CN118956406A

CN118956406A - Soil conditioner for remediation of heavy metal-pesticide combined pollution and its application

Info

Publication number: CN118956406A
Application number: CN202410873479.3A
Authority: CN
Inventors: 蒋少军; 刘忠珍; 李翔; 黄玉芬; 王艳红; 尹贻龙; 徐卓
Original assignee: Institute of Agricultural Resources and Environment of Guangdong Academy of Agricultural Sciences
Current assignee: Institute of Agricultural Resources and Environment of Guangdong Academy of Agricultural Sciences
Priority date: 2024-07-01
Filing date: 2024-07-01
Publication date: 2024-11-15

Abstract

The present invention belongs to the technical field of soil pollution remediation, and discloses a soil conditioner for remediating soil contaminated by heavy metal-pesticide composite pollution, and a preparation method and remediation method thereof. The soil conditioner of the present invention mainly uses urban domestic garbage and waste as raw materials, turns waste into treasure, and then applies it to soil pollution remediation, realizing waste recycling, not only cleaning up waste, but also remediating pesticide and heavy metal pollution in the soil at the same time.

Description

Soil conditioner for restoring heavy metal-pesticide composite pollution and application thereof

Technical Field

The invention relates to the technical field of soil pollution remediation, in particular to a soil conditioner for heavy metal-pesticide composite polluted soil remediation and a preparation and remediation method thereof.

Background

Soil is easy to acidify and activate heavy metals after long-term fertilization, and in order to ensure the quality of vegetables, the pesticide application amount of farmers is large, so that the pesticide residue content in vegetable soil is relatively high. Most pesticides can enter vegetable soil and form short-term or long-term residues. In addition, unreasonable use of fertilizers and organic fertilizers also results in heavy metals becoming a common contaminant in vegetable fields. At present, vegetable soil heavy metal-pesticide composite pollution becomes a common pollution form, and because complex interaction exists between heavy metal and pesticide, and the repairing mechanisms are different, effective treatment is not performed, and accumulation of toxic and other harmful substances can cause great influence on human health and soil environment. The hosting and behavior of pesticides in the soil is dependent on the physicochemical properties of the pesticide, the nature of the soil and the surrounding environmental conditions. In addition, the rate, frequency and route of application of the pesticide also determines the formation of pesticide residues in the soil. However, most of the existing researches on contaminated vegetable fields are still focused on single pollutant researches, and the research on the repair technology of heavy metal-pesticide composite contaminated soil is less. Therefore, the method has important significance in the aspects of ensuring ecological environment, human health and the like when effectively adopting technical measures to treat the heavy metal-high-residue pesticide composite polluted soil.

The iron-carbon-based restoration material, the preparation method and the use method thereof are developed for the soil which is related to organic matter-heavy metal composite pollution by the prior researchers, and the iron-carbon-based restoration material in China patent application CN 115011352A comprises the following components: iron-carbon based composite material, pH adjuster, oxidant and adsorption auxiliary; the iron-carbon-based composite material comprises a biochar-nano zero-valent iron composite material and an iron-based oxide-hydrothermal carbon composite material. The iron-carbon-based restoration material utilizes the synergistic effect among the components to simultaneously solidify and stabilize the heavy metals in the composite polluted soil, and can reduce the leaching concentration of the heavy metals, thereby further reducing the mobility of the heavy metals, and also can oxidize and decompose the organic matters in the polluted soil, and has restoration effect on various organic matters and heavy metal composite polluted soil. According to the method, organic pollutants in soil are degraded and adsorbed and removed simultaneously through the synergistic effect of various components, but the addition of a large amount of oxidants and other substances has an influence on soil health and organic matter protection, and the method is not suitable for vegetable soil with production functions.

CN 115532816a discloses a method for promoting the rapid degradation of an organochlorine and organophosphorus pesticide in soil. The method comprises the following steps: firstly preparing a soil restoration agent, and then applying the soil restoration agent to soil polluted by organic chlorine and organic phosphorus pesticides at different depths from the soil surface. The soil restoration agent contains a composite microbial agent, a soil improvement agent, a microbial carrier and nano iron powder, wherein the composite microbial agent can simultaneously degrade organic chlorine and organophosphorus pesticides in soil; under the synergistic effect of the soil conditioner, the microbial carrier and the nano iron powder, microbial thalli stably survive and reproduce, and the continuous normal operation of the organic chlorine and organic phosphorus degradation reaction is ensured; the soil restoration agent is applied in multiple layers according to different depths, so that organic chlorine and organic phosphorus pesticides in soil can be degraded in multiple layers and more comprehensively, and the soil can be restored more thoroughly. The remediation method has the advantages that the flora has more severe requirements on soil, and the pollution is simultaneously recovered by heavy metal pollution and the production task of safely and high quality vegetable soil is realized.

At present, aiming at the composivity and diversity of the heavy metal-pesticide pollution of vegetable fields, a conditioner and a restoration method which are low in cost, easy to obtain, convenient to use, environment-friendly, efficient and capable of guaranteeing the safe and high-quality production of the vegetable fields with the heavy metal-pesticide compound pollution are provided, and the technical problem to be solved by the person skilled in the art is still needed.

Disclosure of Invention

The invention aims at solving the problems and provides a soil conditioner for restoring heavy metal-pesticide composite polluted soil and a preparation and restoration method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

the first aspect of the invention provides a preparation method of a soil conditioner for restoring heavy metal-pesticide composite polluted soil, which comprises the following steps:

S1, preparing a silicon-based carbon isomer:

S1.1, preparing silicon-based biochar: 10-20 parts of animal and plant biomass waste and 3-5 parts of construction waste are put into a pulverizer to be pulverized into particles, so as to obtain a mixed material; then spraying silicate solution with the concentration of 0.1-0.5M into the obtained mixed material, wherein the volume-mass ratio of the silicate solution to the mixed material is 20-50 mL:1000g; then placing the mixed material sprayed with the silicate solution into a hydrothermal reactor, and fully reacting at 210-270 ℃ to obtain the silicon-based biochar;

s1.2, preparing a silicon-based carbon isomer: mixing the prepared silicon-based biochar with a cross-linking agent solution with the concentration of 8-12 g/L according to the mass ratio of 30-45:5-10, and fully reacting to obtain silicon-based carbon isomer;

The animal and plant biomass waste comprises: plant biomass waste and animal biomass waste;

the construction waste comprises waste bricks, cement blocks, sand, waste ceramic tiles, lime and the like;

The cross-linking agent is selected from polyacrylamide, epoxy resin, polytriallyl isocyanate, acrylic acid, hydroxyethyl acrylate, methacrylic acid and hydroxypropyl methacrylate;

s2, preparing alkali activated electrolytic manganese slag:

mixing electrolytic manganese slag and an alkali activator according to the mass ratio of 10:1-2, uniformly mixing, calcining and activating at a high temperature of 500-750 ℃, cooling and crushing into particles to obtain alkali activated electrolytic manganese slag;

s3 preparation of soil conditioner

Fully mixing 30-45 parts by weight of the silicon-based carbon isomer prepared in the step S1, 15-20 parts by weight of alkali activated electrolytic manganese slag and 8-12 parts by weight of effervescent disintegrating agent, and drying to prepare a granular soil conditioner;

The effervescent disintegrating agent comprises an acid source and an alkali source, wherein the molar ratio of the acid source to the alkali source is 1: (0.8-1.3); the acid source is selected from the group consisting of citric acid, salicylic acid, tartaric acid, caffeic acid, malic acid, and fumaric acid; the alkali source is selected from one or more of NaHCO ₃、K₂CO₃、Na₂CO₃、Ca(HCO3)2、KHCO₃ and CaCO ₃.

Preferably, in the preparation method, the following steps are adopted:

The silicate is sodium silicate or potassium silicate;

the alkali activator is selected from potassium hydroxide, sodium hydroxide and calcium oxide;

the animal and plant biomass waste is used for preparing biochar;

The plant biomass waste comprises plant residues, crop straws, weeds, branches, leaves, wood chips, bamboo chips, sawdust, pericarps and fruit pits;

The animal biomass waste comprises livestock slaughter waste, seafood food waste, animal carcasses and animal feces.

Preferably, in step S1.1, the animal and plant biomass waste and the construction waste are crushed to pass through a 10-mesh sieve; the concentration of the silicate solution is 0.1-0.3M; the hydrothermal reactor is a microwave supercritical reactor; placing the mixed material sprayed with the silicate solution into a hydrothermal reactor, and performing an activation reaction for 1-2 hours at 210-270 ℃ to obtain silicon-based biochar;

S1.2, preparing a silicon-based carbon isomer: and (3) reacting the prepared silicon-based biochar with a cross-linking agent solution for 16-18 h under the environmental condition that the volume ratio of protective gas (such as nitrogen) to oxygen is 80% -100% to 0-20%, so as to prepare the silicon-based carbon isomer.

In the step S2, the electrolytic manganese slag and the alkali activator are calcined for 1-2 hours at 500-750 ℃, cooled and ground into 200-300 mesh particles;

And in the step S3, drying the silicon-based carbon isomer, the alkali-activated electrolytic manganese slag and the effervescent disintegrating agent at 60-75 ℃ for 1.5-2 hours, and then putting the dried silicon-based carbon isomer, the alkali-activated electrolytic manganese slag and the effervescent disintegrating agent into a granulator to prepare the granular soil conditioner.

The second aspect of the invention provides a soil conditioner for restoring heavy metal-pesticide composite polluted soil, which is prepared by adopting the method of any one of the above steps.

Preferably, the particle diameter of the soil conditioner is 2 mm-5 mm, and the mass of single particles is 0.2-0.8 g.

The third aspect of the invention provides an ectopic remediation method for heavy metal-pesticide composite contaminated soil, which comprises the following steps: taking heavy metal-pesticide composite polluted soil, adding the soil conditioner, uniformly mixing, adding water for curing for 7-20 days, and keeping the water content of the soil to be 50-70% of the field water holding capacity during the curing period; the addition amount of the soil conditioner is 0.5-5% or 0.5-3% or 0.5-1% or 1-3% of the mass of the polluted soil, and the soil conditioner is preferably added and then water is added for maintenance for 10-20 days.

The fourth aspect of the invention provides an in-situ remediation method for heavy metal-pesticide composite contaminated soil, which adopts the soil conditioner to remedy the soil and comprises the following steps:

applying a soil conditioner into heavy metal-pesticide composite polluted soil according to the application amount of 0.2 kg-0.5 kg/m ², and then watering for maintenance, wherein the water content of the soil is kept to be 50-70% of the field water holding capacity of the soil during the maintenance period, and the maintenance treatment time is more than or equal to 7 days, preferably 10-20 days or 14-20 days; preferably, the repair is carried out under weather conditions of 0 to 40 ℃.

In the in-situ restoration method, the soil conditioner is applied by a broadcast application method, a hole application method or a columnar irrigation method, and the specific method is as follows:

Broadcasting: sprinkling a soil conditioner into vegetable fields, and then rotary tillage the fields by adopting a rotary cultivator to mix the soil conditioner uniformly; the rotary cultivator has a rotary cultivation depth of 10-20 cm.

Hole application: applying the soil conditioner into the holes, and then covering the soil conditioner by covering soil, wherein the depth of the holes is 10-20 cm;

columnar irrigation: the soil is perforated, and the soil conditioner is applied to the soil at a depth of 5-10 cm.

Preferably, 20 to 30 holes are dug per square meter of land during hole application, and 10 to 20 holes are punched per square meter of land during columnar irrigation;

preferably, the dosage of the soil conditioner is 0.5kg/m ²; the field water holding capacity is 70% during maintenance; the curing temperature is 20-28 ℃.

The beneficial effects of the invention are as follows:

The soil conditioner mainly uses municipal domestic waste and waste as raw materials, changes waste into valuable, and is applied to soil pollution restoration to realize recycling of the waste, namely, the waste is cleaned, and the polluted soil is restored. The soil conditioner takes a silicon-based biochar material as a carrier, and silicon hydroxyl groups rich in the structure of the silicon-based biochar material are crosslinked with a crosslinking agent after the silicon-based biochar material is activated to prepare silicon-based carbon isomers; the animal and plant biomass waste plays a role in serving as a biochar source, the urban building waste mainly provides minerals such as calcium oxide and silicate for the conditioner, and has a promoting effect on the granulating and forming process of the soil conditioner, and in addition, a green path is provided for the treatment and disposal of the urban building waste, the minerals in the building waste are released into the soil to have a stronger passivation effect on heavy metals, and the recycling of the waste also reduces the exploitation of mineral resources.

The silicon-based carbon isomer bridges alkali modified electrolytic manganese slag, and the effervescent disintegrating agent is embedded into the silicon-based carbon isomer through coordination compounding to form the soil conditioner. The soil conditioner is directly applied to the soil, moisture is absorbed in the maintenance process to disintegrate and effervesce, on one hand, gas production forms a loose and porous structure in the soil, and on the other hand, active reaction components (including active silicon, colloidal biochar, iron oxide, manganese oxide and the like in modified electrolytic manganese slag) are released, silicon-based carbon isomers form multiple adsorption sites in the soil, the adsorption effect on heavy metals in the soil is enhanced, and the released alkaline modified electrolytic manganese slag has the effects of removing and degrading pesticides in the soil: on one hand, iron oxide and manganese oxide in the alkali modified electrolytic manganese slag react with organic pollutants such as pesticides in soil, and the generation of non-free radical substances (hydrogen peroxide and singlet oxygen, 1O ₂) is promoted, so that the alkaline modified electrolytic manganese slag shows outstanding pesticide degradation performance in the soil; on the other hand, when the sun is illuminated, the ferromanganese composite mineral structure can initiate oxidation-reduction reaction in the soil electron storage place, so that a large amount of free radicals OH and superoxide (O ₂·^-) are generated through a double electron oxygen reduction way, and the free radicals can promote the removal and degradation of pesticides in the soil. Therefore, the soil conditioner disclosed by the invention can be used for simultaneously repairing heavy metal and pesticide pollution in soil.

The soil conditioner disclosed by the invention improves the characteristics of the gas environment, conductivity, pore structure and the like of the crop root soil, promotes the absorption of crops to nutrients such as nitrogen, phosphorus, potassium and the like, realizes the optimization of soil properties, and simultaneously improves the yield and quality of crops.

The soil conditioner disclosed by the invention is low in cost and easy to obtain, simple in preparation method, convenient to use, environment-friendly and good in pollution remediation effect.

Drawings

Fig. 1 is a physical diagram of sample 5, sample 10 and sample 15.

Fig. 2 is an SEM characterization of sample 5.

FIG. 3 observations of the surface condition of soil conditioner applied in soil.

Detailed Description

The invention is further illustrated, but is not limited, by the following examples.

The experimental methods in the following examples are conventional methods unless otherwise specified.

Main materials and raw material sources:

Electrolytic manganese slag: is a solid waste generated in the production process of electrolytic manganese metal. The method mainly comprises manganese slag generated by solid-liquid separation after ore acid leaching and sulfide slag generated in the purifying and impurity removing process. These wastes contain higher concentrations of elements such as manganese, iron, silicon, etc. The experimental electrolytic manganese slag in the embodiment of the invention is purchased from Shaoguan City, corp. And ecological environmental protection technology Co.

Silicate solution preparation: silicate (sodium silicate or potassium silicate) is dissolved in water to prepare an aqueous solution.

Preparing a cross-linking agent solution: the cross-linking agent is dissolved in water to prepare an aqueous solution.

EXAMPLE 1 preparation of soil conditioner of the present invention

The preparation method of the soil conditioner comprises the following steps:

S1, preparing a silicon-based carbon isomer:

S1.1, preparing silicon-based biochar: 10-20 parts of animal and plant biomass waste and 3-5 parts of construction waste are put into a pulverizer to be pulverized, and then dried and screened by a 10-mesh sieve to obtain a mixed material; then spraying silicate (sodium silicate or potassium silicate) with concentration of 0.1M into the mixture with concentration of 20-50 mL to 1000 g; then placing the mixed material sprayed with the silicate solution into a microwave supercritical reactor, and activating and reacting for 1-2 hours at 210-270 ℃ to obtain the silicon-based biochar.

S1.2, preparing a silicon-based carbon isomer: mixing the silicon-based biochar with a cross-linking agent solution (the concentration is 10 g/L) according to the mass ratio of 30-45:5-10, and reacting for 16-18 h in a three-way reactor under the environmental condition of the volume ratio of nitrogen to oxygen (10:1) to obtain the silicon-based carbon isomer. Because part of the crosslinking agent is unstable in nature and is easily oxidized in the natural environment, the reaction atmosphere is regulated to reduce the oxidation, and the oxygen concentration is reduced, so that the reaction is carried out in the atmosphere mainly of inert gas.

The animal and plant biomass waste comprises: plant biomass waste and animal biomass waste. Plant biomass waste includes plant residues (e.g., waste from the end vegetables), crop stalks, weeds, branches, leaves, wood chips, bamboo chips, sawdust, fruit peel, pit, and the like. The animal biomass waste comprises livestock slaughter waste, seafood food waste (such as shrimp shell, crab shell, fish skin and scale, etc.), animal carcasses, animal feces, etc.

Construction waste includes waste bricks, cement blocks, sand (e.g., river sand), waste tiles, etc., lime, etc.

The cross-linking agent is one of polyacrylamide, epoxy resin, poly-triallyl isocyanurate, acrylic acid, hydroxyethyl acrylate, methacrylic acid and hydroxypropyl methacrylate.

S2, preparing alkali activated electrolytic manganese slag:

mixing electrolytic manganese slag and an alkali activator according to the mass ratio of 10:1-2, and uniformly mixing by a mixer to obtain pretreated electrolytic manganese slag; and (3) carrying out high-temperature calcination on the pretreated electrolytic manganese slag, wherein the calcination temperature is 500-750 ℃, the calcination time is 1h, cooling, and grinding the pretreated electrolytic manganese slag to pass through a 200-300 mesh sieve by a ball mill to obtain the alkali activated electrolytic manganese slag.

The alkali activator is one or more of potassium hydroxide, sodium hydroxide and calcium oxide.

S3 preparation of the soil conditioner of the invention

And (2) fully mixing 30-45 parts by weight of the silicon-based carbon isomer prepared in the step (S1), 15-20 parts by weight of alkali-activated electrolytic manganese slag and 8-12 parts by weight of effervescent disintegrating agent, drying at 60 ℃ for 2 hours, and then placing into a granulator to prepare the granular soil conditioner, wherein the particle diameter of the conditioner is 2-5 mm, and the mass of single particle is about 0.2-0.8 g.

The effervescent disintegrating agent comprises an acid source and an alkali source, wherein the molar ratio of the acid source to the alkali source is 1: (0.8-1.3); the acid source is one or more selected from citric acid, salicylic acid, caffeic acid, tartaric acid, malic acid and fumaric acid (fumaric acid); the alkali source is selected from one or more of NaHCO ₃、K₂CO₃、KHCO₃ and CaCO ₃.

Samples 1-25 of soil conditioner were prepared as described above, with the raw materials used for each sample being specifically shown in Table 1, and the raw material ratios and process parameters being shown in Table 2. The silicate used in samples 1-12 was sodium silicate and the silicate used in samples 13-25 was potassium silicate.

TABLE 1

* And (3) injection: the various mixtures of construction waste in table 1 are mixtures of waste bricks, cement blocks, sand, and waste tiles.

And measuring performance parameters of the prepared soil conditioner, including the pH value of the soil conditioner, the content of heavy metal Cd, as, pb, cr, hg and the like, and evaluating the safety of the soil conditioner. Heavy metal content determination: 0.2g of the sample is placed in a digestion tank pretreated by 10% nitric acid, 10ml of diluted aqua regia is added to ensure that the sample is completely removed and pre-reacted for 10min, and then the digestion tank is placed in a digestion instrument (MARS, USA) for digestion. The digestion temperature is set to 200 ℃, the digestion time is 20min, the digestion tank is taken out after the complete digestion, the digestion tank is cooled, the pipe wall is rinsed with ultrapure water, about 10mL of ultrapure water is added, the digestion tank is kept stand for 30min, filtered and transferred to a centrifuge pipe, the volume is fixed to 5mL, and an inductively coupled plasma mass spectrometer (ICP-MS) is used for measuring the metal content of Cd, as, pb, cr, hg and the like.

As can be seen from table 2, the prepared soil conditioner product is slightly alkaline, which is favorable for improving acid soil, and in addition, the content of heavy metals in a series of prepared passivating agents is lower than the 'soil pollution risk management and control standard (trial) of agricultural land with soil environment quality' (GB 15618-2018), which indicates that the soil conditioner prepared by utilizing waste meets the agricultural requirement.

The soil conditioner disclosed by the invention is different from the prior powdery conditioner in appearance analysis, uniform in particles, favorable for broadcasting the soil conditioner, and darker in color under the condition of higher animal and plant biomass waste addition, and is related to more generated carbon materials. By further microstructural characterization analysis of the soil conditioner, the conditioner contains carbon material, which is similar to the pure biochar structure reported by other inventions, and additionally, the conditioner is rough in appearance as a whole due to the presence of the cross-linking agent and the effervescent agent, which can provide more active sites for contaminant reaction.

Table 2 analysis of soil conditioner product properties

* And (3) injection: in Table 2, the mass ratio of A to B to C in the column of "S1 material ratio parameter" means the mass ratio of kitchen waste, garden waste and construction waste in Table 1, and the volume in brackets means the volume of silicate solution of 0.1M concentration used per 1000g of the mixture in step S1.1. For example, in sample 1, the mass ratio of 5:5:3 refers to the mass ratio of cabbage refuse, branches and cement blocks, and 20ml of silicate solution with the concentration of 0.1M is used for each 1000g of the mixture of cabbage refuse, branches and cement blocks; samples 2-25 and so on. And S3, the material proportion parameter refers to the mass ratio of the silicon-based carbon isomer and the alkali-activated electrolytic manganese slag to the effervescent disintegrating agent.

Example 2

1. Soil culture experiment

Sample 5, sample 10 and sample 15 were selected from example 1 for use in soil culture experiments. FIG. 1 is a pictorial view of sample 5, sample 10 and sample 15; fig. 2 is an SEM characterization of sample 5.

Soil is collected from degenerated vegetable fields (namely pesticide-heavy metal polluted and soil acidized soil) for a soil culture experiment, the pH and heavy metal Cd, as, pb, cr and Hg content of the soil are measured after natural air drying, and meanwhile the residual content of pesticide in the soil is analyzed to evaluate the safety of the soil.

The heavy metal content detection method is carried out according to the technical Specification for soil environmental monitoring (HJ/T166-2004).

The content of organophosphorus pesticides was determined using a triple four-bar gas chromatograph-mass spectrometer, with reference to Zhangqing (Zhang Chaoqing, guangdong chemical, 2023,50 (16): 185-188). The determination of the neonicotinoid pesticide paichongding adopts a solid phase extraction-high performance liquid chromatography method for detection.

The detection result is as follows: the pH of the test soil was 5.24, the ω (Cd) of the soil was 2.32mg/kg, ω (Cr) was 85mg/kg, ω (Pb) was 444mg/kg, ω (Hg) was 0.170mg/kg, and ω (As) was 154mg/kg.

Soil culture experiment: weighing 50g of degenerated vegetable field soil sample, placing the degenerated vegetable field soil sample into a beaker, adding sample 5, sample 10 and sample 15 into the soil sample according to the dosage ratio of (0%, 0.5%, 1% and 3%, w/w), fully and uniformly mixing the soil sample and the soil conditioner sample, adding deionized water for maintenance, keeping the water content of the soil to be 70% of the field water holding capacity during maintenance, observing the gas production condition of the soil surface, and sampling for analysis of related indexes after 14d of soil maintenance treatment. On the one hand, the basic physicochemical properties of the soil are measured, and on the other hand, the effective state of the heavy metals in the soil and the residual quantity of the soil pesticides are measured.

2. Soil conditioner performance test

1. Measurement method

The measurement of the pH value of the soil was carried out by using the standard "potential measurement method for pH value of soil" (HJ 962-2018).

The heavy metal content of soil is measured by a method in soil environment monitoring technical Specification (HJ/T166-2004), 0.5g of soil sample is weighed and placed in a tetrafluoroethylene digestion tube, the tetrafluoroethylene digestion tube is inserted into a digestion hole of an intelligent graphite digestion instrument, 10ml of concentrated HCl is added after a few drops of water are wetted, 15ml of concentrated nitric acid is added when the controller sets low-temperature (80-100 ℃) heating evaporation to about 5ml, heating is continued (100-120 ℃) until the soil sample is sticky, 10ml of hydrofluoric acid is added until the soil sample is heated to 120 ℃, and the digestion tube is timely shaken. 5ml of perchloric acid was added and heated (130 ℃) until the white smoke had been exhausted, and the decomposition product was white or pale yellow viscous substance. After cooling, the inner wall and the digestion tube cover of the digestion tube were rinsed with a dilute acid solution (10% nitric acid), the residue was dissolved by warming, and after cooling, the volume was set to 50ml, and analysis was performed by ICP-MS.

The effective state of the soil heavy metals was extracted with 0.01M CaCl ₂, a soil sample (2.0 g) was extracted with 0.01M CaCl ₂ at a ratio of 1:5, then stirred at 25℃for 2 hours, centrifuged, filtered through 0.45 μm aqueous filter, and analyzed by ICP-MS.

The content of organophosphorus pesticides was determined using a triple four-bar gas chromatograph-mass spectrometer, with reference to Zhangqing (Zhang Chaoqing, guangdong chemical, 2023,50 (16): 185-188).

The determination of the neonicotinoid pesticide paichongding adopts a solid phase extraction-high performance liquid chromatography method for detection: the determination is made with reference to the method in Bolli et al (Bolli et al. Agricultural environmental sciences. Https:// link. Cnki. Net/urlid/12.1347. S.20240227.1639.004).

The contents of quick-acting potassium, available phosphorus, organic matters and total nitrogen in the soil are measured by referring to the method in soil agrochemical analysis method (Lu Rukun main code).

2. Experimental results

The experimental result of soil culture shows that a large amount of bubbles are generated on the surface (shown in figure 3) of the soil after the soil is added with the soil conditioner, the bubbles are related to bubbles generated by the reaction of effervescent substances in the soil conditioner, the bubbles carry active components in the soil conditioner, including active silicon, iron and manganese oxides with high reactivity, calcium, magnesium, biochar particles and the like, and the active components in the soil react with heavy metals and pesticides in a contact manner, on one hand, substances such as biochar particles, active silicon, silicate minerals, iron and manganese and the like in the soil conditioner can react with free heavy metals directly to form more stable heavy metals, so that the bioavailability of the heavy metals in the soil is reduced, and the passivation of the heavy metals is realized; in addition, the ferro-manganese oxidizable substances in the electrolytic manganese slag can react with pesticides in the soil through the generation of non-free radicals (H ₂O₂ and 1O ₂) and free radicals (OH and superoxide (O ₂·^-), so that the content of residual pesticides in the soil is removed or reduced, the repair of heavy metal-pesticide polluted soil is realized, and the generated carbon dioxide gas can be used as a gaseous fertilizer for crop plants to supply for plant growth.

From table 3 it can be seen that applying samples 5, 10 and 15 all significantly increased the nutrient content in the soil, mainly because the raw materials for preparing the soil conditioner are rich in nutrients and contain higher organic carbon. On the basis of supplying nutrients to the soil, the effective state content of heavy metals in the soil is obviously reduced along with the increase of the broadcast dosage (table 4), mainly because the carbon materials in the soil conditioner can effectively adsorb the heavy metals, and the alkaline active materials which are additionally rich and the released silicon-based carbon isomers form multiple adsorption sites in the soil, so that the pH of the soil can be effectively improved, and the movable and dynamic heavy metals can be converted into stable states. Compared with the control, the soil organophosphorus removal rate and the paichongding removal rate of the soil conditioner are remarkably improved (table 4), and the alkaline modified electrolytic manganese slag released by the soil conditioner is mainly used for strengthening the dispersion process of pesticides in the soil and promoting the conversion of the pesticides, wherein the alkaline modified electrolytic manganese slag is mainly used for promoting the conversion of the pesticides due to the fact that electrons are transferred from naturally abundant reduced iron manganese minerals in the electrolytic manganese slag to oxygen, mineral compositions with different contents have strong effects on the generation of superoxide (O ₂ -), hydrogen peroxide (H ₂O₂) and hydroxyl free radicals (OH), the spontaneous generation of OH is caused by the Fenton-like activation of contact electrification and hydrogen peroxide (H ₂O₂) at a mineral interface in the water-electrolytic manganese slag, and the generation of the free radicals can greatly influence the conversion process of residual pesticides in the soil.

Table 3 effect of soil conditioner application on soil nutrients

TABLE 4 Effect of soil conditioner application on soil heavy metal availability

Example 3 vegetable field experiment

1. Experimental method

Sample 5 of example 1 was used to develop a field test, the test soil was the soil sampling soil of example 2, and the prepared soil conditioner was applied to the degraded vegetable soil by broadcasting, hole-application or column-irrigation at a rate of 0.5kg/m ².

And (3) broadcasting treatment: according to the dosage of 0.5kg/m ², the soil conditioner is scattered into vegetable fields, and then the rotary cultivator is adopted to rotary tillage the soil so as to mix the soil conditioner uniformly; the rotary cultivator has a rotary cultivation depth of 10-20 cm.

Hole application treatment: the soil conditioner was applied to the wells and then covered with soil, calculated as 0.5kg/m ² of soil per well. Digging 20-30 holes per square meter of land, wherein the depth of each hole is 10-20 cm.

Columnar irrigation: the hand-held earth auger is used for punching holes on the ground, 10 to 20 holes are punched in each square meter of the ground, the application depth of the soil conditioner is 5 to 10cm, and the application amount of each hole is calculated according to the application amount of the soil conditioner of 0.5kg/m ².

And curing the soil after the soil conditioner is applied, wherein the water content of the soil during the soil curing is 70% of the field water holding capacity of the soil. At the same time, a control group was set, and no soil conditioner application was performed.

The amaranth is planted after the soil is maintained for 10 days, the amaranth is planted in a sowing mode, the planting process follows daily management, the amaranth is harvested after 30 days, and amaranth and soil samples are collected in the amaranth harvesting stage.

2. Soil sample analysis

After the amaranth is harvested, the soil of the vegetable field is collected, and the effective state content of heavy metals and the residual quantity of pesticides in the soil are analyzed according to the method of the example 2.

The results are shown in Table 5, the effective state content of heavy metals in soil can be effectively reduced by different methods of applying the soil conditioner, and the transformation of pesticides (organophosphorus pesticides and paichongding) in the soil can be synchronously and synergistically promoted. Although the hole and columnar pot methods do not come into full contact with all of the soil, the effervescing agent acts to carry the active components of the soil conditioner (e.g., active silicon, biochar particulates, ferro manganese oxides, etc., and non-radicals and radicals generated, etc.) to the soil-pollutant interface, including solidification to stabilize heavy metals and enhance the pesticide dissipation (including removal, volatilization, degradation, etc.) process during the soil maintenance phase.

TABLE 5 Effect of soil conditioner application on soil heavy metals and pesticides

3. Amaranth assay

Sampling during the harvest period of the amaranth, randomly selecting 5 plants, digging out, cleaning with tap water, drying, and measuring the dry weight of the amaranth root system and the upper part of the root. Analyzing and measuring the yield of amaranth, the residual quantity of pesticide on stems and leaves and the content of enriched heavy metals.

As shown in table 6, after the soil conditioner was applied, the content of heavy metals in the stem and leaf parts of amaranth was significantly reduced, and the concentration of agricultural chemicals in the stem and leaf was also significantly reduced, which was lower than the limit specified in the limit of pollutants in food safety national Standard food (GB 2762-2022).

Table 6 effect of soil conditioner application on amaranth

Claims

1. A method for preparing a soil conditioner for remediation of heavy metal-pesticide composite contaminated soil, characterized in that it comprises the following steps:

S1 Preparation of silicon-based carbon isomers:

S1.1 Preparation of silicon-based biochar: 10-20 parts of animal and plant biomass waste and 3-5 parts of construction waste are placed in a pulverizer and crushed into particles to obtain a mixed material; then a silicate solution with a concentration of 0.1-0.5M is sprayed into the obtained mixed material, and the volume mass ratio of the silicate solution to the mixed material is 20-50mL:1000g; then the mixed material sprayed with the silicate solution is placed in a hydrothermal reactor, and fully reacted at 210-270°C to obtain silicon-based biochar;

S1.2 Preparation of silicon-based carbon isomers: The prepared silicon-based biochar and a cross-linking agent solution with a concentration of 8 to 12 g/L are mixed in a mass ratio of 30 to 45:5 to 10, and the mixture is fully reacted to obtain silicon-based carbon isomers;

The plant and animal biomass waste includes: plant biomass waste and animal biomass waste;

The construction waste includes waste bricks, cement blocks, sand and gravel, waste tiles, and lime;

The crosslinking agent is selected from polyacrylamide, epoxy resin, polytriallyl isocyanurate, acrylic acid, hydroxyethyl acrylate, methacrylic acid, hydroxypropyl methacrylate;

S2 Preparation of alkaline activated electrolytic manganese slag:

The electrolytic manganese slag and the alkali activator are mixed in a mass ratio of 10:1-2, and then calcined at high temperature for activation at a temperature of 500°C-750°C. After cooling, the slag is crushed into particles to obtain alkali-activated electrolytic manganese slag.

S3 Preparation of soil conditioner

Fully mix 30-45 parts by weight of the silicon-based carbon isomer prepared in step S1, 15-20 parts by weight of alkali-activated electrolytic manganese slag, and 8-12 parts by weight of an effervescent disintegrant, and dry them to prepare a granular soil conditioner;

The effervescent disintegrant comprises an acid source and an alkali source, wherein the molar ratio of the acid source to the alkali source is 1:(0.8-1.3); the acid source is selected from citric acid, salicylic acid, tartaric acid, caffeic acid, malic acid and fumaric acid; the alkali source is selected from one or more of NaHCO ₃ , K ₂ CO ₃ , Na ₂ CO ₃ , Ca(HCO 3 ) 2 , KHCO ₃ and CaCO ₃ .

2. The preparation method according to claim 1, characterized in that:

The silicate is sodium silicate or potassium silicate;

The alkaline activator is selected from potassium hydroxide, sodium hydroxide, and calcium oxide;

The animal and plant biomass waste is used to prepare biochar;

The plant biomass waste includes plant residues, crop straw, weeds, branches, leaves, wood chips, bamboo chips, sawdust, fruit peels, and fruit cores;

The animal biomass waste includes livestock and poultry slaughter waste, seafood food waste, animal carcasses, and animal feces.

3. The preparation method according to claim 1, characterized in that:

In step S1.1, animal and plant biomass waste and construction waste are crushed to pass through a 10-mesh sieve; the concentration of the silicate solution is 0.1-0.3M; the hydrothermal reactor is a microwave supercritical reactor; the mixed material sprayed with the silicate solution is placed in the hydrothermal reactor, and after activation reaction at 210-270° C. for 1-2 hours, silicon-based biochar is obtained;

S1.2 Preparation of silicon-based carbon isomers: The prepared silicon-based biochar is reacted with a cross-linking agent solution under environmental conditions with a protective gas: oxygen volume ratio of 80% to 100% to 0 to 20% for 16 to 18 hours to obtain silicon-based carbon isomers.

4. The preparation method according to claim 1, characterized in that:

In step S2, the electrolytic manganese slag and the alkaline activator are calcined at 500° C. to 750° C. for 1 to 2 hours, and ground into 200 to 300 mesh particles after cooling;

In step S3, the silicon-based carbon isomer, the alkali-activated electrolytic manganese slag and the effervescent disintegrant are dried at 60-75° C. for 1.5-2 hours and then placed in a granulator to prepare a granular soil conditioner.

5. A soil conditioner for remediation of soil contaminated by heavy metals and pesticides, characterized in that it is prepared by the method described in any one of claims 1 to 4.

6. The soil conditioner according to claim 5, characterized in that the particle diameter of the soil conditioner is 2 mm to 5 mm, and the mass of a single particle is 0.2 to 0.8 g.

7. A method for ex situ remediation of heavy metal-pesticide composite contaminated soil, characterized in that it comprises the following steps: taking heavy metal-pesticide composite contaminated soil, adding the soil conditioner according to claim 5 or 6, mixing, adding water for curing for 7 to 20 days, and maintaining the soil moisture content at 50 to 70% of the field water holding capacity during the curing period; the amount of soil conditioner added is 0.5 to 5% or 0.5 to 3% or 0.5 to 1% or 1 to 3% of the mass of the contaminated soil, preferably adding water after adding the soil conditioner for curing for 10 to 20 days.

8. An in-situ remediation method for heavy metal-pesticide composite contaminated soil, characterized in that the soil conditioner according to claim 5 or 6 is used for remediation, comprising the following steps:

The soil conditioner is applied at a dosage of 0.2kg to 0.5kg/ ^m2 into the heavy metal-pesticide composite contaminated soil, and then watered for maintenance. During the maintenance period, the soil moisture content is maintained at 50-70% of the soil field water holding capacity. The maintenance treatment time is ≥ 7 days, preferably 10-20 days or 14-20 days; preferably, the remediation is carried out under weather conditions of 0-40℃.

9. The in-situ remediation method according to claim 8, characterized in that the soil conditioner is applied by broadcasting, hole application or column irrigation, and the specific method is:

Spreading: Spread the soil conditioner into the vegetable field, and then use a rotary tiller to till the land to mix the soil conditioner; the tillage depth of the rotary tiller is 10 to 20 cm.

Hole application: Apply the soil conditioner into the hole, then cover it with soil, the hole depth should be 10-20cm;

Column irrigation: Drill holes in the ground and apply the soil conditioner to a depth of 5 to 10 cm.

10. The in-situ repair method according to claim 8, characterized in that: when applying the fertilizer in holes, 20 to 30 holes are dug per square meter of land, and when applying the fertilizer in columnar form, 10 to 20 holes are drilled per square meter of land;

The preferred amount of soil conditioner is 0.5 kg/m ² ; the field water holding capacity during the curing period is 70%; and the curing temperature is 20-28°C.