Microscopic Analysis of Magnetite Dissolution into Cu 2 S–FeS Matte with Gas Generation Using In Situ Observation

Solid magnetite inhibits suspended matte in slag from being absorbed into the matte phase during copper smelting using flash furnaces, leading to copper losses. Therefore, rapid magnetite removal by reaction with the matte is desirable; however, the dissolution behavior of magnetite into Cu 2 S–FeS matte has rarely been investigated. Herein, the dissolution mechanism of magnetite is investigated by in situ observation of the magnetite/matte interface at elevated temperatures. The in situ observations reveal that gas generation at the interface is inevitable for any matte composition. Furthermore, image analyses enable the evaluation of the time-dependent reaction area and dissolution rate of magnetite. The kinetic analysis reveals that magnetite dissolution is governed by the mass transfer of oxygen in the matte phase. Furthermore, fine bubbles evidently inhibit mass transfer, and we obtain apparent mass transfer coefficients of 2.6 × 10 –6 m/s (20 mass% FeS) and 2.2 × 10 –6 m/s (35 mass% FeS), both of which are approximately one order of magnitude smaller than those reported for FeS without gas generation. Although only a small fraction of the consumed magnetite contributes to gas generation, it significantly affects magnetite dissolution. Graphic Abstract