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

The present paper reports the application of ammonium persulfate ((NH4)(2)S2O8) 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 (S2O82-) and the oxidative sulfate ion (SO42-), 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 systemS(2)O(8)(2)-/O-2 was studied under the addition of oxygen (0.1-1.0 L/min) with (NH4)(2)S2O8 concentration (0.66-131 M), and liquid/solid ratio (15-25 mL/g). Secondly, the system S2O82-/Pressure was evaluated increasing pressure (101-203 kPa) with (NH4)(2)S2O8 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 theS(2)O(8)(2)-/O-2 system and 5 min in the S2O82-/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 S2O82-/Pressure could be applied to release and recover gold from e-waste with an effective reduction of the agent consumption and minimum time. (C) 2017 Elsevier Ltd. All rights reserved.