Mechanism of Hg(II) Immobilization in Sediments by Sulfate-Cement Amendment.
Mechanism of Hg(II) Immobilization in Sediments by Sulfate-Cement Amendment.
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DOI：
10.1016/j.apgeochem.2016.01.007
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发表时间：
2016-04-01
期刊：
影响因子：
--
通讯作者：
O'Day PA
中科院分区：
文献类型：
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作者：
Serrano S;Vlassopoulos D;O'Day PA
活性改良剂，如波特兰和超硫酸盐水泥提供了一种有前途的技术，通过以生物可利用性较低的固体形式螯合来固定土壤和沉积物中的准金属污染物，如汞（Hg）。潮汐沼泽沉积物与溶解的汞（II）在合成的海水和淡水溶液中进行反应，用波特兰水泥和硫酸亚铁修正案处理，并老化长达90天。反应后的固体进行了分析与批量顺序提取方法，其特征在于粉末X射线衍射（XRD），电子显微镜，和同步辐射X射线吸收光谱在Hg LIII-和S K-边缘。在修改后的沉积物中，XRD，SEM和硫K边XANES表明在海水实验中形成石膏或在淡水实验中形成钙矾石型（Ca 6Al 2（SO 4）3（OH）12.26H2O）相，这取决于最终溶液的pH值（海水pH值为8.5;淡水pH值为10.5）。汞EXAFS光谱分析表明，氯和汞配体在第一和第二配位壳层的距离特性的多核氯汞（II）盐，也许作为一个纳米颗粒相，在海水和淡水实验。除了氯汞物种，一个较小的分数（20%-25%）的汞结合到淡水样品光谱中的氧原子，表明存在一个小的吸附汞馏分。在没有修正案的治疗，汞吸附和提取阻力可以占相对较强的约束力，减少S种存在于沼泽沉积物中的S XANES检测。热力学计算预测稳定的水溶液中的汞-氯物种在海水中的最终pH值，但在淡水中的最终pH值较高，有利于水溶液中的汞-氢氧化物物种。水相和固相之间的Hg配位的差异表明，初始的Hg-Cl配位在水泥水化产物中是稳定的，并且随着老化不会与本体溶液重新平衡。总的来说，结果表明物理封装汞作为多核氯汞（II）盐作为主要的固定机制。
Reactive amendments such as Portland and super-sulfate cements offer a promising technology for immobilizing metalloid contaminants such as mercury (Hg) in soils and sediments through sequestration in less bioavailable solid forms. Tidal marsh sediments were reacted with dissolved Hg(II) in synthetic seawater and fresh water solutions, treated with Portland cement and FeSO4 amendment, and aged for up to 90 days. Reacted solids were analyzed with bulk sequential extraction methods and characterized by powder X-ray diffraction (XRD), electron microscopy, and synchrotron X-ray absorption spectroscopy at the Hg LIII- and S K-edge. In amended sediments, XRD, SEM and sulfur K-edge XANES indicated formation of gypsum in seawater experiments or ettringite-type (Ca6Al2(SO4)3(OH)12.26H2O) phases in fresh water experiments, depending on the final solution pH (seawater ∼8.5; freshwater ∼10.5). Analysis of Hg EXAFS spectra showed Cl and Hg ligands in the first- and second-coordination shells at distances characteristic of a polynuclear chloromercury(II) salt, perhaps as a nanoparticulate phase, in both seawater and fresh water experiments. In addition to the chloromercury species, a smaller fraction (∼20-25%) of Hg was bonded to O atoms in fresh water sample spectra, suggesting the presence of a minor sorbed Hg fraction. In the absence of amendment treatment, Hg sorption and resistance to extraction can be accounted for by relatively strong binding by reduced S species present in the marsh sediment detected by S XANES. Thermodynamic calculations predict stable aqueous Hg-Cl species at seawater final pH, but higher final pH in fresh water favors aqueous Hg-hydroxide species. The difference in Hg coordination between aqueous and solid phases suggests that the initial Hg-Cl coordination was stabilized in the cement hydration products and did not re-equilibrate with the bulk solution with aging. Collectively, results suggest physical encapsulation of Hg as a polynuclear chloromercury(II) salt as the primary immobilization mechanism.