Fe(II)-Induced Mineral Transformation of Ferrihydrite–Organic Matter Adsorption and Co-precipitation Complexes in the Absence and Presence of As(III),ACS Earth and Space Chemistry

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Fe(II)-Induced Mineral Transformation of Ferrihydrite–Organic Matter Adsorption and Co-precipitation Complexes in the Absence and Presence of As(III)
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2018-09-13 00:00:00 , DOI: 10.1021/acsearthspacechem.8b00041
Chunmei Chen ₁ , Donald L. Sparks ₁

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The poorly crystalline ferrihydrite (Fh) is often associated with organic matter (OM) and metal(loid)s, such as arsenic (As). The transformation of Fh to more stable and, hence, less reactive phases is catalyzed by the surface reaction with Fe(II). However, little is known regarding the impact of various specific OM types and the co-existence of OM and As on the secondary mineralization of Fh. Accordingly, we explored the extent and the resulting secondary minerals of Fe(II)-induced transformation of [As(III)-adsorbed] OM–Fh adsorption and co-precipitation complexes, which were synthesized using two types of OM: dissolved organic matter (DOM) extracted from the O horizon of an ultisol and polygalacturonic acid (PGA) as a proxy for polysaccharides. Regardless of OM type, increased contents of the co-precipitated or adsorbed OM led to a decrease in Fh transformation in both the absence and presence of As(III). Adsorbed As(III) caused a decrease in Fh conversion for both pure Fh and OM–Fh complexes. We observed only small differences in Fe(II)-induced transformation of OM–Fh co-precipitates versus adsorptive complexes. However, without adsorbed As(III), OM types strongly influenced the secondary mineral products: DOM impeded goethite (Gt) and stimulated lepidocrocite (Lp) formation, while only Gt was formed for PGA. When As(III) and OM coexists, As(III) favored Lp over Gt formation for both DOM–Fh and PGA–Fh complexes. These findings provide evidence that the mineral evolution of Fh largely depends upon the potential additive/competing influence of coexisting constituents.

中文翻译：

铁（II）的存在与不存在下铁（II）诱导的铁水铁矿-有机质吸附和共沉淀复合物的矿物转化

结晶性较差的三水铁矿（Fh）通常与有机物（OM）和金属（金属）（如砷）相关。通过与Fe（II）的表面反应可催化Fh转变为更稳定的反应相，从而使反应相更少。但是，关于各种特定的OM类型以及OM和As的共存对Fh二次矿化的影响知之甚少。因此，我们探讨了Fe（II）诱导的[As（III）吸附的] OM-Fh吸附和共沉淀复合物的转变的程度和所产生的次生矿物，它们是使用两种类型的OM合成的：溶解有机物（DOM）是从ultisol和聚半乳糖醛酸（PGA）的O层中提取的，作为多糖的代用品。不论是OM类型在不存在和存在As（III）的情况下，共沉淀或吸附的OM的含量增加导致Fh转化率降低。对于纯Fh和OM–Fh络合物，吸附的As（III）导致Fh转化率降低。我们观察到Fe（II）引起的OM-Fh共沉淀物与吸附复合物的转化只有很小的差异。但是，在没有吸附As（III）的情况下，OM类型对次生矿物产物有很大影响：DOM阻止针铁矿（Gt）和刺激纤铁矿（Lp）的形成，而PGA仅形成Gt。当As（III）和OM共存时，对于DOM-Fh和PGA-Fh络合物，As（III）都更倾向于Lp而不是Gt的形成。这些发现提供了证据，表明Fh的矿物演化很大程度上取决于共存成分的潜在加性/竞争性影响。

更新日期：2018-09-13

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