Controlled electrochemical dissolution of hydrothermal and sedimentary pyrite

Electrochemically controlled pyrite dissolution was performed with three pyrite materials from different geological origins under mixed potential and high overpotential conditions. Both solid electrodes and C paste electrodes of powdered pyrite were used. The rate of pyrite dissolution increased with applied positive potential and was strongly affected by temperature. Current density measurements over the applied potential range successfully described the rate of pyrite dissolution of each pyrite electrode. Controlled dissolution performed under mixed potential conditions on the solid electrodes successfully reflected the same pyrite reactivity and dissolution rate order as in batch reactor dissolution studies with the same pyrite materials. Therefore, the relative reactivity of different pyrite materials can be determined through current density measurements on their solid electrodes under mixed potential conditions. This technique could be a useful tool to compare rapidly the relative reactivity for different pyrite materials. In contrast, electrochemically controlled dissolution studies with C paste electrodes constructed with fine-grained pyrite and paraffin/graphite mixture did not result in accurate ranking of pyrite samples by dissolution rate.