Abstract
Light-emitting diode (LED) lamps are rapidly replacing fluorescent lamps in the global lighting market. Consequently, the generation of end-of-life LED waste is increasing, driven by premature loss of luminescence and repair-unfriendly product designs. Waste LED lamps are known to contain significant concentrations of strategic and critical metals, including gallium, rare earth elements, and various base metals. Recovering these materials can support circular economy objectives, promote material conservation, and mitigate environmental risks associated with hazardous components in LED waste.
A range of extraction routes, including pyrometallurgy, hydrometallurgy, and biohydrometallurgy, have been investigated for gallium recovery from waste LEDs. Pyrometallurgical approaches have demonstrated high gallium recovery efficiencies; however, their reliance on elevated processing temperatures results in substantial energy consumption. In contrast, hydrometallurgical studies on gallium extraction from waste LEDs remain scarce and underexplored. This is largely attributed to the inherently low leaching efficiency of conventional wet-chemical methods, as gallium predominantly occurs in LEDs as gallium nitride (GaN), a chemically refractory compound with strong resistance to acid attack.
In this work, several hydrometallurgical approaches were systematically evaluated to improve understanding of the wet chemistry governing gallium dissolution from GaN-containing LED waste. Rather than emphasizing recovery yields, the study focuses on identifying key barriers, limitations, and common misconceptions encountered during leaching experiments, to inform future process development. Multiple inorganic and organic lixiviants were examined in combination with various oxidizing agents, including sulfuric acid, hydrochloric acid, oxalic acid, citric acid, gluconic acid, ferric sulfate, ferric chloride, copper chloride, and hydrogen peroxide. In addition, the effectiveness of advanced oxidative systems and highly aggressive leaching media, such as the Fenton process and aqua regia, was assessed for gallium dissolution. Analytical barriers in Ga measurement with ICP-OES are detailed. The performance of common acidophilic bacteria (Acidithiobacillus ferrooxidans and thiooxidans) was compared with the above-mentioned acids.
The findings provide practical insights into the fundamental challenges associated with hydrometallurgical processing of GaN and highlight critical considerations for the design of more sustainable and effective gallium recovery routes from waste LEDs.