Activity of Silver in Molten Copper Sulfide Saturated with Copper

Abstract

A double Knudsen cell configuration combined with a mass spectrometer has been adopted to determine the activity of silver as a minor element in the equilibrium Cu-Cu 2 S immiscible liquids at 1373, 1423 and 1473 K to analyze the silver behavior in the copper smelting process. The phase relation and distribution ratio of silver between the molten copper and copper matte phases in the copper rich corner of the Cu-Ag-S system have also been determined experimentally at 1473 K by the quenching method and the boundaries of the miscibility gap were determined. Silver activities in the Cu-Ag binary system have been measured using both the double Knudsen cell and the conventional single cell methods in order to obtain the required reference activity value for activity measurements in the Cu-Ag-S system. The activity measurements in both binary and ternary systems indicate that silver deviates positively from the ideal behavior with the Raoultian activity coefficient at infinite dilution of 3.3 and 9.9 at 1473 K in the copper rich and copper matte phases, respectively. It is found that the activity coefficients of silver at infinite dilution in the molten copper and in the copper rich phase saturated with matte are the same at 1473 K, giving e S Ag =0. Assuming copper sulfide with minor amounts of silver to be a CuS 0-5-x -AgS 0.5 solution, activity coefficient of AgS 0.5 at infinite dilution is estimated to be 0.81 at 1473 K. Although silver proves to have the highest vapor pressure among the components in the Cu-Ag-S ternary system, it is concluded that the removal of silver to the gas phase is not likely to occur during the converting process of copper matte.