Material recovery from electronic waste using pyrolysis: Emissions measurements and risk assessment

Abstract

Electronic waste (e-waste) generation has been growing in volume worldwide, and the diversity of its material composition is increasing. Sustainable management of this material is critical to achieving a circular-economy and minimizing environmental and public health risks. This study's objective was to investigate the use of pyrolysis as a possible technique to recover valuable materials and energy from different components of e-waste as an alternative approach for limiting their disposal to landfills. The study includes investigating the potential environmental impact of thermal processing of e-waste. The mass loss and change in e-waste chemicals during pyrolysis were also considered. The energy recovery from pyrolysis was made in a horizontal tube furnace under anoxic and isothermal conditions of selected temperatures of 300 °C, 400 °C, and 500 °C. Critical metals that include the rare earth elements and other metals (such as In, Co, Li) and valuable metals (Au, Ag, Pt group) were recovered from electronic components. Pyrolysis produced liquid and gas mixtures of organic compounds that can be used as fuels. Still, the process also emitted particulate matter and semi-volatile organic products, and the remaining ash contained leachable pollutants. Furthermore, toxicity characteristics leaching procedure (TCLP) of e-waste and partly oxidized products were conducted to measure the levels of pollutants leached before and after pyrolysis at selected temperatures. TCLP result revealed the presence of heavy metals like As, Cr, Cd, and Pd. Lead was found at 160 mg/L in PCBs leachate, which exceeded the toxicity characteristics (TC) limit of 5 mg/L. Liquid sample analysis from TCLP also showed the presence of C₁₀-C₁₉ components, including benzene. This study's results contribute to the development of practical recycling alternative approaches that could help reduce health risks and environmental problems and recover materials from e-waste. These results will also help assess the hazard risks that workers are exposed to semi-formal recycling centers.

Keywords: E-waste recycling; Heavy metals; Metals recovery; Organic pollutants; Pyrolysis; VOC/PAH emission and health risks.

Fig. 1.

Conceptual representation of pollutants emission and exposure from e-waste pyrolysis.

Fig. 2.

Schematic diagram of experimental system for E-waste pyrolysis study.

Fig. 3.

Thermogravimetric analysis results obtained for e-waste components (a) casings, (b) peripheral, and (c) printed circuit boards; and differential thermal analysis, (d) for casings, (e) for peripheral, and (f) for printed circuit boards.

Fig. 4.

Weight loss of e-waste during pyrolysis at selected temperature (a) Casings, (b) peripheral, and (c) printed circuit board.

Fig. 5.

FTIR spectra of e-waste before and after pyrolysis at selected temperatures for electronic components from (a) cell phone casing, (b) keyboard, (c) plastic cable cord, (d) printed circuit board.

Fig. 6.

X-ray fluorescence (XRF) analysis of the chemical composition of showing major elements of (a) printed circuit board from devices different manufactures, (b) effect of pyrolysis temperatures; log scale inserts show the presence of heavy metals at low concentration.

Fig. 7.

Particle emissions from pyrolysis of e-waste at select temperatures (a) electronic plastic casing, (b) plastic desktop cover, (c) plastic cable cord covers, and (d) printed circuit board.

Fig. 8.

Comparison of heavy metal leaching from electronics components (a) casings, (b) peripherals, and (c) printed circuit board; log scale inserts show the distribution of leaching metals at lower concentration.

Fig. 9.

Energy recovery from pyrolysis and burning of e-waste.

Fig. 10.

Hazard quotient of adults chronically exposed to toxic emission of e- aste pyrolysis.