Nickel Adsorption by Biogenic Selenium Nanoparticles (Senps) : Characterization and Simulation of Non-Symmetric Breakthrough Curves in Continuous-Flow Packed-Bed Columns

Nickel adsorption by biogenic selenium nanoparticles (SeNPs) is presented in this work. Native SeNPs and entrapped in a calcium alginate matrix are used as adsorbent in batch experiments and continuous flow packed bed columns. The nature and morphology of the adsorbent were characterized using FTIR, SEM and rheological analysis. Nickel (Ni) adsorption is best fitted by the Langmuir isotherm with maximum loading Q 0 of 29.411 mg Ni/g SeNPs and 0.6506 mg Ni/g alginate-SeNPs. Adsorption is fast and equilibrium is attained within one hour contact time at Ni concentration between 10 to 100 mg/L Ni 2+ at a sorbent to liquid ratio 7.5 g/100 mL. The pseudo-first, pseudo-second and pseudo-nth order kinetic models describe equally well the kinetic data. Continuous flow experiments in packed beds with variable length of 10, 20 and 30 cm at a flow rate of 10 mL/min and with variable flow rates of 20 and 30 mL/min at 30 cm bed length have shown early breakthrough points and non-symmetric sigmoidal profiles. The Bohart-Adams equation fits adequately the main sigmoidal part of the breakthrough curves, while it fails to predict the early breakthrough data. The model accuracy is significantly improved by applying the advection-dispersion-reaction equation (ADR) under the concepts of: (a) the rapid equilibrium with the introduction of an efficiency coefficient accounting for all the kinetic limitations and (b) the split flow accounting for any non-uniform flow conditions in the column. Alginate-SeNPs keep also 59% of the original adsorption characteristics even after eight repeated sorption-desorption cycles. The rheological properties of the alginate-SeNPs were consistent even after eight adsorption-desorption cycles