Catch and release: Gold adsorption and sorbent electrochemical regeneration

Mohamed A Ganzoury; Christina M Hanna; Nan Zhang; Yichen Wu; Charles-François de Lannoy

doi:10.1016/j.jhazmat.2023.132721

Catch and release: Gold adsorption and sorbent electrochemical regeneration

J Hazard Mater. 2024 Jan 15:462:132721. doi: 10.1016/j.jhazmat.2023.132721. Epub 2023 Oct 4.

Authors

Mohamed A Ganzoury¹, Christina M Hanna², Nan Zhang¹, Yichen Wu¹, Charles-François de Lannoy³

Affiliations

¹ Department of Chemical Engineering, McMaster University, 1280 Main St. W., Hamilton, ON, Canada.
² Department of Nanotechnology Engineering, Waterloo University, 200 University Ave W., Waterloo, ON, Canada.
³ Department of Chemical Engineering, McMaster University, 1280 Main St. W., Hamilton, ON, Canada. Electronic address: delannoy@mcmaster.ca.

PMID: 37865077
DOI: 10.1016/j.jhazmat.2023.132721

Abstract

Wastewater generated from e-waste leaching is rich in precious metals including gold, silver and platinum. Conventional precipitation and solvent extraction are chemically intensive separations with concerning environmental externalities. Sorbents, in particular carbon nanotubes, have low chemical consumption, and have shown promise for gold adsorption due to their high specific surface area and chemical functionalization potential. However, regenerating sorbents used to adsorb Au is hazardous requiring strong acids. Herein, we delineate the effect of various functional groups on the sidewalls of multiwall carbon nanotubes (MWCNTs) on gold adsorption, and we introduced an acid-free electrochemical technique for Au elution from MWCNTs. Pristine MWCNTs (P-MWCNTs), carboxylic functionalised MWCNTs (COOH-MWCNTs) and amide functionalised MWCNTs (NH₂-MWCNTs) were compared for their affinity for Au adsorption from acidic AuCl₄^-solutions mimicking acidic e-waste leachate. Au adsorption affinity onto MWCNTs followed the order of P-MWCNT > NH₂-MWCNT > COOH-MWCNTs. Au elution from Au-saturated MWCNTs was subsequently achieved up to 65%, using acid-free electrochemical desorption in neutral aqueous brine. The Au electro-desorption was shown to have a direct relationship with both the applied current and the mass of the Au adsorbed on the MWCNTs. This study demonstrates enhanced adsorption-based preconcentration of gold and acid-free regeneration of sorbents.

Keywords: E-waste leachate; Electrochemical regeneration; Functionalised CNTs; Gold adsorption; Precious metals.