Transport and deposition of CeO₂ nanoparticles in water-saturated porous media

Ceria nanoparticles are used for fuel cell, metal polishing and automobile exhaust catalyst; however, little is known about the impact of their release to the environment. The stability, transport and deposition of engineered CeO₂ nanoparticles through water-saturated column packed with sand were studied by monitoring effluent CeO₂ concentration. The influence of solution chemistry such as ionic strength (1-10 mM) and pH (3-9) on the mobility and deposition of CeO₂ nanoparticles was investigated by using a three-phase (deposition-rinse-reentrainment) procedure in packed bed columns. The results show that water chemistry governs the transport and deposition of CeO₂ nanoparticles. Transport is significantly hindered at acidic conditions (pH 3) and high ionic strengths (10 mM and above), and the deposited CeO₂ particles may not be re-entrained by increasing the pH or lowering the ionic strength of water. At neutral and alkaline conditions (pH6 and 9), and lower ionic strengths (below 10 mM), partial breakthrough of CeO₂ nanoparticles was observed and particles can be partially detached and re-entrained from porous media by changing the solution chemistry. A mathematical model was developed based on advection-dispersion-adsorption equations and it successfully predicts the transport, deposition and re-entrainment of CeO₂ nanoparticles through a packed bed. There is strong agreement between the deposition rate coefficients calculated from experimental data and predicted by the model. The successful prediction for attachment and detachment of nanoparticles during the deposition and re-entrainment phases is unique addition in this study. This work can be applied to access the risk of CeO₂ nanoparticles transport in contaminated ground water.