Initial Vanadium Research Articles

Adsorption of vanadium(V) from acidic solutions by using octylamine functionalized magnetite nanoparticles as a novel adsorbent

Adsorption of vanadium(V) from acidic solutions was investigated by using octylamine functionalized magnetite nanoparticles as a novel adsorbent of vanadium. Batch experiments were conducted to determine the effects of initial pH, nanoparticles to octylamine weight ratio, amount of adsorbent, stirring time and initial vanadium(V) concentration in aqueous solution on adsorption efficiency. The adsorption was highly pH dependent, and the optimal pH was 3.2. The weight ratio of magnetite nanoparticles to octylamine was studied in optimum pH, and the best result was 3 : 2. More than 88% of vanadium(V) in solution was removed by 38.4 mg of adsorbent. In kinetics studies, the adsorption equilibrium could be achieved within 10minutes, and the experimental data were well fitted by the pseudosecond-order model. Comparison of Langmuir and Freundlich isotherm models indicated a better fit of Langmuir model to the adsorption of vanadium(V) and the mono-layer adsorption capacity for vanadium(V) was 25.707 mg g−1.

Synthesis of protonated chitosan flakes for the removal of vanadium(III, IV and V) oxyanions from aqueous solutions

Vanadium is included in the USEPA Contaminant Candidate List (CCL). Protonated chitosan flakes (PCF) were shown to effectively remove vanadium(III, IV, and V) oxyanions from aqueous solutions at high yields. It was also proven that the adsorption capacity of vanadium increases when using PCF instead of chitosan beads (CB). A 99–100% removal of vanadium oxyanions was achieved during the first 2h of contact when using 5g/L PCF adsorbent and the initial vanadium concentration of 0.500mg/L, while CB only removed 4–18%. Adsorption experiments were performed by varying contact time, pH of the aqueous solution and adsorbent suspension solution, and analyzing the effect of common anions. Vanadium(III, IV and V) adsorption is favored in the Langmuir's model. These species of vanadium were removed efficiently without the need of pretreatment process, even when common anions were added, such as chloride, carbonate, sulfate and phosphate. The proposed mechanism for the removal of vanadium, when adding PCF, is by the process of electrostatic attraction.

Microstructure of nanocrystalline nonstoichiometric vanadium carbide VC0.875

A nanocrystalline powder of nonstoichiometric vanadium carbide VC0.875 has been prepared by the high-energy ball milling method. The crystal structure, microstructure, morphology, and size distribution of particles of the initial and milled powders have been investigated using X-ray diffraction, laser diffraction, and scanning electron microscopy. For vanadium carbide, the model calculation of the particle size of a VC0.875 nanopowder as a function of the milling duration has been performed for the first time. A comparison of the experimental and theoretical results has demonstrated that a nanopowder with an average particle size of 40–80 nm can be obtained by a 10-h high-energy ball milling of the initial vanadium carbide powder with an average particle size of ∼6 μm.

Thermal oxidation of InP with V2O5 + PbO nanolayers of different compositions

Data are presented on the thermal oxidation of (V2O5 + PbO)/InP structures which demonstrate that the combined effect of the oxides deposited by magnetron sputtering does not follow the additivity rule and that this behavior is due to the formation of a quasi-liquid phase (maximum) and lead vanadate (minimum) (IR spectroscopy, Auger electron spectroscopy). The effective activation energy for the oxidation of the (V2O5 + PbO)/InP structures is shown to systematically decrease with increasing initial vanadium oxide content. The oxidation of the structures follows a partially catalytic mechanism, with V2O5 acting as a catalyst (oxidation kinetics, IR spectroscopy, ultrasoft X-ray emission spectroscopy).

Vanadium nanoclusters on Si(1 1 1) 7 × 7 surface studied by scanning tunneling microscopy

The size distribution and shape transition of self-assembled vanadium silicide clusters on Si(1 1 1) 7 × 7 have been investigated by scanning tunneling microscopy. Nanoclusters were formed by submonolayer vanadium deposition at room temperature followed by subsequent annealing (solid phase epitaxy – SPE). At room temperature, initially V-nanoclusters are formed which occupy sites avoiding the corner hole parts of the unit cells in the Si(1 1 1) 7 × 7 surface. Upon annealing, strong metal–silicon reaction occur leading to the formation of vanadium silicide nanoclusters. As a function of temperature, both, flat (2D) and three dimensional (3D) clusters have been obtained. After annealing at temperatures around 900 K many faceted clusters are created, whereas at higher annealing temperature, around 1300 K, predominantly 3D clusters are formed. The size distribution of SPE grown clusters could be well controlled in the range of 3–10 nm. The cluster size depends on the annealing temperature as well as on the initial vanadium coverage. Based on high resolution STM images a structure model for one kind of vanadium disilicide clusters exposing atomically flat surfaces was proposed.

Selective separation and concentration of vanadium(V) by a chemical pumping hollow-fiber supported liquid membrane

A hollow fiber supported liquid membrane (HFSLM) system for the separation and concentration of vanadium (V) has been developed and characterized by using tricaprylylmethylammonium chloride (Aliquat 336®) dissolved in dodecane as carrier. The transport of vanadium through the liquid membrane is based on a pH gradient between feed and stripping solutions to provide an appropriate change on the chemical species of aqueous vanadate, i.e., aqueous metavanadate, VO 2(OH) 2 −1 (4.0 < pH < 7.0) is extracted by Aliquat 336 and VO 3OH 2− (pH > 8.0) is not extracted. Selective separation and concentration experiments were carried out at low vanadium(V) concentration (mg 1 −1 level). The study of the HFSLM includes the influence of hydrodynamic, physical and chemical conditions, i.e., flow rate of feed solution through the fibers, number and length of fibers, lifetime of the system, initial vanadium concentration in the feed solution, and pH of aqueous phases. Transport of V(V) increases with the flow rate of the feed solution through the fibers until a ‘plateau’ is reached (> 0.2 ml min −1 in a single fiber). It has been shown that in a HFSLM module, the membrane area increases with the number of fibers but also there is an increase of the sterical hindrance between the fibers which reduces the expected increase of vanadium transport. On the other hand, the length of the fibers has a scarce influence on the transport process. The effect of the acidity of the feed solution on the vanadium transport shows a similar behavior to that obtained previously for liquid-liquid distribution and laminar SLM studies. The results obtained indicate that vanadium(V) can be effectively concentrated and selectively separated by hollow fiber SLM containing Aliquat 336® as carrier.

Vanadium(V) reduction in Thiobacillus thiooxidans cultures on elemental sulfur

We describe the reduction of vanadium (V) to vanadium (IV) in cultures of Thiobacillus thiooxidans on elemental sulfur, for initial vanadium (V) concentrations up to 5 mM. The vanadium (V) is reduced by intermediate compounds generated by bacterial oxidation of elemental sulfur. The limit of initial vanadium (V) allowing bacterial action seems to be related to the inhibition caused by such vanadium species, rather than connected to the vanadium (IV) species, which did not show inhibitory effects up to concentrations of about 0.1 M. This reduction mechanism of vanadium (V) is potentially applicable in the recovery of vanadium from spent solid catalysts, by a low-cost methodology.

Formation of an active surface on oxide systems containing vanadium used for dehydrogenation of hydrocarbons in the presence of hydrogen acceptors. 4. Catalytic and physicochemical properties of vanadium-zirconium and vanadium-titanium catalysts for the oxidative dehydrogenation of ethylbenzene in the presence of nitrobenzene

A study has been made of the catalytic and physicochemical properties of vanadium-zirconium and vanadium-titanium oxide systems in the oxidative dehydrogenation of ethylbenzene in the presence of nitrobenzene. The degree of conversion to styrene was less than 10% and to aniline 60%. The methods used to study the physicochemical properties of the catalysts were diffuse reflection electron spectroscopy (DRES), x-ray and differential thermogravimetric analysis. The presence of surface VTd5+, VOh5+, and VQ4+ ions has been established, their ratios depending on the initial vanadium concentrations, the nature of the carrier, and the thermal treatment conditions. In the vanadium—zirconium systems VTd5+ predominate, but in the vanadium-titanium ones VQ4+. The VOh5+ ions appear to be present in the form of clusters. A chemical compound between the active components and ZrO2 and a V2O5 phase have been detected, which take no part in the dehydrogenation reaction.

Neonatal behavior & mother-neonate interaction

In this work, 2-ethyl-1-hexanol, a long chain alcohol, is used to extract pentavalent vanadium V(V) from both sodium metavanadate solution and a synthetic leach liquor. At first, effects of process parameters on the extraction of V(V) from a solution free from the other metals are examined and discussed. The maximum extraction yield has been achieved at initial pH (pH0) about 2.0. Moreover, the influences of the concentration of extracting reagent, initial vanadium concentration, and organic/aqueous (O/A) phase ratio on the extraction are investigated. Subsequently, recovery of V(V) from a synthetic leach solution in the presence of Fe(III), U(VI), Si(IV), and Al(III) was explored. Under the extraction conditions of initial pH of 1.9, 2-ethyl-1-hexanol concentration of 70 v/v%, extraction temperature of 60 °C, and phase ratio (O/A) of 2/1; about 93% of V(V) was extracted while the extraction of the other coexisting metals was lower than 8%. The present results showed that 2-ethyl-1-hexanol is a suitable solvent for the selective separation of V(V) from the acidic sulfate solutions. Moreover, a method for the stripping and precipitation of the V(V) compound was proposed to achieve the complete recovery of vanadium. The presented method led to the selective stripping of V(V) from the organic phase and its complete precipitation in the form of ammonium metavanadate.

The formation of austenite in a low-alloy steel

Austenite formation from different microstructural conditions has been studied in an Fe-lV-0.2C steel. The starting microstructures of ferrite, bainite, and martensite, and the morphology of austenite formation have been examined in detail by light microscopy and transmission electron microscopy. Retained austenite in quenched martensitic areas has been used to establish the crystallographic relationships during austenite nucleation, and to indicate the behavior of the initial vanadium carbide dispersion present in the ferrite starting microstructure. Limited measurements were also made of the kinetics of austenitization.

Condition of titanium and vanadium mononitride particles after nitriding and heat treatment

1. It was established that, in the initial condition, titanium and vanadium mononitride preparations produced by direct nitriding techniques are never in a state of equilibrium. The cross section of each grain has a nitrogen concentration gradient which may reach the limiting composition in the surface layer under certain nitriding conditions. 2. It is shown that, to obtain equilibrium preparations, specimens of the mononitrides must be subjected to additional annealing for several hours at 1200–1400°C under conditions precluding their further nitriding. 3. Using equilibrium specimens, the boundaries of existence of titanium and vanadium mononitrides at temperatures ranging from ∼800 to 1400°C were redefined with greater precision.

Mechanism of the reaction of vanadium(III) with mercury(II) in aqueous perchloric acid solutions

Kinetic studies on the reaction of vanadium(III) with mercury(II), 2VIII+ 2HgII→ 2VIV+(HgI)2, in perchloric acid solutions of ionic strengths 2·0M(LiClO4) and 3·0M(NaClO4) are consistent with the mechanism (i)–(iii). VIII+ HgII [graphic omitted] VIV+ HgI(i), VIII+ HgI [graphic omitted] VIV+ Hg0(ii), VIV+ HgI [graphic omitted] VV+ Hg0(iii), Subsequent reactions Hg0+ HgII→(HgI)2, and VIII+ VV→ 2VIV are more rapid and are not rate determining. The rate law corresponding to (i)–(iii) is given by (iv). At low initial vanadium(IV) concentrations the [graphic omitted] second term in (iv) is negligible, but at high vanadium(IV) concentrations (>0·1M) the second term becomes dominant. Although the kinetics do not rule out the two-electron reaction VIII+ HgII→ VV+ Hg0 as an alternative to (iii), the consecutive one-electron changes V3+→ VO2+→ VO2+ are considered more likely.