Synthesis and characterizations of Zr(IV)-loaded orange waste for effective sequestration of Mo(VI) and W(VI) from water

An efficient and environmentally benign biosorbent for Mo(VI) and W(VI) sequestration was developed by loading Zr(IV) ions onto Saponified Orange Juice Residue (SOJR). An energy-dispersive X-ray (EDX) spectroscopy, Fourier Transform Infra-Red (FTIR) spectroscopy, Thermo-Gravimetric/Differential Thermo-Gravimetric Analysis (TG/DTA), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and chemical analysis techniques were employed to characterize investigated biosorbents. Zr(IV)-loaded SOJR was able to remove oxoanionic species of both the metal ion efficiently at wide pH range, however, pH 5 was preferable for maximum sequestration in batch mode. Langmuir, Freundlich, and Temkin isotherm models were used to examine the equilibrium biosorption, with the Langmuir model having the best correlations with the experimental data. Maximum sequestration capacity of Zr(IV)-SOJR for Mo(VI) and W(VI) were evaluated to be 0.83 and 0.70 mmol/g, respectively. The order of interference caused by investigated co-existing ions were in the order of Cl − < NO 3 − < CO 3 2− < SO 4 2− < PO 4 3− during Mo(VI) sequestration. Zr(IV)-SOJR having co-ordinated hydroxide ligand were inferred to be substituted by oxoanionic species of Mo(VI) and W(VI) during the sequestration. Elution of adsorbed metal ions could be done using dilute alkali solution and regenerate biosorbent. Therefore, Zr(IV)-SOJR studied in this work is projected to be a low-cost, efficient, and environmentally benign material for effective sequestration of Mo(VI) and W(VI) from water. Graphical abstract