The Synergistic Effect of Cu2+ Fe2+ Fe3+ Acidic System on the Oxidation Kinetics of Ag-Doped Pyrite

The impurities contained in the structure of natural pyrite have been reported to introduce variation in its semiconducting properties and oxidation behavior. However, there is no direct study about the effect of specific impurities on the pyrite electrodissolution process kinetics. Among the impurity elements, silver is of particular interest and is often found in natural pyrite. Silver is shown to be capable of catalysis of sulfide mineral dissolution in an acidic environment. In the present study, Ag-doped pyrite was fabricated by a hydrothermal method. X-ray powder diffraction and X-ray photoelectron spectroscopy analyses of the pyrite showed a homogeneous silver distribution in the pyrite. The electrochemical dissolution kinetics of the Ag-doped pyrite were studied in different sulfuric acid electrolytes, with or without the addition of Fe and Cu cations. A variety of electrochemical techniques, including linear sweep voltammetry, cyclic voltammetry, chronoamperometry, and impedance analysis were applied to evaluate the electrochemical response of the pyrite minerals. The experimental results showed a reduced pyrite electrochemical reactivity with increasing Ag content of the Ag-doped pyrites. The exchange current density of the pyrite electrodes in the sulfuric acid electrolytes decreased from 4.0 x 10(-6) to 1.0 X 10(-6) A/cm(2) by increasing the silver content of the pyrites from 138 to 3820 ppm. However, the anodic dissolution of the Ag-doped pyrite electrode showed a substantial increase in the Cu Fe-containing sulfuric acid solution. For instance, 4) of a pyrite electrode with 138 ppm Ag increased from 9.6 X 10(-6) A/cm(2) in the Fe-containing sulfuric acid solution to 2.3 X 10(-s) A/cm(2) in the Fe Cu-containing sulfuric acid solution. In the electrochemical impedance spectroscopy analysis, the Ag-doped pyrite with a higher concentration of Ag showed smaller charge -transfer resistances.