Dissolution of hematite in acidic oxalate solutions

The dissolution of hematite in acidic oxalate solutions has been studied under various experimental conditions. The effect of temperature, oxalate concentration and pH on hematite dissolution were studied. In order to study the effect of atmospheric oxygen and light on the dissolution reaction, experiments were carried out in an inert atmosphere (purging with argon), in an 'oxidising atmosphere' (without purging), in the presence of visible light and in darkness. It was found that the dissolution process is much faster in an inert atmosphere under visible light. The dissolution process in all other cases was very slow, including a characteristic induction period, attributed to ferrous ion generation in solution through a heterogeneous, time-consuming reductive pathway. In an oxidising atmosphere the dissolution process is seriously retarded due to the oxidation of ferrous to ferric ions by the dissolved atmospheric oxygen. Iron dissolution is highly dependent on temperature and pH of the solution, while it is practically independent of the total oxalate concentration.