Invited lecture: Abiotic vs. biotic dissolution of hornblende

In this work, the rates and mechanisms of weathering and Fe release from hornblende were investigated under abiotic and biotic conditions. Under abiotic conditions, the dissolution rate of hornblende increased from pH 6 to 1, and stoichiometry of Fe and Si release rates varied with pH. For biotic experiments, bacteria from an Adirondack soil were isolated that could extract Fe from the hornblende in minimal media. We showed that these bacteria enhanced the release rate of Fe from hornblende over rates in sterile culture, produced low molecular weight organic acids and acidic biofilms, enhanced etching of hornblende underneath biofilms, produced catecholate siderophores, changed the stoichiometry of hornblende dissolution compared to abiotic dissolution, and (perhaps) recycled siderophores for Fe transport. Enhanced Fe release rates from hornblende are also reported for experiments without bacteria but with a commercially available derivative of a natural hydroxamate siderophore added to the solution.