Effect of activation pretreatment of limonitic laterite ores using sodium fluoride and sulfuric acid on water leaching of nickel and cobalt

- H2SO4 and NaF activating laterite for improving Ni/Co leaching over Fe was proposed.
- Optimum conditions for leaching target elements were determined.
- Ni/Co leaching can be obviously improved compared with directly H2SO4 leaching.
- Thermodynamic basis and phase transformation of activation process were clarified.

This study investigated the effect of activation pretreatment of limonitic laterite ores using sodium fluoride and sulfuric acid on water leaching of nickel (Ni) and cobalt (Co) over iron at atmospheric pressure. X-ray diffraction, thermogravimetric and differential scanning calorimetry, scanning electron microscopy/energy-dispersive spectroscopy, and optical microscopy were used to characterize ore samples before and after activation. Results showed that iron oxides are the major minerals of the original ore, as well as the major Ni- and Co-bearing minerals. Activation pretreatment can break these mineral lattices and expose their Ni and Co to the reaction interface, thereby facilitating easy and selective extraction of both metals over iron under mild leaching conditions. Ni and Co leaching reached 85.3% and 93.9%, respectively, and the Fe dissolution was < 8% under optimal conditions. Furthermore, behaviors of Fe, Ni, and Co in the activation process were illustrated. The effects of such behaviors on their leaching were also discussed.