In the reaction shaft of the flash furnaceFlash furnace, particle-particle interactionsParticle interaction are known to be significant, and collision and coalescenceCollision and coalescence of the droplets are thought to dominate the matteMatte yield in the settler. Although it is essential to understand this behavior for efficient copper recoveryCopper recovery and sustainable production, the mechanisms of concentrateConcentrate combustionCombustion, particle collision, and coalescence have not yet been fully understood due to a phenomenon based on very fast reactions of fine concentratesConcentrate. In this study, to reveal the mechanisms of combustionCombustion, collision, and coalescence of the concentrateConcentrate, a microscopic observation method was developed using high-speed imaging. A small, vertical laminar flow furnaceFurnace made of quartz, the micro-drop tube furnaceFurnace, was supplied with heated oxygen, and a small amount of concentrateConcentrate was continuously fed from the top of the furnaceFurnace and combusted. Using a high-speed camera and microscope lens, direct observationDirect observation of the combustionCombustion behavior and morphological change of single particle in the concentrateConcentrate was successfully achieved. The knowledge obtained from this direct observationDirect observation would be highly useful for estimating concentrateConcentrate combustionCombustion behavior and matteMatte droplet growth in the reaction shaft of the flash furnaceFlash furnace.