Comprehensive utilization method for multi-source rare earth-containing waste

Abstract

The invention discloses a high-universality and high-integration-level recovery method suitable for waste materials with different sources and different composition rare earth contents and an intelligent system of the high-universality and high-integration-level recovery method. The method sequentially comprises the six steps of mechanical pretreatment, microbiological leaching, deep eutectic / ionic liquid selective extraction, rare earth enrichment, purification and product preparation and tail liquid circulation, and real-time optimization of leaching parameters and separation conditions is achieved through programmable sensing-machine learning closed-loop control. Compared with a traditional acid leaching-solvent extraction technology, the method has the advantages that the total recovery rate (larger than or equal to 95%) and selectivity (Y / Fe separation coefficient larger than or equal to 300) of rare earth elements are remarkably improved, energy consumption is reduced by 30% or above, various solid wastes such as permanent magnets, polishing dust, tailings and waste batteries can be compatible, and green, economical, modularized and self-adaptive rare earth resource regeneration is achieved.

Description

Technical Field

[0001] The present invention belongs to the field of comprehensive utilization of rare earth resources and solid waste treatment, and specifically relates to a method and system for efficiently recovering various types of rare earth waste, integrating mechanical, chemical, biological, and digital technologies. Background Art

[0002] Rare earth elements are metal elements with unique chemical and physical properties due to their unique 4f electron structure. They are widely used in key technical fields such as high-performance permanent magnet materials (such as NdFeB magnets), fluorescent materials, optical glass, hydrogen storage alloys, electric vehicle batteries, wind power generation, electrolytic capacitors, and optical communication devices. They are strategic resources indispensable for modern information technology, green energy, and national defense industries. With the rapid development of industries such as new energy vehicles, wind power, and electronic products, the demand for rare earth materials continues to grow, and the contradiction between supply and demand of rare earth resources has become increasingly prominent.

[0003] In the traditional rare earth mining and smelting processes, there are problems such as serious resource waste, high energy consumption, and heavy pollution. Especially in the mining of ionic rare earths in southern China, a large amount of ammonium salt solution has been used for in-situ leaching for a long time, resulting in serious water pollution and soil degradation. At the same time, with the large-scale retirement of rare earth application products, the quantity of rare earth secondary resources (such as waste permanent magnets, fluorescent powders, battery cathode materials, catalysts, polishing powders, tailings, etc.) has increased rapidly. Statistical data shows that the recycling rate of some rare earth application materials is less than 1%, and a large amount of rare earth-containing waste has not been effectively utilized, which not only causes resource waste but also brings potential environmental pollution risks.

[0004] Most of the existing rare earth recycling technologies continue the traditional hydrometallurgical process, mainly including strong acid leaching and organic solvent extraction processes. For example, in the recycling of NdFeB permanent magnets, hydrochloric acid or sulfuric acid is generally used to leach rare earth elements, and then separation and purification are carried out through extractants such as tributyl phosphate (TBP) or P2O4. Such processes have multiple problems:

[0005] 1) Strong specificity and poor adaptability: For different types of waste (such as permanent magnets and battery powders), independent process flows often need to be designed, lacking unity and modularity capabilities;

[0006] 2) High environmental pollution risk: A large amount of strong acid is used in the leaching process, and the extractant is highly toxic and volatile, which is extremely likely to generate waste gas and waste liquid, increasing the difficulty of treating the three wastes;

[0007] 3) High energy consumption and cost: High-temperature roasting and the use of concentrated acid significantly increase energy consumption and operating costs, which is not conducive to large-scale promotion;

[0008] 4) Long process chain and low automation: There are many operation links, complex control variables, lack of real-time monitoring and optimization means, and the overall efficiency is limited.

[0009] In recent years, with the advancement of the concepts of green chemistry, resource recycling, and intelligent manufacturing, researchers at home and abroad have attempted to adopt some new technologies for the recycling and utilization of rare earths, including:

[0010] 1) Biohydrometallurgy technology: Leaching is achieved through the metabolic action of bacteria or fungi on metal minerals. It has the advantages of mild operation, low energy consumption, and no pollution, and has made progress in the fields of metals such as copper, nickel, and uranium. However, it still faces challenges such as strain screening and leaching efficiency in the rare earth field;

[0011] 2) Deep eutectic solvents (DES) and ionic liquids (IL): As green and designable solvents, they can accurately and selectively extract specific metals by regulating the composition, showing good thermal stability, low vapor pressure, and renewability, and are considered an important direction to replace traditional solvents;

[0012] 3) Integration of physical and chemical methods: Such as the combination of mechanical activation and leaching, selective reduction / oxidation, etc., to enhance the separation effect between rare earths and impurities;

[0013] 4) Digital and intelligent technologies: Real-time process parameters are obtained through online sensors, and the leaching and separation conditions are optimized by combining machine learning and data-driven modeling to enhance the adaptability and controllability of the process.

[0014] Although these emerging methods have their own advantages, it is still difficult for a single technology to simultaneously meet the requirements of waste diversity, process selectivity, environmental protection, and automatic control. Therefore, constructing a "composite" rare earth recycling process system, that is, organically integrating mechanical pretreatment, bioleaching, green solvent extraction, and digital control technologies, is the key development direction for the future utilization of rare earth secondary resources. This process can achieve the goals of "wide raw material adaptability, good pollution control, high recovery rate, and low energy consumption cost". Especially when facing industrial waste with complex sources and large component differences, it can provide a more flexible solution.

[0015] In summary, the existing technologies still have obvious deficiencies such as poor adaptability, insufficient greenness, and lack of intelligent control in the process of rare earth recycling. There is an urgent need to develop a new rare earth recycling method and system with high versatility, high selectivity, environmental friendliness, and self-adaptive ability to achieve the efficient, safe, and sustainable treatment of various rare earth wastes. The present invention is proposed under this background, aiming to construct an innovative rare earth recycling and utilization technology system integrating "multi-source adaptation - hybrid process - green solvent - intelligent optimization". Summary of the Invention

[0016] The object of the present invention is to overcome and solve the huge environmental burden brought about by rare earth mineral mining and the increasing problem of waste rare earth-containing materials. A rare earth recovery method and system that can simultaneously process various rare earth wastes, reduce the consumption of chemical reagents, and have an adaptive control ability are provided, including the following steps.

[0017] S1. Mechanical pretreatment. Crushing, ball milling or jet milling is used to make the particle size of the waste ≤ 100 μm. Air classification is used to remove low-value inorganic impurities to improve the subsequent leaching efficiency.

[0018] S2. Microbial leaching. Acidithiobacillus ferrooxidans and a bacteria-fungi complex system are used as leaching strains; the pH is maintained at 1.8 - 2.2, the temperature is 30 ± 2 °C, and aeration is 0.5 vvm; through the bacterial oxidation of Fe 2+ / S 2- to generate H + and complexing agents to achieve in-situ destruction of rare earth-oxide / metal bonds.

[0019] S3. Deep eutectic / ionic liquid selective extraction.

[0020] After adjusting the Fe 3+ content in the leaching solution to ≤ 0.1 mol·L-1, it is contacted and extracted with the hydrophobic quaternary ammonium phosphate ionic liquid [P 66614 [Cl] or chiral DES (ChCl / oxalic acid 1:1); a multi-stage countercurrent process is adopted, and after extraction saturation, it is back-extracted with a weakly acidic nitric acid-ethanol system to achieve a rare earth enrichment multiple ≥ 30.

[0021] S4. Rare earth enrichment and purification

[0022] The enriched solution is oxidized and precipitated (H2O2 / H2O2-NH3·H2O) to generate RE(OH)3, and calcined at 750 °C to obtain the main product RE2O3; associated metals such as Fe and Al are separated by adjusting the pH, sequential precipitation or electrodeposition.

[0023] S5. Tail liquid recycling and reagent recovery

[0024] DES / IL is regenerated by vacuum distillation - water washing, and the recycling rate ≥ 95%; the mother liquor is recycled by electrodialysis for strain cultivation and mineralized carbon dioxide conversion to achieve near-zero emissions.

[0025] S6. Digital monitoring and machine learning optimization

[0026] Online probes for ORP, pH, conductivity, UV-Vis and an ICP-OES rapid detection module are installed in the process; a parameter-yield prediction model based on XGBoost is used, combined with an improved Bayesian optimization algorithm to adjust key variables such as the solid-liquid ratio, aeration volume, and phase ratio in real time to achieve adaptability to different wastes.

[0027] The beneficial effects of the present invention are as follows:

[0028] (1) The method developed in the present invention has high generality, and one process is adaptable to more than 10 kinds of rare earth-containing raw materials such as magnet powder, tailings, dust, and spent battery electrodes.

[0029] (2) The method developed in the present invention is green and low-carbon, without strong corrosive inorganic acids and IL / DES can be recycled, and the carbon emission is reduced by 40% compared with the existing acid leaching-extraction route.

[0030] (3) The method developed in the present invention has high selectivity and high recovery rate. The total rare earth recovery rate ≥ 95%, and the separation coefficient from the main associated metals is increased by 2-3 orders of magnitude.

[0031] (4) The method developed in the present invention has adaptive intelligent control. ML-driven reduces the average debugging time from 3 days to 6 hours.

[0032] (5) The method developed in the present invention has modular and scalable characteristics. Each sub-module can be upgraded or replaced separately, and is applicable to a production capacity of 10 t / a - 10000 t / a. Detailed implementation mode

[0033] The technical solution of the present invention will be described in detail below. However, it is necessary to point out here that the following embodiments are only for further illustration of the present invention, and cannot be understood as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention still fall within the protection scope of the present invention.

[0034] Example 1

[0035] Retired fan NdFeB permanent magnet

[0036] S1. Mechanical pretreatment

[0037] (1) Take 500 g of retired rotor magnet and crush it with a liquid nitrogen embrittlement machine to <1 cm;

[0038] (2) Planetary ball milling (ZrO2 tank, ball:material = 6:1) at 400 rpm for 120 min, dry method

[0039] (3) Air classification to obtain d 50 ≈25 μm powder.

[0040] S2. Biological leaching

[0041] (1) Prepare a slurry in a 5 L glass-lined PTFE reactor, with a solid-liquid ratio of 200 g·L -1 ;

[0042] (2) Inoculate *A. ferrooxidans* and *A. niger* (live bacteria = 1×10 8 mL -1 ) at a volume ratio of 1:3;

[0043] (3) Control the pH at 1.9, temperature at 30°C, stirring speed at 400 rpm, and aeration rate at 0.6 vvm;

[0044] (4) Online ORP > 650 mV, Fe 3+ ≤0.08 mol·L -1 ;

[0045] (5) After 72 h, filter. The RE in the leaching solution is 3+ = 23.6 g·L -1 , and the leaching rate is 96.8%.

[0046] S3. IL extraction

[0047] (1) Take 2 L of the leaching solution and treat it with [P 66614 \[Cl] in a 4-stage countercurrent microchannel mixer (residence time 45 s) at O / A = 1:1;

[0048] (2) After phase separation, the RE loading in the organic phase is 115 g·L -1 .

[0049] S4. Stripping and enrichment

[0050] (1) Use 0.8 mol·L -1 HNO3 + 20 vol% ethanol, O / A = 1:2, 2-stage countercurrent;

[0051] (2) The RE in the enrichment solution is 3+ ≈68 g·L -1 , and the enrichment multiple is 34 times.

[0052] S5. Precipitation and roasting

[0053] (1) At 60°C, add 30% H2O2 dropwise to adjust the ORP > 700 mV;

[0054] (2) Add 25% NH3·H2O to adjust the pH to 9.5 and keep warm for 30 min;

[0055] (3) Filter, dry at 60°C, and roast at 750°C for 2 h to obtain 114.2 g of RE2O3 product with a purity of 99.92%.

[0056] S6. Recycling

[0057] The IL is subjected to vacuum distillation at 65°C and washed with water; the recovery rate is 96.4%, and the attenuation in 50 batches is < 2%.

[0058] Key indicators: Dy / Nd separation coefficient 530; specific energy consumption 3.4 kWh·kg -1 REO; carbon emission 4.1 kg CO2e·kg - 1 REO.

[0059] Example 2

[0060] Phosphate rock tailings (southern ionic type)

[0061] S1. Mechanical / alkalization pretreatment

[0062] (1) Take 5 kg of tailings (Nd 0.20%, Y 0.15%).

[0063] (2) Pre-roast in a blast furnace at 850 °C with 2 wt% Na2CO3 for 30 min to break the phosphate-rare earth lattice;

[0064] (3) After cooling, grind to d 50 ≈35 μm.

[0065] S2. Bioleaching

[0066] (1) Solid-liquid ratio 150 g·L -1 , pH 2.1; single strain of Acidithiobacillus ferrooxidans 1×10 8 mL -1 ;

[0067] (2) 28 °C, 0.4 vvm;

[0068] (3) Collect the liquid after 96 h, Y leaching rate 93.2%, Nd 90.4%.

[0069] S3. DES extraction

[0070] Use ChCl / oxalic acid / urea (1:1:0.5 mol), O / A = 1:1.2, 5-stage countercurrent, contact for 5 min; Y / Nd is enriched in DES.

[0071] S4. Stripping

[0072] (1) 0.6 mol·L -1 HNO3 + 10% methanol, O / A = 1:1;

[0073] (2) Enrichment factor 28 times.

[0074] S5. Precipitation and roasting

[0075] Same as Example 1, product Y2O3 purity 99.8%.

[0076] S6. DES regeneration

[0077] Oxalic acid is recovered by washing with water at 40°C and vacuum evaporation, and the efficiency remains 97% after 10 batches of cycles.

[0078] Example 3

[0079] CeO2 polishing dust

[0080] S1. Pretreatment

[0081] (1) The particle size d of the dust itself 50 ≈3μm, no further grinding is required;

[0082] (2) Dry at 105°C for 4h to remove free moisture.

[0083] S2. Biological leaching

[0084] (1) Solid-liquid ratio 100g·L -1 , pH 2.0;

[0085] (2) Dominated by A.niger fungus, add 1g·L -1 glucose to promote the formation of organic acids;

[0086] (3) Leach for 48h, Ce 3+ 30.8g·L -1 .

[0087] S3. DES extraction

[0088] Same as Example 2, O / A = 1:1, 4 stages; Ce transfer rate 97%.

[0089] S4. Stripping

[0090] (1) 0.5mol·L -1 HNO3 (alcohol-free), 1 stage is enough;

[0091] (3) Enriched liquid Ce 3+ 61g·L -1 .

[0092] S5. Precipitation and roasting

[0093] Add a small amount of excessive oxalic acid to quantitatively precipitate Ce2(C2O4)3·10H2O → 850°C for 2h → CeO2 (specific surface area 4.6m 2 ·L -1 ).

[0094] S6. Recycling

[0095] The extraction rate of DES remains >95% after being reused for 30 batches.

[0096] Example 4

[0097] Scrapped positive electrode of nickel-metal hydride battery

[0098] S1. Pretreatment

[0099] (1) Disassemble 2 kg of batteries, wash with water - dry and then crush to <0.5 mm;

[0100] (2) Use magnetic separation to remove Fe - Ni foil.|

[0101] S2. Bioleaching

[0102] (1) Solid - liquid ratio 250 g·L -1 , pH 2.1;

[0103] (2) 30 °C; 48 h; La 3+ 19.7 g·L -1 , Nd 3+ 4.2 g·L -1 .

[0104] (3) Ni 2+ remains in the solid residue >85%.

[0105] S3. IL Extraction

[0106] (1) [P 66614 \[Cl], O / A = 1:0.8, 3 stages;

[0107] (2) La / Nd migration rate 98%.|

[0108] S4. Back - extraction

[0109] (1) 0.7 mol·L -1 HNO3 / ethanol = 80 / 20 (v / v);

[0110] (2) Enrichment multiple 31 times.

[0111] S5. Precipitation and Calcination

[0112] (1) The same as Example 1;

[0113] (2) La2O3 + Nd2O3 alloy oxide, purity 99.7%.

[0114] S6. Recycling[[ID=,66]]

[0115] The residue is electro - deposited with 2M NH3·H2O - NH4Cl, and the Ni recovery rate is 98.2%.

[0116] Comparative Example 1

[0117] Traditional hydrochloric acid - TBP process (NdFeB)

[0118] S1. Crushing

[0119] 500 g of NdFeB powder (not ball-milled).

[0120] S2. Leaching

[0121] (1) 4 mol·L -1 HCl (30% in excess), stir at 80 °C for 2 h;

[0122] (2) The rare earth leaching rate is 89.1%, and Fe 3+ is 38.5 g·L -1 .

[0123] S3. Extraction

[0124] (1) 30 vol% TBP / kerosene (O / A = 1:1), three-stage stirring clarifier;

[0125] (2) Fe and rare earths are co-extracted, and the separation factor is <10.

[0126] S4. Stripping

[0127] (1) Two stages of deionized water;

[0128] (2) The rare earth concentration is only 6.3 g·L -1 .

[0129] S5. Precipitation

[0130] (1) Precipitate with oxalic acid → calcine at 800 °C;

[0131] (2) The purity of the product RE2O3 is 97.8%.

[0132] (3) 12 kg·t of acid is used -1 , the energy consumption is 5.1 kWh·kg -1 REO, and the carbon emission is 7.4 kg CO2 e·kg -1 REO. Performance test:

[0133] Table 1 Performance test - specific methods and parameters

[0134]

[0135] Table 2 Performance of examples and comparative examples

[0136] Performance Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Total rare earth recovery rate / % 96.8±0.9 92.0±1.1 97.5±0.6 94.6±0.8 85.4±1.3 Separation coefficient α(RE / Fe) 530±15 480±18 260±9 310±12 <10 Energy consumption / kWh·kg-1REO 3.4 3.8 3.2 3.7 5.1 <![CDATA[Carbon emissions / kgCO2 e·kg-1 REO]]> 4.1 4.5 3.9 4.3 7.4 Main XRD phase <![CDATA[Nd2O3]]> <![CDATA[Y2O3]]> <![CDATA[CeO2]]> <![CDATA[(La,Nd 2) O3]]> <![CDATA[Nd2O3+α-Fe]]> Total amount of impurities by ICP - OES / ppm 480 520 360 510 2200

[0137] According to the test results of Comparative Example 1 and Examples 1-4 in Table 2, it can be seen that the process of the present invention achieves high recovery rate, high selectivity, low energy consumption and low carbon emission under different waste types, while the comparative example process has defects such as high acid consumption, poor separation and heavy environmental protection burden, verifying the significant technical advantages and universality of the present invention.

[0138] The above are only the preferred embodiments of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be changed within the scope of the concept described herein through the above teachings or the technology or knowledge in the relevant field. As long as the changes and variations made by those skilled in the art do not depart from the spirit and scope of the present invention, they should all be within the protection scope of the appended claims of the present invention.

Claims

1. A comprehensive utilization method for multi-source rare earth-containing waste materials, characterized in that It includes the following steps carried out in sequence: a) Mechanical pretreatment: Crushing, grinding or jet milling the rare earth-containing solid waste to d 90 ≤ 50 μm; b) Microbial leaching: Under the conditions of pH 1.8 - 2.2 and 28°C - 32°C, an acidophilic oxidation bacteria - fungi complex system acts for 48 - 96 h to obtain a rare earth leaching solution; c) Selective extraction with deep eutectic or ionic liquid: The leaching solution from step b) is contacted with quaternary ammonium phosphate ionic liquid [P 66614 [Cl], or choline chloride-oxalic acid deep eutectic solvent with a molar ratio of 1:1 for 3 - 10 min, and a rare earth-containing organic phase is obtained through 2 - 6 stages of countercurrent extraction; d) Stripping and enrichment: Stripping the organic phase with a 0.5 - 1.0 mol / L nitric acid - ethanol mixed solution to obtain a rare earth enrichment solution, and the rare earth enrichment multiple ≥ 30; e) Purification and preparation: Performing H2O2 - NH3·H2O oxidation - precipitation on the enrichment solution and calcining at 650 - 800°C to obtain a rare earth oxide product; f) Solvent regeneration and tail liquid recycling: Performing vacuum distillation - water washing regeneration on the ionic liquid or deep eutectic solvent, with a recycling utilization rate ≥ 95%, and recycling the mother liquid for strain cultivation after electrodialysis treatment; Among them, the solid - liquid ratio, aeration volume, contact time, and pH in steps a) - e) are detected in real - time by on - line pH, ORP, UV - Vis, and ICP - OES sensors, and closed - loop optimization is realized through machine learning algorithms to adapt to rare earth waste materials from different sources and with different compositions.

2. The method according to claim 1, wherein the waste material to be treated is selected from one or more of permanent magnet powder, polishing dust, phosphate ore tailings, waste nickel - metal hydride battery positive electrode powder, fluorescent powder, or rare earth smelting slag.

3. The method according to claim 1, wherein the mechanical pretreatment employs air classification combined with planetary ball milling, and the resulting particle size d 50 is 10 - 30 μm.

4. The method according to claim 1, wherein the microbial leaching strains are Acidithiobacillus ferrooxidans and Aspergillus niger compounded at a viable cell number ratio of 1:(2 - 5).

5. The method according to claim 4, wherein 0.1 - 0.3 g / L of elemental sulfur is added during the microbial leaching process to maintain the activity of the microbial community.

6. According to the method described in claim 1, wherein the leaching solution is controlled by the Fe 2+ / Fe 3+ ratio before entering step c), and the Fe 3+ concentration is adjusted to ≤ 0.1 mol / L to improve the extraction selectivity.

7. According to the method described in claim 1, wherein the mass fraction of water in the ionic liquid [P 66614 [Cl] is controlled to be 0.1% - 0.5%, and the extraction efficiency decay is ≤ 2% after 50 batches of continuous operation.

8. The method according to claim 1, wherein the deep eutectic solvent is a choline chloride - oxalic acid - urea ternary system with a molar ratio of 1:1:0.

5.

9. The method according to claim 1, wherein the stripping solution is subjected to low - pressure flash evaporation at 5 - 15 kPa to recover ethanol, and the ethanol recovery rate ≥ 90%.

10. According to the method described in claim 1, wherein the calcination process in step e) is carried out in an air atmosphere and kept warm for 2-4 h to obtain rare earth oxide powder with a specific surface area of 3-5 m 2 ·g-1.

11. A rare earth waste recycling system for implementing the method according to claim 1, characterized in that, It includes: Mechanical pretreatment module; Continuous - flow biological leaching reactor with aeration and stirring; Micro - channel static mixing - clarification type liquid - liquid extraction device; Stripping - precipitation - calcination unit; Ionic liquid / deep eutectic regeneration unit; Multi - sensor network signal - connected to the above - mentioned units; XGBoost - based parameter prediction model and improved Bayesian optimization controller.

12. The system according to claim 11, wherein the multi - sensor network includes pH, ORP, conductivity, dissolved oxygen, UV - Vis absorption, on - line ICP - OES, and solid content laser scattering sensors.

13. The system according to claim 11, wherein the controller outputs the optimal solid - liquid ratio, aeration flow rate, stirring speed, and phase ratio that are iterated every 10 seconds and is connected to the PLC through OPC - UA for execution.

14. The system according to claim 11, wherein the liquid - liquid extraction device adopts a micro - channel parallel structure with a residence time of 20 - 60 seconds per stage and a pressure drop < 5 kPa.

15. A rare earth oxide-containing product, characterized in that Prepared by the method according to any one of claims 1 - 10, the total rare earth purity ≥ 99.9%, and the total amount of impurity metals ≤ 500 ppm.

16. The rare earth oxide product according to claim 15, wherein 80% of the particle size (d 80 ) is 0.5 - 1.5 μm, and the specific saturation magnetization is increased by more than 5% compared with the primary ore product.

17. The method according to claim 1 has a carbon footprint (in terms of CO2 equivalent) reduced by ≥ 40% compared to the conventional process using 4 mol / L hydrochloric acid - TBP extraction.

18. According to the method described in claim 1, the energy consumption per unit of rare earth oxide is ≤ 4 kWh·kg-1, and the water consumption is ≤ 2 m 3 ·t -1 raw material.

19. The method according to claim 1, wherein the associated iron is recovered as metallic iron deposit by electrodeposition on a stainless - steel cathode with a recovery rate ≥ 95%.

20. When the method according to claim 1 is applied to the positive electrode powder of spent nickel - metal hydride batteries, the total recovery rate of La and Nd is ≥ 94%, and the recovery rate of nickel by subsequent aqueous electrodeposition is ≥ 98%.

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