A double Knudsen cell configuration combined with a mass spectrometer has b
een adopted to determine the activity of silver as a minor element in the e
quilibrium Cu- Cu2S 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 pha
ses in the copper rich corner of the Cu-Ag-S system have also been determin
ed experimentally at 1473 K by the quenching method and the boundaries of t
he miscibility gap were determined. Silver activities in the Cu-Ag binary s
ystem have been measured using both the double Knudsen cell and the convent
ional single cell methods in order to obtain the required reference activit
y 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 activ
ity 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 epsi
lon(Ag)(S) = 0. Assuming copper sulfide with minor amounts of silver to be
a CuS0.5-x-AgS0.5 solution, activity coefficient of AgS0.5 at infinite dilu
tion 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 t
o occur during the converting process of copper matte.