Properties of fluoroantimonates(III) complexes with amino acids

Crystalline complex fluoroantimonates(III) with amino acids (glycine, β-alanine, DL-serine, DL-valine, L-leucine, and L-phenylalanine) have been prepared. The complexes stability in aqueous solutions has been studied with the cementation method. ¹H NMR studies of aqueous solutions of the amino acids complexes with SbF₃ at pH 1–6 and room temperature are reported. Preparation of polycrystalline metal antimony in aqueous solutions of tetrafluoroantimonates(III) complexes with the protonated amino acids has been demonstrated.     

The separation of aluminum(III) ions from the aqueous solution on membrane filter using Alizarin Yellow R

The membrane filtration was examined as an effective and selective method for collection of Al(III) ions from aqueous solutions using Alizarin Yellow R, one of a pH-indicator, as a precipitating reagent. For preparation of aqueous solutions without precipitate or turbidity, a non-ionic surfactant, Triton X-100, was used as a solubilizing reagent for insoluble materials. Three metal ions, Al(III), V(III) and Cu(II) ions, were able to be collected as yellow-orange precipitates from aqueous solutions controlled in a range of pH 4-7, pH 4-9, and pH 5.5-12, respectively, on a membrane filter by filtration under suction. Hydrogen peroxide and o-phenanthroline were found to be capable of masking V(III) and Cu(II) ions in a range of pH 5.5-8 in which Al(III) ions were collected. This membrane filtration was applied to selective separation and determination of Al(III) ions in tap water.     

Selective extraction of iron(III) from aqueous nitrate solution in the presence of cobalt(II), copper(II) and nickel(II) ions using bis(delta2-2-imidazolinyl)-5,5'-dioxime.

The feasibility of using bis(delta2-2-imidazolinyl)-5,5'-dioxime (H2L) for the selective extraction of iron(III) from aqueous solutions was investigated by employing an solvent-extraction technique. The extraction of iron(III) from an aqueous nitrate solution in the presence of metal ions, such as cobalt(II), copper(II) and nickel(II), was carried out using H2L in binary and multicomponent mixtures. Iron(III) extraction has been studied as a function of the pH, equilibrium time and extractant concentration. From the extracted complex species in the organic phase, iron(III) was stripped with 2 M HNO3, and later determined using atomic-absorption spectrometry. The extraction was found to significantly depend on the aqueous solution pH. The extraction of iron(III) with H2L increases with the pH value, reaching a maximum in the zone of pH 2.0, remaining constant between 2 and 3.5 and subsequently decreasing. The quantitative extraction of iron(III) with 5 x 10(-30 M H2L in toluene is observed at pH 2.0. H2L was found to react with iron(III) to form ligand complex having a composition of 1:2 (Fe:H2L).     

Extraction of group VIII elements with 1-phenyl-3-methyl-4-trifluoroacetyl-pyrazolone-5

The extraction of group VIII elements with 1-phenyl-3-methyl-4-trifluoracetyl-pyrazolone-5 from aqueous solutions in chloroform has been studied as a function of pH. Fe(III), Ni(II), Pd(II) and Rh(III) show partial extraction whereas Co(II) is extracted quantitatively. The effect of citrate, cyanide, fluoride, iodide, thiosulphate and thiourea on the extraction of metal ions has been investigated. Back-extraction studies were carried out to strip metal ions from organic phase into appropriate aqueous solutions. Based on these findings some useful analytical separations have been proposed and a few of their possible applications have been discussed.     

Selective separation and extraction of copper(II), iron(II,III), and Cerium(III,IV) ions from aqueous solutions by electroflotation method

Possibility of the electroflotation separation and extraction of cerium(II, IV), copper(II), and iron(II, III) from aqueous solutions is demonstrated. The optimal pH value and the concentration ratio of ions of the metals being separated, at which their electroflotation separation and extraction from aqueous solutions is the most efficient, was determined. It was shown that the electroflotation method is promising for selective separation and extraction of metal ions with various hydrate-formation pH values from aqueous solutions.     

Conditions for the formation of copper nanoparticles by reduction of copper(II) ions with hydrazine hydrate solutions

Optimal conditions were found for the preparation of copper nanoparticles in aqueous solution via reduction of copper(II) ions with hydrazine hydrate. The effects of ligand environment of copper(II) in the initial solution (hydrate, ammonia, citrate, and glycine complexes), concentration, pH, surfactants, temperature, and mode of heating were examined. The obtained colloidal systems were studied by optical spectroscopy, X-ray photoelectron spectroscopy, X-ray powder diffraction, and atomic force microscopy. The examined colloids were found to contain generally spherical copper nanoparticles with a diameter of about 10 nm, which were coated with a copper(I) or copper(II) oxide and hydroxide film.     

Formation of amorphous zinc citrate spheres and their conversion to crystalline ZnO nanostructures

We report a method for synthesizing zinc citrate spheres at a low temperature (90 °C) under normal atmospheric pressure. The spherical structures were amorphous and had an average diameter of ～1.7 μm. The amorphous zinc citrate spheres could be converted into crystalline ZnO nanostructures in aqueous solutions by heating at 90 °C for 1 h. By local dissolution of the zinc citrate spheres, nucleation and growth of ZnO occurred on the surfaces of the amorphous zinc citrate spheres. The morphologies and exposed crystal faces of the crystalline ZnO nanostructures (structure I: oblate spheroid; structure II: prolate spheroid; structure III: hexagonal disk; structure IV: sphere) could be controlled simply by varying the solution composition (solutions I, II, III, or IV) in which the as-prepared amorphous zinc citrate spheres were converted. The concentration of citrate anions and solution pH played a decisive role in determining the morphologies and exposed crystal faces of the crystalline ZnO nanostructures. On the basis of experimental results, we propose a plausible mechanism for the conversion of amorphous zinc citrate spheres into the variety of observed ZnO structures.     

Complexes formed in the chloroform extraction of cobalt(II) with oxine

Absorption spectra of cobalt-oxine complexes-extractedinto chloroform indicate that two cobalt(II) and one cobalt(III) complexes can be extracted depending on pH and the initial concentrations of oxine in the organic phase or cobalt(II) ion in the aqueous phase. The oxidation state of cobalt in the complexes was determined by treatment of organic extracts with an 0.001 M EDTA solution at pH 4–5; cobalt(II) complexes were back-extracted, and the cobalt(III) complex was not. The equilibrium distribution ratios of cobalt(II) between aqueous perchlorate solutions and oxine solutions in chloroform were determined at 20°. A plot of logD_co-log[HO_x]_o vs. pOx gave a single curve for different concentrations of oxine; it was concluded that cobalt(II) is extracted as C_oOx₂HOx.     

Extraction of thiocyanate complexes of cobalt(II) by diphenyl-2-pyridylmethane in benzene from mineral acid solutions

Extraction of Co(II) by diphenyl-2-pyridylmethane (DPPM) in benzene form mineral acid solutions containing potassium thiocyanate has been studied at room temperature (23±2°C). Its extraction from mineral acids alone is rather poor. Optimal aqueous phase composition for the quantitative extraction of Co(II) by 0.1M DPPM is 0.1M acid+0.2M KSCN. Stoichiometric studies indicate that an ionic type complex, (DPPM·H)₂·Co(SCN)₄, is responsible for extraction. The metal can be back-extracted from the organic phase by aqueous acetate, citrate or oxalate solutions. Separation factors from other metals determined under optimal conditions reveal that Co(II) can be quantitatively separated from CsI), Sr(II), Cr(III), Ln(III), Zr(IV), Hf(IV), Cr(VI) and Tc(VII), Mo(VI), Zn(II), Au(III), Hg(II) and U(VI) are, however, coextracted and hence should be previously removed by other techniques or reagents.     

Polymer-Enhanced Ultrafiltration of Fe(III) and Cu(II) Aqueous Solutions Using Poly(Vinyl Alcohol)-Alginic Acid/Cellulose Membranes

This study deals with the removal of Fe(III) and Cu(II) from dilute aqueous solutions using a polymer-enhanced ultrafiltration process. The ultrafiltration studies were carried out in batch stirred cell and the applied pressure was controlled by nitrogen gas. Properties of the composite membranes and its application in metal removal from aqueous solutions were studied. A composite poly(vinyl alcohol)-alginic acid/cellulose membranes were prepared by coating poly(vinyl alcohol)-alginic acid mixture solutions on the filter paper. Poly(vinyl alcohol) and alginic acid were also used as complexing agents to enhance the retention of metal ions. In the filtration of Fe(III) and Cu(II) solutions, the effects of membrane contents, pressure and pH on the retention and the flux were studied. The maximum retention of metals was found as 99% for Fe(III) solution at pressure of 45 psi, pH of 3 in the presence of poly(vinyl alcohol) as complexing agent by using 0.50 (w/v)% [(75 Poly(vinyl alcohol)/25 Alginic acid) (w/w)]/cellulose composite membranes.     

Oxygenation of Fe(II) in the presence of citrate in aqueous solutions at pH 6.0-8.0 and 25 degrees C: interpretation from an Fe(II)/citrate speciation perspective

The kinetics of Fe(II) oxidation in the presence of various citrate concentrations have been investigated in aqueous solutions over the pH range 6.0-8.0 using colorimetry and speciation modeling. Oxidation of Fe(II) was interpreted and quantitatively modeled in terms of oxidation of various Fe(II)-citrate species. Using the model, it is possible to predict whether the presence of citrate would dominate the Fe(II) oxidation and thus enhance/retard the oxidation rate of Fe(II) and vice versa. The study also supports the presence of other Fe(II)-citrate species rather than just the monomeric species at circumneutral pH. At low pH and in a system where complexation of Fe(II) by citrate is dominant, oxidation of Fe(II) is controlled by the oxidation of both Fecit- and Fecit24-. As the pH increases, the oxidation of Fe(OH)cit25- becomes increasingly important and dominates the oxidation of Fe(II) at pH 8.0. Rate constants for the oxidation of all five suggested Fe(II)-citrate species have been estimated and may be used to predict the rate of Fe(II) oxidation at any combination of pH and citrate concentration.     

Biodegradation of Eu(III)-citrate complexes by Pseudomonas fluorescens

Summary We have investigated the structure of Eu(III)-citrate complexes in aqueous solution and their degradability by Pseudomonas fluorescens. Analysis of 1:1, 1:2, and 1:5 Eu(III):citrate solutions at pH 7 by electrospray ionization mass spectrometry (ESI-MS) showed that the 2:2 Eu(III)-citrate complex is the predominant complex species at a low citrate/Eu(III) ratio, while at a high ratio, a 1:2 Eu(III)-citrate complex is formed preferably. Studies on the biodegradation of Eu(III)-citrate complex by P. fluorescens have shown that a 2:2 Eu(III)-citrate complex is resistent to degradation while a 1:2 complex transforms to a 2:2 complex with the degradation of excess citric acid.     

Photocatalytic reaction by Fe(III)–citrate complex and its effect on the photodegradation of atrazine in aqueous solution

The photodegradation of atrazine in aqueous solutions containing citrate and Fe(III) was studied under Xe lamp irradiation on a time scale of hours. It was found that the presence of Fe(III)–citrate complex enhanced the photodegradation rate of atrazine as a result of OH attack. Atrazine photodegradation followed first-order reaction kinetics and the rate depended upon pH and light intensity. High citrate concentrations led to increased photodegradation of atrazine due to the fact that citrate not only acted as a carboxylate ligand but also a reductant of Fe(III). The interaction of Fe(III) with citrate was characterized using UV–visible absorption and Fourier-transform infrared (FTIR) spectroscopy, indicating that the hydrogen ions on the carboxyl groups were exchanged for Fe(III) ions. On the basis of these results, a reaction scheme was proposed in which the cycling of iron and carbon, the depletion of citrate and O₂, and the formation of reactive oxygen species (ROS) were involved.     

Biosorption of Au (III) and Cu (II) from aqueous solution by a non-living Cetraria islandica (L.) Ach

Biosorption of Au(III) and Cu(II) from dilute aqueous solutions was investigated by biomass of the non-living Cetraria islandica (L.) Ach. The removal and recovery of gold and copper were studied by applying batch technique. The experimental parameters such as the pH of the solution, contact time, the amount of Cetraria islandica (L.) Ach. (dried lichen), the concentration of metals on retention and eluents kind and amount have been investigated. Au(III) and Cu(II) were adsorbed on the dried lichen at pH 3 and pH 8, respectively. Quantitative retention (> or = 90%) was obtained within 60 minutes for metals. Maximum capacity of 1.0 g of dried lichen for biosorption of Au(III) and Cu(II) were found as 7.4 mg of Au(III) and 19.2 mg of Cu(II). It was seen that the adsorption equilibrium data conformed well to the Langmuir model and Freundlich equation for Au(III) and only Freundlich equation for Cu(II). The method proposed in this study was applied to spiked mineral water analysis and metals adsorbed on the lichens were quantitatively (> or = 90%) recovered from mineral water samples by using 0.5 mol L(-1) HCl.     

Influence of tartrate ions on the coprecipitation of some trace metal inner complex compounds with bis(8-quinolyl)disulphide

The coprecipitation of Fe(III) quinoline-8-thiolate (QT) with bis (8-quinolyl) disulphide has been investigated with 1 mol × dm^–3 potassium tartrate and 0.001 mol × dm^–3 aqueous tartaric acid solutions in dependence on their pH. In return QTs of Cu(II), Cd(II) and Hg(II) have been coprecipitated from 0.2, 0.1, 0.01 and 0.001 mol × dm^–3 aqueous solutions of tartaric acid after adjusting the pH to 6–7. These tartaric acid concentrations relate to their initial concentrations before the coprecipitation. The presence of tartrate ions influences the recovery of the coprecipitated Fe(III), Cd(II) and Hg(II) QTs. A complete coprecipitation of the Cu(II) inner complex compound can be achieved from the aqueous solutions indicated.     

Some synthesized polymeric composite resins for the removal of Co(II) and Eu(III) from aqueous solutions

Summary The ion-exchange and sorption characteristics of new polymeric composite resins, prepared by gamma radiation were experimentally studied. The composite resins show high uptake for Co(II) and Eu(III) ions in aqueous solutions in a wide range of pH. The selectivity of the resins for Co(II) or Eu(III) species in presence of some competing ions and complexing agents (as Na⁺, Fe³⁺, EDTANa₂, etc.) was compared. Various factors that could affect the sorption behavior of metal ions (Co(II) and Eu(III)) on the prepared polymeric composite resins were studied such as ionic strength, contact time, volume mass ratio.     

Effect of Pyruvate on the Redox Behavior of the Iron (III)-(II) Couple

Abstract

Evidence for the formation of Fe(III) and Fe(II) complexes with pyruvate ion is presented. Complexes with a 1:2 ratio of Fe(II) to pyruvate and 1:1 ratio of Fe(III) to pyruvate were identified by spectrophotometry. The complexation results in partial kinetic control of the electrochemical oxidation of Fe(II) in citrate buffer. In addition, Fe(III) was found to be chemically reduced by pyruvate. The apparent first order rate constant at 25[ddot]C is 7.12 × 10^?2 s ^?1in pH 4.0 pyruvate buffer and 1.24 × 10^?1 s ^?1 in pH 3.2 pyruvate buffer. In pH 4.0 citrate buffer the reaction is not first order and is significantly slower.     

Extraction behavior of Tm(III), Dy(III) and Sm(III) lanthanide with N-benzoyl-N-phenylhydroxalamine

The extraction of Sm(III), Dy(III) and Tm(III) with N-benzoyl-N-phenylhydroxalamine (BPHA) in benzene at pH range (1–10) has been studied. Quantitative separation was found in borate media at pH 8. The slope analysis showed that the extracted complex was M(BPHA)₃, where M=Sm(III), Dy(III) and Tm(III). The effect of various masking agents indicated that EDTA, oxalate, fluoride, phosphate and citrate, interfered in this study. Decontamination study showed that Cu(II), Zn(II), Ni(II), Co(II), Cr(III), Sc(III) and Fe(III) had very poor separation factors, whereas Sn(II), Cd(II), In(III), Ru(II), Hg(II), Ag(I), Ta(V) and Hf(IV) had very large separation factor. The effect of different diluents showed that carbontetrachloride, chloroform, benzene, toluene, nitrobenzene dichloromethane, MIBK and cyclohexanone were equally good for extraction except TBP due to ion association.     

Sorption of small amounts of cobalt(II) on iron(III) oxide

Summary The sorption of small amounts of cobalt(II) on iron (III) oxide has been studied as a function of pH. The mechanism of sorption is discussed. Iron (III) oxide carrier can be used for the preconcentration of small or trace amounts of cobalt(II). The influence of EDTA, glycine,L(+)-arginine andL(+)-cysteine on the sorption yields of cobalt(II) has also been studied.

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Zusammenfassung Die Abhängigkeit der Adsorption geringer Mengen Co (II) an Eisen (III)-hydroxid vom pH wurde untersucht und der Mechanismus der Adsorption erörtert. Eisen (III) oxidträger kann für die Anreicherung kleiner Mengen oder Spuren Co(II) verwendet werden. Der Einfluß von ÄDTA, Glycin, L(+)-Arginin und L(+)-Cystein auf die sorbierte Menge Co(II) wurde gleichfalls geprüft.