Fixed-bed column adsorption of Ge(IV) using catechol-based adsorbents and aqueous complexation modeling to understand Ge(IV) selectivity

Abstract

An efficient production process that can selectively recover the critical element germanium (Ge) from dilute sources is necessary to address the criticality of Ge. In this study, functionalized polystyrenic beads with catechol (A-Cat), nitro-catechol (A-Cat-N), and pyrogallol (A-Py) were used in a fixed-bed column to recover Ge and the Ge selectivity in the presence of competing ions, the effect of flow rate and inlet concentration, breakthrough modeling, and regeneration and reuse were investigated. Additionally, the synthesized adsorbent A-Cat was compared with commercially available N-methylglucamine resin for recovering Ge from synthetic Zn refinery residues solution. All three adsorbents showed Ge adsorption (>25 mg/g) and good desorption in single-element solution. The adsorbents were selective for Ge(IV) in a multiple-element solution containing 15 elements, and concentrated Ge solution was obtained with A-Cat after elution. The Modified Dose-Response model best explained the breakthrough curve compared to the Thomas and Yoon-Nelson model. Lower flow rates and higher inlow concentration both resulted in higher Thomas adsorption capacity (30 mg/g at 9 bed volumes per hour (BVH) and 62.8 mg/g at 80 mg/L Co). The adsorbent A-Cat showed great regeneration while retaining >70 % capacity at the end of 5 adsorption–desorption cycles. A-Cat was also selective for Ge in synthetic Zn refinery residue solution containing 10 times Fe and 20 times Cu and Zn. Commercial N-methylglucamine resin showed low selectivity for Ge and reached saturation at very low bed volumes (BV) (<10BV). The current work shows that the A-Cat can be used for industrial applications to recover Ge selectively. A Linear Free Energy Relationship (LFER) was used to estimate log KML, followed by aqueous complexation modeling. The modeling showed the Ge(IV) selectivity but underestimated the extent of ion complexations, indicating that the apparent stability constants for grafted ligands are higher than solution log KML.