The increasing demand for green energy has created great demand for high purity lanthanide elements because of their wide range of applications, such as in permanent magnets, batteries, and high-energy capacitors. Solvent extraction, which transfers ions from aqueous solutions to organic liquid phases with the support of extractant molecules, is widely used to extract and separate lanthanide ions. Because of poor selectivity, hundreds of cycles of solvent extraction are needed to reach industrially relevant purity, which leads to intensive energy and organic solvent usage that contribute to environmental pollution. It is crucial to study the fundamentals of the ion transfer mechanism and ion-extractant interactions during the solvent extraction process to improve the selectivity and make the lanthanide acquisition process more eco-friendly.We have studied the spontaneous complexation of lanthanide ions with floating molecules of dihexadecyl phosphate (DHDP) at the air-water interface with X-ray techniques and isotherm measurements. These studied have revealed that the DHDP monolayer is compressed and forms an inverted bilayer structure at the air-water interface when there is a high concentration (>10-5 M) of heavier lanthanides (Z > 65) in the aqueous subphase. On the other hand, only a monolayer structure is observed with lighter lanthanide elements at any concentration. X-ray fluorescence measurements show that the formation of the bilayer structure doubles the density of the adsorbed ions. We propose that the inverted bilayer structure is advantageous for separating heavier lanthanide elements for two reasons: it is selectively formed with heavier lanthanides, and its hydrophobic surface makes itself easily detachable from the water and transferable to the organic phase. To study the role of the interface structure in the solvent extraction system, the solvent extraction of Er and Nd from the mixture and pure solutions with the same molecule (DHDP) was studied with Inductively Coupled Plasma Mass Spectrometry (ICP-MS). From the mixture extraction samples, a better selectivity of Er over Nd was observed with DHDP compared to the same system but with octdadecyl phosphate (ODP), which forms a monolayer with both Er and Nd. Also, the selectivity during the extraction is enhanced when there is less extractant than needed for complete extraction of the ions present. Faster and better extraction of Er ions compared to Nd ions from the pure solution was observed. This means that interfaces covered with monolayers and bilayers undergo different transport mechanisms, which affects the extraction's kinetics differently.

Creator

• Yoo, Sangjun

DOI

• https://doi.org/10.21985/n2-dc0r-g453

Subject

• Physics

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:16334
• etdadmin_upload_942685

Keyword

• Interfacial structure
• X-rays
• Lanthanide
• Solvent Extraction
• Synchrotron

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright