Department of Geology, University of Huelva , Campus "El Carmen", 21071 Huelva, Spain.
CNRS , ISTerre, F-38041 Grenoble, France.
Environ Sci Technol. 2017 Jan 3;51(1):28-37. doi: 10.1021/acs.est.6b03315. Epub 2016 Dec 20.
Basaluminite precipitation may play an important role in the behavior of trace elements in water and sediments affected by acid mine drainage and acid sulfate soils. In this study, the affinity of basaluminite and schwertmannite for arsenate and selenate is compared, and the coordination geometries of these oxyanions in both structures are reported. Batch isotherm experiments were conducted to examine the sorption capacity of synthetic schwertmannite and basaluminite and the potential competitive effect of sulfate. In addition, synchrotron-based techniques such as differential pair distribution function (d-PDF) analysis and extended X-ray absorption fine structure (EXAFS) were used to determine the local structure of As(V) and Se(VI) complexes. The results show that oxyanion exchange with structural sulfate was the main mechanism for removal of selenate, whereas arsenate was removed by a combination of surface complexes and oxyanion exchange. The arsenate adsorption capacity of basaluminite was 2 times higher than that of schwertmannite and 3 times higher than that of selenate in both phases. The sulfate:arsenate and sulfate:selenate exchange ratios were 1:2 and 1:1, respectively. High sulfate concentrations in the solutions did not show a competitive effect on arsenate sorption capacity but had a strong impact on selenate uptake, suggesting some kind of specific interaction for arsenate. Both d-PDF and EXAFS results indicated that the bidentate binuclear inner sphere was the most probable type of ligand for arsenate on both phases and for selenate on schwertmannite, whereas selenate forms outer-sphere complexes in the aluminum octahedral interlayer of basaluminite. Overall, these results show a strong affinity of poorly crystalline aluminum phases such as basaluminite for As(V) and Se(VI) oxyanions, with adsorption capacities on the same order of magnitude as those of iron oxides. The results obtained in this study are relevant to the understanding of trace element behavior in environments affected by acid water, potentially opening new research lines focused on remediation by natural attenuation processes or engineered water treatment systems.
方钠石沉淀可能在受酸性矿山排水和酸性硫酸盐土壤影响的水中和沉积物中痕量元素的行为中发挥重要作用。在这项研究中，比较了方钠石和水羟铁锰矿对砷酸盐和硒酸盐的亲和力，并报道了这两种结构中这些含氧阴离子的配位几何形状。进行了批量等温实验，以研究合成水羟铁锰矿和方钠石的吸附能力以及硫酸盐的潜在竞争效应。此外，还使用基于同步加速器的技术，如差分对分布函数（d-PDF）分析和扩展 X 射线吸收精细结构（EXAFS），来确定 As(V)和 Se(VI)配合物的局部结构。结果表明，与结构硫酸盐的氧阴离子交换是硒酸盐去除的主要机制，而砷酸盐则是通过表面络合物和氧阴离子交换的组合去除的。方钠石对砷酸盐的吸附容量是水羟铁锰矿的 2 倍，是硒酸盐的 3 倍，在两相中都是如此。硫酸盐：砷酸盐和硫酸盐：硒酸盐的交换比分别为 1:2 和 1:1。溶液中高浓度的硫酸盐对砷酸盐的吸附容量没有表现出竞争效应，但对硒酸盐的吸收有很强的影响，这表明砷酸盐可能存在某种特殊的相互作用。d-PDF 和 EXAFS 的结果均表明，双核内双齿配位是两种相中砷酸盐最可能的配体类型，而硒酸盐在水羟铁锰矿中则形成外层络合物。总的来说，这些结果表明，结晶度差的铝相（如方钠石）对 As(V)和 Se(VI)含氧阴离子具有很强的亲和力，其吸附容量与氧化铁的吸附容量相当。本研究的结果对于理解受酸性水影响的环境中痕量元素的行为具有重要意义，可能开辟新的研究方向，侧重于自然衰减过程或工程水处理系统的修复。
