Part of tin in the magnetite-type tin-bearing ores existed as isomorphous Sn4+ in the lattice of magnetite (Fe3-xSnxO4, X = 0-1.0), which was impossible to separate and recover by physical beneficiation methods In this study, a calcified roasting process under CO-CO2 atmosphere was applied to separate tin from the magnetite-type tin-bearing tailings, and the results indicated that the isomorphous Sn4+ in the magnetite was removed effectively. Then, Fe2.6Sn0.4O4 was synthesized to investigate the interface reaction mechanisms between CaO and Fe3-xSnxO4. The results indicated that the calcified roasting process can be divided into three stages: the ionic migration of Sn4+ on the interface between CaO and Fe3-xSnxO4 and formation of calcium stannates (Ca2SnO4/CaSnO3), diffusion of Sn4+ through the product layer (CaSnO4/Ca2SnO4), the oxidation of FeO to Fe3O4 by CO2. These findings can provide theoretical support for the utilization of magnetite-type tin-bearing tailings by the calcified roasting process. (C) 2017 Elsevier B.V. All rights reserved.