Mechanisms of goethite dissolution in the presence of desferrioxamine B and Suwannee River fulvic acid at pH 6.5
Mechanisms of goethite dissolution in the presence of desferrioxamine B and Suwannee River fulvic acid at pH 6.5
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DOI：
10.1016/j.gca.2013.04.006
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发表时间：
2013-08-15
影响因子：
5
通讯作者：
Dubbin, William E.
中科院分区：
文献类型：
--
作者：
Stewart, Angela G.;Hudson-Edwards, Karen A.;Dubbin, William E.
铁载体是微生物响应铁胁迫而分泌的 Fe3+ 特异性低分子量螯合配体。低分子量有机酸（例如草酸盐）已被证明可以增强铁载体介导的 Fe3+ 氧化物的溶解。然而，黄腐酸的存在对铁载体功能的影响仍然未知。我们使用批量溶解实验研究了针铁矿-黄腐酸-去铁胺 B（针铁矿-SRFA-DFOB）三元体系中针铁矿的 Fe 释放。实验在 pH 6.5 下进行，同时改变试剂添加顺序。采用 FTIR 和紫外-可见光谱来表征 Fe-DFOB、Fe-SRFA 和 DFOB-SRFA 复合物。仅在 SRFA 存在的情况下，从针铁矿中释放的铁低于检测限。在 SRFA 和 DFOB 均存在的情况下，溶解的 Fe 随着反应时间、DFOB-SRFA 复合物的存在以及 SRFA 先于 DFOB 引入而增加。 FTIR数据显示，在三元体系中，Fe3+主要与DFOB异羟肟酸基团的氧络合，而SRFA的羧酸盐C=O与DFOB的末端NH3+形成静电缔合。我们认为，吸附到针铁矿上的 SRFA 会降低氧化物表面的净正电荷，从而促进阳离子 DFOB 的吸附以及随后的 Fe3+ 螯合和释放。此外，吸附的 SRFA 削弱了针铁矿表面的 Fe-O 键，增加了动力学不稳定的 Fe 的数量。这项工作证明了 SRFA 在提高 Fe3+ 生物利用度方面的积极但间接的作用。皇冠版权所有 (C) 2013 由 Elsevier Ltd 出版。保留所有权利。
Siderophores are Fe3+ specific low MW chelating ligands secreted by micro-organisms in response to Fe stress. Low MW organic acids such as oxalate have been shown to enhance siderophore mediated dissolution of Fe3+ oxides. However, the effect of fulvic acid presence on siderophore function remains unknown. We used batch dissolution experiments to investigate Fe release from goethite in the goethite-fulvic acid-desferrioxamine B (goethite-SRFA-DFOB) ternary system. Experiments were conducted at pH 6.5 while varying reagent addition sequence. FTIR and UV-Vis spectroscopy were employed to characterise the Fe-DFOB, Fe-SRFA and DFOB-SRFA complexes. Iron released from goethite in the presence of SRFA alone was below detection limit. In the presence of both SRFA and DFOB, dissolved Fe increased with reaction time, presence of the DFOB-SRFA complex, and where SRFA was introduced prior to DFOB. FTIR data show that in the ternary system, Fe3+ is complexed primarily to oxygen of the DFOB hydroxamate group, whilst the carboxylate C=O of SRFA forms an electrostatic association with the terminal NH3+ of DFOB. We propose that SRFA sorbed to goethite lowers the net positive charge of the oxide surface, thus facilitating adsorption of cationic DFOB and subsequent Fe3+ chelation and release. Furthermore, the sorbed SRFA weakens Fe-O bonds at the goethite surface, increasing the population of kinetically labile Fe. This work demonstrates the positive, though indirect role of SRFA in increasing the bioavailability of Fe3+. Crown copyright (C) 2013 Published by Elsevier Ltd. All rights reserved.