Catrouillet Charlotte, Davranche Mélanie, Dia Aline, Bouhnik-Le Coz Martine, Demangeat Edwige, Gruau Gérard
Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France.
Géosciences Rennes UMR 6118, Université Rennes 1, CNRS, 35042 Rennes cedex, France.
J Colloid Interface Sci. 2016 May 15;470:153-161. doi: 10.1016/j.jcis.2016.02.047. Epub 2016 Feb 20.
Up until now, only a small number of studies have been dedicated to the binding processes of As(III) with organic matter (OM) via ionic Fe(III) bridges; none was interested in Fe (II). Complexation isotherms were carried out with As(III), Fe(II) or Fe(III) and Leonardite humic acid (HA). Although PHREEQC/Model VI, implemented with OM thiol groups, reproduced the experimental datasets with Fe(III), the poor fit between the experimental and modeled Fe(II) data suggested another binding mechanism for As(III) to OM. PHREEQC/Model VI was modified to take various possible As(III)-Fe(II)-OM ternary complex conformations into account. The complexation of As(III) as a mononuclear bidentate complex to a bidentate Fe(II)-HA complex was evidenced. However, the model needed to be improved since the distribution of the bidentate sites appeared to be unrealistic with regards to the published XAS data. In the presence of Fe(III), As(III) was bound to thiol groups which are more competitive with regards to the low density of formed Fe(III)-HA complexes. Based on the new data and previously published results, we propose a general scheme describing the various As(III)-Fe-MO complexes that are able to form in Fe and OM-rich waters.
到目前为止，仅有少数研究致力于通过离子态铁（III）桥来研究三价砷（As(III)）与有机物（OM）的结合过程；而没有人关注二价铁（Fe(II)）。用As(III)、Fe(II)或Fe(III)以及风化煤腐殖酸（HA）进行了络合等温线实验。尽管使用OM硫醇基团的PHREEQC/模型VI能够重现Fe(III)的实验数据集，但实验数据与模拟的Fe(II)数据之间拟合不佳，这表明As(III)与OM之间存在另一种结合机制。对PHREEQC/模型VI进行了修改，以考虑各种可能的As(III)-Fe(II)-OM三元络合物构象。已证实As(III)作为单核双齿络合物与双齿Fe(II)-HA络合物发生络合。然而，由于双齿位点的分布与已发表的X射线吸收光谱（XAS）数据相比似乎不切实际，因此该模型需要改进。在存在Fe(III)的情况下，As(III)与硫醇基团结合，而硫醇基团对形成的低密度Fe(III)-HA络合物更具竞争力。基于新数据和先前发表的结果，我们提出了一个通用方案，描述了在富含铁和有机物的水体中能够形成的各种As(III)-Fe-OM络合物。
