Despite their importance on Earth and Mars, sulfate minerals have largely escaped notice in the recent flurry of studies regarding alternative mechanisms of solution-mediated mineral precipitation. An exception is calcium sulfate, where experiments have revealed a complex mineralization process involving many different stages and precursors depending on the physicochemical solution conditions. Motivated by these observations, a suite of in and ex situ experimental techniques have been applied to conduct an in-depth study of the formation mechanisms of strontium sulfate, in particular celestine and its meta-stable precursor phase. Experiments at high supersaturations show the formation of a metastable hemihydrate phase. In situ FTIR, XRD, and optical microscopy illustrate how the kinetic persistence of the hydrate is highly dependent upon the local physico-chemical environment, particularly ionic strength and hydrodynamic shear forces. Additionally, in situ Raman and potentiometric monitoring show the transformation reaction from metastable hemihydrate to stable celestine is driven by a dissolution-reprecipitation process. At lower supersaturations, potentiometric co-titrations show evidence for a nanoparticle-aggregation nucleation mechanism during celestine precipitation. Finally, it was found that the critical supersaturation for nucleation varies predictably with supersaturation rate. These results form a detailed picture of nucleation reactions in the SrSO4-H2O system that will serve as the foundation for ongoing work on the effects of confinement on nucleation processes.

Multi-step nucleation in strontium sulfate: Reaction mechanisms and a hemihydrated precursor

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.