Kinetic studies of adsorption

To investigate the sorption mechanism, the constants of sorption were determined by using pseudo-first and second order equations. The plot of log(qe-qt) and t/ qt against time were used and all data were tested against both models. The results from Table 1 show that the correlation coefficients obtained from pseudo-first order were

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Calculation from the intercept and slope of the straight line of pseudo-second order equation (Fig. 2(a), 2(b) and 2(c)), the initial rate of adsorption (h, mg g-1min-1) was obtained (Table 1). The highest initial sorption rate (0.462 mg g-1min-1) was obtained from nickel sorption at 5% adsorbent dosage and initial pH 5.0. By increasing biomass dosage (from 3 to 5%), the metal removal tended to increase. These results are in agreement with the finding of Galedar and Younesi (2013). For the effect of initial pH, Sujatha et al. (2013) explained that at higher pH (>4.5), the cell wall surface becomes more negatively charged when compared to surface negative charges at lower

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2(a), 2(b) and 2(c) shows the extremely linear variation of t/qt with time, t, for a large initial fraction of the sorption period. The pseudo-second order model gave the best correlation of these data, this supported that the adsorption's mechanism is chemically rate controlling or chemisorption (Ho and McKay, 1999b). The pseudo-second order rate expression has also been applied successfully in many studies on heavy metal biosorption. Buranaboripan et al. (2009) used dead chitosan-immobilized and grown fungal beads for Pb(II) biosorption. The kinetic biosorption model of pseudo-second order fitted better than pseudo-first order and modified pseudo-first order models. In contrast, chitosan beads encapsulated with dead biomass of Rhizopus arrhizus were used to study the biosorption of nonylphenol, the authors found that pseudo first-order kinetics gave the best fit with the experimental data (Lang et