Boron removal by a composite sorbent: Polyethylenimine/tannic acid derivative immobilized in alginate hydrogel beads

ABSTRACT

A novel composite material was prepared by the grafting of tannic acid on polyethylenimine (PEI), which allows an efficient sorption of boron (sorption capacity close to 0.89 mmol B g⁻¹). The encapsulation of this chelating sorbent (finely crushed) facilitates its use (readily solid/liquid separation, use in fixed-bed columns) at the expense of a loss in sorption capacity (proportionally decreased by the introduction of alginate having poor efficiency for boron uptake). Sorption isotherms are modeled using the Langmuir equation, while the kinetic profiles are presented a good fit by pseudo-second order rate equation. In addition, the encapsulating matrix introduces supplementary resistance to intraparticle diffusion, especially when the resin is dried without control: freeze-drying partially limits this effect. The stability (at long-term storage) of the sorbent is improved when the sorbent is stored under nitrogen atmosphere. The presence of an excess of NaCl was investigated. The degradation of the hydrogel (by ion-exchange of Ca(II) with Na(I)) leads to a decrease in the sorption performance of composite material but the action of Ca(II) ions in the solutions re-stabilizes the hydrogel.

KEYWORDS:

• Alginate encapsulation
• boron
• polyethylenimine
• sorption isotherms
• tannic acid
• uptake kinetics

Acknowledgments

The authors thank Jean-Marie Taulemesse for SEM analysis.

Funding

This work is part of EU research project (BIOMETAL-DEMO). The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) managed by REA-Research Executive Agency (http://ec.europa.eu/research/rea) under grant agreement n° 619101.