Experimental study of imidazolium-based polymers for the efficient enrichment of low-concentration Nb(V) from sulfuric acid-oxalate solutions

Imidazolium-based polymer (ImPOP-2) can efficiently enrich low-concentration Nb (V) in sulfuric acid-oxalate solutions. • ImPOP-2 exhibited high capacity and fast kinetics for Nb (Ⅴ) via anion exchange. • ImPOP-2 demonstrated superior selectivity towards Nb (V). • The weak interaction between Nb(V) and ImPOP-2 was revealed. Common solvent extraction methods are uneconomical for large volumes of low-concentration Nb(V) leachate, whereas ion exchange exhibits clear advantages. Nevertheless, studies on ion-exchange materials for the recovery of low-concentration niobium in non-fluoride systems are still limited, particularly in the sulfuric acid-oxalate leaching system. Emerging imidazolium-based cationic porous organic polymers have demonstrated great potential for capturing anions. However, few studies have explored their use for Nb(V) capture. In this study, a cationic organic polymer named ImPOP-2 was synthesized and used for batch adsorption experiments in sulfuric acid-oxalate solutions. ImPOP-2 exhibited a high adsorption capacity (212.20 mg·g⁻¹), rapid kinetics (reaching 79.66% of the equilibrium adsorption capacity within 10 min at an initial concentration of 400 mg·L⁻¹) and good reusability (maintaining 91.62% of the original capacity following five regeneration cycles). Even in the presence of 10 times higher concentrations of Fe(III) and 2 times higher concentrations of Ti(IV), ImPOP-2 exhibited good selectivity for Nb(V) over these competing ions, with selectivity coefficients (adsorbed mass ratio) of 1.27 and 1.67, respectively. ImPOP-2 demonstrated superior adsorption performance compared to existing adsorbents used in non-fluoride systems. The interactions between ImPOP-2 and Nb(V) were analyzed using scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier Transform infrared spectroscopy and independent gradient model based on Hirshfeld partition analysis. The results indicated that the adsorption mechanism was primarily ion exchange driven by electrostatic forces, with van der Waals forces and hydrogen bonding also contributing to the adsorption. This study aims to provide a feasible strategy for the efficient enrichment of low-concentration niobium in the sulfuric acid-oxalate leaching system. Download: Download high-res image (214KB) Download: Download full-size image