REMOVAL OF CONGO RED FROM WASTEWATER BY ADSORPTION ONTO WASTE RED MUD

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Waste generated for the during the red mud, an industrial ore, aqueous the byproduct, is recycled solution. such processing of were congo of bauxite red from adsorption kinetics Adsorption studied using dose, parameters time as dye concentration, Adsorption adsorption isotherms. dye was followed data The 4.05 adsorbent first rate both agitation The and red to and pH.

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Nội dung Text: REMOVAL OF CONGO RED FROM WASTEWATER BY ADSORPTION ONTO WASTE RED MUD

1997 Chemosphere, Vol. 34. No. 2, pp. 401417, Copyright 0 1997 Elsevier Science Ltd Printed in Great Britain. All rights reserved PII: SOO45-6535(96)00385-Z 0045.6535/97 $17.00+0.00 REMOVAL OF CONGO RED FROM WASTEWATER BY ADSORPTION ONTO WASTE RED MUD C. NAMASIVAYAM* and D. J. S. E. ARASI Environmental Chemistry Division Department of Environmental Sciences Bharathiar University Coimbatore - 641 046 Tamil Nadu - INDIA. (Received in USA 23 June 1996; accepted 23 August 1996) ABSTRACT industrial byproduct, Waste red mud, an generated during the processing of bauxite ore, is recycled for the adsorption of congo red from aqueous solution. Adsorption kinetics were studied using the parameters such as dye concentration, adsorbent dose, agitation time and pH. Adsorption followed first rate expression. The equilibrium data obeyed both Langmuir and Freundlich adsorption The adsorption capacity of the red mud for the isotherms. dye was 4.05 mg/g. Adsorption was found to be nearly quantitative at pH 2.0. Effect of pH and desorption studies is mostly ion suggest that the mechanism of adsorption Elsevier exchange.0 1997 Science Ltd. All rights reserved : Waste Key words congo red, adsorption isotherms red mud, pH effect. * Author to whom correspondence should be addressed. sandflas250.bharathi.ernet.in E-mail: 401
402 INTRODUCTION Colour is one of the characteristics of an effluent which is easily detected and readily traced back to its source. Most dyes are stable to biological degradation. Coloured waters are often objectionable on aesthetic grounds for drinking and other agricultural purposes. Colour affects the nature of the water by inhibiting sunlight penetration thus reducing photosynthetic action. Some dyes are carcinogenic and mutagenic (1). Hence there is a need to remove dyes from wastewaters before it mixing with receiving waters. The treatment of dyes in industrial wastewaters poses several problems since dyes are generally stable to photodegradation and oxidation (2); hence, they cannot be aerobic digestion. treated by conventional methods of Adsorption of dyes provides an attractive alternative for readily adsorbent is inexpensive and the removal if the most efficient and Activated carbon is available. popular adsorbent and has been used with great success. However, high costs in the procurement of activated carbon in developing countries like India. restricts its use Namasivayam (3) has recently, reviewed non-conventional adsorbents used for the removal of dyes and heavy metals. solid wastes such as biogas include agricultural These residual slurry (4), banana pith (5), orange peel (6),
403 bagasse and paddy straw (7) and industrial solid waste such as Fe(III)/Cr(III) hydroxide(8) and fly ash and coal(g). Namasivayam and coworkers employed red mud for the treatment of dairy wastewater (10) and for the removal of chlorophenol (11) from aqueous solutions. Zouboulis et al. (12) have employed red mud for the removal of nickel. The objective of this study was to evaluate the feasibility of using red mud for the treatment of wastewater containing congo red, a textile dye as a typical case (13). EXPERIMENTAL Materials Waste red mud obtained from Mettur M/S Aluminium Factory (Mettur, Tamil Nadu, India) was used as thoroughly washed with distilled the adsorbent. It was particulate ( < 53 /A) and dried water to remove very fine at 60°C for 5 h. The powder was then used for adsorption Congo red was obtained from CIBA - GEIGY (Bombay, studies. India). Methods Batch adsorption experiments were carried out by agitating 50 mL of dye solution at natural pH (7.3) with 250 mg of adsorbent in glass bottles at 140 rpm at room temperature (30 ? 2'C) using a shaker machine. The dye solution was separated from the adsorbent by centrifugation The dye removal was estimated spectro- at 8,600 x g.
404 photometrically by monitoring the absorbance changes at the wavelength of maximum absorption (495.8 nm) using a Hitachi spectrophotometer (Model U-3210, Tokyo). For studies on the effect of pH upon dye removal, the initial pH of the dye solution was varied from 2 to 11. In the pH range 7.3 to 11.0 there was no change in absorbance with pH. But in acidic conditions the absorbance Hence the per cent removal of the dye of the dye changed. was determined from absorbance values of dye solutions after adjusting the final pH to 7.3. The data for Langmuir and Freundlich adsorption isotherms were taken from batch adsorption experiments evaluating effect of agitation time, and initial dye concentration and adsorbent dose on per cent removal, respectively. Batch desorption studies were carried out as follows: After adsorption experiments with 50 mL of dye solution of 10 mg/L and 250 mg of adsorbent for an agitation time greater than the equilibrium time i.e. 100 min, the dye loaded supernatant dye solution was discarded. The adsorbent was washed gently to remove any unadsorbed dye. Then the spent adsorbent Several such samples were prepared. samples were agitated with 50 mL of water adjusted to different pH values for 100 min. The desorbed dye was separated from the adsorbent by centrifugation and estimated as before.
405 RJZ!3ULTSANDDISCUSSION Effect of contact time and concentration Figure 1 shows effect of agitation time and initial concentration on adsorption of congo red by red mud. The removal of dye was rapid in the initial stages of contact time and gradually decreased with lapse of time until equilibrium. The equilibrium time was 90 min for all the dye concentrations used. The equilibrium uptake of dye decreased from 36.5 $ to 25.7 % as dye concentrations increased from 10 to 40 mg/L. The removal curves were single, smooth and continuous indicating monolayer coverage of dye on outer surface of adsorbent. 20 40 60 80 l oo 120 140 160 180 200 Agdatlon lime (min) 1. Effect of agitation time and dye concentration on Fig. removal: Dye concentration:(O)- 10 mg/L,(D) - 20 mg/L,(A)- mg/L,(e)40 mg/L, Adsorbent dose - 250 30 mg/50 mL; pH - 7.3.
406 Adsorption dynamics The rate constant for adsorption of congo red by red mud was studied using Lagergren rate equation (4), kadt (1) (qe - 9) = log10 qe ___ log10 2.303 and q are the amounts of dye adsorbed (mg/g) at where qe is equilibrium and at time t (sin), respectively, and kad Linear the rate constant of adsorption. plots of loglo for different were obtained dye (qe - 9) vs t concentrations, which indicate that the adsorption process follows the first order rate expression (Fig. 2). Adsorption 2. Lagergreen plots for dye adsorption Pig.
407 rate constants (kad) are presented in Table 1. Adsorption (50 mg/L) rate constants for congo red on biogas waste slurry (4) waste banana pith (5), orange peel (6) and waste Fe(III)/Cr(III) hydroxide (8) were reported to be 0.028, 0.106, 0.0406 and 0.34 l/min, respectively. Table - 1 Rate constants for adsorption Concentration Adsorption of congo red rate constant k ad (I/min) (mg/L) 10 3.34 x 1o-2 20 6.66 x 1o-2 30 7.55 x 1o-2 40 3.57 x 1o-2 Langmuir isotherm Langmuir isotherm is valid for monolayer finite number of adsorption on a surface containing a identical sites. The model assumes uniform energies of adsorption on the surface and no transmigration of adsorbate The Langmuir isotherm is in the plane of the surface. represented by the equation (6) 1 ‘e 'e -=-+ (2)
408 where, C e is the concentration of dye (mg/L) at equilibrium. The constant Q, signifies the adsorption capacity and b is related to the energy of adsorption. Linear plot of C,/q, vs shows that the adsorption follows Langmuir isotherm 'e (Fig. 3). The values of Q, and b were calculated from the slope and intercept of the linear plot and are presented in Table 2. The applicability of Langmuir isotherm suggests the monolayer coverage of congo red on the surface of red mud. The Q, and b values for the adsorption of congo red by some non-conventional adsorbents are shown in Table 2. 1: 10 15 20 25 30 35 5 Ce hg/L) Fig. 3. Langmuir plot for dye adsorption
409 Table -2 Langmuir constants Q b Adsorbent Ref. L/w4 w9g Waste Fe(III)/Cr(III) hydroxide 44.00 0.0505 9 Waste Orange peel 22.44 0.0680 7 Waste banana pith 20.29 0.0900 6 Biogas waste slurry 9.50 0.2116 5 Waste red mud 4.05 0.0360 This work Paddy straw 1.01 0.8700 8 characteristics of Langmuir The essential expressed by a dimensionless constant, isotherm can be called equilibrium parameter, RL, which is defined by, l SC 1 + bco where b is the Langmuir constant and Co is the initial dye The RL values were found to be between concentration (mg/L). 1, indicating favourable adsorption for congo red on 0 and red mud for all the concentrations studied(6). Freundlich isotherm Freundlich equation was also applied for the adsorption of congo red on red mud (5).
410 X 1 log10 - = log10 kf + - (4) log10 ce m n (mg), m is the weight where x is the amount of dye adsorbed of the adsorbent used (g), is the equilibrium dye Ce concentration in solution (mg/L) and kf and n are constants incorporating all factors affecting the adsorption process, such as adsorption capacity and intensity. Linear plot of x/m vs shows that the adsorption also log10 'e log10 follows Freundlich isotherm (Fig. 4). In general, higher the greater will be the adsorption capacity. The value, kf of k, and n are shown in Table 3 along with those of values L in literature. other non-conventional adsorbents reported 05 Corr coetft=0.9904 o-4 1 03- o- \- -0 -3 2 - I I I -0 3. 0 10 i6 02 0.4 06 08 12 14 kl;c,Ce Fig. 4. Freundlich plot for dye adsorption
411 Table -3 Freundlich constants Adsorbent n Ref. k, Paddy straw 4.79 7.69 7 Waste Fe(III)/Cr(III) hydroxide 2.01 1.93 8 Waste banana pith 1.20 1.46 5 Biogas waste slurry I.20 1.50 4 Wollestonite 1.21 1.82 14 Waste red mud 0.22 1.46 This work Effect of pH initial pH of the dye solution was When increased from 2 to 11 the per cent removal decreased from The final pH after adsorption was higher 98 to 9 (Fig. 5). than the initial pH in the initial pH range 2 to 7. This is due to the contribution of alkalinity of red mud (13); hence, final pH is important to explain the per cent removal. The per cent removal vs final pH is also shown in Fig. 5c. The explained decrease in adsorption with increase in pH may be on the basis of aqua complex formation and subsequent acid- base dissociation at solid/solution interface (13).
412 ,& , 0 I I I I I 3 L 5 6 7 8 9 10 II Final pH 13 100 80 11 1: ,. "P O9++rk 10 12 14 16 pH I nitial Fig. 5. A. Effect of initial pH on per cent removal of dye B. Effect of initial pH on Final pH C. Per cent removal vs Final pH In acid medium, positive charge develops on the surface of oxides of adsorbent and may be written as H+ "\ M - OHZ+ H-OH--> + OH- M-O + (5) / /
413 where M stands for Al or Si present in the red mud. Since the solution is acidified by hydrochloric acid, the outer surface of positively charged interface will be associated with Cl- ions. The chloride ions are exchanged with dye anions. "\ M - OH2+ M- OHa+ / Cl- + Dye- --> / Dye- + Cl- 0/ O/ (6) With an increase in pH, positive charge on the oxide/solution interface decreases. At pHs above the pH-zpc 8 - 10, the adsorbent surface becomes of the adsorbent i.e. negatively charged and will be associated with positively charged ions of the solution in the following manner: (7) the Thus there are no exchangeable anions on higher and surface of the adsorbent at outer pHs was consequently the adsorption decreases. Similar trend observed in the adsorption of congo red on wollastonite (14) and waste Fe(III)/Cr(III) hydroxide(8).
414 Desorption studies Desorption studies help elucidating the mechanism of adsorption and recovery of dyes and adsorbent. This may make the treatment process economical. The per cent desorption increases with increase in the pH of the aqueous medium (Fig. 6). This is just opposite to the pH effect. The observation in the desorption studies again confirms the mechanism of adsorption stated in the pH effect. 01 I I I I I I I I I 3 4 5 6 10 7 11 8 9 PH 6. Effect of pH on per cent desorption Fig.
415 CONCLUSIONS Red mud, a waste byproduct, from a bauxite processing 1. industry, can be effectively used as an adsorbent for the removal of congo red from wastewaters. 2. The adsorption followed both Langmuir and Freundlich isotherms. The Langmuir adsorption capacity was 4.05 m9/9. 3. Almost quantitative dye removal occurred at the initial pH of 2.0. The kinetic data may be useful for environmental 4. technologist in designing treatment plants for colour removal from wastewaters enriched with congo red. i.5 discarded as waste in bauxite 5. As the adsorbent the treatment method is expected processing industry, to be economical. ACKNOWLEDGEMENT Authors are thankful to Bharathiar University Instrumentation Lab authorities for providing Central facilities.
416 REFERENCES 1. McKay, G., Otterburn, M. S. and Jamal, Aga, J. A. Fuller's earth and fired clay as adsorbents for dye stuffs. Equilibrium and Rate constants. Water, Air, 24 : 307 - 3.22. (1985). Soil pollution, 2. Low, K. S. and Lee, C. K. The removal of cationic dyes using coconut husk as an adsorbent. Pertanika, 13, 221 - 228 (1990). 3. Namasivayam, C. Adsorbents for the treatment of : Environmental wastewaters, In Encyclopedia of Pollution and Control, Vol. 1, Ed.: Trivedy, R. K. Enviro-Media, Karad, Maharastra, India, 1995. pp. 30 - 49. Removal of congo red C. and Yamuna, R. T. 4. Namasivayam, from aqueous solutions by biogas waste slurry. J. 53 : 153 - 157 (1992). Bio Technol, Technol. Chem. Removal of congo red 5. Namasivayam, C. and Kanchana, N. pith. waste banana solutions by from aqueous 1 : 32 - 42. Pertanika J. Sci. Technol. (1993). Namasivayam, C., Muniasamy, N.. Gayathri, K., Rani, M. 6. Removal of dyes from aqueous and Ranganathan, K. Biores. solutions by celluosic waste orange peel. (1996). Technol.,
417 Deo, N. and Ali, M. Dye Adsorption by a new low cost 7. : Congo : Indian material red -1 J. Environ. Prot. (1993). 13 : 496 - 508 8. Namasivayam, C., Jeyakumar, R. and Yamuna, R. T. Dye removal from wastewater by adsorption on waste : Fe(III)/ Cr(II1) hydroxide. Waste Management, 14 643 - 648 (1994). Gupta, G. S., Prasad, G. and Singh, V. N. Removal of 9. chrome dye from aqueous solutions by mixed adsorbents : : fly ash and coal.Water Research, 24 45 - 50 (1990). and Ranganathan, Treatment of dairy 10. Namasivayam, C. K. : 165 - 167 waste water using red mud. Res. Ind. 37 (1992). and Thamaraiselvi, K. Adsorption of 2- 11. Namasivayam, C. International J. chlorophenol by waste red mud, Environ. Studies. (1995) Communicated. Zouboulis, A. I. and Kydros, K. A. Use of red mud for 12. toxic metals removal, The case of nickel. J. Chem. Technol. Bio Technol, 58 101 (1993). : 95 - E. Overcoming the salinity and sodicity of red 13. HO, G. mud and application for rehabilitation and reuse, Conf., Proceedings 43rd Purdue Industrial Waste Chelsea, M. I., (1989) pp. 641 - 649. Lewis, Singh, V. N., Mishra, G. and Panday, K. K. Removal of 14. 22 : 70 congo red by wollastonite, Indian J. Technol. - 71 (1984).