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Kinetics of Coupled Primary- and Secondary-Minimum Deposition of Colloids under Unfavorable Chemical Conditions
journal contribution
posted on 2007-10-15, 00:00 authored by Chongyang Shen, Baoguo Li, Yuanfang Huang, Yan JinThis 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.
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flow interruptiontransport modelsAdditional column experimentsUnfavorable Chemical ConditionsThis studybulk solutioncolumn experimentscolloid retentionlaboratory column experimentse.gforce boundary layer approximationtravel timeflow rateestimate collision efficiencies accountingMaxwell model predictionscolloid depositionExperimental collision efficiencies1156 nmMaxwell approachnanosized particlesTheoretical analysis
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