Gold recovery from printed circuit boards by selective breaking of internal metallic bonds using activated persulfate solutions

Abstract The present paper reports the application of ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) assisted with oxygen and pressure to recover gold from electronic waste (e-waste). This process suggests the selective breaking of metallic bonds to release gold from its substrate without grinding stages or pollutants generation. Waste printed circuit boards were analyzed to determinate base metals (Ni, Fe, Cu) and gold (Au) using microwave plasma atomic emission spectroscopy. After chemical characterization, aqueous commercial grade ammonium persulfate was used to produce the persulfate anion (S 2 O 8 2− ) and the oxidative sulfate ion (SO 4 2− ), which partially oxidized and leached the base metals breaking the Au Ni Fe Cu bonds and allowing gold to be recovered in its original non-leaching state. The influence of oxygen and pressure in the base metals oxidation and gold recovery were separately studied in two different oxidative systems and evaluated by analysis of variance. Firstly, the system S 2 O 8 2− /O 2 was studied under the addition of oxygen (0.1–1.0 L/min) with (NH 4 ) 2 S 2 O 8 concentration (0.66–1.31 M), and liquid/solid ratio (15–25 mL/g). Secondly, the system S 2 O 8 2− /Pressure was evaluated increasing pressure (101–203 kPa) with (NH 4 ) 2 S 2 O 8 concentration (0.66–1.31 M), and liquid/solid ratio (15–25 mL/g). The recovery of gold was made using optimal conditions and reaction times of 30 min in the S 2 O 8 2− /O 2 system and 5 min in the S 2 O 8 2− /Pressure system. At those reaction times, gold was recovered in its solid state and was analyzed using scanning electron microscopy. The findings presented in this paper suggest that the oxidative reaction produced by the system S 2 O 8 2− /Pressure could be applied to release and recover gold from e-waste with an effective reduction of the agent consumption and minimum time.