Directional crystallization of Fe-Ni sulfide melts within the crystallization field of monosulfide solid solution

A method is proposed for conducting the quasiequilibrium directional crystallization of Cu-Ni sulfide melts and the use of this process for constructing a fragment of the phase diagram of the Fe-Ni-S system (x(S) < 0.51) in the region of the primary crystallization of the monosulfide solid solution (mss). A combination of directional crystallization and DTA allowed us (i) to construct the liquid line of descent and the compositional trend of the solid solution during crystallization, which corresponded to segments of trajectories in the liquidus and solidus surfaces; (ii) to constrain the position of the tie lines and determine the distribution coefficients of components, and (iii) to refine the coordinates of points on the monovariant line corresponding to the phase reaction mss + melt -> heazlewoodite solid solution. The first data were obtained on the detailed topography of the liquidus and solidus surfaces near this reaction with the two solid solutions and melt, a fan-shaped arrangement of the tie lines was discovered, and mss fields that behave differently during cooling were discovered, with the boundary between them located between 27 and 37 mol % Ni. Pentlandite in the part of the phase diagram in question was demonstrated to be produced by a solid-phase mechanism. The results can be efficiently used in studying the genesis of minerals at sulfide Cu-Ni deposits like Norilsk and Sudbury.