Reduction remediation method for cadmium-polluted rice field soil and application of reduction remediation method

Abstract

The invention provides a reduction remediation method for cadmium-polluted rice field soil and application of the reduction remediation method, and relates to the technical field of soil remediation. According to the method, the activating agent is added into the soil to activate cadmium in the soil, then the surface of the soil is covered with the composite adsorption material, the activated cadmium in the soil can move towards the soil surface along with water under the action of solar radiation and wind power and is absorbed and retained by the adsorption material, and therefore separation of cadmium and the soil is achieved; and the purpose of reducing and repairing the cadmium-polluted soil is achieved. And in combination with a green-energy-driven infrared heating method, the reduction repair efficiency of the method on the cadmium in the rice field at night can be further improved. On one hand, the total cadmium content in soil can be rapidly reduced, and meanwhile, the multifunctional activating agent can increase soil nutrients while activating cadmium, promote plant growth and improve farmland productivity.

Description

Technical Field

[0001] The invention belongs to the technical field of soil remediation, and in particular relates to a method for reducing and remediating cadmium-contaminated paddy field soil and an application thereof. Background Art

[0002] The treatment and remediation of farmland soil contaminated by heavy metals has always been one of the hot spots and difficulties in soil science and environmental science research. At present, the remediation of farmland soil contaminated by heavy metals mainly focuses on reducing the effectiveness of heavy metals and reducing the absorption and accumulation of heavy metals by crops, including water and fertilizer management, planting low-accumulation crops, and applying passivation modifiers. Although this type of technology has a low single cost and obvious effect, heavy metals still exist in the soil, making it difficult to cure the root cause, and long-term monitoring and treatment are required. Therefore, soil heavy metal reduction and remediation technology aimed at reducing the total amount of heavy metals in the soil has gradually attracted the attention of researchers, and is also one of the urgent needs for the treatment and remediation of farmland heavy metal contaminated soil.

[0003] The existing technologies for reducing and repairing heavy metals in farmland soil mainly include phytoremediation technology, magnetic adsorption and separation technology, etc., in addition to some costly engineering repair measures (such as soil replacement, leaching, electric repair, etc.). Phytoremediation technology uses hyperaccumulators or enrichment plants to absorb heavy metals in the soil and transfer them to the aboveground part, thereby achieving the purpose of removing heavy metals in the soil. This technology has low cost but a long repair cycle. Magnetic adsorption and separation technology uses magnetic adsorption materials to adsorb non-stable heavy metals in the soil, and then removes the magnetic materials from the soil by magnetic separation methods, thereby achieving the reduction of heavy metals in the soil. This technology is simple to operate and removes quickly, but the magnetic material is difficult to completely separate from the soil, is easy to remain in the soil, and is difficult to achieve the adsorption and removal of stable heavy metals in the soil. Therefore, there is an urgent need for a new reduction and repair technology for heavy metal pollution in the surface layer of farmland. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a method for reducing and repairing cadmium-contaminated paddy field soil and its application. The method of the present invention has a short repair time and has a good removal effect on both non-stable heavy metals and stable heavy metals in the soil.

[0005] The present invention provides a method for reducing and restoring cadmium-contaminated paddy soil, comprising the following steps: adding an activator to the soil, spraying irrigation water to make the field water holding capacity of the soil 100%, and covering the soil surface with a composite adsorption material;

[0006] The activator comprises one or more of tetrasodium glutamate diacetate, tetrasodium hydroxyethylene diphosphate, trisodium N-(1-carboxyethyl)iminodiacetate, tetrasodium iminodisuccinate, trisodium ethylenediamine disuccinate, citric acid and oxalic acid;

[0007] The molar concentration ratio of the dosage of the activator to the heavy metal cadmium in the soil is 16:1 to 1:1.

[0008] Preferably, the activator is prepared into an activator solution and then sprayed on the soil surface.

[0009] More preferably, the pH of the activator solution is 4-5.

[0010] Preferably, the composite adsorbent material comprises a water-absorbing material and a heat-absorbing material.

[0011] More preferably, the water-absorbing material includes Toyobo, needle-punched cotton, super absorbent fiber or absorbent cotton; and the heat-absorbing material is polyethylene material.

[0012] Preferably, when the field water holding capacity of the soil drops below 70%, the composite adsorption material is removed, and irrigation water is sprayed so that the field water holding capacity of the soil is 100%.

[0013] Preferably, the reduction and remediation method also includes the activated cadmium in the soil migrating to the soil surface with water under natural and artificial effects and being absorbed and retained by the composite adsorption material, thereby achieving separation of cadmium from the soil.

[0014] More preferably, the natural action refers to solar radiation and wind action; the artificial action refers to setting up infrared heating facilities on the soil surface.

[0015] Preferably, the reduction-based restoration further comprises tidying up the paddy field soil to be restored, wherein the soil particles are smaller than 5 mm and the land is kept flat.

[0016] The present invention also provides an application of the reduction repair method in repairing and / or treating heavy metal contaminated soil.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides a method for reducing and restoring cadmium-contaminated paddy field soil, and the restoration time of the method is short, which is much shorter than the time required for plant restoration; the restoration method of the present invention can not only remove non-stable heavy metal cadmium in the soil, but also has a good removal effect on stable heavy metal cadmium; the composite activators used in the present invention are all biodegradable activators, which can not only effectively activate the heavy metal cadmium in the soil, but also increase soil nutrients and improve farmland productivity; the present invention can strengthen the upward migration of soil pore water at night and improve the removal efficiency of heavy metal cadmium by setting up photovoltaic power generation facilities and using the electric energy stored during the day for infrared heating facilities at night. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the principle of reduction and restoration technology for cadmium-contaminated paddy soil;

[0020] Figure 2 are scanning electron microscope images of different water-absorbing materials, in which a is a scanning electron microscope image of filter paper, b is a scanning electron microscope image of gauze, c is a scanning electron microscope image of needle-punched cotton, d is a scanning electron microscope image of super absorbent fiber, e is a scanning electron microscope image of absorbent cotton, and f is a scanning electron microscope image of Toyobo;

[0021] Figure 3 The effects of different activators on soil cadmium removal;

[0022] Figure 4 The effects of different molar ratios of activator to soil cadmium on soil cadmium removal;

[0023] Figure 5 The effects of different activators on germination rate and germination index of ryegrass;

[0024] Figure 6 is the removal efficiency of cadmium in different cadmium-contaminated soils;

[0025] Figure 7 Effects of different environmental conditions on soil cadmium removal. DETAILED DESCRIPTION

[0026] The present invention provides a method for reducing and restoring cadmium-contaminated paddy soil, comprising the following steps: adding an activator to the soil, spraying irrigation water to make the field water holding capacity of the soil 100%, and covering the soil surface with a composite adsorption material;

[0027] In the present invention, the activator preferably includes one or more of tetrasodium glutamate diacetate (GLDA), tetrasodium hydroxyethyl diphosphate (HEDP), trisodium N-(1-carboxyethyl) iminodiacetate (MGDA), tetrasodium iminodisuccinate (IDS), trisodium ethylenediamine disuccinate (EDDS), citric acid and oxalic acid. In the present invention, as an operative method, the activator may be any combination of the above two activators, such as GLDA+citric acid or MGDA+citric acid or EDDS+citric acid or GLDA+oxalic acid or MGDA+oxalic acid. In the present invention, when the activator is a combination of any two activators, the two activators are preferably mixed in a molar ratio of 1:1 to obtain a composite activator. In the present invention, as another operative method, the type and addition amount of the activator are determined by measuring the cadmium content in the soil to be repaired.

[0028] In the present invention, the molar concentration ratio of the dosage of the activator to the heavy metal cadmium in the soil is preferably 16:1 to 1:1; more preferably 8:1 or 10:1 to 1:1 or 12:1 to 1:1 or 5:1 to 1:1.

[0029] In the present invention, the activator is prepared into an activator solution and then sprayed on the soil surface. The solvent used in the preparation can be selected according to actual conditions. In the present invention, the solvent used in the preparation is preferably water. In a specific embodiment of the present invention, the activator is preferably prepared into an activator solution with water, and after adjusting the pH to 4-5, it is evenly sprayed on the soil surface. In the present invention, the pH of the activator solution is more preferably 4.5. In the present invention, as an operative method, after the activator is prepared, if the original pH is higher than 4.5, the pH is adjusted to 4.5, and if it is lower than 4.5, it is not adjusted.

[0030] In the present invention, the composite adsorbent material includes a water-absorbing material and a heat-absorbing material. In the present invention, the water-absorbing material preferably includes Toyobo, needle-punched cotton, super absorbent fiber or cotton wool; the heat-absorbing material is preferably a black polyethylene material. In the present invention, the composite adsorbent material can be purchased through conventional channels. In a specific embodiment of the present invention, the polyethylene material is more preferably a black mesh polyethylene film. In the present invention, as an implementable method, after covering the soil surface with a water-absorbing material, a layer of heat-absorbing material is covered to form a composite adsorbent material, which can improve the heat absorption capacity, accelerate water evaporation, and improve the removal efficiency of heavy metal cadmium.

[0031] In the present invention, when the field water holding capacity of the soil drops below 70%, the composite adsorption material is removed, and irrigation water is sprayed to make the field water holding capacity of the soil 100%.

[0032] In the present invention, the reduction remediation method preferably also includes the activated cadmium in the soil migrating to the soil surface with water under natural and artificial action and being absorbed and retained by the composite adsorption material, so as to achieve the separation of cadmium from the soil. In the present invention, the natural action refers to solar radiation and wind action; the artificial action refers to the installation of infrared heating facilities on the soil surface. In the present invention, it is preferred to use the electric energy stored during the day for infrared heating facilities by installing photovoltaic power generation facilities and energy storage batteries. In the present invention, the infrared heating facilities can be conventionally selected according to actual conditions. In the present invention, the infrared heating facilities are preferably infrared lamps. In the present invention, the infrared heating facilities can be used both during the day and at night to enhance the upward migration efficiency of cadmium-containing pore water in the soil.

[0033] In the present invention, the reduction-volume restoration preferably also includes tidying up the paddy field soil to be restored, with the soil particles being smaller than 5 mm and the land being kept flat so that the soil has the ability to store water.

[0034] The present invention also provides an application of the reduction repair method in repairing and / or treating heavy metal contaminated soil.

[0035] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0036] The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are commercially available products unless otherwise specified.

[0037] Example 1

[0038] A method for reducing and restoring cadmium-contaminated paddy soil, the specific steps are as follows:

[0039] (1) Land preparation: The soil of the paddy field to be restored is prepared so that the soil particles are smaller than 5 mm and the land is kept flat and has water storage capacity;

[0040] (2) Adding activator: Determine the cadmium content in the soil, prepare the activator GLDA into a solution with water, adjust the pH to 4.5, and evenly spray it on the soil surface. The molar ratio of activator GLDA to cadmium is 16:1;

[0041] (3) Regulate soil moisture: spray irrigation water into the soil to make the soil's field water holding capacity reach 100%;

[0042] (4) Covering with composite adsorbent material: Cover the water-absorbing material Toyobo on the soil surface to fit the soil surface, and then cover it with a layer of black mesh polyethylene material to form a composite adsorbent material;

[0043] (5) By setting up photovoltaic power generation facilities and energy storage batteries, the electricity stored during the day can be used for infrared heating facilities at night to enhance the upward migration efficiency of Cd-containing pore water in the soil at night;

[0044] (6) When the soil field water holding capacity drops below 70%, remove the composite adsorption material on the surface and repeat steps (3) to (5) for 2 to 3 cycles. Figure 1 .

[0045] Example 2

[0046] The difference from Example 1 is that the water-absorbing material covering the soil surface is needle-punched cotton, and the remaining steps are the same as Example 1.

[0047] Example 3

[0048] The difference from Example 1 is that the water-absorbing material covering the soil surface is super absorbent fiber, and the remaining steps are the same as Example 1.

[0049] Example 4

[0050] The difference from Example 1 is that the water-absorbing material covering the soil surface is absorbent cotton, and the remaining steps are the same as Example 1.

[0051] Example 5

[0052] The difference from Example 1 is that the activator is HEDP, and the remaining steps are the same as Example 1.

[0053] Example 6

[0054] The difference from Example 1 is that the activator is MGDA, and the remaining steps are the same as those of Example 1.

[0055] Example 7

[0056] The difference from Example 1 is that the activator is IDS, and the remaining steps are the same as Example 1.

[0057] Example 8

[0058] The difference from Example 1 is that the activator is EDDS, and the remaining steps are the same as those of Example 1.

[0059] Example 9

[0060] The difference from Example 1 is that the activator is citric acid, and the remaining steps are the same as those of Example 1.

[0061] Example 10

[0062] The difference from Example 1 is that the activating agent is oxalic acid, and the remaining steps are the same as those of Example 1.

[0063] Embodiment 11

[0064] The difference from Example 1 is that the activator is GLDA+citric acid (molar ratio is 1:1), and the remaining steps are the same as Example 1.

[0065] Example 12

[0066] The difference from Example 1 is that the molar ratio of the activator GLDA to cadmium is 12:1, and the remaining steps are the same as Example 1.

[0067] Example 13

[0068] The difference from Example 1 is that the molar ratio of the activator GLDA to cadmium is 8:1, and the remaining steps are the same as Example 1.

[0069] Embodiment 14

[0070] The difference from Example 1 is that the molar ratio of the activator GLDA to cadmium is 6:1, and the remaining steps are the same as Example 1.

[0071] Embodiment 15

[0072] The difference from Example 1 is that the molar ratio of the activator GLDA to cadmium is 2:1, and the remaining steps are the same as Example 1.

[0073] Example 16

[0074] The difference from Example 1 is that the molar ratio of the activator GLDA to cadmium is 1:1, and the remaining steps are the same as Example 1.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that the water-absorbing material covering the soil surface is gauze, and the remaining steps are the same as those of Example 1.

[0077] Comparative Example 2

[0078] The difference from Example 1 is that the water-absorbing material covering the soil surface is filter paper, and the remaining steps are the same as Example 1.

[0079] Comparative Example 3

[0080] The difference from Example 1 is that the activator is EDTA, and the remaining steps are the same as those of Example 1.

[0081] Comparative Example 4

[0082] The difference from Example 1 is that irrigation water is sprayed into the soil so that the field water holding capacity of the soil reaches 70%.

[0083] Test Example 1

[0084] Six absorbent materials were selected as test materials, including filter paper, gauze, needle-punched cotton, super absorbent fiber, cotton wool and Toyobo, to study their absorption properties of heavy metal solutions. Figure 2 The following are scanning electron microscope (SEM) images of different materials. It can be seen from the figure that there are great differences in the apparent morphology of different materials. The surface of the filter paper is dense and irregular, and the surface fibers of the gauze and the cotton wool are flat, but the spacing between the cotton wool fibers is large, which is related to the fact that the cotton wool itself is relatively soft and fluffy. The SEM images of needle-punched cotton, super absorbent fiber and Toyobo are similar, all of which are composed of tubular fibers, but the tubular fibers of super absorbent fiber and Toyobo are smoother, which is related to the similar composition of the two.

[0085] 0.2mmol / L CdCl2, EDTA-Cd and GLDA-Cd solutions were prepared respectively (the molar ratio of EDTA (tetrasodium ethylenediaminetetraacetic acid) and GLDA (tetrasodium glutamate diacetate) to cadmium in the latter two solutions was 1:1), and the absorption performance of different composite water-absorbing materials of Examples 1 to 3 and Comparative Examples 1 to 3 on cadmium solution was studied. Table 1 shows the absorption of cadmium solution by different materials. Regardless of the form of cadmium solution, Toyobo has the strongest absorption capacity, and the solution absorption per unit mass of Toyobo is 46.2-49.2mL / g, which is significantly higher than other materials; the filter paper has the smallest liquid absorption capacity, which is only 8.82-11.8mL / g, and the solution absorption of Toyobo is 4.16-5.42 times that of filter paper. The order of the absorption performance of the six materials is: Toyobo> needle-punched cotton> super absorbent fiber≈absorbent cotton> gauze> filter paper.

[0086] Table 1 Absorption performance of different materials for cadmium solution (mL / g)

[0087] Material Cd ion solution EDTA-Cd solution GLDA-Cd solution filter paper 11.8Ae 8.92Bd 8.82Bd gauze 14.8Ad 10.3Bd 10.2Bd Needle-punched cotton 26.7Ab 25.6Ab 26.8Ab Super absorbent fiber 21.7Ac 19.2Bc 17.6Ac Cotton wool 17.9Bd 20.9Ac 19.7ABc Toyobo 49.2Aa 46.2Aa 47.8Aa

[0088] Note: Different capital letters in the table indicate significant differences among treatments in the same row, and different lowercase letters indicate significant differences among treatments in the same column (p<0.05).

[0089] Table 2 shows the absorption of cadmium in solution by different materials per unit mass. Among the six materials, the absorption of cadmium per unit mass of Toyobo is the highest, reaching 0.009-0.016mmol / g, which is significantly higher than other materials. In cadmium ion solution, the absorption of cadmium in solution by filter paper and gauze is only lower than that of Toyobo; in GLDA-Cd solution, the absorption capacity of cadmium in solution by filter paper and gauze is in the middle; and in EDTA-Cd solution, the absorption capacity of cadmium in solution by filter paper and gauze is low, at 0.003mmol / g, but it is not much different from needle-punched cotton (0.005mmol / g) and absorbent cotton (0.004mmol / g).

[0090] Table 2 Absorption of cadmium in solution by different materials (mmol / g)

[0091] Cd ion solution EDTA-Cd solution GLDA-Cd solution filter paper 0.009Ab 0.003Ad 0.006Ab gauze 0.010Ab 0.003Bd 0.004Bb Needle-punched cotton 0.009Ab 0.005Ab 0.008Aa Super absorbent fiber 0.005Ac 0.003Bd 0.004ABb Cotton wool 0.005Bc 0.004Ac 0.004Bb Toyobo 0.016Aa 0.009Ca 0.011Ba

[0092] Note: Different capital letters in the table indicate significant differences among treatments in the same row, and different lowercase letters indicate significant differences among treatments in the same column (p<0.05).

[0093] In summary, the materials with good absorption performance for different forms of cadmium solutions are Toyobo and needle-punched cotton, among which Toyobo is the best. In addition, a layer of black mesh polyethylene material is covered on the above absorbent materials to form a composite adsorption material, which can improve the heat absorption capacity and accelerate the evaporation of water.

[0094] Test Example 2

[0095] The test soil was collected from farmland soil around a mining area in Fuyang, Zhejiang. The soil pH was 7.93, the total Cd content in the soil was 19.1 mg / kg, and the Cd content in the hydrochloric acid extract state was 13.2 mg / kg. Take 200g of the test soil and put it into a 200mL beaker, add different activators and stir evenly, keep it in a flooded state, let it stand for 1 day, cover the surface with adsorption material Toyobo, put it in an oven and bake it at 45℃ for 2 days; after taking out the absorbent material, add water to the flooded state, then let it stand for 1 day, put in the new absorbent material, and bake it at 45℃ for 2 days; after taking it out, use a small soil drill to collect 2 samples in each beaker and mix them together for use; the above 6 days is one cycle, and then repeat the same cycle 2 times for a total of 18 days. The test treatment is as follows:

[0096] Treatment with different activators: Due to the poor biodegradability of EDTA, the heavy metal complex after activation is not easy to degrade and easily causes secondary pollution, which is not suitable for use in farmland soil. Therefore, the present invention mainly selects biodegradable activators, including GLDA (tetrasodium glutamate diacetate), HEDP (tetrasodium hydroxyethyl diphosphate), MGDA (trisodium N-(1-carboxyethyl) iminodiacetic acid), IDS (tetrasodium iminodisuccinate), EDDS (trisodium ethylenediamine disuccinate), citric acid (CA), oxalic acid (OA), GLDA+citric acid (molar ratio 1:1), a total of 8 activators, and the added amount is 0.02 mol / kg soil. After the activator is prepared, if the original pH is higher than 4.5, the pH is adjusted to 4.5, and if it is lower than 4.5, it is not adjusted.

[0097] Molar ratios of different activators to heavy metals: GLDA was selected as the activator. According to the total Cd content in the soil, the molar ratios of GLDA and total cadmium were set to 1:1, 2:1, 6:1, 8:1, 12:1 and 16:1, and the corresponding GLDA addition amounts were 0.01, 0.02, 0.06, 0.08, 0.12 and 0.16 mol / kg soil, respectively.

[0098] After the treatment, the total Cd and hydrochloric acid extractable Cd content in the soil were determined, and the changes in soil organic matter, cation exchange capacity (CEC), and available nutrients were also determined. The root elongation experiment was used to evaluate the effect of the repaired soil on plant growth. The specific method was as follows: ryegrass was selected as the test plant, 35g of the above-mentioned test soil and original soil were placed in each culture dish, and deionized water was added with a watering can to adjust the soil moisture to 70% of the field water holding capacity; 15 ryegrass seeds were placed and cultured at 25 degrees in the dark for 3 days. Water was added every day during the culture process to maintain the moisture content of the soil. Another culture dish was taken, filter paper was placed, moistened with deionized water, and 15 seeds were placed in the same culture dish. It was cultured under the same conditions as the control group. After the culture was completed, the germination rate and root elongation of ryegrass in each culture dish were measured, and the germination index was calculated.

[0099] Figure 3 (a) is the removal effect of different activators on soil heavy metals. The results show that due to the different activators, there are certain differences in the content of residual heavy metals in the soil. In the GLDA and MGDA treatments, the removal rates of total soil Cd were 51% and 41%, respectively. The order of the removal rate of total soil Cd by different activators is GLDA>MGDA>GLDA+CA>CA>IDS>EDDS>HEDP>OA. From the results after each sampling, the degree of decrease in the total Cd content in the soil of each treatment after the first sampling is not much different, and the total Cd content in the soil after the second and third samplings is more obvious. Figure 3 (b) Changes in the content of hydrochloric acid-extractable Cd in soil. The three activators, GLDA, EDDS and MGDA, can remove more than 70% of the hydrochloric acid-extractable Cd in soil, which are 72%, 75% and 73% respectively. The combined reagents of IDS and GLDA+CA (1:1) can also remove more than 60% of the hydrochloric acid-extractable Cd in soil, with removal rates of 65% and 63% respectively. In general, the decrease in the hydrochloric acid-extractable Cd is significantly higher than the total amount. Since the hydrochloric acid-extractable state can extract non-exchangeable or adsorbed Cd (i.e., stable heavy metals) in the soil, these activators can remove some stable heavy metals in the soil, which is beneficial to the reduction of the total Cd content in the soil.

[0100] Figure 4 (a) It can be seen that compared with the treatment before remediation, each treatment has a better effect on the removal of Cd in the soil, and the more activators are added to the soil, the higher the removal rate. When the molar ratio of activator to heavy metal is the highest, the removal effect of heavy metal Cd in the soil is the best, and the removal rate reaches 68%. Other treatments can also achieve good results in soil remediation, and the removal rate can reach 37% to 59%. The change in the content of Cd in the hydrochloric acid extractable state of soil is not as obvious as the change in the total amount of heavy metals, see Figure 4(b). During the third sampling, the removal rate of soil hydrochloric acid-extractable Cd was 63% to 71%, and the difference between different treatments was less than the total Cd removal rate of 37% to 68%. The greater the amount of activator added, the higher the removal rate of hydrochloric acid-extractable Cd. When the molar ratio of activator to Cd was 16:1, the removal effect of hydrochloric acid-extractable Cd in the soil was the best, and the removal rate could reach 71%. When the activator and heavy metals were in other ratios, there was also a good remediation effect on Cd in the soil, and the removal rate could reach 50% to 58%. Considering the amount of activator input and the removal efficiency of Cd, 8:1 was selected as the optimal activator input molar ratio.

[0101] The changes in soil nutrients after treatment with different activators are shown in Table 3. Soil organic matter is an important component of soil and an important indicator of soil fertility, while soil CEC is also an important indicator for evaluating soil water and fertilizer retention and buffering capacity. After treatment, the content of soil organic matter decreased, but the amplitude was not large, and there was no significant difference between most activator treatments and the original soil, while the soil organic matter increased slightly after GLDA treatment. For soil CEC, except for the increase in HEDP treatment, the soil CEC decreased slightly after other activators, but the decrease was very small. Soil nitrogen, phosphorus and potassium are also three essential elements for agricultural soil and crops. The content of alkaline nitrogen, available phosphorus and available potassium in the soil has a strong correlation with the absorption of soil nutrients by agricultural plants and agricultural output, and is an important soil nutrition indicator. The results in Table 3 show that the content of alkaline nitrogen, available phosphorus and available potassium in the treated soil is increased compared with the original soil. Among them, the content of alkaline nitrogen is significantly higher than that of the original soil, and its content reaches 1.63 to 2.05 times that of the original soil. This is mainly because the biodegradable activator used in the present invention releases nitrogen during the decomposition process. The effective phosphorus content in the soil has also increased significantly, reaching 1.28 to 1.74 times that of the original soil. This is because the added activator dissolves some phosphate minerals in the soil, causing the stable form of phosphorus in the soil to be released and converted into effective phosphorus. The content of quick-acting potassium in the soil has also increased, which is also related to the dissolution of potassium-containing minerals in the soil by the added activator, that is, converting some slow-acting potassium into quick-acting potassium.

[0102] Table 3 Changes in soil nutrients after treatment with different activators

[0103]

[0104] Note: Different letters in the same column indicate significant differences among treatments (p<0.05)

[0105] Figure 5The effect of soil treated with different activators on the germination rate and germination index of ryegrass. Compared with the original soil, the germination rate and germination index of the soil were significantly improved. For the germination rate, the germination rate of ryegrass in the soil treated with activators was higher than that of the original soil, among which the MGDA treatment was the highest, reaching 100%, and the germination rates after other activators were also higher than 90%, and higher than 80% of the original soil. For the germination index, the germination index of all activators was higher than that of the original soil, among which the germination index of ryegrass after GLDA, MGDA, IDS, EDDS and GLDA+CA (1:1) combination agents were all higher.

[0106] Based on the above research results, the soil treated with different activators did not have an adverse effect on the soil. On the contrary, it increased the content of available nutrients in the soil and improved the plant growth conditions. Among them, MGDA, GLDA, CA and GLDA+CA (1:1) had a better effect on promoting soil nutrients and plant growth. This patented technology can not only significantly reduce the content of heavy metals in the soil, but also improve the soil properties, which is conducive to plant growth. It is a promising farmland soil remediation technology.

[0107] Test Example 3

[0108] In actual application, different environmental conditions have different effects on the application effect of the technology. Therefore, this test example uses an experimental method similar to that of Test Example 2 to study the effect of different environmental conditions on soil Cd removal. The test soil was collected from farmland soil around a mining area in Fuyang, Zhejiang. The soil pH was 7.93, the total soil Cd content was 19.08 mg / kg, and the hydrochloric acid extractable Cd content was 13.18 mg / kg. The test treatment is as follows:

[0109] Different heating methods: activator GLDA was selected with an addition amount of 0.02 mol / kg; the initial water content was flooding (depth of 0.5 cm); two heating methods, infrared lamp radiation and oven heating (temperature of 45°C), were used, for a total of 2 treatments.

[0110] Different temperatures: the activator is GLDA, and two temperatures are set at 45℃ and 30℃; the molar ratio of activator to heavy metal is 2:1, the corresponding GLDA addition amount is 0.02mol / kg, the heating method is infrared heating, the initial moisture content is flooding, and there are 2 treatments in total.

[0111] Different moisture contents: activator GLDA was selected with an addition amount of 0.02 mol / kg; three moisture contents were set, namely flooding, 100% field water capacity (WHC) and 70% WHC, and infrared warming was used, with a total of 3 treatments.

[0112] Figure 6The results show the influence of different environmental conditions on the removal of soil Cd by the present invention. Although the removal rate of Cd by oven heating is higher than that by infrared heating ( Figure 6 (a)), but the difference between the two is not big, and the infrared heating method is closer to the solar radiation under natural conditions, so infrared radiation is used to enhance the repair effect when applied at night. From the effect of different temperatures ( Figure 6 (b)), the removal rate of heavy metals in the 45℃ treatment is slightly higher than that in the 30℃ treatment, but the energy consumed in the 45℃ treatment is much higher than that in the 30℃ treatment, so a better remediation effect can be obtained when the temperature is above 30℃. Figure 6 (c)) There is little difference in the removal rate of heavy metals between the flooding and 100% WHC treatments, while the removal rate of heavy metals in the 70% WHC treatment is significantly lower, only 14%. Therefore, in actual operation, the use of 100% WHC can reduce the use of water without affecting the removal rate of heavy metals. When the soil moisture content drops to 70% WHC, water needs to be added again to 100% WHC to ensure that the removal rate of heavy metals is maintained at a high level.

[0113] Test Example 4

[0114] Two typical Cd-contaminated soils were selected to study the adaptability of the present invention to remove Cd from different soils. Test soil 1 was collected from a polluted farmland in Jiujiang, Jiangxi Province, with a soil pH of 4.60, a total soil Cd content of 3.06 mg / kg, and a hydrochloric acid-extractable Cd content of 2.63 mg / kg; test soil 2 was collected from farmland soil around a mining area in Fuyang, Zhejiang Province, with a soil pH of 7.93, a total soil Cd content of 19.1 mg / kg, and a hydrochloric acid-extractable Cd content of 13.2 mg / kg.

[0115] This experiment was conducted in a solar greenhouse, and an experimental method similar to that of Experimental Example 2 was used to study the removal efficiency of Cd in different soils by the present invention, wherein the adsorbent material was a composite adsorbent material of Toyobo and black mesh polyethylene, the heating method was daytime solar radiation + nighttime infrared lamp radiation, the activator was GLDA, and the dosage was 0.02 mol / kg soil. Antoine infrared lamp (100-300W adjustable) was used for nighttime infrared radiation, and the time was from 7 pm to 7 am the next day. A 2m×1m solar panel was used, with a battery (24V, 100AH), and the solar power generated during the day could be stored in the battery for use by the infrared lamp at night.

[0116] from Figure 7 It can be seen that no matter what kind of soil, the present invention can effectively reduce the total Cd content of the soil ( Figure 7(a)), the total Cd removal rate of Zhejiang soil reached 51%, while that of Jiangxi soil reached 40%; from the perspective of Cd content extracted by hydrochloric acid, the removal rate of Zhejiang soil was 72%, while that of Jiangxi soil was 63% ( Figure 7 (b)). This result shows that when the Cd concentration in the soil is high, the removal rate of Cd by the present invention will be higher, so the present invention is more suitable for contaminated soil with a higher Cd concentration.

[0117] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for reducing and restoring cadmium-contaminated paddy soil, characterized in that: The method comprises the following steps: adding an activator to the soil and then spraying irrigation water to make the field water holding capacity of the soil 100%, and covering the soil surface with a composite adsorption material; The activator comprises one or more of tetrasodium glutamate diacetate, tetrasodium hydroxyethylene diphosphate, trisodium N-(1-carboxyethyl)iminodiacetate, tetrasodium iminodisuccinate, trisodium ethylenediamine disuccinate, citric acid and oxalic acid; The molar concentration ratio of the dosage of the activator to the heavy metal cadmium in the soil is 16:1 to 1:

1.

2. The reduction repair method according to claim 1, characterized in that: The activator is prepared into an activator solution and then sprayed on the soil surface.

3. The reduction repair method according to claim 2, characterized in that: The pH of the activator solution is 4-5.

4. The reduction repair method according to claim 1, characterized in that: The composite adsorption material comprises a water-absorbing material and a heat-absorbing material.

5. The reduction repair method according to claim 4, characterized in that: The water-absorbing material includes Toyobo, needle-punched cotton, super absorbent fiber or absorbent cotton; the heat-absorbing material is black polyethylene material.

6. The reduction repair method according to claim 1, characterized in that: When the field water holding capacity of the soil drops below 70%, the composite adsorption material is removed, and irrigation water is sprayed to make the field water holding capacity of the soil 100%.

7. The reduction repair method according to claim 1, characterized in that: The reduction and restoration method also includes the following steps: under natural and artificial action, the activated cadmium in the soil moves to the soil surface along with the water and is absorbed and retained by the composite adsorption material, thereby achieving separation of the cadmium from the soil.

8. The reduction repair method according to claim 7, characterized in that: The natural action refers to solar radiation and wind action; the artificial action refers to setting up infrared heating facilities on the soil surface.

9. The reduction repair method according to claim 1, characterized in that: The reduction-based restoration also includes tidying up the paddy field soil to be restored, ensuring that the soil particles are smaller than 5 mm and the land is kept flat.

10. Use of the reduction remediation method according to any one of claims 1 to 9 in remediating and / or treating heavy metal contaminated soil.

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