Some ideas for promoting the metal separation process are proposed based on the consideration of the force caused by interfacial tension gradient as a driving force. The force drives the particle toward the direction of the lower interfacial tension side, which has been confirmed by water model experiments. Therefore, it is possible to move fine metal particles by producing interfacial tension gradient between fine metal particles and molten slag. The force in molten slag–metal (iron) system was evaluated under some assumptions. The evaluation indicates that the force is enough large to engulf the fine metal particle by the interface between metal particle and slag for promoting metal separation process.