Chemical condition for the appearance of a negative Ce anomaly in stream waters and groundwaters

Abstract

Nine publications showing REE data in groundwaters and river water were examined to understand the general condition of terrestrial water where a negative Ce anomaly develops. It was found that the negative Ce anomaly only appeared when Fe, Mn and dissolved organic carbon (DOC) concentrations were low (Fe and Mn <5 × 10-5 mol/L and DOC < 10 mg/L). Assuming that Ce3+ and Fe2+ concentrations were limited by the formation of cerianite and ferrihydrite, respective redox potential (Eh) was calculated from each of Ce3+ and Fe2+ concentrations. For data sets displaying Ce anomalies, the calculated Ehs (cEhs) showed a 1:1 relationship between Ce and Fe. This relationship indicates that the absolute concentration of Ce in natural water may be thermodynamically determined in situ by Eh and pH when concentrations of Fe, Mn and DOC are poor. Copyright © 2008 by The Geochemical Society of Japan.