A method for preparing, using and applying a composite soil conditioner

Abstract

The application discloses a preparation method and use method of a composite soil conditioner and application thereof, relates to the technical field of soil remediation, and can improve soil structure, improve the composition of organic matter in soil, increase the Eh value of the rhizosphere soil of crops, increase the biomass of crops, and significantly reduce the biological availability and toxicity of arsenic and the arsenic content absorbed and accumulated by crops in edible parts of stems and leaves by multiple effects such as in-situ passivation of soil, formation of iron-arsenic precipitation, and formation of iron film / titanium film, so that arsenic is intercepted in inedible root parts.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a preparation method, a use method and an application of a composite soil conditioner. Background Art

[0002] Arsenic, a metalloid, enters soil and water bodies through atmospheric deposition and surface runoff. Planting crops on arsenic-contaminated land can affect their normal growth and development, leading to reduced yields and even death. Furthermore, arsenic accumulated in the edible parts of crops can enter the human body through the food chain, causing acute or chronic arsenic poisoning, impacting the respiratory and nervous systems, and ultimately leading to diseases such as liver cancer, bladder cancer, and skin cancer. Therefore, soil remediation research to reduce arsenic accumulation in crops has become an urgent need to ensure safe crop production and promote the sustainable development of agricultural ecosystems.

[0003] Soil conditioners, because they are rich in organic matter, can effectively improve soil structure, replenish soil organic matter content, increase soil fertility, thereby promoting crop growth and improving crop resistance to growth stress caused by arsenic pollution. However, due to the high pH value of soil conditioners, after application to the soil, the mobility of arsenic will gradually increase, accelerating the dissolution of arsenic and aggravating soil arsenic pollution. Long-term use will also cause soil compaction and the accumulation of certain elements and chemicals in the soil, affecting the ecological balance of the soil. Summary of the Invention

[0004] The main purpose of the present invention is to provide a preparation method of a composite conditioner, which can be simply applied to arsenic-contaminated soil to increase the Eh value of rhizosphere soil, reduce the bioavailability and toxicity of arsenic, increase crop biomass and yield, and reduce the arsenic content absorbed and accumulated in the edible parts of agricultural products. The present invention aims to solve the technical problems that soil conditioners in the existing technology easily lead to a gradual increase in arsenic mobility, accelerate arsenic dissolution, aggravate arsenic contamination in the soil, and cause soil compaction after long-term use; at the same time, the accumulation of arsenic in the edible parts of crops leads to health risks.

[0005] A method for preparing a composite soil conditioner comprises the following steps:

[0006] S1. According to the mass percentage, 35% to 40% of oyster shell, 35% to 40% of limestone, 20% to 25% of biochar, 5% to 8% of organic activated carbon and 3% to 5% of mineral humic acid are mixed to prepare a soil conditioner;

[0007] Oyster shells and limestone are pre-treated by calcination: calcination at high temperature, crushing and grinding to a particle size of 125-147 μm;

[0008] S2. Add ilmenite in an amount of 10% to 15% by mass of the soil conditioner, and mix well to obtain a composite soil conditioner; the ilmenite is crushed, ground, and sieved before mixing, and the sieve diameter is 1 to 3 mm.

[0009] The composite soil conditioner is made by calcining, crushing and grinding oyster shells and limestone at high temperature, and then compounding them with biochar, organic activated carbon and mineral humic acid to form a soil conditioner. The single limestone is calcined and applied to the soil in contact with water, which usually generates a pH of 12 to 13.4% of the strong alkaline substance calcium hydroxide, while calcined lime is mixed with calcined oyster shells at a lower mass percentage, which can not only neutralize the acidic soil, but also reduce the strong alkalinity. In addition, the calcined oyster shells under the particle size of this scheme have an obvious multi-porous structure. In addition to effectively adsorbing heavy metals, they can also well adsorb harmful hydroxides, sodium, chlorides, etc., inhibit the increase in soil pH, so that the soil conditioner can bidirectionally adjust the soil pH to achieve the purpose of making the soil environment suitable for plant growth; mineral humic acid has good stability, and its main component is a multi-component organic acid. It is adsorbed on calcined lime and calcined oyster shells, further enhancing the performance of its complex functional groups, and forming a protective film layer in the soil to inhibit soil loss. It can be combined with biochar, organic activated carbon, calcined oyster shells, etc. to improve soil structure, improve the organic matter composition in the soil, and improve the soil Eh value, thereby making the soil have an in-situ passivation effect on arsenic.

[0010] By combining ilmenite with soil conditioners, its trivalent iron minerals can react with arsenic in the soil to form iron-arsenic precipitates, reducing the mobility of arsenic in water and soil and promoting the formation of stable arsenic. When crops are iron deficient, titanium can also help induce the expression of iron-related genes in crops, thereby promoting the absorption and utilization of iron. The application of composite soil conditioners can effectively promote crop growth; the iron and titanium in ilmenite can form iron films and titanium films under arsenic pollution conditions to surround the roots of plants in the form of a "barrier", thereby reducing the absorption of arsenic by crops and significantly reducing the transport of arsenic to the aboveground parts of crops.

[0011] Simply applying the composite soil conditioner to arsenic-contaminated soil for crop planting can improve soil structure, improve the organic matter composition in the soil, increase the Eh value of the crop rhizosphere soil, and increase the crop biomass. It also significantly reduces the bioavailability and toxicity of arsenic through the multiple effects of in-situ soil passivation, formation of iron-arsenic precipitation, and formation of iron film / titanium film. The arsenic content accumulated in the edible parts of the crops' stems and leaves is absorbed and retained in the inedible root parts. The present invention realizes the resource utilization of solid waste, is low-cost, and is environmentally friendly.

[0012] Mineral-derived humic acid is prepared by oxidizing and activating the mineral raw materials, followed by high-speed crushing, followed by alkaline extraction and acid precipitation, and finally differential centrifugation. The active ingredients of mineral-derived humic acid are one or more of fulvic acid, fulvic acid, and palmitic acid.

[0013] Preferably, the biochar is prepared by drying and pulverizing stevia residue, then calcining it in a muffle furnace at 330-370°C for 1.8-2.5 hours. Stevia residue, as a solid waste, is rich in organic acids, proteins, organic matter, fats, cellulose, and other components. After being prepared into biochar, it can be used in a composite soil conditioner as a nutritionally balanced organic fertilizer. When applied to the soil, the trace elements and nutrients it contains not only improve and fertilize the soil, promoting crop growth and development, but also increase the bacterial abundance in the soil and enhance the diversity of the soil microbial community, further achieving resource utilization.

[0014] Preferably, the organic activated carbon is prepared by crushing sawdust and coconut shells to 1.5-2.5 cm and treating them at 350-450°C for 3-5 hours. Further preferably, the sawdust and coconut shells are mixed in a 1:1 weight ratio. Sawdust and coconut shells are widely available carbon-containing materials. After being prepared into activated carbon, they can be used as adsorbents and catalysts in composite soil conditioners for arsenic-contaminated soils. This helps adsorb and fix arsenic in the soil, reducing its mobility, further promoting the normal growth and development of crops, and replenishing the soil's total carbon content.

[0015] The present invention provides a method for using a composite soil conditioner. The composite soil conditioner is applied to arsenic-contaminated soil at a dosage of 280 to 320 kg per mu (approximately 280 to 320 kg) and then aged for 14 to 16 days after thoroughly mixing the composite soil conditioner with the surface soil. This simple application of the composite soil conditioner to arsenic-contaminated soil can increase the Eh value of the rhizosphere soil and reduce the bioavailability and toxicity of arsenic. Surface soil generally refers to the soil within the top layer (0 to 20 cm thick).

[0016] Preferably, crops are planted in the aged arsenic-contaminated soil, wherein the crops are selected from round-leaved red amaranth. This can increase the biomass and yield of crops in the arsenic-contaminated soil and reduce the arsenic content absorbed and accumulated in the edible parts of the agricultural products.

[0017] The present invention provides an application of a composite soil conditioner, wherein the arsenic contamination value of arsenic-contaminated soil using the composite soil conditioner is between 150 and 180 mg kg -1 In my country's soil environmental quality standard GB15618-2018, the background value of soil arsenic is limited to 15 mg / kg, while the first-level standard is limited to 25 mg / kg and the second-level standard is limited to 40 mg / kg. The composite soil conditioner prepared by the present invention can be used to treat arsenic pollution at a level of 150-180 mg·kg.-1 It is more effective in arsenic-contaminated soil within a certain range.

[0018] Compared with the prior art, the composite soil conditioner of the present invention is prepared by mixing calcined oyster shells and limestone with biochar, activated organic carbon and mineral humic acid to form a soil conditioner, and then adding ilmenite and mixing evenly to obtain the composite soil conditioner. The composite soil conditioner is simply applied to arsenic-contaminated soil, thereby improving the soil structure, improving the organic matter composition in the soil, increasing the Eh value of the crop rhizosphere soil, and increasing the biomass of the crop. The composite soil conditioner significantly reduces the bioavailability and toxicity of arsenic through multiple effects such as in-situ soil passivation, formation of iron-arsenic precipitation, and formation of iron film / titanium film. The arsenic content accumulated in the edible parts of the stems and leaves of the crop is absorbed and retained in the inedible root parts, thereby realizing waste resource utilization, low cost, and green environmental protection. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0020] This application proposes a method for preparing a composite soil conditioner, comprising the following steps:

[0021] S1. According to the mass percentage, 35% to 40% of oyster shell, 35% to 40% of limestone, 20% to 25% of biochar, 5% to 8% of organic activated carbon and 3% to 5% of mineral humic acid are mixed to prepare a soil conditioner;

[0022] Oyster shells and limestone are pre-treated by calcination: calcination at high temperature, crushing and grinding to a particle size of 125-147 μm;

[0023] The biochar is prepared by drying and crushing stevia residue and then calcining it at a high temperature of 330-370°C in a muffle furnace for 1.8-2.5 hours; the effective components of the mineral humic acid are one or more of fulvic acid, black humic acid and palmitic acid.

[0024] The organic activated carbon is prepared by crushing sawdust and coconut shell into 1.5-2.5 cm and treating them at a high temperature of 350-450°C for 3-5 hours.

[0025] S2. Add ilmenite in an amount of 10% to 15% by mass of the soil conditioner, and mix well to obtain a composite soil conditioner; the ilmenite is crushed, ground, and sieved before mixing, and the sieve diameter is 1 to 3 mm.

[0026] In order to verify the effect of the above-mentioned composite soil conditioner on arsenic-contaminated soil and crops, this program conducted the following experiments:

[0027] The following examples and comparative examples describe a method for using the composite soil conditioner in arsenic-contaminated soil: applying 300 kg per mu (approximately 300 kg) of the composite soil conditioner to the arsenic-contaminated soil, thoroughly mixing the composite soil conditioner with the surface soil, and then aging the mixture for 14 days. Crops are planted in the aged arsenic-contaminated soil, wherein the selected crop is amaranth with round leaves and red flowers.

[0028] (1) Test location

[0029] The test site is located in an arsenic-contaminated farmland in Longgang District, Shenzhen City, Guangdong Province. The site has a subtropical monsoon climate with an average annual temperature of 22.3°C and an average annual rainfall of 1933 mm. Due to the poor site conditions, thin soil layer, poor soil quality, and location in a low mountainous and hilly area surrounded by mountains, rock weathering and leaching are intense. The arsenic content of the soil parent material is high, exceeding the As pollution risk screening value specified in the "Environmental Risk Assessment Standard for Soil Pollution Risk in Agricultural Land" (GB15618-2018) (As <30 mg / kg when 6.5 < pH ≤ 7.5). The basic physical and chemical properties of the soil in the test site are shown in the following table:

[0030] Table 1 Basic physical and chemical properties of soil in the test plots

[0031]

[0032] (2) Test materials

[0033] Ilmenite mineral was provided by Guangxi Jinmao Titanium Co., Ltd. The basic cost of the material is shown in Table 2. Raw materials without special instructions were obtained from the market, and the same batch of raw materials was used in both the examples and comparative examples.

[0034] Table 2 Basic composition of ilmenite

[0035]

[0036] (3) Experimental treatment and index determination

[0037] Each example and comparative example is divided into cells (2 m×3 m) in a random manner, and a 50 cm isolation zone is set between adjacent cells and covered with a film to prevent mutual influence between cells.

[0038] At 40 days of amaranth growth, plant height was uniformly measured in the field, followed by sampling of the plant and rhizosphere soil. The harvested samples were divided into roots, stems, and leaves, rinsed with tap water, and then dried in a 105°C oven for 30 minutes to a constant weight. The dry weight of each amaranth part was measured and recorded. The samples were then thoroughly ground in a grinder and placed in sealed bags for testing of arsenic concentrations in each part of the amaranth.

[0039] Determination of As content in plant samples

[0040] 0.2g of the crushed plant sample was weighed and placed in a polytetrafluoroethylene digestion tube. 10ml of nitric acid was added, and the tube was pre-digested in a graphite furnace. The tube was then capped and placed in a microwave digester for sample digestion. After digestion, the sample was removed from the sample in the graphite furnace until 1-2ml of liquid remained. After cooling, the sample was transferred to a 25ml volumetric flask, filtered to volume, and the filtered liquid was placed in a 30ml small square bottle for storage. The arsenic content in the digestion solution was measured using an atomic fluorescence spectrometer. A commercially available arsenic standard solution (CFGG-AA-060033-0201) was used to construct a standard curve. Quality control was performed using a rice flour standard (GBW(E)-100349) and a blank sample.

[0041] Determination of soil pH and Eh in rhizosphere soil

[0042] 10 g of rhizosphere soil passed through a 2 mm sieve was weighed into a centrifuge tube, 25 ml of pure water was added, and the tube was placed in a shaker for 1 hour and then allowed to stand for 3 hours. The pH and Eh values ​​of the supernatant were measured using a portable pH meter (SX620, Sanxin Instrument Co., Ltd., China) and an Eh meter (SX630, Sanxin Instrument Co., Ltd., China).

[0043] Heavy metal transport coefficient (Translocation Factor, TF)

[0044] The heavy metal transport coefficient can reflect the ability of a certain heavy metal to be transported from the underground part of a plant to various organs above ground. The calculation formula of TF is:

[0045] TF=C shoot / C root

[0046] Among them C shoot is the heavy metal concentration in various parts of the aboveground plant (such as stems and leaves), C root Heavy metal concentrations in the roots of this plant.

[0047] Example 1

[0048] A method for preparing a composite soil conditioner comprises the following steps:

[0049] S1, 35% oyster shell, 35% limestone, 20% biochar, 6% organic activated carbon and 4% mineral humic acid are mixed according to the mass percentage to prepare a soil conditioner;

[0050] The oyster shell and limestone are calcined and pretreated: calcined at a high temperature of 500-600 DEG C, crushed and ground to a particle size of 125-147 μm;

[0051] The biochar is prepared by drying and crushing sweet leaf residue, and then calcining at a high temperature of 350 DEG C for 2 hours in a muffle furnace;

[0052] The organic activated carbon is prepared by crushing wood chips and coconut shells to about 2 cm in length at a weight ratio of 1:1, and then treating at a high temperature of 400 DEG C for 4 hours.

[0053] S2, 10% ilmenite is added according to the mass percentage of the soil conditioner, and the mixture is uniformly obtained to obtain a composite soil conditioner; the ilmenite is crushed, ground and sieved before mixing, and the screen diameter is 2 mm.

[0054] The following comparative examples are also provided for the above embodiments, and the preparation method and planting method of the composite soil conditioner of the following comparative examples are consistent with example 1, and the differences are shown in the following table:

[0055] Blank Rowed amaranth without any conditioner Comparative Example 1 Rowed amaranth with the same amount of soil conditioner as in Example 1 applied Comparative Example 2 Rowed amaranth with the same amount of ilmenite as in Example 1 applied Comparative Example 3 Rowed amaranth with a composite soil conditioner (oyster shell without calcination treatment) applied

[0056] Test data table 1

[0057]

[0058] (Different lowercase letters represent significant differences between groups (P<0.05))

[0059] Test data table 2

[0060] Group TF / root to stem TF / root to leaf Rhizosphere soil pH Rhizosphere soil Eh Blank 20.86±0.25a 22.53±0.25a 6.76±0.11b 362.5±4.5c Example 1 0.82±0.01b 0.98±0.1c 6.81±0.4b 459±2.83a Comparative Example 1 20.87±3.62a 15.22±3.85b 7.18 ± 0.14ab 417.5 ± 31.82ab Comparative Example 2 0.94±0.09b 1.03±0.39c 6.8±0.03b 431.5 ± 20.51ab Comparative Example 3 2.23±0.13b 1.84±0.25c 7.35±0.06a 390.5 ± 7.78bc

[0061] (Different lowercase letters represent significant differences between groups (P<0.05))

[0062] From the above data, it can be seen that:

[0063] Comparing the blank group with example 1, comparative examples 1-3.

[0064] From the data of the stem and leaf biomass of each part, by comparing the blank group with Example 1, Comparative Example 1 and Comparative Example 3, it can be seen that the application of the composite soil conditioner or the soil conditioner significantly promotes the growth of the edible parts (stems and leaves) of amaranth. By comparing the blank group with Comparative Example 1 and Comparative Example 2, it can be seen that although the biomass of the edible parts of amaranth applied only with ilmenite has a certain increase, the increase is not as good as that of the composite soil conditioner or the soil conditioner, among which the increase effect of the composite soil conditioner is the best; secondly, from the plant height data, by comparing Comparative Example 3 with Example 1 and Compared with the blank group, it can be seen that the composite soil conditioner of calcined oyster shell increases the plant height of amaranth compared with the composite soil conditioner of uncalcined oyster shell. The plant height of the composite soil conditioner of uncalcined oyster shell is not significantly different from that of the blank group. By comparing the blank group with Comparative Example 1 and Comparative Example 2, the plant height growth of amaranth applied only with ilmenite is not as good as that of amaranth applied with soil conditioner. By comparing the overall biological data of the blank group with Example 1 and Comparative Examples 1 to 3 (plant height, biomass), Example 1 has a significantly better effect on improving plant height and biomass of various parts.

[0065] From the data of As content and transport coefficient of each part, the blank group was compared with Example 1 and Comparative Examples 1 to 3. The addition of ilmenite significantly reduced the transport coefficient and accumulated arsenic content of the edible part of amaranth, and significantly increased the arsenic content accumulated in the root of amaranth. There was no significant difference in the transport coefficient between amaranth with only soil conditioner added and the blank group. However, since the soil conditioner improved the soil structure and enhanced the in-situ passivation of arsenic in the soil, the arsenic content in each part of amaranth also decreased, but it was significantly less than the decrease in the arsenic content in amaranth with ilmenite added. The comparison shows that the synergistic effect of ilmenite makes amaranth absorb more arsenic. The arsenic content is accumulated as much as possible in the roots of amaranth. The addition of ilmenite in the present application can intercept the As absorbed by the amaranth root system in the roots, significantly reduce the arsenic content in the stems and leaves of amaranth, and further regulate the safe production of the edible parts of amaranth. Comparing Comparative Example 3 with Example 1 and the blank group, it can be seen that after adding calcined oyster shells, due to the good combination of calcined oyster shells and other components in the composite soil conditioner and the synergistic effect of ilmenite, there is a significant gain effect on reducing the transport coefficient and As content in the edible parts of amaranth (stems and leaves). Example 1 is significantly better than Comparative Examples 1 to 3.

[0066] From the data of rhizosphere soil pH and rhizosphere soil Eh, compared with the blank group, only adding ilmenite (Comparative Example 2) or only adding a soil conditioner (Comparative Example 1) can increase the rhizosphere soil Eh. In terms of soil pH, Comparative Example 2 is not much different from the blank group, and the soil pH of Comparative Example 1 is increased. When the oyster shell in the composite soil conditioner is not calcined (Comparative Example 3), the bidirectional regulating effect of the calcined oyster shell on the soil pH is lost, and the soil pH is significantly increased. The composite soil conditioner containing calcined oyster shell and ilmenite (Example 1) is not much different from the blank group in soil pH, while the rhizosphere soil Eh is significantly better than Comparative Examples 1 to 3, indicating that calcined oyster shell and ilmenite play a synergistic role in the composite soil conditioner, increasing the Eh value of the crop rhizosphere soil, balancing the pH value of the soil, and providing a good soil environment for crop growth.

[0067] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent structural transformations made by using the contents of the present invention specification under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a composite soil conditioner, characterized in that: The following steps are involved: S1. Mix 35% to 40% of oyster shell, 35% to 40% of limestone, 20% to 25% of biochar, 5% to 8% of organic activated carbon, and 3% to 5% of mineral humic acid according to mass percentage to prepare a soil conditioner, wherein the sum of the mass percentages of the components of the soil conditioner is 100%; The oyster shells and the limestone are subjected to calcination pretreatment: calcination at high temperature, crushing and grinding, and crushed to a particle size of 125-147 μm; S2. Add ilmenite in an amount of 10% to 15% by mass of the soil conditioner and mix well to obtain a composite soil conditioner; The ilmenite is crushed, ground and sieved before mixing, and the diameter of the sieve is 1-3 mm; The biochar is prepared by drying and crushing stevia residue, and then calcining it at a high temperature of 330-370° C. in a muffle furnace for 1.8-2.5 hours. The active ingredient of the mineral-source humic acid is one or more of fulvic acid, fulvic acid, and palmitic acid. The organic activated carbon is prepared by crushing sawdust and coconut shells to 1.5-2.5 cm and treating them at a high temperature of 350-450° C. for 3-5 hours.

2. A method for using a composite soil conditioner, characterized in that: The composite soil conditioner according to claim 1 is applied to arsenic-contaminated soil at a dosage of 280-320 kg per mu, and the composite soil conditioner is fully mixed with the surface soil and then aged for 14-16 days.

3. The method for using the composite soil conditioner according to claim 2, wherein: Crops are planted in the aged arsenic-contaminated soil, wherein the crop is selected round-leaved red amaranth.

4. Application of the composite soil conditioner, characterized in that: The arsenic contamination value of the arsenic-contaminated soil using the composite soil conditioner as claimed in claim 1 is between 150 and 180 mg kg -1 scope.

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