O. Pourret, M. Davranche, G. Gruau
Jun 1, 2008
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Quality indicators
Journal
Chemical Geology
Abstract
Abstract Cerium anomaly development in natural waters is commonly related to the mechanism of oxidative scavenging of tetravalent cerium by iron and/or manganese oxides. In this study, a new mechanism for the development of Ce anomalies is described, which combines the oxidation of Ce at high pH by carbonate and the preferential adsorption of Ce(IV) to humic acids. This new mechanism was experimentally elucidated by studying the competition between carbonate and humic acids for complexing rare earth elements (REE). These experiments showed that above pH 8.2, 8.6 or 8.7 (with decreasing alkalinity from 10 − 2 to 10 − 3 mol L − 1 ), Ce(III) is readily oxidized into Ce(IV), which is then preferentially adsorbed onto humic acids. This preferential uptake of Ce results in the development of a negative Ce anomaly (as low as 0.05) in the “truly” dissolved part of the solution (i.e.,