Marine Science Faculty Publications


The Influence of Solution Chemistry on REE Uptake by Ulva Lactuca L. in Seawater

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Simultaneous uptake of Ce(III), Eu(III), Gd(III), Yb(III), and Zn(II) by an organic substrate, Ulva lactuca L., was examined in seawater. REE behavior was observed to be strongly dependent on solution complexation. Over a range of carbonate ion concentrations between 10−6 mol kg-soln−1 and 7 × 10−3 mol kg-soln−1, the affinity of Ulva lactuca for Gd(III) decreased by approximately two orders of magnitude. The influence of carbonate complexation on REE solid/solution distributions was much larger for Yb(III) than for Gd(III) and was larger for Gd(III) than for Ce(III). At carbonate ion concentrations greater than about 6 × 10−5molkg-soln−1, REE solid/solution partition coefficients, DT(M) = (REEactivityg−1Ulva)/(REEactivityg−1seawater) exhibited the order Ce(III) > Eu(III) > Gd(III) > Yb(III). At carbonate ion concentrations less than about 3 × 10=−5molkg-soln−1, the affinity of Ulva lactuca L. for REEs exhibited the order Eu(III) >Gd(III) >Ce(III) >Yb(III). Our partition coefficient observations are in general accord with shale-normalized REE abundance patterns in seawater. Adsorption by organic substrates can produce heavy REE enrichments in seawater relative to the LREEs, Gd(III) solution enrichments relative to Eu(III), and, at relatively low carbonate ion concentrations, enrichments of very light REEs compared to their immediate neighbors. The behavior of Zn(II) in our study differed considerably from the REEs. The partition of Zn(II) between Ulva and seawater is not strongly dependent on carbonate ion concentration.

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Geochimica et Cosmochimica Acta, v. 54, issue 6, p. 1587-1595