Akbari Alavijeh Mozhgan, Schindler Michael, Wirth Mark G, Qafoku Odeta, Kovarik Libor, Perea Daniel E
Department of Earth Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
Environmental Molecular Sciences Laboratory (EMSL), Pacific Northwest National Laboratory, Richland, WA 99354, USA.
Environ Sci Process Impacts. 2023 Mar 22;25(3):577-593. doi: 10.1039/d2em00332e.
This study investigates the sequestration and transformation of silver (Ag) and arsenic (As) ions in soil organic matter (OM) at the nanoscale using the combination of atom probe tomography (APT), transmission electron microscopy (TEM), focused ion beam (FIB), ion mill thinning and scanning electron microscopy (SEM). Silver-arsenic contaminated organic-rich soils were collected along the shore of Cobalt Lake, a former mining and milling site of the famous Ag deposits at Cobalt, Ontario, Canada. SEM examinations show that particulate organic matter (OM grains) contains mineral inclusions composed of mainly Fe, S, and Si with minor As and traces of Ag. Four OM grains with detectable concentrations of Ag (by SEM-EDS) were further characterized with either a combination of TEM and APT or TEM alone. These examinations show that As is predominantly sequestered by OM through either co-precipitation with Fe-(hydr)oxide inclusions or adsorption on Fe-(hydr)oxides and their subsequent transformation into scorodite (FeAsO·2HO)/amorphous Fe-arsenate (AFA). Silver nanoparticles (NPs) with diameters in the range of ∼5-20 nm occur in the organic matrix as well as on the surface of Fe-rich inclusions (Fe-hydroxides, Fe-arsenates, Fe-sulfides), whereas Ag sulfide NPs were only observed on the surfaces of the Fe-rich inclusions. Rims of Ag-sulfides on Ag NPs (TEM data), accumulation of S atoms within and around Ag NPs (APT data), and the occurrence of dendritic as well as euhedral acanthite NPs with diameters in the range of ∼100-400 nm (TEM data) indicate that the sulfidation of the Ag NPs occurred a mineral-replacement reaction (rims) or a complete dissolution of the Ag NPs, the subsequent precipitation of acanthite NPs and their aggregation (dendrites) and Ostwald ripening (euhedral crystals). These results show the importance of OM and, specifically the mineral inclusions in the sequestration of Ag and As to less bioavailable forms such as acanthite and scorodite, respectively.
本研究结合原子探针断层扫描（APT）、透射电子显微镜（TEM）、聚焦离子束（FIB）、离子磨减薄技术和扫描电子显微镜（SEM），在纳米尺度上研究了土壤有机质（OM）中银（Ag）和砷（As）离子的固存和转化。沿着加拿大安大略省科博尔特著名银矿床的一个 former 采矿和选矿场地科博尔特湖岸边，收集了富含银砷的富含有机质的土壤。SEM 检查表明，颗粒状有机质（OM 颗粒）含有主要由 Fe、S 和 Si 组成的矿物包裹体，含有少量 As 和痕量 Ag。对四个可检测到 Ag 浓度（通过 SEM-EDS）的 OM 颗粒，进一步采用 TEM 和 APT 组合或单独使用 TEM 进行表征。这些检查表明，As 主要通过与 Fe-（氢）氧化物包裹体共沉淀或吸附在 Fe-（氢）氧化物上，随后转化为臭葱石（FeAsO·2H₂O）/无定形铁砷酸盐（AFA）而被 OM 固存。直径在约 5-20 nm 范围内的银纳米颗粒（NPs）存在于有机基质中以及富铁包裹体（氢氧化铁、铁砷酸盐、铁硫化物）表面，而硫化银 NPs 仅在富铁包裹体表面观察到。Ag NPs 上的硫化银边缘（TEM 数据）、Ag NPs 内部和周围 S 原子的积累（APT 数据）以及直径在约 100-400 nm 范围内的树枝状和自形辉银矿 NPs 的出现（TEM 数据）表明，Ag NPs 的硫化发生了矿物置换反应（边缘）或 Ag NPs 的完全溶解，随后辉银矿 NPs 的沉淀及其聚集（树枝状）和奥斯特瓦尔德熟化（自形晶体）。这些结果表明了 OM 的重要性，特别是矿物包裹体在分别将 Ag 和 As 固存为生物可利用性较低的形式（如辉银矿和臭葱石）方面的重要性。
