Environmental Molecular Sciences Laboratory

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Unraveling chemical speciation and interfacial dynamics in complex, heterogeneous

Science Theme: 
Date: 
Tuesday, October 15, 2019
Principal Investigator: 
Jian-zhi Hu
Lead Institution: 
Pacific Northwest National Laboratory
Closed Date: 
Wednesday, September 30, 2020
Project ID: 
51194
Abstract: 

We propose to use NMR in combination with computational modeling, to study the conversion of soluble tetrahedral aluminum (Al) species to octahedrally coordinated Al-bearing mineral precipitates under strongly basic conditions typical of high-level nuclear wastes such as those at the Hanford Site. Key to efficient processing of these wastes is the ability to control the reaction mechanisms and kinetics that lead to stable solid precipitates, such as the Al-bearing minerals gibbsite and boehmite, in highly alkaline systems of concentrated electrolytes. We hypothesize that this control can be achieved by (i) manipulating solvation structures of key cations and anions; (ii) understanding solvent dynamics and solute organization; and (iii) determining the extent to which fluid phase dynamics influence pre-nucleation species, nucleation, and interfacial reactivity. We will test this hypothesis by conducting in-situ analyses under conditions of variable solution composition, pH and temperature. The complexity of these wastes is further exacerbated by the addition of megatons of organic compounds, such as glycolate and ethylenediaminetetraacetic acid (EDTA). We further hypothesize that the breakdown products of these organic compounds, such as CO2, HCO3- etc., will affect the reactivity and kinetics of Al tetrahedral to octahedral transformations, through incorporation into the solvation structures of electrolytes.