Nickel removal by biogenic selenium nanoparticles (SeNPs): Characterization and simulation of non-symmetric breakthrough curves in continuous-flow packed-bed columns

Abstract

Nanoparticles offer an alternative mean for heavy metals removal from aquatic environment. In this work we study the sequestering of nickel by biogenic selenium nanoparticles (SeNPs) both in native and in immobilized form in alginate matrix (alginate-SeNPs). The apparent sorption like process is attributed to the coordination chemistry of Ni with the functional groups of the extracellular polymeric substances (EPS) covering the SeNPs. The kinetics and the equilibrium of the process are presented, while the morphology and the properties of the adsorption beads are studied by SEM, FTIR and rheological analysis. Langmuir isotherm describes the adsorption equilibrium with maximum loading Q0 29.411 mg Ni/g SeNPs and 0.651 mg Ni/g alginate-SeNPs. The adsorption of nickel is fast and equilibrium is attained within one hour. Continuous flow experiments in packed beds reveal early elution patterns and non-symmetric sigmoidal profiles due to the reduced adsorption capacity of the immobilized SeNPs, the short depth of the beds and the apparent non-uniform flow pattern. The Bohart-Adams equation fits adequately the main sigmoidal part of the breakthrough curves, however fails to predict the early breakthrough data. By using the advection–dispersion-reaction equation (ADR) under two novel aspects: (a) the rapid equilibrium model with the introduction of an efficiency coefficient accounting for all the kinetic and sorption limitations and (b) the split flow model accounting for any non-uniform flow conditions in the column, the model accuracy is significantly improved. Repeated sorption–desorption experiments show that alginate-SeNPs retain 59% of the original adsorption capacity even after eight cycles.