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Mechanism of Hg(II) immobilization in sediments by sulfate-cement amendment
Applied Geochemistry ( IF 3.4 ) Pub Date : 2016-04-01 , DOI: 10.1016/j.apgeochem.2016.01.007
Susana Serrano 1 , Dimitri Vlassopoulos 2 , Peggy A O'Day 1
Affiliation  

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.

中文翻译:

硫酸盐水泥改良剂固定沉积物中Hg(II)的机理

反应性改良剂(例如波特兰水泥和超硫酸盐水泥)提供了一种很有前景的技术,可通过以生物可利用性较低的固体形式进行封存来固定土壤和沉积物中的类金属污染物,例如汞 (Hg)。潮汐沼泽沉积物与合成海水和淡水溶液中溶解的 Hg(II) 反应,用波特兰水泥和 FeSO4 改良剂处理,并老化长达 90 天。反应后的固体用大量连续萃取方法进行分析,并通过粉末 X 射线衍射 (XRD)、电子显微镜和同步加速器 X 射线吸收光谱在 Hg LIII 和 S K 边缘进行表征。在修正后的沉积物中,XRD、SEM 和硫 K-edge XANES 表明在海水实验中形成了石膏或在淡水实验中形成了钙矾石型 (Ca6Al2(SO4)3(OH)12.26H2O) 相,取决于最终溶液的 pH 值(海水~8.5;淡水~10.5)。Hg EXAFS 光谱的分析表明,在海水和淡水实验中,第一和第二配位壳中的 Cl 和 Hg 配体在多核氯汞 (II) 盐的特征距离处,可能作为纳米颗粒相。除了氯汞物质外,在淡水样品光谱中,一小部分 (~20-25%) 的 Hg 与 O 原子键合,表明存在少量吸附的 Hg 部分。在没有修正处理的情况下,可以通过 S XANES 检测到的沼泽沉积物中存在的还原 S 物质的相对强结合来解释汞吸附和提取抗性。热力学计算预测在海水最终 pH 值下稳定的含水 Hg-Cl 物质,但淡水中较高的最终 pH 值有利于水合氢氧化物物种。水相和固相之间 Hg 配位的差异表明,初始 Hg-Cl 配位在水泥水化产物中是稳定的,并且不会随着老化而与本体溶液重新平衡。总的来说,结果表明 Hg 作为多核氯汞 (II) 盐的物理封装是主要的固定机制。
更新日期:2016-04-01
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