Separation Of Dyes From Cotton Dyeing
Effluent Using Cationic Polyelectrolytes
By A.K. Mukherjee, Bhuvanesh Gupta,
S.M.S. Chowdhury, Department of Textile
Technology, Indian Institute of Technology,
New Delhi, India
Abstract
The separation of reactive, sulfur,
and vat dyes from cotton dyeing effluent
was investigated by a coagulation
process using a cationic polymer electrolyte (PE). The coagulation of dyes
was found to be considerably influenced
by the amount of added PE and pH of
the effluent. High degree of separation,
(i.e.-90-99%) could be achieved for all
the dyes. The secondary treatment of
the PE treated (primary treatment) with
Alum was investigated. This treatment
was effective in increasing the dye separation by removing the last traces of
the dye from the primary treated effluent. The reuse of recovered dye for subsequent cotton dyeing operations has
been explored.
Introduction
Textile wet processing involves the
use of a variety of chemicals comprising
various classes of dyes and other
chemicals, known as auxiliary chemicals. The waste water stream from the
textile dyeing operation, therefore, contains unutilized dyes and auxiliary
chemicals along with a large amount of
Water. The pollution load on the liquid
effluent increases with subsequent
steps of chemical processing where the
contribution of one single dyeing step
amounts to about 8-20% of the total pollution load due to incomplete exhaustion of the dye.'
The water consumption in chemical
Processing operation varies from 50300 L for every kg of the processing
goods. A mill processing 100,000 MT of
cotton per day may require water varying from 2.5 to 4.0 million liters per day.
About 40,000to 80,000 tons of dyes are
American Dyestuff Reporter
0 February 19
rable I: Four dye types studied.
Procion" Red M5B
CI Reactive Red 2
Remazol" Brilliant Orange 3 8
CI Reactive Orange 16
Sulfur Black
I
CI Sulfur Black 1
Novatic@Golden Orange 3G
I
CI Vat Orange 15
rable II: Dyeinn conditions and other parameters.
Dye
M:L
Procion
Red M5B
1:lO
35
45
Remazol
Briliiant
Orange 3B
1:lO
60
45
Sulfur
Black
1:lO
95
50
Novatic
Golden
Orange 3G
1.5
60
30
I
I
Dyeing Dyeing
Temp.,% time, min
I
stimated to be discharged every year
iy textile processing units on a global
ia~is.2.~
Therefore, the problem is not only
issociated with the toxicity of the dyes
eleased, also the colored effluent flowi g through drains. The large quantity of
r e effluent from a dyeing unit and the
!xtent of pollution in it can adversely
iffect acquatic life. Such waste streams
ieed, therefore, desired treatment prior
3 their disposal which calls for the most
ippropriate treatment option. Recently,
there has been great emphasis on the
development of low-cost polymeric floc.
culants for the textile effluent treat.
mer~t.~
These
,~
polymers basically are
polyacrylamide and its copolymers with
other monomers containing cationic
groups.6+'
In the present investigation, the
treatment of the dye effluent obtained
from the dyeing of cotton with differeni
classes of dyes has been undertaken by
coagulation with a cationic polyelectrolytes, and the optimum conditions for
the dye separation have been established.
Experimental
Materials
Cationic polyelectrolyte (PE) was
received from Dai-ichi, Karkaria. The
following four types of dyes were used
for this study (Table I).
The industrial effluent, supplied by
Sartaj Processors, New Delhi, contained Procion" reactive dyes-Yellow
MR, Blue MR.
Sodium hydroxide, sodium chloride,
sodium carbonate, sodium sulfide, and
alum were used, as received. Water
was distilled before use.
Dyeing procedure
The fabric used for this study was
plain weave 100% cotton. The dyeing
parameters to produce the effluent for
different dyes are shown in Table II.
The optical density of the dye sohtion was measured using a Perkin
Elmer Lamda 38" UV-VIS spectrophotometer. The percent exhaustion of the
dye was calculated as per the following
equation.
ODi-ODf
x 100
Percent exhaustion = ODi
where, ODI and OD1 are the optical density of dye bath liquor and spent liquor,
respectively.
Reuse of the recovered dye
The effluent received after the primary and secondary treatments was filtered and dried at 80°C. The recovered
dye was utilized for cotton dyeing. The
dyeing conditions were as follows.
percent shade - 1%
liquor ratio - 1:30
Results and Discussion
Dye effluent for the present study
was generated by lab-scale dyeing of
cotton with four different classes of dyes
as per the composition and conditions
mentioned in Table II. For comparison,
effluent from a cotton dyeing industry
was used. The dye concentration in all
five effluents is presented in Table HI. It
may be seen from the results that the
percent exhaustion of the reactive dye
was lower than for the sulphur and vat
dyes. This is due to the relatively lower
affinity of reactive dyes towards cotton
dyeing as compared to the sulfur and
vat dyes.* As a result, the dye concen26
Table 111: Percent exhaustion of various dyes.
Exhaustion
Dye
Dye in spent liquor
(PPW
("4
65
Remazol Brilliant Orange 3B
65
69 1
711
Sulphur Black
80
400
Novatic Golden Orange 3G
75
500
Industrial effluent
65
156
Procion Red 5MB
Table I V Percent exhaustion of recovered dye on cotton.
Dye
Procion Red 5MB
(Reactive Dye)
Sulphur Black
Novatic Orange 3G
(Vat Dye)
Exhaustion (%)
Fabric
30
Washfastness
1
.-
67
70
Cotton
2-3
4-5
tration in reactive dye effluent tends to
be higher than other dyes. The concentration of reactive-dye in the industrial
effluent was similar to the effluent prepared on a lab scale.
The influence of the polyelectrolytes
on the dye separation from the effluent
is presented in Figures 1-3. The trend in
separation of two reactive dyes in
Figure 1 is similar to each other. The
separation increases with the increase
in PE content but slows down after it
reaches 80% at a PE concentration of
150 ppm. More than 90% of the dyes
are separated by the addition of 250
ppm of PE to the effluent. The difference in the extent of separation of both
the reactive dyes may be attributed to
the difference in their chemical structure. However, at comparable level of
PE (150 ppm) addition, the difference in
percent separation of the two dyes is
4%.
On the other hand, the industrial
effluent shows much higher dye separation at the same level of the PE addition.
This may be due to the difference in the
chemical structure of the dye as well as
much lower concentration of dye in the
effluent as compared tg the other two
reactive dyes. The sulphur dye still
shows better separation as compared to
the reactive dye (Figure 2). Here, more
than 90% separation is achieved by the
addition of 50 ppm of PE..
The influence of settling time on percent dye separation is presented in
Figure 4. The pH of the effluent w,is
maintained at 6.5. The extent of dye
separation varies with the increase in
the settling time, reaching a maximum
at 12 h. It may, therefore, be stated that
the coagulation in the present system is
optimum at the settling time of 12 h.
This stands applicable for the reactive
dyes, for example, Procion Red M5B.
The effect of pH on dye separation IS
presented in Figure 5. It may be seen
that the pH has a strong influence on
the efficiency of the PE. The lower the
pH, the higher is the dye separation.
Such a behavior may be attributed to
the greater ionization of the cationic
polyelectrolytes at a lower pH which
results in its better accessibility to the
anionic dye species. This is very important since by reducing the pH, lower
amounts of PE are needed to achieve
the same dye separation. This could
eventually be translated as a cost-effective approach. The dye separation was
95% at a pH of 5.5, as compared to
75% at a pH of 10.5. It may, therefore,
be stated that the cationic PE used in
this study is highly effective at a pH of
5.5.
For sulphur dye as well, the decreasing pH enhances the dye separation.
The influence of pH in Novatic" dye is
not visible and the dye separation is at
American Dyestuff Reporter
0 February 199!
A
Figure 1-Variation of the percent separation with the polyelectrolyte concentration in different dye effluents-(0)
Procion Red M5B; (13) Ramazol Orange 3B; (0) industrial
effluent; pH, 10.5.
LO
Figure %Variation of the percent separation with the poly
electrolyte concentration in Novatic Golden Orange 3G; pH
10.5.
-
-
CI
OO
I
50
I
100
I
150
I
200
I
2%
I
OO
I
I
I
I
I
20
LO
60
80
100
300
P P M OF E L E C T R O L Y T E
P P M OF POLYELECTROLYTE
:igure 2-Variation of the percent separation with the polymlectrolvte concentration in Sulfur Black 1; aH, 10.5.
100
-
98
-
Figure &Variation of the percent separation with the poly
electrolvte concentration in Procion Red M5B; pH, 6.5.
z
?!
%
96-
U
n
9Lc
Y
z
92n
80
0
.
0
I
&
9 00
I
8
SETTING
I
12
TIME
I
16
I
20
I
24
_
Ih I
P P M OF POLYELECTROLYTE
l e maximum (-100%).
The pH related behavior in dye sepration may be attributed to the fact that
l e formation of polyelectrolytes
epends on the pH of the solution. At a
Iwer pH, the ionization of PE tends to
)crease and the ionic sites are protoated along the molecular backbone. As
result of the cationic charge, the con-
American Dyestuff Reporter
0 February 1999
formation of PE changes in such a way
that the molecular chains assume an
extended conformation. The availability
of these cationic sites to the dye molecules is therefore facilitated.
The further treatment of the PE treated effluent, (i.e.-secondary treatment
with alum was studied to remove the
last traces of the dye. The primary treat-
ment does not remove -100% of thc
dye. Therefore, alum was used as i
secondary coagulant, and the result
have been produced in Figure 6 . For a
of the dyes, the addition of alum result!
further separation of the dye from thc
effluent. The higher the amount of alum
the more the dye separation. Certainl)
the amount of alum needed to achievc
Figure SVariation of the percent separation with the pH of
the effluent. (M) Procion Red M5B; ( 0 )Ramazol Orange 3B;
0) Sulfur dye; (0)Navatic dye; PE, 100 ppm.
Figure GVariation of the percent separation with alum con
centartion for different dye effluent. (0) Procion Red M5E
0 ) Ramazol Orange 38;(M) Sulfur dye; (0)Navatic dye
7 ) Industrial effluent; primary treatment, 100 ppm PE.
1
AL
70
a
t
thi
SE
'0
100
PH
2W
300
LOO
500
600
ALUM I P P M l
thi
(F
Tic
ON
nii
ir.
fc
tc:
-99% dye separation is different for all
the dyes. For Procion Red 400 ppm
alum is required to achieve 99.6% separation. Other dyes needed a relatively
higher amount of alum to achieve similar separation. It's important to keep in
mind that the effluents after primary
treatment have different amounts of
dyes. Alum is a well-known coagulant
and flocculant and is in use in the secondary treatment of the effluent in the
chemical industry.
The percent exhaustion of treated
dye on cotton is presented in Table IV.
The results showed that percent
exhaustion in recovered sulfur and vat
dyes is much higher than in the reactive
dye. This may be understood from the
hydrolysis of the reactive dye which
takes place during the dyeing operation.
During the previous dyeing itself, a significant fraction of the dye gets
hydrolyzed. As a result, the reactive dye
acts as the direct dye on cotton. Since
the interaction of dye with the fiber is in
the form of weak Van der Waal's forces,
the washfastness is poor. The high
washfastness of the vat dyes is due to
the relatively large particles of insoluble
colorant in the fiber.
The recovered sulfur and vat dyes,
therefore, can be reused in the dye bath
due to reasonable exhaustion and good
wash fastness properties. Thus, the
problem of solid sludge disposal is minimized. Moreover, the dyeing cost of the
fabric decreases because a part of the
dye is reusable.
Conclusions
The addition of cationic polyelectrolytes (PE) to cotton dyeing effluent
containing reactive, sulfur and vat dyes
is very effective in the separation of the
dyes. The extent of separation IS strongly influenced by the amount of added
polyelectrolytes and >90% dye separation can be achieved. The efficiency of
the coagulation process strongly
depends on the pH of the spent liquor
for the reactive and sulfur dyes. The efficiency increases with the decrease in
the pH of the effluent. However, for vat
dyes, the pH variation did not show any
impact on the extent of dye separation.
The effluent, after primary treatment
with PE, still has some dye left in it.
Further separation of the dye could be
achieved by a secondary treatment with
alum. A combination of the primary
treatment with PE and the secondary
treatment of the effluent with alum leads
to a dye separation close to 99%.
The recovered dye from the effluent
treatment has been reused for the dyeing of cotton fabric by standard dyeing
procedures. Percent exhaustion and
washfastness are very good for sulfur
and vat dyes. However, in reactivt
dyes, the percent exhaustion and wast
fastness are rather poor. The high effi
ciency (Yo)of the dye separation fron
the liquid effluent by using this proces:
and the possibility of reutilizing tht
recovered dye for cotton dyeing make:
the process attractive, having little soli(
sludge disposal problems and bein(
cost effective. n EIn
f ai
nz
in1
acc
a:
Ir.
F
re.
iv
off
References
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Colour.. 100 (1 984) 383.
(2) G. Horstmann, J. SOC. Dyen
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(3) Th. Bohme, DyeinglPrinting
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(4) J.A. Laszlo, Text. Chem. Color.
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(5) H.F. Mark, N.M. Bikales and G
Overburger, Encyclopedia of Polyme
Science and Technology, Vol. 7.
(6)
D.A.
Mortimer,
Polym
International, 25 (1991) 29.
(7) M.H. Abo-Shosha, N.A. lbrahim
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(8) J.E. Bothe, H.Q. Flock, and M.F
Hoover, J. Macromol. Sci.-Chem., A 1
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Oii
bit
rc:
HI
ti"
F:
t
.ir
in!
e
tc.
M.
fE
tt
C
t
fL
tt
ti
ir
28
American Dyestuff Reporter
0 February 1999
An