Fly ash를 이용한 2,4-Dichlorophenoxyacetic acid의 흡착

Theories and Applications of Chem. Eng., 2002, Vol. 8, No. 1

김미희, 송형석, 문희, 양재호

전남대학교 화학공학부, 전남대학교 응용화학부

Adsorption of 2,4-Dichlorophenoxyacetic acid on Fly ash

M. H. Kim, H. S. Song, H. Moon*, J. H. Yang

Dep. of Chem. Eng., Chonnam Nat'l Univ., Kwangju 500-757, Korea

Faculty of Applied Chem. Chonnam Nat'l Univ., Kwangju 500-757, Korea*

Introduction

Surface water pollution by pesticides has been receiving much attention in recent years. 2,4-Dichlorophenoxyacetic acid(2,4-D) is a class of manufactured chemicals that do not occur naturally in the environment. 2,4-D has been widely used in making dyes, wood preservatives, explosives, insect control substances, and other chemicals, and as a photographic developer. 2,4-D enters the air, water, and soil during its manufacture and use. It may be formed from reaction of other chemicals in the air. It may also enter the environment through landfill and storage tank leaks, or accidental spills during manufacture or transport. The amount 2,4-D ingested that causes harmful effects varies among people. Among the several currently known physical, chemical, and biological method for wastewater reuse, adsorption is one of the key processes. The available literature pertaining to the adsorption process used in wastewater treatment primarily deals with activated carbon.

However, in recent years, research interest has increased in terms of the production of low-cost alternatives to activated carbon, which remains an expensive material in spite of its prolific use[1-2]. The major solid waste byproducts from various power plants are ash. It is produced as a fine, noncombustible residue carried off in the flue gas with relatively uniform particle size distribution. Today fly ash is predominantly used in soil stabilization, as a source of metals, and as a cement additive.[3-4]. Environmental concerns have prompted both the government and industry to find effective ways to utilize fly ash and reduce the solid waste volume that is landfilled.   Earlier, we have successfully used wastes of several prime industries to remove metals and other toxic substances[5-6]. Continuing the efforts in that direction, we have now tried fly ash, after converting into an adsorbent, for the removal and recovery of 2,4-D from aqueous solutions. The results are described in this paper.

Experimental Section

The fly ash samples(F-330 and F-660) used in this study were obtained from the Yeochun plant of LG Chem Ltd.. The properties of 2,4-D are given in Table 1.

Equilibrium experiments were carried out by contacting a given amount of sorbent with 2,4-D solution and keeping in a constant temperature shaking incubator. After equilibrium was reached, the concentration of 2,4-D was analyzed using a UV-visible spectrophotometer(Shimadzu, model 1601) at 283 nm. The adsorption capacity of the activated carbon was calculated from the material balance. For kinetic study, the

화학공학의 이론과 응용 제8권 제1호 2002년

batch experiments were made in a carberry-type

Table 1. Properties of 2,4-Dichlorophenoxyacetic acid
	structural formula	molecular weight	solubility in water(g/L)	density
2,4-Dichlorophenoxy- acetic acid		221.04	0.89	1.563

batch adsorber. The vessel had a water circulating jacket in a constant temperature bath. A stirring speed of 500 rpm was adopted because above that speed the stirring has little effect on the adsorption process. At predetermined time intervals, the concentration of 2,4-D was analyzed as described previously.

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Results and Discussion

In this study, three isotherm models - Langmuir, Freundlich, Sips - were used to correlate the experimental equilibrium data. As illustrated in Fig. 1 and 2, the experimental data are well correlated by Sips equation. The experimental equilibrium adsorption isotherms obtained at the different initial pHs for the adsorption of 2,4-D on two fly ash(F-330 and F-660) respectively. As shown in those figures, the equilibrium adsorption amounts of 2,4-D on fly ash decreased with increasing initial pH of solution, for pH range of 3.0-10.0. Sips model was fitted successfully for all of the pH conditions. The calculated parameters of Sips equation are listed in Table 2.

In general, the influence of pH is attributed to the electrostatic interaction between the adsorbent surface and the adsorbate molecule. This suggests that effective separation could be achieved by the adjustment of pH.

Table 2. Adsorption equilibrium of 2,4-D on Fly ash for different initial pHs at 298.15K
Isotherm	Parameters	pH 3		pH 7		pH 10
		F-330	F-660	F-330	F-660	F-330
Langmuir	qm	0.3714	0.1636	0.0575	0.5409	0.0460
	b	0.3972	1.2298	4.8499	0.0652	5.3516
	Error(%)	15.2339	6.2253	7.4800	4.2981	4.5497
Freundlich	k	0.1248	0.1196	0.0583	0.0331	0.0473
	n	1.0671	1.2092	2.1191	1.0409	2.2462
	Error(%)	16.0135	7.4184	3.9990	4.1906	3.4732
Sips	qm	0.0464	0.0711	0.0611	0.0361	0.0633
	b	634.63	11.5489	3.6630	2.3270	1.6536
	n	0.2992	0.6492	1.1193	0.6905	1.5358
	Error(%)	9.2127	5.6593	6.3611	4.8882	2.6563

Fig. 3 and 4 represent the experimental data for 2,4-D in a batch adsorber at different revolution speed. These show that the equilibrium for 2,4-D is attained in 2 hour. Fig. 5 and 6 show the experimental data for 2,4-D on each fly ash in batch adsorber at different initial pH. The presence of high concentration of hydroxyl ions does not have much influence on the initial rate of adsorption of 2,4-D.

References

1. V.K. Gupta, D. Mohan, S. Sharma, Sep. Sci. Technol. (1998) 33, 1331.

2. V.K. Gupta, S. Sharma, I.S. Yadav, D. Mohan, J. Chem. Technol. Biotechnol. (1998) 71, 180.

3. E.E. Berry, V.M. Malhotra, ACI J. (1982) 2, 59.

4. Y. Halse, P.L. Pratt, Cem. Concr. Res. (1984) 14, 491.

5. D. Koeppenkastrop, E.H De Careo, Environ. Sci. Technol. (1993) 27, 1796.

6. S.K. Srivastava, V.K Gupta, D. Mohan, J. Environ. Eng.(ASCE) (1997) 123, 461.

화학공학의 이론과 응용 제8권 제1호 2002년