Continuous removal of Cr(VI) by lab-scale fixed-bed column packed with chitosan-nanomagnetite particles

Hexavalent Chromium species are classified as hazardous compounds due to their high toxic potential, considering also their remarkable solubility and redox potential. Various processes have been developed to remove/recover Cr(VI) species from polluted groundwater, such as membrane processes, ion-exchange and adsorption and chemical or biochemical reduction. Indeed, the reduction/removal process of Cr(VI) through iron-based materials usually leads to a pH increase of the reaction medium, allowing to facilitate the subsequent precipitation of the Cr(III) species. In this context, the use of iron based nano-particles (IBNs) supported on bio-polymer matrix allowed to maximize the Cr(VI) removal capacities of iron-based materials, leading to the production of high active and eco-compatible nano-materials. The use of chitosan as surface-modified agent, allows the reduction of aggregation forces among the produced IBNs, leading to higher surface active areas and chemical reactivity. At the same time, the use of a bio-polymer increases the eco-compatibility of the IBNs, reducing the possible interaction with bacteria and microorganisms during the treatment process. In this work chitosan-nanomagnetite particles were synthetized and employed as packing material inside fixed-bed lab-scale column (height 25 cm and diameter of 1.5 cm) to remove, in continuous, Cr(VI) species from synthetic wastewaters. The tests were performed at different inlet flow-rate values (2, 5 and 7 mL/min) at fixed Cr(VI) initial concentration (20 mg/L) and varying the solution pH (pH=4 and 7). The obtained breakthrough curves were then modeled according to the classical dynamic Thomas model.