Color removal via adsorption on wood shaving

The Science of the Total Environment, 66 (1987) 26~273 Elsevier Science Publishers B.V,, Amsterdam -- Printed in The Netherlands

269

Short Communication COLOR REMOVAL VIA ADSORPTION ON WOOD SHAVING

SOHAIR I. ABO-ELELAand M.A. EL-DIB Water Pollution Control Laboratories, National Research Centre, Cairo (Egypt)

(Received November 25th, 1986; accepted May 25th, 1987)

ABSTRACT Factors affecting the adsorption capacity of dyes on wood shavings, such as the mesh size of the adsorbent, wood dosages, contact time, and the structure of the adsorbant, were studied. Adsorption of dye on wood follows the classical Freundlich's isotherm. Available results indicated that wood shaving is a good adsorbent. Its capacity varies according to the structure of the dye and mesh size. Powdered activated carbon was used as a reference adsorbent for the same dyes under investigation.

INTRODUCTION The d i s c h a r g e of h i g h l y colored w a s t e is n o t only a e s t h e t i c a l l y displeasing, b u t also impedes light p e n e t r a t i o n , t h u s u p s e t t i n g biological processes and p r o d u c t i v i t y w i t h i n a stream. In addition, m a n y dyes m a y be toxic to some organisms. A c c o r d i n g to the U.S. E n v i r o n m e n t a l P r o t e c t i o n A g e n c y , a maximum effluent color c o n c e n t r a t i o n of 300 A P H A u n i t s c a n be p e r m i t t e d (EPA, 1974). C o n s i d e r a b l e r e s e a r c h h a s been c a r r i e d o u t on the r e m o v a l of c o l o r from textile w a s t e via c h e m i c a l a n d / o r biological t e c h n i q u e s ( J u d k i n s and J o h n , 1978; M r i g a n k a et al., 1978). A d s o r p t i o n tends to be a p r o m i s i n g t r e a t m e n t ( M c k a y et al., 1979). The use of w o o d as a c h e a p a d s o r b e n t for c o l o r in textile effluents was explored by P o o t s et al. (1978). This s t u d y e v a l u a t e s the adsorption c a p a c i t y of wood s h a v i n g with r e s p e c t to dyes, especially those used in the finishing of c o t t o n goods. EXPERIMENTAL Material

L a b o r a t o r y tests were c o n d u c t e d u s i n g direct-soluble Congo-red C.I 22120, a n d d i a p h t a m i n e l i g h t o r a n g e EG, were used in t h e i r pure form. W o o d shaving, o b t a i n e d as c a r p e n t e r shop, was used as the adsorbent. The w o o d was

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© 1987 Elsevier Science Publishers B.V.

acidic dyes, n a m e l y C.I 40225. The dyes a solid w a s t e from a n o t subjected to a n y

270 form of pretreatment and was sieved into different size ranges prior to use. The maximum wavelength (~max) for Congo-red and light orange EG were found to be 500 and 405 nm, respectively. All tests were carried out at room temperature (20 + 2°C) and tap water was used for the preparation of dye solution. Powdered carbon (Merck, Darmstadt, Germany) was used as a reference for the adsorption capacity of wood shaving.

Determination of equilibrium time Equilibrium time was determined by shaking a 0.6 g sample of wood shaving with 50ml of dye solution using a known concentration of dye (15mg1-1) at different time intervals ranging from 0 to 4 h. For light orange EG, filtration was carried out using 0.45 ttm filter paper. In the case of activated carbon, the supernatant was separated by adding 2 mg of alum to the slightly alkaline solution then rapid solid-liquid separation was achieved. Residual color was determined and the amount of adsorbed dye was plotted versus time. The effect of mesh size of wood on the equilibrium time was also investigated.

Determination of adsorption isotherms Adsorption isotherms were determined by shaking a fixed amount of wood (0.6 g) with 50 ml of different concentrations of dye ranging from 5 to 20 mg l-1 pure dye stuff, at the predetermined equilibrium time. The adsorption isotherm was also determined for dyes using activated carbon as an adsorbent. Freundlich's equation was employed to plot the adsorption isotherms, as follows: _

log x m

=

1

logK +-logC n

where x is the amount of dye adsorbed (mgl-1), m the weight of wood used (g l- i), C the equilibrium concentration of dye (mg 1 1) and K and n are constants including all factors affecting the adsorption process, namely properties of adsorbent, adsorbate and the solvent. In general, as the value of K increases the adsorption capacity of wood increases. RESULTS AND DISCUSSION

Effect of contact time Use of wood shaving The relationship between the amount of dye adsorbed and contact time is shown in Fig. 1A and B. Figure 1A shows that the contact time necessary for Congo-red to reach equilibrium ranges between 60 and 120 min, depending on the particle size of the adsorbing material. However, the equilibrium time for light orange EG was almost 2 h, regardless of the particle size of the wood (Fig.

271

E

14

-5 u 10

-6

6

~6 E

H 500)J C"-----O 800.U e-- X"e 1000p

~red

nH

C~ 4

I

I

I

S03Na I I

I

I

L

I

S03Na I I

~8 E

7

-66 u

o

3

rr"

2

E

CH N 3 I

I 40

I

I 80

I

[ 120

I

I I 1150

I 200

I

I 240

Time,rain.

Fig. 1. Effect of time on adsorption of studied dyes on wood shaving.

1B). Available results are in agreement with those obtained by Asfour et al. (1985) and Poots et al. (1978).

Use of powdered activated carbon The equilibrium time necessary for dyes to reach saturation using powdered activated carbon was obtained after 10 min, for both dyes under investigation. ADSORPTION ISOTHERMS

Use of wood shaving Adsorption of the studied dyes on wood shaving was found to conform to Freundlich's equation, as presented in Fig. 2A and 2B. The results show that wood shaving has a greater adsorption capacity for Congo-red than for light orange EG. The percentage removal of Congo-red reached 82%. However, in the case of light orange EG, the removal of color did not exceed 39.3%. The value of the constant "K" of Freundlich's isotherm is considerably greater for Congo-red than for diaphtamine light orange EG (Table 1).The amount of wood required to remove any given amount of the studied dyes is much less in the case of Congo-red. Reduction of dye concentration from 15 to 0.5 mg l-1 (97%) requires wood shaving doses of 1.9-2.1 g 1 1 for Congo-red and 8.2-15.7gl 1 for light orange EG.

272

40 30

E

{A Conc.l~-red

11111

)~------o ---.-o500g 800J~

=o

I~r/

7 (B)

xlE B

5

3 2

tO

20

Ce equilib, cone. mg/l Fig. 2. Freundlieh's adsorption isotherm for the studied dyes on wood shaving.

The high adsorption capacity of wood shaving for Congo-red compared with light orange EG (Table 1) suggests that chemical adsorption is involved. The chemical structure of Congo-red (Fig. 1A) satisfies the conditions required for adsorption of an effective direct dye on adsorbent. These results are in agreement with those obtained by Sadov et al. (1978).

Use of activated carbon Adsorption of dyes on powdered carbon was found to proceed in accordance with Freundlich's isotherms (Fig. 2). Reduction of dye concentration from 15 to TABLE 1 Adsorption parameters and doses required for removal of dyes using wood shaving

of woo shaving~ (g l- ~)

slope Mesh size ~u)

Congo-red Direct light orange EG

Mesh size Cu)

500

800

1000

500

800

0.4309 0.683

0.4780 0.65

0.3995 0.633

10.9297 10.066 2.85 1.45

Mesh size (~) 1000

500

800

10.034 1.45

1.85 8.169

2.07 2.08 15.69 15.69

a Amount of wood shaving required to reduce dye concentration from 15 to 0.5 mg l-1.

1000

273 0 . 5 m g l 1 requires c a r b o n doses of 0.130gl 1 for Congo-red and 0.139gl ~ for light o r a n g e EG. These doses are m u c h lower t h a n t h o s e for wood shaving. This m a y be a t t r i b u t e d to the h i g h v a l u e o f " K " in the case of carbon. The a d s o r p t i o n p a r a m e t e r s are similar for b o t h dyes. This indicates t h a t the m e c h a n i s m of a d s o r p t i o n a n d / o r u p t a k e by wood s h a v i n g differs from t h a t p r e v a i l i n g in the case of a c t i v a t e d carbon. CONCLUSION The results o b t a i n e d are in f a v o u r of the use of wood s h a v i n g as an available c h e a p m a t e r i a l for the r e m o v a l of c o l o r i n g m a t e r i a l s and dyes from i n d u s t r i a l w a s t e w a t e r s . T h e y show a h i g h a d s o r p t i o n c a p a c i t y of wood s h a v i n g for Congored c o m p a r e d with light o r a n g e EG. The results s u g g e s t t h a t c h e m i c a l adsorption m a y be involved. Also, the efficiency of the a d s o r p t i o n process depends p r i m a r i l y on the s t r u c t u r e of the dye. REFERENCES Asfour, H.M., O.A. Fadali, M.M. Nassar and M.S. E1-Geundi, 1985. Equilibrium studies on adsorption of basic dyes on hardwood. J. Chem. Technol. Biotechnol. Chem. Technol., 35A: 21 27. Judkins, Jr., J.F. and S.H. John, 1978. Color removal from textile dye waste using magnesium carbonate. JWPCF, 50: 2446-2456. Mckay, G., M.S. Otterburn and A.G. Sweeney, 1979. The removal of color from effluent using various adsorbants. III. Silica: rate Processes. Water Res., 10: 15~20. Mriganka, M.G., E.W. Franklin, J.S. Otis, B.K. Peter and D.G. Paul, 1978. Treatability studies and design consideration for textile wastewater. J. Water Pollut. Control Fed., 50: 1976-1985. Poots, V.J.P., G. Mckay and J.J. Healy, 1978. Removal of basic dye from effluent using wood as an adsorbent. JWPC 5: 926-935. Sadov, F., M. Korchagin and A. Matetsky, 1978. Chemical technology of fibrous materials. Translated from Russian by N. Cherny Shova. Mir. Publishers, Moscow. U.S. EPA, 1974. Development for effluent limitations guidelines and new source performance standards for textile mills point source category, pp. 238~32.