Wenchen Song

The effective management of High-Level Liquid Waste (HLLW) is critical for environmental and human health protection. The presence of platinum group metals (PGMs) in HLLW, particularly their refractory nature due to their high melting points, complicates vitrification processes. This study presents a targeted adsorption strategy using COF-42 for Pd²⁺ sequestration in HLLW systems. The comprehensive characterization of COF-42 and its Pd-loaded counterpart (Pd@COF-42) via PXRD, FT-IR, TGA, XPS, and SEM confirms structural robustness and successful Pd²⁺ incorporation. Kinetic and thermodynamic analyses reveal pseudo-second-order adsorption behavior with a maximum capacity of 170.6 mg/g, highlighting the exceptional Pd²⁺ affinity. Systematic optimization identifies HNO₃ concentration (≤3 M) and adsorbent dosage (≤30 mg) as critical parameters governing adsorption efficiency through protonation–deprotonation equilibria. Furthermore, COF-42 exhibits superior selectivity for Pd²⁺ over 13 competing metal ions and maintains ~80% adsorption efficiency after four regeneration cycles. These performance metrics originate from the synergistic interplay of (1) framework flexibility enabling adaptive Pd²⁺ coordination, (2) hierarchical porosity facilitating ion diffusion, and (3) dense –NH/–NH₂ groups acting as electron-rich chelation sites.

Zirconium, a critical rare metal with exceptional corrosion resistance and nuclear applications, is conventionally produced via the energy-intensive Kroll process. The electrolysis of ZrC_xO_y soluble anodes has been extensively investigated due to its advantages in having a short process flow and resulting in high-quality products. In particular, during the electrolysis of zirconium oxycarbide with a C:O molar ratio of 1:1, gaseous CO can be released, and no residual anodes are generated, which is extremely appealing. In this regard, this paper explores the feasibility of preparing zirconium metal through high-temperature vacuum reduction to produce zirconium oxycarbide using ZrO₂ as the raw material, followed by direct molten-salt electrolysis. Firstly, the reduction products were characterized using an X-ray diffractometer (XRD) and a scanning electron microscope (SEM). The results showed that under a vacuum of xO_y and a small amount of ZrO₂, and they exhibited good electrical conductivity (0.0169 Ω·cm). Subsequently, the cyclic voltammetry test results of the reduction products revealed the reversible redox behavior of ZrC_xO_y. There were characteristic oxidation peaks at −0.53 V and −0.01 V (vs. Pt), corresponding to the formation of Zr²⁺ and Zr⁴⁺, respectively, and a reduction peak at −1.51 V, indicating the conversion from Zr²⁺ to Zr. Finally, β-zirconium metal with a purity of 99.2 ± 0.3 wt.% was obtained through potentiostatic electrolysis, and its quality met the R60704 grade specified in ASTM B551-12 (2021). This study offers a novel approach for the short-flow preparation of zirconium metal, which is conducive to expanding its applications.

The proper management of High-Level Liquid Waste (HLLW) is essential for safeguarding the environment and human health. The presence of platinum group metals (PGMs) in HLLW can impact its disposal due to their high melting points. Therefore, it is vital to eliminate PGMs during the initial treatment phase. Thus, this research introduces an adsorption method using COF-42 as an adsorbent to target palladium (Pd). The molecular structure, integrity, and morphology of COF-42 and Pd@COF-42 are thoroughly assessed using various techniques such as PXRD, FT-IR, TGA, XPS, and SEM. The study further investigates the adsorption kinetics and thermodynamics of Pd by COF-42, revealing that the adsorption process follows a Freundlich model. The maximum adsorption capacity of COF-42 is 170.6mg/g, demonstrating a superb adsorption capacity for palladium. Additionally, the study also explores the impact of adjusting HNO3 concentration, and COF-42 dosage on the adsorption performance, highlighting the influence of acidity levels on the final outcome. Lastly, the selectivity of COF-42 towards Pd in the presence of different metal ions and its ability to be reused underscore its effectiveness in Pd(II) adsorption, attributed to the synergistic effects of its flexible ligand, framework porosity, and concentrated –NH/–NH2 groups with a strong affinity for Pd2+.