Fe <sup>2+</sup>引起的水铁矿转化过程中砷的吸附和还原,ACS Earth and Space Chemistry

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Fe ²⁺引起的水铁矿转化过程中砷的吸附和还原
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2019-04-25 00:00:00 , DOI: 10.1021/acsearthspacechem.9b00031
Jeffrey Paulo H. Perez _{1,

2} , Dominique J. Tobler ₃ , Andrew N. Thomas ₄ , Helen M. Freeman _{1,

5} , Knud Dideriksen _{3,

6} , Jörg Radnik ₇ , Liane G. Benning _{1,

2,

8}

Affiliation

氧化铁在控制受污染的土壤和地下水中砷（As）的迁移率和毒性方面起着重要作用。地下地球化学条件的动态变化会影响As的固存和迁移，因为As的命运高度依赖于存在的主要铁矿物相，特别是这些元素形成或转化的途径。为了评估地下环境中砷酸盐[As（V）]的命运，我们研究了Fe ²⁺诱导的在与环境有关的缺氧条件下含As（V）的亚铁水合物（As（V）-FH）向更多结晶相的转变。地下条件。具体来说，我们研究了变化的Fe ²⁺_（aq） / Fe（III）_{固体的影响}在环境pH条件下，As（V）-FH向含铁结晶态相转变过程中，与矿物结合的As物种的行为和形态的比率（0.5、1、2）。在所有的Fe ²⁺_（aq） / Fe（III）_固体比下，针脚石（GT），绿锈硫酸盐（GR _SO4）和纤铁矿（LP）都在反应的前2小时内形成。在低比例（0.5：1）下，最初形成的GR _SO4和/或LP随着反应的进行而溶解，并且24小时后仅保留了GT和一些未反应的FH。在Fe ²⁺_（aq） / Fe（III）的_固体比为2，GR _SO4在整个反应的24小时内保持稳定，与GT和未反应的As（V）-FH保持一致。尽管大多数起始As（V）-FH转化为其他相，但在转化反应过程中，最初吸附的As并未释放到溶液中，约有99.9％仍与矿物结合。然而，最初的As（V）部分还原为As（III），最可能是由于与表面相关的Fe ²⁺ -GT氧化还原对。随着Fe ²⁺_（aq） / Fe（III）_{固体的形成}，As（V）的还原程度从约34％增至约40％比率从0.5增加到2。总体而言，我们的研究结果提供了重要的洞察力，帮助我们了解砷（As）污染的缺氧土壤和沉积物中铁（羟基）氧化物的转化途径，并证明此类转化可能对砷的迁移率以及重要的氧化态和氧化态产生影响。因此，在这些环境中具有毒性。

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Adsorption and Reduction of Arsenate during the Fe2+-Induced Transformation of Ferrihydrite

Iron (oxyhydr)oxides play an important role in controlling the mobility and toxicity of arsenic (As) in contaminated soils and groundwaters. Dynamic changes in subsurface geochemical conditions can impact As sequestration and remobilization since the fate of As is highly dependent on the dominant iron mineral phases present and, specifically, the pathways through which these form or transform. To assess the fate of arsenate [As(V)] in subsurface settings, we have investigated the Fe²⁺-induced transformation of As(V)-bearing ferrihydrite (As(V)-FH) to more crystalline phases under environmentally relevant anoxic subsurface conditions. Specifically, we examined the influence of varying Fe²⁺_(aq)/Fe(III)_solid ratios (0.5, 1, 2) on the behavior and speciation of mineral-bound As species during the transformation of As(V)-FH to crystalline iron-bearing phases at circumneutral pH conditions. At all Fe²⁺_(aq)/Fe(III)_solid ratios, goethite (GT), green rust sulfate (GR_SO4), and lepidocrocite (LP) formed within the first 2 h of reaction. At low ratios (0.5 to 1), initially formed GR_SO4 and/or LP dissolved as the reaction progressed, and only GT and some unreacted FH remained after 24 h. At Fe²⁺_(aq)/Fe(III)_solid ratio of 2, GR_SO4 remained stable throughout the 24 h of reaction, alongside GT and unreacted As(V)-FH. Despite the fact that majority of the starting As(V)-FH transformed to other phases, the initially adsorbed As was not released into solution during the transformation reactions, and ∼99.9% of it remained mineral-bound. Nevertheless, the initial As(V) became partially reduced to As(III), most likely because of the surface-associated Fe²⁺-GT redox couple. The extent of As(V) reduction increased from ∼34% to ∼40%, as the Fe²⁺_(aq)/Fe(III)_solid ratio increased from 0.5 to 2. Overall, our results provide important insights into transformation pathways of iron (oxyhydr)oxide minerals in As contaminated, anoxic soils and sediments and demonstrate the impact that such transformations can have on As mobility and also importantly oxidation state and, hence, toxicity in these environments.

更新日期：2019-04-25

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