Solvent extraction of chromium(VI) from base metal ions with diphenyl-2-pyridylmethane as a liquid anion exchanger

The extraction of chromium(VI) from aqueous hydrochloric, nitric and sulfuric acid solutions by diphenyl-2-pyridylmethane(DPPM) dissolved in chloroform has been studied. Chromium(VI) is quantitatively extracted from hydrochloric acid solutions in the range 0.1–1M. With increasing acid concentration, the extraction of chromium diminishes and in concentrated acid solutions practically all the chromium remains in the aqueous phase. The quantitative back-extraction of chromium from the organic phase is possible with HCl or HNO₃ at concentrations higher than 5M through the use of reducing agents. The composition of the extracted chromium(VI) species was studied in solution. The complexes (DPPMH)⁺HCrO ₄ ⁻ and (DPPMH)₂Cr₂O ₇ ⁻ are extracted for tracer and macro amounts of chromium(VI) respectively. The data have been utilized for the separation of chromium(VI) from base metal ions.     

Extraction of iron(III) with diphenyl-2-pyridylmethane dissolved in benzene from aqueous chloride solutions

The mechanism of extraction has been investigated by partition, slope analysis and loading-ratio data. The results obtained give a picture of the mechanism of extraction of FeCl ₄ ⁻ ions in relation to the hydration and solvation of the compound extracted. The possible formula of the extracted species is (DPPM)₃H₃O⁺(H₂O)_n−FeCl ₄ ⁻ . In dilute aqueous hydrochloric acid systems the influence of the concentration of a number of salts with cations of different electrical potentials (Ze/r), on iron(III) extraction, has been studied. Splitting of the organic phases occurs at high acid and/or high salt concentrations. The phenomenon is explained on the basis of the variability of the hydration number. Investigations have been made to understand the parameters controlling the extraction of the metal and its is shown that the extraction offers a simple, fast and selective separation method of iron from solutions.     

Liquid-liquid extraction of protactinium(V) using tri-iso-octylamine

Solvent extraction of protactinium with tri-iso-octyl-amine (TIOA) in xylene, benzene, carbon tetrachloride and chloroform from HCl, HF, HNO₃, HClO₄ and H₂SO₄ media was studied using ²³³Pa as a radiotracer. The extraction efficiencies of protactinium were determined as a function of shaking time, concentrations of mineral acids in aqueous phase, extractant concentrations and diluents in organic phase. The extraction mechanism was discussed. The results show that the extracted species in the organic phase is [(R₃N⁻H)_nPa(OH)_xCl _y ^5−x−y ].     

The extraction of Cr(III) from aqueous thiocyanate solutions and its separation from Co(II) and Ni(II)

For the system liquid anion-exchanger—Cr(III)−NCS⁻, an investigation has been made of the dependence of the percentage extraction of Cr(III) on parameters such as standing time of the Cr(III)−NCS⁻ solution, temperature, pH and type of exchanger. Quantitative extraction of e.g. 4·10⁻⁴ M Cr(III) by 0.1M Aliquat in CCl₄ is easily achieved at room temperature, using 4.75M KNCS−0.05N HCl as aqueous phase. At high Cr(III) concentrations, the complex anion present in the organic phase is Cr(NCS) ₆ ³⁻ ; when working with dilute metal ion solutions, the species extracted is Cr(NCS)₄ (H₂O) ₂ ⁻ . Separations of mixtures containing 10⁻²−10⁻⁴ M Co(II), Ni(II) and Cr(III) have successfully been accomplished.     

Selective solvent extraction of chromium(VI) using 2-hexylpyridine

The extraction behaviour of trace and macroamounts of chromium(VI) from different mineral acid solutions by 2-hexylpyridine in chloroform has been investigated. In the chloride system, the extracted species is apparently (HPyH⁺)₂ (Cr₂O₇)²⁻ or HPy⁺(HCrO ₄ ⁻ ) for macro and trace amounts of chromium(VI), respectively. Among the common anions chloride and sulphate have little effect on extraction up to 1M concentration, while in the case of nitrate there is a continuous decrease in the extraction with the increase of salt concentration in the aqueous phase. The effect of ascorbate, acetate, citrate, oxalate, thiosulphate, thiocyanate ions on the extraction from 1M HCl was also examined. Separation factors of several elements relative to chromium(VI) have been described and the separation of chromium(IV) from a large number of elements has been achieved.     

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.     

Extraction-spectrophotometric investigations on two ternary ion-association complexes of gallium(III)

Complex formation and liquid-liquid extraction were studied in systems containing Ga(III), azoderivative of resorcinol {4-(2-pyridylazo)resorcinol (PAR) or 4-(2-thiazolylazo)resorcinol (TAR)}, 2,3,5-triphenyltetrazolium chloride (TTC), water and chloroform. The optimum conditions w.r.t. pH, extraction time, concentration of ADR and concentration of TTC for the extraction of Ga(III) as an ion-associate complex were found.. The composition of the extracted complexes, (TT⁺)[Ga(PAR)₂] (I), (TT⁺)[Ga(TAR)₂] (II) or (TT⁺)₂[Ga(OH)(TAR)₂] (III), and the constants of association (β) between 2,3,5-triphenyltetrazolium cation (TT⁺) with corresponding anionic chelates were established by several methods. The constants of distribution (K_D) and extraction (K_ex) of the principal species I and III were determined as well. The apparent molar absorptivities of the chloroform extract at the optimum extraction-spectrophotometric conditions were ɛ′₅₁₀=9.5×10⁴ L mol⁻¹ cm⁻¹ (I) and ɛ′₅₃₀=4.6×10⁴ L mol⁻¹ cm⁻¹ (III). The validity of Beer’s law was checked and analytical characteristics that were calculated are reported herein.      

Extraction of HCl,HBr, HNO3, HClO4, H2SO4 and CH3COOH by 4-(5-Nonyl)pyridine and 2-hexylpyridine in benzene and determination of their pKBH+ values

The extraction of HCl, HBr, HNO₃, HClO₄, H₂SO₄ and CH₃COOH into solutions of 4-(5-nonyl)pyridine (NPy) and 2-hexylpyridine (HPy) dissolved in benzene has been studied. The results show that the larger, less basic anions extract better (ClO ₄ ⁻ >CH₃COO⁻≥NO ₃ ⁻ >Br⁻>Cl⁻>HSO ₄ ⁻ ) due to their low aqueous hydration. The ionization constants of NPyH⁺ and HPyH⁺ as determined spectrophotometrically were found to be 5.97±0.06 and 5.94±0.05, respectively, at 25°C.     

Extraction of rhodium(III) with sulfoxides from hydrochloric acid solutions

Extraction of rhodium(III) from hydrochloric acid solutions with dihexyl sulfoxide (DHSO) and with petroleum sulfoxides (PSOs) was studied, and the optimal conditions for its recovery were found. At a phase contact time of up to 0.5 h, the extraction of rhodium(III) with sulfoxides occurred mainly by an ionassociation scenario. If the phase contact time exceeds 0.5 h, a mixed extraction scenario predominated to form the extracted complexes (L · H⁺) · [RhCl₄L₂]-(DHSO)_o and PSO (LH⁺) · [RhCl₄(H₂O) · L]⁻. The protonation of the extraction agents occurred at the donor oxygen atoms of the sulfoxide group. When rhodium was extracted with PSOs, the coordination of the extractant molecule in the inner coordination sphere of the acido complex to the metal ion occurred through the donor sulfur atom of the sulfoxide group, while with the use of DHSO, through the donor atoms of sulfur and oxygen of the sulfoxide group. Electronic, ¹H NMR, and IR spectroscopy and elemental analysis were used to determine the composition of the extracted compounds and suggest their structure.     

Separation of Tc(VII) from Tc(IV) by solvent extraction

The solvent extraction of Tc(IV) and Tc(VII) by isoamyl alcohol has been studied. The TcCl ₆ ²⁻ and TcO ₄ ⁻ ions are both extracted from 3M H₂SO₄ solution but hydrolyzed Tc(IV) species are not. This permits the separation of the two valence states of technetium. The air oxidation of carrier-free hydrolyzed^99mTc(IV) may be limited by the presence of⁹⁹Tc carrier in the same chemical form. Paper chromatography and electrophoresis were used to identify TcCl ₆ ²⁻ , TcO ₄ ⁻ and hydrolyzed species. It was also found that the hydrolyzed ReCl ₆ ²⁻ can reduce TcO ₄ ⁻ to Tc(IV).     

Solvent extraction of zirconium from hydrochloric acid solutions by sulphoxides and their mixtures

The solvent extraction of zirconium from HCl solutions by dipentyl sulphoxide (DPSO), dioctyl sulphoxide (DOSO), tributyl phosphate (TBP), and their mixtures in various solvents has been studied. At a given H⁺ strength, the extraction coefficient η of the metal increases with an increase in Cl⁻ activity whereas it is almost independent of H⁺ at constant Cl⁻. Under otherwise identical conditions, η increases with an increase in the extractant concentration but is virtually independent of the metal ion concentration over a wide range. The species extracted are ZrCl₄·DPSO, ZrCl₄·DOSO, and ZrCl₄·2TBP. In the case of mixtures, the slope of the log η−log M extractant plot for one component decreases with an increase in the concentration of the second component, the lines crossing at a common point. Extraction is favoured by solvents of low dielectric constant. It is possible to separate zirconium from thorium and uranium by solvent extraction with sulphoxides.     

Solvent extraction of uranium(VI) by p-tert-butylcalix[n]-arene acetate

The solvent extraction of U(VI) by p-tert-butylcalix[n]-arene acetate (H _n L) (n=4, 6, 8) has been studied. The effects of acidity in aqueous phase and concentration of extractant in organic phase on the distribution ratio were examined. It has been found that the distribution ratio is proportional to [H⁺]⁻² and [H _n L]_(O) and the extracted complex species is UO₂H _n ⁻²L. The equilibrium constants of the extraction reactions have been determined. The reaction mechanism is discussed.     

Extraction of pertechnetate with tetraphenylphosphonium in the presence of various acids, salts and hydroxides

Solvent extraction of pertechnetate anions from aqueous solutions of some mineral acids (HCl, HNO₃, HClO₄, H₂SO₄), (NaCl, NaNO₃, NaClO₄, K₂CrO₄, NaCO₃), NaOH and NH₄OH by tetraphenylphosphonium chloride in chloroform and nitrobenzene was studied. The results are presented in the form of the dependencies of extraction characteristics of TcO ₄ ⁻ (distribution ratio, percentage of extraction) on the (C₆H₅)₄PCl, H⁺ and competitive anion concentrations. The solvent extraction of sub-and super-stoichiometric ratio of TcO ₄ ⁻ : (C₆H₅)₄P⁺ was performed. The extraction constant values of ion pairs TcO ₄ ⁻ −Cl⁻, TcO ₄ ⁻ −NO ₃ ⁻ , TcO ₄ ⁻ −ClO ₄ ⁻ and of individual anions TcO ₄ ⁻ , Cl⁻, NO ₃ ⁻ , ClO ₄ ⁻ were calculated.     

Determination of stability constants of U(VI), Np(VI) and Pu(VI) with chloride ions by extraction chromatography

The complex formation of U(VI), Np(VI) and Pu(VI) with chloride ions was studied in HClO₄−HCl solutions at ionic strength of 2.0 and [H⁺]=2.0M by the method of extraction chromatography using dilute HDEHP as the stationary phase.     

Ternary ion-association complexes between the indium(III) - 4-(2-pyridylazo)resorcinol anionic chelate and some tetrazolium cations

Complex formation and liquid-liquid extraction were studied in systems containing indium(III), 4-(2-pyridylazo)resorcinol (PAR), tetrazolium salt (TZS), water and chloroform. Two different TZS were used: 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT). The optimum conditions for extraction of In(III) as a ternary complex, (TT⁺)[In(PAR)₂] or (MTT⁺)[In(PAR)₂], were found: pH, extraction time, concentration of PAR and concentration of TZS. The constants of extraction (K_ex), constants of association (β), constants of distribution (K_D) and recovery factors (R%) were determined. The apparent molar absorptivities in chloroform were calculated to be ɛ′₅₂₀=6.6×10⁴ L mol⁻¹ cm⁻¹ and ɛ′₅₁₅=7.1×10⁴ L mol⁻¹ cm⁻¹ for the systems with TTC (I) and MTT (II), respectively. Beer’s law was obeyed for In(III) concentrations up to 3.4 μg mL⁻¹ in both the cases. The limits of detection (LOD=0.07 μg mL⁻¹ I and LOD=0.12 μg mL⁻¹ II), limits of quantification (LOQ=0.24 μg mL⁻¹ I and LOQ=0.41 μg mL⁻¹ II) and Sandell’s sensitivities (SS) were estimated as well.      

Solubility of neptunium oxide in the KURT (KAERI Underground Research Tunnel) groundwater

The solubilities of NpO₂(s) in the KURT (KAERI Underground Research Tunnel) granitic groundwater with low ionic strength were measured experimentally and calculated by a geochemical code. Then these results were compared with each other as well as with foreign results. The concentrations of neptunium were measured as 6·10⁻⁸−2·10⁻⁸ mol/L at a pH = 9.5–11.1 and Eh = −0.2 V, and less than 5·10⁻⁹ mol/L at a pH = 11.8–13.0 and Eh = −0.3–0.44 V. The dominant aqueous species were presumed as Np(OH)_x(CO₃)_y ^4−x−2y complexes and Np(OH)₄(aq) at pH = 9.5–13 under the Eh<−0.2 V reducing condition.     

Kinetic studies on H+-catalysed aquation of some chromium(III)-oxalato-amino acid complexes

The following chromium(III) complexes with serine (Ser) and aspartic acid (Asp) were obtained and characterized in solution: [Cr(ox)₂(Aa)]²⁻ (where Aa = Ser or Asp), [Cr(AspH₋₁)₂]⁻ and [Cr(ox)(Ser)₂]⁻. In acidic solutions, [Cr(ox)₂(Aa)]²⁻ undergoes acid-catalysed aquation to cis-[Cr(ox)₂(H₂O)₂]⁻ and the appropriate amino acid. [Cr(ox)(Ser)₂]⁻ undergoes consecutive acid-catalysed Ser liberation to give [Cr(ox)(H₂O)₄]⁺, and the [Cr(Asp)₂]⁻ ion is converted into [Cr(Asp)(H₂O)₄]²⁺. Kinetics of these reactions were studied under isolation conditions. The determined rate expressions for all the reactions are of the form: k _obs = a + b[H⁺]. Reaction mechanisms are proposed, and the meaning of the determined parameters has been established. Evidence for the formation of an intermediate with O-monodentate amino acid is given. The effect of the R-substituent at the α-carbon atom of the amino acid on the complex reactivity is discussed.     

Solvent extraction of cobalt(II), zinc(II) and europium(III) with 4-thiobenzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one (SBMPP)

Solvent extraction of⁶⁵zinc,⁶⁰cobalt and^152+154europium from aqueous buffers into benzene containing 4-thiobenzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one (SBMPP) has been investigated in detail (μ=0.1, T=26±1°C). The species extracted and the values of log K_ex, where K_ex refers to the extraction equilibrium, are ZnL₂ (−2.68) CoL₂(−3.08) and EuL₃(−7.08), where L is the anion of the ligand. The sulfur analog appears to be more effective than the parent ligand 4-benzoyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-one in the extraction of zinc(II) and cobalt(II), whereas the reverse is true with europium(III).     

Extraction of pertechnetate anion as a ligand in metal complexes with tributylphosphate

The extraction of the pertechnetate anion has been investigated in the systems tributylphosphate (TBP)—solvent (carbon tetrachloride, n-heptane, chloroform)—metal salt (uranyl nitrate and chloride, thorium nitrate)—ammonium salt. In the absence of a metal, the solvates HTeO₄. iTBP (i=4) are extracted, while in the presence of uranium and thorium, the distribution of technetium corresponds to the formation of the mixed complexes: UO₂(NO₃)(TeO₄)·2TBP, UO₂Cl(TcO₄)·2TBP and Th(NO₃)₃ (TcO₁)·2TBP. The effective constants of the reactions H⁺+TcO ₄ ⁻ +i(TBP)_org←(HTcO₁·iTBP)_org, and (ML_n·2TBP)_org+TcO ₄ ⁻ ←(ML_n−1TcO₄·2TBP)_org+L were established in the above systems. The extraction of pertechnetate ion is more effective when it is coordinated to a cation solvated by TBP than the extraction in the form of pertechnetate acid solvated by TBP.     

Extraction of Pd(II) by some petrochemical products from nitrate media

Liquid-liquid extraction of divalent palladium by solutions of Diesel oil (D.O.) and gas oil II (G.O.II) in benzene and lacquer petroleum from nitrate media has been studied. Palladium in concentrations of ∼10⁻³M is very effectively extracted by dilute solutions of extraction reagents and the distribution of palladium is almost independent of the acidity and nitrate concentration of the aqueous phase. Of other common salts, chlorides, thioeyanates and nitrites affect the palladium distribution. In many cases high concentrations of salts completely suppress the extraction of palladium. The rate of palladium extraction by dilute solutions of extractants is relatively small. Some substances such as dimethyl sulfoxide (DMSO) were found to accelerate the extraction. Palladium extraction from nitric acid media also has been studied from the points of view of chemical and radiation stability. Diesel oil was found to be a more stable extraction reagent in acid media than gas oil II.