Studies on the extraction behaviour of zirconium from mixed aqueous media with TBP

A systematic study is presented on the extraction of Zr(IV) by tri-n-butylphosphate from H₂SO₄, HNO₃, HCl and HBr solutions as well from binary mixtures of H₂SO₄ and halogen acids. It has been found that Zr(IV) extraction is appreciably increased by addition of halogen acid to sulphuric acid solutions. On the other hand, the presence of water-miscible alcohols and acetone was found to enhance Zr(IV) extraction from HCl and HNO₃ solutions. An investigation of extracted Zr complexes from pure acids and mixed aqueous media enabled an explanation of the observed enhancements. In the light of the obtained results, an extraction mechanism is suggested.     

Studies on plutonium(IV) hydroxosuccinate

The precipitation behaviour of basic plutonium(IV) compounds from dilute nitric acid medium with aliphatic dicarboxylic acids has been investigated. Unlike plutonium(IV) oxalate, which is precipitated in acid medium (1–4M), the higher dicarboxylates precipitate in 0.9–2.5 pH range and their elemental analysis indicate Pu/dicarboxylate ratio of 11. The mode of formation, composition, solubility and thermal degradation behaviour for plutonium(IV) hydroxosuccinate has been studied. The hydroxy group determination by kinetic titration using fluoride complexing revealed that the compound has a Pu:OH ratio of 11 and determination of bridging oxygen group gave a Pu:O ratio of 10.5 suggest its formation as hydroxysuccinate having an oxobridged formula.     

Solvent extraction of neptunium(IV) from nitric acid solutions by sulphoxides and their mixtures

Studies have been performed on the liquid-liquid extraction of neptunium from nitric acid solutions by di-n-hexylsulphoxide (DHSO) di-no-octylsulphoxide (DOSO) and di-iso-amylsulphoxide (DISO) and their mixtures over a wide range of conditions. At a given strength of the extractant, extraction of Np(IV) increases initially rapidly with increase in the acid concentration; at high acidities, above 8M HNO₃, the extraction decreases. Under otherwise identical conditions, extraction increases with an increase in the extractant concentration. The species extracted would appear to be Np(NO₃)₄·2(R₂SO). A mixture of two extractants extracts more than the sum of the extractions due to the individual components at concentrations corresponding to those of the mixture. After loading the organic phase with uranium(VI), extractability of Np(IV) becomes considerably lower. The diminution in extraction with increase in temperature is small. A comparison of the extraction behaviour of Np(IV) with those of Pu(IV), U(VI) and some associated fission products has been made.     

Studies on extraction of zirconium(IV) by tricapryl methyl ammonium chloride from sulphate media and its separation from hafnium(IV)

The distribution of Zr(IV) between aqueous H₂SO₄ solutions and organic phases of tricapryl methyl ammonium chloride has been described. The dependence of extraction on acidity, metal and solvent concentration, diluent type and temperature was thoroughly investigated. The possible extraction mechanism is discussed in the light of results obtained. A method for the separation of Hf(IV) from Zr(IV) is also suggested.     

Thermodynamics of extraction of U(VI), Np(IV) and Pu(IV) with some long chain aliphatic sulphoxides

Distribution data for U(VI), Np(IV) and Pu(IV) from 2 M nitric acid medium with 0,2 M di-n-hexyl sulphoxide (DHSO) and di-n-octyl sulphoxide (DOSO) in Solvesso-100 have been obtained in the temperature range 20–50°C. From these data, the enthalpy, entropy and free energy changes associated with their extraction were evaluated. Extraction of Np(IV) and Pu(IV) with both sulphoxides is favoured by negative enthalpy and positive entropy changes whereas the extraction of U(VI) is favoured only by high negative enthalpy change. This behaviour has been explained as arising due to the higher hydration of Np⁴⁺ and Pu⁴⁺ ions as compared to the UO₂²⁺ ion.     

Studies on the adsorption of plutonium (IV) on alumina from phosphoric acid-nitric acid solution

Results of experiments on the adsorption of plutonium (IV) on alumina and their application to the recovery of plutonium from analytical waste solutions containing phosphoric-nitric acid are reported. Distribution ratios of plutonium (IV) between alumina and solutions containing varying concentrations of phosphoric acid and nitric acid are determined. The influence of various ions like UO₂ ²⁺, Fe³⁺, MoO₄ ^2–, VO²⁺ and SO₄ ^2– on the distribution ratio is evaluated. Saturation values of adsorption of plutonium (IV) on alumina and optimum conditions for loading and elution of plutonium on a column packed with alumina are described.     

Solvent extraction of tetraphenylarsonium ion pairs from mixed aqueous-organic solutions

Ion pairs of tetraphenylarsonium cation with iodide, bromide, and perrhenate anions were extracted into chloroform from mixed aqueous-organic solutions. The extraction of these ion pairs was found to increase in the presence of polar aprotic solvents in the mixed aqueous-organic phase. This effect was correlated with literature data on free energy of transfer of the Ph₄As⁺ ion, and ascribed to ion pair/solvent and/or ion/solvent interactions in the organic phase.     

Studies on extraction of thorium(IV) from sulfate media with mixtures of long-chain primary amines and tributyl phosphate

The partition of Th(IV) from H₂SO₄ solutions with extractant mixtures of long-chain primary amine (Primene JMT, PrJT) and tributyl phosphate (TBP) is described. Exraction was optimized at PrJT/TBP molar ratio of about 3. The dependence of extraction on acidity, salting agent, extractant concentration, diluent type and temperature, was investigated. From the results obtained, the extracted species are suggested and enthalpy data determined.     

Liquid-liquid extraction of copper (II) with dialkyl sulphoxides

The extraction behaviour of Cu(II) from hydrochloric acid and lithium chloride solutions with di-n-pentyl sulphoxide (DPSO) and di-n-octyl sulphoxide (DOSO) has been investigated over a wide range of conditions. At a given strength of the extradant, the extraction increases with increase in HCl and LiCl concentrations. The extraction of the metal also increases with increase in extractant concentration at constant [HCl] or [LiCl]. The species extracted would appear to be CuCl₂·2DPSO/2DOSO and CuCl ₄ ²⁻ ·2DPSO. The extraction of the metal decreases with increase in initial aqueous metal concentration and also with increase in temperature. The extraction also depends on the nature of the diluent employed.     

Solvent extraction studies on the recovery of plutonium(IV) from phosphoric acid solution using monooctylphenylphosphoric acid

Extraction of plutonium from analytical waste solutions containing phosphoric acid using a solution of monooctylphenylphosphoric acid (MOPPA) is described. Effect of reagent concentration, presence of uranium, plutonium loading and back extraction of plutonium from the organic phase are described. Using a solution of 0.05 F MOPPA in xylene, more than 90% plutonium could be extracted in one cycle.     

Solvent extraction of uranium(VI) into toluene by dicyclohexano-18-crown-6 from mixed aqueous-organic solutions

Extraction behaviour of uranium(VI) from mixed organo-aqueous solutions containing water-miscible protic aliphatic alcohols and several aprotic solvents was investigated by using dicyclohexano-18-crown-6(DC18C6) as an extractant. The organic phase was a binary solution of DC18C6 and toluene while the polar phase was a three component solution of uranyl nitrate, polar additive and aqueous nitric acid. Methanol, ethanol, isobutanol, dioxane, acetone, propylene carbonate and acetonitrile were used as the organic components of the mixed (polar) phase. Propylene carbonate, acetone, acetonitrile and dioxane increased the extractability of U(VI), whereas alcoholic additives showed only an antagonistic effect. The relative increase in extraction was found to be more at lower nitric acid concentrations. Possible reasons for such behaviour are briefly discussed. Recovery of U(VI) from loaded organic phase was easily accomplished using dilute perchloric acid and sulphuric acid. A sample method was standardized for the separation of plutonium(IV) from uranium(VI) based on its reductive stripping.     

Studies on the solvent extraction behaviour of Pu(IV) from sulfuric acid medium into di-2-ethylhexyl phosphoric acid (HDEHP)

Extraction of plutonium(IV) from aqueous sulfuric and sulfuric-nitric acid into di-2-ethylhexyl phosphoric acid (HY) in the diluents n-dodecane, toluene or chloroform has been investigated. The composition of the Pu(IV) species extracted from H₂SO₄ was found to be PuH₂Y₆, which changed to Pu(NO₃)H₂Y₅ and Pu(NO₃)₂H₂Y₄ with increasing concentration of nitrate ion in the aqueous medium. These three species can be represented as PuY₂(HY₂)₂, Pu(NO₃)Y(HY₂)₂ and Pu(NO₃)₂(HY₂)₂, respectively, where Y represents the anion of monomeric HY, and HY₂ the anion of dimeric H₂Y₂. Synergism in the extraction of Pu(IV) by the addition of thenoyltrifluoroacetone (HTTA) to HY was also investigated and attributed to extraction of the additional species, Pu(TTA)Y(HY₂)₂ and Pu(TTA)₂(HY₂)₂. The addition of the neutral extractant tri-n-octylphosphine oxide (TOPO) to HY did not result in synergism in the extraction of Pu(IV) from aqueous sulfuric acid. With aqueous nitric acid under similar conditions, however, synergism was observed. The possible equilibria in these systems were identified and the corresponding equilibrium constants were determined.     

Solvent extraction of zinc/II/ with sulphoxides: Theoretical analysis of extraction behaviour

This paper describes a theoretical method for analyzing the behaviour of⁶⁵Zn during solvent extraction from ammonium thiocyanate solutions with dialkyl sulphoxides. The mechanism of extraction of Zn/II/ from thiocyanate medium by sulphoxides may be represented by the following general equation: $$xM_{aq}^{m + } + ySCN_{aq}^ - + zS_{org} \rightleftharpoons [M_x /SCN/_y ]^{mx - y} .zS_{org} $$ where M^m+ is the metal ion and S is the extractant. Expressions for the distribution coefficients were derived taking into account complexation of the metal in the aqueous phase by inorganic ligands and also the dissociation of the extracted ion-pairs in the organic phase. Using these expressions, the values of the extraction constants were determined by a least-squares fit with the experimental extraction data. From these extraction constants, the various species extracted into the organic phase were resolved. The influence of the metal concentration, temperature and the diluent on the extraction of Zn/II/ has been investigated.     

The effect of temperature on the extraction of plutonium(IV) from nitric acid by tri-n-butyl phosphate

The extraction of Pu(VI) from varying concentration of nitric acid into TBP in dodecane was studied at different temperatures in the range 20–60°C. From the distribution coefficient data, the enthalpy changes for the extraction of Pu(VI) under different conditions were determined. All the data obtained showed that the extraction of Pu(VI) from nitric acid into TBP is exothermic in nature. An attempt was made to evaluate the thermodynamic free energy and entropy changes.     

New substrates in the ferroin-catalyzed bromate system in aqueous-organic mixed media

A large number of substrates have hitherto been employed in the Belousov-Zhabotinsky (B-Z) oscillatory system in pure aqueous medium. A systematic study of aromatic bromate oscillators is limited by solubility problem relating to the compounds and the brominated derivatives. The use of aqueous-organic mixed media for the oscillatory study is found to be highly useful for the study of water insoluble substances. A comparative study of the oscillatory behavior of gallic acid as substrate in pure aqueous as well as in a number of mixed media have been made in order to ascertain the suitability of mixed media in oscillatory systems. The alteration of oscillatory characteristics in the presence of organic solvent can be understood in terms of the Field-Koros-Noyes (FKN) mechanism. The oscillatory behavior of seventeen new substrates in the ferroin-catalyzed bromate system in 20% (v) acetonitrile is also presented and discussed in this communication. The reactivity of structurally related substrates has been correlated to the structure in terms of the relevant oscillatory parameters. The use of aqueous-organic mixed media in oscillatory systems would enable the investigation of new classes of substrates since getting them into the solution phase would no longer be a limitation. © 1993 John Wiley & Sons, Inc.     

Studies on the extraction of americium(III) from aqueous nitrate media by sulfoxides

Solvent extraction behaviour of Am(III) from dilute nitric acid media with sulfoxides (R₂SO) in Solvesso-100 has been investigated over a wide range of conditions. Very poor extractability of Am necessitated the use of salting-out agents, viz., nitrates of Al, Mg, Ca, Li and NH ₄ ⁺ . Effects of certain variables such as acidity, extractant concentration, saltingout agent, temperature etc., on metal extraction by sulfoxides have been examined systematically. For a fixed sulfoxide concentration, extraction attains a maximum value up to around 0.2–0.4M HNO₃ and decreasing above 1M HNO₃. In contrast, increasing the concentration of sulfoxide (0.8M DISO, 1.3M DBuSO) gives almost quantitative Am extraction up to 1M HNO₃. For satisfactory extraction, di-n-octyl as well as di-n-hexyl sulfoxide are the most suitable extracting agents. Extractability of Am increases with increasing amounts of all the salting-out agents studied and their effect follows the sequence: Al³⁺>Mg²⁺>Ca²⁺>Li⁺>NH ₄ ⁺ ; this is also the relative dehydrating effect of the cations. The species extracted would appear to be Am(NO₃)₃.3R₂SO. Americium is easily stripped with 1–3M HNO₃ solutions from the loaded organic phase. Extraction decreases with increasing temperature, indicating the extraction to be exothermic. Extraction from partially non-aqueous solutions was also investigated.     

Studies on enzymatic peptide synthesis in biphasic aqueous-organic systems with product extraction

The dipeptide derivativesZ-Tyr-Leu-NH₂ andMca-Tyr-Leu-NH₂ were synthesized by -chymotrypsin-catalyzed coupling reactions in solvent systems consisting of buffer and ethyl acetate. In comparison to a pure aqueous medium, in which only insignificant synthesis takes place, the product formation is greatly enhanced in a biphasic medium due to extraction of the dipeptide into the organic phase. The influence of several reaction parameters, such as buffer concentration, reaction time, volume ratio of organic and aqueous phase, and reagent concentration on the yield ofZ-Tyr-Leu-NH₂ was investigated. Replacement of the hydrophobicZ-group by the more hydrophilic chloroacetyl group resulted in better dipeptide yields at higher reaction rates. Abbreviations: IUPAC-IUB rules for peptides are followed, see Eur J Biochem 27: 201 (1972).Ac = acetyl,Glt = 4-carboxybutyryl (glutaryl),Mca = monochloroacetyl,Z = benzyloxycarbonyl, –OMe = methyl ester, –Nan = 4-nitroanilide, TLC = thin layer chromatography. All amino acids are ofL-configuration.     

Mixed-ligand chelate extraction of neodymium(III) with thenoyltrifluoroacetone and various sulphoxides

Mixed-ligand chelate extraction of Nd(III) into benzene with mixtures of thenoyltrifluoroacetone (HTTA) and bis-2-ethylhexyl sulphoxide (B2EHSO) or di-n-octyl sulphoxide (DOSO) or diphenyl sulphoxide (DPhSO) or trioctylphosphine oxide (TOPO) from thiocyanate solutions has been studied. A very high synergistic enhancement of the order 10(3) has been observed in these systems. Thus this mixed-ligand chelate system may be useful in the extraction and separation of Nd(III) from other metal ions. The mechanism of extraction can be explained by a simple chemically based model presented in this paper.