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Carbochlorination kinetics of tantalum and niobium pentoxides  [cached]
Allain, E.,Gaballah, I.,García, F.,Ferreira, S.
Revista de Metalurgia , 1999,
Abstract: The carbochlorination kinetics of pure Nb2O5 and Ta2O5 by gas mixture (C12 + CO + N2) between 380 and 1,000 °C is studied. A calculation of the standard free energy of the carbochlorination reactions is made. A diagram of the phases stability is drawn. The influence of the gas flow, temperature and the pardal pressure of Cl2 and CO at temperatures below 650 °C on the reaction rate is studied. The apparent activation energy is approximately 75 and 110 kJ/mol for Nb2Os and Ta2O5, respectively. At temperatures above 650°C the Arrhenius diagram presents an anomaly which may be attributed to the decomposition of the COCl2 formed in situ. The apparent reaction order of the carbochlorination of these oxides against Cl2+CO is approximately 2. The carbochlorination rates of these oxides are much greater than those of chlorination by Cl2 + N2. The carbochlorination kinetics of tin furnace slag leaching concentrates containing tantalum and niobium compounds are also studied and compared with the carbochlorination kinetics of the pure oxides. En este trabajo se estudia la cinética de carbocloruración del Nb2O5 y del Ta2O5 por la mezcla de gases (Cl2 + CO + N2) entre 380 y 1000°C. Se hace un cálculo de la energía libre estándar de carbocloruración y se dibujan los diagramas de equilibrio de fases. Se estudia la influencia del flujo de gas, la temperatura y la presión parcial de Cl2 y CO a temperaturas por debajo de 650°C sobre la velocidad de reacción. La energía de activación es aproximadamente 75 y 110 kJ/mol para el Nb2O5 y el Ta2O5, respectivamente. A temperaturas por encima de 650°C, el diagrama de Arrhenius presenta una anomalía que puede ser atribuida a la descomposición del COCl2 formado in situ. El orden aparente de reacción de la carbocloruración de estos óxidos frente a Cl2 + CO es aproximadamente 2. La velocidad de carbocloruración de estos óxidos es mucho más grande que la que se conseguía con una mezcla de Cl2 y N2. Se ha comparado la cinética de carboclururación de los compuestos de niobio y tantalio contenidos en los concentrados de lixiviación de las escorias de hornos de esta o con la cinética de carbocloruración de los óxidos puros.
A Review of Niobium-Tantalum Separation in Hydrometallurgy  [PDF]
Olushola S. Ayanda, Folahan A. Adekola
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2011, DOI: 10.4236/jmmce.2011.103016
Abstract: Niobium and tantalum are chemically similar and are associated with each other in nature which makes it very difficult to separate. For many years, the separation of tantalum from niobium involved the fractional crystallization of potassium heptafluorotantalate away from potassium oxypentafluoroniobate monohydrate, this method has been supplanted by solvent extraction from fluoride-containing solutions by the use of solvent extractants such as Octanol, bis(2-ethylhexyl)phosphoric acid (DEHPA), Alamine 336, methyl isobutyl ketone (MIBK), tri-nbutyl phosphate (TBP) or cyclohexanone. A detailed review of the various processes involved in the breakdown treatment of niobium and tantalum primary sources, extraction and separation and newer processes of extraction as well as the various technique involved were discussed.
Potash Breakdown of Poly-Mineralized Niobium-Tantalum-Lanthanides Ore Material  [PDF]
Mona N. El Hazek, Nawal H. Mohamed, Azza A. Gabr
American Journal of Analytical Chemistry (AJAC) , 2019, DOI: 10.4236/ajac.2019.103009
Abstract: The potentiality of the alkali breakdown of the poly mineralized ore material south Gabal El-A’urf area, central Eastern Desert, Egypt is investigated. It includes the multiple oxide mineral tanteuxenite, monazite, bastnasite, anatase, as well as zircon. This ore material assaying lanthanides (RE2O3 1.9%), niobium (Nb2O5 1.25%) as well as titanium and zirconium (TiO2 and ZrO2 1.23% and 1.12%) respectively besides tantalum (Ta2O5 0.13%), were used for the present work. This sample has thus been subjected to two alkali breakdown techniques using potash; namely agitation leaching and fusion. The latter technique was found to be preferred as it gives higher leaching efficiency. The optimum leaching conditions are weight ratio of the ore/potassium hydroxide 1/2 at 400°C for 1 h. The realized leaching efficiencies attained 95.0% and 93.7% for Nb and Ta respectively as well as 96% for lanthanides and 75% for Ti while that for Zr did not exceed 10%.
Lewis Acid Catalysis of the Diels–Alder Reaction Using Niobium and Tantalum Chlorides in the Presence of Coordinating Ligands  [PDF]
Joshua Howarth,Kevin Gillespie
Molecules , 2000, DOI: 10.3390/50800993
Abstract: The Jacobsen and pybox type ligands effect chiral induction in the presence of niobium(V) chloride and tantalum(V) chloride in the Lewis acid catalysed Diels–Alder reaction.
Extraction of Tantalum from locally sourced Tantalite using Polyethylene glycol solution
NS Maina, MS Ahmad
Nigerian Journal of Basic and Applied Sciences , 2009,
Abstract: The ability of polyethylene glycol solution to extract tantalum from locally sourced tantalite ore was studied. The amount of tantalum pentoxide extracted increased with increase in concentration of Polyethylene glycol (PEG) solution from 28.08% to 60.23%. However, the amount of niobium pentoxide extracted increased from 0.1194% to a maximum of 40.52% at increasing concentration of PEG and dropped to 26.1477% at PEG solution concentration of 60%. The separation factor of tantalum pentoxide and niobium pentoxide at 30, 40, 50, and 60% PEG concentrations were 0.0031, 0.3110, 0.7874 and 0.2338 respectively. The distribution coefficient (D1) of tantalum pentoxide at 30, 40, 50 and 60% PEG concentrations were 0.3904, 0.6477, 0.8651 and 1.5145 respectively; while at 30, 20, 30, 40, 50 and 60% PEG concentration the distribution coefficients (D2) of niobium pentoxide were 0.0012, 0.2014, 0.6812 and 0.3541 respectively. KEYWORDS: Tantalum, tantalite, extraction, niobium, polyethylene glycol (PEG).
Semiconductive properties of anodic niobium oxides
,A.I. de; Rangel,C.M.; Skeldon,P.; Thompson,G.E.;
Portugaliae Electrochimica Acta , 2006,
Abstract: the semiconductive properties of anodic niobium oxides formed at constant potential and constant current density to different final voltages have been examined by mott-schottky analysis. thin anodic oxides were formed on sputtered niobium specimens at constant potential in the range of 2.5 to 10 vag/agcl in a borate buffer solution. thicker oxides were formed, also on sputtered niobium specimens, at a constant current density of 5 ma cm-2 in 0.1 m ammonium pentaborate solution to final voltages of 10, 50 and 100 v. capacitance measurements were performed in a borate buffer solution of ph 8.8, at a frequency range of 200 to 2000 hz, at a sweep rate of 5 mv s-1 from +2.5 to -1 vag/agcl. the results obtained show n-type semiconductor behaviour with a carrier density in the range of 8 ′ 1018 - 6 ′ 1019 cm-3 on films formed to 10 v. thicker films showed lower carrier densities in the range of 1 ′ 1018 - 2 ′ 1018 cm-3 with a calculated charge depletion layer of 33-36 nm.
Semiconductive properties of anodic niobium oxides  [cached]
A.I. de Sá,C.M. Rangel,P. Skeldon,G.E. Thompson
Portugaliae Electrochimica Acta , 2006,
Abstract: The semiconductive properties of anodic niobium oxides formed at constant potential and constant current density to different final voltages have been examined by Mott-Schottky analysis. Thin anodic oxides were formed on sputtered niobium specimens at constant potential in the range of 2.5 to 10 V Ag/AgCl in a borate buffer solution. Thicker oxides were formed, also on sputtered niobium specimens, at a constant current density of 5 mA cm-2 in 0.1 M ammonium pentaborate solution to final voltages of 10, 50 and 100 V. Capacitance measurements were performed in a borate buffer solution of pH 8.8, at a frequency range of 200 to 2000 Hz, at a sweep rate of 5 mV s-1 from +2.5 to -1 V Ag/AgCl. The results obtained show n-type semiconductor behaviour with a carrier density in the range of 8 ′ 10(18) - 6 ′ 10(19) cm-3 on films formed to 10 V. Thicker films showed lower carrier densities in the range of 1 ′ 10(18) - 2 ′ 10(18) cm-3 with a calculated charge depletion layer of 33-36 nm.
Tantalum, Niobium and Titanium Coatings for Biocompatibility Improvement of Dental Implants
Mohammad Hossein Fathi,Vajihesadat Mortazavi
Dental Research Journal , 2007,
Abstract: Introduction: Metals have a wide range of applications in implant and prosthetic materials in dentistry.Corrosion resistance and biocompatibility of metals should be improved in order to utilizethem as biomaterials. The aim of this work was to prepare metallic coatings on 316L stainless steel dental implants, to evaluate the corrosion characteristics of the uncoated and metallic coated dentalimplants as an indication of biocompatibility and, to compare the effect of the type of the coatings on biocompatibility.Materials and Methods: In this in vitro evaluation, three types of metallic coatings including tantalum, niobium and titanium coatings were compared using a physical vapor deposition process on 316L stainless steel dental implants. Structural characterization techniques including X-ray diffraction, scanning electron microscopy and energy dispersive X-ray analysis were utilized to investigatethe microstructure and morphology of the coatings. Electrochemical potentiodynamic tests were performed in two types of physiological solutions at 37±1°C in order to determine and compare the corrosioncurrent density and corrosion potential characteristics. The mean values were statistically compared by ANOVA at a 95% level of confidence.Results: the findings showed that all of the three types of metallic coatings had a positive effect on improvement of the corrosion behavior. The coatings could increase the corrosion resistance of 316L stainless steel and this trend was independent of the type of physiological environment.Conclusion: The biocompatible metallic coatings could decrease the corrosion current density and is a distinct advantage for prevention of ion release. Decreasing ion release can improve the biocompatibility of the dental implant, and consequently can prevent tissue damage, tissue inflammation and irritation, and can also lead to obtaining a desirable histopathological response.
Extraction of metals from complex sulfide nickel concentrates by low-temperature chlorination roasting and water leaching  [PDF]
Cong Xu,Hong-wei Cheng,Guang-shi Li,Chang-yuan Lu,Xiong-gang Lu,Xing-li Zou,Qian Xu
- , 2017, DOI: https://doi.org/10.1007/s12613-017-1417-2
Abstract: The recovery of valuable metals from complex sulfide concentrates was investigated via chlorination roasting followed by water leaching. A reaction process is proposed on the basis of previous studies and the results of our preliminary experiments. During the process, various process parameters were studied, including the roasting temperature, the addition of NH4Cl, the roasting time, the leaching time, and the liquid-to-solid ratio. The roasted products and leach residues were characterized by X-ray diffraction and vibrational spectroscopy. Under the optimum condition, 95% of Ni, 98% of Cu, and 88% of Co were recovered. In addition, the removal of iron was studied in the water leaching stage. The results demonstrate that this process provides an effective approach for extracting multiple metals from complex concentrates or ores.
AN INVESTIGATON OF THE SUBSTITUTED AMIDETYPE A-101 EXTRACTANT AND ITS APPLICATIONS

Res GP of Solvent Extraction,Changsha Institute of Mining,Metallurgy Research,

金属学报 , 1977,
Abstract: Under the guidance of the principle of independence and self-reliance, thesubstituted amide-type A-101 extractant has been successfully synthesized. Thistype extractant showed easy synthesis, better physico-chemical properties andhigher selectivity. Dialkylacetamide is one of weakly basic extractant with car-bonyl as functional group. Examples are given in which A-101 type extractanthas been used to extract and separate rare metals from ore concentrates, e.g.niobium-tantalum separation, thallium extraction, molybdenum-rhenium separa-tion, gallium extraction etc., in every case satisfactory results on industrial scalehave been obtained.
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