Civil and Environmental Engineering, Duke University ,118A Hudson Hall, Box 90287,Durham, North Carolina 27708, United States.
Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
Environ Sci Technol. 2023 Aug 22;57(33):12388-12397. doi: 10.1021/acs.est.3c00694. Epub 2023 Aug 10.
Liquid elemental mercury (Hg) pollution can remain in soils for decades and, over time, will undergo corrosion, a process in which the droplet surface oxidizes soil constituents to form more reactive phases, such as mercury oxide (HgO). While these reactive coatings may enhance Hg migration in the subsurface, little is known about the transformation potential of corroded Hg in the presence of reduced inorganic sulfur species to form sparingly soluble HgS particles, a process that enables the long-term sequestration of mercury in soils and generally reduces its mobility and bioavailability. In this study, we investigated the dissolution of corroded Hg in the presence of sulfide by quantifying rates of aqueous Hg release from corroded Hg droplets under different sulfide concentrations (expressed as the S:Hg molar ratio). For droplets corroded in ambient air, no differences in soluble Hg release were observed among all sulfide exposure levels (S:Hg mole ratios ranging from 10 to 10). However, for droplets oxidized in the presence of a more reactive oxidant (hydrogen peroxide, HO), we observed a 10- to 25-fold increase in dissolved Hg when the oxidized droplets were exposed to low sulfide concentrations (S:Hg ratios from 10 to 10) relative to droplets exposed to high sulfide concentrations. These results suggest two critical factors that dictate the release of soluble Hg from Hg in the presence of sulfide: the extent of surface corrosion of the Hg droplet and sufficient sulfide concentration for the formation of HgS solids. The mobilization of Hg in porous media, therefore, largely depends on aging conditions in the subsurface and chemical reactivity at the Hg droplet interface.
液态元素汞（Hg）污染可在土壤中存在数十年，随着时间的推移，它将经历腐蚀过程，在此过程中，液滴表面会氧化土壤成分，形成更具反应性的相，如氧化汞（HgO）。虽然这些反应性涂层可能会增强地下水中 Hg 的迁移，但对于腐蚀 Hg 在还原无机硫物种存在下转化为难溶性 HgS 颗粒的转化潜力知之甚少，这一过程使汞在土壤中长期固定，通常降低其迁移性和生物可利用性。在这项研究中，我们通过量化腐蚀 Hg 液滴在不同硫化物浓度（表示为 S:Hg 摩尔比）下从腐蚀 Hg 液滴中释放出的水溶态 Hg 速率，研究了硫化物存在下腐蚀 Hg 的溶解。对于在环境空气中腐蚀的液滴，在所有硫化物暴露水平下（S:Hg 摩尔比范围从 10 到 10），可溶态 Hg 的释放没有差异。然而，对于在更具反应性氧化剂（过氧化氢，HO）存在下氧化的液滴，当氧化液滴暴露于低硫化物浓度（S:Hg 比从 10 到 10）时，与暴露于高硫化物浓度的液滴相比，可溶态 Hg 的释放增加了 10 到 25 倍。这些结果表明，有两个关键因素决定了硫化物存在下 Hg 从 Hg 中的可溶性释放：Hg 液滴表面腐蚀的程度和形成 HgS 固体所需的硫化物浓度。因此，多孔介质中 Hg 的迁移在很大程度上取决于地下的老化条件和 Hg 液滴界面的化学活性。
