Finck Nicolas, Dardenne Kathy
Institute for Nuclear Waste Disposal (INE), Karlsruhe Institute of Technology (KIT), P.O. Box 3640, D-76021 Karlsruhe, Germany.
Institute for Nuclear Waste Disposal (INE), Karlsruhe Institute of Technology (KIT), P.O. Box 3640, D-76021 Karlsruhe, Germany.
J Contam Hydrol. 2016 May;188:44-51. doi: 10.1016/j.jconhyd.2016.03.001. Epub 2016 Mar 10.
In this study, we investigated the interaction between selenite and either Fe((II))aq or S((-II))aq in solution, and the results were used to investigate the interaction between Se((IV))aq and FeS in suspension. The reaction products were characterized by a combination of methods (SEM, XRD and XAS) and the reaction mechanisms were identified. In a first experiment, Se((IV))aq was reduced to Se((0)) by interaction with Fe((II))aq which was oxidized to Fe((III)), but the reaction was only partial. Subsequently, some Fe((III)) produced akaganeite (β-FeOOH) and the release of proton during that reaction decreased the pH. The pH decrease changed the Se speciation in solution which hindered further Se((IV)) reduction by Fe((II))aq. In a second experiment, Se((IV))aq was quantitatively reduced to Se((0)) by S((-II))aq and the reaction was fast. Two sulfide species were needed to reduce one Se((IV)), and the observed pH increase was due to a proton consumption. For both experiments, experimental results are consistent with expectations based on the oxidation reduction potential of the various species. Upon interaction with FeS, Se((IV))aq was reduced to Se((0)) and minute amounts of pyrite were detected, a consequence of partial mackinawite oxidation at surface sulfur sites. These results are of prime importance with respect to safe deep disposal of nuclear waste which contains the long-lived radionuclide (79)Se. This study shows that after release of (79)Se((IV)) upon nuclear waste matrix corrosion, selenite can be reduced in the near field to low soluble Se((0)) by interaction with Fe((II))aq and/or S((-II))aq species. Because the solubility of Se((0)) species is significantly lower than that of Se((IV)), selenium will become much less (bio)available and its migration out of deep HLW repositories may be drastically hindered.
在本研究中，我们研究了溶液中硒酸盐与二价铁离子（Fe((II))aq）或硫离子（S((-II))aq）之间的相互作用，并将结果用于研究悬浮液中四价硒离子（Se((IV))aq）与硫化亚铁（FeS）之间的相互作用。通过多种方法（扫描电子显微镜、X射线衍射和X射线吸收光谱）对反应产物进行了表征，并确定了反应机理。在第一个实验中，四价硒离子（Se((IV))aq）通过与被氧化为三价铁离子（Fe((III))）的二价铁离子（Fe((II))aq）相互作用被还原为零价硒（Se((0))），但该反应只是部分反应。随后，一些三价铁离子（Fe((III))）生成了针铁矿（β - FeOOH），并且该反应过程中质子的释放降低了pH值。pH值的降低改变了溶液中硒的形态，这阻碍了二价铁离子（Fe((II))aq）对四价硒离子（Se((IV))）的进一步还原。在第二个实验中，四价硒离子（Se((IV))aq）被硫离子（S((-II))aq）定量还原为零价硒（Se((0))），且反应迅速。还原一个四价硒离子（Se((IV))）需要两个硫化物分子，观察到的pH值升高是由于质子的消耗。对于这两个实验，实验结果与基于各种物种氧化还原电位的预期一致。与硫化亚铁（FeS）相互作用时，四价硒离子（Se((IV))aq）被还原为零价硒（Se((0))），并且检测到微量的黄铁矿，这是表面硫位点部分马基诺矿氧化的结果。这些结果对于含有长寿命放射性核素（79）Se的核废料安全深地质处置至关重要。本研究表明，核废料基质腐蚀后释放出（79）Se((IV))，亚硒酸盐可通过与二价铁离子（Fe((II))aq）和/或硫离子（S((-II))aq）物种相互作用在近场中还原为低溶解度的零价硒（Se((0))）。由于零价硒（Se((0))）物种的溶解度远低于四价硒离子（Se((IV))），硒的（生物）有效性将大大降低，并且其从高放废物深地质处置库中的迁移可能会受到极大阻碍。
