人工纳米颗粒在饱和石英砂介质中的运移行为

Transport of artificial nanoparticles in saturated sand media

以生物炭为代表的人工碳材料广泛应用于环境污染的控制和修复,而其中产生的纳米级颗粒可能会迁移或携带污染物共迁移进入地下水环境而加剧污染风险.通过室内一维砂柱实验,研究离子强度(ionic strength,IS)、pH、流速和共存有机污染物(对乙酰氨基酚(acetaminophen,AP))对生物炭纳米颗粒在饱和多孔介质中运移和滞留行为的影响程度和机理.结果表明,纳米级生物炭颗粒在饱和多孔介质中的运移能力较强.生物炭和石英砂的电负性均随着IS的降低、pH的增加而增强,两者之间的静电斥力作用随之增大,造成生物炭在砂粒表面的附着减少从而促进了运移,降低了生物炭在饱和砂柱中的滞留量.流速的增加同样对生物炭的运移具有促进作用,这主要是由增强的水流剪切作用所致.此外,有机污染物AP的存在对生物炭颗粒的运移性具有抑制作用,其在石英砂介质中的滞留量随AP浓度的升高而增大.

Artificial carbonaceous materials,such as biochar,have been widely used in the environmental pollution control and remediation.During the application,nanoparticles(NPs)of these carbonaceous materials will inevitably be produced,and these particles may migrate into the subsurface eventually or even facilitate the transport of contaminants into groundwater,increasing the risk of environmental pollution.Therefore,a comprehensive understanding of the transport and retention behaviors of NPs in porous media is critical to the development of remediation technology using carbonaceous materials.In this study,laboratory saturated columns were packed with silica sand to elucidate the transport and retention behaviors of biochar NPs in saturated porous media under various physicochemical conditions,and the effect of ionic strength(IS),pH,and flow velocity was investigated.Furthermore,acetaminophen(AP),a representative non⁃steroidal anti⁃inflammatory drug that has been widely detected in the subsurface,was chosen as the model organic contaminant in this study,so as to explore the influence of co⁃existing organic contaminant on the transport of NPs in sand columns.The results showed that the mobility of biochar NPs was relatively high in saturated sand media.Both biochar NPs and sand became more negatively charged at decreased IS and increased pH,which would introduce stronger electrostatic repulsions between biochar NPs and sand grains.As a result,the attachment of biochar onto the sand surface was decreased and thus promoted the transport of biochar NPs,and particles were less retained in saturated sand columns.Higher mobility of biochar NPs was observed with the increase of flow velocity,mainly owing to the enhanced hydrodynamic shear.In addition,the presence of AP was found to inhibit the transport of biochar NPs,which could be attributed to the decreased electrostatic repulsions due to compression of electrical double layer,as well as masking of the negatively charged sites on particles due to AP adsorption.The deposition of biochar NPs in saturated sand media increased with increasing AP concentrations.Overall,the results from this study give insight into the transport behaviors of biochar NPs in porous media,and have implications to the prediction and assessment of the risks of NPs in the subsurface.