Activation pretreatment of limonitic laterite ores by alkali-roasting method using sodium carbonate

Activation pretreatment of Cr-containing limonitic laterite ores by Na₂CO₃ roasting to remove Cr and Al, as well as its effect on Ni and Co extraction in the subsequent pressure acid leaching process were investigated. X-ray diffraction (XRD), thermogravimetric (TG), and scanning electron microscopy/X-ray energy dispersive spectroscopy (SEM/XEDS) techniques were used to characterize the laterite ores and the water leaching residues of alkali roasting and found that goethite is the major Ni-bearing mineral and chromite the minor one. Alkali-roasting pretreatment breaks the mineral lattices of the laterite, exposing their Ni and Co, which leads to higher extraction of these two metals under milder operation conditions in the subsequent pressure acid leaching process. Experimental results showed that the leaching of Cr and Al were up to 99 wt% and 80 wt%, respectively, under optimal alkali roasting and water leaching conditions. Compared with the direct pressure acid leaching of the raw laterite ores, leaching of Ni and Co increased from 79.96 wt% to 97.52 wt% and 70.02 wt% to 95.33 wt%, respectively, after alkali-roasting activation pretreatment was performed. Meanwhile, the grade of acid leaching iron residues increased from 55.31 wt% to 62.92 wt%, and these residues with low Cr content could be more suitable as the raw materials for iron-making.