Rice field soil conditioner, its preparation method and application

Abstract

The application provides a paddy field soil conditioner, a preparation method and application thereof. The soil conditioner comprises a carrier and a hexavalent iron compound loaded on the carrier; the carrier is biochar, and the hexavalent iron compound is distributed on the surface layer of the biochar; and the mass ratio of the hexavalent iron compound to the carrier in the soil conditioner is (1-20):100. The soil conditioner can realize the synergistic effect of soil cadmium pollution remediation and guarantee of rice yield.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil pollution remediation, in particular to a paddy soil conditioner, a preparation method and application thereof. BACKGROUND

[0002] Cadmium is the most common and toxic heavy metal pollution element in soil, which poses a great threat to food security and even human health. Environmental and human factors have exacerbated cadmium pollution, resulting in the continuous accumulation of cadmium in soil, which affects the health of humans and animals through the food chain.

[0003] The use of paddy soil conditioner can effectively improve the physical and chemical properties of soil and reduce the active components of cadmium in soil, providing favorable conditions for crop growth. At present, most of the remediation methods for cadmium-contaminated soil use imported soil method and replacement of cultivated soil method. Although these methods can reduce soil cadmium pollution in the short term, they affect the soil structure. Biological remediation methods can help eliminate or reduce the toxicity of environmental pollutants, accelerate or strengthen the degradation or transformation processes that occur slowly or not under natural conditions. However, such methods have a long repair time and are limited by the type, concentration and environmental conditions of pollutants, making it difficult to achieve the desired goal. Chemical remediation methods such as chemical washing can efficiently remove cadmium from soil, but the high price and residual chemical agents can easily cause additional environmental pollution problems.

[0004] Currently, studies have shown that different valence iron modified biochar can be used to reduce the bioavailability of cadmium and other heavy metals in soil. For example, iron hydroxide and biochar can be mixed to precipitate heavy metals such as arsenic in soil. In addition, biochar materials loaded with magnetic iron can also effectively inhibit heavy metal components in soil. However, the application of excessive iron-containing biochar amendment can affect the growth of rice and even cause rice yield reduction. Therefore, it is of great significance to coordinate the environmental effects of iron-modified biochar with rice growth to achieve cadmium pollution remediation in paddy soil and ensure rice yield and quality. SUMMARY

[0005] To solve the above technical problems, the present application provides a paddy soil conditioner, a preparation method and application thereof, which can comprehensively improve the problem of cadmium pollution in soil and solve the problem of resource utilization of agricultural by-products.

[0006] To solve the above problems, the present application adopts the following technical solutions:

[0007] A soil conditioner, which comprises a carrier and a hexavalent iron compound loaded on the carrier; the carrier is biochar, and the hexavalent iron compound is distributed on the surface layer of the biochar.

[0008] According to the present application, the biochar is obtained after pyrolysis and carbonization of the agroforestry by-product raw material.

[0009] Preferably, the agroforestry by-product raw material is at least one selected from pine needles, rice straw, common cattail, reed, rice husk, rapeseed straw, wheat straw and sugarcane.

[0010] Preferably, the preparation method of the biochar comprises: after crushing the agroforestry by-product raw material, pyrolysis and carbonization at 400-700℃ for 1-12h using a gas atmosphere furnace to obtain the biochar.

[0011] According to the present application, the specific surface area of the biochar is not less than 8m 2 / g, preferably 8-700m 2 / g, for example 8m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 16.055m 2 / g, 17m 2 / g, 18m 2 / g, 19m 2 / g, 20m 2 / g, 23.519m 2 / g, 25m 2 / g, 30m 2 / g, 40m 2 / g, 50m 2 / g, 60m 2 / g, 70m 2 / g, 80m 2 / g, 90m 2 / g, 100m 2 / g, 200 m 2 / g, 300m 2 / g, 400m 2 / g, 500m 2 / g, 600m 2 / g, 700m 2 / g.

[0012] According to the present application, the pore volume of the biochar is not less than 0.03cm 3 / g, preferably 0.03-1cm 3 / g, for example 0.03cm 3 / g, 0.04cm3 / g, 0.05 cm 3 / g, 0.06 cm 3 / g, 0.07 cm 3 / g, 0.08 cm 3 / g, 0.09 cm 3 / g, 0.1 cm 3 / g, 0.2 cm 3 / g, 0.3 cm 3 / g, 0.4 cm 3 / g, 0.5 cm 3 / g, 0.6 cm 3 / g, 0.7 cm 3 / g, 0.8 cm 3 / g, 0.9 cm 3 / g, 1 cm 3 / g.

[0013] According to the present application, the average pore size of the biochar is not more than 15 nm, preferably 0.1-12 nm, for example 0.1 nm, 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm.

[0014] According to the present application, the hexavalent iron compound is selected from at least one of the group consisting of ferric acid, sodium ferrate and potassium ferrate.

[0015] According to the present application, the mass ratio of the hexavalent iron compound to the carrier in the soil conditioner is (1-20):100, preferably (1-10):100, more preferably (2-4):100.

[0016] According to the present application, the purity of the hexavalent iron compound in the soil conditioner is ≥95%.

[0017] The present application also provides a preparation method of the above-mentioned soil conditioner, which comprises the following steps:

[0018] (1) crushing the agroforestry by-product raw material, then pyrolyzing and carbonizing to obtain biochar;

[0019] (2) mixing the biochar prepared in step (1) with a hexavalent iron compound to obtain the soil conditioner.

[0020] According to the present application, the agroforestry by-product raw material comprises at least one of the group consisting of pine needles, rice straw, southern cattail, reed, rice husk, rape straw, wheat straw and sugarcane.

[0021] Preferably, the agroforestry by-product raw material comprises rice husk and rice straw, and the mass ratio of rice husk to rice straw is (1-20):(99-80), for example, 20:80.

[0022] According to the present application, the pyrolytic carbonization is performed under a vacuum atmosphere (oxygen-free atmosphere).

[0023] Preferably, the vacuum atmosphere can be selected from atmospheres known in the art, for example, at least one selected from the group consisting of, but not limited to, nitrogen, helium, argon, and ammonia.

[0024] According to the present application, the pyrolytic carbonization can be performed under conditions known in the art. Illustratively, the temperature of the pyrolytic carbonization is 400-700°C, for example, 500°C or 600°C. Illustratively, the time of the pyrolytic carbonization is 1-12h, for example, 2h or 4h.

[0025] According to the present application, in step (2), the mass ratio of the biochar to the hexavalent iron compound is 100:(1-20), preferably 100:(1-10), more preferably 100:(2-4).

[0026] According to the present application, the hexavalent iron compound has the meaning as described above, for example, at least one selected from the group consisting of, but not limited to, ferric acid, sodium ferrate, and potassium ferrate.

[0027] Preferably, the purity of the hexavalent iron compound is ≥95%.

[0028] According to the present application, in step (2), the mixing can be performed by methods known in the art, for example, by ball milling.

[0029] The present application also provides a soil conditioner prepared by the above preparation method, which has the meaning as described above.

[0030] The present application also provides use of the above soil conditioner or the soil conditioner prepared by the above preparation method in soil improvement, for example, in rice field soil improvement.

[0031] The present application also provides a soil improvement method, preferably a rice field soil improvement method, which specifically comprises: applying the soil conditioner to soil.

[0032] According to the present application, applying the above soil conditioner or the soil conditioner prepared by the above preparation method to soil can be achieved by mixing the soil conditioner with soil. Specifically, the mixing can be achieved by ploughing, for example. By ploughing, the mixing of the soil conditioner with 0-20cm surface layer soil can be achieved.

[0033] According to the application, the water content in the soil is 0.1-100%.

[0034] According to the application, the cadmium content in the soil is 0-10 mg / kg, for example 0.1 mg / kg, 0.2 mg / kg, 0.3 mg / kg, 0.4 mg / kg, 0.5 mg / kg, 0.6 mg / kg, 0.7 mg / kg, 0.8 mg / kg, 0.89 mg / kg, 0.9 mg / kg, 1 mg / kg, 1.5 mg / kg, 2.0 mg / kg, 2.5 mg / kg, 3.0 mg / kg, 3.5 mg / kg, 4 mg / kg, 4.5 mg / kg, 5 mg / kg, 5.5 mg / kg, 6 mg / kg, 6.5 mg / kg, 7 mg / kg, 7.5 mg / kg, 8 mg / kg, 8.5 mg / kg, 9 mg / kg, 9.5 mg / kg, 10 mg / kg.

[0035] According to the application, in the improved method, the mass-area ratio of the soil improver to the soil is (100-2000) kg / (1-66.66667) m 2 .

[0036] Preferably, the mass-area ratio of the soil improver to the soil is 2000 kg / 66.66667 m 2 .

[0037] According to the application, the improved method can achieve the synergistic effect of soil cadmium pollution remediation and ensuring rice yield.

[0038] Advantages:

[0039] (1) The soil improver of the application uses hexavalent iron compounds to form iron-containing compound colloids when water is added, and the biochar has a high specific surface area and various oxygen-containing functional groups, so that the adsorption of cadmium ions in the soil is achieved through the combination of colloids and biochar materials;

[0040] (2) The soil improver of the application can undergo redox reactions with other organic or inorganic pollutants to form effective adsorption effects, effectively fixing cationic heavy metal components in the soil, thereby further reducing the cadmium content in the soil and improving the overall soil cadmium reduction efficiency of the material. Moreover, the soil improver of the application can achieve the synergistic effect of soil cadmium pollution remediation and ensuring rice yield. In addition, the preparation method of the soil improver of the application is simple, which saves a lot of time and economic cost. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 SEM image (a) and element distribution image (b-f) of the biochar prepared at 500℃.

[0042] Figure 2 The influence of the soil conditioner of Comparative Example 1 and Example 2 on the cadmium accumulation amount of rice grain.

[0043] Figure 3 The rice yield in the application example. DETAILED DESCRIPTION

[0044] The technical solutions of the present application will be further described in detail below in combination with specific examples. It should be understood that the following examples are only illustratively described and explained the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above content of the present application is covered in the scope of the present application intended to be protected.

[0045] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0046] It should be noted that the specific surface area, pore volume and pore size are obtained by BET test.

[0047] The carbon yield is calculated using the following formula:

[0048] Carbon yield = V0 / V1*100%

[0049] Wherein, V0 is the mass of the material after carbonization, and V1 is the mass of the biomass material.

[0050] Preparation Example

[0051] Preparation of biochar: rice hulls and rice straw (mass ratio 20:80) were ground into powder by a powder grinder, and pyrolysis carbonization was carried out at 400℃, 500℃ and 600℃ respectively for 2h in an argon gas atmosphere furnace to obtain biochar. The parameters of the biochar are shown in Table 1.

[0052] As can be seen from Table 1, when the pyrolysis carbonization temperature is 500℃, the specific surface area of the biochar can reach more than 16 m 2 / g, which is suitable for preparing soil conditioners. Figure 1 SEM (a) and element distribution (b-f) of the biochar prepared at a pyrolysis carbonization temperature of 500℃. As can be seen from the figure, in addition to C and O elements, there are also obvious P, N and K elements on the surface of the biochar material after carbonization at 500℃.

[0053] Table 1

[0054]

[0055] Example 1

[0056] The preparation method of the soil conditioner of the present example comprises the following steps:

[0057] (1) The biochar was prepared according to the pyrolysis carbonization temperature of 500°C in the preparation example;

[0058] (2) The biochar prepared in step (1) was mixed with sodium ferrate (purity 95%) at a mass ratio of 100:2, and then ball-milled to obtain the soil conditioner, which is recorded as conditioner 1.

[0059] The soil conditioner of the present example is composed of biochar and sodium ferrate modified on the biochar, wherein the loading amount of sodium ferrate in the biochar is 2wt%, and the biochar is obtained by carbonization of a mixture of rice husk and rice straw as raw material.

[0060] Example 2

[0061] The preparation method of the soil conditioner of the present example comprises the following steps:

[0062] (1) The biochar was prepared according to the pyrolysis carbonization temperature of 500°C in the preparation example;

[0063] (2) The biochar prepared in step (1) was mixed with sodium ferrate (purity 95%) at a mass ratio of 100:4, and then ball-milled to obtain the soil conditioner, which is recorded as conditioner 2.

[0064] The soil conditioner of the present example is composed of biochar and sodium ferrate modified on the biochar, wherein the loading amount of sodium ferrate in the biochar is 4wt%, and the biochar is obtained by carbonization of a mixture of rice husk and rice straw as raw material.

[0065] Comparative Example 1

[0066] The difference between the present comparative example and Example 1 is that the biochar is prepared according to the pyrolysis carbonization temperature of 500°C in the preparation example, and no sodium ferrate is added, and the biochar is used as the soil conditioner, which is recorded as comparative conditioner 1.

[0067] Application Example

[0068] The present test was carried out in the base of Beishan Town, Changsha City, Hunan Province, East longitude 112°56'15", North 27°54'55". It is located in the East Asian monsoon region, belongs to subtropical monsoon humid climate, the climate is mild, the heat is rich, the rainfall is sufficient, the sunshine is sufficient, and the four seasons are distinct. In the rice field of the present test, the cadmium content in the soil is 0.89 mg / kg. 12 plots were randomly selected, and the area of each plot was 30 m 2 , the plots were separated by soil ridge covered with plastic film, single row and single irrigation, and the protection row was set outside, and every 3 plots was a group, which was recorded as experimental group 1, experimental group 2, comparative group 1 and blank group respectively.

[0069] The soil conditioners of Examples 1-2 and Comparative Example 1 were taken respectively, and the following improvement methods were used to improve the paddy soil of Experimental Group 1, Experimental Group 2 and Comparative Group 1. The improvement methods specifically included: mixing the paddy soil conditioner with the paddy soil in each plot evenly, wherein the dosage of the paddy soil conditioner in the soil was 100-2000 kg / mu, mixing it evenly with the top 20cm of soil using a tiller, and after stabilizing for 4 days, transplanting rice.

[0070] Blank group: Rice was transplanted directly without the above soil improvement.

[0071] With consistent field management, the seed soaking date for the single-season rice in the field trial was May 15th, the transplanting size was 15cm × 25cm, and the harvest date was September 20th. The application rates of N, P2O5, and K2O were 120 kg·hm². -2 60kg·hm -2 120kg·hm -2 .

[0072] Freshly harvested rice was tested for cadmium content in rice treated with different methods using an NX-100FA food heavy metal detector. The cadmium accumulation in the rice after soil amendment using the soil conditioners of Examples 1-2 and Comparative Example 1 is shown in Table 2.

[0073] Table 2

[0074]

[0075] like Figure 2 The image shows the effect of the paddy soil conditioner of Comparative Example 1 and Example 2 on cadmium accumulation in rice paddies. (The image is presented in the original text.) Figure 2 It is known that after using the soil conditioner of the present invention, the cadmium content in rice grains is significantly reduced. Among them, the soil conditioner of Example 2 resulted in a cadmium content in rice grains as low as 0.03 mg / kg, thus achieving the best effect.

[0076] Figure 3 The rice yield of paddy fields improved with the soil conditioners of Examples 1-2 and Comparative Example 1 was 8.5 t / hm². -2 10.5t hm -2 11t hm -2 8thm -2 ).from Figure 3As can be seen from Table 2, the rice yield in paddy fields improved with the soil conditioners of Examples 1 and 2 was higher than that in the control and blank groups. This demonstrates that the soil conditioner of the present invention can achieve a synergistic effect, reducing cadmium content in paddy fields without affecting rice yield. Furthermore, Table 2 and... Figure 3 It can be seen that, compared with the blank group, although the use of biochar as a soil conditioner in control group 1 can reduce the cadmium content in paddy fields, the rice yield is reduced. That is, adding biochar alone to improve the soil cannot achieve the above-mentioned synergistic effect. In contrast, the use of the soil conditioner of the present invention to improve paddy fields can achieve the above-mentioned synergistic effect and has obvious advantages.

[0077] The exemplary embodiments of the present invention have been described above. However, the scope of protection of this application is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a soil conditioner, characterized in that, The preparation method includes the following steps: (1) After crushing the agricultural and forestry by-product raw materials, pyrolysis and carbonization are carried out to obtain biochar; the agricultural and forestry by-product raw materials include rice husks and rice straw, and the mass ratio of rice husks to rice straw is 1-20:99-80; the temperature of pyrolysis and carbonization is 400-700℃; the time of pyrolysis and carbonization is 1-12h. (2) The biochar prepared in step (1) is mixed with a hexavalent iron compound to obtain the soil conditioner; The soil conditioner includes a carrier and a hexavalent iron compound loaded on the carrier; the carrier is biochar, and the hexavalent iron compound is distributed on the surface of the biochar; in the soil conditioner, the mass ratio of the hexavalent iron compound to the carrier is 1-20:

100. The specific surface area of ​​the biochar is not less than 8 m². 2 / g; The biochar has a pore volume of not less than 0.03 cm³. 3 / g; The average pore size of the biochar is no greater than 15 nm.

2. The preparation method according to claim 1, characterized in that, The specific surface area of ​​the biochar is 8-700 m². 2 / g; The biochar has a pore volume of 0.03-1 cm³. 3 / g; The average pore size of the biochar is 0.1-12 nm.

3. The preparation method according to claim 1, characterized in that, The hexavalent iron compound is selected from at least one of ferric acid, sodium ferrate and potassium ferrate; The mass ratio of the hexavalent iron compound to the support is 1-10:100; In the soil conditioner, the purity of the hexavalent iron compound is ≥95%.

4. The preparation method according to claim 1, characterized in that, The mass ratio of the hexavalent iron compound to the support is 2-4:

100.

5. The preparation method according to claim 1, characterized in that, The pyrolysis carbonization is carried out under a vacuum atmosphere.

6. The preparation method according to claim 5, characterized in that, The vacuum atmosphere is selected from at least one of nitrogen, helium, argon and ammonia.

7. The preparation method according to claim 1, characterized in that, In step (2), the mass ratio of the biochar to the hexavalent iron compound is 100:1-20; The purity of the hexavalent iron compound is ≥95%.

8. The preparation method according to claim 1, characterized in that, In step (2), the mixing is carried out by ball milling.

9. The application of the soil conditioner prepared by the preparation method according to any one of claims 1-8 in paddy field soil improvement.

10. A method for soil improvement, characterized in that, The soil improvement method is a paddy field soil improvement method, which specifically includes: applying the soil conditioner prepared by the preparation method according to any one of claims 1-8 to the soil; The soil conditioner is applied to the soil by mixing it with the soil. The soil contains 0.1% to 100% water. The cadmium content in the soil is 0-10 mg / kg; In the aforementioned improvement method, the mass-to-area ratio of the soil conditioner to the soil is 100-2000 kg / m³-66.66667 m². 2 ; The improved method achieves a synergistic effect of soil cadmium pollution remediation and ensuring rice yield.

11. The soil improvement method according to claim 10, characterized in that, The mass-to-area ratio of the soil conditioner to the soil is 2000 kg / 66.66667 m². 2 .

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