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New data on dikes of rare metal topaz–"zinnwaldite" granites of the Salmi anorthosite–rapakivigranite complex are presented. The U–Pb (ID-TIMS) isotopic age of Ta–Nb mineralization: the columbite-(Fe)–tantalite-(Fe) series and tapiolite is 1541 ± 2.5 Ma. Conclusions are given on the age limitations of associated rocks, intersected by analogous dikes, and the discreteness of the rare-metal magmatism manifestation in the studied area. [ABSTRACT FROM AUTHOR]

Accessory columbite-(Fe) to tantalite-(Fe) from three granitic pegmatites of the Tatric Superunit (Bratislava Massif of the Malé Karpaty Mts., Bojná Massif of the Považský Inovec Mts. and Suchý Massif of the Strážovské Mts.) was used for dating by the in-situ LA–ICP–MS U–Pb method. The columbite–tantalite crystals were sampled from the most fractionated pegmatite dykes of the beryl–columbite subtype situated in the pre-Alpine, Paleozoic crystalline basement of the Tatric Superunit, Western Carpathians (western and central Slovakia). The obtained columbite–tantalite Concordia ages are as follows: 354.5 ± 4.5 Ma (Jezuitské Lesy pegmatite, the Bratislava granite Massif), 360 ± 5.0 Ma (Moravany nad Váhom, Striebornica Ridge pegmatite, the Bojná Massif), and 352 ± 8.5 Ma (Liešťany, Bystrý Hill pegmatite, the Suchý Massif). The columbite–tantalite ages show Mid-Variscan formation of rare-element pegmatites from the Devonian/Carboniferous boundary to Tournaisian stage, which is coeval with the emplacement of cogenetic granites during the main phase of Variscan intracontinental subduction and collision. The obtained columbite–tantalite age interval of rare-element granitic pegmatites of the Tatric Superunit (~360 to 350 Ma) is generally older than the ages of Be- and Li-rich rare-element pegmatites of the Moldanubian Superunit in the Bohemian Massif (~340 to 320 Ma). The rare-element granitic pegmatites of the Austroalpine Superunit (Eastern Alps) are significantly younger (~290 to 240 Ma) because they were formed in an extension regime during the Permian to Early Triassic post-Variscan orogenic collapse. [ABSTRACT FROM AUTHOR]

LCT (lithium–cesium–tantalum) pegmatites from the Kaustinen and Kolmozero regions contain columbite–tantalite mineralization, which has been presented in this study. Crystal structure, Raman microscopy, and optical property analyses of these minerals were performed. As a result of the structural studies and micro-area analyses, it was determined that these minerals in the pegmatites in question constitute a solid solution with numerous Mn-Fe and Nb-Ta substitutions within a single crystal. The ratio between Mn-Fe and Nb-Ta can change from crystal to crystal, which makes it impossible to find precise stechiometry between these ions. The crystallization conditions of these minerals were also determined by studying the associations of other rock-forming minerals and accessory minerals in the discussed rocks. [ABSTRACT FROM AUTHOR]

The paper presents experimental data on tantalite solubility in water-saturated granitoid melts with various alumina and alkaline elements concentrations at T = 650–850°C and P = 100 MPa. The maximum Ta concentration (effective solubility) in melt is shown to be always higher than the Nb concentration. As the melt composition is changed from alkaline to Al2O3-enriched, the Ta and Nb concentrations decrease by one to two orders of magnitude, and the Nb/Ta ratio simultaneously decreases (from ~0.8–0.7 to ~0.4–0.1) because the Nb concentration decreases notably more rapidly than that of Ta. This effect is enhanced at decreasing temperature. The effective Ta solubility in melt is demonstrated to be practically independent of the composition of the dissolving mineral of the columbite-tantalite series. The Ta, Nb, Mn, and Fe diffusion coefficients in granitoid melts are estimated. The Ta and Nb diffusion coefficients at T = 750°C and P = 100 MPa are ~10–10 cm2/s, and those of Fe and Mn are ~10–8.5 cm2/s. With an increase in temperature from 740 to 980°C, all of the diffusion coefficients increase by approximately 1.5 orders of magnitude. The configurations of the diffusion profiles of Ta concentration in melts change differently depending on change in the composition of the melt, temperature, or pressure. [ABSTRACT FROM AUTHOR]

There is concern that work scenarios on the tantalite mining sites in Oke-Ogun, Oyo State, Nigeria may cause occupational radiation exposure of workers due to enhanced concentrations of naturally occurring radionuclides in some process materials. A prior radiological assessment of the mining activities was carried out to determine if and which exposure scenarios may require radiation protection measures. Samples of the materials involved, comprising tantalite (tantalum ores), soil and waste rock were collected and analyzed for activity concentrations of 40K, 226Ra, 238U and 232Th using a hyper pure germanium detector gamma-ray spectrometer. Radon concentrations in the mines were also measured using a continuous radon monitor - Radon-Scout Plus (Sarad, GmbH). Activity concentrations of 40K are below 10 Bqg-1 in all the samples but all the tantalite samples contain more than 1 Bqg-1 of 226Ra and 238U. Hence tantalite is regarded as naturally occurring radioactive material (NORM) and the mining activity as a practice. The requirements for planned exposure situations apply to all the mining sites but, on the basis of graded approach, the optimum radiation protection measures vary from one mine to another, ranging from exemption to authorization. Exposures to radon in the underground mines pose the greatest radiological risks and portend the greatest need for regulatory control in the mining operations. The results further underscore the need to integrate radiation protection with the other health and safety measures in the mining sector. [ABSTRACT FROM AUTHOR]

The concentration and temperature dependences of the solubility of tantalite, pyrochlore, and tantalum and niobium oxides in fluoride–chloride aqueous (mHF + mHCl) solutions at 300–550°C and 100 MPa (Co–CoO buffer) were studied experimentally. The initial concentration of HF varied from 0.01m to 2m, while the HCl concentration remained constant and was 0.5m. A comparative analysis of the equilibrium contents of Nb and Ta upon dissolution of tantalum and niobium oxides and natural tantalite and pyrochlore in fluoride, chloride, and mixed (mHF + mHCl) solutions was carried out. [ABSTRACT FROM AUTHOR]

In this study, phase transformations were examined during low temperature interactions of natural tantalite with powders of aluminum and Ca–Al addition alloy (69.4 wt% Ca) using thermography, X-ray diffraction, and X-ray spectral microanalysis. The phase and elemental compositions of the initial mineral and the products of its metallothermic reduction were determined. Thermodynamic modeling of "mineral–reducing agent" interactions in the systems was performed in the temperature range of 500°C–3000°C, and the temperatures of the resulting products were calculated without taking into account heat losses. Experimental studies on reduction processes were performed under conditions of continuous heating of the mineral with reagents to 1200°C–1550°C in an argon flow. The studied mineral sample was manganotantalite with the composition of Mn0.94(Nb0.495Ta0.505)2.14O6 with a melting point of 1506°C. The aluminothermic reduction proceeded with the formation of intermetallic phases based on the Ta–Nb, Ta–Nb–Mn, and Nb–Mn–Al systems, and upon interaction with the Ca–Al alloy, the metal phase included solid solutions, such as (Nb,Ta)-ss. In both cases, a predominant reduction of niobium and the formation of intermediate suboxides and composite oxides containing niobium and tantalum were noted as a result of the incomplete transformation of manganotantalite during nonisothermal heating in the temperature range under study. [ABSTRACT FROM AUTHOR]

Three mineral types of the columbite group have been revealed at the Kester Deposit (Eastern Yakutia), that is, columbite-(Fe), columbite-(Mn) and tantalite-(Mn), which are part of rare-metal granites, ongonites, albitites, and greisens. Columbite-(Mn) prevails: Ta/(Ta + Nb) = 0.30, and Mn/(Mn + Fe) = 0.64. The generalized formula of columbite–tantalite of the deposit is (Mn0.61Fe0.34)0.95(Nb1.37Ta0.58Ti0.04W0.03Sn0.01)2.03O6. Columbite–tantalite forms polymineral individuals with concentric growth zonality (from the core to the rim): columbite-(Fe) → columbite-(Mn) → tantalite-(Mn) + uranmicrolite → columbite-(Mn). In columbite of the Kester Deposit, WO3 is a typomorphic impurity, which is 2.67%, on average (formula coefficent, apfu is 0.04); the maximum value is 7.12% (apfu is 0.11). The isomorphic replacement of cations in the B position is assumed according to the following scheme: 2(Nb, Ta)5+ ↔ W6+ + Ti4+. In tantalite, SnO2 is a typomorphic impurity, which is 1.01%, on average (apfu is 0.03); the maximum value is 3.74% (apfu is 0.21). The paragenesis of the columbite group minerals includes albite, topaz, lepidolite, Nb-Ta-bearing cassiterite, wolframoixiolite, wolframite, U-Hf-bearing zircon, and struverite. At the Kester Deposit, the evolution of columbite–tantalite is accompanied by an increase in Ta/Nb, Mn/Fe, and Sn/W ratios manifested in the change of columbite by tantalite both in the process of the formation of ore-bearing rocks and in the rock series: rare-metal granites → albitites → greisens. The variation limits of Ta/(Ta + Nb) and Mn/(Mn + Fe) ratios are 0.07–0.74 and 0.16–0.96, respectively. The diversity and evolution of the columbite group minerals of the Kester Deposit indicate their belonging to the rare-metal ore-magmatic system, which includes ore-bearing rare-metal granites, albitites, and greisens. The presence of small intrusions of rare-metal granites and ongonites in the deposit area allows the forecasting of new objects with bedrock and placer columbite–tantalite mineralization. [ABSTRACT FROM AUTHOR]

LCT (lithium–cesium–tantalum) pegmatites from the Kaustinen and Kolmozero regions contain columbite–tantalite mineralization, which has been presented in this study. Crystal structure, Raman microscopy, and optical property analyses of these minerals were performed. As a result of the structural studies and micro-area analyses, it was determined that these minerals in the pegmatites in question constitute a solid solution with numerous Mn-Fe and Nb-Ta substitutions within a single crystal. The ratio between Mn-Fe and Nb-Ta can change from crystal to crystal, which makes it impossible to find precise stechiometry between these ions. The crystallization conditions of these minerals were also determined by studying the associations of other rock-forming minerals and accessory minerals in the discussed rocks.

Microlite-group minerals occur as common replacement products after primary and secondary columbite-group minerals (CGM) in albitised blocky K-feldspar and in coarse-grained, muscovite-rich units of the Schinderhübel I, Scheibengraben and Bienergraben beryl–columbite pegmatites in the Maršíkov District (Silesian Unit, Bohemian Massif, Czech Republic). Textural and compositional variations of microlite-group minerals were examined using electron probe micro-analyses and microRaman spectroscopy (μRS). A complex post-magmatic evolution of the pegmatites and the following microlite populations (Mic) and related processes were found: (1) precipitation of U, Na-rich and F-poor Mic I on cracks in CGM; (2) alteration of Mic I to U-rich together with Na- and F-poor Mic II; and (3) partial replacement of Mic I and II by Mic III with a distinct Na, U and Ti loss and Ca and F gain. Stage (2) includes an extensive leaching of Na, without U loss. The final stage (3) produced euhedral-to-subhedral oscillatory zoned Ca and F enriched Mic III with distinctly different composition to the previous F-poor and A-site vacant Mic II. Aggregates of fersmite are associated commonly with Mic III. Distal Mic IIId occurs locally on cracks in K-feldspar or quartz, with compositions analogous to Mic III. Compositional variations and textural features of microlite-group minerals during dissolution–reprecipitation processes serve as sensitive tracers of post-magmatic evolution in granitic pegmatites recording complex interactions between magmatic pegmatite units and externally derived, hydrothermal metamorphic fluids. [ABSTRACT FROM AUTHOR]

The decay time of magnesium tantalate (Mg4Ta2O9 ) crystal is shorter than that of CdWO4 crystal, and its light yield and energy resolution are slightly higher than that of CdWO4 crystal respectively. Its afterglow is 0. 01% /3 ms as low as that of CdWO4. In addition, the Mg4Ta2O9 crystal has no toxic elements, and will be one of the best candidate materials in the field of container security inspection for replacing CdWO4 crystal which containing toxic element Cd. The research progresses in the structural properties, crystal growth, scintillation properties and doping modification of Mg4Ta2O9 crystals are reviewed. The research show that Mg4Ta2O9 doping with Zn2+ or Nb5+ ions can significantly increase its light yield. [ABSTRACT FROM AUTHOR]

Spontaneous parametric down-conversion is an essential tool for a quantum light source in the infrared region ranging 2–5 µm for the purpose of material identification, chemical analysis, and gas sensing. So far, photon pairs from the process in a nonlinear crystal have low tunability and a narrow spectral range because of the phase-matching condition. Here, we propose a novel type of spontaneous parametric down-conversion processes that overcomes these challenges, where two photon pairs are simultaneously produced in the visible and infrared regions in periodically poled stoichiometric lithium tantalite. It allows broadband and tunable generation of infrared photon pairs that can be employed as an alternative light source for quantum infrared spectroscopy. [ABSTRACT FROM AUTHOR]

NORM minerals generate, after metallurgical processing, radioactive slags that can be controlled by CNEN. Thus, it is necessary to establish a reprocessing route to make the material exemption. The route necessarily passes through the characterization of the slag from its physical properties. In this paper the results of the variation of the concentrations of U and Th oxides with the electrical, and magnetic properties of the slag, with their granulometry and with their density are presented. It has been observed that the metallurgical processing produces as slag a slag with molecular connections between the oxides that constitute it. In this way, the separation of the oxides will only be possible with the leaching of the slag.

The mining sector's share in Ethiopia's economy is gradually increasing. Among metallic mines, Legadembi for gold and Kenticha for tantalum are the main contributors. At Kenticha, the Ethiopian Mineral Development Share Company is producing tantalite concentrate of 40-60% grade by open pit mining. The mine area is comprised of the rocks of Neoproterozoic age, pegmatite, granite, serpentinite, and talc-chlorite schist. The ore-bearing pegmatite intruding the basement serpentinite, and talc schist rocks, is asymmetric, N-S trending, and locally affected by fractures and local faults. Mining, at present, is being done using conventional methods not by developing benches. An optimum open pit design is developed and its impact on the run of mine is evaluated based on the field data, technical mine report data, borehole data, tonnage data, grade data and mine survey. The suggested design has taken into account the mine drainage, bench design, haul road design, and mine waste dump design. Also keeping in view the future mining and production requirements. The suggested open pit mine design can minimize the dilution and improve the ore recovery. [ABSTRACT FROM AUTHOR]

Cubic potassium tantalite niobate [KTa1-xNbxO3 (KTN)] crystals of large size, good quality, and varying Nb concentration have been grown by the Czochralski method and their thermal properties have been systematically studied. The melting point, molar enthalpy of fusion, and molar entropy of fusion of the crystals were determined to be: 1536.9 K, 12 068.521 J mol-1, and 7.85 J K-1 mol-1 for KTa0.67Nb0.33O3; and 1520.61 K, 15 352.511 J mol-1, and 10.098 J K-1 mol-1 for KTa0.67Nb0.33O3, respectively. Based on the data, the Jackson factor was calculated to be 0.994f and 1.214f for KTa0.67Nb0.33O3 and KTa0.63Nb0.37O3, respectively. The thermal expansion coefficients over the temperature range of 298.15-773.15 K are: α=4.0268×10-6/K, 6.4428×10-6/K, 6.5853×10-6/K for KTaO3, KTa0.67Nb0.33O3, and KTa0.63Nb0.37O3, respectively. The density follows an almost linear decrease when the temperature increases=from 298.15 to 773.15 K. The measured specific heats at 303.15 K are: 0.375 J g-1 K-1 for KTaO3; 0.421 J g-1 K-1 for KTa0.67Nb0.33O3, and 0.430 J g-1 K-1 for KTa0.63Nb0.37O3 The thermal diffusion coefficients of the crystals were measured over the temperature range from 303.15-563.15 K. The calculated thermal conductivity values of KTaO3, KTa0.67Nb0.33O3, and KTa0.63Nb0.37O3 at 303.15 K are 8.551, 5.592, and 4.489 W m-1 K-1, respectively. The variation of these thermal properties versus Nb concentration is qualitatively analyzed. These results show that crystalline KTN is a promising material for optical applications. [ABSTRACT FROM AUTHOR]

Based on experimental data (T = 650-800 °C, P = 1-2 kbar) on the solubility of columbite and tantalite in silicate melt and on the distribution of Ta and Nb among coexisting silicate melt, aqueous fluid, and aluminum fluoride melt, we calculated a possible change in the Ta/Nb indicator ratio in residual deeply differentiated granite melts. The Clarke values of these metals in acid rocks of the Earth's crust were taken as their initial contents. The calculations were made by the mass balance method. It is shown that the separation of fluid in the closed magmatic system rock-forming minerals-silicate melt-water can lead to an approximately twice increase in Ta/Nb in the residual melt as compared with the initial Clarke value. In the system rock-forming minerals-silicate melt-aluminum fluoride melt with the initial content of fluorine close to that in biotite granites, the Ta/Nb ratio in the residual melt can increase to ~1. Successive crystallization of minerals of the isomorphic columbite-tantalite series can lead to Ta/Nb > 2 in the residual melt. Crystallization of biotite causes a significant increase in Ta/Nb and prevents the accumulation of these metals in the residual silicate melt. [ABSTRACT FROM AUTHOR]

A novel double perovskite tantalite orange–red light emitting Sr2LuTaO6:Sm3+ phosphor was synthesized by the solid state reaction. The phase, crystal structure, photoluminescence properties, thermal stability and decay curves were studied. The X-ray diffraction patterns indicated that the phosphor has a pure phase of cubic phase structure. Excited by near-ultraviolet light at 407 nm, the sample exhibited three sharp emission peaks at 564 nm, 600 nm, 645 nm corresponding to the 4G5/2 → 6HJ (J = 5/2, 7/2 and 9/2) transitions, respectively. The optimum doping concentration of Sm3+ ions was determined to be 5 mol% and the concentration quenching process comes from the energy transfer among nearest-neighbor ions. The as-prepared phosphors showed excellent thermal stability, the integral intensity at 423 K is about 91.10% of the initial intensity. The CIE chromaticity coordinates of Sr2LuTaO6:Sm3+ phosphors located in orange–red region. The results suggest that Sr2LuTaO6:Sm3+ phosphors have great potential application in white light-emitting diodes. [ABSTRACT FROM AUTHOR]

This study focused on the leaching of uranium and thorium from a high grade Ethiopian tantalite ore using sulfuric acid. The effects of variables such as acid concentration, temperature and leaching time were studied. In general, the leaching efficiency of uranium increases with increasing temperature from 100 to 300°C whereas the opposite trend was observed for thorium. The amount of uranium leached increased from 69.1% at contact time of 1 hr to 88.6% when the tantalite ore was leached for 3 hrs. On the other hand, for the experiments conditions considered in this study, the leaching behavior of uranium and thorium did not change significantly with varying sulphuric acid concentration from 70 to 90 wt%. Overall, the highest dissolution of uranium and thorium were achieved at 100°C, 70 wt% H2SO4 concentration and 1 hr contact time. [ABSTRACT FROM AUTHOR]

In this study, Zn 1- x Ca x TiTa 2 O 8 (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) ceramics were sintered from 1225 °C to 1325 °C via the solid-state reaction route. A mixture of trirutile and ixiolite phases was confirmed by the XRD and Raman spectra. The ratio of these two phases was determined by x , which was also a critical impact factor for the microwave dielectric properties. It was noticed that the × f value increased to a maximum at x = 0.02, then deteriorated gradually with further increases of x. The improved permittivity value with x was attributed to the higher polarizability of Ca2+ than that of Zn2+. Optimal microwave dielectric performance was observed in the Zn 0.98 Ca 0.02 TiTa 2 O 8 ceramics sintered at 1250 °C: ε r = 36.5, × f = 73,865 GHz, and τ f = 14 ppm/°C. The experimental results suggest that the Ca-modified ZnTiTa 2 O 8 ceramics are promising for miniaturized microwave device applications. • Ca2+ substituted A-site ion of the ZnTiTa 2 O 8 ceramics were prepared. • The ratio of the ixiolite and trirutile phases was determined by the amount of Ca2+ substitution level, which also contributed to the microwave dielectric properties. • Compared with pure ZnTiTa 2 O 8 , the Q × f value was increased from 33,679 GHz to 73,865 GHz and the τ f value was decreased from 26.13 ppm/°C to 14.02 ppm/°C. [ABSTRACT FROM AUTHOR]

Abstract The processes involved in the magmatic–hydrothermal transition in rare-element pegmatite crystallization are obscure, and the role of hydrothermal mechanisms in producing economic concentrations of rare elements such as tantalum remains contentious. To decipher the paragenetic information encoded in zoned minerals crystallized during the magmatic–hydrothermal transition, we applied SEM-EDS and LA-ICP-MS chemical mapping to muscovite- and columbite-group minerals (CGM) from a rare-element pegmatite of the albite-spodumene subtype from Aclare, southeast Ireland. We present a three-stage model for the magmatic–hydrothermal transition based on petrography, imaging and quantification of rare-element (Li, B, Rb, Nb, Sn, Cs, Ba, Ta, W, U) zoning, integrated with geochemical modeling and constraints from published literature. Stage I marks the end of purely magmatic crystallization from a peraluminous granitic melt. In stage II, polymerized silicic melt and depolymerized alkaline aqueous melt coexist as immiscible media, both of which influence muscovite and CGM crystallization. Stage II also marks the onset of phyllic alteration of primary mineral assemblages. Hydrothermal fluid release causes further resorption of primary minerals and eventual precipitation of fine-grained albite in stage III. Muscovite and CGM both exhibit trace-element zoning, while CGM also show major-element zoning. Petrographic relationships and geochemical markers such as Ta# (=Ta/[Ta + Nb]) of individual mineral zones reveal that both mineral species crystallized contemporaneously over all three stages. Furthermore, Rayleigh fractional crystallization of muscovite is efficient in fractionating Ta from Nb. Tantalum and Nb are additionally fractionated by halogen-rich aqueous media, which remobilize both elements, but redeposit preferentially Ta-enriched oxides. Columbite–tantalite mineralization is therefore both magmatic and hydrothermal. Albite associated with stage-III muscovite and CGM was likely precipitated from a hydrothermal fluid when pH changed due to hydrolysis of primary minerals. The complex zoning and resorption of minerals indicates that bulk analyses and conventional LA-ICP-MS spot ablation analyses of muscovite in rare element pegmatites may lead to erroneous modelling of element partitioning and fluid evolution. Combined petrographic and high-resolution geochemical analysis of two mineral species (which co-crystallize and incorporate the same elements of interest) is an effective tool to assess the complex processes of crystal–melt–fluid interaction. Our three-stage model may also be applicable to the still not well understood magmatic–hydrothermal transition from fertile granitic melts to formation of Sn-W veins and greisens or porphyry-type deposits. [ABSTRACT FROM AUTHOR]

Mining activities cause disequilibrium in the bound states of heavy metals in rocks, soils and mineral ore. These heavy and toxic metals find their ways into the food chain thereby posing health risks along the chain. Furthermore, the work scenarios in mining activities have exposure pathways such as inadvertent ingestion and inhalation of dust and materials from the sites. The dose levels due to heavy metals in tantalite samples from Oke-Ogun, Oyo State have been estimated. Twelve samples of tantalite ore [(Fe, Mn) Ta2O6], were obtained from the mining sites. 500mg of the pulverized samples were pelletized for their elemental analysis using proton Induced X-ray Emission technique. Hazard indices due to exposure to carcinogenic elements in Tantalite were estimated based on United State Environmental Protection Agency (USEPA) dose model. Chromium, Lead and Arsenic are the only carcinogenic elements found in the samples and average concentrations 311.05, 2533.26 and 127.35 ppm respectively and are higher than permissible limit recommended by Abundance elements in average crustal rock (AEACR) (100, 10.1 and 2-0 ppm respectively). The summation of hazard indices values estimated for carcinogenic elements are greater than unity. The estimated Life time average daily dose for the carcinogenic elements is 6.86E-06 mg/kg. The cancer risk estimated for the carcinogenic elements in Komu and Eluku is of the order Cr (1.32E-05) > Pb (5.83E-08). The total risk for these elements is 1.32E-05 and this value is within the permissible limit range of 10-4 - 10-6 recommended by USEPA, 1998. [ABSTRACT FROM AUTHOR]

The results of geochronological studies on columbite-tantalite and monazite from the rare metal pegmatites of the Kawadgaon-Challanpara area in Bastar craton, central India are presented. Columbite-tantalite yielded U-Pb concordia upper intercept age of 1978±16 Ma (MSWD = 0.18). Radiogenic 207Pb*/206Pb* (T7/6) ages on 4 out of 5 columbite-tantalite vary in a narrow range of 1903 to 2077 Ma and are similar to U-Pb age, whereas, one sample shows younger 207Pb*/206Pb*(T7/6) age of 1728 Ma. Younger Pb-Pb age of 1744 ± 250 Ma (MSWD = 150) has also been indicated by these columbite-tantalite samples. Four out of five monazite samples define Pb-Pb errorchron age of 2050±370 Ma (MSWD = 165) and radiogenic 207Pb*/206Pb* (T7/6) ages on 3 out of 5 monazites show a narrow range of 1983 to 2083 Ma. Other two samples show younger 207Pb*/206Pb*(T7/6) ages as 1254 Ma and 1592Ma. Both monazite and columbite-tantalite indicate disturbance in Pb and U isotopic systematics as revealed by high MSWD. However, selected samples from both monazite and columbite-tantalite indicate age of their formation as c. 2000 Ma. Younger ages, i.e., 1254 to 1744 Ma are indicative of later geological disturbances. Reported age of c. 2000 Ma is comparable to Rb-Sr date of pegmatitic muscovite (1850-2330 Ma) from this area and is younger to intrusive granites of c. 2500 Ma. By analogy, therefore, it may be inferred that the age of the rare element mineralization may be ~2000 Ma old, and linked with younger granitic activity that spanned over the period from 2300 to 2100 Ma in the Bastar craton. [ABSTRACT FROM AUTHOR]

The simply zoned Šejby pegmatite of beryl-columbite subtype is enclosed in migmatitized gneisses - country rocks of the southern part of the Central Moldanubian Plutonic Complex, Bohemian Massif, Czech Republic. The columbite-group minerals (CGM) occur mostly in blocky K-feldspar unit. Primary magmatic CGM [columbite-(Fe)-tantalite-(Fe)], show an interesting compositional and textural evolution. Subhomogeneous cores of columbite-(Fe)-tantalite-(Fe) (A) are surrounded by heterogeneous intermediate zones (B) and (C) with irregular to oscillatory zoning and mutually comparable compositions. Zone (B) contains grains of tapiolite-(Fe) and inclusions of pyrite decomposed into a mixture of secondary jarosite-group minerals. In the next zone (C), irregular Mn-enriched patches occur and in the outermost thin zone (D) CGM exhibit fine oscillatory zoning typically developed at crystal terminations. The late, subsolidus CGM include patchy-zoned Mn-enriched columbite-(Fe) and late columbite-(Fe) veinlets both formed at the expense of their magmatic precursors in the zone C,the veinlets are also present in the zone D. Similar but fine patches and veinlets are developed around jarosite pseudomorphs after pyrite. The compositional evolution of CGM shows a slight increase in Ta/ Nb and Mn/Fe in the zones A and B followed by a reverse trend to elevated Nb and Fe in the zone C and, in particular, in the zone D. Complex subsolidus fluid-melt interactions that generated patches and veinlets caused only minor changes in Ta/Nb and slight Mn-enrichment. Tantalum depletion in veins close to jarosite pseudomorphs after pyrite indicates higher mobility of Ta in acidic low-temperature fluids. [ABSTRACT FROM AUTHOR]

The Chinese Altai is renowned for its rich rare-element resources. Nine representative rare-element (REL) pegmatites were dated using LA-ICP-MS and 40Ar-39Ar methods. The columbite grains yield a weighted mean 206Pb/238U age of 239.6±3.8 Ma for the Dakalasu (Be-Nb-Ta) pegmatite and concordia U-Pb ages of 258.1±3.1 Ma and 262.3±2.5 Ma for the Xiaokalasu (Li-Nb-Ta) pegmatite. The zircons display a weighted mean 206Pb/238U age of 198.5±2.5 Ma for the Husite (Be) pegmatite and concordia U-Pb ages of 194.3±1.6 Ma and 248.2±2.2 Ma for the Qunkuer (Be) and Taerlang (barren) pegmatites. The muscovite 40Ar-39Ar dating gives plateau ages of 286.4±1.6 Ma, 297.0±2.6 Ma, 265.2±1.5 Ma, 178.8±1.0 Ma, 162.2±0.9 Ma, 237.7±1.3 Ma, 237.4±1.2 Ma and 231.9±1.2 Ma for the Talate (Li-Be-Nb-Ta), Baicheng (Nb-Ta), Kangmunagong (barren), Husite (Be), Qunkuer (Be-Nb-Ta), Xiaokalasu (Li-Nb-Ta), Weizigou (Be) and Taerlang (barren) pegmatites, respectively. These new ages coupled with previous geochronological work suggest that the REL pegmatites in the Chinese Altai formed during early Permain - Late Jurassic time. The REL pegmatites located in the Central Altaishan terrane are younger than those in the Qiongkuer-Abagong terrane, showing a correlation with the coeval and adjacent granites. The formation of the REL pegmatites and these granites indicates frequent and strong magmatic activity in the post-orogenic and anorogenic setting. The spatial and temporal distribution of pegmatites and granites reveals a magmatism path from the SE (of age early-middle Permian), to the NW (middle Permian - Middle Triassic) and finally to the central part (Middle Triassic - Jurassic) of the Chinese Altai. [ABSTRACT FROM AUTHOR]

In this study, the decomposition behavior of Ta and Nb from the mangano-tantalite ore was investigated using HF/H2SO4 mixture and KOH fusion. The effects of reaction time, decomposition temperature, acid and alkaline concentrations, and particle size on the dissolution process were examined. Higher decomposition rates were achieved at 6:2 mol/dm3 ratio of HF and H2SO4, and with the addition of 10 g KOH in the alkali fusion step. In addition, similar trends in decomposition rates between two agents (HF/H2SO4 and KOH) and comparable dissolution performances were observed. The increase in the decomposition temperature initially increased the decomposition rate of manganotantalite for the two systems considered in this study. However, no significant change in the leaching rate of Ta and Nb was observed beyond 50 °C for the HF/H2SO4 system and above 400 °C when using the KOH fusion process. The elemental and compositional analyses of the leached residues using XRF, XRD, and FT-IR spectroscopy indicated that the acid (mixture of HF and H2SO4) decomposition resulted in slightly better dissolution performance for Ta compared with the alkaline fusion method. Overall, the results indicated that KOH can be a suitable alternative decomposition agent to the volatile, corrosive and toxic HF in the hydrometallurgical processing of tantalite ores. [ABSTRACT FROM AUTHOR]

Europium ion incorporation, and the effect of its concentration in the relative population of Eu 3+ ions for each host site, was investigated using atomistic simulations based on the Mott–Littleton and Mean Field approaches. We predicted the most favorable sites occupied by the europium ion and the related charge-compensation mechanisms involved in these substitutions. It was found that Eu ions are the most energetically favorable for incorporation at both Li and Ta sites. A series of the occupation fraction, which was set as the relative population of Eu ions for each site, for different Eu concentrations in LiTaO 3 , also was considered. Several schemes for the distribution of the Eu dopant were also calculated and compared with experimental results. [ABSTRACT FROM AUTHOR]

The study involved the separation of Ta and Nb in a phosphate matrix using ion exchange chromatography. Experimental variations included different types of Ta/Nb containing samples, types of resin, phosphoric acid concentration as eluent, flow rate and column dimensions. Experimental conditions were developed and refined using a pure 1:1 (Ta/Nb) 2 O 5 synthetic mixture and the optimum conditions were then applied to a real tantalite mineral sample. Experimental results indicated the successful separation of the Ta and Nb in the synthetic sample using the weak basic Dowex Mathon and Dowex 66 free base resins. Almost complete recovery of Nb was achieved with 200 mL of 8 M H 3 PO 4 . It was found that Ta was more strongly absorbed but by using a stronger acid concentration of 10 M H 3 PO 4 , almost complete recovery was also obtained for Ta. Excellent elemental separation (α = 11.5) and recoveries were also obtained with tantalite mineral as sample under identical experimental conditions. Almost complete recoveries for both Nb and Ta were obtained after elution with 8.0 M and 10.0 M H 3 PO 4 respectively. Apart from the complete separation of Ta and Nb, minor elements which are also present in tantalite like Fe, Mn and U could also be successfully separated and quantitatively recovered. However, the Nb fraction was contaminated with Ti because under these conditions these two elements are simultaneously eluted. The successful separation and recovery of both Ta and Nb from a phosphate matrix suggest a possible alternative to the conventional fluoride beneficiation methods. This method also has the potential of industrial applications. [ABSTRACT FROM AUTHOR]

The aim of this work is to evaluate the genesis and tectonic setting of the Kenticha rare metal granite-pegmatite deposit using petrography and whole-rock geochemical analysis. The samples were analysed for major elements, and trace and rare earth elements by ICP-AES and ICP-MS, respectively. The Kenticha rare metal granite-pegmatite deposit is controlled by the N-S deep-seated normal fault that allow the emplacement of the granite-pegmatite in the study area. Six main mineral assemblages have been identified: (a) alaskitic granite (quartz + microcline + albite with subordinate muscovite), (b) aplitic layer (quartz + albite), (c) muscovite-quartz-microcline-albite pegmatite, (d) spodumene-microcline-albite pegmatite, partly albitized or greisenized, (e) microcline-albite-green and pink spodumene pegmatite with quartz-microcline block, which is partly albitized and greisenized, and (f) quartz core. This mineralogical zonation is also accompanied by variation in Ta ore concentration and trace and rare earth elements content. The Kenticha granite-pegmatite is strongly differentiated with high SiO2 (72–84 wt %) and enriched with Rb (∼689 ppm), Be (∼196 ppm), Nb (∼129 ppm), Ta (∼92 ppm) and Cs (∼150 ppm) and depleted in Ba and Sr. The rare earth element (REE) patterns of the primary ore zone (below 60 m depth) shows moderate enrichment in light REE ((La/Yb) N = ∼8, and LREE/HREE = ∼9.96) and negative Eu-anomaly (Eu/Eu* = ∼0.4). The whole-rock geochemical data display the Within Plate Granite (WPG) and syn-Collisional Granite (syn-COLG) suites and interpret as its formation is crustal related melting. The mineralogical assemblage, tectonic setting and geochemical signatures implies that the Kenticha rare metal bearing granite pegmatite is formed by partial melting of metasedimentary rocks during post-Gondwana assembly and further tantalite enrichment through later hydrothermal-metasomatic processes. [ABSTRACT FROM AUTHOR]

Ilmenite-pyrophanite crystals from a garnet pegmatite dyke from the Upper Codera Valley (Sondrio, Italian Alps) showing exsolutions of titanohematite and columbite-tantalite were investigated by scanning and transmission electron microscopy. The titanohematite precipitates share the same crystallographic orientation of the ilmenite-pyrophanite host, are bean-shaped when observed on sections inclined to the pinacoidal section, and are elongated when observed on sections closer to the prism section, possibly because of their discoidal shape parallel to (001). The columbite-tantalite precipitates form a hexagonal network of needles elongated along [110] of the ilmenite-pyrophanite and titanohematite host. The following crystallographic relationship was established: [100]Col//[001]Ilm; [001]Col//[110]Ilm; [010]Col//[110]Ilm, which can be explained in terms of preservation of the oxygen close packing between the ilmIlmenite and columbite structures. The interfaces between any two of the three different phases are coherent but show lattice strain contrast and sometimes dislocations because of their different unit-cell dimensions. On the basis of textural observations, titanohematite is supposed to exsolve first, followed by columbite-tantalite at temperatures below 500°C. The addition of MnO to the Fe2O3-FeTiO3 system is supposed to considerably influence the topology of the related T-X phase diagram and the solubility of Nb2O5 and Ta2O5 in this system. [ABSTRACT FROM AUTHOR]

The authors have studied the mechanism of controlled modification of composition, structure, chemistry, physicochemical and process properties of columbite, tantalite, zircon and feldspar at the meso-, micro- and nanoscales after nonthermal treatment by high-voltage nanosecond electromagnetic pulses. The studies used methods: X-ray photoelectron spectroscopy, scanning electron and atomic force microscopy, potentiometric titration, electromigration chromatography, Kelvin probe force microscopy, microhardness metering and assessment of hydrophobic behavior and flotation activity of the minerals. It is found that changes in the chemical state of atoms on the surface of minerals are mainly connected with the sequential transformation of stages in the process of formation and modification of a functional cover of mineral surface, with variation in a ratio of different type hydroxyl groups on the surface of columbite, zircon and feldspar, which conditions contrast physicochemical properties of rare metal minerals and improves selectivity of their separation by flotation. [ABSTRACT FROM AUTHOR]

The beneficiation methods for Ethiopian Kenticha pegmatite-spodumene ores were assessed through mineralogical and quantitative analyses with X-ray diffraction (XRD) and energy-dispersive X-ray fluorescence (EDXRF). The tantalite in the upper zone of the Kenticha pegmatite-spodumene deposit is 58.7wt% higher than that in the inner zone. XRD analysis revealed that the upper zone is dominated by manganocolumbite, whereas the inner zone is predominantly tantalite−Mn. Repeated cleaning and beneficiation of the upper-zone ore resulted in concentrate compositions of 57.34wt% of TaO and 5.41wt% of NbO. Washing the tantalite concentrates using 1vol% KOH and 1 M HSO led to the removal of thorium and uranium radioactive oxides from the concentrate. The findings of this study suggest that the beneficiation and alkaline washing of Kenticha pegmatite-spodumene ores produce a high-grade export-quality tantalite concentrate with negligible radioactive oxides. [ABSTRACT FROM AUTHOR]

The results of experimental studies and scientific substantiation of an effect of directional change in the chemical and phase composition of the surface and increase in the contrast of physicochemical and electrical properties of tantalite, columbite, and zircon in the course of treatment with anolyte (pH < 5) and a hydrochloric acid solution (HCl, pH 3-3.5) are reported. The mechanism of structural and chemical transformations of the mineral surface in the process of leaching with acid solutions are studied. This mechanism includes the activation of oxidation of iron atoms in the surface layer of tantalite and columbite with the transition from Fe(II) to Fe(III), destruction of the zircon surface with the formation of oxygen-vacancy defects of the SiO- and SiO-types, and intense dissolution of iron- and silicate-bearing films from the surface of rare-metal minerals. [ABSTRACT FROM AUTHOR]

Objectives: The aim of this study was to evaluate the effect of root canal irrigants on the compressive strength of hydraulic tricalcium silicate cements. Materials and methods: Specimens ( n = 60) of tricalcium silicate materials-Group 1: White ProRoot mineral trioxide aggregate (MTA), Group 2: NeoMTA Plus, Group 3: White MTA Angelus, and Group 4: Biodentine were exposed to one of the solutions ( n = 20): Phosphate buffered saline (PBS; control), 3 % NaOCl, or 17 % EDTA for 5 min while being suspended in PBS. Compressive strength values were evaluated after 7 days of storage. The data were statistically analyzed by two-way ANOVA and Tukey's multiple comparison test ( P = 0.05). Results: Biodentine (BD) showed significantly higher compressive strength than the other materials (P < 0.05) in the control group. When exposed to NaOCl, compressive strength of WMTA and WMTA-A decreased significantly (P < 0.05), while EDTA decreased the compressive strength of all the cements compared to the control (P < 0.05). There was no significant difference in the compressive strength of BD and NMTA-P when exposed to NaOCl or EDTA. Conclusions: Biodentine and NeoMTA Plus did not show a significant reduction in compressive strength when exposed to NaOCl. EDTA reduced the compressive strength of the cements tested. Clinical significance: Tricalcium silicates were differentially influenced by root canal irrigants. It is essential to understand the composition of these materials prior to clinical use. Traces of irrigants from the root canal wall must be thoroughly removed. [ABSTRACT FROM AUTHOR]

The conditions of tantalite (Congo deposit) and the decomposition of columbite (Zashikhinsk deposit) using an HF and HSO mixture when heated to 80°C have been found. The extraction of Ta and Nb into solutions achieved levels of more than 99% and ∼94% for tantalite and columbite, accordingly. It has been found that operation with filtrates that were obtained during the decomposition of concentrates and sent for the Ta and Nb extraction was radiation-proof. Schemes for the Ta and Nb separation and cleaning by octanol-1 extraction have been proposed. [ABSTRACT FROM AUTHOR]