Separation of silver from bismuth melt in a centrifugal separator with zinc as an additive

Abstract

Silver is massively present in the pyrometallurgical refining of bismuth, for the aim of effectively removing it, an innovative physical method of centrifugal separation was proposed in this work. And a two-step separation process was conducted according to the theoretical analysis of Bi-Ag and Bi-Ag-Zn phase diagrams. The micro-structure and macro-morphology of the samples obtained from the two-step separation were introduced. And the removal mechanism of silver from bismuth melt was investigated. The filtrated bismuth and bismuth-rich phase concentrated from the preliminary and secondary separation experiments mainly migrated to the lower part of the crucible, whereas the residues of precipitated Ag-Bi phase and Ag-Zn phase were found in the upper part of the crucible. In contrast, there was no separation of phases when it was in the normal-gravity field. After centrifugal separation with the theoretical amount of zinc addition at T = 543 K (270 °C) and G = 400, the purity and yield of bismuth-rich phase were up to 99.38 wt% and 83.92%, respectively. And the removal rate of silver and zinc reached 99.84% and 91.16%. Accordingly, the separation of silver from bismuth melt was found to be practical in a centrifugal separator, which featured the high-efficiency, environmental friendliness and low energy consumption.