Removal of hazardous hexavalent chromium from aqueous phase using zirconium oxide-immobilized alginate beads

The present study addresses the aqueous phase removal of hexavalent chromium [Cr(VI)] using a composite adsorbent. An adsorbent was prepared by immobilizing hydrous zirconium oxide (HZO) into alginate beads (HZO@AB). The material was characterized via scanning electron microscopy (SEM), which showed an increase in surface roughness after HZO immobilization. The impregnation of alginate beads with HZO and successful adsorption of Cr(VI) onto HZO@AB were analyzed by X-ray photoelectron spectroscopy (XPS). The adsorption of Cr(VI) was well described by a pseudo-second-order kinetic model (R2 > 0.99). The Langmuir model provided the best correlation with adsorption of Cr(VI) on HZO@AB (R2 > 0.99), supporting the nature of adsorption as a monolayer. The adsorption of Cr(VI) [as CrO42− and HCrO4−)] was effective between pH 3 and 6 and decreased at higher pH. The maximum equilibrium sorption capacity of HZO@AB for Cr(VI) was 9.8 mg g-1 at pH 5. The thermodynamic parameters (ΔG°, ΔH°, ΔS°) were evaluated, and the process of Cr(VI) adsorption on HZO@AB was identified as endothermic, thermodynamically feasible, and spontaneous (‒ΔG°). The adsorbent was satisfactorily reused for three consecutive cycles. The adsorption capacity of regenerated composite adsorbent for Cr(VI) was 6.92 mg g-1 in the third cycle, and the adsorbent retained approximately 73% of its original Cr(VI) adsorption capacity. The results of this study indicate that the developed adsorbent (HZO@AB) could be a potential candidate for treating wastewater containing Cr(VI).