A study on extraction of rare earth elements from end-of-life electronic waste using environmentally benign organic acids

The increasing volume of electronic waste and the growing demand for rare earth elements (REEs) underscore the need for sustainable and scalable resource recovery technologies. The objective of this study was to develop and evaluate an integrated slow pyrolysis and organic-acid leaching process for the selective recovery of REEs from end-of-life printed circuit boards (PCBs), while assessing its scalability and environmental performance. Thermogravimetric analysis of PCB size fractions ranging from 75 to 600 μm indicated that the major decomposition of polymeric components commenced at 260 °C and approached completion near 600 °C. Accordingly, a pyrolysis temperature of 550 °C was selected for the subsequent batch processing of pulverised PCBs. Slow pyrolysis effectively decomposed epoxy resins and halogenated flame retardants, yielding a metal–rich solid residue. Ultimate (CHNS) analysis showed that approximately 64% of hydrogen, 22.4% of carbon, and 29.4% of nitrogen were removed during pyrolysis, with a substantial fraction of the organic mass transferred to the condensed pyrolysis oil and gas. Gas chromatography revealed that the pyrolysis gas became increasingly hydrogen–rich as the temperature increased from 400 to 550 °C, accompanied by a decline in C 2 – C 4 hydrocarbons due to enhanced secondary cracking. X–ray fluorescence analysis confirmed silicon, aluminium, copper, and bromine as the dominant inorganic constituents, consistent with the glass–fibre–reinforced and metal–rich nature of PCBs and the presence of brominated flame retardants. Leaching experiments, in 100 mL batch mode, using environmentally benign organic acids demonstrated distinct differences in REE extraction efficiency. Although citric (tri–carboxylic) and maleic (di–carboxylic) acids showed high extraction efficiencies, mono–carboxylic acetic acid consistently achieved superior REE recovery. Under optimal conditions (2 M acetic acid, 90 °C, 1:80 solid–to–liquid ratio, 10 min), >99% of Nd was recovered, a performance that was successfully replicated and scaled up at the 30–L reactor scale, while Dy and Y exhibited lower recoveries. The high selectivity, rapid kinetics, and effectiveness of environmentally mild reagents indicate that this combined pyrolysis − leaching approach provides a scalable and environmentally responsible pathway for recovering critical REEs from PCB while generating energy dense gaseous and liquid by–products.