Urban mining by flash Joule heating

Bing Deng,James M Tour,Zhe Wang,Emily A Mchugh,Carter Kittrell,Duy Xuan Luong

doi:10.1038/s41467-021-26038-9

Abstract

Precious metal recovery from electronic waste, termed urban mining, is important for a circular economy. Present methods for urban mining, mainly smelting and leaching, suffer from lengthy purification processes and negative environmental impacts. Here, a solvent-free and sustainable process by flash Joule heating is disclosed to recover precious metals and remove hazardous heavy metals in electronic waste within one second. The sample temperature ramps to ~3400 K in milliseconds by the ultrafast electrical thermal process. Such a high temperature enables the evaporative separation of precious metals from the supporting matrices, with the recovery yields >80% for Rh, Pd, Ag, and >60% for Au. The heavy metals in electronic waste, some of which are highly toxic including Cr, As, Cd, Hg, and Pb, are also removed, leaving a final waste with minimal metal content, acceptable even for agriculture soil levels. Urban mining by flash Joule heating would be 80× to 500× less energy consumptive than using traditional smelting furnaces for metal-component recovery and more environmentally friendly.

Highlights

Precious metal recovery from electronic waste, termed urban mining, is important for a circular economy
The metals in e-waste were heated and evaporated by ultrahigh-temperature flash Joule heating (FJH), the metal vapors were transported under vacuum and collected by condensation
The printed circuit board (PCB) was ground to small powder and mixed with carbon black (CB), which served as the conductive additive (Fig. 1b, inset)

Summary

Introduction

Precious metal recovery from electronic waste, termed urban mining, is important for a circular economy. The sample temperature ramps to ~3400 K in milliseconds by the ultrafast electrical thermal process Such a high temperature enables the evaporative separation of precious metals from the supporting matrices, with the recovery yields >80% for Rh, Pd, Ag, and >60% for Au. The heavy metals in electronic waste, some of which are highly toxic including Cr, As, Cd, Hg, and Pb, are removed, leaving a final waste with minimal metal content, acceptable even for agriculture soil levels. Compared with directly leaching e-waste raw materials, by leaching the residual solids after FJH, the recovery yield is significantly improved with tens of times increase for Ag and few times increase for Rh, Pd, and Au. The toxic heavy metals, including Cd, Hg, As, Pb, and Cr, could be removed and collected, minimizing the health risks and environmental impact of the recycling process

Methods

Results

Conclusion