Americium and curium, present in spent nuclear fuel, are carried forward to the high-level wastes (HLW) upon its reprocessing within the closed nuclear fuel cycle strategy. These minor actinides are required to be extracted efficiently to mitigate the long-term radiotoxicity of the HLW, which in some countries is the proposed strategy for the safe management of radioactive wastes emanating from the reprocessing of spent nuclear fuel. While both Am and Cm are co-extracted by most of extractants used for actinide partitioning and lanthanide-actinide separations, their mutual separation makes Am transmutation less complicated. In their most stable (trivalent) oxidation state, these elements are very difficult to separate. In this review, solvent extraction systems for the mutual separation of Am(III) and Cm(III) from nitric acid solutions are discussed. The extraction systems for the separation of americium directly from high-level liquid waste and from isolated mixtures of americium and curium are considered. Abbreviations: D:distribution ratio, $D=\frac{C_{org}}{C_{aq}}$, where C_org – total concentration of a metal in the organic phase, C_aq – total concentration of a metal in the aqueous phase; DF: decontamination factor, $DF=\frac{C_{x,feed}\cdot Q_{feed}}{C_{x,product}\cdot Q_{product}}$, where C_x,feed, C_x,product – concentrations of an impurity in the initial feed solution and the product solution (raffinate or back-extract), Q_feed, Q_product – flow rates of the initial feed solution and the product solution; GW×day/tHM: burn-up of nuclear fuel, where tHM – tons of heavy metal; HAC: high active concentrate; HLW: high level waste; HSAB: Hard and Soft Lewis Acids and Bases; K_ex: constant of extraction, for the reaction M³⁺ _(aq) + 3NO₃ ⁻ _(aq) +nL_(org) = M(NO₃)₃L_{n (org)}, K_ex: [M³⁺][NO₃ ⁻]³[L]ⁿ/[M(NO₃)₃L_n]; PUREX: Plutonium Uranium Reduction EXtraction; GANEX: Grouped ActiNide EXtraction; REE: rare earth element; SF: separation factor, SF = D₁/D₂, D₁>D₂; SNF: spent nuclear fuel; TRLIFS: time-resolved laser induced fluorescence spectrometry; β: constant of complex formation; List of ligands: ADAAM(EH): tetra-(2-ethylhexyldiamide-(2-ethylhexyl)-amine; BTPhen: bis-triazinylphenanthroline; (Cl-Ph)2PS2H: bis-(chlorophenyl)-dithiophosphinic acid; CMPO: Carbamoylmethylphosphine oxide DMDOHEMA: N,N’-dimethyl-N,N’-dioctyl-2-(hexyloxy)ethylmalonamide; DOODa: N,N,N’,N’-tetraalkyl-3,6-dioxaoctanediamide; H2BP18C6: N,N’-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-18-crown-6; H4TPAEN: N,N,N’,N’-tetrakis-[(6-carboxypyridin-2-yl)-ethylenediamine; HDEHP: di-(2-ethylhexyl)phosphoric acid; HEDTA: hydroxyethylethylenediaminetriacetic acid; HEH[EHP]: 2-ethylhexylphosphonic acid; NTAamide: N,N,N,N’,N’,N’-hexaalkylnitrilotriacetamide; PhPyPO: phenyl-pyridine phosphine oxide; TBP: tri-(n-butyl)phosphate; TEDGA: tetraethyldiglycolamide; TEHP: tri-(2-ethylhexyl) phosphate; TODGA: tetraoctyldiglicolamide; TPH: hydrogenated tetrapropylene List of terms: CHON-principle: An idea that the extractant molecule should consist only of carbon, hydrogen, oxygen and nitrogen atoms, so that the spent ligand can be easily incinerated without the formation of any solid waste. Salting out-agent: An inorganic salt with the same counter-ion as an extracted complex has.Counter-current process: A process in which the solvent and the aqueous feed streams, in contact with each other, flow in opposite directions.

Development of efficient extractants for the separation of actinides and lanthanides in the technologies of nuclear fuel cycle is one of the most urgent and complex tasks in modern nuclear energetics. New family of 4,7-dichloro-1,10-phenanthroline-2,9-dicarboxylic acid diamides based on cyclic amines was synthesized and shown to exhibit high selectivity in the La/Am pair separation (SF (Am/La ≈ 10)) and in the Am/Eu pair separation (SF (Am/Eu ≈ 12)). It was shown that pyrrolidine derived diamide is more efficient extractant for americium, curium and lanthanides from highly acidic HNO₃ solution than its non-cyclic N,N,N′,N′-tetraalkyl analogues. The structures of synthesized compounds were studied in details by IR, NMR spectroscopy, and single crystal X-ray diffraction. According to spectroscopy data, incorporation of aromatic rings to the amide fragment of ligand leads to complex dynamic behavior in solutions what is believed to strongly affect the extraction ability of synthesized ligands.

A new phosphine oxide ligand demonstrates high selectivity for the Am–Cm pair with SF = 2.9–3.5 and the Am–Eu pair with SF = 7.3–8.5 in a range of 0.1–3 M nitric acid. Thermodynamic measurements show that the entropy factor is responsible for selectivity observed in the extraction experiment. The most prevalent complexes of all three metal ions were (Ph₂PyPO)₂M(NO₃)₃. According to their DFT modelling, the M–N distances for the Cm ion were larger than those for Am, so the last ion enters deeper into the pseudo-cavity of the ligand, which causes the observed selectivity.

Predicted by DFT simulation dilactams (B) are selective and efficient extractants for the separation of Eu³⁺ and Am³⁺.

In this work we report on new examples of phenanthrolindiamides containing asymmetric centers in amide substituents.