Weidong Guo’s research while affiliated with Wuhan Institute of Technology and other places

The recovery of rare earth elements (REEs) from discharged electronic devices or mineral waste water is highly essential but still facing challenges. In this work, two amino-functionalized carboxyl-UiO-66 (UiO-66-COOH-TETA and UiO-66-(COOH)2-ED) prepared via the postmodification method were employed as the adsorbents for Yb(III) capture. The experimental results revealed their superior adsorption capacities of 161.5 and 202.6 mg/g, respectively. Meanwhile, their adsorption processes can be described by the pseudo-second-order kinetic model and Langmuir model. Effects of initial pH and temperature on adsorptions were systematically evaluated, affording an optimal operating condition (i.e., pH of 5.5-6, T of 65 °C, t of 10 h). Moreover, the fabricated materials exhibited great reusability after five adsorption-regeneration cycles. UiO-66-COOH-TETA demonstrated good separation selectivity for Yb(III) over light REEs (i.e., 3.98 of Yb/Ce, 3.51 of Yb/Nd). Based on the density functional theory calculations and characterization analysis (XPS, Zeta, mapping, and IR), the adsorption mechanisms were mainly attributed to significant electrostatic attraction and strong surface complexation between N and O sites and Yb(III).

The removal of rare earth elements in mineral processing wastewater is highly desirable but still challenging. In this study, three bimetallic Prussian blue analogues (PBA) and six corresponding oxides are prepared by co-precipitation and calcination methods, and then utilized to adsorb aqueous Yb(III) solution. The results of XRD, SEM, BET, and XPS indicate the successful synthesis of all the adsorbents. Among them, three PBA-oxide samples (PBO-800) exhibit the superior adsorption capacities (˃250 mg/g). The adsorption processes of Yb(III) are in accordance with the pseudo-second-order kinetic model and Langmuir model, simultaneously showing the spontaneous and endothermic thermodynamics. Moreover, PBO-800 can be reused after alkaline solution regeneration with less than 10% degradation after five consecutive adsorption-desorption cycles. More importantly, PBO-800 exhibits the impressive separation selectivity of Yb(III) and most light rare earth ions (e.g., 5.51 of Yb/La, 4.03 of Yb/Pr), as well as the selectivity of Yb(III) and alkali metal ions (e.g., 300.5 of Yb/Na, 256.2 of Yb/Ca). According to the characterization analysis and DFT calculation, the adsorption mechanism of Yb(III) by PBO-800 is mainly attributed to the strong interaction between the abundant active-oxygen sites and Yb(III), and the significant electrostatic attraction.

Two novel N-rich covalent organic frameworks (COFs), named COF-TZ-TP and COF-TA-TP, were prepared via a one-step solvothermal method and employed as the adsorbent to remove rare earth (RE) ions from solution. The as-prepared materials were characterized with XRD, FESEM, ATR-IR, BET, TGA and XPS analysis. The results show the rapid adsorption kinetics of La(III) with capacities of 165.6 and 89.8 mg/g for COF-TZ-TP and COF-TA-TP after 3 h. Moreover, Langmuir isotherm model and pseudo-second-order kinetic model are well fitted to describe the La(III) adsorption process. The analysis of the adsorption thermodynamic shows that the adsorption process is a spontaneous exothermic process with ΔS⁰ of 57.22 and 84.09 J/(mol ∙ K) for COF-TZ-TP and COF-TA-TP, respectively. In addition, the fabricated COFs exhibit the better adsorption results towards the light RE ions compared with heavy ones and the excellent reusability after five adsorption-regeneration cycles. The adsorption mechanism reveals that the splendid adsorption performance of RE for our N-rich COFs is mainly attributed to the surface coordination interaction between the N element and La(III) according to the characterization analysis for COF-TZ-TP before and after the adsorption process with elemental mapping, EDS and XPS. Therefore, these COFs with abundant active N sites offer the highly efficient adsorption capacity of La(III), and provide the promising strategy for the recovery of light RE from waste rare earth devices.

Developing the novel ionic liquids as the potential substitutes for conventional organic solvents in extraction of the rare-earth metals is highly desirable but remains facing challenges. In this study, the well-designed carboxylic acid functionalized phosphonium based ionic liquids, (4-carboxyl)butyl-trioctyl-phosphonium chloride/nitrate, are synthesized and characterized. The as-prepared samples are tested as the undiluted hydrophobic acidic extractant for rare-earth metal ions, affording the maximal loading of 3 mol/mol towards Nd(III) in aqueous solution and the remarkable stripping performance. The results also reveal their excellent extractability and selectivity for Sc(III) in the mixtures of six rare-earth ions, as well as the outstanding separation properties between rare-earth and first row transition-metal ions (i.e., La/Ni, Sm/Co). Moreover, the extraction mechanism indicates that the extracted rare-earth complex via a proton exchange in the ionic liquid phase is structurally similar to the complexes obtained with neutral extractants. This work presents a prototype for the fabrication of the hydrophobic cation-functionalized ionic liquids for highly efficient rare-earth extraction and provides the future application in recycling of rare-earth metals from the spent magnets.