Volume shrinkage of ludwigite/coal composite pellet during isothermal and non-isothermal reduction

Highlights: • Ludwigite is boron containing iron ore and can be used for boron extraction. • Isothermal and non-isothermal reduction of ludwigite/coal pellet was performed. • Volume shrinkage of the pellet highly depends on reduction temperature. • Activation energy for volume shrinkage during isothermal reduction is 276.0 kJ/mol. - Abstract: The volume shrinkage and bulk density evolution of ludwigite/coal composite pellet during solid state isothermal and non-isothermal reduction was investigated. It was found that the volume shrinkage and bulk density highly depended on reduction temperature. The volume shrinkage and density of the pellet increased with the increasing of reduction temperature and the increasing rate was fast within 15 min. The volume shrinkage and density kept stable when the reduction temperature was higher than 1250 °C. The highest volume shrinkage and density were 55.55% and 3.43 g/cm³ at the temperature of 1300 °C when reduced for 30 min. The shrinking and densifying of the composite pellet were mainly due to the loss of carbon and oxygen and the sintering of gangue oxides and metallic iron particles. The kinetics of volume shrinkage of ludwigite/coal composite pellet in the reduction process was also deduced and the value of the activation energy was 276.0 ± 59.52 kJ/mol from 1150 °C to 1250 °C.