Browsing by Author "Cheng, WP"

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Adsorption behavior of iron-cyanide onto gamma-Al2O3 interface: A coagulation approach
(1999-05-01)
Cheng, WP
;
Huang, CP
;
Pan, JRS
;
環境工程研究所
;
Institute of Environmental Engineering
Ferrocyanide and ferricyanide ions have strong coagulation ability in a natural water system due to their high valences. Studies with aluminum oxide turbid waters showed significant differences in coagulation between simple ions (Cl-, SO42-, Fe(CN)(6)Fe3-(CN)(6)(4-)) and other species (H2PO4-) that interact chemically with the oxide surface. The evidence suggested that the adsorption of ferrocyanide and ferricyanide on aluminum oxide surface is an outer-sphere reaction. The linear relationship between the logarithm of the significant coagulation concentration and Schultz-Hardy ratios indicated that the coagulation obeyed the DLVO rule. Therefore, it is concluded that the coagulation of aluminum oxide by ferrocyanide and ferricyanide is essentially caused by compression of the electric double layer rather than by charge neutralization. (C) 1999 Academic Press.
Adsorption characteristics of iron-cyanide complex on gamma-Al2O3
(1996-08-10)
Cheng, WP
;
Huang, CP
;
環境工程研究所
;
Institute of Environmental Engineering
The adsorption behavior of ferrocyanide and ferricyanide toward aluminum oxide with a 0.01 M NaClO4 background electrolyte at 25 degrees C was investigated. Results obtained from different pH values demonstrated that the adsorption of these complex ions could be described by a modified Langmuir isotherm in the concentration range 0.5 X 10(-4) to 4 X 10(-4) M. This modified Langmuir isotherm developed here could accurately predict the equilibrium partition between solid and liquid phases while taking proton competition into account. Also, the apparent equilibrium constant (K-app) derived from the Langmuir equation for ferrocyanide or ferricyanide adsorption on aluminum oxide was compared with the intrinsic constant (K-int) calculated by triple-layer model simulation. This comparison revealed a strong correlation between the apparent equilibrium constant and the intrinsic constant. Moreover, in comparing K-app with K-int, we can infer that the adsorption of either ferrocyanide or ferricyanide complexes onto aluminum oxide is achieved through outer-sphere complexation. (C) 1996 Academic Press, Inc.
Adsorption characteristics of iron-cyanide complex on gamma-Al2O3
(1996-08-10)
Cheng, WP
;
Huang, CP
;
環境工程研究所
;
Institute of Environmental Engineering
The adsorption behavior of ferrocyanide and ferricyanide toward aluminum oxide with a 0.01 M NaClO4 background electrolyte at 25 degrees C was investigated. Results obtained from different pH values demonstrated that the adsorption of these complex ions could be described by a modified Langmuir isotherm in the concentration range 0.5 X 10(-4) to 4 X 10(-4) M. This modified Langmuir isotherm developed here could accurately predict the equilibrium partition between solid and liquid phases while taking proton competition into account. Also, the apparent equilibrium constant (K-app) derived from the Langmuir equation for ferrocyanide or ferricyanide adsorption on aluminum oxide was compared with the intrinsic constant (K-int) calculated by triple-layer model simulation. This comparison revealed a strong correlation between the apparent equilibrium constant and the intrinsic constant. Moreover, in comparing K-app with K-int, we can infer that the adsorption of either ferrocyanide or ferricyanide complexes onto aluminum oxide is achieved through outer-sphere complexation. (C) 1996 Academic Press, Inc.
Competitive adsorption of ferricyanide and ferrocyanide on gamma-Al2O3 surface
(2000-04-15)
Cheng, WP
;
Huang, C
;
Chien, YC
;
環境工程研究所
;
Institute of Environmental Engineering
In the past 3 decades, research has proven the significance of competitive adsorption in the equilibrium of pollutants between solid and liquid phases. However, studies on the competitive adsorption of complex ions are very limited in spite of its important role in transporting pollutants in the natural environment. The objective of this study is to derive the thermodynamic parameters of the competitive adsorption between ferricyanide and ferrocyanide from the modified Langmuir isotherm and the triple-layer model (TLM) to determine the location of adsorption. The effects of pH, temperature, and ion concentration on competitive adsorption onto gamma-Al2O3 were investigated. The results demonstrate that ferrocyanide is more competitive than ferricyanide. By comparing the derived K-app with K-int, we inferred that the adsorption of ferricyanide and ferrocyanide onto gamma-Al2O3 was achieved through outer-sphere complexation. The negative Delta H-3 indicated that the adsorption was exothermic, The positive entropy (Delta S degrees) was caused by the replacement and release of a greater number of smaller surface ions by adsorbed ferricyanide and ferrocyanide ions of larger size. (C) 2000 Academic Press.
Thermodynamic parameters of iron-cyanide adsorption onto gamma-Al2O3
(1997-04-15)
Huang, CP
;
Cheng, WP
;
環境工程研究所
;
Institute of Environmental Engineering
In this study, we describe the adsorption of ferricyanide (Fe(CN)(6)(3-)) on gamma-Al2O3 by a modified Langmuir adsorption isotherm. The modified Langmuir isotherm developed herein can accurately predict the apparent equilibrium constant (K-app) at different pH values and temperatures. In the experimental pH range of 5-6.5, adsorption capacity and apparent equilibrium constants decrease as the temperature increases. Because surface protonation increases as pH decrease, a more positively charged site on the surface increases the attraction force that exists between gamma-Al2O3 and the adsorbate. According to the Gibbs-Hehmholtz equation, these apparent equilibrium constants at various temperatures and pH conditions can be applied to determine enthalpy changes (Delta H-0) for the adsorption at different pH conditions. The result indicates that enthalpy change at different pH values is near -5 kcal/mol which indicates that the enthalpy change is in the order of hydrogen bonding and confirms the exothermic nature of the adsorption process. The results also indicate that other thermodynamic parameters change of ferricyanide adsorption. The positive entropy change (Delta S-0) has been explained from the viewpoint of exchange reaction in this study. The negative free energy change (Delta G(ads)(0)) for ferricyanide adsorption shows the spontaneous nature of the adsorption process. (C) 1997 Academic Press.
Thermodynamic parameters of iron-cyanide adsorption onto gamma-Al2O3
(1997-04-15)
Huang, CP
;
Cheng, WP
;
交大名義發表
;
環境工程研究所
;
National Chiao Tung University
In this study, we describe the adsorption of ferricyanide (Fe(CN)(6)(3-)) on gamma-Al2O3 by a modified Langmuir adsorption isotherm. The modified Langmuir isotherm developed herein can accurately predict the apparent equilibrium constant (K-app) at different pH values and temperatures. In the experimental pH range of 5-6.5, adsorption capacity and apparent equilibrium constants decrease as the temperature increases. Because surface protonation increases as pH decrease, a more positively charged site on the surface increases the attraction force that exists between gamma-Al2O3 and the adsorbate. According to the Gibbs-Hehmholtz equation, these apparent equilibrium constants at various temperatures and pH conditions can be applied to determine enthalpy changes (Delta H-0) for the adsorption at different pH conditions. The result indicates that enthalpy change at different pH values is near -5 kcal/mol which indicates that the enthalpy change is in the order of hydrogen bonding and confirms the exothermic nature of the adsorption process. The results also indicate that other thermodynamic parameters change of ferricyanide adsorption. The positive entropy change (Delta S-0) has been explained from the viewpoint of exchange reaction in this study. The negative free energy change (Delta G(ads)(0)) for ferricyanide adsorption shows the spontaneous nature of the adsorption process. (C) 1997 Academic Press.