Dissolution Of Niobium Research Articles

Kinetics of hydrochloric acid leaching of niobium from TiO2 residues

Production of TiO2 generates waste containing significant quantities of valuable metals which if recovered, could have a positive impact on the economics of TiO2 production and waste management. In this investigation, the kinetics of HCl leaching of niobium from TiO2 residues are studied. The complex mineralisation of niobium in its primary ores makes economic recovery very difficult, often demanding the use of chlorination, carbochlorination or fusion with alkali fluxes for breakdown of its mineral concentrates and upgrading before leaching in acid, usually hydrofluoric acid. The effects of parameters leaching temperature (25–90°C), HCl concentration (0.5–4M), stirring speed (100–500rpm) and solid–liquid ratio were determined in the experiments. A maximum niobium extraction rate >90% was achieved within 60min of leaching the residues in 4M HCl at 70°C. The kinetics analysis showed that the dissolution of niobium in HCl is governed by pore diffusion of the random pore model, with an activation energy of 16.8±1.2kJmol−1 Nb.

Solution of niobium in iron during arc surfacing

The solution of niobium in iron during arc surfacing is simulated. The model is based on diffusional dissolution of niobium particles in metals. It includes diffusion equations, initial and boundary conditions, and also the equations of motion of the boundary between the media. The diffusion coefficient in liquid iron is assumed to much exceed that in the solid solution. The solution of the Stefan diffusional problem within the solid is found as a Fourier series in terms of cosines; the solution within the liquid is found in terms of error functions. The time for the dissolution of niobium is determined. It is 10–100 s for 10-μm particles at high temperatures.

Niobium, tantalum, and titanium fluoride solutions

Parameters for the preparation of concentrated tantalum, niobium, and titanium fluoride solutions by dissolution of their oxides or hydroxides in hydrofluoric acid were studied. Anatase titania, niobium oxide, and tantalum oxide calcined to 900°C were found to have high dissolution rates. Solid phases separated upon the dissolution of niobium, tantalum, and titanium oxides in hydrofluoric acid were identified as NbO2F, TaO2F, Ta3O7F, and TiOF2. Niobium hydroxide dissolution in an autoclave at the atmospheric pressure gave various complex salts: NH4NbOF4 and (NH4)3Nb2OF11.

Electrochemical synthesis of sodium hexamethoxyniobate

Anodic dissolution of niobium in anhydrous methanol in the presence of sodium methylate was studied. A method for recovery of niobium methylate from sodium hexamethoxyniobate by the reaction with ammonium chloride was developed.

Electrochemical synthesis of niobium methylate

The formation of niobium(V) methylate in methanol against the background of lithium chloride is studied. It is found that, in the anodic dissolution of niobium in the diaphragmless electrolyzer, formed niobium(V) methylate is partially reduced to the four-valent state at the cathode. In order to suppress the reduction of Nb(V), an electrolyzer was designed, which enabled one to separate the anolyte from the catholyte using the difference between their densities. Niobium methylate was not found in the anolyte; however, it forms as a result of mixing the anolyte with the catholyte after completion of electrolysis. The current efficiency of niobium methylate of 96–97% was achieved. Possible mechanism of the process is discussed.

Electrochemical synthesis of niobium(V) ethylate

The effect exerted by the supporting electrolyte and cathode material on the anodic dissolution of niobium in ethanol solutions was studied.

EQCM Study of Anodic Film Growth on Valve Metals

A comparative study of anodic film growth on niobium, zirconium, and tungsten in was performed using the rotating electrochemical quartz crystal microbalance (EQCM). Potential sweep as well as potential step and hold experiments were performed in the range between open circuit and 8 Significant differences in the mass transients between the three metals were observed. During the formation of anodic films on niobium and zirconium, the dissolution was negligible and the fraction of the current serving for film growth was always close to unity. On tungsten, anodic dissolution in combination with film growth led to a growth fraction that diminished with time. The results obtained by the double potential step technique were compared with numerical simulations based on models considering either high field conduction or an interface reaction as limiting the kinetics of film growth. The growth of anodic films on niobium and zirconium was found limited by high field conduction, whereas film growth on tungsten was interface controlled. Film growth on tungsten was accompanied by important anodic dissolution, while dissolution of niobium and zirconium was negligible. © 2004 The Electrochemical Society. All rights reserved.

NbMCM-41 mesoporous molecular sieves in oxidative dehydrogenation of ethane and propane

It has been evidenced that the dissolution of niobium in silica mesoporous matrix significantly increases the catalytic effectiveness in the oxidative dehydrogenation of alkanes as compared with unsupported Nb2O5.

Macrokinetics of thermal explosion in a niobium-aluminum system. II. Phase-formation dynamics

The thermal explosion in a gas-free mixture of metal powders has been studied for the first time using the method of dynamic x-ray structural analysis. The dynamics of formation of new crystalline phases at all stages of the process is determined. It is shown that melting of aluminum is followed by dissolution of niobium in the melt and crystallization of the intermediate product NbAl3, and the melt does not wet niobium particles. A dramatic improvement in wetting is observed at a temperature of ≈ 1040 K (apparently, due to the destruction of oxide films). This results in a thermal explosion, and the Nb2Al phase is formed. The reaction during the thermal explosion also follows the dissolution-crystallization mechanism.

Microstructures and crystallographic relationships in aluminized coatings on IN713LC and MAR-M247

The crystallographic relationships among γ, β and σ phases at the interfaces between aluminized coatings and the substrates IN-713LC and MAR-M247 are the same as those identified previously in the coatings on René 80. In the outer zone of the coatings on the two substrates, the existence of the same crystallographic relationships between the β phase and the α-Cr and the misfit dislocations at the phase boundary indicate that the α-Cr precipitates directly from the β phase. The dissolution of niobium and tantalum together with other elements in the α-Cr precipitates explains why the β matrix does not form the Ni 2AlNB and Ni 2AlTa phases in the outer zone of the coatings on IN713LC and MAR-M247 respectively. The Kurdjumov-Sachs relationships between the β phase and the carbides MC and M 23C 6 were recognized in the coating on IN713LC.

Dissolution of niobium and tantalum matrix and their separation from trace elements by means of extraction with diantipyrylmethanes

The separation of niobium and tantalum as matrices from other elements that appear as trace impurities was systematically examined by extraction with diantipyrylmethane and hexyl-diantipyrylmethane. The decomposition of the matrices in the HF/HNO3 mixture was optimised by using the smallest possible quantities of nitric acid, because the presence of nitric acid hindered the efficiency of the separation. For the same reason the elimination of nitric acid from the sample solution by evaporation and also by decomposition with formic acid and urea was examined.

Niobium Dissolution by Hydrofluoric Acid and Potassium Iodate Prior to Nitrogen Determination.

Niobium Dissolution by Hydrofluoric Acid and Potassium Iodate Prior to Nitrogen Determination.

Complexes of niobium and tantalum hydroxides with di-ols

The dissolution of niobium and tantalum hydroxides in alkaline solutions of catechol and other 1–2,di-ols has been studied and solid crystalline products isolated. These show some variability in composition consequent upon the polynucleation of the metal hydroxide through ageing. Under appropriate conditions such compounds as (NH 4) 3[Nb(OH) 2(C 6H 4O 2) 3].H 2O may be isolated. This compound absorbs at 340 mμ in ethanol but is immediately hydrolysed in water or aqueous alkali and subsequently, within certain limits of OH- concentration, a species absorbing at 310 mμ — probably a 1: 1 complex and containing polynuclear niobic acid units — is slowly formed. Infra-red absorption measurements give no evidence of the presence of a niobyl radicle, NbO, in the solids. Tantalum hydroxide is much less easily dissolved in catechol than niobium hydroxide and the products contain about 5 moles of catechol to each tantalum atom.