Adsorption kinetics of cupric and cadmium ions on corncob particles

The effects of the pH, agitation speed, particle size, and concentration of corncob particle on the adsorption kinetics of cupric and cadmium ions were investigated in this study. It was found that the uptakes of cupric and cadmium ions on corncob particles increased with increasing the initial pH and agitation speed, and with decreasing the particle size. The amount of adsorbed ions also increased with increasing the concentration of corncob particles, but the amount of the adsorbed ions/unit mass of adsorbent diminished. Based on the elimination of the external and intraparticle diffusions, the intrinsic forward and backward rate constants in a reversible surface reaction model combined with an effectiveness factor were estimated for cadmium ions to be 2.88/(mmol min) and 0.184/min. The maximum adsorption capacity and the effectiveness factor in this model were determined for copper and cadmium ions as a function of the initial pH and particle size. Both values increased with increasing the initial pH, and decreasing the size and concentration of corncob particle. The simple external diffusion model can describe only the solute change in solution for initial 5 min, which suggested that adsorption of cadmium on corncob particles was controlled first by the external diffusion, and then by the intraparticle diffusion. The external mass transfer coefficients first increased with increasing the modified Reynolds number, and then reached a maximum value.