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首页> 外文期刊>Environmental Science & Technology >Competing Fe(Ⅱ)-Induced Mineralization Pathways of Ferrihydrite
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Competing Fe(Ⅱ)-Induced Mineralization Pathways of Ferrihydrite

机译：竞争性铁（Ⅱ）诱导的水铁矿成矿途径

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Owing to its high surface area and intrinsic reactivity, ferrihydrite serves as a dominant sink for numerous metals and nutrients in surface environments and is a potentially important terminal electron acceptor formicrobial respiration. Introduction of Fe(Ⅱ), by reductive dissolution of Fe(Ⅲ) minerals, for example, converts ferrihydrite to Fe phases varying in their retention and reducing capacity. While Fe(Ⅱ) concentration is the master variable dictating secondary mineralization pathways of ferrihydrite, here we reveal that the kinetics of conversion and ultimate mineral assemblage are a function of competing mineralization pathways influenced by pH and stabilizing ligands. Reaction of Fe(Ⅱ) with ferrihydrite results in the precipitation of goethite, lepidocrocite, and magnetite. The three phases vary in their precipitation extent, rate, and residence time, all of which are primarily a function of Fe(Ⅱ) concentration and ligand type (Cl, SO_4, CO_3). While lepidocrocite and goethite precipitate over a large Fe(Ⅱ) concentration range, magnetite accumulation is only observed at surface loadings greater than 1.0 mmol Fe(Ⅱ)/g ferrihydrite (in the absence of bicarbonate). Precipitation of magnetite induces the dissolution of lepidocrocite (presence of Cl) or goethite (presence of SO_4), allowing for Fe(Ⅲ)-dependent crystal growth. The rate of magnetite precipitation is a function of the relative proportions of goethite to lepidocrocite; the lower solubility of the former Fe (hydr)oxide slows magnetite precipitation. A one unit pH deviation from 1, however, either impedes (pH 6) or enhances (pH 8) magnetite precipitation. In the absence of magnetite nucleation, lepidocrocite and goethite continue to precipitate at the expense of ferrihydrite with near complete conversion within hours, the relative proportions of the two hydroxides dependent upon the ligand present. Goethite also continues to precipitate at the expense of lepidocrocite in the absence of chloride. In fact, the rate and extent of both goethite and magnetite precipitation are influenced by conditions conducive to the production and stability of lepidocrocite. Thus, predicting the secondary mineralization of ferrihydrite, a process having sweeping influences on contaminantutrient dynamics, will need to take into consideration kinetic restraints and transient precursor phases (e.g., lepidocrocite) that influence ensuing reaction pathways.
机译：由于其高的表面积和固有的反应性，三水铁矿是表面环境中许多金属和营养物质的主要汇，并且是微生物呼吸的潜在重要的末端电子受体。例如，通过还原性溶解Fe（Ⅲ）矿物引入Fe（Ⅱ），可将水铁矿转变为Fe相，其保留和还原能力各不相同。尽管Fe（Ⅱ）浓度是决定水铁矿次生矿化途径的主要变量，但在此我们发现转化动力学和最终矿物组合是受pH和稳定配体影响的竞争矿化途径的函数。 Fe（Ⅱ）与水铁矿的反应导致针铁矿，纤铁矿和磁铁矿的沉淀。这三个阶段的沉淀程度，速率和停留时间各不相同，所有这些主要是Fe（Ⅱ）浓度和配体类型（Cl，SO_4，CO_3）的函数。当纤铁矿和针铁矿在较大的Fe（Ⅱ）浓度范围内析出时，仅在表面载荷大于1.0 mmol Fe（Ⅱ）/ g亚铁酸盐（在没有碳酸氢盐的情况下）时才观察到磁铁矿堆积。磁铁矿的沉淀诱导了纤铁矿（Cl的存在）或针铁矿（SO_4的存在）的溶解，从而使依赖于Fe（Ⅲ）的晶体生长。磁铁矿的沉淀速率是针铁矿与纤铁矿的相对比例的函数。前铁（氢）氧化物的较低溶解度会减慢磁铁矿沉淀。从1偏离一个单位的pH值会阻碍（pH 6）或增强（pH 8）磁铁矿沉淀。在没有磁铁矿成核的情况下，纤铁矿和针铁矿继续沉淀，以亚铁酸盐为代价，在数小时内几乎完全转化，两种氢氧化物的相对比例取决于存在的配体。在没有氯化物的情况下，针铁矿还继续以锂铁蒙脱石为代价沉淀。实际上，针铁矿和磁铁矿沉淀的速率和程度都受到有利于纤铁矿的生产和稳定性的条件的影响。因此，预测水铁矿的二次矿化是一个对污染物/营养物动力学具有广泛影响的过程，将需要考虑动力学约束和影响后续反应路径的瞬态前体相（例如，纤铁矿）。

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