Correlation of the extraction constants of the system Cd(II)–H3PO4/Cyanex 302–kerosene at different ionic strengths

Bromley's theory for calculating activity coefficients in order to correlate the values of cadmium extraction constant by Cyanex 302 from phosphoric acid solutions at different ionic strengths has been applied. A chemical model for the aqueous phase including the species H₃PO₄, H₂PO₄⁻, H₅P₂O₈⁻, H₆P₂O₈, CdHPO₄ and CdH₂PO₄⁺ has been considered. The increase observed for the extraction constant value when increasing the phosphoric acid concentration is probably due to the significant increase of the cadmium activity coefficient. A reaction extraction including water as a component has been proposed, and the value of the thermodynamic extraction constant of log K⁰=7.02 for the formation of CdR₂(HR) species, HR being the major component of Cyanex 302, has been obtained.     

Correlation of the extraction constant values of Cu(II) by 5-dodecylsalicylaldoxime from phosphoric acid media

The equilibrium constant values of copper(II) extraction from phosphoric acid media by LIX 622 (67.7% 5-dodecylsalicylaldoxime, Cognis Ireland) taking into account the formation in the organic phase of the complex CuL₂, HL being 5-dodecylsalicylaldoxime, at different ionic strengths have been calculated. Elmore's model has been considered for the speciation of the aqueous phase. A new approach for the calculation of the activity coefficient of H₂PO₄⁻ has also been proposed. The extraction equilibrium constant values obtained at the different ionic strengths have been successfully correlated considering the activity coefficients of the species in solution as well as the release of water molecules in the extraction process. The extraction constant value at infinite dilution of the complex CuL₂ is also reported.     

Extraction of sulfuric acid with TOPO

A study on solvent extraction of sulfuric acid by tri-octylphosphine oxide (TOPO) in n-heptane has been made. Extraction coefficients of H₂SO₄ as a function of H₂SO₄ concentration in aqueous phase, and extractant concentrations in organic phase have been studied. The composition of extracted species, equilibrium constants of extraction reaction have been evaluated. These results are important for interpreting extraction equilibrium data of uranium(VI) or other metal ions with TOPO in sulfuric acid media.     

LIX 84 as an extractant for throium(IV), uranium(VI) and molybdenum(VI)

The extraction order of Th(IV), U(VI) and Mo(VI) based on pH_0.5 values is Mo(VI)>U(VI)>Th(IV). Quantitative extraction has been observed for U(VI) by mixture of 10% (v/v) LIX 84 and 0.1M dibenzoylmethane at pH 4.2 and by mixture of 10% LIX 84 and 0.05M HTTA in the pH range 5.5–7.3 and for Mo(VI) by 10% LIX 84 from chloride media at pH 1.5. The order of extraction of Mo(VI) from 1N acid solutions is HCl>H₂SO₄>HNO₃>HClO₄ and extraction decreases very rapidly with increase in the concentration of HCl as compared to that from H₂SO₄, HNO₃ and HClO₄ acid solutions. The diluents C₆H₆, CCl₄ and CHCl₂ are found to be superior ton-butyl alcohol and isoamyl alcohol for extraction of Mo(VI). Influence of concentration of different anions on the extraction of U(VI) and Mo(VI) has been studied. Very little extraction has been observed in case of Th(IV) by LIX 84 or its mixtures with other chelating extractants or neutral donors.     

Extraction with benzene and its derivatives

The extractability of selenium halides with benzene and some of its derivatives has been investigated using a radioactive tracer technique in order to establish the optimum conditions for its extraction. It has been found that Se(IV) is poorly extracted from HCl, HBr or H₂SO₄ solutions but high distribution ratios are observed with binary mixtures of 9M H₂SO₄ and acid halides. The extraction of some other elements is also studied under the conditions selected for Se(IV) extraction and it has been found that only antimony follows Se(IV) in the organic phase. In view of the data obtained, analytical advantages are mentioned and separation procedures are recommended. The extraction mechanism is also discussed and the role of sulfuric acid in the extraction system is explained.     

Rhenium(VII) extraction with Versatic hydrazides and <Emphasis Type="Italic">N',N'</Emphasis>-Dialkylhydrazides

Rhenium(VII) and molybdenum(VI) extraction with kerosene solutions of α-branched tertiary carboxylic Versatic acids derivatives containing hydrazide C(O)NHNH2 and C(O)NHNCH₃)₂ fragments instead of carboxyl group has been studied. Optimal extraction conditions have been determined depending on H₂SO₄, HCl, and extractant concentrations and composition of extracted complexes has been established. The mechanism of extraction and back extraction of perrhenate ion with ammonia solutions has been suggested.     

Screening, optimization and validation of microwave-assisted extraction for the determination of persistent organochlorine pesticides

In the present study, a microwave-assisted extraction method has been investigated for the extraction of persistent organochlorine pesticides from sediment in comparison to the classical Soxhlet extraction. The extraction procedure has been screened by a complete factorial design for statistically significant parameters. Thereafter, the identified parameters, composition of extraction solvent (mixtures of n-hexane-acetone), extraction temperature and time were optimized by a Box-Behnken design. Finally, the optimized microwave-assisted procedure has been validated by extraction of two different matrix reference materials, a sediment and a mallow powder. The data obtained for both materials were in good agreement with those obtained by Soxhlet extraction and published values. Special emphasis has been given to an accurate determination of p,p′-DDT, since DDT is known as instable during GC-injection. In order to evaluate the DDT-degradation, ¹³C₁₂-p,p′-DDT-solutions were analyzed and the degradation rates during GC-injection were calculated. Furthermore, ¹³C₁₂-p,p′-DDT was added to the sediment samples prior to extraction and the degradation rates during the optimization experiment have been investigated.     

Composition of extraction products from alkylated high-sulphur coals

Products of reductive and non-reductive methylation of two high-sulphur coals (Mequinenza and Illinois No. 6) have been extracted by dichloromethane. It has been established that the efficiency of the transformation of coal to the products soluble in CH₂Cl₂ is higher for coals subjected to non-reductive methylation by the Liotta method than for those after reduction in the potassium/liquid ammonia system. The extracts and the extraction residues were subjected to elemental analysis, IR spectroscopy, and AP-TPR (Atmospheric Pressure-Temperature Programmed Reduction) measurements. It has been shown that the main species undergoing extraction by CH₂Cl₂ are aliphatic compounds or aromatic structures of low degree of condensation. The effect of the extraction on the sulphur groups in coal has been discussed.     

The extraction of iron(III) by dioctylarsinic acid in chloroform

Dioctylarsinic acid, HDOAA, in chloroform solution has been investigated as a reagent for the extraction of iron(III) chloride. The extraction coefficient reaches two maxima, one of 1.5 at 8.5 M hydrochloric acid and another of 7 at pH 2.3. Experiments in the range 4–8 M for sulfuric, nitric and perchloric acids showed no extraction of iron(III) from these solutions for extraction times of 6 h. Evidence for the extraction of H₃FeCl₆ from 4–9 M hydrochloric acid solutions as [(H₂DOAA)⁺]₃FeCl₆^3- is presented. The species extracted from aqueous solutions of pH 1–2.3 is probably a hydroxy complex of the composition [Fe₂(DOAA)₂(HDOAA)X₄(H₂0)₂ ](X = OH and/or Cl).     

Extraction of Ce(III), Gd(III) and Yb(III) from Citrate Medium by High Molecular Weight Amines

Abstract

High molecular weight amines have been used for the extraction of citrate complexes of Ce(III), Gd(III) and Yb(III). The effect of different variables on extraction has been studied. The citrate species extracted in the organic phase have been proposed as [(RNH₃ ⁺)₃] [M(Cit)₂]^3-.     

Extraction of uranium(VI) through reversed micelle by primary amine N1923

A study on extraction of uranium(VI) from sulfuric acid media by the primary amine N₁₉₂₃ in chloroform is described. Extraction coefficients of uranium(VI) as a function of aqueous H₂SO₄ concentration, extractant concentration and temperature have been studied. From the data, the compositions of extracted species, equilibrium constants and enthalpies of extraction reaction have been evaluated. A new extraction mechanism of amine has been suggested, that is the formation of reversed micelle as a result of the aggregation of ammonium salt in the organic phase of the extraction. This assumption may be used for interpreting extraction data satisfactorily, which can not be explained by the slope analysis method.     

Extraction of Zr(IV) by TBP-DMSO and TBP-Py from aqueous solutions containing monobasic acids

The distribution ratios for the extraction of Zr(IV) by TBP and its binary mixtures with DMSO or Py in n-dodecane in the presence of HNO₃, and HClO₄ have been determined. Based on stoichiometric and slope analysis methods a possible mechanism for the extraction has been proposed.     

Solvent extraction studies on tetravalent selenium

A systematic study has been carried out on the extraction of SeI₄, by various water-immiscible organic solvents. Extraction has been investigated as a function of H₂SO₄ and Kl concentrations. It has been found that Se(IV) extraction is appreciably increased by addition of iodide ion to sulfuric acid solutions. On the other hand, the presence of water-miscible alcohols and acetone was found to enhance Se(IV) extraction from H₂SO₄–Kl solutions. In the light of the results, an extraction mechanism is suggested.     

Synergistic extraction of uranium from acidic sulfate leach liquor using D2EHPA mixed with TOPO

Uranium extraction from sulfate leach liquor acid by D₂EHPA and TOPO mixture in kerosene was investigated. The effect of different factors affecting the extraction mechanism such as sulfate leach liquor acid, D₂EHPA and TOPO concentrations and temperature have been studied. The mathematical treatment for the obtained date suggested that the composition of synergistic extraction species is (UO₂(D)₂T). The logarithm of the apparent equilibrium constant, log Kex, of synergistic extraction reaction has been evaluated, to be 3.35 ± 0.1. The effect of temperature on extraction process was investigated and the apparent values of the thermodynamics parameters (?H, ?G and ?S) were 38.2 kJ/mol, ?19.1 kJ/mol and 192.5 J/mol respectively.     

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.     

Selective extraction of Hg(II) from aqueous mineral acid solution containing iodide ions using 2-benzylpyridine in benzene

A method for the selective extraction of mercury has been developed. The extraction of Hg(II) by 2-benzylpyridine (BPy) in benzene from dilute mineral acid solution containing iodide ions has been investigated, and variables such as concentration of acids, iodide and the extractant have been optimized. The optimum conditions for the extraction of Hg(II) by 0.1M BPy/benzene are: 0.01M (HCl, HNO₃, H₂SO₄)+0.01M KI. The distribution coefficients and separation factors of 19 elements relative to Hg(II), have been reported. Effect of anions such as ascorbate, acetate, citrate, oxalate and thiosulfate has also been studied. The method developed could find useful applications in selective extraction of small amounts of mercury from environmental samples.     

Extraction of micro- and macroconcentrations of rare earth ions with the mixture of D2EHPA and TBP in n-hexane and cyclohexane

The synergistic solvent extraction of Eu(III) and some other rare earth elements from nitrate solutions (HNO₃+LiNO₃) by a mixture of (TBP+D2EHPA) in n-hexane and cyclohexane has been investigated at 22 °C. Antagonism found in europium extraction from 0.1M HNO₃ transforms into a synergistic effect. The synergistic effects existing for all investigated metals in extraction from 0.1M HNO₃+3M LiNO₃ were caused by formation of mixed complexes of the type Ln(D2EHPA)_2nH_2n–3+1(NO₃)₁TBP_m, where 1=1 or 2. The selectivity of the extraction in a synergistic system is lower for the La–Yb pair than in the case of D2EHPA extraction under the same conditions. On the other hand, the application of the synergistic mixture is more suitable for Eu–Ho separation. Thus the synergistic effect can be used for the separation or refining of some lanthanides.     

Synergic extraction of divalent iron,cobalt, copper and zinc with thenoyltrifluoroacetone-dibenzylamine in chloroform

The solvent extraction of divalent iron, cobalt, copper and zinc from perchlorate medium of constant ionic strength (0.1 H⁺, NaClO₄) into a mixture of thenoyltrifluoroacetone (HTTA) and dibenzylamine (DBA) in chloroform has been studied. The extraction of the different cations were found to increase by more than 10³ order of magnitude in presence of DBA. Slope analysis of the extraction results assumed a general formula of M(TTA)₂·DBA for the extractable adduct. A stability order of Fe(TTA)₂·DBA>Co(TTA)₂ ·DBA>Zn(TTA)₂·DBA>Cu(TTA)₂·DBA has been decumented.     

Extraction of copper(II) ions from ammonia solutions with a β-diketone extractant

The extraction of copper(II) ions from ammonia solutions with a new β-diketone extractant, DX-510A, has been studied. Kinetic features of the copper(II) extraction and back extraction have been established: the reaction orders have been determined, and extraction and stripping rate constants have been calculated to be k_e1 = 4.14 × 10^–2 s^–1 and k_be1 = 3.20 × 10^–2 s^–1, respectively. It has been demonstrated that the extraction of copper(II) ions is not accompanied by the coextraction of ammonia. The type of extracted complex has been determined and its formula has been suggested.     

Investigations on the use of 4-(5-Nonyl) pyridine as an extractant for chlorocomplexes of gallium(III)

A study of the distribution of gallium(III) between hydrochloric acid solutions and 0.1M 4-(5-nonyl)-pyridine in benzene has been undertaken. Gallium can be quantitatively extracted from moderate to concentrated acid solutions and also from dilute acid solutions containing high concentrations of neutral cations of high charge density. The effects of acidity, the solvent concentration and diverse ions on the extraction have been investigated. An attempt has been made to elucidate the stoichiometry of the extracted species. The formulation of (NP_y H)⁺ GaCl ₄ ⁻ ) and (NP_y−H−NP_y)⁺ GaCl ₄ ⁻ is expected at macro and trace concentrations of the metal. The extraction coefficients of several elements have been recorded under conditions optional for the extraction of gallium; and their factors for separations are estimated.