New Insights into the Recovery of Strategic and Critical Metals by Solvent Extraction

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Experimental and numerical investigation of PWR Tube Support Plate (TSP) clogging formation mechanisms

International audienceCorrosion product deposits in the secondary side of PWR Steam Generators (SG) may result in Tube Support Plate (TSP) clogging majorly composed of magnetite (Fe3O4), which can lead to heavy consequences for nuclear reactor operation and safety issues such as primary-to-secondary leaks. It appears that TSP clogging is mainly driven by magnetite particle deposition and iron precipitation, which can be strengthened by flashing and electrokinetics mechanisms under the specific TSP geometric configuration. TSP clogging formation involves thus complex thermohydraulic, physical and chemical processes while the contribution of each phenomenon and the influence of operating conditions such as secondary fluid velocity, pH and temperature on TSP clogging are still unheralded. COLENTEC two-phase flow loop tests in 2015 provided the first representative experimental results of TSP clogging build-up and showed deposit growth rate in accordance with French power plant feedbacks. Numerical calculations showed the electrokinetics may play a predominant role in TSP clogging formation whereas no significant contribution of magnetite particle deposition occurs provided that the size of magnetite particles is close to 1 µm and the total iron concentration is less than 1 ppm

Direct precipitation of niobium and tantalum from alkaline solutions using calcium-bearing reagents

The recovery of Nb(V) and Ta(V) from alkaline solutions was investigated using calcium-bearing reagents (CaCl2(aq), Ca(CH3COO)+(aq), Ca(NTA)−(aq), Ca(EDTA)2 −(aq), CaCO3(s) and Ca(OH)2(s)) at 25 °C. It was found that hexaniobate and hexatantalate ions (HxNb6O19x − 8 and HxTa6O19x − 8; 0 ≤ x ≤ 3) can be quantitatively precipitated with calcium chloride, calcium acetate or calcium hydroxide when the ratio (Ca/M)initial is at least 0.4 mol/mol (M = Nb, Ta). Precipitation yields higher than 95% are obtained for solutions that contain, as low as, 3 ∗ 10− 4 mol/L of Nb and 1 ∗ 10− 4 mol/L of Ta. Moreover, the proposed precipitation method can be operated in a wide pH range and consumes two times less reactant than the classical way for recovering Nb and Ta which consists of neutralizing their alkaline solutions with a mineral acid. The amorphous calcium niobate concentrate was characterized by elemental analysis (ICP-OES), thermogravimetric analysis (TGA-MS) and Raman spectroscopy and the solid phase K3Ca2.2(H0.6Nb6O19)·nH2O was identified under specific conditions

Spéciation du palladium dans les opérations de retraitement du combustible nucléaire usé

International audienceLe combustible nucléaire usé est retraité industriellement par le procédé PUREX afin d’extrairesélectivement l’uranium (U) et le plutonium (Pu). Ce procédé met en œuvre un solvant organiquecomposé de tri-$n$-butylphosphate (TBP) dilué dans un mélange d’hydrocarbures aliphatiques (TPH).À l’issue de l’étape de dissolution du combustible usé, le palladium (Pd) ainsi que les autresproduits de fission sont séparés de l’U et du Pu puis immobilisés dans une matrice de verre. Aucours des différents cycles d’extraction, le solvant est soumis à des agressions chimiques etradiolytiques et peut se dégrader. Les produits de dégradation formés sont éliminés grâce à destraitements du solvant. Cependant, après quelques dizaines d’années de fonctionnement du procédé,des précipités contenant du palladium ont été observés dans certains équipements de l’usine.La présence de ces solides dans les cycles d’extraction peut être expliquée par la réaction chimique decertains produits de dégradation avec le palladium conduisant à la formation de précipités. Lesobjectifs de cette thèse sont de caractériser les précipités afin de comprendre leur présence dans lescycles d’extraction liquide-liquide et de proposer des mécanismes de formation de ces solides

Recovery of Metal Values from Ni-Cd Cake Waste Residue of an Iranian Zinc Plant by Hydrometallurgical Route

This paper concerns the development of an environment-friendly hydrometallurgical flowsheet dedicated to the recovery of zinc and nickel from a waste residue collected from an Iranian zinc plant. In particular, valuable metals from Ni-Cd cake waste generated at this plant were recovered by a simple hydrometallurgical process using minimum acid for leaching, and solvent extraction step was designed such that addition of sodium hydroxide was not required and the effluent generated is safe to dispose off. The waste was leached with a mixture of hydrochloric acid and sulfuric acid in the presence of hydrogen peroxide in order to achieve a good selectivity towards iron and calcium. Afterwards, cementation was performed at pH 5 in order to remove cadmium. Liquid-liquid extraction was then implemented to produce high-purity solutions of zinc and nickel. Zinc-nickel separation was obtained at pH 2 by using a mixture of bis-(2-ehtyl-hexyl)-phosphoric acid (HDEHP) and tris-2-ethylhexyl amine (TEHA) diluted in an aliphatic kerosene. TEHA did not directly participate but helped in the extraction of zinc by scavenging the protons released by HDEHP. Therefore, no alkaline solution was necessary for maintaining the equilibrium pH during liquid-liquid extraction. Finally, this flowsheet allowed to recover more than 95% of zinc and nickel from the residue with more than 99% purity

Liquid-Liquid Extraction of Cobalt(II), Nickel(II) and Manganese(II) from Acidic Chloride Media

International audienceThe extraction properties of two synthesized cationic exchangers, i.e. bis(1,3-dibutoxypropan-2-yl) phosphoric acid (BiDiBoPP) and bis(1,3-diisobutoxypropan-2-yl) phosphoric acid (IPA), have been studied for the liquid-liquid extraction of Co(II), Ni(II) and Mn(II) contained in 1 M HCl. A comparison of the extraction properties of these extractants diluted in kerosene with Cyanex ® 272 shows BiDiBoPP and IPA extract advantageously at lower pH than Cyanex ® 272 and a better Co(II)-Mn(II) separation is achieved using BiDiBoPP or IPA than with Cyanex ® 272

A density functional theory study of uranium(vi) nitrate monoamide complexes

Density functional theory calculations were performed on uranyl complexed with nitrate and monoamide ligands (L) [UO 2(NO 3) 2·2L]. The obtained results show that the complex stability is mainly governed by two factors: (i) the maximization of the polarizability of the coordinating ligand and (ii) the minimization of the steric hindrance effects. Furthermore, the electrostatic interaction between ligands and uranium(vi) was found to be a crucial parameter for the complex stability. These results pave the way to the definition of (quantitative) property/structure relationships for the in silico screening of monoamide ligands with improved extraction efficiency of uranium(vi) in nitrate acidic solution