Affiliation:
1. Institute of Experimental Mineralogy, Russian Academy of Sciences
Abstract
The concentration and temperature dependences of the solubility of natural pyrochlore and columbite, tantalum and niobium oxides in alkaline aqueous solutions of NaOH and (mNaF + mNaOH) at 300–550°C, 100 and 50 MPa and low oxygen fugacity (Co-CoO and Ni-NiO buffers) were experimentally studied. . The initial concentration of NaOH varied from 0.01 to 2 m, and the concentration of NaF from 0.01 to 1 m. It has been established that the content of Nb in alkaline solutions in the entire studied range of concentrations is higher than the content of Ta by approximately one and a half orders of magnitude. At the same time, the solubility of pyrochlore in alkaline sodium solutions is noticeably higher than the solubility of columbite, which suggests that Nb is more capable of forming complexes in alkaline solutions, while Ta complexation is mainly suppressed. The solubility of pyrochlore and columbite decreases with increasing temperature. The presence of the F-ion in the form of NaF low concentrations has a positive effect on the solubility of minerals and oxides of Ta and Nb at high temperatures (500–550°C). It has been established that in NaOH solutions, the deposition of Nb is favored by a situation with a decrease in oxygen fugacity (Co-CoO buffer). The study of pressure effect at 50 and 100 MPa on the solubility of pyrochlore, columbite, and oxides of Ta and Nb in sodium alkaline solutions showed that the solubility of pyrochlore increases with increasing pressure. The solubility of columbite does not change much in this case. Thus, a decrease in pressure favors the deposition of Nb in the form of tantalum niobates upon dissolution of pyrochlore. For columbite, there is no such dependence.
Publisher
The Russian Academy of Sciences
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