Reduction of Nitro Aromatic Compounds by Zero-Valent Iron Metal

Abstract

The properties of iron metal that make it useful in remediation of chlorinated solvents may also lead to reduction of other groundwater contaminants such as nitro aromatic compounds (NACs). Nitrobenzene is reduced by iron under anaerobic conditions to aniline with nitrosobenzene as an intermediate product.Coupling products such as azobenzene and azoxybenzene were not detected. First-order reduction rates are similar for nitrobenzene and nitrosobenzene, but aniline appearance occurs more slowly (typical pseudo-first-order rate constants 3.5 × 10 -2 , 3.4 × 10 -2 , and 8.8 × 10 -3 min -1 , respectively, in the presence of 33 g/L acid-washed, 18-20 mesh Fluka iron turnings). The nitro reduction rate increased linearly with concentration of iron surface area, giving a specific reaction rate constant (3.9 ( 0.2 × 10 -2 min -1 m -2 L). The minimal effects of solution pH or ring substitution on nitro reduction rates, and the linear correlation between nitrobenzene reduction rate constants and the square-root of mixing rate (rpm), suggest that the observed reaction rates were controlled by mass transfer of the NAC to the metal surface. The decrease in reduction rate for nitrobenzene with increased concentration of dissolved carbonate and with extended exposure of the metal to a particular carbonate buffer indicate that the precipitation of siderite on the metal inhibits nitro reduction.

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

“…Although encouraging treatment efficiency has been documented (Gu et al, 1998;Morrison et al, 2001;Su and Puls, 2003), reactions between ZVI and groundwater constituents causing ZVI corrosion and subsequent secondary mineral precipitation contribute to long term performance reduction of ZVI PRBs (Liang et al, 2003;Slater and Binley, 2003;Wilkin et al, 2003;Jin Suk et al, 2009). Carbonate minerals (often precipitated concurrent with iron oxides (Mackenzie et al, 1999;Phillips et al, 2000;Liang et al, 2003)), are known to significantly impact ZVI reactivity and hydraulic efficiency in systems with frequently encountered high carbonate groundwater conditions through surface passivation and pore clogging (Agrawal and Tratnyek, 1996;Phillips et al, 2000;Liang et al, 2003;Slater and Binley, 2003;Wilkin et al, 2003;Jeen et al, 2006;Jeen et al, 2007;Jin Suk et al, 2009). …”

Decolourization of azo dyes using magnesium–palladium system

“…Thus the overall reaction is: [16][17][18][19][20][21][22][23][24][25][26][27]. Although Fe 0 has been applied extensively for remediation of several pollutants, the major drawbacks are slow reaction rates, rapid passivation of the metal and requirement for strict anaerobic conditions.…”

Enhanced Biological Treatment of Industrial Wastewater With Bimetallic Zero-Valent Iron

“…It should be noted that the efficacy of ZVI for the transformation of chlorinated hydrocarbons, azo dyes, and nitroaromatic compounds has been extensively investigated over the past 15 years (5)(6)(7)(8). ZVI exhibits a strong tendency to donate electrons in water:…”