Phase Transformation during Metallothermic Reduction of Tantalite

In this study, phase transformations were examined during low temperature interactions of natural tantalite with powders of aluminum and Ca–Al addition alloy (69.4 wt% Ca) using thermography, X-ray diffraction, and X-ray spectral microanalysis. The phase and elemental compositions of the initial mineral and the products of its metallothermic reduction were determined. Thermodynamic modeling of “mineral–reducing agent” interactions in the systems was performed in the temperature range of 500°C–3000°C, and the temperatures of the resulting products were calculated without taking into account heat losses. Experimental studies on reduction processes were performed under conditions of continuous heating of the mineral with reagents to 1200°C–1550°C in an argon flow. The studied mineral sample was manganotantalite with the composition of Mn_0.94(Nb_0.495Ta_0.505)_2.14O₆ with a melting point of 1506°C. The aluminothermic reduction proceeded with the formation of intermetallic phases based on the Ta–Nb, Ta–Nb–Mn, and Nb–Mn–Al systems, and upon interaction with the Ca–Al alloy, the metal phase included solid solutions, such as (Nb,Ta)-ss. In both cases, a predominant reduction of niobium and the formation of intermediate suboxides and composite oxides containing niobium and tantalum were noted as a result of the incomplete transformation of manganotantalite during nonisothermal heating in the temperature range under study.