 95%.

Test standard: National Environmental Protection Industry Standard "Solid Waste Leaching Toxic Leaching Method Sulfuric Acid Nitric Acid Method" (HJ/T 299-2007).

Test process: Weigh 50g of the solidified contaminated soil after curing, place it in 105°C and dry it, keep the weight constant until the error of the two weighing values is less than ±1%, and calculate the moisture content of the sample. Calculate the dry weight of the remediation soil according to the moisture content, weigh a remediation soil sample with a dry basis mass of 10g, and conduct the test according to the methods and procedures stipulated in the "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid Nitric Acid Method" (HJ/T 299-2007). The test results are shown in Table 4.

Table 4 Toxicity leaching test results (mg/L)

The sulfuric acid and nitric acid leaching method is used as a standard to evaluate whether solid waste is hazardous waste, and it is also a common method for analyzing the toxicity characteristics of pollutants leached from solid waste under the action of acidic rainfall. From the toxicity leaching test result of table 4, can find out by comparing embodiment 1-3, embodiment 4-6 and embodiment 7-9: be mixed with the restoration soil of the present invention's improver, Zn, Pb, Ni in its leachate The leaching concentration of Cu and Cu all decreased with the increase of the amount of modifier. From Comparative Example 1, it can be seen that the heavy metals in the untreated source polluted soil have strong mobility, and the leaching amount of heavy metals Zn, Pb, Ni and Cu It is much higher than the limit value in the "Identification of Hazardous Waste Identification Standards for Leaching Toxicity" (GB 5085.3-2007). In combination with Examples 1-9, it can be found that the addition of modifiers can significantly reduce the leaching of heavy metals and increase environmental safety. Contrast from embodiment 3 and comparative example 2 as can be known, add the improving agent among the present invention and after maintenance 28 days, the stability of heavy metal all improves to some extent, and the stabilizing effect in embodiment 3 is more obvious, and its leaching amount is far lower than << Hazardous waste identification standard leaching toxicity identification "(GB 5085.3-2007), and the steel slag powder in the improvement agent in comparative example 2 is not activated and only prepared by phosphate-loaded biochar, which can be used to a certain extent Reduce the migration characteristics of heavy metals Zn, Pb, Ni and Cu in the soil, reduce their harm to environmental safety, and still meet the basic requirements of the present invention. It can be seen from this that the activation modification treatment of the used steel slag can be effectively To enhance the solidification and stabilization effect of the improver on heavy metals, if the steel slag does not undergo activation treatment, the technical effect of the present invention can also be achieved to a certain extent.

Example 11

To embodiment 1, embodiment 2, embodiment 3, comparative example 1, comparative example 2, embodiment 4, embodiment 5, embodiment 6, embodiment 7, embodiment 8 and embodiment 9 by the method for embodiment 10 After curing, the solidified contaminated soil is used for the pH test of the remediation soil:

Test standard: Test method for pH value of soil 4972-01.

Test process: Weigh 50g of the solidified contaminated soil after curing, place it in 105°C and dry it, keep the weight constant until the error of the two weighing values is less than ±1%, and calculate the moisture content of the sample. Calculate the dry weight of the remediation soil according to the moisture content, pass through a 1mm sieve and weigh 10g of the remediation soil sample on a dry basis, mix it with 10g of distilled water, and test the pH value of the solution after standing for 1 hour. The test results are shown in Table 5.

Table 5 pH test results

The pH of the solidified soil is an important index to evaluate the effect of the modifier on the solidification of heavy metals, and it has a great influence on the development mode and degree of the secondary utilization of the restoration site. From the results of the pH test in Table 5, the comparison of Examples 1-3 and Comparative Example 1 shows that after adding the modifier, the pH of the solidified soil is significantly improved, and after 28 days of curing, the pH value of the contaminated soil is between 6 and 9. between, close to neutral, which is conducive to the utilization of the restoration site, and the pH of the solidified soil in Examples 4-9 is also significantly improved. After 28 days of maintenance, the pH value of the polluted soil is also between 6 and 9, close to the middle Compared with Example 3, the pH value of comparative example 2 is slightly higher because the steel slag is not activated, but it can basically realize the technical solution of the present invention. If the pH continues to rise, it will bring many problems to the development and utilization of land .

Example 12

To embodiment 1, embodiment 2, embodiment 3, comparative example 1, comparative example 2, embodiment 4, embodiment 5, embodiment 6, embodiment 7, embodiment 8 and embodiment 9 by the method for embodiment 10 The polluted soil of the conservation carries out phytotoxicity test (seed germination rate test):

Test process: The seed germination rate test uses soybeans that are more sensitive to the content of heavy metal pollutants in the soil. The germination rate is used as an ecological indicator to analyze the toxicity of heavy metal and organic compound polluted soil. It is a common method to measure the soil environment from the perspective of ecotoxicology. Important methods of quality and soil contamination. First of all, the plain soil and repair soil after 28 days of curing should be air-dried naturally and passed through a 2mm sieve for later use. Take 4kg of soil (plain soil or repair soil) for each sample and put it into a pot (the diameter of the upper mouth is 25cm, the diameter of the bottom is 20cm, and the height is 20cm), and the height of the soil is 18cm; use distilled water to pour the soil in the pot until it holds water. The rate is 60%, and then keep the water holding rate unchanged and place it in the room for 2 days; finally sow soybeans, the soybeans are sown at a depth of about 0.3cm, and 100 seeds are sown in each pot; after sowing, spray regularly to maintain suitable soil moisture , so that the seeds germinate in a sunny place indoors, at a room temperature of 18-22°C, and under natural lighting. Germination rate=(number of germinated seeds/number of tested seeds)×100%. The test results are shown in Table 6.

Table 6 seed germination rate (%)

The seed germination rate test can reflect the toxic effect of soil on plants. As can be seen from Table 6: heavy metal content is very high in plain soil (comparative example 1, the polluted soil that does not add improver), has a strong impact on the germination rate of seed, and the soybean seed germination rate in polluted soil is only 8% and 12% %. The improver in comparative example 2 has improved the germination rate to a certain extent, but the improvement range is limited, and can only reach the germination rates of 49% and 52%. It has a certain stabilizing effect on the heavy metals in the polluted soil, but the effect was limited at that time; on the contrary, the germination rate of the seeds of the improvement agent repairing soil in the embodiments of the present invention 1-9 is all greater than 85% under the situation of various dosages, the highest or even Can reach 99%. The difference between Examples 1, 2, 3 and Comparative Example 1 shows that the improvement agent of the present invention repairs the composite heavy metal contaminated soil and is eco-friendly, which is conducive to the development and growth of plants and microorganisms around the site after restoration. The comparison of Example 3 and Comparative Example 2 shows that the The activation treatment of steel slag can also effectively reduce the poisonous effect of soil on plants, which reflects its ability to solidify and stabilize heavy metals from the side.

Claims (9)

1. A modifier for composite heavy metal polluted soil, characterized in that: it is made up of the following mass percent materials: steel slag powder 30-55%; superphosphate powder 20-50%; phosphate-loaded biochar 5-5% 30%. 2. The improvement agent for composite heavy metal polluted soil according to claim 1, characterized in that: 35-50% of said steel slag powder; 25-45% of superphosphate powder; 10-25% of biochar loaded with phosphate %. 3. The improver for composite heavy metal polluted soil according to claim 1 or 2, characterized in that: the steel slag powder is activated steel slag powder prepared by the following method: (1) crushing and sieving one or more of magnetically separated converter slag, open hearth furnace slag and electric furnace oxide slag; (2) taking the material with a particle size of less than 2mm in the obtained product and drying it until its moisture content is less than 2%; (3) The obtained product is ground and passed through a 150-200 mesh sieve, and then calcined at 500-700° C. for 1-2 hours to obtain activated steel slag powder. 4. The improver for composite heavy metal-contaminated soil according to claim 1, characterized in that: the biochar loaded with phosphate is prepared by the following method: (1) preparing a phosphate solution with a concentration of 0.01-0.05mol/L, grinding the biochar through a 0.1-0.3mm sieve to obtain biochar powder; (2) Biochar powder and aluminum sulfate are mixed according to a mass ratio of 20-30:1 to obtain a biochar powder mixture; (3) Immerse the obtained biochar powder mixture into the phosphate solution, stir for 10-15min, vibrate and stir at 20-30°C for 10-15h, and then let it stand for 36-48h to obtain a gel-like precipitate; (4) Drying the gelatinous precipitate with an air flow at 100-250° C. until its moisture content is less than 2%, and grinding the obtained product through a 150-200 mesh sieve to obtain biochar loaded with phosphate. 5. The improver for compound heavy metal-contaminated soil according to claim 1 or 4, characterized in that: the biochar is made of one or more of coffee grounds, tea foam and traditional Chinese medicine residues at 100-105°C After drying at high temperature until its quality is constant, it is made by pyrolysis at 400-700°C under anaerobic conditions. 6. The improvement agent for composite heavy metal polluted soil according to claim 1, characterized in that: said superphosphate powder is prepared by the following method: P ₂ O ₅ content is 14-20% superphosphate Use airflow at 100-250°C to dry until the moisture content is less than 2%, and grind through a 150-200 mesh sieve. 7. the preparation method of the improvement agent that is used for composite heavy metal polluted soil as claimed in claim 1 is characterized in that comprising the steps: steel slag powder, superphosphate powder and the biological charcoal of load phosphate are mixed by weight percentage, adopt Stir in a dry method for 0.5-1h until the mixture is uniform and pass through a 150-200 mesh sieve to obtain the improver. 8. The method for using the modifier for composite heavy metal-contaminated soil according to claim 1, characterized in that: the modifier is mixed with heavy metal-contaminated soil, wherein the amount of the modifier is the dry weight of heavy metal-contaminated soil 5-15%, and the moisture content of the heavy metal-contaminated soil is 16-30%. 9. The method for using the modifier for composite heavy metal-contaminated soil according to claim 8, characterized in that: the content of particles with a particle diameter less than 0.075mm in the heavy metal-contaminated soil is 65-100%, wherein the content of heavy metal lead More than 2000mg/kg, the content of heavy metal zinc is more than 2000mg/kg, the content of heavy metal copper is more than 2000mg/kg, and the content of heavy metal nickel is more than 2000mg/kg.