A method for enriching rare earth elements in rare earth tailings area

Abstract

The present application discloses a method for enriching rare earth elements in a rare earth tailings area, comprising the following steps: first applying basal fertilizer to the soil in the rare earth tailings area, direct-seeding the seeds of the royal millet in the soil 7 days later, and performing the first topdressing when the plants grow to the tillering stage, and performing the second topdressing 3 days after mowing, wherein the fertilizers used in the basal fertilizer, the first topdressing and the second topdressing are biogas residue or biogas liquid, and the biogas residue is applied directly or after pretreatment; the pretreatment method of the biogas residue comprises: drying and crushing the biogas residue, adding a sugar compound and stirring evenly. The present invention can significantly improve the enrichment of rare earth elements in the rhizosphere soil of plants and improve the rare earth element enrichment capacity of plants.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth element enrichment, and in particular relates to a method for enriching rare earth elements in a rare earth tailings area. Background Art

[0002] Rare earth tailings are an important strategic mineral resource in southern my country, but due to strong market demand and the continuous expansion of production scale, the consumption rate of rare earth resources in my country is accelerating. The rare earth elements in the soil of ionic rare earth tailings in southern my country are difficult to extract by traditional mining processes, and their presence will also cause harm to the surrounding ecosystem.

[0003] Rare earth elements (REEs) refer to the 15 lanthanide elements with atomic numbers 57-71 in the periodic table (in order of atomic number from small to large: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and yttrium (Y) and scandium (Sc) which are closely related to the lanthanide elements.

[0004] Planting energy plants on rare earth contaminated soil can not only repair the contaminated soil and restore vegetation, but also enrich the rare earth elements in the soil to a certain extent. Harvesting the aboveground parts of the plants can realize metal resource utilization, providing an economical and effective solution for the ecological management of rare earth contaminated areas and the utilization of rare earth resources. The factors that affect the accumulation of rare earth elements are as follows: (1) The species of the plant is the main factor that determines the absorption of rare earth elements by the plant, which not only affects the accumulation of rare earth elements, but also affects the differentiation of rare earth elements. (2) The rare earth elements in plants mainly come from the soil. Therefore, whether it is a rare earth element hyperaccumulator or an ordinary plant, the rare earth element content in the soil directly determines the accumulation and differentiation of rare earth elements in the body. (3) Season and age will also affect the accumulation of rare earth elements in plants. (4) The composition and content of inorganic or organic ligands in the soil solution and inside the plant body will also affect the accumulation of rare earth elements in the plant.

[0005] Yugu (scientific name: Pennisetum americanum(L. ) Leeke.) is an annual herbaceous plant of the Poaceae family and the genus Pennisetum. Royal millet has the characteristics of wide adaptability and strong stress resistance. It is a forage crop that can be used as both forage and forage, and has high yields of both grain and grass. Although the rare earth element enrichment efficiency of energy plants is generally lower than that of rare earth element hyperaccumulators (referring to plants with a rare earth element content of not less than 1000µg / g in the aboveground parts, or plants with a rare earth element absorption coefficient of not less than 1 in the aboveground parts), it can be compensated by the high biomass of energy plants. However, the growth of energy plants in tailings areas requires the support of exogenous nutrients, otherwise the restored vegetation will decline due to insufficient nutrients. The growth of energy plants is closely related to the type and amount of fertilization.

[0006] Biogas slurry and biogas residue are rich in organic matter, nitrogen, phosphorus, potassium and other nutrients, which can provide the nutrients required by plants. At present, the research on the application of biogas slurry / biogas residue mainly focuses on the impact on crop yield, quality, pests and diseases, and soil environmental quality, while there are few reports on the impact of rare earth tailings on the enrichment of rare earth elements in soil. In addition, most of the existing technologies do not take into account the impact of the application amount, physical and chemical properties, and pretreatment of biogas slurry or biogas residue on the enrichment of rare earth elements in plants, resulting in an insufficiently obvious enrichment effect.

[0007] In addition, biogas sludge is the solid part obtained after solid-liquid separation of anaerobic fermentation residues. Its own shape and the characteristics of rare earth elements result in its rare earth element enrichment effect being inferior to that of biogas slurry.

[0008] In summary, how to provide a method for enriching rare earth elements in rare earth tailings areas, improve the enrichment effect of rare earth elements in rare earth tailings areas by selecting suitable energy plants and rationally applying exogenous nutrients to energy plants, is a problem that urgently needs to be solved. Summary of the invention

[0009] The first purpose of the present invention is to use biogas slurry or biogas residue as exogenous nutrients and millet as energy plants to study the effects of different application amounts of biogas slurry or biogas residue on the enrichment of rare earth elements, so as to determine the application range of biogas slurry or biogas residue.

[0010] The second purpose of the present invention is to study the influence of different pH values ​​of biogas slurry or biogas residue on the rare earth element enrichment of corn, so as to determine the range of physical and chemical properties of biogas slurry or biogas residue.

[0011] The third purpose of the present invention is to pretreat biogas residue to overcome the deficiency of biogas residue as exogenous nutrient in enriching rare earth elements for energy plants.

[0012] The technical solution of the present invention is as follows:

[0013] A method for enriching rare earth elements in a rare earth tailings area specifically comprises the following steps:

[0014] First, basal fertilizer was applied to the soil in the rare earth tailings area. Seven days later, the seeds of the royal millet were directly sown in the soil. When the plants grew to the tillering stage, the first topdressing was carried out. When the best growing plants reached a height of 1.2 m, they were mowed. The second topdressing was carried out on the third day after mowing. The application rates of the basal fertilizer, the first topdressing and the second topdressing were the same, and the pure nitrogen was 800-1000 kg / hm 2 , preferably 960 kg / hm 2 The fertilizers used in the base fertilizer, the first topdressing fertilizer and the second topdressing fertilizer are biogas residue or biogas liquid.

[0015] Preferably, the physicochemical properties of the biogas slurry are: pH 7.72-8.28, organic matter OM content of 0.22-0.37%, total nitrogen TN content of 0.16-0.30%, P2O5 content of 0.03-0.18%, and K2O content of 0.13-0.25%.

[0016] Preferably, the physical and chemical properties of the biogas residue are: moisture content 61.75-69.22%, pH 7.90-8.33, organic matter OM content 23.08-32.89%, total nitrogen TN content 2.23-3.33%, P2O5 content 12.04-14.02%, and K2O content 0.54-0.88%.

[0017] Preferably, the planting density of the royal millet is 1-30 plants / m 2 .

[0018] Preferably, the rare earth tailings area is an ionic rare earth tailings area.

[0019] The biogas residue is applied directly or after pretreatment. The pretreatment method of the biogas residue comprises the following steps: drying the biogas residue (to a water content of 30-40%), crushing the biogas residue, adding a sugar compound and stirring evenly. The amount of the sugar compound added is 4-8% of the mass of the biogas residue.

[0020] Preferably, the carbohydrate compound comprises starch and UDP-glucose in a mass ratio of 1:(0.5-0.8).

[0021] Beneficial effects of the present invention:

[0022] 1. Planting royal millet in rare earth tailings areas and using the exogenous nutrient biogas slurry or biogas residue at a specific application amount of the present invention can significantly promote the accumulation of rare earth elements in the rhizosphere soil of plants, thereby promoting the enrichment of rare earth elements in royal millet plants. Compared with biogas residue, the royal millet after applying biogas slurry has a more obvious enrichment effect on rare earth elements in the tailings area.

[0023] 2. The present invention selects biogas slurry or biogas residue with suitable physical and chemical properties and can effectively improve the enrichment effect of rare earth elements by controlling its pH.

[0024] 3. When biomass raw materials are fermented for biogas, most of the rare earth elements in the raw materials remain in the biogas residue, and the content in the biogas liquid is relatively small. However, in the current technology, when biogas residue is applied to energy plants as exogenous nutrients, the release of rare earth elements in the biogas residue and their enrichment in plants are generally not considered. In addition, the solid-based form and chemical composition of biogas residues cause it to have a certain adsorption capacity for rare earth elements, which affects the enrichment of rare earth elements by plants. As a result, after the biogas residue is applied, the rare earth element enrichment effect of energy plants is not obvious (lower than biogas liquid). Therefore, when the biogas residue is applied to the royal millet, the present invention first pre-treats the biogas residue, adds sugar compounds and mixes with the biogas residue, and the hydroxyl groups in the sugar compounds can coordinate with the rare earth elements in the biogas residue and soil to form an easily absorbable form, thereby promoting the enrichment of rare earth elements in plants.

[0025] The carbohydrate compounds of the present invention are specifically selected as starch and UDP-glucose, which not only contain a large number of hydroxyl groups, but also contain phosphoric acid, which can form stable ligands with rare earth elements. UDP-glucose as a biological molecule is more easily absorbed and transported by plants after combining with rare earth elements. In addition, when applying biogas residue, it is generally applied to the soil close to the plant part. In the pretreated biogas residue, starch and UDP-glucose form colloids in the biogas residue, which promotes the plants to focus on enriching the rare earth elements in the biogas residue.

[0026] When the present invention pretreats the biogas residue, the uridine diphosphate glucose used has affinity to the soil, can quickly adhere to the soil surface, can enhance the combination of the biogas residue and the soil, and promote the absorption of biogas residue nutrients by plants. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the chondrite-standardized (Boynton (1984)) distribution diagram of the Dingnan rare earth tailings sample. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0029] The experimental methods and materials in the following examples are conventional methods and commonly available materials unless otherwise specified. If no specific techniques or conditions are specified in the examples, the experiments were carried out according to the techniques or conditions described in the literature in the art or according to the product instructions. Example 1

[0030] This embodiment provides a method for enriching rare earth elements in a rare earth tailings area, wherein the rare earth tailings area is planted with corn at a planting density of 20 plants / m 2 , specifically including the following steps:

[0031] First, basal fertilizer was applied to the soil of the rare earth tailings area to be treated. Seven days later, the seeds of the royal millet were directly sown in the soil. When the plants grew to the tillering stage, the first topdressing was carried out. When the best growing plants reached a height of 1.2 m, they were mowed. The second topdressing was carried out on the third day after mowing. The application rates of the basal fertilizer, the first topdressing and the second topdressing were the same, and the pure nitrogen conversion rate was 960 kg / hm 2 The fertilizer used for the base fertilizer, the first topdressing and the second topdressing is biogas slurry. The treatment period is two years (2019-2020).

[0032] The physicochemical properties of the biogas slurry are as follows:

[0033] Example 2

[0034] This embodiment provides a method for enriching rare earth elements in a rare earth tailings area, wherein the rare earth tailings area is planted with corn at a planting density of 20 plants / m 2 Specifically, basal fertilizer is first applied to the soil of the rare earth tailings area to be treated. Seven days later, the seeds of the royal millet are directly sown in the soil. When the plants grow to the tillering stage, the first topdressing is carried out. When the best growing plants reach a height of 1.2 m, they are mowed. The second topdressing is carried out on the third day after mowing. The application rates of the basal fertilizer, the first topdressing and the second topdressing are the same, and the pure nitrogen conversion rate is 960 kg / hm 2 The fertilizer used for the base fertilizer, the first topdressing and the second topdressing is biogas residue. The treatment period is two years (2019-2020).

[0035] The physicochemical properties of the biogas residue are as follows:

[0036] Example 3

[0037] This embodiment provides a method for enriching rare earth elements in a rare earth tailings area. The application amounts of the base fertilizer, the first topdressing and the second topdressing are the same, and the pure nitrogen content is 800 kg / hm 2 , the fertilizer used is biogas slurry, and the rest is the same as in Example 1.

[0038] Example 4

[0039] This embodiment provides a method for enriching rare earth elements in a rare earth tailings area. The application amount of the base fertilizer, the first topdressing fertilizer and the second topdressing fertilizer is the same, and the pure nitrogen equivalent is 1000 kg / hm 2 , the fertilizer used is biogas slurry, and the rest is the same as in Example 1.

[0040] Example 5

[0041] This embodiment provides a method for enriching rare earth elements in a rare earth tailings area. The application amounts of the base fertilizer, the first topdressing and the second topdressing are the same, and the pure nitrogen content is 800 kg / hm 2 The fertilizer used is biogas residue, and the rest is the same as in Example 1.

[0042] Example 6

[0043] This embodiment provides a method for enriching rare earth elements in a rare earth tailings area. The application amount of the base fertilizer, the first topdressing fertilizer and the second topdressing fertilizer is the same, and the pure nitrogen equivalent is 1000 kg / hm 2 The fertilizer used is biogas residue, and the rest is the same as in Example 2.

[0044] Example 7

[0045] Based on Example 2, this example provides a method for enriching rare earth elements in a rare earth tailings area. The biogas sludge used is pretreated before use. The pretreatment method is: the biogas sludge is dried (to a moisture content of 30-40%), crushed, and then a sugar compound is added and stirred evenly. The amount of the sugar compound added is 6% of the mass of the biogas sludge, and the sugar compound includes starch and uridine diphosphate glucose in a mass ratio of 1:0.65.

[0046] The rest is the same as Example 2.

[0047] Example 8

[0048] Based on Example 2, this example provides a method for enriching rare earth elements in a rare earth tailings area. The biogas sludge used is pretreated before use. The pretreatment method is: the biogas sludge is dried (to a moisture content of 30-40%), crushed, and then a sugar compound is added and stirred evenly. The amount of the sugar compound added is 4% of the mass of the biogas sludge, and the sugar compound includes starch and uridine diphosphate glucose in a mass ratio of 1:0.5.

[0049] The rest is the same as Example 2.

[0050] Example 9

[0051] Based on Example 2, this example provides a method for enriching rare earth elements in a rare earth tailings area. The biogas sludge used is pretreated before use. The pretreatment method is: the biogas sludge is dried (to a moisture content of 30-40%), crushed, and then a sugar compound is added and stirred evenly. The amount of the sugar compound added is 8% of the mass of the biogas sludge, and the sugar compound includes starch and uridine diphosphate glucose in a mass ratio of 1:0.8.

[0052] The rest is the same as Example 2.

[0053] Comparative Example 1-2 (Energy Plant Change):

[0054] The difference between Comparative Example 1 and Example 1 is that the royal aril is replaced by hybrid Pennisetum, and the rest remains unchanged.

[0055] The difference between Comparative Example 2 and Example 2 is that the royal aril is replaced by hybrid Pennisetum, and the rest remains unchanged.

[0056] Comparative Examples 3-6 (change in the amount of biogas slurry or biogas residue applied):

[0057] The difference between Comparative Examples 3 and 4 and Example 1 is that the amount of biogas slurry applied each time is changed, while the rest remains unchanged.

[0058] The difference between Comparative Examples 5 and 6 and Example 2 is that the amount of biogas residue applied each time is changed, while the rest remains unchanged.

[0059] The details are as follows:

[0060]

[0061] Comparative Examples 7 and 8 (pH changes of biogas slurry):

[0062] The difference between Comparative Example 7 and Example 1 is that the pH value of the biogas slurry applied each year is adjusted to 7.40 using acid (sulfuric acid).

[0063] The difference between Comparative Example 8 and Example 1 is that the biogas slurry applied each year is adjusted to a pH value of 8.50 using alkali (sodium hydroxide).

[0064] Comparative Examples 9 and 10 (pH change of digestate):

[0065] The difference between Comparative Example 9 and Example 2 is that the pH value of the biogas residue applied each year is adjusted to 7.50 using acid (sulfuric acid).

[0066] The difference between Comparative Example 10 and Example 2 is that the pH value of the biogas residue applied each year is adjusted to 8.50 using alkali (sodium hydroxide).

[0067] Comparative Examples 11-13 (Changes in the pretreatment method of biogas residue):

[0068] Comparative Example 11

[0069] The difference between this comparative example and Example 7 is that in the biogas residue pretreatment method, the carbohydrate compound only includes starch.

[0070] Comparative Example 12

[0071] The difference between this comparative example and Example 7 is that in the biogas residue pretreatment method, the sugar compound only includes uridine diphosphate glucose.

[0072] Comparative Example 13

[0073] The difference between this comparative example and Example 7 is that in the biogas residue pretreatment method, the uridine diphosphate glucose in the sugar compound is replaced by chitosan.

[0074] Pot test

[0075] 1. Test Materials

[0076] Energy plants used in pot experiments (Pennis fasciatus hybrids ( Pennisetum hybrid , PH), Migu ( Pennisetum americanum , PA) and exogenous nutrients (biogas slurry (BS), biogas residues (BR)) are all provided by Ganzhou Ruiyuan Biotechnology Co., Ltd. The company has built a super-large biogas project (with a total fermentation volume of 20,000 m 3 ). In 2017, the research team and the company jointly established an energy plant sustainable restoration area in the abandoned mining area around the biogas project. The biogas slurry and biogas residue were taken from the fermentation tank of the biogas project and stored at 4 ℃ for future use. After testing, the heavy metal content in the biogas slurry and biogas residue did not exceed the limit value in the agricultural industry standard "Biogas Fertilizer" (NY / T 2596-2022).

[0077] 1. Rare earth element content in the soil tested by rare earth tailings

[0078] Rare earth tailings test soil PS (Primary soil): The soil samples required for the potted test were taken from an abandoned rare earth tailings restoration area in Dingnan County, Ganzhou City, Jiangxi Province (115.054917°E, 24.979109°N). The area was originally a rare earth tailings dump, with sandy red soil, poor nutrients, and extremely high rare earth element content, with a total amount of 705.85 mg / kg, which is 3.78 times the national soil background value (186.76 mg / kg) (see Table 1).

[0079] Table 1 Rare earth element content in the tested soil (mg / kg)

[0080]

[0081] Note: GM refers to the background value of rare earth elements in Chinese soil, refer to "Characteristics of Background Values ​​of Rare Earth Elements in Chinese Soil"; REE is rare earth element, ∑LREE is light rare earth elements La~Eu, ∑HREE is heavy rare earth elements Gd~Lu+Y, ∑REE is the total content of 15 rare earth elements excluding Sc and Pm.

[0082] The Dingnan rare earth tailings were standardized for the rare earth element content of chondrites as recommended by Boynton (1984) (see Figure 1 ) found that the REE distribution pattern of Dingnan rare earth tailings has the characteristics of light rare earth element enrichment and negative Eu anomaly. Further analysis of the REE characteristic parameters (Table 2) found that the light and heavy rare earths in the Dingnan rare earth tailings left over from mining were significantly fractionated, with light rare earth enrichment; both light and heavy rare earth elements were obviously differentiated, and the differentiation of light rare earth elements was more obvious; Eu showed obvious negative anomaly, moderate loss, and Ce was generally normal.

[0083] Table 2 Geochemical characteristic parameters of rare earth elements in the tested soils

[0084]

[0085] 2. Rare earth element content in biogas slurry and biogas residue in 2019-2020

[0086] As shown in Table 3, the rare earth element contents of biogas slurry and biogas residue did not differ much within two years, with the ∑REE of biogas slurry ranging from 0.98 to 1.13 mg / L and that of biogas residue ranging from 41.55 to 44.10 mg / kg. In addition, the ratio of light to heavy rare earth elements L / H was greater than 1, which showed the characteristics of enrichment of light rare earth elements.

[0087] Table 3 Rare earth element content in biogas slurry and biogas residue in 2019-2020

[0088]

[0089] 2. Test methods

[0090] The outdoor potted plant experiment was carried out at the experimental base of Jiangxi Academy of Agricultural Sciences from 2019 to 2020. The energy plants were selected from royal millet (hereinafter referred to as PA) and the control plant hybrid Pennisetum (hereinafter referred to as PH), and NCK (blank control group, no fertilizer, no energy plants planted) and PACK (no fertilizer, royal millet planted) were set up, and the methods of Examples 1, 2, 7 and Comparative Examples 1-13 were respectively carried out.

[0091] Potted operation process: ① Base fertilizer: Mix the biogas slurry and biogas residue with 8 kg of soil respectively, put them in pots and let them stand for 7 days; ② Planting: Soak the seeds of the royal millet in 10% hydrogen peroxide solution for 15 minutes, rinse them with sterile water 5 times, and soak them for 4 hours. Sow 10 seeds directly, and thin out the seedlings after 3-4 leaves grow, leaving the 3 best growing plants; transplant 3 hybrid Pennisetum seed nodes into pots, and thin out the seedlings after 2 leaves grow, leaving only 1 plant; ③ First topdressing: When the plants grow to the tillering stage, apply the first topdressing according to the application ratio. ④ Mowing and second topdressing: Mowing the best growing experimental treatment groups when the plant height reaches 1.5 m (hybrid Pennisetum) and 1.2 m (royal millet), and the second topdressing is carried out 3 days after mowing.

[0092] 3. Rare Earth Elements Determination Method

[0093] After pretreatment with tetrabasic acids (HNO3, HCl, HF and HClO4), the concentrations of rare earth elements (REEs) were determined by inductively coupled plasma mass spectrometry (ICP-MS, Agilent 7900, Japan), including 15 rare earth elements: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. Among them, light rare earth elements (LREE) were La~Eu; heavy rare earth elements (HREE) were Gd~Lu+Y.

[0094] 4. Test results

[0095] 1. Effects of different fertilization rates of biogas slurry or biogas residue on rare earth element enrichment in royal millet

[0096] According to the above-mentioned test method (Examples 1, 2 and Comparative Examples 3-6), after the energy plant Royal Millet was planted in the test soil with biogas slurry or biogas residue for 2 years, the rare earth element content in the rhizosphere soil of the plant and the above-ground part of the energy plant was tested in the second year (2020). The results are shown in Tables 4, 5, 6 and 7.

[0097] (1) Rare earth element content in the test soil

[0098] Table 4 Effects of different biogas slurry application rates on rare earth element content (mg / kg) in soil of rice cultivation

[0099]

[0100] Table 5 Effects of different application rates of biogas residue on the rare earth element content (mg / kg) in the soil of rice cultivation

[0101]

[0102] It can be seen from Tables 4 and 5 above that through the comparison of NCK (blank control group, no fertilizer, no energy plants planted) and PACK (no fertilizer, planted with pearl millet), the total amount of rare earth elements ∑REE in the rhizosphere soil of plants increased significantly after planting pearl millet, indicating that planting pearl millet can form rare earth element REEs aggregation in the rhizosphere soil.

[0103] Compared with the PACK group, the total amount of rare earth elements ∑REE in the rhizosphere soil of Examples 1 and 2 of the present invention further increased significantly after the application of biogas slurry and biogas residue, indicating that the application of biogas slurry and biogas residue will promote the accumulation of rare earth elements in the rhizosphere soil of plants. Compared with Comparative Examples 3 and 4 and Comparative Examples 5 and 6, the amount of biogas slurry and biogas residue fertilizer in Examples 1 and 2 of the present invention is both 960 kg / hm 2 The effect is better when the soil is treated with fertilizer, and the rare earth elements in the rhizosphere soil accumulate more.

[0104] (2) Rare earth element content in royal grains

[0105] Table 6 Effects of different biogas slurry application rates on rare earth element content in rice plants (mg / kg)

[0106]

[0107] Table 7 Effects of different application rates of biogas residue on the rare earth element content (mg / kg) of the rice plants

[0108]

[0109] It can be seen from Tables 6 and 7 that, compared with the PACK group, after the biogas slurry was applied in Example 1 of the present invention, the total amount of rare earth elements ∑REE in the above-ground plant part of the corn increased, indicating that the application of biogas slurry would improve the rare earth element enrichment capacity of the corn. Compared with the PACK group, after the biogas residue was applied in Example 2, the total amount of rare earth elements ∑REE in the above-ground plant part of the corn decreased, indicating that the application of biogas residue affected the enrichment of rare earth elements in the corn plants (therefore, the biogas residue needs to be pretreated later to reduce this effect). Moreover, compared with Comparative Examples 3 and 4 and Comparative Examples 5 and 6, the amount of biogas slurry and biogas residue fertilizer applied in Examples 1 and 2 of the present invention is both 960 kg / hm 2 The effect is better when the rare earth elements are enriched in the rice.

[0110] 2. Effects of different energy plants on rare earth element enrichment in Migu

[0111] According to the above-mentioned test method (Examples 1 and 2 and Comparative Examples 1 and 2), after the energy plants Achyranthes bidentata and hybrid Pennisetum were planted in the test soil for 2 years after the application of biogas slurry or biogas residue, the content of rare earth elements in the rhizosphere soil of the plants and the above-ground parts of the energy plants were tested in the second year (2020). The results are shown in Tables 8 and 9.

[0112] (1) Rare earth element content in the test soil

[0113] Table 8 Rare earth element content in soil when using biogas slurry or biogas residue to plant royal millet and hybrid Pennisetum (mg / kg)

[0114]

[0115] It can be seen from Table 8 that compared with the comparative examples 1 and 2 in which hybrid Pennisetum was planted, the total amount of rare earth elements ∑REE in the rhizosphere soil of the plants after planting Mirella vulgaris in Examples 1 and 2 of the present invention is higher, indicating that the present invention uses biogas slurry or biogas residue to plant Mirella vulgaris, and the phenomenon of rare earth element REEs aggregation in the rhizosphere part of the plants is more obvious.

[0116] (2) Rare earth element content in energy plants

[0117] Table 9 Rare earth element content in energy plants when biogas slurry or biogas residue is used (mg / kg)

[0118]

[0119] It can be seen from Table 9 that compared with the comparison examples 1 and 2 in which hybrid Pennisetum was planted, the total amount of rare earth elements ∑REE in the aboveground plant part of the Pennisetum after planting the Pennisetum in Examples 1 and 2 of the present invention was higher, indicating that the present invention, in which the Pennisetum is planted with biogas slurry or biogas residue, has a better rare earth element enrichment ability than hybrid Pennisetum.

[0120] 3. Effects of different pH values ​​of biogas slurry or biogas residue and biogas residue pretreatment methods on rare earth element enrichment in maltose

[0121] According to the test method (Examples 1, 2, 7 and Comparative Examples 7-13), after the energy plant Migu was planted in the test soil with biogas slurry or biogas residue for 2 years, the rare earth element content in the rhizosphere soil of the plant and the above-ground part of the energy plant was tested in the second year (2020). The results are shown in Tables 10, 11, 12 and 13.

[0122] (1) Rare earth element content in the test soil

[0123] Table 10 Effects of different biogas slurries or biogas residues on the rare earth element content (mg / kg) in the soil when planting royal millet

[0124]

[0125] It can be seen from Table 10 that after the application of the biogas slurry and biogas residue of Examples 1 and 2 of the present invention to plant millet, the total amount of rare earth elements ∑REE, the total amount of light rare earth elements ∑LREE and the total amount of heavy rare earth elements ∑HREE in the rhizosphere soil of the plants are higher than those in Comparative Examples 7-10 (the pH of the biogas slurry and biogas residue was changed), indicating that controlling the pH of the biogas slurry or biogas residue within an appropriate pH range can promote the enrichment of rare earth elements REEs in the rhizosphere of plants.

[0126] Compared with Example 2, after the pretreatment of the biogas residue in Example 7, the phenomenon of rare earth element REEs enrichment in the rhizosphere of the plant was more obvious. And after changing the biogas residue pretreatment method (Comparative Examples 11-13), the phenomenon of rare earth element REEs enrichment in the rhizosphere of the plant was weakened, indicating the specific effect of the biogas residue pretreatment of the present invention.

[0127] (2) Rare earth element content in energy plants

[0128] Table 11 Effects of different biogas slurries or biogas residues on the rare earth element content (mg / kg) in the rice plants

[0129]

[0130] It can be seen from Table 11 that after the use of the biogas slurry and biogas residue of Examples 1 and 2 of the present invention to plant pearl millet, the total amount of rare earth elements ∑REE, the total amount of light rare earth elements ∑LREE and the total amount of heavy rare earth elements ∑HREE in the aboveground plant part of pearl millet are all higher than those in Comparative Examples 7-10 (the pH of the biogas slurry and biogas residue was changed), indicating that controlling the pH of the biogas slurry or biogas residue within an appropriate pH range can improve the rare earth element enrichment capacity of pearl millet.

[0131] Compared with Example 2, after the pretreatment of the biogas residue in Example 7, the rare earth element enrichment of the above-ground plant part of the millet significantly increased, indicating that the pretreatment of the biogas residue in the present invention weakened the effect of the biogas residue application on the rare earth element enrichment of the millet plant. After changing the biogas residue pretreatment method (Comparative Examples 11-13), the rare earth element enrichment capacity of the millet was weakened, indicating the specific effect of the biogas residue pretreatment of the present invention.

Claims

1. A method for enriching rare earth elements in a rare earth tailings area, characterized in that: Planting royal millet in the rare earth tailings area and applying biogas residue, which is applied after being pre-treated; The pH of the biogas residue is 7.90-8.33; The biogas residue pretreatment method comprises the following steps: drying and crushing the biogas residue, adding a sugar compound and stirring evenly, wherein the amount of the sugar compound added is 4-8% of the mass of the biogas residue; The sugar compound includes starch and UDP-glucose in a mass ratio of 1:(0.5-0.8).

2. The method according to claim 1, characterized in that: The specific steps for planting royal millet in rare earth tailings areas include: First, basal fertilizer was applied to the soil in the rare earth tailings area. Seven days later, the seeds of the royal millet were directly sown in the soil. When the plants grew to the tillering stage, the first topdressing was carried out. When the best growing plants reached a height of 1.2 m, they were mowed. The second topdressing was carried out on the third day after mowing. The application rates of the basal fertilizer, the first topdressing and the second topdressing were the same, and the pure nitrogen content was 800-1000 kg / hm 2 The fertilizers used for the base fertilizer, the first topdressing and the second topdressing are the biogas residue obtained by pretreatment.

3. The method according to claim 1, characterized in that: The physical and chemical properties of the biogas residue are as follows: moisture content 61.75-69.22%, organic matter OM content 23.08-32.89%, total nitrogen TN content 2.23-3.33%, P2O5 content 12.04-14.02%, and K2O content 0.54-0.88%.

4. The method according to claim 1, characterized in that: The planting density of the royal millet is 1-30 plants / m 2 .

5. The method according to claim 1, characterized in that: The rare earth tailings area is an ionic rare earth tailings area.

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