Colour removal from textile effluents by adsorption techniques

EL-GEUNDI Department of Chemical Engineering, Faculty of Engineering, Minia University, E1-Minia, Egypt First received January 1990; accepted in revised form September 1990 Abstract--Th

Wat Res Vol 25, No 3, pp 271-273, 1991 0043-1354/91 $3.00 + 0.00

COLOUR REMOVAL FROM TEXTILE EFFLUENTS BY

ADSORPTION TECHNIQUES

MOHAMMAD S EL-GEUNDI Department of Chemical Engineering, Faculty of Engineering, Minia University, E1-Minia, Egypt

(First received January 1990; accepted in revised form September 1990)

Abstract The adsorption of two basic dyestuffs (Atrazon Blue and Maxilon Red) and two acid dyestuffs (Telon Blue and Erionyl Red) onto maize cob was studied High adsorptive capacities were observed for the adsorption of basic dyestuffs, namely, 160 and 94.5 mg dye per g maize cob for Astrazon Blue and Maxilon Red, respectively Lower capacities were obtained with the acid dyestuffs, namely, 47.7 and 41.4 nag dye per g maize cob for Erionyl Red and Telon Blue, respectively A series of contact-time experiments was undertaken in an agitated batch adsorber to assess the effect of the system variables, namely, agitation speed, maize cob particle size and maize cob mass The experimental results for these contact-time experiments were discussed

Key words dyestuffs, maize cob, adsorption capacity, adsorption rate

NOMENCLATURE

a~ = Langmuir isotherm constant (dm 3 mg- t )

Co = initial liquid-phase concentration (rag dm -3)

C, = equilibrium liquid-phase concentration (mg dm -3)

Ct = liquid-phase concentration at time t (mg dm -3)

KL = Langmuir isotherm constant (dm 3 g- i )

M = mass of adsorbent (g)

qc = equilibrium solid-phase concentration (mg g- ~ )

t = time (min)

I N T R O D U C T I O N

Adsorption is rapidly gaining prominence as a

m e t h o d o f treating aqueous effluents The treatment

o f aqueous effluents in countries in the Middle and

F a r East is extremely i m p o r t a n t as a means of

conserving and recycling water The rapidly growing

textile industries in these areas o f the world produce

large quantities o f effluents M o s t conventional

adsorption systems use activated carbon which is

expensive and necessitates regeneration (McKay,

1981, 1982)

In Egypt, a vast a m o u n t of maize cob is available

as agricultural waste The aim of the present work is

to test the ability o f maize cob to adsorb dyestuffs

The maize cob plus adsorbed dye could then be

burned as much o f it is used as a fuel already

Isotherm studies have been undertaken to determine

the m a x i m u m adsorption capacity o f maize cob for

dyestuffs, namely Astrazon Blue F R R , Maxilon Red

BL-N, Telon Blue A N L and Erionyl Red RS In

addition a series o f contact-time experiments was

undertaken using an agitated batch adsorber to

study the effects o f a n u m b e r o f factors on the rate

o f adsorption These factors are agitation speed,

adsorbent mass and maize cob particle size range

EXPERIMENTAL

Maize cob used in this study as an adsorbent was collected from EI-Minia Governorate, Egypt It was cut to particle size ranges 250-355, 355-500, 500-710 and 710-1000#m

It was left (for 3 days) to equilibrate to a fixed moisture content (14 + 0.3%) prior to sieving and experimental work Maize cob was not subjected to any form of pretreatment prior to use

Four dyestuffs were used as adsorbates The dyestuffs used in the experiments are listed in Table 1

All concentrations were measured at the wavelength corresponding to maximum absorbance, 2m~, using spectro- photometer (Spectro-Plus MK1A) Dilutions were under- taken when absorbance exceeded 0.6

Adsorption isotherms were determined by the bottle- point method (El-Geundi, 1987) A constant mass of maize cob was added to bottles containing 50-ml of dye solution (different initial concentrations) The bottles were sealed and, together with appropriate controls, mechanically shaken for a period of 5 days Resultant solution concen- trations were then determined, the equilibrium data from each such bottle representing one point on an adsorption isotherm

Several contact-time experiments were undertaken in an agitated batch adsorber to study the effect of a number of the system variables contact-time The design and details of the batch adsorber used in the kinetic studies have been reported previously (EI-Geundi, 1987)

RESULTS AND DISCUSSION

Equilibrium isotherms

The capacity of maize cob for various dyestuffs can

be determined by measuring equilibrium isotherms Adsorption isotherms were analysed according to the linear form o f the Langmuir isotherm:

Ce/qo = I/K~ + (aL/KL) Co

The plots of the isotherms are shown in Fig 1 and are seen to be linear over the whole concentration

271

272

Table 1 List of dyestuffs chosen for the present study

Type Supplied 2ma x

/ / 4.8

.,/~ / A Astrazon BLue

~ o / • Moxiton Red

d

1.6

i • "D" ~ dp • 250- 355/.¢m

T=25°C

0 80 160 240

C e ( mg.drr; 3)

Fig 1 Langmuir plot for the adsorption of dyestuffs onto

maize cob

range The parameters, KL and a L of the Langmuir

have been calculated for various dyestuffs and are

listed in Table 2 The values of the ratios gL/a L

represent the maximum adsorption capacity of

adsorbent for a particular dyestuff Table 2 shows

that Erionyl Red has an adsorption capacity of

4 7 7 m g g -1 while that of Telon Blue is 4 1 4 m g g -~

These two acid dyes would therefore appear to have

similar adsorption capacities while Astrazon Blue

and Maxilon Red have much greater affinities, for

the maize cob adsorption capacities of 160 and

9 4 5 m g g -1, respectively This difference between

the adsorption capacities of basic and acid dyes is

connected to the nature of maize cob

The structure of maize cob is cellulose based, and

the surface of cellulose in contact with water is

negatively charged (McKay et al., 1988) Most dyes

are ionized in solution many being salts or sulphonic

or carboxylic acids While others contain acidic phen-

olic groups Teion Blue (Acid Blue 25) is an example

of a dye which ionizes to an anionic coloured com-

ponent D - and a cation of Na + The approach of an

acidic dye anion will suffer coulombic repulsion due

to the presence of the strong anionic groups in maize

cob Astrazon Blue (Basic Blue 69) is an example of

a dye which will ionize to give the coloured cationic

dye base and this will undergo attraction on approaching the anionic maize cob structure The molecular volumes of dyes are 650 x 10 -24 and

690 × 10 -:4 cm 3 molecule -~ for Astrazon Blue and Telon Blue, respectively (McKay, 1982), then there

is not much difference in size between the dye molecules Consequently, the molecular mobility in solution and in the adsorbent must be similar and therefore not responsible for the different adsorption capacities

Batch contact-time studies

Four series of experiments were undertaken to study the influence of agitation The dyes studied were Astrazon Blue, Maxilon Red, Telon Blue and Erionyl Red, and the agitation speeds varied from 75

to 600 rev rain- i

Experimental results for the adsorption of Astra- zon Blue on maize cob are shown in Fig 2 Similar trends were obtained for all four dyes and the rate of dye removal was influenced by the degree of agitation and the uptake increases with stirring rate The mechanism of colour removal from effluent involved four steps: (i) migration of dye molecules from the bulk solution to the surface of the adsorbent; (ii) diffusion through the boundary layer to the surface

of the maize cob; (iii) adsorption at a site; (iv) intraparticle diffusion into the interior of the maize

1.0 ~ Co'300 mg.a r~3

L~:I~q,~,.~ m I.0 q.d~ 3

~ ~ : ~ v ' l ~ dp • 355-500p.m

0.6 RPM ~

O 250 ,',, 4OO

0 60 120 180

Time (min)

Fig 2 Effect of agitation on the adsorption of Astrazon

Blue onto maize cob

Table 2 Parameters in Langmuir isotherm

No Adsorbate (dm 3 g - t ) (dm 3 r a g - i ) (mg g - i ) coefficient

Adsorption capacities of dyestuffs 273

1.O0

®(p.m)

[] 2 5 0 - 355

; R ' N , o 5oo-rlO

0.84

0.76

T i m e ( m i n i

Fig 3 Effect of particle size range on the adsorption o f

Telon Blue onto maize cob

1.00

0.92

o

0.84 & 0.85

E] 1.275 Co, lOOmg.d~3 • ~ A

o 1.70 dp, 500-710/J.m

• 3.40

Time (rain)

Fig 4 Effect of maize cob mass on the adsorption of Erionyl

Red onto maize cob

observation is in agreement with the proposed mech- anism, since the large external surface area (for small particles) removes more dye in the initial stages of the adsorption process than the large particles

The effect of maize cob mass on the adsorption rate was studied when other experimental conditions were maintained constant In all cases the rate of dye adsorption increased with increasing maize cob mass; the results are shown in Fig 4 as a plot of (Ct/Co)

against time for the adsorption of Erionyl Red on maize cob

Rate of dye adsorption depends on the driving force per unit area, and in this case, since Co is constant, increasing the mass of maize cob increases the surface area for adsorption and hence the rate of dye adsorption is increased Since the particle size range is constant the surface area will be directly proportional to the mass of maize cob in the system

CONCLUSION

In laboratory-scale studies, the data show that maize cob has considerable potential for the removal

of dyestuffs from wastewater over a wide range of concentrations The effect of the system variables on the adsorption of dyestuffs onto maize cob has been studied, increasing the rate of agitation and the maize cob mass increases the rate of dye adsorption In- creasing particle size decreases the adsorption rate

cob The boundary layer resistance will be affected by

the rate of adsorption and increasing the degree of

agitation will reduce this resistance and increase the

mobility of the system

The influence of contact-time on the four ranges

of particle size of maize cob investigated using

the size ranges 250-355, 355-500, 500-710 and

710-1000/~m The experimental results are shown in

Fig 3 as a plot of (C,/C0) against time for the

adsorption of Telon Blue on maize cob The data

show an increase in the rate of dye uptake as the

mean diameter of the adsorbent decreases This

REFERENCES

E1-Geundi M S (1987) Mass transfer processes during colour removal from effluents using adsorption tech- niques Ph.D thesis, The Queen's University of Belfast, Belfast, U.K

McKay G (1981) Design models for adsorption system in wastewater treatment J chem tech Biotechnol 31, 717-731

McKay G (1982) Adsorption of dyestuffs from aqueous solutions with activated carbon I: equilibrium and batch contact-time studies J chem tech Biotechnol 32, 759-772

McKay G., E1-Geundi M S and Nassar M M (1988) External mass transport processes during the adsorption

of dyes onto bagasse pith Wat Res 22, 1527-1533