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A selective reduction volatilization (SRV) process developed by the authors could remove excessive tin from the complex tin-bearing iron concentrates. But it was especially noteworthy that the volatilization ratio of Sn and the residual tin content were obviously influenced by the variation of roasting parameters during the SRV process. Hence, the existence form of residual tin in the roasted products and the possible reactions between SnO2 and Fe3O4 need to be further determined. In the present study, the effect of roasting parameters on the reduction of SnO2 in the tin-bearing iron concentrates was first investigated. Then, samples with diverse cassiterite/magnetite (C/M) mass ratios were used to determine the effect of magnetite on phase transformation of SnO2 by using XRD, SEM–EDS, etc. The results indicated that magnetite markedly affected the tin volatilization and phase transformation of SnO2 under CO–CO2 atmospheres. Fe–Sn spinel was easily formed during the reduction process, and higher roasting temperatures promoted the formation of Fe–Sn spinel, which had an adverse effect on the Sn volatilization ratio.

Calcite (CaCO3), one of the main impurities, has an uncertain effect on the volatilization behavior of tin oxide in the tin-bearing iron ore concentrates during the selective reduction volatilization process. In this study, natural calcite powders were added into the tin-bearing iron ore concentrates to investigate tin volatilization behavior affected by CaCO3 under different roasting temperature, CO content, and roasting time. In addition, the effect of CaCO3 on the phase transformation of SnO2 was determined using XRD, SEM-EDS combined with thermodynamics calculation. The results indicated that CaCO3 had a significantly adverse effect on the Sn volatilization ratio, because Ca2SnO4 was easily formed under CO-CO2 atmosphere. It was also found from the study that the generation of SnO(s) was the most critical intermediate for promoting the formation of Ca2SnO4.

Tin is an indispensable metal in the modern industry. The current tin smelting processes, however, have the disadvantages of high smelting temperature, long smelting time, especially high tin loss ratio (>10 wt%). The tin loss attributes to the volatilization as gaseous SnO and stannous silicate (SnO?SiO2) residual in the slag. An innovative approach for preparing metallic tin effectively from cassiterite in the presence of Na2CO3, named gas-based reduction roasting followed by water leaching process, is under development in Central South University, China. The present study, using chemically pure SnO2 and SiO2, aims to determine the impact of Na2CO3 on the metallic tin preparation from cassiterite by the novel process using XRD, SEM-EDS, chemical analysis, etc. It was found that Na2CO3 effectively restrained the tin volatilization as SnO and the formation of hardly reductive SnO?SiO2 during the reduction roasting process. In the presence of Na2CO3, most of SnO2 in the raw materials (mixture of SnO2+SiO2) was directly reduced to metallic tin, and part of SnO2 reacted with Na2CO3 to form intermediate Na2SnO3, which was then reduced to metallic tin. The SiO2 was transformed into Na2SiO3 and then went into the water solution in the following water-leaching process. The main reactions of the SnO2 + SiO2 system in the presence of Na2CO3 under reductive atmosphere were ascertained.

Iron, tin-bearing tailings is a kind of hazardous solid waste generated from cassiterite dressing operation. It is difficult to utilize the tailings by present mineral processing methods due to the complex dissemination characteristics. In this study, a process of gas-based magnetizing roasting followed by magnetic separation was studied for separating and recovering iron from the tailings. The effects of roasting and magnetic separation parameters on the recovery of iron were systematically investigated. The optimum parameters were proposed as follows: CO/(CO+CO2) content of 5%, roasting temperature of 850 “C, roasting time of 60 min, grinding particle size of 90% less than 45 µm and magnetic field intensity of 800 Gs. Under these conditions, the magnetic concentrate containing 68.5% Fe and 0.06% Sn was achieved, which can be used as high-quality raw materials for direct reduction iron production.