From sonotrode to tube transducer for flow-based sonoprocessing: ultrasonically-enhanced metal recovery from electronic waste

Li, Shida (2026) From sonotrode to tube transducer for flow-based sonoprocessing: ultrasonically-enhanced metal recovery from electronic waste. PhD thesis, University of Glasgow.

Abstract

Electronic waste (E-waste) generation reached 62 Mt in 2022, with the total value of technology critical metals (TCMs) amounting to $91 billion. Printed circuit boards (PCBs) and lithium-ion batteries (LiBs), account for 3-5% and 3-4% of the total mass, respectively, and represent two of the most important targets for resource recovery. Traditional recycling routes generally suffer from high energy consumption, limited selectively, and environmental risks. Power ultrasound offers a promising pathway for improving E-waste recycling processes. Improved mass transport and acoustic cavitation mediated effects have demonstrated the ability to enhance material delamination, thereby providing significant potential for green recycling applications.

Deep eutectic solvent (DES)-based ionometallurgical methods offer several advantages, including low-temperature operation, reduced toxicity, and the potential for selective metal recovery. However, their high viscosity leads to limited mass transfer and slow dissolution/delamination kinetics, making it difficult to meet high-throughput processing requirements. Using the delamination of TCM-containing layers from PCB surfaces in Ethaline-DES as a case study, this thesis first demonstrates the intensification effect of power ultrasound on green-solvent recycling processes. By combining sonotrode-induced acoustic cavitation with Ethaline-DES, the delamination rate of TCM was increased by more than thirtyfold compared with passive treatment without sonication.

However, the development of high-throughput applications for sonochemistry and sonoprocessing remains one of the major challenges in ultrasonic engineering. Conventional power-ultrasound devices are typically based on Langevin transducers and are commonly implemented as sonotrodes or ultrasonic baths. This creates an inherent trade-off between cavitation intensity and spatial distribution, limiting the scalability of conventional ultrasonic configurations for high-load and continuous-flow processing.

This thesis presents the first comprehensive study of the development, testing, optimisation and application of a novel tube transducer comprising a single, element radially poled tubular piezoceramic element. The transducer is designed to generate an intense, inward-focused cavitation field within the tube bore. Acoustic measurements, high-speed imaging (HSI), and sonochemiluminescence (SCL) demonstrated that the tube transducer can produce highintensity cavitation throughout the entire bore, with peak activity concentrated along the central axis. Compared with the highly localised cavitation field generated by a conventional sonotrode, this geometry is inherently more suitable for flow-through processing applications.

Graphite delamination from LIB anodes was employed as the primary application case study to evaluate the practical sonoprocessing capability of the tube transducer. Under geometrically comparable conditions, the static tube-transducer configuration achieved higher graphite-delamination efficiencies than a sonotrode for both sheet and flake samples, demonstrating that its broader cavitation field can be translated into improved materials-processing performance.

To investigate flow-based processing, a recirculation system containing three tube transducers in series was designed and constructed. Pulsed excitation was introduced under flow conditions, and the effects of operation duration, processing load, and flow rate on graphite delamination efficiency were systematically investigated. Complete graphite delamination of flake samples was achieved within an operation duration of 2 min. The processable load per unit reactor volume was increased to approximately three times that of the static configuration. Furthermore, the principal limitation at high processing loads was identified as blockage caused by abrupt pipe contractions within the circulation loop, providing a clear direction for future system optimisation and scale-up.

Overall, this thesis demonstrates that transitioning from localised sonotrode-based processing to a modular tube-transducer configuration can effectively mitigate the structural limitations of conventional power-ultrasound systems associated with the trade-off between cavitation intensity and spatial coverage. Through modular integration and series connection, the tube-transducer concept provides a route towards a future continuous-flow sonoprocessing platform. These findings indicate that tube transducer-based sonoprocessing represents a promising and scalable approach for LiB anode recycling and, more broadly, for the sustainable recovery of valuable materials from electronic waste.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Subjects: T Technology > TD Environmental technology. Sanitary engineering; T Technology > TK Electrical engineering. Electronics Nuclear engineering
• Colleges/Schools: College of Science and Engineering > School of Engineering
• Funder's Name: Engineering and Physical Sciences Research Council (EPSRC)
• Supervisor's Name: Prentice, Dr. Paul and Feeney, Professor Andrew
• Date of Award: 2026
• Depositing User: Theses Team
• Unique ID: glathesis:2026-86221
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 09 Sep 2026 16:23
• Last Modified: 09 Sep 2026 16:24
• Thesis DOI: 10.5525/gla.thesis.86221
• URI: https://theses.gla.ac.uk/id/eprint/86221

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