Thermodynamics and kinetics of glyphosate adsorption on resin D301

Fei-xiong Chen; Cai-rong Zhou; Guo-peng Li; Fei-fei Peng

doi:10.1016/j.arabjc.2012.04.014

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Original article

9 (

2_suppl

); S1665-S1669

doi:

10.1016/j.arabjc.2012.04.014

Thermodynamics and kinetics of glyphosate adsorption on resin D301

Fei-xiong Chen^{^a}, Cai-rong Zhou^{^a,⁎}, Guo-peng Li^{^a}, Fei-fei Peng^{^b}

a School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450001, Henan, China

b School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China

⁎Corresponding author. Address: School of Chemical Engineering & Energy, Zhengzhou University, 100 of Science Road, Zhengzhou 450001, Henan, China. Tel./fax: +860 37167781034. zhoucairong@zzu.edu.cn (Cai-rong Zhou)

Received: 2011-11-29, Accepted: 2012-4-22, Published: 2012-11-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

The adsorption isotherms, kinetics, and thermodynamics are investigated in batch experiments. The adsorption isotherms and kinetics in the range of 303.15–318.15 K are determined. Langmuir, Freundlich, and Temkin isotherms are employed to describe the adsorption process, indicating that the Langmuir isotherm fits the data better. By thermodynamic functions, ΔH^θ, ΔG^θ and ΔS^θ are calculated. The kinetics of the adsorption follows a pseudo-second order model. The apparent activation energy is calculated to be 83.11 kJ mol⁻¹ by Arrhenius equation.

Keywords

Adsorption

Separation

Thermodynamics

Kinetics

Glyphosate

Resin D301

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1 Introduction

Glyphosate (N-carboxy methyl phosphonic glycine) is a highly effective herbicide, which is widely used in agricultural production. A quantity of inorganic salts and some organic compounds, such as glyphosate and glycine, exist in the wastewater drained from the production of glyphosate. Therefore, it is an urgent subject to treat the product of glyphosate from this wastewater. The methods of chemical oxidation, electrolysis, biochemical, evaporation have been used to treat wastewater. And adsorption is a kind of potential and effective method in enrichment or recycling of glyphosate and treatment of wastewater. The research on adsorption of glyphosate mainly focused on the adsorption behavior in the soil (Li et al., 2008) or on the adsorption of trace amounts of glyphosate on the clay, aluminum oxide and iron oxide, aluminum hydroxide and iron hydroxide in the environmental protection (Gimsing and Borggaard, 2007, 2002; Glass, 1987 ).

After comparison with adsorption properties of glyphosate on resins, activated carbon and activated aluminas (Ge et al., 2009; Peng et al., 2007), the resin D301 is selected as adsorbent and its properties of adsorption in aqueous solution of glyphosate are studied in this paper. The thermodynamics and kinetics of adsorption process are also investigated in detail.

2 Experimental

2.1

2.1 Materials and experiment apparatuses

2.1.1

2.1.1 Reagents

All chemicals are of analytical grade and used as received without any purification. Resin D301 is purchased from Changzhou Bo Yan adsorption material Technology Co. Ltd., (China) and glyphosate (mass fraction is 95%) is provided by a chemical factory (Zhejiang, China). The solution of glyphosate (1.0% mass fraction, pH = 6.0 is adjusted with NaOH) is prepared, to some extent, which is similar to the properties of original wastewater of glyphosate supplied by the chemical factory (Zhejiang, China), especially in pH value and concentration. So it can be used to simulate the original wastewater. Resin D301 is prepared according to a previous work (Peng et al., 2007). Distilled-deionized water is used throughout the experiments.

2.1.2

2.1.2 Apparatus

FA1004 Electronic Analytical Balance (Shanghai Precision & Scientific Instruments Co. Ltd., Shanghai, China); UV–visible spectrophotometer (UV-2401PC, Shimadzu Corporation, Japan); THZ-98A type Constant-temperature Shaker (Scientific Instruments Co. Ltd., Shanghai, China).

2.1.3

2.1.3 Adsorption procedures

In a typical adsorption procedure, 0.5 g of Resin D301 mixed with 45 mL of glyphosate solution in an iodine number flask is shaken under a controlled temperature and at 150 rpm (r min⁻¹) of constant-temperature shaker. After reaching the adsorption equilibrium, the concentration of glyphosate in the liquid phase is determined with spectrophotometry. The capacity of static equilibrium adsorption could be kept as the main observation index. The formula is written by the following equation:

(1)

q = \frac{(c_{o} - c_{1}) \times V_{1}}{m}

where q is the equilibrium capacity of adsorption (mg g⁻¹); c₀ and c₁ are the concentrations of both initial and after adsorbing glyphosate (mg mL⁻¹); V₁ is the volume of adsorption solution (mL); m is the amount of resin D301 (g).

2.1.4

2.1.4 Determination procedures

Three solutions are prepared, i.e., S₁ (250 g L⁻¹ potassium bromide solution), S₂ (6.99 g L⁻¹ sodium nitrite solution), and S₃ (50% sulfuric acid solution). Some amount of glyphosate solution is mixed with 5 mL of S₁, 1 mL of S₂, and 5 mL of S₃ and diluted to 100 mL with deionized water. After settling for 20 min, the concentration of glyphosate is determined at 243 nm (Peng et al., 2007).

2.2

2.2 The basic models

2.2.1

2.2.1 Adsorption isotherm models

To analyze the equilibrium data of absorption, the isotherm models of Langmuir, Freundlich, and Temkin are used. Eqs. (2)–(4) are in turn the linear forms of them (Khenifi et al., 2010):

(2)

\frac{1}{q_{e}} = \frac{1}{q_{\max} c_{e} b} + \frac{1}{q_{\max}}

(3)

\ln q_{e} = \ln k_{f} + \frac{1}{n} \ln c_{e}

(4)

q_{e} = B_{T} \ln A_{T} + B_{T} \ln c_{e}

where c_e is the equilibrium concentration in equilibrium aqueous phase (mg L⁻¹), q_e is the amount adsorbed at equilibrium (mg g⁻¹) in Eqs. (2)–(4). In addition to that, in Eq. (2) b is the equilibrium adsorption coefficient (L g⁻¹) and q_max is the maximum adsorption capacity (mg g⁻¹). In Eq. (3) k_f is expressed as adsorption capacity coefficient. n is adsorption intensity, reflecting the trend of isotherm, and the value of n is usually greater than 1. If the value of 1/n is greater than 2, it is believed that the process of absorption is difficult to go on. In Eq. (4), B_T = RT/b_T, T is the absolute temperature in Kelvin and R is the universal gas constant (8.314 J mol⁻¹ K⁻¹), the constant B_T is related to the heat of adsorption; A_T is the equilibrium association constant (L min⁻¹), corresponding to the maximum bonding energy.

2.2.2

2.2.2 Adsorption kinetics models (Khenifi et al., 2010)

The pseudo-first order kinetic model, pseudo-second order model, Elovich equation and the intraparticle diffusion model are used, in order to analyze the kinetics data of absorption. Eqs. (5)–(8) are listed blew:

(5)

\ln (q_{e} - q_{t}) = \ln (q_{e}) - k_{1} t

(6)

\frac{t}{q_{t}} = \frac{1}{k_{2} q_{e}^{2}} + \frac{t}{q_{e}}

(7)

q_{t} = β \ln (α β) + β \ln t

(8)

q_{t} = k_{p} \times \sqrt{t} + c

where q_t and q_e are the amount of adsorbate at any time t and at equilibrium time (mg g⁻¹) respectively, and k₁ is the rate constant of pseudo-first order adsorption (min⁻¹). k₂ is the rate constant of pseudo-second order adsorption (g mg⁻¹ min⁻¹). In Eq. (7), α is the initial rate of adsorption (g mg⁻¹ min⁻¹), β is the desorption constant (g mg⁻¹). k_p is the rate constant of intraparticle transport (mg g⁻¹ min^−0.5) and c (mg g⁻¹).

3 Results and discussion

3.1

3.1 Adsorption isotherms and adsorption models

The equilibrium adsorption isotherm is fundamental for describing the interactive behavior between adsorbate and adsorbent. To achieve this goal, the adsorption data are analyzed with Langmuir, Freundlich and Temkin isotherms.

The values of isotherms calculated by using different models are listed in Table 1. From Table.1, the results show that:

Langmuir isotherm is the best effective, according to the correlation coefficient (r²). So the Langmuir model is more appropriate to express the adsorption isotherm of resin D301 absorbing glyphosate from the aqueous solution.
From value of q_max in Langmuir isotherm, the maximum capacity of adsorption increases with the temperature increasing.
n is less than 1 in Freundlich isotherm. Therefore, it is difficult for resin D301 to absorb glyphosate.

Table 1 Langmuir, Freundlich and Temkin isotherms constants for the adsorption of glyphosate.

Models		Langmuir			Freundlich			Temkin
		q_max (mg g⁻¹)	b × 10³ (L mg⁻¹)	r²	k_f (mg g⁻¹)	n	r²	B_T (L g⁻¹)	A_T (L min⁻¹)	r²
T/K	308.15	400.00	0.07645	0.9803	0.001284	0.5743	0.9728	100.00	0.5763	0.9622
	313.15	625.00	0.04188	0.9529	0.008370	0.7348	0.9366	143.05	0.3716	0.9379
	318.15	833.33	0.02454	0.9366	0.03472	0.8946	0.9041	130.13	0.3733	0.8158

3.2

3.2 The thermodynamics parameters of adsorption

Thermodynamic parameters are essential to evaluate the adsorption process since they provide in-depth information on inherent energetic changes. Assuming that the activity coefficient does not change in the low temperature, the Gibbs energy (ΔG^θ), enthalpy (ΔH^θ), and entropy (ΔS^θ) changes are calculated by the following equations (Peng et al., 2005; Zhou et al., 2009):

(9)

Δ G^{θ} = - RT \ln (K)

(10)

\ln K = \frac{Δ S^{θ}}{R} - \frac{Δ H^{θ}}{RT}

where K is distribution coefficient, R is the thermodynamic gas constant (8.314 J mol⁻¹ K⁻¹). In the Langmuir equation, K = b, b is the theoretical adsorption coefficient of Langmuir.

ΔH^θ and ΔS^θ can be obtained from Eq. (10) and ΔG^θ can be calculated by ln K at different temperatures. The results obtained by Langmuir model are shown in Table 2.

Table 2 Thermodynamics parameters of Langmuir.

T (K)	b × 10³ (L mg⁻¹)	ΔH^θ (kJ mol⁻¹)	ΔG^θ (kJ mol⁻¹)	ΔS^θ J mol K⁻¹	r²
308.15	0.07645	−92.64	24.31	−379.52	0.9994
313.15	0.04188		26.20
318.15	0.02454		28.10

From Table 2, it reveals that the adsorption is an exothermic process (ΔH^θ < 0), and the capacity of adsorption increases with temperature increasing. ΔH^θ is calculated to be −92.64 kJ mol⁻¹. When ΔH^θ is in the range of (5–10) kJ mol⁻¹, the adsorption mechanism is physiosorption; i.e., the bond between adsorbent and adsorbate is van der Waals interactions. When ΔH^θ is in the range of (30–70) kJ mol⁻¹, the adsorption belongs to chemisorption; i.e., a chemical bond is formed between the adsorbate and the surface. In the present system, the value of ΔH^θ demonstrates that neither fully physical nor fully chemical and some complex mechanism dictated the adsorption process, and it also reveals that chemical adsorption is the dominant process of adsorption (Li et al., 2011). ΔS^θ is also negative, which implies that the degree of freedom decreased at the solid–liquid interface during the adsorption process. It also suggests that there are some structural changes in both the adsorbate and adsorbent.

According to the adsorption exchange theory, for the solid–liquid exchange adsorption, the adsorption process of solute exchange from liquid to an interface of solid–liquid will lose some degree of freedom (including translation and rotation). So the entropy of process is reduced; but in the liquid phase, the solute exchange adsorption tends to make the resin contraction occur, making part of the water of the hydration in the resin get released into the liquid phase, and the desorption process of water molecule makes the entropy of process increased. The value of entropy depends on the sum of those phenomena.

Based on the values of both enthalpy and entropy, ΔG^θ is obtained to be positive by Eqs. (9) and (10). The results account for the reason that the entropy of adsorption plays a leading role, namely the driving force of adsorption process is more dominant than that of chemical bonding force. Therefore, even if the adsorption process is exothermic, sometimes, it is not conducive to an adsorption process. And the higher the temperature is, the more difficult the adsorption is. But it is still able to initiate the adsorption process, which is consistent with experiments (Li and Li, 2009).

As the temperature increases, from the model of Langmuir, it shows that q_max is increasing, but from Table 2, it is clear that the adsorption process will become non-spontaneous by the main driving force of chemical bonding force. It is important to make a balance between q_max and spontaneity, so the process of absorption benefits in the low temperature.

3.3

3.3 Results of kinetics and discussion

Adsorption kinetic is investigated to examine the controlling mechanism for this adsorption process. The pseudo-first order and the pseudo-second order kinetics equations basically contain all the process. By using both kinetics equations, the simulation analysis of experimental data reveals the truth of the adsorption kinetic mechanism of glyphosate on resin D301. To further study on the adsorption kinetics, models of both Elovich and intraparticle diffusion are applied, simultaneously. The results are listed in Table 3. Table 3 shows that the correlation coefficient value of the pseudo-second order kinetic equation is higher than that of other models. Therefore, the pseudo-second order kinetic equation is suitable to model the adsorption curve of glyphosate on resin D301.

Table 3 Different kinetics models constants for resin D301 in different temperature (concentration of glyphosate is 1.0%; pH = 6.0).

Models	Parameters of pseudo-second order model			Parameters of pseudo-first order model
T (K)	k₂ (min⁻¹)	q_e (mg g⁻¹)	r²	k₁ (min⁻¹)	q_e (mg g⁻¹)	r²
303.15	2.52 × 10^–4	161.29	0.9910	4.60 × 10^–3	181.44	0.9786
308.15	3.91 × 10^–4	166.67	0.9948	2.70 × 10^–3	463.59	0.9894
313.15	6.95 × 10^–4	169.49	0.9892	1.30 × 10^–3	380.28	0.9732
318.15	1.17 × 10^–3	131.58	0.9952	8.00 × 10^–3	364.24	0.9262

	Parameters of Elovich model			Parameters of intraparticle diffusion model
	β (g mg⁻¹)	α (mg g⁻¹ min⁻¹)	r²	k_p (mg g⁻¹ min^−0.5)	c (mg g⁻¹)	r²
303.15	30.39	0.020	0.9642	7.826	42.39	0.9244
308.15	46.93	0.0086	0.8914	14.64	30.36	0.9051
313.15	47.13	0.011	0.9166	11.98	62.48	0.8157
318.15	24.46	0.030	0.9107	4.42	57.35	0.8371

The correlation coefficient value of the pseudo-first order kinetic equation is little lower than the pseudo-second order kinetic equation, indicating that this adsorption is mainly controlled by the surface control, rather than the adsorbate diffusion. The adsorption rate constant of pseudo-second order in Table 3 shows that its rate constant of adsorption increases with the increasing temperature, which reveals that this adsorption may be controlled by chemical adsorption.

3.4

3.4 Calculation and analysis of the apparent activation energy

The linear form of Arrhenius equation (Wang et al., 2010) can be expressed by the following equation:

(11)

\ln k = - \frac{E_{a}}{RT} + \ln A

where E_a (J mol⁻¹) is the apparent activation energy of the reaction; k is a coefficient. The data in Table 3 to plot ln k vs 1/T (see Fig. 1) show that the adsorption process is in accordance with pseudo-second order kinetic model. So, for this reaction, the apparent activation energy is calculated by the coefficient of k₂ in pseudo-second order kinetic model.

The linear fitting of Arrhenius equation.

Activation energy is an important factor for determining the reaction rate. In a certain temperature, if the activation energy is greater, the reaction is slower; if activation energy is smaller, the reaction is faster. In room temperature, if the activation energy calculated is less than 40 kJ mol⁻¹, the rate of the reaction is quick; if it is greater than 120 kJ mol⁻¹, the rate of the reaction is rather slow (Zhou et al., 2009).

For the ion exchange reaction of glyphosate on resin D301, the apparent activation energy of the pseudo-second order kinetic model is obtained to be 83.11 kJ mol⁻¹. According to the experimental data, the apparent rate constant (k₂) increased with increasing temperature, which can account for the reason that the higher the temperature is, the more complete the exchange reaction of drug and resin is. In consideration of the reason that this reaction is an exothermic reaction as well as that E_a is between 40 and 120 kJ mol⁻¹ which shows that this adsorption process is slow, the conclusion is in accordance with that of Freundlich isotherm as in Table 2.

4 Conclusions

Resin D301 has a high capacity of adsorption. Adsorption of glyphosate on resin D301 meets well with Langmuir model and is a single-layer adsorption. And thermodynamic functions of ΔH^θ, ΔG^θ, ΔS^θ are calculated in the process of resin D301 adsorbing glyphosate. They are ΔH^θ = −92.64 kJ mol⁻¹, ΔG^θ > 0, and ΔS^θ < 0, respectively, which indicated that the adsorption process is exothermic, entropy decreased, and dominated by some complex mechanism, neither fully physical nor fully chemical adsorption. Moreover, adsorption of glyphosate on resin D301 meets well with the pseudo-second order kinetic model, and the apparent activation energy of this adsorption is 83.11 kJ mol⁻¹.

References

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Introduction

Experimental

Materials and experiment apparatuses
The basic models

Results and discussion

Adsorption isotherms and adsorption models
The thermodynamics parameters of adsorption
Results of kinetics and discussion
Calculation and analysis of the apparent activation energy

Conclusions

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[1] Ge Lei, Wang Jing, Chen Huan, Cui Hao, Tao Xiancong, Zheng Jianzhong, . Adsorption of glyphosate from aqueous solutions by hydrous ferric oxide preloaded into activated carbon. Chin. J. Environ. Eng.. 2009;13:1745-1748.
[Google Scholar]

[2] Gimsing A.L., Borggaard O.K., . Phosphate and glyphosate adsorption by hematite and ferrihydrite and comparison with other variable charge minerals. Clays Clay Miner.. 2007;55:110-116.
[Google Scholar]

[3] Gimsing A.L., Borggaard O.K., . Competitive adsorption and desorption of glyphosate and phosphate on clay silicates and oxides. Clay Miner.. 2002;37:509-515.
[Google Scholar]

[4] Glass R.L., . Adsorption of glyphosate by soils and clay minerals. J Agric. Food Chem.. 1987;35:497-500.
[Google Scholar]

[5] Khenifi A., Derriche Z., Mousty C., Prévot V., Forano C., . Adsorption of glyphosate and glufosinate by Ni2AlNO3 layered double hydroxide. Appl. Clay Sci.. 2010;47:362-371.
[Google Scholar]

[6] Li Yan, Yang Min, Wang Hongbin, Sun Yanfang, Feng Guiquan, . Study on thermodynamics of soil adsorbing glyphosate. J. Anhui Agric. Sci.. 2008;36:10061-10062.
[Google Scholar]

[7] Li Xiqian, Zhou Xiao, Mu Jun, Lu Lijun, Han Dachuan, Lu Chunmei, Wang Mingtai, . Thermodynamics and kinetics of p-aminophenol adsorption on poly(aryl ether ketone) containing pendant carboxyl groups. J. Chem. Eng. Data. 2011;56:4274-4277.
[Google Scholar]

[8] Li Qingguo, Li Weimin, . Study on thermodymamics of adsorbing timosaponin by resin. J. Liaoning Univ. Tradit. Chin. Med.. 2009;11:232-233.
[Google Scholar]

[9] Peng Shuchuan, Wang Shisheng, Chen Tianhu, Jiang Shaotong, Qing Chengsong, . Thermodynamics study of adsorption of water soluble dyestuffs onto purified palygorskite. J. Chin. Ceram. Soc.. 2005;33:1012-1017.
[Google Scholar]

[10] Peng Bo, Chen Jian, Wang Jing, Zhang Jianzhong, Wang Xiaoyan, Chen Jinlong, . Comparison of adsorption properties of glyphosate on resins and activated aluminas. J. Hebei Univ. (Nat. Sci. Ed.). 2007;27:505-510.
[Google Scholar]

[11] Wang Guizhen, Li Lixin, Li Yongzhen, Xue Quanmin, . Study on the preparation of bamboo activated carbon and its phenol adsorption properties. J. Chem. Chin. Univ.. 2010;24:700-704.
[Google Scholar]

[12] Zhou Wei, Tang Yu, Xie Huan, Liu Cha, Yang Dajian, Chen Xinzi, . Kinetics and thermodynamics of absorption of ganciclovir by ion exchange resin. J. Chin. Pharm.. 2009;17:1327-1331.
[Google Scholar]

Thermodynamics and kinetics of glyphosate adsorption on resin D301

Abstract

Keywords

Adsorption

Separation

Thermodynamics

Kinetics

Glyphosate

Resin D301

1 Introduction

2 Experimental

2.1 Materials and experiment apparatuses

2.1.1 Reagents

2.1.2 Apparatus

2.1.3 Adsorption procedures

2.1.4 Determination procedures

2.2 The basic models

2.2.1 Adsorption isotherm models

2.2.2 Adsorption kinetics models (Khenifi et al., 2010)

3 Results and discussion

3.1 Adsorption isotherms and adsorption models

3.2 The thermodynamics parameters of adsorption

3.3 Results of kinetics and discussion

3.4 Calculation and analysis of the apparent activation energy

4 Conclusions

References

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