2,4-디클로로페녹시아세틱 에시드와 2,4-디니트로페놀의 평형특성

김숙진, 심왕근*, 김태영, 문 희*, 김승재, 조성용

전남대학교 환경공학과, *전남대학교 응용화학부

Equilibrium Characteristics of 2,4-Dichlorophenoxyacetic acid and 2,4-Dinitrophenol

Sook Jin Kim, Wang Geun Shim*, Tae Young Kim,

Hee Moon*, Seong Jae Kim, Sung Yong Cho

Department of Environmental Engineering, Chonnam National University, *Faculty of Applied Chemistry, Chonnam National University

Introduction

Environmental contamination by toxic xenobiotic chemicals is a serious worldwide problem. The widespread usage of pesticides has a potential negative impact on public health and the ecosystem.

Among the numerous agrochemicals in use today, the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), a member of the phenoxy herbicide group, has been widely applied to control broad leaf weeds[1]. 2,4-D is a regulated compound due to its toxicity; solids containing 2,4-D in excess of 1,000ppm are classified as hazardous.

2,4-Dinitrophenol (2,4-DNP) has been used in the manufacture of dyes and wood preservatives and as a pesticide. It is also used as an indicator for the detection of potassium and ammonium ions. The acute (short-term) effects of 2,4-DNP in human through oral exposure consist of nausea, vomiting, sweating, dizziness, headaches, and loss of weight. Long-term oral exposure to 2,4-DNP in human has resulted in the formation of cataracts and skin lesions and has caused effects on the bone marrow, central nervous system(CNS), and cardiovascular system[2].

Various treatment techniques have been employed to treat the wastewater, including precipitation, adsorption, ion exchange, and reverse osmosis. The adsorption equilibria data are one of utmost importance for modeling the wastewater treatment process. Hence, this paper presents experimental results for the adsorption of 2,4-D and 2,4-DNP on various activated carbons. The pH dependency has also been incorporated into a Sips equation.

Theory

·Adsorption isotherms

There are various single-species isotherms reported in literatures[3]. In this study, single-species equilibria data were correlated by the Langmuir, Freundlich, Sips and Redlich-Peterson equation.

Langmuir equation : [eqn: q= { q}_{m }bC/(1+bC)]

Freundlich equation : [eqn: q=k {C }^{1/n }]

Sips equation : [eqn: q= {q }_{m }b { C}^{1/n }/(1+b{ C}^{1/n })]

Redlich-Peterson equation : [eqn: q=aC/(1+ b{ C}^{m })]

Materials and methods

·Activated carbon

The adsorbents used in this study were granular actvated carbon(GAC) F400, SLS103 and WPL manufactured by Calgon, Samchully and Union Carbon Ltd, respectively. GAC which was used as the adsorbent was sieved into a narrow range of particle sizes(0.055∼0.065 cm in dia.), before washing it with distilled water a few times to remove impurities and carbon powder and then stored after drying it in the vaccume oven at 120□1 □ for 24hr. The physical properties of F-400, SLS103 and WPL are shown in Table 1, respectively.

Table 1. Physical Properties of Different Adsorbents

Physical properties	Unit	F400	SLS103	WPL
Particle diameter	mm	0.37∼0.54	0.37∼0.54	0.37∼0.54
Multi point BET	m2/g	840	1000	650
Average pore radius	□	14.93	11.98	12.56

·Adsorbates

The adsorbates were 2,4-D and 2,4-DNP. The purity and manufacturer of each adsorbate are as follows: 2,4-D, 99.0% (Acros Co.); 2,4-DNP, 99.0% (Yakuri Co.). All chemicals were used without further treatment. The solution pH was adjusted to 3.5, 7, 10 by the addition of NaOH and HCl.

·Isotherm test

Adsorption isotherms were determined by contacting a volume(200ml) of solution of 100mg/l with a carefully weighed activated carbon in a conical flask. The amount of carbon was varied (0.001∼0.25g) in single solute test. The flaskes were continually shaked for 7day to provide good mixing and contact of the carbon and the solution until an constant liquid phase concentraion of adsorbate was achieved in a thermostated bath at 25□1□.

The concentration of organic solution was determined with a UV(Shimadzu 1601) at □=284nm and 325nm, respectively.

Results and discussions

Adsorption isotherms play a key role in the design of the adsorption-based process for treatment of wastewater disposal. In this study, four isotherm models were used to correlate the experimental equilibrium data. To find the isotherm parameters for each isotherm equation, a linear least square method was used. The value of the mean percentage error has been used as a test criterion for the fit of the correlation. The estimated values of the adsorption parameters are summarized in Table 2. Among four equations, the Sips and Redlich-Peterson equations gives the best fit but it is likely to be an inevitable result since this equation contains three adjustable parameters. Fig. 1 shows the adsorption amounts of 2,4-D onto three different adsorbents. According to experimental results, the magnitude of adsorption capacity was the order of F400> SLS103> WPL.

The surface heterogeneity and chemical nature of the adsorbent surface are important factors for the determination of the influence of pH on the adsorption of single systems. In general high pH depresses the equilibrium amount adsorbed but neutral salt addition increases adsorption. Each experimental isotherm was plotted in terms of Sips to obtain the pH dependent parameters, qm and b. The pH dependence of these parameters was assumed to obey the following empirical expression:

[eqn: { q}_{ m}= { q}_{m0 }exp( alpha CDOT z), ~b= { b}_{0 }exp(- beta CDOT z),~z= LEFT ( 1/ { pH}_{ } -1/ { pH}_{m } RIGHT )]

Fig. 2 shows the experimental equilibrium adsorption isotherms obtained at the different pHs for 2,4-D and 2,4-DNP and corresponding amounts fitted with the pH dependent Sips isotherm. A Sips model with pH-dependent parameters was fitted successfully to all of the pH adsorption isotherms.

Reference

1. S.S.mangat and P.Elefsiniotis, Wat. Res. 33, 3, 861-867, 1999.

2. EPA Health Effects Notebook for Hazardous Air Pollutants-Draft.

3. Duong D. Do, Adsorption analysis : Equilibria and kinetics, Series on        Chemical Engineering Vol. 2, Imperial College Press., 1998.

Fig. 1. Adsorption equilibrium of 2,4-D onto various adsorbents

at initial pH3.5 and 298.15K

Table 2. Adsorption equilibrium constants of 2,4-D onto various adsorbents

at initial pH3.5 and 298K

Isotherm	Parameters	F400	SLS103	WPL
Langmuir	qm	1.857	1.384	1.431
	b	33.86	61.79	17.95
	Error(%)	3.111	8.451	7.660
Freundlich	k	2.369	2.011	1.807
	n	3.974	3.798	2.836
	Error(%)	1.354	2.989	4.800
Sips	qm	3.025	3.458	2.460
	b	2.361	1.137	1.738
	n	2.164	2.664	1.900
	Error(%)	0.638	2.434	4.375
Redlich-Peterson	a	197.3	547.3	82.99
	b	87.23	279.3	49.43
	m	0.808	0.762	0.744
	Error(%)	0.561	2.602	4.855

(a) 2,4-DNP	(b) 2,4-D

Fig. 2. pH dependence of the adsorption of 2,4-D and 2,4-DNP onto F400