Abstract:
The exponential growth of electronic waste (e-waste) has become a critical environmental
concern, requiring innovative approaches for resource recovery. Among the valuable metals
contained within the e-waste, copper holds particular significance due to its abundance and
widespread application in electronic devices. Traditional extraction methods often involve
environmentally detrimental processes and become ineffective in complex metal mixtures,
leading to the necessity of selective, greener methods. Deep eutectic solvents (DES) can be
defined as a class of solvents formed by the combination of two or more components, which have
been reported as alternative solvents for various applications, with hydrophobic deep eutectic
solvent (HDES), those that are immiscible with water, being reported as an innovative alternative
solvent for extractions from water. The primary aim of the project is to evaluate the effect of using
HDESs for the extraction of copper from complex aqueous electronic waste streams and use this
understanding to improve the extraction system. 24 HDESs were assessed for their ability to
extract copper from both a pure copper sulfate solution and a mixed metal e-waste lixiviant.
While high copper removal from the mixed metal solution could be obtained with lidocaine based
HDES, these formed a precipitate which contained a complex mixture of metals, likely as a result
of the formation of metal complexes with lidocaine and carboxylate ligands. The HDES
methyltrioctylammonium chloride : decanoic acid (N8881Cl : C10A) was found to be the most
effective at extracting copper from the aqueous electronic waste stream without forming a
precipitate. The molar ratio of the N8881Cl : C10A HDES system had a surprisingly large impact
on extraction efficiency, with the optimal hydrogen bond acceptor : hydrogen bond donor
(HBA:HBD) molar ratio of 2:1. A model was proposed for the molar ratio dependence of the
extraction. Further, attempts to optimize the extraction conditions using DOE were unsuccessful
with the optimized conditions proposed by the model not leading to the highest extraction yield.
An attempt at the electrodeposition of copper and the recycling of the HDES was made. Finally,
further investigation is required to elaborate the mechanisms dominating the copper extraction
and optimize extraction conditions for enhanced metal extraction efficiency. By approaching a
sustainable solution to copper extraction and recovery from e-waste, this study contributes to
advancing the field of resource recovery and environmental sustainability not only limited in
metal but other material recycling.