Geology Club Seminar
Ion exchange in microporous minerals is a widely used process for industrial and environmental applications, but little progress has been made to predict how each mineral might exchange different cations and what their ionic selectivities will be. As a result, many laborious and time-consuming experiments must be performed to find the optimal mineralogical conditions to sequester a cation of interest. A challenging aspect of predicting ion exchange mechanisms is that the underlying phenomena that control the exchange processes must be empirically determined. Crystal and aqueous solution properties, such as mineral pore size/shape and framework composition and fluid cation concentration gradients, can only describe part of the story. Other mineral properties such as thermal expansion, polyhedral distortion, electronic structure(e.g., Jahn-Teller, crystal field splitting), molecular gate effects, and others also have critical roles in determining cation selectivity. To tackle this problem, I am working on describing the fundamental aspects of ion exchange in a suite of functional titanium and zirconium silicate microporous materials (e.g., zorite, sitinakite, and gaidonnayite) for application toward radioactive waste sequestration, pharmaceutical development, and heavy metal entrapment. I will discuss the capture of cesium, strontium, and rare earth elements by microporous titanium and zirconium silicates using time-resolved techniques such as in situ X-ray diffraction, Raman spectroscopy, neutron scattering, and molecular dynamics simulations, and show that many of these minerals share some fundamental ion exchange properties.