Thernmodynamics and Phase Equilibria in the (Ni, Cu, Zn)-(As, Sb, Bi)-S Systems at Elevated Temperature (300-900 C)

Abstract

Stable phase relations in the (Ni, Cu)-(As, Sb)-S, Cu-Bi-S and Zn-As-S systems and their thermodynamic properties, at the presence of the impurities, are reviewed. The Cu-based systems are relatively intensively studied. Among the sulfosalts of these systems tetrahedrite (Cu12+xSb4+yS13, where 0 < x < 1.92 and -0.02 < y < 0.27) and tennantite (Cu12+xAs4+yS13, where 0 < x < 1.72 and 0 < y < 0.08) are reported to be the most stable relative to other sulfosalts and certain other sulfide phases, which accounts for their common occurrence in a variety of mineral ore deposits. Natural tetrahedrite and tennantite in equilibrium with other minerals commonly constitute other chemical elements as a substitution for Cu, As and Sb and both are described by the general formula:(Cu, Ag)10(Fe, Zn, Cu, Hg, Cd, Co, Au)2(Sb, As)4S13. According to the literature data the Ni-based systems comprise a single stoichiometric ternary stable phase for their respective impurities (gersdorffite, NiAsS, and ullmannite, NiSbS), and both experience a wide solid solubility range. At favorable conditions substitution of As for S in the gersdorffite and Co for Ni and Sb for As in the ullmennite are the main mechanisms of solid solution formations. Thermodynamic properties and phase equilibria studies in the Zn-As-S system are rare among published litrature. A study about this system, below 760 oC, has shown that there is no ternary phase stable. In general, the ternary systems have complex phase relations, which may be as a result of the very low differences in their Gibbs energies of formation.