Strategies to Enable a Circular Economy in the Electronics Industry: Electrochemical Recovery of Metals

Abstract

<p>Advanced electronics and the clean energy industries increasingly rely on rare earth and specialty metals (e.g., yttrium, osmium, and indium; RESE). This may cause a bottleneck effect where demand for these metals cannot keep up with supply from primary extraction alone. Furthermore, few management strategies exist across the life cycle, leading to low recycling rates of less than 1% and little to no reuse of materials. These factors have led the U.S. Department of Energy to label these metals as “critical”, with respect to their importance to clean energy. </p><p>The goal of this thesis was to target the problem of material criticality and provide specific scientific advancements needed to mitigate this issue to enable a circular economy within the electronics industry. After identifying these needs across the life cycle, it was apparent that the manufacturing and end-of-life stages were where technological contributions could have the biggest impact. In response to this need, I then focused on building a device capable of recycling RESE for direct reuse in industrial manufacturing. </p><p>First, I outlined the technical objectives and advancements needed across the electronics life cycle to enable a closed-loop system. Here, I focused on detailing tasks including: (1) design devices for disassembly, (2) materials for substitution, (3) manufacturing processes that enable the use of recycled materials, (4) fabrication efficiency, (5) technology interventions to enable e-waste recovery, (6) methods to collect and separate e-waste components, (7) technologies to digest and recover RESE, and (8) technologies to separate commercially desirable, high-purity outputs. </p><p>Second, I developed a technology to tackle one of these necessary advancements, which was developing a device to recycle RESE from industrial waste streams. The objective was to build a technology capable of selectively recovering and separating RESE on individual filters to enable direct reuse. Here, I successfully built a carbon nanotube (CNT)-enabled filter device that electrochemically recovered and separated RESE from bulk metals, recovering them as metal oxides. I also detailed the mechanism of recovery, which was determined to be an oxygen reduction mechanism, and separation was based on hydroxide stability. </p><p>To increase the selectivity of the device, I then tested redox mediators (i.e., organic molecules that facilitate electron transfer and redox equilibrium) in the system to obtain direct metal reduction to reclaim zero-valent metal instead of metal oxides. Here, the goal was to develop a method to separate these metals based on their reduction potentials instead of their hydroxide stabilities. Results indicated that these mediators did not transfer electrons to the metals as anticipated, but instead were binding to the metals themselves, or were transferring the electrons to the oxygen, providing another pathway for enhanced oxide deposition.</p><p>Next, a variety of metal recovery techniques were tested to reclaim the metals off the CNT filters to provide metals for reuse in industrial manufacturing. Here, solution-based and solid-based methods were utilized, with acid washing and full filter combustion giving the highest recovery values, near 100%. Metal selectivity between acids indicated potential for further separation capability. Finally, my observations from the other chapters identified many key design modifications needed to enable the successful scale up of this technology. Here, I detail the specific designs modifications needed and provide rationale for each.</p><p>The contributions from my work include providing specific scientific advancements needed to enable a circular economy in the electronics industry, as well as providing a technology to recover and separate RESE from mixed metal streams. I also detail other strategies to further advance this technology, as well provide a detailed outline of design modifications needed for scale up. This set of work provides motivation and an outline of research needed to encourage academia and industry to pursue work in this critically important field.</p><p>Overall, this technology could offer several advantages including: enhanced recovery of high-value specialty minerals using low-cost CNT filters, reduced need for mining Earth-rare minerals in politically unstable or environmentally undesirable locations, and reduced emissions of toxic elements or nascent industrial minerals that have yet unknown toxicities or environmental impacts.</p>