Microwave-Mediated Extraction of Critical Metals from LED E-Waste
Abstract
1. Introduction
2. Materials and Methods
2.1. Microwave-Mediated Processing of LED E-Waste
2.2. Acid Treatment of the Recovered LED Chips
2.3. Characterizations
3. Results and Discussion
3.1. Microwave Separation Mechanism and Materials Characterization
3.2. Acid Leaching of Critical Metals from LED Chips
3.3. Microwave-Mediated Incineration vs. Direct Incineration
- (i)
- Thermal heating reduces the recovery efficiency within the reflective cavity, as some of the LED chip materials deform, adhere, or become trapped, making the separation and extraction of the chip more difficult. In particular, after conventional heat treatment, the LED chip was only partially recovered (with an efficiency of 45%, determined through mass measurements using a five-digit precision scale), with some material remaining trapped in the cavity (Figure 7). In the case of microwave treatment, the LED chip is 100% recoverable, with a mass remarkably close to the expected value of 0.1 mg per LED, leaving the reflective cavity completely empty (Figure 3D).
- (ii)
- Conventional heat treatment causes severe oxidation of the metallic pins into iron oxides, which compromises their structural integrity and renders them non-conductive (Figure 8). Silver can be detected in small amounts using XRF but not in the XRD in this case. When heated in air at 800 °C, the iron core oxidizes, forming a thick iron oxide layer. This layer, along with the fact that silver is present in small amounts, can completely obscure the detection of silver by XRD. Thus, direct heating is less favorable as it does not fully recover the LED chip material and causes irreversible damage to the metallic pins, ultimately reducing the recovery efficiency of the LED components.
3.4. Scalability, Limitations, and Challenges
4. Conclusions
- Microwave irradiation converts the plastic LED lens into a brittle char and weakens chip-to-metal pin bonds, enabling easy mechanical separation;
- A deflagration-like reaction initiated by the microwaves rapidly decomposes the plastic enclosure and enables the release of the LED chip;
- During microwave treatment, the LED chip becomes embedded in the charred lens residue, aiding its recovery;
- Calcination of the charred material produces a solid material containing critical elements such as Ga, As, In, Y, and Au;
- A two-step acid leaching process (aqua regia followed by hot HCl) efficiently extracts valuable metals;
- The method achieves an extraction efficiency of up to 96%, confirming its high effectiveness;
- The process is rapid and scalable, completing component separation in approximately one minute—making it well-suited for industrial recycling applications.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
References
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Element | Elemental Concentrations (% w/w) 1 | Leaching Efficiencies (%) 2 | ||||
---|---|---|---|---|---|---|
PNLED | SMLED | SMLEDH | SMLEDHH | SMLEDH | SMLEDHH | |
Fe | 61.0 | 26.7 | 36.8 | 7 | 100 | |
Ni | 37.0 | |||||
Cu | 10.8 | 0.3 | 98 | 100 | ||
Ga | 2.5 | 3.4 | 6.0 | 9 | 91 | |
As | 1.3 | 327 * | 98 | 100 | ||
Sr | 406 * | 92 * | 704 * | 85 | 93 | |
Y | 0.24 | 0.32 | 10 | 100 | ||
Zr | 202 * | 161 * | 0.1 | 46 | 81 | |
Ru | 269 * | 138 * | 65 | 100 | ||
Rh | 39 * | 100 | ||||
Ag | 1.0 | 1.5 | 0.6 | 614 * | 73 | 96 |
In | 570 * | 142 * | 83 | 100 | ||
Sn | 2.0 | 1.3 | 0.5 | 59 | 99 | |
Ba | 185 * | 40 * | 85 | 100 | ||
La | 140 * | 158 * | 994 * | 24 | 73 | |
Ce | 224 * | 265 * | 20 | 100 | ||
Gd | 344 * | 567 * | 0 | 100 | ||
Au | 1.0 | 1.5 | 100 | 100 | ||
Pb | 426 * | 403 * | 443 * | 36 | 96 |
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Bourlinos, A.B.; Papachristodoulou, C.; Markou, A.; Chalmpes, N.; Giannelis, E.P.; Gournis, D.P.; Salmas, C.E.; Karakassides, M.A. Microwave-Mediated Extraction of Critical Metals from LED E-Waste. ChemEngineering 2025, 9, 47. https://doi.org/10.3390/chemengineering9030047
Bourlinos AB, Papachristodoulou C, Markou A, Chalmpes N, Giannelis EP, Gournis DP, Salmas CE, Karakassides MA. Microwave-Mediated Extraction of Critical Metals from LED E-Waste. ChemEngineering. 2025; 9(3):47. https://doi.org/10.3390/chemengineering9030047
Chicago/Turabian StyleBourlinos, Athanasios B., Christina Papachristodoulou, Anastasios Markou, Nikolaos Chalmpes, Emmanuel P. Giannelis, Dimitrios P. Gournis, Constantinos E. Salmas, and Michael A. Karakassides. 2025. "Microwave-Mediated Extraction of Critical Metals from LED E-Waste" ChemEngineering 9, no. 3: 47. https://doi.org/10.3390/chemengineering9030047
APA StyleBourlinos, A. B., Papachristodoulou, C., Markou, A., Chalmpes, N., Giannelis, E. P., Gournis, D. P., Salmas, C. E., & Karakassides, M. A. (2025). Microwave-Mediated Extraction of Critical Metals from LED E-Waste. ChemEngineering, 9(3), 47. https://doi.org/10.3390/chemengineering9030047