Sn–Pb alloy processing for commercial tin production

Abstract

The aim of the research is to develop an optimal method for Sn–Pb alloy processing to obtain a marketable product – high-grade tin O1–O3 (Sn  98.5 %). Laboratory studies were conducted on the refining of the Sn–Pb alloy with the following composition, wt.%: 53–60 Sn; 18–29 Pb, first by vacuum distillation (t = 1085÷1300 °C, P = 15÷100 Рa; τ = 3÷36 h) for As, Sb and Pb sublimation, then by reagent deposition with elemental sulfur and aluminum as part of the Al–Sn master alloy in the presence of NH4Cl for Cu, Fe and Sb separation. This resulted in obtaining a Sn-containing residue (yield ~60 %) of the following composition, wt.%: 92.39 Sn; 0.46 Pb that was subjected to reagent refining to obtain O3 grade tin (metal yield ~68 %) with the following composition, wt.%: 99.5 Sn; 0.009 Pb. It was found that it is feasible to carry out refining from a preliminarily decopperized Sn–Pb alloy to obtain a finished O1 grade product with a direct extraction of 90 %. A schematic diagram was developed and recommendations were formulated for the process regulations on Sn–Pb alloy processing to obtain commercial tin and recover resulting intermediate products and waste. A furnace with separate production of As, Sb, Pb condensates with the following composition, wt.%: 94.2–98.3 As; 5.1–14.5 Sb; 78.9–86.4 Pb, respectively, was chosen as a vacuum distillation unit. The economic effect of processing ~480 ton/year of Sn–Pb alloy (~50.8 % Sn) with the production of ~235 ton/year of O1–O3 grade tin is ~39 million rubles/year.