Document Type



Master of Science


Mechanical Engineering

First Adviser

Alparslan Oztekin


Rare earth elements (REEs) are valuable raw materials for various applications in modern high technology industries. For most countries, the majority of REEs are imported from abroad. Therefore, developing an alternative method to produce REEs is significant to the national security of those countries. The extraction of selected REEs from acid mine drainage (AMD) by supercritical CO2 (sCO2) was investigated in this study. The solubility of different ligands in sCO2 has significant impact on the extraction efficiency of REEs. Static equilibrium experiments were performed to measure the solubility of organometallic complexing agent in sCO2. Solid Manganese acetoacetate (Mn(acac)3) was selected to conduct the study of the solubility testing of metallic organic compounds in sCO2 and identify optimal operating conditions for REEs extraction tests. The measurements were conducted at various temperatures of 40℃, 60℃, and 80℃, and in the pressure range from 100 to 200 bar. The results demonstrate that temperature and pressure are essential factors which affect the solubility of the manganese organic compound. Higher the temperature and pressure, higher the solubility it is. Conditions of 80℃ and 200 bar were used to test selected REEs (Ce, La, Nd) organic complexes in the study.

Sodium aluminate (NaAlO2) was verified to be able to fully precipitate the metal components in AMD samples from Blashak Coal Corp. at pH values reaching 13. In addition, dynamic sCO2 experiments were carried out to measure extraction efficiencies of Ce, La, and Nd in sCO2 under conditions of 40℃, 200 bar, with a sCO2 flow rate of 0.104 L/min. The coagulation and complexation processes of AMD samples were investigated before the dynamic sCO2 experiments. Complexes were prepared from the AMD precipitate, using nitric acid (HNO3) and tributyl phosphate (TBP). The overall extraction efficiency of REEs was determined by both the complexation process and the dynamic sCO2 extraction experiment process. For selected REEs, the testing results indicate that light REEs can achieve overall extraction efficiencies in the 40 – 60% range. Larger molecular weights REEs could achieve larger extraction efficiencies. The conditions of the concentration of H ion (H+) in the REEs-HNO3/TBP complex product, the operating temperature and pressure of the system, and the number of extraction cycles were identified to affect the extraction efficiency of REEs in the dynamic extraction experiments. This study provides encouraging result in extracting REEs from AMD using a multi-step process that includes coagulation - complexation - sCO2 extraction. Furthermore, it needed to optimize the process to efficiencies in the 90% range, as well as access the economics of the process.

Available for download on Sunday, May 22, 2022