Biosciences Division, Argonne National Laboratory, Argonne, Illinois 60439-4843, USA.
Environ Sci Technol. 2013 Aug 20;47(16):9157-66. doi: 10.1021/es400627j. Epub 2013 Aug 2.
Natural Fe(III) oxides typically contain a range of trace elements including P. Although solution phase and adsorbed P (as phosphate) have been shown to impact the bioreduction of Fe(III) oxides and the formation of "biogenic" secondary minerals, little is known about the potential effects of occluded/incorporated phosphate. We have examined the bioreduction of Fe(III) oxides (lepidocrocite (γ-FeOOH) and maghemite (γ-Fe2O3)) containing 0-3 mass% P as "bound" (a term we use to include both adsorbed and occluded/incorporated) phosphate. Kinetic dissolution studies showed congruent release of Fe and P, suggesting that the phosphate in these materials was incorporated within the particles; however, 53% or 86% of the total phosphate associated with the lepidocrocites containing 0.7 or 3 mass% P, respectively, was extracted with 0.1 M NaOH and can be considered to be adsorbed, both to exterior surfaces and within micropores. In the absence of phosphate, lepidocrocite was rapidly reduced to magnetite by Shewanella putrefaciens CN32, and over time the magnetite was partially transformed to ferrous hydroxy carbonate (FHC). The presence of 0.2-0.7 mass% P significantly inhibited the initial reduction of lepidocrocite but ultimately resulted in greater Fe(II) production and the formation of carbonate green rust. The bioreduction of maghemite with and without bound phosphate resulted in solid-state conversion to magnetite, with subsequent formation of FHC. We also examined the potential redox cycling of green rust under alternating Fe(III)-reducing and oxic conditions. Oxidation of biogenic green rust by O2 resulted in conversion to ferric green rust, which was readily reduced back to green rust by S. putrefaciens CN32. These results indicate the potential for cycling of green rust between reduced and oxidized forms under redox dynamics similar to those encountered in environments that alternate between iron-reducing and oxic conditions, and they are consistent with the identification of green rust in soils/sediments with seasonal redox cycling.
天然 Fe(III) 氧化物通常含有一系列痕量元素，包括 P。尽管溶液相和吸附的 P（如磷酸盐）已被证明会影响 Fe(III) 氧化物的生物还原和“生物成因”次生矿物的形成，但对于封闭/固溶磷酸盐的潜在影响知之甚少。我们研究了含有 0-3 质量%P 的作为“结合态”（我们用于包括吸附和封闭/固溶）磷酸盐的 Fe(III) 氧化物（针铁矿（γ-FeOOH）和磁赤铁矿（γ-Fe2O3））的生物还原。动力学溶解研究表明 Fe 和 P 同时释放，表明这些材料中的磷酸盐是在颗粒内固溶的；然而，分别含有 0.7 和 3 质量%P 的针铁矿中与总磷相关的 53%或 86%，可以用 0.1 M NaOH 提取出来，可认为是吸附在表面和微孔内。在没有磷酸盐的情况下，针铁矿被 Shewanella putrefaciens CN32 快速还原为磁铁矿，随着时间的推移，磁铁矿部分转化为亚铁羟基碳酸盐（FHC）。存在 0.2-0.7 质量%P 显著抑制了针铁矿的初始还原，但最终导致更多的 Fe(II)生成和碳酸盐绿锈的形成。含结合态磷酸盐的磁赤铁矿和不含结合态磷酸盐的磁赤铁矿的生物还原导致固相反转化为磁铁矿，随后形成 FHC。我们还研究了在交替的 Fe(III)还原和有氧条件下绿锈潜在的氧化还原循环。O2 对生物绿锈的氧化导致其转化为高铁绿锈，高铁绿锈很容易被 S. putrefaciens CN32 还原回绿锈。这些结果表明，在类似于在铁还原和有氧条件交替的环境中遇到的氧化还原动力学下，绿锈可能在还原和氧化形式之间循环，并且与在具有季节性氧化还原循环的土壤/沉积物中识别出绿锈的结果一致。
