EVOLUTION OF HEMATITE SURFACE MICROTOPOGRAPHY UPON DISSOLUTION BY SIMPLE ORGANIC-ACIDS

The surface microtopography of hematite over the course of dissolution in oxalic and citric acids was examined by in-situ and ex-situ atomic -force microscopy. In-situ imaging of the basal-plane surface of a cen timeter-scale natural hematite sample immersed in 2 mM citric acid dem onstrated that the basal-plane surface was relatively unreactive; rath er, dissolution occurred along step edges and via etch-pit formation. Ex-situ imaging of synthetic hematite particles following batch dissol ution in 1 mM oxalic acid showed similar dissolution features on basal -plane surfaces; in addition, etching along particle edges was apparen t. The presence of etch features is consistent with a surface-controll ed dissolution reaction. The results are in agreement with previous in vestigations suggesting that the basal-plane surface is relatively unr eactive with respect to ligand exchange. Both in-situ and ex-situ imag ing of particle surfaces can provide valuable information on the roles of surface structures and microtopographic features in mineral dissol ution.