PNNL

Abstract

Nitrilotriacetamides are an emerging class of extractants that have been identified as promising candidates for a variety of separation schemes. Systems incorporating these ligands are prone to third-phase formation at high loading, but this can be mitigated by increasing the alkyl chain length or adding a phase modifier (e.g., 1-octanol). In this work, the impacts of these modifications on HNO3 extraction, H2O extraction, and physiochemical properties (interfacial tension, viscosity, and density) are examined. The studies show that ligand alkyl chain length has very little impact on HNO3 and H2O extraction, whereas the addition of 10% octanol significantly increases extraction of both HNO3 and H2O. Viscosity and interfacial ten-sion are impacted by HNO3 concentration, alkyl chain length, and the presence of phase modifier but remain in a range that should be compatible with commonly used solvent contacting equipment. Additional studies of physiochemical properties at variable ligand concentration suggest that a change in aggregation occurs above approximately 10-50 mM ligand. Thermodynamic modeling of distribution ratios and spectroscopic studies aimed at understanding speciation in the presence of HNO3 are also reported. These experiments suggest that the first equivalent of extracted HNO3 interacts with both the central amine and carbonyl groups of the ligand. The spectroscopic changes at higher HNO3 concentrations are relatively minor, suggesting additional HNO3 is associated in an outer-sphere manner