Off-campus WSU users: To download campus access dissertations, please use the following link to log into our proxy server with your WSU access ID and password, then click the "Off-campus Download" button below.

Non-WSU users: Please talk to your librarian about requesting this dissertation through interlibrary loan.

Access Type

WSU Access

Date of Award

January 2022

Degree Type


Degree Name



Civil and Environmental Engineering

First Advisor

Timothy Dittrich


The demand of rare earth elements (REEs) is increasing due to their multiple technological applications in communication devices and industrial magnets, among other applications. There are multiple challenges to ensuring a reliable supply of REEs. As a result, the US Department of Energy has classified REEs as a critical vulnerability to US economic security. Current methods for separating and isolating individual REEs utilizes large amounts of organic solvents and 100s to 1000s of individual steps which are complicated and raise concerns over environmental impacts. For these reasons, other sources of domestic REEs are being pursued. Coal fly ash (CFA) is one alternative source of REEs that has received attention as a potentially more environmentally friendly source of REEs. This dissertation addresses several REEs issues: by 1) developing a sorbent media capable of concentrating REEs from CFA leachate with a preference toward the more valuable heavy REEs, 2) concentrating REEs from CFA using fixed bed columns, and 3) separating individual REEs using sequential columns and understanding the functions using complexation and reactive transport modeling. Our process provides an organic solvent-free and environmentally friendly method of extracting and separating REEs. The main results of this research were: (1) the successful development of a bisethyhexylamido DTPA-associated organosilica sorbent media that is capable of binding REEs even with competing elements such as iron and aluminum present in several orders of magnitude higher concentrations, (2) the development of an ash-to-oxide process that extracts REEs from coal fly ash and enriches them from a starting concentration of 0.038 wt% up to >10wt% by using DTPA-associated sorbent media, (3) the development of a sequential extraction technique using a mixed solution of 16 rare-earth elements plus thorium, which was able to separate >90% pure Th and >80% pure Sc solutions in one pass through a packed bed column. Surface complexation modeling and reactive transport modeling with PHREEQC was used to help predict packed bed column performance and interpret how the DPTA ligand interacts with the REEs in various solutions.

Off-campus Download