The nature of Zn precipitates formed in the presence of pyrophyllite
The nature of Zn precipitates formed in the presence of pyrophyllite
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DOI：
10.1021/es991330q
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发表时间：
2000-06-15
影响因子：
11.4
通讯作者：
Sparks, DL
中科院分区：
文献类型：
--
作者：
Ford, RG;Sparks, DL
在长达4个月的时间里，研究了锌在叶蜡石表面的分配与表面负荷的关系。利用x射线吸收精细结构光谱（XAFS）对反应产物进行检测表明，在每次表面加载时都形成Zn沉淀。将表面析出相的局部结构与各种含氢氧化物相和含碳酸盐相的结构进行比较，表明形成了Zn-Al层状双氢氧化物（LDH）。老化后Zn在叶叶石体系中的溶解度表明，初始Zn- al LDH析出物转变为更稳定的形式。这些实验体系中锌稳定性的提高可能归因于LDH结晶度的增加（奥斯特瓦尔德成熟）或LDH中间层中Si的掺入导致转变为层状硅酸盐样相。我们的研究结果支持在富含铝硅酸盐矿物的土壤中形成LDH沉淀作为锌固定的前驱物。这些结果增强了最近的发现，过渡金属在粘土矿物吸附过程中可能形成层状氢氧化物和层状硅酸盐样沉淀。认识到这一过程在某些土壤类型中是一种潜在的金属固存机制，对于评估污染物的衰减是很重要的。为这些地表沉淀物建立一个更全面的溶解度数据库将有助于作出更可靠的估计。
The partitioning of Zn to the pyrophyllite surface was studied as a function of surface loading for periods up to 4 months. Examination of the reaction products using X-ray absorption fine structure spectroscopy (XAFS) indicated the formation of a Zn precipitate at each surface loading. Comparison of the local structure of the surface precipitates to the structure of various hydroxide- and carbonate-bearing phases indicates the formation of a Zn-Al layered double hydroxide (LDH). The solubility of Zn following aging in pyrophyllite systems indicated that the initial Zn-Al LDH precipitates transformed to a more stable form. Increased Zn stability in these experimental systems may be attributed to an increase in LDH crystallinity (Ostwald ripening) or incorporation of Si within the LDH interlayer leading to transformation to a phyllosilicate-like phase. Our results support formation of an LDH precipitate as a precursor to Zn fixation in soils abundant in aluminosilicate minerals. These results augment recent findings that transition metals may form layered hydroxide and phyllosilicate-like precipitates during sorption to clay minerals. Acknowledgment of this process as a potential metal sequestration mechanism in certain soil types is important to assessment of contaminant attenuation. Development of a more comprehensive database of solubilities for these surface precipitates will facilitate more reliable estimates.