Isolation of Rare-Earth Elements from Mixtures of Calcium and Lanthanide Oxalates

The temperature regions for separate crystallization of rare-earth element (REE) oxides of the cerium group in the presence of CaCO₃ have been determined using X-ray diffraction, differential thermogravimetric analysis, inductively coupled plasma mass spectroscopy, and X-ray fluorescence. The possibility to separate REE oxides from CaCO₃ in H₂SO₄ solutions after heat treatment (450–600°C) has been studied. The solid phase of the precipitate is represented by slightly soluble calcium sulfate, whereas the REE oxides pass into the liquid phase in the form of highly soluble sulfates. After heat treatment of the test mixture of REE oxalates and calcium oxalate at a temperature higher than 750°C, calcium compounds pass into 1–2% HNO₃ liquid phase in the form of nitrates, whereas lanthanide oxides remain in the insoluble phase of REE oxide solid solution having CeO₂ structure.     

Extraction of Nitric Acid from Chloride-Nitrate Solutions

The extraction of nitric acid from chloride-nitrate solutions simulating solutions that result from eudialyte breakdown with hydrochloric acid after extractive recovery of rare-earth elements was studied. A general flowsheet was suggested for the extraction of rare-earth elements from chloride solutions and utilization of nitrate ions as concentrated solutions of nitrates used in recycling.     

Sorption Recovery of Transplutonium Elements from Nitric Acid Solutions with Arsenazo Group Reagents

Sorption recovery of actinides and lanthanides from nitric acid solution with arsenazo group reagents, activated carbon modified with these reagents, and chelating sorbents containing arsenazo functional groups was studied.     

酒石酸与La~(3+)对草酸钙结晶的影响

采用X射线衍射(XRD)、傅立叶红外光谱(FTIR)和扫描电镜(SEM)分析了凝胶体系中混合添加剂酒石酸和La~(3+)对草酸钙(Ca Oxa)晶体生长的影响。研究结果显示,酒石酸可以抑制Ca Oxa晶体的生长、聚集,并诱导二水草酸钙(COD)生成;La~(3+)不仅可诱导COD生成,而且可使一水草酸钙(COM)的形貌发生变化;而酒石酸和La~(3+)的联合作用则不仅增强了对COD的诱导能力,并使COM的聚集程度降低、比表面积减小。酒石酸和La~(3+)的联合疗法对尿石病的预防和治疗有较大的参考价值。     

Forms of Rh(III) in Nitric Acid Solutions

The forms of Rh(III) in nitric acid solutions are studied by ¹⁴N, ¹⁵N, ¹⁷O, and ¹⁰³Rh NMR and electronic absorption spectra. At HNO₃concentrations below 5 mol/l, rhodium mainly exists as low-nuclear oligomers with a bridging fragment Rh(-OH)(-ONO₂)Rh; terminal positions of the central atoms are occupied by water molecules. It was found that the isotopic equilibrium ¹⁴NO^– ₃/¹⁵NO^– ₃of the bridging ligand sets in at an abnormally high rate, at which the isotopic exchange H₂ ¹⁷O/H₂ ¹⁶O of the terminal ligands also occurs in the dimers and trimers. The formation of low-nuclear oligomers is a common feature of Rh(III) complexes in aqueous solutions with ligand deficiency in the system. The possibility of isolating rhodium from nitric acid solutions using different methods is predicted.     

Nitrogen Trioxide in Irradiated Aqueous Nitric Acid Solutions of Hydrazine

The rate constants of reactions of the NO₃ radical with hydrazoic acid (7.6 × 10⁶l mol^–1s^–1) and the hydrazonium ion (2.3 × 10⁶l mol^–1s^–1) in 6 M nitric acid at 290 ± 2 K were measured by a pulse radiolysis technique. The reaction scheme was refined by the computer simulation of the -radiolysis of aqueous nitric acid solutions of hydrazine with the use of the measured rate constants and published data on the reactivity of intermediates. The results of computations were compared with experimental data on the continuous radiolytic degradation of hydrazine in aqueous 2 M nitric acid solutions at 313 K.     

酒石酸镁对水合草酸钙晶体生长的调控作用

本文在凝胶模拟体系中研究了Mgtart对草酸钙生长、 聚集和晶型、 晶相等的影响, 以期阐明Mgtart防治泌尿系结石形成的可能机理, 为临床医学提供参考.     

Dissolution of Calcium Carbonate in Aqueous Solutions of Acetic Acid

A kinetic equation for the calcium carbonate dissolution, fitting the experimental data to within 8.1%, was obtained. The additional diffusion hindrance caused by the CO₂ evolution in the course of the dissolution was considered.     

Solubility of Lead Nitrate in Aqueous Solutions of Nitric Acid and Zinc Nitrate

Solubility of lead nitrate in the system H₂O-Zn(NO₃)₂-HNO₃ was studied using the simplexlattice design method. The equations describing the effect of nitric acid and zinc nitrate concentrations on the content of lead nitrate in solution at 25 and 55°C were derived.     

Solubility of Calcium Sulfate Dihydrate in Nitric Acid at 20°C

The solubility of gypsum in 0-30 wt % nitric acid solutions at 20°C was studied. The data were compared with the results obtained at 60°C.     

Kinetic Characteristics of Xylitol Crystallization from Aqueous-Ethanolic Solutions

The kinetics of xylitol crystallization from aqueous-ethanolic solutions as a function of the initialsolution supersaturation, solvent composition, temperature was studied. The effect of solvent compositionon the rate of the xylitol bulk crystallization was considered.     

Reduction of Np(VI) in Irradiated Solutions of Nitric Acid

The reliable separation of neptunium from dissolved nuclear fuel assumes the ability to maintain a preferred oxidation state. However, regardless of its initial redox speciation, a series of reactions occurs in nitric acid to create a mixture of oxidation states including Np(V), Np(VI) and sometimes Np(IV). To further complicate the situation, irradiated solutions such as fuel dissolution contain both transient and long-lived radiolysis products which may be strongly oxidizing or reducing. Thus, irradiation may be expected to impact the equilibrium distributions of the various neptunium valences.We have irradiated nitric acid solutions of neptunium with ⁶⁰Co gamma-rays, and measured radiolytically-induced changes in neptunium valences, as well as the nitrous acid concentration, by UV/Vis spectroscopy. It was found that in 4 M HNO3 at low absorbed doses, the oxidizing radicals oxidized Np(V) to Np(VI). However, as the irradiation proceeded the concentration of nitrous acid became sufficient to reduce Np(VI) to Np(V), and then continued irradiation favored this reduction until an equilibrium was achieved in balance with the oxidation of Np(V) by nitric acid itself. The starting abundances of the two neptunium valences did not affect the final equilibrium concentrations of Np(V) and Np(VI), and no Np(IV) was detected.     

Stability of Fibrous Carbon Materials in Cathodic Polarization in Nitric Acid Solutions

Stability and electrical conductivity of graphitized and carbonized fibrous carbon materials are studied in cathodic polarization in nitric acid solutions.     

Cerium(III) Electrooxidation in Nitric Acid Solutions of Rare-earth Elements

The electrochemical behavior of cerium(III) in nitric acid solutions of rare-earth elements was studied. The activation energy and reaction order of cerium(III) oxidation were determined for various levels of anodic polarization.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 928–932.Original Russian Text Copyright © 2005 by Sedneva.     

Complex Formation of Calcium Ions and Monosubstituted Succinic Acid Derivatives in Aqueous Solutions

Complex formation of calcium ions with succinic acid monoamide, methyl hydrogen succinateat 25°C and ionic strength I = 0.3 (KCl) was studied by pH-potentiometric titration. The stability constants ofthe complexes were determined.     

Electrodeposition of Rhodium on Cathodes of Carbon-Fiber Material from Rh(III) Complexes in Nitric Acid Solutions

Rhodium electrodeposition on cathodes of a carbon-fiber material from nitric acid solutions containing various complex forms of Rh(III) is studied. Depending on the Rh(III) form, the deposition degree varies by several times, all other factors being the same. The charge of a complex species prevailing in solution is presumably a factor determining the electrochemical behavior of Rh(III).     

Leaching of Lanthanides from Phosphohemihydrate with Nitric Acid

Factors were examined that determine passing of lanthanides into solution during nitric acid leaching of phosphohemihydrate obtained in the course of production of wet-process phosphoric acid from Khibiny apatite concentrate by the hemihydrate technique. The data obtained were compared to the results of sulfuric acid leaching.     

Syntheses,Structures and Properties of Lanthanide Coordination Polymers Constructed from Mixed Acid

Two new coordination polymers,[Ln(oba)(ox)0.5(H2O)2]n(Ln = Ho(1),Eu(2);H2oba = 4,4?-oxybis(benzoic acid),H2ox = oxalic acid) have been synthesized under hydrothermal conditions.According to single-crystal X-ray diffraction analyses,complex 1 crystallizes in the monoclinic system,space group P21/c with a = 13.783(2),b =10.0120(15),c = 12.1974(18) ,β = 105.217(2)°,V = 1624.2(4) 3,C15H12O9Ho,Mr = 501.18,Z = 4,Dc = 2.050 g/cm3,F(000) = 964,μ = 4.919 mm-1,λ(MoKα) = 0.71073 ?,GOOF = 1.124,the final R = 0.0239 and wR = 0.0570 for 3310 independent reflections with Rint = 0.0298.Complexes 2 and 1 are isostructural.Oba and ox ligands bridge the Ln(III) ions into 2D layers with(4,4) topology,which are further interlinked into a 3D supramolecular network by hydrogen bonds.TG curves of the two complexes are studied to examine their thermal stabilities.Additionally,complex 2 shows red fluorescence in the solid state at room temperature.