Optimization of Tin Recovery From Concentrates Through a Model for Prediction of Slag Composition

Abstract

Processing of tin slags in reduction furnaces was studied in order to optimize tin recovery and reduce recirculation rates of slags containing thorium and uranium oxides. A theoretical approach considering a mass balance of the process was developed and adjusted by experimental results in order to predict the final slag composition. A metallic phase (FeSnSi) was discovered trapped in the slag due to high apparent viscosity, raising the FeO and SnO2 contents of the slag sample. This FeSnSi alloy is rich in tin and its recovery would help to reduce the slags recirculation. High contents of ZrO2 were found in the slag, restricting it from reaching complete fluid phase. Through an analysis of the slag in the CaO-FeOx-SiO2 and ZrO2-CaO-SiO2 phase systems it can be concluded that final slags should be modeled aiming fluid phase at working conditions and additions should be planned in order to control ZrO2 levels.

Study of Ferrous Residue From the Brazilian Tin Industry and Perspectives of Its Recovery

“…In general, the alloy contains traces of contaminants such as Pb, S, Al, Nb, Cr and Mn, higher levels of contaminants such as W, P, Ca, and, of course, Sn, Si and Fe. Regarding this last element, compared to Wright [12] all samples have higher Fe contents and lower Sn contents, which are in accordance with Clemente (2017) [17] and indicate that these levels are characteristic of the Brazilian industry.…”

“…According to the literature [12,16], the FeSn alloy, also known as 'hardhead', has Sn amounts at least comparable to Fe amounts and the alloy is recirculated alongside with cassiterite. However, Clemente (2017) [17], showed the production of FeSn with much higher Fe and lower Sn contents, which can be a specific attribute from the Brazilian industry. As can be expected, recirculation leads to lower furnace capacity, something undesirable in a production process.…”

“…Wright (1982) [12] stated that part of Si could be obtained from SiO 2 in an EAF under very reducing conditions. However, Clemente (2017) [17] conducted experiments regarding reduction of ferrous tin slags and concluded that part of the Si added to the charge oxidized in the furnace. Although many other aspects should be analyzed for a better conclusion, this inconsistence shows that the recovery of Sn from FeSn is not an ordinary process and demands further investigation.…”