Multicavity triethylenetetramine-chitosan/alginate composite beads for enhanced Cr(VI) removal

A novel triethylenetetramine (TEAE) modified chitosan microbeads with multicavity structure encapsulated in alginate backbone (named as HCTA) was fabricated for Cr(VI) removal from aqueous solution. Cr(VI) removal was investigated in batch and column modes. FTIR, SEM-EDS, XRD and XPS, etc. were utilized for characterization of the composites. Multiple mechanisms such as electrostatic interaction, reduction reaction, chelation and cation-exchange involved in the adsorption process. Binary combination of matrix and fillers contributed to highly efficient Cr(VI) removal in a wide pH range (2-10), whereas Na+, Ca2+, Al3+, Cl-, NO3- and SO42- had minimal effects on the removal performance. The experimental maximum adsorption capacity was similar to 291.3 mg/g at the optimal pH 3.0, much higher than that of alginate beads (similar to 26.1 mg/g); a three-stage kinetics behavior was observed with similar to 50% of the maximum Cr(VI) adsorption capacity within 60 min; the increase of temperature was favorable for adsorption. The experimental data were fitted well to the Freundlich model and the pseudo-second-order model in batch system. The Thomas model was fitted better than Bohart-Adams model with breakthrough curves under different influent flow rate in a column system. Moreover, HCTA beads showed good chemical and mechanical stability for alkali resistance even at high saline conditions. Crucially, excellent reusability of HCTA beads was observed after nine cycles. These results make the novel HCTA beads a promising candidate for Cr(VI) removal in certain practical wastewater. (C) 2019 Elsevier Ltd. All rights reserved.