Niobium concentration

Spectroscopic methods for the deterrnination of impurities in niobium include the older arc and spark emission procedures (53) along with newer inductively coupled plasma source optical emission methods (54). Some work has been done using inductively coupled mass spectroscopy to determine impurities in niobium (55,56). X-ray fluorescence analysis, a widely used method for niobium analysis, is used for routine work by niobium concentrates producers (57,58). Paying careful attention to matrix effects, precision and accuracy of x-ray fluorescence analyses are at least equal to those of the gravimetric and ion-exchange methods. 

The optimal temperature range for the interaction was found to be 150-230°C. The cake resulting from the fluorination process was also successfully leached with water, dissolving ammonium oxyfluoroniobate, (NH4)3NbOF6. The solution was separated from the precipitate of lithium fluoride. The main parameters of the solution were a niobium concentration of about 75 g/1 Nb205, pH = 3—4. 

Niobium occurs, usually with tantalum, in columbite Fe(NbC>3)2, (80% Nb205). pyrochlore (50% Nb2C>5). samarskne (50% Nb2Oj). chiefly found in western Australia, and South Dakota. Recovered along with tantalum by fusion with potassium bisulfate, and obtained in the residue after subsequent extraction with II20. Niobium and tantalum are separated by fractional crystallization uf the potassium fluorides, niobium concentrating in the mother liquid and tantalum in the crystals. 

Toxicity data on niobium and its compounds are sparse. The most common materials, e.g., niobium concentrates, ferroniobium, niobium metal and niobium alloys, appear to be relatively inert biologically. Limited animal experiments show high toxicity for some salts, which arc related to disturbance of enzyme action, Niobium hydride lias moderate fibiogenic and general toxic action. Recommended maximum allowable concentrations arc 6 mg/m3. Recommended maximum permissible concentration of Nb ill reservoir water is 0.01 mg/L. The threshold for affecting clarity and biological oxygen demand (BOD) is 0.1 mg/L. 

While tantalum and niobium are relatively depleted, compared to other incompatible elements, many primitive arc magmas have higher tantalum and niobium concentrations than MORE (Figure 14). This is particularly true of primitive, continental arc lavas, both basalts and andesites. Oceanic arc lavas tend to have tantalum and niobium concentrations as low as, or lower than MORBs, and elevated lanthanum concentrations compared to MORBs. 

Several electrodeposits were formed at potentials ranging from 0 to -O.IV. EDS examination of the as-deposited surface indicated the presence of aluminum and niobium in all of the electrodeposits examined. Chlorine was not detected in any of the samples indicating that the deposits contained no entrained electrolyte. Figure 7 is a plot of alloy composition as a function of deposition potential. The highest niobium concentration detected was 13.5% (atomic fraction). This was observed at a deposition potential of O.OV. As the deposition potential is made more negative, the niobium concentration is dramatically reduced. This implies that the kinetics for aluminum deposition are much faster than that of niobium, or that the niobium reduction is simply mass transport limited in the potential range examined. The fact that pure niobium deposits are apparently not achievable at potentials more positive of the aluminum deposition potential may be an indication that the codeposition of niobium and aluminum at negative potentials follows an mduced codeposition mechanism i.e., niobium deposition is only possible when aluminum is codeposited. 

All of the deposits examined had dense, compact morphologies. The deposits containing low levels of niobium had surface morphologies quite similar to that of pure aluminum. These deposits were nodular and exhibited extensive crystallographic faceting. When the niobium concentration increased, the nodules become quite smooth... 

However, at relatively high niobium concentrations in the melt NbClg" partly decomposed, yielding NbCls " and chlorine gas ... 

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