Thermal behaviors and growth of reduced ferronickel particles in carbon-laterite composites

The thermal behaviors of single laterite ore and graphite-laterite mixtures were investigated by thermogravimetry (TG),derivative thermogravimetry (DTG),and differential thermal analysis (DTA).Four mass loss steps maximized at about 78,272,583,and 826℃ are observed for the laterite ore,representing the vaporization of free water,the dehydroxylation of goethite,the decomposition of serpentines,and the second dehydroxylation of serpentines,respectively.The reduction reactions of the graphite-laterite mixtures start at around 700℃ and can be divided into three major temperature regions.Coal-laterite composites with an addition of 10 wt.％ CaO were roasted at 1100-1350℃ for 30 min,and the reduced samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The results indicate that the reduction reactions proceed more completely at higher temperatures.The growth of the reduced ferronickel particles is greatly influenced by the roasting temperature.Obvious growth of the reduced ferronickel particles appears with the formation of worm-like crystals for the sample reduced at 1250℃,and spheric particles are observed for the sample reduced at 1300℃.When the reduction temperature increases to 1350℃,the reduced ferronickel particles agglomerate to ferronickel granules of 3-8 mm in diameter.The main elements in the granules include iron,nickel,chromium,carbon,and sulfur,with the content of nickel and that of iron of 9.08 wt.％ and 85.21 wt.％,respectively.