Evidence of a critical content in Fe(0) on FoCa7 bentonite reactivity at 80 °C
Evidence of a critical content in Fe(0) on FoCa7 bentonite reactivity at 80 °C
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DOI：
10.1016/j.clay.2007.03.002
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发表时间：
2008-02-01
影响因子：
5.6
通讯作者：
Bruno, Gerard
中科院分区：
文献类型：
--
作者：
Perronnet, Murielle;Jullien, Michel;Bruno, Gerard
为了评估粘土工程屏障(EBS)在与装有放射性废物的金属罐接触时的约束性能的演变，需要评估Fe(0)-膨润土相互作用。使用粉状FoCa7膨润土和金属铁进行了45天-80摄氏度的测试。由于一个基本参数可能是Fe(0)的有效含量，因此使用了从0到1/3的较大范围的铁/粘土质量比(I/C)。粘土材料的约束能力取决于其膨胀性和滞留能力。因此，在本研究中，选择阳离子交换容量(CEC)的变化作为评价约束性质演变的主要标准。同时，利用X射线衍射仪和能谱仪对膨润土的物理化学演化进行了研究。利用Fe-57穆斯堡尔谱研究了膨润土中高岭石和蒙脱石与Fe(0)接触时，高岭石和蒙脱石转变为SiAlFe凝胶的过程。当I/C=1/3时，这些凝胶成熟为富铁的双八面体层状硅酸盐，其组成与Fe-M+-4Si图中的橄榄石和绿帘石的组成相一致。最重要的是，该反应取决于Fe(0)的有效含量。当I/C比在1/30~1/7.5时，FoCa7膨润土的交换容量开始下降，Fe(0)的消耗变大，蒙脱石发生变化，形成二次氧化物。当I/C从1/7.5到1/5时，可以观察到富铁的层状硅酸盐的结晶。当I/C=1/3.75以上，初始的铁氧化物被强烈消耗，并参与凝胶或新的层状硅酸盐八面体中Fe2+和Fe3+的掺入。这些实验结果被作为输入数据，用于使用Crunch反应-传输模型预测EBS的长期演化。(C)2007 Elsevier B.V.保留所有权利。
In order to assess the evolution of the confinement properties of clay engineered barriers (EBS) when in contact with metallic canisters containing radioactive wastes, Fe(0)-bentonite interactions need to be assessed. "45 days-80 degrees C" tests were performed using powdered FoCa7 bentonite and metallic iron. Since one fundamental parameter may be the available quantity of Fe(0), a wide range of Iron/Clay mass ratios (I/C) from 0 to 1/3 is used. The confinement power of clay material results from the swelling properties and the retention capacity. Thus, the major criterion which is chosen to assess the evolution of the confinement properties in this study is the variation of Cation Exchange Capacity (CEC). In parallel, the physico-chemical evolution of bentonite is studied using XRD and EDS-TEM microanalyses. The evolution of the distribution of iron environments is obtained by Fe-57 Mossbauer spectroscopy.This study evidences that both kaolinite and smectite from the bentonite are altered into SiAlFe gels when in contact with Fe(0). These gels maturates into Fe-rich di-trioctahedral phyllosilicates, whose composition is bounded by the one of odinite and greenalite in a Fe-M+-4Si diagram when I/C=1/3. Most of all, it is evidenced that the reaction depends on the available quantity of Fe(0). When the I/C ratio is between 1/30 and 1/7.5, the exchange capacity of FoCa7 bentonite starts decreasing, the consumption of Fe(0) becomes significant, the alteration of smectites occurs and secondary oxides are formed. The crystallization of Fe-rich phyllosilicates is observable when I/C ratio is higher, from a threshold between 1/7.5 and 1/5. Above I/C=1/3.75, initial iron oxides are strongly consumed and participate in the incorporation of Fe2+ and Fe3+ in gels or new phyllosilicates octahedra.These experimental results were used as input data for the prediction of the long-term evolution of the EBS using Crunch reaction-transport model. (C) 2007 Elsevier B.V. All rights reserved.