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ARS Home » Pacific West Area » Riverside, California » Agricultural Water Efficiency and Salinity Research Unit » Research » Publications at this Location » Publication #374379

Research Project: Identifying, Quantifying and Tracking Microbial Contaminants, Antibiotics and Antibiotic Resistance Genes in Order to Protect Food and Water Supplies

Location: Agricultural Water Efficiency and Salinity Research Unit

Title: Impact of phosphate adsorption on the mobility of PANI-supported nano zero-valent iron

item LIN, DANTONG - Tsinghua University
item Bradford, Scott
item HU, LIMING - Tsinghua University
item LO, IRENE - Hong Kong University Of Science

Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2020
Publication Date: 1/18/2021
Citation: Lin, D., Bradford, S.A., Hu, L., Lo, I. 2021. Impact of phosphate adsorption on the mobility of PANI-supported nano zero-valent iron. Vadose Zone Journal. 20(2). Article e20091.

Interpretive Summary: Groundwater contamination is an important problem in many regions of the United States, and remediation can be greatly enhanced by injection of nano-sized iron particles at these sites. However, adsorption of groundwater contaminants on the iron particles may enhance their groundwater mobility and thereby create a pollution source. Studies were undertaken to assess the potential risks from contaminant adsorption on iron particles. Results demonstrate that adsorption of a negatively charged contaminant like phosphate increased the mobility of iron particles and facilitated contaminant transport. This information indicates a potential risk from using nano-sized iron to remediate contaminated sites. This information will be of interest to scientists and engineers concerned with protecting groundwater quality and remediating hazardous waste sites with iron particles.

Technical Abstract: Nano zero-valent iron (nZVI) has been used for in situ groundwater remediation due to its strong adsorption and reaction characteristics. However, oxyanion contaminants in groundwater can ready adsorbed onto the surface of nZVI. This can potentially alter the mobility of nZVI and create a secondary pollution source, but these issues have not yet been systematically investigated. In this study, polyaniline-supported nZVI (PnZVI) and phosphate-sorbed PnZVI (PS-PnZVI) were synthesized in the laboratory. The sedimentation and transport behavior of these two nZVI particles were investigated, compared, and mathematically modeled to better understand the impact of phosphate adsorption on these processes. Results showed that phosphate adsorption can enhance the stability and mobility of PnZVI. Interaction energy calculations that considered van der Waals and magnetic attraction, electrostatic double layer and Born repulsion, and the influence of nanoscale roughness and binary charge heterogeneity were conducted to better infer mechanisms causing nZVI particle sedimentation and retention. Nanoscale roughness and binary charge heterogeneity were found to significantly decrease the energy barrier, but not to low enough levels to explain the observed behavior. The rapid settling of PnZVI was attributed to strong magnetic attraction between particles, which produced rapid aggregation and retention due to straining and/or hydrodynamic bridging. Phosphate adsorption enhanced the mobility of PS-PnZVI in comparison with PnZVI due to a decrease in particle size and aggregation, and an increase in the energy barrier with the porous media. A potential risk of nZVI particles to facilitate oxyanion contaminant transport was demonstrated for phosphate.