Adsorption isotherm, mechanism, and geometry of Pb(II) on magnetites substituted with transition metals
Adsorption isotherm, mechanism, and geometry of Pb(II) on magnetites substituted with transition metals
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Pb(II) 在过渡金属取代的磁铁矿上的吸附等温线、机理和几何形状
DOI：
10.1016/j.chemgeo.2017.09.003
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发表时间：
2017-10-20
期刊：
影响因子：
3.9
通讯作者：
Zhang, Jing
中科院分区：
文献类型：
--
作者：
Liang, Xiaoliang;Wei, Gaoling;Zhang, Jing
天然水体和土壤中氧化铁含量丰富，对Pb（II）具有很强的吸附清除能力，影响了Pb在地表的迁移和归宿。我们研究了用Cr、Mn、Co和Ni等常见过渡金属取代的磁铁矿对Pb （II）的吸附。采用传统的宏观研究方法，即酸碱滴定和批量吸附实验，辅以x射线吸收精细结构（XAFS）光谱分析和表面络合模型（SCM），研究了Pb（II）的吸附能力、吸附机理和局部配位。取代增加了表面位点密度，而pHpzc没有变化。背景电解质的存在不抑制对Pb（II）的吸附，并随着pH的增加而增强。等温线符合Langmuir吸附模型。XAFS分析表明，Pb（II）离子主要通过内球络合作用吸附在磁铁矿表面，吸附的Pb（II）呈双齿双核共享角几何形状，与吸附量无关。这种吸附几何结构可以很好地拟合实验吸附数据与扩散层模型（DLM）。吸附量的提高顺序为Cr > Ni > Mn > Co，并对吸附Pb（II）的活性位点密度和局部配位的测量值进行了讨论。本文首次研究了不同取代磁铁矿对Pb（II）的吸附。所得结果对理解Pb（II）在磁铁矿表面的络合反应具有重要意义。
Iron oxides are abundant in natural waters and soils and have high capacities for scavenging Pb(II) by adsorption, which affects the transport and fate of Pb on the earth's surface. We investigated the adsorption of Pb (II) on magnetites substituted with commonly incorporated transition metals such as Cr, Mn, Co, and Ni. The adsorption capacity, mechanism, and local coordination of Pb(II) were investigated by traditional macroscopic studies, i.e., acid-base titration and batch adsorption experiment, complemented with X-ray absorption fine structure (XAFS) spectrum analysis and surface complexation model (SCM). The substitution increased the surface site density, while pHpzc did not vary. Pb(II) adsorption was not suppressed by the presence of background electrolyte and improved as pH increased. The isotherms were well fit to the Langmuir adsorption model. The XAFS analysis demonstrated that Pb(II) ions were adsorbed on magnetite surface predominantly via innersphere complexation, where the adsorbed Pb(II) species was in bidentate binuclear corner-sharing geometry, independent of the adsorption capacity. This adsorption geometry can be applied to fit the experimental adsorption data well with the diffuse layer model (DLM). The substitutions improved the adsorption capacity in the following order: Cr > Ni > Mn > Co, and were discussed regarding the measured values of active site density and local coordination of adsorbed Pb(II). This study is the first documentation of Pb(II) adsorption on magnetite with different substitutions. The obtained results are of great significance for the understanding of Pb(II) surface complexation reactions on magnetite surface.