Mechanisms of TiO2 nanoparticle transport in porous media: Role of solution chemistry, nanoparticle concentration, and flowrate

► Removal mechanisms depend on nanoparticle concentration, flowrate, pH and ionic strength. ► Combination of mechanisms including straining, blocking, and aggregate breakup. ► Aggregate size is important parameter for removal under unfavorable conditions. ► Under favorable conditions, blocking leads to greater elution with nanoparticle concentration. ► Increased flowrate leads to more elution due to aggregate breakup.