(235c) Treatment and Extraction of Metals from Electronic Wastes Using a Novel Solvent Containing Supercritical CO2

The management of wastes, particularly electronic waste (e-waste), has become a significant challenge faced by humanity. The number of discarded computers, phones, and other appliances, often defined as Waste Electrical and Electronic Equipment (WEEE), doubled between 2009 and 2014 to 41.8 million tons per year globally. Currently, e-waste disposal factories tend to recycle the non-toxic, valuable components of e-waste (metals) and release the toxic components into the surroundings via pyrometallurgy (burning). Chemical treatment, known as hydrometallurgy, is an alternative method that involves large amounts of hazardous, corrosive acids. As more and more e-waste is landfilled and disposed, the availability of easily mineable elements, particularly metals, decreases, disturbing the overall material cycle. Therefore, new, environmentally-friendly approaches to recycle and recover valuable components from e-waste are urgently needed. This study focuses on the use of supercritical CO₂ (scCO₂) and piranha acid as a novel solvent system for the treatment of e-waste, specifically in the extraction of metals, such as copper, iron and aluminum. Printed circuit board (PCB) was used as the e-waste of study and is generally composed of 40% metals, 30% plastics, and 30% refractory material. Through the synthesis of metal and polymer model composite particles, which reduced the complexity of PCB, the effects of scCO₂ in the solvent system were investigated. The results suggested that the role of scCO₂ is not the direct extraction of metal from e-waste particles but rather swelling of the polymer (organics) component within the e-waste particles. The swelling of polymers induced permanent morphological changes, and thus, seems to have enhanced the transport phenomena and ultimately improved the kinetics of the metal leaching into the solvent. A transport model was developed for the metal extraction from the complex e-waste particles consisting of layers with distinct organic and metallic components and a kinetics study was performed to gain a fundamental understanding of the multiphase interactions between the scCO₂, acid, and metal/polymer particle matrix. The scCO₂ solvent system was found to be a promising treatment scheme for metal extraction from e-waste with improved environmental sustainability.