Fig. 4: Removal of heavy metals in e-waste by flash Joule heating (FJH) process.

a Vapor pressure–temperature relationships of toxic heavy metals and carbon. b Concentrations of toxic heavy metals in the printed circuit board (PCB). c Concentrations of toxic heavy metals in PCB after FJH. d Removal efficiency and collection yield of heavy metals. The efficiency and yield were the average of three independent FJH experiments (n = 3). e Concentration of Hg in the residues after multiple FJH reactions. f Concentration of Cd in the residues after multiple FJH reactions. The dashed lines in (e, f) represent the starting contents and the approved World Health Organization (WHO) level for safe limits of agricultural soils.