Preparation method, use method and application of composite soil conditioner

Abstract

The invention discloses a preparation method, a use method and application of a composite soil conditioner, and relates to the technical field of soil remediation. Compared with the prior art, the composite soil conditioner is prepared by uniformly mixing calcined oyster shells and limestone with biochar, organic activated carbon and mineral source humic acid; the composite soil conditioner is simply applied to arsenic-polluted soil, and can improve the soil structure, improve the composition of organic matters in the soil, increase the Eh value of crop rhizosphere soil and increase the biomass of crops, so that the soil quality is improved. The biological availability and toxicity of arsenic are remarkably reduced through multiple effects of soil in-situ passivation, iron-arsenic precipitation forming, iron film / titanium film forming and the like, the content of arsenic absorbed and accumulated at edible parts of stems and leaves of crops is reduced, arsenic is intercepted at unedible root parts, solid waste resource utilization is achieved, and the method is low in cost and environmentally friendly.

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, as a metalloid, enters soil and water bodies through atmospheric deposition and surface runoff. Planting crops on arsenic-contaminated land will affect the normal growth and development of crops, resulting in reduced yields or even death. In addition, arsenic accumulated in the edible parts of crops will enter the human body through the amplification effect of the food chain, causing acute or chronic arsenic poisoning in the human body, affecting the respiratory and nervous systems of the human body and ultimately leading to diseases such as liver cancer, bladder cancer and skin cancer. Therefore, research on soil remediation 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 propose a preparation method of a composite conditioner, which is simply applied to arsenic-contaminated soil, can improve the Eh value of rhizosphere soil, reduce the biological effectiveness and toxicity of arsenic, increase the biomass and yield of crops, and reduce the arsenic content absorbed and accumulated in the edible parts of agricultural products. The invention aims to solve the technical problems that the soil conditioners in the prior art are prone to cause the mobility of arsenic to gradually increase, accelerate the dissolution of arsenic and aggravate the arsenic pollution in the soil, and cause soil compaction if used for a long time; at the same time, the accumulation of arsenic in the edible parts of crops causes health hazards.

[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 subjected to calcination pretreatment: after high-temperature calcination, crushing and grinding, the particles are crushed to a particle size of 125 to 147 μm;

[0008] S2. Add ilmenite at 10% to 15% of the mass percentage of the soil conditioner, 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 and contacts with water to form a pH value of 1. 12 to 13.4 of the strong alkaline substance calcium hydroxide, while calcined lime and calcined oyster shells are mixed with 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-microporous structure. In addition to effectively adsorbing heavy metals, they can also well adsorb harmful hydroxides, sodium, chlorides, etc., inhibit the increase of 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, which is adsorbed on calcined lime and calcined oyster shells, further enhancing the performance of its complexing 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 the 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] The composite soil conditioner is simply applied to arsenic-contaminated soil for crop planting, which can improve the soil structure, improve the organic matter composition in the soil, increase the Eh value of the crop rhizosphere soil, and increase the crop biomass. The bioavailability and toxicity of arsenic are significantly reduced 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 stems and leaves of the crops is absorbed and retained in the inedible root parts. The present invention realizes the resource utilization of solid waste, is low-cost, and is green and environmentally friendly.

[0012] The preparation of mineral humic acid is to oxidize and activate the mineral raw materials, then crush them at high speed, then perform alkali extraction and acid precipitation, and finally perform differential centrifugation. The effective components of mineral humic acid are one or more of fulvic acid, black humic acid and palmitic acid.

[0013] Preferably, the preparation of biochar is to dry and crush stevia residue, and then calcine it at 330-370°C in a muffle furnace for 1.8h-2.5h. Stevia residue, as solid waste, contains rich organic acids, proteins, organic matter, fat, cellulose and other components. After being prepared into biochar, it can be used as a nutritionally comprehensive and balanced organic fertilizer in a composite soil conditioner. After being applied to the soil, the trace elements and nutrients it contains can not only improve and fertilize the soil, promote the growth and development of crops, but also increase the abundance of bacteria in the soil, improve the diversity of soil microbial communities, and further achieve the purpose of resource utilization.

[0014] Preferably, the organic activated carbon is prepared by crushing sawdust and coconut shell to 1.5-2.5 cm and treating at 350-450°C for 3-5 hours. Further preferably, sawdust and coconut shell are mixed in a weight ratio of 1:1. Sawdust and coconut shell are widely available carbon-containing substances. After being prepared into activated carbon, they are used as adsorbents and catalysts in composite soil conditioners for arsenic-contaminated soil, which can help adsorb and fix arsenic in the soil, reduce the mobility of arsenic in the soil, and further promote the normal growth and development of crops and supplement the total carbon content of the soil.

[0015] The present invention provides a method for using a composite soil conditioner, wherein the composite soil conditioner is applied to arsenic-contaminated soil at a dosage of 280 to 320 kg per mu, and the composite soil conditioner is fully mixed with the surface soil and then aged for 14 to 16 days. The composite soil conditioner is applied to the arsenic-contaminated soil in a simple manner, which can increase the Eh value of the rhizosphere soil and reduce the biological effectiveness and toxicity of arsenic. The surface soil generally refers to the soil within the surface layer of 0 to 20 cm in thickness.

[0016] Preferably, crops are planted in the aged arsenic-contaminated soil, and the crops are selected round-leaved red amaranth, which can increase the biomass and yield of crops on the arsenic-contaminated soil and reduce the arsenic content absorbed and accumulated in the edible parts of 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 mg·kg 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 primary standard is limited to 25 mg / kg and the secondary standard is limited to 40 mg / kg. The composite soil conditioner prepared by the present invention can be used in the arsenic pollution value 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 to mix evenly to obtain the composite soil conditioner. The composite soil conditioner is simply applied to arsenic-contaminated soil, which can improve the soil structure, improve the organic matter composition in the soil, increase the Eh value of the crop rhizosphere soil, increase the biomass of the crop, and significantly reduce the biological effectiveness 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, as well as the absorption of the accumulated arsenic content in the edible parts of the stems and leaves of the crops, and retain the arsenic 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 in the present invention, all other embodiments obtained by ordinary technicians in this field without 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 considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0020] The present 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: calcined at high temperature, crushed and ground to a particle size of 125 to 147 μm;

[0023] The preparation of biochar is to dry and crush stevia residue, and then calcine it at a high temperature of 330-370°C in a muffle furnace for 1.8h-2.5h; the effective components of 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 at 10% to 15% of the mass percentage of the soil conditioner, 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 method of using the composite soil conditioner in arsenic-contaminated soil in the following embodiments and comparative examples is as follows: applying the composite soil conditioner to the arsenic-contaminated soil at a dosage of 300 kg per mu, mixing the composite soil conditioner with the surface soil thoroughly and then aging for 14 days, and planting crops in the aged arsenic-contaminated soil, wherein the selected crop is Taiwan-selected round-leaved red amaranth.

[0028] (I) 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 of the experimental site, the thin soil layer, the poor soil quality, and the location in the low mountain and hilly area, surrounded by mountains, the rock weathering and leaching are strong, and 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) (6.5<pH≤7.5, As<30mg / kg). 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 plot

[0031]

[0032] (II) 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 were used in the examples and comparative examples.

[0034] Table 2 Basic composition of ilmenite

[0035]

[0036] (III) Experimental treatment and index determination

[0037] Each example and comparative example divides the cells (2 m×3 m) into small areas 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 the cells.

[0038] When the growth period of amaranth reached 40 days, the plant height was uniformly measured in the field, and then the plant and rhizosphere soil were sampled. The harvested samples were divided into three parts: roots, stems, and leaves, and washed with tap water. After being dried in an oven at 105°C for 30 minutes, they were dried to constant weight. The dry weight of each part of the amaranth in each treatment was weighed and the data was recorded. The samples were then put into a grinding machine to be fully crushed and put into sealed bags to detect the arsenic concentration in each part of the amaranth.

[0039] Determination of As content in plant samples

[0040] Weigh 0.2g of the crushed plant sample, put it into a polytetrafluoroethylene digestion tube, add 10ml nitric acid and put it into a graphite furnace for pre-digestion, then cover it and put it into a microwave digestion instrument for sample digestion, and after digestion, drive the acid in the graphite furnace until 1-2ml of liquid remains, transfer it to a 25ml volumetric flask for constant volume filtration after cooling, and store the filtered liquid in a 30ml small square bottle for testing. The As content in the digestion solution was measured by an atomic fluorescence photometer, and the standard curve was configured with a purchased arsenic standard solution (CFGG-AA-060033-0201) during the measurement process, and the rice flour standard (GBW(E)-100349) and blank samples were used for quality control.

[0041] Soil rhizosphere pH and Eh determination

[0042] 10 g of rhizosphere soil passed through a 2 mm sieve was weighed into a centrifuge tube, and 25 ml of pure water was added. The tube was placed in a shaker and shaken for 1 hour, 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 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 the 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. According to the mass percentage, 35% of oyster shell, 35% of limestone, 20% of biochar, 6% of organic activated carbon and 4% of mineral humic acid are mixed to prepare a soil conditioner;

[0050] Oyster shells and limestone are pre-treated by calcination: calcined at a high temperature of 500-600°C, crushed and ground to a particle size of 125-147 μm;

[0051] The biochar was prepared by drying and crushing the stevia residue and then calcining it at 350°C in a muffle furnace for 2 h.

[0052] The organic activated carbon is prepared by crushing sawdust and coconut shell in a weight ratio of 1:1 to about 2 cm and treating at a high temperature of 400°C for 4 hours.

[0053] S2. Add ilmenite according to 10% of the mass percentage of the soil conditioner, mix evenly to obtain a composite soil conditioner; the ilmenite is crushed, ground and sieved before mixing, and the sieve diameter is 2 mm.

[0054] The following comparative examples are also provided for the above examples. The preparation method and planting method of the composite soil conditioner in the following comparative examples are consistent with those in Example 1. The differences are detailed in the following table:

[0055] Blank Group Amaranth is grown in rows without adding any conditioning agents Comparative Example 1 Drilling amaranth only applied the same amount of soil conditioner as in Example 1 Comparative Example 2 Drilling amaranth only applied the same amount of ilmenite as in Example 1 Comparative Example 3 Application of composite soil conditioner to row-sown amaranth (oyster shells not calcined)

[0056] Test data table 1

[0057]

[0058] (Different lowercase letters indicate significant differences among treatment 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 Group 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 indicate significant differences among treatment groups (P<0.05))

[0062] From the above data, we can see that:

[0063] Compare the blank group with Example 1 and Comparative Examples 1 to 3.

[0064] From the data of 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 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 shells increases the plant height of Amaranth compared with the composite soil conditioner of uncalcined oyster shells, and there is no significant difference in the plant height of the composite soil conditioner of uncalcined oyster shells compared with the blank group. By comparing the blank group with Comparative Examples 1 and 2, the plant height growth of Amaranth applied only with ilmenite is not as good as that of Amaranth applied with soil conditioners. 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 significantly better effect on improving plant height and biomass of each part.

[0065] From the data of As content and transport coefficient of each part, by comparing the blank group 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 accumulated arsenic content in the root of amaranth. There was no significant difference between the transport coefficient of amaranth added with soil conditioner and the blank group. However, since the soil conditioner improved the soil structure and enhanced the in-situ passivation of arsenic by the soil, the arsenic content of each part of amaranth also decreased, but it was obviously less than the decrease in the arsenic content of amaranth added with ilmenite. 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 roots of amaranth 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 ingredients in the composite soil conditioner and the synergistic effect of ilmenite, the transport coefficient of the edible parts of amaranth (stems and leaves) is reduced and the As content is reduced. There is a significant gain effect, and 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 soil conditioner (Comparative Example 1) can improve 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 improved. 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 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, improve the Eh value of crop rhizosphere soil, balance the pH value of the soil, and provide 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 changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied 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. 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; The oyster shell and the limestone are subjected to calcination pretreatment: high-temperature calcination, crushing and grinding treatment, and crushed to a particle size of 125 to 147 μm; S2, adding ilmenite according to 10% to 15% of the mass percentage of the soil conditioner, and mixing evenly to obtain a composite soil conditioner; The ilmenite is crushed, ground and sieved before mixing, and the diameter of the sieve is 1 to 3 mm.

2. The method for preparing the composite soil conditioner according to claim 1, characterized in that: 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 h to 2.5 h; the effective components of the mineral humic acid are one or more of fulvic acid, black humic acid and palmitic acid.

3. The method for preparing the composite soil conditioner according to claim 1, characterized in that: 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.

4. A method for using a composite soil conditioner, characterized in that: The composite soil conditioner according to any one of claims 1 to 3 is applied to arsenic-contaminated soil at a dosage of 280 to 320 kg per mu, and the composite soil conditioner is fully mixed with the surface soil and then aged for 14 to 16 days.

5. The method for using the composite soil conditioner according to claim 4, characterized in that: Crops are planted in the aged arsenic-contaminated soil, wherein the crop is selected round-leaved Amaranth.

6. Application of composite soil conditioner, characterized in that: The arsenic contamination value of the arsenic-contaminated soil using the composite soil conditioner as claimed in any one of claims 1 to 3 is between 150 mg·kg and 180 mg·kg -1 scope.

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