Molybdenum(VI) Coordination in Tributyl Phosphate Chloride Based System

Mechanistic Insights into Molybdenum-Iron-Catalyzed Neptunium Reduction and Extraction

Neptunium (Np), as a critically regarded actinide in nuclear waste, is of great significance for environmental hazard mitigation and the resource-oriented management of nuclear waste. The reduction of Np(V) to Np(IV) represents a pivotal step toward efficient Np recovery. However, this process is profoundly influenced by the intricate redox chemistry of Np itself and the diverse concomitant fission products in spent nuclear fuel, with the underlying mechanistic details remaining inadequately elucidated. In this study, we demonstrated that molybdenum (Mo) and iron (Fe) dramatically accelerated the reduction rate of Np(V) by approximately 2 × 104-fold. Additionally, by integrating analytical techniques including absorption spectroscopy, stopped-flow spectroscopy, inductively coupled plasma-mass spectrometry, and solvent extraction, we deciphered the electron transfer interactions between Mo and Fe, as well as their synergistic catalytic mechanism in driving the Np(V)-Np(IV) conversion. This study not only advances the fundamental understanding of Np redox chemistry in complex nuclear waste matrices but also offers technical support for optimizing nuclear waste treatment protocols.

An insightful study on the reduction and extraction of neptunium assisted by molybdenum

High-level liquid waste (HLLW) generated through nuclear reactions and spent fuel reprocessing contains the critical transuranic element neptunium (Np). Thus, the efficient recovery of Np from HLLW via the TRPO (trialkylphosphine oxide) process is not only beneficial for radioactive contamination remediation but also boosts the recycling of precious nuclear resources. However, this process including Np(V)-Np(IV) conversion is highly dependent on the components coexisting in HLLW, and its underlying mechanism is still not clear, restricting the recovery of Np in multiple scenarios. Herein, the effect of coexisting metal ions on the reduction and extraction of Np(V) was studied, and molybdenum (Mo) was identified to play a vital role in this course. Additionally, in combination with absorption spectral analysis, X-ray photoelectron spectroscopy and solvent extraction, the promotion of the extraction of Np by Mo was elucidated to be due to the catalytic reduction effect both in the aqueous phase and organic phase. This study can help researchers better understand the redox chemistry of Np in the treatment of HLLW.

Adsorption behavior of Mo(VI) from aqueous solutions using tungstate-modified magnetic nanoparticle

A new magnetic nanoparticle modified with sodium tungstate (Mnp-Si-W) was synthesized and employed for the sorption of molybdenum from aqueous solutions. The prepared nanoparticles (Mnp-Si-W) were characterized by different advanced techniques. Different parameters that influenced the adsorption percent of Mo(VI) were investigated using a batch process. Based on a systematic investigation of the adsorption isotherms and kinetics models, Mo(VI) adsorption follows the Langmuir model and pseudo-second-order kinetics. According to the Langmuir isotherm model, the Mnp-Si-W nanoparticles exhibited a maximum adsorption capacity of 182.03 mg g-1 for Mo(VI) at pH 2.0. The effect of competing ions showed that the prepared nanoparticles have a high selectivity for the sorption of molybdenum. Moreover, the effect of some interfering anions on Mo(VI) ion sorption is found in the following order: phosphate < sulfate < chromate. Finally, the nanoparticle (Mnp-Si-W) can be successfully reused five times.

Structural Investigation of Technetium Dibutylphosphate Species Using X-ray Absorption Fine Structure Spectroscopy

The speciation of Tc after the extraction of Tc(IV) from H2O and 1 M HNO3 by dibutylphosphoric acid (HDBP) in dodecane has been studied by X-ray absorption fine structure (XAFS) spectroscopy. Results show the formation of dimeric species with Tc2O2 and Tc2O units, and the formulas [Tc2O2(DBP·HDBP)4] (1) and [Tc2O(NO3)2(DBP)2(DBP·HDBP)2] (2) were, respectively, proposed for the species extracted from H2O and 1 M HNO3. The interatomic Tc-Tc distances found in the Tc2O2 and Tc2O units [2.55(3) and 3.57(4) Å, respectively] are similar to the ones found in Tc(IV) dinuclear species. It is likely that the speciation of Tc(IV) in dodecane is due to the extraction of a species with a Tc2O unit for (2) and to the redissolution of a Tc(IV)-DBP solid for (1). The XAFS results for (1) and (2) were compared to that obtained for the extraction of Tc(IV) with TBP/HDBP/dodecane from 0.5 M HNO3, (3) which highlight the formation of Tc mononuclear nitrate species {i.e., [Tc(NO3)3(DBP)] or [Tc(NO3)2(DBP·HDBP)]}. These results confirm the importance of the preparation and speciation of the Tc(IV) aqueous solutions prior to extraction and how much this influences and drives the final Tc speciation in organic extraction. These studies outline the complexity of Tc separation chemistry and provide insights into the behavior of Tc during the reprocessing of used nuclear fuel.

Novel Styrene-Based Polyamine Sorbent for Efficient Selective Separation of Molybdenum

Tungsten (W) and molybdenum (Mo) are important strategic resources but the two coexist in both primary ore and waste. Before a single metal product is obtained, it is often necessary to separate the two. In this work, we reported two new polyamine resins (D301@PA and D301@TA), which can be obtained by an assembled amine (primary amine or tertiary amine) and traditional D301 resin by the dipping method. Then, the sorption experiments with the amine resins were carried out, and the selectivity and sorption capacity of the two new polyamine resins for MoS₄ ^2- have been significantly improved. Among them, D301@TA showed the highest sorption capacity of 414 mg·g^-1 and a separation factor of 108. Finally, the sorption mechanism can be inferred through scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) analysis, and X-ray photoemission spectroscopy (XPS); the Cl^- ions in the amine resin and the MoS₄ ^2- ions were subjected to ion exchange. This work provides a green and efficient approach for separating tungsten and molybdenum.

Speciation of Molybdenum(VI) in Chloride Media at Elevated Mo Concentrations

Speciation of Mo(VI) in chloride media (0.5-11 M HCl) at elevated Mo concentrations (0.1-300 mM Mo) was investigated using UV spectroscopy. In addition to five major monomeric species, H₂MoO₄, H₃MoO₄ ⁺, H₃MoO₄Cl, MoO₂Cl₂, and MoO₂Cl₃ ^-, chemometric analysis of UV spectra suggests the presence of three cationic dinuclear species that predominate in solutions of 1-4.5 M HCl at >20 mM Mo concentrations. Thermodynamic values and molar absorptivity spectra were calculated from UV spectrophotometric data using refined numerical methods. The stability constants determined for three Mo dimers are log β = 3.53 ± 0.05 (H₂Mo₂O₅ ²⁺), log β = 3.60 ± 0.04 (H₃Mo₂O₅ ³⁺), and log β = 2.91 ± 0.03 (H₃Mo₂O₆Cl²⁺).