Influence of Non-stoichiometric Serpentine in Saprolite Ni-ore on a Softening Behavior of Raw Materials in a Rotary Kiln for Production of Ferro-nickel Alloy
The investigation of influence of non-stoichiometric serpentine in saprolite Ni-ore on a softening behavior of raw materials has been successfully carried out by SEM-EDS analysis. Serpentine in ore is classified into the low-MgO and high-FeO, high-MgO and low-FeO type. The ratio of that depends on the degree of leaching of MgO during the weathering. The crystal lattice of serpentine is significantly disturbed by the leaching of MgO, and has cation component much lower than stoichiometric composition, which allows replacement of much Mg2+ by Fe3+ to be enhanced during weathering. This leads to the formation of non-stoichiometric low-MgO type serpentine with much Fe2O3. The recrystallization of that continually takes place in accordance with equilibrium. Therefore, it is not until 1300°C that olivine (2(Mg1–xFex)·SiO2) occurs, in that case, low-MgO and high-SiO2-FeO amorphous silicate is simultaneously formed as the residual melt. Further, CaO in flux and Al2O3 in spinel melt into that melt, which allows melting temperature of melt to be still more reduced. In the recrystallization of non-stoichiometric high-MgO type of serpentine, olivine occurs from around 900°C. High-MgO-SiO2 and low-FeO amorphous silicate is simultaneously formed as the residual of recrystallization. Whereas, the contents of higher-MgO and lower-FeO than Ore-A leads to difficulty in melt generation. Thus, melt generation in saprolite Ni-ore occurs as the residual in the recrystallization (i.e., formation of olivine) of non-stoichiometric serpentine, being enhanced by the amount of MgO leached and Fe3+ by which Mg2+ is emplaced in the weathering.