Mechanism of Ring Formation in Nickel Ore During Rotary Kiln Processing and Its Mitigation Strategies

Ring formation in rotary kilns is a major operational problem in the ferronickel dry smelting process, in which nickel laterite ore undergoes drying, calcination, and partial reduction. Excessive ring accretion reduces thermal efficiency and disrupts stable kiln operation. In this study, the mechanism of ring formation was investigated through a combined approach integrating laboratory-scale experiments and long-term operational data obtained from a large-scale industrial rotary kiln. The effects of ore composition, particle size, and temperature on melting and sintering behavior were examined, and their correlations with operating variables such as fuel input and kiln rotational speed were analyzed. The results show that ring formation is governed by the selective melting and adhesion of low-melting constituents, particularly in ores with low basicity (MgO/SiO2 < 0.55) and high Fe content (>14 wt.%). A high fraction of fine particles (<75 μm) further promotes adhesion due to their lower melting temperature and enhanced mechanical retention on the refractory surface. In industrial operation, localized overheating near the burner zone and low kiln rotational speeds (0.9–1.1 rpm) significantly accelerate ring growth. These findings provide a mechanistic understanding of ring formation and suggest that appropriate ore blending and optimized control of fuel input and kiln rotation are effective strategies for mitigating ring accretion in commercial ferronickel rotary kilns.