A soil conditioner for simultaneous cadmium and arsenic remediation, its preparation method and application

Abstract

This invention provides a soil conditioner for simultaneous remediation of cadmium and arsenic, its preparation method, and its application, relating to the field of soil conditioner technology. The method includes: S1, using waste backwash iron sludge pyrolysis to produce porous iron-based sludge char, then loading DTC onto it to obtain DTC covalently loaded iron-based sludge char; S2, using waste traditional Chinese medicine residue for aerobic high-temperature composting to obtain fermented carbonized traditional Chinese medicine residue; S3, using aluminum extraction waste residue for dealkalization to obtain fly ash aluminum extraction and dealkalization activated white mud; S4, mixing the products obtained in S1-S3 with mineral-derived potassium humate, adding sodium-based bentonite, and granulating to obtain the soil conditioner. This soil conditioner has the functions of adjusting soil pH, simultaneously remediating cadmium and arsenic in the soil, and increasing soil organic matter. This invention, through precise matching of multiple mechanisms, can solve multiple problems of existing soil conditioners, such as single and mediocre remediation effects, poor stability, and inability to increase soil organic matter, and can also realize the resource utilization of various types of waste.

Description

Technical Field

[0001] This invention relates to the field of soil conditioner technology, specifically to a soil conditioner for simultaneous cadmium and arsenic remediation, its preparation method, and its application. Background Technology

[0002] According to statistics, over 2 million km² of arable land has been contaminated by cadmium and arsenic. 2 In major rice-producing areas and farmland surrounding industrial and mining areas, Cd-As co-existing compound pollution is a typical characteristic. The synergistic exceedance of cadmium and arsenic seriously threatens food security and farmland ecological security. However, the simultaneous treatment of cadmium and arsenic faces natural antagonistic contradictions: conventional alkaline passivating agents that fix arsenic easily activate cadmium, while thiol chelating agents that fix cadmium easily affect arsenic stability; and single remediation materials cannot achieve long-term stable synergistic effects between cadmium and arsenic.

[0003] Among existing cadmium and arsenic remediation agents, dithiocarbamate (DTC) is commonly used as a highly efficient cadmium chelating material. However, conventional physical mixing methods often suffer from drawbacks such as easy leaching of DTC, poor stability, high risk of secondary pollution, and ineffective arsenic remediation. For example, Chinese patent application CN105754610A discloses a remediation agent for soil contaminated with heavy metals cadmium, lead, and arsenic, and its preparation method. This remediation agent is composed of the following components by weight ratio: 30-50% biochar, 5-10% diatomaceous earth, 5-10% sodium bentonite, 5-10% activated alumina, 10-20% dithiocarbamate, 5-10% ethylenediaminetetraacetic acid, 5-10% tartaric acid, 5-10% polyacrylamide, and 5-10% sodium dodecyl sulfonate. Although the solution uses dithiocarbamate (DTC) as one of the main components, it adopts a conventional physical mixing method, directly mixing DTC with biochar, diatomaceous earth, bentonite, etc. The DTC in the remediation agent has poor stability and is easily leached, lacking long-term effectiveness in the treatment of cadmium and arsenic.

[0004] Secondly, while single iron-based biochar materials can also fix arsenic and reduce cadmium levels to some extent in soil remediation agents, the effect is generally limited. For example, Chinese patent application CN104388094A discloses an iron-based biochar material, its preparation process, and its application in soil pollution remediation. This iron-based biochar material uses biomass as raw material and incorporates iron-containing compounds during the high-temperature carbonization process, doping iron in a specific ratio to form an iron-based biochar material with a special structure and function. It can reduce cadmium and arsenic content to some extent, but the effective cadmium content in the soil is reduced by only about 20%.

[0005] In addition, bentonite, potassium humate, and industrial white mud are also widely used in soil remediation agents, but they are mostly used alone or in simple combinations. They can only achieve single improvement or single heavy metal fixation, without a precise synergistic mechanism. They are just conventional material stacking, lacking creativity and long-term effectiveness, and cannot solve the core pain point of simultaneous stabilization of cadmium and arsenic in acidic paddy fields.

[0006] Furthermore, the aforementioned cadmium-reducing and arsenic-fixing materials are relatively expensive. Based on these shortcomings of existing technologies, developing a specialized soil conditioner that simultaneously and synergistically passivates cadmium and arsenic, is non-antagonistic, long-lasting and stable, utilizes solid waste resources, is low-cost, and also improves soil conditions, has significant engineering value and innovative implications. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a soil conditioner for simultaneous treatment of cadmium and arsenic, which addresses the shortcomings of the existing technology. This soil conditioner has the functions of adjusting soil pH, simultaneously treating cadmium and arsenic in the soil, and increasing soil organic matter. It can solve multiple problems of existing soil conditioners, such as single and general treatment effect, poor stability, and inability to increase soil organic matter. At the same time, it can also realize the resource utilization of solid waste and reduce the cost of soil conditioners.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a soil conditioner for simultaneous cadmium and arsenic remediation, specifically comprising the following steps: S1. Preparation of DTC (sodium diethyldithiocarbamate) covalently supported iron-based sludge char: S101. Dry the waste backwash iron sludge generated from the iron and manganese removal process of the sewage treatment plant to a moisture content of less than 10%, crush and sieve it, and then pyrolyze it under an inert protective atmosphere. After the pyrolysis is completed, keep the inert protective atmosphere and cool it naturally to room temperature to obtain a porous iron-based sludge carbon. S102. The iron-based sludge carbon obtained from DTC and S101 is reacted at room temperature and stirred in a closed manner at a mass ratio of 1:2 for 30-60 minutes. Then, the free water is removed by vacuum drying to obtain DTC covalently supported iron-based sludge carbon. S2. Preparation of fermented carbonized Chinese medicine residue: Waste Chinese medicine residue dehydrated to a moisture content of ≤60% is subjected to aerobic high-temperature composting fermentation. The material temperature is controlled at 55~65℃ throughout the fermentation process, and the initial carbon-nitrogen ratio (C / N) of the compost is controlled at 20:1~25:1. The composting cycle is 25~30 days. During the fermentation period, the compost is turned over every 5~7 days. After the fermentation is completed, it is dried to a moisture content of <15%, crushed and sieved to obtain fermented carbonized Chinese medicine residue. S3. Preparation of fly ash alumina extraction and alkali removal white mud: S301, Dealkali removal: Take the aluminum extraction waste residue produced by the acid method of fly ash aluminum extraction process, remove impurities, mix it with clean water at a solid-liquid mass ratio of 1:4~1:5, continuously stir and wash with water until the pH value of the slurry stabilizes in the range of 8.5~9.5 and the fluctuation is ≤±0.1 after two consecutive water washes, and the dealkali removal process is judged to be completed, and dealkali removal slurry is obtained. S302, dehydrate the dealkali slurry, dry it at a constant temperature until the moisture content is ≤5%, crush and sieve to obtain fly ash aluminum extraction and dealkali removal activated white mud; S4. Preparation of soil conditioner: Weigh the following components by weight: DTC covalently loaded iron-based sludge char obtained in S1, fermented carbonized Chinese medicinal residue obtained in S2, fly ash alumina extraction and dealkali removal white mud obtained in S3, and mineral-derived potassium humate; add them sequentially, rotate at 200-400 rpm for 15-30 minutes to form a stable composite, then add the following components by weight: sodium-based bentonite, rotate for 5-10 minutes, granulate, and dry to obtain the soil conditioner.

[0009] Furthermore, the weight parts of each component in the soil conditioner are as follows: DTC covalently loaded iron-based sludge carbon: 40-50 parts; Fermented and carbonized Chinese medicinal herb residue: 15-20 parts; Sodium-based bentonite: 10-15 parts; Fly ash aluminum extraction and alkali removal white mud: 10-15 parts; 5-8 parts of mineral-derived potassium humate.

[0010] Furthermore, the pyrolysis conditions in S101 are as follows: high-purity nitrogen is introduced as a protective gas to prevent oxidation of the iron component, and the nitrogen volume flow rate is controlled at 0.8~1.5L / min; the heating rate is set at 5~10℃ / min, and the temperature is gradually increased from room temperature to the final pyrolysis temperature of 350~400℃. After reaching the set temperature, the temperature is kept constant for pyrolysis for 2~3 hours.

[0011] Furthermore, the drying conditions in S101 are: drying at 105℃ for 6~8 hours until the moisture content is less than 10%, and then pulverizing through a 100~200 mesh sieve.

[0012] Furthermore, the inert protective atmosphere in S101 is nitrogen or argon, preferably nitrogen.

[0013] Furthermore, the vacuum drying conditions in S102 are as follows: control the drying temperature ≤50℃, vacuum degree ≥-0.08MPa, and vacuum drying for 4~6h.

[0014] Furthermore, the water washing and dealkali removal operation in S301 is as follows: the aluminum extraction waste residue is thoroughly stirred with clean water to form a suspension slurry. Under normal temperature conditions, the mixture is continuously stirred and washed for 15-25 minutes to fully dissolve the soluble sodium salts and free alkaline substances in the pores of the waste residue. After stirring, the mixture is allowed to settle for 10-15 minutes to separate the upper alkaline washing waste liquid, completing the first water washing. The water washing operation is repeated 3-5 times. After each round of water washing and remixing of the slurry, the pH value of the slurry is measured.

[0015] Furthermore, the mixing conditions for forming a stable complex of DTC covalently loaded iron-based sludge carbon, fermented carbonized Chinese medicinal residue, dealkalized white mud, and mineral-derived potassium humate in S4 are: rotating at 200~400 rpm for 15~30 min.

[0016] Furthermore, the granulation process of S4 is as follows: the material is put into the disc granulator for granulation, and the disc rotation speed is controlled at 25~35r / min; an appropriate amount of water is sprayed in during the granulation process to maintain the material moisture content at 20~25% and the granulation particle size at 2~5mm.

[0017] Furthermore, the drying process of S4 is as follows: After granulation, the drying temperature of the granules is kept constant at 40℃, and forced ventilation is turned on throughout the process with a ventilation speed of 0.3~0.6m / s. Low-temperature ventilation drying can avoid high temperature damage to the covalent bond structure of DTC, the microporous structure of bentonite, and the activity of organic matter.

[0018] Furthermore, the potassium fulvic acid content in the mineral-derived potassium fulvicate is ≥50%, the potassium oxide content is ≥8%, and it passes through an 80~100 mesh sieve.

[0019] Furthermore, the fermented and carbonized Chinese medicinal residue is sieved through a 60-100 mesh sieve; sodium-based bentonite is sieved through a 100-200 mesh sieve; and the fly ash aluminum extraction, dealkali removal, and activated white mud is sieved through a 100-200 mesh sieve.

[0020] Secondly, the present invention provides a soil conditioner for simultaneous cadmium and arsenic remediation prepared by the above method.

[0021] Thirdly, the present invention also provides an application of the soil conditioner as described above in paddy field soil improvement. Specifically, the soil conditioner is evenly spread on the field surface by manual or mechanical application 5 to 7 days before plowing, and then plowed with a rotary tiller to mix it evenly with the soil. After watering with an appropriate amount of water to stabilize and mature for 3 to 5 days, rice is transplanted. This method is used to adjust the pH of paddy field soil, simultaneously achieve soil cadmium and arsenic treatment, and improve soil organic matter.

[0022] The working principle of each component in the soil conditioner provided by this invention: 1. DTC Covalently Loaded Iron-Based Sludge Charcoal: Iron-based sludge charcoal retains a large number of hydroxyl active sites after low-temperature oxygen-limited pyrolysis. In-situ iron doping provides ample arsenic adsorption sites, serving as an anchoring point for DTC covalent loading. After DTC loading, the highly stable thiol chelating groups in the iron-based sludge charcoal can specifically capture free Cd from the soil. 2+ This generates extremely difficult-to-dissolve and stable complexes, significantly reducing the bioavailability of cadmium in the soil.

[0023] 2. Fermented and carbonized Chinese medicinal residue: Provides active organic matter and extracellular polymers (EPS), which can optimize the soil micro-ecological environment, promote the biopassivation of heavy metals in the soil, and slow down soil acidification.

[0024] 3. Fly ash aluminum extraction and dealkalization white mud: It can gently regulate soil pH, replenish the silicon and calcium content in the soil, inhibit the reduction and activation of arsenic under flooded conditions, and stabilize the arsenic fixation effect.

[0025] 4. Mineral-derived potassium humate: enhances the stability of heavy metal complexation, promotes the formation of soil aggregates, and increases soil organic matter content.

[0026] 5. Sodium-based bentonite: Its microporous structure can lock in viable repair components, slow down component loss, and ensure long-term stable effects.

[0027] This invention has the following beneficial effects and innovations: 1. Covalent loading to improve stability: The solution of this invention abandons the traditional physical impregnation and mixing method. It utilizes the abundant Fe-OH active sites on the surface of iron-based sludge carbon to covalently coordinate with DTC thiol groups, thereby achieving DTC molecule anchoring and fixation. This completely solves the problems of DTC leaching, short duration, and secondary pollution, and significantly improves the long-term stability of cadmium.

[0028] 2. Achieving simultaneous cadmium and arsenic remediation: In this invention, DTC covalent complexation is used to target and lock in effective cadmium, iron-based active oxides are used to specifically adsorb and fix arsenic, dealkalized white mud is used to moderately adjust alkali to inhibit the reduction and activation of arsenic in flooded areas, traditional Chinese medicine residue is used to promote soil microbial solidification of heavy metals, potassium humate is used to enhance complexation stability, and bentonite micropores are used to lock in and maintain efficacy. By using multiple mechanisms for precise matching, the antagonistic problem of cadmium and arsenic remediation can be solved.

[0029] 3. Realizing Solid Waste Resource Utilization: In this invention, three types of waste resources are integrated: municipal iron and manganese removal sludge (water treatment solid waste), fly ash aluminum extraction white mud (industrial solid waste), and waste Chinese medicine residue (agricultural by-product). These are combined with pharmaceutical-grade derivative chelating materials and mineral source improvement materials to form a cross-border composite system. This not only solves the resource utilization problem of multiple types of waste and reduces raw material costs, but also forms a complete system of precise modification, covalent loading, and synergistic compounding for the cadmium and arsenic antagonism problem in acidic paddy fields through raw material combination and innovative modification processes. The raw material combination, preparation process, and synergistic mechanism between the components are all beyond existing common knowledge.

[0030] 4. Diverse functions: The soil conditioner provided by this invention can not only passivate heavy metals, but also replenish soil carbon sources, silicon and calcium nutrients, and active organic matter, improve the structure of acidic soil, enhance soil fertility, and achieve the integration of "remediation + improvement + yield increase". Detailed Implementation

[0031] Unless otherwise defined, 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0032] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variation thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0033] When a parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1~5” is disclosed, the described range should be interpreted as including the ranges “1~4”, “1~3”, “1~2”, “1~2 and 4~5”, “1~3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0034] To facilitate understanding of the present invention, preferred embodiments are provided below to provide a more complete description of the invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to enable a thorough and complete understanding of the disclosure of the present invention.

[0035] The main raw materials used in the following examples are from the following sources: DTC, purchased from Shaoguan Dingfeng Biotechnology Co., Ltd., CAS: 148-18-5, purity ≥95%.

[0036] Sodium-based bentonite was purchased from Tuoyi New Materials (Guangzhou) Co., Ltd., CAS: 1302-78-9. The sodium-based bentonite was first dried at 105℃ and passed through a 100-200 mesh sieve for later use.

[0037] Potassium humate sourced from Jinan Hongrun Chemical Co., Ltd. Humic acid content ≥50%, potassium oxide content ≥8%, passed through a 100-mesh sieve.

[0038] Unless otherwise specified, follow standard conditions or the manufacturer's recommendations. Reagents or instruments without a manufacturer's name are all commercially available standard products.

[0039] Example 1: Preparation of DTC covalently supported iron-based sludge carbon This invention provides a method for preparing DTC covalently supported iron-based sludge char, specifically including the following steps: (1) Preparation of iron-based sludge carbon: Waste backwash sludge generated from the iron and manganese removal process of a municipal wastewater treatment plant was collected. Its main components were hydrated iron oxide (Fe2O3nH2O, content ≥65%), manganese oxide (MnO2, content about 5%~10%), a small amount of calcium magnesium carbonate and quartz sand impurities. In this invention, the waste backwash sludge is mainly used to retain a large number of hydroxyl active sites through low-temperature oxygen-limited pyrolysis. In-situ iron doping can provide sufficient arsenic adsorption sites, providing anchoring points for DTC covalent loading.

[0040] The waste backwashed iron sludge was dried in a 105℃ drying oven for 6-8 hours until the moisture content was less than 10%, and then pulverized through a ball mill and passed through a 100-200 mesh sieve. The sieved iron sludge powder was placed in a tubular pyrolysis furnace, and high-purity nitrogen was introduced as a protective gas. The nitrogen volume flow rate was controlled at 0.8-1.5 L / min, and air was isolated throughout the process to prevent oxidation of the iron components. The heating rate was set to 5-10℃ / min, and the temperature was gradually increased from room temperature to the final pyrolysis temperature of 350-400℃. After reaching the set temperature, the pyrolysis was maintained at a constant temperature for 2 hours. After the pyrolysis was completed, nitrogen was continued to be introduced, and the furnace was naturally cooled to room temperature. The discharged material was a porous iron-based sludge carbon.

[0041] (2) Add DTC and the iron-based sludge carbon obtained in (1) to a high-speed mixer at a ratio of 1:2. Stir at 200-400 rpm at room temperature (20-25℃) for 30-60 minutes in a closed environment. This system utilizes the large number of hydroxyl (Fe-OH) active sites on the surface of the iron-based sludge carbon to coordinate and covalently bind with the thiol (-SH) groups in the DTC molecule. The reaction process does not require the addition of external acids, bases, or catalysts. The closed environment at room temperature can prevent the oxidation and decomposition of DTC, ensuring that the coordination reaction continues.

[0042] As a preferred embodiment, the specific parameters of this embodiment are set as follows: (1) The waste backwash iron sludge is dried in a drying oven at 105℃ for 8 hours until the moisture content is less than 10%, and then crushed through a ball mill and passed through a 100-mesh sieve. The nitrogen volume flow rate is controlled at 1.5L / min, the heating rate is set at 10℃ / min, and the temperature is gradually increased from room temperature to the final pyrolysis temperature of 400℃. After reaching the set temperature, it is kept at a constant temperature for 2 hours for pyrolysis. (2) The stirring speed is 400rpm, and the reaction is carried out in a closed environment for 60 minutes.

[0043] Example 2 Preparation of fermented carbonized Chinese medicinal residue This invention provides a method for preparing fermented carbonized Chinese medicinal residue, comprising the following steps: This invention collects a mixture of plant residues produced by a traditional Chinese medicine extraction factory during the production of traditional Chinese medicine preparations such as Isatis root granules, Astragalus injection, and Danshen dripping pills. The mixture mainly contains residues of rhizomes and other root-like medicinal herbs such as Isatis root, Astragalus, and Danshen. Its main components are: fiber content approximately 50%–65%, crude protein approximately 8%–12%, and lignin approximately 15%–20%. The invention primarily utilizes the active organic matter and extracellular polymeric substances (EPS) that can be provided after the fermentation and carbonization of these plant residues. These EPS can optimize the soil microecological environment, promote the biopassivation of heavy metals in the soil, and mitigate soil acidification.

[0044] The collected waste medicinal herb residue is dehydrated to a moisture content of ≤60% and then subjected to aerobic high-temperature composting fermentation. The material temperature is controlled at 55-65℃ throughout the fermentation process, with a composting cycle of 25-30 days. The initial carbon-to-nitrogen ratio (C / N) of the compost is adjusted to 20:1-25:1. No additional exogenous fermentation bacteria are needed; the composting relies on the indigenous microorganisms inherent in the medicinal herb residue. During fermentation, the compost is turned every 5-7 days to ensure sufficient oxygen supply and uniform composting (seed germination rate >80%). The fully composted material is dried at 60-80℃ to a moisture content of <15%, then pulverized and passed through a 60-100 mesh sieve to obtain fermented carbonized medicinal herb residue.

[0045] As a preferred embodiment, the specific parameters of this embodiment are set as follows: the material temperature is controlled at 65℃ throughout the fermentation process, and the composting cycle is 30 days; the initial carbon-nitrogen ratio of the material is adjusted to 25:1, and the compost is turned over once every 7 days during the fermentation period; the material after decomposition is dried at 80℃ until the moisture content is <15%, crushed and passed through a 100-mesh sieve to obtain fermented carbonized Chinese medicine residue.

[0046] Example 3 Preparation of white mud for aluminum extraction and alkali removal from fly ash This invention provides a method for preparing white mud for aluminum extraction and alkali removal from fly ash, comprising the following steps: (1) Aluminum extraction waste residue produced by the acid process of fly ash extraction in a certain factory was collected. Its main chemical components are silicon dioxide (SiO2, 60.0%~78.0%), aluminum oxide (Al2O3, 12.0%~20.0%), calcium oxide (CaO, 0.4%~1.0%), magnesium oxide (MgO, 0.2%~0.8%), and contains a small amount of unreacted residual sulfate and soluble sodium salt (Na). + (Approximately 0.5%~2.0%). This invention mainly utilizes the aluminum extraction waste residue after dealkalization and activation to gently adjust the soil pH, replenish the silicon and calcium content in the soil, inhibit the reduction and activation of arsenic under flooded conditions, and stabilize the arsenic fixation effect.

[0047] Remove lumpy impurities and floating debris from the collected aluminum extraction waste. Mix the pretreated aluminum extraction waste with clean water at a solid-liquid mass ratio of 1:4 to 1:5, and stir thoroughly to form a suspension slurry. Continue stirring and washing at room temperature for 15 to 25 minutes to fully dissolve soluble sodium salts and free alkaline substances from the pores of the waste. After stirring, allow to settle for 10 to 15 minutes, separating the upper alkaline washing waste liquid to complete the first water wash. Repeat the water washing operation 3 to 5 times using a step-by-step clean water replacement method, thoroughly draining the waste liquid after each round to prevent residual alkali from refluxing and accumulating. After each round of water washing and remixing the slurry, immediately measure the pH value of the slurry using a potentiometric method. Continue washing until the pH value stabilizes in the range of 8.5 to 9.5 for two consecutive tests, with fluctuations ≤ ±0.1, indicating that the dealkali removal process is complete and a dealkali-removed slurry is obtained.

[0048] (2) After the dealkali slurry is dehydrated by pressure filtration, it is placed in a constant temperature drying equipment and dried at 60~80℃ until the material moisture content is ≤5%. After ultrafine grinding, it is passed through a 100~200 mesh sieve to obtain fly ash aluminum extraction and dealkali activation white mud.

[0049] As a preferred embodiment, the specific parameters of this embodiment are set as follows: (1) In this embodiment, the pretreated aluminum extraction waste residue is mixed with clean water at a solid-liquid mass ratio of 1:5 and continuously stirred and washed for 25 minutes at room temperature; after stirring, it is allowed to settle for 15 minutes, and the upper alkaline washing waste liquid is separated to complete one water washing; the water washing operation is repeated; the water washing is continued until the pH value is stable in the range of 8.5~9.5 and the fluctuation is ≤±0.1 for two consecutive tests. (2) In this embodiment, the dehydrated material is dried at 80℃ until the material moisture content is ≤5%, and after ultrafine grinding, it is passed through a 100-mesh sieve to obtain fly ash aluminum extraction and dealkali removal activated white mud. According to the test, the product contains 60.0%~78.0% silicon dioxide, 0.4%~1.0% calcium oxide, and 0.2%~0.8% magnesium oxide.

[0050] Example 4 Preparation of Soil Conditioner This invention provides a method for preparing a soil conditioner, comprising the following steps: (1) Add 40-50 parts of DTC covalently loaded iron-based sludge carbon prepared in Example 1, 15-20 parts of fermented carbonized Chinese medicine residue prepared in Example 2, 10-15 parts of fly ash aluminum extraction and dealkali removal white mud prepared in Example 3, and 5-8 parts of mineral-derived potassium humate in sequence. Rotate at 200-400 rpm for 15-30 min to form a stable composite. Then add 10-15 parts of sodium-based bentonite and rotate for another 5-10 min. Utilize the well-developed microporous structure and adsorption properties of sodium-based bentonite to form a coating layer on the surface of the composite, locking in DTC, active iron oxide and other easily lost active repair components, slowing down component leaching loss, and ensuring the long-term stable effect of the soil conditioner.

[0051] (2) Granulation: After thorough mixing and reaction, the material is placed in a disc granulator for granulation. The rotation speed of the disc is controlled at 25~35 r / min. During the granulation process, an appropriate amount of water is sprayed in to maintain the moisture content of the material at 20~25%. The particle size is maintained between 2~5 mm. After granulation, the material is placed in a drying oven. The drying temperature is kept constant at 40℃. Forced ventilation is turned on throughout the process (ventilation speed is controlled at 0.3~0.6 m / s). Low-temperature ventilation drying can avoid high temperature damage to the covalent bond structure of DTC, the microporous structure of bentonite, and the activity of organic matter. After drying until the moisture content of the particles reaches the standard, the material is discharged to obtain the soil conditioner.

[0052] As a preferred embodiment, the specific parameters of this embodiment are set as follows: (1) 50 parts of DTC covalently loaded iron-based sludge carbon, 20 parts of fermented carbonized Chinese medicine residue prepared in Example 2, 15 parts of fly ash alumina extraction and dealkali removal white mud prepared in Example 3, and 8 parts of mineral-derived potassium humate are rotated at 400 rpm for 30 min, and then 15 parts of sodium-based bentonite are added, and the mixture is rotated for another 10 min to obtain 15 parts of sodium-based bentonite. (2) The rotation speed of the disc granulator is controlled at 35 r / min. During the granulation process, an appropriate amount of water is sprayed in to maintain the material moisture content at 20~25%, and the granulation particle size is maintained at 5 mm. After granulation, the material is placed in a drying oven and dried at 40℃ to obtain the soil conditioner.

[0053] Referring to the preparation method provided in Example 4, the composition and ratio of soil conditioner components were adjusted to obtain different soil conditioners. The control group was prepared by replacing or removing the corresponding components according to the method in Example 4. The specific composition is shown in Table 1 below. To verify the feasibility and effectiveness of the present invention, the soil conditioners of the above treatment groups were subjected to the following tests: First, to eliminate the influence of heavy metals in the raw material components, the heavy metal content of each major component was tested. All heavy metal contents were below the limits specified in the "Limits for Toxic and Hazardous Substances in Fertilizers" (GB 38400-2019) (Total arsenic (As) ≤ 50 mg / kg, total cadmium (Cd) ≤ 10 mg / kg, total lead (Pb) ≤ 200 mg / kg, total chromium (Cr) ≤ 500 mg / kg, and total mercury (Hg) ≤ 5 mg / kg). The results are shown in Table 2 below.

[0054] I. Rice Plot Experiment with Soil Conditioner A small-plot experiment was conducted in an acidic paddy field contaminated with cadmium and arsenic near a town in Yizhang County, Chenzhou City. The experiment consisted of 11 treatments, each replicated three times, for a total of 33 plots arranged in a randomized block design. Each plot was 6m long and 4m wide, with a 2.5m wide protective row surrounding the experimental field. The field ridges were separated by agricultural film, and single-row irrigation was implemented to prevent water and fertilizer cross-contamination between plots.

[0055] Basic physicochemical properties of the tested soil: soil pH 5.98, organic matter 29.43 g / kg, total cadmium 1.34 mg / kg, available cadmium 0.83 mg / kg, total arsenic 136 mg / kg, available arsenic 14.5 mg / kg. The rice variety was Jingliangyou Huazhan (late-season rice).

[0056] Treatment 1-T1 (CK): Conventional fertilization, without the application of any conditioners.

[0057] Treatment 2-T2: Apply conventional fertilizer + 100 kg / mu of soil conditioner prepared by T2 as basal application.

[0058] Treatment 3-T3: Apply conventional fertilizer + 100 kg / mu of soil conditioner prepared by T3 as basal application.

[0059] Treatment 4-T4: Apply conventional fertilizer plus 100 kg / mu of soil conditioner prepared with T4 as a base fertilizer.

[0060] Treatment 5-T5: Apply conventional fertilizer plus 100 kg / mu of soil conditioner prepared by T5 as a base fertilizer.

[0061] Treatment 6-T6: Apply conventional fertilizer plus 100 kg / mu of soil conditioner prepared with T6 as a base fertilizer.

[0062] Treatment 7-T7: Apply conventional fertilizer plus 100 kg / mu of soil conditioner prepared with T7 as a base fertilizer.

[0063] Treatment 8-T8: Apply conventional fertilizer plus 100 kg / mu of soil conditioner prepared with T8 as a base fertilizer.

[0064] Treatment 9-T9: Apply conventional fertilizer plus 100 kg / mu of soil conditioner prepared by T9 as a base fertilizer.

[0065] Treatment 10-T10: Apply conventional fertilizer plus 100 kg / mu of soil conditioner prepared by T10 as a base fertilizer.

[0066] Treatment 11-T11: Apply conventional fertilizer + 100 kg / mu of soil conditioner prepared by T11 as basal application.

[0067] On the basis of conventional fertilization, 5-7 days before plowing, the conditioner is evenly spread on the field surface by manual or mechanical means, and then plowed with a rotary tiller to mix it evenly with the soil. After watering appropriately for 3-5 days to stabilize and mature, the rice is transplanted. During the rice growth period, weeding, fertilization, pesticide spraying, and irrigation are carried out according to local production management methods.

[0068] When the rice matures, collect 1.5 kg of soil samples, air dry them naturally, grind them, and then pass them through a 20-mesh sieve (for pH value) and a 100-mesh sieve (for analyzing the content of available cadmium, available arsenic, and organic matter in the soil). Mix them well, pack them into sealed bags according to their numbers, and store them for later use.

[0069] A 1.5 kg rice sample was collected. The rice was dehulled using a dehulling machine to obtain rice grains. After drying, the rice grains were ground and passed through an 80-mesh sieve (used to analyze the cadmium and arsenic content of the rice grains) to remove impurities and particles. The rice grains were then placed in sealed bags for storage and future use.

[0070] Soil pH, available cadmium, available arsenic, and organic matter were measured; rice yield, cadmium, and arsenic content in rice were determined. The detection methods are as follows: Soil pH determination method: Using water as the extraction solvent, a small amount of soil is collected and mixed with water at a mass ratio of 2.5:1. The pH is then determined by potentiometric method (refer to NY / T1377-2007).

[0071] Determination of available cadmium in soil: Refer to the "Determination of available lead and cadmium in soil by atomic absorption spectrometry" (GB / T23739-2009).

[0072] Determination of available arsenic in soil: DTPA extraction-atomic fluorescence spectrometry (a general method for the detection of available arsenic in agricultural soils) was used.

[0073] Determination of soil organic matter: determined according to the potassium dichromate titration method (NY / T 1121.6-2006).

[0074] Rice yield determination: Refer to the "Operating Specifications for Rice Yield Determination" (DB33 / T 2517-2022).

[0075] Method for determining cadmium in rice: Refer to the National Food Safety Standard for the Determination of Cadmium in Food (GB 5009.15).

[0076] Method for determining arsenic in rice: Refer to the National Food Safety Standard for the Determination of Arsenic in Food (GB 5009.11).

[0077] All experimental data were analyzed by one-way ANOVA using SPSS 22.0, and differences between treatments were compared using Duncan's new multiple range method (α=0.05).

[0078] 1. Effects of different treatments on soil pH The results of the tests on the effects of different treatment groups on soil pH are shown in Table 3 below: As shown in Table 3, the soil pH value of treatment 1 (CK) was 5.98. Compared with treatment 1, treatments 2, 3, 4, 5, 6, 8, 9, 10, and 11 all increased the soil pH value to some extent, with the order being: treatment 9 > treatment 11 > treatment 10 > treatment 7 > treatment 8 > treatment 5 > treatment 4 > treatment 6 > treatment 3 > treatment 2. The soil conditioner treatment groups (treatments 9-10) provided by this invention showed significant pH improvement efficiency.

[0079] 2. Effects of different treatments on soil organic matter The results of the tests on the effects of different treatment groups on soil organic matter are shown in Table 4 below: As shown in Table 4, the soil organic matter content of treatment 1 (CK) was 29.43%. Compared with treatment 1, treatment 2 slightly reduced the soil organic matter content (mainly because DTC itself does not contain organic matter, and DTC alone may accelerate the consumption of organic matter). Treatments 3, 4, 5, 6, 8, 9, 10, and 11 all increased the soil organic matter content to some extent. Among the treatment groups with the same weight components, the soil conditioner treatment groups (treatments 9-10) provided by this invention showed a significant increase in soil organic matter, with treatment 9 > treatment 8 > treatment 6 > treatment 4 > treatment 7 > treatment 5.

[0080] 3. Effects of different treatments on available cadmium and arsenic content in soil The results of the tests on the effects of different treatment groups on the available cadmium and available arsenic content in the soil are shown in Table 5 below: As shown in Table 5, the available cadmium content in soil of treatment 1 (CK) was 0.83 mg / kg and the available arsenic content was 14.5 mg / kg. Compared with treatment 1, treatments 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11 all reduced the available cadmium and available arsenic content in the soil to some extent.

[0081] Soil effective cadmium reduction effect: treatment 9 > treatment 11 > treatment 10 > treatment 7 > treatment 8 > treatment 5 > treatment 3 > treatment 6 > treatment 4 > treatment 2 > treatment 1; the soil conditioner treatment groups (treatments 9-10) provided by this invention have significant cadmium reduction effects, and are all superior to the other component compound control groups (T5-T8).

[0082] Soil effective arsenic reduction effect: treatment 9 > treatment 11 > treatment 10 > treatment 8 > treatment 6 > treatment 7 > treatment 5 > treatment 4 > treatment 3 > treatment 2 > treatment 1; the soil conditioner treatment groups (treatments 9-10) provided by this invention have significant arsenic reduction effects, and are all superior to the other component compound control groups (T5-T8).

[0083] 4. Effects of different treatments on rice yield The results of the experiment on the effects of different treatment groups on rice yield are shown in Table 6 below: As can be seen from Table 6, the rice yield of treatment 1 (CK) was 521.6 kg / mu. Compared with treatment 1, treatments 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11 all improved the rice yield to a certain extent. In particular, compared with the compound treatments of the same weight components, the rice yield of the soil conditioner treatment group provided by this invention was significantly improved.

[0084] 5. Effects of different treatments on cadmium and arsenic content in rice. The effects of different treatment groups on the cadmium and arsenic content of rice were tested, and the results are shown in Table 7 below: As can be seen from Table 7, the cadmium content of rice in treatment 1 (CK) was 0.36 mg / kg and the arsenic content was 0.91 mg / kg. Compared with treatment 1, treatments 2 to 11 all reduced the cadmium and arsenic content of rice to some extent.

[0085] The effect of reducing cadmium in rice was as follows: Treatment 9 > Treatment 11 > Treatment 10 > Treatment 7 > Treatment 8 > Treatment 5 > Treatment 3 > Treatment 6 > Treatment 4 > Treatment 2 > Treatment 1; The soil conditioner treatment group provided by this invention showed a significant reduction in cadmium content in rice.

[0086] Arsenic reduction effect in rice: Treatment 9 > Treatment 11 > Treatment 10 > Treatment 8 > Treatment 6 > Treatment 7 > Treatment 5 > Treatment 4 > Treatment 3 > Treatment 2 > Treatment 1; The arsenic content in rice treated with the soil conditioner provided by this invention was significantly reduced.

[0087] II. Stability Monitoring Test of Soil Conditioner To verify the long-term stability of soil conditioners, a second-year field monitoring experiment was conducted based on the previous plot experiment. The control group received no conditioner, and the nine treatment groups received no supplemental conditioner, only routine fertilization and water management, with all other agricultural operations remaining the same as the previous season.

[0088] After the rice matured in the second year, soil and rice samples were collected to determine the pH, available cadmium, available arsenic, and organic matter content in the soil, as well as the cadmium and arsenic content in the rice. All sampling and testing methods were consistent with those used in the first year's plot experiment.

[0089] The results comparing the first and second years are shown in Table 8: The formulas for calculating the persistence factor and the reduction rate are as follows: Persistence Factor PF = (Reduction rate in quarter n / Reduction rate in quarter 1) × 100%.

[0090] Reduction rate (%) = (treatment group - CK) / CK × 100%.

[0091] The results showed that in the second year after applying the soil conditioner of the present invention (without reapplication), the soil pH, organic matter, and rice yield of treatment 9 decreased by 2.6%, 3.8%, and 1.8% respectively compared to the first season. The available cadmium was 0.33 mg / kg, the available arsenic was 6.6 mg / kg, the rice cadmium was 0.13 mg / kg, and the rice arsenic was 0.31 mg / kg, which were 13.8%, 17.9%, 18.2%, and 14.8% respectively compared to the first season. The persistence factor was >70%, indicating that the conditioner has good residual effect.

[0092] In summary, this invention provides a soil conditioner that uses DTC covalent complexation to target and lock in available cadmium, iron-based active oxides to specifically adsorb and fix arsenic, dealkalized white mud to moderately adjust alkali and inhibit the reduction and activation of arsenic in flooded areas, traditional Chinese medicine residue to promote soil microbial solidification of heavy metals, potassium humate to enhance complexation stability, and bentonite micropores to lock in and maintain efficacy. By utilizing multiple mechanisms for precise matching, this invention solves the difficulties in the cadmium and arsenic remediation industry.

[0093] The above description is only a part of the preferred embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a soil conditioner for simultaneous cadmium and arsenic remediation, characterized in that, Specifically, the steps include the following: S1. Preparation of DTC covalently supported iron-based sludge char: S101. Dry the waste backwash iron sludge generated from the iron and manganese removal process of the sewage treatment plant to a moisture content of less than 10%, crush and sieve it, and then pyrolyze it under an inert protective atmosphere. After pyrolysis, keep the inert protective atmosphere and cool it naturally to room temperature to obtain porous iron-based sludge char; S102. Mix DTC and the iron-based sludge char obtained in S101 at a mass ratio of 1:2 and stir at room temperature for 30-60 minutes. Then, vacuum dry to remove free water to obtain DTC covalently supported iron-based sludge char. S2. Preparation of fermented carbonized Chinese medicine residue: Waste Chinese medicine residue dehydrated to a moisture content of ≤60% is subjected to aerobic high-temperature composting fermentation. The material temperature is controlled at 55~65℃ during the fermentation process, and the initial carbon-nitrogen ratio of the composting material is controlled at 20:1~25:

1. The composting cycle is 25~30 days. During the fermentation period, the compost is turned over every 5~7 days. After the fermentation is completed, it is dried to a moisture content of <15%, crushed and sieved to obtain fermented carbonized Chinese medicine residue. S3. Preparation of fly ash aluminum extraction and dealkali removal white mud: S301. Dealkali removal: Take the aluminum extraction waste residue produced by the acid process of fly ash aluminum extraction, remove impurities, mix it with clean water at a solid-liquid mass ratio of 1:4~1:5, continuously stir and wash with water until the pH value of the slurry is stable in the range of 8.5~9.5 and the fluctuation is ≤±0.1 after two consecutive water washes, and the dealkali removal process is judged to be completed, and dealkali removal slurry is obtained; S302. Dehydrate the dealkali removal slurry, dry it at a constant temperature until the moisture content is ≤5%, crush and sieve, and fly ash aluminum extraction and dealkali removal activated white mud is obtained; S4. Preparation of soil conditioner: Weigh the following components by weight: DTC covalently loaded iron-based sludge char obtained in S1, fermented carbonized Chinese medicinal residue obtained in S2, fly ash alumina extraction and dealkali removal white mud obtained in S3, and mineral-derived potassium humate; add them sequentially, rotate at 200-400 rpm for 15-30 minutes to form a stable composite, then add the following components by weight: sodium-based bentonite, rotate for 5-10 minutes, granulate, and dry to obtain the soil conditioner.

2. The method for preparing the soil conditioner for simultaneous cadmium and arsenic remediation according to claim 1, characterized in that, The weight parts of each component in the soil conditioner are as follows: DTC covalently loaded iron-based sludge carbon: 40-50 parts; Fermented and carbonized Chinese medicinal herb residue: 15-20 parts; Sodium-based bentonite: 10-15 parts; Fly ash aluminum extraction and alkali removal white mud: 10-15 parts; 5-8 parts of mineral-derived potassium humate.

3. The method for preparing the soil conditioner for simultaneous cadmium and arsenic remediation according to claim 1, characterized in that, The pyrolysis conditions in S101 are as follows: high-purity nitrogen is introduced as a protective gas to prevent oxidation of the iron component, and the nitrogen volume flow rate is controlled at 0.8~1.5L / min; the heating rate is set at 5~10℃ / min, and the temperature is gradually increased from room temperature to the final pyrolysis temperature of 350~400℃. After reaching the set temperature, the temperature is kept constant for pyrolysis for 2~3 hours.

4. The method for preparing the soil conditioner for simultaneous cadmium and arsenic remediation according to claim 1, characterized in that, The drying conditions in S101 are: drying at 105℃ for 6~8 hours until the moisture content is less than 10%, and then pulverizing through a 100~200 mesh sieve; the vacuum drying conditions in S102 are: controlling the drying temperature to ≤50℃, the vacuum degree to ≥-0.08MPa, and vacuum drying for 4~6 hours.

5. The method for preparing the soil conditioner for simultaneous cadmium and arsenic remediation according to claim 1, characterized in that, The specific steps of the water washing and dealkali removal operation in S301 are as follows: The aluminum extraction waste residue is thoroughly mixed with clean water to form a suspension slurry. Under normal temperature conditions, the mixture is continuously stirred and washed for 15-25 minutes to fully dissolve the soluble sodium salts and free alkaline substances in the pores of the waste residue. After stirring, the mixture is allowed to settle for 10-15 minutes, and the upper alkaline washing waste liquid is separated to complete the first water washing. The water washing operation is repeated 3-5 times. After each round of water washing and remixing of the slurry, the pH value of the slurry is measured.

6. The method for preparing the soil conditioner for simultaneous cadmium and arsenic remediation according to claim 1, characterized in that, The mixing conditions for forming a stable complex of DTC covalently loaded iron-based sludge carbon, fermented carbonized Chinese medicinal residue, dealkalized white mud, and mineral-derived potassium humate in S4 are: rotating at 200~400 rpm for 15~30 min.

7. The method for preparing the soil conditioner for simultaneous cadmium and arsenic remediation according to claim 1, characterized in that, The granulation process of S4 is as follows: the material is put into the disc granulator for granulation, and the disc rotation speed is controlled at 25~35r / min; an appropriate amount of water is sprayed in during the granulation process to maintain the material moisture content at 20~25% and the granulation particle size at 2~5mm.

8. The method for preparing the soil conditioner for simultaneous cadmium and arsenic remediation according to claim 1, characterized in that, The drying process of S4 is as follows: After granulation, the drying temperature of the granules is kept constant at 40℃, and forced ventilation is turned on throughout the process with a ventilation speed of 0.3~0.6m / s.

9. A soil conditioner for simultaneous cadmium and arsenic remediation prepared by the method according to any one of claims 1 to 8.

10. The application of the soil conditioner as described in claim 9 in paddy field soil improvement, characterized in that, Specifically, the soil conditioner is applied evenly to the field surface 5-7 days before tilling, either manually or mechanically. Then, it is tilled with a rotary tiller to mix it evenly with the soil. After watering with an appropriate amount of water for 3-5 days to stabilize and mature, rice is transplanted. This method is used to adjust the pH of paddy field soil, simultaneously treat cadmium and arsenic in the soil, and improve soil organic matter.

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