School of Physical Sciences

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Browsing School of Physical Sciences by Author "Atu, A. Ayuk"

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    Equilibrium, thermodynamic and kinetic studies on adsorption of zinc (II) from solutions using different low-cost adsorbents
    (Open Science, 2015-11-05) Njoku, Pascal C.; Atu, A. Ayuk; Atulegwu, P. Uzoije; Justus I. Okolie
    Many industrial wastewaters contain numerous toxic metals such as zinc, which must be removed before reuse of the water or discharge into the environment. In this present study, unripe plantain peel activated carbon (UPPAC), pineapple peel activated carbon (PPAC) and commercial activated carbon (CAC) were utilized as low cost adsorbents for the removal of Zn (II) from aqueous solutions. Batch adsorption methodology was used to evaluate the effect of solution pH, initial metal ion concentration, adsorbent dose, contact time and temperature on adsorption. Scanning Electron Microscope (SEM) and Fourier Transform Infrared Spectrophotometer (FTIR) were used to characterize the adsorbents. The equilibrium isotherm data were analyzed using the Langmuir, Freundlich and Temkin isotherm model. The kinetic data were analyzed using the pseudo-first order, pseudo-second order equations, Elovich equation and intraparticle rate equation. Maximum adsorption of Zn (II) on UPPAC, PPAC and CAC (82.45%, 89.95% and 93.45%) was observed at pH 6 and pH 7. The adsorbed amount of Zn (II) increased with increase in contact time and reached equilibrium within 180 minutes. The maximum adsorption was found to be 200 mg/L in the studied range (200 – 1000 mg/L). The adsorption capacity and percent removal of Zn (II) were found to increase with increase in temperature. The Freundlich isotherm models provided the best fit to the experimental data for Zn (II) as indicated by the regression coefficient values (R2> 0.97). The pseudo-second order equation gave the best fit to the experimental data for the metal ion (R2 > 0.99). Thermodynamic analysis showed a spontaneous adsorption process as negative values of ∆Go (-1.269 to -5.530) were obtained at all temperatures. The positive enthalpy change ∆Ho, 18.00, 20.46 and 23.45 kJ mol-1 for UPPAC, PPAC and CAC indicated an endothermic process. A highly disordered process was indicated by the positive entropy change ∆So .