Thermodynamics of the miscibility gap in the Ag-Se system

The miscibility gap in the Ag-Cu-Se system plays a central role in the smel ting of copper anode slimes for the recovery of silver; however, its positi on in the Ag-Se and Cu-Se component binary systems is poorly defined. In th is work, the miscibility gap in the Ag-Se system has been accurately define d by holding samples at selected temperatures, then quenching them and anal yzing the two phases. The miscibility gap has been shown to extend from 6.7 to 25.0 pet at the monotectic temperature of 890 degrees C. As the tempera ture increases to 1150 degrees C, the boundaries do not converge very rapid ly. The limiting activity coefficient of Ag2Se in molten silver was calcula ted to be 7.8 at 1100 degrees C, confirming earlier work. The limiting acti vity coefficient of hypothetical liquid selenium at the same temperature wa s found to be approximately 0.008, Finally, the activity of hypothetical li quid selenium in the liquids on either side of the miscibility gap, from th e monotectic temperature to 1150 degrees C, was mapped.