Leaching rate of hematite in hydrochloric acid solutions in agitated vessel

A kinetic study on the leaching of Fe₂O₃ in HCl solutions has been made by using agitated vessel to clarify the mechanism of the rate acceleration which was found in the previous study for Fe₂O₃-HNO₃ system. Powder specimens with various sizes were prepared by a wet classification of ground powder obtained from pellets sintered at 1623 K (I) and 1523 K (II). The specific areas of these specimens were measured before and after the leaching experiments. Leaching rates were found to be independent of the agitation speed. Leaching rates under various conditions were correlated by the following relationship: r = 20.0(1+5.4α^1.6) S_w0 exp (-94000/RT)C_H(+)C_Cl(-), where α is the fraction dissolved, S_w0 the initial specific area of the specimen, T temperature, C concentration of ionic species. As seen in the above correlation, the leaching rate increased with increasing α. In order to clarify the mechanism of the rate acceleration, a leaching experiment was carried out by using a sintered Fe₂O₃ disk of which surface was polished and exposed to a HCl solution. Same as the previous study, only the (0001) oriented crystal planes were found to dissolve and its dissolution rate increased with time. The fractional area of the (0001) plane was about 25%. Assuming the same fractional area for the powder specimen, the increase in the overall surface area was well estimated.