A new look at microbial leaching patterns on sulfide minerals

Leaching patterns on sulfide minerals were investigated by high-resolution scanning electron microscopy (SEM). Our goal was to evaluate the relative c ontributions of inorganic surface reactions and reactions localized by atta ched cells: to surface morphology evolution. Experiments utilized pyrite (F eS2), marcasite (FeS2) and arsenopyrite (FeAsS), and two iron-oxidizing pro karyotes in order to determine the importance of cell typo, crystal structu re, and mineral dissolution rate in microbially induced pit formation. Pyri te surfaces were reacted with the iron-oxidizing bactulium Acidithiobacillu s ferrooxidans (at 25 degreesC), the iron-oxidizing archoeon 'Ferroplasma a cidarmanus' (at 37 degreesC), and abiotically in the presence of Fe3+ ions. In ail three experiments, discrete bacillus-sized (1-2 mum) and -shaped (e lliptical) pits developed on pyrite surfaces within 1 week; of reaction. Re sults show that attaching cells are not necessary fur pit formation on pyri te. Marcasite and arsenopyrite surfaces were reacted with A. ferrooxidans , (at 25 degreesC) and 'F. acidaranus' (at 37 degreesC). Cell-sized and cell -shaped dissolution pits were not observed oil marcasite or arsenopylite at any point during reaction with A. ferrooxidans, or on marcasite surfaces r eacted with 'F. acidarmanus'. However, individual 'F. acidarmanus' cells we re found within individual shallow (< 0.5 <mu>m deep) pits. The size and sh ape (round rather than elliptical) of the pits conformed closely to the sha pe of F. acidarmanus (cells) pits on arsenopyrite. We infer these pits to b e cell-induced. We attribute the formation of pits readily detectable (by S EM) to thr higher rt activity of arsenopyrite compared to pyrite and marcas ite under the conditions the experiment was conducted. These pits contribut ed little to the overall surface topographical evolution, and most likely d id nor significantly increase surface area during reaction. Our results sug gest that overall sulfide mineral dissolution may be dominated by surface r eactions with Fe3+ rather than by reactions: at the cell-mineral interface. (C) 2001 Federation of European Microbiological Societies. Published by El sevier Science B.V. All rights reserved.