Acid-base properties of kaolinite, montmorillonite and illite at marine ionic strength
Acid-base properties of kaolinite, montmorillonite and illite at marine ionic strength
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DOI：
10.1016/j.chemgeo.2018.01.018
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发表时间：
2018-04
期刊：
影响因子：
3.9
通讯作者：
Yuxia Liu;D. Alessi;S. Flynn;Md Samrat Alam;Weiduo Hao;M. Gingras;Huazhang Zhao;K. Konhauser
中科院分区：
文献类型：
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作者：
Yuxia Liu;D. Alessi;S. Flynn;Md Samrat Alam;Weiduo Hao;M. Gingras;Huazhang Zhao;K. Konhauser
在边缘海洋环境中，如果现代泥浆的成分被用作古代页岩沉积物前体的替代物，那么了解粘土矿物在金属阳离子从水柱转移到海底中的作用是很重要的。在这项研究中，我们进行了三个自然丰富的粘土矿物（高岭石，蒙脱石和伊利石）在0.56 M NaCl电解质溶液的电位滴定，以确定在海水离子强度的每个粘土矿物的表面反应性。我们的研究结果表明，所有三种粘土矿物越来越阴离子的pH值从3增加到9，蒙脱石具有最高的负电荷。使用非静电（NEM）和静电（恒电容模型，CCM）表面络合模型（SCM）的电位滴定和吸附数据进行建模。双中心表面络合模型，包括一个基础硅氧烷表面中心（≡X-）和一个两性边缘中心（≡SOH），为每种矿物的质子化数据提供了极好的拟合。进行了镉（II）吸附实验来量化阳离子的大小吸附，结果表明10 g蒙脱石、伊利石和高岭石粉末可以结合4.7 × 10 - 4g的当量，4.3 × 10−4g和4.0 × 10−4g的Cd，在海水相关条件下（初始Cd浓度为8.9 × 10− 6 M，pH = 8）。为了将这一数值纳入现代河流粘土输入海洋的背景下，每年沉积13.5 × 109吨总悬浮沉积物（Milliman和米德，1983年），其中10 - 25%是粘土（曼海姆等人，1970; Schroeder等人，2015年）。吸附在悬浮粘土矿物上进入现代海洋的镉总量可能达到每年约104至105吨。这项研究的结果突出了粘土矿物在将金属从海洋水柱输送到海底方面的潜在作用。
In marginal marine settings, understanding the role that clay minerals play in the transfer of metal cations from the water column to the seafloor is important if the composition of modern muds is to be used as a proxy for the precursors of ancient shale deposits. In this study, we conducted potentiometric titrations of three naturally abundant clay minerals (kaolinite, montmorillonite and illite) in 0.56 M NaCl electrolyte solutions to ascertain the surface reactivity of each clay mineral at seawater ionic strength. Our results demonstrate that all three clay minerals were increasingly anionic as pH increases from 3 to 9, with montmorillonite having the highest negative-charge. The potentiometric titrations and adsorption data were modeled using both non-electrostatic (NEM) and electrostatic (constant-capacitance model, CCM) surface complexation models (SCMs). A two-site surface complexation model, that included one basal siloxane surface site (≡X−) and one amphoteric edge site (≡SOH), provided an excellent fit for the protonation data of each mineral. Cd(II) adsorption experiments were conducted to quantify the magnitude of cation adsorption, which showed that 10 g montmorillonite, illite, and kaolinite powder could bind an equivalent of 4.7 × 10−4g, 4.3 × 10−4g, and 4.0 × 10−4g of Cd, respectively, under conditions relevant to seawater (initial Cd concentration of 8.9 × 10−6M, and pH = 8). To place this value into the context of modern riverine clay inputs to the ocean, 13.5 × 109tons of total suspended sediment are deposited annually (Milliman and Meade, 1983) of which 10 to 25% is clay (Manheim et al., 1970; Schroeder et al., 2015). The total amount of Cd adsorbed to suspended clay minerals entering the modern oceans could then amount to approximately 104to 105tons per year. The results of this study highlight the potential role of clay minerals in transporting metals from the ocean water column to the seafloor.