Electrochemical behaviour of the dissolution and passivation of arsenopyrite in 9K culture medium

The behaviour of arsenopyrite (FeAsS) in the acidic iron-free 9K culture medium was investigated using a combination of electrochemical and analytical techniques. The results demonstrated that the oxidative dissolution of arsenopyrite was accompanied by its surface passivation from the beginning of the arsenopyrite dissolution at potentials from OCP to 1000 mV, which limited further dissolution of arsenopyrite. The dissolution was complex and different under different applied potentials. The leaching kinetics of Fe, As and S, as well as the physicochemical properties of the formed passive film, varied with the potentials. A dissolution rate was found to be likely Fe > As > S from FeAsS. The passive film consisted mainly of As2S2 and As2S3 (<= 800 mV), and S-0 (> 800 mV). The passive film was also shown to have a two-layer structure, i.e. a porous outer layer and a compact inner barrier layer that appeared to impart its strongest resistance to the dissolution of arsenopyrite at 750 mV. An applied potential higher than 800 mV could observably improve the dissolution of the film and thus reduce its passivating action.