Transport of aluminum oxide nanoparticles in saturated sand: Effects of ionic strength, flow rate, and nanoparticle concentration

The effect of ionic strength (IS), flow rate, and nanoparticle concentration on the transport and deposition of aluminum oxide nanoparticles (Al2O3 NPs) in saturated sand was investigated. Mobility of Al2O3 NPs was influenced by IS, the highest mobility was observed in DI water (97% elution of the influent) and decreased with increasing ionic strength. Decreased mobility of the NPs was due to aggregation as the IS increased. Varying flow conditions did not have a significant effect on mobility. However, increased and faster elution was observed when the influent concentration was increased from 50 mg/L to 400 mg/L. The influent and effluent nanoparticle sizes were also measured using dynamic light scattering. For most conditions, the size was observed to be below 100 nm and there was no significant change to the influent and effluent particle sizes. Significant elution was observed although conditions were electrostatically favorable, which was attributed to the small, stable size (~ 82 nm) of the particles and blocking. DLVO theory was also applied to the data to better understand the mechanisms of mobility. It is necessary to consider these mechanisms for a reliable prediction of transport through the subsurface and potential removal methods such as filtration.