A comprehensive study of atmospheric pressure leaching of saprolitic laterites in acidic media

The mineralogy of saprolitic laterites has been characterised using X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis and X-ray fluorescence. The results showed that the ore consists mainly of nickel-and iron-substituted lizardite and minor quantities of magnetite. Several experiments were conducted to investigate the extraction of nickel and cobalt from lizardite at atmospheric pressure in acidic media as a function of particle size, sulphuric acid concentration, reaction time, temperature and liquid to solid ratio. Generally, as much as 69.6% Ni and 30.8% Co were extracted under the experimental condition of 10% (v/v) H2SO4, reaction temperature 90 degrees C, reaction time 2 h, particle size 59.9% passing through 74 mm, stirring at 500 rev min(-1) and liquid to solid ratio 3 mL g(-1). Increased extraction of Ni and Co from lizardite with sulphuric acid could be obtained by introducing leaching additives such as ferric chloride (Ni leaching rate 74.8%, Co leaching rate 45.4%), organic acid (Ni leaching rate 76.3%, Co leaching rate 48.7%) and fluoride (Ni leaching rate 81.7%, Co leaching rate 52.3%).