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首页> 外文期刊>Environmental Science & Technology >Three-parameter empirical isotherm model: Its application to sorption onto organoclays
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Three-parameter empirical isotherm model: Its application to sorption onto organoclays

机译：三参数经验等温线模型：在吸附到有机粘土上的应用

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摘要

A new three-parameter empirical isotherm model (the Song isotherm model, hereinafter) is proposed. This model satisfies the Henry's law and the Freundlich isotherm model in the low and high concentration ranges, respectively. We applied this model to the single-solute sorption of 2-chloro-, 3-cyano-, and 4-nitrophenol from water to montmorillonites organically modified with either hexadecyltrimethylammonium (HDTMA) cation or both HDTMA and tetra methylammonium (TMA) dual cations. Sorption to organoclays (i.e., organically modified clays) modified with the long-hydrocarbon chain organic cations or the short- and long-hydrocarbon chain dual organic cations usually occurs by a partition mechanism. Sorption of polar organic compounds to organoclays, however, becomes nonlinear when the solution-phase concentration covered is more than 3 orders of magnitude. The three parameters contained in the presently proposed model could be estimated from the plot, log(q/c) versus log c. The partition coefficient in the Henry's law region (K) can be estimated from the ordinate value of the asymptote in the low concentration region, the Freundlich index (n) can be estimated from the slope of the asymptote in the high concentration region, and the parameter (beta) corresponding to the crossover point can be estimated from the intersection point of the two asymptotes. By performing nonlinear curve fitting to the raw data, q versus c, using the initial guesses estimated from the manipulated data, log(q/c) versus log c, the optimum set of parameters could be determined without worrying much over the annoying local minima. The Song model was compared with other existing two- and three-parameter isotherm models. The Song model fitted our experimental data better than the Langmuir and Freundlich models and showed nearly the same goodness-of-fit as the Redlich-Peterson and dual-mode models. The obvious merit of the Song model is that it provides us with the partition 'coefficient in the Henry's law region. The organic carbon-normalized partition coefficients in the Henry's law region were found to be about 1 order of magnitude higher than the corresponding octanol-water partition coefficients, at least for the phenolic compounds covered in this study.
机译：提出了一种新的三参数经验等温线模型（以下称为Song等温线模型）。该模型分别在低和高浓度范围内满足亨利定律和Freundlich等温线模型。我们将此模型应用于从水中到通过十六烷基三甲基铵（HDTMA）阳离子或HDTMA和四甲基铵（TMA）双阳离子有机改性的蒙脱石上的2-氯-，3-氰基-和4-硝基苯酚的单质吸附。通常通过分配机理吸附到用长烃链有机阳离子或短烃链和长烃链双重有机阳离子改性的有机粘土（即，有机改性的粘土）上。但是，当所覆盖的溶液相浓度超过3个数量级时，极性有机化合物对有机粘土的吸附将变为非线性。当前提出的模型中包含的三个参数可以从曲线log（q / c）与log c进行估计。亨利定律区域（K）的分配系数可以从低浓度区域的渐近线的坐标值估算出来，弗氏指数（n）可以从高浓度区域的渐近线的斜率估算出来，可以从两个渐近线的交点估计与交点对应的参数β。通过使用从操纵数据log（q / c）到log c估计的初始猜测值对原始数据q和c进行非线性曲线拟合，可以确定最佳参数集，而不必担心烦人的局部最小值。将Song模型与其他现有的两参数和三参数等温线模型进行了比较。 Song模型比Langmuir和Freundlich模型更好地拟合了我们的实验数据，并且显示出与Redlich-Peterson模型和双模式模型几乎相同的拟合优度。 Song模型的明显优点是，它为我们提供了亨利定律区域中的分区系数。至少对于本研究覆盖的酚类化合物，亨利定律区域的有机碳归一化分配系数比相应的辛醇-水分配系数高约1个数量级。

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