LGIT-OSUG, University of Grenoble-I, BP 53, F-38041 Grenoble Cedex 9, France.
Environ Sci Technol. 2010 Feb 15;44(4):1288-94. doi: 10.1021/es903037s.
The reductive immobilization of Se(IV) by micrometer-sized (100-200 microm) calcite containing sorbed or coprecipitated Fe(II) was investigated at pH 7 under anoxic conditions (O(2) < 1 ppmv) using X-ray absorption near-edge structure (XANES) spectroscopy. The Se(IV) sorption on calcite increased in the presence of sorbed Fe(II) compared to that of Fe-free pure calcite. XANES spectra of Se K-edge shows that nearly half of the total sorbed Se(IV) is reduced to Se(0) by Fe(II) sorbed on calcite within 24 h. The extent of reduction decreases with increasing equilibration time of calcite with Fe(II) solution before Se(IV) addition. The combined results of field emission scanning electron microscopy and X-ray diffraction have shown that needle-shaped red monoclinic elemental Se with diameters of 30-50 nm and lengths of up to 100 nm is precipitated on the calcite surface. Fe(II) coprecipitated calcite does not contribute to Se(IV) reduction within 72 h. Therefore, the reduction capacity of Fe(II) linked to calcite critically depends on its location (either on the surface or in the bulk solid), and less extensively on the pre-equilibration time of calcite with Fe(II) solution. Such understanding is important to predict the transport, transformation, and attenuation of Se in subsurface and in nuclear waste repositories.
采用 X 射线吸收近边结构（XANES）光谱法，在缺氧条件（O2<1ppmv）下，研究了 pH 7 时微米级（100-200 微米）方解石中吸附或共沉淀的 Fe（II）对 Se（IV）的还原固定作用。与不含 Fe 的纯方解石相比，在存在吸附 Fe（II）的情况下，方解石对 Se（IV）的吸附增加。Se K 边的 XANES 谱表明，在 Se（IV）加入之前，方解石与 Fe（II）溶液平衡 24 小时内，近一半的总吸附 Se（IV）被吸附在方解石上的 Fe（II）还原为 Se（0）。随着方解石与 Fe（II）溶液预平衡时间的增加，还原程度降低。场发射扫描电子显微镜和 X 射线衍射的综合结果表明，在方解石表面沉淀出直径为 30-50nm、长度可达 100nm 的针状红色单斜元素 Se。72 小时内，共沉淀的 Fe（II）方解石对方解石表面吸附的 Se（IV）没有还原作用。因此，与方解石结合的 Fe（II）的还原能力主要取决于其位置（表面或体相），而与方解石与 Fe（II）溶液的预平衡时间关系不大。这种理解对于预测地下和核废料库中 Se 的迁移、转化和衰减非常重要。
