Soil Chemistry Group, Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, ETH Zürich, Universitätstrasse 16, CHN, CH-8092 Zürich, Switzerland.
Environ Sci Technol. 2024 Nov 12;58(45):20224-20234. doi: 10.1021/acs.est.4c09261. Epub 2024 Nov 3.
The transformation of the mineral ferrihydrite in reducing environments, and its impact on the mobility of incorporated trace metals, has been investigated in model laboratory studies, but studies using complex soil or sediment matrices are lacking. Here, we studied the transformation of zinc (Zn)-bearing ferrihydrite labeled with Fe and mixed with natural sediments, incubated in reducing conditions for up to six months. We tracked the evolution of Fe and Zn speciation with Fe Mössbauer spectroscopy and with bulk and micro-X-ray absorption spectroscopy. We show that Fe was readily reduced and incorporated into a poorly crystalline mixed-valence Fe(II)-Fe(III) phase resembling green rust. In parallel, Zn was released in the surrounding porewater and scavenged by precipitation with available ligands, particularly as zinc sulfide (ZnS) or Zn-carbonates. Early in the mineral transformation process, the chemical behavior of Fe was decoupled from Zn, suppressing the impact of Zn on the rates and products of the ferrihydrite transformation. Our results underline the discrepancy between model experiments and complex field-like conditions and highlight the importance of sediment and soil geochemistry and ligand competition on the fate of divalent metal contaminants in the environment.
在还原环境中，矿物水铁矿的转化及其对所结合痕量金属迁移性的影响，已在模型实验室研究中进行了研究，但缺乏使用复杂土壤或沉积物基质的研究。在这里，我们研究了用 Fe 标记并与天然沉积物混合的含 Zn 水铁矿在还原条件下长达六个月的转化。我们使用 Fe Mössbauer 光谱法以及整体和微 X 射线吸收光谱法跟踪 Fe 和 Zn 形态的演变。我们表明，Fe 很容易被还原并掺入类似于绿锈的非晶混合价态 Fe(II)-Fe(III)相。与此同时，Zn 在周围的孔隙水中释放出来，并与可用配体（特别是硫化锌 (ZnS) 或 Zn 碳酸盐）一起沉淀而被捕获。在矿物转化过程的早期，Fe 的化学行为与 Zn 分离，抑制了 Zn 对水铁矿转化速率和产物的影响。我们的结果强调了模型实验与复杂现场条件之间的差异，并强调了沉积物和土壤地球化学以及配体竞争对环境中二价金属污染物命运的重要性。
