Physical Simulation of Phase Separation at the Slag-Metal Interface During Pellet Melting: A Phenomenological Study

Metallized pellets are spherical iron-bearing burden materials obtained by treating iron ore pellets through processes such as direct reduction. They contain a certain proportion of metallic iron and mainly consist of metallic iron, incompletely reduced oxides, gangue, and other nonmetallic components. They are one of the commonly used iron-bearing materials in electric smelting furnaces. The melting process of metallized pellets not only affects the melting efficiency of the charge but is also accompanied by slag-metal separation and gangue separation, which is directly related to mass transfer, heat transfer, and production efficiency during the smelting process. However, existing studies have mainly focused on the melting behavior of pellets in a single-phase molten pool, while studies on gangue separation, interfacial migration, and slag-metal separation during pellet melting at the slag-metal two-phase interface remain rare. Because this region involves complex interfacial heat transfer, fluid flow, and interfacial interactions, investigating only the overall melting process of pellets is insufficient to reveal the actual gangue separation mechanism. Therefore, a systematic investigation of the melting and separation processes of pellets at the slag-metal interface is necessary. Based on the principle of similarity, a water-oil-ice three-phase physical model was employed in this study, in which water, silicone oil, and ice balls containing dyed silicone oil samples were used to simulate molten iron, slag, and pellets, respectively. The dyed silicone oil is specially designed to simulate the gangue in the pellet. Visualization experiments were conducted to investigate the evolution of pellet melting morphology, oil droplet (gangue) release behavior, and diffusion characteristics in the oil layer under different initial oil droplet positions and static or parallel flow conditions. The results show that the initial position of the oil droplet and the parallel flow significantly affect the local melting behavior of the ice ball and the oil droplet release process. In particular, the release time of the oil droplet located above the ice ball is significantly longer than that of the oil droplet located below the ice ball. The parallel flow significantly changes the melting sequence of the ice ball and the oil droplet release path by enhancing convective heat transfer in the lower region of the ice ball. According to the initial position of the oil droplet and the flow conditions, the oil droplet release process can be classified into five typical separation types, including (1) lateral release of the upper oil droplet after the ice shells on both sides melt through, (2) release of the upper oil droplet through a hole at the bottom of the upper hemisphere, (3) direct release of the lower oil droplet through a local hole, (4) two-stage release of the lower oil droplet controlled by interfacial constraint, and (5) single-stage release of the oil droplet on the downstream flow side driven by parallel flow. The oil droplet release time in the parallel flow cases is shorter than that in the static conditions. The diffusion behavior of the oil droplet after entering the oil layer is weakly affected by the parallel flow and is mainly characterized by inertial diffusion along the initial release direction, followed by spreading toward the surrounding area. This study reveals the slag-metal separation mechanism during pellet melting at the slag-metal interface under the combined control of flow, ice shell morphology, and interfacial interactions, providing experimental evidence for optimizing the melting and separation behavior of pellet charges in electric smelting furnaces and related smelting processes.