A method for reducing the arsenic content in rice grown in alkaline arsenic-contaminated paddy fields

Abstract

This application discloses a method for reducing the arsenic content of rice grown in alkaline arsenic-polluted paddy fields, belonging to the field of soil remediation technology. The method involves pretreating air-dried electrolytic manganese slag, zeolite, and desulfurized gypsum. The pretreated electrolytic manganese slag, natural zeolite, and desulfurized gypsum are then mixed uniformly to obtain an EMR-ZL-FGD mixed sample. This mixed sample can alter the speciation of arsenic in the soil and effectively reduce the available arsenic content. When the EMR-ZL-FGD addition is 2 wt%, the available arsenic content in the soil is reduced by 50.34%. Soil pH and cation exchange capacity are positively correlated with available arsenic content, while redox potential is negatively correlated. The passivating material EMR-ZL-FGD can effectively reduce the arsenic content in the underground roots, aboveground stems and leaves, and grains. Furthermore, the higher the EMR-ZL-FGD addition, the less arsenic is accumulated in the rice.

Description

Technical Field

[0001] This invention belongs to the field of soil remediation technology, specifically relating to a method for reducing the arsenic content of rice grown in alkaline arsenic-contaminated paddy fields. Background Technology

[0002] There are two main approaches to soil arsenic remediation: one is to reduce the arsenic content in the soil, and the other is to reduce its bioavailability. Currently, common soil arsenic pollution remediation technologies can be divided into physical remediation, chemical remediation, and bioremediation.

[0003] Physical remediation includes methods such as soil replacement, topsoil replacement, deep tillage, thermal treatment, electrokinetic remediation, and adsorption. Soil replacement, topsoil replacement, and deep tillage share the same principle. Specifically, soil replacement and topsoil replacement involve replacing or diluting the contaminated soil with clean soil, suitable for soils with severe arsenic contamination. Deep tillage involves turning the soil layers upside down, mixing deep clean soil with contaminated soil to dilute the contamination, suitable for low-concentration arsenic contamination. These three methods are technically simple, but they do not remove heavy metals and are costly. Thermal treatment involves heating the soil to volatilize and separate arsenic. Besides arsenic, it can also be applied to other volatile heavy metal pollutants such as mercury (Hg) and selenium (Se). Thermal treatment consumes a large amount of energy. Studies show that arsenic volatilizes at 800℃ under aerobic conditions and 600℃ under anaerobic conditions. Such high temperatures can damage soil structure and chemical properties, alter soil pH, reduce organic matter (SOM) content, and decrease cation exchange capacity (CEC). Improper treatment may also cause airborne arsenic pollution. Electrokinetic remediation involves applying a low-level direct current to electrodes, causing contaminants to move towards the electrodes. Electrokinetic remediation is low-cost and has minimal environmental disturbance, but it is only suitable for soils with good conductivity and permeability. Adsorption methods involve adding adsorbents to adsorb soil contaminants. The key to adsorption methods is material development; currently, research on arsenic adsorption materials mainly focuses on various natural minerals and agricultural byproducts.

[0004] Chemical remediation mainly includes leaching and passivation / stabilization techniques. Leaching uses a leaching solution to treat arsenic-contaminated soil, separating arsenic from the soil through dissolution, chelation, and desorption. Leaching agents typically include strong acids and bases, chelating agents, organic acids, and salts. Currently, the most commonly used artificial chelating agents for soil arsenic pollution are EDTA (ethylenediaminetetraacetic acid) and EDDS (trisodium ethylenediaminedisuccinate). However, artificial chelating agents are expensive and can easily cause secondary pollution if they remain in the soil. Passivation / stabilization techniques involve adding passivating agents. Through adsorption, precipitation, complexation, and redox reactions, the passivating agents convert arsenic in the soil into a less mobile, chemically stable, and less toxic form, fixing it in the soil. Soil passivation technology is simple to operate, low in cost, and highly efficient, making it a widely researched and applied soil arsenic remediation technology. Various iron and manganese oxides, natural minerals, and biomass materials can all be used for soil arsenic fixation.

[0005] Bioremediation technologies include phytoremediation and microbial remediation. Phytoremediation utilizes arsenic hyperaccumulating plants to extract arsenic from the soil for treatment. This is a sustainable and green remediation technology with advantages such as simple operation and no secondary pollution. Bioremediation technologies require less investment, have good results, and are easy to manage, but they are highly specific and difficult to adapt to the remediation of soils with complex contamination.

[0006] Passivation technology reduces the bioavailability of arsenic in soil by adding soil passivating agents. Therefore, the core of passivation remediation is the research and application of low-cost, high-efficiency passivation materials. While there is abundant research on heavy metal passivation materials, the chemical properties and passivation mechanisms of arsenic differ from those of typical heavy metals such as lead, cadmium, and copper. Many passivation materials that can fix heavy metal cations can actually activate arsenic oxyanions, posing a significant challenge to the passivation and remediation of arsenic-contaminated soil. Due to the unique properties of arsenic pollutants, the development and research of targeted passivation materials is essential. Electrolytic manganese slag (EMR), as a large-scale industrial solid waste requiring resource utilization, is rich in iron, aluminum, manganese, and other metal cations that adsorb arsenic. Its porous surface structure also gives it great potential for arsenic passivation in soil. EMR is also rich in nitrogen, phosphorus, and potassium, which promote plant growth. Furthermore, electrolytic manganese slag has an acidic pH, which can improve the pH of clean soil. Summary of the Invention

[0007] Technical problems to be solved:

[0008] To address the shortcomings of existing technologies, this application solves the problems of current methods such as soil replacement, topsoil replacement, and deep tillage, which fail to remove heavy metals and have high engineering costs; thermal treatment consumes a large amount of energy and may cause air arsenic pollution if not handled properly; electrokinetic remediation is only suitable for soils with good conductivity and permeability; chemical remediation uses expensive artificial chelating agents that can easily cause secondary pollution if left in the soil; bioremediation is not suitable for remediating soils with complex pollution; and passivation technology faces significant challenges in the passivation remediation of soil with arsenic pollution. This application provides a method for reducing the arsenic content of rice grown in alkaline arsenic-polluted paddy fields.

[0009] Technical solution:

[0010] To achieve the above objectives, this application provides the following technical solution:

[0011] A method for reducing the arsenic content in rice grown in alkaline arsenic-contaminated paddy fields includes the following steps:

[0012] Step 1, Pretreatment of electrolytic manganese slag: The air-dried electrolytic manganese slag is ground by EMR and passed through a 100-mesh sieve, then placed in an oven at 105°C.

[0013] Dry at ℃ to constant weight; Zeolite pretreatment: Grind natural zeolite ZL and pass it through a 100-mesh sieve, then put it in an oven and dry at 105℃ to constant weight; Desulfurized gypsum FGD pretreatment: Dry and dehydrate the desulfurized gypsum, then crush and grind it through a 100-mesh sieve.

[0014] Step 2: The pretreated electrolytic manganese slag, natural zeolite and desulfurized gypsum are shaken in a constant temperature shaking box at 240 rpm for 150 min in a mass ratio of 1:2:1 to make them completely and evenly mixed, so as to obtain the EMR-ZL-FGD mixed sample.

[0015] The third step is soil pretreatment: After the soil samples with an arsenic content of 60-90 mg / kg are collected, they are naturally air-dried in a cool place, coarse residues are picked out, crushed and mixed evenly, and then passed through a 2 mm sieve for later use.

[0016] The fourth step is to take pretreated soil samples to determine soil moisture content and field capacity: Take 1 kg of pretreated air-dried soil and put it into four sets of plastic flower pots with a diameter of 15 cm. Based on the mass of air-dried soil, add 0.5% to 2% of EMR-ZL-FGD mixed sample and mix it thoroughly with the soil. Each treatment is repeated three times. Spray deionized water to make the soil moisture content 80% of the field capacity. The soil moisture content is maintained by weighing. Deionized water is added every 24 hours.

[0017] The fifth step was to determine the passivation effect of EMR on soil arsenic: the available arsenic content in the soil was measured after 15, 30, 60 and 90 days of passivation reaction.

[0018] Step 6, Rice seedling raising and soil passivation preparation: After being selected by water flotation, rice seeds are soaked in 35℃ warm water for 8 hours to promote germination.

[0019] After removing and drying for 1 hour, the seeds are evenly sown into seedling trays. The bottom of the seedling trays is pre-filled with 5cm of clean soil free of arsenic contamination and 0.1wt% of N:P2O5:K2O=1:1:1 compound fertilizer is applied. After sowing rice seeds, a layer of pre-treated soil is covered to maintain the soil moisture content at 80% of the field maximum water holding capacity. Soil passivation preparation is carried out 15 days before transplanting. 0.5% to 2% of EMR-ZL-FGD mixed sample is added to the soil pre-treated in the third step and thoroughly mixed. The soil moisture content is maintained at 80% of the field maximum water holding capacity by weighing method for 15 days, and water is added every 24 hours.

[0020] Step 7: Take 15 kg of the soil that has been passivated for 15 days and place it in a pot with a radius of 20 cm and a height of 40 cm. Apply 20 g of N:P2O5:K2O = 1:1:1 compound fertilizer to each pot as a base fertilizer. Select rice seedlings with uniform growth and transplant them into the pots, 3 holes per pot, 3 seedlings per hole. Supplement with 2 g of N:P2O5:K2O = 1:1:1 compound fertilizer every 15 days, for three times. Irrigate the rice with flood water during its growth process.

[0021] Irrigation was stopped at the beginning of the grain-filling period, and watering was resumed after the water had dried naturally. The treatment groups were placed randomly, and their positions were randomly changed every three days to ensure uniform light exposure. The rice growing period was 5 months.

[0022] Step 8: After the rice matures, harvest the rice grains and sun-dry them naturally, then store them in sealed bags. Pull up the remaining rice plants by the roots, rinse the soil around the roots with tap water, then rinse three times with deionized water. Place them in an oven at 105℃ for 30 minutes to kill the green, then dry them at 65℃ until constant weight. Finally, cut them off at the root tip with scissors.

[0023] The rice plant was divided into aboveground and underground parts; the arsenic content of the aboveground and underground parts and rice grains was measured separately.

[0024] Furthermore, in the third step, the coarse residue consists of one or more of the following: gravel, grass roots, and animal remains.

[0025] Furthermore, the method for determining the available arsenic content in the soil in the fifth step is as follows: Available arsenic in the soil is extracted using NaHCO3 solution. Weigh 5g of soil that has been ground through a 1mm mesh sieve into a 50mL centrifuge tube, add 25mL of 0.5mol / L NaHCO3 solution, place the tube in a constant temperature shaking incubator, and shake and extract for 2h at 25℃ and 250rpm. After centrifugation, take the supernatant, filter it, and determine the arsenic content using ICP-MS.

[0026] Furthermore, the amount of the electrolytic manganese slag-zeolite-desulfurized gypsum mixed sample added was 2 wt% based on the air-dried soil mass.

[0027] Furthermore, the method for determining the arsenic content of the aboveground and underground parts of rice and rice grains in the eighth step is as follows: crush each part of the rice using a crusher, take 0.5g in a tetrafluoroethylene crucible, add 5ml of concentrated hydrochloric acid, 4ml of concentrated nitric acid and 1ml of perchloric acid, and heat on a graphite hot plate at 120℃ for 2 hours until completely dissolved; dilute the digest to 50ml and filter using a 45μm filter membrane, and determine the arsenic content of the digest using inductively coupled plasma mass spectrometry (ICP-MS).

[0028] Beneficial effects:

[0029] This application provides a method for reducing the arsenic content of rice grown in alkaline arsenic-contaminated paddy fields, which has the following advantages compared with the prior art:

[0030] 1. The mixed sample of electrolytic manganese slag-zeolite-desulfurized gypsum can change the speciation of arsenic in the soil and effectively reduce the content of available arsenic in the soil. When the addition amount of EMR-ZL-FGD is 2wt%, the content of available arsenic in the soil is reduced by 50.34%. The remediation mechanism of EMR on arsenic-contaminated soil is mainly redox reaction, coprecipitation, ion exchange and changes in soil charge. Soil pH and cation exchange capacity are positively correlated with available arsenic content, while redox potential is negatively correlated with available arsenic content. EMR can reduce the content of available arsenic in the soil by reducing pH and cation exchange capacity and increasing redox potential.

[0031] 2. The passivating material EMR-ZL-FGD can effectively reduce the arsenic content in the underground roots, aboveground stems and leaves, and grains. The higher the dosage of EMR-ZL-FGD, the less arsenic is accumulated in rice. When the dosage is 2wt%, the arsenic content in rice grains is reduced by 79.53% and 74.07%, respectively. The trend of arsenic content in rice is the same as that of available arsenic content in soil, proving that EMR-ZL-FGD mainly reduces the arsenic content in rice by fixing available arsenic in the soil.

[0032] 3. The addition of EMR-ZL-FGD can effectively reduce the translocation of arsenic in rice, thereby reducing the arsenic enrichment coefficient of rice. Calculations of translocation coefficients between different parts of rice revealed that EMR had no significant effect on the translocation coefficient from the underground roots to the aboveground stems and leaves, but it significantly reduced the translocation coefficient from the aboveground stems and leaves to the grains. EMR also reduced the TF of SA and NJ. g / sThe values ​​decreased from 0.0858 to 0.0361 and from 0.0839 to 0.0455, respectively, reflecting that EMR can affect the arsenic translocation from rice stems and leaves to grains, allowing arsenic to remain in the stems and leaves and reducing the risk of arsenic contamination in rice grains. Attached Figure Description

[0033] Figure 1 This is a diagram illustrating the impact of EMR-ZL-FGD on available arsenic content in soil in this application.

[0034] Figure 2 This is a graph showing the effect of EMR-ZL-FGD on the arsenic content of different parts of Shuangliangyou in this application;

[0035] Figure 3 This is a graph showing the effect of EMR-ZL-FGD on the arsenic content of different parts of the Nanjing japonica plant. Detailed Implementation

[0036] The present invention will be further described below with reference to embodiments. The following description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make equivalent modifications to the disclosed technical content to create equivalent embodiments. Any simple modifications or equivalent changes made to the following embodiments based on the technical essence of the present invention without departing from the scope of the invention are all within the protection scope of the present invention.

[0037] The soil samples used in this application were collected from paddy fields in a village near a coal-fired power plant in Xuzhou City. Soil testing revealed arsenic content of 60-90 mg / kg, exceeding the risk screening values ​​for agricultural land soil pollution stipulated in the "Soil Environmental Quality Standard for Agricultural Land Soil Pollution Risk Control" (GB15618-2018) and the limits in the "Safety Thresholds for Cadmium, Chromium, Lead, Mercury, and Arsenic in Soil for Rice Production" (GBT36869-2018), posing a hazardous risk. After collection, the soil samples were naturally air-dried in a cool place, and coarse debris such as gravel, grass roots, and animal remains were removed. The samples were then crushed, mixed evenly, and passed through a 2mm sieve for later use. The basic physicochemical properties of the soil are shown in Table 1 below.

[0038] Table 1 Basic physical and chemical properties of soil

[0039]

[0040] The indica rice seed selected in this application is the salt-alkali tolerant rice (SA) Shuangliangyou 138;

[0041] The Japonica rice seed used was Nanjing (NJ)46.

[0042] Example 1

[0043] The method for reducing the arsenic content in rice grown in alkaline arsenic-contaminated paddy fields includes the following steps:

[0044] Step 1, Electrolytic manganese slag pretreatment: Grind the air-dried electrolytic manganese slag (EMR) and pass it through a 100-mesh sieve. Then, dry it in an oven at 105°C until constant weight. Zeolite pretreatment: Grind natural zeolite (ZL) and pass it through a 100-mesh sieve. Then, dry it in an oven at 105°C until constant weight. Desulfurized gypsum (FGD) pretreatment: Dry and dehydrate the desulfurized gypsum, then crush and grind it through a 100-mesh sieve.

[0045] Step 2: The pretreated electrolytic manganese slag, natural zeolite and desulfurized gypsum are shaken in a constant temperature shaking box at 240 rpm for 150 min in a mass ratio of 1:2:1 to make them completely and evenly mixed, so as to obtain the EMR-ZL-FGD mixed sample.

[0046] The third step is soil pretreatment: After the soil samples with an arsenic content of 60-90 mg / kg are collected, they are naturally air-dried in a cool place, and coarse residues are picked out. The coarse residues are gravel, grass roots, and animal remains. After being crushed and mixed evenly, they are passed through a 2 mm sieve for later use.

[0047] The fourth step is to take pretreated soil samples to determine soil moisture content and field capacity: Take 1 kg of pretreated air-dried soil and put it into four sets of plastic flower pots with a diameter of 15 cm. Based on the mass of air-dried soil, add 0.5% to 2% of EMR-ZL-FGD mixed sample and mix it thoroughly with the soil. Each treatment is repeated three times. Spray deionized water to make the soil moisture content 80% of the field capacity. The soil moisture content is maintained by weighing. Deionized water is added every 24 hours.

[0048] The fifth step was to determine the effect of EMR on soil arsenic: After 15, 30, 60 and 90 days of passivation, the available arsenic content in the soil was measured.

[0049] Step 6, Rice Seedling Raising and Soil Passivation Preparation: Prepare salt-tolerant rice seeds (Shuangliangyou 13). After water flotation, soak them in 35℃ warm water for 8 hours to promote germination. After drying for 1 hour, evenly sow them into seedling trays. The bottom of the seedling trays is filled with 5cm of clean soil free of arsenic contamination and 0.1wt% of N:P2O5:K2O=1:1:1 compound fertilizer (15-15-15) is applied. Cover the rice seeds with a layer of soil pretreated in Step 1, maintaining the soil moisture content at 80% of the field capacity. 15 days before transplanting, perform soil passivation preparation by adding 0.5%–2% of the EMR-ZL-FGD mixed sample to the soil pretreated in Step 3 and mixing thoroughly. Maintain the soil moisture content at 80% of the field capacity by weighing for 15 days, replenishing water every 24 hours.

[0050] Step 7: Take 15 kg of the soil that has been passivated for 15 days and place it in a pot with a radius of 20 cm and a height of 40 cm. Apply 20 g of N:P2O5:K2O = 1:1:1 compound fertilizer to each pot as a base fertilizer. Select rice seedlings with uniform growth and transplant them into the pots, 3 holes per pot, 3 seedlings per hole. Replenish with 2 g of N:P2O5:K2O = 1:1:1 compound fertilizer every 15 days, for three times. Irrigate the rice by flooding during its growth process, stopping irrigation at the grain-filling stage and allowing the water to dry naturally before watering again. Place the treatment groups randomly, rotating their positions every three days to ensure even light exposure. The rice growth period is 5 months.

[0051] Step 8: After the rice matures, harvest the rice grains and sun-dry them naturally, then store them in sealed bags. Uproot the remaining rice plants, rinse the soil around the roots with tap water, then rinse three times with deionized water. Place them in an oven at 105℃ for 30 minutes to kill the green, then dry them at 65℃ to constant weight. Cut the rice plants along the root tips with scissors to separate them into above-ground and underground parts. Determine the arsenic content in the above-ground and underground parts and the rice grains separately.

[0052] Step 9: Calculation of arsenic enrichment factor and translocation factor: The ability of rice grains to enrich arsenic in the soil is represented by the bioconcentration factor (BCF), and the calculation formula is as follows: In the formula, C 籽粒 C represents the arsenic concentration in the grain. 土壤 The concentration of arsenic in the soil; the arsenic translocation capacity in rice is represented by the translocation factor (TF), calculated using the following formula: In the formula, TF x / y C represents the transfer coefficient from part y to part x. x C represents the arsenic concentration at site x. y The arsenic concentration at location y;

[0053] Effects of EMR-ZL-FGD mixed sample on available arsenic content in soil: Electrolytic manganese slag contains abundant iron, manganese, and aluminum oxides, and the geochemical behavior of arsenic in soil is mainly influenced by metal oxides. On the one hand, iron and manganese metal oxides can form iron-manganese nodules, which have both oxidizing and adsorption capabilities for arsenic; on the other hand, iron and aluminum, as Lewis acids, can combine with arsenate, as Lewis bases, to form amorphous ferric arsenate, ferrous arsenate, and aluminum arsenate. Natural zeolite and dehydrated gypsum are rich in porous structures and have good adsorption effects on arsenic. The EMR-ZL-FGD mixed sample reduced the available arsenic content in the soil by 62.7%, as shown in the test results. Figure 1 As shown.

[0054] Effects of EMR-ZL-FGD mixed samples on arsenic content in different parts of rice: Arsenic content in different parts of rice variety Shuangliangyou 138 is as follows Figure 2 As shown, after adding the EMR-ZL-FGD mixed sample, the arsenic content in the underground parts of Shuangliangyou SA rice decreased by 43.21% compared with the control group. The arsenic content in both the aboveground parts and grains of rice was significantly lower than that in the underground parts, and the trends in arsenic content in the aboveground parts and grains were consistent with those in the underground parts. The arsenic content in the aboveground parts of SA rice decreased by 44.22% compared with the control group. The arsenic content in the grains of SA rice decreased by 79.53% compared with the control group, and the differences between the treatment groups were statistically significant (p<0.05). By comparing the arsenic content in various parts of the treatment and control groups, it can be concluded that the EMR-ZL-FGD mixed sample can effectively reduce the accumulation of arsenic in rice.

[0055] Effects of EMR-ZL-FGD on Arsenic Accumulation and Translocation Coefficients in Rice: Since the absorption and translocation of arsenic in rice is regulated by relevant genes, there are significant differences in arsenic accumulation and translocation among different rice genotypes. Some substances can affect the translocation of arsenic at key nodes in rice, such as γ-aminobutyric acid (GABA). GABA can reduce the expression of Lsi-1 and Lsi-2 translocation genes, ultimately reducing arsenic accumulation in rice seedlings. Applying silicon to rice leaves can also reduce the translocation of arsenic from roots to stems. To gain a deeper understanding of the mechanism by which the passivating agent EMR reduces arsenic content in rice, this application calculated the accumulation and translocation coefficients of rice. The changes in the accumulation and translocation coefficients are shown in Table 2.

[0056] Table 2. Effects of EMR-ZL-FGD on the enrichment and translocation coefficient of rice.

[0057]

[0058] The passivating agent EMR-ZL-FGD significantly altered the enrichment factor (BCF) of *Symplocos bisporus* (SA) (p<0.05), decreasing it by 0.0179 compared to the control group. Analysis of the effect of EMR-ZL-FGD on the translocation coefficient of rice revealed that EMR-ZL-FGD significantly affected the translocation coefficient (TF) of both the aboveground and underground parts of SA. s / r The effect was not significant, but it did affect the translocation coefficient TF between grains and aboveground parts. g / s The effect was significant (p<0.05), indicating that for SA, EMR-ZL-FGD mainly reduces arsenic accumulation by decreasing arsenic translocation from stems and leaves to grains. EMR-ZL-FGD significantly reduced the accumulation coefficient of rice and, to some extent, reduced the translocation coefficient, suggesting that EMR-ZL-FGD not only reduces the available arsenic content in soil to lower the arsenic content in rice, but also reduces arsenic translocation, causing arsenic to be retained in roots and stems and leaves, thus reducing the arsenic content in grains.

[0059] Effects of EMR-ZL-FGD on the number of tillers and effective panicles in rice:

[0060] Table 3 Effects of EMR-ZL-FGD on the number of tillers and effective panicles in rice.

[0061]

[0062] Table 3 shows the effects of EMR-ZL-FGD on the number of tillers and effective panicles in rice. The addition of EMR-ZL-FGD increased the number of tillers and effective panicles in Shuangliangyou SA rice. This may be due to the large amount of ammonia nitrogen introduced into the soil by the application of EMR-ZL-FGD. According to previous studies, higher ammonia nitrogen can promote tillering and jointing and heading in rice.

[0063] Effects of EMR-ZL-FGD on rice biomass: Table 4 shows that the plant height, fresh weight, and dry weight of rice in the EMR-ZL-FGD treatment group were significantly higher than those in the control group without EMR-ZL-FGD. For Shuangliangyou SA rice, EMR-ZL-FGD significantly increased plant height, fresh weight, and dry weight, achieving statistical significance. EMR-ZL-FGD did not show a regular effect on root length.

[0064] Table 4. Effects of EMR-ZL-FGD on rice biomass

[0065]

[0066]

[0067] Effects of EMR-ZL-FGD on Rice Yield and Grain Quality: Table 5 shows that EMR-ZL-FGD significantly increased the panicle length of SA (sweet rice). EMR-ZL-FGD had no significant effect on the 100-grain weight of rice, with only minor variations. Combined with the results of the study on the effect of EMR-ZL-FGD on the number of effective panicles in rice, EMR-ZL-FGD can promote panicle growth and slightly increase rice yield and grain quality.

[0068] Table 5. Effects of EMR-ZL-FGD on Rice Yield and Grain Quality

[0069]

[0070] Effects of EMR-ZL-FGD on chlorophyll content in rice: The results of chlorophyll fluorescence tests on rice leaves are shown in Table 6. EMR-ZL-FGD significantly increased the chlorophyll content of rice, with SA chlorophyll fluorescence increasing by 0.0194 Fv / Fm. Moshe analyzed the effects of manganese, iron, copper, and zinc on chlorophyll concentration and plant growth, and the results showed that the chlorophyll level of plants was mainly affected by manganese content. Manganese ions are present in every photosynthetic unit of chloroplasts, and manganese has special activity in the photosynthetic reaction of green plants, including the function of releasing oxygen. Therefore, EMR provides manganese ions to promote chlorophyll synthesis in rice leaves.

[0071] Table 6. Effects of EMR-ZL-FGD on chlorophyll content in rice.

[0072]

[0073] Example 2:

[0074] The method for reducing the arsenic content in rice grown in alkaline arsenic-contaminated paddy fields includes the following steps:

[0075] Step 1, Electrolytic manganese slag pretreatment: The air-dried electrolytic manganese slag EMR is ground through a 100-mesh sieve and placed in an oven to dry at 105℃ to constant weight; Zeolite pretreatment: Natural zeolite ZL is ground through a 100-mesh sieve and placed in an oven to dry at 105℃ to constant weight; Desulfurized gypsum FGD pretreatment: The desulfurized gypsum is dried and dehydrated, then crushed and ground through a 100-mesh sieve.

[0076] Step 2: The pretreated electrolytic manganese slag, natural zeolite and desulfurized gypsum are shaken in a constant temperature shaking box at 240 rpm for 150 min in a ratio of 1:2:1 to make them completely and evenly mixed, so as to obtain the EMR-ZL-FGD mixed sample.

[0077] The third step is soil pretreatment: After the soil sample with an arsenic content of 60-90 mg / kg is collected, it is naturally air-dried in a cool place, and the coarse residue is picked out. The coarse residue is gravel, grass roots, and animal remains. After being crushed and mixed evenly, it is passed through a 2 mm sieve for later use.

[0078] The fourth step is to take pretreated soil samples to determine soil moisture content and field capacity: Take 1 kg of pretreated air-dried soil and put it into four sets of plastic flower pots with a diameter of 15 cm. Based on the mass of air-dried soil, add 0.5% to 2% of EMR-ZL-FGD mixed sample and mix it thoroughly with the soil. Each treatment is repeated three times. Spray deionized water to make the soil moisture content 80% of the field capacity. The soil moisture content is maintained by weighing. Deionized water is added every 24 hours.

[0079] The fifth step was to determine the passivation effect of EMR on soil arsenic: the available arsenic content in the soil was measured after 15, 30, 60 and 90 days of passivation reaction.

[0080] Step 6, Rice Seedling Raising and Soil Passivation Preparation: Prepare Nanjing 46 rice seeds, and after water flotation, soak them in 35℃ warm water for 8 hours to promote germination. After removing and drying for 1 hour, evenly sow them into seedling trays. The bottom of the seedling trays is filled with 5cm of clean soil free of arsenic contamination and 0.1wt% of N:P2O5:K2O=1:1:1 compound fertilizer (15-15-15) is applied. After the rice seeds, cover them with a layer of soil pretreated in Step 1, maintaining the soil moisture content at 80% of the field capacity. 15 days before transplanting, perform soil passivation preparation by adding 0.5% to 2% of the EMR-ZL-FGD mixed sample to the soil pretreated in Step 3 and mixing thoroughly. Maintain the soil moisture content at 80% of the field capacity by weighing for 15 days, replenishing water every 24 hours.

[0081] Step 7: Take 15 kg of the soil that has been passivated for 15 days and place it in a pot with a radius of 20 cm and a height of 40 cm. Apply 20 g of N:P2O5:K2O = 1:1:1 compound fertilizer to each pot as a base fertilizer. Select rice seedlings with uniform growth and transplant them into the pots, 3 holes per pot, 3 seedlings per hole. Replenish with 2 g of N:P2O5:K2O = 1:1:1 compound fertilizer every 15 days, for three times. Irrigate the rice by flooding during its growth process, stopping irrigation at the grain-filling stage and allowing the water to dry naturally before watering again. Place the treatment groups randomly, rotating their positions every three days to ensure even light exposure. The rice growth period is 5 months.

[0082] Step 8: After the rice matures, harvest the rice grains and sun-dry them naturally, then store them in sealed bags. Uproot the remaining rice plants, rinse the soil around the roots with tap water, then rinse three times with deionized water. Place them in an oven at 105℃ for 30 minutes to kill the green, then dry them at 65℃ to constant weight. Cut the rice plants along the root tips with scissors to separate them into above-ground and underground parts. Determine the arsenic content in the above-ground and underground parts and the rice grains separately.

[0083] Step 9: Calculation of arsenic enrichment factor and translocation factor: The ability of rice grains to enrich arsenic in the soil is represented by the bioconcentration factor (BCF), and the calculation formula is as follows: In the formula, C 籽粒 C represents the arsenic concentration in the grain. 土壤 The concentration of arsenic in the soil; the arsenic translocation capacity in rice is represented by the translocation factor (TF), calculated using the following formula: In the formula, TF x / yC represents the transfer coefficient from part y to part x. x C represents the arsenic concentration at site x. y The arsenic concentration at location y;

[0084] Effects of EMR-ZL-FGD mixed samples on arsenic content in different parts of rice: Arsenic content in different parts of Nanjing 46 rice variety is as follows Figure 3 As shown, after adding the EMR-ZL-FGD mixed sample, the arsenic content in the underground parts of Nanjing rice (NJ) decreased by 43.61% compared with the control group. The arsenic content in both the aboveground parts and grains of rice was significantly lower than that in the underground parts, and the trends in arsenic content in the aboveground parts and grains were consistent with those in the underground parts. The arsenic content in the aboveground parts of NJ decreased by 52.15% compared with the control group. The arsenic content in the grains of SA rice decreased by 74.07% compared with the control group, and all treatment groups showed statistically significant differences (p<0.05).

[0085] Effects of EMR-ZL-FGD on the Accumulation and Translocation Coefficients of Rice: The changes in the accumulation and translocation coefficients of Nanjing japonica rice (NJ) are shown in Table 7. The passivating agent EMR-ZL-FGD significantly altered the accumulation coefficient (BCF) of NJ (p<0.05), decreasing it by 0.0139 compared to the control group. Analysis of the effect of EMR on the translocation coefficient of rice revealed that EMR significantly affected both the translocation of arsenic from the underground parts to the aboveground parts and from the aboveground parts to the grains (p<0.05).

[0086] Table 7. Effects of EMR-ZL-FGD on the enrichment and translocation coefficient of rice.

[0087]

[0088] Effects of EMR-ZL-FGD on the number of tillers and effective panicles in rice:

[0089] Table 8 Effects of EMR-ZL-FGD on Tiller Number and Effective Panicle Number in Rice

[0090]

[0091]

[0092] Table 8 shows the effects of EMR-ZL-FGD on the number of tillers and effective panicles in rice. The addition of EMR-ZL-FGD increased the number of tillers and effective panicles in Nanjing NJ rice. This may be due to the large amount of ammonia nitrogen introduced into the soil by the application of EMR-ZL-FGD. According to previous studies, higher ammonia nitrogen can promote tillering and jointing and heading in rice.

[0093] Effects of EMR-ZL-FGD on rice biomass: Table 9 shows that the plant height, fresh weight, and dry weight of rice in the EMR-ZL-FGD treatment group were significantly higher than those in the control group without EMR-ZL-FGD. For rice (NJ), EMR-ZL-FGD significantly increased plant height, fresh weight, and dry weight, achieving statistical significance. EMR-ZL-FGD did not show a regular effect on root length.

[0094] Table 9. Effects of EMR-ZL-FGD on rice biomass

[0095]

[0096] Table 10 shows that EMR-ZL-FGD significantly increased the panicle length of SA (sweet rice). EMR-ZL-FGD had no significant effect on the 100-grain weight of rice, with only minor variations. Combined with the results of the study on the effect of EMR-ZL-FGD on the number of effective panicles in rice, EMR-ZL-FGD can promote the growth of rice panicles and slightly increase rice yield and grain quality.

[0097] Table 10. Effects of EMR-ZL-FGD on Rice Yield and Grain Quality

[0098]

[0099] Effects of EMR-ZL-FGD on chlorophyll content in rice: The results of chlorophyll fluorescence tests on rice leaves are shown in Table 11. EMR-ZL-FGD significantly increased the chlorophyll content in rice, and the chlorophyll fluorescence of NJ increased by 0.017 Fv / Fm.

[0100] Table 11 Effects of EMR-ZL-FGD on Chlorophyll Content in Rice

[0101]

[0102] This application conducted passivation experiments on actual arsenic-contaminated soil, investigating the effects of different addition ratios of EMR-ZL-FGD passivating material EMR on the content of available arsenic in the soil and the arsenic content in rice. The experiments also measured the growth of rice, providing a reference for rice cultivation.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method of reducing arsenic content of rice grown in a rice field contaminated with basic arsenic, characterized by, The steps are as follows: Step 1, Electrolytic manganese slag pretreatment: Grind the air-dried electrolytic manganese slag (EMR) and pass it through a 100-mesh sieve. Then, dry it in an oven at 105°C until constant weight. Zeolite pretreatment: Grind natural zeolite (ZL) and pass it through a 100-mesh sieve. Then, dry it in an oven at 105°C until constant weight. Desulfurized gypsum (FGD) pretreatment: Dry and dehydrate the desulfurized gypsum, then crush and grind it through a 100-mesh sieve. Step 2: The pretreated electrolytic manganese slag, natural zeolite and desulfurized gypsum are shaken in a constant temperature shaking box at 240 rpm for 150 min in a mass ratio of 1:2:1 to make them completely and evenly mixed, so as to obtain the EMR-ZL-FGD mixed sample. The third step is soil pretreatment: After the soil samples with an arsenic content of 60-90 mg / kg are collected, they are naturally air-dried in a cool place, coarse residues are picked out, crushed and mixed evenly, and then passed through a 2 mm sieve for later use. The fourth step is to take pretreated soil samples to determine soil moisture content and field capacity: Take 1 kg of pretreated air-dried soil and put it into four sets of plastic flower pots with a diameter of 15 cm. Based on the mass of air-dried soil, add 0.5% to 2% of EMR-ZL-FGD mixed sample and mix it thoroughly with the soil. Each treatment is repeated three times. Spray deionized water to make the soil moisture content 80% of the field capacity. The soil moisture content is maintained by weighing. Deionized water is added every 24 hours. The fifth step was to determine the passivation effect of EMR on soil arsenic: the available arsenic content in the soil was measured after 15, 30, 60 and 90 days of passivation reaction. Step 6, Rice seedling raising and soil passivation preparation: After being floated in clean water, rice seeds are soaked in warm water at 35℃ for 8 hours to promote germination. After being taken out and dried for 1 hour, they are evenly sown into seedling trays. The bottom of the seedling trays is filled with 5cm of clean soil free of arsenic pollution and 0.1wt% of N:P2O5:K2O=1:1:1 compound fertilizer is applied. After sowing rice seeds, a layer of pre-treated soil is covered to maintain the soil moisture content at 80% of the field maximum water holding capacity. Soil passivation preparation is carried out 15 days before transplanting. 0.5% to 2% of EMR-ZL-FGD mixed sample is added to the soil pre-treated in step 3 and thoroughly mixed. The soil moisture content is maintained at 80% of the field maximum water holding capacity by weighing method for 15 days, and water is added every 24 hours. Step 7: Take 15 kg of the soil that has been passivated for 15 days and put it into a pot with a radius of 20 cm and a height of 40 cm. Apply 20 g of N:P2O5:K2O = 1:1:1 compound fertilizer to each pot as a base fertilizer. Select rice seedlings with uniform growth and transplant them into the pots, with 3 holes per pot and 3 seedlings per hole. Replenish with 2 g of N:P2O5:K2O = 1:1:1 compound fertilizer every 15 days, for three times. Flood irrigation is carried out during the rice growth process. Flood irrigation is stopped at the beginning of the grain-filling stage, and watering is resumed after the water has dried naturally. The treatment groups are randomly placed and their positions are randomly changed every three days to ensure uniform light exposure. The rice growth period is 5 months. Step 8: After the rice matures, harvest the rice grains, dry them naturally in the sun, and store them in sealed bags. Pull up the rest of the rice plants by the roots, rinse the soil around the roots with tap water, rinse three times with deionized water, put them in an oven at 105℃ for 30 minutes to kill the green, and then dry them at 65℃ to constant weight. Cut them off along the root tip with scissors to separate them into above-ground and underground parts, and measure the arsenic content of the above-ground and underground parts and the rice grains respectively.

2. The method for reducing arsenic content of rice grown in a rice field contaminated with basic arsenic according to claim 1, characterized by: The coarse slag in the third step is one or more of the following: gravel, grass roots, and animal remains.

3. The method for reducing arsenic content of rice grown in a rice field contaminated with basic arsenic according to claim 1, characterized by: The method for determining the available arsenic content in the soil in the fifth step is as follows: Available arsenic in the soil is extracted using NaHCO3 solution. Weigh 5g of soil that has been ground through a 1mm mesh sieve into a 50mL centrifuge tube, add 25mL of 0.5mol / L NaHCO3 solution, place the tube in a constant temperature shaking oven, and shake and extract for 2h at 25℃ and 250rpm. After centrifugation, take the supernatant, filter it, and determine the arsenic content using ICP-MS.

4. The method for reducing arsenic content of rice grown in a rice field contaminated with basic arsenic according to claim 1, characterized by: The addition amount of the electrolytic manganese slag-zeolite-desulfurized gypsum mixed sample was 2 wt% based on the air-dried soil mass.

5. The method for reducing arsenic content of rice grown in a rice field contaminated with basic arsenic according to claim 1, characterized by: The method for determining the arsenic content of rice aboveground and underground parts and rice grains in the eighth step is as follows: crush each part of the rice using a crusher, take 0.5g and put it in a tetrafluoroethylene crucible, add 5ml of concentrated hydrochloric acid, 4ml of concentrated nitric acid and 1ml of perchloric acid, heat and digest at 120℃ on a graphite hot plate for 2 hours until completely dissolved; dilute the digest to 50ml and filter it using a 45μm filter membrane, and determine the arsenic content of the digest using inductively coupled plasma mass spectrometry (ICP-MS).

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