At low surfactant concentrations often non-linear sorption processes are observed when natural adsorbents like sediment or soil are involved. This sorption process is often explained by a Dual-Model (DM) model, which assumes sorption to an adsorbent to be based on a combined ionic-polar and non-polar sorption interaction term. An Independent-Mode (IM) model, however, could treat surfactant sorption as two independent sorption processes to which the non-polar and ionic-polar features of the surfactant molecule contribute differently. For both models the overall exact partition coefficient, K^total_p, and its corresponding total standard free enthalpy of adsorption, Δ_sG⁰_total, are derived. We tested the outcome of both models against multiple published experimental sorption data sets by, (i) varying the organic carbon fraction, (ii) constructing sorption and partition isotherms over different concentration ranges, (iii) removing the organic carbon fraction, (iv) applying different types of mixtures of surfactants, and (v) explaining sorption hysteresis in desorption studies based on either continuous and successive washing steps. It turned out that only the IM model was able to explain the reported sorption phenomena. We also show that when one interaction is dominating, e.g. non-polar over ionic-polar, the Δ_sG⁰_total of the IM model can be approximated by the sum of the different Δ_sG⁰ values, the Δ_sG⁰_total of the DM model. The exact partition coefficient, K_p(C_w) (L kg⁻¹) = dC_s (mmol kg⁻¹)/dC_w (mmol L⁻¹), is turning each sorption isotherm into a partition isotherm that provides the K_p values required in environmental risk assessment models.

中文翻译：

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表面活性剂以与环境相关的浓度吸附到沉积物上：以独立模式作为统一概念。

在低表面活性剂浓度下，当涉及天然吸附剂（如沉积物或土壤）时，通常会观察到非线性吸附过程。该吸附过程通常由双重模型（DM）模型解释，该模型假定对吸附剂的吸附基于离子-极性和非极性吸附相互作用项的组合。但是，独立模式（IM）模型可以将表面活性剂的吸附视为两个独立的吸附过程，表面活性剂分子的非极性和离子极性特征对它们的贡献不同。两个模型的总体精确分配系数，ķ^总_p，和吸附的其相应的总的标准自由焓，Δ_小号ģ ⁰_总，是派生的。我们针对以下多个公开的实验吸附数据集测试了两个模型的结果，方法是：（i）改变有机碳分数，（ii）构建不同浓度范围内的吸附和分配等温线，（iii）去除有机碳分数，（iv）使用不同类型的表面活性剂混合物，以及（v）在基于连续和连续洗涤步骤的解吸研究中解释吸附滞后。事实证明，只有IM模型才能解释所报道的吸附现象。我们还表明，当一个相互作用支配，例如非极性过离子极性的，所述Δ_小号ģ ⁰_总的IM模型可以通过不同的Δ的总和近似_小号ģ⁰值时，Δ_小号ģ ⁰_总的DM模式。精确的分配系数K _p（ C _w）（L kg ^-1）= d C _s（mmol kg ^-1）/ d C _w（mmol L ^-1），正在将每个吸附等温线转变为提供等值线的分配等温线。环境风险评估模型中要求的K _p值。