abstract
Hydrophobic eutectic solvents (HES) emerged as promising substitutes to the conventional organic phase used in the solvent extraction (SX) of metal ions due to the avoidance of diluents and the suppression of third-phase manifestation. However, HES present a highly structured liquid phase defined by hydrogen-bonded interactions such that intercomponent interactions are expected to play a greater role in SX using HES compared to a diluted extractant solution. In this work, the extraction of lanthanides from nitrate media by the non-ideal solvent composed of decanoic acid (C10OOH) and trioctylphosphine oxide (TOPO) was determined as a function of the lanthanide cation selection, HES molar fraction, HNO3 concentration, and temperature. Through the systematic variation of these parameters, the delicate balance between complexation and solvent reorganisation and its influence on the extraction and metal selectivity is determined by metal partition experiments, time resolved fluorescence and Raman spectroscopy, and small-angle X-ray scattering (SAXS). A compromise between maximum Ln3+ loading and selectivity was observed, driven by the variation in the quantity of weakly H-bonded TOPO and the change in the configurational entropy of the mixture. All results point towards the need to explicitly consider the HES phase structuration and its compositional changes with solute co-extraction on the Ln3+ extraction as no change in the extracted complex speciation was observed across all tested conditions. The C10OOH + TOPO was used as a model system due as lanthanide extraction using TOPO and carboxylic extractants is well described whilst the phase diagram and properties of the eutectic are reported. Nevertheless, the derived conclusions are translatable to other systems and can help guide the design and application of possible HES combinations for SX.
keywords
N-OCTYLPHOSPHINE OXIDE; RARE-EARTH-METALS; TRIOCTYLPHOSPHINE OXIDE; TRIVALENT LANTHANIDES; LANTHANOID(III) IONS; MOLECULAR-DYNAMICS; INDIUM EXTRACTION; WEAK-INTERACTIONS; ORGANIC PHASES; THERMODYNAMICS
subject category
Engineering
authors
Favero, UG; Schaeffer, N; Passos, H; Cruz, KAML; Ananias, D; Dourdain, S; Hespanhol, MC
our authors
Duarte Ananias
Assistant Researcher
Helena Isabel Sousa Passos
Junior Researcher
Nicolas Schaeffer
Assistant ResearcherProjects
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
CICECO - Aveiro Institute of Materials (UIDP/50011/2020)
Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)
acknowledgements
This work was partly developed within the scope of the project CICECO-Aveiro Institute of Materials, UIDB/50011/2020, UIDP/50011/2020, and LA/P/0006/2020, financed by national funds through the FCT/MCTES. This work was supported by the Instituto Nacional de Ciencias e Tecnologias Analiticas Avancadas (INCTAA) /Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq) [grant number 465768/2014-8] ; Fundacao de Amparo a Pesquisa do Estado de Minas Gerais (FAPEMIG) [grant number CEX-PPM-00585-17] ; CNPq [grant number 305649/2021-3, 131790/2020-0] ; Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES) /Fundacao para a Ciencia e Tecnologia (FCT) [grant number 88881.309048/2018-01] ; CAPES [grant number 88882.437092/2019-01] .