Influence of natural soil colloid’s stability on transport of copper-based nanoparticles in saturated porous media

Abstract

Subsurface transport of metal-based nanoparticles (NPs) is dominantly governed by soil colloids and pore water chemistry. The current understanding of colloid-aided transport of metal oxide NPs is very limited. Therefore, the present study has explored clay colloid-aided transport of CuO-NPs in saturated porous-sand media under the influence of various environmental parameters such as ionic strength (IS), and dissolved organic matter (DOM). The role of soil pore water (SPW) chemistry and natural-colloids (NC) extracted from different types of soil on the transport of CuO-NPs has also been investigated. Results suggest stable bentonite clay colloids (BCC) significantly enhance the transport of CuO-NPs in the saturated porous media, whereas an increase in the IS has decreased the mobility of CuO-NPs due to increased aggregation of BCC along with NPs. The introduction of DOM at a concentration of 1 mg/L resulted in 70.4% retention of CuO-NPs at 10 mM NaCl in the absence of BCC. Whereas, in the presence of BCC the retention has increased to 91.7% due to aggregation of BCC. In the case of SPW, the lower mobility of CuO-NPs was observed for alluvial and black soils having higher clay content with high salinity both in the presence and absence of NC. In contrast, higher mobility of CuO-NPs was found in the presence of NC in lateritic and red soils. Whereas, absence of NC in SPW from lateritic and red soils caused almost 100% retention. The impact of flow velocity was observed only in the case of a stable suspension system. The current study suggests NC extracted from four different soils has shown significant variations in their stability that impacted the co-transport of metal oxide NPs. Also, the soil having low salinity with higher clay content possess greater risk for the release of sorbed CuO-NPs in the surface and subsurface environment.