Time-resolved scattering and diffraction studies of mineral reactions
The formation and transformation of minerals occurs within a wide variety of terrestrial, marine, freshwater and crustal environments, including soils, aquifers and hydrothermal systems. Examples of the types of reactions that occur within these environments include the crystallisation of clay minerals during aquifer diagenesis, zeolite formation under hydrothermal conditions and the nucleation and growth of nanoparticulate ferric oxyhydroxides in soils. These processes occur on a wide variety of time-scales from seconds to years and are often key components of the geochemical cycle within their respective environments. Quantifying the kinetics and mechanisms of these reactions using in situ measurements can be challenging due to the wide variety of chemical and physical environments in which they occur. The development of beamlines and ends station at synchrotron sources in the UK and across the world now provide facilities to perform in situ time-resolved studies on a wide variety mineral reactions.
This lecture will describe the use of synchrotron radiation to conduct time resolved in situ measurements on mineral reactions using a variety of techniques including Powdered X-ray Diffraction (PXRD), Energy Dispersive X-Ray Diffraction (EDXRD) and Small and Wide Angle X-ray Scattering (SAXS/WAXS). We will review the information that can be obtained using these techniques, data analysis protocols and theories useful for extracting kinetic and mechanistic information from the data. In addition, we will discuss the use and specification of environmental cells used to perform different types of experiments including stopped-flow cells, hydrothermal synthesis apparatus, high temperature reaction furnaces and chemostat systems. Finally, examples from a number of case studies characterising reactions in a variety of mineral systems will be examined e.g. zeolites, iron oxides, sulphide minerals and hydrated silicate phases.