Biosorption studies of Cu(II) onto Mansonia sawdust: Process design to minimize biosorbent dose and contact time

The aim of this paper is to examine the various operating processes and determine the overall biosorption rate and how each of the processes influences biosorption. The results revealed that external mass transfer, film diffusion and ion exchange were predominant at the initial 5 min of biosorption and their rate constants were measured. The pseudo-second order model rate constants were determined and the relationship between these constants and the biosorption performance such as the approaching equilibrium factor, Rw, the rate factor k2qe, the biosorption half-life (t0.5) and the operating time (tx) were determined. The pore and film diffusion coefficients decreased with increasing copper(II) concentration. The values of initial biosorption factor, Ri, for the biosorption process showed that for all initial copper(II) concentrations, initial biosorption was faster than intraparticle diffusion. The activation energies, enthalpies, entropies and free energies for each of the operating processes were determined and the results showed that film diffusion had the highest activation energy and may be the overall rate limiting step. Mathematical models for the optimization of multistage process for minimum biosorbent mass and contact time were also developed.