引用本文:王 锐,许海娟,魏世勇,方 敦,杨小洪.针铁矿和针铁矿—胡敏酸复合体对Se(Ⅳ)吸附机制[J].土壤学报,2018,55(2):399-410.
WANG Rui,XU Haijuan,WEI Shiyong,FANG Dun,YANG Xiaohong.Selenite Adsorption Mechanisms of Goethite and Goethite-Humic Acid Complex[J].Acta Pedologica Sinica,2018,55(2):399-410
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针铁矿和针铁矿—胡敏酸复合体对Se(Ⅳ)吸附机制
王 锐, 许海娟, 魏世勇, 方 敦, 杨小洪
湖北民族学院化学与环境工程学院
摘要:
研究了针铁矿和针铁矿—胡敏酸复合体对Se(Ⅳ)的吸附机制。结果表明:针铁矿和复合体对Se(Ⅳ)的最大吸附容量分别为0.202 mmol g-1和0.159 mmol g-1。针铁矿的等温吸附数据适合用Langmuir模型拟合,而Freundlich模型更适合描述复合体的等温吸附过程。针铁矿的等电点(IEP)在7.0附近,复合体的IEP<3.0;当pH=4.0时,它们的表面电位分别为46.6 mV和-40.5 mV。X—射线光电子能谱(XPS)分析显示,针铁矿和复合体表面Fe2p3/2的电子结合能(B.E.)分别为711.4 eV和711.5 eV,复合体表面C1s的B.E.值为284.8 eV。初始pH=4.0时,样品与Se(Ⅳ)相互作用后的主要变化体现在:①针铁矿和复合体的悬浮液pH分别升高至4.4和4.2,表面电位分别降低了39.08 mV和升高了1.8 mV;②针铁矿表面Fe(Ⅲ)的B.E.值降低了0.4 eV,但吸附态Se(Ⅳ)的B.E.值无明显变化;③复合体表面Fe(Ⅲ)的B.E.值降低了0.3 eV,表面C-O中C的B.E.值由285.7 eV升高至286.5 eV,吸附态Se(Ⅳ)的B.E.值升高了0.6 eV。针铁矿和复合体吸附Se(Ⅳ)的主要机制包括表面配合反应(复合体表面铁羟基与HSeO3-之间存在双齿配位)、静电引力、氢键等作用。此外,复合体表面吸附态Se(Ⅳ)同时与针铁矿和胡敏酸发生了作用,形成了针铁矿—Se(Ⅳ) —胡敏酸三元体。
关键词:  针铁矿  针铁矿—胡敏酸复合体  等温吸附  硒(Ⅳ)  X—射线光电子能谱(XPS)
DOI:10.11766/trxb201710090405
分类号:
基金项目:国家自然科学基金项目(41561053,41261060,21565013)资助
Selenite Adsorption Mechanisms of Goethite and Goethite-Humic Acid Complex
WANG Rui, XU Haijuan, WEI Shiyong, FANG Dun, YANG Xiaohong
Department of Chemistry and Environmental Engineering, Hubei University for Nationalities
Abstract:
【Objective】Selenium (Se) is an essential micronutrient for human and animals. Ingestion of either an inadequate or excessive amount of Se tends to lead to health problems. Bioavailability of Se in soils depends on its forms. Iron oxides and humic acid are important components of soils and may interact with Se through desorption/adsorption. Iron oxides and humic acid in soils are often cemented together forming aggregates, thus significantly affecting translsocation and transformation of nutrient elements and contaminants in the soils. However, in-depth knowledge about the effects of iron oxides-humic acid complex on speciation and bioavailability of Se in soils is still rarely available. 【Method】In this study, goethite-humic acid complex was prepared through a modified co-precipitation procedure for analysis of selenite (Se(IV) adsorption characteristics in aqueous solutions through a series of tests, like pH, Zeta potential and X-ray photoelectron spectrum(XPS) and isothermal adsorption. 【Result】 At the initial pH=4, the adsorption capacity (Qm), as fitted with the Langmuir model, was 0.202 mmol g-1 and 0.159 mmol g-1 for goethite and the complex, respectively. The Langmuir model was suitable for use to describe isotherm adsorption of Se(Ⅳ) for goethite (R2=0.970), while the Freundlich model was for the complex (R2=0.980). As for goethite and the complex, the isoelectric point (IEP) was about 7.0 and less 3.0, and zeta potential at pH=4.0 was 46.6 mV and -40.5 mV, respectively. X-ray photoelectron spectrum (XPS) showed that the electronic binding energy (B.E.) of the Fe2p3/2 on the surface of goethite and the complex was 711.4 eV and 711.5 eV respectively, and the B.E. of the C1s on the complex surface was 284.8 eV. With the initial pH being 4.0, changes in interactions between the samples and Se(Ⅳ) were embodied mainly in the following aspects: (1) pH rose up to 4.4 and 4.2, respectively in the suspensions of goethite and the complex, while surface potential decreased by 39.08 mV in goethite, but increased by 1.8 mV the complex; (2) B.E. of Fe(Ⅲ) dropped by 0.4 eV on the surface of goethite, but remained almost unchanged in adsorbed Se(Ⅳ); (3) B.E. of Fe(Ⅲ) decreased by 0.3 eV on the surface of the complex , but increased by 0.6 eV on adsorbed Se(Ⅳ), and the B.E. of C in C-O bonds rised to 286.5 eV. 【Conclusion】The complex is lower than goethite in Qm of Se(Ⅳ) and affinity for absorbed Se(Ⅳ). But their adsorptions of Se(Ⅳ) occur mainly through the following mechanisms, i.e. surface coordination reaction and hydrogen bonding. The electrostatic attraction would contribute to improve the Qm of Se(Ⅳ) on goethite, while the electrostatic repulsion was the reason that decreased the Qm of Se(Ⅳ) on complex. Moreover, for surface coordination in the complex, bidentate coordination existed between iron hydroxyl groups (≡FeOH) on the surface of the complex and HSeO3-. In addition, the adsorbed Se(Ⅳ) on the surface of the complex interacted with both goethite and humic acid, forming a goethite-Se(Ⅳ)-humic acid ternary system.
Key words:  Goethite  Goethite-humic acid complex  Isothermal adsorption  Selenite  X-ray photoelectron spectrum (XPS)