Distribution And Accumulation Of Silver In Crude Tin Alloy

Silver as a precious metal is widely used in electronic materials, photosensitive materials, solder, battery materials, silver paste, decorations etc. On one side with people’s demand for silver is increasing and on the other side the silver resources are decreasing, so it is particularly pressing to recover of silver from crude tin.There were two kinds of raw materials in these experients, one was the Sn-Ag alloy the other was Sn-Ag-Pb alloy. At present, the main treatment process is pyrometallurgy combined with hydrometallurgy. But these processes has drawbacks, such as long process flow, great investment, great consumption of reagent, pollution, et al. Experiments were done based on the advantage of zinc desilverization which has characteristic of simple, effective process and with no pollution.The possibility of using zinc enrichment of silver from Sn-Ag alloy was analyzed combined with the phase diagrams, thermodynamics and dynamics. The combination and distribution of Ag before and after zinc added was investigated using SEM, XRD, EDS and chemical analysis. Adding zinc, cooling rate, holding time on the influence of silver enrichment were studied by orthogonal experiment.The reaction mechanism was realized through the microstructure analysis. For Sn-Ag-Pb alloy experiments about zinc desilverization were attempted.The results of phase diagram analysis and thermodynamic calculation shows that enrichment of silver in crude tin with Zn is possible, for the Ag-Zn compounds are much easier to be formed than Ag-Sn compounds. Dynamics show that the reaction process can be speeded up by mixing. Experimental results show that Ag exists in the form of Ag3Sn in Sn-1.5wt%Ag alloys, no obvious segregation can be seen; zinc can not effectively spread to the whole melt and reacted with Ag3Sn without stirring, after stirring Ag will exists in the form of Ag-Zn compounds and enrichment of the bottom of the samples affected by the gravity; Orthogonal experiment results show that the grow up of Ag-Zn compounds were greatly effected by the amount of zinc and stirring conditions, less effected by cooling rates;The best level combination for Ag enrichment is that nzn:nAg=5, stiring20minutes, cooling rate1.5℃/min. Microstructure analysis shows the big Ag-Zn compounds were formed by small Ag-Zn compounds which generated in Zn reacting with Ag-Sn compound and tend to sinking into the bottom of sample. Experimental results of Sn-Ag-Pb alloy show that Ag could be enrichmented by zinc desilverization, the enrichment ratio is higher than eighty persents.