Acetate enhanced selective recovery of vanadium by amidoxime-functionalized cellulose

A novel green solid-liquid extraction strategy is developed for the selective extraction of vanadium from sulfate solutions containing chromium and other heavy metals, typical of vanadium leachates of primary and secondary resources. The strategy uses bio-based biodegradable materials such as amidoximated cellulose as an adsorbent in tandem with acetate, as an auxiliary soluble ligand that improves the adsorption capacity and selectivity of the adsorbent. The amidoximation of the biopolymer is achieved using a fast green synthetic method that does not use toxic swelling agents or organic solvents. Acetate increases the adsorption capacity of the functionalized cellulose to tetravalent vanadyl V(IV) from 70 to 330 mg g-1, decreases the co-adsorption of chromium(III) from 50 to 25 mg g-1, while there is practically no co-adsorption of copper(II) and nickel(II). We demonstrate that this method can be scaled up in an adsorption column using amidoximated cellulose beads. In contrast to acetate, citrate inhibits vanadium adsorption. Macroscopic techniques (zeta potential, adsorption isotherms, speciation modelling), X-ray photoelectron spectroscopy (XPS), and computational quantum mechanical modelling of the vanadium complexes were used to provide insights into the mechanisms of the adsorption enhancement by acetate. For comparison, we also study the adsorption of pentavalent vanadium V(V). The results suggest that acetate enhances the adsorption of V(IV) by weakening of its hydration. The inhibiting effects of citrate on the adsorption of V(IV) and acetate on the adsorption of Cr(III) are explained by the closed coordination shells of the central atoms in the corresponding chelating complexes. Overall, the use of a biopolymer functionalized with chelating groups in tandem with acetate is a novel strategy to improve the sustainability of hydrometallurgy and wastewater treatment.