Gangue minerals of siliceous nickel ores, raw material of Fe-Ni smelting, occupy some 80 % of each ore and changes of the mineral compositions of blended ores due to mines as well as working places are apt to make smelting operations unsteady. The effect of the mineral compositions and flux on softening temperatures of the ores was investigated and the following results were obtained.
(1) Fe2SiO4 inevitably formed in reducing process of the ore creates olivine slag with low melting point, reacting with CaO, Al2O3 and SiO2 of the flux as well as the ore and generates local molten phases above some 1,473K.
(2) Melting temperature of the ore is influenced in the beginning by the amount of Fe2SiO4, that is index of Fe / SiO2 and later by index of (Al2O3 + CaO) / SiO2, along with proceeding of FeO reduction.
(3) The ore with higher value of Fe / SiO2 gives better reduction fractions of Ni and Fe due to progress of direct reduction by solid C in the local molten phases from lower temperature.
(4) Fe of goethite plays essential roles both in slag formation and in Ni recovery.
