Potential of zirconium-based materials for the removal and recovery of tungsten ions from the aqueous phase

Tungsten(W), which exists as oxoanion species in water, is regarded as a water pollutant and is a valuable material in various industrial fields. Therefore, the adsorption (removal) of W ions from aqueous solutions and their subsequent desorption (recovery) are important processes. Inspired by the ability of zirconium (Zr)-based materials to adsorb phosphate and arsenic (As) ions—both oxoanion species in water—we hypothesized that these materials would also be effective for the adsorption of W ions. In this study, ZrO 2 , Zr(OH) 4 , and ZrO(OH) 2 were synthesized, and their surface morphology, crystallinity, thermogravimetric–differential thermal behavior, specific surface area, hydroxyl group content, and point of zero charge were examined. The W-ion adsorption capacity of the materials followed the order ZrO 2 < Zr(OH) 4 < ZrO(OH) 2 . The adsorption kinetics data indicated that equilibrium was reached within 6 h, and the results fit the pseudo-second-order model (correlation coefficient: 0.999–1.000) more closely than the pseudo-first-order model (correlation coefficient: 0.898–0.997). The adsorption isotherm data were better described by the Langmuir model (correlation coefficient: 0.999–1.000) compared to the Freundlich model (correlation coefficient: 0.933–0.998). Elemental analysis confirmed the adsorption of W ions using the Zr-based materials. Acidic conditions were optimal for W adsorption using Zr-based materials, reflecting the influence of the adsorbent's surface charge. In addition, phosphate ions affected the W-ion adsorption capacity in complex solution systems. In contrast, chloride, nitrate, and sulfate ions were not adsorbed under the same conditions. Finally, W ions adsorbed onto ZrO(OH) 2 were readily desorbed using sodium hydroxide solutions of varying concentrations, with desorption efficiency increasing as the NaOH concentration increased. Overall, the effective W-ion removal performance of the proposed Zr-based materials demonstrates their potential as promising candidates for the adsorption of W ions in aqueous systems. • W adsorption capacity was in the order: ZrO 2 < Zr(OH) 4 < ZrO(OH) 2 . • The intensity of W onto ZrO(OH) 2 significantly increased after adsorption. • ZrO(OH) 2 demonstrated promising characteristics as an adsorbent for the recovery of W.