I/EC W
O
R
INDUSTRIAL K
B
by N. L Nemerow
O
O
K
F
WASTES E
A
T
U
R
E
and W. L. Wilson, North Carolina State College
Color Removal from Azo Dye Wastes Stannous chloride is an effective reducing agent for removing color from azo dyes
V^VER
5 0 % of all t h e dyes con
sumed by t h e textile a n d other in dustries is of t h e azo type. W h e n color is present in a n y industrial effluent, it signifies to t h e public t h a t pollution exists. It, therefore, is a p p a r e n t to industry a n d stream regulatory agencies t h a t color should be removed from plant effluents, b u t w i t h a m i n i m u m of expense. T h e r e is n o tangible return on a n investment expended on color removal; how ever, there a r e intangible benefits such as t h e prevention of law suits, the improvement of public relations, and t h e increase in value of proper ties adjoining a river, in which waste flows a r e ever present. Effective Reducing A g e n t
O n e very promising m e t h o d for removing color from azo-type dyes involves the reduction of t h e nitro-
gen to nitrogen ( — N = N — ) bond with stannous chloride, a powerful reducing agent. T h e degree of color removal, a n d t h e most practical m e t h o d of effecting this reduction, a r e of utmost importance to industries discharging colored wastes. Preliminary tests were m a d e with methyl orange (a monoazo d y e ) , Calcomine Diazo Black B H D (a disazo dye), a n d Calcomine Black 2 0 0 % (a trisazo d y e ) , to determine the o p t i m u m dosage of stannous chloride required to achieve com plete color reduction. T h e d y e concentration ranged from 0 . 0 0 5 % for Calcomine Black 2 0 0 % to 0 . 1 2 5 % for methyl orange. O n e h u n d r e d milliliter samples were heated at 212° F . for a m a x i m u m of 2 hours after t h e addition of various quanti ties of a \M solution of stannous chloride.
During t h e reduction, t h e samples were agitated with a magnetic stirrer, operating at m e d i u m speed, to achieve better contact between t h e molecules. T h e volume a n d tem perature were held constant. Color was measured by visual means only. Following successful preliminary tests, final pilot studies were m a d e with 2-liter samples of each azo dye. Stannous chloride is equally effec tive in removing color from mono-, dis-, a n d trisazo-type dyes. Color removals ranged from 96 to 9 9 . 5 % a t the wave length of m a x i m u m absorp tion (Table I) on dyes treated with heat a n d stannous chloride. Heat ing alone reduced t h e color concen tration from 1.0 to 9 . 0 % in five of t h e 10 dyes. W i t h the other five dyes, heat h a d n o effect on color concentration. Costs of Color R e m o v a l
100 100 TREATED DYE
70
UNTRE CTED DY
3C
500 550 600 650 WAVE LENGTH ( Γημ )
400
450
500 550 600 WAVE LENGTH [πιμ)
650
700
Graphs show the t r e a t e d dyes to b e almost colorless, their light transmittance approaches 1 0 0 %
As d y e waste treatment results in an expenditure of money with seldom any return, the economics of t h e method employed assumes a lead ing role. A greater quantity of stannous chloride was required for disazo dyes t h a n for monoazo types (Table I ) . Similarly, more reducing agent was used for trisazo dyes t h a n the disazo types. T h e r e were excep tions to these findings, however. For example, Diphenyl Fast R e d B, a disazo dye, required 25 pounds of stannous chloride per pound of dye while the other three disazo types used less t h a n 4 pounds. O n the other h a n d , Erie Green M T 1 5 0 % , a trisazo dye, required only 5 pounds of stannous chloride p e r p o u n d of dye while t h e other three trisazo types used 10 to 25 pounds. T h e average time required to achieve complete color reduction inVOL. 49, NO. 12 ·
DECEMBER 1957
77 A
I/EC
INDUSTRIAL WASTES
Table I.
·
A Workbook
Feature
Color Removal Efficiencies with Stannous Chloride
Type Dye
SnCh Required (Mg./ Mg. Dye)
Chem. Cost Chem. (SnCl 2 )/Lb. Cost/100 Lb Time Color Dye in Goods Dyed Required, Removed, Waste, Av. Shade, Hr.
%
$
$"
98.5 99.5 99.0
2.38 2.38 2.38
0.0928 0.238 0.165
97.0 99.5 98.0 99.0 98.4
1.59 3.18 19.87 3.18 6.95
0.095 0.095 0.745 0.018 0.238
MONOAZO
Methyl orange Erie Pink 2B Av.
3.0 3.0 3.0
Calcomine Diazo Black BHD Direct Blue RW Diphenyl Fast Red Β 125% Niagara Sky Blue 6B 200% Av.
2.0 4.0
1.0 2.0 1.5 DISAZO 1.0 1.5 3.5 1.0
25.0 4.0
8.75
1.75 TRISAZO
Erie Brown CN 200% Erie Fast Brown GR 200% Erie Green MT 150% Calcomine Black 200% Av.
19.87 96.0 2.190 99.0 7.95 0.596 5.0 2.0 99.5 3.97 0.149 1.5 25.0 99.0 19.87 4.170 16.2 2.06 98.4 12.91 1.780 ° Dye bath concentrations and exhaustion figures taken from 'Direct Dyes on Cotton," published by E. I. du Pont de Nemours & Co., Inc. 25.0 10.0
2.0
2.75
creases as the n u m b e r of ( — N = N — ) azo groups goes u p ; however, there are exceptions. For example Di phenyl Fast R e d B, a disazo dye, required 3.5 hours and Niagara Sky Blue 6B, a disazo dye, required only 1 hour, while the average time re quired was 1.75 hours. T h e cost of stannous chloride (based on $0.795 per pound) for each pound of dye in the waste averaged $2.38 for m o n o
Table II.
azo dyes, $6.95 for disazo dyes, a n d $12.91 for trisazo dyes. T h e ten dyes were investigated as to the quantity of dye used per 100 pounds of cotton goods to obtain a medium shade for each color (Table II). T h e amounts required vary from 0.375 to 1.0 p o u n d of dye per 100 pounds of cotton dyed. I n addi tion, dyes vary according to the ease with which a n d extent to which
Quantity of Dye Used to Obtain Medium Shade for Each Color Medium Shade Dye
Dye
Color Index No."
Methyl orange 6 Erie Pink 2B
142 128
Calcomine Diazo Black BHD
401
Direct Blue RW Diphenyl Fast Red Β 125% Niagara Sky Blue 6B 200%
512 419 518
Erie Brown CN 200%
596
Erie Fast Brown GR 200%
598
Erie Green MT 150%
593
Calcomine Black 200%
581
Mfr. National Aniline American Cyanamid Co., Inc. Ciba Geigy National Aniline National Aniline National Aniline National Aniline American Cyanamid Co., Inc.
Concn., Lb./100 Lb. Goods 0.390
Dye Exhaustion, Max.,
% 90 (est)
1.0"
90"*
o^s*
92d
0.50* 0.75·*
94"* 95*
0.375d
98.5d
0.5
