MODELING BATCH KINETICS OF CADMIUM REMOVAL BY A RECYCLED IRON ADSORBENT

The kinetics of cadmium adsorption onto a recycled iron-bearing materi al is investigated. Batch rate data are analyzed using a surface react ion rate model, solved analytically, and a dual rate diffusion model s olved numerically. Experimental investigations examined the effects of sorbent particle size in the 0.06-0.5 mm diameter range and pH in the 4-7 range. While both rate models can describe time-concentration dat a for cadmium well, particularly for the larger granular sizes of sorb ent, the analysis reveals a substantial variation in the relevant rate coefficients with particle radius, r, suggesting diffusion versus sur face-controlled reaction kinetics. The second-order rate constant for the surface reaction model and the intraparticle diffusion coefficient of the dual rate diffusion model, represented as surface diffusion, w ere proportional to 1/r.