Method for inhibiting rice field soil cadmium activation and reducing rice cadmium content

Abstract

The invention relates to the technical field of soil and food heavy metal pollution prevention and control, and provides a method for inhibiting rice field soil cadmium activation and reducing rice cadmium content, which comprises the following steps: before rice planting flooding, mixing an electron shuttle material with adsorption performance with a metal sulfide with electrochemical potential lower than that of CdS, scattering the mixture into rice field soil and fully and uniformly mixing the mixture with plough layer soil. Planting rice in a conventional mode after the soil is drowned, and harvesting rice grains one week after drainage and field baking in the later stage of filling. According to the invention, a Cd fixation coefficient and a two-stage regulation index are constructed and are used for evaluating the adsorption and vulcanization effects of the composite regulation agent on Cd < 2 + > in a flooding stage and the promotion effects of the composite regulation agent on electron transfer and CdS stability in a drainage stage. Normal moisture management is adopted, the ratio of Zn in ZnS to the concentration of extractable Cd in soil and the proportion of nano-biochar are optimized, activation of Cd in different stages is accurately inhibited, and the content of Cd in rice is reduced. The method is high in stability and high in universality and has popularization value.

Description

Technical Field

[0001] The present invention relates to the technical field of prevention and control of heavy metal pollution in soil and food, and more specifically, to a method for inhibiting cadmium activation in paddy soil and reducing cadmium content in rice. Background Art

[0002] Due to the accelerated industrialization process, mining, improper use of chemical fertilizers and pesticides, and unreasonable treatment of waste, a large amount of cadmium (Cd)-containing pollutants enter the environment and accumulate in the soil, and the heavy metal cadmium (Cd) pollution situation in paddy soil is severe. Cd pollution in paddy soil easily leads to the Cd concentration in rice exceeding the limit value of China's food hygiene and health standard (0.2 mg kg -1 ), thus threatening human health through the dietary route. Paddy fields have a periodic flooding and drainage process, and the drainage stage contributes more than 90% to the Cd accumulation in rice. Therefore, it is crucial to reduce the availability of Cd in the soil drainage and oxidation stage. Current measures for reducing soil Cd pollution mainly focus on passivating soil Cd, including increasing soil pH by adding a single alkaline material (such as CaCO3, CaO, etc.) to reduce the solubility of Cd, passivating Cd by adding iron and manganese oxides 2+ , enhancing the adsorption and fixation of Cd by increasing soil organic matter through exogenous application of organic fertilizers 2+ , etc. However, these methods basically reduce the availability of Cd in the overall flooding and drainage stages by strengthening the physical adsorption effect, without fully considering the contribution of the flooding and drainage stages of paddy fields to Cd pollution in rice, resulting in the underutilization of the added remediation materials. Therefore, the above methods have problems such as low universality and poor stability in inhibiting soil Cd activation and alleviating Cd accumulation in rice, and cannot ensure that the Cd concentration in rice is reduced from a high-risk level to the safety standard level. In particular, the existing technology lacks a means for quantitatively evaluating the synergistic effect of adsorption effect, sulfide redox potential difference, and electron transfer efficiency, making it difficult to dynamically optimize the ratio of remediation materials and water management strategies, resulting in the inability to accurately inhibit the Cd activation process in different stages. For the flooding and drainage stages with different contributions, specifically reducing the availability of soil Cd in different stages will have a more significant effect. Therefore, there is an urgent need for a method that can make full use of the flooding and drainage characteristics of paddy soil and their significant differences in the contribution to Cd accumulation in rice, effectively reduce the availability of Cd in the soil drainage and oxidation stage and then reduce the Cd accumulation in rice on the basis of ensuring no secondary pollution, so as to ensure food safety and human health. Summary of the Invention

[0003] To overcome the above-mentioned defects of the prior art, the present invention provides a method for inhibiting cadmium activation in paddy soil and reducing cadmium content in rice. Innovatively, an electron shuttle with adsorption properties is incorporated into the formation of metal sulfides and the synergistic system of the galvanic cell effect between different metal sulfides. By quantifying the combined contributions of adsorption, potential difference, and adsorption enhancement effect through the Cd fixation coefficient, and combining the two-stage regulation index to dynamically evaluate the coupling effect of adsorption / sulfidation efficiency during the flooding stage and electron transfer / stability during the drainage stage, the cadmium concentration in rice is effectively reduced to below the limit value of China's food hygiene and health standards.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A method for inhibiting cadmium activation in paddy soil and reducing cadmium content in rice. Before flooding for rice cultivation, an electron shuttle material with adsorption properties (denoted as "Component A") is mixed with a metal sulfide (denoted as "Component B") whose electrochemical potential (open circuit potential value measured compared to the standard hydrogen electrode) is lower than that of CdS. The mixture (denoted as "composite regulator") is scattered into the paddy soil and thoroughly mixed with the plow layer soil. After the soil is flooded, rice is cultivated according to the conventional cultivation method and water management requirements. After draining and drying the field for 1 week in the late filling stage of rice, rice grains are harvested.

[0006] To evaluate the effect of the composite regulator on the reduction of Cd 2+ activity in soil pore water, the present invention defines the Cd fixation coefficient, and its calculation formula is:

[0007]

[0008] In the formula, CFS is the Cd fixation coefficient; C Cd,p is the Cd 2+ concentration in soil pore water before application; C Cd,t is the Cd 2+ concentration in soil pore water after application; is the redox potential of ZnS to CdS; E ref is the standard reference potential, with the CdS potential of 346.3 - 362.8 mV as the benchmark; Q Cd,nano is the Cd 2+ adsorption capacity of nano-biochar; Q Cd,bulk is the Cd 2+ adsorption capacity of ordinary biochar; ω1, ω2, and ω3 are weight coefficients, satisfying ω1 + ω2 + ω3 = 1..

[0009] The Cd fixation coefficient of the present invention evaluates the comprehensive performance of the composite regulator through the weighted calculation of the adsorption reduction rate, potential difference contribution rate, and nano-adsorption enhancement rate.

[0010] In the present invention A three - electrode system (working electrode: ZnS / CdS composite electrode; reference electrode: saturated calomel electrode; auxiliary electrode: platinum electrode) was used to scan the open - circuit potential in a pH 5.5 buffer solution.

[0011] In the present invention Determined by batch adsorption experiments, the conditions were 25 °C, initial Cd 2+ concentration of 5 mg L -1 , adsorption time of 24 hours, and the adsorption amount ratio per unit mass of biochar was calculated.

[0012] The above - mentioned is aimed at paddy field environments where the contribution of the soil drainage stage to Cd accumulation in rice is significantly more than that of the soil flooding stage. Since most paddy fields have this characteristic, the method of the present invention has universality for Cd - contaminated paddy field soil.

[0013] The component A - an electron - shuttle material with adsorption properties, mainly mediates the adsorption effect during the paddy field flooding stage. The types include micro / nano - sized pyrolytic biochar, hydrothermal biochar, etc., among which nano - sized pyrolytic biochar is the best preference. The raw materials for preparing and obtaining these biochars can be uncontaminated agricultural bulk crop wastes (such as rice, wheat straw, etc.) or livestock and poultry manure wastes, etc., and uncontaminated rice straw raw materials are the best preference. That is, nano - sized straw - sourced pyrolytic biochar is the best preference.

[0014] The component B - metal sulfide, needs to meet two conditions: (1) The metal element should be a beneficial macro, meso, or microelement, (2) Its electrochemical potential should be significantly lower than that of CdS (346.3 - 362.8 mV, measured under pH conditions of 4.5 - 6.5). According to the galvanic cell effect, metal sulfides with low electrochemical potential are prone to preferentially oxidize and dissolve, thereby inhibiting the oxidation and dissolution process of metal sulfides with higher electrochemical potential around them, and thus inhibiting the activation of metal ions in the latter. Among the feasible metal sulfides that meet the above conditions, ZnS or MnS is preferred.

[0015] The composite regulator - a mixture of an electron - shuttle material with adsorption properties and metal sulfide. Taking nano - biochar as an example of the electron - shuttle material, it is added at 0.2 - 0.8% (w / w) of the mass of the paddy field plow layer soil; for metal sulfide, taking ZnS or MnS as an example, first, the Cd in the soil extracted by 0.1 mol L -1 CaCl2 (pH 7.0) reagent is denoted as "extractable Cd", and the Zn in the externally added ZnS or Mn in the MnS is set to 28 - 120 times the concentration of extractable Cd. 2+

[0016] In the described method, under the conventional water management in paddy fields, during the pulping period, a composite regulator is scattered and completely mixed with the plow layer soil, and flooding is continuously maintained for 3 - 5 days, with the water surface exceeding the water - soil interface by 3 - 5 cm during the flooding period. After draining the paddy fields for 1 week during the late filling stage of rice, rice grains are harvested. As a preferred embodiment of the method of the present invention, the electron shuttle material with adsorption properties is nano - sized, porous pyrolytic biochar, and its preparation source material is conventional uncontaminated rice straw. With the existing preparation devices and technical support, the preparation cost of nano - biochar is relatively economical. The metal sulfide is ZnS particles or a fertilizer rich in ZnS. The ZnS fertilizer can be a general agricultural fertilizer or can be replaced by a sphalerite mineral fertilizer rich in ZnS. The ZnS fertilizer is the best preference.

[0017] The efficiency of the composite regulator during the flooding stage and the drainage stage is evaluated through the two - stage regulation index, and its calculation formula is:

[0018]

[0019] In the formula, DPSI is the two - stage regulation index, A1 is the adsorption amount of Cd by the composite regulator during the flooding stage 2+ ; A0 is the adsorption amount of Cd when component A is used alone 2+ ; S1 is the content of CdS promoted to form by the composite regulator during the flooding stage; S0 is the generation amount of CdS without adding the composite regulator; E1 is the rate of electron transfer between ZnS / MnS and CdS promoted by the composite regulator during the drainage stage; E0 is the electron transfer rate between ZnS / MnS and CdS when component B (ZnS / MnS) is used alone; P1 is the percentage of stable CdS maintained by the composite regulator during the drainage stage; P0 is the percentage of CdS that still stably exists without adding the composite regulator; is the ratio of the Cd 2+ adsorption amounts of the composite regulator and the nano - biochar alone, calculated by fitting the adsorption isotherm with the Langmuir model; is the ratio of the CdS generation amounts of the composite regulator and without adding the regulator, analyzed by quantitatively analyzing the peak area through X - ray diffraction (XRD); is the ratio of the electron transfer rates of the composite regulator and ZnS alone, calculated by measuring the charge transfer resistance using alternating current impedance (EIS); is the percentage of stable CdS of the composite regulator and without adding the regulator, calculated by combining the CdS dissolution experiment and measuring the dissolved amount of Cd 2+ using ICP - OES / AAS.

[0020] Among the two - stage regulation indexes, the adsorption amount ratio during the flooding stage It is positively correlated with the addition amount of nano-biochar, and the electron transfer rate ratio in the drainage stage is related to the conductivity of nano-biochar (≥10 S / m -1 ).

[0021] The two-stage regulation index of the present invention calculates the coupling of adsorption and sulfidation effects in the flooding stage and electron transfer and stability in the drainage stage, and dynamically optimizes the water management strategy.

[0022] As a further solution of the present invention, a method for inhibiting cadmium activation in paddy soil and reducing cadmium content in rice includes the following steps:

[0023] S1: Evaluate the contribution of the flooding and drainage stages of paddy fields to the Cd accumulation in rice, determine the feasibility of applying the composite regulator in this method, and optimize the addition amounts of the two components in the composite regulator.

[0024] S2: Prepare component A - nano-biochar. The mass of the soil in the regulated block can be calculated according to the area of the plough layer soil in the paddy field, and the ratio of the mass of the added nano-biochar to the soil mass is controlled to be 0.2 - 0.8%. Prepare component B - ZnS particles, and control the ratio of Zn in the added ZnS to the extractable Cd concentration in the soil to be 28 - 120. Specifically, 0.1 mol / L -1 CaCl2 (pH 7.0) reagent can be used to extract the mixed sample of the plough layer soil and measure the content of extractable Cd in the soil, so that the ratio of Zn in the externally added ZnS to the concentration of extractable Cd in the background soil reaches between 28 and 120.

[0025] S3: Manually and fully mix the above component materials, and sprinkle them on the soil surface during the slurry making of paddy soil, so that they are completely and evenly mixed with the plough layer soil.

[0026] S4: The paddy field adopts conventional water management measures. The above composite regulator is mixed into the plough layer soil and flooded for 3 - 5 days, and the water surface exceeds the water-soil interface by 3 - 5 cm during the flooding period. After draining and drying the paddy field for 1 week in the late stage of rice filling, the rice grains are harvested.

[0027] For the water management, normal water management is adopted. Flood for 3 - 5 days in the early stage. On the one hand, it protects the externally added ZnS fertilizer from being oxidized and denatured. On the other hand, the externally added nano-biochar can directly adsorb Zn 2+ and Cd 2+ or promote the stable existence and increase of their contents by adsorbing ZnS, CdS, etc. formed in the flooding stage. In the drainage stage, nano-biochar improves the electron transfer efficiency between ZnS and CdS through its own electron shuttle property. The method of the present invention not only effectively reduces the free Cd in the pore water in the flooding stage 2+The concentration also significantly inhibited the activation of soil Cd during the drainage stage, thereby reducing the Cd content in rice to below the limit value of the national food hygiene and health standard.

[0028] Compared with the prior art, the beneficial effects of the method for inhibiting the activation of cadmium in paddy soil and reducing the cadmium content in rice of the present invention are as follows:

[0029] By applying a mixture of an electron shuttle material with adsorption properties (such as nano-biochar) and a metal sulfide with an electrochemical potential lower than that of CdS (such as ZnS fertilizer) to the soil, controlling the ratio of Zn in the exogenous ZnS to the concentration of extractable Cd in the soil and the proportion content of the exogenous nano-biochar, the activation of soil Cd during the flooding and drainage stages can be specifically inhibited, and then the Cd content in rice can be reduced.

[0030] By constructing the calculation formulas of the Cd fixation coefficient and the two-stage regulation index, the quantitative evaluation of the regulation effect of Cd pollution in paddy fields is realized. Among them, the calculation formula of the Cd fixation coefficient can guide the rapid judgment of the rationality of the compound regulator ratio in the field; the calculation formula of the two-stage regulation index provides a dynamic optimization basis for water management. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic flow chart of the method for inhibiting the activation of cadmium in paddy soil and reducing the cadmium content in rice of the present invention.

[0032] Figure 2 It is the effect of the method for inhibiting the activation of cadmium in paddy soil and reducing the cadmium content in rice of the present invention Figure 1 .

[0033] Figure 3 It is the effect of the method for inhibiting the activation of cadmium in paddy soil and reducing the cadmium content in rice of the present invention Figure 2 . DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] Example 1

[0036] S1: Extract the soil with 0.1 mol L -1 CaCl2 reagent and measure the concentration of extractable Cd to be 1.5 mg kg -1, 3.0 kg of soil was added to each pot for each treatment of the potted plants. Calculated according to the addition amount of 0.5% (w / w), the addition amount of nano-biochar (component A) was 15 g; calculated according to the ratio of exogenous ZnS-Zn to the concentration of extractable Cd in the soil background of 116, the addition amount of ZnS (component B) was 0.78 g.

[0037] S2: Components A and B were first mixed and then added to the soil to make it completely mixed with the soil.

[0038] S3: After the soil was flooded for 5 days, rice seedlings were planted. With the conventional water management method, the water was drained in the late tillering stage to prevent ineffective tillering and facilitate the jointing growth of the plants, and then flooded again. During the flooding period, the water layer above the water-soil interface was maintained at 3 - 5 cm. After the rice was in the filling stage and the grains were plump, the water was drained and dried for 1 week, and then the rice grains were harvested. The Cd activity in the soil at different growth stages during the rice growth period and the accumulation content of heavy metal elements such as Cd in the rice grains were detected in the laboratory environment, and the grain yield was counted.

[0039] Figure 2 For the effect diagram of Example 1 (potted plant experiment I), the soil was collected from Xiangtan, Hunan. The total Cd concentration in the soil was 3.0 mg / kg -1 , pH 5.5. Four treatments were set: (1) Control, (2) the soil added with ZnS (+ZnS), where the ratio of exogenous ZnS-Zn to the extractable Cd concentration in the soil background was 116, (3) the soil added with nano-biochar (+nBC), with an addition amount of 0.5% (w / w), (4) the soil added with a mixture of ZnS and nano-biochar, and the addition amounts of the two components were the same as those in (2) and (3) respectively. Figure 2 (a) and (b) are the changes in the Cd concentration in the soil pore water and the extractable Cd concentration over time in the four groups of potted plant treatments respectively; Figure 2 (c), (d), (e), (f), (g) are the concentrations of elements such as Cd, Zn, Fe, Mn, and As in the rice grains in the four groups of potted plant treatments respectively; Figure 2 (h) is the rice grain yield in the four groups of potted plant treatments.

[0040] As Figure 2 shown, through the above method, a greenhouse rice potted plant experiment was carried out using the soil from Xiangtan, Hunan. Compared with the control (Control) without adding any regulator, the application of the composite regulator (nano-biochar + ZnS mixture) effectively reduced the Cd concentration in the soil pore water and the extractable Cd concentration, and the reduction rates could reach 12 - 81% and 1.2 - 83% respectively. The Cd concentration in the rice grains decreased by 86% (i.e., 0.15 mg / kg -1 ) and was lower than the limit value of the national food hygiene and health standard (0.2 mg / kg -1)。In addition, the As content in the grains was not affected, the nutritional quality indexes such as Zn, Fe, and Mn in the grains were not affected, and the grain yield was effectively increased by 68%.

[0041] In the embodiment of the present invention, the Cd fixation coefficient calculation formula is used to evaluate the inhibition effect of the composite regulator on soil cadmium activation. The Cd fixation coefficient calculation formula quantifies the inhibition ability of the composite regulator on Cd activation through the weighted combination of adsorption effect, potential difference effect, and adsorption enhancement effect. Among them, the adsorption effect term is determined based on the change in the Cd 2+ concentration in soil pore water. The pore water is extracted by centrifugation and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The percentage of the concentration difference before and after application in the initial concentration is calculated to reflect the direct adsorption contribution of component A, and its weight is set to 0.75; the potential difference effect term is determined by scanning the open circuit potential in a pH 5.5 buffer solution using a three-electrode system (the working electrode is a ZnS / CdS composite electrode, and the reference electrode is a saturated calomel electrode), and calculating the potential difference ratio in combination with the standard CdS potential. Its weight is set to 0.15; the adsorption enhancement term is determined by comparing the Cd 2 + adsorption amounts of nano-biochar and ordinary biochar through a batch adsorption experiment. Specifically, at 25 °C, a solution with an initial Cd 2+ concentration of 5 mg L -1 is used, and the adsorption time is 24 hours. The adsorption amount ratio per unit mass of biochar is calculated, and the promotion effect of the nanomaterial on the adsorption ability is characterized by this ratio. Its weight is set to 0.10. The calculation parameters and results of the Cd fixation coefficient under different treatments are shown in Table 1.

[0042] Table 1. Parameters and results of Cd fixation coefficient calculation under different treatments

[0043]

[0044]

[0045] In the embodiment of the present invention, the two-stage regulation index calculation formula is used to evaluate the action efficiency of the composite regulator in different stages. The two-stage regulation index calculation formula dynamically evaluates the synergistic effect of the composite regulator through the product of the regulation factors in the flooding stage and the drainage stage. Among them, the flooding stage factor is determined by combining the Langmuir adsorption model and X-ray diffraction (XRD) quantitative analysis, and calculating the adsorption amount increase multiple of the composite regulator to Cd 2+ and the CdS production amount increase multiple respectively, reflecting the synergistic effect of adsorption and sulfidation; the drainage stage factor The charge transfer resistance was measured by AC impedance to calculate the electron transfer rate ratio, and the CdS dissolution experiment was combined with ICP-OES / AAS to determine the Cd 2+ The dissolution amount was calculated to calculate the percentage change of stable CdS, and to quantify the enhancement of CdS stability by the electron shuttle effect of nano-biochar; the construction of the two-stage regulation index was based on the dual mechanism of inhibiting Cd activation in the flooding stage and maintaining CdS stability in the drainage stage. Its value was positively correlated with the reduction of rice Cd and the increase in yield, providing a theoretical basis for the dynamic optimization of water management strategies. The calculation parameters and results of the two-stage regulation index of each treatment group are shown in Table 2.

[0046] Table 2. Parameters and results of the calculation of the two-stage regulation index under different treatments

[0047]

[0048]

[0049] In the embodiment of the present invention, component A added is nano pyrolytic biochar, and component B is ZnS reagent particles. However, in actual production, component A can be replaced by adding micron-sized pyrolytic biochar or micron / nano-sized hydrothermal biochar with adsorption performance. Component B can be replaced by adding general agricultural fertilizers rich in ZnS or mineral fertilizers such as sphalerite rich in ZnS, and the addition form does not affect the effect of the present invention.

[0050] Example 2

[0051] S1: Use 0.1 mol L -1 The soil was leached with CaCl2 reagent and the extractable Cd concentration was determined to be 1.5 mg kg -1 3.0 kg of soil was added to each pot under each pot treatment. The amount of nano-biochar (component A) added was calculated to be 15 g based on the addition amount of 0.5% (w / w); the amount of MnS (component B) added was calculated to be 0.84 g based on the ratio of exogenous MnS-Mn to the background extractable Cd concentration in the soil of 116.

[0052] S2: Mix components A and B first and then add them to the soil to mix them thoroughly.

[0053] S3: Plant rice seedlings 5 ​​days after the soil is flooded. Combined with conventional water management methods, drainage is performed in the late tillering stage to prevent ineffective tillering and facilitate jointing growth of plants. Then, the soil is flooded again. During the flooding period, the water layer above the water-soil interface is maintained at 3-5 cm. After the rice is filled and the grains are full, the soil is drained and dried for 1 week, and then the rice grains are harvested. In the laboratory environment, the soil Cd activity and the accumulation content of heavy metal Cd and other elements in rice at different growth stages during rice growth are detected, and the grain yield is counted.

[0054] Figure 3 For the effect diagram of Example 2 (Pot experiment II), the soil was collected from Xiangtan, Hunan. The total Cd concentration in the soil was 3.0 mg / kg -1 , and the pH was 5.5. Four treatments were set: (1) Control, (2) soil added with MnS (+MnS), where the ratio of exogenous MnS-Mn to the background extractable Cd concentration in the soil was 116, (3) soil added with nano-biochar (+nBC) with an addition amount of 0.5% (w / w), (4) soil added with a mixture of MnS and nano-biochar, and the addition amounts of the two components were the same as those in (2) and (3) respectively. Figure 3 (a) and (b) are the changes in the Cd and extractable Cd concentrations in the soil pore water over time in the four groups of pot experiments respectively; Figure 3 (c), (d), (e), (f), and (g) are the concentrations of elements such as Cd, Zn, Fe, Mn, and As in the rice in the four groups of pot experiments respectively; Figure 3 (h) is the rice yield in the four groups of pot experiments.

[0055] As Figure 3 shown, through the above method, a greenhouse rice pot experiment was carried out using the soil from Xiangtan, Hunan. Compared with the control (Control) without adding any regulator, the application of the composite regulator (nano-biochar + MnS mixture) effectively reduced the Cd and extractable Cd concentrations in the soil pore water, and the reduction rates could reach 4.7 - 76% and 6.7 - 75% respectively. The Cd concentration in the rice grains decreased by 83% accordingly (i.e., 0.18 mg / kg -1 ) and was lower than the limit value of the national food hygiene and health standard (0.2 mg / kg -1 ). In addition, the As content in the grains was not affected, the Zn in the grains was not negatively affected, the quality indexes such as Fe and Mn in the grains were not affected, and the grain yield was effectively increased by 48%.

[0056] In the embodiment of the present invention, the Cd fixation coefficient calculation formula is used to evaluate the inhibitory effect of the composite regulator on soil cadmium activation. The Cd fixation coefficient calculation formula quantifies the inhibitory ability of the composite regulator on Cd activation through the weighted combination of adsorption effect, potential difference effect, and adsorption enhancement effect. Among them, the adsorption effect term is determined based on the change in the Cd 2+ concentration in the soil pore water. The pore water is extracted by centrifugation and analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The percentage of the concentration difference before and after application in the initial concentration is calculated to reflect the direct adsorption contribution of component A, and its weight is set to 0.75; the potential difference effect term The measurement was carried out using a three - electrode system (the working electrode was a ZnS / CdS composite electrode, and the reference electrode was a saturated calomel electrode) to scan the open - circuit potential in a pH 5.5 buffer solution. The potential difference ratio was calculated by combining with the standard CdS potential, and its weight was set to 0.15; the adsorption enhancement term The measurement was carried out through batch adsorption experiments to compare the Cd adsorption amounts of nano - biochar and ordinary biochar 2 + Specifically, at 25 °C, a solution with an initial Cd 2+ concentration of 5 mg / L -1 was used, and the adsorption time was 24 hours. The adsorption amount ratio per unit mass of biochar was calculated, and the enhancement effect of the nanomaterial on the adsorption capacity was characterized by this ratio. Its weight was set to 0.10. The calculation parameters and results of the Cd fixation coefficient under different treatments are shown in Table 3.

[0057] Table 3. Parameters and results of Cd fixation coefficient calculation under different treatments

[0058]

[0059] In the examples of the present invention, a two - stage regulation index calculation formula was used to evaluate the action efficiency of the composite regulator at different stages. The two - stage regulation index calculation formula dynamically evaluated the synergistic effect of the composite regulator through the product of the regulation factors in the flooding stage and the drainage stage. Among them, the flooding - stage factor The measurement was carried out by combining the Langmuir adsorption model and X - ray diffraction (XRD) quantitative analysis to calculate the adsorption amount increase multiple of the composite regulator for Cd 2+ and the CdS production amount increase multiple, reflecting the synergistic effect of adsorption and sulfidation; the drainage - stage factor The measurement was carried out by using alternating current impedance to measure the charge transfer resistance to calculate the electron transfer rate ratio, and through the CdS dissolution experiment combined with ICP - OES / AAS to measure the Cd 2+ dissolution amount, calculating the percentage change of stable CdS to quantify the enhancement effect of the electron shuttle effect of nano - biochar on the stability of CdS; the construction of the two - stage regulation index was based on the dual mechanisms of inhibiting Cd activation in the flooding stage and maintaining CdS stability in the drainage stage. Its value was positively correlated with the Cd reduction in rice and the yield increase, providing a theoretical basis for the dynamic optimization of the water management strategy. The calculation parameters and results of the two - stage regulation index for each treatment group are shown in Table 4.

[0060] Table 4. Parameters and results of two - stage regulation index calculation under different treatments

[0061]

[0062] In the embodiments of the present invention, the added component A is nano pyrolytic biochar, and the component B is MnS reagent particles. However, in actual production, component A can be replaced with micron-sized pyrolytic biochar or micron / nano-sized hydrothermal biochar with adsorption properties, etc. Component B can be respectively replaced with general agricultural fertilizers rich in MnS or mineral fertilizers such as manganous sulfide ore rich in MnS. The addition form does not affect the effect of the present invention.

[0063] Example 3

[0064] To verify the correlation between the established evaluation indicators and the actual prevention and control effects, a comparative analysis was carried out on the evaluation index results of Examples 1 and 2 and the measured Cd content and yield data of rice. The results are shown in Table 5.

[0065] Table 5 Relationship between evaluation indicators and Cd content and yield of rice

[0066]

[0067]

[0068] As can be seen from Table 5, with the increase of the Cd fixation coefficient and the two-stage regulation index, the Cd concentration in rice gradually decreases, and the Cd reduction rate and the yield increase rate show an upward trend. The linear regression method was used to analyze the relationship between the Cd fixation coefficient, the two-stage regulation index and the Cd concentration, Cd reduction rate, and yield increase rate of rice. The results show that there is an obvious negative correlation between the Cd fixation coefficient, the two-stage regulation index and the change of the Cd concentration in rice, indicating that the higher the index value, the lower the Cd concentration; there is a positive correlation with the Cd reduction rate and the yield increase rate. The higher the index value, the higher the Cd reduction rate and the yield increase rate. The above relationship has a linear correlation in statistics (R 2 > 0.9).

[0069] As mentioned above, only the specific embodiments of the present application are described, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0070] Finally: The above description is only the preferred embodiments of the present invention and is not used to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should all be included within the protection scope of the present invention.

Claims

1. A method for inhibiting cadmium activation in paddy soil and reducing cadmium content in rice, characterized in that: The following steps are involved: Before flooding for rice planting, an electron shuttle material with adsorption performance is used as component A and mixed with a metal sulfide with an electrochemical potential lower than CdS as component B, wherein the electrochemical potential is an open circuit potential value measured relative to a standard hydrogen electrode; the obtained mixture is sprinkled into paddy field soil as a composite regulator to be fully mixed with the plough layer soil; after the soil is flooded, rice is planted according to conventional planting methods and water management requirements, and the rice grains are harvested after draining the field in the late rice filling period and 1 week later; the effect of the composite regulator on Cd in soil pore water is evaluated by the Cd fixation coefficient 2 +The effect of reduced activity, calculated as: Where, CFS is the Cd fixed coefficient; C Cd,p is the Cd content in soil pore water before application 2+ Concentration; C Cd,t is the Cd content in soil pore water after application 2+ concentration; is the redox potential of ZnS to CdS; E ref is the standard reference potential, based on the CdS potential of 346.3-362.8 mV; Q Cd,nano Cd in nano-biochar 2+ Adsorption capacity; Q Cd,bulk Cd in ordinary biochar 2+ Adsorption amount; ω1, ω2 and ω3 are weight coefficients, satisfying ω1+ω2+ω3=1.

2. The method for inhibiting cadmium activation in paddy soil and reducing cadmium content in rice according to claim 1, characterized in that: The paddy field environment satisfies that the contribution rate of soil drainage stage to Cd accumulation in rice is greater than the contribution rate of soil flooding stage.

3. The method for inhibiting cadmium activation in paddy soil and reducing cadmium content in rice according to claim 1, characterized in that: The component A is an electron shuttle material with adsorption performance, which mainly mediates the adsorption effect during the flooding stage of the rice field. The component A includes micron-scale or nano-scale pyrolysis biochar and hydrothermal biochar.

4. The method of claim 1, wherein: The component B is a metal sulfide, which must meet the following requirements: the metal element of the metal sulfide must be a large, medium or trace amount of beneficial elements; and the electrochemical potential of the metal sulfide must be significantly lower than that of CdS.

5. The method of claim 1, wherein: The composite regulator is a mixture of an electron shuttle material with adsorption performance and a metal sulfide. The electron shuttle material is selected from biochar with micron to nanometer sizes, and the addition amount is 0.2-0.8% of the mass of the paddy field plough layer soil. When the metal sulfide is ZnS or MnS, firstly, 0.1 mol L -1 Soil Cd extracted by calcium chloride reagent 2+ The concentration was recorded as "extractable Cd", and the exogenously added Zn in ZnS or Mn in MnS was set to 28-120 times the concentration of extractable Cd.

6. The method according to claim 1, characterized in that The method comprises the following steps: under conventional water management in the paddy field, during the beating period, the composite regulator is sprinkled and completely mixed with the tillage layer soil, and the field is continuously flooded for 3-5 days, during which the water surface exceeds the water-soil interface by 3-5 cm. The field is drained and baked in the late rice filling period, and the rice grains are harvested after one week.

7. The method of claim 1, wherein: The dual-stage regulation index is used to evaluate the efficiency of the compound regulator during the flooding stage and the drainage stage. The calculation formula is: In the formula, A1 is the effect of the compound regulator on Cd in the flooding stage. 2 + adsorption; A0 is the adsorption of Cd when component A is used alone 2 + adsorption amount; S1 is the CdS content promoted by the composite regulator in the flooding stage; S0 is the amount of CdS generated when the composite regulator is not added; E1 is the rate of electron transfer between component B and CdS promoted by the composite regulator in the drainage stage; E0 is the electron transfer rate between component B and CdS when component B is used alone; P1 is the percentage of CdS that remains stable in the drainage stage by the composite regulator; P0 is the percentage of CdS that still exists stably when the composite regulator is not added.

8. A method for inhibiting cadmium activation in paddy soil and reducing cadmium content in rice according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1: Evaluate the contribution of flooding and drainage to the accumulation of Cd in rice, determine the feasibility of applying the compound regulator in this method, and optimize the addition amount of the two components in the compound regulator; S2: Prepare nano-biochar as component A, and calculate the soil mass of the controlled block according to the area of ​​the paddy field soil, and control the added nano-biochar mass to 0.2-0.8% of the soil mass; prepare ZnS particles as component B, and control the ratio of Zn in the added ZnS to the extractable Cd concentration in the soil to be 28-120. The specific operation can be to add 0.1 mol L -1 Calcium chloride reagent was used to extract the mixed sample of the topsoil and the content of Cd extracted from the soil was determined, so that the ratio of Zn in the exogenously added ZnS to the background soil extracted Cd concentration reached between 28 and 120; S3: The above two components are mixed manually and sprinkled on the soil surface during the paddy field soil beating process to make them completely and evenly mixed with the tillage layer soil; S4: Conventional water management measures were adopted in the rice fields. The above-mentioned compound regulator was mixed into the soil tillage layer and flooded for 3-5 days. During the flooding period, the water surface exceeded the water-soil interface by 3-5 cm. The rice grains were harvested after the rice was drained and baked for 1 week in the late stage of rice filling. The water management adopts normal water management, and flooding for 3-5 days in the early stage can protect the exogenously added ZnS fertilizer from being oxidized and denatured, and the exogenous nano-biochar can directly absorb Zn 2+ 、Cd 2+ Or by adsorbing ZnS and CdS formed in the flooding stage; in the drainage stage, nano-biochar improves the electron transfer efficiency between ZnS and CdS through its own electron shuttling properties.

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