Rate Determining Steps Study in Cadmium Sorption from Aqueous Solutions by Sunflower Leaves

Batch studies of cadmium ion sorption by dried sunflower leaves were carried out to identify the main rate controlling steps in the overall uptake mechanism, using a single external mass transfer diffusion model and intraparticle mass transfer diffusion model. Many classical parameters influencing cadmium sorption mechanisms namely: initial cadmium concentration, agitation speed, initial solution pH, particle size, temperature, sorbent mass and cadmium salt nature were investigated. The approach chosen in this study was restricted to an interpretation and subsequent identification of mass transfer coefficients by separating the two mechanisms, based on the adequacy of correspondence models with experimental data of these parameters. The process mechanism was found to be complex, consisting of external mass transfer and intraparticle mass transfer diffusion. Analysis of mechanistic steps involved in the sorption process confirms that the sorption process is particle-diffusion-controlled, with some predominance of some external mass transfer at the initial stages for the different experimental parameters studied.