Diffusion is the main transport process of water and solutes in clay-rich porous media owing to their very low permeability, so they are widely used as barriers against contaminant spreading. However, the prediction of contaminant mobility can be very complicated when these media are partially water-saturated. We conducted diffusion experiments for water (HTO and HDO) and ions (²²Na⁺ and ¹²⁵I⁻) through partially water saturated compacted kaolinite, a weakly charged clay material, to quantify the distinct diffusive behavior of these species. The osmosis method was used to set kaolinite samples at 67, 86 and 100% saturation. The results showed that desaturation led to a sharp decrease in diffusive rates by factors of 6.5, 18 and 35 for HTO, ¹²⁵I⁻ and ²²Na⁺, respectively, from 100 to 67% of the degree of saturation. Thus, to interpret water diffusivities, we proposed a model taking into account the diffusion of water in both gas and liquid phases, using diffusion data obtained for ions, considered as inert species. This model was capable of properly predicting water diffusive flux, especially at a low degree of saturation (67% saturation), for which the assumption made for the occurrence of air phase continuity throughout the sample appears to be more relevant than at 86% saturation.

扩散是水和溶质在富含粘土的多孔介质中的主要传输过程，由于其渗透率非常低，因此它们被广泛用作防止污染物扩散的屏障。然而，当这些介质部分水饱和时，污染物流动性的预测可能非常复杂。我们对水（HTO 和 HDO）和离子（²² Na ⁺和¹²⁵ I ^- ）通过部分水饱和的压实高岭石（一种弱电荷粘土材料）进行了扩散实验，以量化这些物种的不同扩散行为。渗透法用于将高岭石样品设置为 67、86 和 100% 的饱和度。结果表明，^{去饱和导致 HTO、 125} I ^-和²² Na ^{+的扩散率}分别从饱和度的 100% 到 67%急剧下降 6.5、18 和 35 倍。因此，为了解释水的扩散率，我们提出了一个模型，该模型考虑了水在气相和液相中的扩散，使用了被认为是惰性物质的离子的扩散数据。该模型能够正确预测水的扩散通量，尤其是在低饱和度（67% 饱和度）下，对于这种情况，整个样品中出现空气相连续性的假设似乎比 86% 饱和度时更相关。