Title

Geochemical Behavior of the Rare Earth Elements in Natural Terrestrial Waters

Date of Award

Spring 2005

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean/Earth/Atmos Sciences

Program/Concentration

Oceanography

Committee Director

Karen H. Johannesson

Committee Director

David J. Burdige

Committee Member

G. Richard Whittecar

Abstract

This dissertation presents three manuscripts describing the following aspects of the geochemical behavior of REEs: (1) solution complexation of REEs with both inorganic and organic ligands in natural terrestrial waters; (2) the geochemical behavior of REEs along the groundwater flow paths in two different aquifer types (i.e., sand vs. carbonate); and (3) surface complexation behavior of REEs in the Carrizo Sand aquifer. In the first manuscript, a solution complexation model of REEs, which includes both inorganic and organic ligands, was developed from an existing code (Humic Ion-Binding Model V; Tipping, 1994). To a first approximation, the role of naturally occurring dissolved organic matter in the speciation of REEs in natural terrestrial waters was evaluated by a modeling approach. The model predicts that organic complexes are the dominant forms for dissolved REEs in bulk river waters draining the continents and are insignificant for a “model” groundwater. The second manuscript thoroughly described the concentrations, fractionation patterns, and speciation of REEs along groundwater flow paths in both sand and carbonate aquifers. The study results show, due to different controlling factors, the concentrations of REEs along groundwater flow paths are different in these two different types of aquifers. However, REE fractionation behaviors are similar in both aquifers and can chiefly be explained by the solution and surface complexation behaviors of REEs. The third manuscript investigated the adsorption behavior of REEs onto Carrizo sand by batch experiments. Experimental data show that REE adsorption onto Carrizo sand increases with increasing atomic number across the REE series. For each REE, adsorption increases with increasing pH. REE adsorption was not sensitive to ionic strength and total REE concentrations at our experimental conditions. However, competitive cations in solution would weaken REE adsorption, especially for LREEs at low pH values. Based on the experiment results, a surface complexation model for REE adsorption onto Carrizo sand was developed. The batch experimental data and the model results indicate that REE was adsorbed onto Carrizo sand not only as free metal ions but also as aqueous dicarbonato complexes in Carrizo groundwaters when pH is above 7.3.

DOI

10.25777/t1mq-xy51

ISBN

9780542157523

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