Trace metal recovery and concentration using ferrites

Ferrites have been used to separate a wide range of substances such as dissolved metal species, particulate matter, and organic and biological materials; they have been used almost exclusively for metal waste treatment applications. However, ferrites can be used to remove and concentrate selected trace metals in a wide variety of feed solutions requiring analysis. A brief overview of ferrite properties and recent applications for trace metal recovery and concentration will be presented.     

Stereospecific incorporation of 13CO into olefinic substituted metal carbonyl compounds

The triene complex, (bicyclo[6.1.0] nona-2,4,6-triene)molybdenum tricarbonyl, has been observed to react with ¹³CO in solution to afford stereospecifically the axially labelled ¹³CO tetracarbonyl derivative. Further reactions of this ¹³CO derivative with triphenylphosphine or bis(1,2-diphenylphosphino)ethane resulted in formation of the cis disubstituted phosphine derivatives with retention of the ¹³CO label.     

Determination of ferrous ion in microsamples of hexagonal ferrites

Summary A sensitive and accurate method is described for determining microgram amounts of ferrous iron associated with a large excess of ferric iron and various bivalent cations, in hexagonal ferrites. Ferrous iron is complexed with bathophenanthroline, extracted into a chloroform-ethanol mixture and spectrophotometrically measured at 540 nm against a 13 v/v chloroform-ethanol mixture. Ferric iron is masked with ammonium dihydrogen phosphate. The analytical conditions are stated for determination of iron(II) in both solvents used for ferrites, viz., hydrochloric and phosphoric acids. Cobalt, copper, and nickel do not interfere if the procedures suggested are used. Ferrous iron down to 0.02% can be determined in samples weighing only a few milligrams.

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Zusammenfassung Eine empfindliche und genaue Methode zur Bestimmung von Mikrogrammengen Eisen(II) in Gegenwart eines großen Überschusses von Eisen(III) und verschiedener zweiwertiger Kationen in hexagonalen Ferriten wurde beschrieben. Eisen(II) wird mit Bathophenanthrolin komplex gebunden, mit einer Chloroform-Äthanol-Mischung extrahiert und bei 540 nm gegen eine Chloroform-Äthanol-Mischung (13 v/v) spektrophotometrisch gemessen. Eisen(III) wird mit NH₄ · H₂PO₄ maskiert. Die Arbeitsbedingungen für die Bestimmung von Eisen(II) in beiden für Ferrite verwendeten Lösungsmitteln — Salzsäure und Phosphorsäure — wurden festgelegt. Co, Cu und Ni stören die empfohlenen Verfahren nicht. Bis zu 0,02% Eisen(II) können in Einwaagen von wenigen Milligramm bestimmt werden.

     

Nucleophilic displacement on 4-nitrophenyl dimethyl phosphinate by ethoxide ion: alkali metal ion catalysis and mechanism

We report on a spectrophotometric kinetic study of the effect of Li(+) and K(+) cations on the ethanolysis of 4-nitrophenyl dimethylphosphinate () in ethanol at 25 [degree]C. The nucleophilic displacement reaction of with LiOEt and KOEt in the absence and presence of 18-crown-6 ether (18-C-6) furnished observed first-order rate constants which increase in the order EtO(-) < KOEt < LiOEt. The kinetic data are analyzed in terms of a scheme which assigns concurrent kinetic activity to free ethoxide and metal alkoxide, to obtain the second-order rate coefficients for reaction of the metal ion-ethoxide pairs, k(MOEt). Derived [small delta]G(ip), [small delta]G(ts) and [capital Delta]G(cat) values quantify ground state and transition state stabilization by the metal ions to give [small delta]G(ts) > [small delta]G(ip) for Li(+) and [small delta]G(ts)[similar][small delta]G(ip) for K(+). These results indicate moderate catalysis by Li(+), with manifesting lesser susceptibility to catalysis than other substrates previously studied. Second-order rate constants for the reaction of the aryl dimethylphosphinates with free EtO(-) were obtained from plots of log k(obs)vs. [KOEt], measured in the presence of excess 18-C-6. Hammett plots with [sigma] and [sigma][degree] substituent constants give significantly better correlation of rates than [sigma](-) and yield a moderately large [small rho]([small rho][degree]) value; this is interpreted in terms of a stepwise mechanism involving rate-limiting formation of a pentacoordinate intermediate. Comparison of the present results with those of Williams on the aqueous alkaline hydrolysis of Me(2)P(O)-OPhX and Ph(2)P(O)-OPhX esters, establishes the rationale for a change in mechanism in the more basic EtO(-)/EtOH nucleophile/solvent system by a stepwise mechanism instead of a concerted one in aqueous base. Structure-reactivity correlations following Jencks show that the change in mechanism is accounted for by cross interactions between the nucleophile and the leaving group in the transition state. The observed duality of mechanism is rationalized on the basis of the More O'Ferrall-Jencks diagram, as a spectrum of transition states covering a wide range of nucleophile and leaving group basicities.     

Possible mechanism of metal ion extraction from aqueous solutions by fibrous polypropylene

Peculiarities of the extraction of metal ions from aqueous solutions by fibrous polypropylene have been investigated. It has been found that metal ion adsorption proceeds owing to the existence of a gas-liquid-hydrophobic polymer boundary line. The process mechanism has been discussed.     

Synthesis of inorganic-organic hybrids by incorporation of inorganic components into organic polymer using metal alkoxides

Inorganic-organic hybrids have been synthesized by incorporation of the inorganic component of Ti(OC₂H₅)₄ into the organic polymer of ethyl cellulose. The inorganic-organic hybrids did not dissolve in toluene used as a solvent for the starting materials. The ethanol was formed as a by-product of the alcoholysis condensation reaction between Ti(OC₂H₅)₄ and ethyl cellulose. These results suggest that ethoxy groups of Ti(OC₂H₅)₄ react with hydroxy groups of ethyl cellulose to form cross-linking bonds of –O–Ti–O–. The reaction of Ti(OC₂H₅)₄ with ethyl cellulose was further investigated by Fourier transform infrared (FT-IR) spectroscopy. The FT-IR spectroscopic experiments revealed that the Ti–O bond state of Ti(OC₂H₅)₄ was changed by refluxing a toluene solution of Ti(OC₂H₅)₄ with ethyl cellulose. The inorganic-organic hybrids have an interesting dielectric property; their dielectric constant is higher than that of ethyl cellulose and that of a simple mixture of TiO₂ and ethyl cellulose.     

Preconcentration of heavy metal ions on reversibly precipitated polymeric systems

A procedure is proposed for the preconcentration of heavy metal ions in the analysis of aqueous media. It consists in the addition of components of reversibly precipitated polymeric systems to the solution, and precipitation of the polymer-metal complex, followed by its dissolution upon changing of the medium’s acidity. The procedure is tested on model solutions of copper, zinc, and lead ions and their mixture (0.001–0.01 mg/L). It is found that the interpolymer complex of poly-N-vinylimidazole with polymethacrylic acid ensures the complete extraction of metal ions and their preconcentration of more than 30-fold.     

Tandem mass spectra of ammonium ion,metal ion and ligated metal ion adducts of acyclic sugar derivatives

The tandem mass (MS/MS) spectra of ammonium ion, metal ion and ligated metal ion adducts of chain-extended acyclic nitro-containing deoxyglucose and deoxygalactose derivatives have been studied. The ammonium adducts fragment primarily by elimination of ammonia followed by acetic acid, thus not giving much structural information. In contrast, cationization of these compounds by metal ions and ligated metal ions gave structurally informative and useful fragment ions on MS/MS. The metal ions and ligated metal ions play an important role in controlling and directing fragmentation. Retro-aldol fragmentation is facilitated by metal ions such as Li(+), Na(+), Ag(+) and Cu(+), whereas the adducts with higher alkali metal ions such as Rb(+) and Cs(+) fragment to give only the corresponding metal ions. The divalent metal ions such as Cu(2+) and Ba(2+) also induce retro-aldol fragmentation. However, the charge is carried by the aldehyde fragment in the case of Cu(2+) adducts, whereas the nitroalkane fragment carries the charge in the case of Ba(2+) adducts. Ligated metal ions such as ZnCl(+), CuCl(+), InCl(2) (+) and BaCl(+) also behave similarly and induce retro-aldol fragmentation in these acyclic sugars. Both the metal ion and ligated metal ion adducts can fragment by elimination of metal-containing neutral molecules.     

Electrical conductivities of potassium ferrites doped with divalent metal oxide

The electronic and ionic conduction in three kinds of potassium ferrites with β-alumina structure was studied. Undoped ferrite, K₂O·6Fe₂O₃, prepared by sintering at 1400°C after prefiring a mixture of potassium carbonate and ferric oxide, was a mixed conductor with about 1% ionic conduction and predominantly electronic conduction. The nickel- or zinc-doped potassium ferrite showed decreasing conductivity in the range of a single phase as the content of dopant increased. Variations of the electronic conduction in the doped potassium ferrites were assigned to changes of ferrous ion concentration accompanied by structural changes in the spinel-like blocks. Potassium ion conductivities of the three sorts of samples were estimated from the total conductivities and the transport numbers obtained by dc-polarization technique and electrolysis method. The decreases of the ionic conductivities were explained by narrowing of the alkali-oxygen slot caused by doping.     

A new incorporation mechanism for trivalent actinides into bioapatite: a TRLFS and EXAFS study

One of the most toxic byproducts of nuclear power and weapons production is the transuranics, which have a high radiotoxicity and long biological half-life due to their tendency to accumulate in the skeletal system. This accumulation is inhomogeneous and has been associated with the chemical properties and structure of the bone material rather than its location or function. This suggests a chemical driving force to incorporation and requires an atomic scale mechanistic understanding of the incorporation process. Here we propose a new incorporation mechanism for trivalent actinides and lanthanides into synthetic and biologically produced hydroxyapatite. Time-resolved laser fluorescence spectroscopy and extended X-ray absorption fine structure have been used to demonstrate that trivalent actinides and lanthanides incorporate into the amorphous grain boundaries of apatite. This incorporation site can be used to explain patterns in uptake and distribution of radionuclides in the mammalian skeletal system.     

Invetigations into the use of an auxiliary metal ion for indirect amperometri detection

Summary A method for determination of metal ions subsequent to separation by ion chromatography has previously been developed. The method is based on Indirect Amperometric Detection whereby the decrease in the oxidation current, due to a dithiocarbamate ligand added post column, is monitored. Upon elution from the chromatographic column the metal ions are complexed by the ligand. As the complexes formed are electroinactive at the applied potential, the background current decreases according to the metal ion concentration. The method developed in this work involves addition to the reagent of Zn(II) as a auxiliary metal ion to displace the analyte metals from the chromatographic eluent ligand complexes after separation. Sodium bis(2-hydroxy-ethyl) dithiocarbamate was used as the postcolumn derivatising reagent. The addition of Zn(II) to the reagent causes some unforeseen behaviour in the chromatographic system.     

Investigations of the thermal transformations of precipitated mixed transition metal hydroxides

The thermal behaviour and phase composition of mixed oxides obtained by oxidation of iron(II) hydroxide in the presence of Mg, Zn, Co, Cu and Ni, is investigated by thermogravimetry, and conventional and high-temperature X-ray diffractometry.     

Quantification of the ion transport mechanism in protective polymer coatings on lithium metal anodes

Protective Polymer Coatings (PPCs) have been proposed to protect lithium metal anodes in rechargeable batteries to stabilize the Li/electrolyte interface and to extend the cycle life by reducing parasitic reactions and improving the lithium deposition morphology. However, the ion transport mechanism in PPCs remains unclear. Specifically, the degree of polymer swelling in the electrolyte and the influence of polymer/solvent/ion interactions are never quantified. Here we use poly(acrylonitrile-co-butadiene) (PAN–PBD) with controlled cross-link densities to quantify how the swelling ratio of the PPC affects conductivity, Li⁺ ion selectivity, activation energy, and rheological properties. The large difference in polarities between PAN (polar) and PBD (non-polar) segments allows the comparison of PPC properties when swollen in carbonate (high polarity) and ether (low polarity) electrolytes, which are the two most common classes of electrolytes. We find that a low swelling ratio of the PPC increases the transference number of Li⁺ ions while decreasing the conductivity. The activation energy only increases when the PPC is swollen in the carbonate electrolyte because of the strong ion–dipole interaction in the PAN phase, which is absent in the non-polar PBD phase. Theoretical models using Hansen solubility parameters and a percolation model have been shown to be effective in predicting the swelling behavior of PPCs in organic solvents and to estimate the conductivity. The trade-off between conductivity and the transference number is the primary challenge for PPCs. Our study provides general guidelines for PPC design, which favors the use of non-polar polymers with low polarity organic electrolytes.

Protective Polymer Coatings (PPCs) protect lithium metal anodes in rechargeable batteries to stabilize the Li/electrolyte interface and to extend the cycle life by reducing parasitic reactions and improving the lithium deposition morphology.     

Diaza-crown ethers—VI : A mechanism for metal ion promoted formation of macrocyclic diazaoligoethers

The mechanism of the formation of 1,7,10,16-tetraoxa - 4,13 - diazacylooctadecane has been studied from both a thermodynamic and a kinetic point of view. The cyclisation is favoured by the presence of an alkali metal ion, which forms a complex with the ring precursor. Both this intermediate and the complex react with starting material, but only the complex forms a cyclic product. The rate constants of these reactions have been determined by using simulation methods.     

Chromium ion incorporation in the crystal structure of BGO

Comprehensive investigations have been performed by EPR and optical spectroscopy for Bi₃GeO₄ crystals doped with chromium ions. It is demonstrated that the known optical absorption spectrum for chromium ions, specifically, the triplet in the region 600–900 nm has an analog in the EPR spectra — the center with electron spin S = 1. The spectrum is described by the spin-Hamiltonian with the parameters D = 550 G, E = 10 G, g _xx = g _yy = 1.915, g _zz = 1.932. The EPR spectrum is dictated by Cr⁴⁺ incorporation at the germanium sites. Luminescence observed in the region 1.2–1.7 μm is also caused by transitions of Cr⁴⁺ with tetrahedral surroundings to germanium sites. Original Russian Text Copyright ? 2005 N. V. Chernei, V. A. Nadolinnyi, N. V. Ivannikova, V. A. Gusev, I. N. Kupriyanov, V. N. Shlegel, and Ya. V. Vasiliev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 444–450, May–June, 2005.