Reductive acid leaching of laterite and metal oxides — A review with new data for Fe(Ni,Co)OOH and a limonitic ore

The reductive leaching of nickel laterite has attracted the interest of many researchers due to the enhanced kinetics of nickel and cobalt dissolution in the presence of acids and reducing agents during atmospheric, pressure, heap or bio leaching processes. Systematic studies on synthetic oxides and natural ores can shed light on the reaction mechanism and lead to investigations of beneficial reagents for further studies. This paper briefly reviews the literature and describes a comparative study of metal leaching from synthetic goethite spiked with nickel or cobalt and a limonitic laterite ore to rationalise the role of reducing agents in acid media. Results are discussed on the basis of the effect of speciation, surface chemical reactivity of oxides and heterogeneous kinetic models.

► FeOOH leaching rates are controlled by a surface reaction mechanism via H+ adsorption.
► Fe/Ni leaching from laterite obeys a shrinking core model due to H+ diffusion through a porous layer.
► SO2, Na2S2O4, SO2/Cu(II), Fe, FeSO4, and FeCl2 enhance metal leaching from laterite.
► Linear correlations between % metal extractions show co-existence of Fe–Ni and Co–Mn.
► Faster rates in HCl than H2SO4 show enhanced H+ activity and metal-chloride complexation.