A method for the restoration and reuse of ionic rare earth tailings

Abstract

The present invention discloses a method for the restoration and reuse of ionic rare earth tailings, which includes pretreatment of the tailing area, planting of energy crops, and reuse of energy crops. During the pretreatment of the tailing area, soil improvers are applied to the ionic rare earth tailings by plowing. The soil improver includes 10-20 parts of modified biochar, 5-8 parts of rice husks, 6-12 parts of ceramsite, and 8-14 parts of attapulgite powder. The present invention improves the soil by adding a soil improver containing modified biochar, promotes the fixation of heavy metals in the soil, and performs seed coating treatment on energy crops. The combination of the two improves the restoration effect of the tailings. In addition, the present invention also removes heavy metals from the plant juice obtained by juicing the restored energy crops and then supplies it for agricultural use, which is safe and reasonable and improves the utilization rate of the restored plants.

Description

Technical Field

[0001] The present invention belongs to the technical field of tailings treatment, and specifically relates to a method for repairing and recycling ionic rare earth tailings. Background Art

[0002] With the increasing demand for rare earths in various industries, the mining volume of rare earths has also been increasing day by day. Although excessive exploitation has brought certain economic benefits, it has caused great damage to the environment and ecological destruction. Especially in the early stage, the mining processes of ionic rare earth tailings are backward pond leaching and heap leaching processes, which are extremely likely to cause environmental problems such as soil fertility degradation, soil desertification, associated heavy metal pollution, and soil erosion. These damaged tailings cannot be used without treatment.

[0003] Among the existing ionic rare earth tailings repair technologies, vegetation restoration is one of the clean, environmentally friendly, and green in-situ restoration technologies. It uses the special physiological functions of plants to transfer pollutants in the soil to the roots, stems, fruits, etc. through absorption, enrichment, precipitation, etc., to achieve the purpose of removing pollutants, and has the characteristics of good effect, small investment, easy management, and no secondary pollution.

[0004] At present, although energy crops have been used for vegetation restoration in many ionic rare earth tailings areas, it has a good effect on tailings areas with general damage conditions, but the overall effect on tailings areas with more serious damage and pollution is not good. The main reason is that the soil desertification in ionic rare earth tailings is serious, there are too many pollutants, and the organic matter content is low, resulting in slow plant growth and high mortality, thus greatly reducing the repair effect and increasing the repair cost. Moreover, many existing vegetation restoration methods do not consider the safe and reasonable utilization methods of energy crops, resulting in certain resource waste.

[0005] The invention patent CN202110160762.8 provides a method for treating ionic rare earth tailings based on a biogas project. It uses the biogas residues and biogas slurry generated by the biogas project, which are used as fertilizers after pretreatment, to plant energy crops in rare earth tailings, and uses ecological restoration technology to transform the soil of rare earth tailings. It only considers improving the physical and chemical properties of the soil by using biogas slurry and biogas residues, but does not consider the influence of the addition of complex biogas slurry and biogas residues on the forms, transformation, and migration of heavy metal ions, making the heavy metal ions unstable and increasing the difficulty of heavy metal treatment in the soil. In addition, there are pollutants in the tailings itself, and the application of biogas slurry and biogas residues to the soil without sterilization further increases the risk of energy crop seed pollution, affecting the germination rate of seeds and the yield of crops, which all have a direct impact on the tailings repair effect.

[0006] The invention patent CN 201210137521.2 provides a substrate formulation suitable for the vegetation restoration of ionic rare earth tailings. Carbendazim, a bactericidal component, is added to the plant growth soil medium. However, it uses organic compounds, lacks environmental friendliness, and does not focus on sterilizing plant seeds.

[0007] In summary, how to provide a method for the restoration and reuse of ionic rare earth tailings, which can improve the tailing restoration effect by improving the soil, enhancing the fixation of heavy metals in the soil, and strengthening the sterilization of plant seeds, and at the same time promote the safe and reasonable reuse of energy crops, is an urgent problem to be solved currently. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for the restoration and reuse of ionic rare earth tailings. By adding a soil conditioner containing modified biochar to improve the soil, promote the fixation of heavy metals in the soil, and perform seed coating treatment on energy crops, not only the sterilization effect of the seeds is improved, the germination and growth of energy crops are promoted, but also the absorption and enrichment of heavy metals by plants are promoted. The combination of the two improves the tailing restoration effect. In addition, the plant juice obtained by juicing the restored energy crops is subjected to heavy metal impurity removal and then supplied for agricultural use, which is safe and reasonable and improves the utilization rate of the restored plants.

[0009] The purpose of the present invention is achieved as follows:

[0010] A method for the restoration and reuse of ionic rare earth tailings includes pre-treatment of the tailing area, planting of energy crops, and reuse of energy crops. During the pre-treatment of the tailing area, the soil is plowed and a soil conditioner is applied to the ionic rare earth tailings. The soil conditioner includes 10 - 20 parts of modified biochar, 5 - 8 parts of rice husks, 6 - 12 parts of ceramsite, and 8 - 14 parts of attapulgite powder.

[0011] The preparation method of the modified biochar includes the following steps:

[0012] (1) Soak the straw in an inorganic iron salt solution for 1 - 2 h. After the soaking is completed, adjust the pH value of the solution to not less than 9.5, perform solid-liquid separation to obtain the treated straw.

[0013] (2) Carbonize the treated straw under anaerobic conditions. Soak the obtained carbonized product in a 2-ethylhexanoic acid ferrous aqueous solution for 1 - 2 h, take it out and dry it, then soak it in an ethanol solution of iron ethanol for 10 - 30 min, and then air-dry to obtain the modified biochar.

[0014] Furthermore, the application amount of the soil conditioner is 1 - 1.8% of the soil quality with a surface depth of 30 - 35 cm in the tailing area.

[0015] Further, in step (1), the inorganic iron salt is ferric chloride or ferric sulfate, the molar concentration of ferric ions in the inorganic iron salt solution is 1.1 - 1.5 mol / L, and the mass of the inorganic iron salt solution is 5 - 10 times the mass of the straw.

[0016] Further, in step (2), the conditions for carbonization treatment are: carbonization at 400 - 450 °C for 2 - 3 h, the molar concentration of ferrous ions in the aqueous solution of ferrous 2 - ethylhexanoate is 0.6 - 0.9 mol / L, the mass ratio of iron ethanolate to ethanol is 1:(2 - 5), and the aqueous solution of ferrous 2 - ethylhexanoate and the ethanol solution of iron ethanolate respectively account for 3 - 6 times and 2 - 4 times the mass of the carbonized product.

[0017] The present invention also provides a seed coating agent for energy crops in a method for the restoration and reuse of ionic rare earth tailings. The energy crops for planting are treated with the coating agent after germination of the energy crop seeds and then sown. The coating agent used for the coating treatment comprises the following raw materials in parts by weight: 2.5 - 4 parts of a bactericide, 1 - 3 parts of a plant growth regulator, 3 - 5 parts of a trace element fertilizer, and 30 - 50 parts of a film - forming agent. The bactericide comprises a neo - gambogic acid derivative and an astragalus flavonoid compound with a mass ratio of 1:(0.4 - 1.2).

[0018] Further, the neo - gambogic acid derivative is 10 - methoxyneo - gambogic acid, and the astragalus flavonoid compound is astragalus isoflavan glycoside.

[0019] Further, the plant growth regulator is Atonik, the trace element fertilizer is one or more of boron fertilizer, zinc fertilizer, and manganese fertilizer, and the film - forming agent is polyvinyl alcohol, starch, polyethylene glycol, or xanthan gum.

[0020] Further, the method for coating agent treatment is: after mixing the film - forming agent with (20 - 50 times) water and mixing evenly, then adding the bactericide, the plant growth regulator, and the trace element fertilizer, and after stirring evenly, coating the energy crop seeds according to a drug - to - seed ratio of 1:(8 - 14).

[0021] The present invention also provides a method for reusing energy crops in a method for the restoration and reuse of ionic rare earth tailings, which specifically comprises the following steps: taking anaerobic fermentation as the post - harvest utilization mode of the restoration plants, constructing a mixed fermentation raw material, optimizing its energy production process, forming a green circular mode for the post - harvest utilization of the restoration plants, harvesting the restored energy crops, juicing the harvested plants, using the obtained solid residue as the fermentation substrate of a biogas station, and concentrating the squeezed plant juice after removing impurities with an impurity - removing agent as livestock and poultry feed.

[0022] The impurity - removing agent is modified lignosulfonate sodium, and its preparation method comprises the following steps:

[0023] S1. After dissolving sodium lignosulfonate in 20 - 40 times of water with stirring, adjust the pH value of the solution to 3 - 4, add hydrogen peroxide and ferrous sulfate, stir and react for 1 - 2 h, and then let it stand still.

[0024] S2. Adjust the pH value of the reaction solution obtained in step S1 to 8 - 9 with 20% sodium hydroxide solution, add phosphonoamine compound, formaldehyde and distilled water under stirring conditions, and heat and react for 1 - 2 h.

[0025] S3. Adjust the pH value of the reaction solution obtained in step S2 to 9 - 10 with 20% sodium hydroxide solution, continue to add long - chain oxygen - containing amine compound, hydroxypropylmalonaldehyde and distilled water under stirring conditions, and heat and react for 2 - 4 h.

[0026] S4. Dropwise add 1 mol / L hydrochloric acid solution into the reaction solution obtained in step S3, wash the precipitated solid with ethanol, filter by suction, wash with water, filter by suction, and dry to obtain modified sodium lignosulfonate.

[0027] Further, the phosphonoamine compound is iminodimethylenephosphonic acid, and the long - chain oxygen - containing amine compound is isodecyloxypropylpropylenediamine.

[0028] Further, in step S1, the mass ratio of sodium lignosulfonate, hydrogen peroxide and ferrous sulfate is 1:(0.3 - 0.8):(0.06 - 0.2).

[0029] In step S2, the mass ratio of the phosphonoamine compound, formaldehyde and distilled water is 1:(0.3 - 0.4):(3 - 6), the molar ratio of the phosphonoamine compound to sodium lignosulfonate is (0.8 - 2):1, and the heating temperature is 70 - 75 °C.

[0030] In step S3, the mass ratio of the long - chain oxygen - containing amine compound, hydroxypropylmalonaldehyde and distilled water is 1:(0.2 - 0.3):(3 - 6), the molar ratio of the long - chain oxygen - containing amine compound to sodium lignosulfonate is (0.6 - 1.4):1, and the heating temperature is 80 - 85 °C.

[0031] The beneficial effects of the present invention are as follows:

[0032] 1. The modified biochar is added to the soil conditioner of the present invention. It not only has the characteristics of large specific surface area, rich mineral component content, high charge density, strong adsorption performance and ion exchange performance of ordinary biochar, which is helpful for plant growth, but also contains iron sources with different valence states in the modified biochar, which can further improve the heavy - metal fixation ability of biochar, thus promoting the tailing restoration effect.

[0033] 2. The modified biochar of the present invention first introduces inorganic iron salts, and then is carbonized and soaked in an aqueous solution of ferrous 2-ethylhexanoate. This not only enables the modified biochar to contain iron sources with different valence states, but also combines inorganic iron sources and organic iron sources, which can meet the compatibility between soil and biochar in different environments. In addition, ferrous 2-ethylhexanoate and inorganic iron salts re-form a certain proportion of iron salts and ferrous salts through redox reactions in the soil, which also changes the number of bindings between 2-ethylhexanoate groups and iron or ferrous ions, thereby changing the spatial morphology on the surface of the modified biochar and making the spatial morphology of the modified biochar adapt to that of the soil, promoting its soil improvement effect.

[0034] 3. Finally, the modified biochar of the present invention is also soaked in an ethanol solution of iron ethanolate. After the obtained modified biochar is placed in the soil, iron ethanolate hydrolyzes and aggregates in the water-containing soil to form a colloid, which has the effect of fixing the soil and has good water and fertilizer retention capabilities. In addition, for the modified biochar containing ferrous 2-ethylhexanoate, inorganic iron salts, and colloid in the soil, it fixes the activities of heavy metal ions in the soil through the colloid, making the fixation effect of iron sources with different valence states on heavy metals more significant.

[0035] 4. In addition, since biochar is prone to generate toxic substances after high-temperature carbonization, and its preparation raw materials are also prone to generate harmful substances when contaminated, the colloid formed by the hydrolysis of iron ethanolate in the modified biochar of the present invention can also inhibit the release of toxic substances after carbonization in the soil, avoiding side effects of the modified biochar on the soil.

[0036] 5. After the energy crop seeds are coated with the treatment of the present invention, the active ingredients in the coating will be gradually absorbed during the seed development process, improving the germination rate of the energy crop seeds. Moreover, the coating contains a bactericide with obvious bactericidal effect, which can prevent the seeds from being infected by miscellaneous bacteria during the germination process. Therefore, the coated seeds grow vigorously at the seedling stage, with dark green leaves, developed roots, and strong plants, enhancing the ecological restoration effect of the tailings.

[0037] 6. The bactericides used in the present invention are neo-gambogic acid derivatives and astragalus flavonoids, which have the advantages of being green and environmentally friendly compared with ordinary synthetic organic bactericides. Moreover, the present invention further selects 10-methoxyneo-gambogic acid and astragalus isoflavan glycoside as bactericides. 10-methoxyneo-gambogic acid has certain lipophilicity, which can enhance the selectivity of the bactericide for bacteria and fungi, making the utilization rate of the bactericide high and the dosage small; astragalus isoflavan glycoside has strong moisturizing properties, and it can improve the moisturizing effect of the seeds in the seed coating and promote seed development.

[0038] 7. The present invention selects the combination of 10 - methoxy gambogic acid and astragalus isoflavan glycoside as a fungicide. The functional groups (hydroxyl group, methoxy group) in the two can adsorb heavy metal ions in the soil, and when they exist in a specific ratio, they can achieve a stable heavy metal adsorption effect and are not easily desorbed. The seed coating of energy crops containing this fungicide can further improve the absorption and enrichment of heavy metal ions by energy crops.

[0039] 8. After the soil conditioner and seed coating of the present invention are used, the absorption and enrichment of heavy metals by energy crops are improved, making the heavy metal content in the planted energy crops relatively high and difficult to be directly used for agriculture. Therefore, the present invention squeezes the repaired energy crops to obtain plant juice, removes heavy metals from the juice and then supplies it for agricultural use, which is safe and effective, and improves the utilization rate of the repaired plants; and the impurity remover used in the present invention is modified sodium lignosulfonate, which will not affect the nutritional components in the plant juice while removing heavy metal ions.

[0040] 9. After the sodium lignosulfonate is subjected to oxidative pretreatment and then amination modification, the obtained modified sodium lignosulfonate has enhanced adsorption force for heavy metals and increased adsorption capacity, significantly enhancing the heavy metal adsorption ability.

[0041] 10. The present invention uses two kinds of amine compounds to modify sodium lignosulfonate, so that the impurity remover contains multiple branched chains for adsorbing heavy metal ions. The phosphate group in the phosphoric acid - based amine compound can further expand the adsorption sites of heavy metal ions and enhance the adsorption effect; the long - chain oxygen - containing amine compound can enhance the surface activity and can adsorb other pollutants except heavy metals, with good decontamination effect.

[0042] 11. The phosphoric acid - based amine compound of the present invention further selects iminodimethylenephosphonic acid, which contains both acidic and basic groups, is not easily affected by the acidity and alkalinity of the system, and can simultaneously remove heavy metal cations and metal anions in the form of acid radicals; and both the N and P atoms in iminodimethylenephosphonic acid contain lone pairs of electrons, which can form coordination with different metal ions, with good adsorption effect; in addition, the modified sodium lignosulfonate containing a symmetric bis - phosphoric acid structure has high biological activity, which is beneficial to the retention of effective components in the plant juice.

[0043] 12. The long - chain oxygen - containing amine compound of the present invention further selects isodecyloxypropyl propylenediamine, which participates in the reaction with hydroxypropyl dialdehyde, so that there are several different reaction sites in the modification reaction of sodium lignosulfonate, and complex product structures can be generated, which is beneficial to the coagulation of modified sodium lignosulfonate after adsorbing heavy metals. Embodiment

[0044] The present invention will be further described below in conjunction with embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0045] Taking a damaged and polluted ion-type rare earth tailing pond in Dingnan, Ganzhou, Jiangxi as the experimental area, with a total area of 28 km 2 , which is evenly divided into 20 sub-experimental areas to implement the following Examples 1-2, 4-5 and Comparative Examples 1-16. Comparative Examples 17-23 utilize the energy crops harvested after the repair of Example 3 by different methods. Example 1

[0046] This example provides a method for the repair and reuse of ion-type rare earth tailings, including:

[0047] Pretreatment of the tailing pond area: The slope of general ion-type tailing areas is between 5°-35°. For areas with a steeper slope, land rectification is required before vegetation restoration can be carried out. For areas with severe soil erosion, such as gully erosion, sheet erosion, and engineering erosion, the degrees of soil erosion are different, and different engineering technology combinations are needed in the rare earth tailings to control soil erosion. The main measures include land leveling, building intercepting ditches, building erosion control revetments, etc. to initially fix the soil, and then crops are cultivated.

[0048] Planting of energy crops: Select energy crops with strong adaptability to rare earth tailings. In this example, Pennisetum hydridum is selected and planted in the pretreated tailing pond area. The specific steps are as follows: The seeds of the energy crops are germinated and then sown (broadcasting can be used), and then covered with soil after sowing; then biogas slurry and biogas residue are used for soil fertilization, with a dosage of 500-1000 kg of the biogas residue and biogas slurry mixture per mu; after fertilization, management is carried out, including weeding, watering, and mowing. During this period, soil samples are collected and tested every 3 months. When the soil organic matter content is stable at 30-40 g / kg, the whole energy crop can be harvested.

[0049] Reuse of energy crops: Anaerobic fermentation is used as the post-harvest utilization method of the restoration plants. A mixed fermentation raw material is constructed, and its energy production process is optimized to form a green circular mode for the post-harvest utilization of the restoration plants. The restoration plants are harvested and processed as the fermentation substrate of the biogas station.

[0050] Among them, during the pretreatment of the tailing pond area, the soil is plowed and a soil conditioner is applied to the ion-type rare earth tailings. The application amount of the soil conditioner is 1% of the soil quality of the 30 cm surface layer of the tailing pond area. The soil conditioner includes 10 parts of modified biochar, 5 parts of rice husks, 6 parts of ceramsite, and 8 parts of attapulgite powder.

[0051] The method for preparing modified biochar comprises the following steps:

[0052] (1) Soak the straw in a 5-fold amount of ferric chloride or ferric sulfate solution (with an iron ion molar concentration of 1.5 mol / L) for 1 hour. After the soaking, adjust the pH value of the solution to no less than 9.5, perform solid-liquid separation, and obtain the treated straw;

[0053] (2) The treated straw was carbonized in a muffle furnace at 400℃ for 3h under oxygen-free conditions, and the obtained carbonized material was immersed in an aqueous solution of ferrous 2-ethylhexanoate (the molar concentration of ferrous ions was 0.9 mol / L) for 1h, taken out and dried, and immersed in an ethanol solution of ethanol iron for 10min, the mass ratio of ethanol iron to ethanol being 1:2, and then surface dried to obtain modified biochar. The ferrous 2-ethylhexanoate aqueous solution and the ethanol solution of ethanol iron accounted for 3 times and 2 times the mass of the carbonized material, respectively. Example 2

[0054] On the basis of Example 1, this example provides a method for repairing and reusing ionic rare earth tailings, wherein energy crop seeds used for energy crop planting are treated with a coating agent after germination and then sown.

[0055] The coating agent used in the coating treatment includes the following raw materials in parts by weight: 2.5 parts of fungicide, 1 part of plant growth regulator (Aidosu), 3 parts of trace element fertilizers (boron fertilizer, zinc fertilizer) and 30 parts of film-forming agent (starch), wherein the fungicide includes 10-methoxyneogamic acid and astragaloside in a mass ratio of 1:0.4.

[0056] The coating agent treatment method is: add 20 times the water to the film-forming agent and mix well, then add the fungicide, plant growth regulator and trace element fertilizer, stir evenly and coat the energy crop seeds according to the drug-seed ratio of 1:8.

[0057] The rest is the same as Example 1. Example 3

[0058] On the basis of Example 2, the energy crop recycling method in this example further includes: squeezing the harvested plants to obtain solid residues as a fermentation substrate for a biogas station, and the squeezed plant juice is decontaminated with an impurity remover and then concentrated to be used as livestock and poultry feed.

[0059] The impurity remover is modified sodium lignin sulfonate, and its preparation method comprises the following steps:

[0060] S1. After adding 20 times of water to sodium lignin sulfonate and stirring to dissolve, adjust the pH value of the solution to 3, add hydrogen peroxide and ferrous sulfate, stir and react for 1 hour and then let it stand; the mass ratio of sodium lignin sulfonate, hydrogen peroxide and ferrous sulfate is 1:0.3:0.06.

[0061] S2. Adjust the pH value of the reaction solution obtained in step S1 to 8 with 20% sodium hydroxide solution, add iminodimethylenephosphonic acid, formaldehyde and distilled water under stirring conditions, and heat the reaction at 70 °C for 1 h; the mass ratio of iminodimethylenephosphonic acid, formaldehyde and distilled water is 1:0.3:3, and the molar ratio of iminodimethylenephosphonic acid to sodium lignosulfonate is 0.8:1.

[0062] S3. Adjust the pH value of the reaction solution obtained in step S2 to 9 with 20% sodium hydroxide solution, continue to add isodecyloxypropyl propanediamine, hydroxypropanedial and distilled water under stirring conditions, and heat the reaction at 80 °C for 2 h; the mass ratio of isodecyloxypropyl propanediamine, hydroxypropanedial and distilled water is 1:0.2:3, and the molar ratio of isodecyloxypropyl propanediamine to sodium lignosulfonate is 0.6:1.

[0063] S4. Dropwise add 1 mol / L hydrochloric acid solution to the reaction solution obtained in step S3, wash the precipitated solid with ethanol, filter by suction, wash with water, filter by suction and dry to obtain modified sodium lignosulfonate.

[0064] The rest is the same as in Example 2. Example 4

[0065] This example provides a method for the restoration and reuse of ionic rare earth tailings, including pretreatment of the tailing area, planting of energy crops and reuse of energy crops. During the pretreatment of the tailing area, the soil is plowed and a soil conditioner is applied to the ionic rare earth tailings. The application amount of the soil conditioner is 1.4% of the soil quality with a surface depth of 32 cm in the tailing area. The soil conditioner includes 15 parts of modified biochar, 6.5 parts of rice husks, 9 parts of ceramsite and 11 parts of attapulgite powder.

[0066] The preparation method of the modified biochar includes the following steps:

[0067] (1) Immerse the straw in a 7-fold amount of ferric chloride or ferric sulfate solution (the molar concentration of iron ions is 1.3 mol / L) for 1.5 h. After the immersion, adjust the pH value of the solution to not less than 9.5, perform solid-liquid separation to obtain the treated straw.

[0068] (2) Carbonize the treated straw in a muffle furnace at 425 °C for 2.5 h under anaerobic conditions. Immerse the obtained carbonized product in an aqueous solution of ferrous 2-ethylhexanoate (the molar concentration of ferrous ions is 0.75 mol / L) for 1.5 h, take it out and dry it, then immerse it in an ethanol solution of iron ethanol for 20 min. The mass ratio of iron ethanol to ethanol is 1:3.5, and then air dry to obtain the modified biochar. The aqueous solution of ferrous 2-ethylhexanoate and the ethanol solution of iron ethanol respectively account for 4.5 times and 3 times the mass of the carbonized product.

[0069] In this embodiment, for the energy crop planting, the energy crop seeds are germinated and then treated with a coating agent before sowing. The coating agent used for the coating treatment comprises raw materials in the following parts by weight: 3.2 parts of a bactericide, 2 parts of a plant growth regulator (Atonik), 4 parts of trace element fertilizers (boron fertilizer, zinc fertilizer, manganese fertilizer), and 40 parts of a film-forming agent (polyvinyl alcohol). The bactericide comprises 10-methoxyhonokiol and astragalus isoflavan glycoside with a mass ratio of 1:0.8.

[0070] The method for the coating agent treatment is as follows: After mixing the film-forming agent with 35 times of water evenly, the bactericide, the plant growth regulator, and the trace element fertilizers are added, and after stirring evenly, the energy crop seeds are coated according to a drug-seed ratio of 1:11.

[0071] In this embodiment, the method for reusing energy crops specifically comprises the following steps: The repaired energy crops are harvested, the harvested plants are juiced, the obtained solid residues are used as fermentation substrates for a biogas station, and the squeezed plant juice is concentrated after being decontaminated by a decontaminant and used as livestock and poultry feed.

[0072] The decontaminant is modified lignosulfonate sodium, and its preparation method comprises the following steps:

[0073] S1. After stirring and dissolving lignosulfonate sodium in 30 times of water, the pH value of the solution is adjusted to 3.5, hydrogen peroxide and ferrous sulfate are added, and after stirring and reacting for 1.5 h, it is left to stand; the mass ratio of lignosulfonate sodium, hydrogen peroxide, and ferrous sulfate is 1:0.5:0.13.

[0074] S2. The pH value of the reaction solution obtained in step S1 is adjusted to 8.5 with a 20% sodium hydroxide solution, iminodimethylenephosphonic acid, formaldehyde, and distilled water are added under stirring conditions, and it is heated and reacted at 72 °C for 1.5 h; the mass ratio of iminodimethylenephosphonic acid, formaldehyde, and distilled water is 1:0.35:4.5, and the molar ratio of iminodimethylenephosphonic acid to lignosulfonate sodium is 1.4:1.

[0075] S3. The pH value of the reaction solution obtained in step S2 is adjusted to 9.5 with a 20% sodium hydroxide solution, isodecyloxypropyl propanediamine, hydroxypropyl dialdehyde, and distilled water are continuously added under stirring conditions, and it is heated and reacted at 82 °C for 3 h; the mass ratio of isodecyloxypropyl propanediamine, hydroxypropyl dialdehyde, and distilled water is 1:0.25:4.5, and the molar ratio of isodecyloxypropyl propanediamine to lignosulfonate sodium is 1:1.

[0076] S4. A 1 mol / L hydrochloric acid solution is dropped into the reaction solution obtained in step S3, and the precipitated solid is rinsed with ethanol, filtered by suction, washed with water, filtered by suction, and dried to obtain modified lignosulfonate sodium.

[0077] The rest is the same as in Example 3. Example 5

[0078] This embodiment provides a method for the restoration and reuse of ionic rare earth tailings, including pretreatment of the tailing area, planting of energy crops, and reuse of energy crops. During the pretreatment of the tailing area, the soil is plowed and a soil conditioner is applied to the ionic rare earth tailings. The application amount of the soil conditioner is 1.8% of the soil quality with a surface depth of 35 cm in the tailing area. The soil conditioner includes 20 parts of modified biochar, 8 parts of rice husks, 12 parts of ceramsite, and 14 parts of attapulgite powder.

[0079] The preparation method of the modified biochar includes the following steps:

[0080] (1) The straw is soaked in a 10-fold amount of ferric chloride or ferric sulfate solution (the molar concentration of ferric ions is 1.1 mol / L) for 2 h. After the soaking is completed, the pH value of the solution is adjusted to not less than 9.5, and solid-liquid separation is carried out to obtain the treated straw.

[0081] (2) Under an oxygen-free condition, the treated straw is carbonized in a muffle furnace at 450 °C for 2 h. The obtained carbide is soaked in an aqueous solution of ferrous 2-ethylhexanoate (the molar concentration of ferrous ions is 0.6 mol / L) for 2 h, taken out and dried, and then soaked in an ethanol solution of iron ethanol for 30 min. The mass ratio of iron ethanol to ethanol is 1:5, and then it is surface-dried to obtain the modified biochar. The aqueous solution of ferrous 2-ethylhexanoate and the ethanol solution of iron ethanol respectively account for 6 times and 4 times the mass of the carbide.

[0082] In this embodiment, for the planting of energy crops, the energy crop seeds are germinated and then treated with a coating agent before sowing. The coating agent used for the coating treatment includes the following raw materials in parts by weight: 4 parts of a bactericide, 3 parts of a plant growth regulator (Atonik), 5 parts of trace element fertilizers (zinc fertilizer, manganese fertilizer), and 50 parts of a film-forming agent (xanthan gum). The bactericide includes 10-methoxyneoagaricic acid and astragalus isoflavan glycoside with a mass ratio of 1:1.2.

[0083] The method for coating agent treatment is as follows: The film-forming agent is mixed with 50 times of water and then the bactericide, plant growth regulator, and trace element fertilizers are added. After stirring evenly, the energy crop seeds are coated according to a drug-seed ratio of 1:14.

[0084] In this embodiment, the method for the reuse of energy crops specifically includes the following steps: The restored energy crops are harvested, the harvested plants are juiced, the obtained solid residue is used as a fermentation substrate for a biogas station, and the squeezed plant juice is concentrated after being decontaminated by a decontaminant and used as livestock and poultry feed.

[0085] The decontaminant is modified lignosulfonate, and its preparation method includes the following steps:

[0086] S1. After dissolving sodium lignosulfonate in 40 times its weight of water with stirring, adjust the pH value of the solution to 4. Then add hydrogen peroxide and ferrous sulfate, stir and react for 2 h, and then let it stand. The mass ratio of sodium lignosulfonate, hydrogen peroxide and ferrous sulfate is 1:0.8:0.2.

[0087] S2. Adjust the pH value of the reaction solution obtained in step S1 to 9 with 20% sodium hydroxide solution. Under stirring conditions, add iminodimethylenephosphonic acid, formaldehyde and distilled water, and heat and react at 75 °C for 2 h. The mass ratio of iminodimethylenephosphonic acid, formaldehyde and distilled water is 1:0.4:6, and the molar ratio of iminodimethylenephosphonic acid to sodium lignosulfonate is 2:1.

[0088] S3. Adjust the pH value of the reaction solution obtained in step S2 to 10 with 20% sodium hydroxide solution. Continue to add isodecyloxypropylpropylenediamine, hydroxypropyl dialdehyde and distilled water under stirring conditions, and heat and react at 85 °C for 4 h. The mass ratio of isodecyloxypropylpropylenediamine, hydroxypropyl dialdehyde and distilled water is 1:0.3:6, and the molar ratio of isodecyloxypropylpropylenediamine to sodium lignosulfonate is 1.4:1.

[0089] S4. Dropwise add 1 mol / L hydrochloric acid solution to the reaction solution obtained in step S3. The precipitated solid is rinsed with ethanol, filtered by suction, washed with water, filtered by suction again, and dried to obtain modified sodium lignosulfonate.

[0090] The rest is the same as in Example 3.

[0091] Comparative Example 1

[0092] The difference between this comparative example and Example 1 is that no soil conditioner is used during the pretreatment of the tailing area.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 1 is that the modified biochar in the soil conditioner is replaced with ordinary biochar, that is, the biochar directly obtained by carbonizing straw.

[0095] Comparative Example 3

[0096] The difference between this comparative example and Example 1 is that the mass fraction of the modified biochar in the soil conditioner is 8 parts.

[0097] Comparative Example 4

[0098] The difference between this comparative example and Example 1 is that the mass fraction of the modified biochar in the soil conditioner is 22 parts.

[0099] Comparative Example 5

[0100] The difference between this comparative example and Example 1 lies in that in step (2) of the preparation method of the modified biochar, ferrous 2-ethylhexanoate and iron ethanolate are not used. Specifically: under an oxygen-free condition, the treated straw is carbonized in a muffle furnace at 400 °C for 3 h, and that's it.

[0101] Comparative Example 6

[0102] The difference between this comparative example and Example 1 lies in that in step (2) of the preparation method of the modified biochar, ferrous 2-ethylhexanoate is not used. Specifically: under an oxygen-free condition, the treated straw is carbonized in a muffle furnace at 400 °C for 3 h. The obtained carbonized product is immersed in an ethanol solution of iron ethanolate for 10 min, and then surface dried to obtain the modified biochar.

[0103] Comparative Example 7

[0104] The difference between this comparative example and Example 1 lies in that in step (2) of the preparation method of the modified biochar, iron ethanolate is not used. Specifically: under an oxygen-free condition, the treated straw is carbonized in a muffle furnace at 400 °C for 3 h. The obtained carbonized product is immersed in an aqueous solution of ferrous 2-ethylhexanoate for 1 h, taken out and dried to obtain the modified biochar.

[0105] Comparative Example 8

[0106] The difference between this comparative example and Example 1 lies in that in step (2) of the preparation method of the modified biochar, ferrous 2-ethylhexanoate is changed to ferrous lactate.

[0107] Comparative Example 9

[0108] The difference between this comparative example and Example 1 lies in that in step (2) of the preparation method of the modified biochar, iron ethanolate is changed to sodium ethoxide.

[0109] Comparative Example 10

[0110] The difference between this comparative example and Example 2 lies in that the fungicide in the seed coating agent is changed to the commonly used carbendazim.

[0111] Comparative Example 11

[0112] The difference between this comparative example and Example 2 lies in that the fungicide in the seed coating agent is changed to gambogic acid.

[0113] Comparative Example 12

[0114] The difference between this comparative example and Example 2 lies in that the fungicide in the seed coating agent is changed to other types of astragalus flavonoids - astragaloside.

[0115] Comparative Example 13

[0116] The difference between this comparative example and Example 2 lies in that the fungicide in the seed coating agent does not contain 10-methoxy-gambogic acid.

[0117] Comparative Example 14

[0118] The difference between this comparative example and Example 2 is that the fungicide in the seed coating agent does not contain astragalus isoflavan glycoside.

[0119] Comparative Example 15

[0120] The difference between this comparative example and Example 2 is that the mass ratio of 10-methoxy gambogic acid to astragalus isoflavan glycoside in the fungicide is 1:0.3.

[0121] Comparative Example 16

[0122] The difference between this comparative example and Example 2 is that the mass ratio of 10-methoxy gambogic acid to astragalus isoflavan glycoside in the fungicide is 1:1.3.

[0123] Comparative Example 17

[0124] The difference between this comparative example and Example 3 is that in the method for reusing energy crops, the impurity removing agent is sodium lignosulfonate.

[0125] Comparative Example 18

[0126] The difference between this comparative example and Example 3 is that in the preparation method of the modified sodium lignosulfonate, sodium lignosulfonate only undergoes an amination reaction with urea, that is, the original step S3 is deleted, and iminodimethylenephosphonic acid in step S2 is changed to urea.

[0127] Comparative Example 19

[0128] The difference between this comparative example and Example 3 is that the preparation method of the modified sodium lignosulfonate does not include step S2, that is, sodium lignosulfonate only undergoes an amination reaction with isodecyloxypropyl propylenediamine.

[0129] Comparative Example 20

[0130] The difference between this comparative example and Example 3 is that the preparation method of the modified sodium lignosulfonate does not include step S3, that is, sodium lignosulfonate only undergoes an amination reaction with iminodimethylenephosphonic acid.

[0131] Comparative Example 21

[0132] The difference between this comparative example and Example 3 is that in step S2 of the preparation method of the modified sodium lignosulfonate, iminodimethylenephosphonic acid is changed to another type of phosphoric acid-based amine compound - aminomethylphosphonic acid.

[0133] Comparative Example 22

[0134] The difference between this comparative example and Example 3 lies in that in step S3 of the preparation method of the modified sodium lignosulfonate, isodecyloxypropyl propylenediamine is changed to another type of long-chain oxygen-containing amine compound - 3-isodecyloxypropylamine.

[0135] Comparative Example 23

[0136] The difference between this comparative example and Example 3 lies in that in step S3 of the preparation method of the modified sodium lignosulfonate, hydroxypropanedial is changed to formaldehyde.

[0137] I. Influence of the tailing restoration of the present invention on soil parameters

[0138] According to the methods of Examples 1-2, 4-5 and Comparative Examples 1-16 of the present invention, the ionic rare earth tailing areas were restored. After a 3-year restoration period, the soils in different experimental areas were tested to obtain various parameters before and after restoration, and the results are shown in Tables 1 and 2 below.

[0139] 1. Soil properties

[0140] Table 1

[0141]

[0142] 2. Changes in heavy metal content

[0143] Table 2 Heavy metal content (mg / kg)

[0144]

[0145] In the national second soil census soil classification, a pH of 6.5-7.5 is classified as rich, and there are research reports. However, when the soil pH is about 6.5, the availability of various nutrients in the soil is relatively high, which can meet the growth of most plants.

[0146] It can be seen from Table 1 that the restoration effect of the examples of the present invention on ionic rare earth tailings is obvious, especially Examples 2, 4, and 5 perform excellently. The pH of the soils after restoration in Examples 1-2, 4-5 is all about 6.5, which can meet the growth requirements of plants; the contents of organic matter, total nitrogen, total phosphorus, available phosphorus, and available potassium are all significantly increased compared with before restoration, and the soil fertility is enhanced, which is beneficial to the planting of ecological plants.

[0147] It can be seen from Table 2 that the examples of the present invention have obvious effects on removing heavy metals in ionic rare earth tailings, especially Examples 2, 4, and 5 perform excellently. The heavy metal contents in the soils after restoration in Examples 1-2, 4-5 are all lower than the lower limit values specified in the "Soil Environmental Quality - Risk Control Standards for Soil Pollution of Agricultural Land" (GB15618-2018), which can significantly improve the soil pollution situation.

[0148] Compared with Comparative Example 1 (prior art), after using the soil conditioner in Example 1, both the soil properties and heavy metal content were significantly improved. Compared with Example 1, in Example 2, the seeds of the energy crop were coated, and neo-gambogic acid derivatives and astragalus flavonoids were used as fungicides in the coating agent. Not only was the bactericidal effect obvious, the germination rate of the energy crop seeds was increased, but also it had the advantages of being green and environmentally friendly, and could promote seed development, improve the absorption and enrichment of heavy metal ions by the energy crop. Therefore, the soil properties and heavy metal content in Example 2 were further improved, and the remediation effect was enhanced.

[0149] Compared with Example 1, in Comparative Examples 2-9, the preparation method of the modified biochar in the soil conditioner was changed; compared with Example 2, in Comparative Examples 10-16, the components of the seed coating agent were changed; as a result, the soil properties in Comparative Examples 2-16 deteriorated to varying degrees, and the heavy metal removal effect also decreased.

[0150] II. Germination rate and yield of the energy crop of the present invention

[0151] According to the methods of Examples 1-2 and Comparative Examples 1-16 of the present invention, the ionic rare earth tailing area was remediated, and the seed germination rate and crop yield of the energy crop (Pennisetum hydridum) were detected. The results are shown in Table 3 below.

[0152] Table 3

[0153]

[0154] As can be seen from Table 3, the seed germination rate of the energy crops planted in Examples 1 and 2 of the present invention reached more than 92.5%, and the crop yield reached 192 t / hm 2 above. The good growth of the energy crop also promoted the remediation effect of the tailing area.

[0155] Compared with Comparative Example 1 (prior art), after using the soil conditioner in Example 1, the improvement of the soil properties also increased the germination rate of the crop seeds and the crop yield. Compared with Example 1, in Example 2, the seeds of the energy crop were coated, and neo-gambogic acid derivatives and astragalus flavonoids were used as fungicides, which not only increased the germination rate of the energy crop seeds, promoted seed development, increased the yield, and thus enhanced the remediation effect.

[0156] Compared with Example 1, in Comparative Examples 2-9, the preparation method of the modified biochar in the soil conditioner was changed; compared with Example 2, in Comparative Examples 10-16, the components of the seed coating agent were changed; as a result, the seed germination rate and crop yield in Comparative Examples 2-16 decreased.

[0157] III. Utilization of the energy crop of the present invention

[0158] According to the methods of Embodiment 3 and Comparative Examples 17 - 23 of the present invention, the energy crops harvested after restoration (after a 3-year restoration period) were utilized by different methods. The obtained plant juice was concentrated, and the heavy metal contents and nutrient contents before and after impurity removal in the concentrate were detected. The results are shown in Tables 4 and 5 below.

[0159] Table 4 Heavy Metal Contents in Plant Juice (mg / kg)

[0160]

[0161] Table 5 Nutrient Component Contents in Plant Juice (%)

[0162]

[0163] It can be seen from Tables 4 and 5 that by utilizing and removing impurities from the restored energy crops in Embodiment 3 of the present invention, the heavy metal content in the plant juice can be significantly reduced, meeting the requirements of the "Hygienic Standard for Feeds" (GB 13078 - 2018). It can be directly used as livestock and poultry feed without significantly affecting its nutrient components, which can improve the rationality and safety of the utilization of energy crops.

[0164] Compared with Embodiment 3, in Comparative Examples 17 - 23, the preparation method of the impurity removal agent modified sodium lignosulfonate was changed. As a result, the heavy metal impurity removal effect decreased, and the nutrient components were also lost to varying degrees.

[0165] It should be noted that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for the restoration and reuse of ionic rare earth tailings, including pretreatment of the tailing area, planting of energy crops, and reuse of energy crops, characterized in that, During the pretreatment process of the tailing area, the soil is plowed and a soil conditioner is applied to the ionic rare earth tailings. The soil conditioner includes 10-20 parts of modified biochar, 5-8 parts of rice husks, 6-12 parts of ceramsite, and 8-14 parts of attapulgite powder; The preparation method of the modified biochar includes the following steps: (1) Soak the straw in an inorganic iron salt solution for 1-2 h. After the soaking is completed, adjust the pH value of the solution to not less than 9.5, and perform solid-liquid separation to obtain the treated straw; (2) Carbonize the treated straw under an oxygen-free condition. Soak the obtained carbonized product in an aqueous solution of ferrous 2-ethylhexanoate for 1-2 h. After taking it out and drying, soak it in an ethanol solution of iron ethanol for 10-30 min, and then dry the surface to obtain the modified biochar; The application amount of the soil conditioner is 1-1.8% of the soil quality with a surface depth of 30-35 cm in the tailing area; in step (1), the inorganic iron salt is ferric chloride or ferric sulfate, the molar concentration of iron ions in the inorganic iron salt solution is 1.1-1.5 mol / L, and the mass of the inorganic iron salt solution is 5-10 times the mass of the straw; In step (2), the carbonization treatment conditions are: carbonize at 400-450 °C for 2-3 h. The molar concentration of ferrous ions in the aqueous solution of ferrous 2-ethylhexanoate is 0.6-0.9 mol / L. The mass ratio of iron ethanol to ethanol is 1:(2-5). The aqueous solution of ferrous 2-ethylhexanoate and the ethanol solution of iron ethanol respectively account for 3-6 times and 2-4 times the mass of the carbonized product.

2. The method for the restoration and reuse of ionic rare earth tailings according to claim 1, characterized in that: The energy crop planting uses energy crop seeds that are germinated and then treated with a coating agent before sowing. The coating agent used for the coating treatment includes the following raw materials in parts by weight: 2.5-4 parts of a fungicide, 1-3 parts of a plant growth regulator, 3-5 parts of a trace element fertilizer, and 30-50 parts of a film-forming agent. The fungicide includes a neo-gambogic acid derivative and an astragalus flavonoid compound with a mass ratio of 1:(0.4-1.2).

3. The method for the restoration and reuse of ionic rare earth tailings according to claim 1, characterized in that: The energy crop reuse method specifically includes the following steps: Harvest the repaired energy crops, juice the harvested plants, use the obtained solid residue as a fermentation substrate for a biogas station, and concentrate the squeezed plant juice after removing impurities with an impurity remover as livestock and poultry feed; The impurity remover is modified lignosulfonate sodium, and its preparation method includes the following steps: S1. After dissolving lignosulfonate sodium in water and stirring, adjust the pH value of the solution to 3-4, add hydrogen peroxide and ferrous sulfate, stir and react for 1-2 h, and then let it stand; S2. Adjust the pH value of the reaction solution obtained in step S1 to 8-9, add a phosphoric acid-based amine compound, formaldehyde, and distilled water under stirring conditions, and heat and react for 1-2 h; S3. Adjust the pH value of the reaction solution obtained in step S2 to 9-10, continue to add a long-chain oxygen-containing amine compound, hydroxypropyl dialdehyde, and distilled water under stirring conditions, and heat and react for 2-4 h; S4. Drop a hydrochloric acid solution into the reaction solution obtained in step S3, wash the precipitated solid with ethanol, filter by suction, wash with water, filter by suction, and dry to obtain modified lignosulfonate sodium.

4. The method for repairing and recycling ionic rare earth tailings according to claim 2, characterized in that: The gambogic acid derivative is 10-methoxy gambogic acid, and the astragalus flavonoid compound is astragaloside II.

5. The method for the repair and reuse of ionic rare earth tailings according to claim 2, characterized in that: The plant growth regulator is Atonik, the trace element fertilizer is one or more of boron fertilizer, zinc fertilizer, and manganese fertilizer, and the film-forming agent is polyvinyl alcohol, starch, polyethylene glycol, or xanthan gum.

6. The method for repairing and recycling ionic rare earth tailings according to claim 2, wherein: The method for treating the coating agent is as follows: After mixing the film-forming agent with water, add the fungicide, plant growth regulator, and trace element fertilizer, stir evenly, and then coat the energy crop seeds according to the drug-seed ratio of 1:(8-14).

7. The method for the restoration and reuse of ionic rare earth tailings according to claim 3, characterized in that: The phosphonic acid-based amine compound is iminodimethylenephosphonic acid, and the long-chain oxygen-containing amine compound is isodecyloxypropyl propanediamine.

8. The method for the restoration and reuse of ionic rare earth tailings according to claim 3, characterized in that: In step S1, the mass ratio of sodium lignosulfonate, hydrogen peroxide, and ferrous sulfate is 1:(0.3-0.8):(0.06-0.2); In step S2, the mass ratio of the phosphonic acid-based amine compound, formaldehyde, and distilled water is 1:(0.3-0.4):(3-6), the molar ratio of the phosphonic acid-based amine compound to sodium lignosulfonate is (0.8-2):1, and the heating temperature is 70-75 °C; In step S3, the mass ratio of the long-chain oxygen-containing amine compound, hydroxypropyl dialdehyde, and distilled water is 1:(0.2-0.3):(3-6), the molar ratio of the long-chain oxygen-containing amine compound to sodium lignosulfonate is (0.6-1.4):1, and the heating temperature is 80-85 °C.

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