The Influence of Redox Reactions on the Uptake of Dissolved Ce by Suspended Fe and Mn Oxide Particles

Laboratory experiments were conducted to evaluate the partitioning ofrare earth elements (REE) between solution and suspended particles. Becauseof their strong tendency to complex, the REE can be used to study a varietyof marine processes and in particular particle scavenging. In this study, anemphasis was placed on examining abiotic redox processes that influence theuptake of dissolved Ce by particles. Batch sorption experiments wereconducted with REE and synthetic mineral phases over the range of pH4–9. The solutions varied in ionic strength between 0 and 0.7 M andconsisted of individual solutes (NaNO₃, NaCl, andNa₂SO₄), ionic mixtures that duplicate theseawater composition, and natural seawater. The uptake of REE from solutionwas also studied at a Pt electrode coated with using cyclic voltametry. Experimental results are consistent with uptake of dissolved Ce onto occurring by a combination of oxidativescavenging and surface complexation. The contribution of oxidativescavenging to the removal of Ce from solution is most pronounced at acidicpH, where the strictly trivalent REE exhibit little propensity for sorptiononto . Sorption of dissolved Ce onto FeOOH occursin a manner analogous to that of the other strictly trivalent REE and nocontribution from oxidative scavenging is observed on this mineral phase atlow pH. Our work also substantiates the hypothesis that anions in solution,particularly and Cl^-, aswell as those adsorbed on the surface of the particles, influence the extentof Ce uptake by . This revised version was published online in July 2006 with corrections to the Cover Date.