Division of Environmental Science and Ecological Engineering, Korea University, Seoul 136-713, Republic of Korea.
Chemosphere. 2013 Sep;93(1):133-9. doi: 10.1016/j.chemosphere.2013.05.005. Epub 2013 May 31.
The cosolvency model was not applicable for predicting the sorption of organic carboxylic acids. The reason of inapplicability was investigated by analyzing the solubility (Sm) and sorption (Km) of benzoic acid, 2,4-dichlorophenoxyacetic acid (2,4-D), and 2,4,6-trichlorophenol (2,4,6-TCP). The Sm and Km by two iron-rich soils was measured as a function of methanol volume fraction (fc), electrolyte compositions, and pH(app). For 2,4,6-TCP, the Km of both neutral and anion species was well-explainable by the cosolvency model, exemplifying the knowledge of cosolvency power (σ) being sufficient to describe its sorption. However, for benzoic acid and 2,4-D, the Km of organic anions increased with fc, illustrating the organic carboxylate to be responsible for the deviation. The Sm of organic anions was not affected by the ionic valence (Ca(2+) vs. K(+)) of liquid phase. Among hydrophilic quantities of the 2,4-D sorption, the fraction of anion exchange increased with fc while the fraction of Ca-bridge decreased in the same range. Adding solvent in soil-water system is likely to render soil surface charge more positive, fortifying the anion exchange, but opposing the formation of Ca-bridging. Therefore, it can be concluded that the positive Km-fc relationship is due to the anion exchange of organic carboxylate with positively charged soil surface, whose contribution is >50% of overall sorption at solvent-free system and becomes greater with fc up to 82%.
共溶剂模型不适用于预测有机羧酸的吸附。通过分析苯甲酸、2,4-二氯苯氧基乙酸（2,4-D）和 2,4,6-三氯苯酚（2,4,6-TCP）的溶解度（Sm）和吸附（Km），研究了不适用性的原因。两种富铁土壤的 Sm 和 Km 作为甲醇体积分数（fc）、电解质组成和 pH（app）的函数进行了测量。对于 2,4,6-TCP，中性和阴离子物种的 Km 均可通过共溶剂模型很好地解释，这表明共溶剂能力（σ）足以描述其吸附。然而，对于苯甲酸和 2,4-D，有机阴离子的 Km 随 fc 增加，这表明有机羧酸根负责偏差。有机阴离子的 Sm 不受液相离子价（Ca(2+) 与 K(+))的影响。在 2,4-D 吸附的亲水性量中，阴离子交换的分数随 fc 增加而增加，而在相同范围内 Ca 桥的分数减少。在土壤-水系统中添加溶剂可能会使土壤表面电荷带更多正电荷，从而加强阴离子交换，但反对 Ca 桥的形成。因此，可以得出结论，Km-fc 关系呈正相关是由于有机羧酸根与带正电荷的土壤表面的阴离子交换，其在无溶剂体系中的贡献>50%，并且随着 fc 增加到 82%而变得更大。
