Electrowinning of gold from a dilute solution using hydrocyclone-type cell

ABSTRACT The redox reaction mechanism of gold−cyanide [Au(CN)2 −] during hydrocyclone electrowinning was investigated in this work by conducting Hull cell test, potentiodynamic polarization, and computational fluid dynamics (CFD) simulations. A leaching solution of waste printed circuit boards (WPCBs) was prepared as an electrolyte, and the effects of flow rate and applied voltage on the recovery of gold and destruction of cyanide through hydrocyclone electrowinning were investigated. A numerical simulation of the flow field in the cell was performed, and the results were visualized by conducting a finite element analysis in FLUENT. The CFD simulations and Hull cell test showed that the cylindrical cathode region had a flow velocity of ~11.05 m·s−1, which was higher than that at the center of the cylindrical part (<6.45 m·s−1). The optimum conditions for electrowinning were found to be as: an electrode distance of 4.9 mm and a current density of 73.78 mA·cm−2. The anodic polarization results showed that an Ir-based mixed metal oxide (MMO) anode could more efficiently oxidize the free cyanide because of its high current density than other types of anodes (Ir-based MMO: 299.3 mA·cm−2 > SS304: 3.5 mA·cm−2 > Pt-coated Ti: 1.3 mA·cm−2). Through the demonstrated hydrocyclone electrowinning test, the gold concentration could be decreased from 100 to 0.24 mg·L−1 within 12 h while destroying almost total amount of free cyanide in a day.