MIREA — Russian Technological University (Lomonosov Institute of Fine Chemical Technologies), Moscow, Russia:

N. A. Permyakova, Assistant Lecturer at the Department of General Chemical Technology, e-mail: permyakovana@mitht.ru
M. V. Tsygankova, Senior Lecturer at the K. A. Bolshakov Department of Chemistry and Technology of Rare Elements, Candidate of Chemical Sciences
E. I. Lysakova, Associate Professor at the K. A. Bolshakov Department of Chemistry and Technology of Rare Elements, Candidate of Chemical Sciences

This paper looks at the pyrochlore-monazite-goethite ores of the Chuktukonsk deposit (0.98wt.% Nb₂O₅) and their processing with the help of acidbased (HNO₃, H₂SO₄) and sulphatization techniques. Nitric-acid pressure leaching was found to be an efficient processing technique for this type of ore: ore size –0.074 mm; CHNO₃ = 25%; CH₂O₂ = 5%; τ = 2 h; solid-to-liquid = 1:9; heat treatment mode: 1 h at 160 ^oC followed by 1 h at 230 ^oC. As a result, rare earth metals and manganese are leached to the solution while all of the contained niobium remains in the cake. Two different techniques were tested to recover niobium from the cake. One is based on the use of alkali (NaOH sintering), the other is an extractive leaching technique that combines acid leaching with liquid-liquid extraction of tributyl phosphate in one stage. It was established that niobium mi nerals can be efficiently decomposed when using a mixture of hydro fluoric and sulphuric acids with the concentrations of 4.08 and 8.46 mol/L, correspon dingly, as a leaching agent. At the weight ratio of 1:2:1 of the solid to aqueous to organic phase and after the slurry has been stirred intensively for 5 minutes, niobium fluorides, which form as a result of interaction between hydrofluoric acid and the cake components, can be recovered with a 50% solution of tributyl phosphate in octane. After that they transfer to an organic phase while impurities get accumulated in the solid residue. As niobium-containing cake has a high concentration of silicon, it is recommended to first remove silicon from the cake using a strong alkaline solution.

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