Pellet-Sintering Process for Limonitic Nickel Laterite: Effects of Operating Parameters and Performance Improvement

Limonitic nickel laterite is difficult to sinter because of its high loss on ignition, high combined-water content, and complex refractory mineral composition, which often result in poor sinter strength and high solid fuel consumption. In this study, a pellet-sintering process was adopted to improve the sintering performance of limonitic nickel laterite. Pot sintering tests were carried out to investigate the effects of key process parameters—including moisture content, solid fuel dosage, return fines dosage, and drying–holding regime—on yield, tumble index, productivity index, and solid fuel consumption. The selected conditions were determined as follows: moisture content of 21%, solid fuel dosage of 5.8%, return fines dosage of 25%, drying at 450 °C for 5 min, and holding at 1000 °C for 10 min, under a fixed basicity of 1.5 and a bed height of 850 mm. Under these conditions, the yield, tumble index, productivity index, and solid fuel consumption reached 70.19%, 57.87%, 1.37 t·m−2·h−1, and 95.86 kg·t−1, respectively. Compared with conventional sintering, pellet sintering increased the yield, tumble index, and productivity index by 24.05%, 35.56%, and 31.73%, respectively, while reducing solid fuel consumption by 22.87%. XRD, OM, quantitative image analysis, and SEM–EDS analyses showed that pellet sintering reduced the average two-dimensional pore area fraction from 33.29% to 18.05% and the large-pore area fraction from 22.25% to 11.61%, while promoting a more continuous bonding structure characterized by a spinel-rich mineral framework, spinel–olivine eutectic-type composite bonding phases, and SFCA-type bonding phases. These results demonstrate that pellet sintering is a feasible route for improving the sintering performance and consolidation behavior of limonitic nickel laterite.