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

Abstract

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).