Kinetics of Coupled Primary- and Secondary-Minimum Deposition of Colloids under Unfavorable Chemical Conditions

Abstract

This study examines the deposition/release mechanisms involved in colloid retention under unfavorable conditions through theoretical analysis and laboratory column experiments. A Maxwell approach was utilized to estimate the coupled effects of primary- and secondary-minimum deposition. Theoretical analysis indicates that the secondary energy minimum plays a dominant role in colloid deposition even for nanosized particles (e.g., 20 nm) and primary-minimum deposition rarely happens for large colloids (e.g., 1000 nm) when diffusion is the dominant process. Polystyrene latex particles (30 and 1156 nm) and clean sand were used to conduct three-step column experiments at different solution ionic strengths, a constant pH of 10, and a flow rate of 0.0012 cm/s. Experimental results confirm that small colloids can also be deposited in secondary minima. Additional column experiments involving flow interruption further indicates that the colloids deposited in the secondary energy well can be spontaneously released to bulk solution when the secondary energy minimum is comparable to the average Brownian kinetic energy. Experimental collision efficiencies are in good agreement with Maxwell model predictions but different from the theoretical values calculated by the interfacial force boundary layer approximation. We propose a priori analytical approach to estimate collision efficiencies accounting for both primary- and secondary-minimum deposition and suggest that the reversibility of colloid (e.g., viruses and bacteria) deposition must be considered in transport models for accurate predictions of their travel time in the subsurface environments.

Transport and Deposition of Carbon Nanoparticles in Saturated Porous Media

“…The zeta potential of carbon ball in distilled water was measured to be −43 mV. Particle concentrations were determined by UV-Vis spectrophotometer (UV-1800, Shimadzu, Kyoto, Japan) based on Beers-lambert law at the wavelength of 320 nm for 200 nm particle and 310 nm for the 5 nm, respectively [45].…”

“…After adding each layer of 1.5 cm glass beads, vibration was applied for 3 min using a vortex mixer. During vibration, proper strength was applied on the top of the column by one hand to keep Particle concentrations were determined by UV-Vis spectrophotometer (UV-1800, Shimadzu, Kyoto, Japan) based on Beers-lambert law at the wavelength of 320 nm for 200 nm particle and 310 nm for the 5 nm, respectively [45].…”

“…According to [45], the experimental sticking efficiency α exp can also be obtained from the following expression derived for the case where particles move across a packed bed of identical collectors with length L:…”

Equilibrium and kinetic models for colloid release under transient solution chemistry conditions

“…Under steady-state flow and solution chemistry conditions low amounts of colloids are slowly released from the solid phase when the kinetic energy of diffusing colloids exceeds the adhesive interaction energy (Ryan and Elimelech, 1996;Ryan and Gschwend, 1994;Shen et al, 2007). Conversely, significant amounts of colloid release may rapidly occur during temporal changes (i.e., transients) in solution chemistry (Grolimund et al, 2001;Roy and Dzombak, 1996) and/or water velocity Grasso, 1998, 2000).…”

“…Colloid immobilization and release at a particular location on the collector surface depend on the strength of the resisting adhesive torque in comparison to the applied hydrodynamic torque Grasso, 1998, 2000), and the adhesive interaction energy relative to the kinetic energy of diffusing colloids (Shen et al, 2007;Simoni et al, 1998). Transients in water velocity alter the hydrodynamic force that acts on immobilized colloids Grasso, 1998, 2000), and is spatially variable because of the complex geometry of the pore space (Bradford et al, 2011).…”