Waste-free green leaching remediation method for rare earth contaminated soil

Abstract

The invention discloses a waste-free green leaching remediation method for rare earth contaminated soil, which comprises the following steps: a biodegradable chelating agent solution is used as an organic leaching agent and is applied to the rare earth contaminated soil to be remedied, and the biodegradable chelating agent is selected from N, N '-dihydroxybenzenesulfonic acid, N'-dihydroxybenzenesulfonic acid, N '-dihydroxybenzenesulfonic acid and N'-dihydroxybenzenesulfonic acid; the component A is one or more than two of N, N-bis (carboxymethyl)-L-glutamic acid, iminodisuccinic acid, polyaspartic acid, methylglycine diacetic acid, ethylenediamine disuccinic acid, and potassium salts and sodium salts thereof; the pH value of a mixed system of the organic eluting agent and the rare earth contaminated soil is 6 or above, soil colloid in the rare earth contaminated soil is dispersed through the organic eluting agent, and leaching and removal of rare earth combined with iron and manganese oxides are promoted. The organic eluting agent is nearly neutral and alkaline, iron oxide colloidal particles enriched with a large number of rare earth elements can be effectively dispersed and dissolved in a leaching solution, acidified soil is improved, application of an alkaline modifier is avoided, and recycling of the eluted soil is facilitated.

Description

Technical Field

[0001] The invention relates to a rare earth contaminated soil restoration method, and in particular to a waste-free green leaching restoration method for rare earth contaminated soil. Background Art

[0002] Rare Earth Elements (REEs) are essential components of various advanced industries, including electronics, petrochemicals, aerospace, medicine, and renewable energy. However, REEs also pose significant environmental and public health risks as emerging pollutants, which can leach from weathering crusts during natural weathering and migrate to agricultural fields.

[0003] In recent years, due to the large-scale development of rare earth resources, rare earth resources have been enriched and migrated in environmental media. The migration and transformation of rare earths in mining areas and surrounding water bodies, soil and other environments have resulted in rare earth content in crops such as vegetables and rice being 10 to 20 times greater than the national food limit standard, and are transmitted through the food chain, leading to increased risks to public health and the ecological environment. In addition, the in-situ leaching process used in the mining of ion-adsorption rare earth deposits leads to widespread migration of rare earth elements, causing non-point source pollution. Increased concentrations of REEs in the soil inhibit crop growth and accumulate in plants, which may affect human health through the food chain. Therefore, effective remediation technology is essential to mitigate the environmental risks of REEs pollution.

[0004] Among the current soil pollution control technologies, how to remove pollutants from the soil efficiently and quickly while avoiding secondary pollution of the soil is the focus of research. Soil leaching remediation has the advantages of fast effect and efficient removal of pollutants. However, traditional leaching technology often requires a large amount of reagents, and the leaching solution remaining in the soil will cause new environmental risks. Commonly used inorganic acid leaching will destroy the soil structure and cause soil nutrient loss. A large amount of residual inorganic salt leaching agents may affect (inhibit) the growth of crops during the reuse of the soil after repair. The strong binding of rare earths with iron / manganese oxides in the soil poses a challenge to traditional leaching agents (such as ammonium salts, magnesium salts, iron salts and rhamnolipids), and these leaching agents have limited effects. Therefore, it is urgent to find an environmentally friendly remediation method with high leaching efficiency, little damage to the soil, no residue in the soil and low toxicity.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute the prior art known to ordinary technicians in the field. Summary of the invention

[0006] The purpose of the present invention is to provide a waste-free green leaching remediation method for rare earth contaminated soil, which solves the problem that traditional leaching agents are difficult to remove rare earth elements strongly bound to iron / manganese oxides in rare earth contaminated soil. The method can reduce damage to the soil while removing rare earths in the soil. In addition, the method also overcomes the difficulty in disposing of leaching waste liquid in traditional remediation technology, increases processing costs, and easily causes secondary pollution. It can achieve waste-free generation in the entire remediation process, and constructs a green, clean and efficient remediation method that combines resource recycling, leaching waste liquid resource utilization and full-process remediation material recycling.

[0007] In order to achieve the above-mentioned object, the present invention provides a waste-free green leaching remediation method for rare earth contaminated soil, which comprises: using a biodegradable chelating agent solution as an organic eluting agent, and spreading it in the rare earth contaminated soil to be remediated, wherein the biodegradable chelating agent is selected from N, N-bis(carboxymethyl)-L-glutamic acid, iminodisuccinic acid, polyaspartic acid, methylglycine diacetic acid and ethylenediamine disuccinic acid, and any one or more of their potassium salts and sodium salts; the pH of the mixed system of the organic eluting agent and the rare earth contaminated soil is above 6, and the soil colloids in the rare earth contaminated soil to be remediated are dispersed by the organic eluting agent, so as to promote the leaching and removal of the rare earth elements combined with iron and manganese oxides.

[0008] Preferably, the concentration of the biodegradable chelating agent solution is 10-100 mmol / L.

[0009] Preferably, when the N, N-bis(carboxymethyl)-L-glutamic acid and iminodisuccinic acid are used, the pH of the organic eluent is above 8; when the polyaspartic acid is used, the pH of the organic eluent is between 6 and 8.

[0010] Preferably, when the N, N-bis(carboxymethyl)-L-glutamic acid is used, the pH of the mixed system is above 6.0; when the iminodisuccinic acid is used, the pH of the mixed system is above 6.5; when the polyaspartic acid is used, the pH of the mixed system is above 6.3.

[0011] More preferably, when the N, N-bis(carboxymethyl)-L-glutamic acid is used, the pH of the mixed system is 6.0-9.5; when the iminodisuccinic acid is used, the pH of the mixed system is 6.5-8.2; when the polyaspartic acid is used, the pH of the mixed system is 6.3-6.7.

[0012] Preferably, the organic eluent is used to treat the rare earth contaminated soil to be remediated for 0.5 to 2 days.

[0013] Preferably, in the organic eluent treatment, the mass ratio of the organic eluent to soil solids is 0.8~5:1.

[0014] Preferably, the method comprises the following steps: S1. Plowing and breaking the rare earth contaminated soil to be repaired, and applying the organic eluent thereto, so that the eluent fully infiltrates the rare earth contaminated soil, and the pH of the mixed system is above 6; S2. Introducing irrigation water into the rare earth contaminated soil and simultaneously tilling the soil, mixing the soaked soil and the irrigation water evenly, and using the disturbance during the tillage process to leach and dissolve the rare earths in the soil and transfer them into the leaching solution; S3, the leachate is passed through the drainage channel into the sedimentation tank, the leachate is allowed to settle, the mud and water are separated, the upper leachate is transferred to the collection tank, and the bottom sludge is transferred to the field for reuse; S4, introducing irrigation water into the washed soil, and simultaneously tilling the soil, so that the washed soil and the irrigation water are fully mixed, and the rare earth remaining in the washed soil is dissolved by water washing; S5, the washing liquid enters the sedimentation tank through the drainage channel, the leaching liquid is allowed to settle, the mud and water are separated, the upper washing liquid is transferred to the sedimentation tank, and the bottom sludge is transferred to the field for reuse; S6, adding a precipitant to the sedimentation tank to precipitate the rare earth in the washing liquid, and after the washing liquid is purified by precipitation, it is transferred to the reservoir for reuse as irrigation water; S7, using the leaching liquid in the collection pool of step S3 as rare earth micro-fertilizer for agricultural production.

[0015] In steps S1 and S2 of the present invention, a high concentration of eluent is used to moisten the soil during the infiltration process, and the high concentration of eluent has a strong reactivity, so that the organic eluent fully reacts with the soil particles and the rare earth therein; then, irrigation water is introduced to leach out the activated rare earth elements in the soil. On the one hand, an efficient reaction is generated between the organic eluent and the soil, and on the other hand, the preparation volume of the organic eluent is reduced, thereby reducing the site occupation and preparation cost caused by the preparation of the eluent.

[0016] Preferably, in step S1, the mass ratio of the organic eluent to the rare earth contaminated soil is 0.4~1:1, and the infiltration time is 0.5~2 days; in step S2, the mass ratio of the irrigation water to the rare earth contaminated soil is 0.4~4:1, and the elution reaction time is 0.5~3 days.

[0017] Preferably, in step S4, the mass ratio of the irrigation water to the washed soil is 0.2-1:1; the washing time is 12-36 h, and the number of washings is 1-5 times.

[0018] Preferably, in step S6, the precipitant includes any one or more of oxalic acid, ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate, magnesium bicarbonate, magnesium carbonate, magnesium oxide, magnesium hydroxide, sodium hydroxide and potassium hydroxide.

[0019] Preferably, in the rare earth contaminated soil, the content of reducible rare earths accounts for more than 50%; or / and, the rare earth elements in the soil to be remediated are any one or more of lanthanide elements, yttrium and scandium.

[0020] Preferably, the rare earth micro-fertilizer is used in crop planting. Rare earth micro-fertilizer can increase crop yield, improve the quality of agricultural products, and enhance the ability of crops to resist stress, coercion and drought.

[0021] Preferably, the crops are food crops, vegetables, tea trees and fruit trees.

[0022] More preferably, the crops include: potato, rapeseed and carrot.

[0023] More preferably, the rare earth micro-fertilizer can promote the plant height, stem thickness, aboveground dry weight, underground dry weight, number of aboveground branches, single potato weight and total chlorophyll of potatoes, as well as any one or more of the activities of superoxide dismutase, peroxidase and catalase in leaves; the rare earth micro-fertilizer can promote the increase of rapeseed fresh weight, dry weight, reducing sugar content and vitamin C content, as well as chlorophyll synthesis; the rare earth micro-fertilizer can promote the growth of carrots, as well as the improvement of yield and / or quality, specifically, the rare earth micro-fertilizer can promote the increase of petiole number, total fresh weight, tuber fresh weight, soluble sugar and vitamin C content of carrots.

[0024] The waste-free green leaching remediation method for rare earth contaminated soil of the present invention solves the problem that traditional leaching agents are difficult to remove rare earth elements strongly bound to iron / manganese oxides in rare earth contaminated soil, and has the following advantages: (1) The present invention uses biodegradable chelating agents, particularly glutamic acid-N, N-diacetic acid (GLDA), iminodisuccinic acid (ISA) and polyaspartic acid (PASP), as alternatives for removing rare earth elements from contaminated agricultural soil. GLDA, ISA and PASP have excellent removal effects on rare earth elements. Methylglycine diacetic acid and ethylenediamine disuccinic acid contain abundant amino and carboxyl groups and have comparable rare earth element removal capabilities to GLDA. (2) The biodegradable chelating agent used in the present invention has an organic elution agent with a pH value of above 6, which is nearly neutral and alkaline. The isoelectric point of iron oxides in the soil is above 6. The biodegradable chelating agent used in the present invention can effectively disperse soil colloids, so that iron oxide colloid particles enriched with a large amount of rare earth elements are effectively dispersed and dissolved in the leaching liquid, thereby effectively removing rare earth elements, solving the problem of low leaching efficiency in traditional rare earth contaminated soil leaching and remediation technology, and avoiding leaching under acidic conditions, thereby improving acidified soil and avoiding the application of alkaline modifiers, which is conducive to the reuse of soil after leaching. At the same time, leaching with the biodegradable chelating agent of the present invention will significantly remove reducible rare earths (rare earths combined with iron / manganese oxides), thereby reducing the mobility and bioavailability of rare earths in the soil. The reduction of bioavailable rare earth elements significantly reduces the environmental risks associated with contaminated soil. (3) The biodegradable chelating agent used in the present invention increases soil enzyme activity after leaching, indicating a positive impact on soil health; (4) The method of the present invention, which washes the soil after leaching, can effectively remove the rare earth elements remaining in the soil after leaching, ensure the leaching remediation effect, improve the rare earth resource recovery efficiency through precipitation treatment, and realize the reuse of irrigation water; not only can the rare earth in the contaminated soil be removed by leaching, but also rare earth micro-fertilizer can be obtained for agricultural production. It can be applied to the planting of potatoes, rapeseed and carrots, which can promote the growth and development of potatoes, rapeseed and carrots, and realize resource recovery and soil improvement; the method of the present invention uses a closed-loop circulation method, so that the waste in the remediation process becomes the raw material of the next production link, thereby realizing "zero waste" remediation and maximizing the utilization of resources. It is a green, environmentally friendly and sustainable method for remediating rare earth contaminated soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the elution removal efficiency of total rare earth elements in contaminated soil by different eluents in Experimental Example 1 of the present invention.

[0026] Figure 2 Results of the single factor experiment of soil leaching in Experimental Example 2 of the present invention; (a) BCs concentration; (b) pH value; (c) L / S ratio; (d) leaching time.

[0027] Figure 3 The REEs content results of REEs-contaminated soil before and after leaching under different BCs in Experimental Example 2 of the present invention (a~c) and I R Value(d).

[0028] Figure 4The results of REEs extractable by TCLP (a), REEs extractable by DTPA (b), and REEs extractable by SEBT (c) in Experimental Example 2 of the present invention, as well as the correlation results therebetween (d-f).

[0029] Figure 5 Transmission electron microscopy characterization images of colloidal minerals in the leaching liquid in Experimental Example 2 of the present invention; (a) transmission electron microscopy image; (b) Fe electron energy spectrum image; (c) Ce electron energy spectrum image; (d) Nd electron energy spectrum image; (e) selected high-resolution transmission electron microscopy image; (f) selected electron diffraction image; (g) Dy electron energy spectrum image; (h) Si electron energy spectrum image.

[0030] Figure 6 This is a flow chart of the waste-free green leaching remediation method for rare earth contaminated soil in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] It should be noted that: if the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. If the manufacturer of the instruments is not specified, they are all conventional products that can be purchased commercially. If the manufacturer of the raw materials and reagents is not specified, they are all commercially available products or can be prepared by known methods.

[0033] In the present invention, all features defined in the form of numerical ranges or percentage ranges, such as values, quantities, contents and concentrations, are only for brevity and convenience. Accordingly, the description of numerical ranges or percentage ranges should be deemed to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0034] The features mentioned in the present invention can be combined arbitrarily, as long as there is no contradiction in the combination of these features, all possible combinations should be considered as the scope of this specification. Each feature disclosed in the specification can be replaced by any alternative feature that can provide the same, equal or similar purpose. Therefore, unless otherwise specified, the disclosed features are only general examples of equal or similar features.

[0035] The present invention provides a waste-free green leaching remediation method for rare earth contaminated soil, based on biodegradable chelating agents (BCs) as organic leaching agents, including: N, N-bis (carboxymethyl) -L-glutamic acid (GLDA), iminodisuccinic acid (ISA), polyaspartic acid (PASP), methylglycine diacetic acid and ethylenediamine disuccinic acid, and one or more of their potassium salts and sodium salts. Although some heavy metal chelating agents have been disclosed, not all of them can be applied to the removal of rare earths, and for the removal of rare earths in soil, biodegradability, soil health and other aspects need to be taken into account. For example, although ethylenediaminetetraacetic acid (EDTA) shows excellent efficiency in removing heavy metals in soil, the poor biodegradability of EDTA will have a negative impact on soil microorganisms and plants. In addition, in rare earth soil remediation, rare earths do not exist in ionic form. There is a strong binding effect between rare earths in the soil and iron / manganese oxides in the soil. The proportion of rare earths bound to iron and manganese oxides in the soil is more than 50%, which poses a challenge to traditional eluents (such as ammonium salts, magnesium salts, iron salts and rhamnolipids), and the effects of these eluents are limited.

[0036] The inventors of the present invention selected BCs with a pH above 6, which are nearly neutral and alkaline, in the study of biodegradable chelating agents (BCs). The inventors found that the selected BCs can disperse soil iron oxide colloids to promote the release of rare earths, solving the problem that rare earths and iron / manganese oxides in the soil have a strong binding effect and are difficult to remove. However, for reducible pollutants, previous studies usually use eluents such as strong acids or strong reducing agents to destroy iron and manganese oxides in the soil, thereby achieving the dissolution and release of reducible pollutants. This practice seriously damages the soil mineral components and soil structure, accelerates nutrient loss, causes soil acidification, and is very unfavorable for agricultural production after repair. In the leaching process of the present invention, no strong acid eluent is applied, and the soil minerals will not be acidified to cause damage, nor will the soil be acidified. On the contrary, the organic eluent used in the present invention will increase the soil pH, improve the acidified soil, and avoid the application of alkaline modifiers, which is conducive to the reuse of the soil after leaching.

[0037] In addition, the inventors also found that different BCs have different removal capabilities for rare earth elements in soil, and BCs are more effective in removing heavy rare earths than light rare earths. The removal efficiency of REEs is positively correlated with the concentration of BCs, liquid-solid ratio and elution time, and higher pH conditions greatly promote the leaching and removal of REEs mediated by BCs. Furthermore, it is found that the BCs used in the present invention have little effect on soil properties, can reduce the environmental risks of rare earth elements in contaminated soil, and improve the safety of its potential reuse.

[0038] The inventors found that BCs, including GLDA, ISA and PASP, have excellent rare earth element removal effects. Methylglycine diacetic acid and ethylenediamine disuccinic acid also contain abundant amino and carboxyl groups and have comparable rare earth element removal capabilities to GLDA.

[0039] Based on this, the inventors of the present invention have developed a green remediation model that combines multiple functions such as "pollution remediation", "resource recovery" and "soil improvement". It is a clean remediation technology with "zero waste" treatment throughout the entire process. First, the rare earth elements in the soil are desorbed and dissolved through chelation and other methods using an organic eluent, and transferred to the leaching solution, thereby effectively removing the rare earth elements in the soil and achieving the remediation of contaminated soil. Subsequently, the leaching solution is collected and recycled after soil-water separation, and used as a rare earth micro-fertilizer in agricultural production to achieve resource recovery and soil improvement. At the same time, water washing treatment of the soil after leaching can effectively remove the rare earth elements remaining in the soil after leaching, ensure the leaching remediation effect, improve the efficiency of rare earth resource recovery through precipitation treatment, and achieve irrigation water reuse. This method uses a closed-loop circulation method to make the waste in the remediation process the raw material for the next production link, thereby achieving "zero waste" remediation and maximizing the utilization of resources. It is a green, environmentally friendly and sustainable method for remediating rare earth contaminated soil.

[0040] The following is a detailed description of a waste-free green leaching and remediation method for rare earth contaminated soil provided by the present invention through experimental examples and embodiments.

[0041] Experimental Example 1 Comparison of elution efficiency between organic and inorganic eluents The total rare earth removal rate of the biodegradable chelating agents N, N-bis(carboxymethyl)-L-glutamic acid (GLDA), iminodisuccinic acid (ISA), polyaspartic acid (PASP) selected in the present invention was compared with that of the traditional inorganic salt eluent under the same conditions. The results are shown in Figure 1 .

[0042] like Figure 1 As shown in Figure 1, it is the elution removal efficiency of different eluents for total rare earth elements in contaminated soil in Experimental Example 1 of the present invention. Figure 1 It can be seen that the elution efficiency of the organic eluent used in the present invention for rare earth elements in the soil is much higher than that of other traditional inorganic eluents. This is related to the pollution characteristics of rare earth contaminated soil. In rare earth contaminated soil, rare earth elements have a strong affinity with iron and manganese oxides, resulting in a high proportion of reducible rare earth content in the contaminated soil (>50%), while the content of highly active exchangeable, carbonate-bound and weakly acid-extractable rare earths accounts for a low proportion (<20%). Traditional inorganic eluents mainly remove pollutants from the soil through ion exchange, and this process can only remove low-content exchangeable, carbonate-bound and weakly acid-extractable rare earths, but cannot remove reducible rare earths that account for the main component.

[0043] The pH of the organic eluent used in the present invention is above 6, which is nearly neutral and alkaline. The isoelectric points (PZC) of iron oxides in the soil (such as ferrihydrite, hematite, goethite and lepidocrocite) are all above 6. The pH of the soil solution can be increased during the elution process, and mineral colloids such as iron oxides can be effectively dispersed, dissolved and released into the soil solution, thereby achieving the removal of rare earth elements. Therefore, the organic eluent used in the present invention (BCs with a pH above 6) can effectively remove rare earth elements with weak binding ability with iron and manganese oxides through chelation on the one hand, and on the other hand, the organic eluent can disperse soil colloids, promote the leaching of iron and manganese oxides and rare earth minerals (such as cerite) enriched with rare earth elements, and enhance the removal of rare earth elements in the soil.

[0044] Experimental Example 2: Contaminated soil leaching experiment 1. Experimental Materials Contaminated soil samples were collected from paddy fields near ion-adsorbed rare earth deposits at a depth of 0 to 20 cm and then dried in the shade. The dried soil was sieved through a 2 mm pore size sieve and mixed evenly for use in the experiment. The total rare earth elements (TREEs) content in the soil was determined to be 736.0 mg / kg. The contents of LREEs (Light REEs, i.e. La to Eu) and HREEs (Heavy REEs, i.e. Gd to Lu, and Y) in the soil were 623.7 and 112.3 mg / kg, respectively. The detailed contents of individual rare earth elements are shown in Table 1, and the soil property indicators are shown in Table 2.

[0045] Table 1 Rare earth element content in contaminated soil (unit: mg / kg) Table 2 Properties of contaminated soil Note: In the table, SOM is soil organic matter, which was determined by potassium dichromate oxidation spectrophotometry; CEC is cation exchange capacity, which was determined by hexaamminecobalt trichloride spectrophotometry; soil pH was measured using a pH meter (PB-10 Sartorius, Germany), and the ratio of soil to deionized water was 1:2.5 (w / v); available P (AP), available K (AK) and available N (AN) were in accordance with Chinese standard schemes HJ 704-2014, LY / T1228-2015 and LY / T 1234-2015.

[0046] The GLDA (content 47% and density 1.40 g / cm 3), ISA and PASP (content 40% and density 1.20g / cm 3 ) are sodium salts. The pH of the sodium salt solutions (50 mM) used were 11.7 (GLDA), 10.5 (ISA), and 8.6 (PASP).

[0047] 2. Experimental process To evaluate the removal effect of different elution conditions on rare earth elements in contaminated soil, batch tests were carried out using polypropylene centrifuge tubes and a single factor experimental method.

[0048] Key parameters such as BCs concentration, BCs solution pH, liquid-to-soil ratio (L / S, referred to as liquid-to-soil ratio) and leaching time were investigated to investigate the removal of rare earth elements. The experimental conditions are as follows:

[0049] The elution conditions were 25°C, BCs concentration was 5-100 mmol / L, BCs solution pH was 3-11, L / S ratio was 1:1-10:1 (mL: g), and elution time was 10-4880 min. In each experiment, the contaminated soil and BCs solution were mixed in a polyvinyl alcohol centrifuge tube at a certain L / S ratio and stirred at 200 rpm. 1M HNO 3 and NaOH solution to adjust the pH of the BCs solution. After elution, the suspension was centrifuged at 6000 rpm for 10 min, filtered through a 0.22 µm filter membrane, and the concentration of rare earth elements in the supernatant was analyzed using an inductively coupled plasma mass spectrometer (ICP-MS).

[0050] In addition, a leaching experiment was conducted under the conditions of 25°C, BCs concentration of 50 mM, L / S ratio of 5:1 and leaching time of 24 h, and the untreated contaminated soil was used as the control (CK) to measure the following items: 1) Rare earth element distribution determination According to the BCR sequential extraction method, the forms of REEs are divided into: weak acid extraction state, reducible state, oxidizable state and residual state. Each form of REEs is extracted sequentially. The specific steps of sequential extraction are as follows: (1) Weak acid extraction: 25℃ with 0.11M CH 3 COOH oscillation for 16 h; (2) Reducible state: Use 20 mL 0.5M HONH 2 HCl (pH = 2.0) at 25 °C with shaking for 16 h; (3) Oxidizable state: let stand at room temperature for 1 hour, then add 5 mL 30% H 2 O 2 (pH = 2.0) was heated in a water bath at 85 °C for 1 hour. 1 M NH4 OAc (pH = 2.0), continue heating for 16 h;

[0051] (4) Residue state: in HNO 3 -HCl-HClO 4 (v1: v2: v3=1: 3: 1) solution.

[0052] Adoption Index I R Used to evaluate the stability of elements in soil. I R A value close to 1 indicates that the element is mostly in a stable residual state, indicating a lower environmental risk. Conversely, a value close to 0 indicates that the element is mainly present in a more bioavailable weakly acid extractable and reducible state, indicating a higher environmental risk. I R According to the BCR extraction results of the above rare earth elements, use formula (1) to calculate:

[0053] (1) In formula (1), i is the number of steps for BCR extraction, k =4; F i For rare earth elements in the extraction step i The percentage of F 1 , F 2 , F 3 and F 4 They correspond to the weakly acid extractable state, reducible state, oxidizable state and residual state of rare earth elements respectively.

[0054] 2) Mobility and bioavailability of rare earth elements in soil The mobility of rare earth elements was evaluated by the Toxicity Characteristic Leaching Procedure (TCLP). The bioavailability of rare earth elements in leached soil was evaluated by the Simplified Bioavailability Extraction Test (SBET). Diethylenetriaminepentaacetic acid (DTPA) solution was used to extract the effective concentration of rare earth elements, and the ratio of soil to the solution was 1:5 (w:v) to obtain DTPA-REE.

[0055] 3) Soil properties and enzyme activity determination The soil properties were determined in the same manner as described in Table 1 above.

[0056] Soil enzyme activity was measured to evaluate soil health, specifically: catalase activity was measured by 240 nm UV spectrophotometry; sucrase activity was measured by 3, 5-dinitrosalicylic acid colorimetry; β-glucosidase activity was measured by p-nitrophenol colorimetry. Throughout the experiment, each treatment included a control sample to ensure accuracy.

[0057] 4) Characterization of nano-minerals in leachate The colloidal minerals in the leaching solution were characterized by transmission electron microscopy.

[0058] 3. Experimental results (1) Rare earth removal efficiency results like Figure 2 The results of a single factor experiment on soil leaching are shown in Figure 2. Figure 2 (a), it can be seen that the removal efficiency of BCs for rare earths in soil increases with the increase of BCs concentration, but eventually tends to be stable. Increasing the GLDA concentration from 1mM to 20mM, the total rare earth removal rate increased significantly from 2.7% to 48.6%. The removal rates of ISA and PASP were lower than that of GLDA. At 20 mM, the removal rate of GLDA was 48.6%, while the removal rates of ISA and PASP were 18.1% and 19.9%, respectively. Among them, GLDA had the highest removal rate (50.8%), which was significantly better than ISA (40.5%) and PASP (23.2%). Therefore, GLDA has more advantages as a chelating agent in removing rare earth elements in soil leaching.

[0059] See also Figure 2 (b) and Table 3, which shows the pH values ​​measured in the mixed system after mixing BCs solutions with different pH and contaminated soil. It can be seen that the pH value of the mixed system significantly affects the removal efficiency of TREEs, and higher pH levels enhance the removal of REEs by all BCs. When using GLDA, increasing the pH of the BCs solution from 3 to 10 (corresponding to the pH value of the mixed system from 3.37 to 9.46), the removal rate increased from 38.0% to 54.0%. Similarly, the removal rates of ISA and PASP increased from 15.1% to 31.2% and 8.2% to 20.9%, respectively. These results indicate that higher pH conditions greatly promote the leaching and removal of REEs mediated by BCs.

[0060] Table 3 pH of the eluent and soil mixture system See also Figure 2(c), it can be seen that increasing the L / S ratio can improve the removal efficiency of TREEs. When the L / S ratio is 1: 1, the removal efficiencies of GLDA, ISA, and PASP are 46.6%, 14.1%, and 9.5%, respectively. When the L / S ratio increases to 5: 1, the removal efficiencies are 54.8%, 28.6%, and 24.8%, respectively. When the L / S ratio is low, the interaction of BCs with the soil is limited, resulting in low removal efficiency. However, increasing the L / S ratio above 5: 1 will not produce significant improvements and may result in excessive water and energy consumption, as well as greater wastewater output. Therefore, the optimal L / S ratio is 5: 1, which can strike a balance between high TREEs removal efficiency and cost-effectiveness.

[0061] See also Figure 2 (d) In the first 120 minutes of elution, the TREEs removal efficiency increases rapidly, and then gets a greater improvement. After 120 minutes, the TREEs removal efficiencies of GLDA, ISA, and PASP reach 47.9%, 30.8%, and 20.7%, respectively. Subsequently, the removal efficiency continues to rise slowly, reaching 62.6%, 35.0%, and 26.3%, respectively, at 2880 minutes. This is because unstable REEs can easily compound with BCs, causing the removal efficiency of REEs to rise sharply, so initial rapid removal occurs, and as elution continues, BCs begin to combine with more stable REE species, resulting in slower removal.

[0062] (2) Results of different rare earth contents in soil like Figure 3 The figure shows the distribution of REEs content in REEs-contaminated soil before and after leaching under different BCs. It can be seen that under the conditions of BCs concentration of 50 mM, L / S ratio of 5:1 and leaching time of 24 h, after BCs leaching, the rare earth element content of each soil component decreased except for the residual state. Among them, under GLDA, ISA and PASP as organic eluting agents, the weak acid extraction state decreased by 69.8%, 22.5% and 49.1%, respectively, and the oxidizable state combined with organic matter decreased by 55.4%, 37.7% and 18.5%, respectively, and the most stable residual state was basically unaffected. REEs mainly exist in the reducible state (81%), which is combined with iron / manganese oxides. The removal of REEs by BCs depends largely on their ability to target and extract the reducible state. Among them, GLDA is the most effective, reducing the reducible state by 77.8%, while ISA reduces the reducible state by 48.5% and PASP reduces the reducible state by 32.1%.

[0063] HREEs are generally more toxic than LREEs, and their different forms affect the environmental risk of REEs contaminating soil. Figure 3As shown in the figure, the removal efficiency of BCs for the weakly acid extractable and reducible forms of HREEs was significantly higher than that for LREEs. After GLDA treatment, the contents of the weakly acid extractable and reducible forms of HREEs decreased by 82.8% and 85.0%, respectively, while those for LREEs only decreased by 66.8% and 76.7%, respectively.

[0064] Mobile toxic element components are the root cause of environmental risks, therefore, it is crucial to evaluate the stability of rare earth elements during BCs leaching. I R The value increases, indicating that the remaining rare earth elements are more strongly bound in the residue state and the mobility decreases. I R The value (YS in the figure) is between 0.38 and 0.54, see Figure 3 (d) After washing with GLDA, ISA and PASP, I R The values ​​increased to 0.54~0.85, 0.44~0.77 and 0.43~0.64 respectively. I R The values ​​increase in the order of GLDA>ISA>PASP, a trend consistent with their respective efficiencies in extracting rare earth elements from soil (see Figure 2 Compared with LREEs, BCs elution significantly improved the stability of HREEs. I R The value increased from 0.26 to 0.35, and the LREEs I R The value increased from 0.16 to 0.25. The weakly acid extractable and reducible forms of rare earth elements can cause soil instability, and BCs showed higher removal efficiency for these forms of HREEs compared to LREEs (see Figure 3 ), thereby increasing the stability of HREEs in water and soil washing.

[0065] (3) Results of mobility and bioavailability of different rare earth elements in soil like Figure 4 The results of the TCLP test to evaluate the mobility of rare earth elements in soil are shown in Figure 2. The results show that leaching with BCs significantly reduced the mobility of rare earth elements compared to untreated soil. GLDA reduced the mobility of TREEs, LREEs, and HREEs by 96.0%, 95.8%, and 96.7%, respectively. ISA and PASP also significantly reduced the mobility of rare earths.

[0066] See also Figure 4In addition to mobility, the bioavailability (i.e., the portion that is bioabsorbable) of REEs was also significantly reduced after BCs elution. Compared with ISA and PASP elutions, GLDA, ISA, and PASP elutions reduced DTPA-extractable TREEs by 94.4%, 76.6%, and 55.0%, and reduced SBET-extractable TREEs by 80.8%, 38.3%, and 32.8%, respectively. GLDA was particularly effective in reducing the bioavailability of remaining REEs compared with ISA and PASP, which is consistent with their respective efficiencies in extracting REEs from soil (see Figure 2 ).

[0067] (4) Soil properties and enzyme activity The results showed that soil pH and CEC, two key indicators of soil quality, were significantly improved after BCs leaching (P<0.05). It is worth noting that BCs leaching caused a significant increase in soil pH, from 4.22 to 6.57~7.66. In addition, as shown in Table 4, BCs leaching also improved soil nutrient levels. GLDA leaching increased AP from 13 mg / kg to 18.45 mg / kg, an increase of 41.9%, while PASP leaching increased AN from 113.7 to 203.1 mg / kg, an increase of 78.7%. Soil catalase, sucrase, and β-glucosidase were all increased after leaching. In the process of removing REEs from the soil by BCs leaching adopted in the present invention, the soil properties were not significantly affected, but the soil enzyme activity indicators were promoted, which was helpful to microbial processes and nutrient cycles.

[0068] Table 4 Soil enzyme activities before and after leaching and remediation Through the above research on the removal of REEs in soil by BCs leaching, it can be seen that the three BCs can effectively remove REEs in soil, among which GLDA has the highest removal rate, which is significantly better than ISA and PASP. The REEs removal rate is positively correlated with BCs concentration, L / S ratio and leaching time, among which BC concentration is the most influential factor. The study also found that higher pH values ​​enhance the complexing ability of BCs. In contaminated soil, REEs mainly exist in a reducible state, which determines their mobility and bioavailability. Removing reducible REEs helps to mitigate environmental risks, especially HREEs, which plays a key role in determining pollution risks. The inventors found that BCs are more effective than LREEs in removing HREEs, thereby helping to reduce soil environmental risks. In addition, BCs leaching maintains the quality and function of the soil, potentially improving soil properties and enzyme activity. These findings indicate that BCs-leached soil may be suitable for sustainable agricultural use and enhance its potential for long-term soil remediation. Therefore, the present invention provides a waste-free green leaching remediation method for rare earth contaminated soil, and applies BCs to the remediation of rare earth contaminated soil.

[0069] (5) Characterization of nanominerals in the leaching solution like Figure 5 As shown, the colloidal mineral structure in the leaching solution characterized by transmission electron microscopy. There are a large number of iron oxides and cerium ore enriched with rare earth elements in the leaching solution. The leaching process of the present invention effectively disperses mineral colloids such as iron oxide, so that the iron oxide carries a large amount of rare earth elements and leaches out of the soil. At the same time, iron oxides are obviously enriched in heavy rare earth elements. Because heavy rare earth elements have stronger ecotoxicity than light rare earth elements, the leaching of iron oxides enriched with rare earth elements by organic eluents greatly promotes the reduction of soil environmental risks after leaching. At the same time, cerium ore is also leached out. This is because the isoelectric point of cerium ore is above 6, and the system pH is above 6 or even above 8 during the leaching process, which promotes the dispersion and dissolution of cerium ore colloidal minerals. cerium ore is also enriched in light rare earths, which is conducive to the efficient removal of residual light rare earths in the soil. cerium ore is the most difficult residual rare earth element component to elute in the soil, so the leaching process of the present invention effectively promotes the elution and removal of residual rare earth elements.

[0070] Example 1 A waste-free green leaching remediation method for rare earth contaminated soil, see Figure 6 , including the following steps: S1. Plow and break the contaminated soil to be repaired, and apply N, N-bis(carboxymethyl)-L-glutamate sodium organic eluent to it, so that the organic eluent fully infiltrates the contaminated soil. Among them, the mass ratio of organic eluent to contaminated soil to be repaired is 1:1, the infiltration reaction is 1 day, the concentration of organic eluent is 40 mmol / L, the pH of N, N-bis(carboxymethyl)-L-glutamate sodium solution is 10.9, and the pH of the eluent and soil mixed system is ~9, so there is no need to adjust the pH of the eluent;

[0071] S2. Introduce irrigation water into the contaminated soil and till it at the same time, mix the soaked soil and irrigation water evenly, and use the disturbance during tillage to leach and dissolve the rare earths in the soil and transfer them into the leaching solution. The mass ratio of irrigation water to contaminated soil is 1:1, and the leaching reaction time is 2 days;

[0072] S3, the leachate is passed through the drainage channel into the sedimentation tank, the leachate is allowed to settle, the mud and water are separated, the upper leachate is transferred to the collection tank, and the bottom sludge is transferred to the field for reuse; S4, introducing irrigation water into the washed soil, plowing the soil at the same time, fully mixing the washed soil and irrigation water, and washing the residual rare earth in the washed soil. The mass ratio of irrigation water to washed soil is 1: 1; the washing time is 12 h, and the number of washings is 2;

[0073] S5, the washing liquid enters the sedimentation tank through the drainage channel, the leaching liquid is allowed to settle, the mud and water are separated, the upper washing liquid is transferred to the sedimentation tank, and the bottom sludge is transferred to the field for reuse; S6, adding sodium bicarbonate to the sedimentation tank to precipitate the rare earth in the washing liquid, and after the washing liquid is purified by precipitation, it is transferred to the reservoir for reuse as irrigation water; S7, using the leaching liquid in the collection pool of step S3 as rare earth micro-fertilizer for agricultural production.

[0074] After testing, the contents of La, Ce, Pr, Nd, Sm and Eu in the rare earth micro-fertilizer obtained in this embodiment are 20, 26.6, 4.14, 4, 2.6 and 0.5 mg / L, respectively.

[0075] Application Case 1: Application of recycled rare earth micro-fertilizer in potato planting The rare earth micro-fertilizer collected from the contaminated soil after leaching and restoration in Example 1 was used for potatoes ( Solanum tuberosum L.) planting production. In the seedling stage, the above-mentioned rare earth micro-fertilizer was added by irrigation, and each plant was irrigated with 100mL of rare earth solution, and a treatment without rare earth micro-fertilizer was set as a control. The results are shown in Table 5. As shown in Table 5, after the treatment with rare earth micro-fertilizer, various indicators such as potato plant height, stem thickness, dry weight of the aboveground part, dry weight of the underground part, number of aboveground branches, single plant potato weight and total chlorophyll increased. In addition, the addition of rare earth micro-fertilizer increased the activity of superoxide dismutase, peroxidase and catalase in the leaves of potato seedlings, enhanced the stress resistance of potatoes, and promoted the growth and development of potatoes.

[0076] Table 5 Effects of rare earth micronutrient fertilizers on the growth and development of potato plants Application Case 2: Application of recycled rare earth micro-fertilizer in rapeseed cultivation The rare earth micro-fertilizer collected from the contaminated soil after leaching and remediation in Example 1 was used for rapeseed cultivation. The rare earth micro-fertilizer containing cerite colloidal mineral was sprayed on the leaves of potted rapeseed, and a treatment without rare earth micro-fertilizer was set as a control. The results are shown in Table 6.

[0077] As shown in Table 6, after treatment with rare earth micro-fertilizer containing ceresite colloidal mineral, the fresh weight and dry weight of rapeseed increased compared with the control, the photosynthesis and chlorophyll synthesis of rapeseed were enhanced, the reducing sugar content was significantly increased, the vitamin C content was improved, and the antioxidant capacity was enhanced.

[0078] Table 6 Effects of rare earth micronutrient fertilizers on rapeseed growth and development Application Case 3: Application of recycled rare earth micro-fertilizer in carrot planting The rare earth micro-fertilizer collected from the contaminated soil after leaching and remediation in Example 1 was used for carrot planting and production. The experiment used three red seven-inch carrots, selected carrot seeds of uniform size and full grains, and after disinfection with 5% sodium hypochlorite for 10 min, rinsed with deionized water 5 times and soaked for 4 h. Then placed in a seedling tray covered with filter paper for seedling cultivation, and kept moist during the period. Stir the soil evenly before planting carrots, and put 1.5kg of soil in each plastic pot. After the seeds are white, they are sown in plastic pots (1 pot 1 kind). After two weeks of growth, the roots are irrigated with rare earth micro-fertilizer containing cerite colloidal minerals for 4 consecutive days. Each plant is irrigated with 100 mL of rare earth solution, and a treatment without rare earth micro-fertilizer is set as a control. The results are shown in Table 7.

[0079] As shown in Table 7, after treatment with rare earth micro-fertilizer containing cerium colloidal mineral, the growth, yield and quality of carrots were improved. This may be due to the fact that cerium (CeO 2) The colloidal particles can be effectively absorbed by carrot seedlings and migrate to the leaves, promoting florigen, light signals and photosynthesis, and improving the formation and growth of tuberous roots. Key nutrients such as β-carotene, soluble sugars and ascorbic acid are significantly improved.

[0080] Table 7 Effects of rare earth micronutrient fertilizers on the growth and development of potato plants Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A waste-free green leaching and remediation method for rare earth contaminated soil, characterized in that: The method includes: A biodegradable chelating agent solution is used as an organic eluent and is spread on rare earth contaminated soil to be repaired. The biodegradable chelating agent is selected from N, N-bis(carboxymethyl)-L-glutamic acid, iminodisuccinic acid, polyaspartic acid, methylglycine diacetic acid and ethylenediamine disuccinic acid, and any one or more of their potassium salts and sodium salts. The pH of the mixed system of the organic eluent and the rare earth contaminated soil is above 6. The soil colloids in the rare earth contaminated soil to be repaired are dispersed by the organic eluent, thereby promoting the leaching and removal of rare earth elements combined with iron and manganese oxides.

2. The waste-free green leaching and remediation method for rare earth contaminated soil according to claim 1 is characterized in that: The concentration of the biodegradable chelating agent solution is 10-100 mmol / L.

3. The waste-free green leaching and remediation method for rare earth contaminated soil according to claim 1 is characterized in that: When the N, N-bis(carboxymethyl)-L-glutamic acid and iminodisuccinic acid are used, the pH of the organic eluent is above 8; when the polyaspartic acid is used, the pH of the organic eluent is between 6 and 8.

4. The waste-free green leaching and remediation method for rare earth contaminated soil according to claim 1 is characterized in that: The time for the organic eluent to treat the rare earth contaminated soil to be repaired is 0.5 to 2 days.

5. The waste-free green leaching and remediation method for rare earth contaminated soil according to claim 1 is characterized in that: In the organic eluent treatment, the mass ratio of the organic eluent to soil solids is 0.8~5:

1.

6. The waste-free green leaching and remediation method for rare earth contaminated soil according to claim 1 is characterized in that: The method comprises the following steps: S1. Plowing and breaking the rare earth contaminated soil to be repaired, and applying the organic eluent thereto, so that the eluent fully infiltrates the rare earth contaminated soil, and the pH of the mixed system is above 6; S2. Introducing irrigation water into the rare earth contaminated soil and simultaneously tilling the soil, mixing the soaked soil and the irrigation water evenly, and using the disturbance during the tillage process to leach and dissolve the rare earths in the soil and transfer them into the leaching solution; S3, the leachate is passed through the drainage channel into the sedimentation tank, the leachate is allowed to settle, the mud and water are separated, the upper leachate is transferred to the collection tank, and the bottom sludge is transferred to the field for reuse; S4, introducing irrigation water into the washed soil, and simultaneously tilling the soil, so that the washed soil and the irrigation water are fully mixed, and the rare earth remaining in the washed soil is dissolved by water washing; S5, the washing liquid enters the sedimentation tank through the drainage channel, the leaching liquid is allowed to settle, the mud and water are separated, the upper washing liquid is transferred to the sedimentation tank, and the bottom sludge is transferred to the field for reuse; S6, adding a precipitant to the sedimentation tank to precipitate the rare earth in the washing liquid, and after the washing liquid is purified by precipitation, it is transferred to the reservoir for reuse as irrigation water; S7, using the leaching liquid in the collection pool of step S3 as rare earth micro-fertilizer for agricultural production.

7. The waste-free green leaching and remediation method for rare earth contaminated soil according to claim 6 is characterized in that: In step S1, the mass ratio of the organic eluent to the rare earth contaminated soil is 0.4-1:1, and the infiltration time is 0.5-2 days; in step S2, the mass ratio of the irrigation water to the rare earth contaminated soil is 0.4-4:1, and the elution reaction time is 0.5-3 days.

8. The waste-free green leaching and remediation method for rare earth contaminated soil according to claim 6 is characterized in that: In step S4, the mass ratio of the irrigation water to the washed soil is 0.2-1:1; the washing time is 12-36 h, and the number of washings is 1-5 times.

9. The waste-free green leaching and remediation method for rare earth contaminated soil according to claim 6 is characterized in that: In step S6, the precipitant includes any one or more of oxalic acid, ammonium bicarbonate, ammonium carbonate, sodium bicarbonate, sodium carbonate, magnesium bicarbonate, magnesium carbonate, magnesium oxide, magnesium hydroxide, sodium hydroxide and potassium hydroxide.

10. The waste-free green leaching remediation method for rare earth contaminated soil according to any one of claims 1 to 9, characterized in that: In the rare earth contaminated soil, the content of reducible rare earths accounts for more than 50%; Or / and, the rare earth element in the soil to be remediated is any one or more of lanthanide elements, yttrium and scandium.

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