大多数原位补救技术的有效性,包括纳米修复,取决于试剂成功输送到地下目标处理区。靶向递送工程纳米颗粒(NP)以处理存在于不饱和区中的石油烃需要了解它们在这些系统中的传输行为。一系列柱实验探索了初始水饱和度的影响,流量,输入剂量,和多孔介质织构上的氧化铁或涂覆有两亲性共聚物的钴铁氧体NP的运输,以及他们对原油区的目标依附。随着初始含水量的增加,空气饱和度随之降低,NP穿透曲线(BTC)中存在的拖尾程度降低,恢复的NP质量增加。空气饱和度与空气-水界面的大小呈正相关,提供额外的NP保留位点。在较低的注射流速下,由于更长的停留时间和相对较高的空气饱和度,NP保留率增加。在测试范围内,NP转运行为对NP注射剂量不敏感。在粘土和粉砂含量较高的沉积物中观察到NPBTC的保留和延迟增加。用较低浓度的Pluronic嵌段共聚物涂覆以促进结合的NP优先保留在原油区内。为了模拟从非饱和系统观察到的不对称NP穿透曲线,需要使用一个模型,该模型既考虑了流动区域,也考虑了固定流动区域,以及具有非线性Langmuirian阻塞的NP附着和脱离。该模型允许检查附着和脱离速率系数,该系数捕获了NP与多孔介质和/或原油的相互作用。发现初始水饱和度和流量对NP附着率系数没有明显影响,随着粘土和粉土含量的增加,它增加了~10×,在原油存在的情况下,大约100倍,表明原油区内优先的NP附着。由于使用了较低的NP聚合物浓度涂层来促进对原油的附着增加,在柱入口附近观察到较高的保留率,并通过向模型中添加深度依赖性应变项来定量捕获。这种保留行为代表了空气-水界面处的不可逆附着和由于NP聚集体的形成而增强的柱入口附近的应变的组合。分离率系数随初始含水饱和度和流量的降低而降低,但随着粘土和粉砂含量的增加而增加。这项研究的发现有助于我们理解Pluronic涂层NP在不饱和条件下的运输和结合行为,特别是,初始含水量的作用,流量和多孔介质质地。NPs向靶区的证明递送是扩大NPs作为治疗试剂的效用的重要步骤。
The effectiveness of most in situ remedial technologies, including nanoremediation, lies on successful delivery of reagents to a subsurface target treatment zone. Targeted delivery of engineered nanoparticles (NPs) to treat petroleum hydrocarbons present in the unsaturated zone requires an understanding of their transport behaviour in these systems. A series of column experiments explored the effect of initial water saturation, flowrate, input dosage, and porous medium texture on the transport of iron oxide or cobalt ferrite NPs coated with an amphiphilic co-polymer, as well as their targeted attachment to a crude oil zone. As the initial water content increased with a concomitant reduction in air saturation, the degree of tailing present in the NP breakthrough curves (BTCs) reduced, and the mass of NPs recovered increased. Air saturation is positively correlated with the magnitude of air-water interfaces, which provide additional NP retention sites. At a lower injection flow rate, NP retention increased due to a longer residence time and comparatively high air saturation. NP transport behaviour was not sensitive to NP injection dose over the range tested. Increased retention and retardation of the NP BTC was observed in sediments with a higher clay and silt content. NPs coated with a lower concentration of a Pluronic block co-polymer to promote binding were preferentially retained within the crude oil zone. To simulate the asymmetrical NP breakthrough curves observed from the unsaturated systems required the use of a model that accounted for both mobile and immobile flow regions as well as NP attachment and detachment with nonlinear Langmuirian blocking. This model allowed examination of attachment and detachment rate coefficients which captured NP interaction with the porous medium and/or crude oil. It was found that the initial water saturation and flow rate did not have an appreciable impact on the NP attachment rate coefficient, while it increased by ~10× with increasing clay and silt content, and by ~100× in the presence of crude oil, indicating preferential NP attachment within the crude oil zone. As a result of the lower NP polymer concentration coating used to promote increased attachment to crude oil, higher retention was observed near the column inlet and was captured quantitatively by adding a depth-dependent straining term to the model. This retention behaviour represents a combination of irreversible attachment at the air-water interfaces and straining near the column inlet enhanced by the formation of NP aggregates. The detachment rate coefficient decreased with a lower initial water saturation and flowrate, but increased with higher clay and silt content. The findings from this study contribute to our understanding of the transport and binding behaviour of Pluronic-coated NPs in unsaturated conditions and, in particular, the role of initial water content, flowrate and porous medium texture. Demonstrated delivery of NPs to a target zone is an important step towards expanding the utility of NPs as treatment reagents.