Date of Award

12-2023

Document Type

Campus Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences

First Advisor

Karen H. Johannesson

Second Advisor

Robert Chen, Crystal Schaaf

Third Advisor

Helen Poynton, Brian Haley

Abstract

We conducted batch absorption experiments to examine the adsorption of the 14 naturally occurring lanthanides and yttrium (Y) onto synthetic goethite (-FeOOH). Following convention, we refer to these elements collectively as the rare earth elements (REEs) and yttrium, or REY for short. Results of the experiments show that the middle REYs (MREE) and heavy REYs (HREE) are preferentially absorbed onto goethite compared to the light REYs (LREE). Yttrium has an ionic radius nearly identical to holmium (Ho) and consequently exhibits chemical properties and behavior like the HREEs. The adsorption data were employed to develop a surface complexation model (SCM) for REYs onto goethite using the generalized double-layer model formalism. The surface complexation species consisted of the weak and strong sites for the free metal ion ( ≡FeOREY^(2+)) and the weak site for the carbonado (≡REYCO_3^+). The SCM predicts REY adsorption onto goethite from pH 2.5-10.5, has been developed, and successfully simulates the sorption of REYs. Combining experimental data coupled SCMs will be highly beneficial to further understanding REY in diagenetic environments (e.g., Equatorial Pacific Basin). Therefore, we also conducted batch absorption experiments to examine the REY in marine sediment cores collected from the south of Hawaii at a water depth > 5000 m. The results of the experiments show that the middle REYs (MREE) and heavy REYs (HREE) are preferentially absorbed onto stations 3 and 4 (STD3 & STD4) compared to the light REYs (LREE). Yttrium has an ionic radius nearly identical to holmium (Ho) and consequently exhibits chemical properties and behavior like the HREEs, with positive Y anomalies reflected in STD3 and station 5 (STD5). The adsorption data were employed to develop a surface complexation model (SCM) for REYs onto these marine sediments using the generalized double-layer model formalism. The surface complexation species consisted of the weak and strong sites for the free metal ion ( ≡FeOREY^(2+)) and the weak site for the carbonado (≡REYCO_3^+). The SCM predicts REY adsorption onto pacific sediments from pH 3-10, has been developed, and successfully simulates the sorption of REYs.

Comments

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