JOlI" lal of Scientifi c & I ndustrial Research
Vol . 60. September 200 I . pp 735-737
Recovery of Indigo from a Textile Effluent in Nigeria
v 0
Aj i bola
Chemi stry Department. A h madu Bello Uni versity, Zaria. N i geria
Received: 3 0 M arch 200 1 ; accepted: 1 8 June 200 I
I ndigo was recovered from
n
text i l e eftluent u.sing a method of acid precipitation fo l l owed by purification w i t h acetonc.
Structural studies usi ng U V\visible spectroscopy showed thm the recovered indigo has A",,, at 600 nm. Thc resu lts showed
a
preponderance of the cis- isomer. Recovery of i ndigo gave better quality effluent.
Introduction
The wide variety of environmental health hazards
assoc iated w i t h dye i n g act i v i ti e s and the ejecti on of
i ndustrial effluent conta i n i n g mai n l y spent indigo dye
from te xtile i ndustries have aroused the concern of many
environmentalists. and the need to reduce t h i s wastes
has become imperative. Dye waste includes residues from
ex hausted dye bath, dye rin se. salt and wax I . The i mpacl
of this i ndl1.�trial effluent, w h ic h include increased total
and suspended s o l i d s , c o l o r, pH a n d d e p l e t i o n of
d i ssolved oxygen content on rivers, streams or acquifers,
has necessitated an abatement by env i ron mental i sts and
the i ndustries themsel ves .
Though i nd i go i s b iodegradabl e i n microbial l y
active environments, the final products o f biodegradation
may be d i ffi c u l t to ascert a i n " . T h i s i s bec au se the
mechanism of degradation and the products formed is
dependent on certai n physicochemical factors such as
temperature, pH, oxygen concentration, surface area, etc .
It is therefore possible to have d i fferent products, some
of which may be more tox i c than the dye waste, thus
al lowing untreated dye wastes to enter the environment
to undergo this n atural treatment is not a good alternati ve
to the waste management p roblem. It i s known that no
single solution to waste management is feasi ble, but
recycling and reuse of materials l i ke i nd i go and other
i nputs are an ev ident preference i n the waste redpct ion
strategy for textile i ndustries" Some success has been
ach ieved i n the recovery of some texti l e i nputs, and this
method, w i l l further sol ve problem faced i n the area of
waste reduction .
Experimental Procedure
(a) Process of Recovery
The scheme g i ven below describes this procedure.
(I)
(4)
(2)
..
Steps ( I ) and (2) constitute rec lamation and steps 0 )
and (4) are recy c l i n g process .
Neutralization-Thi s i s the addition of a non-oxidizing
acid to the effluent, bringing the pH to about 6.4.
Precipitation-After neutral i zation t he dye i s al l owed
to settle u nder atmospheric pressure, or faster by suction .
The precipitation is usual l y fast, which i s less than I
m i n for about 4 L of the effluent. The precipi tate is
washed with water and can be kept for l on ger duration,
provided i t i s kept wet.
Purification-Impurities such as wax and gum Arabic
are removed, using a l ight organic sol vent l i ke acetone
or petroleum spiri t (40 to 60). The organ i c sol vent, which
c o n t a i n s m a i n l y g u m A r a b i c , m ay be rec o v e red
i mmediately by d i st i l l at i o n , l eav i ng the gum beh i nd,
which may also be reused .
J SCI IND RES VOL 60 SEPTEMBER 200 I
736
0.7
.!':
::
0.6
Gl
0
I:
III
-€
0
'"
.0
c(
·
·
·
0.5
.
.
.
0.4
unused
indigo
,.
..
.
:
0.3
.
0.2
0.1
0
200
Figure I
300
-
4 00
500
Wavelength (nm)
600
700
UV -visible spectra of the recovered and the fresh unused indigo
Table I -Comparative results for some parameters obtained before and after recovery of indigo
Parameters measured
Before recovery of indigo
After recovery of indigo
Suspended solids (mglL)
74 1 5
Dissolved solids (mglL)
2945
1 382.4
Total solids (mglL)
1 0360
1 382.4
288
Colour (Hazens)
20
Organics (mglL)
Not determined
Inorganics (mg/L)
Not determined
PH
1 0.94
(b) Structural Analysis
IR and UVIvisible spectroscopy was used for the
structural elucidation of the indigo samples . About 1 0
3
mg of the recovered dye was dissolved in 50 cm of
chloroform, and filtered. The UV/visi ble spectrum
between 200 and 700 nm was studied . S imi larly the
spectrum for the fresh unused dye belonging to the same
batch as the recovered dye was determined.
Results and Discussion
The prevention of pollution, resu lting from the
overburdening of surface and underground water with
wastes from industries, or from intermittent pollution
incidents is of prime importance for protecting and
enhancing the quality of this resource. The approach,
based on the recovery and reuse of some materials in the
waste is one of the viable and economical strategies for
454.4
6.32
waste reduction3 • The quality of the effluent before and
after the recovery of the indigo i s given in Table I . The
recovery of indigo from effluent streams of textile
industries showed an improvement in the quality of the
effluent to be discharged into the environment, as shown
in Table I . For example the colour and total solids were
reduced by about 82.6 and 86.7 per cent, respectively.
The c o lo u r and pH of the effl u e n t a l s o redu ced
significantly.
Results obtained from the UV/visible spectroscopy
showed that the recovered indigo has ",max in the region
of 600 nm (Figure 1 ) and the fresh unused indigo around
6 1 0 nm. The "'max in b oth the cases are same as
reported4 • This indicates that the conjugation of the
double bonds in the molecule was restored after recovery.
The absorption peaks at 248 nm and 288 nm, respectively,
in the recovered indigo, corresponds to the peaks at 254
nm 300 nm, respectively, for the fresh unused indigo.
AJIBOLA : RECOVERY OF INDIGO FROM TEXTILE EFFLUENT
Indigo exists in two isomeric forms, i.e. the cis- and
trans-forms, as shown in compounds 1 and 2, and these
two forms exist in the fresh unused dye and the recovered
dye in different proportions5.
0
o:K:o
o
N�
�
0-- N
�
o
cis-form (1)
trans-fOlTI1(2)
The two peaks at shorter wavelengths are as a result
of these isomeric forms . The absorption peaks at 248
nm (for the recovered dye) are as a result of the more
energetic cis-isomer, while the absorption peaks at longer
wavelength (i e, 288 nm and 300 nm for recovered and
fresh indigo, respectively) are ascribed to the more stable
trans-isomer. Comparing the spectra in Figure I , it can
be noticed that there is a preponderance of the ci,5-isomer
in the recovered indigo as compared with the fresh indigo.
This may be explained by considering the structure of
the leuco form (i.e. reduced form), produced during
vatting at 60-80 °C6 (3 and 4).
c4=}0
0
I
N
N
�
o
OJ==<;O
N
",
'
N
o
0
"' ,
'"
�
10}
�
101
Under this condition, compounds 3 and 4 are formed
and enough energy is available to cause a rotation about
737
the single bond, thus resulting in the conversion of the
trans-isomer to the cis-isomer.
Conclusions
The procedure for the recovery of indigo,
described in this study, is quite simple and also enhances
the efficient use of energy. It is, therefore, important to
consider waste minimization strategy in this direction
and also make it feasible. Companies that generate large
amount of wastes should, as a matter of urgency, respond
to environmental pressures pro-actively, if they want to
remain economically competi tive. Where waste is
produced, it should be looked upon as an indicator of
inefficiency, and inefficient use of resources is not only
harmful for commercial use but also to the environment.
Waste minimization imperative should be central to many
companies' environmental policies and strategies.
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2
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3
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4
Aldrich Catalog, Handbook offine chemicals (Aldrich Chemical
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5
Venkataraman K, The chemistry of synthetic dyes, Vol. 3
(Academic Press, London) 1 970, pp 385 - 400.
6
Nkeonye P 0, Fundamental principles oftextile dyeing, printing
and fin ishing (ABU Press Ltd., Nigeria) 1 987, pp 2 - I I .