The Interactions between Ta-Nb Ferroalloys and Sulfate-carbonate Melts

Abstract

The oxidation of Ta-Nb containing ferroalloys takes place during pyrochemical processing of tantalum-niobium ores and secondary raw materials [1, 2]. Molten salts, in particular sulfates, carbon­ ates and their mixtures can be used as oxidizers. In the present work we studied the interaction between sodium and calcium sulfates (carbonates) and multicomponent Ta-Nbcontaining ferroalloys as well as their individual components. Thermodynamic modelling, thermogravimetric (TG), differential-thermal (DT), and high-temperature X-ray diffraction (XRD) methods were employed in the present study. The X-ray diffraction patterns were measured on heating with linear heating rate of 10 degrees/min. The extent of interaction (a) was cal­ culated from the ratio of the measured mass change of the molten mixture to the initial S 0 3 content of the system. The metals and alloys were used as powders (parti­ cle size < 0.1 mm). The purity of the individual metals was > 99.9%. The experiments were performed un­ der an inert atmosphere or under vacuum. Chemically pure sodium and calcium sulfates and sodium carbon­ ate were calcined for 2 h at 973 K prior to use. Thermodynamic analysis of the systems M Na2S 0 4 (M = Ta, Nb or V) has indicated many pos­ sible reactions. Some of the basic ones are:

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