Characterizing the reactivity of metallic iron in Fe/As-rock/H2O systems by long-term column experiments

The intrinsic reactivity of four metallic iron materials (Fe) was investigated in batch and column experiments. The Fe reactivity was characterized by the extent of aqueous fixation of in-situ leached arsenic (As). Air-homogenized batch experiments were conducted for 1 month with 10.0 g/l of an As-bearing rock (ore material) and 0.0 or 5.0 g/l of Fe. Column experiments were performed for 2 and 3 months. Each dynamic experiment was made up of 2 glass columns in series. The first column contained 2.5 or 5.0 g of the ore material and the second column 0.0 or 5.0 g of a Fe material. Results showed no significant reactivity difference in batch studies for all 4 materials, ZVI2 was by far the most reactive material in column experiments. This observation was attributed to the relative kinetics of production of aqueous As and Fe species under the experimental conditions and their impact on the formation of a protective film on Fe. Accordingly, no protective film could be built at the surface of the least reactive materials. The results corroborated the urgent need for unified experimental procedures to characterize Fe materials.