Authors: Tanapon Phenrat Navid Saleh Kevin Sirk HyeJin Kim Robert D Tilton Gregory V Lowry
Publish Date: 2007/10/26
Volume: 10, Issue: 5, Pages: 795-814
Abstract
Nanoscale zerovalent iron NZVI particles are 5–40 nm sized Fe0/Feoxide particles that rapidly transform many environmental contaminants to benign products and are a promising in situ remediation agent Rapid aggregation and limited mobility in watersaturated porous media limits the ability to deliver NZVI dispersions in the subsurface This study prepares stable NZVI dispersions through physisorption of commercially available anionic polyelectrolytes characterizes the adsorbed polymer layer and correlates the polymer coating properties with the ability to prevent rapid aggregation and sedimentation of NZVI dispersions Polystyrene sulfonate with molecular weights of 70 k and 1000 k g/mol PSS70K and PSS1M carboxymethyl cellulose with molecular weights of 90 k and 700 k g/mol CMC90K and CMC700K and polyaspartate with molecular weights of 25 k and 10 k g/mol PAP25K and 10K were compared Particle size distributions were determined by dynamic light scattering during aggregation The order of effectiveness to prevent rapid aggregation and stabilize the dispersions was PSS70K83 ≈PAP10K82 PAP25K72 CMC700K52 where stability is defined operationally as the volume percent of particles that do not aggregate after 1 h CMC90K and PSS1M could not stabilize RNIP relative to bare RNIP A similar trend was observed for their ability to prevent sedimentation with 40 34 32 20 and 5 wt of the PSS70K PAP10K PAP25K CMC700K and CMC90K modified NZVI remaining suspended after 7 h of quiescent settling respectively The stable fractions with respect to both aggregation and sedimentation correlate well with the adsorbed polyelectrolyte mass and thickness of the adsorbed polyelectrolyte layers as determined by Oshima’s soft particle theory A fraction of the particles cannot be stabilized by any modifier and rapidly agglomerates to micron sized aggregates as is also observed for unmodified NZVI This nondispersible fraction is attributed to strong magnetic attractions among the larger particles present in the polydisperse NZVI slurry as the magnetic attractive forces increase as r6
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