Method for improving rare earth waste residue by microorganism and application thereof

Abstract

The present application relates to the technical field of microbial remediation, and particularly relates to a microbial improvement method and application of rare earth waste residue, the microbial improvement method of the rare earth waste residue comprises the following steps: S1-preprocessing of the rare earth waste residue: selecting the rare earth ore dressing waste residue with pH of 7-9, and removing large impurities therein; S2-mixing of raw materials: adding a microbial improver to the pretreated rare earth waste residue and mixing sufficiently until uniform; S3-microbial improvement: stacking the mixture of step S2 into a heap with a height of 1-1.5 m, and fermenting at 25-30 DEG C for 3-7 days, thereby obtaining the microbial improved rare earth waste residue. The microbial improvement method disclosed in the present application effectively improves the organic matter content of the rare earth waste residue, has an excellent application prospect in the fields of mine reclamation or landscaping, and conforms to the green development concept of solid waste resource utilization and ecological circulation.

Description

Technical Field

[0001] This invention relates to the field of microbial remediation technology, specifically to a method and application for the microbial improvement of rare earth waste residue. Background Technology

[0002] Rare earth elements, as strategically critical mineral resources, are widely used in high-tech fields such as new energy, electronic information, and national defense. With the continuous expansion of rare earth resource mining and the advancement of smelting and separation processes, a large amount of solid waste, namely rare earth slag, is generated during rare earth production. It is estimated that for every ton of rare earth oxides produced, several to tens of tons of slag are generated. The accumulated slag in my country's rare earth producing areas has reached millions of tons and is showing a year-on-year growth trend. This slag is usually stored in the open in tailings ponds or dedicated storage yards, occupying a large amount of land resources and posing a long-term potential threat to the surrounding ecological environment.

[0003] Rare earth waste residue has extremely poor physical and chemical properties, mainly manifested in poor physical structure, nutrient deficiency, and excessive levels of heavy metals and radioactive elements. Physically, the waste residue particles are typically angular, with uneven particle size distribution, low porosity, and poor aggregate stability, resulting in extremely low water and fertilizer retention capacity, making it difficult to form a good soil structure. Chemically, the waste residue contains almost zero organic matter, nitrogen, phosphorus, and other nutrients; its pH value is often acidic or alkaline; and its high salt content makes it difficult for plants to establish and grow. Furthermore, toxic and harmful substances can easily migrate and spread under natural conditions through rainwater leaching, wind dispersion, and surface runoff, polluting the surrounding soil, surface water, groundwater, and atmospheric environment, and even threatening human health through the food chain. Therefore, the ecological restoration of rare earth waste residue dumps has become a bottleneck restricting the green and sustainable development of the rare earth industry.

[0004] Currently, the main traditional technologies for the improvement and ecological restoration of rare earth waste residue are physical remediation and chemical remediation. Physical remediation mainly includes measures such as topsoil covering, landfilling, and engineering isolation. While these methods can control the spread of pollutants in the short term, they suffer from problems such as large engineering workload, high cost, and land resource occupation, and do not fundamentally improve the physicochemical properties of the waste residue. Chemical remediation adjusts the pH of the waste residue, precipitates and fixes heavy metals, or reduces its bioavailability by adding modifiers (such as lime, phosphates, and organic matter). However, chemical remediation often has limitations such as large dosage of remediation agents, high cost, potential introduction of secondary pollution, and difficulty in achieving lasting remediation effects. Against this backdrop, microbial remediation technology, with its advantages of being environmentally friendly, having low operating costs, being easy to operate, and having lasting remediation effects, has gradually become a research hotspot in the field of rare earth waste residue improvement. Invention patent CN110172004A discloses a soil conditioner for ion-type rare earth tailings and its preparation method. The raw materials for this soil conditioner include pig manure, mushroom bran, wheat bran, humic acid, soybean meal, water hyacinth, *Erigeron annuus*, microbial compound inoculants, straw, rice husks, cow manure, sawdust, lignite, coconut shell, graphene, and hydrogel. This soil conditioner can efficiently replenish nutrients in the soil of ion-type rare earth tailings. Combined with plant cultivation and the conversion and absorption of harmful substances in the soil by the soil conditioner, it achieves stable and efficient remediation of ion-type rare earth tailings soil, while significantly controlling soil remediation costs. However, this conditioner mainly targets soil remediation and lacks specific treatment effects for the resource-based remediation and reuse of rare earth ore beneficiation waste. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention provides a method for microbial improvement of rare earth waste residue and its application. The microbial improvement method disclosed in this invention effectively increases the organic matter content of rare earth waste residue, showing excellent application prospects in fields such as mine reclamation and landscaping, and conforming to the green development concept of solid waste resource utilization and ecological recycling.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first aspect of this invention provides a method for microbial modification of rare earth waste residue, comprising the following steps: S1 - Pretreatment of rare earth waste residue: Select rare earth beneficiation waste residue with pH of 7~9 and remove large impurities. S2 - Raw material mixing: Add microbial modifier to the pretreated rare earth waste residue from step S1 and mix thoroughly until homogeneous; S3-Microbial Improvement: The mixture from step S2 is piled into a heap with a height of 1-1.5m and fermented at 25-30℃ for 3-7 days to obtain microbially improved rare earth waste residue.

[0007] In some embodiments of the present invention, the mass ratio of the pretreated rare earth waste residue to the microbial modifier is 1:(0.005-0.02).

[0008] In some embodiments of the present invention, the microbial improver comprises the following raw materials in parts by weight: 1-5 parts of high-protein raw material powder, 0.5-3 parts of compound enzyme, 0.1-1 parts of fungal powder, 0.1-2 parts of plant growth regulator, 10-15 parts of compound carrier, and 10-30 parts of water.

[0009] In some embodiments of the present invention, the high-protein raw material powder is one or more of soybean meal powder, duckweed powder, and fish meal.

[0010] In some embodiments of the present invention, the complex enzyme is a mixture of protease, cellulase, and β-glucanase.

[0011] In some embodiments of the present invention, the fungal powder is one or more of Trichoderma viride powder, Geotrichum candida powder, Aspergillus oryzae powder, Rhizocystis mosieboldii powder, and Rhizocystis pilosa powder, with a viable count ≥1×10⁻⁶. 8 CFU / g.

[0012] In some embodiments of the present invention, the plant growth regulator is fulvic acid and / or brassinolide.

[0013] In some embodiments of the present invention, the preparation steps of the composite carrier are as follows: (1) Mix attapulgite, polyglutamic acid and deionized water, adjust the pH to 7-8, grind and shake for 1-2 hours, let stand to settle and discard the supernatant to obtain pre-modified attapulgite. (2) Mix the pre-modified attapulgite from step (1) with deionized water, then add itaconic acid and N,N′-methylenebisacrylamide and mix by shaking for 0.5-1h, then add an initiator, heat to 65-70℃ under an inert atmosphere, react for 4-6h with stirring, and then wash and dry to obtain the modified attapulgite. (3) The modified attapulgite and sodium carbonate from step (2) are mixed and added to deionized water. After shaking and mixing for 1-2 hours, the supernatant is discarded after standing and settling. The mixture is then ground and sieved to obtain the composite carrier.

[0014] In some embodiments of the present invention, in step (1), the mass ratio of attapulgite clay to polyglutamic acid is 1:(0.05-0.2).

[0015] In some embodiments of the present invention, in step (2), the mass ratio of the pre-modified attapulgite to itaconic acid is 1:(0.06-0.08).

[0016] In some embodiments of the present invention, in step (3), the mass ratio of the modified attapulgite to sodium carbonate is 1:(0.05-0.1).

[0017] This invention modifies attapulgite by preparing a modifier mainly composed of hydrophilic polymers, introducing a large number of hydrophilic groups into its main chain. On the one hand, electrostatic repulsion and steric hindrance effects promote the uniform dispersion of the components of the microbial modifier; on the other hand, hydrogen bonding with water molecules forms a stable hydration layer, maintaining a suitable moisture content of the material and avoiding problems such as mass transfer obstruction and local anaerobic conditions caused by excessive viscosity, thus ensuring the remediation effect and functionality for subsequent applications. At the same time, the three-dimensional cross-linked network structure formed by the modified carrier provides sufficient microenvironment space for the attachment and colonization of microbial communities, which is conducive to the long-term survival and maintenance of metabolic activity of functional microorganisms. Furthermore, through the synergistic effect of multiple mechanisms with high-protein raw material powder, compound enzymes, and fungal powder, the agglomeration of rare earth waste particles is promoted. The presence of attapulgite and the introduction of sodium ions further reduce the density of rare earth waste, thereby improving soil structure and effectively increasing organic matter and nutrient content.

[0018] The applicant also discovered that some of the active groups introduced during hydrophilic modification, such as itaconic acid and polyglutamic acid structures, may undergo partial degradation while chelating and fixing heavy metals, releasing active substances that can then be absorbed and utilized by plants, promoting root development and growth metabolism, further enhancing the application value of the invention, and conforming to the green development concept of solid waste resource utilization and ecological recycling.

[0019] In another aspect, the present invention provides the application of rare earth waste residue modified by a microbial modification method in the fields of mine reclamation or landscaping.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. The microbial improvement method disclosed in this invention effectively increases the organic matter content of rare earth waste residue, and has excellent application prospects in fields such as mine reclamation or landscaping, which is in line with the green development concept of solid waste resource utilization and ecological cycle.

[0021] 2. This invention modifies attapulgite soil with hydrophilic polymers, introducing a large number of hydrophilic groups. This promotes the dispersion of the amendment and maintains a suitable moisture content, avoiding mass transfer obstruction and localized anaerobic conditions. Furthermore, the modified three-dimensional network may provide colonization space for microorganisms, synergistically promoting waste aggregation with high-protein, enzyme, and fungal powder, reducing waste density, improving soil structure, and enhancing nutrient content. Simultaneously, the active groups such as itaconic acid and polyglutamic acid may partially degrade after complexing and fixing heavy metals, releasing active substances that are absorbed by plants, thereby promoting root growth and aligning with the concepts of solid waste resource utilization and ecological recycling. Detailed Implementation

[0022] The present invention will be described below with reference to specific embodiments. It should be noted that the examples and comparative examples below are for illustrative purposes only and are not intended to limit the invention. Other combinations and various modifications within the scope of the invention can be made without departing from its spirit or scope.

[0023] To facilitate implementation of this invention by those skilled in the art, the following description is provided regarding some of the raw materials and manufacturers used in the embodiments and comparative examples: The compounds and related reagents used in the following specific embodiments are all commercially available. The attapulgite clay used has a pH of 7-8 and was purchased from Hengyi Construction Machinery Co., Ltd. in Hangjin Banner, Inner Mongolia. The polyglutamic acid used is γ-polyglutamic acid with a weight-average molecular weight of 200 kDa. The high-protein raw material powder used is an equal mass mixture of soybean meal powder, duckweed powder, and fish meal. The complex enzyme used is an equal mass mixture of protease, cellulase, and β-glucanase. The fungal powder used is an equal mass mixture of *Trichoderma viride* powder and *Geotrichum candida* powder, with a total viable count of 4 × 10⁻⁶. 8 CFU / g; the plant growth regulator used was brassinolide.

[0024] It should be noted that the post-processing steps such as "grinding", "vibration", "washing" and "drying" mentioned in the following embodiments are routine operations for those skilled in the art, and should be selected according to actual operations.

[0025] Preparation Example 1 The preparation steps of the composite carrier are as follows: (1) Mix 20g of attapulgite, 3g of polyglutamic acid and 180mL of deionized water, adjust the pH to 7.5, grind (ball-to-material ratio of 10:1, rotation speed of 300r / min, 30min) and shake (temperature of 25℃, rotation speed of 180r / min, 1h), let stand to settle and discard the supernatant, crush to 100 mesh to obtain pre-modified attapulgite; (2) Mix 10g of the pre-modified attapulgite from step (1) with 200mL of deionized water, then add 0.7g of itaconic acid and 0.04g of N,N′-methylenebisacrylamide and mix by shaking (temperature 25℃, speed 180r / min) for 0.8h, then add 0.015g of ammonium persulfate, heat to 68℃ under nitrogen atmosphere, react for 5h with stirring, wash 3 times with anhydrous ethanol and dry to obtain modified attapulgite; (3) Mix 5g of modified attapulgite from step (2) and 0.4g of sodium carbonate in 30mL of deionized water, shake and mix for 1.5h, let stand to precipitate and discard the supernatant, grind until >95% passes through a 200-mesh sieve to obtain the composite carrier.

[0026] Preparation Example 2 The specific implementation method of the composite carrier is the same as that of Preparation Example 1, except that the amount of polyglutamic acid added in step (1) is 5g.

[0027] Preparation Example 3 The specific implementation method of the composite carrier is the same as that of Preparation Example 1, except that the amount of itaconic acid added in step (2) is 0.85g.

[0028] Preparation Example 4 The specific implementation method of the composite carrier is the same as that of Preparation Example 1, except that the amount of sodium carbonate added in step (3) is 0.6g.

[0029] Preparation Example 5 The preparation steps of the composite carrier are as follows: (1) Mix 20g of attapulgite, 3g of polyglutamic acid and 180mL of deionized water, adjust the pH to 7.5, grind (ball-to-material ratio of 10:1, rotation speed of 300r / min, 30min) and shake (temperature of 25℃, rotation speed of 180r / min, 1h), let stand to settle and discard the supernatant, crush to 100 mesh to obtain pre-modified attapulgite; (2) Mix 10g of the pre-modified attapulgite from step (1) with 200mL of deionized water, then add 0.7g of itaconic acid and 0.04g of N,N′-methylenebisacrylamide and mix by shaking (temperature 25℃, speed 180r / min) for 0.8h, then add 0.015g of ammonium persulfate, heat to 68℃ under nitrogen atmosphere, react for 5h with stirring, wash 3 times with anhydrous ethanol and dry to obtain the composite carrier.

[0030] Preparation Example 6 The microbial improver contains the following raw materials in parts by weight: 3 parts high-protein raw material powder, 2 parts compound enzyme, 0.5 parts fungal powder, 1 part plant growth regulator, 12 parts compound carrier and 25 parts water.

[0031] The preparation steps of the microbial modifier are as follows: The microbial improver is obtained by mixing high-protein raw material powder, compound enzyme, fungal powder, plant growth regulator, compound carrier and water at 30°C until homogeneous.

[0032] The composite carrier used in this preparation example was obtained from Preparation Example 1.

[0033] Preparation Example 7 The specific implementation method of the microbial modifier and its preparation steps is the same as that of Preparation Example 6, except that the composite carrier used in this preparation example is obtained from Preparation Example 2.

[0034] Preparation Example 8 The specific implementation method of the microbial modifier and its preparation steps is the same as that of Preparation Example 6, except that the composite carrier used in this preparation example is obtained from Preparation Example 3.

[0035] Preparation Example 9 The specific implementation method of the microbial modifier and its preparation steps is the same as that of Preparation Example 6, except that the composite carrier used in this preparation example is obtained from Preparation Example 4.

[0036] Preparation Example 10 The specific implementation method of the microbial modifier and its preparation steps is the same as that of Preparation Example 6, except that the composite carrier used in this preparation example is obtained from Preparation Example 5.

[0037] Preparation Example 11 The specific implementation method of the microbial modifier and its preparation steps is the same as that of Preparation Example 6, except that in this preparation example, attapulgite clay is used to replace the composite carrier in an equal amount.

[0038] Example 1 A method for microbial modification of rare earth waste residue includes the following steps: S1 - Pretreatment of rare earth waste residue: Select rare earth beneficiation waste residue with pH of 7~9 and remove large impurities. S2 - Raw material mixing: Add 1.3% of the mass of the microbial modifier to the pretreated rare earth waste residue from step S1 and mix thoroughly until homogeneous; S3 - Microbial Improvement: The mixture from step S2 is piled into a heap with a height of 1.2m and fermented at 28℃ for 5 days to obtain microbially improved rare earth waste residue.

[0039] The microbial modifier used in this embodiment was obtained from Preparation Example 6.

[0040] Example 2 A method for microbial modification of rare earth waste residue includes the following steps: S1 - Pretreatment of rare earth waste residue: Select rare earth beneficiation waste residue with pH of 7~9 and remove large impurities. S2 - Raw material mixing: Add 0.5% of the mass of the microbial modifier to the pretreated rare earth waste residue from step S1 and mix thoroughly until homogeneous; S3-Microbial Improvement: The mixture from step S2 is piled into a heap with a height of 1m and fermented at 30℃ for 3 days to obtain microbially improved rare earth waste residue.

[0041] The microbial modifier used in this embodiment was obtained from Preparation Example 6.

[0042] Example 3 A method for microbial modification of rare earth waste residue includes the following steps: S1 - Pretreatment of rare earth waste residue: Select rare earth beneficiation waste residue with pH of 7~9 and remove large impurities. S2 - Raw material mixing: Add 2% of the mass of the microbial modifier to the pretreated rare earth waste residue from step S1 and mix thoroughly until homogeneous; S3 - Microbial Improvement: The mixture from step S2 is piled into a heap with a height of 1.5m and fermented at 25℃ for 7 days to obtain microbially improved rare earth waste residue.

[0043] The microbial modifier used in this embodiment was obtained from Preparation Example 6.

[0044] Example 4 A method for microbial modification of rare earth waste residue, the specific implementation method is the same as that in Example 1, the difference being that the microbial modifier used in this example is obtained from Preparation Example 7.

[0045] Example 5 A method for microbial modification of rare earth waste residue is described, with the specific implementation method being the same as in Example 1, except that the microbial modifier used in this example is obtained from Preparation Example 8.

[0046] Example 6 A method for microbial modification of rare earth waste residue, the specific implementation method is the same as that in Example 1, the difference being that the microbial modifier used in this example is obtained from Preparation Example 9.

[0047] Example 7 A method for microbial modification of rare earth waste residue is described, with the specific implementation method being the same as in Example 1, except that the microbial modifier used in this example is obtained from Preparation Example 10.

[0048] Example 8 A method for microbial modification of rare earth waste residue is described, with the specific implementation method being the same as in Example 1, except that the microbial modifier used in this example is obtained from Preparation Example 11.

[0049] Example 9 A method for microbial modification of rare earth waste residue, the specific implementation method is the same as in Example 1, the difference being that the mass ratio of pretreated rare earth waste residue to microbial modifier in this example is 1:0.025.

[0050] Performance testing (1) The organic matter content of each rare earth waste residue after the improvement of Examples 1-9 and the rare earth waste residue raw material without microbial improvement were used as control groups. (2) Under the moisture conditions (50% water content) of each rare earth waste residue after the above-mentioned improvements in Examples 1-9, record the time required for the corresponding water to completely evaporate in order to characterize the water retention capacity. The specific test results are shown in Table 1.

[0051] Table 1

[0052] As shown in Table 1, the experimental data of Examples 1-3 and the control group indicate that the organic matter content of the rare earth waste residue repaired by the microbial modification method of the present invention is significantly increased. Comparing Example 4 with Example 1, the change in the amount of polyglutamic acid added slightly reduces the organic matter content and water retention capacity. This may be because excessive polyglutamic acid competes with itaconic acid during polymerization, affecting the formation efficiency of the three-dimensional network structure. Comparing Example 5 with Example 1, the change in the amount of itaconic acid added may lead to excessive cross-linking, resulting in excessively high cross-linking density and excessively small network pore size in the polymer's three-dimensional network structure. This restricts the free diffusion and storage space of water molecules and inhibits the effective loading and synergistic effect of various active components in the carrier network, thus affecting the organic matter retention capacity and water retention capacity. The following are examples of improvements: Example 6, compared to Example 1, shows that the amount of sodium carbonate added changes, which may disrupt the hydration layer structure formed by the hydrophilic polymer, reducing the binding capacity of the hydrogen bond network to water molecules, making water more easily evaporate and lose, and the organic matter content also decreases slightly; Example 7, compared to Example 1, shows that without further compounding with sodium carbonate, the improvement effect decreases to varying degrees due to the influence of the composite carrier's structural stability and adsorption capacity; Example 8, compared to Example 1, shows that when commercially available attapulgite is used to replace the composite carrier in equal amounts, the organic matter content and water retention capacity of the improved rare earth waste residue decrease, and the effect is significantly insufficient; Example 9, compared to Example 1, shows that when the mass ratio of the pretreated rare earth waste residue to the microbial improver changes, the improvement effect is limited.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for microbial modification of rare earth waste residue, characterized in that, Includes the following steps: S1 - Pretreatment of rare earth waste residue: Select rare earth beneficiation waste residue with pH of 7~9 and remove large impurities. S2 - Raw material mixing: Add microbial modifier to the pretreated rare earth waste residue from step S1 and mix thoroughly until homogeneous; S3-Microbial Improvement: The mixture from step S2 is piled into a heap with a height of 1-1.5m and fermented at 25-30℃ for 3-7 days to obtain microbially improved rare earth waste residue.

2. The method for microbial improvement of rare earth waste residue according to claim 1, characterized in that, The microbial improver comprises the following raw materials in parts by weight: 1-5 parts high-protein raw material powder, 0.5-3 parts compound enzyme, 0.1-1 parts fungal powder, 0.1-2 parts plant growth regulator, 10-15 parts compound carrier, and 10-30 parts water.

3. The method for microbial improvement of rare earth waste residue according to claim 2, characterized in that, The high-protein raw material powder is one or more of soybean meal powder, duckweed powder, and fish meal.

4. The method for microbial improvement of rare earth waste residue according to claim 2, characterized in that, The complex enzyme is a mixture of protease, cellulase, and β-glucanase.

5. The method for microbial improvement of rare earth waste residue according to claim 2, characterized in that, The fungal powder is one or more of the following: *Trichoderma viride* powder, *Geotrichum candida* powder, *Aspergillus oryzae* powder, *Dendrobium moss* powder, and *Rhizocystis radicans* powder, with a viable count ≥ 1 × 10⁻⁶. 8 CFU / g.

6. The method for microbial improvement of rare earth waste residue according to claim 2, characterized in that, The plant growth regulator is fulvic acid and / or brassinolide.

7. The method for microbial improvement of rare earth waste residue according to claim 2, characterized in that, The preparation steps of the composite carrier are as follows: (1) Mix attapulgite, polyglutamic acid and deionized water, adjust the pH to 7-8, grind and shake for 1-2 hours, let stand to settle and discard the supernatant to obtain pre-modified attapulgite. (2) Mix the pre-modified attapulgite from step (1) with deionized water, then add itaconic acid and N,N′-methylenebisacrylamide and mix by shaking for 0.5-1h, then add an initiator, heat to 65-70℃ under an inert atmosphere, react for 4-6h with stirring, and then wash and dry to obtain the modified attapulgite. (3) The modified attapulgite and sodium carbonate from step (2) are mixed and added to deionized water. After shaking and mixing for 1-2 hours, the supernatant is discarded after standing and settling. The mixture is then ground and sieved to obtain the composite carrier.

8. The method for microbial improvement of rare earth waste residue according to claim 7, characterized in that, In step (1), the mass ratio of attapulgite clay to polyglutamic acid is 1:(0.05-0.2).

9. The method for microbial improvement of rare earth waste residue according to claim 7, characterized in that, In step (2), the mass ratio of the pre-modified attapulgite to itaconic acid is 1:(0.06-0.08).

10. The application of rare earth waste residue modified by the microbial modification method according to any one of claims 1-9 in the fields of mine reclamation or landscaping.

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