Humic Acid Facilitates the Transport of ARS-Labeled Hydroxyapatite Nanoparticles in Iron Oxyhydroxide-Coated Sand

Abstract

Hydroxyapatite nanoparticles (nHAP) have been widely used to remediate soil and wastewater contaminated with metals and radionuclides. However, our understanding of nHAP transport and fate is limited in natural environments that exhibit significant variability in solid and solution chemistry. The transport and retention kinetics of Alizarin red S (ARS)-labeled nHAP were investigated in water-saturated packed columns that encompassed a range of humic acid concentrations (HA, 0-10 mg L(-1)), fractional surface coverage of iron oxyhydroxide coatings on sand grains (λ, 0-0.75), and pH (6.0-10.5). HA was found to have a marked effect on the electrokinetic properties of ARS-nHAP, and on the transport and retention of ARS-nHAP in granular media. The transport of ARS-nHAP was found to increase with increasing HA concentration because of enhanced colloidal stability and the reduced aggregate size. When HA = 10 mg L(-1), greater ARS-nHAP attachment occurred with increasing λ because of increased electrostatic attraction between negatively charged nanoparticles and positively charged iron oxyhydroxides, although alkaline conditions (pH 8.0 and 10.5) reversed the surface charge of the iron oxyhydroxides and therefore decreased deposition. The retention profiles of ARS-nHAP exhibited a hyperexponential shape for all test conditions, suggesting some unfavorable attachment conditions. Retarded breakthrough curves occurred in sands with iron oxyhydroxide coatings because of time-dependent occupation of favorable deposition sites. Consideration of the above effects is necessary to improve remediation efficiency of nHAP for metals and actinides in soils and subsurface environments.

Do Goethite Surfaces Really Control the Transport and Retention of Multi-Walled Carbon Nanotubes in Chemically Heterogeneous Porous Media?

“…This result is consistent with bacteria transport studies in various fractions of iron oxide-coated sands, 25,26 but a linear increase in k sw1 with λ has been reported for nanoparticles. 27,64 This discrepancy is likely related to differences in the size of the a IS was 1 mM KCl. The input concentration of MWCNT was 1 mg L −1 .…”

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“…The first kinetic Site-1 colloid , time-dependent retention, assumes reversible retention using first-order retention (k 1a ) and detachment (k 1d ) coefficients, and a Langmuirian approach blocking function (Adamczyk et al, 1994;Wang et al, 2012) to account for maximum soil colloid content on Site-1 colloid of sand (S max1 ). The second kinetic Site-2 colloid , depth-dependent retention, assumes irreversible retention using a first-order retention coefficient (k 2a ) and a depthdependent blocking function (Bradford et al, 2003;Wang et al, 2012). s 1 and s 2 are the retained colloid contents in column sand associated with Site-1 colloid and Site-2 colloid , respectively.…”

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“…Many researchers pointed out that taking into consideration of model-fitted parameters is vital to gain insight in understanding colloid deposition mechanisms (Wang et al, 2012;Gamerdinger and Kaplan, 2001;van Genuchten and Wagenet, 1989). They demonstrated that the breakthrough curves (BTCs) of colloids can be adequately fitted using a variety of models.…”