Supergravity process for enriching and separating Ag from Sn–Ag–Zn melts

Abstract

The feasibility of applying supergravity technology to enhance desilverization of crude Sn with Zn was studied using the model Sn–1.5Ag–xZn alloys. The solidification characteristics of the alloys were examined using differential scanning calorimetry and scanning electron microscopy. In addition, the effect of the supergravity field on the enrichment and separation behavior of Ag in the alloy samples was investigated. Upon cooling, Ag–Zn compounds crystallized first from the alloy melts, followed by the proeutectic Sn phase and Sn–Zn eutectic phase. A greater number of Ag–Zn compounds were formed with increasing Zn content. After supergravity enrichment, the Ag–Zn compounds were concentrated at the bottom of the samples. The Ag content gradually increased along the supergravity direction, and the distribution gradient of Ag in the sample became steeper with increasing gravity coefficient (G). The Ag–Zn compounds were effectively separated from the alloy melt by filtration under supergravity fields. After separating the Sn–1.5Ag–7.5Zn alloy at 230 °C and G = 400, Ag content of molten Sn which passed through the filter was decreased by 15.6 times to 0.102 wt%, while the majority of the Ag–Zn compounds were retained by the filter, resulting in a 93.6% separation rate of Ag.