Phase relations in the Cu2S-FeS-ZnS and Cu2S-PbS-ZnS ternary systems at 1473°K: Extraction of zinc from sulphide ore using liquid copper as a reagent

CIM Bulletin, Vol. 95, No. 1059, 2002

C.M. Nyamai, S. Surapunt and K. Itagaki

The use of liquid copper as a medium for zinc extraction has been used in the Warner Process as a method of processing zinc-lead sulphide ore. The recovery of zinc metal is based on the reaction: ZnS(s) + 2Cu(l) = Zn(g) + Cu2S(l) In this method, thermodynamic and phase equilibria investigations of the Cu2S-FeS-ZnS and Cu2S-PbS-ZnS systems are of importance and form the basis for the liquid sulphide phase which appears as a product and is used as a solvent in the Warner Process. Phase relations in the Cu2S-FeS-ZnS and Cu2S-PbS-ZnS ternary systems were determined experimentally at 1473°K to provide a fundamental basis for the new zinc smelting process. The results show that the solid solubility of ZnS in the two systems is very small (2 wt% to 3 wt% ZnS in FeS, 4 wt% ZnS in Cu2S for the u2S-FeS-ZnS system; less than 0.5 wt% ZnS in both PbS and Cu2S for the Cu2S-PbS-ZnS system). The Raoultian Activity Coefficient of ZnS in the liquid mixtures and the vapour pressure of zinc over the matte in both systems is relatively large (g° = 7.7 – 15.8, Pzn(atm) = 0.088 – 1.026 or the Cu2S-FeS-ZnS system; g° = 8.9 – 12.9, PZn(atm) = 0.075 – 0.214 for the Cu2S-PbS-ZnS system). On the FeS-ZnS join, the only phases detected are FeS and iron-rich sphalerite (Zn, Fe)S. The binary join mixture occurs at about 92 wt% FeS-8 wt% ZnS at 1473°K. Electron microprobe examination of the quenched samples indicate about 47 wt% to 48 wt% FeS in sphalerite and about 2 wt% to 3 wt% ZnS in the iron sulphide phase. On the Cu2S-ZnS join, microprobe analysis reveals that the maximum solubility is 4 wt% Zn in liquid Cu2S and 3.6 wt% Cu in solid ZnS. In the Cu2S-PbS-ZnS ternary system, microprobe analysis of the quenched samples indicate on average, 5 wt% ZnS in the liquid phase region. The only phases detected on the PbS- ZnS join are ZnS and PbS. The eutectic phase contains, on average, 13 wt% ZnS. The phase relationships, very low solid solubilities of zinc sulphide in the liquid mixtures of both Cu2S-FeS-ZnS and Cu2S-PbS-ZnS systems, coupled with the high Raoultian Activity Coefficient of ZnS as well as the high vapour pressure of zinc over matte all favour the partitioning of zinc metal into the vapour phase. This new process is cost effective and bypasses the expensive and tedious conventional technique of zinc production involving oxidation of the sulphide ore by roasting followed by a reduction process to extract the zinc. The results indicate that a new zinc smelting technology using the Warner Process would be more efficient and preferable over the traditional methods of zinc extraction.
Keywords: Extraction, Sulphide, Zinc, Liquid copper, Smelting