Formation of Crystalline Zn-Al Layered Double Hydroxide Precipitates on γ-Alumina: The Role of Mineral Dissolution
Formation of Crystalline Zn-Al Layered Double Hydroxide Precipitates on γ-Alumina: The Role of Mineral Dissolution
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DOI：
10.1021/es3018094
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发表时间：
2012-11-06
影响因子：
11.4
通讯作者：
Sparks, Donald L.
中科院分区：
文献类型：
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作者：
Li, Wei;Livi, Kenneth J. T.;Sparks, Donald L.
为了更好地理解镍（Ni）、锌（Zn）和钴（Co）等有毒金属在土壤中作为层状双氢氧化物（LDH）相的螯合作用，我们系统地研究了Al的存在以及Zn在γ-Al 2 O3上吸附/沉淀过程中矿物溶解的作用使用扩展X射线吸收精细结构光谱（EXAFS），高分辨率透射电子显微镜（HR-TEM），同步辐射粉末X射线衍射（SR-XRD）和Al-27固态NMR。EXAFS分析表明在Zn浓度>= 0.4mM时形成Zn-Al LDH沉淀，HR-TEM和SR-XRD均表明这些沉淀是结晶的。这些沉淀物在Al-27固态NMR谱中在δ（Al-27）=+12.5ppm处产生小肩，与典型Zn-Al LDH中的混合八面体Al/Zn化学环境一致。NMR分析为Al在沉淀物中的存在和γ-氧化铝基体溶解后的迁移提供了直接证据。为了进一步解决这个问题，我们比较了一系列具有相似化学组成的铝（氢）氧化物上的锌吸附机制。但使用EXAFS和TEM的溶解性不同。这些结果表明，在相同的实验条件下，Zn-Al LDH在γ-Al_2O_3和Al_2O_3上形成沉淀，而在三羟铝石、勃姆石和三水铝石等难溶矿物上不形成沉淀，表明基质矿物表面溶解在Zn-Al LDH沉淀的形成过程中起着重要作用。
To better understand the sequestration of toxic metals such as nickel (Ni), zinc (Zn), and cobalt (Co) as layered double hydroxide (LDH) phases in soils, we systematically examined the presence of Al and the role of mineral dissolution during Zn sorption/precipitation on gamma-Al2O3 (gamma-alumina) at pH 7.5 using extended X-ray absorption fine structure spectroscopy (EXAFS), high resolution transmission electron microscopy (HR-TEM), synchrotron-radiation powder X-ray diffraction (SR-XRD), and Al-27 solid-state NMR. The EXAFS analysis indicates the formation of Zn-Al LDH precipitates at Zn concentration >= 0.4 mM, and both HR-TEM and SR-XRD reveal that these precipitates are crystalline. These precipitates yield a small shoulder at delta(Al-27) = +12.5 ppm in the Al-27 solid-state NMR spectra, consistent with the mixed octahedral Al/Zn chemical environment in typical Zn-Al LDHs. The NMR analysis provides direct evidence for the existence of Al in the precipitates and the migration from the dissolution of gamma-alumina substrate. To further address this issue, we compared the Zn sorption mechanism on a series of Al (hydr)oxides with similar chemical composition. but differing dissolubility using EXAFS and TEM. These results suggest that, under the same experimental conditions, Zn-Al LDH precipitates formed on gamma-alumina and corundum but not on less soluble minerals such as bayerite, boehmite, and gibbsite, which point outs that substrate mineral surface dissolution plays an important role in the formation of Zn-Al LDH precipitates.