Adsorptive recovery of vanadium(V) from chromium(VI)-containing effluent by Zr(IV)-loaded orange juice residue

• Zr(VI)-SOW is a promising biomass adsorbent for the adsorption of V(V).
• The adsorption mechanism is anion exchange between OH− and metal oxo-anions.
• Adsorption efficiency was found to be strongly dependent on pH.
• βV/Cr of Zr(IV)-SOW is much higher than the commercial resin D201.
• Column adsorption can realize the higher enrichment factors for V than Cr.

Dried orange juice residue marketed as cattle food was converted into an economical and environmentally benign sorbent through chemical loading with zirconium(IV). Its adsorption properties for vanadium(V) and chromium(VI) from synthetic and actual waste water were investigated. The adsorption of V(V) is strongly dependent on solution pH, and the maximum separation coefficient (βV/Cr = 45) between V(V) and Cr(VI) takes place at pH 2.85. The anion exchange or nucleophilic substitution reaction between OH− and metal oxo-anions was proposed as the main adsorption mechanism. Langmuir adsorption and pseudo-second-order rate equations can describe well the adsorption of V(V) onto the gel. The maximum adsorption capacities for V(V) and Cr(VI) were estimated as 1.003 and 0.288 mmol/g, respectively. The adsorbed vanadium was effectively desorbed using a diluted NaOH solution. The negligible interference of coexisting anions, such as nitrates and chlorides, durability, reproducibility of the gel, and the column adsorption test through the mixture of V(V) and Cr(VI) followed by elution make the Zr(IV)-SOW a promising sorbent for the recovery of a small quantity of vanadium from chromium(VI)-containing effluent. Finally, a preliminary attempt to selectively enrich V(V) from the real dilute industrial effluent that contains Cr(VI) using the present gel has been carried out, and it was confirmed to be successfully achieved.