The mechanisms governing the transport and retention kinetics of @entity6701 ( @entity3759 , rutile) nanoparticle (NP) aggregates were investigated in saturated porous media. Experiments were carried out under a range of well-controlled ionic strength (from DI water up to 1 mM) and ion valence ( @entity1219 vs @entity3282 ) comparable to the low end of environmentally relevant solution chemistry conditions. Solution chemistry was found to have a marked effect on the electrokinetic properties of NP aggregates and the sand and on the resulting extent of NP aggregate transport and retention in the porous media. Comparable transport and retention patterns were observed for NP aggregates in both @entity1219 and @entity3282 solutions but at much lower ionic strength with @entity3282 . Transport experimental results showed temporal and spatial variations of NP aggregate deposition in the column. Specifically, the breakthrough curves displayed a transition from blocking to ripening shapes, and the NP retention profiles exhibited a shift of the maximum NP retention segment from the end toward the entrance of the column gradually with increasing ionic strength. Additionally, the deposition rates of the NP aggregates in both @entity4338 and @entity3282 solutions increased with ionic strength, a trend consistent with traditional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Upon close examination of the results, it was found that the characteristics of the obtained transport breakthrough curves closely followed the general trends predicted by the DLVO interaction-energy calculations. However, the obtained NP retention profiles were found to deviate severely from the theory. We propose that a NP aggregate reconformation through collision between NP aggregates and sand grains reduced the repulsive interaction energies of NP-NP and NP-sand surfaces, consequently accelerating NP deposition with transport distance and facilitating approaching NP deposition onto NPs that had already been deposited. It is further suggested that @entity3759 NP transport and retention are determined by the combined influence of NP aggregate reconformation associated with solution chemistry, travel distance, and DLVO interactions of the system.

Transport and retention of XXXX rutile nanoparticles in saturated porous media under low-ionic-strength conditions: measurements and mechanisms.

@entity1219 :: ('CHEBI:26710', 'Chemical') :: ['NaCl'] @entity3759 :: ('CHEBI:32234', 'Chemical') :: ['TiO(2)'] @entity6701 :: ('MESH:C009495', 'Chemical') :: ['titanium dioxide'] @entity3282 :: ('CHEBI:3312', 'Chemical') :: ['CaCl(2)'] @entity4338 :: ('CHEBI:32588', 'Chemical') :: ['KCl']
@entity3759 :: (CHEBI:32234,Chemical) :: ['TiO2']
