BIOSYNTHESIS OF SELF-INCORPORATED METAL-GRAPHITIC COMPOSITES FROM ELECTRONIC WASTE USING Eleocharis acicularis

Abstract

The consumer demand for strategic elements such as cobalt, indium, lithium, and rare earth elements has been constantly on the rise in the past decade. Due to market volatility and supply-chain disruption, the recovery of strategic elements from secondary sources, such as electronic waste (e-waste), has received substantial attention globally. The current e-waste recycling and metal recovery methods consume considerable amounts of energy and chemicals, resulting in large environmental footprints. The use of biological systems, including bacterial leaching and hyperaccumulator plants, offers alternative techniques to mitigate adverse environmental impacts by reducing chemical and energy consumption and gaseous emissions. Here, we used a hyperaccumulator plant, Eleocharis acicularis, to extract strategic elements such as indium, cobalt, lithium, and rare earth elements (europium, neodymium, erbium, gadolinium, and yttrium) directly from e-waste slurries or aqueous solutions. E.acicularis was shown as a superior candidate for its metal bioaccumulation capacity from e-waste slurries and its tolerance to extreme environmental and operational conditions for the first time. The plant biomass, having a high concentration of incorporated metals, was used as a carbon-rich precursor to synthesize value-added metal-graphitic composites. The objective was to develop a cradle-to-cradle biology-based system to synthesize novel value-added carbon-metal composites and recover strategic elements from secondary sources. Indium-, lithium-, cobalt-, and gadolinium-graphitic materials had higher conductivity than commercial graphite. Indium-graphitic material had high thermal stability, and gadolinium-graphitic materials had significant paramagnetic properties. Rare earth-graphitic material maintained a stable capacitance between 100Hz to 300kHz, making it a potential capacitor for high-frequency applications. The optical properties of the metal-graphitic material were also comparable to the commercial graphite. Additionally, we characterized the economic viability and environmental implications of this process via two scenarios, baseline and optimized. The baseline scenario was assumed to be the process of recovering indium from Liquid Crystal Display (LCD) screen slurry and subsequent pyrolysis for indium-graphitic material synthesis. The optimized scenario was a hypothetical derivative of the baseline scenario that might allow for improved sustainable practice. The costs and global warming potential (GWP) of the optimized scenario were also compared to processes of graphite synthesis and indium recovery in acidic leachate. Overall, the comparison demonstrated that biomass-based resource recovery and graphite synthesis could provide a low-cost and sustainable alternate technique for recovery and remanufacturing.