Kinetics modelling of Cu(II) biosorption onto coconut shell and Moringa oleifera seeds from tropical regions

100Adsorption kinetic studies are of great significance to evaluate the performance of a given adsorbent and to gain insight into the underlying mechanism. This work investigated the sorption kinetics of Cu(II) onto coconut shell and Moringa oleifera seeds using batch techniques. In order to understand the mechanisms of the biosorption process and the potential rate controlling steps, kinetic models were used to fit the experimental data. The results indicate that kinetic data were best described by the pseudo second-order model with correlation coefficient (R²) of 0.9974 and 0.9958 for the coconut shell and Moringa oleifera seeds, respectively. The initial sorption rates obtained for coconut shell and Moringa oleifera seeds were 9.6395 × 10⁻¹ and 8.3292 × 10⁻² mg g⁻¹ min⁻¹, respectively. The values of the mass transfer coefficients obtained for coconut shell (β_l = 1.2106 × 10⁻³ cm s⁻¹) and Moringa oleifera seeds (β_l = 8.965 × 10⁻⁴ cm s⁻¹) indicate that the transport of Cu(II) from the bulk liquid to the solid phase was quite fast for both materials investigated. The results indicate that intraparticle diffusion controls the rate of sorption in this study; however film diffusion can not be neglected, especially at the initial stage of sorption.