A selenium-rich cadmium-contaminated soil passivator and its preparation method and use method

Abstract

The present invention belongs to the technical field of soil selenium enrichment and cadmium reduction, and specifically relates to a selenium-rich cadmium contaminated soil passivator, and a preparation method and a use method thereof. The raw materials of the selenium-rich cadmium contaminated soil passivator include: nano-calcium carbonate modified biochar, limestone powder or dolomite powder, and calcium magnesium phosphate fertilizer; the selenium-rich cadmium contaminated soil passivator is obtained by mixing and granulating the above raw materials. The passivator proposed by the present invention is mainly aimed at selenium-rich cadmium contaminated soil. Continuous multiple applications according to the use method can significantly increase the effective selenium content of selenium-rich soil and reduce the effective cadmium content of selenium-rich soil. Compared with the existing soil cadmium passivator, the passivator prepared by the present invention can not only increase crop yields and increase economic benefits, but also is convenient and efficient, low-cost, fast-acting, green and pollution-free, and truly achieves the goal of simultaneous cadmium reduction and selenium enrichment.

Description

Technical Field

[0001] The invention belongs to the technical field of soil selenium-enriched cadmium reduction, and particularly relates to a selenium-enriched cadmium-contaminated soil passivator and a preparation method and a use method thereof. Background Art

[0002] Selenium is a trace element necessary for the human body. It is closely related to human health and is the source of human life. It is known as the "element of life". It has multiple biological functions such as anti-oxidation and enhancing the immune system. It is a recognized anti-cancer substance in the international medical community. According to statistics, 72% of counties and cities in my country are selenium-deficient to varying degrees, of which 1 / 3 are severely selenium-deficient areas. For people with selenium deficiency, dietary selenium intake is one of the important ways to supplement selenium, and the safest and most effective way to supplement selenium for the human body is usually natural selenium-rich agricultural products. The selenium content of agricultural products mainly comes from soil, and soil parent material is the key factor in determining the selenium content in soil.

[0003] A large number of studies have found that due to the influence of geological movements, selenium often co-exists with cadmium in the soil, resulting in the threat of widespread cadmium pollution in selenium-rich areas. Cadmium is one of the persistent pollutants in the environment and is easy to enter biological systems, which may cause harm to the health of humans and other organisms. In order to ensure the high-quality development of selenium-rich agriculture, it is of great significance and urgent to carry out prevention and control and governance of selenium-rich soil cadmium pollution risk areas. The commonly used paddy field soil cadmium passivators often passivate the activity of selenium in the soil while reducing the effective cadmium in the soil and preventing crops from absorbing cadmium, thereby reducing the biological effectiveness of selenium in the soil and reducing the absorption of selenium by crops, making it difficult to achieve a win-win situation for both. Therefore, how to achieve selenium-enriched agricultural products while reducing the absorption of cadmium in selenium-rich cadmium-contaminated soil has become a technical problem. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and provide a selenium-rich cadmium contaminated soil passivator, which specifically adopts the following technical solutions:

[0005] A selenium-rich cadmium-contaminated soil passivator, the raw materials of which include, by weight: 25-50 parts of nano-calcium carbonate-modified biochar, 35-60 parts of limestone powder or dolomite powder, and 30-55 parts of calcium magnesium phosphate fertilizer; the nano-calcium carbonate-modified biochar is prepared by the following process: calcium chloride, sodium hydroxide, dimethyl carbonate, polyacrylic acid and biochar are stirred and mixed in a solution system for 2.5-5 minutes, and the resulting precipitate is the nano-calcium carbonate-modified biochar. Generally speaking, soil with a total selenium content greater than 0.4 mg / kg is selenium-rich soil.

[0006] In the present invention, the nano-calcium carbonate modified biochar proposed by the inventor is a new material, and its crystal structure has certain similarities with calcite. It is different from the traditional addition of calcium carbonate for adjusting the pH. Experiments have proved that compared with the existing passivators, the cadmium reduction effect of this material is more obvious. More importantly, compared with the existing passivators, the nano-calcium carbonate modified biochar proposed by the present invention has a significantly lower impact on selenium, achieving the effect of reducing cadmium while avoiding a greater impact on selenium.

[0007] The nano calcium carbonate modified biochar of the present invention has a great influence on the degradation of Cd 2+ The adsorption mechanism of Cd 2+ Ion exchange and precipitation reactions between calcium carbonate nanoparticles and biochar. Nano-calcium carbonate occurs on the surface of nano-calcium carbonate particles in the form of adsorption or precipitation, and biochar mainly adsorbs Cd by ion exchange. 2+ Compared with nano-calcium carbonate modified biochar materials, unmodified biochar has limited surface functional groups and mineral components (CO3 2- ,PO4 3- ) is low, resulting in a generally smaller adsorption capacity; natural calcite (calcium carbonate) has a dense crystal structure for Cd 2+ The adsorption efficiency of Cd is very low, so only by preparing nano calcium carbonate can the adsorption of Cd be greatly improved in the form of Cd-CaCO3. 2+ Nano-calcium carbonate modified biochar can not only absorb a large amount of Cd in the soil 2+ It can also promote the transformation of soil selenium and increase the effective selenium content in the soil, mainly based on the following two reasons: (1) Nano-calcium carbonate increases the transformation of aluminum from the exchange state to the hydroxyl adsorption state and the organic coordination state, and promotes the transformation of selenium from the organic bound state to the water-soluble state; (2) Nano-calcium carbonate changes the existence form of iron-manganese oxides, and promotes the transformation of iron-manganese oxide-bound selenium to water-soluble selenium. Under the action of these two aspects, the effective selenium content in the soil is significantly improved.

[0008] The calcium magnesium phosphate fertilizer added by the present invention can further activate the selenium in the soil. The chemical behaviors of phosphorus and selenium in the soil are similar and both exist in the form of anions. Under acidic conditions, the corresponding anions are easily adsorbed by iron manganese oxides and clay minerals, and there is a competitive adsorption between the two. Therefore, applying calcium magnesium phosphate fertilizer to the soil increases the content of hydrogen phosphate ions, and the hydrogen phosphate ions in the soil compete with selenite for adsorption, which is an internal ligand exchange mechanism. Relative to selenite, hydrogen phosphate ions are stronger ligand ions. When they exist simultaneously, hydrogen phosphate ions are preferentially adsorbed by the soil, thereby reducing the adsorption of selenite by the soil and increasing the effectiveness of selenium in the soil.

[0009] In addition, the limestone powder or dolomite powder added in the present invention is mainly to quickly increase the pH in the soil to above 6.2, so that the effective selenium content in the soil reaches the maximum while the effective cadmium content is reduced to the minimum, truly achieving the goal of reducing cadmium and enriching selenium simultaneously. The effective selenium content in the soil is positively correlated with the pH, that is, the larger the pH of the soil, the higher the effectiveness of its selenium. When the soil pH is low (pH<5), the selenium in the soil is easily fixed by iron and manganese oxides, which reduces the effectiveness of selenium; when the pH in the soil increases, the negative charge increases on the surface of the soil particles, and the hydroxide can replace the selenate ions on the adsorption site, so that the selenate ions are released into the soil solution, and the biological effectiveness of selenium increases.

[0010] In the preparation process of the above-mentioned nano-calcium carbonate modified biochar, the ratio of calcium chloride, sodium hydroxide, dimethyl carbonate, polyacrylic acid and biochar is (0.0005mol-0.003mol): (0.01mol-0.02mol): (0.005mol-0.015mol): (0.004mol-0.006mol): (2.0g-5.0g). By adjusting the amount of biochar, a nano-calcium carbonate modified biochar containing 3.5wt%-6wt% (optimally 5wt%) of nano-calcium carbonate is prepared. If the content of nano-calcium carbonate is too low, the passivation effect will be poor. If the content is too high, the nano-particle size will be too large, which will also affect the passivation effect. The biochar is preferably straw biochar.

[0011] In some preferred implementations, the raw materials of the selenium-rich cadmium contaminated soil passivator also include 20-40 parts of modified zeolite by weight; the modified zeolite is preferably alkali-modified zeolite. The preparation process is as follows: slowly add the zeolite to a Ca(OH)2 solution (preferably a concentration of 2mol / L-5mol / L), maintain the temperature at 60°C-80°C (can be by hot steam), and fully contact the zeolite with the Ca(OH)2 solution under stirring (can be by a stirrer), filter after 10h-12h (the filtrate can be recycled), and dry the filter residue at 105°C to obtain the modified zeolite.

[0012] The modified zeolite added in the present invention can further reduce cadmium and activate selenium in the soil, increase the content of effective selenium, and better achieve the simultaneous reduction of cadmium and enrichment of selenium. The effect of activating selenium by using alkali-modified zeolite is better than that by acid-modified zeolite, because acid-modified zeolite may also partially adsorb anions including selenate.

[0013] In some preferred implementations, the raw materials of the selenium-rich cadmium contaminated soil passivator also include 20-50 parts of calcium magnesium nitro humate in parts by weight. The preparation process is as follows: add weathered coal to a nitric acid solution with a mass fraction of 25-30%, the weight ratio of weathered coal to nitric acid solution is 1:0.5-0.8, and stir for 30min-40min to obtain activated humic acid; add 100 parts of activated humic acid on a dry basis and then add 50 parts of 60-mesh calcined dolomite to water at the same time, the weight of water is 70%-80% of the total weight of activated humic acid and calcined dolomite, stir well and react at 90°C for 4h to obtain the calcium magnesium nitro humate.

[0014] The inventors have found that calcium magnesium nitro humate also has the effect of reducing the cadmium content without affecting the selenium content. Therefore, in order to further improve the effect of the solution, calcium magnesium nitro humate can also be preferably added as a raw material.

[0015] In some preferred implementations, the raw materials of the selenium-rich cadmium contaminated soil passivator also include 0.1-1 parts of AM bacterial agent by weight; the AM bacterial agent is preferably a composite bacterial agent composed of Glomus mosseae, Glomus versifor m and Glomus intraradices, with an effective ingredient of ≥ 70wt.%, and an effective viable count of ≥ 10 billion per gram. This combination has the best effect on reducing soil bulk density, increasing the proportion of soil macroaggregates, and improving soil physical properties.

[0016] In order to further improve the implementation effect of the scheme, the present invention also adds AM bacterial agent as a raw material. After being added to the soil, it can promote the increase of aggregates in the soil, thereby increasing the air permeability of the soil, and then can change the redox potential of the soil, which is more conducive to selenium enrichment and cadmium reduction.

[0017] The present invention also provides a preparation method of the selenium-rich cadmium contaminated soil passivator, comprising the following steps: mixing the above raw materials in parts by weight and granulating. Specifically, the above raw materials are fully mixed, granulated and dried after adding a binder (when the raw materials contain AM bacterial agent, the AM bacterial agent solution is sprayed into the masterbatch after it is basically formed, and dried at low temperature).

[0018] The present invention also provides a method for using the selenium-rich cadmium contaminated soil passivator, which is applied in a one-time bottom application. The amount of the selenium-rich cadmium contaminated soil passivator required to be added when the pH of the soil is adjusted from pHi to pHt is Q; when the organic matter content in the soil is not more than 30 g / kg, Q=EXP(1.52×(pHt-4.8))-EXP(1.52×(pHi-4.8)); when the organic matter content in the soil is more than 30 g / kg, Q=EXP(1.39×(pHt-4.4))-EXP(1.39×(pHi-4.4)). pHt is greater than pHi.

[0019] The beneficial effects of the present invention are as follows: the passivator proposed by the present invention is mainly aimed at selenium-rich cadmium-contaminated soil. According to the method of use, continuous multiple applications every season or every year can significantly increase the effective selenium content of selenium-rich soil, reduce the effective cadmium content of selenium-rich soil, increase the effective selenium-cadmium molar ratio of selenium-rich soil, reduce crop absorption and accumulation of cadmium in soil, increase crop absorption and accumulation of selenium, and finally reach the safety production standard of selenium-rich soil. Compared with the existing soil cadmium passivator, the passivator prepared by the present invention can not only increase crop yield and increase economic benefits, but also is convenient and efficient, low cost, fast-acting, green and pollution-free, and truly achieves the goal of simultaneous cadmium reduction and selenium enrichment. DETAILED DESCRIPTION

[0020] The following will provide a clear and complete description of the concept and technical effects of the present invention in conjunction with the embodiments, so as to fully understand the purpose, scheme and effects of the present invention.

[0021] The nano-calcium carbonate modified biochar, calcium magnesium nitrohumate, and modified zeolite in the following examples are respectively prepared by the following processes:

[0022] (1) Preparation of nano-calcium carbonate modified biochar

[0023] 10 mL of 0.1 mol / L calcium chloride solution was quickly mixed with 90 mL of an aqueous solution containing 0.01 mol sodium hydroxide, 0.005 mol dimethyl carbonate, 0.004 mol polyacrylic acid and 2.0 g biochar, and the reaction solution was stirred at room temperature for about 2.5 minutes. The precipitate was then quickly separated by centrifugation, washed with distilled water, and the washed sample was dried to obtain nano-calcium carbonate modified biochar.

[0024] (2) Preparation of calcium magnesium nitrohumate

[0025] The weathered coal is added to a nitric acid solution with a mass fraction of 25%, the weight ratio of the weathered coal to the nitric acid solution is 1:0.5, and the activated humic acid is obtained after stirring for 35 minutes; 100 parts of the activated humic acid on a dry basis are added to water at the same time as 50 parts of 60-mesh calcined dolomite, the weight of the water being 70% of the total weight of the activated humic acid and the calcined dolomite, and the mixture is stirred and reacted at 90°C for 4 hours to obtain the calcium magnesium nitro humate.

[0026] (3) Preparation of modified zeolite

[0027] 800 kg of zeolite was slowly added into 2 mol / L Ca(OH)2 solution. The reaction solution was kept at 70°C by hot steam and the zeolite was fully contacted with the solution under the action of a stirrer. After 10 hours, the solution was filtered and the filtrate was recycled. The filter residue was dried at 105°C to obtain the modified zeolite.

[0028] The binder in the following embodiments is bentonite.

[0029] Embodiment 1:

[0030] A selenium-rich cadmium-contaminated soil passivator, whose raw materials include, by weight: 40 parts of nano-calcium carbonate-modified biochar, 40 parts of calcium magnesium phosphate fertilizer, 30 parts of modified zeolite, 30 parts of calcium magnesium nitro humate, 45 parts of limestone / dolomite powder, 0.5 parts of AM bacterial agent solution, and 7 parts of a binder.

[0031] The preparation process is as follows: nano calcium carbonate modified biochar, calcium magnesium phosphate fertilizer, modified zeolite, calcium magnesium nitro humate, and limestone / dolomite powder are mixed, and then a binder is added in a granulator for granulation. After the masterbatch is basically formed, the AM bacterial agent solution is sprayed until the particles are completely formed, and then dried and sieved. The particles with a particle size greater than 5 mm and less than 1 mm are returned to the crusher for re-crushing and granulation. The particles with a particle size of 2-5 mm are sieved out, measured, and packaged to obtain a selenium-rich cadmium contaminated soil passivator.

[0032] The AM microbial agent is a composite microbial agent composed of arbuscular mycorrhizal fungi of the genus Glomus mosseae, Glomus versiform and Glomus intrar adices, with an effective ingredient ≥ 70wt.%, and an effective live bacterial count ≥ 10 billion / gram.

[0033] Embodiment 2:

[0034] A selenium-rich cadmium-contaminated soil passivator, whose raw materials include, by weight: 35 parts of nano-calcium carbonate-modified biochar, 40 parts of calcium magnesium phosphate fertilizer, 30 parts of modified zeolite, 30 parts of calcium magnesium nitro humate, 45 parts of limestone / dolomite powder, 0.5 parts of AM bacterial agent solution, and 7 parts of a binder.

[0035] The preparation process is as follows: nano calcium carbonate modified biochar, calcium magnesium phosphate fertilizer, modified zeolite, calcium magnesium nitro humate, and limestone / dolomite powder are mixed, and then a binder is added in a granulator for granulation. After the masterbatch is basically formed, the AM bacterial agent solution is sprayed until the particles are completely formed, and then dried and sieved. The particles with a particle size greater than 5 mm and less than 1 mm are returned to the crusher for re-crushing and granulation. The particles with a particle size of 2-5 mm are sieved out, measured, and packaged to obtain a selenium-rich cadmium contaminated soil passivator.

[0036] The AM microbial agent is a composite microbial agent composed of arbuscular mycorrhizal fungi of the genus Glomus mosseae, Glomus versiform and Glomus intrar adices, with an effective ingredient ≥ 70wt.%, and an effective live bacterial count ≥ 10 billion / gram.

[0037] Embodiment 3:

[0038] A selenium-rich cadmium-contaminated soil passivator, whose raw materials include, by weight: 30 parts of nano-calcium carbonate-modified biochar, 40 parts of calcium magnesium phosphate fertilizer, 30 parts of modified zeolite, 30 parts of calcium magnesium nitro humate, 45 parts of limestone / dolomite powder, 0.5 parts of AM bacterial agent solution, and 7 parts of a binder.

[0039] The preparation process is as follows: nano calcium carbonate modified biochar, calcium magnesium phosphate fertilizer, modified zeolite, calcium magnesium nitro humate, and limestone / dolomite powder are mixed, and then a binder is added in a granulator for granulation. After the masterbatch is basically formed, the AM bacterial agent solution is sprayed until the particles are completely formed, and then dried and sieved. The particles with a particle size greater than 5 mm and less than 1 mm are returned to the crusher for re-crushing and granulation. The particles with a particle size of 2-5 mm are sieved out, measured, and packaged to obtain a selenium-rich cadmium contaminated soil passivator.

[0040] The AM microbial agent is a composite microbial agent composed of arbuscular mycorrhizal fungi of the genus Glomus mosseae, Glomus versiform and Glomus intrar adices, with an effective ingredient ≥ 70wt.%, and an effective live bacterial count ≥ 10 billion / gram.

[0041] Embodiment 4:

[0042] A selenium-rich cadmium-contaminated soil passivator, whose raw materials include, by weight: 25 parts of nano-calcium carbonate-modified biochar, 40 parts of calcium magnesium phosphate fertilizer, 30 parts of modified zeolite, 30 parts of calcium magnesium nitro humate, 45 parts of limestone / dolomite powder, 0.5 parts of AM bacterial agent solution, and 7 parts of a binder.

[0043] The preparation process is as follows: nano calcium carbonate modified biochar, calcium magnesium phosphate fertilizer, modified zeolite, calcium magnesium nitro humate, and limestone / dolomite powder are mixed, and then a binder is added in a granulator for granulation. After the masterbatch is basically formed, the AM bacterial agent solution is sprayed until the particles are completely formed, and then dried and sieved. The particles with a particle size greater than 5 mm and less than 1 mm are returned to the crusher for re-crushing and granulation. The particles with a particle size of 2-5 mm are sieved out, measured, and packaged to obtain a selenium-rich cadmium contaminated soil passivator.

[0044] The AM microbial agent is a composite microbial agent composed of arbuscular mycorrhizal fungi of the genus Glomus mosseae, Glomus versiform and Glomus intrar adices, with an effective ingredient ≥ 70wt.%, and an effective live bacterial count ≥ 10 billion / gram.

[0045] Comparative Example:

[0046] A selenium-rich cadmium-contaminated soil passivator, whose raw materials include, by weight: 35 parts of biochar, 40 parts of calcium magnesium phosphate fertilizer, 30 parts of modified zeolite, 30 parts of calcium magnesium nitro humate, 45 parts of limestone / dolomite powder, 0.5 parts of AM bacterial agent solution, and 7 parts of a binder.

[0047] The preparation process is as follows: biochar, calcium magnesium phosphate fertilizer, modified zeolite, calcium magnesium nitro humate, and limestone / dolomite powder are mixed, and then a binder is added in a granulator for granulation. After the masterbatch is basically formed, the AM bacterial agent solution is sprayed until the particles are completely formed, and then dried and sieved. The particles with a particle size greater than 5 mm and less than 1 mm are returned to the crusher for re-crushing and granulation. The particles with a particle size of 2-5 mm are screened out, measured, and packaged to obtain a selenium-rich cadmium contaminated soil passivator.

[0048] The AM microbial agent is a composite microbial agent composed of arbuscular mycorrhizal fungi of the genus Glomus mosseae, Glomus versiform and Glomus intrar adices, with an effective ingredient ≥ 70wt.%, and an effective live bacterial count ≥ 10 billion / gram.

[0049] Compared with Example 1, the comparative example replaces the nano-calcium carbonate-modified biochar with ordinary biochar.

[0050] Effect experiment:

[0051] The experiment was carried out on mid-season rice and late rice using a potted test method, with no passivation agent (CK), ordinary biochar (rice biochar), ordinary calcium carbonate, nano-calcium carbonate-modified biochar, comparative example, Examples 1-4 and Tebei calcium soil conditioner (the raw material is oyster shell, provided by Xiamen Mata Ecology Co., Ltd., which is the mainstream soil cadmium passivator product currently circulating in the market), a total of 10 treatments, each treatment was repeated 3 times, and a total of 30 pots. Each pot was filled with 10 kg of soil (on an oven-dried basis). The soil was mixed with fertilizers and passivators and then potted. The pots were irrigated with water and the rice was transplanted after soaking for about a week. Three rice stalks were transplanted in each pot. Soil and plant samples were collected after the harvest of mid-season rice and late rice. The rice yield, effective selenium in soil, soil selenium form, effective cadmium in soil, soil cadmium form, brown rice selenium, and brown rice cadmium content were determined. The relative cadmium reduction rate and relative selenium enrichment rate were calculated based on the cadmium and selenium contents in the brown rice. The soil cadmium passivation rate and soil selenium activation rate were calculated based on the effective cadmium and effective selenium contents in the soil.

[0052] Soil type for test: Both mid-season and late-season rice are paddy soils. The basic physical and chemical properties of the basic soil in the mid-season rice season are: pH = 5.67, organic matter 2.94%, total cadmium 1.14 mg / kg, total selenium 0.65 mg / kg, and the basic physical and chemical properties of the basic soil in the late-season rice season are: pH = 4.88, organic matter 4.17%, total cadmium 0.71 mg / kg, total selenium 0.82 mg / kg. According to the limit value of my country's "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)" (GB 15618-2018) (pH <6.5, cadmium 0.30 mg / kg), the total cadmium content of the test site soil is 2-3 times the standard limit, which is moderately polluted soil. According to the standard of soil total selenium content: less than 0.125mg / kg is selenium-deficient soil, between 0.125-0.175mg / kg is low-selenium soil, between 0.175-0.450mg / kg is selenium-rich soil, and between 0.450-3.000mg / kg is high-selenium soil. The total selenium content of the tested soil is between 0.450-3.000mg / kg, which is high-selenium soil.

[0053] The selenium-rich cadmium contaminated soil passivator is a one-time bottom application. The soil passivator is applied to adjust the soil pH to above 6.5. The amount of the selenium-rich cadmium contaminated soil passivator that needs to be added when the soil pH is adjusted from pHi before fertilization to a preset pHt is Q; when the organic matter content in the soil is not more than 30g / kg, Q=EXP(1.52×(pHt-4.8))-EXP(1.52×(pHi-4.8)); when the organic matter content in the soil is more than 30g / kg, Q=EXP(1.39×(pHt-4.4))-EXP(1. 39×(pHi-4.4)), the results calculated according to the formula are: the application amount of each treatment in the comparative example and the embodiment on mid-season rice is 72.21 g / pot, and the application amount on late rice is 73.66 g / pot; the application amount of the terbium calcium soil conditioner on mid-season rice is 19.66 g / pot, and the application amount on late rice is 34.73 g / pot, the application amount of nano-calcium carbonate-modified biochar on mid-season rice and late rice is converted according to the amount and proportion of Example 1, and the application amount of ordinary biochar and ordinary calcium carbonate is consistent with that of nano-calcium carbonate-modified biochar.

[0054] Compared with ordinary biochar and ordinary calcium carbonate, nano-calcium carbonate modified biochar can significantly increase the yield of mid-season rice and late rice, which is 9.57% and 2.73% higher than ordinary biochar on mid-season rice and late rice, and 4.12% and 1.43% higher than ordinary calcium carbonate on mid-season rice and late rice, respectively.

[0055] The present invention can significantly increase rice yield by compounding nano calcium carbonate modified biochar with other materials calcium magnesium phosphate fertilizer, modified zeolite, calcium magnesium nitro humate, limestone / dolomite powder. As shown in Table 1, compared with the comparative example (without adding nano calcium carbonate modified biochar), the embodiment increases the yield of mid-season rice and late rice by 1.75-8.8% and 1.82-9.88%, respectively.

[0056] Compared with the passivating agent sold on the market, the soil conditioner of Tebecalcium, the present invention also shows a significant yield-increasing effect, among which Example 1 has the largest yield increase, reaching 10.49% and 12.94% on mid-season rice and late rice respectively, and Example 4 has the smallest yield increase, reaching 3.51% and 4.65% on mid-season rice and late rice respectively.

[0057] Table 1 Effect of soil passivators on rice yield

[0058] deal with Medium Rice(g / pot) Late Rice(g / pot) CK (without passivation agent) 42.72 48.74 Ordinary biochar 45.11 49.96 Ordinary calcium carbonate 47.47 50.59 Nano-calcium carbonate modified biochar 49.43 51.32 Comparative Example 54.76 58.60 Example 1 59.57 64.39 Example 2 58.57 62.30 Example 3 55.72 61.52 Example 4 55.80 59.66 Tebei calcium soil conditioner 53.91 57.01

[0059] As can be seen from Table 2, compared with ordinary biochar and ordinary calcium carbonate, nano-calcium carbonate modified biochar significantly reduced the cadmium content in mid-season rice and late rice brown rice, and the relative cadmium reduction rate increased from 7.61% and 10.13% of ordinary biochar to 66.3% and 58.23%, respectively, an increase of 58.7 and 48.1 percentage points, respectively; from 26.09% and 30.38% of ordinary calcium carbonate to 66.3% and 58.23%, an increase of 40.22 and 27.85 percentage points, respectively. The reason is that nano-calcium carbonate modified biochar mainly reduces the ion exchange cadmium content and increases the carbonate-bound, iron-manganese oxide-bound, organic-bound and residual cadmium contents, thereby reducing the effective cadmium content in the soil, increasing the soil cadmium passivation rate, reducing the cadmium content in rice, and increasing the relative cadmium reduction rate of rice (see Tables 3, 4 and 5). Nano-calcium carbonate modified biochar can effectively reduce the cadmium content in brown rice and increase the selenium content in mid-season and late-season brown rice. The relative selenium enrichment rate increased by 37.25 and 40.63 percentage points respectively compared with ordinary biochar, and increased by 11.76 and 20.83 percentage points respectively compared with ordinary calcium carbonate. Further research shows that nano-calcium carbonate modified biochar mainly increases the effective selenium content and selenium activation rate in soil by increasing the content of water-soluble and exchangeable selenium and reducing the content of iron-manganese oxide-bound and organic-bound selenium, thereby increasing the selenium content in brown rice and the selenium enrichment rate of rice (see Tables 3, 4 and 5).

[0060] The present invention prepares Example 1, Example 2, Example 3 and Example 4 by compounding nano calcium carbonate modified biochar with other materials calcium magnesium phosphate fertilizer, modified zeolite, calcium magnesium nitro humate, limestone / dolomite powder. As shown in Table 2, compared with the comparative example (no nano calcium carbonate modified biochar added), the example shows obvious cadmium reduction effect on mid-season rice and late rice, and the relative cadmium reduction rate increases by 40.22-44.57 percentage points and 34.18-45.57 percentage points, respectively, and the soil cadmium passivation rate increases by 13.11-24.59 percentage points and 13.79-20.69 percentage points, respectively, indicating that adding a certain amount of nano calcium carbonate modified biochar to the passivator can effectively passivate the effective cadmium in paddy soil and significantly reduce the cadmium content of rice. The embodiment effectively increases the selenium content in rice while reducing the cadmium content in rice. The relative selenium enrichment rate increases by 13.73-33.33 percentage points and 10.42-31.25 percentage points respectively compared with the control example, and the soil selenium activation rate increases by 1.08-1.54 percentage points and 1.71-2.68 percentage points respectively compared with the control example. This shows that adding nano-calcium carbonate modified biochar can further activate the activity of selenium in selenium-rich soil and increase the biologically effective selenium content in soil.

[0061] As shown in Table 2, compared with the treatment without the passivation agent, the cadmium content of the brown rice of the mid-season rice and late rice in Examples 1, 2, 3 and 4 was reduced from 0.92 and 0.79 mg / kg without the passivation agent to 0.14-0.18 and 0.1-0.19 mg / kg, and the cadmium reduction rate reached 80.43%-84.78% and 75.95%-87.34%, respectively. The present invention can reduce the cadmium content in rice mainly due to reducing the ion exchange state cadmium content, increasing the carbonate-bound, iron-manganese oxide-bound, organic-bound and residual cadmium content, thereby reducing the effective cadmium content in the soil, improving the soil cadmium passivation rate, and achieving the purpose of reducing cadmium in rice. The present invention can not only greatly reduce the cadmium content of rice, but also significantly enrich selenium in mid-season rice and late rice. As shown in Table 2, the selenium content in the mid-season brown rice of Example 1, Example 2, Example 3 and Example 4 is increased from 0.051 mg / kg without the treatment of the passivating agent to 0.066-0.076 mg / kg, and the selenium content in the late rice brown rice is increased from 0.077 mg / kg without the treatment of the conditioning agent to 0.11-0.13 mg / kg. The relative selenium enrichment rates in mid-season rice and late rice reach 29.41-49.02% and 45.83-66.67% respectively. Research on the selenium forms and effective selenium in the soil shows that the embodiments mainly increase the water-soluble and exchangeable selenium contents and reduce the iron-manganese oxide-bound and organic-bound selenium contents, thereby increasing the effective selenium content and selenium activation rate in the soil.

[0062] Compared with the passivating agent Tebecalcium soil conditioner sold on the market, the invention shows obvious selenium-enriched cadmium-reducing effect on both mid-season rice and late-season rice, and the relative cadmium-reducing rates are increased by 30.43-26.09 percentage points and 24.05-35.44 percentage points, respectively, and the soil cadmium passivation rates are increased by 4.92-16.39 percentage points and 15.52-22.41 percentage points, respectively. This is mainly attributed to the fact that the effective cadmium content in the soil is reduced, the cadmium content in the soil is increased, the cadmium passivation rate in the soil is increased, and the cadmium content in the rice is reduced by reducing the ion-exchange cadmium content and increasing the carbonate-bound, iron-manganese oxide-bound, organic-bound and residual cadmium contents. The invention realizes effective selenium enrichment while reducing the cadmium content in brown rice. The relative selenium enrichment rate is increased by 19.61-39.22 percentage points and 31.25-52.08 percentage points on mid-season rice and late rice respectively compared with the Tebei calcium soil conditioner, and the soil selenium activation rate is increased by 1.69-2.15 percentage points and 2.07-3.05 percentage points. Studies on the selenium forms and effective selenium in the soil show that the invention mainly increases the water-soluble and exchangeable selenium contents and reduces the iron-manganese oxide-bound and organic-bound selenium contents, thereby increasing the effective selenium content and selenium activation rate in the soil, thereby achieving the purpose of selenium enrichment in rice (Table 3, Table 4, Table 5).

[0063] Table 2 Effects of soil passivators on cadmium and selenium content, cadmium reduction rate and selenium enrichment rate in rice

[0064]

[0065] Note: Relative cadmium reduction rate (RE) = (1-C T / C CK )×100%, where: C T is the cadmium content of brown rice in the passivation treatment area, C CK is the cadmium content of brown rice in the control area (without passivation agent); relative selenium enrichment rate (SEE) = (S T / S CK -1)×100%, where: S T is the selenium content of brown rice in the treatment area, S CK is the selenium content of brown rice in the control area.

[0066] Table 3 Effects of soil passivators on soil selenium forms

[0067]

[0068]

[0069] Table 4 Effects of soil passivators on soil cadmium forms

[0070]

[0071] Table 5 Effects of soil passivators on soil effective cadmium and selenium content, cadmium passivation rate and selenium activation rate

[0072]

[0073]

[0074] Note: The passivation rate of heavy metal cadmium in soil (IE) = (1-C T / C CK )×100%, where: C T is the soil cadmium available content (DTPA extraction state) in the passivation treatment area, C CK To repair the effective cadmium content in the soil of the control area (DTPA extracted state); soil selenium activation rate (AE) = effective selenium content in the soil / total selenium content in the soil × 100%.

[0075] The above is only a preferred embodiment of the present invention. The present invention is not limited to the above implementation. As long as the technical effect of the present invention is achieved by the same means, it should belong to the protection scope of the present invention. Within the protection scope of the present invention, its technical scheme and / or implementation method can have various modifications and changes.

Claims

1. A selenium-rich cadmium contaminated soil passivator, characterized in that: The raw materials include, by weight: 25-50 parts of nano calcium carbonate modified biochar, 35-60 parts of limestone powder or dolomite powder, 30-55 parts of calcium magnesium phosphate fertilizer, 20-40 parts of modified zeolite, 20-50 parts of nitro humic acid calcium magnesium, 0.1-1 parts of AM bacterial agent, and 7 parts of binder; The nano-calcium carbonate modified biochar is prepared by the following process: calcium chloride, sodium hydroxide, dimethyl carbonate, polyacrylic acid and biochar are stirred and mixed in a solution system for 2.5-5 minutes, and the resulting precipitate is the nano-calcium carbonate modified biochar, wherein the content of nano-calcium carbonate in the nano-calcium carbonate modified biochar is 3.5-6 wt%; The ratios of calcium chloride, sodium hydroxide, dimethyl carbonate, polyacrylic acid and biochar are (0.0005 mol-0.003 mol): (0.01 mol-0.02 mol): (0.005 mol-0.015 mol): (0.004 mol-0.006 mol): (2.0 g-5.0 g).

2. The selenium-rich cadmium contaminated soil passivator according to claim 1, characterized in that The modified zeolite is alkali-modified zeolite.

3. The selenium-rich cadmium contaminated soil passivator according to claim 1, characterized in that: In the nano-calcium carbonate modified biochar, the content of nano-calcium carbonate is 5 wt %.

4. The selenium-rich cadmium contaminated soil passivator according to claim 1, characterized in that: The AM bacterial agent is a composite bacterial agent composed of Glomus mosseae, Glomus versiform and Glomus intraradices, with an effective ingredient of ≥70 wt.%, and an effective live bacterial count of ≥10 billion / gram.

5. A method for preparing a selenium-rich cadmium contaminated soil passivator according to any one of claims 1 to 4, characterized in that: The following steps are involved: The raw materials are mixed and granulated according to weight parts.

6. A method for using the selenium-rich cadmium contaminated soil passivator according to any one of claims 1 to 4, characterized in that: The application method is one-time bottom application. The amount of the selenium-rich cadmium contaminated soil passivator required to be added when the pH of the soil is adjusted from pHi to pHt is Q; when the organic matter content in the soil is not more than 30 g / kg, Q=EXP(1.52×(pHt-4.8))-EXP(1.52×(pHi-4.8)); when the organic matter content in the soil is more than 30 g / kg, Q=EXP(1.39×(pHt-4.4))-EXP(1.39×(pHi-4.4)).

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