Columbite - tantalite composition

Columbite - tantalite chlorination, 5-6 composition, 4 decomposition by H2S04, 6, 259-263 HF, 6,256-263... 

The elements themselves require little comment. Niobium is 10 to 12 times more abundant in the earth s crust than tantalum. The main commercial sources of both are the columbite-tantalite series of minerals, which have the general composition (Fe/Mn)(Nb/Ta)206, with the ratios Fe/Mn and Nb/Ta continuously variable. Niobium is also obtained from pyrochlore, a mixed calcium-sodium niobate. Separation and production of the metals is complex. Both metals are bright, high melting (Nb, 2468°C Ta, 2996°C), and very resistant to acids. They can be dissolved with vigor in an HN03—HF mixture, and very slowly in fused alkalis. 

Table 60. Initial dissolution rates (RJ of niobium and tantalum dissolved from columbite or tantalite in different solutions, at 80% . (Compositions of solutions are given in mol/l)(qfter Majima et al. [415]).

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