There are a variety of solvent extraction based separation processes under investigation for advanced nuclear fuel cycle development, particularly processes to remove lanthanides from the minor trivalent actinides. A principle defining feature for any new extraction system is the optimization of movement of the target species across the liquid-liquid boundary and into the bulk organic phase. Suitable extractant molecules share the properties of conventional surfactant molecules: a polar “head” for interfacial activity and a greasy “tail” for organic phase compatibility. Such “amphiphilic” molecules display a tendency to mask their bipolar behavior by hiding (via head-to-head interactions in the lipophilic medium) as hydrogen bonded dimers or reverse micelles in the nonpolar organic phase. Their movements and organization of these molecules (and their metal complexes) is of significant interest but challenging to probe. Most methods used to characterize these interactions rely on optical spectroscopy or indirect methods like freezing point depression or vapor pressure osmometry. NMR spectroscopy is a versatile technique that can be used to directly probe organic phases and the interactions occurring in situ without many of the limitations of other techniques. Diffusion Ordered Spectroscopy (DOSY) is an advanced NMR technique used to determine the diffusion coefficients of species by tracking an NMR active nucleus. The diffusion coefficient can be used to infer the size of species in solution. Recent research at WSU has focused on using DOSY to investigate the self-aggregation of extractants along with their interactions with phase modifiers, water, acids, and extracted lanthanide complexes. The results obtained from DOSY are comparable to small angle neutron scattering and the relative ubiquity of NMR makes DOSY a far more accessible technique to smaller institutions. The nondestructive nature of DOSY makes it a versatile tool in organic extractant development and characterization. In this report, recent results featuring the application of DOSY to the characterization of extractants of interest in nuclear separations (and their metal complexes) will be discussed.

Utilizing Diffusion Ordered Spectroscopy (DOSY) to probe organic phases in liquid-liquid solvent extraction systems

253rd National Meeting (2017)

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