The study of Ni–Co alloy deposition on iron powder particles in a fluidized bed from sulphate bath

This paper describes a process of electrolytic deposition of nickel–cobalt (Ni–Co) binary alloy on Fe powder. Electrochemical behavior of this binary alloy was studied by cyclic voltammetry with a paraffin impregnated graphite electrode as a working electrode. Deposition of individual metals (Ni, Co), as well as the simultaneous nickel–cobalt co-deposition, was performed in aqueous solutions (Watts-type electrolyte) both with and without Fe powder. Special attention was paid to the influence of suspension density on the electrode process. This density affects on the quality of iron powder electroplating. Preferential deposition of the less noble metal (Co) leading to its higher content in the deposit was observed in contrast to the more noble one (Ni) in spite of higher content of Ni in the plating solution. This anomalous phenomenon–known already for other metals (Zn, Cd, Sn)–has been confirmed and investigated for iron-group metals (Fe, Co, Ni) in this work. Electrolytic deposition of Ni–Co binary alloys, including anomalous behavior is a complicated process. Understanding the anomalous behavior would lead to better control of the deposition process and to explanation of the mechanism of Ni–Co co-deposition.     

Effect of platinum,palladium and rhodium on the activity and sulfur resistance of catalysts based on ZrO<Subscript>2</Subscript> in the oxidative conversion of methane

A study was carried out on the effect of noble metals (Pd, Pt, and Rh) on the activity and sulfur resistance of a Cu-Ni-Ce oxide composite on yttrium-stabilized zirconium in the oxidation of methane by oxygen. The enhancement in activity in the deep oxidation of methane, which is greatest for the pallaldium sample, is related to the oxidation-reduction properties of the composites. The platinum catalyst displayed greatest sulfur resistance, which may be attributed to the mechanism for the oxidation of SO₂ on platinum-group metals. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 3, pp. 170–174, May–June, 2008.     

Application of fluoroxidants for the decomposition and analysis of platinum metals and gold in black shale ores

In order to develop a reliable method for the platinum group metals (PGMs) determination in ores of organic origin like carbonaceous black shale a decomposition method with fluoroxidants like BrF₃ and KBrF₄ was established which avoids the commom losses of PGM organometallic compounds by volatilazation or chemisorption. The recovery from different trapping solutions is discussed. Platinum metals are evidently found in the carbonaceous black shale ores from the “Natalka” deposit situated in the Magadan area. PGMs are very inhomogenously distributed in the ores and ore concentrates and their total contents in ore are 5–18 g/t. The carbonaceous concentrate of black shale ore contains up to 23 g/t of the sum of platinum metals. ≥ 8% of the sum of platinum and palladium contained in this carbonaceous concentrate are soluble in organic solvents. Received: 16 July 1998 / Revised: 16 April 1999 / Accepted: 5 May 1999     

Application of fluoroxidants for the decomposition and analysis of platinum metals and gold in black shale ores

In order to develop a reliable method for the platinum group metals (PGMs) determination in ores of organic origin like carbonaceous black shale a decomposition method with fluoroxidants like BrF₃ and KBrF₄ was established which avoids the commom losses of PGM organometallic compounds by volatilazation or chemisorption. The recovery from different trapping solutions is discussed. Platinum metals are evidently found in the carbonaceous black shale ores from the “Natalka” deposit situated in the Magadan area. PGMs are very inhomogenously distributed in the ores and ore concentrates and their total contents in ore are 5–18 g/t. The carbonaceous concentrate of black shale ore contains up to 23 g/t of the sum of platinum metals. ≥ 8% of the sum of platinum and palladium contained in this carbonaceous concentrate are soluble in organic solvents. Received: 16 July 1998 / Revised: 16 April 1999 / Accepted: 5 May 1999     

Ternary complexes in the spectrophotometric determination of trace amounts of platinum(IV)

A simple, rapid, reproducible, sensitive and selective method is proposed for the spectrophotometric determination of submicrogram amounts of platinum(IV) in aqueous media. The proposed method involves the formation of a ternary complex between the hexa-ammine-platinum(IV) cationic complex, and the counter-ion 2,4,5,7-tetrabromofluorescein ethyl ester. The reaction is instantaneous and the red ternary complex remains stable for ca. 1 hr. Beer's law is obeyed over the range 39-1170 ppM with molar absorptivity of ca. 8.0 x 10(4) at 555 nm and pH 10. A relative standard deviation of 1.1% was found for the reproducibility of the method. Even without the use of masking agents, no interference is encountered from other noble metals except rhodium(III). Of 13 other cations and 8 anions tested, only iron(III) interferes.     

The Surface Tension and Density of Liquid Ag–Bi, Ag–Sn, and Bi–Sn Alloys

Summary. The sessile drop method has been used to measure density and surface tension for pure Ag, Bi, Sn, and their mixtures. For pure metals and Bi–Sn alloys negative temperature coefficients of surface tension have been obtained. In case of Ag–Bi and Ag–Sn alloys the temperature coefficients of surface tension take negative or positive values depending on composition. Experimental values of the surface tension for Ag–Bi, Ag–Sn, and Bi–Sn are compared with those computed from Butler’s model. A relatively good agreement is observed.     

Determination of metformin based on amplification of its voltammetric response by a combination of molecular wire and carbon nanotubes

Molecular wires containing copper(II) (CuMW), in the form of the coordination polymer (Cu(II)₄(bpp)₄(maa)₈(H₂O)₂).2H₂O (bpp=1,3-bis(4-pyridyl)propane, maa=2-methylacrylic acid), and multiwalled carbon nanotubes (CNT) have been combined to prepare a paste electrode (CuMW/CNT/PE). The voltammetric response of the CuMW/CNT/PE to metformin (MET) was significantly greater than that of electrodes prepared from other materials, because of both the surface effect of CuMW and CNT and coordination of MET with the Cu(II) ion in the CuMW. A novel voltammetric method for determination of MET is proposed. In pH 7.2 Britton–Robinson buffer, using single sweep voltammetry, the second-order derivative peak current for oxidation of MET at 0.97 V (relative to SCE) increased linearly with MET concentration in the range 9.0 × 10⁻⁷–5.0 × 10⁻⁵ mol L⁻¹ and the detection limit was 6.5 × 10⁻⁷ mol L⁻¹. Figure When a combination of molecular wires containing copper(II) (CuMW) and multiwalled carbon nanotubes (CNT) was used to prepare a paste electrode (CuMW/CNT/PE) the voltammetric response to metformin (curve c) was significantly higher than that at a carbon/PE (curve a) or a CNT/PE (curve b), because of the amplification effect of CNT and CuMW. A novel voltammetric method is proposed for determination of MET     

A Voltammetric Electronic Tongue for the Quantitative Analysis of Quality Parameters in Wastewater

The use of a voltammetric electronic tongue for the quantitative analysis of quality parameters in influent wastewater from a wastewater treatment plant (WWTP) that treats domestic and industrial wastewater is proposed. The electronic voltammetric tongue consists of a set of four noble electrodes (iridium, rhodium, platinum and gold) housed inside a stainless steel cylinder. These noble metals have high durability and are low maintenance‐demanding, as required for developing future automated equipment. A pulse voltammetry study was conducted in 35 wastewater samples to determine ammonia (NH₄⁺‐N), nitrates (NO₃⁻‐N), total phosphate (tot‐P), soluble chemical oxygen demand (CODs) and conductivity. These parameters were also determined in these samples by routine analytical methods in the WWTP laboratory. A partial least squares (PLS) analysis was run to obtain a model to predict each parameter. Twenty‐five samples were included in the calibration set and 10 in the validation set. Calibration and validation sets were selected randomly, except for the extreme values of each parameter, which were included in the calibration set. Variable selection was performed on the voltammetric data using Genetic Algorithms in the calibration data set for each parameter. The electronic tongue showed good predictive power to determine the concentrations of NH₄⁺‐N, NO₃⁻‐N and tot‐P and CODs.     

Validation of an analytical method to determine trace metal impurities in fluoride compounds by flame atomic absorption spectroscopy

 The development of an analytical method for the determination of some heavy metals (Fe, Cu, Co, Zn and Ni) in fluoride compounds [Cu(BF₄)₂, Sn(BF₄)₂, Pb(BF₄)₂ and HBF₄] by flame atomic absorption spectroscopy is described. This method is to be used as a routine analytical method in an industrial quality control laboratory. To this end the "performance characteristics" of an instrumental analytical method such as matrix effects, sensitivity, linearity, detection and quantitation limits, precision and accuracy were evaluated for every system under study. The results of these investigations showed that non-spectral interferences (due to the presence of large concentrations of major metals such as Cu, Sn and Pb) were observed. Nevertheless it was possible to define a matrix concentration interval where matrix effects were not statistically significant, and therefore a direct calibration approach could be used as the calibration tool whenever the major metal concentration was not higher than 40×10^–3 kg l^–1. A guide to the developement of an analytical method for trace metal determination is provided. General tools for quality control have been used in order to show how an analytical method can be tested daily and evaluated in a convenient manner. Received: 29 January 1997 Accepted: 11 March 1997     

Stripping voltammetric determination of platinum metals at a carbon paste electrode modified with cationic surfactants

In this contribution, a novel method is described for the determination of platinum metals. The procedure developed employs a carbon paste electrode modified in situ with cationic surfactants of the quaternary ammonium salt type. The pre-concentration step is based on a specific accumulation mechanism involving ion-pair formation; the detection being performed by cathodic scanning in the differential pulse voltammetric mode. Regarding the individual forms of platinum metals, the method has been found convenient for the determination of three heavy platinum metals in the form of Pt(IV), Ir(III) and Os(IV), whereas for the remaining elements (Ru, Rh, and Pd) was almost inapplicable. Platinum metals of the former group can be pre-concentrated in chloride-containing supporting media via PtCl₆²⁻, IrCl₆³⁻ and OsCl₆²⁻ complex anions, the central atom of each species being fairly reducible during the voltammetric scan. Stripping signals for both platinum and iridium were proportional to the concentration in a range of 1-10 × 10⁻⁶ M Pt(IV) and Ir(III); the response for osmium being linear within 0.1-6 × 10⁻⁷ M Os(IV) with a detection limit of about 5 × 10⁻⁹ mol l⁻¹. During optimisation, special attention was paid to the accumulation mechanism, choice of key experimental conditions, and to interference effects from foreign ions with potentially ion-pairing capabilities (AuCl₄⁻, TlCl₄⁻, CrO₄²⁻, MnO₄⁻, SCN⁻, and I⁻). The method elaborated has been tested on both model solutions and real samples of industrial waste water, showing in both cases satisfactory analytical performance.     

Determination of trace platinum by supramolecular catalytic kinetic spectrofluorimetry of β–cyclodextrin–platinum–KBrO3–salicylaldehyde furfuralhydrazone

A supramolecular catalytic kinetic spectrofluorimetric method was developed for the determination of platinum(IV) and the possible mechanism of catalytic reaction was discussed. The method was based on the fluorescence-enhancing reaction of salicylaldehyde furfuralhydrazone (SAFH) with potassium bromate, which was catalysed by platinum(IV) in a water–ethanol medium. β–Cyclodextrin (β-CD) obviously sensitized the determination at pH 5.20 and 25°C. Under optimum conditions, the β-CD–platinum–KBrO₃–SAFH supramolecular kinetic catalytic reaction system had excitation and emission maxima at 372 and 461 nm, respectively. The linear range of this method was 0.60–180 ng ml⁻¹ with a relative standard deviation of 1.2%, and the detection limit was 0.18 ng ml⁻¹. Investigation of the mechanism and the effects of interferences is presented. The proposed method was applied successfully to determine trace platinum(IV) in the chemotherapeutic drug cisplatin and serum from patients with satisfactory results.      

Oxidation of thiophene over copper-manganese mixed oxides

Commercial hopcalite calcined at different temperatures and hopcalite modified with noble metals (Pt, Pd, and Au) were studied in oxidation of thiophene. Surface and bulk properties of catalysts were studied using temperature-programmed reduction (TPR_H2), X-ray diffraction method (XRD) and thermal analysis (TG-DTA-MS). It was shown that calcined samples displayed higher activity in comparison with commercial untreated hopcalite; however, a lower temperature of calcination was favourable. High temperature of thermal treatment induced an increase in the crystallinity and a decrease in the surface area of the samples, and, as a consequence, the loss of catalysts activity. Moreover, marked improvement in the catalytic performance of platinum and palladium modified catalysts in relation to base hopcalite was observed. The obtained results indicate that the higher activity of samples containing Pt and Pd was accompanied by better reducibility of the catalysts. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

A biomonitoring study: 210Po and heavy metals in marine organisms from the Adriatic Sea (Italy)

In various samples of marine organisms from the central Adriatic Sea ²¹⁰Po was determined by alpha spectrometry and thirteen heavy metals (Mn, Fe, Co, Cr, V, Ni, Cu, Zn, Cd, As, Sn, Hg and Pb) by energy dispersive, polarised X ray fluorescence spectrometry (EDPXRF). ²¹⁰Po activity concentration ranged between 0.3 and 44.6 Bq kg⁻¹ fresh weight. The data obtained depend upon the type of the marine organism; among the pelagic species, anchovy displayed the highest polonium concentration. Typical concentration ( \upmu \textg·\textg_(\textfresh) ^{- 1} ) \left( {\upmu {\text{g}}\cdot{\text{g}}_{{({\text{fresh}})}}^{ - 1} } \right) ranges were as follows: Mn: <1.32–1.73; Fe: 4.11–94.27; Co < 0.13–0.23; Ni: <0.13–0.52; Cu: 0.37–145.31; Zn: 0.46–16.46; Cd: <0.10–0.25; As: 0.36–60.52; Hg: <0.13–0.70; Pb: <0.13–0.35, Sn: <0.20–12.67; V and Cr were always <1.32. The data obtained are also compared with those obtained by other authors for the same organism coming from other Italian seas.     

Codeposition of copper and tin from acidic sulfate solutions containing polyethylene glycols. Effect of length of the hydrocarbon chain

Voltammetry and electrochemical impedance spectroscopy technique were applied to study the effect of polyethylene glycols (PEG) with different molecular mass on Cu(II) and Sn(II) reduction kinetics in acidic sulfate solutions. Tetraethylene glycol was found to be the surface-active oligomer on both Cu and Sn substrates that holds the shortest (–CH₂–CH₂–O–)_m chain. The exchange current density of the rate-limiting step Cu²⁺ + e → Cu⁺ falls drastically with an increase in the molecular mass of PEG. An addition of PEG into halide-free Sn(II) solutions results in the significant inhibition of Sn(II) reduction in the entire range of cathodic polarizations including the region of limiting current. Inhibition degree also increases with PEG molecular mass. In contrast with Cu|Cu(II) system, formation of adsorption layers on Sn electrodes proceeds significantly slower. Underpotential deposition of Sn(II) is observed in the region of Cu(II)-limiting current. The characteristic current minimum arises in the region where free Sn phase is thermodynamically stable. It deepens with the length of the hydrocarbon chain of PEG. The fall of current density seems to arise from the inhibitive PEG adsorption on tin atoms that are still not incorporated into general Cu–Sn lattice.     

Hydration of platinum(II) complexes: a molecular mechanics study using atom-based force-field parameters

 This work is related to the interaction of water with two platinum(II) complexes, [Pt(NH₃)₄]²⁺ (denoted 1) and trans-[Pt(OH)₂(NH₃)₂] (denoted 2). We have considered two approaches of a water molecule to complexes 1 and 2 along the z-axis normal to the platinum(II) coordination plane: approach I, with the water oxygen oriented towards Pt, and approach II, with one water hydrogen directed towards Pt. Calculations have been performed within a molecular mechanics method based upon the interaction potentials proposed earlier by Claverie et al. and subsequently adjusted to results obtained with symmetry – adapted perturbational theory as well as with supermolecule (up to second-order M?ller–Plesset, MP2) methods. We discuss some possible simplifications of the potentials mentioned. The results relative to the hydration of Pt complexes 1 and 2 following approach I or II are discussed and compared to recent (MP2) ab initio energy–distance curves that we have recently determined. The MP2 calculations have shown that besides exchange–repulsion contributions, which are very similar in all hydrated complexes, approach I is mainly governed by electrostatics, whereas for approach II both electrostatic and dispersion contributions are important. Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 5 June 2000     

The rapid isolation and determination of iridium after simultaneous liquid-liquid extraction and determination of platinum,palladium, rhodium and gold

The proposed method provides a rapid isolation of iridium form the other noble metals, as well as from Ni, Cu, Fe, Cr, Co and Na. The scheme comprises an initial removal of ruthenium and osmium by volatilization of their tetroxides followed by the simultaneous extraction of platinum, palladium, rhodium and gold as their 2-mercaptobenzothiazole—tin(II) chloride complexes into chloroform. Iridium in the raffinate is complexed by the same reagent system, after boiling, and extracted into chloroform. The extracts after evaporation of the solvent are converted to hydrochloric acid solutions and the noble metals are determined by atomic absorption spectrometry. Satisfactory results are obtained for various noble metal solutions, and for a solid platiniferous sample.     

Voltammetric study of Sn(II) reduction on a glassy-carbon electrode from sulfate-tartrate baths

The reduction of Sn(II) from sulfate-tartrate baths on a glassy-carbon electrode is studied. The influence of the tartrate anion and Sn(II) concentrations and the solution pH on the shape of the voltamograms and on the efficiency of the electrodeposition process is examined. A reaction scheme to explain the results is proposed. The voltammetric and anodic stripping analysis of the electrodeposition process shows that the optimal efficiency conditions to obtain Sn deposits are bath solutions without excess of tartrate ligand, not excessively high pH, and low overpotentials. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 2, pp. 165–171. The text was submitted by the authors in English.     

Sequential determination of platinum, ruthenium, and molybdenum in carbon-supported Pt, PtRu, and PtMo catalysts by atomic absorption spectrometry

A simple accurate and precise analytical method for the determination of platinum, ruthenium, and molybdenum in Pt, PtRu, and PtMo nanoparticles catalysts deposited on high-surface area carbon by flame atomic absorption spectrometry (FAAS) and graphite furnace atomic absorption spectrometry (GFAAS) is described. The complete digestion of samples (0.010-0.020 g), which contain noble metals (NMs) in the range between 0 and 30% in combination among them or with other non-NMs, is obtained under mild conditions using both concentrated HCl and HCl+HNO₃ (1+1 (v/v)) mixture to boiling for 30 min in an open vessel. Carbon is separated from the solution by filtering it. Under optimized conditions of the flame, the poor sensitivity of platinum is enhanced 50-fold in presence of 1% (m V⁻¹) ascorbic acid, whereas the analytical signal of ruthenium increased by the presence of co-existing platinum. Any kind of interference is observed on the analytical signal of molybdenum. Recovery test obtained by analyzing commercial powder catalysts ranged from 99 to 101%. The precision, expressed as relative standard deviation of five measurements, is better than 1%. Electrode catalysts, made by using the carbon-supported platinum-based powder catalysts, have been analyzed for the metal loadings onto the electrode by GFAAS after dissolution under the same conditions used for the powder catalysts. The precision, expressed as relative standard deviation of three measurements, is better than 2%.     

Deposition and characterisation of a porous Sn(IV) semiconductor nanofilm on boron-doped diamond

Nanofilm deposits of a porous Sn(IV) oxide are formed by anodic electrodeposition on a polished boron-doped diamond electrode immersed in an aqueous Sn²⁺ solution. Mechanically and electrochemically stable deposits of 10–15 nm thickness are formed irrespective of the Sn²⁺ concentration and mass-transport enhancement by power ultrasound. Atomic force microscopy images indicate the presence of a smooth and noncrystalline film, which is stable under ambient conditions. n-type semiconducting characteristics are observed for the aqueous solution redox couples Fe(CN)₆ ^3–/4– and Ru(NH₃)₆ ^3+/2+. However, preliminary results from voltammetric experiments indicate that the small and neutral organic molecule N,N,N′,N′-tetramethylphenylenediamine is able to diffuse through the porous film to undergo oxidation directly at the surface of the boron-doped diamond electrode. Electronic Publication     

Systematic investigation of some metal cation interferences on the determination of molybdenum by flame atomic absorption spectrometry

The interference effects of some metal cations on the absorbance of Mo during its determination by flame AAS have been investigated, in air-acetylene flame, at a fuel flow rate of 1.8 L/min. While the interfering ion concentration was changing between 5 and 40 000 mg/L, the Mo concentration was taken as 10, 20 and 40 mg/L. It was shown that even at low concentrations of interfering ion there was a large suppression of Mo absorbance. No absorbance was observed for Mo in the presence of 50 time higher concentration of Mg, Ca, Sr, and Ba. These interference effects were suppressed by additions of 0.04% (m/v) sodium diethyldithiocarbamate (Na-DDTC), 2% (m/v) ammonium chloride, and 0.4% (m/v) sodium hydrogen phosphate. The interference from another group of elements, Mn, Fe, Al, Cd, Ni, Cr, Co, Cu and Zn, has been also investigated. In the presence of above mentioned metals, except Mn, the reproducibility of Mo absorption signal was not satisfactory. In the presence of Mn (5–40000 mg/L) the absorbance of Mo decreased significantly, however, the reproducibility was high. Molybdenum absorbance decreased under the influence of 5000–40000 mg/L of Fe, Co, Ni, 500–40000 mg/L of Cr. On the other hand, the absorption signal of Mo increased at about 20–40% in the presence of Zn and Cd. By the addition of 2% NH₄Cl the interference of these metals could be eliminated completely for all mass ratios of Mn: Mo and up to Mo: M mass ratio of 1: 10–1: 100 for the other metals, and reliable absorbance signals of Mo were obtained. The text was submitted by the authors in English.