Wat Res Vol 25, No 3, pp 271-273, 1991 Printed in Great Britain 0043-1354/91 $3.00 + 0.00 Pergamon Press pie 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 revisedform 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~ = Co = C, = Ct = KL = M = qc = t= 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 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 All concentrations were measured at the wavelength corresponding to maximum absorbance, 2m~, using spectrophotometer (Spectro-Plus MK1A) Dilutions were undertaken when absorbance exceeded 0.6 Adsorption isotherms were determined by the bottlepoint 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 days Resultant solution concentrations 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) Langmuir isotherm constant (dm 3mg- t ) initial liquid-phase concentration (rag dm -3) equilibrium liquid-phase concentration (mg dm -3) liquid-phase concentration at time t (mg dm -3) Langmuir isotherm constant (dm 3g- i ) mass of adsorbent (g) equilibrium solid-phase concentration (mg g- ~) time (min) INTRODUCTION Adsorption is rapidly gaining prominence as a method of treating aqueous effluents The treatment of aqueous effluents in countries in the Middle and Far East is extremely important as a means of conserving and recycling water The rapidly growing textile industries in these areas of the world produce large quantities of effluents Most conventional adsorption systems use activated carbon which is expensive and necessitates regeneration (McKay, 1981, 1982) In Egypt, a vast amount of maize cob is available as agricultural waste The aim of the present work is to test the ability of maize cob to adsorb dyestuffs The maize cob plus adsorbed dye could then be burned as much of it is used as a fuel already Isotherm studies have been undertaken to determine the maximum adsorption capacity of 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 of contact-time experiments was undertaken using an agitated batch adsorber to study the effects of a number of factors on the rate of adsorption These factors are agitation speed, adsorbent mass and maize cob particle size range 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 of the Langmuir isotherm: Ce/qo = I/K~ + (aL/KL) Co The plots of the isotherms are shown in Fig and are seen to be linear over the whole concentration 271 272 MOHAMMAD S EL-GEUNDI Table List of dyestuffs chosen for the present study No Colour Type of dye Supplied by 2max (nm) Telon Blue A N L Erionyl Red RS Maxilon Red BL-N Astrazon Blue F R R 62055 23635 11055 Blue Red Red Blue Acid Acid Basic Basic Bayer Ciba Geigy Ciba-Geigy Bayer 600 522 538 585 // 4.8 ,/~ / ~o / A/" d C.I Commercial name 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 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 A AstrazonBLue • Moxiton Red ~ Etionyt Red 1.6 Batch contact-time studies i • "D" ~ I dp • 250- 355/.¢m T=25°C I 80 160 Ce ( mg.drr; 3) I I 240 Fig 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 The values of the ratios gL/a L represent the maximum adsorption capacity of adsorbent for a particular dyestuff Table shows that Erionyl Red has an adsorption capacity of 47.7mgg -1 while that of Telon Blue is 41.4mgg -~ 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 94.5mgg -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 phenolic groups Teion Blue (Acid Blue 25) is an example of a dye which ionizes to an anionic coloured component 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 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 Astrazon Blue on maize cob are shown in Fig 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 ~ L~:I~q,~,.~ ~~:~v'l~ 0.6 RPM Co'300 mg.ar~3 m I.0 q.d~ dp • 355-500p.m ~ °~o O 7'5 O 250 ,',, 4OO 0.4 I I 60 120 Time (min) I 180 Fig Effect of agitation on the adsorption of Astrazon Blue onto maize cob Table Parameters in Langmuir isotherm No Adsorbate KL (dm g - t ) aL (dm r a g - i ) qm~ (mg g - i ) Correlation coefficient Astrazon Blue Maxilon Red Erionyl Red Telon Blue 6.08 2.93 0.668 0.497 0.038 0.031 0.014 0.012 160.0 94.5 47.7 41.4 0,99 0,99 0,99 0,97 Adsorption capacities of dyestuffs 1.O0 ®(p.m) [] - 355 ;R'N, ° 0.92 o 5oo-rlO ,,o-,ooo 0.84 0.76 I l 60 120 180 Time(mini Fig Effect of particle size range on the adsorption of Telon Blue onto maize cob 1.00 0.92 273 observation is in agreement with the proposed mechanism, 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 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 o 0.84 & 0.85 E] 1.275 o 1.70 • 2.125 • 3.40 0.76 Co, lOOmg.d~3 dp, 500-710/J.m RPM, 400 I 60 I 120 • ~ A I 180 Time (rain) Fig Effect of maize cob mass on the adsorption of Erionyl Red onto maize cob 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 Increasing particle size decreases the adsorption rate REFERENCES 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 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 E1-Geundi M S (1987) Mass transfer processes during colour removal from effluents using adsorption techniques 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