Abstract: In this study, we conducted bulk and dynamic experiments to investigate the efficiency of Ce (III) oxidation and fixation by Mn-contained limonite and goethite. Based on experimental results, the mechanism of Ce oxidation and fixation by coexisting iron and manganese, and its geological significance, are discussed. Results of bulk experiments show that Mn-contained limonite has a high performance on the oxidation and fixation of Ce; Ce was totally removed after 48 hours under solution with Ce concentration of 6000 μg/L and limonite concentration of 1 g/L. For experiments with initial Ce concentrations of 300 to 4500 μg/L, Ce removal is positively correlated with Mn content for limonite experiments. As for goethite, it decreased Ce removal when comparing to the control experiments. Results of dynamic adsorption experiments show that for high-Mn limonite, the distribution of Ce is constrained not by Mn minerals, but by iron oxides. The results of this study indicates that: (1) the process of Ce oxidation and precipitation is adsorption of Ce (III) -oxidation of Ce(III) to Ce(IV)-precipitation of Ce(IV) minerals-autocatalytic oxidation of Ce(III) to Ce(IV) by CeO₂, and (2) the contributions of coexisted Mn and Fe oxides to Ce oxidation and fixation are Mn oxides promoting the oxidation of Ce(III) and Fe oxides promoting the precipitation of CeO₂ through electrostatic attraction. This study is significant in explaining the geological phenomenon that although Mn oxides have higher Ce(III) oxidation ability than that of Fe oxides, under Fe- and Mn-oxides coexisting conditions, Ce tends to be fixed by Fe oxides.

Key words: limonite, manganese oxide, goethite, Ce(III), CeO₂, autocatalytic oxidation