Semester

Spring

Date of Graduation

2025

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Edward Sabolsky

Committee Co-Chair

Terence Musho

Committee Member

Konstantinos Sierros

Abstract

The efficient recovery of critical metals such as tantalum (Ta), manganese (Mn), gallium (Ga), and indium (In) from electronic waste (e-waste) is essential for resource sustainability and environmental protection. This research uses microwave-assisted treatment to investigate the carbothermal reduction of these four specific metals from their oxides in a simulated e-waste mixture, with carbon black serving as both a microwave coupling and reduction agent. Microwave processing is used specifically because it offers a rapid and energy-efficient alternative to conventional thermal methods, with the benefits of intrinsic heating and selective heating of materials. The first experiments centered on understanding the effects of carbon weight and packing density on the heating rate and maximum achievable temperature under a variable microwave input power. It was found that the carbon black used was highly efficient as a heating agent when in powder form as opposed to a pellet, demonstrating a 45% increase in temperature achieved. The carbon powder also heated 6 times quicker than pellets and had an 80% energy conversion rate when input power was increased, proving it to be an effective internal heating source for the experiments. Once the microwave coupling of carbon black was characterized, the carbon powder was mixed with the individual target oxides at various loadings and heated up to the specific reduction temperatures that were priorly established using a designed Ellingham diagram. The products of the reactions were analyzed using XRD analysis to determine the reduction efficiency and product composition. In the final phase, oxides were combined with carbon powder in stages: first, a binary mixture of Ta and Mn oxides representing tantalum capacitors, and second, a complex blend of all four oxides, simulating typical e-waste composition. The experimental matrix for the final phase consisted of staged heating and time holds at reduction temperatures. The results demonstrated that the metal oxides reduce to lower forms that include carbides, lower valence oxides and pure metals, though challenges such as hot-spot formation, temperature measurement accuracy, and atmospheric control were noted for further optimization. In conclusion, this thesis offers a comprehensive investigation into the microwave assisted carbothermal reduction of critical metal oxides derived from e-waste. The study demonstrates the effectiveness of microwave-assisted carbothermal reduction for recovering these metals in the form of lower oxides, carbides, alloys, or pure metals. By recovering these valuable metals, this approach contributes significantly to a more circular economy and reduces reliance on primary resource extraction.

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