a b s t r a c tActivity of uranium was determine d in gallium, indium and gallium-indium eutectic (21.8 wt.% In) based alloys between 573 and 1073 K employing the electromotive force method. In two-phase U-Ga-In alloys, uranium forms the intermetallic compound UGa 3 . Activity coefficients and solubility of uranium in Ga-In eutectic were also determine d in the same temperature range. Partial thermodynamic functions of c-U in saturate d alloys wit h gallium, indium and Ga-In eutectic were calculated.

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High reactivity of powdered aluminium together with its relatively low price are the main reasons for the application of this metal as a reducing agent for the reduction of oxides and fluorides of rare and rare earth metals by the aluminothermal method. This technology is widely used in the production of master alloys for ferrous metallurgy. The "out-of-furnace" process (i.e. without external heat access) is the prevailing technology for metallic niobium production worldwide. However, aluminothermal reduction for industrial production of metallic tantalum has been limited because of the high required temperature, over 2800 °C.In this paper the results of simultaneous reduction of tantalum(V) and iron(III) oxides by calcium-aluminothermal "out-offurnace" process are presented. Powdered aluminium and metallic calcium were used as reductants. The pickup of tantalum at smeltings with the mass of raw materials over 1 kg reached 94%. The metal was obtained in the form of compact ingot; separation of metallic and slag phases was excellent. Crushed melt underwent refining remelting in an electron beam furnace.For thermodynamic studies and optimization of the aluminothermal reduction processes of Ta 2 O 5 and Fe 2 O 3 in the temperature range of 1000-3000 °C a licensed computer simulation program "HSC Chemistry 6.1, 2007", elaborated by the company Outotec Oy, was applied.