Silver loss during the oxidative refining of silver–copper alloys

The high temperature oxidative refining of molten silver–copper alloys is accompanied by silver losses to the slag. Typically, borosilicate slags are utilized as a flux and air or oxygen is injected into the molten alloy. The majority of the copper can be selectively oxidized to copper oxide, but some silver is also lost to the slag. In this research, the mechanism of silver loss has been investigated. Firstly, TGA and DTA studies of molten silver–copper alloys were performed, in order to elucidate the oxidation processes occurring at the gas–metal interface in the bubble. Secondly, the silver losses to the slag in the high temperature refining tests were quantified. Thirdly, the slag was characterized using XRD and the morphology of the silver in the slag was examined. Fourthly, a pseudo-equilibrium model of the refining process was developed and this was utilized to suggest methods for minimizing the silver loss to the slag. Finally, possible methods for recovering the silver from the slag are discussed.

Research highlights
► During the high temperature oxidative refining of silver–copper alloys under a borosilicate slag, silver is lost to the slag.
► It was shown that the silver losses to the slag increased with the copper oxide content of the slag and this was attributed to a decrease in the activity coefficient of silver oxide with increasing copper oxide content.
► The Equilibrium module of Outokumpu HSC Chemistry 6.1 was used to predict the changes in the silver content of the slag as a function of the operating variables in the refining process.
► A number of potential processes were considered for recovering the silver from the refining slag.