A.S. Kertes

Synergic extraction of some lanthanides and transition metals by two bidentate chelating agents

Abstract The combination of two bidentate ligands, the acidic thenolytrifluoroacetone and the Lewis base phenanthroline or dipyridyl, produces a very strong synergic effect in solvent extraction of lanthanides and bivalent transition metals. The stability constants of the mixed adducts have been determined in benzene, cyclohexane, carbon tetrachloride and chloroform at 25°C. In some cases, values of enthalpy and entropy changes associated with the formation of the synergic adducts have been derived from stability constants calculated at different temperatures.

SOLUTE-SOLVENT INTERACTION IN THE SYSTEM HYDROCHLORIC ACID-WATER-TRI-n- BUTYL PHOSPHATE

Abstract Attempts have been made to identify the species formed in a heterogeneous equilibrium between aqueous hydrochloric acid and pure tributyl phosphate. In addition to the conventional distribution and water content determination, physical-chemical measurements of density, viscosity and conductivity of the organic layer were carried out. Two well defined species were found to exist as a result of solute-solvent interactions in the system studied. The first, formed at lower initial aqueous acid concentrations has the composition [(TBP)2·HCl·(H2O)]6]; the second, formed at higher acid concentrations, has the general formula [TBP·HCl·(H2O)3]. The reactions involved have been suggested. The system studied is of interest in connection with the extraction of inorganic chlorides from hydrochloric acid solutions into tributyl phosphate.

Extraction equilibria in the system aqueous hydrochloric acid-uranyl chloride-tri-n-butyl phosphate

Abstract The distribution of uranyl chloride between aqueous hydrochloric acid solutions and indiluted tri-n-butyl phosphate (TBP) was examined as a function of increasing acid concentration in the initial aqueous solution, the metal concentration being kept constant, and as a function of increasing uranyl chloride concentration for constant acid content of the initial aqueous solution. The pregnant organic layers involved were investigated by means of volume-swelling determinations, and by viscosity, density, conductivity and spectrophotometric measurements. The water content of the tri-butyl phosphate layer was also determined. It was found that the chemical mechanism governing the extraction of uranyl chloride is largely dependent upon the hydrochloric acid concentration in the initial aqueous solutions. For low acid concentrations the mutual salting-out effect of thr two solutes controls the mechanism; at medium acid concentrations (1–7 M HCl) the acid concentration has no marked influence on the extraction mechanism involved; at high acid concentrations it is the competition between two complex-solvates, namely the hydrochloric acid-monosolvate-trihydrate and the uranyl chloride-disolvate, which controls the extraction of uranyl chloride from aqueous solutions.

Distribution of nitric acid between water and amberlite LA-1 liquid anion exchanger

Abstract The solute-solvent interaction between Amberlite LA-1, a long-chain secondary amine extractant dissolved in carbon tetrachloride or benzene and aqueous nitric acid solution up to ∼ 16 M has been investigated by physical and chemical measurements. The first reaction is an acid-base equilibrium leading to the formation of amine nitrate. The quilibrium constants were evaluated as K1 = 3·8 × 105 and 5·4 × 105 in carbon tetrachloride and benzene respectively. The second and third reactions postulated involve amine nitrate and associated nitric acid molecules, leading to the formation of a molecular addition compound identified as R2HNHNO3·HNO3 and to the physical partition of associated nitric acid between the aqueous and organic phases. The equilibrium concentration product quotients have the values K2 = 1·85 for carbon tetrachloride and K2 = 2·24 for benzene, and the distribution constant has the value Kd = 0·1±0·02 for 1 M amine solution in both diluents. The effects of the formation of the amine nitrate aggregates or of the extracted molecular addition compound, or both, are not taken into account. Evidence was obtained that the aggregation of the species in the organic phase is largely a post-equilibrium phenomenon.

Hydrochloric acid promoted hydrolysis of tri-n-butyl phosphate

Abstract This study, an extension of a previous note, (6) revealed that the fundamental reaction in the hydrolysis of tri-butyl phosphate accelerated by hydrochloric acid is the cleavage of the OC linkage, and it has been shown that the dealkylation reaction in the organic phase yields butyl chloride and acid esters. First-order rate constants were calculated and compared with those for a similar nitric acid system. A mechanism for the acidolytic degradation, based on the new data, is proposed. Previous observations of a greatly increased rate of hydrolysis of the organic phase as its water content increases have been confirmed, and the differences in rate in parallel nitric and hydrochloric acid systems explained accordingly.

Aggregation equilibria in solvent extraction of iron(III) halides

Osmometric measurements on benzene solutions containing trilaurylammonium chloride or bromide, TLAHX. and tetrachloro or tetrabromoferrate, TLAHFeX4, (X = Cl and Br) and data on the partition of iron(III) chloride between aqueous hydrochloric acid solutions and benzene solutions of trilaurylammonium chloride indicate that in the equilibrium organic phase the predominate metal complexes are TLAHFeX4 and TLAHX·TLAHFeX4 in addition to the various homogeneous oligomers of both TLAHX and TLAHFeX4. Their formation constants are given. The water content of the benzene phase has no significant effect upon the aggregation equilibria.

Cationic surfactants in organic solvents. III. Critical micelle concentration of dodecylammonium halides in benzene and toluene

Abstract The behavior of primary, secondary, tertiary and quaternary dodecylammonium chloride and bromide in benzene and toluene was investigated by surface tension measurements, the dye-solubilization and iodine-complex formation method and vapor pressure osmometry at 37° and 50°C. The smooth continuity in the measured properties of these solutions as a function of concentration has been interpreted in terms of a progressive oligomerization of the cationic surfactants rather than in terms of a monomer ⇄, micelle equilibrium, familiar in aqueous solutions. No indication for the phenomenon of critical micelle concentration could be observed.

HYDROLYTIC AND PHOTOLYTIC REACTIONS IN THE SYSTEM: WATER-HYDROCHLORIC ACID- URANYL CHLORIDE-BUTYL PHOSPHORIC ESTERS

Thc phenomenon of the homogeneous organic layer. initially uranium (VI), turning from yellow to a greenish tinge, characteristic of uranium(IV), while forming the gel precipitate in thc extraction of uranium, is described. The homogeneous equilibrium organic layers, previously separated from the opposing equilibrium aqueous phases, and containing both hydrochloric acid and uranyl chloride in various concentrations, could not be kept unchanged after a period of 8 to l0 days under normal laboratory conditions of light and temperature. After this period a solid began to separate out. Once the transformation starts it proceeds quite rapidly and is usually complete in a few days. The green gel is completely soluble in chloroform and partially soluble in toluene. It is also soluble in hot, concentrated nitric acid. The mechanism of the phenomenon is discussed. (P.C.H.)

Thermodynamics of solvent extraction processes: Synergic adducts of copper and zinc diketonates with bidentate nitrogen bases

Abstract By direct titration calorimetry, the equilibrium constants and the enthalpy, entropy and free energy changes of the reaction MA 2 + L → MA 2 L, leading to the formation of synergic adducts of 1,10-phenanthroline, 2,2′-dipyridyl and 4,4′-dipyridyl with several bis-(β-diketonato) copper and zinc chelates have been determined in chloroform solution at 25°C. The thermodynamic functions indicate that the lower the stability of the metal diketonate and the greater basicity of the donor atom, the greater the stability of the adduct formed. In most cases the adducts are stalilized by large exothermic enthalpy changes. In some copper compounds, however, the Jahn-Teller distortion affects the enthalpy and entropy contributions to the free energy changes.

Spectra of neodymium(III) in nitrate-water and nitrate-chloride melts

Abstract The absorption spectra of neodymium have been recorded in LiNO 3 KNO 3 eutectic and its mixtures with water or chloride ions in the temperature range between 80 and 350°C. While the positions of the absorption bands in the visible region are not substantially different in the various media studied, the molar absorptivities of some of the bands are sensitive to the environment. This medium effect has been quantitatively followed by a stepwise addition of water or chloride ions to the nitrate melt.