Effective intraparticle diffusion coefficients of CoCl2 in mesoporous functionalized silica adsorbents

The scope of this work is to determine the effective intraparticle diffusion coefficient of CoCl₂ over mesoporous functionalized silica. Silica is selected as a carrier of the functionalized groups for its rigid structure which excludes troublesome swelling, often found in polymeric adsorbents. 2-(2-pyridyl)ethyl-functionalized silica is selected as a promising affinity adsorbent for the reversible adsorption of CoCl₂. The adsorption kinetics is investigated with the Zero Length Column (ZLC) method. Initially, experiments were performed at different flow rates to eliminate the effect of external mass transfer. The effect of pore size (60 Å and 90 Å), particle size (40?10^?6 m–1000?10^?6 m) and initial CoCl₂ concentration (1 mol/m³–2.0 mol/m³) on the mass transfer was investigated. A model was developed to determine the pore diffusion coefficient of CoCl₂ by fitting the experimental data to the model. The pore diffusion coefficients determined for two different pore sizes of silica are D _p (60 Å) =1.95?10^?10 m²/s] and D _p (90 Å) =5.8?10^?10 m²/s]. The particle size and the initial CoCl₂ concentration do not have an influence on the value of diffusion coefficient. However, particle size has an influence on the diffusion time constant. In comparison with polymer adsorbents, silica based adsorbents have higher values of diffusion coefficients, as well as a more uniform and stable pore structure.