1. Pseudo-Second Order Model for Lead Ions Removal from Water
Chien-Chou Yeha, Jui-Hsin Chena, Yuh-Shan Hob#* and Wen-Ta Chiua
aTaipei Medical University – Wan Fang Hospital,
bSchool of Public Health, Taipei Medical University
Introduction
Equilibrium studies described by a sorption isotherm characterized by certain constants whose values express the surface properties and affinity of the sorbent. In many cases, the equilibrium sorption capacity is unknown and when chemisorption tends to become immeasurably slow and the amount sorbed is still significantly smaller than the equilibrium amount [1]. However, the pseudo-second order equation has the following advantages: it allowed an effective sorption capacity; the sorption capacity and rate constant of pseudo-second order and initial sorption rate can all be determined from the equation without knowing any parameter beforehand.
Materials and Methods
Palm kernel fiber was obtained from the Nigerian institute for oil palm research (N.I.F.O.R) Benin City, Nigeria. A range of initial solution pH (pH = 3, 4, 5 and 6) were used and the flasks were agitated for 20 min. A 0.6 g sample of fiber was added to 400 ml volume of lead ion solution and agitated. Initial lead concentration 120 mg/dm3 were used. Samples (2.5 ml) were withdrawn at suitable time interval, filtered and the filtrate analyzed for the remaining lead concentration with AAS. A range of fibre dose from 1.5 to 5 g/dm3 were used for effect of fibre dose.
Results and Discussion
Table 1. Isotherms and Their Linear Forms
Table 2. Pseudo-second order rate parameters for sorption of lead on fibre at varies initial solution pH
Fig. 1. Plot of sorbed amount versus time for lead ion at varies fibre doses
Fig. 2. Plot of the experimental sorption capacity curves for the sorption of lead ion at varies fibre doses
Table 3. Pseudo-second order rate parameters for sorption of lead on fibre at varies fibre doses
Fig. 3. Variation of sorption capacity and percent lead removal against fibre dose
Fig. 4. Pseudo-isotherms of sorption lead on fibre with operating lines
Table 4. Comparison of linear regression coefficient of determination, r2, and non-linear 2 test analysis
Conclusion
This investigation was based on the assumption of a pseudo-second order mechanism in relation to the sorption of lead on palm kernel fibre. The results showed high coefficient of determination. The pseudo-second order rate constant, the initial sorption rate and the equilibrium sorption capacity, were a function of palm kernel fibre dose. An isotherm was obtained by changing fibre doses using equilibrium concentration and equilibrium capacity obtained based on the pseudo-second order constants. It is not appropriate to use the coefficient of determination of linear regression analysis for comparing the best-fitting of Freundlich and both linear Langmuir isotherms. Non-linear Chi-square analysis could be a better method. Freundlich is a special case of Redlich-Peterson isotherm when constants A and B are high. It was clear that both two-parameter pseudo-Freundlich and three-parameter pseudo-Redlich-Peterson isotherms were the best-fitting models for the experiment results.