2.3 Decolorization of Dye Compounds
Fe0
has recently been studied to decolorize textile wastewater [42-45]. The destruction of the
azo bond (N=N) in the chromophore of azo dyes leads to decolorization of the dye solutions
as shown in figure 1. The iron particle is oxidized while the dye molecule is reduced. The dye
molecule receives electrons from the iron and combines with H+
from an acid to form the
transitional product. This product gains electrons and combines with H+
again, forming the
terminal products [43]. Additionally, in the presence of Fe0
, aromatic azo compounds are
susceptible to reduction to produce aromatic amines which are easily degraded by
microorganisms [45]. Several experiments [46-47] also confirm that under reactive conditions,
azo dyes are decomposed through N-N cleavage with the formation of aromatic amines such
as aniline. As aromatic amines are toxic, a combination treatment of zero-valent technique
with other wastewater treatment technologies may be required. Batch kinetic studies show that
the decolorization rate follows first order equation [45]. It was found that only small amount
of dyes was adsorbed on the iron surface [45] and sorption data of dyes on the iron surfaces
fitted with Langmuir isotherm [43].