Separation of Silicon Isotopes by Silicon Tetrafluoride–Silane Technology

Silane enriched in silicon isotopes was obtained in high yield by reacting SiF₄ with a solution of NaAlH₄ in diethylene glycol dimethyl ether in a purpose-designed apparatus. Chemical analyses are presented for isotopically enriched silicon obtained by the thermal decomposition of silane.     

Extraction of Mo from solutions in HNO<Subscript>3</Subscript> and other mineral acids with solutions of dibutyl hydrogen phosphate in a diluent

Extraction of Mo from HNO₃ solutions with solutions of HDBP in xylene and CCl₄ in a wide range of Mo concentrations was studied. The Mo distribution ratios are considerably higher with CCl₄ diluent compared to xylene, but the extractant capacity in both cases is the same and corresponds to the ratio HDBP: Mo = 2. The active species in the Mo extraction is the HDBP dimer. In the first step, an acidic molybdenyl salt with HDBP of the composition MoO₂(DBP)₂(HDBP)₂, exhibiting certain secondary extraction properties toward rare-earth elements, is formed in all the cases. The dependence of the Mo extraction on the aqueous solution acidity passes through a minimum at 3–4 M HNO₃. The subsequent increase in the Mo distribution ratios is associated with the simultaneous extraction of HNO₃ (or nitrate ion) whose concentration in the extract is considerably lower than the Mo concentration. With an increase in the loading of the extract with molybdenum, the acidic molybdenum salt of HDBP undergoes restructurization, probably associated with additional coordination of H₂MoO₄ to it. The dependence of the Mo distribution ratio on the acid concentration in the extraction from sulfuric acid solutions passes through a minimum at 3–4 M H₂SO₄, which correlates with the first step of the acid dissociation, and in the extraction from HClO₄ the dependence passes through a minimum and a maximum. In the extraction from hydrochloric acid solutions, the Mo extractability decreases with an increase in the acid concentration, owing to complexation in the aqueous phase. The nature of processes occurring at various loadings of the extract with molybdenum are discussed.     

Extraction of HNO3 with solutions of zirconium salt of dibutyl hydrogen phosphate in 30% tributyl phosphate and in xylene

Zirconium salt of dibutyl hydrogen phosphate (ZS HDBP) dissolved in xylene or 30% tributyl phosphate (TBP) + xylene mixture extracts noticeable amounts of HNO₃ at its low concentrations in the aqueous phase, when extraction of HNO₃ with straight HDBP itself is not observed. IR data show that DBP^? and NO ₃ ^? ions compete for coordination to Zr, which also adds from 2 to 4 HDBP molecules. With a further increase in the HDBP concentration, the HDBP and HNO₃ molecules compete for coordination in the outer coordination sphere of zirconium. Inflections in the S-shaped dependence of the HNO₃ concentration in the organic phase on the [Zr]:[HDBP] molar ratio lie within the interval from 1:8 to 1:12, which corresponds to filling of the Zr outer sphere with HDBP molecules. In the presence of TBP, these curves become smooth and have no apparent inflection.     

First Observation of the Cation-Cation Interaction of Actinides in Melts: NpO2 +-UO2 2+ System

Study of the absorption spectra of the NpO ₂ ⁺ ion in a CsCl melt containing 2 M UO ₂ ²⁺ , as well as in K₂UO₂Cl₄ and Cs₂UO₂Cl₄ melts (T = 700°C), allowed the first detection of the cation-cation interaction of actinides in melts. In all the molten salts studied, the cation-cation interaction of NpO ₂ ⁺ and UO ₂ ²⁺ is manifested most clearly (via appearance of an additional band) in the ³ H ₅ ³ H ₄ magnetic-dipole transition of the 5f ² configuration of the NpO₂ ⁺ ion (D _4h symmetry) near 1.6 m: Along with a sharp peak of unbound neptunyl(V) at 1660 nm, there is an equally sharp peak at 1633 nm belonging to the cation-cation complex. The intensity ratio for the peaks at 1633 and 1660 nm increases in the series of melts (UO ₂ ²⁺ in CsCl) < K₂UO₂Cl₄ < Cs₂UO₂Cl₄ by two orders of magnitude.     

Chemiluminescence of Luminol Induced by NpO2F4OH3- Complexes Excited with Nitrogen Laser Radiation (λ = 337.1 nm)

Chemiluminescence of luminol induced by NpO₂ ^{2 +} complexes excited with nitrogen laser radiation was studied in 42% solutions of CsF with different pH. The absorption spectra of solutions of NpO₂F₄OH^{3 -} complexes and the chemiluminescence spectra of these solutions containing luminol and having different pH were recorded.     

Extraction of zirconium with tributyl phosphate from nitric acid solutions

The extraction of zirconium with tributyl phosphate (TBP) in organic diluent was studied. The dependence of the distribution ratio of Zr on the TBP concentration in the organic phase and also the IR spectra of Zr-TBP extracts obtained at different concentrations of Zr and HNO₃ in the aqueous phase show that at least two kinds of extractable zirconium nitrate solvates with TBP are formed in extraction with 30% TBP. The solvate formed at HNO₃ concentration not exceeding 3 M contains water molecules. The extract-able species formed at higher nitric acid concentration in the aqueous phase is anhydrous zirconium nitrate disolvate with TBP.     

A spectroscopic study of molybdenum extracts in organic solutions of dibutyl hydrogen phosphate in equilibrium with aqueous nitric acid solutions

The Mo extracts prepared by contacting dibutyl hydrogen phosphate (HDBP, HA) dissolved in xylene or CCl₄ with HNO₃ solutions of various concentrations in a wide range of Mo concentrations, and also the third phase formed in the analogous extraction system with tridecane as diluent were examined by IR and UV spectroscopy. The data obtained confirm the conclusion that, at the ratios HDBP: Mo ≥ 4 in the extract, molybdenum is extracted in the form of the acidic salt MoO₂(HA₂)₂. The spectroscopic data obtained at higher extract loading were interpreted assuming the formation of binuclear complexes (HA₂)MoO₂A₂MoO₂(HA₂) and, at HDBP: Mo < 3, of complexes of hydroxomolybdenyl and/or dimolybdenyl, and finally of polymeric complexes with bridging Mo-O-Mo bonds. In strongly acidic media, coextraction of outer-sphere molecular HNO₃ and the presence of coordinated nitrate ion in the extract (probably in the form of molybdenyl nitrate complexes) are observed. A multistep extraction mechanism involving formation in the aqueous phase of an asymmetric monomeric complex MoO₂(OH)(H₂O)(HA₂) was suggested.     

The Role of Hydroxide Ions in Reduction of Uranyl Ion Stimulated by Nitrogen Laser Radiation (337.1 nm)

The behavior of the UO₂ ²⁺ ion excited by radiation of pulse nitrogen laser in aqueous solutions with a high content of CsF was studied at various pH. Chemiluminescence of luminol under the action of OH radicals appearing in the solution was considered.     

Interaction of HDBP with Zr in extraction

Complexes of Zr with dibutyl hydrogen phosphate (HDBP) formed in extraction from 1–6 M HNO₃ solutions were studied by extraction methods and differential IR spectrometry. The study revealed formation of a single complex Zr(NO₃)₂A₂, or “core” (where A is DBP anion). Additional HDBP molecules are linked to the “core” via phosphoryl oxygen atoms to form associates Zr(NO₃)₂A₂(HA) _n with no definite stoichiometry. A differential spectrometric study revealed the band ν_s(POO^?) = 1010 cm^?1, which in the spectra of neat HDBP is obscured by the P-OC vibration frequency. The difference ν_as(POO^?) ? ν_s(POO^?) decreases as the HDBP: Zr ratio is decreased from 6 to 2. Extraction of Eu with the associate Zr(NO₃)₂A₂(HA)₆ occurs owing to interaction with both phosphoryl oxygen atoms of HDBP linked to the “core” by a strong hydrogen bond.     

Extraction Properties of Dibutylphosphoric Acid Zirconium Salt in Recovery of Transplutonium and Rare-Earth Elements from Nitric Acid Solution

The structures of dibutylphosphoric acid zirconium salt (Zr-DBP) and of the complexes formed in the organic phase in extraction of rare-earth elements with Zr-DBP were suggested on the basis of the extraction and IR data. The influence exerted by the acidity, Zr-DBP concentraiton, and degree of extractant saturation with the metal on the structure of the complexes was examined. The contributions of various extraction mechanisms for all the rare-earth elements and also for Am and Cm were revealed by mathematical simulation. Irrespective of the diluent, addition of TBP to Zr-DBP decreases the distribution factors of Ce, Eu, and Am but increases the extractant capacity for rare-earth elements by a value that considerably exceeds the extraction of the elements with TBP taken separately.