High-gravity continuous preparation of chitosan-stabilized nanoscale zero-valent iron towards Cr(VI) removal

Abstract

Nanoscale zero-valent iron (nZVI) is easy to agglomerate and be oxidized by surrounding media, and even can't be prepared continuously, which have seriously restricted its application in environmental restoration. Herein, we report a facile technique for the continuous preparation of nZVI with excellent dispersion and stability on a large scale using impinging stream-rotating packed bed (IS-RPB) as the reactor and chitosan as the stabilizer. The effects of high-gravity factor, liquid flow and the additive amount of chitosan on the removal capacity of the chitosan-stabilized nZVI (CS-nZVI) were investigated. It was discovered that the removal capacity toward Cr(VI) was firstly increased and then reduced with each operating parameter increasing. The reactivity of CS-nZVI prepared via different reactors (traditional stirred tank reactor (STR) and IS-RPB) was studied through the removal of Cr(VI). With enhancement mass transfer and rapid micromixing capacities of IS-RPB reactor, CS-nZVI prepared in IS-RPB (CS-nZVI-R) had higher reaction rate constant (0.0836 min−1) and adsorption capacity (101.837 mg g−1) than that prepared in STR. CS-nZVI-R was shown higher stability and reusability, and it could be reused more than four times. Furthermore, this as-prepared CS-nZVI-R can be used for the selective removal of Cr(VI) in the presence of NO3–. In short, it provides an effective route for the controllable continuous preparation of high reactive nZVI, which would expand the application of nZVI in the field of heavy metal pollution remediation.