Activation pretreatment of limonitic laterite ores by alkali-roasting using NaOH

Activation pretreatment of Cr-containing limonitic laterite ores by NaOH roasting to remove Cr, Al, and Si, as well as its effect on Ni and Co extraction in the subsequent pressure acid leaching process was investigated. Characterization results of X-ray diffraction (XRD) and scanning electron microscopy/X-ray energy dispersive spectroscopy (SEM/XEDS) show that goethite is the major Ni-bearing mineral, and chromite is the minor one. Experimental results show that the leaching rates of Cr, Al, and Si are 95.6wt%, 83.8wt%, and 40.1wt%, respectively, under the optimal alkali-roasting conditions. Compared with the direct pressure acid leaching of laterite ores, the leaching rates of Ni and Co increase from 80.1wt% to 96.9wt% and 70.2wt% to 95.1wt% after pretreatment, respectively. Meanwhile, the grade of acid leaching iron residues increases from 54.4wt% to 62.5wt%, and these residues with low Cr content are more suitable raw materials for iron making.