Impact of Sodium Humate Coating on Collector Surfaces on Deposition of Polymer-Coated Nanoiron Particles

Abstract

The affinity between nanoscale zerovalent iron (nano-ZVI) and mineral surfaces hinders its mobility, and hence its delivery into contaminated aquifers. We have tested the hypothesis that the attachment of poly(acrylic acid)-coated nano-ZVI (PAA-nano-ZVI) to mineral surfaces could be limited by coating such surfaces with sodium (Na) humate prior to PAA-nano-ZVI injection. Na humate was expected to form a coating over favorable sites for PAA-nano-ZVI attachment and hence reduce the affinity of PAA-nano-ZVI for the collector surfaces through electrosteric repulsion between the two interpenetrating charged polymers. Column experiments demonstrated that a low concentration (10 mg/L) Na humate solution in synthetic water significantly improved the mobility of PAA-nano-ZVI within a standard sand medium. This effect was, however, reduced in more heterogeneous natural collector media from contaminated sites, as not an adequate amount of the collector sites favorable for PAA-nano-ZVI attachment within these media appear to have been screened by the Na humate. Na humate did not interact with the surfaces of acid-washed glass beads or standard Ottawa sand, which presented less surface heterogeneity. Important factors influencing the effectiveness of Na humate application in improving PAA-nano-ZVI mobility include the solution chemistry, the Na humate concentration, and the collector properties.

Groundwater Chemistry Has a Greater Influence on the Mobility of Nanoparticles Used for Remediation than the Chemical Heterogeneity of Aquifer Media

“…the range and magnitude of repulsive double-layer interactions between particles . This reduced particle stability, increased the particle size distribution to d 10 / d 50 / d 90 = 1.7/5.8/31.6 μm, and resulted in a less negative particle ζ-potential of −24.2 ± 4.5 mV at a pH of 8.7 ± 0.2 (as reported previously). Moreover, Ca 2+ in MHW can induce aggregation by the specific complexation or bridging interactions with polyelectrolytes in the coatings …”

“…The concentrations of Cl – , SO 4 2– , NO 3 – , and HCO 3 – were 0.1, 0.8, 1.1, and 1.0 mM, respectively. A complete chemical analysis of this synthetic water has been reported in a previous publication …”

“…A complete chemical analysis of this synthetic water has been reported in a previous publication. 12 2.2. Preparation and Characterization of the Nanoparticle Suspension.…”

“…Chemical and physical heterogeneities of the collector surfaces due, for example, to variations in the mineral composition and roughness affect the affinity of nanoparticles for the collector surfaces. , Chemical heterogeneities of collector surfaces have a marked effect on the surface charge distribution, which governs nanoparticle transport and deposition onto collector surfaces. , Preferential deposition of nanoparticles occurs when the electric double-layer repulsion between particles and sites on the collector surfaces is sufficiently small. It also occurs at favorable sites on the collector surfaces, i.e.…”

Environmental Transformations and Algal Toxicity of Single-Layer Molybdenum Disulfide Regulated by Humic Acid

“…The transformations of nanomaterials in environmental media, including changes in the physical structure, chemical dissolution (ion release), and sulfidation, are factors that determine the biocompatibility and risk assessment of nanomaterials. − The cytotoxicity of Ag and CuO has been shown to be attenuated with partial physical release and chemical transformations in environmental media. − Therefore, whether environmental or biological transformations are beneficial for the biological safety of SLMoS 2 -based nanomaterials is worth investigation. A deep understanding of the environmental transformations of SLMoS 2 nanosheets must be gained prior to their large-scale applications.…”