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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 SnO 2 and Fe 3 O 4 need to be further determined. In the present study, the effect of roasting parameters on the reduction of SnO 2 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 SnO 2 by using XRD, SEM–EDS, etc. The results indicated that magnetite markedly affected the tin volatilization and phase transformation of SnO 2 under CO–CO 2 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. [ABSTRACT FROM AUTHOR]