Thermodynamic parameters of iron-cyanide adsorption onto {gamma}-Al{sub 2}O{sub 3}

Journal Article · Tue Apr 15 04:00:00 EDT 1997 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1006/jcis.1997.4758· OSTI ID:483814

Huang, C; Cheng, W P ^[1]

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1. National Chiao Tung Univ., Hsinchu (Taiwan, Province of China). Inst. of Environmental Engineering

In this study, the authors describe the adsorption of ferricyanide (Fe(CN){sub 6}{sup 3{minus}}) on {gamma}-Al{sub 2}O{sub 3} by a modified Langmuir adsorption isotherm. The modified Langmuir isotherm developed herein can accurately predict the apparent equilibrium constant (K{sup 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}-Al{sub 2}O{sub 3} and the adsorbate. According to the Gibbs-Helmholtz equation, these apparent equilibrium constants at various temperatures and pH conditions can be applied to determine enthalpy changes ({Delta}H{sup 0}) for the adsorption at different pH conditions. The result indicates that enthalpy change at different pH values is near {minus}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{sup 0}) has been explained from the viewpoint of exchange reaction in this study. The negative free energy change ({Delta}G{sub ads}{sup 0}) for ferricyanide adsorption shows the spontaneous nature of the adsorption process.

• OSTI ID: 483814
• Journal Information: Journal of Colloid and Interface Science, Journal Name: Journal of Colloid and Interface Science Journal Issue: 2 Vol. 188; ISSN 0021-9797; ISSN JCISA5
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ADSORPTION
ADSORPTION HEAT
ADSORPTION ISOTHERMS
ALUMINIUM OXIDES
FERRICYANIDES
MATHEMATICAL MODELS
PH VALUE
SORPTIVE PROPERTIES
THERMODYNAMICS