Gold recovery from secondary waste of PCBs by electro-Cl2 leaching in brine solution and solvo-chemical separation with tri-butyl phosphate

In the present study, sustainable recycling of gold from the secondary stream of waste printed circuit boards using brine leaching with electro-Cl-2 and solvo-chemical strategies was investigated. More than 99% of gold was leached in 2.0 mol.L-1 NaCl solution at pH, 1.0; electro-Cl-2 rate, 0.62 mmol min(-1); temperature, 50 degrees C; and time, 75 min. The kinetic data best fitted to the logarithmic model, while activation energy (16.3 kJ mol(-1)) indicated an intermediate-controlled leaching process. Results corroborated with the solution chemistry and reaction thermodynamics of the AueNaCl-(electro)Cl-2 system could reveal the stepwise reaction mechanism. In-situ generated Cl-2(g) first dissolved in a brine solution that forming Cl-2(aq), which subsequently converted to NaClO and diffused on gold particles to liberate the gold-chloro complex. Gold from the brine leach liquor was quantitatively separated using 0.5 mol.L-1 TBP at pH((eq)) = 0.5 and O:A = 1:1. The formation of ([HAuCl4 center dot 2TBP center dot H2O) over bar complex through the ion-pair solvation into the organic phase was supported by advanced spectral analysis. Finally, a highpurity gold with >99% efficiency was stripped by contacting the Au-loaded organic phase with 0.2 mol.L-1 thiosulfate solution; however, using the same concentration of thiourea yielded only a 94% efficacy. This study successfully eliminates the use of highly toxic lixiviants (like aqua-regia and cyanide) in gold metallurgy along with the regeneration and reusable benefits of the organic solvent (TBP). (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study investigated sustainable recycling of gold from the secondary stream of waste printed circuit boards using brine leaching with electro-Cl-2 and solvo-chemical strategies. The gold leaching efficiency reached over 99% under specific conditions, and the study successfully eliminated the use of highly toxic lixiviants in gold metallurgy while promoting the regeneration and reusability of the organic solvent TBP.