Carbon paste electrodes in mineral processing: an electrochemical study of sphalerite

Abstract

The electrochemical behaviour of two sphalerite samples with 0.8% and 8.2% iron, respectively, have been studied with the carbon paste electrode technique. Potentiodynamic sweeps with rotating disc electrodes were performed in acidic perchlorate, chloride and sulphate solutions in the temperature range 23–85°C. In order to investigate the nature of the overall anodic dissolution reaction of the sphalerite samples, chronocoulometry, in combination with atomic absorption spectrometry 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 overpotentials, while a total of 6 electrons were needed at high overpotentials. The activation energy was determined as a function of potential. For chloride 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/mol, indicating a transition to diffusion-controlled reactions. In perchlorate solutions the activation energy was 60±2 kJ/mol in the entire potential region studied: 0.25-1 V. In sulphate solutions the activation 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 the same minerals is given.