Analysis of Cadmium Adsorption on Novel Organo-Ceramic Adsorbents with a Thiol Functionality

The adsorption characteristics of cadmium ions from aqueous solutions onto two organo-ceramic adsorbents synthesized in our laboratories were studied. The main species participating in the adsorption process, determined from the chemical equilibrium, is Cd 2+ . Formation of a bidentate cadmium−thiol complex is proposed to explain the experimental isotherms. The kinetics of adsorption onto the sol−gel-synthesized adsorbent was studied in a differential batch reactor with recycle. Two kinetic models were tested with experimental data: chemical reaction and film/pore mass-transfer resistances. The results indicate that either model can be used to explain the adsorption process as observed from the AARD values and from the F -test. The values of fitted parameters are k 1 = 0.0021 L·g/mmol 2 ·min, D p = 1.4 × 10 -7 cm 2 /s, and τ = 5.0. The last two parameters can be used to satisfactorily predict the breakthrough curve in a fixed bed by the film/pore diffusion model. A sensitivity analysis shows that pore diffusion resistances control the adsorption process.