Potential- und Stromoszillationen an Pyrit-Elektroden in sulfidischer Lösung

Abstract

The anodic oxidation of pyrite in alkaline sulfide solution at room temperature leads to regular current-potential oscillations at potentials of about 0.5 V. The potentials oscillate with a frequency between ν=8.4ċ10−2 s−1 and ν=1.45 s−1 in the range of 0.2 V to 0.7 V. The higher potential is accompanied by a decrease of the current from 30 mA to 15 mA. Stirring of the solution doesn’t change the characteristics of the oscillations. The oscillations stop by increasing the temperature at roughly 50°C at the lower potential or by decreasing the temperature at roughly −5°C at the higher potential.. A potential of about 0.5 V on the pyrite electrode results in the formation of a surface layer of iron(III) sulfide. This layer is relatively passivating; the potential increases and the current decreases. Subsequently, the layer of iron(III) sulfide decomposes into iron(II) sulfide and disulfide ions, and a new oscillation cycle begins. Iron(III) sulfide is stable at temperatures below 0°C and doesn’t exist at temperatures above 50°C. Therefore, no oscillations are observed at temperatures higher than 50°C and lower than −5°C..