Date of Award

12-2025

Document Type

Thesis

Degree Name

Master of Science (MS)

Degree Statement

Master of Science in Mining Engineering

Department

Department of Mining Engineering

Granting Institution

University of Alaska Fairbanks

Committee Chair

Fan, Long

Committee Member

Ghosh, Tathagata

Committee Member

Farzadnia, Nima

Table of Contents

Chapter 1: Introduction.

1.1 Introduction

1.2 Research objectives

1.3 Thesis outline

Chapter 2: Literature review.

2.1 Coal and coal ash rank

2.2 Fundamentals of Supercritical Carbon Dioxide (SC-CO2)

2.3 Ligand chemistry of SC-CO2 for REE extraction

2.4 Solubility and compatibility of ligands with HNO3 and SC-CO2

2.5 Complex formation between REEs and ligands in SC-CO2

2.6 Role of ligand functional groups in the extraction mechanism

2.7 Influence of water in adducts for extraction

Chapter 3: Methodology.

3.1 Methods and materials

3.2 Apparatus and experimental design

3.2.1 Helium leakage test

3.2.2 Solubility studies

3.2.3 Extraction experimental run

3.2.4 Complex preparation and FTIR analysis

3.3 Analytical techniques employed for characterization (FTIR, UV-vis, ICP-MS)

Chapter 4: Discussion

4.1 Result and discussions

4.1.1 Effects of pressure on CO2 solubility on various TBP: HNO3 ratios

4.1.2 Solubility of CO2 at varying temperatures

4.2 Preliminary REE extraction confirmation/validation

4.2.1 ICP-MS analysis

4.2.2 FTIR analysis for solubility of SC-CO2 in TBP: HNO3 complex

4.3 Thermodynamics and kinetics on REE extraction efficiency

4.3.1 Effect of temperature and pressure on REE extraction efficiency

Chapter 5: Conclusions and future works.

5.1 Conclusions

5.2 Future works

References.

Abstract

This thesis introduced the essence of REE application in the modern world, the primary and secondary sources of REEs. It revised the fundamentals of supercritical carbon dioxide (SC- CO2), its application in REE extraction as green technology, the complex formation of tributyl phosphate (TBP)- nitric acid (HNO3), and temperature-pressure effects in REE extraction. The methodology systematically examined the thermodynamic solubility of CO2 in TBP-nitric acid (HNO3) complexes at three molar ratios (2:1, 1:1, and 1:2), temperatures between 40-60 degrees Celsius, and at a maximum pressure of 12 MPa, respectively. Preliminary extraction experimental runs were conducted to validate solubility studies. Data analysis used mole balance calculations to quantify solubility. In addition, Fourier Transform infrared spectroscopy (FTIR) was employed to clarify the molecular interactions triumphing within the solvent system. The findings of this study showed a robust positive correlation between pressure and carbon dioxide solubility, with a steep increase being observed above the critical pressure of CO2 (about 7.38 MPa). Contrarily, temperature and CO2 solubility showed an inverse relation; for the 1:2 TBP: HNO3 complex, the maximum CO2 absorption was consistently recorded at 40 degrees Celsius across the investigated pressure range. Results from the ICP-MS report confirmed that high solubility favours effective REE extraction, especially Cerium and Neodymium, and a complex ratio of 2:1 resulted in a higher yield of extraction. Consequential spectral shifts in the phosphorylation (P=O) and nitrate (N-O) regions were revealed and detected by Fourier Transform infrared (FTIR) spectroscopy. Conclusively, these research findings revealed that solubility is a crucial mechanism for good extraction performance and have provided valuable thermodynamic understanding that can inform the future development of more environmentally benign and solvent-efficient extraction technologies.

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