Electrochemical methods to measure gold leaching current in an alkaline thiosulfate solution

Rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE) were employed to measure leaching current of gold in an alkaline thiosulfate solution. First, the leaching current was determined with the help of RDE by measuring currents around the open circuit potential (ocp) and applying the mixed potential theory. The leaching current measured by this method may have contribution from another parasitic reaction such as oxidation of the leaching reagent. Therefore, a second method that employs RRDE was applied to verify that the leaching current measured at the RDE represents the gold dissolution reaction. In this approach gold was used for the disk and the ring was made of a glassy carbon. The gold ions produced at the disk during the leaching reaction were reduced at the ring. The collection efficiency allowed then to calculate the rate of gold ions production at the disk from the measured ring current. The leaching currents measured using this procedure were in excellent agreement with currents measured using RDE and the mixed potential theory confirming that the leaching currents measured by the first method were free of parasitic reactions and could be used as a measure of gold dissolution rate.