Aggregation and Sedimentation of Aqueous Nanoscale Zerovalent Iron Dispersions

Abstract

Nanoscale zerovalent iron (NZVI) rapidly transforms many environmental contaminants to benign products and is a promising in-situ remediation agent. To be effective, NZVI should form stable dispersions in water such that it can be delivered in water-saturated porous media to the contaminated area. Limited mobility of NZVI has been reported, however, attributed to its rapid aggregation. This study uses dynamic light scattering to investigate the rapid aggregation of NZVI from single nanoparticles to micrometer size aggregates, and optical microscopy and sedimentation measurements to estimate the size of interconnected fractal aggregates formed. The rate of aggregation increased with increasing particle concentration and increasing saturation magnetization (i.e., the maximum intrinsic magnet moment) of the particles. During diffusion limited aggregation the primary particles (average radius = 20 nm) aggregate to micrometer-size aggregates in only 10 min, with average hydrodynamic radii ranging from 125 nm to 1.2 microm at a particle concentration of 2 mg/L (volume fraction(phi= 3.2 x 10(-7)) and 60 mg/L (phi = 9.5 x 10(-6)), respectively. Subsequently, these aggregates assemble themselves into fractal, chain-like clusters. At an initial concentration of just 60 mg/L, cluster sizes reach 20-70 microm in 30 min and rapidly sedimented from solution. Parallel experiments conducted with magnetite and hematite, coupled with extended DLVO theory and multiple regression analysis confirm that magnetic attractive forces between particles increase the rate of NZVI aggregation as compared to nonmagnetic particles.

Metal‐based nanoparticles in soil: Fate, behavior, and effects on soil invertebrates

“…1). Using iron NPs, Phenrat et al [40] found that higher concentrations (60 mg/L) resulted in higher aggregation rates and stability of aggregate size in comparison with lower concentrations (2 mg/L). Zinc oxide NPs dispersed in aqueous solution aggregated in a wide range of sizes, resulting in aggregates almost 10-fold larger than the primary NPs [41,42].…”

Characterization of green zero-valent iron nanoparticles produced with tree leaf extracts

“…It is also known that nZVIs have the tendency to agglomerate, forming bigger structures that tend to settle, reducing their reactivity due to the decrease of the surface area (Phenrat et al, 2006). Therefore, the study of the agglomeration/settling tendency of the different green nZVIs is essential.…”

“…These nanomaterials have the capacity to percolate through very small pores in the soil subsurface, or to remain suspended in the groundwater, allowing the nanoparticles to react longer, disperse better and reach locations farther than bigger particles. However, in real situations, and because of agglomeration and adsorption processes, the nanomaterials have a limited radius of influence (Phenrat et al, 2006). Nevertheless, nanomaterials have an enormous potential for environmental remediation.…”

Application of green zero-valent iron nanoparticles to the remediation of soils contaminated with ibuprofen

“…Efficiencies of ibuprofen degradation in aqueous solution using nZVIs produced from different extracts (nZVI concentrations of 2.7, 9.8 and 14 mmol L −1 for tea leaves, grape marc, and vine leaves, respectively) at different pHs (3 and 7). zones (Schrick et al, 2004;Phenrat et al, 2007). The degradation firstly occurs at the more superficial zone of the soil and, as the nZVIs move downwards, its surface oxidizes through the reaction with ibuprofen and oxygen, located in the soil pores or dissolved in the soil moisture, decreasing their reactivity.…”