C.F. Coleman

Mechanism of the slow extraction of iron(III) from acid perchlorate solutions by di(2-ethylhexyl)phosphoric acid in n-octane☆

Abstract The rate of iron(III) extraction by di(2-ethylhexyl)phosphoric acid (HDEHP, HA) in n-octane from acid perchlorate solutions, as FeA3. 3HA, is controlled by series and parallel reactions in the introduction of the first and second anion ligands, all occurring at the interface. (In the following subscripts, 1 and 2 refer to first and second anion ligands, m to extractant monomer, d and df to extractant dimer, s to interface saturation.) The measured rate [Fe] , r  −d[ Fe ] [ Fe ] dt , is well fitted by the step rates (25°C) r 1m = 5·5 × 10 −4 [∑HA] 0·5 /[H + ] r 1d = 1·8 × 10 −3 [∑HA]/[H + ] for parallel reactions introducing the first anion ligand, in series with r 2 ≈ 4 × 10 −4 /[H + ] 2 r 2s = 1·5 × 10 −7 /[H + ] [Fe] r 2d = 9·0 × 10 −6 [∑HA] 1·5 /[H + ] 2 r 2df = 1·2 × 10 −5 [∑HA] 2 /[H + ] 2 for parallel reactions introducting the second anion ligand. Step 2s is zero order, while all the other steps are first order, with respect to the aqueous iron concentration. In extractions through a quiescent interface these step rates combine so that r = (r 1m + r 1d ) (r 2s + r 2d + r 2df )/∑r i and in extractions with dispersion mixing so that r = (r 1m + r 1d ) r 2 / (r 1m + r 1d + r 2 ) . The rate decreases slightly with increasing ionic strength, increases with increasing temperature (heat of activation ≈ 10–15 kcal/mole) and with conditions that increase the ionization of HA, and increases sometimes markedly with addition of proton-accepting complexers that can bypass the interface steps 1m and 1d with analogous reactions homogeneous in the aqueous phase.

Sodium and strontium extraction by di(2-ethylhexyl)phosphate: Mechanisms and equilibria☆

Abstract Extraction of sodium and strontium by di(2-ethylhexyl)phosphoric acid (HA or HDEHP) in benzene was examined over the complete loading range from trace concentration to reagent saturation, i.e., formation of the normal salt NaA (NaDEHP) or SrA2 (Sr(DEHP)2). Trace strontium extraction from 0·50 and 4·00 M NaNO3 by mixtures of HA and its sodium salt, NaA, was examined from zero to 100% NaA. Extraction equilibrium curves (organic vs. aqueous concentration), hydrogen ion and reagent-concentration dependences have been examined in all cases, and, for strontium extraction by mixed HA-NaA, sodium-ion dependence was examined. The data indicate that the reaction for sodium extraction by the acid dimer, (HA)2, is Na+ + 2(HA)2·3HA + H+ up to 25% NaA. Additional sodium extraction results in tetramer destruction to yield the salt NaA. The reaction for strontium extraction by (HA)2 is similar: Sr2+ + SrA2·4HA + 2H+. Also similarly, ultimate loading leads to the salt SrA2. Both these salts are polymerized. Trace strontium extraction by mixed HANaA is most readily described by the equation: Sr2+ + (n/y)(aHA·bNaA)y (1/x)(SrA2·(n − 2))(αHA·βNaA))x + iH+ + jNa+, where the extractant is characterized as a mixed, y-fold polymer containing a fraction of HA and b fraction of NaA. The data indicate that strontium extracts as SrA2·4HA at least up to organic-phase compositions of 40% NaA. At higher NaA concentrations the interpretation is less certain but suggests the extraction of strontium into NaA micelles.

The sulfate complexes of some trivalent transplutonium actinides and europium

Abstract The sulfate complexes of Eu, Am, Cm, Bk, Cf and Es were investigated by a solvent extraction method using neutral species distribution between a benzene solution of a long-chain amine sulfate and aqueous sulfuric acid-sodium sulfate solutions. Sulfate was the only anion present and the ionic strength varied with the ligand concentration. Activity coefficient effects over the ligand concentration range examined (up to 0·5 M ) were estimated by a Debye-Huckel expression. The use of the Debye-Huckel equation is justified since the γ ± Na 2 SO 4 data can be fitted to 0·5 M and even higher concentrations with the same equation. Evidence for important amounts of the heretofore unreported trisulfate species of these elements was found, but no evidence was found for tetrasulfate species. The equilibrium constants for all of the actinides are close together and show a smooth periodicity as Z varies. The equilibrium constants for europium are close to those for the actinides. Overall formation constants at zero ionic strength for the mono-, di- and trisulfates of each of the elements are given. Percent distribution of each actinide as a function of sulfate ion concentration is shown.

The tetrad effect: The thiocyanate complex stability constants of some trivalent actinides

Abstract A solvent extraction technique, using bis(2-ethylhexyl)phosphoric acid as the extractant, was employed to examine the formation of Am(III), Cm(III), Bk(III), Cf(III), and Es(III) thiocyanate complexes in a NaSCNNaClO 4 medium at ionic strength I = 1·0 M and pH = 2·00. Mathematical analysis of the data led to the conclusion that the mono-, di-, and trithiocyanate species exist in the thiocyanate concentration range studied in this work. Values of the overall stability constants β 1 , β 2 , and β 3 were calculated. As the atomic number of the actinides increased, the β 1 values exhibited a gradual increase in stability, which is consistent with the expected effect on complex stability due to the actinide contraction. The β 2 values decreased rapidly across the series from americium to einsteinium, with a concomitant increase in β 3 . In addition, there was evidence of the tetrad effect in the β 3 values, and this led to the tentative conclusion that the Act(SCN) 3 (where Act = Am, Cm, Bk, Cf, and Es) complexes are of the inner-sphere type. The thermodynamic parameters of the Am(III) thiocyanate complexes were calculated from temperature dependence measurements. The enthalpy and entropy changes were used to aid in the distinction between inner-sphere and outer-sphere complex formation.

Extraction of alkaline earths from sodium nitrate solutions by di(2-ethylhexyl) phosphate in benzene: mechanisms and equilibria☆

Abstract The extraction of the alkaline earths, excluding radium, by di(2-ethylhexyl)phosphate (DEHP) in benzene from 0·50 and 4·0 M sodium nitrate solutions has been examined as a function of pH and DEHP concentration. Curves with a characteristic maximum in the region of pH 5, similar to that already observed for strontium, were found in all cases. Log plots of E M = [ M ] org [ M ] aq . vs 3 pH gave a slope of +2 at low pH indicating exchange of M2+ with 2H+. The relative extractability was Be ⪢ Ca > Mg > Sr > Ba from 4 M NaNO3 and Be ⪢ Ca > Mg ≈ Sr > Ba from 0·5 M NaNO3. Reagent concentration dependences at low pH where DEHP is in the acid dimer form (HDEHP)2 indicate the following number of DEHP monomers associated with each metal atom: From 4·0 M NaNO3: Be, ∼4; Ca, 5–6; Mg, uncertain; Ba, 6; and from 0·5 M NaNO3: Be, uncertain; Ca, 4–5; Mg, 4–6; Ba, 4–6. The lower number always obtained at the lower reagent concentration and the higher number at the higher reagent concentration. The s ame association ratios and also indicated by the organic phase composition NaDEHP Σ DEHP at which maximum extraction occurs.

INTERFACE MECHANISM FOR URANIUM EXTRACTION BY AMINE SULPHATE.

Abstract In the extraction of metal ions by organic solutions of aqueous-insoluble alkyl ammonium salts the mechanism by which the metal species transfers across the aqueous-organic interface cannot be determined by the usual equilibrium studies. In an effort to elucidate this mechanism, interfacial tension of the two-phase system and kinetics of the transfer of35SO4 between organic (di-n-decylamine sulphate in benzene) and aqueous (acid-sodium sulphate) phases were studied. The kinetic experiments were designed so as to offer the possibility of detecting the transfer of anionic uranium species from aqueous to organic phase. Several different aqueous phase situations were examined, covering the range from low sulphate where most of the uranium exists as the uranyl ion to 1·0 M sulphate where most of the uranium exists as the disulphate complex. At the higher aqueous sulphate concentrations (>0·025 M) an increased rate of35S transfer during uranium extraction (at a given organic/aqueous total sulphate ratio) gave strong evidence for an anion exchange mechanism such as Download : Download full-size image (dotted underlines indicating the organic phase). At aqueous sulphate concentration below 0·01 M, the35S transfer rate was decreased during uranium extraction, and the explanation offered for this result suggests transfer by a neutral mechanism such as Download : Download full-size image Thus, it appears that neutral species transfer is possible where aqueous neutral or cationic species predominate and anionic species transfer is possible where aqueous anionic species predominate, with no implication that the two mechanisms are mutally exclusive. These conclusions are supported by calculations of the number of sulphates transferred per uranium based on35S transfer aq → org during uranium transfer aq → org.

Plutonium polymerization—III The nitrate precipitation of Pu(IV) polymer☆

Abstract The precipitation of aged Pu(IV) polymer by HNO3, LiNO3, Al(NO3)3 and NaNO3 has been observed. With the exception of LiNO3, the precipitation of 0·00678M Pu(IV) polymer was independent of the source of NO3−, and the maximum amount of precipitated polymer occurred at 1·8 NO3−. Further addition of NO3− redissolved the polymer. The nitrate precipitation of Pu(IV) polymer has been analyzed according to the solubility product principle and has been found to closely resemble a solubility product mechanism.

The extraction of water by tri-n-octylamine and several of its salts in benzene and phenylcyclohexane

Abstract The variation in water content of tri-n-octylamine (TOA) and several of its salts with water vapor pressure was determined by isopiestic and liquid-liquid equilibrium. In addition, the type of bonding was investigated with infrared absorption. Water was determined by Karl Fischer titration, by weight gain, and by use of titrated water as an analytical tracer. Benzene solutions of TOA extract water to form the monohydrate, with no indication of the formation of a dimer hydrate even at 0·5 M TOA. The value obtained for the equilibrium quotient with its standard error of fitting is 0·858 ± (σ = 0·006). At a fixed amine concentration, the water extracted by TOA bisulfate (TOAHS) varied nearly linearly with water activity up to aw = 0·9. That extracted by the normal sulfate (TOAS) and mixed TOA-TOAS also varied linearly with aw up to 0·4–0·7, then increased more steeply. The effect of hydration at saturation (aw = 1) depended on the amine salt form and concentration. There was little difference between benzene and phenylcyclohexane as diluents. In undiluted TOAS, water molarity varied linearly with aw up to aw = 0·7), but the mole fraction of water did not follow Henrys law above aw = 0·2). In this binary system, both TOAS and H2O showed negative deviations from Raoults law. Infrared absorption spectra suggest both hydrogen bonding of water to the anion and simple dissolution of unbonded water, but indicate no direct interaction between the oxygen of the water and the alkylammonium ion. Benzene solutions of other TOA salts tested extract less water than solutions of TOAS, Cl > NO3 > ClO4 > OAc. They follow Henrys law, from aw = 0 to 0·85 for the nitrate and to aw = 1 for the others.

Reference solutes for isopiestic and dynamic vapor pressure osmometry in organic solvents: Triphenylmethane, azobenzene, and benzil in dry benzene☆

Abstract The vapor pressure lowering of benzene solutions of azobenzene (AZO), triphenylmethane (TPM), and benzil (BZL) was measured at 20°C by two methods, one a direct differential measurement of the difference between vapor pressures of solution and solvent, and the other a direct measurement of the total vapor pressure of the solution. The results were cross-checked by isopiestic measurements at 25°C on the three pairs of benzene solutions, AZOTPM, AZOBZL, and TPMBZL. Each solute-benzene system shows some deviation from ideality. The osmotic coefficients are well-fitted by φ TPM = 0·9847−0·1120m TPM +0·00077 (m TPM +0·0504 φ AZO = 0·8795−0·0530m AZO +0·0520 (m AZO +0·4313 φ BZL = 0·7713−0·0112m BZL +0·1200 (m BZL +0·5247 The non-ideality of these solutions is not accounted for by regular solution theory, and only partially by assumption of association. With TPM (but not with AZO or BZL) it is well-accounted for by Guggenheims lattice model.

Phosphine oxide and quaternary ammonium extraction of americium(III) from concentrated chloride solutions

Abstract The extraction of Am(III) and Eu(III) by tri-n-octylphosphine oxide (TOPO) and methyl trialkyl(C8C10) ammonium chloride (Adogen 464) from HCl and slightly acidic LiCl solutions was investigated. Linear extraction isotherms showed that macro Eu(III) specoes exist with the same degree of assocition in both organic and aqueous phases suggesting the same behavior for the actinide analog Am(III). Reagent dependences indicated the extraction of primarily AmCl3·TOPO and AmCl3·3TOPO from 1 and 5 M LiCl, respectively, and the extraction of only R4NAmCl4 (where R4N+ is the quaternary ammonium cation of Adogen 464) from both 1 and 5 M LiCl. However, detailed studies of the TOPO-LiCl and Adogen 464-LiCl systems showed wide variations in lithium and water extraction as a function of aqueous LiCl molarity, so that these systems are not suitable for investigating the aqueous chloride complex equilibria.