Influence of hydrogeochemical processes on zero-valent iron reactive barrier performance: A field investigation

Abstract

Geochemical and mineralogical changes were evaluated at a field Fe0-PRB at the Oak Ridge Y-12 site concerning operation performance during the treatment of U in high NO3- groundwater. In the 5-year study period, the Fe0 remained reactive as shown in pore-water monitoring data, where increases in pH and the removal of certain ionic species persisted. However, coring revealed varying degrees of cementation. After 3.8-year treatment, porosity reduction of up to 41.7% was obtained from mineralogical analysis on core samples collected at the upgradient gravel-Fe0 interface. Elsewhere, Fe0 filings were loose with some cementation. Fe0 corrosion and pore volume reduction at this site are more severe due to the presence of NO3- at a high level. Tracer tests indicate that hydraulic performance deteriorated: the flow distribution was heterogeneous and under the influence of interfacial cementation a large portion of water was diverted around the Fe0 and transported outside the PRB. Based on the equilibrium reductions of NO3- and SO4(2-) by Fe0 and mineral precipitation, geochemical modeling predicted a maximum of 49% porosity loss for 5 years of operation. Additionally, modeling showed a spatial distribution of mineral precipitate volumes, with the maximum advancing from the interface toward downgradient with time. This study suggests that water quality monitoring, coupled with hydraulic monitoring and geochemical modeling, can provide a low-cost method for assessing PRB performance.

Role of Phosphate in the Remediation and Reuse of Heavy Metal Polluted Wastes and Sites

“…The goal is to have contaminant levels below target concentration at compliance points down gradient of the barrier. The barriers also prevent groundwater contaminants from migrating to uncontaminated aquifers, which may be difficult to locate and remedy [87][88][89][90][91][92].…”

Calcite precipitation dominates the electrical signatures of zero valent iron columns under simulated field conditions

“…iron oxides or calcite) on the electrical responses. Yet PRB precipitate mineralogy is normally complex, being dependent on the groundwater chemistry at the site, in many cases including both iron oxides and calcite (Furukawa et al, 2002;Morrison et al, 2002;Liang et al, 2003;Phillips et al, 2003;Liang et al, 2005 and electronic (iron metal) conductors causing decreases in electrical conduction and polarization and, presumably, in surface reactivity.…”

ZVI (Fe0) Desalination: Stability of Product Water

“…Zero valent iron (Fe 0 , ZVI) has been placed in permeable reactive barriers (PRB's) and injected into aquifers in order to effect aquifer remediation since the 1970s (e.g., [6][7][8][9][10]70,71,[93][94][95][96][97][98]). The principle historical remediation focus has been on the removal of organo-chlorides, organo-nitrates, phosphates, nitrates, arsenic and heavy metals (e.g., [26,70,71,93,94,[99][100][101][102]).…”

“…Desalination associated with zero valent iron (ZVI, Fe 0 ) has been demonstrated in more than 160 batch trials (utilizing 0.2-240 L/batch [1][2][3][4][5]) and by monitoring the salinity of water flowing through granular Fe 0 permeable reactive barriers (PRB) [6][7][8][9][10]. These trials have demonstrated that ZVI desalination has potential applications for groundwater management, road runoff water management, agricultural water management, municipal and domestic water, emergency and disaster water requirements, feed and waste water treatment associated with conventional desalination plants, waste water associated with the extractive industries and environmental damage mitigation [1][2][3][4][5][6][7][8][9][10].…”

“…These trials have demonstrated that ZVI desalination has potential applications for groundwater management, road runoff water management, agricultural water management, municipal and domestic water, emergency and disaster water requirements, feed and waste water treatment associated with conventional desalination plants, waste water associated with the extractive industries and environmental damage mitigation [1][2][3][4][5][6][7][8][9][10].…”