Sustainable reduction of Cr (VI) and its elemental mapping on chitosan coated citrus limetta peels biomass in synthetic wastewater

In the present study, biosorption-cum-biotransformation of Cr (VI) to less toxic Cr (III) on chitosan-coated Citrus limetta peel biomass has been studied. Energy dispersive X-ray and elemental mapping indicated the homogeneous distribution of chromium together with other major elements like carbon, nitrogen and oxygen which are considered as major elemental constituent of chitosan and play a significant role in Cr (VI) biotransformation. The surface of synthesized adsorbent was observed to be rough and porous. pHzpc of chitosan-coated Citrus limetta peel biomass was estimated as 3.69. Atomic forced microscopy showed that the roughness of chitosan-coated Citrus limetta peel biomass increased up to 146.62 nm as compared to uncoated one (28.62 nm). Freundlich isotherm (R2 = 0.99) and pseudo second-order kinetic model (R2 = 0.99) were found to be better fitted in the experimental data as compared to other isotherm and kinetic models. Thermodynamics indicated that Cr (VI) adsorption was spontaneous and endothermic. Results showed that chitosan coated Citrus limetta peels biomass has high Cr (VI) removal capacity (99.34%). A combination of two batch reactors in series was capable in removing 100% Cr (VI). This adsorbent showed a high regeneration capacity and regenerated adsorbent was used in consecutive five adsorption-desorption cycles.