Properties and reactivity of Fe-organic matter associations formed by coprecipitation versus adsorption: Clues from arsenate batch adsorption
Properties and reactivity of Fe-organic matter associations formed by coprecipitation versus adsorption: Clues from arsenate batch adsorption
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共沉淀与吸附形成的铁-有机物缔合物的性质和反应性：来自砷酸盐批量吸附的线索
DOI：
10.1016/j.gca.2014.08.026
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发表时间：
2014
影响因子：
5
通讯作者：
Freund A.
中科院分区：
文献类型：
--
作者：
Mikutta R;Lorenz D;Guggenberger G;Haumeier L;Freund A.
羟基氧化铁在控制土壤中含氧阴离子如砷酸根和磷酸根的生物有效性方面起着重要作用。尽管如此，很少有人知道的属性和反应性的Fe（III）-有机物相来自吸附（有机物（OM）的反应后合成氧化铁）versuscoprecipitation（形成的氧化铁在OM的存在下）。共沉淀物和吸附复合物的合成在pH 4使用两种天然有机质（NOM）类型提取的森林地面层（Oi和Oa地平线）的Haplic灰壤。铁（III）共沉淀物在1.0和0.1的初始摩尔金属与碳（M/C）比和0.2的铝（Al）与Fe（III）比下形成。通过X射线衍射、X射线光电子能谱（XPS）、N2气体吸附、动态光散射和电泳迁移率测量研究了样品的性质。在批实验中研究了砷[As（V）]在Fe-OM相中的吸附（168 h，pH 4，100 μM As）。共沉淀物的有机碳（OC）含量（82-339 mg g−1）高于吸附复合物（31和36 mg g−1），导致比表面积的显著变化（9-300 m2 g-1），平均孔半径（1-9 nm），和总孔隙体积（11-374 mm 3g-1），但与NOM类型或Al的存在无关。（XPS表面浓度：60-82原子% C）引起相当的吸附络合物和共沉淀物的pHPZC（1.5-2）。合成条件导致不同的Fe-OM缔合模式：“M/C0.1”共沉淀物中的Fe氧化物颗粒在较大程度上覆盖最外聚集体表面，对于某些“M/C1.0”共沉淀物，OM有效地包裹Fe氧化物，而吸附复合物中的OM主要覆盖外聚集体表面。尽管他们的OC含量较大，吸附的As（V）是最快的共沉淀物形成在低Fe的可用性（M/C 0.1），并促进弱键合OC的解吸和解聚。与此相反，“M/C 1.0”共沉淀物表现出相当的吸收率作为吸附复合物。虽然小的中孔（2-10 nm）促进了快速的As吸收，特别是对于“M/C 0.1”共沉淀物，但微孔（<2 nm）的存在似乎削弱了As解吸。这项研究表明，在陆地和水生系统中的不良结晶铁（III）氧化物的环境反应性可以在很大程度上取决于形成条件。富碳Fe相沉淀在低M/C比可能发挥更重要的作用，在含氧阴离子固定和Fe和C循环比在较高的M/C比或各自的吸附络合物形成的阶段。
Ferric oxyhydroxides play an important role in controlling the bioavailability of oxyanions such as arsenate and phosphate in soil. Despite this, little is known about the properties and reactivity of Fe(III)-organic matter phases derived from adsorption (reaction of organic matter (OM) to post-synthesis Fe oxide)versuscoprecipitation (formation of Fe oxides in presence of OM). Coprecipitates and adsorption complexes were synthesized at pH 4 using two natural organic matter (NOM) types extracted from forest floor layers (Oi and Oa horizon) of a Haplic Podzol. Iron(III) coprecipitates were formed at initial molar metal-to-carbon (M/C) ratios of 1.0 and 0.1 and an aluminum (Al)-to-Fe(III) ratio of 0.2. Sample properties were studied by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), N2gas adsorption, dynamic light scattering, and electrophoretic mobility measurements. Arsenic [As(V)] adsorption to Fe-OM phases was studied in batch experiments (168 h, pH 4, 100 μM As). The organic carbon (OC) contents of the coprecipitates (82–339 mg g−1) were higher than those of adsorption complexes (31 and 36 mg g−1), leading to pronounced variations in specific surface area (9–300 m2g−1), average pore radii (1–9 nm), and total pore volumes (11–374 mm3g−1) but being independent of the NOM type or the presence of Al. The occlusion of Fe solids by OM (XPS surface concentrations: 60–82 atom% C) caused comparable pHPZC(1.5–2) of adsorption complexes and coprecipitates. The synthesis conditions resulted in different Fe-OM association modes: Fe oxide particles in ‘M/C 0.1’ coprecipitates covered to a larger extent the outermost aggregate surfaces, for some ‘M/C 1.0’ coprecipitates OM effectively enveloped the Fe oxides, while OM in the adsorption complexes primarily covered the outer aggregate surfaces. Despite of their larger OC contents, adsorption of As(V) was fastest to coprecipitates formed at low Fe availability (M/C 0.1) and facilitated by desorption of weakly bonded OC and disaggregation. In contrast, ‘M/C 1.0’ coprecipitates showed a comparable rate of As uptake as the adsorption complexes. While small mesopores (2–10 nm) promoted the fast As uptake particularly to ‘M/C 0.1’ coprecipitates, the presence of micropores (<2 nm) appeared to impair As desorption. This study shows that the environmental reactivity of poorly crystalline Fe(III) oxides in terrestrial and aquatic systems can largely vary depending on the formation conditions. Carbon-rich Fe phases precipitated at low M/C ratios may play a more important role in oxyanion immobilization and Fe and C cycling than phases formed at higher M/C ratios or respective adsorption complexes.
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