Experimental study of solubility of columbite and pyrochlore, tantalum and niobium oxides in alkaline hydrothermal fluids at 300–550°C, 50 and 100 MPa

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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.

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N. Kotova

Institute of Experimental Mineralogy, Russian Academy of Sciences

编辑信件的主要联系方式.
Email: kotova@iem.ac.ru
俄罗斯联邦, Chernogolovka

V. Korzhinskaya

Institute of Experimental Mineralogy, Russian Academy of Sciences

Email: kotova@iem.ac.ru
俄罗斯联邦, Chernogolovka

Yu. Shapovalov

Institute of Experimental Mineralogy, Russian Academy of Sciences

Email: kotova@iem.ac.ru

Corresponding Member of the RAS

俄罗斯联邦, Chernogolovka

参考

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2. Fig. 1. Concentration dependences of the equilibrium content of: a) niobium during dissolution of pyrochlore (Pchl), columbite (Col) and Nb2O5 in NaOH solutions; b) tantalum during dissolution of pyrochlore (Pchl) and Ta2O5 in NaOH solutions (T = 550 °C, P = 100 MPa, Co–CoO buffer).

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3. Fig. 2. Concentration dependences of the equilibrium content of niobium during dissolution of: a) pyrochlore (Pchl) and columbite (Col) in (1mNaOH + mNaF) solutions; b) Nb2O5 in NaOH solutions and (mNaOH + mNaF) solutions with equimolar contents of NaOH and NaF (T = 550°C, P = 100 MPa (Co–CoO buffer).

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4. Fig. 3. Concentration dependence of Ta2O5 solubility in (mNaOH + mNaF) solutions: unshaded squares – in (1mNaOH + mNaF) solutions; shaded squares – in (mNaOH + mNaF) solutions with equimolar contents of NaOH and NaF (T = 550°C, P = 100 MPa, Co–CoO buffer).

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5. Fig. 4. Temperature dependences of the equilibrium contents of niobium in NaOH and (mNaOH + mNaF) solutions at a pressure of 100 MPa: a) for pyrochlore: shaded figures – 0.1m and 1m NaOH solutions; unshaded figures – (mNaOH + 0.1m NaF); b) for Nb2O5: asterisks – 0.1m NaOH; squares – 1m NaOH; triangles – (1m NaOH + 0.5m NaF) solution.

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6. Fig. 5. Temperature dependence of Ta2O5 solubility: a) in 0.1m NaOH; b) in solutions (m NaOH + m NaF) (T = 550°C, P = 100 MPa (Co–CoO buffer).

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7. Fig. 6. a) Temperature dependence of the equilibrium content of niobium during dissolution of pyrochlore in 1m and 0.1m NaOH at different pressures (shaded figures at 100 MPa; unshaded figures at 50 MPa); b) concentration dependence of the equilibrium content of niobium during dissolution of columbite and pyrochlore in NaOH solutions at different pressures (shaded figures – 100 MPa; unshaded figures – 50 MPa) (T = 550oC, Co–CoO buffer).

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8. Fig. 7. Effect of NaOH concentration and fluid pressure on solubility: a) Nb2O5 at different pressures (shaded figures at 100 MPa; open figures at 50 MPa); b) Ta2O5 at different pressures (shaded figures at 100 MPa; open figures at 50 MPa) (T = 550oC, Co–CoO buffer).

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9. Fig. 8. Crystals formed during dissolution of: a) columbite in 0.1 m NaOH solution; b) pyrochlore in 1 m NaOH solution (T = 550 °C, P = 100 MPa, Co–CoO buffer).

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10. Fig. 9. a) Natrotantite Na2Ta4O11 crystals formed by dissolving Ta2O5 in a 0.01m NaOH solution; b) NaTaO3 crystals formed by dissolving Ta2O5 in a 0.5m NaOH solution (T = 550°C, P = 100 MPa, Co–CoO buffer).

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