Fast dissolution of nickel from a lizardite-rich saprolitic laterite by sulphuric acid at atmospheric pressure

Mineralogical analyses of a saprolitic laterite has been studied by particle size analysis, thermal analysis, X-ray fluorescence (XRF), scanning electron microscope (SEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. The results showed that the saprolitic laterite consists mainly of nickel-substituted lizardite revealing the elliptic morphology. The fast rate of nickel dissolution from this saprolitic laterite by sulphuric acid at atmospheric pressure has been investigated at different temperatures. As much as 91.3% Ni could be leached after 12 min with 10%(v/v) H2SO4, particle size d50 = 25 µm, reaction temperature 90 °C, stirring at 500 rpm and liquid to solid ratio 3:1. Extending the leaching time results in a loss of nickel to the residue. To prevent the re-adsorption of dissolved nickel by re-precipitated amorphous silica, it may be appropriate to leach saprolitic laterites at a lower temperature for a longer time and maintain high free acidity.