(537b) Treatment and Extraction of Copper from Electronic Waste Via Induced Morphological Changes Utilizing Supercritical CO2

The management of electronic waste (e-waste) has become a significant challenge faced by humanity. Globally, 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. 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 also used and involves large amounts of corrosive acids. As the amount of e-waste grows, the availability of easily mineable elements, particularly metals, decreases, disturbing the overall material cycle. Thus, new, environmentally-friendly approaches to recover valuable components from e-waste are urgently needed. This study focuses on the use of supercritical CO₂ (scCO₂) and sulfuric acid, 2 M H₂SO₄, as a novel solvent system for the treatment of e-waste, specifically in the extraction of copper. 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 composites, which reduced the complexity of PCB, the effects of scCO₂ in the solvent system were investigated. The results showed that scCO₂ and acid induced a permanent morphological change in the polymer component, creating voids and causing delamination. This finding was translated to the actual waste PCB system and a novel two-step process was developed. This two-step process involved the pre-treatment of small pieces of waste PCB with scCO₂ and 2 M sulfuric acid at 120 °C and 148 atm for 30 minutes followed by leaching of the pre-treated PCB in a solvent containing 2 M H₂SO₄ and 0.2 M H₂O₂ at ambient conditions.Experimental results showed that 82% of the copper contained in the PCB was extracted in under 4 hours. The characterization of the PCB demonstrated that the pre-treatment with scCO₂ and acid induced the crystallization of the plastics (polymer component), creating pores and weakening the structure of the PCB, thus enhancing transport of the solvent to the buried metal interfaces. This novel process utilizing scCO₂ minimizes intensive physical processing (e.g. grinding of the PCB) and reduces acid usage during the extraction of Cu from e-waste, presenting a greener alternative to the current methods of recycling of metals from e-waste, which tend to be energy-intensive and hazardous.