Fe(II) 催化矿物转化过程中硅酸盐对水铁矿和纤铁矿的稳定作用：对颗粒形态和硅酸盐分布的影响,Environmental Science & Technology

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Fe(II) 催化矿物转化过程中硅酸盐对水铁矿和纤铁矿的稳定作用：对颗粒形态和硅酸盐分布的影响
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2022-04-18 , DOI: 10.1021/acs.est.1c08789
Katrin Schulz ₁ , Laurel K ThomasArrigo ₁ , Ralf Kaegi ₂ , Ruben Kretzschmar ₁

Affiliation

含水亚铁 (Fe(II)) 和次生 Fe 羟基氧化物之间的相互作用在缺氧土壤和沉积物中催化矿物重结晶和/或转化过程，其中氧阴离子（如硅酸盐）丰富。然而，硅酸盐在铁矿物重结晶和转化过程中的作用和归宿尚未完全清楚，尤其是纤铁矿仍不清楚。在本研究中，我们将 (Si-) 水铁矿 (Si/Fe = 0、0.05 和 0.18) 和 (Si-) 纤铁矿 (Si/Fe = 0 和 0.08) 与同位素标记的^57反应Fe(II) (Fe(II)/Fe(III) = 0.02 和 0.2) 在 pH 7 下长达 4 周。我们通过 X 射线衍射跟踪 Fe 矿物的转变，并通过测量水相和固相 Fe 同位素分数来跟踪 Fe 原子交换。我们的研究结果表明，在 Fe(II) 存在下水铁矿转变的程度受固相 Si/Fe 比的强烈影响，而增加 Fe(II)/Fe(III) 比（从 0.02 到 0.2）只有一个轻微的影响。硅酸盐的存在增加了新形成的纤铁矿晶体的厚度，Fe(II) 反应的水铁矿元素分布图显示，与新形成的纤铁矿相比，与剩余水铁矿相关的硅更多。纯纤铁矿在低 Fe(II) 处理中经历重结晶，并在高 Fe(II)/Fe(III) 比率下转变为磁铁矿。吸附的硅酸盐使纤铁矿表面失活，这大大降低了铁原子交换并抑制了矿物转化。总的来说，这项研究的结果表明，Fe(II) 催化的 Si-水铁矿转变导致硅酸盐在固相中重新分布并形成更厚的纤铁矿片晶，而吸附的硅酸盐可以完全抑制纤铁矿转变。因此，在考虑还原条件下土壤中的铁矿物动力学时，硅酸盐是一个重要的因素。本研究结果表明，Fe(II)催化的水铁矿转变导致硅酸盐在固相中的重新分布，形成较厚的纤铁矿片晶，而吸附的硅酸盐可以完全抑制纤铁矿的转变。因此，在考虑还原条件下土壤中的铁矿物动力学时，硅酸盐是一个重要的因素。本研究结果表明，Fe(II)催化的水铁矿转变导致硅酸盐在固相中的重新分布，形成较厚的纤铁矿片晶，而吸附的硅酸盐可以完全抑制纤铁矿的转变。因此，在考虑还原条件下土壤中的铁矿物动力学时，硅酸盐是一个重要的因素。

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Stabilization of Ferrihydrite and Lepidocrocite by Silicate during Fe(II)-Catalyzed Mineral Transformation: Impact on Particle Morphology and Silicate Distribution

Interactions between aqueous ferrous iron (Fe(II)) and secondary Fe oxyhydroxides catalyze mineral recrystallization and/or transformation processes in anoxic soils and sediments, where oxyanions, such as silicate, are abundant. However, the effect and the fate of silicate during Fe mineral recrystallization and transformation are not entirely understood and especially remain unclear for lepidocrocite. In this study, we reacted (Si-)ferrihydrite (Si/Fe = 0, 0.05, and 0.18) and (Si-)lepidocrocite (Si/Fe = 0 and 0.08) with isotopically labeled ⁵⁷Fe(II) (Fe(II)/Fe(III) = 0.02 and 0.2) at pH 7 for up to 4 weeks. We followed Fe mineral transformations with X-ray diffraction and tracked Fe atom exchange by measuring aqueous and solid phase Fe isotope fractions. Our results show that the extent of ferrihydrite transformation in the presence of Fe(II) was strongly influenced by the solid phase Si/Fe ratio, while increasing the Fe(II)/Fe(III) ratio (from 0.02 to 0.2) had only a minor effect. The presence of silicate increased the thickness of newly formed lepidocrocite crystallites, and elemental distribution maps of Fe(II)-reacted Si-ferrihydrites revealed that much more Si was associated with the remaining ferrihydrite than with the newly formed lepidocrocite. Pure lepidocrocite underwent recrystallization in the low Fe(II) treatment and transformed to magnetite at the high Fe(II)/Fe(III) ratio. Adsorbed silicate inactivated the lepidocrocite surfaces, which strongly reduced Fe atom exchange and inhibited mineral transformation. Collectively, the results of this study demonstrate that Fe(II)-catalyzed Si-ferrihydrite transformation leads to the redistribution of silicate in the solid phase and the formation of thicker lepidocrocite platelets, while lepidocrocite transformation can be completely inhibited by adsorbed silicate. Therefore, silicate is an important factor to include when considering Fe mineral dynamics in soils under reducing conditions.

更新日期：2022-04-18

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