Time-Resolved Structural Analysis of Heavy Metal Cation Exchange Reactions in Anionic Clay and Manganese Oxide Nanoparticles

Heaney

EAR-0125908

Anionic clays and manganese oxides occur abundantly as nanocrystalline coatings on soil and sediment particles in surficial environments. They exhibit a remarkable facility for exchanging ions dissolved in aqueous fluids and act as major traps for anions and cations. The investigators of this proposal will apply a novel crystallographic approach to resolve mechanisms of cation exchange in layered double hydroxide and Mn oxide materials. Powdered samples will be monitored by synchrotron X-ray diffraction during the process of cation exchange. These experiments will yield the first time-resolved analyses of the structural distortions that occur to accommodate substitutions by transition metals in low-temperature minerals. Additionally, in concert with high-temperature infrared spectroscopy, synchrotron XRD analyses will be performed as samples are heated, allowing the structural manifestations of thermal decomposition to be correlated with cation exchange capacity.

These studies will allow the investigators to capture intermediate transition steps that are overlooked by a more conventional static analysis of final run products. As the structural perturbations that are associated with chemical substitutions tend to stabilize the exchanged phases, these studies will indicate which factors limit the degree of exchange for selected cations. Consequently, these experiments will suggest approaches to the design of new remediation materials with amplified exchange characteristics.