CARBON-PASTE ELECTRODES IN MINERAL PROCESSING - AN ELECTROCHEMICAL STUDY OF SPHALERITE

The electrochemical behaviour of two sphalerite samples with 0.8% and 8.2% iron, respectively, have been studied with the carbon paste elect rode technique. Potentiodynamic sweeps with rotating disc electrodes w ere performed in acidic perchlorate, chloride and sulphate solutions i n the temperature range 23-85 degrees C. In order to investigate the n ature of the overall anodic dissolution reaction of the sphalerite sam ples, chronocoulometry, in combination with atomic absorption spectrom etry was used. The dissolution of sphalerite with 0.8% iron was found to be independent of potential. The dissolution of sphalerite with 8.2 % iron was found to follow a two-electron process at low overpotential s, while a total of 6 electrons were needed at high overpotentials. Th e activation energy was determined as a function of potential. For chl oride solutions the activation energy was found to be 58 +/- 3 kJ/mol at 0.25-0.8 V. At 1.0 V the activation energy was found to be 43 kJ/mo l, indicating a transition to diffusion-controlled reactions. In perch lorate solutions the activation energy was 60 +/- 2 kJ/mol in the enti re potential region studied: 0.25-1 V. In sulphate solutions the activ ation energy was found to be 43 +/- 2 kJ/mol in the region 0.25-0.5 V and 34 +/- 1 kJ/mol at potentials up to 1 V. The results indicate that the rate-determining process changes with the potential and solution composition. A comparison with the result of leaching experiments on t he same minerals is given.