A. Agrawal et Pg. Tratnyek, REDUCTION OF NITRO AROMATIC-COMPOUNDS BY ZERO-VALENT IRON METAL, Environmental science & technology, 30(1), 1996, pp. 153-160
The properties of iron metal that make it useful in remediation of chl
orinated solvents may also lead to reduction of other groundwater cont
aminants such as nitro aromatic compounds (NACs). Nitrobenzene is redu
ced by iron under anaerobic conditions to aniline with nitrosobenzene
as an intermediate product. Coupling products such as azobenzene and a
zoxybenzene were not detected. First-order reduction rates are similar
for nitrobenzene and nitrosobenzene, but aniline appearance occurs mo
re slowly (typical pseudo-first-order rate constants 3.5 x 10(-2), 3.4
x 10(-2), and 8.8 x 10(-3) min(-1), respectively, in the presence of
33 g/L acid-washed, 18-20 mesh Fluka iron turnings). The nitro reducti
on rate increased linearly with concentration of iron surface area, gi
ving a specific reaction rate constant (3.9 +/- 0.2 x 10(-2) min(-1) m
(-2) L). The minimal effects of solution pH or ring substitution on ni
tro reduction rates, and the linear correlation between nitrobenzene r
eduction rare constants and the square-root of mixing rate (rpm), sugg
est that the observed reaction rates were controlled by mass transfer
of the NAC to the metal surf:ace. The decrease in reduction rate for n
itrobenzene with increased concentration of dissolved carbonate and wi
th extended exposure of the metal to a particular carbonate buffer ind
icate that the precipitation of side rite on the metal inhibits nitro
reduction.