Silicon-sulfur-iron-based synergistic passivation of heavy metal composite contaminated soil remediation materials and methods

Abstract

The present application provides a silicon-sulfur-iron-based cooperative heavy metal compound contaminated soil remediation material and method, which comprises: basalt powder and binary compound passivation material; the binary compound passivation material is a mixture of ball-milled sulfidized hematite and hydro ferrite modified biomass charcoal. The basalt powder and the binary compound passivation material are used cooperatively before and after, which can comprehensively and efficiently passivate cadmium, lead, zinc and other heavy metals in the soil, can provide a passivation effect of 3-5 years, is long-acting and stable, the raw materials for preparation are all natural minerals or agricultural and forestry waste, is environment-friendly, can supplement beneficial elements such as silicon, calcium, magnesium and iron in the soil after application, is beneficial to improve the soil microenvironment, and has simple preparation process, low cost, easy to scale industrial production and popularization.

Description

Technical Field

[0001] This invention relates to the field of soil remediation materials, and in particular to remediation materials and methods for silicon-sulfur-iron-based synergistic passivation of heavy metal-contaminated soil. Background Technology

[0002] During mining, wastewater discharge, tailings and waste rock accumulation, chemical smelting, and leaching lead to the enrichment of heavy metals in the soil of mining areas and surrounding regions. The "National Soil Pollution Status Survey Bulletin" indicates that a significant portion of the polluted soil is located in areas with high geological backgrounds. Generally, while the total heavy metal content in soils with high geological backgrounds is relatively high, it is mostly present in the form of iron and manganese oxides in a bound or residual state, with relatively low overall activity. The main enriched elements in background soils are Cd and As. According to investigations by relevant scholars, the Cd content in red clay formed from carbonate rocks is 0.164-0.276 mg / kg, and the As content is 12.73-13.42 mg / kg, followed by Pb, Zn, Cr, Hg, Cu, Ni, etc. Figure 1 The figure is cited from: Li Yanan, Xia Xueqi, Yang Zhongfang, et al., High background of heavy metals in carbonate rock-developed soils: formation factors and risk characteristics [J]. China Environmental Science, 2026, 46(1): 11-19. For example, although Cd and As have different geochemical properties, Cd is mainly enriched by clay minerals and iron-manganese oxides after dissolution of carbonate minerals, while As is retained by forming stable complexes with iron-manganese oxides. The strong weathering under the hot and humid climate of Southwest China promotes the dissolution of carbonates and accelerates the generation of iron-manganese oxides. Therefore, both migrate and enrich in the same area. The main factor for the formation of such high background elements is the "secondary enrichment" during the weathering process of the parent rock, that is, the leaching of macroelements such as Ca and Mg causes the relative enrichment of trace elements such as Cd. In this process, iron-manganese minerals play an important role in the in-situ enrichment of these elements. From a macroscopic perspective, hot and humid climates are more conducive to the formation of higher background contents. Due to frequent human production activities, especially in the southern regions, the physical and chemical properties of soil have changed dramatically. Particularly in alluvial areas, soil acidification has led to a significant increase in the proportion of some heavy metal elements in their ionic and other available forms, posing a risk of activation and potential threats to human health.

[0003] Currently, soil pollution remediation technologies mainly include physical remediation, bioremediation, and chemical remediation. Physical remediation primarily alters the physical structure of the soil to reduce or remove heavy metals by precisely controlling their migration within a specific range. Key measures include soil replacement, isolation, heat treatment, and physical isolation. It is often suitable for small-area industrial contaminated sites but has high treatment costs. Bioremediation utilizes microorganisms and enriching plants to bio-adsorb, bio-reduce, and bio-transform heavy metals, improving the contaminated soil environment. It is often used in conjunction with other methods; using it alone results in long remediation cycles and significant uncertainties. Chemical remediation involves adding adsorbents, complexing agents, and reducing agents to alter the chemical properties of elements in the soil, fixing or transforming them into stable, non-migrating substances. Among these three remediation methods, in-situ passivation is the most widely used technology. The selection of passivation materials is crucial to the passivation effect. In the remediation of polymetallic mining areas and surrounding land contaminated with Cd, Pb, Zn, As, etc., the commonly used passivating agents fall into six categories: First, alkaline passivating agents such as lime, calcium carbonate, and fly ash, which promote the removal of Cd by increasing soil pH. 2+ Pb 2+ Zn 2+ The first method generates hydroxide or carbonate precipitates, simultaneously reducing their solubility and bioavailability. It is inexpensive, widely available, and simple to operate. However, it has disadvantages such as simultaneous sedimentation of beneficial trace elements, poor long-term effectiveness (decreasing with rainwater leaching or soil acidity recovery), requiring repeated application and large dosages. The second method involves phosphate passivating agents such as phosphate rock powder and hydroxyapatite, which react with Pb... 2+ The first type generates extremely stable, insoluble compounds with good long-lasting effects and high stability, while also having a phosphate fertilizer effect, which can improve soil fertility. Its disadvantages include a significantly weaker passivation effect on cadmium and zinc compared to lead, and excessive application can easily lead to phosphorus loss and eutrophication; it is also relatively expensive. The second type uses clay minerals such as zeolite and attapulgite, which are natural mineral materials, environmentally friendly, stable, and have slow-release and long-term passivation potential; some can even improve soil structure. However, their ability to treat high concentrations of heavy metal pollution is weak, and they can easily cause soil compaction. The third type uses organic passivating agents such as biochar, woody peat, and humic acid, which complex heavy metals through surface functional groups while increasing soil organic matter, promoting the conversion of heavy metals to organic forms. These are generally prepared using agricultural waste and are low-cost. The disadvantages are that the passivation effect is greatly affected by the raw materials and pyrolysis temperature, and the quality is unstable. Long-term and repeated use can increase soluble organic matter in the soil, which in turn can complex and activate some heavy metals. It is generally used in combination with other passivating agents. Fifth, there are metal oxides or hydroxides such as iron and manganese oxides, which form complexes with heavy metals through surface hydroxyl groups, exhibiting strong adsorption capacity for Cd, Pb, and Zn, and are very common in the treatment of polluted water. The disadvantages are that natural materials have low purity, artificial synthesis is costly, and the effect is limited when used alone. Sixth, there are sulfide passivating agents such as sodium sulfide and ferrous sulfide, S... 2- with cd2+ Pb 2+ Zn 2+ It generates sulfide precipitates with extremely low solubility products, exhibiting a very high degree of stabilization. In neutral soil environments, its passivation effect on Cd, Pb, and Zn is very significant. Disadvantages include its tendency to aggregate and poor dispersibility when used alone; the need for combination with a passivating agent matrix carrier in small quantities; and the release of toxic gases in strongly acidic soil environments.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a remediation material and method for silicon-sulfur-iron based synergistic passivation of heavy metal composite contaminated soil. This material and method can achieve long-lasting, safe, and efficient remediation of high-concentration Cd, Pb, Zn and other heavy metal composite contaminated soil in geologically high background mining areas.

[0006] In a first aspect, the present invention provides a remediation material for silicon-sulfur-iron based synergistic passivation of heavy metal-contaminated soil, comprising: basalt powder and a binary composite passivation material; wherein the binary composite passivation material is a mixture of ball-milled hematite sulfide and ferroalloy modified biochar.

[0007] Preferably, the mass ratio of the ball-milled hematite sulfide to the modified biochar of ferrohydrate is 1:(1-2).

[0008] Preferably, the heavy metal is one or more of cadmium (Cd), lead (Pb), and zinc (Zn).

[0009] Preferably, the preparation of the basalt powder includes the following steps: crushing natural basalt, grinding it, passing it through a 200-mesh sieve, and drying it at 100℃-150℃ to obtain basalt powder.

[0010] Preferably, the preparation of the ball-milled hematite sulfide includes the following steps: Natural hematite is crushed, ground, passed through a 200-mesh sieve, and dried at 100℃-150℃ to obtain hematite powder. Hematite powder was mixed with sodium sulfide solution and reacted under constant temperature shaking at 50°C. After the reaction was completed, the product was separated by centrifugation. The separated product was washed until neutral, freeze-dried, ball-milled, and passed through a 200-mesh sieve to obtain ball-milled hematite sulfide.

[0011] Preferably, the preparation of the modified biochar from ferrohydrate includes the following steps: Agricultural and forestry waste is crushed, sieved, and pyrolyzed at 600℃-700℃ to obtain biochar, which is then ground and sieved again. Biochar and Fe(NO3)3·9H2O were dispersed in deionized water at a mass ratio of 1:(20-30), and then continuously stirred to allow Fe to...3+ It is fully adsorbed onto the surface and pores of biochar without causing accumulation; Slowly add NaOH solution to the continuously stirred mixture, adjust the pH to about 7.5, allow the precipitate to age, filter and wash until neutral; The washed product was dried, ground, and passed through a 100-mesh sieve to obtain ferroalloy modified biochar.

[0012] Preferably, the agricultural and forestry waste includes one or more of corn cobs, coconut shells, and sesame stalks.

[0013] In a second aspect, the present invention provides a method for remediating soil contaminated with heavy metals, using the aforementioned silicon-sulfur-iron-based synergistic passivation material for remediating soil contaminated with heavy metals, wherein the basalt powder and the binary composite passivation material are used synergistically in two separate applications.

[0014] Preferably, it includes the following steps: Loosen the topsoil, sprinkle some basalt powder, loosen it again, sprinkle another part of basalt powder, and till it. Water it to keep the soil moisture content above 70% of field capacity. Cultivate it for a period of time (preferably about one month) without disturbing it and adjust the soil pH to above 6.5. Sprinkle the binary composite passivation material onto the surface, till, and water to keep the soil moisture content above 70% of field capacity. Cultivate for a period of time (preferably about one month) without disturbing the soil.

[0015] Preferably, the method also includes the following steps: after 3-5 years of normal crop cultivation, monitor the passivation effect; after 3-5 years, apply half the amount of binary composite passivation material.

[0016] The present invention has at least the following beneficial effects: (1) Multi-mechanism synergistic passivation: Basalt powder and binary composite passivation material (ball milled hematite + ferroalloy modified biochar) are applied twice in a synergistic manner before and after the application, which comprehensively and efficiently passivates Cd, Pb and Zn heavy metals. The basalt powder releases active silicon to form insoluble silicates with Pb, Cd and Zn. The ball milled hematite provides sulfur ions to form CdS, PbS and ZnS precipitates. The active iron-based sites provided by the ball milled hematite and ferroalloy modified biochar can firmly bind Cd, Pb and Zn ions through surface complexation, co-precipitation and lattice embedding. The high specific surface area of ​​the ferroalloy modified biochar specifically adsorbs Cd, Pb and Zn ions. The CaO and MgO in basalt powder and the alkaline groups in ferruginous modified biochar work together to maintain a neutral to slightly alkaline microenvironment in the soil, which is conducive to precipitation formation and long-term stability. During the weathering process of basalt powder, secondary clay minerals formed in situ can exchange ions and be fixed between layers with ferruginous modified biochar. The synergistic use of basalt powder and binary composite passivation materials, each performing its specific function while promoting each other, overcomes the shortcomings of single materials being ineffective for a particular metal and having insufficient complexation stability.

[0017] (2) Outstanding long-term stability: The silicate and sulfide precipitates formed are extremely difficult to dissolve in the natural environment, and have strong resistance to acid rain leaching and microbial degradation. Basalt powder itself is a natural mineral that weathers slowly and can continuously release active ingredients. The carbon skeleton of the modified biochar of ferroalloy protects the ball-milled hematite from excessive oxidation and extends the life of sulfides. The mixed and synergistic use can provide a passivation effect of up to 3 to 5 years.

[0018] (3) Environmentally friendly and improves soil microenvironment: All raw materials are natural minerals or agricultural and forestry waste. After application, they can simultaneously replenish beneficial elements such as silicon, calcium, magnesium, and iron in the soil, improve soil pH and nutrient availability, improve soil aggregate structure, increase organic carbon content, and enhance soil fertility. At the same time, they stimulate the growth of beneficial microorganisms such as sulfate-reducing bacteria, enhance crop stress resistance, and reduce crop absorption of heavy metals.

[0019] (4) Strong adaptability, low cost, simple preparation process, and easy to scale up: In sulfide polymetallic mining areas, the soil is mostly acidic. Basalt powder can neutralize the acid, and sulfide precipitation remains stable under alkaline conditions. The selective adsorption of Cd by ferroalloy-modified biochar is better than that of competing ions such as Ca and Mg. Binary composite passivation materials can simultaneously treat Cd, Pb, and Zn composite pollution without the need for separate formulations for different heavy metals. Basalt costs about 200-300 yuan / ton, hematite costs about 1000 yuan / ton, and biochar can be prepared using agricultural waste. The preparation process of ball milling hematite sulfide and ferroalloy-modified biochar is simple. Binary composite passivation materials only require physical mixing of the two, which is convenient for industrial production. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 The spatial correspondence diagram of soil Cd spatial content and lithological distribution in a typical area of ​​Southwest China provided by the present invention; wherein, (1) is a spatial diagram of Cd content and (2) is a spatial distribution diagram of lithology.

[0022] Figure 2 A schematic diagram of the preparation process and remediation method of the silicon-sulfur-iron based synergistic passivation material for heavy metal composite contaminated soil provided by the present invention.

[0023] Figure 3 The images show experimental rice cultivation fields under different conditions provided by the present invention, wherein 1 is comparative example 1; 2 is comparative example 2; 3 is example 2; and 4 is control example 3.

[0024] Figure 4 The graph shows the percentage results of the removal passivation rate of the effective state of heavy metals provided by the present invention; where (1) is Cd; (2) is Pb; and (3) is Zn. Detailed Implementation

[0025] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0026] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 This embodiment provides a remediation material for silicon-sulfur-iron based synergistic passivation of heavy metal composite contaminated soil, including: basalt powder and binary composite passivation material; the binary composite passivation material is a mixture of ball-milled hematite sulfide and ferroalloy modified biochar at a mass ratio of 1:(1~2).

[0029] In this embodiment, the preparation of basalt powder includes the following steps: natural basalt is crushed and ground, then passed through a 200-mesh sieve to obtain fine basalt powder, which is then dried at 100℃~150℃ for 2~3 hours to obtain basalt powder. Its main chemical composition is: SiO2 45~52%, Al2O3 12~18%, Fe2O3+FeO 5~12%, CaO 5~10%, MgO 3~8%, Na2O+K2O <5%, with the remainder being other oxides.

[0030] In this embodiment, the preparation of ball-milled hematite sulfide includes the following steps: 1) After crushing and grinding natural hematite (Fe2O3 content of 85%~90%), pass it through a 200-mesh sieve to screen out hematite powder, and dry it at 100℃~150℃ for 2~3 hours for later use; 2) Prepare a 2mol / L sodium sulfide solution using sodium sulfide nonahydrate (Na2S·9H2O) with a purity >98%. Mix 100g of hematite powder with 1L of sodium sulfide solution. Seal the mixture in a glass bottle of a certain size and transfer it to a constant temperature shaker at 50℃ for at least 24 hours. Set the shaking speed to 200~300rpm. After the reaction is complete, use a low-speed centrifuge to separate the product. 3) Wash with deionized water until neutral, then freeze-dry in a freeze dryer for more than 6 hours, then ball-mill in a ball mill, and finally pass through a 200-mesh sieve to screen out the ball-milled hematite sulfide.

[0031] In this embodiment, the preparation of modified biochar from ferrohydrate includes the following steps: 1) After crushing and grinding waste corn cobs, coconut shells and sesame stalks with a high-speed pulverizer, pass them through a 100-mesh sieve, and then pyrolyze them in a tube furnace at 650℃ under N2 protection for 2 hours to obtain biochar. Grind the biochar through a 100-mesh sieve and set it aside for later use. 2) Disperse biochar and ferric nitrate nonahydrate (Fe(NO3)3·9H2O) in deionized water at a mass ratio of 1:(20~30), and stir continuously for more than 1 hour to allow the Fe... 3+ It is fully adsorbed onto the surface and pores of biochar without causing accumulation; 3) Slowly add 1 mol / L NaOH solution to the continuously stirred mixture, adjust the pH to about 7.5, let the precipitate age for 2 hours, and then filter and wash until neutral. 4) Dry the washed product in a vacuum drying oven at 60℃ for more than 24 hours. After taking it out, grind it gently and pass it through a 100-mesh sieve to obtain ferroalloy modified biochar. Seal and store it for later use.

[0032] In this embodiment, the preparation of the binary composite passivation material includes the following steps: Ball-milled hematite sulfide and modified biochar were added to a three-dimensional oscillating mixer at a mass ratio of 1:1 and oscillated at a speed of 30-50 rpm for at least 0.5 hours. The mixture was then passed through a 100-mesh sieve to obtain the binary composite passivation material.

[0033] Example 2 This embodiment provides a method for remediating soil contaminated with heavy metals, employing the silicon-sulfur-iron-based synergistic passivation material for heavy metal contaminated soil described in Example 1. The basalt powder and the binary composite passivation material are used synergistically in two stages. During application, it is important to maintain appropriate soil moisture content and ambient temperature.

[0034] Taking a heavy metal-contaminated abandoned field near a lead-zinc mine in Yunnan Province as a case study, the topsoil layer was intact, with a depth ranging from approximately 25cm to 45cm and a pH between 5 and 6.3. Ten soil samples were randomly collected from the top 20cm layer for testing and analysis of Cd, Pb, Zn, and Cu content. The experimental field measured 1m x 12m, as shown in Table 1. The risk of Cu exceeding the standard in the soil was low, and no further testing or research on Cu was conducted in subsequent experiments.

[0035] Table 1. Content of heavy metals Cd, Pb, Zn, and Cu in soil

[0036] Specifically, such as Figure 2 As shown, the method for remediating soil contaminated with heavy metals includes the following steps: (1) First time: In summer, from July to August, first loosen the top 20cm of soil, then spread half of the basalt powder evenly at a rate of 300kg / mu, loosen it again, and then spread the other half. Rotary tillage twice to ensure that the basalt powder is fully mixed with the topsoil within 20cm. Water thoroughly to keep the soil moisture content above 70% of field capacity. Maintain the soil for 1 month without disturbing it, and adjust the soil pH to above 6.5.

[0037] (2) Second step: Apply the binary composite passivation material (modified biochar from ferroalloy + ball-milled hematite sulfide) evenly at a rate of 150 kg / mu, then rotary till twice. Water thoroughly to maintain the soil moisture content at or above 70% of field capacity, keep the soil humidity and temperature constant, and maintain the soil for 1 month without disturbance. The passivation repair base year is recorded as 0 years.

[0038] (3) Plant rice normally the following year (the first year of planting), such as Figure 3 The position S3 is shown in the diagram.

[0039] Comparative Example 1 (1) First time: In the summer months of July and August, first loosen the top 20cm of soil, then spread half of the fine slaked lime powder evenly at a rate of 150kg / mu, loosen it again, and then spread the other half. Rotary tillage twice to ensure that the slaked lime is fully mixed with the topsoil within 20cm. Water thoroughly to keep the soil moisture content above 70% of field capacity. Maintain the soil for 1 month without disturbing it, and adjust the soil pH to above 6.8.

[0040] (2) Second step: Spread biochar evenly at a rate of 150 kg / mu, then rotary till twice. Water thoroughly to maintain soil moisture content above 70% of field capacity, keep soil humidity and temperature constant, and maintain for 1 month without disturbance. The passivation and repair period is recorded as 0 years.

[0041] In this comparative example, the preparation method of biochar is as follows: waste corn cobs, coconut shells, and sesame stalks are crushed and ground using a high-speed pulverizer, passed through a 100-mesh sieve, and then pyrolyzed in a tube furnace at 650℃ under N2 protection for 2 hours to obtain biochar, which is then ground and passed through a 100-mesh sieve.

[0042] (3) Plant rice normally the following year (the first year of planting), such as Figure 3 The position of S1 is shown in the diagram.

[0043] Comparative Example 2 (1) In the summer months of July and August, spread the binary composite passivation material (modified biochar of ferrophosphate + ball-milled hematite sulfide) evenly at a rate of 150 kg / mu, and then rotary till twice. Water thoroughly to keep the soil moisture content above 70% of the field capacity, maintain soil humidity and temperature, and maintain the soil for 1 month without disturbing it.

[0044] (2) Plant rice normally the following year (the first year of planting), such as Figure 3 The position of S2 is shown in the diagram.

[0045] Comparative Example 3 Without making any improvements, rice will be planted normally the following year (the first year of planting) as a blank control. Figure 3 As shown in CK.

[0046] Detection example In Example 2 and Comparative Examples 1-3, five sampling points were set up for each point. The content of effective heavy metals (mainly water-soluble and ion-exchangeable forms) was analyzed once a year in October.

[0047] In the third and fourth years, no continuous testing and analysis data were available after the three-year project implementation period ended. However, two samples of wild shepherd's purse grown in the third year were collected, and the Pb, Cd, and Zn contents in the shepherd's purse from the two different locations are shown in Table 2. The Pb and Cd contents did not exceed the limits specified in GB 2762-2022 "National Food Safety Standard: Limits of Contaminants in Food".

[0048] Table 2. Content of Pb, Cd and Zn in shepherd's purse

[0049] In the fifth year, three sites were set up in each area, with chili peppers, corn and sweet potatoes mainly planted on site.

[0050] The average removal passivation rate of heavy metals Cd, Pb, and Zn is as follows: Figure 4 As shown in Table 3-5.

[0051] Table 3 Average Cd removal passivation rate

[0052] Table 4 Average Pb removal passivation rate

[0053] Table 5 Average Zn removal passivation rate

[0054] In Example 2 (S3 position), the average passivation removal rate of Cd was 76% in the first year, 87% in the second year (an increase of 11%), and remained at around 76% in the fifth year; the average passivation removal rate of Pb was 74% in the first year, 76% in the second year (an increase of 2%), and decreased to 65% in the fifth year; the average passivation removal rate of Zn was 81% in the first year, 73% in the second year (a decrease of about 8%), and decreased to 65% in the fifth year.

[0055] Comparative Example 1 (S1 position): The average removal passivation rate of Cd was 62% in the first year, 70% in the second year (an increase of 8%), and dropped to 64% in the fifth year; the average removal passivation rate of Pb was 65% in the first year, 63% in the second year, and dropped to 56% in the fifth year; the average removal passivation rate of Zn was 73% in the first year, 63% in the second year, and dropped to 57% in the fifth year.

[0056] Comparative Example 2 (S2 position): The average removal passivation rate of Cd was 57% in the first year, 73% in the second year (an increase of 16%), and dropped to 65% in the fifth year; the average removal passivation rate of Pb was 51% in the first year, 73% in the second year (an increase of 22%), and dropped to 65% in the fifth year; the average removal passivation rate of Zn was 68% in the first year, 65% in the second year, and dropped to 61% in the fifth year.

[0057] In summary, the passivation effect is ranked as Cd > Zn > Pb, and the stability after passivation is ranked as Cd > Pb > Zn. Example 2 showed an overall passivation effect exceeding 10% compared to Comparative Example 1, with better stability. Comparative Example 1 showed poor sustained stability and unstable passivation with significant variations. Compared to Comparative Examples 1 and 2, Example 2 revealed that basalt powder adjusts soil pH slowly but has a long duration, which is extremely important for Zn passivation. Furthermore, Zn's later activation is faster, resulting in the fastest decrease in passivation rate, while Pb passivation is less affected by soil pH changes. Based on rice growth (… Figure 3 The synergistic use of basalt powder and binary composite passivation material (modified biochar from ferroalloy + ball-milled hematite sulfide) resulted in significantly better rice growth. In Example 2 and Comparative Example 1, the Cd and Pb contents in the rice of the second year both met the national food safety standards. In Comparative Example 2, one point showed that Pb exceeded the standard, while Cd did not exceed the standard. A thorough analysis of the three sets of data shows that soil acidification (without adjusting soil pH) has a certain promoting effect on the absorption of heavy metals by plants. The specific comparison is shown in Table 6.

[0058] Table 6

[0059] In summary, this invention provides a silicon-sulfur-iron based remediation material for heavy metal contaminated soil, which combines silicate precipitation, sulfide precipitation, surface complexation and adsorption of heavy metal elements, soil pH buffering, and long-term stability. This material enhances the long-term stability of heavy metals after passivation, enabling long-lasting, safe, and efficient remediation of high-concentration Cd, Pb, Zn, and other composite contaminated soils in geologically high-background mining areas.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silicon-sulfur-iron based synergistic passivation remediation material for heavy metal composite contaminated soil, characterized in that, include: Basalt powder and binary composite passivation material; the binary composite passivation material is a mixture of ball-milled hematite sulfide and ferroalloy modified biochar.

2. The remediation material for silicon-sulfur-iron based synergistic passivation of heavy metal composite contaminated soil according to claim 1, characterized in that, The mass ratio of ball-milled hematite sulfide to modified ferrophosphate biochar is 1:(1-2).

3. The remediation material for silicon-sulfur-iron based synergistic passivation of heavy metal composite contaminated soil according to claim 1, characterized in that, The heavy metal is one or more of cadmium, lead, and zinc.

4. The remediation material for silicon-sulfur-iron based synergistic passivation of heavy metal composite contaminated soil according to claim 1, characterized in that, The preparation of the basalt powder includes the following steps: crushing, grinding, sieving, and drying natural basalt to obtain basalt powder.

5. The remediation material for silicon-sulfur-iron based synergistic passivation of heavy metal composite contaminated soil according to claim 1, characterized in that, The preparation of the ball-milled hematite sulfide includes the following steps: Natural hematite is crushed, ground, sieved, and dried to obtain hematite powder; Iron powder was mixed with sodium sulfide solution and the mixture was subjected to constant temperature and shaking reaction. After the reaction was completed, the product was separated by centrifugation. The separated product was washed until neutral, freeze-dried, ball-milled, and sieved to obtain ball-milled hematite sulfide.

6. The remediation material for silicon-sulfur-iron based synergistic passivation of heavy metal composite contaminated soil according to claim 1, characterized in that, The preparation of the modified biochar from ferrohydrate includes the following steps: Agricultural and forestry waste is crushed, sieved, and pyrolyzed to obtain biochar, which is then ground and sieved again. After dispersing biochar and Fe(NO3)3·9H2O in deionized water, the mixture was continuously stirred to allow Fe to... 3+ It is fully adsorbed onto the surface and pores of biochar without causing accumulation; Slowly add NaOH solution to the continuously stirred mixture, adjust the pH, allow the precipitate to age, filter and wash until neutral; The washed product was dried, ground, and sieved to obtain ferrophosphate-modified biochar.

7. The remediation material for silicon-sulfur-iron based synergistic passivation of heavy metal composite contaminated soil according to claim 6, characterized in that, The agricultural and forestry waste includes one or more of the following: corn cobs, coconut shells, and sesame stalks.

8. A method for remediating soil contaminated with heavy metals, characterized in that, The remediation material for silicon-sulfur-iron based synergistic passivation of heavy metal composite contaminated soil according to any one of claims 1-7 is used, wherein the basalt powder and the binary composite passivation material are used synergistically in two stages.

9. The method for remediating heavy metal-contaminated soil according to claim 8, characterized in that, Includes the following steps: Loosen the topsoil, sprinkle some basalt powder, loosen it again, sprinkle another part of basalt powder, and rotary till; water it to keep the soil moisture content above 70% of field capacity, maintain it for a period of time without disturbing it, and adjust the soil pH to above 6.

5. Spread the binary composite passivation material on the surface, till the soil, and water it to keep the soil moisture content above 70% of field capacity. Maintain the soil for a period of time without disturbing it.

10. The method for remediating heavy metal-contaminated soil according to claim 8, characterized in that, It also includes the following steps: After 3-5 years of normal crop cultivation, monitor the passivation effect; after 3-5 years, reduce the application of binary composite passivation material by half.

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